arXiv subjects

R. Biswas

Publications and source records attributed to R. Biswas.

At least 37 records · Page 2Linked to original sources

arXiv2019

Influence of probe geometry of optical fibers in sensing volatile liquids through localized surface plasmon resonance

A comprehensive analysis of influence of probe geometry on localized surface plasmon resonance phenomenon is presented. Plasmonic responses of noble metal nanoparticles such as AuNPs and AgNPs have been exclusively examined by adopting D-type and tapered optical fiber probes for the detection of methanol. With increase in concentration of methanol, the effective refractive index of the medium changes which leads to alter absorbance characteristics of the NPs; thereby modulating the eventual output responses of the proposed sensor. A comparative study has been presented with respective change in geometrical shapes of the probes to detect methanol. The sensitivity in case of D-type probe for detection of methanol is found to be ~0.09644 mV/ppm with AuNPs and ~0.03038 mV/ppm with AgNPs. On the other hand, the sensitivity for AgNPs coated probe is found to be ~0.00389 mV/ppm and 0.00379 mV/ppm for AuNPs in case of tapered probe.

physics.app-ph↗

arXiv2019

Role of radon as a precursor to earthquakes:An appraisal

Radon monitoring has recently gained extensive attention among seismologists. It is now widely reported as a precursssory signal prior to occurrence of a seismic event. The enhanced estimation of radon in soil gas is basically attributed to the strain changes which arise within the earth surface. In this chapter, the role of radon as a precurssor is eleborated, acompanied by the anomalies which come across during observation. Additionally, the recent studies done in Himalayan Belt is also reviewd along with future perspectives in radon estimation.

physics.geo-ph↗

arXiv2019

Laser induced suppression of transmission in magnetically strained black phosphorus

Charge transport through a rectangular vector potential barrier modulated by a continuum laser in monolayer phosphorene is studied theoretically in the ballistic regime along the line of Floquet formalism. Laser free transmission profile displays strong directional behavior exhibiting collimation depending on the incident energy and width of the barrier. However, the application of laser, polarized along the zig-zag direction, creates a sharp anti-resonance in the transmission spectrum and reveals a strong light matter interaction due to broken symmetry in presence of the magnetic vector potential. Transmission properties through a vector barrier are found to be sensitive particularly for lower frequency and higher intensity of the laser. For a thin barrier, the laser assisted conductance is suppressed remarkably in contrast to its oscillatory nature for a thicker one.

cond-mat.mes-hall↗

arXiv2019

A next-generation LHC heavy-ion experiment

The present document discusses plans for a compact, next-generation multi-purpose detector at the LHC as a follow-up to the present ALICE experiment. The aim is to build a nearly massless barrel detector consisting of truly cylindrical layers based on curved wafer-scale ultra-thin silicon sensors with MAPS technology, featuring an unprecedented low material budget of 0.05% X$_0$ per layer, with the innermost layers possibly positioned inside the beam pipe. In addition to superior tracking and vertexing capabilities over a wide momentum range down to a few tens of MeV/$c$, the detector will provide particle identification via time-of-flight determination with about 20~ps resolution. In addition, electron and photon identification will be performed in a separate shower detector. The proposed detector is conceived for studies of pp, pA and AA collisions at luminosities a factor of 20 to 50 times higher than possible with the upgraded ALICE detector, enabling a rich physics program ranging from measurements with electromagnetic probes at ultra-low transverse momenta to precision physics in the charm and beauty sector.

physics.ins-det↗

arXiv2019

Inexpensive hetero-core spliced fiber optic setup for assessing strain

We report here a novel experimental scheme for the measurement of strain that utilizes a simple intensity based interrogation system, based on optical fibers. Corresponding to splicing of a multimode fiber between two single mode fibers, the transmittance was measured by subjecting them to strain at multi points. The results corresponding to those multi points are found to mimic MMI interfere considerably. The set-up has the potential to be applied in crack propagation analysis.

physics.ins-det↗

arXiv2017

Dynamic cloaking effect of a vector barrier in bilayer graphene

Transmission profiles in bilayer graphene have been studied theoretically in presence of a pair of delta function magnetic barriers. Two types of asymmetric Fano resonances are discussed in connection to the electronic cloaking effect in graphene nanostructures. One arises in a static (time independent) vector barrier due to the quantum interference between the discrete hole like state inside the barrier and the electron like continuum outside. In this case the computed results for normal incidence indirectly verify that the cloaking effect is a manifestation of the chirality conservation in charge transport through bilayer graphene scalar barriers. While the other arising due to discrete continuum coupling via the exchange of photon under the application of an external time periodic scalar potential. The study of Fano resonances in transmission spectrum is very much urgent in regards of localization of charge carriers in graphene nano structures for its application in digital device fabrication.

cond-mat.mes-hall↗

arXiv2017

How Many Kilonovae Can Be Found in Past, Present, and Future Survey Datasets?

