Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Probability Theory”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,801 records · Page 100Linked to original sources
PubMed1998

Lung-volume reduction surgery for diffuse emphysema: radiologic assessment of changes in thoracic dimensions.

Patients with severe, diffuse emphysema may be candidates for pneumectomy (lung-volume reduction surgery, LVRS) to improve lung and respiratory muscle function. To identify candidates who might benefit from this surgery, it is necessary to understand how lung volumes and respiratory function are effected. In this article, the authors demonstrate a significant difference in lung size on chest radiographs obtained before and after surgery. Thirty-five of 71 consecutive patients undergoing LVRS had both preoperative and postoperative chest radiographs and pulmonary function tests available for retrospective review. Preoperative and postoperative measurements of lung height, transthoracic diameters, mediastinal width, heart size, diaphragmatic arc, and intercostal spaces were compared using paired t-tests. Radiographic measurements where also correlated with changes in lung volumes as measured by pulmonary function tests. Lung heights (right, left, mean lateral) and coronal diameter at the aortic arch were reduced after surgery (all p < 0.05). Forced vital capacity, forced expiratory volume in 1 second (FEV1), and vital capacity increased, and total lung capacity and residual volume decreased after surgery (all p < 0.05). Left lung height showed a significant correlation (p = 0.025) with FEV1; all other correlations between radiographic changes and pulmonary function test changes were not significant. The explanation for improved lung function in patients after LVRS is not completely clear and is probably multifactorial. Radiologic alterations reflect anatomic changes caused by surgery and support the theory that modifications of chest wall configuration occur and are likely responsible, in part, for improved symptomatology and respiratory function.

Adult↗
PubMed2001

Conductivity of continuum percolating systems.

We study the conductivity of a class of disordered continuum systems represented by the Swiss-cheese model, where the conducting medium is the space between randomly placed spherical holes, near the percolation threshold. This model can be mapped onto a bond percolation model where the conductance sigma of randomly occupied bonds is drawn from a probability distribution of the form sigma(-a). Employing the methods of renormalized field theory we show to arbitrary order in epsilon expansion that the critical conductivity exponent of the Swiss-cheese model is given by t(SC)(a) = (d-2)nu + max[phi,(1-a)(-1)], where d is the spatial dimension and nu and phi denote the critical exponents for the percolation correlation length and resistance, respectively. Our result confirms a conjecture that is based on the "nodes, links, and blobs" picture of percolation clusters.

Journal Article↗
PubMed2002

Granular polymer solution.

We have measured the spectrum of fluctuations in the size of a granular polymer in a granular solvent. The system consists of a linear chain of plastic spheres immersed in a planar fluid of self-propelled balls. The time average of the end-to-end length r of the chain scales with the number of links N according to approximately N2nu, with nu=0.75+/-0.01. This provides an experimental test of the theoretical value nu=3 / 4 of the critical exponent for a self-avoiding random walk in two dimensions. The measured probability distribution P(r) is compared with the universal function of the scaling theory.

Journal Article↗
PubMed2006

Fundamentals of pair diffusion in kinematic simulations of turbulence.

We demonstrate that kinematic simulation (KS) of three-dimensional homogeneous turbulence produces fluid element pair statistics in agreement with the predictions of L F. Richardson [Proc. R. Soc. London, Ser. A 110, 709 (1926)] even though KS lacks explicit modeling of turbulent sweeping of small eddies by large ones. This scaling is most clearly evident in the turbulent diffusivity's dependence on rms pair separation and, to a lesser extent, on the pair's travel time statistics. It is also shown that kinematic simulation generates a probability density function of pair separation which is in good agreement with recent theory [S. Goto and J. C. Vassilicos, New J. Phys. 6, 65 (2004)] and with the scaling of the rms pair separation predicted by L. F. Richardson [Proc. R. Soc. London, Ser. A 110, 709 (1926)]. Finally, the statistical persistence hypothesis (SPH) is formulated mathematically and its validity tested in KS. This formulation introduces the concept of stagnation point velocities and relates these to fluid accelerations. The scaling of accelerations found in kinematic simulation supports the SPH, even though KS does not generate a Kolmogorov scaling for the acceleration variance (except for a specific case and a limited range of outer to inner length-scale ratios). An argument is then presented that suggests that the stagnation points in homogeneous isotropic turbulence are on average long-lived.

