Carrier-phase time transfer

We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code, as is done in current GPS-based time-transfer systems. Atomic clocks were connected to geodetic GPS receivers; we then used the GPS carrier-phase observations to estimate relative clock behavior at 6-minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common view time transfer and agrees, within the experimental uncertainty, with two-way satellite time-transfer measurements for a 2400 km baseline. GPS carrier-phase time transfer has a stability of 100 ps, which translates into a frequency uncertainty of about two parts in 10(-15) for an average time of 1 day.     

Time and time again

In the study of human-machine systems, the need to have a model of the user is by now taken for granted. The model can be used both as support for design and analysis and as a representation of the user that resides somewhere in the machine. When it comes to the practice of modelling, two characteristic approaches can be recognized. The first focuses on the how of modelling, and is concerned mainly with the structure and contents of models. The second focuses on what is being modelled, and is concerned mainly with the functioning or performance of the model. The first approach has dominated human-machine systems research for several decades, and has led to orthodoxy in modelling by which certain structural characteristics are accepted without questioning. This unreflective attitude to modelling has been criticised several times, although with little effect. In taking the second approach and focusing on what should be modelled, two important issues are that human performance varies in level of control, i.e. in terms of how orderly it is, and that thinking and acting take time-- and occur in a context where time is limited. Although it is clearly essential that user models can account for these characteristics, very few existing models are capable of doing so because they focus on internal information processing rather than on performance in a dynamic environment. The paper describes a type of functional model, called contextual control models, which shows how it is possible to account for both different control modes and how performance is affected by time. Indeed, control and time are intimately linked and loss of one may lead to a loss of the other. The contextual control model distinguishes among four characteristic control modes (strategic, tactical, opportunistic and scrambled) and two time parameters (time to evaluate, time to select) that are seen relative to the available time. Finally, a number of applications of contextual control models are described.     

Cost-based optimal relation between inspection time and assessment time for random fatigue crack growth

Optimal inspection time for random fatigue crack growth is theoretically investigated based upon cost-minimization, using a diffusive crack growth model. The optimal inspection time is defined so as to minimize the expected total cost expended up to the assessment time, at which the effect of an inspection is quantified. Assuming that (i) only one inspection is done up to the assessment time, and (ii) the component is immediately replaced if a crack is detected by the inspection, we formulate the expected total cost by the use of the diffusive crack growth model, where randomness associated with the material inhomogeneity, the initial crack length and crack-detection is taken into analysis. Through numerical calculations, we derive the optimal inspection time as well as the optimal expected cost. Finally, we perform parameter sensitivity analyses, and discuss the optimal selection of the assessment time.     

Coupling subdomains with heterogeneous time integrators and incompatible time steps

The work presented in this publication can be categorized among domain decomposition methods of the dual Schur type applied to structural dynamics. This approach leads to lower CPU times and better control of the accuracy of the time discretization and allows to take into account multi-time-scale effects which arise in transient structural dynamics. In order to consider incompatible time scales, one has to enforce continuity at the interfaces between the subdomains. Here, we propose a general formalism which enables the coupling of subdomains with their own numerical time integration scheme. The proposed method enables one to take into account possible nonlinearities which may present different time scale between the subdomains in a general manner for a wide range of time numerical scheme. This method also offers an important improvement for industrial software with easy implementation. Linear and nonlinear numerical examples are proposed in order to show the efficiency and the robustness of the method.     

How do time pressured drivers estimate speed and time?

The purpose of this laboratory study was to investigate the influence of time pressure on the perception of speed and duration in driving situations. Participants provided estimations of speed and performed both productions and reproductions of time durations, based on traffic films. The experimental films were made from a driver's point of view within a moving car, and audio-recorded instructions invited participants to imagine that they were driving while under time pressure or while relaxed. The results obtained using this within-participant design support the hypothesis that time pressure promotes fast driving, and may induce an underestimation of speed and trip-related durations, the latter of which suggests that time pressure modulates time perception. Some of these effects were mediated by the emotional impact of time pressure. Links between time perception and speed were also observed. The discussion makes reference to internal clock models and focuses on the practical consequences of these results.     

