Convective Regime of Filtration Combustion of Energetic Materials in a Cocurrent Flow of Their Combustion Products

The convective regime of filtration combustion of energetic materials in a cocurrent flow of their combustion products is studied using a model with extremely simplified kinetics and heat transfer, which shows instability of the process. It is shown that the more accurate twotemperature model describes a steadystate regime. In this regime, the gas temperature on the hot boundary of the heating zone is well below the combustion temperature, and the solidphase temperature is well below the temperature proposed in recent studies on this topic. It is pointed out that the twotemperature approach is unjustified and intragranular nonisothermicity must be taken into account for convective regimes. It is shown that the threetemperature model, which takes into account this effect, does not give a stable steadystate solution.     

Isolation of a lactone,structurally related to the esterifying acids of pyrrolizidine alkaloids,from the costal fringes of male Ithomiinae

Adult male Ithomiinae feed at plants containing pyrrolizidine alkaloids. Certain species secrete on hairs of the costal fringe, a specialized organ on their hindwings, a novel -lactone structurally related to the unusual branched-chain acids that are unique to these alkaloids.     

Properties ofSrMO 3-δ(M=Fe,Co) as oxygen electrodes in alkaline solution

Strontium ferrates and cobaltates with compositions SrFeO_3- (0.060.40) and SrCoO_3- (0.040.30) were synthesized. The dependence of the oxygen electrode properties on the value was examined in 1 mol dm^–3 KOH solution. In the SrFeO_3- series, the samples with 0.24<<0.29, showed the highest activity in both oxygen evolution and reduction reactions. In contrast, no strong dependence on the value was observed in SrCoO_3-, which also showed a high catalytic activity for oxygen evolution.     

Effect of framework aluminum in proton‐ or copper‐exchanged MFI ferrialuminosilicates on their activity for the reduction of nitric oxide with ammonia

Reduction of NO with ammonia in excess oxygen has been carried out on protonform and Cu²⁺exchanged MFI ferrialuminosilicate. Though HZSM5 showed very low activity, the framework Al in Hferrialuminosilicate greatly enhanced the activity. The framework Al in Cu²⁺exchanged ferrialuminosilicate also enhanced the activity to some extent.     

Soldier defense secretions of malaysian free-ranging termite of the genusLacessititermes (Isoptera,Nasutitermitinae)

Soldiers of free-ranging termites of the genusLacessititermes (Isoptera, Nasutitermitinae) secrete from their frontal glands a mixture of monoterpenes, sesquiterpenes, and diterpenes.Lacessititermes ransoneti, L. laborator, andL. species A produce species-specific secretions, the composition being most complex forL. laborator. Apart from known mono- and dihydroxytrinervitadienes, the following new diterpenes were isolated and tentatively assigned as trinervita-1(15),8(19)-dien-2,3,9,14-tetraol 2,3,14-O-triacetate, trinervita-1(15),8(19)-dien-2,3,9,14-tetraol 2,3,14-O-triacetate, 2,3,9, 14-tetraacetoxy-1 (15), 8(19)-trinervitadiene, and 2,3,11,13-tetraacetoxy-1(15),8(19)-trinervitadiene. Data on intragenus chemical variations were subjected to canonical discriminant analysis and genetic distances among the species were calculated to depict intragenus identities and affinities.     

Fertilizer requirements for specified yield targets. I. Theoretical derivation of mathematical models for the computation of soil and fertilizer nutrient efficiencies

The conventional deduction procedure of computation of soil () and fertilizer () nutrient efficiencies for the amount of fertilizer required for specified yield targets does not make provision of the amount of soil nutrient derived by crops from the available pool of soil nutrients not accounted for in the amount extracted by a soil test procedure. The derivation of two mathematical models, viz., Tamil Nadu Agricultural University Model I [TNAU Model I] and Model II [TNAU Model II] is reported in this paper which aim at computing the soil () and fertilizer () nutrient efficiencies not accounted for by the conventional method.In the case of TNAU Model I, the relationship between the nutrient uptake (U) and the soil (S) and the fertilizer (F) nutrients was established by assuming a functional relationship of the type U =S +F such that 0 1 and 0 1. In TNAU Model II the same relationship was established as U =S +F + such that 0 1, 0 1 and > 0. The term in the latter model is a measure of the amount of soil nutrient the crop absorbs from a slowly available pool of nutrients not accounted for in the amounts extracted by the soil test procedure employed or applied through fertilizer.The field verification of these models is reported elsewhere.     

