Dynamics and transport properties of Kondo insulators

A many-body theory of paramagnetic Kondo insulators is described, focusing specifically on single-particle dynamics, scattering rates, d.c. transport and optical conductivities. This is achieved by development of a non-perturbative local moment approach to the symmetric periodic Anderson model within the framework of dynamical mean-field theory. Our natural focus is the strong coupling, Kondo lattice regime; in particular the resultant `universal' scaling behaviour in terms of the single, exponentially small low-energy scale characteristic of the problem. Dynamics/transport on all relevant ($\omega, T$) scales are considered, from the gapped/activated behaviour characteristic of the low-temperature insulator through to explicit connection to single-impurity physics at high $\omega$ and/or $T$; and for optical conductivities emphasis is given to the nature of the optical gap, the temperature scale responsible for its destruction, and the consequent clear distinction between indirect and direct gap scales. Using scaling, explicit comparison is also made to experimental results for d.c. transport and optical conductivites of Ce_3Bi_4Pt_3, SmB_6 and YbB_{12}. Good agreement is found, even quantitatively; and a mutually consistent picture of transport and optics results.Comment: 49 pages, 23 figure

The Raman spectrum of gallium phosphide

The first and second-order Raman spectra of gallium phosphide recorded recently by Russell and Hobden using a He-Ne laser source, are discussed in the light of current theories on the dynamics of crystal lattices. The observed spectra of GaP is examined in detail with a calculation of the phonon frequencies from the critical points Γ, L and X, using the Raman supercell modes and their frequency expressions as given by Ramanathan for ZnS lattice. Satisfactory explanations have been given for the observed second-order frequencies in the case of GaP

The second order Raman spectrum of calcium fluoride

The second-order Raman spectrum of calcium fluoride recorded recently by Russell, using a He-Ne laser source, is discussed in the light of current theories on the dynamics of crystals. The observed spectrum of CaF2 is examined in detail with a calculation of the frequencies of the supercell modes using the lattice dynamic models of Ramanathan and Ganesan and Srinivasan, with the selection rules for the combinations from the critical points X for CaF2 structures. Satisfactory explanations have been given for most of the observed second-order frequency shifts

Coarsening and Slow-Dynamics in Granular Compaction

We address the problem of the microscopic reorganization of a granular medium under a compaction process in the framework of Tetris-like models. We point out the existence of regions of spatial organization which we call domains, and study their time evolution. It turns out that after an initial transient, most of the activity of the system is concentrated on the boundaries between domains. One can then describe the compaction phenomenon as a coarsening process for the domains, and a progressive reduction of domain boundaries. We discuss the link between the coarsening process and the slow dynamics in the framework of a model of active walkers on active substrates.Comment: Revtex 4 pages, 4 figures, in press in PRL. More info http://axtnt3.phys.uniroma1.it/Tetri

Seaweed and their importance

Agar agar and algin serve as stabilizers, emulsifiers, thickeners, and gelling agents

Correlation between Local Structure Distortions and Martensitic Transformation in Ni-Mn-In alloys

The local structural distortions arising as a consequence of increasing Mn content in Ni_2Mn_1+xIn_1-x (x=0, 0.3, 0.4, 0.5 and 0.6) and its effect on martensitic transformation have been studied using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Using the room temperature EXAFS at the Ni and Mn K-edges in the above compositions, the changes associated with respect to the local structure of these absorbing atoms are compared. It is seen that in the alloys exhibiting martensitic transformation ($x \ge 0.4$) there is a significant difference between the Ni-In and Ni-Mn bond lengths even in the austenitic phase indicating atomic volume to be the main factor in inducing martensitic transformation in Ni-Mn-In Heusler alloys.Comment: 8 pages, 2 figure

Marine Algal Flora From Selected Centres Along The Madras Coast

A survey was made on the marine algae occurring at Pulicat, Kovalam, Muthukadu andMahabalipuram along the Madras coast. A total of 22 species were collected of which six species belonged to Chlorophyta, three to Phaeophyta, 10 to Rhodophyta and three to Cyanophyta. Out of the 22 species, 16 are recorded for the first time along the Madras coas

Seaweed recipes and other practical uses of Seaweeds

Seaweeds (a plant group of the sea) in botanical terms "Algae" form an important food item in many countries of the East as well as West. In China, marine algae bears the name sea-vegetable and it is not uncommon for coastal inhabitants of Japan, Malaya, China and Phillippines to be seen on the seashore during low tide collecting these sea-vegetables. Korea and Japan are the two ceuntries where algae are farmed but only in Japan extensive seaweed cultivation is done

Growth, Reproduction and Liberation of Oospores in Turbinaria ornata (Turner) J. Agardh

Young plants of T. ornata appeared in April and grew to maximum size during October to December. Plants were mostly unbranched between February and June and thereafter branching started reaching maximum during September to November. Reproductive plants were found throughout the year with a peak spore output in November (33810 oospores/plant). There was no periodicity in the liberation of oospores. T. ornate may be harvested during the peak growth period from October to December for the manufacture of alginic acid

Seaweed culture in India-an appraisal

In recent years there has been a steady increase in the demand for naturally occuring seaweeds as a result of many seaweed based industries coming up. In order to meet the raw material requirement of these industries attempts have been made in this country to develop suitable seaweed farming techniques by some Institutes notably the CMFRI at its Mandepam. Regional Centre and CSMCRI at its field centre, Mandapam. Experimental culture of economically important seaweeds such as Gracllaria edulis, Gelidiella acerosa and other species was undertaken since 1972 at Mandapam- in these experiments production rates ranging from 3 to 8 times the initial wet weight were obtained. The techniques of seaweed culture, the favourable seasons optimum duration of culture period and the influence of environmental parameters are discussed in this account with notes on economics of seaweed culture. General information on the seaweed resources slong our coasts, their potential for exploitation and culture are also highlighted