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Relativistic compact stars with charged anisotropic matter

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Chinese Physics C 2018年第5期42卷 104-116页

作者： s.K.Maurya Ayan banerjee Phongpichit Channuie Department of Mathematical & Physical sciences College of Arts & Science University of Nizwa Department of Mathematics Faculty of Applied Sciences Durban University of Technology school of science Walailak University

In this article, we perform a detailed theoretical analysis of new exact solutions with anisotropic fluid distribution of matter for compact objects subject to hydrostatic equilibrium. We present a family solution to the Einstein-Maxwell equations describing a spherically symmetric, static distribution of a fluid with pressure *** implement an embedding class one condition to obtain a relation between the metric functions. We generalize the properties of a spherical star with hydrostatic equilibrium using the generalised Tolman-Oppenheimer-Volkoff(TOV)equation. We match the interior solution to an exterior Reissner-Nordstr?m one, and study the energy conditions,speed of sound, and mass-radius relation of the star. We also show that the obtained solutions are compatible with observational data for the compact object Her X-1. Regarding our results, the physical behaviour of the present model may serve for the modeling of ultra compact objects.

关键词： Class I spacetime exact solutions compact objects electromagnetic mass models

Propagating disturbances along a coronal loop from simultaneous EUV imaging and spectroscopic observations

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Research in Astronomy and Astrophysics 2015年第7期15卷 1027-1035页

作者： Ajanta Datta s.Krishna Prasad Dipankar banerjee HKBK College of Engineering Indian Institute of Astrophysics Astrophysics Research Centre School of Mathematics and Physics Queen's University Belfast

Propagating disturbances（PDs） were studied along an active region loop using simultaneous imaging and spectroscopy. An image sequence recorded in the Fe Ⅸ/Fe X 171  channel, from TRACE and spectral data in the si Ⅻ 520.6  line obtained from CDs/sOHO, are analyzed. A space-time map constructed from the TRACE image sequence shows the presence of PDs close to the loop foot point propagating with an apparent speed of 39 km s-1. The periodicity was found to be 5.4 *** corresponding spectroscopic data from CDs, at a location away from the foot point, show oscillations in all three line parameters roughly at the same period. At locations farther from the foot point, the line width oscillation seems to disappear while the Doppler velocity oscillation becomes prominent. We attribute this to the signature of propagating slow waves that get affected by flows/other events close to the foot point. spectral line profiles do not show much asymmetry, however, it is difficult to infer anything due to the broadened Gaussian shape of the CDs line profiles.

关键词： sun: corona -- oscillations -- UV radiation -- imaging spectroscopy

Potentiality of semiconducting diamond as the base material of millimeter-wave and terahertz IMPATT devices

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Journal of semiconductors 2014年第3期35卷 39-49页

作者： Aritra Acharyya suranjana banerjee J.P.banerjee Institute of Radio Physics and Electronics University of Calcutta Academy of Technology West Bengal University of Technology

An attempt is made in this paper to explore the potentiality of semiconducting type-IIb diamond as the base material of double-drift region（DDR） impact avalanche transit time（IMPATT） devices operating at both millimetre-wave（mm-wave） and terahertz（THz） frequencies. A rigorous large-signal（L-s） simulation based on the non-sinusoidal voltage excitation（NsVE） model developed earlier by the authors is used in this study. At first,a simulation study based on avalanche response time reveals that the upper cut-off frequency for DDR diamond IMPATTs is 1.5 THz, while the same for conventional DDR si IMPATTs is much smaller, i.e. 0.5 THz. The L-s simulationresultsshowthattheDDRdiamondIMPATTdevicedeliversapeakRFpowerof7.79Wwithan18.17%conversion efficiency at 94 GHz; while at 1.5 THz, the peak power output and conversion efficiency decrease to6.19mWand8.17%respectively,taking50%*** diamond and si shows that the former excels over the later as regards high frequency and high power performance at both mm-wave and THz frequency bands. The effect of band to band tunneling on the L-s properties of DDR diamond and si IMPATTs has also been studied at different mm-wave and THz frequencies.