Journal Article↗
PubMed2005

Statistics of real eigenvalues in Ginibre's ensemble of random real matrices.

The integrable structure of Ginibre's orthogonal ensemble of random matrices is looked at through the prism of the probability p(n,k) to find exactly k real eigenvalues in the spectrum of an n x n real asymmetric Gaussian random matrix. The exact solution for the probability function p(n,k) is presented, and its remarkable connection to the theory of symmetric functions is revealed. An extension of the Dyson integration theorem is a key ingredient of the theory presented.

Journal Article↗
PubMed1990

Lumbar puncture headache: a review.

August Bier, the father of spinal anesthesia, suffered and reported the first lumbar puncture (LP) headache. On August 24, 1898 his assistant, a Dr. Hildebrandt, attempted to administer a spinal anesthetic to Dr. Bier; it was never completed because the syringe did not fit the already implanted spinal needle. Bier himself suggested that continued leakage of cerebrospinal fluid (CSF) through the dural puncture site was the cause of headache, a theory that has been embraced by the medical community; however, the mechanism is probably more complex. Nearly 50 years ago, J. Lawrence Pool, using an endoscopic technique to visualize the surface of the spinal cord and the cauda equina, frequently observed large collections of epidural fluid two to four days following lumbar puncture in patients without headache. Evidence that will be presented below suggests that CSF volume alterations may be the signal closest to the headache mechanism.

Age Factors↗
PubMed1983

Conservation in soil of h(2) liberated from n(2) fixation by hup nodules.

Pigeon peas (Cajanus cajan) were grown in large soil columns (90-cm length by 30-cm diameter) and inoculated with four different strains of cowpea rhizobia, which varied with respect to hydrogen uptake activity (Hup). Despite the profuse liberation of H(2) from Hup nodules in vitro, H(2) gas was not detected in any of the soil columns. When H(2) was injected into the columns, the rates of consumption were highest in the treatments (including control) containing Hup nodules (218 and 177 nmol . h . cm) and lowest in the Hup treatments (158, 92, and 64 nmoles . h . cm). In situ H(2) uptake rates in small soil cores at fixed distances from the nodules decreased exponentially with distance from the nodule (R = 0.99). This decrease in H(2) consumption was associated with a similar decrease in numbers of H(2)-oxidizing chemolithotrophic bacteria as determined by the most-probable-number method. On the basis of two equations derived separately upon diffusive theory (Fix's Law) and kinetic theory (Michaelis-Menten), the empirically derived rate constants and coefficients indicated that all of the H(2) emitted from Hup nodules would be consumed by H(2)-oxidizing bacteria within a 3- to 4.5-cm radius of the nodule surface. It is concluded that H(2) is not lost from the soil-plant ecosystem during N(2) fixation in C. cajan but is conserved by H(2)-oxidizing bacteria.

Journal Article↗
PubMed1982

Homogeneity of large-field color matches in congenital red-green color deficients.

Rayleigh matches obtained from red-green color deficients with conventional methods show large individual differences within diagnostic categories. Similar matches obtained from the same observers with a large-field substitution method show much less variability and suggest that the differences observed among simple anomals, extreme anomals, and dichromats with conventional methods are probably not solely due to the visual pigments contained in the cones. A theory that attributes these differences to the relative number of abnormal cones present in the observer's retina is described.

Color Perception↗
PubMed1980

Surgical treatment for chest pain in mitral valve prolapse.

