Center Of Cavities Research Articles

Hydrogen Uptake by {H[Mg(HCOO)3]⊃NHMe2}∞ and Determination of Its H2 Adsorption Sites through Monte Carlo Simulations

A detailed analysis of the solvothermal synthesis in DMF of the polymeric magnesium formate {H[Mg(HCOO)(3)]⊃NHMe(2)}(∞) (1) from Mg(ClO(4))(2)·6H(2)O revealed that the final crystalline product is formed after an acid-catalyzed DMF hydrolysis, producing formic acid and dimethylamine. The former bridges magnesium(II) centers, creating the 3D scaffold, while the latter is trapped inside the cubic cavities of the polymer, engaging in strong hydrogen bonding with the formate ions of the cage. After thermal activation and guest removal, the material was tested for hydrogen uptake at T = 77 K over the 0-80 bar pressure range, and the existence of preferred H(2) adsorption sites was assessed through grand canonical Monte Carlo (GCMC) simulations. No specific low-energy site was found, and the H(2) molecules positions within the framework cavities are mainly dependent on packing effects. Thus, at low H(2) loadings the most populated site is the center of the cubic cavities, even though, at higher pressures, two more "localized" positions have been found by the simulation because of the reduced freedom of movement. The maximum experimental H(2) uptake corresponds to 8.8 mg/g or 13.5 mg/cm(3).

An Unexpected Role for the Clock Protein Timeless in Developmental Apoptosis

BackgroundProgrammed cell death is critical not only in adult tissue homeostasis but for embryogenesis as well. One of the earliest steps in development, formation of the proamniotic cavity, involves coordinated apoptosis of embryonic cells. Recent work from our group demonstrated that c-Src protein-tyrosine kinase activity triggers differentiation of mouse embryonic stem (mES) cells to primitive ectoderm-like cells. In this report, we identified Timeless (Tim), the mammalian ortholog of a Drosophila circadian rhythm protein, as a binding partner and substrate for c-Src and probed its role in the differentiation of mES cells.Methodology/Principal FindingsTo determine whether Tim is involved in ES cell differentiation, Tim protein levels were stably suppressed using shRNA. Tim-defective ES cell lines were then tested for embryoid body (EB) formation, which models early mammalian development. Remarkably, confocal microscopy revealed that EBs formed from the Tim-knockdown ES cells failed to cavitate. Cells retained within the centers of the failed cavities strongly expressed the pluripotency marker Oct4, suggesting that further development is arrested without Tim. Immunoblots revealed reduced basal Caspase activity in the Tim-defective EBs compared to wild-type controls. Furthermore, EBs formed from Tim-knockdown cells demonstrated resistance to staurosporine-induced apoptosis, consistent with a link between Tim and programmed cell death during cavitation.Conclusions/SignificanceOur data demonstrate a novel function for the clock protein Tim during a key stage of early development. Specifically, EBs formed from ES cells lacking Tim showed reduced caspase activity and failed to cavitate. As a consequence, further development was halted, and the cells present in the failed cavity remained pluripotent. These findings reveal a new function for Tim in the coordination of ES cell differentiation, and raise the intriguing possibility that circadian rhythms and early development may be intimately linked.

High-quality acoustic cavities based on radial sonic crystals.

Radial sonic crystals are radially inhomogeneous systems that present a dispersion relation similar to one dimensional sonic crystals, with the peculiarity of having low-frequency band gaps. These structures are here employed to design high-quality circularly symmetric acoustic cavities. The presence of band gaps in their dispersion relation allows to localize sound in the cavity centers, leading to strong resonances whose frequency depends on the symmetry of the field. Therefore, it is possible to design cavities with monopolar, dipolar, quadrupolar, etc., symmetry. A proposal for its physical realization is also described, showing that radial sonic crystals are possible to build by using the concept of acoustic metamaterials. [Work supported by MCIIN of Spain and ONR.]

Atomic-Scale Distribution of Water Molecules at the Mica-Water Interface Visualized by Three-Dimensional Scanning Force Microscopy

We have developed a method referred to as three-dimensional scanning force microscopy (3D-SFM) which enables us to visualize water distribution at a solid-liquid interface with an atomic-scale resolution in less than 1 min. The 3D-SFM image obtained at a mica-water interface visualizes 3D distributions of adsorbed water molecules above the center of hexagonal cavities and the laterally distributed hydration layer. The atomically resolved 3D-SFM image showing mirror symmetry suggests the existence of surface relaxation of the cleaved mica surface next to the aqueous environment.

