2,906 research outputs found
Molecular gyroscopes and biological effects of weak ELF magnetic fields
Extremely-low-frequency magnetic fields are known to affect biological
systems. In many cases, biological effects display `windows' in biologically
effective parameters of the magnetic fields: most dramatic is the fact that
relatively intense magnetic fields sometimes do not cause appreciable effect,
while smaller fields of the order of 10--100 T do. Linear resonant
physical processes do not explain frequency windows in this case. Amplitude
window phenomena suggest a nonlinear physical mechanism. Such a nonlinear
mechanism has been proposed recently to explain those `windows'. It considers
quantum-interference effects on protein-bound substrate ions. Magnetic fields
cause an interference of ion quantum states and change the probability of
ion-protein dissociation. This ion-interference mechanism predicts specific
magnetic-field frequency and amplitude windows within which biological effects
occur. It agrees with a lot of experiments. However, according to the
mechanism, the lifetime of ion quantum states within a protein
cavity should be of unrealistic value, more than 0.01 s for frequency band
10--100 Hz. In this paper, a biophysical mechanism has been proposed that (i)
retains the attractive features of the ion interference mechanism and (ii) uses
the principles of gyroscopic motion and removes the necessity to postulate
large lifetimes. The mechanism considers dynamics of the density matrix of the
molecular groups, which are attached to the walls of protein cavities by two
covalent bonds, i.e., molecular gyroscopes. Numerical computations have shown
almost free rotations of the molecular gyros. The relaxation time due to van
der Waals forces was about 0.01 s for the cavity size of 28 angstr\"{o}ms.Comment: 10 pages, 7 figure
Accretion Disks and Dynamos: Toward a Unified Mean Field Theory
Conversion of gravitational energy into radiation in accretion discs and the
origin of large scale magnetic fields in astrophysical rotators have often been
distinct topics of research. In semi-analytic work on both problems it has been
useful to presume large scale symmetries, necessarily resulting in mean field
theories. MHD turbulence makes the underlying systems locally asymmetric and
nonlinear. Synergy between theory and simulations should aim for the
development of practical mean field models that capture essential physics and
can be used for observational modeling. Mean field dynamo (MFD) theory and
alpha-viscosity accretion theory exemplify such ongoing pursuits. 21st century
MFD theory has more nonlinear predictive power compared to 20th century MFD
theory, whereas accretion theory is still in a 20th century state. In fact,
insights from MFD theory are applicable to accretion theory and the two are
artificially separated pieces of what should be a single theory. I discuss
pieces of progress that provide clues toward a unified theory. A key concept is
that large scale magnetic fields can be sustained via local or global magnetic
helicity fluxes or via relaxation of small scale magnetic fluctuations, without
the kinetic helicity driver of 20th century textbooks. These concepts may help
explain the formation of large scale fields that supply non-local angular
momentum transport via coronae and jets in a unified theory of accretion and
dynamos. In diagnosing the role of helicities and helicity fluxes in disk
simulations, each disk hemisphere should be studied separately to avoid being
misled by cancelation that occurs as a result of reflection asymmetry. The
fraction of helical field energy in disks is expected to be small compared to
the total field in each hemisphere as a result of shear, but can still be
essential for large scale dynamo action.Comment: For the Proceedings of the Third International Conference and
Advanced School "Turbulent Mixing and Beyond," TMB-2011 held on 21 - 28
August 2011 at the Abdus Salam International Centre for Theoretical Physics,
Trieste, http://users.ictp.it/~tmb/index2011.html Italy, To Appear in Physica
Scripta (corrected small items to match version in print
Closure tests for mean field magnetohydrodynamics using a self consistent reduced model
The mean electromotive force and alpha effect are computed for a forced
turbulent flow using a simple nonlinear dynamical model. The results are used
to check the applicability of two basic analytic ansatze of mean-field
magnetohydrodynamics - the second order correlation approximation (SOCA) and
the tau approximation. In the numerical simulations the effective Reynolds
number Re is 2-20, while the magnetic Prandtl number varies from 0.1 to
. We present evidence that the approximation may be appropriate
in dynamical regimes where there is a small-scale dynamo. Catastrophic
quenching of the effect is found for high . Our results
indicate that for high SOCA gives a very large value of the
coefficient compared with the ``exact'' solution. The discrepancy depends on
the properties of the random force that drives the flow, with a larger
difference occuring for -correlated force compared with that for a
steady random force.Comment: submitted to MNRA
