The synthesis of magnetic recording trellis codes with good hamming distance properties

In this paper we present, by means of an example, a systematic procedure to synthesize combined modulation/error correcting trellis codes, suitable for Viterbi decoding. This synthesis is based on firstly selecting a suitable linear convolutional code, secondly by analysing the state system of this code to determine the important Hamming distance building properties, and finally by mapping a code with the desired restrictions on its sequences onto this state system. As an example we develop a R = 3/6 dc free (b,l,c) = (0,3,2) code withd_{min} = 4. This code improves on the best codes in [1]. Codes havingb geq 1, and which will thus be more suitable for magnetic recording, can also be synthesized following the proposed procedure.     

Multiplexed systems for the detection of ionizing radiation

Twelve different versions of integrating encoding (multiplexed) measurement systems for recording the spatial and angular characteristics of ionizing radiation are presented. Spatial, temporal, and binary modulation of the valid signal is performed by the multiplexed measurement system, which thereby suppresses the contribution of noise to the test results and, in a number of cases, makes it possible to obtain tomographic information. Different types of periodioc (0, 1), (– 1, 1), and (– 1, 0, 1) codes and tables, methods of constructing encoders based on these codes and tables, and the basic parameters of the encoders are described.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 49–54, November, 1995.     

Channel selection of atmospheric remote sensing

We introduce a channel selection method for atmospheric remote-sensing problems described by a Fredholm integral equation of the first kind. Whether one set of channels (CH) is more suitable than another (CH') can be judged by whether (1) the degree of predominance (DP) value of CH is larger than that of CH', i.e., if the number of channels is the same and (2) the number of channels of CH is more than that of CH', if the DP values of both are acceptable. One can calculate the DP of the unknown function f (y) for a set of remote-sensing channels by DP = [1 + (Rf?(a)(2) - 1) R(d)(2)](-1/2), Rf?(a)(2) = R(c)(2)[ R(b)(2) + R(a)(2)(1 + R(b)(2))], where R(a), R(b), R(c), and (1 - R(d)(2))(1/2) of this channel set represent the influences on the ability to recover the unknown function caused by various measurement errors, the noise parameter, the relativity of the kernel functions, and the blindness of remote sensing means, respectively. Our channel selection method can be simplified to a conventional method when there are no differences in the relative measurement errors, no blind components of the unknown function and no noise parameters in the kernel function.     

Bit error ratio performance of a receiver diversity scheme with channel estimation

The performance of diversity combining techniques with channel estimation for the case of unequal power branches is discussed. The performance of binary phase shift keying (BPSK), pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM) formats is investigated and their performance with nonideal channel estimation is explored. The case of combining multiple branches with unequal power levels is considered and optimal weighting factors for a log likelihood ratio test (LLRT) detector for the BPSK case are presented. These weights are shown to operate in a similar manner to those obtained by the linear minimum mean squared error (LMMSE) criterion and are compared with the well known maximal ratio combining (MRC) technique. The probability of error of this receiver is derived and simplifications for high signal-to-noise ratios are presented. Finally, numerical results are presented to compare the performance of the LLRT, LMMSE and MRC based receivers     

Vertical MOS-gated pin-diodes: MOS-gated tunneling transistors in Si(100) and Si(111)

Tunneling devices are an interesting alternative to conventional MOS-devices due to their high speed switching capabilities. Recently, it was shown that tunneling transistors based on vertical MOS-gated pin-diodes can be fabricated. The pin-diodes themselves were grown by means of UHV-MBE on highly n⁺-doped Si(100)-substrates with a 100 nm thick intrinsic channel region. The top contact was formed by the deposition of a highly-doped B δ-layer with a peak doping amount of approximately 10²¹ cm⁻³ for the necessary abrupt pn-junction and 300-nm p⁺-contact region. At a low supply voltage of −0.2 V, a current gain of three orders of magnitude with saturation behavior is achieved [1]. In the present contribution, we have shown the influence of the amount of B in the δ-layer and of the abruptness of the drain-channel-junction on the transistor behavior. For that, we have discussed the characteristics of MOS-gated pin-diodes on Si(111) with ultra-sharp B δ's with a peak doping amount between 10²⁰ and 10²¹ cm⁻³ and a peak width <3 nm, in comparison with MOS-gated pin-diodes on Si(100) presented in Hansch et al. [1]. In order to obtain these highly doped ultra-sharp B δ-layers, a phase-transition from an electrically inactive Si(111)- -R30° B surface phase into an electrically active one was induced by rapid thermal annealing.     

