Showing papers by "University of Fribourg published in 1992"

Responses of monkey dopamine neurons during learning of behavioral reactions.

Abstract: 1. Previous studies have shown that dopamine (DA) neurons respond to stimuli of behavioral significance, such as primary reward and conditioned stimuli predicting reward and eliciting behavioral reactions. The present study investigated how these responses develop and vary when the behavioral significance of stimuli changes during different stages of learning. Impulses from DA neurons were recorded with movable microelectrodes from areas A8, A9, and A10 in two awake monkeys during the successive acquisition of two behavioral tasks. Impulses of DA neurons were distinguished from other neurons by their long duration (1.8-5.0 ms) and low spontaneous frequency (0.5-7.0 imp/s). 2. In the first task, animals learned to reach in a small box in front of them when it opened visibly and audibly. Before conditioning, DA neurons were activated the first few times that the empty box opened and animals reacted with saccadic eye movements. Neuronal and behavioral responses disappeared on repeated stimulus presentation. Thus neuronal responses were related to the novelty of an unexpected stimulus eliciting orienting behavior. 3. Subsequently, the box contained a small morsel of apple in one out of six trials. Animals reacted with ocular saccades to nearly every box opening and reached out when the morsel was present. One-third of 49 neurons were phasically activated by every door opening. The response was stronger when food was present. Thus DA neurons responded simultaneously to the sight of primary food reward and to the conditioned stimulus associated with reward. 4. When the box contained a morsel of apple on every trial, animals regularly reacted with target-directed eye and arm movements, and the majority of 76 DA neurons responded to door opening. The same neurons lacked responses to a light not associated with task performance that was illuminated at the position of the food box in alternate sessions, thus demonstrating specificity for the behavioral significance of stimuli. 5. The second task employed the operant conditioning of a reaction time situation in which animals reached from a resting key toward a lever when a small light was illuminated. DA neurons lacked responses to the unconditioned light. During task acquisition lasting 2-3 days, one-half of 25 DA neurons were phasically activated when a drop of liquid reward was delivered for reinforcing the reaching movement. In contrast, neurons were not activated when reward was delivered at regular intervals (2.5-3.5 s) but a task was not performed.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronal activity in monkey ventral striatum related to the expectation of reward

Abstract: Projections from cortical and subcortical limbic structures to the basal ganglia are predominantly directed to the ventral striatum. The present study investigated how the expectation of external events with behavioral significance is reflected in the activity of ventral striatal neurons. A total of 420 neurons were studied in macaque monkeys performing in a delayed go-no-go task. Lights of different colors instructed the animal to do an arm-reaching movement or refrain from moving, respectively, when a trigger light was illuminated a few seconds later. Task performance was reinforced by liquid reward in both situations. A total of 60 ventral striatal neurons showed sustained increases of activity before the occurrence of individual task events. In 43 of these neurons, activations specifically preceded the delivery of reward, independent of the movement or no-movement reaction. In a series of additional tests, these activations were time locked to the subsequent reward, disappeared within a few trials when reward was omitted, and were temporally unrelated to mouth movements. Changes in the appetitive value of the reward liquid modified the magnitude of activations, suggesting a possible relationship to the hedonic properties of the expected event. Activations also occurred when reward was delivered in a predictable manner outside of any behavioral task. These data suggest that neurons in the ventral striatum are activated during states of expectation of individual environmental events that are predictable to the subject through its past experience. The prevalence of activations related to the expectation of reward suggests that ventral striatal neurons have access to central representations of reward and thereby participate in the processing of information underlying the motivational control of goal-directed behavior.

Role of primate basal ganglia and frontal cortex in the internal generation of movements. III. Neuronal activity in the supplementary motor area.

