Spanning in de plant

Plantencelfysiologi

A collaborative approach to improving academic honesty

Mouse gene Ptprr encodes multiple protein tyrosine phosphatase receptor type R (PTPRR) isoforms that negatively regulate mitogen-activated protein kinase (MAPK) signaling pathways. In the mouse brain, PTPRR proteins are expressed in cerebellum, olfactory bulb, hippocampus, amygdala and perirhinal cortex but their precise role in these regions remains to be determined. Here, we evaluated phenotypic consequences of loss of PTPRR activity and found that basal smell was normal for Ptprr(-/-) mice. Also, spatial learning and fear-associated contextual learning were unaffected. PTPRR deficiency, however, resulted in impaired novel object recognition and a striking increase in exploratory activity in a new environment. The data corroborate the importance of proper control of MAPK signaling in cerebral functions and put forward PTPRR as a novel target to modulate synaptic processes

No Longer Discrete:Modeling the Dynamics of Social Networks and Continuous Behavior

The dynamics of individual behavior are related to the dynamics of the social structures in which individuals are embedded. This implies that in order to study social mechanisms such as social selection or peer influence, we need to model the evolution of social networks and the attributes of network actors as interdependent processes. The stochastic actor-oriented model is a statistical approach to study network-attribute coevolution based on longitudinal data. In its standard specification, the coevolving actor attributes are assumed to be measured on an ordinal categorical scale. Continuous variables first need to be discretized to fit into such a modeling framework. This article presents an extension of the stochastic actor-oriented model that does away with this restriction by using a stochastic differential equation to model the evolution of a continuous attribute. We propose a measure for explained variance and give an interpretation of parameter sizes. The proposed method is illustrated by a study of the relationship between friendship, alcohol consumption, and self-esteem among adolescents

Onderzoek naar vermindering van de bijvangst van een boomkortuig

In het kader van EU-project RECOVERY werden vergelijkende visserij- en selectiviteitsproeven uitgevoerd in 2002 en 2003 aan boord van MS “Tridens” aan 12 m boomkortuigen. De resultaten van een negental vistuigproeven zijn hier gegeven, gericht op het bepalen van het effect van een grote mazen kap en/of een vierkante mazen paneel achter in het net op vangst-verschillen in vergelijking met een conventioneel boomkornet. Het conventionele net werd in een aantal proeven zo uitgevoerd, dat het kan worden geacht de totale vispopulatie te vangen. Hiertoe werd een binnenzak van 40 mm maaswijdte aangebracht en een kap met 100 mm mazen. De proeven geven hetzelfde beeld als voorheen gevonden: een belangrijke afname (-30%) in wijtingvangsten voor de grote mazen kap. De kabeljauwvangsten waren gering, maar toch lijkt er sprake van een afname met de grote mazen kap. Het vierkante mazen paneel achterin voor de kuil lijkt weinig effect op de selectiviteit te hebben. De binnenzakken geven een sterke toename (+70%) van de vangst van ondermaatse vis, maar ook een aanzienlijke toename (+30%) van de aanlanding. Uit oogpunt van ecosysteembeheer dient eventueel gebruik ervan natuurlijk te worden vermeden

Oxygen transport and consumption in germinating seeds

Three mathematical models were formulated to describe the oxygen con-sumption of seeds during germination. These models were fitted to measure-ment data of oxygen consumption curves for individual germinating seeds of Savoy cabbage, barley and sugar beet provided by Fytagoras. The first model builds on a logistic growth model for the increasing population of mitochondria in the embryo during growth. The other two take the anatomy and physiologi-cal properties of the seed into account. One describes the oxygen uptake during the germination phase only. An extension of this model is capable of fitting the complete oxygen consumption curve, including the initial ‘repair’ phase in which the embryonic cells recover from their dormant state before extensive cell division and growth commences. Keywords: Modelling, seed germination, cellular respiration, oxygen transpor

Competitive tendering and deregulation in the British bus

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Geometrical quadrupolar frustration in DyB4_4

Physical properties of DyB$_4$ have been studied by magnetization, specific heat, and ultrasonic measurements. The magnetic entropy change and the ultrasonic properties in the intermediate phase II indicate that the degeneracy of internal degrees of freedom is not fully lifted in spite of the formation of magnetic order. The ultrasonic attenuation and the huge softening of $C_{44}$ in phase II suggests existence of electric-quadrupolar (orbital) fluctuations of the 4$f$-electron. These unusual properties originate from the geometrical quadrupolar frustration.Comment: 4 pages, 4 figures, accepted for publication in Journal of the Physical Society of Japa