bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon‐13 NMR spectroscopy. It was not always easy
Authors: Traficante Daniel D. 
Published: March 2007

AbstractThe development of carbon‐13 NMR spectroscopy is presented from a historical perspective. The problems that were associated with instrumental limitations are reviewed, as are experimental techniques used to circumvent or minimize them. Sweeping, instrument maintenance, probe modifications, proton decoupling, and time averaging are among the topics of discussion.
Uses of shaped pulses in NMR: A primer
Authors: McDonald Sylvia , Warren Warren S. 
Published: March 2007

AbstractThis is an overview of the effects of shaped radiofrequency pulses and instrumental requirements for pulse shaping. We summarize what is known in general about pulse shaping and the tradeoffs involved in choosing a pulse shape for specific experiments. We also discuss computerized optimization, which is the method used to derive most of the pulse shapes in common use, and present a program which optimizes pulse shapes for any desired excitation profile. We also summarize the current literature by listing representative papers with detailed and useful waveforms.
A new approach to avoid excessive numerical diffusion in Eulerian–Lagrangian methods
Authors: Younes A. , Fahs M. , Ackerer P. 
Published: March 2007

AbstractLumping is often used to avoid non‐physical oscillations for advection–dispersion equations but is known to add numerical diffusion. A new approach is detailed in order to avoid excessive numerical diffusion in Eulerian–Lagrangian methods when several time steps are used. The basic idea of this approach is to keep the same characteristics during all time steps and to interpolate only the concentration variations due to the dispersion process. In this way, numerical diffusion due to the lumping is removed at the end of each time step. The method is combined with the Eulerian–Lagrangian localized adjoint method (ELLAM) which is a mass conservative characteristic method for solving the advection–dispersion equation.Two test problems are modelled to compare the proposed method to the consistent, the full and the selective lumping approaches for linear and non‐linear transport equations. Copyright © 2007 John Wiley & Sons, Ltd.
Performing great and the purpose of performing better than others: on the recursiveness of the achievement goal adoption process
Authors: Van Yperen Nico W. , Renkema Lennart J. 
Published: March 2007

AbstractThe purpose of the present research is to complement and extend previous achievement goal research by emphasizing that great performance may serve as an antecedent of performance‐approach goal adoption, that is, the wish to outperform others. A consistent finding across the three studies is, indeed, that great (perceived) performance and high performance expectancies are associated with the adoption of performance‐approach goals. It is concluded that the process of goal adoption is a dynamic, recursive process in which performance attainment is most likely to operate as both an antecedent and a consequence of goal adoption. Copyright © 2007 John Wiley & Sons, Ltd.
Estimation of a two‐dimensional seismic compressional‐wave velocity distribution by iterative tomographic imaging
Authors: Zhu Xianhuai , McMechan George A. 
Published: March 2007

AbstractTwo‐dimensional velocity distributions may be estimated using iterative tomographic imaging. The medium is parameterized as a grid of small rectangular elements, each of which has constant (unknown) slowness (s); the data are refraction travel‐times (t) picked from the real data, which are transmitted between sources and recorders both located on the Earth's surface. Slowness estimation is performed by solution of the system of equations t = DsT where D is a matrix of ray segment lengths, and T denotes the vector transpose. The solution involves minimization of the difference between the real and predicted travel‐times and is equally applicable to under and over‐determined problems. As matrix D is very large it cannot be inverted directly, and a row‐action, simultaneous iterative reconstruction technique is used. Predicted travel‐times are obtained by vectorized ray tracing. Rays are updated every few iterations so that they are internally consistent with the velocity estimated by tomography. The wider the source and recording apertures, the greater the depths that can be imaged. Rays refracted at the shallowest depths contain independent constraints that cannot be replaced by increasing the amount of data refracted at greater depths.
Tomographic imaging in hydrocarbon reservoirs
Authors: Justice J. H. , Vassiliou A. A. , Singh S. , Logel J. D. , Hansen P. A. , Hall B. R. , Hutt P. R. , Solanki J. J. 
Published: March 2007

