Photoionization study of L-valine in the gas phase by vacuum ultraviolet synchrotron radiation

The photoionization and photodissociation of L-valine are studied by tunable synchrotron vacuum ultraviolet photoionization mass spectrometry at the photon energy of 13 eV. The ionization energy of L-valine and the appearance energies of major fragments are measured by the photoionization efficiency spectrum in the photon energy range of 8-11 eV. Possible formation pathways of the major fragments, NH(2)CHC(OH)(2)(+) (m/z=75), NH(2)(CH(3))(2)(CH)(2)(+) (m/z=72) and NH(2)CHCO(+) (m/z=57), are discussed in detail with the theoretical calculations at the B3LYP/6-31++G (d, p) level. Hydrogen migration is considered as the key way for the formation of NH(2)CHC(OH)(2)(+) (m/z=75) and NH(2)CHCO(+) (m/z=57). Furthermore, other fragments, NH(2)CHCOOH(+) (m/z=74), (CH(3))(2)(CH)(2)(+) (m/z=56), C(4)H(7)(+) (m/z=55), NH(2)CHOH(+) (m/z=46), NH(2)CH(2)(+) (m/z=30) and m/z=18, species are also briefly described.     

A three-layer PMMA electrophoresis microchip with Pt microelectrodes insulated by a thin film for contactless conductivity detection

A three-layer poly (methyl methacrylate) (PMMA) electrophoresis microchip integrated with Pt microelectrodes for contactless conductivity detection is presented. A 50 μm-thick PMMA film is used as the insulating layer and placed between the channel plate (containing the microchannel) and the electrode plate (containing the microelectrode). The three-layer structure facilitates the achievement of a thin insulating layer, obviates the difficulty of integrating microelectrodes on a thin film, and does not compromise the integration of microchips. To overcome the thermal and chemical incompatibilities of polymers and photolithographic techniques, a modified lift-off process was developed to integrate Pt microelectrodes onto the PMMA substrate. A novel two-step bonding method was created to assemble the complete PMMA microchip. A low limit of detection of 1.25 μg ml(-1) for Na(+) and high separation efficiency of 77,000 and 48,000 plates/m for Na(+) and K(+) were obtained when operating the detector at a low excitation frequency of 60 kHz.     

Strain stiffening of non-colloidal hard sphere suspensions dispersed in Newtonian fluid near liquid-and-crystal coexistence region

Concentrated hard sphere suspensions often show an interesting nonlinear behavior, called strain stiffening, in which the viscosity or modulus starts to increase at critical strain amplitude. Sudden increase of rheological properties is similar to shear thickening; however, the particle dynamics in the strain stiffening under oscillatory shear flow does not necessarily coincide with the mechanism of shear thickening under step shear flow. In this study, we have systematically investigated the nonlinear rheology of non-colloidal (>1???m) hard sphere suspensions dispersed in Newtonian fluid near liquid-and-crystal coexistence region in order to better understand the strain stiffening behavior. The suspensions near liquid-and-crystal coexistence region are known to locally form the closed packing structure. The critical strain amplitude which is the onset of strain stiffening was different for the storage and loss modulus. But they converged to each other as the suspension forms a more crystalline structure. The critical strain amplitude was independent of medium viscosity, imposed angular frequency, and particle size, but was strongly dependent upon particle volume fraction. The onset of strain stiffening was explained in terms of shear-induced collision due to particle motion in the closed packing structure. Nonlinear stress wave-forms, which reflect the micro-structural change, were observed with the onset of strain stiffening. During the strain stiffening, enhanced elastic stress before and after flow reversal was observed which originates from changes in the suspension microstructure. Nonlinearity of the shear stress in terms of Fourier intensity was extremely increased up to 0.55. Beyond the strain stiffening, the suspension responded liquid-like and the nonlinearity decreased but the elastic shear stress was still indicating the microstructure rearrangement within a cycle.     

A node-to-surface linear complementarity problem approach for general three-dimensional contact analysis

Meccanica - Contact between two deformable bodies is a complex nonlinear problem especially when rigid-body motion and geometric errors of components are taken into consideration. In this paper, an...     

Further Apéry-Like Series for Riemann Zeta Function

Mathematical Notes - By means of two transformation formulas of classical hypergeometric series, several Apéry-like series involving harmonic numbers of higher order are derived for the...     

Determinantal Evaluation of Four Wronskian Matrices

Ukrainian Mathematical Journal - Two determinants of Wronskian matrices are evaluated for the case where the matrix rows are partitioned into n blocks. Similar formulae are derived for the matrices...     

