Initial Linear Portion Research Articles

Dual clumped isotope thermometry of coral carbonate

The stable (δ18O and δ13C) and clumped (Δ47) isotope compositions of coral carbonate are valuable archives for paleoclimate reconstructions. However, the Δ47-temperature relationships of warm and cold-water corals deviate from that of inorganic carbonate precipitated at equilibrium. Dual clumped isotope thermometry of carbonates (i.e., simultaneous Δ47 and Δ48 measurements on a single carbonate) has the potential to achieve more accurate paleotemperature reconstruction, identifying and correcting for kinetically driven isotopic disequilibrium. Here we present the first extensive dual clumped isotope dataset of coral carbonate, spanning a broad range of cold and warm-water coral species. We confirm that corals are enriched in Δ47 and depleted in Δ48 relative to equilibrium, a pattern corresponding to the mixing of an equilibrium DIC pool with kinetically derived HCO3– produced by hydration and hydroxylation of CO2. Dual clumped isotope measurements of cold-water corals fall on the initial linear portion of model (IsoDIC) predicted departure from equilibrium. The dual clumped isotope composition of cold-water corals, corrected by the model-predicted Δ47/Δ48 offset slope (−0.78), yield accurate reconstruction of coral growth temperature with a precision of <3 °C at the 68% confidence level. In contrast, disequilibrium offsets in the Δ47 and Δ48 of warm-water corals correspond to precipitation from a more equilibrated DIC pool, which we attribute to the action of carbonic anhydrase in the calcifying fluid. It may be possible to correct warm-water coral growth temperatures, using an empirically derived correction (Δ47/ Δ48 offset slope of −0.4). Dual clumped isotope thermometry of coral carbonate opens new possibilities to reconstruct both sea surface temperatures and ocean dynamics of intermediate to deep water masses.

An Enhanced Flume Testing Procedure for the Study of Rill Erosion

This paper presents the development and verification of an improved and cost-effective flume apparatus and corresponding testing methodology. A rigorous analysis of the flow conditions during testing was considered and an interpretation of test results was carried out following the premises of the Water Erosion Prediction Project (WEPP) rill erosion model. The apparatus and methodology were verified using statically compacted specimens of a latosol from the central region of Brazil. Tests were performed on samples with void ratios of 1.0 and 1.5 and under variable hydraulic conditions to verify the repeatability and ideal analysis time for the soil loss curves. The soil loss curves presented hyperbolic behavior, with a maximum value that appeared to be randomly behaved, which can be attributed to the complex nature of the erosion processes at later stages. The equipment and testing methodology produced erosion curves with repeatability that were superior with respect to their initial linear and transition portions. Recommendations are made regarding the adequate interpretation of the testing data and the selection of the ideal elapsed time for soil loss analysis.

γH2AX, 53BP1 and Rad51 protein foci changes in mesenchymal stem cells during prolonged X-ray irradiation.

At high exposure levels ionizing radiation is a carcinogen. Little is known about how human stem cells, which are known to contribute to tumorigenesis, respond to prolonged radiation exposures. We studied formation of DNA double strand breaks, accessed as γH2AX and 53BP1 foci, in human mesenchymal stem cells (MSCs) exposed to either acute (5400 mGy/h) or prolonged (270 mGy/h) X-irradiation. We show a linear γH2AX and 53BP1 dose response for acute exposures. In contrast, prolonged exposure resulted in a dose-response curve that had an initial linear portion followed by a plateau. Analysis of Rad51 foci, as a marker of homologous recombination, in cells exposed to prolonged irradiation revealed a threshold in a dose response. Using Ki67 as a marker of proliferating cells, we show no difference in the γH2AX distribution in proliferating vs. quiescent cells. However, Rad51 foci were found almost exclusively in proliferating cells. Concurrent increases in the fraction of S/G2 cells were detected in cells exposed to prolonged irradiation by scoring CENPF-positive cells. Our data suggest that prolonged exposure of MSCs to ionizing radiation leads to cell cycle redistribution and associated activation of homologous recombination. Also, proliferation status may significantly affect the biological outcome, since homologous repair is not activated in resting MSCs.

