bluuebunny/crossref_metadata_2025_split huggingface dataset:
Latent photochromism (pseudothermochromism) and photofatigue of crystalline 2‐(2′,4′‐dinitrobenzyl)pyridine
Authors: Naumov Panče , Ohashi Yuji 
Published: August 2004

AbstractAlong with the metastable 2‐(2′,4′‐dinitrophenylmethylidene)‐1,2‐dihydropyridine (NH) and the unstable 6‐aci‐nitro‐2‐nitro‐5‐(2′‐pyridylmethylene)‐1,3‐cyclohexadiene (OH), the stable form of 2‐(2′,4′‐dinitrobenzyl)pyridine (DNBP), CH, is photochemically converted into small amounts of 1,2‐bis(2′,4′‐dinitrophenyl)‐1,2‐bis(2′‐pyridyl)ethane, trans‐bis[5‐nitro‐2‐(pyridine‐2‐carbonyl)phenyl]diazene N‐oxide, 6‐nitro‐3‐(2′‐pyridyl)‐2,1‐benzisoxazole and 3‐nitropyrido[1,2‐b]quinolin‐6‐ium‐11‐olate. The latent photochromism of DNBP, as shown by x‐ray analysis of the structures of the side‐products and ESR/IR measurements, is attributed to open‐shell reactions that are initiated by hydrogen photoabstraction and subsequent creation of two monoradicals, NH. and OH.. Large amounts of the radicals (ca 50% NH. and 70% OH.) confined in the crystalline interior are persistent under ambient conditions. Through quasi‐periodic reactions, the remaining radicals partially recover the ground‐state isomers CH, NH and OH, or decay to the side‐products, which results in crystalline photofatigue. Together with proton tunneling from the excited CH, the radical reactions represent dominant mechanism for the creation of NH and OH in the low‐temperature regimes, but are successfully competed by the closed‐shell reactions at higher temperatures. The precursor state, whose existence was assumed previously from transient absorption spectroscopy, may be identified as the radical OH.. The present work represents the first study of the photofatigue of a 2‐(2′,4′‐dinitrobenzyl)pyridine compound and extends the ‘classical’ mechanism of the photochromic reactions of nitrobenzylpyridines with a set of open‐shell radical reaction routes. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis and surface properties of fluorinated block copolymers containing sulfonic groups
Authors: Wang Feng , Li Hong , Zhang Zhao Bin , Hu Chun Pu , Wu Shu Sen 
Published: August 2004

AbstractA series of fluorinated block copolymers with different fluorinated block lengths and compositions were synthesized by atom transfer radical polymerization (ATRP), and then the block copolymers containing sulfonic groups with various sulfonation levels were successfully prepared further via a sulfonation reaction. These well‐defined block copolymers were characterized by means of Fourier transform infrared (FTIR), 1H‐nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The surface activities of the fluorinated block copolymers containing sulfonic groups in N‐methyl pyrrolidone solution and the surface properties of the films prepared from such a solution were examined, and the experimental results showed that the fluorinated block copolymers exhibited a high surface activity in solution and quite a low solid surface energy of films, even though they contain hydrophilic sulfonic groups. The critical surface tensions of these copolymers were estimated and were comparable to that of polytetrafluoroethylene. Even more interestingly, the surface activities of the block copolymers containing sulfonic groups or sodium sulfonate groups in aqueous solution were also measured. It was found that the surface activity in aqueous solution was weaker than that in N‐methyl pyrrolidone solution and depended on both the length of the fluorinated block and the sulfonation level of the block copolymers. The surface properties of the films prepared from the block copolymers in aqueous solution were tested, and most of these films exhibited a hydrophilic surface property. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4809–4819, 2004
Thermal stability of the fullerene‐chain link in 6‐arm PS stars with a C60 core
Authors: Audouin Fabrice , Nuffer Richard , Mathis Claude 
Published: August 2004

