Is neurogenesis reparative after status epilepticus?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65863/1/j.1528-1167.2007.01355.x.pd

Analysis of planetary analogue materials by laser-induced breakdown spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) is a promising tool for elemental chemical analysis in planetary science, because it allows real-time and fast in-situ determination of the elemental composition of materials down to minute concentrations. The technique requires no special preparation of samples, can provide high lateral resolution (as low as several tenths μm), depth profiling (down to mm) and, therefore, is not disturbed by dust layers. Miniaturized LIBS instruments are currently considered for the next NASA (Mars Science Laboratory) and ESA (ExoMars) missions to Mars, as well as studied for the international Europa Lander Mission. Here we present the LIBS laboratory facility at the German Aerospace Center in Berlin for the chemical elemental analysis under simulated planetary (Mars, Europa) conditions. The main purpose of the system is the study of the LIBS capability for in-situ spectroscopy for diverse planetary missions as well as the development of a LIBS spectral database under simulated planetary conditions for planetary analogue materials

Modelling polarization properties of comet 1P/Halley using a mixture of compact and aggregate particles

Recently, the result obtained from `Stardust' mission suggests that the overall ratio of compact to aggregate particles is 65:35 (or 13:7) for Comet 81P/Wild 2 (Burchell et al. 2008). In the present work, we propose a model which considers cometary dust as a mixture of compact and aggregate particles, with composition of silicate and organic. We consider compact particles as spheroidal particles and aggregates as BCCA and BAM2 aggregate with some size distribution. For modeling Comet 1P/ Halley, the power-law size distribution n(a)= a^{-2.6}, for both compact and aggregate particles is taken. We take a mixture of BAM2 and BCCA aggregates with a lower and upper cutoff size around 0.20$\mu m$ and 1$\mu m$. We also take a mixture of prolate, spherical and oblate compact particles with axial ratio (E) from 0.8 to 1.2 where a lower and upper cutoff size around 0.1$\mu m$ and 10$\mu m$ are taken. Using T-matrix code, the average simulated polarization curves are generated which can best fit the observed polarization data at the four wavelengths $\lambda$ = 0.365$\mu m$, 0.485$\mu m$, 0.670$\mu m$ and 0.684$\mu m$. The suitable mixing percentage of aggregates emerging out from the present modeling corresponds to 50% BAM2 and 50% BCCA particles and silicate to organic mixing percentage corresponds to 78% silicate and 22% organic in terms of volume. The present model successfully reproduces the observed polarization data, especially the negative branch, more effectively as compared to other work done in the past. It is found that among the aggregates, the BAM2 aggregate plays a major role, in deciding the cross-over angle and depth of negative polarization branch.Comment: 7 pages, 5 figures (accepted for publication in MNRAS on May 4, 2011

Dust observations of Comet 9P/Tempel 1 at the time of the Deep Impact

On 4 July 2005 at 05:52 UT, the impactor of NASA's Deep Impact (DI) mission crashed into comet 9P/Tempel 1 with a velocity of about 10 km/s. The material ejected by the impact expanded into the normal coma, produced by ordinary cometary activity. The characteristics of the non-impact coma and cloud produced by the impact were studied by observations in the visible wavelengths and in the near-IR. The scattering characteristics of the "normal" coma of solid particles were studied by comparing images in various spectral regions, from the UV to the near-IR. For the non-impact coma, a proxy of the dust production has been measured in various spectral regions. The presence of sublimating grains has been detected. Their lifetime was found to be about 11 hours. Regarding the cloud produced by the impact, the total geometric cross section multiplied by the albedo was measured as a function of the color and time. The projected velocity appeared to obey a Gaussian distribution with the average velocity of the order of 115 m/s. By comparing the observations taken about 3 hours after the impact, we have found a strong decrease in the cross section in J filter, while that in Ks remained almost constant. This is interpreted as the result of sublimation of grains dominated by particles of sizes of the order of some microns.Comment: Accepted by A&

A Spitzer Survey of Mid-Infrared Molecular Emission from Protoplanetary Disks II: Correlations and LTE Models

