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Systematic Differences (systematic + difference)
Selected AbstractsThe intrinsic shape of the human lumbar spine in the supine, standing and sitting postures: characterization using an active shape modelJOURNAL OF ANATOMY, Issue 2 2009Judith R. Meakin Abstract The shape of the lumbar spine in the sagittal plane varies between individuals and as a result of postural changes but it is not known how the shape in different postures is related. Sagittal images of the lumbar spines of 24 male volunteers were acquired using a positional magnetic resonance scanner. The subjects were imaged lying supine, standing and sitting. An active shape model was used to characterize shape in terms of independent modes of variation. Two modes were identified that described the total (mode 1) and distribution (mode 2) of the curvature. The spinal shape was found to be intercorrelated between the three postures for both modes, suggesting that the lumbar spine has an element of shape that is partially maintained despite postural alterations. Mode 1 values indicated that the spine was straightest when standing and curviest when sitting. Mode 2 values indicated that the distribution in the curvature was most even when sitting and least even when lying supine. Systematic differences in the behaviour of the spine, when changing posture, were found that suggest that the shape of the spine may affect its biomechanics. [source] In Vivo Determination of Bone Structure in Postmenopausal Women: A Comparison of HR-pQCT and High-Field MR Imaging,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2008Galateia J Kazakia PhD Abstract Bone structural measures obtained by two noninvasive imaging tools,3T MRI and HR-pQCT,were compared. Significant but moderate correlations and 2- to 4-fold discrepancies in parameter values were detected, suggesting that differences in acquisition and analysis must be considered when interpreting data from these imaging modalities. Introduction: High-field MRI and high resolution (HR)-pQCT are currently being used in longitudinal bone structure studies. Substantial differences in acquisition and analysis between these modalities may influence the quantitative data produced and could potentially influence clinical decisions based on their results. Our goal was to compare trabecular and cortical bone structural measures obtained in vivo by 3T MRI and HR-pQCT. Materials and Methods: Postmenopausal osteopenic women (n = 52) were recruited for this study. HR-pQCT imaging of the radius and tibia was performed using the XtremeCT scanner, with a voxel size of 82 × 82 × 82 ,m3. MR imaging was performed on a 3T Signa scanner using SSFP imaging sequences, with a pixel size of 156 × 156 ,m2 and slice thickness of 500 ,m. Structure parameters were calculated using standard HR-pQCT and MRI analysis techniques. Relationships between measures derived from HR-pQCT, MRI, and DXA were studied. Results: Significant correlations between HR-pQCT and MRI parameters were found (p < 0.0001) and were strongest for Tb.N (r2 = 0.52), Ct.Th (r2 = 0.59), and site-specific Tb.Sp (r2 = 0.54,0.60). MRI and HR-pQCT provided statistically different values of structure parameters (p < 0.0001), with BV/TV and Tb.Th exhibiting the largest discrepancies (MR/HR-pQCT = 3,4). Although differences in the Tb.N values were statistically significant, the mean differences were on the order of our reproducibility measurements. Systematic differences between MRI and HR-pQCT analysis procedures leading to discrepancies in cortical thickness values were observed, with MRI values consistently higher. Minimal correlations were found between MRI or HR-pQCT parameters and DXA BMD or T-score, except between HR-pQCT measures at the radius and the ultradistal radius T-scores, where moderate correlations were found (r2 = 0.19,0.58). Conclusions: This study provides unique insight into two emerging noninvasive tools for bone structure evaluation. Our findings highlight the significant influence of analysis technique on results of in vivo assessment and underscore the importance of accounting for these differences when interpreting results from these modalities. [source] The impact of cross-sectional data aggregation on the measurement of vertical price transmission: An experiment with German food pricesAGRIBUSINESS : AN INTERNATIONAL JOURNAL, Issue 4 2006Stephan von Cramon-Taubadel The impact of cross-sectional aggregation over individual retail stores on the estimation and testing of vertical price transmission between the wholesale and retail levels is investigated using a unique data set of individual retail prices in Germany. Systematic differences between the results of estimations using aggregated data on the one hand, and disaggregated data on the other, are discussed theoretically and confirmed empirically. The results suggest that estimation with aggregated data can generate misleading conclusions about price transmission behavior at the level of the individual units (i.e., retail stores) that underlie these aggregates. [JEL classifications: C22, L11, D40] © 2006 Wiley Periodicals, Inc. Agribusiness 22: 505,522, 2006. [source] Refinement of protein crystal structures using energy restraints derived from linear-scaling quantum mechanicsACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2005Ning Yu A novel method is proposed in which combined restraints derived from linear-scaling semiempirical quantum-mechanical (QM) calculations and X-ray diffraction data are combined to refine crystal structures of proteins. Its performance has been tested on a small protein molecule, bovine pancreatic trypsin inhibitor (BPTI). The refinement involves minimization of the sum of a geometric energy function and an X-ray target function based on either the least-squares residual or the maximum-likelihood