bluuebunny/crossref_metadata_2025 huggingface dataset:
The Chemistry of Fireworks
Authors: Russell Michael
Published: January 2009

"For centuries fireworks have been a source of delight and amazement in cultures around the world. But what produces their dazzling array of effects? This book takes you behind the scenes to explore the chemistry and physics behind the art of pyrotechnics. Topics covered include history and characteristics of gunpowder; principles behind each of the most popular firework types: rockets, shells, fountains, sparklers, bangers, roman candles and wheels; special effects, including sound effects, coloured smokes and electrical firing; firework safety for private use and displays; and firework legislation. The Chemistry of Fireworks is aimed at students with A level qualifications or equivalent. The style is concise and easy to understand, and the theory of fireworks is discussed in terms of well-known scientific concepts wherever possible. It will also be a useful source of reference for anyone studying pyrotechnics as applied to fireworks. Review Extracts ""a worthwhile addition to the pyrotechnist's library"" Fireworks ""a useful source of information which makes absorbing reading."" Angewandte Chemie, International Edition"
Human calcium/calmodulin-dependent serine protein kinase regulates the expression of p21 via the E2A transcription factor
Authors: Sun Rongju , Su Yongyue , Zhao Xiaodong , Qi Jie , Luo Xiaofeng , Yang Zongcheng , Yao Yongming , LUO Xiangdong , Xia Zhaofan
Published: January 2009

CASK (calcium/calmodulin-dependent serine protein kinase) is a kind of scaffolding protein that recruits or organizes other proteins at the plasma membrane to co-ordinate signal transduction pathways within the cytoplasm and nucleus. We have previously found that hCASK (human CASK) binds Id1 (inhibitor of DNA binding 1) through hCASK's GUK (guanylate kinase) domain and inhibits cell growth, probably via interactions with Id1. Overexpression of hCASK resulted in a reduced rate of cell growth, although inhibition of CASK via RNAi (RNA interference) promoted cell proliferation in ECV304 cells. This study revealed that hCASK regulates the protein and mRNA level of p21wafi/cip1 (referred to throughout as p21), and activated the expression of p21 in a time-dependent manner. Two E-boxes in the proximal region at the TSS (transcription start site) play key roles in regulating hCASK-mediated p21 expression. We suggest that E2A (E12 and E47), a representative of the E proteins that binds the E-box elements, is a participant in the mediation of p21 expression by hCASK. The results of the present study suggest that hCASK regulation of cell growth might involve p21 expression, and that the bHLH (basic helix–loop–helix) transcription factor E2A probably participates in hCASK regulation of p21 expression. From these findings, we propose a novel proliferation signalling pathway mediated by hCASK.
Chondroitin 4-O-sulfotransferase-1 is required for somitic muscle development and motor axon guidance in zebrafish
Authors: Mizumoto Shuji , Mikami Tadahisa , Yasunaga Daiki , Kobayashi Naoki , Yamauchi Hajime , Miyake Ayumi , Itoh Nobuyuki , Kitagawa Hiroshi , Sugahara Kazuyuki
Published: January 2009

CS (chondroitin sulfate) has been implicated in a variety of biological processes during development. Its biological functions are closely associated with characteristic sulfated structures. Here, we report the characterization of a zebrafish counterpart of C4ST-1 (chondroitin 4-O-sulfotransferase-1) and its functional importance in embryogenesis. Recombinant C4ST-1 showed a substrate preference for chondroitin and catalysed the 4-O-sulfation of GalNAc residues, a highly frequent modification of CS in the embryos of zebrafish as well as other vertebrates. Whole-mount in situ hybridization revealed that C4ST-1 showed a distinct spatiotemporal expression pattern in the developing zebrafish embryo. During the segmentation stages, strong expression was observed along the body axis including the notochord and somites. Functional knockdown of C4ST-1 with specific antisense morpholino-oligonucleotides led to a marked decrease in the 4-O-sulfation and amount of CS in the embryos. Consistent with the preferential expression in the rostrocaudal axis, C4ST-1 morphants displayed morphological defects exemplified by a ventrally bent trunk and a curled and/or kinky tail, largely due to misregulated myotomal myod expression, implying perturbation of axial muscle differentiation in somites. Furthermore, the aberrant projection of spinal motor axons, which extended ventrally at the interface between the notochord and individual somites, was also observed in C4ST-1 morphants. These results suggest that 4-O-sulfated CS formed by C4ST-1 is essential for somitic muscle differentiation and motor axon guidance in zebrafish development.
Nitration of cathepsin D enhances its proteolytic activity during mammary gland remodelling after lactation
Authors: Zaragozá Rosa , Torres Luis , García Concha , Eroles Pilar , Corrales Fernando , Bosch Ana , Lluch Ana , García-Trevijano Elena R. , Viña Juan R.
Published: January 2009

