10,121 research outputs found
Probing the electron EDM with cold molecules
We present progress towards a new measurement of the electron electric dipole
moment using a cold supersonic beam of YbF molecules. Data are currently being
taken with a sensitivity of . We
therefore expect to make an improvement over the Tl experiment of Commins'
group, which currently gives the most precise result. We discuss the systematic
and statistical errors and comment on the future prospect of making a
measurement at the level of .Comment: 8 pages, 6 figures, proceedings of ICAP 200
Chemically engineering ligand selectivity at the free fatty acid receptor 2 based on pharmacological variation between species orthologs
When it is difficult to develop selective ligands within a family of related G-protein-coupled receptors (GPCRs), chemically engineered receptors activated solely by synthetic ligands (RASSLs) are useful alternatives for probing receptor function. In the present work, we explored whether a RASSL of the free fatty acid receptor 2 (FFA2) could be developed on the basis of pharmacological variation between species orthologs. For this, bovine FFA2 was characterized, revealing distinct ligand selectivity compared with human FFA2. Homology modeling and mutational analysis demonstrated a single mutation in human FFA2 of C4.57G resulted in a human FFA2 receptor with ligand selectivity similar to the bovine receptor. This was exploited to generate human FFA2-RASSL by the addition of a second mutation at a known orthosteric ligand interaction site, H6.55Q. The resulting FFA2-RASSL displayed a >100-fold loss of activity to endogenous ligands, while responding to the distinct ligand sorbic acid with pEC(50) values for inhibition of cAMP, 5.83 ± 0.11; Ca(2+) mobilization, 4.63 ± 0.05; ERK phosphorylation, 5.61 ± 0.06; and dynamic mass redistribution, 5.35 ± 0.06. This FFA2-RASSL will be useful in future studies on this receptor and demonstrates that exploitation of pharmacological variation between species orthologs is a powerful method to generate novel chemically engineered GPCRs
Space-based geoengineering: challenges and requirements
The prospect of engineering the Earth's climate (geoengineering) raises a multitude of issues associated with climatology, engineering on macroscopic scales, and indeed the ethics of such ventures. Depending on personal views, such large-scale engineering is either an obvious necessity for the deep future, or yet another example of human conceit. In this article a simple climate model will be used to estimate requirements for engineering the Earth's climate, principally using space-based geoengineering. Active cooling of the climate to mitigate anthropogenic climate change due to a doubling of the carbon dioxide concentration in the Earth's atmosphere is considered. This representative scenario will allow the scale of the engineering challenge to be determined. It will be argued that simple occulting discs at the interior Lagrange point may represent a less complex solution than concepts for highly engineered refracting discs proposed recently. While engineering on macroscopic scales can appear formidable, emerging capabilities may allow such ventures to be seriously considered in the long term. This article is not an exhaustive review of geoengineering, but aims to provide a foretaste of the future opportunities, challenges, and requirements for space-based geoengineering ventures
Nodal Quasiparticle Lifetimes in Cuprate Superconductors
A new generation of angular-resolved photoemission spectroscopy (ARPES)
measurements on the cuprate superconductors offer the promise of enhanced
momentum and energy resolution. In particular, the energy and temperature
dependence of the on-shell nodal (k_x=k_y) quasiparticle scattering rate can be
studied. In the superconducting state, low temperature transport measurements
suggest that one can describe nodal quasiparticles within the framework of a
BCS d-wave model by including forward elastic scattering and spin-fluctuation
inelastic scattering. Here, using this model, we calculate the temperature and
frequency dependence of the on-shell nodal quasiparticle scattering rate in the
superconducting state which determines the momentum width of the ARPES momentum
distribution curves. For a zero-energy quasiparticle at the nodal momentum k_N,
both the elastic and inelastic scattering rate show a sudden decrease as the
temperature drops below Tc, reflecting the onset of the gap amplitude. At low
temperatures the scattering rate decreases as T^3 and approaches a zero
temperature value determined by the elastic impurity scattering. For T>T_c, we