Effect of openings on in-plane structural behavior of reinforced concrete floor slabs

To determine the inelastic seismic response of reinforced concrete (RC) buildings, typically a tri-linear in-plane load-displacement idealization is used for modeling the behavior of RC floor diaphragms, to account for cracking and yielding prior to failure. In the 1980s, solid (without openings) beam-supported RC two-way slab panels were experimentally studied at Lehigh University under in-plane monotonic and cyclic loads, with and without service gravity loads, to determine their in-plane load-displacement and hysteretic characteristics. Subsequently, these results could be implemented in nonlinear damage analysis computational tools developed for analyzing RC buildings with flexible floor diaphragms, ignoring the effect of openings. Due to the lack of experimental data, in the present study a finite element (FE) approach is used to investigate the inelastic behavior of RC floor diaphragms with openings. A general purpose FE software was initially used to create a nonlinear 3D model of the solid panels tested at Lehigh University, and the obtained results from the actual experiment were used to verify the validity of the FE model. This model uses eight-node concrete brick elements (SOLID65) combined with embedded steel reinforcement elements (REIN264). After the accuracy of the solid (with no opening) FE model was verified, openings were placed in the model, and then a sensitivity study has been conducted where the effects of varying opening sizes (0, 6.25%, 14%, and 25% of the floor panel area) and out-of-plane loading (zero and full service load) on the in-plane load-displacement characteristics of the floor panels are investigated. Results indicate that the drop in ultimate in-plane load capacity of the floor diaphragm due to the presence of out-of-plane service loading becomes less significant as the opening size increases (4% for 25% opening vs. 15% for the solid slab). Also, the first significant variation from the initial linear portion of the in-plane load-displacement curve moves up from 30% to about 50% of the ultimate load capacity for the slab with the larger size opening. The failure mechanisms changed due to the presence of the openings, where yielding of the bars around the opening corners appeared to significantly affect the behavior of the slabs. The positive contribution of inclined reinforcing bars, placed at opening corners, in strengthening the in-plane capacity of the slab panels with opening, is effectively demonstrated by use of the FE model.

Lacertus Fibrosis versus Achilles Allograft reconstruction for Chronic Distal Biceps Tears

Objectives:Chronic distal biceps tears can be difficult to treat as in many cases, the remaining biceps tendon is significantly retracted and an allograft may be required to provide length for reconstruction. The lacertus fibrosis (LF), being a local, stout, fibrous sheath, can potentially be used as a reconstruction graft, obviating the need for allograft tissue. The purpose of this study is to evaluate the strength of the lacertus fibrosis compared to achilles allograft (AA) for distal biceps reconstruction.Methods:10 fresh-frozen matched cadaveric pairs of elbows were used in this study. The distal biceps tendon was isolated and 3 centimeters of tendon was resected. In Group 1, the LF was identified and released from its distal attachment, maintaining its attachment to the biceps muscle. This was then tubularized and repaired to the radius via button fixation. In Group 2, an AA tendon graft was sutured to the biceps muscle via Pulvertaft weave and similarly repaired to the ulna via button fixation. The prepared radii were rigidly mounted at a 45-degree angle in a MTS electromechanical test frame (MTS Systems, Eden Prairie, MN). The proximal biceps muscle was secured in a custom fabricated cryogenic grip and allowed to freeze for 60s prior to testing. Two differential variable reluctance transducers (DVRTs) were mounted on the specimens, one at the radius-soft tissue junction and the second in the muscle or muscle allograft tissue junction proximal to the repair. Specimens were then loaded at a displacement rate of 20 mm/min until failure. Failure was defined as a 3 mm displacement of the DVRT located at the radius-soft tissue junction. Stiffness was calculated from the initial linear portion of the load versus radial DVRT curve. A t-test was used to determine if any observed differences were significant (p≤0.05)Results:Load to failure, as defined as a 3mm gap formation by DVRT was similar between both groups. Load to failure in Group 1 (LF) was 20.17 ± 5.52 N versus 16.89 ±4.54 N in Group 2 (AA) (p=0.18). Stiffness of the construct was also not statistically different, with Group 1 (LF) averaging 12.32± 7.11 KPa versus 10.48 ± 5.66 KPa in Group 2 (AA) (p=0.34).Conclusion:Lacertus fibrosis reconstruction for chronic distal biceps tears was as strong biomechanically as the commonly used achilles tendon allograft in terms of load to failure and construct stiffness. This may be a reasonable alternative for chronic distal biceps reconstruction in which primary repair is not possible.

