Polymer-Mode-Coupling Theory of Finite-Size-Fluctuation Effects in Entangled Solutions, Melts and Gels. I. General Formulation and Predictions

The transport coefficients of dense polymeric fluids are approximately calculated from the microscopic intermolecular forces. The following finite molecular weight effects are discussed within the Polymer-Mode-Coupling theory (PMC) and compared to the corresponding reptation/ tube ideas: constraint release mechanism, spatial inhomogeneity of the entanglement constraints, and tracer polymer shape fluctuations. The entanglement corrections to the single polymer Rouse dynamics are shown to depend on molecular weight via the ratio N/N_e, where the entanglement degree of polymerization, N_e, can be measured from the plateau shear modulus. Two microscopically defined non-universal parameters, an entanglement strength 1/alpha and a length scale ratio, delta= xi_rho/b, where xi_rho and b are the density screening and entanglement length respectively, are shown to determine the reduction of the entanglement effects relative to the reptation- -like asymptotes of PMC theory. Large finite size effects are predicted for reduced degrees of polymerization up to N/N_e\le10^3. Effective power law variations for intermediate N/N_e of the viscosity, eta\sim N^x, and the diffusion constant, D\sim N^{-y}, can be explained with exponents significantly exceeding the asymptotic, reptation-like values, x\ge 3 and y\ge2, respectively. Extensions of the theory to treat tracer dielectric relaxation, and polymer transport in gels and other amorphous systems, are also presented.Comment: Latex, figures and styles files included; Macromolecules, in press (1997

Polymer-Mode-Coupling Theory of Finite-Size-Fluctuation Effects in Entangled Solutions, Melts and Gels. II. Comparison with Experiment

The predictions of the polymer mode coupling theory for the finite size corrections to the transport coefficients of entangled polymeric systems are tested in comparisons with various experimental data. It is found that quantitative descriptions of the viscosities, eta, dielectric relaxation time, tau_e, and diffusion coefficients, D, of polymer melts can be achieved with two microscopic structural fit parameters whose values are in the range expected from independent theoretical or experimental information. An explanation for the (apparent) power law behaviors of eta, taue, and D in (chemically distinct) melts for intermediate molecular weights as arising from finite size corrections, mainly the self-consistent constraint release mechanism, is given. The variation of tracer dielectric relaxation times from Rouse to reptation-like behavior upon changes of the matrix molecular weight is analyzed. Self and tracer diffusion constants of entangled polymer solutions can be explained by the theory as well, if one further parameter of the theory is adjusted. The anomalous scaling of the tracer diffusion coefficients in semidilute and concentrated polystyrene solutions, D\sim N^{-2.5}, is predicted to arise due to the spatial correlations of the entanglement constraints, termed ``constraint porosity''. Extensions of the theory to polymer tracer diffusion through polyvinylmethylether and polyacrylamide gels provide an explanation of the observation of anomalously high molecular weight scaling exponents in a range where the size of the tracer, R_g, already considerably exceeds the gel pore size, xi_g.Comment: Latex, figures and styles files included; Macromolecules, in press (1997

Strain gradient visco-plasticity with dislocation densities contributing to the energy

We consider the energetic description of a visco-plastic evolution and derive an existence result. The energies are convex, but not necessarily quadratic. Our model is a strain gradient model in which the curl of the plastic strain contributes to the energy. Our existence results are based on a time-discretization, the limit procedure relies on Helmholtz decompositions and compensated compactness

Fifty Shades of Erns: Innate Immune Evasion by the Viral Endonucleases of All Pestivirus Species.

The genus Pestivirus, family Flaviviridae, includes four historically accepted species, i.e., bovine viral diarrhea virus (BVDV)-1 and -2, classical swine fever virus (CSFV), and border disease virus (BDV). A large number of new pestivirus species were identified in recent years. A common feature of most members is the presence of two unique proteins, Npro and Erns, that pestiviruses evolved to regulate the host's innate immune response. In addition to its function as a structural envelope glycoprotein, Erns is also released in the extracellular space, where it is endocytosed by neighboring cells. As an endoribonuclease, Erns is able to cleave viral ss- and dsRNAs, thus preventing the stimulation of the host's interferon (IFN) response. Here, we characterize the basic features of soluble Erns of a large variety of classified and unassigned pestiviruses that have not yet been described. Its ability to form homodimers, its RNase activity, and the ability to inhibit dsRNA-induced IFN synthesis were investigated. Overall, we found large differences between the various Erns proteins that cannot be predicted solely based on their primary amino acid sequences, and that might be the consequence of different virus-host co-evolution histories. This provides valuable information to delineate the structure-function relationship of pestiviral endoribonucleases

