Electronic structure and magnetism in the frustrated antiferromagnet LiCrO2

LiCrO2 is a 2D triangular antiferromagnet, isostructural with the common battery material LiCoO2 and a well-known Jahn-Teller antiferromagnet NaNiO2. As opposed to the latter, LiCrO2 exibits antiferromagnetic exchange in Cr planes, which has been ascribed to direct Cr-Cr d-d overlap. Using LDA and LDA+U first principles calculations I confirm this conjecture and show that (a) direct d-d overlap is indeed enhanced compared to isostructural Ni and Cr compounds, (b) p-d charge transfer gap is also enhanced, thus suppressing the ferromagnetic superexchange, (c) the calculated magnetic Hamiltonian maps well onto the nearest neighbors Heisenberg exchange model and (d) interplanar inteaction is antiferromagnetic.Comment: 5 pages, 4 figure

Brittle fracture of polymer transient networks

We study the fracture of reversible double transient networks, constituted of water suspensions of entangled surfactant wormlike micelles reversibly linked by various amounts of telechelic polymers. We provide a state diagram that delineates the regime of fracture without necking of the filament from the regime where no fracture or break-up has been observed. We show that filaments fracture when stretched at a rate larger than the inverse of the slowest relaxation time of the networks. We quantitatively demonstrate that dissipation processes are not relevant in our experimental conditions and that, depending on the density of nodes in the networks, fracture occurs in the linear viscoelastic regime or in a non-linear regime. In addition, analysis of the crack opening profiles indicates deviations from a parabolic shape close to the crack tip for weakly connected networks. We demonstrate a direct correlation between the amplitude of the deviation from the parabolic shape and the amount of non linear viscoelasticity

New Approximability Results for the Robust k-Median Problem

We consider a robust variant of the classical $k$-median problem, introduced by Anthony et al. \cite{AnthonyGGN10}. In the \emph{Robust $k$-Median problem}, we are given an $n$-vertex metric space $(V,d)$ and $m$ client sets $\set{S_i \subseteq V}_{i=1}^m$. The objective is to open a set $F \subseteq V$ of $k$ facilities such that the worst case connection cost over all client sets is minimized; in other words, minimize $\max_{i} \sum_{v \in S_i} d(F,v)$. Anthony et al.\ showed an $O(\log m)$ approximation algorithm for any metric and APX-hardness even in the case of uniform metric. In this paper, we show that their algorithm is nearly tight by providing $\Omega(\log m/ \log \log m)$ approximation hardness, unless ${\sf NP} \subseteq \bigcap_{\delta >0} {\sf DTIME}(2^{n^{\delta}})$. This hardness result holds even for uniform and line metrics. To our knowledge, this is one of the rare cases in which a problem on a line metric is hard to approximate to within logarithmic factor. We complement the hardness result by an experimental evaluation of different heuristics that shows that very simple heuristics achieve good approximations for realistic classes of instances.Comment: 19 page

Frequency-dependent polarizabilities of alkali atoms from ultraviolet through infrared spectral regions

We present results of first-principles calculations of the frequency-dependent polarizabilities of all alkali atoms for light in the wavelength range 300-1600 nm, with particular attention to wavelengths of common infrared lasers. We parameterize our results so that they can be extended accurately to arbitrary wavelengths above 800 nm. This work is motivated by recent experiments involving simultaneous optical trapping of two different alkali species. Our data can be used to predict the oscillation frequencies of optically-trapped atoms, and particularly the ratios of frequencies of different species held in the same trap. We identify wavelengths at which two different alkali atoms have the same oscillation frequency.Comment: 6 pages, 2 figure

On the NP-Hardness of Approximating Ordering Constraint Satisfaction Problems

We show improved NP-hardness of approximating Ordering Constraint Satisfaction Problems (OCSPs). For the two most well-studied OCSPs, Maximum Acyclic Subgraph and Maximum Betweenness, we prove inapproximability of $14/15+\epsilon$ and $1/2+\epsilon$. An OCSP is said to be approximation resistant if it is hard to approximate better than taking a uniformly random ordering. We prove that the Maximum Non-Betweenness Problem is approximation resistant and that there are width-$m$ approximation-resistant OCSPs accepting only a fraction $1 / (m/2)!$ of assignments. These results provide the first examples of approximation-resistant OCSPs subject only to P $\neq$ \NP

State-insensitive bichromatic optical trapping

We propose a scheme for state-insensitive trapping of neutral atoms by using light with two independent wavelengths. In particular, we describe the use of trapping and control lasers to minimize the variance of the potential experienced by a trapped Rb atom in ground and excited states. We present calculated values of wavelength pairs for which the 5s and 5p_{3/2} levels have the same ac Stark shifts in the presence of two laser fields.Comment: 5 pages, 4 figure