formalism. For comparison, similar refinement runs have also been performed using energy restraints derived from the force field available in the Crystallography & NMR System (CNS) program. The QM refinements were carried out with weights that were varied by several orders of magnitude and the optimal weights were identified by observing the trend in the final free R values, QM heats of formation and coordinate root-mean-square deviations (r.m.s.d.s) from the crystal structure. It is found that the QM weights are typically smaller but generally on the same scale as the molecular-mechanics (MM) weights for the respective X-ray target functions. The crystallographic R, free R, real-space R values and correlation coefficients based on the structures refined with the energy restraints derived from our QM calculations and Engh and Huber parameters are comparable, suggesting that the QM restraints are capable of maintaining reasonable stereochemistry to a similar degree as the force-field parameters. A detailed inspection of the structures refined with the QM and MM energy restraints reveals that one of the common differences between them and the crystal structure is that the strained bond angles in the crystal structure are corrected after energetically restrained refinements. Systematic differences in certain bond lengths between the QM-refined structures and the statistical averages of experimental structures have also been observed and discussed. [source] The impact of metabolic state on Cd adsorption onto bacterial cellsGEOBIOLOGY, Issue 3 2007K. J. JOHNSON ABSTRACT This study examines the effect of bacterial metabolism on the adsorption of Cd onto Gram-positive and Gram-negative bacterial cells. Metabolically active Gram-positive cells adsorbed significantly less Cd than non-metabolizing cells. Gram-negative cells, however, showed no systematic difference in Cd adsorption between metabolizing and non-metabolizing cells. The effect of metabolism on Cd adsorption to Gram-positive cells was likely due to an influx of protons in and around the cell wall from the metabolic proton motive force, promoting competition between Cd and protons for adsorption sites on the cell wall. The relative lack of a metabolic effect on Cd adsorption onto Gram-negative compared to Gram-positive cells suggests that Cd binding in Gram-negative cells is focused in a region of the cell wall that is not reached, or is unaffected by this proton flux. Thermodynamic modeling was used to estimate that proton pumping causes the pH in the cell wall of metabolizing Gram-positive bacteria to decrease from the bulk solution value of 7.0 to approximately 5.7. [source] Relationship between the IQ of people with Prader,Willi syndrome and that of their siblings: evidence for imprinted gene effectsJOURNAL OF INTELLECTUAL DISABILITY RESEARCH, Issue 5 2009J. Whittington Abstract Background Genetic disorders occasionally provide the means to uncover potential mechanisms linking gene expression and physical or cognitive characteristics or behaviour. Prader,Willi syndrome (PWS) is one such genetic disorder in which differences between the two main genetic subtypes have been documented (e.g. higher verbal IQ in one vs. higher performance IQ in the other; slower than normal reaction time in one vs. normal in the other). In a population study of PWS, the IQ distribution of people with PWS was approximately normal. This raises the question of whether this distribution arose from a systematic effect of PWS on IQ (hypothesis 1) or whether it was the fortuitous result of random effects (hypothesis 2). Method The correlation between PWS and sibling IQ was determined in order to discriminate between the two hypotheses. In the first case we would expect the correlation to be similar to that found in the general population (0.5); in the second case it would be zero. Results It was found that the overall PWS,sibling IQ correlation was 0.3 but that the two main genetic subtypes of PWS differed in their familial IQ relationships. As expected, the IQs of normal siblings correlated 0.5, and this was also the case with one genetic subtype of PWS (uniparental disomy) and their siblings, while the other subtype IQ correlated ,0.07 with sibling IQ. Conclusions This is a potentially powerful result that gives another clue to the role of genes on chromosome 15 in the determination of IQ. It is another systematic difference between the genetic subtypes of PWS, which needs an explanation in terms of the very small genetic differences between them. [source] Global Market Segmentation and Patterns in Stock Market Reaction to US Earnings Announcements: Further EvidenceJOURNAL OF INTERNATIONAL FINANCIAL MANAGEMENT & ACCOUNTING, Issue 2 2005Tony Kang The purpose of this study is to investigate why the information content of US earnings announcements of non-US firms cross-listing in the US varies with the degree of capital market segmentation in the cross-listing firms' countries of domicile. My evidence shows that indirect barriers to investing (i.e., accounting rules and liquidity differences) rather than direct investment barriers (i.e., investment restrictions) mainly account for this difference. After controlling for the level of accounting disclosure in a firm's country of domicile, I do not observe a systematic difference in the size of market's reaction to earnings announcements depending on the degree of market segmentation in the firm's country of domicile. This study contributes to the literature by providing evidence that accounting disclosure plays an important role in the integration of global capital markets. [source] Comparison between three-dimensional volume-selective turbo spin-echo imaging and two-dimensional ultrasound for assessing carotid artery structure and functionJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2005Lindsey