bluuebunny/crossref_metadata_2025_split huggingface dataset:
PD‐L1 (B7‐H1) expression by urothelial carcinoma of the bladder and BCG‐induced granulomata
Authors: Inman Brant A. , Sebo Thomas J. , Frigola Xavier , Dong Haidong , Bergstralh Eric J. , Frank Igor , Fradet Yves , Lacombe Louis , Kwon Eugene D. 
Published: March 2007

AbstractBACKGROUNDPD‐L1 (programmed death ligand 1, B7‐H1) is a cell surface glycoprotein that can impair T‐cell function. PD‐L1 is aberrantly expressed by multiple human malignancies and has been shown to carry a highly unfavorable prognosis in patients with kidney cancer. The role of PD‐L1 was evaluated as a mechanism for local stage progression in urothelial carcinoma (UC) of the bladder.METHODSUsing immunohistochemistry, PD‐L1 expression was evaluated in a cohort of 280 high‐risk UCs of the bladder. PD‐L1 was modeled as a predictor of bladder cancer stage using ordinal logistic regression. Other covariates evaluated as potential confounders included age, gender, tumor grade, and lymphocytic infiltration. Further, PD‐L1 was evaluated as a potential mechanism of bacillus Calmette‐Guerin (BCG) failure in the subset of high‐risk nonmuscle‐invasive tumors that received this treatment.RESULTSPD‐L1 expression was observed in 7% of pTa, 16% of pT1, 23% of pT2, 30% of pT3/4, and 45% of carcinoma in situ (CIS) tumors. PD‐L1 expression was associated with high‐grade tumors (odds ratio [OR] = 2.4, P = .009) and tumor infiltration by mononuclear cells (OR = 5.5, P = .004). We observed that the key determinants of stage progression in this cohort were World Health Organization/International Society of Urologic Pathology (WHO/ISUP) high‐grade tumor pathology (OR = 4.77, 95% confidence interval [CI]: 2.73–8.34; P < .001) and PD‐L1 expression (OR = 2.20, P = .012). PD‐L1 expression was found to be extremely abundant in the BCG‐induced bladder granulomata in 11 of 12 patients failing BCG treatment.CONCLUSIONSCollectively, these data indicate that tumor PD‐L1 may facilitate localized stage‐advancement of UC and attenuate responses to BCG immunotherapy by neutralizing T cells that normally guard against cancer invasion from the epithelium into the bladder musculature. Cancer 2007. © 2007 American Cancer Society.
Characterization of Pericyclic Reactions Using Multicenter Electron Delocalization Analysis
Authors: Mandado Marcos , González‐Moa María J. , Mosquera Ricardo A. 
Published: March 2007

AbstractThis work investigates the applicability of multicenter delocalization analysis to the characterization of pericyclic reactions. The results indicate that multicenter delocalization indices are a powerful tool for studying concerted processes, allowing the characterization of aromatic transition states with a significant increase in the electron delocalization. Moreover, an advantage over magnetic‐based indices is that multicenter delocalization indices are not influenced by local electron currents but by the electron delocalization along the multiple (n) centers, and provide, in a quantitative sense, more reliable results. A thorough comparison with magnetic‐based indices is carried out for the trimerization reaction of acetylene. Tracking the values of multicenter delocalization indices along the reaction path allows investigation of the nature of concerted mechanisms. Six‐center electron delocalization displays a maximum at the transition state of the Diels–Alder reaction, whereas a similar maximum of four‐center electron delocalization is slightly displaced to butadiene for the ring opening of cyclobutene. The profile of multicenter electron delocalization indices along the reaction path of [2+2] cycloaddition of ketene to ethene shows the presence of the two independent mechanisms that agree with the two HOMO/LUMO orbital interactions previously proposed to dominate this reaction.
Pivotal Steps Towards Quantification of Molecular Diffusion Coefficients by NMR
Authors: Zhang Shanmin 
Published: March 2007

