| 41. |
- Abbas, Zareen, 1962, et al.
(författare)
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Monte Carlo Simulations of Salt Solutions: Exploring the Validity of Primitive Models
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:17, s. 5905-5916
-
Tidskriftsartikel (refereegranskat)abstract
- An extensive series of Monte Carlo (MC) simulations were performed in order to explore the validity of simple primitive models of electrolyte solutions and in particular the effect of ion size asymmetry on the bulk thermodynamic properties of real salt solutions. Ionic activity and osmotic coefficients were calculated for 1:1, 2:1, and 3:1 electrolytes by using the unrestricted primitive model (UPM); i.e., ions are considered as charged hard spheres of different sizes dissolved in a dielectric continuum. Mean ionic activity and osmotic coefficients calculated by the MC simulations were fitted simultaneously to the experimental data by adjusting only the cation radius while keeping the anion radius fixed at its crystallographic value. Ionic radii were further optimized by systematically varying the cation and anion radii at a fixed sum of ionic radii. The success of this approach is found to be highly salt specific. For example, experimental data (mean ionic activity and osmotic coefficients) of salts which are usually considered as dissociated such as HCl, HBr, LiCl, LiBr, LiClO4, and KOH were successfully fitted up to 1.9, 2.5, 1.9, 3, 2.5, and 4.5 M concentrations, respectively. In the case of partially dissociated salts such as NaCl, the successful fits were only obtained in a more restricted concentration range. Consistent sets of the best fitted cation radii were obtained for acids, alkali, and alkaline earth halides. A list of recommended ionic radii is also provided. The reliability of the optimized ionic radii was further tested in simulations of the osmotic coefficients of LiCl−NaCl−KCl salt mixtures. A very good agreement between the simulated and experimental data was obtained up to ionic strength of 4.5 M.
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| 42. |
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| 43. |
- Abbas, Zareen, 1962, et al.
(författare)
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Size-Dependent Surface Charging of Nanoparticles
- 2008
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Ingår i: J of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:15, s. 5715-5723
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental interest in the possible curvature dependence of particle charging in electrolyte solutions is subjected to theoretical analysis. The corrected Debye-Hückel theory of surface complexation (CDH-SC) and Monte Carlo (MC) simulation are applied to investigate the dependence of surface charging of metal oxide nanoparticles on their size. Surface charge density versus pH curves for spherical metal oxide nanoparticles in the size range of 1-100 nm are calculated at various concentrations of a background electrolyte. The surface charge density of a nanoparticle is found to be highly size-dependent. As the particle diameter drops to below 10 nm there is considerable increase in the surface charge density as compared with the limiting values seen for particles larger than 20 nm. This increase in the surface charge density is due to the enhanced screening efficiency of the electrolyte solution around small nanoparticles, which is most prominent for particles of diameters less than 5 nm. For example, the surface charge densities calculated for 2 nm particles at 0.1 M concentration are very close to the values obtained for 100 nm particles at 1 M concentration. These predictions of the dependence of surface charge density on particle size by the CDH-SC theory are in very good agreement with the corresponding results obtained by the MC simulations. A shift in the pH value of the point of zero charge toward higher pH values is also seen with a decreasing particle size.
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| 44. |
- Abbasi, Morteza, 1982, et al.
(författare)
-
A Broadband 60-to-120 GHz single-chip MMIC multiplier chain
- 2009
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. ; , s. 441-444
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a single-chip 60 GHz to 120 GHz frequency multiplier chain based on 0.1 ?m GaAs mHEMT. The MMIC can deliver 3 to 5 dBm of output power from 110 GHz to 130 GHz with 2 dBm input power and consumes only 65 mW of DC power. The signal at the fundamental frequency is suppressed more than 20 dB over the band of interest. The impedance matching networks are realized using coupled transmission lines.
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| 45. |
- Abbasi, Morteza, 1982, et al.
(författare)
-
An E-Band(71-76, 81-86 GHz) Balanced Frequency Tripler for High-Speed Communications
- 2009
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Ingår i: APMC: 2009 ASIA PACIFIC MICROWAVE CONFERENCE. - 9781424428014 ; 1-5, s. 1184-1187
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An E-Band transistor-based balanced frequency tripler is implemented using a 0.15 mu m GaAs mHEMT process which can be integrated into a single-chip RF front-end. The balanced configuration with 90 degrees hybrids at the input and output improves the port impedance matching which is measured to be better than 15 dB at the input and 10 dB at the output over the frequencies of interest. The tripler has a conversion loss of 11.5 dB from 71 GHz to 76 GHz and 14 dB from 81 GHz to 86 GHz. The second and forth harmonics are suppressed by more than 30 dB and the fundamental frequency by 20 dB. The tripler can deliver -2 dBm output power.
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| 46. |
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| 47. |
- Abbasi, Morteza, 1982, et al.
(författare)
-
Single-Chip Frequency Multiplier Chains for Millimeter-Wave Signal Generation
- 2009
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 57:12, s. 3134-3142
-
Tidskriftsartikel (refereegranskat)abstract
- Two single-chip frequency multiplier chains targeting 118 and 183 GHz output frequencies are presented. The chips are fabricated in a 0.1 mu m GaAs metamorphic high electron-mobility transistor process. The D-band frequency doubler chain covers 110 to 130 GHz with peak output power of 5 dBm. The chip requires 2 dBm input power and consumes only 65 mW of dc power. The signal at the fundamental frequency is suppressed more than 25 dB compared to the desired output signal over the band of interest. The G-band frequency sextupler (x6) chain covers 155 to 195 GHz with 0 dBm peak output power and requires 6.5 dBm input power and 92.5 mW dc power. The input signal to the multiplier chain can be reduced to 4 dBm while the output power drops only by 0.5 dB. The unwanted harmonics are suppressed more than 30 dB compared to the desired signal. An additional 183 GHz power amplifier is presented to be used after the x6 frequency multiplier chain if higher output power is required. The amplifier delivers 5 dBm output power with a small-signal gain of 9 dB from 155 to 195 GHz. The impedance matching networks are realized using coupled transmission lines which is shown to be a scalable and straightforward structure to use in amplifier design. Microstrip transmission lines are used in all the designs.
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| 48. |
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| 49. |
- Abdelzaher, T., et al.
(författare)
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The aperiodic multiprocessor utilization bound for liquid tasks
- 2002
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Ingår i: 8th IEEE Real-Time and Embedded Technology and Applications Symposium, 2002. Proceedings. - 1545-3421. - 0769517390 ; , s. 173-184
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Konferensbidrag (refereegranskat)abstract
- Real-time scheduling theory has developed powerful tools for translating conditions on aggregate system utilization into per-task schedulability guarantees. The main breakthrough has been Liu and Layland's utilization bound for schedulability of periodic tasks. In 2001 this bound was generalized by Abdelzaher and Lu to the aperiodic task case. In this paper we further generalize the aperiodic bound to the case of multiprocessors, and present key new insights into schedulability, analysis of aperiodic tasks. We consider a special task model, called the liquid task model, representative of high-performance servers with aperiodic workloads, such as network routers, web servers, proxies, and real-time databases. For this model, we derive the optimal multiprocessor utilization bound, defined on a utilization-like metric we call "synthetic utilization". This bound allows developing constant-time admission control tests that provide utilization-based absolute delay, tees. We show that the real utilization of admitted tasks can be close to unity even when synthetic utilization is kept below the bound. Thus, our results lead to multiprocessor systems which combine constant-time admission control with high utilization while making no periodicity assumptions regarding the task arrival pattern.
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| 50. |
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