Presence Of Dust Particles Research Articles

Ordinary hot-wire/hot-film method for spirography application

Although hot-wire/hot-film has lots of advantages, but some problems like flow direction detection, variation of temperature and ambient pressure and presence of dust particles in the vicinity of the sensor, cause errors in medical application measurement. This paper describes an innovative way for using ordinary hot-wire/hot-film method in spirography. The innovation includes an obstacle between two hot-film sensors and a procedure for data processing considering all hot-wire/hot-film problems. In addition a calibration syringe with definite volume is used to modify the calibration of spirometer under different working conditions.

Free convection of a dusty‐gas flow along a semi‐infinite vertical cylinder

AbstractAn analysis is performed to study the free convection of a dusty‐gas flow along a semi‐infinite isothermal vertical cylinder. The governing equations of the flow problem are transformed into non‐dimensional form and the resulting nonlinear, coupled parabolic partial differential equations have been solved numerically using an implicit finite difference scheme of Crank–Nicholson type. The flow variables such as gas–velocity, dust‐particle velocity and temperature, shearing stress and heat transfer coefficients are calculated numerically for various parameters occurring in the problem. It is observed that due to the presence of dust particles, the gas velocity is found to decrease. Copyright © 2009 John Wiley & Sons, Ltd.

Electrostatic vortices in inhomogeneous pair-ion-electron and dusty plasmas

Pair-ion plasma in the presence of dust particles and electrons has been studied. A coupled linear dispersion relation containing dust ion acoustic, dust acoustic and drift waves has been found. Many standard dispersion relations have been discussed in different limits. In the nonlinear regime, the stationary solution in the form of dipolar vortices has been obtained. It is noticed that the formation of these nonlinear structures depends on the acoustic speed and diamagnetic drift speed.

"Self rather seedy": Climate and Colonial Pathography in Conrad's African Fiction

Upon first arriving in the Congo, Marlow, the narrator of Conrad’s Heart of Darkness, discovers that the steamship meant to be his mode of travel is disabled. After obtaining the necessary tools and repair ing it, he sets off on his journey to retrieve Kurtz. Marlow finds the climate oppressive: “Going up that river . . . The air was warm, thick, heavy, sluggish. There was no joy in the brilliance of sunshine.” 1 As the steamship nears Kurtz’s camp, Marlow is advised by the manager to set anchor for one last night before proceeding up the final part of the river. The crew spends the night onboard and awakens at dawn, a scene which Marlow describes in a short passage rife with climatic imagery: When the sun rose there was a white fog, very warm and clammy, and more blinding than the night. It did not shift or drive; it was just there, standing all round you like something solid. At eight or nine, perhaps, it lifted as a shutter lifts. We had a glimpse of the towering multitude of trees, of the immense matted jungle, with the blazing little ball of the sun hanging over it—all perfectly still—and then the white shutter came down again, smoothly, as if gliding into greased grooves. (67-68) In Conrad in the Nineteenth Century, Ian Watt links the “persistent image” of “mist or haze” in Conrad’s work to his impressionistic writing style. As evidence, Watt cites Conrad’s warning that “Marlow’s tale will be not centered on, but surrounded by, its meaning; and this meaning will be only as fitfully and tenuously visible as a hitherto unnoticed presence of dust particles and water vapour.” 2 Watt also argues that Conrad presents the world around his narrators filtered

Effect of magnetic field dependent viscosity on ferroconvection in the presence of dust particles

