| 1. |
- Salam, Abdus, et al.
(författare)
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Measurement of the atmospheric aerosol particle size distribution in a highly polluted mega-city in Southeast Asia (Dhaka-Bangladesh)
- 2012
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 59, s. 338-343
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol particle size distribution was measured with an aerodynamic particle sizer (APS) spectrometer continuously from January 21 to April 24, 2006 in Dhaka, Bangladesh. Particles number, surface and mass distributions data were stored automatically with Aerosol Instrument Manager (AIM) software on average every half an hour in a computer attached to the APS. The grand total average of number, surface and mass concentrations were 8.2 x 10(3) +/- 7.8 x 10(3) particles cm(-3), 13.3 x 10(3) +/- 11.8 x 10(3) mu m(2) cm(-3) and 3.04 +/- 2.10 mg m(-3), respectively. Fine particles with diameter smaller than 1.0 mu m aerodynamic diameter (AD) dominated the number concentration, accounted for 91.7% of the total particles indicating vehicular emissions were dominating in Dhaka air either from fossil fuel burning or compressed natural gas (CNGs). The surface and mass concentrations between 0.5 and 1.0 mu m AD were about 56.0% and 26.4% of the total particles, respectively. Remarkable seasonal differences were observed between winter and pre-monsoon seasons with the highest monthly average in January and the lowest in April. Aerosol particles in winter were 3.79 times higher for number, 3.15 times for surface and 2.18 times for mass distributions than during the pre-monsoon season. Weekends had lower concentrations than weekdays due to less vehicular traffic in the streets. Aerosol particles concentrations were about 15.0% (ranging from 9.4% to 17.3%) higher during traffic peak hours (6:00am-8:00pm) than off hours (8:00pm-6:00am). These are the first aerosol size distribution measurements with respect to number, surface and mass concentrations in real time at Dhaka, Bangladesh.
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| 2. |
- Al-Mamun, Abdullah, et al.
(författare)
-
Multitaper spectrum : A promising method in spectrum sensing cognitive radio
- 2010
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Konferensbidrag (refereegranskat)abstract
- Cognitive radio (CR) has been proposed as a promising and effective technology to improve radio spectrum utilization. The primary objective of the CR is to handle the non-interference rules with any primary users (PUs). Highly sensitive and optimal spectrum sensing detectors are required in order to avoid harmful interference to PUs. Multitaper spectrum seems to be the most appealing one for spectrum sensing CR because of its accurate identification and estimation and low computational complexity. Mulitaper uses small set of tapers and multiple orthogonal prototype filters to reduce the variance. The Fourier transform of a Slepian sequence, originally known as discrete prolate spheroidal sequences (DPSS), gives maximum energy density inside a given bandwidth and less spectral leakage with better specifications has been investigated in this paper and shows that no other window in signal processing can satisfy this property
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| 3. |
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| 4. |
- Antzutkin, Oleg, et al.
(författare)
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Ionic-liquid-based lubricants and lubrication additives comprising ions
- 2012
-
Patent (populärvet., debatt m.m.)abstract
- Anti-wear and friction-reducing lubricants and additives to lubricants for both ferrous and non-ferrous materials with/without DLC (diamiond-like-coatings) or graphene-based coatings, which are halogen free boron based ionic liqs. comprising a combination of an anion chosen from a mandelato borate anion, a salicylato borate anion, an oxalato borate anion, a malonato borate anion, a succinato borate anion, a glutarato borate anion and an adipato borate anion, with at least one cation selected from a tetraalkylphosphonium cation, a choline cation, an imidazolium cation and a pyrrolidinium cation, wherein said at least one cation has at least one alkyl group substituent with the general formula CnH2n+1 , wherein 1≤n≤80. Advantages of the invention include that it provides halogen free ionic liqs. for lubrication and that sensitivity for hydrolysis is reduced.
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| 5. |
- Arabi, A., et al.
(författare)
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Proteomic screen reveals Fbw7 as a modulator of the NF-kappa B pathway
- 2012
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 3, s. 976-
-
Tidskriftsartikel (refereegranskat)abstract
- Fbw7 is a ubiquitin-ligase that targets several oncoproteins for proteolysis, but the full range of Fbw7 substrates is not known. Here we show that by performing quantitative proteomics combined with degron motif searches, we effectively screened for a more complete set of Fbw7 targets. We identify 89 putative Fbw7 substrates, including several disease-associated proteins. The transcription factor NF-κB2 (p100/p52) is one of the candidate Fbw7 substrates. We show that Fbw7 interacts with p100 via a conserved degron and that it promotes degradation of p100 in a GSK3 2 phosphorylation-dependent manner. Fbw7 inactivation increases p100 levels, which in the presence of NF-κB pathway stimuli, leads to increased p52 levels and activity. Accordingly, the apoptotic threshold can be increased by loss of Fbw7 in a p100-dependent manner. In conclusion, Fbw7-mediated destruction of p100 is a regulatory component restricting the response to NF-κB2 pathway stimulation.
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| 6. |
- Balram, Pavan, 1986, et al.
(författare)
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Power system islanding operation support by wind power plants
- 2011
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Ingår i: 4th EPE Joint Wind Energy and T and D Chapters Seminar 2011; Trondheim; Norway; 9 May 2011 through 11 May 2011. - 9781612841670
-
Konferensbidrag (refereegranskat)abstract
- Power system islanding operation support by wind power plants during an underfrequency, undervoltage event is studied. Influence of inertia control and active power control is analyzed in the presence and absence of voltage control by WPP. Effects of variation in wind speed on the frequency and voltage support is observed.
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| 7. |
- Bano, Humara, et al.
(författare)
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Evaluation of provision and support for disabled students in libraries of special education professional degree awarding institutions (DAIs) and rehabilitation centers (RCs).
- 2013
-
Ingår i: Library Philosophy and Practice. - : University of Idaho Library. - 1522-0222. ; :1013
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- This study presents census data of provision and support for students with special needs (usually known as disabled students) in libraries of special education professional degree awarding institutions (DAIs) and rehabilitation centers (RCs) acting in Lahore. Questionnaire was used as research instrument in this quantitative study. Provisions and supports in libraries of DAIs and RCs were illustrated on graphs covering overall students with disabilities and different disability areas – physical impairments, hearing impairments, and visual impairments. Non-parametric tests were used for data analysis. Analysis of collected data confirmed that there was no association or relationship between provisions and supports for students with disabilities in libraries of DAIs and RCs, and type of disabilities. Similarly, Chi-square analysis showed that there was no association between sector and type of disability for provisions and supports for students with disabilities in libraries of DAIs and RCs. Findings of this study have theoretical and practical implications for patrons with special needs’ education and librarianship in Pakistan. This research contributes its part for better attitudes, interactions, and understandings in libraries for students with special needs. Furthermore, this study guides librarians and administration of DAIs and RCs working for students with special needs regarding better provisions and supports in libraries for them.
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| 8. |
- Bengtsson, Maria, et al.
