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Top 20 Most Read Articles
August 2011
The 20 articles with the most full-text downloads during the month, in descending order.
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Characterization of ultra-thin oxides using electrical C-V and I-V measurements AIP Conf. Proc. 449, pp. 235-239; doi:http://dx.doi.org/10.1063/1.56801 (5 pages) Online Publication Date: 27 March 2008
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The measurement of electrical parameters from capacitance-voltage (C-V) and current-voltage (I-V) curves provides a fast means of characterizing oxides in MOS capacitors or transistor structures. For ultra-thin oxides (<2 nm), conventional, well-established techniques must be reconsidered and modified due to several increasingly important physical effects including polysilicon depletion and surface quantum mechanical effects. In this work these effects have been incorporated into a rapid analysis program for extracting ultra-thin oxide parameters from measured C-V and I-V data. The technique uses a physically based model of structure charge and potential combined with a non-linear least squares fitting technique to extract device parameters. © 1998 American Institute of Physics. |
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Fundamentals of Radiation Dosimetry AIP Conf. Proc. 1345, pp. 5-23; doi:http://dx.doi.org/10.1063/1.3576156 (19 pages) Online Publication Date: 11 July 2011
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The basic concepts of radiation dosimetry are reviewed on basis of ICRU reports and text books. The radiation field is described with, among others, the particle fluence. Cross sections for indirectly ionizing radiation are defined and indicated is how they are related to the mass energy transfer and mass energy absorption coefficients. Definitions of total and restricted mass stopping powers of directly ionizing radiation are given. The dosimetric quantities, kerma, absorbed dose and exposure together with the relations between them are discussed in depth. Finally it is indicated how the absorbed dose can be measured with a calorimeter by measuring the temperature increase and with an ionisation chamber measuring the charge produced by the ionizing radiation and making use of the Bragg‐Gray relation. |
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FREDHOLM‐VOLTERRA INTEGRAL EQUATION WITH A GENERALIZED SINGULAR KERNEL AND ITS NUMERICAL SOLUTIONS AIP Conf. Proc. 1309, pp. 33-46; doi:http://dx.doi.org/10.1063/1.3525135 (14 pages) Online Publication Date: 3 December 2010
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In this paper, the existence and uniqueness of solution of the Fredholm‐Volterra integral equation (F‐VIE), with a generalized singular kernel, are discussed and proved in the spaceL2(Ω)×C(0,T). The Fredholm integral term (FIT) is considered in position while the Volterra integral term (VIT) is considered in time. Using a numerical technique we have a system of Fredholm integral equations (SFIEs). This system of integral equations can be reduced to a linear algebraic system (LAS) of equations by using two different methods. These methods are: Toeplitz matrix method and Product Nyström method. A numerical examples are considered when the generalized kernel takes the following forms: Carleman function, logarithmic form, Cauchy kernel, and Hilbert kernel. |
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AIP Conf. Proc. 1345, pp. 1-1; doi:http://dx.doi.org/10.1063/1.3576154 (1 page) Online Publication Date: 11 July 2011
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Advanced Semiconductor Dosimetry in Radiation Therapy AIP Conf. Proc. 1345, pp. 48-74; doi:http://dx.doi.org/10.1063/1.3576159 (27 pages) Online Publication Date: 11 July 2011
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Modern radiation therapy is very conformal, resulting in a complexity of delivery that leads to many small radiation fields with steep dose gradients, increasing error probability. Quality assurance in delivery of such radiation fields is paramount and requires real time and high spatial resolution dosimetry. Semiconductor radiation detectors due to their small size, ability to operate in passive and active modes and easy real time multichannel readout satisfy many aspects of in vivo and in a phantom quality assurance in modern radiation therapy. Update on the recent developments and improvements in semiconductor radiation detectors and their application for quality assurance in radiation therapy, based mostly on the developments at the Centre for Medical Radiation Physics (CMRP), University of Wollongong, is presented. |
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Fundamentals of Materials, Techniques, and Instrumentation for OSL and FNTD Dosimetry AIP Conf. Proc. 1345, pp. 274-302; doi:http://dx.doi.org/10.1063/1.3576173 (29 pages) Online Publication Date: 11 July 2011
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The optically stimulated luminescence (OSL) technique has already become a successful commercial tool in personal radiation dosimetry, medical dosimetry, diagnostic imaging, geological and archeological dating. This review briefly describes the history and fundamental principles of OSL materials, methods and instrumentation. The advantages of OSL technology and instrumentation in comparison with thermoluminescent technique are analyzed. Progress in material and detector engineering has allowed new and promising developments regarding OSL applications in the medical field. Special attention is dedicated to Al2O3:C as a material of choice for many dosimetric applications. Different aspects of OSL theory, materials optical and dosimetric properties, instrumentation, and data processing algorithms are described. The next technological breakthrough was done with Fluorescent Nuclear Track Detectors (FNTD) that have some important advantages in measuring fast neutron and high energy heavy charge particles that have become the latest tool in radiation therapy. New Mg‐doped aluminum oxide crystals and novel type of imaging instrumentation for FNTD technology are discussed with regard to application in mixed neutron‐gamma fields, medical dosimetry and radiobiological research. |