A. Crowe PhD Abstract Purpose To compare a volume-selective three-dimensional turbo spin echo (TSE) technique with ultrasound (US) for assessing carotid artery wall structure and function. Materials and Methods A three-dimensional volume-selective TSE technique was used to image the carotid artery in 10 healthy subjects and five hypertensive subjects (each of whom were scanned three times while they received different hypertension treatments). Lumen and wall area were measured on MR images. Two-dimensional US measurements of the intima-media thickness (IMT) and lumen diameter were taken in three orientations through a single cross section. The lumen area change over the cardiac cycle was used to determine distension. For validation, a Bland-Altman analysis was used to compare the vessel wall and lumen areas measured by three-dimensional MRI volumes with those obtained by US scans. Results Agreement between the two methods was found. The mean difference in distension between US and MRI was 1.2% (±5.1%). For the wall area measurements, good agreement was shown, but there was a systematic difference due to the visualization of the adventitia by MRI. Both techniques offer an easy way to objectively measure lumen indices. MRI can provide the complete circumference over the length of a vessel, while US is flexible and relatively inexpensive. The application of US is limited, however, when subjects are poorly echogenic. A difference between hypertensive and healthy subjects was found. Conclusion There was a good agreement between MRI and the clinically established two-dimensional US method. The MRI method has the advantage of providing increased vessel coverage, which permits one to assess localized abnormalities without assuming vessel uniformity. J. Magn. Reson. Imaging 2005;21:282,289. © 2005 Wiley-Liss, Inc. [source] A data base for partition of volatile organic compounds and drugs from blood/plasma/serum to brain, and an LFER analysis of the dataJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2006Michael H. Abraham Abstract Literature values of the in vivo distribution (BB) of drugs from blood, plasma, or serum to rat brain have been assembled for 207 compounds (233 data points). We find that data on in vivo distribution from blood, plasma, and serum to rat brain can all be combined. Application of our general linear free energy relationship (LFER) to the 207 compounds yields an equation in log BB, with R2,=,0.75 and a standard deviation, SD, of 0.33 log units. An equation for a training set predicts the test set of data with a standard deviation of 0.31 log units. We further find that the invivo data cannot simply be combined with in vitro data on volatile organic and inorganic compounds, because there is a systematic difference between the two sets of data. Use of an indicator variable allows the two sets to be combined, leading to a LFER equation for 302 compounds (328 data points) with R2,=,0.75 and SD,=,0.30 log units. A training equation was then used to predict a test set with SD,=,0.25 log units. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:2091,2100, 2006 [source] Agency conflicts between board and managerNONPROFIT MANAGEMENT & LEADERSHIP, Issue 2 2009A discrete choice experiment in Flemish nonprofit schools Detecting agency problems is an important task when assessing the effectiveness of a nonprofit organization's governance. A first step is to examine the objectives of principals and agents and determine whether there is a systematic difference between them. Using a discrete choice experiment, we identify the objectives of board chairpersons (principals) and headmasters (agents) of Flemish nonprofit schools. We find systematic differences between the two groups. Of the seven possible objectives set out in the experiment, six are relevant for both headmasters and board chairpersons. For four of these, the preferences of both groups differ significantly. Whereas ideological values play an important role for both the board and the headmaster, they are significantly more important for the board. Both parties dislike having a large number of pupils, and the disutility is larger for the board. With respect to job satisfaction and pupil satisfaction, we find the opposite: while the board is prepared to give up pupil and job satisfaction in favor of the other objectives, these two objectives score very high on the priority list of the headmasters. [source] Reconsidering the Northwest European Family System: Living Arrangements of the Aged in Comparative Historical PerspectivePOPULATION AND DEVELOPMENT REVIEW, Issue 2 2009Steven RugglesArticle first published online: 12 JUN 200 During the past four decades, historians and demographers have argued that historical Northwest Europe and North America had a unique weak-family system characterized by neolocal marriage and nuclear family structure. This analysis uses newly available micro-data from 84 historical and contemporary censuses of 34 countries to evaluate whether the residential behavior of the aged in historical Northwest Europe and North America was truly distinctive. The results show that with simple controls for agricultural employment and demographic structure, comparable measures of the living arrangements of the aged show little systematic difference between nineteenth-century Northwest Europe and North America and twentieth-century developing countries. These findings cast doubt on the hypothesis that Northwest Europeans and North Americans had an exceptional historical pattern of preference for nuclear families. [source] Comparing mass-consistent atmospheric moisture budgets on an irregular grid: An Arctic exampleTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 592 2003M. Göber Abstract We present a method to minimize the effects of different resolution and mass imbalance when comparing atmospheric energy