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

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

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Spintronics: Fundamentals and applications

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then-despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of approximately 2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.

Thin-film thermoelectric devices with high room-temperature figures of merit

In 1974 an article appeared in Science magazine with the dry-sounding title “Judgment Under Uncertainty: Heuristics and Biases” by a pair of psychologists who were not well known outside their discipline of decision theory. In it Amos Tversky and Daniel Kahneman introduced the world to Prospect Theory, which mapped out how humans actually behave when faced with decisions about gains and losses, in contrast to how economists assumed that people behave. Prospect Theory turned Economics on its head by demonstrating through a series of ingenious experiments that people are much more concerned with losses than they are with gains, and that framing a choice from one perspective or the other will result in decisions that are exactly the opposite of each other, even if the outcomes are monetarily the same. Prospect Theory led cognitive psychology in a new direction that began to uncover other human biases in thinking that are probably not learned but are part of our brain’s wiring.

Thinking fast and slow.

Passive iron-oxide nanocrystals are grown on Fe(100) and Fe(110) facets of single-crystal Fe whiskers. Transmission electron microscopy and electron diffraction characterize the oxide spinel structure and their epitaxial growth on Fe whiskers. Iron-oxide nanocrystals grown on Fe(100) facets have sizes close to that of the single magnetic domain Fe3O4 particles, which is supported by our preliminary magnetic force microscopy measurement at room temperature.

Characterization of spinel iron-oxide nanocrystals grown on Fe whiskers

We present a quantitative study of the second voltage derivative (SD) of ballistic electron emission spectra of Au/GaAs/AlGaAs heterostructures to probe the effect of electron scattering on these spectra. Our analysis of the SD spectra shows that strong electron scattering occurs at the nonepitaxial Au/GaAs interface, leading to an experimentally observed redistribution of current among the electron transport channels. We also show that the effects of hot-electron scattering inside the semiconductor modify the spectra and are sensitive to the heterojunction band structure, its geometry, and temperature. {copyright} {ital 1999} {ital The American Physical Society}

Effect of Electron Scattering on Second Derivative Ballistic Electron Emission Spectroscopy in Au/GaAs/AlGaAs Heterostructures

The pressure dependence of the lowest-lying 4f→ 5d absorption band in crystalline films of YbTe, YbSe, and YbS has been studied. The absorption edge which occurs at about 1.8 eV in YbTe, 1.5 eV in YbSe, and 1.1 eV in YbS at zero pressure is shown to close at a rate of 11.0, 9.8, and 6.5 meV/kbar, respectively, for pressures up to 8 kbar. The measurements predict gap collapses in all the three chalcogenides at pressures of the order of 175 kbar, in good agreement with pressure-volumes studies and qualitative changes in the reflectivity at high pressures.

Optical absorption in ytterbium monochalcogenides under pressure

Using the heat-pulse technique, we have measured the velocity spectrum of atoms evaporating from a free liquid $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ surface. In the ballistic regime (at sufficiently low ambient temperatures) this spectrum is found to be Maxwell-Boltzmann in nature with no effects evident owing to the quasiparticle nature of the liquid. At higher vapor pressures (higher temperatures) the transition from ballistic atomic propagation to collective adiabatic sound in $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ has been studied.

Velocity Spectrum of Atoms Evaporating from a Liquid He Surface at Low Temperatures

An optical spin-valve effect is observed using sub-bandgap internal photoemission to generate and collect hot electrons in magnetic multilayers grown on n-Si. Approximately 1.5%-2.5% magnetoresistance is observed in this two-terminal device at low temperature, and this effect is reduced only to 1.1% at room temperature. A simple model is presented to explain the results.

Venkatesh Narayanamurti

Papers

Characterization of spinel iron-oxide nanocrystals grown on Fe whiskers

Effect of Electron Scattering on Second Derivative Ballistic Electron Emission Spectroscopy in Au/GaAs/AlGaAs Heterostructures

Optical absorption in ytterbium monochalcogenides under pressure

Velocity Spectrum of Atoms Evaporating from a Liquid He Surface at Low Temperatures

Spin-valve photodiode