Net Fence Research Articles

Design and research of automatic fishing machine based on acoustic adjustment

In this paper, an automatic fishing machine based on acoustic conditioning was developed and tested in a reservoir. The floating catcher is remotely and automatically controlled to operate underwater speakers, feeders and underwater cameras that monitor fish behavior in real time. The open net fence installed underneath the system can be automatically closed to catch captured fish. And in this paper, we monitor and discuss the dynamics of fish populations in the net box. With classic conditional reflexes, fish can associate sound signals with food. Also, in order to strengthen the conditioned behavior of fish swimming freely in the reservoir, we employ regular training. With the utility of an audible signal which is to attract fish around the catcher, the catcher can catch fish and automatically close the net fence around them: fish catches in this particular event are 2.5 times as much as ones in a controlled event. In controlled events, the net fence is automatically closed without summoning fish.

Reliability-Based Design of Protection Net Fences: Influence of Rockfall Uncertainties through a Statistical Analysis

Net fences are among the most widespread passive protective measures to mitigate the risk from rockfall events. Despite the current design approach being based on partial safety factors, a more efficient time-dependent reliability approach has been recently introduced by the authors. This method is influenced by various parameters related to the geometry and the kinematics of the block, i.e., the uncertainty related to the distribution of the size of the impacting block, its occurrence probability, and the shape of the right-tail of the distributions of its velocity and trajectory height at the location of the net fence. Furthermore, the block size distribution of the deposit greatly affects the results. The present work focuses on the possible range of such parameters to encompass the great majority of real events. The obtained results are compared with the current design approaches based on fixed partial safety factors. It emerges that the choice of the characteristic mass of the block and the failure probability greatly influence the results. Moreover, if a set of partial safety factors is assigned to different sites, an intrinsic variability in the failure probability has to be accepted. Suggestions for an accurate procedure and future developments are provided.

Dislocation of the metacarpophalangeal joint in a female red deer: Case report

The paper presents a post-traumatic anomaly of the metacarpal joint of a front limb of a female red deer, which was the cause of joint dislocation. This anomaly arose due to an incorrect positioning of the limb during movement, especially during fast running, most probably when the frightened animal was escaping from danger. Other mechanical causes cannot be excluded, such as entrapment of the limb in a net fence for crops and forest youngsters, which is commonly used to protect the forest from wild animals. The study showed that the resulting injury had led to secondary degenerative changes and deformities of the lopsided axis of the limb. The result was an incorrect directional orientation of the metacarpal bone and toes, and consequently of the hooves of the third and fourth fingertips. At the same time, the second and fifth toes, residual in this species, became retarded. The joint dislocation led to an incorrect positioning of the hooves during the animal’s movement and, consequently, to their excessive growth. These changes, however, despite their long-standing character, did not affect the animal’s condition, as evidenced by its carcass weight, which was above average for a female deer of this age and in this region of Poland.

Wind tunnel test on the effect of metal net fences on sand flux in a Gobi Desert, China

The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions: no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m (i.e., 13H, where H denotes the fence height) downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.

Efficiency of fishing gears in the river Halda, Chittagong, Bangladesh

To determine the catch efficiency of fishing gears, catch per unit effort (CPUE)data were collected for two years during January 2007 to December 2008 from the river Halda. Analyses were done to examine the variation of CPUE among gears, studied sections, months and years. The mean CPUE for pooled data of all gears was 2.247±0.265 kg.gear-1day-1 and 2.697±0.355 kg.gear-1day-1 for 2007 and 2008 respectively. Among eight gear categories, bag nets yielded the highest CPUE during 2007 (5.957±0.704 kg.gear-1day-1) and seine nets during 2008 (7.288±1.477 kg.gear-1day-1). Among 31 gear types, small meshed bag nets yielded the highest CPUE (18.065±6.660 and 15.69±4.479 kg.gear-1day-1 during 2007 and 2008 respectively). CPUE was highest during March-April and September-November periods. Analysis of variance showed significant difference among catch rates of different fishing gears. The CPUE differed significantly among different months for net fence, gill net, cast net and scoop net during 2007; and for seine net, net fence, bag net and cast net during 2008.

Efficiency of fishing gears in the river Halda, Chittagong, Bangladesh

To determine the catch efficiency of fishing gears, catch per unit effort (CPUE) data were collected for two years during January 2007 to December 2008 from the river Halda. Analyses were done to examine the variation of CPUE among gears, studied sections, months and years. The mean CPUE for pooled data of all gears was 2.247±0.265 kg.gear-1day-1 and 2.697±0.355 kg.gear-1day-1 for 2007 and 2008 respectively. Among eight gear categories, bag nets yielded the highest CPUE during 2007 (5.957±0.704 kg.gear-1day-1) and seine nets during 2008 (7.288±1.477 kg.gear-1day-1). Among 31 gear types, small meshed bag nets yielded the highest CPUE (18.065±6.660 and 15.69±4.479 kg.gear-1day-1 during 2007 and 2008 respectively). CPUE was highest during March-April and September-November periods. Analysis of variance showed significant difference among catch rates of different fishing gears. The CPUE differed significantly among different months for net fence, gill net, cast net and scoop net during 2007; and for seine net, net fence, bag net and cast net during 2008.

