Publications
2021

(2021) Physics Letters B. 813, 136042. Abstract
We introduce a general variational framework to address the tunneling of hot Fermi systems. We use the representation of the trace of the imaginary time τ=it propagator as a functional integral type of a sum over complete sets of states at intermediate propagation slices. We assume that these states are τdependent and generated by an arbitrary trial Hamiltonian H_{0}(τ). We then use the convexity inequality to derive H_{0}(τ) controlled variational bound for a trial action functional. This functional has a general structure consisting of two parts  statistically weighted quantum penetrability and dynamical tunneling entropy. We examine how this structure incorporates the basic physics of tunneling of hot Fermi systems. Using the variational inequality one can optimise the dynamical parameters controlling the action functional for any choice of the trial problem. As an application we take H_{0}(τ) to describe imaginary time dynamics of non interacting Bogoliubovde Gennes (BdG) quasiparticles. Optimising its dynamical parameters we extend the tunneling theory of hot Fermi systems to the HartreeFockBogoliubov (HFB) frame and derive the corresponding generalisation of imaginary time temperature dependent BdG mean field equations. As in the trial action the prominent feature of these equations is an inseparable interplay between quantum dynamical and entropic statistical effects. In the zero temperature limit these equations describe the \u201cfalse ground state\u201d tunneling decay of superfluid Fermi systems (spontaneous fission in nuclear physics). With increasing excitation energy (effective temperature) the decay process is gradually evolving from pure quantum tunneling to statistical \u201cbottle neck\u201d escape mechanism. Correspondingly the statistically weighted dynamical penetrability part in the action gradually decreases while the tunneling entropy increases with increasing effective temperature.
2012

(2012) European Physical Journal D. 66, 9, 231. Abstract
Techniques to deal with Feshbach resonances are applied to describe resonant light scattering off one dimensional photonic crystal slabs. Accurate expressions for scattering amplitudes, free of any fitting parameter, are obtained for isolated as well as overlapping resonances. They relate the resonance properties to the properties of the optical structure and of the incident light. For the most common case of a piecewise constant dielectric function, the calculations can be carried out essentially analytically. After establishing the accuracy of this approach we demonstrate its potential in the analysis of the reflection coefficients for the diverse shapes of overlapping, interacting resonances.
2010

(2010) Journal Of The Optical Society Of America BOptical Physics. 27, 5, p. 899903 Abstract
We develop a path integral approach for analyzing the stationary light propagation in general dielectric media. The Hermitian form of the stationary Maxwell equations is transformed into a quantum mechanical problem of a spin 1 particle with spinorbit coupling and position dependent mass. After appropriate ordering several path integral representations of a solution are constructed. First we keep the propagation of the polarization degrees of freedom in an operator form integrated over paths in a coordinate space. The use of spin 1 coherent states allows representing this part as a path integral over such states. Finally a path integral in a transversal momentum space with explicit transversality enforced at every time slice is also given. As an example the geometrical optics limit is discussed and the ray equation is recovered together with the Rytov rotation of the polarization vector.
2009

(2009) Physical Review A. 80, 3, 033803. Abstract
We study the use of squeezed light for qubit coherent control and compare it with the coherentstate control field case. We calculate the entanglement between a short pulse of resonant squeezed light and a twolevel atom in free space and the resulting operation error. We find that the squeezing phase, the phase of the light field, and the atomic superposition phase all determine whether atompulse mode entanglement and the gate error are enhanced or suppressed. When averaged over all possible qubit initial states, the gate error would not decrease by a practically useful amount and would in fact increase in most cases. However, the enhanced entanglement may be of use in quantum communication schemes. We discuss the possibility of measuring the increased gate error as a signature of the enhancement of entanglement by squeezing.

