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2005

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Articles 4591 - 4620 of 4759

Full-Text Articles in Physical Sciences and Mathematics

Stable Motions Of Vehicle Formations, Anca Williams, Gerardo Lafferriere, J. J. P. Veerman Jan 2005

Stable Motions Of Vehicle Formations, Anca Williams, Gerardo Lafferriere, J. J. P. Veerman

Mathematics and Statistics Faculty Publications and Presentations

We investigate stable maneuvers for a group of autonomous vehicles while moving in formation. The allowed decentralized feeback laws are factored through the Laplacian matrix of the communication graph. We show that such laws allow for stable circular or elliptical motions for certain vehicle dynamics. We find necessary and sufficient conditions on the feedback gains and the dynamic parameters for convergence to formation. In particular, we prove that for undirected graphs there exist feedback gains that stabilize rotational (or elliptical) motions of arbitrary radius (or eceentricity). In the directed graph case we provide necessary and sufficient conditions on the curvature …

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A Solvable Model For Gravity Driven Granular Dynamics, J. J. P. Veerman Jan 2005

A Solvable Model For Gravity Driven Granular Dynamics, J. J. P. Veerman

Mathematics and Statistics Faculty Publications and Presentations

We discuss a toy model to study the dynamics of individual particles in avalanches. The model describes a particle launched from an inclined infinite staircase. The particle is not allowed to bounce when it collides with the staircase. During the collision, the particle loses some energy, and after that slides on to the end of the step it landed on. The process then repeats itself. The dynamics of this no-bounce model can essentially be completely understood. Partial versions of some results were stated and argued in previous work. Here we give a full description together with all the proofs. We …

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Flocks And Formations, J. J. P. Veerman, Gerardo Lafferriere, John S. Caughman Iv, A. Williams Jan 2005

Flocks And Formations, J. J. P. Veerman, Gerardo Lafferriere, John S. Caughman Iv, A. Williams

Mathematics and Statistics Faculty Publications and Presentations

Given a large number (the “flock”) of moving physical objects, we investigate physically reasonable mechanisms of influencing their orbits in such a way that they move along a prescribed course and in a prescribed and fixed configuration (or “in formation”). Each agent is programmed to see the position and velocity of a certain number of others. This flow of information from one agent to another defines a fixed directed (loopless) graph in which the agents are represented by the vertices. This graph is called the communication graph. To be able to fly in formation, an agent tries to match the …

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Measurement Of Lipid Peroxidation In Biology Models Using Gas-Chromatography-Aass Spectrometry, Madhavi Lokireddy Jan 2005

Measurement Of Lipid Peroxidation In Biology Models Using Gas-Chromatography-Aass Spectrometry, Madhavi Lokireddy

Master's Theses and Doctoral Dissertations

C2C12 mouse myoblast cells, grown in glass vials, were connected to a cryofocusing unit to trap volatile organic compounds (VOCs). The VOCs were eluted from the trap by capacitive discharge into a gas chromatograph with time-of-flight mass spectral capabilities (GC-TOFMS) and were found to include the lipid peroxidation product hexanal. The pro-oxidant cumene hydroperoxide elevated the levels of these lipid peroxidation products, whereas the anti-oxidant butylated hydroxy toluene (BHT) impaired their production. Derivatization of the aldehyde products of lipid peroxidation in the same myoblast cells with pentafluorobenzyl hydroxylamine hydrochloride (PFB) provided evidence for formation of non-volatile products of lipid peroxidation …

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A Robust Controller For The Manipulation Of Micro Scale Objects, Qinmin Yang, Jagannathan Sarangapani Jan 2005

A Robust Controller For The Manipulation Of Micro Scale Objects, Qinmin Yang, Jagannathan Sarangapani

Electrical and Computer Engineering Faculty Research & Creative Works

A suite of novel robust controllers is presented for the manipulation and handling of micro-scale objects in a micro-electromechanical system (MEMS) where adhesive, surface tension, friction and van der Waals forces are dominant. Moreover, these forces are typically unknown. The robust controller overcomes the unknown system dynamics and ensures the performance in the presence of actuator constraints by assuming that the upper bounds on these forces are known. On the other hand, for the robust adaptive controller, the unknown forces are estimated online. Using the Lyapunov approach, the uniformly ultimate boundedness (UUB) of the closed-loop manipulation error is shown for …

