691 research outputs found
The benefit of a 1-bit jump-start, and the necessity of stochastic encoding, in jamming channels
We consider the problem of communicating a message in the presence of a
malicious jamming adversary (Calvin), who can erase an arbitrary set of up to
bits, out of transmitted bits . The capacity of such
a channel when Calvin is exactly causal, i.e. Calvin's decision of whether or
not to erase bit depends on his observations was
recently characterized to be . In this work we show two (perhaps)
surprising phenomena. Firstly, we demonstrate via a novel code construction
that if Calvin is delayed by even a single bit, i.e. Calvin's decision of
whether or not to erase bit depends only on (and
is independent of the "current bit" ) then the capacity increases to
when the encoder is allowed to be stochastic. Secondly, we show via a novel
jamming strategy for Calvin that, in the single-bit-delay setting, if the
encoding is deterministic (i.e. the transmitted codeword is a deterministic
function of the message ) then no rate asymptotically larger than is
possible with vanishing probability of error, hence stochastic encoding (using
private randomness at the encoder) is essential to achieve the capacity of
against a one-bit-delayed Calvin.Comment: 21 pages, 4 figures, extended draft of submission to ISIT 201
Upper Bounds on the Capacity of Binary Channels with Causal Adversaries
In this work we consider the communication of information in the presence of
a causal adversarial jammer. In the setting under study, a sender wishes to
communicate a message to a receiver by transmitting a codeword
bit-by-bit over a communication channel. The sender and the receiver do not
share common randomness. The adversarial jammer can view the transmitted bits
one at a time, and can change up to a -fraction of them. However, the
decisions of the jammer must be made in a causal manner. Namely, for each bit
the jammer's decision on whether to corrupt it or not must depend only on
for . This is in contrast to the "classical" adversarial
jamming situations in which the jammer has no knowledge of , or
knows completely. In this work, we present upper bounds (that
hold under both the average and maximal probability of error criteria) on the
capacity which hold for both deterministic and stochastic encoding schemes.Comment: To appear in the IEEE Transactions on Information Theory; shortened
version appeared at ISIT 201
Evaluation of allelopathic potential of selected plant species on Parthenium hysterophorus
The phytotoxicity of shoot leachates of selected plant species was assessed on germination, and on shootcut and seedling bioassays of Parthenium hysterophorus. Shoot leachates of selected plant species were effective in inhibiting germination of Parthenium seeds, with Azardirachta indica the most effective. Shoot growth was inhibited most, and shoots damaged the most, by leachates of Solanum nigrum
An algorithm for the estimation of bounds on the emissivity and temperatures from thermal multispectral airborne remotely sensed data
The effective flux incident upon the detectors of a thermal sensor, after it has been corrected for atmospheric effects, is a function of a non-linear combination of the emissivity of the target for that channel and the temperature of the target. The sensor system cannot separate the contribution from the emissivity and the temperature that constitute the flux value. A method that estimates the bounds on these temperatures and emissivities from thermal data is described. This method is then tested with remotely sensed data obtained from NASA's Thermal Infrared Multispectral Scanner (TIMS) - a 6 channel thermal sensor. Since this is an under-determined set of equations i.e. there are 7 unknowns (6 emissivities and 1 temperature) and 6 equations (corresponding to the 6 channel fluxes), there exist theoretically an infinite combination of values of emissivities and temperature that can satisfy these equations. Using some realistic bounds on the emissivities, bounds on the temperature are calculated. These bounds on the temperature are refined to estimate a tighter bound on the emissivity of the source. An error analysis is also carried out to quantitatively determine the extent of uncertainty introduced in the estimate of these parameters. This method is useful only when a realistic set of bounds can be obtained for the emissivities of the data. In the case of water the lower and upper bounds were set at 0.97 and 1.00 respectively. Five flights were flown in succession at altitudes of 2 km (low), 6 km (mid), 12 km (high), and then back again at 6 km and 2 km. The area selected with the Ross Barnett reservoir near Jackson, Mississippi. The mission was flown during the predawn hours of 1 Feb. 1992. Radiosonde data was collected for that duration to profile the characteristics of the atmosphere. Ground truth temperatures using thermometers and radiometers were also obtained over an area of the reservoir. The results of two independent runs of the radiometer data averaged 7.03 plus or minus .70 for the first run and 7.31 plus or minus .88 for the second run. The results of the algorithm yield a temperature of 7.68 for the low altitude data to 8.73 for the high altitude data
Multi-resolution processing for fractal analysis of airborne remotely sensed data
