11,232 research outputs found
A trapped mercury 199 ion frequency standard
Mercury 199 ions confined in an RF quadrupole trap and optically pumped by mercury 202 ion resonance light are investigated as the basis for a high performance frequency standard with commercial possibilities. Results achieved and estimates of the potential performance of such a standard are given
On Exchange of Orbital Angular Momentum Between Twisted Photons and Atomic Electrons
We obtain an expression for the matrix element for a twisted
(Laguerre-Gaussian profile) photon scattering from a hydrogen atom. We consider
photons incoming with an orbital angular momentum (OAM) of ,
carried by a factor of not present in a plane-wave or pure
Gaussian profile beam. The nature of the transfer of units of OAM from
the photon to the azimuthal atomic quantum number of the atom is investigated.
We obtain simple formulae for these OAM flip transitions for elastic forward
scattering of twisted photons when the photon wavelength is large
compared with the atomic target size , and small compared the Rayleigh range
, which characterizes the collimation length of the twisted photon beam.Comment: 16 page
Evaluation of large area crop estimation techniques using LANDSAT and ground-derived data
The results of the Domestic Crops and Land Cover Classification and Clustering study on large area crop estimation using LANDSAT and ground truth data are reported. The current crop area estimation approach of the Economics and Statistics Service of the U.S. Department of Agriculture was evaluated in terms of the factors that are likely to influence the bias and variance of the estimator. Also, alternative procedures involving replacements for the clustering algorithm, the classifier, or the regression model used in the original U.S. Department of Agriculture procedures were investigated
Lunar particle shadows and boundary layer experiment: Plasma and energetic particles on the Apollo 15 and 16 subsatellites
The lunar particle shadows and boundary layer experiments aboard the Apollo 15 and 16 subsatellites and scientific reduction and analysis of the data to date are discussed with emphasis on four major topics: solar particles; interplanetry particle phenomena; lunar interactions; and topology and dynamics of the magnetosphere at lunar orbit. The studies of solar and interplanetary particles concentrated on the low energy region which was essentially unexplored, and the studies of lunar interaction pointed up the transition from single particle to plasma characteristics. The analysis concentrated on the electron angular distributions as highly sensitive indicators of localized magnetization of the lunar surface. Magnetosphere experiments provided the first electric field measurements in the distant magnetotail, as well as comprehensive low energy particle measurements at lunar distance
Bulk Superconductivity at 14 K in Single Crystals of Fe1+yTexSe1-x
Resistivity, magnetic susceptibility and heat capacity measurements are
reported for single crystals of Fe1+yTexSe1-x grown via a modified Bridgeman
method with 0 < y < 0.15, and x= 1, 0.9, 0.75, 0. 67, 0.55 and 0.5. Although
resistivity measurements show traces of superconductivity near 14 K for all x
except x=1, only crystals grown with compositions near x=0.5 exhibit bulk
superconductivity. The appearance of bulk superconductivity correlates with a
reduction in the magnitude of the magnetic susceptibility at room temperature
and smaller values of y, the concentration of Fe in the Fe(2) site.Comment: Submitted to Phys. Rev.
Criminal law as a security project
This paper asks how criminal might be understood as a security project. Following Valverde’s lead, it does this not by trying to define the concept of security, but by looking at the operation of the temporal and spatial logics of the criminal law. It looks first at the basic logics of time and space in conceptions of criminal liability and jurisdiction, before reviewing some recent developments which challenge these practices and what these might mean for criminal law as a security project
VLA Survey of Dense Gas in Extended Green Objects: Prevalence of 25 GHz Methanol Masers
We present resolution Very Large Array (VLA) observations of four
CHOH - 25~GHz transitions (=3, 5, 8, 10) along with 1.3~cm
continuum toward 20 regions of active massive star formation containing
Extended Green Objects (EGOs), 14 of which we have previously studied with the
VLA in the Class~I 44~GHz and Class~II 6.7~GHz maser lines (Cyganowski et al.
2009). Sixteen regions are detected in at least one 25~GHz line (=5), with
13 of 16 exhibiting maser emission. In total, we report 34 new sites of
CHOH maser emission and ten new sites of thermal CHOH emission,
significantly increasing the number of 25~GHz Class I CHOH masers observed
at high angular resolution. We identify probable or likely maser counterparts
at 44~GHz for all 15 of the 25~GHz masers for which we have complementary data,
providing further evidence that these masers trace similar physical conditions
despite uncorrelated flux densities. The sites of thermal and maser emission of
CHOH are both predominantly associated with the 4.5 m emission from
the EGO, and the presence of thermal CHOH emission is accompanied by 1.3~cm
continuum emission in 9 out of 10 cases. Of the 19 regions that exhibit 1.3~cm
continuum emission, it is associated with the EGO in 16 cases (out of a total
of 20 sites), 13 of which are new detections at 1.3~cm. Twelve of the 1.3~cm
continuum sources are associated with 6.7~GHz maser emission and likely trace
deeply-embedded massive protostars
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