Parallel Excluded Volume Tempering for Polymer Melts

We have developed a technique to accelerate the acquisition of effectively uncorrelated configurations for off-lattice models of dense polymer melts which makes use of both parallel tempering and large scale Monte Carlo moves. The method is based upon simulating a set of systems in parallel, each of which has a slightly different repulsive core potential, such that a thermodynamic path from full excluded volume to an ideal gas of random walks is generated. While each system is run with standard stochastic dynamics, resulting in an NVT ensemble, we implement the parallel tempering through stochastic swaps between the configurations of adjacent potentials, and the large scale Monte Carlo moves through attempted pivot and translation moves which reach a realistic acceptance probability as the limit of the ideal gas of random walks is approached. Compared to pure stochastic dynamics, this results in an increased efficiency even for a system of chains as short as $N = 60$ monomers, however at this chain length the large scale Monte Carlo moves were ineffective. For even longer chains the speedup becomes substantial, as observed from preliminary data for $N = 200$

Polaron Hopping in Nano-scale Poly(dA)–Poly(dT) DNA

<p>Abstract</p> <p>We investigate the current&#8211;voltage relationship and the temperature-dependent conductance of nano-scale samples of poly(dA)&#8211;poly(dT) DNA molecules. A polaron hopping model has been used to calculate the I&#8211;V characteristic of nano-scale samples of DNA. This model agrees with the data for current versus voltage at temperatures greater than 100 K. The quantities <it>G</it> _<it>0</it>, <it>i</it> _<it>0</it>, and <it>T</it> _<it>1d</it> are determined empirically, and the conductivity is estimated for samples of poly(dA)&#8211;poly(dT).</p

Lithographically cut single-walled carbon nanotubes: Controlling length distribution and introducing end-group functionality

Single-walled carbon nanotubes are efficiently cut to precise submicrometer lengths and very narrow length distributions. Chemical functional groups are placed selectively only at the ends without the nanotube walls being modified or damaged. The new methodology includes lithography to place protective photoresist patterns over the nanotubes and reactive ion etching to remove the unprotected nanostructure. This approach enables critical dimensional and chemical control for integrated nanodevice manufacturing based on chemical self-assembly under ambient conditions

Resolved versus confirmed ARDS after 24 h: insights from the LUNG SAFE study

Purpose: To evaluate patients with resolved versus confirmed ARDS, identify subgroups with substantial mortality risk, and to determine the utility of day 2 ARDS reclassification.Methods: Our primary objective, in this secondary LUNG SAFE analysis, was to compare outcome in patients with resolved versus confirmed ARDS after 24 h. Secondary objectives included identifying factors associated with ARDS persistence and mortality, and the utility of day 2 ARDS reclassification.Results: Of 2377 patients fulfilling the ARDS definition on the first day of ARDS (day 1) and receiving invasive mechanical ventilation, 503 (24%) no longer fulfilled the ARDS definition the next day, 52% of whom initially had moderate or severe ARDS. Higher tidal volume on day 1 of ARDS was associated with confirmed ARDS [OR 1.07 (CI 1.01-1.13), P = 0.035]. Hospital mortality was 38% overall, ranging from 31% in resolved ARDS to 41% in confirmed ARDS, and 57% in confirmed severe ARDS at day 2. In both resolved and confirmed ARDS, age, non-respiratory SOFA score, lower PEEP and P/F ratio, higher peak pressure and respiratory rate were each associated with mortality. In confirmed ARDS, pH and the presence of immunosuppression or neoplasm were also associated with mortality. The increase in area under the receiver operating curve for ARDS reclassification on day 2 was marginal.Conclusion: ARDS, whether resolved or confirmed at day 2, has a high mortality rate. ARDS reclassification at day 2 has limited predictive value for mortality. The substantial mortality risk in severe confirmed ARDS suggests that complex interventions might best be tested in this population