Proteomic studies in the mammary gland of control lactating and weaned rats have shown that there is an increased pattern of nitrated proteins during weaning when compared with controls. Here we report the novel finding that cathepsin D is nitrated during weaning. The expression and protein levels of this enzyme are increased after 8 h of litter removal and this up-regulation declines 5 days after weaning. However, there is a marked delay in cathepsin D activity since it does not increase until 2 days post-weaning and remains high thereafter. In order to find out whether nitration of cathepsin D regulates its activity, iNOS (inducible nitric oxide synthase)−/− mice were used. The expression and protein levels of this enzyme were similar to WT (wild-type) animals, but the proteolytic activity was significantly reduced during weaning in knockout compared to WT mice. in vitro treatment of recombinant human cathepsin D or lactating mammary gland homogenates with relatively low concentrations of peroxynitrite enhances the nitration as well as specific activity of this enzyme. Using MS, it has been shown that the residue Tyr168 was nitrated. All of these results show that protein nitration during weaning might be a signalling pathway involved in mammary gland remodelling.
The inositol phosphatase MTMR4 is a novel target of the ubiquitin ligase Nedd4
Authors: Plant Pamela J. , Correa Judy , Goldenberg Neil , Bain James , Batt Jane
Published: January 2009

The inositol phosphatase, MTMR4 (myotubularin-related protein 4), was identified as a novel interactor of the ubiquitin ligase Nedd4 (neural-precursor-cell-expressed developmentally down-regulated 4). hMTMR4 (human MTMR4) and Nedd4 co-immunoprecipitated and co-localized to late endosomes. The PY (Pro-Tyr) motif of hMTMR4 binds to WW (Trp-Trp) domains of hNedd4. MTMR4 expression was decreased in atrophying muscle, whereas Nedd4 expression was increased and hMTMR4 was ubiquitinated by hNedd4, suggesting that this novel interaction may underlie the biological process of muscle breakdown.
FoxO proteins: cunning concepts and considerations for the cardiovascular system
Authors: Maiese Kenneth , Chong Zhao Zhong , Shang Yan Chen , Hou Jinling
Published: January 2009

Dysfunction in the cardiovascular system can lead to the progression of a number of disease entities that can involve cancer, diabetes, cardiac ischaemia, neurodegeneration and immune system dysfunction. In order for new therapeutic avenues to overcome some of the limitations of present clinical treatments for these disorders, future investigations must focus upon novel cellular processes that control cellular development, proliferation, metabolism and inflammation. In this respect, members of the mammalian forkhead transcription factors of the O class (FoxOs) have increasingly become recognized as important and exciting targets for disorders of the cardiovascular system. In the present review, we describe the role of these transcription factors in the cardiovascular system during processes that involve angiogenesis, cardiovascular development, hypertension, cellular metabolism, oxidative stress, stem cell proliferation, immune system regulation and cancer. Current knowledge of FoxO protein function combined with future studies should continue to lay the foundation for the successful translation of these transcription factors into novel and robust clinical therapies.
Role of TNF-α in vascular dysfunction
Authors: Zhang Hanrui , Park Yoonjung , Wu Junxi , Chen Xiu ping , Lee Sewon , Yang Jiyeon , Dellsperger Kevin C. , Zhang Cuihua
Published: January 2009

Healthy vascular function is primarily regulated by several factors including EDRF (endothelium-dependent relaxing factor), EDCF (endothelium-dependent contracting factor) and EDHF (endothelium-dependent hyperpolarizing factor). Vascular dysfunction or injury induced by aging, smoking, inflammation, trauma, hyperlipidaemia and hyperglycaemia are among a myriad of risk factors that may contribute to the pathogenesis of many cardiovascular diseases, such as hypertension, diabetes and atherosclerosis. However, the exact mechanisms underlying the impaired vascular activity remain unresolved and there is no current scientific consensus. Accumulating evidence suggests that the inflammatory cytokine TNF (tumour necrosis factor)-α plays a pivotal role in the disruption of macrovascular and microvascular circulation both in vivo and in vitro. AGEs (advanced glycation end-products)/RAGE (receptor for AGEs), LOX-1 [lectin-like oxidized low-density lipoprotein receptor-1) and NF-κB (nuclear factor κB) signalling play key roles in TNF-α expression through an increase in circulating and/or local vascular TNF-α production. The increase in TNF-α expression induces the production of ROS (reactive oxygen species), resulting in endothelial dysfunction in many pathophysiological conditions. Lipid metabolism, dietary supplements and physical activity affect TNF-α expression. The interaction between TNF-α and stem cells is also important in terms of vascular repair or regeneration. Careful scrutiny of these factors may help elucidate the mechanisms that induce vascular dysfunction. The focus of the present review is to summarize recent evidence showing the role of TNF-α in vascular dysfunction in cardiovascular disease. We believe these findings may prompt new directions for targeting inflammation in future therapies.
Genital warts at the site of healed herpes progenitalis: the isotopic response
Authors: Ruocco Eleonora
Published: January 2009

A 53‐year‐old man presented with a crop of papular and somewhat warty lesions on the internal aspect of his prepuce ( Fig. 1). They had appeared over the last 3 months and lately had been enlarging; this persuaded the patient to seek dermatovenereologic advice. The patient, who was uncircumcised, denied any extramarital intercourse, but reported a clear medical history of recurrent herpes progenitalis that had afflicted him and his spouse for many years. Recurrent attacks of this infection, each lasting about 2 weeks, had occurred with variable frequency in his forties, and the last episode could be dated exactly to the age of 49 years. The herpetic infection had been managed with topical and sometimes oral acyclovir, but no considerable therapeutic benefit had been noticed. On admission, the patient's main concern was that the new lesions could represent a relapse of the herpes progenitalis. Although they were completely different from the herpetic lesions objectively (solid and not vesicular), subjectively (asymptomatic and not tingling or painful), and in their course (lasting unmodified for months and not evolving into erosions), they had arisen in the area in which the herpetic vesicles had appeared in the past.

