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PurposeThis study aims to propose a novel viscoelastic–viscoplastic combined constitutive model for glassy amorphous polymers within the framework of thermodynamics at finite strain that is capable of capturing their rate-dependent inelastic mechanical behavior in wide ranges of deformation rate and amount.Design/methodology/approachThe rheology model whose viscoelastic and viscoplastic elements are connected in series is set in accordance with the multi-mechanism theory. Then, the constitutive functions are formulated on the basis of the multiplicative decomposition of the deformation gradient implicated by the rheology model within the framework of thermodynamics. Dynamic mechanical analysis (DMA) and loading/unloading/no-load tests for polycarbonate (PC) are conducted to identify the material parameters and demonstrate the capability of the proposed model.FindingsThe performance was validated in comparison with the series of the test results with different rates and amounts of deformation before unloading together. It has been confirmed that the proposed model can accommodate various material behaviors empirically observed, such as rate-dependent elasticity, elastic hysteresis, strain softening, orientation hardening and strain recovery.Originality/valueThis paper presents a novel rheological constitutive model in which the viscoelastic element connected in series with the viscoplastic one exclusively represents the elastic behavior, and each material response is formulated according to the multiplicatively decomposed deformation gradients. In particular, the yield strength followed by the isotropic hardening reflects the relaxation characteristics in the viscoelastic constitutive functions so that the glass transition temperature could be variant within the wide range of deformation rate. Consequently, the model enables us to properly represent the loading process up to large deformation regime followed by unloading and no-load processes.

Cellulose triacetate (CTA)-based hollow fiber (HF) membrane is one of the commercially successful semipermeable membranes that has had a long progress since the time the excellent semi-permeable feature of cellulose-based polymers was found in 1957. Because of the reliable and excellent performances, especially for drinking water production from seawater, CTA-HFs have been widely used as reverse osmosis (RO) membranes, especially in arid regions. In this review, recent developments and research trends on CTA-HF membranes for seawater reverse osmosis (SWRO) plants were presented. A flux analytical model, an optimization strategy for chlorine injection without losing salt rejection performance, and a module of current high performance CTA RO membranes along with its plant operation data were updated in this paper. Furthermore, a newly developed CTA-HF membrane for brine concentration (BC) application (called BC membrane) was also addressed. Finally, RO/BC hybrid operation was introduced as an effective SWRO desalination technique that enables minimizing the volume of brine disposal from the RO plant by increasing the recovery ratio and the subsequent amount of produced freshwater, without an additional energy input.

Polymeric liquids exhibit a crossover from the nonentangled to entangled behavior on an increase of the molecular weight M. For example, it has been established that the zero-shear viscosity h0(M ) of non-entangled low-M chains is proportional to M as described by Rouse model, whereas h0(M ) of well-entangled high-M chains is proportional to M a with a = ~ 3.4. 2) Not only for the linear viscoelastic property, the crossover has been observed also for nonlinear viscoelasticity, specifically in the shear damping function h(g), where g is a magnitude of step shear strain. h(g ) is insensitive to M and close to the Doi-Edwards (DE) prediction for high-M chains. This universal damping behavior was classified by Osaki as the type-A behavior. In contrast, the g dependence of h(g) considerably weakens with decreasing M when M is below a critical value ~ 2Me (with Me being the entanglement molecular weight), as reported by Takatori et al. and Inoue et al. for polystyrene (PS) solutions and by Vega et al. for polystyrene (PS) melts. This weak damping was classified by Osaki as the type-B behavior. A couple of theoretical attempts has been made for explaining the origin of type-B damping behavior. Kapnistos et al. have reported a weak damping of h(g ) for scarcely entangled polymer deduced from their slip-spring model where a Rouse chain is confined in a tube shaped parabolic potential. The confinement is realized by some springs having one end anchored in space and the other end connected to the chain. The spring end connected to the chain slides along the chain backbone to mimic the entanglement. Kapnistos et al. reported that if the number of slip-springs on the chain, which reflects the number of entanglement per chain, is decreased, the strain dependence of h(g) is weakened. Since there is no damping in the limit of free Rouse chain, it is rather natural that the strain dependence of h(g ) becomes weaker when the number of springs on the chain becomes smaller. They discussed that their simulation results are consistent with those for comb polymers with a small number of backbonebackbone entanglements. Another explanation of the type-B behavior was given by Kharlamov et al. They derived the distribution function of the end-to-end vector of a whole chain Ree after the chain contraction along the primitive path, and then calculated the stress from the second moment of Nonlinear Stress Relaxation of Scarcely Entangled Chains in Primitive Chain Network Simulations