and water budgets from different datasets. Sizeable differences between re-analysis- and radiosonde-based atmospheric budgets had been found in earlier studies and it had been suspected that the different resolutions of the datasets strongly contributes to these discrepancies. Furthermore, most studies so far had used mass-imbalanced wind fields, which can lead to serious errors. We balance the wind field by using a variational modification algorithm combined with a finite-element discretization which allows the use of data on a grid defined by the radiosonde network. This method permits the computation of flux divergences in integral form and gives a consistent numerical method to get a mass-balanced wind field with minimum modifications. Applying this method to Arctic radiosonde and re-analysis data on the same grid leads to a better agreement with respect to the horizontal distribution and the mean annual cycle of the moisture flux convergence. The constraint of mass balance on the wind field leads to a greatly reduced and more realistic variability in space and time. However, a systematic difference of about 20% remains between the estimate based on a re-analysis dataset sampled only on the coarse grid of the radiosonde network and an estimate based on the use of the full, fine grid of the re-analysis. These systematic differences can be significantly reduced by creating a simulated radiosonde dataset from the re-analysis with doubled resolution. We undertake an extensive analysis of the uncertainty of the estimates originating from the choices made in the specification of the algorithm. Based solely on radiosonde data, which are likely to result in a low bias, we estimate the net water gain of the Arctic atmosphere as 164 ± 10 mm yr,1 (0.45 ± 0.03 mm d,1) for 1979,93. Copyright © 2003 Royal Meteorological Society. [source] Case-controlled structure validationACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2009Randy J. Read Although many factors influence the quality of a macromolecular crystal structure, validation criteria are usually only calibrated using one of these factors, the resolution. For many purposes this is sufficient, but there are times when one wishes to compare one set of structures with another and the comparison may be invalidated by systematic differences between the sets in factors other than resolution. This problem can be circumvented by borrowing from medicine the idea of the case-matched control: each structure of interest is matched with a control structure that has similar values for all relevant factors considered in this study. In addition to resolution, these include the size of the structure (as measured by the volume of the asymmetric unit) and the year of deposition. This approach has been applied to address two questions: whether structures from structural genomics efforts reach the same level of quality as structures from traditional sources and whether the impact factor of the journal in which a structure is published correlates with structure quality. In both cases, once factors influencing quality have been controlled in the comparison, there is little evidence for a systematic difference in quality. [source] Using diffusion MRI for measuring the temperature of cerebrospinal fluid within the lateral ventriclesACTA PAEDIATRICA, Issue 2 2010LR Kozak Abstract Aim:, Hypothermia is often induced to reduce brain injury in newborns, following perinatal hypoxic,ischaemic events, and in adults following traumatic brain injury, stroke or cardiac arrest. We aimed to devise a method, based on diffusion-weighted MRI, to measure non-invasively the temperature of the cerebrospinal fluid in the lateral ventricles. Methods:, The well-known temperature dependence of the water diffusion constant was used for the estimation of temperature. We carried out diffusion MRI measurements on a 3T Philips Achieva Scanner involving phantoms (filled with water or artificial cerebrospinal fluid while slowly cooling from 41 to 32°C) and healthy adult volunteers. Results:, The estimated temperature of water phantoms followed that measured using a mercury thermometer, but the estimates for artificial cerebrospinal fluid were 1.04°C lower. After correcting for this systematic difference, the estimated temperature within the lateral ventricles of volunteers was 39.9°C. Using diffusion directions less sensitive to cerebrospinal fluid flow, it was 37.7°C, which was in agreement with the literature. Conclusion:, Although further improvements are needed, measuring the temperature within the lateral ventricles using diffusion MRI is a viable method that may be useful for clinical applications. We introduced the method, identified sources of error and offered remedies for each. [source] Evaluation of some factors affecting the agreement between the Proview Eye Pressure Monitor and the Goldmann applanation tonometer measurementsCLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 4 2007Pinakin Gunvant BS Optom PhD FAAO Background:, Our aim was to examine whether training level and ocular factors could account for part of the difference in intraocular pressure (IOP) measured using the Goldmann applanation tonometer (GAT) and Proview Eye Pressure Monitor (PPT). Methods:, One hundred and nineteen individuals (238 eyes) were enrolled in the study. The mean age was 35.8 years (range 21 to 79). All study participants obtained IOP measurements using the PPT after hearing instructions on how to perform PPT. Glaucoma patients obtained additional IOP measurements using PPT after viewing an instructional video and after 30 days of home use. IOP was also measured using the GAT at each experimental session. Results:, The difference in IOP measured by the GAT and the PPT was 0.55 ± 3.38 mmHg, 0.17 ± 3.79 mmHg and -1.30 ± 3.79 mmHg for myopic, emmetropic and hypermetropic groups, respectively, which