2,570 research outputs found
Environmental Toxins Linked to Neurodegeneration and Autism Activate the Brainâs Immune System
Microglia are the primary immune cells of the central nervous system and become activated in response to noxious stimuli, leading to a cycle of inflammation and cell death that has been implicated in the development of Parkinsonâs disease and autism. This study examines the effects of environmental toxins, at levels commonly found in humans, on microglial cell survival and activation. The toxins used in this study include polybrominated diphenyl ether (PBDE) flame retardants, the food additive propionic acid (PPA), and the organochlorine pesticide dieldrin. These chemicals have been linked to neuronal damage, although their effects on microglial cells have not been fully studied. Our results indicate that microglial cell survival could be decreased by as much as 50% due to exposure to these toxins, without the production of certain cytokines produced by lipopolysaccharide (LPS)-induced activation. These effects are significant as further understanding of the role of microglia in neuronal damage could provide a pharmacologic target for future drug development as well as elucidate the pathology of neurodegenerative diseases
Aharonov-Bohm interferences from local deformations in graphene
One of the most interesting aspects of graphene is the tied relation between
structural and electronic properties. The observation of ripples in the
graphene samples both free standing and on a substrate has given rise to a very
active investigation around the membrane-like properties of graphene and the
origin of the ripples remains as one of the most interesting open problems in
the system. The interplay of structural and electronic properties is
successfully described by the modelling of curvature and elastic deformations
by fictitious gauge fields that have become an ex- perimental reality after the
suggestion that Landau levels can form associated to strain in graphene and the
subsequent experimental confirmation. Here we propose a device to detect
microstresses in graphene based on a scanning-tunneling-microscopy setup able
to measure Aharonov-Bohm inter- ferences at the nanometer scale. The
interferences to be observed in the local density of states are created by the
fictitious magnetic field associated to elastic deformations of the sample.Comment: Some bugs fixe
Ripple Texturing of Suspended Graphene Atomic Membranes
Graphene is the nature's thinnest elastic membrane, with exceptional
mechanical and electrical properties. We report the direct observation and
creation of one-dimensional (1D) and 2D periodic ripples in suspended graphene
sheets, using spontaneously and thermally induced longitudinal strains on
patterned substrates, with control over their orientations and wavelengths. We
also provide the first measurement of graphene's thermal expansion coefficient,
which is anomalously large and negative, ~ -7x10^-6 K^-1 at 300K. Our work
enables novel strain-based engineering of graphene devices.Comment: 15 pages, 4 figure
Acute ECG ST-segment elevation mimicking myocardial infarction in a patient with pulmonary embolism
Pulmonary embolism is a common cardiovascular emergency, but it is still often misdiagnosed due to its unspecific clinical symptoms. Elevated troponin concentrations are associated with greater morbidity and mortality in patients with pulmonary embolism. Right ventricular ischemia due to increased right ventricular afterload is believed to be underlying mechanism of elevated troponin values in acute pulmonary embolism, but a paradoxical coronary artery embolism through opened intra-artrial communication is another possible explanation as shown in our case report
Symmetric diffusions with polynomial eigenvectors
25 pagesInternational audienceWe describe symmetric diffusion operators where the spectral decomposition is given through a family of orthogonal polynomials. In dimension one, this reduces to the case of Hermite, Laguerre and Jacobi polynomials. In higher dimension, some basic examples arise from compact Lie groups. We give a complete description of the bounded sets on which such operators may live. We then provide a classification of those sets when the polynomials are ordered according to their usual degree
Modeling Supply Networks and Business Cycles as Unstable Transport Phenomena
Physical concepts developed to describe instabilities in traffic flows can be
generalized in a way that allows one to understand the well-known instability
of supply chains (the so-called ``bullwhip effect''). That is, small variations
in the consumption rate can cause large variations in the production rate of
companies generating the requested product. Interestingly, the resulting
oscillations have characteristic frequencies which are considerably lower than
the variations in the consumption rate. This suggests that instabilities of
supply chains may be the reason for the existence of business cycles. At the
same time, we establish some link to queuing theory and between micro- and
macroeconomics.Comment: For related work see http://www.helbing.or
Osseointegration of zirconia implants: an SEM observation of the bone-implant interface
Background The successful use of zirconia ceramics in orthopedic surgery led to a demand for dental zirconium-based implant systems. Because of its excellent biomechanical characteristics, biocompatibility, and bright tooth-like color, zirconia (zirconium dioxide, ZrO2) has the potential to become a substitute for titanium as dental implant material. The present study aimed at investigating the osseointegration of zirconia implants with modified ablative surface at an ultrastructural level. Methods A total of 24 zirconia implants with modified ablative surfaces and 24 titanium implants all of similar shape and surface structure were inserted into the tibia of 12 Gottinger minipigs. Block biopsies were harvested 1 week, 4 weeks or 12 weeks (four animals each) after surgery. Scanning electron microscopy (SEM) analysis was performed at the bone implant interface. Results Remarkable bone attachment was already seen after 1 week which increased further to intimate bone contact after 4 weeks, observed on both zirconia and titanium implant surfaces. After 12 weeks, osseointegration without interposition of an interfacial layer was detected. At the ultrastructural level, there was no obvious difference between the osseointegration of zirconia implants with modified ablative surfaces and titanium implants with a similar surface topography. Conclusion The results of this study indicate similar osseointegration of zirconia and titanium implants at the ultrastructural level
Chrobak Normal Form Revisited, with Applications
Abstract. It is well known that any nondeterministic finite automata over a unary alphabet can be represented in a certain normal form called the Chrobak normal form [1]. We present a very simple conversion pro-cedure working in O(n3) time. Then we extend the algorithm to improve two trade-offs concerning conversions between different representations of unary regular languages. Given an n-state NFA, we are able to find a regular expression of size O ( n2 logn) describing the same language (which improves the previously known O(n2) size bound [8]) and a context-free grammar in Chomsky normal form with O(ân logn) nonterminals (which improves the previously known O(n2/3) bound [3]). As a byproduct of our conversion procedure, we get an alternative proof of the Chrobak normal form theorem. We believe that its efficiency and simplicity make the effort of reproving an already known result worth-while. Key-words: unary automata, descriptional complexity
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