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PubMed2002

Settling and deformation of a thin elastic shell on a thin fluid layer lying on a solid surface.

placement of a soft contact lens onto the cornea, the upper eyelid deforms and settles the lens by squeezing fluid out of the post-lens tear film or POLTF (i.e., the tear fluid layer sandwiched between the lens and the cornea). This paper studies the physical mechanisms that control the dynamic state of the contact lens during blinking, i.e., its shape and its distance from the cornea, especially a long time after insertion. We model the lens as a deformable elastic shell and the cornea as a flat nondeformable body. The tear fluid is assumed to be Newtonian, and the lens is characterized by an elastic modulus and a Poisson ratio. Lubrication equations under creeping flow are used to solve the fluid problem, while the thin-shell approximation is applied to the solid lens. The solid and fluid mechanics problems are coupled by maintaining continuity of stress and velocity at the solid/liquid interface. Lid applied pressure causes the lens to approach the cornea by squeezing tear fluid out and also leads to the deformation of the lens. Subsequently, in the interblink period, since there is no applied force, the elastic energy stored in the lens due to its deformation is released causing it to move away from the cornea by imbibing tear fluid into the POLTF. If the POLTF thickness is large, the inward motion of the lens in the blink is more than the outward motion during interblink, and this causes the lens to settle closer to the cornea. Eventually, there may be a balance of the inward motion during the blink and the outward motion during the interblink. If so, the lens subsequently exhibits periodic steady-state motion. However, it is also possible that a balance of inward and outward motion is never achieved, and the lens continues to settle endlessly. If this happens, then the thinfilm interactions between the mucin-covered corneal surface and the lens material determine whether the lens actually touches the cornea and possibly adheres. Our elastohydrodynamic analysis serves as a useful tool to elucidate the effects of various lens parameters on the final settled state of the lens. In particular, we are concerned about eventual adherence and/or mechanical abrasion to the cornea, which is very important to the ocular health of soft contact lens wearers.

Journal Article↗

PubMed2002

Textural and chemical characterizations of adsorbent prepared from palm shell by potassium hydroxide impregnation at different stages.

Preparation and characterization of activated carbon from palm shell, a carbonaceous agricultural solid waste, by potassium hydroxide treatment at different stages were studied. The effects of activation temperature and chemical to sample ratio on the characteristics of the activated carbon were investigated. Fixed-bed adsorption of sulfur dioxide (SO(2)) gas was carried out to evaluate the adsorptive capacity of the samples. Desorption tests were conducted to verify the occurrence of chemisorption due to some surface functional groups or of chemical reaction between SO(2) and KOH. It was found that pre-impregnation of raw palm shell was involved in replacement of some hydrogen ions with potassium ions to form cross-linked complexes, which retarded the tar formation during carbonization, resulting in a relatively high yield. Moreover, these potassium ions accelerated the reaction as catalysts during gasification of chars by carbon dioxide. For chars with mid-impregnation, potassium hydroxide acted in two ways: (i) formation of metallic potassium by dehydration and (ii) conversion into potassium carbonate. Metallic potassium intercalated to the carbon matrix accounted for pore development and potassium carbonate layer prevented the sample from over burn-off. Post-impregnation of final products modified the textural characteristics of the sample as some pore entrances were blocked by chemicals. However, potassium hydroxide enhanced the amount of SO(2) uptaken via formation of potassium sulfite.

Adsorption↗

PubMed2002

From heterocoagulated colloids to core-shell particles.

Heterocoagulation of large and small oppositely charged colloid particles, accompanied by spreading of small beads over the surface of large spheres, offers a promising alternative to synthesis of core-shell particles via interfacial polymerization. In this paper, conditions required for complete spreading of the shell-forming polymer over the surface of the core-forming material (CFM) are predicted in terms of a critical distance, x(cr), between the small particles on the surface of the CFM. The theoretical value of x(cr) is tested in experiments conducted for polypyrrole/polyacrylic and silica-titanyl sulfate/polyacrylic heterocoagulate units.

