2,479 research outputs found
Opto-mechanical micro-macro entanglement
We propose to create and detect opto-mechanical entanglement by storing one
component of an entangled state of light in a mechanical resonator and then
retrieving it. Using micro-macro entanglement of light as recently demonstrated
experimentally, one can then create opto-mechanical entangled states where the
components of the superposition are macroscopically different. We apply this
general approach to two-mode squeezed states where one mode has undergone a
large displacement. Based on an analysis of the relevant experimental
imperfections, the scheme appears feasible with current technology.Comment: 7 pages, 6 figures, to appear in PRL, submission coordinated with
Sekatski et al. who reported on similar result
Characterizing the Rigidly Rotating Magnetosphere Stars HD 345439 and HD 23478
The SDSS III APOGEE survey recently identified two new Ori E type
candidates, HD 345439 and HD 23478, which are a rare subset of rapidly rotating
massive stars whose large (kGauss) magnetic fields confine circumstellar
material around these systems. Our analysis of multi-epoch photometric
observations of HD 345439 from the KELT, SuperWASP, and ASAS surveys reveals
the presence of a 0.7701 day period in each dataset, suggesting the
system is amongst the faster known Ori E analogs. We also see clear
evidence that the strength of H-alpha, H I Brackett series lines, and He I
lines also vary on a 0.7701 day period from our analysis of multi-epoch,
multi-wavelength spectroscopic monitoring of the system from the APO 3.5m
telescope. We trace the evolution of select emission line profiles in the
system, and observe coherent line profile variability in both optical and
infrared H I lines, as expected for rigidly rotating magnetosphere stars. We
also analyze the evolution of the H I Br-11 line strength and line profile in
multi-epoch observations of HD 23478 from the SDSS-III APOGEE instrument. The
observed periodic behavior is consistent with that recently reported by Sikora
and collaborators in optical spectra.Comment: Accepted in ApJ
Metal-insulator transition at B=0 in a dilute two dimensional GaAs-AlGaAs hole gas
We report the observation of a metal insulator transition at B=0 in a high
mobility two dimensional hole gas in a GaAs-AlGaAs heterostructure. A clear
critical point separates the insulating phase from the metallic phase,
demonstrating the existence of a well defined minimum metallic conductivity
sigma(min)=2e/h. The sigma(T) data either side of the transition can be
`scaled' on to one curve with a single parameter (To). The application of a
parallel magnetic field increases sigma(min) and broadens the transition. We
argue that strong electron-electron interactions (rs = 10) destroy phase
coherence, removing quantum intereference corrections to the conductivity.Comment: 4 pages RevTex + 4 figures. Submitted to PRL. Originally posted 22
September 1997. Revised 12 October 1997 - minor changes to referencing,
figure cations and figure
Viruses, variants and vaccines
The current SARS-CoV-2 pandemic has brought a number of major global clinical, sociological and economic issues into sharp focus. We address some of these issues, focusing on short-term factors such as virus mutations and vaccine efficacy, and also considering the longer-term implications of the current pandemic. We discuss societal responses to the presence of a pathogen that will probably remain in circulation for decades or longer, and to future new emergent viruses
Back gating of a two-dimensional hole gas in a SiGe quantum well
A device comprising a low-resistivity, n-type, Si substrate as a back gate to a p-type (boron), remote-doped, SiGe quantum well has been fabricated and characterized. Reverse and forward voltage biasing of the gate with respect to the two-dimensional hole gas in the quantum well allows the density of holes to be varied from 8 × 1011 cm–2 down to a measurement-limited value of 4 × 1011 cm–2. This device is used to demonstrate the evolution with decreasing carrier density of a re-entrant insulator state between the integer quantum Hall effect states with filling factors 1 and 3
The LAEX and NASA portals for CoRoT public data
* Aims. We describe here the main functionalities of the LAEX (Laboratorio de
Astrofisica Estelar y Exoplanetas/Laboratory for Stellar Astrophysics and
Exoplanets) and NASA portals for CoRoT Public Data. The CoRoT archive at LAEX
was opened to the community in January 2009 and is managed in the framework of
the Spanish Virtual Observatory. NStED (NASA Star and Exoplanet Database)
serves as the CoRoT portal for the US astronomical community. NStED is a
general purpose stellar and exoplanet archive with the aim of providing support
for NASA planet finding and characterisation goals, and the planning and
support of NASA and other space missions. CoRoT data at LAEX and NStED can be
accessed at http://sdc.laeff.inta.es/corotfa/ and
http://nsted.ipac.caltech.edu,respectively.
