Net Transition Research Articles

Labor force status transitions at older ages in the Philippines, Singapore, Taiwan, and Thailand, 1970-1990.

While there is considerable evidence of a trend toward earlier retirement in the United States and Europe, trends in rapidly growing economies in other parts of the world have not been closely examined. This paper traces the labor force participation rates of older men and women in four Asian countries, the Philippines, Singapore, Taiwan, and Thailand, over the period of 1970 to 1990. Aggregate census data are used to calculate net transitions into and out of the labor force so as to permit the analysis of differences by country and cohort as well as change over time. Results show that, although men exhibit a general trend toward earlier net labor force exit, labor force participation rates at older ages remain high. Older women are found to be increasingly engaged in economic activity, especially in Singapore and Taiwan.

Analysis of Deadlock and Circular Waits Using a Matrix Model for Flexible Manufacturing Systems

The problem of deadlock in a large class of reentrant flowline systems is analysed based on a Petri net model. The relation between deadlock and circular waits is established by rigorously defining the situation of circular blocking. Deadlock analysis is then performed in terms of circular waits and their associated structures, the so-called critical siphons and critical subsystems. A dynamical system representation obtained by coupling the Petri net marking transition equation with the matrix rule-based controller equations is adopted. The task of computing the Petri net structures of deadlock analysis is largely simplified (operations involved are of polynomial complexity) by using the matrices of this system description. An on-line maximally permissive control policy for deadlock avoidance (MAXWIP) is then devised. This can be efficiently implemented by incorporating the “outer-loop” control decisions via certain dispatching control inputs. The result is a dispatching control with deadlock avoidance, which is a generalized kanban scheme.

AND/OR net representation for robotic task sequence planning

The paper describes a framework for task sequence planning for a generalized robotic work cell. The AND/OR net provides a compact, distributed, domain-specific representation of geometric configurations of parts and devices in the work cell. The approach maintains a correspondence from geometric state information to task and motion plans and on-line discrete-event control that is not available in traditional action-based planners. The feasibility criteria for each AND/OR net transition guide the geometric reasoning required in the planning of feasible sequences. The resulting search space for plans is often much smaller (due to explicit representation of geometric constraints) than the state space of an action-based task planner. For purposes of analysis, the AND/OR net is mapped into a Petri net and the resulting Petri net is shown to be bounded and have guaranteed properties of liveness, safeness, and reversibility. In this form, the AND/OR net may be viewed as a Petri net synthesis tool in which the resulting Petri net representation may be used for on-line scheduling and control of the system.

Elastic and inelastic scattering of4dinner-shell electrons in(Y,Gd)2O3studied by synchrotron-radiation excitation

Excitations within the $4f$ shell of ${\mathrm{Gd}}^{3+}$ in $({\mathrm{Y},\mathrm{G}\mathrm{d})}_{2}{\mathrm{O}}_{3}$ are observed by resonant elastic and inelastic soft x-ray scattering with synchrotron radiation. Inelastic scattering takes place when exciting ${4d}^{10}{4f}^{7}\ensuremath{\rightarrow}{4d}^{9}{4f}^{8}$ transitions and extends over an energy range of about 10 eV. The features can be assigned to the net transition from the ${}^{8}{S}_{7/2}$ ground state to the sextet multiplets of the ${4f}^{7}$ configuration in ${\mathrm{Gd}}^{3+},$ which have the same parity as the ground state. The inelastic scattering is maximal when the excitation energy is tuned to the ${4d}^{9}{4f}^{8}{(}^{6}D)$ intermediate state.

Waves of democratization

The term, “waves of democratization,” popularized by Huntington (1991), can be conceptualized in at least three ways: as rises in the global level of democracy, as periods of positive net transitions to democracy, and as linked sets of transitions to democracy. Each of these approaches to the concept carries distinct theoretical implications and generates somewhat different historical patterns. The three approaches are examined using four cross-national, time-series operationalizations of democracy.

A new matrix model for discrete event systems: application to simulation

Simulation schemes for discrete event (DE) systems based on a new DE matrix formulation are presented. This new formulation is a hybrid system with logical and algebraic components that allows fast, direct design and reconfiguration of rule-based controllers for manufacturing systems. It applies to general DE systems that include shared resources, dispatching, circular waits, and variable part routing. A certain DE matrix state equation together with the familiar Petri net marking transition equation yield a complete dynamical description of a DE system. Our goal in this article is to show that this provides a simplified computer tool that allows efficient simulation and modeling for DE systems.

