Wa Values Research Articles

Comparison of binderless boards produced with different tissues of totora (Schoenoplectus californicus (C.A. Mey) Soják) stems

Different types of non-wood forest products have been used to produce binderless boards with potential environmental benefits. Totora (Schoenoplectus californicus) is a macrophyte that has long been used for traditional constructions in the Americas; however, its contemporary applications are limited. In this study, the feasibility of producing binderless boards using different tissues of totora stems was studied. The physical characteristics, lower lignin content, and lower solvent extractives content of pith particles caused better particle's interactions that promoted their self-bonding effect that generated better MOR and IB values of pith binderless boards. However, the hygroscopic nature of pith particles also created high TS and WA for pith boards, whereas boards made with the rind, which has higher extractives and lignin content showed the lowest TS and WA values but also lower mechanical resistance. These findings may help understand the potentialities of these biomass resources and optimize the industrial processes for producing construction materials with them.

Wettability of Phosphonium Benzene Sulfonate on Parafilm

Abstract The wettability of phosphonium benzene sulfonate on parafilm has been investigated by means of dynamic contact angle measurement. Based on the surface tension data, the spreading coefficient, adhesion tension (γlg cosθ), and adhesion work (WA) were further analyzed. It was revealed that the surface tension and contact angle decreased with the increase in concentration, and remained constant when the concentration was higher than the critical micelle concentration (CMC). Furthermore, the spreading coefficient increased with increase in concentration then stays unchanged. In the studied concentration range, the value of spreading coefficient is negative, indicating that it cannot rapidly spread the surfactant on the parafilm surface to an uniform film. The measurements show a linear relationship between the adhesion tension γlg cosθ and the surface tension in the concentration range of 2 × 10−6 mol L−1 to 1 × 10−4 mol L−1. The adsorbed amount of surfactant molecules at the parafilm-solution interface is lower than that at the gas-liquid interface. The value of WA was initially decreased then increased as the concentration was increasing and reaches a minimum value at the concentration near the CMC.

ANALISIS MODEL ANTRIAN MULTIPLE CHANNEL MULTIPLE PHASE SERVICE DALAM PROSES PEMBUATAN KARTU MAHASISWA (KTM) PADA BANK BNI UNTAD

The queue is a common situation that is common in our daily lives as consumers waited in front of the booth to get a turn to the service or service facilities. One example is the manufacture queue Student Identity Card (KTM) Tadulako in Bank BNI UNTAD. The purposes of this research is to analyze the characteristics of the making of queue Student Identity Card (KTM) Tadulako in Bank BNI of UNTAD. By calculating the probability were no queues (𝑃0 ),the average customer in the queue (𝐿𝑎),the average customer in the system (𝐿𝑠 ),the average waiting time for customers in the queue (Wa ),the average time waiting for customers in the system (W𝑠 ). The results showed that the model type of queue that is used in the manufacture of Student Card (KTM) Tadulako in Bank BNI UNTAD is a model of multiple channels-multiple phase (M / M / S) with a Poisson arrival pattern distribution and exponential distribution service time. The analysis shows the performance characteristics of a queuing system manufacture KTM BANK BNI of UNTAD can be said to have been effective, because of the steady state in each stage. On Wednesday, the value of (𝑃0 ) at CS is 0,145 and the teller is 0.8879,for the value of (𝐿𝑎) in CS is 1.8821 and the teller customer is a customer 0.0004 tothe value (𝐿𝑠 ) 3.4948is the customer, to the value of (Wa ) on CS is 33.5373 minutes and the teller was 0.0075 minutes, to the value of (W𝑠 ) is 74.1952 minutes. On Thursday, the value of (𝑃0 ) on CS was 0.121 and the teller is 0.8837,for the value of (𝐿𝑎) in CS is 2.4998 and the teller customer is a customer 0.0005 tothe value (𝐿𝑠 ) 4.1918is the customer, to the value of (Wa ) on CS is 42.4061 minutes and the teller was 0.0081 minutes, to the value of (W𝑠 ) is 71.1808 minutes.Keywords : Exponential Distribution, Poisson Distribution, Queue Multi Phase

Airway quantification using adaptive statistical iterative reconstruction-V on wide-detector low-dose CT: a validation study on lung specimen.