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Diamond and Cubic Boron Nitride: Properties, Growth and Applications AIP Conf. Proc. 1292, pp. 191-196; doi:http://dx.doi.org/10.1063/1.3518293 (6 pages) Online Publication Date: 15 November 2010
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Since their first synthesis, cubic boron nitride (c‐BN) and diamond thin films have triggered a vivid interest in these wide band gap materials for many different applications. Because of superior properties, c‐BN and diamond can be applied in optic, electronic and acoustic for high performances devices. In this discussion, we first describe briefly the properties of c‐BN and diamond and we review both the growth techniques and the progresses achieved in the synthesis of c‐BN and diamond, and in a second part, characteristics of new c‐BN and diamond UV detectors for solar observation are reported. These photo‐detectors present extremely low dark current, high breakdown voltage, high responsivity and stability under UV irradiation. Finally, diamond based acoustic devices and sensors are presented. High frequency acoustic wave devices can be design for high frequency filtering or sensing applications. Diamond∕AlN micro‐cantilevers are excellent platform for sensor applications. |
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Electrical conductivity in inhomogeneous media AIP Conf. Proc. 40, pp. 2-45; doi:http://dx.doi.org/10.1063/1.31150 (44 pages) Online Publication Date: 9 July 2008
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The history of this field is reviewed, with emphasis on the relationship to the development of molecular field concepts in dielectric theory, in the last century, and with emphasis on the relationship to the study of disordered structures, in recent decades. A few of the many methods for calculating effective conductivities will be presented and discussed. One of these is based on the direct macroscopic application of the Clausius‐Mossotti relationship. In that connection we emphasize the shortcomings of the commonly accepted Lorentz derivation for the internal field and restate a less well known existing alternative derivation. The symmetrical and unsymmetrical effective medium theories of Bruggeman are presented. Connection is made to transport in randomly chosen resistor networks, to percolation threshold problems, and to transport in magnetic fields in the presence of inhomogeneities. Two more specialized topics are also discussed. One of these is the variability in field effect transistor thresholds arising from the limited size of the samples in which threshold is determined by the onset of percolation. The other specialized topic: The occurrence of strong spatial inhomogeneities in fields and currents in metals, in the presence of lattice defects, even though the mean free path is large compared to the extent of the defect. |
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Metrology for Emerging Materials, Devices, and Structures: The Example of Graphene AIP Conf. Proc. 1173, pp. 3-11; doi:http://dx.doi.org/10.1063/1.3251256 (9 pages) Online Publication Date: 14 October 2009
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New switches are being designed based on carrier spin, excitons, and other properties. Graphene is considered a strong candidate for many of these applications. New phenomena abound at nanoscale dimensions, and graphene is no exception. Quantum confinement impacts materials properties and measurement itself. Berry Phase corrections to carrier transport measurements are widely recognized. New materials such as graphene are difficult to find, manipulate, and measure. One key question is the number of graphene layers in a sample and the stacking of multilayer samples. Multiple characterization methods are necessary including transmission electron microscopy (TEM), Low Energy Electron Microscopy (LEEM), nano‐Raman, and several scanned probe methods. Multislice simulations are a useful guide in determining TEM capability and imaging conditions. Initial simulation work points to the ability to distinguish stacking patterns. Recent work indicates that LEEM can determine the number of layers and the morphology of a graphene sample.[1] Raman provides an excellent means of determining the number of layers in a stack of graphene. Single electron transistors have mapped electron‐hole puddles across a sample area.[2] Quantum confinement and Berry Phase corrections are two examples of quantum phenomena that alter the properties of nano‐scale structures.[3] Optical and electrical properties must be understood before they are measured. This paper will cover the research and development of metrology for CMOS Extension and Beyond CMOS using graphene as an example. |
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Medical Radiation Dosimetry: Concepts and Needs AIP Conf. Proc. 1345, pp. 24-35; doi:http://dx.doi.org/10.1063/1.3576157 (12 pages) Online Publication Date: 11 July 2011
