2,417 research outputs found
Short-recurrence Krylov subspace methods for the overlap Dirac operator at nonzero chemical potential
The overlap operator in lattice QCD requires the computation of the sign
function of a matrix, which is non-Hermitian in the presence of a quark
chemical potential. In previous work we introduced an Arnoldi-based Krylov
subspace approximation, which uses long recurrences. Even after the deflation
of critical eigenvalues, the low efficiency of the method restricts its
application to small lattices. Here we propose new short-recurrence methods
which strongly enhance the efficiency of the computational method. Using
rational approximations to the sign function we introduce two variants, based
on the restarted Arnoldi process and on the two-sided Lanczos method,
respectively, which become very efficient when combined with multishift
solvers. Alternatively, in the variant based on the two-sided Lanczos method
the sign function can be evaluated directly. We present numerical results which
compare the efficiencies of a restarted Arnoldi-based method and the direct
two-sided Lanczos approximation for various lattice sizes. We also show that
our new methods gain substantially when combined with deflation.Comment: 14 pages, 4 figures; as published in Comput. Phys. Commun., modified
data in Figs. 2,3 and 4 for improved implementation of FOM algorithm,
extended discussion of the algorithmic cos
Étale motivic cohomology and algebraic cycles
We consider etale motivic or Lichtenbaum cohomology and its relation to algebraic cycles. We give an geometric interpretation of Lichtenbaum cohomology and use it to show that the usual integral cycle maps extend to maps on integral Lichtenbaum cohomology. We also show that Lichtenbaum cohomology, in contrast to the usual motivic cohomology, compares well with integral cohomology theories. For example, we formulate integral etale versions of the Hodge and the Tate conjecture, and show that these are equivalent to the usual rational conjectures
The impact of on-site cardiac rhythm on mortality in patients supported with extracorporeal cardiopulmonary resuscitation: A retrospective cohort study.
BACKGROUND
Extracorporeal cardiopulmonary resuscitation (ECPR) is increasingly used in patients with out-of-hospital or in-hospital cardiac arrest in whom conventional cardiopulmonary resuscitation remains unsuccessful. The aim of this study was to analyze the impact of initial cardiac rhythm - detected on-site of the cardiac arrest - on mortality.
METHODS
We performed a retrospective cohort study of patients who received ECPR in our tertiary care cardiac arrest center. Patients were divided into three groups depending on their cardiac rhythm: shockable rhythm, pulseless electrical activity, and asystole. The primary endpoint was mortality within the first 7 days after ECPR deployment. Secondary endpoints were mortality within 28 days and impact of pre-ECPR potassium, serum lactate, pH and pCO2 on mortality. The association of the initial cardiac rhythm and the location of arrhythmia detection (patient monitored in hospital [category: monitored], not monitored but hospitalized [in-hospital], not monitored, not hospitalized [out-of hospital]) with the primary and secondary outcome was examined by means of univariable and multivariable logistic regression.
RESULTS
Sixty-five patients could be included in the final analysis. Thirty-two patients (49.2%, 95%CI 36.6% - 61.9%) died within the first 7 days. In terms of 7-day-mortality patients differed in the initial cardiac rhythm (p=0.040) and with respect of the location of arrhythmia detection (p=0.002). Shockable cardiac rhythm (crude OR 0.21; 95%CI 0.03 - 0.98) and pulseless electrical activity (0.13; 0.02 - 0.61) as the initial rhythm on-site showed better odds for survival compared to asystole. However, this association did neither persist in adjusted analysis nor in pairwise comparison.
DISCUSSION
The study could not demonstrate a better outcome with shockable rhythm after ECPR. More homogeneous and adequately powered cohorts are needed to better understand the impact of cardiac rhythm on patient outcome after ECPR
Non-Invasive Assessment of Intra-Abdominal Pressure Using Ultrasound Guided Tonometry - a Proof-of-Concept Study.
BACKGROUND
Intra-abdominal hypertension jeopardizes abdominal organ perfusion and venous return. Contemporary recognition of elevated intra-abdominal pressure (IAP) plays a crucial role in reducing mortality and morbidity. We evaluated ultrasound guided tonometry in this context hypothesizing that the vertical chamber diameter of this device inversely correlates with intra-abdominal pressure.