Path integrals for light propagation through dielectrics  a full vector version(2009) Theoretical And Computational Nanophotonics (TaconaPhotonics 2009). 1176, p. 5456 Abstract
We develop a path integrals approach for analyzing stationary light propagation through dielectrics. The hermitian form of the stationary Maxwell equations is transformed into a quantum mechanical problem of a spin 1 particle with spinorbit coupling and position dependent mass. As an example the geometrical optics limit is discussed and the ray equation is recovered together with the Rytov rotation. Possible other applications are indicated.
2008

(2008) Physical Review B. 78, 20, 205204. Abstract
We calculate the dynamical fluctuation spectrum of electronic spins in a semiconductor under a steadystate illumination by light containing polarization squeezing correlations. Taking into account quasiparticle lifetime and spin relaxation for this nonequilibrium situation we consider up to fourth order optical effects which are sensitive to the squeezing phases. We demonstrate the possibility to control the spin fluctuations by optically modulating these phases as a function of frequency, leading to a nonLorentzian spectrum which is very different from the thermal equilibrium fluctuations in n doped semiconductors. Specifically, in the timedomain spinspin correlation can exhibit time delays and sign flips originating from the phase modulations and correlations of polarizations, respectively. For higher light intensity we expect a regime where the squeezing correlations will dominate the spectrum.

(2008) Journal Of The Optical Society Of America AOptics Image Science And Vision. 25, 6, p. 14351443 Abstract
Polarization independence in a onedimensional resonant grating waveguide structure involves the simultaneous excitation of two guided modes propagating in different directions. Possible simultaneous excitations occur when the two excited guided modes have either the same polarization, i.e., TETE (transverse electric) or TMTM (transverse magnetic), or different polarizations, i.e., TETM. Simultaneous excitations may result in bandgaps and singularities. We confirm and show that in order to achieve polarization independence, it is necessary to find the conditions that minimize the effects of such bandgaps and singularities and experimentally demonstrate tunable polarization independence for simultaneously excited TETMguided modes.

(2008) Physical Review B. 77, 3, 035307. Abstract
We calculate the transfer rate of correlations from polarization entangled photons to the collective spin of a manyelectron state in a twoband system. It is shown that when a semiconductor absorbs pairs of photons from a twomode squeezed vacuum, certain fourthorder electronphoton processes correlate the spins of the excited electron pairs of different quasimomenta. Different distributions of the quantum Stokes vector of the light lead to either enhancement or reduction of the collective spin correlations, depending on the symmetry of the distribution. We find that as the squeezing of the light becomes nonclassical, the spin correlations exhibit a crossover from being positive with an ∼ N2 (N is the average photon number) scaling to being negative with ∼N scaling, even when N is not small. Negative spin correlations mean a preponderance of spin singlets in the optically generated state. We discuss the possibility to measure the collective spin correlations through the measurement of the Faraday rotation fluctuation spectrum in a steadystate configuration.
2007

(2007) Physical Review A. 76, 1, Abstract
A broadband squeezed vacuum photon field is characterized by a complex squeezing function. We show that by controlling the wavelength dependence of its phase it is possible to change the dynamics of the atomic polarization interacting with the squeezed vacuum. Such a phase modulation effectively produces a finite range temporal interaction kernel between the two quadratures of the atomic polarization yielding the change in the decay rates as well as the appearance of additional oscillation frequencies. We show that decay rates slower than the spontaneous decay rate can be achieved even for a squeezed bath in the classical regime. For "piecewise linear" and quadratic phase modulations the power spectrum of the scattered light exhibits narrowing of the central peak due to the modified decay rates. For strong phase modulations, side lobes appear symmetrically around the central peak reflecting additional oscillation frequencies.
2005

(2005) Physical Review B. 72, 7, 075333. Abstract
We consider a semiconductor quantumwell placed in a waveguide microcavity and interacting with the broadband squeezed vacuum radiation, which fills one mode of the waveguide with a large average occupation. The waveguide modifies the optical density of states so that the quantum well interacts mostly with the squeezed vacuum. The vacuum is squeezed around the externally controlled central frequency ω0, which is tuned above the electronhole gap Eg, and induces fluctuations in the interband polarization of the quantum well. The power spectrum of scattered light exhibits a peak around ω0, which is moreover nonLorentzian and is a result of both the squeezing and the particlehole continuum. The squeezing spectrum is qualitatively different from the atomic case. We discuss the possibility of observing the above phenomena in the presence of additional nonradiative (ee, phonon) dephasing.
2003

