Search

Hot electrons, far above the lattice temperature of a material, present opportunities for enhanced solar energy harvesting or performance of otherwise unfavorable chemistry. The spectroscopic signatures and dynamics of hot carrier absorption and emission have been extensively studied in bulk and nanoscopic semiconductors, but the effects on intraband transitions are largely unexplored. Here, the effect of hot electrons on the properties of colloidal quantum wells made of cadmium selenide is examined using ultrafast spectroscopy. Similar to expitaxial quantum wells, these atomically precise materials support intersubband transitions (a class of intraband transitions in 1D and 2D materials) in the near-infrared spectral window. Using energy-dependent photoexcitation, it is shown that electrons reach effective temperatures of 2000 K or greater. This results in a substantial transient shift in the oscillator strength of the instersubband transition to lower energies on a sub-picosecond time-scale. Similar heating of electrons is achieved under mid-infrared re-excitation, which permits ultrafast transmittance modulation throughout the near-infrared.

We develop a framework for price-mediated contagion in financial systems where banks are forced to liquidate assets to satisfy a risk-weight based capital adequacy requirement. In constructing this modeling framework, we introduce a two-tier pricing structure: the volume weighted average price that is obtained by any bank liquidating assets and the terminal mark-to-market price used to account for all assets held at the end of the clearing process. We consider the case of multiple illiquid assets and develop conditions for the existence and uniqueness of clearing prices. We provide a closed-form representation for the sensitivity of these clearing prices to the system parameters, and use this result to quantify: (1) the cost of regulation, in stress scenarios, faced by the system as a whole and the individual banks, and (2) the value of providing bailouts to consider when such notions are financially advisable. Numerical case studies are provided to study the application of this model to data.

We propose a model-based predictive estimator of the finite population proportion of a misclassified binary response, when information on the auxiliary variable(s) is available for all units in the population. Asymptotic properties of the misclassification-adjusted predictive estimator are also explored. We propose a computationally efficient bootstrap variance estimator that exhibits better performance compared to usual analytical variance estimator. The performance of the proposed estimator is compared with other commonly used design-based estimators through extensive simulation studies. The results are supplemented by an empirical study based on literacy data.

Count data arising in various fields of applications are often under‐reported. Ignoring undercount naturally leads to biased estimators and inaccurate confidence intervals. In the presence of undercount, in this paper, we develop likelihood‐based methodologies for estimation of mean using validation data. The asymptotic distributions of the competing estimators of the mean are derived. The impact of ignoring undercount on the coverage and length of the confidence intervals is investigated using extensive numerical studies. Finally an analysis of heat mortality data is presented.

Indian Railways is the fourth-largest railway network in the world by size, with 121,407 kilometers of total track over a 67,368-kilometre route. Mostly the railway tracks in India have joined by bolted and large welded joints, susceptible to derailment and fractures due to the longitudinal tensile stresses (hence strain) as the temperature falls below the distressing temperature. This problem caused from mechanical sources such as braking, rolling friction and wheel flanging on curves. Usually once them temperature varies anchoring temperature, causes the compressive and tensile stress in rail tracks and rail joints, more vulnerable to thermal buckling. This paper aims to characterize the in situ thermal stress detection for different rail and rail joints. The strain gauges were employed for strain monitor. This paper examines the potential of the strain gauges for in situ thermal stress levels for increasing temperature. For economical growing countries like India, railway infrastructure plays a critical role. The resistances were monitored for incremental thermal loading.

