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Articles 1 - 19 of 19

Full-Text Articles in Physics

Magnetotaxis And Magnetic Particles In Bacteria, Richard B. Frankel, Dennis A. Bazylinski Dec 1994

Magnetotaxis And Magnetic Particles In Bacteria, Richard B. Frankel, Dennis A. Bazylinski

Physics

Magnetotactic bacteria contain magnetic particles that constitute a permanent magnetic dipole and cause each cell to orient and migrate along geomagnetic field lines. Recent results relevant to the biomineralization process and to the function of magnetotaxis are discussed.


Mössbauer Spectroscopic And Magnetic Studies Of Magnetoferritin, Q. A. Pankhurst, S. Betteridge, D. P. E. Dickson, T. Douglas, Stephen Mann, Richard B. Frankel Dec 1994

Mössbauer Spectroscopic And Magnetic Studies Of Magnetoferritin, Q. A. Pankhurst, S. Betteridge, D. P. E. Dickson, T. Douglas, Stephen Mann, Richard B. Frankel

Physics

Mössbauer spectroscopic and magnetic measurements have been made on a novel magnetic protein produced by the controlled reconstitution of ferritin. The data indicate that the predominant mineral form in the iron-containing cores is maghemite (γ-Fe2O3) rather than magnetite (Fe3O4).


Iron Core Formation In Horse Spleen Ferritin: Magnetic Susceptibility, Ph, And Compositional Studies, S. Hilty, B. Webb, Richard B. Frankel, G. D. Watt Nov 1994

Iron Core Formation In Horse Spleen Ferritin: Magnetic Susceptibility, Ph, And Compositional Studies, S. Hilty, B. Webb, Richard B. Frankel, G. D. Watt

Physics

Horse spleen ferritin (HoSF) reconstituted with small iron cores ranging in size from 8 to 500 iron atoms was studied by magnetic susceptibility and pH measurements to determine when the added Fe3+ begins to aggregate and form antiferromagnetically coupled clusters and also to determine the hydrolytic state of the iron at low iron loading. The Evans NMR magnetic susceptibility measurements showed that at iron loadings as low as 8 Fe3+/HoSF, at least half of the added iron atoms were involved in antiferromagnetic exchange interactions and the other half were present as isolated iron atoms with S = 5 ...


Particle Conjugation And The 1/N_C Corrections To G_A, Joseph Schechter, H. Weigel Oct 1994

Particle Conjugation And The 1/N_C Corrections To G_A, Joseph Schechter, H. Weigel

Physics

We impose the requirement that the isovector axial vector current for the soliton sector of the chiral quark model transforms correctly under particle conjugation. This forces us to choose an otherwise arbitrary ordering of collective space operators in such a way that the next--to--leading 1/N_C correction to g_A vanishes.


Excited Heavy Baryons In The Bound State Picture, Joseph Schechter, Anand Subbaraman Oct 1994

Excited Heavy Baryons In The Bound State Picture, Joseph Schechter, Anand Subbaraman

Physics

The orbitally excited heavy quark baryons are studied in the Callan Klebanov bound state model with heavy spin symmetry. First, a compact description of the large N_c, infinite heavy quark mass bound state wavefunctions and the collective quantization is given. In order to study the kinematical corrections due to finite masses we motivate an approximate Schrodinger-like equation for the bound state. The effective potential in this equation is compared with the quadratic approximation (spherical harmonic oscillator) to it. This oscillator approximation is seen to be not very accurate. It is noted that the present experimental information cannot be even qualitatively ...


Interface Motion In Random Media At Finite Temperature, Lee-Wen Chen, M. Cristina Marchetti Aug 1994

Interface Motion In Random Media At Finite Temperature, Lee-Wen Chen, M. Cristina Marchetti

Physics

We have studied numerically the dynamics of a driven elastic interface in a random medium, focusing on the thermal rounding of the depinning transition and on the behavior in the

T = 0 pinned phase. Thermal effects are quantitatively more important than expected from simple dimensional estimates. For sufficient low temperature the creep velocity at a driving force equal to the T = 0 depinning force exhibits a power-law dependence on T, in agreement with earlier theoretical and numerical predictions for CDW’s. We have also examined the dynamics in the T = 0 pinned phase resulting from slowly increasing the driving force ...


Non-Perturbative Renormalization Group Flows In Two-Dimensional Quantum Gravity, Simon Catterall, Ray L. Renken, John B. Kogut Aug 1994

Non-Perturbative Renormalization Group Flows In Two-Dimensional Quantum Gravity, Simon Catterall, Ray L. Renken, John B. Kogut

Physics

Recently a block spin renormalization group approach was proposed for the dynamical triangulation formulation of two-dimensional quantum gravity. We use this approach to examine non-perturbatively a particular class of higher derivative actions for pure gravity.


