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Search Results: 1 - 10 of 14074 matches for " Priyamvada Singh "
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High prevalence of Arginine to Glutamine Substitution at 98, 141 and 162 positions in Troponin I (TNNI3) associated with hypertrophic cardiomyopathy among Indians
Rani Deepa,Nallari Pratibha,Priyamvada Singh,Narasimhan Calambur
BMC Medical Genetics , 2012, DOI: 10.1186/1471-2350-13-69
Abstract: Background Troponin I (TNNI3) is the inhibitory subunit of the thin filament regulatory complex Troponin, which confers calcium-sensitivity to striated muscle actomyosin ATPase activity. Mutations (2-7%) in this gene had been reported in hypertrophic cardiomyopathy patients (HCM). However, the frequencies of mutations and associated clinical presentation have not been established in cardiomyopathy patients of Indian origin, hence we have undertaken this study. Methods We have sequenced all the exons, including the exon-intron boundaries of TNNI3 gene in 101 hypertrophic cardiomyopathy patients (HCM), along with 160 healthy controls, inhabited in the same geographical region of southern India. Results Our study revealed a total of 16 mutations. Interestingly, we have observed Arginine to Glutamine (R to Q) mutation at 3 positions 98, 141 and 162, exclusively in HCM patients with family history of sudden cardiac death. The novel R98Q was observed in a severe hypertrophic obstructive cardiomyopathy patient (HOCM). The R141Q mutation was observed in two familial cases of severe asymmetric septal hypertrophy (ASH++). The R162Q mutation was observed in a ASH++ patient with mean septal thickness of 29 mm, and have also consists of allelic heterogeneity by means of having one more synonymous (E179E) mutation at g.4797: G → A: in the same exon 7, which replaces a very frequent codon (GAG: 85%) with a rare codon (GAA: 14%). Screening for R162Q mutation in all the available family members revealed its presence in 9 individuals, including 7 with allelic heterogeneity (R162Q and E179E) of which 4 were severely affected. We also found 2 novel SNPs, (g.2653; G → A and g.4003 C → T) exclusively in HCM, and in silico analysis of these SNPs have predicted to cause defect in recognition/binding sites for proteins responsible for proper splicing. Conclusion Our study has provided valuable information regarding the prevalence of TNNI3 mutations in Indian HCM patients and its risk assessment, these will help in genetic counseling and to adopt appropriate treatment strategies.
Study of the dynamics of the core of A2218
Priyamvada Natarajan
Physics , 1995,
Abstract: We report the results of an attempt to study the velocity structure of the core of the cluster A2218 in order to probe its dynamical state. The aim is to understand if the core is indeed virialized? relaxed? or in hydrodynamic equilibrium? We use cluster lensing data in conjunction with the optical galaxy data to solve in detail for the nature of galaxy orbits and the velocity anisotropy in the core. We present our preliminary results below.
Do cluster galaxies have extended dark halos?
Priyamvada Natarajan
Physics , 1997,
Abstract: We present the results of the application of the methodology introduced by Natarajan & Kneib (1997) to interpret local perturbations to the cluster shear field resulting from mass associated with individual cluster galaxies. The lensing signal is used to place new constraints on the average mass-to-light ratio and spatial extents of the dark matter halos associated with morphologically-classified early-type cluster members in the Abell cluster AC114. The total mass of a fiducial $L^\ast$ cluster spheroidal galaxy is found to be largely contained within $\sim$ 15 kpc radius halo ($\sim$~8--10 $R_e$) with a mass-to-light ratio ${M/L_V} \sim {15^{+10}_{-4}} $ (90 % c.l.) in solar units within this radius. Comparisons with similar estimates for field galaxies suggests that the cluster galaxies in AC114 may possess less extensive and less massive halos. Additionally, there is some indication that, at a fixed luminosity, S0 galaxies are less extended than ellipticals, suggesting a difference in the efficiency of tidal stripping for different galaxy types. These results enable us to probe the variation of the mass-to-light ratio with scale via gravitational lensing methods. Therefore, the prospects for constraining the mass density of the Universe and understanding galaxy evolution using these gravitational lensing methods are very promising.
Consequences of feedback from early supernovae for disk assembly
Priyamvada Natarajan
Physics , 1998, DOI: 10.1086/311877
Abstract: In this letter we examine the role of the first supernovae in proto-galaxies, their role in feedback and the consequences for disk assembly. Extending the picture proposed by Dekel & Silk (1986), we argue that energetic supernovae winds can expel baryons from all proto-galaxies with varying degrees of efficiency. The fraction of baryons retained and hence available to assemble into the baryonic disk is therefore, a function of the central velocity dispersion of the halo. Such a coupling of the baryonic component to the dark halo leads to the following interesting consequence, a prediction for a weak scaling of the zero-point of the Tully-Fisher relation or alternatively, the mass-to-light ratio with the central velocity dispersion of the halo. On applying to the case of the Milky Way halo, this feedback mechanism implies: (i) that the Milky Way halo lost approximately 10% of its original gas content; (ii) a range in the inferred redshift of formation $z_f$, and the local baryon fraction $f_b$ for the Milky Way that depends on the initial spin parameter of the halo. We find that for a low spin halo - $z_f < 1$, $f_b \sim 2%$; for a median spin halo - $z_f \sim 1 - 2.5$, $f_b \sim 5%$; and for a high spin halo - $z_f \sim 4 - 8$, $f_b \sim 20%$. The observationally determined ages for the oldest disk stars in the Milky Way seem to rule out a low value for the spin parameter. Given the shape of the spin distribution of halos obtained in N-body simulations, while a high value of the spin parameter is not very probable, it is interesting to note that if this is indeed the case for the Milky Way halo, then feedback processes can cause the local baryon fraction to differ significantly from the universal value.
