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1.
  • Cindemir, Umut, et al. (författare)
  • Porous Nickel Oxide Sensor for Formaldehyde Detection
  • 2014
  • Ingår i: European Materials Society (E-MRS) Spring Meeting, Lille, France, May 26-30, 2014. : Symposium B: Advanced functional materials for environmental monitoring and applications..
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Formaldehyde is a volatile organic compound, which is a harmful indoor pollutant, causing sick building syndrome (SBS) and is released from household and building materials. Since higher concentrations of formaldehyde are considered to be carcinogenic, monitoring them indoors is of great importance. Advanced gas deposition has here been used to fabricate highly porous nickel oxide (NiO) thin films for formaldehyde sensing. The films were deposited on Al2O3 substrates with prefabricated comb-structured electrodes, and a resistive heater at the opposite face. The morphology of the films was investigated with scanning electron microscopy, and the porosity was determined by nitrogen adsorption isotherms with the Brunauer-Emmett-Teller method. The particle size was found to be less than 10 nm, as determined by x-ray diffraction. X-ray photoelectron spectroscopy of the NiO films was also done. Gas sensing measurements were done using a total gas flow rate of 200 ml/min. Resistivity values of sensors were recorded with formaldehyde diluted in synthetic air. Sensor resistances were recorded at 50 ppm, 25ppm, 10ppm and 5 ppm formaldehyde concentration. NiO films showed promising formaldehyde gas sensing properties implying lower levels of detection limit.
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2.
  • Österlund, Lars, 1967-, et al. (författare)
  • Photocatalytic oxide films in the built environment
  • 2014
  • Ingår i: INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices. - Institute of Physics (IOP). ; s. 012009
  • Konferensbidrag (refereegranskat)abstract
    • The possibility to increase human comfort in buildings is a powerful driving force for the introduction of new technology. Among other things our sense of comfort depends on air quality, temperature, lighting level, and the possibility of having visual contact between indoors and outdoors. Indeed there is an intimate connection between energy, comfort, and health issues in the built environment, leading to a need for intelligent building materials and green architecture. Photocatalytic materials can be applied as coatings, filters, and be embedded in building materials to provide self-cleaning, antibacterial, air cleaning, deodorizing, and water cleaning functions utilizing either solar light or artificial illumination sources – either already present in buildings, or by purposefully designed luminaries. Huge improvements in indoor comfort can thus be made, and also alleviate negative health effects associated with buildings, such as the sick-house syndrome. At the same time huge cost savings can be made by reducing maintenance costs. Photocatalytic oxides can be chemical modified by changing their acid-base surface properties, which can be used to overcome deactivation problems commonly encountered for TiO2 in air cleaning applications [2, 3]. In addition, the wetting properties oxides can be tailored by surface chemical modifications and made e.g. oleophobic and water repellent [5]. Here we show results of surface acid modified TiO2 coatings on various substrates. In particular, we show that advanced surface treatment of photocatalytic cement yields surfaces with beneficial self-cleaning properties by means of photo-fixation of surface sulfate groups. We propose that such approaches are feasible for a number of applications in the built environment, including windows, tiles, sheet metals, plastics, etc.
3.
  • Midya, Surajit, et al. (författare)
  • Pantograph Arcing in Electrified Railways-Mechanism and Influence of Various Parameters-Part I : With DC Traction Power Supply
  • 2009
  • Ingår i: IEEE Transactions on Power Delivery. - 0885-8977. ; 24:4, s. 1931-1939
  • Tidskriftsartikel (refereegranskat)abstract
    • Pantograph arcing is a common phenomenon in electrified railway systems. This is also a source of broadband-conducted and radiated electromagnetic interference (EMI) for vehicle as well as traction power and signaling systems. In this paper and the companion paper, experimental analyses of pantograph arcing phenomena are presented for dc and ac feeding systems, respectively. Influences of different parameters on dc traction system, such as supply-voltage polarity, relative motion between pantograph and overhead contact wire, namely, forward motion along the track (longitudinal), and lateral sliding motion of the pantograph (zigzag) are presented here. From the voltage and current waveforms of the test runs, it is shown that pantograph arcing is a polarity-dependent phenomenon. For the positive-fed overhead traction system, where pantograph is cathode, the supply interruptions due to zigzag motion are comparatively less compared to negatively fed traction systems. As a result, the transients, due to pantograph arcing, are more frequent in negatively fed traction systems. It is found that the arc root movement along the electrode surfaces (pantograph-contact wire) is governed by the relative motion and polarity of the electrodes. The analyses presented in this paper also form a foundation to understand the pantograph arcing process and the corresponding influential parameters with the ac supply presented in the companion paper. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the EMI due to pantograph arcing in dc-fed traction systems.
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4.
  • Midya, Surajit, et al. (författare)
  • Pantograph Arcing in Electrified Railways-Mechanism and Influence of Various Parameters-Part II : With AC Traction Power Supply
  • 2009
  • Ingår i: IEEE Transactions on Power Delivery. - 0885-8977. ; 24:4, s. 1940-1950
  • Tidskriftsartikel (refereegranskat)abstract
    • Pantograph arcing with ac supply generates transients, cause asymmetries and distortion in supply voltage and current waveforms and can damage the pantograph and the overhead contact line. The asymmetry generates a net dc component and harmonics, which propagate within the traction power and signalling system and causes electromagnetic interference. Unlike dc-fed systems (Part I), the arcing in ac supply is complex because of the zero crossing of currents and voltages. In this paper, we discuss the mechanisms of sliding contact and arcing between pantograph-contact wire using the experimental setup described in Part I. Influences of various parameters and test conditions on arcing phenomenon and their signature patterns on the supply voltage and current waveforms are presented. It is shown how the arcing mechanism and corresponding asymmetry in the voltage and current waveforms are governed by line speed, current, supply voltage, inductive load, and pantograph material. The asymmetry in the current waveform is mainly due to the difference in the duration of successive zero-current regions and uneven distortion of the waveshapes. This, in turn, creates the asymmetry in the voltage waveform. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the electromagnetic interference due to pantograph arcing in ac traction systems.
