Time Partitioning Research Articles

Population analyses of kinetic partitioning in protein folding.

A simple lattice model of protein folding is studied in order to analyze the kinetic partitioning phenomena in the energy landscape perspective. By restricting the area of conformational space, it becomes possible to follow many Monte Carlo trajectories until they reach equilibrium. Alteration of population of trajectories is monitored and the relations between the energy landscape and kinetics are examined. Kinetic partitioning phenomena are categorized into different types in terms of characteristic time constants and partitioning ratio. In a specific partitioning process, refolding proceeds along the parallel pathways; the time constants have a temperature dependence similar to that observed in hen lysozyme. High-energy conformations are classified into groups according to the probability that the trajectories starting from those conformations will reach each energy valley. The partitioning ratio is determined by the way in which the conformational space is organized into these groups.

Retention time of macerated alfalfa hay and silage in sheep.

Fresh alfalfa was mowed and conditioned mechanically at four levels: a control (rubber rolls), macerated once (a single passage through three finely corrugated rolls set at 1-mm clearance), macerated twice (two passages), and macerated thrice (three passages). Alfalfa was then field-wilted either for 45 h and conserved as chopped silage at 30% dry matter (DM) or for 94 h and stored as baled hay at 85% DM. The eight forage treatments (four mechanical conditioning levels x two conservation systems) were fed to 24 sheep (three replications per treatment) during 5 wk. At the beginning of wk 5, a 15-g sample of chromium-mordanted forage (3.5% Cr) was fed to each sheep, and feces samples were collected at 30 different times over 7 d, between 10 h and 168 h after Cr ingestion. Four models were used to estimate the passage rates, the time delay, and the mean retention time (MRT). A two-compartment time-dependent model and a multicompartment model produced the best fit (average r2 of 0.96) to represent the Cr concentration in the feces over time. When compared with alfalfa hay, alfalfa silage had a higher (P < 0.01) time-dependent turnover rate (0.0949 vs 0.0733/h), a lower (P = 0.03) time delay (9.1 vs 11 h), and a lower (P = 0.04) MRT (57.8 vs 64.4 h). Maceration did not affect significantly (P > 0.10) the time delay or the MRT. However, the MRT of macerated alfalfa hay tended to be higher than the MRT of control hay. Experimental data based on marker concentration in the feces can be used satisfactorily to assess differences in MRT between treatments, but they should be used with caution to estimate the partition of retention time within the gastrointestinal tract.

On the Use of the Time Axis for Ecological Separation: Diel Rhythms as an Evolutionary Constraint

On the Use of the Time Axis for Ecological Separation: Diel Rhythms as an Evolutionary Constraint

Group-based estimation of missing hydrological data: II. Application to streamflows

The group approach that treats hydrological data as groups rather than as single-valued observations was proposed in a companion paper. Various models representing four techniques are briefly presented and applied to single series and bi-series cases, respectively, in this paper. The techniques represented by these models are regression, time series analysis, partitioning modelling, and artificial neural networks. The utility of the models for estimating missing streamflow data using the group approach is investigated. It turns out that the group approach is valid for estimating missing values, and possibly other applications, when data are significantly auto-correlated.

Group-based estimation of missing hydrological data: I. Approach and general methodology

In this first paper in a set of two, the problem of estimating missing segments in streamflow records is described. The group approach, different from the traditional single-valued approach, is proposed and explained. The approach perceives the hydrological data as sequence of groups rather than single-valued observations. The techniques suggested to handle the group approach are regression, time series analysis, partitioning modelling, and artificial neural networks. Pertinent literature is reviewed and background material is used to support the group approach. Implementation and comparisons of models' performance are deferred to the second paper.

