3,809 research outputs found
Selfish traffic allocation for server farms
We study the price of selfish routing in noncooperative networks like the Internet. In particular, we investigate the price of selfish routing using the price of anarchy (a.k.a. the coordination ratio) and other (e.g., bicriteria) measures in the recently introduced game theoretic parallel links network model of Koutsoupias and Papadimitriou. We generalize this model toward general, monotone families of cost functions and cost functions from queueing theory. A summary of our main results for general, monotone cost functions is as follows: 1. We give an exact characterization of all cost functions having a bounded/unbounded price of anarchy. For example, the price of anarchy for cost functions describing the expected delay in queueing systems is unbounded. 2. We show that an unbounded price of anarchy implies an extremely high performance degradation under bicriteria measures. In fact, the price of selfish routing can be as high as a bandwidth degradation by a factor that is linear in the network size. 3. We separate the game theoretic (integral) allocation model from the (fractional) flow model by demonstrating that even a very small or negligible amount of integrality can lead to a dramatic performance degradation. 4. We unify recent results on selfish routing under different objectives by showing that an unbounded price of anarchy under the min-max objective implies an unbounded price of anarchy under the average cost objective and vice versa. Our special focus lies on cost functions describing the behavior of Web servers that can open only a limited number of Transmission Control Protocol (TCP) connections. In particular, we compare the performance of queueing systems that serve all incoming requests with servers that reject requests in case of overload. Our analysis indicates that all queueing systems without rejection cannot give any reasonable guarantee on the expected delay of requests under selfish routing even when the injected load is far away from the capacity of the system. In contrast, Web server farms that are allowed to reject requests can guarantee a high quality of service for every individual request stream even under relatively high injection rates
Sequential Filtering Processes Shape Feature Detection in Crickets: A Framework for Song Pattern Recognition.
Intraspecific acoustic communication requires filtering processes and feature detectors in the auditory pathway of the receiver for the recognition of species-specific signals. Insects like acoustically communicating crickets allow describing and analysing the mechanisms underlying auditory processing at the behavioral and neural level. Female crickets approach male calling song, their phonotactic behavior is tuned to the characteristic features of the song, such as the carrier frequency and the temporal pattern of sound pulses. Data from behavioral experiments and from neural recordings at different stages of processing in the auditory pathway lead to a concept of serially arranged filtering mechanisms. These encompass a filter for the carrier frequency at the level of the hearing organ, and the pulse duration through phasic onset responses of afferents and reciprocal inhibition of thoracic interneurons. Further, processing by a delay line and coincidence detector circuit in the brain leads to feature detecting neurons that specifically respond to the species-specific pulse rate, and match the characteristics of the phonotactic response. This same circuit may also control the response to the species-specific chirp pattern. Based on these serial filters and the feature detecting mechanism, female phonotactic behavior is shaped and tuned to the characteristic properties of male calling song.Supported by the Biotechnology and Biological Sciences Research Council (BB/J01835X/1) and the Isaac Newton Trust (Trinity College, Cambridge).This is the final version of the article. It first appeared from Frontiers via http://dx.doi.org/10.3389/fphys.2016.0004
and systems at threshold: II. The effect of D waves
Using the two-body interactions obtained from a chiral constituent quark
model we study all and states with I=0,1,2 and
J=1/2,3/2 at threshold, taking into account all three-body configurations with
S and D wave components. We constrain further the limits for the
spin-triplet scattering length a_{1/2,1}. Using the hypertriton binding energy
we find a narrow interval for the possible values of the
spin-singlet scattering length a_{1/2,0}. We found that the system
has a quasibound state in the (I,J) = (1,1/2) channel very near threshold with
a width of about 2.1 MeV.Comment: 19 pages, 4 tables, 6 figures. Accepted for publication in Phys. Rev.
