尿素分子团簇线性和一阶非线性光学极化率的理论计算

检验分子晶体非线性光学极化率的可加性,对于确认有向气体模型(Oriented-Gas Model) 具有重要的科学意义,对探索新型实用的分子非线性光学材料也有实际的意义。本文对尿素晶体中分子簇非线性光学极化率的可加性做了详尽的理论研究。首次做到了尿素分子最近邻排布团簇的非线性光学极化率的从头算,从而扩展了前人的工作。研究结果有效地确认了有向气体模型。同时,我们还提出了壳层结构模型 (Shell-Structure Model),用以解决有向气体模型中的缺陷,可实现更为有效可靠地计算晶体宏观非线性光学系数。     

Could the New Absorption Cross Section of J/ψ Change the Aspect of Nuclear Absorption Mechanism

The enlarged new absorption cross sections of J/ψ by π and ρ were put into the hadron and string cascade model, JPCIAE, and the J/ψ suppression factors in P-A, O-U, S-U and Pb-Pb minimum bias collisions at 200A GeV/c were calculated with nuclear absorption mechanism only. The results seem to indicate that, with new enlarged cross section it is still hard to change the aspect that nuclear absorption mechanism itself could not easily account for the J/ψ anomalous suppression in Pb-Pb collisions.     

核形变对J/ψ压低的效应

用强子和弦级联模型,JPCIAE,研究(200A GeV)U+U中心碰撞中核形变对J/ψ压低的效应.结果表明:在两形变核的长轴都沿束流方向的碰撞中,J/ψ压低因子约为两长轴都垂直于束流方向碰撞时的二分之一.     

Comparison of inter- and intramolecular cyclodextrin complexes

Abstract

We present the first comparative steady-state and time-resolved fluorescence studies of inter- and intramolecular cyclodextrin complexes. Specifically, we report equilibrium and kinetic results for dansyl-glycine complexed with β-cyclodextrin (intermolecular) and the dansyl-glycine-β-cyclodextrin adduct (intramolecular). The fluorescence intensity decay profile for the intermolecular system is best described by a discrete triple exponential decay law. This is consistent with stepwise 1:1 and 2:1 (β-cyclodextrin:guest) inclusion complexation. Equilibrium constants are in line with previous results on similar species. In contrast, we found that the intramolecular case was described by a doubly exponential decay law—consistent with a single intramolecular inclusion complex. Displacement experiments, with borneol, confirm the simplicity of the intramolecular complex. In all cases, continuous distribution models failed to fit the experimental data.     

5-Bromobarbituric Acid : A Mild and Selective Monobrominating Agent Employed in the Synthesis of the Gastrin Antagonist GR174152

5-Bromobarbituric acid (5) is a convenient reagent for the selective bromination of cyclic imine 3. A facile, in situ synthesis of this reagent involving a disproportionation reaction between barbituric acid and dibromobarbituric acid is described.     

Irradiation and measurement devices and methods development for LSNAA applications at the TRIGA-ACPR core

A Large Sample Neutron Activation Analysis (LSNAA) facility has been developed at the TRIGA-Annular Core Pulsed Reactor (ACPR) operated by the Institute for Nuclear Research in Pitesti. The central irradiation cavity of ACPR can accommodate a large irradiation device. The ACPR neutron flux characteristics are well known and spectrum adjustment techniques have been successfully applied to enhance the thermal component of the neutron flux in the central irradiation cavity. An analysis methodology was developed by employing the MCNP (a general Monte Carlo N-particle transport code) code in order to estimate counting efficiency and correction factors for the major perturbing phenomena. The paper presents the development of the experimental device, the results of the neutron flux-spectrum characterization, and preliminary steps to validate the analysis methodology.     

Templated xerogels as platforms for biomolecule-less biomolecule sensors

We designed and synthesized new armed 12-oxacrown-3s bearing oxygen donor arms and forming encapsulated complexes with metal ions. The ISEs based on the single armed 12-oxacrown-3s exhibited Na⁺ ion selectivity, while the ISE based on the double armed 12-oxacrown-3 exhibited Li⁺ ion selectivity. The conformational analysis was performed on the free armed 12-oxaciown-3s and the non-encapsulated and the encapsulated armed 12-oxacrown-3 complexes using a semi-empirical method. The conformational analysis indicated that all armed 12-oxacrown-3s structurally prefer the Na⁺ ion rather than the Li⁺ ion. Further, it became apparent that the single armed 12-oxacrown-3s without a guest cation have the C_3v 12-oxaciown-3 ring and the double armed 12-oxacrown-3 without a guest cation has the bent 12-oxacrown-3 ring. The oxygens except carbonyl oxygens were directed toward the cation center in the structures of the complexes. It was clear that the ether and ester oxygens participate in the sidearm coordination.     

