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In this paper we introduce a quotient structure on topological ternary semigroup by defining a congruence suitably. We have found conditions under which this quotient structure becomes a topological ternary semigroup. We have also obtained conditions that make this quotient a topological ternary group, whenever the base structure is a topological ternary group.

In this short review, we provide an overview of recent progress in deploying advanced characterization techniques to understand the effects of local inhomogeneities in moir\'e heterostructures over multiple length scales. Particular emphasis is placed on correlating the impact of twist angle misalignment, nano-scale disorder, and atomic relaxation on the moir\'e potential and its collective excitations, particularly moir\'e excitons. Finally, we discuss future technological applications leveraging based on moi\'e excitons., Comment: Submitted to Small in response to an invitation for the special issue that celebrates the scientific accomplishments of Prof. P M Ajayan

Laser-driven neutron sources are routinely produced by the interaction of laser-accelerated protons with a converter. They present complementary characteristics to those of conventional accelerator-based neutron sources (e.g. short pulse durations, enabling novel applications like radiography). We present here results from an experiment aimed at performing a global characterization of the neutrons produced using the Titan laser at the Jupiter Laser Facility (Livermore, USA), where protons were accelerated from 23 $\mu m$ thick plastic targets and directed onto a LiF converter to produce neutrons. For this purpose, several diagnostics were used to measure these neutron emissions, such as CR-39, activation foils, Time-of-Flight detectors and direct measurement of $^{7}$Be residual activity in the LiF converters. The use of these different, independently operating diagnostics enables comparison of the various measurements performed to provide a robust characterization. These measurements led to a neutron yield of $2.10^{9}$ neutrons per shot with a modest angular dependence, close to that simulated.

The Quantum Materials group at Indian Institute of Technology Patna is working on a range of topics relating to nanoelectronics, spintronics, clean energy and memory design etc. The PI has past experiences of working extensively with superconducting systems like cuprates [1, 2], ruthanate [3], pnictide [4, 5], thin film heterostructures [6, 7] etc and magnetic recording media [8, 9] etc. In this report, we have summarised the ongoing works in our group. We explored a range of functional materials like two-dimensional materials, oxides. topological insulators, organic materials etc. using a combination of experimnetal and computational tools. Some of the useful highlights are as follows: (a) tuning and control of the magnetic and electronic state of 2D magentic materials with rapid enhancement in the Curie temperature, (b) Design and detection of single electron transistor based nanosensors for the detection of biological species with single molecular resolution, (c) Observation of non-volatile memory behaviour in the hybrid structures made of perovskite materials and 2D hybrids. The results offer useful insight in the design of nanoelectronic architecrures for diverse applications.

Here a real life optimal control problem under fuzzy time period using variational principle is formulated and Solved. The unit production cost is a function of production rate and also dependent on raw material cost, development cost due to durability and wear-tear cost. The holding cost is assumed to be non-linear, dependent on time. The profit function which consists of revenue, production cost and holding cost is formulated as a Fuzzy-Final Time and Fixed State System optimal control problem with fuzzy time period. Here production rate is unknown and considered as a control variable and stock level is taken as a state variable. It is formulated to optimize the production rate so that total profit is maximum. The non-linear optimization technique-Generalised Reduced Gradient Method (LINGO 11.0) is used. The optimum results are illustrated both numerically and graphically., Comment: arXiv admin note: substantial text overlap with arXiv:2006.01740

We demonstrate a scheme for enhanced proton acceleration from near-critical-density targets by splitting a laser pulse into a linearly and a circularly polarized laser pulse. The combination of two laser pulses generates a shock wave as well as hole boring effect at the front surface of the target. Protons at the front get combined acceleration from the two acceleration mechanisms. 2D-PIC simulation shows nearly two-fold enhancement in proton energy from this mechanism for a near-critical density target. The acceleration mechanism is also studied with different target density and thickness to ascertain the target parameters over which the acceleration process shows dominant behaviour.

