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1.
Design of a novel LED collimating element based on freeform surface   总被引:3,自引:0,他引:3  
A novel element for collimating LED light is designed based on non-imaging optics. It is composed of a refraction lens and a reflector. The upper surface of the lens is freeform and calculated by geometrical optics and iterative process. The lens makes the rays in the range of 0°-45°from the optical axis collimated. The rays in the range of 45°-90°from the optical axis are collimated by the reflector. The inner surface of the reflector is parabolic with its focus located in the LED chip. The designed element is applicable to LED source of any emitting type. For a certain application, the simulation results of the designed element in Tracepro show that it has a very compact structure and good collimating performance. Just investigating the loss in the lens surfaces, this element has high light output efficiency of nearly 99%. Most lighting area radii are no more than 20 mm when the illuminated plane is 5 m away from the LED source.  相似文献
2.
Junction network is a special type of roadwork pattern that scatters and distributes around the specific zone of metropolitan and in that contains different grade and functional roads of arterial road, urban freeway and expressway. Intelligent control is new development where the control problem is to find the combination of control measures that result for the best road performance and control effectiveness. The problems of multi-objective coordinated metering and evaluation for local ramp is considered. This paper discusses the optimal coordination of mainline and ramp, a modified ramp latency model is posed using the method of queuing theory, and a ramp control with better mechanism compare to artificial neural network using radical based function-support vector machine algorithm is designed. With in-situ traffic flow data of Beijing ring and radial freeway during high-density period, three known and the designed novel methodologies are compared, the intensive simulations show the effectiveness of the proposed approach, particularly at the aspect of minimize reduplicated waiting time for junction network. using these methodologies demonstrates the comparative control efficiency and accuracy.  相似文献
3.
Anisotropy is ubiquitous in solids and enhanced in low-dimensional materials. In response to an electromagnetic wave, anisotropic absorptive and refractive properties result in dichroic and birefringent optical phenomena both in the linear and nonlinear optics regimes. Such material properties have led to a diverse array of useful polarization components in the visible and near-infrared, but mature technology is non-existent in the terahertz (THz). Here, we review several novel types of anisotropic material responses observed in the THz frequency range, including both linear and circular anisotropy, which have long-term implications for the development of THz polarization optics. We start with the extreme linear anisotropy of macroscopically aligned carbon nanotubes, arising from their intrinsically anisotropic dynamic conductivity. Magnetically induced anisotropy will then be reviewed, including the giant Faraday effects observed in semiconductors, semimetals, and two-dimensional electron systems.  相似文献
4.
For conventional subcarrier pairing schemes in cooperative orthogonal frequency division multiplexing amplify and forward multi-relay networks, to avoid interference, each subcarrier pair (SP) is assigned to only one relay. Over a specific subcarrier, the destination receives signals transmitted from only one relay. In our subcarrier pairing scheme, we assign each SP to all the relays. Thus, over a specific subcarrier, the destination receives signals transmitted from all the relays. Since it is assumed that there exists the direct link from the source to the destination, we assume that the source also transmits signals during the second time slot for the direct transmission mode. We propose an enhanced joint subcarrier pairing and power allocation optimization scheme which maximizes the transmission rate subject to total network power constraint. The problem is simplified and solved by using dual method. It is shown from simulation results that our proposed scheme outperforms the other schemes.  相似文献
5.
Impulse radio is a low-complexity ultra-wideband system which is suitable for highly dispersive multipath channel. In this paper, we propose a random correlation-based receiver for impulse radio communications. The proposed receiver correlates the received pilot symbols with the randomly generated base functions according to channel statistics and forms the detection template by combining several base functions which have larger correlation coefficients with the pilot symbols. The proposed receiver demodulates the received signal by employing a symbol rate sampling. Computer simulation results have shown that the proposed receiver outperforms the conventional correlator-based receiver, compressive sensing correlator-based receiver, weighted energy detector and autocorrelation receiver.  相似文献
6.
For multiple-input multiple-output cognitive radio systems, we propose an optimal single transmit and receive antenna selection scheme which maximizes the signal-to-interference-and-noise ratio. Considering peak interference power constraint, peak transmit power constraint, and interference from primary transmitter to cognitive receiver, we theoretically derive the exact system outage probability. It is shown that the theoretical results match simulation results.  相似文献
7.
In this paper, considering the interferences from primary transmitter to secondary receiver and from secondary transmitter to primary receiver, we derive the upper and lower bounds of outage probability for underlay cognitive opportunistic multi-relay networks. Theoretical and simulation results show the upper and lower bounds converge to the exact outage probability at high interference-to-noise (INR) region. Because the interference from primary transmitter to secondary receiver is considered, an outage floor at high signal-to-noise ratio (SNR) occurs when INR increases proportionally with SNR.  相似文献
8.
Ultra-wideband (UWB) communication systems are expected to operate in a highly frequency-selective multipath fading environment. To exploit multipath diversity gains in a multiuser scenario, we developed a differentially-encoded, di-symbol time-division multiuser impulse radio (d2TD-IR) system with delay-sum autocorrelation receivers. In traditional time-division multiple access systems, each user transmits a single pulse during a symbol duration in a pre-assigned chip which is longer than maximum excess delay of the channel. However, due to the exponential decay property of UWB channel, we proposed the use of much shorter chip duration, which significantly increases the transmission rate. Because dense pulse transmission will induce multiuser interference, two time-hopping access sequences, which alternately encode the odd- and even-index symbols, are employed with delay-sum autocorrelation receivers to maximally suppress the interference. It was shown that when the chip duration is properly chosen, the proposed system outperforms the conventional time-hopping impulse radio system at high signal-to-noise ratio. This paper also proposed a method to estimate the optimal chip duration when only the average power decay profile of the UWB channel is known.  相似文献
9.
For transmitted-reference impulse radio, it has been experimentally shown that multiple transmit antennas can provide an energy boost in the received signal. Here, we propose a 2-transmit and Q-receive differential space-time block coded impulse radio with autocorrelation receiver. A mathematical model for predicting the system bit-error-rate (BER) performance is derived for intersymbol interference-free transmission over an ultra-wideband channel, and validated with computer simulated results. From the results, it is observed that in migrating from 1-transmit to 2-transmit antennas, a signal-to-noise ratio gain of 3 dB, 2 dB and 1 dB at BER = 10-5 can be achieved, respectively, for the case of 1-, 2- and 4-receive antennas.  相似文献
10.
由材料参数测试和器件响应率测试证实,LiNbO_3晶体的热释电响应率优值Mv为一般公认值的二倍。而且当温度升高时,Mv缓慢降低,并不出现某些文献所预示的明显增加。着重研究了LiNbO_3探测器在高功率密度连续激光辐照下的输出特性。研究结果表明,在相同条件下,LiNbO_3探测器的输出开始偏离线性所对应的最大功率密度远高于LiTaO_3。仔细测定了LiNbO_3晶体的固有介质损耗,并据此估计LiNbO_3器件探测率的极限值。分析表明,就制备背景限探测率的器件的潜力而言,LiNbO_3不低于TGS。  相似文献
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