1,225 research outputs found
Scanning Tunneling Spectroscopy of Bi2Sr2CuO6+d: New Evidence for the Common Origin of the Pseudogap and Superconductivity
Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped Bi2Sr2CuO6+δ between 275 mK and 82 K. Below Tc = 10 K, the spectra show a gap with well-defined coherence peaks at ±Δp≃12 meV, which disappear at Tc. Above Tc, the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at T*≃68 K. The comparison with Bi2Sr2CaCu2O8+δ demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin
Exclusive channels in semi-inclusive production of pions and kaons
We investigate the role of exclusive channels in semi-inclusive
electroproduction of pions and kaons. Using the QCD factorization theorem for
hard exclusive processes we evaluate the cross sections for exclusive
pseudoscalar and vector meson production in terms of generalized parton
distributions and meson distribution amplitudes. We investigate the
uncertainties arising from the modeling of the nonperturbative input
quantities. Combining these results with available experimental data, we
compare the cross sections for exclusive channels to that obtained from quark
fragmentation in semi-inclusive deep inelastic scattering. We find that rho^0
production is the only exclusive channel with significant contributions to
semi-inclusive pion production at large z and moderate Q^2. The corresponding
contribution to kaon production from the decay of exclusively produced phi and
K^* is rather small.Comment: 33 pages, 18 figure
First direct observation of the Van Hove singularity in the tunneling spectra of cuprates
In two-dimensional lattices the electronic levels are unevenly spaced, and
the density of states (DOS) displays a logarithmic divergence known as the Van
Hove singularity (VHS). This is the case in particular for the layered cuprate
superconductors. The scanning tunneling microscope (STM) probes the DOS, and is
therefore the ideal tool to observe the VHS. No STM study of cuprate
superconductors has reported such an observation so far giving rise to a debate
about the possibility of observing directly the normal state DOS in the
tunneling spectra. In this study, we show for the first time that the VHS is
unambiguously observed in STM measurements performed on the cuprate Bi-2201.
Beside closing the debate, our analysis proves the presence of the pseudogap in
the overdoped side of the phase diagram of Bi-2201 and discredits the scenario
of the pseudogap phase crossing the superconducting dome.Comment: 4 pages, 4 figure
Vortex Imaging in the pi-Band of Magnesium Diboride
We report scanning tunneling spectroscopy imaging of the vortex lattice in
single crystalline MgB2. By tunneling parallel to the c-axis, a single
superconducting gap (Delta = 2.2 meV) associated with the pi-band is observed.
The vortices in the pi-band have a large core size compared to estimates based
on Hc2, and show an absence of localized states in the core. Furthermore,
superconductivity between the vortices is rapidly suppressed by an applied
field. These results suggest that superconductivity in the pi-band is, at least
partially, induced by the intrinsically superconducting sigma-band.Comment: 4 pages, 3 figure
Development of a theory-based questionnaire to assess structure and control in parent feeding (SCPF)
Abstract
Background
Parents shape children\u2019s eating environments and act as powerful socialization agents, impacting young children\u2019s behavioral controls of food intake. Most feeding measures assess parents\u2019 use of control to manage children\u2019s intake of energy dense foods. The Structure and Control in Parent Feeding (SCPF) questionnaire was developed to assess more positive aspects of feeding practices with their young children \u2014setting limits, providing routines\u2014that promote self-regulation, as well as controlling feeding practices.
Methods
A mixed method approach was used to develop the SCPF. In 2013, cognitive interviews informed the modification, deletion and/or replacement of items. In 2014, the survey was distributed statewide to mothers of toddlers aged 12 to 36\ua0months participating in the Women, Infants, and Children program. In 2016, exploratory factor analyses was conducted to test our theoretical parenting model and content validity and criterion validity were assessed ( n \u2009=\u2009334).
Results
Exploratory factor analysis (EFA) and second-order EFA revealed a 2-factor, 22-item Structure model and a 2-factor, 12-item Control model. Internal consistencies for all factors exceeded 0.70. As predicted, the Structure superfactor was positivity associated with responsiveness, whereas the Control superfactor was positively associated with demandingness on the Caregiver\u2019s Feeding Styles Questionnaire. The Structure subscales were also positively associated with mealtime behaviors and Control subscales were positively associated with control-oriented feeding measures from the Control in Parent Feeding Practices questionnaire.