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Radiation is used widely used in medicine for diagnostic and therapeutic applications. Both the desired effects and the potential detrimental side effects depend on the radiation dose delivered. As such it is essential to determining the radiation dose received by patients as accurately as needed to optimise the radiation procedure. Solid state dosimeters are increasingly used in medicine because of their small physical size, high sensitivity and usually low cost. Combining multiple detectors allows the detection of radiation dose distributions, an application where the distinction between radiation dosimeter and image detector starts to blur. Given the rapid development of detector technology it can be expected that the utilisation of solid‐state dosimeters in medicine will continue to increase. |
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Radiochromic Film Dosimetry and its Applications in Radiotherapy AIP Conf. Proc. 1345, pp. 75-99; doi:http://dx.doi.org/10.1063/1.3576160 (25 pages) Online Publication Date: 11 July 2011
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Radiochromic film can be a fast and inexpensive means for performing accurate quantitative radiation dosimetry. The development of new radiochromic compositions that have greater dose sensitivity and fewer environmental dependencies has led to an ever increasing use of the film in radiotherapy applications. In this report the various physical and dosimetric properties of radiochromic film are presented and the strategies to adequately manage these properties when using radiochromic film for radiotherapy applications are discussed. |
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The Principles of Phototransferred Thermoluminescence AIP Conf. Proc. 1345, pp. 323-334; doi:http://dx.doi.org/10.1063/1.3576175 (12 pages) Online Publication Date: 11 July 2011
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The principles of phototransferred thermoluminescence (PTTL) are described, and some of the basic theoretical ideas underlying this technique are presented. It is demonstrated that the PTTL efficiency is dependent on the photon energy as well as on the activation energies of the various traps involved in the process. A simple two‐traps‐one‐recombination‐center model is capable of predicting a variety of different PTTL behaviors, some already were observed experimentally. |
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Strongly Correlated Electron Materials: Dynamical Mean‐Field Theory and Electronic Structure AIP Conf. Proc. 715, pp. 3-74; doi:http://dx.doi.org/10.1063/1.1800733 (72 pages) Online Publication Date: 13 September 2004
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These are introductory lectures to some aspects of the physics of strongly correlated electron systems. I first explain the main reasons for strong correlations in several classes of materials. The basic principles of dynamical mean‐field theory (DMFT) are then briefly reviewed. I emphasize the formal analogies with classical mean‐field theory and density functional theory, through the construction of free‐energy functionals of a local observable. I review the application of DMFT to the Mott transition, and compare to recent spectroscopy and transport experiments. The key role of the quasiparticle coherence scale, and of transfers of spectral weight between low‐ and intermediate or high energies is emphasized. Above this scale, correlated metals enter an incoherent regime with unusual transport properties. The recent combinations of DMFT with electronic structure methods are also discussed, and illustrated by some applications to transition metal oxides and f‐electron materials. © 2004 American Institute of Physics |
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WAVE PROPAGATION IN ELASTIC MEDIUM WITH HETEROGENEOUS QUADRATIC NONLINEARITY AIP Conf. Proc. 1335, pp. 43-50; doi:http://dx.doi.org/10.1063/1.3591838 (8 pages) Online Publication Date: 21 June 2011
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This paper studies the one‐dimensional wave propagation in an elastic medium with spatially non‐uniform quadratic nonlinearity. Two problems are solved analytically. One is for a time‐harmonic wave propagating in a half‐space where the displacement is prescribed on the surface of the half‐space. It is found that spatial non‐uniformity of the material nonlinearity causes backscattering of the second order harmonic, which when combined with the forward propagating waves generates a standing wave in steady‐state wave motion. The second problem solved is the reflection from and transmission through a layer of finite thickness embedded in an otherwise linearly elastic medium of infinite extent, where it is assumed that the layer has a spatially non‐uniform quadratic nonlinearity. The results show that the transmission coefficient for the second order harmonic is proportional to the spatial average of the nonlinearity across the thickness of the layer, independent of the spatial distribution of the nonlinearity. On the other hand, the coefficient of reflection is proportional to a weighted average of the nonlinearity across the layer thickness. The weight function in this weighted average is related to the propagating phase, thus making the coefficient of reflection dependent on the spatial distribution of the nonlinearity. Finally, the paper concludes with some discussions on how to use the reflected and transmitted second harmonic waves to evaluate the variance and autocorrelation length of nonlinear parameter β when the nonlinearity distribution in the layer is a stochastic process. |
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AIP Conf. Proc. 1345, pp. 187-206; doi:http://dx.doi.org/10.1063/1.3576167 (20 pages) Online Publication Date: 11 July 2011
