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Background and Objective: A double-blind phase 3 study was conducted to compare posaconazole 300 mg intravenously (IV)/300 mg orally once daily (twice daily day 1) with voriconazole 4 mg/kg IV twice daily/200 mg orally twice daily (6 mg/kg day 1) for treatment of invasive aspergillosis. This analysis was conducted to summarize the pharmacokinetics and exposure-response relationships of posaconazole and voriconazole using plasma trough concentration (C trough ) as a surrogate for exposure from the double-blind phase 3 study., Methods: The pharmacokinetic evaluable population included all intention-to-treat (ITT) participants with at least one plasma concentration during the treatment period. Treatment blinding was maintained without therapeutic drug monitoring. C trough sampling occurred throughout treatment; efficacy and safety were evaluated using quartiles determined by mean C trough concentrations. Exposure efficacy variables included day 42 all-cause mortality (primary study endpoint) and global clinical response. Exposure safety variables included all adverse events and treatment-related adverse events., Results: The pharmacokinetic analysis population included 506 of 575 ITT participants (437 with C trough concentrations: 228 posaconazole, 209 voriconazole). No trend was seen across quartiles of posaconazole C trough for the key efficacy endpoint of all-cause mortality through day 42. Participants in the highest quartile of voriconazole C trough had higher all-cause mortality through day 42 than participants in the lower three quartiles of voriconazole C trough . Similar findings were observed for global clinical response and C trough . No clear exposure safety trend by quartile was seen for posaconazole or voriconazole., Conclusions: A strong exposure-response relationship was not observed across the range of exposure from the administered doses and formulations for posaconazole or voriconazole., Trial Registration: NCT01782131; registered January 30, 2013., (© 2023. The Author(s).)

Bimetallic Ag@Au nanoparticles (NPs) have received significant research interest because of their unique optical properties and molecular sensing ability through surface-enhanced Raman scattering (SERS). However, the synthesis of Ag@Au core-shell plasmonic nanostructures with precisely controlled size and shape remained a great challenge. Here, we report a simple approach for the synthesis of bimetallic Ag@Au nanodisks of about 13.5 nm thickness and different diameters through a seed-mediated growth process. The synthesis involves the conformal deposition of Au atoms at the corner sites of Ag nanoplate (AgNPL) seeds coupled with site-selective oxidative etching of AgNPL edges to generate Ag@Au nanodisks. The resultant Ag@Au nanodisks manifest significantly improved chemical stability and tunable localized surface plasmon resonance from the visible to the near-infrared spectral range. Moreover, in comparison to AgNPLs, the Ag@Au nanodisks showed greatly enhanced SERS performance with an enhancement factor up to 0.47 × 10 5 , which is nearly 3-fold higher than that of the original AgNPLs (0.18 × 10 5 ). Furthermore, the Ag@Au nanodisks show a high sensitivity for detecting probe molecules such as crystal violet of concentration as low as 10 -9 M and excellent reproducibility, with the SERS intensity fluctuation less than 12.5%. The synthesis route adapted for the controlled fabrication of Ag@Au nanodisks can be a potential platform for maneuvering other bimetallic plasmonic nanostructures useful for plasmonics and sensing applications., Competing Interests: The authors declare no competing financial interest.

This work reports the results of in vivo assays of an implant composed of the hydrogel Chitosan-g-Glycidyl Methacrylate-Xanthan [(CTS-g-GMA)-X] in Wistar rats. Degradation kinetics of hydrogels was assessed by lysozyme assays. Wistar rats were subjected to laminectomy by cutting the spinal cord with a scalpel. After the surgical procedure, hydrogels were implanted in the injured zone (level T8). Somatosensory evoked potentials (SEPs) obtained by electric stimulation onto periphery nerves were registered in the corresponding central nervous system (CNS) areas. Rats implanted with the biomaterials showed a successful recovery compared with the non-implanted rats after 30days. Lysozyme, derived from egg whites, was used for in vitro assays. This study serves as the basis for testing the biodegradability of the hydrogels (CTS-g-GMA)-X that is promoted by enzymatic hydrolysis. Hydrogels' hydrolysis was studied via lysozyme kinetics at two pH values, 5 and 7, under mechanical agitation at 37°C. Results show that our materials' hydrolysis is slower than pure CTS possibly due to the steric hindrance imposed by the GMA grafting of functionalization. This hydrolysis helps degrade the biomaterial and at the same time it provides support for spinal cord recovery. Combination of these results may prove useful in the use of these hydrogels as scaffolds for cells proliferation and their application as implants in living organisms., (Copyright © 2017. Published by Elsevier B.V.)

