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At least 1,603 records · Page 89Linked to original sources
PubMed1999

Crystallization of hepatitis B virus core protein shells: determination of cryoprotectant conditions and preliminary X-ray characterization.

Hepatitis B virus causes liver cirrhosis and hepatocellular cancer and is a major cause of death, particularly in Asia and sub-Saharan Africa. The virus consists of an inner core or nucleocapsid, which encloses the viral nucleic acid, with an outer lipid envelope containing surface-antigen proteins. The core protein, when expressed in E. coli, assembles into spherical shells containing 180 or 240 subunits, arranged with T = 3 or T = 4 icosahedral symmetry. The C-terminal region of the protein is involved in nucleic acid binding, and deletion of this region does not prevent capsid formation. C-terminally deleted hepatitis B core shells containing 240 subunits have been crystallized and data has been collected to 3. 6 A resolution from frozen crystals, using butanediol as a cryoprotectant. The crystals have C2 symmetry, with unit-cell parameters a = 538.0, b = 353.0, c = 369.6 A, beta = 132.3 degrees.

Cold Temperature↗
PubMed2001

Multiple ionization upon K-shell photoabsorption of the CO and N2 molecules.

The spectra of multiple ionization of CO and N2 in the gas phase in the region of the K-shell ionization thresholds of C and N are studied theoretically. The processes of additional excitation/ionization from 1pi and 5sigma-shells are included. The effects of many-electron correlations on the extention of multiplet structure for some configurations of multiple excitations is studied. Absolute values of photoabsorption cross sections are calculated in some of the channels of multiple ionization.

Journal Article↗
PubMed2001

The temperature dependence for the third shell's Fourier-peak of Nb-EXAFS in KNbO3 as additional source of information on the local atomic structure.

The information on the structure of tetragonal KNbO3 is extracted from the temperature dependence of the third shell's Fourier-peak of Nb-EXAFS. It is shown that this dependence can be explained by two effects: 1) rigid rotations of the O6-octahedron and 2) increase of the third shell's DW-parameter. However, diffraction data on the temperature dependence of the DW-parameter permit us to conclude that the last effect only is sufficient and the O6-octahedron rotation doesn't occur in the high-temperature phases of KNbO3. Using EXAFS it is revealed that in the neighboring cells Nb-atoms are parallel shifted closely to [211] direction in tetragonal phase.

Journal Article↗
PubMed2002

Lumen pressure within obliquely insonated absorbent solid cylindrical shells with application to Doppler flow phantoms.

Flow phantoms used in medical ultrasound usually employ a plastic tube as a blood vessel mimic. These tubes often have acoustic properties differing significantly from the tissue and blood-mimicking media, which results in distortion of the acoustic pressure field within the tubes and, hence, of the Doppler flow spectra. Previous analyses of this problem have used some form of the infinite plate transmission coefficient, although at least one ray-based analysis has considered a cylindrical interface but with zero wall thickness. In this paper, we compare these approximate pressure fields with the exact solution for oblique incidence on a viscoelastic cylindrical shell at 5 MHz to find for which materials the plate approximation is valid. The shell has water both inside and outside, but it can be modified to use a different fluid inside and also to include absorption in either fluid. We find the plate approximation is reasonable for soft tubes such as the copolymer Cflex (Cole-Palmer, Niles, IL) but much less so for hard tubes such as polymethylmethacrylate (PMMA).

Blood Flow Velocity↗
PubMedDate not supplied

Meshless thin-shell simulation based on global conformal parameterization.

This paper presents a new approach to the physically-based thin-shell simulation of point-sampled geometry via explicit, global conformal point-surface parameterization and meshless dynamics. The point-based global parameterization is founded upon the rigorous mathematics of Riemann surface theory and Hodge theory. The parameterization is globally conformal everywhere except for a minimum number of zero points. Within our parameterization framework, any well-sampled point surface is functionally equivalent to a manifold, enabling popular and powerful surface-based modeling and physically-based simulation tools to be readily adapted for point geometry processing and animation. In addition, we propose a meshless surface computational paradigm in which the partial differential equations (for dynamic physical simulation) can be applied and solved directly over point samples via Moving Least Squares (MLS) shape functions defined on the global parametric domain without explicit connectivity information. The global conformal parameterization provides a common domain to facilitate accurate meshless simulation and efficient discontinuity modeling for complex branching cracks. Through our experiments on thin-shell elastic deformation and fracture simulation, we demonstrate that our integrative method is very natural, and that it has great potential to further broaden the application scope of point-sampled geometry in graphics and relevant fields.

Algorithms↗
PubMed2003

Encapsulated yeast cells inside Paramecium primaurelia: a model system for protection capability of polyelectrolyte shells.

