7,896 research outputs found
Millimeter Wave Localization: Slow Light and Enhanced Absorption
We exploit millimeter wave technology to measure the reflection and
transmission response of random dielectric media. Our samples are easily
constructed from random stacks of identical, sub-wavelength quartz and Teflon
wafers. The measurement allows us to observe the characteristic transmission
resonances associated with localization. We show that these resonances give
rise to enhanced attenuation even though the attenuation of homogeneous quartz
and Teflon is quite low. We provide experimental evidence of disorder-induced
slow light and superluminal group velocities, which, in contrast to photonic
crystals, are not associated with any periodicity in the system. Furthermore,
we observe localization even though the sample is only about four times the
localization length, interpreting our data in terms of an effective cavity
model. An algorithm for the retrieval of the internal parameters of random
samples (localization length and average absorption rate) from the external
measurements of the reflection and transmission coefficients is presented and
applied to a particular random sample. The retrieved value of the absorption is
in agreement with the directly measured value within the accuracy of the
experiment.Comment: revised and expande
Evidence of Skyrmion excitations about in n-Modulation Doped Single Quantum Wells by Inter-band Optical Transmission
We observe a dramatic reduction in the degree of spin-polarization of a
two-dimensional electron gas in a magnetic field when the Fermi energy moves
off the mid-point of the spin-gap of the lowest Landau level, . This
rapid decay of spin alignment to an unpolarized state occurs over small changes
to both higher and lower magnetic field. The degree of electron spin
polarization as a function of is measured through the magneto-absorption
spectra which distinguish the occupancy of the two electron spin states. The
data provide experimental evidence for the presence of Skyrmion excitations
where exchange energy dominates Zeeman energy in the integer quantum Hall
regime at
Segregation, precipitation, and \alpha-\alpha' phase separation in Fe-Cr alloys: a multi-scale modelling approach
Segregation, precipitation, and phase separation in Fe-Cr systems is
investigated. Monte Carlo simulations using semiempirical interatomic
potential, first-principles total energy calculations, and experimental
spectroscopy are used. In order to obtain a general picture of the relation of
the atomic interactions and properties of Fe-Cr alloys in bulk, surface, and
interface regions several complementary methods has to be used. Using Exact
Muffin-Tin Orbitals method the effective chemical potential as a function of Cr
content (0-15 at.% Cr) is calculated for a surface, second atomic layer and
bulk. At ~10 at.% Cr in the alloy the reversal of the driving force of a Cr
atom to occupy either bulk or surface sites is obtained. The Cr containing
surfaces are expected when the Cr content exceeds ~10 at.%. The second atomic
layer forms about 0.3 eV barrier for the migration of Cr atoms between bulk and
surface atomic layer. To get information on Fe-Cr in larger scales we use
semiempirical methods. Using combined Monte Carlo molecular dynamics
simulations, based on semiempirical potential, the precipitation of Cr into
isolated pockets in bulk Fe-Cr and the upper limit of the solubility of Cr into
Fe layers in Fe/Cr layer system is studied. The theoretical predictions are
tested using spectroscopic measurements. Hard X-ray photoelectron spectroscopy
and Auger electron spectroscopy investigations were carried out to explore Cr
segregation and precipitation in Fe/Cr double layer and Fe_0.95Cr_0.05 and
Fe_0.85Cr_0.15 alloys. Initial oxidation of Fe-Cr was investigated
experimentally at 10^-8 Torr pressure of the spectrometers showing intense
Cr_2O_3 signal. Cr segregation and the formation of Cr rich precipitates were
traced by analysing the experimental spectral intensities with respect to
annealing time, Cr content, and kinetic energy of the exited electron.Comment: 16 pages, 14 figures, 52 reference
Inclusive 2H(3He,t) reaction at 2 GeV
The inclusive 2H(3He,t) reaction has been studied at 2 GeV for energy
transfers up to 500 MeV and scattering angles from 0.25 up to 4 degrees. Data
are well reproduced by a model based on a coupled-channel approach for
describing the NN and N Delta systems. The effect of final state interaction is
important in the low energy part of the spectra. In the delta region, the
cross-section is very sensitive to the effects of Delta-N interaction and Delta
N - NN process. The latter has also a large influence well below the pion
threshold. The calculation underestimates the experimental cross-section
between the quasi-elastic and the delta peaks; this is possibly due to
projectile excitation or purely mesonic exchange currents.Comment: 9 pages, 9 figures, accepted for publication in EPJ
Optimizing individual benefits of pulmonary rehabilitation including a multifaceted dietary intervention – A single-arm feasibility study
IntroductionFew studies have examined the effectiveness of nutrition interventions in municipal COPD rehabilitation programs. The objectives of this study were to examine the feasibility of implementation in practice (primary) and the feasibility of study methods and potential effectiveness (secondary) of a multidisciplinary dietary intervention offered to patients who start municipal rehabilitations program.MethodsThis study was a single arm intervention study with a pre-post design. Participant were recruited from five different municipal rehabilitation centers and received three individualized dietary counselling's. The primary outcome was retention, compliance to the intervention and complement of data collection. Secondary outcomes included changes in dietary intake, body composition and physical function. Analysis of the primary and secondary outcomes was primarily based on descriptive statistics.ResultsIn total, 111 (77%) of 145 eligible patients from five different municipalities consented to participate. Of them 99 (89%) completed. Before the intervention 67 (63%) of the participants had 75% or more of their requirement of energy covered, and 48 (45%) had 75% or more of their protein requirements covered. At the end of the intervention, 76 (77%) of the participants had 75% or more coverage of energy requirements and 80 (83%) had 75% or more coverage of their protein requirements. In general, the level of completeness was high.ConclusionWe found recruitment to be feasible, a high rate of retention, a high compliance to the intervention and high completeness of the data collection
Dirac-harmonic maps from index theory
We prove existence results for Dirac-harmonic maps using index theoretical
tools. They are mainly interesting if the source manifold has dimension 1 or 2
modulo 8. Our solutions are uncoupled in the sense that the underlying map
between the source and target manifolds is a harmonic map.Comment: 26 pages, no figur
Influence of dietary administration of organic acids and increased feed structure on S. typhimurium infection in pigs
Several epidemiological investigations and reports from advisors practicing in swine herds have independent of each other pointed out commercial feed mixes compared to home mixed feed and dry feed compared to wet fermented feed to be the most important risk factors for increased Salmonella infection levels in Danish slaughter pigs (Dahl (1997), Stege (1997))
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