34,103 research outputs found
Effects of External Loads on Human Head Movement Control Systems
The central and reflexive control strategies underlying movements were elucidated by studying the effects of external loads on human head movement control systems. Some experimental results are presented on dynamic changes weigh the addition of aviation helmet (SPH4) and lead weights (6 kg). Intended time-optimal movements, their dynamics and electromyographic activity of neck muscles in normal movements, and also in movements made with external weights applied to the head were measured. It was observed that, when the external loads were added, the subject went through complex adapting processes and the head movement trajectory and its derivatives reached steady conditions only after transient adapting period. The steady adapted state was reached after 15 to 20 seconds (i.e., 5 to 6 movements)
Prospects for Mirage Mediation
Mirage mediation reduces the fine-tuning in the minimal supersymmetric
standard model by dynamically arranging a cancellation between anomaly-mediated
and modulus-mediated supersymmetry breaking. We explore the conditions under
which a mirage "messenger scale" is generated near the weak scale and the
little hierarchy problem is solved. We do this by explicitly including the
dynamics of the SUSY-breaking sector needed to cancel the cosmological
constant. The most plausible scenario for generating a low mirage scale does
not readily admit an extra-dimensional interpretation. We also review the
possibilities for solving the mu/Bmu problem in such theories, a potential
hidden source of fine-tuning.Comment: 14 page
Variational study of a two-level system coupled to a harmonic oscillator in a ultrastrong coupling regime
The nonclassical behaviors of a two-level system coupled to a harmonic
oscillator is investigated in the ultrastrong coupling regime. We revisit the
variational solution of the ground state and find that the existing solution do
not account accurately for nonclassical effects such squeezing. We suggest a
new trial wave function and demonstrate that it has an excellent accuracy on
the quantum correlation effects as well as on energy.Comment: 4 pages; 3 figures; to appear in Phys. Rev.
The Gaugino Code
Gauginos might play a crucial role in the search for supersymmetry at the
Large Hadron Collider (LHC). Mass predictions for gauginos are rather robust
and often related to the values of the gauge couplings. We analyse the ratios
of gaugino masses in the LHC energy range for various schemes of supersymmetry
breakdown and mediation. Three distinct mass patterns emerge.Comment: 42 pages, Latex; a discussion of deflected anomaly mediation added,
references adde
Partial scaling transform of multiqubit states as a criterion of separability
The partial scaling transform of the density matrix for multiqubit states is
introduced to detect entanglement of quantum states. The transform contains
partial transposition as a special case. The scaling transform corresponds to
partial time scaling of subsystem (or partial Planck's constant scaling) which
was used to formulate recently separability criterion for continous variables.A
measure of entanglement which is a generalization of negativity measure is
introduced being based on tomographic probability description of spin states.Comment: 16 pages, 5 figures, submitted to J. Phys. A: Math. Ge
Kondo resonance of a Co atom exchange coupled to a ferromagnetic tip
The Kondo effect of a Co atom on Cu(100) was investigated with a
low-temperature scanning tunneling microscope using a monoatomically sharp
nickel tip. Upon a tip-Co contact, the differential conductance spectra exhibit
a spin-split asymmetric Kondo resonance. The computed ab initio value of the
exchange coupling is too small to suppress the Kondo effect, but sufficiently
large to produce the splitting observed. A quantitative analysis of the line
shape using the numerical renormalization group technique indicates that the
junction spin polarization is weak.Comment: 5 pages, 4 figure
Weibull-type limiting distribution for replicative systems
The Weibull function is widely used to describe skew distributions observed
in nature. However, the origin of this ubiquity is not always obvious to
explain. In the present paper, we consider the well-known Galton-Watson
branching process describing simple replicative systems. The shape of the
resulting distribution, about which little has been known, is found essentially
indistinguishable from the Weibull form in a wide range of the branching
parameter; this can be seen from the exact series expansion for the cumulative
distribution, which takes a universal form. We also find that the branching
process can be mapped into a process of aggregation of clusters. In the
branching and aggregation process, the number of events considered for
branching and aggregation grows cumulatively in time, whereas, for the binomial
distribution, an independent event occurs at each time with a given success
probability.Comment: 6 pages and 5 figure
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Neuronal SIRT1 Regulates Metabolic and Reproductive Function and the Response to Caloric Restriction.
Sirt1 is an NAD-dependent, class III deacetylase that functions as a cellular energy sensor. In addition to its well-characterized effects in peripheral tissues, emerging evidence suggests that neuronal Sirt1 activity plays a role in the central regulation of energy balance and glucose metabolism. In this study, we generated mice expressing an enzymatically inactive form (N-MUT) or wild-type (WT) SIRT1 (N-OX) in mature neurons. N-OX male and female mice had impaired glucose tolerance, and N-MUT female, but not male, mice had improved glucose tolerance compared with that of WT littermates. Furthermore, glucose tolerance was improved in all mice with caloric restriction (CR) but was greater in the N-OX mice, who had better glucose tolerance than their littermates. At the reproductive level, N-OX females had impaired estrous cycles, with increased cycle length and more time in estrus. LH and progesterone surges were absent on the evening of proestrus in the N-OX mice, suggesting a defect in spontaneous ovulation, which was confirmed by the ovarian histology revealing fewer corpora lutea. Despite this defect, the mice were still fertile when mated to WT mice on the day of proestrus, indicating that the mice could respond to normal pheromonal or environmental cues. When subjected to CR, the N-OX mice went into diestrus arrest earlier than their littermates. Together, these results suggested that the overexpression of SIRT1 rendered the mice more sensitive to the metabolic improvements and suppression of reproductive cycles by CR, which was independent of circadian rhythms
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