1,135 research outputs found
Response of an Excitatory-Inhibitory Neural Network to External Stimulation: An Application to Image Segmentation
Neural network models comprising elements which have exclusively excitatory
or inhibitory synapses are capable of a wide range of dynamic behavior,
including chaos. In this paper, a simple excitatory-inhibitory neural pair,
which forms the building block of larger networks, is subjected to external
stimulation. The response shows transition between various types of dynamics,
depending upon the magnitude of the stimulus. Coupling such pairs over a local
neighborhood in a two-dimensional plane, the resultant network can achieve a
satisfactory segmentation of an image into ``object'' and ``background''.
Results for synthetic and and ``real-life'' images are given.Comment: 8 pages, latex, 5 figure
Gene expression of serotonergic markers in peripheral blood mononuclear cells of patients with late-onset Alzheimer's disease
Serotonin or 5-hydroxytryptamine (5-HT) is primarily involved in the regulation of learning and memory. Pathological changes in metabolism or functional imbalance of 5-HT has been associated with Alzheimer's disease (AD). The hypothesis tested is that in peripheral blood, markers of the serotonergic pathway can be used as a diagnostic tool for AD. The current study measured the relative expression of 5-HT receptors (5-HTR2A and 5-HTR3A) as well as the 5-HT catalytic enzyme, Monoamine oxidase A (MAO-A) mRNA in Peripheral Blood Mononuclear Cells (PBMCs) of patients with late-onset Alzheimer's disease (LOAD) and age-matched controls. 5-HTR2A, 5-HTR3A, and MAO-A mRNA expressions were examined in PBMCs of 30 patients with LOAD and 30 control individuals. Real-time quantitative PCR was used to measure mRNA expression. The dementia status of patients in this study was assessed using a Mini-Mental State Examination (MMSE). Mean data of relative mRNA expression of 5-HTR2A, 5-HTR3A and MAO-A were significantly lower in PBMCs of patients with LOAD compared with controls. Based on the down-regulation of serotonergic markers in PBMCs, our findings may be another claim to the systemic nature of LOAD. The role of peripheral serotonergic downregulation, in the pathogenesis of AD, needs to be further studied. Given the extremely convenient access to PBMCs, these molecular events may represent more complete dimensions of AD neuropathophysiology or possibly lead to a new direction in studies focused on blood-based markers. © 2020 The Authors Alzheimer's disease, 5-HT2A receptor, 5-HT3A receptor, Monoamine oxidase-A (MAO-A), Gene expression, Load, Neuroscience, Immunology, Genetics, Gene mutation, Molecular biology, Immune system © 2020 The Author
Singularities In Scalar-Tensor Cosmologies
In this article, we examine the possibility that there exist special
scalar-tensor theories of gravity with completely nonsingular FRW solutions.
Our investigation in fact shows that while most probes living in such a
Universe never see the singularity, gravity waves always do. This is because
they couple to both the metric and the scalar field, in a way which effectively
forces them to move along null geodesics of the Einstein conformal frame. Since
the metric of the Einstein conformal frame is always singular for
configurations where matter satisfies the energy conditions, the gravity wave
world lines are past inextendable beyond the Einstein frame singularity, and
hence the geometry is still incomplete, and thus singular. We conclude that the
singularity cannot be entirely removed, but only be made invisible to most, but
not all, probes in the theory.Comment: 23 pages, latex, no figure
Kinks in the discrete sine-Gordon model with Kac-Baker long-range interactions
We study effects of Kac-Baker long-range dispersive interaction (LRI) between
particles on kink properties in the discrete sine-Gordon model. We show that
the kink width increases indefinitely as the range of LRI grows only in the
case of strong interparticle coupling. On the contrary, the kink becomes
intrinsically localized if the coupling is under some critical value.
Correspondingly, the Peierls-Nabarro barrier vanishes as the range of LRI
increases for supercritical values of the coupling but remains finite for
subcritical values. We demonstrate that LRI essentially transforms the internal
dynamics of the kinks, specifically creating their internal localized and
quasilocalized modes. We also show that moving kinks radiate plane waves due to
break of the Lorentz invariance by LRI.Comment: 11 pages (LaTeX) and 14 figures (Postscript); submitted to Phys. Rev.