Off-nadir antenna bias correction using Amazon rain sigma(0) data
The radar response from the Amazon rain forest was studied to determine the suitability of this region for use as a standard target to calibrate a scatterometer like that proposed for the National Oceanic Satellite System (NOSS). Backscattering observations made by the SEASAT Scatterometer System (SASS) showed the Amazon rain forest to be a homogeneous, azimuthally-isotropic, radar target which was insensitive to polarization. The variation with angle of incidence was adequately modeled as scattering coefficient (dB) = a theta b with typical values for the incidence-angle coefficient from 0.07 to 0.15 dB/deg. A small diurnal effect occurs, with measurements at sunrise being 0.5 dB to 1 dB higher than the rest of the day. Maximum-likelihood estimation algorithms presented here permit determination of relative bias and true pointing angle for each beam. Specific implementation of these algorithms for the proposed NOSS scatterometer system is also discussed
Mutually unbiased bases for the rotor degree of freedom
We consider the existence of a continuous set of mutually unbiased bases for
the continuous and periodic degree of freedom that describes motion on a circle
(rotor degree of freedom). By a singular mapping of the circle to the line, we
find a first, but somewhat unsatisfactory, continuous set which does not relate
to an underlying Heisenberg pair of complementary observables. Then, by a
nonsingular mapping of the discrete angular momentum basis of the rotor onto
the Fock basis for linear motion, we construct such a Heisenberg pair for the
rotor and use it to obtain a second, fully satisfactory, set of mutually
unbiased bases.Comment: 9 pages, 4 figure
Off-nadir antenna bias correction using Amazon rain forest sigma deg data
The radar response from the Amazon rain forest was studied to determine the suitability of this region for use as a standard target to calibrate a scatterometer like that proposed for the National Ocean Satellite System (NOSS). Backscattering observations made by the SEASAT-1 scatterometer system show the Amazon rain forest to be a homogeneous, azimuthally-isotropic, radar target which is insensitive to polarization. The variation with angle of incidence may be adequately modeled as sigma deg (dB) = alpha theta + beta with typical values for the incidence-angle coefficient from 0.07 dB deg to 0.15 dB/deg. A small diurnal effect occurs, with measurements at sunrise being 0.5 dB to 1 dB higher than the rest of the day. Maximum likelihood estimation algorithms are presented which permit determination of relative bias and true pointing angle for each beam. Specific implementation of these algorithms for the proposed NOSS scatterometer system is also discussed
Deep resequencing of the voltage-gated potassium channel subunit KCNE3 gene in chronic tinnitus
Membrane-stabilizing drugs have long been used for the treatment of chronic tinnitus, suggesting an underlying disturbance of sensory excitability due to changes in ion conductance. The present study addresses the potassium channel subunit gene KCNE3 as a potential candidate for tinnitus susceptibility. 288 Caucasian outpatients with a diagnosis of chronic tinnitus were systematically screened for mutations in the KCNE3 open reading frame and in the adjacent region by direct sequencing. Allele frequencies were determined for 11 known variants of which two (F66F and R83H) were polymorphic but were not associated with the disorder. No novel variants were identified and only three carriers of R83H were noted. However, owing to a lack of power, our study can neither rule out effects of KCNE3 on the risk for developing chronic tinnitus, nor can it exclude a role in predicting the severity of tinnitus. More extensive investigations are invited, including tests for possible effects of variation in this ion channel protein on the response to treatment
Codes for Key Generation in Quantum Cryptography
As an alternative to the usual key generation by two-way communication in
schemes for quantum cryptography, we consider codes for key generation by
one-way communication. We study codes that could be applied to the raw key
sequences that are ideally obtained in recently proposed scenarios for quantum
key distribution, which can be regarded as communication through symmetric
four-letter channels.Comment: IJQI format, 13 pages, 1 tabl
Mutually unbiased bases in dimension six: The four most distant bases
We consider the average distance between four bases in dimension six. The
distance between two orthonormal bases vanishes when the bases are the same,
and the distance reaches its maximal value of unity when the bases are
unbiased. We perform a numerical search for the maximum average distance and
find it to be strictly smaller than unity. This is strong evidence that no four
mutually unbiased bases exist in dimension six. We also provide a two-parameter
family of three bases which, together with the canonical basis, reach the
numerically-found maximum of the average distance, and we conduct a detailed
study of the structure of the extremal set of bases.Comment: 10 pages, 2 figures, 1 tabl
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