Cycle time estimation for semiconductor final testing processes with Weibull-distributed waiting time

Accurate cycle time is an essential planning basis required for many production applications, especially on due date commitments, performance metrics analysing, capacity planning, and scheduling. The re-entrant final testing process is the final stage of the complicated semiconductor manufacturing process. To enhance the ability of quick responses and to achieve better on-time delivery in final testing factories, it is essential to develop an accurate cycle time estimation method. In this paper, we provide a statistical approach to calculate the cycle time for multi-layer semiconductor final testing involving the sum of multiple Weibull-distributed waiting times. In addition, percentiles of the cycle time are obtained which are useful to industrial practitioners for due date commitments satisfying the targeted on-time delivery rate. To demonstrate the applicability of the proposed cycle time estimation model, a real example in a semiconductor final testing factory which is located on the Science-based Industrial Park in Hsinchu, Taiwan, is presented.     

The burn-in test scheduling problem with batch dependent processing time and sequence dependent setup time

The burn-in test scheduling problem (BTSP) is a variation of the complex batch processing machine scheduling problem, which is also a generalisation of the liquid crystal injection scheduling problem with incompatible product families and classical identical parallel machine problem. In the case we investigated on the BTSP, the jobs are clustered by their product families. The product families can be clustered by different product groups. In the same product group, jobs with different product families can be processed as a batch. The batch processing time is dependent on the longest processing time of those jobs in that batch. Setup times between two consecutive batches of different product groups on the same batch machine are sequentially dependent. In addition, the unequal ready times are considered in the BTSP which involves the decisions of batch formation and batch scheduling in order to minimise the total machine workload without violating due dates and the limited machine capacity restrictions. Since the BTSP involves constraints on unequal ready time, batch dependent processing time, and sequence dependent setup times, it is more difficult to solve than the classical parallel batch processing machine scheduling problem with compatible product families or incompatible product families. These restrictions mean that the existing methods cannot be applied into real-world factories directly. Consequently, this paper proposes a mixed integer programming model to solve the BTSP exactly. In addition, two efficient solution procedures which solve the BTSP are also presented.     

Acceleration and time to fail

A physical model of the growth of chemically related failures in electronic components is developed. This model is used to demonstrate that time to failure is as much a function of the component geometry as it is of the activation energy of the reaction. Further interpretation suggests that for any specified failure mechanism the acceleration achieved in a high temperature stress environment will appear to be a variable. Finally, using a simulation technique, a statistical distribution of the times to fail can be generated which resembles very closely the classical exponential failure curve.     

Space–time computation techniques with continuous representation in time (ST-C)

We introduce space–time computation techniques with continuous representation in time (ST-C), using temporal NURBS basis functions. This gives us a temporally smooth, NURBS-based solution, which is desirable in some cases, and a more efficient way of dealing with the computed data. We propose two versions of ST-C. In the first version, the smooth solution is extracted by projection from a solution computed with a different temporal representation, typically a discontinuous one. We use a successive projection technique with a small number of temporal NURBS basis functions at each projection, and therefore the extraction can take place as the solution with discontinuous temporal representation is being computed, without storing a large amount of time-history data. This version is not limited to solutions computed with ST techniques. In the second version, the solution with continuous temporal representation is computed directly by using a small number of temporal NURBS basis functions in the variational formulation associated with each time step.     

First passage time control charts assuming power law intensity for time to jointly monitor time and magnitude

Control charts are essential tools to monitor the quality of a process and commonly used in many industries besides industrial production. Due to the industrial revolution, many products have very low failure chances and labeled as the high-quality products, where the time-between-events (TBE) charts are commonly used to monitor such processes. This study purposes control charts to monitor time and magnitude assuming the power law process for the TBE whereas the magnitude is assumed cumulative as well as noncumulative over time. Besides two illustrative examples, a comparison to the existing rate and first passage time (FPT) charts is also presented in this study. It is shown numerically that the proposed charts are more efficient than the existing FPT and rate charts.     

