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PubMed1976

Characterization of 80-million-year-old mollusk shell proteins.

Fossil glycoproteins of the soluble organic matrix are present in an 80-million-year-old mollusk shell from the Late Cretaceous Period. Discrete molecular weight components, as determined by gel electrophoresis, are preserved. The fossil organic matrix was compared with the organic matrix of a living representative species of the same superfamily. A particular repeating amino acid sequence, found in contemporary mollusk shell proteins, was identified in the fossil glycoproteins. The ultrastructure, mineralogy, and chemistry of the inorganic components of the fossil and contemporary shells provide information on the state of preservation of the fossil. The use of fossil shell proteins to further our understanding of molecular evolution is discussed.

Amino Acids↗

PubMed1979

Interior remodeling of the shell by a gastropod mollusc.

As the Conus shell grows by spiraling of the outer lip around the axis, profound internal shell dissolution thins the walls of the protected penultimate whorl from several millimeters to <50mum. Shell material is added to the inside of the spire and the anterior part of the columella. The resulting shell has a uniformly thick last whorl and thickened spire that enhance defense against crushing predators and a greatly expanded interior living space for the animal.

Journal Article↗

PubMedDate not supplied

Time domain 1H NMR as a new method to monitor softening of gelatin and HPMC capsule shells.

Defined mechanical properties are an essential requirement for any pharmaceutical dosage form and this is particularly important in the case of liquid-filled capsules. Changes in the mechanical properties may be induced by exposure of the capsules to humidity or by a shift of the water equilibrium that typically occurs when hydrophilic or amphiphilic fill masses are used, for example, in self-emulsifying drug delivery systems. This study aims to characterize the softening of empty hard gelatin and hydroxypropyl methylcellulose (HPMC) capsules by means of mechanical tests, a Bareiss hardness test, and a stiffness test using a texture analysis method. A benchtop time domain NMR method is applied in addition to characterize the physico-chemical state of water in the capsule shells and to correlate this with the results of the mechanical tests. Hardness and stiffness measurements resulted in corresponding values, showing a softening for both capsule materials in a humid environment, which was most pronounced beyond 60% relative humidity. The capsules made of gelatin exhibited in general higher stiffness and hardness values compared to the HPMC capsules. The physico-chemical state of water in the capsule shells, as probed by a time domain NMR method, was interpreted in terms of a population balance model. Three different water populations were identified that differ in their molecular mobility, as indicated by their characteristic spin-lattice relaxation times, T1. The most loosely bound water fraction dominated in the capsule shells in the range beyond 60% relative humidity. Numerical correlation of the data led to a heuristic equation between the NMR-derived fraction of loosely bound water in the capsule shells and their mechanical stiffness and hardness. Adequate models were obtained for both capsule types, gelatin, and HPMC. Mechanical measurements of pharmaceutical capsules are generally destructive and time consuming. Testing is usually performed in an analytical laboratory, off-line from the manufacturing process, and involves only a small number of samples. Based on the here presented correlation between mechanical stiffness measurements and benchtop time domain NMR data, the latter method may be used as a nondestructive alternative for mechanical testing. This study also opens the possibility to investigate liquid-filled capsules and to establish a process analytical technology (PAT) during manufacturing.

Capsules↗

PubMedDate not supplied

Fouling deterrence on the bivalve shell Mytilus galloprovincialis: a physical phenomenon?

The physical nature of fouling deterrence by the mussel Mytilus galloprovincialis was investigated using high-resolution biomimics of the bivalve surface. The homogeneous microtextured surface of M. galloprovincialis (1.94 +/- 0.03 microm), the smooth surface of the bivalve Amusium balloti (0 microm), and moulds of these surfaces (biomimics) were compared with controls of smooth (0 microm) and sanded moulds, (55.4 +/- 2.7 microm) and PVC strips (0 microm) in a 12-week field trial. The shell and mould of M. galloprovincialis were fouled by significantly fewer species and had significantly less total fouling cover than the shell and mould of A. balloti over a 12-week period. However, the major effects were between surfaces with and without microtopography. Surface microtopography, be it structured as in the case of M. galloprovincialis shell and mould, or random as in the case of the sanded mould, had a lower cover of fouling organisms than treatments without microtopography after 6 weeks. There was also no difference between the effect of the M. galloprovincialis mould and the sanded mould. The strong fouling deterrent effects of both these surfaces diminished rapidly after 6 to 8 weeks while that of M. galloprovincialis shell remained intact for the duration of the experiment suggesting factors in addition to surface microtopography contribute to fouling deterrence.