Differences on herringbone molecular arrangement in two forms of long-chain 1,ω-alkanediols (C n H 2 n +2 O₂ with n = 10, 11, 12, 13) are explained from the analysis of O-H···O hydrogen-bond sequences in infinite chains and the role of a C-H···O intramolecular hydrogen-bond in stabilization of a gauche defect, as well as the inter-grooving effectiveness on molecular packing. GIXD (Glancing Incidence X-ray Diffraction) experiments were conducted on polycrystalline monophasic samples. Diffracted intensities were treated with the multi-axial March-Dollase method to correlate energetic and geometrical features of molecular interactions with the crystalline morphology and textural pattern of samples. The monoclinic (P 2 ₁/ c , Z = 2) crystals of the even-numbered members ( n = 10, 12; DEDOL and DODOL, respectively) are diametrical prisms with combined form {104}/{-104}/{001} and present a two-fold platelet-like preferred orientation, whereas orthorhombic (P 2 ₁ 2 ₁ 2 ₁, Z = 4) odd-numbered members ( n = 11, 13; UNDOL and TRDOL, respectively) present a dominant needle-like orientation on direction [101] (fiber texture). We show that crystalline structures of medium complexity and their microstructures can be determined from rapid GIXD experiments from standard radiation, combined with molecular replacement procedure using crystal structures of compounds with higher chain lengths as reference data.

We investigate the system-size dependence of the thermodynamic properties of ionic fluids under periodic boundary conditions. Following an approach previously developed in the context of quantum Monte Carlo simulations of many-electron systems, we show that the leading-order finite-size artifact in the Coulomb energy per particle of a classical fluid of N structureless ions at given density and temperature is simply -k B T(2N) -1 . Analytical approximations for the periodicity-induced size dependence of the excess thermodynamic properties of the fluid in the weak-coupling regime are obtained within the linearized Debye-Hückel theory. Theoretical results are compared with published simulations of the one-component plasma and our own simulations of a primitive-model electrolyte solution. Our work is directly relevant to estimating finite-size corrections in simulations of charged fluids comprising structureless ions embedded in continuous media. We outline in the Appendix how some of our formal results may be generalized to molecular fluids with mobile ions; e.g., electrolyte solutions with explicit solvent.

Using a chemical potential route, the square-well (SW) fluid model is solved in a quasichemical approximation (QCSW). At low temperatures, the liquid reaches a limiting density greater than the triple point density of a SW fluid but less than the equilibrium liquid-to-solid transition density for hard spheres. As this unique density is approached with decreasing temperature, the liquid entropy also approaches an asymptotic value, thus averting the "entropy catastrophe". Mean-field models in the van der Waals (VDW) genre fail to predict this type of behavior. In VDW models, attractive force contributions to the equation of state incorrectly diverge with decreasing temperature as 1/T, whereas those for the QCSW model asymptote to a fixed value. The QCSW model posits the intuitively pleasing idea that, at high densities, attractive contributions to the configurational energy begin to saturate well before zero temperature is reached. As a consequence, the force balance between repulsive and attractive forces stabilizes the liquid density, which thereafter becomes effectively independent of temperature. This fixed density in turn fixes all other density-dependent thermodynamic properties. These low-temperature, force-stabilized states are identified as glass states.

