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In recent years, the transition metal trichalcogenides (TX3) of Group IVB, VB and VIB have received much more attention because of the considerable diversity in their physical properties. The most striking feature of these compounds is that the structure here may be classified into three types depending on the number of different TX3 chains present in the unit cell. Thus ZrSe3, TaSe3 and NbSe3 are the representative compounds having one, two and three types of chain based on the different bond lengths for the (X2)2– pairs in the base of the TX3 trigonal prismatic framework. A similar model is also applicable in the case of NbS3, with the addition of a 2b-superstructure associated with the formation of niobium pairs. The chain structure also facilitates the process of intercalation which has been most effectively used in secondary batteries. These compounds exhibit the superconductivity phenomena and charge density wave, etc. and also find application in photoelectrochemical cells. An attempt has been made here to review the up-to-date chemistry of transition metal trichalcogenides related with their preparation, structure and properties such as physical and chemical, thermodynamic, electrical, magnetic and optical properties, intercalation and use in the photoelectrochemical cells. 93 相似文献
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The radical copolymerization of acyclic terpene namely geraniol [GER] with acrylonitrile [AN] in DMF at (70 ± 0.1)°C for 1 h, using benzoylperoxide (BPO) as an initiator has been carried out under inert atmosphere of nitrogen. The kinetic expression for reaction is Rp ∝ [BPO]0.5 [AN]1.0 [GER]1.0. The IR spectrum of the copolymer shows bands at 3432 and at 2244 cm?1 due to ? OH group of GER and ? CN group of AN, respectively. The 13C‐NMR spectrum shows peaks at 73–75 δ ppm and 116–120 δ ppm due to ? OH group of GER and ? CN group of AN, respectively. The thermogravimetric analysis and differential scanning calorimetry study shows that copolymer is thermally stable up to 407°C and has glass transition temperatures (Tg) 56°C. The reactivity ratios r1 (AN) and r2 (GER) have been calculated as 0.05 and 0.005, respectively. The Alfrey‐Price Q‐e parameter for GER has been calculated as 0.094 and ?2.0, respectively. The molecular weights of the copolymers have been evaluated by gel‐permeation chromatography. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
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This paper considers the estimation of both the intercept term and the slope parameter in a linear ultrastructural model using
direct regression and reverse regression methods. Without assuming the errors to be normally distributed, asymptotic expressions
for the bias and the variance of the estimators are derived and analyzed. The effect of departure of the errors from normality
is also studied. 相似文献
17.
SZ Zhou S Cooper LY Kang L Ruggieri S Heimfeld A Srivastava HE Broxmeyer 《Canadian Metallurgical Quarterly》1994,179(6):1867-1875
Recombinant adeno-associated virus 2 (AAV) virions were constructed containing a gene for resistance to neomycin (neoR), under the control of either the herpesvirus thymidine kinase (TK) gene promoter (vTK-Neo), or the human parvovirus B19 p6 promoter (vB19-Neo), as well as those containing an upstream erythroid cell-specific enhancer (HS-2) from the locus control region of the human beta-globin gene cluster (vHS2-TK-Neo; vHS2-B19-Neo). These recombinant virions were used to infect either low density or highly enriched populations of CD34+ cells isolated from human umbilical cord blood. In clonogenic assays initiated with cells infected with the different recombinant AAV-Neo virions, equivalent high frequency transduction of the neoR gene into slow-cycling multipotential, erythroid, and granulocyte/macrophage (GM) progenitor cells, including those with high proliferative potential, was obtained without prestimulation with growth factors, indicating that these immature and mature hematopoietic progenitor cells were susceptible to infection by the recombinant AAV virions. Successful transduction did not require and was not enhanced by prestimulation of these cell populations with cytokines. The functional activity of the transduced neo gene was evident by the development of resistance to the drug G418, a neomycin analogue. Individual high and low proliferative colony-forming unit (CFU)-GM, burst-forming unit-erythroid, and CFU-granulocyte erythroid macrophage megakaryocyte colonies from mock-infected, or the recombinant virus-infected cultures were subjected to polymerase chain reaction analysis using a neo-specific synthetic oligonucleotide primer pair. A 276-bp DNA fragment that hybridized with a neo-specific DNA probe on Southern blots was only detected in those colonies cloned from the recombinant virus-infected cells, indicating stable integration of the transduced neo gene. These studies suggest that parvovirus-based vectors may prove to be a useful alternative to the more commonly used retroviral vectors for high efficiency gene transfer into slow or noncycling primitive hematopoietic progenitor cells, without the need for growth factor stimulation, which could potentially lead to differentiation of these cells before transplantation. 相似文献
18.
The main purpose of this article is to show how one can integrate statistical and nonstatistical items of evidence in the belief function framework. First, we use the properties of consonant belief functions to define the belief that the true mean of a variable lies in a given interval when a statistical test is performed for the variable. Second, we use the above definition to determine the sample size for a statistical test when a desired level of belief is needed from the sample. Third, we determine the level of belief that the true mean lies in a given interval when a statistical test yields certain values for the sample mean and the standard deviation of the mean for the variable. Finally, we use the auditing situation to illustrate the process of integrating statistical and nonstatistical items evidence. © 1994 John Wiley & Sons, Inc. 相似文献
19.
Dielectric behaviour of hot pressed AIN ceramic is studied before and after exposing the samples to inorganic acid (HCl and HNO3) vapours with a specific aim to study the effect of these vapours on the dielectric constant () and dissipation factor (tan ). Four samples having different volume percentage of porosity (0.2 to 15%) are selected for this study. Dielectric dispersion increases after exposing the samples to the above acid vapours. Tan also increases quite appreciably; the increase being more at higher porosity. Recovery studies show that the exposure effect is reversible. The exposure time dependence of and tan indicates that these parameters show a maxima at a particular exposure time. However, no such maxima is observed in the gravimetric measurements. The increase in dielectric parameters after exposure to acid vapours is explained in terms of the ionic conduction due to the dissociation of these vapours in the presence of moisture. The porosity dependence of this effect is discussed in terms of closed and open porosity reported by other workers. 相似文献
20.
R. Shukla P. Khurana K. K. Srivastava 《Journal of Materials Science: Materials in Electronics》1992,3(2):132-137
A possible application of AgInTe2 for optoelectronic switching is reported. Alternating and direct current (a.c. and d.c.) response of the material has been studied over a wide frequency range (5 Hz to 1 MHz) through measurements of conductance, capacitance and photocurrent at different temperature and illumination levels. The switching/recovery time has been analysed in terms of time constant and found to be of the order of microseconds for this material. Higher frequencies of operation (>40 kHz) are preferable because, at such frequencies, becomes almost independent of illumination level and temperature. Furthermore, the switching speed can be conveniently controlled with d.c. bias applied across the sample. Elliott's CBH model has been satisfactorily used to explain the switching behaviour for AgInTe2. 相似文献