Papular lesions, in a ring‐like arrangement, at the site of a prior recurrent herpes simplex

image

Despite the obvious clinical diagnosis of genital warts and in compliance with the patient's explicit request, a punch biopsy was made. The epithelium showed moderate parakeratosis, pronounced acanthosis, diffuse cell vacuolization, and no signs of nuclear dysplasia ( Fig. 2). Mild edematous changes, dilated capillaries, and a discrete lymphocytic infiltrate were observed in the dermis.

Histologic examination of a papular lesion. Acanthotic epithelium with diffuse perinuclear vacuolization (hematoxylin and eosin staining, × 200)

image

The diagnosis of genital warts was made and the lesions were successfully treated with liquid nitrogen.
Influence of stress on the magnetic domain structure in Fe81Ga19 alloys
Authors: Song H. Z. , Li Y. X. , Zhao K. Y. , Zeng H. R. , Hui S. X. , Li G. R. , Yin Q. R. , Wu G. H.
Published: January 2009

Grains, grain boundaries, magnetic domain distributions, and their correlations in Fe81Ga19 alloys as-cast, annealed, and under compressive and grinding stresses were investigated using scanning electron acoustic microscopy (SEAM) and magnetic force microscopy (MFM). For as-cast and annealed samples, the main domain structure obtained using SEAM is not clear. For samples under stresses, the main domains are obvious and regular. For the sample under compressive stress, its stripe domains array orderly and perpendicularly to the stress direction. The subdomains of as-cast sample observed using MFM show a clear dendritic structure. However, for the sample under compressive stress, the subdomains are irregular. These results may be helpful to understand the magnetostrictive behavior of Fe–Ga alloys under stress.
Electrically induced deflective amplification for adaptive sensing of chemicals
Authors: Tian Ruhai , Ma Liyuan , Su Ming
Published: January 2009

An adaptive strategy for sensitive detection of chemicals is proved in electrically induced deflections of an optical fiber. The surface of the fiber, close to one end, is modified by a sensing polymer film. Upon contact with solutions, the adsorption of ions onto the polymer changes the surface charge and bends the fiber in an electric field. The concept has been confirmed in several systems including detections of pH and metal ion, nanoparticles, and self-assembled monolayers. The dependence of the sensitivity on the strength of electric field provides an adaptive approach with adjustable sensitivity for chemical sensing.
Spectral investigations on Dy3+-doped transparent oxyfluoride glasses and nanocrystalline glass ceramics
Authors: Babu P. , Jang Kyoung Hyuk , Kim Eun Sik , Shi Liang , Seo Hyo Jin , Rivera-López F. , Rodríguez-Mendoza U. R. , Lavín V. , Vijaya R. , Jayasankar C. K. , Rama Moorthy L.
Published: January 2009

Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and studied by x-ray diffraction, absorption, and visible and near-infrared emission spectra. The samples emit intense white light when populating the F49/2 level with a 451 nm laser light and, from the visible emission spectra, yellow to blue intensity ratios and chromaticity color coordinates have been calculated and their relative variation have been discussed based on the concentration of Dy3+ ions and the heat treatment conditions used to prepare the glass ceramics. Infrared emission has also been observed in glasses and glass ceramics after laser excitation at 800 nm, showing bands at 1.33 and 1.67 μm, useful for optical amplification in fiber amplifiers.
Effects of anion concentration on ion-transport pressure in nanopores
Authors: Kim Taewan , Lu Weiyi , Han Aijie , Punyamurtula Venkata K. , Chen Xi , Qiao Yu
Published: January 2009

In an experiment on pressure-driven ion transport in nanopores of a zeolite, the anion concentration is varied in a broad range. As the anion concentration is relatively low, its influence on the ion transport pressure, which reflects the system free energy variation rate, is negligible. When the anion concentration is relatively high, it has a pronounced effect on the ion transport pressure, which should be attributed to the unique surface ion structure in the confining nanoenvironment. The testing data also indicate that the effective interfacial tension is highly dependent on the anion size.
S
expansion of higher-order Lie algebras
Authors: Caroca R. , Merino N. , Salgado P.
Published: January 2009

By means of a generalization of the S-expansion method we construct a procedure to obtain expanded higher-order Lie algebras. It is shown that the direct product between an Abelian semigroup S and a higher-order Lie algebra (G,[,…,]) is also a higher-order Lie algebra. From this S-expanded Lie algebra are obtained resonant submultialgebras and reduced multialgebras of a resonant submultialgebra.
Breather solutions of the discrete nonlinear Schrödinger equations with unbounded potentials
Authors: Zhang Guoping
Published: January 2009

In this paper I investigate the existence of nontrivial breather solutions of the discrete nonlinear Schrödinger equation with the unbounded potential at infinity. First I derive a discrete version of compact embedding theorem. Then combining the Nehari manifold approach and the compact embedding theorem, I show the existence of breather solutions without Palais–Smale condition. The results on the exponential decay of breather solutions are also provided in this paper.
Chopper system for time resolved experiments with synchrotron radiation
Authors: Cammarata Marco , Eybert Laurent , Ewald Friederike , Reichenbach Wolfgang , Wulff Michael , Anfinrud Philip , Schotte Friedrich , Plech Anton , Kong Qingyu , Lorenc Maciej , Lindenau Bernd , Räbiger Jürgen , Polachowski Stephan
Published: January 2009

