A New Ignition Criterion Based Upon a Critical Thermal Energy Density

It has long been known that various ignition criteria of energetic materials have been limited in applicability to small regions. In order to explore the physical nature of ignition, we calculated how much thermal energy per unit mass of energetic materials was absorbed under different external stimuli. Hence, data of several typical sensitivity tests were analyzed by order of magnitude estimation. Then a new concept on critical thermal energy density was formulated. Meanwhile, the chemical nature of ignition was probed into by chemical kinetics.

Orientation-based Continuum Damage Models for Rocks

A general formulation of the Helmholtz free energy used in thermodynamics of damage process of rocks is derived within a multi-scale framework. Such a physically-based thermodynamic state potential has a hybrid, discrete/continuum, nature in the sense tha

Flow similariy applied in convection-based tilt sensor

The environment temperature has inevitable effects on property of the convect ion-based tilt sensors. It not only redefines the application, but also prevents the improvement of the sensor performance. Numerical simulation of the fluid flow in the chamber of a sensor was performed and the influence of the environment temperature was studied in this paper. At zero tilt angle, the temperature distribution along the perpendicular line cross the heat source at various environment temperatures was presented. It was found that the flow varied dramatically at different environment temperatures, which would cause the output signal vary accordingly, even when the tilt angle was kept at a constant, because this device works by sensing the change of flow. At the same condition, we present the numerical results when the temperature difference across the heat source and the environment was kept at the same, in those results, it was found that the temperature difference at every point along the perpendicular line cross the heat source keep the same, this result confirms the similarity principle of nature convection. Second, A method of eliminating environment temperature infect on property of convect ion-based tilt sensor, which is based on the theory of flow similarity, is proposed. It was found that a thermal transistance can be piped on the circuit of heat source to compensate the temperature of the heat source. A compensative circuit was specially designed which can keep flow similarity by changing heat source temperature in order to eliminate the influence of environment temperature. The experiment results show that above 70% temperature drift can be eliminated by this compensative circuit.

Near-field hexagonal array illumination based on fractional Talbot effect

Hexagonal array is a basic structure widely exists in nature and adopted by optoclectronic device. A phase plate based on the fractional Talbot effect that converts a single expanded laser beam into a regular hexagonal array of uniformly illuminated apertures with virtually 100% efficiency is presented. The uniform hexagonal array illumination with a fill factor of 1/12 is demonstrated by the computer simulation. (C) 2006 Elsevier GmbH. All rights reserved.

Structure of macrozoobenthos of the East Dongting nature reserve, with emphasis on relationships with environmental variables

Ecological survey of macrozoobenthos assemblages was carried out at 32 sites in the East Dongting Nature Reserve, located in the northern region of the East Dongting Lake in the middle basin of the Yangtze River, China. All total 51 taxa including 18 oligochaetes, 15 mollusks, 14 insects and four other animals were recorded. Mollusks composed the dominant group and accounted for more than 70% of the total abundance. Assemblages were composed mainly of scrapers (66.7%) and collector-gatherers (nearly 20%), and to a lesser extent collector-filterers (roughly 12%), predators (ca. 7%), and shredders (ca. 6%). Two-way indicator species analysis, detrended correspondence, and canonical correspondence analysis (CCA) were employed to identify the relationships between macrozoobenthos assemblages and environmental variables. Thirty-two sites were separated into four site groups based on composition and relative abundance of benthic macroinvertebrates. CCA detected that water depth, pH, conductivity, SiO2, total nitrogen, total phosphorus, alkalinity, hardness, and Ca2+, were significant environmental factors influencing the pattern of macozoobenthos. In this minimal subset, water depth, pH, alkalinity and hardness were the most influential variables.

Investigation on multiple-port microcylinder lasers based on coupled modes

Microcylinder resonators with multiple ports connected to waveguides are investigated by 2D finite-difference time-domain (FDTD) simulation for realizing microlasers with multiple outputs. For a 10 mu m radius microcylinder with a refractive index of 3.2 and three 2 mu m wide waveguides, confined mode at the wavelength of 1542.3 nm can have a mode Q factor of 6.7 x 10(4) and an output coupling efficiency of 0.76. AlGaInAs/InP microcylinder lasers with a radius of 10 mu m and a 2 mu m wide output waveguide are fabricated by planar processing techniques. Continuous-wave electrically injected operation is realized with a threshold current of 4 mA at room temperature, and the jumps of output power are observed accompanying a lasing mode transformation.

Design and Fabrication of AlGaN-Based Resonant-Cavity-Enhanced p-i-n UV PDs

AlGaN-based resonant-cavity-enhanced (RCE) p-i-n photodetectors (PDs) for operating at the wavelength of 330 nm were designed and fabricated. A 20.5-pair AlN/Al0.3Ga0.7N distributed Bragg reflector (DBR) was used as the back mirror and a 3-pair AlN/Al0.3Ga0.7N DBR as the front one. In the cavity is a p-GaN/i-GaN/n-Al0.3Ga0.7N structure. The optical absorption of the RCE PD structure is at most 59.8% deduced from reflectance measurement. Selectively enhanced by the cavity effect, a response peak of 0.128 A/W at 330 nm with a half-peak breadth of 5.5 nm was obtained under zero bias. The peak wavelength shifted 15 nm with the incident angle of light increasing from 0 degrees to 60 degrees.