This paper deals with the theoretical investigation of the effect of magnetic field dependent (MFD) viscosity on the thermal convection in a ferromagnetic fluid in the presence of dust particles. For a flat ferromagnetic fluid layer contained between two free boundaries, the exact solution is obtained using a linear stability analysis and a normal mode analysis method. For the case of stationary convection, dust particles always have a destabilizing effect, whereas the MFD viscosity has a stabilizing effect on the onset of convection. In the absence of MFD viscosity, the destabilizing effect of magnetization is depicted but in the presence of MFD viscosity, non-buoyancy magnetization may have a destabilizing or a stabilizing effect on the onset of convection. The critical wave number and critical magnetic thermal Rayleigh number for the onset of stationary convection are also determined numerically for sufficiently large values of buoyancy magnetization parameter M 1. Graphs have been plotted by giving numerical values to the parameters to depict the stability characteristics. It is observed that the critical magnetic thermal Rayleigh number is reduced solely because the heat capacity of clean fluid is supplemented by that of the dust particles. The principle of exchange of stabilities is found to hold true for the ferromagnetic fluid heated from below in the absence of dust particles. The oscillatory modes are introduced due to the presence of the dust particles, which were non-existent in their absence. A sufficient condition for the non-existence of overstability is also obtained.

On the role of dust in the cometary plasma

The cometary coma consists of neutral gas, plasma, and dust grains. The dust grains can influence both the neutral and charged coma’s constituents. Usually, the presence of dust particles in a plasma results in additional losses of both electrons and ions due to the plasma recombination on the particle surfaces. Solar radiation makes the impact of dust even more complicated depending on the solar flux, the dust number density, the photoelectric properties of the dust particles, the dust particle composition, the distribution of the sizes, etc. We propose a simple kinetic model evaluating the role of dust particles in the coma plasma chemistry and demonstrate that this role can be crucial, resulting in a nontrivial behavior of both the electron and ion densities of the plasma. We show that a coma’s dust particles can be negatively as well as positively charged depending on their composition. These opposite charges of the grains can result in fast coagulation of dust particles, thus, forming complex aggregate shapes of cometary grains.

The 3D Simulation of Dust Particle Transport

Recently, the presence of dust particles in tokamak plasma and the role of dust in material re-deposition, core contamination, and tritium inventory brought significant attention of the fusion community. The physical model for dust transport in fusion devices and the newly developed 3D code DUSTT are discussed. The DUSTT code takes into account both the dust dynamics due to dust-plasma interactions as well as the effects of dust charging, heating and evaporation. The code allows tracking of test dust particle in realistic plasma background calculated with edge-plasma transport code UEDGE. Some results on dust transport in DIII-D tokamak are presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of magnetic-field-dependent viscosity and rotation on ferrothermohaline convection saturating a porous medium in the presence of dust particles

This paper deals with the theoretical investigation of the combined effect of magnetic-field-dependent (MFD) viscosity and rotation on ferrothermohaline convection saturating a porous medium in the presence of dust particles subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linearized stability theory and the normal mode analysis method. For the case of stationary convection, dust particles always have a destabilizing effect, whereas rotation, stable solute gradient and magnetic-field-dependent viscosity always have a stabilizing effect on the onset of convection. In the absence of rotation, the destabilizing effect of medium permeability is depicted, but in the presence of rotation, medium permeability may have a destabilizing or a stabilizing effect on the onset of convection. In the absence of MFD viscosity, the destabilizing effect of non-buoyancy magnetization is depicted, but in the presence of MFD viscosity, non-buoyancy magnetization may have a destabilizing or a stabilizing effect on the onset of convection. The critical wave number and critical magnetic thermal Rayleigh number for the onset of instability are also determined numerically for sufficiently large values of magnetic parameter M1 and results are depicted graphically. The principle of exchange of stabilities is found to hold true for the ferromagnetic fluid saturating a porous medium heated from below in the absence of dust particles, stable solute gradient and rotation. The oscillatory modes are introduced due to the presence of the dust particles, stable solute gradient and rotation, which were non-existent in their absence. The sufficient conditions for the non-existence of overstability are also obtained.

