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PubMed2005

A novel method to make regenerable core-shell calcium-based sorbents.

A sorbent having a calcium oxide core and a clay shell was prepared and shown to be capable of reusable applications in absorption and desorption processes for carbon dioxide. The novelty of this sorbent is that only calcium carbonate and clay are used for its preparation with water as a binder. A two-step granulation procedure is used to get the core and then another step to coat the shell layer with the clay powder. A repeated wet-and-dry procedure probably makes the core porous yet strong enough to serve as a sorbent. The pellet is then calcined at 1200 degrees C for 2h to reach its final structure. The core-shell pellets have an overall diameter of 4.4mm with average shell thickness of 0.45 mm, crush load of 35 N and attrition index of 0.035 wt%/h. These results indicate that the pellets will probably be capable of withstanding the stress in future applications. Carbon dioxide absorption at or below 300 degrees C showed a maximum weight gain of 38% for our pellets. Finally, desorption in nitrogen at 800 degrees C can restore the pellet to its original state and hence it is ready for re-use as a sorbent.

Absorption↗

PubMed2005

Crab shell-based biosorption technology for the treatment of nickel-bearing electroplating industrial effluents.

This paper discusses the possible application of a biosorption system with acid-washed crab shells in a packed bed up-flow column for the removal of nickel from electroplating industrial effluents. Between two nickel-bearing effluents, effluent-1 is characterized by considerable amount of light metals along with trace amounts of lead and copper. Effluent-2 is characterized by relatively low conductivity, total dissolved solids and total hardness compared to effluent-1. Crab shells exhibited uptakes of 15.08 and 20.04 mg Ni/g from effluent-1 and effluent-2, respectively. The crab shell bed was regenerated using 0.01 M EDTA (pH 9.8, aq. NH3) and reused for seven sorption-desorption cycles. The EDTA elution provided elution efficiencies up to 99% in all the seven cycles. This, together with the data from regeneration efficiencies for seven cycles, provided evidence that the reusability of crab shell in the treatment of nickel-bearing electroplating industrial effluents is viable.

Adsorption↗

PubMed2005

Removal of nickel from aqueous solutions using crab shells.

Partially converted crab shell waste, which contains chitosan, was used to remove nickel from water. The chelating ability of chitosan makes it an excellent adsorbent for removing pollutants. Advantages of chitosan in crab shells include availability, low cost, and high biocompatibility. The metal uptake by partially converted crab shell waste was successful and rapid. The sorption occurred primarily within 5 min. The sorption mechanism appears to be quite complicated and cannot be adequately described by either the Langmuir or Freundlich theories. Various anions, including chloride, bromide, fluoride, acetate, sulfate, nitrate, and phosphate, were found to have a very small effect on the capacity of the crab shells for uptake of nickel. The effect of pH was also found not to be prominent.

Adsorption↗

PubMed2005

The distribution of chitin in larval shells of the bivalve mollusk Mytilus galloprovincialis.

The insoluble matrix of larval shells of the marine bivalve mollusk Mytilus galloprovincialis is investigated by confocal laser scanning microscopy using a GFP fusion protein with a chitin-binding domain for labeling of chitinous structures. We show that chitinous material is present in the larval shell, presumably as a chitin-protein complex. We further show that the structure of the chitinous material changes with the development of the larvae. We conclude from the presence of characteristic chitinous structures in certain shell regions that chitin fulfills an important function in the formation and functionality of larval bivalve shells.

Animals↗

PubMed2024

Dynamic structural determinants in bacterial microcompartment shells.

Bacterial microcompartments (BMCs) are polyhedral structures that segregate enzymatic cargo from the cytosol via encapsulation within a protein shell. Unlike other biological polyhedra, such as viral capsids and encapsulins, BMC shells can exhibit a highly advantageous structural and functional plasticity, conforming to a variety of anabolic (CO2 fixation in carboxysomes) and catabolic (nutrient assimilation in metabolosomes) roles. Consequently, understanding the subunit properties and associated protein-protein interaction processes that guide shell assembly and function is a necessary step to fully harness BMCs as modular, biotechnological nanomachines. Here, we describe the recent insights into the dynamics of structural features of the key BMC domain (Pfam00936)-containing proteins, which serve as a structural template for BMC-H and BMC-T shell building blocks.

