Presence Of Nonuniformities Research Articles

Evaluation of the influence of surface irregularity of optical crystal microresonators on their dispersion characteristics

Advantages and prospects of using optical microresonators for the development of measuring instruments based on frequency combs are described. A principle of a frequency comb generator based on an optical microresonator is considered. An example of modeling the properties of microresonators used to generate optical frequency combs is considered. The influence of the nonuniformity of the optical microresonator’s generatrix on the value of the total dispersion has been studied. It is shown that the presence of nonuniformity on the surface affects the dispersion parameters and can also lead to the effect of mode shape splitting in microresonators. We have shown that this effect is particularly dependent on the position and the value of the depth of nonuniformity.

Magnetic response of a two-dimensional viscous electron fluid

It has been established that the Coulomb interactions can transform the electron gas into a viscous fluid. This fluid is realized in a number of platforms, including graphene and two-dimensional semiconductor heterostructures. The defining characteristic of the electron fluid is the formation of layers of charge carriers that are in local thermodynamic equilibrium, as in classical fluids. In the presence of nonuniformities, whirlpools and nontrivial flow profiles are formed, which have been directly imaged in recent experiments. In this paper, we theoretically study the response of the electron fluid to localized magnetic fields. We find that the electric current is suppressed by viscous vortices in regions where magnetic field is sharply varying, causing strong transport signatures. Experimentally, our considerations are relevant since local magnetic fields can be applied to the system through implanting adatoms or embedding micromagnets in the top-gate. Our theory is essential for the characterization and future applications of electron fluids in hydrodynamic spin transport.

Wear of elastic tube with nonuniform coating by rigid bush

This article is devoted to the statement and construction of analytical solution of the wearcontact problem for a rigid bush and elastic pipe with a coating in the case when the coating is nonuniform. The presence of nonuniformity leads us to the necessity of constructing a solution in a special form over special functions, since standard methods does not allow us to effectively take into account the complex properties of the coating. Analytical representation for contact stresses under the bush is presented in series with separate factor, which connect with complex properties of coating. This allows provide effective calculation even if these properties are described by rapidly changing or discontinuous functions. It is also shown that contact stresses will be negligible over time.

Quantitative Susceptibility Mapping of Magnetic Quadrupole Moments

We modeled the magnetic field up to the quadrupole term to investigate not only the average susceptibility (dipole), but also the susceptibility distribution (quadrupole) contribution. Expanding the magnetic field up to the 2nd order provides the quadrupole (0th: monopole, 1st: dipole). Numerical simulations were performed to investigate the quadrupole contribution with subvoxel nonuniformity. Conventional dipole and our dipole + quadrupole models were compared in the simulation, the phantom and human brain. Furthermore, the quadrupole field was compared with the anisotropic susceptibility field in the dipole tensor model. In a nonuniformity case, numerical simulations showed a nonnegligible quadrupole field contribution. Our study showed a difference between the two methods in the susceptibility map at the edges; both the phantom and human studies showed sharper structural edges with the dipole + quadrupole model. Quadrupole moments showed contrast mainly at the structural boundaries. The quadrupole moment field contribution was smaller but nonnegligible compared to the anisotropic susceptibility contribution. Nonuniform and uniform source distributions can be separately considered by quadrupole expansion, which were mixed together in the dipole model. In the presence of nonuniformity, the susceptibility maps may be different between the two models. For a comprehensive field model, the quadrupole might need to be considered along with susceptibility anisotropy and microstructure effects.

The structural features of fluorinated paraffins

A systematic study of the molecular and supramolecular structural features of fluorinated paraffins has been conducted with the use of a set of physical methods and quantum-chemical calculations of the parameters of the IR and NMR spectra. The presence of nonuniformity in the morphological structures of samples obtained from different initial products has been shown. Incomplete substitution of fluorine for hydrogen during synthesis has been revealed, and the types of structural groups in which the substitution occurs have been determined. Fluoroparaffins have been found to effectively dissolve in supercritical carbon dioxide, a phenomenon that opens new fields of application for these materials.