Study of neonatal outcome in multiple gestation

Background:Development of more than one fetus inside the uterus is called multifetal gestation or multiple pregnancy. It’s a great challenge to the concerned obstetricians, due to late diagnosis and related complications. The main causes of perinatal mortality are prematurity, congenital defects, malpresentations, placental insufficiency and traumatic deliveries. Therefore understanding of twinning phenomenon is needed to improve perinatal outcome of this high risk pregnancy. The aims and objectives were to study fetal outcome in patients with multiple gestation.Methods:A prospective observational study carried out during the period of 1 year. A total of 200 patients with antenatal clinical and ultrasound confirmed diagnosis of multiple gestation were enrolled for the study. After taking proper consent for the study, proper history, clinical and obstetrical examinations were conducted and findings noted. Mothers and neonates were followed till discharge from the hospital.Results:Most common presentation was vertex of both foetuses (62.63%). 70.14% patients underwent spontaneous vaginal delivery and 20.32% underwent LSCS with malpresentation being the most common indication of LSCS. 40.70% patients delivered foetuses of opposite sex. 78.89% had dichorionic and diamniotic placenta. 78.89% had binovular twins. 33.66% foetuses had birth weight between 1.6 to 2 kgs (low birth weight). Prematurity was the most common fetal complication (34.91%). Total perinatal mortality rate is 14.21%. Prematurity was most common cause of neonatal mortality. 6.73% are still birth rate. IUGR was the most common cause of still births.Conclusions: Multiple gestation is a mixed blessing and if successful, allows a couple to rapidly expand their family with a minimum number of pregnancies but it’s a great challenge to the concerned obstetricians. Complications due to multiple gestation are associated with adverse maternal outcome.1.       Cunningham FG. William obstetrics. 23rd edn, McGraw Hill; 2010:859-888.2.       Jewell SE, Yip R. Increasing trends in plural births in U.S. -obstet. Gynecol. 1995;85;229-32.3.       Chevernak FA, Johnson RE, Youcha S. Intrapartum external version of the second twin. Obstet Gynecol. 1983;62:160. 4.       Patel F, Hall DR. Twin pregnancies, risks and complications: a review article. Obstetrics and Gynecology Forum. 2004;14(3):13-9.5.       Bhargava J. Review of 291 cases of multiple pregnancy. J Obstet Gynecol. 1973;23:302-11.6.       Katke RD, Thakre NN. Multifetal Pregnancy: Maternal and Neonatal Outcome. Obstet Gynecol Int J. 2015;3(1):00068.7.       Sarojini, Radhika, Bhanu BT, Kavyashree KS. Evaluation of perinatal outcome in twin pregnancy at tertiary care centre. Int J Reprod Contracept Obstet Gynecol. 2014 Dec;3(4):1015-21.8.       Yuel VI, Kaur V. An analytical study of pregnancy outcome in multifetal gestation. J Obstet Gynecol India. 2007;57(6):509-12.9.       Erdemoglu M, Kale A, Akdeniz N, Yalinkaya A, Ozcan Y. Retrospective Analysis of Multiple Pregnancies. Perinatal Journal. 2005;13(4).10.    Gandye LM. Maternal and Perinatal outcome among multiple pregnancies delivering at Bugando Medical Centre and Sekou Toure Regional Hospital in Mwanza, Tanzania. 2013.11.    Tempe A, Batra S, Nankana J. Twin versus singleton pregnancy: A comparison of morbidity and mortality. J. Obstet. Gynecol. Ind. 1993;43(4):518-23.12.    Bhatia G. Twin pregnancy of 500 cases. Obstet Gynecol. 1978;57:25.13.    Guttamcher AF. An analysis of 521 cases of twin pregnancy. Differences in single ovum and double ovum twinning, Am J Obstet Gynaecol. 34:76-84.14.    Joseph K. Perinatal Mortality in twin pregnancy. Obstetrics and Gynecology: Wolters Kluwer. 1964;23(5):738-44.Cite this article as: Arora GG, Bagga GR, Arora GC. Study of neonatal outcome in multiple gestation.Int J Reprod Contracept Obstet Gynecol 2016;5:4025-30. Su RN, Zhu WW. Maternal and Neonatal outcomes in multiple pregnancy: A multicenter study in the Beijing population. Chronic Diseases and Translational Medicine. 2015;1:197-202.

Study of maternal outcome in multiple gestation

Background: Development of more than one fetus inside the uterus is called multifetal gestation or multiple pregnancy. It’s a great challenge to the concerned obstetricians, due to late diagnosis and related complications. Ignorance on the part of patients themselves puts this group in great peril. The increase in multiple births increases the rate of maternal morbidity and mortality. Aims and objectives of the study were to study maternal outcome in patients with multiple gestation.Methods: A prospective observational study carried out during the period of 1 year. A total of 200 patients with antenatal clinical and ultrasound confirmed diagnosis of multiple gestation were enrolled for the study. After taking proper consent for the study, proper history, clinical and obstetrical examinations were conducted and findings noted. Mothers were followed till discharge from the hospital.Results: Most of the patients (49.5%) were in 21-25 years age group. 65% of patients were multigravida. Undue enlargement of abdomen was the most common physical finding (62%). 79% patients had normal vaginal delivery. Fetal Malpresentation was the most common indication for caesarian section. A hypertensive disorder was the most common complication during pregnancy (23.5%) and pre-term labour was the most common intra-partum complication (38%). Incidence of maternal mortality was 1.5%.Conclusions: Multiple gestation is a mixed blessing and if successful, allows a couple to rapidly expand their family with a minimum number of pregnancies but it’s a great challenge to the concerned obstetricians. Complications due to multiple gestation are associated with adverse maternal outcome