1,550 research outputs found
Quantum Entanglement in the S=1/2 Spin Ladder with Ring Exchange
In this paper we study the concurrence and the block-block entanglement in
the spin ladder with four-spin ring exchange by the exact
diagonalization method of finite cluster of spins. The relationship between the
global phase diagram and the ground-state entanglement is investigated. It is
shown that the block-block entanglement of different block size and geometry
manifests richer information of the system. We find that the extremal point of
the two-site block-block entanglement on the rung locates a transition point
exactly due to SU(4) symmetry at this point. The scaling behavior of the
block-block entanglement is discussed. Our results suggest that the block-block
entanglement can be used as a convenient marker of quantum phase transition in
some complex spin systems.Comment: 5 pages, 7 figure
Weak gravity conjecture in the asymptotical dS and AdS background
The cosmological observations provide a strong evidence that there is a
positive cosmological constant in our universe and thus the spacetime is
asymptotical de Sitter space. The conjecture of gravity as the weakest force in
the asymptotical dS space leads to a lower bound on the U(1) gauge coupling
, or equivalently, the positive cosmological constant gets an upper bound
in order that the U(1) gauge theory can survive in four
dimensions. This result has a simple explanation in string theory, i.e. the
string scale should not be greater than the size of the
cosmic horizon. Our proposal in string theory can be generalized to U(N) gauge
theory and gives a guideline to the microscopic explanation of the de Sitter
entropy. The similar results are also obtained in the asymptotical anti-de
Sitter space.Comment: 4 pages; version for publication in JHEP (title changed
PT Symmetry as a Generalization of Hermiticity
The Hilbert space in PT-symmetric quantum mechanics is formulated as a linear
vector space with a dynamic inner product. The most general PT-symmetric matrix
Hamiltonians are constructed for 2*2 and 3*3 cases. In the former case, the
PT-symmetric Hamiltonian represents the most general matrix Hamiltonian with a
real spectrum. In both cases, Hermitian matrices are shown to be special cases
of PT-symmetric matrices. This finding confirms and strengthens the early
belief that the PT-symmetric quantum mechanics is a generalization of the
conventional Hermitian quantum mechanics.Comment: 13 page
Controlling the spin orientation of photoexcited electrons by symmetry breaking
We study reflection of optically spin-oriented hot electrons as a means to
probe the semiconductor crystal symmetry and its intimate relation with the
spin-orbit coupling. The symmetry breaking by reflection manifests itself by
tipping the net-spin vector of the photoexcited electrons out of the light
propagation direction. The tipping angle and the pointing direction of the
net-spin vector are set by the crystal-induced spin precession, momentum
alignment and spin-momentum correlation of the initial photoexcited electron
population. We examine non-magnetic semiconductor heterostructures and
semiconductor/ferromagnet systems and show the unique signatures of these
effects.Comment: 4 pages, 3 figures, resubmitte
Pituitary Adenylate-Cyclase Activating Polypeptide Regulates Hunger- and Palatability-Induced Binge Eating
While pituitary adenylate cyclase activating polypeptide (PACAP) signaling in the hypothalamic ventromedial nuclei (VMN) has been shown to regulate feeding, a challenge in unmasking a role for this peptide in obesity is that excess feeding can involve numerous mechanisms including homeostatic (hunger) and hedonic-related (palatability) drives. In these studies, we first isolated distinct feeding drives by developing a novel model of binge behavior in which homeostatic-driven feeding was temporally separated from feeding driven by food palatability. We found that stimulation of the VMN, achieved by local microinjections of AMPA, decreased standard chow consumption in food-restricted rats (e.g., homeostatic feeding); surprisingly, this manipulation failed to alter palatable food consumption in satiated rats (e.g., hedonic feeding). In contrast, inhibition of the nucleus accumbens (NAc), through local microinjections of GABA receptor agonists baclofen and muscimol, decreased hedonic feeding without altering homeostatic feeding. PACAP microinjections produced the site-specific changes in synaptic transmission needed to decrease feeding via VMN or NAc circuitry. PACAP into the NAc mimicked the actions of GABA agonists by reducing hedonic feeding without altering homeostatic feeding. In contrast, PACAP into the VMN mimicked the actions of AMPA by decreasing homeostatic feeding without affecting hedonic feeding. Slice electrophysiology recordings verified PACAP excitation of VMN neurons and inhibition of NAc neurons. These data suggest that the VMN and NAc regulate distinct circuits giving rise to unique feeding drives, but that both can be regulated by the neuropeptide PACAP to potentially curb excessive eating stemming from either drive
On the existence and uniqueness of solutions to stochastic differential equations driven by G-Brownian motion with integral-Lipschitz coefficients
In this paper, we study the existence and uniqueness of solutions to
stochastic differential equations driven by G-Brownian motion (GSDEs) with
integral-Lipschitz conditions on their coefficients
Stress Promotes Drug Seeking Through Glucocorticoid-Dependent Endocannabinoid Mobilization in the Prelimbic Cortex
Background
Clinical reports suggest that rather than directly driving cocaine use, stress may create a biological context within which other triggers for drug use become more potent. We hypothesize that stress-induced increases in corticosterone “set the stage” for relapse by promoting endocannabinoid-induced attenuation of inhibitory transmission in the prelimbic cortex (PL).