Level Set Method for Image Segmentation: A Survey

A considerable challenge in image segmentation in real world images is intensity inhomogenity. The existing image segmentation algorithms rely on region based and it typically features similarity of image intensities in the region of interest. Due to the presence of intensity non uniformity the segmentation results are not accurate. So this survey paper gives a novel region based techniques for image segmentation in the presence of intensity inhomogenity. Intensity non uniformity occurs in real world images due to various factors such as spatial variations on illumination, imperfections of imaging devices, noise and of low contrast, causes many problems in image processing and computer vision. Image segmentation is a very difficult task in the presence of non uniformity of intensities. Intensity non uniformity is caused by the overlaps between the ranges of intensities in the region to be segmented. This paper covers segmentation techniques to overcome the intensity inhomogenity with the help of Level Set Method. The aim is to implement a level set approach for active contour image segmentation for MRI images. No requirement about object's shape and allowances for very flexible topology change are key advantages for this method. As an application our method can be used for

Degradation of a geared bearing of a stacker

Large size rolling-element bearings used for turning of upper body of machines used in open-pit mining are made in form of single-row or double-row ball bearings. Section diameter of those bearings may be as large as 20 m and rolling elements have diameters of 100 to 250 mm, while they are under eccentric axial load from few to tens of MN. Due to low stiffness of supportive elements and its non-uniform presence all over the circumference of the bearing, the load upon rolling elements is rather unequal in those bearings. The flow of load stream concentrates in points which are in the areas with highest stiffness. This may be achieved using modern computer-assisted design tools. The specificity of these custom made machines makes obtaining credible data for numeric models possible only by applying analyses of the already existing bearings and their support structures which had been in operation for many years. Was introduced applied to opinion of effect of long-lasting exploitation on change of parameters of bearing.

Radial angular temperature distributions for nonisothermal two-phase filtration of oil and water

The distributions of phase saturations, pressure, and temperature in a porous medium of nonuniform permeability are studied by numerical modeling of nonisothermal two-phase filtration of oil and water with the Joule-Thomson effect and adiabatic effect taken into account. It is shown that the presence of nonuniformity in the near-well zone of the reservoir results in nonmonotonic angular and radial distributions of temperature and phase saturations. During oil and water filtration, there is transition from negative to positive temperature anomalies or vice versa, depending on the ratio of the reservoir permeabilities and the presence of a segment on which the angular temperature distribution in the well is nonuniform.

Generalization of the rainbow Airy theory to nonuniform spheres

Rainbow techniques permit measurement of refractive indices, and hence the temperatures of liquid droplets through determination of the absolute angular position of a rainbow interference image in space. The Airy theory, which is commonly used to explain the rainbow effect, permits the determination of a unique refractive-index value, even in the presence of nonuniformities in the droplet. An extension of this theory to spheres that exhibit internal refractive-index gradients is proposed. The case of burning droplets is considered as an example of such spheres, and the results obtained are successfully compared with those presented in the literature.

Fractal model to predict the crack roughness effect on the local bending compliance of circular shafts

In this paper the local compliance due to a transverse fractal crack in a shaft under pure bending is investigated. In a fractal crack, the surface is considered irregular and it is characterized by the presence of nonuniformities at different scales. Therefore, the crack surface can be modeled as a fractal surface with fractal dimension D. An analytical model for the compliance coefficient is presented with and without the effect of the surface roughness. The results obtained shows that as the dimension of the fractal surface increases the compliance increases as well. It is shown that this behavior conforms well with existing experimental results.

Solution of Unsteady-State Shrinking-Core Models by Means of Spectral/Fixed-Point Methods: Nonuniform Reactant Distribution and Nonlinear Kinetics

We present a method for solving moving-boundary problems in the presence of nonuniformities and nonlinearities. The method is based on the spectral decomposition of the concentration field of reacting/diffusing species in a suitable system of eigenfunctions and on the solution of the corresponding system of ordinary differential equations for the Fourier coefficients by means of fixed-point methods. The method proposed by Selim and Seagrave is improved upon and extended to solve moving-boundary problems in the presence of position-dependent diffusion coefficients and nonlinearities in kinetic rates. We apply this method to solve isothermal and nonisothermal shrinking-core models for fluid−solid noncatalytic reactions by focusing on the influence of spatial nonuniformities in the solid reactant distribution.

Uniaxial true stress-true strain curve for a ductile metal

It is well known and has been shown qualitatively and quantitatively that the necking phenomenon in uniaxial tensile ductile metal specimens is caused by the presence of non-uniformities in the initial geometry and initial strength. It is shown in this paper that a uniaxial true stress-true strain curve for an idealized perfect specimen could be constructed from experimental data which is available for uniaxial tensile tests on ductile metal specimens having a known initial non-uniformity.