The discovery of a kilonova (KN) associated with the Advanced LIGO (aLIGO)/Virgo event GW170817 opens up new avenues of multi-messenger astrophysics. Here, using realistic simulations, we provide estimates of the number of KNe that could be found in data from past, present and future surveys without a gravitational-wave trigger. For the simulation, we construct a spectral time-series model based on the DES-GW multi-band light-curve from the single known KN event, and we use an average of BNS rates from past studies of $10^3 \rm{Gpc}^{-3}/\rm{year}$, consistent with the $1$ event found so far. Examining past and current datasets from transient surveys, the number of KNe we expect to find for ASAS-SN, SDSS, PS1, SNLS, DES, and SMT is between 0 and $0.3$. We predict the number of detections per future survey to be: 8.3 from ATLAS, 10.6 from ZTF, 5.5/69 from LSST (the Deep Drilling / Wide Fast Deep), and 16.0 from WFIRST. The maximum redshift of KNe discovered for each survey is z = 0.8 for WFIRST, z = 0.25 for LSST and z = 0.04 for ZTF and ATLAS. For the LSST survey, we also provide contamination estimates from Type Ia and Core-collapse supernovae: after light-curve and template-matching requirements, we estimate a background of just 2 events. More broadly, we stress that future transient surveys should consider how to optimize their search strategies to improve their detection efficiency, and to consider similar analyses for GW follow-up programs.

astro-ph.IM↗

arXiv2017

Delineating site response from microtremors: A case study

We report estimation of site response in the form of fundamental frequency. Towards this objective, we deploy widely established receiver function technique. Taking locally recorded events as inputs, we implement this technique to estimate resonance frequency in three receiver sites, characterized by varying lithology underneath. It is observed that resonance frequencies varies from 3 to 7 Hz, which is also confirmed by our previous studies of estimates from ambient noise recordings with reference to identical sites. Variation of frequency implies existence of heterogeneity in the study area.

physics.geo-ph↗

arXiv2016

Electron transmission through a periodically driven graphene magnetic barrier

The kinetic transport of electrons through graphene magnetic barriers is studied theoretically in presence of an external time harmonic scalar potential. The transmission coefficients are calculated in the framework of the non-perturbative Floquet theory using transfer matrix method. The time dependent scalar potential is found to suppress the usual Fabry-Perot oscillations occurring in the transmission through a constant vector potential barrier (corresponding to two oppositely directed delta-function magnetic barriers). Two types of asymmetric Fano resonances (FR) are noted and are discussed for the narrow barrier structure. One of them arises due to the oscillatory mode while the other due to the evanescent mode of the electron wave inside the barrier. In contrast, the oscillating field favors the transmission for rectangular magnetic barrier structure and also exhibits the FR due to the presence of bound state inside the barrier. The characteristic Fano line shape can be tuned by varying the amplitude of the oscillating potential. The detection of such FR offers an efficient tool for the identification of the quasi-bound and evanescent extended states inside the barrier not reported in the literature so far, for the case of graphene magnetic barrier structures.

cond-mat.mes-hall↗

arXiv2016

Beating oscillation and Fano resonance in the laser assisted electron transmission through graphene δ- function magnetic barriers

We investigate theoretically the transmission of electrons through a pair of δ- function magnetic barriers in graphene in presence of external monochromatic, linearly polarised and CW laser field. The transmission coefficients are calculated in the framework of non-perturbative Floquet theory using the transfer matrix method. It is noted that the usual Fabry-Perot oscillations in transmission through the graphene magnetic barriers with larger inter barrier separation takes the shape of beating oscillations in presence of the external laser field. The laser assisted transmission spectra are also found to exhibit the characteristic Fano resonances (FR) for smaller values of the inter barrier separation. The appearance of the perfect node in the beating oscillation and the asymmetric Fano line shape can be controlled by varying the intensity of the laser field. The above features could provide some useful and potential information about the light - matter interactions and may be utilized in the graphene based optoelectronic device applications.

cond-mat.mes-hall↗

arXiv2015

Spin orbit splitting of the photon induced Fano Resonance in an oscillating graphene electrostatic barrier

