Geometry Factors Research Articles

Feasibility study of GNSS as navigation system to reach the Moon

Reaching the Moon poses very strict requirements in terms of performance, flexibility and cost for all the spacecraft subsystems. These requirements become more stringent if the mission is designed to be accomplished using a small spacecraft. The navigation subsystem is without any doubts essential and nowadays, several systems offer different solutions to the navigation problem. Global Navigation Satellite Systems (GNSSs) such as GPS, GLONASS, or the future Galileo and BeiDou systems, introduce an easier way to provide an autonomous on-board orbit determination system; they only require an on-board GNSS receiver, with low-cost, low-power consumption and limited mass and volume. While GNSS receivers have been already exploited with success for Low Earth Orbit (LEO), their use for very High Earth Orbit (HEO) up to the Moon altitude is still at the research stage. In this context, the purpose of the present work is to determine the potential achievable accuracy of a code-based GNSS receiver solution, during the whole trajectory to reach the Moon. GPS, Galileo, and GPS-Galileo combined (dual constellation) solutions are estimated, by considering constellations availability, pseudorange error factors and geometry factors. Unlike previous investigations, our study is making use of the very accurate multi-GNSS constellation simulator “Spirent GSS8000”, which supports simultaneously the GPS and Galileo systems with L1, L5, E1, and E5 frequency bands. The contribution of this study, clearly demonstrates that GNSS signals can be tracked up to the Moon׳s surface, but not with the current GNSS receiver׳s technology for terrestrial use. We consider and discuss a possible navigation solution that uses a double constellation GPS-Galileo receiver aided by an on board orbital filter system in order to improve the accuracy of the navigation solution and achieve the required sensitivity.

Role of street patterns in zone-based traffic safety analysis

Although extensive analyses of road segments and intersections located in urban road networks have examined the role of many factors that contribute to the frequency and severity of crashes, the explicit relationship between street pattern characteristics and traffic safety remains underexplored. Based on a zone-based Hong Kong database, the Space Syntax was used to quantify the topological characteristics of street patterns and investigate the role of street patterns and zone-related factors in zone-based traffic safety analysis. A joint probability model was adopted to analyze crash frequency and severity in an integrated modeling framework and the maximum likelihood estimation method was used to estimate the parameters. In addition to the characteristics of street patterns, speed, road geometry, land-use patterns, and temporal factors were considered. The vehicle hours was also included as an exposure proxy in the model to make crash frequency predictions. The results indicate that the joint probability model can reveal the relationship between zone-based traffic safety and various other factors, and that street pattern characteristics play an important role in crash frequency prediction.

Sediment–flow interactions at channel confluences: A flume study

Sediment transport and bed morphology at channel confluences with different confluence angles and discharge ratios are analyzed through a series of flume experiments. Bed topography and sediment transport rate are measured and results are compared among different conditions. Sediment transport is intermittent and pulsating as the tributary flow mixes with the mainstream, and the sediment transport rate goes up with the increase in discharge ratio and confluence angle. With no sediment supplied from upstream of the flume, a central scour hole will form along the shear plane and develop toward the right bank, and the depth of the central scour hole increases as the confluence angle and discharge ratio increase. With heavy upstream sediment supplement, deposition will happen in the separation zone and upstream of the confluence area because of the tributary. And the deposition height is related to the discharge ratio and confluence angle. Results indicate the significant impact of confluence geometry, sediment, and flow factors on fluvial processes.

Signal-to-noise ratio and parallel imaging performance of commercially available phased array coils in 3.0T brain magnetic resonance imaging.

