18,562 research outputs found
Features in Evanescent Aharonov-Bohm interferometry
In this work we analyze an Aharonov-Bohm interferometer in the tunneling
regime. In this regime, current magnification effect which arises in presence
of transport currents is absent. A slight modification in the form of a quantum
well incorporated in one of the arms leads to revival of current magnification.
Systematics in magneto-conductance oscillations are observed in this evanescent
wave geometry. In this framework we also see absence of Fano lineshapes in
transmission resonances but once again one can recover these if the direct path
supports propagating modes.Comment: 7 pages, 7 figures. Minor changes made. Accepted for publication in
Phys. Rev.
Current magnification effect in mesoscopic systems at equilibrium
We study the current magnification effect and associated circulating currents
in mesoscopic systems at equilibrium. Earlier studies have revealed that in the
presence of transport current(non-equilibrium situation), circulating currents
can flow in a ring even in the absence of magnetic field. This was attributed
to current magnification which is quantum mechanical in origin. We have shown
that the same effect can be obtained in equilibrium systems, however, in the
presence of magnetic flux. For this we have considered an one-dimensional open
mesoscopic ring connected to a bubble, and the system is in contact with a
single reservoir. We have considered a special case where bubble does not
enclose magnetic flux, yet circulating currents can flow in it due to current
magnification.Comment: 4 pages, 4 figures. Minor corrections made and journal reference
adde
Equilibrium currents in quantum double ring system: A non-trivial role of system-reservoir coupling
Amperes law states that the magnetic moment of a ring is given by current
times the area enclosed. Also from equilibrium statistical mechanics it is
known that magnetic moment is the derivative of free energy with respect to
magnetic field. In this work we analyze a quantum double ring system
interacting with a reservoir. A simple S-Matrix model is used for
system-reservoir coupling. We see complete agreement between the aforesaid two
definitions when coupling between system and reservoir is weak, increasing the
strength of coupling parameter however leads to disagreement between the two.
Thereby signifying the important role played by the coupling parameter in
mesoscopic systems.Comment: 6 pages, 3 figure
The local dayside reconnection rate for oblique interplanetary magnetic fields
We present an analysis of local properties of magnetic reconnection at the
dayside magnetopause for various interplanetary magnetic field (IMF)
orientations in global magnetospheric simulations. This has heretofore not been
practical because it is difficult to locate where reconnection occurs for
oblique IMF, but new techniques make this possible. The approach is to identify
magnetic separators, the curves separating four regions of differing magnetic
topology, which map the reconnection X-line. The electric field parallel to the
X-line is the local reconnection rate. We compare results to a simple model of
local two-dimensional asymmetric reconnection. To do so, we find the plasma
parameters that locally drive reconnection in the magnetosheath and
magnetosphere in planes perpendicular to the X-line at a large number of points
along the X-line. The global magnetohydrodynamic simulations are from the
three-dimensional Block-Adaptive, Tree Solarwind Roe-type Upwind Scheme
(BATS-R-US) code with a uniform resistivity, although the techniques described
here are extensible to any global magnetospheric simulation model. We find that
the predicted local reconnection rates scale well with the measured values for
all simulations, being nearly exact for due southward IMF. However, the
absolute predictions differ by an undetermined constant of proportionality,
whose magnitude increases as the IMF clock angle changes from southward to
northward. We also show similar scaling agreement in a simulation with oblique
southward IMF and a dipole tilt. The present results will be an important
component of a full understanding of the local and global properties of dayside
reconnection.Comment: 12 pages, 7 figures, 1 table, Submitted to Journal Geophysical
Research Space Physics February 12, 2016; Revised April 28, 201
Study of quantum current enhancement, eigenenergy spectra and magnetic moments in a multiply connected system at equilibrium
A multiply connected system in both its open and closed form variations but
in equilibrium is studied using quantum waveguide theory. The system exhibits
remarkable features, in its open form variation we see current enhancement,
hitherto seen only in non-equilibrium systems in absence of magnetic flux. In
its closed form analog parity effects are broken. Further we analyse the global
and local current densities of our system and also show that the orbital
