Solid Fragments Research Articles

Effect of solvent on racemization in carbodiimide mediated solid phase fragment condensations

The Izumiya tripeptide was used to assess racemization in solid-phase fragment condensations. Boc-Gly-Ala-OH 1 was coupled to Leu-PAM resin DIC in a variety of solvents, both with and without HOBt. After cleavage from the resin, the extent of racemization was determined using C18 RP-HLPC to separate the epimers. Solvents used were DMF, NMP, TFE and each of these as mixtures with DCM. Also tested was a mixture of NMP and DMSO (85:15). Couplings in DMF/DCM (1:1) and NMP/DCM (1:1) in the presence of HOBt were in excess of 98% and racemization was undetectable. (<0.1%).

Electron Microscopy Study on Zirconia and Alumina Ceramic Powders Synthesized by Microwave Plasma Pyrolysis

ABSTRACTMorphology, chemistry and microstructure of zirconia and alumina based ceramic powders synthesized by microwave plasma pyrolysis were studied by transmission electron microscopy. Electron diffraction was used to determine the phases present, while conventional bright field and dark field imaging were used to characterize grain size and density variations. Materials analyzed in this study were either pure zirconia, pure alumina, or a ternary zirconia-yttria-alumina oxide. Solid spheres, hollow spheres, and fragments of hollow spheres were observed. All three modifications of zirconia were observed in the pure zirconia powder. In alumina, the predominant phase was cubic, gamma alumina. In the ternary oxide, most structures exhibited cubic zirconia diffraction patterns. Energy dispersive x-ray spectroscopy revealed chemical inhomogeneities in the ternary oxide powder.

Sterically hindered fragmentation in reactive solids

A two-dimensional model of a two-phase solid which undergoes a reaction at its surface is used to study the fragmentation of reactive materials in which the marphalagi- CBI hindering of fragment release is considered. Scaling concepts of cluster percolation theory are used to evaluate Monte Carlo data generated from a Simulation of the hindered fragmentation process. By defining a hierarchy of fragmentation objects, different scaling exponents arc computed for each of these objects as measured by the number of sub-objects they contain. In addition, it appears that each of the different measures of object size exhibits optimum scaling at a different critical reactive-phase mas fraction; simulation data indicate that the critical mass fractions follow a trend consistent with expected physical behaviour of the system. In addition, the critical mass fractions reported correspond to 'virtual' criticalities, i.e. the critical points cannot result in actual divergences in size, but rather are properties of the scaling fundion.

Fragmentation and attrition of carbonaceous particles generated from the fluidized bed combustion of fuel—water slurries

Char aggregates and bed particles covered by carbon deposits are formed as the result of injection of Fuel—Water Slurries (FWS) into hot fluidized beds. Fragmentation and attrition behaviour of these carbonaceous solids has been investigated using two bench-scale fluidized bed units, both 40 mm ID. The first is equipped with a basket for retrieval of fragments, the second with a two-exit head for measurement of time-resolved carbon elutriation rates. Fragmentation and attrition rates have been determined under combustion and inert conditions. They have been correlated with the external surface of carbon particles present in the bed when the size of carbonaceous solids was larger than the bed solids, or with the mass of carbon present in the bed when bed solids were also the test material. Rate equation constants have been estimated and compared with those previously obtained for various coal chars and cokes by means of the same experimental apparatus and technique.