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The parameters, Dth, Dc, Dm, f(D) and f(D)max., describing the characteristics of TL dose response are defined and a short survey of the literature concerning the dose response of the major TL glow peaks in LiF:Mg,Ti (TLD‐100), peaks 5, 7 and 8 is presented. The experimental parameters and details of the analysis affecting the dose response are outlined. The importance of theoretical interpretation of the dose response in the determination of the dose response parameters is demonstrated and an in‐depth introduction to the Unified Interaction Model is described. The dose response as a function of photon energy is analysed for peaks 5, 7 and 8 and the impact of the method of data analysis on the description of f(D) and especially the determination of Dc is emphasized. |
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Dosimetry of Radiopharmaceuticals for Diagnostic and Therapeutic Nuclear Medicine AIP Conf. Proc. 1345, pp. 36-47; doi:http://dx.doi.org/10.1063/1.3576158 (12 pages) Online Publication Date: 11 July 2011
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A standard formalism for radionuclide internal radiation dosimetry was developed in the 1960s and continues to be refined today. Early work was based on a mathematical phantom but this is being replaced by phantoms developed from whole‐body CT scans to give more realistic dose estimates. The largest contributors to the uncertainties in these dose estimates are the errors associated with in vivo activity quantitation, the variability of the biokinetics between patients and the limited information that can be obtained on these kinetics in individual patients. Despite these limitations, pre‐treatment patient‐specific dosimetry is being increasing used, particularly to limit the toxicity to non‐target organs such as the bone marrow. |
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Nanodosimetry: Principle and Current Status AIP Conf. Proc. 1345, pp. 249-261; doi:http://dx.doi.org/10.1063/1.3576171 (13 pages) Online Publication Date: 11 July 2011
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Due to the success of theoretical track structure Monte Carlo simulations, showing that features of ionization patterns on the nanometer level are important for the biological effectiveness of ionizing radiation, several new methods for experimental track structure investigations have been developed in recent years. These methods all use the principle of density scaling in low‐pressure gas to probe track structure in macroscopic dimensions, ideally with single‐ionization resolution. The new field of experimental track structure investigation, which has been called nanodosimetry, can be approached in two ways: (1) the number of ionizations in a defined, ideally wall‐less, sensitive volume is registered per single primary particle and cluster size distributions are obtained, or (2) the full track structure of an ion track segment is “imaged”. Existing nanodosimetric methods are based on the first approach, but a track structure imaging detector is currently under development at Loma Linda University. This contribution will review the principle and existing technical approaches to nanodosimetry and will give an outlook on future developments and applications. |
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AIP Conf. Proc. 1335, pp. 1-3; doi:http://dx.doi.org/10.1063/1.3595982 (3 pages) Online Publication Date: 21 June 2011
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Logarithmic decay in a two‐component model AIP Conf. Proc. 708, pp. 559-564; doi:http://dx.doi.org/10.1063/1.1764224 (6 pages) Online Publication Date: 14 June 2004
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The correlation functions near higher‐order glass‐transition singularities are discussed for a schematic two‐component model within the mode‐coupling theory for ideal glass‐transitions. The correlators decay in leading order like −ln(t/τ) and the leading correction introduces characteristic convex and concave patterns in the decay curves. The time scale τ follows a Vogel‐Fulcher type law close to the higher‐order singularities. © 2004 American Institute of Physics |
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Implementation Of Fuzzy Automated Brake Controller Using TSK Algorithm AIP Conf. Proc. 1324, pp. 1-3; doi:http://dx.doi.org/10.1063/1.3526193 (3 pages) Online Publication Date: 3 December 2010
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In this paper an application of Fuzzy Logic for Automatic Braking system is proposed. Anti‐blocking system (ABS) brake controllers pose unique challenges to the designer: a) For optimal performance, the controller must operate at an unstable equilibrium point, b) Depending on road conditions, the maximum braking torque may vary over a wide range, c) The tire slippage measurement signal, crucial for controller performance, is both highly uncertain and noisy. A digital controller design was chosen which combines a fuzzy logic element and a decision logic network. The controller identifies the current road condition and generates a command braking pressure signal Depending upon the speed and distance of train. This paper describes design criteria, and the decision and rule structure of the control system. The simulation results present the system’s performance depending upon the varying speed and distance of the train. |
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GBR - Devon
Chair and Lecturer (2 posts)
Sandia National Laboratories
US - NM - Albuquerque
Post Doc – Nuclear/ Nanoparticle Materials
Syracuse University
US - NY - Syracuse
Postdoc in Experimental CM Physics
University of Rochester
US - NY - Rochester
Biomedical Optics
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