Showing papers in "Pramana in 2010"

Measurements of plasma temperature and electron density in laser-induced copper plasma by time-resolved spectroscopy of neutral atom and ion emissions

Abstract: Plasma produced by a 355 nm pulsed Nd:YAG laser with a pulse duration of 6 ns focussed onto a copper solid sample in air at atmospheric pressure is studied spectroscopically. The temperature and electron density characterizing the plasma are measured by time-resolved spectroscopy of neutral atom and ion line emissions in the time window of 300-2000 ns. An echelle spectrograph coupled with a gated intensified charge coupled detector is used to record the plasma emissions. The temperature is obtained using the Boltzmann plot method and the electron density is determined using the Saha-Boltzmann equation method. Both parameters are studied as a function of delay time with respect to the onset of the laser pulse. The results are discussed. The time window where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the laser-induced breakdown spectroscopy (LIBS) analysis of samples, is deduced from the temporal evolution of the intensity ratio of two Cu I lines. It is found to be 700-1000 ns.

Characterization of the Lovelock gravity by Bianchi derivative

Abstract: We prove the theorem: The second-order quasilinear differential operator as a second-rank divergence-free tensor in the equation of motion for gravitation could always be derived from the trace of the Bianchi derivative of the fourth-rank tensor, which is a homogeneous polynomial in curvatures. The existence of such a tensor for each term in the polynomial Lagrangian is a new characterization of the Lovelock gravity.

Investigation of bending loss in a single-mode optical fibre

Abstract: Loss of optical power in a single-mode optical fibre due to bending has been investigated for a wavelength of 1550 nm. In this experiment, the effects of bending radius (4–15 mm, with steps of 1 mm), and wrapping turns (up to 40 turns) on loss have been studied. Twisting the optical fibre and its influence on power loss also have been investigated.

Development of underwater laser cutting technique for steel and zircaloy for nuclear applications

Abstract: In nuclear field, underwater cutting and welding technique is required for post-irradiation examination, maintenance, decommissioning and to reduce storage space of irradiated materials like used zircaloy pressure tubes etc., of nuclear power plants. We have developed underwater cutting technique for 4.2 mm thick zircaloy pressure tubes and up to 6 mm thick steel using fibre-coupled 250 W average power pulsed Nd:YAG laser. This underwater cutting technique will be highly useful in various nuclear applications as well as in dismantling/repair of ship and pipe lines in water.

Picosecond optical nonlinearities in symmetrical and unsymmetrical phthalocyanines studied using the Z-scan technique

Abstract: We present our experimental results on the picosecond nonlinear optical (NLO) studies of symmetrical and unsymmetrical phthalocyanines, examined using the Z-scan technique. Both the open-aperture and closed-aperture Z-scan curves for three samples were recorded and the nonlinear coefficients were extracted from the theoretical fits. The nonlinear absorption/refraction contribution from the solvent was also identified. The observed open aperture behaviour for these molecules is understood in terms of the absorption coefficients of these molecules near 800 nm and the peak intensities used. It is established that these phthalocyanines exhibit large optical nonlinearities and, hence, are suitable for optical limiting applications.

Characteristics of the aluminum alloy plasma produced by a 1064 nm Nd:YAG laser with different irradiances

Abstract: The plasma generated by 1064 nm Nd:YAG laser irradiation of aluminum alloy in air at atmospheric pressure was studied spectroscopically. The electron density inferred by measuring the Stark-broadened line profile of Si(I) 288.16 nm decreases with increasing distance from the target surface. The electron temperature was determined using the Boltzmann plot method with nine strong neutral aluminum lines. Due to the thermal conduction towards the solid target and radiative cooling of the plasma as well as conversion of thermal energy into kinetic energy, the electron temperature decreases both at the plasma edge and close to the target surface. Electron density and electron temperature were also studied as functions of laser power density. At the same time, the validity of the assumption of local thermodynamic equilibrium and the effect of selfabsorption were discussed in light of the results obtained.

Chameleon field and the late time acceleration of the Universe

Abstract: In the present work, it is shown that a chameleon scalar field having a non-minimal coupling with dark matter can give rise to a smooth transition from a decelerated to an accelerated phase of expansion for the Universe. It is surprising to note that the coupling with the chameleon scalar field hardly affects the evolution of the dark matter sector, which still redshifts as a.