The case of a 40-year-old woman with mitral valve prolapse and severe atypical chest pain is presented. The diagnosis was confirmed by phonocardiographic, echocardiographic, and angiocardiographic studies. The electrocardiogram revealed an ischemic pattern of ST-T on the anterior and inferior wall. Coronary angiographic studies showed normal coronary arteries. The patient's long-standing, prolonged, disabling atypical chest pain could not be relieved with medical therapy, despite the administration of beta-adrenergic blocking agents, calcium antagonists, and short-acting nitrites during a 30-month period. Thus, the prolapsed mitral valve was replaced with a Hancock xenograft. After 12 months the patient is totally free of symptoms, without any treatment and with a normal ECG. This excellent surgical result could be explained on the basis of the valvular theory of chest pain in mitral valve prolapse, suggesting that pain is promoted probably by a regional imbalance between oxygen availability and consumption, because of the excessive papillary muscular stretching produced by the prolapse. To our knowledge, this is the first published report of successful surgical treatment of chest pain in mitral valve prolapse.

Adult↗
PubMed2003

Using satellite imagery to locate innovative forest management practices in Nepal.

There is a critical need to locate innovative forest management institutions that significantly impact forest cover change. This research presents an initial "proof of concept" methodology which combines deforestation theory with satellite image change analysis to identify forested areas that, theoretically, should probably not be there. Ten such "forest anomalies" are identified using temporal analysis of Landsat TM imagery of the Chitwan district in Nepal, linked with a GIS database on roads and a visual estimation of topography. A rapid field reconnaissance is undertaken to determine which of these anomalies exhibit interesting forest management innovations. Based on this information, one case is selected for detailed field study: this turns out to be a major case of community forestry and a premier ecotourism initiative that we were not aware of until we undertook this analysis. The utility and limitations of the method are described for monitoring trends in forest cover change.

Conservation of Natural Resources↗
PubMed2005

Use of multi-objective air pollution monitoring sites and online air pollution monitoring system for total health risk assessment in Hyderabad, India.

A consensus has been emerging among public health experts in developing countries that air pollution, even at current ambient levels, aggravates respiratory and cardiovascular diseases and leads to premature mortality. Recent studies have also presented well-founded theories concerning the biological mechanisms involved and the groups of people that are probably more susceptible to health effects caused or exacerbated by inhalation of ambient particulate matter (PM.). On the basis of prognostic studies carried out in Center for Environment, JNT University, Hyderabad "it has been estimated that in Hyderabad some 1,700 to 3,000 people per year die prematurely as a result of inhaling PM". These figures reflect only the effects of acute exposure to air pollution. If the long-term effects of chronic exposure are taken into account, 10,000-15,000 people a year could die prematurely in Hyderabad. This estimate of the chronic effects is based on other studies, which are not completely comparable with the Hyderabad situation. While the study designs and analyses in these other studies may indeed be different or irrelevant to Hyderabad, the fact they were carried out in other countries is irrelevant. Taking into account these considerations, a model for total health risk assessment for the city of Hyderabad, and its state of Andhra Pradesh in India has been developed using a multi-objective air pollution monitoring network and online and real time air pollution monitoring stations. For the model studies a number of potential monitoring sites were screened for general and site-specific criteria in a geographic information system (GIS) environment that may, on a local basis, affect the representativeness of the data collected. Local features that may affect either the chemical or meteorological parameters are evaluated to assure a minimum of interference. Finally, for monitoring air pollution, an online and real-time monitoring system was designed using advanced electrochemical sensor systems (sulphur dioxide, oxides of nitrogen, carbon monoxide, hydrocarbons, ozone, mercaptans and hydrogen sulphide) and a particulate matter analyzer (total suspended particulate matter TSPM), PM2.5 and PM10). The sensor and data acquisition systems are programmed to monitor pollution levels at 1/2 hour durations during peak hours and at 1-hour intervals at other times. Presently, extensive statistical and numerical simulations are being carried out at our center to correlate the individuals living in the monitored areas with respiratory infections with air pollution.