Journal Article↗

PubMed1993

Isolation of a phospholipid-free protein shell of bacteriophage PRD1, an Escherichia coli virus with an internal membrane.

PRD1 is a double-stranded DNA virus infecting Escherichia coli and Salmonella typhimurium. It has an icosahedral outer protein capsid which encloses the viral membrane, inside of which resides the phage genome. In this investigation we demonstrate the detergent resistance of the intact virus particles. The membrane of empty DNA-free particles, however, is very sensitive to detergent action. We assume that their sensitivity is due to the access of detergents through a portal structure to the virus interior. Using the anionic detergent sodium dodecyl sulfate, it is possible to obtain a shell structure composed of the major coat protein P3 alone. The treatment of empty particles with the milder nonionic detergents n-octyl beta-D-glucopyranoside and Triton X-100 yielded P3 particles which retained the membrane-associated proteins P7 and P11. Deoxycholic acid treatment yielded shells of intermediate composition between those obtained with the nonionic detergents and sodium dodecyl sulfate.

Capsid↗

PubMed1994

Fullerene-like organization of HIV gag-protein shell in virus-like particles produced by recombinant baculovirus.

Virus-like particles produced by a recombinant baculovirus containing the HIV gag gene were examined by negative staining after delipidization. This technique demonstrated that the gag-protein shell consisted of radially arranged short rods which formed a network of ring-like structures. Similar structures were observed at the plasma membrane of infected cells which had been opened by wet-cleaving. Occasionally five or six subunits were observed forming a ring. These findings suggest that the gag-encoded precursor (pr55) is a rod-like molecule about 34 A in diameter and 85 A in length. A protein cylinder of such dimensions would have a molecular weight of 56K. The center-to-center distance of two neighboring rings formed by the rods was 66 +/- 8 A (N = 200) by direct measurements and 65 A as obtained from averaged images. This morphology and these dimensions indicate that the virus-like particles contain the gag precursor in the form of a near-spherical "fullerene-like" icosahedral shell. Our data indicate that the triangulation number of the rings equals 63. However, since one rod of pr55 is shared by two rings, the number of copies of the precursor will be 1890 as opposed to 2522 if the molecules were closely packed. The particle diameter of 102 nm deduced from the proposed model was close to the diameter obtained from thin sections of low-temperature-embedded specimens (103-108 nm).

Animals↗

PubMed1997

A cucumber necrosis virus variant deficient in fungal transmissibility contains an altered coat protein shell domain.

Little is currently known regarding the specific interactions that govern transmission of plant viruses by their vectors. A cucumber necrosis virus (CNV) variant (LL5) deficient in fungal transmissibility has been isolated from mechanically passaged CNV and characterized. Although LL5 accumulates to wild-type (WT) levels, is capable of rapid systemic infection, and produces stable, highly infectious particles, it is only inefficiently transmitted by Olpidium bornovanus zoospores. The LL5 coat protein (CP) gene was amplified by RT-PCR and cloned in place of the WT CNV CP gene in an infectious CNV cDNA clone. Particles derived from this construct also failed to be efficiently transmitted. The LL5 CP gene was sequenced and found to contain two amino acid substitutions relative to WT CNV CP. One substitution (Phe to Cys) occurred in the arm region and another (Glu to Lys) in the shell domain. These amino acid changes were separately introduced into the WT CNV genome through in vitro mutagenesis and it was found that the Glu to Lys change in the LL5 CP shell domain is largely responsible for the loss of transmissibility. In vitro binding assays were developed to determine if the defect in transmissibility was due to a defect in binding zoospores. LL5 particles were found to bind less efficiently than WT CNV. Furthermore, the nontransmissible tomato bushy stunt virus did not detectably bind zoospores. These binding studies suggest that the specificity of CNV transmission by O. bornovanus occurs through specific recognition of a putative zoospore receptor.