Conclusion
The SCPF questionnaire is a reliable tool that can be used to assess aspects of structure- and control-based feeding practices to better understand how parents feed their toddlers
Comparison between a prenatal sonographic scoring system and a clinical grading at delivery for Placenta Accreta Spectrum disorders
OBJECTIVE: Placenta Accreta Spectrum (PAS) disorders have become a major iatrogenic obstetric complication worldwide. Data on the accuracy of ultrasound examination diagnosis are limited by incomplete confirmation and variability in the description of the different grades of PAS at delivery. The aim of this study was to compare our prenatal routine sonographic screening and diagnostic scoring system with a standardized clinical grading system at birth in patient at risk of PAS. STUDY DESIGN: This is a retrospective cohort study of 607 pregnant patients with at least one prior cesarean delivery between December 2013 and December 2018. All patients were assessed for PAS using our institutional prenatal sonographic scoring system and the corresponding ultrasound findings were compared with those of a standardized clinical intra-operative macroscopic grading system of the degree of accreta placentation at vaginal birth or laparotomy. RESULTS: PAS was diagnosed clinically at birth in 50 (8.2%) cases, 17 of which were confirmed by histopathology. A low (score ≤ 5), medium (score 6-7), high (score ≥ 8) probability for PAS was reported in 502, 61 and 44 cases, respectively. The probability score increased significantly (p < .001) in women ≥2 prior cesarean deliveries, with an anterior low-lying/placenta previa, with absent clear space, increased in retroplacental vascularity and with the size and numbers of lacunae. The number of cases classified clinically as grade 1 (non-PAS) and 3 (adherent PAS) was significantly (p < .001) lower in women with a high probability score whereas the rates of the other grades was significantly (p < .001) higher. The widest discrepancy between ultrasound probability score and clinical grade was found for grade 2 which, describes a partial placental adherence and grades 4 and 5 which, refer to placental percreta which describes tissue having invade trough the uterine serosa and beyond. CONCLUSIONS: Both ends of the spectrum of accreta placentation remain difficult to diagnose antenatal and clinically at birth, in particular when no histopathologic confirmation is available. There is a need to develop ultrasound accuracy score systems that can differentiate between the different grades of PAS and which are validated by standardized clinical and pathology protocols
Evolution of the resistivity anisotropy in Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} single crystals for a wide range of hole doping
To elucidate how the temperature dependence of the resistivity anisotropy of
the cuprate superconductors changes with hole doping, both the in-plane and the
out-of-plane resistivities (\rho_{ab} and \rho_{c}) are measured in a series of
high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} (BSLCO) single crystals for a
wide range of x (x = 0.23 - 1.02), which corresponds to the hole doping per Cu,
p, of 0.03 - 0.18. The anisotropy ratio, \rho_{c}/\rho_{ab}, shows a systematic
increase with decreasing p at moderate temperatures, except for the most
underdoped composition where the localization effect enhances \rho_{ab} and
thus lowers \rho_{c}/\rho_{ab}. The exact p dependence of \rho_{c}/\rho_{ab} at
a fixed temperature is found to be quite peculiar, which is discussed to be due
to the effect of the pseudogap that causes \rho_{c}/\rho_{ab} to be
increasingly more enhanced as p is reduced. The pseudogap also causes a rapid
growth of \rho_{c}/\rho_{ab} with decreasing temperature, and, as a result, the
\rho_{c}/\rho_{ab} value almost reaches 10^6 in underdoped samples just above
T_c. Furthermore, it is found that the temperature dependence of \rho_{c} of
underdoped samples show two distinct temperature regions in the pseudogap
phase, which suggests that the divergence of \rho_{c} below the pseudogap
temperature is governed by two different mechanisms.Comment: 10 pages, 10 figures, revised version. Discussions are expanded with
a new analysis of the T-dependence of \rho_{c} and the resulting new phase
diagra
Electromagnetic Calorimeter for HADES
We propose to build the Electromagnetic calorimeter for the HADES di-lepton
spectrometer. It will enable to measure the data on neutral meson production
from nucleus-nucleus collisions, which are essential for interpretation of
dilepton data, but are unknown in the energy range of planned experiments (2-10
GeV per nucleon). The calorimeter will improve the electron-hadron separation,
and will be used for detection of photons from strange resonances in elementary
and HI reactions.
Detailed description of the detector layout, the support structure, the
electronic readout and its performance studied via Monte Carlo simulations and
series of dedicated test experiments is presented.
The device will cover the total area of about 8 m^2 at polar angles between
12 and 45 degrees with almost full azimuthal coverage. The photon and electron
energy resolution achieved in test experiments amounts to 5-6%/sqrt(E[GeV])
which is sufficient for the eta meson reconstruction with S/B ratio of 0.4% in
Ni+Ni collisions at 8 AGeV. A purity of the identified leptons after the hadron
rejection, resulting from simulations based on the test measurements, is better
than 80% at momenta above 500 MeV/c, where time-of-flight cannot be used.Comment: 40 pages, 38 figures version2 - the time schedule added, information
about PMTs in Sec.III update
Phase-fluctuation induced reduction of the kinetic energy at the superconducting transition
Recent reflectivity measurements provide evidence for a "violation" of the
in-plane optical integral in the underdoped high-T_c compound
Bi_2Sr_2CaCu_2O_{8+\delta} up to frequencies much higher than expected by
standard BCS theory. The sum rule violation may be related to a loss of
in-plane kinetic energy at the superconducting transition. Here, we show that a
model based on phase fluctuations of the superconducting order parameter can
account for this change of in-plane kinetic energy at T_c. The change is due to
a transition from a phase-incoherent Cooper-pair motion in the pseudogap regime
above T_c to a phase-coherent motion at T_c.Comment: 5 pages, 3 eps-figure
Emission patterns of neutral pions in 40 A MeV Ta+Au reactions
Differential cross sections of neutral pions emitted in 181Ta + 197Au
collisions at a beam energy of 39.5A MeV have been measured with the photon
spectrometer TAPS. The kinetic energy and transverse momentum spectra of
neutral pions cannot be properly described in the framework of the thermal
model, nor when the reabsorption of pions is accounted for in a
phenomenological model. However, high energy and high momentum tails of the
pion spectra can be well fitted through thermal distributions with unexpectedly
soft temperature parameters below 10 MeV.Comment: 16 pages (double-spaced), 5 figures; corrections after referee's
comments and suggestion
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