Evidence for continuous visible chemical lasing from the fast nearresonant energy transfer pumping of atomic sodium

Energy transfer from selectively formed metastable states of SiO is used to pump sodium-atom laser amplifiers at λ≈569 nm (4d²D-3p²P), λ≈616 nm (5s²S-3p² P), and λ≈819 nm (3d²D -3p²P). The a³Σ⁺ and b³Π states of SiO are generated in high yield from the Si+N₂O→SiO+N₂ reaction. The energy stored in the triplet states is transferred in a highly efficient collisional process to pump sodium atoms to their lowest excited 3d² D, 4d²D, and 5s²S states. Adopting a sequence in which high concentrations of silicon and sodium atoms are mixed and oxidized, a continuous amplification (gain condition) is monitored which suggests the creation of a population inversion among the receptor sodium-atom energy levels and forms the basis for full cavity oscillation on the Na4 d²D-3p²P transition at 569 nm     

Reliability theory for large linear systems with helping neighbors

Ways to model large systems, whose redundancy consists of the ability of neighbors to help (replace faulty units), at least for a degraded mode of operation, are shown. A general approach of determining and evaluating a fault-tree for such systems is given. One-dimensional (linear) arrays of components are emphasized, and linear consecutive quasi-3-out-of-n:F systems and circular consecutive 3-out-of- n:F systems are discussed. In all cases, explicit formulas-most of them recursive-are given for system unavailability and for mean system-failure frequency for nonidentical s-independent components. As to methodology, the good adaptation of the Shannon decomposition to finding recursive results is amply demonstrated     

Pipelined recursive filter with minimum order augmentation

Pipelining is an efficient way for improving the average computation speed of an arithmetic processor. However, for an M-stage pipeline, the result of a given operation is available only M clock periods after initiating the computation. In a recursive filter, the computation of y(n) cannot be initiated before the computations of y(n-1) through y(n-N) are completed. H.B. Voelcker and E.E. Hartquist (1970) and P.M.Kogge and H.S. Stone (1973) independently devised augmentation techniques for resolving the dependence problem in the computation of y(n). However, the augmentation required to ensure stability may be excessively high, resulting in a very complex numerator realization. A technique which results in a minimum order augmentation is presented. The complexity of the resulting filter design is very much lower. Various pipelining architectures are presented. It is demonstrated by an example that when compared to the prototype filter, the augmented filter has a lower coefficient sensitivity and better roundoff noise performance     

Optimal `series-parallel' networks of 3-state devices

A 3-state component is one which can fall in two different modes: an open mode and a shorted mode. Systems built from such components can also experience either of these two failure modes. For a given number of s-identical s-independent components, a pure `series' or pure `parallel' configuration would be most reliable if only one of the two failure modes were possible. This paper treats the problem of designing the most reliable configuration of a given number of s-identical components that can experience both failure modes. Two simple algorithms for designing an optimal configuration are presented, and by analysis of 6, 8, and 20-component systems they illustrate the extent to which other configurations can be more reliable than `series-parallel' or `parallel-series' arrays     

Computing the probability of undetected error for shortened cycliccodes

The authors present a general technique for computing P _e for all possible shortened versions of cyclic codes generated by any given polynomial. The technique is recursive, i.e. computes P_e for a given code block length n from that of the code block length n-1. The proposed computation technique for determining P_e does not require knowledge of the code weight distributions. For a generator polynomial of degree r, and |g| nonzero coefficients, the technique yields P_e for all code block lengths up to length n in time complexity O(n|g |2^r+|g|). Channels with variable bit error probabilities can be analyzed with the same complexity. This enables the performance of the code generator polynomials to be analyzed for burst errors     

A fast recursive least squares adaptive second order Volterrafilter and its performance analysis

A fast, recursive least squares (RLS) adaptive nonlinear filter modeled using a second-order Volterra series expansion is presented. The structure uses the ideas of fast RLS multichannel filters, and has a computational complexity of O(N³) multiplications, where N-1 represents the memory span in number of samples of the nonlinear system model. A theoretical performance analysis of its steady-state behaviour in both stationary and nonstationary environments is presented. The analysis shows that, when the input is zero mean and Gaussian distributed, and the adaptive filter is operating in a stationary environment, the steady-state excess mean-squared error due to the coefficient noise vector is independent of the statistics of the input signal. The results of several simulation experiments show that the filter performs well in a variety of situations. The steady-state behaviour predicted by the analysis is in very good agreement with the experimental results     

