5,318 research outputs found
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 ()
scales are considered, from the gapped/activated behaviour characteristic of
the low-temperature insulator through to explicit connection to single-impurity
physics at high and/or ; 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 () 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
- …