31,761 research outputs found
Kinetics of the reactions of the acid anhydrides with aromatic amines in aprotic solvents
Work has revealed that diamine derivatives of diphenylmethane (IV), diphenyl ether (V), benzophenone (IV), fluorene (VII), and fluorenone (VIII) polymerizations with pyromellitic dianhydride in DMA were dependent on the basicity of the amine compound. The correlation between the basicity of the amine and its reactivity with phthalic anhydride was determined. Basicity measurements were made by potentiometric titration of each amine in an acetonitrile-water solvent system, from which the pKa of the amine could be determined. Reactivity was defined in terms of the second order rate constant derived form spectrophotometric examination of the reaction between each amine and phthalic anhydride in DMA. This reaction was expected to proceed in either one (for a monoamine) or two (for a diamine) stages
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Radiative transfer modelling for the NOMAD-UVIS instrument on the ExoMars Trace Gas Orbiter mission
The NOMAD (Nadir and Occultation for MArs Discovery) instrument is a 3-channel (2 IR, 1 UV/Vis) spectrometer due to fly on the 2016 ExoMars Trace Gas Orbiter mission. A radiative transfer model for Mars has been developed providing synthetic spectra to simulate observations of the UVIS channel in both solar occultation and nadir viewing geometries. This will allow for the characterization and mitigation of the influence of dust on retrievals of ozone abundance
Searching for links between magnetic fields and stellar evolution. I. A survey of magnetic fields in open cluster A- and B-type stars with FORS1
About 5% of upper main sequence stars are permeated by a strong magnetic
field, the origin of which is still matter of debate.
With this work we provide observational material to study how magnetic fields
change with the evolution of stars on the main sequence, and to constrain
theory explaining the presence of magnetic fields in A and B-type stars.
Using FORS1 in spectropolarimetric mode at the ESO VLT, we have carried out a
survey of magnetic fields in early-type stars belonging to open clusters and
associations of various ages.
We have measured the magnetic field of 235 early-type stars with a typical
uncertainty of about 100 G. In our sample, 97 stars are Ap or Bp stars. For
these targets, the median error bar of our field measurements was about 80 G. A
field has been detected in about 41 of these stars, 37 of which were not
previously known as magnetic stars. For the 138 normal A and B-type stars, the
median error bar was 136 G, and no field was detected in any of them.Comment: Accepted by A&A; 15 pages (article)+15 pages (tables), 8 figure
Modulated Amplitude Waves in Collisionally Inhomogeneous Bose-Einstein Condensates
We investigate the dynamics of an effectively one-dimensional Bose-Einstein
condensate (BEC) with scattering length subjected to a spatially periodic
modulation, . This "collisionally inhomogeneous" BEC is
described by a Gross-Pitaevskii (GP) equation whose nonlinearity coefficient is
a periodic function of . We transform this equation into a GP equation with
constant coefficient and an additional effective potential and study a
class of extended wave solutions of the transformed equation. For weak
underlying inhomogeneity, the effective potential takes a form resembling a
superlattice, and the amplitude dynamics of the solutions of the
constant-coefficient GP equation obey a nonlinear generalization of the Ince
equation. In the small-amplitude limit, we use averaging to construct
analytical solutions for modulated amplitude waves (MAWs), whose stability we
subsequently examine using both numerical simulations of the original GP
equation and fixed-point computations with the MAWs as numerically exact
solutions. We show that "on-site" solutions, whose maxima correspond to maxima
of , are significantly more stable than their "off-site" counterparts.Comment: 25 pages, 10 figures (many with several parts), to appear in Physica
D; higher resolution versions of some figures are available at
http://www.its.caltech.edu/~mason/paper
Arkansas Wheat Cultivar Performance Tests 2013-2014
Wheat cultivar performance tests are conducted each year in Arkansas by the Arkansas Agricultural Experiment Station, Department of Crop, Soil and Environmental Sciences. The tests provide information to companies developing cultivars and/or marketing seed within the state and aid the Arkansas Cooperative Extension Service in formulating cultivar recommendations for small-grain producers
The mixing of interplanetary magnetic field lines: A significant transport effect in studies of the energy spectra of impulsive flares
Using instrumentation on board the ACE spacecraft we describe short-time scale (~3 hour) variations observed in the arrival profiles of ~20 keV nucleon^(–1) to ~2 MeV nucleon^(–1) ions from impulsive solar flares. These variations occurred simultaneously across all energies and were generally not in coincidence with any local magnetic field or plasma signature. These features appear to be caused by the convection of magnetic flux tubes past the observer that are alternately filled and devoid of flare ions even though they had a common flare source at the Sun. In these particle events we therefore have a means to observe and measure the mixing of the interplanetary magnetic field due to random walk. In a survey of 25 impulsive flares observed at ACE between 1997 November and 1999 July these features had an average time scale of 3.2 hours, corresponding to a length of ~0.03 AU. The changing magnetic connection to the flare site sometimes lead to an incomplete observation of a flare at 1 AU; thus the field-line mixing is an important effect in studies of impulsive flare energy spectra
Arkansas Wheat Cultivar Performance Tests 2018-2019
Wheat cultivar performance tests are conducted each year in Ark- ansas by the University of Arkansas System Division of Agriculture’s Arkansas Agricultural Experiment Station, Department of Crop, Soil and Environmental Sciences. The tests provide information to companies developing cultivars and marketing seed within the state and aid the Arkansas Cooperative Extension Service in formulating cultivar recommendations for small-grain producers. The tests are conducted at the Northeast Research and Extension Center at Keiser, the Vegetable Substation near Kibler, the Lon Mann Cotton Research Station near Marianna, the Newport Extension Center near Newport, the Rohwer Research Station near Rohwer, the Pine Tree Research Station near Colt, and the Hope Research and Extension Center. In addition, entries are evaluated in a stripe rust (Puccinia striiformis f.sp. tritici) inoculated nursery in Fayetteville and a Fusarium head blight (FHB) inoculated nursery in Newport and Fayetteville. Specific location and cultural practice information accompany each table
Dynamics and Manipulation of Matter-Wave Solitons in Optical Superlattices
We analyze the existence and stability of bright, dark, and gap matter-wave
solitons in optical superlattices. Then, using these properties, we show that
(time-dependent) ``dynamical superlattices'' can be used to controllably place,
guide, and manipulate these solitons. In particular, we use numerical
experiments to displace solitons by turning on a secondary lattice structure,
transfer solitons from one location to another by shifting one superlattice
substructure relative to the other, and implement solitonic ``path-following'',
in which a matter wave follows the time-dependent lattice substructure into
oscillatory motion.Comment: 6 pages, revtex, 6 figures, to appear in Physics Letters A; minor
modifications from last versio
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