6,422 research outputs found
Nonlinear superhorizon perturbations in Horava-Lifshitz gravity
We perform a fully nonlinear analysis of superhorizon perturbation in
Ho\v{r}ava-Lifshitz gravity, based on the gradient expansion method. We present
a concrete expression for the solution of gravity equations up to the second
order in the gradient expansion, and prove that the solution can be extended to
any order. The result provides yet another example for analogue of the
Vainshtein effect: the nonlinear solution is regular in the limit and recovers general relativity coupled to dark matter at low energy.
Finally, we propose a definition of nonlinear curvature perturbation
in Ho\v{r}ava-Lifshitz gravity and show that it is conserved up to the first
order in the gradient expansion.Comment: 11 page
Superluminal Propagation and Acausality of Nonlinear Massive Gravity
Massive gravity is an old idea: trading geometry for mass. Much effort has
been expended on establishing a healthy model, culminating in the current
ghost-free version. We summarize here our recent findings -- that it is still
untenable -- because it is locally acausal: CTC solutions can be constructed in
a small neighborhood of any event.Comment: Contribution to Conference in Honour of the 90th Birthday of Freeman
Dyson -- To Appear in Proceeding. v2: Explicit CTC example, and other
improvements, adde
Entanglement of Indistinguishable Particles
We present a general criterion for entanglement of N indistinguishable
particles decomposed into arbitrary s subsystems based on the unambiguous
measurability of correlation. Our argument provides a unified viewpoint on the
entanglement of indistinguishable particles, which is still unsettled despite
various proposals made mainly for the s = 2 case. Even though entanglement is
defined only with reference to the measurement setup, we find that the
so-called i.i.d. states form a special class of bosonic states which are
universally separable.Comment: 6 pages, 3 figures, major revisio
Midazolam inhibits hippocampal long-term potentiation and learning through dual central and peripheral benzodiazepine receptor activation and neurosteroidogenesis
Benzodiazepines (BDZs) enhance GABA(A) receptor inhibition by direct actions on central BDZ receptors (CBRs). Although some BDZs also bind mitochondrial receptors [translocator protein (18 kDa) (TSPO)] and promote the synthesis of GABA-enhancing neurosteroids, the role of neurosteroids in the clinical effects of BDZs is unknown. In rat hippocampal slices, we compared midazolam, an anesthetic BDZ, with clonazepam, an anticonvulsant/anxiolytic BDZ that activates CBRs selectively. Midazolam, but not clonazepam, increased neurosteroid levels in CA1 pyramidal neurons without changing TSPO immunostaining. Midazolam, but not clonazepam, also augmented a form of spike inhibition after stimulation adjacent to the pyramidal cell layer and inhibited induction of long-term potentiation. These effects were prevented by finasteride, an inhibitor of neurosteroid synthesis, or 17PA [17-phenyl-(3α,5α)-androst-16-en-3-ol], a blocker of neurosteroid effects on GABA(A) receptors. Moreover, the synaptic effects were mimicked by a combination of clonazepam with FGIN (2-[2-(4-fluorophenyl)-1H-indol-3-yl]-N,N-dihexylacetamide), a selective TSPO agonist, or a combination of clonazepam with exogenous allopregnanolone. Consistent with these in vitro results, finasteride abolished the effects of midazolam on contextual fear learning when administrated 1 d before midazolam injection. Thus, dual activation of CBRs and TSPO appears to result in unique actions of clinically important BDZs. Furthermore, endogenous neurosteroids are shown to be important regulators of pyramidal neuron function and synaptic plasticity
Final Evolution and Delayed Explosions of Spinning White Dwarfs in Single Degenerate Models for Type Ia Supernovae
We study the occurrence of delayed SNe~Ia in the single degenerate (SD)
scenario. We assume that a massive carbon-oxygen (CO) white dwarf (WD) accretes
matter coming from a companion star, making it to spin at the critical rate. We
assume uniform rotation due to magnetic field coupling. The carbon ignition
mass for non-rotating WDs is M_{ig}^{NR} \approx 1.38 M_{\odot}; while for the
case of uniformly rotating WDs it is a few percent larger (M_{ig}^{R} \approx
1.43 M_{\odot}). When accretion rate decreases, the WD begins to lose angular
momentum, shrinks, and spins up; however, it does not overflow its critical
rotation rate, avoiding mass shedding. Thus, angular momentum losses can lead
the CO WD interior to compression and carbon ignition, which would induce an
SN~Ia. The delay, largely due to the angular momentum losses timescale, may be
large enough to allow the companion star to evolve to a He WD, becoming
undetectable at the moment of explosion. This scenario supports the occurrence
of delayed SNe~Ia if the final CO WD mass is 1.38 M_{\odot} < M < 1.43
M_{\odot}. We also find that if the delay is longer than ~3 Gyr, the WD would
become too cold to explode, rather undergoing collapse.Comment: 6 pages, 5 figures, published in the Astrophysical Journal Letters,