Methods
We have established a rat model for these stage-setting effects of stress. In this model, neither a stressor (electric footshock) nor stress-level corticosterone treatment alone reinstates cocaine seeking following self-administration and extinction, but each treatment potentiates reinstatement in response to an otherwise subthreshold cocaine priming dose (2.5 mg/kg, intraperitoneal). The contributions of endocannabinoid signaling in the PL to the effects of stress-level corticosterone on PL neurotransmission and cocaine seeking were determined using intra-PL microinfusions. Endocannabinoid-dependent effects of corticosterone on inhibitory synaptic transmission in the rat PL were determined using whole-cell recordings in layer V pyramidal neurons.
Results
Corticosterone application attenuated inhibitory synaptic transmission in the PL via cannabinoid receptor type 1 (CB1R)– and 2-arachidonoylglycerol–dependent inhibition of gamma-aminobutyric acid release without altering postsynaptic responses. The ability of systemic stress-level corticosterone treatment to potentiate cocaine-primed reinstatement was recapitulated by intra-PL injection of corticosterone, the CB1R agonist WIN 55,212-2, or the monoacylglycerol lipase inhibitor URB602. Corticosterone effects on reinstatement were attenuated by intra-PL injections of either the CB1R antagonist, AM251, or the diacylglycerol lipase inhibitor, DO34.
Conclusions
These findings suggest that stress-induced increases in corticosterone promote cocaine seeking by mobilizing 2-arachidonoylglycerol in the PL, resulting in CB1R-mediated attenuation of inhibitory transmission in this brain region
Mass-Varying Massive Gravity
It has recently been shown that the graviton can consistently gain a constant
mass without introducing the Boulware-Deser ghost. We propose a gravity model
where the graviton mass is set by a scalar field and prove that this model is
free of the Boulware-Deser ghost by analyzing its constraint system and showing
that two constraints arise. We also initiate the study of the model's cosmic
background evolution and tentatively discuss possible cosmological implications
of this model. In particular, we consider a simple scenario where the scalar
field setting the graviton mass is identified with the inflaton and the
graviton mass evolves from a high to a low energy scale, giving rise to the
current cosmic acceleration.Comment: 16 page
Observation of an unusual field dependent slow magnetic relaxation and two distinct transitions in a family of new complexes
An unusual field dependent slow magnetic relaxation and two distinct
transitions were observed in a family of new rare earth-transition metal
complexes, [Ln (bipy) (HO) M(CN)] 1.5 (bipy) 4HO (bipy = 2,2'-bipyridine; Ln = Gd,Y; M = Fe,
Co). The novel magnetic relaxation, which is quite different from those
in normal spin glasses and superparamagnets but very resembles qualitatively
those in single-molecule magnet Mn-Ac even if they possess different
structures, might be attributed to the presence of frustration that is
incrementally unveiled by the external magnetic field. The two distinct
transitions in [GdFe] were presumed from DC and AC susceptibility as well as
heat capacity measurements.Comment: Revtex, 6 figure
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