Bacterial Proteins↗

PubMed2006

Consideration of the three-dimensional structure of core shells (capsids) in spherical retroviruses.

The problem of three-dimensional organization of retroviral cores has been a matter of interest for the past 30 years. The general opinion in favor of icosahedral symmetry based on electron microscopy observations was questioned when cryo-electron microscopy failed to provide convincing evidence in its favor. More recent studies by cryo-electron microscopy, X-ray crystallography and in vitro assembly of the CA domain of Human immuno deficiency virus (HIV), Murine leukemia virus (MuLV) and Rous sarcoma virus (RSV) threw new light on the organization of retroviral cores. In this communication we report how we produced a three-dimensional (3D) model of MuLV core using data from CA assembly on a lipid film [Ganser, B.K., Cheng, A., Sundquist, W.I., Yeager, M., 2003. Three-dimensional structure of the M-MuLV CA protein on a lipid monolayer: a general model for retroviral capsid assembly. EMBO J. 22, 2886-2892]. The resulting structure revealed that the molecular organization of the core shell is specific and the presence of a 5,3,2 rotational symmetry of the 3D model provides support for icosahedral shape of MuLV cores. The model made it possible to determine the diameter of the cores and calculate the number of CA copies as well as the molecular mass of a core of specific diameter. Thus MuLV cores 68 (or 81.6) nm in diameter consist of 1500 (or 2160) copies of CA. About 12% of molecules from fullerene-like Gag shells versus 71% of molecules of closely packed (core-like). Gag shells were not incorporated into the core shells (capsids). Our 3D models received support from X-ray data of MuLV CA NTD domain published by Mortuza et al. [Mortuza, G., Haire, L.F., Stevens, A., Smerdon, S.J., Stoye, J.P., Taylor, I.A., 2004. High resolution structure of a retroviral capsid hexameric amino-terminal domain. Nature 431, 481-485].

Animals↗

PubMed2006

Motion correction properties of the shells k-space trajectory.

The feasibility of a k-space trajectory that samples data on a set of 3D shells is demonstrated with phantom and volunteer experiments. Details of an interleaved multi-shot, helical spiral pulse sequence and a gridding reconstruction algorithm that uses Voronoi diagrams are provided. The motion-correction properties of the shells k-space trajectory are described. It is shown that when used in conjunction with three point markers, k-space data acquired with the shells trajectory provide a generalization of the RINGLET method, allowing for correction of arbitrary rigid-body motion with six degrees of freedom. Use of dedicated navigator echoes or redundant acquisitions of k-space data are not required. Retrospective motion correction is demonstrated with controlled phantom experiments and with seven healthy human volunteers. The motion correction is shown to improve the images, both qualitatively and quantitatively with a metric calculated from image entropy. Advantages and challenges of the shells trajectory are discussed, with particular attention to acquisition efficiency.

Algorithms↗

PubMed2004

Dopamine and drug addiction: the nucleus accumbens shell connection.

Microdialysis studies in animals have shown that addictive drugs preferentially increase extracellular dopamine (DA) in the n. accumbens (NAc). Brain imaging studies, while extending these finding to humans, have shown a correlation between psychostimulant-induced increase of extracellular DA in the striatum and self-reported measures of liking and 'high' (euphoria). Although a correlate of drug reward independent from associative learning and performance is difficult to obtain in animals, conditioned taste avoidance (CTA) might meet these requirements. Addictive drugs induce CTA to saccharin most likely as a result of anticipatory contrast of saccharin over drug reward. Consistently with a role of DA in drug reward, D2 or combined D1/D2 receptor blockade abolishes cocaine, amphetamine and nicotine CTA. Intracranial self-administration studies with mixtures of D1 and D2 receptor agonists point to the NAc shell as the critical site of DA reward. NAc shell DA acting on D1 receptors is also involved in Pavlovian learning through pre-trial and post-trial consolidation mechanisms and in the utilization of spatial short-term memory for goal-directed behavior. Stimulation of NAc shell DA transmission by addictive drugs is shared by a natural reward like food but lacks its adaptive properties (habituation and inhibition by predictive stimuli). These peculiarities of drug-induced stimulation of DA transmission in the NAc shell result in striking differences in the impact of drug-conditioned stimuli on DA transmission. It is speculated that drug addiction results from the impact exerted on behavior by the abnormal DA stimulant properties acquired by drug-conditioned stimuli as a result of their association with addictive drugs.

