On the possibility of oscillatory electrodynamic instability in nematic liquid crystal in a constant inhomogeneous electric field

It is shown that electrodynamic instability in a nematic liquid crystal in constant inhomogeneous electric field can exhibit an oscillatory character. A frequency has been found that is close to that of oscillations observed in experiments.

     

Physical model for shock-wave initiation of detonation in pressed fine crystalline xplosives

A physical model is proposed for the reaction kinetics of heterogeneous explosives under shock-wave initiation of detonation. The model is based on the assumption that the molecular crystals of the explosive materials have semiconductor properties. The model can account for the experimentally observed strong dependence of the shock-wave sensitivity of pressed explosives on their initial density and temperature. The proposed model can be checked by measuring the band gaps of triaminotrinitrobenzene (TATB) and comparing with the value of 40 kcal/mole obtained in the present study from an analysis of explosion experiments. Pis’ma Zh. Tekh. Fiz. 24, 1–5 (October 26, 1998)     

Rapid mass spectrometric analysis of fragments of trinitrotoluene,picric acid and tetryl generated by laser irradiation

Experiments have been made in which single crystals of nitroaromatic explosives such as trinitrotoluene, picric acid and tetryl were irradiated with a focused laser beam of wavelength 266 nm and of duration of 5 n sec in an ultra-high vacuum system housing a sensitive and fast (microsecond time resolution) time-of-flight mass spectrometer. Both positive and negative ions of the products of decomposition were mass-analysed and it has been possible to propose the decomposition schemes of the different explosives. An important finding is that the substituents on the phenyl ring do not affect the breakdown schemes of the different explosives. This has important implications for understanding the different impact sensitivities of these explosives.     

Primary explosives: electrostatic discharge initiation, additive effect and its relation to thermal and explosive characteristics

All explosives, under all conditions must be considered vulnerable to generation, accumulation and discharge of static charge. The low energy static hazards of the order as low as 2-3 mJ need to be guarded against in case of highly sensitive compounds namely primary explosives. The hazard is normally associated with manufacturing and filling operations due to discharge of static charge accumulated on a person supplying energy up to 20 mJ. To reduce the risk associated with static initiation hazard in the processing and handling of the explosives, the electrostatic sensitivity tests can provide an important input regarding electrostatic hazards. This paper presents electrostatic sensitivity data in terms of zero ignition probability data (E(SE0)) of some of the initiatory explosives such as nickel/cobalt hydrazinium nitrate, silver azide, lead azide and mercury salt of 5-nitro tetrazole. Similar data has also been presented for samples coated with polyvinyl pyrrolidone to study its effect on electrostatic sensitivity. The electrostatic spark sensitivity of some conventional and novel made to explain the increased spark sensitivity behavior on the basis of the possible primary explosives has been studied. The electrostatic spark sensitivity of primary explosives decreased in the order of AgN3 = NHN > PbN6 > MNT > CoHN > BNCP. A possible correlation of spark energy with approximation and assumption has been drawn with thermal, detonation and mechanical properties. The polyvinyl pyrrolidone coated samples followed the same order but interestingly with increased spark sensitivity. An attempt has been reasoning of dielectric nature of the materials or exothermic effects of decomposition products of PVP. The present work also reports the electrostatic spark sensitivity of cap compositions.     

Inverse analysis of flow behaviour of AISI 304 stainless steel casing and Nd–Fe–B magnet at different strain rates

Abstract

Nanocrystalline Nd–Fe–B magnets are the most promising permanent magnets for high value applications. Strain rate and temperature have been established as the important parameters under dynamic processing for the development of texture and optimisation of magnetic properties. Experiments have been carried out at the constant true strain rates of 0·01, 0·5 and 5·0 s^–1 at 800°C. Flow stress generated from the experiments represents the combined effect of casing and magnet. To isolate the effect of stainless steel casing, composite deformation has been studied using finite element method. In this way, flow behaviour of steel and Nd–Fe–B magnet has been evaluated.     

静态乳化器

为提高乳化炸药生产过程的安全性,开发新的本质安全的静态乳化器势在必行。静态乳化器由敞口、低转速的粗乳器和精乳器组成,精乳器为静态混合器,两者之间由螺杆泵衔接。通过理论计算和试验研究,确定了静态乳化器的主要技术参数。目前,静态乳化器已成功用于乳化地面站,产品性能稳定,完全满足有关国家标准的要求。静态乳化器的研发可以大大改善乳化炸药生产过程中的安全性,避免因设备自身设计缺陷引起的爆炸等恶性安全事故,提高炸药生产企业的安全生产水平,提升我国工业炸药的生产技术水平。     

Structural transitions in directionally solidified graphitic cast irons

Abstract

Magnesium fading in conjunction with directional solidification has been used to determine the conditions for the structural transition from flake to compacted to nodular graphite in a hypoeutectic and a hypereutectic cast iron. Results are presented in terms of predominance-area diagrams and the conditions for stability are given. Magnesium fading has also been studied during the experiments and a mass transfer coefficient has been determined.