Pricing and promised delivery lead time decisions with a risk-averse agent

This paper studies how a risk-averse firm determines promised delivery lead time and price in a circumstance where the market demand depends not only on the selling price but also on the promised delivery lead time. Two scenarios, one in which the price and promised delivery lead time are independent and the other in which the price is promised delivery lead time sensitive, are analysed. Under conditional value-at-risk criterion, we examine how the risk aversion of decision-makers influences the optimal selection of price, promised delivery lead time and the overall utility of a risk-averse decision-maker. Moreover, by conducting comprehensive sensitivity analyses, we investigate the interaction effects of the decision-maker’s risk aversion and different parameters, including the price and lead time elasticity indexes, the inventory costs, as well as the capacity parameters on the optimal decisions and utilities, so as to offer managerial implications for practitioners under time-based competition environment.     

Inventory and lead time planning with lead-time-sensitive demand

Supply and order lead times can have substantial effects on operations performance and perceived customer service, particularly under uncertain customer demand. Certain customers place a high premium on shorter order lead times, while others may be willing to trade a longer lead time for a lower price. This paper studies a problem in which a supplier wishes to determine the best positioning of a product with respect to order lead time and price. We consider a continuous review inventory replenishment system, where the difference between the procurement lead time and promised sales order lead time influences both cycle stock and safety stock costs, and procurement costs may increase as a result of investment in procurement lead time reduction. We provide models and methods for determining the best combination of price and sales lead time for systems with high economies of scale when demand depends on both sales lead time and price. Our results indicate that for a broad range of practical settings, such systems employ a pure make-to-stock policy or a policy that sets sales lead time equal to the procurement lead time at optimality.     

Shape optimization using time evolution equations

In this study, we deal with a numerical solution based on time evolution equations to solve the optimization problem for finding the shape that minimizes the objective function under given constraints. The design variables of the shape optimization problem are defined on a given original domain on which the boundary value problems of partial differential equations are defined. The variations of the domain are obtained by the time integration of the solution to derive the time evolution equations defined in the original domain. The shape gradient with respect to the domain variations are given as the Neumann boundary condition defined on the original domain boundary. When the constraints are satisfied, the decreasing property of the objective function is guaranteed by the proposed method. Furthermore, the proposed method is used to minimize the heat resistance under a total volume constraint and to solve the minimization problem of mean compliance under a total volume constraint.     

Evaluating order throughput time with variable time window batching

Given increased pressure to provide short delivery times, minimising customer order throughput time is a very important objective in warehousing operations. There are many factors that may affect the performance of an order picking system, such as layout of the warehouse, the storage strategy, the routing policy, the zoning method and the batching policy. In this study, we propose a simple travel time model and analyse the effect of order batching on the expected customer order throughput time with variable time window batching. In addition, we discussed the impact of some parameters on the batch size and the expected customer order throughput time. In the practice of Wuhan Dong Hon Logistics co. Ltd, the storage rack in the warehouse has two levels: the low storage level and the high storage level. These two levels are visited by pickers and forklifts, respectively. The classification improves the performance of order picking. In this study, we build the model based on this practice.     

Quantum state diffusion and time correlation functions

Abstract

In computing the spectra of quantum mechanical systems one encounters the Fourier transforms of time correlation functions, as given by the quantum regression theorem for systems described by master equations. Quantum state diffusion (QSD) gives a useful method of solving these problems by unravelling the master equation into stochastic trajectories; but there is no generally accepted definition of a time correlation function for a single QSD trajectory. In this paper we show how QSD can be used to calculate these spectra directly; by formally solving the equations which arise, we arrive at a natural definition for a two-time correlation function in QSD, which depends explicitly on the stochastic noise of the particular trajectory, and which agrees in the mean with the ensemble average definition of correlation functions.     

