1,981 research outputs found
Wandering globular clusters: the first dwarf galaxies in the universe?
In the last decade we witness an advent of new types of dwarf stellar systems
in cluding ultra-compact dwarfs, ultra-faint dwarf spheroidals, and exotic
globular clusters, breaking the old simple paradigm for dwarf galaxies and
globular clusters. These objects become more intriguing, and understanding of
these new findings be comes more challenging. Recently we discovered a new type
of large scale structure in the Virgo cluster of galaxies: it is composed of
globular clusters. Globular clusters in Virgo are found wandering between
galaxies (intracluster globular clusters) as well as in galaxies. These
intracluster globular clusters fill a significant fraction in the area of the
Virgo cluster and they are dominated by blue globular clusters. These
intracluster globular clusters may be closely related with the first dwarf
galaxies in the universe.Comment: 6 pages, 3 figures, Conference Proceedings: "A Universe of Dwarf
Galaxies", 14-18 June 2010, Lyon, Franc
Phonon effects in molecular transistors: Quantum and classical treatment
We present a comprehensive theoretical treatment of the effect of
electron-phonon interactions in molecular transistors, including both quantal
and classical limits and we study both equilibrated and out of equilibrium
phonons. We present detailed results for conductance, noise and phonon
distribution in two regimes. One involves temperatures large as compared to the
rate of electronic transitions on and off the dot; in this limit our approach
yields classical rate equations, which are solved numerically for a wide range
of parameters. The other regime is that of low temperatures and weak
electron-phonon coupling where a perturbative approximation in the Keldysh
formulation can be applied. The interplay between the phonon-induced
renormalization of the density of states on the quantum dot and the
phonon-induced renormalization of the dot-lead coupling is found to be
important. Whether or not the phonons are able to equilibrate in a time rapid
compared to the transit time of an electron through the dot is found to affect
the conductance. Observable signatures of phonon equilibration are presented.
We also discuss the nature of the low-T to high-T crossover.Comment: 20 pages, 19 figures. Minor changes, version accepted for publication
in Phys. Rev.
Orochi: Investigating Requirements and Expectations for Multipurpose Daily Used Supernumerary Robotic Limbs
Supernumerary robotic limbs (SRLs) present many opportunities for daily use. However, their obtrusiveness and limitations in interaction genericity hinder their daily use. To address challenges of daily use, we extracted three design considerations from previous literature and embodied them in a wearable we call Orochi. The considerations include the following: 1) multipurpose use, 2) wearability by context, and 3) unobtrusiveness in public. We implemented Orochi as a snake-shaped robot with 25 DoFs and two end effectors, and demonstrated several novel interactions enabled by its limber design. Using Orochi, we conducted hands-on focus groups to explore how multipurpose SRLs are used daily and we conducted a survey to explore how they are perceived when used in public. Participants approved Orochi's design and proposed different use cases and postures in which it could be worn. Orochi's unobtrusive design was generally well received, yet novel interactions raise several challenges for social acceptance. We discuss the significance of our results by highlighting future research opportunities based on the design, implementation, and evaluation of Orochi
Suction feeding preceded filtering in baleen whale evolution
The origin of baleen, the key adaptation of modern whales (Mysticeti), marks a profound yet poorly understood transition in vertebrate evolution, triggering the rise of the largest animals on Earth. Baleen is thought to have appeared in archaic tooth-bearing mysticetes during a transitional phase that combined raptorial feeding with incipient bulk filtering. Here we show that tooth wear in a new Late Oligocene mysticete belonging to the putatively transitional family Aetiocetidae is inconsistent with the presence of baleen, and instead indicative of suction feeding. Our findings suggest that baleen arose much closer to the origin of toothless mysticete whales than previously thought. In addition, they suggest an entirely new evolutionary scenario in which the transition from raptorial to baleen-assisted filter feeding was mediated by suction, thereby avoiding the problem of functional interference between teeth and the baleen rack
Possibility of an ultra-precise optical clock using the transition in Yb atoms held in an optical lattice
We report calculations designed to assess the ultimate precision of an atomic
clock based on the 578 nm transition in Yb atoms
confined in an optical lattice trap. We find that this transition has a natural
linewidth less than 10 mHz in the odd Yb isotopes, caused by hyperfine
coupling. The shift in this transition due to the trapping light acting through
the lowest order AC polarizability is found to become zero at the magic trap
wavelength of about 752 nm. The effects of Rayleigh scattering, higher-order
polarizabilities, vector polarizability, and hyperfine induced electronic
magnetic moments can all be held below a mHz (about a part in 10^{18}), except
in the case of the hyperpolarizability larger shifts due to nearly resonant