Fractal geometry is increasingly becoming a useful tool for modeling natural phenomenon. As an alternative to Euclidean concepts, fractals allow for a more accurate representation of the nature of complexity in natural boundaries and surfaces. Since they are characterized by self-similarity, an ideal fractal surface is scale-independent; i.e. at different scales a fractal surface looks the same. This is not exactly true for natural surfaces. When viewed at different spatial resolutions parts of natural surfaces look alike in a statistical manner and only for a limited range of scales. Images acquired by NASA's Thermal Infrared Multispectral Scanner are used to compute the fractal dimension as a function of spatial resolution. Three methods are used to determine the fractal dimension - Schelberg's line-divider method, the variogram method, and the triangular prism method. A description of these methods and the results of applying these methods to a remotely-sensed image is also presented. Five flights were flown in succession at altitudes of 2 km (low), 6 km (mid), 12 km (high), and then back again at 6 km and 2 km. The area selected was the Ross Barnett reservoir near Jackson, Mississippi. The mission was flown during the predawn hours of 1 Feb. 1992. Radiosonde data was collected for that duration to profile the characteristics of the atmosphere. This corresponds to 3 different pixel sizes - 5m, 15m, and 30m. After, simulating different spatial sampling intervals within the same image for each of the 3 image sets, the results are cross-correlated to compare the extent of detail and complexity that is obtained when data is taken at lower spatial intervals
Superconducting-coil--resistor circuit with electric field quadratic in the current
It is shown for the first time that the observed [Phys. Lett. A 162 (1992)
105] potential difference Phi_t between the resistor and the screen surrounding
the circuit is caused by polarization of the resistor because of the kinetic
energy of the electrons of the superconducting coil. The proportionality of
Phi_t to the square of the current and to the length of the superconducting
wire is explained. It is pointed out that measuring Phi_t makes it possible to
determine the Fermi quasimomentum of the electrons of a metal resistor.Comment: 2 pages, 1 figur
Approche markovienne pour la segmentation 3D des tissus cérébraux en IRM
La segmentation des matières grise, blanche et liquide céphalo-rachidien (LCR) en IRM est rendue difficile due à l'effet de volume partiel. Pour s'affranchir de ce problème, nous proposons un modèle de classes mixtes. Le nombre de classes dans un volume d'encéphale est choisi égal à cinq, ce qui est confirmé par l'analyse de l'histogramme. En utilisant une modélisation par champs aléatoires de Markov, notre méthode estime les pourcentages de trois tissus purs dans chaque voxel en deux étapes. Dans un premier temps, les cinq classes ( trois classes purs et deux classes supplémentaires correspondant aux mélanges matières grise-matière blanche et matière grise-LCR) sont segmentées. Les volumes partiels sont ensuite estimés sur les deux classes mixtes. La méthode a été testée sur plusieurs volumes cérébraux en IRM anatomique
Circulating microRNAs are associated with Paroxysmal or Persistent Atrial Fibrillation
Introduction: Novel methods of identifying individuals at risk for atrial fibrillation (AF) are needed. MicroRNAs (MiRNAs) regulate gene expression in a number of cardiovascular diseases, including AF. It is unknown, however, if key circulating, cardiac-specific miRNAs differ between individuals with paroxysmal or persistent AF and those in sinus rhythm.
Methods: 17 individuals with a history of AF were recruited prior to catheter ablation. 24 hospitalized patients in normal sinus rhythm and no history of AF comprised the control group. 94 plasma miRNAs were selected based on a priori associations with processes implicated in AF for evaluation using the TaqMan miRNA expression profiling system.
Results:We found that miRNA expression differed by at least 2-fold for 14 miRNAs, including several previously implicated in cardiovascular remodeling and disease (Figure 1). Levels of miR-7, miR-208, and miR-302b were statistically significantly up- or down-regulated in AF patients relative to controls (p
Application: Although power was limited by the modest sample size, these data support the rationale for using circulating miRNA as AF biomarkers. Moreover, since miRNA can modulate disease pathways, miRNA-based therapeutics would theoretically enable targeting of novel gene regulatory pathways implicated in AF in a unique and powerful manner.
Next Steps/ Future: Further investigations involving well-characterized, large samples from longitudinal studies with standardized miRNA assessment and evaluation for AF are required to validate the observed associations
Extraction et partitionnement de l'encéphale par un modèle de contours actifs
La segmentation des structures anatomiques à partir d'IRM fait maintenant l'objet d'un intérêt certain. Pour améliorer la qualité de la segmentation, l'idée proposée est de combiner la segmentation région et la segmentation contour. La segmentation région permet d'avoir une initialisation automatique approximative pour l'approche contours. Cette dernière assimile le contour à un certain nombre de masses ponctuelles reliées par des ressorts , converge vers un état d'équilibre sous l'action d 'une déformation élastique. Les résultats sont présentés pour l'extraction et le partitionnement de l'encéphale sur des données IRM 3D chez l'être humain et le primate. Ces résultats sont ensuite validés par des mesures comme le taux de recouvrement et la carte de distance
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