The role of cosmic rays in the Earth’s atmospheric processes

Abstract: In this paper, we have provided an overview of cosmic ray effects on terrestrial processes such as electrical properties, global electric circuit, lightning, cloud formation, cloud coverage, atmospheric temperature, space weather phenomena, climate, etc. It is suggested that cosmic rays control short-term and long-term variations in climate. There are many basic phenomena which need further study and require new and long-term data set. Some of these have been pointed out.

Comparative performance of some popular artificial neural network algorithms on benchmark and function approximation problems

Abstract: We report an inter-comparison of some popular algorithms within the artificial neural network domain (viz., local search algorithms, global search algorithms, higher-order algorithms and the hybrid algorithms) by applying them to the standard benchmarking problems like the IRIS data, XOR/N-bit parity and two-spiral problems. Apart from giving a brief description of these algorithms, the results obtained for the above benchmark problems are presented in the paper. The results suggest that while Levenberg-Marquardt algorithm yields the lowest RMS error for the N-bit parity and the two-spiral problems, higher-order neuron algorithm gives the best results for the IRIS data problem. The best results for the XOR problem are obtained with the neuro-fuzzy algorithm. The above algorithms were also applied for solving several regression problems such as cos(x) and a few special functions like the gamma function, the complimentary error function and the upper tail cumulative x2-distribution function. The results of these regression problems indicate that, among all the ANN algorithms used in the present study, Levenberg-Marquardt algorithm yields the best results. Keeping in view the highly nonlinear behaviour and the wide dynamic range of these functions, it is suggested that these functions can also be considered as standard benchmark problems for function approximation using artificial neural networks.

Relativistic star solutions in higher-dimensional pseudospheroidal space-time

Abstract: We obtain relativistic solutions of a class of compact stars in hydrostatic equilibrium in higher dimensions by assuming a pseudospheroidal geometry for the spacetime. The space-time geometry is assumed to be (D − 1) pseudospheroid immersed in a D-dimensional Euclidean space. The spheroidicity parameter (λ) plays an important role in determining the equation of state of the matter content and the maximum radius of such stars. It is found that the core density of compact objects is approximately proportional to the square of the space-time dimensions (D), i.e., core of the star is denser in higher dimensions than that in conventional four dimensions. The central density of a compact star is also found to depend on the parameter λ. One obtains a physically interesting solution satisfying the acoustic condition when λ lies in the range λ > (D + 1)/(D − 3) for the space-time dimensions ranging from D = 4 to 8 and (D + 1)/(D − 3) 1). We note that in the case of a superdense compact object the number of space-time dimensions cannot be taken infinitely large, which is a different result from the braneworld model.

Development of evanescent wave absorbance-based fibre-optic biosensor

Abstract: Development of chemical and biochemical sensors is the current need of the society. In this report, we present our investigation on the development of a label-free fibre-optic biosensor based on evanescent wave absorbance to detect the presence of analytes such as bacteria, virus and some clinically important proteins. A simple UV-LED (280 nm) and photodetector combination along with a fibre probe was used for developing cost-effective, user-friendly and field applicable device. To improve the sensitivity of the detection technique, the probe design was modified and the U-bent probe was fabricated by simple procedure. Further, to overcome the problems for using UV light source in the fibre, the localized surface plasmon resonance of noble metal nanoparticles at visible wavelength was exploited as a sensing medium for the biochemical reactions. Our systematic studies in this regard presented in this communication may bring the excitement for developing the waterborne pathogen detection device for house-hold as well as field applications.

Many-body Hamiltonian with screening parameter and ionization energy

Abstract: We prove the existence of a Hamiltonian with ionization energy as part of the eigenvalue, which can be used to study strongly correlated matter. This eigenvalue consists of total energy at zero temperature (E 0) and the ionization energy (ξ). We show that the existence of this total energy eigenvalue, E 0±ξ, does not violate the Coulombian atomic system. Since there is no equivalent known Hamilton operator that corresponds quantitatively to ξ, we employ the screened Coulomb potential operator (Yukawa-type), which is a function of this ionization energy to analytically calculate the screening parameter (σ) of a neutral helium atom in the ground state. In addition, we also show that the energy level splitting due to spin-orbit coupling is inversely proportional to ξ eigenvalue, which is also important in the field of spintronics.