Mixing rules for the specific heat capacities of several HFC-mixtures

The specific heat capacity at constant pressure (c_p) of some relevant HFCs as replacements for R12, R502 and R22 was measured. The liquids investigated are binary or ternary mixtures of R134a, R152a, R125, R32 and R143a. Empirical functional relations in polynomial forms between the temperature, specific heat capacity and concentration are established and the coefficients of the polynomial correlations are presented. These equations can be used to calculate the c_p-values for the mixtures investigated over the whole concentration range and the predicted properties generally agree with the source data to ca ± 0.1% for the pure substances. The accuracy of the measurements is better than <1% for the pure fluids and <1.5% for the mixtures. Differences between 1 and 2% can occur only at temperatures >40°C and < −50°C.     

Design and evaluation of a high data rate optical wireless system for the diffuse indoor channel using barker spreading codes and RAKE reception [optical wireless communications]

The performance of a high data rate optical wireless system (OWS) over the diffuse indoor infrared channel based on direct sequence spread spectrum (DSSS) techniques is highly sensitive to the properties of the aperiodic autocorrelation function and the spreading factor of the spreading sequence used. Ideally, the aperiodic autocorrelation function should have zero sidelobes in order to eliminate intersymbol interference caused by multipath propagation. In practice, such an ideal sequence does not exist in the binary field when data modulation is applied. For high data rates, a small spreading factor is desired in order to avoid an excessive system bandwidth. The family of Barker sequences is investigated in a DSSS-OWS. The Barker sequences are binary spreading sequences which exhibit small aperiodic autocorrelation values and short spreading factors. The system bit error rate (BER) performance is characterized on the diffuse indoor infrared channel when using RAKE reception. Results of BER against Eh/NQ are presented with data rate and spreading factor as parameters. The results demonstrate that of the seven Barker sequences existing, the length three Barker sequence {0 0 1} provides the best system design trade-off in respect of good BER performance and low implementation complexity.     

Experimental demonstration of gray-scale sparse modulation codes in volume holographic storage

We discuss experimental results of a versatile nonbinary modulation and channel code appropriatefor two-dimentional page-oriented holographic memories. An enumerative permutation code is used to provide a modulation code that permits a simple maximum-likelihood detection scheme. Experimental results from the IBM Demon testbed are used to characterize the performance and feasibility of the proposed modulation and channel codes. A reverse coding technique is introduced to combat the effects of error propagation on the modulation-code performance. We find experimentally that level-3 pixels achieve the beet practical result, offering an 11-35% improvement in capacity and a 12% increase in readout rate as compared with local binary thresholding techniques.     

ISI‐mitigating modulation scheme using ion reaction for molecular communications

Here, according to the type‐based modulation technique, the authors develop a novel modulation scheme by utilising ion collision and reaction to mitigate inter‐symbol interference (ISI) in diffusive molecular communication (MC) systems. Two types of ions are employed as messenger molecules that cause a chemical reaction in the medium. According to the residual molecules and chemical reaction, the proposed modulation scheme adaptively adjusts the number of emitted molecules, thereby guaranteeing that the number of molecules that arrived at the receiver remains at a stable level. The authors evaluate the performance of the proposed scheme by comparing it with the conventional binary molecule shift keying (BMoSK), BMoSK with power adjustment (BMoSK‐PA), and ideal BMoSK (without ISI) modulation techniques via diffusion. Numerical results show that the bit error probability and channel capacity of the proposed modulation scheme are much closer to the ideal BMoSK modulation scheme compared to the conventional BMoSK and the BMoSK‐PA modulation schemes.Inspec keywords: channel capacity, intersymbol interference, error statisticsOther keywords: ISI‐mitigating modulation scheme, ion reaction, molecular communications, type‐based modulation technique, novel modulation scheme, ion collision, inter‐symbol interference, diffusive molecular communication systems, messenger molecules, chemical reaction, residual molecules, emitted molecules, conventional binary molecule shift, ideal BMoSK modulation scheme, conventional BMoSK, BMoSK‐PA modulation schemes

