4,095 research outputs found
Identification of hydrogen bonds using quantum electrodynamics
A method for the identification of hydrogen bonds was investigated from the viewpoint of the stress tensor density proposed by Tachibana and following other works in this field. Hydrogen bonds are known to exhibit common features with ionic and covalent bonds. In quantum electrodynamics, the covalent bond has been demonstrated to display a spindle structure of the stress tensor density. Importantly, this spindle structure is also seen in the hydrogen bond, although the covalency is considerably weaker than in a typical covalent bond. Distinguishing it from the ionic bond is most imperative for the identification of the hydrogen bond. In the present study, the directionality of the hydrogen bond is investigated as the ionic bond is nearly isotropic, while the hydrogen bond exhibits the directionality. It was demonstrated that the hydrogen bond can be distinguished from the ionic bond using the angle dependence of the largest eigenvalue of the stress tensor density
Oncologic outcomes following surgical management of clinical stage II sex cord stromal tumors
Objective
To investigate the clinical history of patients with clinical stage II sex cord stromal tumors who underwent RPLND at our institution.
Methods
Our prospectively maintained testicular cancer database was queried to identify patients who presented with or developed clinical stage II sex cord stromal tumors and underwent RPLND at our institution between 1980 and 2018. Demographic, clinical and pathological characteristics were reviewed. Kaplan-Meier curves were graphed to assess recurrence-free and overall survival.
Results
Fourteen patients were included in the study with a median age of 44.2 years. Four patients presented with clinical stage II disease and 10 patients developed metastatic disease during follow-up of initial clinical stage I disease with a median time to metastasis of 2.7 years (range: 0.4-19.5 years). Of the 10 patients with orchiectomy pathology data available, all patients had at least 1 risk factor on testis pathology (mean: 2.9 risk factors). Nine patients received treatment prior to referral to our institution. All patients recurred post-RPLND at Indiana University. Median recurrence-free survival was 9.8 months. Twelve patients died of disease with a median overall survival of 14.4 months.
Conclusions
Metastatic sex cord stromal tumors are rare and are more resistant to standard treatment modalities than metastatic germ cell tumors. Patients presenting with sex cord stromal tumors should consider prophylactic primary RPLND in the setting of one or more pathological predictor of malignancy
A Morphological Classification Model to Identify Unresolved PanSTARRS1 Sources: Application in the ZTF Real-Time Pipeline
In the era of large photometric surveys, the importance of automated and
accurate classification is rapidly increasing. Specifically, the separation of
resolved and unresolved sources in astronomical imaging is a critical initial
step for a wide array of studies, ranging from Galactic science to large scale
structure and cosmology. Here, we present our method to construct a large, deep
catalog of point sources utilizing Pan-STARRS1 (PS1) 3 survey data, which
consists of 3 sources with mag. We develop a
supervised machine-learning methodology, using the random forest (RF)
algorithm, to construct the PS1 morphology model. We train the model using
5 PS1 sources with HST COSMOS morphological classifications
and assess its performance using 4 sources with Sloan Digital
Sky Survey (SDSS) spectra and 2 \textit{Gaia} sources. We
construct 11 "white flux" features, which combine PS1 flux and shape
measurements across 5 filters, to increase the signal-to-noise ratio relative
to any individual filter. The RF model is compared to 3 alternative models,
including the SDSS and PS1 photometric classification models, and we find that
the RF model performs best. By number the PS1 catalog is dominated by faint
sources (mag), and in this regime the RF model significantly
outperforms the SDSS and PS1 models. For time-domain surveys, identifying
unresolved sources is crucial for inferring the Galactic or extragalactic
origin of new transients. We have classified 1.5 sources
using the RF model, and these results are used within the Zwicky Transient
Facility real-time pipeline to automatically reject stellar sources from the
extragalactic alert stream.Comment: Published in PASP Focus Issue on the Zwicky Transient Facility (doi:
10.1088/1538-3873/aae3d9). 17 Pages, 9 Figure
Electronic stress tensor analysis of hydrogenated palladium clusters
We study the chemical bonds of small palladium clusters Pd_n (n=2-9)
saturated by hydrogen atoms using electronic stress tensor. Our calculation
includes bond orders which are recently proposed based on the stress tensor. It
is shown that our bond orders can classify the different types of chemical
bonds in those clusters. In particular, we discuss Pd-H bonds associated with
the H atoms with high coordination numbers and the difference of H-H bonds in
the different Pd clusters from viewpoint of the electronic stress tensor. The
notion of "pseudo-spindle structure" is proposed as the region between two
atoms where the largest eigenvalue of the electronic stress tensor is negative
and corresponding eigenvectors forming a pattern which connects them.Comment: 22 pages, 13 figures, published online, Theoretical Chemistry
Account
Color Superconductivity from Supersymmetry
A supersymmetric composite model of color superconductivity is proposed.