AbstractUsing nuclear magnetic resonance (NMR) spectroscopy with a pair of pulsed field gradients (PFGs), Stajeskal and Tanner successfully measured molecular diffusion coefficients in solution in 1965. This method has since been used extensively in various applications, especially after the PFG was implemented in commercial NMR probes. Due to the nonuniformity of the PFG and radio frequency (RF) fields, molecules distributed throughout the sample experience different PFG and RF fields and contribute unevenly to the measured diffusion coefficients, resulting in considerable errors in conventional NMR diffusion experiments. By selective excitation of a central sample region with an offset‐independent adiabatic inversion pulse and a PFG, a uniform RF field can be assumed, and the PFG can be represented as a linear approximation. Under these conditions, the molecules diffuse as if they were all experiencing the same effective gradient ge, leading to a Gaussian signal decay as a function of the PFG strength. Quantitative measurement of molecular diffusion coefficients is therefore made possible. From the diffusion coefficient of a 90 % H2O/10 % D2O sample, it is convenient to calibrate ge with a Java program. In a similar way the nonlinearity of the PFG can be corrected.
Recovery of boron from borax sludge using solid–liquid extraction followed by ion exchange with amberlite resin
Authors: Özdemir Mine , Kıpçak İlker 
Published: March 2007

AbstractTo recover boron from borax sludge, initially solid–liquid extraction with dilute sulfuric acid was utilized in a batch reactor. The optimum working conditions for boron extraction were determined. A maximum extraction yield of 85.0% for boron was obtained. In the process, 9.14% of the calcium and 16.8% of the magnesium contained in the solid waste passed to the extraction solution. Subsequently, batch ion‐exchange studies were performed using Amberlite IRA‐743‐boron specific resin for the separation of boron from the calcium and magnesium components in the extraction solution. The effects of contact time and resin dosage on the ion‐exchange process were investigated. A second order kinetic model seemed to be appropriate for the boron ion‐exchange. The boron, which was sorbed on the resin, was eluted completely using a 0.5 M sulfuric acid solution. It was seen that the calcium and magnesium components were not present in the elution solution. In this process, boron was successfully separated from the calcium and magnesium species. It was determined that approximately 98.70% of the boron in the extraction solution could be recovered at a pH value of 8, a contact time of 24 h, an initial boron concentration of 500 mg/L, a resin dosage of 2.5 g of resin/50 mL of extraction solution, and a temperature of 25°C. © 2007 American Institute of Chemical Engineers Environ Prog, 2007
The effect of single vegetation elements on wind speed and sediment transport in the Sahelian zone of Burkina Faso
Authors: Leenders J. K. , Boxel J. H. van , Sterk G. 
Published: March 2007

AbstractSoil loss caused by wind erosion is a widespread phenomenon in the Sahelian zone of West Africa. According to Sahelian farmers, scattered vegetation standing in amongst the crop has the potential for a wind erosion control strategy. This study was conducted to study the effect of single vegetation elements on the pattern of average wind speed and sediment transport. This was done by two experiments that were carried out during the rainy seasons of 2002 and 2003 in north Burkina Faso, West Africa. Wind speeds were measured using three sonic anemometers, at a sampling frequency of 16 Hz. Sediment transport was determined by calculating the mass fluxes from 17 MWAC catchers. In this study, a shrub was defined as a vegetation element with branches until ground and a tree as a vegetation element with a distinctive trunk below a canopy.Behind shrubs wind speed near the soil surface was reduced up to approximately seven times the height of the shrub. The observed reduction in wind speed in the area where wind speed was reduced was 15 per cent on average. At the sides of the shrub, wind speed was increased, by on average 6 per cent. As the area of increase in wind speed is one‐third of the area of decrease in wind speed, the net effect of a shrub is a reduction in wind speed. A similar pattern was visible for the pattern of sediment transport around a shrub. Downwind of a shrub, sediment transport was diminished up to seven times the height of the shrub. Probably most of this material was trapped by the shrub. Trees showed a local increase of wind around the trunk, which is expected to relate to an increase in sediment transport around the trunk. Mass flux measurements of sediment transport were not made, but visual observations in the field substantiate this. Behind the canopy of a tree, a tree acts similarly to a shrub regarding its effects on average wind speed, but as a tree is generally a larger obstacle than a shrub the extent of this effect is larger than for shrubs. Thus, whereas shrubs are more effective than trees regarding their direct effect on soil loss by trapping sand particles near the soil surface, trees are more effective in affecting soil loss indirectly by reducing the wind speed downwind more effectively than shrubs. Therefore, to reduce soil loss in an area, the presence of both trees and shrubs is crucial. Copyright © 2007 John Wiley & Sons, Ltd.
A historical view of imaging systems and technology
Authors: Robinson Enders A. 
Published: March 2007