Water vapor absorption and aqueous retention of hydrolyzed starch polyacrylonitrile graft copolymers — “superabsorbent starch”

Summary Starch copolymers with polyacrylonitrile grafts were prepared using the Mn³⁺ initiation method and different amounts of acrylonitrile. The product was hydrolyzed in aqueous alkali (nitrile groups to amide and carboxyl groups) to enhance the hydrophilic character of the copolymer and achieve superabsorbent properties. At relative humidities (RH) up to 95–97 % the modified starch shows normal water vapor absorption like cellulose and other polysaccharides. When in contact with liquid distilled water, the modified starch forms a superabsorbent gel which retains very large amounts of water (up to 800 g/g). At low and high pH and in aqueous salt solutions (NaCl, CaCl₂ and synthetic urine) the water retention is strongly reduced. This is interpreted as due to the ionic strength (salt effect) and for Ca²⁺ ions probably also crosslinking by salt formation with carboxyl groups on adjacent chains or chain segments.     

Factors governing the electrochemical synthesis of α-nickel (ii) hydroxide

The electrodeposition of -nickel hydroxide is promoted by the simultaneous chemical corrosion of the electrode by an acidic nitrate bath. Chemical corrosion results in the formation of a poorly ordered layered phase which is structurally similar to -nickel hydroxide and provides nucleation sites for the deposition of the latter. Therefore under conditions which enhance corrosion rates such as low current density (<1.3 mA cm–2), high temperature (60 C), high nickel nitrate concentration ( 1M) and the resultant low pH (1.7), -nickel hydroxide electrodeposition is observed, while -nickel hydroxide forms under other conditions. Further, -nickel hydroxide deposition is more facile on an iron electrode compared to nickel or platinum.     

Sugars in Mediterranean Floral Nectars: An Ecological and Evolutionary Approach

High-pressure liquid chromatography analyses of 73 plant species showed that the nectars of phrygana (East Mediterranean garrigue) mainly contain sucrose, glucose, and fructose, and traces of 10 minor sugars. Although the sucrose/hexose ratio was not related to plant life habit, ecological constraints had a detectable effect in shaping sugar composition. This was detected by distinguishing the phryganic plant species into spring–summer and winter flowering, with the distinction made on the basis of the water deficit in the study area. Plants flowering in spring–summer had a higher rate of high sucrose (i.e., sucrose/hexose ratio 0.5; 60.8% of the plant species) vs. low hexose nectars (i.e., ratio <0.5; 39.2%). The ratio was reversed in winter flowering species (36.4% vs. 63.6% with high sucrose and high hexose, respectively). Sucrose/hexose ratios were associated with plant family. The highest values were those of Lamiaceae, which differed significantly from the low sucrose Liliaceae and Apiaceae. Based on recorded plant–pollinator interactions in the community, the present data provide evidence of a partitioning of nectar resources by the existing pollinator guilds within the community, based on the sugar profiles of nectar (all sucrose/hexose ratios for all interactions). Among all major groups, bees and wasps (aculeates) preferred high sucrose nectars, which differed significantly from syrphids, anthomyid a.o. flies, and beetles that visited low sucrose nectars. Similarly, butterflies visited lower sucrose nectars compared to bees. Within families, only Megachilidae could be clearly characterized as high sucrose consumers, differing in this respect from all the remaining insect groups including most other bee families. This confirms previous findings that Megachilidae have a key position in Mediterranean communities where they probably constitute a selective factor for high sucrose nectars.     

High resolution transmission electron microscopic (HRTEM) determination of the preferentially exposed faces onγ-Al2O3 andη-Al2O3

High resolution transmission electron microscopy has been used to examine the crystallites in -Al₂O₃ and -Al₂O₃. -Al₂O₃ has been found to be nearly hexagonally shaped crystallites whose identity distances and angles of fringe patterns indicate that (110) planes are preferentially exposed. -Al₂O₃ showed preferentially exposed surfaces of (100), (110) and super imposed (111)/(211). This information is valuable to the catalyst researcher trying to model the surfaces of these two supports.     

