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Search Results: 1 - 10 of 297555 matches for " Jürgen Bolz "
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GABA through the Ages: Regulation of Cortical Function and Plasticity by Inhibitory Interneurons
Konrad Lehmann,André Steinecke,Jürgen Bolz
Neural Plasticity , 2012, DOI: 10.1155/2012/892784
Abstract: Inhibitory interneurons comprise only about 20% of cortical neurons and thus constitute a clear minority compared to the vast number of excitatory projection neurons. They are, however, an influential minority with important roles in cortical maturation, function, and plasticity. In this paper, we will highlight the functional importance of cortical inhibition throughout brain development, starting with the embryonal formation of the cortex, proceeding by the regulation of sensory cortical plasticity in adulthood, and finishing with the GABA involvement in sensory information processing in old age. 1. Introduction The functioning of the cerebral cortex depends critically on the precise balance between excitatory and inhibitory neurotransmitter systems. Excitation is mediated via glutamate by pyramidal neurons, the projection neurons of the cortex, and by a special class of local neurons in cortical layer IV, the spiny stellate cells. Inhibition is mediated via γ-aminobutyric acid (GABA) by cortical interneurons, which regulate the degree of glutamatergic excitation, filtering the input and regulate the output of projection neurons. GABAergic interneurons, the “nonpyramidal cells” of the cerebral cortex, take many different forms of dendritic and axonal arborization, which have been used for their morphological classification ever since their first description by Ramon Cajal [1–5]. Moreover, interneurons also differ in their firing patterns, the neuropeptides they express, their calcium-binding protein content, and other molecular markers such as ion channels, receptors, and transporters. Based on the combination of structural, functional, and biochemical criteria, interneurons have been subdivided into many different subclasses and it is still a matter of hot debate among the experts of how many interneuron subtypes exist in the cortices of different species [6–8]. At the circuit level, interneurons control the flow of information and synchronization in the cerebral cortex. There are about five times more glutamatergic neurons than GABAergic neurons in the neocortex; this ratio is consistently observed across many mammalian species. This then suggests that the numerical balance of excitatory and inhibitory neurons may be important for normal brain function and behavior. Even though GABAergic interneurons comprise only a small fraction of the cells in the neocortex, disturbances in their development, and hence the delicate balance between excitation and inhibition, can lead to neurological or neuropsychiatric diseases such as epilepsy, autism, and
A dual role of EphB1/ephrin-B3 reverse signaling on migrating striatal and cortical neurons originating in the preoptic area: should I stay or go away ?
André Steinecke,Annika D?ding,Jürgen Bolz
Frontiers in Cellular Neuroscience , 2014, DOI: 10.3389/fncel.2014.00185
Abstract: During embryonic development the preoptic area (POA) gives rise to two populations of neurons which are generated at the same time, cortical interneurons and striatal cells. POA-derived cortical interneurons take a superficial path and avoid the developing striatum when they migrate to their target region. We found that EphB1, which is expressed in the striatal anlage, prevents cortical interneurons from entering the striatum via ephrin-B3 reverse signaling. In contrast, for striatal neurons which also express ephrin-B3, EphB1 acts as a stop signal. This dual role of EphB1 is due to differences in ephrin-B3 reverse signaling cascades. For striatal neurons, binding of EphB1 to ephrin-B3 reduces endogenously high levels of pSrc and pFAK, which then causes the cells to stop migration. In contrast, in cortical interneurons EphB1-ephrin-B3 reverse signaling leads to phosphorylation of Src and FAK which then mediates repulsion. Consistent with these in vitro findings, in an ephrin-B3 knockout mouse line, we discovered misrouted cortical interneurons in the striatum and an over-migration of striatal neurons in their target region. Thus, EphB1/ephrin-B3 reverse signaling has a different impact on two sets of neurons which are generated at the same time and place: it can act as a repulsive cue for migrating neurons or it can terminate neuronal migration, a novel role of the Eph/ephrin system.