Abstract: This study is a part of a project investigating neuronal activity in the basal ganglia and frontal cortex and describes externally and internally induced preparatory activity in the supplementary motor area (SMA), which forms a closed neuronal loop with the striatum. Monkeys made self-initiated arm reaching movements toward a constant target in the absence of phasic external stimuli. In separate blocks of trials, animals performed in a delayed go no-go task in which an instruction cue prepared for subsequent movement or no-movement to a trigger stimulus. A total of 328 neurons were tested in the delay task. Of these, 91 responded transiently to the instruction light with a median latency of 262 ms. Three quarters of these responses were restricted to the instruction preparing for arm movement, as opposed to with-holding it, and thus may be involved in movement preparation processes. Sustained activation during the instruction-trigger interval was found for 67 neurons and occurred nearly exclusively in movement trials. Activation usually increased gradually after the cue and ended abruptly upon movement onset and thus could be related to the setting and maintenance of processes underlying the preparation of movement. Time-locked responses to the trigger stimulus were found in 38 neurons and were usually restricted to movement trials (median latency 80 ms). Activity time-locked to movement execution occurred in 67 neurons, beginning up to 252 ms before movement onset. A total of 266 neurons were tested with self-initiated arm movements. Of these, 43 showed premovement activity beginning 610–3030 ms before movement onset (median 1430 ms). The activity increased slowly and reached its peak at 370 ms before movement onset. It ended before movement onset or continued until the arm began to move or reached the target. This activity appears to reflect neuronal processes related to the internal generation of movements. Two thirds of activations preceding self-initiated movements occurred in neurons not activated before externally instructed movements, suggesting a selectivity for the internal generation process. Activity related to the execution of self-initiated movements occurred in 67 neurons: it began during and up to 420 ms before movement onset and was usually not associated with pre-movement activity. Most of these neurons were also activated with stimulus-triggered movements, suggesting a lack of selectivity for the execution of self-initiated movements. In comparison with the striatum, more SMA neurons showed preparatory activity preceding externally instructed movements (transient 27% vs 16%, sustained 20% vs 12%) and self-initiated movements (16% vs 11%). Whereas transient responses showed similar latencies and durations in the two structures, sustained preparatory activity preceding externally instructed or self-initiated movements began and reached its peak earlier in SMA compared to striatal neurons. However, due to the long durations, sustained activation largely overlapped in the two structures, and thus essentially occurred simultaneously. Instruction-induced or internally generated preparatory activity may originate outside of the SMA and striatum or may derive from activity reverberating in cortico-basal ganglia loops, possibly in conjunction with other, closely associated cortical and subcortical structures. These data would favor a conjoint role for SMA and striatum in the internal generation of individual behavioral acts and the preparation of behavioral reactions.

Neuronal activity in monkey striatum related to the expectation of predictable environmental events.

Abstract: 1. This study investigated neuronal activity in the striatum preceding predictable environmental events and behavioral reactions. Monkeys performed in a delayed go-nogo task that included separate time periods during which animals expected signals of behavioral significance, prepared for execution or inhibition of arm reaching movements, and expected the delivery of reward. In the task, animals were instructed by a green light cue to perform an arm reaching movement when a trigger stimulus came on approximately 3 s later (go situation). Movement was withheld after the same trigger light when the instruction cue had been red (nogo situation). Liquid reward was delivered on correct performance in both situations. 2. A total of 1,173 neurons were studied in the striatum (caudate nucleus and putamen) of 3 animals, of which 615 (52%) showed some change in activity during task performance. This report describes how the activity of 193 task-related neurons increased in advance of at least 1 component of the task, namely the instruction cue, the trigger stimulus, or the delivery of liquid reward. These neurons were found in dorsal and anterior parts of caudate and putamen and were slightly more frequent in the proximity of the internal capsule. 3. The activity of 16 neurons increased in both go and nogo trials before the onset of the instruction and subsided shortly after this signal. These activations may be related to the expectation of the instruction as the first signal in each trial. 4. The activity of 15 neurons increased between the instruction and the trigger stimulus in both go and nogo trials. These activations may be related to the expectation of the trigger stimulus independent of an arm movement. Further 56 neurons showed sustained activations only when the instruction requested a movement reaction. Activations were absent in trials in which the movement was withheld. Twenty-one of these neurons were tested with 2 different movement targets, 5 of which showed activity related to the direction of movement. These activations may be related to the preparation of movement or expectation of the specific movement triggering signal. The activity of an additional 20 neurons was unmodulated before the trigger stimulus in movement trials but increased in the interval between the no-movement instruction and the trigger stimulus for withholding the movement. These activations may be related to the preparation of movement inhibition as specific nogo reaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of primate basal ganglia and frontal cortex in the internal generation of movements. I. Preparatory activity in the anterior striatum.

