皮皮学，免费搜题
登录
搜题
【单选题】
当电梯运行到顶层或底层平层位置仍不能停产，继续向上或运行时，在没有（），以防电梯冲顶或墩底造成事故。
A.
供电系统断相、错相保护装置
B.
超越上、下极限工作位置的保护装置
C.
层门锁与轿门电气联锁装置
D.
慢速移动轿厢装置
拍照语音搜题，微信中搜索"皮皮学"使用
参考答案：
参考解析：
知识点：
.
..
皮皮学刷刷变学霸
举一反三
【单选题】听力原文：W: Did you meet the new teacher yesterday? M: I've been sick for three days. What does the man mean?
A.
The new teacher is sick.
B.
He hasn't met the teacher yet.
C.
He didn't like the teacher.
查看完整题目与答案
【简答题】Fill in the blanks by selecting suitable words from the word bank. You may not use any of the words more than once. A. hinge B. vary C. much D. particulates E. locating F. s...
查看完整题目与答案
【单选题】Write MATLAB codes to implement DSSS system sinmulation, The system is a 2-user system with a 2-path frequency selective fadingchannel for each user, The power for each path is half the total transmit...
A.
N_Trials=300; N_number=100; N_snr=10; N_users=2; N_path=2; Delay=1; Q=16; N_samples=N_number*Q; E_M=0; for trials=1:N_Trials trials noise=randn(N_users.*N_path,Q*N_number)+j.*randn(N_users*N_path,Q*N_number); s10=round(rand(N_users,N_number)); ss_user=s10*2-1;  % without consideration of delayed path pn01=round(rand(N_users,Q)); pn=(pn01.*2-1)./sqrt(Q); S_spread=[]; for user=1:N_users s=kron(ss_user(user,:), pn(user,:)); S_spread=[S_spread; s]; end S_multipath=[]; for user=1:N_users s_user=S_spread(user,:); Suser_delayed=[zeros(1,Delay), s_user(1,1:(N_samples-Delay))]; S_multipath=[S_multipath; [s_user;Suser_delayed]]; end %___________the following is to generate Rayleigh fading coefficients N=N_users.*N_path; fad_c=fading(8,0.005,N_samples, N); fad=fad_c.'; % only use the amplitude; %phase is not used, which is equivalent to have an ideal phase %compensation by using channel equalization S_spread=S_multipath.*fad; %S_spread is the signal matrix of size users x N_number sgma=1; Error_M=[ ]; for snr_db=0:1:N_snr snr=10.^(snr_db./10)/2;  %Evaluate the SNR from SNR in dB N0=2*sgma.^2; Eb=snr.*N0; yy=sqrt(Eb./2)*S_spread+noise;      %received spread signals in the baseband Error_v_user=[]; for user=1:N_users y_path1=yy((user-1).*N_path+1, :); y_path_temp=yy((user-1).*N_path+2, :); y_path2=[y_path_temp(1,Delay+1:N_samples), zeros(1,Delay)]; Y_M_path1=[ ]; Y_M_path2=[]; for k=1:N_number ym1=y_path1(1,(k-1)*Q+1:k*Q); ym2=y_path2(1,(k-1)*Q+1:k*Q); Y_M_path1=[Y_M_path1;ym1]; Y_M_path2=[Y_M_path2;ym2]; end % Y_M is a matrix of size N_number x Q, each row correspinding to a % BPSK symbol ys=Y_M_path1*pn(user,:).'+Y_M_path2*pn(user,:).'; %despreading for a user y=ys.'; y_real=real(y); s_e=sign(y_real); s_e10=(s_e+1)./2; Error_snr=sum(abs(s10(user,:)-s_e10)); Error_v_user=[Error_v_user;Error_snr./N_number]; %A BER collumn vector for all the users and for each snr end  %for user Error_M=[Error_M,Error_v_user]; %BER matrix for all users and for all the SNRs end  % end for snr E_M=E_M+Error_M ; end   % end for trials BER=E_M./N_Trials; BER_T=[ ]; for snr_db=0:1:N_snr snr=10.^(snr_db./10); temp=sqrt(snr./(1+snr)); BER_THEROY=(1-temp)/2; BER_T=[BER_T,BER_THEROY]; end i=0:1:N_snr; semilogy(i,BER(1,:),'-r',i,BER(2,:),'ob',i,BER_T ,'*g'); xlabel('E_b/N_0(dB)') ylabel('BER') legend('User1 RAKE','User2 RAKE', 'Theoretical flat fading');
B.
no need
C.
no need
D.
no need
查看完整题目与答案
【单选题】听力原文：Members of the I.M.F. approved reform. measures that aim to increase the voting power of countries with growing economies. As a first step, they agreed to increases in the voting rights for China...
A.
正确
B.
错误
查看完整题目与答案
【单选题】崔永元在讲父母对自己的影响时,没有提到的是
A.
与人为善
B.
诚实
C.
承担责任
D.
坦诚处事
查看完整题目与答案
【简答题】探视病人我们如何做才不失礼仪呢？
查看完整题目与答案
【单选题】What view did the three Milesian philosophers share?
A.
They all believed that the mythology had a basis in fact.
B.
They introduced a scientific approach to explaining nature.
C.
They thought that water was the original element.
D.
They all agreed with the teachings of Socrates.
查看完整题目与答案
【单选题】What did All egheny College in Meadvilledo three years ago?
A.
It tried to implement a novel financial aid program.
B.
It added $ 2.5 million to its need-based aid program.
C.
It phased out its merit-based scholarships altogether.
D.
It cuts its merit-based aid to help the needy students.
查看完整题目与答案
【判断题】姜半夏和法半夏的主要区别是:前者炮制所用辅料为姜和白矾,而后者所用辅料为甘草和白矾。
A.
