1,680 research outputs found
Disorder induced local density of states oscillations on narrow Ag(111) terraces
The local density of states of Ag(111) has been probed in detail on
disordered terraces of varying width by dI/dV-mapping with a scanning tunneling
microscope at low temperatures. Apparent shifts of the bottom of the
surface-state band edge from terrace induced confinement are observed.
Disordered terraces show interesting contrast reversals in the dI/dV maps as a
function of tip-sample voltage polarity with details that depend on the average
width of the terrace and the particular edge profile. In contrast to perfect
terraces with straight edges, standing wave patterns are observed parallel to
the step edges, i.e. in the non-confined direction. Scattering calculations
based on the Ag(111) surface states reproduce these spatial oscillations and
all the qualitative features of the standing wave patterns, including the
polarity-dependent contrast reversals.Comment: 19 pages, 12 figure
Snell's law for surface electrons: Refraction of an electron gas imaged in real space
On NaCl(100)/Cu(111) an interface state band is observed that descends from
the surface-state band of the clean copper surface. This band exhibits a
Moire-pattern-induced one-dimensional band gap, which is accompanied by strong
standing-wave patterns, as revealed in low-temperature scanning tunneling
microscopy images. At NaCl island step edges, one can directly see the
refraction of these standing waves, which obey Snell's refraction law.Comment: 4 pages, 4 figure
On the effects of turbulence on a screw dynamo
In an experiment in the Institute of Continuous Media Mechanics in Perm
(Russia) an non--stationary screw dynamo is intended to be realized with a
helical flow of liquid sodium in a torus. The flow is necessarily turbulent,
that is, may be considered as a mean flow and a superimposed turbulence. In
this paper the induction processes of the turbulence are investigated within
the framework of mean--field electrodynamics. They imply of course a part which
leads to an enhanced dissipation of the mean magnetic field. As a consequence
of the helical mean flow there are also helical structures in the turbulence.
They lead to some kind of --effect, which might basically support the
screw dynamo. The peculiarity of this --effect explains measurements
made at a smaller version of the device envisaged for the dynamo experiment.
The helical structures of the turbulence lead also to other effects, which in
combination with a rotational shear are potentially capable of dynamo action. A
part of them can basically support the screw dynamo. Under the conditions of
the experiment all induction effects of the turbulence prove to be rather weak
in comparison to that of the main flow. Numerical solutions of the mean--field
induction equation show that all the induction effects of the turbulence
together let the screw dynamo threshold slightly, at most by one per cent,
rise. The numerical results give also some insights into the action of the
individual induction effects of the turbulence.Comment: 15 pages, 7 figures, in GAFD prin
Mean-field diffusivities in passive scalar and magnetic transport in irrotational flows
Certain aspects of the mean-field theory of turbulent passive scalar
transport and of mean-field electrodynamics are considered with particular
emphasis on aspects of compressible fluids. It is demonstrated that the total
mean-field diffusivity for passive scalar transport in a compressible flow may
well be smaller than the molecular diffusivity. This is in full analogy to an
old finding regarding the magnetic mean-field diffusivity in an electrically
conducting turbulently moving compressible fluid. These phenomena occur if the
irrotational part of the motion dominates the vortical part, the P\`eclet or
magnetic Reynolds number is not too large, and, in addition, the variation of
the flow pattern is slow. For both the passive scalar and the magnetic cases
several further analytical results on mean-field diffusivities and related
quantities found within the second-order correlation approximation are
presented, as well as numerical results obtained by the test-field method,
which applies independently of this approximation. Particular attention is paid
to non-local and non-instantaneous connections between the turbulence-caused
terms and the mean fields. Two examples of irrotational flows, in which
interesting phenomena in the above sense occur, are investigated in detail. In
particular, it is demonstrated that the decay of a mean scalar in a
compressible fluid under the influence of these flows can be much slower than
without any flow, and can be strongly influenced by the so-called memory
effect, that is, the fact that the relevant mean-field coefficients depend on
the decay rates themselves.Comment: 13 pages, 10 figures, published on PR
Erprobung eines SQUID-Systems zur Messung des Spannungs-/Dehnungsverhaltens von Spannstahl : AbschluĂbericht / Ferdinand S. RostĂĄsy ; Karim Hariri ; Karl-Heinz Sprenger
Editorial: Development of study programmes
21.03.2014 | Karl-Heinz Gerholz (Paderborn), Dieter Euler (St. Gallen) & Peter F. E. Sloane (Paderborn
Influence of adversarial training on super-resolution turbulence reconstruction
Supervised super-resolution deep convolutional neural networks (CNNs) have
gained significant attention for their potential in reconstructing velocity and
scalar fields in turbulent flows. Despite their popularity, CNNs currently lack
the ability to accurately produce high-frequency and small-scale features, and
tests of their generalizability to out-of-sample flows are not widespread.