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Block Phase Correlation-Based Automatic Drift Compensation For Atomic Force Microscopes, Qinmin Yang, Eric W. Bohannan, Jagannathan Sarangapani Jan 2005

Block Phase Correlation-Based Automatic Drift Compensation For Atomic Force Microscopes, Qinmin Yang, Eric W. Bohannan, Jagannathan Sarangapani

Electrical and Computer Engineering Faculty Research & Creative Works

Automatic nanomanipulation and nanofabrication with an Atomic Force Microscope (AFM) is a precursor for nanomanufacturing. In ambient conditions without stringent environmental controls, nanomanipulation tasks require extensive human intervention to compensate for the many spatial uncertainties of the AFM. Among these uncertainties, thermal drift is especially hard to solve because it tends to increase with time and cannot be compensated simultaneously by feedback. In this paper, an automatic compensation scheme is introduced to measure and estimate drift. This information can be subsequently utilized to compensate for the thermal drift so that a real-time controller for nanomanipulation can be designed as if …

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Marketing Locally Produced Foods: Consumer And Farmer Opinions In Washington County, Nebraska, Mindi L. Schneider, Charles A. Francis Jan 2005

Marketing Locally Produced Foods: Consumer And Farmer Opinions In Washington County, Nebraska, Mindi L. Schneider, Charles A. Francis

Department of Agronomy and Horticulture: Faculty Publications

Local food system potentials were studied in Washington County, Nebraska, United States. As a departure from most studies of locally based systems, farmers were surveyed in addition to consumers for potential participation. Data about the current food system and opinions and preferences for local production, marketing, and purchasing of food were collected using self-administered mail questionnaires. The response rate was 35% for the farmer survey and 37% for the consumer survey. Results indicated that, on the farming side of the food system, conventional corn and soybean production and marketing predominated in Washington County, and farmer interest in producing for local …

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Optimization Of Ultraviolet Emission And Chemical Species Generation From A Pulsed Dielectric Barrier Discharge At Atmospheric Pressure, Xinpei Lu, Mounir Laroussi Jan 2005

Optimization Of Ultraviolet Emission And Chemical Species Generation From A Pulsed Dielectric Barrier Discharge At Atmospheric Pressure, Xinpei Lu, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

One of the attractive features of nonthermal atmospheric pressure plasmas is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. This attractive characteristic recently led to their extensive use in applications that require low temperatures, such as material processing and biomedical applications. The agents responsible for the efficient plasma reactivity are the ultraviolet (UV) photons and the chemically reactive species. In this paper, in order to optimize the UV radiation and reactive species generation efficiency, the plasma was generated by a dielectric barrier discharge driven by unipolar submicrosecond square pulses. To keep the discharge …

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A Multi-Hypothesis Approach For Salient Object Tracking In Visual Surveillance, Filiz Bunyak, Ilker Ersoy, S. R. Subramanya Jan 2005

A Multi-Hypothesis Approach For Salient Object Tracking In Visual Surveillance, Filiz Bunyak, Ilker Ersoy, S. R. Subramanya

Electrical and Computer Engineering Faculty Research & Creative Works

In this paper, a multiple object tracking method for visual surveillance applications is presented. Moving objects are detected by adaptive background subtraction and tracked by using a multi-hypothesis testing approach. Object matching between frames is done based on proximity and appearance similarity. a new confidence measure is assigned to each possible match. This information is arranged into a graph structure where vertices represent blobs in consecutive frames and edges represent match confidence values. This graph is later used to prune and refine trajectories to obtain the salient object trajectories. Occlusions are handled through position prediction using Kalman filter and robust …

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The Architecture Of A Proteomic Network In The Yeast, Emad Ramadan, Christopher Osgood, Alex Pothern Jan 2005