AbstractThe thermal stability of well‐defined hexa‐adducts (PS)6C60 in solution at temperatures around 100 °C has been studied by multi‐detector Size Exclusion Chromatography. The degradation reaction corresponds to a quantitative release of the polystyrene arms from the fullerene core through thermal cleavage of the PS‐C60 link. From the kinetics of formation of cut arms and the progressive decrease of the stars' functionality, we could establish that the reaction follows a stepwise “breaking” mechanism where a 6‐arm star is first converted to a 5‐arm star, then to a 4‐arm star, and so on down to the ungrafted arm. Furthermore, not only does the thermal stability of the PSC60 bond increase if the functionality of the star decreases, but the difference is large enough to allow determination of the kinetics constants for the first three steps. The activation energy for the breaking of an arm‐C60 link is about 65 kJ/mol. The stability of (PS)6C60 slightly decreases with an increase of the arm length. MALDI‐TOF mass spectroscopy has shown that both CC bonds in α and β positions to C60 can be cut, but the breaking of the direct fullerene‐arm bond is favored. We have also found that a polyisopreneC60 bond is about seven times less stable than a PS‐fullerene link upon heating. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4820–4829, 2004
Preparation and characterization of SBA‐15 supported iron(II)‐bisimine pyridine catalyst for ethylene polymerization
Authors: Guo Chao , Jin Guo‐Xin , Wang Fusong 
Published: August 2004

Abstract2,6‐Diacetylpyridinebis (2,6‐diisopropylani) iron dichloride, a late‐transition metal catalyst for olefin polymerization, was supported on SBA‐15 successfully and the property of the supported catalyst was carefully studied. Ethylene polymerization was systematically investigated in the presence of MAO under various conditions employing this type of catalyst system. In general, after support, a decrease in the catalytic activity was observed and higher molecular weight and fibrous morphology of polyethylene were obtained. The “extrusion polymerization” phenomenon was observed in ethylene polymerization by using the supported catalyst system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4830–4837, 2004
Polyampholytes
Authors: Dobrynin Andrey V. , Colby Ralph H. , Rubinstein Michael 
Published: August 2004

AbstractPolyampholytes are charged polymers with both positively and negatively charged groups. The conformation of these polymers in solutions strongly depends on the distribution of charged monomers along the polymer backbone and their environment. In this review we summarize the current level of understanding of such amphoteric polymers in solutions and their interactions with surfaces and polyelectrolytes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3513–3538, 2004
Familial susceptibility to severe respiratory infection in early life
Authors: Goetghebuer Tessa , Kwiatkowski Dominic , Thomson Anne , Hull Jeremy 
Published: August 2004

AbstractLower respiratory tract infections (LRTI) are common in the first year of life and are mostly caused by viruses. Severity of LRTI in infants is associated with early‐life environmental factors. Genetic association studies also suggest a role of heredity in susceptibility to acute bronchiolitis. We designed a case control study to further investigate relative importance of familial influences in risk of LRTI in early childhood compared to environmental factors. From a hospital database, we selected 1,308 children (436 cases; 872 controls) living in Oxfordshire. Cases were children under age 5 years admitted to hospital with LRTI. Parental history and other exposures were recorded in cases and controls by postal questionnaire. Maternal history of asthma increased the risk of severe LRTI in the first year of life, independent of subsequent asthma in a child. History of maternal bronchiolitis also increased the risk of infant LRTI. These results further suppoprt the possibility that genetic factors play an important role in susceptibility to severe viral respiratory infections in early life, and suggest that this effect may be independent of subsequent childhood asthma. Pediatr Pulmonol. 2004; 38:321–328. © 2004 Wiley‐Liss, Inc.
Effect of inhalation times on exhaled NO
Authors: Zacharasiewicz Angela , Wilson Nicola , Lex Christiane , Li Albert , Bush Andrew 
Published: August 2004

AbstractRecent work suggests that exhaled nitric oxide (eNO) can be divided into airway and alveolar components, using varying expiratory flow rates. It is known that higher values of eNO are found with lower expiratory flow rates, thought to be due to prolonged contact of the expirate with the bronchial epithelium. However, whether a prolonged inspiratory time could contaminate the alveolar signal with bronchial derived NO, by the same mechanism, is unknown. We aimed to study the effect, including repeatability, of inhalation time on eNO measurements performed at three different flow rates. We measured eNO in 21 children with asthma of different severity (no steroids, n = 2; inhaled corticosteroid (IC) dose up to 200 mcg/day, n = 3; IC up to 500 mcg/day, n = 3; IC >500 mcg/day, n = 6; IC >500 mcg/day and oral steroid, n = 7) and 24 normal adult controls at 50, 100, and 200 ml/s expiratory flow rate. The effect of either a rapid or a slow inhalation on measured eNO was studied at each flow rate. Furthermore, 12 asthmatic children and 12 adults had repeated measurements 1 hr apart. Repeatability within 1 day was assessed by calculating the single‐determination standard deviation (SD) and 95% range. Our results showed that repeatability was equally good for the three expiratory flow rates, and inhalation time had no influence on the results. The inhalation maneuver does not influence eNO measurements using the variable expiratory flow technique. Pediatr Pulmonol. 2004; 38:335–338. © 2004 Wiley‐Liss, Inc.
Fourier Transform Raman Spectroscopy of the Four Crystallographic Phases of α, β, γ and ε 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐hexaazatetracyclo[5.5.0.05,9.03,11]dodecane (HNIW, CL‐20)
Authors: Goede Patrick , Latypov Nikolaj V. , Östmark Henric 
Published: August 2004