To evaluate the accuracy of airway quantification of adaptive statistical iterative reconstruction (ASIR)-V on low-dose CT using a human lung specimen. A lung specimen was scanned on Revolution CT with low-dose settings (20mAs, 40mAs and 60mAs/100kV) and standard-dose setting (100mAs/120kV). CT images were reconstructed using lung kernel with eleven ASIR-V levels from 0 to 100% with 10% interval. ASIR-V level from 0 to 100% with 10% interval was reconstructed on lung kernel. Wall area percentage (%WA) and wall thickness (WT) were measured. Radiation dose of 20mAs, 40mAs and 60mAs low-dose settings reduced by 87.6%, 75.2% and 62.8% compared to that on standard dose, respectively. Low-dose settings significantly decreased image SNR (p < 0.05) and increased noise (p < 0.001). ASIR-V level exponentially improved image SNR and linearly decreased image noise (all p < 0.001). The mean airway measurement ratios of low-dose to standard-dose were within 2% variation for %WA and within 3% variation for WT. Most %WA and WT values showed no obvious correlation with ASIR-V levels. ASIR-V showed to improve image quality in low radiation dose. However, low-dose settings and ASIR-V strength did not significantly influence airway quantification values, although variation in measurements slightly increased with dose reduction.

Wettability and Adhesion Work Prediction in the Polymer–Aqueous Solution of Surface Active Agent Systems

The wettability of solids by aqueous solutions of surfactants is very important in many practical applications. Thus, the measured advancing contact angles of aqueous solutions of chosen surfactants on polyethylene (PE) and those taken from the literature on polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), and polyamide (nylon 6) were analyzed. Based on the measured values of the contact angles and the literature data of the surface tensions of the studied surfactant solutions, their adsorption at the PE–water interface and the work of adhesion (Wa) were determined. The values of Wa to PE calculated on the basis of the contact angles and surface tensions of these solutions were compared to those determined by applying the new Lifshitz–van der Waals component of the water–PE surface tension. There was a good agreement between the Wa values determined in two different ways. Their contact angles were calculated using the values of PE surface tension, the new Lifshitz–van der Waals component of the water surface tension, and the surface tension of aqueous solutions of the studied surfactants. The contact angle values calculated in such a way were close to the measured values. In the case of PTFE, the same relations were obtained. The values of Wa to PMMA and nylon 6 could be also predicted.

Relationship between lung function and quantitative computed tomographic parameters of airway remodeling, air trapping, and emphysema in patients with asthma and chronic obstructive pulmonary disease: A single-center study

BackgroundThere is a paucity of studies comparing asthma and chronic obstructive pulmonary disease (COPD) based on thoracic quantitative computed tomographic (QCT) parameters.ObjectivesWe sought to compare QCT parameters of airway remodeling, air trapping, and emphysema between asthmatic patients and patients with COPD and explore their relationship with airflow limitation.MethodsAsthmatic patients (n = 171), patients with COPD (n = 81), and healthy subjects (n = 49) recruited from a single center underwent QCT and clinical characterization.ResultsProximal airway percentage wall area (%WA) was significantly increased in asthmatic patients (62.5% [SD, 2.2]) and patients with COPD (62.7% [SD, 2.3]) compared with that in healthy control subjects (60.3% [SD, 2.2], P < .001). Air trapping measured based on mean lung density expiratory/inspiratory ratio was significantly increased in patients with COPD (mean, 0.922 [SD, 0.037]) and asthmatic patients (mean, 0.852 [SD, 0.061]) compared with that in healthy subjects (mean, 0.816 [SD, 0.066], P < .001). Emphysema assessed based on lung density measured by using Hounsfield units below which 15% of the voxels lie (Perc15) was a feature of COPD only (patients with COPD: mean, −964 [SD, 19.62] vs asthmatic patients: mean, −937 [SD, 22.7] and healthy subjects: mean, −937 [SD, 17.1], P < .001). Multiple regression analyses showed that the strongest predictor of lung function impairment in asthmatic patients was %WA, whereas in the COPD and asthma subgrouped with postbronchodilator FEV1 percent predicted value of less than 80%, it was air trapping. Factor analysis of QCT parameters in asthmatic patients and patients with COPD combined determined 3 components, with %WA, air trapping, and Perc15 values being the highest loading factors. Cluster analysis identified 3 clusters with mild, moderate, or severe lung function impairment with corresponding decreased lung density (Perc15 values) and increased air trapping.ConclusionsIn asthmatic patients and patients with COPD, lung function impairment is strongly associated with air trapping, with a contribution from proximal airway narrowing in asthmatic patients.

