2,580 research outputs found
Density and of surface and bulk spins in diamond in high magnetic field gradients
We report on surface and bulk spin density measurements of diamond, using
ultra-sensitive magnetic force microscopy with magnetic field gradients up to
0.5 T/m. At temperatures between 25 and 800 mK, we measure the shifts in
the resonance frequency and quality factor of a cantilever with a micromagnet
attached to it. A recently developed theoretical analysis allows us to extract
a surface spin density of 0.072 spins/nm and a bulk spin density of 0.4 ppm
from this data. In addition, we find an increase of the time of the
surface spins in high magnetic field gradients due to the suppression of spin
diffusion. Our technique is applicable to a variety of samples other than
diamond, and could be of interest for several research fields where surface,
interface or impurity bulk spin densities are an important factor.Comment: 7 pages, 6 figure
Semi-Invariant Terms for Gauged Non-Linear Sigma-Models
We determine all the terms that are gauge-invariant up to a total spacetime
derivative ("semi-invariant terms") for gauged non-linear sigma models.
Assuming that the isotropy subgroup of the gauge group is compact or
semi-simple, we show that (non-trivial) such terms exist only in odd dimensions
and are equivalent to the familiar Chern-Simons terms for the subgroup .
Various applications are mentioned, including one to the gauging of the
Wess-Zumino-Witten terms in even spacetime dimensions. Our approach is based on
the analysis of the descent equation associated with semi-invariant terms.Comment: section 6 expande
Superfield Noether Procedure
We develop a superspace Noether procedure for supersymmetric field theories
in 4-dimensions for which an off-shell formulation in ordinary superspace
exists. In this way we obtain an elegant and compact derivation of the various
supercurrents in these theories. We then apply this formalism to compute the
central charges for a variety of effective actions. As a by-product we also
obtain a simple derivation of the anomalous superconformal Ward-identity in N=2
Yang-Mills theory. The connection with linearized supergravity is also
discussed.Comment: 47 pages, Latex, improved pedagogical presentation and references
adde
Geometric Interpretation of the Quantum Master Equation in the BRST--anti-BRST Formalism
The geometric interpretation of the antibracket formalism given by Witten is
extended to cover the anti-BRST symmetry. This enables one to formulate the
quantum master equation for the BRST--anti-BRST formalism in terms of
integration theory over a supermanifold. A proof of the equivalence of the
standard antibracket formalism with the antibracket formalism for the
BRST--anti-BRST symmetry is also given.Comment: 12 page
Natural Choline from Egg Yolk Phospholipids Is More Efficiently Absorbed Compared with Choline Bitartrate; Outcomes of A Randomized Trial in Healthy Adults
Choline is a vitamin-like essential nutrient, important throughout one’s lifespan. Therefore,
choline salts are added to infant formula, supplements and functional foods. However, if choline
is present in a natural form, e.g. bound to phospholipids, it may be more efficiently absorbed.
The study’s aim was to evaluate if choline uptake is improved after consumption of an egg yolk
phospholipid drink, containing 3 g of phospholipid bound choline, compared to a control drink
with 3 g of choline bitartrate. We performed a randomized, double blind, cross-over trial with
18 participants. Plasma choline, betaine and dimethylglycine concentrations were determined before
and up to six hours after consumption of the drinks. The plasma choline response, as determined
by the incremental area under the curve, was four times higher after consumption of the egg yolk
phospholipid drink compared with the control drink (p < 0.01). Similar outcomes were also observed
for choline’s main metabolites, betaine (p < 0.01) and dimethylglycine (p = 0.01). Consumption of
natural choline from egg yolk phospholipids improved choline absorption compared to consumption
of chemically produced choline bitartrate. This information is of relevance for the food industry,
instead of adding choline-salts, adding choline from egg yolk phospholipids can improve choline
uptake and positively impact health
On The Gauge-Fixed BRST Cohomology
A crucial property of the standard antifield-BRST cohomology at non negative
ghost number is that any cohomological class is completely determined by its
antifield independent part. In particular, a BRST cocycle that vanishes when
the antifields are set equal to zero is necessarily exact.\ \ This property,
which follows from the standard theorems of homological perturbation theory,
holds not only in the algebra of local functions, but also in the space of
local functionals. The present paper stresses how important it is that the
antifields in question be the usual antifields associated with the gauge
invariant description. By means of explicit counterexamples drawn from the free
Maxwell-Klein-Gordon system, we show that the property does not hold, in the
case of local functionals, if one replaces the antifields of the gauge
invariant description by new antifields adapted to the gauge fixation. In terms
of these new antifields, it is not true that a local functional weakly
annihilated by the gauge-fixed BRST generator determines a BRST cocycle; nor
that a BRST cocycle which vanishes when the antifields are set equal to zero is
necessarily exact.Comment: 14 pages Latex fil
Homological Algebra and Yang-Mills Theory
The antifield-BRST formalism and the various cohomologies associated with it
are surveyed and illustrated in the context of Yang-Mills gauge theory. In
particular, the central role played by the Koszul-Tate resolution and its
relation to the characteristic cohomology are stressed.Comment: 20 pages in LaTe
Factors associated with the continuum of care of HIV infected patients in Belgium
BREACHinfo:eu-repo/semantics/nonPublishe
A note on spin-s duality
Duality is investigated for higher spin (), free, massless, bosonic
gauge fields. We show how the dual formulations can be derived from a common
"parent", first-order action. This goes beyond most of the previous treatments
where higher-spin duality was investigated at the level of the equations of
motion only. In D=4 spacetime dimensions, the dual theories turn out to be
described by the same Pauli-Fierz (s=2) or Fronsdal () action (as it
is the case for spin 1). In the particular s=2 D=5 case, the Pauli-Fierz action
and the Curtright action are shown to be related through duality. A crucial
ingredient of the analysis is given by the first-order, gauge-like,
reformulation of higher spin theories due to Vasiliev.Comment: Minor corrections, reference adde
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