Queueing analyses of traffic access control strategies withpreemptive and nonpreemptive disciplines in wideband integrated networks

A multiserver queueing model of access control strategies for a wideband integrated services digital network (ISDN) is considered. There are two types of service requests (SRs): Type 1 SR requires b servers (basic bandwidth units, BBUs) of the c available servers, while Type 2 SR requires a single server. Both types of SRs are queuable in two separate infinite-size buffers. A Type 1 SR is allowed to seize d(⩽b) servers at first and then acquire additional servers as they become available to meet the original requirement of b servers. The arrival processes of both types of SRs are Poisson and the service times are exponentially distributed with mean b/dμ₁ and 1/μ₂ for Type 1 SR and Type 2 SR, respectively. Preemptive and nonpreemptive priority disciplines with movable boundary are analyzed using the Neuts' matrix-analytic approach. Numerical examples of the queue length distribution and the mean waiting time of the SRs are presented     

Reliability of a consecutivek-out-of-r-from-n:F system

The reliability of the consecutive k-out-of-r-from-n:F system is studied. For k=2 an explicit solution is given for n components in line or in cycle in the i.i.d. case. For k⩾3 sharp lower and upper bounds are given for the reliability of the system and demonstrated for different values of n, k, r, p. These bounds are exact for r=n, n-1, n-2, n-3, and for these values the exact analytic solution is also given     

Longitudinal and transverse current distributions on coupledmicrostrip lines

The normalized longitudinal and transverse current distributions on coupled microstrip lines are obtained for even and odd modes by using the charge conservation formula and the charge distributions calculated by a Green's function technique. Their dependence on the shape ratios w/h and s/h and on the relative permittivity ε* of the substrate is shown     

Effective recursive algorithm for computing multiplicative inversesin GF(2m)

Presents an effective recursive algorithm for computing multiplicative inverses in GF(2^m), where m=2^k, employing normal bases. The proposed algorithm requires m-1 cyclic shifts and two multiplications in GF (2^m) and in each subfield of GF(2^m): GF(2^m/2), GF(2^m/4),. . ., GF (2⁸) and GF(2⁴)     

Modulatable orthogonal sequences and their application to SSMAsystems

A set of N-1 orthogonal sequences of period N ² is proposed, where N is a natural number. Each orthogonal sequence proposed can be modulated by N complex numbers of absolute value 1, so the modulated sequence is also orthogonal. When N is an odd prime number, the absolute value of the cross-correlation function between any two of the N-1 orthogonal sequences is constant and satisfies the mathematical lower bound. This property of the cross-correlation function is not changed when each of the two orthogonal sequences is modulated by N complex numbers of absolute value 1. Two spread-spectrum multiple-access (SSMA) systems using these sequences are proposed. One system is an asynchronous SSMA system, using the proposed sequences unmodulated. The cochannel interference peak between any two channels in this system realizes the mathematical lower bound for an asynchronous SSMA system using a set of orthogonal sequences. The other system is a synchronous SSMA system without cochannel interference which uses the modulated form of the proposed sequences     

On the existence of optimum cyclic burst correcting codes over GF(q)

A cyclic b-burst correcting code over GF(q) of redundancy r and length n=(q^r-b+1-1)/(q-1) is said to be optimum. It is proved that a necessary condition for the existence of such a code is the existence of a square-free polynomial in GF(q)[x] of degree b-1 which is not divisible by x such that its period and the degrees of its irreducible factors are relatively prime to q-1. Moreover, if such a polynomial exists, then there are an infinite number of optimum cyclic b-burst correcting codes over GF(q)     

Limiting efficiencies of burst-correcting array codes

The author evaluates the limiting efficiencies e(-S ) of burst-correcting array codes A(n₁,n₂, -s) for all negative readouts -s as n₂ tends to infinity and n₁ is properly chosen to maximize the efficiency. Specializing the result to the products of the first i primes donated by s_i (1⩽i<∞), which are optimal choices for readouts, gives the expression e(-s_i)=(2p_i+1 -2)/(2p_i+1-1) where p_i+1 is the next prime. Previously, it was known only that e(-2)⩾4/5 and e(-1)⩾2/3. This result reveals the existence of burst-correcting array codes with efficiencies arbitrarily close to 1 and with rates also arbitrarily close to 1     