Animals↗

PubMed2004

Role of glutamate receptors in nucleus accumbens core and shell in spatial behaviour of rats.

The nucleus accumbens (NAC) is considered to be an important neural interface between corticolimbic and motor systems of the brain. Several studies have shown that the NAC is not only involved in motivation and reward-related processes but also in spatial behavior. We here investigated the involvement of different glutamate receptor subclasses within NAC core and shell subregions on behavior in a radial-maze. Rats were first trained in a four-arm-baited eight-arm radial maze task for baseline performance. Thereafter, the effects of microinjection of the nonselective glutamate receptor antagonist kynurenic acid (4.5 microg), the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (1 microg) and the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (0.75 microg) in NAC core and shell were tested on reference memory errors (RME) and working memory errors (WME). Moreover, the choice pattern of entries and duration of arm-entries were evaluated. Microinjection of all drugs increased RME. Additionally, non-NMDA receptor blockade in NAC shell but not core increased WME. After microinjection of all drugs into NAC core and shell rats preferentially choose the arms next to the previously visited arm. This work shows that glutamate receptors in both NAC subregions are important for spatial behavior. The deficits seen after glutamate receptor blockade may not be working- or reference memory-related but caused by a switch from a memory-dependent allocentric strategy to an egocentric response strategy.

2-Amino-5-phosphonovalerate↗

PubMed2005

D1-like and D2 dopamine receptor antagonists administered into the shell subregion of the rat nucleus accumbens decrease cocaine, but not food, reinforcement.

Cocaine self-administration experiments were designed to assess the respective roles of D1-like and D2-like dopamine receptors in the ventral forebrain in cocaine reinforcement. D1-like or D2-like dopamine receptor antagonists were microinjected into the nucleus accumbens core, nucleus accumbens shell, neostriatum or lateral septum prior to sessions in which cocaine was self-administered under a progressive ratio schedule by rats. The results indicated that administration of a D1/5 (SCH-23390) or a D2/D3/D4 (eticlopride), but not a D3 (U99194A) or D4 (L-750,667), dopamine receptor antagonist into the core and shell of the nucleus accumbens decreased the reinforcing efficacy of cocaine. However, in control experiments intra-accumbal core administration of SCH-23390 or eticlopride decreased food self-administration, whereas administration of these drugs into the accumbens shell had no effect on food reinforcement. Neither SCH-23390 nor eticlopride influenced cocaine reinforcement when administered into the neostriatum or lateral septum. Collectively, these results indicate that D1-like and D2 dopamine receptors in the nucleus accumbens shell selectively modulate the reinforcing efficacy of cocaine, whereas D1-like and D2 dopamine receptors in the accumbens core have a more general influence on reinforced behaviors.

Animals↗

PubMed2005

Latent inhibition of conditioned taste aversion is not disrupted, but can be enhanced, by selective nucleus accumbens shell lesions in rats.

