• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 173
  • Tagged with
  • 173
  • 173
  • 173
  • 165
  • 162
  • 162
  • 162
  • 124
  • 121
  • 119
  • 119
  • 93
  • 49
  • 47
  • 24
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
161

Interindividual Differences in Mid-Adolescents in Error Monitoring and Post-Error Adjustment

Rodehacke, Sarah, Mennigen, Eva, Müller, Kathrin U., Ripke, Stephan, Jacob, Mark J., Hübner, Thomas, Schmidt, Dirk H. K., Goschke, Thomas, Smolka, Michael N. 14 July 2014 (has links)
A number of studies have concluded that cognitive control is not fully established until late adolescence. The precise differences in brain function between adults and adolescents with respect to cognitive control, however, remain unclear. To address this issue, we conducted a study in which 185 adolescents (mean age (SD) 14.6 (0.3) years) and 28 adults (mean age (SD) 25.2 (6.3) years) performed a single task that included both a stimulus-response (S-R) interference component and a task-switching component. Behavioural responses (i.e. reaction time, RT; error rate, ER) and brain activity during correct, error and post-error trials, detected by functional magnetic resonance imaging (fMRI), were measured. Behaviourally, RT and ER were significantly higher in incongruent than in congruent trials and in switch than in repeat trials. The two groups did not differ in RT during correct trials, but adolescents had a significantly higher ER than adults. In line with similar RTs, brain responses during correct trials did not differ between groups, indicating that adolescents and adults engage the same cognitive control network to successfully overcome S-R interference or task switches. Interestingly, adolescents with stronger brain activation in the bilateral insulae during error trials and in fronto-parietal regions of the cognitive control network during post-error trials did have lower ERs. This indicates that those mid-adolescents who commit fewer errors are better at monitoring their performance, and after detecting errors are more capable of flexibly allocating further cognitive control resources. Although we did not detect a convincing neural correlate of the observed behavioural differences between adolescents and adults, the revealed interindividual differences in adolescents might at least in part be due to brain development.
162

Contribution of Small-Scale Gum and Resin Commercialization to Local Livelihood and Rural Economic Development in the Drylands of Eastern Africa

Abtew, Asmamaw Alemu, Pretzsch, Jürgen, Secco, Laura, Mohamod, Tarig Elshikh 21 July 2014 (has links)
This paper examines the extent to which the economic gains derived from gum and resin commercialization impact rural livelihood improvement under different resource management regimes in the drylands of Ethiopia and Sudan. Primary data were collected through semi-structured interviews with 240 randomly selected small-scale producers in four regions with gradients of resource management regimes. The survey was supplemented by secondary data, group discussions and key informant interviews. In the four regions, gum and resin income contributes to 14%–23% of the small-scale producers’ household income. Absolute income was positively correlated with resource management regime and commercialization level. It was higher from cultivated resources on private lands, followed by regulated access to wild resources. In open-access resources, the producers’ income was the lowest, although accessed by the poor and women. However, dependence on gum and resin was higher in open-access resource areas. Households’ socioeconomic characteristics, resource access, production and marketing variables determining income from gum and resin were identified and their variation across the cases is discussed. Overall, gum and resin commercialization in the study areas play a potential poverty alleviation role as a source of regular income, a safety net, and a means of helping producers move out of poverty.
163

Soil Chemical and Microbial Properties in a Mixed Stand of Spruce and Birch in the Ore Mountains (Germany) - A Case Study

