380 research outputs found
Sequences and filters of characters characterizing subgroups of compact abelian groups
Let H be a countable subgroup of the metrizable compact abelian group G and
f:H -> T=R/Z a (not necessarily continuous) character of H. Then there exists a
sequence (chi_n)_n of (continuous) characters of G such that lim_n chi_n(alpha)
= f(alpha) for all alpha in H and (chi_n(alpha))_n does not converge whenever
alpha in G\H. If one drops the countability and metrizability requirement one
can obtain similar results by using filters of characters instead of sequences.
Furthermore the introduced methods allow to answer questions of Dikranjan et
al.Comment: laTex2e, 10 page
Leptin signalling, obesity and prostate cancer: molecular and clinical perspective on the old dilemma
The prevalence of global obesity is increasing. Obesity is associated with general cancer-related morbidity and mortality and is a known risk factor for development of specific cancers. A recent large systematic review of 24 studies based on meta-analysis of 11,149 patients with prostate cancer showed a significant correlation between obesity and the risk of advanced prostate cancer. Further, a sustained reduction in BMI correlates with a decreased risk of developing aggressive disease. On the other hand, the correlation between consuming different products and prostate cancer occurrence/risk is limited. Here, we review the role of adipose tissue from an endocrine perspective and outline the effect of adipokines on cancer metabolism, with particular focus on leptin. Leptin exerts its physiological and pathological effects through modification of intracellular signalling, most notably activating the Janus kinase (JAK) 2/signal transducer and activator of transcription (STAT) 3 pathway and recently shown sphingolipid pathway. Both high levels of leptin in circulation and leptin receptor mutation are associated with prostate cancer risk in human patients; however, the in vivo mechanistic evidence is less conclusive. Given the complexity of metabolic cancer pathways, it is possible that leptin may have varying effects on prostate cancer at different stages of its development, a point that may be addressed by further epidemiological studies
Dynamic spin-Hall effect and driven spin helix for linear spin-orbit interactions
We derive boundary conditions for the electrically induced spin accumulation
in a finite, disordered 2D semiconductor channel. While for DC electric fields
these boundary conditions select spatially constant spin profiles equivalent to
a vanishing spin-Hall effect, we show that an in-plane ac electric field
results in a non-zero ac spin-Hall effect, i.e., it generates a spatially
non-uniform out-of-plane polarization even for linear intrinsic spin-orbit
interactions. Analyzing different geometries in [001] and [110]-grown quantum
wells, we find that although this out-of-plane polarization is typically
confined to within a few spin-orbit lengths from the channel edges, it is also
possible to generate spatially oscillating spin profiles which extend over the
whole channel. The latter is due to the excitation of a driven spin-helix mode
in the transverse direction of the channel. We show that while finite
frequencies suppress this mode, it can be amplified by a magnetic field tuned
to resonance with the frequency of the electric field. In this case, finite
size effects at equal strengths of Rashba- and Dresselhaus SOI lead to an
enhancement of the magnitude of this helix mode. We comment on the relation
between spin currents and boundary conditions.Comment: 10 pages, 5 figures, added references, corrected typos, extended
section V, VI
Coarse-graining collective skyrmion dynamics in confined geometries
Magnetic skyrmions are magnetic quasi-particles with enhanced stability and
different manipulation mechanisms using external fields and currents making
them promising candidates for future applications for instance in neuromorphic
computing. Recently, several measurements and simulations have shown that
thermally activated skyrmions in confined geometries, as they are necessary for
device applications, arrange themselves predominantly based on commensurability
effects. In this simulational study, based on the Thiele model, we investigate
the enhanced dynamics and degenerate non-equilibrium steady state of a system
in which the intrinsic skyrmion-skyrmion and skyrmion-boundary interaction
compete with thermal fluctuations as well as current-induced spin-orbit
torques. The investigated system is a triangular-shaped confinement geometry
hosting four skyrmions, where we inject spin-polarized currents between two
corners of the structure. We coarse-grain the skyrmion states in the system to
analyze the intricacies of skyrmion arrangements of the skyrmion ensemble. In
the context of neuromorphic computing, such methods address the key challenge
of optimizing read-out positions in confined geometries and form the basis to
understand collective skyrmion dynamics in systems with competing interactions
on different scales.Comment: 11 pages, 4 figure
- âŠ