STUDY ON THE OPTIMUM DISTANCE BETWEEN CUTTING SLOTS FOR WEDGE PICKS

r The effect of the distance between cutting slots on the cutting specific energy consumption experimentally through cutting artificial coal samples with wedge picks is discussed in this paper. The optimum distances between cutting slots in different cut depths are presented, and the theoretical values are in good agreement with the experimental resurts.     

岩质边坡楔形体破坏的离心模型试验方法研究

叙述了岩质边坡楔形体破坏的离心模型试验,较详细地介绍了试验中模型材料选择和试块加工的过程,最后采用Hook方法和机动位移法对离心模型试验的结果进行了分析,得到了预期的试验成果。     

A torque evaluation for a rotary subsoiler

There are many models describing the work of rotary tillers, including torque evaluation. However, the work of a rotary subsoiler is different from that of a rotary tiller, which cuts the soil into pieces and throws them behind the machine. The rotary subsoiler acts on the soil with pressure similar to passive narrow tines. However, the existing models of forces acting on passive implements refer only to their linear movement. In this paper, a hypothesis has been made that the methods used in predicting the forces on soil cutting narrow tines may be applied to a rotary subsoiler, taking into consideration the subsequent positions of the working element in soil and including some corrections connected to the rotary movement of such a tine. On this basis a new mathematical model for predicting torque for a rotary subsoiler in different soils has been developed. Because no theoretical models describing the work of rotary subsoilers can be found, the prediction of the torque requirement may be very important for designers, as well as for other experts applying such machines in the field operations. After development the model was verified in experiments performed in a soil bin, which proved the model to be reliable.     

The effects of grading on the growth and survival of juvenile Dover sole (Solea solea L.)

A 3-month study was carried out to investigate the effects of grading on the overall production, growth performance and survival of juvenile Dover sole (Solea solea L.). Juvenile fish (4.0–40.4 g) were sorted into three size groups: small (4.0–15.5 g), medium (16.0–21.5 g) and large (22.0–40.5 g). In addition, a group of unsorted fish was followed for comparison. The fish from each sorted group and the unsorted group were divided between triplicate tanks at a stocking density of 1.5 kg m⁻². The fish were weighed and counted 21, 42, 63 and 92 days after stocking. In addition, 30 randomly chosen fish in each tank (=90 from each group) were individually tagged. The survival, size distribution, growth and productivity were calculated for small, medium, large and unsorted groups. In addition, comparisons were made between combined sorted and unsorted fish. There was no significant difference between the mean weight and distribution of sorted and unsorted fish by the end of the trial. An increased overall productivity in combined sorted fish was observed. Regular grading could therefore still be beneficial for sole farming as long as the grading interval supports maximum growth (in this case over 90 days). Survival was not significantly affected by the grading process.     

经济鳎类的疾病研究进展

近年来，随着经济鳎类养殖规模的不断扩大，各种病害也随之频繁发生。本文就国内外经济鳎类的疾病研究情况，阐述了引起鳎类爆发流行疾病的病原体，及该类疾病的病原检测、鉴定方法、防治方法、抗病基因的研究进展，以期为经济鳎类的疾病防治提供参考依据。     

杉木刨切试验研究

在对杉木节子进行水热软化试验和硬度测试基础上，对用杉木小径材制作的140mm×140mm×2000mm木方进行了刨切试验。结果表明：由于杉木节子多、硬度大，刨切前必须进行充分的水热软化处理，同时加大刨刀的楔角。建议刨刀楔角采用22°，当刨切厚度为1-2mm时水热处理的时间为28天；刨切厚度为3-4mm时水热处理时间为42天。     

An outbreak of toe ulcers,sole ulcers and white line disease in a group of dairy heifers immediately after calving

Abstract

CASE HISTORY: An outbreak of severe lameness was reported on a 780-cow spring-calving dairy herd in the Manawatu region within 1–3 weeks of calving, which affected over 90% of a group of 150 dairy heifers. Approximately 3 weeks before the planned start of calving heifers had been fed maize and grass silage on a concrete feed pad for 3–4 h per day, and mixed with a group of adult cows.

