409 research outputs found
Magnetic Field Uniformity Across the GF 9-2 YSO, L1082C Dense Core, and GF 9 Filamentary Dark Cloud
The orientation of the magnetic field (B-field) in the filamentary dark cloud
GF 9 was traced from the periphery of the cloud into the L1082C dense core that
contains the low-mass, low-luminosity Class 0 young stellar object (YSO) GF 9-2
(IRAS 20503+6006). This was done using SOFIA HAWC+ dust thermal emission
polarimetry (TEP) at 216 um in combination with Mimir near-infrared background
starlight polarimetry (BSP) conducted at H-band (1.6 um) and K-band (2.2 um).
These observations were augmented with published I-band (0.77 um) BSP and
Planck 850 um TEP to probe B-field orientations with offset from the YSO in a
range spanning 6000 AU to 3 pc. No strong B-field orientation change with
offset was found, indicating remarkable uniformity of the B-field from the
cloud edge to the YSO environs. This finding disagrees with weak-field models
of cloud core and YSO formation. The continuity of inferred B-field
orientations for both TEP and BSP probes is strong evidence that both are
sampling a common B-field that uniformly threads the cloud, core, and YSO
region. Bayesian analysis of Gaia DR2 stars matched to the Mimir BSP stars
finds a distance to GF 9 of 270 +/- 10 pc. No strong wavelength dependence of
B-field orientation angle was found, contrary to previous claims.Comment: 18 pages, 6 figures ApJ, accepte
Application of Pseudo-Hermitian Quantum Mechanics to a Complex Scattering Potential with Point Interactions
We present a generalization of the perturbative construction of the metric
operator for non-Hermitian Hamiltonians with more than one perturbation
parameter. We use this method to study the non-Hermitian scattering
Hamiltonian: H=p^2/2m+\zeta_-\delta(x+a)+\zeta_+\delta(x-a), where \zeta_\pm
and a are respectively complex and real parameters and \delta(x) is the Dirac
delta function. For regions in the space of coupling constants \zeta_\pm where
H is quasi-Hermitian and there are no complex bound states or spectral
singularities, we construct a (positive-definite) metric operator \eta and the
corresponding equivalent Hermitian Hamiltonian h. \eta turns out to be a
(perturbatively) bounded operator for the cases that the imaginary part of the
coupling constants have opposite sign, \Im(\zeta_+) = -\Im(\zeta_-). This in
particular contains the PT-symmetric case: \zeta_+ = \zeta_-^*. We also
calculate the energy expectation values for certain Gaussian wave packets to
study the nonlocal nature of \rh or equivalently the non-Hermitian nature of
\rH. We show that these physical quantities are not directly sensitive to the
presence of PT-symmetry.Comment: 22 pages, 4 figure
Light scattering and optical diffusion from willemite spherulites
Willemite is a zinc silicate mineral used in modern day pottery as a decorative feature within glazes. It is produced by controlled heat treatment of zinc oxide-containing ceramic glazes. The heat-treated glazes devitrify, producing thin nanoscale needle-like willemite crystals growing in spherulitic morphologies through branching of the needles. We show here that this resulting morphology of willemite crystals in an inorganic glass matrix has a previously unreported strong interaction with light, displaying remarkable optical diffraction patterns. Thin sections of such spherulites act as optical diffusers, enabling light beams to be spread up to 160° in width. Analysis of the interaction between the willemite spherulites and light suggests that the high density of willemite crystals in the spherulites and the length scales associated with both the thickness of the needles and the spacings between branches are together responsible for this optical diffusion behaviour.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.optmat.2015.12.02
Proper Motion of the Faint Star near KIC 8462852 (Boyajian's Star) - Not a Binary System
A faint star located 2 arcsec from KIC 8462852 was discovered in Keck 10 m
adaptive optics imaging in the near-infrared (NIR) in 2014 by Boyajian et
al. (2016). The closeness of the star to KIC 8462852 suggested the two could
constitute a binary, which might have implications for the cause of the
brightness dips seen by {\it Kepler} (Boyajian et al. (2016) and in
ground-based optical studies Boyajian et al. (2018). Here, NIR imaging in 2017
using the Mimir instrument resolved the pair and enabled measuring their
separation. The faint star had moved milliarcsec (mas) relative to
KIC 8462852 since 2014. The relative proper motion of the faint star is mas yr, for a tangential velocity of km s if
it is at the same 390 pc distance as KIC 8462852. Circular velocity at the 750
AU current projected separation is km s, hence the star pair
cannot be bound.Comment: 10 pages, 2 figure
Sudden Infant Death Syndrome and prenatal maternal smoking: rising attributed risk in the Back to Sleep era
BACKGROUND: Parental smoking and prone sleep positioning are recognized causal features of Sudden Infant Death. This study quantifies the relationship between prenatal smoking and infant death over the time period of the Back to Sleep campaign in the United States, which encouraged parents to use a supine sleeping position for infants. METHODS: This retrospective cohort study utilized the Colorado Birth Registry. All singleton, normal birth weight infants born from 1989 to 1998 were identified and linked to the Colorado Infant Death registry. Multivariable logistic regression was used to analyze the relationship between outcomes of interest and prenatal maternal cigarette use. Potential confounders analyzed included infant gender, gestational age, and birth year as well as maternal marital status, ethnicity, pregnancy interval, age, education, and alcohol use. RESULTS: We analyzed 