Effects of clay platelets and natural nanotubes on mechanical properties and gas permeability of Poly (lactic acid) nanocomposites

Environmental concerns have resulted in the increased use of biodegradable polymers and their nanocomposites. We have developed a facile method for measuring the work of adhesion (Wa) between nanoparticles and their matrix, which we showed can be used to determine their degree of intercalation within the matrix. This method was then applied to Poly (lactic acid) (PLA) nanocomposites with either sodium montmorillonite clays (C-Na+), organically modified clays (C-30B), resorcinol di (phenyl phosphate) (RDP) coated C-Na+ (C-RDP), Halloysite nanotubes (HNTs) and RDP coated HNTs (H-RDP). The C-30B showed the highest Wa within the PLA matrix, followed by the C-RDP and the C-Na+. X-ray diffraction and TEM indicated that the C-30B platelets were highly exfoliated, the C-RDP were intercalated, while the C-Na+ were aggregated in the PLA matrix. Oxygen gas permeability measurements showed the largest decrease in permeability for the C-30B nanocomposites, followed by the C-RDP, and the C-Na+ nanocomposites. The values of the particle aspect ratios obtained using Nielsen model were consistent with the TEM images. In contrast to clay platelets, HNTs and H-RDP were not effective in decreasing oxygen gas permeability of PLA matrix, which was in excellent agreement with the model we derived. Despite the higher degree of exfoliation, the C-30B nanocomposites had a significantly lower Izod impact than the C-RDP nanocomposites. SEM images showed numerous micro-voids on the Izod impact fracture surface of C-30B nanocomposites. On the other hand, the nanotubes were much more effective in reinforcing the mechanical properties, with RDP coated tubes having the better performance, consistent with their higher value of Wa with PLA matrix. These results showed that RDP coated silicate nanoparticles can provide environmentally safe alternatives for modifying the mechanical and gas barrier properties of PLA.

RELATIONSHIP BETWEEN CONTACT ANGLE HYSTERESIS AND WORK OF ADHESION OF OIL DROPLETS ON PERFLUOROMETHACRYLATESTYRENE THIN FILMS

Water and oil repellencies of flat films are crucial properties of solid materials and some biomimetric surfaces that significantly depend on surface topography and chemical compositions [1,2]. The surface wettability is expressed indirectly by the contact angle (CA) measurements of a specific liquid droplet on these surfaces [1-4]. However, in practical systems, measurement of only equilibrium CA (θe) is not enough to explain polymer surface characteristics, so advancing (θa), receding (θr) CA’s and thus the contact angle hysteresis (CAH= θa – θr) are required to accurately characterize the dewetting properties of the surfaces [1-9]. CAH of a surface is strongly affected from surface chemical heterogeneity and roughness. In addition, the relationship between the equilibrium and dynamic states (work of adhesion, Wa and CAH) is also an important parameter for the characterization of solid surfaces. Basically, the estimate of drop movement on a surface can be represented by Wa values, i.e., a higher Wad value causes a higher tendency of the droplet to stick on the tilt surface. In this study, the oil repellencies of flat perfluoroethyl alkyl methacrylate-styrene (Zonyl-TM-S) random copolymers, which were synthesized in a CO2-expanded monomer medium at 250 bar pressure and 80 oC were investigated with various perfluoroethylalkyl contents. Flat and transparent copolymer surfaces were formed by using dip-coated on glass slides from THF as solvent. The increase in the perfluoromethacrylate content of the flat copolymers resulted in a decrease of the total surface free energy of the flat copolymer surfaces from 19.0 to 14.2 mJ/m2. The oil repellencies of (Zonyl-TM-S) copolymers in the terms of contact angle hysteresis was compared with perfluoroethyl alkyl methacrylate-methyl methacrylate copolymer (Zonyl-TM-ran-MMA) by using oil drops with varying surface tensions between 20.9 mN/m and 26.9 mN/m. The effect of liquid surface tension and wt.% content of Zonyl-TM on oleophobicities of the surfaces were also examined. Increase in hydrocarbon chain lengths also caused an increase in the measured CA values due to the weaker adhesion interactions between the liquid drop and the solid surface. Increase in wt.% Zonyl-TM content of the copolymers resulted in a decrease in Wa values due to the increase of fluorine atoms in copolymer surfaces. The relationship between ( r a ) cosθ = cosθ − cosθ and Wa values, liquid surface tensions and also perfluoro alkyl wt.% content of the copolymer were also investigated. Furthermore, the CAH and oil repellency differences between the p(Zonyl-TM-ran-S) and p(Zonyl-TM-ran- MMA) thin copolymer films with similar Zonyl-TM contents were also compared within this work. An increase was found in CAH values with the increase of hydrocarbon liquid chain length and thus liquid surface tension. This is due to the increase in cohesion interactions between liquid molecules and resulted in a decrease in adhesion interactions between the solid surface and the liquid drop.