AbstractClastic reservoirs saturated with heavy oils have been observed to exhibit a marked relationship between velocity of propagation of acoustic waves and changes introduced by certain kinds of enhanced oil recovery procedures, including heating of the reservoir. This observation forms the basis for a method of monitoring the changes which occur in the reservoir when these enhanced oil recovery (EOR) procedures are used. New developments in diffraction tomographic imaging allow accurate, high‐resolution images to be obtained in hydrocarbon reservoirs, clearly delineating the zones affected by these enhanced oil recovery procedures. When both compressional and shear wave data can be obtained, additional physical parameters such as Poissons ratio can be reconstructed.
Algebraic methods in 3‐d motion estimation from two‐view point correspondences
Authors: Netravali A. N. , Huang T. S. , Krishnakumar A. S. , Holt R. J. 
Published: March 2007

AbstractWe consider the problem of determining motion (3‐D rotation and translation) of rigid objects from their images taken at two time instants. We assume that the locations of the perspective projection on the image plane of n points from the surface of the rigid body are known at two time instants. For n = 5, we show that there are at most ten possible motion values (in rotation and translation) and give many examples. For n ≥ 6, we show that the solution is generally unique. We derive a variety of necessary and sufficient conditions a solution must satisfy, show their equivalence, and use algebraic geometry to derive the bound on the number of solutions. A homotopy method is then used to compute all the solutions. Several examples are worked out and our computational experience is summarized.
On a problem in radiotherapy: Questions of non‐negativity
Authors: Cormack A. M. , Quinto Eric Todd 
Published: March 2007

AbstractA well‐known result is used to show that if g is a non‐negative function and the radiation field, f, is its Radon transform, the dose field, f̂, is the convolution of g with (1/πr) and is necessarily non‐negative. Simple series expansions of f and f̂ are given, and the series for f is written as a finite Fourier series. Known properties of finite Fourier series are used to seek, fruitlessly, for useful conditions on the coefficients to ensure the non‐negativity of f.
New spherical PET design with fresnel aperture orientation
Authors: Cho Z. H. , Kim Y. S. , Hilal S. K. , Kim Y. H. 
Published: March 2007

AbstractA new spherical PET using Fresnel aperture is being designed, and construction is in progress. In the new design, the original spherical geometry is modified to accommodate a more flexible gantry construction and data processing while preserving the focused geometry of the original design. The performance of this new Fresnel aperture‐SPET (F‐SPET) is expected to follow closely with that of the original S‐PET design. An analysis of an F‐SPET designed with nine modular layers, with each modular layer being four rings, was performed in terms of the counting statistics and solid angle and compared with the original S‐PET as well as the conventional cylindrical PET. According to the simulation results, the sensitivity gain of the Fresnel aperture‐SPET remains a factor of 2 over the equivalent cylindrical system and has nearly the same performance as the original S‐PET, while offering a simpler means in construction and data handling for the image reconstruction.
The nuclear magnetic resonance imaging of short t2 material using solid echoes
Authors: Attard J. J. , McDonald P. J. 
Published: March 2007

AbstractThe application of solid echoes to the nuclear magnetic resonance (NMR) imaging of short T2 materials is demonstrated by means of two‐dimensional (19F) images. A closed‐form, exact and generally applicable expression for solid echo imaging is derived and a procedure for on‐the‐fly data analysis given.
Beam profiling by vibrating knife edge: Implications for near‐field optical scanning microscopy
Authors: Korpel A. , Mehrl D. J. , Samson S. 
Published: March 2007

AbstractWe show theoretically and experimentally that beam profiling with a vibrating knife exhibits spatial resolution equal to the knife‐edge excursion. We discuss the implications of this for near‐field optical scanning microscopy, propose an extension of the method to two dimensions, and calculate impulse response, step response, and spatial frequency response.
Microwave imaging of moving objects
Authors: Li Hsueh‐Jyh , Yang Sheng‐Hui , Liu Ta‐Yung , Yen Shih‐Liang , Shen Yuhsyen , Farhat Nabil H. 
Published: March 2007