A chopper system for time resolved pump-probe experiments with x-ray beams from a synchrotron is described. The system has three parts: a water-cooled heatload chopper, a high-speed chopper, and a millisecond shutter. The chopper system, which is installed in beamline ID09B at the European Synchrotron Radiation Facility, provides short x-ray pulses for pump-probe experiments with ultrafast lasers. The chopper system can produce x-ray pulses as short as 200 ns in a continuous beam and repeat at frequencies from 0 to 3 kHz. For bunch filling patterns of the synchrotron with pulse separations greater than 100 ns, the high-speed chopper can isolate single 100 ps x-ray pulses that are used for the highest time resolution. A new rotor in the high-speed chopper is presented with a single pulse (100 ps) and long pulse (10 μs) option. In white beam experiments, the heatload of the (noncooled) high-speed chopper is lowered by a heatload chopper, which absorbs 95% of the incoming power without affecting the pulses selected by the high speed chopper.
A note on the Klein–Gordon equation in the background of a rotating black hole
Authors: Beyer Horst R.
Published: January 2009

This short paper should serve as a basis for further analysis of a previously found new symmetry of the solutions of the wave equation in the gravitational field of a Kerr black hole. Its main new result is the proof of essential self-adjointness of the spatial part of a reduced normalized wave operator of the Kerr metric in a weighted L2-space. As a consequence, it leads to a purely operator theoretic proof of the well posedness of the initial value problem of the reduced Klein–Gordon equation in that field in that L2-space and in this way generalizes a corresponding result of Kay [“The double-wedge algebra for quantum fields on Schwarzschild and Minkowski spacetimes,” Commun. Math. Phys. 100, 57 (1985)] in the case of the Schwarzschild black hole. It is believed that the employed methods are applicable to other separable wave equations.
Ballistic electron transport in hybrid ferromagnet/two-dimensional electron gas sandwich nanostructure: Spin polarization and magnetoresistance effect
Authors: Wang Y. , Chen N. F. , Jiang Y. , Zhang X. W.
Published: January 2009

We have theoretically investigated ballistic electron transport through a combination of magnetic-electric barrier based on a vertical ferromagnet/two-dimensional electron gas/ferromagnet sandwich structure, which can be experimentally realized by depositing asymmetric metallic magnetic stripes both on top and bottom of modulation-doped semiconductor heterostructures. Our numerical results have confirmed the existence of finite spin polarization even though only antisymmetric stray field Bz is considered. By switching the relative magnetization of ferromagnetic layers, the device in discussion shows evident magnetoconductance. In particular, both spin polarization and magnetoconductance can be efficiently enhanced by proper electrostatic barrier up to the optimal value relying on the specific magnetic-electric modulation.
Rotational UV lithography device for cylindrical substrate exposure
Authors: Lima de Miranda Rodrigo , Zamponi Christiane , Quandt Eckhard
Published: January 2009

Optical photolithograhy is a well developed technique, which is normally restricted to planar substrates used in microelectronics or microelectromechanical system fabrication. For other applications—e.g., patterning of stents—photolithography would be an attractive alternative to techniques such as laser structuring provided that the planar technique could be adapted to cylindrical geometries. This study presents the development of a three-dimensional UV photolithography exposure method using a synchronizing movement between a planar Cr mask and a circular substrate. This technique was successfully applied to tubes with outer diameters between 1 and 5 mm. A lateral resolution for a 5 μm feature size of 4.8 μm was achieved, which is close to the resolution of 4.6 μm for similar planar films.
Analytic modal solution to transmission and collimation of light by one-dimensional nanostructured subwavelength metallic slits
Authors: Hua Yi-Lei , Li Zhi-Yuan
Published: January 2009

Light transmitting through a subwavelength slit on an ordinary metal plate is diffracted to all directions but if the exit plane of the slit is patterned with periodical nanostructures, the diffracted light may be compressed into a collimated beam within a small angle. In this paper, we develop a rigorous theoretical method for solving the surface wave induced beam collimation in nanostructured subwavelength metallic slits. The method combines the analytical modal expansion method, the supercell technique, the transfer-matrix method, and the conventional Kirchhoff’s diffraction theory. It allows for quantitative investigation of coupling of the incident light into the guided wave of the slit and coupling of the guided wave out of the nanostructured exit plane. We have used the method to examine light transmission through the nanostructured metallic slit and the corresponding diffraction and beam collimation behaviors. We have extensively analyzed the angular transmission spectrum as a function of the nanostructure period and the incident light wavelength and revealed the condition at which good beam collimation can take place. The result shows that the beam collimation is caused by the excitation of the surface waves supported on the periodical nanostructured pattern and subsequent coupling into the radiation light. Several scattering channels can coexist for coupling the surface waves into the observed diffraction waves and they can act constructively to create one or more collimation beams with excellent directionality and high brightness. The diffraction field patterns in the large area confirm the angular spectrum analysis.
Photoluminescence properties of Eu3+ and Bi3+ in YBO3 host under vacuum ultraviolet/ultraviolet excitation
Authors: Chen Lei , Yang Guangtao , Liu Jiaqin , Shu Xia , Zhang Guobin , Jiang Yang
Published: January 2009