Analysis of Variance↗

PubMed1991

Formation and contraction of a microfilamentous shell in saponin-permeabilized platelets.

To study the mechanism of granule centralization in platelets, we permeabilized with saponin in either EGTA (5 mM) or calcium (1 or 10 microM). Under all conditions, platelets retained 40-50% of their total actin and greater than 70% of their actin-binding protein (ABP) but lost greater than 80% of talin and myosin to the supernatant. Thin sections of platelets permeabilized in EGTA showed a microfilament network under the residual plasma membrane and throughout the cytoplasm. Platelets permeabilized in calcium contained a microfilament shell partly separated from the residual membrane. The shell stained brightly for F-actin. A less dense microfilament shell was also seen in sections of ADP-stimulated intact platelets subsequently permeabilized in EGTA. In the presence of 1 mM ATP gamma S and calcium, myosin was retained (70%) and was localized by indirect immunofluorescence in bright central spots that also stained intensely for F-actin. Electron micrographs showed centralized granules surrounded by a closely packed mass of microfilaments much like the structures seen in thrombin-stimulated intact platelets subsequently permeabilized in EGTA. Permeabilization in calcium, ATP, and okadaic acid, produced the same configuration of centralized granules and packed microfilaments; myosin was retained and the myosin regulatory light chain became phosphorylated. Microtubule coil disassembly before permeabilization did not inhibit granule centralization. These results suggest a possible mechanism for granule centralization in these models. The cytoskeletal network first separates from some of its connections to the plasma membrane by a calcium-dependent mechanism not involving ABP proteolysis. Phosphorylated myosin interacts with the microfilaments to contract the shell moving the granules to the platelet's center.

Actin Cytoskeleton↗

PubMed1976

Coated-vesicle shells, particle/chain material, and tubulin in brain synaptosomes. An electron microscope and biochemical study.

Coated vesicles (CVs), plain synaptic vesicles (PSVs), and nonvesicular flocculent material were isolated from synaptosomes and examined with goniometry and high-resolution electron microscopy after either negative staining or various biochemical procedures. The flocculent material (i.e. the presynaptic matrix material except CV shells) is largely composed of particulate or elongated (chainlike) structures; some of this material (here referred to as particle/chain material) is attached to PSVs. The results obtained were: (a) the proteinaceous properties of the CV coat (also referred to as CV shell) and the particle/chain material were demonstrated with chymotrypsin; (b) the CV shell, studied with various negative-staining techniques, differs from the particle/chain material since it has no 3-4-nm globular subunits and reacts differently to alkaline pH; (c) the particle/chain material consists of aggregates of 3-4-nm globular subunits, four of which yield 8-10-nm fine particles; and these particles can be further aggregated into chains 8-10 nm wide and up to 30-60 nm long showing a "hollow" core; (d) vinblastine sulfate induced ringlike or helical crystalloid precipitates closely resembling the vinblastine-induced microtubule crystals reported in the literature, but vinblastine had no effect on either the CV shell material or the particle/chain material.

Animals↗

PubMed1989

Theoretical studies of the infrared emission from circumstellar dust shells: the infrared characteristics of circumstellar silicates and the mass-loss rate of oxygen-rich late-type giants.

