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Ambulance deployment with the hypercube queuing model.

A computer-implemented mathematical model has been developed to assist planners in the spatial deployment and dispatching of ambulances. The model incorporates uncertainties in the arrival times, locations, and service requirements of patients, building on the branch of operations research known as queuing theory. Several system-performance measures are generated by the model, including mean neighborhood-specific response times, mean utilization of each ambulance, and statistical profiles of ambulance response patterns. This model has been implemented by the Department of Health and Hospitals of the City of Boston.

Ambulances↗
PubMed2003

Some extensions of the Gaussian beam expansion: radiation fields of the rectangular and the elliptical transducer.

A straightforward extension of Gaussian beam expansion is presented for calculation of the Fresnel field integral [J. J. Wen and M. A. Breazeale, J. Acoust. Soc. Am. 83, 1752-1756 (1988)]. The source distribution function is expanded into the superposition of a series of two-dimensional Gaussian functions. The corresponding radiation field is expressed as the superposition of these two-dimensional Gaussian beams and is then reduced to the computation of these simple functions. This treatment overcomes the limit that the shape of source is of circular axial-symmetry. The numerical examples are presented for the field of the (uniform) elliptical and the rectangular piston transducers and agree well with the results given by complicated computation.

Equipment Design↗
PubMed1976

Computer simulation of leukemia therapy: combined pharmacokinetics, intracellular enzyme kinetics, and cell kinetics of the treatment of L1210 leukemia by cytosine arabinoside.

An integrated mathematic computer-based model of the pharmacokinetics, intracellular enzyme kinetics, and cell kinetics of the treatment of L1210 leukemia by cytosine arabinoside (ara-C) is described. The compartment model of Bischoff and Dedrick is extended to the intracellular level by inclusion of equations describing the phosphorylation, dephosphorylation, and deamination of ara-C with enzymatic feedback control. The activities of kinase, deaminase, and phosphatase are explicitly included in the models and are estimated from relevant data. Cell proliferation is described by a continuous-flow mathematic model in which cellular maturation and cell-to-cell variability in maturation rates are key variables. Cell proliferation is related to intracellular biochemistry through mathematic expressions which relate cell lethality and progression delay to the time course of intracellular ara-CTP. In vitro and in vivo experiments performed in a number of laboratories are compared by simulation. The most sensitive parameters in dose-response and cell-survival simulations are deoxycytidine kinase activity, ara-CTP half-life, renal clearance of ara-C, and cell-kinetic parameters for proliferation and cell killing. Progression delay is vital to the realistic simulation of divided-dose schedules. By comparative simulation we have identified areas of uncertainty which can be classified by a few additional measurements. The applications of simulations combining pharmacokinetic, biochemical, and cell-kinetic data in vitro and in vivo are discussed, exploring consistency among different measurements, and relating experimental protocols to clinical treatment.

Animals↗
PubMed2003

White matter hyperintensity progression and late-life depression outcomes.

CONTEXT: White matter hyperintensities (WMHs) are bright foci seen in the parenchyma of the brain on T2-weighted cranial magnetic resonance imaging (MRI) scans and are associated with geriatric depression. Because they are associated with age, they should increase in number and size over time. To our knowledge, this is the first longitudinal, volumetric MRI study of WMHs in depression. OBJECTIVE: To determine if WMH progression over 2 years influences depression outcomes. DESIGN: Over 2 years, depressed subjects received antidepressant treatment according to a naturalistic somatic treatment algorithm designed to offer the best possible treatment to the individual. After the treatment period, depressed subjects were dichotomized based on whether they had reached and sustained remission during this period. PARTICIPANTS: One hundred thirty-three subjects aged 60 years or older meeting DSM-IV criteria for major depressive disorder. MEASURES: Cranial MRI was obtained at baseline and approximately 2 years later. White matter hyperintensity volume was measured in each hemisphere using a semiautomated segmentation process. OUTCOMES: Subjects were dichotomized based on achieving or not achieving remission of depressive symptoms, defined as a Montgomery-Asberg Depression Rating Scale score of 8 or less. RESULTS: The depressed subgroup that achieved and sustained remission had significantly less increases in WMH volume (11.5%) than did the group that did not achieve or sustain remission (31.6%) (P =.01). In a regression model, greater change in WMH volume was significantly associated with failure to sustain remission (P =.004) even when controlling for baseline depression severity, medical illness severity, age, sex, and race. Education was associated with achieving and sustaining remission (P =.02). CONCLUSIONS: Greater progression of WMH volume is associated with poor outcomes in geriatric depression. Future work is needed to develop means of slowing the rate of WMH progression and to determine whether this will lead to improved depression outcomes in elderly persons.

