Command Interneurons in the Crayfish Central Nervous System

The motor effects evoked by stimulation of each of eight command fibres in the circumoesophageal commissures of the crayfish are described. The fibres obtained appeared to have widespread connexions in all or most of the lower ganglia. For certain fibres the response was stronger on the homolateral side of the animal; for others it was symmetrical. The frequency of stimulation of a command fibre generally had a pronounced influence on the speed of the evoked response. In addition, segments of the total response could be elicited selectively by alteration of the frequency and duration of stimulation. Although the responses associated with most of the fibres were not sensitive to the fine temporal pattern of the applied stimulation, for one fibre the motor output depended clearly on the spacing of the stimulating pulses

Gender Patterns in Vietnam's Child Mortality

We analyze child mortality in Vietnam focusing on gender aspects. Contrary to several other countries in the region, mortality rates for boys are substantially larger than for girls. A large rural-urban mortality difference exists, but much more so for boys than for girls. A higher education level of the mother reduces mortality risk, but the effect is stronger for girls than for boys.child mortality, gender differences, hazard rate, frailty model

Sediment management and the renewability of floodplain clay for structural ceramics

The Netherlands has vast resources of clay that are exploited for the fabrication of structural ceramic products such as bricks and roof tiles. Most clay is extracted from the so-called embanked floodplains along the rivers Rhine and Meuse, areas that are flooded during high-discharge conditions. Riverside clay extraction is-at least in theory-compensated by deposition. Based on a sediment balance (deposition versus extraction), we explore the extent to which clay can be regarded as a renewable resource, with potential for sustainable use. Beyond that, we discuss the implications for river and sediment management, especially for the large engineering works that are to be undertaken to increase the discharge capacities of the Rhine and Meuse. Extraction rates are based on production statistics for clay, as well as those for fired end-products. Deposition rates are estimated from published and unpublished geological data (clay volumes and thicknesses, datings, etc.) and from morphological modeling studies. Comparisons between extraction and deposition are made at three different time-space scales: (1) long term (post-1850)/large scale (all Dutch floodplains), (2) present/large scale, and (3) present/site scale. The year 1850 is relevant because it approximately marks the beginning of the current, fully engineered river systems, in which depositional processes are constrained by dikes and groynes. As the Industrial Revolution began in the same period, post-1850 sediments can be identified by their pollution with heavy metals. (1) We estimate the post-1850 clay volume in situ at about 0.20 km(3), and the total extracted volume in the same period at about 0.17 km(3). This puts the net long-term average deposition rate of clay at similar to 1.3 million m(3)/year and the corresponding extraction rate at similar to 1.1 million m(3)/year. (2) Current accumulation is approximately 0.4 million m(3)/year and expected to increase, and current extraction is about 0.7 million m(3)/year and expected to decrease. (3) Clay extraction creates a depression that has an increased sediment-trapping efficiency. This local effect is not considered explicitly in large-scale morphological modeling. Based on maximum observed sedimentation rates, we estimate that replenishment of a clay site takes in the order of 150 years. As clay extraction lowers some 0.5 km(2) of floodplain yearly, a surface area of approximately 75 km(2) would be required for sustainable clay extraction. This is about 1/6 of the total surface area of the embanked floodplains. On the long term, clay extraction from the embanked floodplain depositional environment has been sustainable. At strongly decreasing deposition rates, the ratio between extraction and replenishment seems to have shifted towards unsustainable. However, current sedimentation is estimated conservatively. The site-scale approach suggests that, even if extraction would currently exceed deposition, this could be resolved with sediment management, that is, with site restoration measures aimed at higher sediment-trapping efficiency. Our results have implications for river engineering, especially where substantial digging is involved (floodplain lowering, high-discharge bypass channels, obstacle removal). First, this inevitably affects the clay resources that we studied, while resource sterilization should be avoided. Secondly, the effect that any form of digging has on subsequent sedimentation-increased rates-relates to long-term river maintenance. We conclude that floodplain clay is a renewable resource, especially if managed accordingly. Beyond that, we established that clay extraction is a significant, lasting factor in floodplain evolution along the Rhine and Meuse Rivers. The interests of the extractive industry and river managers could be served jointly with sediment management plans that are based on sediment-budget analyse

Vibronic relaxation in molecular mixed crystals:Pentacene in naphthalene and p-terphenyl

Picosecond photon echo techniques are used to measure directly vibronic relaxation times in the first excited singlet state of pentacene in naphthalene and p-terphenyl. In regions of low (< 300 cm–1) and high (> 1000 cm–1) vibrational energy, relaxation is fast (τ <2 ps) due to direct phonon emission (low energy) and fast vibrational energy redistribution (high energy). In the intermediate region relaxation times vary drastically. Effects of isotope substitution of guest and host suggest intramolecular relaxation in this region. Changes in local environment are shown to influence the relaxation rate quite drastically, indicating large host-induced anharmonic coupling between different vibrations