Over the last twenty five years, advances in the collection and analysis of functional magnetic resonance imaging (fMRI) data have enabled new insights into the brain basis of human health and disease. Individual behavioral variation can now be visualized at a neural level as patterns of connectivity among brain regions. As such, functional brain imaging is enhancing our understanding of clinical psychiatric disorders by revealing ties between regional and network abnormalities and psychiatric symptoms. Initial success in this arena has recently motivated collection of larger datasets which are needed to leverage fMRI to generate brain-based biomarkers to support the development of precision medicines. Despite numerous methodological advances and enhanced computational power, evaluating the quality of fMRI scans remains a critical step in the analytical framework. Before analysis can be performed, expert reviewers visually inspect individual raw scans and preprocessed derivatives to determine viability of the data. This Quality Control (QC) process is labor intensive, and the inability to adequately automate at large scale has proven to be a limiting factor in clinical neuroscience fMRI research. In this paper, we present a novel method for automating the QC of fMRI scans. We train machine learning classifiers using features derived from brain MR images to predict the “quality” of those images, which is based on the ground truth of an expert’s opinion. Specifically, we emphasize the importance of these classifiers’ ability to generalize their predictions across data collected in different studies. To address this, we propose a novel approach entitled “FMRI preprocessing Log mining for Automated, Generalizable Quality Control” (FLAG-QC), in which features derived from mining runtime logs are used to train the classifier. We show that classifiers trained on FLAG-QC features perform much better (AUC = 0.79) than previously proposed feature sets (AUC = 0.56) when testing their ability to generalize across studies.

The fusion evaporation residue (ER) excitation function has been measured for $^{35,37}\mathrm{Cl}+^{181}\mathrm{Ta}$ reactions at energies above the Coulomb barrier. The measurements were performed using the HYbrid Recoil mass Analyzer at IUAC, New Delhi. Comparable ER cross sections have been observed in both reactions and there is no isotopic dependence. Measured ER cross sections were compared with theoretical calculations employing the dinuclear system model at projectile and target nuclei interaction and statistical model for the deexcitation of the formed compound nucleus. Larger ER cross sections at the complete deexcitation cascade of the formed compound nucleus are noticed in both reactions at higher excitation energies $({E}^{*}g80 \mathrm{MeV})$ over the calculated results. Fusion probability varies from $95%$ to $40%$ in the excitation energy range of the study. No appreciable difference in the fusion probability is noticed in the two reactions. Comparison of our results with other reactions populating $^{216}\mathrm{Th}$ shows a very strong entrance channel dependence.

Rail track derailment has been proven to be the cause of most of the rail accidents in recent years. High-temperature strains in railways caused by rail traction and thermal variation are the main causes of derailment, which lead to buckling. The likelihood of passenger deaths and maintenance costs will be reduced if thermal strains and failure in rails are detected early. This research attempts to provide a preventative strategy for detecting thermal strains and deformation caused by temperature fluctuations at railways. Using the electromechanical impedance (EMI) technique, piezoelectric sensors were used to acquire piezo coupled structural signatures for lab-sized rail samples, i.e. plain rail and rail joints, for gradual temperature escalation and repeat heat cycle. The experimental conductance signatures were obtained for the incremental rise in temperature (30–80 °C) in ambient conditions, and repetitive thermal cycles. To better diagnose structural problems induced only by the effect of heat on the host structure, thermal compensation is proposed. The piezo–coupled signatures for thermal changes in rail and rail junctions (weld and bolt) were found to be particularly effective in detecting incipient structural alterations for both steady and cyclic temperature variations. Statistical damage index was used to quantify the damage for all types of rail-joint bar caused due to temperature variation. Overall, this study has paved an experimental technique that can be used to detect early damage in rail and rail joints due to thermal loading.