The photoluminescence properties of Bi3+/Eu3+ doped YBO3 phosphors under 147, 168, 185, 222, and 262 nm excitation were studied in this paper. The sensitization luminescence of Eu3+ by Bi3+ was demonstrated and a useful concentration scope, which is 0.05–0.25 mol %, for Bi3+ doped into YBO3:Eu3+ as candidate of plasma display panel red phosphor was optimized. The relative emission intensity of Bi3+ ions occupying C3 sites in YBO3 crystal increases gradually with Bi3+ concentration increasing, while the emission of Bi3+ occupying S6 sites decreases because of energy transfer from S6 sites to C3 sites. The peak of emission band changes from 295 to 320 nm as Bi3+ concentration increases from 0.1 to 0.25 mol %. Therefore, 0.25 mol % is the critical concentration for Bi3+ ions to transfer their absorption energy between different sites at room temperature. As a result, the luminescence of YBO3:Bi3+, Eu3+ decreases as Bi3+ concentration increases further.
Uniaxial magnetic anisotropy of quasi-one-dimensional Fe chains on Pb∕Si
Authors: Sun Da-Li , Wang De-Yong , Du Hai-Feng , Ning Wei , Gao Jian-Hua , Fang Ya-Peng , Zhang Xiang-Qun , Sun Young , Cheng Zhao-Hua , Shen Jian
Published: January 2009

We fabricated quasi-one-dimensional Fe chains on a 4° miscut Si (111) substrate with a Pb film as a buffer layer. The magnetic properties and morphology of Fe chains were investigated by means of scanning tunneling microscope (STM) and surface magneto-optical Kerr effect (SMOKE). STM images show that Fe chains are formed by Fe random islands along the steps of the Pb film due to step decoration. SMOKE data indicate that the Fe chains exhibit in-plane uniaxial magnetic anisotropy along the step direction. The effective in-plane uniaxial anisotropy constant at room temperature was determined by means of electron spin resonance.
Metallic slit aperture as a near-field optical head for heat-assisted magnetic recording
Authors: Omodani Satoshi , Saiki Toshiharu , Obara Minoru
Published: January 2009

Heat assisted magnetic recording (HAMR) technique requires an optical head that can efficiently generate a subwavelength optical spot. The results of finite difference time domain simulation shows that two subwavelength rectangular holes adjacent to a metallic slit aperture make an optical spot from the slit smaller and its peak intensity higher. A subwavelength spot of 82×46 nm2 (full width at half maximum) in the recording medium is obtainable when a pair of rectangular holes is flanked adjacent to the slit aperture with a much smaller distance than the optical wavelength. This configuration provides a high transmittance of the slit aperture and a high expectation for a high controllability of both a thickness of the slit and a distance between the slit and the rectangular hole by the use of the planar process. By using a plasmon waveguide to guide light into the metallic slit aperture, a thin and efficient optical head for HAMR is achieved.
Hermeticity and diffusion investigation in polysilicon film encapsulation for microelectromechanical systems
Authors: Kim Bongsang , Candler Rob N. , Melamud Renata , Hopcroft Matthew A. , Yoneoka Shingo , Lee Hyung Kyu , Agarwal Manu , Chandorkar Saurabh A. , Yama Gary , Kenny Thomas W.
Published: January 2009

The hermeticity and diffusion behavior of “epi-seal” encapsulation [R. N. Candler et al., J. Microelectromech. Syst. 15, 1446 (2006); B. Kim et al., Proceedings of the ASME 2007 InterPACK Conference (InterPACK’07), 33234 (2007)], an epitaxially deposited polysilicon film encapsulation for microelectromechanical systems (MEMSs), were investigated. MEMS resonators with pressure sensitive quality factor were fabricated inside episeal cavities. By measuring the quality factor and inferring cavity pressure, leakage through the encapsulation was studied as a continuation of previous hermeticity investigations [B. Kim et al., Proceedings of the 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE, pp. 413–416 (2004)]. During long-term monitoring performed at 100 °C in a normal atmosphere, the encapsulated cavity pressure increased at a rate of 5–10 mTorr/yr, whereas no measurable pressure change could be detected in our previous room temperature measurement performed with identically designed and encapsulated resonators. To identify the cause of this pressure increase, the diffusive gas species and diffusion pathways in the epi-seal encapsulation were investigated experimentally. Various gas species in the atmosphere were tested in a 400 °C accelerated environment. These tests identified hydrogen and helium as highly diffusive gas species and showed argon and nitrogen to be much less diffusive under these conditions. Also, a series of devices with modifications of encapsulation geometry was tested in a hydrogen environment at 400 °C. Silicon dioxide, used for sacrificial and passivation layers, was identified as the primary diffusion pathway through the epi-seal encapsulation. These experimental results and diffusion pathway models were compared with the diffusion activation energy of various gas species in semiconductor materials, enabling design and process optimization for improved hermeticity of wafer-scale thin-film encapsulation for MEMS devices.
Nanomechanical cantilever active probes for ultrasmall mass detection
Authors: Salehi-Khojin Amin , Bashash Saeid , Jalili Nader , Müller Maren , Berger Rüdiger
Published: January 2009