(författare)
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A systematic review of coopetition : levels and effects on different levels
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- While the field of coopetition has grown the multi-level nature of the phenomena have not been systematically addressed. The purpose of this systematic review is to organize extant research by distinguishing between level of coopetition and the effects of coopetition. Through a search of two databases, 99 articles were identified addressing coopetition, or collaboration and competition. The articles were classified by the method used, the level of coopetition addressed and on what level the effects were described. Within the different combinations of level and effect a content analysis was made of the articles. We suggest that additional clarification of the concept is needed to consolidate the field and give direction for future research.
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| 9. |
- Bengtsson, Maria, et al.
(författare)
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Linking coopetition tensions with performance : the mediating role of ambidexterity
- 2014
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Konferensbidrag (refereegranskat)abstract
- By viewing coopetition as a paradox, this paper provides a conceptual model for examining the mediating role of managers’ ambidextrous orientation in linking coopetition tensions with firm’s performance. With a focus on two kinds of tensions that managers usually experience in the coopetition relationship (i.e., external tensions) as well as perceive inside the organization (i.e., internal tensions), we conceptualize their materialization from the coopetition paradox and how ambidextrous managers can mitigate their potential destructive effects on performance. This conceptual model is tested on a representative sample of 1,532 firms in Sweden. The results show that coopetition paradox associates with external tensions but weakly relates to internal tensions. A key contribution is that there is no significant direct relation between coopetition tensions and performance but that an ambidextrous orientation of managers provides a strong mediating effect between the two.
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| 10. |
- Bubnova, Olga, et al.
(författare)
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Corrigendum: Semi-metallic polymers
- 2014
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Ingår i: Nature Materials. - : Springer Science and Business Media LLC. - 1476-1122 .- 1476-4660. ; 13, s. 662-662
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Tidskriftsartikel (refereegranskat)
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| 11. |
- Bubnova, Olga, et al.
(författare)
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Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene)
- 2011
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Ingår i: NATURE MATERIALS. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 10:6, s. 429-433
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 degrees C, the best commercially available inorganic semiconductors are bismuth telluride (Bi2Te3)-based alloys, which possess a figure of merit ZT close to one(1). Most of the recently discovered thermoelectric materials with ZT andgt; 2 exhibit one common property, namely their low lattice thermal conductivities(2,3). Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (lambda = D 0.37W m(-1) K-1) yields a ZT = 0.25 at room temperature that approaches the values required for efficient devices.
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| 12. |
- Bubnova, Olga, et al.
(författare)
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Semi-metallic polymers
- 2014
-
Ingår i: Nature Materials. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 13:2, s. 190-194
-
Tidskriftsartikel (refereegranskat)abstract
- Polymers are lightweight, flexible, solution-processable materials that are promising for low-cost printed electronics as well as for mass-produced and large-area applications. Previous studies demonstrated that they can possess insulating, semiconducting or metallic properties; here we report that polymers can also be semi-metallic. Semi-metals, exemplified by bismuth, graphite and telluride alloys, have no energy bandgap and a very low density of states at the Fermi level. Furthermore, they typically have a higher Seebeck coefficient and lower thermal conductivities compared with metals, thus being suitable for thermoelectric applications. We measure the thermoelectric properties of various poly( 3,4-ethylenedioxythiophene) samples, and observe a marked increase in the Seebeck coefficient when the electrical conductivity is enhanced through molecular organization. This initiates the transition from a Fermi glass to a semi-metal. The high Seebeck value, the metallic conductivity at room temperature and the absence of unpaired electron spins makes polymer semi-metals attractive for thermoelectrics and spintronics.
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| 13. |
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| 14. |
- Erdegren, Mikael, et al.
(författare)
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Simulation of surface solidification in direct-chill 6xxx aluminum billets
- 2012
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Ingår i: IOP Conference Series. - : Institute of Physics (IOP). ; , s. Art. no. 012013-
-
Konferensbidrag (refereegranskat)abstract
- Using the Bridgman technique, the solidification of aluminum alloys of types 6005, 6063, and 6082, was studied. The solidification process differs both between the alloys and between billet surface and bulk, due to higher concentrations of Fe, Si, Mn and Mg near the surface. Previously determined surface concentrations were used to calculate the Fe, Si, Mn and Mg additions needed for Bridgman experiments that simulate surface region solidification. Microstructures were studied and grain size, secondary dendrite arm spacing, intermetallic particles, segregation, and coarsening were evaluated. The increased alloy element concentrations at the surface were found to influence both the structure coarseness and the kind of intermetallic precipitation. In addition, clear differences could be determined between the alloy types, depending on their pull rate in the furnace.
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| 15. |
- Filippov, Andrei, et al.
(författare)
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NMR self-diffusion study of a phosphonium bis(mandelato)borate ionic liquid
- 2013
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 15:23, s. 9281-9287
-
Tidskriftsartikel (refereegranskat)abstract
- Newly synthesized halogen-free boron based ionic liquids (hf-BILs) composed of chelated orthoborate anionsand phosphonium cations have hydrolytic stability, low melting point and outstanding wear and frictionreducing properties. We report here the peculiarities of self-diffusion in one representative from this class,trihexyltetradecylphosphonium bis(mandelato)borate, [P6,6,6,14][BMB], in the temperature range of itspractical interest, 20–100 1C. NMR techniques demonstrated complicated diffusional behaviour – the ionicliquid can exist in one or two liquid ‘‘phases’’. In the low-temperature range (20–50 1C), two phases coexistwhere the cations, [P6,6,6,14], are contained mainly in the phase with slower diffusion coefficients while theanions, [BMB], are in the phase with faster diffusion coefficients. Cations have lower diffusion coefficientswith a factor of 20 as compared with the anions, an effect which is caused by aggregation of cations intodomains due to so-called ‘‘hydrophobic interaction’’ of their hydrocarbon chains. As the temperature risesabove 60 1C, the two phases merge into one where both ions have equal diffusion coefficients. This iscaused by thermal motion making the cation domains smaller in size and more easily interacting withanions. As a result, anions and cations diffuse in this high-temperature range as a pair.
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| 16. |
- Filippov, Andrei, et al.
(författare)
-
The effect of the cation alkyl chain length on density and diffusion in dialkylpyrrolidinium bis(mandelato)borate ionic liquids
- 2014
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:48, s. 26798-26805
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Tidskriftsartikel (refereegranskat)abstract
- The physicochemical properties of ionic liquids are strongly affected by the selective combination of the cations and anions comprising the ionic liquid. In particular, the length of the alkyl chains of ions has a clear influence on the ionic liquid's performance. In this paper, we study the self-diffusion of ions in a series of halogen-free boron-based ionic liquids (hf-BILs) containing bis(mandelato)borate anions and dialkylpyrrolidinium cations with long alkyl chains CnH2n+1 with n from 4 to 14 within a temperature range of 293-373 K. It was found that the hf-BILs with n = 4-7 have very similar diffusion coefficients, while hf-BILs with n = 10-14 exhibit two liquid sub-phases in almost the entire temperature range studied (293-353 K). Both liquid sub-phases differ in their diffusion coefficients, while values of the slower diffusion coefficients are close to those of hf-BILs with shorter alkyl chains. To explain the particular dependence of diffusion on the alkyl chain length, we examined the densities of the hf-BILs studied here. It was shown that the dependence of the density on the number of CH2 groups in long alkyl chains of cations can be accurately described using a "mosaic type" model, where regions of long alkyl chains of cations (named 'aliphatic' regions) and the residual chemical moieties in both cations and anions (named 'ionic' regions) give additive contributions. Changes in density due to an increase in temperature and the number of CH2 groups in the long alkyl chains of cations are determined predominantly by changes in the free volume of the 'ionic' regions, while 'aliphatic' regions are already highly compressed by van der Waals forces, which results in only infinitesimal changes in their free volumes with temperature.
