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1.
The dielectric constant ?' and loss tangent tan δ of chlorobenzene-cis-decalin mixtures have been measured in the temperature range 77 K to 330 K and frequency range 0.1 to 100 kHz. On cooling, ?' increases with decreasing temperature upto about 135 K, after which it drops rapidly with decreasing T followed by a slow decrease. This indicates that the liquid mixture goes to an amorphous phase which transforms to a glass phase of restricted dipole rotation below Tg; however, the peak in ?' is due to relaxation in the amorphous phase (α relaxation) and does not give an exact Tg. On heating, the behaviour of the cooling curve is retraced upto 160 K, after which ?' drops suddenly to a value lower than that at 77 K in the glass phase. This indicates the transition to a crystalline phase in which dipole rotational freedom is completely lost. The crystalline phase changes to a eutectic liquid phase of high ?' at a temperature (200 K) lower than the melting point of chlorobenzene and cis-decalin. Dielectric dispersion is observed only in the glass and amorphous phases. The dielectric relaxation time is independent of the concentration of chlorobenzene. 相似文献
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3.
Kanhaiya L. Yadav Amarjeet K. Narula Ramadhar Singh Subhas Chandra 《Applied biochemistry and biotechnology》2001,96(1-3):119-124
The direct current (dc) conductivity of poly(3-methyl thiophene) was measured in the temperature range of 77–300 K. The observed dc conductivity data were analyzed in the light of Mott’s variable range hopping model. Different Mott’s parameters such as
characteristic temperature (T
0), average hopping distance (R), average hopping energy (W), and density of states at the Fermi level (N [E
F
]) were evaluated. By taking the inverse of the coefficient of exponential decay of the localized states involved in the hopping
process as 0.5 nm, a realistic value of density of states at the Fermi level (N [E
F
]) was obtained that agrees well with the values reported earlier for other conjugated polymers. 相似文献
4.
Jitendra Kumar P.K. Siwach Ramadhar Singh O.N. Srivastava 《Solid State Communications》2006,138(8):422-425
We report a large enhancement (∼90%) in magnetoresistance in La0.82Sr0.18MnO3 (LSMO) layers by incorporating a π-conjugated semiconducting polymer layer in between them. The epitaxial LSMO layers were deposited by DC magnetron sputtering on SrTiO3 single crystal substrates and have FM transition temperature (TC)∼310 K. A semiconducting polymer poly(3-octylthiophene) (P3OT) layer was deposited over the epitaxial LSMO layer by solution dip coating technique and with subsequent deposition of another epitaxial LSMO layer, forming a LSMO-P3OT-LSMO heterostructure. The effect of P3OT incorporation on magnetotransport properties of this heterostructure has been examined in the temperature range 77-350 K. Large MR enhancement observed near room temperature in the FM regime is explained in terms of efficient magnetic field dependent carrier injection at LSMO/P3OT interface. 相似文献
5.
S. Balaji Ramadhar Kumar R. Sripriya Urmila Rao Abhishek Mandal Prachi Kakkar P. NeelaKanta Reddy Praveen Kumar Sehgal 《先进技术聚合物》2012,23(3):500-507
Fabrication of keratin–collagen (KC) 3D scaffold with improved thermal denaturation rate is reported. In vitro application of (KC) scaffold stimulates basic extra cellular matrix constituents. KC Scaffold considerably reduced undesirable properties of both collagen and keratin while collagen incorporation reduces the fragility with increases of strength and flexibility in the scaffold. In addition to this, the scaffold showed homogenous well‐interconnected pores in the range of 10–100 µm when observed in scanning electron microscope. Usage of keratin in KC scaffold offers increased biodegradation rate and higher denaturation rate in addition to its rapid cell growth with normal morphology ultimately reaching cell population of 3.9–9.7 million per cm3 after 48 hr in KC scaffold. Circular dichroism (CD) and Fourier transform spectroscopy (FT‐IR) of KC showed presence of helical structure of collagen and ß‐turns of keratin confirming retention of native structures of both the proteins KC scaffold showed good swelling behavior and water uptake. Our study strongly supports the superidity of KC scaffold over the collagen or keratin when they are independently used for tissue engineering applications. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
6.
Ramadhar Singh Rajiv K. Singh Jitendra Kumar Rama Kant Vikram Kumar 《Journal of Polymer Science.Polymer Physics》2010,48(10):1047-1053
We present here the evidence for the origin of dc electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) (P3HT) films. P3HT has been synthesized and purified to obtain pristine P3HT polymer films. P3HT films are chemically doped to make conducting P3HT films with different conductivity level. Temperature (77–350 K) dependent dc conductivity (σdc) and dielectric constant (ε′(ω)) measurements on pristine and doped P3HT films have been conducted to evaluate dc and ac electrical conduction parameters. The relaxation frequency (fR) and static dielectric constant (ε0) have been estimated from dielectric constant measurements. A correlation between dc electrical conduction and dielectric relaxation data indicates that both dc and ac electrical conductions originate from the same hopping process in this system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1047–1053, 2010 相似文献
7.