Compactons versus solitons

Abstract: We investigate whether the recently proposed PT-symmetric extensions of generalized Korteweg-de Vries equations admit genuine soliton solutions besides compacton solitary waves. For models which admit stable compactons having a width which is independent of their amplitude and those which possess unstable compacton solutions the Painleve test fails, such that no soliton solutions can be found. The Painleve test is passed for models allowing for compacton solutions whose width is determined by their amplitude. Consequently, these models admit soliton solutions in addition to compactons and are integrable.

Hybrid recoil mass analyzer at IUAC — First results using gas-filled mode and future plans

Abstract: Hybrid recoil mass analyzer (HYRA) is a unique, dual-mode spectrometer designed to carry out nuclear reaction and structure studies in heavy and medium-mass nuclei using gas-filled and vacuum modes, respectively and has the potential to address newer domains in nuclear physics accessible using high energy, heavy-ion beams from superconducting LINAC accelerator (being commissioned) and ECR-based high current injector system (planned) at IUAC. The first stage of HYRA is operational and initial experiments have been carried out using gas-filled mode for the detection of heavy evaporation residues and heavy quasielastic recoils in the direction of primary beam. Excellent primary beam rejection and transmission efficiency (comparable with other gas-filled separators) have been achieved using a smaller focal plane detection system. There are plans to couple HYRA to other detector arrays such as Indian national gamma array (INGA) and 4π spin spectrometer for ER tagged spectroscopic/spin distribution studies and for focal plane decay measurements.

Mueller matrix polarimetry for the characterization of complex random medium like biological tissues

Abstract: The polarization parameters of light scattered from biological tissues contain wealth of morphological and functional information of potential biomedical importance. But, in optically thick turbid media such as tissues, numerous complexities due to multiple scattering and simultaneous occurrences of many polarization events present formidable challenges, in terms of both accurate measurement and unique interpretation of the individual polarimetry characteristics. We have developed and validated an expanded Mueller matrix decomposition approach to overcome this problem. The approach was validated theoretically with a polarization-sensitive Monte Carlo light propagation model and experimentally by recording Mueller matrices from tissue-like complex random medium. In this paper, we discuss our comprehensive turbid polarimetry platform consisting of the experimental polarimetry system, forward Monte Carlo modelling and inverse polar decomposition analysis. Initial biomedical applications of this novel general method for polarimetry analysis in random media are also presented.

The (G'/G)-expansion method for a discrete nonlinear Schrödinger equation

Abstract: An improved algorithm is devised for using the (G′/G)-expansion method to solve nonlinear differential-difference equations. With the aid of symbolic computation, we choose a discrete nonlinear Schrodinger equation to illustrate the validity and advantages of the improved algorithm. As a result, hyperbolic function solutions, trigonometric function solutions and rational solutions with parameters are obtained, from which some special solutions including the known solitary wave solution are derived by setting the parameters as appropriate values. It is shown that the improved algorithm is effective and can be used for many other nonlinear differential-difference equations in mathematical physics.

An irrational trial equation method and its applications

Abstract: An irrational trial equation method was proposed to solve nonlinear differential equations. By this method, a number of exact travelling wave solutions to the Burgers-KdV equation and the dissipative double sine-Gordon equation were obtained. A more general irrational trial equation method was discussed, and many exact solutions to the Fujimoto-Watanabe equation were given.

Nuclear symmetry energy: An experimental overview

Abstract: The nuclear symmetry energy is a fundamental quantity important for studying the structure of systems as diverse as the atomic nucleus and the neutron star. Considerable efforts are being made to experimentally extract the symmetry energy and its dependence on nuclear density and temperature. In this article, the experimental studies carried out up-to-date and their current status are reviewed.

Effect of curvature on a statistical model of quark-gluon-plasma fireball in the hadronic medium

Abstract: The free energy of a quark-gluon plasma fireball in the hadronic medium is calculated in the Ramanathan et al statistical model after incorporating the effect of curvature. The result with the inclusion of curvature is found to produce significant improvements in all the parameters we calculated with respect to the earlier results. The surface tension with this curvature effect is found to be 0.17Tc3, which is two times the earlier value of surface tension which is 0.078Tc3, and this new result is nearly close to the lattice value 0.24Tc3. As far as transition is concerned, a thermodynamic variable like entropy shows weakly first-order phase transition and it shows continuity in the behaviour of specific heat.