Characteristics and performance of a HYbrid Telescope ARray (HYTAR) detector system for heavy ions are presented. The system has been developed for the study of reaction mechanisms in nuclear physics experiments around the Coulomb barrier. HYTAR apparatus is an array of hybrid telescopes, each unit comprising of a gas ionization chamber followed by a silicon detector. Gas ionization chamber, operated in axial field mode, measures the differential energy loss ( Δ E ), while the residual energies are measured by silicon detector. Particle identification is realized by implementing Δ E -E technique. Use of gas ionization chamber as Δ E detector allows identification of reaction channels down to low energy thresholds ∼ 0.1 MeV/A in A ∼ 100 region. The detector system has been developed to investigate the fusion and fusion–fission dynamics by performing quasi-elastic scattering and fission angular distribution experiments. Processing of the detector signals is realized with compact and simple high density front-end electronics, which consists of custom developed low noise charge sensitive preamplifiers (operated inside vacuum) and differential driver NIM modules, followed by commercially available spectroscopy amplifiers, logic modules, analog to digital converters etc. Design features of the HYTAR and measurements performed with it are described in this article.

A statistical model description of heavy ion induced fusion-fission reactions is presented where shell effects, collective enhancement of level density, tilting away effect of compound nuclear spin and dissipation are included. It is shown that the inclusion of all these effects provides a consistent picture of fission where fission hindrance is required to explain the experimental values of both pre-scission neutron multiplicities and evaporation residue cross-sections in contrast to some of the earlier works where a fission hindrance is required for pre-scission neutrons but a fission enhancement for evaporation residue cross-sections., 14 pages, 2 figures

The problem of testing equality of means of a bivariate normal distribution on the basis of a sample of size n has been considered when the labels of the observations are either missing or not known. The problem may arise in many applied settings, especially in genetics. Classical likelihood ratio test fails here because of identifiability problems. We propose a two-stage testing procedure using a recently developed test in the context of penalized splines. The proposed testing procedure is found to outperform the tests proposed in the literature. Copyright © 2017 John Wiley & Sons, Ltd.

Evaporation residue cross sections for the $^{16}\mathrm{O}+^{203,205}\mathrm{Tl}$ reactions were measured at laboratory beam energies in the range of 82--113 MeV using a gas-filled separator. Transmission efficiency of the separator was estimated using a calibration reaction $^{16}\mathrm{O}+^{197}\mathrm{Au}$ and by simulating the evaporation residues angular distributions. Statistical model calculations were performed for both the measured systems. These calculations overestimate the experimental evaporation residue cross sections. This could be attributed to the presence of noncompound nuclear fission. An estimation of noncompound nuclear fission contribution was carried out. Comparison with neighboring systems shows that a slight change in the entrance channel or the compound nucleus properties makes a large difference in evaporation residue cross sections.

Background: Despite remarkable success of the statistical model (SM) in describing decay of excited compound nuclei (CN), reproduction of the observables from heavy ion-induced fusion-fission reactions is often quite challenging. Ambiguities in choosing the input parameters, lack of clarity about inclusion of various physical effects in the model, and contradictory requirements of input parameters while describing different observables from similar reactions are among the major difficulties of modeling decay of fissile CN.Purpose: This work attempts to overcome the existing inconsistencies by inclusion of important physical effects in the model and through a systematic analysis of a large set of data over a wide range of CN mass (${A}_{\mathrm{CN}}$).Method: The model includes the shell effect in the level density (LD) parameter, shell correction in the fission barrier (${B}_{\mathrm{f}}$), the effect of the orientation degree of freedom of the CN spin (${K}_{\mathrm{or}}$), collective enhancement of level density (CELD), and dissipation in fission. Input parameters are not tuned to reproduce observables from specific reaction(s) and the reduced dissipation coefficient ($\ensuremath{\beta}$) is treated as the only adjustable parameter. Calculated evaporation residue (ER) cross sections (${\ensuremath{\sigma}}_{\mathrm{ER}}$), fission cross sections (${\ensuremath{\sigma}}_{\mathrm{fiss}}$), and particle, i.e., neutron, proton, and $\ensuremath{\alpha}$ particle, multiplicities are compared with data covering ${A}_{\mathrm{CN}}=156$--248.Results: The model produces reasonable fits to ER and fission excitation functions for all the reactions considered in this work. Pre-scission neutron multiplicities (${\ensuremath{\nu}}_{\mathrm{pre}}$) are underestimated by the calculation beyond ${A}_{\mathrm{CN}}\ensuremath{\sim}200$. An increasingly higher value of $\ensuremath{\beta}$, in the range of 2--$4\ifmmode\times\else\texttimes\fi{}{10}^{21}\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, is required to reproduce the data with increasing ${A}_{\mathrm{CN}}$. Proton and $\ensuremath{\alpha}$-particle multiplicities, measured in coincidence with both ERs and fission fragments, are in qualitative agreement with model predictions.Conclusions: The present work mitigates the existing inconsistencies in modeling statistical decay of the fissile CN to a large extent. Contradictory requirements of fission enhancement---obtained by scaling down the fission barrier to reproduce ${\ensuremath{\sigma}}_{\mathrm{ER}}$ or ${\ensuremath{\sigma}}_{\mathrm{fiss}}$ and fission suppression realized by introducing dissipation in the fission channel to reproduce ${\ensuremath{\nu}}_{\mathrm{pre}}$, for similar reactions---have now become redundant. There are scopes for further refinement of the model, as is evident from the mismatch between measured and calculated particle multiplicities in a few cases.