Abstract: The purpose of these studies was to investigate neuronal activity in the basal ganglia and frontal cortex in relation to the internal generation of goal-directed movements. Monkeys performed goal-directed arm movements at a self-chosen moment in the absence of phasic stimuli providing external temporal reference. They were rewarded with a small morsel of food for each movement, although automatic or repetitive behavior was not reinforced. For reasons of comparison, animals were also trained in a delayed go no-go task in which visual cues instructed them to perform or refrain from an arm movement reaction to a subsequent trigger stimulus. This report describes the activity of neurons in the head of the caudate nucleus and rostral putamen preceding self-initiated arm movements and compares it with instruction-induced preparatory activity preceding movements in the delay task. A total of 497 caudate and 354 putamen neurons were tested in the delay task. Two types of preparatory activity were observed: (1) transient responses to the instruction cue, and (2) sustained activity preceding the trigger stimulus or movement onset. Transient responses were found in 48 caudate and 50 putamen neurons, occurring twice as often in movement ('go') as compared to no-movement ('no-go') trials, but rarely in both. These responses may code the information contained in the instruction relative to the forthcoming behavioral reaction. Sustained activity began after instruction onset and lasted until the trigger stimulus or the arm movement occurred, this being for periods of 2-7 s, 12-35 s, or up to 80 s, depending on the task requirements. This activity was seen in 47 caudate and 45 putamen neurons, was largely confined to go trials, and was unrelated to the preparation of saccadic eye movements. In some cases, this activity began as direct responses to the instruction stimulus, but in the majority of cases developed more gradually before the movement. Thus, both transient and sustained activations appear to be related to the preparation of movements. A total of 390 caudate and 293 putamen neurons were tested during self-initiated movements. Activity preceding earliest movement-related muscle activity was found in 32 caudate and 42 putamen neurons. This premovement activity began 0.5-5.0 s before movement onset (median 1160 ms), increased slowly, reached its peak close to movement onset, and subsided rapidly thereafter. It was unrelated to the preparation of saccadic eye movements. Comparisons between the two tasks were made on 53 neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

The Selective innervation by serotoninergic axons of calbindin‐containing interneurons in the neocortex and hippocampus of the marmoset

Abstract: The serotoninergic input to the mammalian cerebral cortex originates in the median and the dorsal raphe nuclei. Median raphe neurons have been previously shown to give rise to beaded varicose axons which form dense pericellular arrays (baskets) surrounding the soma and the proximal dendrites of certain cortical neurons. In the present study, we have searched for specific markers characterizing the neurons of the marmoset neocortex and hippocampus surrounded by these thick varicose serotonin-containing fibers. The non-pyramidal nature of these neurons, suggested by their dendritic arborization, was correlated, in immunocytochemical experiments with double-labelling to demonstrate their surrounding serotonin-containing basket and their content of glutamic acid decarboxylase (GAD) or of the calcium-binding protein calbindin. Another calcium-binding protein common in numerous non-pyramidal cortical neurons, parvalbumin, was never found in neurons surrounded by serotonin-containing baskets. This organization was found in all areas of the neocortex and of the hippocampus where serotonin-containing baskets were present. One of the serotoninergic cortical inputs which originates from the brainstem tegmentum, traditionally described as «diffuse,» proves to be highly selective in that a subset of its axons terminates preferentially on a subpopulation of inhibitory interneurons of the cerebral cortex. It may be emphasized that this subset of cortical interneurons has now been shown to be characterized not only by its axonal and dendritic arborization and its neurotransmitter, but also by a specific type of input which can modulate cortical function in a unique manner.