One of the most promising applications of encapsulated living cells is their use as protected transplanted tissue into the human body. A suitable system for the protection of living cells is the use of nano- or microcapsules of polyelectrolytes. These shells can be deposited easily on top of the cells by means of a layer-by-layer technique. An interesting feature of the capsules is the possibility to control their properties on a nanometre level, tuning their wall texture via the preparation conditions. Here we introduce a model system to test the protection ability of polyelectrolyte capsules. Common bakery yeast cells were encapsulated. They were coated with a fluorescently labelled shell at conditions known to guarantee cell survival, and the cell interior was stained with DAPI. The protozoan Paramecium primaurelia was incubated with this double-stained living yeast and visualized by means of two-photon excitation fluorescence microscopy. Cross-sections of the dye-stained material as well as autofluorescence of the fixed protozoan allowed us to follow the digestion of the coated yeast with time. Our investigation reveals that capsules prepared under these deposition conditions are permeable to lysosomal enzymes, leading to degradation of the yeast inside the intact capsules. Our preliminary results indicate the suitability of the introduced model as a test system of this permeability.

Animals↗
PubMed1989

Hyposensitization to poison ivy after working in a cashew nut shell oil processing factory.

19 adults were patch tested to urushiol, the allergen in poison ivy/oak, to determine their sensitivity to this allergen after working in a cashew nut shell oil (CNSO) processing plant. The cashew nut tree and poison ivy/oak are in the same botanical family. Anacardiaceae, and they share similar chemicals which cause allergic contact dermatitis. 13 of the 19 workers had a preemployment history of poison ivy sensitivity, with 10 developing CNSO dermatitis. After working in this factory for several months, 9 of the 13 noticed a decreased sensitivity or no sensitivity to poison ivy/oak. When tested to urushiol extract, only 3 reacted positively, 2 minimally. These results imply that hyposensitization to poison ivy/oak occurred in these employees after development of hardening to cashew nut shell oil.

Catechols↗
PubMed2000

Resonant response of complex shell structures

Resonances of shell structures play a prominent role in determining their acoustic characteristics. Among the most important of such characteristics are radiated noise, scattering, and self-noise levels. The nature of the structural resonances, for example the number of modes within a particular frequency band or the overall spatial dependence of the response, determines the importance of these phenomena in various contexts and what steps may be taken to modify their acoustic impact. In the past, knowledge of the resonant response of highly idealized systems has been used to guide the development of quiet platforms. The results of a scale model investigation of the effects of increased complexity on the nature of the resonances of submerged shell structures are reported. Effects presented here are flexural Bloch mode resonances, localized resonances resulting from structural irregularity, and the effects of non-axisymmetry on these phenomena. The implications of these results on acoustic design and the development of systems is discussed.

Journal Article↗
PubMed2001

Wave localization on a submerged cylindrical shell with rib aperiodicity.

The results of a numerical study of vibration localization due to stiffener variability in a framed shell are reported. An axisymmetric finite element (FE)-infinite element model is used to obtain predictions in good general agreement with previously reported experimental results. Over the frequency band of this study, up to three times the ring frequency, two structural resonances dominate the vibratory response of the shell for high circumferential orders (n > 10). Localization is shown to be linked to the sensitivity of the local resonance frequencies of the system to specific geometrical parameters. Specifically, rib thickness variations strongly affect the first pass band, while rib spacing variations strongly affect the second pass band.

Journal Article↗
PubMed2001

Acoustic radiation of cylindrical elastic shells subjected to a point source: investigation in terms of helical acoustic rays.

The paper deals with the acoustic radiation of a cylindrical elastic shell with no internal loading surrounded by a fluid medium when its external surface is subjected to a point source. The problem is addressed via the use of the spatial Fourier transform. An expression is obtained for the radiated pressure that is evaluated for the far field using both the stationary phase method and the fast Fourier transform (FFT). The acoustic field calculated from the FFT is much more complicated than that obtained by using only the stationary phase method. In agreement with the geometrical theory of diffraction (GTD), alternative interpretations of the radiated field in terms of helical acoustic rays allows one to understand the reason for this result. The outstanding phenomenon underlined by the use of the FFT is the emergence of an infinite number of spatial dispersion curves associated with each leaky wave propagating in shells when excited by a point source.

Journal Article↗
PubMed2002

Scattering from a ribbed finite cylindrical shell with internal axisymmetric oscillators.

A theoretical formalism is elaborated to determine the acoustic field scattered from a finite cylindrical shell reinforced by a set of ribs with internal axisymmetric oscillators, the locations and properties of which can vary arbitrarily along the cylinder axis. Analytical expressions are derived for the scattered pressure and approximate expressions are proposed to calculate the backscattered field. Some applications have been carried out to investigate the problem of backscattering from a periodically ribbed finite cylindrical shell in the presence of rib aperiodicity or axisymmetric internal oscillators. The modifications of the main features associated with scattering from helical and Bloch-Floquet waves are examined and numerical results are presented with respect to the mean rib spacing and to the total mass of the internal structures.