A Zeno line is a straight line in a fluid's temperature-density plane where the compressibility factor equals unity and stretches from supercritical to subcritical regimes. A second unexpected linearity also occurs in liquids in their normal liquid range (NLR) where the compressibility factor approaches zero. This Zeno-like line includes liquids as diverse as monatomic and diatomic elements to hydrogen bonding liquids, with water and helium being the only currently known exceptions. Remarkably, this second linearity is also present in polymeric liquids, molten metals, and salts, i.e., it is a generic characteristic of liquids with negligible or low vapor pressures. This observation yields the following new corresponding states principle: Saturated liquid densities are a linear function of temperature in the NLR for molecular, polymeric, inorganic, ionic, and metallic liquids and superpose to form a single master curve. Another Zeno-like linearity in the NLR has also been identified for the configurational energy of many liquids. Extension of this line to zero temperature defines the ground state configurational energy of the hypothetical disordered liquid (glass).

We report a case of a 14-year-old female with primary adenocarcinoma of the transverse colon. She was hospitalized after presenting with abdominal pain and signs of intestinal obstruction. There was no health antecedent or family history of neoplasia. Physical examination revealed a distended abdomen. Tenderness was elicited to palpation of the right lower quadrant. Magnetic resonance imaging of the abdomen revealed obstructive signs, with a constricting lesion in the mid-transverse colon of probable neoplastic nature. Laparoscopic segmental resection of the colon was followed by standard right hemicolectomy. A circumferential mid-transverse tumor was diagnosed as primary colorectal carcinoma (CRC) of signet-ring cell type, AJCC stage IIIC, Dukes' C stage. On the basis of immunohistochemistry and clinical data, hereditary nonpolyposis and hamartomatous colorectal cancer syndromes were excluded. Involvement of either the p53, BRAF, or K-RAS genes was ruled out by immunohistochemistry profiling and genetic testing. The neoplasm was categorized as sporadic. The possibility of activation of the Wnt signaling pathway was suspected, because of a defective turnover of the β-catenin protein. Postoperatively, the patient was treated with both systemic and intra-abdominal adjuvant chemotherapy, including oxaliplatin. Between 18 and 24 months after diagnosis, intra-abdominal tumor recurrences were detected. The patient underwent bilateral oophorectomies for Krukenberg tumors and received salvage chemotherapy. Recently, additional recurrent metastatic retroperitoneal disease caused hydronephrosis. The retroperitoneal mass was debulked and a ureteric stent was placed. At the time of this writing, 43 months after diagnosis, the patient is receiving FOLFOX chemotherapy combined with panitumumab. CRC of childhood is exceedingly rare, generally develops in the setting of unrecognized genetic predisposing factors to cancer, presents with advanced disease, is high grade, and tends to have dismal prognosis.

For 68 fluids that include hydrogen bonding and quantum fluids, the fugacity coefficient that defines the residual chemical potential adopts a near universal value of 2/3 at the critical point. More precisely, the reciprocal of the fugacity coefficient equals 1.52 ± 0.02 and includes fluids as diverse as helium (1.50), dodecafluoropentane (1.50), and water (1.53). For 65 classical fluids, a dimensionless thermal pressure coefficient and internal pressure attain critical values of 1.88 ± 0.11 and 1.61 ± 0.11, respectively. From equations of state, values of these new critical constants have been calculated and agree favorably with experimental values. Specifically, for the critical fugacity coefficient, the following results were obtained for its reciprocal: van der Waals (1.44), lattice gas (1.43), scaled particle theory (1.46), and the Redlich-Kwong eq (1.50). The semiempirical Redlich-Kwong equation is also the most accurate for the thermal pressure coefficient (1.86) and internal pressure (1.53). Physical interpretations of these results are discussed as well as their implications for other critical phenomena.

Molecular relaxations of chitosan films have been investigated in the wide frequency range of 0.1 to 3 × 10(9) Hz from -10 °C to 110 °C using dielectric spectroscopy. For the first time, two high-frequency relaxation processes (in the range 10(8) to 3 × 10(9) Hz) are reported in addition to the low frequency relaxations α and β. These two relaxation processes are related to the vibrations of OH and NH2/NH3(+), respectively. The high-frequency relaxations exhibit Arrhenius-type dependencies in the temperature range 10 °C to 54 °C with negative activation energy; this observation is traceable to hydrogen bonding reorientation. At temperatures above the glass transition temperature (54 °C), the activation energy changes from negative to positive values due to breaking of hydrogen bonding and water loss. Upon cooling in a sealed environment, the activation energies of two relaxation processes are nearly zero. FTIR and XRD analyses reveal associated structural changes upon heating and cooling. These two new high-frequency relaxation processes can be attributed to the interaction of bound water with OH and NH2/NH3(+), respectively. A plausible scenario for these high-frequency relaxations is discussed in light of impedance spectroscopy, TGA, FTIR and XRD measurements.