were statistically significant (ANCOVA; p = 0.014). The difference in IOP between GAT and PPT was not significantly different for measurements obtained after verbal instructions, instructional video or after 30 days of home use (Repeated-ANCOVA; p = 0.30). The overall agreement between the GAT and the PPT was poor. Intra-class correlation coefficient was 0.575, and the 95% confidence interval (CI) of agreement was -6.93 to +6.73 mmHg. Conclusion:, There was a small systematic difference in IOP measured by the GAT and PPT when comparing the different refraction groups; however, this level of difference between the groups is unlikely to be of clinical significance. The level of training in using the PPT did not influence its measurements. The limits of agreement between the PPT and the GAT were wide and long-term use of PPT did not improve its agreement. [source] Evaluation of left ventricular volumes and ejection fraction by automated gated myocardial SPECT versus cardiovascular magnetic resonanceCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 3 2005Eva Persson Summary Background:, Electrocardiogram-gated myocardial single-photon emission computed tomography (SPECT) with 99mTc-tetrofosmin allows simultaneous evaluation of myocardial perfusion and function. In this study, left ventricular volumes, ejection fraction (LVEF), and left ventricular wall volume (LVWV) derived from gated SPECT were compared with measurements from cardiovascular magnetic resonance (CMR), performed within a few hours. Methods:, The study population included 55 patients with known or suspected coronary artery disease, including 13 patients with recent acute myocardial infarction. End-diastolic (EDV) and end-systolic (ESV) volumes, LVEF and LVWV were derived automatically from gated SPECT using commercially available software (QGS). In the CMR studies, manually delineated endocardial and epicardial borders on short-axis slices were used to calculate the volumes. Results:, Gated SPECT underestimated EDV by 35 ± 14 ml (mean ± SD) (P<0·001), ESV by 10 ± 13 ml (P<0·001), and LVEF by 4 ± 7 percentage points (P<0·001). There were no systematic difference in EDV, ESV or LVEF between the methods. SPECT underestimated LVWV by 49 ± 30 ml (P<0·001), with a trend towards increasing underestimation by SPECT for larger wall volumes. Conclusion:, These findings show that gated SPECT slightly underestimates EDV, ESV and LVEF compared with CMR. This underestimation is systematic, however, indicating that ventricular volumes derived from gated SPECT are robust enough to guide clinical management. Estimates of LVWV in patients with large wall volumes are less accurate. [source] With a Little Help from Their Friends: Exploring the Advice Networks of Software EntrepreneursCREATIVITY AND INNOVATION MANAGEMENT, Issue 1 2003Cathleen A. McGrath This field interview study examined patterns and content of advice sharing networks among 20 software executives to provide a clearer understanding of how advice relationships are established, the types of advice that are shared and the role that relationships play in the support of information exchange and diffusion. Most advice relationships were formed from strong tie relationships, while systematic differences were found among the types of advice sought from advice relationships resulting from strong ties, business ties and weak ties. The preference of software executives for rich communication media supports the importance of establishing trust in advice sharing relationships. [source] Estimation of the burden of active and life-time epilepsy: A meta-analytic approachEPILEPSIA, Issue 5 2010Anthony K. Ngugi Summary Purpose:, To estimate the burden of lifetime epilepsy (LTE) and active epilepsy (AE) and examine the influence of study characteristics on prevalence estimates. Methods:, We searched online databases and identified articles using prespecified criteria. Random-effects meta-analyses were used to estimate the median prevalence in developed countries and in urban and rural settings in developing countries. The impact of study characteristics on prevalence estimates was determined using meta-regression models. Results:, The median LTE prevalence for developed countries was 5.8 per 1,000 (5th,95th percentile range 2.7,12.4) compared to 15.4 per 1,000 (4.8,49.6) for rural and 10.3 (2.8,37.7) for urban studies in developing countries. The median prevalence of AE was 4.9 per 1,000 (2.3,10.3) for developed countries and 12.7 per 1,000 (3.5,45.5) and 5.9 (3.4,10.2) in rural and urban studies in developing countries. The estimates of burden for LTE and AE in developed countries were 6.8 million (5th,95th percentile range 3.2,14.7) and 5.7 million (2.7,12.2), respectively. In developing countries these were 45 (14,145) million LTE and 17 (10,133) million AE in rural areas and 17 (5,61) million LTE and 10 (5,17) million AE in urban areas. Studies involving all ages or only adults showed higher estimates than pediatric studies. Higher prevalence estimates were also associated with rural location and small study size. Conclusions:, This study estimates the global burden of epilepsy and the proportions with AE, which may benefit from treatment. There are systematic differences in reported prevalence estimates, which are only partially explained by study characteristics. [source] Taxon-specific variation in the stable isotopic signatures (,13C and ,15N) of lake phytoplanktonFRESHWATER BIOLOGY, Issue 5 2006KRISTIINA VUORIO Summary 1. The variability in the stable isotope signatures of carbon and nitrogen (,13C and ,15N) in different phytoplankton taxa was studied in one mesotrophic and three eutrophic lakes in south-west Finland. The lakes were sampled on nine to 16 occasions over 2,4 years and most of the time were dominated by cyanobacteria and diatoms. A total of 151 taxon-specific subsamples covering 18 different phytoplankton taxa could be isolated by filtration through a series of sieves and by flotation/sedimentation, followed by microscopical identification and screening for purity. 