Nomenclature

Nc

number of molecules received in the current bit interval

Np

number of molecules received in current bit interval due to the molecules released in the previous bit interval

Nn

the Additive White Gaussian Noise

τ1

the detection thresholds of bit 1

τ2

the detection thresholds of bit 0

     

Closed-form expressions for symbol error probability of orthogonal space?time block codes over Rician?Nakagami channels

The performances of orthogonal space-time block codes (OSTBCs) over Rician- Nakagami channels are investigated. In particular, we derive closed-form symbol error probability (SEP) expressions for OSTBC systems in which M-ary phase-shift-keying modulation and M-ary quadrature-amplitude modulation are used. These SEP results are expressed in terms of Lauricella's multivariate hypergeometric functions, which can be easily evaluated numerically. When the Rician-Nakagami channel degenerates to the Rician-Rayleigh channel, or equivalently the Rayleigh fading channel, the closed-form SEP expressions are rewritten in terms of higher transcendental functions, that is, Gauss hypergeometric function and Appell hypergeometric function.     

Irradiance-variance behavior by numerical simulation for plane-wave and spherical-wave optical propagation through strong turbulence

We have simulated optical propagation through atmospheric turbulence in which the spectrum near the inner scale follows that of Hill and Clifford [J. Opt. Soc. Am. 68, 892 (1978)] and the turbulence strength puts the propagation into the asymptotic strong-fluctuation regime. Analytic predictions for this regime have the form of power laws as a function of beta0(2), the irradiance variance predicted by weak-fluctuation (Rytov) theory, and l0, the inner scale. The simulations indeed show power laws for both spherical-wave and plane-wave initial conditions, but the power-law indices are dramatically different from the analytic predictions. Let sigmaI(2) - 1 = a(beta0(2)/betac(2))-b(l0/Rf)c, where we take the reference value of beta0(2) to be betac(2) = 60.6, because this is the center of our simulation region. For zero inner scale (for which c = 0), the analytic prediction is b = 0.4 and a = 0.17 (0.37) for a plane (spherical) wave. Our simulations for a plane wave give a = 0.234 +/- 0.007 and b = 0.50 +/- 0.07, and for a spherical wave they give a = 0.58 + /- 0.01 and b = 0.65 +/- 0.05. For finite inner scale the analytic prediction is b = 1/6, c = 7/18 and a = 0.76 (2.07) for a plane (spherical) wave. We find that to a reasonable approximation the behavior with beta0(2) and l0 indeed factorizes as predicted, and each part behaves like a power law. However, our simulations for a plane wave give a = 0.57 +/- 0.03, b = 0.33 +/- 0.03, and c = 0.45 +/- 0.06. For spherical waves we find a = 3.3 +/- 0.3, b = 0.45 +/- 0.05, and c = 0.8 +/- 0.1.     

Composite detector for mixed radiations based on CsI(Tl) and dispersions of small ZnSe(Te) crystals

A new large area detector of high-energy X-ray and β-radiation has been designed and studied. A composite material based on small-crystalline ZnSe(Te) was applied onto the wide surface of a light guide. An experimental specimen has been prepared, which showed β-sensitivity . The spectrograms of a ⁹⁰Sr+⁹⁰Y β-source obtained with the specimen under study make it possible to evaluate the age of the source by the ratio of low- and high-energy regions of the spectrum.

The combined detector (CD) comprises a single crystalline plate of ZnSe(Te) placed onto the output window of a scintillating transparent light guide made of CsI(Tl) in the shape of a truncated pyramid. The CsI(Tl) light guide is used to create an additional channel for detection of γ-radiation, as well as for protecting the photodiode from the penetrating radiation. It is shown that introduction of the light guide does not worsen the energy resolution characteristics of ZnSe(Te). Separate detection of - and γ-radiation has been achieved under simultaneous excitation by ²³⁹Pu (ZnSe(Te), R=6%) and ²⁴¹Am (CsI(Tl), R_γ=20%). The use of selective optical filters allows separation of the peaks of total absorption (p.t.a.) in the case of their superposition.     

