1,522 research outputs found
Power and spectrally efficient M-ARY QAM schemes for future mobile satellite communications
An effective method to compensate nonlinear phase distortion caused by the mobile amplifier is proposed. As a first step towards the future use of spectrally efficient modulation schemes for mobile satellite applications, we have investigated effects of nonlinearities and the phase compensation method on 16-QAM. The new method provides about 2 dB savings in power for 16-QAM operation with cost effective amplifiers near saturation and thereby promising use of spectrally efficient linear modulation schemes for future mobile satellite applications
A novel scheme to aid coherent detection of GMSK signals in fast Rayleigh fading channels
A novel scheme to insert carrier pilot to Gaussian Minimum Shift Keying (GMSK) signal using Binary Block Code (BBC) and a highpass filter in baseband is proposed. This allows the signal to be coherently demodulated even in a fast Rayleigh fading environment. As an illustrative example, the scheme is applied to a 16 kb/s GMSK signal, and its performance over a fast Rayleigh fading channel is investigated using computer simulation. This modem's 'irreducible error rate' is found to be Pe = 5.5 x 10(exp -5) which is more than that of differential detection. The modem's performance in Rician fading channel is currently under investigation
Requirements for regional short-haul air service and the definition of a flight program to determine neighborhood reactions to small transport aircraft
An evaluation of the current status and future requirements of an intraregional short haul air service is given. A brief definition of the different types of short haul air service is given. This is followed by a historical review of previous attempts to develop short haul air service in high density urban areas and an assessment of the current status. The requirements for intraregional air service, the need for economic and environmental viability and the need for a flight research program are defined. A detailed outline of a research program that would determine urban community reaction to frequent operations of small transport aircraft is also given. Both the operation of such an experiment in a specific region (San Francisco Bay area) and the necessary design modifications of an existing fixed wing aircraft which could be used in the experiment are established. An estimate is made of overall program costs
Effect of external magnetic field on electron spin dephasing induced by hyperfine interaction in quantum dots
We investigate the influence of an external magnetic field on spin phase
relaxation of single electrons in semiconductor quantum dots induced by the
hyperfine interaction. The basic decay mechanism is attributed to the
dispersion of local effective nuclear fields over the ensemble of quantum dots.
The characteristics of electron spin dephasing is analyzed by taking an average
over the nuclear spin distribution. We find that the dephasing rate can be
estimated as a spin precession frequency caused primarily by the mean value of
the local nuclear magnetic field. Furthermore, it is shown that the hyperfine
interaction does not fully depolarize electron spin. The loss of initial spin
polarization during the dephasing process depends strongly on the external
magnetic field, leading to the possibility of effective suppression of this
mechanism.Comment: 10 pages, 2 figure
Multi-angle pulse shape detection of scattered light in flow cytometry for label-free cell cycle classification
Flow cytometers are robust and ubiquitous tools of biomedical research, as they enable high- throughput fluorescence-based multi-parametric analysis and sorting of single cells. How- ever, analysis is often constrained by the availability of detection reagents or functional changes of cells caused by fluorescent staining. Here, we introduce MAPS-FC (multi-angle pulse shape flow cytometry), an approach that measures angle- and time-resolved scattered light for high-throughput cell characterization to circumvent the constraints of conventional flow cytometry. In order to derive cell-specific properties from the acquired pulse shapes, we developed a data analysis procedure based on wavelet transform and k-means clustering. We analyzed cell cycle stages of Jurkat and HEK293 cells by MAPS-FC and were able to assign cells to the G1, S, and G2/M phases without the need for fluorescent labeling. The results were validated by DNA staining and by sorting and re-analysis of isolated G1, S, and G2/M populations. Our results demonstrate that MAPS-FC can be used to determine cell properties that are otherwise only accessible by invasive labeling. This approach is technically com- patible with conventional flow cytometers and paves the way for label-free cell sorting
Error Rate of the Kane Quantum Computer CNOT Gate in the Presence of Dephasing
We study the error rate of CNOT operations in the Kane solid state quantum
computer architecture. A spin Hamiltonian is used to describe the system.
Dephasing is included as exponential decay of the off diagonal elements of the
system's density matrix. Using available spin echo decay data, the CNOT error
rate is estimated at approsimately 10^{-3}.Comment: New version includes substantial additional data and merges two old
figures into one. (12 pages, 6 figures
The radical cation of bacteriochlorophyll b. A liquid-phase endor and triple resonance study
The previous termradical cationnext term of bacterioehlorophyll b (BChl b) is investigated by ENDOR and TRIPLE resonance in liquid solution. The experimental hyperfine coupling constants, ten proton and three nitrogen couplings, are compared with the predictions from advanced molecular-orbital calculations (RHF INDO/SP). The detailed picture obtained of the spin density distribution is a prerequisite for the investigation of the primary electron donor previous termradical cationnext term in BChl b containing photosynthetic bacteria
Proton endor study of the photoexcited triplet state PT in Rps. sphaeroides R-26 photosynthetic reaction centres
The photoexcited triplet state PT of Rhodopseudomonas sphaeroides R-26 has been investigated by ENDOR measurements performed on frozen photosynthetic reaction centre solutions. For the first time hyperfine data could be obtained for PT. These data indicate a delocalisation of the triplet state over two bacteriochlorophyll a molecules
Fast Non-Adiabatic Two Qubit Gates for the Kane Quantum Computer
In this paper we apply the canonical decomposition of two qubit unitaries to
find pulse schemes to control the proposed Kane quantum computer. We explicitly
find pulse sequences for the CNOT, swap, square root of swap and controlled Z
rotations. We analyze the speed and fidelity of these gates, both of which
compare favorably to existing schemes. The pulse sequences presented in this
paper are theoretically faster, higher fidelity, and simpler than existing
schemes. Any two qubit gate may be easily found and implemented using similar
pulse sequences. Numerical simulation is used to verify the accuracy of each
pulse scheme
Mena, a new available marker in tumors of salivary glands?
Mena (mammalian Ena) is an actin regulatory protein involved in cell motility and adhesion. Based on its potential role in malignant transformation revealed in other organs, we analyzed the Mena expression in normal salivary glands (SG) and salivary tumors. Mena expression was determined in normal SG (n=10) and also benign (n=20) and malignant (n=35) lesions of SG. For the immunohistochemical staining we used the anti-Mena antibody. All normal SG and the benign lesions (10 pleomorphic adenomas, 10 Warthin's tumors) were Mena negative. Salivary duct carcinomas (n=5), carcinomas in pleomorphic adenoma (n=5), acinic cell carcinomas (n=5), squamous cell carcinomas (n=10) and high-grade mucoepidermoid carcinomas (n=2) were positive. The lymphomas (n=5) and low-grade mucoepidermoid carcinomas (n=1) were Mena negative. In one case the lymphoblastic cells stained positive for Mena. Some of the endothelial cells, in the peritumoral vessels, were Mena positive. To the best of our knowledge, this is the first study in the literature about Mena expression in salivary tumors. Our study suggests that Mena protein seems to play a role in malignant transformation and its intensity is correlated with the type and grade of tumor and also with vascular invasion. Its positivity in endothelial cells may suggest its potential role in tumor angiogenesis
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