In general, clothing pressure is measured using a sensor set on the surface of a human body or dummy, and it is not possible to measure clothing pressure without the sewing process. We have developed a numerical-analysis-based technique to simulate clothing pressure without having to sew the cloth into clothes. We presupposed that clothing made of knitted fabric was applied to a mannequin in close contact with its surface. Based on this simulation, this paper proposes a model for fabric deformation, by extension applicable to large deformation, with anisotropy and non-linearity taken into account. In this model, the fabric is separated into isotropic and anisotropic elements, and non-linearity is assigned to both the isotropic and anisotropic elements. Furthermore, to use this model, we propose a method for fitting the knitted fabric tightly to a human body model while sewing the knitted fabric model reflecting the paper pattern. To prevent excessive extension of the knitted fabric model reflecting the paper pattern during the process of fitting, we adopted the two-step fitting method involving application of the fabric to a temporary human body model (intermediary) followed by its application to a formal human body model. The clothing pressure values calculated with this method were very close to the actually measured values using a rigid mannequin.

Effect of Blended Ionomers on the Strain Hardening of Polyester-Type Elastomer/Ionomer Blends

Orientation and stretch of entangled polymers under large step shear deformations were investigated through primitive chain network simulations. In the simulations, entangled polymer dynamics is described by 3D motion of entanglements, 1D sliding of monomers along the chain, and creation/destruction of entanglements described by hooking/unhooking with surrounding chains at chain ends. In addition to the conventionally proposed relaxation mechanisms that are reptation, contour length fluctuations, and constraint release (both thermal and convective), the simulations also account for force balance among entanglement strands converging to an entanglement node, and nodes also fluctuate in space. Nonlinear step strain data for monodisperse polystyrene melts (Ferri and Greco, Macromolecules, 37:5931, 2006) were quantitatively reproduced by using the same two molecular-weight-independent parameters already adopted by Masubuchi et al. (J Non-Newt Fluid Mech, 149:87, 2008) to fit linear viscoelastic data of several monodisperse polystyrene melts. Analysis of the orientation tensor and of the chain stretch ratio indicates that the segment orientation and stretch realized in the simulation are quantitatively described by a simple three-chain model (Marrucci et al., Macromol Symp, 158:57, 2000a).

The purpose of this study was to evaluate the role of combined CT hepatic angiography (CTHA) and CT during arterial portography (CTAP) in the diagnosis and management of patients with hepatocellular carcinomas (HCC) and liver metastases. Fifty patients with HCC and 19 patients with liver metastases were referred for CTHA and CTAP prior to surgery or interventional therapy. Diagnosis was established by either surgery or clinical observation. Alterations of diagnosis and management resulting from CTHA and CTAP information were recorded. In patients with HCC, diagnosis was altered either by number, location or extent of lesions in 46% of patients and was 78% correct. Alterations of management were performed in 32% of the patients in total, and were correct in all but one. In patients with liver metastases, diagnosis was altered regarding either number, location or extent of lesions in 21% of patients and were 50% correct. Management was not altered after CTHA and CTAP in the patients with liver metastases. We conclude that CTHA and CTAP provide valuable clinical information for patients with HCC and significantly corrected their previous diagnosis and plans of management. CTHA and CTAP should be performed in patients with HCC when either surgical or interventional therapy is the treatment option.

