8,590 research outputs found
Sample-specific and Ensemble-averaged Magnetoconductance of Individual Single-Wall Carbon Nanotubes
We discuss magnetotransport measurements on individual single-wall carbon
nanotubes with low contact resistance, performed as a function of temperature
and gate voltage. We find that the application of a magnetic field
perpendicular to the tube axis results in a large magnetoconductance of the
order of e^2/h at low temperature. We demonstrate that this magnetoconductance
consists of a sample-specific and of an ensemble-averaged contribution, both of
which decrease with increasing temperature. The observed behavior resembles
very closely the behavior of more conventional multi-channel mesoscopic wires,
exhibiting universal conductance fluctuations and weak localization. A
theoretical analysis of our experiments will enable to reach a deeper
understanding of phase-coherent one-dimensional electronic motion in SWNTs.Comment: Replaced with published version. Minor changes in tex
On the Origin of Pluto's Small Satellites by Resonant Transport
The orbits of Pluto's four small satellites (Styx, Nix, Kerberos, and Hydra)
are nearly circular and coplanar with the orbit of the large satellite Charon,
with orbital periods nearly in the ratios 3:1, 4:1, 5:1, and 6:1 with Charon's
orbital period. These properties suggest that the small satellites were created
during the same impact event that placed Charon in orbit and had been pushed to
their current positions by being locked in mean-motion resonances with Charon
as Charon's orbit was expanded by tidal interactions with Pluto. Using the
Pluto-Charon tidal evolution models developed by Cheng et al. (2014), we show
that stable capture and transport of a test particle in multiple resonances at
the same mean-motion commensurability is possible at the 5:1, 6:1, and 7:1
commensurabilities, if Pluto's zonal harmonic . However, the test
particle has significant orbital eccentricity at the end of the tidal evolution
of Pluto-Charon in almost all cases, and there are no stable captures and
transports at the 3:1 and 4:1 commensurabilities. Furthermore, a non-zero
hydrostatic value of destroys the conditions necessary for multiple
resonance migration. Simulations with finite but minimal masses of Nix and
Hydra also fail to yield any survivors. We conclude that the placing of the
small satellites at their current orbital positions by resonant transport is
extremely unlikely.Comment: 22 pages, including 7 figures; accepted for publication in Icaru
Complete Tidal Evolution of Pluto-Charon
Both Pluto and its satellite Charon have rotation rates synchronous with
their orbital mean motion. This is the theoretical end point of tidal evolution
where transfer of angular momentum has ceased. Here we follow Pluto's tidal
evolution from an initial state having the current total angular momentum of
the system but with Charon in an eccentric orbit with semimajor axis (where is the radius of Pluto), consistent with its impact origin.
Two tidal models are used, where the tidal dissipation function
1/frequency and constant, where details of the evolution are strongly
model dependent. The inclusion of the gravitational harmonic coefficient
of both bodies in the analysis allows smooth, self consistent
evolution to the dual synchronous state, whereas its omission frustrates
successful evolution in some cases. The zonal harmonic can also be
included, but does not cause a significant effect on the overall evolution. The
ratio of dissipation in Charon to that in Pluto controls the behavior of the
orbital eccentricity, where a judicious choice leads to a nearly constant
eccentricity until the final approach to dual synchronous rotation. The tidal
models are complete in the sense that every nuance of tidal evolution is
realized while conserving total angular momentum - including temporary capture
into spin-orbit resonances as Charon's spin decreases and damped librations
about the same.Comment: 36 pages, including 18 figures; accepted for publication in Icaru
Bounds for Kloosterman sums on GL(n)
This paper establishes power-saving bounds for Kloosterman sums associated
with the long Weyl element for GL(n), as well as for another type of Weyl
element of order 2. These bounds are obtained by establishing an explicit
representation as exponential sums. As an application we go beyond Sarnak's
density conjecture for the principal congruence subgroup of prime level. We
also bound all Kloosterman sums for GL(4).Comment: 20 page
Thirty-fold: Extreme gravitational lensing of a quiescent galaxy at
We report the discovery of eMACSJ1341-QG-1, a quiescent galaxy at
located behind the massive galaxy cluster eMACSJ1341.92442 (). The
system was identified as a gravitationally lensed triple image in Hubble Space
Telescope images obtained as part of a snapshot survey of the most X-ray
luminous galaxy clusters at and spectroscopically confirmed in
ground-based follow-up observations with the ESO/X-Shooter spectrograph. From
the constraints provided by the triple image, we derive a first, crude model of
the mass distribution of the cluster lens, which predicts a gravitational
amplification of a factor of 30 for the primary image and a factor of
6 for the remaining two images of the source, making eMACSJ1341-QG-1 by
far the most strongly amplified quiescent galaxy discovered to date. Our
discovery underlines the power of SNAPshot observations of massive, X-ray
selected galaxy clusters for lensing-assisted studies of faint background
populations
