Studies of chemisorbed tetracene on si(111)-7x7

The chemisorption of tetracene on the Si(111)-7x7 surface was studied using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. On the basis of the STM results and dimension analysis, two types of binding configurations were proposed. One of the configurations involves the di-sigma reaction between two C atoms of an inner ring with an adatom-rest atom pair on the substrate to give rise to an unsymmetrical butterfly structure. Tetracene in another configuration possesses four C-Si bonds that are formed via di-sigma reactions between the C atoms at the terminal rings with two center adatom-rest atom pairs within one-half of the surface unit cell. Besides, two other binding modes were proposed based on the dimension compatibility between the tetracene C and the substrate Si dangling bonds even though their identifications through the STM images are nonexclusive. Structural modeling and adsorption energies calculations were carried out using the DFT method. Factors affecting the relative thermodynamic stabilities based on the calculation results and the relative populations of tetracene in the different binding configurations as observed experimentally were discussed.     

Reversible switching of substrate activity of poly-N-isopropylacrylamide peptide conjugates

The activity of smart polymer peptide conjugates towards chymotrypsin catalyzed hydrolysis was reversibly switched on and off using temperature as the trigger.     

Regioselective hydroformylation of allylic alcohols

A highly regioselective hydroformylation of allylic alcohols is reported toward the synthesis of β-hydroxy-acid and aldehyde products. The selectivity is achieved through the use of a ligand that reversibly binds to alcohols in situ, allowing for a directed hydroformylation to occur. The application to trisubstituted olefins was also demonstrated, which yields a single diastereomer product consistent with a stereospecific addition of CO and hydrogen.     

Time- and wavelength-interleaved optical pulse train generation based on dispersion spreading and sectional compression

A method to generate time- and wavelength-interleaved optical pulse trains based on dispersion spreading and sectional compression is proposed and demonstrated. A 4×2 GHz time- and wavelength-interleaved pulse train is generated from an input 2 GHz mode-locked pulse train. The advantages of the proposed scheme are its simplicity and robustness, since no microwave component or multiwavelength laser source is required. In addition, we demonstrate supercontinuum generation of an ultraflat 18 nm bandwidth spectrum with less than 0.5 dB fluctuation over the 3.2 nm central bandwidth.     

Localized insulator-conductor transformation of graphene oxide thin films via focused laser beam irradiation

By scanning a focused laser beam over graphene oxide (GO) film deposited on SiO₂/Si substrates, conductive strips as small as 1 μm can be patterned directly either as a channel in the insulating matrix, or as a stand-alone micro belt. The conductivity was increased by at least two orders of magnitude with the mobility estimated in the range of 1–10 cm²/V s. Raman mapping and X-ray photoelectron spectroscopy studies demonstrated the reduction of GO in the laser-irradiated area. The conductance of the patterned channel was independent of the change in oxide-electrode contact resistance of the graphene, and increased linearly with increasing channel width. Increasing irradiation power by repeated scanning initially increased the conductivity of the irradiated area and saturated at a conductivity of ∼36 S/cm. Partial oxidative burning combined with photothermal reduction was identified as the underlying mechanism for the enhancement of the conductivity after laser irradiation on the GO film. Oxidative burning can be controlled by varying the film thickness and laser power.     

Noise conversion from pump to the passively mode-locked fiber lasers at 1.5 μm

We characterize the noise conversion from the pump relative intensity noise (RIN) to the RIN and phase noise of passively mode-locked lasers at 1.5 μm. Two mode locking mechanisms, nonlinear polarization rotation (NPR) and semiconductor saturable absorber mirror (SESAM), are compared for noise conversion for the first time. It is found that the RIN and the phase noise of both types of lasers are dominated by the noise converted from the pump RIN and thus, can be predicted with the measured pump RIN and noise conversion ratios. The SESAM laser is found to show an excess noise conversion from the laser RIN to the laser phase noise due to the slow saturable absorber effect.     