AbstractFourier transform Raman Spectroscopy (Nd : YAG laser at 1064 nm) was used to characterize the four stable phases of 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐hexaazatetracyclo[5.5.0.05,9.03,11]dodecane (HNIW, CL‐20). Raman spectra are reported over the region from 0–4000 cm−1, relative to the laser line. A tentative assignment of the most predominant Raman peaks was made with the aid of QM calculations at the B3LYP/6‐31G(d) level. A method for detecting polymorphic impurities in ε‐CL‐20 was also developed. The detection level for polymorphic impurities was determined to be below 2%. A method for producing γ‐CL‐20 is also presented.
Combustion Mechanism of Consolidated Mixtures of 5‐amino‐1H‐tetrazole with Potassium Nitrate or Sodium Nitrate
Authors: Miyata Yasuyoshi , Date Shingo , Hasue Kazuo 
Published: August 2004

AbstractRecently, 5‐amino‐1H‐tetrazole is developed for practical use as a substitute for sodium azide, which is conventionally used as a fuel component of gas generating agents for automobile airbags. In this study, the combustion mechanisms of the mixtures 5‐amino‐1H‐tetrazole/potassium nitrate and 5‐amino‐1H‐tetrazole/sodium nitrate have been examined. It has been found that the Granular Diffusion Flame model is applicable to the tested samples even when a molten layer exists at the burning surface. In addition, it is shown that within the pressure range of 1–5 MPa, the greatest factor which affects the burning rate is the diffusion process. It is also demonstrated that the fuel component decomposes first, and the oxidizer decomposes next. Meanwhile, it has also been confirmed that the burning rate increases with an increase in pressure because the flame approaches the burning surface and the amount of heat transfer to the solid phase increases. In spite of a decrease in the amount of heat transfer from the gas phase to the solid phase and an increase in the thickness of the condensed phase reaction zone for a mixture with higher fuel content, there are little differences in the burning rates probably because of an increase in the rate of decomposition of the solid phase.
Dynamic Plate Thickness of ERA Sandwiches against Shaped Charge Jets
Authors: Held Manfred 
Published: August 2004

AbstractThe equation for the dynamic plate thickness is derived as a function of standoff distance Z0, jet tip velocity vj0, cutoff velocity vjc, plate velocities vPI and NATO angle of the ERA sandwich. The dynamic thickness is presented as functions of the different parameters for the front plate – flying against the shaped charge jet – and the rear plate – flying with the shaped charge jet. But the dynamic thickness is only one of the reduction factors of ERA sandwiches.
Theoretical Calculation and Molecular Design for High Explosives: Theoretical Study on Polynitropyrazines and Their N‐oxides
Authors: Li Jinshan , Huang Yigang , Dong Haishan 
Published: August 2004

AbstractThe geometries of polynitropyrazines and their N‐oxides have been fully optimized employing the density functional B3LYP method and the 6‐31++G** basis set. For polynitropyrazines and their N‐oxides we have obtained the enthalpies of formation (at p=1.013×105 Pa and T=298.15 K) by designing isodesmic reactions and the detonation velocities by using the Stine method. Calculated results show that the aromaticity of the pyrazine ring of polynitropyrazine is lower than that of its N‐oxide. From the acquired relationship between the experimental impact sensitivity H50 (12B type) and the least CNO2 bond order the predicted H50 values for compounds 2,5‐diamino‐3,6‐dinitropyrazine and 2,5‐diamino‐3,6‐dinitropyrazine‐1‐oxide are 83 cm and 59 cm, respectively, implying that they are low sensitive explosives. The enthalpy of formation of polynitropyrazine is much less than that of its N‐oxide. The calculated density (1.90 g/cm3) for 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) is close to the experimental value (1.918 g/cm3), and from both sensitivity and detonation velocity it has been deduced that LLM‐105 is superior to other diaminodinitropyrazines and their N‐oxides. The largest density and detonation velocity obtained in this work are 2.02 g/cm3 (2‐amino‐3,5,6‐trinitropyrazine) and 9.34 km/s (2,3,5,6‐tetranitropyrazine), respectively.
Combustion of Propellants with Ammonium Dinitramide
Authors: Chakravarthy Satyanarayanan R. , Freeman Jeffrey M. , Price Edward W. , Sigman Robert K. 
Published: August 2004

