923 resultados para Large Size


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Within the project “Tiefenschärfe – hochauflösende Vermes- sung Bodensee” a high-resolution seamless terrain model is created using airborne topobathymetric laserscanning and multibeam echosounder (MBES) techniques. The project visu- alizes the enormous wealth of features of underwater land- scapes of lakes. The combination of hydroacoustic (multibeam echosounder) and laser-optic (topobathymetric laserscan- ning) methods was used for the first time in a freshwater body of this size. Opportunities, limitations and restrictions of these high-resolution methods are presented.

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Performance on interval timing is often explained by the assumption of an internal clock based on neural counting. According to this account, a neural pacemaker generates pulses, and the number of pulses relating to a physical time interval is recorded by a counter. Thus, the number of accumulated pulses is the internal representation of this interval. Several studies demonstrated that large visual stimuli are perceived to last longer than smaller ones presented for the same duration. The present study was designed to investigate whether nontemporal visual stimulus size directly affects the internal clock. For this purpose, a temporal reproduction task was applied. Sixty participants were randomly assigned to one of two experimental conditions with stimulus size being experimentally varied within either the target or the reproduction interval. A direct effect of nontemporal stimulus size on the pacemaker-counter system should become evident irrespective of whether stimulus size was experimentally varied within the target or the reproduction interval. An effect of nontemporal stimulus size on reproduced duration only occurred when stimulus size was varied during the target interval. This finding clearly argues against the notion that nontemporal visual stimulus size directly affects the internal clock. Furthermore, our findings ruled out a decisional bias as a possible cause of the observed differential effect of stimulus size on reproduced duration. Rather the effect of stimulus size appeared to originate from the memory stage of temporal information processing at which the timing signal from the pacemaker-counter component is encoded in reference memory.

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We studied sediment cores from Lake Vens (2,327 m asl), in the Tinée Valley of the SW Alps, to test the paleoseismic archive potential of the lake sediments in this particularly earthquake-sensitive area. The historical earthquake catalogue shows that moderate to strong earthquakes, with intensities of IX–X, have impacted the Southern Alps during the last millennium. Sedimentological (X-ray images, grain size distribution) and geochemical (major elements and organic matter) analyses show that Lake Vens sediments consist of a terrigenous, silty material (minerals and organic matter) sourced from the watershed and diatom frustules. A combination of X-ray images, grain-size distribution, major elements and magnetic properties shows the presence of six homogenite-type deposits interbedded in the sedimentary background. These sedimentological features are ascribed to sediment reworking and grain sorting caused by earthquake-generated seiches. The presence of microfaults that cross-cut the sediment supports the hypothesis of seismic deposits in this system. A preliminary sediment chronology is provided by 210Pb measurement and AMS 14C ages. According to the chronology, the most recent homogenite events are attributable to damaging historic earthquakes in AD 1887 (Ligure) and 1564 (Roquebillière). Hence, the Lake Vens sediment recorded large-magnitude earthquakes in the region and permits a preliminary estimate of recurrence time for such events of ~400 years.

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Tef [Eragrostis tef (Zucc.) Trotter] is the major cereal crop in the Horn of Africa particularly in Ethiopia where it is staple food for about 50 million people. Its resilience to extreme environmental conditions and high in nutrition makes tef the preferred crop among both farmers and consumers. The efficiency of in vitro regeneration plays significant role in the improvement of crops. We investigated the efficiency of regeneration in 18 tef genotypes (15 landraces and three improved varieties) using three sizes of immature embryos (small, intermediate and large) as an explant. In vitro regeneration was significantly affected by the genotype and the size of the immature embryo used as a donor. Intermediate-size immature embryos which were 101-350 µm long led to the highest percentage of regeneration. Interestingly, the three improved varieties presented very low regeneration efficiencies whereas the landrace Manyi resulted in consistently superior percentage of in vitro regeneration from all three sizes of explants. The findings of this work provide useful insight into the tef germplasm amenable for the regeneration technique which has direct application in techniques such as transformation. It also signifies the importance of using tef landraces instead of improved varieties for in vitro regeneration.

