AfricanClarias catfish elicits long-lasting weak electric pulses

The African catfishClarias is generally considered to possess electroreceptors but not electric organs. It is reported here that at least one species of the genus,C. gariepinus, can produce weak monophasic discharges during aggressive interactions with conspecifics. These irregular pulse discharges are substantially longer than the electric organ discharges (EODs) of all other pulse-generating freshwater electric fishes. It is also shown that the optimal sensitivity ofClarias' ampullary receptors just corresponds to the modal pulse duration. TheClarias catfish, with its very specific EOD, may be of special interest in the evolution of the electrogenic system in the siluriforms, comprising many electroreceptive but nonelectrogenic catfish species.     

Topische Bestimmung des zerebralen Angriffs von Reserpin (Serpasil)

Summary The impact of Reserpine (Serpasil) has been investigated by stimulating different parts of the rabbit's brain (Cortex, Diencephalon, Rhinencephalon,Subst. reticularis). Simultaneously the spontaneous brain activity and the electrically induced discharge have been recorded and studied in the cortex, the thalamus (Nucl. dors. med. andlat.), the rhinencephalon and theSubst. reticularis of the brain stem.Reserpine has a depressing influence on the diencephalo-cortical system. It raises the threshold of the afterdischarge induced by stimulation of the cortex and of the thalamus.Nevertheless the drug induces no electrographic sleep pattern. It maintains a steady electric pattern of alertness and increases the electrical ground activity of the rhinencephalon.Reserpine also depresses the spikes induced in the cortex and in the thalamus by stimulation of the pontobulbar reticular system. This effect is supposed to be due to a pharmacological action located at the thalamocortical level rather than in the bulbar segment of the arousal system.     

Sonnenflecken und ihre terrestrischen Wirkungen

Summary After a discussion of the 11-year solar-cycle as regarded from the standpoint of the eruption-hypothesis, which offers a possibility to predict the solar activity for several years and after a review of the magnetic properties of the sun and the sunspots, the paper deals with the new theories of the spots and the solar-cycle as suggested byAlfvén andWalén.The terrestrial effects of the phenomena associated with the solar cycle are classified into 4 groups: effects produced by a) a wave radiationW _k emitted continuously by the sun, b) a wave radiationW _e emitted from the chromospheric eruptions, c) a particle radiationP _k emitted by the so-called M-regions, and d) a particle radiationP _e ejected from the eruptions. The connection between the solar eruptions and the radiationsP _e ,W _e is a well established fact; on the other hand the radiationsW _k ,P _k could be connected by the author with the solar corona and the stationary solar prominences respectively.To account for the intensity of theW _k -radiation a temperature of the solar corona of one million degree is required in agreement with the observed temperature. The heating of the corona occurs in the electric field around an increasing sunspot. As in the corona the mean free path amounts to several kilometers, particles may be accelerated up to 1000 eV, so far the conditionh=0 is fulfilled. Generally speaking acceleration is possible only in such regions whereh andh are not perpendicular to each other.     

No sex difference in the waveform of the pulse type electric fish,Gnathonemus petersii (Mormyridae)

Summary A communication signal in an African freshwater electric fish, its pulse-like Electric Organ Discharge (EOD), was investigated in order to determine whether inter- or intraindividual variability of the EOD waveform provides a putative cue for communication, in addition to the electric cues already identified. In contrast to an individual's highly stereotyped EODs showing extremely low variation (fig. 1), variability between individuals was considerable (fig. 2). The dependence of an individual's EOD duration on temperature was weak with a Q₁₀ of close to 1.5. In none of four quantitative EOD waveform measures can a sexual dimorphism be discerned (table).Gnathonemus petersii very likely relies on mechanisms other than discrimination of intraspecific EOD waveforms for mate recognition.     

Anatomical identification of the presumed electroreceptors of two air breathing catfishes,Clarias batrachus andHeteropneustes fossilis

Summary Histological preparations for light microscopy have revealed for the first time the structure of the electroreceptor ofClarias batrachus andHeteropneustes fossilis, the 2 Indian air-breathing catfishes. These sensory organs are found to resemble the ampullary organs of many weakly electric and nonelectric electroreceptive teleost.The work was in part supported by grant of SCST (U.P.) during the period 1974–76 which is acknowledged.     

