An Algorithm for Universal Lossless Compression With Side Information

This paper proposes a new algorithm based on the Context-Tree Weighting (CTW) method for universal compression of a finite-alphabet sequence x₁ ⁿ with side information y₁ ⁿ available to both the encoder and decoder. We prove that with probability one the compression ratio converges to the conditional entropy rate for jointly stationary ergodic sources. Experimental results with Markov chains and English texts show the effectiveness of the algorithm     

Chemically produced XeF(B) electronic excited state

Ultraviolet (UV) emission has been observed in the reactions of XeF₂+F₂+SiH₄ and XeF₂+F₂+F+B₂H₆. The emission spectra have been identified with the B²Σ→X²Σ transition of XeF. The emission intensity has also been examined as functions of the XeF₂, F₂, SiH₄, and Ar concentrations. Possible mechanisms of XeF(B) production are discussed     

Strongly consistent online forecasting of centered Gaussianprocesses

An estimator Eˆ(d_n,n) of the conditional expectation E[X_n+1|X_n,...,X(n-d_n+1)] in a centered, stationary, and ergodic Gaussian process {X_i}_i with absolutely summable Wold coefficients is constructed on the basis of having observed X₁,...,X_n . For a suitable choice of the length dn→∞ (n→∞) of the past covered by the conditional expectation, it is established that |Eˆ(d_n,n)-E[X_n+1|X_n ,...,X(n-d_n+1)]|→0 with probability 1. In addition, sufficient conditions for |E[X_n+1|X_n,X _n-1,...]-E[X_n+1|X_n,...,X(n-d_n +1)]| →0 to hold with probability 1 are given, that is, conditions under which Eˆ(d_n,n) can be used as a strongly consistent forecaster for |E[X_n+1|X_n,X _n-1,...]     

Exact analysis of a class of GI/G/1-type performability models

We present an exact decomposition algorithm for the analysis of Markov chains with a GI/G/1-type repetitive structure. Such processes exhibit both M/G/1-type & GI/M/1-type patterns, and cannot be solved using existing techniques. Markov chains with a GI/G/1 pattern result when modeling open systems which accept jobs from multiple exogenous sources, and are subject to failures & repairs; a single failure can empty the system of jobs, while a single batch arrival can add many jobs to the system. Our method provides exact computation of the stationary probabilities, which can then be used to obtain performance measures such as the average queue length or any of its higher moments, as well as the probability of the system being in various failure states, thus performability measures. We formulate the conditions under which our approach is applicable, and illustrate it via the performability analysis of a parallel computer system.     

A super self-aligned selectively grown SiGe base (SSSB) bipolartransistor fabricated by cold-wall type UHV/CVD technology

A novel selective epitaxial growth (SEG) technology for fabricating the intrinsic SiGe-base layer of a double poly-Si self-aligned bipolar transistor has been developed. Selectively grown Si and SiGe-alloy layers were obtained by using Si₂H₆+GeH₄+Cl₂+B₂ H₆ gas system using cold-wall ultra-high vacuum (UHV)/CVD. We have optimized the growth conditions so that Si or SiGe grows selectively against Si₃N₄ both on single crystalline Si and on poly-Si of a structure consisting of a poly-Si layer overhanging the single crystalline Si substrate. The selective growth is maintained until the growth from the bottom Si and the top poly-Si coalesce. This selective growth permits a novel emitter-base self-aligned transistor which we call a super self-aligned selectively grown SiGe base (SSSB) HBT     

Statistics of the binary quantizer error in single-loop sigma-deltamodulation with white Gaussian input

Representations and statistical properties of the process e¯ defined by e¯_n+1=λ(e¯_n+ξ_n ), are given. Here λ(u):=u-b·sign(u)+m and {ξ_n}_n=0^+∞ is Gaussian white noise. The process e¯ represents the binary quantizer error in a model for single-loop sigma-delta modulation. The innovations variables are found and the existence and uniqueness of an invariant probability measure, ergodicity properties, as well as the existence of the exponential moment with respect to the invariant probability are proved using Markov process theory. We consider also e¯ as a random perturbation, for small values of the variance of ξ_n, Of the orbits of s_n+1=λ(s_n). Here s_n has the uniform invariant distribution on the interval [m-h, m+b]. Analytical approximations to the structure of the power spectrum of e¯ are obtained using a linear prediction in terms of the innovations variables and the perturbation approach     

Spectral Analysis of Digital Messages Through Finite-Memory Transformations

The spectral analysis is performed for the stochastic sequence{b_{n}} = {h(a_{n}, a_{n-1},cdots, a_{n-M+1})}, where{a_{n}}is an independent identically distributed digital sequence andhis an arbitrary complex function. The computation of the spectrum is based on a general matrix method for the spectral analysis of memoryless functions of Markov chains. The approach employs a recursive algorithm, whose computational time and storage requirements are sufficiently small for the algorithm to be implemented on a modern general purpose computer, even for moderately high values of both the size of the source alphabet and the parameterM. The method is also extended to the case in which the input sequence{a_{n}}is a stationary finite Markov chain.     