The Architecture Of A Proteomic Network In The Yeast, Emad Ramadan, Christopher Osgood, Alex Pothern

Biological Sciences Faculty Publications

We describe an approach to clustering the yeast protein-protein inter-action network in order to identify functional modules, groups of proteins forming multi-protein complexes accomplishing various functions in the cell. We have developed a clustering method that accounts for the small-world nature of the network. The algorithm makes use of the concept of k-cores in a graph, and employs recursive spectral clustering to compute the functional modules. The computed clusters are annotated using their protein memberships into known multi-protein complexes in the yeast. We also dissect the protein interaction network into a global subnetwork of hub proteins (connected to several clusters), …

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Comparison Of Phytoplankton And Autotrophic Picoplankton Populations Over A 24-Hour Period From A Pond's Surface And Subsurface Waters, Harold G. Marshall, Lubomira Burchardt, Elżbieta Wilk-Woźniak Jan 2005

Comparison Of Phytoplankton And Autotrophic Picoplankton Populations Over A 24-Hour Period From A Pond's Surface And Subsurface Waters, Harold G. Marshall, Lubomira Burchardt, Elżbieta Wilk-Woźniak

Biological Sciences Faculty Publications

Phytoplankton abundance and composition relationships within the surface layer changed over short time periods (4-6 hours) in comparison with more constant associations at 2 cm below the surface. Both strata had a diverse algal flora (>50 taxa), but no distinct neuston assemblage characterized the surface layer algal composition over the 24-hour study. The similarity between the two strata indicated the floral composition of the surface layer came from the water column algae below the surface. Chlorophytes, diatoms, cyanobacteria, and cryptophytes represented the most abundant algal categories for both strata with a total mean phytoplankton abundance of 3,566 cells ml …

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Effects Of Human Disturbances On The Behavior Of Wintering Ducks, Melissa L. Pease, Robert K. Rose, Mark J. Butler Jan 2005

Effects Of Human Disturbances On The Behavior Of Wintering Ducks, Melissa L. Pease, Robert K. Rose, Mark J. Butler

Biological Sciences Faculty Publications

Human activity causes wintering waterfowl to expend energy to avoid humans at a time in their annual cycle when energy conservation is important to survival, migration, and breeding reserves. Understanding the effects of recreational activities on waterfowl is important to managing natural resource areas where migratory birds depend on wetland habitat for resting and feeding. We investigated responses of 7 species of dabbling ducks to 5 different experimental human activities, (a pedestrian, a bicyclist, a truck traveling at 2 different speeds, and an electric passenger tram). Responses of ducks depended on type of disturbance, species, and distance from disturbances. Most …

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A Review Of Phytoplankton Composition Within Chesapeake Bay And Its Tidal Estuaries, Harold G. Marshall, Lubomira Burchardt, Richard Lacouture Jan 2005

A Review Of Phytoplankton Composition Within Chesapeake Bay And Its Tidal Estuaries, Harold G. Marshall, Lubomira Burchardt, Richard Lacouture

Biological Sciences Faculty Publications

Based on a continuous 20-year data base ofmonthly sampling in Chesapeake Bay and tidal regions of its major tributaries, 1454 phytoplankton taxa have been identified in these waters. They represent a diverse assemblage of species with a dominant diatom flora throughout the year, in addition to large seasonal representation by chlorophytes, cyanobacteria, cryptophytes and dinoflagellates. Included among this flora were 34 potential harmful or toxin producing species. The phytoplankton compositions associated with the seasonal successional patterns are discussed, in addition to characterizing the dominant floral relationships, with comparison to early composition records within the Bay. Several of the present day …

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Feeding Ecology Of Juvenile Spiny Lobster, Panulirus Interruptus, On The Pacific Coast Of Baja California Sur, Mexico, Verónica Castañeda‐Fernández‐De‐Lara, Elisa Serviere‐Zaragoza, Sergio Hernández‐Vázquez, Mark J. Butler Iv Jan 2005

Feeding Ecology Of Juvenile Spiny Lobster, Panulirus Interruptus, On The Pacific Coast Of Baja California Sur, Mexico, Verónica Castañeda‐Fernández‐De‐Lara, Elisa Serviere‐Zaragoza, Sergio Hernández‐Vázquez, Mark J. Butler Iv

