914 research outputs found
Is the P300 Speller Independent?
The P300 speller is being considered as an independent brain-computer
interface. That means it measures the user's intent, and does not require the
user to move any muscles. In particular it should not require eye fixation of
the desired character. However, it has been shown that posterior electrodes
provide significant discriminative information, which is likely related to
visual processing. These findings imply the need for studies controlling the
effect of eye movements. In experiments with a 3x3 character matrix, attention
and eye fixation was directed to different characters. In the event-related
potentials, a P300 occurred for the attended character, and N200 was seen for
the trials showing the focussed character. It occurred at posterior sites,
reaching its peak at 200ms after stimulus onset. The results suggest that gaze
direction plays an important role in P300 speller paradigm. By controlling gaze
direction it is possible to separate voluntary and involuntary EEG responses to
the highlighting of characters.Comment: 7 pages, 5 figure
Effective Theory for a Heavy Scalar Coupled to the SM via Vector-Like Quarks
We illustrate the application of the recently developed SCET
framework in the context of a specific model, in which the Standard Model (SM)
is supplemented by a heavy scalar and three generations of heavy,
vector-like quarks . We construct the appropriate effective field theory
for two-body decays of into SM particles. We explicitly compute the Wilson
coefficients of the SCET operators appearing at leading and
next-to-leading order (NLO) in an expansion in powers of , as well as
for a subset of operators arising at NNLO, retaining the full dependence on the
ratio . For the phenomenologically most relevant decay channels of
the heavy scalar, we study the impact of resummation effects of Sudakov
logarithms on the decay rates.Comment: 11 pages, 6 figure
Exclusive Radiative Decays of Z Bosons in QCD Factorization
We discuss the very rare, exclusive hadronic decays of a Z boson into a meson
and a photon. The QCD factorization approach allows to organize the decay
amplitude as an expansion in powers of , where the
leading terms contain convolutions of perturbatively calculable hard functions
with the leading-twist light-cone distribution amplitudes of the meson. We find
that power corrections to these leading terms are negligible since they are
suppressed by the small ratio .
Renormalization-group effects play a crucial role as they render our
theoretical predictions less sensitive to the hadronic input parameters which
are currently not known very precisely. Thus, measurements of the decays at the LHC or a future lepton collider provide a theoretically very
clean way to test the QCD factorization approach. The special case where
is complicated by the fact that the decay amplitude receives
an additional contribution where the meson is formed from a two-gluon state.
The corresponding branching ratios are very sensitive to the hadronic
parameters describing the system. Future measurements of these
decays could yield interesting information about these parameters and the gluon
distribution amplitude.Comment: 6 pages, 3 figures, 1 table, contribution to the proceedings of the
38th International Conference on High Energy Physics, 3-10 August 2016,
Chicago, US
Shortest Distances as Enumeration Problem
We investigate the single source shortest distance (SSSD) and all pairs
shortest distance (APSD) problems as enumeration problems (on unweighted and
integer weighted graphs), meaning that the elements -- where
and are vertices with shortest distance -- are produced and
listed one by one without repetition. The performance is measured in the RAM
model of computation with respect to preprocessing time and delay, i.e., the
maximum time that elapses between two consecutive outputs. This point of view
reveals that specific types of output (e.g., excluding the non-reachable pairs
, or excluding the self-distances ) and the order of
enumeration (e.g., sorted by distance, sorted row-wise with respect to the
distance matrix) have a huge impact on the complexity of APSD while they appear
to have no effect on SSSD.
In particular, we show for APSD that enumeration without output restrictions
is possible with delay in the order of the average degree. Excluding
non-reachable pairs, or requesting the output to be sorted by distance,
increases this delay to the order of the maximum degree. Further, for weighted
graphs, a delay in the order of the average degree is also not possible without
preprocessing or considering self-distances as output. In contrast, for SSSD we
find that a delay in the order of the maximum degree without preprocessing is
attainable and unavoidable for any of these requirements.Comment: Updated version adds the study of space complexit
Subleading Shape Functions in Inclusive B Decays
The contributions of subleading shape functions to inclusive decay
distributions of B mesons are derived from a systematic two-step matching of
QCD current correlators onto soft-collinear and heavy-quark effective theory.
