1/f noise and resistivity of spin glasses

Electrical resistivityρ(T) of spin glasses within the framework of Mookerjee and Chowdhury’s percolation model where there is a distribution of relaxation times (drt) is calculated.ρ(T) thus calculated is in better qualitative agreement with experimental results than that in the single relaxation time model.     

High-p t and jet physics from RHIC to LHC

The observation of the strong suppression of high-p t hadrons in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) at BNL has motivated a large experimental program using hard probes to characterize the deconfined medium created. However, what can be denoted as “leading particle” physics accessible at RHIC presents some limitations which motivate at higher energy the study of much more penetrating objects: jets. The gain in center-of-mass energy expected at the Large Hadron Collider (LHC) at CERN will definitively improve our understanding on how the energy is lost in the system, opening a major new window of study: the physics of jets on an event-by-event basis. We will concentrate on the expected performance for jet reconstruction in ALICE using the EMCal calorimeter. (for the ALICE Collaboration) The text was submitted by the author in English.     

Charge division mechanism in low energy binary fission and the passage of prompt fragments towards theβ-stable products in terms of the double core model

The postulates of the double core model of binary fission are examined against the two well-known charge division mechanisms of fission, namelyucd andecd. An analytic expression of the modifieducd formula is obtained. Radiochemical distribution of mass and charge, formulated from the model, is found to agree satisfactorily with available experimental results. Finally, the most probable charge and mass values of the radiochemical heavy and light products, the average number of neutron andβ-emissions per fragment, are calculated, and found to agree with experimental observations.     

Configurational energies of different A7B types of the long-range order in Fe-Si alloys

In order to examine the existence of the long-range order of A₇B types in Fe-Si alloys with composition less than 12·5 at.% Si, the configurational energies of several superstructures in b.c.c. alloys with the cubic elementary cell having the lattice parameter 2a are calculated on the basis of a simple model with a pairwise interaction between atoms extending to the third neighbours. From the proposed model it follows that the superstructure of A₇B type suggested byFallot can be expected if the interaction parameter for the third neighboursv ₃>0. On the other hand, the two-phase structure (DO₃ order and pure Fe) will be favoured by the alloy crystal ifv ₃<0.The author is indebted to Dr. F.Kroupa and Dr. A.Gemperle for stimulating discussions.     

Two-photon excitation spectrum of benzonitrile vapour

The two-photon excitation spectrum of benzonitrile in the gas phase at about 1 torr has been recorded and analysed in the total energy region of 36300 to 40500 cm⁻¹ using both linearly and circularly polarised light from a Nd-YAG pumped dye laser. The two-photon spectrum consists of strong Franck Condon (fc) transitions bearing a good resemblance to the one-photon spectrum and also vibronic coupling (vc) transitions essentially arising out of the analogue of the benzeneν ₁₄. By a comparative study of thetp spectra of various other monosubstituted benzenes, it has been inferred that the strongtp spectrum of benzonitrile should be ascribed to a considerableπ charge delocalization over the phenyl and nitrile groups.     

Pressure and volume dependence of thelo-to phonons in InAs

The pressure dependence of thelo-to phonons in InAs has been investigated by Raman scattering using the diamond anvil cell. Indium arsenide transforms, presumably to the rock-salt structure at 70±1 kbar. The mode Grüneisen parameters for thelo-to phonons are γ _lo =0.99±0.03, γ _to =1.2±0.03 respectively. The effective charge,e* _T , for InAs decreases slightly with pressure and this trend is in accordance with the behaviour of other III–V zinc blende structured semiconductors: The structural phase transition is discussed in the light of theoretical calculations for phase stability of III–V compounds, as well as recent high pressure x-ray diffraction studies.     

Chemical freeze-out temperature in the hydrodynamical description of Au + Au collisions at $$ \sqrt {^S NN} = 200 GeV $$

We study the effect of separate chemical and kinetic freeze-outs to the ideal hydrodynamical flow in Au + Au collisions at RHIC ( energy). Unlike earlier studies we explore how these effects can be counteracted by changes in the initial state of the hydrodynamical evolution. We conclude that the reproduction of pion, proton and antiproton yields necessitates a chemical freeze-out temperature of T ≈ 150MeV instead of T = 160–170 MeV motivated by thermal models. Contrary to previous reports, this lower temperature makes it possible to reproduce the p T spectra of hadrons if one assumes very small initial time, τ ₀ = 0.2 fm/c. However, the p T differential elliptic flow, v ₂(p T) remains badly reproduced. This points to the need to include dissipative effects (viscosity) or some other refinement to the model.     