(2003) IEEE Photonics Technology Letters. 15, 11, p. 15311533 Abstract
We present the development of an ultrafast twodimensional (288 × 132 elements) reflection modulator array based on GaAsAlGaAs multiple quantumwells embedded in asymmetric FabryPérot structure. The array has low operation voltage (

(2003) Europhysics Letters. 62, 1, p. 103109 Abstract
In this work we analyze how coherent transport through a quantum dot (QD) in the Kondo regime is affected by the weak capacitive interaction with a nearby biased quantum point contact (QPC). We find that when the QDQPC interaction is weak, the width of the resonance at the Fermi level is hardly affected by it, suggesting the absence of dephasing. However, the spectral weight of such resonance is reduced leading to an observable suppression of the conductance and the elastic transmission probability through the QD.
2001

(2001) Physical Review B  Condensed Matter and Materials Physics. 63, 20, Abstract
In controlled dephasing a controlled environment causes dephasing of transport through a mesoscopic system. As a result of their interaction the states of the two subsystems are entangled. In this paper we discuss how their entanglement influences dephasing using as an example the \u201cwhich path detector,\u201d where the dephasing of transport through a quantum dot (QD) due to the interaction with a quantum point contact (QPC) is detected by means of an AharonovBohm (AB) interferometer. In particular, we calculate the suppression ν of AB oscillations as a function of the bias eV applied to the QPC and the coupling Γ of the QD to the leads. At low temperatures the entanglement produces a smooth crossover from ν ∝ (eV/Γ)^{2}, when e V ≪ Γ to ν ∝ eV/Γ, for e V ≫ Γ.
1999

(1999) Physical Review B  Condensed Matter and Materials Physics. 60, 8, p. 55495560 Abstract
We study the statistics of quasiparticle and quasihole levels in small interacting disordered systems within the HartreeFock approximation. The distribution of the inverse compressibility, given according to Koopmans theorem by the distance between the two levels across the Fermi energy, evolves from a Wigner distribution in the noninteracting limit to a shifted Gaussian for strong interactions. On the other hand, the nature of the distribution of spacings between neighboring levels on the same side of the Fermi energy (corresponding to energy differences between excited states of the system with one missing or one extra electron) is not affected by the interaction and follows WignerDyson statistics. These results are derived analytically by isolating and solving the appropriate HartreeFock equations for the two levels. They are substantiated by numerical simulations of the full set of HartreeFock equations for a disordered quantum dot with Coulomb interactions. We find enhanced fluctuations of the inverse compressibility compared to the prediction of the random matrix theory, possibly due to the localization of the wave functions around the edge of the dot. The distribution of the inverse compressibility calculated from the discrete second derivative with respect to the number of particles of the HartreeFock ground state energy deviates from the distribution of the level spacing across the Fermi energy. The two distributions have similar shapes but are shifted with respect to each other. The deviation increases with the strength of the interaction thus indicating the breakdown of Koopmans theorem in the strongly interacting limit.
1997

(1997) Nuclear Physics B. 488, 3, p. 735774 Abstract
Matrices are said to behave as free noncommuting random variables if the action which governs their dynamics constrains only their eigenvalues, i.e. depends on traces of powers of individual matrices. The authors use recently developed mathematical techniques in combination with a standard variational principle to formulate a new variational approach for matrix models. Approximate variational solutions of interacting largeN matrix models are found using the free random matrices as the variational space. Several classes of classical and quantum mechanical matrix models with different types of interactions are considered and the variational solutions compared with exact Monte Carlo and analytical results. Impressive agreement is found in a majority of cases.
1996

(1996) Surface Science. 361362, p. 489492 Abstract
The energy relaxation rate due to onephonon processes for 2D electrons is calculated. An explicit dependence on the characteristics of random potential, magnetic field, and electron energy is obtained.

