Increase In Collision Frequency Research Articles

Modulational instability of electromagnetic waves in a collisional quantum magnetoplasma

The modulational instability of right-hand circularly polarized electromagnetic electron cyclotron (CPEM-EC) wave in a magnetized quantum plasma is studied taking into account the collisional effects. Employing quantum hydrodynamic and nonlinear Schrödinger equations, the dispersion relation of modulated CPEM-EC wave in a collisional plasma has been derived. It is found that this wave is unstable in such a plasma system and the growth rate of the associated instability depends on various parameters such as electron Fermi temperature, plasma number density, collision frequency, and modulation wavenumber. It is shown that while the increase of collision frequency leads to increase of the growth rate of instability, especially at large wavenumber limit, the increase of plasma number density results in more stable modulated CPEM-EC wave. It is also found that in contrast to collisionless plasma in which modulational instability is restricted to small wavenumbers, in collisional plasma, the interval of instability occurrence can be extended to a large domain.

Solitary and shock waves in magnetized electron-positron plasma

An Ohm's law for electron-positron (EP) plasma is obtained. In the framework of EP magnetohydrodynamics, we investigate nonrelativistic nonlinear waves' solutions in a magnetized EP plasma. In the collisionless limit, quasistationary propagating solitary wave structures for the magnetic field and the plasma density are obtained. It is found that the wave amplitude increases with the Mach number and the Alfvén speed. However, the dependence on the plasma temperature is just the opposite. Moreover, for a cold EP plasma, the existence range of the solitary waves depends only on the Alfvén speed. For a hot EP plasma, the existence range depends on the Alfvén speed as well as the plasma temperature. In the presence of collision, the electromagnetic fields and the plasma density can appear as oscillatory shock structures because of the dissipation caused by the collisions. As the collision frequency increases, the oscillatory shock structure becomes more and more monotonic.

Transit Bus and Pedestrian Safety Analysis in the Context of Operator Improvements and Traffic Volume Assessment

Pedestrian safety related to public bus transit is an integral part of promoting sustainability especially in the urban setting. This concept has received significant attention within the last decade as transit agencies strive to make their systems more sustainable and safer at the same time. This study examined pedestrian collisions related to public transit buses in Philadelphia over a three-year study period from 2008 to 2011. The objective is to perform a detailed analysis on crash records, which provides the foundation on statistics for bus-pedestrian collision to allow for future studies in modeling work in this field. Results of this research provided insights on bus-pedestrian collisions in terms of bus maneuver, cause of crash, impact point of bus, and relation to hourly traffic volume. A strong correlation was found between traffic volume and bus-pedestrian collision rate in terms of hours of the day. For any given hour, an increase in collision frequency was found if the traffic volume exceeds a threshold of 5% of its average annual daily traffic. This serves as an indicator of locations that pedestrians are vulnerable at. Analyses were conducted to the fullest extent allowable by the limited dataset. This study presents findings that can be future developed and investigated in future studies. Additionally, countermeasures are recommended in each section that presents a critical area to address.

One-dimensional plasma photonic crystals with sinusoidal densities

Properties of electromagnetic waves with normal and oblique incidence have been studied for one-dimensional plasma layers with sinusoidal densities. Wave transmittance as a function of wave frequency exhibits photonic band gaps characteristic of photonic crystals. For periodic structures, increasing collision frequency is demonstrated to lead to greater absorption, increasing the modulation factor enlarges the gap width, and increasing incidence angle can change the gap locations of the two polarizations. If a defect layer is introduced by inserting a new plasma layer in the center, a defect mode may appear within the gap. Periodic number, collision frequency, and modulation factor can affect magnitude of the defect mode. The incidence angle enables the frequency to be tuned. Defect layer thickness affects both frequency and number of defect modes. These results may provide theoretical guidance in designing tunable narrow-band filters.

Super-Atmospheric Pressure Ion Sources: Application and Coupling to API Mass Spectrometer.