* Methods. Based on considerable experience with astronomical archives, the
aforementioned archives are designed with the aim of delivering science-quality
data in a simple and efficient way.
* Results. LAEX and NStED not only provide access to CoRoT Public Data but
furthermore serve a variety of observed and calculated astrophysical data. In
particular, NStED provides scientifically validated information on stellar and
planetary data related to the search for and characterization of extrasolar
planets, and LAEX makes any information from Virtual Observatory services
available to the astronomical community.Comment: Accepted for publication in Astronomy & Astrophysic
The Nature of Electronic States in Atomically Thin MoS2 Field-Effect Transistors
We present low temperature electrical transport experiments in five field
effect transistor devices consisting of monolayer, bilayer and trilayer MoS2
films, mechanically exfoliated onto Si/SiO2 substrate. Our experiments reveal
that the electronic states in all films are localized well up to the room
temperature over the experimentally accessible range of gate voltage. This
manifests in two dimensional (2D) variable range hopping (VRH) at high
temperatures, while below \sim 30 K the conductivity displays oscillatory
structures in gate voltage arising from resonant tunneling at the localized
sites. From the correlation energy (T0) of VRH and gate voltage dependence of
conductivity, we suggest that Coulomb potential from trapped charges in the
substrate are the dominant source of disorder in MoS2 field effect devices,
which leads to carrier localization as well.Comment: 10 pages, 5 figures; ACS Nano (2011
Searching for Transiting Planets in Stellar Systems
We analyze the properties of searches devoted to finding planetary transits
by observing simple stellar systems, such as globular clusters, open clusters,
and the Galactic bulge. We develop the analytic tools necessary to predict the
number of planets that a survey will detect as a function of the parameters of
the system, the observational setup, site properties, and planet properties. We
find that the detection probability is generally maximized for I-band
observations. The signal-to-noise ratio of a planetary transit is weakly
dependent on the mass of the primary for sources with flux above the sky
background, and falls very sharply for sources below sky. Therefore the number
of detectable planets is roughly proportional to the number of stars with
fluxes above sky (and not necessarily the number of sources with photometric
error less a given threshold). In order to maximize the number of detections,
experiments should be tailored such that stars near sky are above the detection
threshold. Once this requirement is met, the number of detected planets is
relatively weakly dependent on the detection threshold, diameter of the
telescope, exposure time, seeing, age of the system, and planet radius. The
number of detected planets is a strongly decreasing function of the distance to
the system, implying that the nearest, richest clusters may prove to be optimal
targets.Comment: 24 pages, 10 figures. Minor changes. Accepted to ApJ, to appear in
the September 20, 2005 issu
Weak localisation, hole-hole interactions and the "metal"-insulator transition in two dimensions
A detailed investigation of the metallic behaviour in high quality
GaAs-AlGaAs two dimensional hole systems reveals the presence of quantum
corrections to the resistivity at low temperatures. Despite the low density
() and high quality of these systems, both weak localisation
(observed via negative magnetoresistance) and weak hole-hole interactions
(giving a correction to the Hall constant) are present in the so-called
metallic phase where the resistivity decreases with decreasing temperature. The
results suggest that even at high there is no metallic phase at T=0 in
two dimensions.Comment: 5 pages, 4 figure
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