1,093 research outputs found
DIGIT survey of far-infrared lines from protoplanetary disks I
[abridged] We present far-infrared spectroscopic observations of PMS stars
taken with Herschel/PACS as part of the DIGIT key project. The sample includes
22 Herbig AeBe and 8 T Tauri sources. Multiple atomic fine structure and
molecular lines are detected at the source position: [OI], [CII], CO, OH, H_2O,
CH^+. The most common feature is the [OI] 63micron line detected in almost all
of the sources followed by OH. In contrast with CO, OH is detected toward both
Herbig AeBe groups (flared and non-flared sources). An isothermal LTE slab
model fit to the OH lines indicates column densities of 10^13 < N_OH < 10^16
cm^-2, emitting radii 15 < r < 100 AU and excitation temperatures 100 < T_ex <
400 K. The OH emission thus comes from a warm layer in the disk at intermediate
stellar distances. Warm H_2O emission is detected through multiple lines toward
the T Tauri systems AS 205, DG Tau, S CrA and RNO 90 and three Herbig AeBe
systems HD 104237, HD 142527, HD 163296 (through line stacking). Overall,
Herbig AeBe sources have higher OH/H_2O abundance ratios across the disk than
do T Tauri disks, from near- to far-infrared wavelengths. Far-infrared CH^+
emission is detected toward HD 100546 and HD 97048. The slab model suggests
moderate excitation (T_ex ~ 100 K) and compact (r ~ 60 AU) emission in the case
of HD 100546. The [CII] emission is spatially extended in all sources where the
line is detected. This suggests that not all [CII] emission is associated with
the disk and that there is a substantial contribution from diffuse material
around the young stars. The flux ratios of the atomic fine structure lines are
consistent with a disk origin for the oxygen lines for most of the sources.Comment: Accepted for publication in A&
Distinguishing and electron pairing symmetries by neutron spin resonance in superconducting NaFeCoAs
A determination of the superconducting (SC) electron pairing symmetry forms
the basis for establishing a microscopic mechansim for superconductivity. For
iron pnictide superconductors, the -pairing symmetry theory predicts the
presence of a sharp neutron spin resonance at an energy below the sum of hole
and electron SC gap energies () below . On the other hand,
the -pairing symmetry expects a broad spin excitation enhancement at an
energy above below . Although the resonance has been observed in
iron pnictide superconductors at an energy below consistent with the
-pairing symmetry, the mode has also be interpreted as arising from the
-pairing symmetry with due to its broad energy width and
the large uncertainty in determining the SC gaps. Here we use inelastic neutron
scattering to reveal a sharp resonance at E=7 meV in SC
NaFeCoAs ( K). On warming towards , the mode
energy hardly softens while its energy width increases rapidly. By comparing
with calculated spin-excitations spectra within the and
-pairing symmetries, we conclude that the ground-state resonance in
NaFeCoAs is only consistent with the -pairing, and
is inconsistent with the -pairing symmetry.Comment: 9 pages, 8 figures. submitted to PR
In-plane polarized collective modes in detwinned YBaCuO observed by spectral ellipsometry
The in-plane dielectric response of detwinned YBaCuO has
been studied by far-infared ellipsometry. A surprisingly lare number of
in-plane polarized modes are observed. Some of them correspond to pure phonon
modes. Others posses a large electronic contribution which strongly increases
in the superconducting state. The free carrier response and the collective
modes exhibit a pronounced a-b anisotropy. We discuss our results in terms of a
CDW state in the 1-d CuO chains and induced charge density fluctuations within
the 2-d CuO planes
On the origin of [NeII] 12.81 micron emission from pre-main sequence stars: Disks, jets, and accretion
(Abridged) We have conducted a study of [NeII] line emission based on a
sample of 92 pre-main sequence stars mostly belonging to the infrared Class II,
including 13 accreting transition disk objects and 14 objects driving jets and
outflows. We find several significant correlations between L[NeII] and stellar
parameters, in particular LX and the wind mass loss rate, dM/dt. Most
correlations are, however, strongly dominated by systematic scatter. While
there is a positive correlation between L[NeII] and LX, the stellar mass
