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31.
The dielectric relaxation phenomena of rigid polar liquid molecules chloral and ethyltrichloroacetate (j) in benzene, n-hexane and n-heptane (i) under 4.2, 9.8 and 24.6 GHz electric fields at 30°C are studied to show the possible existence of double relaxation times τ 2 and τ 1 for rotations of the whole and the flexible parts of molecules. The probability of showing double relaxation is more in aliphatic solvents indicating their nonrigidity. The symmetric and asymmetric distribution parameters γ and δ are obtained from X ij ′ /X 0ij and X ij ″ /X 0ij and w j →0 where X ij ′ and X ij ″ are real and imaginary parts of the complex orientational susceptibility X i * and X 0ij is the low frequency susceptibility which is real. X ij ’s are involved with the measured dielectric relative permittivities ε ij ′ , ε in ″ , ε 0ij and ε ∞ij of solutions. The theoretical weighted contributions c 1 and c 2 towards dielectric dispersions by Fröhlich’s method are compared with the experimental ones obtained from the graphical variation of X ij ′ /X 0ij and X ij ″ /X 0ij with weight fractions w j ’s at w j → 0. The measured dipole moments μ 2 and μ 1 of the whole and the flexible part of a polar molecule in terms of the linear coefficients β’s of X ij ′ ’s with w j ’s and the estimated τ 2 and τ 1 reveal their associations with aliphatic solvents. The theoretical dipole moments μ theo’s from the available bond angles and bond moments of the substituent polar groups of the molecules with the estimated μ’s suggest the mesomeric, inductive and electromeric effects in them under GHz electric field. 相似文献
32.
Back Cover: Effect of the Bulkiness of the End Functional Amide Groups on the Optical,Gelation, and Morphological Properties of Oligo(p‐phenylenevinylene) π‐Gelators (Chem. Asian J. 7/2014) 下载免费PDF全文
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34.
MK Bhide RM Kadam MD Sastry Ajay Singh Shashwati Sen Manmeet Kaur DK Aswal SK Gupta VC Sahni 《Pramana》2002,58(5-6):799-802
Microwave absorption studies have been carried out on MgB2 superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for
polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave
absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime. 相似文献
35.
S Chopra N S Pawar M P Singh Rakesh Kumar J Prasad V P Patel Raj Pal B Kumar S Ojha K Devarani T Nandi M Sota P Barua S Gargari R Joshi D Kanjilal SK Datta 《Pramana》2002,59(5):753-759
The 15 UD pelletron at NSC has been operational and performed well during the last 11 years. There have been major modifications
performed for upgradation of pelletron system over this period. Major upgradations which have been implemented are new resistor
network system for voltage gradient, doublet to singlet unit conversion for accelerator units, turbopump based gas stripper
system etc. In addition accelerator mass spectroscopy program has also been started. A new multi-cathode source, Wien filter
etc. have been procured and will be added soon in the system. An overview of the most significant upgradations undertaken
and other activities for the system are being reported in the present paper. 相似文献
36.
Epitaxial La1−x
Pb
x
MnO3 (LPMO) thin films, grown on (100) SrTiO3 substrates by laser ablation technique at different temperatures between 600 and 850°C, have been characterized for electrical
and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature
(T
MI) decreases with increasing substrate temperature, which has been attributed to decrease in Pb content in the filsm. The YBa2Cu3O
x
/La1−x
MnO3 heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated. 相似文献
37.