We report a measurement of the $C\!P$-violating parameters $A$ and $S$ in $B^{0}\to K_{S}^{0} \pi^{0}$ decays at Belle II using a sample of $387\times 10^{6}$ $B\bar{B}$ events recorded in $e^{+}e^{-}$ collisions at a center-of-mass energy corresponding to the $\Upsilon(4S)$ resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain $A = 0.04^{+0.15}_{-0.14}\pm 0.05$ and $S = 0.75^{+0.20}_{-0.23}\pm 0.04$, where the first uncertainties are statistical and the second are systematic.

The response of the BAS-TR image plate (IP) was absolutely calibrated using CR-39 track detector for high linear energy transfer (LET) Au ions up to $\sim$1.6 GeV (8.2 MeV/nucleon), accelerated by high-power lasers. The calibration was carried out by employing a high-resolution Thomson parabola spectrometer, which allowed resolving Au ions with closely spaced ionization states up to 58$^+$. A response function was obtained by fitting the photo-stimulated luminescence (PSL) per Au ion for different ion energies, which is broadly in agreement with that expected from ion stopping in the active layer of the IP. This calibration would allow quantifying the ion energy spectra for high energy Au ions, which is important for further investigation of the laser-based acceleration of heavy ion beams., Comment: 6 pages; 4 figures. Submitted to journal for review

High power lasers have proven being capable to produce high energy gamma rays, charged particles and neutrons to induce all kinds of nuclear reactions. At ELI, the studies with high power lasers will enter for the first time into new domains of power and intensities.

We report the signatures of dynamic spin fluctuations in the layered honeycomb Li$_3$Cu$_2$SbO$_6$ compound, with a 3$d$ S = 1/2 $d^9$ Cu$^{2+}$ configuration, through muon spin rotation and relaxation ($\mu$SR) and neutron scattering studies. Our zero-field (ZF) and longitudinal-field (LF)-$\mu$SR results demonstrate the slowing down of the Cu$^{2+}$ spin fluctuations below 4.0 K. The saturation of the ZF relaxation rate at low temperature, together with its weak dependence on the longitudinal field between 0 and 3.2 kG, indicates the presence of dynamic spin fluctuations persisting even at 80 mK without static order. Neutron scattering study reveals the gaped magnetic excitations with three modes at 7.7, 13.5 and 33 meV. Our DFT calculations reveal that the next nearest neighbors (NNN) AFM exchange ($J_{AFM}$ = 31 meV) is stronger than the NN FM exchange ($J_{FM}$ = -21 meV) indicating the importance of the orbital degrees of freedom. Our results suggest that the physics of Li$_3$Cu$_2$SbO$_6$ can be explained by an alternating AFM chain rather than the honeycomb lattice., Comment: 5 pages, 4 figures

Magnetized plasma interactions are ubiquitous in astrophysical and laboratory plasmas. Various physical effects have been shown to be important within colliding plasma flows influenced by opposing magnetic fields, however, experimental verification of the mechanisms within the interaction region has remained elusive. Here we discuss a laser-plasma experiment whereby experimental results verify that Biermann battery generated magnetic fields are advected by Nernst flows and anisotropic pressure effects dominate these flows in a reconnection region. These fields are mapped using time-resolved proton probing in multiple directions. Various experimental, modelling and analytical techniques demonstrate the importance of anisotropic pressure in semi-collisional, high-$\beta$ plasmas, causing a reduction in the magnitude of the reconnecting fields when compared to resistive processes. Anisotropic pressure dynamics are crucial in collisionless plasmas, but are often neglected in collisional plasmas. We show pressure anisotropy to be essential in maintaining the interaction layer, redistributing magnetic fields even for semi-collisional, high energy density physics (HEDP) regimes

