1,798 research outputs found
Breaking time-reversal symmetry with a superconducting flux capacitor
We present the design of a passive, on-chip microwave circulator based on a
ring of superconducting tunnel junctions. We investigate two distinct physical
realisations, based on either Josephson junctions (JJ) or quantum phase slip
elements (QPS), with microwave ports coupled either capacitively (JJ) or
inductively (QPS) to the ring structure. A constant bias applied to the center
of the ring provides the symmetry breaking (effective) magnetic field, and no
microwave or rf bias is required. We find that this design offers high
isolation even when taking into account fabrication imperfections and
environmentally induced bias perturbations and find a bandwidth in excess of
500 MHz for realistic device parameters.Comment: 10 pages, 11 figures, including supplementary material - published as
"Passive on-chip, superconducting circulator using rings of tunnel junctions
Multimodal Generative Learning Utilizing Jensen-Shannon-Divergence
Learning from different data types is a long-standing goal in machine
learning research, as multiple information sources co-occur when describing
natural phenomena. However, existing generative models that approximate a
multimodal ELBO rely on difficult or inefficient training schemes to learn a
joint distribution and the dependencies between modalities. In this work, we
propose a novel, efficient objective function that utilizes the Jensen-Shannon
divergence for multiple distributions. It simultaneously approximates the
unimodal and joint multimodal posteriors directly via a dynamic prior. In
addition, we theoretically prove that the new multimodal JS-divergence (mmJSD)
objective optimizes an ELBO. In extensive experiments, we demonstrate the
advantage of the proposed mmJSD model compared to previous work in
unsupervised, generative learning tasks.Comment: Accepted at NeurIPS 2020, camera-ready versio
Generalized Multimodal ELBO
Multiple data types naturally co-occur when describing real-world phenomena
and learning from them is a long-standing goal in machine learning research.
However, existing self-supervised generative models approximating an ELBO are
not able to fulfill all desired requirements of multimodal models: their
posterior approximation functions lead to a trade-off between the semantic
coherence and the ability to learn the joint data distribution. We propose a
new, generalized ELBO formulation for multimodal data that overcomes these
limitations. The new objective encompasses two previous methods as special
cases and combines their benefits without compromises. In extensive
experiments, we demonstrate the advantage of the proposed method compared to
state-of-the-art models in self-supervised, generative learning tasks.Comment: 2021 ICL
Atelectasis in obese patients undergoing laparoscopic bariatric surgery are not increased upon discharge from Post Anesthesia Care Unit.
BACKGROUND
Obese patients frequently develop pulmonary atelectasis upon general anesthesia. The risk is increased during laparoscopic surgery. This prospective, observational single-center study evaluated atelectasis dynamics using Electric Impedance Tomography (EIT) in patients undergoing laparoscopic bariatric surgery.
METHODS
We included adult patients with ASA physical status I-IV and a BMI of ≥40. Exclusion criteria were known severe pulmonary hypertension, home oxygen therapy, heart failure, and recent pulmonary infections. The primary outcome was the proportion of poorly ventilated lung regions (low tidal variation areas) and the global inhomogeneity (GI) index assessed by EIT before discharge from the Post Anesthesia Care Unit compared to these same measures prior to initiation of anesthesia.
RESULTS
The median (IQR) proportion of low tidal variation areas at the different analysis points were T1 10.8% [3.6-15.1%] and T5 10.3% [2.6-18.9%], and the mean difference was -0.7% (95% CI: -5.8% -4.5%), i.e., lower than the predefined non-inferiority margin of 5% (p = 0.022). There were no changes at the four additional time points compared to T1 or postoperative pulmonary complications during the 14 days following the procedure.
