Quasi-exact solvability of Dirac equation with Lorentz scalar potential

We consider exact/quasi-exact solvability of Dirac equation with a Lorentz scalar potential based on factorizability of the equation. Exactly solvable and $sl(2)$-based quasi-exactly solvable potentials are discussed separately in Cartesian coordinates for a pure Lorentz potential depending only on one spatial dimension, and in spherical coordinates in the presence of a Dirac monopole.Comment: 10 pages, no figure

A comparative cost-effectiveness analysis of mechanical and pharmacological VTE prophylaxis after lower limb arthroplasty in Australia

Background Venous thromboembolism (VTE) is a complication following surgery. Low-molecular-weight heparin (LMWH) or direct oral anticoagulants (DOACs) are efficacious but come with inherent bleeding risk. Mechanical prophylaxis, such as intermittent pneumatic compression (IPC), does not induce bleeding but may be difficult to implement beyond the immediate post-operative period. This study compared the cost and quality-adjusted life years (QALYs) saved of commonly used VTE prophylaxis regimens after lower limb arthroplasty. Methods A previously published cost-utility model considering major efficacy and safety endpoints was updated to estimate the 1-year cost-effectiveness of different VTE prophylaxis regimens. The VTE strategies assessed included apixaban, dabigatran, rivaroxaban, LMWH, IPC, IPC + LMWH and IPC + apixaban. Efficacy data were derived from studies in PubMed, and cost data came from the 2017 Australian AR-DRG and PBS pricing schemes. Results Costs for VTE prophylaxis including treatment of its associated complications over the first year after surgery ranged from AUD $644 (IPC) to AUD$956 (rivaroxaban). Across 500 simulations, IPC was the cheapest measure in 73% of simulations. In 97% of simulations, a DOAC was associated with the highest resulting QALYs. Compared to IPC, apixaban was cost-effective in 76.4% of simulations and apixaban + IPC in 87.8% of simulations. For VTE events avoided, the DOACs and IPC were on par. LMWH and LMWH + IPC were negatively dominated. Conclusions Apixaban, IPC or a sequential/simultaneous combination of both is currently the most cost-effective VTE prophylaxis regimens. The choice between them is best guided by the relative VTE and bleeding risks of individual patients

Dichotomous development of the gut microbiome in preterm infants.

BackgroundPreterm infants are at risk of developing intestinal dysbiosis with an increased proportion of Gammaproteobacteria. In this study, we sought the clinical determinants of the relative abundance of feces-associated Gammaproteobacteria in very low birth weight (VLBW) infants. Fecal microbiome was characterized at ≤ 2 weeks and during the 3rd and 4th weeks after birth, by 16S rRNA amplicon sequencing. Maternal and infant clinical characteristics were extracted from electronic medical records. Data were analyzed by linear mixed modeling and linear regression.ResultsClinical data and fecal microbiome profiles of 45 VLBW infants (gestational age 27.9 ± 2.2 weeks; birth weight 1126 ± 208 g) were studied. Three stool samples were analyzed for each infant at mean postnatal ages of 9.9 ± 3, 20.7 ± 4.1, and 29.4 ± 4.9 days. The average relative abundance of Gammaproteobacteria was 42.5% (0-90%) at ≤ 2 weeks, 69.7% (29.9-86.9%) in the 3rd, and 75.5% (54.5-86%) in the 4th week (p < 0.001). Hierarchical and K-means clustering identified two distinct subgroups: cluster 1 started with comparatively low abundance that increased with time, whereas cluster 2 began with a greater abundance at ≤ 2 weeks (p < 0.001) that decreased over time. Both groups resembled each other by the 3rd week. Single variants of Klebsiella and Staphylococcus described variance in community structure between clusters and were shared between all infants, suggesting a common, hospital-derived source. Fecal Gammaproteobacteria was positively associated with vaginal delivery and antenatal steroids.ConclusionsWe detected a dichotomy in gut microbiome assembly in preterm infants: some preterm infants started with low relative gammaproteobacterial abundance in stool that increased as a function of postnatal age, whereas others began with and maintained high abundance. Vaginal birth and antenatal steroids were identified as predictors of Gammaproteobacteria abundance in the early (≤ 2 weeks) and later (3rd and 4th weeks) stool samples, respectively. These findings are important in understanding the development of the gut microbiome in premature infants

Occurrence of Kanamycin-Resistant Bacteria Relative to Anthropogenic Pollution Along Richland Creek in Nashville, TN​

The overuse of antibiotics has caused an increase in antibiotic-resistant (AR) bacteria, which is a serious public health concern. Previous studies showed a significant correlation between anthropogenic pollution and AR bacteria. This project aims to identify AR bacteria in Richland Creek relative to local anthropogenic pollution. Water samples were collected at four locations along Richland Creek in Nashville, Tennessee. Bacteria resistant to the antibiotic kanamycin were isolated from the water samples, identified to genera using DNA barcoding, and compared among the sites. We expect to see a greater abundance and diversity of kanamycin-resistant bacteria closer to the end than near the head of the creek. This research project can help describe the diversity of AR bacteria species present in the stream in different areas of Nashville and has public health consequences if the disparities in the distribution of AR bacteria correlate to human activity and/or socioeconomic differences along the stream