In this paper we study the implications of contingent payments on the clearing wealth in a network model of financial contagion. We consider an extension of the Eisenberg–Noe financial contagion model in which the nominal interbank obligations depend on the wealth of the firms in the network. We first consider the problem in a static framework and develop conditions for existence and uniqueness of solutions as long as no firm is speculating on the failure of other firms. In order to achieve existence and uniqueness under more general conditions, we introduce a dynamic framework. We demonstrate how this dynamic framework can be applied to problems that were ill-defined in the static framework.

We consider the estimation of the prevalence of a rare disease, and the log-odds ratio for two specified groups of individuals from group testing data. For a low-prevalence disease, the maximum likelihood estimate of the log-odds ratio is severely biased. However, Firth correction to the score function leads to a considerable improvement of the estimator. Also, for a low-prevalence disease, if the diagnostic test is imperfect, the group testing is found to yield more precise estimate of the log-odds ratio than the individual testing.

Using information from multiple surveys to produce better pooled estimators is an active research area in recent days. Multiple surveys from same target population is common in many socioeconomic and health surveys. Often all the surveys do not contain same set of variables. Here we consider a standard situation where responses are known for all the samples from multiple surveys but the same set of covariates (or auxiliary variables) is not observed in all the samples. Moreover, in our case we consider a finite population set up where samples are drawn from multiple finite populations using same or different probability sampling designs. Here the problem is to estimate the parameters (or superpopulation parameters) of underlying regression model. We propose quadratic inference function estimator by combining information related to the underlying model from different samples through design weighted estimating functions (or score functions). We did a small simulation study for comprehensive understanding of our approach.

Valuing Debt and Equity in Interbank Networks Valuation adjustments to account for, for example, counterparty risk, have become an important part of derivative valuation by any bank since the 2007–2009 financial crisis. As evidenced by that crisis, considering the risk of a single firm alone can cause gross misspecification of firm health. In “Pricing of Debt and Equity in a Financial Network with Comonotonic Endowments,” Banerjee and Feinstein construct an analytical formulation for a valuation adjustment that takes the entire network of counterparty obligations into account when all institutions have comonotonic endowments. From the perspective of stress testing, such a setting corresponds to a systematic shock to all firms. This comonotonic setting is then shown to provide computationally tractable upper and lower bounds to the general network valuation problem. The authors demonstrate that the comonotonic endowment setting arises endogenously in a system of equity maximizing firms.

The characteristics and performance of a new detector system based on CsI(TI) scintillators, and its front-end electronics are presented. The detector system has been developed for the detection of light charged particles to investigate fusion–fission dynamics, and will also serve as ancillary detector for an array of neutron detectors. CsI scintillators are read by photo-diodes. The main feature of the array is its compact and simple high density front-end electronics which includes custom developed low noise charge sensitive preamplifiers (with very low power consumption for operation inside vacuum), NIM differential drivers, and commercially available Mesytec amplifiers with two different time constants for particle identification using a ballistic deficit technique.

