Comprehensive structural characterization of MCM-41: From mesopores to particles

In the present work the meso- and macro-structural characteristics of the mesoporous adsorbent MCM-41 have been estimated with the help of various techniques. The structure is found to comprise four different length scales: that of the mesopores, the crystallites, the grains and of the particles. It was found that the surface area estimated by the use of small angle scattering techniques is higher, while that estimated by mercury porosimetry is much lower, than that obtained from gas adsorption methods. Based on the macropore characterization by mercury porosimetry, and the considerable macropore area determined, it is seen that the actual mesopore area of MCM-41 may be significantly lower than the BET area. TEM studies indicated that MCM-41 does not have an ideal mesopore structure; however, it may still be treated as a model mesoporous material for gas adsorption studies because of the large radius of curvature of the channels.

Simultaneous steady state and dynamic design of process systems using structural indicators

The simultaneous design of the steady-state and dynamic performance of a process has the ability to satisfy much more demanding dynamic performance criteria than the design of dynamics only by the connection of a control system. A method for designing process dynamics based on the use of a linearised systems' eigenvalues has been developed. The eigenvalues are associated with system states using the unit perturbation spectral resolution (UPSR), characterising the dynamics of each state. The design method uses a homotopy approach to determine a final design which satisfies both steady-state and dynamic performance criteria. A highly interacting single stage forced circulation evaporator system, including control loops, was designed by this method with the goal of reducing the time taken for the liquid composition to reach steady-state. Initially the system was successfully redesigned to speed up the eigenvalue associated with the liquid composition state, but this did not result in an improved startup performance. Further analysis showed that the integral action of the composition controller was the source of the limiting eigenvalue. Design changes made to speed up this eigenvalue did result in an improved startup performance. The proposed approach provides a structured way to address the design-control interface, giving significant insight into the dynamic behaviour of the system such that a systematic design or redesign of an existing system can be undertaken with confidence.

Ultrasound evaluation of polymer gel dosimeters

A new method for the evaluation of radiotherapy 3D polymer gel dosimeters has been developed using ultrasound to assess the significant structural changes that occur following irradiation of the dosimeters. The ultrasonic parameters of acoustic speed of propagation, attenuation and transmitted signal intensity were measured as a function of absorbed radiation dose. The dose sensitivities for each parameter were determined as 1.8 x 10(-4) s m(-1) Gy(-1), 3.9 dB m(-1) Gy(-1) and 3.2 V-1 Gy(-1) respectively. All parameters displayed a strong variation with absorbed dose that continued beyond absorbed doses of 15 Gy. The ultrasonic measurements demonstrated a significantly larger dynamic range in dose response curves than that achieved with previously published magnetic resonance imaging (MRI) dose response data. It is concluded that ultrasound shows great potential as a technique for the evaluation of polymer gel dosimeters.

Large amplitude folding in finely layered viscoelastic rock structures

We analyze folding phenomena in finely layered viscoelastic rock. Fine is meant in the sense that the thickness of each layer is considerably smaller than characteristic structural dimensions. For this purpose we derive constitutive relations and apply a computational simulation scheme (a finite-element based particle advection scheme; see MORESI et al., 2001) suitable for problems involving very large deformations of layered viscous and viscoelastic rocks. An algorithm for the time integration of the governing equations as well as details of the finite-element implementation is also given. We then consider buckling instabilities in a finite, rectangular domain. Embedded within this domain, parallel to the longer dimension we consider a stiff, layered plate. The domain is compressed along the layer axis by prescribing velocities along the sides. First, for the viscous limit we consider the response to a series of harmonic perturbations of the director orientation. The Fourier spectra of the initial folding velocity are compared for different viscosity ratios. Turning to the nonlinear regime we analyze viscoelastic folding histories up to 40% shortening. The effect of layering manifests itself in that appreciable buckling instabilities are obtained at much lower viscosity ratios (1:10) as is required for the buckling of isotropic plates (1:500). The wavelength induced by the initial harmonic perturbation of the director orientation seems to be persistent. In the section of the parameter space considered here elasticity seems to delay or inhibit the occurrence of a second, larger wavelength. Finally, in a linear instability analysis we undertake a brief excursion into the potential role of couple stresses on the folding process. The linear instability analysis also provides insight into the expected modes of deformation at the onset of instability, and the different regimes of behavior one might expect to observe.