MST/474     

复合乳化剂对乳化炸药贮存稳定性分析

影响乳化炸药贮存期的因素很多,而乳化剂是其中最主要的因素之一.试验中采用了复合型乳化剂,对比试验表明,STL复合乳化剂克服了单一乳化剂的不足,具有良好的乳化作用;生产工艺与使用安全可靠,乳化炸药的贮存稳定性明显改善.     

Highly effective H2/D2 separation in a stable Cu-based metal-organic framework

A three-dimensional copper metal-organic framework with the rare chabazite(CHA)topology namely FJI-Y11 has been constructed with flexibly carboxylic ligand 5,5'-[(1,4-phenylenebis(methylene))bis(oxy)]diisophthalic acid(H₄L).FJI-Y11 exhibits high water stability with the pH range from 2 to 12 at temperature as high as 373 K.Importantly,FJI-Y11 also shows high efficiency of hydrogen isotope separation using dynamic column breakthrough experiments under atmospheric pressure at 77 K.Attributed to its excellent structural stability,FJI-Y11 possesses good regenerated performance and maintains high separation efficiency after three cycles of breakthrough experiments.     

New method for calculating densities of nitroaromatic explosive compounds

A new model has been introduced for simple calculation of crystal density of an important class of organic explosives, namely nitroaromatic energetic compounds. This model is based on the fundamental correlation. The introduced procedure has been applied to 60 well-known and new synthesized organic nitroaromatic explosives. The results show that the present method gives comparable prediction respect to well-developed group additivity method for estimation of crystal density of organic explosives. The introduced simple method can be applied to any complex nitroaromatic explosive that contains the elements of carbon, hydrogen, nitrogen and oxygen with no difficulties.     

Recrystallisation of single crystal superalloy CMSX–4

Abstract

A series of experiments investigating the recrystallisation of single crystal superalloy CMSX-4 have been carried out. Indentation atroom temperature has been used to study the effects of annealing time and temperature, and it has been found that a very strong dependence upon temperature is evident. Annealing above the γ′ solvus temperature results in very rapid growth of recrystallised grains whereas annealing below the γ′ solvus greatly suppresses the advancing grain boundaries. Additionally experiments have been carried out using an electrothermal mechanical test (ETMT) machine, to study the effects of degree of plastic strain and the temperature at which the strain is introduced. The strain threshold for recrystallisation under various annealing conditions has been determined and it has been found that recrystallisation occurs more readily if strain is introduced above 950°C. Finally, apparent activation energies for recrystallisation have been determined by measuring the change in resistivity that occurs during recrystallisation.     

Detecting Explosions with Ionizing-Radiation Measurement of Scattered 137Cs γ-Rays

Measurements have been made on the spectra of the rays scattered by trotyl and by substances similar to it in density and composition placed behind various shielding materials. The experiments check the scope for implementing -tomography for observing and identifying explosives.     

Formulation Optimization of a Hydrocolloid Dressing

Abstract

A methodology of mixture experiments has been applied to the formulation of a multicomponent hydrocolloid dressing. Using an extreme vertices statistical design, a semi-occlusive dressing composed of dextran, phospholipid, glycerol and sodium lauryl sulphate has been formulated, which checks evaporative water loss (EWL) from the excised wound surface of rats to an optimum level.     

Modelling the flow behaviour of steel under non-isothermal conditions

Abstract

A mathematical model is proposed for evaluating flow behaviour under hot deformation conditions. The effects of dynamic recovery and recrystallisation as well as temperature and strain rate variations are considered in the model by means of Bergstrom's approach and the additivity rule for strain. To verify the model, hot compression tests for three grades of steel together with upsetting experiments are carried out. Comparison between experimental and theoretical results confirms the reliability of the model.     

CONTINUOUS COOLING OF WET FOUNDRY SAND USING A FLUIDIZED BED

Abstract

In order to establish the optimum cooling system for hot returned sand in metal casting processes, a mathematical model including simultaneous heat and mass transfer has been constructed. The present study is especially directed towards clarifying the dynamical behavior of sand cooling in a one-pass fluidized bed. A series of continuous cooling experiments has been made for various conditions. Characteristics of both transient and steady-state bed temperature are explained reasonably by the present model. Furthermore, a possible proposal has been given on the optimal operation, which raises heat exchange efficiency in fluidization cooling of hot molding sand.     