Magnetic Phase Diagram of GdNi2B2C: Two-ion Magnetoelasticity and Anisotropic Exchange Couplings
Extensive magnetization and magnetostriction measurements were carried out on
a single crystal of GdNi2B2C along the main tetragonal axes. Within the
paramagnetic phase, the magnetic and strain susceptibilities revealed a weak
anisotropy in the exchange couplings and two-ion tetragonal-preserving
alpha-strain modes. Within the ordered phase, magnetization and
magnetostriction revealed a relatively strong orthorhombic distortion mode and
rich field-temperature phase diagrams. For H//(100) phase diagram, three
field-induced transformations were observed, namely, at: Hd(T), related to the
domain alignment; Hr(T), associated with reorientation of the moment towards
the c-axis; and Hs(T), defining the saturation process wherein the exchange
field is completely counterbalanced. On the other hand, For H//(001) phase
diagram, only two field-induced transformations were observed, namely at: Hr(T)
and Hs(T). For both phase diagrams, Hs(T) follows the relation
Hs[1-(T/Tn)^2]^(1/2)kOe with Hs(T-->0)=128.5(5) kOe and Tn(H=0)=19.5 K. In
contrast, the thermal evolution of Hr(T) along the c-axis (much simpler than
along the a-axis) follows the relation Hr[1-T/Tr]^(1/3) kOe where
Hr(T-->0)=33.5(5) kOe and Tr(H=0)=13.5 K. It is emphasized that the
magnetoelastic interaction and the anisotropic exchange coupling are important
perturbations and therefore should be explicitly considered if a complete
analysis of the magnetic properties of the borocarbides is desired
Study of star formation in RCW 106 using far infrared observations
High resolution far-infrared observations of a large area of the star forming
complex RCW 106 obtained using the TIFR 1-metre balloon-borne telescope are
presented. Intensity maps have been obtained simultaneously in two bands
centred around 150 & 210 micron. Intensity maps have also been obtained at the
4 IRAS bands using HIRES processed IRAS data. From the 150 & 210 micron maps,
reliable maps of dust temperature and optical depth have been generated. The
star formation in this complex has occured in five linear subclumps. Using the
map at 210 micron, which has a spatial resolution superior to that of the IRAS
at 100 micron, 23 sources have been identified. The SED and luminosity of these
sources have been determined using the associations wit hthe IRAS maps.
Luminosity distribution of these sources has been obtained. Assuming these
embedded sources to be ZAMS stars and using the mass-luminosity relation, the
power law slope of the Initial Mass Function is found to be -1.73+-0.5. This
index for this very young complex is about the same as that for more evolved
complexes and clusters. Radiation transfer calculations in spherical geometry
have been undertaken to fit the SEDs of 13 sources with fluxes in both the TIFR
and IRAS bands. From this, the r^-2 density distribution in the envelopes is
ruled out. Finally, a correlation is seen between the luminosity of embedded
sources and the computed dust masses of the envelopes.Comment: Accepted for publication in MNRAS (21 pages, 8 figures & 3 tables
Gluino Production in Electron-Positron Annihilation
We discuss the pair production of gluinos in electron-positron annihilation
at LEP, in a model with soft supersymmetry breaking, allowing for mixing
between the squarks. In much of the parameter space of the Minimal
Supersymmetric Model (MSSM) the cross section corresponds to a branching
ratio above , even up to . A non-observation of gluinos at
this level restricts the allowed MSSM parameter space. In particular, it leads
to lower bounds on the soft mass parameters in the squark sector.Comment: 24 pages LATEX plus 10 pages of figures (not included, available on
request). Full postscript version available by anonymous ftp at node
VSFYS1.FI.UIB.NO in subdirectory OSLAND, file BERGEN94-10.PS), Bergen
Scientific/Technical Report No. 1994-1
What is a β cell? - Chapter I in the Human Islet Research Network (HIRN) review series
BACKGROUND: The pancreatic β cell, as the sole source of the vital hormone insulin, has been under intensive study for more than a century. Given the potential of newly created insulin-producing cells as a treatment or even cure of type 1 diabetes (T1D) and possibly in severe cases of type 2 diabetes (T2D), multiple academic and commercial laboratories are working to derive surrogate glucose-responsive, insulin-producing cells. SCOPE OF REVIEW: The recent development of advanced phenotyping technologies, including molecular, epigenomic, histological, or functional, have greatly improved our understanding of the critical properties of human β cells. Using this information, here we summarize the salient features of normal, fully functional adult human β cells, and propose minimal criteria for what should rightfully be termed 'β cells' as opposed to insulin-producing but not fully-functional surrogates that we propose should be referred to as 'β-like' cells or insulin-producing cells. MAJOR CONCLUSIONS: Clear criteria can be established to differentiate fully functional, mature β cells from 'β-like' surrogates. In addition, we outline important knowledge gaps that must be addressed to enable a greater understanding of the β cell
Domain Wall Spacetimes: Instability of Cosmological Event and Cauchy Horizons
The stability of cosmological event and Cauchy horizons of spacetimes
associated with plane symmetric domain walls are studied. It is found that both
horizons are not stable against perturbations of null fluids and massless
scalar fields; they are turned into curvature singularities. These
singularities are light-like and strong in the sense that both the tidal forces
and distortions acting on test particles become unbounded when theses
singularities are approached.Comment: Latex, 3 figures not included in the text but available upon reques
Big Bang Baryogenesis
An overview of baryogenesis in the early Universe is presented. The standard
big bang model including big bang nucleosynthesis and inflation is breifly
reviewed. Three basic models for baryogenesis will be developed: The
``standard" out-of-equilibrium decay model; the decay of scalar consensates
along flat directions in supersymmetric models; and lepto-baryogenesis, which
is the conversion of a lepton asymmetry into a baryon asymmetry via
non-perturbative electroweak interactions.Comment: 36 pages, LaTeX, UMN-TH-1249, Lectures given at the 33rd
International Winter School on Nuclear and Particle Physics, ``Matter Under
Extreme Conditions", Feb. 27 - March 5 1994, Schladming Austri
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