Journal Article↗
PubMed2002

The effect of internal point masses on the radiation of a ribbed cylindrical shell.

A finite element analysis is performed on a submerged cylindrical shell with internal frames and point masses attached to the frames. A point force on the shell is shown to excite resonances of the frames. Without the point masses, most of these resonances are evanescent and do not radiate to the far field. With the point masses, the high circumferential order resonances couple with those at low circumferential order with the result of increasing radiation to the far field. In this investigation, the radiation increase is about 10 dB over a broad frequency range (1.5 to 3 times the ring resonance).

Journal Article↗
PubMed2002

Analysis of flexural wave velocity and vibration mode in thin cylindrical shell.

The relationship between the flexural wave velocity and the excited vibration mode of a thin cylindrical shell is investigated. The natural frequency corresponding to the vibration mode is obtained as the solution of characteristic equation of thin cylindrical shell. However, all of these vibration modes are not excited actually. To estimate the excited vibration mode, the concept of "modified bending stiffness" is introduced, and the influence of each stress component upon the modified bending stiffness is analyzed. The excited mode is theoretically discriminated from the nonexcited mode based on the smallness of this modified bending stiffness. The validity of our theory is confirmed by an excellent agreement between theoretical and experimental results on flexural wave velocity.

Journal Article↗
PubMed1992

Sound scattering by a cylindrical shell reinforced by lengthwise ribs and walls.

An analytical solution is derived for the acoustic response of submerged thin-walled ring cylindrical shell containing lengthwise stiffening members: internal stringers and walls. On the basis of the analysis of the acoustic pressure versus time diagrams the stiffener-borne wave-generation mechanisms are traced. Shown is that the shell/stiffener junctions act as additional entry and exit points of circumferential waves circulating in the shell and the fluid. The stiffening members cause transformations of circumferential waves from one propagation type to another.

Acoustics↗
PubMed2000

Influence of circumferential partial coating on the acoustic radiation from a fluid-loaded shell

Acoustic compliant coatings are a common approach to mitigate the radiation and scattering of sound from fluid-loaded submerged structures. An acoustic compliant coating is a coating that decouples an acoustic source from the surrounding acoustic medium; that is, it provides an acoustic impedance mismatch (different density and speed of sound product). Such a coating is distinct from an ordinary compliant coating in that it may not be resilient in the sense of low stiffness, but still provides an acoustic impedance mismatch. Ideally, the acoustic coating is applied uniformly over the entire surface of the fluid-loaded structure to minimize the acoustic radiation and scattering. However, in certain instances, because of appendages, it may not be practically possible to completely cover the surface of a fluid-loaded structure to decouple it from the adjacent acoustic medium. Furthermore, there may be some inherent advantages to optimizing the distribution of the coating around areas from which the acoustic radiation appears to be dominant. This would be analogous to the application of damping treatment to a vibrating structure in areas where the vibration levels are highest. In the case of the acoustic radiation the problem is more complex because of the coupling between the acoustic fluid and the structure. In this paper, the influence of a partial coating on the acoustic radiation from a fluid-loaded, cylindrical shell of infinite extent and excited by either a line force or an incident plane acoustic wave is examined. The solution to the response and scattered pressure is developed following the procedure used by the authors in previous work on the scattering from fluid-loaded plates and shells. The coating is assumed to be normally reacting providing a decoupling layer between the acoustic medium and the structure; that is, it does not add mass or stiffness to the base structure. The influence of added mass or stiffness of the coating can be included as an added inhomogeneity and treated separately in the solution.

Journal Article↗
PubMed2006

Imaging the Mott insulator shells by using atomic clock shifts.

Microwave spectroscopy was used to probe the superfluid-Mott insulator transition of a Bose-Einstein condensate in a three-dimensional optical lattice. By using density-dependent transition frequency shifts, we were able to spectroscopically distinguish sites with different occupation numbers and to directly image sites with occupation numbers from one to five, revealing the shell structure of the Mott insulator phase. We used this spectroscopy to determine the onsite interaction and lifetime for individual shells.

Journal Article↗
PubMed1963

Amino acids in the proteins from aragonite and calcite in the shells of Mytilus californianus.

Hydroxylysine and hydroxyproline are absent in the calcified proteins of Mytilus. The organic matrices from the calcite layers have a consistently higher ratio of acidic to basic amino acids than the aragonitic shell units. The uncalcified shell units periostracum and outer ligament, have very few acidic residues, which may in part account for the lack of mineralization.

Acids↗