Net Opening Research Articles

심해 저층트롤망의 수중형상에 관한 모형실험

A model experiment using circulation water channel was carried out to investigate the dynamic characteristics of bottom trawl net which can be used in sea mount of North Pacific. Hydrodynamic resistance and shape variation according to the flow velocity and angle of hand rope transformation for net were measured, and experimental value was analyzed as the value of full-scale bottom trawl net. The results summarized are as follows; At the <TEX>$30^{\circ}$</TEX> of angle of hand rope to net, hydrodynamic resistance varied from 0.5kgf to 2.68kgf as the flow velocity increased between 0.31m/s and 0.92m/s, and formula of hydrodynamic resistance for the model net was <TEX>$F_m=3.04\;{\cdot}\;{\upsilon}^{1.53}$</TEX>. At the fixed angle of hand rope, Net height was low and Net width was high according to the increase of flow velocity, and in addition, vertical opening was low and Net width was high by the increase of angle of hand rope at the fixed flow velocity. At the <TEX>$30^{\circ}$</TEX> of angle of hand rope to net, net opening area was <TEX>$0.214m^2$</TEX> as flow velocity was 0.61m/s, and formula of net opening area for the model net was <TEX>$S_m=-0.22{\upsilon}+0.35$</TEX>. At the <TEX>$30^{\circ}$</TEX> of angle of hand rope to net, catch efficiency seemed to be highest as <TEX>$0.319m^3/s$</TEX> of filtering volume at the 0.76m/s(51kt's) of flow velocity. Shape variation of net showed the gradual laminar transform for the variation of flow velocity but there needed some improvements due to the occurrence of shortening at the ahead of wing net.

Echolocating bats can use acoustic landmarks for spatial orientation

We investigated the echolocating bat's use of an acoustic landmark for orientation in a complex environment with no visual information. Three bats of the species Eptesicus fuscus were trained to fly through a hole in a mist net to receive a food reward on the other side. In all experiments, the vocal behavior of the bats was recorded simultaneously using a high-speed video recording system, allowing for a 3D reconstruction of the flight path. We ran three types of experiments, with different spatial relations between the landmark and net hole. In the first experiment, the bat's behavior was studied in test trials with the landmark placed 10 cm to the left of the net opening; between test trials, the positions of the net opening and landmark were moved, but the spatial relationship between the two remained fixed. With the landmark adjacent to the net opening, the bats quickly found the hole. In the second experiment, bats were tested in control trials in which the landmark was moved independently of the hole, breaking the established spatial relationship between the two. In control trials the bats repeatedly crashed into the net next to the landmark, and inspected the area around it. In the final experiment, the landmark was removed altogether from the set-up. Here the bats spent more time per trial searching for the net opening with an increased number of inspections as well as crashes into the net. However, over the course of a test day without the landmark, bats reduced the time spent per trial and focused inspections and crashes around the hole. The behavioral data show for the first time that the echolocating bat can learn to rely on an acoustic landmark to guide spatial orientation.

ECHO-ORIENTATION

Bats zooming through the air at dusk know where they're going, despite flying in near darkness; they detect their ultrasound calls bouncing off objects and use these echoes to find their way around. Marianne Jensen,Cynthia Moss and Annemarie Surlykke decided to see which of these numerous echoes bats rely on for orientation(p. 4399).Collecting big brown bats from attics in America and a colony in Canada,the team trained the animals to fly through a hole in a large net suspended across a dark room, rewarding them with a juicy mealworm. They placed a camera tripod next to the hole for the bats to use as an `acoustic landmark' that reflects their calls. To reconstruct the bats' flight path as the animals tried to locate their dinner, the team filmed them with high-speed cameras. They recorded the bats' calls to correlate these with their flight behaviour. When the team placed the tripod near the hole in the net, the bats had no trouble finding the hole. But when the team moved the tripod to another position, the bats crashed into the net next to the tripod and inspected the area of the net where the hole should have been; they clearly ignored the net's faint echoes and used the tripod as an acoustic landmark. When the team took the tripod out of the room, the frustrated bats spent even longer desperately searching for the net opening. The team concludes that bats can learn to rely on a single echo-reflecting object to figure out where to go.

