glial cells missing and gcm2 Cell Autonomously Regulate Both Glial and Neuronal Development in the Visual System of Drosophila

SummaryThe transcription factors Glial cells missing (Gcm) and Gcm2 are known to play a crucial role in promoting glial-cell differentiation during Drosophila embryogenesis. Our findings reveal a central function for gcm genes in regulating neuronal development in the postembryonic visual system. We demonstrate that Gcm and Gcm2 are expressed in both glial and neuronal precursors within the optic lobe. Removal of gcm and gcm2 function shows that the two genes act redundantly and are required for the formation of a subset of glial cells. They also cell-autonomously control the differentiation and proliferation of specific neurons. We show that the transcriptional regulator Dachshund acts downstream of gcm genes and is required to make lamina precursor cells and lamina neurons competent for neuronal differentiation through regulation of epidermal growth factor receptor levels. Our findings further suggest that gcm genes regulate neurogenesis through collaboration with the Hedgehog-signaling pathway

Entropy generation in a model of reversible computation

We present a model in which, due to the quantum nature of the signals controlling the implementation time of successive unitary computational steps, \emph{physical} irreversibility appears in the execution of a \emph{logically} reversible computation.Comment: 13 pages, 6 figure

An Uncertainty Relation of Space-Time

We propose an uncertainty relation of space-time. This relation is characterized by GhT \lesssim \delta V, where T and \delta V denote a characteristic time scale and a spatial volume, respectively. Using this uncertainty relation, we give qualitative estimations for the entropies of a black hole and our universe. We obtain qualitative agreements with the known results. The holographic principle of 't Hooft and Susskind is reproduced. We also discuss cosmology and give a relation to the cosmic holographic principle of Fischler and Susskind. However, as for the maximal entropy of a system with an energy E, we obtain the formula \sqrt{EV/Gh^2}, with V denoting the volume of the system, which is distinct from the Bekenstein entropy formula ER/h with R denoting the length scale of the system.Comment: 13 pages, Journal Version, PTPTe

Localized Netrins Act as Positional Cues to Control Layer-Specific Targeting of Photoreceptor Axons in Drosophila

SummaryA shared feature of many neural circuits is their organization into synaptic layers. However, the mechanisms that direct neurites to distinct layers remain poorly understood. We identified a central role for Netrins and their receptor Frazzled in mediating layer-specific axon targeting in the Drosophila visual system. Frazzled is expressed and cell autonomously required in R8 photoreceptors for directing their axons to the medulla-neuropil layer M3. Netrin-B is specifically localized in this layer owing to axonal release by lamina neurons L3 and capture by target neuron-associated Frazzled. Ligand expression in L3 is sufficient to rescue R8 axon-targeting defects of Netrin mutants. R8 axons target normally despite replacement of diffusible Netrin-B by membrane-tethered ligands. Finally, Netrin localization is instructive because expression in ectopic layers can retarget R8 axons. We propose that provision of localized chemoattractants by intermediate target neurons represents a highly precise strategy to direct axons to a positionally defined layer

A efetividade dos instrumentos da Política Estadual de Recursos Hídricos e do Sistema de Recursos Hídricos do Rio Grande do Sul no 26º ano da Lei n° 10.350/94 : relatório final de pesquisa

