Theory and simulations of rigid polyelectrolytes

We present theoretical and numerical studies on stiff, linear polyelectrolytes within the framework of the cell model. We first review analytical results obtained on a mean-field Poisson-Boltzmann level, and then use molecular dynamics simulations to show, under which circumstances these fail quantitatively and qualitatively. For the hexagonally packed nematic phase of the polyelectrolytes we compute the osmotic coefficient as a function of density. In the presence of multivalent counterions it can become negative, leading to effective attractions. We show that this results from a reduced contribution of the virial part to the pressure. We compute the osmotic coefficient and ionic distribution functions from Poisson-Boltzmann theory with and without a recently proposed correlation correction, and also simulation results for the case of poly(para-phenylene) and compare it to recently obtained experimental data on this stiff polyelectrolyte. We also investigate ion-ion correlations in the strong coupling regime, and compare them to predictions of the recently advocated Wigner crystal theories.Comment: 32 pages, 15 figures, proceedings of the ASTATPHYS-MEX-2001, to be published in Mol. Phy

Third-hand smoking: indoor measurements of concentration and sizes of cigarette smoke particles after resuspension

International audienc

Outcome of Colonic Surgery in Elderly Patients with Colon Cancer

Introduction. Colonic cancer is one of the most commonly diagnosed malignancies and most often occurs in patients aged 65 years or older. Aim. To evaluate the outcome of colonic surgery in the elderly in our hospital and to compare five-year survival rates between the younger and elderly patients. Methods. 207 consecutive patients underwent surgery for colon cancer. Patients were separated in patients younger than 75 and older than 75 years. Results. Elderly patients presented significantly more (P < .05) as a surgical emergency, had a longer duration of admission and were more often admitted to the ICU (P < .01). Also, elderly patients had significant more co-morbidities, especially cardiovascular pathology (P < .01). Post-operative complications were seen more often in the elderly, although no significant difference was seen in anastomotic leakage. The five-year survival rate in the younger group was 62% compared with 36% in the elderly (P < .05). DFS was 61% in the younger patients compared with 32% in the elderly (P < .05). Conclusion. Curative resection of colonic carcinoma in the elderly is well tolerated and age alone should not be an indication for less aggressive therapy. However, the type and number of co-morbidities influence post-operative mortality and morbidity

Characterization of the Soluble Nanoparticles Formed through Coulombic Interaction of Bovine Serum Albumin with Anionic Graft Copolymers at Low pH

A static light scattering (SLS) study of bovine serum albumin (BSA) mixtures with two anionic graft copolymers of poly (sodium acrylate-co-sodium 2-acrylamido-2-methyl-1-propanesulphonate)-graft-poly (N, N-dimethylacrylamide), with a high composition in poly (N, N-dimethylacrylamide) (PDMAM) side chains, revealed the formation of oppositely charged complexes, at pH lower than 4.9, the isoelectric point of BSA. The core-corona nanoparticles formed at pH = 3.00, were characterized. Their molecular weight and radius of gyration were determined by SLS, while their hydrodynamic radius was determined by dynamic light scattering. Small angle neutron scattering measurements were used to determine the radius of the insoluble complexes, comprising the core of the particles. The values obtained indicated that their size and aggregation number of the nanoparticles, were smaller when the content of the graft copolymers in neutral PDMAM side chains was higher. Such particles should be interesting drug delivery candidates, if the gastrointestinal tract was to be used

Counterion adsorption on flexible polyelectrolytes: comparison of theories

Counterion adsorption on a flexible polyelectrolyte chain in a spherical cavity is considered by taking a "permuted" charge distribution on the chain so that the "adsorbed" counterions are allowed to move along the backbone. We compute the degree of ionization by using self-consistent field theory (SCFT) and compare with the previously developed variational theory. Analysis of various contributions to the free energy in both theories reveals that the equilibrium degree of ionization is attained mainly as an interplay of the adsorption energy of counterions on the backbone, the translational entropy of the small ions, and their correlated density fluctuations. Degree of ionization computed from SCFT is significantly lower than that from the variational formalism. The difference is entirely due to the density fluctuations of the small ions in the system, which are accounted for in the variational procedure. When these fluctuations are deliberately suppressed in the truncated variational procedure, there emerges a remarkable quantitative agreement in the various contributing factors to the equilibrium degree of ionization, in spite of the fundamental differences in the approximations and computational procedures used in these two schemes. Nevertheless, since the significant effects from density fluctuations of small ions are not captured by the SCFT, and due to the close agreement between SCFT and the other contributing factors in the more transparent variational procedure, the latter is a better computational tool for obtaining the degree of ionization

