102,482 research outputs found
Metabolic control of stemness and differentiation
No full textProve crescenti evidenziano un ruolo fondamentale per il metabolismo nella fisiologia delle cellule staminali e nella specifica del lignaggio [1, 2]. Il metabolismo, infatti, non è più considerato solo una fonte di energia né un endpoint della regolazione genica. Invece, i metaboliti e l'ambiente nutritivo sono attori attivi nel determinare la segnalazione intracellulare e le attività enzimatiche e di conseguenza modulatori del destino delle cellule staminali. Inoltre, gli intermedi metabolici del metabolismo cellulare regolano i meccanismi epigenetici, comprese le modificazioni degli istoni, la metilazione del DNA e gli RNA non codificanti, modulando in tal modo il paesaggio e lo staminali dell'epigenoma globale [3].
Questo numero speciale riunisce 9 documenti per evidenziare i recenti sviluppi nel campo.Increasing evidence highlights a pivotal role for metabolism in stem cell physiology and lineage specification [1, 2]. Metabolism, indeed, is no longer considered merely an energy source nor an endpoint of gene regulation. Instead, metabolites and the nutrient environment are active players in determining intracellular signaling and enzymatic activities and consequently modulators of stem cell fate. Moreover, metabolic intermediates of cellular metabolism regulate epigenetic mechanisms, including histone modifications, DNA methylation, and noncoding RNAs, thereby modulating the global epigenome landscape and stemness [3].
This special issue brings together 9 papers to highlight recent developments in the field
Steel Frames Optimization Considering Beam-Column Joint Stiffness and Geometric Constraints
No full textStructural optimization is an active research branch in engineering, especially dealing with complex and concomitant aspects likewise in seismic design. Capacity design criteria for seismic design and detailing must be respected, e.g. according to the “strong-column weak-beam” principle. In steel structures, the choice of a specific beam-column joint typology may strongly affect its behavior under horizontal actions. In this study, the authors investigated the role of beam-column joint stiffness within an optimization paradigm related to steel structure frames. Specifically, the authors adopted simplified modeling assumptions for analysis under lateral loads in the Python environment and Computer and Structures inc. SAP2000 finite element software. Indeed, the main focus hitherto is oriented toward the problem definition accounting for geometric constraints and beam-column rotational stiffness capacity. Future investigations will adopt more realistic modeling procedures accounting for the typical non-linearities involved during strong dynamic actions
Acquisition and influence of expectations about visual speed
No full textIt has been long hypothesized that due to the inherent ambiguities of visual input
and the limitations of the visual system, vision is a form of “unconscious inference”
whereby the brain relies on assumptions (aka expectations) to interpret the external
world. This hypothesis has been recently formalized into Bayesian models of perception
(the “Bayesian brain”) that represent these expectations as prior probabilities. In
this thesis, I focus on a particular kind of expectation that humans are thought to
possess – that objects in the world tend to be still or move slowly – known as the
“slow speed prior”. Through a combination of experimental and theoretical work, I
investigate how the speed prior is acquired and how it impacts motion perception.
The first part of my work consists of an experiment where subjects are exposed to
simple "training" stimuli moving more often at high speeds than at low speeds. By
subsequently testing the subjects with slow-moving stimuli of high uncertainty (low
contrast), I find that their perception gradually changes in a manner consistent with
the progressive acquisition of an expectation that favours progressively higher speeds.
Thus subjects appear to gradually internalize the speed statistics of the stimulus ensemble over the duration of the experiment. I model these results using an existing
Bayesian model of motion perception that incorporates a speed prior with a peak
at zero, extending the model so that the mean gradually shifts away from zero.
Although the first experiment presents evidence for the plasticity of the speed prior,
the experimental paradigm and the constraints of the model limit the accuracy and
precision in the reconstruction of observers’ priors. To address these limitations, I
perform a different experiment where subjects compare the speed of moving gratings
of different contrasts. The new paradigm allows more precise measurements of
the contrast-dependent biases in perceived speed. Using a less constrained Bayesian
model, I extract the priors of subjects and find considerable interindividual variability.
Furthermore, noting that the Bayesian model cannot account for certain subtleties in
the data, I combine the model with a non-Bayesian, physiologically motivated model
of speed tuning of cortical neurons and show that the combination offers an improved
description of the data. Using the paradigm of the second experiment, I then explore
the role of visual experience on the form of the speed prior. By recruiting avid video
gamers (who are routinely exposed to high speeds) and nongamers of both sexes, I
study the differences in the prior among groups and find, surprisingly, that subjects’
speed priors depend more on gender than on gaming experience. In a final series of
experiments similar to the first, I also test subjects on variations of the trained stimulus
configuration – namely different orientations and motion directions. Subjects’
responses suggest that they are able to apply the changed prior to different orientations
and, furthermore, that the changed prior persists for at least a week after the
end of the experiment. These results provide further support for the plasticity of the
speed prior but also suggest that the learned prior may be used only across similar
stimulus configurations, whereas in sufficiently different configurations or contexts a
“default” prior may be used instead
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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3346: Samuel G. Freedman, author, 2013
No full textPhotograph of author Samuel G. Freedman, at NT Daily Slash meeting in the Mayborn School of Journalism at UNT
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