Economic Value of Agricultural Land for Community Livelihoods within the Context of REDD+

A study was carried out in two villages of Mughunga and Pohama in Singida Rural District, central Tanzania, to assess the economic value of agricultura l land for community livelihoods within the context of Reducing Emissions from Deforestation and Forest Degradation (REDD+). Market price valuation method was used to assess the economic value of agricultural land. Findings showed that a good number of pe ople in both villages depend on agriculture (96.4%) and livestock keeping (90.1%) for their livelihoods. The economic value of agriculture land wa s revealed to be 35,871,750 and 49,259,382Tsh per acre for Mughunga and Pohama villages respectively, with hig h contribution from sunflower, followed by sorghum and maize crops. The study results revealed lower economic value, mainly of food crops such as maize and bulrush millet. This implicates changes in the agricultural land as these crops were valued high in the past. The major reasons for such changes include decline in agricultural production and increased pressure for land resources. For sustainability of agricultural land in the study area, efforts need to be scaled up towards conservation of agricultural land by all parties, that is, communities, government and private entities.

Charge-storage process in IrO2-SnO2 mixed-oxide electrodes. Role of coating composition, solution pH and Temperature

The effects of both pH and temperature on the kinetics of redox processes that involve the charging/discharging of electrocatalytic sites, at dimensionally stable anodes, have been investigated. At first, electrodes based on Ir and Sn oxides, having different molar compositions, were studied by X-ray diffraction in order to characterize the system under investigation, and with the four-probe method to evaluate how the film resistivity varies with the oxide composition. Then, cyclic voltammetric experiments were carried out at different temperatures to estimate the apparent activation energy (Wa) of the charging/discharging process of active sites. The Wa values obtained were rather low (about 0.5kcalmol−1) and thus realistically not attributable to any chemical reaction. By excluding a role for the various physicochemical parameters that could influence the process, we suggest that the “double injection/double ejection” mechanism is related to a Grotthuss-type movement of protons, which takes its advantage from an electrode-electrolyte interface extending for a few monolayers within the oxide coating. The interface thus represents a relatively rigid and organized structure in which protons can move without any hindrance.

Effect of resin type and content on properties of composite particleboard made of a mixture of wood and rice husk

This study investigated the effect of resin type and content on the dimensional stability and mechanical properties of single-layer composite particleboards made of a mixture of wood particles (70wt%) and rice husk particles (30wt%). Two types of resin, urea–formaldehyde (UF) resin and phenol–formaldehyde (PF) resin, were used in the experiments at three different contents which were 8, 10, or 12wt%. The dimensional stability of the samples was significantly improved by increasing the resin content. When the contents of the UF and PF resins increased from 8 to 12wt%, the WA values of the samples decreased to18% and 33%, respectively. Similar results were also observed for the TS values. The UF resin bonded samples swelled two times more than the PF resin bonded particleboard. The mechanical properties of the PF resin bonded samples were better than the UF resin bonded samples. When the contents of the UF and PF resins increased from 8% to 12wt%, the internal bond strength values of the samples increased to 21% and 41%, respectively. The bending strength and modulus of elasticity of the samples were not significantly increased by increasing contents of the UF and PF resins, except for the 12wt% content.