488,918 birth records after excluding 5835 records with missing smoking status. Smokers were more likely to be single, non-Hispanic, less educated, and to report alcohol use while pregnant (p < 0.001). The study included 598 SIDS cases of which 172 occurred in smoke-exposed infants. Smoke exposed infants were 1.9 times (95% CI 1.6 to 2.3) more likely to die of SIDS. The attributed risk associating smoking and SIDS increased during the study period from approximately 50% to 80%. During the entire study period 59% (101/172) of SIDS deaths in smoke-exposed infants were attributed to maternal smoking. CONCLUSIONS: Due to a decreased overall rate of SIDS likely due to changing infant sleep position, the attributed risk associating maternal smoking and SIDS has increased following the Back to Sleep campaign. Mothers should be informed of the 2-fold increased rate of SIDS associated with maternal cigarette consumption
Scleroderma Renal Crisis: A Pathology Perspective
Scleroderma renal crisis (SRC) is an infrequent but serious complication of systemic sclerosis (SSc). It is associated with increased vascular permeability, activation of coagulation cascade, and renin secretion, which may lead to the acute renal failure typically associated with accelerated hypertension. The histologic picture of SRC is that of a thrombotic microangiopathy process with prominent small vessel involvement manifesting as myxoid intimal changes, thrombi, onion skin lesions, and/or fibrointimal sclerosis. Renal biopsies play an important role in confirming the clinical diagnosis, excluding overlapping/superimposed diseases that might lead to acute renal failure in SSc patients, helping to predict the clinical outcome and optimizing patient management. Kidney transplantation may be the only treatment option available for a subset of SRC patients who develop end-stage renal failure despite aggressive angiotensin-converting enzyme inhibitor therapy. However, the posttransplant outcome for SSc patients is currently suboptimal compared to the general renal transplant population
On design and tribological behaviour of laser textured surfaces
The paper reports an investigation into the functional response of textured surfaces with different designs that incorporated arrays of micro-dimples and grooves (40 μm diameter/width and 15 μm depth for both patterns) produced on tungsten carbide (WC) blocks by employing nanosecond (ns) and femtosecond (fs) lasers. In particular, the tribological performance of the textured WC blocks against stainless steel (SS316L) counterbody was evaluated in terms of friction and wear under dry condition compared to an untextured specimen. Friction tests were carried out on a reciprocating sliding tester while unidirectional ball-on-disc method was utilised to assess wear on the mating surfaces. The untextured surface exhibited a continuous rise in the friction coefficient from 0.15 to 0.5 from the start of the cycle to the end while the specimens textured with ns and fs lasers reached steady-state condition after 100 and 200 cycles with values between 0.35-0.45 and 0.3-0.4, respectively. Energy dispersive spectroscopy following wear tests showed a pronounced material transfer from the balls to the textured surfaces with stainless steel filling up some of the dimple and groove cavities; however, the reverse phenomenon was not apparent. Additionally, texturing with the fs laser exhibited formation of nano-ripples/structures in the produced dimples and grooves that can be further studied for creating nano-textured cutting tools or surfaces with super-hydrophobic/anti-ice properties
NuSTAR Observations of the Black Hole GS 1354-645: Evidence of Rapid Black Hole Spin
We present the results of a NuSTAR study of the dynamically confirmed
stellar-mass black hole GS 1354-645. The source was observed during its 2015
"hard" state outburst; we concentrate on spectra from two relatively bright
phases. In the higher-flux observation, the broadband NuSTAR spectra reveal a
clear, strong disk reflection spectrum, blurred by a degree that requires a
black hole spin of a = cJ/GM^2 > 0.98 (1 sigma statistical limits only). The
fits also require a high inclination: theta = 75(2) degrees. Strong "dips" are
sometimes observed in the X-ray light curves of sources viewed at such an
angle; these are absent, perhaps indicating that dips correspond to flared disk
structures that only manifest at higher accretion rates. In the lower-flux
observation, there is evidence of radial truncation of the thin accretion disk.
We discuss these results in the context of spin in stellar-mass black holes,
and inner accretion flow geometries at moderate accretion rates.Comment: Accepted for publication in ApJ Letter
Isolation, synthesis and optimization of cyclopropanation process of 4-allyl-2-methoxyphenol
The synthesis of 4-((2,2-dichlorocyclopropyl)methyl)-2-methoxyphenol 2 have been accomplished by using cyclopropanation process and Reponse Surface Methodology [1,2]. This methodology was used to determine the optimal conditions for the cyclopropanation reaction of eugenol 1. The reaction time (X1) and the ratio of the reaction mixture’s solvent (X2) were the two investigated factors. The statistical analysis of this study indicates that both of these factors had significant effects on the cyclopropanation yield. The central composite design showed that polynomial regression models were in good agreement with the experimental results of the coefficient determination (0.95) of product 2 yield. The optimal conditions were 17.44 and 5.78 hours. In such condition, the predicted yield of the product 2 was 43.96%. Keywords: Eugenol; 4-((2,2-dichlorocyclopropyl)methyl)-2-methoxyphenol; Central composite design; Optimization experiment
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