Transport in quantum wires

With a brief introduction to one-dimensional channels and conductance quantisation in mesoscopic systems, we discuss some recent experimental puzzles in these systems, which include reduction of quantised conductances and an interesting {\it odd-even} effect in the presence of an in-plane magnetic field. We then discuss a recent non-homogeneous Luttinger liquid model proposed by us, which addresses and gives an explanation for the reduced conductances and the {\it odd-even} effect. We end with a brief summary and discussion of future projects.Comment: Talk presented at the International Discussion Meeting on Mesoscopic and Disordered systems, December, 2000, 16 pages, 2 figure

Field Theories of Frustrated Heisenberg Antiferromagnets

We study the Heisenberg antiferromagnetic chain with both dimerization and frustration. The classical ground state has three phases: a Neel phase, a spiral phase and a colinear phase. In each phase, we discuss a non-linear sigma model field theory governing the low energy excitations. We study the theory in the spiral phase in detail using the renormalization group. The field theory, based on an $SO(3)$ matrix-valued field, becomes $SO(3) \times SO(3)$ and Lorentz invariant at long distances where the elementary excitation is analytically known to be a massive spin-$1/2$ doublet. The field theory supports $Z_2 ~$ solitons which lead to a double degeneracy in the spectrum for half-integer spins (when there is no dimerization).Comment: Latex, 12 pages, 2 figures (gzipped and uuencoded

Bosonic Mean Field Theory of the Spiral Phases of Heisenberg Antiferromagnets on a Chain

We develop a novel bosonic mean field theory to describe the spiral phases of a Heisenberg antiferromagnet on a one-dimensional chain, in terms of three bosons at each site. The ground state is disordered and for large values of the spin $S$, two different and exponentially small energy gaps are found. The spin-spin correlation function is computed and is shown to decay exponentially at large distances. Our mean field theory is also shown to be exact in a large-$N$ generalization.Comment: plain.tex, TIFR/TH/92-66, IISc/CTS/92-1

Renormalization group study of the conductances of interacting quantum wire systems with different geometries

We examine the effect of interactions between the electrons on the conductances of some systems of quantum wires with different geometries. The systems include a wire with a stub in the middle, a wire containing a ring which can enclose a magnetic flux, and a system of four wires which are connected in the middle through a fifth wire. Each of the wires is taken to be a weakly interacting Tomonaga-Luttinger liquid, and scattering matrices are introduced at all the junctions. Using a renormalization group method developed recently for studying the flow of scattering matrices for interacting systems in one dimension, we compute the conductances of these systems as functions of the temperature and the wire lengths. We present results for all three regimes of interest, namely, high, intermediate and low temperature. These correspond respectively to the thermal coherence length being smaller than, comparable to and larger than the smallest wire length in the different systems, i.e., the length of the stub or each arm of the ring or the fifth wire. The renormalization group procedure and the formulae used to compute the conductances are different in the three regimes. We present a phenomenologically motivated formalism for studying the conductances in the intermediate regime where there is only partial coherence. At low temperatures, we study the line shapes of the conductances versus the electron energy near some of the resonances; the widths of the resonances go to zero with decreasing temperature. Our results show that the conductances of various systems of experimental interest depend on the temperature and lengths in a non-trivial way when interactions are taken into account.Comment: Revtex, 17 pages including 15 figure

Junction of several weakly interacting quantum wires: a renormalization group study

We study the conductance of three or more semi-infinite wires which meet at a junction. The electrons in the wires are taken to interact weakly with each other through a short-range density-density interaction, and they encounter a general scattering matrix at the junction. We derive the renormalization group equations satisfied by the S-matrix, and we identify its fixed points and their stabilities. The conductance between any pair of wires is then studied as a function of physical parameters such as temperature. We discuss the possibility of observing the effects of junctions in present day experiments, such as the four-terminal conductance of a quantum wire and crossed quantum wires.Comment: RevTeX, 13 pages, including 4 eps figure

Transport through quasi-ballistic quantum wires: the role of contacts

We model one-dimensional transport through each open channel of a quantum wire by a Luttinger liquid with three different interaction parameters for the leads, the contact regions and the wire, and with two barriers at the contacts. We show that this model explains several features of recent experiments, such as the flat conductance plateaux observed even at finite temperatures and for different lengths, and universal conductance corrections in different channels. We discuss the possibility of seeing resonance-like structures of a fully open channel at very low temperatures.Comment: revtex, 5 pages, 1 eps figure; clarifications added in light of new experiment