Self-Organized Criticality In Non-Conserved Systems, Alan Middleton, Chao Tang Jul 1994

Self-Organized Criticality In Non-Conserved Systems, Alan Middleton, Chao Tang

Physics

The origin of self-organized criticality in a model without conservation law (Olami, Feder, and Christensen, Phys. Rev. Lett. {\bf 68}, 1244 (1992)) is studied. The homogeneous system with periodic boundary condition is found to be periodic and neutrally stable. A change to open boundaries results in the invasion of the interior by a ``self-organized'' region. The mechanism for the self-organization is closely related to the synchronization or phase-locking of the individual elements with each other. A simplified model of marginal oscillator locking on a directed lattice is used to explain many of the features in the non-conserved model: in particular ...


Twin-Boundary Pinning Of Superconducting Vortex Arrays, M. Cristina Marchetti, Valerii M. Vinokur Jul 1994

Twin-Boundary Pinning Of Superconducting Vortex Arrays, M. Cristina Marchetti, Valerii M. Vinokur

Physics

We discuss the low-temperature dynamics of magnetic flux lines in high-temperature superconductors in the presence of a family of parallel twin planes that contain the $c$ axis. A current applied along the twin planes drives flux motion in the direction transverse to the planes and acts like an electric field applied to {\it one-dimensional} carriers in disordered semiconductors. As in flux arrays with columnar pins, there is a regime where the dynamics is dominated by superkink excitations that correspond to Mott variable range hopping (VRH) of carriers. In one dimension, however, rare events, such as large regions void of twin ...


Comparison Of Magnetic Properties Of Polysaccharide Iron Complex (P.I.C.) And Ferritin, M. E. Y. Mohie-Eldin, Richard B. Frankel, L. Gunther Jul 1994

Comparison Of Magnetic Properties Of Polysaccharide Iron Complex (P.I.C.) And Ferritin, M. E. Y. Mohie-Eldin, Richard B. Frankel, L. Gunther

Physics

The synthetic polysaccharide iron complex (PIC) molecule has been suggested as a ‘biomimic’, i.e. a counterpart, to the naturally occurring biological molecule ferritin with respect to its magnetic properties based on the identification of ferrihydrite as the major mineral in both. Magnetization measurements were used to investigate the magnetic properties of PIC in relation to those of ferritin, as well as to identify differences in such properties between naturally occurring ferritin, which we designate here as Ferritin I, and ferritin with an artificially high content of Fe2+ ions bound to its core, which is designated here as Ferritin ...


Heavy Meson Radiative Decays And Light Vector Meson Dominance, Joseph Schechter, Pankaj Jain, Arshad Momen Jun 1994

Heavy Meson Radiative Decays And Light Vector Meson Dominance, Joseph Schechter, Pankaj Jain, Arshad Momen

Physics

Electromagnetic interactions are introduced in the effective chiral Lagrangian for heavy mesons which includes light vector particles. A suitable notion of vector meson dominance is formulated. The constraints on the heavy meson -light vector and heavy meson-light pseudoscalar coupling constants are obtained using experimental D^* \ra D \, \gamma branching ratios. These constraints are compared with values estimated from semi-leptonic transition amplitudes as well as from extension of the light meson coupling pattern. Application to the heavy baryon spectrum in the ``bound state " model is made.


Low-Temperatures Vortex Dynamics In Twinned Superconductors, M. Cristina Marchetti, Valerii M. Vinokur May 1994

Low-Temperatures Vortex Dynamics In Twinned Superconductors, M. Cristina Marchetti, Valerii M. Vinokur

Physics

We discuss the low-temperature dynamics of magnetic flux lines in samples with a family of parallel twin planes. A current applied along the twin planes drives flux motion in the direction transverse to the planes and acts like an electric field applied to {\it one-dimensional} carriers in disordered semiconductors. As in flux arrays with columnar pins, there is a regime where the dynamics is dominated by superkink excitations that correspond to Mott variable range hopping (VRH) of carriers. In one dimension, however, rare events, such as large regions void of twin planes, can impede VRH and dominate transport in samples ...


