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排序方式: 共有3888条查询结果,搜索用时 15 毫秒
911.
Xuan Hoang Khoa Le Hakan F. Oztop Fatih Selimefendigil Mikhail A. Sheremet 《Entropy (Basel, Switzerland)》2022,24(4)
Heat transport augmentation in closed chambers can be achieved using nanofluids and extended heat transfer surfaces. This research is devoted to the computational analysis of natural convection energy transport and entropy emission within a closed region, with isothermal vertical borders and a heat-conducting solid fin placed on the hot border. Horizontal walls were assumed to be adiabatic. Control relations written using non-primitive variables with experimentally based correlations for nanofluid properties were computed by the finite difference technique. The impacts of the fin size, fin position, and nanoadditive concentration on energy transfer performance and entropy production were studied. It was found that location of the long fin near the bottom wall allowed for the intensification of convective heat transfer within the chamber. Moreover, this position was characterized by high entropy generation. Therefore, the minimization of the entropy generation can define the optimal location of the heat-conducting fin using the obtained results. An addition of nanoparticles reduced the heat transfer strength and minimized the entropy generation. 相似文献
912.
913.
914.
通过在钛宝石激光腔内引入望远镜长腔系统增加腔长,实现了重复频率低到10?MHz的飞秒激光振荡,在5?W的抽运功率下获得了平均输出功率200?mW、单脉冲能量20?nJ的稳定输出. 在此基础上分析了腔内不同色散情况下的输出脉冲光谱和脉宽特性,结果表明在腔内存在一定负色散的情况下,锁模脉宽可接近转换极限,最短脉宽可达56?fs. 而在正色散的情况下,锁模输出的脉宽较宽,并且随着腔内正色散的增多,脉宽可到大于600?fs,锁模光谱也呈马鞍形.
关键词:
钛宝石激光器
飞秒脉冲
低重复频率
望远镜腔 相似文献
915.
S. Unnikrishnan Nair C.D. Shete A. Subramoniam K.L. Handoo C. Padmanabhan 《Applied Acoustics》2010,71(1):61-67
Launch vehicle noise is broadband in nature and the noise transmitted into the payload fairing is reduced by treating its interior with an acoustic absorption layer. The latest generation payload fairings are made from composite material which offer poor noise attenuation at low frequencies. One possible solution for reducing the low frequency noise is to use Helmholtz resonators tuned to a few of the dominant low frequency components, such as shell ring frequency or the first few cavity modes of the fairing. The paper presents a simplified modelling approach for numerical simulation of a coupled cavity–resonator system which is validated by experiments. The influence of damping and resonator volume fraction on the coupled system performance, to suppress the first axial mode in a cylindrical cavity, is shown and the resonator volume fraction required for significantly (more than 5 dB) suppressing the cavity axial mode is established. 相似文献
916.
An experimentally feasible scheme for implementing
four-atom quantum dense coding of an atom--cavity system
is proposed. The cavity is only virtually excited and no quantum information will be
transferred from the atoms to the cavity. Thus the scheme is
insensitive to cavity decay and the thermal field. In the
scheme, Alice can send faithfully 4 bits of classical information to
Bob by sending two qubits. Generalized Bell states can be exactly
distinguished by detecting the atomic state, and quantum dense
coding can be realized in a simple way. 相似文献
917.
A novel Yb3+-doped fiber ring cavity laser pumped by a 977 nm laser diode is presented with its output laser wavelength of 1060 nm. Based on a fiber Bragg grating (FBG), the laser exhibits 0.20 nm line-width, 7.5 mW laser output power, 40 dB signal-to-noise ratio (SNR) and 66% slope efficiency. 相似文献
918.
Pranab K. Mukhopadhyay J. George S. K. Sharma K. Ranganathan T. P. S. Nathan 《Optics & Laser Technology》2002,34(5)
A practical method is described and used for determination of the effective stimulated emission cross-section (σe) in an operating diode pumped Nd:YVO4 micro-laser at 1064 nm with various doping concentrations. In this method a micro-laser is formed by keeping a small piece of the sample in a plane–plane resonator under semi-monolithic configuration and a fiber coupled diode laser (808 nm) was used for pumping. The pump power induced thermal lensing effect was used to make the cavity stable. In thermally stabilized solid-state lasers the cavity parameters change dynamically with the pump power and hence the overlap integrals become a function of the absorbed pump power. In our method the overlap integrals were estimated by measuring the thermal lens focal length at the threshold. The value of σe of Nd:YVO4 crystal with different doping concentrations obtained by this method were in well agreement with the reported values. 相似文献
919.
利用有限元方法求解:S-参数矩阵,研究了过模慢波结构对圆波导TM01,TM02模的反射特性,分析了在慢波结构末端加入谐振腔后,由于两端口的不对称性而造成的对反射特性影响。结果表明,在TM01的π模频率附近,慢波结构和谐振腔组成的系统对无谐振腔一侧端口入射TM01模的反射增大,而对有谐振腔一侧端口入射TM01模的反射减小。根据计算结果,解释了普通多波切伦柯夫振荡器所用慢波结构周期数较多的原因,说明了在多波切伦柯夫振荡器中引入谐振腔后,不但可以减少所用慢波结构周期数,而且有利于提高微波输出效率。 相似文献
920.