16,019 research outputs found
The wicked problems of British cities: how New Labour sought to develop a new integrated approach
Strong enhancement of transport by interaction on contact links
Strong repulsive interactions within a one dimensional Fermi system in a
two-probe configuration normally lead to a reduced off-resonance conductance.
We show that if the repulsive interaction extends to the contact regions, a
strong increase of the conductance may occur, even for systems where one would
expect to find a reduced conductance. An essential ingredient in our
calculations is a momentum-space representation of the leads, which allows a
high energy resolution. Further, we demonstrate that these results are
independent of the high-energy cutoff and that the relevant scale is set by the
Fermi velocity.Comment: Published version -- references correcte
Giant coherence in driven systems
We study the noise-induced currents and reliability or coherence of transport
in two different classes of rocking ratchets. For this, we consider the motion
of Brownian particles in the over damped limit in both adiabatic and
non-adiabatic regimes subjected to unbiased temporally symmetric and asymmetric
periodic driving force. In the case of a time symmetric driving, we find that
even in the presence of a spatially symmetric simple sinusoidal potential,
highly coherent transport occurs. These ratchet systems exhibit giant coherence
of transport in the regime of parameter space where unidirectional currents in
the deterministic case are observed. Outside this parameter range, i.e., when
current vanishes in the deterministic regime, coherence in transport is very
low. The transport coherence decreases as a function of temperature and is a
non-monotonic function of the amplitude of driving. The transport becomes
unreliable as we go from the adiabatic to the non-adiabatic domain of
operation.Comment: 15 pages, 9 figures, replaced by the version to appear in JSTA
Pressure study of nematicity and quantum criticality in SrRuO for an in-plane field
We study the relationship between the nematic phases of SrRuO and
quantum criticality. At ambient pressure, one nematic phase is associated with
a metamagnetic quantum critical end point (QCEP) when the applied magnetic
field is near the \textit{c}-axis. We show, however, that this metamagnetic
transition does not produce the same nematic signatures when the QCEP is
reached by hydrostatic pressure with the field applied in the
\textit{ab}-plane. Moreover, a second nematic phase, that is seen for field
applied in the \textit{ab}-plane close to, but not right at, a second
metamagnetic anomaly, persists with minimal change to the highest applied
pressure, 16.55 kbar. Taken together our results suggest that metamagnetic
quantum criticality may not be necessary for the formation of a nematic phase
in SrRuO
How Algorithmic Confounding in Recommendation Systems Increases Homogeneity and Decreases Utility
Recommendation systems are ubiquitous and impact many domains; they have the
potential to influence product consumption, individuals' perceptions of the
world, and life-altering decisions. These systems are often evaluated or
trained with data from users already exposed to algorithmic recommendations;
this creates a pernicious feedback loop. Using simulations, we demonstrate how
using data confounded in this way homogenizes user behavior without increasing
utility
Parity Doubling and SU(2)_L x SU(2)_R Restoration in the Hadron Spectrum
We construct the most general nonlinear representation of chiral SU(2)_L x
SU(2)_R broken down spontaneously to the isospin SU(2), on a pair of hadrons of
same spin and isospin and opposite parity. We show that any such representation
is equivalent, through a hadron field transformation, to two irreducible
representations on two hadrons of opposite parity with different masses and
axial couplings. This implies that chiral symmetry realized in the
Nambu-Goldstone mode does not predict the existence of degenerate multiplets of
hadrons of opposite parity nor any relations between their couplings or masses.Comment: 4 pages, 1 figure; v3: Note added to clarify implications for hadrons
that do not couple to pions: Chiral symmetry can be realized linearly on such
states, leading to parity doubling. To the extent that they are parity
doubled, these hadrons must decouple from pions, a striking prediction that
can be tested experimentally. This applies to the work of L. Glozman and
collaborator
Energetics of rocked inhomogeneous ratchets
We study the efficiency of frictional thermal ratchets driven by finite
frequency driving force and in contact with a heat bath. The efficiency
exhibits varied behavior with driving frequency. Both nonmonotonic and
monotonic behavior have been observed. In particular the magnitude of
efficiency in finite frequency regime may be more than the efficiency in the
adiabatic regime. This is our central result for rocked ratchets. We also show
that for the simple potential we have chosen, the presence of only spatial
asymmetry (homogeneous system) or only frictional ratchet (symmetric potential
profile), the adiabatic efficiency is always more than in the nonadiabatic
case.Comment: 5 figure
Implications of CoGeNT and DAMA for Light WIMP Dark Matter
In this paper, we study the recent excess of low energy events observed by
the CoGeNT collaboration, and discuss the possibility that these events
originate from the elastic scattering of a light (m_DM ~ 5-10 GeV) dark matter
particle. We find that such a dark matter candidate may also be capable of
generating the annual modulation reported by DAMA, as well as the small excess
recently reported by CDMS, without conflicting with the null results from other
experiments, such as XENON10. A dark matter interpretation of the CoGeNT and
DAMA observations favors a region of parameter space that is especially
attractive within the context of Asymmetric Dark Matter models. In such models,
the cosmological dark matter density arises from the baryon asymmetry of the
universe, naturally leading to the expectation that m_DM ~ 1-10 GeV. We also
discuss neutralino dark matter from extended supersymmetric frameworks, such as
the NMSSM. Lastly, we explore the implications of such a dark matter candidate
for indirect searches, and find that the prospects for detecting the neutrino
and gamma ray annihilation products of such a particle to be very encouraging.Comment: 16 pages, 14 figures. v2: references added, fig 4 and surrounding
discussion modified
The Cerebellum and SIDS: Disordered Breathing in a Mouse Model of Developmental Cerebellar Purkinje Cell Loss during Recovery from Hypercarbia.
The cerebellum assists coordination of somatomotor, respiratory, and autonomic actions. Purkinje cell alterations or loss appear in sudden infant death and sudden death in epilepsy victims, possibly contributing to the fatal event. We evaluated breathing patterns in 12 wild-type (WT) and Lurcher mutant mice with 100% developmental cerebellar Purkinje cell loss under baseline (room air), and recovery from hypercapnia, a concern in sudden death events. Six mutant and six WT mice were exposed to 4-min blocks of increasing CO2 (2, 4, 6, and 8%), separated by 4-min recovery intervals in room air. Breath-by-breath patterns, including depth of breathing and end-expiratory pause (EEP) durations during recovery, were recorded. No baseline genotypic differences emerged. However, during recovery, EEP durations significantly lengthened in mutants, compared to WT mice, following the relatively low levels of CO2 exposure. Additionally, mutant mice exhibited signs of post-sigh disordered breathing during recovery following each exposure. Developmental cerebellar Purkinje cell loss significantly affects compensatory breathing patterns following mild CO2 exposure, possibly by inhibiting recovery from elevated CO2. These data implicate cerebellar Purkinje cells in the ability to recover from hypercarbia, suggesting that neuropathologic changes or loss of these cells contribute to inadequate ventilatory recovery to increased environmental CO2. Multiple disorders, including sudden infant death syndrome (SIDS) and sudden unexpected death in epilepsy (SUDEP), appear to involve both cardiorespiratory failure and loss or injury to cerebellar Purkinje cells; the findings support the concept that such neuropathology may precede and exert a prominent role in these fatal events
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