Substantia nigra grafts and Parkinson's disease: from animal experiments to human therapeutic trials

During the decade since the first reports of functional effects of substantia nigra (SN) transplantation in animal models of Parkinson's disease, the procedure has progressed to human clinical trials. There is evidence that SN grafts can produce some alleviation of the manifestations of SN lesions in animal models, and by several measures these grafts appear to function in a manner similar to the normal SN. There do, however, appear to be limitations on the efficacy of SN allografts in rodent models, that may be related to an inability of fetal SN transplants to fully integrate into the host brain structure. No method of overcoming this limitation has yet been found. Studies of transplantation of human fetal SN to immunosuppressed rat hosts suggest that human donor tissue exerts proportionately greater effects than rat tissue, and is similarly effective when transplanted as solid tissue fragments or as dissociated cells. Only recently, a few controlled studies have obtained evidence for positive effects of SN grafts in primate models of Parkinson's disease. In the few clinical studies reported thus far, there are indications that some clinical improvements can be produced by SN grafts, although there is little or no evidence that the clinical changes found so far are larger than the changes that have been seen after adrenal medulla grafts. The possibility of a role of striatal injury in the clinical changes has not been resolved. It is noteworthy that nearly all of the studies of SN transplantation in rodents, primates, and humans have employed methodologies similar to those developed in the course of the first few reports on SN transplantation, and that the effects obtained by these methods are limited, even in rats. The possibility is raised that fundamental advances in SN transplantation techniques may be important for the development of a more efficacious clinical procedure.

Some aspects of the photoluminescence properties of solid argon: Solids versus clusters in a supersonic beam

Selectively excited photoluminescence spectra of Ar clusters are presented. They contain information concerning fragmentation of the clusters following primary exciton-type excitation. Excited Ar 2 ∗ molecules are identified as the main excited fragments. Close similarities between desorption of excited species from solid Ar and fragmentation of Ar clusters are found. Lifetime measurements of the wavelength-selected cluster luminescence bands indicate cluster-specific properties of the cluster luminescence center. It turns out that time- and spectrally resolved luminescence spectroscopy under selective photon excitation is a powerful tool to investigate electronic cluster excitation.

Intraoperative bronchial aspiration of ruptured pulmonary hydatid cysts

Ruptured pulmonary hydatid cysts are seen clinically and radiologically as persistent cavitary lesions of the lung. Bronchi opening into the pericyst cavity allow for discharge of fluid matter but not the escape of solid remnants of the collapsed parasite. Operative manipulation of the involved lung in the course of surgical management of chronic ruptured pulmonary hydatids can force fragments of the laminated membrane or small daughter cysts into the bronchial tree. Such extruded solid fragments lodge in bronchi of the same or opposite lung with resulting acute obstruction of airways. Intraoperative bronchial aspiration of hydatid material was seen in 7 patients with ruptured hydatid cysts of the lung, either primary or secondary to transdiaphragmatic extension of liver hydatids. The first clinical sign can be unexplained difficulty in ventilation. Effective management consists of prompt exposure of the stem bronchus on the operative side, with bronchotomy for suction retrieval of escaped solid fragments of the parasite.

The extraordinary radar echoes from Europa, Ganymede, and Callisto: A geological perspective

This outline of plausible geologic explanations for the icy Galilean satellites' radar properties takes into consideration electromagnetic scattering models for the echoes, available empirical and theoretical information about regolith formation, and ice physics. The strange radar signatures arise because (1) ice is electrically different from silicates and/or (2) icy regoliths contain bulk-density (and hence refractive-index) structures absent within silicate regoliths. Ice's relatively high radar-frequency transparency compared with that of silicates permits longer photon path lengths, deeper radar sounding, and a greater number of scattering events. Consequently, scattering mechanisms that cannot contribute significantly to lunar echoes can dominate icy-satellite echoes. Possible phenomena unique to icy regoliths include (1) smoothing out of discontinuities between solid ejecta fragments and more porous surroundings under the action of thermal annealing to form refraction-scattering (RS) “lenses” and (2) formation of density enhancements in the shape of crater floors that result in RS and/or total internal reflection (TIR). In either case, high-order multiple scattering is more likely to be responsible for the echoes than low-order scattering. Radar/radio observations can constrain the order of the scattering and the scale of the structures responsible for the echoes but might not determine whether TIR or RS dominates the scattering. Multiwavelength investigations of the degree of correlation between radar properties and geologic terrain type should prove most useful, because inter- and intrasatellite variations in radar properties probably correspond to variations in ice purity, regolith thickness, and regolith thermal history and age.