关键词： diamond IMPATTs DDR large-signal simulation millimeter-wave terahertz

Effect of junction temperature on the large-signal properties of a 94 GHz silicon based double-drift region impact avalanche transit time device

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Journal of semiconductors 2013年第2期34卷 19-30页

作者： Aritra Acharyya suranjana banerjee J.P.banerjee Institute of Radio Physics and Electronics University of Calcutta92APC RoadKolkata-700009India Academy of Technology West Bengal University of TechnologyAdisaptagramHooghly-712121West BengalIndia

The authors have developed a large-signal simulation technique extending an in-house small-signal simulation code for analyzing a 94 GHz double-drift region impact avalanche transit time device based on silicon with a non-sinusoidal voltage excitation and studied the effect of junction temperature between 300 and 550 K on the large-signal characteristics of the device for both continuous wave （CW） and pulsed modes of operation. Results show that the large-signal RF power output of the device in both CW and pulsed modes increases with the increase of voltage modulation factor up to 60%, but decreases sharply with further increase of voltage modulation factor for a particular junction temperature; while the same parameter increases with the increase of junction temperature for a particular voltage modulation factor. Heat sinks made of copper and type-IIA diamond are designed to carry out the steady-state and transient thermal analysis of the device operating in CW and pulsed modes respectively. Authors have adopted Olson＇s method to carry out the transient analysis of the device, which clearly establishes the superiority of type-IIA diamond over copper as the heat sink material of the device from the standpoint of the undesirable effect of frequency chirping due to thermal transients in the pulsed mode.

关键词： admittance characteristics chirp bandwidth frequency chirping junction temperature large-signal analysis transient thermal analysis

Vitreous haemorrhage as the first presentation of undiagnosed Waldenstrom macroglobulinemia

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International Journal of Ophthalmology(English edition) 2021年第10期14卷 1639-1641页

作者： Christina s Lim Huzaifa Malick somnath banerjee Department of Ophthalmology University Hospitals of Leicester NHS TrustInfirmary SquareLeicester LE15WWUnited Kingdom

Dear Editor, Waldenstrom macroglobulinemia(WM) is a rare type of non-Hodgkin’s lymphoma, commonly associated with hyperviscosity syndrome. Unlike non-Hodgkin’s lymphoma, its ocular manifestations are less well described in the literature. Here we present the first case of undiagnosed WM presenting with dense vitreous haemorrhage. The study was conducted in accordance with the principles of the Declaration of Helsinki. The informed consent was obtained from the subject.

关键词： globulin lymphoma Waldenstr

Emerging Challenges in Atolls for sustainable Groundwater Management

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地学前缘 2009年第S1期16卷 22-23页

作者： Pallavi banerjee V.s.singh National Geophysical Research Institute

Tropical islands,about 50000 in number,are distributed over the Pacific,Indian and Atlantic *** groundwater resources in the form of lens shaped aquifers,in atolls,are extremely vulnerable to natural processes and human *** increasing population on these islands has worsened the groundwater demand supply ratio significantly. This deteriorating ground water condition has come

关键词： coral islands groundwater numerical modeling groundwater level sea level

Nucleosynthesis in the accretion disks of Type Ⅱ collapsars

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Research in Astronomy and Astrophysics 2013年第9期13卷 1063-1074页

作者： Indrani banerjee Banibrata Mukhopadhyay Department of Physics Indian Institute of Science

