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.

We have measured the tunnelingI–V characteristics of Al-oxide-Al superconducting tunnel junctions in the presence of pair-breaking microwaves, ħω>2Δ. The junctions show an excess current below a bias of 2Δ/e. Photon-assisted tunneling (ħω>2Δ) may account for the excess current.

Superconducting tunneling in a pair-breaking microwave field

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A case study of a world-class research project accomplished in China: discovery of the quantum anomalous Hall effect

GeAu films operating near the metal insulator transition are ideally suited for high magnetic field thermometry. Until now, difficulties in fabrication, unpredictable temperature responsivity and their inherently high impedances(R up to 100M ohms) have prevented their uses as fast heat pulse detectors. It has been found [1] that within a narrow window of Au concentration that these films have excellent temperature responses. However, these concentrations were determined by Rutherford backscattering after fabrication. Variations on either side of this window resulted in films that are metallic(small R(T)) or insulating (exceedingly large resistances). In addition the responsivity was strongly dependent on whether or not these films were amorphous or polycrystalline.

Fast Response GeAu Heat Pulse Bolometers for Use in Ballistic Phonon, High Magnetic Field Experiments

A knowledge of the vibration spectrum in GaAs is of importance for explaining a variety of phonon transport and scattering experiments. [1] Recently two-phonon Raman Scattering [2] has been used to probe the non-equilibrium phonon population of optically excited GaAs. This work has led to the most precise determination of the phonon spectrum at the critical points of GaAs. It is therefore appropriate to fit the parameters of a lattice vibration model by comparing the computed two-phonon density of states against the experimental Raman data. The comparison is presented here for both the overtones and the sum and difference frequency combinations. Although calculations have been previously presented [3] for overtones in GaAs, we are not aware of any calculations for the combinations. The latter, particularly the difference frequencies, provide the most sensitive and rigorous test of the analysis. Finally, the model can then be used to compute the one-phonon spectrum for comparison with neutron scattering results and for calculating transport properties.

Raman Scattering and the Two-Phonon Density of States in GaAs

Our current study focuses on an analysis of the ballistic electron emission microscopy (BEEM) spectra of Au/(AlGa)As heterostructures to estimate quantitatively the effect of the carrier scattering in the metal, at the metal-semiconductor (m-s) interface and in the semiconductor on the multivalley carrier transport. The second derivative (SD)-BEEM spectra, representing the heterostructure transmission coefficient, show explicit partitioning of the contribution of different transport channels (Γ, L and X conduction valleys). Our analysis of SD-BEEM spectra by the developed theoretical model indicates that about 85–92% of the BEEM electrons are scattered at the nonepitaxial Au/GaAs interface. We also show that initial electron distribution among the conduction bands of the semiconductor, specified by the m-s interface scattering, is modified by the further hot-electron transport inside the semiconductor.

Venkatesh Narayanamurti

Papers

Superconducting tunneling in a pair-breaking microwave field

A case study of a world-class research project accomplished in China: discovery of the quantum anomalous Hall effect

Fast Response GeAu Heat Pulse Bolometers for Use in Ballistic Phonon, High Magnetic Field Experiments

Raman Scattering and the Two-Phonon Density of States in GaAs

Second Derivative Ballistic Electron Emission Spectroscopy in Au/(AlGa)As