77 research outputs found
Role of heavy-meson exchange in pion production near threshold
Recent calculations of -wave pion production have severely underestimated
the accurately known \ total cross section near
threshold. In these calculations, only the single-nucleon axial-charge operator
is considered. We have calculated, in addition to the one-body term, the
two-body contributions to this reaction that arise from the exchange of mesons.
We find that the inclusion of the scalar -meson exchange current (and
lesser contributions from other mesons) increases the cross section by about a
factor of five, and leads to excellent agreement with the data. The results are
neither very sensitive to changes in the distorting potential that generates
the wave function, nor to different choices for the meson-nucleon form
factors. We argue that \ data provide direct
experimental evidence for meson-exchange contributions to the axial current.Comment: 28 Pages, IU-NTC #93-0
Derivative-Coupling Models and the Nuclear-Matter Equation of State
The equation of state of saturated nuclear matter is derived using two
different derivative-coupling Lagrangians. We show that both descriptions are
equivalent and can be obtained from the sigma-omega model through an
appropriate rescaling of the coupling constants. We introduce generalized forms
of this rescaling to study the correlations amongst observables in infinite
nuclear matter, in particular, the compressibility and the effective nucleon
mass.Comment: 16 pages, 6 figures, 36 kbytes. To appear in Zeit. f. Phys. A
(Hadrons and Nuclei
QCD Sum Rules for Hyperons in Nuclear Matter
Within finite-density QCD sum-rule approach we investigate the self-energies
of hyperons propagating in nuclear matter from a correlator of
interpolating fields evaluated in the nuclear matter ground state. We
find that the Lorentz vector self-energy of the is similar to the
nucleon vector self-energy. The magnitude of Lorentz scalar self-energy of the
is also close to the corresponding value for nucleon; however, this
prediction is sensitive to the strangeness content of the nucleon and to the
assumed density dependence of certain four-quark condensate. The scalar and
vector self-energies tend to cancel, but not completely. The implications for
the couplings of to the scalar and vector mesons in nuclear matter and
for the spin-orbit force in a finite nucleus are discussed.Comment: 20 pages in revtex, 6 figures available under request as ps files,
UMD preprint #94--11
Strangeness nuclear physics: a critical review on selected topics
Selected topics in strangeness nuclear physics are critically reviewed. This
includes production, structure and weak decay of --Hypernuclei, the
nuclear interaction and the possible existence of bound
states in nuclei. Perspectives for future studies on these issues are also
outlined.Comment: 63 pages, 51 figures, accepted for publication on European Physical
Journal
A Decommissioned LHC Model Magnet as an Axion Telescope
The 8.4 Tesla, 10 m long transverse magnetic field of a twin aperture LHC
bending magnet can be utilized as a macroscopic coherent solar axion-to-photon
converter. Numerical calculations show that the integrated time of alignment
with the Sun would be 33 days per year with the magnet on a tracking table
capable of in the vertical direction and in the horizontal
direction. The existing lower bound on the axion-to-photon coupling constant
can be improved by a factor between 50 and 100 in 3 years, i.e.,
for axion masses
1 eV. This value falls within the existing open axion mass window.
The same set-up can simultaneously search for low- and high-energy celestial
axions, or axion-like particles, scanning the sky as the Earth rotates and
orbits the Sun.Comment: Final version, accepted for publication in Nucl. Instr. Meth. A. More
information can be found at http://wwwinfo.cern.ch/~collar/SATAN/alvaro.htm
Experimental Search for Solar Axions via Coherent Primakoff Conversion in a Germanium Spectrometer
Results are reported of an experimental search for the unique, rapidly
varying temporal pattern of solar axions coherently converting into photons via
the Primakoff effect in a single crystal germanium detector. This conversion is
predicted when axions are incident at a Bragg angle with a crystalline plane.
The analysis of approximately 1.94 kg.yr of data from the 1 kg DEMOS detector
in Sierra Grande, Argentina, yields a new laboratory bound on axion-photon
coupling of GeV, independent of
axion mass up to ~ 1 keV.Comment: RevTeX, 11 pages, figures can be obtained by fax from
[email protected]. Submitted to Phys. Lett.
