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Biomedical subjects

D E Newman

Publications and source records attributed to D E Newman.

At least 19 recordsLinked to original sources
PubMed2006

Renormalization of tracer turbulence leading to fractional differential equations.

For many years quasilinear renormalization has been applied to numerous problems in turbulent transport. This scheme relies on the localization hypothesis to derive a linear transport equation from a simplified stochastic description of the underlying microscopic dynamics. However, use of the localization hypothesis narrows the range of transport behaviors that can be captured by the renormalized equations. In this paper, we construct a renormalization procedure that manages to avoid the localization hypothesis completely and produces renormalized transport equations, expressed in terms of fractional differential operators, that exhibit much more of the transport phenomenology observed in nature. This technique provides a first step toward establishing a rigorous link between the microscopic physics of turbulence and the fractional transport models proposed phenomenologically for a wide variety of turbulent systems such as neutral fluids or plasmas.

Journal Article↗
PubMed2006

Bone ALP and OC reference standards in adult baboons (Papio hamadryas) by sex and age.

BACKGROUND: Serum bone-specific alkaline phosphatase (bone ALP) and intact osteocalcin (OC) are markers of bone formation of interest because of easy measurability and potential utility as identifiers of those at risk for fractures associated with bone metabolism disorders. The baboon (Papio hamadryas) exhibits extensive biological similarities to humans making it particularly well suited to studies of bone maintenance and turnover. METHODS: We measured serum bone ALP and OC in 591 baboons. RESULTS: We report significant sex and age effects and present reference ranges and percentile distributions for these markers. CONCLUSIONS: This study is the first to characterize normal variation in bone ALP and OC levels in baboons and to assess the age and sex effects on this variation. The results provide much-needed reference standards to allow researchers to evaluate the status of their animals in cross-sectional studies and assess the meaning of changes in bone ALP and OC levels in longitudinal studies.

Age Factors↗
PubMed2004

Complex dynamics of blackouts in power transmission systems.

In order to study the complex global dynamics of a series of blackouts in power transmission systems a dynamical model of such a system has been developed. This model includes a simple representation of the dynamical evolution by incorporating the growth of power demand, the engineering response to system failures, and the upgrade of generator capacity. Two types of blackouts have been identified, each having different dynamical properties. One type of blackout involves the loss of load due to transmission lines reaching their load limits but no line outages. The second type of blackout is associated with multiple line outages. The dominance of one type of blackout over the other depends on operational conditions and the proximity of the system to one of its two critical points. The model displays characteristics such as a probability distribution of blackout sizes with power tails similar to that observed in real blackout data from North America.

Models, Theoretical↗
PubMed2003

Quiet-time statistics of electrostatic turbulent fluxes from the JET tokamak and the W7-AS and TJ-II stellarators.

The statistics of the quiet times between successive turbulent flux bursts measured at the edge of the JET tokamak and the W7-AS and TJ-II stellarators are analyzed in search for evidence of self-organized critical behavior. The results obtained are consistent with what would be expected in the situation where the underlying plasma is indeed in a near critical state.

Journal Article↗
PubMed2002

Quiet-time statistics: a tool to probe the dynamics of self-organized-criticality systems from within the strong overlapping regime.

A method is presented that allows one to obtain information about the underlying dynamics of a self-organized-criticality system even when the strong-overlapping or hydrodynamic regime (in which individual avalanches are no longer distinguishable) is the only one amenable of probing. The method is based on the analysis of the statistics of the lapses of time between activity bursts or quiet times. The case of a randomly driven running sandpile is used to illustrate the use and capabilities of this technique.

Journal Article↗
PubMed2002

Avalanche structure in a running sandpile model.

The probability distribution function of the avalanche size in the sandpile model does not verify strict self-similarity under changes of the sandpile size. Here we show the existence of avalanches with different space-time structure, and each type of avalanche has a different scaling with the sandpile size. This is the main cause of the lack of self-similarity of the probability distribution function of the avalanche sizes, although the boundary effects can also play a role.

Journal Article↗
PubMed2002

Transition in the dynamics of a diffusive running sandpile.

A running sandpile is shown to undergo a dynamical transition as diffusion is increased from zero. The transition takes place after the local diffusion has become so large as to erase the local inhomogeneities, caused by the intermittent rain of sand, before they can trigger avalanche activity. The system then undergoes an abrupt change with the self-similar structure of the dynamics being replaced with quasiperiodic, near system-size transport events. These results may have significant implications for many of the driven physical systems for which self-organized criticality based dynamical models have been proposed.

Journal Article↗
PubMed2002

Waiting-time statistics of self-organized-criticality systems.

It is argued that a system governed by self-organized-criticality (SOC) dynamics can lack Poisson waiting-time statistics not only when the experimental resolution lies within the self-similar scale range but also if the system is slowly driven in a correlated way. This result thus suggests that waiting time statistics cannot be used as a necessary test for SOC behavior in real physical systems.

Journal Article↗
PubMed2000

Development of inhibitory circuitry in visual and auditory cortex of postnatal ferrets: immunocytochemical localization of calbindin- and parvalbumin-containing neurons.