(1996) Physical Review B. 53, 12, p. 79647969 Abstract
Longrange Coulomb interaction between the edges of a Hall bar changes the nature of the gapless edge excitations. Instead of independent modes propagating in opposite directions on each edge as expected for a shortrange interaction one finds elementary excitations living simultaneously on both edges, i.e., composed of correlated density waves propagating in the same direction on opposite edges. We discuss the microscopic features of this Coulomb drag of excitations in the fractional quantum Hall regime within the framework of the bosonic ChernSimons LandauGinzburg theory. The dispersion law of these excitations is nonlinear and depends on the distance between the edges as well as on the current that flows through the sample. The latter dependence indicates a possibility of parametric excitation of these modes. The bulk distributions of the density and currents of the edge excitations differ significantly for short and longrange interactions.

(1996) Physical review letters. 77, 4, p. 719722 Abstract
We consider the process of parametric excitation of gapless edge modes in a Hall bar by an alternating current. We find that such a process can be realized provided both an interedge interaction and a constant current are present in the bar. The expected experimental signatures of this phenomenon are discussed.
1995

(1995) Zeitschrift für Physik. 353, 2, p. 213225 Abstract
The \u201cbody fixed frame\u201d with respect to local gauge transformations is introduced. Rigid gauge \u201crotations\u201d in QCD and their Schrödinger equation are studied for static and dynamic quarks. Possible choices of the rigid gauge field configuration corresponding to a nonvanishing static colormagnetic field in the \u201cbody fixed\u201d frame are discussed. A gauge invariant variational equation is derived in this frame. For large number N of colors the rigid gauge field configuration is regarded as random with maximally random probability distribution under constraints on macroiscopiclike quantities. For the uniform magnetic field the joint probability distribution of the field components is determined by maximizing the appropriate entropy under the area law constraint for the Wilson loop. In the quark sector the gauge invariance requires the rigid gauge field configuration to appear not only as a background but also as inducing an instantaneous quarkquark interaction. Both are random in the large N limit.
1993

HALL TUNNELING OF VORTICES IN HIGHTEMPERATURE SUPERCONDUCTORS(1993) JETP Letters. 57, 11, p. 711716 Abstract
Quantum tunneling of vortices in very clean typeII superconductors is shown to be governed by the Hall term in the equation of motion. An effective action determining the tunneling probability is calculated. It is argued that hightemperature superconductors may belong to a class of very clean materials, and that they may have Hall tunneling at low temperatures.
1992

(1992) Physical Review B. 46, 7, p. 39533965 Abstract
We present a semiclassical theory of charged interacting anyons in a strong magnetic field. We derive the appropriate generalization of the WKB quantization conditions and determine the corresponding wave functions for nonseparable integrable anyonic systems. This theory is applied to a system of two interacting anyons, two interacting anyons in the presence of an impurity, and three interacting anyons. We calculate the dependence of the semiclassical energy levels on the statistical parameter and find regions in which this dependence follows very different patterns. The semiclassical treatment allows us to find the correlation between these patterns and the changes in the character of the classical motion of the system. We also test the accuracy of the meanfield approximation for low and highenergy states of the threeanyon system.

(1992) Physical review letters. 69, 21, p. 30013004 Abstract
Landau level mixing by external potentials is considered in a BornOppenheimer expansion which separates the dynamics of the fast velocities of cyclotron rotation and the slow coordinates of the guiding centers. Level mixing is present already in the extreme adiabatic limit and in transitions at avoided crossings. Nonvanishing Berrys phase adds effective magnetic field depending on external potential. Explicit results are given for weakly inhomogeneous potentials. The projection on a single Landau level appears as an extreme limit of the formalism.