We have modeled the infrared emission of spherically symmetric, circumstellar dust shells with the aim of deriving the infrared absorption properties of circumstellar silicate grains and the mass-loss rates of the central stars. As a basis for our numerical studies, a simple semianalytical formula has been derived that illustrates the essential characteristics of the infrared emission of such dust shells. A numerical radiative transfer program has been developed and applied to dust shells around oxygen-rich late-type giants. Free parameters in such models include the absorption properties and density distribution of the dust. An approximate, analytical expression is derived for the density distribution of circumstellar dust driven outward by radiation pressure from a central source. A large grid of models has been calculated to study the influence of the free parameters on the emergent spectrum. These results form the basis for a comparison with near-infrared observations. Observational studies have revealed a correlation between the near-infrared color temperature, Tc, and the strength of the 10 micrometers emission or absorption feature, A10. This relationship, which essentially measures the near-infrared optical depth in terms of the 10 micrometers optical depth, is discussed. Theoretical A10-Tc relations have been calculated and compared to the observations. The results show that this relation is a sensitive way to determine the ratio of the near-infrared to 10 micrometers absorption efficiency of circumstellar silicates. These results as well as previous studies show that the near-infrared absorption efficiency of circumstellar silicate grains is much higher than expected from terrestrial minerals. We suggest that this enhanced absorption is due to the presence of ferrous iron (Fe2+) color centers dissolved in the circumstellar silicates. By using the derived value for the ratio of the near-infrared to 10 micrometers absorption efficiency, the observed A10-Tc relation can be calibrated in terms of the total dust column density of the circumstellar shell and thus the mass-loss rate of late-type giants can easily be derived. Detailed models have been made of the infrared emission of three well-studied Miras: R Cas, IRC 10011, and OH 26.5+0.6, with the emphasis on the shape of the 10 micrometers emission or absorption feature. The results show that the intrinsic shape of the 10 micrometers resonance varies from a very broad feature in R Cas to a relatively narrower feature in OH 26.5+0.6, with IRC 10011 somewhere in between. Possible origins of this variation are discussed. The mass-loss rates from these objects are calculated to be 3 x 10(-7), 2 x 10(-5), and 2 x 10(-4) M Sun yr-1 for R Cas, IRC 10011, and OH 26.5+0.6, respectively. These results are compared to other determinations in the literature.

Astronomical Phenomena↗

PubMed1989

Successful use of shell vial centrifugation and 16 to 18-hour immunofluorescent staining for the detection of influenza A and B in clinical specimens.

The rapid diagnosis of influenza A and B infections is beneficial for the proper management of patients with acute respiratory illness. The authors evaluated a shell vial centrifugation method to detect these viruses 16-18 hours postinoculation and compared it with conventional tube cell culture. Rhesus monkey kidney cells were used in both methods. Conventional culture of 334 respiratory specimens recovered 64 influenza isolates; the average time to positivity was 4.1 days. Low-speed shell vial centrifugation with polyclonal immunofluorescent staining 16-18 hours postinoculation was performed on 96 fresh specimens and on an additional 38 frozen specimens. These 134 specimens contained 49 of the 64 total influenza-positive specimens. The shell vial method yielded a sensitivity of 90.9% and 87.5% for fresh and frozen specimens, respectively, as compared with conventional tube cell culture. The authors conclude that the shell vial method is an important adjunct to conventional culture for the rapid detection of influenza A and B in clinical specimens.

Bronchoalveolar Lavage Fluid↗

PubMed1994

Conditioned media produced by follicular shells of different maturity affect maturation of pig oocytes.

The objective of this study was to further test the hypothesis that follicular secretions produced by follicular cells with different maturity affect oocyte cytoplasmic maturation differently. A group of nine gilts were slaughtered on Day 17 of the estrous cycle and another group of ten were slaughtered on Day 20. The five largest and five smallest follicles were selected from the fifteen largest healthy follicles dissected from each pair of ovaries and categorized as large and small follicles, respectively. The five follicular shells in each category were pooled and cultured in 10 ml of modified TCM 199 supplemented with 2.5 micrograms FSH/ml for 48 h with use of a mobile culture system. Afterwards, conditioned media were collected and used for maturing immature porcine oocytes. Each of six replicated experiments consisted of two culture dishes for each conditioned medium: Day 17 small (S17) and Day 17 large (L17), and Day 20 small (S20) and Day 20 large (L20) follicular shells. After 47 h culture, oocytes were inseminated with boar spermatozoa and were fixed 11 h post-insemination to examine fertilization. The average diameters of follicles used were 4.4, 5.7, 6.2, and 7.5 mm for S17, L17, S20, and L20, respectively. Nuclear maturation was slightly higher in oocytes matured in conditioned media produced by large follicular shells than in those produced by small follicular shells (97.0 vs. 93.5%, p = 0.045). Penetrability of oocytes was not affected by treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2003

Gene transcripts selectively down-regulated in the shell of the nucleus accumbens long after heroin self-administration are up-regulated in the core independent of response contingency.

