750,483 research outputs found
Monte Carlo simulations of pulse propagation in massive multichannel optical fiber communication systems
We study the combined effect of delayed Raman response and bit pattern
randomness on pulse propagation in massive multichannel optical fiber
communication systems. The propagation is described by a perturbed stochastic
nonlinear Schr\"odinger equation, which takes into account changes in pulse
amplitude and frequency as well as emission of continuous radiation. We perform
extensive numerical simulations with the model, and analyze the dynamics of the
frequency moments, the bit-error-rate, and the mutual distribution of amplitude
and position. The results of our numerical simulations are in good agreement
with theoretical predictions based on the adiabatic perturbation approach.Comment: Submitted to Physical Review E. 8 pages, 5 figure
State Amplification
We consider the problem of transmitting data at rate R over a state dependent
channel p(y|x,s) with the state information available at the sender and at the
same time conveying the information about the channel state itself to the
receiver. The amount of state information that can be learned at the receiver
is captured by the mutual information I(S^n; Y^n) between the state sequence
S^n and the channel output Y^n. The optimal tradeoff is characterized between
the information transmission rate R and the state uncertainty reduction rate
\Delta, when the state information is either causally or noncausally available
at the sender. This result is closely related and in a sense dual to a recent
study by Merhav and Shamai, which solves the problem of masking the state
information from the receiver rather than conveying it.Comment: 9 pages, 4 figures, submitted to IEEE Trans. Inform. Theory, revise
Topoisomerase expression and amplification in solid tumours: Analysis of 24,262 patients.
BackgroundTopoisomerase I (TOPO1) and topoisomerase IIα (TOP2A) are specific targets of multiple chemotherapy drugs. Increased expression of TOPO1 protein and amplification of the TOP2A gene have been associated with treatment response in colorectal and breast cancers, respectively. TOPO1 and TOP2A may be potential therapeutic targets in other malignancies as well.Summary of methodsWe analysed TOPO1 protein expression and TOP2A gene amplification in patients (n = 24,262 specimens) with diverse cancers. Since HER2 and TOP2A co-amplification have been investigated for predictive value regarding anthracycline benefit, we analysed specimens for HER2 amplification as well.ResultsOverexpressed TOPO1 protein was present in 51% of the tumours. Four percent of the tumours had TOP2A amplification, with gallbladder tumours and gastroesophageal/oesophageal tumours having rates over 10%. Overall, 4903 specimens were assessed for both TOP2A and HER2 amplification; 129 (2.6%) had co-amplification. High rates (>40%) of HER2 amplification were seen in patients with TOP2A amplification in breast, ovarian, gastroesophageal/oesophageal and pancreatic cancer.ConclusionOur data indicate that increased TOPO1 expression and TOP2A amplification, as well as HER2 co-alterations, are present in multiple malignancies. The implications of these observations regarding sensitivity to chemotherapy not traditionally administered to these tumour types merits investigation
Dualism between Optical and Difference Parametric Amplification
Breaking the symmetry in a coupled wave system can result in unusual
amplification behavior. In the case of difference parametric amplification the
resonant pump frequency is equal to the difference, instead of the sum,
frequency of the normal modes. We show that sign reversal in the symmetry
relation of parametric coupling give rise to difference parametric
amplification as a dual of optical parametric amplification. For optical
systems, our result can potentially be used for efficient XUV amplification
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