Complex system reliability with general repair time distributions under preemptive repeat repair discipline

The behaviour of a complex system having “N” components in series in class L₁ and “m” identical components in parallel redundancy in class L₂, has been investigated. It has been assumed that a failure in L₁ brings about the complete break-down of the system whereas the failure of any two components of class L₂ causes the system to work in a state of reduced efficiency. The repair of the failed components in the class L₁ and L₂ is carried out under Preemptive Repeat Repair Discipline⁽⁵⁾. Laplace Transforms of various state probabilities, viz. the system is in up state, reduced efficiency state and down state, have been obtained. In the end, asymptotic behaviour of the complex system, has also been discussed.     

Complex system reliability with exponential repair time distributions under head-of-line-repair-discipline

In this paper the behaviour of a complex system, composed of two classes of components L₁ and L₂, has been investigated. It has been assumed that the repair of the failed components in classes L₁ and L₂ is carried out under the “head-of-line-repair-discipline”. Laplace transforms of the various state probabilities have been obtained. Inversions have also been carried out to obtain time-dependent probabilities. In the end, the behaviour of this system under steady state has also been examined.     

Operational behaviour of a complex system having shelf-life of the components under preemptive resume repair discipline

Complex system comprised of two types of components (I and II), has been considered. Type I consists of N components connected in series whereas type II consists of components connected in stand-by redundancy. It has been assumed that stand-by component may also fail in its shelf-life. The operational behaviour of such a system has been investigated under preemptive Resume Repair discipline using supplementary variable technique and Laplace Transforms.     

Reliability Model with 1 or 2 Repair Channels

Two models have been considered for a complex system with two classes of components L1 and L2. L1 components are connected in series; failure of an L1 component causes failure of the system. Class L2 consists of large number of components. Failure of any one L2 component reduces the efficiency of the system. Repairs of L2 components are followed by post-repairs. In Model I, repairs and post-repairs are done by a single channel; in Model II, there are separate channels for the two. Failure and repair times are exponentially distributed. Laplace transforms of the various probability states are obtained.     

Availability of a complex system having shelf-life of the components and common-cause failures

In this paper, a complex system comprised of two types of component is considered. Type I consists of N components connected in series, whereas type II consists of components connected in standby redundancy. It is assumed that a standby component may also fail in its shelf-life. Further, the system experiences two modes of failure—the first due to change in performance characteristics and the second due to a common cause. The availability of such a system is investigated using supplementary variable techniques and Laplace transforms. Finally, a number of interesting particular cases are discussed.     

Systems in reduced efficiency and alternating periods

We discuss here 2-unit systems working in alternating periods of normal and abnormal periods. The system consists of two units L₁ and L₂. In a normal period only the failure of the unit L₂ causes system failure. If the unit L₁ fails in this period the system works in reduced efficiency. In an abnormal period the failure of any one of the two units produces a complete failure of the system. This is model I. In model II the failure of L₂ causes a failure of the system irrespective of the periods. On the failure of unit L₁ in a normal period the system works in reduced efficiency as in model I. But in an abnormal period when the unit L₁ fails the system does not fail immediately. It is able to work for a certain short period, called the sustenance period. In an abnormal period a failed unit cannot be repaired. If the sustenance period expires, the system is considered as a total failure. If in the meanwhile the system enters the normal period it continues to work in reduced efficiency. The normal and abnormal periods alternate. The reliability of these two models are discussed using the Markov renewal technique. Certain particular cases are analysed.     