Improved relaxation time coverage in ramp-strain histories

Standard methods for deriving relaxation data from measurements invariably involve some form of ramp-type deformation history, the initial portion of which is typically not employed for modulus evaluation. In fact, the “ten-times-rule” or a variant thereof is widely used at the expense of short term data acquisition. This paper suggests a simple if (not) obvious method to extend the range of relaxation data that can be acquired from a single test at a single temperature. The method draws on new computational developments for inverting ill-conditioned systems of equations which allows the determination of relaxation parameters nearly routinely and trouble-free. We demonstrate this process for extraction of relaxation characterization from ramp strain histories through (a) numerical evaluation with a virtual test sequence, as well as through (b) data measured in the laboratory. Limitations regarding the time range over which the relaxation modulus can be extracted from laboratory measurements in terms of equipment resolution and stability are discussed. With these constraints in mind it appears feasible to extend the time range by three to four decades towards shorter times when compared with the application of the “ten-times-rule”. Similar treatments apply to the acquisition of creep compliance data.     

Extended failure time in the creep of frozen soils

A new concept of defining the failure time in creep as that at which the slope of a straight line from the origin becomes a tangent to the creep curve in the tertiary creep region is proposed. Using this concept, the data from several creep tests carried out in frozen soils are analyzed. It is shown that the estimated useful life of a foundation for a structure built in perenially frozen ground is larger by a factor of at least 1.5 compared to that based on the conventional failure time taken as the time to reach the minimum creep rate or the end of the steady state creep. The exponent of the power law creep in the tertiary region is also calculated.     

Time-redundant system reliability under randomly constrained time resources

The paper considers the time-redundant system where the system total task is a sequence of n phases and the total task must be executed during constrained time. For every phase, there is its own server, which executes the phase task during randomly distributed time. The server is not perfectly reliable and two types of failure (“open” and “closed”) are possible. Redundant servers may be used in any phase. The time–probability characteristics are introduced for any task, based on which the system reliability is treated as a probability that the system total task will be correctly completed during a corresponding time resource, which also may be randomly distributed. The adequate model is presented and a semi-Markov process is used as a mathematical technique. The closed-form solution was derived based on an acyclic Semi-Markov process. The numerical example of the elaborated approach is presented.     

On time distortion under stress

Under conditions of extreme and life-threatening stress, people often report distortions of time. These distortional experiences are critical since, axiomatically, they occur in circumstances where small variations in behavior can mean the difference between survival and extinction. The present work examines the spectrum of evidence concerning such phenomena including observations from real-world events such as combat, ejection from high-performance aircraft, driving in dangerous environments and from less stressful, yet informative laboratory procedures. A contextual theory is promulgated which postulates that in addition to draining attentional resources, stress prevents the efficient production of such resources. The stress-depleted resources which remain are directed to task-relevant activities and consequently attention to time-based cues is minimized resulting in distortion effects for both time-in-passing and for time recollection in memory. A number of practical observations are advanced concerning the performance of professionals who are likely to meet such conditions in their occupations including those in aerospace, military, fire-fighting, law enforcement, and medical emergency service operations. In conclusion, we present a number of future research strategies that may be enacted in order to evaluate this ephemeral, real-world phenomenon.     

A subnanosecond time discriminator system

A time discriminator is described, which gives an output if two pulses on separate input lines (which overlap) have their leading edges separated by a time greater than a preset value. Three channels are packaged in a single-width NIM module. Also described is a digitally controlled delay circuit used in calibration of the discriminator. The time discriminator provides 200 ps resolution, 60 ns (15 MHz) double pulse resolution, better than 1% linearity over a 20 ns range, and ECL and NIM outputs with adjustable width control.