The crystalline structures of carboxylic acid monolayers adsorbed on graphite

X-ray and neutron diffraction have been used to investigate the formation of solid crystalline monolayers of all of the linear carboxylic acids from C(6) to C(14) at submonolayer coverage and from C(8) to C(14) at multilayer coverages, and to characterize their structures. X-rays and neutrons highlight different aspects of the monolayer structures, and their combination is therefore important in structural determination. For all of the acids with an odd number of carbon atoms, the unit cell is rectangular of plane group pgg containing four molecules. The members of the homologous series with an even number of carbon atoms have an oblique unit cell with two molecules per unit cell and plane group p2. This odd-even variation in crystal structure provides an explanation for the odd-even variation observed in monolayer melting points and mixing behavior. In all cases, the molecules are arranged in strongly hydrogen-bonded dimers with their extended axes parallel to the surface and the plane of the carbon skeleton essentially parallel to the graphite surface. The monolayer crystal structures have unit cell dimensions similar to certain close-packed planes of the bulk crystals, but the molecular arrangements are different. There is a 1-3% compression on increasing the coverage over a monolayer.     

水热法制备近红外发光NaLa(WO4)2∶Ln(Ln=Er, Nd)球形粒子的研究

利用水热法制备了NaLa（WO4）2∶Ln（Ln=Er,Nd）球形粉末,分别用XRD,TEM和发光光谱等对粉末的物相、形貌、发光性质进行研究。XRD和SEM结果表明：制得的NaLa（WO4）2∶Ln（Ln=Er,Nd）粉末为白钨矿晶型,分散性良好,粒度均匀,呈规则的球形,粒径为1μm左右。发光光谱的测试表明：样品的最佳掺杂浓度为1.0%;随着煅烧温度的增加,样品发光强度逐渐增大;700℃下煅烧时最佳煅烧时间是4 h。     

1.54 and 1.75 μm infrared luminescence of Y2O3:Er

A new 1.75 μm infrared emission transition of Y₂O₃:Er³⁺ is assigned to the ⁴S_3/2 → ⁴I_9/2 transition of Er³⁺ ions situated at the C₂ sites of cubic RE₂O₃ (RE = Y, Gd, Lu). The intensities of features in the 1.54 μm ⁴I_15/2–⁴I_13/2 absorption transition due to Er³⁺ at S₆ and C₂ sites are consistent with the site occupation ratio and the relative magnetic dipole–electric dipole intensity contributions of Er³⁺ at the different sites. The 1.54 μm emission lines are predominantly from Er³⁺ ions at C₂ sites. The different behaviours of the emission intensities 1.75 and 1.54 μm groups with change in Er³⁺ dopant ion concentration, preparation technique, Yb³⁺ co-doping, temperature change and different excitation line are rationalized.     

Interfacial constraints on water and proton transport across nafion membranes

Water and proton transport across a Nafion membrane are measured as functions of water activity and applied electric potential with a polymer electrolyte hydrogen pump. Water and proton transport across the membrane must match water and proton transport entering and leaving the electrode/membrane/vapor three phase interfaces at the anode and cathode. At low applied electric potential proton and water fluxes are correlated. At moderate to high applied electric potential the proton current is constant, independent of applied electric potential, while the water transport increases with increasing electric potential. At high applied electric potential water and proton transport become uncoupled at the membrane interfaces; water is transported across the membrane/vapor interface and protons are transported across the membrane/electrode interface. The applied electric potential drives electro‐osmosis to redistribute the water in the membrane. Water redistribution is limited by the interfacial transport of water across the membrane/vapor interface. © 2015 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2015 , 53, 1580–1589     

A new approach for calculating the real stability radius

We present a new fast algorithm to compute the real stability radius with respect to the open left half plane which is an important problem in many engineering applications. The method is based on a well-known formula for the real stability radius and the correspondence of singular values of a transfer function to pure imaginary eigenvalues of a three-parameter Hamiltonian matrix eigenvalue problem. We then apply the implicit determinant method, used previously by the authors to compute the complex stability radius, to find the critical point corresponding to the desired singular value. This corresponds to a two-dimensional Jordan block for a pure imaginary eigenvalue in the parameter dependent Hamiltonian matrix. Numerical results showing quadratic convergence of the algorithm are given.     

High-throughput analysis by SP-LDI-MS for fast identification of adulterations in commercial balsamic vinegars

Balsamic vinegar (BV) is a typical and valuable Italian product, worldwide appreciated thanks to its characteristic flavors and potential health benefits. Several studies have been conducted to assess physicochemical and microbial compositions of BV, as well as its beneficial properties. Due to highly-disseminated claims of antioxidant, antihypertensive and antiglycemic properties, BV is a known target for frauds and adulterations. For that matter, product authentication, certifying its origin (region or country) and thus the processing conditions, is becoming a growing concern. Striving for fraud reduction as well as quality and safety assurance, reliable analytical strategies to rapidly evaluate BV quality are very interesting, also from an economical point of view. This work employs silica plate laser desorption/ionization mass spectrometry (SP-LDI-MS) for fast chemical profiling of commercial BV samples with protected geographical indication (PGI) and identification of its adulterated samples with low-priced vinegars, namely apple, alcohol and red/white wines.     

Temperature effect on porous silicon luminescence

A theoretical surface-state model of porousilicon luminescence is proposed. The temperature effect on the PhotoLuminescence (PL) spectrum for pillar and spherical structures is considered, and it is found that the effect is dependent on the doping concentration, the excitation strength, and the shape and dimensions of the Si microstructure. The doping concentration has an effect on the PL intensity at high temperatures and the excitation strength has an effect on the PL intensity at low temperatures. The variations of the PL intensity with temperature are different for the pillar and spherical structures. At low temperatures the PL intensity increases in the pillar structure, while in the spherical structure the PL intensity decreases as the temperature increases, at high temperatures the PL intensities have a maximum for both models. The temperature, at which the PL intensity reaches its maximum, depends on the doping concentration. The PL spectrum has a broader peak structure in the spherical structure than in the pillar structure. The theoretical results are in agreement with experimental results.