The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is thought to play an important role in activity-dependent stages of brain development. Previous studies have shown that different functional subclasses of cortical GABA-containing neurons can be distinguished by antibodies to the calcium-binding proteins parvalbumin and calbindin. Thus insight into the development of distinct subsets of inhibitory cortical circuits can be gained by studying the development of these calcium-binding protein-containing neurons. Previous studies in several mammalian species have suggested that calcium-binding proteins are upregulated in sensory cortex when thalamocortical afferents arrive. In ferrets, the ingrowth of thalamic axons into cortex occurs well into postnatal development, allowing access to early stages of cortical development and calcium-binding protein expression. We find in ferrets that both parvalbumin- and calbindin-immunoreactivity are present in primary visual and primary auditory cortex long before thalamocortical synapse formation, but that there is a sharp decline in immunoreactivity by postnatal day 20. Day 20 in ferrets corresponds to postnatal day 1 in cats, and thus previous studies in postnatal cats would have missed this early pattern of calcium-binding protein distribution. Another surprising finding is that the proportion of parvalbumin- and calbindin-immunoreactive neurons peaks secondarily late in development, between P60 and adulthood. This result suggests that the parvalbumin- and calbindin-containing subclasses of nonpyramidal neurons remain immature until late in the critical period for cortical plasticity, and that they are positioned to play an important role in experience-dependent modification of cortical circuits.

Animals↗
PubMed1999

Development of inhibitory circuitry in visual and auditory cortex of postnatal ferrets: immunocytochemical localization of GABAergic neurons.

The goal of this study was to describe the development of gamma-aminobutyric acid (GABA)-containing neurons in visual and auditory cortex of ferrets. The laminar and tangential distribution of neurons containing excitatory, inhibitory, and neuromodulatory substances constrain the potential circuits which can form during development. Ferrets are born at an early stage of brain development, allowing examination of inhibitory circuit formation in cerebral cortex prior to thalamocortical ingrowth and cortical plate differentiation. Immunocytochemically labelled nonpyramidal GABA neurons were present from postnatal day 1 throughout development, in all cortical layers, and generally followed the inside-out pattern of neuronal migration into the cortical plate. Prior to postnatal day 14, pyramidal neurons with transient GABA immunoreactivity were also observed. The density of Nissl-stained and GABA-immunoreactive neurons was high early in development, declined markedly by postnatal day 20, then remained relatively constant until adulthood. However, examination of the proportion of GABA neurons revealed an unexpected late peak at postnatal day 60, then a decrease in adulthood. Visual and auditory cortex were similar in most respects, but the peak at postnatal day 60 and the final proportion of GABA neurons was higher in auditory cortex. The late peak suggests that inhibitory circuitry is stabilized relatively late in sensory cortical development, and thus that GABA neurons could provide an important substrate for experience-dependent plasticity at late stages of development.

Animals↗
PubMed1999

Anomalous diffusion in a running sandpile model.

To explore the character of underlying transport in a sandpile, we have followed the motion of tracer particles. Moments of the distribution function of the particle positions, =D(0)t(nnu(n)), are determined as a function of the elapsed time. The numerical results show that the transport mechanism for distances less than the sandpile length is superdiffusive with an exponent nu(n) close to 0.75, for n<1.

Journal Article↗
PubMed1989

Radiographic findings in liveborn triploidy.

The detailed radiographic features of triploidy, a fatal congenital disorder with 69 chromosomes, have not previously been reported. Radiographs of ten liveborn infants with chromosomally confirmed triploidy showed six findings highly suggestive of this diagnosis: harlequin orbits, small anterior fontanelle, gracile ribs, diaphyseal overtubulation of long bones, upswept clavicles and antimongoloid pelvis. Sixteen other less specific findings showed many similarities to those found in trisomy 18.

Abnormalities, Multiple↗
PubMed1985

Bacteriuria screening by use of acridine orange-stained smears.

Acridine orange (AO)-stained smears of 1,042 urine specimens were examined for the presence of bacteria and compared with quantitative culture results. The detection of one or more organisms per three AO fields at X200 magnification was noted in 161 of 162 and 193 of 195 urine specimens that grew greater than 10(5) and 10(4) CFU/ml, respectively, of a clinically relevant organism. However, a high number of false-positive AO smears (356 and 324, respectively) was observed among urines that failed to grow organisms at 10(5) and 10(4) CFU/ml. Sensitivity, specificity, and positive and negative predictive values of AO smears were 99, 58, 26, and 99%, respectively, for cultures of greater than or equal to 10(5) CFU/ml and 98, 59, 32, and 99%, respectively for cultures of greater than or equal to 10(4) CFU/ml. Despite the poor specificity of the AO smear, the very high negative predictive value would allow for the ruling out of bacteriuria defined at 10(4) CFU/ml and would eliminate the need for culture of ca. 50% of the urine specimens in this study. Employment of the rapid, inexpensive AO procedure only as a means to eliminate specimens for culture would allow significant cost savings and permit the laboratory to send out a large number of potentially negative or low-count urine results within a short time of specimen receipt.

Acridine Orange↗
PubMed1985

Leg length determination by CT digital radiography.

CT digital radiography is a new accurate technique for measuring leg length discrepancy. It is easily performed on commercially available equipment with a radiation dose of 3-6 times less than the conventional technique. Because of the short time required to complete the examination, charges are comparable with those for existing procedures. Good correlation in total limb length measurements between this new technique and spot scanography was noted in 24 patients. CT digital radiography should be the preferred method for evaluation for limb length discrepancy, particularly in children, because of the simple technique and lowering of radiation dose.

Child↗
PubMed1984

Genetics of sonographically detected intrauterine fetal cystic hygromas.

Turner syndrome has been the only genetic abnormality reported in which intrauterine cystic hygromas occur. We have recently seen three patients in whom cystic hygromas were detected in utero, and which turned out to be due to Turner, Down, and Noonan syndromes respectively. As the finding of a fetal cystic hygroma occurs in a spectrum of genetic disorders, anatomic and cytogenetic studies are indicated for definitive diagnosis.

Adult↗