CONCLUSION
We found that obese patients undergoing laparoscopic bariatric surgery do not leave the Post Anesthesia Care Unit with increased low tidal variation areas compared to the preoperative period
Improvement of productivity for aqueous biphasic hydroformylation of methyl 10-undecenoate
The overall productivity of the aqueous biphasic hydroformylation of the castor oil-derived methyl 10-undecenoate is increased. To increase the reaction rate, the miscibility of water and the fatty compound is increased by addition of the green solvent 1-butanol as co-solvent. For the first time, the concentration of solvents, substrate, and product within the reaction process is experimentally examined in a biphasic system under 20 bar pressure of synthesis gas and 140 °C. A reactor to get samples of both phases is developed to determine the quarternary mixture of the reaction system presented in a four-dimensional tetrahedron diagram. With the knowledge gained about the reaction and its drivers, it is possible to increase the efficiency of the reaction process reported so far. With simultaneously high reaction rates (turn over frequency = >5000 h−1), the space–time yield of the reaction reaches values of >120 g L−1h−1 and can be improved significantly without negatively affecting catalyst leaching
Improving aqueous biphasic hydroformylation of unsaturated oleochemicals using a jet-loop-reactor
In two case studies, the reaction performance of the aqueous biphasic hydroformylation of two industrially relevant oleochemicals, namely methyl 10-undecenoate (case 1) and methyl oleate (case 2), is significantly improved by the use of a Jet-Loop Reactor concept. Based on previously reported studies, only the two green and benign co-solvents, 1-butanol and isopropanol are applied, respectively, in the absence of any additional auxiliary. Both reactions benefit highly from using this special piece of equipment, specifically designed for improving gas–liquid–liquid mixing to create large interfacial areas with no moving internals. In case 1, the loading of the co-solvent 1-butanol is successfully reduced. For the first time significant yields (>40% after 1 h) are obtained in the absence of any co-solvent, which is very beneficial, since aldehyde products and substrate form a pure product phase enabling straightforward separation. In case 2, the loading of the substrate methyl oleate is successfully increased from 6 to 30 wt% still showing satisfying productivity. At 15 wt%, the yield of the desired internal aldehydes in the jet-loop reactor is increased by a factor of five compared to a stirred tank reactor after 3 h
The Leading Particle Effect from Heavy-Quark Recombination
The leading particle effect in charm hadroproduction is an enhancement of the
cross section for a charmed hadron D in the forward direction of the beam when
the beam hadron has a valence parton in common with the D. The large D+/D-
asymmetry observed by the E791 experiment is an example of this phenomenon. We
show that the heavy-quark recombination mechanism provides an economical
explanation for this effect. In particular, the D+/D- asymmetry can be fit
reasonably well using a single parameter whose value is consistent with a
recent determination from charm photoproduction.Comment: Revtex file, 4 pages, 3 figure
Structure and Thermodynamics of the Mixed Alkali Alanates
The thermodynamics and structural properties of the hexahydride alanates
(M2M'AlH6) with the elpasolite structure have been investigated. A series of
mixed alkali alanates (Na2LiAlH6, K2LiAlH6 and K2NaAlH6) were synthesized and
found to reversibly absorb and desorb hydrogen without the need for a catalyst.
Pressure-composition isotherms were measured to investigate the thermodynamics
of the absorption and desorption reactions with hydrogen. Isotherms for
catalyzed (4 mol% TiCl3) and uncatalyzed Na2LiAlH6 exhibited an increase in
kinetics, but no change in the bulk thermodynamics with the addition of a
dopant. A structural analysis using synchrotron x-ray diffraction showed that
these compounds favor the Fm-3m space group with the smaller ion (M') occupying
an octahedral site. These results demonstrate that appropriate cation
substitutions can be used to stabilize or destabilize the material and may
provide an avenue to improving the unfavorable thermodynamics of a number of
materials with promising gravimetric hydrogen densities.Comment: 6 pages, 7 figures,3 tables, submitted to PR
Spin structure of the nucleon: QCD evolution, lattice results and models
The question how the spin of the nucleon is distributed among its quark and
gluon constituents is still a subject of intense investigations. Lattice QCD
has progressed to provide information about spin fractions and orbital angular
momentum contributions for up- and down-quarks in the proton, at a typical
scale \mu^2~4 GeV^2. On the other hand, chiral quark models have traditionally
been used for orientation at low momentum scales. In the comparison of such
model calculations with experiment or lattice QCD, fixing the model scale and
the treatment of scale evolution are essential. In this paper, we present a
refined model calculation and a QCD evolution of lattice results up to
next-to-next-to-leading order. We compare this approach with the Myhrer-Thomas
scenario for resolving the proton spin puzzle.Comment: 11 pages, 6 figures, equation (9) has been corrected leading to a
revised figure 1b. Revision matches published versio
Expression of heterologous proteins flanked by NS3-4A cleavage sites within the hepatitis C virus polyprotein
AbstractHepatitis C virus (HCV) contributes substantially to human morbidity and mortality world-wide. The development of HCV genomes expressing heterologous proteins has enhanced the ability to study viral infection, but existing systems have drawbacks. Recombinant viruses often require adaptive mutations to compensate for reduced viral titers, or rely on an artificial genomic organization that uncouples viral protein expression from recombinant gene expression. Here, we sought to exploit the viral polyprotein processing machinery to express heterologous proteins within the context of the HCV polyprotein. We show that HCV genotypes 2a and 1b permit insertion of reporter proteins between NS5A and NS5B with minimal impact on viral fitness. Using this strategy we constructed reporter genomes exhibiting a wide dynamic range, simplifying analysis of HCV infection in primary hepatocytes. Expression of heterologous proteins within the HCV genome offers new opportunities to analyze HCV infection in experimental systems without perturbing functions of individual viral proteins
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