AbstractThis paper reports a series of experiments involving ammonium dinitramide (ADN), a new energetic oxidizer of potential use in composite solid propellants. The experiments include (a) self‐deflagration of pressed pellets of ADN; (b) combustion of sandwiches with ADN laminae on both sides of a binder lamina that is either “pure” or filled with particulate oxidizer and other additives; and, (c) combustion of propellants with a bimodal oxidizer size distribution, wherein, combustion of coarse ADN and fine AP (ammonium perchlorate) and vice versa were used, in addition to mixtures of coarse ADN and AP, fine ADN and AP, and all‐ADN or all‐AP formulations.
A Dde resin based strategy for inverse solid‐phase synthesis of amino terminated peptides, peptide mimetics and protected peptide intermediates
Authors: Rai Aman , Gutheil William G. 
Published: August 2004

AbstractThis report describes a Dde resin based attachment strategy for inverse solid‐phase peptide synthesis (ISPPS). This attachment strategy can be used for the synthesis of amino terminated peptides with side chains and the carboxyl terminus either protected or deprotected. Amino acid t‐butyl esters were attached through their free amino group to the Dde resin. The t‐butyl carboxyl protecting group was removed by 50% TFA, and inverse peptide synthesis cycles performed using an HATU/TMP based coupling method. Protected peptides were cleaved from the resin with dilute hydrazine. Side chain protecting groups could then be removed by treatment with TFMSA/TFA. The potential of this approach was demonstrated by the synthesis of several short protected and unprotected peptides in good yield and with low epimerization. Its potential for peptide mimetic synthesis was demonstrated by the synthesis of two peptide trifluoromethylketones. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd.
Electronic properties of Co and Ni silicides: a theoretical approach using extended Huckel method
Authors: Galvan D. H. , Posada Amarillas A. , Samaniego Reyna J. C. , García‐Méndez M. , Farías M. H. 
Published: August 2004

AbstractCalculations of electronic structure, total and projected density of states (DOS), crystal orbital overlap population (COOP), and average net charge, and also Mulliken population analysis, were performed to study electronic properties of Co and Ni silicides. Analysis of the energy bands depicts metallic behavior for both silicides.The projected DOS yields an indication that hybridization occurs for Co and Ni silicides. The hybridized band in CoSi2 is composed of Co d and p orbitals and Si p and s orbitals, while in NiSi2 the hybridized band is formed by Ni d and p orbitals with Si p orbitals. The fact that the Fermi energy crosses a small part of the DOS, as is the case of CoSi2, yields an indication of the different electronic properties of CoSi2 when compared to NiSi2. The hybridization is stronger in CoSi2 than in NiSi2. Mulliken population analysis provides an indication that a smaller charge distribution exists in NiSi2 when compared to CoSi2. This difference in charge distribution accounts for the different electronic behavior, in agreement with the DOS analysis. Moreover, COOP analysis provides an indication of the existence of covalent bonding between M and Si (M = Ni, Co), this being stronger in Co than in Ni silicides. Furthermore, the average net charge in both compounds yields an indication that there is a charge transfer from M towards Si. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First‐principles elastic constants and electronic structure of BP, BAs, and BSb
Authors: Meradji H. , Drablia S. , Ghemid S. , Belkhir H. , Bouhafs B. , Tadjer A. 
Published: August 2004

AbstractWe have carried out a first‐principles total‐energy calculation of the structural and the elastic properties for the series of boron compounds BP, BAs, and BSb. We have applied the augmented plane‐wave plus local‐orbitals method with both the local‐density approximation (LDA) and the generalized gradient approximation (GGA). Since there have been no previous theoretical or experimental determinations, our calculations provide the first available information on the elastic constants of these materials. The elastic constants have been derived by the stress‐strain relation. We have calculated all of the equilibrium structural parameters for both phases: rock salt and zinc blende structures. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interstitial substitutions of vanadyl ions doped in single crystals of hexaimidazole cobalt sulphate: An EPR study
Authors: Sougandi I. , Velavan K. , Venkatesan R. , Sambasiva Rao P. 
Published: August 2004