Long-term drug-induced alterations in neurotransmission within the nucleus accumbens (NAc) shell and core may underlie relapse to drug-seeking behavior and drug-taking upon re-exposure to drugs and drug-associated stimuli (cues) during abstinence. Using an open screening strategy, we recently identified 25 gene transcripts, encoding for proteins involved in neuronal functioning and structure that are down-regulated in rat NAc shell after contingent (active), but not after non-contingent (passive), heroin administration. Studying the expression of the same transcripts in the NAc core by means of quantitative PCR, we now demonstrate that most of these transcripts are up-regulated in that NAc subregion long (3 weeks) after heroin self-administration in rats. A similar up-regulation in gene expression was also apparent in the NAc core of animals with a history of non-contingent heroin administration (yoked controls). These data indicate that heroin self-administration differentially regulates genes in the NAc core as compared with the shell. Moreover, whereas cognitive processes involved in active drug self-administration (e.g., instrumental learning) seems to direct gene expression in the NAc shell, neuroplasticity in the NAc core may be due to the pharmacological effects of heroin (including Pavlovian conditioning), as expressed in rats upon contingent as well as non-contingent administration of heroin.

Adaptation, Physiological↗

PubMed1998

Revision knee arthroplasty with patella replacement versus bony shell.

A study was undertaken to assess the clinical results of revision total knee arthroplasty in which an unresurfaced bony shell was left after removing a patellar component versus those in which a patellar component was implanted. Followup was obtained in 123 of 130 consecutive revision total knee replacements (94%) from three centers. In 21 knees a shell of patellar bone was left and 92 knees had a patellar component in place. Ten patients had a patellectomy and were excluded from consideration. The group with the bony shell had a lower postoperative knee score but the preoperative Knee Society clinical score was significantly lower as well in this group of patients. Compared with the group of patients with the patellar component in place, the group of patients with knees left with a bony shell had a significantly higher percentage of patients who had difficulty using stairs, a higher percentage of patients who were not satisfied with their surgery, and a higher percentage of patients who rated their surgery as unsuccessful in returning them to normal daily activities. When a patellar component was not able to be implanted in revision total knee arthroplasty, a lower quality result was observed.

Arthroplasty, Replacement, Knee↗

PubMed1995

Histologic comparison of breast implant shells with smooth, foam, and pillar microstructuring in a rat model from 1 day to 6 months.

The purpose of this study was to determine the soft-tissue response to silicone breast implants with different surface morphologies and to correlate implant microtexturing with capsular formation. Using a rat model, we inserted breast implants having three types of shells: micropillared, silicone foam, and smooth silicone (control). We used 96 adult male Sprague-Dawley rats weighing between 250 and 300 gm. Thirty-two rats were assigned to each of the three shell groups. Within each shell group, 4 rats were implanted for 24 hours, 4 for 4 weeks, 4 for 8 weeks, 4 for 12 weeks, 4 for 16 weeks, 4 for 20 weeks, and 4 for 24 weeks. The rats were sacrificed at the end of each time interval, and periprosthetic tissue was obtained for histologic analysis. Our results show a stable soft-tissue response with some macrophages and fibroblasts for the smooth silicone shell group; capsule thicknesses were 10 to 12 cells with interwoven collagen. The silicone foam prolonged the active cellular response with regard to macrophages, fibroblasts, and multinucleated giant cells, along with random collagen deposition and alternating thin and thick capsular areas. The micropillar group had a more stable cellular response, with macrophages and fibroblasts, along with disruption of the long-range orientation of collagen fibers.