The target development laboratory at Inter-University Accelerator Centre (IUAC) is one of the main facilities for the fabrication of nuclear physics targets in India. Vacuum evaporation and cold rolling technique are mainly used for the production of isotopically pure targets at IUAC. Targets of Gd, Pt, W, Mo, Ta, Ni, Ag and Sn have been developed in the form of self-supporting targets and with thin carbon backing. Recent progress in target development laboratory at IUAC will be discussed in the report.

Fission fragment angular distributions for three reactions, $^{19}\mathrm{F}+^{182}\mathrm{W},^{19}\mathrm{F}+^{187}\mathrm{Re}$, and $^{19}\mathrm{F}+^{193}\mathrm{Ir}$, are measured in the laboratory energy range of 82--120 MeV. Extracted fission cross sections of the present systems as well as those of three others from literature $(^{19}\mathrm{F}+^{192}\mathrm{Os},^{19}\mathrm{F}+^{194}\mathrm{Pt}$, and $^{19}\mathrm{F}+^{197}\mathrm{Au})$ are compared with the predictions of a statistical model which takes into account the effects of shell, orientation degree of freedom, and collective enhancement in level density (CELD). In all the cases, the standard statistical model predictions overestimate the measured fission cross section, indicating the presence of some amount of dynamical effects in the exit channel. A dissipation strength of $2\ifmmode\times\else\texttimes\fi{}{10}^{21}\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ is found to be sufficient to reproduce the data of all the reactions. No scaling of fission barrier height to fit the data is required.

Background: It is a well established fact that nuclear deformation and vibration influence fusion dynamics around the Coulomb barrier. This effect was observed for several systems with the inclusion of inelastic excitations in coupled-channels calculations. Sub-barrier fusion cross sections were also observed to be affected by neutron transfer in systems carrying positive $Q$ value for transfer channels. However, recent experimental analysis with a few systems showed that inelastic excitations are enough to explain the sub-barrier fusion behavior, and no effect was noticed due to positive $Q$-value transfer channels.Purpose: The motivation behind present investigation is to explore the effects of colliding nuclei structure and the transfer channel on enhancement of sub-barrier fusion cross sections.Method: An experiment was performed with Heavy Ion Reaction Analyzer (HIRA) at New Delhi to measure the fusion cross sections for $^{28}\mathrm{Si}+^{92,96}\mathrm{Zr}$ systems. These cross sections were later compared with quantum mechanical coupled-channels calculations. In order to explore the effects of nuclear deformation on fusion cross sections, the present data were compared with those of other researchers on fusion who have used various projectiles of different structural properties on a $^{96}\mathrm{Zr}$ target.Results: Experimental fusion cross sections have been extracted around the Coulomb barrier. In the coupled-channels framework, inclusion of inelastic excitations of both projectile $(^{28}\mathrm{Si})$ and targets $(^{92,96}\mathrm{Zr})$ could reproduce the experimental cross sections around the Coulomb barrier, but they deviated substantially in the sub-barrier region. This indicates that positive $Q$-value neutron transfer channels may need to be included in the calculations to reproduce the experimental cross sections at sub-barrier energies.Conclusions: The nuclear structure of interacting nuclei has a strong influence on sub-barrier fusion enhancement. The effect of multineutron transfer channels was observed to be significant for fusion, especially for those systems where interacting nuclei are less deformed or spherical.