CLINICAL FINDINGS: During treatment for lameness, the feet of 28 lame heifers were closely examined. Seventy lesions were recorded in the claws of these heifers. The predominant lesion was severe solar and white line haemorrhage, with much of the haemorrhage focussed at the site at which sole ulcers are normally seen. White line disease was seen in nine claws and sole ulcers in four. Additionally, a lesion which is not commonly recorded in New Zealand, a toe abscess arising from separation of the white line from the sole in the abaxial region of tip of the toe was recorded in 11 claws. The clinical impression was that the soles of the affected heifers were very thin. This was supported by examination of the feet of eight heifers using ultrasonography that indicated heifers with hoof horn haemorrhages had very thin soles (estimated mean 4.1 mm) and that these soles were thinner than those in non-lame heifers without haemorrhages.

DIAGNOSIS: The pattern of disease seen in these heifers closely matched that seen in an outbreak of lameness in heifers in Florida, which was linked to thin soles resulting from excess hoof horn wear. The clinical signs and findings of the examination using ultrasonography strongly implicated thin soles as the underlying cause of lameness on this farm. An on-farm investigation revealed a combination of heifer behaviour and prolonged exposure to wet concrete on the feed pad were the primary causes of excess wear that resulted in thin soles.

CLINICAL RELEVANCE: This was an unusual outbreak of lameness in a group of newly calved heifers. The problem highlights the value of good management during the transition of heifers at pasture to the lactating herd standing on concrete for long periods, in the control of lameness.     

养殖密度对半滑舌鳎成鱼生长的影响

采用单因素试验方法,研究了不同养殖密度对半滑舌鳎生长的影响。试验设置400、500、600尾,池三种养殖密度梯度,选择同源、同批次且体重均为600g左右的半滑舌鳎成鱼在闭合式循环养殖系统中养殖153d。结果表明：不同养殖密度对半滑舌鳎体重的增长有显著影响（P〈0．05）,低密度组、中密度组和高密度组半滑舌鳎的体重平均增长量分别为671．35g、650．94g、474．07g,高密度组显著低于低、中密度组（P〈0．05）。随养殖密度的增大,半滑舌鳎的生长呈现减慢的趋势,并且出现了生长离差。分析表明,500尾,池的乔殖富度在实际养殖生产中较为适宜。结果提示,养殖密度是影响半滑舌鳎生长的一个重要因素,过高的密度会抑制半滑舌鳎的生长。     

供水及丁香酚对间作小麦蚕豆生长速率及籽粒产量的影响

为了寻求人工调控存在化感物质间作群体的理论依据,通过盆栽试验,探讨不同供水水平下(田间持水量的75%、60%和45%),小麦根系分泌物丁香酚对单作和间作蚕豆、小麦生长速率(Crop Growth Rate,CGR)及籽粒产量的影响。结果表明:在蚕豆苗期-始花期、结荚-成熟期2个生育阶段,丁香酚对蚕豆生长速率整体表现为抑制作用,但结荚-成熟期75%供水水平下的单作、60%供水水平下的间作除外,增加供水缓解了单作蚕豆的抑制作用、加剧了间作蚕豆的抑制作用,间作模式可缓解抑制;自苗期以后,丁香酚对小麦生长速率表现为抑制作用,且增加供水亦不能缓解抑制,但在开花-成熟期间作模式可以缓解抑制。在同等供水水平下,间作籽粒产量与单作籽粒产量的加权平均相比增加了24.92%-52.74%。丁香酚除对45%供水水平下小麦籽粒产量有化感促进作用以外,对两种作物的其他处理均呈现化感抑制作用。间作可弱化丁香酚对小麦、蚕豆籽粒产量的化感作用。