Binding Sites↗

PubMed1996

A hypothesis about the mechanism of assembly of double-shelled rotavirus particles.

During double-shelled (ds) particle assembly, subviral particles [possibly single-shelled (ss) particles] acquire the outer capsid protein during their transport across the endoplasmic reticulum (ER) membrane by an exocytosis-like process, probably by a fusion-like mechanism. Fine reticular material is observed around the junction area between virus particles and the ER membrane on the cytoplasmic side of projecting ss particles, suggesting this is the site of assembly of ds particles. It is assumed that the reticular material may correspond to the hetero-oligometric complexes consisting of the non-structural glycoprotein NSP4, the structural proteins VP4 and VP7, and that both VP7 and VP4 may fold onto ss particles as a complex. On the other hand, the budding process simply serves as a vehicle to transport ss particles from the cytoplasm to the ER lumen. Thus, it is assumed that the production of protein complexes may be indispensable for virion assembly, in which NSP4 regulates VP4 folding as an ER chaperone and also the exocytosis-like or fusion-like transport systems through the ER membrane.

Animals↗

PubMed1978

Scanning electron microscope studies of the egg shell in some anostraca (Crustacea: Branchiopoda).

The tertiary shell of the eggs of anostracan crustaceans consists of two layers, an outer cortex and an inner alveolar layer. Scanning electron microscope studies show that, in most species, these layers are separated by a subcortical space which intercommunicates with spaces in the cortex and with the meshwork of the alveolar layer. No evidence was found for direct communication between pores on the surface of Branchipus stagnalis eggs and the subcortical space. No surface pores were found in the eggs of Branchinecta packardi, Chirocephalus diaphanus, Artemia salina, nor in eggs of the notostracan Triops cancriformis. Similarities in structure and possible functions of the egg shells of anostracan crustaceans and certain insects are discussed in relation to similarities in certain features of their environments.

Animals↗

PubMed1976

Ultrastructural study of the shell-repair membrane in the snail, Helix pomatia L..

The shell-repair membrane of the snail, Helix pomatia, has been studied with the transmission electron microscope (TEM). The ultrastructure of the repair membrane, in the initial stages of calcification, revealed the presence of a fibrillar protein, proteoglycan granules, osmiophilic vesicles, and cytoplasmic dense bodies of different size and structure. The involvement of the cell constituents in the formation of calcifying centra and initial crystal formation is discussed. The amoebocytes present within the repair membrane appeared to be involved in three different functions: (1) phagocytosis, (2) release of granules, vesicles and dense bodies, and (3) secretin of a fibrillar protein. The possible lytic function of the amoebocytes is mentioned. The common features in the minearlizing process of the shell-repair membrane of the snail and the epiphyseal cartilage of the mammals were noted.

Animals↗

PubMed1989

The calcium-phosphorus metabolism expert system module: a program developed in the ALEX Smalltalk/V shell.

The object-oriented computing model of Smalltalk/V proved to be very well suited for the creation of a medical expert system on the diagnosis of calcium-phosphorus metabolism abnormalities. A major reason for this was that a disease could be viewed as a self-contained, active, entity. The expert system is implemented in ALEX, an expert system shell that is written in Smalltalk/V. The shell consists of classes and methods that can be modified, as needed, by the developer. The expert system is, at present, 140,000 bytes in size, and includes 43 diseases, arranged in 7 contexts. Sixty case reports were used to test the expert system. In 30 cases, there was complete agreement between clinician and expert system; in 12 cases, the expert system responded appropriately when presented with diseases that were not known to the system; and in 18 cases, the system gave plausible results.

Calcium↗

PubMed1993

Using ILIAD system shell to create an expert system for differential diagnosis of renal masses.