Lymphocytes Are the Major Reservoir for Foamy Viruses in Peripheral Blood

AbstractSimian and human foamy virus (FV) DNA can be readily detected in peripheral blood leukocytes. However, it is unknown which leukocyte populations harbor the virusin vivo.We, therefore, analyzed blood samples from nine African green monkeys, four chimpanzees, and two humans for the presence of foamy virus proviral DNA in different FACS-purified leukocyte populations, using a highly sensitive nested polymerase chain reaction (PCR). The CD8+lymphocytes were PCR positive in all 15 samples and the average viral burden was highest in this population. FV DNA was detected in 10 of 15 cell samples enriched for B lymphocytes, and 4 of 9 CD4+lymphocyte, 3 of 13 CD14+monocyte, and 4 of 13 polymorphonuclear leukocyte samples. A highly sensitive reverse transcriptase PCR was performed to detect viral transcripts in peripheral blood leukocytes. All samples were negative. In conclusion, lymphocytes, and especially CD8+T lymphocytes, were found to be a major target for foamy virus in the peripheral blood, but viral gene expression was not detected

The Significance of Vascular Alterations in Acute and Chronic Rejection for Vascularized Composite Allotransplantation.

Vascularized composite allotransplantation (VCA) has emerged as a useful reconstructive option for patients suffering from major tissue defects and functional deficits. While the technical feasibility has been optimized and more than 130 VCAs have been performed during the last two decades, hurdles such as acute and chronic allograft rejection, graft deterioration, and eventual functional impairment need to be addressed. Recently, chronic graft rejection and progressive failure have been linked to vascular alterations observed in the allografts. Graft vasculopathy (GV) may play a pivotal role in long-term graft deterioration. The understanding of the underlying pathophysiological processes and their initial triggers is of utmost importance in the prevention, attenuation, and therapy of GV. While there are reports on the etiology and development of GV in solid organ transplantation, there are limited data with respect to chronic rejection and GV in the realm of VCA. Nevertheless, recent reports from long-term VCA recipients suggest that GV could truly jeopardize allografts in the follow-up evaluation. Chronic rejection and GV include different entities and might have different pathways in distinct organs. Herein, we reviewed the current literature on vascular changes during both acute and chronic allograft rejection, with a focus on their clinical and translational significance for VCA

Abdominal, perineal, and genital soft tissue reconstruction with pedicled anterolateral thigh perforator flaps

Background Pedicled perforator flaps have become a contemporary alternative to muscle flaps for soft tissue reconstruction as they have reduced donor site morbidity, avoid the need for microsurgical transfer, and are versatile and reliable. The anterolateral thigh (ALT) flap was first introduced as a free flap and has since gained popularity as a pedicled flap. Here we review our experience using pedicled ALT flaps for regional soft tissue reconstruction. Methods We retrospectively reviewed all patients who underwent loco-regional soft tissue reconstruction using pedicled ALT flaps between March 2014 and October 2018, with the goal of identifying potential applications of pedicled ALT flaps. The following aspects of each case were reviewed: patient demographics, defect location and size, comorbidities such as previous radiotherapy, flap details, clinical follow-up, and postoperative complications. Results Our analysis demonstrates the versatility of pedicled ALT flaps in a variety of indications to successfully cover large abdominal, perineal, and genital soft tissue defects. Depending on the patient’s needs to achieve more bulk or stability in the reconstruction, the ALT flap was individually tailored with underlying muscle or fascia. The average follow-up was 7 months (range: 3–13 months). Conclusions Pedicled ALT flaps are a valuable reconstructive option for soft tissue defects located within the pedicle’s range, from the lower abdomen to the perianal region. These flaps are usually raised from a non-irradiated donor site and are sufficient for covering extensive soft tissue defects. Three-dimensional reconstruction of the defect using pedicled ALT flaps allows for anatomical function and minor donor sites