Ionospheric effects on one-way timing signals

A proposed navigation concept requires that a user measure the time-delay that satellite-emitted signals experience in traversing the distance between satellite and user. Simultaneous measurement of the propagation time from four different satellites permits the user to determine his position and clock bias if satellite ephemerides and signal propagation velocity are known. A pulse propagating through the ionosphere is slowed down somewhat, giving an apparent range that is larger than the equivalent free space range. The difference between the apparent range and the true range, or the free space velocity and the true velocity, is the quantity of interest. This quantity is directly proportional to the total electron content along the path of the propagating signal. Thus, if the total electron content is known, or is measured, a perfect correction to ranging could be performed. Faraday polarization measurements are continuously being taken at Fort Monmouth, N. J., using beacon emissions of the ATS-3 (137.35 MHz) satellite. Day-to-day variability of the diurnal variation of total electron content values is present with differences of up to 50% or more not being uncommon. In addition, superposed on the overall diurnal variation are smaller scale variations of approximately 5 to 10% of the total content which are attributed to ionospheric density irregularities

Plasmaspheric effects on one way satellite timing signals

The effects of the ionospheric retardation of satellite-emitted timing signals was presented. The retardation at the navigation frequencies, which is proportional to the total ionospheric electron content (TEC), was determined by Faraday polarization measurements of VHF emissions of a geostationary satellite. The polarization data yielded TEC up to approximately 1200 km only, since the measurement technique is based on the Faraday effect which is weighted by the terrestrial magnetic field

Optical response of grain boundaries in upgraded metallurgical-grade silicon for photovoltaics

Using upgraded metallurgical-grade silicon (UMG-Si) is a cost-effective and energy-efficient approach for the production of solar cells. Grain boundaries (GBs) play a major role in determining the device performance of multicrystalline Si (mc-Si) solar cells. In this study two UMG-Si wafers, one from the middle part of a brick and the other from the top part of the same brick, were investigated. An excellent correlation was found between the grain misorientation and the corresponding optical response of GBs as indicated by photoluminescence (PL) imaging, electron backscattered diffraction (EBSD), and cross-sectional transmission electron microscopy (TEM). In addition, the PL features at random GBs depend also on the impurity levels in the wafer. In particular the PL emission was greatly enhanced in the narrow regions close to the random GB in the top wafer, which is an interesting phenomenon that may have potential application in high efficiency light-emission diodes (LEDs) based on Si. © 2011 Elsevier B.V.postprin

Computational Sensitivity Investigation of Hydrogel Injection Characteristics for Myocardial Support

Biomaterial injection is a potential new therapy for augmenting ventricular mechanics after myocardial infarction (MI). Recent in vivo studies have demonstrated that hydrogel injections can mitigate the adverse remodeling due to MI. More importantly, the material properties of these injections influence the efficacy of the therapy. The goal of the current study is to explore the interrelated effects of injection stiffness and injection volume on diastolic ventricular wall stress and thickness. To achieve this, finite element models were constructed with different hydrogel injection volumes (150 µL and 300 µL), where the modulus was assessed over a range of 0.1 kPa to 100 kPa (based on experimental measurements). The results indicate that a larger injection volume and higher stiffness reduce diastolic myofiber stress the most, by maintaining the wall thickness during loading. Interestingly, the efficacy begins to taper after the hydrogel injection stiffness reaches a value of 50 kPa. This computational approach could be used in the future to evaluate the optimal properties of the hydrogel

Reduced Order Modeling of an Adaptive Mesh Ocean Model

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

The diversity of bioactive proteins in Australian snake venoms

Australian elapid snakes are among the most venomous in the world. Their venoms contain multiple components that target blood hemostasis, neuromuscular signaling, and the cardiovascular system. We describe here a comprehensive approach to separation and identification of the venom proteins from 18 of these snake species, representing nine genera. The venom protein components were separated by two-dimensional PAGE and identified using mass spectrometry and de novo peptide sequencing. The venoms are complex mixtures showing up to 200 protein spots varying in size from 10. These include many proteins identified previously in Australian snake venoms, homologs identified in other snake species, and some novel proteins. In many cases multiple trains of spots were typically observed in the higher molecular mass range (> 20 kDa) (indicative of post-translational modification). Venom proteins and their post-translational modifications were characterized using specific kantibodies, phosphoprotein- and glycoprotein-specific stains, enzymatic digestion, lectin binding, and antivenom reactivity. In the lower molecular weight range, several proteins were identified, but the predominant species were phospholipase A(2) and alpha-neurotoxins, both represented by different sequence variants. The higher molecular weight range contained proteases, nucleotidases, oxidases, and homologs of mammalian coagulation factors. This information together with the identification of several novel proteins (metalloproteinases, vespryns, phospholipase A(2) inhibitors, protein-disulfide isomerase, 5'-nucleotidases, cysteinerich secreted proteins, C-type lectins, and acetylcholinesterases) aids in understanding the lethal mechanisms of elapid snake venoms and represents a valuable resource for future development of novel human therapeutics

Measurement of competing pathways in a shock-induced phase transition in zirconium by femtosecond diffraction

