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Search Results: 1 - 10 of 321692 matches for " W. B?k "
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Characterization of Ba1-xNaxTi1-xNbxO3
W. Bk
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: The purpose of this paper was characterization of electric properties of polycrystalline nanograin solidsolution of Ba1-xNaxTi1-xNbxO3, x = 0.65 (BNTN65) within the temperature range 153 K-573 K.Design/methodology/approach: The dielectric spectroscopy method (DSM) has been applied to measuredielectric and electric parameters within frequency range from 20 Hz to 1 MHz and within the temperature rangeof diffused ferroelectric – paraelectric transition and above within paraelectric state.Findings: Analysis of temperature and frequency dependences of real (ε’) and imaginary (ε”) parts of dielectricpermittivity and electric modulus provided the new details about specific features of paraelectric properties ofceramic BNTN65 sample. They involve weak relaxational diffused processes as well as dielectric losses. Specifictwo steps increase of ε’ values turned out to be frequency dependent and of thermal activated character.Research limitations/implications: Above specified new details of polarizability of paraelectric phase forceramic sample should be treated as a base for new modelling approach and quantitative description of polarclusters dependence on temperature and frequency.Originality/value: For the first time, details of polarizability of paraelectric phase, which are temperature andfrequency dependent in such specific manner were described.
Characteristics of phase transitions in Ba0.995Na0.005Ti0.995Nb0.005O3 ceramics
W. Bk
Archives of Materials Science and Engineering , 2009,
Abstract: Purpose: The purpose of this work was to prepare ceramic material BaTiO3 (BT) as well as solid solution of Ba1-xNaxTi1-xNbxO3 (for x = 0.005) (BNTN05) type and correlate their structural (polycrystalline) properties with phase transitions within the temperature range from 153 K to 473 K.Design/methodology/approach: The dielectric spectroscopy method has been applied to measure dielectric and electric parameters within the frequency from 20 Hz to 1 MHz.Findings: The measured dependences of: complex dielectric permittivity and its phase angle (between measuring voltage and current response) points out on complex phase transition character for both investigated materials. Experimental outcomes for BT are consistent with those already published. Achieved results in the case of BNTN05 are published here for the first time. They were correlated with those of BT as unmodified one. Phase transitions parameters of both materials were described by means of generalised Curie-Weiss rule including step of phase transition diffusivity. Small amount (x = 0.005) of NaNbO3 (NN) admixture makes sharp, classical transition of first order kind occurring in the case of BT, to be a diffusive one and shifted by about 20 K towards lower temperatures.Research limitations/implications: Further investigations should be carried out in a broaden frequency range (up to 1.8 GHz) in order to establish the influence of network dynamics on ferroelectric-paraelectric phase transition as well as others low–temperature phase transitions. In order to complete structural data of new BNTN05 material additional X-ray and calorimetric measurements will be performed.Originality/value: The same method and components were used for preparation of BT and new BNTN05 material. Thermally induced phase transitions, mutually related in both materials were measured and described.
Relaxor properties of Ba1-xNaxTi1-xNbxO3 at low temperatures
W. Bk
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: The purpose of this paper is to investigate ferroelectric relaxor behavior of polycrystalline solidsolutions of Ba1-xNaxTi1-xNbxO3 (for x = 0.3 and x = 0.4) at low temperatures (113 K - 473 K).Design/methodology/approach: The dielectric spectroscopy method has been applied to measure dielectricand electric parameters within the frequencies from 20 Hz to 1 MHz.Findings: Temperature dependences of real (ε’) and imaginary (ε”) parts of dielectric permittivity confirm relaxortype of polarization behavior for both investigated materials. Experimental findings are in good agreement withdata published in literature. Diffused phase transition of relaxor character is analysed in the terms of departurefrom Curie-Weiss rule. A dependence of the temperature related to the maximum of dielectric permittivity on thefrequency has activated character. Different thermal activation energies found for the investigated materials maybe related to their different microstructures.Research limitations/implications: Further investigations should be carried on in a broaden frequency range(up to 1.8 GHz) in order to establish an influence of network dynamics on ferroelectric-paraelectric phase transition.Originality/value: Relaxor behaviour in polycrystalline solid solution of Ba1-xNaxTi1-xNbxO3 (for x = 0.3 andx = 0.4) is described.