Nature of interfacial defects and their roles in strain relaxation at highly lattice mismatched 3C-SiC/Si (001) interface

Misfit defects in a 3C-SiC/Si (001) interface were investigated using a 200 kV high-resolution electron microscope with a point resolution of 0.194 nm. The [110] high-resolution electron microscopic images that do not directly reflect the crystal structure were transformed into the structure map through image deconvolution. Based on this analysis, four types of misfit dislocations at the 3C-SiC/Si (001) interface were determined. In turn, the strain relaxation mechanism was clarified through the generation of grow-in perfect misfit dislocations (including 90 degrees Lomer dislocations and 60 degrees shuffle dislocations) and 90 partial dislocations associated with stacking faults. (C) 2009 American Institute of Physics. [doi:10.1063/1.3234380]

A novel face recognition method based on hypersausage neural networks

In this paper, we firstly give the nature of 'hypersausages', study its structure and training of the network, then discuss the nature of it by way of experimenting with ORL face database, and finally, verify its unsurpassable advantages compared with other means.

Characterization and analysis of two-dimensional GaAs-based photonic crystal nanocavities at room temperature

This paper describes the design and fabrication process of a two-dimensional GaAs-based photonic crystal nanocavity and analyzes the optical characterization of cavity modes at room temperature. Single InAs/InGaAs quantum dots (QDs) layer was embedded in a GaAs waveguide layer grown on an Al0.7Ga0.3As layer and GaAs substrate. The patterning of the structure and the membrane release were achieved by using electron-beam lithography, reaction ion etching, inductively coupled plasma etching and selective wet etching. The micro-luminescence spectrum is recorded from the fabricated nanocavities, and it is found that some high-order cavity modes are clearly observed besides the lowest-order resonant mode is exhibited in spite of much high rate of nonradiative recombination. The variance of resonant modes is also discussed as a function of r/a ratio and will be used in techniques aimed to improve the probability of achieving spectral coupling of a single QD to a cavity mode.

Quasiparticle nature of rotational bands in Pt-187

The high-spin states in Pt-187 have been studied experimentally by means of in-beam gamma-ray spectroscopy techniques via the Yb-173(O-18, 4n) fusion-evaporation reaction. The high-spin level scheme of Pt-187 has been established, including three rotational bands. Based on the systematics of level structure in neighboring nuclei and by comparing the experimental and theoretical B(M1)/B(E2) ratios, configurations of 11/2+ [615], 7/2(-)[5031 and 1/2(-)[521] have been proposed for the three rotational bands, respectively. Band properties of band crossing frequency, alignment gain and signature splitting have been discussed.

On the induction period of methane aromatization over Mo-based catalysts

The behavior of different species during the temperature-programmed surface reaction (TPSR) of methane over various catalysts is traced by an online mass spectrometer, It is demonstrated that the transformation of MoO3 to molybdenum carbide hinders the activation of methane as well as the succeeding aromatization in the TPSR, If this transformation process is done before the reaction, the temperature needed for methane activation and benzene formation will be greatly lowered (760 and 847 K, respectively). On the basis of comparison of the catalytic behavior of molybdenum supported on different zeolites, it is suggested that the initial activation of methane is the rate-determining step of this reaction. For the cobalt catalysts supported on HMCM-22 or Mo catalysts supported on TiO2, no benzene formation could be observed during the TPSR, However, the prohibition of benzene formation is different in nature over these two catalysts: the former lacks the special properties exhibited by molybdenum carbide, which can continuously activate methane even when multiple layers of carbonaceous species are formed on its surface, while the latter cannot accomplish the aromatization reaction since there are no Bronsted acid sites to which the activated intermediates can migrate, although the activation of methane can be achieved on it. Only for the catalysts that possess both of these properties, together with the special channel structure of zeolite, can efficient methane aromatization be accomplished. (C) 2000 Academic Press.

High-performance dye-sensitized solar cells based on solvent-free electrolytes produced from eutectic melts

Low-cost excitonic solar cells based on organic optoelectronic materials are receiving an ever-increasing amount of attention as potential alternatives to traditional inorganic photovoltaic devices. In this rapidly developing field, the dye-sensitized solar cell(1) (DSC) has achieved so far the highest validated efficiency of 11.1% (ref. 2) and remarkable stability(3).

Origin of negative differential resistance and memory characteristics in organic devices based on tris(8-hydroxyquinoline) aluminum

Negative differential resistance (NDR) and memory phenomenon have been realized in current-voltage (I-V) characteristics of indium tin oxide/tris(8-hydroxyquinoline) aluminum/aluminum devices. The I-V curves have been divided into three operational regions that are associated with different working regimes of the devices: (i) bistable region, (ii) NDR region, and (iii) monotonic region. The bistable region disappeared after a couple of voltage sweeps from zero to a positive voltage. The bistable nature can be reinstated by applying a suitable negative voltage.

Studies on the nature of the macromolecular condensed state of "nascent" ultra high molar mass polyethylene

Ultra high molar mass polyethylene (UHPE) powder as polymerized in a slurry process has been studied, in its nascent state, after recrystallization on rapid cooling from the melt and after hot compression molding to a film, by DSC, effect of annealing the recrystallized specimen at 120 similar to 130 degreesC, morphology by polarizing optical microscopy and small angle X-ray scattering. Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains, involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers. On melting, a nematic rubbery state of nanometer size domain resulted. The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC, possibly higher than 300 degreesC, the exact temperature is however not sue because of chain degradation at such high temperatures. The recrystallization process from the melt is a crystallization from a nematic rubbery state. The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity. The remelting peak temperature could be returned close to that of the nascent state by annealing at 120 similar to 130 degreesC.