Defect passivation with potassium trifluoroborate for efficient spray-coated perovskite solar cells in air

Defects as non-radiative recombination centers hinder the further efficiency improvements of perovskite solar cells (PSCs). Additive engineering has been demonstrated to be an effective method for defect passivation in perovskite films. Here, we employed (4-methoxyphenyl) potassium trifluoroborate (C₇H₇BF₃KO) with \begin{document}${{\rm{BF}}_3^-}$\end{document} and K⁺ functional groups to passivate spray-coated (FAPbI₃)_x(MAPbBr₃)_1–x perovskite and eliminate hysteresis. It is shown that the F of \begin{document}${{\rm{BF}}_3^-}$\end{document} can form hydrogen bonds with the H atom in the amino group of MA⁺/FA⁺ ions of perovskite, thus reducing the generation of MA⁺/FA⁺ vacancies and improving device efficiency. Meanwhile, K⁺ and reduced MA⁺/FA⁺ vacancies can inhibit ion migration, thereby eliminating hysteresis. With the aid of C₇H₇BF₃KO, we obtained hysteresis-free PSCs with the maximum efficiency of 19.5% by spray-coating in air. Our work demonstrates that additive engineering is promising to improve the performance of spray-coated PSCs.     

Feedback capacity of the first-order moving average Gaussian channel

Despite numerous bounds and partial results, the feedback capacity of the stationary nonwhite Gaussian additive noise channel has been open, even for the simplest cases such as the first-order autoregressive Gaussian channel studied by Butman, Tiernan and Schalkwijk, Wolfowitz, Ozarow, and more recently, Yang, Kavccaronicacute, and Tatikonda. Here we consider another simple special case of the stationary first-order moving average additive Gaussian noise channel and find the feedback capacity in closed form. Specifically, the channel is given by Y_i=X_i+Z_i, i=1,2,..., where the input {X _i} satisfies a power constraint and the noise {Z_i} is a first-order moving average Gaussian process defined by Z_i=alphaU_i-1+U_i, |alpha|les 1, with white Gaussian innovations U_i, i=0,1,.... We show that the feedback capacity of this channel is C_FB=-log x₀ where x₀ is the unique positive root of the equation rhox²=(1-x²)(1-|alpha|x)² and rho is the ratio of the average input power per transmission to the variance of the noise innovation U_i. The optimal coding scheme parallels the simple linear signaling scheme by Schalkwijk and Kailath for the additive white Gaussian noise channel-the transmitter sends a real-valued information-bearing signal at the beginning of communication and subsequently refines the receiver's knowledge by processing the feedback noise signal through a linear stationary first-order autoregressive filter. The resulting error probability of the maximum likelihood decoding decays doubly exponentially in the duration of the communication. Refreshingly, this feedback capacity of the first-order moving average Gaussian channel is very similar in form to the best known achievable rate for the first-order autoregressive Gaussian noise channel given by Butman     

Epitaxial growth of β-SiC on Si by RTCVD with C3H8 and SiH4

The authors established that β-SiC thin films can be grown epitaxially on (100) Si substrates by rapid thermal chemical vapor deposition (RTCVD) employing carbonization with C₃H₈ , as well as post-carbonization growth using SiH₄ and C ₃H₈ in H₂. They determined the optimum carbonization conditions with respect to reaction temperature and ramp rate, gas flow rates, etc. A possible mechanism, based on nucleation density and Si surface diffusion, has been proposed for the effect of C ₃H₈ flow rate in film thickness, morphology, and void formation. Void-free SiC films have been grown on Si at high C₃H₈ flow rates. The authors determined the optimum conditions for subsequent SiC growth with respect to temperature and Si/C ratio in the gas phase. They established that the resulting SiC thin films are monocrystalline by X-ray and electron diffraction. The SiC-Si interface was investigated by cross-section transmission electron microscopy and found to be sharp and intimate where no voids are present     