Este trabalho busca demonstrar a efetividade da Lei n° 10.350/94, conhecida como a Lei das Águas gaúcha. Muito se tem dito sobre os motivos da não implantação dos instrumentos da referida lei na totalidade e o quanto esse fato prejudica não só os seus atores como também a garantia do acesso à água de qualidade e em quantidade para todos. O próprio desenvolvimento do Estado do Rio Grande do Sul tem sido atrapalhado pela degradação dos recursos hídricos. Este estudo teve como base a análise de 26 anos da lei, até dezembro de 2020. O recorte territorial foi a região hidrográfica do Guaíba. Os resultados da pesquisa demostram que muito já foi feito pelos atores e que as possíveis alterações na lei devem ter o objetivo de atualização e não de alteração em seus fundamentos. Pretendemos que este trabalho, com seu produto ordenado de evidências documentais, suas conclusões e recomendações, possa contribuir no nivelamento dos entendimentos quanto às adequações necessárias da lei. Boa parte do objetivo proposto já terá sido cumprido caso esse nivelamento facilite os necessários acordos entre as partes abrangidas. O certo é que precisamos do envolvimento de mais pessoas na defesa desse bem natural e essencial à manutenção da vida.Este trabajo busca demostrar la efectividad de la ley de aguas de Rio Grande do Sul. Mucho se ha hablado de las razones para no implementar los instrumentos de la Ley 10.350 / 94 en su totalidad y cuánto ha perjudicado a sus actores y al objetivo de garantizar agua en calidad y cantidad para todos. El desarrollo del Estado de Rio Grande do Sul se ha visto obstaculizado, al menos por la degradación de los recursos hídricos. La base de análisis fueron los veintiséis años de la Ley, hasta diciembre de 2020, y el enfoque territorial fue la región hidrográfica de Guaíba. Los resultados de la investigación y su análisis muestran que ya se ha hecho mucho por los actores y que los posibles cambios en la Ley deben actualizarse y no cambiar los fundamentos. Pretendemos que la utilización de esta obra, con su producto ordenado de prueba documental, sus conclusiones y recomendaciones, contribuya a nivelar los entendimientos respecto a los necesarios ajustes de la Ley. Ya habremos cumplido buena parte de nuestro objetivo si esta nivelación facilita los acuerdos necesarios entre las partes cubiertas. Lo cierto es que necesitamos la participación de más personas en la defensa de este bien natural y esencial para el mantenimiento de la vida

Analyse des Angebots deutsch- und fremdsprachiger Tageszeitungen im Internet

Das Internet ist das größte und auch wohl meist genutzte Computernetz der Welt. Mittlerweile sind sehr viele Zeitungsverlage mit einer Online-Ausgabe ihrer Printzeitung im WWW vertreten. Diese Diplomarbeit liefert eine umfassende Bestandsaufnahme und Analyse von Tageszeitungen im WWW, anhand der das Engagement der Zeitungsverlage einzelner Länder im Internet aufgezeigt werden kann. Außerdem erläutert sie das notwendige Basiswissen bezüglich Internet und Online-Publishing

Space-Time Localisation with Quantum Fields

We introduce observables associated with the space-time position of a quantum point defined by the intersection of two light pulses. The time observable is canonically conjugated to the energy. Conformal symmetry of massless quantum fields is used first to build the definition of these observables and then to describe their relativistic properties under frame transformations. The transformations to accelerated frames of the space-time observables depart from the laws of classical relativity. The Einstein laws for the shifts of clock rates and frequencies are recovered in the quantum description, and their formulation provides a conformal metric factor behaving as a quantum observable.Comment: 11 pages, to appear in Physics Letters

Evolving fuzzy CP^n and lattice n-simplex

Generalizing the previous works on evolving fuzzy two-sphere, I discuss evolving fuzzy CP^n by studying scalar field theory on it. The space-time geometry is obtained in continuum limit, and is shown to saturate locally the cosmic holographic principle. I also discuss evolving lattice n-simplex obtained by `compactifying' fuzzy CP^n. It is argued that an evolving lattice n-simplex does not approach a continuum space-time but decompactifies into an evolving fuzzy CP^n.Comment: Typos corrected, 13 pages, no figures, LaTe

Measurement of Time-of-Arrival in Quantum Mechanics

It is argued that the time-of-arrival cannot be precisely defined and measured in quantum mechanics. By constructing explicit toy models of a measurement, we show that for a free particle it cannot be measured more accurately then $\Delta t_A \sim 1/E_k$, where $E_k$ is the initial kinetic energy of the particle. With a better accuracy, particles reflect off the measuring device, and the resulting probability distribution becomes distorted. It is shown that a time-of-arrival operator cannot exist, and that approximate time-of-arrival operators do not correspond to the measurements considered here.Comment: References added. To appear in Phys. Rev.

Drosophila Photoreceptor Axon Guidance and Targeting Requires the Dreadlocks SH2/SH3 Adapter Protein

AbstractMutations in the Drosophila gene dreadlocks (dock) disrupt photoreceptor cell (R cell) axon guidance and targeting. Genetic mosaic analysis and cell-type-specific expression of dock transgenes demonstrate dock is required in R cells for proper innervation. Dock protein contains one SH2 and three SH3 domains, implicating it in tyrosine kinase signaling, and is highly related to the human proto-oncogene Nck. Dock expression is detected in R cell growth cones in the target region. We propose Dock transmits signals in the growth cone in response to guidance and targeting cues. These findings provide an important step for dissection of signaling pathways regulating growth cone motility