2,711 research outputs found
Triangle-generation in topological D-brane categories
Tachyon condensation in topological Landau-Ginzburg models can generally be
studied using methods of commutative algebra and properties of triangulated
categories. The efficiency of this approach is demonstrated by explicitly
proving that every D-brane system in all minimal models of type ADE can be
generated from only one or two fundamental branes.Comment: 34 page
Preliminary results using a P300 brain-computer interface speller: a possible interaction effect between presentation paradigm and set of stimuli
FernĂĄndez-RodrĂguez Ă., Medina-JuliĂĄ M.T., Velasco-Ălvarez F., Ron-Angevin R. (2019) Preliminary Results Using a P300 Brain-Computer Interface Speller: A Possible Interaction Effect Between Presentation Paradigm and Set of Stimuli. In: Rojas I., Joya G., Catala A. (eds) Advances in Computational Intelligence. IWANN 2019. Lecture Notes in Computer Science, vol 11506. Springer, ChamSeveral proposals to improve the performance controlling a P300-based BCI speller have been studied using the standard row-column presentation (RCP) par-adigm. However, this paradigm could not be suitable for those patients with lack of gaze control. To solve that, the rapid serial visual presentation (RSVP) para-digm, which presents the stimuli located in the same position, has been proposed in previous studies. Thus, the aim of the present work is to assess if a stimuli set of pictures that improves the performance in RCP, could also improve the per-formance in a RSVP paradigm. Six participants have controlled four conditions in a calibration task: letters in RCP, pictures in RCP, letters in RSVP and pictures in RSVP. The results showed that pictures in RCP obtained the best accuracy and information transfer rate. The improvement effect given by pictures was greater in the RCP paradigm than in RSVP. Therefore, the improvements reached under RCP may not be directly transferred to the RSVP.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
Heat-flux footprints for I-mode and EDA H-mode plasmas on Alcator C-Mod
IR thermography is used to measure the heat flux footprints on C-Modâs outer target in I-mode and EDA H-mode plasmas. The footprint profiles are fit to a function with a simple physical interpretation. The fit parameter that is sensitive to the power decay length into the SOL, λ[subscript SOL], is ~1â3Ă larger in I-modes than in H-modes at similar plasma current, which is the dominant dependence for the H-mode λ[subscript SOL]. In contrast, the fit parameter sensitive to transport into the private-flux-zone along the divertor leg is somewhat smaller in I-mode than in H-mode, but otherwise displays no obvious dependence on I[subscript p], B[subscript t], or stored energy. A third measure of the footprint width, the âintegral widthâ, is not significantly different between H- and I-modes. Also discussed are significant differences in the global power flows of the H-modes with âfavorableâ âB drift direction and those of the I-modes with âunfavorableâ âB drift direction.United States. Dept. of Energy (Cooperative Agreement DE-FC02-99-ER54512
BNCI systems as a potential assistive technology: ethical issues and participatory research in the BrainAble project
This paper highlights aspects related to current research and thinking about ethical issues in relation to Brain Computer Interface (BCI) and Brain-Neuronal Computer Interfaces (BNCI) research through the experience of one particular project, BrainAble, which is exploring and developing the potential of these technologies to enable people with complex disabilities to control computers. It describes how ethical practice has been developed both within the multidisciplinary research team and with participants. Results: The paper presents findings in which participants shared their views of the project prototypes, of the potential of BCI/BNCI systems as an assistive technology, and of their other possible applications. This draws attention to the importance of ethical practice in projects where high expectations of technologies, and representations of âideal typesâ of disabled users may reinforce stereotypes or drown out participant âvoicesâ. Conclusions: Ethical frameworks for research and development in emergent areas such as BCI/BNCI systems should be based on broad notions of a âduty of careâ while being sufficiently flexible that researchers can adapt project procedures according to participant needs. They need to be frequently revisited, not only in the light of experience, but also to ensure they reflect new research findings and ever more complex and powerful technologies
Tree-Level Stability Without Spacetime Fermions: Novel Examples in String Theory
Is perturbative stability intimately tied with the existence of spacetime
fermions in string theory in more than two dimensions? Type 0'B string theory
in ten-dimensional flat space is a rare example of a non-tachyonic,
non-supersymmetric string theory with a purely bosonic closed string spectrum.
However, all known type 0' constructions exhibit massless NSNS tadpoles
signaling the fact that we are not expanding around a true vacuum of the
theory. In this note, we are searching for perturbatively stable examples of
type 0' string theory without massless tadpoles in backgrounds with a spatially
varying dilaton. We present two examples with this property in non-critical
string theories that exhibit four- and six-dimensional Poincare invariance. We
discuss the D-branes that can be embedded in this context and the type of gauge
theories that can be constructed in this manner. We also comment on the
embedding of these non-critical models in critical string theories and their
holographic (Little String Theory) interpretation and propose a general
conjecture for the role of asymptotic supersymmetry in perturbative string
theory.Comment: harvmac, 29 pages; v2 minor changes, version to appear in JHE
Supersymmetric Orientifolds of Gepner Models
Supersymmetric orientifolds of four dimensional Gepner Models are constructed
in a systematic way. For all levels of the Gepner model being odd the generic
expression for both the A-type and the B-type Klein bottle amplitude is
derived. The appearing massless tadpoles are canceled by introducing
appropriate boundary states of Recknagel/Schomerus(RS). After determining the
Moebius strip amplitude we extract general expressions for the tadpole
cancellation conditions. We discuss the issue of chirality for such
supersymmetric orientifold models and finally present a couple of examples in
detail.Comment: 38 pages, TeX harvmac, ref. adde
Probing Orientifold Behavior Near NS Branes
The effect of NS 5 branes on an orientifold is studied. The orientifold is
allowed to pass through a pile of k NS branes forming a regularized CHS
geometry. Its effect on open strings in its vicinity is used to study the
change in the orientifold charge induced by the NS branes.Comment: Important references added, 30 pages, 8 figure
DBI analysis of generalised permutation branes
We investigate D-branes on the product GxG of two group manifolds described
as Wess-Zumino-Novikov-Witten models. When the levels of the two groups
coincide, it is well known that there exist permutation D-branes which are
twisted by the automorphism exchanging the two factors. When the levels are
different, the D-brane charge group demands that there should be
generalisations of these permutation D-branes, and a geometric construction for
them was proposed in hep-th/0509153. We give further evidence for this proposal
by showing that the generalised permutation D-branes satisfy the
Dirac-Born-Infeld equations of motion for arbitrary compact, simply connected
and simple Lie groups G.Comment: 19 pages, computation in section 3.5.1 corrected, conclusions
unchange
Brane Boxes: Bending and Beta Functions
We study the type IIB brane box configurations recently introduced by Hanany
and Zaffaroni. We show that even at finite string coupling, one can construct
smooth configurations of branes with fairly arbitrary gauge and flavor
structure. Limiting our attention to the better understood case where NS-branes
do not intersect over a four dimensional surface gives some restrictions on the
theories, but still permits many examples, both anomalous and non-anomalous. We
give several explicit examples of such configurations and discuss what
constraints can be imposed on brane-box theories from bending considerations.
We also discuss the relation between brane bending and beta-functions for
brane-box configurations.Comment: latex, 18 pages, 8 figure
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