Abstract C218: Novel therapeutic potential in targeting micro tubules by naturally occurring anti cancer agent withaferin A in human cancers.

Abstract Background: Chemical compounds from natural sources continue to serve as important pharmacological tools for the understanding of biological pathways and also provide chemical platform for new drug discovery. The utility of various anti-microtubule agents from natural origins are the best examples that continuously serve these two purposes. In this study, we have identified a novel tubulin-targeting activity of a natural product Withaferin-A. Though several groups have already shown that Withaferin-A is a potent anti-cancer agent, can kill variety of carcinomas by inducing apoptosis, but not much is known about its molecular targets inside the cell. This study is to evaluate the therapeutic efficacy of WA towards human cancer, in relation to its ability to directly targeting microtubule dynamics within cell. Methods: The IC-50 value of WA was determined by MTT assay, apoptosis and cell cycle assay was performed by FACS analysis, wound healing assay was done to see cellular migration, immune fluorescent detection was done to check microtubular network of WA treated cells. Effect of WA on tubulin polymerization in cell free system was studied by light scattering assay, binding measurements of WA to tubulin was determined by flurometric assay and probable WA-tubulin interaction site was proposed by molecular modeling method. Results: We have identified WA as a novel anti-microtubule agent that inhibits proliferation, migration and cellular progression by affecting mitosis in HeLa and MCF-7 cells. Brief incubation with nontoxic concentrations of WA induced significant depolymerization of interphase and mitotic spindle microtubules. It inhibits tubulin polymerization, induces conformational changes in tubulin by directly binding to purified tubulin. Both in silico and in-vitro studies indicated that WA preferably binds to a novel site on tubulin. Conclusion: It is evident that WA suppresses microtubule dynamics by directly binding to tubulin which sheds light on mechanisms behind its anti-proliferative activity towards cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C218.

Influence of varied surface texture of dentin porcelain on optical properties of porcelain specimens

Differences in the texture of dentin porcelain surfaces may change the direction of incident light at the enamel-dentin porcelain interface and affect the optical properties of a ceramic crown. The purpose of this study was to measure optical parameters of enamel-dentin porcelain complexes with different dentin porcelain surface textures, and to analyze the relationship between optical parameters and surface texture. Eighty dentin porcelain (ShoFu Vintage Halo, shade A2) disks (1.0 × 10.0 mm) were fabricated and assigned to 10 groups (n=8). The dentin porcelain specimens were given different surface textures with modified surface roughnesses (Ra) and different levels of waviness (Wa). Measurements of transmittance, reflectance, and CIE L*a*b* values were made with a spectrocolorimeter (PR-650) after standard finishing of the enamel-dentin porcelain complex. Translucency parameters (TP) and color difference (ΔE) were calculated with CIE L*a*b* values, respectively. The data were statistically analyzed by 1-way ANOVA and Fisher's LSD (least significant difference) post hoc tests (α=.05). Transmittance, reflectance, and the translucency parameter were influenced significantly by surface roughness (P<.05) and waviness values (P<.01). With a decrease in the Ra value from 1.23 μm to 0.15 μm, mean reflectance values increased from 37.01% to 38.63%, while mean values of transmittance and the translucency parameter decreased from 1.04% to 0.87% and 19.44 to 18.03, respectively. With an increase of the Wa value from 0.0 mm to 0.2 mm, mean values of reflectance decreased from 37.06% to 30.30%, while transmittance and the translucency parameter increased from 1.10% to 2.05% and 19.15 to 20.01, respectively. Color difference values (ΔE) ranged from 0.30 to 1.45 (Ra group) and from 1.46 to 4.16 (Wa group), respectively. Surface texture of dentin porcelain significantly influenced the optical properties of enamel-dentin porcelain specimens, and surface waviness (Wa) had higher correlation coefficients with optical parameters than did roughness (Ra).

