2-噻吩乙酸的HPLC分析测定

建立了一种2-噻吩乙酸的反相高效液相色谱-紫外检测法.研究了流动相的组成、流速及色谱柱温度等因素对测定的影响.采用色谱柱为VARIAN C18(250 mm×4.6 mm,5μm)反相色谱柱,流动相为甲醇-水(V∶V=70∶30),流速1.0 mL/min,柱温为室温,紫外检测波长235 nm,在6 min内可完成分析.该方法的回收率为98.4%~99.8%,RSD<1%.其优点为2-噻吩乙酸与其同分异构体3-噻吩乙酸得到较好的分离,明显不重叠,且操作简单、快速和准确可靠,用于2-噻吩乙酸产品的纯度测定,结果令人满意.     

Studies on physicochemical characteristics of chitosan derivatives with dicarboxylic acids

Chitosan (N-deacetylated derivative of chitin) was solubilised in different aqueous dicarboxylic acid solutions, including oxalic acid, malonic acid, adipic acid, azelaic acid and also in monocarboxylic acetic acid. These dicarboxylic acid solutions were used with the objective that they not only act as solvents but also enhance material properties of chitosan gel films through chemical cross-linking. The properties including conformational changes of chitosan, chemical interaction, and mechanical, morphological and thermal characteristics of selected chitosan samples studied in this work. The circular dichroism study indicated that the intensity of the broad negative transition of chitosan helical structure in the wavelength region of 190–230 nm decreased with decreasing the chain length of the dicarboxylic acids. The infrared spectra revealed the formation of amide linkage between chitosan and carboxylic acids in solid state. The cross-sections of the films produced from malonic acid and acetic acid solutions of chitosan exhibited granular morphologies with different granule sizes and hill-valley-structures under atomic force microscope. The chitosan/malonic acid film showed improved water resistance and decreased tensile properties compared with the chitosan/acetic acid and chitosan/adipic acid films. These physical characteristics of chitosan/malonic acid film are attributed to the dual effects of malonic acid, which acts as a chemical cross-linker and also as a plasticizer. A strong glass transition (T _g) peak at 166 °C in differential scanning calorimetric analysis was observed, indicating the possible plasticizing effect with malonic acid.     

Fracture strength of ion-exchange silicate-containing dental glass ceramics

Dental glass ceramics with the composition of (0.2K, 0.8Na)₂O–xAl₂O₃–ySiO₂ (x = 0.4–0.8, y = 4–6) were studied for their mechanical properties. Different ion-exchange practices were used to modify the sub-surface concentration distributions of K⁺, Na⁺, and H⁺ of these glass ceramics. Specimens were heat-treated in molten KNO₃, and NaNO₃ + KNO₃ salt baths at 350–450 °C for the ion exchanges of K⁺ and Na⁺, or in the 4% acetic aqueous solution at 85 °C for a hydration treatment. Some glass ceramics contained a feldspar crystalline phase, which was not affected by different ion-exchange practices. Specimens with a single ion-exchange process or with the hydration treatment had higher flexural strength than those without either of these two treatments. For double ion-exchange specimens, the flexural strength increased with decreasing ion-exchange temperature. The double ion-exchange specimens had flexural strength up to 280 MPa, which was slightly lower than that of the single ion-exchange specimens, but much higher than that of the as-annealed specimens. However, the Weibull modulus of these double ion-exchange specimens was 5–8 because of the presence of large defects. For further increasing mechanical reliability, silicate-containing dental glass ceramics were required to have appropriate flaw controls and ion-exchange processes.     

Low-temperature immobilization of liquid radioactive waste using silica from concentrated hydrothermal solutions

Experiments on vitrification of simulated liquid radioactive waste (LRW) were performed. To obtain solid glass-like phases, LRW components were treated with aqueous-alcoholic hydrochloric acid solutions containing hydrolyzates of alkyl silicates and aqueous silica sols obtained by membrane concentration of a natural hydrothermal solution. The pH of the mixture was 1.5–4. The characteristics of the solid samples obtained were studied by X-ray phase analysis, thermogravimetry, and scanning electron microscopy. A procedure was developed for low-temperature (5–60°C) immobilizaiton of low-level LRW using aqueous silica sols.     

Mathematical simulation of the azimuthal-radial distribution of temperature in a well in the presence of heat sources

The results of theoretical investigations of radial and azimuthal distributions of temperature in a well-rock system in the presence of heat sources are presented. The problem considered is connected with determination of the intervals of fluid motion outside the column by thermal methods. It is shown that in the case of long existence of the channel of fluid overflow outside the column, useful information can be obtained by creating a “contrast” temperature, for example, by heating the fluid inside the casing and subsequently measuring the azimuthal distribution of temperature in the process of its recovery on disconnection of a heater. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 80–82, September–October, 2006.     