Fragmentation statistics from Eulerian hydrocode calculations

In this paper, we discuss a procedure for computing discrete fragmentation information for terminal ballistics events from the continuum data that emerges from two-dimensional Eulerian hydrocode simulations of these events. The present examples deal with the normal impact of lead cylinders on lead plates at velocities below 1600 m/s. In this regime, the resulting debris is almost exclusively solid lead fragments. We have experimental data of sufficient accuracy to evaluate the extraction of such fragmentation information from code simulations. The problem is interesting because the observed distribution of fragment size would require extreme subgrid resolution in the hydrocode if the statistics were computed directly. Our approach is different. We ask whether or not the general continuum description predicted by the code contains enough information to allow coupling of an analytic fragmentation theory that successfully predicts fragmentation statistics. We believe that this approach is valid, and discuss our current success in matching experimental data.

The Fc binding site for streptococcal protein G is in the C gamma 2-C gamma 3 interface region of IgG and is related to the sites that bind staphylococcal protein A and human rheumatoid factors.

The isolated 35 kDa fragment of protein G obtained by papain digestion of group G streptococci was found to bind solid phase intact IgG, Fc (2C gamma 2 + 2C gamma 3 domains), F(ab')2 and F(acb)2 (F(ab')2 + 2C gamma 2 domains) fragments but not pFc' (2C gamma 3 domains) fragments. The level of binding to rabbit F(acb)2 and rabbit F(ab')2 fragments was similar. Protein G binding to solid phase Fc fragments was inhibited by IgG, Fc, staphylococcal protein A and its monovalent fragment D, but was enhanced by F(ab')2 fragments. Chemical modification of tyrosine but not histidine residues of IgG abrogated its ability to inhibit the binding of protein G to solid phase Fc fragments. Protein G was found to strongly inhibit the binding of a monoclonal and a polyclonal human rheumatoid factor to IgG. These findings indicate that protein G binds with separate sites to the Fc and F(ab')2 fragments of IgG, that the interaction with the Fc fragment occurs at the C gamma 2-C gamma 3 domain interface region and that tyrosine but not histidine residues in this area are likely involved. The relationship of the Fc fragment-binding site specificity of protein G to that of other microbial IgG binding proteins and human rheumatoid factors is discussed.

Intra- and Extracellular Localization of Lignin Peroxidase during the Degradation of Solid Wood and Wood Fragments by Phanerochaete chrysosporium by Using Transmission Electron Microscopy and Immuno-Gold Labeling

The distribution of lignin peroxidase during degradation of both wood and woody fragments by the white rot fungus Phanerochaete chrysosporium was investigated by using anti-lignin peroxidase in conjunction with postembedding transmission electron microscopy and immuno-gold labeling techniques. The enzyme was localized in the peripheral regions of the fungal cell cytoplasm in association with the cell membrane, fungal cell wall, and extracellular slime materials. In solid wood, lignin peroxidase was detected in low concentrations associated with both superficial and degradation zones within secondary cell walls undergoing fungal attack. A similar but much greater level of extracellular peroxidase activity was associated with wood fragments degraded by the fungus grown under liquid culture conditions optimal for production of the enzyme. Efforts to infiltrate degraded wood pieces with high levels of lignin peroxidase showed the enzyme to be restricted to superficial regions of wood decay and to penetrate wood cell walls only where the wall structure had been modified. In this respect the enzyme was able to penetrate characteristic zones of degradation within the secondary walls of fibers to sites of lignin attack. This suggests a possibility for a close substrate-enzyme association during wood cell wall degradation.