Discussions of three-dimensional models for mixed-mode fatigue crack growth

This technical note discusses several three-dimensional models for mixed-mode fatigue crack growth that were developed recently by Bian and coauthors [1], [2], [3], [4] and [5]. However, these models are found being formulated from a generally incorrect three-dimensional crack-front stress field for embedded elastic elliptical cracks. The corresponding correct crack-front stress field for the elliptical cracks is thus presented, and then the three-dimensional fatigue crack growth models are corrected and expressed in much simpler functions.     

Onset of strong scintillation with application to remote sensing of turbulence inner scale

Numerical simulation of propagation through atmospheric turbulence of an initially spherical wave is used to calculate irradiance variance σ(2)(I), variance of log irradiance σ(2)(ln I), and mean of log irradiance ?In I? for 13 values of l(0)/R(f) (i.e., of turbulence inner scale l(0) normalized by Fresnel scale R(F)) and 10 values of Rytov variance σ(2)(Rytov), which is the irradiance variance, including the inner-scale effect, predicted by perturbation methods; l(0)/R(f) was varied from 0 to 2.5 and σ(2)(Rytov) from 0.06 to 5.0. The irradiance probability distribution function (PDF) and, hence, σ(2)(I), σ(2)(In I), and ?ln I? are shown to depend on only two dimensionless parameters, such as l(o)/R(F) and σ(2)(Rytov). Thus the effects of the onset of strong scintillation on the three statistics are characterized completely. Excellent agreement is obtained with previous simulations that calculated σ(2)(I). We find that σ(2)(I), σ(2)(In I), and ?ln I? are larger than their weak-scintillation asymptotes (namely, σ(2)(Rytov), σ(2)(Rytov), and - σ(2)(Rytov)/2, respectively) for the onset of strong scintillation for all l(0)/R(f). An exception is that for the largest l(0)/R(f), the onset of strong scintillation causes σ(2)(ln I) to decrease relative to its weak-scintillation limit, σ(2)(Rytov). We determine the efficacy of each of the three statistics for measurement of l(0), taking into account the relative difficulties of measuring each statistic. We find that measuring σ(2)(I) is most advantageous, although it is not the most sensitive to l(0) of the three statistics. All three statistics and, hence, the PDF become insensitive to l(0) for roughly 1 < β0(2) < 3 (where β0(2) is σ (2)(Rytov) for l(0) = 0); this is a condition for which retrieval of l(0) is problematic.     

Binary Two-Error-Correcting Codes are Better than Quaternary

Codes over large fields can be used to construct codes over subfields. Such constructions of covering and error-correcting codes are discussed. In particular, packings and coverings with spheres of radius two are considered. A new construction of binary two-error-correcting codes from quaternary two-error-correcting codes is presented. This construction maintains the density, showing that such binary codes are at least as good as quaternary codes. The same construction is used to arrive at a similar conclusion for covering codes. Keywords:Bounds on codes, Covering code, Error-correcting code, Finite field.     

Performances d'une machine tritherme à éjecteur utilisant des mélanges de fluides frigorigènesPerformance analysis of a jet cooling system using refrigerant mixtures

The optimisation of a jet cooling system using refrigerant mixtures as substitutes of pure refrigerants has been investigated. A steady-state simulation program, for given temperatures of the sources, integrating simple models of each component has been developed. A Peng-Robinson equation of state assuming equality of the fugacities of the two phases was used to model the thermodynamic properties of the vapour and liquid-vapour equilibrium. The refrigerants investigated in this study are: the pure refrigerants R142b, R152a, RC318, R124, R134a, R22 and the binary refrigerants R22/RC318, R22/R142b, R22/R124, R22/R152a, R22/R134a, R134a/R142b, R152a/R142b and R134a/R152a. Results show that the use of a binary mixture does not always increase the performance of system. Generally, when the mixture is strongly zeotropic (e.g.: R22/RC318), the cooling efficiency of the system decreases. However, when the mixture is mildly zeotropic (e.g. R134a/R142b) or almost azeotropic (e.g. R134a/R152a), efficiency and energetic efficiency increase.     

