The Development of a Method to Extract High Purity Oxygen From the Martian Atmosphere

A glow-discharge in an ambient Mars atmosphere (total pressure of 5 torr, composed of 95% carbon dioxide) results in the dissociation of carbon dioxide molecules into carbon monoxide and oxygen. If the glow-discharge zone is maintained adjacent and close to a silver membrane, operated at temperatures above 400°C, atomic and molecular oxygen, produced by the glow-discharge, can be separated from the other species by atomic diffusion through the membrane to an ultrahigh vacuum region where the desorbed O2 is then collected. Experiments have been conducted to study the behavior of the glow discharge in both molecular oxygen and carbon dioxide environments, and to study the interaction of atomic and molecular oxygen with silver. It was found that, with this geometry, more than 75% of the CO2 was dissociated into CO and O with only 5 mA discharge current and that the permeation flux increased linearly with discharge current. Only 0.65% of the generated atomic oxygen was adsorbed at the membrane because it quickly recombined to form O2as it migrated toward the membrane. The atomic oxygen arriving at the membrane, bypassed the thermal dissociative adsorption and therefore had a much higher sticking coefficient. This higher sticking coefficient resulted in a greatly increased surface concentration of oxygen which greatly increased the oxygen flux through the membrane. The sticking coefficient of the atomic oxygen on silver was estimated by using a Langmuir type model and was found to be close to 1 at room temperature. Since most of the gas phase atomic oxygen quickly recombined to form O2 as it migrated toward the silver membrane, both a small amount of atomic oxygen and a relative large amount of molecular oxygen components will adsorb on the hot Ag membrane. But because of the much higher sticking coefficient for atomic oxygen on silver, the atomic component dominated the adsorption. It was also found that the oxygen flux through the Ag membranes is diffusion controlled and therefore proportional to the reciprocal of the membrane thickness. Supported pin hole free Ag membranes with thicknesses of 12 μm have been developed in this work. Furthermore, a pin hole free Ag membrane that was grown by a combination of At ion bombardment assisted physical vapor deposition and intermediate burnishing with a thickness less than 1μm is being developed which will substantially improve the oxygen flux level. Thickness of 1 pm will permit flux levels of at least 1016 molecules/cm2s. With this flux level, less than 1.5 m2 membrane surface area would be needed to support an astronaut on a continual basis on the Mars surface. The results of this work show that this approach of producing oxygen from the CO2 Martian atmosphere can eliminate mechanical filtration, compression and high temperature heating of the Mars atmosphere proposed previously by electrochemical method

The Study of Oxygen Transport Through Polycrystalline, Single Crystal and Alloyed Silver

The permeation of oxygen through large grain polycrystalline silver, through the (110), (111) and (100) single crystals of silver and through Ag0.05Zr alloy have been studied over the temperature range of 400 - 800 °C. In addition, studies were also conducted using glow discharge dissociation of the supply side ( upstream ) molecular oxygen in order to examine whether normal dissociative adsorption is a limiting step in the overall transport process. The permeability of oxygen through polycrystalline silver was found to be quite linear and quite repeatable. The diffusivity measurements were found to exhibit two distinct linear regions, one above and one below a critical temperature of 630 °C. The high-temperature data have an activation energy (11.1 kcal/mole ) similar to that reported by others, but the low-temperature data have a comparatively larger activation energy ( 15.3 kcal/mole ) which is probably due to the higher efficiency of traps. The permeability of oxygen through the (110), (111) and (100) single ·crystals of silver· all fell along a linear Arrhenius plot with the activation energy and the preexponential very similar to that found for the polycrystalline silver. This indicates that the transport limitation is approximately the same, even though there is some substantial difference in the microstructure. The magnitude of the diffusivity was found to be different for the three different crystal orientations which is inconsistent with the relation of K = DS since the solubility must be the same. The variation in the diffusivity can be explained by the relative displacement along a given crystallographic direction for a given number of jumps. The diffusivity ratios were in reasonable agreement with the ratio of the displacements squared. The permeability for Ag0.05Zr alloy was found to be a fact of 1 .86 higher than polycrystalline silver. The 0.05 percent Zr gives a much higher grain boundary and defect density to provide more reservoirs for oxygen which will increase the solubility and give the higher permeability. The diffusivity data have a higher activation energy but are very close in magnitude to the polycrystalline silver. The effect of the surface limitation on the transport was further examined by using a glow discharge on the upstream side to enhance the formation of oxygen atoms. It was found that the flux of oxygen substantially increased from the steady state dissociative adsorption level by a factor of 6. This indicates that there is a definite surface limitation for normal dissociative adsorption. The increased signal during the glow discharge suggests that the adsorption and dissolution rate for oxygen atoms is substantially greater than for the previously conducted permeation experiments where 02 molecules are dissociatively adsorbed