Modelling the nucleon wave function from soft and hard processes
J. Bolz,P. Kroll
Physics , 1996, DOI: 10.1007/s002180050186
Abstract: Current light-cone wave functions for the nucleon are unsatisfactory since they are in conflict with the data of the nucleon's Dirac form factor at large momentum transfer. Therefore, we attempt a determination of a new wave function respecting theoretical ideas on its parameterization and satisfying the following constraints: It should provide a soft Feynman contribution to the proton's form factor in agreement with data; it should be consistent with current parameterizations of the valence quark distribution functions and lastly it should provide an acceptable value for the $\jp \to N \bar N$ decay width. The latter process is calculated within the modified perturbative approach to hard exclusive reactions. A simultaneous fit to the three sets of data leads to a wave function whose $x$-dependent part, the distribution amplitude, shows the same type of asymmetry as those distribution amplitudes constrained by QCD sum rules. The asymmetry is however much more moderate as in those amplitudes. Our distribution amplitude resembles the asymptotic one in shape but the position of the maximum is somewhat shifted.
l=0 to l=1 Transition Form Factors
J. Bolz,P. Kroll,J. G. Koerner
Physics , 1994, DOI: 10.1007/BF01290682
Abstract: A method is proposed to extend the hard scattering picture of Brodsky and Lepage to transitions between hadrons with orbital angular momentum l=0 and l=1. The use of covariant spin wave functions turns out to be very helpful in formulating that method. As a first application we construct a light-cone wave function of the nucleon resonance $N^*(1535)$ in the quark-diquark picture. Using this wave function and the extended hard scattering picture, the $N$--$N^*$ transition form factors are calculated at large momentum transfer and the results compared to experimental data. As a further application of our method we briefly discuss the $\pi$--$a_1$ form factors in an appendix.
Colour-octet contributions to exclusive charmonium decays
J. Bolz,P. Kroll,G. A. Schuler
Physics , 1996, DOI: 10.1016/S0370-2693(96)01515-8
Abstract: We investigate the theoretical uncertainties of $P$-wave charmonium decays into two pions, $\chi_{\c J}\rightarrow \pi^+\pi^-$, $\pi^0\pi^0$. Constraining the pion distribution-amplitude from the recent precise data on $F_{\pi\gamma}(Q^2)$, we find an order-of-magnitude discrepancy between data and prediction. The disagreement persists even after inclusion of transverse degrees of freedom and Sudakov suppressions. We propose the colour-octet mechanism as the solution to the puzzle. The colour-octet decay contribution arising from the higher Fock component $|\c \cbar \g >$ of the $\chi_{\c J}$ wave function is actually not power suppressed with respect to the usual colour-singlet decay arising from the dominant $|\c \cbar >$ Fock state. An explicit calculation yields an agreement with the data for a very reasonable value for the single extra non-perturbative parameter.
Operator Splitting Method for Coupled Problems:Transport and Maxwell Equations  [PDF]
Jürgen Geiser
American Journal of Computational Mathematics (AJCM) , 2011, DOI: 10.4236/ajcm.2011.13019
Abstract: In this article a new approach is considered for implementing operator splitting methods for transport problems, influenced by electric fields. Our motivation came to model PE-CVD (plasma-enhanced chemical vapor deposition) processes, means the flow of species to a gas-phase, which are influenced by an electric field. Such a field we can model by wave equations. The main contributions are to improve the standard discretization schemes of each part of the coupling equation. So we discuss an improvement with implicit Runge- Kutta methods instead of the Yee’s algorithm. Further we balance the solver method between the Maxwell and Transport equation.
Development of a computer vision system to monitor pig locomotion  [PDF]
Jrgen Kongsro
Open Journal of Animal Sciences (OJAS) , 2013, DOI: 10.4236/ojas.2013.33038
Abstract: Avoiding lameness or leg weakness in pig production is crucial to reduce cost, improve animal welfare and meat quality. Detection of lameness detection by the use of vision systems may assist the farmer or breeder to obtain a more accurate and robust measurement of lameness. The paper presents a low-cost vision system for measuring the locomotion of moving pigs based on motion detection, frame-grabbing and multivariate image analysis. The first step is to set up a video system based on web camera technology and choose a test area. Secondly, a motion detection and data storage system are used to build a processing system of video data. The video data are analyzed measuring the properties of each image, stacking them for each animal and then analyze these stacks using multivariate image analysis. The system was able to obtain and decompose information from these stacks, where components could be extracted, representing a particular motion pattern. These components could be used to classify or score animals according to this pattern, which might be an indicator of lameness. However, further improvement is needed with respect to standardization of herding, test area and tracking of animals in order to have a robust system to be used in a farm environment.