Photon echoes stimulated from an accumulated grating:Theory of generation and detection

We present a theoretical description of the generation and detection of photon echoes, stimulated from an accumulated frequency grating in the inhomogeneous distribution. We show that detection of the echoes takes place via interference in the sample between a properly phased and directed probe pulse and the echo polarization. In this description the echo phenomenon emerges as an induced transparency of the sample rather than a burst of coherent radiation. By solving simultaneously the optical Bloch and Maxwell equations, an expression is obtained which correlates quantitatively the echo intensity to the decay parameters, pulse intensity, and the transition moment. As an application of the theory we present results on the intersystem crossing of pentacene in naphthalene at 1.5 K

Diphenylamino Radical Dimer as a Color Center in a Molecular Crystal

Radical pairs of diphenylamino (DPA) can be formed in a single crystal of tetraphenylhydrazine (TPH) by uv photolysis. The structure of these radical dimers can be elucidated by ESR measurements. These studies show that eight configurationally different dimers occur, which fall into two classes with 3- and 4-Å separation, respectively. Optical measurements reveal long-wavelength charge resonance absorptions arising from the dimers; this interpretation is supported by polarization measurements. Temperature-dependent ESR measurements were used to determine the singlet–triplet splittings of the two spin systems, yielding about 130 and 40 cm–1 for the 3- and 4-Å dimers, respectively. The radical dimer crystal defect can be regarded as a color center in a molecular crystal

Mapping Societal Risk. Main report

Het RIVM heeft in samenwerking met TNO twee methoden uitgewerkt om in een bepaald gebied de kans op een ongeval met een groot aantal slachtoffers (het groepsrisico) inzichtelijker te maken. Uitgangspunt is een zogeheten gebiedsgerichte benadering. Het groepsrisico wordt veroorzaakt door de aanwezige gevaarlijke stoffen in een gebied, zoals bij bedrijven en tijdens het transport ervan. De nieuwe benadering maakt het groepsrisico op een kaart inzichtelijk. In de oorspronkelijke, wetenschappelijke weergave in een grafiek ontbreekt dit overzicht. De methoden geven het groepsrisico (GR) weer op twee kaarten: de GR-gebiedskaart en de GR-bijdragekaart. De GR-gebiedskaart geeft inzicht in de grootte van het groepsrisico in een bepaald gebied. De GR-bijdragekaart zoomt in op de deelgebieden die het meeste bijdragen aan het groepsrisico. De twee kaarten zijn een aanvulling op de oorspronkelijke weergave, die het groepsrisico in een grafiek weergeeft. De kaarten worden bij voorkeur samen gebruikt bij het maken van beleid, zoals vergunningaanvragen of bestemmingsplannen. Daarnaast kunnen de kaarten worden ingezet bij de ontwikkeling van veiligheidsbeleid en de verantwoording van het groepsrisico door overheden. De methoden zijn in drie casussen getoetst op hun bruikbaarheid. Een voorbeeld is het vervoer van gevaarlijke stoffen over het spoor in Dordrecht. De resultaten van het onderzoek zijn in workshops voorgelegd aan betrokken partijen. Het onderzoek is in twee rapporten weergegeven. Het hoofdrapport beschrijft hoe je de methoden kunt toepassen. Het toelichtende rapport gaat in op de onderzoeksmethode.In collaboration with TNO, RIVM has elaborated two methods aimed at providing improved insight into the risk of a large number of individuals (societal risk) being involved in an accident in a certain area. The basic principle of these methods is the so-called area-specific approach in which societal risk is caused by hazardous materials present at a location, such as at industrial complexes or on units of a transportation system. By presenting societal risk on a map, this new approach provides increased insight, which was lacking in the graphical representation of the original, scientific presentation. Both methods present societal risk (SR) on a map: the SR-area map and the SR-contribution map. The SR-area map shows the level of the societal risk in a specified area; the SR-contribution map zooms in on the locations that contribute most to the societal risk. Both maps are supplements to the original presentation, which represents societal risk in graphical form. The maps are preferably used together when applied to policy-making, such as licence requests and land use planning. They can also be used by the appropriate governmental authorities for developing safety policy and in the justification process for policy-making on societal risk. The methods have been validated for usefulness in three case-studies, one of which is the transportation of hazardous materials by rail through the city of Dordrecht. The results of the study have been presented to all concerned parties. The study is described in two reports. The main report describes the usefulness of the methods. The explanatory report delves more deeply into the research methods used.VRO