Breakability rate of fragile item depends on the accumulated stress of heaped stock level. So breakablility rate can be considered as dependent parameter of stock variable. The unit production cost is a function of production rate and also dependent on raw material cost, development cost and wear-tear cost. The holding cost is assumed to be non-linear, dependent on time. Here optimal control problem for a fragile item under finite time horizon is considered. The profit function which consists of revenue, production and holding costs is formulated as a Fixed-Final Time and Fixed State System(cf. Naidu (2000)) optimal control problem with finite time horizon. Here production rate is unknown and considered as a control variable and stock level is taken as a state variable. It is formulated to optimize the production rate so that total profit is maximum. As particular cases, models are evaluated with and without breakability. The models are solved by using conventional Variational Principle along with the non-linear optimization technique-Generalised Reduced Gradient Method (LINGO 12.0). The optimum results are illustrated both numerically and graphically. Some sensitivity analysis on breakability coefficient are presented., Comment: 14 pages 5 figures

The Time-of-Flight (ToF) technique coupled with semiconductor-like detectors, as silicon carbide and diamond, is one of the most promising diagnostic methods for high-energy, high repetition rate, laser-accelerated ions allowing a full on-line beam spectral characterization. A new analysis method for reconstructing the energy spectrum of high-energy laser-driven ion beams from TOF signals is hereby presented and discussed. The proposed method takes into account the detector's working principle, through the accurate calculation of the energy loss in the detector active layer, using Monte Carlo simulations. The analysis method was validated against well-established diagnostics, such as the Thomson Parabola Spectrometer, during an experimental campaign carried out at the Rutherford Appleton Laboratory (RAL, UK) with the high-energy laser-driven protons accelerated by the VULCAN Petawatt laser.

We establish the primary decomposition and uniqueness of primary decomposition for k-ideals in commutative Noetherian semirings., Comment: 6 pages

We derive an effective Hamiltonian for the two-dimensional Hubbard-Holstein model in the regimes of strong electron-electron and strong electron-phonon interactions by using a nonperturbative approach. In the parameter region where the system manifests the existence of a correlated singlet phase, the effective Hamiltonian transforms to a $t_1-V_1-V_2-V_3$ Hamiltonian for hard-core-bosons on a checkerboard lattice. We employ quantum Monte Carlo simulations, involving stochastic-series-expansion technique, to obtain the ground state phase diagram. At filling $1/8$, as the strength of off-site repulsion increases, the system undergoes a first-order transition from a superfluid to a diagonal striped solid with ordering wavevector $\vec{Q}=(\pi/4,3\pi/4)$ or $(\pi/4,5\pi/4)$. Unlike the one-dimensional situation, our results in the two-dimensional case reveal a supersolid phase (corresponding to the diagonal striped solid) around filling $1/8$ and at large off-site repulsions. Furthermore, for small off-site repulsions, we witness a valence bond solid at one-fourth filling and tiny phase-separated regions at slightly higher fillings., Comment: Accepted in EPJ B

We study M1-transitions involving mesons: $B_c(1s)$, $B_c^*(1s)$, $B_c(2s)$, $B_c^*(2s)$, $B_c(3s)$ and $B_c^*(3s)$ in the relativistic independent quark (RIQ) model based on a flavor independent average potential in the scalar-vector harmonic form. The transition form factor for $B_c^*\to B_c\gamma$ is found to have analytical continuation from spacelike to physical timelike region. Our predicted coupling constant $g_{B_c^* B_c}$ = 0.34 Ge$V^{-1}$ and decay width $\Gamma(B_c^*\to B_c\gamma)$ = 23 eV agree with other model predictions. In view of possible observation of $B_c$ and $B_c^*$ s-wave states at LHC and Z-factory and potential use of theoretical estimate on M1-transitions, we investigate the allowed as well as hindered transitions of orbitally excited $B_c$-meson states and predict their decay widths in overall agreement with other model predictions. We consider the typical case of $B_c^*(1s)\to B_c(1s)\gamma$, where our predicted decay width which is found quite sensitive to the mass difference between $B_c^*$ and $B_c$ mesons may help in determining the mass of $B_c^*$ experimentally.