Accretion history of super-massive black holes
Priyamvada Natarajan
Physics , 1998,
Abstract: We show that the luminosity function of the actively star-forming Lyman break galaxies and the B-band quasar luminosity function at $z = 3$ can be fit reasonably well with the mass function of collapsed galaxy scale dark matter haloes predicted by viable variants of hierarchical cold dark matter dominated cosmological models for lifetimes $t_Q$ of the optically bright phase of QSOs in the range $10^{6}$ to $10^{8}$ yr. There is a strong correlation between $t_Q$ and the required degree of non-linearity in the relation between black hole and host halo mass. Such a non-linear relation is motivated by suggesting that the mass of supermassive black holes may be limited by the back-reaction of the emitted energy on the accretion flow in a self-gravitating disc. This would imply a relation of black hole to halo mass of the form $M_{\rm bh} \propto v_{\rm halo}^5 \propto M_{\rm halo}^{5/3}$ and a typical duration of the optically bright QSO phase of the order of the Salpeter time, $\sim 10^{7}$ yr. The high integrated local mass density of black holes inferred from recent kinematic determinations of black hole masses in nearby galaxies seem to indicate that the overall efficiency of supermassive black holes for producing blue light is lower than was previously assumed. We discuss three possible accretion modes with low optical emission efficiency: (i) accretion well above the Eddington rate, (ii) accretion obscured by dust, and (iii) accretion below the critical rate leading to an advection dominated accretion flow lasting for a Hubble time. We further argue that accretion with low optical efficiency might be closely related to the origin of the hard X-ray background.
The mass assembly history of black holes in the Universe
Priyamvada Natarajan
Physics , 2011,
Abstract: We track the growth and evolution of high redshift seed black holes over cosmic time. This population of massive, initial black hole seeds form at these early epochs from the direct collapse of pre-galactic gas discs. Populating dark matter halos with seeds formed in this fashion, we follow their mass assembly history to the present time using a Monte-Carlo merger tree approach. Using this formalism, we predict the black hole mass function at the present time; the integrated mass density of black holes in the Universe; the luminosity function of accreting black holes as a function of redshift and the scatter in observed, local Mbh{\sigma}s relation. Signatures of these massive seed models appear predominantly at the low mass end of the present day black hole mass function. In fact, our prediction of the shape of the Mbh{\sigma}s relation at the low mass end and increased scatter has recently been corroborated by observations. These models predict that low surface brightness, bulge-less galaxies with large discs are least likely to be sites for the formation of massive seed black holes at high redshifts. The efficiency of seed formation at high redshifts also has a direct influence on the black hole occupation fraction in galaxies at z = 0. This effect is more pronounced for low mass galaxies today as we predict the existence of a population of low mass galaxies that do not host nuclear black holes. This is the key discriminant between the models studied here and the Population-III remnant seed model.
The formation and evolution of massive black hole seeds in the early Universe
Priyamvada Natarajan
Physics , 2011,
Abstract: Tracking the evolution of high redshift seed black hole masses to late times, we examine the observable signatures today. These massive initial black hole seeds form at extremely high redshifts from the direct collapse of pre-galactic gas discs. Populating dark matter halos with seeds formed in this fashion, we follow the mass assembly history of these black holes to the present time using a Monte-Carlo merger tree approach. Utilizing this formalism, we predict the black hole mass function at high redshifts and at the present time; the integrated mass density of black holes in the Universe; the luminosity function of accreting black holes as a function of redshift and the scatter in observed, local M-sigma relation. Comparing the predictions of the `light' seed model with these massive seeds we find that significant differences appear predominantly at the low mass end of the present day black hole mass function. However, all our models predict that low surface brightness, bulge-less galaxies with large discs are least likely to be sites for the formation of massive seed black holes at high redshifts. The efficiency of seed formation at high redshifts has a direct influence on the black hole occupation fraction in galaxies at z=0. This effect is more pronounced for low mass galaxies. This is the key discriminant between the models studied here and the Population III remnant `light' seed model. We find that there exists a population of low mass galaxies that do not host nuclear black holes. Our prediction of the shape of the M-sigma relation at the low mass end and increased scatter has recently been corroborated by observations.