Biological Sciences Faculty Publications

Many aspects of the early life history of the red lobster Panulirus interruptus are little known, including the relationship between habitat structure, food resource availability, and nutrition of juveniles. We investigated the spatial and temporal differences in food intake, diet composition, and nutritional condition of juveniles at two sites along the Pacific coast of the Baja California Peninsula (Mexico) with contrasting oceanographic and biological conditions. One site (Arvin) is located inside a protected bay, Bahia Tortugas, where the waters are cooler and temperate seagrasses and macroalgae are the dominant benthic flora. The second site (Queen) in Bahia Sebastian Vizcaino was …

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Population Dynamics Of Oryzomys Palustris And Microtus Pennsylvanicus In Virginia Tidal Marshes, Christopher P. Bloch, Robert K. Rose Jan 2005

Population Dynamics Of Oryzomys Palustris And Microtus Pennsylvanicus In Virginia Tidal Marshes, Christopher P. Bloch, Robert K. Rose

Biological Sciences Faculty Publications

Oryzomys palustris (marsh rice rat) and Microtus pennsylvanicus (meadow vole) cohabit coastal marshes in the mid-Atlantic US. Both were live-trapped for 23 months at two tidal marsh sites in Virginia to assess their demography near the margins of their distributions. In the presence of dense vegetation, population dynamics of the two species were seasonal and positively correlated, with densities declining through the winter. At the more sparsely vegetated site, densities of both species were lower, and densities of M. pennsylvanicus were negatively correlated with those of O. palustris. Patterns of reproduction differed between the species. O. palustris was reproductively …

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Hydrographic And Biological Changes In The Taiwan Strait During The 1997-1998 El Niño Winter, S. Shang, C. Zhang, H. Hong, Q. Liu, G. T. F. Wong, C. Hu, B. Huang Jan 2005

Hydrographic And Biological Changes In The Taiwan Strait During The 1997-1998 El Niño Winter, S. Shang, C. Zhang, H. Hong, Q. Liu, G. T. F. Wong, C. Hu, B. Huang

OES Faculty Publications

During the 1997–1998 El Niño event, the average sea surface temperature (SST) in the Taiwan Strait (TWS) in the winter was ~1.4°C higher than that of the winter climatological mean. The areal ratio of the warm water (≥2°C above the regional mean) to the cold water (≥2°C below the regional mean) in the TWS increased by 25% while the area of the eutrophic water (chlorophyll a >1 mg m-3) was halved. Field observations also indicate that the mixed layer in the TWS became more nutrient-poor during this winter. These observations are consistent with a diminished advection of the …

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Do Viruses Affect Fecundity And Survival Of The Copepod Acartia Tonsa Dana?, Lisa A. Drake, Fred C. Dobbs Jan 2005

Do Viruses Affect Fecundity And Survival Of The Copepod Acartia Tonsa Dana?, Lisa A. Drake, Fred C. Dobbs

OES Faculty Publications

Naturally occurring viruses are extremely abundant in aquatic systems, and they infect bacteria, cyanobacteria, prokaryotic and eukaryotic phytoplankton, heterotrophic nanoflagellates, fish and mammals. Viral infections of single-celled organisms have been studied intensively in the past decade, but little is known about the effects of viruses on aquatic metazoans, other than for some economically important species. Because zooplankton assemblages are often dominated in number and biomass by copepods, we used them as model organisms to study the effects of naturally occurring viruses on higher trophic levels. We attempted to induce viral infection in laboratory-reared cultures of the estuarine copepod Acartia tonsa …

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Variability Of Sea Ice Cover In The Chukchi Sea (Western Arctic Ocean) During The Holocene, Anne De Vernal, Claude Hillaire-Marcel, Dennis A. Darby Jan 2005

Variability Of Sea Ice Cover In The Chukchi Sea (Western Arctic Ocean) During The Holocene, Anne De Vernal, Claude Hillaire-Marcel, Dennis A. Darby

