Study of Early Predictors of Fatality in Mechanically Ventilated Neonates in NICU

Objective: To evaluate the risk factors associated with fatality in mechanically ventilated neonates using multiple regression analysis. Design & settings: Prospective study conducted at Neonatal ICU at New Civil Hospital, Surat – a tertiary care centre, from December, 2007 to May, 2008 for 6 months. Methods: Fifty neonates in NICU consecutively put on mechanical ventilator during study period were enrolled in the study. The pressure limited time cycled ventilator was used. All admitted neonates were subjected to an arterial blood gas analysis along with a set of investigations to look for pulmonary maturity, infections, renal function, hyperbilirubinemia, intraventricular hemorrhage and congenital anomalies. Different investigation facilities were used as and when required during ventilation of neonates. Multiple logistic regression analysis was done to find out the predictors of fatality among these neonates. Results: Various factors suspected as predictors of fatality of mechanically ventilated neonates were assessed. Hypothermia, prolonged capillary refill time (CRT), initial requirement of oxygen fraction (FiO2) >0.6, alveolar to arterial PO2 difference (AaDO2) >250, alveolar to arterial PO2 ratio (a/A) <0.25, & oxygenation index (OI) >10 were found statistically highly significant predictors of mortality among mechanically ventilated neonates. Conclusion: Hypothermia and prolonged capillary refill time were independent predictors of fatality in neonatal mechanical ventilation. Risk of fatality can be identified in mechanically ventilated neonates

Radiative interactions in laminar duct flows

Analyses and numerical procedures are presented for infrared radiative energy transfer in gases when other modes of energy transfer occur simultaneously. Two types of geometries are considered, a parallel plate duct and a circular duct. Fully developed laminar incompressible flows of absorbing-emitting species in black surfaced ducts are considered under the conditions of uniform wall heat flux. The participating species considered are OH, CO, CO2, and H2O. Nongray as well as gray formulations are developed for both geometries. Appropriate limiting solutions of the governing equations are obtained and conduction-radiation interaction parameters are evaluated. Tien and Lowder's wide band model correlation was used in nongray formulation. Numerical procedures are presented to solve the integro-differential equations for both geometries. The range of physical variables considered are 300 to 2000 K for temperature, 0.1 to 100.0 atm for pressure, and 0.1 to 100 cm spacings between plates/radius of the tube. An extensive parametric study based on nongray formulation is presented. Results obtained for different flow conditions indicate that the radiative interactions can be quite significant in fully developed incompressible flows

Antiferromagnetism and phase separation in the t-J model at low doping: a variational study

Using Gutzwiller-projected wave functions, I estimate the ground-state energy of the t-J model for several variational states relevant for high-temperature cuprate superconductors. The results indicate antiferromagnetism and phase separation at low doping both in the superconducting state and in the staggered-flux normal state proposed for the vortex cores. While phase separation in the underdoped superconducting state may be relevant for the stripe formation mechanism, the results for the normal state suggest that similar charge inhomogeneities may also appear in vortex cores up to relatively high doping values.Comment: 4 pages, 3 figures, reference adde

Inhomogeneous metallic phase upon disordering a two dimensional Mott insulator

We find that isoelectronic disorder destroys the spectral gap in a Mott-Hubbard insulator in 2D leading, most unexpectedly, to a new metallic phase. This phase is spatially inhomogeneous with metallic behavior coexisting with antiferromagnetic long range order. Even though the Mott gap in the pure system is much larger than antiferromagnetic exchange, the spectral gap is destroyed locally in regions where the disorder potential is high enough to overcome the inter-electron repulsion thereby generating puddles where charge fluctuations are enhanced. With increasing disorder, these puddles expand and concomitantly the states at the Fermi energy get extended leading to a metallic phase. We discuss the implications of our results for experiments.Comment: (4 pages, 5 figures

Weak Mott insulators on the triangular lattice: possibility of a gapless nematic quantum spin liquid

We study the energetics of Gutzwiller projected BCS states of various symmetries for the triangular lattice antiferromagnet with a four particle ring exchange using variational Monte Carlo methods. In a range of parameters the energetically favored state is found to be a projected $d_{x^2-y^2}$ paired state which breaks lattice rotational symmetry. We show that the properties of this nematic or orientationally ordered paired spin liquid state as a function of temperature and pressure can account for many of the experiments on organic materials. We also study the ring-exchange model with ferromagnetic Heisenberg exchange and find that amongst the studied ans\"atze, a projected $f-$wave state is the most favorable.Comment: Longer version, 7+ pages, 5 figure