17,997 research outputs found
Improved Second-Order Bounds for Prediction with Expert Advice
This work studies external regret in sequential prediction games with both
positive and negative payoffs. External regret measures the difference between
the payoff obtained by the forecasting strategy and the payoff of the best
action. In this setting, we derive new and sharper regret bounds for the
well-known exponentially weighted average forecaster and for a new forecaster
with a different multiplicative update rule. Our analysis has two main
advantages: first, no preliminary knowledge about the payoff sequence is
needed, not even its range; second, our bounds are expressed in terms of sums
of squared payoffs, replacing larger first-order quantities appearing in
previous bounds. In addition, our most refined bounds have the natural and
desirable property of being stable under rescalings and general translations of
the payoff sequence
Suzaku Confirms NGC~3660 is an Unabsorbed Seyfert 2
An enigmatic group of objects, unabsorbed Seyfert 2s may have intrinsically
weak broad line regions, obscuration in the line of sight to the BLR but not to
the X-ray corona, or so much obscuration that the X-ray continuum is completely
suppressed and the observed spectrum is actually scattered into the line of
sight from nearby material. NGC 3660 has been shown to have weak broad
optical/near infrared lines, no obscuration in the soft X-ray band, and no
indication of "changing look" behavior. The only previous hard X-ray detection
of this source by Beppo-SAX seemed to indicate that the source might harbor a
heavily obscured nucleus. However, our analysis of a long-look Suzaku
observation of this source shows that this is not the case, and that this
source has a typical power law X-ray continuum with normal reflection and no
obscuration. We conclude that NGC 3660 is confirmed to have no unidentified
obscuration and that the anomolously high Beppo-SAX measurement must be due to
source confusion or similar, being inconsistent with our Suzaku measurements as
well as non-detections from Swift-BAT and RXTE.Comment: Accepted to PAS
Anti-Fall: A Non-intrusive and Real-time Fall Detector Leveraging CSI from Commodity WiFi Devices
Fall is one of the major health threats and obstacles to independent living
for elders, timely and reliable fall detection is crucial for mitigating the
effects of falls. In this paper, leveraging the fine-grained Channel State
Information (CSI) and multi-antenna setting in commodity WiFi devices, we
design and implement a real-time, non-intrusive, and low-cost indoor fall
detector, called Anti-Fall. For the first time, the CSI phase difference over
two antennas is identified as the salient feature to reliably segment the fall
and fall-like activities, both phase and amplitude information of CSI is then
exploited to accurately separate the fall from other fall-like activities.
Experimental results in two indoor scenarios demonstrate that Anti-Fall
consistently outperforms the state-of-the-art approach WiFall, with 10% higher
detection rate and 10% less false alarm rate on average.Comment: 13 pages,8 figures,corrected version, ICOST conferenc
RealPen: Providing Realism in Handwriting Tasks on Touch Surfaces using Auditory-Tactile Feedback
We present RealPen, an augmented stylus for capacitive tablet screens that recreates the physical sensation of writing on paper with a pencil, ball-point pen or marker pen. The aim is to create a more engaging experience when writing on touch surfaces, such as screens of tablet computers. This is achieved by regenerating the friction-induced oscillation and sound of a real writing tool in contact with paper. To generate realistic tactile feedback, our algorithm analyzes the frequency spectrum of the friction oscillation generated when writing with traditional tools, extracts principal frequencies, and uses the actuator's frequency response profile for an adjustment weighting function. We enhance the realism by providing the sound feedback aligned with the writing pressure and speed. Furthermore, we investigated the effects of superposition and fluctuation of several frequencies on human tactile perception, evaluated the performance of RealPen, and characterized users' perception and preference of each feedback type
Massive higher spins and holography
We review recent progress towards the understanding of higher spin gauge
symmetry breaking in AdS space from a holographic vantage point. According to
the AdS/CFT correspondence, N=4 SYM theory at vanishing coupling constant
should be dual to a theory in AdS which exhibits higher spin gauge symmetry
enhancement. When the SYM coupling is non-zero, all but a handful of HS
currents are violated by anomalies, and correspondingly local higher spin
symmetry in the bulk gets spontaneously broken. In agreement with previous
results and holographic expectations, we find that, barring one notable
exception (spin 1 eating spin 0), the Goldstone modes responsible for HS
symmetry breaking in AdS have non-vanishing mass even in the limit in which the
gauge symmetry is restored. We show that spontaneous breaking a' la
Stueckelberg implies that the mass of the relevant spin s'=s-1 Goldstone field
is exactly the one predicted by the correspondence.Comment: 8 pages, talk presented by M.B. at the "Fourth Meeting on Constrained
Dynamics and Quantum gravity" held in Cala Gonone (Sardinia, Italy),
September 12-16, 200
Simple model for quantum general relativity from loop quantum gravity
New progress in loop gravity has lead to a simple model of `general-covariant
quantum field theory'. I sum up the definition of the model in self-contained
form, in terms accessible to those outside the subfield. I emphasize its
formulation as a generalized topological quantum field theory with an infinite
number of degrees of freedom, and its relation to lattice theory. I list the
indications supporting the conjecture that the model is related to general
relativity and UV finite.Comment: 8 pages, 3 figure
An efficient algorithm for learning with semi-bandit feedback
We consider the problem of online combinatorial optimization under
semi-bandit feedback. The goal of the learner is to sequentially select its
actions from a combinatorial decision set so as to minimize its cumulative
loss. We propose a learning algorithm for this problem based on combining the
Follow-the-Perturbed-Leader (FPL) prediction method with a novel loss
estimation procedure called Geometric Resampling (GR). Contrary to previous
solutions, the resulting algorithm can be efficiently implemented for any
decision set where efficient offline combinatorial optimization is possible at
all. Assuming that the elements of the decision set can be described with
d-dimensional binary vectors with at most m non-zero entries, we show that the
expected regret of our algorithm after T rounds is O(m sqrt(dT log d)). As a
side result, we also improve the best known regret bounds for FPL in the full
information setting to O(m^(3/2) sqrt(T log d)), gaining a factor of sqrt(d/m)
over previous bounds for this algorithm.Comment: submitted to ALT 201
Thermal-Hall conductivity and long-lived quasiparticles in CeCoIn
In CeCoIn, the thermal conductivity and Hall conductivity
below display large anomalies below . The strong
suppression of the anomalies in weak fields implies the existence of long-lived
quasiparticles. We also discuss briefly the Wiedemann-Franz ratio and the
existence of a strongly field-dependent spin-fluctuation heat current.Comment: 2 pages, 2 figures, proceedings of M2S-HTSC-VIII, Dresden 200
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