METHODS
IAP was increased in six 5 mmHg steps to 40 mmHg by instillation of normal saline into the peritoneal cavity of eight anesthetized pigs. Liver and renal blood flows (ultrasound transit time), intra-vesical, intra-peritoneal and end-inspiratory plateau pressures were recorded. For ultrasound-based assessment of intra-abdominal pressure (ultrasound guided tonometry), a pressure transducing, compressible chamber was fixed at the tip of a linear ultrasound probe, and the system was applied on the abdominal wall using different pre-determined levels of external pressure. At each IAP level (reference: intra-vesical pressure), two investigators measured the vertical diameter of this chamber.
RESULTS
All abdominal flows decreased (by 39% to 58%), and end-inspiratory plateau pressure increased from 15 mbar (14-17 mbar) to 38 mbar (33-42 mbar) (median, range) with increasing IAP (all p < 0.01). Vertical chamber diameter decreased from 14.9 (14.6-15.2) mm to12.8 (12.4-13.4) mm with increasing IAP. Coefficients of variations between and within observers regarding change of the vertical tonometry chamber diameter were small (all < 4%), and the results were independent of the externally applied pressure level on the ultrasound probe. Correlation of IAP and vertical pressure chamber distance was highly significant (r: -1, p: 0.0004). Ultrasound guided tonometry could discriminate between normal (baseline) pressure and 15 mmHg, between 15 and 25mmHg) and between 25 and 40 mmHg IAP (all p≤0.18). Similar results were obtained for end-inspiratory plateau pressures.
CONCLUSIONS
In our model, values obtained by ultrasound guided tonometry correlated significantly with intra-abdominal pressures. The method was able to discriminate between normal, moderately and markedly increased IAP values
Non-Invasive Assessment of Intra-Abdominal Pressure Using Ultrasound Guided Tonometry - a Proof-of-Concept Study.
BACKGROUND
Intra-abdominal hypertension jeopardizes abdominal organ perfusion and venous return. Contemporary recognition of elevated intra-abdominal pressure (IAP) plays a crucial role in reducing mortality and morbidity. We evaluated ultrasound guided tonometry in this context hypothesizing that the vertical chamber diameter of this device inversely correlates with intra-abdominal pressure.
METHODS
IAP was increased in six 5 mmHg steps to 40 mmHg by instillation of normal saline into the peritoneal cavity of eight anesthetized pigs. Liver and renal blood flows (ultrasound transit time), intra-vesical, intra-peritoneal and end-inspiratory plateau pressures were recorded. For ultrasound-based assessment of intra-abdominal pressure (ultrasound guided tonometry), a pressure transducing, compressible chamber was fixed at the tip of a linear ultrasound probe, and the system was applied on the abdominal wall using different pre-determined levels of external pressure. At each IAP level (reference: intra-vesical pressure), two investigators measured the vertical diameter of this chamber.
RESULTS
All abdominal flows decreased (by 39% to 58%), and end-inspiratory plateau pressure increased from 15 mbar (14-17 mbar) to 38 mbar (33-42 mbar) (median, range) with increasing IAP (all p < 0.01). Vertical chamber diameter decreased from 14.9 (14.6-15.2) mm to12.8 (12.4-13.4) mm with increasing IAP. Coefficients of variations between and within observers regarding change of the vertical tonometry chamber diameter were small (all < 4%), and the results were independent of the externally applied pressure level on the ultrasound probe. Correlation of IAP and vertical pressure chamber distance was highly significant (r: -1, p: 0.0004). Ultrasound guided tonometry could discriminate between normal (baseline) pressure and 15 mmHg, between 15 and 25mmHg) and between 25 and 40 mmHg IAP (all p≤0.18). Similar results were obtained for end-inspiratory plateau pressures.