Millions of surveillance cameras operate at 24x7 generating huge amount of visual data for processing. However, retrieval of important activities from such a large data can be time consuming. Thus, researchers are working on finding solutions to present hours of visual data in a compressed, but meaningful way. Video synopsis is one of the ways to represent activities using relatively shorter duration clips. So far, two main approaches have been used by researchers to address this problem, namely synopsis by tracking moving objects and synopsis by clustering moving objects. Synopses outputs, mainly depend on tracking, segmenting, and shifting of moving objects temporally as well as spatially. In many situations, tracking fails, thus produces multiple trajectories of the same object. Due to this, the object may appear and disappear multiple times within the same synopsis output, which is misleading. This also leads to discontinuity and often can be confusing to the viewer of the synopsis. In this paper, we present a new approach for generating compressed video synopsis by grouping tracklets of moving objects. Grouping helps to generate a synopsis where chronologically related objects appear together with meaningful spatio-temporal relation. Our proposed method produces continuous, but a less confusing synopses when tested on publicly available dataset videos as well as in-house dataset videos.

We report on the experimental observation of beam-like neutron emission with peak flux of the order of 10^9 n/sr, from light nuclei reactions in a pitcher-catcher scenario, by employing MeV ions driven by high power laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHM divergence angle of 70 degrees, with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitcher-catcher materials indicates the dominant reactions being d(p, n+p)^1H and d(d,n)^3He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons' spatial and spectral profiles are most likely related to the directionality and high energy of the projectile ions., Comment: 6 pages, 7 figures

Calibration of three scintillators (EJ232Q, BC422Q and EJ410) in a time-of-flight (TOF) arrangement using a laser drive-neutron source is presented. The three plastic scintillator detectors were calibrated with gamma insensitive bubble detector spectrometers, which were absolutely calibrated over a wide range of neutron energies ranging from sub MeV to 20 MeV. A typical set of data obtained simultaneously by the detectors are shown, measuring the neutron spectrum emitted from a petawatt laser irradiated thin foil.

The paper is concerned with distributed learning and optimization in large-scale settings. The well-known Fictitious Play (FP) algorithm has been shown to achieve Nash equilibrium learning in certain classes of multi-agent games. However, FP can be computationally difficult to implement when the number of players is large. Sampled FP is a variant of FP that mitigates the computational difficulties arising in FP by using a Monte-Carlo (i.e., sampling-based) approach. The Sampled FP algorithm has been studied both as a tool for distributed learning and as an optimization heuristic for large-scale problems. Despite its computational advantages, a shortcoming of Sampled FP is that the number of samples that must be drawn in each round of the algorithm grows without bound (on the order of $\sqrt{t}$, where $t$ is the round of the repeated play). In this paper we propose Computationally Efficient Sampled FP (CESFP)---a variant of Sampled FP in which only one sample need be drawn each round of the algorithm (a substantial reduction from $O(\sqrt{t})$ samples per round, as required in Sampled FP). CESFP operates using a stochastic-approximation type rule to estimate the expected utility from round to round. It is proven that the CESFP algorithm achieves Nash equilibrium learning in the same sense as classical FP and Sampled FP. Simulation results suggest that the convergence rate of CESFP (in terms of repeated-play iterations) is similar to that of Sampled FP., Comment: Submitted for publication. Initial Submission: Jun. 2015. 15 pages