Air Pollutants↗
PubMed1976

The postpericardiotomy and similar syndromes.

A syndrome of pericardial and often pleural reaction with effusions and with fever occurs in three different settings. It bears the descriptive term of the condition which it follows: the postpericardiotomy syndrome, the postmyocardial infarction syndrome, and the postpericardial trauma syndrome. The manifestations, incidence, theories of etiology, treatment, and possibility of prevention were discussed. The syndrome is probably due to an immunologic response with an associated viral illness, since in a prospective study of children undergoing cardiac surgery in which the pericardium was entered, we found that the development of heart-reactive antibody in high titer and a significant rise in antiviral antibody occurred in patients with clinically evident syndrome.

Adolescent↗
PubMed1996

Health care 2015: flight of the butterfly.

Projecting out to the year 2015 sounds presumptuous. Who can predict that far ahead? Perhaps no one can. Social and organizational arrangements come slowly. It takes five years or so to implement simple concepts, sometimes decades for more radical changes. Once you have the ideas in tangible form, it can take another five years to get it working right. Early adopters bring others into the movement and, over 15-25 years, new directions dominate. It takes at least a generation of new practitioners to take on the new values and methods so what is likely to dominate in 2015 is beginning to be taken somewhat seriously as the successor movement to our current fad with externally imposed managed care. Put another way, entire generations of people will resist new ideas, making implementation unlikely until their control fades and a new generation takes the helm. The exciting challenge for the observer is to address the issue of where health is and should be going. Both are difficult challenges. Agreeing on what is important and what is not represents a competitive challenge. How do we perceive the world? Surely our value sets will color what we see. Who is not predisposed to select a future where they fit and their pet theories are likely to become reality. For these and other reasons, it is probably easier to agree on what we would like to see happen in the future than on what is happening. Unfortunately, unless we see the world as it is, we are less likely to be able to shift it in a direction we would like to see.

Delivery of Health Care↗
PubMedDate not supplied

[Sleep disorders as a risk factors for stroke].

Sleep-disordered breathing seems to play a role in pathogenesis of stroke: for example, it was showed that snoring is a risk factor for stroke. Sleep disorders and sleep-disordered breathing increase the risk for stroke, probably by influencing systemic and cerebral blood circulation, causing hypoxaemia during night. This theory is supported by the fact of higher prevalence of stroke in the morning. During REM sleep there is a higher requirement for oxygen; as most sleep apnoeas occur during REM, it is possible that there is a relative hypoxaemia during this sleep stage. Stroke, including hemispheric stroke, can cause or aggravate the pre-existing sleep-disordered breathing. There are contradictory data in the literature regarding the influence of stroke on sleep architecture. Sleep disorders are associated with poorer stroke outcome, so their detection and treatment can be important in secondary stroke prophylaxis and will improve the patient's functioning and quality of life.

Brain↗
PubMed2004

[Change in service provision and availability under the list patient system reform].

BACKGROUND: In this article, we analyse the relationship between length of patient lists and general practitioners' (GPs') service provision in order to investigate whether the list patient system reform has led to reduced accessibility and/or supplier inducement. MATERIAL AND METHODS: The data were collected from a comprehensive questionnaire survey among GPs in the list patient system in 2002 (2306 GPs) and from the National Insurance Administration in 2001 (1637 GPs). The relationship between length of patient lists and service provision was analysed using regression analysis. RESULTS: The relationship between length of patient lists and number of consultations per GP was almost proportional, as was the relationship between length of patient list and number of consultations initiated by GPs. GPs who wanted more patients on their list had fewer consultations than those who were satisfied with the length of their lists and they did not compensate by taking more laboratory tests per consultation. Analysis of the two independent sets of data gave almost identical results. INTERPRETATION: Patients' access to their GPs is independent of the length of his or her patient list. Even GPs with long lists do not ration consultations. This probably reflects efficient organisation of the practice. Our results do not support the theory that GPs induce demand for their services; one explanation is that GPs with short lists have chosen to have precisely that and have no need to induce demand.

