Microwave Frequency Quadrupling Based on Distributed Feedback Laser and a Single Intensity Modulator

In this article, we have proposed and experimentally demonstrated a directly modulated distributed feedback laser (DFB-LD) to generate microwave and millimeter-wave signals. The proposed scheme uses DFB-LD and intensity modulator (IM) biased at null point. A radio frequency (RF) signal from a signal generator is split into two branches and one branch directly modulates the DFB-LD, while the other branch drives the IM. Two second-order sidebands separated by four times the frequency of the input RF signal are generated. Experimental results indicated that we can generate a four-fold microwave signal with a good optical signal to noise ratio.     

Non-revisiting genetic algorithm with adaptive mutation using constant memory

The continuous non-revisiting genetic algorithm (cNrGA) uses the entire search history and parameter-less adaptive mutation to significantly enhance search performance. Storing the entire search history is natural and costs little when the number of fitness evaluations is small or moderate. However, if the number of evaluations required is substantial, some memory management is desirable. In this paper, we propose two pruning mechanisms to keep the memory used constant. They are least recently used pruning and random pruning. The basic idea is to prune a unit of memory when the memory threshold is reached and some new search information is required to be stored, thus keeping the overall memory used constant. Meanwhile, both pruning strategies naturally form parameter-less adaptive mutation operators. A study is carried out to evaluate the impact on performance caused by loss of search history information. Experimental results show that (1) both strategies can maintain the performance of cNrGA, up to the empirical limit when 90 % of the search history is not recorded, (2) cNrGA and its variants with constant memory outperform the real-coded genetic algorithm and the standard particle swarm optimization. By pre-extracting all the current prune-able history information and storing them into a list, namely, to-prune-list, the overhead of both pruning strategies becomes small. This suggests that cNrGA can be extended to use in situations when the number of fitness evaluations is much larger than before with no significant effect on statistical performance. This widens the applicability of cNrGA to include more practical problems that require larger number of fitness evaluations before converging to the global optima.     

以交叉分子束及时间切片离子速度成像法研究产物成对相关讯息

研发了一种新颖的实验方法 ,用以在交叉分子束条件下测量双分子反应产物的成对相关 (paircorrela tion)讯息 .作为尝试 ,首先选取了F +CD4/CHD3 /CH4反应体系 .结合时间切片离子速度成像与交叉分子束技术 ,可直接测得产物态分辨且成对相关的角分布 .已研究了产物成对相关的几个方面 ,阐释了碰撞能效应 .测量表明 ,产物角分布对HF/DF产物振动态有极强的相关性 ,同时对甲基产物的振动态也有不可忽视的相关性 .在低碰撞能时 ,在F +CH4多原子反应中 ,首度发现了反应动态共振的证据 .     

Synthesis and Structures of d10–d10 M2(μ‐dppm)2 Complexes with Sensitive Metal–Metal Distances in Response to the Binding of Sigma Donors

Diphosphine‐bridged dicopper(I) acetate complexes [Cu₂(μ‐dppm)₂(μ‐OAc)]X ( 2 X; X^? = , ) and [Cu₂(μ‐dppm)₂(μ‐OAc)(MeCN)]X ( 4 X) were prepared and the structures of 2 (PF₆ ) and 4 (PF₆ ) determined by X‐ray crystallography. The ground‐state geometries of [Cu₂(μ‐dppm)₂(μ‐OAc)]⁺ and [Cu₂(μ‐dppm)₂(μ‐OAc)(L)]⁺ (L = py, MeCN, THF, acetone, MeOH) were also obtained using density functional theory (DFT). The increased Cu – Cu distances found experimentally and theoretically by comparing the structures of cation [Cu₂(μ‐dppm)₂(μ‐OAc)]⁺ and its derivatives [Cu₂(μ‐dppm)₂(μ‐OAc)(L)]⁺ reflect the binding of various sigma donors (L). When using [Cu₂(μ‐dppm)₂(μ‐OAc)]⁺ as a structure sensor, the electron‐donating strength of a sigma donor can be quantitatively expressed as a DFT‐calculated Cu – Cu distance with the relative strength in the order py > MeCN > THF > acetone > MeOH, as determined.     

Nanofluidic system for the studies of single DNA molecules

Here, we describe a simple and low-cost lithographic technique to fabricate size-controllable nanopillar arrays inside the microfluidic channels for the studies of single DNA molecules. In this approach, nanosphere lithography has been employed to grow a single layer of well-ordered close-packed colloidal crystals inside the microfluidic channels. The size of the polymeric colloidal nanoparticles could be trimmed by oxygen plasma treatment. These size-trimmed colloidal nanoparticles were then used as the etching mask in a deep etching process. As a result, well-ordered size-controllable nanopillar arrays could be fabricated inside the microfluidic channels. The gap distance between the nanopillars could be tuned between 20 and 80 nm allowing the formation of nanofluidic system where the behavior of a single lambda-phage DNA molecule has been investigated. It was found that the lambda-phage DNA molecule could be fully stretched in the nanofluidic system formed by nanopillars with 50 nm gap distance at a field of 50 V/cm.     

Preparation of cobalt-containing bulky monodentate phosphines with electron-withdrawing/donating substituents on bridged arylethynyl and their applications in Suzuki coupling reactions

Several cobalt-containing bulky monodentate phosphines (μ-PPh₂CH₂PPh₂)Co₂(CO)₄(μ,η-(^tBu)₂PCC(C₆H₄R)) (4a: R=H; 4b: R=p-F; 4cp: R=p-CF₃; 4cm: R=m-CF₃; 4d: R=p-OMe) were prepared from the reactions of (^tBu)₂PCC(R-C₆H₄) (2a: R=H; 2b: R=p-F; 2cp: R=p-CF₃; 2cm: R=m-CF₃; 2d: R=p-OMe) with Co₂(CO)₆(μ-PPh₂CH₂PPh₂) 3. Further reactions of 4a, 4b, 4cp, 4cm, and 4d with Pd(OAc)₂ yielded unique palladium complexes (μ-PPh₂CH₂PPh₂)Co₂(CO)₄(μ,η-(^tBu)₂PCC(C₆H₃R)-κC¹)Pd(μ-OAc) (5a: R=H; 5b: R=p-F; 5cp: R=p-CF₃; 5cm: R=m-CF₃; 5d: R=p-OMe, respectively). The strong electron-withdrawing substituents, -F and -CF₃, assist the ortho-metalation process during the formation of 5b, 5cp, and 5cm. The more positively charged palladium center in 5b (or 5cp, 5cm) enhances the probability for PhB(OH)₃⁻ to attack the metal center and the rate of reduction thereafter. DFT studies on the charges of these palladium centers support this assumption. The enhancement of the reaction rates of the Suzuki-Miyaura cross-coupling reactions using 5b, 5cp, and 5cm is thereby attributed to this effect.     

Ultrafast Spectroscopy Studies on Thickness Dependence of Acoustic Phonon Modes in Silver Nanoprisms

Time-resolved transient absorption technique is used to investigate the thickness dependence of acoustic phonon modes of silver nanoprisms with two thicknesses, 7.8 ± 1.2 and 8.5 ± 0.69 nm, and a similar bisector length of 31.4 ∼ 31.6 nm. Coherent acoustic phonon signals are observed. A new acoustic phonon frequency within 7.81 cm⁻¹ ∼ 11.7 cm⁻¹ is found and this phonon mode is associated with the thickness of the nanoprism. Another phonon frequency between 1.95 cm⁻¹ and 1.71 cm⁻¹ is also observed, and its origin can be associated with the bisector length of the nanoprism.