2. Substantial and systematic differences between phytoplankton taxa, seasons and lakes were observed for both ,13C and ,15N. The values of ,13C ranged from ,34.4, to ,5.9, and were lowest in chrysophytes (,34.4, to ,31.3,) and diatoms (,30.6, to ,26.6,). Cyanobacteria were most variable (,32.4, to ,5.9,), including particularly high values in the nostocalean cyanobacterium Gloeotrichia echinulata (,14.4, to ,5.9,). For ,13C, the taxon-specific amplitude of temporal changes within a lake was usually <1,8, (<1,4, for microalgae alone and <1,8, for cyanobacteria alone), whereas the amplitude among taxa within a water sample was up to 31,. 3. The values of ,15N ranged from ,2.1, to 12.8, and were high in chrysophytes, dinophytes and diatoms, but low in the nitrogen-fixing cyanobacteria Anabaena spp., Aphanizomenon spp. and G. echinulata (,2.1, to 1.6,). Chroococcalean cyanobacteria ranged from ,1.4, to 8.9,. For ,15N, the taxon-specific amplitude of temporal changes within a lake was 2,6,, (2,6, for microalgae alone and 2,4, for cyanobacteria alone) and the amplitude among taxa within a water sample was up to 11,. 4. The isotopic signatures of phytoplankton changed systematically with their physical and chemical environment, most notably with the concentrations of nutrients, but correlations were non-systematic and site-specific. 5. The substantial variability in the isotopic signatures of phytoplankton among taxa, seasons and lakes complicates the interpretation of isotopic signatures in lacustrine food webs. However, taxon-specific values and seasonal patterns showed some consistency among years and may eventually be predictable. [source] Hydraulic differentiation of Ponderosa pine populations along a climate gradient is not associated with ecotypic divergenceFUNCTIONAL ECOLOGY, Issue 4 2002H. Maherali Summary 1.,Pinus ponderosa occurs in a range of contrasting environments in the western USA. Xeric populations typically have lower leaf : sapwood area ratio (AL/AS) and higher whole-tree leaf specific hydraulic conductance (KL) than mesic populations. These climate-driven shifts in hydraulic architecture are considered adaptive because they maintain minimum leaf water potential above levels that cause xylem cavitation. 2.,Using a common garden study, we examined whether differences in biomass allocation and hydraulic architecture between P. ponderosa populations originating from isolated outcrops in the Great Basin desert and Sierran montane environments were caused by ecotypic differentiation or phenotypic plasticity. To determine if populations were genetically differentiated and if phenotypic and genetic differentiation coincided, we also characterized the genetic structure of these populations using DNA microsatellites. 3.,Phenotypic differentiation in growth, biomass allocation and hydraulic architecture was variable among populations in the common garden. There were no systematic differences between desert and montane climate groups that were consistent with adaptive expectations. Drought had no effect on the root : shoot and needle : stem ratio, but reduced seedling biomass accumulation, leaf area ratio, AL/AS and KL. Stem hydraulic conductance (KH) was strongly size-dependent, and was lower in droughted plants, primarily because of lower growth. 4.,Although microsatellites were able to detect significant non-zero (P < 0·001) levels of differentiation between populations, these differences were small and were not correlated with geographic separation or climate group. Estimates of genetic differentiation among populations were low (<5%), and almost all the genetic variation (>95%) resided within populations, suggesting that gene flow was the dominant factor shaping genetic structure. 5.,These results indicate that biomass allocation and hydraulic differences between desert and montane populations are not the result of ecotypic differentiation. Significant drought effects on leaf : sapwood allocation and KL suggest that phenotypic differentiation between desert and montane climates could be the result of phenotypic plasticity. [source] Further Characterisation of the 91500 Zircon CrystalGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2004Michael Wiedenbeck zircon 91500; matériau de référence; intercomparaison entre techniques; valeurs de travail This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 in both backscattered electron and cathodoluminescence images is described in detail. Blind intercomparison data reported by both LA-ICP-MS and SIMS laboratories indicate that only small systematic differences exist between the data sets provided by these two techniques. Furthermore, the use of NIST SRM 610 glass as the calibrant for SIMS analyses was found to introduce little or no systematic error into the results for zircon. Based on both laser fluorination and SIMS data, zircon 91500 seems to be very well suited for calibrating in situ oxygen isotopic analyses. Cet article présente les résultats d'une nouvelle caractérisation du zircon 91500, dont des données de microanalyse par sonde électronique, d'analyse par ablation laser en couplage à un ICP-MS, d'analyse par sonde ionique (SIMS) et d'analyse par fluorination laser. Le but de cette étude etait de démontrer que ce large monocristal de zircon pouvait être utilisé pour la calibration d'analyses in situ de Terres Rares et des isotopes de I'Oxygène, et en même temps de fournir des valeurs "de travail" pour un certain nombre de systémes géochimiques cruciaux. En complément des tests systématiques d'homogénéité de I'échantillon, tant chimiquement que structurellement, /'ex/sfence, dans le zircon 91500, de zonages