1,064 research outputs found
Twists of K-theory and TMF
We explore an approach to twisted generalized cohomology from the point of
view of stable homotopy theory and quasicategory theory provided by
arXiv:0810.4535. We explain the relationship to the twisted K-theory provided
by Fredholm bundles. We show how our approach allows us to twist elliptic
cohomology by degree four classes, and more generally by maps to the four-stage
Postnikov system BO. We also discuss Poincare duality and umkehr maps in
this setting
Diagnosis and Location of Pinhole Defects in Tunnel Junctions using only Electrical Measurements
In the development of the first generation of sensors and memory chips based
on spin-dependent tunneling through a thin trilayer, it has become clear that
pinhole defects can have a deleterious effect on magnetoresistance. However,
current diagnostic protocols based on Andreev reflection and the temperature
dependence of junction resistance may not be suitable for production quality
control. We show that the current density in a tunnel junction in the
cross-strip geometry becomes very inhomogeneous in the presence of a single
pinhole, yielding a four-terminal resistance that depends on the location of
the pinhole in the junction. Taking advantage of this position dependence, we
propose a simple protocol of four four-terminal measurements. Solving an
inverse problem, we can diagnose the presence of a pinhole and estimate its
position and resistance.Comment: 9 pages, eplain TeX, other macro files included; some versions of TeX
epsf may have trouble with figures, in which case try the Postscript or PDF
generated automatically by the Archiv
Parametrized spectra, multiplicative Thom spectra, and the twisted Umkehr map
We introduce a general theory of parametrized objects in the setting of
infinity categories. Although spaces and spectra parametrized over spaces are
the most familiar examples, we establish our theory in the generality of
objects of a presentable infinity category parametrized over objects of an
infinity topos. We obtain a coherent functor formalism describing the
relationship of the various adjoint functors associated to base-change and
symmetric monoidal structures.
Our main applications are to the study of generalized Thom spectra. We obtain
fiberwise constructions of twisted Umkehr maps for twisted generalized
cohomology theories using a geometric fiberwise construction of Atiyah duality.
In order to characterize the algebraic structures on generalized Thom spectra
and twisted (co)homology, we characterize the generalized Thom spectrum as a
categorification of the well-known adjunction between units and group rings.Comment: Submission draft. Various changes, including rewrite in terms of
infinity topoi and corrected discussion of functoriality of Atiyah dualit
Conserved Quantities in Models of Classical Chaos
Quantum chaos is a major subject of interest in condensed matter theory, and
has recently motivated new questions in the study of classical chaos. In
particular, recent studies have uncovered interesting physics in the
relationship between chaos and conserved quantities in models of quantum chaos.
In this paper, we investigate this relationship in two simple models of
classical chaos: the infinite-temperature Heisenberg spin chain, and the
directed polymer in a random medium. We relate these models by drawing
analogies between the energy landscape over which the directed polymer moves
and the magnetization of the spin chain. We find that the coupling of the chaos
to these conserved quantities results in, among other things, a marked
transition from the rough perturbation profiles predicted by analogy to the KPZ
equation to smooth, triangular profiles with reduced wandering exponents. These
results suggest that diffusive conserved quantities can, in some cases, be the
dominant forces shaping the development of chaos in classical systems.Comment: This was an undergraduate research paper by Henry Ando, which we are
posting now because it is relevant to some continuing wor
Optical trapping with "on-demand" two-photon luminescence using Cr:LiSAF laser with optically addressed saturable Bragg reflector
We demonstrate a diode-pumped Cr:LiSAF laser with controllable and reliable fast switching between its continuous-wave and mode-locked states of operation using an optically-addressed semiconductor Bragg reflector, permitting dyed microspheres to be continuously trapped and monitored using a standard microscope imaging and on-demand two-photon-excited luminescence techniques
IP3 receptor isoforms differently regulate ER-mitochondrial contacts and local calcium transfer
Contact sites of endoplasmic reticulum (ER) and mitochondria locally convey calcium signals between the IP3 receptors (IP3R) and the mitochondrial calcium uniporter, and are central to cell survival. It remains unclear whether IP3Rs also have a structural role in contact formation and whether the different IP3R isoforms have redundant functions. Using an IP3R-deficient cell model rescued with each of the three IP3R isoforms and an array of super-resolution and ultrastructural approaches we demonstrate that IP3Rs are required for maintaining ER-mitochondrial contacts. This role is independent of calcium fluxes. We also show that, while each isoform can support contacts, type 2 IP3R is the most effective in delivering calcium to the mitochondria. Thus, these studies reveal a non-canonical, structural role for the IP3Rs and direct attention towards the type 2 IP3R that was previously neglected in the context of ER-mitochondrial calcium signaling
Network sensitivity to geographical configuration
Gravitational wave astronomy will require the coordinated analysis of data
from the global network of gravitational wave observatories. Questions of how
to optimally configure the global network arise in this context. We have
elsewhere proposed a formalism which is employed here to compare different
configurations of the network, using both the coincident network analysis
method and the coherent network analysis method. We have constructed a network
model to compute a figure-of-merit based on the detection rate for a population
of standard-candle binary inspirals. We find that this measure of network
quality is very sensitive to the geographic location of component detectors
under a coincident network analysis, but comparatively insensitive under a
coherent network analysis.Comment: 7 pages, 4 figures, accepted for proceedings of the 4th Edoardo
Amaldi conference, incorporated referees' suggestions and corrected diagra
Parallelism and divergence in immune responses: a comparison of expression levels in two lakes
Question: How do immune phenotypes differ between infected and uninfected wild individuals, and is the effect the same in different populations?
Organisms: Threespine stickleback (Gasterosteus aculeatus) from two lake populations on the island of North Uist, Scotland, sampled in May 2015.
Methods: For each fish, we recorded length, sex, reproductive status, condition, and parasitic infection. We measured the expression levels of eight genes that act as key markers of immune system function using qPCR, and then examined the relationship between measured factors and immune gene expression profiles within each population.
Conclusions: Populations differed significantly in their immune gene expression profiles. Within each population, multiple factors, including condition, reproductive status, and Schistocephalus solidus infection levels, were found to correlate with expression levels of different arms of the immune system
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