Ways of devising low-waste technology in units for freeing gas-air mixtures from hydrogen sulfide and carbon disulfide

Conclusions A calculation of the coefficient of utilization of material resources performed for the gas clean-up works of one of the plants in the sub-branch — the Cherkassk Khimvolokno Sci.-Ind. Assoc. (for the gas purifiers of the first and second manufacturing units) — has shown that, at present, the waste-freedom coefficient is 0.64. Thereupon, this gas clean-up works has been assigned to the ordinary manufacturing category.On transition of the gas clean-up units to low-waste technology on introduction of the measures indicated above, the waste-freedom coefficient is increased to 0.8 and the gas clean-up works becomes a low-waste operation.Translated from Khimicheskie Volokna, No. 6, pp. 3–5, November–December, 1988.     

Synthesis of statistical polydiene networks by reaction of liquid polyenes with telechelic siloxanes

The present investigation concerns the synthesis of statistical networks similar to vulcanized rubber. We have used liquid precursor polymers: polybutadiene (PB) and polyisoprene (PI) with telechelic siloxanes. The reactivity of the polydienes can be classified as follows: PB units 1,2 PI units 3,4 PI units 1,4 0. The network formation is a function of the ratio R = nb, of pendent double bonds/nb. of SiH. For R 1 the networks are rather hard and brittle, for 8 R 10 they are soft and elastic, whereas for R 16 the gels obtained are very soft and sticky.     

Synthesis of new metal-containing side-chain monomers and polymers

New metal-containing vinyl monomers, hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hexyl-6-oxy-{4-[4-(4-ferrocenoyl phenyl)phenyl]benzoyloxy}methacrylate, and the corresponding homopolymers and random copolymers with hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate were synthesized. The compounds were characterized by¹H NMR; their thermal behavior was investigated by means of differential scanning calorimetry. Monomers and polymers containing the ferrocene unit melt at lower temperatures than those derived from the cyclopentadienyl managanese tricarbonyl moiety. The melting temperatures of the monomers and polymers ranged from 399 to about 515 K, Both monomers and polymers failed to exhibit mesogenic behavior. Values ofM _n,M _w,M _w/M _n, and degree of polymerization were obtained by gel permeation chromatography. TheM _n ranged from 16,500 for the copolymer containing hexyl-6-oxy-{4-[4-(4-ferrocenoyl phenyl)phenyl] benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio to 26,000 for the copolymer containing hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio.M _w/M _n ranged from 1.6 in the case of the copolymer containing hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio to 2.2 in the case of poly(hexyl-6-oxy{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate).     

Fabrication and characterization of the Ag‐based high‐technology model nanocluster catalyst for ethylene epoxidation manufactured by electron beam lithography

Nanocluster catalysis is an area where greater fundamental knowledge is needed to understand the behavior of aggregates of metal atoms in determining product selectivity of chemical reactions. While catalysis is practiced industrially with economic success there is still a great need to eliminate wasteful sidereactions which hurt overall yields. Here we report on fabrication of a Agbased hightechnology model nanocluster catalyst by using electron beam lithography (EBL) designed for systematic studies of the ethylene epoxidation reaction. The catalyst is made of a square array of cylindershaped Ag nanoclusters that are 200 Å in diameter, deposited on a four inch silicon wafer, precovered with a 100 Å thick film of alumina. The height of the particles and interparticle distance can vary, and were chosen to be 150–300 and 1000 Å, respectively. The high technology catalyst was characterized by Xray photoelectron spectroscopy (XPS), highresolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The thermal stability of Ag nanoclusters in vacuo was investigated.     

Deactivation of ferrierite during the skeletal isomerization of linear butenes

Deactivation of ferrierite during the skeletal isomerization of 1-butene at atmospheric pressure and 0.15 atm 1-butene partial pressure was studied. At 300°C, the carbon content shows a sharp increase during the first 30 min-on-stream, with a slower growth thereafter. Temperature-programmed oxidation profiles corresponding to different times-on-stream are similar, showing two well-defined combustion peaks centered at about 325 and 640°C, respectively. When starting the 1-butene feed with the catalytic bed at 100 or 200°C and then increasing the temperature up to 300°C, no significant difference is observed, neither in carbon content nor in oxidation profiles. Important differences in the profiles are observed by comparing at the same time at each temperature. The lower the temperature, the higher the reactivity toward oxidation at low temperature. The carbonaceous deposit formed at 100°C shows the main combustion peak at the lowest temperature (135°C) and a more olefinic character; it could be related to a strong adsorption of reactant molecules. At 200°C, the proportion of saturated species associated to oligomers increases; while at 300°C, coke shows both aromatic and olefinic species.     

