129 research outputs found
Studies of auroral X-ray imaging from high altitude spacecraft
Results of a study of techniques for imaging the aurora from a high altitude satellite at X-ray wavelengths are summarized. The X-ray observations allow the straightforward derivation of the primary auroral X-ray spectrum and can be made at all local times, day and night. Five candidate imaging systems are identified: X-ray telescope, multiple pinhole camera, coded aperture, rastered collimator, and imaging collimator. Examples of each are specified, subject to common weight and size limits which allow them to be intercompared. The imaging ability of each system is tested using a wide variety of sample spectra which are based on previous satellite observations. The study shows that the pinhole camera and coded aperture are both good auroral imaging systems. The two collimated detectors are significantly less sensitive. The X-ray telescope provides better image quality than the other systems in almost all cases, but a limitation to energies below about 4 keV prevents this system from providing the spectra data essential to deriving electron spectra, energy input to the atmosphere, and atmospheric densities and conductivities. The orbit selection requires a tradeoff between spatial resolution and duty cycle
The effects of mass transferin the liquid phase on the rate of aluminium evaporation from the Ti-6Al-7Nb alloy
In the present paper, the rate of aluminium evaporation from the Ti-6Al-7Nb alloy during smelting with the use of VIM method at 5 to 1 000 Pa and 1 973 to 2 023 K has been discussed. It has been observed that pressure reduction and temperature rise affect aluminium elimination from the alloy. Based on the determined values of overall mass transfer coefficients and mass transfer coefficients in the liquid phase, it has been found that the resistance related to aluminium mass transfer in the liquid phase is about 8 % of the overall process resistance
First results of material charging in the space environment
A satellite experiment, designed to measure potential charging of typical thermal control materials at near geosynchronous altitude, was flown as part of the SCATHA program. Direct observations of charging of typical satellite materials in a natural charging event ( 5 keV) are presented. The results show some features which differ significantly from previous laboratory simulations of the environment
Should We Learn Probabilistic Models for Model Checking? A New Approach and An Empirical Study
Many automated system analysis techniques (e.g., model checking, model-based
testing) rely on first obtaining a model of the system under analysis. System
modeling is often done manually, which is often considered as a hindrance to
adopt model-based system analysis and development techniques. To overcome this
problem, researchers have proposed to automatically "learn" models based on
sample system executions and shown that the learned models can be useful
sometimes. There are however many questions to be answered. For instance, how
much shall we generalize from the observed samples and how fast would learning
converge? Or, would the analysis result based on the learned model be more
accurate than the estimation we could have obtained by sampling many system
executions within the same amount of time? In this work, we investigate
existing algorithms for learning probabilistic models for model checking,
propose an evolution-based approach for better controlling the degree of
generalization and conduct an empirical study in order to answer the questions.
One of our findings is that the effectiveness of learning may sometimes be
limited.Comment: 15 pages, plus 2 reference pages, accepted by FASE 2017 in ETAP
Multiple Polar Cap Arcs: Akebono (Exos D) Observations
Akebono (Exos D) observations demonstrate that polar cap arcs sometimes have a fine structure, that is, multiple (double or triple) arcs with spacing of a few tens of kilometers. The multiple polar cap arcs are dominantly observed in the nightside polar cap region, suggesting that low background conductance favors the appearance of the structured arcs. A relationship between the spacing and the average energy of the precipitating electrons is investigated. Results show that a higher energy leads to a wider spacing. Akebono observations also show the existence of a downward current region embedded between upward current regions (arcs). Comparison of the observations with results from a coupled magnetosphere-ionosphere Sun-aligned arc model is made, which shows good qualitative agreement between the modeling and observational results on the spacing-energy dependence and the effect of background ionospheric conductance
Characterization of crop residues from false banana/Ensete ventricosum/in Ethiopia in view of a full-resource valorization
Research ArticleFalse banana /Ensete ventricosum [Welw.] Cheesman/ is exploited as a food crop in
Ethiopia where it represents an important staple food. The plant is harvested and large
amounts of biomass residues are originated, mainly from the pseudo stem (i.e., fiber bundles
obtained from the leaf sheaths after being scrapped to produce starchy food) and the
inflorescence stalk. These materials were studied in relation to their summative chemical
composition, composition of lignin, lipophilic and polar extracts. Moreover, their structural
characteristics, in view of their valorization, were scrutinized. The analytical studies were
performed with the aid of FTIR, GC/MS, Py-GC/MS and SEM. The fiber bundles are aggregates
of mainly long and slender fibers with low ash, extractives and lignin contents (3.8%.
4.4% and 10.5% respectively) and high holocellulose and α-cellulose contents (87.5% and
59.6% respectively). The hemicelluloses in the fibers are mostly highly acetylated xylans
and the lignin is of the H-type (H:G:S, 1:0.7:0.8). This lignin composition is in line with the
FTIR peaks at 1670 cm-1 and 1250 cm-1.The inflorescence stalk has high ash content
(12.3% in the main stalk and 24.6% in fines) with a major proportion of potassium, high
extractives (25.9%), and low lignin and α-cellulose contents (5.8% and 17.9% respectively).
The stalk includes numerous starch granules in the cellular structure with the predominant
presence of parenchyma. The potential valorization routes for these materials are clearly different.
The fiber bundles could be used as a fiber source for paper pulp production with the
possibility of a prior hemicelluloses removal while the inflorescence stalk has nutritional
value for food and fodder. Furthermore, it can also be used for sugar fermentation productsinfo:eu-repo/semantics/publishedVersio
Statistical Inference for Valued-Edge Networks: Generalized Exponential Random Graph Models
Across the sciences, the statistical analysis of networks is central to the
production of knowledge on relational phenomena. Because of their ability to
model the structural generation of networks, exponential random graph models
are a ubiquitous means of analysis. However, they are limited by an inability
to model networks with valued edges. We solve this problem by introducing a
class of generalized exponential random graph models capable of modeling
networks whose edges are valued, thus greatly expanding the scope of networks
applied researchers can subject to statistical analysis
Enhanced pharmacological efficacy of sumatriptan due to modification of its physicochemical properties by inclusion in selected cyclodextrins
The study focused on the pharmacological action of sumatriptan, in particular its antiallodynic and antihyperalgesic properties, as an effect of cyclodextrinic inclusion of sumatriptan, resulting in changes of its physicochemical qualities such as dissolution and permeability through artificial biological membranes, which had previously been examined in vitro in a gastro-intestinal model. The inclusion of sumatriptan into β-cyclodextrin and 2-hydroxylpropylo-β-cyclodextrin by kneading was confirmed with the use of spectral (fourier-transform infrared spectroscopy (FT-IR); solid state nuclear magnetic resonance spectroscopy with magic angle spinning condition, 1H and 13C MAS NMR) and thermal (differential scanning calorimetry (DSC)) methods. A precise indication of the domains of sumatriptan responsible for its interaction with cyclodextrin cavities was possible due to a theoretical approach to the analysis of experimental spectra. A high-performance liquid chromatography with a diode-array detector method (HPLC-DAD) was employed to determine changes in the concentration of sumatriptan during dissolution and permeability experiments. The inclusion of sumatriptan in complex with cyclodextrins was found to significantly modify its dissolution profiles by increasing the concentration of sumatriptan in complexed form in an acceptor solution compared to in its free form. Following complexation, sumatriptan manifested an enhanced ability to permeate through artificial biological membranes in a gastro-intestinal model for both cyclodextrins at all pH values. As a consequence of the greater permeability of sumatriptan and its increased dissolution from the complexes, an improved pharmacological response was observed when cyclodextrin complexes were applied
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