We investigate theoretically the effect of a time dependent oscillating potential on the transport property of the Dirac Fermion through a monolayer graphene electrostatic barrier under the influence of the Rashba spin orbit interaction. The time dependent problem is solved in the frame work of the non perturbative Floquet approach. It is noted that the dynamic condition of the barrier may be controlled by tuning the Rashba parameter. Introduction of the spin orbit interaction causes splitting of the Fano resonance(FR), a characteristic feature in photon assisted tunneling. The separation between the spin split FR gives an indirect measure of the fine structure of the quasihole bound state inside the barrier. The present findings on the Rashba splitting of the FR and its external control by tuning the oscillating field parameters might have potential for applications in spintronic devices, especially in the spin field effect transistors. The spin polarization of different Floquet sidebands is found to be quite sensitive to the spin pseudospin interaction.

cond-mat.mes-hall↗

arXiv2015

DES13S2cmm: The First Superluminous Supernova from the Dark Energy Survey

We present DES13S2cmm, the first spectroscopically-confirmed superluminous supernova (SLSN) from the Dark Energy Survey (DES). We briefly discuss the data and search algorithm used to find this event in the first year of DES operations, and outline the spectroscopic data obtained from the European Southern Observatory (ESO) Very Large Telescope to confirm its redshift (z = 0.663 +/- 0.001 based on the host-galaxy emission lines) and likely spectral type (type I). Using this redshift, we find M_U_peak = -21.05 +0.10 -0.09 for the peak, rest-frame U-band absolute magnitude, and find DES13S2cmm to be located in a faint, low metallicity (sub-solar), low stellar-mass host galaxy (log(M/M_sun) = 9.3 +/- 0.3); consistent with what is seen for other SLSNe-I. We compare the bolometric light curve of DES13S2cmm to fourteen similarly well-observed SLSNe-I in the literature and find it possesses one of the slowest declining tails (beyond +30 days rest frame past peak), and is the faintest at peak. Moreover, we find the bolometric light curves of all SLSNe-I studied herein possess a dispersion of only 0.2-0.3 magnitudes between +25 and +30 days after peak (rest frame) depending on redshift range studied; this could be important for 'standardising' such supernovae, as is done with the more common type Ia. We fit the bolometric light curve of DES13S2cmm with two competing models for SLSNe-I - the radioactive decay of 56Ni, and a magnetar - and find that while the magnetar is formally a better fit, neither model provides a compelling match to the data. Although we are unable to conclusively differentiate between these two physical models for this particular SLSN-I, further DES observations of more SLSNe-I should break this degeneracy, especially if the light curves of SLSNe-I can be observed beyond 100 days in the rest frame of the supernova.

astro-ph.HE↗

arXiv2014

Cosmological Parameter Uncertainties from SALT-II Type Ia Supernova Light Curve Models

We use simulated SN Ia samples, including both photometry and spectra, to perform the first direct validation of cosmology analysis using the SALT-II light curve model. This validation includes residuals from the light curve training process, systematic biases in SN Ia distance measurements, and the bias on the dark energy equation of state parameter w. Using the SN-analysis package SNANA, we simulate and analyze realistic samples corresponding to the data samples used in the SNLS3 analysis: 120 low-redshift (z < 0.1) SNe Ia, 255 SDSS SNe Ia (z < 0.4), and 290 SNLS SNe Ia (z <= 1). To probe systematic uncertainties in detail, we vary the input spectral model, the model of intrinsic scatter, and the smoothing (i.e., regularization) parameters used during the SALT-II model training. Using realistic intrinsic scatter models results in a slight bias in the ultraviolet portion of the trained SALT-II model, and w biases (winput - wrecovered) ranging from -0.005 +/- 0.012 to -0.024 +/- 0.010. These biases are indistinguishable from each other within uncertainty; the average bias on w is -0.014 +/- 0.007.

astro-ph.CO↗

arXiv2014

Improved cosmological constraints from a joint analysis of the SDSS-II and SNLS supernova samples

