146 research outputs found
Versatile transporter apparatus for experiments with optically trapped Bose-Einstein condensates
We describe a versatile and simple scheme for producing magnetically and
optically-trapped Rb-87 Bose-Einstein condensates, based on a moving-coil
transporter apparatus. The apparatus features a TOP trap that incorporates the
movable quadrupole coils used for magneto-optical trapping and long-distance
magnetic transport of atomic clouds. As a stand-alone device, this trap allows
for the stable production of condensates containing up to one million atoms. In
combination with an optical dipole trap, the TOP trap acts as a funnel for
efficient loading, after which the quadrupole coils can be retracted, thereby
maximizing optical access. The robustness of this scheme is illustrated by
realizing the superfluid-to-Mott insulator transition in a three-dimensional
optical lattice
Radiation Hydrodynamical Instabilities in Cosmological and Galactic Ionization Fronts
Ionization fronts, the sharp radiation fronts behind which H/He ionizing
photons from massive stars and galaxies propagate through space, were
ubiquitous in the universe from its earliest times. The cosmic dark ages ended
with the formation of the first primeval stars and galaxies a few hundred Myr
after the Big Bang. Numerical simulations suggest that stars in this era were
very massive, 25 - 500 solar masses, with H II regions of up to 30,000
light-years in diameter. We present three-dimensional radiation hydrodynamical
calculations that reveal that the I-fronts of the first stars and galaxies were
prone to violent instabilities, enhancing the escape of UV photons into the
early intergalactic medium (IGM) and forming clumpy media in which supernovae
later exploded. The enrichment of such clumps with metals by the first
supernovae may have led to the prompt formation of a second generation of
low-mass stars, profoundly transforming the nature of the first protogalaxies.
Cosmological radiation hydrodynamics is unique because ionizing photons coupled
strongly to both gas flows and primordial chemistry at early epochs,
introducing a hierarchy of disparate characteristic timescales whose relative
magnitudes can vary greatly throughout a given calculation. We describe the
adaptive multistep integration scheme we have developed for the self-consistent
transport of both cosmological and galactic ionization fronts.Comment: 6 pages, 4 figures, accepted for proceedings of HEDLA2010, Caltech,
March 15 - 18, 201
Radial Construction of an Arterial Wall
SummarySome of the most serious diseases involve altered size and structure of the arterial wall. Elucidating how arterial walls are built could aid understanding of these diseases, but little is known about how concentric layers of muscle cells and the outer adventitial layer are assembled and patterned around endothelial tubes. Using histochemical, clonal, and genetic analysis in mice, here we show that the pulmonary artery wall is constructed radially, from the inside out, by two separate but coordinated processes. One is sequential induction of successive cell layers from surrounding mesenchyme. The other is controlled invasion of outer layers by inner layer cells through developmentally regulated cell reorientation and radial migration. We propose that a radial signal gradient controls these processes and provide evidence that PDGF-B and at least one other signal contribute. Modulation of such radial signaling pathways may underlie vessel-specific differences and pathological changes in arterial wall size and structure.Video Abstrac
Creating, moving and merging Dirac points with a Fermi gas in a tunable honeycomb lattice
Dirac points lie at the heart of many fascinating phenomena in condensed
matter physics, from massless electrons in graphene to the emergence of
conducting edge states in topological insulators [1, 2]. At a Dirac point, two
energy bands intersect linearly and the particles behave as relativistic Dirac
fermions. In solids, the rigid structure of the material sets the mass and
velocity of the particles, as well as their interactions. A different, highly
flexible approach is to create model systems using fermionic atoms trapped in
the periodic potential of interfering laser beams, a method which so far has
only been applied to explore simple lattice structures [3, 4]. Here we report
on the creation of Dirac points with adjustable properties in a tunable
honeycomb optical lattice. Using momentum-resolved interband transitions, we
observe a minimum band gap inside the Brillouin zone at the position of the
Dirac points. We exploit the unique tunability of our lattice potential to
adjust the effective mass of the Dirac fermions by breaking inversion symmetry.
