Melting of polymer single crystals studied by dynamic Monte Carlo simulations

We report dynamic Monte Carlo simulations of lattice polymers melting from a metastable chain-folded lamellar single crystal. The single crystal was raised and then melted in an ultrathin film of polymers wetting on a solid substrate, mimicking the melting observations made by using Atomic Force Microscopy. We observed that the thickness distribution of the single crystal appears quite inhomogeneous and the thickness increases gradually from facetted edges to the center. Therefore, at low melting temperatures, melting stops at a certain crystal thickness, and melting-recrystallization occurs when allowing crystal thickening; at intermediate temperatures, melting maintains the crystal shape and exhibits different speeds in two stages; at high temperatures, fast melting makes a melting hole in the thinnest region, as well as a saw-tooth-like pattern at the crystal edges. In addition, the linear melting rates at low temperatures align on the curve extrapolated from the linear crystal growth rates. The temperature dependence of the melting rates exhibits a regime transition similar to crystal growth. Such kinetic symmetry persists in the melting rates with variable frictional barriers for c -slip diffusion in the crystal as well as with variable chain lengths. Visual inspections revealed highly frequent reversals upon melting of single chains at the wedge-shaped lateral front of the lamellar crystal. We concluded that the melting kinetics is dominated by the reverse process of intramolecular secondary crystal nucleation of polymers.

Engineer’s role in resolving disputes in offshore projects

Offshore construction and supply projects involve complex contractual arrangements regulating the relationships of operators, contractors, subcontractors and suppliers. Although every effort is made to prevent the occurrence of disputes when parties enter into contract, it is a fact of life that disputes do arise. This paper explains the role of engineers in the dispute resolution process. It highlights the features of disputes which arise out of the offshore construction and supply industry by way of inclusion of a description of: the life cycle of a typical offshore development; a typical engineering, procurement, construction, installation and commissioning project; the engineer’s involvement in the contractual process; types of frequently occurring disputes; and the role of engineers in dispute avoidance. By way of introducing the various methods of disputes resolution, including litigation, arbitration, adjudication, expert determination, mediation, the engineers’ functions in these processes are highlighted.’The paper concludes that engineers are indeed important if not crucial to every stage of an oil and gas construction project. They have every opportunity to assist in dispute avoidance by being more aware of the contractual relationship between various parties and the project procedure. They can be factual witnesses to set out the chain of events that happened, expert witnesses to assist the court or tribunal in understanding the technical issues, and they are also well placed to judge the rights and wrongs of the parties given their technical backgrounds in understanding the day-to-day running of a project.

Correlations between clinical and physiological consequences of the novel mutation R878C in a highly conserved pore residue in the cardiac Na+ channel

Aim:

We compared the clinical and physiological consequences of the novel mutation R878C in a highly conserved pore residue in domain II (S5-S6) of human, hNa_v1.5, cardiac Na⁺ channels.

Methods:

Full clinical evaluation of pedigree members through three generations of a Chinese family combined with SCN5A sequencing from genomic DNA was compared with patch and voltage-clamp results from two independent expression systems.

Results:

The four mutation carriers showed bradycardia, and slowed sino-atrial, atrioventricular and intraventricular conduction. Two also showed sick sinus syndrome; two had ST elevation in leads V1 and V2. Unlike WT-hNa_v1.5, whole-cell patch-clamped HEK293 cells expressing R878C-hNa_v1.5 showed no detectable Na⁺ currents (i_Na), even with substitution of a similarly charged lysine residue. Voltage-clamped Xenopus oocytes injected with either 0.04 or 1.5 μg μL⁻¹ R878C-hNa_v1.5 cRNA similarly showed no i_Na, yet WT-hNa_v1.5 cRNA diluted to 0.0004–0.0008 ng μL⁻¹resulted in expression of detectable i_Na. i_Na was simply determined by the amount of injected WT-hNa_v1.5: doubling the dose of WT-hNa_v1.5 cRNA doubled i_Na. i_Na amplitudes and activation and inactivation characteristics were similar irrespective of whether WT-hNa_v1.5 cRNA was given alone or combined with equal doses of R878C-hNa_v1.5 cRNA therefore excluding dominant negative phenotypic effects. Na⁺ channel function in HEK293 cells transfected with R878C-hNa_v1.5 was not restored by exposure to mexiletine (200 μm) and lidocaine (100 μm). Fluorescence confocal microscopy using E3-Nav1.5 antibody demonstrated persistent membrane expression of both WT and R878C-hNa_v1.5. Modelling studies confirmed that such i_Na reductions reproduced the SSS phenotype.

