6,115 research outputs found
A microbiological method for the determination of choline by use of a mutant of Neurospora
Previous communications from this laboratory have described the production of biochemical mutants in the mold Neurospora by means of ultraviolet and x-rays (1, 2). Such mutants are characterized by the inability to carry out specific chemical syntheses which normally occur in the unmutated, or wild type, strain. In each case which has been genetically analyzed the failure of the synthesis has been found to be related to the mutation of a single gene. The strain to be described, known as No. 34486, or cholineless, arose from a culture of wild type Neurospora crassa which had been irradiated with ultraviolet light. It was found to be unable to grow in a medium containing only salts, sugar, and biotin, but it grew normally on the addition of a mixture of water-soluble vitamins. When the components of the mixture were tested singly, it was found that the addition of choline alone permitted normal growth.
Up to the present, no completely satisfactory method for the determination of choline in natural products and tissue extracts has been described. Chemical methods, such as precipitation of the reineckate, lack specificity, while the biological method of Fletcher, Best, and Solandt (3) is time-consuming and difficult, and “possesses many dangerous pitfalls for the chemist” (4). The whole subject has been critically reviewed by Best and Lucas (4). It was therefore of interest to determine whether the Neurospora mutant is a suitable test organism in a quantitative assay for choline. The experiments to be described show that this is the case and form the basis of a simple, sensitive, and specific method for the determination of choline in natural products. By this procedure it is possible to determine choline in a concentration of 0.02 mg. per liter; routine analyses can be run on 100 mg. samples of material
Quenching and Tomography from RHIC to LHC
We compare fully perturbative and fully nonperturbative pictures of high-pT
energy loss calculations to the first results from LHC. While over-suppressed
compared to published ALICE data, parameter-free pQCD predictions based on the
WHDG energy loss model constrained to RHIC data simultaneously describe well
the preliminary CMS hadron suppression, ATLAS charged hadron v2, and ALICE D
meson suppression; we also provide for future reference WHDG predictions for B
meson RAA. However, energy loss calculations based on AdS/CFT also
qualitatively describe well the RHIC pion and non-photonic electron suppression
and LHC charged hadron suppression. We propose the double ratio of charm to
bottom quark RAA will qualitatively distinguish between these two energy loss
pictures.Comment: 4 pages, 3 figures. Proceedings for Quark Matter 201
Charge-conjugation violating neutrino interactions in supernovae
The well known charge conjugation violating interactions in the Standard
Model increase neutrino- and decrease anti-neutrino- nucleon cross sections.
This impacts neutrino transport in core collapse supernovae through "recoil"
corrections of order the neutrino energy over the nucleon mass . All
corrections to neutrino transport deep inside a protoneutron star are
calculated from angular integrals of the Boltzmann equation. We find these
corrections significantly modify neutrino currents at high temperatures. This
produces a large mu and tau number for the protoneutron star and can change the
ratio of neutrons to protons. In addition, the relative size of neutrino mean
free paths changes. At high temperatures, the electron anti-neutrino mean free
path becomes {\it longer} than that for mu or tau neutrinos.Comment: 14 pages, 2 included ps figures, subm. to Phys. Rev.
Tyrocidin inhibition: effect of Tween 80 and conidial density
Tyrocidin inhibition: effect of Tween 80 and conidial densit
Dilaton test of connection between AdS_3 X S^3 and 5D black hole
A 5D black hole(M) is investigated in the type IIB superstring theory
compactified on ST. This corresponds to AdSST in the near horizon with asymptotically flat space. Here the
harmonic gauge is introduced to decouple the mixing between the dilaton and
others. On the other hand we obtain the BTZ balck
hole(AdSST) as the non-dilatonic solution. We calculate
the greybody factor of the dilaton as a test scalar both for a 5D black
hole(MST) and the BTZ black hole(AdSST). The result of the BTZ black hole agrees with the greybody
factor of the dilaton in the dilute gas approximation of a 5D black hole.Comment: revised version to appear in classical and quantum gravity, 15 pages
with RevTe
pQCD vs. AdS/CFT Tested by Heavy Quark Energy Loss
We predict the charm and bottom quark nuclear modification factors using
weakly coupled pQCD and strongly coupled AdS/CFT drag methods. The
log(pT/M_Q)/pT dependence of pQCD loss and the momentum independence of drag
loss lead to different momentum dependencies for the R_{AA} predictions. This
difference is enhanced by examining a new experimental observable, the double
ratio of charm to bottom nuclear modification factors,
R^{cb}=R^c_{AA}/R^b_{AA}. At LHC the weakly coupled theory predicts R^{cb} goes
to 1; whereas the strongly coupled theory predicts R^{cb} .2 independent of pT.
At RHIC the differences are less dramatic, as the production spectra are
harder, but the drag formula is applicable to higher momenta, due to the lower
temperature.Comment: 6 pages, 4 figures. Proceedings for the International Conference on
Strangeness in Quark Matter (SQM 2007), Levoca, Slovakia, 24-29 June 200
Dispersion -box correction to the weak charge of the proton
We consider elastic scattering of electrons off a proton target. The parity
violating (PV) asymmetry arises at leading order in due to
interference of and exchange. The radiative corrections to this
leading mechanism were calculated in the literature and included in
experimental analyses, except for box and cross-box contributions.
We present here a dispersion calculation of these corrections in forward
kinematics. We demonstrate that at the GeV energies of current PV experiments,
such corrections are not suppressed by the small vector weak charge of the
electron, as occurs in the atomic PV. Our results suggest that the current
theoretical uncertainty in the analysis of the QWEAK experiment might be
substantially underestimated, and more accurate account of the dispersion
corrections are needed in order to interprete the PV data.Comment: 4 pages, 3 figures, revtex
Neutrino Trapping in a Supernova and Ion Screening
Neutrino-nucleus elastic scattering is reduced in dense matter because of
correlations between ions. The static structure factor for a plasma of
electrons and ions is calculated from Monte Carlo simulations and parameterized
with a least squares fit. Our results imply a large increase in the neutrino
mean free path. This strongly limits the trapping of neutrinos in a supernova
by coherent neutral current interactions.Comment: 9 pages, 1 postscript figure using epsf.st
When Black Holes Meet Kaluza-Klein Bubbles
We explore the physical consequences of a recently discovered class of exact
solutions to five dimensional Kaluza-Klein theory. We find a number of
surprising features including: (1) In the presence of a Kaluza-Klein bubble,
there are arbitrarily large black holes with topology S^3. (2) In the presence
of a black hole or a black string, there are expanding bubbles (with de Sitter
geometry) which never reach null infinity. (3) A bubble can hold two black
holes of arbitrary size in static equilibrium. In particular, two large black
holes can be close together without merging to form a single black hole.Comment: 23 pages, 5 figures, v2: few comments on stability modifie
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