Aqueous Solution Structure at the Cleaved Mica Surface: Influence of K+, H3O+, and Cs+ Adsorption

Monte Carlo simulations of the interface between the cleaved surface of muscovite mica and aqueous solution containing K+, Cs+, and/or H3O+ ions compensating negative charge of muscovite and Cl− ions at ambient conditions are reported. Simulation results reveal that, in dependence on surface concentration, K+ is preferentially adsorbed above ditrigonal cavity centers or substituted tetrahedrons ∼1.7 A or ∼2.15 A from the surface, respectively, whereas Cs+ is preferentially adsorbed above ditrigonal cavity centers ∼2.0−2.2 A from the surface. Adsorption of K+ and Cs+ in excess of the surface concentration compensating the negative charge of muscovite leads to a coadsorption of Cl− as an outer sphere complex on the solution side of the Stern layer. This study also suggests that H3O+ is the only species adsorbing as close as ∼1.3 A from the mica surface in contact with deionized water and contributing to the first adsorbed layer observed recently with X-ray reflectivity. On the basis of available experimenta...

Met‐Enkephalin Involvement in Morphine‐Modulated Peritonitis in Swiss Mice

Morphine coinjection with zymosan inhibits pain and leukocyte accumulation during peritonitis in several strains of mice, and affects systems of endogenous opioids. Present investigations focus on Met-enkephalin (Met-ENK) in the inflamed peritoneal cavity and brain centers of Swiss mice. Males of Swiss mice were IP injected with zymosan or zymosan supplemented with morphine. At the selected time points the peritoneal leukocytes were counted and the Met-ENK level was measured in exudatory fluid and leukocytes, striatum, hypothalamus, and pituitary gland. The Met-ENK content in peritoneal fluid rised sharply after zymosan injection, which corresponded with its decline in exudatory leukocytes, hypothalamus, and striatum. Morphine coinjection enhanced intraperitoneal accumulation of Met-ENK and its release from exudatory leukocytes, but inhibited its early fluctuations in hypothalamus and striatum. Effects of morphine-modulated inflammation on the Met-ENK system lasted longer than 7 days.

Extensive intrazeolitic hydrolysis of Zn(II): partial structures of partially and fully hydrated Zn(II)-exchanged zeolite X

Complete Zn 2+ exchange of two single crystals of zeolite X (Na 92Si 100Al 92O 384) was attempted at 80°C from aqueous Zn(NO 3) 2 (pH=5.5 at 23°C). The structures of crystal 1 (partially dehydrated by evacuation at 23°C and 10 −3 Torr for two days) and crystal 2 (fully hydrated) were determined by X-ray diffraction techniques in the cubic space group Fd 3 ̄ at 23°C ( a o=24.750(5) and 24.872(6) Å, respectively). They were refined using all intensities to the final error indices R 1=0.126 and 0.116 based on the 428 and 348 reflections, respectively, for which F o>4 σ( F o). Each crystal has about 54 Zn 2+ ions per unit cell, indicating the uptake of eight excess Zn(OH) 2 molecules. In both crystals, further extensive hydrolysis of Zn 2+ is seen. Many non-framework oxygens were not found. In crystal 1, 34 Zn 2+ ions per unit cell occupy conventional cationic sites: 10 are at site I ′, 12 at site II, and 12 at site III ′. Three Zn 2+ ions each coordinate to a framework oxygen at a non-conventional site in the supercages. Three Zn 2+ ions at the centers of sodalite cavities each coordinate tetrahedrally to four non-framework oxygens to give (likely) Zn(OH) 2(H 2O) 2 which hydrogen bonds multiply to the zeolite framework. At three supercage positions, about 14 Zn 2+ ions that do not coordinate to the zeolite framework are found. Per unit cell, 37 H 3O + ions are found: 20 at site I ′ and 17 at site II. It is presumed, considering the number of H 3O + ions, that the latter 14 Zn 2+ ions are hydrolyzed Zn 2+ ions, likely hydrated Zn(OH) 2 molecules, some likely bridging. In crystal 2, 33 Zn 2+ ions per unit cell are found at conventional cationic sites: two at site I, 14 at two different sites I ′, seven at site II, and 10 at site III ′. As in crystal 1, three Zn 2+ ions each coordinate to a framework oxygen at a non-conventional site in the supercage. At three supercage positions, about 18 Zn 2+ ions that do not coordinate to the zeolite framework are found. Per unit cell, 40 H 3O + ions are found: 18 at site II ′ and 22 at site II. Only about 16 non-framework oxygens were found per unit cell: eight water molecules in the supercages and, in the sodalite cages, eight hydroxide ions which participate in the formation of two nearly cubic Zn 4(OH) 4 4+ clusters.