Schua, Karoline, Wende, Stefan, Wagner, Sven, Feger, Karl-Heinz 27 July 2015 (has links)
A major argument for incorporating deciduous tree species in coniferous forest stands is their role in the amelioration and stabilisation of biogeochemical cycles. Current forest management strategies in central Europe aim to increase the area of mixed stands. In order to formulate statements about the ecological effects of mixtures, studies at the stand level are necessary. In a mixed stand of Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth) in the Ore Mountains (Saxony, Germany), the effects of these two tree species on chemical and microbial parameters in the topsoil were studied at one site in the form of a case study. Samples were taken from the O layer and A horizon in areas of the stand influenced by either birch, spruce or a mixture of birch and spruce. The microbial biomass, basal respiration, metabolic quotient, pH-value and the C and N contents and stocks were analysed in the horizons Of, Oh and A. Significantly higher contents of microbial N were observed in the Of and Oh horizons in the birch and in the spruce-birch strata than in the stratum containing only spruce. The same was found with respect to pH-values in the Of horizon and basal respiration in the Oh horizon. Compared to the spruce stratum, in the birch and spruce-birch strata, significantly lower values were found for the contents of organic C and total N in the A horizon. The findings of the case study indicated that single birch trees have significant effects on the chemical and microbial topsoil properties in spruce-dominated stands. Therefore, the admixture of birch in spruce stands may distinctly affect nutrient cycling and may also be relevant for soil carbon sequestration. Further studies of these functional aspects are recommended.
164

Surface Conductance of Five Different Crops Based on 10 Years of Eddy-Covariance Measurements

Spank, Uwe, Köstner, Barbara, Moderow, Uta, Grünwald, Thomas, Bernhofer, Christian 16 January 2017 (has links)
The Penman-Monteith (PM) equation is a state-of-the-art modelling approach to simulate evapotranspiration (ET) at site and local scale. However, its practical application is often restricted by the availability and quality of required parameters. One of these parameters is the canopy conductance. Long term measurements of evapotranspiration by the eddy-covariance method provide an improved data basis to determine this parameter by inverse modelling. Because this approach may also include evaporation from the soil, not only the ‘actual’ canopy conductance but the whole surface conductance (gc) is addressed. Two full cycles of crop rotation with five different crop types (winter barley, winter rape seed, winter wheat, silage maize, and spring barley) have been continuously monitored for 10 years. These data form the basis for this study. As estimates of gc are obtained on basis of measurements, we investigated the impact of measurements uncertainties on obtained values of gc. Here, two different foci were inspected more in detail. Firstly, the effect of the energy balance closure gap (EBCG) on obtained values of gc was analysed. Secondly, the common hydrological practice to use vegetation height (hc) to determine the period of highest plant activity (i.e., times with maximum gc concerning CO2-exchange and transpiration) was critically reviewed. The results showed that hc and gc do only agree at the beginning of the growing season but increasingly differ during the rest of the growing season. Thus, the utilisation of hc as a proxy to assess maximum gc (gc,max) can lead to inaccurate estimates of gc,max which in turn can cause serious shortcomings in simulated ET. The light use efficiency (LUE) is superior to hc as a proxy to determine periods with maximum gc. Based on this proxy, crop specific estimates of gc,maxcould be determined for the first (and the second) cycle of crop rotation: winter barley, 19.2 mm s−1 (16.0 mm s−1); winter rape seed, 12.3 mm s−1 (13.1 mm s−1); winter wheat, 16.5 mm s−1 (11.2 mm s−1); silage maize, 7.4 mm s−1 (8.5 mm s−1); and spring barley, 7.0 mm s−1 (6.2 mm s−1).
165

Comparative Analysis of Behavioral Models for Adaptive Learning in Changing Environments

