Interactive volume rendering of thin thread structures within multivalued scientific data sets

We present a threads and halos representation for interactive volume rendering of vector-field structure and describe a number of additional components that combine to create effective visualizations of multivalued 3D scientific data. After filtering linear structures, such as flow lines, into a volume representation, we use a multilayer volume rendering approach to simultaneously display this derived volume along with other data values. We demonstrate the utility of threads and halos in clarifying depth relationships within dense renderings and we present results from two scientific applications: visualization of second-order tensor valued magnetic resonance imaging (MRI) data and simulated 3D fluid flow data. In both application areas, the interactivity of the visualizations proved to be important to the domain scientists. Finally, we describe a PC-based implementation of our framework along with domain specific transfer functions, including an exploratory data culling tool, that enable fast data exploration.     

Correlation entre les courbes courant-tension et la morphologie des dépôts électrolytiques d'étain

Résumé En contrÔlant le transport de matière par diffusion au sein de l'électrolyte au moyen d'une électrode à disque tournant, on étudie le mécanisme de lélectrocristallisation de l'étain en milieu phénolsulfonique. Les courbes courant-tension stationnaires et les diagrammes d'impédance peuvent s'expliquer par la coexistence d'au moins trois espèces adsorbées à l'interface métal-electrolyte. L'apparition des trois variétés morphologiques (spongieuse, compacte, puis dendritique) de dépÔt observées lorsqu'on augmente la densité de courant suggère, d'une manière analogue à l'électrocristallisation du zinc, l'intervention d'un processus autocatalytique dans le mécanisme réactionnel de décharge des ions Sn²⁺ et son couplage avec la diffusion superficielle d'adions du type Sn _ads ⁺ . La compétition entre l'adsorption d'hydrogène, capable d'inhiber la décharge des ions Sn²⁺, et ce processus autocatalytique explique que, dans les conditions stationnaires, la courbe courant-tension soit parallèle à l'axe des courants dans une certaine gamme de densités de courant.L'addition de dihydroxydiphenylsulfone dans l'électrolyte, qui élargit le domaine des densités de courant intermédiaires où le dépÔt reste compact, modifie la cinétique de l'électrocristallisation en ayant pour effet de réduire l'importance relative du processus autocatalytique dans le mécanisme réactionnel.

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The mechanism of the electrocrystallization of tin in a phenolsulphonic bath is studied by using a rotating disc electrode. The current-voltage curves plotted under steady-state conditions and the impedance diagrams can be explained by the coexistence of at least three adsorbed species at the metal-electrolyte interface. The three kinds of deposit morphology (spongy, compact, and dendritic) which are observed with increasing current density suggests, as in the case of zinc electrocrystallization, the coupling of an autocatalytic step occurring at the interface with the surface diffusion of adions such as Sn _ads ⁺ . The competition between this autocatalytic step and the hydrogen adsorption, which is able to inhibit the discharge of Sn²⁺ ions, explains why the steady-state current-voltage curves are parallel to the current axis in a certain range of current density.With small amounts of dihydroxydiphenylsulphone in the electrolyte, the range of current density leading to compact deposits is widened. It is shown that the additive changes the coupling of the processes taking place at the interface and seems to decrease the importance of the autocatalytic step in the reaction mechanism.

     

Evaluation of bent-crystal x-ray backlighting and microscopy techniques for the Sandia Z machine

X-ray backlighting and microscopy systems for the 1-10-keV range based on spherically or toroidally bent crystals are discussed. These systems are ideal for use on the Sandia Z machine, a megajoule-class x-ray facility. Near-normal-incidence crystal microscopy systems have been shown to be more efficient than pinhole cameras with the same spatial resolution and magnification [Appl. Opt. 37, 1784 (1998)]. We show that high-resolution (< or = 10 microm) x-ray backlighting systems using bent crystals can be more efficient than analogous point-projection imaging systems. Examples of bent-crystal-backlighting results that demonstrate 10-microm resolution over a 20-mm field of view are presented.     

Reduction of carbamylated albumin by extended hemodialysis

Introduction Among conventional hemodialysis (CHD) patients, carbamylated serum albumin (C‐Alb) correlates with urea and amino acid deficiencies and is associated with mortality. We postulated that reduction of C‐Alb by intensive HD may correlate with improvements in protein metabolism and cardiac function. Methods One‐year observational study of in‐center nocturnal extended hemodialysis (EHD) patients and CHD control subjects. Thirty‐three patients receiving 4‐hour CHD who converted to 8‐hour EHD were enrolled, along with 20 controls on CHD. Serum C‐Alb, biochemistries, and cardiac MRI parameters were measured before and after 12 months of EHD. Findings EHD was associated with reduction of C‐Alb (average EHD change ?3.20 mmol/mol [95% CI ?4.23, ?2.17] compared to +0.21 [95% CI ?1.11, 1.54] change in CHD controls, P < 0.001). EHD was also associated with increases in average essential amino acids (in standardized units) compared to CHD (+0.38 [0.08, 0.68 95%CI]) vs. ?0.12 [?0.50, 0.27, 95% CI], P = 0.047). Subjects who reduced C‐Alb more than 25% were found to have reduced left ventricular mass, increased urea reduction ratio, and increased serum albumin compared to nonresponders, and % change in C‐Alb significantly correlated with % change in left ventricular mass. Discussion EHD was associated with reduction of C‐Alb as compared to CHD, and reduction of C‐Alb by EHD correlates with reduction of urea. Additional studies are needed to test whether reduction of C‐Alb by EHD also correlates with improved clinical outcomes.     

Fast Image‐Based Modeling of Astronomical Nebulae

Astronomical nebulae are among the most complex and visually appealing phenomena known outside the bounds of the Solar System. However, our fixed vantage point on Earth limits us to a single known view of these objects, and their intricate volumetric structure cannot be recovered directly. Recent approaches to reconstructing a volumetric 3D model use the approximate symmetry inherent to many nebulae, but require several hours of computation time on large multi‐GPU clusters. We present a novel reconstruction algorithm based on group sparsity that reaches or even exceeds the quality of prior results while taking only a fraction of the time on a conventional desktop PC, thereby enabling end users in planetariums or educational facilities to produce high‐quality content without expensive hardware or manual modeling. In principle, our approach can be generalized to other transparent phenomena with arbitrary types of user‐specified symmetries.     

DES-GENERATED CHECKSUMS FOR ELECTRONIC SIGNATURES

Secrecy and authentication are two important features of a secure communication system. Public Key Cryptosystems, based, e.g., on the Rivest-Shamir-Adleman (RSA) algorithm, provide a very elegant solution to the problem of authenticity verification or true electronic signatures. Practical problems, however, mainly the lack of execution speed, prevent a straightforward application. In order to sign a long message it is much faster to first calculate a short digest or checksum and then sign the compressed message. For this checksum calculation the fast, inexpensive and extensively tested Data Encryption Standard (DES) can be used. But care must be taken that this additional processing step does not introduce any weakness into the signature scheme. This paper investigates two DES-based hashing methods. It is shown that neither method seems to introduce any statistical regularities in the generated checksums. The “Cipher/Message to Plain Feedback,” however, is not secure under a modification compensation attack. It is further shown how the second method, the “Cipher to Plain Feedback” proposed by Davies and Price, can be broken by a “meet in the middle attack.” This checksum method, however, can be used safely with a slight modification.