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Results for “Deterministic Measurement”

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At least 487 records · Page 27Linked to original sources

PubMed1999

Test for low-dimensional determinism in electroencephalograms.

We tested low-dimensional determinism in an electroencephalogram (EEG), based on the fact that smoothness (continuity) on an embedded phase space is enough to imply determinism within time series. A modified version of the method developed by Salvino and Cawley [Phys. Rev. Lett. 73, 1091 (1994)] was used. In our method, we chose a box randomly and then estimated the mean directional element in the box containing the d+1 data points, where d is the embedding dimension. The global average for the mean local directional elements over the boxes, W, is a measure for smoothness. The nonlinear noise reduction method developed by Sauer [Physica D 58, 193 (1992)] is then applied to the EEG. We also compared the results for the EEG with those for its surrogate data. We found that the W values for the noise-reduced EEG had stable values around 0.35, which means that the EEG is not a low-dimensional deterministic signal. However, this method may not be applicable to the time series generated from high-dimensional deterministic systems. We cannot exclude the possibility that the determinism in the EEG may be too high-dimensional to be detected with current methods.

Algorithms↗

PubMed2006

Complete deterministic linear optics Bell state analysis.

We show how hyperentanglement allows us to deterministically distinguish between all four polarization Bell states of two photons. In this proof-of-principle experiment, we employ the intrinsic time-energy correlation of photon pairs generated with high temporal definition in addition to the polarization entanglement obtained from parametric down-conversion. For the identification, no nonlinear optical elements or auxiliary photons are needed. The new possibilities this complete Bell measurement offers are demonstrated by realizing an optimal dense coding protocol.

Journal Article↗

PubMed2005

A model (in)validation approach to gait classification.

This paper addresses the problem of human gait classification from a robust model (in)validation perspective. The main idea is to associate to each class of gaits a nominal model, subject to bounded uncertainty and measurement noise. In this context, the problem of recognizing an activity from a sequence of frames can be formulated as the problem of determining whether this sequence could have been generated by a given (model, uncertainty, and noise) triple. By exploiting interpolation theory, this problem can be recast into a nonconvex optimization. In order to efficiently solve it, we propose two convex relaxations, one deterministic and one stochastic. As we illustrate experimentally, these relaxations achieve over 83 percent and 86 percent success rates, respectively, even in the face of noisy data.

Algorithms↗

PubMed1998

Fetal dose evaluation during breast cancer radiotherapy.

PURPOSE: The aim of the work was to estimate the radiation dose delivered to the fetus in a pregnant patient irradiated for breast cancer. METHODS AND MATERIALS: A 45-year woman was treated for left breast cancer using a 6 MV photon beam with two isocentric opposing tangential unwedged fields. Daily dose was 2.3 Gy at 95% isodose line given by two fields/day, 5 days/week. A total dose of 46 Gy was given in 20 fractions over a 4-week period. Pregnancy confirmed during the second therapeutic week. Treatment lasted between the second and sixth gestation week. Radiation dose to fetus was estimated from in vivo and phantom measurements using thermoluminescence dosimeters and an ionization chamber. In vivo measurements were performed by inserting either a catheter with TL dosimeters or ionization chamber into the patient's rectum. Phantom measurements were performed by simulating the treatment conditions on an anthropomorphic phantom. RESULTS: TLD measurements (in vivo and phantom) revealed fetal dose to be 0.085% of the tumor dose, corresponding to a cumulative fetal dose of 3.9 cGy for the entire treatment of 46 Gy. Chamber measurements (in vivo and phantom) revealed a fetal dose less than the TLD result: 0.079 and 0.083% of the tumor dose corresponding to cumulative fetal dose of 3.6 cGy and 3.8 cGy for in vivo and phantom measurement, respectively. CONCLUSIONS: It was concluded that the cumulative dose delivered to the unshielded fetus was 3.9 cGy for a 46 Gy total tumor dose. The estimated fetal dose is low compared to the total tumor dose given due to the early stage of pregnancy, the large distance between fundus-radiation field, and the fact that no wedges and/or lead blocks were used. No deterministic biological effects of radiation on the live-born embryo are expected. The lifetime risk for radiation-induced fatal cancer is higher than the normal incidence, but is considered as inconsequential.