AbstractWhen approached from a historical viewpoint the development of many important imaging systems throughout history often share common ground. Extremely important was the development of the idea of mathematical projection which provides methods for making an image that conformally represents the object. The prime example is the discovery of the stereographic projection by Hipparchus of Nicaea in the second century BC. The stereographic projection provided the basis for the astrolabe, an astronomical device that acted both as an instrument of observation and as an analog computer. The stereographic projection and similar ones also provided the basis for the world maps of the ancients which utilized a grid of longitude and latitude. When the ancient Greek books were rediscovered in the Renaissance, the maps provided the impetus for the age of exploration. The Mercator projection of the sixteenth century was obtained as a logarithmic transformation of the stereographic projection. The Mercator projection provided sea captains with maps that had a rectangular grid of latitude and longitude and also had the property that straight lines represented courses of constant compass directions. The development of the telescope and microscope in the early seventeenth century provided means to obtain images that could not be seen by the unaided eye. Galileo's discovery of the moons of Jupiter led to Roemer's determination in 1676 that light travels at a finite velocity. Unknowingly, Roemer also discovered the relativistic Doppler effect, which in the present century helped to establish our concept of the expanding universe. The relativistic Doppler factor mathematically is none other than the expression for the stereographic projection of Hipparchus. The development of high energy physics in this century has led to images of the microworld of subatomic particles. In this environment Einstein's equation E = mc2 finds verification. This equation is a result of the theory of special relativity. The basic mathematics of special relativity is contained in the Lorentz transform. Again we can return to Hipparchus, because the Lorentz transform follows from a sequential application of the stereographic projection.
An iterative reconstruction algorithm for single photon emission computed tomography with cone beam geometry
Authors: Gullberg Grant T. , Zeng Gengsheng L. , Tsui Benjamin M. W. , Hagius John T. 
Published: March 2007

AbstractAn iterative EM reconstruction algorithm for single photon emission computed tomography is implemented for cone beam geometry that uses a ray‐driven projector‐backprojector. The cone beam projector‐backprojector models the attenuated Radon transform of a source distributed within an attenuator as line integrals of discrete voxels representing the source and attenuation distributions. The attenuation coefficient distribution for each voxel is assumed to be equal to the average value over a cubical region, and the integral of the source concentration through each voxel is obtained by interpolating between the source values at eight neighboring voxels. The calculation of the attenuation factors requires a specification of the attenuation distribution, estimated either from an assumed constant distribution with an estimated body outline or from transmission measurements. The distribution of attenuation coefficients is stored in memory, and the attenuation factors are calculated for each voxel during the projection and backprojection operations instead of using precalculated values. Computer simulations of half‐scan and full‐scan reconstructions show that the algorithm is able to compensate for attentuation and to suppress the propagation of artifacts that can result with limited angular sampling. The simulations verify that the algorithm has important application to cardiac SPECT imaging; because of variable attentuation through the thorax, it is necessary to use an iterative algorithm with an attenuation map in order to quantify radiopharmaceutical distributions in the heart.
Developments in high‐resolution positron emission tomography at MGH
Authors: Brownell G. L. , Burnham C. A. , Stearns C. W. , Chesler D. A. , Brownell A.‐L. , Palmer M. R. 
Published: March 2007