Suppression of Multiple Scattering by Photon Cross-correlation Techniques

Abstract

With growing scientific interest in concentrated colloidal systems, multiple scattering becomes a major obstacle in many light-scattering experiments. Stimulated by work of Phillies and Drewel, three different dual-beam dual-detector dynamic light scattering experiments are discussed, which all achieve the isolation of singly scattered light by photon cross-correlation. All three experiments allow for a large variation of the scattering angle—an important requirement for studies of interacting systems.     

Transition between two steady states of unidirectional solidification of lanthanum modified Al–Si eutectic

Abstract

The transition between two steady states of unidirectional solidification of Al–Si eutectic modified with 0·5 wt-%La has been investigated experimentally by abruptly changing the solidification rate. The addition of lanthanum results in only partial modification of the eutectic microstructure, fiakelike and fibrelike silicon phases being always present after solidification. The interflake spacing and the interfibre spacing are shown to have a continuous but retarded response to an abrupt change of solidification rate, the retardation of the interflake spacing being the greater. A model of the response dynamics governing the transition has been developed to interpret the results of the experiments.

MST/1237     

Desorption electrospray ionization of explosives on surfaces: sensitivity and selectivity enhancement by reactive desorption electrospray ionization

Desorption electrospray ionization (DESI), an ambient mass spectrometry technique, is used for trace detection of the explosives trinitrohexahydro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2,4,6-trinitrotoluene (TNT), Pentaerythritol tetranitrate (PETN), and their plastic compositions (Composition C-4, Semtex-H, Detasheet) directly from a wide variety of surfaces (metal, plastic, paper, polymer) without sample preparation or pretreatment. Analysis of the explosives is performed under ambient conditions from virtually any surface in very short times (<5 s) including confirmatory tandem mass spectrometry (MS/MS) experiments, while retaining the sensitivity and specificity that mass spectrometry offers. Increased selectivity is obtained both by MS/MS and by performing additional experiments in which additives are included in the spray solvent. These reactive DESI experiments (reactions accompanying desorption) produce such ions as the chloride and trifluoroacetate adducts of RDX and HMX or the Meisenheimer complex of TNT. Desorption atmospheric pressure chemical ionization, a variant of DESI that uses gas-phase ions generated by atmospheric pressure corona discharges of toluene or other organic compounds, provides evidence for a heterogeneous-phase (gaseous ion/absorbed analyte) charge-transfer mechanism of DESI ionization in the case of explosives. Plastic explosives on surfaces were analyzed directly as fingerprints, without sample preparation, to test DESI as a possible method for in situ detection of explosives-contaminated surfaces. DESI also allowed detection of explosives in complex matrixes, including lubricants, household cleaners, vinegar, and diesel fuel. Absolute limits of detection for the neat explosives were subnanogram in all cases and subpicogram in the case of TNT. The DESI response was linear over 3 orders of magnitude for TNT. Quantification of RDX on paper gave a precision (RSD) of 2.3%. Pure water could be used as the spray solution for DESI, and it showed ionization efficiencies for RDX in the negative ion mode similar to that given by methanol/water. DESI represents a simple and rapid way to detect explosives in situ with high sensitivity and specificity and is especially useful when they are present in complex mixtures or in trace amounts on ordinary environmental surfaces.     

Development of a technique using MCNPX code for determination of nitrogen content of explosive materials using prompt gamma neutron activation analysis method

Nuclear-based explosive detection methods can detect explosives by identifying their elemental components, especially nitrogen. Thermal neutron capture reactions have been used for detecting prompt gamma 10.8 MeV following radioactive neutron capture by ¹⁴N nuclei. We aimed to study the feasibility of using field-portable prompt gamma neutron activation analysis (PGNAA) along with improved nuclear equipment to detect and identify explosives, illicit substances or landmines. A ²⁵²Cf radio-isotopic source was embedded in a cylinder made of high-density polyethylene (HDPE) and the cylinder was then placed in another cylindrical container filled with water. Measurements were performed on high nitrogen content compounds such as melamine (C₃H₆N₆). Melamine powder in a HDPE bottle was placed underneath the vessel containing water and the neutron source. Gamma rays were detected using two NaI(Tl) crystals. The results were simulated with MCNP4c code calculations. The theoretical calculations and experimental measurements were in good agreement indicating that this method can be used for detection of explosives and illicit drugs.