기선권현망어업의 3척식 자동화 양망시스템 개발

This study was conducted in order to improve the automatic fishing operation system for anchovy boat seine by comparison with the fishing gear geometry and efficiency using the labor saving nets and the combined type net with midwater trawl. Field experiments were carried out to observe the geometry of nets and improve the fishing operation system by catcher boats. The vertical net opening of fore wing net, square, fore bag net and after bag net of the combined type net were varied in the range of 9.9~12.9. 16.2~28.2, 6.8~12.1 and 9.5~15.2m respectively, when the towing speed was 1.0m/sec and the distance between boats were 100m, 200m, 300m. The vertical net opening of the combined type nets was gradually decreased as function of with increasing the distance between catcher boats. Labor saving net which was maintained the net opening and towing depth stable was more suitable for the automatic hauling operation system by improvement of bag net rather than the combined type nets which was impossible in swallow depth and near to anchovy school. 3 boats hauling operation system of the labor saving net was carried out by crane with power block in 2 catcher boats for improvement of hauling operation and pushing equipment of anchovy cooking system in the processing boat for maintain more anchovy in dry frame. From the results of field experiments, 3 boats hauling operation system with power block and improved cooking system was very 3 boats hauling operation system with power block and improved cooking system was very useful and more practical as hauling time 20~35min and No. of fishermen 12~13 in comparison with the traditional system such as hauling time 30~50 min and No. of fishmen 28~38.

생력형 기선권현망 어구의 전개성능

기선권현망어업의 어구 개량과 조업시스템 개선을 목적으로 생력형어구를 제작하여 현장조업선에 의한 해상실험을 실시하여 어구의 형상과 조업시스템을 관찰한 결과를 요약하면 다음과 같다. 1. 생력형 어구의 양선간격에 따른 오비기 앞끝, 오비기, 수비, 앞창, 자루그물 입구, 깔때기, 자루그물 뒤끝의 망고 변화폭은 각각 5.0<TEX>${\sim}$</TEX>7.8, 14.4<TEX>${\sim}$</TEX>21.1, 16.2<TEX>${\sim}$</TEX>21.2, 14.0<TEX>${\sim}$</TEX>17.3, 11.7<TEX>${\sim}$</TEX>13.9, 5.4<TEX>${\sim}$</TEX>6.9, 8.2<TEX>${\sim}$</TEX>9.8m이었고, 각 부분의 실제 전개율은 50<TEX>${\sim}$</TEX>78, 25<TEX>${\sim}$</TEX>36, 24<TEX>${\sim}$</TEX>31, 31<TEX>${\sim}$</TEX>38, 61<TEX>${\sim}$</TEX>73, 71<TEX>${\sim}$</TEX>91, 87<TEX>${\sim}$</TEX>104%로 나타났다. 2. 생력형 어구는 그물목줄 부착으로 오비기 앞끝의 전개가 신속하게 이루어지고 있으며, 개량된 나발그물 부착으로 축소형 개량어구보다 포켓형상을 대폭 개선시켜 어군의 유도가 매우 원활하였다. 또한, 양선간격 및 예망속도 변화에 따른 어구 형상이 매우 안정되었으며, 망고의 변화 폭이 크지 않아 어구의 전개성능이 향상되었다. 3. 자루그물의 개량으로 어구저항 감소, 예망속도 증대 및 입망된 어군의 도피가 현저히 감소하여 어획량이 현용어구보다 증가하였으며, 조업시스템의 개선이 가능하였다. This study was conducted in order to improvement of fishing gear and fishing operating system for anchovy boat seine by labor saving improved nets. Field experiments were carried out observe geometry of nets and fishing operating system by catcher boats. The obtained results are summarized as follows : The Vertical net opening of fore wing net, wing net, inside wing net, square, fore bag net, flapper, after bag net of the labor saving improved net according to the distance between catcher boats were varied in the range of 5.0<TEX>${\sim}$</TEX>7.8, 14.4<TEX>${\sim}$</TEX>21.1, 16.2<TEX>${\sim}$</TEX>21.2, 14.0<TEX>${\sim}$</TEX>17.3, 11.7<TEX>${\sim}$</TEX>13.9, 5.4<TEX>${\sim}$</TEX>6.9, 8.2<TEX>${\sim}$</TEX>9.8m respectively, varied in the range of 50<TEX>${\sim}$</TEX>78, 25<TEX>${\sim}$</TEX>36, 24<TEX>${\sim}$</TEX>31, 31<TEX>${\sim}$</TEX>38, 61<TEX>${\sim}$</TEX>73, 71<TEX>${\sim}$</TEX>91, 87<TEX>${\sim}$</TEX>104% of the actual ratio of net opening in each part. Labor saving improved net was performed instant net opening in fore wing net and maintained stable net opening and towing depth by means of attached net pendant. Also, it was minimized as net pocket phenomenon leading to guide anchovy for more catch by means of attached body net. The opening in accordance with distance between catcher boats and towing speed. The catch of labor saving improved net was increased than traditional net due to decrement of net resistance by improvement of bag net leading to increasement of towing speed and reduction of escape anchovy as well as improve nets of whole operation system.