Study of the relaxor behaviour in Ba0.68Na0.32Ti0.68Nb0.32O3 ceramic
w. Bk
Journal of Achievements in Materials and Manufacturing Engineering , 2009,
Abstract: Purpose: The purpose of this work was to synthesize a new ceramic solid solution Ba0.68Na0.32Ti0.68Nb0.32O3 (BNTN32), as well as to measure and analyse its dielectric properties within the temperature range 123 K-473 K, where dielectrically active phase transition was supposed to occur.Design/methodology/approach: The new ceramic composition was prepared by means of conventional method. Dependence of phase transition features on temperature and frequency of measuring field were measured using dielectric spectroscopy method within the frequency range from 20 Hz to 1 MHz.Findings: The electric susceptibility along with temperature decrease generally rises up and has transient dispersion vanishing at about 230 K. At higher and low temperatures, frequency dependence of dispersion differs in character: at temperatures at ~400 K, low frequency values dominate. Dielectric energy losses are very high at ~high temperature, they decline down while temperature decrease, and at about 200 K range its frequency dependence is reversed and less scattered with maximum at ~150 K. The whole transition of ferroelectric - paraelectric (FE - PE) type can be described by means of Curie-Weiss law and it gets diffused character.Research limitations/implications: For modelling purposes the structure parameters of BNTN32 have to be measured by X-ray diffraction in order to establish the dielectric/structural activities of transitions taking place within used the temperature range. Additionally, dielectric measurements within broader frequency range up to 1.8 GHz will be performed.Originality/value: The new type of ceramic material was prepared with interesting dielectric properties. Dispersion reverse of energy losses activated thermally and low frequency memory of barium titanate (BT) transition effect visible at ~400 K is to be a subject of modelling further work.
A Study of Design Optimization Using Response Surface Analysis and Fabricaiton MEMS Probe Tip  [PDF]
K. B. Kim, J. W. Lee, S. J. Ha, Y. K. Cho, M. W. Cho
Journal of Applied Mathematics and Physics (JAMP) , 2015, DOI: 10.4236/jamp.2015.32030
Abstract:

In semiconductor manufacturing process, probe station that is testing equipment is important. Inspection step is for detecting defects on semiconductor before the packaging. Probe card is a part of probe station and contains probe tip that contacts to semiconductor. Through probe tip, it can inspect defects of semiconductor. In this paper, optimization method is used with response surface analysis to design MEMS type probe tip. And fabricating probe tip uses maskless lithography, electro-plating and lapping process.

Factors controlling upper tropospheric relative humidity
B. K rcher ,W. Haag
Annales Geophysicae (ANGEO) , 2004,
Abstract: Factors controlling the distribution of relative humidity in the absence of clouds are examined, with special emphasis on relative humidity over ice (RHI) under upper tropospheric and lower stratospheric conditions. Variations of temperature are the key determinant for the distribution of RHI, followed by variations of the water vapor mixing ratio. Multiple humidity modes, generated by mixing of different air masses, may contribute to the overall distribution of RHI, in particular below ice saturation. The fraction of air that is supersaturated with respect to ice is mainly determined by the distribution of temperature. The nucleation of ice in cirrus clouds determines the highest relative humdity that can be measured outside of cirrus clouds. While vertical air motion and ice microphysics determine the slope of the distributions of RHI, as shown in a separate study companion (Haag et al., 2003), clouds are not required to explain the main features of the distributions of RHI below the ice nucleation threshold. Key words. Atmospheric composition and structure (pressure, density and temperature; troposphere – composition and chemistry; general or miscellaneous)
Monte Carlo Study of Maghemite Nanoparticles
K. Adebayo,B. W. Southern
Physics , 2010,
Abstract: We consider a simple model of maghemite nanoparticles and study their magnetic properties using Monte Carlo methods. The particles have a spherical geometry with diameters ranging from 3 nm to 8 nm. The interior of the particles consists of core spins with exchange interactions and anisotropy given by the values in the bulk material. The outer layer of the particles consists of surface spins with weaker exchange interactions but an enhanced anisotropy. The thermal behaviour of the total, core and surface magnetizations are calculated as well as the hysteresis loops due to the application of an applied field. The effect of the surface anisotropy on the blocking temperature, the coercive and exchange bias fields is studied.