Nephronophthisis
Nephronophthisis (NPH) is an autosomal recessive disease characterized by a chronic tubulointerstitial nephritis that progress to terminal renal failure during the second decade (juvenile form) or before the age of 5 years (infantile form). In the juvenile form, a urine concentration defect starts during the first decade, and a progressive deterioration of renal function is observed in the following years. Kidney size may be normal, but loss of corticomedullary differentiation is often observed, and cysts occur usually after patients have progressed to end-stage renal failure. Histologic lesions are characterized by tubular basement membrane anomalies, tubular atrophy, and interstitial fibrosis. The infantile form is characterized by cortical microcysts and progression to end-stage renal failure before 5 years of age. Some children present with extrarenal symptoms: retinitis pigmentosa (Senior-Løken syndrome), mental retardation, cerebellar ataxia, bone anomalies, or liver fibrosis. Positional cloning and candidate gene approaches led to the identification of eight causative genes (NPHP1, 3, 4, 5, 6, 7, 8, and 9) responsible for the juvenile NPH and one gene NPHP2 for the infantile form. NPH and associated disorders are considered as ciliopathies, as all NPHP gene products are expressed in the primary cilia, similarly to the polycystic kidney disease (PKD) proteins
Physiology and pathophysiology of the vasopressin-regulated renal water reabsorption
To prevent dehydration, terrestrial animals and humans have developed a sensitive and versatile system to maintain their water homeostasis. In states of hypernatremia or hypovolemia, the antidiuretic hormone vasopressin (AVP) is released from the pituitary and binds its type-2 receptor in renal principal cells. This triggers an intracellular cAMP signaling cascade, which phosphorylates aquaporin-2 (AQP2) and targets the channel to the apical plasma membrane. Driven by an osmotic gradient, pro-urinary water then passes the membrane through AQP2 and leaves the cell on the basolateral side via AQP3 and AQP4 water channels. When water homeostasis is restored, AVP levels decline, and AQP2 is internalized from the plasma membrane, leaving the plasma membrane watertight again. The action of AVP is counterbalanced by several hormones like prostaglandin E2, bradykinin, dopamine, endothelin-1, acetylcholine, epidermal growth factor, and purines. Moreover, AQP2 is strongly involved in the pathophysiology of disorders characterized by renal concentrating defects, as well as conditions associated with severe water retention. This review focuses on our recent increase in understanding of the molecular mechanisms underlying AVP-regulated renal water transport in both health and disease
Cycles of vascular plexus formation within the nephrogenic zone of the developing mouse kidney
Effects of Anacetrapib in Patients with Atherosclerotic Vascular Disease
BACKGROUND:
Patients with atherosclerotic vascular disease remain at high risk for cardiovascular events despite effective statin-based treatment of low-density lipoprotein (LDL) cholesterol levels. The inhibition of cholesteryl ester transfer protein (CETP) by anacetrapib reduces LDL cholesterol levels and increases high-density lipoprotein (HDL) cholesterol levels. However, trials of other CETP inhibitors have shown neutral or adverse effects on cardiovascular outcomes.
METHODS:
We conducted a randomized, double-blind, placebo-controlled trial involving 30,449 adults with atherosclerotic vascular disease who were receiving intensive atorvastatin therapy and who had a mean LDL cholesterol level of 61 mg per deciliter (1.58 mmol per liter), a mean non-HDL cholesterol level of 92 mg per deciliter (2.38 mmol per liter), and a mean HDL cholesterol level of 40 mg per deciliter (1.03 mmol per liter). The patients were assigned to receive either 100 mg of anacetrapib once daily (15,225 patients) or matching placebo (15,224 patients). The primary outcome was the first major coronary event, a composite of coronary death, myocardial infarction, or coronary revascularization.
RESULTS:
During the median follow-up period of 4.1 years, the primary outcome occurred in significantly fewer patients in the anacetrapib group than in the placebo group (1640 of 15,225 patients [10.8%] vs. 1803 of 15,224 patients [11.8%]; rate ratio, 0.91; 95% confidence interval, 0.85 to 0.97; P=0.004). The relative difference in risk was similar across multiple prespecified subgroups. At the trial midpoint, the mean level of HDL cholesterol was higher by 43 mg per deciliter (1.12 mmol per liter) in the anacetrapib group than in the placebo group (a relative difference of 104%), and the mean level of non-HDL cholesterol was lower by 17 mg per deciliter (0.44 mmol per liter), a relative difference of -18%. There were no significant between-group differences in the risk of death, cancer, or other serious adverse events.
CONCLUSIONS:
Among patients with atherosclerotic vascular disease who were receiving intensive statin therapy, the use of anacetrapib resulted in a lower incidence of major coronary events than the use of placebo. (Funded by Merck and others; Current Controlled Trials number, ISRCTN48678192 ; ClinicalTrials.gov number, NCT01252953 ; and EudraCT number, 2010-023467-18 .)
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