1,841 research outputs found
The effect of carbacyclin, a prostaglandin analogue, on adenylate cyclase activity in platelet membranes
AbstractThe effect of carbacyclin, a chemically stable analogue of prostacyclin, on the activity of adenylate cyclase in platelet membrane was measured, and compared with the effect of PGE1. When GTP was added in concentrations up to 10 μM the activation of adenylate cyclase by carbacyclin was increased, whereas higher concentrations of GTP were inhibitory. The addition of a non-hydrolysable analogue of GDP, guanosine 5′-[β-thio]diphosphate (GDP[βS]) resulted in a dose-dependent inhibition of adenylate cyclase activation by carbacyclin; this inhibition was relieved by adding increased amounts of GTP
Leading-twist light cone distribution amplitudes for p-wave heavy quarkonium states
In this paper, a study of light-cone distribution amplitudes for p-wave heavy
quarkonium states are presented. Within the light-front framework, the leading
twist light-cone distribution amplitudes, and their relevant decay constants,
have some simple relations. These relations can be further simplified when the
non-relativistic limit and the wave function as a function of relative momentum
|\vec\kappa| are taken into consideration. In addition, the \kappa_\perp
integrations in the equations of LCDAs and \xi-moments can be completed
analytically when the Gaussian-type wave function is considered. After fixing
the parameters that appear in the wave function, the curves and the
corresponding decay constants of the LCDAs are plotted and calculated for the
charmonium and bottomonium states. The first three \xi-moments of the LCDAs are
estimated and are consistent with those of other theoretical approaches.Comment: 25 pages, 2 figures, some details and one reference added; version to
appear in JHE
Two centuries of southwest Iceland annually-resolved marine temperature reconstructed from Arctica islandica shells
Iceland's exposure to major ocean current pathways of the central North Atlantic makes it a useful location for developing long-term proxy records of past marine climate. Such records provide more detailed understanding of the full range of past variability which is necessary to improve predictions of future changes. We constructed a 225-year (1791–2015 CE) master shell growth chronology from 29 shells of Arctica islandica collected at 100 m water depth in southwest Iceland (Faxaflói). The growth chronology provides a robust age model for shell oxygen isotope (δ18Oshell) data produced at annual resolution for 251 years (1765–2015 CE). The temperature reconstruction derived from δ18Oshell shows coherence with May–October local surface temperature records and sea surface temperatures in the North Atlantic region, suggesting it is a useful proxy indicator of water temperature variability at 100 m depth within Faxaflói. Field correlations between the shell-based records and gridded sea surface temperature data reveal strong positive correlations between the 1-year lagged shell growth and temperatures within the subpolar gyre post-1972, suggesting a delayed influence of subpolar gyre dynamics on ecological indicators in southwest Iceland in recent decades. However, the shell growth chronology and δ18Oshell record generally show relatively weak and insignificant correlations with larger region climate indices including the Atlantic Multidecadal Variability, North Atlantic Oscillation, and East Atlantic pattern. Therefore the interannual variations in the newly produced shell-based records appear to reflect more local to regional dynamics around southwest Iceland than large-scale modes of climate variability.publishedVersio
An amplitude analysis of the reaction
A simple partial wave amplitude analysis of has been performed for data in the range p_{\sl lab} = 360 -- 1000
MeV/c. Remarkably few partial waves are required to fit the data, while the
number of required values barely changes over this energy range. However,
the resulting set of partial wave amplitudes is not unique. We discuss possible
measurements with polarized beam and target which will severely restrict and
help resolve the present analysis ambiguities. New data from the reaction
alone, are insufficient for that
purpose.Comment: 16 pages (revtex), 8 figures available on request, submitted to Phys.
Rev.
QCD Predictions for the Transverse Energy Flow in Deep-Inelastic Scattering in the Small x HERA Regime
The distribution of transverse energy, , which accompanies
deep-inelastic electron-proton scattering at small , is predicted in the
central region away from the current jet and proton remnants. We use BFKL
dynamics, which arises from the summation of multiple gluon emissions at small
, to derive an analytic expression for the flow. One interesting
feature is an increase of the distribution with
decreasing , where . We perform a
numerical study to examine the possibility of using characteristics of the
distribution as a means of identifying BFKL dynamics at HERA.Comment: 16 pages, REVTEX 3.0, no figures. (Hardcopies of figures available on
request from Professor A.D. Martin, Department of Physics, University of
Durham, DH1 3LE, England.) Durham preprint : DTP/94/0
Ellipsometric detection of transitional surface structures on decapped GaAs(001)
Structural and optical properties of MBE-grown GaAs(001) surface have been
studied by reflection high-energy electron diffraction and single-wavelength
ellipsometry under dynamic conditions of ramp heating after desorption of
passivating As-cap-layer with and without As4 beam applied to the surface. For
a number metastable reconstruction transitions a clear correlation is
stablished between diffraction and optical data. Boundary lines for
transitional superstructures are determined as a function of As flux and
corresponding activation energies are estimated. For the first time it is shown
ellipsometrically that optical response of the surface is drastically different
for transitions of the order->order and order->disorder type.Comment: 6 pages, 6 figures Keywords: GaAs, surface reconstructions,
ellipsometr
National innovation and knowledge performance: The role of higher education teaching and training
This paper acknowledges the role of the higher education system (HES) in the production of knowledge and human capital. However, most of the literature attributes this production to the second (research activities) and third (exploitation of teaching and research activities) mission. This paper proposes to investigate the under explored role of the first mission (teaching) of HES in the production of national innovation
Power Corrections and Renormalons in Deep Inelastic Structure Functions
We study the power corrections (infrared renormalon contributions) to the
coefficient functions for non-singlet deep inelastic structure functions due to
gluon vacuum polarization insertions in one-loop graphs. Remarkably, for all
the structure functions , , and , there are only two such
contributions, corresponding to and power corrections. We
compute their dependence on Bjorken . The results could be used to model the
dominant higher-twist contributions.Comment: Latex 2e, 9 pages including 2 Postscript figure
Configuration Complexities of Hydrogenic Atoms
The Fisher-Shannon and Cramer-Rao information measures, and the LMC-like or
shape complexity (i.e., the disequilibrium times the Shannon entropic power) of
hydrogenic stationary states are investigated in both position and momentum
spaces. First, it is shown that not only the Fisher information and the
variance (then, the Cramer-Rao measure) but also the disequilibrium associated
to the quantum-mechanical probability density can be explicitly expressed in
terms of the three quantum numbers (n, l, m) of the corresponding state.
Second, the three composite measures mentioned above are analytically,
numerically and physically discussed for both ground and excited states. It is
observed, in particular, that these configuration complexities do not depend on
the nuclear charge Z. Moreover, the Fisher-Shannon measure is shown to
quadratically depend on the principal quantum number n. Finally, sharp upper
bounds to the Fisher-Shannon measure and the shape complexity of a general
hydrogenic orbital are given in terms of the quantum numbers.Comment: 22 pages, 7 figures, accepted i
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