기선권현망 축소형 개량어구의 전개성능

기선권현망어업의 어구 개량과 조업시스템 개선을 목적으로 자루그물을 A, B 2가지로 달리한 축소형 개량어구를 설계, 제작하여 현장조업선에 의한 해상실험을 실시하여 어구의 형상을 관찰한 결과를 요약하면 다음과 같다. 1. 축소형 개량어구의 실제 전개율은 오비기에서 20% 정도로 가장 작았고, 뒤쪽으로 갈수로 커지며, 자루그물에서는 110% 정도로 가장 컸으며, B형이 A형에 비하여 5~10%정도 크게 나타났다. 자루그물 입구와 뒤끝의 망고 변화폭은 A형이 9.0~13.6, 9.3·10.4m이고, B형이 10.9~14.8, 5.8~8.0m로 나타나서 B형이 A형에 비하여 자루그물 입구는 1~2m 크고, 뒤끝은 2~3m 작았다. 2. 축소형 개량어구는 오비기의 수직방향 전개성능이 개선되어 수비에 이르기까지의 예망수층이 완만하게 형성되었으며, 예망수층의 변화폭이 기존어구에 비해 적게 나타났다. 나발 그물이 포켓형상을 개선시켜 그물코의 날림현상 감소와 수비에서 자루그물까지의 어구형상이 완만하게 이루어졌으며, 예망속도가 느린 경우에도 어구의 형상이 안정되었다. 3. 축소형 개량어구 B형은 자루그물의 변화폭이 적었고, 이중깔대기의 부착으로 인해 입망된 어군의 도피율이 감소하였다. This study was conducted in order to improvement of fishing gear and fishing operating system for anchovy boat seine by bag net A-type and B-type was attached with half size modified nets. Field experiments were carried out observe geometry of nets by catcher boats. The obtained results are summarized as follows : The actual ratio of net opening in each part of the half size modified nets was increased from fore part to back part of the nets as shown the smallest value about 20% in wing net and the biggest value about 110% in bag net. In addition, vertical net opening of B-type net as measured as 10.9~11.8m in fore bag net and 5.8~8.0m in after bag net were 1~2m greater than 9.0~13.6m of A-type one, and 2~3m less than 9.3~10.4m of A-type one, respectively. Vertical net opening of half size modified net was shown as less variation of towing depth from wing net to inside wing net than those of traditional nets due to stable vertical performance. The mesh distortion or drift and variation of vertical net opening were decreased by improvement of bag nets in order to minimized shape of net pocket phenomenon whenever towing speed is slow. Bag net B-Type attached with dual flapper was shown as less variation in width of bag net and less escapement of anchovy.

Refined calculation model for NaLA, a fishing net shape simulator, applicable to gill nets

: The purpose of the present paper was to describe the dynamic behavior of gill nets using the computer-aided simulation NaLA (net shape and loading analysis), a system that was developed for determining net shape and load. The general calculation model of the system was refined after considering gill net construction and the environment during operation, such as wave motion and the boundary conditions of the water surface and bottom. This method models a gill net as a group of lumped masses interconnected by springs without mass, which are arranged as knots, mesh bars, netting lines, and other rigging components. Equations of motion are then derived for each lumped mass point. Net shape, mesh opening angle, and tension distribution are estimated at each time-step by using a PC to solve the system of equations. To examine the applicability of the refined calculation model of NaLA to gill nets, experiments were conducted with a gill net in a water channel. The experimental and calculated net shape, loading, and mesh opening angles were compared. The results agreed well, confirming that the refined calculation model of NaLA for gill nets is applicable to estimate the dynamic behavior of gill nets.

