The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983

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The molecular basis of retinotectal topography

Five tests on battery cells were performed.

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The results revealed that in all of the test conditions investigated, the battery cells simply vented their hydrogen gas and some electrolyte, but did not burst or generate any large debris fragments. Theoretical model for plasma expansion generated by hypervelocity impact.

The hypervelocity impact experiments of spherical LY12 aluminum projectile diameter of 6. The impact velocity of the projectile is 5. The experimental results show that the plasma phase transition appears under the current experiment conditions, and the plasma expansion consists of accumulation, equilibrium, and attenuation. The plasma characteristic parameters decrease as the plasma expands outward and are proportional with the third power of the impact velocity, i. Based on the experimental results, a theoretical model on the plasma expansion is developed and the theoretical results are consistent with the experimental data.

Ju, Yuanyuan; Zhang, Qingming, E-mail: qmzhang bit. Mass spectrometry of hyper-velocity impacts of organic micrograins. The study of hyper-velocity impacts of micrometeoroids is important for the calibration of dust sensors in space applications. For this purpose, submicron-sized synthetic dust grains comprising either polystyrene or poly[bis 4-vinylthiophenyl sulfide] were coated with an ultrathin overlayer of an electrically conductive organic polymer either polypyrrole or polyaniline and were accelerated to speeds between 3 and 35 km s -1 using the Heidelberg Dust Accelerator facility.

Depending on the projectile type and the impact speed, both aliphatic and aromatic molecular ions and cluster species were identified in the mass spectra with masses up to u. Clusters resulting from the target material silver and mixed clusters of target and projectile species were also observed. Impact velocities of between 10 and 35 km s -1 are suitable for a principal identification of organic materials in micrometeoroids, whereas impact speeds below approximately 10 km s -1 allow for an even more detailed analysis.

Molecular ions and fragments reflect components of the parent molecule, providing determination of even complex organic molecules embedded in a dust grain.

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In contrast to previous measurements with the Cosmic Dust Analyser instrument, the employed LAMA instrument has a seven times higher mass resolution--approximately which allowed for a detailed analysis of the complex mass spectra. These fundamental studies are expected to enhance our understanding of cometary, interplanetary and interstellar dust grains, which travel at similar hyper-velocities and are known to contain both aliphatic and aromatic organic compounds.

Metallic pressure tanks used in space missions are inherently vulnerable to hypervelocity impacts from micrometeoroids and orbital debris; thereby knowledge of impact damage and its effect on the tank integrity is crucial to a spacecraft risk assessment. This paper describes tests that have been performed to assess the effects of hypervelocity impact HVI damage on Titanium alloy Ti-6Al-4V pressure vessels burst pressure and characteristics. The tests consisted of a pair of HVI impact tests on water-filled Ti-6Al-4V tanks water being used as a surrogate to the actual propellant and subsequent burst tests as well as a burst test on an undamaged control tank.

The resulting impact debris plumes partially penetrated the Ti-6Al-4V tank surfaces resulting in a distribution of craters. During the burst tests, the tank that failed at a lower burst pressure did appear to have the failure initiating at a crater site with observed spall cracks. A fracture mechanics analysis showed that the tanks failure at the impact location may have been due to a spall crack that formed upon impact of a fragmentation on the Titanium surface. This result was corroborated with a finite element analysis from calculated Von-Mises and hoop stresses.

Design and testing of miniaturized plasma sensor for measuring hypervelocity impact plasmas. Goel, A. An increasingly notable component of the space environment pertains to the impact of meteoroids and orbital debris on spacecraft and the resulting mechanical and electrical damages. In order to measure the flux, composition, energy distribution, and temperature of ions and electrons in this plasma, a miniaturized plasma sensor has been developed for carrying out in-situ measurements in space.

