15,531 research outputs found
Lema\^{i}tre's Hubble relationship
Edwin Hubble is often credited with discovering the expanding Universe based
on spectra taken by him. This statement is incorrect and we feel that it is the
responsibility of those who are aware of the historical facts to set the record
straight.Comment: 3 page letter, more accurately reflects letter published in Physics
Today, August 201
Electroweak phase transition in technicolor
Several phenomenologically viable walking technicolor models have been
proposed recently. I demonstrate that these models can have first order
electroweak phase transitions, which are sufficiently strong for electroweak
baryogenesis. Strong dynamics can also lead to several separate transitions at
the electroweak scale, with the possibility of a temporary restoration and an
extra breaking of the electroweak symmetry. First order phase transitions will
produce gravitational waves, which may be detectable at future experiments.Comment: 6 pages, 4 figures. Talk at PASCOS 2010 conference, Valencia, 19-23
July 201
A REGIONAL COMPARISON OF FARM COSTS AND RETURNS AMONG TOP DAIRY PRODUCERS
The purpose of this paper is to compare costs and returns of the top dairy producers in the Upper Midwest to those in other major dairy regions of the U.S. The analysis is based on the 1989 Farm Costs and Returns Survey conducted by the U.S. Department of Agriculture. The top dairy farmers are defined in several ways, including: (1) highest returns to capital and management, (2) lowest total cash costs, and (3) highest milk marketings per cow.Livestock Production/Industries,
Homochirality in an early peptide world
A recently proposed model of non-autocatalytic reactions in dipeptide
reactions leading to spontaneous symmetry breaking and homochirality is
examined. The model is governed by activation, polymerization, epimerization
and depolymerization of amino acids. Symmetry breaking is primarily a
consequence of the fact that the rates of reactions involving homodimers and
heterodimers are different, i.e., stereoselective, and on the fact that
epimerization can only occur on the N-terminal residue and not on the Cterminal
residue. This corresponds to an auto-inductive cyclic process that works only
in one sense. It is argued that epimerization mimics both autocatalytic
behavior as well as mutual antagonism - both of which were known to be crucial
for producing full homochirality.Comment: 19 pages, 7 figures, 3 boxe
Role of hydrogen in hydrogen-induced layer exfoliation of germanium
The role of hydrogen in the exfoliation of Ge is studied using cross-sectional transmission electron microscopy, atomic force microscopy, and multiple-internal transmission mode Fourier-transform infrared absorption spectroscopy and compared with the mechanism in silicon. A qualitative model for the physical and chemical action of hydrogen in the exfoliation of these materials is presented, in which H-implantation creates damage states that store hydrogen and create nucleation sites for the formation of micro-cracks. These micro-cracks are chemically stabilized by hydrogen passivation, and upon annealing serve as collection points for molecular hydrogen. Upon further heating, the molecular hydrogen trapped in these cracks exerts pressure on the internal surfaces causing the cracks to extend and coalesce. When this process occurs in the presence of a handle substrate that provides rigidity to the thin film, the coalescence of these cracks leads to cooperative thin film exfoliation. In addition to clarifying the mechanism of H-induced exfoliation of single-crystal thin Ge films, the vibrational study helps to identify the states of hydrogen in heavily damaged Ge. Such information has practical importance for the optimization of H-induced layer transfer as a technological tool for materials integration with these materials systems
Spectroscopic studies of the mechanism for hydrogen-induced exfoliation of InP
The motion and bonding configurations of hydrogen in InP are studied after proton implantation and subsequent annealing, using Fourier transform infrared (FTIR) spectroscopy. It is demonstrated that, as implanted, hydrogen is distributed predominantly in isolated pointlike configurations with a smaller concentration of extended defects with uncompensated dangling bonds. During annealing, the bonded hydrogen is released from point defects and is recaptured at the peak of the distribution by free internal surfaces in di-hydride configurations. At higher temperatures, immediately preceding exfoliation, rearrangement processes lead to the formation of hydrogen clusters and molecules. Reported results demonstrate that the exfoliation dynamics of hydrogen in InP and Si are markedly different, due to the higher mobility of hydrogen in InP and different implant-defect characteristics, leading to fundamental differences in the chemical mechanism for exfoliation
Nitric Oxide Bioavailability and Its Potential Relevance to the Variation in Susceptibility to the Renal and Vascular Complications in Patients With Type 2 Diabetes
OBJECTIVE—We compared the renal and systemic vascular (renovascular) response to a reduction of bioavailable nitric oxide (NO) in type 2 diabetic patients without nephropathy and of African and Caucasian heritage. RESEARCH DESIGN AND METHODS—Under euglycemic conditions, renal blood flow was determined by a constant infusion of paraminohippurate and changes in blood pressure and renal vascular resistance estimated before and after an infusion of l-Ng-monomethyl-l-arginine. RESULTS—In the African-heritage group, there was a significant fall in renal blood flow (Δ−46.0 ml/min per 1.73 m(2); P < 0.05) and rise in systolic blood pressure (Δ10.0 mmHg [95% CI 2.3–17.9]; P = 0.017), which correlated with an increase in renal vascular resistance (r(2) = 0.77; P = 0.004). CONCLUSIONS—The renal vasoconstrictive response associated with NO synthase inhibition in this study may be of relevance to the observed vulnerability to renal injury in patients of African heritage
- …