We present an analysis of Spitzer-IRS observations of H2O, OH, HCN, C2H2, and CO2 emission, and Keck-NIRSPEC observations of CO emission, from a diverse sample of T Tauri and Herbig Ae/Be circumstellar disks. We find that detections and strengths of most mid-IR molecular emission features are correlated with each other, suggesting a common origin and similar excitation conditions. We note that the line detection efficiency is anti-correlated with the 13/30 um SED spectral slope, which is a measure of the degree of grain settling in the disk atmosphere. We also note a correlation between detection efficiency and H-alpha equivalent width, and tentatively with accretion rate, suggesting that accretional heating contributes to line excitation. If detected, H2O line fluxes are correlated with the mid-IR continuum flux, and other co-varying system parameters, such as L_star. However, significant sample variation, especially in molecular line ratios, remains. LTE models of the H2O emission show that line strength is primarily related to the best-fit emitting area, and this accounts for most source-to-source variation in H2O emitted flux. Best-fit temperatures and column densities cover only a small range of parameter space, near 10^{18} cm-2 and 450 K for all sources, suggesting a high abundance of H2O in many planet-forming regions. Other molecules have a range of excitation temperatures from ~500-1500 K, also consistent with an origin in planet-forming regions. We find molecular ratios relative to water of ~10^{-3} for all molecules, with the exception of CO, for which n(CO)/n(H2O)~1. However, LTE fitting caveats and differences in the way thermo-chemical modeling results are reported make comparisons with such models difficult, and highlight the need for additional observations coupled with the use of line-generating radiative transfer codes

Human Adult Neurogenesis: Evidence and Remaining Questions

Renewed discussion about whether or not adult neurogenesis exists in the human hippocampus, and the nature and strength of the supporting evidence, has been reignited by two prominently published reports with opposite conclusions. Here, we summarize the state of the field and argue that there is currently no reason to abandon the idea that adult-generated neurons make important functional contributions to neural plasticity and cognition across the human lifespan

Prox1 Is Required for Granule Cell Maturation and Intermediate Progenitor Maintenance During Brain Neurogenesis

The transcription factor Prox1 plays a crucial role in intermediate progenitor maintenance and hippocampal neuron differentiation during adult neurogenesis in the dentate gyrus region of the hippocampus

Measurements of the vertical fluxes of atomic Fe and Na at the mesopause: implications for the velocity of cosmic dust entering the atmosphere

The downward fluxes of Fe and Na, measured near the mesopause with the University of Colorado lidars near Boulder, and a chemical ablation model developed at the University of Leeds, are used to constrain the velocity/mass distribution of the meteoroids entering the atmosphere and to derive an improved estimate for the global influx of cosmic dust. We find that the particles responsible for injecting a large fraction of the ablated material into the Earth's upper atmosphere enter at relatively slow speeds and originate primarily from the Jupiter Family of Comets. The global mean Na influx is 17,200 ± 2800 atoms/cm2/s, which equals 298 ± 47 kg/d for the global input of Na vapor and 150 ± 38 t/d for the global influx of cosmic dust. The global mean Fe influx is 102,000 ± 18,000 atoms/cm2/s, which equals 4.29 ± 0.75 t/d for the global input of Fe vapor

Modulation of aberrant CDK5 signaling rescues impaired neurogenesis in models of Alzheimer's disease

Recent studies show that in Alzheimer's disease (AD), alterations in neurogenesis contribute to the neurodegenerative process. Neurodegeneration in AD has been associated with aberrant signaling through the cyclin-dependent kinase-5 (CDK5) pathway via its activators p35/p25; however, the role of CDK5 in the mechanisms of defective adult neurogenesis in AD is unknown. First, to study AD-like abnormal activation of CDK5 signaling in an in vitro model of neurogenesis, neuronal progenitor cells (NPCs) were infected with a viral vector expressing p35, and exposed to amyloid-β protein (Aβ1−42). These conditions resulted in impaired maturation and neurite outgrowth in vitro, and these effects were reversed by pharmacological or genetic inhibition of CDK5. Similarly, neurogenesis was impaired in a transgenic mouse model of AD that expresses high levels of amyloid precursor protein (APP), and this effect was reversed in transgenic mice crossed with a CDK5 heterozygous-deficient mouse line. A similar rescue effect was observed in APP transgenic mice treated with Roscovitine, a pharmacological inhibitor of CDK5. Taken together, these data suggest that the CDK5 signaling pathway has a critical role in maintaining the integrity of NPCs and neuronal maturation in the adult hippocampus. Moreover, potential therapeutic approaches could focus on modulating the aberrant activity of CDK5 to target the neurogenic and neurodegenerative alterations in AD

The production of platinum-coated silicate nanoparticle aggregates for use in hypervelocity impact experiments

We present a method for producing metal-coated low-density (?3) aggregate silicate dust particles for use in hypervelocity impact (HVI) experiments. Particles fabricated using the method are shown to have charged and electrostatically accelerated in the Max Planck Institut für Kernphysik (MPI-K) 2 MV Van de Graaff accelerator, allowing the production of impact ionization mass spectra of silicate particles (impacting at velocities ranging from ?1 to >30 km s?1, corresponding to sizes of >1 ?m to <0.1 ?m) using the Large Area Mass Analyser (LAMA) instrument, designed for cosmic dust detection in space. Potential uses for the coated grains, such as in the calibration of aerogel targets similar to those used on the Stardust spacecraft, are also discussed