AbstractMicrowave images for objects in motion can be obtained with quality as good as those obtained in the stationary case if the signal waveforms, data acquisition systems, and image reconstruction algorithms are cleverly designed. The principle of imaging for objects in motion is to eliminate the gross Doppler effect of the echo signals and only reserve the differential Doppler information to reconstruct the image. Accordingly, requirements for parameters of the signal waveform are established. Two steps are involved in the image reconstruction algorithm: range alignment and phase compensation. Focused images of complex‐shaped targets with simulated motion have been obtained experimentally.
Visible and infrared mapping spectrometer for exploration of comets, asteroids, and the saturnian system of rings and moons
Authors: Juergens David W. , Duval James E. , Lockhart Robert F. , Langevin Yves , Formisano Vittorio , Bellucci Giancarlo 
Published: March 2007

AbstractThe science objectives and system design for a Visible and Infrared Mapping Spectrometer (VIMS), an imaging spectrometer for planetary exploration, are described. The instrument development is the result of a collaboration between scientists and engineers from the United States, Italy, and France. NASA has selected VIMS as a facility instrument for the Comet Rendezvous Asteroid Flyby (CRAF) Mission, and as a candidate facility instrument for the Cassini Mission to explore Saturn and its rings and moons. (A facility instrument is provided by the project for the use of a science team which was selected on the basis of individual competitive science proposals.) VIMS covers the spectral range from 0.35 to 5.2 μm with a nominal spatial resolution of 0.5 milliradians (pixel size) and spectral resolutions (spectral width) of 7 nm at 0.35–1.0‐ μm wavelength and 16nm at 1.0–5.2‐μm wavelength. The nominal pixel size is 0.5 × 0.5 mrad2. The two separate missions are scheduled to be launched by NASA from the Eastern Test Range at Cape Canaveral, Florida, using the Titan IV Launch Vehicle. The planned launch date for the Cassini Mission is November 1995. The planned launch date for the CRAF Mission is February 1996.
Moderate resolution imaging spectrometer‐tilt (modis‐t)
Authors: Magner Thomas J. , Salomonson V. V. 
Published: March 2007

AbstractThe Moderate Resolution Imaging Spectrometer‐Tilt (MODIS‐T) instrument is being constructed for flight on the Earth Observing System (EOS). It is an imaging spectrometer utilizing a grating‐type, reflecting Schmidt optical design that must provide a 1.1‐km spatial resolution at nadir from a spacecraft altitude of 705 km with a 1500‐km cross‐track swath and a ±50° fore and aft tilt capability. The instrument is required to cover the wavelength range from 400 to 880 nm in approximately 15‐nm steps with less than 2.3% instrument‐induced polarization. The absolute radiometric accuracy must be at least 5% over the full dynamic range of the instrument.
Spaceborne imaging radars
Authors: Elachi Charles 
Published: March 2007

AbstractThe Seasat and Shuttle imaging radars flown in the 1970s and 1980s established a strong scientific and technical base for a number of imaging radars that are flying or under development. Recent advances in understanding wave‐surface interactions, utilization of multispectral and polarimetric data, as well as advances in microwave and electronic technology, are allowing the development of a new generation of multiparameter imaging radars that will allow quantitative measurements of surface and near‐surface geophysical parameters and monitoring of surface processes over long‐term duration. This article is an overview of spaceborne imaging radars presently flying or under development.
Character recognition via critical points
Authors: Shchepin E. V. , Nepomnyashchii G. M. 
Published: March 2007

AbstractA new approach to image coding, based on ordinate‐preserving plane homoeomorphism invariants, is presented. A critical‐points graph bearing full information on these invariants is outlined. Appropriate noise‐smoothing techniques are developed. The proposed method has been implemented and tested with a new optical character recognition program, CRIPT.
Comparison of the born iterative method and tarantola's method for an electromagnetic time‐domain inverse problem
Authors: Moghaddam M. , Chew W. C. , Oristaglio M. 
Published: March 2007