The signal-to-noise ratio (SNR) and parallel imaging (PI) performance of two commercial phased-array coils (PACs) were examined in magnetic resonance imaging (MRI) of the brain. All measurements were performed on a 3.0T MRI instrument. The SNR and PI performance were evaluated with 32-channel and 15-channel PACs. A gradient echo sequence was used for obtaining images of a phantom. SNR and geometry factor (g-factor) maps were calculated from two images with identical parameters. Horizontal and vertical profiles were taken through the SNR maps in the axial plane. The average g-factor was measured in a circular region of interest in the g-factor maps for the axial plane. The SNR map of the 32-channel coil showed a higher SNR than that of the 15-channel coil at the phantom's posterior and lateral surfaces. The SNR profiles for the 32-channel coil also showed a 1.3-fold increase at the phantom's center. The average g-factor of the 32-channel coil was lower than that of the 15-channel coil at the same acceleration factor. These results indicate that the 32-channel coil can provide a higher spatial resolution and/or a faster imaging speed. Horizontal and vertical profiles are useful for evaluation of the performance of commercially available PACs.

Preliminary Discussion Regarding SVM Kernel Function Selection in the Twofold Rock Slope Prediction Model

AbstractThe kernel function, which is an important component of support vector machine (SVM) theory, directly affects the results of a prediction model. When establishing an effective prediction slope model, analysis factors such as slope angle, slope height, potential sliding body height and inclination, and cohesion and friction angle of each potential sliding surface need to be considered. As the results of an example design show, there is an appropriate regularity between analysis factors and kernel functions. For example, the radial basis function (RBF) kernel function is suitable for the geometry factors of a rock slope analysis, whereas the Sigmoid kernel function is better than RBF for analyzing the cohesion and friction angle of the back potential sliding surface; likewise, the linear kernel function is suitable for the material factors of a bottom sliding surface analysis. For these reasons, a combination of kernel functions is necessary for an overall analysis of complex rock slope problems. A ...

Slurry erosion of surface imperfections in pipeline systems

This paper highlights erosion studies on two sizes of circular cavities as well as a regular and an irregular weld bead-configurations commonly encountered on pipeline surfaces. The novelty of combining physical experiments and computational fluid dynamics simulation methods provides new insights into the erosive effect of surface imperfections in pipes. The erosion results for each case are normalised with the maximum erosion occurring on a reference cylinder sample placed in-line during the tests. This ratio is defined as the geometric factor. The results suggest that the maximum erosion occurs on the forward-facing edge of the pipe cavities, while the maximum erosion rate occurs on the wind-ward side of the weld. The geometric factor for direct particle impact on the forward-facing edges of surface cavities in water–sand mixtures is found to be nominally half that of air–sand erosion experiments. However, when coupled with more complex systems in low Stokes number flows (e.g. presence of extraneous peaks in irregular weld ridges) the geometry factor can be twice that of direct impact air-based configurations due to the generation of trailing vortices shed from these geometric features. Computational fluid dynamics simulation of the flow field further illustrates the flow complexities that accompany these simple geometric features.

A general optimized geometry of angled ribs for enhancing the thermo-hydraulic behavior of a solar air heater channel – A Taguchi approach

The thermo-hydraulic behavior of the air flow through a solar air heater is numerically simulated and then optimized by use of Taguchi method. An innovative general geometry is introduced for the rib that variation in its parameters can generate triangular, trapezoidal and rectangular geometries simultaneously. A L16 (44) orthogonal array is used to optimize the geometry factors accounts for the maximum thermal performance of the ribbed channel. Thermal performance concept includes maximization of heat transfer coefficient and minimization of friction factor. Maximization of thermal enhancement factor is taken as the criteria of optimization. At a constant flow Reynolds number of 10,000, rib relative pitch (P/H), rib relative height (e/H), rib relative tip width (a/H) and rib front projection (s) are employed as the design factors. Results show that rib pitch, rib height, rib tip width and rib front projection have the greatest influences on the thermo-hydraulic performance, respectively. A triangular rib geometry with rib height of 0.2H and P = 2H in which the rib front is normal to the flow direction (i.e. s = 0) is recognized as the optimum configuration.

