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1.
2.
K. Dasgupta P. Barat A. Sarkar P. Mukherjee D. Sathiyamoorthy 《Applied Physics A: Materials Science & Processing》2007,87(4):721-726
The use of graphite as a moderator in a low temperature thermal nuclear reactor is restricted due to accumulation of energy
caused by displacement of atoms by neutrons and high energetic particles. Thermal transients may lead to a release of stored
energy that may raise the temperature of the fuel clad above the design limit. Disordered carbon is thought to be an alternative
choice for this purpose. Two types of disordered carbon composites, namely, CB (made up of 15 wt. % carbon black dispersed
in carbonized phenolic resin) and PAN (made up of 20 vol. % chopped polyacrylonitrile carbon fibre dispersed in carbonized
phenolic resin matrix) have been irradiated with 145 MeV Ne6+ ions at three fluence levels of 1.0×1013, 5.0×1013 and 1.5×1014 Ne6+/cm2, respectively. The XRD patterns revealed that both the samples remained disordered even after irradiation. The maximum release
of stored energy for CB was 212 J/g and that of PAN was 906 J/g. For CB, the release of stored energy was a first order reaction
with activation energy of 2.79 eV and a frequency factor of 3.72×1028 per second. 13% of the defects got annealed by heating up to 700 °C. PAN showed a third-order release rate with activation
energy of 1.69 eV and a frequency factor of 1.77×1014 per second. 56% of the total defects got annealed by heating it up to 700 °C. CB seems to be the better choice than PAN as
it showed less energy release with a slower rate.
PACS 61.80.Jh; 61.80.-x; 61.43Er; 61.43.-j; 68.43.Vx 相似文献
3.
The study of the angular distribution of slow particles during high energy hadron-nucleus interaction indicates that emission of slow particles takes place from a thermally non-equilibrated system. This evidence has come out from the presence of intermittency - a phenomenon that reveals a fractal structure and represents a self-similarity in the particle production process. Hence, this study highlights inadequacy of cascade-evaporation model and advocates the need of its refinement. 相似文献
4.
S. Sarkar A. D. Thakur C. V. Tomy G. Balakrishnan D. McK Paul S. Ramakrishnan A. K. Grover 《Pramana》2006,66(1):193-207
New experimental data are presented on the scan rate dependence of the magnetization hysteresis width ΔM(H) (∞ critical current densityJ
c(H)) in isothermalMH scans in a weakly pinned single crystal of Ca3Rh4Sn13, which displays second magnetization peak (SMP) anomaly as distinct from the peak effect (PE). We observe an interesting
modulation in the field dependence of a parameter which purports to measure the dynamical annealing of the disordered bundles
of vortices injected through the sample edges towards the destined equilibrium vortex state at a givenH. These data, in conjunction with the earlier observations made while studying the thermomagnetic history dependence inJ
c(H) in the tracing of the minor hysteresis loops, imply that the partially disordered state heals towards the more ordered state
between the peak field of the SMP anomaly and the onset field of the PE. The vortex phase diagram in the given crystal of
Ca3Rh4Sn13 has been updated in the context of the notion of the phase coexistence of the ordered and disordered regions between the
onset field of the SMP anomaly and the spinodal line located just prior to the irreversibility line. A multi-critical point
and a critical point in the (H,T) region of the Bragg glass phase have been marked in this phase diagram and the observed behavior is discussed in the light
of recent data on multi-critical point in the vortex phase diagram in a single crystal of Nb. 相似文献
5.
Pongaglabol [8-hydroxy-5-phenyl-furo[2,3-h]benzo(b)pyran-7-one] was synthesized and tested for antibacterial effects againstShigella dysenteriae, Salmonella typhi, Streptococcus β-haemolyticus andStaphylococcus aureus. The synthesized compounds were characterized using UV, IR and1H NMR spectral data 相似文献
6.
Studies on the thermal stability of FeCr2O4 in air show that surface oxidation preceeds bulk oxidation. Electrical resistivity and thermoelectric power measurements show that above 47 K, Fe2+ ions are oxidised by the oxygen adsorbed on the surface and above 523K diffusion of the ions into the bulk occur. DTA and TG show that the bulk oxidation starts above 673 K and the change from the defect spinel phase to the rhombohedral phase occurs during oxidation and is not a sharp transition.
The authors wish to thank DST for some financial help. 相似文献
Zusammenfassung Untersuchungen der thermischen Stabilität von FeCr2O4 in Luft zeigen, daß der Masseoxidation eine Oxidation an der Oberfläche vorangeht. Messungen des elektrischen Widerstandes und der thermo-elektromotorischen Kraft zeigen, daß die Fe2+-Ionen oberhalb 47 K durch den an der Oberfläche adsorbierten Sauerstoff oxidiert werden und daß oberhalb 523 K eine Diffusion der Ionen in das Innere abläuft. DTA- und TG- Untersuchungen zufolge setzt die Masseoxidation oberhalb 673 K ein und während der Oxidation verläuft ein unscharfer Übergang von der defekten Spinellphase in die rhomboedrische Phase.
The authors wish to thank DST for some financial help. 相似文献
7.