Efficiency, Organizational↗
PubMed1992

Relative risk of early and late death in infancy among offspring of non-native-born parents residing in Washington State.

It has been suggested that geographic variation in the early neonatal (0-6 days) and postperinatal (7-364 days) mortality rates for the United States derives from positive and negative associations, respectively, with the probability of an average couple sharing one or more HLA antigens. If this theory is correct, then the ratio of 0-6-day deaths to 7-364-day deaths among the offspring of migrant parents should be similar to that seen in the area from which the mother and the father originally migrated. Information on deaths among the offspring of migrant couples by the mother's region of birth was obtained from computerized vital statistics for Washington state for the period 1968-1977. Information on infant deaths occurring in the mother's region of birth was obtained from published vital statistics for the United States for 1980-1984. Ratios of 0-6-day deaths to 7-364-day deaths in 9 geographic regions for the period 1980-1984 were placed in 4 intervals. These intervals became the standard against which the 0-6/7-364-day ratios in the offspring of migrant parents were compared by means of a test for trend in proportions. As predicted, a significant positive trend was observed when the mother and the father were born in the same region but not when they were born in different regions.

Emigration and Immigration↗
PubMedDate not supplied

Aneurysms of spinal arteries associated with intramedullary arteriovenous malformations. II. Results of AVM endovascular treatment and hemodynamic considerations.

PURPOSE: To evaluate the changes occurring in spinal aneurysm (SA) size related to modification of endovascularly treated AVMs. METHODS: Fourteen patients with an intramedullary AVM and associated SA underwent endovascular treatment of their AVM with particles. Embolization sessions numbered from one to 14 (mean five) in each patient. RESULTS: Four patients had SAs with size changes mirroring those of the AVM with embolization: these decreased in size or disappeared after AVM reduction or cure and increased or recurred after AVM recanalization. A second group of patients had SAs that remained unchanged despite AVM changes (six of seven of these were in patients with metameric angiomatosis). CONCLUSIONS: Results in the first group lend support to the hemodynamic theory of associated aneurysm formation. On the other hand, aneurysms that remained unchanged probably are not AVM flow-related and could be an expression of an extensive vascular disorder such as metameric angiomatosis; however, hemodynamic and developmental factors could be concurrent.

Aneurysm↗
PubMed1986

The pathogenesis and pathophysiology of rectal prolapse and solitary rectal ulcer syndrome.

Rectal prolapse and solitary rectal ulcer syndrome are both benign conditions affecting the rectum, mainly in women; prolapse tends to occur late in life, while solitary rectal ulcer syndrome has a predilection for the younger adult. Complete rectal prolapse probably starts as a mid-rectal intussusception, although a combination of this theory and the 'sliding hernia' theory has been proposed by Altemeier et al (1971). The pelvic floor weakness associated with prolapse, which gives rise to incontinence, is most likely due to a traction injury to the pudendal nerve. Anorectal manometry will indicate those incontinent patients likely to benefit from rectopexy. Abnormal descent of the perineum may be found in rectal prolapse and solitary rectal ulcer syndrome as well as descending perineum syndrome per se. The clinical features of these three conditions can overlap. Solitary rectal ulcer syndrome is essentially due to prolapse and traumatization of the rectal mucosa. Inappropriate puborectalis contraction, abnormal perineal descent, and overt rectal prolapse have all been cited as possible mechanisms of development of the condition. Defecography is the radiologic investigation of choice. Electromyography, as in rectal prolapse, may show evidence of pudendal nerve damage although incontinence is rare.

Adult↗

Refine your search to explore more results.