Slip partitioning in the Sea of Marmara pull-apart determined from GPS velocity vectors

Dislocation modelling is used to examine the GPS velocity vectors for the Marmara Sea region. First, the vectors due to the known Anatolia/Eurasia rotation are reproduced by introducing structures that approximate the large-scale tectonics. Observed features of the smaller scale fault system in the Marmara region are then progressively included with slip amplitudes and directions adjusted to fit an 80-vector subset of the GPS data. The motion in the Marmara Sea region is partitioned with the faults that bound the north of the basin carrying more strike-slip motion than predicted from the Anatolia-Eurasia plate motion and faults to the south having a greater perpendicular component. Taken together however, there is no net opening across the Marmara Sea perpendicular to the overall trend of the boundary and thus deformation in the Marmara region results only from the pull-apart geometry of the North Anatolian fault. No extension related to the Aegean system is needed to explain the observations. The GPS results are consistent with motion over the last 5 Myr that has been determined from geological reconstructions.

Surface flocking as a possible anti-biofoulant

Fouling organisms create difficulties for aquaculturists by weighing down materials and constricting net openings. Research on anti-fouling began with toxic chemicals and has more recently moved to non-toxic methods focusing on settlement cues of invertebrates. Surface texture is one physical cue to which both invertebrate larvae and algal spores respond. Flocking is a process that makes smooth surfaces fibrous by adding electrostatically charged fibers to an adhesive coated surface. To test the effects of flocking on recruitment, polyvinyl chloride (PVC) plastic panels that were untreated, primed with adhesive, and flocked were deployed subtidally in the Westport River estuary, Westport, MA, USA for 1 month exposure periods in 1998. Species composition was determined and compared among treatments. To test for effects only on barnacle recruitment, wood panels were deployed subtidally in Clarks Cove, New Bedford, MA and PVC panels were deployed in the subtidal of Eel Pond, Woods Hole, MA; Cape Cod Canal at Massachusetts Maritime Academy, Bourne, MA; and in Point Judith Pond, RI. Flocking surfaces resulted in lower recruitment of green and brown algae, but had no effect on red algae. For invertebrates, flocking was effective at inhibiting the recruitment of encrusting animals, had no effect on stoloniferous animals, and increased the abundance of tube-building polychaetes and solitary ascidians.

Inhibitors of ethylene synthesis inhibit auxin-induced stomatal opening in epidermis detached from leaves of Vicia faba L.

Using leaf epidermis from Vicia faba, we tested whether auxin-induced stomatal opening was initiated by auxin-induced ethylene synthesis. Epidermis was dark-incubated in buffered KNO3 containing 0.1 mM alpha-napthalene acetic acid or 1 mM indole-3-acetic acid. Maximum net opening was ca. 4 micron after 6 h. Opening was reversed by 20 microM ABA, 0.1 mM CaCl2. 1-Aminocyclopropane carboxylic acid (ACC) synthase catalyzes synthesis of ACC, the immediate precursor to ethylene. Auxin-induced stomatal opening was fully inhibited by 10 microM 1-aminoethoxyvinylglycine (AVG), an ACC synthase inhibitor. In solutions containing AVG, auxin-induced opening was restored in a concentration-dependent manner by exogenous ACC, but not in control solutions lacking an auxin. ACC-mediated reversal of AVG-inhibition of stomatal opening was inhibited by alpha-aminoisobutyric acid (AIB), an inhibitor of ACC oxidase, the last enzyme in the ethylene biosynthetic pathway, by 10 microM silver thiosulfate (STS), an inhibitor of ethylene action, and by 20 microM ABA, 0.1 mM CaCl2. CoCl2, an inhibitor of ethylene synthesis, also inhibited auxin-induced opening. Both STS and CoCl2 inhibited opening induced by light or by fusicoccin, but neither light- nor fusicoccin-induced opening was inhibited by AVG. These results support the hypothesis that auxin-induced stomatal opening is mediated through auxin-induced ethylene production by guard cells.

