4,811 research outputs found
Radiations from RaD and RaE
The electron and gamma-spectra from RaD and RaE have been thoroughly investigated. The gamma-radiation from RaD was studied with both krypton and argon proportional counters with brass and aluminum cathodes. The L alpha, L beta, and L gamma radiations of Bi were observed and identified with a critical absorber. The intensity ratios of L alpha:L beta:L gamma are 1:1:0.2. The previously reported 7.8-kev (10 percent) line was not found but could be strongly excited by copper backing. The weak 23-kev line (10^-3 per disintegration in our measurements) could be contributed from the piling effect of the detecting system.
The conversion electrons of RaD were investigated in a solenoid magnetic spectrometer to obtain the L and (M+N) conversion coefficients. The results are: NeL / N beta =64 percent, NeM+N / N beta =21 percent, NeL+M+N / N beta =(85±5) percent.
The conversion electrons of RaD were again investigated with a 180° beta-spectrometer with a resolution of 0.8 percent and a counter window of ~6 µg/cm2. The LI, LII, and LIII conversion lines of the 46.5-kev gamma-ray were resolved. The ratio of LI:LII:LIII:MI-III:MIV-V:NI-V:NVI-VIII+0 are 1:0.075:0.007: 0.25:0.006:0.07:0.007. From the ratios of the L-subshell conversion electrons, the 46.5-kev transition is interpreted as an M1 type.
The upper limit of the intensity of the reported lines at 42 kev, at 37 kev, and at 31 kev must be less than 0.5 percent per disintegration if the same conversion coefficient is assumed.
The unconverted 46.5-kev gamma-radiation is 0.07±0.02 per disintegration. Thus the excited state of 46.5 kev in RaE can account for (92±5) percent of the disintegrations.
Neither internal conversion electrons nor nuclear gamma-radiations are found in RaE. A faint x-ray (~80 kev) of the order of 10-4 per disintegration due to the ionization effect was observed in RaE.
A brief discussion of the decay scheme of RaD and the possible spin assignments of various levels is included
Casimir interactions in graphene systems
The non-retarded Casimir interaction (van der Waals interaction) between two
free standing graphene sheets as well as between a graphene sheet and a
substrate is determined. An exact analytical expression is given for the
dielectric function of graphene along the imaginary frequency axis within the
random phase approximation for arbitrary frequency, wave vector, and doping.Comment: 4 pages, 4 figure
"Drinking in the Dark" (DID): a simple mouse model of binge-like alcohol intake
One of the greatest challenges that scientists face when studying the neurobiology and/or genetics of alcohol (ethanol) consumption is that most preclinical animal models do not voluntarily consume enough ethanol to achieve pharmacologically meaningful blood ethanol concentrations (BECs). Recent rodent models have been developed that promote binge-like levels of ethanol consumption associated with high BECs (i.e., ≥100 mg/dl). This unit describes procedures for an animal model of binge-like ethanol drinking which has come to be called "drinking in the dark" (DID). The "basic" variation of DID involves replacing the water bottle with a bottle containing 20% ethanol for 2 to 4 hr, beginning 3 hr into the dark cycle, on cages of singly-housed C57BL/6J mice. Using this procedure, mice typically consume enough ethanol to achieve BECs >100 mg/dl and to exhibit behavioral evidence of intoxication. An alternative two-bottle (ethanol and water) procedure is also described
Determination of Strong-Interaction Widths and Shifts of Pionic X-Rays with a Crystal Spectrometer
Pionic 3d-2p atomic transitions in F, Na, and Mg have been studied using a bent crystal spectrometer. The pionic atoms were formed in the production target placed in the external proton beam of the Space Radiation Effects Laboratory synchrocyclotron. The observed energies and widths of the transitions are E=41679(3) eV and Γ=21(8) eV, E=62434(18) eV and Γ=22(80) eV, E=74389(9) eV and Γ=67(35) eV, in F, Na, and Mg, respectively. The results are compared with calculations based on a pion-nucleus optical potential
PT-symmetry in honeycomb photonic lattices
We apply gain/loss to honeycomb photonic lattices and show that the
dispersion relation is identical to tachyons - particles with imaginary mass
that travel faster than the speed of light. This is accompanied by PT-symmetry
breaking in this structure. We further show that the PT-symmetry can be
restored by deforming the lattice
Investigating the pre-main sequence magnetic chemically peculiar system HD 72106
The origin of the strong magnetic fields observed in chemically peculiar Ap
and Bp stars stars has long been debated. The recent discovery of magnetic
fields in the intermediate mass pre-main sequence Herbig Ae and Be stars links
them to Ap and Bp stars, providing vital clues about Ap and Bp stars and the
origin and evolution of magnetic fields in intermediate and high mass stars. A
detailed study of one young magnetic B star, HD 72106A, is presented. This star
appears to be in a binary system with an apparently normal Herbig Ae star. A
maximum longitudinal magnetic field strength of +391 +/- 65 G is found in HD
72106A, as are strong chemical peculiarities, with photospheric abundances of
some elements ranging up to 100x above solar.Comment: 8 pages, 6 figures. Proceeding of the 2006 conference of the Special
Astrophysical Observatory of the Russian Academy of Science
PAMELA and FERMI-LAT limits on the neutralino-chargino mass degeneracy