Marković, Dimitrije, Kiebel, Stefan J. 16 January 2017 (has links)
Probabilistic models of decision making under various forms of uncertainty have been applied in recent years to numerous behavioral and model-based fMRI studies. These studies were highly successful in enabling a better understanding of behavior and delineating the functional properties of brain areas involved in decision making under uncertainty. However, as different studies considered different models of decision making under uncertainty, it is unclear which of these computational models provides the best account of the observed behavioral and neuroimaging data. This is an important issue, as not performing model comparison may tempt researchers to over-interpret results based on a single model. Here we describe how in practice one can compare different behavioral models and test the accuracy of model comparison and parameter estimation of Bayesian and maximum-likelihood based methods. We focus our analysis on two well-established hierarchical probabilistic models that aim at capturing the evolution of beliefs in changing environments: Hierarchical Gaussian Filters and Change Point Models. To our knowledge, these two, well-established models have never been compared on the same data. We demonstrate, using simulated behavioral experiments, that one can accurately disambiguate between these two models, and accurately infer free model parameters and hidden belief trajectories (e.g., posterior expectations, posterior uncertainties, and prediction errors) even when using noisy and highly correlated behavioral measurements. Importantly, we found several advantages of Bayesian inference and Bayesian model comparison compared to often-used Maximum-Likelihood schemes combined with the Bayesian Information Criterion. These results stress the relevance of Bayesian data analysis for model-based neuroimaging studies that investigate human decision making under uncertainty.
166

Tic Frequency Decreases during Short-term Psychosocial Stress – An Experimental Study on Children with Tic Disorders

Buse, Judith, Enghardt, Stephanie, Kirschbaum, Clemens, Ehrlich, Stefan, Rößner, Veit 06 February 2017 (has links)
It has been suggested that psychosocial stress influences situational fluctuations of tic frequency. However, evidence from experimental studies is lacking. The current study investigated the effects of the Trier Social Stress Test (TSST-C) on tic frequency in 31 children and adolescents with tic disorders. A relaxation and a concentration situation served as control conditions. Patients were asked either to suppress their tics or to “tic freely.” Physiological measures of stress were measured throughout the experiment. The TSST-C elicited a clear stress response with elevated levels of saliva cortisol, increased heart rate, and a larger number of skin conductance responses. During relaxation and concentration, the instruction to suppress tics reduced the number of tics, whereas during stress, the number of tics was low, regardless of the given instruction. Our study suggests that the stress might result in a situational decrease of tic frequency.
167

PRONTOX – proton therapy to reduce acute normal tissue toxicity in locally advanced non-small-cell lung carcinomas (NSCLC): study protocol for a randomised controlled trial

Zschaeck, Sebastian, Simon, Monique, Löck, Steffen, Troost, Esther G. C., Stützer, Kristin, Wohlfahrt, Patrick, Appold, Steffen, Makocki, Sebastian, Bütof, Rebecca, Richter, Christian, Baumann, Michael, Krause, Mechthild 17 March 2017 (has links)
Background Primary radiochemotherapy with photons is the standard treatment for locally advanced-stage non-small cell lung cancer (NSCLC) patients. Acute radiation-induced side effects such as oesophagitis and radiation pneumonitis limit patients’ quality of life, and the latter can be potentially life-threatening. Due to its distinct physical characteristics, proton therapy enables better sparing of normal tissues, which is supposed to translate into a reduction of radiation-induced side effects. Methods/design This is a single-centre, prospective, randomised controlled, phase II clinical trial to compare photon to proton radiotherapy up to 66 Gy (RBE) with concomitant standard chemotherapy in patients with locally advanced-stage NSCLC. Patients will be allocated in a 1:1 ratio to photon or proton therapy, and treatment will be delivered slightly accelerated with six fractions of 2 Gy (RBE) per week. Discussion The overall aim of the study is to show a decrease of early and intermediate radiation-induced toxicity using proton therapy. For the primary endpoint of the study we postulate a decrease of radiation-induced side effects (oesophagitis and pneumonitis grade II or higher) from 39 to 12%. Secondary endpoints are locoregional and distant failure, overall survival and late side effects. Trial registration Registered at ClinicalTrials.gov with Identifier NCT02731001 on 1 April 2016.
168

The Link between Corporate Environmental and Corporate Financial Performance: Viewpoints from Practice and Research