OES Faculty Publications

Dinocysts from cores collected in the Chukchi Sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques. Holocene sequences have been recovered in a down-slope core (B15: 2135 m, 75°44'N, sedimentation rate of ~1cm kyr-1) and in a shelf core (P1: 201 m, 73°41'N, sedimentation rate of ~22 cm kyr-1). The shelf record spanning about 8000 years suggests high-frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar (cal) …

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Burial Of Terrestrial Organic Matter In Marine Sediments: A Re-Assessment, David J. Burdige Jan 2005

Burial Of Terrestrial Organic Matter In Marine Sediments: A Re-Assessment, David J. Burdige

OES Faculty Publications

Calculations based on recent observations indicate that approximately one third of the organic matter presently being buried in marine sediments may be of terrestrial origin, with the majority of this terrestrial organic matter (TOM) burial occurring in muddy, deltaic sediments. These calculations further suggest that the remineralization of terrestrial organic matter in the oceans is also much less efficient than that of marine organic matter. These two underappreciated observations have important implications in terms of our understanding of the controls on the global carbon cycle. From a paleoceanographic perspective, the results presented here also suggest that changes in TOM burial …

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Iron In The Sargasso Sea (Bermuda Atlantic Time-Series Study Region) During Summer: Eolian Imprint, Spatiotemporal Variability, And Ecological Implications, Peter N. Sedwick, T. M. Church, A. R. Bowie, C. M. Marsay, S. J. Ussher, K. M. Achilles, P. J. Lethaby, R. J. Johnson, M. M. Sarin, D. J. Mcgillicuddy Jan 2005

Iron In The Sargasso Sea (Bermuda Atlantic Time-Series Study Region) During Summer: Eolian Imprint, Spatiotemporal Variability, And Ecological Implications, Peter N. Sedwick, T. M. Church, A. R. Bowie, C. M. Marsay, S. J. Ussher, K. M. Achilles, P. J. Lethaby, R. J. Johnson, M. M. Sarin, D. J. Mcgillicuddy

OES Faculty Publications

We report iron measurements for water column and aerosol samples collected in the Sargasso Sea during July-August 2003 (summer 2003) and April-May 2004 (spring 2004). Our data reveal a large seasonal change in the dissolved iron (dFe) concentration of surface waters in the Bermuda Atlantic Time-series Study region, from ∼1-2nM in summer 2003, when aerosol iron concentrations were high (mean 10 nmol/m-3), to ∼0.1-0.2nM in spring 2004, when aerosol iron concentrations were low (mean 0.64 nmol/m-3). During summer 2003, we observed an increase of ∼0.6nM in surface water dFe concentrations over 13 days, presumably due to …

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Chemistry Of Surface Waters: Distinguishing Fine-Scale Differences In Sea Grass Habitats Of Chesapeake Bay, Emmanis Dorval, Cynthia M. Jones Jan 2005

Chemistry Of Surface Waters: Distinguishing Fine-Scale Differences In Sea Grass Habitats Of Chesapeake Bay, Emmanis Dorval, Cynthia M. Jones

OES Faculty Publications

We tested the hypothesis that the physical and chemical processes acting in sea grass habitats of the lower Chesapeake Bay are spatially structured and that dissolved elemental chemistry of sea grass-habitat surface waters have their own unique identity. We sampled surface waters from July to September 2001 in five sea grass habitats of the lower bay: Potomac, Rappahannock, York, Island (Tangier-Bloodsworth), and Eastern Shore. Dissolved Mg, Mn, Sr, and Ba concentrations were measured by sector field inductively coupled plasma-mass spectrometry. As expected, Mg, Sr, and Ba exhibited conservative behavior, but Mn exhibited nonconservative behavior along the salinity gradient. Spatial differences …

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Dirac Sextic Oscillator In The Constant Magnetic Field, Ramazan Koç, Mehmet Koca Jan 2005

Dirac Sextic Oscillator In The Constant Magnetic Field, Ramazan Koç, Mehmet Koca

Turkish Journal of Physics

We introduce a Dirac equation which reproduces the usual radial sextic oscillator potential in the non-relativistic limit. We determine its energy spectrum in the presence of the magnetic field. It is shown that the equation is solved in the context of quasi-exactly-solvable problems. The equation possesses hidden sl_2-algebra and the destroyed symmetry of the equation can be recovered for specific values of the magnetic field which leads to exact determination of the eigenvalues.