First Report of Bell Pepper (Capsicum annuum) as a Host of Sclerotinia minor in California.

In 1997, commercially grown bell pepper in the Salinas Valley (Monterey County), California, developed a previously undescribed disease. Plant foliage became pale green and wilted. Crowns developed brown lesions that girdled the plants, resulting in plant death. White mycelia and small (2 to 3 mm), black, irregularly shaped sclerotia were observed on the outside of plant crowns and in the centers of stem cavities. Isolations consistently resulted in the recovery of Sclerotinia minor. Pathogenicity was tested by inoculating 2-month-old bell pepper plants (cv. California Wonder) with sclerotia from three pepper and three lettuce (Lactuca sativa) isolates of S. minor (seven plants per isolate). Six to 10 sclerotia were placed 1 cm below the soil line and adjacent to the plant crowns. After 8 days, plants inoculated with pepper and lettuce isolates developed symptoms similar to those found in commercial fields, and S. minor was recovered from all peppers. The uninoculated control plants developed no symptoms. This is the first report of bell pepper as a host of S. minor.

Parametric optimization of neutron drum counter

We optimize the efficiency of neutron counter designs for 208-1 drums when counting totals neutrons by using MCNP. Design parameters, including the number of 3He tubes and the tube pitch, depth, and gas-fill pressure, were investigated. Both cylindrical and rectilinear geometries with and without cadmium liners were examined. Fission spectra from both 240Pu and 252Cf were modeled as isotropic point sources located in the geometric center of the detector cavities.

Rapid Method for Detection ofAspergillus5S Ribosomal RNA Using a Genus-specific Oligonucleotide Probe

Ribosomal RNA (rRNA) is present in all prokaryotic and eukaryotic cells. Although sequences are conserved, variations in nucleic acid composition are known to be species specific. Formalin or Bouin's fixed, paraffin-embedded tissue specimens from 17 cases of culture proven Aspergillus sp infections were studied by a rapid (< 30 minutes) in situ hybridization procedure using a biotinylated oligonucleotide DNA probe complementary to nucleic acids 1-22 of Aspergillus sp 5S rRNA sequence. Positivity was noted within fungal organisms in all 17 cases and was identified in both hyphal forms and within fruiting bodies. Signal was weak or absent within the center of Aspergillus abscess cavities with increasing signal located toward the periphery of the cavity, suggesting that rRNA in situ hybridization may detect viable fungal forms. In situ hybridization with the oligonucleotide probe on tissues containing several different organisms including Candida sp, Histoplasma capsulatum, Cryptococcus neoformans, Pneumocystis carinii, Pseudallescheria boydii, Fusarium sp, and Mucor were negative. Use of site specific oligonucleotide probes specific for a variety of rRNA sequences may aid in the diagnosis of several medically important bacterial, fungal, and protozoal pathogens.

Moderate heat treatment of bone allografts. Experimental results of osteointegration.

The use of bone allografts is often essential in orthopedic surgery. Strict donor screening, including HIV testing 3 months postoperatively, is mandatory before a transplant may be used. Yet these measures do not definitely rule out the possibility of HIV transmission, as there is a window period before infection is revealed by blood testing. Accordingly, there is a need for virus inactivation methods that can be used on bone allografts. As radiation treatment and chemical methods have a number of disadvantages, we chose a moderate heat treatment of 65 degrees C for a series of animal experiments. In 12 rabbit femoral condyles, moderate-heat-treated bone allografts were implanted into 6-mm drill holes. Twelve normal allografts and 12 empty drill holes served as controls. Radiologic and histological evaluation up to 12 weeks postoperatively revealed slow spontaneous bone remodeling from the rim to the center of the empty cavities. Normal deep frozen allografts were quickly intergrated after a short period of osteoclast reaction around the transplant, with occasional bone bridges between host and allograft. The examination of heat-treated allografts showed no differences to the controls, including morphologic aspects and the time course of osteointegration. Five zones of bone repair and osteointegration were distinguished. We conclude that thermal treatment of bone allografts has adverse effects on osteointegration in the rabbit femoral condyle. Thus, it may contribute to improving safety in human bone transplantation.