visibles en électrons retro diffusés et en cathodoluminescence, est décrite en détail, line comparaison en aveugle des résultats obtenus par LA-ICP-MS et par SIMS, dans des laboratoires différents, montre que les différences systématiques entre les ensembles de données obtenues par ces deux techniques sont très faibles. De plus, I'utilisation du verre NIST SRM 610 comme calibrant lors de I'analyse par SIMS n'introduit qu'une erreur systématique très faible si ce n'est inexistante sur les résultats du zircon. Sur la base des analyses par fluorination laser et par SIMS, le zircon 91500 semble être parfaitement adapte a son utilisation pour la calibration d'analyses isotopiques in situ d'oxygène. [source] Multilevel models for estimating incremental net benefits in multinational studiesHEALTH ECONOMICS, Issue 8 2007Richard Grieve Abstract Multilevel models (MLMs) have been recommended for estimating incremental net benefits (INBs) in multicentre cost-effectiveness analysis (CEA). However, these models have assumed that the INBs are exchangeable and that there is a common variance across all centres. This paper examines the plausibility of these assumptions by comparing various MLMs for estimating the mean INB in a multinational CEA. The results showed that the MLMs that assumed the INBs were exchangeable and had a common variance led to incorrect inferences. The MLMs that included covariates to allow for systematic differences across the centres, and estimated different variances in each centre, made more plausible assumptions, fitted the data better and led to more appropriate inferences. We conclude that the validity of assumptions underlying MLMs used in CEA need to be critically evaluated before reliable conclusions can be drawn. Copyright © 2006 John Wiley & Sons, Ltd. [source] An epigenetic induction of a right-shift in hippocampal asymmetry: Selectivity for short- and long-term potentiation but not post-tetanic potentiationHIPPOCAMPUS, Issue 1 2008Akaysha C. Tang Abstract In humans, it is well established that major psychological functions are asymmetrically represented between the left and right cerebral cortices. The developmental origin of such functional lateralization remains unknown. Using the rat as a model system, we examined whether exposing neonates briefly to a novel environment can differentially affect synaptic plasticity in the left and right hippocampi during adulthood. During the first 3 weeks of life, one half of the pups from a litter spent 3 min daily away from their familiar home environment (Novel) while their littermates remained in that familiar environment (Home). At adulthood (7-months old), post-tetanic potentiation (PTP) of excitatory post-synaptic potentials (EPSPs), a very short-lasting form of plasticity, was greater among the Novel than the Home rats in both left and right hippocampi. In contrast, the novelty-induced increases in short- and long-term potentiation (STP, LTP), two relatively longer-lasting forms of plasticity, were found only in the right hippocampus. These findings demonstrate that a phase-selective asymmetry in hippocampal synaptic plasticity can be induced epigenetically by seemingly small systematic differences in early life environment. The selectivity of this asymmetry for the longer-lasting forms of synaptic plasticity suggests that the observed asymmetry in plasticity may contribute specifically to an asymmetric learning process which, in turn, may contribute to a functional asymmetry in the neocortex. © 2007 Wiley-Liss, Inc. [source] Graduates' career aspirations and individual characteristicsHUMAN RESOURCE MANAGEMENT JOURNAL, Issue 1 2005Wolfgang Mayrhofer Using the basic distinction between organisational and post-organisational career orientation, this article examines preferences of business school graduates for different types of career fields and systematic differences between people with different career orientations in terms of behavioural characteristics as well as personality traits. The results show that business school graduates clearly distinguish between organisational and post-organisational career fields. Graduates with post-organisational career aspirations display attributes of high flexibility, leadership motivation, selfpromotion/self-assertion, self-monitoring, networking and less self-consciousness. For individuals preferring an organisational career pattern, inverse relationships apply. Some implications of the findings for HR practice are discussed. [source] Where Infants Look Determines How They See: Eye Movements and Object Perception Performance in 3-Month-OldsINFANCY, Issue 2 2004Scott P. Johnson A fundamental question of perceptual development concerns how infants come to perceive partly hidden objects as unified across a spatial gap imposed by an occluder. Much is known about the time course of development of perceptual completion during the first several months after birth, as well as some of the visual information that supports unity perception in infants. The goal of this investigation was to examine the inputs to this process. We recorded eye movements in 3-month-old infants as they participated in a standard object unity task and found systematic differences in scanning patterns between those infants whose post-habituation preferences were indicative of unity perception versus those infants who did not perceive unity. Perceivers, relative to nonperceivers, scanned more reliably in the vicinity of the visible rod parts and scanned more frequently across the range of rod motion. These results suggest that emerging object concepts are tied closely to available visual information in the environment, and the process of information pickup. [source] Intercomparison of global cloud cover fields over oceans from the VOS observations and NCEP/NCAR reanalysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2007Ernst