Net and total transition costs: The timing of economic reform

Countries face an ongoing need for fiscal adjustment and economic reform — adjustment and reforms that involve short-term transition costs. Thus economic agents, depending on their time preference for present consumption or on the level of economic populism in a given society, will postpone the required measures. On the other hand, if the corrective measures are not adopted, after a certain lapse of time procrastination costs arise. The net transition costs of adjustment and reform are the difference between these two costs: they may explain the timing of reform. If adjustment and reform is undertaken soon after economic distortions appear, the net transition costs will be high, but, as a tradeoff, recovery will come sooner. As economic agents show a greater preference for present consumption, they will postpone adjustment and reform. Then, the procrastination costs will start to rise. This trend may reach a point where the cost curve of adjustment and reform cross the procrastination cost curve. At this point net transition costs turn negative, so that even for the more populist economic agents that give full preference for present consumption, it becomes rational to adjust and reform.

A Survey of Petri Net Methods for Controlled Discrete EventSystems

This paper surveys recent research on the application of Petri net models to the analysis and synthesis of controllers for discrete event systems. Petri nets have been used extensively in applications such as automated manufacturing, and there exists a large body of tools for qualitative and quantitative analysis of Petri nets. The goal of Petri net research in discrete event systems is to exploit the structural properties of Petri net models in computationally efficient algorithms for computing controls. We present an overview of the various models and problems formulated in the literature focusing on two particular models, the controlled Petri nets and the labeled nets. We describe two basic approaches for controller synthesis, based on state feedback and event feedback. We also discuss two efficient techniques for the on-line computation of the control law, namely the linear integer programming approach which takes advantage of the linear structure of the Petri net state transition equation, and path-based algorithms which take advantage of the graphical structure of Petri net models. Extensions to timed models are briefly described. The paper concludes with a discussion of directions for future research.

Median attractor and transients in random boolean nets

Variants of a random boolean network of binary gates called the Kauffman net are studied. Each gate receives two random inputs from the other gates in the network and is assigned a transition function from a non-uniform distribution. Fine upper bounds on the attractor and transient lengths as the behavioral characteristics of the network are determined for large net size, N, and different transition function distributions. The effects of these distributions on the localization property of the net is shown. Analysis of nets with N > 1000 was shown to be very difficult. We also determine the scaling properties of attractors and transients with the net size. Our results exhibit strong “antichaos” behavior even for very large N for some of the networks.

Quantum interference in microwave multiphoton transitions.

We observe interference in the resonant microwave multiphoton transition probability between the 21s state and the 19,3 Stark state of K in a static field as a function of the duration and intensity of a microwave pulse at 9 GHz. The 19,3 state adiabatically connects to the 19f state in zero field. The ac Stark effect shifts the 21s state through a multiphoton resonance with the 19,3 Stark state during both the rising and falling edges of the microwave pulse. The transitions that occur during each traversal of the resonance lead to an interference in the net transition probability as a function of the relative phase accumulated by each state during the pulse. We measure both the frequency of the interference oscillations for different detunings from resonance and the amplitude of the fringes for different degrees of pulse asymmetry. The latter results are in complete agreement with the predictions of a Landau-Zener model for the resonance transitions.

A theory of tension fluctuations due to muscle cross-bridges

We present an analytical theory for the spectrum of tension fluctuations due to muscle cross-bridges. The theory is based upon the Langevin theory of brownian motion, and is illustrated using a simplified three-state model for the cross-bridge cycle, which is intended to model cross-bridges in fibrillar insect flight muscle. Langevin white-noise sources, representing fluctuations in the net transition rates for each step in the cycle, are introduced into the rate equations, and their strengths are adjusted to give the correct mean-square fluctuations in the occupation probabilities. The Langevin theory shows that the noise is closely related to the elastic properties of cross-bridges, and it also shows in detail how each step in the cross-bridge cycle contributes differently to the noise spectrum. We find that the total noise increases with filament displacement. For small filament displacements, the noise is dominated by the power stroke and by dissociation at the end of the cycle. These contributions increase in the region of stretch activation, whilst at larger displacements, where the cross-bridge becomes locked in the strong-binding state, the noise is much larger and is dominated by attachment and detachment at the beginning of the cycle. The cross-bridge properties in this regime are strongly affected by free inorganic phosphate. Finally, we show how the noise spectrum is modified by the inclusion of a series compliance representing a practical force transducer.