A solvent extraction approach to recover acetic acid from mixed waste acids produced during semiconductor wafer process

Recovery of acetic acid (HAc) from the waste etching solution discharged from silicon wafer manufacturing process has been attempted by using solvent extraction process. For this purpose 2-ethylhexyl alcohol (EHA) was used as organic solvent. In the pre-treatment stage >99% silicon and hydrofluoric acid was removed from the solution by precipitation. The synthesized product, Na(2)SiF(6) having 98.2% purity was considered of commercial grade having good market value. The waste solution containing 279 g/L acetic acid, 513 g/L nitric acid, 0.9 g/L hydrofluoric acid and 0.030 g/L silicon was used for solvent extraction study. From the batch test results equilibrium conditions for HAc recovery were optimized and found to be 4 stages of extraction at an organic:aqueous (O:A) ratio of 3, 4 stages of scrubbing and 4 stages of stripping at an O:A ratio of 1. Deionized water (DW) was used as stripping agent to elute HAc from organic phase. In the whole batch process 96.3% acetic acid recovery was achieved. Continuous operations were successfully conducted for 100 h using a mixer-settler to examine the feasibility of the extraction system for its possible commercial application. Finally, a complete process flowsheet with material balance for the separation and recovery of HAc has been proposed.     

Nano structures through self-assembly of protected hydrophobic amino acids: encapsulation of rhodamine B dye by proline-based nanovesicles

The development of novel molecules for the creation of nanometer structures with specific properties has been the current interest of this research. We have developed a set of molecules from hydrophobic ω- and α-amino acids by protecting the –NH₂ with Boc (t-butyloxycarbonyl) group and –CO₂H with para-nitroanilide such as BocHN–Xx–CONH–(p–NO₂)·C₆H₄, where Xx is γ-aminobutyric acid (γ-Abu), (l)-isoleucine, α-aminoisobutyric acid, proline, etc. These molecules generate various nanometer structures, such as nanofibrils, nanotubes and nanovesicles, in methanol/water through the self-assembly of bilayers in which the nitro benzene moieties are stacked in the middle and the Boc-protected amino acids parts are packed in the outer surface. The bilayers can be further stacked one over the other through hydrophobic interactions to form multilayer structure, which helps to generate different kinds of nanoscopic structures. The formation of the nanostructures has been facilitated through the participation of various noncovalent interactions, such as hydrophobic interactions, hydrogen bonding and aromatic π-stacking interactions. Fluorescence microscopy and UV studies reveal that the nanovesicles generated from pro-based molecule can encapsulate dye molecules which can be released by addition of acid (at pH 2). These single amino acid based molecules are both easy to synthesize and cost-effective and therefore offer novel scaffolds for the future design of nanoscale structures.     

Templated synthesis of mesoporous aluminas by <Emphasis Type="Italic">graft</Emphasis> copolymer and their CO<Subscript>2</Subscript> adsorption capacities

Mesoporous aluminas were synthesized via a sol–gel process by templating an amphiphilic graft copolymer, PVC–g–POEM, consisting of a poly(vinyl chloride) (PVC) backbone and poly(oxyethylene methacrylate) (POEM) side chains. The mesoporous structures of aluminas with large surface areas were confirmed by X-ray diffraction, transmission electron microscopy, and nitrogen adsorption/desorption analysis. Aluminas synthesized with PVC–g–POEM graft copolymer exhibited higher CO₂ adsorption capacities (0.7 mol CO₂/kg sorbent) than aluminas synthesized without graft copolymer (0.6 mol CO₂/kg sorbent). The adsorption capacity of alumina strongly depends on its structure and calcination temperature; amorphous (400 °C) > γ phase (800 °C) > α phase (1000 °C).     

Bioconversion of poly(vinyl alcohol) to vanillin in a <Emphasis Type="Italic">Phanerochaete chrysosporum</Emphasis> culture medium

The bioconversion of Phanerochaete chrysosporium cultures in aqueous poly(vinyl alcohol) – PVAL – solutions was studied. A 50% weight loss was observed within 20 days, caused by a ligninperoxidase – LiP – enzyme which is produced during the secondary metabolism of Phanerochaete chrysosporium. The changes of the chemical structure of PVAL were studied by UV- and IR-spectroscopy. The presence of vanillin – the major metabolic reaction product, benzaldehyde, and veratrylalcohol was determined chromatographically (HPLC) in the extra cellular medium after different reaction times. A possible mechanism of the biological degradation is outlined.     

Liquid-liquid phase transition in aqueous solutions of <Emphasis Type="Italic">n</Emphasis>-hydrocarbons and amphiphiles

Phase transitions in ensembles of water clusters in aqueous solutions of C11–C28 n-hydrocarbons and C2–C12 amphiphiles have been studied as dependent on the concentration and size of dissolved molecules. A critical size (approximately corresponding to the volume of undecane molecule) for water clusters is determined, which triggers the phase transition that leads to the formation of bistable amphiphile micelles.     

