Persistence of internal representations of alternative voluntary actions.

We have investigated a situation in which externally available response alternatives and their internal representations could be dissociated, by suddenly removing some action alternatives from the response space during the interval between the free selection and the execution of a voluntary action. Choice reaction times in this situation were related to the number of initially available response alternatives, rather than to the number of alternatives available effectively available after the change in the external environment. The internal representations of response alternatives appeared to persist after external changes actually made the corresponding action unavailable. This suggests a surprising dynamics of voluntary action representations: counterfactual response alternatives persist, and may even be actively maintained, even when they are not available in reality. Our results highlight a representational basis for the counterfactual course of action. Such representations may play a key role in feelings of regret, disappointment, or frustration. These feelings all involve persistent representation of counterfactual response alternatives that may not actually be available in the environment

Bound electron contribution to soft x-ray laser interferograms of dense plasmas

Unpublished manuscript. Dated: April 15, 2004.Includes bibliographical references (pages 7-8).We present experimental evidence showing that the contribution of bound electrons to the index of refraction can significantly affect soft x-ray laser interferograms of laser-created plasmas. We report picosecond resolution soft x-ray laser interferograms of Al laser-created plasmas that late in their evolution display negative fringe shifts in the plasma periphery. Simulated density maps show that this results from the dominant contribution of low charge ions to the index of refraction. If neglected, the presence of significant densities of low charge ions in laser-created plasmas may result in the overestimation of the measured electron density for most materials

Volition and inhibition: Objective and subjective aspects of human volitional control

Action decisions can be directly driven by the current state of the external environment (instructed decisions); or they can be driven by internal mental states and goals, independently of the current environment (intentional decisions). Neural, behavioural and subjective data suggests that two separate neural systems may drive instructed and intentional action respectively. The distinction can be generalized beyond action itself to action inhibition, also classifiable as either instructed or intentional. However, the validity of the instructed/intentional distinction remains controversial. This thesis presents three linked sets of experiments that explored the validity and generality of the distinction, extending it in two key directions: action inhibition and subjective experience. The first group of experiments concerned decision making processes related to action and inhibition; the second focused on the period between decision making and action execution and the third on the subjective experience of intentional actions. Decision making processes were addressed by comparing electrophysiological and subjective measures prior to, during and after decisions to act or inhibit action. In the absence of external imperatives, intentional decisions may capitalize on spontaneous neural fluctuations, and show a weaker neural code than their instructed counterparts. To further explore the relative strength of intentional decisions, the period between decision making and action execution was addressed with EEG and behavioural methods. No evidence for unstable intentional decisions was found, during decision maintenance. Intentional action decisions may be strong, and persistent. Finally, two experiments directly compared the subjective experience of intentional and instructed actions. Neuroimaging results revealed possible mechanisms associated with the subjective experience of acting intentionally. Together, results support the broad distinction between instructed and intentional decisions. In particular, the coding of intentional actions may involve partial activations of alternative responses. Importantly, the thesis also demonstrates the feasibility of experimental studies addressing the subjective experience of intentional behaviour

Simulation of Water Cerenkov Detectors Using {\sc geant4}

We present a detailed simulation of the performance of water Cerenkov detectors suitable for use in the Pierre Auger Observatory. Using {\sc geant4}, a flexible object-oriented simulation program, including all known physics processes, has been developed. The program also allows interactive visualization, and can easily be modified for any experimental setup.Comment: Talk to be presented at the XI Symposium on Very High Energy Cosmic Ray Interaction

A Study of the Water Cherenkov Calorimeter

The novel idea of water Cherenkov calorimeter made of water tanks as the next generation neutrino detector for nu factories and nu beams is investigated. A water tank prototype with a dimension of 1*1*13m^3 is constructed, its performance is studied and compared with a GEANT4 based Monte Carlo simulation. By using measured parameters of the water tank, including the light collection efficiency, attenuation length, angular dependent response etc, a detailed Monte Carlo simulation demonstrates that the detector performance is excellent for identifying neutrino charged current events while rejecting neutral current and wrong-flavor backgrounds.Comment: 19 pages, 14 figures, submitted to NI

A Water Tank Cerenkov Detector for Very High Energy Astroparticles

Extensive airshower detection is an important issue in current astrophysics endeavours. Surface arrays detectors are a common practice since they are easy to handle and have a 100% duty cycle. In this work we present an experimental study of the parameters relevant to the design of a water Cerenkov detector for high energy airshowers. This detector is conceived as part of the surface array of the Pierre Auger Project, which is expected to be sensitive to ultra high energy cosmic rays. In this paper we focus our attention in the geometry of the tank and its inner liner material, discussing pulse shapes and charge collections.Comment: Accepted in Nucl. Instr. and Meth. A, LaTex 18 pages, 7 figure

Limited metacognitive access to one’s own facial expressions

As humans we communicate important information through fine nuances in our facial expressions, but because conscious motor representations are noisy, we might not be able to report these fine but meaningful movements. Here we measured how much explicit metacognitive information young adults have about their own facial expressions. Participants imitated pictures of themselves making facial expressions and triggered a camera to take a picture of them while doing so. They then rated confidence (how well they thought they imitated each expression). We defined metacognitive access to facial expressions as the relationship between objective performance (how well the two pictures matched) and subjective confidence ratings. Metacognitive access to facial expressions was very poor when we considered all face features indiscriminately. Instead, machine learning analyses revealed that participants rated confidence based on idiosyncratic subsets of features. We conclude that metacognitive access to own facial expressions is partial, and surprisingly limited

Multiphoton Reactive Surfaces Using Ruthenium(II) Photocleavable Cages

Photoreactive surfaces derived from a new photocleavable surface modification agent and with photosensitivity in the Vis and IR region are described. A ruthenium(II) caged aminosilane, [Ru(bpy)₂(PMe₃)(APTS)](PF₆)₂, was synthesized and attached to silica surfaces. Light irradiation removed the cage and generated surface patterns with reactive amine groups. The photosensitivity of this compound under single (460 nm) and two-photon (900) excitation is demonstrated. Functional patterns with site-selective attachment of other molecular species are described.A.d.C., O.F., and R.E. thank the DFG (444ARG113/8/1-0) for financial support. The authors thank Beatriz García (INQUIMAE) for helping with the synthesis part, Andreas Best (MPIP) for the laser scanning experiments, and Juan P. Fernández-Blázquez (MPIP) for help the contrast measurements. R.E. is staff member of CONICET

Dense plasma interferometry with a tabletop soft X-ray laser and an amplitude division interferometer based on diffraction gratings

Includes bibliographical references (page 486).We have demonstrated a novel Mach-Zehnder soft x-ray interferometer that uses diffraction gratings as beam splitters. The interferometer was used together with a 46.9nm tabletop soft x-ray laser, to map the evolution of the electron density distribution of a large-scale laser created plasma