1,016 research outputs found
The south-central United States magnetic anomaly
The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced to pole and derivative maps provide constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the anomaly, but are rather indicative of a crustal zone which was disturbed during a Middle Proterozoic thermal event which enriched magnetic material deep in the crust
Characterization of All-Chromium Tunnel Junctions and Single Electron Tunneling Devices Fabricated by Direct-Writing Multilayer Technique
We report about the fabrication and analysis of the properties of Cr/CrO_x/Cr
tunnel junctions and SET transistors, prepared by different variants of
direct-writing multilayer technique. In all cases, the CrO_x tunnel barriers
were formed in air under ambient conditions. From the experiments on single
junctions, values for the effective barrier height and thickness were derived.
For the Cr/CrO_x/Cr SET transistors we achieved minimal junction areas of 17 x
60 nm^2 using a scanning transmission electron microscope for the e-beam
exposure on Si_3N_4 membrane substrate. We discuss the electrical performance
of the transistor samples as well as their noise behavior.Comment: 19 pages, 9 figure
Gravitational waves from stochastic relativistic sources: primordial turbulence and magnetic fields
The power spectrum of a homogeneous and isotropic stochastic variable,
characterized by a finite correlation length, does in general not vanish on
scales larger than the correlation scale. If the variable is a divergence free
vector field, we demonstrate that its power spectrum is blue on large scales.
Accounting for this fact, we compute the gravitational waves induced by an
incompressible turbulent fluid and by a causal magnetic field present in the
early universe. The gravitational wave power spectra show common features: they
are both blue on large scales, and peak at the correlation scale. However, the
magnetic field can be treated as a coherent source and it is active for a long
time. This results in a very effective conversion of magnetic energy in
gravitational wave energy at horizon crossing. Turbulence instead acts as a
source for gravitational waves over a time interval much shorter than a Hubble
time, and the conversion into gravitational wave energy is much less effective.
We also derive a strong constraint on the amplitude of a primordial magnetic
field when the correlation length is much smaller than the horizon.Comment: Replaced with revised version accepted for publication in Phys Rev
Decay of scalar variance in isotropic turbulence in a bounded domain
The decay of scalar variance in isotropic turbulence in a bounded domain is
investigated. Extending the study of Touil, Bertoglio and Shao (2002; Journal
of Turbulence, 03, 49) to the case of a passive scalar, the effect of the
finite size of the domain on the lengthscales of turbulent eddies and scalar
structures is studied by truncating the infrared range of the wavenumber
spectra. Analytical arguments based on a simple model for the spectral
distributions show that the decay exponent for the variance of scalar
fluctuations is proportional to the ratio of the Kolmogorov constant to the
Corrsin-Obukhov constant. This result is verified by closure calculations in
which the Corrsin-Obukhov constant is artificially varied. Large-eddy
simulations provide support to the results and give an estimation of the value
of the decay exponent and of the scalar to velocity time scale ratio
Constructing applicative functors
Applicative functors define an interface to computation that is more general, and correspondingly weaker, than that of monads. First used in parser libraries, they are now seeing a wide range of applications. This paper sets out to explore the space of non-monadic applicative functors useful in programming. We work with a generalization, lax monoidal functors, and consider several methods of constructing useful functors of this type, just as transformers are used to construct computational monads. For example, coends, familiar to functional programmers as existential types, yield a range of useful applicative functors, including left Kan extensions. Other constructions are final fixed points, a limited sum construction, and a generalization of the semi-direct product of monoids. Implementations in Haskell are included where possible
Adult-Child Sexual Contact: Examining Mental Health Trainees’ Perception of the Impact on Adult Psychological-Emotional Status
Thirty-eight graduate students enrolled in mental health-related programs completed the Brief Symptom Inventory (BSI) indicating anticipated impact of adult-child sexual contact on the psychological status of a young adult woman from positive family environment and one from a negative family environment. BSI subscale scores were significantly higher than the BSI general population’s mean scores in both cases. Multiple regression analyses found that: in the healthy family scenario, practitioners’ background variables (parent education, family of origin climate, prior childhood sexual contact with an adult, and education) did not contribute significantly to the variance in their prediction of expectation of client’s overall psychological distress; and, in the dysfunctional family case, practitioners’ background (childhood experience with adult sexual contact, education level, and professional experience) contributed to 40% of the variance in their prediction of the client’s emotional state. Results of qualitative analyses are presented, and implications for training and service delivery discussed
On the Nature of Incompressible Magnetohydrodynamic Turbulence
A novel model of incompressible magnetohydrodynamic turbulence in the
presence of a strong external magnetic field is proposed for explanation of
recent numerical results. According to the proposed model, in the presence of
the strong external magnetic field, incompressible magnetohydrodynamic
turbulence becomes nonlocal in the sense that low frequency modes cause
decorrelation of interacting high frequency modes from the inertial interval.
