A sequential nanopore-channel device for polymer separation.

In this work, we investigated whether a series of nanopores connected by channels can be used to separate polymer mixtures by molecular size. We conducted multiscale coarse-grained simulations of semiflexible polymers driven through such a device. Polymers were modelled as chains of beads near the nanopores and as single particles in the bulk of the channels. Since polymers rarely escape back into the bulk of the channels after coming sufficiently close to the nanopores, the more computationally expensive simulations near the pores were decoupled from those in the bulk. The distribution of polymer positions after many translocations was deduced mathematically from simulations across a single nanopore-channel pair, under the reasonable assumption of identical and independent dynamics in each channel and each nanopore. Our results reveal rich polymer dynamics in the nanopore-channel device and suggest that it can indeed produce polymer separation. As expected, the mean time to translocate across a single nanopore increases with the chain length. Conversely, the mean time to cross the channels from one nanopore to the next decreases with the chain length, as smaller chains explore more of the channel volume between translocations. As such, the time between translocations is a function of the length and width of the channels. Depending on the channel dimensions, polymers are sorted by increasing length, decreasing length, or non-monotonically by length such that polymers of an intermediate size emerge first.

Translocation Time through a Nanopore with an Internal Cavity Is Minimal for Polymers of Intermediate Length.

The translocation of polymers through nanopores with large internal cavities bounded by two narrow pores is studied via Langevin dynamics simulations. The total translocation time is found to be a nonmonotonic function of polymer length, reaching a minimum at intermediate length, with both shorter and longer polymers taking longer to translocate. The location of the minimum is shown to shift with the magnitude of the applied force, indicating that the pore can be dynamically tuned to favor different polymer lengths. A simple model balancing the effects of entropic trapping within the cavity against the driving force is shown to agree well with simulations. Beyond the nonmonotonicity, detailed analysis of translocation uncovers rich dynamics in which factors such as going to a high force regime and the emergence of a tail for long polymers dramatically change the behavior of the system. These results suggest that nanopores with internal cavities can be used for applications such as selective extraction of polymers by length and filtering of polymer solutions, extending the uses of nanopores within emerging nanofluidic technologies.

Randomized Controlled Trial of Radiation Protection With a Patient Lead Shield and a Novel, Nonlead Surgical Cap for Operators Performing Coronary Angiography or Intervention.

BACKGROUND: Interventional cardiologists receive one of the highest levels of annual occupational radiation exposure. Further measures to protect healthcare workers are needed. METHODS AND RESULTS: We evaluated the efficacy of a pelvic lead shield and a novel surgical cap in reducing operators' radiation exposure. Patients undergoing coronary angiography or percutaneous coronary intervention (n=230) were randomized to have their procedure with or without a lead shield (Ultraray Medical, Oakville, Canada) placed over the patient. During all procedures, operators wore the No Brainer surgical cap (Worldwide Innovations and Technology, Kansas City, KS) designed to protect the head from radiation exposure. The coprimary outcomes for the lead shield comparison were (1) operator dose (µSv) and (2) operator dose indexed for air kerma (µSv/mGy). For the cap comparison, the primary outcome was the difference between total radiation dose (µSv; internal and external to cap). The lead shield use resulted in a 76% reduction in operator dose (mean dose, 3.07; 95% confidence interval [CI], 2.00-4.71 µSv lead shield group versus 12.57; 95% CI, 8.14-19.40 µSv control group; P<0.001). The mean dose indexed for air kerma was reduced by 72% (0.004; 95% CI, 0.003-0.005 µSv/mGy lead shield group versus 0.015; 95% CI, 0.012-0.019 µSv/mGy control group; P<0.001). The cap use resulted in a significant reduction in operator head radiation exposure (mean left temporal difference [external-internal] radiation dose was 4.79 [95% CI, 3.30-6.68] µSv; P<0.001). CONCLUSIONS: The use of a pelvic lead shield and the cap reduced significantly the operator radiation exposure and can be easily incorporated into clinical practice. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02128035.

Design of a hybrid computational fluid dynamics-monte carlo radiation transport methodology for radioactive particulate resuspension studies.

There are numerous scenarios where radioactive particulates can be displaced by external forces. For example, the detonation of a radiological dispersal device in an urban environment will result in the release of radioactive particulates that in turn can be resuspended into the breathing space by external forces such as wind flow in the vicinity of the detonation. A need exists to quantify the internal (due to inhalation) and external radiation doses that are delivered to bystanders; however, current state-of-the-art codes are unable to calculate accurately radiation doses that arise from the resuspension of radioactive particulates in complex topographies. To address this gap, a coupled computational fluid dynamics and Monte Carlo radiation transport approach has been developed. With the aid of particulate injections, the computational fluid dynamics simulation models characterize the resuspension of particulates in a complex urban geometry due to air-flow. The spatial and temporal distributions of these particulates are then used by the Monte Carlo radiation transport simulation to calculate the radiation doses delivered to various points within the simulated domain. A particular resuspension scenario has been modeled using this coupled framework, and the calculated internal (due to inhalation) and external radiation doses have been deemed reasonable. GAMBIT and FLUENT comprise the software suite used to perform the Computational Fluid Dynamics simulations, and Monte Carlo N-Particle eXtended is used to perform the Monte Carlo Radiation Transport simulations.

MEDECOR--a medical decorporation tool to assist first responders, receivers, and medical reach-back personnel in triage, treatment, and risk assessment after internalization of radionuclides.

After a radiological dispersal device (RDD) event, it is possible for radionuclides to enter the human body through inhalation, ingestion, and skin and wound absorption. From a health physics perspective, it is important to know the magnitude of the intake to perform dosimetric assessments. From a medical perspective, removal of radionuclides leading to dose aversion (hence risk reduction) is of high importance. The efficacy of medical decorporation strategies is extremely dependent upon the time of treatment delivery after intake. The "golden hour," or more realistically 3-4 h, is optimal when attempting to increase removal of radionuclides from extracellular fluids prior to cellular incorporation. To assist medical first response personnel in making timely decisions regarding appropriate treatment delivery modes, it is desirable to have a software tool that compiles existing radionuclide decorporation therapy data and allows a user to perform simple diagnosis leading to optimized decorporation treatment strategies. In its most simple application, the software is a large database of radionuclide decorporation strategies and treatments. The software can also be used in clinical interactive mode, in which the user inputs the radionuclide, estimated activity, route of intake and time since exposure. The software makes suggestions as to the urgency of treatment (i.e., triage) and the suggested therapy. Current developments include risk assessment which impacts the potential risk of delivered therapy and resource allocation of therapeutic agents. The software, developed for the Canadian Department of National Defence (DND), is titled MEDECOR (MEdical DECORporation). The MEDECOR tool was designed for use on both personal digital assistant and laptop computer environments. The tool was designed using HTML/Jscript, to allow for ease of portability amongst different computing platforms. This paper presents the features of MEDECOR, results of testing at a major NATO exercise, and future development of this tool into MEDECOR2.