Latent inhibition is a form of negative priming in which repeated non-reinforced pre-exposures to a stimulus retard subsequent learning about the predictive significance of that stimulus. The nucleus accumbens shell and the anatomical projection it receives from the hippocampal formation have been attributed a pivotal role in the control or regulation of latent inhibition expression. A number of studies in rats have demonstrated the efficacy of selective shell lesions to disrupt latent inhibition in different associative learning paradigms, including conditioned active avoidance and conditioned emotional response. Here, we extended the test to the conditioned taste aversion paradigm, in which the effect of direct hippocampal damage on latent inhibition remains controversial. We demonstrated the expected effect of selective shell lesions on latent inhibition of conditioned emotional response and of conditioned active avoidance, before evaluating in a separate cohort of rats the effect of comparable selective lesions on latent inhibition of conditioned taste aversion: a null effect of the lesions was first obtained using parameters known to be sensitive to amphetamine treatment, then an enhancement of latent inhibition was revealed with a modified conditioned taste aversion procedure. Our results show that depending on the associative learning paradigm chosen, shell lesions can disrupt or enhance the expression of latent inhibition; and the pattern is reminiscent of that seen following hippocampal damage.

Animals↗

PubMed2006

Structure and in vitro cytocompatibility of the gastropod shell of Helix pomatia.

Distinguishing features of biological constructions are high stability and adaptation to their environment. Beside biocompatibility, nontoxicity and degradability these characteristics are demanded for new biomaterials in the field of tissue engineering. This study investigated the chemical composition, the organization and the in vitro osteoconductive potential of the terrestrial gastropod shell (Helix pomatia) on CAL72 and human osteoblast-like cells. Chemical composition of the biomaterial was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) was performed to analyze the architecture of the snail shell and the morphology of the seeded cells. A double staining procedure (FDA/PI) and a proliferation test (EZ4U) assessed the viability of the cells. Microscopical images showed the multilayered architecture of the aragonite shell with hexagonal crystals on the inner side. The cells spread well on the biomaterial and the highest proliferation rate could be measured with CAL72 cells on the inner shell surface. The osteoconductive effects of this natural biomaterial could encourage further experiments in the field of tissue engineering.

Animals↗

PubMed2003

Resonant acoustic scattering by a finite linear grating of elastic shells.

Theoretical and experimental studies of the acoustic scattering by a finite linear grating of elastic cylindrical shells are performed. It is observed that a resonant interaction takes place at low frequency when the shells are very close to each other. This phenomenon can be clearly associated to the Scholte-Stoneley wave that propagates around a single shell. It is shown that each resonance of the Scholte-Stoneley wave is split up into N resonances when N shells compose the grating.

Acoustics↗

PubMed2004

Space-time-wave number-frequency Z(x, t, k, f) analysis of SAW generation on fluid filled cylindrical shells.

A new 4D space-time-wave number-frequency representation Z(x,t,k,f) is introduced. The Z(x,t,k,f) representation is used for processing 2D space-time signal collection issued from wave propagation along a 1D medium. This representation is an extension along the time dimension of the space-wave number-frequency representation. The Z(x,t,k,f) representation is obtained by short time-space 2D Fourier transforming the space-time collection. The Z(x,t,k,f) representation allows the characterization transient aspects of wave generation and propagation in both space and time dimensions. The Z(x,t,k,f) representation is used to experimentally investigate Lamb wave generation and propagation around a cylindrical shell (relative thickness is equal to 0.03) surrounded by water and excited by a pulse (0.1 micros duration with 1-5 MHz transducers). Three kinds of fluids have been used inside the shell: air, water, propanol. In all the cases, the Z(x,t,k,f) analysis clearly identify the reflected field on the insonified side of the shell and it allows the measurement of the local reflection coefficients R(x,t,k,f). The generation and the propagation of Lamb waves are also quantified. For the liquid filled shells, the multiple internal reflections are revealed by Z(x,t,k,f) analysis: the local transmission coefficients T(x,t,k,f) are also measured. When local matching conditions allows Lamb wave generation, the multiple regeneration of Lamb wave is observed. Based on these results, a link is establish toward the theoretical results obtained by steady state approach and Sommerfeld-Watson transform.

Journal Article↗

PubMed2006

Amplitude-modulated acoustic radiation force experienced by elastic and viscoelastic spherical shells in progressive waves.