AbstractThe development of high resolution PET systems is important for the wider application of this techniques. The resolution of PET is limited by a number of physical factors such as positron range, small angle deviation, and sampling frequency. The design of the detector array and its sensitivity remain critical factors; designs incorporating analog coding have proven to be useful. PCR‐I, a single plane PET system, has demonstrated the concept and has produced useful images in animal studies. PCR‐II will extend the concept to a two dimensional detector array resulting in a system with high resolution and high sensitivity.
New examples of a recursive algorithm for calculating the echo pattern from a multilayered structure: Application to four‐layered structures
Authors: Lees Sidney 
Published: March 2007

AbstractIt was previously shown that the sonic echo wave pattern from a thin layer embedded between two thick layers can be readily and accurately calculated using a recursive expression (1). Two three‐layered experimental structures were described where the calculated and experimental wave patterns were successfully compared. It was shown that marked drastic changes in the echo wave pattern result from a layer much thinner than the pulse length.The mathematical technique lends itself readily to computer calculation and can be employed in situations with an arbitrary number of layers. The power of the algorithm will be demonstrated here on a four‐layered structure. The material in the next section is taken directly from Ref. 1.
Estimating rigid‐body motion from three‐dimensional data without matching point correspondences
Authors: Lin Zse‐Cherng , Lee Hua , Huang Thomas S. 
Published: March 2007

AbstractThe estimation of the three‐dimensional (3‐D) motion parameters of a rigid body is a very important subject in scene analysis and trajectory prediction. Motion parameters can be estimated from two sets of object feature points before and after the motion. In general, the matching correspondences of the feature points are available, and the motion parameters can be estimated by solving equations associated with the correspondences. In this paper, we present a new method for motion estimation from 3‐D data without requiring the knowledge of matching correspondences.In the noise‐free case, this approach identifies four candidates for the rotation matrix. The rotation matrix giving the best match of the point features can then be selected from the four candidates, and the matching correspondences are subsequently established. Possible ambiguities due to symmetrical feature points are also discussed in this paper. In the presence of noise, this method provides an initial estimate of the motion, which is then used to establish the matching correspondences. Subsequently, a new estimate of the motion parameters can be obtained with the established matching correspondence information. The effects of random zero‐mean noise are studied. Simulated results are shown to demonstrate the effectiveness and accuracy of this technique.
Inverse scattering, seismic traveltime tomography, and neural networks
Authors: Lu Shin‐Yee , Berryman James G. 
Published: March 2007

AbstractInverse scattering methods for reconstructing sound‐wave‐speed structure in the dimensions have been shown to be equivalent to inverting line integrals when the scattered field is of sufficiently high frequency and the scattering is sufficiently weak. Seismic traveltime tomography uses first arrival traveltime data to invert for wave‐speed structure. Of course, the traveltime is itself a line integral along a refracting ray path through the medium being probed. The similarity between these two inversion problems is discussed. One type of neural network‐the Hopfield net‐may be used to improve the traveltime inversion. We find that, by taking advantage of the general relationship between least‐squares solution and generalized inverses, the neural networks approach eliminates the need for inverting singular or poorly conditioned matrices and therefore also eliminates the need for the damping term often used to regularize such inversions. This procedure produces reconstructions with fewer artifacts and faster convergence than those attained previously using damped least‐squares methods.
Contour reconstruction in diffraction tomography
Authors: Ladas Kostas T. , Tsihrintzis George A. 
Published: March 2007

AbstractWe address the problem of reconstructing the directional derivative and/or the Laplacian of an object function f characterizing a weakly inhomogeneous scatterer directly from data collected in a set of scattering experiments. We employ the Rytov approximation to model the complex phase of the scattered wavefields and show that a minimum‐norm least‐squares solution can be obtained from the well known filtered backpropagation algorithm of diffraction tomography with appropriate modification of the tomographic filters employed in the filtering step of the algorithm. The procedure is illustrated by a computer simulation study.
Imaging of earthquake sources
Authors: Morales Jorge , McMechan George A. 
Published: March 2007