This work describes the preparation and characterization of biomimetic chitosan/multiwall carbon nanotubes/nano-hydroxyapatite (CTS/MWCNT/nHAp) scaffolds and their viability for bone tissue engineering applications. The cryogenic process ice segregation-induced self-assembly (ISISA) was used to fabricate 3D biomimetic CTS scaffolds. Proper combination of cryogenics, freeze-drying, nature and molecular ratio of solutes give rise to 3D porous interconnected scaffolds with clusters of nHAp distributed along the scaffold surface. The effect of doping in CNT (e.g. with oxygen and nitrogen atoms) on cell viability was tested. Under the same processing conditions, pore size was in the range of 20-150 μm and irrespective on the type of CNT. Studies on cell viability with scaffolds were carried out using human cells from periosteum biopsy. Prior to cell seeding, the immunophenotype of mesenchymal periosteum or periosteum-derived stem cells (MSCs-PCs) was characterized by flow cytometric analysis using fluorescence-activated and characteristic cell surface markers for MSCs-PCs. The characterized MSCs-PCs maintained their periosteal potential in cell cultures until the 2nd passage from primary cell culture. Thus, the biomimetic CTS/MWCNT/nHAp scaffolds demonstrated good biocompatibility and cell viability in all cases such that it can be considered as promising biomaterials for bone tissue engineering., (© 2013 Wiley Periodicals, Inc.)

Equations of state in the van der Waals genre suggest that saturated liquids should adhere to the following corresponding states principle (CSP): saturated liquids at the same reduced density (ρR = ρ/ρc) have comparable dimensionless thermodynamic properties. This CSP is shown to be applicable to a variety of thermodynamic properties that include entropy of vaporization, cohesive energy density, thermal expansion coefficient, isothermal compressibility, thermal pressure coefficient, compressibility factor, temperature coefficient of the vapor pressure, heat capacity difference, and surface tension. For two classes of liquids, all properties rendered dimensionless by the proper choice of scaling variables superpose to form "master curves" that illustrate the CSP. Using scaled particle theory, an improved van der Waals model is developed whose results are compared with existing experimental thermodynamic data in dimensionless form. Properly expressing thermodynamic properties in dimensionless form acts to consolidate and harmonize liquid state properties.

Globular proteins contain cavities/voids that play specific roles in controlling protein function. Elongated cavities provide migration channels for the transport of ions and small molecules to the active center of a protein or enzyme. Using Monte Carlo and Molecular Dynamics on fully atomistic protein/water models, a new computational methodology is introduced that takes into account the protein's dynamic structure and maps all the cavities in and on the surface. To demonstrate its utility, the methodology is applied to study cavity structure in myoglobin and five of its mutants. Computed cavity and channel size distributions reveal significant differences relative to the wild type myoglobin. Computer visualization of the channels leading to the heme center indicates restricted ligand access for the mutants consistent with the existing interpretations. The new methodology provides a quantitative measure of cavity structure and distributions and can become a valuable tool for the structural characterization of proteins.