Magnetohydrodynamically generated velocities in confined plasma

We investigate by numerical simulation the rotational flows in a toroid confining a conducting magnetofluid in which a current is driven by the application of externally supported electric and magnetic fields. The computation involves no microscopic instabilities and is purely magnetohydrodynamic (MHD). We show how the properties and intensity of the rotations are regulated by dimensionless numbers (Lundquist and viscous Lundquist) that contain the resistivity and viscosity of the magnetofluid. At the magnetohydrodynamic level (uniform mass density and incompressible magnetofluids), rotational flows appear in toroidal, driven MHD. The evolution of these flows with the transport coefficients, geometry, and safety factor are described.

Composition of inner-source heavy pickup ions at 1 AU: SOHO/CELIAS/CTOF observations

Context. Pickup ions in the inner heliosphere mainly originate in two sources, one interstellar and one in the inner solar system. In contrast to the interstellar source that is comparatively well understood, the nature of the inner source has not been clearly identified. Former results obtained with the Solar Wind Ion Composition Spectrometer on-board the Ulysses spacecraft revealed that the composition of inner-source pickup ions is similar, but not equal, to the elemental solar-wind composition. These observations su ered from very low counting statistics of roughly one C + count per day. Aims. Because the composition of inner-source pickup ions could lead to identifying their origin, we used data from the Charge-TimeOf-Flight sensor on-board the Solar and Heliospheric Observatory. It o ers a large geometry factor that results in about 100 C + counts per day combined with an excellent mass-per-charge resolution. These features enable a precise determination of the inner-source heavy pickup ion composition at 1 AU. To address the production mechanisms of inner-source pickup ions, we set up a toy model based on the production scenario involving the passage of solar-wind ions through thin dust grains to explain the observed deviations of the inner-source PUI and the elemental solar-wind composition. Methods. An in-flight calibration of the sensor allows identification of heavy pickup ions from pulse height analysis data by their mass-per-charge. A statistical analysis was performed to derive the inner-source heavy pickup ion relative abundances of N + , O + , Ne + , Mg + , Mg 2+ , and Si + compared to C + . Results. Our results for the inner-source pickup ion composition are in good agreement with previous studies and confirm the deviations from the solar-wind composition. The large geometry factor of the Charge-Time-of-Flight sensor even allowed the abundance ratios of the two most prominent pickup ions, C + and O + , to be investigated at varying solar-wind speeds. We found that the O + /C + ratio increases systematically with higher solar-wind speeds. This observation is an unprecedented feature characterising the production of inner-source pickup ions. Comparing our observations to the toy model results, we find that both the deviation from the solar-wind composition and the solar-wind-speed dependent O + /C + ratio can be explained.

Source geometry factors for HDR 192Ir brachytherapy secondary standard well-type ionization chamber calibrations

Well-type ionization chambers are used for measuring the source strength of radioactive brachytherapy sources before clinical use. Initially, the well chambers are calibrated against a suitable national standard. For high dose rate (HDR) 192Ir, this calibration is usually a two-step process. Firstly, the calibration source is traceably calibrated against an air kerma primary standard in terms of either reference air kerma rate or air kerma strength. The calibrated 192Ir source is then used to calibrate the secondary standard well-type ionization chamber.Calibration laboratories are usually only equipped with one type of HDR 192Ir source. If the clinical source type is different from that used for the calibration of the well chamber at the standards laboratory, a source geometry factor, ksg, is required to correct the calibration coefficient for any change of the well chamber response due to geometric differences between the sources.In this work we present source geometry factors for six different HDR 192Ir brachytherapy sources which have been determined using Monte Carlo techniques for a specific ionization chamber, the Standard Imaging HDR 1000 Plus well chamber with a type 70010 HDR iridium source holder. The calculated correction factors were normalized to the old and new type of calibration source used at the National Physical Laboratory. With the old Nucletron microSelectron-v1 (classic) HDR 192Ir calibration source, ksg was found to be in the range 0.983 to 0.999 and with the new Isodose Control HDR 192Ir Flexisource ksg was found to be in the range 0.987 to 1.004 with a relative uncertainty of 0.4% (k = 2). Source geometry factors for different combinations of calibration sources, clinical sources, well chambers and associated source holders, can be calculated with the formalism discussed in this paper.