An efficient numerical method for performance analysis ofcontention MAC protocols: a case study (PRMA++)

Several multiple access control (MAC) protocols of industrial interest can be modeled by discrete-state discrete-time Markov chains, with finite lower block Hessenberg probability transition matrices P_N, where the diagonal blocks have a size which decreases while passing from the top left block (A_0,0) down to the right bottom block (A_N,N). Such matrices have been identified in the literature as funnel matrices. In general, for meaningful systems of engineering interest, the size of P_N is so large that the computation of the P_N stationary probabilities (π) with common numerical methods cannot be performed due to the computational cost involved. To calculate the stationary probabilities of P_N we have developed an innovative computational method which fully exploits the block Hessenberg structure of the matrix I-P_N . In this way, we drastically reduce the overall computational cost with respect to the customarily used LU factorization, while still keeping the strong numerical stability of Gaussian elimination with diagonal adjustment. The potential of the new method is exploited to assess the performance of an access protocol for third-generation mobile systems, called PRMA++ (packet reservation multiple access protocol). This was designed within the European project RACE and has so far been studied, to the best of our knowledge, via simulative analysis. PRMA++ has received a lot of attention from manufacturers in the ongoing fifth framework program of the European Community     

A universal predictor based on pattern matching

We consider a universal predictor based on pattern matching. Given a sequence X₁, ..., X_n drawn from a stationary mixing source, it predicts the next symbol X_n+1 based on selecting a context of X_n+1. The predictor, called the sampled pattern matching (SPM), is a modification of the Ehrenfeucht-Mycielski (1992) pseudorandom generator algorithm. It predicts the value of the most frequent symbol appearing at the so-called sampled positions. These positions follow the occurrences of a fraction of the longest suffix of the original sequence that has another copy inside X₁X₂···X_n ; that is, in SPM, the context selection consists of taking certain fraction of the longest match. The study of the longest match for lossless data compression was initiated by Wyner and Ziv in their 1989 seminal paper. Here, we estimate the redundancy of the SPM universal predictor, that is, we prove that the probability the SPM predictor makes worse decisions than the optimal predictor is O(n^-ν) for some 0<ν<½ as n→∞. As a matter of fact, we show that we can predict K=O(1) symbols with the same probability of error     

On universal hypotheses testing via large deviations

A prototype problem in hypotheses testing is discussed. The problem of deciding whether an i.i.d. sequence of random variables has originated from a known source P₁ or an unknown source P₂ is considered. The exponential rate of decrease in type II probability of error under a constraint on the minimal rate of decrease in type I probability of error is chosen for a criterion of optimality. Using large deviations estimates, a decision rule that is based on the relative entropy of the empirical measure with respect to P₁ is proposed. In the case of discrete random variables, this approach yields weaker results than the combinatorial approach used by Hoeffding (1965). However, it enables the analysis to be extended to the general case of Rⁿ-valued random variables. Finally, the results are extended to the case where P₁ is an unknown parameter-dependent distribution that is known to belong to a set of distributions (P⁰₁, &thetas;∈Θ)     

Theoretical analysis of word-level switching activity in thepresence of glitching and correlation

This paper presents a novel analytical approach to compute the switching activity in digital circuits at the word level in the presence of glitching and correlation. The proposed approach makes use of signal statistics such as mean, variance, and autocorrelation. It is shown that the switching activity α_f at the output node f of any arbitrary circuit in the presence of glitching and correlation is computed as α_f=Σ_i=1^S-1α(f _i,i+1)=Σ_i=1^{S- 1}p(f_i+1)(1-p(f_i))(1-ρ(f_i,i+1 )) (1) where ρ(f_i,i+1)=ρ(f_i,i+1)=(E[f_i(Sn)f _i+1(Sn)]- p(f_i)p(f_i+1))/(√(p(f _i)-p(f_i)²)(p(f_i+1)- p(f_i+1²))) (2). S number of time slots in a cycle; ρ(f_i,+1) time-slot autocorrelation coefficient; E[x]=expected value of x; p_x=probability of the signal x being “one”. The switching activity analysis of a signal at the word level is computed by summing the activities of all the individual bits constituting the signal. It is also shown that if the correlation coefficient of the higher order bits of a normally distributed signal x is ρ(x_c), then the bit P₀ where the correlation begins and the correlation coefficient is related hy ρ(x_c)=erfc{(2(P₀-1)-1)/(√2σ_x )} where erfc(x)=complementary error function; σ_x=variance of x. The proposed approach can estimate the switching activity in less than a second which is orders of magnitude faster than simulation-based approaches. Simulation results show that the errors using the proposed approach are about 6.1% on an average and that the approach is well suited even for highly correlated speech and music signals     