The traditional picture of solid-solid phase transformations assumes an ordered parent phase transforms into an ordered daughter phase via a single unique pathway. Zirconium and its prototypical phase transition from hexagonal close-packed (hcp) to simple hexagonal (hex-3) structure has generated considerable controversy over several decades regarding which mechanism mediates the transformation. However, a lack of in situ measurements over the relevant atomistic timescales has hindered our ability to identify the true pathway. In this study, we exploit femtosecond X-ray diffraction coupled with nanosecond laser compression to give unprecedented insights into the complexities of how materials transform at the lattice level. We observe single-crystal zirconium changing from hcp to a hex-3 structure via not one but three competing pathways simultaneously. Concurrently, we also observe a broad diffuse background underlying the sharp Bragg diffraction during the transition. We corroborate our observation of the diffuse signal with multimillion-atom molecular dynamics simulations using a machine-learned interatomic potential. Our study demonstrates that the traditional mechanistic view of transitions may fail for even an elemental metal and that the mechanisms by which materials transform are far more intricate than generally thought

Beyond small-scale transients: a closer look at the diffuse quiet solar corona

Within the quiet Sun corona imaged at 1 MK, much of the field of view consists of diffuse emission that appears to lack the spatial structuring that is so evident in coronal loops or bright points. We seek to determine if these diffuse regions are categorically different in terms of their intensity fluctuations and spatial configuration from the more well-studied dynamic coronal features. We analyze a time series of observations from Solar Orbiter's High Resolution Imager in the Extreme Ultraviolet to quantify the characterization of the diffuse corona at high spatial and temporal resolutions. We then compare this to the dynamic features within the field of view, mainly a coronal bright point. We find that the diffuse corona lacks visible structuring, such as small embedded loops, and that this is persistent over the 25 min duration of the observation. The intensity fluctuations of the diffuse corona, which are within +/-5%, are significantly smaller in comparison to the coronal bright point. Yet, the total intensity observed in the diffuse corona is of the same order as the bright point. It seems inconsistent with our data that the diffuse corona is a composition of small loops or jets or that it is driven by discrete small heating events that follow a power-law-like distribution. We speculate that small-scale processes like MHD turbulence might be energizing the diffuse regions, but at this point we cannot offer a conclusive explanation for the nature of this feature.Comment: Accepted for publication in A&A. 10 pages, 8 figure

From knock-out phenotype to three-dimensional structure of a promising antibiotic target from streptococcus pneumoniae

Given the rise in drug-resistant Streptococcus pneumoniae, there is an urgent need to discover new antimicrobials targeting this pathogen and an equally urgent need to characterize new drug targets. A promising antibiotic target is dihydrodipicolinate synthase (DHDPS), which catalyzes the rate-limiting step in lysine biosynthesis. In this study, we firstly show by gene knock out studies that S. pneumoniae (sp) lacking the DHDPS gene is unable to grow unless supplemented with lysine-rich media. We subsequently set out to characterize the structure, function and stability of the enzyme drug target. Our studies show that sp-DHDPS is folded and active with a kcat = 22 s-1 , KM PYR = 2.55 ± 0.05 mM and KM ASA = 0.044 ± 0.003 mM. Thermal denaturation experiments demonstrate sp-DHDPS exhibits an apparent melting temperature (TM app) of 72 °C, which is significantly greater than Escherichia coli DHDPS (Ec-DHDPS) (TM app = 59 °C). Sedimentation studies show that sp-DHDPS exists in a dimer-tetramer equilibrium with a KD 4→2 = 1.7 nM, which is considerably tighter than its E. coli ortholog (KD 4→2 = 76 nM). To further characterize the structure of the enzyme and probe its enhanced stability, we solved the high resolution (1.9 Å) crystal structure of sp-DHDPS (PDB ID 3VFL). The enzyme is tetrameric in the crystal state, consistent with biophysical measurements in solution. Although the sp-DHDPS and Ec-DHDPS active sites are almost identical, the tetramerization interface of the s. pneumoniae enzyme is significantly different in composition and has greater buried surface area (800 Å2 ) compared to its E. coli counterpart (500 Å2 ). This larger interface area is consistent with our solution studies demonstrating that sp-DHDPS is considerably more thermally and thermodynamically stable than Ec-DHDPS

Paradoxical regulation of human argininosuccinate synthetase cDNA minigene in opposition to endogenous gene: Evidence for intragenic control sequences

Human somatic cell variants resistant to the arginine analog, canavanine, express 200-fold increased levels of argininosuccinate synthetase (AS) mRNA as compared to parental cells. In this study we examined whether AS cDNA sequences contain cis- acting regulatory elements that are involved in the induction of AS mRNA in canavanine-resistant cells. Minigene constructs containing AS cDNA sequences under the transcriptional control of a viral promoter were stably transfected into the human squamous cell carcinoma line, RPMI 2650. Upon conversion of cells to canavanine-resistance, expression of the endogenous AS gene increased by two orders of magnitude as expected. Surprisingly, however, expression of AS cDNA minigenes decreased 10- to 15- fold in canavanine-resistant cell variants. The observed down-modulation of AS cDNA minigene expression was dependent upon a concomitant induction of the endogenous AS gene and not simply expression of the canavanine-resistant phenotype. This paradoxical regulation was specific for AS gene sequences since a minigene containing the neomycin-resistance gene in place of AS cDNA sequences failed to regulate. Furthermore, minigenes lacking a substantial portion of the AS cDNA also failed to exhibit the down-modulation. These findings suggest that expression of the human AS gene is regulated by a specific and limiting, positively-acting , trans- acting mechanism in canavanine-resistant cells and that exogenous AS cDNA (mRNA) sequences can compete for this mechanism .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45538/1/11188_2005_Article_BF01535072.pd