290 research outputs found
Accuracy of B(E2; 0+ -> 2+) transition rates from intermediate-energy Coulomb excitation experiments
The method of intermediate-energy Coulomb excitation has been widely used to
determine absolute B(E2; 0+ -> 2+) quadrupole excitation strengths in exotic
nuclei with even numbers of protons and neutrons. Transition rates measured
with intermediate-energy Coulomb excitation are compared to their respective
adopted values and for the example of 26Mg to the B(E2; 0+ -> 2+) values
obtained with a variety of standard methods. Intermediate-energy Coulomb
excitation is found to have an accuracy comparable to those of long-established
experimental techniques.Comment: to be published in Phys. Rev.
Photophysics of the electronic states S0 and S1 for the coplanar molecular structures of the α,ω-diphenylpolyenes DPH and DPO
Spectroscopy of the monoclinic and orthorhombic crystalline forms of all-trans-diphenylhexatriene (DPH) and all-trans-diphenyloctatetraene (DPO) show absorption and emission bands that do not generate the widely known Stokes shift of the polyene compounds, discovered by Hausser et al. in 1953 and repeatedly studied over the last 60 years. It can be concluded from our study that the crystallization system, whether in a monoclinic or orthorhombic system, does not significantly influence the photophysics of DPH and DPO in the crystal phas
Magneto-Optic Trapping of β-Decaying 38Km, 37K From an On-Line Isotope Separator
A magneto-optic trap (MOT) can provide a well-polarized, backing-free, localized source of radioactive atoms for β-decay experiments. We have trapped approximately 6000 atoms of 38Km ( t1/2 = 0.925s) and 2000 atoms of 37K (1.226 s) produced at the TRIUMF on-line separator TISOL in a vapor-cell MOT. We have measured optical isotope shifts and deduced the nuclear charge radii, which show an unusual lack of change at the neutron number N = 20 shell closure. Plans include a search for scalar contributions to the β+- ν correlation in the 0+→0+ decay of 38Km
Measurement of Angular Distributions and R= sigma_L/sigma_T in Diffractive Electroproduction of rho^0 Mesons
Production and decay angular distributions were extracted from measurements
of exclusive electroproduction of the rho^0(770) meson over a range in the
virtual photon negative four-momentum squared 0.5< Q^2 <4 GeV^2 and the
photon-nucleon invariant mass range 3.8< W <6.5 GeV. The experiment was
performed with the HERMES spectrometer, using a longitudinally polarized
positron beam and a ^3He gas target internal to the HERA e^{+-} storage ring.
The event sample combines rho^0 mesons produced incoherently off individual
nucleons and coherently off the nucleus as a whole. The distributions in one
production angle and two angles describing the rho^0 -> pi+ pi- decay yielded
measurements of eight elements of the spin-density matrix, including one that
had not been measured before. The results are consistent with the dominance of
helicity-conserving amplitudes and natural parity exchange. The improved
precision achieved at 47 GeV,
reveals evidence for an energy dependence in the ratio R of the longitudinal to
transverse cross sections at constant Q^2.Comment: 15 pages, 15 embedded figures, LaTeX for SVJour(epj) document class
Revision: Fig. 15 corrected, recent data added to Figs. 10,12,14,15; minor
changes to tex
Ecological challenges for the buffer zone management of protected areas of forest-savannah mosaic in West Africa
In sub-Saharan Africa, the management of buffer zones around protected areas does not often take into serious account the needs of resource exploitation by the local populations or the conservation needs of these areas. We described the ecological characteristics and management issues affecting the buffer zone around the Fazao-Malfakassa National Park; a 192,000-ha protected area in central-western Togo of utmost conservation importance within the Dahomey Gap region. Within the buffer zone (10 km radius, 334,800 ha), we focussed on four high conservation value areas totalling 65,594 ha (20% of the total buffer zone area). Using 2015 sentinel-2 images we analyzed land cover patterns and described existing ecological zones. We complemented these with field surveys and interviews with 300 people living in 22 villages within the buffer zone to describe the conditions affecting the resident human population. Although over 60% of the total buffer zone area is degraded, we identified four areas of high conservation value (total area = 65,594 ha). Interviewees recognized that slash-and-burn was the most common form of land use, followed by agroforestry practices. Agriculture, charcoal, and firewood production were the main drivers affecting habitats, and land conflicts were recurrent due to the rise in human population. The decline in agriculture, reported by interviewees in some sectors, was attributable to ravages of crops by elephants. Three independent diversity indices showed that, in preserved zones, a greater diversity of animals (with similar utilization frequencies) were hunted than in degraded sites (where grasscutters were the dominant hunted species). There were also significant differences between degraded and preserved zones in terms of plants used for charcoal production and for non-timber forest products. We advocate the development of community-controlled hunting areas to enhance the conservation value of the four well-preserved zones. Instead, promoting sustainable agricultural production systems in the degraded areas can help to further stabilize the agricultural front and reduce land pressure on the park
Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction
Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H,
3He, and 14N targets has been studied by the HERMES experiment at squared
four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20
GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the
nuclear transparency, was found to decrease with increasing coherence length of
quark-antiquark fluctuations of the virtual photon. The data provide clear
evidence of the interaction of the quark- antiquark fluctuations with the
nuclear medium.Comment: RevTeX, 5 pages, 3 figure
Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron
The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2]
for the proton and neutron have been determined from measurements of polarised
cross section asymmetries in deep inelastic scattering of 27.5 GeV
longitudinally polarised positrons from polarised 1H and 3He internal gas
targets. The data were collected in the region above the nucleon resonances in
the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the
proton the contribution to the generalised Gerasimov-Drell-Hearn integral was
found to be substantial and must be included for an accurate determination of
the full integral. Furthermore the data are consistent with a QCD
next-to-leading order fit based on previous deep inelastic scattering data.
Therefore higher twist effects do not appear significant.Comment: 6 pages, 3 figures, 1 table, revte
Approximations in the quasiparticle random phase evaluation of double beta decay rates
Sphingomyelin Synthases Regulate Protein Trafficking and Secretion
Sphingomyelin synthases (SMS1 and 2) represent a class of enzymes that transfer a phosphocholine moiety from phosphatidylcholine onto ceramide thus producing sphingomyelin and diacylglycerol (DAG). SMS1 localizes at the Golgi while SMS2 localizes both at the Golgi and the plasma membrane. Previous studies from our laboratory showed that modulation of SMS1 and, to a lesser extent, of SMS2 affected the formation of DAG at the Golgi apparatus. As a consequence, down-regulation of SMS1 and SMS2 reduced the localization of the DAG-binding protein, protein kinase D (PKD), to the Golgi. Since PKD recruitment to the Golgi has been implicated in cellular secretion through the trans golgi network (TGN), the effect of down-regulation of SMSs on TGN-to-plasma membrane trafficking was studied. Down regulation of either SMS1 or SMS2 significantly retarded trafficking of the reporter protein vesicular stomatitis virus G protein tagged with GFP (VSVG-GFP) from the TGN to the cell surface. Inhibition of SMSs also induced tubular protrusions from the trans Golgi network reminiscent of inhibited TGN membrane fission. Since a recent study demonstrated the requirement of PKD activity for insulin secretion in beta cells, we tested the function of SMS in this model. Inhibition of SMS significantly reduced insulin secretion in rat INS-1 cells. Taken together these results provide the first direct evidence that both enzymes (SMS1 and 2) are capable of regulating TGN-mediated protein trafficking and secretion, functions that are compatible with PKD being a down-stream target for SMSs in the Golgi
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