Electronically Tunable RC Sinusoidal Oscillators

This paper presents two types of active configurations for realizing electronically tunable RC sinusoidal oscillators. The type-1 network employs two grounded scaled resistances KR1 and KR2, where K is a scaling factor. The frequency of oscillation Wo is controlled conveniently by adjusting K, since Wo appears in the form W0 = l/K/?R1C1R2C2. For realizing the scaled resistances, an active configuration is proposed, which realizes KRi = Ri/1 + f(VB), where f(VB) denotes a function of a controlling voltage VB. Thus the frequency tuning can be effected by controlling a voltage VB. The type-2 oscillator uses two periodically switched conductances. It is shown that the tuning of oscillation frequency can be done by varying the pulsewidth-to-period ratio (?/T) of the periodically switched conductances.     

CVD Tungsten and Tungsten-Rhenium Alloys for Structural Applications

The microstructures of CVD tungsten and tungsten-rhenium alloys have been investigated to evaluate their suitability as high temperature materials. We found that the partial pressure in the reaction chamber affected the microstructure and surface roughness of deposited pure tungsten and tungsten-rhenium alloys. Grain sizes smaller than 0.5 im were obtained for both deposited pure tungsten and tungsten-rhenium alloys. Fine-grained tungsten proved to have greater hardness (Hv>1000 at room temperature (R.T.)) bending strength (δ = 700-1230 MPa at R.T.-l 175 K) and thermal coefficient of linear expansion (β = 4.5-4.9 xl0⁶K^-1 at 575-1175 K) characteristics than tungsten with columnar structure.     

Microstructure and mechanical properties of in situ TiB reinforced titanium matrix composites based on Ti–FeMo–B prepared by spark plasma sintering

The in situ synthesized TiB reinforced titanium matrix composites have been prepared by spark plasma sintering at 800–1200 °C under 20 MPa for 5 min. The effects of sintering temperature and reinforcement volume fraction on flexural strength, Young’s modulus and fracture toughness of the composites are investigated. The titanium matrix consists of -Ti and β-Ti phases, and the volume fraction of β-Ti increases with increasing sintering temperatures. The in situ synthesized TiB reinforcements are distributed randomly and uniformly in matrix. The transverse section of TiB has a hexagonal shape aligned along [0 1 0] direction, and the crystallographic planes of the TiB needles are always of the type . The 10 vol% TiB reinforced composite sintered at 1000 °C exhibits excellent mechanical properties. The flexural strength, Young’s modulus and fracture toughness of this composite are 1560 MPa, 137 GPa and 8.64 MPa · m^1/2, respectively.     

前驱体制备途径对PFN-PMN二元铅基铁电陶瓷性能的影响

综合运用 ＸＲＤ、ＳＥＭ、ＴＥＭ、ＥＤＳ和介电测量等方法,考察了一步预煅烧法和二步预煅烧法等前驱体制备途径对Ｐｂ（Ｆｅ_１／２Ｎｂ_１／２）Ｏ_３（ＰＦＮ）－Ｐｂ（Ｍｇ_１／３Ｎｂ_２／３）Ｏ_３（ＰＭＮ）二元系铁电陶瓷显微结构和介电性能的影响．研究结果表明,对（１－Ｘ）ＰＦＮ－ＸＰＭＮ二元系而言,在所考查的组成范围内（Ｘ＝０～０.５）;其居里温度与ＰＭＮ的含量近似成线性关系,且随Ｘ的增加,居里温度向低温方向移动.峰值介电常数随Ｘ的增加而降低．（预）煅烧和烧结条件对显微结构和介电性能都有不可忽视的影响．对用一步预煅烧法和二步预煅烧法得到的样品的介电性能和其他性能进行了比较,并对其差异产生的可能机制进行了讨论．