Accurate and Efficient Calculation of the Inductance of an Arbitrary-Shaped Coil Using Surface Current Model

In this paper, we present a novel approach for efficient calculation of the inductance of an arbitrary shaped coil with circular cross section using finite element method coupled with an analytical method. To reduce the simulation time and the memory requirement, the surface current model (SCM) instead of the volume current model (VCM) for the conductor modeling is used. According to the magnetic energy formulation and Ampere’s law, a geometry factor to determine the equivalent height of the SCM for the self-inductance is obtained numerically. To calculate the mutual inductances, further two factors for determining the equivalent distances between adjacent windings are evaluated. Finally, the accuracy and the computational cost of this approach compared with the VCM are presented.

A semi-empirical model relating micro structure to acoustic properties of bimodal porous material

Complex morphology of open cell porous media makes it difficult to link microstructural parameters and acoustic behavior of these materials. While morphology determines the overall sound absorption and noise damping effectiveness of a porous structure, little is known on the influence of microstructural configuration on the macroscopic properties. In the present research, a novel bimodal porous structure was designed and developed solely for modeling purposes. For the developed porous structure, it is possible to have direct control on morphological parameters and avoid complications raised by intricate pore geometries. A semi-empirical model is developed to relate microstructural parameters to macroscopic characteristics of porous material using precise characterization results based on the designed bimodal porous structures. This model specifically links macroscopic parameters including static airflow resistivity (σ), thermal characteristic length (Λ′), viscous characteristic length (Λ), and dynamic tortuosity (α∞) to microstructural factors such as cell wall thickness (2t) and reticulation rate (Rw). The developed model makes it possible to design the morphology of porous media to achieve optimum sound absorption performance based on the application in hand. This study makes the base for understanding the role of microstructural geometry and morphological factors on the overall macroscopic parameters of porous materials specifically for acoustic capabilities. The next step is to include other microstructural parameters as well to generalize the developed model. In the present paper, pore size was kept constant for eight categories of bimodal foams to study the effect of secondary porous structure on macroscopic properties and overall acoustic behavior of porous media.

オリフィス下流における物質移行係数の直接測定およびLESによる乱流スカラー輸送の解析

It is necessary to evaluate the geometry factor for predicting the flow accelerated corrosion (FAC) of carbon steel piping in a complicated flow field. Geometry factor is defined as the ratio of wall mass transfer coefficient in the piping systems such as orifice to that in a straight pipe. The mass transfer coefficient behind the orifice is computed by large eddy simulation (LES) and is also measured by electrochemical method. The experimental measurement is conducted with the pipe of the test section made of Ni, in which the whole pipe surface acts as electrode (referred as ’overall electrode condition’). The obtained results are compared with the previous experiments, in order to clarify the effect of the area of the electrode, with a point electrode embedded in an insulated pipe (referred as ‘point electrode condition’). Geometry factor obtained from the overall electrode condition is larger than that of a point electrode measurement. In order to simulate the mass transfer coefficient in pipe flow, we adopt the analogy between mass transfer and heat transfer, and calculate the unsteady temperature field using the numerical data of LES. Geometry factor predicted by heat transfer coefficient agrees well with that measured in overall electrode condition. The large scale motions with vortex structure of separated flow from the orifice influence the instantaneous scalar fields. Analyses of turbulent scalar transport and space-time correlation between wall scalar transfer and flow fields reveal that the mean wall scalar transfer is affected by not only near the wall region but also the coherent scalar fields away from the wall.