Modeling forest fire by a paper-burning experiment, a realization of the interface growth mechanism

Abstract: We present an experiment on the propagation front of a flameless fire on a thin piece of paper. We find that fire fronts on a piece of paper follow quite well self-affine scaling statistics, with the roughening exponent χ around 0.70, well above the value 1 2 in the theoretical interface growth model using Gaussian noise. This discrepancy may be due to an anomalously singular behavior of the noise distribution, consistent with some recent studies.

Soybean lectin binding neurons in the visual cortex of the rat contain parvalbumin and are covered by glial nets.

Abstract: We carried out qualitative and quantitative studies on the distribution of soybean agglutinin-labelled cells in the visual cortex of the rat. Lectin-positive nerve cells mostly showed the morphological characteristics of small and large multipolar basket cells. Only a few cells appeared to be bipolar with a vertical or horizontal orientation. By light microscopy, soybean agglutinin binding sites were seen as discontinuous, punctate perineuronal staining (or pericellular nets) on the surface of about 9% of cortical neurons. Lectin-positive cells were predominantly localized in layers IV and V (16.9 and 12.4% of all neurons), where the intensity of staining was also the strongest. Combining lectin- and immunohistochemistry on cryo semithin sections, lectin-positive cells were shown to contain parvalbumin. Nerve cells in the visual cortex containing the related calcium binding-proteins, calbindin or calretinin were never soybean agglutinin-positive. Some glial cells and their processes were also soybean agglutinin-positive. The structure of the soybean agglutinin-positive pericellular nets was similar to that of glial nets visualized with the Golgi-method. Electron microscopy revealed that lectin binding sites were localized on the membranes and cytoplasm of glial processes ensheathing the axon terminals that impinged upon neurons and their proximal dendrites. Synaptic clefts and axon terminals were never reactive, thus explaining the discontinuous punctate labelling of the neuronal surface. Lectin binding sites were also found on the trans-face of the Golgi-complex of some lectin positive neurons suggesting that N-acetylgalactosamine-containing glycoconjugates, which are selectively detected by the lectin, are synthesized, at least partly, within the labelled neurons. We therefore consider possible the existence of specific interactions between parvalbumin positive basket cells and the glial network surrounding them, by which the neuron may determine the conditions of its own microenvironment.

Raman optical activity instrument for biochemical studies

Abstract: A simple and fully computer-controlled backscattering incident circular polarization Raman optical activity (ICP ROA) instrument suitable for chioptic studies of biologically significant molecules in aqueous solution is described. It consists of a fast single-stage monochromator equipped with a holographic edge filter, a highly efficient holographic difiaction grating and a thinned back illuminated thermoelectrically cooled charge-coupled device detector as the key spectral elements. A longitudinal electro-optic modulator is employed to switch between orthogonal circular polarization states in the incident laser radiation within a backscattering geometry. A thick Lyot depolarizer is used for the depolarization of the backscattered Raman radiation. High-quality backscattering ICP ROA spectra of (1S)-( − )-trans-pinane, (1R)-( + )-trans-pinane, L-alanine, L-alanyl-L-alanine, lysozyme, D-glucose, α-D-cyclodextrin and 2′-deoxycytidine are presented as typical examples of the excellent performance characteristics.

Structure, electronic properties, and defects of amorphous gallium arsenide

Abstract: We have constructed a structural model of amorphous gallium arsenide by quenching from the melt, via first-principles molecular-dynamics simulations. The properties of our structure agree well with the available experimental information. We find that the predominant defects in this system are not wrong bonds, but threefold-coordinated atoms. Because of a relaxation mechanism similar to that occurring on the GaAs(110) surface, these do not yield states in the gap, but yield empty Ga and filled As dangling-bond states near the band edges.