Pressurizing the ionization source to gas pressure greater than atmospheric pressure is a new tactic aimed at further improving the performance of atmospheric pressure ionization (API) sources. In principle, all API sources, such as ESI, APCI and AP-MALDI, can be operated at pressure higher than 1 atm if suitable vacuum interface is available. The gas pressure in the ion source can have different role for different ionization. For example, in the case of ESI, stable electrospray could be sustained for high surface tension liquid (e.g., pure water) under super-atmospheric pressure, owing to the absence of electric discharge. Even for nanoESI, which is known to work well with aqueous solution, its stability and sensitivity were found to be enhanced, particularly in the negative mode when the ion source was pressurized. For the gas phase ionization like APCI, measurement of gaseous compound also showed an increase in ion intensity with the ion source pressure until an optimum pressure at around 4-5 atm. The enhancement was due to the increased collision frequency among reactant ion and analyte that promoted the ion/molecule reaction and a higher intake rate of gas to the mass spectrometer. Because the design of vacuum interface for API instrument is based on the upstream pressure of 1 atm, some coupling aspects need to be considered when connecting the high pressure ion source to the mass spectrometer. Several coupling strategies are discussed in this paper.

Single and mixed oxide and clay particle agglomeration: Influence of feed mineralogy and percent drum volume loading

Agglomeration of fine particles into coarse and robust product with desired attributes is a key precursor to a number of industrial processes and unit operations. This study investigates isothermal, batch, drum agglomeration behaviour and agglomerate attributes of model, single and mixed oxide (hematite and quartz) and clay (kaolinite and smectite) minerals, the nature of which reflects mineral feed ore preparation for heap leaching. Particularly, the influence of per cent drum volume loading and feed mineralogical composition on agglomeration behaviour and product structural properties was examined. 5–40mm size agglomerates produced with 30% w/w H2SO4 solution as a binding medium displayed drum volume loading and mineralogy dependent structure and properties. Increasing the per cent drum volume loading from 2.9 to 8.6 led to the formation of larger agglomerates due to a concomitant increase in particles' collision frequency. Furthermore, clay-rich (single and mixed minerals) feeds exhibited slower growth rates than the oxide-rich ones, despite the higher binder dosages used in the agglomeration of the former. For mineral type (clay vs. oxide) particle–binder interactions during agglomeration, NMR analysis showed that H2SO4 adsorption by kaolinite was considerably greater than that of quartz. On equivalent feed masses, the differences in agglomerate growth rates of the oxide and clay minerals can be attributed to the differences in their intrinsic properties (e.g., plasticity, ore mineralogy/chemistry). Dry agglomerates' compressive strengths for kaolinite and hematite were quite similar and greater than those for quartz and smectite. Their re-wetting stability, however, decreased in the order: kaolinite>quartz>hematite=smectite. Oxide and clay minerals mixing and synergistic particles' interactions resulted in agglomerates which displayed markedly enhanced compressive strength and re-wetting stability.

Systematic Investigation of Parameters Affecting the Performance of an Agitated Filter-Dryer

A systematic experimental investigation of contact drying operation was carried out in an agitated Charles Thompson filter-dryer. In this study, the effect of process parameters (wall temperature, impeller speed, fill level) on the drying performance in the filter-dryer is quantified as a function of bed temperature and solvent concentration. In addition, the impact of drying conditions on the particle size distribution was also examined. It was found that in the range of parameters investigated, drying rate increased with wall temperature and reduced bed depth. The effect of impeller speed was variable where favorable drying conditions were strongly dependent on the particle properties. Moreover, decrease in the particle size was evident with an increase in impeller speed and decrease in the bed depth due to increased collision frequency and reduction in the fill volume both leading to particle attrition respectively. Besides, the average wall to solid heat transfer coefficient is also estimated for variable operating conditions.

Large amplitude inertial compressional Alfvénic shock and solitary waves, and acceleration of ions in magnetohydrodynamic plasmas

Large amplitude inertial compressional Alfvénic shock and solitary waves in magnetohydrodynamic plasmas are investigated. Dispersive effect caused by non-ideal electron inertia currents perpendicular to the ambient magnetic field can balance the nonlinear steepening of waves leading to the formation of a soliton. A Sagdeev-potential formalism is employed to derive an energy-balance like equation. The range of allowed values of the soliton speed, M (Mach number), plasma β (ratio of the plasma thermal pressure to the pressure in the confining magnetic field), and electron inertia, wherein solitary waves may exist, are determined. Depth of the potential increases with increasing the Mach number and plasma β, however decreases with the increasing electron inertia. The height of soliton increases with increasing in Mach number and decreases with plasma β. And with increasing electron inertial length, the width of soliton increases. The electron-ion collisional dissipation results a dissipative inertial compressional Alfvén wave, which can produce a shock like structure and can efficiently accelerate ions to the order of the local Alfvén velocity. The shock height increases with the increasing collision frequency, but shock height decreases with increasing plasma β.

