7,325 research outputs found
Intracerebral Implantation of Ionic Synthetic Hydrogels: Effect of Polar Substrata on Astrocytosis and Axons
In previous studies, hyperporous synthetic
hydrogels of poly(glyceryl methacrylate) or
p(GMA), containing bioadhesive substrates of
collagen, were implanted into rat cerebral tissue
in order to provide systems of oriented guidance
channels for directing the growth of the scar and
axons /28/. In the present study, ionic p(GMA)-
collagen hydrogels containing polar chemical
groups, either basic amino groups or acidic
carboxyl groups, were evaluated for their
tolerance and their effects on the brain scarring
response and axonal reactivity after long-term
implantation in the cerebral cortex. In all
animals, the implants were well tolerated.
Although both types of gels influenced the
astroglial reaction near the bioimplant,
hydrogels carrying carboxyl groups had the
strongest influence on the elongation, the
direction and the organization of astrocytic
processes so that a glial matrix could form in
regions of the gel. Extracellular material (e.g.
reticulin) was also deposited into the gels
carrying carboxyl groups. Although cortical nerve fibers .in the surrounding tissue showed a
regenerative response, extending onto or into the
matrices, this behavior seemed to depend more
on the organization of the .astrocytic scar
imposed by the gel than on the type of gel. We
conclude that matrices carrying negatively
charged groups influence favorably the astrocytosis
and the deposition of connective tissue,
and that this approach represents a new avenue
in attempting to modulate the brain scar
formation
Multiangle observations of Arctic clouds from FIRE ACE: June 3, 1998, case study
In May and June 1998 the Airborne Multiangle Imaging Spectroradiometer (AirMISR) participated in the FIRE Arctic Cloud Experiment (ACE). AirMISR is an airborne instrument for obtaining multiangle imagery similar to that of the satellite-borne MISR instrument. This paper presents a detailed analysis of the data collected on June 3, 1998. In particular, AirMISR radiance measurements are compared with measurements made by two other instruments, the Cloud Absorption Radiometer (CAR) and the MODIS airborne simulator (MAS), as well as to plane-parallel radiative transfer simulations. It is found that the AirMISR radiance measurements and albedo estimates compare favorably both with the other instruments and with the radiative transfer simulations. In addition to radiance and albedo, the multiangle AirMISR data can be used to obtain estimates of cloud top height using stereoimaging techniques. Comparison of AirMISR retrieved cloud top height (using the complete MISR-based stereoimaging approach) shows excellent agreement with the measurements from the airborne Cloud Lidar System (CLS) and ground-based millimeterwave cloud radar
The Coulomb Sum and Proton-Proton Correlations in Few-Body Nuclei
In simple models of the nuclear charge operator, measurements of the Coulomb
sum and the charge form factor of a nucleus directly determine the
proton-proton correlations. We examine experimental results obtained for
few-body nuclei at Bates and Saclay using models of the charge operator that
include both one- and two-body terms. Previous analyses using one-body terms
only have failed to reproduce experimental results. However, we find that the
same operators which have been used to successfully describe the charge form
factors also produce substantial agreement with measurements of the Coulomb
sum.Comment: 11 pages, Revtex version 3.0 with 3 Postscript figures appended, ANL
preprint PHY-7473-TH-9
SPIRAL2 cryomodule production result and analyses
THIOB02International audienceThe production and qualification of the SPIRAL2 cryomodules are close to the end. Their performances arenow well established. This paper will explain the path followed to the good achievements, and show somestatistical analyses to be used for future projects. How far can we push the performances? What cryogenicsconsumption shall we take as design values
Blunted cardiovascular responses to acute psychological stress predict low behavioral but not self-reported perseverance