Thermal ecology and structural habitat use of two sympatric lizards (Carlia vivax and Lygisaurus foliorum) in subtropical Australia

The thermal ecology and structural habitat use of two closely related sympatric lizards, Carlia vivax (de Vis) and Lygisaurus foliorum de Vis, were examined in an open sclerophyll forest in subtropical Australia. Comparable mean body temperatures (T-b) and habitat temperatures (T-hab) at the point of capture were recorded for both species. However, sex- related differences in the thermal variables for C. vivax, with females displaying higher temperatures than males, resulted in some significant differences in T-b and T-hab between the species. Variation in T-b and T-hab within and between species was unrelated to time of capture. The difference in T-hab within C. vivax suggested that females were selecting warmer thermal environments than males. Both C. vivax and L. foliorum used most structural features of their habitat randomly as indicated by a similarity in canopy, shrub, ground, log and litter cover and litter depth between habitat surveys and random surveys. However, C. vivax displayed a preference for ground vegetation (height

Structural development of silicated films self-assembled at the air-water interface

The development of structure perpendicular to and in the plane of the interface has been studied for mesoporous silicate films self-assembled at the air/water interface. The use of constrained X-ray and neutron specular reflectometry has enabled a detailed study of the structural development perpendicular to the interface during the pre-growth phase. Off-specular neutron reflectometry and grazing incidence X-ray diffraction has enabled the in-plane structure to be probed with excellent time resolution. The growth mechanism under the surfactant to silicate source ratios used in this work is clearly due to the self-assembly of micellar and molecular species at the air/liquid interface, resulting in the formation of a planar mesoporous film that is tens of microns thick. (C) 2003 Elsevier Science B.V. All rights reserved.

Structural change, balance-of-payments constraint, and economic growth: evidence from the multisectoral Thirlwall`s law

This paper contributes to the literature on balance-of-payments constrained growth by investigating how structural change identified with changes in the sectoral composition of exports and imports affects the external constraint We test both the original and a multisectoral version of Thirlwall`s law for a sample of Latin American and Asian countries The original Thirlwall s law is found to hold for all sample countries except South Korea, whereas the multisectoral analogue holds for all of them As the sectoral composition of exports and imports is found to matter for growth we analyze the evolution of each country`s weighted trade income elasticities

STRUCTURAL INTERDEPENDENCE AMONG COLOMBIAN DEPARTMENTS

This paper analyzes structural interdependence among Colombian departments. The results show that Bogota has a large influence on the other regional economies through the power of its purchases. Additionally, a center-periphery pattern emerges in the spatial concentration of the effects of the hypothetical extraction of any territory. From a policy point of view, the main findings reaffirm the role played by Bogota in the recent polarization process observed in the regional economies in Colombia. Any policy action oriented to reduce these regional disparities should take into account that, given the structural interdependence among Colombian departments, the effects of new investment in the lagged regions would flow through Bogota and the major regional economies.

Evaluating the efficiency of fractional integration parameter estimators

This article deals with the efficiency of fractional integration parameter estimators. This study was based on Monte Carlo experiments involving simulated stochastic processes with integration orders in the range]-1,1[. The evaluated estimation methods were classified into two groups: heuristics and semiparametric/maximum likelihood (ML). The study revealed that the comparative efficiency of the estimators, measured by the lesser mean squared error, depends on the stationary/non-stationary and persistency/anti-persistency conditions of the series. The ML estimator was shown to be superior for stationary persistent processes; the wavelet spectrum-based estimators were better for non-stationary mean reversible and invertible anti-persistent processes; the weighted periodogram-based estimator was shown to be superior for non-invertible anti-persistent processes.

Use of bulk density profiles from X-radiography to examine structural crust models

Exponential and sigmoidal functions have been suggested to describe the bulk density profiles of crusts. The present work aims to evaluate these conceptual models using high resolution X-radiography. Repacked seedbeds from two soil materials, air-dried or prewetted by capillary rise, were subjected to simulated rain, which resulted in three types of structural crusts, namely, slaking, infilling, and coalescing. Bulk density distributions with depth were generated using high-resolution (70 mum), calibrated X-ray images of slices from the resin-impregnated crusted seedbeds. The bulk density decreased progressively with depth, which supports the suggestion that a crust should be considered as a nonuniform layer. For the slaking and the coalescing crusts, the exponential function underestimated the strong change in bulk density across the morphologically defined transition between the crust and the underlying material; the sigmoidal function provided a better description. Neither of these crust models effectively described the shape of the bulk density profiles through the whole seedbed. Below the infilling and slaking crusts, bulk density increased linearly with depth as a result of slumping. In the coalescing crusted seedbed, the whole seedbed uniformly collapsed and most of the bulk density change within the crust could be ascribed to slumping (0.33 g cm(-3)) rather than to crusting (0.12 g cm(-3)). Finally, (i) X-radiography appears as a unique tool to generate high resolution bulk density profiles and (ii) in structural crusts, bulk density profiles could be modeled using the existing exponential and sigmoidal crusting models, provided a slumping model would be coupled.