The sensor comprises an array of electrostatic analyzer wells split into 16 different channels, catering to different species and energy ranges in the plasma. We present results from numerical simulation based optimization of sensor geometry. A novel approach of fabricating the sensor using printed circuit boards is implemented. We also describe the test setup used for calibrating the sensor and show results demonstrating the energy band pass characteristics of the sensor. In addition to the hypervelocity impact plasmas, the plasma sensor developed can also be used to carry out measurements of ionospheric plasma, diagnostics of plasma propulsion systems, and in other space physics experiments.

Hypervelocity dust impact craters on photovoltaic devices imaged by ion beam induced charge. Photovoltaic PV arrays are especially vulnerable because of their large surface area and the performance can be degraded owing to the disruption of the structure of the junction in the cells making up the array. Extensive prior work has been done on the analysis of the morphology of craters in PV cells to understand the origin of the micrometeoroid that caused the crater and to study the corresponding mechanical damage to the structure of the cell. Generally, about half the craters arise from natural micrometeoroids, about one third from artificial Al-rich debris, probably from solid rocket exhausts, and the remainder from miscellaneous sources both known and unknown.

However to date there has not been a microscopic study of the degradation of the electrical characteristics of PV cells exposed to hypervelocity dust impacts.

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We are able to extrapolate the charge collection efficiency degradation rate of unbiased cells in space based on our current measurements and the. The electromagnetic properties of plasma produced by hypervelocity impact. The change of electron density in moving plasma in this paper is empirically determined according to multiple ground-based experimental results and the assumption of the Maxwell distribution. Moreover, the equation of the magnetic field intensity, dominated by the current due to the collective electron movement during the expansion, is presented on the basis of the Biot-Savart law, and its relationship with time and space is subsequently depicted.

In addition, hypervelocity impact experiments on a 2AL12 target have been carried out using a two-stage light gas gun to accelerate a 2AL12 projectile of 6. Spiral coils are designed to measure the intensity of the electromagnetic field induced by this impact.

Lastly, numerical simulation of the magnetic field intensity using this experimental parameter reveals that the intensity in our estimation from our theory tends to be well consistent with the experimental data in the first peak of the pulse signal.

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Emission spectroscopy of hypervelocity impacts on aluminum, organic and high-explosive targets. Verreault, J. Laboratory experiments of hypervelocity impacts on aluminum, nylon and high-explosive targets are presented. Spectral measurements of the impact flash are recorded, together with radiometric measurements to derive the temperature of the flash. Such experiments aim at demonstrating that the impact.

Hypervelocity impact events mobilize and redistribute fine-grained regolith dust across the surfaces of planetary bodies.

The ejecta mass-velocity distribution controls the location and emplacement of these materials. The current flux of material falling on the moon is dominated by small bolides and should cause frequent impacts that eject dust at high speeds. When scaled to lunar conditions, the high-speed component of ejecta from hypervelocity impacts can be lofted for significant periods of time as evidenced by the LCROSS mission results, c.

Even at laboratory scales, ejecta can approach orbital velocities; the higher impact speeds and larger projectiles bombarding the lunar surface may permit a significant portion of material to be launched closer to escape velocity. When these ejecta return to the surface or encounter local topography , they impact at hundreds of meters per second or faster, thereby "scouring" the surface with low mass oblique impacts. While these high-speed ejecta represent only a small fraction of the total ejected mass, the lofting and subsequent ballistic return of this dust has the highest mobilization potential and will be directly applicable to the upcoming LADEE mission.

This study incorporates both canonical sand targets and air-fall pumice dust to simulate the mechanical properties of lunar regolith. The implementation of a Particle Tracking Velocimetry PTV technique permits non-intrusive measurement of the ejecta velocity distribution within the ejecta curtain by following the path of individual ejecta particles.

Hydrocode modeling of the spallation process during hypervelocity impacts : Implications for the ejection of Martian meteorites.

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Hypervelocity ejection of material by impact spallation is considered a plausible mechanism for material exchange between two planetary bodies. The Tillotson equations of state, which are able to treat the nonlinear dependence of density on pressure and thermal pressure in strongly shocked matter, were used to study the hydrodynamic-thermodynamic response after impacts.