Numerical analysis of contact electrification using DEM–CFD

Contact electrification occurs in many powder handling processes and involves electrostatic charges that are transferred between contacting particles during collisions. In the current paper, a successive condenser model was developed and implemented into a discrete element method coupled with computational fluid dynamics (DEM–CFD) to analyse the charge transfer during powder processing. The numerical results for the contact electrification between a dielectric particle and a neutral conductive surface were in excellent agreement with experimental data reported in the literature. It was also shown that, during single collisions, the transferred charge is proportional to the maximum contact area but decreases linearly as the initial charge of the particle increases. In a successive impact process, charge accumulation on a particle increases exponentially with the number of collisions and eventually reaches an equilibrium state. During these processes, larger particles gain higher steady state charge but the charge-to-mass ratio is smaller. Nevertheless, particles of different sizes have identical surface charge density and charging coefficient when the impact velocity is identical. In the case of gas fluidization, the electrostatic charge gradually accumulates on particles and eventually reaches an equilibrium state. Non-uniform charge distribution is generally induced. A higher superficial gas velocity results in a faster charge accumulation due to increased collision frequency and impact velocity.

Thermal Performance of a Vapor Chamber-Based Plate of High-Power Light-Emitting Diodes Filled with Al<SUB>2</SUB>O<SUB>3</SUB> Nanofluid

Nanofluid that contains Al2O3 nanoparticles evenly dispersed in deionized water is considered to have superior heat transfer characteristics due to the significant increase in both collision frequency and contact surface area between the nanoparticles and the deionized water. The thermal performance of the vapor chamber-based plate of a high power light-emitting diode (LED) filled with Al2O3 nanofluid was experimentally investigated. The thermal characteristics of the vapor chamber were also compared with those of copper- and aluminum-based plates exposed to the heating source of four single-crystal LEDs. The experimental results show that the effective thermal conductivity of the vapor chamber increased with an increase in heat flux. A higher heating power caused an increase in the temperature variation in the vapor chamber, the illumination of the vapor chamber-, copper-, and aluminum-based plates, and the material resistance of the copper- and aluminum-based plates. In contrast, the spreading, convective, and total thermal resistance all decreased with an increase in heating power for all three base plates. The total thermal resistance of the vapor chamber is mostly due to its spreading thermal resistance, and appeared to be lower than that of the copper- and aluminum-based plates under a heating power of over 5 Watts.

A Geographic Analysis of Collisions Involving Child Pedestrians in a Large Southern California County

Objectives: The goal of this study is to explore the relationship between child pedestrian injuries and socioeconomic characteristics of neighborhoods in the context of local traffic volume. Methods: Child pedestrian collisions were identified in the data of the California Statewide Integrated Traffic Records System (SWITRS). Nine hundred sixty crashes over a 5-year period were identified, geocoded, and mapped to Orange County census tracts. Census data from 2000 were used to identify tracts, population, and population characteristics in the county of approximately 3,000,000 individuals. Pedestrian collision maps were merged with census characteristics and analyzed using STATA (Version 10.1, Stata Corp, College Station, IX) to determine correlations between socioeconomic factors and collision rates within census tracts. Results: The percentage of the population living in households with low income (less than 185% of the federal poverty level) was the strongest predictor of pedestrian injuries. One fourth of census tracts had less than 9 percent of residents with low income and averaged 6 per 100,000 child pedestrian crashes annually. One fourth of the census tracts had more than 32 percent of residents with low income and an average of 56 child pedestrian crashes per 100,000 annually. These data indicate an 8.8-fold increase in collision frequency in the lowest income quartile over the highest income quartile. Other socioeconomic correlates strongly associated with increased child collisions include population density, proportion of population speaking English less than very well, lack of high school education, number of multifamily residences, and Latino ethnicity. Conclusions: Our study showed that child pedestrian collisions are nearly 9 times more frequent in the poorest quartile of neighborhoods than in the richest quartile. Other factors associated with increased pediatric collision risk include increased neighborhood crowding, low levels of education and English speaking ability, and Latino ethnicity.

