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

The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

/pdf/a-comprehensive-review-of-zno-materials-and-devices-21a3zjadem.pdf

A comprehensive review of zno materials and devices

Additive manufacturing of metallic components – Process, structure and properties

Zinc oxide is a unique material that exhibits semiconducting and piezoelectric dual properties. Using a solid–vapour phase thermal sublimation technique, nanocombs, nanorings, nanohelixes/nanosprings, nanobelts, nanowires and nanocages of ZnO have been synthesized under specific growth conditions. These unique nanostructures unambiguously demonstrate that ZnO probably has the richest family of nanostructures among all materials, both in structures and in properties. The nanostructures could have novel applications in optoelectronics, sensors, transducers and biomedical sciences. This article reviews the various nanostructures of ZnO grown by the solid–vapour phase technique and their corresponding growth mechanisms. The application of ZnO nanobelts as nanosensors, nanocantilevers, field effect transistors and nanoresonators is demonstrated.

/pdf/zinc-oxide-nanostructures-growth-properties-and-applications-8d5hcz3lg8.pdf

Zinc oxide nanostructures: growth, properties and applications

There is a widespread discussion concerning the ‘better’ wavelength for laser ablation chemical analysis. Wavelength is believed to be an important parameter based on the sample’s optical penetration depth as well as photon energy for bond breaking. The lasers most widely employed for analytical applications are the excimer, based on an ArF mixture with a wavelength of 193 nm, and the solid state Nd:YAG, with wavelengths of 266 nm and 213 nm. NIST glasses were ablated to test the effects of these wavelengths on fractionation and transport efficiency. Crater geometry and volume were measured by using a white-light interference microscope. For all three wavelengths, linear calibration curves were obtained using NIST glasses as standards. The 208Pb/238U ratio in a tuff rock sample was measured using all three wavelengths; the value obtained using the NIST-glass calibration was compared to that measured using liquid nebulization.

Comparison of 193, 213 and 266 nm laser ablation ICP-MS

The influence of plasma shielding on the coupling of laser energy to a target surface during picosecond pulsed laser–material interactions is demonstrated using a He and Ar gas atmosphere. An inductively coupled plasma‐atomic emission spectrometer (ICP‐AES) is used to monitor the quantity of copper material removed during picosecond and nanosecond pulsed‐laser sampling. The intensity of Cu i emission from the ICP‐AES was found to be 16.4 times larger with He as the gas medium compared to Ar during picosecond laser sampling. It was also observed that depth of craters in the copper targets decreased as the gas pressure was increased beyond 10 Torr in Ar and 100 Torr in He. Possible mechanisms of shock waves, multiphoton ionization, and plasma shielding to explain these observations are discussed. For plasma shielding to occur in the picosecond time regime, the existence of high‐energy photoelectrons emitted from a Cu sample during the leading edge of laser pulse is postulated. These electrons form a plasma ...

Plasma shielding during picosecond laser sampling of solid materials by ablation in He versus Ar atmosphere

Preferential vaporization and plasma shielding during nano-second laser ablation

A probe beam deflection technique was utilized to measure the propagation of a shock wave and material vapour plume generated during excimer laser ablation of aluminium samples. The measured transit time of the laser-induced shock wave was compared with the prediction based on an ideal blast-wave model, using the Sedov-Taylor solution. The prediction of the incident laser energy converted into the laser-induced gasdynamic flow utilizing this blast-wave model overestimated the efficiency, even under conditions when the measured shock-wave velocity follows the correct model relation. The propagation of material vapour was measured from the deflection of the probe beam at later times. The propagation velocity of material vapour ranged from 20-40 m s-1 with a greater velocity near the target surface.

https://iopscience.iop.org/article/10.1088/0022-3727/32/19/316/pdf

Shock wave and material vapour plume propagation during excimer laser ablation of aluminium samples

The Zn-to-Cu ratio in brass was measured by laser ablation inductively coupled plasma atomic emission spectroscopy. The influence of laser beam properties (pulse width, wavelength, and power density) on fractional laser ablation was investigated. The behavior of the Zn/Cu ratio vs. laser power density shows that there are different mechanisms influencing ps and ns laser ablation. With the use of a 30 ns pulse duration from an excimer laser, thermal vaporization appears to be the dominant process in the low-power density region. The Zn/Cu ratio approaches stoichiometry at higher power density, but the ablated mass still remains Zn rich. With a 35 ps pulse Nd:YAG laser, a nonthermal mechanism appears to govern the laser ablation process. When a 3 ns Nd:YAG laser is used, both thermal and nonthermal processes exist. For both 3 ns and 30 ps Nd:YAG lasers, stoichiometric ablation can be achieved at higher power densities.

Richard E. Russo

Papers

Comparison of 193, 213 and 266 nm laser ablation ICP-MS

Plasma shielding during picosecond laser sampling of solid materials by ablation in He versus Ar atmosphere

Preferential vaporization and plasma shielding during nano-second laser ablation

Shock wave and material vapour plume propagation during excimer laser ablation of aluminium samples

Preferential Vaporization during Laser Ablation Inductively Coupled Plasma Atomic Emission Spectroscopy