New class of dynamics in concentrated polymer gels.

We show that concentrated poly(methyl methacrylate) solution exhibits a new class of coupled dynamics, which can be regarded as an intermediate between the collective diffusion of solutions and the structural relaxations of glasses. This class of dynamics have a relaxation rate that is directly proportional to the wave vector. The transition from diffusive to coupled collective dynamics occurs at smaller length scales with increasing polymer concentration and decreasing temperature. The experimental observations can be understood by considering the contributions from physical cross-links interconnected by stiff polymer segments.

Influence of chain length on the alpha-beta bifurcation in oligomeric glass formers.

A series of oligo(propylene glycol) dimethyl ethers has been investigated using dielectric spectroscopy in order to relate features of the glass transition dynamics to the number of monomer units N in the chain. The results show that (i) when scaled with the glass transition temperature, the beta relaxations systematically become faster for larger N whereas the alpha relaxations display nearly identical temperature evolutions, i.e., the alpha-beta bifurcation shifts towards shorter times for larger N, (ii) the bifurcation scenario displays a crossover in behavior at N approximately 10 monomer units, signaling the transition from oligomeric to polymeric behavior, and (iii) the beta relaxation has a cooperative nature.

Power laws in polymer solution dynamics.

The dynamical screening length xi(h) in semidilute to highly concentrated polymer solutions of poly(methyl methacrylate) in propylene carbonate has been examined using photon correlation spectroscopy and pulsed field gradient nuclear magnetic resonance. A crossover between different concentration dependent regimes, xi(h) approximately phi(-alpha), where alpha is found to be approximately 0.5, approximately 1, and approximately 2, is observed when the local viscosity is taken into account. Here phi is the volume fraction of polymer in the solution. Well-defined crossovers between alpha=0.5 and alpha=1 corresponding to a transition from a marginal solvent to a theta solvent behavior have been predicted to occur due to the reduction of excluded-volume effects between the spatially correlated polymer segments with increasing polymer volume fraction. However, a clear experimental validation of the crossover has never been presented before. The third regime (alpha approximately 2) is observed in the highly concentrated region where the static screening length is comparable to the persistence length of the polymer. The observation indicates that the rigid rod model previously used to describe concentrated solutions is an oversimplification valid only in the very high concentration limit. The obtained results at high concentrations are discussed in the frame of a simple physical model where segments at the persistence length scale are treated as flexible rodlike segments.

Chain-length-dependent relaxation scenarios in an oligomeric glass-forming system: from merged to well-separated alpha and beta loss peaks.

We have studied the relaxation dynamics of a homologous series of propylene glycol based dimethyl ethers in the supercooled regime by means of broadband dielectric spectroscopy. The system is chosen in order to minimize changes of the intermolecular interactions with varying molecular weight, M. A gradual transformation from a scenario of well-separated to one of merged alpha and beta loss peaks was observed with decreasing M. The results give strong evidence for the currently debated excess wing being due to an underlying beta relaxation. The study suggests that the main difference between glass formers with and without excess wings is the relaxation time at the merging temperature.

Is profound peripheral insulin resistance in patients with pancreatic cancer caused by a tumor-associated factor?

Diabetes in patients with pancreatic cancer occurs in 70% to 80% of the patients and is characterized by high plasma levels of insulin. In type II diabetes that is not associated with pancreatic cancer, peripheral insulin resistance and impaired muscle glycogen synthesis are major pathogenic factors. We investigated peripheral insulin sensitivity in patients with pancreatic cancer before and after tumor removal. The effects of pancreatic tumor extracts on glycogen synthesis in skeletal muscle in vitro and the tumor content of pancreatic islet hormones were also investigated. Marked peripheral insulin resistance was found in the patients with pancreatic cancer and was more pronounced in the diabetic patients than in the nondiabetic patients. Insulin sensitivity was not correlated with weight loss, tumor size, or bilirubin levels but improved after surgery. Tumor extracts from diabetic patients with pancreatic cancer caused a marked reduction of glycogen synthesis in skeletal muscle in vitro. All tumors contained islet hormones but not in concentrations sufficient to explain the effect on glycogen synthesis. These findings indicate that a diabetogenic factor associated with pancreatic adenocarcinomas could be involved in the development of the profound peripheral insulin resistance and thereby could contribute to the high incidence of diabetes observed in patients with pancreatic cancer.

Erythrocythemia following renal transplantation: influence of diuretic therapy.

Post-transplant erythrocythemia (PTE) is a common finding in renal allograft recipients, although the etiology of this disorder has not been clearly established. We identified 22 patients (9.8%) with PTE from among 225 renal transplant recipients followed for an average of 5.5 years. To characterize possible predisposing factors and to study the clinical significance of PTE, these patients were compared with a control group matched for age, race, sex and etiology of renal failure. Plasma volume (PV) and red blood cell mass (RBCM) were measured in the majority of patients with PTE. Peripheral serum erythropoietin (Ep) levels were determined in the majority of patients in the control and PTE groups. PTE occurred an average of 11.4 months after transplantation. Risk factors for the development of PTE were pretransplant hypertension, retention of native kidneys, higher pretransplant hematocrit, and diuretic use for treatment of post transplant hypertension. Ep levels in the PTE and control groups were not significantly different. Twenty of the 22 patients with PTE were receiving concurrent diuretic therapy, and hematocrits fell to normal levels in all of these patients following cessation or dose reduction of diuretic. No other treatment of PTE was utilized, excluding the phlebotomy of a single unit of blood from one patient. No thromboembolic complications were noted during the follow-up period. We conclude that PTE is frequently induced by overzealous diuretic therapy for treatment of post-transplant hypertension. Discontinuation or reduction of diuretic therapy results in resolution of PTE in nearly all patients. From this experience we have developed an algorithm for the investigation and management of PTE.

Identification of an enteric adenovirus by immunoelectroosmophoresis (IEOP) technique.

Infantile gastroenteritis can be caused by several of the established adenovirus types. There are also adenoviruses that defy in vitro cultivation but have been recognized by electron microscopy. One isolate of these viruses, which have been designated enteric adenoviruses, has been characterized. Several of the established adenovirus types are shed in stools over long periods. The conditions for direct identification of enteric adenoviruses by immunoelectroosmophoresis (IEOP) have therefore been evaluated. Application of this technique requires highly specific reagents. However, a high prevalence of antibodies in rabbits reacting with human rotavirus was noted. For these reasons, immunoadsorbent purified antibodies were prepared. Because of the difficulty in purifying immunogens from stools, an immunization procedure characterized by immunization with adenovirus subunits bound to affinity chromatography beads was elaborated. An identification procedure for adenoviruses causing infantile gastroenteritis based a) on IEOP using group-specific and monospecific antibodies and b) on the determination of the in vitro cultivatability is suggested.

Preparation of specific antisera against adenoviruses by affinity bead immunization (ABI).

Certain adenovirus types can be replicated only to low titer in tissue cultures. Other, such as adenovirus strains associated with infantile gastroenteritis, cannot be replicated in vitro. A method which allows preparation of specific antisera has therefore been evaluated. The procedure involves coupling of group-specific antibodies against adenovirus capsid subunits to CNBr-activated Sepharose 4B; reaction of crude virus suspensions with immobilized adenovirus-specific IgG; elimination of contaminating material by extensive washing using a wide pH range; and immunization with adenovirus immunogens immobilized on the beads. Efficient immunization was obtained with immunogen doses of both 50 ng and 50 microgram. The immunization procedure which has been designated affinity bead immunization (ABI) could therefore have a wide applicability in cases where the relevant immunogen constitutes a minor fraction of a crude preparation.