Isocytosine (ICH) exists in solution as two major tautomers, the keto form with N1 carrying a proton (1a) and the keto form with N3 being protonated (1b). In water, 1a and 1b exist in equilibrium with almost equal amounts of both forms present. Reactions with a series of Pd(II) and Pt(II) am(m)ine species such as (dien)Pd(II), (dien)Pt(II), and trans-(NH(3))(2)Pt(II) reveal, however, a distinct preference of these metals for the N3 site, as determined by (1)H NMR spectroscopy. Individual species have been identified by the pD dependence of the ICH resonances. pK(a) values (calculated for H(2)O) for deprotonation of the individual tautomers complexes are 6.5 and 6.4 for the N3 linkage isomers of dienPd(II) and dienPt(II), respectively, as well as 6.2 and 6.0 for the N1 linkage isomers. The dimetalated species [(dienM)(2)(IC-N1,N3)](3+) (M = Pd(II) or Pt(II)) are insensitive over a wide range of pD. The crystal structure analysis of [(dien)Pd(ICH-N3)](NO(3))(2) is reported. Ab initio calculations have been performed for tautomer compounds of composition [(NH(3))(3)Pt(ICH)](2+), cis- and trans-[(NH(3))(2)PtCl(ICH)](+), as well as trans-[(NH(3))(2)Pt(ICH)(2)](2+). Without exception, N3 linkage isomers are more stable, in agreement with experimental findings. As to the reasons for this binding preference, an NBO (natural bond orbital) analysis for [(NH(3))(3)Pt(ICH-N3)](2+)strongly suggests that intramolecular hydrogen bonding between trans-positioned NH(3) ligands and the two exocyclic groups of the ICH is of prime importance. The calculations furthermore show a marked pyramidalization of the NH(2) group of ICH in the complex once the heterocyclic ligand forms a dihedral angle <90 degrees with the Pt coordination plane. 相似文献
8.
Dinabandhu Pramanick Jyotish Sarkar Ramanath Bhattacharyya 《Journal of polymer science. Part A, Polymer chemistry》1988,26(5):1457-1463
The reactions of OH radical with Cl?, Br?, I?, and F? ions have been studied by entrapping the product radicals as polymer endgroup which have been detected and estimated by the sensitive dye partition technique. The rate constants of the reactions with Br?, Cl?, and F? ions have been determined to be 1.51 × 109, 1.32 × 109, and 0.92 × 109 L mol?1 s?1, respectively at 25°C and pH 1.00. Oxidation of I? ions liberates I, which inhibits the polymerization and the reaction could not be followed by polymer endgroup analysis. The observed order of reactivity Br? > Cl? > F? is in accordance with the electron affinities of the halide ions. The acidity of the reaction medium has a strong influence on the rate of reaction. With Br? ions, the rate constant of the reaction falls from 1.51 × 109 to 0.75 × 109 L mol?1 s?1 at 25°C as the pH is raised from 1.0 to 2.8. The method is simple and accurate and can be applied to study very reactive radicals. 相似文献
9.
The isolation and the X-ray crystal structure of physiological copper(II)-L-histidine complex are reported. The neutral five-coordinate complex shows distorted square pyramidal geometry with bidentate and tridentate L-histidine ligands. The basic character of the pendent imidazole group and H-bonding interactions of bidentate L-histidine ligand are important for copper transport. The unique structural features help explain the origin of its thermodynamic stability and kinetic reactivity in human blood along with the ternary copper(II)-amino acid complexes. The role of L-histidine in interaction with copper(II)-albumin, in cellular uptake of copper, and in treatment of Menkes disease can be studied using these results. 相似文献
10.
Gupta D Roitzsch M Lippert B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(22):6643-6652
Isocytosine (ICH; 1) exists in solution in an equilibrium of tautomers 1a and 1b with the N1 and N3 positions carrying the acidic proton, respectively. In the solid state, both tautomers coexist in a 1:1 ratio. As we show, the N3H tautomer 1b can selectively be crystallized in the presence of the model nucleobase 1-methylcytosine (1-MeC). The complex 1b x (1-MeC)2 x H2O (2) forms pairs through three hydrogen bonds between the components; hydrogen bonds between identical molecules are also formed, leading to an infinite tape structure. On the other hand, the N1H tautomer 1a co-crystallizes with protonated ICH to give [1a x ICH2]NO3 (3), again with three hydrogen bonds between the partners, yet the acidic proton is disordered over the two entities. With M(II)(dien) (M=Pt, Pd; dien=diethylenetriamine) preferential coordination of tautomer 1a through the N3 position is observed. DFT calculations, which were also extended to Pt(II)(tmeda) linkage isomers (tmeda=N,N,N',N'-tetramethylethylenediamine), suggest that intramolecular hydrogen bonding between the ICH tautomers and the co-ligands at M, while adding to the preference for N3 coordination, is not the major determining factor. Rather it is the inherently stronger Pt-N3 bond which favors complexation of 1a. With an excess of M(II)(dien), dinuclear species [M2(dien)2(IC-N1,N3)]3+ (M=Pd(II), 4 and Pt(II), 5) also form and were isolated as their ClO4(-) salts and structurally characterized. In strongly acidic medium 5 is converted to [Pt(dien)(ICH-N1)]2+ (6), that is, to the Pt(II) complex of tautomer 1b. 相似文献