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Features Of Daily Variation In Cosmic Ray Intensity During High/Low Amplitude Events, Rajesh K. Mishra, Rekha Agarwal Mishra Jan 2005

Features Of Daily Variation In Cosmic Ray Intensity During High/Low Amplitude Events, Rajesh K. Mishra, Rekha Agarwal Mishra

Turkish Journal of Physics

A detailed study has been conducted on the long-term changes in the diurnal, semi-diurnal and tri-diurnal anisotropy of cosmic rays in terms of the high/low amplitude anisotropic wave train events (HAE/LAE) during the period 1981--94 using the neutron monitor data from the Deep River neutron monitoring station. In all, 38 HAE and 28 LAE cases have been studied. An inter-comparison of the first three harmonics during these events has been made so as to understand the basic reason causing the occurrence of these types of events. It has been observed that the phase of diurnal anisotropy shifts towards earlier hours …

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Standard Ubv Observations At The Çanakkale University Observatory (Çuo), Hi̇cran Bakiş, Volkan Bakiş, Osman Demi̇rcan, Edwin Budding Jan 2005

Standard Ubv Observations At The Çanakkale University Observatory (Çuo), Hi̇cran Bakiş, Volkan Bakiş, Osman Demi̇rcan, Edwin Budding

Turkish Journal of Physics

By using standard and comparison star observations carried out at different times of the year, at Çanakkale Onsekiz Mart University Observatory, we obtained the atmospheric extinction coefficients at the observatory. We also obtained transformation coefficients and zero-point constants for the transformation to the standard Johnson UBV system, of observations in the local system carried out with the SSP5A photometer and T40 telescope. The transmission curves and the mean wavelengths of the UBV filters as measured in the laboratory appear not much different from those of the standard Johnson system and found inside the transmission curve of the standard mean atmosphere.

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Some Physical Properties Of \Gamma Irradiated Ge_X(As_2te_3)_{100 - X} Chalcogenide System, Afaf Abdel-Aal, Bahiga Abdel-Hameed Mansour, Hoda Mohamed Eissa Jan 2005

Some Physical Properties Of \Gamma Irradiated Ge_X(As_2te_3)_{100 - X} Chalcogenide System, Afaf Abdel-Aal, Bahiga Abdel-Hameed Mansour, Hoda Mohamed Eissa

Turkish Journal of Physics

The effect of \gamma -radiation on the electrical conductivity, switching, and optical properties of the chalcogenide amorphous system Ge_x(As_2Te_3)_{100 - x} (where x = 0,1,5,10 atm %) have been studied. The results show that the radiation causes a shift of the optical gap,as well as a change in the electrical activation energy and the threshold voltage. As the \gamma -doses increase, the values of the allowed indirect optical energy gap E_{opt} for the different compositions decreases and the tail energy width increases.

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Photoconductivity Of Selenium And Sulphur Doped A-Si:H Thin Films, Sanjeev Kumar Sharma, Himanshu Gupta, Rajendra Kumar, Ram Mohan Mehra Jan 2005

Photoconductivity Of Selenium And Sulphur Doped A-Si:H Thin Films, Sanjeev Kumar Sharma, Himanshu Gupta, Rajendra Kumar, Ram Mohan Mehra

Turkish Journal of Physics

This paper presents a study of photoconductivity of S- and Se-doped a-Si:H as a function of composition and temperature. Temperature dependence of photoconductivity of the films was measured under the illumination of white light at 100~mW/cm^2. The room temperature photoconductivity for the same doping concentration of 10^{-4} (to develop H_2Se/SiH_4 and H_2S/SiH_4) is found to be higher in Se-doped -- than S-doped -- a-Si:H film due to a low defect density. From the measurement of intensity dependence of photoconductivity, it is found that the addition of Se and S changes the recombination mechanism from monomolecular, for low-doped films, to bimolecular …