Studies of terahertz wave propagation in non-magnetized plasma

The space crafts, such as spaceship, space shuttle and so on, will face a famous blackout problem when they re-enter the earth's atmosphere at high velocity. The plasma sheath severely affects the propagation of the incident electromagnetic wave and causes severe electromagnetic wave attenuation, which results in the communication failures between the space crafts and the ground control center. It is important to study the properties of terahertz wave propagation in non-magnetized plasma, for using the terahertz wave communication is an alternative method to solve the reentry blackout problem. The terahertz wave propagation characteristics in non-magnetized plasma are studied in this paper. The variations of the terahertz wave propagation properties with the terahertz wave frequency, plasma density, plasma collision frequency and the thickness of the plasma are acquired. Some new phenomena are found i.e., there appears periodic oscillation on the reflectivity curve with the increase of terahertz wave frequency, and the period of oscillation is 0.03THz. The oscillation amplitude increases with the increase of terahertz frequency, decreases with the increase of plasma density, and increases with the increase of plasma collision frequency. The oscillation is attributed to the multiple reflections of the electromagnetic wave at the interfaces at z=0 and z=-d. The terahertz wave propagation properties in plasma are studied experimentally with the shock tube, and the experimental results match well with the theoretical ones. Both the theoretical and experimental results indicate that using terahertz wave communication is an effective way to solve the reentry blackout problem.

Side Magnet Designs and Magnetic Field Effects on Effective Gap Filling of Longthrow Sputtering PVD for 3DIC Application

This study used Finite Volume Method to simulate the magnetic profile of PVD (physical vapor deposition) chamber. It can be applied to different kinds of magnet arrangements to the longthrow sputtering PVD. For this long throw PVD, the best optimized process conditions and results from simulations included effects from chamber adaptor height, side magnet space, and magnet arangements. The side magnets consist of a total of 44 sets for one supporter around the chamber adaptor. Each set has three magnets. Each magnet has the magnetic field strength of 5,500 Gauss. The adaptor of gap filling chamber has a height of 120 mm and 44 sets of magnets around the adaptor. The polarity of side magnets is the same as the top magnets of the chamber. These magnets can very effectively increase of electron mobility and collision frequency with sputtered atoms. The plasma simulation result shows that the ionization rate on supttered atoms can be up to 26% from such a longthrow PVD system along with such magnets arrangement. Therefore, it shows a significant improvement on bottom side-wall step coverage in via hole up to 45%. The deposition rate increases by 40%. In addition, by adjusting RF bias and resputtering power, further improvement with 3/4 depth of side-wall step coverage by 30% and corner step coverage by 70% can be obtained. This study uses a simple method to apply to 3DIC gap filling capability for an increase of aspect ratio (AR). The improvement from this longthrow sputtering PVD with side magnets design around the adaptor not only results in low cost target design but also provides a very effective gap filling capability with higher deposition rate for 3DIC application.

Near-wall conductivity effect under a space—charge-saturated sheath in the Hall thruster

In this paper, we adopt the modified Morozov secondary electron emission model to investigate the influence of the characteristic of a space—charge-saturated sheath near the insulated wall of the Hall thruster on the near-wall conductivity, by the method of two-dimensional (2D) particle simulation (2D+3V). The results show that due to the sharp increase of collision frequency between the electrons and the wall under the space—charge-saturated sheath, the near-wall transport current under this sheath is remarkably higher than that under a classical sheath, and equals the near-wall transport current under a spatially oscillating sheath in order of magnitude. However, the transport currents under a space—charge-saturated sheath and a spatially oscillating sheath are different in mechanism, causing different current density distributions under the above two sheaths, and a great influence of channel width on the near-wall transport current under a space—charge-saturated sheath.

Friedel Screening Effects on the Entanglement Fidelity for Elastic Collisions in Degenerate Quantum Plasmas

The Friedel screening effects on the entanglement fidelity for the elastic electron–ion collision are investigated in degenerate quantum collisional plasmas. The partial wave analysis and effective interaction including the far-field terms caused by the quantum screening and Kohn singularities are employed to obtain the entanglement fidelity function in dense quantum plasmas. It is found that the Friedel screening effects enhance the entanglement fidelity in quantum plasmas. It is also found that the entanglement fidelity decreases with increasing collision frequency. The Friedel screening effect is found to be more significant in small collision energy and high Fermi wave number domains.