One of the most important challenges in the injection molding process of the short-glass fiber/thermoplastic composite parts is being able to predict the fiber orientation, since it controls the mechanical and the physical properties of the final parts. Folgar and Tucker included into the Jeffery equation a diffusive type of term, which introduces a phenomenological coefficient for modeling the randomizing effect of the mechanical interactions between the fibers, to predict the fiber orientation in concentrated suspensions. Their experiments indicated that this coefficient depends on the fiber volume fraction and aspect ratio. However, a definition of the fiber interaction coefficient, which is very necessary in the fiber orientation simulations, hasn't still been proven yet. Consequently, this study proposed a developed fiber interaction model that has been introduced a fiber dynamics simulation in order to obtain a global fiber interaction coefficient. This supposed that the coefficient is a sum function of the fiber concentration, aspect ratio, and angular velocity. The proposed model was incorporated into a computer aided engineering simulation package C-Mold. Short-glass fiber/polyamide-6 composites were produced in the injection molding with the fiber weight concentration of 30 wt.%, 50 wt.%, and 70 wt.%. The physical properties of these composites were examined, and their fiber orientation distributions were measured by micro-computed-tomography equipment μ-CT. The simulation results showed a good agreement with experiment results.

Computed tomography demonstrates the precise anatomy and various pathologic processes of the gastrointestinal tract in the ileocecal-appendiceal region. The examination should be performed with intravenous contrast approximately 1 hour after the oral administration of 700 to 1000 mL diluted barium.

Between April 1, 1987 and August 7, 1997, a total of 128 abutment teeth associated with 34 telescope removable partial dentures in 28 patients (22 females and 6males) who had a mean age of 57.4±9.3 years was observed. The survival time (with extraction being the endpoint) for each abutment tooth was calculated using Kaplan-Meier analysis. Significance levels were determined using 8 prognostic factors for 4 statistical tests, i. e., the generalized Wilcoxon, the Cox-Mantel, the Logrank, and the Mantel-Haenszel tests. Furthermore, survival estimates and relative risks were calculated by Cox hazard regression.The results conclusively indicated a higher survival for vital as compared to endodontically-treated teeth. The relative risk of an abutment tooth adjacent to a free-end saddle was 5.81. The risk increased by 2.79 for each group from molar to cuspid, to premolar, and to incisor. The survival estimate was 89.8% at 9-10 years after placement of the denture.

To assist in developing a “normal” electromyographic (EMG) envelope, various amplitude normalization procedures for surface EMG signals have been used to reduce the inter- and intrasubject variability of collected data. The effect of two normalization methods (normalization to mean ensemble average: NME, and peak ensemble average: NPE) on intersubject variability and reproducibility of surface EMG profiles from masticatory muscles during unilateral gum chewing was examined. The EMG profiles for anterior temporal (Ta), posterior temporal (Tp), masseter (M) and anterior belly of digastric (Da) muscles on chewing side from 5 asymptomatic dentate subjects were made on 3 different sessions. Coefficients of variation and intraclass correlation coefficients, ICC (3, 1), were used to assess the variability and reproducibility. Each normalization procedure reduced the intersubject variability of unnormalized EMG profiles for Ta, Tp and M. NME procedure provided lower intersubject variability for Da. Reproducibility of unnormalized profiles for Ta, Tp and M was significantly improved by the two procedures. The NME procedure on Da was more reproducible than the NPE procedure. These results showed that phasic characteristics of muscular activity influenced the outcome of amplitude normalization. These methods used. were reliable and reproducible for measuring phasic muscle activity of masticatory muscles during gum chewing.