An empirical model and an inversion technique for radar scatteringfrom bare soil surfaces

Polarimetric radar measurements were conducted for bare soil surfaces under a variety of roughness and moisture conditions at L -, C-, and X-band frequencies at incidence angles ranging from 10° to 70°. Using a laser profiler and dielectric probes, a complete and accurate set of ground truth data was collected for each surface condition, from which accurate measurements were made of the rms height, correlation length, and dielectric constant. Based on knowledge of the scattering behavior in limiting cases and the experimental observations, an empirical model was developed for σ°_hh, σ°_vv, and σ° _hv in terms of ks (where k=2π/λ is the wave number and s is the rms height) and the relative dielectric constant of the soil surface. The model, which was found to yield very good agreement with the backscattering measurements of the present study as well as with measurements reported in other investigations, was used to develop an inversion technique for predicting the rms height of the surface and its moisture content from multipolarized radar observations     

Prediction intervals based on partial observations for somediscrete distributions

Prediction limits of the following type are considered for the binomial, hypergeometric, and negative-binomial distributions. For the binomial distribution, suppose X_r successes have occurred in the first r trials, and based on this partial information it is desired to predict the total number of successes X _s (r<s), which will have occurred by trial s. Similar results are considered for the Poisson and negative-binomial distributions. The results are expressed in terms of well known distributions which have been tabulated, but it is quite tedious to carry out the procedures based on available tables. Normal (Gaussian) approximations are provided which make these methods convenient to apply     

Information rates for magnetic recording channels with peak- andslope-limited magnetization

A model for magnetic recording is proposed which uses two parameters to describe the limitations on the remanent magnetization in the medium: the dimensionless peak value A_m and the steepest slope B(s^-1). A low-pass bandwidth restriction W(s^-1) due to read circuits is also included. Lower and upper bounds on the achievable transmission rates are derived in terms of the signal-to-noise ratio. For the case of ideal low-pass restriction with B≪W, the bounds increase linearly, logarithmically, and as the cube root, with low, medium, and large ρ_B, respectively. With B≪ W the problem reduces to the one with no restriction on the slope     

Impact of noise of linearity of SQUID feedback loops at high slewrate

A simplified digital DC SQUID (superconducting quantum interference device) system has been simulated to determine the degree of linearity in a digital flux-locked-loop (FLL), with 12-b D/A converter. The influence of comparator noise and quantization noise on the feedback loops corresponding to single- and two-pole integrators is investigated as a function of the normalized slew rate s_N =s/s_max. A simple approximation describing the attainable linearity up to a specific slew rate range is suggested. Measurements with and without a DC SQUID magnetometer in a digital FLL system yielded a satisfying agreement with simulations in the range 0.3<s_n⩽1     

Studies of diffused phosphorus emitters: saturation current,surface recombination velocity, and quantum efficiency

The surface recombination velocity s for silicon surfaces passivated with thermal oxide was experimentally determined as a function of surface phosphorus concentration for a variety of oxidation, anneal, and surface conditions. This was accomplished by measuring the emitter saturation current density J₀ of transparent diffusions for which the J₀ is strongly dependent on s. At the lowest doping levels, the value of s was confirmed by measurements of s on substrates with uniform phosphorus doping. The impact of these measurements on solar cell design is discussed     

On the capacity region of the discrete additive multiple-accessarbitrarily varying channel

The discrete additive multiple-access arbitrarily varying channel (AVC) with two senders and one receiver is considered. Necessary and sufficient conditions are given for its deterministic-code average-probability-of-error capacity region under a state constraint to have a nonempty interior. In the case that no state constraint is present, the capacity region is characterized exactly. In the case of the noiseless mod-2 adder AVC using state constraint function l(s)=s and subject to a state constraint L less than or equal to 0.13616917, the capacity region is shown to be a 45-degree triangle whose legs have length 1-h(L), where h denotes the binary entropy function     

Invariant permutations for consecutive k-out-of-ncycles

Consecutive-k-out-of-n cycles are proposed as topologies for k-loop computer networks and describe a circular system of n components where the system fails if and only if any k consecutive components all fail. Suppose that the components are interchangeable. The the question arises as to which permutation maximizes the system reliability, assuming that the components have unequal reliabilities. If there exists on optimal permutation which depends on the ordering, but not the values, of the component reliabilities, then the system (and the permutation) is called invariant. The circular system is found to be not invariant except for k=1, 2, n-2, n-1, and n