Perennial névés and the hydrology of rock glaciers

Abstract: From 1986 to 1990 water tracing was carried out in three rock glaciers in the Upper Val de Rechy. Results indicate different patterns of circulation depending on the size and degree of activity of the rock glaciers. Two rock glaciers show rapid superficial flow and one has slow interstitial flow. This is analogous to supra- and subglacial flow. Intra-flow is also seen in one rock glacier. The importance of perennial neves at the roots of rock glaciers is demonstrated. Meltwater supplies the risings and, by refreezing, probably also increases the ice mass of the rock glaciers. De 1986 a 1990, des tracages des eaux ont ete realises dans trois glaciers rocheux de la vallee superieure de Rechy. Les resultats indiquent l'existence de differents reseaux de circulation des eaux qui peuvent ětre mis en relation avec la taille et le degre d'activite des glaciers rocheux. Deux glaciers rocheux actifs montrent un ecoulement superficiel rapide et l'un d'entre eux montre, en outre, un ecoulement intersticiel lent. Ceux-ci sont semblables aux ecoulements supra et sous-glaciaire. Un ecoulement interne a ete aussi observe dans un glacier rocheux inactif. L'importance des neves perennes localises a la partie superieure des glaciers rocheux est demontree. Leurs eaux de fonte alimentent les crues et, par regel, augmentent probablement la masse de glace qui se trouve au sein du glacier rocheux.

The assignment of functions to decentralized government: from theory to practice

Abstract: The question of why key academic economic arguments for the assignment of functions to decentralized government have not informed the political debate in Switzerland is examined in this paper. In the first section the most relevant theoretical factors of optimal government organization for service delivery are reviewed. A catalogue of criteria that have been debated in the Swiss context at both federal–cantonal and cantonal–local levels are covered in the second section. The main point is that the discussion is focused on rather different criteria from those noted in orthodox economic theory. The analysis of the causes and discrepancies between theory and practice permits a more general conclusion, addressed to fiscal federalism. The conclusion is that there is no general answer to how functions should be assigned to a particular level of government, as the solution depends upon the relevant value-judgments of the polity as well as the resources-use required to provide given services. The outcome is a set...

Characterization of the cellulolytic enzyme system from the brown-rot fungus Coniophora puteana

Abstract: The cellulolytic enzymes of various strains of the brown-rot fungus Coniophora puteana were studied. The organism was grown in an air-lift fermentor in mineral medium containing glucose, cellobiose or amorphous cellulose. The specific growth rate varied between 0.082 and 0.062 h−1. On amorphous cellulose as sole carbon source, the organism secreted various proteins, some of which were characterized. The mixture contained inter alia four endocellulases, two exo-cellobiohydrolases and a cellobiose dehydrogenase. Three endocellulases (named type I) were active on soluble cellulose derivatives but inactive on p-nitrophenyllactoside (p-NPL), whereas a fourth endocellulase (named type II) was active on both. The two exo-cellobiohydrolases released cellobiose from amorphous cellulose; they were inactive on soluble cellulose derivatives but hydrolyzed p-NPL with strong cellobiose inhibition. A cellobiose dehydrogenase having spectral characteristics compatible with a flavo b-cytochrome was also identified. Neither the exo-cellobiohydrolase nor the type II endocellulase were secreted during growth on cellobiose whereas type I endocellulases and cellobiose dehydrogenase were formed at a reduced rate. No formation of cellulolytic enzymes was observed during growth on glucose alone.

M- and L-shell ionization in near-central collisions of 5.5-MeV/amu 16O ions with Mo atoms deduced from theoretical analysis of high-resolution K x-ray spectra.