Doi and Edwards (DE) proposed that the relaxation of entangled linear polymers under large deformation occurs in two steps: the fast chain contraction (via the longitudinal Rouse mode of the chain backbone) and the slow orientational relaxation (due to reptation). The DE model assumes these relaxation processes to be independent and decoupled. However, this decoupling is invalid for a generalized convective constraint release (CCR) mechanism that releases the entanglement on every occasion of the contraction of surrounding chains. Indeed, the decoupling does not occur in the sliplink models where the entanglement is represented by the binary interaction (hooking) of chains. Thus, we conducted primitive chain network simulations based on a multichain sliplink model to investigate the chain contraction under step shear. The simulation quantitatively reproduced experimental features of the nonlinear relaxation modulus G(t, γ). Namely, G(t, γ) was cast in the time-strain separable form, G(t, γ) = h(γ)G(t) with h(γ) = damping function and G(t) = linear modulus, but this rigorous separability was valid only at times t comparable to the terminal relaxation time, although a deviation from this form was rather small (within ±10%) at t>τR (longest Rouse relaxation time). A molecular origin of this delicate failure of time-strain separability at t ∼ τR was examined for the chain contour length, subchain length, and subchain stretch. These quantities were found to relax in three steps, the fast, intermediate, and terminal steps, governed by the local force balance between the subchains, the longitudinal Rouse relaxation, and the reptation, respectively. The contributions of the terminal reptative mode to the chain length relaxation as well as the subchain length/stretch relaxation, not considered in the original DE model, emerged because the sliplinks (entanglement) were removed via the generalized CCR mechanism explained above and the reformation of the sliplinks was slow at around the chain center compared to the more rapidly fluctuating chain end. The number of monomers in the subchain were kept larger at the chain center than at the chain end because of the slow entanglement reformation at the center, thereby reducing the tension of the stretched subchain at the chain center compared to the DE prediction. This reduction of the tension at the chain center prevented completion of the length equilibration of subchains at t ∼ τR (which contradicts to the DE prediction), and it forces the equilibration to complete through the reptative mode at t⪢τR. The delicate failure of time-strain separability seen for G(t, γ) at t ∼ τR reflects this retarded length equilibration.

Molecular theories for polymer rheology are based on conformational dynamics of the polymeric chain. Hence, measurements directly related to molecular conformations appear more appealing than indirect ones obtained from rheology. In this study, primitive chain network simulations are compared to experimental data of entangled DNA solutions [Teixeira et al., Macromolecules 40, 2461 (2007)]. In addition to rheological comparisons of both linear and nonlinear viscoelasticities, a molecular extension measure obtained by Teixeira et al. through fluorescent microscopy is compared to simulations, in terms of both averages and distributions. The influence of flow on conformational distributions has never been simulated for the case of entangled polymers, and how DNA molecular individualism extends to the entangled regime is not known. The linear viscoelastic response and the viscosity growth curve in the nonlinear regime are found in good agreement with data for various DNA concentrations. Conversely, the molecular extension measure shows significant departures, even under equilibrium conditions. The reason for such discrepancies remains unknown.

Damping functions of entangled polymers for shear, uniaxial, biaxial, and planar deformations, as well as normal stress ratios for shear deformations, were obtained from Brownian simulations making use of the primitive chain network model. To investigate the effect of the force balance over the entanglements and of the convective constraint release mechanism, comparisons with predictions of earlier theories and with experimental data in the literature were performed. It was found that the obtained damping functions are close to the three-chain theory [Marrucci, Greco, and Ianniruberto, Macromol Symp, 158, 57 (2000)] suggesting that the force balance is a dominant correction over the basic Doi-Edwards theory as compared with the effect of convective constraint release. Furthermore, the predicted normal stress ratio in shear, i.e., a quantity very sensitive to the different assumptions, is in good agreement with experiments, suggesting that the combination of force balance, convective constraint release, and other relaxation modes, as accounted for through the primitive chain network model, is quite acceptable.

