322 research outputs found
A new beamline for laser spin-polarization at ISOLDE
A beamline dedicated to the production of laser-polarized radioactive beams
has been constructed at ISOLDE, CERN. We present here different simulations
leading to the design and construction of the setup, as well as technical
details of the full setup and examples of the achieved polarizations for
several radioisotopes. Beamline simulations show a good transmission through
the entire line, in agreement with observations. Simulations of the induced
nuclear spin-polarization as a function of atom-laser interaction length are
presented for Na, [1] and for Ar, which is studied in this
work. Adiabatic spin rotation of the spin-polarized ensemble of atoms, and how
this influences the observed nuclear ensemble polarization, are also performed
for the same nuclei. For Ar, we show that multiple-frequency pumping
enhances the ensemble polarization by a factor 1.85, in agreement with
predictions from a rate equations model.
[1] J. Phys. G: Nucl. Part. Phys./174408400
Recommended from our members
Excitonic Properties of Low-Band-Gap Lead-Tin Halide Perovskites
The MAPb1–xSnxI3 (x = 0–1) (MA = methylammonium)
perovskite family comprises a range of ideal absorber band gaps for
single- and multijunction perovskite solar cells. Here, we use spectroscopic
measurements to reveal a range of hitherto unknown fundamental properties
of this materials family. Temperature-dependent transmission results
show that the temperature of the tetragonal to orthorhombic structural
transition decreases with increasing tin content. Through low-temperature
magnetospectroscopy, we show that the exciton binding energy is lower
than 16 meV, revealing that the dominant photogenerated species at
typical operational conditions of optoelectronic devices are free
charges rather than excitons. The reduced mass increases approximately
proportionally to the band gap, and the mass values (0.075–0.090me) can be described with a two-band k·p
perturbation model extended across the broad band gap range of 1.2–2.4
eV. Our findings can be generalized to predict values for the effective
mass and binding energy for other members of this family of materials
Wannier-function description of the electronic polarization and infrared absorption of high-pressure hydrogen
We have constructed maximally-localized Wannier functions for prototype
structures of solid molecular hydrogen under pressure, starting from LDA and
tight-binding Bloch wave functions. Each occupied Wannier function can be
associated with two paired protons, defining a ``Wannier molecule''. The sum of
the dipole moments of these ``molecules'' always gives the correct macroscopic
polarization, even under strong compression, when the overlap between nearby
Wannier functions becomes significant. We find that at megabar pressures the
contributions to the dipoles arising from the overlapping tails of the Wannier
functions is very large. The strong vibron infrared absorption experimentally
observed in phase III, above ~ 150 GPa, is analyzed in terms of the
vibron-induced fluctuations of the Wannier dipoles. We decompose these
fluctuations into ``static'' and ``dynamical'' contributions, and find that at
such high densities the latter term, which increases much more steeply with
pressure, is dominant.Comment: 17 pages, two-column style with 14 postscript figures embedded. Uses
REVTEX and epsf macro
Pattern formation of reaction-diffusion system having self-determined flow in the amoeboid organism of Physarum plasmodium
The amoeboid organism, the plasmodium of Physarum polycephalum, behaves on
the basis of spatio-temporal pattern formation by local
contraction-oscillators. This biological system can be regarded as a
reaction-diffusion system which has spatial interaction by active flow of
protoplasmic sol in the cell. Paying attention to the physiological evidence
that the flow is determined by contraction pattern in the plasmodium, a
reaction-diffusion system having self-determined flow arises. Such a coupling
of reaction-diffusion-advection is a characteristic of the biological system,
and is expected to relate with control mechanism of amoeboid behaviours. Hence,
we have studied effects of the self-determined flow on pattern formation of
simple reaction-diffusion systems. By weakly nonlinear analysis near a trivial
solution, the envelope dynamics follows the complex Ginzburg-Landau type
equation just after bifurcation occurs at finite wave number. The flow term
affects the nonlinear term of the equation through the critical wave number
squared. Contrary to this, wave number isn't explicitly effective with lack of
flow or constant flow. Thus, spatial size of pattern is especially important
for regulating pattern formation in the plasmodium. On the other hand, the flow
term is negligible in the vicinity of bifurcation at infinitely small wave
number, and therefore the pattern formation by simple reaction-diffusion will
also hold. A physiological role of pattern formation as above is discussed.Comment: REVTeX, one column, 7 pages, no figur
Spin chains with dynamical lattice supersymmetry
Spin chains with exact supersymmetry on finite one-dimensional lattices are
considered. The supercharges are nilpotent operators on the lattice of
dynamical nature: they change the number of sites. A local criterion for the
nilpotency on periodic lattices is formulated. Any of its solutions leads to a
supersymmetric spin chain. It is shown that a class of special solutions at
arbitrary spin gives the lattice equivalents of the N=(2,2) superconformal