Optical properties of carbon nanotube gas sensor

A kinetic theory combined with an effective medium theory in a nonlinear basis is used to compute the effective dielectric of single-walled carbon nanotubes (SWNTs) in the presence of gas molecules. The effect of the change of SWNT volume fraction on the response to gas molecules is investigated to find the optimum SWNTs embedded in the system. The computational results obtained show that the effective dielectric of the system increases explicitly with increasing dielectric and volume fraction of SWNTs. The effects of molecular adsorption on the effective dielectric of the system are also examined. This investigation showed that the effective dielectric of the system increases with increasing collision frequency and decreases with increasing electron density. This work is helpful for designing SWNT gas sensors.

Propagation and Absorption of Electromagnetic Waves in Inhomogeneous Helicon Plasmas with a Lower Hybrid Resonance Layer

Propagation and absorption of radiofrequency waves are numerically studied for radially inhomogeneous helicon plasmas with a lower hybrid resonance layer. The rf power is absorbed outside the resonance layer and the peak absorption occurs near the resonance at a low collision frequency. As the collision frequency increases, the absorption peak moves toward the plasma boundary. The plasma resistance is examined as functions of the density and the magnetic field. The density giving a high plasma resistance is proportional to the magnetic field for a wide range of the magnetic field, including the lower hybrid resonance, if the density profile is suciently steep.

Features of electron-wall collision frequency with saturated sheath in Hall thruster

In the paper we study the electron-wall collision frequency in Hall thruster using the two-dimensional particle-in-cell method. It is found that electron-wall collision frequency is greatly increased in the state of saturated sheath compared with in the state of classic sheath, and even two orders of magnitude higher. Thus, the contribution of electron-wall collision frequency in the state of saturated sheath to near-wall current will be non-ignorable. In this paper the reason why the electron-wall collision frequency is increased in the state of saturated sheath is further analysed. It is believed that the increase of electron-wall collision frequency is caused by rather low sheath potential drop and the backflow of secondary electron emitted from the wall.

Properties of obliquely incident electromagnetic wave in one-dimensional magnetized plasma photonic crystals

Properties of obliquely incident electromagnetic wave in one-dimensional (1D) magnetized plasma photonic crystals (PPCs) are studied in this paper. Based on the continuous boundary condition of electromagnetic wave in 1D PPC, transfer matrix equation and dispersion equation of transverse magnetic polarization are deduced, and the properties of dispersion and transmission relation in terms of external magnetic field, collision frequency, and dielectric constant of dielectric and incident angles are investigated, respectively. Results show that gap location and gap width can be effectively controlled by adjusting external magnetic field as well as incident angle, and increasing collision frequency has little effect on gap width while larger dielectric constant of dielectric leads to more gaps.

Increased [ PSI + ] Appearance by Fusion of Rnq1 with the Prion Domain of Sup35 in Saccharomyces cerevisiae

During propagation, yeast prions show a strict sequence preference that confers the specificity of prion assembly. Although propagations of [PSI(+)] and [RNQ(+)] are independent of each other, the appearance of [PSI(+)] is facilitated by the presence of [RNQ(+)]. To explain the [RNQ(+)] effect on the appearance of [PSI(+)], the cross-seeding model was suggested, in which Rnq1 aggregates act as imperfect templates for Sup35 aggregation. If cross-seeding events take place in the cytoplasm of yeast cells, the collision frequency between Rnq1 aggregates and Sup35 will affect the appearance of [PSI(+)]. In this study, to address whether cross-seeding occurs in vivo, a new [PSI(+)] induction method was developed that exploits a protein fusion between the prion domain of Sup35 (NM) and Rnq1. This fusion protein successfully joins preexisting Rnq1 aggregates, which should result in the localization of NM around the Rnq1 aggregates and hence in an increased collision frequency between NM and Rnq1 aggregates. The appearance of [PSI(+)] could be induced very efficiently, even with a low expression level of the fusion protein. This study supports the occurrence of in vivo cross-seeding between Sup35 and Rnq1 and provides a new tool that can be used to dissect the mechanism of the de novo appearance of prions.