Anomalies on capture nets of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae) following a sublethal chronic exposure to cadmium

A laboratory study on the sublethal effects of cadmium (Cd) on the net-spinning process of the larvae of Hydropsyche slossonae was conducted in order to assess the potential of net anomalies as an indicator of chronic exposure to Cd. Two major anomalies with different frequency levels were identified after chronic exposure to 0.37, 1.2, 11.6, 21.4 and 43.3 μg l −1 of Cd. The first was a distortion of the midline meshes where the diamond-shape structure is disrupted and the meshes are separated by extra strands (called ‘midline’ anomaly). The second aberration consisted of a distortion of the rectilinear structure of net opening by strands being fused or added over the meshes (called ‘crossover’ anomaly). The midline distortion may be linked to a physiological stress caused by Cd, which can affect the control of the net-spinning process. It was not possible to relate the crossover aberrations to a specific toxic action of Cd, but data indicated that both anomalies are independent from each other and that two modes of action could be implicated. Protein analyses of capture nets have revealed silk polypeptide modifications at the highest Cd concentration tested, indicating a possible effect of Cd interaction with silk proteins. However, neither a gradient-concentration nor a time-dependent response could be established with both aberration frequencies. Silk protein modifications would rather play a secondary role in the appearance of both net anomalies, and mostly at a high concentration level. Finally, the toxicity curves (EC 50) show that the sensitivity threshold for both types of aberration ranged from 1 to 5 μg l −1 which is highly sensitive compared with other sublethal effects of Cd on other macroinvertebrate species. Hence, the use of capture-net anomalies of hydropsychid larvae would represent a valuable indicator of sublethal toxicity induced by Cd and possibly by other metals in running waters.

Efficiency of the bottom trawl used for the Mediterranean international trawl survey (MEDITS)

The aim of the work presented in this paper was to assess the relative efficiency of the GOC 73 sampling trawl used for the Mediterranean international trawl survey programme (MEDITS) compared with that of a typical Italian commercial trawl. The latter was chosen because it is commonly used by fishermen in the central Adriatic, where the experiment was conducted, and therefore appeared as the best possible sampler of the commercial species present in those areas. Moreover, this trawl is similar to the various trawls used for the Italian national survey programme (GRUND). Four fishing trips were conducted between 1996 and 1997 in different areas and seasons to sample different species. Each trip was conducted in the same fishing area. A codend cover mounted on the commercial trawl ensured that the codends of the two nets had the same mesh opening. The two trawls were alternated daily. Net geometry (horizontal and vertical net opening) was measured during all tows. Catch data were converted into abundance per swept area before comparing the trawls. Efficiency comparisons were performed on ten fish species, one crustacean and four molluscs belonging to the MEDITS list of main reference species. The MEDITS trawl was significantly less efficient in terms of both weight and numbers of individuals fished for hake ( Merluccius merluccius), common sole ( Solea vulgaris) and Norway lobster ( Nephrops norvegicus). A highly significant difference in favour of the commercial trawl was found in the weight, but not the numbers, of common pandora ( Pagellus erythrinus). Efficiency differences were negligible for red mullet ( Mullus barbatus), while the MEDITS trawl was significantly more efficient for the numbers of Atlantic horse mackerel ( Trachurus trachurus). For all the other main reference species differences were not significant. The commercial trawl was more efficient for large individuals of some species. The relative efficiency of the MEDITS trawl was especially low for small-size classes of N. norvegicus. The results confirm the lower efficiency of the MEDITS compared with the commercial Italian trawl for benthic species, and its greater efficiency for some others released from the bottom as well as for the pelagic ones. These data allow the results of the MEDITS surveys to be compared with those of the GRUND programme and with commercial-fleet catches in areas where the commercial trawls used are similar to the one studied here.

Collection characteristics of a solar air heater with built-in net.