Differential diagnosis of renal masses is an important and difficult process. A renal mass diagnostic system (RMDS) developed by using the ILIAD expert system shell has been created for diagnostic consultations and patient simulations. Seventy-two cases of renal mass have been tested on this system and the diagnostic accuracy was compared to that of residents. The overall diagnostic accuracy (75%) for renal masses is significantly better than second-year urological residents (60%) and not worse than urological chief residents (71%). The expert system also displays the cost of the diagnostic procedures so that the user can choose the most cost-effective diagnostic process. We conclude that this powerful renal mass diagnosis system developed by using ILIAD system shell can be used as a teaching, self-training and clinical tool for urological residents.

Artificial Intelligence↗

PubMed1990

Mycoflora and nutritional value of shelled melon seeds (Citrulus vulgaris Schrad.) in Nigeria.

Thirteen fungi were isolated from mouldy shelled melon seeds. The fungi more frequently isolated included species of Mucor (11.25%), Rhizopus (13.75%), Aspergillus (36.25%), Macrophoma (2.50%), Penicillium (8.75%), Alternaria (5.00%), Fusarium (8.75%), Botrytis (6.25%), Torula (3.75%) and Geotrichum (3.75%). Healthy, shelled melon seeds inoculated with Fusarium solani for 7 or 14 days caused increases in the free fatty acid (f.f.a.) content of the healthy seeds from an initial value of 1.06% to 2.19% after 7 days and 4.23% after 14 days. Similar results were obtained when other fungal isolates were used as inocula but Fusarium solani effected the greatest increase in the f.f.a. content followed by Aspergillus niger and Penicillium notatum. The fungi also caused decreases in the crude protein from 35.51% to 25.16%, crude fibre from 4.30% to 1.35% and total carbohydrate content from 4.28% to 3.01% of the seeds after 14 days infection. Aflatoxin was detected (0.20 micron/g) in the infected seeds being sold in the markets and also from seeds inoculated with spores (0.40 micron/g) of A/ flavus and 0.50 micron/g) from a mixture of spores of various Aspergillus strains after incubation for 14 days.

Aflatoxins↗

PubMed1997

Differential effects of acute and chronic nicotine on dopamine output in the core and shell of the rat nucleus accumbens.

Like several drugs of abuse, nicotine increase dopamine (DA) release in the nucleus accumbens (NAC). In the present study, the effects of acute and chronic nicotine on DA output in two subdivisions of the NAC, the core and the shell, which are largely associated with motor control and limbic functions, respectively, were examined by means of in vivo differential normal pulse voltammetry in anesthetized, pargyline-treated rats. In the first experiment, acute administration of nicotine (25, 50 and 100 micrograms/kg, cumulative doses; i.v.) was found to increase DA levels in the NACshell to 163% of baseline, whereas DA output in the NACcore was not significantly affected. In the second experiment, animals were pretreated with twelve daily injections of saline or nicotine (0.5 mg/kg, i.p.); about 24 hours after the last injection, the animals were challenged with nicotine (50 micrograms/kg and 100 micrograms/kg, cumulative doses; i.v.). Under these conditions, nicotine increased DA output in the NACshell in saline-pretreated animals to 248% and in nicotine-pretreated rats to 180%. Also, nicotine increased DA output in the NACcore in saline-pretreated animals to 185%, whereas no significant effect was observed in nicotine-pretreated rats. The results of the present experiments indicate (i) that acutely administered nicotine or nicotine challenge in chronically pretreated animals with either saline or nicotine consistently increases DA release to a greater extent in the NACshell than in the NACcore, and (ii) that chronic nicotine pretreatment reduces the stimulatory-action of nicotine on DA output in either the shell or the core subdivision of the NAC.

Animals↗

PubMed1995

Conventional viral cultures and shell vial assay for diagnosis of apparently culture-negative Coxiella burnetii endocarditis.

