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Fractional Change (fractional + change)
Selected AbstractsThe accuracy of matrix population model projections for coniferous trees in the Sierra Nevada, CaliforniaJOURNAL OF ECOLOGY, Issue 4 2005PHILLIP J. VAN MANTGEM Summary 1We assess the use of simple, size-based matrix population models for projecting population trends for six coniferous tree species in the Sierra Nevada, California. We used demographic data from 16 673 trees in 15 permanent plots to create 17 separate time-invariant, density-independent population projection models, and determined differences between trends projected from initial surveys with a 5-year interval and observed data during two subsequent 5-year time steps. 2We detected departures from the assumptions of the matrix modelling approach in terms of strong growth autocorrelations. We also found evidence of observation errors for measurements of tree growth and, to a more limited degree, recruitment. Loglinear analysis provided evidence of significant temporal variation in demographic rates for only two of the 17 populations. 3Total population sizes were strongly predicted by model projections, although population dynamics were dominated by carryover from the previous 5-year time step (i.e. there were few cases of recruitment or death). Fractional changes to overall population sizes were less well predicted. Compared with a null model and a simple demographic model lacking size structure, matrix model projections were better able to predict total population sizes, although the differences were not statistically significant. Matrix model projections were also able to predict short-term rates of survival, growth and recruitment. Mortality frequencies were not well predicted. 4Our results suggest that simple size-structured models can accurately project future short-term changes for some tree populations. However, not all populations were well predicted and these simple models would probably become more inaccurate over longer projection intervals. The predictive ability of these models would also be limited by disturbance or other events that destabilize demographic rates. [source] The Use of Anatomic M-Mode Echocardiography to Determine the Left Atrial Appendage Functions in Patients with Sinus RhythmECHOCARDIOGRAPHY, Issue 2 2005Yekta Gurlertop M.D. Left atrial appendage (LAA) contractile dysfunction is associated with thrombus formation and systemic embolism. LAA function is determined by its flow velocities and fractional area change. This study was performed in order to determine the LAA functions with the anatomic M-mode echocardiography (AMME). Our study comprised 74 patients who had sinus rhythm and underwent transesophageal echocardiography (TEE) for various reasons. LAA fractional change (LAAFAC) was measured by manual planimetry in a transverse basal short-axis approach and LAA emptying and filling velocities also were measured. The AMME values were determined by an M-mode cross section from a cursor placed beneath the orifice of the LAA in transverse basal short-axis imaging. From these values LAA fractional shortening (LAAFS) and ejection fraction (LAAEF) were calculated. LAAEF was calculated by the Teicholz method. The comparisons were conducted, and no correlations between the LAA late filling and the anatomic M-mode values were found (for LAAFS r = 0.18; P > 0.05 and for LAAEF r = 0.19; P > 0.05). There were significant but poor correlations among the LAA late emptying with the anatomic M-mode measurements (for LAAFS r = 0.26; P < 0.05 and for LAAEF r = 0.30; P < 0.01), whereas, there were significant and good correlations between the LAAFAC and the anatomic M-mode values (for LAAFS r = 0.75; P < 0.01 and for LAAEF r = 0.78; P < 0.01). There were significant differences between the valvular heart disease group and the normal group, and between the valvular heart disease group and the ASD group (for LAAFAC P < 0.01, for LAAEF P < 0.01, for LAAFS P < 0.01). There was no difference between the normal group and the ASD group. Our study showed that the LAAEF and LAAFS in patients with sinus rhythm obtained via anatomical M-mode echocardiography is a new method, which can be used instead of left atrial appendage area change. [source] Adsorption of 3- and 4-benzoylpyridine on colloidal silver particles: a surface-enhanced Raman scattering studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2004Joydeep Chowdhury Abstract Surface-enhanced Raman scattering (SERS) spectra of 3- and 4-benzoylpyridine (BP) adsorbed on silver hydrosols were compared with the FTIR and normal Raman spectra in bulk and in solution. With a small fractional change in adsorbate concentration, the SER spectra of isomeric BPs show significant changes in their features, indicating different orientational changes of the different parts of the flexible molecule on the colloidal silver surface with adsorbate concentration. The appearance of a broad, long-wavelength band in the absorption spectra of the silver sol due to solute-induced coagulation of colloidal silver particles is found to be red shifted with increase in adsorbate concentration. The SER excitation profiles indicate that the resonance of the Raman excitation radiation with the new aggregation band contributes more to the SERS intensity than that with the original sol band. Copyright © 2004 John Wiley & Sons, Ltd. [source] Influence of lee waves on the near-surface flow downwind of the PenninesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 627 2007P. F. Sheridan Abstract The results of a recent field experiment focusing on the near-surface pressure and flow fields downstream of the Pennines in northern England are presented. The main aim of the experiment is the improvement of wind forecasts downstream of orography. Trapped lee waves commonly occur in westerly flow in this region, and during the experiment there were numerous instances of apparent flow separation, indicating the formation of lee-wave rotors. The spatial variability of the near-surface flow in these circumstances is closely linked to the positions of lee-wave crests and troughs aloft, and appears to be a response to pressure gradients induced by the lee waves. For large-amplitude waves, it has been possible to demonstrate a correlation between the fractional change of the flow speed across the measurement array (which if large enough may lead to flow separation) and a normalized pressure-perturbation amplitude. For a group of lee-wave cases during which the cross-mountain flow is strong, a rapid decrease in the Scorer parameter within the lower portion of the troposphere appears to be a prerequisite for rotors to form. However, this does not guarantee their occurrence. For a fixed Scorer-parameter profile, idealized two-dimensional simulations indicate that the lee-wave-induced pressure-perturbation amplitude, and hence the occurrence of rotors, is controlled largely by the strength of the wind upstream close to the mountain-top level. It seems that the combination of a favourable Scorer-parameter profile and sufficiently strong low-level winds is required for rotors to develop. © Crown Copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd. [source] Determining the dilation factor in 4D monitoring of compacting reservoirs by rock-physics modelsGEOPHYSICAL PROSPECTING, Issue 6 2007José M. Carcione ABSTRACT Hydrocarbon depletion and fluid injection cause compaction and stretching of the reservoir and overburden layers. 4D prestack seismic data can be used to detect these changes because compaction/stretching causes changes in traveltimes and seismic velocities. We show that, by using two different petro-elastic models at varying effective pressures, a good approximation is to assume that the fractional changes in layer thickness, ,L/L, and seismic velocity, ,v/v, are related by a linear function of ,L/L. The slope of this function (the dilation factor, ,= (,v/v)/(,L/L)) is negative and its absolute value generally decreases (shale, low porosity) or increases (sandstone, high porosity) with increasing layer thickness and decreasing effective pressure. The analysis is mainly performed for isotropic deformations. The dilation factor for uniaxial deformations is smaller in absolute value. The dilation factor, which can be calculated from time-lapse data, can be used to predict reservoir compaction/stretching as a function of depth and surface subsidence. [source] Rate Responsive Pacing Using Transthoracic Impedance Minute Ventilation Sensors: A Multicenter Study on Calibration StabilityPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 12 2002FIRAT DURU DURU, F., et al.: Rate Responsive Pacing Using Transthoracic Impedance Minute Ventilation Sensors: A Multicenter Study on Calibration Stability. Previous studies showed that transthoracic impedance. Previous studies showed that transthoracic impedance minute ventilation (IMV), as measured by a pacemaker sensor, is closely correlated to actual minute ventilation (VE·) determined by standard methods. The aim of this study was to analyze the changes in the calibration between IMV and VE· at rest and during exercise over time. Fifteen patients (age 60 ± 13 years) with Medtronic Kappa 400 pacemakers completed a baseline visit followed by two visits separated by 1 month and 1 week, respectively. In each patient, VE· (L/min) was monitored at rest in the supine and sitting positions and during graded bicycle ergometer exercise using a standard cardiopulmonary metabolic gas analysis system with simultaneous recording of IMV (,/min) using DR-180 extended telemetry monitors. Calibration at rest was defined as the ratio of IMV to VE·, calculated from 1-minute average values in the supine and sitting positions. Calibration during bicycle exercise was defined as intercept (IMV value at VE·= 10 L/min-typical VE· value at beginning of exercise), and slope of the IMV/VE· regression line. The calibration of IMV showed individual variability over time. The magnitude (absolute value) of observed fractional changes in calibration at 1 month was 0.23 ± 0.20 (rest-supine), 0.20 ± 0.15 (rest-sitting), 0.18 ± 0.19 (exercise-intercept), 0.28 ± 0.35 (exercise-slope), and 0.18 ± 0.15, 0.15 ± 0.09, 0.28 ± 0.39, and 0.27 ± 0.15, respectively, at 1 week. The magnitude of change at 1 month was not statistically different from the magnitude of change at 1 week. In conclusion, the calibration of IMV, as measured by a pacemaker sensor, versus actual VE· may demonstrate variability. However, this study also suggests that the observed changes are not cumulative over time. These results have implications for patient monitoring applications using these sensors and for development of future pacemaker rate response algorithms. [source] | |||||||||||||