A solar air heater with a built-in net was proposed and the collection characteristics were experimentally investigated. Eight kinds of metallic nets, which had different transmissivity and opening fraction, were configured parallel in the space between the transparent cover plate and absorber. The temperature distribution within the air layer and pressure drop were measured, and the effects of the net transmissivity and opening fraction on the temperature distribution, collection efficiency and pressure drop were examined.When the metallic net was inserted in the solar air heater, the temperature distribution within the air layer was quite different and the collection efficiency became 16 to 35% higher than those of conventional solar air heaters and solar air heaters without a net. The collection efficiency had a maximum against the net transmissivity. By changing the net setting position, the pattern of temperature distribution was much affected while the collection efficiency was hardly affected. The pressure drop in the present solar air heater was higher than those in the conventional solar air heater and the solar air heater without a net, and had a maximum against the net transmissivity, i.e. the net opening fraction.

Sugar and Organic Acid Accumulation in Guard Cells of Vicia faba in Response to Red and Blue Light.

Changes in neutral sugar and organic acid content of guard cells were quantitated by high-performance liquid chromatography during stomatal opening in different light qualities. Sonicated Vicia faba epidermal peels were irradiated with 10 [mu]mol m-2 s-1 of blue light, a fluence rate insufficient for the activation of guard cell photosynthesis, or 125 [mu]mol m-2 s-1 of red light, in the presence of 1 mM KCl, 0.1 mM CaCl2. The low-fluence-rate blue light stimulated an average net stomatal opening of 4.7 [mu]m in 2 h, whereas the saturating fluence rate of red light stimulated an average net opening of 3.8 [mu]m in 2 h. Under blue light, the malate content of guard cells increased to 173% of the initial level during the first 30 min of opening and declined as opening continued. Sucrose levels continuously rose throughout the blue light-stimulated opening, reaching 215% of the initial level after 2 h. The starch hydrolysis products maltose and maltotriose remained elevated at all times. Under red light, guard cells showed very little increase in organic acid or maltose levels, whereas sucrose levels increased to 208% of the initial level after 2 h. Total measured organic metabolite concentrations were correlated with stomatal apertures in all cases except where substantial malate increases occurred. These results support the hypothesis that light quality modulates alternative mechanisms of osmotic accumulation in guard cells, including potassium uptake, photosynthetic sugar production, and starch breakdown.

Curved vein fibres: an alternative explanation

Veins occurring at the edge of the dextral Indian Islands Fault (Newfoundland) are folded in response to a fault-parallel, ductile shear. The veins, which locally constitute a penetrative fabric element at outcrop scale, are composed mainly of calcite and have a narrow rim of quartz and chlorite. Both the calcite and quartz are generally fibrous and lattice distortion in the calcite is not commensurate with the observed degree of fibre curvature. This observation supports the popular view that curved fibres grow curved as they track the vein opening vector. It is demonstrated, however, that the curvature in the material described here is due to deformation and that the lack of strong lattice distortion is due, in part, to polygonization and to recrystallization. All observations are consistent with both the calcite and the quartz fibres having grown perpendicular to the vein walls. The chlorite orientation is controlled by the orientation of mica grains in the country rock. In some veins, markers make it possible to define the net opening direction and, in all examples, it is demonstrated that the direction has not been tracked by the fibres. Since this conclusion may be more generally applicable, caution should be exercised in interpreting kinematics on the basis of fibre geometry. Where vein density is high, the veins and country rock screens separating them form a multilayer sequence that is folded into fairly harmonic folds. The folds appear to have a cleavage transected relationship to the regional cleavage, but the cleavage is shown to predate the folds.