Women in Sahitya Academy Award-winning novels

From 2012 to 2020 (excluding 2013), the Sahitya Akademi explores their status based on some of the female characters in the award-winning novels. In the novel 'Thol', a female character named Arukkani goes to work in a leather factory due to her family situation.  Love blossoms for her at work. Without respecting her feelings for the place, she abandons love, thinking of the consequences of continuing that love.  A third victim of superstition is the neck stretching. The situation arises where she meets her boyfriend one day.  She protects the culture and culture without going with him in that situation.  In the novel 'Anjadi', a woman named Veerammal marries a man of her choice to her mother and father. The mother maintains her husband's respect in the home, no matter how poor her husband may be. When Veerammal offers to give her grains at her birth house, Wendy refuses to buy them to protect the house. The husband behaves like a mature woman at home. In the novel 'Sancharam', Veena Soundarammal lends a helping hand to a helpless blind Nataswara artist and marries him. She does the work he needs to do and expresses humanity. The blister character in the novel 'Chool' is a woman who cannot give birth and at the same time is a mother to many buffaloes and lives with mental courage and self-confidence. Their friendship emerges from the characterization of Arunmozhi in the novel 'Invalid Money', who cries after meeting his friend in danger.  The status of such women has been explored in this article

Isolation and Screening of bacteriocin producing lactic acid bacteria from milk and milk products

One of the most important groups of acid producing bacteria in food industry is the lactic acid bacteria,(LAB). LAB are widespread in nature and predominate in microflora of milk and its products LAB are known to produce bacteriocin and have great potential in food bio preservatives. In the present study a total of 160 strains of LAB were isolated from eight different milk and milk products collected from Dairy Farm, Annamalai University. They were screened for the production of bacteriocin active against Listeria monocytogenes. Among the 160 strains 22 strains were observed as positive bacteriocin producers. The highest percent (25.0%) of bacteriocin producers was recorded in butter followed by yoghurt (20%), curd (18.75%) buffalo milk (16.66%), Goat milk (13.88%) Cheese (11.11%) cow milk (10%) and dairy milk (6.25%). The bacteriocin producers were identified upto generic level as Enterococcus, Lactococcus, Lactobacillus and Streptococcus.  There was a striking predominance of  the genus Enterococcus (55%) followed by Lactococcus (22%) in the milk and milk products. The spectrum of inhibitory activity of the bacteriocin producers against Gram positive and Gram negative pathogens were tested and observed that, activity is restricted to Gram positive organisms, but Lactobacillus and Streptococcus were active against both Gram positive and Gram negative organisms. The bacteriocins produced by LAB are to be characterized in the further studies

Transport in Double-Crossed Luttinger Liquids

We study transport through two Luttinger liquids (one-dimensional electrons interacting through a Coulomb repulsion in a metal) coupled together at {\it two} points. External voltage biases are incorporated through boundary conditions. We include density-density couplings as well as single-particle hops at the contacts. For weak repulsive interactions, transport through the wires remains undisturbed by the inter-wire couplings, which renormalise to zero. For strong repulsive interactions, the inter-wire couplings become strong. For symmetric barriers and no external voltage bias, a single gate voltage is sufficient to tune for resonance transmission in both wires. However, for asymmetric couplings or for finite external biases, the system is insulating.Comment: Latex file, 11 pages, one eps figur

Transcription profiling reveals potential mechanisms of dysbiosis in the oral microbiome of rhesus macaques with chronic untreated SIV infection.

A majority of individuals infected with human immunodeficiency virus (HIV) have inadequate access to antiretroviral therapy and ultimately develop debilitating oral infections that often correlate with disease progression. Due to the impracticalities of conducting host-microbe systems-based studies in HIV infected patients, we have evaluated the potential of simian immunodeficiency virus (SIV) infected rhesus macaques to serve as a non-human primate model for oral manifestations of HIV disease. We present the first description of the rhesus macaque oral microbiota and show that a mixture of human commensal bacteria and "macaque versions" of human commensals colonize the tongue dorsum and dental plaque. Our findings indicate that SIV infection results in chronic activation of antiviral and inflammatory responses in the tongue mucosa that may collectively lead to repression of epithelial development and impact the microbiome. In addition, we show that dysbiosis of the lingual microbiome in SIV infection is characterized by outgrowth of Gemella morbillorum that may result from impaired macrophage function. Finally, we provide evidence that the increased capacity of opportunistic pathogens (e.g. E. coli) to colonize the microbiome is associated with reduced production of antimicrobial peptides