The Motley World of “International Values”: Modes of Production on the World Market  [PDF]
Jrgen Sandemose
Theoretical Economics Letters (TEL) , 2016, DOI: 10.4236/tel.2016.63058
Abstract: I venture to describe the world market from the viewpoint of those different extant modes of production which deliver commodities in “foreign” trade. The world market is, then, understood strictly in its basic feature, as a market for material products, all called commodities. The term “exchange”, which has to be used with some indeterminacy to begin with, is explained in greater detail as I proceed. In this regard, the most important sections are nos. 2 and 3. The term “modes of production” will also be clarified in due place, and primarily in Sections 9 and 10. I find such a concept necessary for an adequate background description of the products which are poured onto any market. I primarily analyze the capitalist mode of production through the concept of intensity of labour (cf. 4 and 9), which plays a main role even in Marx’s theory of the “modifications” of the law of value on the world market. Also, I find what is often labelled “Karl Marx’s theory of international values” to be correct in its foundations, and I will take a point of departure in it—especially apparent in sections 1, 2 and 3. A target for criticism in this article is the modern mainstream theory of “factors of production” in so far as it is found feasible for an analysis of the movements on the world market. This is briefly done in Section 8. In Section 6, I consider David Ricardo’s theory of “comparative advantages” as a counter-example to that theory. I use some terrain to show that the real historical and social background of the economic functioning of the so-called “factors”—capital, land and labour—must be a measuring rod for whether a factor theory is viable or not. To do this, I depend (cf. again Sections 9 and 10) to a high degree of Marx’s theory of those factors considered as forms of organized class forces—a viewpoint which played a central role in his preparing of the three volumes of Capital. While the Marxian theory insofar is adequate, it is also useful in analyzing the aborted or undeveloped state of those modes of production which, beneath the advanced capitalist one, supply the world market with material products. This ought to become clear especially in Sections 10 and 11. As my text expands, I try to show how the said inconsistency in the Ricardian model is based on
On the Exposition of the Transformation of Commodity-Values into Production Prices in the Third Volume of Capital—A Textual Analysis  [PDF]
Jrgen Sandemose
Theoretical Economics Letters (TEL) , 2016, DOI: 10.4236/tel.2016.65098
Abstract: The article is about the exposition of the Karl Marx’s concept of production prices in his main work Capital. It focuses on the structure of the central text in question, Chapter 9 of the third volume, on “transformation [Verwandlung] of commodity-values into production prices”. The actual content and structure of the chapter has to some degree been overlooked or distorted in the literature. The aim of the article is to establish (or re-establish) a sound view of the chapter, freed from prejudices nurtured by—especially—a theory of price formation which, albeit “modernized” by i.a. Walras, dates back to Steuart and Ricardo. These prejudices have had an immense significance for misunderstandings of the Marxian theory of measure of value and standard of prices reflected in the text of the chapter mentioned. For this reason, the article is furnished with an Appendix, underlining the difficult situation for Marxist-minded research today. It should be noted that it is not an objective of the article to discuss any extant interpretation of Marx’s exposition. However, the paradigm of criticism that was introduced early in the 20th century by Ladislaus von Bortkiewicz is used as a perspective. Specific references—other than to Marx’s own texts—are held at a minimum in the article proper. I have chosen such a mode of approach because I find that misunderstandings of the chapter are evenly distributed among authors regardless of how their views on the “transformation” collide. On the other hand, such a consciousness of “misunderstandings” among commentators certainly does imply that the author should at least shortly clarify his own view of the main problems in the paradigmatic criticism mentioned above. In the first section, I point out the importance of Marx’s way of presenting his concept of the composition of capital. In the next, I make some remarks on the concept of the socially necessary labour time and its relation to abstract labour. In the third and fourth, I investigate Marx’s different models of analysis. In the fifth section, it will be shown how Marx, contrary to
Paradoxes, Self-Referentiality, and Hybrid Systems: A Constructive Approach  [PDF]
Jürgen Klüver
Open Journal of Philosophy (OJPP) , 2017, DOI: 10.4236/ojpp.2017.71004
Abstract:
Since the discovery of the paradoxes of self-referentiality or self-reference respectively logicians and mathematicians tried to avoid self-reference when constructing formal systems. Yet “real” complex systems like the mind are characterized by self-reference and can accordingly only be modeled by formal systems that are also basically self-referential. In this article I show that and how self-referential computer programs, understood as algorithmic formal systems, are not only possible but also since some time quite common in special branches of computer science. Examples for this argument are neural networks and so-called hybrid systems, i.e. combination of different sub systems. The hybrid system SOCAIN, a combination of a cellular automaton, a neural network and a genetic algorithm is an example for the fruitfulness of using self-reference in a systematic way. In particular, such systems consist of mutually dependent sub systems, i.e. form no static hierarchy.
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