Time-Resolved Structural Kinetics of an Organic Mixed Ionic–Electronic Conductor

The structure and packing of organic mixed ionic–electronic conductors have an especially significant effect on transport properties. In operating devices, this structure is not fixed but is responsive to changes in electrochemical potential, ion intercalation, and solvent swelling. Toward this end, the steady-state and transient structure of the model organic mixed conductor, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is characterized using multimodal time-resolved operando techniques. Steady-state operando X-ray scattering reveals a doping-induced lamellar expansion of 1.6 Å followed by 0.4 Å relaxation at high doping levels. Time-resolved operando X-ray scattering reveals asymmetric rates of lamellar structural change during doping and dedoping that do not directly depend on potential or charging transients. Time-resolved spectroscopy establishes a link between structural transients and the complex kinetics of electronic charge carrier subpopulations, in particular the polaron–bipolaron equilibrium. These findings provide insight into the factors limiting the response time of organic mixed-conductor-based devices, and present the first real-time observation of the structural changes during doping and dedoping of a conjugated polymer system via X-ray scattering.     

Organochlorines in Greenland lake sediments and landlocked Arctic char (Salvelinus alpinus)

Lake sediments and landlocked Arctic char (Salvelinus alpinus) were sampled in 1994 and 1995 at four different locations in Greenland, three at the west coast and one at the east coast. Sediments, char muscle and char liver were analysed for PCBs (10 congeners), DDTs (pp'), HCHs (alpha, beta, gamma), dieldrin, HCB and chlordanes (5) and char in addition to toxaphene (total and 4 congeners). All organochlorines in the sediment samples were below the detection limit of 0.1 microgram kg-1 dry wt., while the overall geometric means in Arctic char muscle were, in microgram kg-1 wet wt., for PCBs 11 (range 1-140), for DDTs 4.0 (1-35), for HCHs 0.4 (0.06-1.5), for dieldrin 0.7 (< 0.1-4.2), for HCB 0.7 (0.09-3.8), for chlordanes 4.8 (1-57) and for total toxaphene 13 (1-180). The sums of PCBs, DDTs, chlordanes and total toxaphene disclosed higher concentrations in muscle of char from the east coast compared to char from the west coast. Dieldrin and HCB showed the same tendency, but less pronounced, while the sum of HCHs were found in highest concentrations at the west coast. PCB, DDT, chlordane and toxaphene concentrations showed a decreasing trend following the East Greenland Current. Principal component analysis on PCB congeners showed that the proportion of higher chlorinated PCBs (Cl > 5) were higher in Qaqortoq in south Greenland compared to the three other sampling areas in Greenland. However, no correlation was seen either between degree of chlorination and latitude or between degree of chlorination and PCB concentrations.     

Neurocognitive signs in prodromal Huntington disease.

Objective: PREDICT-HD is a large-scale international study of people with the Huntington disease (HD) CAG-repeat expansion who are not yet diagnosed with HD. The objective of this study was to determine the stage in the HD prodrome at which cognitive differences from CAG-normal controls can be reliably detected. Method: For each of 738 HD CAG-expanded participants, we computed estimated years to clinical diagnosis and probability of diagnosis in 5 years based on age and CAG-repeat expansion number (Langbehn, Brinkman, Falush, Paulsen, & Hayden, 2004). We then stratified the sample into groups: NEAR, estimated to be ≤9 years; MID, between 9 and 15 years; and FAR, ≥15 years. The control sample included 168 CAG-normal participants. Nineteen cognitive tasks were used to assess attention, working memory, psychomotor functions, episodic memory, language, recognition of facial emotion, sensory–perceptual functions, and executive functions. Results: Compared with the controls, the NEAR group showed significantly poorer performance on nearly all of the cognitive tests and the MID group on about half of the cognitive tests (p = .05, Cohen's d NEAR as large as ?1.17, MID as large as ?0.61). One test even revealed significantly poorer performance in the FAR group (Cohen's d = ?0.26). Individual tasks accounted for 0.2% to 9.7% of the variance in estimated proximity to diagnosis. Overall, the cognitive battery accounted for 34% of the variance; in comparison, the Unified Huntington's Disease Rating Scale motor score accounted for 11.7%. Conclusions: Neurocognitive tests are robust clinical indicators of the disease process prior to reaching criteria for motor diagnosis of HD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimizing Thermal-Optical Methods for Measuring Atmospheric Elemental (Black) Carbon: A Response Surface Study