At tree-level, the results can be expressed in terms of forward matrix elements
of bi-local light-cone operators. Four-quark operators, which arise at O(g^2),
are included. Their effects can be absorbed entirely into a redefinition of
other shape functions. Our results are in disagreement with some previous
studies of subleading shape-function effects in the literature. A numerical
analysis of B->X_u+l+nu decay distributions suggests that power corrections are
small, with the possible exception of the endpoint region of the charged-lepton
energy spectrum.Comment: 22 pages, 2 figures; several typos corrected; version published in
JHE
Proposal for a Precision Measurement of |Vub|
A new method for a precision measurement of the CKM matrix element |Vub| is
discussed, which combines good theoretical control with high efficiency and a
powerful discrimination against charm background. The resulting combined
theoretical uncertainty on |Vub| is estimated to be 10%.Comment: 4 pages, 2 figures, RevTe
Radiatively corrected shape function for inclusive heavy hadron decays
We discuss the non-perturbative and the radiative corrections to inclusive B
decays from the point of view known from QED corrections to high energy e^+ e^-
processes. Here the leading contributions can be implemented through the so
called ``radiator function'' which corresponds to the shape function known in
heavy hadron decays. In this way some new insight into the origin of the shape
function is obtained. As a byproduct, a parameterization of the radiatively
corrected shape function is suggested which can be implemented in Monte Carlo
studies of inclusive heavy hadron decays.Comment: LaTeX, uses a4, graphicx and psfrag, 10 pages. The complete paper is
also available at http://www-ttp.physik.uni-karlsruhe.de/Preprints
Niche differentiation of two sympatric species of Microdochium colonizing the roots of common reed
<p>Abstract</p> <p>Background</p> <p>Fungal endophyte communities are often comprised of many species colonizing the same host. However, little is known about the causes of this diversity. On the one hand, the apparent coexistence of closely related species may be explained by the traditional niche differentiation hypothesis, which suggests that abiotic and/or biotic factors mediate partitioning. For endophytes, such factors are difficult to identify, and are therefore in most cases unknown. On the other hand, there is the neutral hypothesis, which suggests that stochastic factors may explain high species diversity. There is a need to investigate to what extent each of these hypotheses may apply to endophytes.</p> <p>Results</p> <p>The niche partitioning of two closely related fungal endophytes, <it>Microdochium bolleyi </it>and <it>M. phragmitis</it>, colonizing <it>Phragmites australis</it>, was investigated. The occurrences of each species were assessed using specific nested-PCR assays for 251 field samples of common reed from Lake Constance, Germany. These analyses revealed niche preferences for both fungi. From three niche factors assessed, i.e. host habitat, host organ and season, host habitat significantly differentiated the two species. <it>M. bolleyi </it>preferred dry habitats, whereas <it>M. phragmitis </it>prevailed in flooded habitats. In contrast, both species exhibited a significant preference for the same host organ, i.e. roots. Likewise the third factor, season, did not significantly distinguish the two species. Differences in carbon utilization and growth temperature could not conclusively explain the niches. The inclusion of three unrelated species of Ascomycota, which also colonize <it>P. australis </it>at the same locations, indicated spatio-temporal niche partitioning between all fungi. None of the species exhibited the same preferences for all three factors, i.e. host habitat, host organ, and time of the season.</p> <p>Conclusions</p> <p>The fungal species colonizing common reed investigated in this study seem to exploit niche differences leading to a separation in space and time, which may allow for their coexistence on the same host. A purely neutral model is unlikely to explain the coexistence of closely related endophytes on common reed.</p
Visual Place Recognition: A Tutorial
Localization is an essential capability for mobile robots. A rapidly growing
field of research in this area is Visual Place Recognition (VPR), which is the
ability to recognize previously seen places in the world based solely on
images. This present work is the first tutorial paper on visual place
recognition. It unifies the terminology of VPR and complements prior research
in two important directions: 1) It provides a systematic introduction for
newcomers to the field, covering topics such as the formulation of the VPR
problem, a general-purpose algorithmic pipeline, an evaluation methodology for
VPR approaches, and the major challenges for VPR and how they may be addressed.
2) As a contribution for researchers acquainted with the VPR problem, it
examines the intricacies of different VPR problem types regarding input, data
processing, and output. The tutorial also discusses the subtleties behind the
evaluation of VPR algorithms, e.g., the evaluation of a VPR system that has to
find all matching database images per query, as opposed to just a single match.
Practical code examples in Python illustrate to prospective practitioners and
researchers how VPR is implemented and evaluated.Comment: IEEE Robotics & Automation Magazine (RAM
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