Die Reizschwelle der Sinnesorgane als physikalisches Problem

Summary A survey is given of recent work on physical aspects of sensory processes. The reasoning which leads to the generally recognized view that one rod of the retina is excited by only one quantum of light is given in par. II. In par. IIIa summary is given of the papers byHecht andVan der Velden on the number of rods which must be struck in order to obtaina sensation of light. Par. III describes the role of the quantum character of light at higher intensities (de Vries), where it sets a limit to intensity discrimination and visual acuity. The influence of Brownian movement on the process of hearing is discussed in par. VI. It is found that the Brownian movement of the inner ear is close to the threshold actually observed (de Vries), whereas the Brownian motion of the air at the eardrum (seeSivian andWhite) is below the audible threshold. The role of the Brownian movementin the sense cells is described in par. VII; the results are used for an analysis of the mechanism of hearing (see alsode Vries); evidence is obtained that electric voltages are generated in the tectorial membrane (the well-known cochlear microphonics) and that they play an important part in the mechanism of energy transfer to the sense cells (similar voltages were also derived from the cupolæ in the lateral lines of fishes by the present author). Finally some physical arguments are sumarized againstYeagley's theory of bird navigation.     

On the solvent-extraction of acetylcholine receptor

Summary Chloroform/methanol rechromatography on Sephadex LH-20 of fractions isolated from organic solvent extracts ofE. electricus electric organs exhibited alterations in elution point compared to the original chromatography. Additionally,³H decamethonium bromide did not coelute with any of the observed fractions. It is concluded that as presently described the organic solvent isolation procedure for the cholinergic receptor exhibits undesirable characteristics.Acknowledgments. The authors thank Dan Burrough and Rick O'Brien for their competent technical assistance. Naval Medical Research Development and Command, Research Work Unit No. MRO41.06.01.0021. The opinions and assertions contained herein are the private ones of the writers and are not to be construed as official or reflecting the views of the Navy Department or the naval service at large.     

Lethal effect of electrolysis on nematodes (Meloidogyne incognita)

Summary Electrolysis of salt solutions produces mortality of a plant-parasitic nematodeMeloidogyne incognita. The mortality depends on the nature and amount of the, products of electrochemical reactions and is enhanced in presence of Cu-electrodes. Application of magnetic fields on electric fields alters nematode mortality in ferro-magnetic electrolytes.     

Captivity affects behavioral physiology: Plasticity in signaling sexual identity

Summary Little is known about the link between captivity, physiology, and behavior in wild-caught vertebrates. Anecdotal evidence suggests that hormonal changes are responsible for behavioral changes in wild animals brought into captivity. Studying the effects of captivity on reproduction is hampered because wild animals often fail to exhibit sexual behavior under captive conditions. In weakly discharging electric fish, field studies have reported sex differences in electric organ discharges which are rarely seen in the laboratory. I now report the results of a series of laboratory investigations which show thatGnathonemus petersii exhibits seasonal, hormone-dependent, phasespecific sex differences in electric organ discharges. Captivity dramatically alters and may even reverse these sex differences as a result of rapid changes in endogenous plasma hormone levels. These findings have broad implications for research on animal physiology and behavior performed in laboratory settings.     

Einfluss des luftelektrischen Feldes auf das Haut-Potential vonRana esculenta

Summary The potential across the skin ofRana esculenta was remarkably reduced under Faraday conditions in comparison to animals kept under normal conditions. A pulsating electric field (10 Hz) practically abolished this effect.     

Effect of acetylhomocysteine thiolactone on nucleolar cytology and lipofuscinogenesis in electric lobe neurons

Summary Treatment with acetylhomocysteine thiolactone significantly reduces the cellular level of lipofuscin in neurons of the electric lobe ofTorpedo marmorata. At the same time, this drug produces a 45% decrease in nucleolar volume in these neurons, reflecting decreased cellular synthetic activity.     