Consolidation Analysis by the Extended Taylor Method ( ETM ).

The Taylor t method is extended for improving the estimation of the end-of-primary (EOP) settlement p  and coefficient of vertical consolidation v c . The extended Taylor method (ETM) utilizes the same graphical procedure of the conventional Taylor method, but this procedure is repeated twice at any two U values greater than 52.6% instead of the one used in the Taylor method at 90%; U is the average degree of consolidation. The ETM explicitly relates v c to the slope of the initial linear portion of the t  - t curve as well as the EOP settlement p  ; t  is the settlement at time t during consolidation. The ETM can be applied with a minimum of four consolidation data points for estimating p  and v c . Two types of EOP settlements are distinguished; firstly, local EOP settlement pi  obtained by matching experimental results to theory at a particular U value; secondly, global EOP settlement p  obtained by extrapolation using two or more local EOP settlements. The ETM explains the observed differences in v c values estimated by the existing methods in terms of the differences in p  values obtained by these existing methods. Experimental results are used to validate and compare the extended Taylor method with the existing methods.

The effect of nano-void on deformation behaviour of Al-Cu intermetallic thin film compounds

In the present study, deformation behaviour of AlCu, Al2 Cu3 intermetallic thin films having a nano-void at its center have been investigated using molecular dynamics (MD) simulation. The results are compared with the thin films of pure Al, Cu metals and intermetallic AlCu, Al2 Cu3 thin films having no defect for estimating the effect of nano-void on the mechanical properties of intermetallic thin film. Simulated tensile tests are performed at different strain rates (108 s-1 , 0.5 × 109 s-1 and 109 s-1 ) and temperatures (10 K, 50 K and 300 K). All the stress-strain curves have zig-zag nature after initial linear elastic portion, which quite resembles with the typical nano-scale material behavior. Al2 Cu3 intermetallic thin film exhibits higher yield strength compared to AlCu intermetallic thin film. The atomic configurations captured during deformation clearly show that deformation is localized near the void, followed by void closure and necking of the thin film. The failure of thin film occurs after straining down to a point indicating its ductile nature. An increase in the magnitude of average stress near the void has been revealed from Von Mises’ stress analysis on the defect surface. The stress around void is increased uptill the attainment of maximum stress. The strain is localized near the void, which actually helps in breaking of the atomic bonds and ultimately causes fracture.

Consolidation Analysis by the Modified Slope Method

Abstract The slope method (Al-Zoubi, 2008, Geotech. Test. J., Vol. 31, No. 6, pp. 526–530) in which the coefficient of consolidation cv was expressed as function of the EOP settlement δp and slope m of the initial linear portion of the observed δt − √t curve is modified for improving the procedure used for estimating the EOP δp. The slope method EOP δp values were estimated using the point at which δt − √t curve starts to deviate from the initial linear portion. In this note, the EOP δp is determined based on a unique relationship between the ratio of the secant slope of δt − √t curve at 50 % consolidation to the secant slope at any time arbitrarily selected beyond the initial linear portion of the δt − √t curve (theoretically, at U ≥ 52.6%) and average degree of consolidation U. The modified slope method requires a minimum of four compression-time data points for better cv estimates. Two types of EOP settlement are identified; local EOP settlement δpi is obtained at a specific Ui value as is the case in the Taylor method and global EOP settlement δp is determined independently of any U value. The modified slope method yields δp and cv values quite similar to those of the Casagrande method.