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We present a record of particulate dust concentration and size distribution in subannual resolution measured on the European Project for Ice Coring in Antarctica (EPICA) Dronning Maud Land (EDML) ice core drilled in the Atlantic sector of the East Antarctic plateau. The record reaches from present day back to the penultimate glacial until 145,000 years B.P. with subannual resolution from 60,000 years B.P. to the present. Mean dust concentrations are a factor of 46 higher during the glacial (~850–4600 ng/mL) compared to the Holocene (~16–112 ng/mL) with slightly smaller dust particles during the glacial comparedto the Holocene and with an absolute minimum in the dust size at 16,000 years B.P. The changes in dust concentration are mainly attributed to changes in source conditions in southern South America. An increase in the modal value of the dust size suggests that at 16,000 years B.P. a major change in atmospheric circulation apparently allowed more direct transport of dust particles to the EDML drill site. We find a clear in-phase relation of the seasonal variation in dust mass concentration and dust size during the glacial (r(conc,size) = 0.8) but no clear phase relationship during the Holocene (0 size)<0.4). With a simple conceptual 1-D model describing the transport of the dust to the ice sheet using the size as an indicator for transport intensity, we find that the effect of the changes in the seasonality of the source emission strength and the transport intensity on the dust decrease over Transition 1 can significantly contribute to the large decrease of dust concentration from the glacial to the Holocene.

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One key hypothesis in the study of brain size evolution is the expensive tissue hypothesis; the idea that increased investment into the brain should be compensated by decreased investment into other costly organs, for instance the gut. Although the hypothesis is supported by both comparative and experimental evidence, little is known about the potential changes in energetic requirements or digestive traits following such evolutionary shifts in brain and gut size. Organisms may meet the greater metabolic requirements of larger brains despite smaller guts via increased food intake or better digestion. But increased investment in the brain may also hamper somatic growth. To test these hypotheses we here used guppy (Poecilia reticulata) brain size selection lines with a pronounced negative association between brain and gut size and investigated feeding propensity, digestive efficiency (DE), and juvenile growth rate. We did not find any difference in feeding propensity or DE between large- and small-brained individuals. Instead, we found that large-brained females had slower growth during the first 10 weeks after birth. Our study provides experimental support that investment into larger brains at the expense of gut tissue carries costs that are not necessarily compensated by a more efficient digestive system.

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BACKGROUND Meta-analyses of continuous outcomes typically provide enough information for decision-makers to evaluate the extent to which chance can explain apparent differences between interventions. The interpretation of the magnitude of these differences - from trivial to large - can, however, be challenging. We investigated clinicians' understanding and perceptions of usefulness of 6 statistical formats for presenting continuous outcomes from meta-analyses (standardized mean difference, minimal important difference units, mean difference in natural units, ratio of means, relative risk and risk difference). METHODS We invited 610 staff and trainees in internal medicine and family medicine programs in 8 countries to participate. Paper-based, self-administered questionnaires presented summary estimates of hypothetical interventions versus placebo for chronic pain. The estimates showed either a small or a large effect for each of the 6 statistical formats for presenting continuous outcomes. Questions addressed participants' understanding of the magnitude of treatment effects and their perception of the usefulness of the presentation format. We randomly assigned participants 1 of 4 versions of the questionnaire, each with a different effect size (large or small) and presentation order for the 6 formats (1 to 6, or 6 to 1). RESULTS Overall, 531 (87.0%) of the clinicians responded. Respondents best understood risk difference, followed by relative risk and ratio of means. Similarly, they perceived the dichotomous presentation of continuous outcomes (relative risk and risk difference) to be most useful. Presenting results as a standardized mean difference, the longest standing and most widely used approach, was poorly understood and perceived as least useful. INTERPRETATION None of the presentation formats were well understood or perceived as extremely useful. Clinicians best understood the dichotomous presentations of continuous outcomes and perceived them to be the most useful. Further initiatives to help clinicians better grasp the magnitude of the treatment effect are needed.

