ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Passing electric currents through a single crystal of La0.77Ca0.23MnO3 causes a marked decrease in the temperature of the insulator–metal transition, TIM, the TIM decreasing with increasing current. The transition exhibits thermal hysteresis, the magnitude of which increases with an increase in applied current. Large negative electroresistance is observed close to room temperature while large positive electroresistance occurs at low temperatures. Similar results are observed with La0.9MnO3 as well.
No abstract is provided for this article.
No abstract is provided for this article.
The effects of modifying the well-known multiferroic BiFeO3 by substituting Fe by Mn and Bi by La have been investigated. It is shown that both the substitutions have a favourable effect on the multiferroic properties of BiFeO3. Thus, both BiFe1−x Mn x O3 and Bi1−x La x FeO3 (x =0.0–0.3) show increased magnetization accompanied by hysteresis loops as well as improved dielectric properties. The ferroelectric transition temperature is lower than that of BiFeO3, but is in a more accessible range. In Bi1−x La x FeO3, there is a change in structure at x =0.2.
The discovery of graphene has aroused great interest in the properties and phenomena exhibited by two‐dimensional inorganic materials, especially when they comprise only a single, two or a few layers. Graphene‐like MoS 2 and WS 2 have been prepared by chemical methods, and the materials have been characterized by electron microscopy, atomic force microscopy (AFM) and other methods. Boron nitride analogues of graphene have been obtained by a simple chemical procedure starting with boric acid and urea and have been characterized by various techniques that include surface area measurements. A new layered material with the composition BCN possessing a few layers and a large surface area discovered recently exhibits a large uptake of CO 2 .
Lifetimes of positrons annihilating in a number of organic compounds consisting of aromatic hydrocarbons, substituted benzenes, phenols, anilines and ketones have been measured. Experimentally measured values of tau 2 and I2 are examined to determine whether positron annihilation takes place at a particular site of the molecule or whether it depends on average properties of the molecules. The intensity I2 seems to be related to the width of Ore gap in organic molecules; the tau 2 values in molecular liquids, however, can be interpreted in terms of additive atomic contributions to pick-off quenching. In substituted benzenes the results show changes due to substituent effects and these changes could be correlated with Hammett's sigma -constant. Results indicate that positron annihilation in organic media is determined by microscopic properties of the molecules such as ionization potentials (or width of Ore gap) and electron densities at the annihilation sites.
During the years preceding India's independence on August 15, 1947, the Indian National Congress focused considerable attention on the importance of science and technology, including scientific planning in an independent country. Jawaharlal Nehru, the first Prime Minister of independent India, held the portfolio for science and technology, as have most of his successors. Nehru was largely responsible for Parliament's adoption of the 1958 Science Policy Resolution. In 1971, the governments of Indira Gandhi and her son, Rajiv Gandhi, took important steps to integrate scientific planning with economic planning. During these years, significant new government institutions were created. The current government of Manmohan Singh, which maintains an active national science advisory committee, has made significant changes in the Indian government's science and technology structure and is creating new institutions for science, technology, and higher education. Currently, India's total investment in research and development is somewhat less than 1% of the gross domestic product, but this ratio is expected to rise to 2% or more in the next few years. The government currently accounts for 85–90% of the country's R&D, but there are indications that private-sector investments will become more important. India has long enjoyed wide-ranging cooperation with several countries, including the US, Western Europe, the Soviet Union, and Russia. During the years immediately following independence, the UK exerted more influence on Indian science than any other country. Today the US has considerable influence, especially as it is also a preferred destination for Indian students and post-doctoral fellows.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The Born-Mayer model with four repulsive parameters has been employed for the study of the pressure transitions in alkali halides. Satisfactory solutions can be obtained only by multiplying the van der Waals term by K, where K > 1 for most alkali halides It has been shown that the ratio of ρ2/ρ1 is equal to the structural constant, a = rii/rij The three- and two-parameter equations are thus special cases of the four-parameter equation and b2 obtained is proportional to (1 25 rl2 + 0 75 rj2)/2.
