Radiation Pressure Induced Instabilities in Laser Interferometric Detectors of Gravitational Waves

The large scale interferometric gravitational wave detectors consist of Fabry-Perot cavities operating at very high powers ranging from tens of kW to MW for next generations. The high powers may result in several nonlinear effects which would affect the performance of the detector. In this paper, we investigate the effects of radiation pressure, which tend to displace the mirrors from their resonant position resulting in the detuning of the cavity. We observe a remarkable effect, namely, that the freely hanging mirrors gain energy continuously and swing with increasing amplitude. It is found that the `time delay', that is, the time taken for the field to adjust to its instantaneous equilibrium value, when the mirrors are in motion, is responsible for this effect. This effect is likely to be important in the optimal operation of the full-scale interferometers such as VIRGO and LIGO.Comment: 27 pages, 11 figures, RevTex styl

Zero Temperature Insulator-Metal Transition in Doped Manganites

We study the transition at T=0 from a ferromagnetic insulating to a ferromagnetic metallic phase in manganites as a function of hole doping using an effective low-energy model Hamiltonian proposed by us recently. The model incorporates the quantum nature of the dynamic Jahn-Teller(JT) phonons strongly coupled to orbitally degenerate electrons as well as strong Coulomb correlation effects and leads naturally to the coexistence of localized (JT polaronic) and band-like electronic states. We study the insulator-metal transition as a function of doping as well as of the correlation strength U and JT gain in energy E_{JT}, and find, for realistic values of parameters, a ground state phase diagram in agreement with experiments. We also discuss how several other features of manganites as well as differences in behaviour among manganites can be understood in terms of our model.Comment: To be published in Europhysics Letter

Optimising the directional sensitivity of LISA

It was shown in a previous work that the data combinations canceling laser frequency noise constitute a module - the module of syzygies. The cancellation of laser frequency noise is crucial for obtaining the requisite sensitivity for LISA. In this work we show how the sensitivity of LISA can be optimised for a monochromatic source - a compact binary - whose direction is known, by using appropriate data combinations in the module. A stationary source in the barycentric frame appears to move in the LISA frame and our strategy consists of "coherently tracking" the source by appropriately "switching" the data combinations so that they remain optimal at all times. Assuming that the polarisation of the source is not known, we average the signal over the polarisations. We find that the best statistic is the `network' statistic, in which case LISA can be construed of as two independent detectors. We compare our results with the Michelson combination, which has been used for obtaining the standard sensitivity curve for LISA, and with the observable obtained by optimally switching the three Michelson combinations. We find that for sources lying in the ecliptic plane the improvement in SNR increases from 34% at low frequencies to nearly 90% at around 20 mHz. Finally we present the signal-to-noise ratios for some known binaries in our galaxy. We also show that, if at low frequencies SNRs of both polarisations can be measured, the inclination angle of the plane of the orbit of the binary can be estimated.Comment: 16 pages, 8 figures, submitted to Phys Rev

Is low amniotic fluid index an indicator of fetal distress and hence delivery?

Background: Amniotic fluid Index (AFI) is an indicator of fetal well-being. Low AFI is considered to be one of the indications for delivery as it may be associated with fetal distress and birth asphyxia. We sought to determine whether low AFI is an indicator of fetal compromise and an indication to deliver.Methods: This prospective, observational study was conducted at Department of Obstetrics & Gynecology, KMC, Manipal University, India, between August 2013 and Aug 2014. A total of 150 subjects that had induced labor or direct caesarean section for various indications and also having low-normal (5-8) / low (<5) AFI, were recruited. Subjects with fetal anomalies were excluded. Outcome variables studied were, fetal distress in labor, thick meconium stained amniotic fluid, mode of delivery in induced labor, perinatal asphyxia, and respiratory distress syndrome.Results: Out of 150 subjects, 68 (45.4%) had low and 82 (54.6%) had low-normal AFI. Both the groups were matched for demographic characteristics and confounding factors for neonatal outcome. In low AFI group the incidence of Low APGAR (11.7%), perinatal asphyxia (11.7%) and RDS (16.1%) were significantly higher compared to those in low-normal group (3.6%, 1.2% and 2.4% respectively) p = 0.057, 0.006 and 0.002. There was no significant difference between the groups with respect to mode of delivery when labor was induced.Conclusions: Low AFI, especially when it is <5, is an indicator of fetal compromise and one may anticipate perinatal asphyxia and RDS. Hence it is prudent to contemplate delivery when the AFI is between 5 and 8

Supersolid and solitonic phases in one-dimensional Extended Bose-Hubbard model

We report our findings on quantum phase transitions in cold bosonic atoms in a one dimensional optical lattice using the finite size density matrix renormalization group method in the framework of the extended Bose-Hubbard model. We consider wide ranges of values for the filling factors and the nearest neighbor interactions. At commensurate fillings, we obtain two different types of charge density wave phases and a Mott insulator phase. However, departure from commensurate fillings yield the exotic supersolid phase where both the crystalline and the superfluid orders coexist. In addition, we obtain signatures for solitary waves and also superfluidity.Comment: 7 pages, 11 figure