accretion rate, dMacc/dt, induces a correlation only if we combine the largely
different subsets of jet sources and stars without jets. Our results suggest
that L[NeII] is bi-modally distributed, with separate distributions for the two
subsamples. The jet sources show systematically higher L[NeII], by 1-2 orders
of magnitude with respect to objects without jets. Jet-driving stars also tend
to show higher mass accretion rates. We therefore hypothesize that the trend
with dMacc/dt reflects a trend with dM/dt that is more physically relevant for
[NeII] emission. L[NeII] measured for objects without known outflows and jets
is found to agree with simplified calculations of [NeII] emission from disk
surface layers if the measured stellar X-rays are responsible for heating and
ionizing of the gas. The large scatter in L[NeII] may be introduced by
variations of disk properties and the irradiation spectrum, as previously
suggested. The systematically enhanced [NeII] flux from jet sources clearly
suggests a role for the jets themselves, as previously demonstrated by a
spatially resolved observation of the outflow system in the T Tau triple.Comment: accepted for Astronomy & Astrophysics, 25 pages, 11 figures -
revisions: affiliation added, NeII flux unit in Table 3 correcte
Oscillations and interactions of dark and dark-bright solitons in Bose-Einstein condensates
Solitons are among the most distinguishing fundamental excitations in a wide
range of non-linear systems such as water in narrow channels, high speed
optical communication, molecular biology and astrophysics. Stabilized by a
balance between spreading and focusing, solitons are wavepackets, which share
some exceptional generic features like form-stability and particle-like
properties. Ultra-cold quantum gases represent very pure and well-controlled
non-linear systems, therefore offering unique possibilities to study soliton
dynamics. Here we report on the first observation of long-lived dark and
dark-bright solitons with lifetimes of up to several seconds as well as their
dynamics in highly stable optically trapped Rb Bose-Einstein
condensates. In particular, our detailed studies of dark and dark-bright
soliton oscillations reveal the particle-like nature of these collective
excitations for the first time. In addition, we discuss the collision between
these two types of solitary excitations in Bose-Einstein condensates.Comment: 9 pages, 4 figure
Warm gas at 50 AU in the disk around Herbig Be star HD 100546
The disk atmosphere is one of the fundamental elements of theoretical models
of a protoplanetary disk. However, the direct observation of the warm gas (>>
100 K) at large radius of a disk (>> 10 AU) is challenging, because the line
emission from warm gas in a disk is usually dominated by the emission from an
inner disk. Our goal is to detect the warm gas in the disk atmosphere well
beyond 10 AU from a central star in a nearby disk system of the Herbig Be star
HD 100546. We measured the excitation temperature of the vibrational transition
of CO at incremental radii of the disk from the central star up to 50 AU, using
an adaptive optics system combined with the high-resolution infrared
spectrograph CRIRES at the VLT. The observation successfully resolved the line
emission with 0".1 angular resolution, which is 10 AU at the distance of HD
100546. Population diagrams were constructed at each location of the disk, and
compared with the models calculated taking into account the optical depth
effect in LTE condition. The excitation temperature of CO is 400-500 K or
higher at 50 AU away from the star, where the blackbody temperature in
equilibrium with the stellar radiation drops as low as 90 K. This is
unambiguous evidence of a warm disk atmosphere far away from the central star.Comment: 7 pages, 5 figures, A&A in pres
Hypertriglyceridemic Waist Phenotype Predicts Increased Visceral Fat in Subjects With Type 2 Diabetes