Smart antenna spatial sweeping for combined directionality and transmit diversity

In this paper, we present a novel application for antenna arrays in wireless communication systems. Here, antenna arrays at the base station are used to create 1) directionality which supports spatial multiplexing and 2) a scanning beam pattern, allowing receivers at the mobile unit to subdivide the symbol time into L partitions, each with independent fades. Combining the signals received in different symbol time partitions (at the mobile unit) results in diversity gains. In this way, diversity benefits (due to an antenna array) are achieved at the mobile unit with the smart antenna array located at the base station (rather than in the mobile itself), a significant cost saving for wireless communication systems.

Free banking and credit creation: Implications for business cycle theory

For the element of Time, which is the center of the chief difficulty of almost every economic problem, is itself absolutely continuous: Nature knows no partition of time into long periods and short; but the two shade into one another by imperceptible gradations, and what is the short period for one problem is a long period for another. (Marshall 1936) W hile the element of time may be the chief difficulty of almost every economic problem, the difficulties are most apparent and most persistently resist generally accepted solutions in the area of monetary theory and macroeconomics. Money, which simultaneously functions as a medium of exchange and a store of value, may be viewed as the quintessential present good or as a future good, the most liquid store of value. This dual nature of money has been the center of macroeconomic controversy since the time of the classical economists. The Austrian business cycle theory is a blend of monetary and capital theory and highlights coordination problems connected to “time and money.” In the framework developed by Ludwig von Mises, banks create money by creating credit. This created credit finances investment in excess of savings, distorts the structure of production, and sets the stage for the boom–bust cycle. But what is created credit and when and how do banks create credit? Different answers to this question yield different implications for business cycle theory, research, and monetary policy, as well as different monetary reform proposals. Section two examines the classical roots of the time, money,

Phylogeny and Speciation of Felids.

The phylogeny of the Felidae is reconstructed using a total evidence approach combining sequences from 12S rRNA, 16S rRNA, NADH-5, and cytochrome b genes with morphological and karyological characters. The 1504-character data set generated two equally parsimonious trees (CI = 0.413, 1795 steps) of which a strict consensus revealed one polytomy in the placement of the bay cat group. The tree supports several traditional groupings such as the genera Panthera and Lynx and the ocelot group of small South American felids, and it provides additional resolution of relationships within and among the major felid lineages. Combining phylogenetic, distributional, and ecological data indicates that vicariant speciation has played a relatively minor role in the diversification of the felids (approximately 26% of events), while sympatric speciation has been more important than expected on theoretical grounds (approximately 51.8% of events), although postspeciation dispersal may have blurred the boundaries between sympatric, parapatric, and peripheral isolate modes. An examination of ecological changes on the felid tree shows repeated patterns of resource partitioning in time (activity patterns), space (preferred habitat type), and food (as measured by body size) among closely related species. The rapid diversification of the cats thus appears to have been associated more with ecological than with geological separation.

Phylogeny and Speciation of Felids

The phylogeny of the Felidae is reconstructed using a total evidence approach combining sequences from 12S rRNA, 16S rRNA, NADH-5, and cytochrome b genes with morphological and karyological characters. The 1504-character data set generated two equally parsimonious trees (CI = 0.413, 1795 steps) of which a strict consensus revealed one polytomy in the placement of the bay cat group. The tree supports several traditional groupings such as the genera Panthera and Lynx and the ocelot group of small South American felids, and it provides additional resolution of relationships within and among the major felid lineages. Combining phylogenetic, distributional, and ecological data indicates that vicariant speciation has played a relatively minor role in the diversification of the felids (approximately 26% of events), while sympatric speciation has been more important than expected on theoretical grounds (approximately 51.8% of events), although postspeciation dispersal may have blurred the boundaries between sympatric, parapatric, and peripheral isolate modes. An examination of ecological changes on the felid tree shows repeated patterns of resource partitioning in time (activity patterns), space (preferred habitat type), and food (as measured by body size) among closely related species. The rapid diversification of the cats thus appears to have been associated more with ecological than with geological separation.