A patient with culture-negative endocarditis was diagnosed with Q fever endocarditis based on the results of serological tests and positive leukocyte cultures obtained using conventional viral cultures and the shell vial technique. This case report suggests that isolation of Coxiella burnetii from blood may allow better diagnostic and therapeutical evaluation of patients with Q fever endocarditis. The use of both conventional and shell vial viral cultures is recommended for the isolation of Coxiella burnetii from the blood of patients with apparently culture-negative endocarditis.

Adult↗

PubMed1990

Orientation of apatite and organic matrix in Lingula unguis shell.

The orientation relationship between apatite and organic matrix in shell of Lingula unguis (inarticulate brachiopod) was studied. The organic layers, mineralized layers, and decalcified mineralized layers were examined layer by layer using microbeam X-ray diffraction technique. Both organic layer and decalcified mineralized layer showed the diffraction pattern of beta-chitin. The degree of orientation of apatite showed correlation to that of beta-chitin: Well oriented diffraction patterns of apatite crystal and organic matrix were observed in the central part. In this part, the fiber axis of beta-chitin was parallel to the c-axis of apatite. A close relationship of unit cell dimension between apatite and chitin was indicated. These strongly suggest that the fibrous structure of organic matrix assists the orientation of apatite crystals in Lingula unguis shell.

Animals↗

PubMed1990

A simple expert system shell for microcomputer-aided radiographic diagnosis.

A simple microcomputer-based expert system shell for radiographic diagnosis is described. The system interrogates the user by means of a simple question--and-answer approach on the radiographic findings in a given case and proffers a differential diagnosis from a database. The system also allows listing of both the radiographic findings pertinent to a specific diagnosis and all diagnoses in which a particular finding or combination of findings occur. The system database can be easily updated or modified by the user. The demonstration application for the expert system shell is the plain film diagnosis of osseous dysplasia.

Expert Systems↗

PubMed2003

How sphingolipids bind and shape proteins: molecular basis of lipid-protein interactions in lipid shells, rafts and related biomembrane domains.

Understanding the molecular mechanisms controlling the association of proteins with lipid rafts is a central issue in cell biology and medicine. A structurally conserved motif (the 'sphingolipid binding domain') has been characterized in unrelated cellular and microbial proteins targeted to lipid rafts. I propose that the structuration of a sphingolipid shell around the sphingolipid binding domain not only extracts the protein from the liquid-disordered phase of the plasma membrane, and ensures its delivery to lipid rafts, but also influences its conformation. The chaperone activity of sphingolipids in shells and rafts may play an important role in infectious and conformational diseases(human immunodeficiency virus-1, prions, Alzheimer).

Alzheimer Disease↗

PubMed1999

Chronic morphine induces long-lasting changes in acetylcholine release in rat nucleus accumbens core and shell: an in vivo microdialysis study.

Previously, only in vitro studies have shown that chronic administration of morphine provokes long-lasting enhanced activity of accumbal cholinergic neurons, which may contribute to the behavioural sensitization, positive reinforcement and aversive effects associated with enhanced drug-seeking. The present study was aimed at clarifying whether these adaptive changes would also be supported by in vivo microdialysis measurements in freely moving rats, distinguishing between the accumbal substructures shell and core, and observing behavioural changes simultaneously. Acute administration of morphine dose-dependently decreased acetylcholine (ACh) release in the nucleus accumbens (NAc), with 10 mg/kg s.c. being most effective, 5 mg/kg ineffective. On day 5 of spontaneous abstinence from chronic morphine treatment (10-40 mg/kg morphine dose once daily for 5 days), when withdrawal symptoms were still present, even a lower morphine dose (5 mg/kg) was effective in decreasing ACh release in the NAc. During the later phase of abstinence, when no withdrawal symptoms were detectable, the opposite effect, i.e. an increase of ACh release was found. This later effect may represent a long-lasting neuroadaptive effect of morphine. These adaptive effects seemed to be more prominent in the NAc shell. Concurrent with these changes in ACh release, morphine challenges produced marked behavioural stereotypes, possibly indicating behavioural sensitization.

Acetylcholine↗