The chemical, physical, and morphological complexity of atmospheric aerosol elemental carbon (EC) presents major problems in assuring measurement accuracy. Since EC and black carbon are often considered equivalent, methods based on thermal-optical analysis (TOA) are widely used for EC in ambient air samples because no prior knowledge of the aerosol's absorption coefficient is required. Nevertheless, different TOA thermal desorption protocols result in wide EC-to-total-carbon (TC) variation. We created three response surfaces with the following response variables: EC/TC, maximum laser attenuation in the He phase ( L max ), and laser attenuation at the end of the He phase ( L He4 ). A two-level central-composite factorial design comprised of four factors considered the temperatures and durations of all desorption steps in TOA's inert (He) phase and the initial step in TOA's oxidizing (O 2 -He) phase. L max was used to assess the positive bias caused by nonvolatile unpyrolized organic carbon (OC char) being measured as native EC. A negative bias that the attenuated laser response does not detect is caused by the loss of native EC in the He phase. L He4 was used as a surrogate indicator for the loss of native EC in the He phase. The intersection between the L max and L He4 surfaces revealed TOA conditions where both the production of OC char in the He phase was maximized and the loss of native EC in the He phase was minimized, therefore leading to an optimized thermal desorption protocol. Based on the sample types used in this study, the following are generalized optimal conditions when TOA is operated in the fixed-step-durations, laser-transmission mode (i.e., TOT): step 1 in He, 190°C for 60 s; step 2 in He, 365°C for 60 s; step 3 in He, 610°C for 60 s; step 4 in He, 835°C for 72 s. For steps 1-4 in O 2 -He, the conditions are 550°C for 180 s, 700°C for 60 s, 850°C for 60 s, and 900°C for 90 s to 120 s, respectively.     

Endothelin receptor blockade prevents the rise in pulmonary vascular resistance after cardiopulmonary bypass in lambs with increased pulmonary blood flow

BACKGROUND: Children with increased pulmonary blood flow may experience morbidity as the result of increased pulmonary vascular resistance after operations in which cardiopulmonary bypass is used. Plasma levels of endothelin-1, a potent vasoactive substance implicated in pulmonary hypertension, are increased after cardiopulmonary bypass. OBJECTIVES: In a lamb model of increased pulmonary blood flow after in utero placement of an aortopulmonary shunt, we characterized the changes in pulmonary vascular resistance induced by hypothermic cardiopulmonary bypass and investigated the role of endothelin-1 and endothelin-A receptor activation in postbypass pulmonary hypertension. METHODS: In eleven 1-month-old lambs, the shunt was closed, and vascular pressures and blood flows were monitored. An infusion of a selective endothelin-A receptor blocker (PD 156707; 1.0 mg/kg/h) or drug vehicle (saline solution) was then begun 30 minutes before cardiopulmonary bypass and continued for 4 hours after bypass. The hemodynamic variables were monitored, and plasma endothelin-1 concentrations were determined before, during, and for 6 hours after cardiopulmonary bypass. RESULTS: After 90 minutes of hypothermic cardiopulmonary bypass, both pulmonary arterial pressure and pulmonary vascular resistance increased significantly in saline-treated lambs during the 6-hour study period (P <.05). In lambs pretreated with PD 156707, pulmonary arterial pressure and pulmonary vascular resistance decreased (P <. 05). After bypass, plasma endothelin-1 concentrations increased in all lambs; there was a positive correlation between postbypass pulmonary vascular resistance and plasma endothelin-1 concentrations (P <.05). CONCLUSIONS: This study suggests that endothelin-A receptor-induced pulmonary vasoconstriction mediates, in part, the rise in pulmonary vascular resistance after cardiopulmonary bypass. Endothelin-A receptor antagonists may decrease morbidity in children at risk for postbypass pulmonary hypertension. This potential therapy warrants further investigation.     

A computational model for tracking subsurface tissue deformation during stereotactic neurosurgery

Recent advances in the field of stereotactic neurosurgery have made it possible to coregister preoperative computed tomography (CT) and magnetic resonance (MR) images with instrument locations in the operating field. However, accounting for intraoperative movement of brain tissue remains a challenging problem. While intraoperative CT and MR scanners record concurrent tissue motion, there is motivation to develop methodologies which would be significantly lower in cost and more widely available. The approach we present is a computational model of brain tissue deformation that could be used in conjunction with a limited amount of concurrently obtained operative data to estimate subsurface tissue motion. Specifically, we report on the initial development of a finite element model of brain tissue adapted from consolidation theory. Validations of the computational mathematics in two and three dimensions are shown with errors of 1%-2% for the discretizations used. Experience with the computational strategy for estimating surgically induced brain tissue motion in vivo is also presented. While the predicted tissue displacements differ from measured values by about 15%, they suggest that exploiting a physics-based computational framework for updating preoperative imaging databases during the course of surgery has considerable merit. However, additional model and computational developments are needed before this approach can become a clinical reality.     