Timing of primary growth harvest affects the yield and nutritive value of timothy-red clover mixtures

The effects of partition of growth time between primary growth and regrowth of organically grown mixed (mainly timothy and red clover) leys were studied over two years in Juva, Finland. Primary growth was harvested at three different dates and regrowth on a single occasion from all plots. Dry matter (DM) yield of primary growth increased by 116 kg per ha per day by delaying harvest (P

Time Discretization of Parabolic Problems by the HP-Version of the Discontinuous Galerkin Finite Element Method

The discontinuous Galerkin finite element method (DGFEM) for the time discretization of parabolic problems is analyzed in the context of the hp-version of the Galerkin method. Error bounds which are explicit in the time steps as well as in the approximation orders are derived and it is shown that the hp-DGFEM gives spectral convergence in problems with smooth time dependence. In conjunction with geometric time partitions it is proved that the hp-DGFEM results in exponential rates of convergence for piecewise analytic solutions exhibiting singularities induced by incompatible initial data or piecewise analytic forcing terms. For the h-version DGFEM algebraically graded time partitions are determined that give the optimal algebraic convergence rates. A fully discrete hp scheme is discussed exemplarily for the heat equation. The use of certain mesh-design principles for the spatial discretizations yields exponential rates of convergence in time and space. Numerical examples confirm the theoretical results.

Modelling of Microsegregation

A numerical model has been developed for the quantitative prediction of microsegregation during solidification of ternary alloys. Due to the computational efficiency of the algorithm, this model can be incorporated into macrosegregation calculations performed at the scale of a whole casting. Solidification and possible remelting are calculated for an open system, i.e., for a small volume element whose average solute contents are not necessarily constant during the casting. Assuming uniform temperature in this small volume element, the variations of average enthalpy and solute contents are assumed to be known functions of time resulting from the average continuity equations solved at the macroscopic scale. This microsegregation model developed for globulitic grain structures considers the diffusion of the solute elements in one dimension with a front-tracking procedure for the primary solid-liquid interface. Solute back-diffusion in the primary phase occurring during the various stages of solidification (primary, eutectic valley and ternary eutectic solidification) are taken into account through an implicit finite difference formulation with a Landau transformation for the mapping of the variable solid comain onto a fixed [0,1] interval. Complete solute mixing in the liquid is assumed and the solid phases different from the primary phase are supposed to be stoechiometric and the most stable. This model also allows the consideration of different specific masses for the liquid and solid, temperature-dependent solute diffusivities in the primary phase and non-linear phase diagram. A coupling with phase diagram calculations obtained ith the Thermo-Cale software [1] has been performed through mapping files. At each microscopic time step, liquidus slopes and partition coefficients of each involved phase are bilinearly interpolated from this file, resulting in an accurate and efficient microsegregation calculation. This model is applied to the case of an Al-Mg-Si alloy. From the enthalpy and average solute content evolutions, it allows to obtain the calculated concentration profiles of the solute elements and the solidification path of the alloy, including the formation of the primary phase, the solidification along a monovariant line and the precipitation of ternary eutectic. The new liquid concentrations, the new temperature, the new average specific mass and the new fraction of each phase calculated by the present model are the input of the next macrosegregation calculation step. Homogenisation treatment of low-concentration alloys can also be predicted by mapping the solvus surfaces of the phase diagram in a similar way. This approach can be extended to more complex alloy systems but direct access to Thermo-Cale [1] should be made in order to avoid too large mapping files.

DISTRIBUIÇÃO NO TEMPO GEOLÓGICO DOS PRINCIPAIS DEPÓSITOS MINERAIS BRASILEIROS: 1. CADASTRO DOS MODELOS GENÉTICOS E IDADES DOS DEPÓSITOS

The knowledge of mineral deposits time partition is an important prospection guide because when restricted to a given epoch, mineral deposits concentrate within one geological unit. In this paper a file with informations about the 194 main brazilian mineral deposits is shown. These deposits were selected mainly by their economic significance, to point out metalogenic processes active during a certain epoch and by their prospective significance as indicators of potential for mineral deposits of the same type, in one region or geological unit. The file contains data about (1) ore composition, (2) deposit name and location, (3) probable genetic model, (4) age of mineralization and (5) references. In the second part of this work these mineral deposits will be grouped and each deposit will be located on geological time accordingly their ore ages. Epochs when groups of mineral deposit formed will be compared with the main brazilian thermo-tectonic events.

