Nature of the spiral state, electric polarisation and magnetic transitions in Sr-doped YBaCuFeO5_5: A first-principles study

Contradictory results on the ferroelectric response of type II multiferroic YBaCuFeO$_{5}$, in its incommensurate phase, has of late, opened up a lively debate. There are ambiguous reports on the nature of the spiral magnetic state. Using first-principles DFT calculations for the parent compound within LSDA+U+SO approximation, the multiferroic response and the nature of spiral state is revealed. The helical spiral is found to be more stable below the transition temperature as spins prefer to lie in ab plane. The Dzyaloshinskii-Moriya (DM) interaction and the spin current mechanism were earlier invoked to account for the electric polarisation in this system. However, the DM interaction is found to be absent, spin current mechanism is not valid in the helical spiral state and there is no electric polarisation thereof. These results are in good agreement with the recent single-crystal data. We also investigate the magnetic transitions in YBa$_{1-x}$Sr$_x$CuFeO$_5$ for the entire range $0\le x\le 1$ of doping. The exchange interactions are estimated as a function of doping and a quantum Monte Carlo (QMC) calculation on an effective spin Hamiltonian shows that the paramagnetic to commensurate phase transition temperature increases with doping till $x=0.5$ and decreases beyond. Our observations are consistent with experimental findings.Comment: 8 pages, 7 figure

Role of biochemical markers in the prediction of osteopenia and osteoporosis in men and women of Sikkim, India

Background: Osteoporosis being a silently progressing disease, the real challenge is to identify the individual at high risk of osteoporosis. Many bone turnover marker have been associated with bone loss even before occurrence of any changes in bone structure. Therefore, this study was aim to evaluate the predictive value of bone turnover marker by correlating with low bone density.Methods: This was a case control study conducted in Sikkim Manipal Institute of Medical Sciences, India. A total of 300 subjects (150 case and 150 control) both male and female between the age group of 35- 65 were enrolled. We measure one bone formation marker serum osteocalcin and two resorption marker urine hydroxyproline (OHP) and urine N- terminal telopeptides of type I collagen (NTX). Calcaneal QUS device (GE Lunar Achilles Express heel- densitometer) was used to determine the bone density.Results: A significant difference of the bone markers i.e. hydroxyproline, NTx and osteocalcin were observed between cases and control of men and women with P<0.001. These variables statistically significantly predicts bone density with F (3, 71) = 5,671, P= 0.002, R2= 0.193 and F (3, 71) = 5.292, P= 0.002, R2= 0.183 in women and men respectively.Conclusions: Study showed that bone turnover markers are able to predict low bone mass. Resorption markers NTx and OHP were the main predictor in men whereas OHP and formation marker Osteocalcin in women. Therefore, BTM measurement along with BMD can provide useful information about the changes in the bone mass which will help to predict the risk of osteoporosis

Microstructural changes induced by ternary additions in a hypo-eutectic titanium-silicon alloy

Hypo-eutectic Ti-6.5 wt % Si alloy modified by separate additions of misch metal and low surface tension elements (Na, Sr, Se and Bi) has been examined by microscopic study and thermal analysis. Addition of third element led to modification of microstructure with apparently no significant enhancement of tensile ductility, with the exception of bismuth. Bismuth enhanced the ductility of the alloy by a factor of two and elastic-plastic fracture toughness to 9 MPa m-&#189; from a value of almost zero. The improved ductility of bismuth modified alloy is attributed to the reduced interconnectivity of the eutectic suicide, absence of significant suicide precipitation in the eutectic region and increase in the volume fraction of uniformly distributed dendrites. These changes are accompanied by a decrease in the temperature of eutectic solidification

On the evaluation of stability of rare earth oxides as face coats for investment casting of titanium

Attempts have been made to evaluate the thermal stability of rare earth oxide face coats against liquid titanium. Determination of microhardness profiles and concentration profiles of oxygen and metallic constituents of oxide in investment cast titanium rods has allowed gradation of relative stability of rare earth oxides. The relative stability of evaluated oxides in the order of increasing stability follows the sequence CeO2 &#8594; ZrO2 &#8594; Gd2O3 &#8594; didymium oxide &#8594; Sm2O3 &#8594; Nd2O3 &#8594; Y2O3. The grading does not follow the free energy data of the formation of these oxides. A better correlation with the experimental observations is obtained when the solubility of the metallic species in titanium is also taken into consideration

Momentum and Heat Transfer in MHD Axisymmetric Stagnation-Point Flow over a Shrinking Sheet

In this paper we present a mathematical analysis for the magneto hydrodynamic (MHD) axi-symmetric stagnation-point flow and heat transfer over a shrinking sheet which shrinks axi-symmetrically in its own plane. The governing partial differential equations along with the boundary conditions are first cast into a dimensionless form and then these equations are solved numerically by shooting technique. Thermal conductivity is assumed to vary linearly with the temperature. Temperature profiles are obtained for two different types of heating process namely (i) the sheet with prescribed surface temperature (PST) and (ii) the sheet with prescribed surface heat flux (PHF). The effects of various physical parameters on the flow and heat transfer characteristics are presented graphically and discussed

Approximation Algorithm for Line Segment Coverage for Wireless Sensor Network

The coverage problem in wireless sensor networks deals with the problem of covering a region or parts of it with sensors. In this paper, we address the problem of covering a set of line segments in sensor networks. A line segment ` is said to be covered if it intersects the sensing regions of at least one sensor distributed in that region. We show that the problem of finding the minimum number of sensors needed to cover each member in a given set of line segments in a rectangular area is NP-hard. Next, we propose a constant factor approximation algorithm for the problem of covering a set of axis-parallel line segments. We also show that a PTAS exists for this problem.Comment: 16 pages, 5 figures

HIV and cancer registry linkage identifies a substantial burden of cancers in persons with HIV in India.