The effect of magnetic-field-dependent viscosity on ferroconvection in a porous medium in the presence of dust particles

This paper deals with the theoretical investigation of the effect of magnetic-field-dependent (MFD) viscosity on the thermal convection in ferromagnetic fluid saturating a porous medium in the presence of dust particles. For a flat ferromagnetic fluid layer contained between two free boundaries, the exact solution is obtained using a linear stability analysis. For the case of stationary convection, medium permeability and dust particles always have a destabilizing effect whereas the MFD viscosity has a stabilizing effect on the onset of convection. In the absence of MFD viscosity, the destabilizing effect of magnetization is depicted but in the presence of MFD viscosity, magnetization may have a destabilizing or stabilizing effect on the onset of convection. The critical wave number and critical magnetic thermal Rayleigh number for the onset of stationary convection are also determined numerically for sufficiently large values of buoyancy magnetization parameter M1. Graphs have been plotted by giving numerical values to the parameters to depict the stability characteristics. It is observed that the critical magnetic thermal Rayleigh number is reduced solely because the heat capacity of clean fluid is supplemented by that of the dust particles. The principle of exchange of stabilities is found to hold true for the ferromagnetic fluid saturating a porous medium heated from below in the absence of dust particles. The oscillatory modes are introduced due to the presence of the dust particles, which were nonexistent in their absence. A sufficient condition for the nonexistence of overstability is also obtained.

Kinetics of an RF low-pressure discharge with a condensed phase

The electron energy distribution function in an RF low-pressure plasma is found in the presence of dust particles. The effect of microscopic objects on the electroneutrality of the plasma and the electron energy distribution is estimated.

Thermal instability of ionized dusty plasmas

We investigate the role of thermal instability, arising from radiative cooling of an optically thin, ionized, dusty plasma, by linear stability analysis. The corresponding isobaric stability condition for condensation mode is found to be modified significantly by the concentration of finite sized, relatively heavy, and negatively charged dust particles. It has been shown that the radiation condensation mode is severely affected by the presence of dust particles. A distinct departure from the classical behavior (Field 1965) is that the existence of unstable acoustic modes depends on the dust-charge fluctuation parameter and is not affected by the cooling through radiation.

The Bohm criterion for the dusty plasma sheath

The Bohm criterion for the dusty plasma sheath is investigated with a fluid model. It is shown that the presence of dust particles near the interface between the bulk plasma and the sheath should have effects upon the ion Mach number. The dust particles charging and density variation are taken into account, and therefore the self-consistent relation between the dust surface potential and ion Mach number at the sheath edge is derived. The numerical results reveal that both the ion critical Mach number and the dust critical Mach number with variation of density ratio of dust-to-electron begin to decline after a maximum.

In-situ study of dust particle formation in Ar/CH 4 and Ar/C 2H 2 mixtures

We have studied the characteristic behaviour of dust particle formation in the capacitively coupled standard GEC cell using Ar/CH 4 methane and Ar/C 2H 2 mixtures. Laser light scattering and absorption by dust particles, plasma emission, spectrum analysis for the change of plasma impedance by the presence of dust particles, atomic spectral emission by argon atoms, and mass spectroscopic measurements are performed in-situ. Using the 7th harmonic signal as an external control parameter, we have successfully deposited two-dimensional periodic structures of ‘dust dots’.

Synthesis and morphology of platinum-coated hollow-fiber carbon membranes

Hollow-fiber carbon membranes were prepared and used as support media for a platinum catalyst. The platinum metal was deposited onto the surface of the hollow-fiber carbon membranes by three different techniques: solution coating with chloroplatinic acid, which is the commonly used technique; vapor deposition, involving the sublimation of the platinum metal; and magnetron sputter coating, the most effective method. The hollow-fiber carbon membranes coated with a chloroplatinic acid solution were studied with scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX). The platinum coating grew on the surface, unevenly, in the form of small crystals. The percentage of platinum on the surface was too low to be detected by EDAX. The high-vacuum evaporation coating of the membranes with platinum was also studied with both SEM and EDAX. Again, because of the low percentage of platinum, EDAX did not reveal any platinum on the surfaces of the membranes. The magnetron sputter coating of platinum onto the membranes was performed and studied with SEM. The thickness of the coated platinum could be varied through variations in the coating time. The cavities observed in the micrographs were formed during the coating operations by the presence of dust particles on the membranes. An SEM micrograph of a hollow-fiber carbon membrane, produced from a polyacrylonitrile-based precursor, spun with a low amount of dimethyl sulfoxide in the bore fluid, and coated with platinum, showed a skin on the outside and a porous elongated structure inside the skin. The distance between the inner and outer skins contained fingerlike pores of various sizes. The largest pores were found near the inside skin, whereas the smallest pores were next to the outside skin. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1051–1058, 2003