AbstractTwo methods of solving the nonlinear two‐dimensional electromagnetic inverse scattering problem in the time domain are considered. These are the Born iterative method and the method originally proposed by Tarantola for the seismic reflection inverse problems. The former is based on Born‐type iterations on an integral equation, whereby at each iteration the problem is linearized, and its solution is found via a regularized optimization. The latter also uses an iterative method to solve the nonlinear system of equations. Although it linearizes the problem at each stage as well, no optimization is carried out at each iteration; rather the problem as a whole is posed as a (regularized) optimization. Each method is described briefly and its computational complexity is analyzed. Tarantola's method is shown to have a lower numerical complexity compared to the Born iterative method for each iteration, but in the examples considered, required more iterations to converge. Both methods perform well when inverting a smooth profile; however, the Born iterative method gave better results in resolving localized point scatterers.
Data processing system for nuclear medicine images
Authors: Kuba A. , Makay A. , Máté E. , Csernay L. 
Published: March 2007

AbstractA software system (MicroSegams) is described which is able to acquire, store, present, and process nuclear medicine images. The most important basic procedures (e.g., image acquisition from a gamma camera, selection of a study from the catalogue, drawing regions of interest, etc.) and complete clinical procedures (e.g., renography, brain perfusion, etc.) can be activated directly from the system menu by mouse. The language sLan (a subset of programming language C containing more than 200 elementary functions) can also be used to write new procedures to be interpreted or compiled. The system is offered as a basic tool for the performance of static, dynamic, gated, or tomographic investigations in clinical practice.
A fourier‐transforming coded aperture
Authors: Patt B. E. , Wade G. , Richardson J. M. 
Published: March 2007

AbstractA Fourier‐transforming coded aperture can be synthesized with a pair of two‐dimensional detector arrays, each preceded by a properly designed sequence of two Gabor‐zone plates. The coded image falling on one of the arrays corresponds to the cosine transform of the object. The coded image falling on the other array corresponds to the sine transform. Thus the Fourier transform of the object can be formed by using the first coded image as the real part, and the second coded image as the imaginary part, of the Fourier transform. Fourier‐transforming coded apertures of this type are capable of producing better resolution than spatial‐domain apertures. Although the system described in this article is specifically applied to a gamma‐ray camera, such a system is generally applicable to a wide varioty of noncoherent imagers.©1993 John Wiley & Sons Inc
Self‐calibration of large phased‐array antennas for radar
Authors: Steinberg Bernard D. 
Published: March 2007

AbstractSelf‐calibration of a phased antenna array is required when distortions in the array are not known a priori and cannot be measured, or when turbulence in the propagation medium perturbs the radiation field. Two types of self‐calibration procedures are discussed that have proved successful in experimental high‐resolution two‐dimensional microwave radar imaging. Each extracts information from the backscattered reradiation field to deduce a compensating weight vector for the phased array antenna. The first depends upon the presence of a strong reflector in the field of view of the transmitter. The second calibrates the array from correlation estimates of wavefront samples in the array. The basic algorithm in each group is described, along with two more sophisticated algorithms in the latter class. Two‐dimensional radar images of airplanes are shown with resolution comparable to human vision. The performance of each algorithm and comparisons between them are illustrated by these images of targets and by simulation experiments.©1993 John Wiley & Sons Inc
A status report on applying discrete inverse theory to ionospheric tomography
Authors: Fremouw E. J. , Secan J. A. , Bussey R. M. , Howe B. M. 
Published: March 2007

AbstractDiscrete inverse theory (DIT) provides an orderly framework in which to combine measurements of total electron content (TEC) with a priori information to image the ionosphere tomographically. We have developed a DIT‐based tomographic processor for use with relative TEC data. The processor's a priori information comprises the global mean of over 17,000 profiles generated from an ionospheric model, for use as a “generic background”; empirical orthogonal functions (EOFs) spanning the same model profiles, for use as vertical basis functions; and a red power‐law horizontal spectrum. Relative TEC data are used to evaluate coefficients multiplying the EOFs and harmonics, thus quantifying a perturbation electron‐density field. The perturbation field, which need not be small, is added to the a priori background to produce the image. We present here several images produced by employing the processor with simulated TEC data based on in situ ionospheric measurements and incoherent‐scatter radar observations.©1994 John Wiley & Sons Inc
Few‐field radiation therapy optimization in the phase space of complication‐free tumor control
Authors: Söderström Svante , Gustafsson Anders , Brahme Anders 
Published: March 2007