The relationship between electrical conductivity, structure and antibacterial properties of chitosan-silver nanoparticles (CS/AgnP) biocomposites has been analyzed. To test the film's antimicrobial activity, Gram-positive and Gram-negative bacteria were studied. The interactions between silver nanoparticles with chitosan suggest the formation of silver ions which plays a major role in nanocomposite's bactericidal potency. In CS/AgnP biocomposites, the bactericide effectiveness increases by increasing AgnP concentrations up to 3 wt%, which is close to the electrical percolation threshold of ca. 3 wt%. As the AgnP concentration increases above this threshold, the bactericidal potency is greatly diminished. The elucidated correlation between electrical conductivity and antibacterial activity could be useful in the design of other nanocomposites that involve polymeric-based matrices., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Objective: To characterize recorded trichinosis cases and outbreaks in Santa Fe Province, Argentina, from 1998 to 2009 from epidemiological, clinical, and laboratory viewpoints., Methods: An analysis was conducted of 1 519 epidemiological records of persons who had signs and symptoms compatible with trichinosis in Santa Fe Province in the period 1998-2009. A descriptive statistical analysis of information in epidemiological records and of clinical and laboratory results, as well as a bifactorial analysis of possible associations with epidemiological and environmental factors were also carried out., Results: Trichinosis symptoms were found in 1 276 cases; 372 met the clinical case definition and 224 samples were positive by indirect immunofluorescence, independent of their clinical case classification. There were 27 outbreaks that involved 1 157 cases identified in eight departments, with greater frequency in the province's center and south. Annual distribution of epidemiologically associated cases was heterogeneous, with greater frequency in the period 2000-2003 and in the months of August to October. Probability of becoming sick was greater with consumption of products from informal sources (OR = 3.69; P = 0.014) and in rural areas (OR = 1.799; P = 0.011). Disease incubation period (median) was 12 days. The risk of becoming sick was 2.06 times greater in persons who ate meat or ate pork by-products than in those who did not., Conclusions: The greatest number of outbreaks occurred in departments that were more populous and where pork production was greater. Specific actions should be designed for prevention and control of the disease in those departments. Epidemiological risk analysis should be considered in evaluating, managing, and communicating trichinosis health risks.

This work reports the synthesis and characterization of a new material obtained by mixing the hybrid natural-synthetic chitosan-g-glycidyl methacrylate (CTS-g-GMA) biopolymer and xanthan gum (X). All materials were characterized by infrared spectroscopy (FTIR), X-ray diffraction, and thermal analysis (DSC and TGA) and the results were contrasted with those of the precursor materials. The swelling index of the hydrogels decreases when the GMA mass percentage increases. The X-ray diffraction patterns show that the hybrid hydrogels are amorphous in contrast to chitosan (CTS), which is semi-crystalline. FTIR analysis confirms the existence of physical interactions among constituents. Rheological properties, η, G', and G", were determined as a function of flow allowing one to conclude that (CTS-g-GMA)-X behaves as physical hydrogel. Additionally, we report viability of fibroblasts when cultured onto the synthesized hydrogels. This study shows that these hydrogels support cell viability and have potential for use in biomedical engineering applications.

Deep Eutectic Solvents (DESs) based upon mixtures of Acrylic Acid (AA) or Methacrylic Acid (MAA) and Choline Chloride (CCl) demonstrated superior performance than regular organic solvents and even ionic liquids for frontal polymerizations (FPs). Full recovering of CCl after FP provided an interesting green character to the process., (© The Royal Society of Chemistry 2011)

An analysis of the expected divergences in thermodynamic properties at the close-pack density (eta(cp) = pi square root(2)/6) along with the known virial coefficients up to 10th order suggests a weak logarithmic singularity in the excess fluid entropy. The corresponding equation of state (EOS) also possesses a singularity at eta(cp). The new EOS accurately describes extant molecular dynamics data up to the fluid-solid transition (eta approximately 0.494) with differences of less than 1 part per thousand. This accuracy is maintained into the metastable fluid regime up to eta approximately 0.52. In terms of accuracy, the new EOS is no better than Pade approximants, but the new EOS, unlike the Pade approximants, diverges at eta(cp). In addition, a new order parameter is defined that enables all system configurations to be classified as either disordered or ordered. Monte Carlo simulations are used to determine this order parameter in the metastable fluid range. Using this new order parameter, evidence is presented to support a thermodynamic glass transition at eta approximately 0.54. With respect to this transition, congruence is found with the traditional ideas espoused by Gibbs and DiMarzio and Adam and Gibbs. It is the rapid disappearance of disordered (random) configurations with increasing density that drives the glass transition and slows the dynamics.

