Equalizing the transmission gain of the energy analyzer-secondary-electron multiplier system

An electric circuit for applying the voltage, determined by the voltage across electrodes of the energy analyzer, to the control grid, placed at the input of the detector of the secondary-electron multiplier, has been designed. With the transmission gains of the analyzer and saw-tooth voltage divider that powers the energy analyzer being equal, the constancy of particle energy at the detector input is maintained and the transmission gain of the section is thereby kept unchanged in the whole energy range of analyzed particles.     

Capacity and coding for the block-independent noncoherent AWGN channel

Communication over the noncoherent additive white Gaussian noise (AWGN) channel is considered, where the transmitted signal undergoes a phase rotation, unknown to the transmitter and the receiver. The effects of phase dynamics are explicitly taken into account by considering a block-independent model for the phase process: the unknown phase is constant for a block of N complex symbols and independent from block to block. In the first part of the paper, the capacity-achieving input distribution is characterized. In particular, it is shown that the maximizing density has circular symmetry, is discrete in amplitude with infinite number of mass points, and always has a mass point at zero. Furthermore, asymptotic expressions and bounds for the capacity are derived. Based on these results, the capacity is evaluated through numerical optimizations for unconstrained and modulation-constrained input distributions. In the second part of this paper, inspired by the capacity results, two classes of coding and modulation schemes are proposed for fast and moderate phase dynamics. In the case of fast phase dynamics (i.e., small N), optimized modulation alphabets are designed having exponential complexity with N at the demodulator. In the case of moderate phase dynamics (i.e., moderate values of N), specially designed modulation alphabets are utilized that have linear complexity with N. These alphabets are used together with optimized irregular low-density parity-check (LDPC) codes. Simulation results show that these codes can achieve close-to-capacity performance with moderate complexity, and outperform the best known codes so far.     

Lattice-matched epitaxial Pb1 − x Mn x Se/PbSe1 − x S x heterojunctions

This paper examines the possibility of producing lattice-matched p-n heterojunctions based on epitaxial n-Pb_{1 ? x} Mn _x Se (x = 0.02) and p-PbSe_{1 ? x} S _x (x = 0.04) films. The heterojunctions have been grown by molecular beam epitaxy in a single processing cycle, without breaking the vacuum, using a compensating Se vapor source in the growth process. Optimal conditions have been found for the growth of structurally perfect (W _1/2 = 90″-100″) epitaxial films and fabrication of lattice-matched heterojunctions based on such films, photosensitive in the IR spectral region.     

On the growth,structure, and surface morphology of epitaxial CdTe films

The structure and surface morphology of epitaxial CdTe films grown on glassy substrates with and without compensation with an additional Te vapor source during growth are studied. The optimal conditions of the production of structurally perfect epitaxial films with a pure smooth surface with no inclusions of another phase (T _so = 1000–1100 K, T _su = 570–670 K) are determined. It is established that, on glassy substrates, the epitaxial films grow via the (111) plane of the face-centered cubic (fcc) lattice with the parameter a = 6.481 Å. By varying the temperature of the main and compensating sources, CdTe films with n- and p-type conductivity are produced.     

Rotationally invariant and rotationally robust codes for the AWGN and the noncoherent channel

The paper investigates the design and robustness of rotationally invariant (RI) codes. First, RI codes are extended to the case of serially concatenated (SC) trellis-coded modulation (TCM) and several high-rate powerful RI-SCTCM codes are designed over 8-phase-shift keying and 16-quadrature amplitude modulation alphabets. The investigation continues by considering more realistic channels that introduce cycle slips during phase estimation, and thus rotate only part of the transmitted codeword. It is proven that RI codes with small state space are robust in these channels, even when traditional coherent decoders are utilized. Furthermore, it is demonstrated through simulations that the addition of a simple stopping criterion to the coherent iterative decoding algorithm is sufficient for robustness of the more powerful RI-SCTCM codes when partial codeword rotations are considered. Finally, it is investigated whether RI codes are useful for transmission in the noncoherent channel. It is proved that RI codes are as good as any other good codes for this channel when the phase dynamics are low, and optimal decoding is performed. However, it is shown that for a certain class of receivers, RI codes are also robust to partial phase rotations in this channel.     

Growth of epitaxial Cd<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Mn<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Te films

We have studied the growth and structure of epitaxial films of Cd_1–xMn_x (x = 0.03) diluted magnetic solid solutions grown on mica substrates by molecular beam epitaxy and identified conditions for producing n- and p-type epitaxial films. Using an additional Te vapor source and optimizing the substrate temperature in the growth process, we were able to obtain structurally perfect p-type Cd_1–xMn_xTe (x = 0.03) films with clean, smooth surfaces. The growth plane of the films on the mica substrates is (111) of a face-centered cubic lattice and their unit-cell parameter is а = 6.477 Å.     

Detection of parallel executable steps for programs with arrays

The detection of informational and logical program step dependencies is a key problem when performing equivalent transformations. In this article we consider this problem for systems of loops which represent concentration of mass computations and are the biggest challenge in parallel execution. The prototype of program formalization is C language just because of it’s popularity and it being an intermediate language for compilation of most programming languages including object-oriented ones.     

Pilot-symbol-assisted coded transmission over the block-noncoherent AWGN channel

In this paper, pilot-symbol-assisted transmission in conjunction with high-performance coding over the block-independent noncoherent additive white Gaussian noise channel is investigated. Several approximate iterative receivers are proposed, which either perform carrier-phase estimation separately from detection, or joint carrier-phase estimation/decoding in an iterative fashion. The performance of the proposed receivers is analyzed using density evolution. The power allocation to the pilot symbol is quantified, and it is shown that an optimal allocation scheme exists that minimizes the overall information bit signal-to-noise ratio required for error-free communication. This optimal power allocation, which could be utilized in code design, is found to be sensitive to the channel coherence interval, as well as to the particular receiver used. In addition, a simple upper bound on the performance of any receiver that performs joint iterative carrier-phase estimation and detection, is derived. The obtained results are compared with the simulated performance of the proposed receivers.