Dynamics of evaporative cooling in magnetically trapped atomic hydrogen

We study the evaporative cooling of magnetically trapped atomic hydrogen on the basis of the kinetic theory of a Bose gas. The dynamics of trapped atoms is described by the coupled differential equations, considering both the evaporation and dipolar spin relaxation processes. The numerical time-evolution calculations quantitatively agree with the recent experiment of Bose-Einstein condensation with atomic hydrogen. It is demonstrated that the balance between evaporative cooling and heating due to dipolar relaxation limits the number of condensates to 9x10^8 and the corresponding condensate fraction to a small value of 4% as observed experimentally.Comment: 5 pages, REVTeX, 3 eps figures, Phys. Rev. A in pres

Microscopic structure and dynamics of glass forming Zr2Co melts and the impact of different late transition metals on the melt properties

We studied the short-range order and the atomic dynamics of stable and undercooled binary Zr2Co alloy melts as well as their density and viscosity. The containerless processing technique of electrostatic levitation was used to achieve deep undercooling and to avoid contaminations. Static structure factors are determined by combining this technique with neutron and high energy X-ray diffraction. Co self-diffusion coefficients are measured by quasielastic neutron scattering. Our results reveal that the short-range order of the Zr2Co melts closely resembles that previously observed for Zr64Ni36. We consider this as the origin of the very similar melt dynamics of these two alloys at same temperatures. On the other hand, the difference in the structure and dynamics when compared with those of Zr2Cu and Zr2Pd shows clearly that not only the atomic sizes, but also electronic properties or chemical bonding have an important influence on the melt properties of Zr-based glass forming melts

Erratum: "A Gravitational-wave Measurement of the Hubble Constant Following the Second Observing Run of Advanced LIGO and Virgo" (2021, ApJ, 909, 218)

[no abstract available

Determinants of mortality in non-neutropenic ICU patients with candidaemia

Introduction: Candidaemia in critically-ill intensive care unit (ICU) patients is associated with high crude mortality. Determinants of mortality – particularly those amenable to potential modification – are incompletely defined. Methods: A nationwide prospective clinical and microbiological cohort study of all episodes of ICU-acquired candidaemia occurring in non-neutropenic adults was undertaken in Australian ICUs between 2001 and 2004. Multivariate Cox regression analyses were performed to determine independently significant variables associated with mortality. Results: 183 episodes of ICU-acquired candidaemia occurred in 183 patients during the study period. Of the 179 with microbiological data, Candida albicans accounted for 111 (62%) episodes and Candida glabrata, 32 (18%). Outcome data were available for 173: crude hospital mortality at 30 days was 56%. Host factors (older age, ICU admission diagnosis, mechanical ventilation and ICU admission diagnosis) and failure to receive systemic antifungal therapy were significantly associated with mortality on multivariate analysis. Among the subset who received initial fluconazole therapy (n = 93), the crude mortality was 52%. Host factors (increasing age and haemodialysis receipt), but not organism- (Candida species, fluconazole MIC), pharmacokinetic- (fluconazole dose, time to initiation), or pharmacodynamic-related parameters (fluconazole dose:MIC ratio) were associated with mortality. Process of care measures advocated in recent guidelines were implemented inconsistently: follow-up blood cultures were obtained in 68% of patients, central venous catheters removed within five days in 80% and ophthalmological examination performed in 36%. Conclusions: Crude mortality remains high in Australian ICU patients with candidaemia and is overwhelmingly related to host factors but not treatment variables (the time to initiation of antifungals or fluconazole pharmacokinetic and pharmacodynamic factors). The role and timing of early antifungal intervention in critically-ill ICU patients requires further investigation.Deborah J.E. Marriott, E. Geoffrey Playford, Sharon Chen, Monica Slavin, Quoc Nguyen, David Ellis and Tania C. Sorrell for the Australian Candidaemia Stud

GW190814: gravitational waves from the coalescence of a 23 solar mass black hole with a 2.6 solar mass compact object

We report the observation of a compact binary coalescence involving a 22.2–24.3 Me black hole and a compact object with a mass of 2.50–2.67 Me (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO’s and Virgo’s third observing run on 2019 August 14 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of - + 241 45 41 Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, - + 0.112 0.009 0.008, and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to �0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1–23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models of the formation and mass distribution of compact-object binaries