We report on the successful demonstration of selective acceleration of deuterium ions by target-normal sheath acceleration (TNSA) with a high-energy petawatt laser. TNSA typically produces a multi-species ion beam that originates from the intrinsic hydrocarbon and water vapor contaminants on the target surface. Using the method first developed by Morrison, et al.,$^{1}$ an ion beam with $>$99$\%$ deuterium ions and peak energy 14 MeV/nucleon is produced with a 200 J, 700 fs, $>10^{20} W/cm^{2}$ laser pulse by cryogenically freezing heavy water (D$_{2}$O) vapor onto the rear surface of the target prior to the shot. Within the range of our detectors (0-8.5$^{\circ}$), we find laser-to-deuterium-ion energy conversion efficiency of 4.3$\%$ above 0.7 MeV/nucleon while a conservative estimate of the total beam gives a conversion efficiency of 9.4$\%$., Comment: 5 pages, 5 figures

Direct investigation of ion-induced dynamics in matter on picosecond (ps, 10-12 s) timescales has been precluded to date by the relatively long nanosecond (ns, 10-9 s) scale ion pulses typically provided by radiofrequency accelerators1. By contrast, laser-driven ion accelerators provide bursts of ps duration2, but have yet to be applied to the study of ultrafast ion-induced transients in matter. We report on the evolution of an electron-hole plasma excited in borosilicate glass by such bursts. This is observed as an onset of opacity to synchronised optical probe radiation and is characterised by the 3.0 +/- 0.8 ps ion pump rise-time . The observed decay-time of 35 +/- 3 ps i.e. is in excellent agreement with modelling and reveals the rapidly evolving electron temperature (>10 3 K) and carrier number density (>10 17cm-3). This result demonstrates that ps laser accelerated ion bursts are directly applicable to investigating the ultrafast response of matter to ion interactions and, in particular, to ultrafast pulsed ion radiolysis of water3-5, the radiolytic decompositions of which underpin biological cell damage and hadrontherapy for cancer treatment6., Comment: 11 pages

A novel method for characterising the full spectrum of deuteron ions emitted by laser driven multi-species ion sources is discussed. The procedure is based on using differential filtering over the detector of a Thompson parabola ion spectrometer, which enables discrimination of deuterium ions from heavier ion species with the same charge-to-mass ratio (such as C6+, O8+, etc.). Commonly used Fuji Image plates were used as detectors in the spectrometer, whose absolute response to deuterium ions over a wide range of energies was calibrated by using slotted CR-39 nuclear track detectors. A typical deuterium ion spectrum diagnosed in a recent experimental campaign is presented., Comment: 7 pages, 7 figures

Spectrally-peaked proton beams ($E_{p}\approx 8$ MeV, $\Delta E\approx 4$ MeV) have been observed from the interaction of an intense laser ($> 10^{19 }$ Wcm$^{-2}$) with ultrathin CH foils, as measured by spectrally-resolved full beam profiles. These beams are reproducibly generated for foil thicknesses (5-100 nm), and exhibit narrowing divergence with decreasing target thickness down to $\approx 8^\circ$ for 5 nm. Simulations demonstrate that the narrow energy spread feature is a result of buffered acceleration of protons. Due to their higher charge-to-mass ratio, the protons outrun a carbon plasma driven in the relativistic transparency regime.

We report on the laser-driven generation of purely neutral, relativistic electron-positron pair plasmas. The overall charge neutrality, high average Lorentz factor ($\gamma_{e/p} \approx 15$), small divergence ($\theta_{e/p} \approx 10 - 20$ mrad), and high density ($n_{e/p}\simeq 10^{15}$cm$^{-3}$) of these plasmas open the pathway for the experimental study of the dynamics of this exotic state of matter, in regimes that are of relevance to electron-positron astrophysical plasmas., Comment: The manuscript is withdrawn from ArXiv because of conflicting interests

The dynamics of magnetic fields with amplitude of several tens of Megagauss, generated at both sides of a solid target irradiated with a high intensity (? 1019W/cm2) picosecond laser pulse, has been spatially and temporally resolved using a proton imaging technique. The amplitude of the magnetic fields is sufficiently large to have a constraining effect on the radial expansion of the plasma sheath at the target surfaces. These results, supported by numerical simulations and simple analytical modeling, may have implications for ion acceleration driven by the plasma sheath at the rear side of the target as well as for the laboratory study of self-collimated high-energy plasma jets., Comment: Accepted for publication in Physical Review Letters

