19,772 research outputs found
The invalidity of a strong capacity for a quantum channel with memory
The strong capacity of a particular channel can be interpreted as a sharp
limit on the amount of information which can be transmitted reliably over that
channel. To evaluate the strong capacity of a particular channel one must prove
both the direct part of the channel coding theorem and the strong converse for
the channel. Here we consider the strong converse theorem for the periodic
quantum channel and show some rather surprising results. We first show that the
strong converse does not hold in general for this channel and therefore the
channel does not have a strong capacity. Instead, we find that there is a scale
of capacities corresponding to error probabilities between integer multiples of
the inverse of the periodicity of the channel. A similar scale also exists for
the random channel.Comment: 7 pages, double column. Comments welcome. Repeated equation removed
and one reference adde
Exoplanetary atmosphere target selection in the era of comparative planetology
The large number of new planets expected from wide-area transit surveys means
that follow-up transmission spectroscopy studies of their atmospheres will be
limited by the availability of telescope assets. We argue that telescopes
covering a broad range of apertures will be required, with even 1m-class
instruments providing a potentially important contribution. Survey strategies
that employ automated target selection will enable robust population studies.
As part of such a strategy, we propose a decision metric to pair the best
target to the most suitable telescope, and demonstrate its effectiveness even
when only primary transit observables are available. Transmission spectroscopy
target selection need not therefore be impeded by the bottle-neck of requiring
prior follow-up observations to determine the planet mass. The decision metric
can be easily deployed within a distributed heterogeneous network of telescopes
equipped to undertake either broadband photometry or spectroscopy. We show how
the metric can be used either to optimise the observing strategy for a given
telescope (e.g. choice of filter) or to enable the selection of the best
telescope to optimise the overall sample size. Our decision metric can also
provide the basis for a selection function to help evaluate the statistical
completeness of follow-up transmission spectroscopy datasets. Finally, we
validate our metric by comparing its ranked set of targets against lists of
planets that have had their atmospheres successfully probed, and against some
existing prioritised exoplanet lists.Comment: 20 pages, 16 figures, 3 tables. Revision 3, accepted by MNRAS.
Improvements include always using planetary masses where available and
reliable, treatment for sky backgrounds and out-of-transit noise and a use
case for defocused photometr
The kinetics of surfactant desorption at the airâsolution interface
The kinetics of desorption of the anionic surfactant sodium dodecylbenzene sulfonate at the airâsolution interface have been studied using neutron reflectivity (NR). The experimental arrangement incorporates a novel flow cell in which the subphase can be exchanged (diluted) using a laminar flow whilst the surface region remains unaltered. The kinetics of the desorption is relatively slow and occurs over many tens of minutes compared with the dilution timescale of approximately 10â30 minutes. A detailed mathematical model, in which the rate of the desorption is determined by transport through a near-surface diffusion layer into a diluted bulk solution below, is developed and provides a good description of the timedependent adsorption data.\ud
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A key parameter of the model is the ratio of the depth of the diffusion layer, Hc , to the depth of the fluid, Hf, and we find that this is related to the reduced PĂ©clet number, Pe*, for the system, via Hc/Hf, = C/Pe* 1/ 2 . Although from a highly idealised experimental arrangement, the results provide an important insight into the ârinse mechanismâ, which is applicable to a wide variety of domestic and industrial circumstances
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Cortical distance determines whether flankers cause crowding or the tilt illusion
Differences between target and flanker orientations become exaggerated in the tilt illusion. However, small differences sometimes go unnoticed. This small-angle assimilation shares many similarities with other types of visual crowding but is typically found only with small and/or hard-to-see stimuli. In Experiment 1, we investigated the effect of stimulus visibility on orientation bias using relatively large stimuli. The introduction of visual noise increased the perceived similarity of target and flanker orientations at retinal eccentricities of 4- and 10-; however, small-angle assimilation was found only at 10-. The effects of eccentricity were reduced in Experiment 2, when our stimuli were âM-scaledâ for equal cortical coverage. Further support for a cortical substrate was obtained in Experiment 3, in which the effects of targetâflanker separation were measured. When biases from all three experiments are expressed as a fraction of the inducing flankersâ angle, and plotted as a function of the approximate cortical separation between the target and its closest flanker, they form a curve like the cross-section of half a Mexican hat. We conclude that the tilt illusion and small-angle assimilation reflect opponent influences on orientation perception. The strength of each influence increases with cortical proximity and stimulus visibility, but the one responsible for assimilation has a lesser extent
The Rewards of Patience: An 822 Day Time Delay in the Gravitational Lens SDSS J1004+4112
We present 107 new epochs of optical monitoring data for the four brightest
images of the gravitational lens SDSS J1004+4112 observed between October 2006
and June 2007. Combining this data with the previously obtained light curves,
we determine the time delays between images A, B and C. We confirm our previous
measurement finding that A leads B by dt_BA=40.6+-1.8 days, and find that image
C leads image A by dt_CA=821.6+-2.1 days. The lower limit on the remaining
delay is that image D lags image A by dt_AD>1250 days. Based on the
microlensing of images A and B we estimate that the accretion disk size at a
rest wavelength of 2300 angstrom is 10^{14.8+-0.3} cm for a disk inclination of
cos{i}=1/2, which is consistent with the microlensing disk size-black hole mass
correlation function given our estimate of the black hole mass from the MgII
line width of logM_BH/M_sun=8.44+-0.14. The long delays allow us to fill in the
seasonal gaps and assemble a continuous, densely sampled light curve spanning
5.7 years whose variability implies a structure function with a logarithmic
slope of gamma = 0.35+-0.02. As C is the leading image, sharp features in the C
light curve can be intensively studied 2.3 years later in the A/B pair,
potentially allowing detailed reverberation mapping studies of a quasar at
minimal cost.Comment: Submitted to ApJ, 12 pages, 3 figure
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Pyrolysis-GCĂGC-TOFMS to characterize carbonaceous chondrites
Using pyrolysis-GCxGC-TOFMS to analyze organic carbon in carbonaceous chondrites gives a massive increase in both sensitivity and structural information from samples when compared to traditional Py-GC-MS
Molecular cloning of a neuron-specific transcript and its regulation during normal and aberrant cerebellar development.
Dynamics of Plume-Triple Junction Interaction: Results from a Series of Three-Dimensional Numerical Models and Implications for the Formation of Oceanic Plateaus
Mantle plumes rising in the vicinity of mid-ocean ridges often generate anomalies in melt production and seafloor depth. This study investigates the dynamical interactions between a mantle plume and a ridge-ridge-ridge triple junction, using a parameter space approach and a suite of steady state, three-dimensional finite element numerical models. The top domain boundary is composed of three diverging plates, with each assigned half-spreading rates with respect to a fixed triple junction point. The bottom boundary is kept at a constant temperature of 1350°C except where a two-dimensional, Gaussian-shaped thermal anomaly simulating a plume is imposed. Models vary plume diameter, plume location, the viscosity contrast between plume and ambient mantle material, and the use of dehydration rheology in calculating viscosity. Importantly, the model results quantify how plume-related anomalies in mantle temperature pattern, seafloor depth, and crustal thickness depend on the specific set of parameters. To provide an example, one way of assessing the effect of conduit position is to calculate normalized area, defined to be the spatial dispersion of a given plume at specific depth (here selected to be 50km) divided by the area occupied by the same plume when it is located under the triple junction. For one particular case modeled where the plume is centered in an intraplate position 100km from the triple junction, normalized area is just 55%. Overall, these models provide a framework for better understanding plateau formation at triple junctions in the natural setting and a tool for constraining subsurface geodynamical processes and plume properties
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