minimal models. The case of spin one is investigated in detail: in particular,
it is shown that the Fateev-Zamolodchikov chain and its off-critical extension
admits a lattice supersymmetry for all its coupling constants. Its
supersymmetry singlets are thoroughly analysed, and a relation between their
components and the weighted enumeration of alternating sign matrices is
conjectured.Comment: Revised version, 52 pages, 2 figure
Microbial DNA fingerprinting of human fingerprints: dynamic colonization of fingertip microflora challenges human host inferences for forensic purposes
Human fingertip microflora is transferred to touched objects and may provide forensically relevant information on individual hosts, such as on geographic origins, if endogenous microbial skin species/strains would be retrievable from physical fingerprints and would carry geographically restricted DNA diversity. We tested the suitability of physical fingerprints for revealing human host information, with geographic inference as example, via microbial DNA fingerprinting. We showed that the transient exogenous fingertip microflora is frequently different from the resident endogenous bacteria of the same individuals. In only 54% of the experiments, the DNA analysis of the transient fingertip microflora allowed the detection of defined, but often not the major, elements of the resident microflora. Although we found microbial persistency in certain individuals, time-wise variation of transient and resident microflora within individuals was also observed when resampling fingerprints after 3 weeks. While microbial species differed considerably in their frequency spectrum between fingerprint samples from volunteers in Europe and southern Asia, there was no clear geographic distinction between Staphylococcus strains in a cluster analysis, although bacterial genotypes did not overlap between both continental regions. Our results, though limited in quantity, clearly demonstrate that the dynamic fingerprint microflora challenges human host inferences for forensic purposes including geographic ones. Overall, our results suggest that human fingerprint microflora is too dynamic to allow for forensic marker developments for retrieving human information
Magnetic moments of short-lived nuclei with part-per-million accuracy: Towards novel applications of -detected NMR in physics, chemistry and biology
We determine for the first time the magnetic dipole moment of a short-lived
nucleus with part-per-million (ppm) accuracy. To achieve this two orders of
magnitude improvement over previous studies, we implement a number of
innovations into our -detected Nuclear Magnetic Resonance (-NMR)
setup at ISOLDE/CERN. Using liquid samples as hosts we obtain narrow, sub-kHz
linewidth, resonances, while a simultaneous in-situ H NMR measurement
allows us to calibrate and stabilize the magnetic field to ppm precision, thus
eliminating the need for additional -NMR reference measurements.
Furthermore, we use ab initio calculations of NMR shielding constants to
improve the accuracy of the reference magnetic moment, thus removing a large
systematic error. We demonstrate the potential of this combined approach with
the 1.1 s half-life radioactive nucleus Na, which is relevant for
biochemical studies. Our technique can be readily extended to other isotopic
chains, providing accurate magnetic moments for many short-lived nuclei.
Furthermore, we discuss how our approach can open the path towards a wide range
of applications of the ultra-sensitive -NMR in physics, chemistry, and
biology.Comment: re-submitte
Fermionic NNLL corrections to b -> s \gamma
In this paper we take the first step towards a complete
next-to-next-to-leading logarithmic (NNLL) calculation of the inclusive decay
rate for . We consider the virtual corrections of order
\alphas^2 n_f to the matrix elements of the operators , and
and evaluate the real and virtual contributions to . These
corrections are expected to be numerically important. We observe a strong
cancelation between the contributions from the current-current operators and
and obtain, after applying naive non-abelianization, a reduction of the
branching ratio of 3.9% (for GeV) and an increase of 3.4% (for
GeV).Comment: 38 pages, result extended to allow for an explicit photon energy
cut-off, appendix and references added, final result and conlclusions
unchange
For whom and under what circumstances do school-based energy balance behavior interventions work? Systematic review on moderators
The aim of this review was to systematically review the results and quality of studies investigating the moderators of school-based interventions aimed at energy balance-related behaviors. We systematically searched the electronic databases of Pubmed, EMBASE, Cochrane, PsycInfo, ERIC and Sportdiscus. In total 61 articles were included. Gender, ethnicity, age, baseline values of outcomes, initial weight status and socioeconomic status were the most frequently studied potential moderators. The moderator with the most convincing evidence was gender. School-based interventions appear to work better for girls than for boys. Due to the inconsistent results, many studies reporting non-significant moderating effects, and the moderate methodological quality of most studies, no further consistent results were found. Consequently, there is lack of insight into what interventions work for whom. Future studies should apply stronger methodology to test moderating effects of important potential target group segmentations
- …