Impact of moisture on thermally induced denaturation and decomposition of lyophilized bovine somatotropin

The nonisothermal transitions of lyophilized recombinant bovine somatotropin (rbSt) as seen via differential scanning calorimetry were evaluated with respect to moisture content. The transition peak temperature of rbSt decreased with increasing moisture from 161 degrees C in the dry state to a plateau of 65 degrees C at 28% moisture, which is similar to that of rbSt in solution. Using high performance liquid chromatography, this irreversible endothermic transition consisted primarily of unfolding, hydrophobic aggregation, and some covalent modifications. In the dry state, covalent modifications, including polymerization into compounds of higher molecular weight, were more prominent, while in the presence of moisture, hydrophobic aggregation was most prominent. The irreversibility and scan rate dependence of the endothermic phenomena supports the kinetic nature of the transition rather than a simple equilibrium between globular and unfolded states. The apparent activation energy for the net transition (i.e., unfolding, hydrophobic aggregation, and covalent modifications) was 57 kcal/mol for rbSt at 9.9% moisture. The observed enthalpy of the transition increased, decreased, then approximately leveled off as a function of increasing moisture content. This can be explained by the increasingly significant contribution of the exothermic aggregation at higher moisture contents.

Kinetics of hepatic bile acid handling in cholestatic liver disease: Effect of ursodeoxycholic acid

Ursodeoxycholic acid (UDCA) is clinically beneficial in chronic cholestatic liver disease, but the underlying mechanisms are unclear. It has been suggested that intrahepatic retention of endogenous hydrophobic bile acids contributes to cholestasis and that the hydrophilic bile acid UDCA reduces this retention; the aim of our study was to test these hypotheses. Twelve patients with primary biliary cirrhosis (PBC) and 5 with primary sclerosing cholangitis (PSC) were studied before and during UDCA (10 mg.kg-1.day-1) and compared with 11 healthy controls. Following intravenous 75Se labeled homocholic acid taurine (75SeHCAT) in the fasting state, abdominal gamma camera imaging was performed for 90 minutes. Initial hepatic uptake, transit time, net, and absolute excretory rates for 75SeHCAT were measured. Mean initial hepatic uptake was not different between patients and controls (17.2% and 19.9% dose/minute, not significant). However, net and absolute excretory rates were significantly reduced in patients (1.4% vs. 3.7% dose/minute, P < 0.0001; and 2.35% vs. 3.96% dose/minute, P < 0.02, respectively), and hepatic transit time was prolonged (18.7 minutes vs. 11.6 minutes, P < 0.002). UDCA improved net and absolute hepatic excretory rates and transit time (1.43% to 1.96% dose/minute, P < 0.001; 2.35% to 3.15% dose/minute, P < 0.005 and 18.7 to 14.7 minutes, P < 0.001, respectively). However, UDCA did not alter initial hepatic uptake. In PBC and PSC, there is a defect in hepatic bile acid excretion but not in uptake, implying bile acid retention. This retention is reduced by UDCA.

Task decomposition and analysis of robotic assembly task plans using Petri nets

This paper describes a framework for robotic task sequence planning which decomposes tasks into operations sequences for a generic robotic workcell. The approach provides robust execution of tasks through properties of: traceability-implicit mapping operations representation, and viability-retaining multiple execution. Given the descriptions of the objects in the system and all feasible geometric configurations and relationships among these objects, an AND/OR net which describes the relationships of all feasible geometric states and associated feasibility criteria for net transitions is generated. This AND/OR net is mapped into a Petri net which incorporates all feasible sequences of high level operations. The resulting Petri net is then decomposed in a stepwise manner into lower level Petri nets of which each transition can be directly implemented by control commands or command sequences based on devices and objects in the system, or, by lower level planning transitions corresponding to path planning, grasp planning, fine motion planning, etc. The property analysis for different levels of decomposition is also presented, and the inheritance of properties between levels is defined. All possible task sequences could be found using a search algorithm based on feasible system states. The shortest sequence may be chosen from the lowest level decomposition and is guaranteed to be the optimal output of the hierarchical planning system to efficiently implement the desired tasks. >

The contribution of DNA single-stranded order to the thermodynamics of duplex formation.