It is shown that the obtained nonlocal spectrum of the inertial range of
incompressible magnetohydrodynamic turbulence represents an anisotropic
analogue of Kraichnan's nonlocal spectrum of hydrodynamic turbulence. Based on
the analysis performed in the framework of the weak coupling approximation,
which represents one of the equivalent formulations of the direct interaction
approximation, it is shown that incompressible magnetohydrodynamic turbulence
could be both local and nonlocal and therefore anisotropic analogues of both
the Kolmogorov and Kraichnan spectra are realizable in incompressible
magnetohydrodynamic turbulence.Comment: Physics of Plasmas (Accepted). A small chapter added about 2D MHD
turbulenc
Development of a Sandwich ELISA to Measure Exposure to Occupational Cow Hair Allergens
Background: Cow hair and dander are important inducers of occupational allergies in cattle-exposed farmers. To estimate allergen exposure in farming environments, a sensitive enzyme immunoassay was developed to measure cow hair allergens. Methods: A sandwich ELISA was developed using polyclonal rabbit antibodies against a mixture of hair extracts from different cattle breeds. To assess the specificity of the assay, extracts from other mammalian epithelia, mites, molds and grains were tested. To validate the new assay, cow hair allergens were measured in passive airborne dust samples from the stables and homes of farmers. Dust was collected with electrostatic dust fall collectors (EDCs). Results: The sandwich ELISA was found to be very sensitive (detection limit: 0.1 ng/ml) and highly reproducible, demonstrating intra-and interassay coefficients of variation of 4 and 10%, respectively. The assay showed no reactivity with mites, molds and grains, but some cross-reactivity with other mammalian epithelia, with the strongest reaction with goat. Using EDCs for dust sampling, high concentrations of bovine allergens were measured in cow stables (4,760-559,400 mu g/m(2)). In addition, bovine allergens were detected in all areas of cattle farmer dwellings. A large variation was found between individual samples (0.3-900 mu g/m(2)) and significantly higher values were discovered in changing rooms. Conclusion: The ELISA developed for the detection of cow hair proteins is a useful tool for allergen quantification in occupational and home environments. Based on its low detection limit, this test is sensitive enough to detect allergens in passive airborne dust. Copyright (C) 2011 S. Karger AG, Base
Some relations between Lagrangian models and synthetic random velocity fields
We propose an alternative interpretation of Markovian transport models based
on the well-mixedness condition, in terms of the properties of a random
velocity field with second order structure functions scaling linearly in the
space time increments. This interpretation allows direct association of the
drift and noise terms entering the model, with the geometry of the turbulent
fluctuations. In particular, the well known non-uniqueness problem in the
well-mixedness approach is solved in terms of the antisymmetric part of the
velocity correlations; its relation with the presence of non-zero mean helicity
and other geometrical properties of the flow is elucidated. The well-mixedness
condition appears to be a special case of the relation between conditional
velocity increments of the random field and the one-point Eulerian velocity
distribution, allowing generalization of the approach to the transport of
non-tracer quantities. Application to solid particle transport leads to a model
satisfying, in the homogeneous isotropic turbulence case, all the conditions on
the behaviour of the correlation times for the fluid velocity sampled by the
particles. In particular, correlation times in the gravity and in the inertia
dominated case, respectively, longer and shorter than in the passive tracer
case; in the gravity dominated case, correlation times longer for velocity
components along gravity, than for the perpendicular ones. The model produces,
in channel flow geometry, particle deposition rates in agreement with
experiments.Comment: 54 pages, 8 eps figures included; contains additional material on
SO(3) and on turbulent channel flows. Few typos correcte
Inertial range scaling of scalar flux spectra in uniformly sheared turbulence
A model based on two-point closure theory of turbulence is proposed and
applied to study the Reynolds number dependency of the scalar flux spectra in
homogeneous shear flow with a cross-stream uniform scalar gradient. For the
cross-stream scalar flux, in the inertial range the spectral behavior agrees
with classical predictions and measurements. The streamwise scalar flux is
found to be in good agreement with the results of atmospheric measurements.
However, both the model results and the atmospheric measurements disagree with
classical predictions. A detailed analysis of the different terms in the
evolution equation for the streamwise scalar flux spectrum shows that nonlinear
contributions are governing the inertial subrange of this spectrum and that
these contributions are relatively more important than for the cross-stream
flux. A new expression for the scalar flux spectra is proposed. It allows us to
unify the description of the components in one single expression, leading to a
classical K^-7/3 inertial range for the cross-stream component and to a new
K^-23/9 scaling for the streamwise component that agrees better with
atmospheric measurements than the K^-3 prediction of J. C. Wyngaard and O. R.
Cot\'e [Quart. J. R. Met. Soc. 98, 590 (1972)]
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