Open data from the third observing run of LIGO, Virgo, KAGRA, and GEO

The global network of gravitational-wave observatories now includes five detectors, namely LIGO Hanford, LIGO Livingston, Virgo, KAGRA, and GEO 600. These detectors collected data during their third observing run, O3, composed of three phases: O3a starting in 2019 April and lasting six months, O3b starting in 2019 November and lasting five months, and O3GK starting in 2020 April and lasting two weeks. In this paper we describe these data and various other science products that can be freely accessed through the Gravitational Wave Open Science Center at https://gwosc.org. The main data set, consisting of the gravitational-wave strain time series that contains the astrophysical signals, is released together with supporting data useful for their analysis and documentation, tutorials, as well as analysis software packages

Chemical short-range order in undercooled Cu-Ni melts

For liquid Cu-Co, which shows a rich phase diagram, it has been shown that Cu and Co demix, if the liquid is undercooled below its binodal line. In contrast Ni-Cu shows a comparatively simple phase diagram of a solid solution and no phase separation in liquid state has been reported so far. On the other hand, measurements of the electrical resistivity show a non-linear temperature dependence for melts of the Cu-rich alloys Ni40Cu60 and Ni20Cu80 [1]. A possible explanation for this non-linear temperature dependence might be concentration fluctuations that increase with increasing undercooling of the liquid, hence indicating a tendency for demixing. Also the slightly positive enthalpy of mixing of Ni-Cu points towards a demixing nature of this system. While these are indirect arguments, in this work we present direct investigations on the short-range order in Ni42.5Cu57.5 alloy melts by elastic neutron diffraction that have been performed on the D20 diffractometer at the Institute Laue-Langevin. An electromagnetic levitation furnace was used as sample environment allowing to undercool the melts below the melting temperature [2]. Partial structure factors have been determined by application of an isotopic substitution technique using samples of the four different isotopic compositions 58Ni42.5natCu57.5, 60Ni42.5natCu57.5, natNi42.5natCu57.5 and 62Ni42.563Cu57.5. The Bhatia-Thornton partial structure factor SNN that describes the topological short-range order of the melt closely resembles the structure factors observed for melts of the pure elements Ni [3] and Cu, indicating a similar topological structure. For the Bhatia-Thornton partial structure factor SCC that describes the chemical short-range order of the melt a rise in intensity is observed at low momentum transfer, q, on top of a relatively large flat background with some smaller oscillations towards larger q. The rise of SCC at low q increases with decreasing temperature. It directly points to the demixing nature of the system with concentration fluctuations on large length scales that become more pronounced with increasing undercooling. Interestingly, the generic behavior of phase separation has recently been studied by means of molecular dynamics simulations on binary symmetric Lennard-Jones mixtures [4,5]. A demixing behavior has been found for attractive Lennard-Jones liquids, if the interaction parameters of the unlike atomic pairs are smaller than those of the like atomic pairs. The shape of SCC and its temperature dependence calculated by the molecular dynamics simulations closely resemble those we observed experimentally for liquid in Ni42.5Cu57.5 showing that main predictions on the dependence of the chemical short-range order on the atomic interactions inferred from this simple generic model are found in real metallic systems like Cu-Ni. References 1) T. Richardsen, G. Lohöfer, Int. J. Thermophys. 23, 1207 (2002). 2) D. Holland-Moritz et. al., Meas. Sci. Techn. 16, 372 (2005). 3) T. Schenk et al., Phys. Rev. Lett. 89, 075507 (2002). 4) S.K. Das et al., J. Chem. Phys. 125, 024506 (2006). 5) S. Amore et al., J. Chem. Phys. 134, 044515 (2011)

Chemical short-range order in liquid Ni-Cu

Neutron diffraction in combination with isotopic substitution on the zero-scatterer 62Ni4363Cu57 shows indications for chemical short-range order in the stable liquid as evidenced by oscillations in the concentration-concentration structure factor SCC(q). This points towards a non-ideal solution behavior of Ni-Cu contrary to common believe but in agreement with measurements of free enthalpy of mixing. The temperature dependence of SCC at small momentum transfer provides evidence of critical compositional fluctuations in Ni43Cu57 melts