Animals↗

PubMed2000

Symmetries, invariants, and cascades in a shell model of turbulence

Reduced wave number models of turbulence, namely shell models, show cascade processes and anomalous scaling of correlators which might be analogous to what is observed in Navier-Stokes (NS) turbulence. The scaling properties of the shell models depend on the specific symmetries and invariants of the models. A shell model is investigated. It is argued that this model might have a closer resemblance than the standard Gledzer-Ohkitani-Yamada model to the NS turbulence. The shell model investigated here coincides with the Sabra model proposed by L'vov et al. [Phys. Rev. E. 58, 1811 (1998)] for a specific choice of the free parameters of their model. For this choice of parameters, besides the energy and the "helicity," the model has a cubic inviscid invariant.

Journal Article↗

PubMed2000

Superdeformation in the N = Z nucleus 36Ar: experimental, deformed mean field, and spherical shell model descriptions

A superdeformed rotational band has been identified in 36Ar, linked to known low-spin states, and observed to its high-spin termination at Ipi = 16(+). Cranked Nilsson-Strutinsky and spherical shell model calculations assign the band to a configuration in which four pf-shell orbitals are occupied, leading to a low-spin deformation beta(2) approximately 0.45. Two major shells are active for both protons and neutrons, yet the valence space remains small enough to be confronted with the shell model. This band thus provides an ideal case to study the microscopic structure of collective rotational motion.

Journal Article↗

PubMed2001

Crossover from electronic to atomic shell structure in alkali metal nanowires.

After making a cold weld by pressing two clean metal surfaces together, upon gradually separating the two pieces a metallic nanowire is formed, which progressively thins down to a single atom before contact is lost. In previous experiments we have observed that the stability of such nanowires is influenced by electronic shell filling effects, in analogy to shell effects in metal clusters. For sodium and potassium at larger diameters there is a crossover to crystalline wires with shell closings corresponding to the completion of additional atomic layers. This observation completes the analogy between shell effects observed for clusters and nanowires.

Journal Article↗

PubMed2003

Growth of three-shell onionlike bimetallic nanoparticles.

We show by molecular dynamics simulations on three systems (B/A=Pd/Ag, Cu/Ag, and Ni/Ag) that three-shell metallic nanoparticles made by a core of a metal A, an intermediate shell of metal B and an external shell of metal A (A-B-A nanoparticles) can be grown by deposition of B atoms onto an A core. The growth of the intermediate B shell is triggered by the fact that the most favorable positions for isolated B impurities inside A clusters are located just one layer below the cluster surface.

Journal Article↗

PubMed2004

Fragmentation of shells.

We present a theoretical and experimental study of the fragmentation of closed thin shells made of a disordered brittle material. Experiments were performed on brown and white hen egg shells under two different loading conditions: impact with a hard wall and explosion by a combustible mixture. Both give rise to power law fragment size distributions. A three-dimensional discrete element model of shells is worked out. Based on simulations of the model, we give evidence that power law fragment mass distributions arise due to an underlying phase transition which proved to be abrupt for explosion and continuous for impact. We demonstrate that the fragmentation of closed shells defines a new universality class of fragmentation phenomena.

Journal Article↗

PubMed2006

Vanishing N = 20 shell gap: study of excited states in (27,28)Ne.

This Letter reports on the (1)H((28)Ne, (28)Ne) and (1)H((28)Ne, (27)Ne) reactions studied at intermediate energy using a liquid hydrogen target. From the cross section populating the first 2(+) excited state of (28)Ne, and using the previously determined BE(2) value, the neutron quadrupole transition matrix element has been calculated to be M(n)=13.8 +/- 3.7 fm(2). In the neutron knockout reaction, two low-lying excited states were populated in (27)Ne. Only one of them can be interpreted by the sd shell model while the additional state may intrude from the fp shell. These experimental observations are consistent with the presence of fp shell configurations at low excitation energy in (27,28)Ne nuclei caused by a vanishing N=20 shell gap at Z=10.

Journal Article↗