11,792 research outputs found
Bicategories of spans as cartesian bicategories
Bicategories of spans are characterized as cartesian bicategories in which
every comonad has an Eilenberg-Moore ob ject and every left adjoint arrow is
comonadic
Research on the application of satellite remote sensing to local, state, regional, and national programs involved with resource management and environmental quality
Project summaries and project reports are presented in the area of satellite remote sensing as applied to local, regional, and national environmental programs. Projects reports include: (1) Douglas County applications program; (2) vegetation damage and heavy metal concentration in new lead belt; (3) evaluating reclamation of strip-mined land; (4) remote sensing applied to land use planning at Clinton Reservoir; and (5) detailed land use mapping in Kansas City, Kansas
Cartesian Bicategories II
The notion of cartesian bicategory, introduced by Carboni and Walters for
locally ordered bicategories, is extended to general bicategories. It is shown
that a cartesian bicategory is a symmetric monoidal bicategory
Semiconductor technology program: Progress briefs
Measurement technology for semiconductor materials, process control, and devices, is discussed. Silicon and silicon based devices are emphasized. Highlighted activities include semiinsulating GaAs characterization, an automatic scanning spectroscopic ellipsometer, linewidth measurement and coherence, bandgap narrowing effects in silicon, the evaluation of electrical linewidth uniformity, and arsenicomplanted profiles in silicon
Photoluminescence quantum efficiency of dense silicon nanocrystal ensembles in SiO2
The photoluminescence decay characteristics of silicon nanocrystals in dense ensembles fabricated by ion implantation into silicon dioxide are observed to vary in proportion to the calculated local density of optical states. A comparison of the experimental 1/e photoluminescence decay rates to the expected spontaneous emission rate modification yields values for the internal quantum efficiency and the intrinsic radiative decay rate of silicon nanocrystals. A photoluminescence quantum efficiency as high as 59%±9% is found for nanocrystals emitting at 750 nm at low excitation power. A power dependent nonradiative decay mechanism reduces the quantum efficiency at high pump intensity
Neutron spin-echo study of the critical dynamics of spin-5/2 antiferromagnets in two and three dimensions
We report a neutron spin-echo study of the critical dynamics in the
antiferromagnets MnF and RbMnF with three-dimensional (3D) and
two-dimensional (2D) spin systems, respectively, in zero external field. Both
compounds are Heisenberg antiferromagnets with a small uniaxial anisotropy
resulting from dipolar spin-spin interactions, which leads to a crossover in
the critical dynamics close to the N\'eel temperature, . By taking
advantage of the energy resolution of the spin-echo
spectrometer, we have determined the dynamical critical exponents for both
longitudinal and transverse fluctuations. In MnF, both the characteristic
temperature for crossover from 3D Heisenberg to 3D Ising behavior and the
exponents in both regimes are consistent with predictions from the
dynamical scaling theory. The amplitude ratio of longitudinal and transverse
fluctuations also agrees with predictions. In RbMnF, the critical
dynamics crosses over from the expected 2D Heisenberg behavior for
to a scaling regime with exponent , which has not been predicted
by theory and may indicate the influence of long-range dipolar interactions
Study of high-speed angular-contact ball bearings under dynamic load
Research program studies behavior of specific high-speed, angular-contact ball bearings. Program is aimed at detailed investigation of ball-separator behavior and lubrication surface-finish effects in a specific gyro wheel
Getting a Full Dose? Reconsidering Sex Chromosome Dosage Compensation in the Silkworm, Bombyx mori
Dosage compensation—equalizing gene expression levels in response to differences in gene dose or copy number—is classically considered to play a critical role in the evolution of heteromorphic sex chromosomes. As the X and Y diverge through degradation and gene loss on the Y (or the W in female-heterogametic ZW taxa), it is expected that dosage compensation will evolve to correct for sex-specific differences in gene dose. Although this is observed in some organisms, recent genome-wide expression studies in other taxa have revealed striking exceptions. In particular, reports that both birds and the silkworm moth (Bombyx mori) lack dosage compensation have spurred speculation that this is the rule for all female-heterogametic taxa. Here, we revisit the issue of dosage compensation in silkworm by replicating and extending the previous analysis. Contrary to previous reports, our efforts reveal a pattern typically associated with dosage compensated taxa: the global male:female expression ratio does not differ between the Z and autosomes. We believe the previous report of unequal male:female ratios on the Z reflects artifacts of microarray normalization in conjunction with not testing a major assumption that the male:female global expression ratio was unbiased for autosomal loci. However, we also find that the global Z chromosome expression is significantly reduced relative to autosomes, a pattern not expected in dosage compensated taxa. This combination of male:female parity with an overall reduction in expression for sex-linked loci is not consistent with the prevailing evolutionary theory of sex chromosome evolution and dosage compensation
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