The acceleration of ions from ultra-thin foils has been investigated using 250 TW, sub-ps laser pulses, focused on target at intensities up to $3\times10^{20} \Wcm2$. The ion spectra show the appearance of narrow band features for proton and Carbon peaked at higher energy (in the 5-10 MeV/nucleon range) and with significantly higher flux than previously reported. The spectral features, and their scaling with laser and target parameters, provide evidence of a multispecies scenario of Radiation Pressure Acceleration in the Light Sail mode, as confirmed by analytical estimates and 2D Particle In Cell simulations. The scaling indicates that monoenergetic peaks with more than 100 MeV/nucleon energies are obtainable with moderate improvements of the target and laser characteristics, which are within reach of ongoing technical developments.

A novel regime is proposed where, employing linearly polarized laser pulses at intensities $10^{21}\textrm{Wcm}^{-2}$ as two order of magnitude lower than earlier predicted [T. Esirkepov et al., Phys. Rev. Lett. 92, 175003 (2004)], ions are dominantly accelerated from ultrathin foils by the radiation pressure, and have monoenergetic spectra. In the regime, ions accelerated from the hole-boring process quickly catch up with the ions accelerated by target normal sheath acceleration (TNSA), and they then join in a single bunch, undergoing a hybrid Light-Sail/TNSA acceleration. Under an appropriate coupling condition between foil thickness, laser intensity and pulse duration, laser radiation pressure can be dominant in this hybrid acceleration. Two-dimensional PIC simulations show that $1.26\textrm{GeV}$ quasimonoenergetic $\textrm{C}^{6+}$ beams are obtained by linearly polarized laser pulses at intensities of $10^{21}\textrm{Wcm}^{-2}$., Comment: 6 pages, 4 figures

The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation. A halo that surrounds the main region of emission is also polarized, and is attributed to the effect of electron recirculation. The variation of the amplitude of the transition radiation with respect to observation angle provides evidence for the presence of {$\mu$m-size} filaments., Comment: 12 pages, 7 figures

The paper studies the problem of filtering a discrete-time linear system observed by a network of sensors. The sensors share a common communication medium to the estimator and transmission is bit and power budgeted. Under the assumption of conditional Gaussianity of the signal process at the estimator (which may be ensured by observation packet acknowledgements), the conditional prediction error covariance of the optimum mean-squared error filter is shown to evolve according to a random dynamical system (RDS) on the space of non-negative definite matrices. Our RDS formalism does not depend on the particular medium access protocol (randomized) and, under a minimal distributed observability assumption, we show that the sequence of random conditional prediction error covariance matrices converges in distribution to a unique invariant distribution (independent of the initial filter state), i.e., the conditional error process is shown to be ergodic. Under broad assumptions on the medium access protocol, we show that the conditional error covariance sequence satisfies a Markov-Feller property, leading to an explicit characterization of the support of its invariant measure. The methodology adopted in this work is sufficiently general to envision this application to sample path analysis of more general hybrid or switched systems, where existing analysis is mostly moment-based., Comment: 8 pages. Submitted to the American Control Conference, ACC 2010

We present electronic transport characteristics of ternary alloy Cd1-xZnxS nanowire networks in the dark and under white light illumination. Compared to the negligible dark current, we observed a photocurrent enhancement up to 4 orders of magnitude at intensity of 460 mW/cm2. The time constant of the dynamic photoresponse is ~5 sec. The current-voltage characteristics at different intensities show Ohmic behavior at low bias and space charge limited conduction (SCLC) at higher bias voltages. The SCLC behavior and slow time response indicate that the charge transport is dominated by tunneling at the percolating inter-nanowire junctions.