Admission Hyperglycemia and Acute Myocardial Infarction: Outcomes and Potential Therapies for Diabetics and Nondiabetics
Anjan K. Chakrabarti,Priyamvada Singh,Lakshmi Gopalakrishnan,Varun Kumar,Meagan Elizabeth Doherty,Cassandra Abueg,Weici Wang,C. Michael Gibson
Cardiology Research and Practice , 2012, DOI: 10.1155/2012/704314
Abstract: Hyperglycemia, in both diabetic and nondiabetic patients, has a significant negative impact on the morbidity and mortality of patients presenting with an acute myocardial infarction (AMI). Contemporary evidence indicates that persistent hyperglycemia after initial hospital admission continues to exert negative effects on AMI patients. There have been a number of studies demonstrating the benefit of tight glucose control in patients presenting with AMI, but a lack of convincing clinical data has led to loose guidelines and poor implementation of glucose targets for this group of patients. The CREATE-ECLA study, which hypothesized that a fixed high dose of glucose, insulin, and potassium (GIK) would change myocardial substrate utilization from free fatty acids to glucose and therefore protect ischemic myocardium, failed to demonstrate improved clinical outcomes in AMI patients. Studies that specifically investigated intensive insulin therapy, including DIGAMI-2 and HI-5, also failed to improve clinical outcomes such as mortality. There are a number of reasons that these trials may have fallen short, including the inability to reach glucose targets and inadequate power. There is now a need for a large placebo-controlled randomized trial with an adequate sample size and adherence to glucose targets in order to establish the benefit of treating hyperglycemia in patients presenting with AMI. 1. Background Major advances in cardiovascular disease, and specifically the treatment of acute coronary syndrome (ACS), have had a significant impact on the morbidity and mortality of patients with acute myocardial infarctions (AMI). Despite these advances, diabetes continues to put patients with and without a prior history of myocardial infarction at significant cardiovascular risk [1]. The presence of diabetes doubled the age-adjusted risk for cardiovascular disease in men and tripled it in women in the Framingham Heart Study, and it remained an independent risk factor even after adjusting for age, hypertension,??smoking, hyperlipidemia, and left ventricular hypertrophy [2]. Furthermore, there is a graded rise in cardiovascular risk with increasing hyperglycemia in patients with overt diabetes. In fact, as demonstrated by a meta-analysis of 13 prospective cohort studies, for every one-percentage point increase in glycosylated hemoglobin (HbA1c), the relative risk for any cardiovascular event was 1.18 (95% CI 1.10–1.26) [3]. It has been well documented that with adequate glycemic control, cardiovascular outcomes improve in patients with both type 1 and type 2 diabetes
Estimating the mass density of neutral gas at $z < 1$
Priyamvada Natarajan,Max Pettini
Physics , 1997, DOI: 10.1093/mnras/291.1.28L
Abstract: We use the relationships between galactic HI mass and B-band luminosity determined by Rao & Briggs to recalculate the mass density of neutral gas at the present epoch based on more recent measures of the galaxy luminosity function than were available to those authors. We find $\Omega_{gas}(z=0) \simeq 5 \times 10^{-4}$ in good agreement with the original Rao & Briggs value, suggesting that this quantity is now reasonably secure. We then show that, if the scaling between H I mass and B-band luminosity has remained approximately constant since $z = 1$, the evolution of the luminosity function found by the Canada-France redshift survey translates to an increase of $\Omega_{gas}$ by a factor of $\approx 3$ at $z = 0.5 - 1$ . A similar value is obtained quite independently from consideration of the luminosity function of Mg II absorbers at $z = 0.65$. By combining these new estimates with data from damped \lya systems at higher redshift, it is possible to assemble a rough sketch of the evolution of $\Omega_{gas}$ over the last 90% of the age of the universe. The consumption of H I gas with time is in broad agreement with models of chemical evolution which include the effects of dust, although more extensive samples of damped \lya systems at low and intermediate redshift are required for a quantitative assessment of the dust bias.
Two-dimensional galaxy-galaxy lensing: a direct measure of the flattening and alignment of light and mass in galaxies
Priyamvada Natarajan,Alexandre Refregier
Physics , 2000, DOI: 10.1086/312808
Abstract: We propose a new technique to directly measure the shapes of dark matter halos of galaxies using weak gravitational lensing. Extending the standard galaxy-galaxy lensing method, we show that the shape parameters of the mass distribution of foreground galaxies can be measured from the two-dimensional shear field derived from background galaxies. This enables the comparison of the ellipticity of the mass distribution with that of the light in galaxies, as well as an estimate of the degree of alignment between the stellar component and dark matter. We choose the specific case of an elliptical, isothermal profile and estimate the feasibility and significance of the detection of this signal. The prospects for applying this technique are excellent with large on-going surveys like the Sloan Digital Sky Survey. The expected signal is smaller, but comparable in significance to that of the mass in standard galaxy-galaxy lensing analyses. Since shapes of halos depend on the degree of dissipation and the transfer of angular momentum during galaxy assembly, constraints obtained from our analysis will provide an important input to models of galaxy formation.
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