AbstractElastic waves, produced by temporally and spatially finite fault ruptures during earthquakes, propagate through the Earth. Recordings of these waves at the Earth's surface provide the data for reconstruction of the source properties, including location, spatial and temporal extents, and rupture velocities. A 2D finite‐difference solution of the elastic wave equation is used to numerically extrapolate synthetic observations backward in time to create images of the energy release during an earthquake.
Solid modeling of space stations in a concurrent processing environment
Authors: Saleh A. , Adeli H. 
Published: March 2007

AbstractThis article presents solid modeling of space station structures in a multiprocessing environment such as the Cray YMP 8/864. A space station is modeled as a collection of space trusses. Elements of trusses are created concurrently using constructive solid geometry. Concurrent solid modeling of large structures can be integrated with parallel algorithms for optimization of such structures in order to fully automate their computer‐aided design in a multiprocessing environment.
Planetary cameras
Authors: Anderson J. L. , Collins S. A. , Klaasen K. P. , Reilly T. H. 
Published: March 2007

AbstractThe “first look” phase of planetary imaging has been completed, with many spectacular discoveries made by a wide variety of cameras and spacecraft. Now that planetary scientists have a better idea about what is out there, new cameras can be developed to address specific questions in greater depth. Ideally, these cameras would be fully optimized to carry out their scientific objectives. In reality, however, the numerous constraints and severe environments of a planetary spacecraft often influence the camera design as strongly as the science. New developments in optics, detectors, microcomputers, and structural materials have greatly expanded the capabilities that can be built into a small, lightweight, low‐power instrument, and further progress is expected in the coming decade. The new camera designs will be used on a variety of flyby, orbiter, lander, and rover missions now in preparation by NASA and other space agencies throughout the world.
Design and development of the mars observer camera
Authors: Malin M. C. , Danielson G. E. , Ravine M. A. , Soulanille T. A. 
Published: March 2007

AbstractThe Mars Observer Camera (MOC) consists of three integrated optical subassemblies (one narrow‐angle and two wide‐angle cameras) with common electronics, designed to take high‐spatial‐resolution pictures of the surface of Mars and lower‐spatial‐resolution, synoptic coverage of the planet's surface and atmosphere. It incorporates several advanced technologies, including the use of graphite/epoxy structural materials, 32‐bit microprocessors, 108‐bit digital buffers, and high‐speed custom integrated circuits. The cameras use the “push broom” technique to build pictures, one line at a time, as the spacecraft orbits the planet. The narrow‐angle camera can acquire images of areas ranging from 2.9 × 2.9 km2 to 2.9 × 25.2 km2 at a resolution of 1.4 m/pixel. Additionally, lowerresolution pictures (to a lowest resolution of about 11 m/pixel) can be acquired through the narrow‐angle camera by pixel averaging; these images can be much longer (up to 2.9 × 500 km at 11 m/pixel). The wide‐angle cameras are capable of viewing Mars from horizon to horizon and, in a single 24‐hour period, can acquire a complete global image of the planet at a resolution of at least 7.5 km/pixel. Regional areas (covering hundreds of kilometers on a side) may be photographed at a resolution of better than 250 m/pixel at the nadir. The two wide‐angle cameras image through a different spectral filter, allowing the construction of color images. The MOC is a cylinder 88 cm in length and about 40 cm in diameter; the redundant electronics, equivalent in complexity and computational power to two engineering workstations, fit within a volume 40 cm in diameter and 10 cm long behind the narrow‐angle primary mirror. NASA's Mars Observer mission has adopted a distributed operations philosophy: all uplink and downlink activities for the MOC and the other payload experiments will occur remote from the Jet Propulsion Laboratory's command centers. Following its year‐long flight to Mars (launch is scheduled for 16 September 1992), Mars Observer is planned to acquire data for one Mars year (687 Earth days). During that time, MOC will acquire about 2 × 1012 bits of image and engineering data. During the last three months of the mission, Mars Observer will use a French‐supplied relay system to acquire an additional 2 × 109 bits of data from balloons deployed as part of the Soviet Mars '94 mission. These data will be collected and transferred to the Earth through the MOC electronics.