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5.
  • Özcelikkale, Ayca, et al. (författare)
  • Transmission Strategies for Remote Estimation with an Energy Harvesting Sensor
  • 2017
  • Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276. ; 16:7, s. 4390-4403
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider the remote estimation of a time-correlated signal using an energy harvesting (EH) sensor. The sensor observes the unknown signal and communicates its observations to a remote fusion center using an amplify-and-forward strategy. We consider the design of optimal power allocation strategies in order to minimize the mean-square error at the fusion center. Contrary to the traditional approaches, the degree of correlation between the signal values constitutes an important aspect of our formulation. We provide the optimal power allocation strategies for a number of illustrative scenarios. We show that the most majorized power allocation strategy, i.e. the power allocation as balanced as possible, is optimal for the cases of circularly wide-sense stationary (c.w.s.s.) signals with a static correlation coefficient, and sampled low-pass c.w.s.s. signals for a static channel. We show that the optimal strategy can be characterized as a water-filling type solution for sampled low-pass c.w.s.s. signals for a fading channel. Motivated by the high-complexity of the numerical solution of the optimization problem, we propose low-complexity policies for the general scenario. Numerical evaluations illustrate the close performance of these low-complexity policies to that of the optimal policies, and demonstrate the effect of the EH constraints and the degree of freedom of the signal.
6.
  • Renman, Viktor, et al. (författare)
  • Structural-electrochemical relations in the aqueous copper hexacyanoferrate-zinc system examined by synchrotron X-ray diffraction
  • 2017
  • Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 369, s. 146-153
  • Tidskriftsartikel (refereegranskat)abstract
    • The storage process of Zn2+ in the Prussian blue analogue (PBA) copper hexacyanoferrate (Cu[Fe(CN)6]2/3-nH2O - CuHCF) framework structure in a context of rechargeable aqueous batteries is examined by means of in operando synchrotron X-ray diffraction. Via sequential unit-cell parameter refinements of time-resolved diffraction data, it is revealed that the step-profile of the cell output voltage curves during repeated electrochemical insertion and removal of Zn2+ in the CuHCF host structure is associated with a non-linear contraction and expansion of the unit-cell in the range 0.36 < x < 1.32 for Znx/3Cu[Fe(CN)6]2/3-nH2O. For a high insertion cation content there is no apparent change in the unit-cell contraction. Furthermore, a structural analysiswith respect to the occupancies of possible Zn2+ sites suggests that the Fe(CN)6 vacancies within the CuHCF framework play an important role in the structural-electrochemical behavior of this particular system. More specifically, it is observed that Zn2+ swaps position during electrochemical cycling, hopping between cavity sites to vacant ferricyanide sites.
7.
  • Russell, Camilla, et al. (författare)
  • Gold Nanowire Based Electrical DNA Detection Using Rolling Circle Amplification
  • 2014
  • Ingår i: ACS Nano. - 1936-0851 .- 1936-086X. ; 8:2, s. 1147-1153
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an electrical sensor that uses rolling circle amplification (RCA) of DNA to stretch across the gap between two electrodes, interact with metal nanoparticle seeds to generate an electrically conductive nanowire, and produce electrical signals upon detection of specific target DNA sequences. RCA is a highly specific molecular detection mechanism based on DNA probe circularization. With this technique, long single-stranded DNA with simple repetitive sequences are produced. Here we show that stretched RCA products can be metalized using silver or gold solutions to form metal wires. Upon metallization, the resistance drops from T Omega to k Omega for silver and to Omega for gold. Metallization is seeded by gold nanoparticles aligned along the single-stranded DNA product through hybridization of functionalized oligonucleotides. We show that combining RCA with electrical DNA detection produces results in readout with very high signal-to-noise ratio, an essential feature for sensitive and specific detection assays. Finally, we demonstrate detection of 10 ng of Escherichia coli genomic DNA using the sensor concept.
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8.
  • Sun, Weiwei, et al. (författare)
  • A new 2D monolayer BiXene, M2C (M = Mo, Tc, Os)
  • 2016
  • Ingår i: Nanoscale. - 2040-3364 .- 2040-3372. ; 8:34, s. 15753-15762
  • Tidskriftsartikel (refereegranskat)abstract
    • The existence of BiXenes, a new family of 2D monolayers, is hereby predicted. Theoretically, BiXenes have 1H symmetry (P (6) over bar m2) and can be formed from the 4d/5d binary carbides. As the name suggests, they are close relatives of MXenes, which instead have 1T symmetry (P (3) over bar m1). The newly found BiXenes, as well as some new MXenes, are shown to have formation energies close to that of germanene, which suggests that these materials should be possible to be synthesised. Among them, we illustrate that 1H-Tc2C and 1T-Mo2C are dynamically stable at 0 K, while 1H-Mo2C, 1T-Tc2C, 1H-Os2C, and 1T-Rh2C are likely to be stabilised via strain or temperature. In addition, the nature of the chemical bonding is analysed, emphasizing that the covalency between the transition metal ions and carbon is much stronger in BiXenes than in MXenes. The emergence of BiXenes can not only open up a new era of conducting 2D monolayers, but also provide good candidates for carrier materials aimed at energy storage and spintronic devices that have already been unveiled in MXenes.
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