Organo-modified magnesium hydroxide nano-needle and its polystyrene nanocomposite

Acrylic acid modified magnesium hydroxide nano-needles (AA–Mg(OH)₂) had been synthesized by alkaline injected into magnesium chloride solution at about 0°C in the presence of acrylic acid (AA). Then the polystyrene/magnesium hydroxide nano-needles composite (PS/Mg(OH)₂) had been prepared by the radical copolymerization with styrene in toluene system using AA–Mg(OH)₂ as a macro-monomer. The elemental analysis (EA) and Fourier transform infrared (FTIR) analyses show that the polystyrene had been grafted onto the surfaces of the nano-needles (AA–Mg(OH)₂). The nano-needles (AA–Mg(OH)₂) had better dispersibility in polystyrene matrix as observed by transmission electron microscope (TEM) analysis. The thermal behavior analysis results from the differential scanning calorimetry (DSC) indicated that the magnesium hydroxide nano-needles had lower thermal decomposition temperature than that of the polymer matrix and it is expected that the nano-needles prepared by the proposed method could be used as an environmental-friendly flame retardant.     

Solar-blind MSM-photodetectors based on Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>N heterostructures

Solar-blind MSM photodetectors based on the AlGaN heterostructures have been fabricated and investigated. The influence of material properties on device parameters is discussed. Effect of different buffer layers on the detector performances has been examined. Detectors exhibit low dark currents and high sensitivity within the range of 250–290 nm. Effect of optical excitation energy on GaN-based MSM-detector performance is analyzed and discussed. At high excitation level the detector speed of response is limited by the field screening caused by the space-charge of the holes. The impulse response of GaN-based MSM-detector is compared favorably with GaAs MSM-device.     

Investigations on Pd:SnO2/porous silicon structures for sensing LPG and NO2 gas

P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions. Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter have been estimated as 25 μm. Pd:SnO₂/PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device. Sensing properties of the device towards liquefied petroleum gas (LPG) and NO₂ gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity and optimum operating temperature of the device towards LPG and NO₂ gas sensing has been estimated as 69% at 180 °C and 52% at 220 °C, respectively. The developed sensor device shows a short response time of 25 and 57 s for sensing LPG and NO₂ gases, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Discrete and Embedded Eigenvalues for One-Dimensional Schrödinger Operators

I present an example of a discrete Schrödinger operator that shows that it is possible to have embedded singular spectrum and, at the same time, discrete eigenvalues that approach the edges of the essential spectrum (much) faster than exponentially. This settles a conjecture of Simon (in the negative). The potential is of von Neumann-Wigner type, with careful navigation around a previously identified borderline situation.     

A conceptual high flux reactor design with scope for use in ADS applications

A 100 MWt reactor design has been conceived to support flux level of the order of 10¹⁵ n/cm²/s in selected flux trap zones. The physics design considers high enriched metallic alloy fuel in the form of annular plates placed in a D₂O moderator tank in a hexagonal lattice arrangement. By choosing a tight lattice pitch in the central region and double the lattice pitch in the outer region, it is possible to have both high fast flux and thermal flux trap zones. By design the flux level in the seed fuel has been kept lower than in the high flux trap zones so that the burning rate of the seed is reduced. Another important objective of the design is to maximize the time interval of refueling. As against a typical refueling interval of a few weeks in such high flux reactor cores, it is desired to maximize this period to as much as six months or even one year. This is possible to achieve by eliminating the conventional control absorbers and replacing them with a suitable amount of fertile material loading in the reactor. Requisite number of seedless thorium-aluminum alloy plates are placed at regular lattice locations vacated by seed fuel in alternate fuel layers. It is seen that these thorium plates are capable of acquiring asymptotic fissile content of 14 g/kg in about 100 days of irradiation at a flux level of 8 × 10¹⁴ n/cm²/s. In summary, the core has a relatively higher fast flux in the central region and high thermal flux in the outer region. The present physics design envisages a flat core excess reactivity for the longest possible cycle length of 6 months to one year. It is also possible to modify the design for constant subcriticality for about the same period or longer duration by considering neutron spallation source at the centre and curtailing the power density in the inner core region by shielding it with a layer of thoria fuel loading.      