Moreover, changing the lattice anisotropy allows us to move the position of the
Dirac points inside the Brillouin zone. When increasing the anisotropy beyond a
critical limit, the two Dirac points merge and annihilate each other - a
situation which has recently attracted considerable theoretical interest [5-9],
but seems extremely challenging to observe in solids [10]. We map out this
topological transition in lattice parameter space and find excellent agreement
with ab initio calculations. Our results not only pave the way to model
materials where the topology of the band structure plays a crucial role, but
also provide an avenue to explore many-body phases resulting from the interplay
of complex lattice geometries with interactions [11, 12]
KLF2 Is a Novel Transcriptional Regulator of Endothelial Proinflammatory Activation
The vascular endothelium is a critical regulator of vascular function. Diverse stimuli such as proinflammatory cytokines and hemodynamic forces modulate endothelial phenotype and thereby impact on the development of vascular disease states. Therefore, identification of the regulatory factors that mediate the effects of these stimuli on endothelial function is of considerable interest. Transcriptional profiling studies identified the Kruppel-like factor (KLF)2 as being inhibited by the inflammatory cytokine interleukin-1β and induced by laminar shear stress in cultured human umbilical vein endothelial cells. Overexpression of KLF2 in umbilical vein endothelial cells robustly induced endothelial nitric oxide synthase expression and total enzymatic activity. In addition, KLF2 overexpression potently inhibited the induction of vascular cell adhesion molecule-1 and endothelial adhesion molecule E-selectin in response to various proinflammatory cytokines. Consistent with these observations, in vitro flow assays demonstrate that T cell attachment and rolling are markedly attenuated in endothelial monolayers transduced with KLF2. Finally, our studies implicate recruitment by KLF2 of the transcriptional coactivator cyclic AMP response element–binding protein (CBP/p300) as a unifying mechanism for these various effects. These data implicate KLF2 as a novel regulator of endothelial activation in response to proinflammatory stimuli
The first spectral line surveys searching for signals from the Dark Ages
Our aim is to observationally investigate the cosmic Dark Ages in order to
constrain star and structure formation models, as well as the chemical
evolution in the early Universe. Spectral lines from atoms and molecules in
primordial perturbations at high redshifts can give information about the
conditions in the early universe before and during the formation of the first
stars in addition to the epoch of reionisation. The lines may arise from moving
primordial perturbations before the formation of the first stars (resonant
scattering lines), or could be thermal absorption or emission lines at lower
redshifts. The difficulties in these searches are that the source redshift and
evolutionary state, as well as molecular species and transition are unknown,
which implies that an observed line can fall within a wide range of
frequencies. The lines are also expected to be very weak. Observations from
space have the advantages of stability and the lack of atmospheric features
which is important in such observations. We have therefore, as a first step in
our searches, used the Odin satellite to perform two sets of spectral line
surveys towards several positions. The first survey covered the band 547-578
GHz towards two positions, and the second one covered the bands 542.0-547.5 GHz
and 486.5-492.0 GHz towards six positions selected to test different sizes of
the primordial clouds. Two deep searches centred at 543.250 and 543.100 GHz
with 1 GHz bandwidth were also performed towards one position. The two lowest
rotational transitions of H2 will be redshifted to these frequencies from
z~20-30, which is the predicted epoch of the first star formation. No lines are
detected at an rms level of 14-90 and 5-35 mK for the two surveys,
respectively, and 2-7 mK in the deep searches with a channel spacing of 1-16
MHz. The broad bandwidth covered allows a wide range of redshifts to be
explored for a number of atomic and molecular species and transitions. From the
theoretical side, our sensitivity analysis show that the largest possible
amplitudes of the resonant lines are about 1 mK at frequencies <200 GHz, and a
few micro K around 500-600 GHz, assuming optically thick lines and no
beam-dilution. However, if existing, thermal absorption lines have the