Stereotactic Aqua Stream and Aspirator for Removal of Intracerebral Hematoma

The stereotactic aqua stream and aspirator is modified from the aqua stream and aspirator for stereotactic evacuation of intracerebral hematoma. The newly designed needles were adapted to Leksell, Patil, Komai and Sugita stereotactic equipment. The new device was used in 14 cases with intracerebral hematoma. The tips of the needles were stereotactically inserted into the center of the hematoma cavities. The ratios of evacuated hematoma against hematoma content varied from 73 to 98%, averaging 87.2%. Hematomas could be satisfactorily and safely evacuated at any stage. Cerebral perfusion pressure was increased by 20 mm Hg during surgery.

Investigation of ammonium sites in proton conducting NH 4TaWO 6/ND 4TaWO 6-ceramics by neutron powder diffraction

Rietveld refinement of high resolution neutron powder diffraction data permitted the location of ammonium groups at 8b positions within the defect pyrochlore structure (space group: Fd3m). The ammonium groups were found to stay at the center of cavities, which are formed by a three-dimensional network of interacting tunnels. At room temperature and at 523 K the deuteria are aligned towards the six nearest oxygens. The evaluation of the data collected indicates the possibility of a Grotthus-type mechanism.

Electron localization in liquid water: A computer simulation study of microscopic trapping sites

Sites at which excess electrons in pure water at 10 °C could become initially localized and subsequently rapidly solvated are identified by scanning a molecular dynamics simulation of pure equilibrium ST2 water with a test charge. Very favorable sites with respect to both volume and electrostatic potential are found in relatively high number density. Although the observed distribution of large cavities spans a wide range with respect to the electrostatic potential at the cavity centers, the calculated potential energy at the most favorable sites is almost as large as the apparent hydration energy of the electron in the equilibrated state.

Structure of a Vermiculite-Aniline Intercalate

AbstractA vermiculite-aniline intercalate with a basal spacing of 14.78 Å was investigated by one- and two-dimensional X-ray diffraction methods. The intercalate, prepared by ion exchange between Na-saturated vermiculite from Llano, Texas, and a 1% aniline hydrochloride solution, contains only one aniline cation per single layer cell. A reduced effective cell-charge is believed to be responsible for this. Structure factor calculations were made in space group C2/c and with unit cell dimensions of a = 5.33, b = 9.18, c = 29.78 Å, and β = 97.0°. However, extra reflections in the a*b* plane, which are similar to those in a vermiculite-benzidine intercalate, showed that after aniline intercalation the true unit cell became primitive. The aniline cations are distributed statistically over equivalent crystallographic sites in the interlayer space. The organic molecules are orientated with their planes vertical and their nitrogen atoms over the projected centers of the ditrigonal cavities into which they key. The aniline cations form ordered arrays upon the silicate layers by packing into rows. Perpendicular to [010], populated and vacant rows alternate. Along populated rows aromatic ring planes are alternately parallel and perpendicular to [010]. With small adjustments this model is similar to that of benzidine-vermiculite.

Giant monopole resonances in the scattering of waves from gas-filled spherical cavities and bubbles

Continuing our previous work on viscoelastic scattering of p waves from fluid-filled spherical cavities in sound-absorbing materials, we now perform the theoretical analysis needed for the complete study of the monopole mode of vibration. Our approach is based on the Breit–Wigner formulation of nuclear scattering theory, and from it we show how the scattering amplitudes consist of two parts, the smooth background of the evacuated cavity and the resonance contribution of the filler fluid. We present a complete analytical study of the giant fundamental resonance and its overtones in the monopole case. The results are then particularized to the Rayleigh region and also to the case of evacuated cavities in lossless rubber and to gas bubbles in water, recovering and extending previous results available in the literature. Studying the sound pressure level at the center of air-filled cavities in lossy materials, we quantitatively determine how absorption shifts the resonance peaks and broadens their width. Using our theory we find that the width of the resonance peaks depends linearly on the resonance frequencies, and we show how this important result can be used to determine the shear absorption parameter of viscoelastic materials. We also find that the giant monopole resonance for air-filled cavities in rubber contains a contribution from the shear waves in the cavity wall and another from the resonance oscillations of the air-filling in a 15:1 ratio, for this particular material combination. We display numerous plots, some obtained from the analytic monopole formulas developed here, and some numerically obtained by computer for dipoles and quadrupoles. Finally, we show graphs of the summed scattering amplitudes fpp and fps accounting for the first twenty multipole contributions, and the dominance of the monopole term emerges again from this result. We have assumed ’’weak’’ absorption to simplify the analytical treatment, but any viscosity level can be handled by computer using this method.