The emission characteristics of intense laser driven protons are controlled using ultra-strong (of the order of 10^9 V/m) electrostatic fields varying on a few ps timescale. The field structures are achieved by exploiting the high potential of the target (reaching multi-MV during the laser interaction). Suitably shaped targets result in a reduction in the proton beam divergence, and hence an increase in proton flux while preserving the high beam quality. The peak focusing power and its temporal variation are shown to depend on the target characteristics, allowing for the collimation of the inherently highly divergent beam and the design of achromatic electrostatic lenses., Comment: 9 Pages, 5 figures

A new regime is described for Radiation Pressure Acceleration of a thin foil by an intense laser beam of above 10^20 W/cm^2. Highly monoenergetic proton beams extending to GeV energies can be produced with very high efficiency using circularly polarized light. The proton beams have a very small divergence angle (less than 4 degrees). This new method allows the construction of ultra-compact proton and ion accelerators with ultra-short particle bursts.

In recent experiments of laser pulse interaction at relativistic intensities with a low density plasma, the proton radiography technique showed evidence of long--lived field structures generated after the self-channeling of the laser pulse. We present 2D particle-in-cell simulations of this interaction regime, where the dynamics of similar structures has been resolved with high temporal and spatial resolution. An axially symmetrical field pattern, resembling both soliton-like and vortex structures, has been observed. A study of the physics of such structures and a comparison with experimental data is in progress., Comment: To appear in the Proceedings of the International Workshop "Collective phenomena in macroscopic systems", Villa Olmo, Como, Italy, December 4-6, 2006; 9 pages, 8 figures submitted in GIF format

The dynamics of transient electric fields generated by the interaction of high intensity laser pulses with underdense plasmas has been studied experimentally with the proton projection imaging technique. The formation of a charged channel, the propagation of its front edge and the late electric field evolution have been characterised with high temporal and spatial resolution. Particle-in-cell simulations and an electrostatic, ponderomotive model reproduce the experimental features and trace them back to the ponderomotive expulsion of electrons and the subsequent ion acceleration., Comment: 5 figures, accepted for publication in New Journal of Physics

The dynamics of electric field generation and radial acceleration of ions by a laser pulse of relativistic intensity propagating in an underdense plasma has been investigated using an one-dimensional electrostatic, ponderomotive model developed to interpret experimental measurements of electric fields [S. Kar et al, New J. Phys. *9*, 402 (2007)]. Ions are spatially focused at the edge of the charge-displacement channel, leading to hydrodynamical breaking, which in turns causes the heating of electrons and an "echo" effect in the electric field. The onset of complete electron depletion in the central region of the channel leads to a smooth transition to a "Coulomb explosion" regime and a saturation of ion acceleration., Comment: 9 pages, 7 figures, final revised version, to appear on Plasma Phys. Contr. Fus., special issue on "Laser and Plasma Accelerators", scheduled for February, 2009

The S-duality invariance of the equations of motion of four dimensional string effective action with cosmological constant, $\Lambda $, is studied. It is demonstrated that the S-duality symmetry of the field equations are broken for nonzero $\Lambda$. The ``naturalness'' hypothesis is invoked to argue that $\Lambda $ should remain small since exact S-duality symmetry will force the cosmological constant to vanish in the string effective action., Comment: 13 pages, RevTex , slightly extended version with more discussions added ( To appear in Phys. Lett. B )

It is shown explicitly, that a number of solutions for the background field equations of the string effective action in space-time dimension D can be generated from any known lower dimensional solution, when background fields have only time dependence. An application of the result to the two dimensional charged black hole is presented. The case of background with more general coordinate dependence is also discussed., Comment: 12 pages

The article presents a report that discusses the way peace and normalcy be restored in the Northeastern regions of India. The topics discussed include controlling insurgency by blocking trafficking routes for supply of weapons, need of physically intervening the illegal manufacturing of drugs of abuse like heroin and methamphetamine tablets by militant outfits, and steps for curbing crimes and violations of law. Other topics include need for ensuring justice for the victims of crime.