1,319 research outputs found
Feshbach Resonance and Growth of a Bose-Einstein Condensate
Gross-Pitaevskii equation with gain is used to model Bose Einstein
condensation (BEC) fed by the surrounding thermal cloud. It is shown that the
number of atoms continuously injected into BEC from the reservoir can be
controlled by applying the external magnetic field via Feshbach resonance.Comment: 4 page
LHC Charge Asymmetry as Constraint on Models for the Tevatron Top Anomaly
The forward-backward asymmetry in top quark production at
the Tevatron has been observed to be anomalously large by both CDF and D0. It
has been suggested that a model with a coupling to and might
explain this anomaly, and other anomalies in mesons. Single-top-quark
production in this model is large, and arguably in conflict with Tevatron
measurements. However the model might still be viable if is
somewhat smaller than its current measured central value. We show that even
with smaller couplings, the model can be discovered (or strongly excluded) at
the LHC using the 2010 data sets. We find that a suitable charge-asymmetry
measurement is a powerful tool that can be used to constrain this and other
sources of anomalous single-top production, and perhaps other new high-energy
charge-asymmetric processes.Comment: 25 pages, 4 figures, note adde
Optical antenna of comb-shaped split ring architecture for increased field localization in NIR and MIR
Cataloged from PDF version of article.We propose and demonstrate novel designs of optical antennas based on comb-shaped split ring architecture that display multi resonance field intensity enhancement spectrum. These nanoantennas achieve substantially increased field localization at longer wavelengths than that of a single or an array of dipoles with the same side length. With these optical antennas, localizing near infrared (NIR) and mid infrared (MIR) lights within a region of tens of nanometers at an intensity enhancement level of the order of thousands of magnitude can be accomplished. (C)2013 Optical Society of America
Three-dimensional study of planar optical antennas made of split-ring architecture outperforming dipole antennas for increased field localization
Cataloged from PDF version of article.Optical antennas are of fundamental importance for the strongly localizing field beyond the diffraction limit. We report that planar optical antennas made of split-ring architecture are numerically found in three-dimensional simulations to outperform dipole antennas for the enhancement of localized field intensity inside their gap regions. The computational results (finite-difference time-domain) indicate that the resulting field localization, which is of the order of many thousandfold, in the case of the split-ring resonators is at least 2 times stronger than the one in the dipole antennas resonant at the same operating wavelength, while the two antenna types feature the same gap size and tip sharpness. (C) 2012 Optical Society of Americ
A Dusty Disk Around WD1150-153: Explaining the Metals in White Dwarfs by Accretion from the Interstellar Medium versus Debris Disks
We report the discovery of excess K-band radiation from a metal-rich DAV
white dwarf star, WD1150-153. Our near infrared spectroscopic observations show
that the excess radiation cannot be explained by a (sub)stellar companion, and
is likely to be caused by a debris disk similar to the other DAZ white dwarfs
with circumstellar debris disks. We find that the fraction of DAZ white dwarfs
with detectable debris disks is at least 14%. We also revisit the problem of
explaining the metals in white dwarf photospheres by accretion from the
interstellar medium (ISM). We use the observed interstellar column densities
toward stars in close angular proximity and similar distance as DAZ white
dwarfs to constrain the contribution of accretion from the ISM. We find no
correlation between the accretion density required to supply metals observed in
DAZs with the densities observed in their interstellar environment, indicating
that ISM accretion alone cannot explain the presence of metals in nearby DAZ
white dwarfs. Although ISM accretion will certainly contribute, our analysis
indicates that it is not the dominant source of metals for most DAZ white
dwarfs. Instead, the growing number of circumstellar debris disks around DAZs
suggests that circumstellar material may play a more dominant role in polluting
the white dwarf atmospheres.Comment: ApJ, in pres
The New Class of Dusty DAZ White Dwarfs
Our mid-infrared survey of 124 white dwarfs with the Spitzer Space Telescope
and the IRAC imager has revealed an infrared excess associated with the white
dwarf WD 2115-560 naturally explained by circumstellar dust. This object is the
fourth white dwarf observed to have circumstellar dust. All four are DAZ white
dwarfs, i.e. they have both photospheric Balmer lines and photospheric metal
lines.
We discuss these four objects as a class, which we abbreviate "DAZd", where
the "d" stands for "dust". Using an optically-thick, geometrically-thin disk
model analogous to Saturn's rings, we find that the inner disk edges are at
>~0.1 to 0.2 Ro and that the outer disk edges are ~0.3 to 0.6 Ro. This model
naturally explains the accretion rates and lifetimes of the detected WD disks
and the accretion rates inferred from photospheric metal abundances.Comment: 27 pages, 7 figures, ApJ accepte
The Future is Now: the Formation of Single Low Mass White Dwarfs in the Solar Neighborhood
Low mass helium-core white dwarfs (M < 0.45 Msun) can be produced from
interacting binary systems, and traditionally all of them have been attributed
to this channel. However, a low mass white dwarf could also result from a
single star that experiences severe mass loss on the first ascent giant branch.