Breast Neoplasms↗

PubMed2000

Hitchhiking under positive Darwinian selection.

Positive selection can be inferred from its effect on linked neutral variation. In the restrictive case when there is no recombination, all linked variation is removed. If recombination is present but rare, both deterministic and stochastic models of positive selection show that linked variation hitchhikes to either low or high frequencies. While the frequency distribution of variation can be influenced by a number of evolutionary processes, an excess of derived variants at high frequency is a unique pattern produced by hitchhiking (derived refers to the nonancestral state as determined from an outgroup). We adopt a statistic, H, to measure an excess of high compared to intermediate frequency variants. Only a few high-frequency variants are needed to detect hitchhiking since not many are expected under neutrality. This is of particular utility in regions of low recombination where there is not much variation and in regions of normal or high recombination, where the hitchhiking effect can be limited to a small (<1 kb) region. Application of the H test to published surveys of Drosophila variation reveals an excess of high frequency variants that are likely to have been influenced by positive selection.

Animals↗

PubMed2002

Minimizing radiation-induced skin injury in interventional radiology procedures.

Skin injury is a deterministic effect of radiation. Once a threshold dose has been exceeded, the severity of the radiation effect at any point on the skin increases with increasing dose. Peak skin dose is defined as the highest dose delivered to any portion of the patient's skin. Reducing peak skin dose can reduce the likelihood and type of skin injury. Unfortunately, peak skin dose is difficult to measure in real time, and most currently available fluoroscopic systems do not provide the operator with sufficient information to minimize skin dose. Measures that reduce total radiation dose will reduce peak skin dose, as well as dose to the operator and assistants. These measures include minimizing fluoroscopy time, the number of images obtained, and dose by controlling technical factors. Specific techniques-dose spreading and collimation-reduce both peak skin dose and the size of skin area subjected to peak skin dose. For optimum effect, real-time knowledge of skin-dose distribution is invaluable. A trained operator using well-maintained state-of-the art equipment can minimize peak skin dose in all fluoroscopically guided procedures.

Dose-Response Relationship, Radiation↗

PubMed2002

A mathematical model of a biological arms race with a dangerous prey.

In a recent paper, Brodie and Brodie provide a very detailed description of advances and counter-measures among predator-prey communities with a poisonous prey that closely parallel an arms race in modern society. In this work, we provide a mathematical model and simulations that provide a theory as to how this might work. The model is built on a two-dimensional classical predator-prey model that is then adapted to account for the genetics and random mating. The deterministic formulation for the genetics for the prey population has been developed and used in other contexts. Adapting the model to allow for genetic variation in the predator is much more complicated. The model allows for the evolution of the poisonous prey and for the evolution of the resistant predator. The biological paradigm is that of the poisonous newt and the garter snake which has been studied extensively although the models are broad enough to cover other examples.

Animals↗

PubMed2005

Sequence learning under dual-task conditions: alternatives to a resource-based account.

In two experiments with the serial reaction-time task, participants were presented with deterministic or probabilistic sequences under single- or dual-task conditions. Experiment 1 showed that learning of a probabilistic structure was not impaired over a first session by performing a counting task, but that such an interference arose over a second session, when the knowledge was tested under single-task conditions. In contrast, the effects of the secondary task arose earlier for participants exposed to deterministic sequences. This difference between deterministic and probabilistic sequences disappeared in Experiment 2, where the counting task was performed on tones associated to the locations. Comparisons between sessions indicated that the secondary task affected not only the expression but also the acquisition of sequence learning, and that greater interference was observed in those conditions that yielded more explicit knowledge. These results suggest that the effects of a dual task on the measures of implicit sequence learning may be partly due to the intrusion of explicit knowledge and partly due to the disruption of the sequence produced by the inclusion of random events.

Cues↗

PubMed2003

Comparison of simulated annealing and mean field annealing as applied to the generation of block designs.