Abstract: The K\ensuremath{\alpha} and K\ensuremath{\beta} x-ray spectra of molybdenum bombarded by 5.5-MeV/amu $^{16}\mathrm{O}$ ions were measured with high resolution. In such heavy-ion--atom collisions, multiple ionization of the M and L shells of the target atoms is extremely likely to occur, resulting in a complex structure of the observed spectra. The ${\mathit{L}}^{\mathit{n}}$-satellite structure was resolved, whereas M vacancies produce only a shift and a broadening of the lines so that it is not possible to obtain in a direct way information about the M-hole distribution. We thus propose a method for the analysis of x-ray spectra of multiply ionized atoms. In this method the measured K\ensuremath{\alpha} and K\ensuremath{\beta} spectra are simultaneously analyzed as a sum of K\ensuremath{\alpha}${\mathit{L}}^{\mathit{n}}$${\mathit{M}}^{\mathit{m}}$ and K\ensuremath{\beta}${\mathit{L}}^{\mathit{n}}$${\mathit{M}}^{\mathit{m}}$ components, respectively, with theoretically determined profiles. A binomial distribution of holes in the M shell is assumed and the M-shell ionization probabilities are treated as adjustable parameters. The profiles are constructed as sums of Voigt functions, whose positions and heights are determined by extensive multiconfiguration Dirac-Fock method calculations. If, in a simultaneous fit to the K\ensuremath{\alpha}${\mathit{L}}^{0}$ and K${\mathrm{\ensuremath{\beta}}}_{1,3}$${\mathit{L}}^{0}$ lines, just one parameter ${\mathit{p}}_{\mathit{M}}^{\mathit{X}}$ describing the M-shell ionization at the moment of the K x-ray transition is used, the experimental data are not reproduced in an entirely satisfactory way (${\mathit{p}}_{\mathit{M}}^{\mathit{X}}$=0.19\ifmmode\pm\else\textpm\fi{}0.02). Therefore, two parameters, one common for the 3s and 3p subshells ${\mathit{p}}_{3\mathit{s}\mathit{p}}^{\mathit{X}}$ and the other for the 3d subshells, were introduced and a much better fit to both lines (${\mathit{p}}_{3\mathit{s}\mathit{p}}^{\mathit{X}}$=0.17\ifmmode\pm\else\textpm\fi{}0.02, ${\mathit{p}}_{3\mathit{d}}^{\mathit{X}}$=0.23\ifmmode\pm\else\textpm\fi{}0.02) was obtained.The importance and influence of alternative ionizing processes as electron-capture and rearrangement processes are discussed and the M-shell ionization probability at the moment of the collision (${\mathit{p}}_{\mathit{M}}$=0.18\ifmmode\pm\else\textpm\fi{}0.02) is deduced from the ${\mathit{p}}_{\mathit{M}}^{\mathit{X}}$ value. It is shown that the differences between ${\mathit{p}}_{3\mathit{s}\mathit{p}}^{\mathit{X}}$ and ${\mathit{p}}_{3\mathit{d}}^{\mathit{X}}$ are mainly due to Coster-Kronig transitions, rather than due to different subshell ionization probabilities. The spectra were also analyzed with respect to the L-shell ionization on the basis of the calculated K\ensuremath{\alpha}${\mathit{L}}^{\mathit{n}}$${\mathit{M}}^{0}$, K${\mathrm{\ensuremath{\beta}}}_{1,3}$${\mathit{L}}^{\mathit{n}}$${\mathit{M}}^{0}$, and K${\mathrm{\ensuremath{\beta}}}_{2}$${\mathit{L}}^{\mathit{n}}$${\mathit{M}}^{0}$ components. The M-shell ionization was taken into account by taking a larger Gaussian width and by shifting the positions of the lines. The intensity yields of the L satellites were determined, the primary vacancy distribution was deduced, and the results from K\ensuremath{\alpha} and K\ensuremath{\beta} spectra are compared.