Mitochondrial DNA Variant for Complex I Reveals a Role in Diabetic Cardiac Remodeling

Myocardial remodeling and dysfunction are serious complications of type 2 diabetes mellitus (T2DM). Factors controlling their development are not well established. To specifically address the role of the mitochondrial genome, we developed novel conplastic rat strains, i.e. strains with the same nuclear genome but a different mitochondrial genome. The new animals were named T2DN(mtFHH) and T2DN(mtWistar), where the acronym T2DN denotes their common nuclear genome (type 2 diabetic nephropathy (T2DN) rats) and mtFHH or mtWistar the origin of their mitochondria, Fawn Hooded Hypertensive (FHH) or Wistar rats, respectively. The T2DN(mtFHH) and T2DN(mtWistar) showed a similar progression of diabetes as determined by HbA1c, cholesterol, and triglycerides with normal blood pressure, thus enabling investigation of the specific role of the mitochondrial genome in cardiac function without the confounding effects of obesity or hypertension found in other models of diabetes. Echocardiographic analysis of 12-week-old animals showed no abnormalities, but at 12 months of age the T2DN(mtFHH) showed left ventricular remodeling that was verified by histology. Decreased complex I and complex IV but not complex II activity within the electron transport chain was found only in T2DN(mtFHH), which was not explained by differences in protein content. Decreased cardiac ATP levels in T2DN(mtFHH) were in agreement with a lower ATP synthetic capacity by isolated mitochondria. Together, our data provide experimental evidence that mtDNA sequence variations have an additional role in energetic heart deficiency. The mitochondrial DNA background may explain the increased susceptibility of certain T2DM patients to develop myocardial dysfunction.

Glutamates 78 and 122 in the Active Site of Saccharopine Dehydrogenase Contribute to Reactant Binding and Modulate the Basicity of the Acid-Base Catalysts

Saccharopine dehydrogenase catalyzes the NAD-dependent oxidative deamination of saccharopine to give l-lysine and alpha-ketoglutarate. There are a number of conserved hydrophilic, ionizable residues in the active site, all of which must be important to the overall reaction. In an attempt to determine the contribution to binding and rate enhancement of each of the residues in the active site, mutations at each residue are being made, and double mutants are being made to estimate the interrelationship between residues. Here, we report the effects of mutations of active site glutamate residues, Glu(78) and Glu(122), on reactant binding and catalysis. Site-directed mutagenesis was used to generate E78Q, E122Q, E78Q/E122Q, E78A, E122A, and E78A/E122A mutant enzymes. Mutation of these residues increases the positive charge of the active site and is expected to affect the pK(a) values of the catalytic groups. Each mutant enzyme was completely characterized with respect to its kinetic and chemical mechanism. The kinetic mechanism remains the same as that of wild type enzymes for all of the mutant enzymes, with the exception of E78A, which exhibits binding of alpha-ketoglutarate to E and E.NADH. Large changes in V/K(Lys), but not V, suggest that Glu(78) and Glu(122) contribute binding energy for lysine. Shifts of more than a pH unit to higher and lower pH of the pK(a) values observed in the V/K(Lys) pH-rate profile of the mutant enzymes suggests that the presence of Glu(78) and Glu(122) modulates the basicity of the catalytic groups.

Dynamin2 GTPase and Cortactin Remodel Actin Filaments

The large GTPase dynamin, best known for its activities that remodel membranes during endocytosis, also regulates F-actin-rich structures, including podosomes, phagocytic cups, actin comet tails, subcortical ruffles, and stress fibers. The mechanisms by which dynamin regulates actin filaments are not known, but an emerging view is that dynamin influences F-actin via its interactions with proteins that interact directly or indirectly with actin filaments. We show here that dynamin2 GTPase activity remodels actin filaments in vitro via a mechanism that depends on the binding partner and F-actin-binding protein, cortactin. Tightly associated actin filaments cross-linked by dynamin2 and cortactin became loosely associated after GTP addition when viewed by transmission electron microscopy. Actin filaments were dynamically unraveled and fragmented after GTP addition when viewed in real time using total internal reflection fluorescence microscopy. Cortactin stimulated the intrinsic GTPase activity of dynamin2 and maintained a stable link between actin filaments and dynamin2, even in the presence of GTP. Filaments remodeled by dynamin2 GTPase in vitro exhibit enhanced sensitivity to severing by the actin depolymerizing factor, cofilin, suggesting that GTPase-dependent remodeling influences the interactions of actin regulatory proteins and F-actin. The global organization of the actomyosin cytoskeleton was perturbed in U2-OS cells depleted of dynamin2, implicating dynamin2 in remodeling actin filaments that comprise supramolecular F-actin arrays in vivo. We conclude that dynamin2 GTPase remodels actin filaments and plays a role in orchestrating the global actomyosin cytoskeleton.