Lithium Polystyrene Sulfonate as a Hole Transport Material in Inverted Perovskite Solar Cells

Despite the exceptional efficiency of perovskite solar cells (PSCs), further improvements can be made to bring their power conversion efficiencies (PCE) closer to the Shockley-Queisser limit, while the development of cost-effective strategies to produce high-performance devices are needed for them to reach their potential as a widespread energy source. In this context, there is a need to improve existing charge transport layers (CTLs) or introduce new CTLs. In this contribution, we introduced a new polyelectrolyte (lithium poly(styrene sulfonate (PSS))) (Li:PSS) polyelectrolyte as an HTL in inverted PSCs, where Li⁺ can act as a counter ion for the PSS backbone. The negative charge on the PSS backbone can stabilize the presence of p-type carriers and p-doping at the anode. Simple Li:PSS performed poorly due to poor surface coverage and voids existence in perovskite film as well as low conductivity. PEDOT:PSS was added to increase the conductivity to the simple Li:PSS solution before its use which also resulted in lower performance. Furthermore, a bilayer of PEDOT:PSS and Li:PSS was employed, which outperformed simple PEDOT:PSS due to high quality of perovskite film with large grain size also the large electron injection barrier (ϕ_e) impeded back diffusion of electrons towards anode. As a consequence, devices employing PEDOT:PSS / Li:PSS bilayers gave the highest PCE of 18.64%.     

Comparison of dansylated aminopropyl controlled pore glass solvated by molecular and ionic liquids

We compare how (i) four ionic liquids (ILs) (1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]), 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpy][Tf2N]), and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P(C6)3C14][Tf2N])) and (ii) two conventional molecular liquids (methanol and 1-octanol) solvate/wet luminescent organic moieties that are covalently attached to the surface of silica controlled pore glass (CPG). A series of aminopropyl CPG particles that have been covalently tagged with the solvatochromic fluorescent probe group dansyl were used in this study. The results demonstrate that ILs solvate/wet the silica surface differently in comparison to molecular liquids (MLs). Specifically, when comparing ILs and MLs that appear to solvate the free probe, dansylpropylsulfonamide (DPSA), equally in solution, we find that ILs do not solvate/wet the silica surfaces as well as the corresponding MLs. The cation component in these ILs is the significant factor in how the ILs solvate/wet silica surfaces. Solvation/wetting of surface-bound species at a silica surface depends on the cation size. Chlorosilane end-capping of the surface silanol and amine residues attenuates the cation's affects.     

Structural and optical properties of thin films porous amorphous silicon carbide formed by Ag-assisted photochemical etching

In this work, we present the formation of porous layers on hydrogenated amorphous SiC (a-SiC: H) by Ag-assisted photochemical etching using HF/K₂S₂O₈ solution under UV illumination at 254 nm wavelength. The amorphous films a-SiC: H were elaborated by d.c. magnetron sputtering using a hot pressed polycrystalline 6H-SiC target. Because of the high resistivity of the SiC layer, around 1.6 MΩ cm and in order to facilitate the chemical etching, a thin metallic film of high purity silver (Ag) has been deposited under vacuum onto the thin a-SiC: H layer. The etched surface was characterized by scanning electron microscopy, secondary ion mass spectroscopy, infrared spectroscopy and photoluminescence. The results show that the morphology of etched a-SiC: H surface evolves with etching time. For an etching time of 20 min the surface presents a hemispherical crater, indicating that the porous SiC layer is perforated. Photoluminescence characterization of etched a-SiC: H samples for 20 min shows a high and an intense blue PL, whereas it has been shown that the PL decreases for higher etching time. Finally, a dissolution mechanism of the silicon carbide in 1HF/1K₂S₂O₈ solution has been proposed.