Fluctuations and the magnetic equation of state

The influence of inhomogeneity of magnetization on the equation of state for a magnetic system has been considered in the approximation of homogeneous fluctuations of magnetic moment. The fluctuations have been described in the molecular field approximation. It has been shown that taking into account the fluctuations of magnetic moment at the derivation of the equation of state changes the relation among the variablesM, H andT, the temperature dependence of the spontaneous magnetization near the critical point, and shifts the critical temperature.The author would like to thank Prof. J.Kocinski and Prof. L.Wojtczak for their interest in the subject of the paper and for numerous elucidating discussions. The author is indebted to Prof. L.Valenta for his helpful remarks concerning this paper.     

Equilibrium theory of two-dimensional simple liquids

Using the Wigner-Kirkwood expansion and bare Lennard-Jones (LJ) (12-6) potential, an effectiveLJ potential is derived, which includes the quantum effects through the expressions of the effective diameter∂(T, λ) and well-depth (T, λ). We use theWCA perturbation theory to calculate the free energy and pressure for theLJ and effectiveLJ potentials. Simple analytic expressions are given for the reference system and the first order correction calculated. The results are quite good at high density. The quantum effects on the free energy and pressure are also discussed.     

Secondary electron emission of sputtered alumina films

Secondary electron emission yieldδ was measured for thin films of alumina prepared byrf sputtering technique. Single pulse method was used along with 4-gridleed optics system to determineδ. Maximum value of 4·3 was obtained at primary energy of 350 eV. The Dionne’s theory was used to analyse the results and the emission probability escape depth and absorption coefficient of secondaries were also estimated. Fairly good correlation is observed between experimental and theoretical values ofδ for beam energies upto 1 keV.     

Isospin violations in largeP T pion inclusive processes in perturbative quantum chromodynamics

We investigate the asymmetries arising due to electromagnetic interactions in largeP _T pion inclusive processes. The hardqcd processes that contribute to such asymmetries areq+g→q+γ,q+q→g+γ etc. which are suspected to be substantial, as indicated by theqcd predictions for a significant and increasingγ/π ^o ratio at largeP _T. We calculate the expected isospin related asymmetries and propose tests that might detect them. Our estimates indicate that the effects are much smaller than may be naively expected. We also observe a remarkable scaling of asymmetries in the variableP _T/(s)^1/2.     

Bethe-Salpeter dynamics for two-photon processes

Recent experimental data on single hadron production by two-photon beams inpetra andpep have provided a unique opportunity for testing specific models of confinement through a study of one of their cleanest predictionsviz the γγ →H amplitudes. Motivated by this new facility, aqcd-oriented Bethe-Salpeter model of harmonic confinement, which has already been found to describe rather well several classes of hadronic data (from mass spectra to electromagnetic and pionic couplings), is now employed for a detailed comparison of its predictions onP → γγ andT → γγ couplings with the data. The agreement is quite good for all cases except one (η → γγ). This paper is offered as a “Festschrift” in honour of Dr Raja Ramanna on the occasion of his sixtieth birthday. The subject is theoretical in content but seeks to exploit an entirely new window opened by the latest experimental technology (on two-photon physics). As such it is appropriately dedicated to one of the main architects of nuclear science in India.     

Perturbation theory for a microemulsion with triangular well potential

The perturbation approach of Barker and Henderson (1967, 1968) has been applied to a microemulsion obeying triangular well potential as a perturbative attractive tail over the Percus-Yevick (PY) hard sphere model by calculating the Rayleigh ratio,R ₉₀, under the mean spherical approximations. The results are in better agreement with experimental values. Presented at the 70th Indian Science Congress, Tirupathi, January 3–8, 1983.     

Gravity-induced weak symmetry breaking and supergravity

We give here a review of the recent developments of grand unified theories based onN=1 supergravity. We start with a brief introduction of supersymmetry and supergravity multiplets, and then discuss the construction of an invariant Lagrangian. The phenomena of gravity-induced weak symmetry breaking via the super Higgs effect at the tree level, corresponding to the conventional SU(5) gauge group, are then considered. We then extend this idea to the larger group SO(10), showing two possible breaking chains given as (i) SO(10)×susy→SU(2) _L ×U(1) _R ×U(1) _B-L ×SU(3) _C (≡ G₂₁₁₃)×susy→U(1)_em×SU(3) _C (G _LE ) predicting a secondZ-boson having mass lower than 1 TeV, and (ii) SO(10)×susy→SU(2) _L ×SU(2) _R ×SU(4)→(≡G₂₂₄)×susy→ SU(2) _L ×U(1) _Y ×SU(3) _C (≡ G₂₁₃)×susy→U(1)_em×SU(3) _C . We also consider the radiative breaking of weak symmetry via renormalisation group effects, which predicts the top quark mass. Some experimental signatures of the supersymmetric particles are investigated and possible future outlook is discussed. Invited talk presented at the International Symposium on Theoretical Physics, Bangalore, November 1984.     