Dynamic mechanical properties of crosslinked polyisoprene under deformation

Summary Molecular motions of elastomers under deformations were observed through dynamic mechanical measurements. Composite master curves of dynamic moduli E and E and loss tangent tan over a wide range of frequency and in a state of elongation were obtained by the time-temperature superposition procedure. It is found that both moduli increase with strain, . The slope of the dispersion curve of E become more gradual with the increase in , while that of E is almost unchanged. The increment of E is generally larger than that of E, which does not agree with the N. W. Tschoegl prediction, E ^* ()=f() E _o ^* (), where E ^* () and E _o ^* () are complex moduli at the strain of and O, respectively, and f() is the function of only . The difference in the strain dependence of E from E was found to correspond to the strain dependence of the equilibrium modulus.     

Gasless Combustion of Ti–Al Bimetallic Multilayer Nanofoils

Ti–Al multilayer foils were produced magnetron vacuum deposition. The microstructure period varied in the range of 5–110 nm, the number of layers was 150–4700, and the total thickness of a multilayer foil reached 15–20 m. The gasless combustion of the foils was studied. Steadystate and pulsating combustion regimes were revealed; combustion temperatures were determined for both regimes. It was shown that the most probable mechanism of the selfpropagating reaction is the diffusion of Al in Ti at a temperature close to the temperature of the transition.     

Intermediate angle scattering functions and local chain configurations of semicrystalline and amorphous polymers

Summary Molecular scattering functions at intermediate scattering vectors, of =(4/ sin/2) in the range 0.03 to 1.0Å^–1, are found to be extremely sensitive to the local configurations of polymer chains in both semicrystalline and amorphous states. Available experimental results of intermediate angle neutron scattering (IANS) from melt-crystallized polyethylene and isotactic polypropylene provide compelling evidence that adjacent re-entry is rare. The rotational isomeric state model satisfactorily accounts for IANS and chain dimensions of polycarbonate in the amorphous state.     

Specific features of the phase transformations occurring during the sintering process of the beta-alumina based ceramics and their properties

Conclusions During the sintering process of beta-alumina obtained using the method of plasmochemical synthesis, the structural transformation occurs and it is accompanied by the separation of the excess Na₂O and the formation of an intergranular meltlike phase that is saturated with sodium and is characterized by high dielectric properties.The quantity of the meltlike phase and the magnitude of the /( + ) ratio determine the degree of stabilization (stability) and the final resistivity of the material and depend on the initial chemical composition and the heating rate maintained during the sintering process.It was shown that when the duration of residence of the material in the hot zone of the furnace is increased or when the specimens sintered maintaining high heating rates are subjected to additional heat treatment, one observes the occurrance of the reverse structural transformation that is characterized by an increase of the phase ratio /( + ) 1, a reduction in the quantity of the meltlike phase right up to its complete disappearance, and a decrease of the electrical resistivity of the material.In the materials having a large excess quantity of sodium oxide, the process of crystallization of the intergranular NaAlO₂ phase occurs simultaneously with the second phase transformation.The best ceramic and electrophysical parameters were obtained when sintering the material contained 7.9% Na₂O.Translated from Ogneupory, No. 3, pp. 13–18, March, 1990.     

Crystal Orientation Dependence of Macropore Formation in n-Si With Backside-Illumination in HF-Electrolyte

The formation of macropores on anodically biased n-type silicon with backside-illumination was investigated as a function of crystal orientation and bias voltage. Specimens were cut from bulk crystals with various orientations from {100} to {111}, polished and subjected to anodic etching in HF. The resulting pores were investigated on cleaved samples by SEM. All pores were found to grow in either a 100 direction or a 113 direction, depending on the misorientation angle. This finding applies also to the branching of a single pore. The results can be understood if the valence for the dissolution reaction is approximately 2.6 in 100 and approximately 4 in the 113 direction, and if all other directions are not allowed for the growth of pores in Si.