(1992) Physical Review B. 46, 4, p. 23192331 Abstract
Quantum mechanics of the guiding centers of charged particles moving in a twodimensional plane perpendicular to a strong magnetic field is semiclassical in character. The inverse of the strength of the field plays the role of the Planck constant. When projected on a single Landau level, the dynamics of three interacting particles is completely integrable. We carry out the semiclassical quantization of the invariant tori of this system and find all the energy levels and the properties of the corresponding wave functions. In the case of Fermi statistics, we compare the eigenenergies with exact numerical results. For identical particles, fermions as well as bosons, we find a strong correlation between otherwise independent quantization conditions controlling the eigenvalues of the angular momentum and the energy of the system. This correlation is responsible for the discontinuous dependence of the groundstate energy on the size of the system. In the fermion case, this is a wellknown feature of the fractional quantum Hall system. Our results indicate that it may also be true for bosonic systems. For fermions, our semiclassical results miss some levels or add some extra levels in several places near the separatrix of the system but are otherwise in a good overall agreement with the exact eigenvalues. The agreement is significantly better when the size of the system is much larger than the magnetic length. For the lowestenergy state corresponding to the onethird filling of the Landau level, we find only a 0.07% error. The problem of missing or extra levels can presumably be also corrected by a proper treatment of tunneling, which is important close to the separatrix. The semiclassical wave function of the system is the Husimi transform of the wave function in the guidingcenter representation. It is concentrated around the quantized invariant tori of the problem in this representation. We compare this function with the Laughlin variational wave function.

(1992) Physical review letters. 69, 2, p. 363366 Abstract
We present a semiclassical theory of charged interacting anyons in a strong magnetic field. We apply this theory to a number of fewanyon systems including two interacting anyons in the presence of an impurity and three interacting anyons. We discuss the dependence of their energy levels on the statistical parameter and find regions in which this dependence follows very different patterns. The semiclassical arguments allow us to correlate these patterns with the change in the character of the classical motion of the system.
1991

(1991) Nuclear Physics B. 361, 3, p. 585625 Abstract
Twodimensional QCD in the largeN limit is formulated as a HartreeFock problem and solved numerically on a lattice. Calculation of singleparticle wave functions and the onebody density matrix displays the structure of baryons. Insight into the Skyrme model is provided by showing that in the limit of small quark mass, the baryon is accurately approximated by a spatially varying chiral rotation of the vacuum wave function, where the chiral angle satisfies the sineGordon equation. The meson spectrum is calculated in the random phase approximation. The same mean field theory is also applied to chiral and nonchiral GrossNeveu models, where it agrees with known analytical results.

(1991) Annals of Physics. 208, 1, p. 189 Abstract
Twodimensional quantum electrodynamics (QED_{2}) and quantum chromodynamics (QCD_{2}) are studied in the framework of canonical quantization on the light cone. The crucial feature of the present approach is the formulation on a finite interval. This allows resolution of the severe infrared ambiguities of twodimensional gauge theories and clarification of the relationship between lightcone and equaltime quantization. In particular, the naive lightcone approach emerges as an effective theory with welldefined limitations. For QED_{2}, it is demonstrated that the known nonperturbative phenomena can be obtained on the lightcone. For QCD_{2}, using the lightcone Coulomb gauge, the role of the gauge degrees of freedom for regularizing the infrared singularity of the gluon propagator is exhibited. The structure of the Hilbert space, the properties of the vacuum and of the elementary excitations are addressed. In the chiral limit (vanishing quark mass), analytical result for both SU(N) and U(N) QCD_{2} are presented. Relativistic manybody techniques are employed to solve the theory in the large N limit, and the quark condensate is evaluated on the lightcone. It is pointed out that the finite interval techniques allow taking advantage of the technical simplification usually attributed to lightcone quantization, even when using ordinary coordinates. This surprising result is intimately connected to Lorentz invariance.
1989

(1989) Physics Letters B. 217, 12, p. 14 Abstract
A hot liquiddrop model which describes equilibrated highly excited nuclei is considered. The model includes the neutron and the proton components of the nuclear liquid and is used to calculate the upper limiting temperature of nuclear stability. Stability of hot nuclei against nonequilibrim particle emission is also investigated. The behaviour of both stability limits is presented for wide regions of the (N, Z) nuclear chart.

