长春单独考试研究生取得的学历是全日制的还是非全...

Copying Birds May Save Aircraft FuelBoth Boeing and Airbus have trumpeted the efficiency of their newest aircraft.The 787 and 350 respectively.Their clever designs and lightweightcompositescertainly make a difference.But a group of researchers at Stanford University,led by Ilan Kroo,has suggested that airlines could take a more naturalisticapproach to cutting jet-fuel use and it would not require them to buy newaircraft.The answer,says Dr Kroo,lies with birds.Since 1914,scientists have known thatbirds flying in formation-a V-shape-expend less energy.The air flowing over abird's wings curls upwards behind the wingtips.a phenomenon known asupwash.Other birds flying in the upwash experience reduced drag,and spendless energy propelling themselves.Peter Lissaman,anaeronautics expert whowas formerly at Caltech and the University of Southern California,has suggestedthat a formation of 25 birds might enjoy a range increase of 71%.When applied to aircraft,the principles are not substantially different.Dr Krooand his team modeled what would happen if three passenger jets departing fromLos Angeles,San Francisco and I as Vegas were to assemble over Utah,assume aninverted V-formation occasionally change places so all could have a turn in themost favourable positions,and proceed to London.They found that the aircraftconsumed as much as 15%less fuel（coupled with a reduction in carbon-dioxideoutput）.Nitrogen-oxide emissions during the cruising portions of the flight fellby around a quarter.There are,of course,knots to be worked out.One consideration is safety,or atleast the perception of it.Would passengers feel comfortable travelling incompanion?Dr Kroo points out that the aircraft could be separated by severalnautical miles,and would not be in the intimate groupings favoured by displayteams like the Red Arrows,A passenger peering out of the window might noteven see the other planes.Whether the separation distances involved wouldsatisfy air-traffic-control regulations is another matter,although a working groupat the International Civil Aviation Organisation has included the possibility offormation flying in a blueprint for new operational guidelines.It remains to be seen how weather conditions affect the air flows that makeformation flight more efficient.In zones of increased turbulence,the planes'wakes will decay more quickly and the effect will diminish.Dr Kroo says this isone of the areas his team will investigate further.It might also be hard for airlinesto co-ordinate the departure times and destinations of passenger aircraft in a waythat would allow them to gain from formation flight.Cargo aircraft,in contrast,might be easier to reschedule,as might routine military flight.As it happens,America's armed forces are on the on case already.Earlier thisyear the country'S Defence Advanced Research Projects Agency announcedplans to pay Boeing to investigate formation flight,though the programme hasyet to begin.There are reports that some military aircraft flew in formation whenthey were low on fuel during the Second World War,but Dr Lissaman says theyare unsubstantiated."My father was an RAF pilot and my cousin the skipper of aLancaster lost over Berlin,"he adds.So he should know
Formation flight is more comfortable because passengers can not see theother plans.

扑翼样震颤可见于肝性脑病的
A. 一期 B. 二期 C.三期 D.四期

男性，45岁。腰痛多年，时轻时重，伴双下肢后外侧痛。10天前搬重物后疼痛加重，并出现麻木与排尿困难。检査：腰活动受限，直腿抬高试验与加强试验阳性，鞍区痛觉减退。
该患者主要的治疗措施是

A.卧硬床休息
B.骨盆牵引及腰部理疗
C.硬脊膜外腰封闭
D.手术治疗

关于消化性溃疡大出血的叙述，下列哪项不正确？
A.胃溃疡出血多见于胃小弯 B.十二指肠溃疡出血多位于球部后壁 C.绝大多数可保守治疗止血 D. 60岁以上的老年患者心肺功能差，多采用保守治疗