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| 17. |
- Freire, Francis, et al.
(författare)
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Acoustic evidence of a submarine slide in the deepest part of the Arctic, the Molloy Hole
- 2014
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Ingår i: Geo-Marine Letters. - : Springer Science and Business Media LLC. - 0276-0460 .- 1432-1157. ; 34:4, s. 315-325
-
Tidskriftsartikel (refereegranskat)abstract
- The western Svalbard continental margin contains thick sediment sequences with areas known to contain gas hydrates. Together with a dynamic tectonic environment, this makes the region prone to submarine slides. This paper presents results from geophysical mapping of the deepest part of the high Arctic environment, the Molloy Hole. The mapping includes multibeam bathymetry, acoustic backscatter and sub-bottom profiling. The geophysical data reveal seabed features indicative of sediment transport and larger-scale mass wasting. The large slide scar is here referred to as the Molloy Slide. It is located adjacent to the prominent Molloy Hole and Ridge system. The slide is estimated to have transported >65 km(3) of sediments over the deep axial valley of the Molloy Ridge, and further into the Molloy Hole. A unique feature of this slide is that, although its run-out distance is relatively short (<5 km), it extends over an enormous vertical depth (>2,000 m) as a result of its position in a complex bathymetric setting. The slide was most likely triggered by seismic activity caused by seafloor spreading processes along the adjacent Molloy Ridge. However, gas-hydrate destabilization may also have played a role in the ensuing slide event.
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| 18. |
- Gebbink, Wouter A., et al.
(författare)
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Polyfluoroalkyl phosphate esters and perfluoroalkyl carboxylic acids in target food samples and packaging - method development and screening
- 2013
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Ingår i: Environmental Science and Pollution Research. - : Springer Science and Business Media LLC. - 0944-1344 .- 1614-7499. ; 20:11, s. 7949-7958
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Tidskriftsartikel (refereegranskat)abstract
- Polyfluoroalkyl phosphate mono-, di-, and tri-esters (mono-, di-, and triPAPs) are used to water- and grease-proof food packaging materials, and these chemicals are known precursors to perfluoroalkyl carboxylic acids (PFCAs). Existing analytical methods for PAPs lack sample clean-up steps in the sample preparation. In the present study, a method based on ultra performance liquid chromatography coupled to tandem mass spectrometry (UPLC/MS/MS) was developed and optimized for the analysis of mono-, di-, and triPAPs, including a clean-up step for the raw extracts. The method was applied to food samples and their PAP-containing packaging materials. The optimized UPLC/MS/MS method enabled the separation and identification of a total of 4 monoPAPs, 16 diPAPs, and 7 triPAPs in the technical mixture Zonyl®-RP. For sample clean-up, weak anion exchange solid phase extraction columns were tested. PAPs standard solutions spiked onto the columns were separated into a fraction containing neutral compounds (triPAPs) and a fraction with ionic compounds (mono- and diPAPs) with recoveries between 72–110 %. Method limits of quantification for food samples were in the sub to low picogram per gram range. For quantitative analysis of PAPs, compound-specific labeled internal standards showed to be essential as sorption and matrix effects were observed. Mono-, di-, and/or triPAPs were detected in all food packaging materials obtained from the Swedish market. Up to nine diPAPs were detected in the food samples, with the 6:2/6:2 and 6:2/8:2 diPAPs as the dominant compounds. DiPAP concentrations in the food samples ranged from 0.9 to 36 pg/g, which was comparable to individual PFCA concentrations in the same samples. Consumption of food packed in PAP-containing materials could be an indirect source of human exposure to PFCAs.
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| 19. |
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| 20. |
- Glynn, Anders, et al.
(författare)
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Perfluorinated Alkyl Acids in Blood Serum from Primiparous Women in Sweden : Serial Sampling during Pregnancy and Nursing, And Temporal Trends 1996-2010
- 2012
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 46:16, s. 9071-9079
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Tidskriftsartikel (refereegranskat)abstract
- We investigated temporal trends of blood serum levels of 13 perfluorinated alkyl acids (PFAAs) and perfluorooctane sulfonamide (FOSA) in primiparous women (N = 413) from Uppsala County, Sweden, sampled 3 weeks after delivery 1996-2010. Levels of the short-chain perfluorobutane sulfonate (PFBS) and perfluorohexane sulfonate (PFHxS) increased 11%/y and 8.3%/y, respectively, and levels of the long-chain perfluorononanoate (PFNA) and perfluorodecanoate (PFDA) increased 4.3%/y and 3.8%/y, respectively. Concomitantly, levels of FOSA (22%/y), perfluorooctane sulfonate (PFOS, 8.4%/y), perfluorodecane sulfonate (PFDS, 10%/y), and perfluorooctanoate (PFOA, 3.1%/y) decreased. Thus, one or several sources of exposure to the latter compounds have been reduced or eliminated, whereas exposure to the former compounds has recently increased. We explored if maternal levels of PFOS, PFOA, and PFNA during the early nursing period are representative for the fetal development period, using serial maternal serum samples, including cord blood (N = 19). PFAA levels in maternal serum sampled during pregnancy and the nursing period as well as in cord blood were strongly correlated. Strongest correlations between cord blood levels and maternal levels were observed for maternal serum sampled shortly before or after the delivery (r = 0.70-0.89 for PFOS and PFOA). A similar pattern was observed for PFNA, although the correlations were less strong due to levels close to the method detection limit in cord blood.
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| 21. |
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| 22. |
- Kashif, Ahsan-Ullah, et al.
(författare)
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A TCAD approach for non-linear evaluation of microwave power transistor and its experimental verification by LDMOS
- 2010
-
Ingår i: Journal of Computational Electronics. - : SpringerLink. - 1569-8025 .- 1572-8137. ; 9:2, s. 79-86
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Tidskriftsartikel (refereegranskat)abstract
- A simulation technique is developed in TCAD to study the non-linear behavior of RF power transistor. The technique is based on semiconductor transport equations to swot up the overall non-linearity’s occurring in RF power transistor. Computational load-pull simulation technique (CLP) developed in our group, is further extended to study the non-linear effects inside the transistor structure by conventional two-tone RF signals, and initial simulations were done in time domain. The technique is helpful to detect, understand the phenomena and its mechanism which can be resolved and improve the transistor performance. By this technique, the third order intermodulation distortion (IMD3) was observed at different power levels. The technique was successfully implemented on a laterally-diffused field effect transistor (LDMOS). The value of IMD3 obtained is −22 dBc at 1-dB compression point (P 1 dB) while at 10 dB back off the value increases to −36 dBc. Simulation results were experimentally verified by fabricating a power amplifier with the similar LDMOS transistor.