potential to be orders of magnitude stronger than the resonant lines. We make a
simple estimation of the sizes and masses of the primordial perturbations at
their turn-around epochs, which previously has been identified as the most
favourable epoch for a detection. This work may be considered as an important
pilot study for our forthcoming observations with the Herschel Space
Observatory.Comment: 15 pages, 9 figures, 3 on-line pages. Accepted for publication in
Astronomy & Astrophysics 8 March 2010
The role impairment associated with mental disorder risk profiles in the WHO World Mental Health International College Student Initiative
OBJECTIVE: The objective of this study is to assess the contribution of mental comorbidity to role impairment among college students. METHODS: Web-based self-report surveys from 14,348 first-year college students (Response Rate [RR] = 45.5%): 19 universities, eight countries of the World Mental Health International College Student Initiative. We assessed impairment (Sheehan Disability Scales and number of days out of role [DOR] in the past 30 days) and seven 12-month DSM-IV disorders. We defined six multivariate mental disorder classes using latent class analysis (LCA). We simulated population attributable risk proportions (PARPs) of impairment. RESULTS: Highest prevalence of role impairment was highest among the 1.9% of students in the LCA class with very high comorbidity and bipolar disorder (C1): 78.3% of them had severe role impairment (vs. 20.8%, total sample). Impairment was lower in two other comorbid classes (C2 and C3) and successively lower in the rest. A similar monotonic pattern was found for DOR. Both LCA classes and some mental disorders (major depression and panic, in particular) were significant predictors of role impairment. PARP analyses suggest that eliminating all mental disorders might reduce severe role impairment by 64.6% and DOR by 44.3%. CONCLUSIONS: Comorbid mental disorders account for a substantial part of role impairment in college students. © 2018 John Wiley & Sons, Ltd
Benefits and harms of perioperative high fraction inspired oxygen for surgical site infection prevention: a protocol for a systematic review and meta-analysis of individual patient data of randomised controlled trials.
INTRODUCTION
The use of high fraction of inspired oxygen (FiO2) intraoperatively for the prevention of surgical site infection (SSI) remains controversial. Promising results of early randomised controlled trials (RCT) have been replicated with varying success and subsequent meta-analysis are equivocal. Recent advancements in perioperative care, including the increased use of laparoscopic surgery and pneumoperitoneum and shifts in fluid and temperature management, can affect peripheral oxygen delivery and may explain the inconsistency in reproducibility. However, the published data provides insufficient detail on the participant level to test these hypotheses. The purpose of this individual participant data meta-analysis is to assess the described benefits and harms of intraoperative high FiO2compared with regular (0.21-0.40) FiO2 and its potential effect modifiers.
METHODS AND ANALYSIS
Two reviewers will search medical databases and online trial registries, including MEDLINE, Embase, CENTRAL, CINAHL, ClinicalTrials.gov and WHO regional databases, for randomised and quasi-RCT comparing the effect of intraoperative high FiO2 (0.60-1.00) to regular FiO2 (0.21-0.40) on SSI within 90 days after surgery in adult patients. Secondary outcome will be all-cause mortality within the longest available follow-up. Investigators of the identified trials will be invited to collaborate. Data will be analysed with the one-step approach using the generalised linear mixed model framework and the statistical model appropriate for the type of outcome being analysed (logistic and cox regression, respectively), with a random treatment effect term to account for the clustering of patients within studies. The bias will be assessed using the Cochrane risk-of-bias tool for randomised trials V.2 and the certainty of evidence using Grading of Recommendations, Assessment, Development and Evaluation methodology. Prespecified subgroup analyses include use of mechanical ventilation, nitrous oxide, preoperative antibiotic prophylaxis, temperature (2.5 hour).
ETHICS AND DISSEMINATION
Ethics approval is not required. Investigators will deidentify individual participant data before it is shared. The results will be submitted to a peer-review journal.
PROSPERO REGISTRATION NUMBER
CRD42018090261
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