We investigate nucleosynthesis inside the gamma-ray burst （GRB） accre- tion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star. After that, an out- ward moving shock triggers a successful supernova. However, the supernova ejecta lacks momentum and within a few seconds the newly formed neutron star gets trans- formed to a stellar mass black hole via massive fallback. The hydrodynamics of such an accretion disk formed from the fallback material of the supernova ejecta has been studied extensively in the past. We use these well-established hydrodynamic models for our accretion disk in order to understand nucleosynthesis, which is mainly ad- vection dominated in the outer regions. Neutrino cooling becomes important in the inner disk where the temperature and density are higher. The higher the accretion rate （M） is, the higher the density and temperature are in the disks. We deal with accre- tion disks with relatively low accretion rates： 0.001 Mo s-1 ~ 3）/~ 0.01 Mo s--1 and hence these disks are predominantly advection dominated. We use He-rich and si- rich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like 31p, 39K, 43sc＇ 35C1 and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthe- sized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they should

关键词： accretion accretion disks -- gamma rays: bursts -- black hole physics-- nuclear reactions nucleosynthesis abundances

Propagating disturbances along fan-like coronal loops in an active region

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Research in Astronomy and Astrophysics 2015年第11期15卷 1832-1842页

作者： sudip Mandal Tanmoy samanta Dipankar banerjee s.Krishna Prasad Luca Teriaca Indian Institute of Astrophysics Astrophysics Research Centre School of Mathematics and Physics Queen’s University Belfast Max-Planck-Institut fuer sonnensystemforschung (MPs)

Propagating disturbances are often observed in active region fan-like coronal loops. They were thought to be due to slow mode magnetohydrodynamic waves based on some of the observed properties. However, recent studies involving spectroscopy indicate that they could be due to high speed quasi-periodic upflows which are difficult to distinguish from upward propagating slow waves. In this context, we have studied a fan loop structure in the active region AR 11465 using simultaneous spectroscopic and imaging observations from the Extreme Ultraviolet Imaging spectrometer onboard Hinode and Atmospheric Imaging Assembly onboard solar Dynamics Observatory. Analysis of the data shows significant oscillations at different locations. We explore the variations in different line parameters to determine whether the waves or flows could cause these oscillations to improve the current understanding of the nature of these disturbances.

关键词： wavelet simultaneous distinguish Extreme propagating solar fitting pixel spectroscopic Roberts

Early Pliocene Paleoceanography of the Vityaz Fracture Zone,Central Indian Ridge

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Acta Geologica sinica(English Edition) 2007年第4期81卷 614-621页

作者： M.V.s.GUPTHA Ranadip banerjee Lina P.MERGULHAO Priyanka banerjee G.PARTHIBAN Manish TEWARI National Institute of Oceanography Dona Paula Goa-403 004India Department of Geological sciences Jadavpur University Kolkata700032India Physical Research Laboratory Navrangpura AhmedabadIndia

Planktic foraminifera from the calcareous substrate of a ferromanganese crust in the Vityaz Fracture Zone （VFZ）, Central Indian Ridge were studied to reconstruct the early Pliocene paleoceanography of this region. Eleven species of planktic foraminifera were encountered, among them Globorotalia menardii, Neogloboquadrina dutertrei, Globigerina bulloides and Globigerinoides tuber are prominent. Predominance of N. dutertrei in the top 3 cm of the carbonate substrate is attributed to an influx of fresh water which eventually triggered their productivity by increasing the nutrient level. The presence of G. bulloides and G. menardii in significant proportions in deeper layers suggests the prevalence of open ocean upwelling. The bulk chemical compositions of the substrate at different depth intervals indicates higher enrichment of trace metals in the upper sections which could have been supplied through oceanic water by the chemical weathering of terrestrial matter during the peak of Pliocene Asian monsoon. Thus, it is concluded that during the early Pliocene the biogenic components of the substrate were distinctly contributed by both upwelling and productivity triggered by an influx of fresh water originating from the intensification of the Asian monsoon during the early Pliocene Period.

关键词： Central Indian Ridge Vityaz Fracture Zone ferromanganese crust biogenic bloom,freshwater influx Neogene climate change spores Asian monsoon