Structure and Evolution of a Novel Dimeric Enzyme from a Clinically Important Bacterial Pathogen

Dihydrodipicolinate synthase (DHDPS) catalyzes the first committed step of the lysine biosynthetic pathway. The tetrameric structure of DHDPS is thought to be essential for enzymatic activity, as isolated dimeric mutants of Escherichia coli DHDPS possess less than 2.5% that of the activity of the wild-type tetramer. It has recently been proposed that the dimeric form lacks activity due to increased dynamics. Tetramerization, by buttressing two dimers together, reduces dynamics in the dimeric unit and explains why all active bacterial DHDPS enzymes to date have been shown to be homo-tetrameric. However, in this study we demonstrate for the first time that DHDPS from methicillin-resistant Staphylococcus aureus (MRSA) exists in a monomer-dimer equilibrium in solution. Fluorescence-detected analytical ultracentrifugation was employed to show that the dimerization dissociation constant of MRSA-DHDPS is 33 nm in the absence of substrates and 29 nm in the presence of (S)-aspartate semialdehyde (ASA), but is 20-fold tighter in the presence of the substrate pyruvate (1.6 nm). The MRSA-DHDPS dimer exhibits a ping-pong kinetic mechanism (k(cat)=70+/-2 s(-1), K(m)(Pyruvate)=0.11+/-0.01 mm, and K(m)(ASA)=0.22+/-0.02 mm) and shows ASA substrate inhibition with a K(si)(ASA) of 2.7+/-0.9 mm. We also demonstrate that unlike the E. coli tetramer, the MRSA-DHDPS dimer is insensitive to lysine inhibition. The near atomic resolution (1.45 A) crystal structure confirms the dimeric quaternary structure and reveals that the dimerization interface of the MRSA enzyme is more extensive in buried surface area and noncovalent contacts than the equivalent interface in tetrameric DHDPS enzymes from other bacterial species. These data provide a detailed mechanistic insight into DHDPS catalysis and the evolution of quaternary structure of this important bacterial enzyme.

Deformation behavior and mechanism of porous PLLA under compression

scaffolds. The PLLA dioxane solutions in test tubes were cooled from the bottom surfaces at a constant rate by using liquid nitrogen to induce solid–liquid phase separation. The phase-separated samples were then dried under vacuum at -5 C for about 6 days to remove the solvent completely. Cylindrical samples were obtained and then trimmed to be a cylinder with 8-mm diameter and 12-mm length. Porosity (volume fraction of pores) of a scaffold was estimated from the densities of PLLA solid and the scaffold. Compression tests were then performed using a conventional mechanical testing machine at a loading rate of 1 mm/min. A fieldemission scanning electron microscope (FE-SEM) was also used to observe the microstructures of the porous samples and the deformation behavior of the porous samples at the critical point. FE-SEM micrographs of the cross-sections in the transverse direction are shown in Fig. 1. Homogeneous distribution of pores is observed, and the size of the pores tends to decrease with increase in the concentration of the solution. The porosities of these porous samples were estimated as 94.7, 90.0, and 88.5% for the concentrations of 3, 5, and 7 wt.%, respectively. FE-SEM micrograph of a crosssection in the vertical direction is shown in Fig. 2. For all the samples, this kind of porous structure was observed. These structures shown in Figs. 1 and 2 suggest that the crystals of the solvent grow in the vertical and transverse directions at a constant speed by the freezing process. Typical stress–strain curves under compression are shown in Fig. 3. The stress– strain relation of this porous structure of PLLA can be characterized by four different regions as shown in Fig. 4. The region A is the initial linear portion corresponding to linear elastic deformation of the porous structure. The end of the region A and the transition point to the region B is recognized as a critical point where localized failures of the wall structures of the pores take place. In the region B, stress