AbstractThe phase space of P+, describing the probability of achieving tumor control without causing severe complications in normal tissues, has been investigated for three different clinically relevant treatment geometries. These include tumors in the head and neck region, thorax, and pelvis. Some general conclusions about the shape and properties of the P+ phase space are given for the selected target volumes. The use of three different radiation beam types‐strictly homogeneous, wedged, and generally nonuniform beams‐has been investigated and the considerable differences in the P+ phase space are shown. One conclusion is that the exact selection of beam entry direction becomes gradually less important as the number of beam portals becomes larger. One of the most important results is that use of appropriately selected nonuniform beam profiles reduces the number of necessary beam portals to such a low level that the treatment technique becomes simple and reliable at the same time as the probability of achieving tumor control without severe complications is almost as high as with an unlimited number of beams This means that most ordinary treatment units equipped with beam compensating filters can be used for closely optimal radiation therapy.
Effects of biophysical and physiologic parameters on brain activation‐induced R2* and R2 changes: Simulations using a deterministic diffusion model
Authors: Bandettini Peter A. , Wong Eric C. 
Published: March 2007

AbstractA central issue in magnetic resonance imaging of human brain function using blood oxygenation level‐dependent (BOLD) contrast is the accurate interpretation of the signal changes that are observed. Using a method that incorporates repeated phase rotation and convolution with a smoothing function to simulate spin diffusion in the presence of magnetic field perturbers, the dependencies of the absolute and relative changes in transverse relaxation rates (δR2* and δR2) on biophysical and physiologic parameters were explored. First we introduce the modeling methodology. Then we simulate δR2* and δR2 as physiologic and biophysical parameters are modulated within the ranges that they vary across subjects and voxels in the brain. The simulations demonstrate that the δR2* and δR2 values that occur with activation‐induced changes in blood oxygenation depend most strongly on the resting state blood volume and field strength. The δR2*/δR2 ratios depend most strongly on the vessel radius and spin diffusion coefficient.
In vivo validation of the bold mechanism: A review of signal changes in gradient echo functional MRI in the presence of flow
Authors: Haacke E. Mark , Lai Song , Yablonskiy Dmitriy A. , Lin Weili 
Published: March 2007

AbstractBrain functional magnetic resonance imaging (FMRI) is possible because of local changes in blood flow and oxygenation levels. Understanding the role of each mechanism is important for interpreting FMRI results as well as for the design of the experiment itself. In this review, we address the role of flow and blood oxygen level dependence (BOLD) and how they can be used in conjunction with each other to enhance the BOLD effect. We also discuss the role of intra/extravascular signal changes in the presence of a vessel for the imaging situation and show how the ratio of these two contributions is likely to change as the blood volume fraction changes. Using the BOLD model itself, along with 3‐D phase imaging, we show that blood oxygenation level in veins in vivo is Y = 0.544 ± 0.029 as measured in 14 vessels in five subjects. Finally, we comment on the use of phase images themselves as a means to discriminate tissues with different levels of blood such as gray matter, white matter, and cerebrospinal fluid.
Susceptibility effect‐enhanced functional MR imaging using tailored RF gradient echo (TRFGE) sequence
Authors: Cho Z. H. , Ro Y. M. , Chung S. C. 
Published: March 2007

AbstractIn this article, we have described a tailored radio frequency gradient echo (TRFGE) technique which is applied to functional imaging. The TRFGE technique is insensitive to the inflow effect, which often complicates the analysis of functional magnetic resonance imaging (FMRI) data, and is also insensitive to nonfunctional backgrounds such as static tissues. The susceptibility effect measurement obtained from the TRFGE technique therefore provides a unique form of functional imaging, namely, susceptibility‐only functional imaging. To examine TRFGE functional imaging systematically, we designed an experiment to determine the flow effect and susceptibility‐dependent signal change by varying the imaging parameters including flip angle α, repetition time TR, and echo time TE. The results obtained were then compared with the data obtained with conventional gradient‐echo (CGE) functional MR imaging. The experimental results shown were all obtained using human volunteers with a 2.0‐T whole‐body MRI system.