terms cannot be ruled out without an accurate measurement of the magic
wavelength.Comment: 4 pages, 1 figur
Long-term trends in tropical cyclone tracks around Korea and Japan in late summer and early fall
This study investigates long-term trends in tropical cyclones (TCs) over the extratropical western North Pacific (WNP) over a period of 35 years (1982-2016). The area analyzed extended across 30-45 degrees N and 120-150 degrees E, including the regions of Korea and Japan that were seriously affected by TCs. The northward migration of TCs over the WNP to the mid-latitudes showed a sharp increase in early fall. In addition, the duration of TCs over the WNP that migrated northwards showed an increase, specifically in early to mid-September. Therefore, more recently, TC tracks have been observed to significantly extend into the mid-latitudes. The recent northward extension of TC tracks over the WNP in early fall was observed to be associated with changes in environmental conditions that were favorable for TC activities, including an increase in sea surface temperature (SST), decrease in vertical wind shear, expansion of subtropical highs, strong easterly steering winds, and an increase in relative vorticity. In contrast, northward migrations of TCs to Korea and Japan showed a decline in late August, because of the presence of unfavorable environmental conditions for TC activities. These changes in environmental conditions, such as SST and vertical wind shear, can be partially associated with the Pacific decadal oscillation
Vacuum solutions of the gravitational field equations in the brane world model
We consider some classes of solutions of the static, spherically symmetric
gravitational field equations in the vacuum in the brane world scenario, in
which our Universe is a three-brane embedded in a higher dimensional
space-time. The vacuum field equations on the brane are reduced to a system of
two ordinary differential equations, which describe all the geometric
properties of the vacuum as functions of the dark pressure and dark radiation
terms (the projections of the Weyl curvature of the bulk, generating non-local
brane stresses). Several classes of exact solutions of the vacuum gravitational
field equations on the brane are derived. In the particular case of a vanishing
dark pressure the integration of the field equations can be reduced to the
integration of an Abel type equation. A perturbative procedure, based on the
iterative solution of an integral equation, is also developed for this case.
Brane vacuums with particular symmetries are investigated by using Lie group
techniques. In the case of a static vacuum brane admitting a one-parameter
group of conformal motions the exact solution of the field equations can be
found, with the functional form of the dark radiation and pressure terms
uniquely fixed by the symmetry. The requirement of the invariance of the field
equations with respect to the quasi-homologous group of transformations also
imposes a unique, linear proportionality relation between the dark energy and
dark pressure. A homology theorem for the static, spherically symmetric
gravitational field equations in the vacuum on the brane is also proven.Comment: 13 pages, no figures, to appear in PR
Performance of the CREAM calorimeter in accelerator beam test
The CREAM calorimeter, designed to measure the spectra of cosmic-ray nuclei from under 1 TeV to 1000 TeV, is a 20 radiation length (X0) deep sampling calorimeter. The calorimeter is comprised of 20 layers of tungsten interleaved with 20 layers of scintillating fiber ribbons, and is preceded by a pair of graphite interaction targets providing about 0.42 proton interaction lengths (\lambda int). The calorimeter was placed in one of CERN's SPS accelerator beams for calibration and testing. Beams of 150 GeV electrons were used for calibration, and a variety of electron, proton, and nuclear fragment beams were used to test the simulation model of the detector. In this paper we discuss the performance of the calorimeter in the electron beam and compare electron beam data with simulation results.The CREAM calorimeter, designed to measure the spectra of cosmic-ray nuclei from under 1 TeV to 1000 TeV, is a 20 radiation length (X0) deep sampling calorimeter. The calorimeter is comprised of 20 layers of tungsten interleaved with 20 layers of scintillating fiber ribbons, and is preceded by a pair of graphite interaction targets providing about 0.42 proton interaction lengths (\lambda int). The calorimeter was placed in one of CERN's SPS accelerator beams for calibration and testing. Beams of 150 GeV electrons were used for calibration, and a variety of electron, proton, and nuclear fragment beams were used to test the simulation model of the detector. In this paper we discuss the performance of the calorimeter in the electron beam and compare electron beam data with simulation results
Scalar-isoscalar excitation in dense quark matter
We study the spectrum of scalar-isoscalar excitations in the color-flavor
locked phase of dense quark matter. The sigma meson in this phase appears as a
four-quark state (of diquark and anti-diquark) with a well-defined mass and
extremely small width, as a consequence of it's small coupling to two pions.
The quark particle/hole degrees of freedom also contribute significantly to the
correlator just above the threshold 2\Delta where \Delta is the superconducting
gap.Comment: RevTeX, 11 pages, 4 fig
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