387 research outputs found
Spectrum of the Velocity Distribution Function in the Slab Ion Temperature Gradient Driven Turbulence
A spectral analysis of the velocity distribution function in the slab ion temperature gradient (ITG) driven turbulence is done by using high-resolution Eulerian kinetic simulation results. It is clarified how the entropy variable associated with the fine-scale structure of the distribution function is produced by the turbulent heat transport in the presence of the temperature gradient, transferred from macro to microscales in the velocity space through phase- mixing processes, and dissipated by collisions. An interesting analogy between the entropy spectrum in the ITG turbulence and the spectrum of a passive scalar quantity in a turbulent fluid is pointed out. The entropy spectral function is analytically derived and confirmed by the simulation result. It is shown that the entropy spectrum obeys a power law in the range that is free from instability sources and collisional dissipation
Strongly Secure Privacy Amplification Cannot Be Obtained by Encoder of Slepian-Wolf Code
The privacy amplification is a technique to distill a secret key from a
random variable by a function so that the distilled key and eavesdropper's
random variable are statistically independent. There are three kinds of
security criteria for the key distilled by the privacy amplification: the
normalized divergence criterion, which is also known as the weak security
criterion, the variational distance criterion, and the divergence criterion,
which is also known as the strong security criterion. As a technique to distill
a secret key, it is known that the encoder of a Slepian-Wolf (the source coding
with full side-information at the decoder) code can be used as a function for
the privacy amplification if we employ the weak security criterion. In this
paper, we show that the encoder of a Slepian-Wolf code cannot be used as a
function for the privacy amplification if we employ the criteria other than the
weak one.Comment: 10 pages, no figure, A part of this paper will be presented at 2009
IEEE International Symposium on Information Theory in Seoul, Korea. Version 2
is a published version. The results are not changed from version 1.
Explanations are polished and some references are added. In version 3, only
style and DOI are edite
Secret Key Agreement by Soft-decision of Signals in Gaussian Maurer's Model
We consider the problem of secret key agreement in Gaussian Maurer's Model.
In Gaussian Maurer's model, legitimate receivers, Alice and Bob, and a
wire-tapper, Eve, receive signals randomly generated by a satellite through
three independent memoryless Gaussian channels respectively. Then Alice and Bob
generate a common secret key from their received signals. In this model, we
propose a protocol for generating a common secret key by using the result of
soft-decision of Alice and Bob's received signals. Then, we calculate a lower
bound on the secret key rate in our proposed protocol. As a result of
comparison with the protocol that only uses hard-decision, we found that the
higher rate is obtained by using our protocol.Comment: 10 pages, 4 figures, to be appear in Proc. of 2008 IEEE International
Symposium on Information Theory in Toronto, Canad
Thermal Infrared and Optical Photometry of Asteroidal Comet C/2002 CE
C/2002 CE is an object in a retrograde elliptical orbit with Tisserand
parameter indicating a likely origin in the Oort Cloud. It appears to
be a rather inactive comet since no coma and only a very weak tail was detected
during the past perihelion passage. We present multi-color optical photometry,
lightcurve and thermal mid-IR observations of the asteroidal comet.
\textcolor{blue}{ With the photometric analysis in , the surface color is
found to be redder than asteroids, corresponding to cometary nuclei and
TNOs/Centaurs. The time-resolved differential photometry supports a rotation
period of 8.190.05 h. The effective diameter and the geometric albedo are
17.90.9 km and 0.030.01, respectively, indicating a very dark
reflectance of the surface. The dark and redder surface color of C/2002
CE may be attribute to devolatilized material by surface aging suffered
from the irradiation by cosmic rays or from impact by dust particles in the
Oort Cloud. Alternatively, C/2002 CE was formed of very dark refractory
material originally like a rocky planetesimal. In both cases, this object lacks
ices (on the surface at least). The dynamical and known physical
characteristics of C/2002 CE are best compatible with those of the
Damocloids population in the Solar System, that appear to be exhaust cometary
nucleus in Halley-type orbits. The study of physical properties of rocky Oort
cloud objects may give us a key for the formation of the Oort cloud and the
solar system.Comment: 9 pages, 4 figures accepted to Icaru
Noise Tolerance of the BB84 Protocol with Random Privacy Amplification
We prove that BB84 protocol with random privacy amplification is secure with
a higher key rate than Mayers' estimate with the same error rate. Consequently,
the tolerable error rate of this protocol is increased from 7.5 % to 11 %. We
also extend this method to the case of estimating error rates separately in
each basis, which enables us to securely share a longer key.Comment: 26 pages, 1 figure, version 2 fills a logical gap in the proof.
Version 3 includes an upper bound on the mutual information with finete code
length by using the decoding error probability of the code. Version 4 adds a
paragraph clarifying that no previous paper has proved that the BB84 with
random privacy amplification can tolerate the 11% error rat
Differences in Risk Factors for Rotator Cuff Tears between Elderly Patients and Young Patients
It has been unclear whether the risk factors for rotator cuff tears are the same at all ages or differ between young and older populations. In this study, we examined the risk factors for rotator cuff tears using classification and regression tree analysis as methods of nonlinear regression analysis. There were 65 patients in the rotator cuff tears group and 45 patients in the intact rotator cuff group. Classification and regression tree analysis was performed to predict rotator cuff tears. The target factor was rotator cuff tears; explanatory variables were age, sex, trauma, and critical shoulder angle≥35°. In the results of classification and regression tree analysis, the tree was divided at age 64. For patients aged≥64, the tree was divided at trauma. For patients aged<64, the tree was divided at critical shoulder angle≥35°. The odds ratio for critical shoulder angle≥35° was significant for all ages (5.89), and for patients aged<64 (10.3) while trauma was only a significant factor for patients aged≥64 (5.13). Age, trauma, and critical shoulder angle≥35° were related to rotator cuff tears in this study. However, these risk factors showed different trends according to age group, not a linear relationship
Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU
We present a unique and significant polarimetric result regarding the
near-Earth asteroid (152679) 1998 KU , which has a very low
geometric albedo. From our observations, we find that the linear polarization
degrees of 1998 KU are 44.6 0.5\% in the R band
and 44.0 0.6\% in the V band at a solar phase angle of 81.0\degr. These
values are the highest of any known airless body in the solar system (i.e.,
high-polarization comets, asteroids, and planetary satellites) at similar phase
angles. This polarimetric observation is not only the first for primitive
asteroids at large phase angles, but also for low-albedo (< 0.1) airless
bodies.
Based on spectroscopic similarities and polarimetric measurements of
materials that have been sorted by size in previous studies, we conjecture that
1998 KU has a highly microporous regolith structure comprising
nano-sized carbon grains on the surface.Comment: 9 pages, 5 figures, and 3 tables, accepted for publication in A&
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