The Role of Cell Interactions in Early Neurogenesis - Cargèse | Anne M. Duprat | Springer

The effects of material strength and gravitational acceleration were not considered. A two-dimensional time-dependent pressure field within a 1. A resolution test was also performed to reject ejected materials with peak pressures that were too low due to artificial viscosity.

The relationship between ejection velocity veject and peak pressure Ppeak was also derived. Our approach shows that "late-stage acceleration" in an ejecta curtain occurs due to the compressible nature of the ejecta, resulting in an ejection velocity that can be higher than the ideal maximum of the resultant particle velocity after passage of a shock wave. We also calculate the ejecta mass that can escape from a planet like Mars i. Although the mass of such ejecta is limited to 0. Finally, we propose that impact spallation is a plausible mechanism for the generation of tektites.

Hyper-velocity impacts on the molten silica of the LMJ facility: experimental results and related simulations. This work presents a damaging study of the molten silica splinter-guards of the experiment chamber of the Megajoule laser facility. Damaging is due to the impact of hyper-velocity particulates coming from the interaction between X-rays and the diagnostic supports. Samples are expertized to measure the craters and damaging characteristics generated by the impact.

Experimental results are compared to numerical simulations in order to check the capability of the model to reproduce the effect of hyper-velocity impacts on molten silica. The final goal is to evaluate the lifetime of splinter-guards. The ballistic limit was defined as the projectile size on the threshold of failure of the OM pressure shell as a function of impact speeds and angle.

This test program provides HVI data on U. Data from this test program was used to update ballistic limit equations used in Soyuz OM penetration risk assessments. The objective of this hypervelocity impact test program was to determine the ballistic limit particle size for C stainless steel spherical projectiles on the Soyuz OM shielding at several impact conditions velocity and angle combinations. Effect of impact angles on ejecta and crater shape of aluminum alloy T6 targets in hypervelocity impacts.

Full Text Available The effect of the impact angle of projectiles on the crater shape and ejecta in thick aluminum alloy targets was investigated in hypervelocity impacts. When polycarbonate projectiles and aluminum alloy T6 target were used, the impact angle of the projectiles clearly affected the crater shape, as expected. The impact angle also affected the ejecta mass, ejecta size and scatter angle. Analysis of simulated hypervelocity impacts on a titanium fuel tank from the Salyut 7 space station. The aim of this project was to gain a better understanding of the microstructural effects of hypervelocity impacts HVI in titanium alloys.

We investigated a titanium fuel tank recovered from the Russian Salyut 7 space station, which was launched on April 19, before being destroyed during an un-controlled re-entry in , reportedly scattering debris over parts of South America. Several sections were cut out from the tank in order to undergo HVI simulations using a two-stage light gas gun. In addition, a Ti-6Al-4V alloy was studied for further comparison. Microstructural alterations were investigated using focused ion beam FIB milling and depth profiling, as well as transmission electron microscopy TEM.

There was evidence of a very high density of dislocations in the vicinity of the crater. The extent of the deformation was localised in a region of about one to two radii of the impact craters. No notable differences were observed between the titanium alloys used during the hypervelocity impact tests. Asteroid deflection using a kinetic impactor: Insights from hypervelocity impact experiments.

The impact crater will be observed from the AIM spacecraft and an observation of the ejecta plume is possible [1]. This allows conclusions to be drawn about the physical properties of the target material, and the momentum transfer will be studied [1]. In preparation for this mission, hypervelocity impact experiments can provide valuable information about the outcome of an impact event as a function of impactor and target material properties and, thus, support the interpretation of the data from the DART impact.

In addition, these impact experiments provide an important means to validate numerical impact simulations required to simulate large-scale impacts that cannot be studied in laboratory experiments. Impact experiments have shown that crater morphology and size, crater growth and ejecta dynamics strongly depend on the physical properties of the target material [2].

The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983
The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983
The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983
The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983
The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983
The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983
The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983
The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983
The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983 The Role of Cell Interactions in Early Neurogenesis: Cargèse 1983

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