Liu C Dobhal MP Ethirajan M Missert JR Pandey RK Balasubramanian S Sukumaran DK Zhang M Kadish KM Ohkubo K Fukuzumi S 《Journal of the American Chemical Society》2008,130(43):14311-14323
The oxidation of bacteriopyropheophorbide with ferric chloride hexahydrate or its anhydrous form produced the ring-D oxidized (ring-B reduced) chlorin in >95% yield. Replacing the five-member isocyclic ring in bacteriopyropheophorbide- a with a fused six-member N-butylimide ring system made no difference in regioselective oxidation, and the corresponding ring-B reduced chlorin was isolated in almost quantitative yield. When the oxidant was replaced by 2,3-dichloro-5,6-dicyano-p-benzoquinone, which is frequently used at the oxidizing stage of the porphyrin synthesis, the ring-B oxidized (ring-D reduced) chlorins were obtained. With both ring-B reduced and ring-D reduced chlorins in hand, their photophysical and electrochemical properties were examined and compared for the first time. The ring-B reduced chlorine 20, with a fused six-member N-butylimide ring, exhibits the most red-shifted absorption band (at lambda(max) = 746 nm), the lowest fluorescence quantum yield (4.5%), and the largest quantum yield of singlet oxygen formation (67%) among the reduced ring-B and ring-D chlorins investigated in this study. Measurements of the one-electron oxidation and reduction potentials show that compound 20 is also the easiest to oxidize among the examined compounds and the third easiest to reduce. In addition, the 1.62 eV HOMO-LUMO gap of 20 is the smallest of the examined compounds, and this agrees with values calculated using the DFT method. Spectroelectrochemical measurements afforded UV-visible absorption spectra for both the radical cations and radical anions of the examined chlorins. The ring-B reduced compound 20, with a fused six-member N-butylimide ring, is regarded as the most promising candidate in this study for photodynamic therapy because it has the longest wavelength absorption and the largest quantum yield of singlet oxygen formation among the compounds investigated. 相似文献
38.
According to linear response theory, all relaxation functions in the linear regime can be obtained using time correlation functions calculated under equilibrium. In this paper, we demonstrate that the cross correlations make a significant contribution to the partial stress relaxation functions in polymer melts. We present two illustrations in the context of polymer rheology using (1) Brownian dynamics simulations of a single chain model for entangled polymers, the slip-spring model, and (2) molecular dynamics simulations of a multichain model. Using the single chain model, we analyze the contribution of the confining potential to the stress relaxation and the plateau modulus. Although the idea is illustrated with a particular model, it applies to any single chain model that uses a potential to confine the motion of the chains. This leads us to question some of the assumptions behind the tube theory, especially the meaning of the entanglement molecular weight obtained from the plateau modulus. To shed some light on this issue, we study the contribution of the nonbonded excluded-volume interactions to the stress relaxation using the multichain model. The proportionality of the bonded/nonbonded contributions to the total stress relaxation (after a density dependent "colloidal" relaxation time) provides some insight into the success of the tube theory in spite of using questionable assumptions. The proportionality indicates that the shape of the relaxation spectrum can indeed be reproduced using the tube theory and the problem is reduced to that of finding the correct prefactor. 相似文献
39.
Provably secure dynamic identity-based three-factor password authentication scheme using extended chaotic maps 总被引:1,自引:0,他引:1
SK Hafizul Islam 《Nonlinear dynamics》2014,78(3):2261-2276
With the aim of guaranteeing secure communication through public networks, three-factor password authentication (TF-PWA) scheme plays a key role in many internet applications. Since in TF-PWA scheme, the communicating entities can mutually authenticate each other and generate a shared session key, which will be used for secure exchange of messages in succeeding communication among them. As a result, the TF-PWA schemes gain enormous consideration in recent years. More recently, due to light-weight features of the extended chaotic map, it is also extensively applied in designing of public key encryption, key agreement, image encryption, S-box, hash function, digital signature, password authentication, etc. The aim of this paper was to design a dynamic identity-based three-factor password authentication scheme using extended chaotic map (ECM-TF-PWA) in the random oracle model. The proposed scheme is provably secure based on the intractability assumption of chaotic map-based Diffie–Hellman problem. The informal security analysis gives the evidence that our scheme protects all attacks and provides functionality attributes that are needed in a three-factor authentication system. Besides, the performance discussion shows that our scheme performs better than others in respect of computation and communication cost. 相似文献
40.