5,226 research outputs found
On the Outage Capacity of Correlated Multiple-Path MIMO Channels
The use of multi-antenna arrays in both transmission and reception has been
shown to dramatically increase the throughput of wireless communication
systems. As a result there has been considerable interest in characterizing the
ergodic average of the mutual information for realistic correlated channels.
Here, an approach is presented that provides analytic expressions not only for
the average, but also the higher cumulant moments of the distribution of the
mutual information for zero-mean Gaussian (multiple-input multiple-output) MIMO
channels with the most general multipath covariance matrices when the channel
is known at the receiver. These channels include multi-tap delay paths, as well
as general channels with covariance matrices that cannot be written as a
Kronecker product, such as dual-polarized antenna arrays with general
correlations at both transmitter and receiver ends. The mathematical methods
are formally valid for large antenna numbers, in which limit it is shown that
all higher cumulant moments of the distribution, other than the first two scale
to zero. Thus, it is confirmed that the distribution of the mutual information
tends to a Gaussian, which enables one to calculate the outage capacity. These
results are quite accurate even in the case of a few antennas, which makes this
approach applicable to realistic situations.Comment: submitted for publication IEEE Trans. Information Theory; IEEEtran
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Interaction effects and charge quantization in single-particle quantum dot emitters
We discuss a theoretical model of an on-demand single-particle emitter that
employs a quantum dot, attached to an integer or fractional quantum Hall edge
state. Via an exact mapping of the model onto the spin-boson problem we show
that Coulomb interactions between the dot and the chiral quantum Hall edge
state, unavoidable in this setting, lead to a destruction of precise charge
quantization in the emitted wave-packet. Our findings cast doubts on the
viability of this set-up as a single-particle source of quantized charge
pulses. We further show how to use a spin-boson master equation approach to
explicitly calculate the current pulse shape in this set-up.Comment: 5+5 pages, 3 figures, fixed typos, update Supplement Material and
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Crossover from Conserving to Lossy Transport in Circular Random Matrix Ensembles
In a quantum dot with three leads the transmission matrix t_{12} between two
of these leads is a truncation of a unitary scattering matrix S, which we treat
as random. As the number of channels in the third lead is increased, the
constraints from the symmetry of S become less stringent and t_{12} becomes
closer to a matrix of complex Gaussian random numbers with no constraints. We
consider the distribution of the singular values of t_{12}, which is related to
a number of physical quantities. Changing the number of channels in the third
lead corresponds to increasing the amount of loss in the system (and is
distinct from prior uses of a third lead to model dephasing)
Developmental regulation of expression of the lactate dehydrogenase (LDH) multigene family during mouse spermatogenesis
Expression of the Lactate Dehydrogenase (LDH) genes during various stages of spermatogenesis was studied by using a combination of Northern blot analyses and in situ hybridization techniques. These studies have indicated that developmentally programmed expression of all three functional LDH genes occurs during differentiation of germ cells. The LDH/C (ldh-3) gene was expressed exclusively during meiosis and spermiogenesis, beginning in leptotene/zygotene spermatocytes and continuing through to the elongated spermatids. LDH/C (ldh-3) gene expression was accompanied by transient expression of the LDH/A (ldh-1) gene in pachytene spermatocytes and round spermatids. The LDH/B (ldh-2) gene was expressed mainly in Sertoli and spermatogonial cells. By using somatic cell hybrids, the LDH/C (ldh-3) gene has been mapped to mouse chromosome 7, establishing that it is syntenic with the LDH/A (ldh-1) gene locus. Experimental observations made in this study provide new insight into the order and sequence of events involved in the regulation of gene expression of the LDH gene family during spermatogenesis
Act quickly, decide later: long latency visual processing underlies perceptual decisions but not reflexive behavior
Jolij J, Scholte H, Van Gaal S, Hodgson TL, Lamme VAF (2011) Act quickly, decide later: Long latency visual processing underlies perceptual decisions but not reflexive behavior. Journal of Cognitive Neuroscience 23(12), p 3734-3745
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