The pi-persistent protocol for unidirectionalbroadcast bus networks

A protocol for multiaccess communication over unidirectional bus networks is proposed, and its performance capabilities are determined. Under this protocol, time is slotted with a slot equaling a packet's transmission time. A station with a packet to send persists in transmitting its packet in an empty slot with probability p_i until it is successful. Three criteria for fairness in selection of the p_i are modeled using Markov chains, which are solved to obtain the proper p_i that satisfy each fairness criterion. Unlike previous studies of unidirectional bus networks, stations are allowed to buffer more than one packet. The average packet delay for this protocol is bounded, and the maximum achievable throughput approaches unity with increasing buffer size. Further, the protocol provides better delay versus throughput behavior for fixed packet lengths than previous round-robin schemes, its performance is insensitive to bus characteristics, and it appears to be particularly well suited for fiber-optic network applications requiring long distances and high bandwidths. Simulation results that confirm the predicted performance are included     

Frequency stabilization of laser diodes using 1.51-1.55 μmabsorption lines of 12C2H2 and 13C2

Frequency stabilization of a 1.55 μm DFB laser diode is demonstrated using vibrational-rotational absorption of ¹²C ₂H₂ and ¹³C₂H₂ molecules (named VRAM). Frequency stability within 2 MHz peak to peak fluctuation can be achieved in the wavelength region of 1.51-1.55 μm. Frequency-stabilized DFB laser compact modules have been constructed. Frequency stabilities are evaluated by measuring the beat spectrum of the two lasers. In addition, the temperature and pressure dependences of the acetylene absorption lines are characterized     

Work function of boron-doped polycrystallineSixGe1-x films

The work function of p-type polycrystalline Si_xGe_1-x films deposited by LPCVD using SiH₄ and GeH₄ was determined by CV measurements on MOS structures. Boron was introduced in the Si_xGe_1-x films either exsitu by ion implantation or insitu by adding B₂H₆ in the reactants during film deposition. The work function of the Si_xGe_1-x films is found to decrease as the Ge content increases; it is 5.16 eV for Si, 4.76 eV for Si_0.49Ge_0.51, and 4.67 eV for Ge. The work function of the Si and Ge films coincides well with that of single crystalline Si and Ge, respectively. It is also found that a thin Si adhesion layer of about 3 nm (nominal thickness), deposited prior to the Si_xGe_1-x, has a negligible effect on the work function determination     

On the dynamics of population inversion for 3 μm Er3+lasers

A generalized model for 3-μm (⁴I_11/2 →⁴I_13/2)Er lasers is proposed. The essential energy transfer processes present in the single-doped Er ³⁺ systems (up-conversion from ⁴I_13/2, up-conversion from ⁴ I_11/2, cross-relaxation from ⁴S _3/2), as well as those present in Cr³⁺ codoped Er ³⁺ systems, are taken into account. In the frame of this model, the main features of 3 μm Er³⁺ lasers, such as long pulse or CW operation, the change of emission wavelength as a function of pumping conditions, and the effects of codoping with Ho³⁺ or Tm³⁺ ions, are explained     

Nonlinear Analysis of Correlative Tracking Systems Using Renewal Process Theory

A new method is presented which describes the behavior of an(N + 1)th-order tacking system in which the nonlinearity is either periodic [phase-locked loop (PLL) type] or a nonperiodic [delay-locked loop (DLL) type]. The cycle slipping of such systems is modeled by means of renewal Markov processes. A fundamental relation between the probability density function (pdf) of the single process and the renewal process is derived which holds in the transient as well as in the stationary state. Based on this relation it is shown that the stationary pdf, the mean time between two cycle slips, and the average number of cycles to the right (left) can be obtained by solving a single Fokker-Planck equation of the renewal process. The method is applied to the special case of a PLL and compared with the so-called periodic-extension (PE) approach. It is shown that the pdf obtained via the renewal-process approach can be reduced to agree with the PE solution for the first-order loop in the steady state only. The reasoning and its implications are discussed. In fact, it is shown that the approach based upon renewal-process theory yields more information about the system's behavior than does the PE solution.