Real-time monitoring and kinetic parameter estimation of the affinity interaction of jArtinM and rArtinM with peroxidase glycoprotein by the electrogravimetric technique

ArtinM is a D-mannose binding lectin that has been arousing increasing interest because of its biomedical properties, especially those involving the stimulation of Th1 immune response, which confers protection against intracellular pathogens The potential pharmaceutical applications of ArtinM have motivated the production of its recombinant form (rArtinM) so that it is important to compare the sugar-binding properties of jArtinM and rArtinM in order to take better advantage of the potential applications of the recombinant lectin. In this work, a biosensor framework based on a Quartz Crystal Microbalance was established with the purpose of making a comparative study of the activity of native and recombinant ArtinM protein The QCM transducer was strategically functionalized to use a simple model of protein binding kinetics. This approach allowed for the determination of the binding/dissociation kinetics rate and affinity equilibrium constant of both forms of ArtinM with horseradish peroxidase glycoprotein (HRP), a N-glycosylated protein that contains the trimannoside Man alpha 1-3[Man alpha 1-6]Man, which is a known ligand for jArtinM (Jeyaprakash et al, 2004). Monitoring of the real-time binding of rArtinM shows that it was able to bind HRP, leading to an analytical curve similar to that of jArtinM, with statistically equivalent kinetic rates and affinity equilibrium constants for both forms of ArtinM The lower reactivity of rArtinM with HRP than jArtinM was considered to be due to a difference in the number of Carbohydrate Recognition Domains (CRDs) per molecule of each lectin form rather than to a difference in the energy of binding per CRD of each lectin form. (C) 2010 Elsevier B V. All rights reserved

Dibucaine effects on structural and elastic properties of lipid bilayers

In this work we report the interaction effects of the local anesthetic dibucaine (DBC) with lipid patches in model membranes by Atomic Force Microscopy (AFM). Supported lipid bilayers (egg phosphatidylcholine, EPC and dimyristoylphosphatidylcholine, DMPQ were prepared by fusion of unilamellar vesicles on mica and imaged in aqueous media. The AFM images show irregularly distributed and sized EPC patches on mica. On the other hand DMPC formation presents extensive bilayer regions on top of which multibilayer patches are formed. In the presence of DBC we observed a progressive disruption of these patches, but for DMPC bilayers this process occurred more slowly than for EPC. In both cases, phase images show the formation of small structures on the bilayer surface suggesting an effect on the elastic properties of the bilayers when DBC is present. Dynamic surface tension and dilatational surface elasticity measurements of EPC and DMPC monolayers in the presence of DBC by the pendant drop technique were also performed, in order to elucidate these results. The curve of lipid monolayer elasticity versus DBC concentration, for both EPC and DMPC cases, shows a maximum for the surface elasticity modulus at the same concentration where we observed the disruption of the bilayer by AFM. Our results suggest that changes in the local curvature of the bilayer induced by DBC could explain the anesthetic action in membranes. (C) 2008 Elsevier B.V. All rights reserved.

Visible and near-infrared luminescent Eu(3+) or Er(3+) doped laponite-derived xerogels and thick films: Structural and spectroscopic properties