Stability of Relativistic Matter with Magnetic Fields for Nuclear Charges up to the Critical Value

We give a proof of stability of relativistic matter with magnetic fields all the way up to the critical value of the nuclear charge Zα = 2/π. This paper may be reproduced, in its entirety, for non-commercial purposes.     

An axial flow cyclone to remove nanoparticles at low pressure conditions

In this study, the axial flow cyclone used in Tsai et al. (2004) was further tested for the collection efficiency of both solid (NaCl) and liquid (OA, oleic acid) nanoparticles. The results showed that the smallest cutoff aerodynamic diameters achieved for OA and NaCl nanoparticles were 21.7 nm (cyclone inlet pressure: 4.3 Torr, flow rate: 0.351 slpm) and 21.2 nm (5.4 Torr, 0.454 slpm), respectively. The collection efficiencies for NaCl and OA particles were close to each other for the aerodynamic diameter ranging from 25 to 180 nm indicating there was almost no solid particle bounce in the cyclone. The 3-D numerical simulation was conducted to calculate the flow field in the cyclone and the flow was found to be nearly paraboloid. Numerical simulation of the particle collection efficiency based on the paraboloid flow assumption showed that the collection efficiency was in good agreement with the experimental data with less than 15% of error. A semi-empirical equation for predicting the cutoff aerodynamic diameter at different inlet pressures and flow rates was also obtained. The semi-empirical equation is able to predict the cutoff aerodynamic diameter accurately within 9% of error. From the empirical cutoff aerodynamic diameter, a semi-empirical square root of the cutoff Stokes number, , was calculated and found to be a constant value of 0.241. This value is useful to the design of the cyclone operating in vacuum to remove nanoparticles.     

Photogreying of TiO<Subscript>2</Subscript> nanoparticles

Photogreying, the change in brightness on UV irradiation in the absence of oxygen, of TiO₂ nanoparticulate dispersions is shown to depend on the nature of the liquid, consistent with a surface reaction. Measurements on a series of TiO₂ particles (mainly 75×10 nm) dispersed in, e.g., alkyl benzoate correlate well with those on the same TiO₂’s dispersed in a second liquid (e.g. propan-2-ol). Photogreying in propan-2-ol is paralleled by photocatalytic-oxidation activity, indicating a common origin – UV-generation of charge carriers. Further, photogreying parallels Ti³⁺ formation. Hence, although appearance and the visible spectra of photogreyed particles both differ from those of Ti³⁺ in ≤10 nm colloidal TiO₂, we suggest that photogreying is caused by capture of UV excited electrons to form Ti³⁺. Surface treatment reduces photogreying, and we speculate that differences between uncoated samples reflect differences in the number of potentially reducible Ti’s.     

用157 nm激光制作的光子晶体光纤法布里-珀罗传感器

157nm准分子激光用于微加工具有单光子能量高,峰值功率高,材料吸收系数高,分辨率高等优点。利用157nm激光微加工的方法,在光子晶体光纤上融切出微小矩形孔,从而构成腔长为45.6μm的微光纤法布里-珀罗干涉腔,得到的干涉条纹平滑,衬比度约为26dB,并从激光与石英材料的相互作用上分析了形成较好干涉条纹的原因。把这种微腔应用于应变测量,在550μm范围内,腔长增量相对于应变的灵敏度为0.32nm/μm,线形度达0.9994。实验证明该微腔对温度不敏感,800℃范围内腔长变化仅20nm。157nm准分子激光加工光纤法布里-珀罗腔方法简单,一次成型,具有较高的加工效率和精度,有望实现光纤法布里-珀罗腔的规模化批量制造,具有较好的应用前景。