AbstractElectron paramagnetic resonance studies on single crystals of hexaimidazole cobalt(II) sulphate doped with VO(II) are carried in the temperature range 77–300 K at X‐band frequencies. Single crystal EPR spectra indicate the presence of vanadyl impurity positioned in four sites with intensity ratios of 45:36:6:1. Angular variation studies in all the three orthogonal planes confirm that both the intense vanadyl sites have occupied interstitial positions in the lattice. The spin Hamiltonian parameters, calculated for the two sites, indicate orthorhombic nature for the impurity. However, the analysis of powder spectrum reveals the presence of only one site. The spin‐lattice relaxation parameters have been calculated at various temperatures from line width measurements. The admixture coefficients have also been calculated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature shift of the Fe2+ absorption band in LiNbO3:Fe crystal
Authors: Yükselici M. H. , Allahverdi Ç. , Tunç A. V. 
Published: August 2004

AbstractThe temperature dependence of the Fe2+ absorption band of a strongly oxidized LiNbO3:Fe crystal is reported over the range from 25 to 350 °C, where the effect of temperature on the band is reversible. The band broadens and shifts to lower energy as temperature is increased. The rate at which the absorption peak energy decreases with increasing temperature is calculated as –6.8 × 10–5 eV/°C from the slope of the straight‐line fit to the temperature against peak position energy graph. We propose that the origin of the temperature shift is due to both a shift of the energetic position of impurities and the decrease of the band gap energy. The consistency between the calculated rate by the help of a simplified model which describes the shift of the band gap energy in the frame of the lattice dilation and the observed rate suggests that the lattice dilation might be responsible for the temperature shift of the band. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Radiative properties of Er(DBM)3(TPPO)2 doped solid poly(methyl methacryate) matrix
Authors: Liang Hao , Chen Biao , Zheng Zhiqiang 
Published: August 2004

AbstractEr(DBM)3(TPPO)2 doped solid poly(methyl methacryate) (PMMA) matrix was prepared and its optical absorption and fluorescence spectra were presented. The Judd–Ofelt parameters obtained for Er3+ in PMMA are 43.84 × 10–20 cm2, 2.31 × 10–20 cm2 and 1.12 × 10–20 cm2. The radiative properties, such as transition probabilities, fluorescence branching ratios and radiative lifetime have been predicted and evaluated. The calculated radiative lifetime and stimulated emission cross section of 4I13/2 → 4I15/2 transition revealed that it is promising for Er(DBM)3(TPPO)2 doped PMMA to be used in rare earth containing polymer based optical devices. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dielectric and optical studies of phase transitions in [(CH3)2NH2]5Cd2CuCl11 crystal
Authors: Elyashevskyy Yu. , Dacko S. , Kosturek B. , Czapla Z. , Kapustyanik V. B. 
Published: August 2004

AbstractSingle crystals of [(CH3)2 NH2]5Cd2CuCl11 have been grown and their dielectric and optical properties have been studied. Electric permittivity, losses and linear optic birefringence measurements have shown that the obtained new crystal is isomorphous with the original one – [(CH3)2 NH2]5Cd3Cl11. Phase transitions were observed at 175 K (continuous) and 120 K (first order). It means that partial replacing of cadmium atoms by copper ones does not change the structure and the heavy Cd2CuCl11–2 anions do not influence significantly the interaction of dimethylammonium cations. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Human tumor suppressor p53 and DNA viruses
Authors: Collot‐Teixeira S. , Bass J. , Denis F. , Ranger‐Rogez S. 
Published: August 2004

AbstractHuman tumor suppressor protein p53 plays a major role in the cell cycle, orchestrating a number of important genes involved in cell‐cycle control and apoptosis, and seems to be one of the most important molecules protecting cells from malignant transformation. Mutations in the p53 gene are observed in about 50% of primary tumors, inducing defective p53 protein no longer capable of binding DNA and of activating transcription. Certain DNA viruses are thought to act in a similar way and may also contribute to the progression of invasive cancer in infected tissue. One of the most effective strategies employed by these viruses is the inhibition of p53 protein by interaction with viral oncoproteins, implying a direct but also an indirect role of these viruses in the impairment of p53 structure and function. This article provides a summary of current knowledge concerning p53 tumor suppressor protein and reviews the different mechanisms adopted by different DNA viruses in undermining p53 function. Copyright © 2004 John Wiley & Sons, Ltd.