Laponite-derived materials represent promising materials for optical applications. In this work, Eu(3+)- or Er(3+)-doped laponite xerogels and films were prepared from colloidal dispersion. Homogeneous, crack-free and transparent single layers were deposited on soda-lime substrates with a thickness of 10 mu m. Structural and spectroscopic properties were analyzed by thermal analyses, X-ray diffractometry, transmission electron microscopy, infrared spectroscopy, and luminescence spectroscopy. The addition of a rare earth ion to the laponite does not promote any changes in thermal stability or phase transition. Laponite clay was identified after annealing up to 500 degrees C, with a decrease in basal spacing when the annealing temperature is changed from 100 degrees C to 500 degrees C. Enstatite polymorphs and amorphous silicate phases were observed after heat treatment at 700 degrees C and 900 degrees C. Stationary and time-dependent luminescence spectra in the visible region for Eu(3+), and (5)D(0) lifetime are discussed in terms of thermal treatment and structural evolution. In the layered host, the Eu(3+) ions are distributed in many different local environments. However, Eu(3+) ions were found to occupy at least two symmetry sites, and the ions are preferentially incorporated into the crystalline enstatite for the materials annealed at 700 degrees C and 900 degrees C. A (5)D(0) lifetime of 1.3 ms and 3.1 ms was obtained for Eu(3+) ions in an amorphous silicate and crystalline MgSiO(3) local environment, respectively. Strong Er(3+) emission at the 1550 nm region was observed for the materials annealed at 900 degrees C, with a bandwidth of 44 nm. (C) 2008 Elsevier B.V. All rights reserved.

Biochemical and structural characterization of a beta-1,3-1,4-glucanase from Bacillus subtilis 168

beta-1,3-1,4-Glucanases (E.C. 3.2.1.73) hydrolyze linked beta-D-glucans, such as lichenan and barley beta-glucan. Recombinant beta-1,3-1,4-glucanase from Bacillus subtilis expressed in Escherichia coil and purified by Ni-NTA chromatography exhibited optimum activity at 50 degrees C and pH 6.0. The catalytic half-life at 60 degrees C decreased from 90 to 5 min when the enzyme was incubated in the presence and absence of Ca(2+) respectively. The kinetic parameters of lichenan hydrolysis were 2695, 3.1 and 1220 for V(max) (mu mol/min/mg), K(m) (mg mL(-1)) and K(cat) (s(-1)), respectively. Analysis by DLS, AUC and SAXS demonstrated the enzyme is monomeric in solution. Chemical denaturation monitored by ITFE and far-UV CD yielded Delta G(H2O) values of 9.6 and 9.1 kcal/mol, respectively, showing that the enzyme has intermediate stability when compared with other Bacillus beta-1,3-1,4-glucanases. The crystal structure shows the anti-parallel jelly-roll beta-sheet conserved in all GH16 beta-1,3-1,4-glucanases, with the amino acid differences between Bacillus sp. enzymes that are likely determinants of stability being distributed throughout the protein. (C) 2011 Elsevier Ltd. All rights reserved.

The use of electrospray ionization tandem mass spectrometry on the structural characterization of novel asymmetric metallo-organic supermolecules, based on pentafluorophenylporphyrins and ruthenium complexes

The novel asymmetric metallo-organic triads cis- and trans-[B(4-py)BPFPH(2){Ru(3)O(Ac)(6)(py)(2)}(Ru(bpy)(2)Cl}](PF(6))(2) (5a,b) for which cis- and trans-B(4-py)BPFPH(2)=5,10-bis(pentafluorophenyl)-15,20-bis(4-pyridyl)porphyrin and 5,15-bis(pentafluorophenyl)-10,20-bis(4-pyridyl)porphyrin, respectively; Ac = acetate; py = pyridine and bpy = 2,2`-bipyridine, as well as their corresponding monosubstituted dyads cis- and trans-[B(4-py)BPFPH(2){Ru(3)O(Ac)(6)(py)(2)}]PF(6) (4a,b) have been structurally characterized via electrospray ionization mass spectrometry (ESI-MS and ESI-MS/MS). The ESI-MS of dyads 4a,b display two characteristic Ru-multicomponent clusters of isotopologue ions corresponding to singly charged ions 4a,b(+) of m/z 1629 and doubly charged ions [4a,b+H](2+) of m/z 815 and the triads 5a,b are detected by ESI-MS as the intact doubly charged cluster of isotopologue ions of m/z 1039 [5a,b](2+). The ESI-MS/MS of 4a,b(+), [4a,b+H](2+) and [5a,b](2+) reveal characteristic dissociation pathways, which confirm the structural assignments providing additional information on the intrinsic binding strengths of the gaseous ions. Although the gas-phase behavior of each pair of isomers was rather similar, the less symmetric dyads 4a,b are distinguished via the (1)H NMR spectral profile of the pyrrolic signals. Exploratory photophysical assays have shown that both modifying motifs alter the porphyrinic core emission profile, opening the possibility to use these asymmetric systems as photophysical devices. (C) 2008 Elsevier Ltd. All rights reserved.