Poly(methyl methacrylate) (PMMA) is one of the most commonly plastics used as dental-base material, due to its good biological compatibility and mechanical properties. Chitosan has wide application in chemical, biochemical and biomedical fields of research. In this work, chitosan (CTS) was functionalized with glycidyl methacrylate (GMA), to ease a further reaction with MMA. The resulting co-polymer was finally blended with PMMA and poly(butyl acrylate) PBA which works as a damper, the polymers were cured by UV to obtain the final resin. Characterization of UV-cured resins was carried out by thermal measurements, X-ray diffraction, atomic force microscopy (AFM), micro and nanoindentation, water absorption and elution in water. As a result a higher thermal stability of the final resin compared with the precursor co-polymer ((CTS-GMA)-g-PMMA) was obtained. The resin presented roughness in the nanometer scale and nanoparticles embedded in the acrylic matrix producing a tough material. However, XRD measurements show that all materials are in an amorphous state. Values of hardness and elastic modulus results were very near to those of the dentine. The results of elution in water of the tested resin samples show them as clinically acceptable as a dental base material.

Polymer adhesion between two immiscible polymers is usually poor because there is little interpenetration of one polymer into the other at the interface. Increasing the width of the interfacial zone can enhance adhesion and mechanical properties. In principle, this can be accomplished by exposing heterogeneous polymer materials to a high-pressure fluid. The fluid can act as a common solvent and promote interpenetration. It also increases chain mobility at the interface, which helps to promote "welding" of the two polymers. A combination of the gradient theory of inhomogeneous systems and the Sanchez-Lacombe equation of state was used to investigate this phenomenon, especially the effect of the high compressibility of supercritical (SC) fluid on the compatibilization of two incompatible polymers. We calculate the interfacial density profile, interfacial thickness, and interfacial tension between the two polymers with and without the SC fluid. We find that the interfacial tension is decreased and the interfacial thickness is increased with high-pressure SC fluid for the ternary systems we have investigated. As the critical point is approached and the SC compressibility becomes large, no enhancement or deleterious effects on compatibilization were observed.

A probabilistic protocol which makes possible the calculation of the diffusivity of light gases in amorphous materials from limited Monte Carlo and molecular dynamics data is presented. Diffusion coefficients are calculated for helium and methane in polystyrene, and for helium, neon, and methane in three pairs of polysulfone isomers. Results include diffusion coefficients as small as 10(-9) cm2/s and are in good agreement with results obtained from traditional molecular dynamics and with available experimental data.

We examine the morphological structures of asymmetric poly(ethylene oxide)-b-poly(1,1'-dihydroperflurooctyl methacrylate) (PEO-b-PFOMA) thin films upon annealing in a compressible fluid, supercritical CO2 (Sc-CO2). The strong affinity between PFOMA and CO2 is found to induce phase segregation when annealing PEO-b-PFOMA films at the same temperature as compared with vacuum. In vacuum, PEO-b-PFOMA films remain disordered from 80 to 180 degrees C, whereas, in Sc-CO2 at 13.9 MPa, an upper order-disorder transition (UODT) between 116 and 145 degrees C is found. In Sc-CO2, the observed ordered structure is layers of PEO spheres embedded in the matrix of PFOMA, followed by a brush layer, in which PEO wets the substrate. The swelling isotherms of PFOMA and PEO in CO2 are correlated with the Sanchez-Lacombe equation of state (SLEOS) to estimate the interaction parameters, XPFOMA-CO2 and XPEO-CO2. The phase segregation (order) induced by CO2 relative to vacuum at a given temperature is explained in terms of two factors: (1) copolymer volume fraction upon dilution with CO2, phi, and (2) the relative interaction parameter, DeltaX= XPEO-CO2 - XPFOMA-CO2. The latter factor favors order and is dominant at low temperatures over the phi factor, which always favors disorder. At high temperatures (above the T(ODT)), the preferential swelling of PFOMA by CO2 is less pronounced ( DeltaX decreases), and the copolymer is disordered.