Emerging evidence relates attenuated physiological stress reactions to poor behavioral regulation. However, only a small number of behaviors such as impulsivity and risk taking have been explored. Nevertheless, one opportunistic study suggested that blunted reactivity might relate to poor perseverance. The present study examined the relationship between cardiovascular reactivity to acute active psychological stress and selfâreported and behavioral perseverance. Participants (N = 64) completed a selfâreport perseverance questionnaire before heart rate (HR) and blood pressure (BP) were measured at rest and in response to 4âmin active (paced auditory serial addition; PASAT) and passive (cold pressor) stress tests. This was followed by an unsolvable Euler puzzle tracing task, with the time spent and number of attempts endeavoring to solve the puzzle recorded as behavioral perseverance measures. Blunted systolic and diastolic BP reactivity to the PASAT was associated with fewer attempts at the impossible puzzle, and lower diastolic BP PASAT reactivity related to less time persevering at the puzzle. Moreover, attenuated diastolic BP and HR PASAT reactivity predicted poorer perseverance at keeping one's hand in the iced water of the cold pressor task. There was no association between reactivity and selfâreported perseverance. These preliminary findings add to the evidence that implicates blunted reactivity as a physiological marker of poor behavioral regulation, and this may indicate why individuals with blunted reactivity are at increased risk of developing negative health outcomes (e.g., obesity and addictions)
Eikonal analysis of Coulomb distortion in quasi-elastic electron scattering
An eikonal expansion is used to provide systematic corrections to the eikonal
approximation through order , where is the wave number. Electron
wave functions are obtained for the Dirac equation with a Coulomb potential.
They are used to investigate distorted-wave matrix elements for quasi-elastic
electron scattering from a nucleus. A form of effective-momentum approximation
is obtained using trajectory-dependent eikonal phases and focusing factors.
Fixing the Coulomb distortion effects at the center of the nucleus, the
often-used ema approximation is recovered. Comparisons of these approximations
are made with full calculations using the electron eikonal wave functions. The
ema results are found to agree well with the full calculations.Comment: 12 pages, 6 Postscript figure
G Electronics and Data Acquisition (Forward-Angle Measurements)
The G parity-violation experiment at Jefferson Lab (Newport News, VA) is
designed to determine the contribution of strange/anti-strange quark pairs to
the intrinsic properties of the proton. In the forward-angle part of the
experiment, the asymmetry in the cross section was measured for
elastic scattering by counting the recoil protons corresponding to the two
beam-helicity states. Due to the high accuracy required on the asymmetry, the
G experiment was based on a custom experimental setup with its own
associated electronics and data acquisition (DAQ) system. Highly specialized
time-encoding electronics provided time-of-flight spectra for each detector for
each helicity state. More conventional electronics was used for monitoring
(mainly FastBus). The time-encoding electronics and the DAQ system have been
designed to handle events at a mean rate of 2 MHz per detector with low
deadtime and to minimize helicity-correlated systematic errors. In this paper,
we outline the general architecture and the main features of the electronics
and the DAQ system dedicated to G forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section
A. It has been written with Latex using \documentclass{elsart}. Nuclear
Instruments and Methods in Physics Research Section A: Accelerators,
Spectrometers, Detectors and Associated Equipment In Press (2007
Pressure-induced amorphization and polyamorphism in one-dimensional single crystal TiO2 nanomaterials
The structural phase transitions of single crystal TiO2-B nanoribbons were
investigated in-situ at high-pressure using the synchrotron X-ray diffraction
and the Raman scattering. Our results have shown a pressure-induced
amorphization (PIA) occurred in TiO2-B nanoribbons upon compression, resulting
in a high density amorphous (HDA) form related to the baddeleyite structure.
Upon decompression, the HDA form transforms to a low density amorphous (LDA)
form while the samples still maintain their pristine nanoribbon shape. HRTEM
imaging reveals that the LDA phase has an {\alpha}-PbO2 structure with short
range order. We propose a homogeneous nucleation mechanism to explain the
pressure-induced amorphous phase transitions in the TiO2-B nanoribbons. Our
study demonstrates for the first time that PIA and polyamorphism occurred in
the one-dimensional (1D) TiO2 nanomaterials and provides a new method for
preparing 1D amorphous nanomaterials from crystalline nanomaterials.Comment: 4 figure
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