leach改进协议
选举方法采取 LEACH 协议的方法：每个节点随机产生一个 0~1 的数，如果这个数小于阈值 T ( n ) ，则该节点向周围节点广播它是簇头的消息
( 广播中包含 ID 和当前量 ) ，并加入候选簇首集合，如果通信范围内的相邻节点也为簇首，则在候选集合中比较两者的能量，能量小的退出集合作为普通节点。
在选举簇首时，考虑节点的剩余能量和节点到基站的距离，如果节点能量充足，距离基站较近则增大阈值
T ( n ) ，提高该节点成为簇首的概率，如果节点能量较低，距离基站较远，则降低阈值 T ( n ) ，减小该节点成为簇首的概率 。 T ( n )的计算公式为：
SHOW FULL COLUMNS FROM `jrk_downrecords` [ RunTime:0.001304s ]
SELECT `a`.`aid`,`a`.`title`,`a`.`create_time`,`m`.`username` FROM `jrk_downrecords` `a` INNER JOIN `jrk_member` `m` ON `a`.`uid`=`m`.`id` WHERE `a`.`status` = 1 GROUP BY `a`.`aid` ORDER BY `a`.`create_time` DESC LIMIT 10 [ RunTime:0.100012s ]
SHOW FULL COLUMNS FROM `jrk_tagrecords` [ RunTime:0.001130s ]
SELECT * FROM `jrk_tagrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 20 [ RunTime:0.001940s ]
SHOW FULL COLUMNS FROM `jrk_member` [ RunTime:0.001145s ]
SELECT `id`,`username`,`userhead`,`usertime` FROM `jrk_member` WHERE `status` = 1 ORDER BY `usertime` DESC LIMIT 10 [ RunTime:0.003622s ]
SHOW FULL COLUMNS FROM `jrk_searchrecords` [ RunTime:0.000957s ]
SELECT * FROM `jrk_searchrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 5 [ RunTime:0.003226s ]
SELECT aid,title,count(aid) as c FROM `jrk_downrecords` GROUP BY `aid` ORDER BY `c` DESC LIMIT 10 [ RunTime:0.014871s ]
SHOW FULL COLUMNS FROM `jrk_articles` [ RunTime:0.001201s ]
UPDATE `jrk_articles` SET `hits` = 1 WHERE `id` = 19674 [ RunTime:0.001454s ]