(1989) Physical review letters. 63, 1, p. 3134 Abstract
The Landau theory of shape transitions in hot rotating nuclei is applied to eveneven rareearth nuclei from cerium to hafnium. The parameters of the Landau expansion are extracted from microscopic calculations based on the NilssonStrutinsky procedure, and are shown to follow simple systematics. In particular, the systematics of the critical temperature and the critical angular momentum of the shape transitions as functions of neutron and proton number are investigated. Simple rules are provided for the behavior of these quantities.

(1989) Physical Review B. 40, 4, p. 21472157 Abstract
We consider a voltagebiased ultrasmallcapacitance Josephson junction, with the coupling to the external source containing both resistive and inductive elements. In addition we include a phenomenological coupling to an external heat bath. Our goal is to extend and generalize previous studies of currentbiased ultrasmall junctions. Charging effects, due to the presence of discrete charge carriers in the junction, play a crucial role. In particular we find an infiniteresistance branch in the IV characteristic for a dc bias, and resistive steps in the IV curve when the external bias contains an additional ac component. These effects are reminiscent of the Coulomb blockade and the inverse Shapiro steps, respectively, predicted earlier in the context of currentbiased circuits. As a response to an ac voltage bias, we also predict spikes of the voltage across the junction and a noisy background when this voltage is plotted as a function of either the external dc biasing voltage or the external frequency. Our analysis shows that various circuitry components may qualitatively affect the response of the junction to an external bias.
1988

(1988) Nuclear Physics A. 482, 12, p. 5764 Abstract
Universal features of evolution of the equilibrium nuclear shapes with temperature and angular momentum are predicted by the Landau theory of nuclear shape transitions. The general dependence of the nuclear free energy on the deformation given by this theory also provides a unified description of thermal fluctuations of all quadrupole degrees of freedom. Using this unified theory we calculate the giant dipole absorption by hot rotating nuclei and investigate its systematics as a function of nuclear spin and temperature. Direct comparison with experimental data is presented.

(1988) Physical review letters. 61, 17, p. 19261929 Abstract
A macroscopic approach to giant dipole resonances (GDR's) in hot rotating nuclei is presented. It is based on the Landau theory of nuclear shape transitions and provides a unified description of thermal fluctuations in all quadrupole shape degrees of freedom. With all parameters fixed by the zerotemperature nuclear properties the theory shows a very good agreement with existing GDR measurements in hot nuclei. The sensitivity of the GDR peak to the shape of hot nuclei is critically examined. Lowtemperature experimental results in Er show clear evidence for changes in the nuclear energy surface, while highertemperature results are dominated by the fluctuations.
1987

(1987) Nuclear Physics A. 469, 2, p. 205238 Abstract
A unified framework of the Landau theory of phase transitions in statistical systems is applied to the description of the shape transitions in hot rotating nuclei. Assuming the temperature dependence of the coefficients of the Landau expansion is consistent with the underlying microscopic theory we derive and discuss the most general features of these transitions which are expected to have a universal character. For nuclei with prolate ground states we find rapid changes of the equilibrium shape from almost prolate to oblate when the excitation energy E^{*} increases in the vicinity of a certain critical value and for a fixed angular momentum J. The rate of these shape transitions depends strongly on the magnitude of J and is faster for smaller J. In the terminology of statistical mechanics the transition is first order when J is less than a certain critical J_{c} and second order for J > J_{c}. On the phase diagram of E^{*} versus J the lines of the first and second order transitions meet at an analog of a tricritical point where large fluctuations around the equilibrium shape are expected. The general theory is illustrated by calculations of the properties and the phase diagram of the ^{166}Er nucleus.
1986

(1986) Physical review letters. 57, 5, p. 539542 Abstract
The Landau theory of shape transitions in hot rotating nuclei is introduced and the universal features of such transitions are derived. The phase diagram of the excitation energy versus angular momentum J for nuclei with prolate ground states shows a transition line from triaxial to oblate shapes. The transition is first order for small values of J and becomes second order above a certain value which is the analog of the tricritical point. Nuclear shapes change very rapidly from near prolate to oblate in the vicinity of this point. The theory is used to calculate the phase diagram of the Er166 nucleus.
1985

