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Standard Templates (standard + templates)

Distribution by Scientific Domains
Medical Sciences50%

Selected Abstracts

Statistical density modification using local pattern matching

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2003
Thomas C. Terwilliger
A method for improving crystallographic phases is presented that is based on the preferential occurrence of certain local patterns of electron density in macromolecular electron-density maps. The method focuses on the relationship between the value of electron density at a point in the map and the pattern of density surrounding this point. Patterns of density that can be superimposed by rotation about the central point are considered equivalent. Standard templates are created from experimental or model electron-density maps by clustering and averaging local patterns of electron density. The clustering is based on correlation coefficients after rotation to maximize the correlation. Experimental or model maps are also used to create histograms relating the value of electron density at the central point to the correlation coefficient of the density surrounding this point with each member of the set of standard patterns. These histograms are then used to estimate the electron density at each point in a new experimental electron-density map using the pattern of electron density at points surrounding that point and the correlation coefficient of this density to each of the set of standard templates, again after rotation to maximize the correlation. The method is strengthened by excluding any information from the point in question from both the templates and the local pattern of density in the calculation. A function based on the origin of the Patterson function is used to remove information about the electron density at the point in question from nearby electron density. This allows an estimation of the electron density at each point in a map, using only information from other points in the process. The resulting estimates of electron density are shown to have errors that are nearly independent of the errors in the original map using model data and templates calculated at a resolution of 2.6,Å. Owing to this independence of errors, information from the new map can be combined in a simple fashion with information from the original map to create an improved map. An iterative phase-improvement process using this approach and other applications of the image-reconstruction method are described and applied to experimental data at resolutions ranging from 2.4 to 2.8,Å. [source]

COPD-intuition or template: nurses' stories of acute exacerbations of chronic obstructive pulmonary disease

JOURNAL OF CLINICAL NURSING, Issue 6 2004
Patricia Hill Bailey MHSc
Study rational., A number of nurse-researchers have examined the experience of dyspnoea reduction during non-acute phases of the chronic obstructive pulmonary disease (COPD). However, nurses working on in-patient hospital units are frequently required to care for individuals suffering from acute exacerbations of their disease (AECOPD). These critically ill individuals present at health care institutions incapacitated by severe shortness of breath/dyspnoea that is frequently refractory to treatment. To date, little is known about the nurses' understanding of the care they provide for individuals hospitalized because of these acute episodes of their chronic illness. Study objectives., The research project was undertaken, in part, to develop an understanding of nurses' experience of caregiving for individuals hospitalized for in-patient care during an AECOPD. Methodological design., This focused ethnographic narrative examined the caregiving stories of 10 nurse caregivers. The 10 nurse caregivers were interviewed while caring for a patient and their family during an experience of an AECOPD characterized by incapacitating breathlessness. Results., The nurse caregivers told a number of caregiving stories that illustrated a common care template that appears to be based on intuition or pattern recognition focusing on anxiety sometimes to the exclusion of dyspnoea. Conclusions., Analysis of these stories emphasized the need to facilitate nurses individualization of standard templates. More importantly, this analysis illustrated the critical need to develop strategies to facilitate the reshaping of inaccurate templates in the presence of new knowledge. [source]

Statistical density modification using local pattern matching

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2003
Thomas C. Terwilliger
A method for improving crystallographic phases is presented that is based on the preferential occurrence of certain local patterns of electron density in macromolecular electron-density maps. The method focuses on the relationship between the value of electron density at a point in the map and the pattern of density surrounding this point. Patterns of density that can be superimposed by rotation about the central point are considered equivalent. Standard templates are created from experimental or model electron-density maps by clustering and averaging local patterns of electron density. The clustering is based on correlation coefficients after rotation to maximize the correlation. Experimental or model maps are also used to create histograms relating the value of electron density at the central point to the correlation coefficient of the density surrounding this point with each member of the set of standard patterns. These histograms are then used to estimate the electron density at each point in a new experimental electron-density map using the pattern of electron density at points surrounding that point and the correlation coefficient of this density to each of the set of standard templates, again after rotation to maximize the correlation. The method is strengthened by excluding any information from the point in question from both the templates and the local pattern of density in the calculation. A function based on the origin of the Patterson function is used to remove information about the electron density at the point in question from nearby electron density. This allows an estimation of the electron density at each point in a map, using only information from other points in the process. The resulting estimates of electron density are shown to have errors that are nearly independent of the errors in the original map using model data and templates calculated at a resolution of 2.6,Å. Owing to this independence of errors, information from the new map can be combined in a simple fashion with information from the original map to create an improved map. An iterative phase-improvement process using this approach and other applications of the image-reconstruction method are described and applied to experimental data at resolutions ranging from 2.4 to 2.8,Å. [source]

Regional cerebral blood flow during hyperventilation in patients with acute bacterial meningitis

CLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 5 2000
K. Møller
Mechanical hyperventilation is often instituted in patients with acute bacterial meningitis when increased intracranial pressure is suspected. However, the effect on regional cerebral blood flow (CBF) is unknown. In this study, we measured regional CBF (rCBF) in patients with acute bacterial meningitis before and during short-term hyperventilation. In 17 patients with acute bacterial meningitis, absolute rCBF (in ml/100 g min,1) was measured during baseline ventilation and hyperventilation by single-photon emission computed tomography (SPECT) using intravenous 133Xe bolus injection. Intravenous 99mTc-HMPAO (hexamethylpropyleneamine oxime) was subsequently given during hyperventilation. In 12 healthy volunteers, rCBF was measured by SPECT and 99mTc-HMPAO during spontaneous ventilation. Using standard templates to identify regions of interest (ROIs), we calculated rCBF in percentage of cerebellar (99mTc-HMPAO images) or mean hemispheric (133Xe images) flow for each ROI, the degree of side-to-side asymmetry for each ROI, and the anterior-to-posterior flow ratio. On 133Xe images, absolute rCBF decreased significantly during hyperventilation compared to baseline ventilation in all regions, but the relative rCBF did not change significantly from baseline ventilation (n=14) to hyperventilation (n=12), indicating that the perfusion distribution was unchanged. On 99mTc-HMPAO images (n=12), relative rCBF and the anterior-to-posterior flow ratio were significantly lower in patients than in controls in the frontal and parietal cortex as well as in the basal ganglia. Focal perfusion abnormalities were present in 10 of 12 patients. Regional cerebral blood flow abnormalities are frequent in patients with acute bacterial meningitis. Short-term hyperventilation does not enhance these abnormalities. [source]