809, L6 (2015), added some corrections for errat
Sense of Self in Baby Chimpanzees
Philippe Rochat and his colleague tentatively proposed that young infants' propensity to engage in self-perception and systematic exploration of the perceptual consequences of their own action plays and is probably at the origin of an early sense of self: the ecological self. Rochat and Hespos (1997) reported that neonates discriminate between external and self-stimulation. Neonate tended to display significantly more rooting responses (i.e., head turn towards the stimulation with mouth open and tonguing) following external compared to self-stimulation. Rochat et al. (1998) also reported that 2-month-olds showed clear sign of modulation of their oral activity on the pacifier as a function of analog versus non-analog condition. Rochat and his colleague concluded that these observations are interpreted as evidence of self-exploration and the emergence of a sense of self-agency by 2-month-olds. We tried to replicate these findings in infant chimpanzees. We observed rooting responses of three baby chimpanzees in two condition, self-stimulation and external stimulation. In external stimulation condition, the index finger of the experimenter or small stick touched one of the infant's cheeks. In self-stimulation condition, the experimenter took infant's hand and touched his or her cheek with their fingers. In Rochat and Hespos, they recorded and analyzed several measures such as state, head movement, mouth activity and so on. How ever, we analyzed only mouth activities tentatively. We found infant chimpanzees tended to show more rooting responses following external stimulation compared to self-stimulation as well as human infants.
We also carried out sucking experiment with two baby chimpanzees. The experimenter held the pacifier and put the artificial nipple into the infant's mouth. A session started when the infant take the nipple inside the his or her mouth. Auditory stimulus, which was a complex tone comprised of six harmonics with equal intensity, was given to the chimpanzee according to the test condition during their sucking. There were four test conditions and each condition consisted with three types of feedback as follows: 1) silent baseline, contingent, and steady, 2) contingent baseline, 1-sec delay, and 3-sec delay, 3) contingent baseline, 6-sec delay, and 12-sec delay, 4) contingent baseline, 1/2 efficiency, and 1/4 efficiency. In test 1, one infant chimpanzee showed decrease of the minimum pressure of sucking in the contingent condition. In test 2, one subject showed shorter intervals of sucking in 3-sec delay condition. This seems to be similar to human infant's. We may be able to postulate ecological self in baby chimpanzees according to the self-exploration. In test 3 and 4, we did not obtain any effects of stimulus conditions. Results of these studies. These studies were conducted as the parts of the chimpanzee development project in Primate Research Institute, Kyoto University, organized by Professor Tetsuro Matsuzawa
Correlation between Tc and Lattice Parameters of Novel Superconducting NaxCoO2 yH2O
We synthesized the five batches of the samples of the novel P3 type
superconductor, Na(HO)CoOHO, by the
soft chemical process starting from -NaCoO. The chemical and
structural properties varied rather widely from batch to batch, with a result
that varied from 4.6 K to 3.2 K. The magnetic susceptibility above
shows upturn at low temperature as in the case of the P2 phase. The
seems to be well correlated to the lattice parameters.Comment: 2 pages, 2 figures, and 1 table, to be published in J. Phys. Soc.
Jpn. 73 (9) with possible minor revision
Classification of minimal actions of a compact Kac algebra with amenable dual
We show the uniqueness of minimal actions of a compact Kac algebra with
amenable dual on the AFD factor of type II. This particularly implies the
uniqueness of minimal actions of a compact group. Our main tools are a Rohlin
type theorem, the 2-cohomology vanishing theorem, and the Evans-Kishimoto type
intertwining argument.Comment: 68 pages, Introduction rewritten; minor correction
Correlation, Breit and Quantum Electrodynamics effects on energy level and transition properties of W ion
The electron correlation effects and Breit interaction as well as Quantum
Electro-Dynamics (QED) effects were expected to have important contribution to
the energy level and transition properties of heavy highly charged ions. The
ground states [Ne] and first excited states
[Ne]3s of W ion have been studied by using
Multi-Configuration Dirac-Fock method with the implementation of Grasp2K
package. A restricted active space was employed to investigate the correlation
contribution from different models. The Breit interaction and QED effects were
taken into account in the relativistic configuration interaction calculation
with the converged wavefunction. It is found that the correlation contribution
from 3s and 3p orbital have important contribution to the energy level,
transition wavelength and probability of the ground and the first excited state
of W ion
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