Biological evaluation of inhibitors of reverse transcriptase from HIV type-1

Article history: Received October 21, 2014 Received in revised form December 02, 2014 Accepted 12 December 2014 Available online 12 December 2014 In the present work, Zn(II), Co(II) and Cr(II) metal complexes (3-5) of N-hydroxy-4[(hydroxyimino)methyl]benzamidine ligand (2) were synthesized and their anti-HIV activity by inhibiting reverse transcriptase was explored. Structural characterization using NMR, FTIR, Mass, UV-Vis spectra, TGA, magnetic moment and elemental analyses were performed. The analyses show that geometry, lipophilicity and steric factor play crucial role. Cell viability test is performed on peripheral blood mononuclear cells to check toxicity of prepared compounds on immune system, shows toxicity only at higher concentration. Antimicrobial activity and DNA cleavage analysis have also been studied and reported. © 2015 Growing Science Ltd. All rights reserved.

Performance Measures to Characterize Corridor Travel Time Delay Based on Probe Vehicle Data

Anonymous probe vehicle data are being collected on roadways throughout the United States. These data are incorporated into local and statewide mobility reports to measure the performance of highways and arterial systems. Predefined spatially located segments, known as traffic message channels (TMCs), are spatially and temporally joined with probe vehicle speed data. Through the analysis of these data, transportation agencies have been developing agencywide travel time performance measures. One widely accepted performance measure is travel time reliability, which is calculated along a series of TMCs. When reliable travel times are not achieved because of incidents and recurring congestion, it is desirable to understand the time and the location of these occurrences so that the corridor can be proactively managed. This research emphasizes a visually intuitive methodology that aggregates a series of TMC segments based on a cursory review of congestion hotspots within a corridor. Instead of a fixed congestion speed threshold, each TMC is assigned a congestion threshold based on the 70th percentile of the 15-min average speeds between 02:00 and 06:00. An analysis of approximately 90 million speed records collected in 2013 along I-80 in northern New Jersey was performed for this project. Travel time inflation, the time exceeding the expected travel time at 70% of measured free-flow speed, was used to evaluate each of the 166 directional TMC segments along 70 mi of I-80. This performance measure accounts for speed variability caused by roadway geometry and other Highway Capacity Manual speed-reducing friction factors associated with each TMC.

A comparative study of SrCo0.8Nb0.2O3−δand SrCo0.8Ta0.2O3−δas low-temperature solid oxide fuel cell cathodes: effect of non-geometry factors on the oxygen reduction reaction

The crystal geometry factor was constrained for the first time to study the non-geometry factors that may affect the oxygen reduction reaction at the operating temperature of solid oxide fuel cells.

Full Bayesian Mixed-Effect Intervention Model for Before–After Speed Data Analysis

The analysis of before–after speed data to evaluate the effectiveness of safety interventions is often limited to a non-model-based comparison of speed-related indicators. Moreover, modeling of speed data often does not take into account the nested nature of the data. The objective of the study was to quantify the effect of posted speed limit (PSL) reductions in an urban, residential context. The study employed a mixed-effect intervention model, which could address limitations of existing methods. To model mean free-flow speed and the probability of a speed being below or equal to various thresholds, mixed-effect normal regression and binomial logistic regression models were used. Use of a comprehensive, unique, and disaggregated data set enabled not only the before–after evaluation of the PSL reduction but also the exploration of the effects of various temporal, traffic, and road geometry factors on speed. Results demonstrated the appropriateness of using the mixed-effect model for speed data. Parameter estimations showed that nighttimes; weekends; a high proportion of vans, buses, and trucks; evening peak periods; collector roads; and low hourly traffic volumes were all associated with an increase in the mean free-flow speed and a decrease in the probability of speeds being below or equal to various thresholds. Evaluation results showed the mean free-flow speed was reduced by 3.85 km/h in the after period and that speeds below or equal to 50, 60, 70, and 80 km/h increased by 20.0%, 9.2%, 2.8%, and 0.9%, respectively. All improvements were statistically significant; this finding implied that the PSL reduction was effective at influencing vehicle speed.

Design and Test of Magnetic Wall Decoupling for Dipole Transmit/Receive Array for MR Imaging at the Ultrahigh Field of 7T.