正确
B.
错误
查看完整题目与答案
【单选题】What did all three main female characters have in common?
A.
Loved to cook.
B.
Depression.
C.
They were all writers.
D.
They loved and appreciated flowers.
查看完整题目与答案
相关题目：
【单选题】听力原文：W: Did you meet the new teacher yesterday? M: I've been sick for three days. What does the man mean?
A.
The new teacher is sick.
B.
He hasn't met the teacher yet.
C.
He didn't like the teacher.
查看完整题目与答案
【简答题】Fill in the blanks by selecting suitable words from the word bank. You may not use any of the words more than once. A. hinge B. vary C. much D. particulates E. locating F. s...
查看完整题目与答案
【单选题】Write MATLAB codes to implement DSSS system sinmulation, The system is a 2-user system with a 2-path frequency selective fadingchannel for each user, The power for each path is half the total transmit...
A.
N_Trials=300; N_number=100; N_snr=10; N_users=2; N_path=2; Delay=1; Q=16; N_samples=N_number*Q; E_M=0; for trials=1:N_Trials trials noise=randn(N_users.*N_path,Q*N_number)+j.*randn(N_users*N_path,Q*N_number); s10=round(rand(N_users,N_number)); ss_user=s10*2-1;  % without consideration of delayed path pn01=round(rand(N_users,Q)); pn=(pn01.*2-1)./sqrt(Q); S_spread=[]; for user=1:N_users s=kron(ss_user(user,:), pn(user,:)); S_spread=[S_spread; s]; end S_multipath=[]; for user=1:N_users s_user=S_spread(user,:); Suser_delayed=[zeros(1,Delay), s_user(1,1:(N_samples-Delay))]; S_multipath=[S_multipath; [s_user;Suser_delayed]]; end %___________the following is to generate Rayleigh fading coefficients N=N_users.*N_path; fad_c=fading(8,0.005,N_samples, N); fad=fad_c.'; % only use the amplitude; %phase is not used, which is equivalent to have an ideal phase %compensation by using channel equalization S_spread=S_multipath.*fad; %S_spread is the signal matrix of size users x N_number sgma=1; Error_M=[ ]; for snr_db=0:1:N_snr snr=10.^(snr_db./10)/2;  %Evaluate the SNR from SNR in dB N0=2*sgma.^2; Eb=snr.*N0; yy=sqrt(Eb./2)*S_spread+noise;      %received spread signals in the baseband Error_v_user=[]; for user=1:N_users y_path1=yy((user-1).*N_path+1, :); y_path_temp=yy((user-1).*N_path+2, :); y_path2=[y_path_temp(1,Delay+1:N_samples), zeros(1,Delay)]; Y_M_path1=[ ]; Y_M_path2=[]; for k=1:N_number ym1=y_path1(1,(k-1)*Q+1:k*Q); ym2=y_path2(1,(k-1)*Q+1:k*Q); Y_M_path1=[Y_M_path1;ym1]; Y_M_path2=[Y_M_path2;ym2]; end % Y_M is a matrix of size N_number x Q, each row correspinding to a % BPSK symbol ys=Y_M_path1*pn(user,:).'+Y_M_path2*pn(user,:).'; %despreading for a user y=ys.'; y_real=real(y); s_e=sign(y_real); s_e10=(s_e+1)./2; Error_snr=sum(abs(s10(user,:)-s_e10)); Error_v_user=[Error_v_user;Error_snr./N_number]; %A BER collumn vector for all the users and for each snr end  %for user Error_M=[Error_M,Error_v_user]; %BER matrix for all users and for all the SNRs end  % end for snr E_M=E_M+Error_M ; end   % end for trials BER=E_M./N_Trials; BER_T=[ ]; for snr_db=0:1:N_snr snr=10.^(snr_db./10); temp=sqrt(snr./(1+snr)); BER_THEROY=(1-temp)/2; BER_T=[BER_T,BER_THEROY]; end i=0:1:N_snr; semilogy(i,BER(1,:),'-r',i,BER(2,:),'ob',i,BER_T ,'*g'); xlabel('E_b/N_0(dB)') ylabel('BER') legend('User1 RAKE','User2 RAKE', 'Theoretical flat fading');
B.
no need
C.
no need
D.
no need
查看完整题目与答案
【单选题】听力原文：Members of the I.M.F. approved reform. measures that aim to increase the voting power of countries with growing economies. As a first step, they agreed to increases in the voting rights for China...
A.
正确
B.
错误
查看完整题目与答案
【单选题】崔永元在讲父母对自己的影响时,没有提到的是
A.
与人为善
B.
诚实
C.
承担责任
D.
坦诚处事
查看完整题目与答案
【简答题】探视病人我们如何做才不失礼仪呢？
查看完整题目与答案
【单选题】What view did the three Milesian philosophers share?
A.
They all believed that the mythology had a basis in fact.
B.
They introduced a scientific approach to explaining nature.
C.
They thought that water was the original element.
D.
They all agreed with the teachings of Socrates.
查看完整题目与答案
【单选题】What did All egheny College in Meadvilledo three years ago?
A.
It tried to implement a novel financial aid program.
B.
It added $ 2.5 million to its need-based aid program.
C.
It phased out its merit-based scholarships altogether.
D.
It cuts its merit-based aid to help the needy students.
查看完整题目与答案
【判断题】姜半夏和法半夏的主要区别是:前者炮制所用辅料为姜和白矾,而后者所用辅料为甘草和白矾。
A.
正确
B.
错误
查看完整题目与答案
【单选题】What did all three main female characters have in common?
A.
Loved to cook.
B.
Depression.
C.
They were all writers.
D.
They loved and appreciated flowers.
查看完整题目与答案