6,414 research outputs found
Sub-Doppler laser cooling of fermionic 40K atoms in three-dimensional gray optical molasses
We demonstrate sub-Doppler cooling of 40K on the D_1 atomic transition. Using
a gray molasses scheme, we efficiently cool a compressed cloud of 6.5x10^8
atoms from ~ 4\mK to 20uK in 8 ms. After transfer in a quadrupole magnetic
trap, we measure a phase space density of ~10^-5. This technique offers a
promising route for fast evaporation of fermionic 40K.Comment: 6 pages; 7 figures; submitted to EP
Molecular dynamics simulations of the evaporation of particle-laden droplets
We use molecular dynamics simulations to study the evaporation of
particle-laden droplets on a heated surface. The droplets are composed of a
Lennard-Jones fluid containing rigid particles which are spherical sections of
an atomic lattice, and heating is controlled through the temperature of an
atomistic substrate. We observe that sufficiently large (but still nano-sized)
particle-laden drops exhibit contact line pinning, measure the outward fluid
flow field which advects particle to the drop rim, and find that the structure
of the resulting aggregate varies with inter-particle interactions. In
addition, the profile of the evaporative fluid flux is measured with and
without particles present, and is also found to be in qualitative agreement
with earlier theory. The compatibility of simple nanoscale calculations and
micron-scale experiments indicates that molecular simulation may be used to
predict aggregate structure in evaporative growth processes
Separated Oscillatory Fields for High-Precision Penning Trap Mass Spectrometry
Ramsey's method of separated oscillatory fields is applied to the excitation
of the cyclotron motion of short-lived ions in a Penning trap to improve the
precision of their measured mass. The theoretical description of the extracted
ion-cyclotron-resonance line shape is derived out and its correctness
demonstrated experimentally by measuring the mass of the short-lived Ca
nuclide with an uncertainty of using the ISOLTRAP Penning
trap mass spectrometer at CERN. The mass value of the superallowed beta-emitter
Ca is an important contribution for testing the conserved-vector-current
hypothesis of the electroweak interaction. It is shown that the Ramsey method
applied to mass measurements yields a statistical uncertainty similar to that
obtained by the conventional technique ten times faster.Comment: 5 pages, 4 figures, 0 table
Significant association of a M129V independent polymorphism in the 5\prime UTR of the PRNP gene with sporadic Creutzfeldt-Jakob disease in a large German case-control study
Background: A single nucleotide polymorphism (SNP) in the coding region of the prion protein gene (PRNP) at codon 129 has been repeatedly shown to be an associated factor to sporadic Creutzfeldt-Jakob disease (sCJD), but additional major predisposing DNA variants for sCJD are still unknown. Several previous studies focused on the characterisation of polymorphisms in PRNP and the prion-like doppel gene (PRND), generating contradictory results on relatively small sample sets. Thus, extensive studies are required for validation of the polymorphisms in PRNP and PRND.Methods: We evaluated a set of nine SNPs of PRNP and one SNP of PRND in 593 German sCJD patients and 748 German healthy controls. Genotyping was performed using MALDI-TOF mass spectrometry.Results: In addition to PRNP 129, we detected a significant association between sCJD and allele frequencies of six further PRNP SNPs. No significant association of PRND T174M with sCJD was shown. We observed strong linkage disequilibrium within eight adjacent PRNP SNPs, including PRNP 129. However, the association of sCJD with PRNP 1368 and PRNP 34296 appeared to be independent on the genotype of PRNP 129. We additionally identified the most common haplotypes of PRNP to be over-represented or under-represented in our cohort of patients with sCJD.Conclusion: Our study evaluated previous findings of the association of SNPs in the PRNP and PRND genes in the largest cohorts for association study in sCJD to date, and extends previous findings by defining for the first time the haplotypes associated with sCJD in a large population of the German CJD surveillance study
Relativistic quark models of baryons with instantaneous forces
This is the first of a series of three papers treating light baryon resonances (up to 3 GeV) within a relativistically covariant quark model based on the three-fermion Bethe-Salpeter equation with instantaneous two- and three-body forces. In this paper we give a unified description of the theoretical background and demonstrate how to solve the Bethe-Salpeter equation by a reduction to the Salpeter equation. The specific new features of our covariant Salpeter model with respect to the usual nonrelativistic quark model are discussed in detail. The purely theoretical results obtained in this paper will be applied numerically to explicit quark models for light baryons in two subsequent papers
Impact of early-stage HIV transmission on treatment as prevention
Timely HIV treatment improves health (1)
and reduces transmission (2). These individual-
level benefits of HIV treatment for both
clinical and preventive purposes are well
established, but several questions remain
about the population-level impact of HIV
treatment as prevention (3). In PNAS, Eaton
and Hallett (4) use a mathematical model to
address one such question: Does the proportion
of transmission during early HIV infection
affect the impact of HIV treatment on
HIV incidence
The effect of flares on total solar irradiance
Flares are powerful energy releases occurring in stellar atmospheres. Solar
flares, the most intense energy bursts in the solar system, are however hardly
noticeable in the total solar luminosity. Consequently, the total amount of
energy they radiate 1) remains largely unknown and 2) has been overlooked as a
potential contributor to variations in the Total Solar Irradiance (TSI), i.e.
the total solar flux received at Earth. Here, we report on the detection of the
flare signal in the TSI even for moderate flares. We find that the total energy
radiated by flares exceeds the soft X-ray emission by two orders of magnitude,
with an important contribution in the visible domain. These results have
implications for the physics of flares and the variability of our star.Comment: accepted in Nature Physic
Cryopreservation of grapevine (Vitis spp.) shoot tips from growth chamber-sourced plants and histological observations
Many genebanks rely on cryopreservation as a method to preserve vulnerable field collections of vegetatively propagated crops. Effective cryopreservation procedures have been identified for Vitis; however, they usually use in vitro plantlets as the shoot tip source materials. It is costly to establish Vitis collections in vitro prior to cryopreservation. We sought to determine if growth chamber derived Vitis plants could serve as the source of shoot tips for cryopreservation. Nodal sections from growth chamber derived plants were surface-disinfected and placed in tissue culture on pre-treatment medium for 2 weeks. Uniform apical shoot tips (1 mm) were first obtained from the nodal sections and then precultured for 3 days on medium containing 0.3 M sucrose, salicylic acid, glutathione (reduced form), ascorbic acid and plant preservative mixture. Half-strength PVS2 was applied for 30 min at 22 °C, prior to full-strength PVS2 treatment at 0 °C. Cryopreserved shoot tips had the highest average regrowth of 50 and 55 % without and with cold-acclimation followed with a full-strength PVS2 exposure duration of 40 and 30 min at 0 °C, respectively. This cryopreservation protocol achieved high percentages of regrowth in V. vinifera 'Chardonnay' and 'Riesling' and V. hybrid 'Oppenheim'. Histological observations revealed that shoot tips from growth chamber plants had apical as well as multiple lateral meristems that survived LN immersion. The preservation of multiple meristems in each shoot tip may increase the capacity of shoot tip regeneration in cryopreserved Vitis that originates from ex vitro sources. The high percentage of regrowth after shoot tip cryopreservation using Vitis shoot tips derived from growth chamber source plants suggest that it may be possible to cryopreserve Vitis shoot tips without first introducing each accession into tissue culture
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