High-precision spectra for dynamical Dark Energy cosmologies from constant-w models

Spanning the whole functional space of cosmologies with any admissibleDE state equations w(a) seems a need, in view of forthcomingobservations, namely those aiming to provide a tomography of cosmicshear. In this paper I show that this duty can be eased and that asuitable use of results for constant-w cosmologies can besufficient. More in detail, I ``assign'' here six cosmologies, aimingto span the space of state equations w(a) = wo+wa(1−a), forwo and wa values consistent with WMAP5 and WMAP7 releases andrun N-body simulations to work out their non-linear fluctuationspectra at various redshifts z. Such spectra are then compared withthose of suitable auxiliary models, characterized by constantw. For each z a different auxiliary model is needed. Spectraldiscrepancies between the assigned and the auxiliary models, up to k ≃ 2–3 h Mpc−1, are shown to keep within 1 %.Quite in general, discrepancies are smaller at greater z and exhibita specific trend across the wo and wa plane. Besides of aimingat simplifying the evaluation of spectra for a wide range of models,this paper also outlines a specific danger for future studies of theDE state equation, as models fairly distant on the w0-wa planecan be easily confused.

A test of Hořava gravity: the dark energy

Recently Hořava proposed a renormalizable gravity theory withhigher spatial derivatives in four dimensions which reduces toEinstein gravity with a non-vanishing cosmological constant inIR but with improved UV behaviors. Here, I consider a non-trivialtest of the new gravity theory in FRW universe by considering an IRmodification which breaks ``softly'' the detailed balance conditionin the original Hořava model. I separate the dark energy partsfrom the usual Einstein gravity parts in the Friedman equations andobtain the formula of the equations of state parameter. The IR modified Hořava gravity seems to be consistent with the current observational data but we need some more refined data setsto see whether the theory is really consistent with our universe.From the consistency of our theory, I obtain some constraints on theallowed values of w0 and wa in the Chevallier, Polarski, andLinder's parametrization and this may be tested in the near future,by sharpening the data sets.

Higher-order aberrations from the internal optics of the eye

To analyze the distribution of human higher-order wavefront aberrations (3rd- to 6th-order) from the internal optics (WA(internal)) and the variations with age and to evaluate the degree of compensation that the internal optics provide for anterior corneal aberrations (WA(cornea)). Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. With assumption of a simple model for the eye, the WA(internal) were obtained by direct subtraction of the WA(cornea) from the ocular aberrations (WA(eye)). The WA(eye) were measured using the WaveScan system (Visx, Inc.), and the WA(cornea) were computed from the topographic data (Humphrey Atlas) using the CTView program (Sarver and Associates, Inc.). In 144 eyes of 114 normal patients (age 20 to 69 years), WA(internal) were calculated for a 6.0 mm pupil and a compensation factor (CF) was computed, with positive values representing compensation of WA(cornea) by WA(internal) and negative values indicating that the internal surfaces add aberrations to those of the cornea. There was wide individual variation in WA(internal). The mean coefficient for 4th-order spherical aberration (Z(4)(0)) was -0.145 microm +/-0.094 (SD) (95% confidence interval [CI], -0.160 to -0.130 microm); 95.1% of eyes had negative values. The mean root-mean-square value for HOAs was 0.334 +/- 0.096 microm (95% CI, 0.319 to 0.350 microm). Moderate to high correlations were found between the right and left eyes in HOAs, 4th-order and 6th-order spherical aberration coefficients (Z(4)(0) and Z(6)(0)). With increasing age, the HOAs did not change, whereas the negative coefficients for Z(4)(0) tended to become less negative. Only the term Z(4)(0) had a CF significantly correlated with increasing age (r=-0.338, P<.05 with Bonferroni correction). WA(internal) varied widely among patients, and a moderate to high degree of mirror symmetry existed between the right and left eyes. Internal surfaces compensated at least partially for the HOA and Z(4)(0) in most eyes, and this compensation decreased only mildly with increasing age.