Radio-frequency coil arrays using dipole antenna technique have been recently applied for ultrahigh field magnetic resonance (MR) imaging to obtain the better signal-noise-ratio (SNR) gain at the deep area of human tissues. However, the unique structure of dipole antennas makes it challenging to achieve sufficient electromagnetic decoupling among the dipole antenna elements. Currently, there is no decoupling methods proposed for dipole antenna arrays in MR imaging. The recently developed magnetic wall (MW) or induced current elimination decoupling technique has demonstrated its feasibility and robustness in designing microstrip transmission line arrays, L/C loop arrays and monopole arrays. In this study, we aim to investigate the possibility and performance of MW decoupling technique in dipole arrays for MR imaging at the ultrahigh field of 7T. To achieve this goal, a two-channel MW decoupled dipole array was designed, constructed and analyzed experimentally through bench test and MR imaging. Electromagnetic isolation between the two dipole elements was improved from about -3.6 dB (without any decoupling treatments) to -16.5 dB by using the MW decoupling method. MR images acquired from a water phantom using the MW decoupled dipole array and the geometry factor maps were measured, calculated and compared with those acquired using the dipole array without decoupling treatments. The MW decoupled dipole array demonstrated well-defined image profiles from each element and had better geometry factor over the array without decoupling treatments. The experimental results indicate that the MW decoupling technique might be a promising solution to reducing the electromagnetic coupling of dipole arrays in ultrahigh field MRI, consequently improving their performance in SNR and parallel imaging.

Fabrication and characterization of joined silicon carbide cylindrical components for nuclear applications

The use of silicon carbide (SiC) composites as structural materials in nuclear applications necessitates the development of a viable joining method. One critical application for nuclear-grade joining is the sealing of fuel within a cylindrical cladding. This paper demonstrates cylindrical joint feasibility using a low activation nuclear-grade joint material comprised entirely of β-SiC. While many papers have considered joining material, this paper takes into consideration the joint geometry and component form factor, as well as the material performance. Work focused specifically on characterizing the strength and permeability performance of joints between cylindrical SiC–SiC composites and monolithic SiC endplugs. The effects of environment and neutron irradiation were not evaluated in this study. Joint test specimens of different geometries were evaluated in their as-fabricated state, as well as after being subjected to thermal cycling and partial mechanical loading. A butted scarf geometry supplied the best combination of high strength and low permeability. A leak rate performance of 2×10−9mbarls−1 was maintained after thermal cycling and partial mechanical loading and sustained applied force of 3.4kN, or an apparent strength of 77MPa. This work shows that a cylindrical SiC–SiC composite tube sealed with a butted scarf endplug provides out-of-pile strength and permeability performance that meets light water reactor design requirements.

Theoretical and experimental evaluation of multi-band EPI for high-resolution whole brain pCASL Imaging

Multi-band echo planar imaging (MB-EPI), a new approach to increase data acquisition efficiency and/or temporal resolution, has the potential to overcome critical limitations of standard acquisition strategies for obtaining high-resolution whole brain perfusion imaging using arterial spin labeling (ASL). However, the use of MB also introduces confounding effects, such as spatially varying amplified thermal noise and leakage contamination, which have not been evaluated to date as to their effect on cerebral blood flow (CBF) estimation. In this study, both the potential benefits and confounding effects of MB-EPI were systematically evaluated through both simulation and experimentally using a pseudo-continuous arterial spin labeling (pCASL) strategy. These studies revealed that the amplified noise, given by the geometry factor (g-factor), and the leakage contamination, assessed by the total leakage factor (TLF), have a minimal impact on CBF estimation. Furthermore, it is demonstrated that MB-EPI greatly benefits high-resolution whole brain pCASL studies in terms of improved spatial and temporal signal-to-noise ratio efficiencies, and increases compliance with the assumptions of the commonly used single blood compartment model, resulting in improved CBF estimates.