Central nervous system distribution kinetics of indinavir in rats

The central nervous system (CNS) distribution kinetics of indinavir were extensively evaluated using a combinational in-vivo model comprising the integration plot method (a single-passage approach) and neuropharmacokinetic method (a multiple-passage approach). A 5 mg kg(-1) dose of indinavir was administered intravenously to rats. Blood and cerebrospinal fluid (CSF) samples and whole brain were collected from the animals at specified time points and the drug concentration in each sample was determined using a high-performance liquid chromatography method. For the neuropharmacokinetic study, the simultaneous plasma, CSF and brain concentrations were fitted to an integrated model, which resulted in the estimation of the influx (K(in)) and efflux (K(out)) rate constants of the drug to/from CSF and brain parenchyma. The integration plot method involved plotting the brain-plasma or CSF-plasma concentration ratios (K(p, app)) against AUC(0-->t)/C(p(t)), and estimating the uptake clearance of the drug by brain/CSF from the slope of the initial linear portion of the plot. The K(in) and K(out) values of the drug to/from CSF were estimated to be 2.42 x 10(-2) and 13.26 x 10(-2)min(-1), respectively, and the corresponding values for brain parenchyma were 1.02 x 10(-2) and 1.32 x 10(-2) min(-1), respectively. The uptake clearances of indinavir by CSF and brain parenchyma were 8.89 and 8.38microL min(-1)g(-1), respectively. The permeability surface area products of the drug for the blood-brain barrier and blood-CSF barrier were estimated as 1.05 x 10(-2) and 2.45 x 10(-2) mLmin(-1)g(-1), respectively. The estimated kinetic parameters indicated limited CNS entry of the drug because of the limited blood-brain barrier permeability and the efficient drug efflux from CNS, particularly from CSF.

Water sorption kinetics in light‐cured poly‐HEMA and poly(HEMA‐co‐TEGDMA); determination of the self‐diffusion coefficient by new iterative methods

AbstractThe present investigation is concerned with the determination of self‐diffusion coefficient (D) of water in methacrylate‐based biomaterials following Fickian sorption by two new methods: the Iterative and the Graphical methods. The D value is traditionally determined by means of the initial slope of the corresponding sorption curve and the so‐called Stefan's approximation. The proposed methods using equations without approximations and data resulting from the whole sorption range reach to accurate values of D, even when the sorption curve does not present an initial linear portion. In addition to D, the Graphical method allows the extrapolation of the mass of the sorbed water at equilibrium (M∞), even when the equilibrium specimen's mass fluctuates around its limited value (m∞). The test of the proposed procedures by means of ideal and Monte Carlo simulated data revealed that these methods are fairly applicable. The obtained D values compared with those determined by means of the Stephan's method revealed that the proposed methods provide more accurate results. Finally, the proposed methods were successfully applied to the experimental determination of the diffusion coefficient of water (50°C) in the homopolymer of 2‐hydroxyethyl methacrylate (HEMA) and in the copolymer of HEMA with triethylene glycol dimethacrylate (98/2 mol/mol). These polymers were prepared by light curing (λ = 470 nm) at room temperature in presence of camphorquinone and N,N‐dimethylaminoethyl methacrylate as initiator. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Grape seed oil supercritical extraction kinetic and solubility data: Critical approach and modeling

This paper focuses on supercritical CO 2 extraction of grape seed oil which has been analyzed both experimentally and theoretically. Extractions on crushed seeds at pressures varying in the range 280–550 bar and at a fixed temperature of 313 K were performed. From the initial linear portion of the experimental curves oil solubility data in the supercritical solvent have been obtained. By modeling the complete curves, the transport parameters regulating the oil mass transfer inside the seed particles have been calculated: the internal transport coefficient and the effective diffusivity. Three different extraction baskets (0.1, 0.2 and 0.5 l) have been utilized: the differences in the extraction curves have been modeled and explained in terms of the different void volume of the apparatus for the various baskets. A procedure to obtain consistent solubility data when dealing with extractor vessel with non-negligible void volume has been described.