Femtosecond laser-fabricated microstructures in bulk poly(methylmethacrylate) and poly(dimethylsiloxane) at 800 nm towards lab-on-a-chip applications

Abstract: Laser direct writing technique is employed to fabricate microstructures, including gratings (buried and surface) and two-dimensional photonic crystal-like structures, in bulk poly(methylmethacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) using ∼100 femtosecond (fs) pulses. The variation of structure size with different writing conditions (focussing, speed and energy) was investigated in detail. Diffraction efficiencies of the gratings were calculated and the changes in diffraction efficiency (DE) as a function of period, energy and scanning speed were evaluated. Highest diffraction efficiencies of 34% and 10%, for the first order, were obtained in PMMA and PDMS respectively. Heat treatment of these gratings demonstrated small improvement in the diffraction efficiency. Several applications resulting from these structures are discussed. Fs modification in PMMA and PDMS demonstrated emission when excited at a wavelength of 514 nm. We attempted to prepare buried waveguides in PMMA with higher refractive index at the core. We have successfully fabricated branched and curved structures in PMMA and PDMS finding impending applications in microfluidics.

Some invariant solutions for non-conformal perfect fluid plates in 5-flat form in general relativity

Abstract: A set of six invariant solutions for non-conformal perfect fluid plates in 5-flat form is obtained using one-parametric Lie group of transformations. Out of the six solutions so obtained, three are in implicit form while the remaining three could be expressed explicitly. Each solution describes an accelerating fluid distribution and is new as far as authors are aware.

Effective atomic numbers of some H-, C-, N- and O-based composite materials derived from differential incoherent scattering cross-sections

Abstract: In this work, we have made an effort to determine whether the effective atomic numbers of H-, C-, N- and O-based composite materials would indeed remain a constant over the energy grid of 280–1200 keV wherein incoherent scattering dominates their interaction with photons. For this purpose, the differential incoherent scattering cross-sections of Be, C, Mg, Al, Ca and Ti were measured for three scattering angles 60°, 80° and 100° at 279.1, 661.6 and 1115.5 keV using which an expression for the effective atomic number was derived. The differential incoherent scattering cross-sections of the composite materials of interest measured at these three angles in the same set-up and substituted in this expression would yield their effective atomic number at the three energies. Results obtained in this manner for bakelite, nylon, epoxy, teflon, perspex and some sugars, fatty acids as well as amino acids agreed to within 2% of some of the other available values. It was also observed that for each of these samples, Z eff was almost a constant at the three energies which unambiguously justified the conclusions drawn by other authors earlier [Manjunathaguru and Umesh, J. Phys. B: At. Mol. Opt. Phys. 39, 3969 (2006); Manohara et al,Nucl. Instrum. Methods B266, 3906 (2008); Manohara et al Phys. Med. Biol. 53, M377 (2008)] based on total interaction cross-sections in the energy grid of interest.

Effect of magnetic field on the impurity binding energy of the excited states in spherical quantum dot

Abstract: The effect of external magnetic field on the excited state energies in a spherical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic field, the energy would be increased. The results obtained by this method were compared with the previous investigations.

Crystal growth and comparison of vibrational and thermal properties of semi-organic nonlinear optical materials

Abstract: Single crystals of urea thiourea mercuric sulphate (UTHS) and urea thiourea mercuric chloride (UTHC), semi-organic nonlinear optical materials, were grown by low-temperature solution growth technique by slow evaporation method using water as the solvent. Good quality single crystals were grown within three weeks. The nonlinear nature of the crystals was confirmed by SHG test. The UV-Vis spectrum showed the transmitting ability of the crystals in the entire visible region. FTIR spectrum was recorded and vibrational assignments were made. The degree of dopant inclusion was ascertained by AAS. The TGA-DTA studies showed the thermal properties of the crystals.

Effect of next-nearest-neighbour interaction on d x 2 − y 2 -wave superconducting phase in 2D t-J model

Abstract: An exact diagonalization calculation of the t-J model on 2D square cluster has been studied for the ground state properties of HTSC. Effect of next-nearest-neighbour hopping and magnetic (both antiferromagnetic and ferromagnetic) interaction on d x 2−y 2-wave pairing has been shown. Relative strength of the next-nearest-neighbour interaction with respect to that of near-neighbour interaction for the strongest d x 2−y 2-wave pairing has been estimated. A schematic phase diagram is shown. It is shown that a two-sublattice model with antiferromagnetic interaction between them and a small intra-ferromagnetictype interaction in one sublattice favours d x 2−y 2-wave superconductivity and moderate negative type NNN hopping adds flavours to this phase.