Intraretinal transplantation of fluorescently labeled retinal cell suspensions

Dissociated cell suspensions of neonatal neural retina, labeled with the fluorescent dyes Fast blue or Fluoro-gold, were transplanted into the retina of normal adult rats or of rats affected by late stage phototoxic retinopathy. Light microscopy showed good survival, differentiation, and integration of the transplants, as well as permanence of the label up to 100 days. The results indicate that the transplantation of dissociated, fluorescently labeled retinal cells has a number of advantages over the transplantion of solid fragments of retinal tissue, previously performed by ourseleves and others. The following are some of the most immediate procedural advantages: the number of transplanted cells can be assessed, the transplanted cells are in a more intimate contact with the host tissue and therefore integrate better with the host, and the fluorescent tags permit precise determination of the survival and distribution of the transplanted cells.

Metastasis of Ocular and Flank Implants of the 13762NF Mammary Adenocarcinoma in Syngeneic Rats&lt;xref ref-type="fn" rid="FN1"&gt;2&lt;/xref&gt;

Solid fragments of a syngeneic tumor of low immunogenicity were implanted on the anterior surface of the iris or posterior surface of the cornea in young Fischer 344 rats. Growth and metastasis of these implants were examined and compared with those occurring following sc tumor implantation in the flank. Corneal implants did not grow well or metastasize. Iridial implants grew well, and tumor typically filled the eye within a few weeks. If tumor-filled eyes were left intact, all rats died or became moribund 7-9 weeks later. Metastasis was seen in the lungs (11/11), cervical lymph nodes (7/11), body wall (5/11), heart (4/11), kidney (4/11), and liver (3/11). Removal (enucleation) of tumor-filled eyes prior to spread to the orbit prevented the development of overt metastatic disease for 1-2 years (11/11). When healthy enucleated rats were necropsied 0 days to 26 weeks post enucleation, small nodules were seen in the lung (9/13), liver (3/13), or spleen (1/13). Nodules were not seen in rats that had been housed in our animal facility for 1-2 years (16/16), had eye surgery with tumor implanted on the posterior surface of the cornea (6/6), or had been subjected to the surgical procedures of corneal implantation and enucleation (3/3). When tumors were implanted sc, rats died after 6-7 weeks. Metastasis was seen in the lung (12/12), lymph nodes (12/12), spleen (1/12), and liver (1/12). Removal of very small flank tumors failed to prevent animals from dying 7-8 weeks later with pulmonary and lymph node metastasis (10/10). In summary, iridial implantation resulted in an altered pattern of metastasis. Animals that had iridial implants and enucleation failed to develop overt metastatic disease and had small nodules in the lung, liver, or spleen.

Rb-Sr-analyses of Apollo 16 melt rocks and a new age estimate for the Imbrium basin: Lunar basin chronology and the early heavy bombardment of the moon

