1,359 research outputs found
Communications Biophysics
Contains reports on four research projects.National Institutes of Health (Grant 1 P01 GM-14940-02)Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E)National Institutes of Health (Grant 5 TO1 GM-01555-02
n-Heptane hydroconversion over nickel-loaded aluminum- and/or boron-containing BEA zeolites prepared by recrystallization of magadiite varieties
Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic aluminum-containing magadiites and conventionally synthesized [B]BEA, were tested, after ion exchange with nickel, as bifunctional catalysts for hydroconversion of n-heptane. The reducibility of nickel ions incorporated into BEA zeolites by ion exchange was investigated by temperature-programmed reduction (TPR). The acidity of the samples was characterized with strong (pyridine (Py), ammonia (NH3)) and weak (nitrogen) bases. The adsorbed bases were studied by transmission FT-IR (Py), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy (N2), and temperature-programmed ammonia evolution (TPAE, NH3). Over Ni/H-[B]BEA the reactants were completely converted via fast hydrogenolysis, whereas this reaction pathway plays only a negligible role in the hydroconversion over Ni/H-[Al]BEA and Ni/H-[Al,B]BEA zeolites. Boron-containing BEA zeolites were less active catalysts than the boron-free catalyst in the principal unimolecular hydroconversion reactions. However, incorporation of boron into the framework of BEA zeolite results in a considerable selectivity shift towards isomerization. Results suggest that the acid strength of bridged hydroxyls, probed with weak (N2) and strong basis (pyridine), was found to be similar in the boron-free and boron-containing BEA samples. The decrease in the isomerization rate and the increase of the apparent activation energy upon incorporation of boron may be attributed to the decrease in the heat of n-heptane adsorption
Correlation Between the Deuteron Characteristics and the Low-energy Triplet np Scattering Parameters
The correlation relationship between the deuteron asymptotic normalization
constant, , and the triplet np scattering length, , is
investigated. It is found that 99.7% of the asymptotic constant is
determined by the scattering length . It is shown that the linear
correlation relationship between the quantities and
provides a good test of correctness of various models of nucleon-nucleon
interaction. It is revealed that, for the normalization constant and
for the root-mean-square deuteron radius , the results obtained with the
experimental value recommended at present for the triplet scattering length
are exaggerated with respect to their experimental counterparts. By
using the latest experimental phase shifts of Arndt et al., we obtain, for the
low-energy scattering parameters (, , ) and for the
deuteron characteristics (, ), results that comply well with
experimental data.Comment: 19 pages, 1 figure, To be published in Physics of Atomic Nucle
Case Report: Modified Thoracoscopic-Assisted Cervical Resection for Retrosternal Goiter
Introduction: The treatment of choice for retrosternal goiters (RSG) is surgical resection to relieve symptoms and rule out malignancy. Although the majority of RSG can be removed by a cervical approach only, an extracervical approach (e.g., sternotomy, thoracotomy or thoracoscopy) may be required. Herein, we describe a refined thoracoscopic-assisted cervical two-team RSG resection without thoracoscopic mediastinal dissection.Technique: A 57-year-old man presented with a large RSG with posterior mediastinal extension (PME) and extensive peritumoral vascularization. Due to its extension below the aortic arch and its small connection with the right thyroid lobe, a combined cervical and thoracoscopic approach was intended. The endocrine surgery unit performed the cervical mobilization of the right thyroid lobe, while the thoracic surgery unit gently pushed the mediastinal tumor through the thoracic inlet without performing mediastinal dissection. This allowed a safe visualization of the inserting vessels by the endocrine surgery team at the neck, followed by a stepwise division of the vessels and resection of the retrosternal nodule through the cervical access.Comment: The described approach is indicated for RSG with posterior mediastinal extension, anteroposterior dimension smaller than the thoracic inlet and inaccessibility from a cervical approach only. This minimally invasive approach is associated with a faster recovery, decreased morbidity and postoperative pain, shorter hospital stay and better cosmetic results
Electron correlations in the antiproton energy-loss distribution in He
We present ab initio calculations of the electronic differential energy-transfer cross sections for antiprotons with energies between 3 keV and 1 MeV interacting with helium. By comparison with simulations employing the mean-field description based on the single-active electron approximation we are able to identify electron correlation effects in the stopping and straggling cross sections. Most remarkably, we find that straggling exceeds the celebrated Bohr straggling limit when correlated shake-up processes are included.The present paper was supported by Grants No. FWF-SFB049 (Nextlite), No. FWF-SFB041 (VICOM), No. WWTF MA14-002, Doctoral College Grant No. FWF-W1243
(Solids4Function), by the National Research, Development and Innovation Office (NKFIH) Grant No. KH 126886, and by the high performance computing resources
of the Babeş-Bolyai University. J.F. acknowledges funding from the European Research Council under Grant No. ERC-2016-STG-714870 and by the Ministerio de Economía y
Competitividad (Spain) through a Ramón y Cajal grant. X.- M.T. was supported by a Grants-in-Aid for Scientific Research (Grant No. JP16K05495) from the Japan Society for the Promotion of Scienc
Electron correlations in the antiproton energy-loss distribution in He
We present ab initio calculations of the electronic differential energy-transfer cross sections for antiprotons with energies between 3 keV and 1 MeV interacting with helium. By comparison with simulations employing the mean-field description based on the single-active electron approximation we are able to identify electron correlation effects in the stopping and straggling cross sections. Most remarkably, we find that straggling exceeds the celebrated Bohr straggling limit when correlated shake-up processes are included
Proton capture cross section of Sr isotopes and their importance for nucleosynthesis of proton-rich nuclides
The (p,) cross sections of three stable Sr isotopes have been
measured in the astrophysically relevant energy range. These reactions are
important for the -process in stellar nucleosynthesis and, in addition, the
reaction cross sections in the mass region up to 100 are also of importance
concerning the -process associated with explosive hydrogen and helium
burning. It is speculated that this -process could be responsible for a
certain amount of -nuclei in this mass region. The (p,) cross
sections of Sr isotopes were determined using an activation
technique. The measurements were carried out at the 5 MV Van de Graaff
accelerator of the ATOMKI, Debrecen. The resulting cross sections are compared
with the predictions of statistical model calculations. The predictions are in
good agreement with the experimental results for Sr(p,)Y
whereas the other two reactions exhibit differences that increase with mass
number. The corresponding astrophysical reaction rates have also been computed.Comment: Phys. Rev. C in pres
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