237 research outputs found
Continuum Singularities of a Mean Field Theory of Collisions
Consider a complex energy for a -particle Hamiltonian and let
be any wave packet accounting for any channel flux. The time independent
mean field (TIMF) approximation of the inhomogeneous, linear equation
consists in replacing by a product or Slater
determinant of single particle states This results, under the
Schwinger variational principle, into self consistent TIMF equations
in single particle space. The method is a
generalization of the Hartree-Fock (HF) replacement of the -body homogeneous
linear equation by single particle HF diagonalizations
We show how, despite strong nonlinearities in this mean
field method, threshold singularities of the {\it inhomogeneous} TIMF equations
are linked to solutions of the {\it homogeneous} HF equations.Comment: 21 pages, 14 figure
Assembly and maturation of the U3 snoRNP in the nucleoplasm in a large dynamic multiprotein complex
Antisymmetrization of a Mean Field Calculation of the T-Matrix
The usual definition of the prior(post) interaction between
projectile and target (resp. ejectile and residual target) being contradictory
with full antisymmetrization between nucleons, an explicit antisymmetrization
projector must be included in the definition of the transition
operator, We derive the
suitably antisymmetrized mean field equations leading to a non perturbative
estimate of . The theory is illustrated by a calculation of forward
- scattering, making use of self consistent symmetries.Comment: 30 pages, no figures, plain TeX, SPHT/93/14
Is T Leonis a superoutbursting intermediate polar?
We present an XMM-Newton analysis of the cataclysmic variable T Leo. The
X-ray light curve shows sinusoidal variation on a period P_x equal to
0.89^{+0.14}_{-0.10} times the previously spectroscopically determined orbital
period. Furthermore, we find a signal in the power spectrum at 414 sec that
could be attributed to the spin period of the white dwarf. If true, T Leo would
be the first confirmed superoutbursting intermediate polar IP). The spin
profile is double-peaked with a peak separation of about 1/3 spin phases. This
appears to be a typical feature for IPs with a small magnetic field and fast
white dwarf rotation. An alternative explanation is that the 414 sec signal is
a Quasi-periodic Oscillation (QPO) that is caused by mass transfer variation
from the secondary, a bright region (``blob'') rotating in the disc at a radius
of approximately ~9 Rwd or - more likely - a travelling wave close to the inner
disc edge of a dwarf nova with a low field white dwarf. The XMM-Newton RGS
spectra reveal double peaked emission for the O VIII Ly alpha line. Scenarios
in the IP and dwarf nova model are discussed (an emitting ring in the disc,
bright X-ray spot on disc edge, or emitting accretion funnels), but the
intermediate polar model is favoured. Supported is this idea by the finding
that only the red peak appears to be shifted and the `blue' peak is compatible
with the rest wavelength. The red peak thus is caused by emission from the
northern accretion spot when it faces the observer. Instead, the peak at the
rest wavelength is caused when the southern accretion funnel is visible just on
the lower edge of the white dwarf - with the velocity of the accreting material
being perpendicular to the line of sight.Comment: 11 pages, 15 figures, accepted by A&
Procedures for the salvage and necropsy of the Dugong (Dugong Dugon)-second edition 2007
This manual provides a detailed guide for dugong (Dugong dugon) carcass handling and
necropsy procedures. It is intended to be used as a resource and training guide for anyone
involved in dugong incidents including management officers, biologists, parks and wildlife field
staff, and veterinarians and pathologists who may lack dugong expertise. Because of the wide
range of professionals this book is targeting, information and the use of technical terms is
extensive. Section 8.0 provides definitions of various terms used which are italicised throughout
the text
When lack of control enhances closeness to others : the case of unemployment and economic threat
When personal control is threatened, people often turn to their own group
and show negativity towards others. In three studies, we tested an alternative prediction that the salient lack of personal control (vs. control) experienced in the context of unemployment can lead to connectedness and
more positive perception of similar others (e.g., members of groups affected
by unemployment or the economic crisis). In two European countries, we
found experimental (Study 1: Poland) and correlational (Study 2: Spain)
evidence that a lowered sense of control of unemployed people was related
to more favorable intergroup evaluations. Furthermore, when lack of control related to unemployment threat was experimentally induced, participants perceived a Greek outgroup more positively, and this effect was
mediated by identification with and similarity to this group (Study 3). We
discuss the role of the shared experience of collective uncontrollability in
promoting positive intergroup relation
Safety and immunogenicity of a self-amplifying RNA vaccine against COVID-19: COVAC1, a phase I, dose-ranging trial