The Accuracy of Clinical Staging of Stage I-IIIa Non-Small Cell Lung Cancer : An Analysis Based on Individual Participant Data

BACKGROUND: Clinical staging of non-small cell lung cancer (NSCLC) helps determine the prognosis and treatment of patients; few data exist on the accuracy of clinical staging and the impact on treatment and survival of patients. We assessed whether participant or trial characteristics were associated with clinical staging accuracy as well as impact on survival. METHODS: We used individual participant data from randomized controlled trials (RCTs), supplied for a meta-analysis of preoperative chemotherapy (+/- radiotherapy) vs surgery alone (+/- radiotherapy) in NSCLC. We assessed agreement between clinical TNM (cTNM) stage at randomization and pathologic TNM (pTNM) stage, for participants in the control group. RESULT: Results are based on 698 patients who received surgery alone (+/- radiotherapy) with data for cTNM and pTNM stage. Forty-six percent of cases were cTNM stage I, 23% were cTNM stage II, and 31% were cTNM stage IIIa. cTNM stage disagreed with pTNM stage in 48% of cases, with 34% clinically understaged and 14% clinically overstaged. Agreement was not associated with age (P = .12), sex (P = .62), histology (P = .82), staging method (P = .32), or year of randomization (P = .98). Poorer survival in understaged patients was explained by the underlying pTNM stage. Clinical staging failed to detect T4 disease in 10% of cases and misclassified nodal disease in 38%. CONCLUSION: This study demonstrates suboptimal agreement between clinical and pathologic staging. Discrepancies between clinical and pathologic T and N staging could have led to different treatment decisions in 10% and 38% of cases, respectively. There is therefore a need for further research into improving staging accuracy for patients with stage I-IIIa NSCLC.Peer reviewe

Genetic Deletion of the Nociceptin/Orphanin FQ Receptor in the Rat Confers Resilience to the Development of Drug Addiction

The nociceptin (NOP) receptor is a G-protein-coupled receptor whose natural ligand is the nociceptin/orphanin FQ (N/OFQ) peptide. Evidence from pharmacological studies suggests that the N/OFQ system is implicated in the regulation of several addiction-related phenomena, such as drug intake, withdrawal and relapse. Here, to further explore the role of NOP system in addiction, we used NOP (-/-) rats to study the motivation for cocaine, heroin and alcohol self-administration in the absence of N/OFQ function. Conditioned place preference (CPP) and saccharin (0.2% w/v) self-administration were also investigated. Results showed that NOP (-/-) rats self-administer less cocaine (0.25, 0.125 or 0.5 mg/infusion) both under a Fixed Ratio 1 and a Progressive Ratio schedule of reinforcement compared to wild type (Wt) controls. Consistently, cocaine (10 mg/kg, i.p.) was able to induce CPP in Wt but not in NOP (-/-). When NOP (-/-) rats were tested for heroin (20 μg/infusion) and ethanol (10% v/v) self-administration, they showeda significantly lower drug intake compared to Wt. Conversely, saccharin self-administration was not affected by NOP deletion, excluding the possibility of nonspecific learning deficits or generalized disruption of reward mechanisms in NOP (-/-) rats. These findings were confirmed with pharmacological experiments using two selective NOP antagonists, SB-612111 and LY2817412. Both drugs attenuated alcohol self-administration in Wt rats but not in NOP (-/-) rats. In conclusion, our results demonstrate that genetic deletion of NOP receptors confers resilience to drug abuse and support a role for NOP receptor antagonism as a potential treatment option for drug addiction.Neuropsychopharmacology accepted article preview online, 26 August 2016. doi:10.1038/npp.2016.171

Unified Homogenization Theory for Magnetoinductive and Electromagnetic Waves in Split Ring Metamaterials

A unified homogenization procedure for split ring metamaterials taking into account time and spatial dispersion is introduced. The procedure is based on two coupled systems of equations. The first one comes from an approximation of the metamaterial as a cubic arrangement of coupled LC circuits, giving the relation between currents and local magnetic field. The second equation comes from macroscopic Maxwell equations, and gives the relation between the macroscopic magnetic field and the average magnetization of the metamaterial. It is shown that electromagnetic and magnetoinductive waves propagating in the metamaterial are obtained from this analysis. Therefore, the proposed time and spatially dispersive permeability accounts for the characterization of the complete spectrum of waves of the metamaterial. Finally, it is shown that the proposed theory is in good quantitative and qualitative agreement with full wave simulations.Comment: 4 pages, 3 figure