Repeated impact response of hand lay-up and vacuum infusion thick glass reinforced laminates

Vacuum infusion (VI) is being considered as a viable alternative to more traditional hand lay-up (HL). Main reason in favor of the more costly technique is the cleaner and friendlier work environment. Moreover, VI potentially offers another important benefit over HL in that prepreg levels of resin may be achieved, resulting in stronger and lighter laminates. The present paper compares the two manufacturing techniques on the basis of the response to repeated impact loading. The laminate is a thick non-symmetric glass-fiber-reinforced plastics intended for nautical application. Four impact velocities (1.5, 2.2, 3.1 and 3.8 m/s) were considered, and a minimum of four specimens for any given velocity were subjected to 40 repeated impacts or up to perforation. The impact response was evaluated in terms of damage progression by visual observation of the impacted specimens, evolution of the peak force and of the bending stiffness with the number of impacts and by calculating the Damage Index (DI), a damage variable recently proposed by the authors to monitor the penetration process in thick laminates. Results point out that for impact velocities for which no perforation occurs within test duration, the experimental data essentially overlap. On the contrary, for perforation tests, HL specimens survived more impacts before perforating absorbing more total energy than VI specimens. Plots of the DI variable against the number of impacts were observed to exhibit an initial linear portion, owing to a stable process of damage accumulation within the laminate, and to undergo an unstable growth a few impacts before perforation. When comparing the VI and HL specimens it was observed that, given an impact energy, the level of damage at first impact as well as the rate of stable damage accumulation is alike for the two sets of specimens. On the contrary, it is the number of impacts of the stable damage accumulation region which is lower for VI specimens.

Investigations on sorption, diffusion and permeation of chloro-alkanes and -alkenes through fluoroelastomeric membranes

Sorption, diffusion and permeation of halogenated liquids such as chloroform, dichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, trichloroethylene and tetrachloroethylene into commercial fluoroelastomer (FC-2177 D) were studied at 30, 40 and 50°C using the sorption gravimetric method. The concentration-independent diffusion coefficients were calculated using Fick's equation from the initial linear portion of the sorption curves. The liquid concentration profiles were also computed using the analytical solution of Fick's equation with the appropriate initial and boundary conditions, and these were presented as a function of penetration depth of molecular migration and time of immersion. These results are discussed in terms of the molecular size of liquid penetrants and temperature. The transport phenomenon was found to follow anomalous behavior. From a temperature dependence of diffusion and permeation coefficients, the Arrhenius activation parameters were estimated. The activation energies for diffusion and permeation did not exhibit any systematic dependence on size of the penetrating molecules, but these were influenced by the nature of the liquids. None of the liquids showed any degradative effects on the membrane.

Relationship of sire expected progeny differences to milk yield in Brangus cows1,2

Milk yield from 160 Brangus cows sired by 65 Brangus bulls was measured over a 3-yr period with a single-cow milking machine to estimate the relationship of actual milk yield of daughters and their calves' BW with cow sire EPD for milk during the preweaning period. Milk yield was measured six times per year at an average 49, 78, 109, 138, 168, and 198 d postpartum. The regression of daughters' milk yield on sire milk EPD was quadratic (P < 0.01), and the initial linear portion of the curve differed among months (P < 0.05) at an average cow BW. Similarly, the regression of 6-mo average 24-h milk yield on sire milk EPD was curvilinear (P < 0.05). When cow BW was fitted as a covariate in the regression of 6-mo average 24-h milk yield on sire milk EPD, there was an interaction of cow BW with linear sire milk EPD and quadratic sire milk EPD (P < 0.10). The associated response surface suggested that the regression was primarily linear in cows weighing < or = 520 kg and curvilinear in cows weighing >520 kg. A trend existed for the regression of calf 205-d weight on grandsire milk EPD to be curvilinear (P < 0.21); however, the regression of calf 205-d weight on milk yield of their dam was linear (P < 0.01). Results from these data suggest that genetic potential for milk yield, and possibly the associated effects on calf BW transmitted through the grandsire, may have a practical maximum because of nutritional limitations that prevent the expression of genetic potential beyond that level, particularly in heavier cows, which suggests the need to match sire milk EPD and cow BW with production environment.

Development and Qualification of an Algorithm for the Determination of the Initial Linear Portion of a Force Versus Displacement Record

Abstract In mechanical tests, the force versus displacement record generally contains an initial linear elastic portion. In the analysis, the accurate determination of this linear part is essential for the identification of characteristic values of force and/or plastic displacement. In this paper, an algorithm for the determination of this linear portion is presented. This algorithm is qualified on several experimental curves and on virtual data sets generated by a computer program. Results demonstrate that the algorithm is very robust and is able to determine the linear portion accurately.