DISTRIBUIÇÃO NO TEMPO GEOLÓGICO DOS PRINCIPAIS DEPÓSITOS MINERAIS BRASILEIROS: 1. CADASTRO DOS MODELOS GENÉTICOS E IDADES DOS DEPÓSITOS

The knowledge of mineral deposits time partition is an important prospection guide because when restricted to a given epoch, mineral deposits concentrate within one geological unit. In this paper a file with informations about the 194 main brazilian mineral deposits is shown. These deposits were selected mainly by their economic significance, to point out metalogenic processes active during a certain epoch and by their prospective significance as indicators of potential for mineral deposits of the same type, in one region or geological unit. The file contains data about (1) ore composition, (2) deposit name and location, (3) probable genetic model, (4) age of mineralization and (5) references. In the second part of this work these mineral deposits will be grouped and each deposit will be located on geological time accordingly their ore ages. Epochs when groups of mineral deposit formed will be compared with the main brazilian thermo-tectonic events.

Time-partitioning heuristics: Application to one warehouse, multiitem, multiretailer lot-sizing problems

We describe effective time partitioning heuristics for dynamic lot-sizing problems in multiitem and multilocation production/distribution systems. In a time-partitioning heuristic, the complete horizon of (say) N periods, is partitioned into smaller intervals. An instance of the problem is solved, to optimality, on each of these intervals, and the resulting solution coalesced into a solution for the complete horizon. The intervals are selected to be of a size which permits the use of exact and effective solution methods (e.g., branch-and-bound methods). Each interval's problem is specified to include options for starting conditions which adequately complement the solutions obtained for prior intervals. The heuristics can usually be designed to be of low polynomial complexity as well as to guarantee ϵ-optimality for any desired precision ϵ > 0, and asymptotic optimality as N goes to infinity. We first give a general description of the design of time-partitioning heuristics for dynamic lot-sizing problems. We subsequently develop such a heuristic in detail, for the one warehouse multiretailer model representing a two-echelon distribution network with m retailers, selling J distinct items. A comprehensive numerical study exhibits that the partitioning heuristics are very efficient and close-to-optimal. Even problems with a planning horizon of up to 150 periods can be solved within 1.5% of optimality, employing intervals of 5–10 periods only and in a matter of CPU seconds, or up to a few minutes, using longer intervals and when the number of items and retailers is large. These CPU times refer to a SUN 4M (SPARC) workstation. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 463–486, 1999

Accurate computation of quantum densities of states and RRKM rate constants for large polyatomic molecules: The STAIR method

A new method is given for the computation of quantum mechanical microcanonical densities of states of large molecules. The method is based on the observation that for large molecules with many vibrational degrees of freedom, the complex time partition function dephases rapidly allowing for a good short-time approximation. The short-time approximation up to third order gives an Airy function expression for the thermal density of states at a given temperature T. The microcanonical density of states is then deduced from the thermal density. The input needed for the method is the first three moments of the Hamiltonian at a series of temperatures, which adequately cover the energy range of interest. These may be computed using quantum Monte Carlo methods. The method is tested for a harmonic model of trans-stilbene, a separable anharmonic model of cyclopropane, and a separable anharmonic model of a system with 50 degrees of freedom. The short-time Airy method is found to give accurate estimates for the density of states, the integrated density of states, and RRKM microcanonical rate constants.