magnetic response of the system calculated from the current densities (and
inherently linked to the topological configuration) is qualitatively not same
as that calculated from the eigenenergy spectra.Comment: 10 pages, 15 figures, 3 table
Proteostasis and ageing: insights from long-lived mutant mice
The global increase in life expectancy is creating significant medical, social and economic challenges to current and future generations. Consequently, there is a need to identify the fundamental mechanisms underlying the ageing process. This knowledge should help develop realistic interventions capable of combatting age-related disease, and thus improving late-life health and vitality. While several mechanisms have been proposed as conserved lifespan determinants, the loss of proteostasis- where proteostasis is defined here as the maintenance of the proteome- appears highly relevant to both ageing and disease. Several studies have shown that multiple proteostatic mechanisms, including the endoplasmic reticulum (ER)-induced unfolded protein response (UPR), the ubiquitin-proteasome system (UPS) and autophagy, all appear indispensable for longevity in many long-lived invertebrate mutants. Similarly, interspecific comparisons suggest that proteostasis may be an important lifespan determinant in vertebrates. Over the last 20 years a number of long-lived mouse mutants have been described, many of which carry single-gene mutations within the growth-hormone, insulin/IGF-1 or mTOR signalling pathways. However, we still do not know how these mutations act mechanistically to increase lifespan and healthspan, and accordingly whether mechanistic commonality occurs between different mutants. Recent evidence supports the premise that the successful maintenance of the proteome during ageing may be linked to the increased lifespan and healthspan of long-lived mouse mutants
Friction and Inertia: Business Change, Corporate Real Estate Portfolios and the U.K. Office Market
It has been asserted that business reorganization and new working practices are transforming the nature of demand for business space. Downsizing, delayering, business process re-engineering and associated initiatives alter the amount, type and location of space required by firms. The literature has neglected the impact of real estate market structures on the ability of organizations to implement these new organizational forms or contemporary working practices successfully. Drawing from research in the United Kingdom, the article demonstrates that, while new working practices are widespread, their impact on the corporate real estate portfolio is less dramatic than often supposed. In part, this is attributed to inflexibility in market structures, which constrains the supply of appropriate space.
Instabilities in Zakharov Equations for Laser Propagation in a Plasma
F.Linares, G.Ponce, J-C.Saut have proved that a non-fully dispersive Zakharov
system arising in the study of Laser-plasma interaction, is locally well posed
in the whole space, for fields vanishing at infinity. Here we show that in the
periodic case, seen as a model for fields non-vanishing at infinity, the system
develops strong instabilities of Hadamard's type, implying that the Cauchy
problem is strongly ill-posed
Role of quantum entanglement due to a magnetic impurity on current magnification effect in mesoscopic open rings
We study the current magnification effect in presence of exchange scattering
of electron from a magnetic impurity placed in one arm of an open mesoscopic
ring. The exchange interaction causes entanglement of electron spin and
impurity spin. Earlier studies have shown that such an entanglement causes
reduction or loss of interference in the Aharonov-Bohm oscillations leading to
decoherence. We find however, that this entanglement, in contradiction to the
naive expectation of a reduction of current magnification, leads to enhancement
as well as suppression of the effect. We also observe additional novel features
like new resonances and current reversals.Comment: 5 pages RevTex, 5 figures include
Instability of fixed, low-thrust drag compensation
FORCED drag compensation using continuous low-thrustpropulsion has been considered for satellites in low Earth orbit. This simple, but nonoptimal, scheme merely requires that the thrust vector is directed opposite to the drag vector and that the magnitude of the two are equal. In principle, the drag force acting on the spacecraft could be determined onboard using accurate accelerometers. However, for small, low-cost spacecraft such sensors may beunavailable. An alternative strategy would be to Ž x the thrust magnitude equal to the expected air drag that would be experienced by the spacecraft. The thrust levelwould be periodically updated based on ground-based orbit determination. In this Engineering Note, it is shown that such a forced circular orbit with a Ž fixed thrust levelis exponentially unstable for all physically reasonable atmosphere models
- …