Step-ahead spot price densities using daily synchronously reported prices and wind forecasts

This paper uses non-linear methodologies to follow the synchronously reported relationship between the Nordic/Baltic electric daily spot auction prices and geographical relevant wind forecasts in MWh from early 2013 to 2020. It is a well-known market (auctions) microstructure fact that the daily wind forecasts are information available to the market before the daily auction bid deadline at 11 a.m. The main objective is therefore to establish conditional and marginal step ahead spot price density forecast using a stochastic representation of the lagged, synchronously reported and stationary spot price and wind forecast movements. Using an upward expansion path applying the Schwarz (Bayesian information criterion [BIC]) criterion and a battery of residual test statistics, an optimal maximum likelihood process density is suggested. The optimal specification reports a significant negative covariance between the daily price and wind forecast movements. Conditional on bivariate lags from the SNP information and using the known market information for wind forecast movements at t₁, the paper establishes one-step-ahead bivariate and marginal day-ahead spot price movement densities. The result shows that wind forecasts significantly influence the synchronously reported spot price densities (means and volatilities). The paper reports day-ahead bivariate and marginal densities for spot price movements conditional on several very plausible price and wind forecast movements. The paper suggests day-ahead spot price predictions from conditional and synchronously reported wind forecasts movements. The information should increase market participants spot market insight and consequently make spot price predictions more accurate and the confidence interval considerably narrower.     

Protein O-GlcNAcylation regulates Drosophila growth through the insulin signaling pathway

Modification of nuclear and cytosolic proteins by O-linked N-acetylglucosamine (O-GlcNAcylation) is ubiquitous in cells. The in vivo function of the protein O-GlcNAcylation, however, is not well understood. Here, we manipulated the cellular O-GlcNAcylation level in Drosophila and found that it promotes developmental growth by enhancing insulin signaling. This increase in growth is due mainly to cell growth and not to cell proliferation. Our data suggest that the increase in the insulin signaling activity is mediated, at least in part, through O-GlcNAcylation of Akt. These results indicate that O-GlcNAcylation is one of the crucial mechanisms involved in control of insulin signaling during Drosophila development.     

On the usefulness of macroeconomic forecasts as inputs to forecasting models

A forecasting model for y_t based on its relationship to exogenous variables (e.g. x?_t) must use x?_t, the forecast of x?_t. An example is given where commercially available x?_t's are sufficiently inaccurate that a univariate model for y_t appears preferable. For a variety of types of models inclusion of an exogenous variable x?_t is shown to worsen the y_t forecasts whenever x?_t must itself be forecast by x?_t and MSE (x?_t) > Var (x?_t). Tests with forecasts from a variety of sources indicate that, with a few notable exceptions, MSE (x?_t) > Var (x?_t) is common for macroeconomic forecasts more than a quarter or two ahead. Thus, either:

• (a) available medium range forecasts for many macroeconomic variables (e.g. the GNP growth rate) are not an improvement over the sample mean (so that such variables are not useful explanatory variables in forecasting models), and/or
• (b) the suboptimization involved in directly replacing x?_t by x?_t is a luxury that we cannot afford.

     

The C4-dicarboxylate transport system ofRhizobium meliloti and its role in nitrogen fixation during symbiosis with alfalfa (Medicago sativa)

TheRhizobium meliloti C₄-dicarboxylate transport (Dct) system is essential for an effective symbiosis with alfalfa plants. C₄-dicarboxylates are the major carbon source taken up by bacteroids. Genetic analysis of Dct^– mutant strains led to the isolation of thedct carrier genedctA and the regulatory genesdctB anddctD. The carrier genedctA is regulated in free-living cells by the alternative sigma factor RpoN and the two-component regulatory system DctB/D. In addition, DctA is involved in its own regulation, possibly by interacting with DctB. In bacteroids, besides the DctB/DctD system an additional symbiotic activator is thought to be involved indctA expression. Further regulation ofdctA in the free-living state is reflected by diauxic growth of rhizobia, with succinate being the preferred carbon source. The tight coupling of C₄-dicarboxylate transport and nitrogen fixation is revealed by a reduced level of C₄-dicarboxylate transport in nitrogenase negative bacteroids.     