Eliminating autocorrelation reduces biological relevance of home range estimates

1. Destructive subsampling or restrictive sampling are often standard procedures to obtain independence of spatial observations in home range analyses. We examined whether home range estimators based upon kernel densities require serial independence of observations, by using a Monte Carlo simulation, antler flies and snapping turtles as models. 2. Home range size, time partitioning and total straight line distances travelled were tested to determine if subsampling improved kernel performance and estimation of home range parameters. 3. The accuracy and precision of home range estimates from the simulated data set improved at shorter time intervals despite the increase in autocorrelation among the observations. 4. Subsampling did not reduce autocorrelation among locational observations of snapping turtles or antler flies, and home range size, time partitioning and total distance travelled were better represented by autocorrelated observations. 5. We found that kernel densities do not require serial independence of observations when estimating home range, and we recommend that researchers maximize the number of observations using constant time intervals to increase the accuracy and precision of their estimates.

Effect of Gestational Stress on Maternal Behavior in Response to Cage Transfer and Handling of Pups in Two Strains of Rat

The influence of gestational stress was determined on the mother's behavior in two rat strains after a disturbance in her routine. Daily 10 min observations were made for 9 days postpartum in Sprague-Dawley (S-D) and Sabra (SB) rats after transfer of the maternal cage to another room or transient pup removal. In response to cage transfer, SB spent much more time than S-D rats in nursing, licking and sitting on their pups, but less time in individual activities. The direction of effect of gestational stress depended on the strain and particular behavior. The duration of nursing was increased in S-D but decreased in SB rats, while that of pup-licking was increased in SB and unchanged or decreased in S-D. Pup-removal reduced the total amount of pup-directed behavior in control and stressed mothers of both strains and eliminated any differences resulting from gestational stress seen in response to cage transfer. It is concluded that the degree and direction of effect of gestational stress on the partition of time by a nursing mother between pup-directed and other behaviors during the early postnatal period is strongly influenced by the strain of rat and the conditions under which it is assessed.

Association rules and data mining in hospital infection control and public health surveillance.

The authors consider the problem of identifying new, unexpected, and interesting patterns in hospital infection control and public health surveillance data and present a new data analysis process and system based on association rules to address this problem. The authors first illustrate the need for automated pattern discovery and data mining in hospital infection control and public health surveillance. Next, they define association rules, explain how those rules can be used in surveillance, and present a novel process and system--the Data Mining Surveillance System (DMSS)--that utilize association rules to identify new and interesting patterns in surveillance data. Experimental results were obtained using DMSS to analyze Pseudomonas aeruginosa infection control data collected over one year (1996) at University of Alabama at Birmingham Hospital. Experiments using one-, three-, and six-month time partitions yielded 34, 57, and 28 statistically significant events, respectively. Although not all statistically significant events are clinically significant, a subset of events generated in each analysis indicated potentially significant shifts in the occurrence of infection or antimicrobial resistance patterns of P. aeruginosa. The new process and system are efficient and effective in identifying new, unexpected, and interesting patterns in surveillance data. The clinical relevance and utility of this process await the results of prospective studies currently in progress.

Optimization of transmission and emission scan duration in 3D whole-body PET

Whole-body PET imaging is being increasingly used to identify and localize malignant disease remote from the site of the primary tumour. Patients are typically scanned at multiple contiguous bed positions over an axial length of 75-100 cm. Ideally, for oncology patients, the total scan duration should not exceed about an hour and therefore only 5-10 minutes of imaging can be performed at each bed position. To minimize the total scan duration, the transmission scan is often omitted and the emission scan reconstructed without attenuation correction. However, whole-body scans reconstructed without attenuation are non-quantitative and can lead to incorrect diagnoses, particularly for tumours located deep within the body. We have performed a series of torso phantom measurements on a 3D PET scanner (ECAT ART) to investigate the optimal partition of scan time between the emission and transmission scans for a fixed total scan duration. We find that 20%-40% of the total scan time should be dedicated to the transmission acquisition to minimize noise in the attenuation-corrected image. The optimal partition depends on the method of calculating the attenuation correction factors and on the reconstruction algorithm.