Background: Lipid nanoparticle (LNP) encapsulated self-amplifying RNA (saRNA) is a novel technology formulated as a low dose vaccine against COVID-19. Methods: A phase I first-in-human dose-ranging trial of a saRNA COVID-19 vaccine candidate LNP-nCoVsaRNA, was conducted at Imperial Clinical Research Facility, and participating centres in London, UK, between 19th June to 28th October 2020. Participants received two intramuscular (IM) injections of LNP-nCoVsaRNA at six different dose levels, 0.1-10.0Οg, given four weeks apart. An open-label dose escalation was followed by a dose evaluation. Solicited adverse events (AEs) were collected for one week from enrolment, with follow-up at regular intervals (1-8 weeks). The binding and neutralisation capacity of anti-SARS-CoV-2 antibody raised in participant sera was measured by means of an anti-Spike (S) IgG ELISA, immunoblot, SARS-CoV-2 pseudoneutralisation and wild type neutralisation assays. (The trial is registered: ISRCTN17072692, EudraCT 2020-001646-20). Findings: 192 healthy individuals with no history or serological evidence of COVID-19, aged 18-45 years were enrolled. The vaccine was well tolerated with no serious adverse events related to vaccination. Seroconversion at week six whether measured by ELISA or immunoblot was related to dose (both p<0.001), ranging from 8% (3/39; 0.1Οg) to 61% (14/23; 10.0Οg) in ELISA and 46% (18/39; 0.3Οg) to 87% (20/23; 5.0Οg and 10.0Οg) in a post-hoc immunoblot assay. Geometric mean (GM) anti-S IgG concentrations ranged from 74 (95% CI, 45-119) at 0.1Οg to 1023 (468-2236) ng/mL at 5.0Οg (p<0.001) and was not higher at 10.0Οg. Neutralisation of SARS-CoV-2 by participant sera was measurable in 15% (6/39; 0.1Οg) to 48% (11/23; 5.0Οg) depending on dose level received. Interpretation: Encapsulated saRNA is safe for clinical development, is immunogenic at low dose levels but failed to induce 100% seroconversion. Modifications to optimise humoral responses are required to realise its potential as an effective vaccine against SARS-CoV-2. Funding: This study was co-funded by grants and gifts from the Medical Research Council UKRI (MC_PC_19076), and the National Institute Health Research/Vaccine Task Force, Partners of Citadel and Citadel Securities, Sir Joseph Hotung Charitable Settlement, Jon Moulton Charity Trust, Pierre Andurand, Restore the Earth
Human Computer Interaction Meets Psychophysiology: A Critical Perspective
Human computer interaction (HCI) groups are more and more often exploring the utility of new, lower cost electroencephalography (EEG) interfaces for assessing user engagement and experience as well as for directly controlling computers. While the potential benefits of using EEG are considerable, we argue that research is easily driven by what we term naĂŻve neurorealism. That is, data obtained with psychophysiological devices have poor reliability and uncertain validity, making inferences on mental states difficult. This means that unless sufficient care is taken to address the inherent shortcomings, the contributions of psychophysiological human computer interaction are limited to their novelty value rather than bringing scientific advance. Here, we outline the nature and severity of the reliability and validity problems and give practical suggestions for HCI researchers and reviewers on the way forward, and which obstacles to avoid. We hope that this critical perspective helps to promote good practice in the emerging field of psychophysiology in HCI
Towards Zero Training for Brain-Computer Interfacing
Electroencephalogram (EEG) signals are highly subject-specific and vary considerably even between recording sessions of the same user within the same experimental paradigm. This challenges a stable operation of Brain-Computer Interface (BCI) systems. The classical approach is to train users by neurofeedback to produce fixed stereotypical patterns of brain activity. In the machine learning approach, a widely adapted method for dealing with those variances is to record a so called calibration measurement on the beginning of each session in order to optimize spatial filters and classifiers specifically for each subject and each day. This adaptation of the system to the individual brain signature of each user relieves from the need of extensive user training. In this paper we suggest a new method that overcomes the requirement of these time-consuming calibration recordings for long-term BCI users. The method takes advantage of knowledge collected in previous sessions: By a novel technique, prototypical spatial filters are determined which have better generalization properties compared to single-session filters. In particular, they can be used in follow-up sessions without the need to recalibrate the system. This way the calibration periods can be dramatically shortened or even completely omitted for these âexperiencedâ BCI users. The feasibility of our novel approach is demonstrated with a series of online BCI experiments. Although performed without any calibration measurement at all, no loss of classification performance was observed
A Generalized Framework for Quantifying the Dynamics of EEG Event-Related Desynchronization
Brains were built by evolution to react swiftly to environmental challenges. Thus, sensory stimuli must be processed ad hoc, i.e., independentâto a large extentâfrom the momentary brain state incidentally prevailing during stimulus occurrence. Accordingly, computational neuroscience strives to model the robust processing of stimuli in the presence of dynamical cortical states. A pivotal feature of ongoing brain activity is the regional predominance of EEG eigenrhythms, such as the occipital alpha or the pericentral mu rhythm, both peaking spectrally at 10 Hz. Here, we establish a novel generalized concept to measure event-related desynchronization (ERD), which allows one to model neural oscillatory dynamics also in the presence of dynamical cortical states. Specifically, we demonstrate that a somatosensory stimulus causes a stereotypic sequence of first an ERD and then an ensuing amplitude overshoot (event-related synchronization), which at a dynamical cortical state becomes evident only if the natural relaxation dynamics of unperturbed EEG rhythms is utilized as reference dynamics. Moreover, this computational approach also encompasses the more general notion of a âconditional ERD,â through which candidate explanatory variables can be scrutinized with regard to their possible impact on a particular oscillatory dynamics under study. Thus, the generalized ERD represents a powerful novel analysis tool for extending our understanding of inter-trial variability of evoked responses and therefore the robust processing of environmental stimuli
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