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Air Moisture Sensing Properties Of Zncr_2o_4--K_2cro_4 Composites, Neşe Kavasoğlu, Murat Bayhan Jan 2005

Air Moisture Sensing Properties Of Zncr_2o_4--K_2cro_4 Composites, Neşe Kavasoğlu, Murat Bayhan

Turkish Journal of Physics

Crystalline structure, surface morphology and the response to air moisture of ceramic system of composition ZnCr_2O_4 - K_rCrO_4 formed by solid state reaction at elevated temperatures were investigated. The fired ceramic body, which proved to be mainly constructed from about 1 \mu m sized ZnCr_2O_4 spinel grains, was found to be porous. The humidity sensing behaviour of the sensors reveals that the electrical conduction is protonic and is controlled through the thin layers of water adsorbed on the surface of the grains, with charge transfer to the electrodes. Only the material containing 20\% K_2CrO_4 in ZnCr_2O_4 exhibited an exponential behaviour …

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Physical Properties Of Holmium Promoted Superconductivity In Nd-Doped Ybco Ht_C-Superconductors, Morsy Abou Sekkina, Abdul Raouf Tawfik, Osama Hemeda, Mohamad Ahmad Taher Dawoud, Samy El-Attar Jan 2005

Physical Properties Of Holmium Promoted Superconductivity In Nd-Doped Ybco Ht_C-Superconductors, Morsy Abou Sekkina, Abdul Raouf Tawfik, Osama Hemeda, Mohamad Ahmad Taher Dawoud, Samy El-Attar

Turkish Journal of Physics

Samples of the nominal composition (Y_{0.5}Nd_{0.5-x}Ho_x) Ba_2Cu_3O_{7- \delta} , 0 \le x \le 0.5, have been prepared using the conventional solid state reaction. The effect of holmium and neodymium substitution on electrical resistivity, transition temperature T_c, lattice parameters, size of crystallite and grain size has been investigated. X-ray diffraction, electron micro-probe, scanning electron microscope and IR spectra, have been used in our investigation. The results show that the transition temperature T_c, electron-hole jump rate and lattice parameters (a, b) have minimum values at x = 0.2, while c increases to maximum at x = 0.2. The size of crystallite, the …

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Study Of Density Of Localized States In A-Se_{100 - X}Sb_X Films By Space Charge Limited Conduction Measurements, V. S. Kushwaha, Santosh Kumar, A. Kumar Jan 2005

Study Of Density Of Localized States In A-Se_{100 - X}Sb_X Films By Space Charge Limited Conduction Measurements, V. S. Kushwaha, Santosh Kumar, A. Kumar

Turkish Journal of Physics

The present paper reports dc conductivity measurements at high electric fields in vacuum evaporated a-Se_{1 - x}Sb_x (x = 0, 0.02, 0.04, 0.06) thin films. At high fields (~ 10^4 V .cm^{-1}), current can be modelled by the theory of space charge-limited conduction in the case of uniform distribution of localised states in the mobility gap of these materials. The addition of Sb in Se results in an increase in the density of localised states.

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Dielectric Properties Of Industrial Polymer Composite Materials, Muhammad Akram, Athar Javed, Tasneem Zahra Rizvi Jan 2005

Dielectric Properties Of Industrial Polymer Composite Materials, Muhammad Akram, Athar Javed, Tasneem Zahra Rizvi

Turkish Journal of Physics

Frequency and temperature dependence of dielectric constant \varepsilon' and dielectric loss \varepsilon" in pure polyester resin and polymer composites with various types of glass fiber are studied in the frequency range 330 Hz-3 MHz and in the temperature range 25-150 °C. The experimental results show that \varepsilon' and \varepsilon'' increased with the addition of glass fiber in polyester resin. The value of \varepsilon' decreased with increasing frequency, which indicates that the major contribution to the polarization comes from orientation polarization. Dielectric loss peaks were also observed in the composite materials at high temperature due to T_g of polyester. The value …

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