Effects of protein-surface interactions on protein ion signals in MALDI mass spectrometry

The influence of polymer surface-protein binding affinity on protein ion signals in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is examined. The surfaces of poly(vinylidene fluoride) and poly(ethylene terephthalate) polymer substrates are modified by pulsed rf plasma deposition of allylamine. By varying the on/off duty cycle of the pulsed rf plasma, the polymer substrate surfaces are coated with thin films having varying densities of surface amine groups. The varying surface amine density is shown to lead to systematic changes in the surface binding affinity for the 125I-radiolabeled peptides angiotensin I and porcine insulin. Unlabeled angiotensin I and porcine insulin are then deposited on the pulsed rf plasma-modified substrates and analyzed by MALDI mass spectrometry. The experimental approach involves applying the peptide to the modified polymer surface in an aqueous phosphate-buffered saline solution and allowing the peptide solution to dry completely under ambient conditions. Subsequently, the MALDI matrix alpha-cyano-4-hydroxycinnamic acid in methanol and 10% trifluoroacetic acid in water are added to the peptide-coated modified polymer surfaces. The results of these studies demonstrate that, for the sample preparation method employed, increases in the surface peptide binding affinity lead to decreases in the peptide MALDI ion signal.     

Salmonella in meat from hunted game: A Central European perspective

The occurrence of Salmonella in meat from game hunted in Europe is reviewed, with a focus on Central Europe. Prevalence in fecal samples is different according to region and game species, ranging from < 5 (wild ruminants) to ca. 20% (wild boar). The pathogen is rarely recovered from carcasses or meat cuts of wild ruminants (< 1%). Prevalences on wild boar carcasses have been reported to range from < 1 to ca. 7%, the tonsils presumably constituting a main reservoir on the eviscerated carcass. On meat cuts from game, recent German and EU (EFSA) reports indicate a prevalence of < 1%. A number of Salmonella enterica serovars can be isolated, with highest prevalences of S. Typhimurium and S. Enteritidis. Persistence of these pathogens in wildlife is a less pressing issue for biology and wildlife conservation than for public health experts, which has been recognized in the framework of zoonoses legislation. On one hand, wildlife is exposed to salmonellae originating from farm animals and humans, and on the other hand, game can be a source of Salmonella in farm animals. Breeding game under intensified conditions (farmed game) as well as extensive breeding of farm animals, notably pigs, can create new epidemiological situations. The pathway of Salmonella from intestinal content of the live animal to individual meat cuts can be described in qualitative terms, yet the relative contribution of the various factors remains to be quantified, which complicates proper risk assessment. Control of Salmonella in the game meat chain is in part based on Good Hygiene Practice from killing and evisceration to chilling and skinning, whereas more detailed data are needed in order to allow risk-based meat inspection.     

A broadband high-frequency electrical impedance tomography system for breast imaging.

Bio-electric impedance signatures arise primarily from differences in cellular morphologies within an organ and can be used to differentiate benign and malignant pathologies, specifically in the breast. Electrical impedance tomography (EIT) is an imaging modality that determines the impedance distribution within tissue and has been used in prior work to map the electrical properties of breast at signal frequencies ranging from a few kHz to 1 MHz. It has been suggested that by extending the frequency range, additional information of clinical significance may be obtained. We have, therefore, developed a new EIT system for breast imaging which covers the frequency range from 10 kHz to 10 MHz. The instrument developed here is a distributed processor tomograph with 64 channels, capable of generating and measuring voltages and currents. Electrical benchmarking has shown the system to have a SNR greater than 94 dB up to 2 MHz, 90 dB up to 7 MHz, and 65 dB at 10 MHz. In addition, the system measures impedances to an accuracy of 99.7 % and has channel-to-channel variations of less than 0.05 %. Phantom imaging has demonstrated the ability to image across the entire frequency range in both single- and multiplane configurations. Further, 96 women have participated safely in breast exams with the system and the associated conductivity spectra obtained from 3-D image reconstructions range from 0.0237 S/m at 10 kHz to 0.2174 S/m at 10 MHz. These findings are consistent with impedance values reported in the literature.