Temperature Regulation in Nestling Cactus Wrens: The Development of Homeothermy

The Cactus Wren is a permanent resident of semi-arid desert-scrub areas of the southwestern part of the United States and northem Mexico. In the Sonoran Desert near Tucson, Arizona, its breeding season usually extends from March to August, during which two and occasionally three broods of three or four young are raised. The Cactus Wren is an ideal subject for developmental studies because of its long nestling period ( 26 days ), convenient size, and accessibility. The development of structural and behavioral features of the Cactus Wren are described in detail by Anderson and Anderson ( 1961). and they were returned to their nests within 24 hours. Individuals were not used more than once. The young were fed ground beef and meal worms (Tenebrio larvae) and were maintained in a replete condition during the experiments. The ages of nestlings were usually known from our observations at nests and were confirmed by comparing wing length with a standard wing length growth curve ( Anderson and Anderson 1961) . Temperature regulation at ambient temperatures below 35°C was studied by placing nestlings in 260-ml plastic jars with air-tight lids. Air was passed through these containers at a.constant rate (one liter/min) after it was dried by passage through tubes of Drierite dessicant ( anhydrous calcium sulfate). Temperatures inside the containers were measured with indwelling mercury thermometers. The nestlings were isolate’d from the walls of the containers by nylon mesh so that a maximum amount of the body surface was exposed to the circulating air. A range of ambient temperatures was obtained by taking measurements at various times during the day throughout the breeding season. After the nestlings had been in the chambers for 45 minutes their body temperatures were measured by inserting a thermistor probe through the mouth deep into the proventriculus. Regulation at temperatures above 35°C was studied by placing nestlings in shallow paper cups in a constant temperature incubator ( ? 0.5C ). Body temperatures were measured over a three-hour interval at ambient temperatures of 36, 40, and 44°C. The relative humidity was not controlled but never exceeded 20 per cent. Temperatures of nestlings in the field were measured with orally inserted thermistors. Temperatures in the center of the nest cavities and in the shade outside the nests were measured with permanently fixed mercury thermometers.

Self-Consistent-Field Calculations of Bound Electron Pairs in Dielectric Media

The potential for an electron trapping center in a dielectric medium is constructed by a multipole expansion and the effect of electronic polarization of the dielectric included in the electron adiabatic approximation. The Hartree—Fock equations are converted to a set of difference equations, which are solved by a matrix method. For a series of alkali halides, the calculated F and F′ centers s—p excitation energies are generally within 20% of the observed values. Calculations are carried out for the one- and two-electron cavity and one-electron positive-ion trapping centers in liquid ammonia. Calculated heats of solution, pairing energies, and s—p excitation energies are compared with experimental results.

Limestone Diagenesis and Dolomitization in Mississippian Carbonate Banks in Montana

ABSTRACT Waulsortian type carbonate banks in central Montana were diagenetically altered in three major stages: before, during, and after subaerial exposure of the tops of the banks. Before subaerial exposure, cloudy radiaxial fibrous drusy mosaic was precipitated as aragonite on all free internal surfaces. Opaline silica was dissolved, and small amounts of chalcedonic chert replaced parts of fossils and the fibrous mosaic. With partial emergence of the banks, the lime mud and fossils were altered, clear equant-grained drusy mosaic calcite and euhedra of dolomite were formed in centers of cavities lined with fibrous crusts, and seepage refluxion of hypersaline water formed an irregular zone of dolostone at the tops of the banks. Other changes involved weathering of the exposed surface, dilatational fracturing, dissolution of cavelike openings within the banks, and filling of the fractures and openings with crinoid debris. After resubmergence, the banks were engulfed by continued Lodgepole limestone deposition. Late in diagenesis a minor amount of dedolomitization occurred, and, perhaps, microspar (Folk, 1965) formed neomorphically.

The structure of synthetic zeolite G

The sodium ions in zeolite G are not located in the openings of the six-membered oxygen windows, but are shifted toward the center of the cubic octahedral cavities.