Amarjeet K. Narula Ramadhar Singh K. L. Yadav K. B. Ravat Subhas Chandra 《Applied biochemistry and biotechnology》2001,96(1-3):109-117
Poly(3-methyl thiophene) was synthesized by oxidative chemical polymerization technique using ferric chloride as the dopant in an inert atmosphere. Samples of different doping levels were prepared and analyzed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and direct current (DC) conductivity measurement at room temperature (300 K). Synthesis of the polymer was confirmed by FTIR studies. FTIR spectra showed a shift in the heterocyclic bands in the region of 700-1200 cm(-1) with a decrease in synthesis temperature. It was evident from the scanning electron micrographs that the surface structure of the polymer became denser with an increase in doping level. The measured DC conductivity increased initially up to the doping level of 0.8 M and then this increase tended to slow down. Samples having a doping level of 0.4 M were synthesized at 300, 280, and 270 K while maintaining the other synthesis parameters. The conductivity and yield were found to increase as the temperature of the polymerization decreased. 相似文献
8.
Jitendra Kumar Rajiv K. Singh P.K. Siwach H.K. Singh Ramadhar Singh O.N. Srivastava 《Journal of magnetism and magnetic materials》2006
The low field magneto-transport has been measured as a function of temperature in the range 77–300 K and magnetic field; H?3.6 kOe for La0.7Ba0.2Sr0.1MnO3 (LBSMO)–x wt% PMMA composites where x=0, 2, 6 and 10. The X-ray diffraction (XRD) study reveals that no structural modification has occurred in the LBSMO in the composite. Scanning electron microscopy (SEM) investigation shows PMMA getting dispersed through the sample volume and some LBSMO grains appear to be coated with the polymer. The metal-like transition observed at ∼150 K in the virgin LBSMO sample disappears in the composite samples and the resistance shows an increase of about three orders of magnitude as the polymer concentration is increased to 10 wt%. Despite this huge increase in the resistance, the low field magneto-resistance (LFMR) shows an enhancement although smaller than the values commonly observed for other manganite-polymer composite systems. Spin polarized tunneling that causes LFMR seems to be enhanced in the composites. 相似文献
9.
Rajiv K. Singh Amit Kumar Khushboo Agarwal Mahesh Kumar H. K. Singh Pankaj Srivastava Ramadhar Singh 《Journal of Polymer Science.Polymer Physics》2012,50(5):347-360
Highly conducting polypyrrole (PPY) films, doped with various anions [pTS?, ClO4?, and NO3? and mixed electrolyte system (pTS? + ClO4?)], have been electrochemically synthesized in aqueous solution at ~275 K in an inert atmosphere. PPY exhibits metallic order dc conductivity at room temperature and shows variation of conductivity with respect to time of polymerization. Effect of dopant anion on growth mechanism of PPY is evident from its surface morphology. X‐ray photoelectron spectroscopy (XPS), used to examine the surface composition and doping level of various PPY films, confirms the anionic doping into the polymer backbone. Both XPS and ultraviolet–visible spectroscopy give evidence of formation of polarons and bipolarons. The temperature (4.2–320 K)‐dependent dc conductivity data of these PPY films have been explained by Mott's 3D variable‐range hopping conduction model. Mott's parameters have been estimated, and structural disorder with doping is correlated for all the samples. Mott's criterion for distant hopping sites prevails in case of moderately doped samples (PPY3, PPY4, and PPY5), whereas the hopping to nearest neighbor sites is found more suitable in case of highly doped samples (PPY1 and PPY2). The origin of these changes is due to the modification in the molecular structure of PPY, which is governed by different growth mechanisms for organic (pTS?) and inorganic (ClO4? and NO3?) counter anions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献
10.
Ramadhar Kumar S. Balaji T. S. Uma A. B. Mandal P. K. Sehgal 《Applied biochemistry and biotechnology》2010,160(1):30-39
A Bacillus subtilis (MTCC9102) isolate was shown to produce significant amount of keratinase under optimized conditions in solid-state fermentation
using Horn meal as a substrate. Optimized value for moisture, inoculum, and aeration were found to be 100% (v/w), 50% (v/w), and 150% (w/w), respectively, and the optimum nitrogen source was peptone and carbon source was dextrose. Maximum keratinolytic activity
was observed at 48 h after incubation, and the optimum age (24 h) of inoculum was significant. The influence of cultivation
temperature and initial pH of the medium on keratinase production revealed the optimum values for the temperature and pH as
37 °C and 7, respectively. Maximum keratinase activity of the crude extract was 15,972 U/mg/ml. These results indicate that
this bacterial strain shows a high biotechnological potential for keratinase production in solid-state fermentation, and use
of the horn meal as the substrate can be implemented for keratinous solid wastes management. 相似文献