This paper describes an experimental comparison between a discrete stochastic optimization procedure (Simulated Annealing, SA) and a continuous deterministic one (Mean Field Annealing), as applied to the generation of Balanced Incomplete Block Designs (BIBDs). A neural cost function for BIBD generation is proposed with connections of arity four, and its continuous counterpart is derived, as required by the mean field formulation. Both strategies are optimized with regard to the critical temperature, and the expected cost to the first solution is used as a performance measure for the comparison. The results show that SA performs slightly better, but the most important observation is that the pattern of difficulty across the 25 problem instances tried is very similar for both strategies, implying that the main factor to success is the energy landscape, rather than the exploration procedure used.

Algorithms↗

PubMed2003

Protection of the environment: how to position radioprotection in an ecological risk assessment perspective.

The development of a system capable of ensuring adequate protection of the environment from the harmful effects of ionising radiation is at present particularly debated. This need comes both from a restrictive consideration of the environment in the so far existing system for human radioprotection, and the planetary-wide growing concerns about man's technogenic influence on his environment which have yielded 'sustainability' and 'precaution' as guiding principles for environmental protection. Whilst evolving from the field of human radioprotection, the radioprotection of the environment needs to be discussed in a wider perspective, with particular emphasis on the most advanced concepts which emerge from the efforts to deriving improved approaches to Ecological Risk Assessment. For the sake of protection, the environment is traditionally addressed through its biota since these are the sensitive components of ecosystems. Similarities between man and biotas reflect the ubiquitous mechanistic effects of radiation on life which disrupt molecules. However, important differences also arise in a number of perspectives, from the large spectrum of different species of biotas to their hierarchical self-organisation as interacting populations within ecosystems. Altogether, these aspects are prone to promote complex arrays of different responses to stress which lie beyond the scope of human radioprotection due to its focus on individuals of a single species. By means of selected illustrations, this paper reviews and discusses the current challenges faced in proper identification of measurable effect endpoints (stochastic/deterministic, individual/population- or ecosystem-relevant), dose limits in chronic exposure (or levels of concern), and their consideration according to radiation type (RBE) and interactions with other contaminants (synergies/antagonisms) which represent critical gaps in knowledge. The system of human radioprotection has conceptually been targeted at limiting cancer induction (stochastic) in human individuals, whereas the current approach in radioprotection of biota targets reproductive success (deterministic) and cytogenetic effects, thought to have the highest significance at population and ecosystem levels. The focus on individuals in a bottom-up approach, due to the ease with which it may be quantified, has prompted the development of current ecotoxicological methods as a scientific foundation for environmental protection regulation. However, the most recent ecological theories, which emphasise on complex systems as a key to modern ecological understanding, call for the additional consideration of more holistic, top-down, approaches. Critically, dose-effect relationships of the subsystem components may lose their predictive ability at the system level.

Animals↗

PubMed1994

Quantification of evolution from order to randomness in practical time series analysis.

The principal focus of this chapter is the description of a recently developed, readily usable regularity statistic, ApEn, that quantifies the continuum from perfectly orderly to completely random in time series data. Several properties of ApEn facilitate its utility for practical time series analysis: (1) ApEn is nearly unaffected by noise of magnitude below a de facto specified filter level; (2) ApEn is robust to outliers; (3) ApEn can be applied to time series of 100 or more points, with good confidence (established by standard deviation calculations); (4) ApEn is finite for stochastic, noisy deterministic, and composite (mixed) processes, the last of which are likely models for complicated biological systems; (5) increasing ApEn corresponds to intuitively increasing process complexity in the settings of (4). This applicability to medium-sized data sets and general stochastic processes is in marked contrast to capabilities of "chaos" algorithms such as the correlation dimension, which are properly applied to low-dimensional iterated deterministic dynamical systems. The potential uses of ApEn to provide new insights in biological settings are thus myriad, from a perspective complementary to that given by classic statistical methods. The ApEn statistic is typically calculated by a computer program, with a FORTRAN listing for a "basic" code referenced above. It is imperative to view ApEn as a family of statistics, each of which is a relative measure of process regularity. For proper implementation, the two input parameters m (window length) and r (tolerance width, de facto filter) must remain fixed in all calculations, as must N, the data length, to ensure meaningful comparisons. Guidelines for m and r selection are indicated above. We have found normalized regularity to be especially useful; "r" is chosen as a fixed percentage (often 15 or 20%) of the SD of the subject rather than of a group SD. This version of ApEn has the property that it is decorrelated from process SD, in that it remains unchanged under uniform process magnification or reduction; thus we can entirely separate the questions of SD change and regularity change in data analysis. Because regularity questions are thematically orthogonal to the type of information that, for example, moment statistics ascertain, we highly recommend that ApEn be used in conjunction with other such statistics, rather than as a sole indicator of process typicality. Last and yet foremost, we recommend the following order of detail in Practical analysis. First, either visually or algorithmically, eliminate outliers.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity Cycles↗