Conclusion:

Clinical consequences of the novel R878C mutation correlate with results of physiological studies.

Integration and the performance of healthcare networks: do integration strategies enhance efficiency, profitability, and image?

Purpose

This study examines the integration effects on efficiency and financial viability of the top 100 integrated healthcare networks (IHNs) in the United States.

Theory

A contingency- strategic theory is used to identify the relationship of IHNs' performance to their structural and operational characteristics and integration strategies.

Methods

The lists of the top 100 IHNs ranked in two years, 1998 and 1999, by the SMG Marketing Group were merged to create a database for the study. Multiple indicators were used to examine the relationship between IHNs' characteristics and their performance in efficiency and financial viability. A path analytical model was developed and validated by the Mplus statistical program. Factors influencing the top 100 IHNs' images, represented by attaining ranking among the top 100 in two consecutive years, were analysed.

Results and conclusion

No positive associations were found between integration and network performance in efficiency or profits. Longitudinal data are needed to investigate the effect of integration on healthcare networks' financial performance.

Equation of state and Raman frequency of diamond from quantum Monte Carlo simulations

We report variational and diffusion quantum Monte Carlo (VMC and DMC) calculations of the equation of state and Raman frequency of diamond. The pressure derivative of the bulk modulus, which has not been accurately determined experimentally, is calculated to be 3.8 (VMC) and 3.7 (DMC). The values of the Raman frequency calculated at the experimental volume are 1373 cm-1(VMC) and 1359 cm-1 (DMC), in good agreement with the experimental value of 1333 cm-1.

A high-resolution anthropomorphic voxel-based tomographic phantom for proton therapy of the eye

Proton therapy is increasingly used in medical treatments for cancer patients due to the sharp dose conformity offered by the characteristic Bragg peak. Proton beam interactions with the eye will be simulated using the MCNPX Monte Carlo code and available nuclear cross-section data to calculate the dose distribution in the eye gel and surrounding organs. A high-resolution eye model will be employed using a 3D geometrical voxel-based anthropomorphic head phantom obtained from the Visible Human Project (female data). Manual segmentation of the eye, carried out by the Medical Physics group at the University of Surrey resulted in 15 identified structures. This work emphasizes the use of a realistic phantom for accurately predicting dose deposition by protons.

A pilot study of ranolazine in patients with intermittent claudication

AIM

This pilot study provides preliminary information regarding safety and changes in exercise performance during treatment with ranolazine extended-release in patients with reproducible claudication during exercise treadmill testing (ETT).

METHODS

We enrolled 45 patients with documented peripheral arterial disease, reproducible claudication on ETT, and ankle-brachial indices <0.85 at rest that decreased by at least 0.15% or 20% immediately postexercise. Randomized patients received double-blind treatment with either ranolazine 1 000 mg b.i.d. (n=22) or placebo (n=23) for 4 weeks.

RESULTS

Compared with baseline, peak walking time (PWT) increased (mean+/-SEM) by 53+/-34 s with ranolazine (P=0.13) and by 41+/-33 s with placebo (P=0.22). Pain-free walking time during ETT increased by 62+/-18 s with ranolazine (P=0.002) and 36+/-18 s with placebo (P=0.045). Supplemental analyses, excluding patients with baseline exercise duration (16 min and (12 min, showed additional improvement with ranolazine on PWT.

CONCLUSIONS

Ranolazine was well tolerated and these data provide a rationale for proceeding with a definitive trial.

Inhomogeneous backflow transformations in quantum Monte Carlo calculations

An inhomogeneous backflow transformation for many-particle wave functions is presented and applied to electrons in atoms, molecules, and solids. We report variational and diffusion quantum Monte Carlo (VMC and DMC) energies for various systems and study the computational cost of using backflow wave functions. We find that inhomogeneous backflow transformations can provide a substantial increase in the amount of correlation energy retrieved within VMC and DMC calculations. The backflow transformations significantly improve the wave functions and their nodal surfaces.