A finite element beam model was used to study the effects of joint bar looseness, rail height mismatch and train speed on the crack driving force for a crack emanating from a bolt hole in the web of ...a railroad rail. The model accounts for looseness by simulating gaps of varying sizes between rail and joint bars, while the effects of height mismatch were simulated by imposing an impulse to the end of one rail and using modal analysis to determine rail forces. The analysis shows that the crack driving force increases by about 25% as the joint loosens, primarily due to the increase in dynamic wheel load. The results also indicate that a rail height mismatch of 0.25 in. could cause fracture at train speeds as low as 10 mph, if the toughness of the rail steel is low.
We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified ...as a resolved overdensity of old and metal-poor stars with a heliocentric distance of , a half-light radius of , an age of , a metallicity of , and an absolute magnitude of . This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of , a half-light radius of , an age of , a metallicity of , and an absolute magnitude of , consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.
Global polarization of Ξ and Ω hyperons has been measured for the first time in Au + Au collisions at √sNN = 200 GeV. The measurements of the Ξ− and ... hyperon polarization have been performed by ...two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay Ξ → Λ + π, as well as by measuring the polarization of the daughter Λ hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over Ξ− and ... is measured to be ⟨PΞ⟩ = 0.47 ± 0.10(stat) ± 0.23(syst)% for the collision centrality 20%–80%. The ⟨PΞ⟩ is found to be slightly larger than the inclusive Λ polarization and in reasonable agreement with a multiphase transport model. The ⟨PΞ⟩ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. The global polarization of Ω, ⟨PΩ⟩ = 1.11 ± 0.87(stat) ± 1.97(syst)% was obtained by measuring the polarization of daughter Λ in the decay Ω → Λ + K, assuming the polarization transfer factor CΩΛ = 1.
We report precision measurements of hypernuclei $^3_ΛH$ and $^4_ΛH$ lifetimes obtained from Au + Au collisions at $\sqrt{sNN}$ = 3.0 GeV and 7.2 GeV collected by the STAR experiment at the ...Relativistic Heavy Ion Collider, and the first measurement of $^3_ΛH$ and $^4_ΛH$ midrapidity yields in Au + Au collisions at $\sqrt{sNN}$ = 3.0 GeV. $^3_ΛH$ and $^4_ΛH$, being the two simplest bound states composed of hyperons and nucleons, are cornerstones in the field of hypernuclear physics. Their lifetimes are measured to be 221 ± 15 (stat) ± 19 (syst) ps for $^3_ΛH$ and 218 ± 6 (stat) ± 13 (syst) ps for $^4_ΛH$. The pT-integrated yields of $^3_ΛH$ and $^4_ΛH$ are presented in different centrality and rapidity intervals. It is observed that the shape of the rapidity distribution of $4_ΛH$ is different for 0%–10% and 10%–50% centrality collisions. Thermal model calculations, using the canonical ensemble for strangeness, describes the $^3_ΛH$ yield well, while underestimating the $^4_ΛH$ yield. Transport models, combining baryonic mean-field and coalescence (jam) or utilizing dynamical cluster formation via baryonic interactions (phqmd) for light nuclei and hypernuclei production, approximately describe the measured $^3_ΛH$ and $^4_ΛH$ yields. Our measurements provide means to precisely assess our understanding of the fundamental baryonic interactions with strange quarks, which can impact our understanding of more complicated systems involving hyperons, such as the interior of neutron stars or exotic hypernuclei.
Abstract
APOGEE is a high-resolution (
R
∼ 22,000), near-infrared, multi-epoch, spectroscopic survey of the Milky Way. The second generation of the APOGEE project, APOGEE-2, includes an expansion of ...the survey to the Southern Hemisphere called APOGEE-2S. This expansion enabled APOGEE to perform a fully panoramic mapping of all of the main regions of the Milky Way; in particular, by operating in the
H
band, APOGEE is uniquely able to probe the dust-hidden inner regions of the Milky Way that are best accessed from the Southern Hemisphere. In this paper we present the targeting strategy of APOGEE-2S, with special attention to documenting modifications to the original, previously published plan. The motivation for these changes is explained as well as an assessment of their effectiveness in achieving their intended scientific objective. In anticipation of this being the last paper detailing APOGEE targeting, we present an accounting of all such information complete through the end of the APOGEE-2S project; this includes several main survey programs dedicated to exploration of major stellar populations and regions of the Milky Way, as well as a full list of programs contributing to the APOGEE database through allocations of observing time by the Chilean National Time Allocation Committee and the Carnegie Institution for Science. This work was presented along with a companion article, Beaton et al. (2021), presenting the final target selection strategy adopted for APOGEE-2 in the Northern Hemisphere.