Aged↗
PubMed2003

Corpus callosum abnormalities in psychopathic antisocial individuals.

CONTEXT: Psychopathic antisocial individuals have previously been characterized by abnormal interhemispheric processing and callosal functioning, but there have been no studies on the structural characteristics of the corpus callosum in this group. OBJECTIVES: To assess whether (1) psychopathic individuals with antisocial personality disorder show structural and functional impairments in the corpus callosum, (2) group differences are mirrored by correlations between dimensional measures of callosal structure and psychopathy, (3) callosal abnormalities are associated with affective deficits, and (4) callosal abnormalities are independent of psychosocial deficits. DESIGN: Case-control study. SETTING: Community sample. PARTICIPANTS: Fifteen men with antisocial personality disorder and high psychopathy scores and 25 matched controls, all from a larger sample of 83 community volunteers. MAIN OUTCOME MEASURES: Structural magnetic resonance imaging measures of the corpus callosum (volume estimate of callosal white matter, thickness, length, and genu and splenium area), functional callosal measures (2 divided visual field tasks), electrodermal and cardiovascular activity during a social stressor, personality measures of affective and interpersonal deficits, and verbal and spatial ability. RESULTS: Psychopathic antisocial individuals compared with controls showed a 22.6% increase in estimated callosal white matter volume (P<.001), a 6.9% increase in callosal length (P =.002), a 15.3% reduction in callosal thickness (P =.04), and increased functional interhemispheric connectivity (P =.02). Correlational analyses in the larger unselected sample confirmed the association between antisocial personality and callosal structural abnormalities. Larger callosal volumes were associated with affective and interpersonal deficits, low autonomic stress reactivity, and low spatial ability. Callosal abnormalities were independent of psychosocial deficits. CONCLUSIONS: Corpus callosum abnormalities in psychopathic antisocial individuals may reflect atypical neurodevelopmental processes involving an arrest of early axonal pruning or increased white matter myelination. These findings may help explain affective deficits and previous findings of abnormal interhemispheric transfer in psychopathic individuals.

Adult↗
PubMed2003

Progressive decrease of left Heschl gyrus and planum temporale gray matter volume in first-episode schizophrenia: a longitudinal magnetic resonance imaging study.

BACKGROUND: The Heschl gyrus and planum temporale have crucial roles in auditory perception and language processing. Our previous investigation using magnetic resonance imaging (MRI) indicated smaller gray matter volumes bilaterally in the Heschl gyrus and in left planum temporale in patients with first-episode schizophrenia but not in patients with first-episode affective psychosis. We sought to determine whether there are progressive decreases in anatomically defined MRI gray matter volumes of the Heschl gyrus and planum temporale in patients with first-episode schizophrenia and also in patients with first-episode affective psychosis. METHODS: At a private psychiatric hospital, we conducted a prospective high spatial resolution MRI study that included initial scans of 28 patients at their first hospitalization (13 with schizophrenia and 15 with affective psychosis, 13 of whom had a manic psychosis) and 22 healthy control subjects. Follow-up scans occurred, on average, 1.5 years after the initial scan. RESULTS: Patients with first-episode schizophrenia showed significant decreases in gray matter volume over time in the left Heschl gyrus (6.9%) and left planum temporale (7.2%) compared with patients with first-episode affective psychosis or control subjects. CONCLUSIONS: These findings demonstrate a left-biased progressive volume reduction in the Heschl gyrus and planum temporale gray matter in patients with first-episode schizophrenia in contrast to patients with first-episode affective psychosis and control subjects. Schizophrenia but not affective psychosis seems to be characterized by a postonset progression of neocortical gray matter volume loss in the left superior temporal gyrus and thus may not be developmentally fixed.