PubMed2006

The ICRU (International Commission on Radiation Units and Measurements): its contribution to dosimetry in diagnostic and interventional radiology.

The ICRU (International Commission on Radiation Units and Measurements was created to develop a coherent system of quantities and units, universally accepted in all fields where ionizing radiation is used. Although the accuracy of dose or kerma may be low for most radiological applications, the quantity which is measured must be clearly specified. Radiological dosimetry instruments are generally calibrated free-in-air in terms of air kerma. However, to estimate the probability of harm at low dose, the mean absorbed dose for organs is used. In contrast, at high doses, the likelihood of harm is related to the absorbed dose at the site receiving the highest dose. Therefore, to assess the risk of deterministic and stochastic effects, a detailed knowledge of absorbed dose distribution, organ doses, patient age and gender is required. For interventional radiology, where the avoidance of deterministic effects becomes important, dose conversion coefficients are generally not yet developed.

Calibration↗

PubMed2004

A method for a real time estimation of entrance skin dose distribution in interventional neuroradiology.

Interventional neuroradiology can involve very high entrance skin doses to patients and has the potential to induce deterministic radiation effects to the skin. A monitoring system indicating the maximum entrance skin dose during procedures could be useful to avoid skin injuries and to optimize technical parameters. Such evaluation is difficult, because exposure conditions change many times during each procedure. A data acquisition system for real time estimation of patient dose was developed, using a transmission ionization chamber connected to a personal computer, simultaneously measuring air kerma and dose area product. Input data were processed by a software that provided a map of entrance skin dose and stored all the information in a database. The method was first applied during 16 interventional procedures and was found to be suitable to this application thanks to the short time necessary for dose measurements, simplicity of use and absence of interference with the procedure execution. The uncertainty of estimation of maximum entrance skin dose was evaluated to be about 20% at the 1 sigma level.

Algorithms↗

PubMed1989

Stochastic models of soil denitrification.

Soil denitrification is a highly variable process that appears to be lognormally distributed. This variability is manifested by large sample coefficients of variation for replicate estimates of soil core denitrification rates. Deterministic models for soil denitrification have been proposed in the past, but none of these models predicts the approximate lognormality exhibited by natural denitrification rate estimates. In this study, probabilistic (stochastic) models were developed to understand how positively skewed distributions for field denitrification rate estimates result from the combined influences of variables known to affect denitrification. Three stochastic models were developed to describe the distribution of measured soil core denitrification rates. The driving variables used for all the models were denitrification enzyme activity and CO(2) production rates. The three models were distinguished by the functional relationships combining these driving variables. The functional relationships used were (i) a second-order model (model 1), (ii) a second-order model with a threshold (model 2), and (iii) a second-order saturation model (model 3). The parameters of the models were estimated by using 12 separate data sets (24 replicates per set), and their abilities to predict denitrification rate distributions were evaluated by using three additional independent data sets of 180 replicates each. Model 2 was the best because it produced distributions of denitrification rate which were not significantly different (P > 0.1) from distributions of measured denitrification rates. The generality of this model is unknown, but it accurately predicted the mean denitrification rates and accounted for the stochastic nature of this variable at the site studied. The approach used in this study may be applicable to other areas of ecological research in which accounting for the high spatial variability of microbiological processes is of interest.

Journal Article↗

PubMed2004

Analysis of sleep-stage characteristics in full-term newborns by means of spectral and fractal parameters.