Rb-Sr-model ages on 7 impact “glass-bombs” and internal Rb-Sr isochrons for two crystalline impact melt rocks from the Apollo 16 collection have been determined. The post-Cayley “glass-bombs” with model ages between 4.75 ± 0.45 AE and 3.97 ± 0.08 AE can be classified according to their calculated single stage (87Rb86Sr)I-ratios: 67728, 67946, and 67627.8 point to a KREEP-free precursor terrain—the Descartes highlands; whereas 63566, 67567, 67627.10 and 67629 are derived from the more heterogeneous Cayley plains. The very feldspar-rich impact melt rock 65795, which is compositionally similar to the group of feldspathic microporphyritic melt breccias (FM-suite), yields a crystallization age of 3.81 ± 0.04 AE (2σ; λ87Rb = 1.42−11yr−) and ISr of .69929 ± 3. In the subophitic impact melt rock 60635.5 two ages were recorded: One isochron with 3.87 ± 0.02AE and ISr of 0.69920 ± 3 gives the crystallization age of a fine-grained internal clast. At 3.75 ± 0.03 AE this fragment was incorporated into the host lithology of 60635 which is a member of the Anorthositic Noritic Melt Rock (ANMR) group. This group has a crystallization age of about 3.75 AE. The ANMR rocks and several samples of Apollo 14 crystalline impact melt rocks belong to a suite of “young crystalline impact melt rocks” ranging in age from 3.71 to 3.81 AE. These ages are in conflict with the canonical age of the Imbrium event (3.85 AE). It is argued that the young Apollo 14 and 16 melt rocks cannot represent solid exotic fragments or melt splashes ejected from post-Imbrium local or distant craters. Instead, these rocks are derived from coherent impact melt sheets of pre-Imbrian craters with diameters larger than 5–7 km. They are interpreted as clasts of the Fra Mauro and Cayley formation breccia deposits, and therefore their ages are used as an upper limit for the age of the Imbrium event. We suggest that the Imbrium basin and the related Fra Mauro and Cayley formations were formed 3.77 ± 0.02 AE ago and could be even as young as 3.75 AE. As a consequence, we adopt 3.92 ± 0.03 AE, 3.87 ± 0.03 AE, and 3.84 ± 0.04 AE as ages for the Nectaris, Serenitatis, and Crisium basins, respectively, in agreement with the relative crater densities measured on the ejecta blankets of these basins (Wilhelms, 1984). The proposed age sequence leads to an average formation interval for the observed 12–13 Nectarian basins of 7 to 14 m.y. leaving ~30 pre-Nectarian basins of unknown age. These facts suggest that there is no “late terminal lunar cataclysm” in the sense of a culmination of the lunar impact rate at ~3.8 AE ago. Rather, the observations are compatible with a steeply and steadily decreasing flux of impactors (Hartmann, 1980) in the sense of an “early heavy bombardment” which started at the time of the moon's accretion and terminated around 3.75 AE ago.

Isolation and Quantification of Cadmium and Copper-Species in Lettuce Plants

Cadmium and copper-species from native lettuce plants were isolated and quantified after Ultra Turrax homogenization in buffer and subsequent ltracentrifugation and gel filtration of the cytosol. From the cytoplasma, a high molecular weight metal binding-protein (>75000g/mol) containing 55% of the cytoplasmic cadmium and 20% of the cytoplasmic copper and a low molecular weight metal binding-protein (3200g/mol) containing 45% of the cytoplasmic cadmium and 70% of the cytoplasmic copper were isolated. Beside these there were two more copper binding-proteins of about 57000 and 25000g/mol, containing only small percentage of copper. The solid fragments of the cell, containing 50% of the total cadmium and 20% of the total copper respectively were not further examined. A broad variation in the metal balance from plant to plant was observed.

Effect of an impact-generated gas cloud on entrained surface boulders and spall ejecta

The purpose of this investigation is to study the effect of an impact-generated gas cloud on the size-velocity distribution of large, solid ejecta fragments that become entrained in it, with particular reference to the possible Martian origin of the SNC meteorites. The entrainment both of loose surface boulders and of the early-time, large-size, high-velocity spall component of the crater ejecta is modeled numerically. Surface boulders from as far as 40 km from the center of impact can be accelerated by the high velocity leading edge of the gas cloud to velocities in excess of Martian escape velocity (5 km/s), but are generally crushed by the acceleration. Spall fragments become entrained later and nearer the center of the gas cloud, where gas velocities are much less. High velocity spalls are decelerated by the gas and low velocity spalls are accelerated by the gas, but no spalls ejected at < 5km/s are accelerated to velocities 5km/s. An impact-generated gas cloud is thus expected to scour the pre-existing surface of loose material and to change the size-velocity distribution of spall ejecta, but does not sufficiently enhance the velocities of crater ejecta to explain the Martian origin of SNC meteorites as large rocks.