Adolescent↗
PubMed1997

A comparison of spatial prediction techniques for an exploratory analysis of human cortical motor representations.

We compare the use of two-dimensional Laplacian smoothing splines and median polish kriging for an exploratory analysis of spatial data sets. Splines were developed originally for modelling a process with determinstic mean structure, while median polish kriging was developed for predicting a spatial random process. We review the fundamentals of both methods, including smoothing parameter selection for splines and variogram estimation and solving the kriging equations for median polish kriging. We demonstrate application of the methods on maps of muscle representations on the human motor cortex (cortical maps). After applying both methods to 20 cortical maps (left and right hemispheres on each of 10 subjects), we compare the fitted surfaces on the basis of predictive ability, aesthetic appeal, and ease of computation.

Analysis of Variance↗
PubMed2001

Stream function optimization for gradient coil design.

This work presents a method applied to the design of short self-shielded gradient coils of cylindrical geometry. The method uses a hybrid technique that combines the simulated annealing and target field methods to optimize the standard stream functions. The optimized stream functions were parameterized using a few degrees of freedom to reduce the computing time. The optima stream function parameters are given for easy coil design purposes. The proposed approach is compared to the target field method. The main advantage of the present method over the target field method is its ability to enlarge the homogeneous gradient volume. In addition, the designs of short coils based on this approach have shown lower inductance than the coil design based on the target field method. The fast-simulated annealing technique presented in this work enables the gradient coil optimization in less than 3 min of computing time. Magn Reson Med 45:505-512, 2001.

Efficiency↗
PubMed2002

Hydration structure of human lysozyme investigated by molecular dynamics simulation and cryogenic X-ray crystal structure analyses: on the correlation between crystal water sites, solvent density, and solvent dipole.

The hydration structure of human lysozyme was studied with cryogenic X-ray diffraction experiment and molecular dynamics simulations. The crystal structure analysis at a resolution of 1.4 A provided 405 crystal water molecules around the enzyme. In the simulations at 300 K, the crystal structure was immersed in explicit water molecules. We examined correlations between crystal water sites and two physical quantities calculated from the 1-ns simulation trajectories: the solvent density reflecting the time-averaged distribution of water molecules, and the solvent dipole measuring the orientational ordering of water molecules around the enzyme. The local high solvent density sites were consistent with the crystal water sites, and better correlation was observed around surface residues with smaller conformational fluctuations during the simulations. Solvent dipoles around those sites exhibited coherent and persistent ordering, indicating that the hydration water molecules at the crystal water sites were highly oriented through the interactions with hydrophilic residues. Those water molecules restrained the orientational motions of adjoining water molecules and induced a solvent dipole field, which was persistent during the simulations around the enzyme. The coherent ordering was particularly prominent in and around the active site cleft of the enzyme. Because the ordering was significant up to the third to fourth solvent layer region from the enzyme surface, the coherently ordered solvent dipoles likely contributed to the molecular recognition of the enzyme in a long-distance range. The present work may provide a new approach combining computational and the experimental studies to understand protein hydration.

Chemical Phenomena↗
PubMed2006

Cortical atrophy in the cerebellar variant of multiple system atrophy: a voxel-based morphometry study.

This study aimed to determine in vivo the atrophy patterns in clinically established cerebellar variant of multiple-system atrophy (MSA-C) using voxel-based morphometry (VBM). Thirteen patients with MSA-C (12 probable, 1 possible) and 13 healthy controls matched for age and sex were included. High-resolution MR images were acquired with a 1.5 T scanner. Images were normalized onto a study-specific template, segmented into the tissue compartments, modulated with the Jacobian determinants, and finally smoothed with a Gaussian kernel filter of 10 mm. The general linear model was used to assess statistical differences in gray and white matter. Infratentorial atrophy was observed in the cerebellar hemispheres, vermis, mesencephalon, and pons of MSA-C patients. Supratentorial volume loss was found in orbitofrontal and mid-frontal regions as well as in temporomesial and insular areas of both hemispheres. A negative correlation was observed between a cerebellar ataxia score and the volume of cerebellar hemispheres, peduncles, and pons. To compare this atrophy pattern to that of spinocerebellar ataxia (SCA2), which was previously reported by our group, a conjunction analysis was assessed. We observed a volume loss shared by both disorders comprising the cerebellum, vermis, pons, mesencephalon, orbitofrontal, mid-frontal, and temporomesial cortex of both hemispheres as well as the left insular cortex.