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Catheter ablation of complex fractionated atrial electrograms (CFAE), also known as defragmentation ablation, may be considered for the treatment of persistent atrial fibrillation (AF) beyond pulmonary vein isolation (PVI). Concomitant antiarrhythmic drug (AAD) therapy is common, but the relevance of AAD administration and its optimal timing during ablation remain unclear. Therefore, we investigated the use and timing of AADs during defragmentation ablation and their possible implications for AF termination and ablation success in a large cohort of patients. Retrospectively, we included 200 consecutive patients (age: 61 ± 12 years, LA diameter: 47 ± 8 mm) with persistent AF (episode duration 47 ± 72 weeks) who underwent de novo ablation including CFAE ablation. In all patients, PVI was performed prior to CFAE ablation. The use and timing of AADs were registered. The follow-ups consisted of Holter ECGs and clinical visits. Termination of AF was achieved in 132 patients (66 %). Intraprocedural AADs were administered in 168/200 patients (84 %) 45 ± 27 min after completion of PVI. Amiodarone was used in the majority of the patients (160/168). The timing of AAD administration was predicted by the atrial fibrillation cycle length (AFCL). At follow-up, 88 patients (46 %) were free from atrial arrhythmia. Multivariate logistic regression analysis revealed that administration of AAD early after PVI, LA size, duration of AF history, sex and AFCL were predictors of AF termination. The administration of AAD and its timing were not predictive of outcome, and age was the sole independent predictor of AF recurrence. The administration of AAD during ablation was common in this large cohort of persistent AF patients. The choice to administer AAD therapy and the timing of the administration during ablation were influenced by AFCL, and these factors did not significantly influence the moderate single procedure success rate in this retrospective analysis.

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INTRODUCTION Left ventricular thrombus (LVT) formation may worsen the post-infarct outcome as a result of thromboembolic events. It also complicates the use of modern antiplatelet regimens, which are not compatible with long-term oral anticoagulation. The knowledge of the incidence of LVT may therefore be of importance to guide antiplatelet and antithrombotic therapy after acute myocardial infarction (AMI). METHODS In 177 patients with large, mainly anterior AMI, standard cardiac magnetic resonance imaging (CMR) including cine and late gadolinium enhancement (LGE) imaging was performed shortly after AMI as per protocol. CMR images were analysed at an independent core laboratory blinded to the clinical data. Transthoracic echocardiography (TTE) was not mandatory for the trial, but was performed in 64% of the cases following standard of care. In a logistic model, 3 out of 61 parameters were used in a multivariable model to predict LVT. RESULTS LVT was detected by use of CMR in 6.2% (95% confidence interval [CI] 3.1%-10.8%). LGE sequences were best to detect LVT, which may be missed in cine sequences. We identified body mass index (odds ratio 1.18; p = 0.01), baseline platelet count (odds ratio 1.01, p = 0.01) and infarct size as assessed by use of CMR (odds ratio 1.03, p = 0.02) as best predictors for LVT. The agreement between TTE and CMR for the detection of LVT is substantial (kappa = 0.70). DISCUSSION In the current analysis, the incidence of LVT shortly after AMI is relatively low, even in a patient population at high risk. An optimal modality for LVT detection is LGE-CMR but TTE has an acceptable accuracy when LGE-CMR is not available.

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This paper examines how the geospatial accuracy of samples and sample size influence conclusions from geospatial analyses. It does so using the example of a study investigating the global phenomenon of large-scale land acquisitions and the socio-ecological characteristics of the areas they target. First, we analysed land deal datasets of varying geospatial accuracy and varying sizes and compared the results in terms of land cover, population density, and two indicators for agricultural potential: yield gap and availability of uncultivated land that is suitable for rainfed agriculture. We found that an increase in geospatial accuracy led to a substantial and greater change in conclusions about the land cover types targeted than an increase in sample size, suggesting that using a sample of higher geospatial accuracy does more to improve results than using a larger sample. The same finding emerged for population density, yield gap, and the availability of uncultivated land suitable for rainfed agriculture. Furthermore, the statistical median proved to be more consistent than the mean when comparing the descriptive statistics for datasets of different geospatial accuracy. Second, we analysed effects of geospatial accuracy on estimations regarding the potential for advancing agricultural development in target contexts. Our results show that the target contexts of the majority of land deals in our sample whose geolocation is known with a high level of accuracy contain smaller amounts of suitable, but uncultivated land than regional- and national-scale averages suggest. Consequently, the more target contexts vary within a country, the more detailed the spatial scale of analysis has to be in order to draw meaningful conclusions about the phenomena under investigation. We therefore advise against using national-scale statistics to approximate or characterize phenomena that have a local-scale impact, particularly if key indicators vary widely within a country.