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| 23. |
- Kashif, Ahsan-Ullah, et al.
(författare)
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A TCAD Approach to Design a Broadband Power Amplifier
- 2010
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Technology Computer Aided Design (TCAD) provides an alternate method to study the power amplifier (PA) design prior to fabrication. It is very useful for the extraction of an accurate large signal model. This paper presents a design approach from device to circuit level to study broadband PA performance of RF-LDMOS using computational load-pull (CLP) analysis. To validate the TCAD approach, we have designed a broadband (1.9 - 2.5 GHz) class AB power amplifier. The concept is verified by designing an output broadband matching network at optimum impedance value (Zf) of RF-LDMOS using ADS software. The large signal results verify this concept and RF output power of 30.8 dBm is achieved with comparable gain and efficiency.
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| 24. |
- Kashif, Ahsan-Ullah
(författare)
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Optimization of LDMOS Transistor in Power Amplifiers for Communication Systems
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emergence of new communication standards has put a key challenge for semiconductor industry to develop RF devices that can handle high power and high data rates simultaneously. The RF devices play a key role in the design of power amplifiers (PAs), which is considered as a heart of base-station. From economical point of view, a single wideband RF power module is more desirable rather than multiple narrowband PAs especially for multi-band and multi-mode operation. Therefore, device modeling has now become much more crucial for such applications. In order to reduce the device design cycle time, the researchers also heavily rely on computer aided design (CAD) tools. With improvement in CAD technology the model extraction has become more accurate and device physical structure optimization can be carried out with less number of iterations.LDMOS devices have been dominating in the communication field since last decade and are still widely used for PA design and development. This thesis deals with the optimization of RFLDMOS transistor and its evaluation in different PA classes, such as linear, switching, wideband and multi-band applications. For accurate evaluation of RF-LDMOS transistor parameters, some techniques are also developed in technology CAD (TCAD) using large signal time domain computational load-pull (CLP) methods.Initially the RF-LDMOS is studied in TCAD for the improved RF performance. The physical intrinsic structure of RF-LDMOS is provided by Infenion Technologies AG. A reduced surface field (RESURF) of low-doped drain (LDD) region is considered in detail because it plays an important role in RF-LDMOS devices to obtain high breakdown voltage (BVDS). But on the other hand, it also reduces the RF performance due to high on-resistance (Ron). The excess interface state charges at the RESURF region are introduced to reduce the Ron, which not only increases the dc drain current, but also improve the RF performance in terms of power, gain and efficiency. The important achievement is the enhancement in operating frequency up to 4 GHz. In LDD region, the effect of excess interface charges at the RESURF is also compared with dual implanted-layer of p-type and n-type. The comparison revealed that the former provides 43 % reduction in Ron with BVDS of 70 V, while the later provides 26 % reduction in Ron together with BVDS of 64 - 68 V.In the second part of my research work, computational load pull (CLP) simulation technique is used in TCAD to extract the impedances of RF-LDMOS at different frequencies under large signal operation. Flexible matching is an issue in the design of broadband or multi-band PAs. Optimum impedance of RF-LDMOS is extracted at operating frequencies of 1, 2 and 2.5 GHz in class AB PA. After this, CLP simulation technique is further developed in TCAD to study the non-linear behavior of RF devices. Through modified CLP technique, non-linear effects inside the transistor structure are studied by conventional two-tone RF signals in time domain. This is helpful to detect and understand the phenomena, which can be resolved to improve the device performance. The third order inter-modulation distortion (IMD3) of RF- LDMOS was observed at different power levels. The IMD3 of −22 dBc is obtained at 1-dB compression point (P1-dB), while at 10 dB back off the value increases to −36 dBc. These results were also verified experimentally by fabricating a linear PA. Similarly, CLP technique is developed further for the analysis of RF devices in high efficiency operation by investigating the odd harmonic effects for the design of class-F PA. RF-LDMOS can provide a power added efficiency (PAE) of 81.2 % in class-F PA at 1 GHz in TCAD simulations. The results are verified by design and fabrication of class-F PA using large signal model of the similar device in ADS. In fabrication, a PAE of 76 % is achieved.
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| 25. |
- Kashif, Ahsan-Ullah, et al.
(författare)
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Switching Behavior of Microwave Power Transistor Studied in TCAD for Switching Class Power Amplifiers and Experimental Verification by LDMOS based Class-F Power Amplifier
- 2010
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a TCAD study of high speed switching behavior of RF power-transistor in class-F Power Amplifier. We utilized finite harmonics loads for achieving maximum efficiency, without external circuitry. The in house developed computational load–pull (CLP) simulation technique is further extended to investigate the odd harmonic effects of RF transistor in class-F operation. An LD-MOSFET is studied which provided 81.2 % power added efficiency (PAE) at 1 GHz. The concept is experimentally verified by fabricating a class-F PA using same transistor. In the measurement, 76 % PAE is achieved, which is close to the TCAD simulated results. TCAD is an excellent tool to study the behavior of active devices. It has an ability to enhance and optimize the performance of transistor according to system specifications before fabrication.
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| 26. |
- Khan, Ershad Ullah, et al.
(författare)
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Techno-economic analysis of small scale biogas based polygeneration systems : Bangladesh case study
- 2014
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Ingår i: Sustainable Energy Technologies and Assessments. - Amsterdam : Elsevier. - 2213-1388 .- 2213-1396. ; 7, s. 68-78
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Tidskriftsartikel (refereegranskat)abstract
- Access to electricity, clean energy, and safe drinking water services are genuine needs of the rural poor for their welfare. These needs can be addressed either individually or in an integrated approach. Biogas digesters are promising in the rural setting and integration of biogas production with power generation and water purification is an innovative concept that could be applied in remote areas of Bangladesh. This paper presents a new concept for integrated biogas based polygeneration and analyzes the techno-economic performance of the scheme for meeting the demand of electricity, cooking energy and safe drinking water of 30 households in a rural village of Bangladesh. The specific technologies chosen for the key energy conversion steps are as follows: plug-flow digester; internal combustion engine; and air-gap membrane distillation. Mass flows and energy balance, levelized cost of producing electricity, cooking gas and safe drinking water as well as the payback period of such a polygeneration system were analyzed. The results indicate that this polygeneration system is much more competitive and promising (in terms of levelized cost) than other available technologies when attempting to solve the energy and arsenic-related problems in Bangladesh. The payback period of such system is between 2.6 and 4 years.
