4,459 research outputs found
The Impact of User Effects on the Performance of Dual Receive Antenna Diversity Systems in Flat Rayleigh Fading Channels
In this paper we study the impact of user effects on the performance of receive antenna diversity systems in flat Rayleigh fading channels. Three diversity combining techniques are compared: maximal ratio combining (MRC), equal gain combining (EGC), and selection combining (SC). User effects are considered in two scenarios: 1) body loss (the reduction of effective antenna gain due to user effects) on a single antenna, and 2) equal body loss on both antennas. The system performance is assessed in terms of mean SNR, link reliability, bit error rate of BPSK, diversity order and ergodic capacity. Our results show that body loss on a single antenna has limited (bounded) impact on system performance. In comparison, body loss on both antennas has unlimited (unbounded) impact and can severely degrade system performance. Our results also show that with increasing body loss on a single antenna the performance of EGC drops faster than that of MRC and SC. When body loss on a single antenna is larger than a certain level, EGC is not a “sub-optimal” method anymore and has worse performance than SC
The non-existence of stable Schottky forms
Let be the Satake compactification of the moduli space of
principally polarized abelian -folds and the closure of the image of
the moduli space of genus curves in under the Jacobian
morphism. Then lies in the boundary of for any . We
prove that and do not meet transversely in , but
rather that their intersection contains the th order infinitesimal
neighbourhood of in . We deduce that there is no non-trivial
stable Siegel modular form that vanishes on for every . In particular,
given two inequivalent positive even unimodular quadratic forms and ,
there is a curve whose period matrix distinguishes between the theta series of
and .Comment: Corrected version, using Yamada's correct version of Fay's formula
for the period matrix of a certain degenerating family of curves. To appear
in Compositio Mathematic
Radiative Decays X(3872) -> psi(2S)+gamma and psi(4040) -> X(3872)+gamma in Effective Field Theory
Heavy hadron chiral perturbation theory (HHchiPT) and XEFT are applied to the
decays X(3872) -> psi(2S) + gamma and psi(4040) -> X(3872) + gamma under the
assumption that the X(3872) is a molecular bound state of neutral charm mesons.
In these decays the emitted photon energies are 181 MeV and 165 MeV,
respectively, so HHchiPT can be used to calculate the underlying D^0
bar{D}^{0*}+ bar{D}^0 D^{0*} -> psi(2S) + gamma or psi(4040) -> (D^0
bar{D}^{0*}+ bar{D}^0 D^{0*}) + gamma transition. These amplitudes are matched
onto XEFT to obtain decay rates. The decays receive contributions from both
long distance and short distance processes. We study the polarization of the
psi(2S) in the decay X(3872) -> psi(2S) + gamma and the angular distribution of
X(3872) in the decay psi(4040) -> X(3872) + gamma and find they can be used to
differentiate between different decay mechanisms as well as discriminate
between 2^{-+} and 1^{++} quantum number assignments of the X(3872).Comment: 13 pages, 4 figure
Black holes admitting a Freudenthal dual
The quantised charges x of four dimensional stringy black holes may be
assigned to elements of an integral Freudenthal triple system whose
automorphism group is the corresponding U-duality and whose U-invariant quartic
norm Delta(x) determines the lowest order entropy. Here we introduce a
Freudenthal duality x -> \tilde{x}, for which \tilde{\tilde{x}}=-x. Although
distinct from U-duality it nevertheless leaves Delta(x) invariant. However, the
requirement that \tilde{x} be integer restricts us to the subset of black holes
for which Delta(x) is necessarily a perfect square. The issue of higher-order
corrections remains open as some, but not all, of the discrete U-duality
invariants are Freudenthal invariant. Similarly, the quantised charges A of
five dimensional black holes and strings may be assigned to elements of an
integral Jordan algebra, whose cubic norm N(A) determines the lowest order
entropy. We introduce an analogous Jordan dual A*, with N(A) necessarily a
perfect cube, for which A**=A and which leaves N(A) invariant. The two
dualities are related by a 4D/5D lift.Comment: 32 pages revtex, 10 tables; minor corrections, references adde
A first step towards on-device monitoring of body sounds in the wild
Body sounds provide rich information about the state of the human body and
can be useful in many medical applications. Auscultation, the practice of
listening to body sounds, has been used for centuries in respiratory and
cardiac medicine to diagnose or track disease progression. To date, however,
its use has been confined to clinical and highly controlled settings. Our work
addresses this limitation: we devise a chest-mounted wearable for continuous
monitoring of body sounds, that leverages data processing algorithms that run
on-device. We concentrate on the detection of heart sounds to perform heart
rate monitoring. To improve robustness to ambient noise and motion artefacts,
our device uses an algorithm that explicitly segments the collected audio into
the phases of the cardiac cycle. Our pilot study with 9 users demonstrates that
it is possible to obtain heart rate estimates that are competitive with
commercial heart rate monitors, with low enough power consumption for
continuous use.ER
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Dynamic Patterns of Transcript Abundance of Transposable Element Families in Maize.
Transposable Elements (TEs) are mobile elements that contribute the majority of DNA sequences in the maize genome. Due to their repetitive nature, genomic studies of TEs are complicated by the difficulty of properly attributing multi-mapped short reads to specific genomic loci. Here, we utilize a method to attribute RNA-seq reads to TE families rather than particular loci in order to characterize transcript abundance for TE families in the maize genome. We applied this method to assess per-family expression of transposable elements in >800 published RNA-seq libraries representing a range of maize development, genotypes, and hybrids. While a relatively small proportion of TE families are transcribed, expression is highly dynamic with most families exhibiting tissue-specific expression. A large number of TE families were specifically detected in pollen and endosperm, consistent with reproductive dynamics that maintain silencing of TEs in the germ line. We find that B73 transcript abundance is a poor predictor of TE expression in other genotypes and that transcript levels can differ even for shared TEs. Finally, by assessing recombinant inbred line and hybrid transcriptomes, complex patterns of TE transcript abundance across genotypes emerged. Taken together, this study reveals a dynamic contribution of TEs to maize transcriptomes
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