The dynamic acoustic radiation force resulting from a dual-frequency beam incident on spherical shells immersed in an inviscid fluid is examined theoretically in relation to their thickness and the contents of their interior hollow regions. The theory is modified to include a hysteresis type of absorption inside the shells' material. The results of numerical calculations are presented for stainless steel and absorbing lucite (PolyMethyMethacrylAte) shells with the hollow region filled with water or air. Significant differences occur when the interior fluid inside the hollow region is changed from water to air. It is shown that the dynamic radiation force function Yd deviates from the static radiation force function Yp when the modulation size parameter deltax = mid R:x2 - x1mid R: (x1 = k1a, x2 = k2a, k1 and k2 are the wave vectors of the incident ultrasound waves, and a is the outer radius of the shell) starts to exceed the width of the resonance peaks in the Yp curves.

Acoustics↗

PubMed1997

Electrorotation of liposomes: verification of dielectric multi-shell model for cells.

The reliability of multi-shell dielectric models, used to describe the ac electrokinetic behaviour of cells, has been tested by performing electrorotation and dielectrophoretic measurements on unilamellar, oligolamellar, and multilamellar liposomes of diameters ranging from 5 to 24 microm. Fluorescence microscopy, flow cytometry and electron spin resonance were used to characterise the morphology and membranes of the liposomes. The dielectric properties of the various types of liposomes, based on appropriate dielectric shell models, were then analysed using a general purpose, recursive, algorithm. Through simulations, the confidence levels that can be assigned to parameters derived through application of simple shell models are estimated. From this, we confirm that electrorotation data enable accurate determinations to be made of the dielectric properties of the outermost membrane of liposomes, and provide good indications of the level of complexity of the shells and internal compartments. We also demonstrate that, used with sufficient additional information, such as that provided by dielectrophoresis, electrorotation data yields unique solutions for the dielectric parameters of liposome-like particles.

Electric Conductivity↗

PubMed2002

Increased conditioned fear response and altered balance of dopamine in the shell and core of the nucleus accumbens during amphetamine withdrawal.

It has been suggested that neuroadaptations within the nucleus accumbens (NAC) dopaminergic (DA) projection contribute to the negative affect associated with psychostimulant withdrawal. The present study assessed the effects of amphetamine (AMPH) withdrawal on behavioral and NAC DA responses to conditioned fear stress. Animals injected with escalating-dose AMPH (1-5mg/kg, three injections/day, 6 days) or saline (SAL) acquired a tone-shock association on withdrawal day 3 and were tested for extinction of conditioned freezing to the tone on withdrawal day 4. Extracellular levels of NAC shell and core DA were monitored using in vivo microdialysis on both days. AMPH-withdrawn animals exhibited more conditioned freezing than SAL animals during both acquisition and extinction. During acquisition, DA increased more in the shell than the core of the NAC in both AMPH and SAL groups. During extinction to the tone, shell DA increased in SAL- but not AMPH-treated animals, whereas core DA activity was greater in AMPH than SAL animals. These data demonstrate that AMPH withdrawal alters the balance between shell and core DA transmission while increasing the behavioral expression of conditioned fear. Such drug-induced neuroadaptations in the NAC stress response may be involved in the exacerbation of negative emotions associated with drug withdrawal and stimulant-induced psychosis.

Amphetamine↗

PubMed2004

Conch shell structure and its effect on mechanical behaviors.

The shell of pink conch is a kind of natural well-designed composite with excellent mechanical properties, which provides us information for material design. In this paper the microstructures of pink conch shell are characterized by using SEM and TEM. The microscopic analysis indicates that the pink conch shell is with crossed-lamellar microstructure and the angle between two second-order lamellae is 70-90 degrees. The cracking and fracture morphologies indicate that the crack deflection, bridge and fiber pullout are the main toughening mechanisms. Bamboo lamellae are employed to make the simple bio-mimetic model materials. In the model material the rotated angle between the fibers of each glued lamella varies from 0 degrees to 90 degrees. Three-point-bending is employed to test the properties of models material, such as the elastic modulus, the flexural strength and the fracture strain energy density. It is found that the fracture strain energy density of the specimens with the rotated angle between the fibers of the layers about 60 degrees exhibits the maximum value, which is close to the angle of the two second-order lamellae of the conch shell.

Animals↗