Parallel simulated annealing

Abstract: This article introduces the notion of restricted parallelism for networks, a generalization of the unlimited parallelism for Boltzmann machines. The convergence of the annealing algorithm in the restricted parallel form is established, for an arbitrary network. © 1992 Wiley Periodicals, Inc.

Complexes of Rhodium(III) with Two Chelating C⁁N Ligands and One Diimine Ligand

Abstract: The synthesis of two series of cyclometalated RhIII compounds is described, namely of 5 dinuclear chlorobridged species [{Rh(C⁁N)2} (μ-Cl)2] A and of 15 mononuclear complexes [Rh(C⁁N)2(N⁁N)]+B; C⁁N stands for five different cyclometalating ligands, ie deprotonated phenylpyridine, deprotonated 2-(thienyl)pyridine, and three deprotonated 1-aryl-1H-pyrazoles, and N⁁N for six diimine ligands such as 2,2-bihyridine, 2,2′-bi-1H-imidazole, and 2,2′-bipyrimidine For (2,2′-bipyridine)bis[2-(thien-2-yl)pyridinato-N,C3′]rhodium(III) chloride, an X-ray structure determination was carried out In the other cases, 1H-NMR spectra established the configuration of the complexes All mononuclear and dinuclear complexes show a C,C cis-configuration The UV/VIS-absorption bands at longest wavelength are most likely due to metal-to-ligand charge-transfer (MLCT) transitions, depending on the nature of the cyclometalating ligand C⁁N and on the diimine ligand N⁁N The receptor orbital is in some cases on the cyclometalating ligand, in others on the diimine All monomer complexes exhibit at least one reversible reduction wave in the cyclovoltammogram in dimethylformamide solutions, attributable to a ligand-centered reduction It is, therefore, concluded that the LUMO in [Rh(C⁁N)2(N⁁N)]+ is of L(π*) character, as opposed to [Rh(bpy)3]3+, where it is a metal d-orbital The crystal system of (2,2′-bipyridine)bis[2-(thien-2-yl)pyridinato-N,C3′]rhodium(III) chloride—water (1/2125) is tetragonal (space group P4; R = 0036, Rw = 0040) The Rh-atom has slightly distorted octahedral environment; the average distances are (RhN/thienylpyridine) = 2060 (3), RhC = 19885 (3), and RhN(bipyridine) = 21415 (3) A Of the three ligands the 2,2′-bipyridine is the most planar

Fractal aspects of the Swiss landscape

Abstract: We systematically examine the Swiss landscape in the search of the self-affine fractal scaling. We find for intermediate horizontal length scale range (250 m - 5 km) a rather well-defined self-affine roughening exponent of about 0.57, averaged over the whole Swiss territory. This value is surprisingly close to that found in other mountain ranges around the world, in spite of their very different geomorphological appearances. For smaller and larger length scales, more complex behaviors than the simple scaling are encountered.

Unusual features of the retroid element PAT from the nematode Panagrellus redivivus.

Abstract: The PAT retroid transposable elements differ from other retroids in that they have a 'split direct repeat' structure, i.e., and internal 300bp sequence is found repeated, about one half at each element extremity. A very abundant transcript of about 900 nt, the start of which maps to the preferentially deleted portion of PAT elements, is detected on total Panagrellus redivius RNA bearing Northern blots. A potentially corresponding ORF encodes a protein of 265 residues having a carboxy terminal Cystein motif, believed to be exclusively characteristic of the GAG protein in retoid elements. A much fainter, 1800nt long transcript, is also detected on Northern blots and maps slightly downstream of the first ORF. The predicted protein sequence of this region bears motifs typical of reverse transcriptase and RNaseH, as found in the Pol genes of retroid elements. Peptide motif similarities are greatest with the DIRS-1 element derived from Dictyostelium discoideum. The possibility of using PAT elements as transposon tagging system for Caenorhabditis elegans is discussed.