Unusual sorption has been reported in thin polymer films exposed to near-critical CO2. When the supercritical fluid approaches the critical point, the film appears to thicken, but it is not clear whether the film swells or there is an adsorption layer on the film surface. A combination of the gradient theory of inhomogeneous systems and the Sanchez-Lacombe equation of state has been used to investigate this phenomenon. It is shown analytically that surface adsorption on an attractive surface is proportional to the compressibility of the fluid. We have also investigated numerically the sorption of supercritical CO2 on poly(dimethylsiloxane) and polyisobutylene, and supercritical 1,1-difluoroethane on polystyrene. By calculating the Gibbs adsorption and adsorption layer thickness of the supercritical fluids, we found in all cases (different substrates, different supercritical fluids) that maximum adsorption occurs when the supercritical fluid is near its compressibility maximum.

Poly(1-trimethylsilyl-1-propyne) (PTMSP), the most permeable polymer known, undergoes rapid physical aging. The permeability of PTMSP to gases and vapors decreases dramatically with physical aging. Cavity size (free volume) distributions were calculated in as-cast and aged PTMSP, using an energetic based cavity-sizing algorithm. The large cavities found in as-cast PTMSP disappear in aged PTMSP, which is consistent with the positron annihilation lifetime spectroscopy (PALS) measurements. We also characterized the connectivity of cavities in both as-cast and aged PTMSP membranes. Cavities are more connected in as-cast PTMSP than in aged PTMSP. The average cavity sizes calculated from computer simulation are in good agreement with PALS measurements. The transport and sorption properties of gases in as-cast and aged PTMSP are also measured by molecular simulation. Computer simulations showed the decrease of permeability and the increase of permeability selectivity in PTMSP membranes with physical aging, which agrees with experimental observations. The reduction in gas permeability with physical aging results mainly from the decrease of diffusion coefficients. Solubility coefficients show no significant changes with physical aging.

Glassy, disubstituted acetylene-based polymers exhibit extremely high gas permeabilities and high vapor/gas selectivities, which is quite unusual for conventional glassy polymers such as polysulfone. Diffusion coefficients of poly[1-phenyl-2-[p-(trimethylsilyl)phenyl]acetylene] (PTMSDPA) and poly[diphenylacetylene] (PDPA) were obtained using both molecular simulation and experimental techniques. PTMSDPA, a disubstituted glassy acetylene-based polymer, exhibits higher diffusivity than its desilylated analogue, PDPA. Simulation results are in good agreement with experimental data. Cavity size (free volume) distributions of both polymers are also obtained using an energetic-based algorithm (in't Veld et al., J. Phys. Chem. B 2000, 104, 12028) developed recently. Larger cavities in PTMSDPA contribute to its higher diffusivity, and higher permeability.

Nonequilibrium molecular-dynamics simulations are performed for linear and branched chain molecules to study their rheological and structural properties under simple shear and Poiseuille flows. Molecules are described by a spring-monomer model with a given intermolecular potential. The equations of motion are solved for shear and Poiseuille flows with Lees and Edward's [A. W. Lees and S. F. Edwards, J. Phys. C 5, 1921 (1972)] periodic boundary conditions. A multiple time-scale algorithm extended to nonequilibrium situations is used as the integration method, and the simulations are performed at constant temperature using Nose-Hoover [S. Nose, J. Chem. Phys. 81, 511 (1984)] dynamics. In simple shear, molecules with flow-induced ellipsoidal shape, having significant segment concentrations along the gradient and neutral directions, exhibit substantial flow resistance. Linear molecules have larger zero-shear-rate viscosity than that of branched molecules, however, this behavior reverses as the shear rate is increased. The relaxation time of the molecules is associated with segment concentrations directed along the gradient and neutral directions, and hence it depends on structure and molecular weight. The results of this study are in qualitative agreement with other simulation studies and with experimental data. The pressure (Poiseuille) flow is induced by an external force F(e) simulated by confining the molecules in the region between surfaces which have attractive forces. Conditions at the boundary strongly influence the type of the slip flow predicted. A parabolic velocity profile with apparent slip on the wall is predicted under weakly attractive wall conditions, independent of molecular structure. In the case of strongly attractive walls, a layer of adhered molecules to the wall produces an abrupt distortion of the velocity profile which leads to slip between fluid layers with magnitude that depends on the molecular structure. Finally, the molecular deformation under flow depends on the attractive force of the wall, in such a way that molecules are highly deformed in the case of strong attracting walls.