Anne, Bergmann 27 March 2017 (has links)
For more than 40 years, a tremendous number of studies have empirically explored the relationship between Corporate Environmental Performance (CEP) and Corporate Financial Performance (CFP). This study considers the relationship from a new perspective—via a qualitative research approach based on expert interviews. First, practitioners are queried for their view on the link between CEP and CFP and how to measure it. Since the vast majority see a positive relationship, this study contributes with a new form of evidence that it pays to be green. The chosen qualitative approach also allows a more detailed analysis of underlying cause-and-effect mechanisms. For instance, interviewed practitioners emphasize a direct and indirect impact from CEP on CFP. Second, the study conducts interviews with experts from research and associations (non-practitioners) and compares the viewpoints of the two interview groups. One prevalent difference refers to the fact that non-practitioners do not focus on the two impact levels. Moreover, business experts perceive the link between CEP and CFP as much less complex and reveal more pragmatically oriented considerations. The study then discusses how the interview results and identified differences can be used to direct future research and to support corporations in their move towards sustainability.
169

Application of a GIS Multi-Criteria Decision Analysis for the Identification of Intrinsic Suitable Sites in Costa Rica for the Application of Managed Aquifer Recharge (MAR) through Spreading Methods.

Bonilla Valverde, José Pablo, Blank, Clemens, Roidt, Mario, Schneider, Lisa, Catalin, Stefan 27 March 2017 (has links)
Costa Rica’s annual mean precipitation is above 3300 mm, but this precipitation is not evenly distributed in time or space, producing clear differentiated wet and dry seasons in most of the country. Droughts are also common phenomena which greatly affect the availability of water resources. Managed aquifer recharge (MAR) schemes are being taken into consideration to enhance the underground water storage capacity of the country. The present study constitutes the first assessment for the identification of suitable sites for the implementation of MAR technology spreading methods (SM) in Costa Rica. The suitable sites are identified by means of a geographic information system multi-criteria decision analysis (GIS-MCDA) based on four criteria: hydrogeological aptitude, terrain slope, top soil texture and drainage network density. Four steps are performed in order to identify these sites: problem definition, screening for suitable areas, suitability mapping, and sensitivity analysis. The suitability map was divided in two zones after the screening: suitable and unsuitable, the first zone was further divided in five classes according to the weighted linear combination (WLC) ranking. The results indicate that 61% of the country is suitable for conducting SM. This map is a tool for future implementation of MAR techniques in the country.
170

Model Based Analysis of Clonal Developments Allows for Early Detection of Monoclonal Conversion and Leukemia

Baldow, Christoph, Thielecke, Lars, Glauche, Ingmar 28 March 2017 (has links)
The availability of several methods to unambiguously mark individual cells has strongly fostered the understanding of clonal developments in hematopoiesis and other stem cell driven regenerative tissues. While cellular barcoding is the method of choice for experimental studies, patients that underwent gene therapy carry a unique insertional mark within the transplanted cells originating from the integration of the retroviral vector. Close monitoring of such patients allows accessing their clonal dynamics, however, the early detection of events that predict monoclonal conversion and potentially the onset of leukemia are beneficial for treatment. We developed a simple mathematical model of a self-stabilizing hematopoietic stem cell population to generate a wide range of possible clonal developments, reproducing typical, experimentally and clinically observed scenarios. We use the resulting model scenarios to suggest and test a set of statistical measures that should allow for an interpretation and classification of relevant clonal dynamics. Apart from the assessment of several established diversity indices we suggest a measure that quantifies the extension to which the increase in the size of one clone is attributed to the total loss in the size of all other clones. By evaluating the change in relative clone sizes between consecutive measurements, the suggested measure, referred to as maximum relative clonal expansion (mRCE), proves to be highly sensitive in the detection of rapidly expanding cell clones prior to their dominant manifestation. This predictive potential places the mRCE as a suitable means for the early recognition of leukemogenesis especially in gene therapy patients that are closely monitored. Our model based approach illustrates how simulation studies can actively support the design and evaluation of preclinical strategies for the analysis and risk evaluation of clonal developments.

Page generated in 0.0785 seconds