Searches for Dark Matter (DM) particles with indirect detection techniques
have reached important milestones with the precise measurements of the
anti-proton and gamma-ray spectra, notably by the PAMELA and FERMI-LAT
experiments. While the gamma-ray results have been used to test the thermal
Dark Matter hypothesis and constrain the Dark Matter annihilation cross section
into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA
experiment remains relatively unexploited. Here we show that the latter can be
used to set a constraint on the neutralino-chargino mass difference. To
illustrate our point we use a Supersymmetric model in which the gauginos are
light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP)
is the neutralino. In this framework the W^+ W^- production is expected to be
significant, thus leading to large anti-proton and gamma-ray fluxes. After
determining a generic limit on the Dark Matter pair annihilation cross section
into W^+ W^- from the anti-proton data only, we show that one can constrain
scenarios in which the neutralino-chargino mass difference is as large as ~ 20
GeV for a mixed neutralino (and intermediate choices of the anti-proton
propagation scheme). This result is consistent with the limit obtained by using
the FERMI-LAT data. As a result, we can safely rule out the pure wino
neutralino hypothesis if it is lighter than 450 GeV and constitutes all the
Dark Matter.Comment: 22page
Magnetism in pre-MS intermediate-mass stars and the fossil field hypothesis
Today, one of the greatest challenges concerning the Ap/Bp stars is to
understand the origin of their slow rotation and their magnetic fields. The
favoured hypothesis for the latter is the fossil field, which implies that the
magnetic fields subsist throughout the different evolutionary phases, and in
particular during the pre-main sequence phase. The existence of magnetic fields
at the pre-main sequence phase is also required to explain the slow rotation of
Ap/Bp stars. However, until recently, essentially no information was available
about the magnetic properties of intermediate-mass pre-main sequence stars, the
so-called Herbig Ae/Be stars. The new high-resolution spectropolarimeter
ESPaDOnS, installed in 2005 at the Canada-France-Hawaii telescope, provided the
capability necessary to perform surveys of the Herbig Ae/Be stars in order to
investigate their magnetism and rotation. These investigations have resulted in
the detection and/or confirmation of magnetic fields in 8 Herbig Ae/Be stars,
ranging in mass from 2 to nearly 15 solar masses. In this contribution I will
present the results of our survey, as well as their implications for the origin
and evolution of the magnetic fields and rotation.Comment: Proceedings of the CP#AP Workshop held in Vienna in September 200
lnfluence of grape variety, climate and soil on grape composition and on the composition and quality of table wines
The influence of grape variety, soil type, climatic area and year of vintage on grape composition and wine quality was studied over a six-year period with three grape varieties in a eo-operative investigation. The wines were made under carefully controlled conditions to eliminate, as far as possible, any effect of winemaking technique. All viticultural and oenological treatments were replicated so that the data could be analysed statistically. When grapes from different viticultural areas were made into table wines, the quality of the wines was most closely related to grape variety, followed by climatic area and least of all by soil type.Reproducible differences in grape and wine composition were found for the grape varieties studied. For fhe same sugar content Riesling grapes and wine contained more acidity and a higher tartaric acid/malic acid ratio than Clare Riesling grapes and wine. They also contained less nitrogen, phosphorus and potassium. Shiraz grapes were relatively high in malic acid.The year of vintage strongly influenced the tartaric acid/malic acid ratio, particularly for Riesling and Clare Riesling, and also certain other constituents. Certain years could be designated as either high or low malic acid years for a particular grape variety.The soil type influenced the amounts of certain of the constituents of grapes and wine, but had no significant effects on the wine quality. Wines from the same varieties grown on two widely different soils in the same area could not be differentiated in replicated taste tests. The soil depth, drainage and waterholding capacity appeared to be more important than composition per se.Wines made from irrigated vineyards in the warm River Murray viticultural region, contained similar amounts of tartaric and malic acids, but were higher in pH, than wines made from the same grape varieties in the cooler non-irrigated Barossa Valley. Wines from irrigated grapes were generally of somewhat lower quality than those made from grapes of the same variety grown without irrigation in a cooler area. The time of harvesting irrigated grapes appeared to be critical to achieve the necessary balance between sugar, acid and flavour. Shiraz grapes grown under irrigation contained considerably less colour than grapes of the same variety grown without irrigation.Aroma was correlated with flavour in assessing wine quality, but numerical values ascribed to these parameters did not correlate generally with the wine constituents measured. A positive correlation existed between high tasting scores and high Ball/acid ratio
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