Adult↗
PubMed2005

'Objective' determination of coupling constants and conformational equilibria by solvent variation: a comment.

Following the preceding paper, the 'objective' method of Abraham et al. for determining the conformational equilibrium between molecules rapidly interconverting between a number of different conformers has been re-evaluated. The method relies on the acquisition of a sufficient data set of nuclear couplings in different solvents to obtain an over-determined system with more equations than unknowns. The example considered by Deutsch and Roberts, of 1,2-dichloro-1-fluoroethane, is re-evaluated here. A simple but mathematically rigorous computer scanning process is used to analyse the data set instead of the iterative but not mathematically rigorous process used previously and the results compared with those of Deutsch and Roberts. It is shown that both treatments give similar solutions. However, it is emphasized that in these multi-dimensional analyses the probable errors in the derived parameters (in this case the conformer couplings) may be much larger than the r.m.s. (observed versus calculated) errors and this error analysis is essential for a considered appraisal of the method.

Journal Article↗
PubMed2001

Bayesian technique for investigating linearity in event-related BOLD fMRI.

Event-related BOLD fMRI data is modeled as a linear time-invariant system. Together with Bayesian inference techniques, a statistical test is developed for rigorously detecting linearity/nonlinearity in the BOLD response system. The test is applied to data collected from eight subjects using an event-related paradigm with a switching checkerboard as the visual stimulus. Analyzed as a group, the results clearly find the response to be nonlinear. When each subject is analyzed individually, however, the results are predominantly nonlinear, but there is some evidence to suggest that there may be a crossover from a linear to a nonlinear regime and vice versa. This could be important when estimating physiological parameters for individuals. Additionally, estimates of the hemodynamic response function and corresponding response were obtained, but there was no consistent appearance of a poststimulus undershoot in the event-related BOLD response.

Adult↗
PubMed1995

Building proteins from C alpha coordinates using the dihedral probability grid Monte Carlo method.

Dihedral probability grid Monte Carlo (DPG-MC) is a general-purpose method of conformational sampling that can be applied to many problems in peptide and protein modeling. Here we present the DPG-MC method and apply it to predicting complete protein structures from C alpha coordinates. This is useful in such endeavors as homology modeling, protein structure prediction from lattice simulations, or fitting protein structures to X-ray crystallographic data. It also serves as an example of how DPG-MC can be applied to systems with geometric constraints. The conformational propensities for individual residues are used to guide conformational searches as the protein is built from the amino-terminus to the carboxyl-terminus. Results for a number of proteins show that both the backbone and side chain can be accurately modeled using DPG-MC. Backbone atoms are generally predicted with RMS errors of about 0.5 A (compared to X-ray crystal structure coordinates) and all atoms are predicted to an RMS error of 1.7 A or better.

Amino Acids↗
PubMed1994

Energy minimization method using automata network for sequence and side-chain conformation prediction from given backbone geometry.

Globular proteins have high packing densities as a result of residue side chains in the core achieving a tight, complementary packing. The internal packing is considered the main determinant of native protein structure. From that point of view, we present here a method of energy minimization using an automata network to predict a set of amino acid sequences and their side-chain conformations from a desired backbone geometry for de novo design of proteins. Using discrete side-chain conformations, that is, rotamers, the sequence generation problem from a given backbone geometry becomes one of combinatorial problems. We focused on the residues composing the interior core region and predicted a set of amino acid sequences and their side-chain conformations only from a given backbone geometry. The kinds of residues were restricted to six hydrophobic amino acids (Ala, Ile, Met, Leu, Phe, and Val) because the core regions are almost always composed of hydrophobic residues. The obtained sequences were well packed as was the native sequence. The method can be used for automated sequence generation in the de novo design of proteins.

Bacterial Proteins↗