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71,262
نتائج ل
"De Marco, Marco"
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Evaluating collinearity effects on species distribution models: An approach based on virtual species simulation
The increasing use of species distribution modeling (SDM) has raised new concerns regarding the inaccuracies, misunderstanding, and misuses of this important tool. One of those possible pitfalls - collinearity among environmental predictors - is assumed as an important source of model uncertainty, although it has not been subjected to a detailed evaluation in recent SDM studies. It is expected that collinearity will increase uncertainty in model parameters and decrease statistical power. Here we use a virtual species approach to compare models built using subsets of PCA-derived variables with models based on the original highly correlated climate variables. Moreover, we evaluated whether modelling algorithms and species data characteristics generate models with varying sensitivity to collinearity. As expected, collinearity among predictors decreases the efficiency and increases the uncertainty of species distribution models. Nevertheless, the intensity of the effect varied according to the algorithm properties: more complex procedures behaved better than simple envelope models. This may support the claim that complex models such as Maxent take advantage of existing collinearity in finding the best set of parameters. The interaction of the different factors with species characteristics (centroid and tolerance in environmental space) highlighted the importance of the so-called \"idiosyncrasy in species responses\" to model efficiency, but differences in prevalence may represent a better explanation. However, even models with low accuracy to predict suitability of individual cells may provide meaningful information on the estimation of range-size, a key species-trait for macroecological studies. We concluded that the use of PCA-derived variables is advised both to control the negative effects of collinearity and as a more objective solution for the problem of variable selection in studies dealing with large number of species with heterogeneous responses to environmental variables.
Journal Article
Freddy's teddy
Little Teddy has a rip, but Freddy's mother has needle, thread, and more than enough stuffing to fix him.
Book
Los poderes emergentes en la política internacional de comienzos del siglo XXI: el caso de Brasil como potencia suramericana
En el presente artículo se analizarán los cambios que han llevado a la irrupción de los poderes emergentes en la geopolítica global. Se centrará el análisis en los países BRICS en una primera instancia y luego se enfocará la atención en el caso de Brasil, para comprender cómo este contexto impactó en América del Sur y qué cambios se dan en el contexto actual. Lo que se demostrará es que estos países lograron consolidar su posición internacional a partir de su peso a nivel regional, pero sus objetivos no estaban vinculados a un cambio sistémico de la política global, sino a obtener un lugar de relevancia en las decisiones mundiales.
Journal Article
رحلات ماركو بولو
من أعماق الغابات والصحراوات والجبال والوديان .. من وسط الشعوب وأعيادهم وعاداتهم .. من فوق لغات عديدة وثقافات مختلفة دائما تأتينا كتب أدب الرحلات، فهى دائما كتب تجوب العالم شرقه وغربه .. تجتمع حبات در ثقافاته فى كتاب واحد، وهو ما جعل لها مذاق خاص وأدب خاص يمتعنا وفى ذات الوقت يطلعنا على كل جديد لم نألفه ولم نعايشه فى بلادنا أيا كانت هذه البلاد. ومن كتب أدب الرحلات الذائعة الصيت والهامة فى ذات الوقت رحلات \"ماركوبولو\" ذلك الرحالة الذى تعد رحلاته مرجعا هاما فيما يتعلق بحضارات آسيا القديمة وشعوبها، فهى رحلات جابت البلاد من إيطاليا للصين مرورا بآسيا وحضاراتها الجذابة مخلفة ورائها صفحات غنية ثرية نافذة فى نظرتها ونافذة يطل منها العالم إلى تلك الحضارات البائدة. ففى هذه الرحلات ومجلداتها الثلاثة قام \"ماركوبولو\" بتسجيل نواحى الحياة العديدة فى هذه البلاد من عادات لسكانها وما اتبعه حكامها فى إدارتها، أيضا وصفها وصفا تفصيليا سواء كان هذا الوصف لطبيعتها الجغرافية أو الإقتصادية أو السياسية أو الإجتماعية. فهو كتاب يقرأه قارئ عادى وقارئ متخصص وباحث فى التاريخ على السواء .. فهو للصغير ممتع وللكبير مرجع، وفى المكتبة الأدبية درة والمكتبة التاريخية تحفة، وهو ما يجعلنا لا نتعجب إذ جاءنا كحلقة من سلسلة \"الأعمال الخاصة\" فهو عمل خاص ذو مذاق متميز متفرد.
Book
Neuronal activity is required for the development of specific cortical interneuron subtypes
Electrical activity has been shown to regulate development in a variety of species and in various structures, including the retina, spinal cord and cortex. Within the mammalian cortex specifically, the development of dendrites and commissural axons in pyramidal cells is activity-dependent. However, little is known about the developmental role of activity in the other major cortical population of neurons, the GABA-producing interneurons. These neurons are morphologically and functionally heterogeneous and efforts over the past decade have focused on determining the mechanisms that contribute to this diversity. It was recently discovered that 30% of all cortical interneurons arise from a relatively novel source within the ventral telencephalon, the caudal ganglionic eminence (CGE). Owing to their late birth date, these interneurons populate the cortex only after the majority of other interneurons and pyramidal cells are already in place and have started to functionally integrate. Here we demonstrate in mice that for CGE-derived reelin (Re)-positive and calretinin (Cr)-positive (but not vasoactive intestinal peptide (VIP)-positive) interneurons, activity is essential before postnatal day 3 for correct migration, and that after postnatal day 3, glutamate-mediated activity controls the development of their axons and dendrites. Furthermore, we show that the engulfment and cell motility 1 gene (Elmo1), a target of the transcription factor distal-less homeobox 1 (Dlx1), is selectively expressed in Re(+) and Cr(+) interneurons and is both necessary and sufficient for activity-dependent interneuron migration. Our findings reveal a selective requirement for activity in shaping the cortical integration of specific neuronal subtypes.
Journal Article