Radiation-condensation instability in a highly ionized dusty plasma

The dynamics of linear perturbations in a radiatively cooling dusty plasma is considered, with the charge of both dust (Zd) and plasma (Zp) components being allowed to vary with their densities. It is shown that in the long-wavelength limit corresponding to the characteristic cooling length, when the plasma can be treated as quasineutral, the presence of dust particles changes the criteria for radiation instability, regardless of the charging process of the dust particles. In particular, the condensation (isobaric) mode is shown to be stabilized (destabilized) if in the equilibrium, the relation between densities of the dust nd and plasma n under the quasineutrality condition, (d ln nd/d ln n)q<1 (>1) is satisfied, while the isentropic mode is stabilized (destabilized) when the opposite inequalities take place; the isochoric mode is unaltered. Numerical estimates show that these effects can be important in hot phases (T∼106 K) of the interstellar plasma, and in tokamak plasma near the walls.

Nonlocal theory of drift type waves in a collisionless dusty plasma

A nonlocal theory is formulated to study drift waves in a collisionless multicomponent (dusty) plasma in a sheared slab geometry. The dynamics of dust particles and ions are treated by fluid models, whereas the electrons are assumed to follow the Boltzmann distribution. It is found that the usual stability of drift waves in a sheared slab geometry is destroyed by the presence of dust particles. A drift wave is excited which propagates with a new characteristic frequency modified by dust particles. This result is similiar to our earlier work for the collisional dusty plasma [Chakraborty et al., Phys. Plasmas 8, 1514 (2001)].

Elastic light scattering with a LiNbO_3 waveguide

We present the measurements of hemispherical elastic scattering of light guided by different modes of a planar LiNbO3 waveguide. It is shown that the fundamental and the lowest-order modes are more sensitive to the scattering properties of the air-core interface, whereas higher-order modes are more sensitive to the optical inhomogeneities of the core-substrate interface. We also demonstrate that because of static polarization of LiNbO3 crystal, the air-core interface is sensitive to the presence of dust particles in air, which causes a change in the scattered light based on time of observation. This sensitivity could be used to elaborate compact sensors of air contamination.

Nonlocal theory of drift type waves in a collisional dusty plasma

A nonlocal theory of low-frequency drift-type waves has been developed in a magnetized collisional dusty plasma in a sheared slab geometry. It is shown that the well-known stability of the drift waves in a sheared slab geometry does not hold in the presence of dust particles and a new unstable mode exists for typical laboratory plasma parameters.

Micro-sphere levitation in a sheath of a low pressure continuous discharge

Electrode sheath profile measurements are reported, with dust particles in suspension and without. With the shape of the unperturbed potential profile, basic characteristics can be predicted as the surface potential, the charge and potential energy of a dust particle in function of its position in the sheath. The dust particle screening length is also estimated analyzing binary collisions in a gas phase cloud. In the presence of dust particles, an average increase of ion drift velocities is measured showing that micron-sized particles whose charge is due to the electron and ion fluxes produce a self-consistent redistribution of the plasma particle fluxes.

Sheath modification in the presence of dust particles

Negatively charged dust particles are expected to modify the local sheath potential where they are in equilibrium. In the conditions of a hot cathode discharge, sheath profiles are deduced from the measurement of ion drift velocities, with dust particles in suspension and without. In the unperturbed potential profile, the surface potential of an isolated dust particle, its charge, and its potential energy can be estimated as a function of the position in the sheath. In the presence of dust particles, an average increase of the ion drift velocity is measured showing a modification of the local sheath profile. This experimental result suggests that the dust particle charge due to the plasma particle fluxes in the sheath, modifies in turn the local plasma particle distributions.