Effects of spatial luminance nonuniformities on visual-task performance and subjective uniformity

The objectives of the experiment described in the paper were the determination of the effects of nonuniformities on operator performance and perception, and the validation of current recommended standards. Subjects performed two tasks in the presence of nonuniformities: an objective visual search task, and a subjective magnitude-estimation task for the determination of perceived uniformity. The results indicated that the nonuniformities did not appreciably affect search performance, and that current recommendations are appropriate, although the magnitude-estimation task results indicated that the subjects were sensitive to the nonuniformities. The subjective impressions of perceived uniformity results follow the contrast threshold function of the visual system.

The formation of multiple fronts

Using two-dimensional semi-geostrophic frontogenesis models and three-dimensional semi-geostrophic baroclinic wave models, it is shown that atmospheric development in the presence of non-uniformities in pre-existing temperature distributions may be expected to lead to the frequent occurrence of multiple frontal structures. In general, such non-uniformities in the temperature distribution will be important if they significantly change the ambient temperature gradient. The frontal structures associated with the irregularities tend to be very shallow. They are possible candidates for the triggering mechanism for frontal troughs well behind a cold front and for shallow rainbands ahead of such a front. However, it seems that a separate mechanism is still necessary for the production of the middle-level banded structures that are frequently observed.

Isotopic oxygen exchange on supported Ru and Au catalysts

The isotopic exchange reaction of molecular oxygen is applied to supported ruthenium and gold catalysts. The results on supported ruthenium are similar to those on RuO 2. The exchange reaction seems to be unaffected by differences in particle size or nature of the support (MgO or SiO 2, respectively). The heterogeneous exchange kinetics deviate from an exponential law. This indicates the presence of nonuniformities on the catalyst surface and/or a contribution of oxygen diffusion. On supported gold, high exchange activity and massive uptake of labeled oxygen by the solid phase are observed. Au MgO is one order of magnitude more active than Au SiO 2 . The activation of support oxygen for the isotopic exchange reaction is related to an interaction between gold and support.

Boiling Heat Transfer in the Presence of Nonuniform, Direct Current Electric Fields

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBoiling Heat Transfer in the Presence of Nonuniform, Direct Current Electric FieldsRonald F. Lovenguth and Deran HanesianCite this: Ind. Eng. Chem. Fundamen. 1971, 10, 4, 570–576Publication Date (Print):November 1, 1971Publication History Published online1 May 2002Published inissue 1 November 1971https://doi.org/10.1021/i160040a005RIGHTS & PERMISSIONSArticle Views83Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (741 KB) Get e-Alerts

Condensation of Freon-114 in the Presence of a Strong Nonuniform, Alternating Electric Field

The condensation of Freon-114 in the presence of a nonuniform, alternating, 60-cycle, electric field was examined experimentally. The condensing surface was a grounded, cooled flat plate, and the electric field was produced by applying a voltage to a second plate placed above the first. Voltages up to 60 kv were imposed, and nonuniformities in the field were created by varying the angle between the plates. Analytical predictions were made of the expected heat-transfer rate, and reasonable agreement with the experimental data was obtained for voltages less than 40 kv. Above 40 kv the results were unpredictable, but increases in the heat-transfer coefficient as high as ten times that for no field were obtained.

Effect of Stiffness and Nonuniformity on Vibroscopic Determination of Filament Cross-Sectional Area

The presence of stiffness in a stretched string vibrating between fixed supports raises all the natural frequencies over those for a perfectly flexible string. The presence of nonuniformity in cross-sectional area along the string changes some or all of the frequencies from those for a perfectly uniform string, the amount and direction of change depending on the form of the nonuniformity. These changes in frequency may introduce error into the calculation of the average cross-sectional area of a fiber by means of the vibroscopic technique, wherein the mechanical resonance of a stretched fiber is observed under oscillating mechanical or electrostatic forces. In this paper the natural frequencies are calculated with both the stiffness and the nonuniformity taken into account to first-order terms. The relation between the average cross-sectional area and the natural frequencies is analyzed. Consideration is given to the manner in which the changes in frequency and shifts of the nodes, due to nonuniformity, determine the detailed form of the area variation. The characterization of nonuniformities in terms of certain arbitrary parameters is shown to lead to the possibility of calculating the average area by measuring the natural frequencies in only the first and second modes and of calculating the maximum or minimum area by measuring also the nodal shift in the second mode.