Stomatal sensing of the environment

The effects of environmental factors on stomatal behaviour are reviewed and the questions of whether photosynthesis and transpiration control stomata or whether stomata themselves control the rates of these processes is addressed. Light affects stomata directly and indirectly. Light can act directly as an energy source resulting in ATP formation within guard cells via photophosphorylation, or as a stimulus as in the case of the blue light effects which cause guard cell H+ extrusion. Light also acts indirectly on stomata by affecting photosynthesis which influences the intercellular leaf CO2 concentration (Ci). Carbon dioxide concentrations in contact with the plasma membrane of the guard cell or within the guard cell acts directly on cell processes responsible for stomatal movements. The mechanism by which CO2 exerts its effect is not fully understood but, at least in part, it is concerned with changing the properties of guard cell plasma membranes which influence ion transport processes. The Ci may remain fairly constant for much of the day for many species which is the result of parallel responses of stomata and photosynthesis to light. Leaf water potential also influences stomatal behaviour. Since leaf water potential is a resultant of water uptake and storage by the plant and transpirational water loss, any factor which affects these processes, such as soil water availability, temperature, atmospheric humidity and air movement, may indirectly affect stomata. Some of these factors, such as temperature and possibly humidity, may affect stomata directly. These direct and indirect effects of environmental factors interact to give a net opening response upon which is superimposed a direct effect of stomatal circadian rhythmic activity.

Horizontal Ichthyoplankton Tow-Net System with Unobstructed Net Opening

Abstract The larval fish sampler described here consists of a modified bridle, frame, and net system with an obstruction-free net opening and is small enough for use on boats 10 m or less in length. The tow net features a square net frame attached to a 0.5-m-diameter cylinder-on-cone plankton net with a bridle designed to eliminate all obstructions forward of the net opening, significantly reducing currents and vibrations in the water directly preceding the net. This system was effective in collecting larvae representing more than 25 species of fish at sampling depths ranging from surface to 10 m and could easily be used at greater depths.

The drag of four-panel demersal trawls

Present techniques for predicting the drag of fishing nets are analysed. They are inaccurate when applied to modern demersal trawls, and they overestimate the significance of netmouth geometry. The measured net drag at constant speed does not vary significantly with the vertical net opening. Experimental results for 12 four-panel polythene trawls are used to derive the coefficients for a simple formula D=R { 61.2 + 46.6 V 2 (1 + 0.0641 V) } giving the net drag D in newtons when the twine area R is in m 2 and the speed V is in knots. The twine area is estimated from information normally found on a net specification. Thus no measured data are required to estimate the drag. The prediction error in applying the formula is typically around 10% and the worst case among the 12 trawls is 16%.

Film Thickness in Gas-Liquid Two-Phase Flow : 3rd Report, Effects of Obstacle Length and Gap between Obstacle and Tube Surface

The effects of a flow obstacle set in an air-water two-phase upward flow system are examined on the minimum film thickness occurring upstream and downstream of the obstacle. The obstacles used are several rings different in length and gap between the outer surface of the ring and the inner surface of the tube. Instantaneous flow appearance near the obstacle strongly depends upon the net opening ratio of the obstacle including the gap, which obviously affects the magnitude of minimum film thickness. With the same gap, the reverse flow through gap is pronounced with an increasing length of the obstacle. This leads to an increase of minimum film thickness upstream of the obstacle. The effects of the various parameters of obstacle such as shape, size and gap are summarized using all the experimental results so far obtained.

Cableを用いた超音波水中情報観測装置(日本航海学会第28回講演会)

This supersonic observing apparatus has a long-distance cable connected with the transducer and is to catch underwater information by transmitting and receiving supersonic waves from the transducer submerged in the water. The experiment as to this apparatus was done and the methods of it are as follows : (1) The method in midwater trawling By the operation of an indicator equipped in the ship, fitting the transducer to the head of a midwater trawling net through a long-distance cabtyre cable and transmitting and receiving the supersonic waves by the transducer, thus it measures the depth of the net, the height of net opening, the entering status of fish group into the net, etc. remotely from the ship. (2) The method in set net This method is to catch the status of fish group in the set net remotely from the land office by fitting the transducer to the buoy in the set net and then operating an indicator at the land office being connected with a long-distance cable. (3) The method of dropping down transducer This method is to observe the status of fish group, fry group, planktons, other living things, etc. by transmitting and receiving the supersonic waves in vertical or horizontal direction, positioning the transducer at each optional depth after dropping down it being connected with cable into the water. Further, it has been confirmed by the above experiment that a "Pre-Osc. Amp." is required in order to compensate the attenuation, which is increased by the cable for the supersonic observing apparatus when such cable used in especially long length and which influences clearly and interferes with their signal transmission.