The synthesis, characterization and degradation of a hybrid chitosan (CTS)/glycidyl methacrylate (GMA) material are reported. These versatile materials (natural-synthetic materials) are potential candidates for dental restoratives. All materials were characterized by infrared spectroscopy (FT-IR), X-ray diffraction and thermal (DSC) analysis. Particular attention was paid to the thermal stability and chemical resistance of the hybrid CTS materials. From dynamical rheological tests, it was concluded that CTS-GMA solutions behave as physical hydrogels. These pH-sensitive gels are an example of stimuli-responsive polymers, also known as 'smart polymers'.

The critical flocculation density (CFD), that is, the CO(2) density below which flocculation occurs, was studied for dilute water-in-CO(2) (W/C) miniemulsions stabilized with poly(1,1-dihydroperfluorooctyl methacrylate)-b-poly(ethylene oxide) (PFOMA-b-PEO) surfactants. The CFD, which was measured by turbidimetry, decreased as the PFOMA molecular weight was increased, the average droplet size was decreased, the surfactant loading was increased, and the temperature was increased. A simple model, which addressed both the van der Waals attraction between droplets and osmotic solvent-tail interactions, was in good qualitative agreement with the experimentally observed trends for the CFD and predicted a decrease in emulsion stability as the CO(2) density was lowered toward the theta density for PFOMA in bulk CO(2).

Single-trial learning and long-term memory of "what" and "who" information were examined in an adult gorilla (Gorilla gorilla gorilla). We presented the gorilla with a to-be-remembered food item at the time of study. In Experiment 1, following a retention interval of either approximately 7 min or 24 h, the gorilla responded with one of five cards, each corresponding to a particular food. The gorilla was accurate on 70% of the short retention-interval trials and on 82% of the long retention-interval trials. In Experiment 2, the food stimulus was provided by one of two experimenters, each of whom was represented by a card. The gorilla identified the food (55% of the time) and the experimenter (82% of the time) on the short retention-interval trials. On the long retention-interval trials, the gorilla was accurate for the food (73%) and for the person (87%). The results are interpreted in light of theories of episodic memory.

A theory of crystallization is formulated for random copolymers which crystallize with the non-crystallizable co-units incorporated into the crystalline lattice as defects. The appropriate melting point equation and other associated thermodynamic properties are derived for this model as a function of crystal thickness and comonomer concentration. The formation of lamellar type morphology is assumed to be a kinetically determined phenomena and nucleation theory is utilized accordingly. The isothermal lamella thickness is predicted to increase in a definitive manner as the noncrystallizable comonomer concentration X increases, while the associated isothermal growth rate is predicted to decrease. The variation of lamella thickness with X when the copolymer is quenched or cooled at a uniform rate is also qualitatively predicted. Under these conditions lamella thickness decreases with increasing X , which is in accord with previous experimental observations on random copolymers of tetrafluoroethylene and hexafluoropropylene as well as other random copolymers. Theory also suggests how the surface free energy parameters σ e and σ can be determined from isothermal crystallization experiments for a series of random copolymers of varying composition.

A nonequilibrium (kinetic) theory of polymer molecular weight (MW) fractionation is formulated and applied to binary and multicomponent polyethylenes crystallized from unstirred xylene solutions. High MW components crystallize more readily than do low MW components. This fractionation effect is enhanced as the crystallization temperature is raised. At low crystallization temperatures (high undercoolings) the polymer tends to fractionate according to the volume fraction distribution of its MW components and thus, the number average MW of the crystal that is formed is approximately equal to the weight average MW of the polymer in solution. It is shown that MW fractionation does not depend on the details of nucleation. but rather on the rates for post-nucleation crystal growth. The effects of MW polydispersity on crystalline properties is considered and in particular it is shown that polydispersity tends to mask the intrinsic dependence of crystal thickness on MW. The variables which govern and influence fractionation are also discussed.