Fluorinated polyimide–silica films with low permittivity and low dielectric loss

A sol–gel process was used to prepare polyimide–silica hybrid films from the fluorinated polyimide precursors (6FDA-ODA) and tetraethylorthosilicate (TEOS) in N,N-dimethyl acetamide. The hybrid film was then treated with hydrofluoric acid to remove the dispersed silica particles, leaving inside the film pores with diameters ranged from 80 nm to 1 μm, which depended on the size of the silica particles. The chemical structures and morphology of the hybrid and porous films were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The synthesized porous fluorinated polyimide films show low relative dielectric permittivity of 1.9, rendering them promising for microelectronic packaging materials.     

Hydrothermal synthesis of a nanostructured TiO<Subscript>2</Subscript>-based material in the presence of chitosan

Quasi-one-dimensional TiO₂-based nanostructures have been produced through hydrothermal treatment-without additives and in the presence of chitosan—of anatase nanopowder synthesized by an electrochemical sol-gel process. The morphology, phase composition, and structure of the hydrothermal synthesis products were studied by various physicochemical characterization techniques, including high-resolution electron microscopy, X-ray diffraction, and IR spectroscopy. The results demonstrate that the forming one-dimensional structures are isostructural with β-titanic acid, H₂Ti₃O₇. Heat treatment at t ≥ 500°C yields a mixture of sodium polytitanates, Na _y Ti _x O_{2x + 1}, with y = 0.5–2 and x = 2–5. The surface morphology and shape of the nanostructures persist up to 700°C. The key features of the formation of quasi-one-dimensional TiO₂-based structures in the presence of chitosan have been identified.     

Measurement of the instantaneous frequency of broadband signals in a short observation interval

A high-speed method of estimating the instantaneous frequency of broadband signals with slowly varying amplitude and phase using a short sample in real time is proposed, and results of numerical modeling of the measurement procedure are presented. The speed of response and noise immunity of the method is compared with the existing method, based on the theory of signal “splitting.” It is shown that in both methods it is possible to use recurrence relations, which considerably reduce the measurement time. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 50–54, February, 2008.     

Enhancement of the efficiency of i-n-GaN light-emitting diodes by electrochemical etching

An investigation was made of the electrochemical etching of i-n-GaN light-emitting diode structures in aqueous solutions of KOH and NaOH to remove parasitic low-resistivity layers and inclusions in the structures which shunt the active current flow channels through the structures and lower the electroluminescence intensity. The electroluminescence intensity of the structures increased by two or three orders of magnitude during the etching process. Pis’ma Zh. Tekh. Fiz. 25, 55–60 (January 26, 1999)     

Magnetoelectric performance of cylindrical Ni–lead zirconate titanate–Ni laminated composite synthesized by electroless deposition

The cylindrical Ni–lead zirconate titanate (PZT)–Ni laminated composites with various magnetostrictive–piezoelectric phase thickness ratios were synthesized by electroless deposition. The influences of the bias magnetic field (H _dc) and the ac magnetic field frequency (f) on magnetoelectric (ME) effect are discussed. It is seen that the ME voltage coefficient depends strongly on H _dc and f. The ME voltage coefficient and electromechanical resonance frequency increase as the magnetostrictive–piezoelectric phase thickness ratio increases. The calculated resonant frequency increases with the magnetostrictive–piezoelectric phase thickness ratio, which agrees well with the experimental results. The maximum ME voltage coefficient of the cylindrical Ni–PZT–Ni laminated composite is 3.256 V cm⁻¹ Oe⁻¹, which is much higher than that of the plate laminated composite with the same magnetostrictive–piezoelectric phase thickness ratio. Electroless deposition is an efficient method to prepare ME laminated composites with complex structures. Proper resonant frequency and stronger ME effect can be obtained by optimizing the structure.     

On laws governing the splitting failure of flat metallic specimens subjected to thermal shock

Computed and experimental data on the splitting failure of copper, nickel, titanium, molybdenum, brass, and bronze metallic foils from 0.005 to 1 mm thick under thermal shock initiated by the x-radiation of a nuclear explosion are presented. It is proposed that the concepts “average energy liberated over the thickness (mass) of the specimen” ε, “specific absorbed energy” W, and “splitting strength of the material” σ be used as criterial characteristics of failure thresholds of optically thin flat metallic specimens (foils). It is demonstrated that the critical average energy liberation ε_*, which results in splitting, decreases logarithmically (ε_* =A _*-B _*log Δ) with increasing thickness Δ of the irradiated specimens in the interval Δ≈0.001–1 mm, and the critical specific potential energy W_* reguired to effect splitting increases with increasing optical mass m of the specimen under the law W_*=−αmlog (βm), where A_*, B_*, α, and β are certain parameters. It is shown that the longevity of the copper, nickel, titanium, molybdenum, brass, and bronze under radiation-induced thermal shock decreases exponentially with increasing amplitude of the failing stress (splitting strength) and can be described on the basis of the kinematic concept of strength. Deceased. Translated from Problemy Prochnosti, No. 1, pp. 37–47, January–February, 1997.     