Nanostructure analysis of protein thin film prepared by wet and dry processes

ABSTRACTSilk fibroin (SF) and bovine serum albumin (BSA) thin films were deposited on Si(100) substrate either by colloid casting method or by pulsed laser deposition (PLD). Emphasis is laid on the comparison of nanostructures, which developed during the deposition. AFM diagrams were evaluated to quantify the nanostructures, parallel and perpendicular to the substrate, by the average wavelength of the profilogram (Wa ) and surface roughness (Rrms ), respectively. The film thickness increased with increasing the concentration of colloids or laser deposition time. The value of Wa increased with the film thickness. We note, however, that the value Wa becomes much less sensitive with decreasing the scanning area due to decreasing probability of the abnormally large agglomerates of the nanometric units. Probability of the agglomeration growth as a consequence of the surface adhesion is higher with higher concentration of random coil, followed by β-sheet and α-helix. BSA with smaller primary units and lower probability of agglomeration give more uniform films.

Fiber-stretching test: a new technique for characterizing the fiber–matrix interface using direct observation of crack initiation and propagation

A new micromechanical technique for experimental determination of fiber-matrix interfacial properties is presented. This technique consists in tensile loading of the fiber, with a matrix droplet on it, at both ends, accompanied by continuous direct observation of interfacial crack propagation. In comparison with the well-known microbond test, the new method has two important advantages. First, crack propagation is stable for any embedded fiber length and any relation between adhesion and friction at the interface. Second, compliance of the test equipment does not affect the results, and specimens with long free fiber ends can be successfully tested. A similar result can be reached using the pull-out or microbond test with an 'infinite' (very long) embedded fiber length. An algorithm for separate determination of the interfacial adhesion and friction from experimental relationships between the crack length and applied load is described. The new test was employed to determine the interfacial parameters for composites of glass fibers with polypropylene, polystyrene, and polycarbonate. For each fiber-polymer system investigated, the following parameters were calculated: ultimate interfacial shear strength; critical energy release rate for crack propagation; and adhesional pressure. Our approach to the estimation of the work of adhesion, WA, from micromechanical tests, based on the concept of adhesional pressure, allowed us to calculate the WA values for several thermoplastic matrix-glass fiber pairs and to obtain values consistent with previous estimations made according to other approaches.

Work of adhesion and local bond strength in glass fibre-thermoplastic polymer systems

The microbond test was employed to determine the interfacial shear strength (IFSS) in glass fibre-polypropylene and glass fibre-polystyrene systems. The experimental IFSS values were analyzed as a function of embedded length. The local bond strength in both systems was calculated as a limit value of IFSS at zero embedded length. For the same systems, the reversible work of adhesion, WA, was determined from wetting angles of polymer melt on single glass fibres and using the Owens-Wendt approach. A method for WA determination from the microbond test data based on the Nardin-Schultz hypothesis and the concept of local bond strength is proposed. This method, applied to the calculation of WA in composites of a non-polar polymer polypropylene (PP) with glass fibres showed a good agreement with the results obtained from wetting measurements. At the same time, the calculated WA value for a polar polymer polystyrene (PS) is much higher than that obtained using wetting data. Besides, bond strength in the glass fibre/PS system is strongly influenced by the contact forming temperature. These results lead to the assumption that an increased number of the local bonds at the interface can contribute to an improved adhesion between a fibre surface and a polar polymer.

Weighting macromolecular diffraction data.

The results from refinements with six different weighting schemes in PROFFT, SHELXL93 and X-PLOR show that experimental weights, and especially unit weights, tend to overweight the low-angle data at the expense of the higher resolution data. This suggests that the use of unit weights are inappropriate except during initial cycles of refinements. Two alternative weighting schemes, one-line and two-line empirical weights, are shown to produce a relatively even distribution of the weighted r.m.s. error [r.m.s. Err = ( summation operator wDeltaF(2)/n)(1/2)] as a function of sin theta/lambda and result in linear delta(R) normal probability plots. Free R values and free weighted r.m.s. errors from the refinement of a scorpion toxin structure show that the alternative weighting schemes are superior to unit weights, and the r.m.s. deviations of bond distances and angles from the target values and G factors, as calculated by PROCHECK, confirm the superiority of the empirical weighting scheme. It was also observed that changing the value of WA, the contribution of the X-ray gradient to the total function minimized, produced little variation in R free but was directly proportional to the r.m.s. deviation of the bond distances from the target values.