The objective of this study is to employ piezoelectrically driven nanomechanical cantilevers (so-called “active probes”) for ultrasmall mass detection. The idea originates from utilizing the unique configuration and the embedded piezoelectricity of active probes for high amplitude vibration, the attribute that is essential for precise measurement of ultrasmall mass by cantilever-based vibratory sensors. In this work, using focused ion beam technique, a small mass in the order of picograms is added at the tip of active probes. To detect the added mass, a precise model for modal characterization of the probe with geometrical discontinuities is utilized along with a parameter estimation technique for system identification. Using the shifts in the resonant frequencies of the identified system, the amount of added tip mass is estimated at the most sensitive mode of operation. Through a sensitivity analysis, it is shown that the second mode of the present configuration of the active probe is the most reliable mode for mass detection. Moreover, the effect of parameters’ uncertainties on the sensitivity of measurements is studied in more detail. Results indicate that system identification procedure proposed in this work is an inevitable step toward achieving precise measurement of ultrasmall masses through active probes with great potential in bio- and chemomass detection applications.
Phonon scattering at a rough interface between two fcc lattices
Authors: Zhao Hong , Freund Jonathan B.
Published: January 2009

Elastic phonon scattering at an atomically rough interface that separates two fcc lattice leads is computed via a Green’s function method. Results are compared to specular and diffuse phonon scattering models, both of which are widely used in the numerical simulations of phonon Boltzmann transport equations. The shape of the discrete interface in the model is quantified by its spectral characteristics. It is found that the amplitude of the interface height fluctuations has strong influence on the effective interface specularity, while the effect of the two-point correlation length is minor. The average phonon transmission coefficient as well as the overall thermal resistance, however, is relatively insensitive to the interface roughness.
Magnetoresistance calculation in current-perpendicular-to-plane giant magnetoresistance spin valves with current-confined paths
Authors: Wang C. C. , Kumar S. Bala , Tan S. G. , Jalil M. B. A. , Han G. C.
Published: January 2009

We compared the magnetoresistance (MR) ratios of current-confined-path (CCP) current-perpendicular-to-plane (CPP) giant MR spin valves (SVs) calculated using the two-current-model. The simplified two-current model, which places the parasitic resistance external to the two-current network, has been inaccurate in determining the overall resistance of a SV in parallel magnetization configuration. The characteristics of the error in MR depend on the parasitic resistance value, the spin asymmetry coefficient, and the spacer layer resistivity. In comparison to the complete two-current model, we found that although the simplified model could generally predict the trend of various MR behaviors, it also overestimates MR for different CCP densities. A more comprehensive calculation on the CCP SVs was then performed using the spin-drift-diffusion equations based on the Valet–Fert model. It was found that the MR behavior upon considering spin relaxation in the ferromagnetic layers has a closer match with results predicted by the simplified model due to the strong reduction in spin accumulation in the parasitic layers. Spin relaxation in the spacer layer, however, shows a competing effect that tends to reduce the MR ratios. Our results in this paper are useful for accurate evaluation of MR performance in a CPP SV sensor with current-confined paths.
Numerical simulations for cold layer formation in an inverse Z-pinch magnetized target fusion system
Authors: Subhash P. V. , Madhavan S. , Chaturvedi S.
Published: January 2009

One-dimensional magnetohydrodynamic simulations have been performed to study cold layer formation in a magnetized target fusion system with an inverse Z-pinch target plasma. Three phases of cold layer evolution has been identified. During the early compression phase, when liner velocities were not high, formation of a “classical” cold layer is observed, with monotonically increasing plasma densities and decreasing temperatures as the liner is approached. During the main compression phase, lasting until close to peak compression, magnetic flux leakage from the plasma to the liner is not important. The cold layer is then characterized by monotonically decreasing plasma temperature, density, and thermal conductivity. This has practical significance, since it would tend to reduce thermal losses to the liner. During the late compression and burn phases, magnetic flux leakage into the liner becomes important. This phase is characterized by a rapid increase in density and a rapid decrease in magnetic field and temperature toward the liner. This yields significantly higher values of thermal conductivity than in the bulk plasma, leading to enhanced thermal losses. During the first two phases, the entire plasma is magnetically confined. During the last phase, the cold layer changes to a wall-confined mode, while the bulk plasma continues to be magnetically confined. This is a major difference from earlier assumptions about wall confinement of such plasmas. These results show that the Kadomtsev stability parameter exceeds unity in the cold layer during the second and third phases, which may be an indication of instability. The choice of the transport model has a significant effect upon plasma evolution and the plasma lifetime. Classical transport yields plasma density levels near the liner that are significantly higher, sometimes by orders of magnitude, than those yielded by Bohm transport. During the main compression phase, Bohm diffusivity yields a lower lifetime, as expected. During the early compression phase, however, the classical lifetime is unexpectedly below the Bohm value. A physical explanation has been provided for these trends.
A band-to-band Coulomb interaction model for refractive index spectra of ternary semiconductors
Authors: Lin E. Y. , Lay T. S.
Published: January 2009

A band-to-band Coulomb interaction model for the refractive index spectra is presented of AlxGa1−xAs for 0<x<0.412 and In0.53Ga0.47As ternary semiconductors at photon energies near and above the band gap. An accurate absorption model is used to calculate the contribution on the refractive index near band-edge region through a complete closed-form Kramers–Kronig transform. In addition, a Sellmeier-type single-oscillator representation provides all the additional absorption at higher energies due to nonparabolicity and higher-energy bands. The refractive index spectra are extended beyond the band-gap energy and are in excellent agreement with the available experimental data. The refractive index spectra of ternary compounds are fully parametrized by interpolation of the fitting parameters. The results will be important for the detailed design of photonic devices, such as electroabsorption modulators and semiconductor optical amplifiers.
Nanosilver enhanced upconversion fluorescence of erbium ions in Er3+: Ag-antimony glass nanocomposites
Authors: Som Tirtha , Karmakar Basudeb
Published: January 2009