Quarks and diquarks are dynamically generated as composite fields by a newly
introduced strong gauge dynamics. It is shown that the condensation of the
scalar component of the diquark supermultiplet occurs when the chemical
potential becomes larger than some critical value. We believe that the model
well captures aspects of the diquark condensate behavior and helps our
understanding of the diquark dynamics in real QCD. The results obtained here
might be useful when we consider a theory composed of quarks and diquarks.Comment: 4 pages, 2 figures, An error in Eq.(10) correcte
Bonding in doped gallium nanoclusters: Insights from regional DFT
The molecular nature (Ga2)n of gallium makes this an interesting metal to investigate for the development of novel nano-materials. However, establishment of a targeted approach to manipulating the properties of gallium clusters requires a detailed understanding of how doping affects the bonding in these species. In this study, the bonding of gallium nanoclusters has been investigated using electron deformation densities and Regional Density Functional Theory (RDFT). Bonding throughout Ga12X clusters is generally intermediate between covalent and metallic. However, the presence of Ga2 subunits is clearly identified in clusters with endohedral dopants (Ga12X, X = Al, Si, P, Ga, Ge, As). Although there is evidence of Ga2 subunits in exohedral doped clusters, localised bonding to the dopant generally leads to significant disruption to the cluster framework. Maps of electronic chemical potential provide understanding for the observed differences in regioselectivity for hydrogen adsorption
Common snook fed in alternate and continuous regimens with diet supplemented with Bacillus subtilis probiotic.
The objective of this work was to evaluate the addition of Bacillus subtilis probiotic to the feed of common snook (Centropomus undecimalis) fingerlings, in alternate and continuous regimens. Six hundred and sixty fish, with verage length of 5.90±0.88 cm and weight of 1.92±0.28g, were stocked in 12 cages of 1.0 m 3 , with 55 fish each. The experimental design was completely randomized, with three treatments and four replicates. The treatments consisted of diet with the addition of probiotic, provided in alternate regimen for 7 days and in continuous regimen; besides a control without probiotic in the feed. Zootechnical performance, body composition, immune response, and blood parameters were evaluated. No significant differences were observed in zootechnical performance indexes and in body composition of fish treated with probiotic, when compared to the control. Fish from the alternate regimen showed an increment in respiratory burst and a lower total erythrocyte count than fish from the continuous regimen and the control. Fish from the continuous regimen did not differ from those of the control. The addition of Bacillus subtilis does not increase growth rates of common snook fingerlings; however, it has an immunostimulant action when supplied in alternate regimen.Título em português: Robalo?flecha alimentado em regimes alternado e contínuo com dieta suplementada com o probiótico Bacillus subtilis
Simultaneous Triggered Collapse of the Presolar Dense Cloud Core and Injection of Short-Lived Radioisotopes by a Supernova Shock Wave
Cosmochemical evidence for the existence of short-lived radioisotopes (SLRI)
such as Al and Fe at the time of the formation of primitive
meteorites requires that these isotopes were synthesized in a massive star and
then incorporated into chondrites within yr. A supernova shock wave
has long been hypothesized to have transported the SLRI to the presolar dense
cloud core, triggered cloud collapse, and injected the isotopes. Previous
numerical calculations have shown that this scenario is plausible when the
shock wave and dense cloud core are assumed to be isothermal at K,
but not when compressional heating to K is assumed. We show here
for the first time that when calculated with the FLASH2.5 adaptive mesh
refinement (AMR) hydrodynamics code, a 20 km/sec shock wave can indeed trigger
the collapse of a 1 cloud while simultaneously injecting shock wave
isotopes into the collapsing cloud, provided that cooling by molecular species
such as HO, CO, and H is included. These calculations imply that
the supernova trigger hypothesis is the most likely mechanism for delivering
the SLRI present during the formation of the solar system.Comment: 12 pages, 4 color figures. Astrophysical Journal Letters (in press
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