OBJECTIVE: Greater accumulation of visceral fat is strongly linked to risk of cardiovascular disease. However, elevated waist circumference by itself does not always identify individuals with increased visceral fat. RESEARCH DESIGN AND METHODS: We examined 375 subjects with type 2 diabetes from the CHICAGO cohort for presence of hypertriglyceridemic waist phenotype (waist circumference >90 cm in men or >85 cm in women, in conjunction with a plasma triglyceride concentration of ≥177 mg/dl) to determine its usefulness for identifying subjects with increased amounts of visceral fat. We divided subjects into three groups: group 1 (low waist circumference and low triglycerides; waist circumference ≤90 cm in men or ≤85 cm in women and triglyceride <177 mg/dl, n = 18), group 2 (high waist circumference and low triglycerides; waist circumference >90 cm in men or >85 cm in women and triglycerides <177 mg/dl, n = 230), and group 3 (high waist circumference and high triglycerides; waist circumference >90 cm in men or >85 cm in women and triglycerides ≥177 mg/dl, n = 127). RESULTS: Subjects in group 3 had significantly higher visceral fat (P < 0.0001), A1C (P < 0.01), and coronary artery calcium (P < 0.05) compared with group 2, despite similar age, BMI, and waist circumference. The relationship of the phenotype to atherosclerosis, however, was attenuated by adjustment for HDL cholesterol, triglyceride-rich lipoprotein cholesterol, apolipoprotein B, or LDL particle number. CONCLUSIONS: The presence of hypertriglyceridemic waist phenotype in subjects with type 2 diabetes identifies a subset with greater degree of visceral adiposity. This subset also has greater degree of subclinical atherosclerosis that may be related to the proatherogenic lipoprotein changes.Takeda Global Research and Development; National Institutes of Health (DK 71711); University of Illinois at Chicag
What Does Free Space Lambda-Lambda Interaction Predict for Lambda-Lambda Hypernuclei?
Data on Lambda-Lambda hypernuclei provide a unique method to learn details on
the strangeness S =-2 sector of the baryon-baryon interaction. From the free
space Bonn-Julich potentials, determined from data on baryon-baryon scattering
in the S=0,-1 channels, we construct an interaction in the S =-2 sector to
describe the experimentally known Lambda-Lambda hypernuclei. After including
short--range (Jastrow) and RPA correlations, we find masses for these
Lambda-Lambda hypernuclei in a reasonable agreement with data, taking into
account theoretical and experimental uncertainties. Thus, we provide a natural
extension, at low energies, of the Bonn-Julich OBE potentials to the S =-2
channel.Comment: 4 pages, 2 figures, revtex4 style. Minor changes in conclusions.
References updated. Accepted in Phys. Rev. Let
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Experimental and Numerical Investigation of the Use of Ultrasonic Waves to Assist Laser Welding
Data Availability Statement: Data are contained within the article.This study evaluates the enhancement of laser welding using ultrasonic waves aimed at reorganising the intermetallic position in such a fashion that leads to increased mechanical properties of welds in battery pack assemblies for electric vehicles. The experiment employed 20 kHz and 40 kHz High-Power Ultrasound Transducers (HPUTs) in both contact and contactless modes. A simplified experimental configuration is suggested to represent conditions similar to those found in electric vehicle battery pack assemblies. Measurements of vibration transmission to aluminium alloy 1050 plates revealed more than a 1000-fold increase in acceleration amplitude in contact mode compared to contactless mode. The 20 kHz transducer in contactless mode demonstrated superior performance, showing a 10% increase in load and 27% increase in extension compared to welding without ultrasonic assistance. On the other hand, the 40 kHz transducer, while still improved over non-ultrasonic methods, showed less pronounced benefits. This suggests that lower-frequency ultrasonic assistance (20 kHz) is more effective in this specific context. The study explores ultrasonic assistance in laser welding copper (Cu101) to aluminium alloy 1050 using 20 kHz and 40 kHz HPUTs, showing that both transducers enhance microstructural integrity by reducing copper homogenisation into aluminium, with the 20 kHz frequency proving more effective in this context. A numerical simulation was conducted to evaluate the transmission of pressure into the molten pool of the weld, correlated with the vibration results obtained from the 20 kHz transducer. The numerical simulation confirms that no cavitation is initiated in the molten pool area, and all improvements are solely due to the ultrasonic waves.This research was funded by Innovate UK, grant number: 10018077. The APC was funded by Brunel University London
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