(1985) Nuclear Physics A. 436, 2, p. 265293 Abstract
Results of temperaturedependent HartreeFock calculations for equilibrated hot nuclei are presented, extending to the highest temperatures at which the nuclei remain stable. A subtraction procedure developed earlier for isolating the properties of the nucleus from the nucleus + vapor system is applied. The temperature dependence of various quantities characterizing hot nuclei is investigated. The influence of different effective interactions in the HartreeFock equations is examined. Special attention is devoted to the study of the hightemperature stability limit of hot nuclei. This limit in nuclei with the Coulomb interaction artificially switched off (i.e. uncharged nuclei) is shown to correspond to the critical temperature of the liquidgas phase transition expected on the basis of hot nuclear matter calculations. In realistic charged nuclei the Coulomb repulsion causes a nucleus to become electrostatically unstable and to fall apart at much lower temperatures than its uncharged partner. The approach to and the temperature of this Coulomb instability are very sensitive to the choice of the nuclear interaction. Studying this instability in compound nuclei with different chargetomass ratio provides a sensitive measure of the temperature dependence of the nuclear surface properties as well as of certain features of the nuclear equation of state.

(1985) Nuclear Physics A. 437, 2, p. 426442 Abstract
Abstract: Coulomb repulsion causes an instability in a hot compound nucleus when its temperature is raised beyond a certain limiting value. We investigate this Coulomb instability using a finitetemperature version of the liquiddrop model. We demonstrate the relation between this instability and the liquidgas phase transition occurring in hot nuclear matter. The instability temperature T_{lim} depends on the critical temperature T_{c} of the transition and is always below it. The value of T_{lim} is, however, not universal and depends also on the mass and the charge of a compound nucleus. T_{lim} is very sensitive to the basic characteristics of the hot nuclear matter: its equation of state and the temperature dependence of its surface tension.
1984

(1984) Nuclear Physics A. 428, C, p. 9599 Abstract
We propose and discuss a prescription suitable to include the contribution of continuum states in meanfield calculations at high temperature.

(1984) Nuclear Physics A. 427, 2, p. 278296 Abstract
A prescription is proposed for calculating the contribution of unbound states in nuclear HartreeFock calculations at finite temperature. The method is based on the remark that a static HartreeFock calculation at finite temperature describes a hot nucleus in equilibrium with an external nucleon vapor. Properties of the hot nucleus including continuum effects are obtained by extracting the contribution of the external gas, which we calculate from a second HartreeFock calculation. We show that for a onebody potential this subtraction procedure yields standard formulae for partition functions in terms of phase shifts. Numerical calculations are performed in ^{56}Fe and ^{208}Pb. The resuls indicate that continuum contributions are large beyond temperatures of the order of 4 MeV. We also find the existence of a critical temperature, of the order of 10 MeV, beyond which solutions of the equations can no longer be found.

(1984) Nuclear Physics A. 413, 3, p. 439474 Abstract
A phenomenological description of the temperaturedriven shape transitions in heavy nuclei is presented. The general framework of the Landau theory is used to establish the free energy and entropy dependence on the deformation and the temperatureenergy variables. This information is used to discuss the equilibrium quantities as well as the fluctuation effects around equilibrium shapes. Calculations are presented for the entropy, energy and the level density in the context of a typical example of a heavy nucleus undergoing shape transition. The results show considerable deviations from the standard dependences which are obtained using the assumption of a fixed nuclear shape.
1982

(1982) Nuclear Physics A. 389, 1, p. 5668 Abstract
The recently proposed algebraic model for collective spectra of diatomic molecules is analysed in terms of conventional geometrical degrees of freedom. We present a mapping of the algebraic hamiltonian onto an exactly solvable geometrical hamiltonian with the Morse potential. This mapping explains the success of the algebraic model in reproducing the lowlying part of molecular spectra. At the same time the mapping shows that the expression for the dipole transition operators in terms of boson operators differs from the simplest IBM expression and in general must include manybody boson terms. The study also provides an insight into the problem of possible interpretations of the bosons in the nuclear IBM.
1980

