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

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

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

/pdf/high-k-gate-dielectrics-current-status-and-materials-zjvba0c4u8.pdf

High-κ gate dielectrics: Current status and materials properties considerations

We propose an electron wave analog of the electro‐optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin‐orbit coupling in narrow‐gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.

Electronic analog of the electro‐optic modulator

A nanopore-based device provides single-molecule detection and analytical capabilities that are achieved by electrophoretically driving molecules in solution through a nano-scale pore. The nanopore provides a highly confined space within which single nucleic acid polymers can be analyzed at high throughput by one of a variety of means, and the perfect processivity that can be enforced in a narrow pore ensures that the native order of the nucleobases in a polynucleotide is reflected in the sequence of signals that is detected. Kilobase length polymers (single-stranded genomic DNA or RNA) or small molecules (e.g., nucleosides) can be identified and characterized without amplification or labeling, a unique analytical capability that makes inexpensive, rapid DNA sequencing a possibility. Further research and development to overcome current challenges to nanopore identification of each successive nucleotide in a DNA strand offers the prospect of 'third generation' instruments that will sequence a diploid mammalian genome for ∼$1,000 in ∼24 h.

/pdf/the-potential-and-challenges-of-nanopore-sequencing-51qxscif85.pdf

The Potential and Challenges of Nanopore Sequencing

The narrowest feature on present-day integrated circuits is the gate oxide—the thin dielectric layer that forms the basis of field-effect device structures. Silicon dioxide is the dielectric of choice and, if present miniaturization trends continue, the projected oxide thickness by 2012 will be less than one nanometre, or about five silicon atoms across1. At least two of those five atoms will be at the silicon–oxide interfaces, and so will have very different electrical and optical properties from the desired bulk oxide, while constituting a significant fraction of the dielectric layer. Here we use electron-energy-loss spectroscopy in a scanning transmission electron microscope to measure the chemical composition and electronic structure, at the atomic scale, across gate oxides as thin as one nanometre. We are able to resolve the interfacial states that result from the spillover of the silicon conduction-band wavefunctions into the oxide. The spatial extent of these states places a fundamental limit of 0.7 nm (four silicon atoms across) on the thinnest usable silicon dioxide gate dielectric. And for present-day oxide growth techniques, interface roughness will raise this limit to 1.2 nm.

The electronic structure at the atomic scale of ultrathin gate oxides

http://www.tau.ac.il/lifesci/courses/molecular_biophysics/2086.pdf

Microscopic Kinetics of DNA Translocation through synthetic nanopores.

http://www.ks.uiuc.edu/Publications/Papers/PDF/HENG2004/HENG2004.pdf

Sizing DNA using a nanometer-diameter pore.

We show that light can be used as a lens to focus a collimated neutral atomic beam to submicron dimensions during deposition onto a substrate. We have used an optical standing wave at 589 nm as an array of cylindrical lenses to focus a perpendicular sodium beam into a grating on a substrate, with a periodicity of 294.3\ifmmode\pm\else\textpm\fi{}0.3 nm. This result is the first direct evidence of submicron focusing of atoms by light, and represents a fundamentally new scheme for submicron lithography.

Using light as a lens for submicron, neutral-atom lithography.

We have produced single, synthetic nanometer-diameter pores by using a tightly focused, high-energy electron beam to sputter atoms in 10-nm-thick silicon nitride membranes. Subsequently, we measured the ionic conductance as a function of time, bath concentration, and pore diameter to infer the conductivity and ionic mobility through the pores. The pore conductivity is found to be much larger than the bulk conductivity for dilute bath concentrations, where the Debye length is larger than the pore radius, whereas it is comparable with or less than the bulk for high bath concentrations. We interpret these observations by using multiscale simulations of the ion transport through the pores. Molecular dynamics is used to estimate the ion mobility, and ion transport in the pore is described by the coupled Poisson–Nernst–Planck and the Stokes equations that are solved self-consistently for the ion concentration and velocity and electrical potential. We find that the measurements are consistent with the presence of fixed negative charge in the pore wall and a reduction of the ion mobility because of the fixed charge and the ion proximity to the pore wall.

https://www.pnas.org/content/pnas/102/30/10445.full.pdf

Gregory Timp

Papers

The electronic structure at the atomic scale of ultrathin gate oxides

Microscopic Kinetics of DNA Translocation through synthetic nanopores.

Sizing DNA using a nanometer-diameter pore.

Using light as a lens for submicron, neutral-atom lithography.

Electrolytic transport through a synthetic nanometer-diameter pore