Exergetic efficiency optimization for an irreversible heat pump working on reversed Brayton cycle

Abstract: This paper deals with the performance analysis and optimization for irreversible heat pumps working on reversed Brayton cycle with constant-temperature heat reservoirs by taking exergetic efficiency as the optimization objective combining exergy concept with finite-time thermodynamics (FTT). Exergetic efficiency is defined as the ratio of rate of exergy output to rate of exergy input of the system. The irreversibilities considered in the system include heat resistance losses in the hot- and cold-side heat exchangers and non-isentropic losses in the compression and expansion processes. The analytical formulas of the heating load, coefficient of performance (COP) and exergetic efficiency for the heat pumps are derived. The results are compared with those obtained for the traditional heating load and coefficient of performance objectives. The influences of the pressure ratio of the compressor, the allocation of heat exchanger inventory, the temperature ratio of two reservoirs, the effectiveness of the hot- and cold-side heat exchangers and regenerator, the efficiencies of the compressor and expander, the ratio of hot-side heat reservoir temperature to ambient temperature, the total heat exchanger inventory, and the heat capacity rate of the working fluid on the exergetic efficiency of the heat pumps are analysed by numerical calculations. The results show that the exergetic efficiency optimization is an important and effective criterion for the evaluation of an irreversible heat pump working on reversed Brayton cycle.

Solitary wave solutions of selective nonlinear diffusion-reaction equations using homogeneous balance method

Abstract: An auto-Backlund transformation derived in the homogeneous balance method is employed to obtain several new exact solutions of certain kinds of nonlinear diffusion-reaction (D-R) equations. These equations arise in a variety of problems in physical, chemical, biological, social and ecological sciences.

Role of next-nearest-neighbour hopping in the internal structure of the ground state and finite temperature quantities of 2D t-J model

Abstract: An exact diagonalization calculation for a small cluster in the two-dimensional t-J model has been studied to calculate two-hole correlation. Calculations reveal dominant hole-hole correlation for holes sitting on next-nearest-neighbour (NNN) sites and critical coupling occurs at J/t = 0.8. With the increase in negative-type NNN hopping, correlation decreases at NNN sites whereas it increases at other sites. The thermodynamic properties such as entropy and specific heat are studied as functions of temperature with various NNN hopping strength. Results show that with the inclusion of negative NNN hopping, the system becomes more ordered. A qualitative transition temperature region has been estimated. It is shown that with the increase in NNN hopping strength, T c increases. Specific heat results show non-Fermi liquid-type behaviour of the system. All our calculations establish the importance of negative-type NNN hopping.

Simultaneous catalytic regime of tritium and helium-3 in D-D fusion without external breeding

Abstract: A catalytic regime of tritium and helium-3 in deuterium-deuterium fusion, including ion-electron collisions, mechanical expansion, bremsstrahlung radiation, inverse Compton scattering losses and reacting particles energy effect has been investigated. In this paper a new fuel configuration, DTx3Hey, is formed by adding 3He to DT fuel. According to our calculations this fuel (DTx=0.01123Hey=0.0399) has greater energy gain than the fuel (DTx=0.0112) used by Eliezer et al [Eliezer et al, Nucl. Fusion40, 195 (2000)] and also it does not require external tritium and helium-3 breeding. Furthermore, neutron yields in D-D and D-T reactions are reduced due to the reduced quantity of initial amount of deuterium and tritium.

Switching behaviour of a nonlinear Mach-Zehnder interferometer

Abstract: In the present paper, a detailed investigation on the switching behaviour of a nonlinear Mach-Zehnder interferometer (NMZI) has been carried out using beam propagation method (BPM). A thorough investigation on input vs. output characteristic has been carried out by varying different parameters like length of the arms, refractive index of the linear/nonlinear arm, wavelength of the input beams and nonlinear coefficient of the material of the nonlinear arm. The input vs. output characteristic has also been investigated by shifting the balance point of the NMZI. The present paper provides a physically intuitive understanding of the effect of change in different parameters of the NMZI on its switching behaviour.