We report a direct determination of the thermodynamic contribution that DNA single-stranded order makes to DNA duplex formation. By using differential scanning calorimetry (DSC) and temperature-dependent UV absorbance spectroscopy, we have characterized thermodynamically the thermally induced disruption of the 13-mer duplex [d(CGCATGAGTACGC)].[d(GCGTACTCATGCG)] (henceforth called S1.S2) and its component single strands, [d(CGCATGAGTACGC)] (henceforth called S1) and [d(GCGTACTCATGCG)] (henceforth called S2). These spectroscopic and calorimetric measurements yield the following thermodynamic profiles at 25 degrees C: delta G degree = 20.0 kcal/mol, delta H degree = 117.0 kcal/mol, and delta S degree = 325.4 cal.degree-1.mol-1 for duplex melting of S1.S2; delta G degree = 0.45 kcal/mol, delta H degrees = 29.1 kcal/mol, and delta S degree = 96.1 cal.degree-1.mol-1 for single-strand melting of S1; delta G degree = 1.44 kcal/mol, delta H degree = 27.2 kcal/mol, and delta S degree = 86.4 cal.degree-1.mol-1 for single-strand melting of S2 (1 cal = 4.184 J). These data reveal that the two single-stranded structures S1 and S2 are only marginally stable at 25 degrees C, despite exhibiting rather substantial transition enthalpies. This behavior results from enthalpy and entropy contributions of similar magnitudes that compensate each other, thereby giving rise to relatively small free energies of stabilization for the single strands at 25 degrees C. By contrast, the S1.S2 duplex state is very stable at 25 degrees C since the favorable transition entropy associated with duplex disruption (325.4 cal.degree-1.mol-1) is more than compensated for by the extremely large duplex transition enthalpy (117.0 kcal/mol). We also measured directly an enthalpy change (delta H degree) of -56.4 kcal/mol for duplex formation at 25 degrees C using isothermal batch-mixing calorimetry. This duplex formation enthalpy of -56.4 kcal/mol at 25 degrees C is very different in magnitude from the duplex disruption enthalpy of 117.0 kcal/mol measured at 74 degrees C by DSC. Since the DSC measurement reveals the net transition heat capacity change to be close to zero, we interpret this large disparity between the enthalpies of duplex disruption and duplex formation as reflecting differences in the single-stranded structures at 25 degrees C (the initial states in the isothermal mixing experiment) and the single-stranded structures at approximately 80 degrees C (the final states in the DSC experiment). In fact, the enthalpy for duplex formation at 25 degree C (-56.4 kcal/mol) can be combined with the sum of the integral enthalpies requires to melt each single strand from 25 to 80 degree C (23.6 kcal/mol for S1 and 27.2 kcal/mol for S2) to calculate a delta H degree of -107.2 kcal/mol for the hypothetical process of duplex formation from "random-coil" "unstacked" single strands at 25 degree C. The magnitude of this predicted delta H degree value for duplex formation is in good agreement with the corresponding parameter we measure directly by DSC for duplex disruption (117.0 kcal/mol), thereby lending credence to our interpretation and analysis of the data. Thus, our results demonstrate that despite being only marginally stable at 25 degree C, single strands can exhibit intramolecular interactions that enthalpically poise them for duplex formation. For the duplex studied herein, prior to association at 25 degree C, the two complementary single strands already possess > 40% of the total enthalpy (50.8/117) that ultimately stabilizes the final duplex state. This feature of single-stranded structure near room temperature can reduce significantly the enthalpic driving force one might predict for duplex formation from nearest-neighbor data, since such data generally are derived from measurements in which the single strands are in their random-coil states. Consequently, potential contributions from single-stranded structure must be recognized and accounted for when designing hybridization experiments and when using isothermal titration and/or batch mixing techniques to study the formation of duplexes and higher-order DNA structures (e.g., triplexes, tetraplexes, etc.) from their component single strands.

Estimating Age-specific Transition Rates for Population Sub-groups from Successive Surveys: Changes in Adult Rates of Cigarette Smoking

Changes in smoking behavior in various population subgroups can be estimated by using a technique that also has applications in other demographic work. The technique is especially valuable where the available aggregate data for such things as age groups or survey intervals are irregular. When tested on smoking statistics from the New Zealand census which is conducted every 5 years and aggregates age group data in 5-year increments the method achieved statistically comparable results using irregular data to estimate the transition rates into and out of the population of smokers in the U.S. The method estimates net transition rates 1st by considering data for regular age groups and then expanding the formula to include irregular age groups. It also considers the special treatment necessary for the final open interval. Underlying the method is the assumption that age-specific growth rates of population subgroups are approximately constant within the age intervals specified by the data population. The technique produces better estimates the smaller the age intervals are and weak results for the open-ended age group. Changes in the proportions of the population married and single employed and unemployed or healthy and sick also may be estimated by the method. The technique can be used to study more than 2 population groups such as the proportion of light medium and heavy smokers.