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| 27. |
- Khan, MD. Ershad Ullah, 1979-
(författare)
-
Feasibility Analysis of Biogas Based Polygeneration for Rural Development in Bangladesh
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Around three-quarters of Bangladeshis (total population 164 million) live in rural areas: only 25% of these households have access to grid electricity with non-reliable supply despite the country’s successful rural electrification program, kerosene is the predominant source for lighting, and woody biomass is virtually the only option available for cooking. Aside from this energy service challenges the rural population also struggles with unsafe drinking water in terms of widespread arsenic contamination of well water. Access to electricity, clean cooking gas, and safe drinking water services are genuine needs of the rural poor and are essential to improving welfare. These needs can be addressed individually or using an integrated approach. Anaerobic digesters are now a proven technology and remain economically promising in the rural setting, where connection to the public electric and gas grids are not available/either not cost effective or feasible, and where energy and water scarcity are severe. As the technologies continue to improve, and as energy and safe water becomes scarce and fossil fuel energy prices rise, renewable energy based services and technological integration becomes more viable techno-economically. In these circumstances, the integration of biogas digester with power generation and water purification unit is an innovative concept that could be applied in remote areas of Bangladesh. This work presents a new concept for integrated polygeneration and analyzes the techno-economic performance of the scheme for meeting the demand of electricity, cooking energy and safe drinking water of 30 households in a rural village of Bangladesh. This study considers a holistic approach towards tackling both of these issues via integrated renewable energy-based polygeneration employed at the community level. The polygeneration unit under consideration provides electricity via cow dung-fed digester, which in turn is coupled to a gas engine. Excess digester gas is employed for cooking, while waste heat from the process drives a membrane distillation unit for water purification. The specific technologies chosen for the key energy conversion steps are as follows: plug-flow digester; internal combustion engine; and air-gap membrane distillation. The technical features, energy consumption, and potential of renewable energy use in driving the main integrated processes are reviewed and analyzed in this thesis. This study also examines one approach by investigating the application of suitable membrane technologies, specifically air gap membrane distillation (AGMD), as a promising method for small-scale, low cost deployment. Experimental results show that the tested AGMD prototype is capable of achieving high separation efficiency, as all product water samples showed arsenic levels below accepted limits. Mass flows and energy balance, life cycle cost (levelized cost) of producing electricity, cooking gas and safe drinking water as well as the payback period of such a polygeneration system were studied. The results indicate that this polygeneration system is much more competitive and promising than other available technologies when attempting to solve the energy and arsenic-related problems in Bangladesh. One of the main encouraging issues of this integrated system is the levelized cost of the three major services: cooking gas (0.015 USD/kWh), electricity (0.042 USD/kWh–an orders of magnitude lower than comparable photovoltaic or wind systems) and safe drinking water (0.003 USD/liter). Additionally, the payback period is between 2.6 to 4 years.
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| 28. |
- Khan, MD. Ershad Ullah, 1979-, et al.
(författare)
-
Hybrid Renewable Energy with Membrane Distillation Polygeneration for Rural Households in Bangladesh : Pani Para Village Case Study
- 2014
-
Ingår i: 2014 INTERNATIONAL CONFERENCE ON RENEWABLE ENERGY RESEARCH AND APPLICATION (ICRERA). - : IEEE. - 9781479937950 ; , s. 359-362
-
Konferensbidrag (refereegranskat)abstract
- Despite the country's rural electrification program, kerosene is the predominant source for lighting, and woody biomass is virtually the only the option available for cooking. Aside from this energy service challenges the rural population also struggles with unsafe drinking water in terms of widespread arsenic contamination of well water. Access to electricity, clean cooking gas, and safe drinking water services are genuine needs of the rural poor and are essential to improving welfare. These needs can be addressed individually or using an integrated approach. This study considers a holistic approach towards tackling both of these issues via integrated renewable energy-based polygeneration employed at the community level. The polygeneration unit under consideration provides electricity via a pV array and cow dung-fed digester, which in turn is coupled to a gas engine. Excess digester gas is employed for cooking and lighting, while waste heat from the process drives a membrane distillation unit for water purification. The system is sized to serve a community of 52 households (Pani Para, Faridpur District) with 14 kWe peak demand and 250 kWh/day primary electricity loads. Technical assessments and optimization have been conducted with HOMER. Results show that electricity demand can be met with such a system while simultaneously providing 0.4 m(3) cooking fuel and 2-3 L pure drinking water per person per day. Cost estimates indicate that this approach is highly favorable to other renewable options.
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| 29. |
- Khan, MD. Ershad Ullah, 1979-, et al.
(författare)
-
Water purification of arsenic contaminated drinking water via air gap membrane distillation (AGMD)
- 2014
-
Ingår i: Periodica Polytechnica, Mechanical Engineering. - : Faculty of Mechanical Engineering of the Budapest University of Technology and Economics. - 1587-379X. ; 58:1, s. 47-53
-
Tidskriftsartikel (refereegranskat)abstract
- Arsenic contamination in shallow tubewell water is a serioushealth issue in Bangladesh and other Southeast Asian countries.Rural and remote areas in these locations continue toface tremendous challenges in providing access to affordableand safe arsenic-free drinking water. In recent years, intensiveefforts have been undertaken to identify appropriate technologiesfor arsenic removal. This study examines one approach byinvestigating the application of suitable membrane technologies,specifically air gap membrane distillation (AGMD), asa promising method for small-scale, low cost deployment. Theobjective of this study was to test an AGMD commercial prototype(nominal capacity of 2 L/hr) with three different feedstocks:arsenic-containing groundwater (medium concentration) andarsenic-spiked tap water (medium and high concentrations).Results show that the tested AGMD prototype is capable ofachieving excellent separation efficiency, as all product watersamples showed arsenic levels well below WHO accepted limits(10 μg/L) even for initial concentrations over 1800 μg/L.Parametric studies with focus on variation of coolant temperatureillustrate the possibility of integrating AGMD in variousthermal systems.
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| 30. |
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| 31. |
- Nair, Srijith K., et al.
(författare)
-
Towards secure cloud bursting, brokerage and aggregation
- 2010
-
Ingår i: 2010 Eighth IEEE European Conference on Web Services. - : IEEE. - 9780769543109 ; , s. 189-196
-
Konferensbidrag (refereegranskat)abstract
- The cloud based delivery model for IT resources is revolutionizing the IT industry. Despite the marketing hype around “the cloud”, the paradigm itself is in a critical transition state from the laboratories to mass market. Many technical and business aspects of cloud computing need to mature before it is widely adopted for corporate use. For example, the inability to seamlessly burst between internal cloud and external cloud platforms, termed cloud bursting, is a significant shortcoming of current cloud solutions. Furthermore, the absence of a capability that would allow to broker between multiple cloud providers or to aggregate them into a composite service inhibits the free and open competition that would help the market mature. This paper describes the concepts of cloud bursting and cloud brokerage and discusses the open management and security issues associated with the two models. It also presents a possible architectural framework capable of powering the brokerage based cloud services that is currently being developed in the scope of OPTIMIS, an EU FP7 project.
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| 32. |
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| 33. |
- Rahmat Ullah Shah, Syed, et al.