Fully integrated 1.2-μA and 13-μA quiescent current LDOs with improved transient response

We introduce two extremely low quiescent current (I _Q ) low-dropout (LDO) voltage regulators. The Low I _Q -LDO (LI _Q -LDO) uses 13 μA of total quiescent current and is designed for a maximum load current of 50 mA. The Micro I _Q -LDO (MI _Q -LDO) uses only 1.2 μA of total quiescent current and is designed for a maximum load current of 5 mA. Detailed pole/zero analysis is performed to aid in the design of the LDOs. Two LHP zeros cancel the two non-dominant poles which extend the bandwidth and improve transient response. Both designs are fully integrated, stabilized with an on-chip capacitive load of 100 pF. In load transient, the total variation in output voltage for LI _Q -LDO and MI _Q -LDO is 1 V and 950 mV, respectively, and the total line transient variation is 668 and 599 mV, respectively. Both designs occupy an area of 0.26 mm² in a 0.5-μm CMOS process. Two process-independent figures of merit are proposed to compare LI _Q -LDO and MI _Q -LDO with other published work.     

Measured mixer noise temperature and conversion loss of a cryogenic Schottky diode mixer near 800 GHz

We accurately measured the noise temperature and conversion loss of a cryogenically cooled Schottky diode operating near 800 GHz, using the UCB/MPE Submillimeter Receiver at the James Clerk Maxwell Telescope. The receiver temperature was in the range of the best we now routinely measure, 3150 K (DSB). Without correcting for optical loss or IF mismatch, the raw measurements set upper limits ofT _M=2850 K andL _M=9.1 dB (DSB), constant over at least a 1 GHz IF band centered at 6.4 GHz with an LO frequency of 803 GHz. Correction for estimated optical coupling and mismatch effects yieldsT _M=1600 K andL _M=5.5 dB (DSB) for the mixer diode itself. These values indicate that our receiver noise temperature is dominated by the corner cube antenna's optical efficiency and by mixer noise, but not by conversion loss or IF mismatch. The small fractional IF bandwidth, measured mixer IF band flatness from 2 to 8 GHz, and similarly good receiver temperatures at other IF frequencies imply that these values are representative over a range of frequencies near 800 GHz.     

Modeling the ESR spectra of a Zn-P two-spin system in Si: The structure of the semiempirical relaxation operator incorporated in the quantum Liouville equation

The structure is examined of the semiempirical relaxation operator R (a tensor of order 4) used to extend the quantum Liouville equation to nonequilibrium processes, particularly to the absorption of microwave quanta by a Zn-P two-spin paramagnetic system in silicon. The transition-matrix elements M _mn representing microwave absorption are directly involved in the modified quantum Liouville equation. The relaxation operator is expressed in terms of the transition rates v _mn and the overlap functions p _mn for the system: R _mjkn = v _mj p _kn + p _mj v _kn. It is assumed that the component representation of the relaxation operator is structurally similar to that of the Liouville operator L _mjkn in the sense that the former can be constructed from the latter by replacing ±iH _mn and δ_mn with v _mn, and p _mn, respectively. This changeover reflects the stochastic nature of the interaction between the Zn-P system on the one hand and the surrounding silicon and microwave radiation on the other. A physical interpretation of the relaxation-operator components is proposed.     

Reliability of a two-way circular consecutively connected system with multistate components

A two-way circular consecutively connected system with multistate components (two-way circular CCSMC) consists of n cyclically ordered components e₁,…,e_n, i.e. e_i+1, succeeds e₁, iε«ng l, …, n − 1ång;, e, succeeds e_n- Each component is capable of sending a signal in left-hand and right-hand directions. All components operate independently. The whole system is functioning if both left-hand and right-hand signals are received by each component. A recursive procedure evaluating the reliability of a two-way circular CCSMC is presented.     

Predictions of frame compliance and apex morphology in sharp nanoindentations

If all components in a nanoindentation system are well calibrated and a reference material has unique hardness, H and reduced modulus, E_r independent of the indentation depths, the load, L and the penetration depth, h in the indentation loading curve of the reference material can be correlated by L=Kh². Here the constant K is expressed by H, E_r and indenter geometry constants. By using H and E_r of a fused silica and the Berkovich geometry, an analytical expression for the indentation loading curve could be derived. To compare with this analytical loading curve, experimental indentation data were measured with two commercial nanoindenters. The experimental loading curves shifted leftward or rightward from the analytical loading curve and this depth deviation was attributed to improper calibration of the nanoindenters. Quantitative calibrations of frame compliance and indenter bluntness were tried for the raw nanoindentation data and this resulted in consistent nanoindentation data regardless of the used nanoindenters.     