Ac Response Of The Flux-Line Liquid In High-Tc Superconductors, Lee-Wen Chen, M. Cristina Marchetti May 1994

Ac Response Of The Flux-Line Liquid In High-Tc Superconductors, Lee-Wen Chen, M. Cristina Marchetti

Physics

We use a hydrodynamics theory to discuss the response of a viscous flux-line liquid to an ac perturbation applied at the surface of the sample. The theory incorporates viscoelastic effects and describes the crossover between liquid-like and solid-like response of the vortex array as the frequency of the perturbation increases. A large viscosity from flux-line interactions and entanglement leads to viscous screening of surface fields. As a result, two frequency-dependent length scales are needed to describe the penetration of an ac field. For large viscosities the imaginary part of the ac permeability can exihibit, in addition to the well-know peak ...


Possible Extension Of The Chiral Perturbation Theory Program, Joseph Schechter Apr 1994

Possible Extension Of The Chiral Perturbation Theory Program, Joseph Schechter

Physics

After a brief discussion of how chiral dynamics has evolved from the ``universal V-A theory of weak interactions'', we present some evidence that symmetry breaking for the vector meson multiplet is not simpler than but rather analogous to that for the pseudoscalar multiplet. This provides a motivation for speculating on how to extend in a systematic way the chiral perturbation theory program to include vectors.


On The Absence Of An Exponential Bound In Four Dimensional Simplicial Gravity, Simon Catterall, John B. Kogut, R. Renken Mar 1994

On The Absence Of An Exponential Bound In Four Dimensional Simplicial Gravity, Simon Catterall, John B. Kogut, R. Renken

Physics

We have studied a model which has been proposed as a regularisation for four dimensional quantum gravity. The partition function is constructed by performing a weighted sum over all triangulations of the four sphere. Using numerical simulation we find that the number of such triangulations containing V simplices grows faster than exponentially with V. This property ensures that the model has no thermodynamic limit.


Tunneling Into Granular Pb Films In The Superconducting And Insulating Regimes, Richard P. Barber Jr., L. Merchant, Porta Arthur La, Robert C. Dynes Feb 1994

Tunneling Into Granular Pb Films In The Superconducting And Insulating Regimes, Richard P. Barber Jr., L. Merchant, Porta Arthur La, Robert C. Dynes

Physics

Tunneling measurements have been performed on both sides of the insulator-superconductor transition in quench-condensed granular Pb films. The results indicate that the Pb film consists of fully superconducting grains with essentially bulk values for the superconducting energy gap and transition temperature, even when the film exhibits insulating behavior in transport measurements. The density of states inferred from measurements in perpendicular magnetic field are consistent with magnetic spin-flip broadening.


Phase Structure Of Four Dimensional Simplicial Quantum Gravity, Simon Catterall, John B. Kogut, R. Renken Jan 1994

Phase Structure Of Four Dimensional Simplicial Quantum Gravity, Simon Catterall, John B. Kogut, R. Renken

Physics

We present the results of a high statistics Monte Carlo study of a model for four dimensional euclidean quantum gravity based on summing over triangulations. We show evidence for two phases; in one there is a logarithmic scaling on the mean linear extent with volume, whilst the other exhibits power law behaviour with exponent 1/2. We are able to extract a finite size scaling exponent governing the growth of the susceptibility peak


Heavy Quark Solitons: Strangeness And Symmetry Breaking, Joseph Schechter, Arshad Momen, Anand Subbaraman Jan 1994

Heavy Quark Solitons: Strangeness And Symmetry Breaking, Joseph Schechter, Arshad Momen, Anand Subbaraman

Physics

We discuss the generalization of the Callan-Klebanov model to the case of heavy quark baryons. The light flavor group is considered to be SU(3) and the limit of heavy spin symmetry is taken. The presence of the Wess-Zumino-Witten term permits the neat development of a picture , at the collective level, of a light diquark bound to a ``heavy" quark with decoupled spin degree of freedom. The consequences of SU(3) symmetry breaking are discussed in detail. We point out that the SU(3) mass splittings of the heavy baryons essentially measure the ``low energy" physics once more and that ...


Gravity And Electromagnetism In Noncommutative Geometry, Giovanni Landi, Nguyen Ai Viet, Kameshwar C. Wali Jan 1994

Gravity And Electromagnetism In Noncommutative Geometry, Giovanni Landi, Nguyen Ai Viet, Kameshwar C. Wali

Physics

We present a unified description of gravity and electromagnetism in the framework of a Z 2 non-commutative differential calculus. It can be considered as a “discrete version” of Kaluza-Klein theory, where the fifth continuous dimension is replaced by two discrete points. We derive an action which coincides with the dimensionally reduced one of the ordinary Kaluza-Klein theory.