Determination of Enantiomeric Compositions of Analytes Using Novel Fluorescent Chiral Molecular Micelles and Steady State Fluorescence Measurements

Novel fluorescent chiral molecular micelles (FCMMs) were synthesized, characterized, and employed as chiral selectors for enantiomeric recognition of non-fluorescent chiral molecules using steady state fluorescence spectroscopy. The sensitivity of the fluorescence technique allowed for investigation of low concentrations of chiral selector (3.0 × 10⁻⁵ M) and analyte (5.0 × 10⁻⁶ M) to be used in these studies. The chiral interactions of glucose, tartaric acid, and serine in the presence of FCMMs poly(sodium N-undecanoyl-l-tryptophanate) [poly-l-SUW], poly(sodium N-undecanoyl-l-tyrosinate) [poly-l-SUY], and poly(sodium N-undecanoyl-l-phenylalininate) [poly-SUF] were based on diastereomeric complex formation. Poly-l-SUW had a significant fluorescence emission spectral difference as compared to poly-l-SUY and poly-l-SUF for the enantiomeric recognition of glucose, tartaric acid, and serine. Studies with the hydrophobic molecule α-pinene suggested that poly-l-SUY and poly-l-SUF had better chiral discrimination ability for hydrophobic analytes as compared to hydrophilic analytes. Partial-least-squares regression modeling (PLS-1) was used to correlate changes in the fluorescence emission spectra of poly-l-SUW due to varying enantiomeric compositions of glucose, tartaric acid, and serine for a set of calibration samples. Validation of the calibration regression models was determined by use of a set of independently prepared samples of the same concentration of chiral selector and analyte with varying enantiomeric composition. Prediction ability was evaluated by use of the root-mean-square percent relative error (RMS%RE) and was found to range from 2.04 to 4.06%. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Quantum chromodynamics predictions in renormalization scheme invariant perturbation theory

It has recently been shown that any physical quantity ℛ, in perturbation theory, can be obtained as a function of only the renormalization scheme (rs) invariants,ρ ₀,ρ ₁,ρ ₂, … Physical predictions, to any given order, are renormalization scheme independent in this approach. Quantum chromodynamics (qcd) predictions to second order, within thisrs-invariant perturbation theory, are given here for several processes. These lead to some novel relations between experimentally measurable quantities, which do not involve the unknownqcd scale parameter Λ. They can therefore be directly confronted with experiments and this has been done wherever possible. It is suggested that these relations can be used to probe the neglected higher order corrections.     

Change of confinement scale in nuclei and the EMC effect

We study a model in which the confinement scale of quarks in a nucleus of massA changes asA ^1/3. This explains theA dependence of structure functions (emc effect) as seen in muon, electron and antineutrino deep inelastic scattering from nuclear targets. We also investigate a prediction of this model—anA dependence of theqcd scale parameter A.     

ac anddc electroluminescence in CaS:Cu,Sm phosphors

Theac anddc electroluminescence in CaS:Cu, Sm have been investigated. The luminescence spectra show three peaks in the visible region. The brightness-voltage dependence satisfies the relationB=B ₀ exp (−b/V ^1/2) with two modes of variation. The nature of this dependence indc andac at different frequencies is discussed. The electroluminescence brightness also depends on the temperature of the phosphors and shows a peak around 80.0;C. The electroluminescence efficiency increases with applied voltage up to 2200 V and this dependence on V is explained on the basis of a transport process of the Schottky emission type.     

The crystal fields inα-alums—A high pressure magnetic resonance study

The origin of the crystal field and its variation with temperature in severalα-alums have been studied bynmr of²⁷Al andepr of Cr³⁺ at high hydrostatic pressures and low temperatures. The results lead to an explanation of the anomalous temperature variation of the axial crystal field at the trivalent ion site. The mechanism of the phase transition in ammonium alum is also explained. A correlation between the axial crystal field as determined bynmr (e ² qQ/h) and that determined byepr (D) has been obtained.     

Infrared studies on ion irradiated quartz

Damage produced inα- and fused quartz bombarded with low energy (∼ 100 keV) D⁺, He⁺ and Ar⁺ ions, has been studied by observing the changes in their spectrum. Besides bulk reflectivity, the attenuated total reflection spectrum has also been studied, the latter with a view to obtaining the surface polariton frequencies. It is observed that for the same fluence, the changes following D⁺ irradiation are much higher compared to that for Ar⁺ irradiation. The variation of the surface polariton frequency inα-quartz with the damage energy deposited has the same trend as observed earlier for refractive index. Some annealing studies have also been performed in argon-irradiated samples. These studies indicate that whereas in fused quartz the damaged layer recovers completely, inα-quartz there is a residual amorphization even after annealing. A two-layer model is proposed which gives a reasonable simulation of the observedir properties.