(författare)
-
Empirical results of academic librarians' attitudes toward knowledge management in Pakistan
- 2013
-
Ingår i: Library Management. - : Emerald. - 0143-5124 .- 1758-7921. ; 34:8/9, s. 619-631
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose – The purpose of this paper is to investigate librarians' attitude toward knowledge management in the academic environment of Pakistan. Personality characteristics and situational characteristics of behaviour were discussed in the context of a Pakistani university setting. Design/methodology/approach – This is quantitative research with closed-ended questionnaire as the tool for data collection. In data analysis, Pearson correlations of self-esteem, self-efficacy, threat and challenge with factors of knowledge management and Pearson correlations of experience with attitudes toward knowledge management were calculated. In addition, independent samples-t tests for gender and sector were applied. Findings – Significant positive correlations of self-efficacy, self-esteem, and challenges with librarians' attitudes toward knowledge management were calculated. On the other hand, research results proved that attitudes toward knowledge management had no relation with experience of librarians. Similarly, no gender wise and sector wise significant differences were observed in librarians' attitudes toward knowledge management. Research limitations/implications – This research suggests new roles, trends, and vocational settings for library and information science professionals in the field of knowledge management as the topic of future research. Practical implications – This research clarifies the personality characteristics and situational characteristics for knowledge management practices with special reference to librarianship and it contributes to the promotion of knowledge culture in Pakistan. Originality/value – This literary contribution is unique in the sense that it presents knowledge management perspectives in Pakistani librarianship. It is useful for decision makers who are involved in knowledge management attempts. It helps in selection of proper person for the proper task for knowledge management.
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| 34. |
- Rahmat Ullah Shah, Syed, et al.
(författare)
-
Knowledge-sharing behavior in dairy sector of Pakistan
- 2013
-
Ingår i: Library Philosophy and Practice. - : University of Idaho Library. - 1522-0222. ; :917
-
Tidskriftsartikel (refereegranskat)abstract
- This study is about knowledge sharing behavior in dairy sector. Two-hundred middle managers (with professional qualifications) from five industrial units in Pakistan were selected for study. Fifty-seven managers participated in the study (29 percent of the sample). Research model and hypotheses were based on behavioral theories, i.e., TRA, TPB, and TAM. Data were collected through a questionnaire using Likert scale. Spearman’s and Pearson’s correlation coefficients and structural equation model among different variables tested hypotheses of the research modal. The study proved that attitude, intention, and behavior had accepted mutual positive direct effects for knowledge sharing in dairy sector. Conversely, subjective norms and perceived behavioral control had non-significant values but weak positive direct effects toward knowledge sharing. Findings of this study are useful for better understanding about behavioral influences for knowledge sharing. Furthermore, it is of practical use for the organizational administration involved in knowledge management initiatives in geographical circumstances of Pakistan.
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| 35. |
- Raza-Ullah, Tatbeeq, 1982-, et al.
(författare)
-
Emotions in paradoxical inter-firm relationships : a conceptual framework
- 2014
-
Ingår i: The 74th Annual Meeting of the Academy of Management. ; , s. 15851-
-
Konferensbidrag (refereegranskat)abstract
- We develop a theory of emotions in inter-firm relationships with specific attention to the context of coopetition in which firms deal with the paradox of simultaneous cooperation and competition with each other. Our theory articulates the antecedents, characteristics, consequences and management of emotions in coopetition. We propose that the cognitive appraisal of paradox in coopetition leads to emotional ambivalence – an emotional state of experiencing simultaneous positive and negative emotions. We introduce the concept of emotional ambidexterity that enables the focal firm to accept, allow, and maintain emotional ambivalence at a moderate level, and enhance performance. Applying an emotional lens on coopetition enhances scholarly understanding of the paradoxical phenomenon and provides intriguing avenues for further research.
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| 36. |
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| 37. |
- Raza-Ullah, Tatbeeq, 1982-, et al.
(författare)
-
The coopetition paradox and tension in coopetition at multiple levels
- 2014
-
Ingår i: Industrial Marketing Management. - : Elsevier. - 0019-8501 .- 1873-2062. ; 43:2, s. 189-198
-
Tidskriftsartikel (refereegranskat)abstract
- This article explores the nature of the paradox inherent in coopetition; that is, the simultaneous pursuit of cooperation and competition between firms, and emanating tensions that develop at individual, organizational, and inter-organizational levels. We dissect the anatomy of the coopetition paradox to discover how it materializes by creating an external boundary (i.e., via unifying forces) and internal boundaries (i.e., via divergent forces). After explaining the coopetition paradox, we distinguish tension from paradox and submit that tension comprises both positive and negative emotions simultaneously, also known as emotional ambivalence. Finally, we recognize that emotional ambivalence in coopetition prevails at different levels, and vary in its level of intensity and persistency in relation to different contexts. We employ illustrative cases to ground our propositions empirically. This article provides understanding on concepts, expects to incite fruitful dialogue, and fuels further studies on inter-firm paradoxes.
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| 38. |
- Rios, R, et al.
(författare)
-
Nonlinear effects in asymmetric amino acid catalysis by multiple interconnected stereoselective catalytic networks
- 2010
-
Ingår i: Chemistry - A European Journal. - Weinheim : Wiley. - 0947-6539 .- 1521-3765. ; 16:47, s. 13935-13940
-
Tidskriftsartikel (refereegranskat)abstract
- A fine line: The generation of significant positive nonlinear effects in asymmetric amino acid catalysis under homogeneous conditions, which can be explained by the model for cooperative catalytic stereoselective pathways, is reported. The addition of an achiral aldehyde generated the multiple interconnected stereoselective catalytic network.
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| 39. |
- Shah, Faiz Ullah, et al.
(författare)
-
Antiwear additives for lubricants
- 2011
-
Patent (populärvet., debatt m.m.)abstract
- The additives are described by the general formula (I) with 2≤k≤20, 1≤n≤20, R1 = CmH2m+1; 1≤m≤80, and R2 = CpH2p+1; 1≤p≤80.
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| 40. |
- Shah, Faiz Ullah, et al.
(författare)
-
Boron in Tribology : From Borates to Ionic Liquids
- 2013
-
Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 51:3, s. 281-301
-
Forskningsöversikt (refereegranskat)abstract
- Boron compounds are widely used in a range of tribological applications such as friction modifiers, antioxidants, antiwear additives, and in many cases as environmentally friendly lubricants. The chemical nature and structure of boron compounds provide multifunctionality. They are used as (1) solid lubricants such as boric acid and hexagonal boron nitride, (2) liquid lubricants such as ionic liquids, (3) lubricant additives such as borate derivatives of various organic and inorganic compounds, and (4) coatings such as cubic boron nitride and different metal borides. Boron is also one of the most favorable elements for coatings and thin films in biotribological and biomedical applications. This review outlines the growing role of boron in lubrication over the past several decades, summarizes the main findings, and identifies future challenges related to boron chemistry.
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| 41. |
- Shah, Faiz Ullah, et al.
