Numerical investigation of high-speed droplet impact using a multiscale two-fluid approach

A single droplet impact onto solid surfaces remains a fundamental and challenging topic in both experimental and numerical studies with significant importance in a plethora of industrial applications, ranging from printing technologies to fuel injection in internal combustion engines. Under high-speed impact conditions, additional complexities arise as a result of the prompt droplet splashing and the subsequent violent fragmentation; thus, different flow regimes and a vast spectrum of sizes for the produced secondary flow structures coexist in the flow field. The present work introduces a numerical methodology to capture the multiscale processes involved with respect to local topological characteristics. The proposed methodology concerns a compressible Σ-Υ two-fluid model with dynamic interface sharpening based on an advanced flow topology detection algorithm. The model has been developed in OpenFOAM® and provides the flexibility of dealing with the multiscale character of droplet splashing, by switching between a sharp and a diffuse interface within the Eulerian-Eulerian framework in segregated and dispersed flow regions, respectively. An additional transport equation for the interface surface area density (Σ) introduces important information for the sub-grid scale phenomena, which is exploited in the dispersed flow regions to provide an insight into the extended cloud of secondary droplets after impact on the target. A high-speed water droplet impact case has been examined and evaluated against new experimental data; these refer to a millimetre size droplet impacting a solid dry smooth surface at velocity as high as 150m/s, which corresponds to a Weber number of ~7.6×10^5. At the investigated impact conditions compressibility effects dominate the early stages of droplet splashing. A strong shock wave forms and propagates inside the droplet, where transonic Mach numbers occur; local Mach numbers up to 2.5 are observed for the expelled surrounding gas outside the droplet. The proposed numerical approach is found to capture relatively accurately the phenomena and provide significant information regarding the produced flow structure dimensions, which is not available from the experiment

Gamma-Ray Burst Phenomenon as Collapse of QED Magnetized Vacuum Bubble: Analogy with Sonoluminescence

We consider the phenomenon of a gamma-ray burst as a nonlinear collapse of a magnetic cavity surrounding a neutron star with very strong magnetic field B = 10^15 - 10^16 G due to the process of the bubble shape instability in a resonant MHD field of the accreting plasma. The QED effect of vacuum polarizability by the strong magnetic field is taken into account. We develop an analogy with the phenomenon of sonoluminescence (SL) when the gas bubble is located in the surrounding liquid with a driven sound intensity. We show that this analogy between GRB and SL phenomena really exists.Comment: 14 pages, submitted to Natur

Algebraic approach to quantum field theory on a class of noncommutative curved spacetimes

In this article we study the quantization of a free real scalar field on a class of noncommutative manifolds, obtained via formal deformation quantization using triangular Drinfel'd twists. We construct deformed quadratic action functionals and compute the corresponding equation of motion operators. The Green's operators and the fundamental solution of the deformed equation of motion are obtained in terms of formal power series. It is shown that, using the deformed fundamental solution, we can define deformed *-algebras of field observables, which in general depend on the spacetime deformation parameter. This dependence is absent in the special case of Killing deformations, which include in particular the Moyal-Weyl deformation of the Minkowski spacetime.Comment: LaTeX 14 pages, no figures, svjour3.cls style; v2: clarifications and references added, compatible with published versio

A Completely Invariant SUSY Transform of Supersymmetric QED

We study the SUSY breaking of the covariant gauge-fixing term in SUSY QED and observe that this corresponds to a breaking of the Lorentz gauge condition by SUSY. Reasoning by analogy with SUSY's violation of the Wess-Zumino gauge, we argue that the SUSY transformation, already modified to preserve Wess-Zumino gauge, should be further modified by another gauge transformation which restores the Lorentz gauge condition. We derive this modification and use the resulting transformation to derive a Ward identitiy relating the photon and photino propagators without using ghost fields. Our transformation also fulfills the SUSY algebra, modulo terms that vanish in Lorentz gauge

Testing the Noncommutative Standard Model at a Future Photon Collider

Extensions of the Standard Model of elementary particle physics to noncommutative geometries have been proposed as a low energy limit of string models. Independent of this motivation, one may consider such a model as an effective field theory with higher-dimensional operators containing an antisymmetric rank-two background field. We study the signals of such a Noncommutative Standard Model (NCSM) and analyze the discovery potential of a future photon collider, considering angular distributions in fermion pair production.Comment: 13 pages RevTeX, Feynman diagrams and figures included, references added, typographical errors in Feynman rules corrected (all results remain unchangend, since correct Feynman rules were used in the calculations), to appear in Phys. Rev.