We present cosmological constraints from a joint analysis of type Ia supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations. The data set includes several low-redshift samples (z<0.1), all 3 seasons from the SDSS-II (0.05 < z < 0.4), and 3 years from SNLS (0.2 <z < 1) and totals \ntotc spectroscopically confirmed type Ia supernovae with high quality light curves. We have followed the methods and assumptions of the SNLS 3-year data analysis except for the following important improvements: 1) the addition of the full SDSS-II spectroscopically-confirmed SN Ia sample in both the training of the SALT2 light curve model and in the Hubble diagram analysis (\nsdssc SNe), 2) inter-calibration of the SNLS and SDSS surveys and reduced systematic uncertainties in the photometric calibration, performed blindly with respect to the cosmology analysis, and 3) a thorough investigation of systematic errors associated with the SALT2 modeling of SN Ia light-curves. We produce recalibrated SN Ia light-curves and associated distances for the SDSS-II and SNLS samples. The large SDSS-II sample provides an effective, independent, low-z anchor for the Hubble diagram and reduces the systematic error from calibration systematics in the low-z SN sample. For a flat LCDM cosmology we find Omega_m=0.295+-0.034 (stat+sys), a value consistent with the most recent CMB measurement from the Planck and WMAP experiments. Our result is 1.8sigma (stat+sys) different than the previously published result of SNLS 3-year data. The change is due primarily to improvements in the SNLS photometric calibration. When combined with CMB constraints, we measure a constant dark-energy equation of state parameter w=-1.018+-0.057 (stat+sys) for a flat universe. Adding BAO distance measurements gives similar constraints: w=-1.027+-0.055.

astro-ph.CO↗

arXiv2013

Parameter estimation for compact binary coalescence signals with the first generation gravitational-wave detector network

Compact binary systems with neutron stars or black holes are one of the most promising sources for ground-based gravitational wave detectors. Gravitational radiation encodes rich information about source physics; thus parameter estimation and model selection are crucial analysis steps for any detection candidate events. Detailed models of the anticipated waveforms enable inference on several parameters, such as component masses, spins, sky location and distance that are essential for new astrophysical studies of these sources. However, accurate measurements of these parameters and discrimination of models describing the underlying physics are complicated by artifacts in the data, uncertainties in the waveform models and in the calibration of the detectors. Here we report such measurements on a selection of simulated signals added either in hardware or software to the data collected by the two LIGO instruments and the Virgo detector during their most recent joint science run, including a "blind injection" where the signal was not initially revealed to the collaboration. We exemplify the ability to extract information about the source physics on signals that cover the neutron star and black hole parameter space over the individual mass range 1 Msun - 25 Msun and the full range of spin parameters. The cases reported in this study provide a snap-shot of the status of parameter estimation in preparation for the operation of advanced detectors.

gr-qc↗

arXiv2013

Search for Gravitational Waves from Binary Black Hole Inspiral, Merger and Ringdown in LIGO-Virgo Data from 2009-2010

We report a search for gravitational waves from the inspiral, merger and ringdown of binary black holes (BBH) with total mass between 25 and 100 solar masses, in data taken at the LIGO and Virgo observatories between July 7, 2009 and October 20, 2010. The maximum sensitive distance of the detectors over this period for a (20,20) Msun coalescence was 300 Mpc. No gravitational wave signals were found. We thus report upper limits on the astrophysical coalescence rates of BBH as a function of the component masses for non-spinning components, and also evaluate the dependence of the search sensitivity on component spins aligned with the orbital angular momentum. We find an upper limit at 90% confidence on the coalescence rate of BBH with non-spinning components of mass between 19 and 28 Msun of 3.3 \times 10^-7 mergers /Mpc^3 /yr.

gr-qc↗

arXiv2012

Swift follow-up observations of candidate gravitational-wave transient events

We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors and their candidate sky locations were observed by the Swift observatory. Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a "blind injection challenge". With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.

astro-ph.HE↗

arXiv2012

Search for gravitational waves associated with gamma-ray bursts during LIGO science run 6 and Virgo science runs 2 and 3

We present the results of a search for gravitational waves associated with 154 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments in 2009-2010, during the sixth LIGO science run and the second and third Virgo science runs. We perform two distinct searches: a modeled search for coalescences of either two neutron stars or a neutron star and black hole; and a search for generic, unmodeled gravitational-wave bursts. We find no evidence for gravitational-wave counterparts, either with any individual GRB in this sample or with the population as a whole. For all GRBs we place lower bounds on the distance to the progenitor, under the optimistic assumption of a gravitational-wave emission energy of 10^-2 M c^2 at 150 Hz, with a median limit of 17 Mpc. For short hard GRBs we place exclusion distances on binary neutron star and neutron star-black hole progenitors, using astrophysically motivated priors on the source parameters, with median values of 16 Mpc and 28 Mpc respectively. These distance limits, while significantly larger than for a search that is not aided by GRB satellite observations, are not large enough to expect a coincidence with a GRB. However, projecting these exclusions to the sensitivities of Advanced LIGO and Virgo, which should begin operation in 2015, we find that the detection of gravitational waves associated with GRBs will become quite possible.

astro-ph.HE↗