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The Janzen–Connell hypothesis proposes that specialized herbivores maintain high numbers of tree species in tropical forests by restricting adult recruitment so that host populations remain at low densities. We tested this prediction for the large timber tree species, Swietenia macrophylla, whose seeds and seedlings are preyed upon by small mammals and a host-specific moth caterpillar Steniscadia poliophaea, respectively. At a primary forest site, experimental seed additions to gaps – canopy-disturbed areas that enhance seedling growth into saplings – over three years revealed lower survival and seedling recruitment closer to conspecific trees and in higher basal area neighborhoods, as well as reduced subsequent seedling survival and height growth. When we included these Janzen–Connell effects in a spatially explicit individual-based population model, the caterpillar's impact was critical to limiting Swietenia's adult tree density, with a > 10-fold reduction estimated at 300 years. Our research demonstrates the crucial but oft-ignored linkage between Janzen–Connell effects on offspring and population-level consequences for a long-lived, potentially dominant tree species.

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Pits have been observed on many cometary nuclei mapped by spacecraft(1-4). It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments(5,6) andmodels(7,8) cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts(8,9). Alternative mechanisms like explosive activity(10) have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface.

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Random Forests™ is reported to be one of the most accurate classification algorithms in complex data analysis. It shows excellent performance even when most predictors are noisy and the number of variables is much larger than the number of observations. In this thesis Random Forests was applied to a large-scale lung cancer case-control study. A novel way of automatically selecting prognostic factors was proposed. Also, synthetic positive control was used to validate Random Forests method. Throughout this study we showed that Random Forests can deal with large number of weak input variables without overfitting. It can account for non-additive interactions between these input variables. Random Forests can also be used for variable selection without being adversely affected by collinearities. ^ Random Forests can deal with the large-scale data sets without rigorous data preprocessing. It has robust variable importance ranking measure. Proposed is a novel variable selection method in context of Random Forests that uses the data noise level as the cut-off value to determine the subset of the important predictors. This new approach enhanced the ability of the Random Forests algorithm to automatically identify important predictors for complex data. The cut-off value can also be adjusted based on the results of the synthetic positive control experiments. ^ When the data set had high variables to observations ratio, Random Forests complemented the established logistic regression. This study suggested that Random Forests is recommended for such high dimensionality data. One can use Random Forests to select the important variables and then use logistic regression or Random Forests itself to estimate the effect size of the predictors and to classify new observations. ^ We also found that the mean decrease of accuracy is a more reliable variable ranking measurement than mean decrease of Gini. ^