Effects of Mg,Fe, Be additions and solution heat treatment on the π-AlMgFeSi iron intermetallic phase in Al–7Si–Mg alloys

The presence of magnesium in Be-free Al–7Si–Mg alloys results in the formation of an undesirable iron-intermetallic known as the π-AlMgFeSi phase. The effect of Mg, Fe, and Be on the formation of this phase in both unmodified and Sr-modified Al–7Si–xMg–yFe alloys containing 0.4–0.8-wt% Mg and 0.1–0.8-wt% Fe has been investigated at a dendrite arm spacing of 65 μm. A qualitative microstructural examination was carried out to study the effect of solution heat treatment (540 °C/8 h) on the decomposition of the π-AlMgFeSi phase (“π-phase”) in Al–7Si–xMg–0.1Fe alloys containing 0.4–1.0-wt% Mg. The results indicate that increasing the Mg and Fe content increases the amount of the π-AlMgFeSi phase formed. Quantitative measurements revealed a reduction in the surface fraction of the π-phase after solution heat treatment. Different levels of decomposition of the π-phase into needles of β-Al₅FeSi iron intermetallic phase (“β-phase”) were observed at 0.4-, 0.6-, and 0.8-wt% Mg, after solution heat treatment.     

The secondary splitting of zero-gradient points in a scalar field

The mechanisms related to the secondary splitting of zero-gradient points of scalar fields are analyzed using the two-dimensional case of a scalar extreme point lying in a region of local strain. The velocity field is assumed to resemble a stagnation-point flow, cf. Gibson (Phys Fluids 11:2305–2315, 1968), which is approximated using a Taylor expansion up to third order. The temporal evolution of the scalar field in the vicinity of the stagnation point is derived using a series expansion, and it is found that the splitting can only be explained when the third-order terms of the Taylor expansion of the flow field are included. The non-dimensional splitting time turns out to depend on three parameters, namely the local Péclet number Pe _δ based on the initial size of the extreme point δ and two parameters which are measures of the rate of change of the local strain. For the limiting casePe _δ → 0, the splitting time is found to be finite but Péclet-number independent, while for the case of Pe _δ → ∞ it increases logarithmically with the Péclet number. The physical implications of the two-dimensional mathematical solution are discussed and compared with the splitting times obtained numerically from a Taylor–Green vortex.     

Effects of the molecular format of collagen on characteristics of electrospun fibres

Electrospinning is a process that is used to create nanofibres, which have the potential to be used in many medical and industrial applications. The molecular structure of the raw material is an important factor in determining the structure and quality of the electrospun fibres. In this study, we extracted collagen from a cold water fish species, hoki (Macruronus novaezelandiae), and prepared it in several different molecular formats (native triple helical collagen, denatured whole chains, denatured atelocollagen chains and gelatin) for electrospinning. Low molecular weight gelatin and atelocollagen did not form fibres. Treatment with 1,1,1,3,3,3 hexafluoro-2-propanol or 40% acetic acid denatured collagen molecules into intact α-chains prior to the electrospinning process. When using intact denatured collagen chains, 10% acetic acid was an effective aqueous-based solvent for producing uniform fibres. This information will be useful for the development of a non-toxic, aqueous solvent system suitable for industrial scale-up of the electrospinning process. Our results show that this low imino marine collagen is a suitable biopolymer for producing electrospun fibres.     

Effect of oxygen to argon ratio on the properties of thin SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films deposited by r.f. sputtering

Energy Dispersive X-ray and X-ray Photoelectron (XPS) spectroscopies show that SiO _x films deposited by reactive r.f. magnetron sputtering at partial pressure ratios R between oxygen and argon in a wide range (1–0.005) have compositions close to the stoichiometric one. For these films high temperature annealing at 1,000 °C shifts the band in the Fourier Transform-Infrared spectrum due to the Si–O–Si stretching vibration to values typical of stoichiometric SiO₂. Further decrease of R leads to splitting of the Si 2p XPS line indicating increase of the Si content and formation of a second phase in a SiO₂ matrix. The electrical properties of test MOS structures with SiO _x gate dielectric, regarding defect density in the oxide and at the SiO _x /c-Si interface, degrade with the decrease of R. High temperature annealing at 1,000 °C strongly improves the properties of all films regarding leakage current and properties of the interface.