Er 3 + :Ag-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix K2O–B2O3–Sb2O3 by a single-step melt-quench technique involving selective thermochemical reduction. The UV-vis-near-infrared absorption spectra show typical surface plasmon resonance (SPR) band of Ag0 nanoparticles (NPs) in addition to the distinctive absorption peaks of Er3+ ion. X-ray diffraction and selected area electron diffraction results indicate formation of Ag0 NPs along the (200) plane direction. The transmission electron microscopic image reveals the formation of spherical, fractal, and rod-shaped Ag0 NPs having maximum size ∼31 nm. The rod-shaped Ag0 NPs have aspect ratio ∼2.4. The field emission scanning electron microscopic image shows development of three dimensional cornlike microstructures. Photoluminescent upconversion under excitation at 798 nm exhibit two prominent emission bands of Er3+ ions centered at 536 (green) and 645 (red) nm due to S43/2→I415/2 and F49/2→I415/2 transitions, respectively. Both the bands undergo a maximum of three- and eightfold intensity enhancement, respectively, at Ag0 concentration of 0.007 wt % (1.8×1018 atoms/cm3). Local field enhancement induced by Ag0 SPR is found to be responsible for enhancement while energy transfer from Er3+→Ag0 and optical reabsorption due to Ag0 SPR for quenching.
Carrier localization degree of In0.2Ga0.8N/GaN multiple quantum wells grown on vicinal sapphire substrates
Authors: Li Zhen-Yu , Lo Ming-Hua , Chiu Ching-Hua , Lin Po-Chun , Lu Tien-Chang , Kuo Hao-Chung , Wang Shing-Chung
Published: January 2009

In this work, we have grown In0.2Ga0.8N/GaN multiple quantum well (MQWs) epitaxial structure on vicinal sapphire substrates by low pressure metal-organic chemical vapor deposition and investigated the relationship between carrier localization degree and vicinal angles of sapphire substrates. The optical analysis confirmed that the In0.2Ga0.8N/GaN MQWs grown on 0.2°-off sapphire substrate exhibited the smallest carrier localization degree and more ordered In0.2Ga0.8N/GaN MQW structure. In addition, mechanisms for carrier localization in In0.2Ga0.8N/GaN MQWs grown on vicinal substrate were discussed based on the results obtained from the power and temperature dependent photoluminescence measurements. The Raman spectrum showing the in-plane compressive stress of the GaN epitaxial structures grown on vicinal sapphire substrates revealed the relation between the dislocation density and the carrier localization degree in MQWs. From transmission electron microscopy images, the threading dislocation density (TDD) of In0.2Ga0.8N/GaN MQWs grown on 0.2° vicinal sapphire substrate at the bottom of n-GaN layer was about 9.4×108 cm−2 and reduced to 3.0×108 cm−2 at the top of n-GaN layer. We also obtained the TDD of 5.6×107 cm−2 in the MQW region and only 1.0×107 cm−2 in the p-GaN region. Based on the results mentioned above, 0.2°-off substrate can offer In0.2Ga0.8N/GaN MQW blue light-emitting diode structures with benefits, such as high crystal quality, low defects, and small carrier localization degree.
Microthermography of diode lasers: The impact of light propagation on image formation
Authors: LeClech Julien , Ziegler Mathias , Mukherjee Jayanta , Tomm Jens W. , Elsaesser Thomas , Landesman Jean-Pierre , Corbett Brian , Mclnerney John G. , Reithmaier Johann Peter , Deubert Stefan , Forchel Alfred , Nakwaski Włodzimierz , Sarzała Robert P.
Published: January 2009

We analyze the effect of propagating infrared thermal radiation within a diode laser on its thermal image taken by a thermocamera. A ray-tracing analysis shows that this effect substantially influences image formation on a spatial scale of 10 μm, i.e., in the domain of microthermography. The main parameter affecting the thermal radiation spread in the semitransparent semiconductor structure is the free carrier concentration in the substrate, governing its absorption. Two applications are presented: a quantum dot laser and a quantum-well laser, where independent thermal models are developed using the finite element method (FEM). Our ray-tracing analysis verifies the FEM simulated temperature profiles by interlinking them to experimental temperature maps obtained through microthermography. This represents a versatile experimental method for extracting reliable bulk-temperature data from diode lasers on a microscopic scale.
Scanning capacitance characterization of potential screening in InAs nanowire devices
Authors: Law J. J. M. , Dayeh S. A. , Wang D. , Yu E. T.
Published: January 2009

We have used scanning capacitance microscopy and spectroscopy to examine the effects of micron-scale metal contacts, typically present in nanowire-based electronic devices, on carrier modulation and electrostatic behavior in InAs semiconductor nanowires. We observe a pronounced dependence of scanning capacitance images and spectra on distance between the scanning capacitance probe tip and nanowire contact up to distances of 3–4 μm. Based on the comparison of these data with results of finite-element electromagnetic simulations, we interpret these results as a consequence of electrostatic screening of the tip-nanowire potential difference by the large metal contact. These results provide direct experimental verification of contact screening effects on the electronic behavior of nanowire devices and are indicative of the importance of assessing and accounting for the effect of large-scale contact and circuit elements on the characteristics of nanoscale electronic devices generally.
Spin transfer switching enhancement in perpendicular anisotropy magnetic tunnel junctions with a canted in-plane spin polarizer
Authors: Sbiaa Rachid , Law Randall , Tan Ei-Leen , Liew Thomas
Published: January 2009