We utilized computerized record-linkage methods to link HIV and cancer databases with limited unique identifiers in Pune, India, to determine feasibility of linkage and obtain preliminary estimates of cancer risk in persons living with HIV (PLHIV) as compared with the general population.Records of 32,575 PLHIV were linked to 31,754 Pune Cancer Registry records (1996-2008) using a probabilistic-matching algorithm. Cancer risk was estimated by calculating standardized incidence ratios (SIRs) in the early (4-27 months after HIV registration), late (28-60 months), and overall (4-60 months) incidence periods. Cancers diagnosed prior to or within 3 months of HIV registration were considered prevalent.Of 613 linked cancers to PLHIV, 188 were prevalent, 106 early incident, and 319 late incident. Incident cancers comprised 11.5% AIDS-defining cancers (ADCs), including cervical cancer and non-Hodgkin lymphoma (NHL), but not Kaposi sarcoma (KS), and 88.5% non-AIDS-defining cancers (NADCs). Risk for any incident cancer diagnosis in early, late, and combined periods was significantly elevated among PLHIV (SIRs: 5.6 [95% CI 4.6-6.8], 17.7 [95% CI 15.8-19.8], and 11.5 [95% CI 10-12.6], respectively). Cervical cancer risk was elevated in both incidence periods (SIRs: 9.6 [95% CI 4.8-17.2] and 22.6 [95% CI 14.3-33.9], respectively), while NHL risk was elevated only in the late incidence period (SIR: 18.0 [95% CI 9.8-30.20]). Risks for NADCs were dramatically elevated (SIR &gt; 100) for eye-orbit, substantially (SIR &gt; 20) for all-mouth, esophagus, breast, unspecified-leukemia, colon-rectum-anus, and other/unspecified cancers; moderately elevated (SIR &gt; 10) for salivary gland, penis, nasopharynx, and brain-nervous system, and mildly elevated (SIR &gt; 5) for stomach. Risks for 6 NADCs (small intestine, testis, lymphocytic leukemia, prostate, ovary, and melanoma) were not elevated and 5 cancers, including multiple myeloma not seen.Our study demonstrates the feasibility of using probabilistic record-linkage to study cancer/other comorbidities among PLHIV in India and provides preliminary population-based estimates of cancer risks in PLHIV in India. Our results, suggesting a potentially substantial burden and slightly different spectrum of cancers among PLHIV in India, support efforts to conduct multicenter linkage studies to obtain precise estimates and to monitor cancer risk in PLHIV in India

Dust and Stellar Populations in the Large Magellanic Cloud

We present an analysis of line-of-sight extinction measurements obtained using data from the Magellanic Clouds Photometric Survey, which provides 4-filter photometry for millions of stars in the Large Magellanic Cloud. We find that visual extinctions are typically larger by several tenths of a magnitude for stars with effective temperatures > 12000 K, than for stars with effective temperatures between 5500 K and 6500 K. Several repercussions of this population-dependent extinction are discussed. In particular, LMC distance measurements that utilize old stellar populations (such as red clump stars), but use extinctions derived from OB stars, may be biased low. Population-dependent extinction affects the interpretation of color-magnitude diagrams and results in an effective absorption law that is steeper than that intrinsic to the dust for unresolved stellar systems. We further explore the relation between the stellar populations and dust by comparing our extinction map to the 100mu image of the region and identifying potential heating sources of the dust. We conclude that 100mu flux should be used with caution as a star formation tracer, particularly for studies of star formation within galaxies. Finally, we reproduce the observed extinction variation between the hot and cold stellar populations with a simple model of the distribution of the stars and dust where the scaleheight of the cooler stars is >> than that of the dust (which is twice that of the OB stars). (Abridged Abstract)Comment: Accepted for publication in AJ (scheduled for Dec. 1999). 31 pgs (including Figures

Relapses of Plasmodium vivax infection usually result from activation of heterologous hypnozoites.

BACKGROUND: Relapses originating from hypnozoites are characteristic of Plasmodium vivax infections. Thus, reappearance of parasitemia after treatment can result from relapse, recrudescence, or reinfection. It has been assumed that parasites causing relapse would be a subset of the parasites that caused the primary infection. METHODS: Paired samples were collected before initiation of antimalarial treatment and at recurrence of parasitemia from 149 patients with vivax malaria in Thailand (n=36), where reinfection could be excluded, and during field studies in Myanmar (n=75) and India (n=38). RESULTS: Combined genetic data from 2 genotyping approaches showed that novel P. vivax populations were present in the majority of patients with recurrent infection (107 [72%] of 149 patients overall [78% of patients in Thailand, 75% of patients in Myanmar {Burma}, and 63% of patients in India]). In 61% of the Thai and Burmese patients and in 55% of the Indian patients, the recurrent infections contained none of the parasite genotypes that caused the acute infection. CONCLUSIONS: The P. vivax populations emerging from hypnozoites commonly differ from the populations that caused the acute episode. Activation of heterologous hypnozoite populations is the most common cause of first relapse in patients with vivax malaria