(författare)
-
Boundary films at metal oxide-ionic liquid interfaces studied by solid-state NMR spectroscopy
- 2013
-
Konferensbidrag (refereegranskat)abstract
- Solid-state NMR spectroscopy is a useful method for elucidating mechanisms of formation of boundary films at solid-liquid interfaces of different metal oxides in contact with different ionic liquids having halogenated anions, such as NTF2- and PF6- [1,2]. However, these halogen-based ionic liquids are susceptible to hydrolysis and generate HF that erode the surface and pollute the environment. In this study, we employed a similar NMR approach to understand the mechanism of film formation by halogen-free orthoborate ionic liquids (hf-BILs) on the metal oxide surfaces.Samples were prepared by grinding the inorganic oxide and 10 wt% of hf-BIL using mortar and pestle. The boundary films on inorganic metal oxides (Al2O3, MgO and SiO2) surfaces in contact with hf-BILs have been characterized using solid-state MAS (11B, 31P and 29Si) NMR spectroscopy. The single pulse 11B NMR data indicate that bis(mandelato)borate anion, [BMB]-, in [P6,6,6,14][BMB] BIL strongly interacts with these metal oxides, in particular, at elevated temperatures (100 °C). In contrast, no products of decomposition were detected for surface of these oxides exposed to [trihexyltetradecylphosphonium][bis(salicylato)borate] ILs at different temperatures. Therefore, it was suggested that the [BScB]- anion is weakly interacting with these oxides. 31P NMR data on the same IL/metal oxide systems revealed strong interactions of the [P6,6,6,14]+ with these oxides. We suggest that [P6,6,6,14]+ cations are also present in immobile surface layers of ILs on particles of these oxides, because 31P resonance lines of ILs were detected using 1H-31P cross polarization MAS NMR giving rise to NMR signals of solid phases with a low molecular mobility only. The existence of strongly adhered surface layers of ILs on particles of metal oxides was further confirmed by 1H-29Si CP/MAS NMR. This study suggests that the boundary film formation between hf-BILs and metal oxide surfaces is a complex process involving various chemical reactions at the interfaces. These findings can be important for understanding of mechanisms of formation and structure of tribofilms in the process of lubrication of nonferrous metal surfaces by hf-BILs.
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| 42. |
- Shah, Faiz Ullah
(författare)
-
Designed boron chemistry for tribological systems
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Boron compounds can be environmentally friendly alternatives for commercially available lubricant additives. Some boron compounds are already used as friction modifiers, corrosion inhibitors, antioxidants and antiwear additives in lubricants. The focus of the present work is on the development and tribological investigations of new boron compounds for these applications. In this work, boron compounds based on dithiophosphates (DTPs), dithiocarbamates (DTCs) and ionic liquids (ILs) were designed, synthesized and tribologically optimized. The work was carried out in the following steps: (1) Synthesis of novel boron based compounds and ionic liquids; (2) Characterization of the compounds with FTIR, liquid-state (1H, 13C, 31P, 11B) and solid-state magic-angle-spinning (MAS) NMR spectroscopy, electrospray ionization mass spectrometery (ESI-MS), elemental analysis, thermal analyses (TG/DTG, DTA, DSC and QMS), viscosity, density and conductivity; (3) Tribological evaluation using four ball and pin-on-disc tribometers; (4) Surface analysis using an optical profiler and Scanning Electron Microscopy coupled with X-ray Energy Dispersive Spectroscopy (SEM/EDS). (i) Antiwear performance of S-di-n-octoxyboron-O,O’-di-n-octyldithiophosphate (DOB-DTP) was found considerably better in comparison with O,O’-di-n-butyl-dithiophosphato-zinc(II) (ZnDTP). However, since DOB-DTP contains B─S bond, which is sensitive to moisture and may be hydrolyzed by water, a novel class of alkylborate-ethyl-dithiophosphates was synthesized, in which boron is covalently bonded to the dialkyldithiophosphate group through the ethyl linker in order to avoid hydrolysis. (ii) Antiwear performance of an alkylborate-ethyl-dithiophosphate with decyl substitutes at both DTP and the borate groups of the molecule (DDB-EDTP) was superior compared with that of the octyl (DOB-EDTP) and the pentyl (DDB-EDTP) analogues. Residues of one representative compound from this class, DPB-EDTP, after thermal analyses were characterized by multinuclear 13C, 31P and 11B MAS and 31P CP/MAS NMR spectroscopy. Solid-state NMR data suggest that a dominant part of the solid residue of DPB-EDTP consists of borophosphates. (iii) It was found that a novel class of compounds containing alkylborate and dithiocarbamate groups with alkyl or methylbenzyl- substitutes in one molecule provide better antiwear performance compared with commercially available packages of ZnDTPs. (iv) Eight compounds belonging to a novel class of halogen-free chelated orthoborate ionic liquids (hf-BILs) with different phosphonium cations were synthesized. Important physical properties of the ILs including glass transition temperatures, density, viscosity and ionic conductivity were measured. As lubricants, these hf-BILs exhibit considerably better antiwear and friction reducing properties under boundary lubrication conditions for steel-aluminum contacts as compared with fully formulated (15W-50 grade) engine oil. (v) Five compounds belonging to another class of hf-BILs comprised of two chelated orthoborate anions, bis(mandelato)borate and bis(salicylato)borate, and three different nitrile cations (cholinium, pyrrolidinium and imidazolium) were prepared. Solid-state NMR spectroscopy was employed to probe interactions between cations and anions in the salts, which are solid at room temperature. Solid-state NMR data suggested a strong interaction between BScB anions and cholinium cations [Chol]+. This interaction was further confirmed by the X-ray diffraction single crystal structure of this salt as hydrogen bonding between OH of [Chol]+ and the carbonyl group of [BScB]-. The [BScB]- exhibited a strong interaction with imidazolium cation [EMIm]+, whereas a weaker interaction was suggested between pyrrolidinium cation [EMPy]+ and [BScB]-. It was found that the novel boron based DTPs and DTCs have considerably better antiwear performance and higher stability of the coefficient of friction with time as compared with ZnDTP. They also have a high thermal stability, good miscibility with oils and positive environmental issues all that make them an attractive alternative to ZnDTPs and other commercial additives to lubricants. It was found that novel halogen-free boron based ionic liquids may be also potentially used as alternative lubricants for ferrous and non-ferrous contact.
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| 43. |
- Shah, Faiz Ullah, et al.
(författare)
-
Halogen-free chelated orthoborate ionic liquids and organic ionic plastic crystals
- 2012
-
Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 22:14, s. 6928-6938
-
Tidskriftsartikel (refereegranskat)abstract
- Five halogen-free orthoborate salts comprised of three different cations (cholinium, pyrrolidinium and imidazolium) and two orthoborate anions, bis(mandelato)borate and bis(salicylato)borate, were synthesised and characterised by DSC, X-ray diffraction and NMR. DSC measurements revealed that glass transition points of these orthoborate salts are in the temperature range from −18 to −2 °C. In addition, it was found that [EMPy][BScB] and [EMIm][BScB] salts have solid–solid phase transitions below their melting points, i.e. they exhibit typical features of plastic crystals. Salts of the bis(salicylato)borate anion [BScB]− have higher melting points compared with corresponding salts of the bis(mandelato)borate anion [BMB]−. Single crystal X-ray diffraction crystallography (for [Chol][BScB] crystals) and solid-state multinuclear (13C, 11B and 15N) NMR spectroscopy were employed for the structural characterisation of [Chol][BScB], [EMPy][BScB] and [EMIm][BScB], which are solids at room temperature: a strong interaction between [BScB]− anions and [Chol]+ cations was identified as (i) hydrogen bonding between OH of [Chol]+ and carbonyl groups of [BScB]− and (ii) as the inductive C–Hπ interaction. In the other salt, [EMIm][BScB], anions exhibit ππ stacking in combination with C–Hπ interactions with [EMIm]+ cations. These interactions were not identified in [EMPy][BScB] probably because of the lack of aromaticity in cations of the latter system. Our data on the formation of a lanthanum complex with bis(salicylato)borate in the liquid mixture of La3+(aq) with [Chol][BScB] suggest that this class of novel ILs can be potentially used in the extraction processes of metal ions of rare earth elements.