Topological aperiodicity for product systems over semigroups of Ore type
B. K. Kwasniewski,W. Szymanski
Mathematics , 2013,
Abstract: We prove a version of uniqueness theorem for Cuntz-Pimsner algebras of discrete product systems over semigroups of Ore type. To this end, we introduce Doplicher-Roberts picture of Cuntz-Pimsner algebras, and the semigroup dual to a product system of 'regular' C*-correspondences. Under a certain aperiodicity condition on the latter, we obtain the uniqueness theorem and a simplicity criterion for the algebras in question. These results generalize the corresponding ones for crossed products by discrete groups, due to Archbold and Spielberg, and for Exel's crossed products, due to Exel and Vershik. They also give interesting conditions for topological higher rank graphs and $P$-graphs, and apply to the new Cuntz C*-algebra $\mathcal{Q}_\mathbb{N}$ arising from the "$ax+b$"-semigroup over $\mathbb{N}$.
Structure and AC conductivity of polycrystalline Pb(Cd1/3Nb2/3)O3
W. Bk,C. Kajtoch,K. Mroczka,K. Wójcik
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: Purpose of this work was to determine crystalline structure and ac electric conductivity of polycrystalline sample Pb(Cd1/3Nb2/3)O3 (PCN) in paraelectric phase. Controversies involving uncertainties of phase transition character were the motivation of our experimental investigation: roentgenostructural, electron microscopy (SEM) and dielectric (ε’) as well as electric (σ’) spectroscopy.Design/methodology/approach: Polycrystalline PCN samples were prepared using hot pressing method. X-ray measurements had been performed with use of DRON3 apparatus (Cu Kα , monochromator: monocrystal LiF, at detector NaI side) with jump of 2Θ angle accounting for 0.02deg within a range 10-120deg. Structure images were made at room temperature with a use of electron microscope Philips SEM 525M. Dielectric measurements were made with a use of automatic measuring system Quatro Cryosystem 4.0 and Agilent Precision LCR meter HP4284A equipped with WinDETA 5.62 software Novocontrol. Before measurements, polycrystalline PCN samples were refreshed by annealing at 700 K. Next, electric measurements were carried out under cooling with 2 K/min speed.Findings: It was established that cubic phase is present within the whole range of temperatures (173 K-723 K) applied in our measurements. The polar component of the electric conductivity was dominate below the Tm temperature (Tm – temperature at which the maximal value of dielectric permittivity takes place). Above this temperature, activation energy (φ) is falling down, along increasing frequency of measuring field.Research limitations/implications: Changes of AC conductivity of PCN were interpreted in terms of polar regions properties evolution.Originality/value: Results obtained have broad the knowledge about phase transitions occurring without crystal structure change, but involving freezing of polar regions under cooling.
Measurement of motion corrected wind velocity using an aerostat lofted sonic anemometer
W. R. Stevens,W. Squier,W. Mitchell,B. K. Gullett
Atmospheric Measurement Techniques Discussions , 2013, DOI: 10.5194/amtd-6-703-2013
Abstract: An aerostat-lofted, sonic anemometer was used to determine instantaneous 3 dimensional wind velocities at altitudes relevant to fire plume dispersion modeling. An integrated GPS, inertial measurement unit, and attitude heading and reference system corrected the wind data for the rotational and translational motion of the anemometer and rotated wind vectors to a global North, West, Up coordinate system. Data were taken at rates of 10 and 20 Hz to adequately correct for motion of the aerostat. The method was applied during a prescribed forest burn. These data were averaged over 15 min intervals and used as inputs for subsequent dispersion modeling. The anemometer's orientation data are demonstrated to be robust for converting the wind vector from the internal anemometer reference system to the global reference system with an average bias between 5 and 7°. Lofted wind data are compared with sonic anemometer data acquired at 10 m on a mast located near the tether point of the aerostat and with local meteorological data.
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