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

Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

http://pubs.acs.org/doi/pdf/10.1021/cr1002326

Solar Water Splitting Cells

2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Semiconductor-based Photocatalytic Hydrogen Generation

Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

Solar cells are attractive candidates for clean and renewable power; with miniaturization, they might also serve as integrated power sources for nanoelectronic systems. The use of nanostructures or nanostructured materials represents a general approach to reduce both cost and size and to improve efficiency in photovoltaics. Nanoparticles, nanorods and nanowires have been used to improve charge collection efficiency in polymer-blend and dye-sensitized solar cells, to demonstrate carrier multiplication, and to enable low-temperature processing of photovoltaic devices. Moreover, recent theoretical studies have indicated that coaxial nanowire structures could improve carrier collection and overall efficiency with respect to single-crystal bulk semiconductors of the same materials. However, solar cells based on hybrid nanoarchitectures suffer from relatively low efficiencies and poor stabilities. In addition, previous studies have not yet addressed their use as photovoltaic power elements in nanoelectronics. Here we report the realization of p-type/intrinsic/n-type (p-i-n) coaxial silicon nanowire solar cells. Under one solar equivalent (1-sun) illumination, the p-i-n silicon nanowire elements yield a maximum power output of up to 200 pW per nanowire device and an apparent energy conversion efficiency of up to 3.4 per cent, with stable and improved efficiencies achievable at high-flux illuminations. Furthermore, we show that individual and interconnected silicon nanowire photovoltaic elements can serve as robust power sources to drive functional nanoelectronic sensors and logic gates. These coaxial silicon nanowire photovoltaic elements provide a new nanoscale test bed for studies of photoinduced energy/charge transport and artificial photosynthesis, and might find general usage as elements for powering ultralow-power electronics and diverse nanosystems.

http://www.eecs.umich.edu/zhonglab/pub/NW_Solar_Lieber.pdf

Coaxial silicon nanowires as solar cells and nanoelectronic power sources

A device physics model has been developed for radial p-n junction nanorod solar cells, in which densely packed nanorods, each having a p-n junction in the radial direction, are oriented with the rod axis parallel to the incident light direction. High-aspect-ratio (length/diameter) nanorods allow the use of a sufficient thickness of material to obtain good optical absorption while simultaneously providing short collection lengths for excited carriers in a direction normal to the light absorption. The short collection lengths facilitate the efficient collection of photogenerated carriers in materials with low minority-carrier diffusion lengths. The modeling indicates that the design of the radial p-n junction nanorod device should provide large improvements in efficiency relative to a conventional planar geometry p-n junction solar cell, provided that two conditions are satisfied: (1) In a planar solar cell made from the same absorber material, the diffusion length of minority carriers must be too low to allow for extraction of most of the light-generated carriers in the absorber thickness needed to obtain full light absorption. (2) The rate of carrier recombination in the depletion region must not be too large (for silicon this means that the carrier lifetimes in the depletion region must be longer than ~10 ns). If only condition (1) is satisfied, the modeling indicates that the radial cell design will offer only modest improvements in efficiency relative to a conventional planar cell design. Application to Si and GaAs nanorod solar cells is also discussed in detail.

/pdf/comparison-of-the-device-physics-principles-of-planar-and-2f89xq46rb.pdf

Comparison of the device physics principles of planar and radial p-n junction nanorod solar cells

Single-nanowire solar cells were created by forming rectifying junctions in electrically contacted vapor-liquid-solid-grown Si nanowires. The nanowires had diameters in the range of 200 nm to 1.5 microm. Dark and light current-voltage measurements were made under simulated Air Mass 1.5 global illumination. Photovoltaic spectral response measurements were also performed. Scanning photocurrent microscopy indicated that the Si nanowire devices had minority carrier diffusion lengths of approximately 2 microm. Assuming bulk-dominated recombination, this value corresponds to a minimum carrier lifetime of approximately 15 ns, or assuming surface-dominated recombination, to a maximum surface recombination velocity of approximately 1350 cm s(-1). The methods described herein comprise a valuable platform for measuring the properties of semiconductor nanowires, and are expected to be instrumental when designing an efficient macroscopic solar cell based on arrays of such nanostructures.

Photovoltaic Measurements in Single-Nanowire Silicon Solar Cells

Alta Devices, Inc. has fabricated a thin-film GaAs device on a flexible substrate with an independently-confirmed solar energy conversion efficiency of 27.6%, under AM1.5G solar illumination at 1 sun intensity. This represents a new record for single-junction devices under non-concentrated sunlight. This surpasses the previous record, for conversion efficiency of a single-junction device under non-concentrated light, by more than 1%. This is due largely to the high open-circuit voltage (V oc ) of this device. The high V oc results from precise control of the dark current. The fact that this record result has been achieved with a thin-film shows that, for GaAs material systems, the majority of the growth substrate is not needed for device performance. This allows one to consider amortizing the potentially high cost of a GaAs growth substrate by growing a thin-film, lifting it off, and reusing the same substrate multiple times. This technology therefore has the potential to be a novel high-performance, thin-film option for terrestrial photovoltaics.

27.6% Conversion efficiency, a new record for single-junction solar cells under 1 sun illumination

Arrays of vertically oriented Si wires with diameters of 1.5 µm and lengths of up to 75 µm were grown over areas >1 cm^2 by photolithographically patterning an oxide buffer layer, followed by vapor-liquid-solid growth with either Au or Cu as the growth catalyst. The pattern fidelity depended critically on the presence of the oxide layer, which prevented migration of the catalyst on the surface during annealing and in the early stages of wire growth. These arrays can be used as the absorber material in novel photovoltaic architectures and potentially in photonic crystals in which large areas are needed.

/pdf/growth-of-vertically-aligned-si-wire-arrays-over-large-areas-57vayhh2ex.pdf

Growth of vertically aligned Si wire arrays over large areas (>1 cm^2) with Au and Cu catalysts

In this letter, vertical GaN transistors fabricated on bulk GaN substrates are discussed. A threshold voltage of 0.5 V and saturation current >2.3 A are demonstrated. The measured devices show breakdown voltages of 1.5 kV and specific ON-resistance of 2.2 mΩ-cm
 2
, which translates to a figure-of-merit of V
 BR
 2
/R
 ON
 ~1 × 10
 9
 V
 2
 Ω
 -1
 · cm
 -2
.

Brendan M. Kayes

Papers

Comparison of the device physics principles of planar and radial p-n junction nanorod solar cells

Photovoltaic Measurements in Single-Nanowire Silicon Solar Cells

27.6% Conversion efficiency, a new record for single-junction solar cells under 1 sun illumination

Growth of vertically aligned Si wire arrays over large areas (>1 cm^2) with Au and Cu catalysts

1.5-kV and 2.2-m \(\Omega \) -cm \(^{2}\) Vertical GaN Transistors on Bulk-GaN Substrates