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 …

I and i

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.

Fast parallel algorithms for short-range molecular dynamics

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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。

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

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.

/pdf/complex-thermoelectric-materials-59e25n2qme.pdf

Complex thermoelectric materials.

Thermoelectric figure of merit of bulk FeSi2–Si0.8Ge0.2 nanocomposite and a comparison with β-FeSi2

In this research, water-soluble thioglycolic acid-capped ZnS quantum dots (QDs) are synthesized by the chemical precipitation method. The prepared QDs are characterized using x-ray diffraction and transmission electron microscopy. Results revealed that ZnS QDs have a 2.73 nm crystallite size, cubic zinc blende structure, and spherical morphology with a diameter less than 10 nm. Photoluminescence (PL) spectroscopy is performed to determine the presence of low concentrations of starch. Four emission peaks are observed at 348 nm, 387 nm, 422 nm, and 486 nm and their intensities are quenched by increasing concentration of starch. PL intensity variations in the studied concentrations range (0–100 ppm) are best described by a Michaelis–Menten model. The Michaelis constant (K
 m) for immobilized α-amylase in this system is about 101.07 ppm. This implies a great tendency for the enzyme to hydrolyze the starch as substrate. Finally, the limit of detection is found to be about 6.64 ppm.

Synthesis, Surface Modification and Optical Properties of Thioglycolic Acid-Capped ZnS Quantum Dots for Starch Recognition at Ultralow Concentration

Thin film thermoelectric coolers are advantageous for their high cooling power density and their potential integrated applications. Si/sub 1-x/Ge/sub x/ is a good thermoelectric material at high temperatures and superlattice structures can further enhance the device performance. Si/sub 1-x/Ge/sub x/ and Si/sub 1-x/Ge/sub x//Si superlattice structures were grown on Si substrates using molecule beam epitaxy. Si/sub 1-x/Ge/sub x/ and Si/sub 1-x/Ge/sub x//Si superlattice thin film microcoolers with film thickness of the order of several microns were fabricated using integrated circuit processing technology. Micro thermocouples and integrated thermistor sensors were used to characterize these coolers. Maximum cooling power density on the order of hundreds of watts per square centimeter was measured at room temperature. It is possible to monolithically integrate these coolers with Si-based microelectronic devices for localized cooling and temperature stabilization.

http://ieeexplore.ieee.org/iel5/7701/21085/00979917.pdf

Integrated cooling for Si-based microelectronics

It is known that the random orientation of crystallites in polycrystalline Bi0.5Sb1.5Te3 reduces its thermoelectric power factor. An efficient method for growing ordered bulk polycrystalline Bi0.5Sb1.5Te3 was used and the enhancement of thermoelectric power factor was demonstrated. For comparison, samples with randomly and preferentially oriented crystallites were sintered from similar powder of Bi0.5Sb1.5Te3. A press process similar to extrusion was used to align the crystallites during the hot press. The crystallites alignment was verified by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dominant orientation in the aligned sample was in c-plane (0,0,15). The aligned sample demonstrated significant increase in electrical conductivity while the Seebeck coefficient remained unchanged. As a result, the thermoelectric power factor of the aligned sample was improved by ∼50%.

Enhancement in thermoelectric power factor of polycrystalline Bi0.5Sb1.5Te3 by crystallite alignment

The effect of hot carriers on the cooling performance of single barrier heterostructure thermionic coolers is studied theoretically. By studying nonequilibrium characteristics of electrons and phonons in the device, fundamental limitation in the cooler performance is analyzed. In particular, we investigated the effect of various boundary conditions at heterojunctions on the electron and phonon temperature distributions. These boundary conditions have a strong impact on the device operation. Thin film devices under high voltage or in high current density are examples of situations where electrons and phonons are not in equilibrium and a coupled transport equation should be solved for an accurate analysis. In a thermoelectric/thermionic device one measures the lattice temperature while cooling occurs in the electron gas. Although at low currents electrons and phonons have the same equilibrium temperature, by increasing the current they may have different temperatures, which can lead to a reduction in coolin...

Daryoosh Vashaee

Papers

Thermoelectric figure of merit of bulk FeSi2–Si0.8Ge0.2 nanocomposite and a comparison with β-FeSi2

Synthesis, Surface Modification and Optical Properties of Thioglycolic Acid-Capped ZnS Quantum Dots for Starch Recognition at Ultralow Concentration

Integrated cooling for Si-based microelectronics

Enhancement in thermoelectric power factor of polycrystalline Bi0.5Sb1.5Te3 by crystallite alignment

Nonequilibrium electrons and phonons in thin film thermionic coolers