Modulation of ligand-gated receptors in the central nervous system

Basal level neuronal excitability in the mammalian brain is fundamental for physiological brain functions. It is primarily maintained by a fine balance between two types of synaptic transmission: the excitatory transmission mediated by glutamate-gated ion channels including α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs) and N-methyl-D-aspartic acid receptors (NMDARs), and the inhibitory transmission mediated by chloride channels including γ-Aminobutyric acid receptors (GABAARs) found in the brain and glycine receptors (GlyRs) orginating in the spinal cord and brainstem. Therefore, understanding mechanisms by which these ligand-gated ion channels (LIGCs) are regulated is critical for our understanding of both brain functions and dysfunctions, and is the major focus of this thesis. In particular, this research project investigates: 1) how rapid alteration of AMPAR trafficking results in changes in strength of synaptic transmission, with a particular emphasis on its contribution to amygdala long-term potentiation (LTP) and depression (LTD), the two most well-characterized forms of synaptic plasticity, and 2) how excitatory transmitter glutamate modulates functions of the inhibitory GABAA and Gly receptors. In chaper 2 and 3, we show in lateral amygdale (LA) slices that the induction of LTP requires NR2A-containing NMDAR activation, while the expression of LTP requires AMPARs insertion (sensitive to TeTx or GluR1-derived peptide). On the contrary, the induction of LTD involves activation of NR2B-containing NMDARs and the expression of LTD involves AMPARs endocytosis (sensitive to GluR2-3Y peptide). The inhibitory receptors GABAARs and GlyRs are respectively activated by binding with their respective transmitters, GABA and glycine. In chapter 4 and 5, we show novel and unexpected findings where glutamate potentiates currents mediated by either GABAARs or GlyRs in neurons and in HEK cells over-expressing recombinant GABAARs and GlyRs. This potentiation was not dependent on activation of any known ionotropic or metabotropic glutamate receptors. Thus, our results strongly suggest that glutamate can allosterically potentiate the function of GABAARs and GlyRs, thereby blurring the traditional distinction between excitatory and inhibitory transmitters. Such a rapid homeostatic regulatory mechanism may have a significant role in tuning functional balance between synaptic excitation and inhibition in the central nervous system (CNS).Medicine, Faculty ofMedicine, Department ofExperimental Medicine, Division ofGraduat

Study on Retrieval of Chlorophyll-a Concentration Based on Landsat OLI Imagery in the Haihe River, China

The optical complexity of urban waters makes the remote retrieval of chlorophyll-a (Chl-a) concentration a challenging task. In this study, Chl-a concentration was retrieved using reflectance data of Landsat OLI images. Chl-a concentration in the Haihe River of China was obtained using mathematical regression analysis (MRA) and an artificial neural network (ANN). A regression model was built based on an analysis of the spectral reflectance and water quality sampling data. Remote sensing inversion results of Chl-a concentration were obtained and analyzed based on a verification of the algorithm and application of the models to the images. The analysis results revealed that the two models satisfactorily reproduced the temporal variation based on the input variables. In particular, the ANN model showed better performance than the MRA model, which was reflected in its higher accuracy in the validation. This study demonstrated that Landsat Operational Land Imager (OLI) images are suitable for remote sensing monitoring of water quality and that they can produce high-accuracy inversion results

Genetic inhibition of glutamate allosteric potentiation of GABAARs in mice results in hyperexcitability, leading to neurobehavioral abnormalities