CONCLUSIONS
In our model, values obtained by ultrasound guided tonometry correlated significantly with intra-abdominal pressures. The method was able to discriminate between normal, moderately and markedly increased IAP values
Transition from a polaronic condensate to a degenerate Fermi gas of heteronuclear molecules
The interplay of quantum statistics and interactions in atomic Bose--Fermi
mixtures leads to a phase diagram markedly different from pure fermionic or
bosonic systems. However, investigating this phase diagram remains challenging
when bosons condense. Here, we observe evidence for a quantum phase transition
from a polaronic to a molecular phase in a density-matched degenerate
Bose--Fermi mixture. The condensate fraction, representing the order parameter
of the transition, is depleted by interactions and the build-up of strong
correlations results in the emergence of a molecular Fermi gas. By driving
through the transition, we ultimately produce a quantum-degenerate sample of
sodium-potassium molecules exhibiting a large molecule-frame dipole moment of
2.7 Debye. The observed phase transition represents a new phenomenon
complementary to the paradigmatic BEC-BCS crossover observed in Fermi systems.Comment: 12 pages, 9 figure
The effects of positive end-expiratory pressure on cardiac function: a comparative echocardiography-conductance catheter study.
BACKGROUND
Echocardiographic parameters of diastolic function depend on cardiac loading conditions, which are altered by positive pressure ventilation. The direct effects of positive end-expiratory pressure (PEEP) on cardiac diastolic function are unknown.
METHODS
Twenty-five patients without apparent diastolic dysfunction undergoing coronary angiography were ventilated noninvasively at PEEPs of 0, 5, and 10 cmH2O (in randomized order). Echocardiographic diastolic assessment and pressure-volume-loop analysis from conductance catheters were compared. The time constant for pressure decay (Ï„) was modeled with exponential decay. End-diastolic and end-systolic pressure volume relationships (EDPVRs and ESPVRs, respectively) from temporary caval occlusion were analyzed with generalized linear mixed-effects and linear mixed models. Transmural pressures were calculated using esophageal balloons.
RESULTS
τ values for intracavitary cardiac pressure increased with the PEEP (n = 25; no PEEP, 44 ± 5 ms; 5 cmH2O PEEP, 46 ± 6 ms; 10 cmH2O PEEP, 45 ± 6 ms; p < 0.001). This increase disappeared when corrected for transmural pressure and diastole length. The transmural EDPVR was unaffected by PEEP. The ESPVR increased slightly with PEEP. Echocardiographic mitral inflow parameters and tissue Doppler values decreased with PEEP [peak E wave (n = 25): no PEEP, 0.76 ± 0.13 m/s; 5 cmH2O PEEP, 0.74 ± 0.14 m/s; 10 cmH2O PEEP, 0.68 ± 0.13 m/s; p = 0.016; peak A wave (n = 24): no PEEP, 0.74 ± 0.12 m/s; 5 cmH2O PEEP, 0.7 ± 0.11 m/s; 10 cmH2O PEEP, 0.67 ± 0.15 m/s; p = 0.014; E' septal (n = 24): no PEEP, 0.085 ± 0.016 m/s; 5 cmH2O PEEP, 0.08 ± 0.013 m/s; 10 cmH2O PEEP, 0.075 ± 0.012 m/s; p = 0.002].
CONCLUSIONS
PEEP does not affect active diastolic relaxation or passive ventricular filling properties. Dynamic echocardiographic filling parameters may reflect changing loading conditions rather than intrinsic diastolic function. PEEP may have slight positive inotropic effects.
CLINICAL TRIAL REGISTRATION
https://clinicaltrials.gov/ct2/show/NCT02267291 , registered 17. October 2014
Collisions of ultracold molecules in bright and dark optical dipole traps
Understanding collisions between ultracold molecules is crucial for making
stable molecular quantum gases and harnessing their rich internal degrees of
freedom for quantum engineering. Transient complexes can strongly influence
collisional physics, but in the ultracold regime, key aspects of their behavior
have remained unknown. To explain experimentally observed loss of ground-state
molecules from optical dipole traps, it was recently proposed that molecular
complexes can be lost due to photo-excitation. By trapping molecules in a
repulsive box potential using laser light near a narrow molecular transition,
we are able to test this hypothesis with light intensities three orders of
magnitude lower than what is typical in red-detuned dipole traps. This allows
us to investigate light-induced collisional loss in a gas of nonreactive
fermionic NaK molecules. Even for the lowest intensities
available in our experiment, our results are consistent with universal loss,
meaning unit loss probability inside the short-range interaction potential. Our
findings disagree by at least two orders of magnitude with latest theoretical
predictions, showing that crucial aspects of molecular collisions are not yet
understood, and provide a benchmark for the development of new theories.Comment: 13 pages, 11 figure
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