Liberation of mineral constituents by high-voltage pulses

Comparison of compressive and explosive disintegration of rocks aimed at the liberation of valuable minerals shows the great advantage of explosive disintegration. This advantage is especially noticeable where it is important to preserve crystals of precious stones. Electrocrushing devices ensure the explosion of rock lumps by means of almost contactless (just a touch of electrodes) methods that generate plasma in solids during the transfer of the electrical pulse through the rock. Analysis of electrical breakdown products of different rocks versus fragmentation of solids and results of mineral liberation by electro-crushing show predominantly tensile breakage of mineral aggregates by explosive electro-crushing. High-voltage pulses induce non-destructive liberation of precious stones and other minerals having a boundary with rock matrices. The examples of liberating diamond, emeralds, gold, platinum and coal are discussed.

Statistics of structure within solid fragments studied by 2D simulation

A strongly fragmented two-dimensional medium was generated by a large number (103–104) of randomly thrown linear cracks. Various properties of fragments (e.g., number, size, shape, perimeter length, number of sides, and internal structure) were analyzed by computational geometry using a plane sweep algorithm. Asymptotically, for high crack density, the simulated fragment sizes follow the Mott distribution formula (cumulative number decreases exponentially with linear fragment size). Fragment structure, due to dangling or fully internal cracks, is identified with internal damage. The magnitude of damage as function of crack density is obtained by computation and analysis and is shown to reach a constant value asymptotically. By our results, a blasting operation leading to crack growth increases the ratio of small fragments in relation to larger ones.

A powder-based approach to semisolid processing of metals for fabrication of die-castings and composites

A technique is presented for the generation of a globular (non-dendritic) array of solid fragments surrounded by a solute-enriched liquid. This is based on the premixing, heat treatment and consolidation of different types of powder. The resultant slurries have then been injected into a die at high velocity. The technique offers promise in terms of the versatility with which the slurry microstructure can be controlled and the soundness of the resulting die-castings has been encouraging. Among the effects investigated are the role of solute diffusion, the importance of globule size and the nature of coarsening phenomena. Experiments have also been carried out on the incorporation of ceramic fibres into the product and this appears to offer promise as a composite fabrication route. The work described here concerns only aluminium-base material alloyed with magnesium, although the principles outlined are expected to apply to many other systems.

Nonlinear optical studies and CO2 laser-induced melting of Zn-doped GaAs

The absorption of CO2 laser radiation in p-type GaAs is dominated by direct free-hole transitions between states in the heavy- and light-hole bands. For laser intensities on the order of 10 MW/cm2, we report that the absorption associated with these transitions in moderately Zn-doped GaAs (∼1017 cm−3) begins to saturate in a manner predicted by an inhomogeneously broadened two-level model. At higher laser intensities surface melting occurs initially at localized sites in moderately doped material and more uniformly in heavily Zn-doped samples (≳1018 cm−3). As the energy density of the CO2 laser radiation is progressively increased further, the surface topography of the samples shows signs of ripple patterns, high local stress, vaporization of material, and exfoliation of solid GaAs fragments. Electron-induced x-ray emission data taken on the laser-melted samples show that there is a loss of As, compared to Ga, from the surface during the high-temperature cycling. By irradiating the samples in air, argon, and vacuum, we find that the vaporization rates are directly influenced by the ambient environment, particularly by the interaction of oxygen with the molten GaAs. Secondary ion mass spectrometry measurements are used to study the diffusion of oxygen from the native oxide and the incorporation of oxygen in the near-surface region of the GaAs samples that have been melted by a CO2 laser pulse. We find that oxygen incorporation does occur, and that the amount and depth of the oxygen incorporation depends on the laser energy density, number of laser shots, and ambient environment. For samples that are irradiated in argon or vacuum, we find that removal of the native oxide can be accomplished with CO2 laser pulses. Similar measurements are performed on Si-implanted GaAs, and results are reported for the redistribution of the implanted silicon atoms, the deviations from stoichiometry, and the incorporation of oxygen in the resolidified layer.