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During "Meteor" Cruise 6/1966 in the northwest Atlantic a systematic survey of the bottom topography of the southeast Greenland continental margin was undertaken. Eighty-seven profiles transverse to the shelf edge at distances of 3-4 nautical miles and two longitudinal profiles parallel to the coast were carried out with the ELAC Narrow Beam Echo-Sounder giving a reliable record of even steep slopes. On the basis of the echo soundings the topography and morphology of the continental shelf and slope are evaluated. A detailed bathymetric chart and a serial profile chart were designed as working material for the morphological research. These maps along with the original echograms are morphometrically evaluated. The analysis of the sea bottom features is the basis of a subsequent morphogenetical interpretation, verified and extended by means of interpretation of magnetic data and sediment analysis (grain size, roundness, lithology). The results of the research are expressed in a geomorphological map. The primary findings can be summarized as follows: 1) The southeast Greenland shelf by its bottom topography can be clearly designated as a glacially formed area. The glacial features of the shelf can be classified into two zones nearly parallel to the coast: glacial erosion forms on the inner shelf and glacial accumulation forms on the outer shelf. The inner shelf is characterized by the rugged and hummocky topography of ice scoured plains with clear west/east slope asymmetry. On the outer shelf three types of glacial accumulation forms can be recognized: ice margin deposits with clearly expressed terminal moraines, glacial till plains and glaciomarine outwash fans. Both zones of the shelf can be subdivided into two levels of relief. The ice scoured plains, with average depths of 240 meters (m), are dissected to a maximum depth of 1060 m (Gyldenloves Trough) by trough valleys, which are the prolongations of the Greenland fjords. The banks of the outer shelf, with an average depth of 180 m, surround glacial basins with a maximum depth of 670 meters. 2) The sediments of the continental shelf can be classified as glacial due to their grain size distribution and the degree of roundness of the gravel particles. The ice margin deposits on the outer shelf can be recognized by their high percentage of gravels. On the inner shelf a rock surface is suggested, intermittently covered by glacial deposits. In the shelf troughs fine-grained sediments occur mixed with gravels. 3) Topography and sediments show that the southeast Greenland shelf was covered by an ice sheet resting on the sea floor during the Pleistocene ice-age. The large end moraines along the shelf edge probably indicate the maximum extent of the Wurm shelf ice resting on the sea floor. The breakthroughs of the end moraines in front of the glacial basins suggest that the shelf ice has floated further seaward over the increasing depths. 4) Petrographically the shelf sediments consist of gneisses, granites and basalts. While gneisses and granites occire on the nearby coast, basalt is not known to exist here. Either this material has been drifted by icebergs from the basalt province to the north or exists on the southeast Greenland shelf itself. The last interpretation is supported bythe high portion of basalt contained in the sediment samples taken and the strong magnetic anomalies probably caused by basaltic intrusions. 5) A magnetic profile allows the recognition of two magnetically differing areas which approximately coincide with the glacial erosion and accumulation zones. The inner shelf shows a strong and variable magnetic field because the glacially eroded basement forms the sea floor. The outer shelf is characterized by a weak and homogenous magnetic field, as the magnetized basement lies at greater depthy, buried by a thick cover of glacial sediments. The strong magnetic anomalies of the inner shelf are probably caused by dike swarms, similar to those observed further to the north in the Kangerdlugssuaq Fjord region. This interpretation is supported by the high basalt content of the sediment samples and the rough topography of the ice scoured plains which correlates in general with the magnetic fluctuations. The dike structures of the basement have been differentially eroded by the shelf ice. 6) The continental slope, extending from the shelf break at 313 m to a depth of 1270 m with an average slope of 11°, is characterized by delta-shaped projections in front of the shelf basins, by marginal plateaus, ridges and hills, by canyons and slumping features. The projections could be identified as glaciomarine sediment fans. This conclusion is supported by the strong decrease of magnetic field intensity. The deep sea hills and ridges with their greater magnetic intensities have to be regarded as basement outcrops projecting through the glaciomarine sediment cover. The upper continental rise, sloping seaward at about 2°, is composed of wide sediment fans and slump material. A marginal depression on the continental rise running parallel to the shelf edge has been identified. In this depression bottom currents capable of erosion have been recorded. South of Cape Farvel the depression extends to the accumulation zone of the "Eirik" sedimentary ridge. 7) By means of a study of the recent marine processes, postglacial modification of the ice-formed relief can be postulated. The retention effect of the fjord troughs and the high velocity of the East Greenland stream prevents the glacial features from being buried by sediments. Bottom currents capable of active erosion have only been found in the marginal depression on the continental rise. In addition, at the time of the lowest glacio-eustatic sea level, the shelf bottom was not situated in the zone of wave erosion. Only on the continental slope and rise bottom currents, sediment slumps and turbidity currents have led to significant recent modifications. Considering these results, the geomorphological development of the southeast Greenland continental terrace can be suggested as follows: 1. initial formation of a "peneplain", 2. fluvial incision, 3. submergence, and finally 4. glacial modification.