Evidence of a semiannual reproductive cycle for the sea scallop, Placopecten magellanicus (Gmelin, 1791), in the mid-Atlantic region

The reproductive cycle of the sea scallop, Placopecten magellanicus in the mid-Atlantic region was studied over a 15 month period. One to 15 samples a month were collected from commercial vessels fishing from Long Island to Cape Hatteras in water depths of 37-68 m. Gonad weights were determined for four shell size intervals as an indicator of the reproductive cycle. A sharp decline in mean gonad weights between April-May 1987 and a subsequent increase and decrease in weights between SeptemberNovember 1987 indicated reproductive processes were occurring on a semiannual cycle. A major spring spawning season was reconfirmed in 1988 by a rapid increase in mean gonad weights between December 1987-January 1988, followed by variable declines in the weights through June. The occurrence of spawning activity for 2 consecutive spring seasons in addition to a fall spawning season suggests that a semiannual reproductive cycle may be a characteristic feature of P. magellanicus in the mid-Atlantic region. The ramifications of spring spawning to the mid-Atlantic sea scallop fishery and management policies are addressed

Gametogenic cycle of sea scallops (Placopecten magellanicus (Gmelin, 1791)) in the mid-Atlantic Bight

Gametogenesis of the sea scallop, Placopecten magellanicus , from 3 areas within the mid-Atlantic Bight was examined from January to December 1988. Histological and morphometric quantification of gonadal tissue concluded that a semiannual gametogenic cycle was characteristic of sea scallops from the mid-Atlantic Bight. The majority of spawning occurred in May and November. Gonadal development in spring comprised a longer period of time and resulted in greater fecundity than in fall. Differences were found in the timing and magnitude of the semiannual gametogenic processes between sex, area, and water depth within the study area. Varying temperature patterns between the mid-Atlantic Bight and more northerly resource areas may be partially responsible for the observed difference in gametogenic cycles. Semiannual spawning has potential implications for management strategies which are currently based on the assumption of annual spawning and recruitment events

The Random Discrete Action for 2-Dimensional Spacetime

A one-parameter family of random variables, called the Discrete Action, is defined for a 2-dimensional Lorentzian spacetime of finite volume. The single parameter is a discreteness scale. The expectation value of this Discrete Action is calculated for various regions of 2D Minkowski spacetime. When a causally convex region of 2D Minkowski spacetime is divided into subregions using null lines the mean of the Discrete Action is equal to the alternating sum of the numbers of vertices, edges and faces of the null tiling, up to corrections that tend to zero as the discreteness scale is taken to zero. This result is used to predict that the mean of the Discrete Action of the flat Lorentzian cylinder is zero up to corrections, which is verified. The ``topological'' character of the Discrete Action breaks down for causally convex regions of the flat trousers spacetime that contain the singularity and for non-causally convex rectangles.Comment: 20 pages, 10 figures, Typos correcte

Complex transitions to synchronization in delay-coupled networks of logistic maps

A network of delay-coupled logistic maps exhibits two different synchronization regimes, depending on the distribution of the coupling delay times. When the delays are homogeneous throughout the network, the network synchronizes to a time-dependent state [Atay et al., Phys. Rev. Lett. 92, 144101 (2004)], which may be periodic or chaotic depending on the delay; when the delays are sufficiently heterogeneous, the synchronization proceeds to a steady-state, which is unstable for the uncoupled map [Masoller and Marti, Phys. Rev. Lett. 94, 134102 (2005)]. Here we characterize the transition from time-dependent to steady-state synchronization as the width of the delay distribution increases. We also compare the two transitions to synchronization as the coupling strength increases. We use transition probabilities calculated via symbolic analysis and ordinal patterns. We find that, as the coupling strength increases, before the onset of steady-state synchronization the network splits into two clusters which are in anti-phase relation with each other. On the other hand, with increasing delay heterogeneity, no cluster formation is seen at the onset of steady-state synchronization; however, a rather complex unsynchronized state is detected, revealed by a diversity of transition probabilities in the network nodes

Multisensory information facilitates reaction speed by enlarging activity difference between superior colliculus hemispheres in rats

Animals can make faster behavioral responses to multisensory stimuli than to unisensory stimuli. The superior colliculus (SC), which receives multiple inputs from different sensory modalities, is considered to be involved in the initiation of motor responses. However, the mechanism by which multisensory information facilitates motor responses is not yet understood. Here, we demonstrate that multisensory information modulates competition among SC neurons to elicit faster responses. We conducted multiunit recordings from the SC of rats performing a two-alternative spatial discrimination task using auditory and/or visual stimuli. We found that a large population of SC neurons showed direction-selective activity before the onset of movement in response to the stimuli irrespective of stimulation modality. Trial-by-trial correlation analysis showed that the premovement activity of many SC neurons increased with faster reaction speed for the contraversive movement, whereas the premovement activity of another population of neurons decreased with faster reaction speed for the ipsiversive movement. When visual and auditory stimuli were presented simultaneously, the premovement activity of a population of neurons for the contraversive movement was enhanced, whereas the premovement activity of another population of neurons for the ipsiversive movement was depressed. Unilateral inactivation of SC using muscimol prolonged reaction times of contraversive movements, but it shortened those of ipsiversive movements. These findings suggest that the difference in activity between the SC hemispheres regulates the reaction speed of motor responses, and multisensory information enlarges the activity difference resulting in faster responses

Standardisierungswettbewerb zwischen parametrisierbarer Standardsoftware und komponentenbasierten Anwendungssystemen

Standardisierungswettbewerb zwischen parametrisierbarer Standardsoftware und komponentenbasierten Anwendungssystemen / Stefan Volkert ; Bernd Reitwiesner. - In: Information age economy / Hans Ulrich Buhl ... (Hrsg.). - Heidelberg : Physica-Verl., 2001. - S. 667-68