Lagrangian evolution of DMS during the Southern Ocean gas exchange experiment: The effects of vertical mixing and biological community shift

Concentrations of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) are highly variable in time and space. What is driving the variability in DMS(P), and can those variability be explained by physical processes and changes in the biological community? During the Southern Ocean Gas Exchange Experiment (SO GasEx) in the austral fall of 2008, two 3He/SF6 labeled patches were created in the surface water. SF6 and DMS were surveyed continuously in a Lagrangian framework, while direct measurements of air-sea exchange further constrained the gas budgets. Turbulent diffusivity at the base of the mixed layer was estimated from SF6 profiles and used to calculate the vertical fluxes of DMS and nutrients. Increasing mixed layer nutrient concentrations due to mixing were associated with a shift in the phytoplankton community structure, which in turned likely affected the sulfur dynamics on timescales of days. DMS concentration as well as air-sea DMS flux appeared to be decoupled from the DMSP concentration, possibly due to grazing and bacterial DMS production. Contrary to expectations, in an environment with high winds and modest productivity, physical processes (air-sea exchange, photochemistry, vertical mixing) only accounted for a small fraction of DMS loss from the surface water. Among the DMS sinks, inferred biological consumption most likely dominated during SO GasEx

A Dynamical Study of the Black Hole X-ray Binary Nova Muscae 1991

We present a dynamical study of the Galactic black hole binary system Nova Muscae 1991 (GS/GRS 1124-683). We utilize 72 high resolution Magellan Echellette (MagE) spectra and 72 strictly simultaneous V-band photometric observations; the simultaneity is a unique and crucial feature of this dynamical study. The data were taken on two consecutive nights and cover the full 10.4-hour orbital cycle. The radial velocities of the secondary star are determined by cross-correlating the object spectra with the best-match template spectrum obtained using the same instrument configuration. Based on our independent analysis of five orders of the echellette spectrum, the semi-amplitude of the radial velocity of the secondary is measured to be K_2 = 406.8+/-2.7 km/s, which is consistent with previous work, while the uncertainty is reduced by a factor of 3. The corresponding mass function is f(M) = 3.02+/-0.06 M_\odot. We have also obtained an accurate measurement of the rotational broadening of the stellar absorption lines (v sin i = 85.0+/-2.6 km/s) and hence the mass ratio of the system q = 0.079+/-0.007. Finally, we have measured the spectrum of the non-stellar component of emission that veils the spectrum of the secondary. In a future paper, we will use our veiling-corrected spectrum of the secondary and accurate values of K_2 and q to model multi-color light curves and determine the systemic inclination and the mass of the black hole.Comment: ApJ accepted version; minor revision; added a subsection about systematic uncertaintie

WZ Cygni: a Marginal Contact Binary in a Triple System?

We present new multiband CCD photometry for WZ Cyg made on 22 nights in two observing seasons of 2007 and 2008. Our light-curve synthesis indicates that the system is in poor thermal contact with a fill-out factor of 4.8% and a temperature difference of 1447 K. Including our 40 timing measurements, a total of 371 times of minimum light spanning more than 112 yr were used for a period study. Detailed analysis of the $O$--$C$ diagram showed that the orbital period has varied by a combination with an upward parabola and a sinusoid. The upward parabola means the continuous period increase and indicates that some stellar masses are thermally transferred from the less to the more massive primary star at a rate of about 5.80$\times10^{-8}$ M$_\odot$ yr$^{-1}$. The sinusoidal variation with a period of 47.9 yr and a semi-amplitude of 0.008 d can be interpreted most likely as the light-travel-time effect due to the existence of a low-mass M-type tertiary companion with a projected mass of $M_3 \sin i_3$=0.26 M$_\odot$. We examined the evolutionary status of WZ Cyg from the absolute dimensions of the eclipsing pair. It belongs to the marginal contact binary systems before broken-contact phase, consisting of a massive primary star with spectral type of F4 and a secondary with the type K1.Comment: 20 pages, including 3 figures and 6 tables, accepted for publication in A

Magnetic Silicon Fullerene

A metal-encapsulating silicon fullerene, Eu@Si20, has been predicted by density functional theory to be by far the most stable fullerene-like silicon structure. The Eu@Si20 structure is a dodecahedron with D2h symmetry in which the europium atom occupies the center site. The calculated results show that the europium atom has a large magnetic moment of nearly 7.0 Bohr magnetons. In addition, it was found that a stable "pearl necklace" nanowire, constructed by concatenating a series of Eu@Si20 units, with the central europium atom, retains the high spin moment. The magnetic structure of the nanowire indicates potential applications in the fields of spintronics and high-density magnetic storage