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| 44. |
- Shah, Faiz Ullah, et al.
(författare)
-
Interfacial Antiwear and Physicochemical Properties of Alkylborate-dithiophosphates
- 2011
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 3:4, s. 956-968
-
Tidskriftsartikel (refereegranskat)abstract
- Boron compounds have become of interest in tribology because of their unique tribochemical and tribological properties. At the same time, dialkyldithiophosphates (DTPs) of transition metals have been extensively used as multifunctional additives in lubricants to control friction and reduce wear in mechanical systems. Because of the environmental pollution and health hazards of these compounds, ashless compounds with reduced amounts of sulfur and phosphorus are desirable. This work reports on the synthesis, characterization, and tribological properties of a new class of compounds, alkylborate-dithiophosphates. This class combines two high-iron-affinity surface active groups, borate and dialkyldithiophosphate, into a single molecule. The final products, viscous liquids, were characterized by FT-IR, multinuclear 1H, 13C, 31P, and 11B NMR spectroscopy and thermal analyses. Residues of one representative compound from this class, DPB-EDTP, after thermal analyses were additionally characterized by multinuclear 13C, 31P and 11B MAS and 31P CP/MAS NMR spectroscopy. Solid-state NMR data suggest that a dominant part of the solid residue of DPB-EDTP consists of borophosphates. Antiwear and friction properties of a mineral oil with these novel additives were evaluated in a four-ball tribometer in comparison with O,O?-di-n-butyl-dithiophosphato-zinc(II), Zn-BuDTP, as a reference lubricant additive. The surface morphology and the elemental composition of the tribofilms were characterized using scanning electron microscopy with energy-dispersive X-rays spectroscopy (SEM/EDS). The results show that alkylborate-dithiophosphates, with substantially reduced amounts of sulfur and phosphorus compared with Zn-BuDTP, have considerably better antiwear and friction performance.
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| 45. |
- Shah, Faiz Ullah, et al.
(författare)
-
Novel alkylborate-dithiocarbamate lubricant additives : Synthesis and tribophysical characterization
- 2012
-
Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 45:1, s. 67-78
-
Tidskriftsartikel (refereegranskat)abstract
- Boron-based lubricant additives have recently received significant attention, because of their wear-reducing and frictional properties and low pollution. At the same time, dithiocarbamate complexes with different metals have a long history of being used as multifunctional additives to lubricants. In this study, novel, environmentally friendly additives containing alkylborate and dithiocarbamate groups with alkyl or methylbenzyl substitutes in one molecule were studied. Tribological tests were performed with the additives admixed in a mineral oil using steel-on-steel contacts in a four-ball tribometer. Borate derivatives of different dithiocarbamate ligands were synthesized by several step reactions to investigate tribochemical properties of boron, sulfur, and nitrogen combined in one selected compound. Viscous liquid products were characterized by multinuclear 1H, 13C, and 11B NMR spectroscopy. The surface morphology and the elemental composition of the tribofilms were investigated using an optical profiler and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). It was found that some of these novel compounds provide better antiwear performance and similar frictional properties compared with a commercially available ZnDTP package. Traces of sulfur in the tribofilms formed with both 0.2 and 1.0 wt% of alkylborate-dithiocarbamate compounds in a mineral oil were detected with EDS.
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| 46. |
- Shah, Faiz Ullah, et al.
(författare)
-
Novel halogen-free chelated orthoborate-phosphonium ionic liquids : synthesis and tribophysical properties
- 2011
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:28, s. 12865-12873
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis, characterisation, and physical and tribological properties of halogen-free ionic liquids based on various chelated orthoborate anions with different phosphonium cations, both without halogen atoms in their structure. Important physical properties of the ILs including glass transition temperatures, density, viscosity and ionic conductivity were measured and are reported here. All of these new halogen-free orthoborate ionic liquids (hf-BILs) are hydrophobic and hydrolytically stable liquids at room temperature. As lubricants, these hf-BILs exhibit considerably better antiwear and friction reducing properties under boundary lubrication conditions for steel–aluminium contacts as compared with fully formulated (15W-50 grade) engine oil. Being halogen free these hf-BILs offer a more environmentally benign alternative to ILs being currently developed for lubricant applications.
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| 47. |
|
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| 48. |
- Sheikh, Zaka Ullah, et al.
(författare)
-
A Technique for Efficient Realization of Wide-Band FIR LTI Systems
- 2012
-
Ingår i: IEEE Transactions on Signal Processing. - : IEEE Press. - 1053-587X .- 1941-0476. ; 60:3, s. 1482-1486
-
Tidskriftsartikel (refereegranskat)abstract
- This correspondence introduces a technique for efficient realization of wide-band finite-length impulse response (FIR) linear and timeinvariant (LTI) systems. It divides the overall frequency region into three subregions through lowpass, bandpass, and highpass filters realized in terms of only one filter. The actual function to be approximated is in the low- and high-frequency regions realized using periodic subsystems. In this way, one can realize an overall wide-band LTI function in terms of three low-cost subblocks, leading to a reduced overall arithmetic complexity as compared to the regular realization. A systematic design technique is provided and a detailed example shows multiplication and addition savings of 62 and 48 percent, respectively, for a fractional-order differentiator with a 96 percent utilization of the bandwidth. Another example shows that the savings increase/decrease with increased/decreased bandwidth.
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| 49. |
- Sheikh, Zaka Ullah, et al.
(författare)
-
Design of Narrow-Band and Wide-Band Frequency-Response Masking Filters Using Sparse Non-Periodic Sub-Filters
- 2010
-
Konferensbidrag (refereegranskat)abstract
- In this work a new technique for design of narrow-band and wide-band linear-phase finite-length impulse response (FIR) frequency-response masking based filters is introduced. The technique is based on a sparse FIR filter design method for both the model (bandedge shaping) filter as well as the masking filter using mixed integer linear programming optimization. The proposed technique shows promising results for realization of efficient low arithmetic complexity structures.
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| 50. |
- Sheikh, Zaka Ullah, et al.
(författare)
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Design of sparse non-periodic narrow-band and wide-band FRM-like FIR filters
- 2010
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Ingår i: Proceedings of the International Conference on Green Circuits and Systems (ICGCS), 2010. - 9781424468775 - 9781424468768 ; , s. 279-282
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Konferensbidrag (refereegranskat)abstract
- In this work, a design method for narrow-band and wide-band frequency-response masking FIR filters is proposed. As opposed to most previous works, the design method is not based on a periodic model filter. Instead, the masking filter is designed for a given stopband edge. The model filter design is based on optimizing the sparseness of the filter, and, hence, the resulting model filter is not required to be periodic.
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