A pressure-based Mach-uniform method for viscous fluid flows

A pressure-based, Mach-uniform method is developed by combining the SLAU2 numerical scheme and the higher temporal order pressure-based algorithm. This hybrid combination compensates the limitation of the SLAU2 numerical scheme in the low-Mach number regime and deficiencies of the pressure-based method in the high-Mach number regime. A momentum interpolation method is proposed to replace the Rhie-Chow interpolation for accurate shock-capturing and to alleviate the carbuncle phenomena. The momentum interpolation method is consistent in addition to preserving pressure–velocity coupling in the incompressible limit . The postulated pressure equation allows the algorithm to compute the subsonic flows without empirical scaling of numerical dissipation at low-Mach number computation. Several test cases involving a broad range of Mach number regimes are presented. The numerical results demonstrate that the present algorithm is remarkable for the calculation of viscous fluid flows at arbitrary Mach number including shock wave/laminar boundary layer interaction and aerodynamics heating problem.     

Relative Entropy of Correct Proximal Policy Optimization Algorithms with Modified Penalty Factor in Complex Environment

In the field of reinforcement learning, we propose a Correct Proximal Policy Optimization (CPPO) algorithm based on the modified penalty factor β and relative entropy in order to solve the robustness and stationarity of traditional algorithms. Firstly, In the process of reinforcement learning, this paper establishes a strategy evaluation mechanism through the policy distribution function. Secondly, the state space function is quantified by introducing entropy, whereby the approximation policy is used to approximate the real policy distribution, and the kernel function estimation and calculation of relative entropy is used to fit the reward function based on complex problem. Finally, through the comparative analysis on the classic test cases, we demonstrated that our proposed algorithm is effective, has a faster convergence speed and better performance than the traditional PPO algorithm, and the measure of the relative entropy can show the differences. In addition, it can more efficiently use the information of complex environment to learn policies. At the same time, not only can our paper explain the rationality of the policy distribution theory, the proposed framework can also balance between iteration steps, computational complexity and convergence speed, and we also introduced an effective measure of performance using the relative entropy concept.     

Tin-free radical alkoxyamine addition and isomerization reactions by using the persistent radical effect: variation of the alkoxyamine structure

Various C-centered radicals can efficiently be generated through thermal C-O-bond homolysis of alkoxyamines. This method is used to perform environmentally benign radical cyclization and intermolecular addition reactions. These alkoxyamine isomerizations and intermolecular carboaminoxylations are mediated by the persistent radical effect (PRE). In the paper, the effect of the variation of the alkoxyamine structure--in particular steric effects in the nitroxide moiety--on the outcome of the PRE mediated radical reactions will be discussed. Fourteen different nitroxides were used in the studies. It will be shown that reaction times can be shortened about 100 times upon careful tuning of the alkoxyamine structure. Activation energies for the C-O-bond homolysis of the various alkoxyamines are provided. The kinetic data are used to explain the reaction outcome of the PRE-mediated processes.     

Selective attachment of 1,4-benzenedimethanethiol on the copper mediated Si(111)-(7 x 7) surface through S-Cu linkage

The well-defined and patterned copper clusters formed on the Si(111)-(7 x 7) surface have been employed as a template for selective binding of 1,4-benzenedimethanethiol (HS-CH2-C6H4-CH2-SH, 1,4-BDMT), to form ordered molecular nanostructures. Scanning tunneling microscopic (STM) studies showed that each 1,4-BDMT molecule preferentially binds to two neighboring copper atoms within one copper cluster through the S-Cu interaction with its molecular plane parallel to the surface, whereas some 1,4-BDMT bond to individually adsorbed copper atoms, resulting in an upright configuration. Large-scale two-dimensional molecular nanostructures can be obtained using this patterned assembly technique. Our experiments demonstrate the feasibility for controllable growth of ordered molecular nanostructures on the Si(111)-(7 x 7) surface.