Processing irrelevant location information: practice and transfer effects in a Simon task.

How humans produce cognitively driven fine motor movements is a question of fundamental importance in how we interact with the world around us. For example, we are exposed to a constant stream of information and we must select the information that is most relevant by which to guide our actions. In the present study, we employed a well-known behavioral assay called the Simon task to better understand how humans are able to learn to filter out irrelevant information. We trained subjects for four days with a visual stimulus presented, alternately, in central and lateral locations. Subjects responded with one hand moving a joystick in either the left or right direction. They were instructed to ignore the irrelevant location information and respond based on color (e.g. red to the right and green to the left). On the fifth day, an additional testing session was conducted where the task changed and the subjects had to respond by shape (e.g. triangle to the right and rectangle to the left). They were instructed to ignore the color and location, and respond based solely on the task relevant shape. We found that the magnitude of the Simon effect decreases with training, however it returns in the first few trials after a break. Furthermore, task-defined associations between response direction and color did not significantly affect the Simon effect based on shape, and no significant associative learning from the specific stimulus-response features was found for the centrally located stimuli. We discuss how these results are consistent with a model involving route suppression/gating of the irrelevant location information. Much of the learning seems to be driven by subjects learning to suppress irrelevant location information, however, this seems to be an active inhibition process that requires a few trials of experience to engage

Operator related attenuation effects in radiometric surveys

Radiometric surveys using airborne, vehicular mounted or backpack detector systems are increasingly used to identify and evaluate complex distributions of radioactivity in the environment. The signals detected depend on the energy and spatial distribution of radioactive sources, the material properties of the environment and the specific properties of the detector systems employed. Materials in close vicinity to the detector such as housings, and intermediate materials may have a critical impact on detection efficiency, and must therefore be taken into account in calibration. This study evaluates the effect of shielding by the body of the operator in backpack surveys. Controlled experiments using point sources and absorbers, chosen to represent the form and composition of human tissue, were conducted, and coupled to an analytical radiation transport model to estimate attenuation factors for mapping of 137Cs. In this way generic factors to correct for this effect using portable spectrometers have been determined. The results compare well with observations at sampled calibration sites in Fukushima and the Solway area in Scotland. Reductions of the 137Cs full-energy peak intensity between 20% and 30% may be expected depending on operator stature and the offset position of backpack systems. Similar effects may be present for other radiometric systems carried by a human operator

Development of Hemic Neoplasia in the Soft-Shell Clam (Mya arenaria) Along the East Coast of the United States

Hemic neoplasia (HN) is a bivalve disease characterized by uncontrolled proliferation of abnormal hemocytes that invade solid tissue, similar to vertebrate leukemia, ultimately leading to death. High disease prevalence has been reported in many bivalve populations, yet disease etiology and development remain minimally understood. In this study, nine East Coast populations of soft-shell clams (Mya arenaria) were evaluated between 2011-2012 to identify environmental and health factors associated with HN. PCA analysis and statistical testing were used to compare data at and between each population based on HN status. The percentage of organisms with terminal stage 4 HN (76-100% neoplastic cells) was used to group sites into those of high and low disease incidence; with average terminal HN of 6.46% and 28.15% and organismal survival of 60.8% and 20.2% detected for low and high HN sites, respectively. Analysis revealed pollutants including PCBs (Aroclor 1221), PAHs (pyrene and fluoranthene), organochlorinated pesticides (methoxychlor, toxaphene, endrin, BHCs, aldrin, Endosulfan, and heptachlor) and heavy metals (iron, aluminum, chromium, copper, nickel, and zinc); as well as sediment organic content were strongly associated with HN prevalence and survival. On average, high HN sites displayed 1422 mg/kg total pollutants and 49.2% organic content, while low HN sites displayed 388 mg/kg and 36.5%, respectively. Water temperature was also associated with HN and mortality, emphasizing concerns about rising ocean temperatures associated with climate change. Overall, higher pollutant levels or elevated water temperatures increased HN incidence indicating disease transmission through viral infection is likely due to reduced immunity in M. arenaria

Mechanisms affecting post-activation potentiation following voluntary isokinetic knee extension