To assess whether liver-specific late-phase contrast-enhanced pulse-inversion (CE-PI) ultrasound imaging improves the detection of hepatocellular carcinoma (HCC) and liver metastasis in comparison with non-enhanced tissue harmonic imaging (THI).Twenty-one patients with HCC or liver metastasis were studied using standardized ultrasound harmonic settings. Sweeps through the hepatic lobes were done by THI, followed by late-phase CE-PI after Levovist injection. The number and segmental location of nodules detected by each method were recorded and compared with dynamic helical computed tomography (CT) as a reference.Sensitivity for the presence of the disease, metastasis or HCC, on a patient basis for each method was 81.0% for THI and 90.5% for CE-PI. Among the 78 metastatic nodules on reference CT, 31 true-positive, three false-positive, and 47 false-negative nodules were found by THI, while CE-PI depicted 54 true-positive, 12 false-positive and 24 false-negative lesions. Sensitivity in the detection of individual lesion was 51.8% for THI and 76.8% for CE-PI (p=0.0273). A total of 58 HCC nodules were detected on CT; 36 true-positive, 15 false-positive, and 22 false-negative lesions were found by THI; while CE-PI depicted 43 true-positive, six false-positive, and 15 false-negative lesions. Sensitivity in the detection of individual HCC was 42.9% by THI and 57.2% by CE-PI (p=0.2249 NS).In patients with liver metastasis, CE-PI statistically improved the sensitivity of lesion detection compared with THI. Conversely, CE-PI did not improve the sensitivity of lesion detection in patients with HCC.

Horseshoe lung is a rare pulmonary anomaly characterized by fusion of the posterobasal portions of the right and left lungs behind the pericardial reflection, anterior to the aorta. The majority of reported cases occur in conjunction with scimitar syndrome, including hypoplasia of the right lung, anomalous right pulmonary venous return and systemic arterial supply to the lung. Horseshoe lung is usually diagnosed on pulmonary arteriography when the right inferior pulmonary artery crosses the midline and extends to the left lung base. Bronchography is also diagnostic when the branch of horseshoe portion arises from the right bronchus and passes within the lung parenchyma to midline of the lung tissue. The only described CT finding of horseshoe lung is the contiguity of the right and left lungs behind the heart. Most cases are infants under 12 months of age and CT images are severely hampered by respiration motion artefacts. Such artefacts are minimized by using electron-beam computed tomography, allowing a more detailed CT appearance of horseshoe lung in this case.

Relaxation process of a stretched tethered polymer chain was investigated using the dynamic mean field technique. We confirmed that the relaxation of the end-to-end distance of the chain is consistent with that of Rouse dynamics.

The development of multi-purpose real time simulator models with suitable plant dynamics was made; these models can be used not only in training operators but also in designing control systems, operation sequences and many other items which must be studied for the development of new type reactors.The prototype fast breeder reactor "Monju" is taken as an example. Analysis is made on various factors affecting the accuracy and computer load of its dynamic simulation. A method is presented which determines the optimum number of nodes in distributed systems and time steps. The oscillations due to the numerical instability are observed in the dynamic simulation of evaporators with a small number of nodes, and a method to cancel these oscillations is proposed.It has been verified through the development of plant dynamics simulation codes that these methods can provide efficient real time dynamics models of fast breeder reactors.

Much attention has been paid heretofore to the dynamic behavior of coupled reactors ever since the design of modular reactors was proposed from the viewpoint of safety. However, very little appears to have been achieved in presenting a unified approach to contribute to a better understanding of such reactor systems.The present work is an attempt to derive nodal kinetic equations from multi-group diffusion equations, taking into account the spatial and spectral coupling effects. The numerical solutions to these nodal kinetic equations are compared with those to the one group-one dimensional diffusion equations, and discussions are presented on the validity of the equations derived and on the time dependence of the kinetic parameters relevant to the change of the neutron flux shape.