A Magnetoresistance Induced by a Nonzero Berry Phase in GeTe/Sb2Te3 Chalcogenide Superlattices

The chalcogenide alloy Ge–Sb–Te (GST) has not only been used in rewritable digital versatile discs, but also in nonvolatile electrical phase change memory as a key recording material. Although GST has been believed for a long time not to show magnetic properties unless doped with magnetic impurities, it has recently been reported that superlattices (SLs) with the structure [(GeTe)_L(Sb₂Te₃)_M]_N (where L, M, and N are usually integers) have a large magnetoresistance at room temperature for particular combinations of L and M. Here it is reported that when [(GeTe)_L(Sb₂Te₃)_M]_N chalcogenide SL films are thermally annealed at 470 K and cooled down to room temperature under an external magnetic field accompanied by current pulse injections, a large magnetoresistance change (>2500 Ω) is induced. This study shows that the phenomenon has a strong correlation with the GeTe thickness and the periodic structure of the SL films, and that it is induced by the structural phase transition between electrically nonpolar and polar phases in the GeTe layers in the SLs. This study proposes that the relationship between the polar (ferroelectric) phase and the Berry curvature in the SLs is responsible for the magnetoresistance change.     

Numerical analysis of hardware architecture for header compression and packet aggregation on wireless networks

This paper proposes a numerical analysis model to predict the processing delay of a hardware architecture for robust header compression and packet aggregation on wireless mesh networks. The analysis model is composed of a series of queue systems such as G/M/1, M ^[K]/M/1, M/M/1, and M/M/∞ that are one-to-one mapped into the constructed hardware components to characterize the concurrent operations and interactional relationship between encoding and decoding paths. Based on the co-simulation method which integrates NS-2 and SystemC, we show the analysis model properly approximates the processing delay of the hardware architecture. Additionally, the variation of processing delay occurring when a part of hardware components are differently configured is suitably characterized by the proposed model, and the overall mesh network behaviors is predicted by applying the numerical results into NS-2 simulations.     

Research on orotron oscillator with dispersive open resonant system

Theoretical and experimental results of an investigation into a new resonant system have been obtained. This system is named the sphere-corner-echelette open resonator (SCEOR) due to the employment of a mirror that was formed by two echelettes at the angles of 45° to the resonator axis. It turns ont that this resonator is excited on the specific modes not unique to others oscillating systems. There are presented the results of the experimental research of the orotron oscillator with the SCEOR. The spectrum of this device contains only the fundamental modes such as theT E M ₀₀₆,T E M ₀₀₇,T E M ₀₀₈. The efficiency of the orotron is improved, when all other factors are the same the orotron with a much used sphere-cylindrical open resonator.     

An algebraic method for reliability calculations

This paper evaluates the reliability behaviour of a complex system consisting of three sub-systems G₁, G₂ and G₃ connected in parallel redundancy (1-out-of-3: G). These sub-systems are nothing but three power generators in a power house which are connected with switching devices. By the application of Boolean function technique and the theorem of summation of probabilities of compatible events, a symbolic expression for reliability of such a complex system has been evaluated by considering that failure times for various components of the complex system follow arbitrary distributions. In particular, reliability has been evaluated for exponential and Weibull distributions. Moreover, an important parameter, viz. MTTF, has also been computed for exponential failure rates of the units comprising the system. A numerical example, along with graphs, is discussed at the end to highlight the important results.     