STUDY OBJECTIVES: In this work, we studied the behavior of the fractal dimension during each of the neonatal electroencephalogram (EEG) sleep phases and during the awake state, comparing the results with those of the classical spectral parameters and with zero crossing values. DESIGN: Fractal dimension, zero crossing, and spectral parameters of the EEG bands were determined for each 2-second frame of the EEG sleep-time series. Eight channels of each EEG recording were examined. PARTICIPANTS: Twenty healthy full-term newborns (10 boys and 10 girls) with normal psychomotor development evaluated at 24 and 36 months of age, were chosen to participate in this study. MEASUREMENTS AND RESULTS: Fractal analysis showed that where rhythmic and regular activity are present, as during quiet sleep, the fractal dimension is low and rises when bioelectric activity is more variable and complex, reaching its maximum value during wakefulness. The discriminative value of this parameter was similar to that of some spectral bands. CONCLUSIONS: This work was an initial attempt to apply techniques derived from the nonlinear deterministic studies used to evaluate system complexity, to the neonatal EEG, in order to acquire a normative database that can be used as a reference in neurological pathologies. Fractal dimension alone or together with zero crossing and theta and delta bands could be used for computerized discrimination of neonatal EEG sleep phases.

Cerebral Cortex↗

PubMed1995

The influence of extracorporeal clearance techniques on elimination of radiocesium after internal contamination.

Radiocesium, an isotope released after nuclear accidents such as Chernobyl, causes damage to the health of humans after internal contamination. As a result of an internal deposit of radiocesium these persons are continuously irradiated and noxious effects may occur. Removal of this internal radiation source will reduce immediate (short-term) and future damage (long-term). In order to obtain data with respect to cesium kinetics in vivo, data obtained in dogs by Nold et al. were fitted by a computer program. On the basis of these data, simulations were carried out to evaluate the influences of extracorporeal clearance on cesium kinetics. The influence of various treatments on the committed effective dose [E(50)] as a measure of radiation harm was simulated. For this purpose an equivalence between the committed effective dose and the area under the curve, a kinetic parameter, was derived. This equivalence only holds when comparisons are made for different treatments of one subject contaminated with one isotope. Treatment with orally administered Prussian Blue salts reduces the committed effective dose by 29% (50 y). This can be insufficient to prevent deterministic effects as a result of a severe internal contamination with radiocesium. For this purpose other methods are evaluated. In simulations, extracorporeal clearance (e.g. hemoperfusion or hemodialysis) proved to be more effective in reducing E(50) (> 50%, 50 y). Extracorporeal clearance also seems to be effective in the early dose reduction and its consequent deterministic effects. Simulations revealed that effectiveness is improved when the treatment is started earlier and continued for a longer period. Effective extracorporeal clearance may be considered to be a promising method to treat victims of nuclear accidents internally contaminated with radiocesium.

Animals↗

PubMed1983

On some stochastic formulations and related statistical moments of pharmacokinetic models.

This paper presents the deterministic and stochastic model for a linear compartment system with constant coefficients, and it develops expressions for the mean residence times (MRT) and the variances of the residence times (VRT) for the stochastic model. The expressions are relatively simple computationally, involving primarily matrix inversion, and they are elegant mathematically, in avoiding eigenvalue analysis and the complex domain. The MRT and VRT provide a set of new meaningful response measures for pharmacokinetic analysis and they give added insight into the system kinetics. The new analysis is illustrated with an example involving the cholesterol turnover in rats.

Animals↗

PubMed2005

Segmentation of fetal ultrasound images.

This paper describes a new method for segmentation of fetal anatomic structures from echographic images. More specifically, we estimate and measure the contours of the femur and of cranial cross-sections of fetal bodies, which can thus be automatically measured. Contour estimation is formulated as a statistical estimation problem, where both the contour and the observation model parameters are unknown. The observation model (or likelihood function) relates, in probabilistic terms, the observed image with the underlying contour. This likelihood function is derived from a region-based statistical image model. The contour and the observation model parameters are estimated according to the maximum likelihood (ML) criterion, via deterministic iterative algorithms. Experiments reported in the paper, using synthetic and real images, testify for the adequacy and good performance of the proposed approach.

Algorithms↗