Craniosynostosis is treated with endoscopic, open, and/or distraction surgical techniques. We assessed institutional variation in the use these techniques for craniosynostosis and compared hospital ...resource use.
Retrospective analysis of 5249 infants age <18 months old undergoing surgical procedures for all types of craniosynostosis in 2016-2020 in 39 freestanding children's hospitals in the Pediatric Health Information System (PHIS) database. Endoscopic vs. open cranial vault surgery (with and without distraction osteogenesis) was identified using ICD-10-CM codes. Inpatient cost and length of stay (LOS) were compared by surgery type with Wilcoxon Rank Sum.
There was significant (p < .001) variation in the percentage of infants who underwent endoscopic repair across hospitals median 23.6% (interquartile range (IQR): 7.6%-37.5%), range: 0% to 80.4% and across regions range: 22.1% (southeast) to 42.5% (northeast). For endoscopic procedures, median LOS and inpatient cost were lower (p < .001) without vs. with distraction 1 day (IQR 1-1) vs. 2 days (IQR 2-2); $14,617 (IQR 11,823-22178) vs. $33,599 (IQR 22,800-38,619). For open interventions, median LOS and inpatient cost were also lower (p < .001) without vs. with distraction 3 days (IQR 2-4) vs. 5 days (IQR 4-6) and $37,251 (IQR 27,114-50.320) vs. $62,247 (IQR 42,124-91,620).
Substantial variation in the surgical approach for craniosynostosis exists across hospitals and regions. Endoscopic repair without distraction had the lowest hospital resource use, while open repair with distraction had the highest hospital resource. Subsequent analysis of short- and long-term outcomes as well as patient-and-family costs is necessary to assess the true cost-effectiveness of each approach.
Abstract
Prompted by peculiar spectroscopic variability observed in SDSS/APOGEE
H
-band spectra, we monitored the Be star HD 55606 using optical spectroscopy and found that it is an exotic ...double-lined spectroscopic binary (SB2) consisting of a Be star and a hot, compact companion that is probably an OB subdwarf (sdOB) star. The motion of the sdOB star is traced by its impact on the strong He
i
lines, observed as radial velocity (
V
r
) variable, double-peaked emission profiles with narrow central absorption cores. Weak He
ii
4686 Å absorption associated with the companion star is detected in most spectra. Use of the emission peaks of low-ionization emission lines to trace the Be star
V
r
and the He
i
lines to trace the companion star
V
r
yields a circular orbital solution with a 93.8 day period and masses of
M
Be
= 6.2
M
⊙
and
M
sdOB
= 0.9
M
⊙
in the case of
i
= 80°. HD 55606 exhibits a variety of phase-locked variability, including the development of shell lines twice per orbit. The shell phases coincide with variation in the double emission peak separations, and both forms of variability are likely caused by a two-armed spiral density perturbation in the Be disk. The intensity ratios of the double emission peaks are also phase-locked, possibly indicating heating by the sdOB star of the side of the Be disk facing it. HD 55606 is a new member of the growing sample of Be+sdOB binaries, in which the Be star’s rapid rotation and ability to form a disk can be attributed to past mass-transfer.
The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field due to imbalanced chirality of quarks in local parity and charge-parity violating domains in quantum ...chromodynamics. The experimental measurement of the charge separation is made difficult by the presence of a major background from elliptic azimuthal anisotropy. This background and the CME signal have different sensitivities to the spectator and participant planes, and could thus be determined by measurements with respect to these planes. We report such measurements in Au+Au collisions at a nucleon-nucleon center-of-mass energy of 200 GeV at the Relativistic Heavy-Ion Collider. It is found that the charge separation, with the flow background removed, is consistent with zero in peripheral (large impact parameter) collisions. Some indication of finite CME signals is seen with a significance of 1–3 standard deviations in mid-central (intermediate impact parameter) collisions. Furthermore, significant residual background effects may, however, still be present.
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