Quantum dense coding in multiparticle entangled states via local measurements
In this paper, we study quantum dense coding between two arbitrarily fixed
particles in a (N+2)-particle maximally-entangled states through introducing an
auxiliary qubit and carrying out local measurements. It is shown that the
transmitted classical information amount through such an entangled quantum
channel usually is less than two classical bits. However, the information
amount may reach two classical bits of information, and the classical
information capacity is independent of the number of the entangled particles in
the initial entangled state under certain conditions. The results offer deeper
insights to quantum dense coding via quantum channels of multi-particle
entangled states.Comment: 3 pages, no figur
Perfect State Transfer, Effective Gates and Entanglement Generation in Engineered Bosonic and Fermionic Networks
We show how to achieve perfect quantum state transfer and construct effective
two-qubit gates between distant sites in engineered bosonic and fermionic
networks. The Hamiltonian for the system can be determined by choosing an
eigenvalue spectrum satisfying a certain condition, which is shown to be both
sufficient and necessary in mirror-symmetrical networks. The natures of the
effective two-qubit gates depend on the exchange symmetry for fermions and
bosons. For fermionic networks, the gates are entangling (and thus universal
for quantum computation). For bosonic networks, though the gates are not
entangling, they allow two-way simultaneous communications. Protocols of
entanglement generation in both bosonic and fermionic engineered networks are
discussed.Comment: RevTeX4, 6 pages, 1 figure; replaced with a more general example and
clarified the sufficient and necessary condition for perfect state transfe
FTO Biology and Obesity: Why Do a Billion of Us Weigh 3 kg More?
Few would dispute that the current obesity epidemic has been driven by lifestyle and environmental changes. However, it is clear that individuals respond differently to these âobesigenicâ changes and this variation in response has a strong genetic element. Genome-wide association studies have revealed that single nucleotide polymorphisms in Fat mass and obesity-associated transcript (FTO) are robustly associated with body mass index and obesity. Although the effect of these risk alleles are modest, with heterozygous and homozygous carriers weighing approximately 1.5 and 3âkg more respectively, there are an estimated one billion homozygous carriers in the world, spanning multiple different ethnicities and populations. Yet despite its broad impact, the biological function of FTO, particularly its role in controlling energy balance, remains unknown. Although the study of severe Mendelian obesity has been invaluable in illuminating critical pathways controlling food intake, the major burden of disease is carried by those of us with âcommon obesity,â which to date has resisted yielding meaningful biological insights. FTO has at last given us a handle on a huge, worldwide, common problem. In this review, we focus on the available genetic and in vivo evidence to date that implicates FTO in the control of energy balance
Parametrical optimization of laser surface alloyed NiTi shape memory alloy with Co and Nb by the Taguchi method
Different high-purity metal powders were successfully alloyed on to a nickel titanium (NiTi) shape memory alloy (SMA) with a 3 kW carbon dioxide (CO2) laser system. In order to produce an alloyed layer with complete penetration and acceptable composition profile, the Taguchi approach was used as a statistical technique for optimizing selected laser processing parameters. A systematic study of laser power, scanning velocity, and pre-paste powder thickness was conducted. The signal-to-noise ratios (S/N) for each control factor were calculated in order to assess the deviation from the average response. Analysis of variance (ANOVA) was carried out to understand the significance of process variables affecting the process effects. The Taguchi method was able to determine the laser process parameters for the laser surface alloying technique with high statistical accuracy and yield a laser surface alloying technique capable of achieving a desirable dilution ratio. Energy dispersive spectrometry consistently showed that the per cent by weight of Ni was reduced by 45 per cent as compared with untreated NiTi SMA when the Taguchi-determined laser processing parameters were employed, thus verifying the laser's processing parameters as optimum
High-Q nested resonator in an actively stabilized optomechanical cavity
Experiments involving micro- and nanomechanical resonators need to be
carefully designed to reduce mechanical environmental noise. A small scale
on-chip approach is to add an additional resonator to the system as a
mechanical low-pass filter. Unfortunately, the inherent low frequency of the
low-pass filter causes the system to be easily excited mechanically. Fixating
the additional resonator ensures that the resonator itself can not be excited
by the environment. This, however, negates the purpose of the low-pass filter.
We solve this apparent paradox by applying active feedback to the resonator,
thereby minimizing the motion with respect the front mirror of an
optomechanical cavity. Not only does this method actively stabilize the cavity
length, but it also retains the on-chip vibration isolation.Comment: Minor adjustments mad
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