We studied the competition between fusion and quasifission by populating the compound nucleus (CN) $^{210}$Rn through different entrance channels - $^{16}$O+$^{194}$Pt and $^{30}$Si+$^{180}$Hf, at energies around the Coulomb barrier. The larger widths of the fission fragment mass distribution in the $^{30}$Si+$^{180}$Hf reaction which could not be explained by using transition state models, indicated the onset of quasifission in this reaction. Further, the evaporation residues (ERs) produced in these reactions were measured using the gas-filled recoil mass separator HYRA at IUAC. The measurements showed reduced ER cross sections for the $^{30}$Si+$^{180}$Hf reaction when compared with that of $^{16}$O+$^{194}$Pt at similar excitation energies, confirming the presence of quasifission in the $^{30}$Si+$^{180}$Hf reaction. The experimental results are analysed using the dinuclear system (DNS) and statistical models to understand the possible influence of potential energy surfaces (PES) and different entrance channel conditions in heavy ion fusion reactions.

Background: Formation of the compound nucleus (CN) is highly suppressed by quasifission in heavy-ion collisions involving massive nuclei. Though considerable progress has been made in the understanding of fusion-fission and quasifission, the exact dependence of fusion probability on various entrance channel variables is not completely clear, which is very important for the synthesis of new heavy and superheavy elements.Purpose: To study the interplay between fusion and quasifission in reactions forming CN in the boundary region where the fusion probability starts to deviate from unity.Methods: Fusion evaporation residue cross sections were measured for the $^{28,30}\mathrm{Si}+^{180}\mathrm{Hf}$ reactions using the Hybrid Recoil Mass Analyser at IUAC, New Delhi. Experimental data were compared with data from other reactions forming the same CN or isotopes of the CN. Theoretical calculations were performed using the dinuclear system and statistical models.Results: Reduced evaporation residue cross sections were observed for the reactions studied compared with the asymmetric reaction forming the same CN, indicating fusion suppression in more symmetric systems. The observations are consistent with fission fragment measurements performed in the same or similar systems. Larger ER cross sections are observed with increase in mass in the isotopic chain of the CN.Conclusions: Fusion probability varies significantly with the entrance channels in reactions forming the same CN. While complete fusion occurs for the $^{16}\mathrm{O}+^{194}\mathrm{Pt}$ reaction, the fusion probability drops to approximately $60--70%$ for the $^{30}\mathrm{Si}+^{180}\mathrm{Hf}$ and less than $20%$ for the $^{50}\mathrm{Ti}+^{160}\mathrm{Gd}$ reactions, respectively, forming the same CN at similar excitation energies.

Abtsrcat Estimating finite population distribution function (hereafter FPDF) is an important problem to the survey samplers since it summarizes almost all the relevant information of interest about the finite population. Chambers and Dunstan (1986) (henceforth CD) in their seminal paper propose a predictive estimator of FPDF incorporating the unit level auxiliary information available for the entire population. CD estimator assumes a linear regression model in the superpopulation. However, even for moderate deviation from linearity assumption, significant performance deterioration of CD estimator is observed. Here we propose a predictive estimator of FPDF based on a semiparametric regression model. For this we use recently developed penalized splines (P-splines) regression. The proposed estimator performs better than CD estimator if the linearity assumption fails. We find its asymptotic bias and variance. Finally, we compare the performance of the proposed estimator with other alternative estimators through simulation studies and illustrate its use with a real data set.

We use compactifications of C*-algebras to introduce noncommutative coarse geometry. We transfer a noncommutative coarse structure on a C*-algebra with an action of a locally compact Abelian group by translations to Rieffel deformations and prove that the resulting noncommutative coarse spaces are coarsely equivalent. We construct a noncommutative coarse structure from a cocompact continuously square-integrable action of a group and show that this is coarsely equivalent to the standard coarse structure on the group in question. We define noncommutative coarse maps through certain completely positive maps that induce *-homomorphisms on the boundaries of the compactifications. We lift *-homomorphisms between separable, nuclear boundaries to noncommutative coarse maps and prove an analogous lifting theorem for maps between the metrisable boundaries of ordinary locally compact spaces.