基于光谱学分析的聚氨酯弹性体/聚磷酸铵/氢氧化铝复合材料阻燃机理研究

采用熔融共混技术,将聚磷酸铵(APP)和氢氧化铝(ATH)引入到聚氨酯弹性体(TPU)中,制备了一系列热塑性聚氨酯/聚磷酸铵/氢氧化铝(TPU/APP/ATH)复合材料。采用傅里叶红外光谱(FTIR)、X-射线光电子能谱(XPS)、扫描电镜(SEM)、激光拉曼光谱研究了TPU和阻燃TPU(FR-TPU)复合材料燃烧后炭渣的微观形貌、表面结构、元素组成、键合状态和石墨化程度,结合阻燃性能测试,揭示APP和ATH的协同阻燃机制。SEM分析表明相较于APP与ATH单独使用,TPU/APP/ATH炭层的空洞结构更少,炭渣的致密性更高。XPS分析表明FR-TPU的炭渣中C元素含量相比于纯TPU有所降低,O元素的含量有所上升,其中TPU/APP10/ATH10的C元素含量从88.2%降至69.24%,O元素的含量从8.07%升至17.78%,P和Al元素含量相较于单独添加分别从11.74%和16.36%下降至3.91%和3.31%。在此基础上,通过对C元素的分峰拟合发现TPU炭渣中C—C/C—H,C—O/C—N和CO/CN含量分别为61.05%,35.65%和3.30%;TPU/APP10/ATH10炭渣中三种结构含量分别为45.38%,45.00%和9.63%,说明ATH和APP复配使用有利于C元素形成酯、醚、羰基、羧酸（盐）、酯基等结构。通过对O元素的分峰拟合发现,TPU炭渣中O₂/H₂O,—O—,O三种结构含量分别为28.75%,44.36%和26.89%;TPU/APP10/ATH10炭渣中O₂/H₂O,—O—,O三种结构含量分别为44.33%,32.78%和22.89%,说明APP和ATH的加入有利于炭渣中O元素形成O₂/H₂O结构。通过对N元素的分峰拟合发现,TPU炭渣中—NH—,N结构的N元素含量分别为40.93%和59.07%;TPU/APP10/ATH10中—NH—,N结构的N元素含量分别47.17%和52.83%,说明ATH与APP复配使用促进了—NH—结构的形成。拉曼测试表明,相比于单独使用,APP和ATH复配使用,炭层的石墨化程度更好,致密性更高。以上分析结合阻燃测试可以得出TPU/APP/ATH复合材料阻燃机制：ATH受热分解生成氧化铝,吸收热量并释放大量水蒸气,有效促进APP降解,生成不燃性的氨气和聚磷酸,氨气和水蒸气稀释可燃性气体的浓度。随着温度继续升高,氧化铝可继续与聚磷酸反应生成偏磷酸铝[Al(PO₃)₃],同步催化聚氨酯基体成炭,形成高度石墨化炭层,石墨化炭层与偏磷酸铝一起覆盖在基体表面,有效抑制燃烧区域物质以及能量的输运,从而达到阻燃目的。     

Homoclinic Orbits of a Quadratic Isochronous System by the Perturbation-incremental Method

In this paper, the perturbation-incremental method is presented for the analysis of a quadratic isochronous system. This method combines the remarkable characteristics of the perturbation method and the incremental method. The first step is the perturbation method. Assume that the parameter $\lambda$ is small, i.e. $\lambda\approx0$, the initial expression of the homoclinic orbit is obtained. The second step is the parameter incremental method. By extending the solution corresponding to small parameters to large parameters, we can get the analytical-expressions of homoclinic orbits.     

Anticancer Activity of 2-O-caffeoyl Alphitolic Acid Extracted from the Lichen,Usnea barbata 2017-KL-10

Colorectal cancer is one of the life-threatening ailments causing high mortality and morbidity worldwide. Despite the innovation in medical genetics, the prognosis for metastatic colorectal cancer in patients remains unsatisfactory. Recently, lichens have attracted the attention of researchers in the search for targets to fight against cancer. Lichens are considered mines of thousands of metabolites. Researchers have reported that lichen-derived metabolites demonstrated biological effects, such as anticancer, antiviral, anti-inflammatory, antibacterial, analgesic, antipyretic, antiproliferative, and cytotoxic, on various cell lines. However, the exploration of the biological activities of lichens’ metabolites is limited. Thus, the main objective of our study was to evaluate the anticancer effect of secondary metabolites isolated from lichen (Usnea barbata 2017-KL-10) on the human colorectal cancer cell line HCT116. In this study, 2OCAA exhibited concentration-dependent anticancer activities by suppressing antiapoptotic genes, such as MCL-1, and inducing apoptotic genes, such as BAX, TP53, and CDKN1A(p21). Moreover, 2OCAA inhibited the migration and invasion of colorectal cancer cells in a concentration-dependent manner. Taken together, these data suggest that 2OCAA is a better therapeutic candidate for colorectal cancer.     

Sn/carbon nanotube composite anode with improved cycle performance for lithium-ion battery

Anode material for lithium-ion battery based on Sn/carbon nanotube (CNT) composite is synthesized via a chemical reduction method. The Sn/CNT composite is characterized by thermogravimetry, X-ray diffraction, and transition electron microscopy. The Sn/CNT composite delivers high initial reversible capacity of 630.5 mAh g^?1 and exhibits stable cycling performance with a reversible capacity of 413 mAh g^?1 at the 100th cycle. The enhanced electrochemical performance of the Sn/CNT composite could be mainly attributed to the well dispersion of Sn nanoparticles on CNT and partially filling Sn nanoparticles inside the CNT. It is proposed that the chemical treatment of CNT with concentrated nitric acid, which cuts carbon nanotube into short pieces and increases the amount of oxygen-functional groups on the surface, plays an important role in the anchoring of Sn nanoparticles on carbon nanotube and inhibiting the agglomeration of Sn nanoparticles during the charge–discharge process.