Daryoosh Vashaee

Bio: Daryoosh Vashaee is an academic researcher from North Carolina State University. The author has contributed to research in topics: Thermoelectric effect & Thermoelectric materials. The author has an hindex of 48, co-authored 225 publications receiving 15724 citations. Previous affiliations of Daryoosh Vashaee include University of California, Santa Cruz & Oklahoma State University–Tulsa.

Thermal and Thermoelectric Properties of Nanostructured versus Crystalline SiGe

Abstract: Nearly 60% of the world's energy is wasted as heat. Thermoelectric materials can play an important role in green energy harvesting with their ability to convert waste heat into electricity. In this report, thermal and thermoelectric properties of p- type nanostructured silicon germanium (SiGe) as an important high temperature thermoelectric material was studied and compared with those of crystalline SiGe. The materials were synthesized via mechanical alloying and sintering approach. The different synthesis procedures resulted in two different conformation of SiGe. The first one was in nanostructure configuration and the other was in crystalline configuration containing large grains. Thermal and thermoelectric properties of both configurations were investigated in this manuscript. Although, differential thermal analysis (DTA) did not show significant differences between the thermal characteristics of nanostructured and crystalline SiGe, there were major changes in their thermoelectric properties. The nanostructured SiGe had lower electrical conductivity owing to the large scattering rate of electron at the grain boundaries. However, the lower mobility was accompanied by small thermal conductivity in nanostructured SiGe. The Seeback coefficient was grown in nanostructured SiGe as a result of lower carrier concentration. Considering the influence of all these factors, the nanostructured SiGe was thermoelectrically preferred as the figure-of-merit was increased specially at high temperatures.

High Cooling Power Density of SiGe/Si Superlattice Microcoolers

Abstract: : Fabrication and characterization of SiGe/Si superlattice microcoolers integrated with thin film resistors are described. Superlattice structures were used to enhance the device performance by reducing the thermal conductivity, and by providing selective emission of hot carriers through thermionic emission. Thin film metal resistors were integrated on top of the cooler devices and they were used as heat load for cooling power density measurement. Various device sizes were characterized. Net cooling over 4.1 K and a cooling power density of 598 W/cm2 for 40 x 40 mm2 devices were measured at room temperature.

High Performance Multi Barrier Thermionic Devices

Abstract: : Thermoelectric transport perpendicular to layers in multiple barrier superlattice structures is investigated theoretically in two limiting cases of no lateral momentum scattering and strong scattering In the latter regime when lateral momentum is not conserved, the number of electrons participating in thermionic emission will dramatically increase The cooling power density is calculated using Fermi-Dirac statistics, density-of-states for a finite quantum well and the quantum mechanical transmission coefficient in the superlattice Calculation results show that metallic based superlattices with tall barriers (>10 eV) can achieve a large power factor on the order of 006W/mK squared with a moderate electronic contribution to thermal conductivity of 18W/mK If the lattice contribution to thermal conductivity is on the order of 1W/mK, ZT values higher than 5 can be achieved at room temperature

Interlamellar organization of phase separated domains in multi-component lipid multilayers: energetic considerations.

Abstract: A recent experimental study [1] has demonstrated the alignment of phase separated domains across hundreds of bilayer units in multicomponent stacked lipid bilayers. The origin of this alignment is the interlamellar coupling of laterally phase separated domains. Here, we develop a theoretical model that presents the energetics description of this phenomenon based on the minimization of the free energy of the system. Specifically, we use solution theory to estimate the competition between energy and entropy in different stacking configurations. The model furnishes an elemental phase diagram, which maps the domain distributions in terms of the strength of the intra- and inter-layer interactions and estimates the value of inter-layer coupling for complete alignment of domains in the stacks of five and ten bilayers. The area fraction occupied by co-existing phases was calculated for the system of the minimum free energy, which showed a good agreement with experimental observations.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Complex thermoelectric materials.

Abstract: Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching. We review recent advances in the field, highlighting the strategies used to improve the thermopower and reduce the thermal conductivity.