find a quasilinear dependence on T. At low reduced temperatures, the elastic
scattering rate for the nodal quasiparticles exhibits a quasilinear increase at
low energy which arises from elastic scattering processes. The inelastic
spin-fluctuation scattering leads to a low energy omega^3 dependence which, for
omega>~Delta_0, crosses over to a quasilinear behavior.Comment: 8 pages, 7 figures, minor revision
Stark deceleration of CaF molecules in strong- and weak-field seeking states
We report the Stark deceleration of CaF molecules in the strong-field seeking
ground state and in a weak-field seeking component of a rotationally-excited
state. We use two types of decelerator, a conventional Stark decelerator for
the weak-field seekers, and an alternating gradient decelerator for the
strong-field seekers, and we compare their relative merits. We also consider
the application of laser cooling to increase the phase-space density of
decelerated molecules.Comment: 10 pages, 8 figure
An extension of Wiener integration with the use of operator theory
With the use of tensor product of Hilbert space, and a diagonalization
procedure from operator theory, we derive an approximation formula for a
general class of stochastic integrals. Further we establish a generalized
Fourier expansion for these stochastic integrals. In our extension, we
circumvent some of the limitations of the more widely used stochastic integral
due to Wiener and Ito, i.e., stochastic integration with respect to Brownian
motion. Finally we discuss the connection between the two approaches, as well
as a priori estimates and applications.Comment: 13 page
First high-resolution look at the quiet Sun with ALMA at 3 mm
We present an overview of high resolution quiet Sun observations, from disk
center to the limb, obtained with the Atacama Large mm and sub-mm Array (ALMA)
at 3 mm. Seven quiet Sun regions were observed with resolution of up to 2.5" by
4.5". We produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full disk solar
images. The images show well the chromospheric network, which, based on the
unique segregation method we used, is brighter than the average over the fields
of view of the observed regions by K while the intranetwork is less
bright by K, with a slight decrease of the network/intranetwork
contrast toward the limb. At 3 mm the network is very similar to the 1600 \AA\
images, with somewhat larger size. We detected for the first time spicular
structures, rising up to 15" above the limb with a width down to the image
resolution and brightness temperature of 1800 K above the local
background. No trace of spicules, either in emission or absorption, was found
on the disk. Our results highlight ALMA's potential for the study of the quiet
chromosphere.Comment: Astronomy and Astrophysics (Letters), in pres
Pulsed beams as field probes for precision measurement
We describe a technique for mapping the spatial variation of static electric,
static magnetic, and rf magnetic fields using a pulsed atomic or molecular
beam. The method is demonstrated using a beam designed to measure the electric
dipole moment of the electron. We present maps of the interaction region,
showing sensitivity to (i) electric field variation of 1.5 V/cm at 3.3 kV/cm
with a spatial resolution of 15 mm; (ii) magnetic field variation of 5 nT with
25 mm resolution; (iii) radio-frequency magnetic field amplitude with 15 mm
resolution. This new diagnostic technique is very powerful in the context of
high-precision atomic and molecular physics experiments, where pulsed beams
have not hitherto found widespread application.Comment: 6 pages, 12 figures. Figures heavily compressed to comply with
arxiv's antediluvian file-size polic
Electron-electron interaction effects on optical excitations in semiconducting single-walled carbon nanotubes
We report correlated-electron calculations of optically excited states in ten
semiconducting single-walled carbon nanotubes with a wide range of diameters.
Optical excitation occurs to excitons whose binding energies decrease with the
increasing nanotube diameter, and are smaller than the binding energy of an
isolated strand of poly-(paraphenylene vinylene). The ratio of the energy of
the second optical exciton polarized along the nanotube axis to that of the
lowest exciton is smaller than the value predicted within single-particle
theory. The experimentally observed weak photoluminescence is an intrinsic
feature of semiconducting nanotubes, and is consequence of dipole-forbidden
excitons occurring below the optical exciton.Comment: 5 pages, 3 figures, To appear in PR
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