Forecasting for the generation of trading signals in financial markets

In this paper we show that optimal trading results can be achieved if we can forecast a key summary statistic of future prices. Consider the following optimization problem. Let the return r_i (over time i=1, 2, ..., n) for the ith day be given and the investor has to make investment decision d_i on the ith day with d_i=1 representing a ‘long' position and d_i=0 a ‘neutral' position. The investment return is given by r=Σⁿ_i=1r_id_i−cΣⁿ⁺¹_i=1∣d_i−d_i−1∣, where c is the transaction cost. The mathematical programming problem of choosing d₁, ..., d_n to maximize r under a given transaction cost c is shown to have an analytic solution, which is a function of a key summary statistic called the largest change before reversal. The largest change before reversal is recommended to be used as an output in a neural network for the generation of trading signals. When neural network forecasting is applied to a dataset of Hang Seng Index Futures Contract traded in Hong Kong, it is shown that forecasting the largest change before reversal outperforms the k‐step‐ahead forecast in achieving higher trading profits. Copyright © 2000 John Wiley & Sons, Ltd.     

Temporal Aggregation in Dynamic Linear Models

One important aspect concerning the analysis and forecasting of time series that is sometimes neglected is the relationship between a model and the sampling interval, in particular, when the observation is cumulative over the sampling period. This paper intends to study the temporal aggregation in Bayesian dynamic linear models (DLM). Suppose that a time series Y_t is observed at time units t and the observations of the process are aggregated over r units of time, defining a new time series Z_k=Σ^r_i=1Y_rk+i. The relevant factors explaining the variation of Z_k can, and in general will, be different, depending on how the sampling interval r is chosen. It is shown that if Y_t follows certain dynamic linear models, then the aggregated series can also be described by possibly different DLM. In the examples, the industrial production of Brazil is analysed under various aggregation periods and the results are compared. © 1997 John Wiley & Sons, Ltd.     

l-Methionin als Regulator der Spannung von Collagen

Summary Collagen fibres produce tension in hypermolar salt solutions such as 5M NaClO₄. This tension can be increased by formaldehyde 0.035M (or more). These reactions are reversible in 0.15M NaCl and can be repeated many times.l-Methionine in 0.01M solution inhibits the reversal. It is supposed that this effect is caused by inhibition of the aldol-aldimin reaction which restitutes the crosslink in the collagen fibre.     

Vorgänge bei pH-Änderung und bei Belichtung eines Anthocyanidins

Summary The anthocyanidin investigated here exists below pH 4 as a cationAH ₂ ⁺ (wave length of absorption maximum _max=459 mµ), between pH 5 and 7 in the neutral formAH ( _max=492 mµ) and above pH 8 as an anionA ^– ( _max=537 mµ). At pH 5 the freshly dissolved substance is partially converted into a colourless formBH ( _max=372 mµ) and a chemical equilibrium betweenAH andBH is reached within 1 h. A kinetic study of the process of formation ofBH shows that an intermediate productZ is formed. This process can be reversed by light exposure. It can be concluded from a kinetic investigation by using flash light thatBH is transformed by the absorbing light into a new substanceL ( _max 275 mµ and 225 mµ), andL changes partially intoBH, partially intoZ, which itself is transformed partially intoAH ₂ ⁺ ,AH,A ^–, partially intoBH. The reactionZ AH,AH ₂ ⁺ ,A ^– is proportional to the concentration of protons [H ⁺], the reactionZ BH independent of [H ⁺]. Thus a photochemical production ofAH ₂ ⁺ ,AH,A ^– fromBH is readily obtained in the presence ofH ⁺ and not obtained in the absence ofH ⁺.     

Electric charge in hyperbolic motion: the early history

The study of an electric charge in hyperbolic motion is an important aspect of Minkowski’s geometrical formulation of electrodynamics. In “Space and Time”, his last publication before his premature death, Minkowski gives a brief geometrical recipe for calculating the four-force with which an electric charge acts on another electric charge. The subsequent work of Born, Sommerfeld, Laue, and Pauli filled in the missing derivation details. Here, we bring together these early contributions, in an effort to provide a more modern, accessible, and unified exposition of the early history of the electric charge in hyperbolic motion.