Overall efficiency of a V-shaped nylon net fence in preventing sand damage to the Mogao Grottoes

Overall efficiency of a V-shaped nylon net fence in preventing sand damage to the Mogao Grottoes

VIABILIDADE ECONÔMICA DA TERMINAÇÃO DE OVINOS EM CAPIM-TANZÂNIA COM QUATRO NÍVEIS DE SUPLEMENTAÇÃO CONCENTRADA

The economic viability of finishing sheep on Tanzania grass under intermittent grazing was evaluated with four concentrate supplementation levels (0; 0.6; 1.2 and 1.8% LW), two herd separation systems (electric and net fence) and three pasture sizes (1.0; 3.0 and 5.0 ha). The analysis was carried out to determine the minimal necessary conditions to have a viable business. Net income, benefitcost ratio, net present value and internal rate of return with an interest of rate of 8.75% per year were verified. The total implantation cost and maintenance to each system was estimated according to Fortaleza/CE market. Sale price between R$ 2.60 to 3.20/kg LW was considered to estimate total budget. The pasture sized 1.0 ha was economically unviable for both kinds of system tested. The system with net fence was more expensive than the one with electric fence. For the systems with supplementation, data showed viability only for a sale price above R$ 3.00/kg LW and, in some cases, in areas above 5.0 ha. KEYWORDS: concentrate supplementation; internal rate of return; Panicum maximum; profitability analysis; production system.

Different methods of using attractive sugar baits (ATSB) for the control of Phlebotomus papatasi

We have previously shown that fermented ripe fruit is a strong attractant for several mosquito species, and when mixed with oral insecticide these attractive toxic sugar baits (ATSB) were highly effective for local mosquito control. In the present study, we compared the effects of ATSB presented in different ways on isolated populations of Phlebotomus papatasi Scopoli. Experiments were carried out in the arid habitat of the Jordan valley, Israel where the effectiveness of three methods was compared: ATSB sprayed on patches of vegetation, net fence coated with ATSB, and bait stations soaked with ATSB. Spraying ATSB reduced the population to about 5% of the control area population. Barrier ATSB coated fences, had a similar effect decreasing the population to about 12% of the concurrent catch in the control site. The effect of ATSB presented on bait stations was much smaller and compared to the control, only caused the population to be reduced to 40%. In the control areas where only food dye marker was used, the solution presented on bait stations only marked an average of 22.3% of female sand flies while spraying vegetation and using barrier fences in the two other experiments marked about 60% of the females. Our experiments show that ATSB either sprayed on the vegetation or on barrier fences is an effective means against sand flies at least in arid areas where attractive plants are scarce or absent.

Technical Note: Design of rockfall net fences and the new ETAG 027 European guideline

Abstract. The need for protection against rockfall has led to the development of different types of technological solutions that are able to both prevent blocks from detaching from rock walls and to control, intercept or deviate the blocks during movement. Of the many devices that are able to intercept and stop a block, one of the most frequently used is net fence. Many different types of full-scale tests have been carried out, with different test site geometries and procedures to study their behaviour and to certify these devices. This has led to a series of data and information that are not easy to compare. The recent endorsement, by the European Organization for Technical Approvals (EOTA), of a European Technical Approval Guideline (ETAG), which defines how to test and assess the performance of a net fence, is therefore a great innovation that will change both the market and the design procedures of these devices. The most important innovations introduced by this new guideline are here presented and discussed and a net fence design procedure for protection against rockfall is provided.

Seasonal occurrence of thrips and its control with net fence and film mulch in fig orchards.

Seasonal occurrence of thrips and its control with net fence and film mulch in fig orchards.

折り曲げネットの囲いによるツケナ類のコナガ及びカブラハバチの侵入抑制

折り曲げネットの囲いによるツケナ類のコナガ及びカブラハバチの侵入抑制

Habitat Preferences of the White‐Tailed Deer and Several Exotic Ungulates in South Texas

During the fall of 1959 and the spring of 1960, 60 whitetailed deer (Odocoileus virginianus texanus), 28 mouflon sheep (Ovis musimon), 15 black-buck antelope (Antilope cerzicapra), 16 sika deer (Cervus nippon), and 6 axis deer (Axis axis) were introduced onto the H. B. Zachry ranch, 13 miles southwest of Laredo, Texas, in the southwestern corner of Webb County. A study2 of the habitat preference of each of these ungulates was conducted in the summer of 1961 on a 5,000-acre area of the ranch, circumscribed by an 8-ft net fence.