Beyond the iron group: heavy metals in hot subdwarfs

We report the discovery of strong photospheric resonance lines of Ga III, Ge IV, Sn IV and Pb IV in the UV spectra of more than two dozen sdB and sdOB stars at temperatures ranging from 22000 K to 40000 K. Lines of other heavy elements are also detected, however in these cases more atomic data are needed. Based on these discoveries, we present a hypothesis to explain the apparent lack of silicon in sdB stars hotter than ~32000 K. The existence of triply ionised Ge, Sn, and Pb suggests that rather than silicon sinking deep into the photosphere, it is removed from the star in a fractionated stellar wind. This hypothesis provides a challenge to diffusion models of sdB stars.Comment: 5 pages, 3 figures, to appear in A&A Letter

Magnetic neutron scattering study of YVO3: Evidence for an orbital Peierls state

Neutron spectroscopy has revealed a highly unusual magnetic structure and dynamics in YVO$_3$, an insulating pseudocubic perovskite that undergoes a series of temperature induced phase transitions between states with different spin and orbital ordering patterns. A good description of the neutron data is obtained by a theoretical analysis of the spin and orbital correlations of a realistic one-dimensional model. This leads to the tentative identification of one of the phases of YVO$_3$ with the ``orbital Peierls state'', a theoretically proposed many-body state comprised of orbital singlet bonds.Comment: final version, to appear in PR

Antibiotic stewardship implementation and patient-level antibiotic use at hospitals with and without on-site Infectious Disease specialists.

Many US hospitals lack Infectious Disease (ID) specialists, which may hinder antibiotic stewardship efforts. We sought to compare patient-level antibiotic exposure at Veterans Health Administration (VHA) hospitals with and without an on-site ID specialist, defined as an ID physician and/or ID pharmacist. This retrospective VHA cohort included all acute-care patient-admissions during 2016. A mandatory survey was used to identify hospitals' antibiotic stewardship processes and their access to an on-site ID specialist. Antibiotic use was quantified as days of therapy (DOT) per days-present and categorized based on National Healthcare Safety Network definitions. A negative binomial regression model with risk adjustment was used to determine the association between presence of an on-site ID specialist and antibiotic use at the level of patient-admissions. Eighteen of 122 (14.8%) hospitals lacked an on-site ID specialist; there were 525,451 (95.8%) admissions at ID hospitals and 23,007 (4.2%) at non-ID sites. In the adjusted analysis, presence of an ID specialist was associated with lower total inpatient antibacterial use [OR 0.92, (95% CI, 0.85-0.99)]. Presence of an ID specialist was also associated with lower use of broad-spectrum antibacterials [OR 0.61 (95% CI, 0.54-0.70)] and higher narrow-spectrum beta-lactam use [OR 1.43 (95% CI, 1.22-1.67)]. Total antibacterial exposure (inpatient plus post-discharge) was lower among patients at ID versus non-ID sites [OR 0.92 (95% CI, 0.86-0.99)]. Patients at hospitals with an ID specialist received antibiotics in a way more consistent with stewardship principles. The presence of an ID specialist may be important to effective antibiotic stewardship

Antibiotic Stewardship Implementation and Antibiotic Use at Hospitals With and Without On-site Infectious Disease Specialists.

BackgroundMany US hospitals lack infectious disease (ID) specialists, which may hinder antibiotic stewardship efforts. We sought to compare patient-level antibiotic exposure at Veterans Health Administration (VHA) hospitals with and without an on-site ID specialist, defined as an ID physician and/or ID pharmacist.MethodsThis retrospective VHA cohort included all acute-care patient admissions during 2016. A mandatory survey was used to identify hospitals' antibiotic stewardship processes and their access to an on-site ID specialist. Antibiotic use was quantified as days of therapy per days present and categorized based on National Healthcare Safety Network definitions. A negative binomial regression model with risk adjustment was used to determine the association between presence of an on-site ID specialist and antibiotic use at the level of patient admissions.ResultsEighteen of 122 (14.8%) hospitals lacked an on-site ID specialist; there were 525 451 (95.8%) admissions at ID hospitals and 23 007 (4.2%) at non-ID sites. In the adjusted analysis, presence of an ID specialist was associated with lower total inpatient antibacterial use (odds ratio, 0.92; 95% confidence interval, .85-.99). Presence of an ID specialist was also associated with lower use of broad-spectrum antibacterials (0.61; .54-.70) and higher narrow-spectrum β-lactam use (1.43; 1.22-1.67). Total antibacterial exposure (inpatient plus postdischarge) was lower among patients at ID versus non-ID sites (0.92; .86-.99).ConclusionsPatients at hospitals with an ID specialist received antibiotics in a way more consistent with stewardship principles. The presence of an ID specialist may be important to effective antibiotic stewardship