Generative adversarial networks (GANs), which consist of two distinct neural
networks (NNs), a generator and discriminator, are a promising alternative,
allowing for both semi-supervised and unsupervised training. The difference in
the flow fields produced by these two NN architectures has not been thoroughly
investigated, and a comprehensive understanding of the discriminator's role has
yet to be developed. This study assesses the effectiveness of the unsupervised
adversarial training in GANs for turbulence reconstruction in forced
homogeneous isotropic turbulence. GAN-based architectures are found to
outperform supervised CNNs for turbulent flow reconstruction for in-sample
cases. The reconstruction accuracy of both architectures diminishes for
out-of-sample cases, though the GAN's discriminator network significantly
improves the generator's out-of-sample robustness using either an additional
unsupervised training step with large eddy simulation input fields and a
dynamic selection of the most suitable upsampling factor. These enhance the
generator's ability to reconstruct small-scale gradients, turbulence
intermittency, and velocity-gradient probability density functions. The
extrapolation capability of the GAN-based model is demonstrated for
out-of-sample flows at higher Reynolds numbers. Based on these findings,
incorporating discriminator-based training is recommended to enhance the
reconstruction capability of super-resolution CNNs
Trends in the incidence of AIDS-defining and non-AIDS-defining cancers in people living with AIDS: a population-based study from Sao Paulo, Brazil
People living with AIDS are at increased risk of developing certain cancers. Since the introduction of the highly active antiretroviral therapy (HAART), the incidence of AIDS-defining cancers (ADCs) has decreased in high-income countries. The objective of this study was to analyse trends in ADCs and non-AIDS-defining cancers (NADCs) in HIV-positive people with a diagnosis of AIDS, in comparison to the general population, in Sao Paulo, Brazil. A probabilistic record linkage between the 'Population-based Cancer Registry of Sao Paulo' and the AIDS notification database (SINAN) was conducted. Cancer trends were assessed by annual per cent change (APC). In people with AIDS, 2074 cancers were diagnosed. Among men with AIDS, the most frequent cancer was Kaposi's sarcoma (469;31.1%), followed by non-Hodgkin lymphoma (NHL;304;20.1%). A decline was seen for ADCs (APC = -14.1%). All NADCs have increased (APC = -7.4%/year) significantly since the mid-2000s driven by the significant upward trends of anal (APC = -24.6%/year) and lung cancers (APC = -15.9%/year). In contrast, in men from the general population, decreasing trends were observed for these cancers. For women with AIDS, the most frequent cancer was cervical (114;20.2%), followed by NHL (96;17.0%). Significant declining trends were seen for both ADCs (APC = -15.6%/ year) and all NADCs (APC = -15.8%/ year), a comparable pattern to that found for the general female population. Trends in cancers among people with AIDS in Sao Paulo showed similar patterns to those found in developed countries. Although ADCs have significantly decreased, probably due to the introduction of HAART, NADCs in men have shown an opposite upward trend
See-saw relationship of the Holocene East Asian-Australian summer monsoon
D.E. and N.M. acknowledge support by the Leibniz Association (WGL) under Grant No. SAW-2013-IZW-2. F.H.M.âs research is funded through an Australian Postgraduate Award. I.O. is financially supported from TUBITAK under 2214/A program and by Ege University under the Research Project number 2015FEN028. This study received funding from the European Unionâs Horizon 2020 Research and Innovation programme under the Marie SkĆodowska-Curie grant agreement No 691037. The publication of this article was funded by the Open Access Fund of the Leibniz Association. K.H.W. thank Rhawn F. Denniston for his wider involvement in the northwest Australian monsoon project and the Kimberley Foundation Australia for financial support for this project and Paul Wyrwoll for helpful comments. We are also grateful to Yanjun Cai for providing the Lake Qinghai record.Peer reviewedPublisher PD
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