?Superconducting? causal nets

The world is described as a relativistic quantum neural net with a quantum condensation akin to superconductivity. The sole dynamical variable is an operator representing immediate causal connection. The net enjoys a quantum principle of equivalence implying local LorentzSL(2,C) invariance and causality. The past-future asymmetry of its cell is similar to that of the neutrino. A net phase transition is expected at temperatures on the order of theW mass rather than the Planck mass, and near gravitational singularities.

Fast charge translocations associated with partial reactions of the Na,K-pump: II. Microscopic analysis of transient currents.

Nonstationary pump currents which have been observed in K+-free Na+ media after activation of the Na,K-ATPase by an ATP-concentration jump (see the preceding paper) are analyzed on the basis of microscopic reaction models. It is shown that the behavior of the current signal at short times is governed by electrically silent reactions preceding phosphorylation of the protein; accordingly, the main information on charge-translocating processes is contained in the declining phase of the pump current. The experimental results support the Albers-Post reaction scheme of the Na,K-pump, in which the translocation of Na+ precedes translocation of K+. The transient pump current is represented as the sum of contributions of the individual transitions in the reaction cycle. Each term in the sum is the product of a net transition rate times a "dielectric coefficient" describing the amount of charge translocated in a given reaction step. Charge translocation may result from the motion of ion-binding sites in the course of conformational changes, as well as from movement of ions in access channels connecting the binding sites to the aqueous media. A likely interpretation of the observed nonstationary currents consists in the assumption that the principal electrogenic step is the E1-P/P-E2 conformational transition of the protein, followed by a release of Na+ to the extracellular side. This conclusion is supported by kinetic data from the literature, as well as on the finding that chymotrypsin treatment which is known to block the E1-P/P-E2 transition abolishes the current transient. By numerical simulation of the Albers-Post reaction cycle, the proposed mechanism of charge translocation has been shown to reproduce the experimentally observed time behavior of pump currents.

Moment canting in the erbium-iron-manganese-boron system: Magnetization effects

We report that Er2Fe14−x MnxB compounds at 4 K have a component of the magnetization which is linear in the applied field. We attribute this to a noncollinear Er moment structure in which the Er moments rotate under application of an external field. The slope becomes very large (dM/dH=0.51μB/f.u./T) at x=2, near the composition where the net Er and transition metal sublattice magnetizations are equal at zero temperature. This enhanced field dependence suggests an additional moment rotation mechanism near compensation. In the compositions x=2.5 and 2.75, just above zero temperature compensation, the slope of the linear field dependence abruptly increases when the field reaches 5 and 7.2 T, respectively. High Mn concentrations have rare-earth-dominated magnetization curves with substantial curvature at low fields and a linear nonsaturating field dependence at high fields. Anomalies are also observed in the initial magnetization behavior above x=2.5.

Effect of bisacodyl on intestinal electrolyte and water net transport and transit. Perfusion studies in men.

The effect of bisacodyl on intestinal electrolyte, glucose, and water transport, and transit was studied in 6 healthy volunteers by intestinal perfusion. A 5-lumen tube with an occluding balloon allowed constant perfusion (10 ml/min) of 30 cm of the upper jejunum and a rapid collection of the perfusate free of contaminants. A phenol red bolus was injected into the tube and its passage through the test segment was calculated by dye dilution formula. A 1-hour control period was followed by a test period with 6 mg/h bisacodyl and followed by 2 other 1-hour control periods. Net absorption of Na+ (0.35 +/- 0.08 mmol/min) and water (1.7 +/- 0.6 ml/min) changed to net secretion (Na+ -0.93 +/- 0.3 ml/min; water -6.6 +/- 1.9 ml/min), glucose absorption decreased from 25.4% +/- 1.1 to 6.3 +/- 0.5 mg/min and K secretion was enhanced. 62 +/- 2.1% of bisacodyl was absorbed in the 30-cm jejunal segment. Mean transit time decreased from 8.5 +/- 1 to 4.4 +/- 0.7 min and mean flow rate increased from 8.4 +/- 0.6 16.6 +/- 1.9 ml/min. There was an inverse linear relationship between mean transit time and mean flow rate. All the effects of bisacodyl were fully or at least partially reversible. Volume and calculated radius of the test segment remained constant and did not change under bisacodyl. It is concluded, that the secretory effect of bisacodyl is mainly responsible for the decreased mean transit time rather than a direct effect on motility.