Abstract The imbalance between neuronal excitation and inhibition (E/I) in neural circuit has been considered to be at the root of numerous brain disorders. We recently reported a novel feedback crosstalk between the excitatory neurotransmitter glutamate and inhibitory γ‐aminobutyric acid type A receptor (GABAAR)‐glutamate allosteric potentiation of GABAAR functions through a direct binding of glutamate to the GABAAR itself. Here, we investigated the physiological significance and pathological implications of this cross‐talk by generating the β3E182G knock‐in (KI) mice. We found that β3E182G KI, while had little effect on basal GABAAR‐mediated synaptic transmission, significantly reduced glutamate potentiation of GABAAR‐mediated responses. These KI mice displayed lower thresholds for noxious stimuli, higher susceptibility to seizures and enhanced hippocampus‐related learning and memory. Additionally, the KI mice exhibited impaired social interactions and decreased anxiety‐like behaviors. Importantly, hippocampal overexpression of wild‐type β3‐containing GABAARs was sufficient to rescue the deficits of glutamate potentiation of GABAAR‐mediated responses, hippocampus‐related behavioral abnormalities of increased epileptic susceptibility, and impaired social interactions. Our data indicate that the novel crosstalk among excitatory glutamate and inhibitory GABAAR functions as a homeostatic mechanism in fine‐tuning neuronal E/I balance, thereby playing an essential role in ensuring normal brain functioning

Rescuing Nucleus Pulposus Cells From Senescence via Dual‐Functional Greigite Nanozyme to Alleviate Intervertebral Disc Degeneration

Abstract High levels of reactive oxygen species (ROS) lead to progressive deterioration of mitochondrial function, resulting in tissue degeneration. In this study, ROS accumulation induced nucleus pulposus cells (NPCs) senescence is observed in degenerative human and rat intervertebral disc, suggesting senescence as a new therapeutic target to reverse intervertebral disc degeneration (IVDD). By targeting this, dual‐functional greigite nanozyme is successfully constructed, which shows the ability to release abundant polysulfides and presents strong superoxide dismutase and catalase activities, both of which function to scavenge ROS and maintain the tissue at physical redox level. By significantly lowering the ROS level, greigite nanozyme rescues damaged mitochondrial function in IVDD models both in vitro and in vivo, rescues NPCs from senescence and alleviated the inflammatory response. Furthermore, RNA‐sequencing reveals ROS‐p53‐p21 axis is responsible for cellular senescence‐induced IVDD. Activation of the axis abolishes greigite nanozyme rescued NPCs senescence phenotype, as well as the alleviated inflammatory response to greigite nanozyme, which confirms the role of ROS‐p53‐p21 axis in greigite nanozyme's function to reverse IVDD. In conclusion, this study demonstrates that ROS‐induced NPCs senescence leads to IVDD and the dual‐functional greigite nanozyme holds strong potential to reverse this process, providing a novel strategy for IVDD management

Molecular level activation insights from a NR2A/NR2B agonist

<div><p>N-methyl D-aspartate receptors (NMDARs), a subclass of glutamate receptors have broad actions in neural transmission for major brain functions. Overactivation of NMDARs leading to “excitotoxicity” is the underlying mechanism of neuronal death in a number of neurological diseases, especially stroke. Much research effort has been directed toward developing pharmacological agents to modulate NMDAR actions for treating neurological diseases, in particular stroke. Here, we report that Alliin, a sulfoxide in fresh garlic, exhibits affinity toward NR2A as well as NR2B receptors based on virtual screening. Biological activities of Alliin on these two receptors were confirmed in electrophysiological studies. Ligand-binding site closure, a structural change precluding ion channel opening, was observed with Alliin during 100 ns molecular dynamics simulation. Alliin interactions with NR2A and NR2B suggest that residues E/A413, H485, T690, and Y730 may play important roles in the conformation shift. Activation of NR2A and NR2B by Alliin can be differentiated from that caused by glutamate, the endogenous neurotransmitter. These characteristic molecular features in NR2A and NR2B activation provide insight into structural requirements for future development of novel drugs with selective interaction with NR2A and NR2B for treating neurological diseases, particularly stroke.</p></div