Bedacht Abstract The paper inter-compares the total cloud cover over the World Ocean from marine visual observations assimilated in the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) and National Centers of Environmental Prediction/National Center of Atmospheric Research (NCEP-NCAR) reanalysis. The Intercomparison covers the period from 1948 to 2002. NCEP-NCAR reanalysis shows about 10% of fractional cloud cover smaller than the visual observations do. The largest differences are observed in the mid and sub-polar latitudes. In the tropics, NCEP-NCAR data show slightly higher cloud cover then ICOADS. These systematic differences are quite persistent through the year with somewhat stronger differences in summer. Comparison of the characteristics of inter-annual variability shows little consistency between visually observed total cloud cover and total cloudiness diagnosed by the reanalysis. Linear trends are primarily positive in the ICOADS cloud data, while in the NCEP-NCAR reanalysis they show downward trends in the tropics and upward tendencies in the mid and high latitudes. Analysis of the effect of sampling in ICOADS shows that sampling inhomogeneity cannot fully explain the disagreements observed. At the same time, the major climate variability patterns such as North Atlantic Oscillation (NAO) and El-Nino,Southern Oscillation (ENSO) are well captured in both ICOADS and NCEP-NCAR cloud cover data sets. Copyright © 2007 Royal Meteorological Society [source] THE RELIABILITY OF NAÏVE ASSESSORS IN SENSORY EVALUATION VISUALIZED BY PRAGMATICAL MULTIVARIATE ANALYSISJOURNAL OF FOOD QUALITY, Issue 5 2002M.G. O'SULLIVAN The first part of this paper demonstrates a simple graphical way to visualize estimated variances, in terms of a plot of the total initial variance ("SIGNAL") versus residual variance ("NOISE"), as a pragmatic alternative to tables of F-tests. The recently developed Procrustes rotation in the bilinear "jack-knifing" form is then presented as a method for simplifying the comparison of PLS Regression models from different data sets. These methods are applied to sensory data in order to study if naïve (untrained) sensory panelists can produce reliable descriptions of systematic differences between various test meals. The results confirm that three panels of 15 naïve assessors each could give repeatable intersubjective description of the most dominant sensory variation dimensions. [source] Family literacy activities in the homes of successful young readersJOURNAL OF RESEARCH IN READING, Issue 1 2000Rhona Stainthorp This paper presents an account of the literacy activities engaged in by the parents of 29 children around the time that the children were about to start school at Key Stage 1. Fifteen of the children were reading fluently before they began school and the remaining fourteen were matched for age, sex, receptive vocabulary scores, pre-school group attended and socio-economic family status, but not reading fluently. In order to ascertain that the fluent readers were not simply coming from homes where literacy activities were more in evidence, parents were asked to report on their own literacy activities. The data obtained indicated that there were no systematic differences in the activities of the two sets of parents. They also showed that there was a considerable amount of literacy activity evident in the homes. It is argued that, whilst the home environment is highly instrumental in nurturing literacy development, it is not enough to account for precocious reading ability. [source] Scopus's source normalized impact per paper (SNIP) versus a journal impact factor based on fractional counting of citationsJOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 11 2010Loet Leydesdorff Impact factors (and similar measures such as the Scimago Journal Rankings) suffer from two problems: (a) citation behavior varies among fields of science and, therefore, leads to systematic differences, and (b) there are no statistics to inform us whether differences are significant. The recently introduced "source normalized impact per paper" indicator of Scopus tries to remedy the first of these two problems, but a number of normalization decisions are involved, which makes it impossible to test for significance. Using fractional counting of citations,based on the assumption that impact is proportionate to the number of references in the citing documents,citations can be contextualized at the paper level and aggregated impacts of sets can be tested for their significance. It can be shown that the weighted impact of Annals of Mathematics (0.247) is not so much lower than that of Molecular Cell (0.386) despite a five-f old difference between their impact factors (2.793 and 13.156, respectively). [source] STORM DISCHARGE, LOADS, AND AVERAGE CONCENTRATIONS IN NORTHWEST OHIO RIVERS, 1975,1995,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2001R. Peter Richards ABSTRACT: A computerized technique was developed to identify storm runoff episodes and calculate storm discharges, storm loads, and storm average concentrations for each event in datasets with up to 10,000 records. This technique was applied to four watersheds within the Lake Erie drainage basin and identified between 160 and 250 runoff events in each. Storm event loads and storm event mean concentrations were calculated for each runoff event for suspended solids, total phosphorus, soluble reactive phosphorus, nitrate, and total Kjeldahl nitrogen. The basic characteristics of the resulting data are described, as are systematic differences as a function of watershed size, seasonal differences, and trends over time. Many of the results of this study reflect the importance of nonpoint processes and improvements in agricultural best management practices in these watersheds. [source] | |||||||||||||||||||||||||||||||