The present research was designed to: 1) determine whether the voluntary PAP effects commonly observed after conditioning activity (CA; i.e. muscular contraction prior to a ‘test’ contraction) are a consequence of acute neuromuscular alterations relating to the CA itself, or whether they simply reflect warm-up and/or familiarisation effects; 2) clarify the influence of the contraction velocity, duration and total work characteristics of the CA on voluntary PAP; 3) determine the factors allowing stronger individuals to express higher level of voluntary PAP; and 4) determine the peripheral and central mechanisms of voluntary PAP in human skeletal muscle. In Study 1, the effects of different contraction velocity, duration and total work characteristics on PAP were examined after a complete warm-up. The contributions of peripheral and central mechanisms to PAP were also examined. Voluntary and electrically-evoked torques and electromyogram (EMG) data were captured before and after five different dynamic (isokinetic) CAs, after the participants had completed an extensive warm-up including extensive task-specific practice to the point where maximal voluntary contractile capacity was achieved. Vastus lateralis (VL) EMG amplitude normalised to the muscle compound action potentiation (M-wave) amplitude (EMG:M), was taken as a measure of central drive whereas twitch peak torque and M-wave amplitude were recorded to assess peripheral function. Even after a plateau in voluntary contractile capacity was achieved after the complete warm-up, the imposition of CAs elicited significant increases in both voluntary and twitch torques (i.e., PAP). CAs with longer total contraction duration (6s) and a minimum total work of ~750-900 J produced PAP, regardless of the velocity of the CA. No changes in EMG:M were detected after any CA suggesting that central drive was not a major factor influencing PAP under the present experimental conditions. However, the increases in twitch peak torques with lack of change in Mwave amplitude suggest that peripheral function, possibly including changes in myosin regulatory light chain (RLC) phosphorylation and increased intracellular Ca2+ release and sensitivity may have contributed to the observed PAP. It is clear from the literature and the results of Study 1 that there is a significant inter-individual variability in the PAP phenomenon. Typically, stronger individuals are able to express higher levels of PAP but it is unclear why this occurs. Therefore, in Study 2 peak knee extensor torque at 60o·s-1, quadriceps and VL crosssectional area (CSA) and volume, and the type II myosin heavy chain (MHC) isoform percentage (VL) were measured to determine their relative contribution to PAP elicited under voluntary conditions. There were large to very large correlations between PAP magnitude and peak knee extensor torque at 60o·s-1 (r=0.62), quadriceps (r=0.68) and VL (r=0.62) CSA, and quadriceps (r=0.63) and VL (r=0.65) volume. Nonetheless, these correlations were not statistically significant after adjusting for the influence of type II MHC percentage (using partial correlation analysis). By contrast, the strongest correlation was observed for type II MHC percentage (r=0.77), and this correlation remained significant (r=0.56-0.66) after adjusting for other variables. This finding suggests that PAP magnitude is most clearly associated with the type II MHC isoform percentage in the human quadriceps femoris. This might be explained by the fact that myosin RLC phosphorylation, one proposed mechanism responsible for PAP, has been shown to be greater in type II MHC isoforms. The results of Study 1 and Study 2 suggest that changes at the peripheral level, possibly including changes in myosin RLC phosphorylation (and increased intracellular Ca2+ release and sensitivity) may be a primary candidate mechanism of PAP induced by a voluntary CA, although more direct measurements are required to test this assumption. Therefore, tetanic stimulations and maximal isokinetic knee extensions at 180o·s-1 were used in Study 3 to provide a more detailed investigation of the role of changes in the excitation-contraction (E-C) coupling process (i.e. changes in myosin RLC phosphorylation or increased intracellular Ca2+ release and sensitivity) to the PAP response induced by a voluntary CA. Torques produced during voluntary knee extensions, 20 Hz and catch-inducing (20-Hz train preceded by a double pulse with 5-ms interval) stimulation trains, the 20- vs. 80-Hz torque ratio (20:80) as well as the force-augmenting effect of the catch-inducing train were recorded before and after a voluntary CA or a control condition (no CA, rest). Statistically significant increases in voluntary torque, torques elicited by 20-Hz and catch-inducing trains, and 20:80 were observed 1, 4 and 7 min after the CA. Moreover, the force-augmenting effects of the catch-inducing train diminished as the magnitude of PAP increased and then increased as the magnitude of PAP diminished. Statistically significant correlations (r=0.50-0.81) were also found between the changes in voluntary torque production (i.e. PAP) and the changes in these variables. These results suggest that increases in PAP following a voluntary CA are strongly associated with changes in peripheral function, most probably changes in the E-C coupling efficiency.

Weak Lensing Reconstruction and Power Spectrum Estimation: Minimum Variance Methods

Large-scale structure distorts the images of background galaxies, which allows one to measure directly the projected distribution of dark matter in the universe and determine its power spectrum. Here we address the question of how to extract this information from the observations. We derive minimum variance estimators for projected density reconstruction and its power spectrum and apply them to simulated data sets, showing that they give a good agreement with the theoretical minimum variance expectations. The same estimator can also be applied to the cluster reconstruction, where it remains a useful reconstruction technique, although it is no longer optimal for every application. The method can be generalized to include nonlinear cluster reconstruction and photometric information on redshifts of background galaxies in the analysis. We also address the question of how to obtain directly the 3-d power spectrum from the weak lensing data. We derive a minimum variance quadratic estimator, which maximizes the likelihood function for the 3-d power spectrum and can be computed either from the measurements directly or from the 2-d power spectrum. The estimator correctly propagates the errors and provides a full correlation matrix of the estimates. It can be generalized to the case where redshift distribution depends on the galaxy photometric properties, which allows one to measure both the 3-d power spectrum and its time evolution.Comment: revised version, 36 pages, AAS LateX, submitted to Ap

The dual parameterization of the proton generalized parton distribution functions H and E and description of the DVCS cross sections and asymmetries

We develop the minimal model of a new leading order parameterization of GPDs introduced by Shuvaev and Polyakov. The model for GPDs H and E is formulated in terms of the forward quark distributions, the Gegenbauer moments of the D-term and the forward limit of the GPD E. The model is designed primarely for small and medium-size values of x_B, x_B \leq 0.2. We examined two different models of the t-dependence of the GPDs: The factorized exponential model and the non-factorized Regge-motivated model. Using our model, we successfully described the DVCS cross section measured by H1 and ZEUS, the moments of the beam-spin A_{LU}^{\sin \phi}, beam-charge A_{C}^{\cos \phi} and transversely-polarized target A_{UT}^{\sin \phi \cos \phi} DVCS asymmetries measured by HERMES and A_{LU}^{\sin \phi} measured by CLAS. The data on A_{C}^{\cos \phi} prefers the Regge-motivated model of the t-dependence of the GPDs. The data on A_{UT}^{\sin \phi \cos \phi} indicates that the u and d quarks carry only a small fraction of the proton total angular momentum.Comment: 33 pages, 11 figure

Reconstruction methods — P‾ANDA focussing-light guide disc DIRC

The Focussing-Lightguide Disc DIRC will provide crucial Particle Identification (PID) information for the P‾ANDA experiment at FAIR, GSI. This detector presents a challenging environment for reconstruction due to the complexity of the expected hit patterns and the operating conditions of the P‾ANDA experiment. A discussion of possible methods to reconstruct PID from this detector is given here. Reconstruction software is currently under development