One-Step Sintering Synthesis Achieving Multiple Structure Modulations for High-Voltage LiCoO2

The structure instability issues of the highly delithiated LiCoO₂ have significantly hindered its high-voltage applications (≥4.55 V vs Li/Li⁺). Herein, for the first time, multiple modifications of Li_0.9Mg_0.05CoO₂ (L_0.9M_0.05CO) via a simple one-step sintering synthesis are reported. A combination of the bulk Li/Co antisites, a Mg-pillar enriched surface, and a thin Mg O coating layer is achieved to maintain both the bulk and surface structural stability of L_0.9M_0.05CO upon cycling at an upper cut-off voltage of 4.6 V. The bulk Li/Co antisites are discovered to enhance the H1-3 phase evolution reversibility, the Mg pillars that substitute the Li sites effectively reinforces the surface structure, and the thin Mg O coating layer can effectively prevent the cathode from severe side reactions. Benefiting from the reduced but reversible H1-3 phase transition and the reinforced surface structure, L_0.9M_0.05CO shows an excellent cycle stability. This work provides a new structure modulation route for developing high-voltage LiCoO₂ cathodes.     

Performance evaluation of MIMO–WCDMA cellular networks in multiuser frequency selective fading environments

This paper investigates the performance of different transmission strategies for multiple input multiple output (MIMO) networks with the wideband code division multiple access (WCDMA) air interface as the physical layer protocol. Performance is evaluated statistically with extended Monte Carlo (MC) simulations in terms of achievable bit‐error (BER) rate in frequency selective fading cellular environments. As results indicate, for a MIMO configuration with M_t antennas at the base station (BS), M_r antennas per mobile station (MS) and L resolvable multipath components, the transmission strategy based on signal to noise ratio (SNR) enhancement is the optimum transmit solution for M_t ≤ M_r. However, the pre‐RAKE maximal ratio combining transmission strategy outerperforms the SNR enhancement strategy with post‐RAKE processing for M_t > M_r, high number of resolvable multipath components and channel estimation error up to 40%. Moreover, a transmission scheme based on the maximization of the ratio of the desired MS's signal to the total amount of interference that causes to the network is proposed, and is shown that outerperforms the conventional transmission schemes for high data rate services. For symmetric MIMO configurations (M_t = M_r) and two resolvable multipath components, this strategy provides 30% BER gain compared to the maximization of SNR strategy. This gain can be further improved by 25% with a proposed adjacent sector cooperation algorithm. Copyright © 2011 John Wiley & Sons, Ltd.     

The role of the polymer solid electrolyte molecular weight in light-emitting electrochemical cells

Different molecular weights (M_w) of poly (methyl methacrylate) (PMMA) were used as the base for the polymer solid electrolyte (PSE) in light-emitting electrochemical cells (LECs). The rheological properties of the LECs formulations are influenced by the M_w of PMMA. The M_w of PMMA also influences the PSE ionic conductivity and therefore affects the threshold voltage of the devices. Furthermore, partial segregation of the two polymers is observed, which correlates directly to the PMMA M_w. The device with the best performance was prepared with a PMMA M_w of 350,000 and exhibited an effective maximum luminance ～3000 cd m^?2.     

Base current and dominant time constant of an n+n−pn+ transistor operating in the upward mode

An attempt will be made to put together all information on I²L base current available from literature. The aim is to get explicit relations for all base current components at low, medium and high injection. This requires knowledge of excess concentration patterns and stored excess charge as well as of the associated time constants. As a final result the upward current amplification β_u and the upward time constant τ_u are obtained. In the latter no depletion charges have been taken along and a quasi-static condition is assumed. Lateral base current effects have not been taken into account.     

An Mθ/G/1 system with hysteretic switching of the service intensity

For an M^θ/G/1 system, two—basic and post-threshold—service modes with distribution functions F(x) and $\tilde F$ (x) of the service time are applied. The post-threshold mode starts functioning if, at instant t of the beginning of the current customer service, number ξ(t) of customers in the system satisfies the condition ξ(t) > h ₂. The basic mode is restored at the instant when the customer such that ξ(t) ≤ h ₁, where h ₁ ≤ h ₂, begins to be served. The mean duration of the busy period is determined, formulas for the stationary distribution of the number of customers in the system and stationary characteristics are derived. The results are verified with the help of simulation models developed with the use of the GPSS World tools.