A large population of low mass He-core white dwarfs has been discovered in the
old metal-rich cluster NGC 6791. There is therefore a mechanism in clusters to
produce low mass white dwarfs without requiring binary star interactions, and
we search for evidence of a similar population in field white dwarfs. We argue
that there is a significant field population (of order half of the detected
systems) that arises from old metal rich stars which truncate their evolution
prior to the helium flash from severe mass loss. There is a consistent absence
of evidence for nearby companions in a large fraction of low mass white dwarfs.
The number of old metal-rich field dwarfs is also comparable with the
apparently single low mass white dwarf population, and our revised estimate for
the space density of low mass white dwarfs produced from binary interactions is
also compatible with theoretical expectations. This indicates that this channel
of stellar evolution, hitherto thought hypothetical only, has been in operation
in our own Galaxy for many billions of years. One strong implication of our
model is that single low mass white dwarfs should be good targets for planet
searches because they are likely to arise from metal-rich progenitors. We also
discuss other observational tests and implications, including the potential
impact on SN Ia rates and the frequency of planetary nebulae.Comment: ApJ published versio
Miniature photonic-crystal hydrophone optimized for ocean acoustics
This work reports on an optical hydrophone that is insensitive to hydrostatic
pressure, yet capable of measuring acoustic pressures as low as the background
noise in the ocean in a frequency range of 1 Hz to 100 kHz. The miniature
hydrophone consists of a Fabry-Perot interferometer made of a photonic-crystal
reflector interrogated with a single-mode fiber, and is compatible with
existing fiber-optic technologies. Three sensors with different acoustic power
ranges placed within a sub-wavelength sized hydrophone head allow a high
dynamic range in the excess of 160 dB with a low harmonic distortion of better
than -30 dB. A method for suppressing cross coupling between sensors in the
same hydrophone head is also proposed. A prototype was fabricated, assembled,
and tested. The sensitivity was measured from 100 Hz to 100 kHz, demonstrating
a minimum detectable pressure down to 12 {\mu}Pa (1-Hz noise bandwidth), a
flatband wider than 10 kHz, and very low distortion
Expression des "activated leukocyte cell adhesion molecule" im Mammakarzinom: Prädiktivität für das Ansprechen auf eine taxanfreie Chemotherapie
Zusammenfassung: Ziele: "Activated leukocyte cell adhesion molecule" (ALCAM) ist ein Oberflächenimmunglobulin und wird in vielen Mammakarzinomen exprimiert. Es wird vermutet, dass ALCAM in der Tumorgenese und -progression eine Rolle spielt. Die Bedeutung des Adhäsionsmoleküls ALCAM für das Ansprechen auf eine taxanfreie adjuvante Chemotherapie wurde untersucht. Material und Methoden: Gewebeproben von 162Patientinnen mit Mammakarzinomen wurden im Hinblick auf die Expression des ALCAM-Proteins untersucht. Immunhistologische Untersuchungen (IHC) und Western-Blot-Analysen (WB) wurden mit einem monoklonalen Antikörper gegen ALCAM durchgeführt. Die Proteinmengen im WB wurden densitometrisch quantifiziert und mit klinischen sowie histologischen Parametern korreliert. Die Ergebnisse wurden auf mRNA-Ebene mithilfe der Microarray-Analysen (Affymetrix) validiert. Ergebnisse: In der normalen Brustdrüse wird ALCAM in den luminalen und den basalen Epithelzellen exprimiert. Die WB-Analysen von Mammakarzinomen zeigen eine positive Korrelation der ALCAM-Expression mit dem Östrogenrezeptorstatus (p=0,04). Bei Patientinnen, die eine taxanfreie Chemotherapie erhalten haben, ist eine hohe ALCAM-Expression (WB, Affymetrix) prädikitiv für das Ansprechen einer Chemotherapie. Der mediane mRNA-Level von ALCAM war bei Patientinnen, die während des Beobachtungszeitraums noch lebten, 4,5-fach höher als bei Patientinnen, die verstarben. Schlussfolgerung: Ein hoher ALCAM-Gehalt korreliert positiv mit dem Östrogenrezeptorstatus. Außerdem ist ALCAM ein prädiktiver Faktor für das Ansprechen einer taxanfreien Chemotherapi
Pulsed Beam Tests at the SANAEM RFQ Beamline
A proton beamline consisting of an inductively coupled plasma (ICP) source,
two solenoid magnets, two steerer magnets and a radio frequency quadrupole
(RFQ) is developed at the Turkish Atomic Energy Authority's (TAEA) Saraykoy
Nuclear Research and Training Center (SNRTC-SANAEM) in Ankara. In Q4 of 2016,
the RFQ was installed in the beamline. The high power tests of the RF power
supply and the RF transmission line were done successfully. The high power RF
conditioning of the RFQ was performed recently. The 13.56 MHz ICP source was
tested in two different conditions, CW and pulsed. The characterization of the
proton beam was done with ACCTs, Faraday cups and a pepper-pot emittance meter.
Beam transverse emittance was measured in between the two solenoids of the
LEBT. The measured beam is then reconstructed at the entrance of the RFQ by
using computer simulations to determine the optimum solenoid currents for
acceptance matching of the beam. This paper will introduce the pulsed beam test
results at the SANAEM RFQ beamline. In addition, the high power RF conditioning
of the RFQ will be discussed.Comment: 6 pages, 6 figures. Proceedings of the International Particle
Accelerator Conference 2017 (IPAC'17), May 14-19, 2017, TUPAB015, p. 134
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