Different Approaches to Managerial Support for Flexible Working: Implications for Public Sector Employee Well-Being
Improving well-being is an important human resource management issue within public sector organizations as it is linked with improved employee and organizational outcomes. A key antecedent to employee well-being is work–life balance, which can be supported or impeded by flexible working. The extent to which flexible working supports work–life balance and, ultimately, well-being depends on how flexible working is implemented, where managers play a central role. Managers can enable work–life balance by providing employees with work-family-specific support, which incorporates a range of behaviors, including facilitating access to flexible working. However, research to date says little about how and why managers engage in these behaviors and whether this differs within the same organizational context. This article addresses this gap, presenting four approaches to managerial support for flexible working: unconditional support, performance contingent support, no support, and support based upon the approval of others (transfer responsibility). It explores the reasons for each approach through the lens of Conservation of Resources (COR) theory. It suggests that different approaches create the potential for employee well-being to vary considerably within the same organizational and team context. These findings inform how to support and manage flexible working arrangements in ways that optimize well-being in the public sector
Twisted plasma waves driven by twisted ponderomotive force
We present results of twisted plasma waves driven by twisted ponderomotive
force. With beating of two, co-propagating, Laguerre-Gaussian (LG) orbital
angular momentum (OAM) laser pulses with different frequencies and also
different twist indices, we can get twisted ponderomotive force.
Three-dimensional particle-in-cell simulations are used to demonstrate the
twisted plasma waves driven by lasers. The twisted plasma waves have an
electron density perturbation with a helical rotating structure. Different from
the predictions of the linear fluid theory, the simulation results show a
nonlinear rotating current and a static axial magnetic field. Along with the
rotating current is the axial OAM carried by particles in the twisted plasma
waves. Detailed theoretical analysis of twisted plasma waves is given too
A novel profiling concept leading to a significant increase in the mechanical performance of metal to composite joints
In this work, we designed metal-CFRP joints with a profiled adherend termination to improve the mechanical performance. We have applied several profiles to the edge of titanium adherends which were adhesively bonded to CFRP substrates. We conducted finite element modelling and experimental 4PB (4-Point-Bend) testing to investigate how the geometry of the adherend edge profile effects the mechanical performance of the joint. This work shows that profiling of the metal adherend can result in increases of at least 27% in the peak load, and of at least 272% in the energy dissipated up to critical failure normalised by the mechanical energy
Ohm's Law for a Relativistic Pair Plasma
We derive the fully relativistic Ohm's law for an electron-positron plasma.
The absence of non-resistive terms in Ohm's law and the natural substitution of
the 4-velocity for the velocity flux in the relativistic bulk plasma equations
do not require the field gradient length scale to be much larger than the
lepton inertial lengths, or the existence of a frame in which the distribution
functions are isotropic.Comment: 12 pages, plain TeX, Phys. Rev. Lett. 71 3481 (1993
Disordered Correlated Kondo-lattice model
We propose a self-consistent approximate solution of the disordered
Kondo-lattice model (KLM) to get the interconnected electronic and magnetic
properties of 'local-moment' systems like diluted ferromagnetic semiconductors.
Aiming at compounds, where magnetic (M) and non-magnetic (A)
atoms distributed randomly over a crystal lattice, we present a theory which
treats the subsystems of itinerant charge carriers and localized magnetic
moments in a homologous manner. The coupling between the localized moments due
to the itinerant electrons (holes) is treated by a modified RKKY-theory which
maps the KLM onto an effective Heisenberg model. The exchange integrals turn
out to be functionals of the electronic selfenergy guaranteeing selfconsistency
of our theory. The disordered electronic and magnetic moment systems are both
treated by CPA-type methods.
We discuss in detail the dependencies of the key-terms such as the long range
and oscillating effectice exchange integrals, 'the local-moment' magnetization,
the electron spin polarization, the Curie temperature as well as the electronic
and magnonic quasiparticle densities of states on the concentration of
magnetic ions, the carrier concentration , the exchange coupling , and
the temperature. The shape and the effective range of the exchange integrals
turn out to be strongly -dependent. The disorder causes anomalies in the
spin spectrum especially in the low-dilution regime, which are not observed in
the mean field approximation.Comment: Accepted by JMM
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