(1980) Physical Review C. 21, 4, p. 15941602 Abstract
A general method for a microscopic description of nuclear dynamical problems is discussed. The method is based on a functional integral representation for the manybody time evolution operator U(tf,ti). In the stationary phase limit, a timedependent meanfield approximation for the matrix elements of U is obtained. Using standard procedures this allows for extraction of quantum mechanical information about bound states, tunneling, or scattering phenomena in a manynucleon system. The approximation represents a natural generalization of the timedependent HartreeFock method. NUCLEAR STRUCTURE, NUCLEAR REACTIONS derived meanfield approximation for matrix elements of exp(iHt) from exact functional integral; discussed relation to static HF, TDHF, and scattering calculations.

1979

(1979) Nuclear Physics A. 315, 12, p. 205232 Abstract
A semiclassical theory based on the path integral formalism is applied to the description of Coulomb fission. Complex classical trajectories are used to compute the classically forbidden transitions from the target's ground state to fission. In a simple model the energy spectrum and angular distributions of the fragments are calculated for the Coulomb fission in the Xe + U collision. Theoretical predictions are made which may be checked experimentally.
1978
1977

(1977) Annals of Physics. 108, 1, p. 165197 Abstract
The generalized path expansion scheme is defined for path integration in phasespace. Within this framework we study the semiclassical limits to the propagator, both in the momentum and the coordinate representations. It is shown that the role played by the Morse operator in the Lagrangian formulation of the path integral method is taken by another differential operator of the Dirac type. The relevant properties of this operator are discussed. The semiclassical approximations are obtained by extending the results of catastrophe theory for the asymptotic evaluation of finitedimensional integrals to the domain of path integration. Various forms of the uniform semiclassical approximations are obtained. Their validity and applicability are discussed. The method is illustrated by a solution of a simple example in which nongeneric catastrophe occurs.

(1977) Proceedings of the American Mathematical Society. 65, 2, p. 299302 Abstract
Infinite products of ratios of eigenvalues of SturmLiouville operators are expressed in a closed form in terms of corresponding solutions of initialvalue problems.

(1977) Annals of Physics. 103, 1, p. 198207 Abstract
The expansion of path variations in terms of solutions of Morse's boundary problem is applied in order to evaluate Gaussian path integrals. Together with a recently discovered theorem on infinite products of eigenvalues of SturmLiouville type operators this yields an expression for the most general semiclassical propagator. The properties of the latter are investigated in the light of the Morse theory. The general methods developed here are illustrated by the example of a charged particle moving in a homogeneous magnetic field.
1976

Ribonuclease Speptide. A model for molecular recognition(1976) Journal of Biological Chemistry. 251, 5, p. 13331339 Abstract
The relationship of structure to function in the recognition of ribonuclease Speptide by Sprotein was studied by several methods. Liquid phase peptide synthesis was employed to generate analogs of Speptide in which from 1 to 8 residues were deleted from the NH2terminal end of the Speptide. Additional derivatives were made by substitutions in the NH2terminal three amino acids or by modifying the Speptide analogs by trifluoroacetylation. The analogs were generated in the following way. SPeptide was cleaved with chymotrypsin. The fragment obtained, RNase(920), was purified and lengthened step by step using liquid phase peptide synthesis. A second set of analogs were prepared by cleavage of CF3COSpeptide with elastase and the resulting CF3CORNase(720), similarly lengthened. The various analogs of Speptide were tested in their capacity to combine with Sprotein and regenerate biological activity as measured by Vmax and Kb. This work shows a positive contribution of every one of the first 8 NH2terminal residues of Speptide to the molecular recognition of Sprotein in the presence of RNA substrate. Substitution of the first 3 residues by alanine or blocking of the free amino groups decreases recognition, indicating that the original primary structure is the most favorable one.
1974

(1974) Physics Letters B. 53, 1, p. 3944 Abstract
A uniform semiclassical approach based on the classical limit of Feynman's pathintegral representation is applied for the case of multiple Coulomb excitation. The resulting excitation probabilities are compared with those obtained from the conventional semiclassical treatment and also with the results of the full quantum mechanical coupled channels treatment.