We have studied spin transfer switching (STS) in a magnetic tunnel junction with perpendicular magnetic anisotropy for the reference and free layers using the Landau–Lifshitz–Gilbert formalism. We propose a multilayer structure in which the insertion of an additional spin polarizer with in-plane anisotropy can enhance the STS efficiency and switching speed of the device. It is revealed that a canted spin polarizer with an angle between 40° and 80° out of the film plane in the correct direction enhances the STS efficiency more than a fixed in-plane or perpendicular polarizer. Furthermore, we show that the spin transfer torque exerted on the in-plane polarizer layer by the free layer automatically tilts the in-plane polarizer in the direction that enhances STS for both magnetization states of the free layer.
Effect of a magnetic field in simulating the plume field of an anode layer Hall thruster
Authors: Choi Yongjun , Boyd Iain D. , Keidar Michael
Published: January 2009

In this study, we present axisymmetric simulations of xenon plasma plume flow fields from a D55 anode layer Hall thruster. A hybrid particle-fluid method is used for the simulations. The magnetic field surrounding the Hall thruster exit is included in the calculation. The plasma properties obtained from a hydrodynamic model are used as boundary conditions for the simulations. The electron properties are calculated using the Boltzmann model and a detailed fluid model, collisions of heavy particle are modeled with the direct simulation Monte Carlo method, and ion transport in the electric field uses the particle-in-cell technique. The accuracy of the simulation is assessed through comparison with various measured data. It is found that a magnetic field significantly affects the profile of the plasma in the detailed model. The plasma has a potential of 80 V at 10 mm from the thruster exit in the case of zero magnetic field, which decreases to 60 V when the magnetic field is included. Results predicted by the detailed model with the magnetic field are found to be in better agreement with experimental data.
Localized and delocalized states in GaNAs studied by microphotoluminescence and photoreflectance
Authors: Kudrawiec Robert , Sęk Grzegorz , Misiewicz Jan , Ishikawa Fumitaro , Trampert Achim , Ploog Klaus H.
Published: January 2009

Optical transitions in GaNAs bulk layer containing 2.2% N have been studied with microphotoluminescence (μ-PL) and photoreflectance. At low temperatures and low excitation conditions, the μ-PL spectra showed sharp PL lines of 100–300μeV widths about 10–20meV below the energy gap. Those lines were attributed to the recombination of localized excitons trapped at local potential minima. When the excitation power was increased, an additional smooth PL band appeared at the higher-energy side. This band corresponds to the light-hole transition in photoreflectance spectrum, i.e., transition between the delocalized states.
Practical implementation of a two-hemisphere plasma absorption probe
Authors: Scharwitz Christian , Böke Marc , Winter Jörg , Lapke Martin , Mussenbrock Thomas , Brinkmann Ralf Peter
Published: January 2009

The plasma absorption probe is a recently developed tool for efficient determination of electron densities of low temperature plasmas. The occurrence of multiple absorption signals was a serious drawback for interpretation of the probe data. To remedy this drawback, a spherically symmetric design of an absorption probe is proposed. A spherical probe is tested in experiment and simulation and the suppression of the multiple absorption signals is demonstrated. The proof of principle for the concept is given.
Effect of grain boundary on local surface conductivity of diamond film
Authors: Li Y. L. , Li J. J. , Xia X. X. , Lu C. , Jin H. , Gu C. Z.
Published: January 2009

In this article, the direct experimental evidences to determine the effect of grain boundary on local surface conductivity (SC) of diamond films were provided by the measurement using double probe scanning electron microscopy (SEM) technology. Undoped diamond films with (001) orientation were first grown by microwave plasma enhanced chemical vapor deposition and were then hydrogenated at different conditions for SC measurement. In the SEM system, double probes with tiny tip radius severed as two leads were moved along and contacted with the diamond film surface to directly test the local SC of diamond film. The surface electrical property results indicate that for the same distance between the two probes, the local SC of the area across grain boundary is much higher than that of area without grain boundary for the same duration of hydrogenation degrees. In addition, local SC of the area between the two probes increases with the number of grain boundaries in this area, which demonstrates that the grain boundaries play an important role in improving the SC of diamond film. The contribution of the grain boundaries on the local SC of diamond film can be mainly attributed to the defects in grain boundaries that can effectively improve electron transport ability at the diamond film surface.
Green photoluminescence from Zn3N2:Tb films prepared by magnetron sputtering
Authors: Zhang Z.-X. , Pan X.-J. , Liu L.-X. , Ma Z.-W. , Zhao H.-T. , Jia L. , Xie E.-Q.
Published: January 2009

Terbium (Tb)-doped Zn3N2 thin films were prepared on glass and Si substrates by direct current magnetron sputtering in a mixture of pure argon and nitrogen gases. Glancing incidence x-ray diffraction patterns indicated that Zn3N2:Tb thin films were of cubic structure. Raman spectra showed only two Raman-active phonon modes located at 258 and 565 cm−1. The indirect optical band gap of Zn3N2:Tb was determined as 2.4 eV. The sharp characteristic emission lines corresponding to Tb3+ intra-4f shell transitions were resolved in the photoluminescence spectra at room temperature. Those results suggest that Tb-doped Zn3N2 may be a suitable material for visible optoelectronic devices.