The gas chromatographic determination of volatile fatty acids in wastewater samples: Evaluation of experimental biases in direct injection method against thermal desorption method

The production of short-chained volatile fatty acids (VFAs) by the anaerobic bacterial digestion of sewage (wastewater) affords an excellent opportunity to alternative greener viable bio-energy fuels (i.e., microbial fuel cell). VFAs in wastewater (sewage) samples are commonly quantified through direct injection (DI) into a gas chromatograph with a flame ionization detector (GC-FID). In this study, the reliability of VFA analysis by the DI-GC method has been examined against a thermal desorption (TD-GC) method. The results indicate that the VFA concentrations determined from an aliquot from each wastewater sample by the DI-GC method were generally underestimated, e.g., reductions of 7% (acetic acid) to 93.4% (hexanoic acid) relative to the TD-GC method. The observed differences between the two methods suggest the possibly important role of the matrix effect to give rise to the negative biases in DI-GC analysis. To further explore this possibility, an ancillary experiment was performed to examine bias patterns of three DI-GC approaches. For instance, the results of the standard addition (SA) method confirm the definite role of matrix effect when analyzing wastewater samples by DI-GC. More importantly, their biases tend to increase systematically with increasing molecular weight and decreasing VFA concentrations. As such, the use of DI-GC method, if applied for the analysis of samples with a complicated matrix, needs a thorough validation to improve the reliability in data acquisition.     

About the computation of the signature of surface singularities <Emphasis Type=Italic>z</Emphasis><Superscript><Emphasis Type=Italic>N</Emphasis></Superscript> + <Emphasis Type=Italic>g</Emphasis>(<Emphasis Type=Italic>x,y</Emphasis>) = 0

In this article we describe our experiences with a parallel Singular implementation of the signature of a surface singularity defined by z ^N + g(x; y) = 0.     

Facile synthesis of zirconia supported nanomaterials for efficient photocatalytic applications

The recent study enlightens the synthesis and characterization of zirconia (ZrO₂), Fe-doped ZrO₂ (Fe@ZrO₂), and Ni-doped ZrO₂ (Ni@ZrO₂) catalysts having new-fangled morphology with tuned band gap as photocatalysts for degradation of textile wastewater dyes methylene blue (MB), malachite green (MG), and their mixtures. SEM imaging of Fe@ZrO₂ and Ni@ZrO₂ is interestingly varied from ZrO₂ as well as doping of transition metals greatly affects the morphology of composites. The optimization study depicts that the pH, time (min) and catalyst amount (g) have a direct relation with degradation efficiency, while the dye concentration (mg/L) has an indirect relation as well. The photocatalytic studies depict that the degradation of MB and MG follows oxidation pathway via hydroxyl radicals (OH^•) and holes. Reusability of catalysts corresponds to a little decrease in degradation efficiency in the first two cycles and decreases to about ∼10% (Ni@ZrO₂) and ∼12% (Fe@ZrO₂) in next three cycles.     

Asymptotic expansions for elliptic-like regularizations of semilinear evolution equations

Consider in a real Hilbert space H the Cauchy problem (_P0$P_0$): u^′(t)+Au(t)+Bu(t)=f(t)$u^{\prime }(t)+Au(t)+Bu(t)=f(t)$, 0≤t≤T$0\le t\le T$; u(0)=_u0$u(0)=u_0$, where −A   is the infinitesimal generator of a _C0$C_0$-semigroup of contractions, B is a nonlinear monotone operator, and f is a given H-valued function. Inspired by the excellent book on singular perturbations by J.L. Lions, we associate with problem (_P0$P_0$) the following regularization (_Pε$P_{\epsilon }$): −εu^″(t)+u^′(t)+Au(t)+Bu(t)=f(t)$-\epsilon u^{″}(t)+u^{\prime }(t)+Au(t)+Bu(t)=f(t)$, 0≤t≤T$0\le t\le T$; u(0)=_u0$u(0)=u_0$, u^′(T)=_uT$u^{\prime }(T)=u_T$, where ε>0$\epsilon >0$ is a small parameter. We investigate existence, uniqueness and higher regularity for problem (_Pε$P_{\epsilon }$). Then we establish asymptotic expansions of order zero, and of order one, for the solution of (_Pε$P_{\epsilon }$). Problem (_Pε$P_{\epsilon }$) turns out to be regularly perturbed of order zero, and singularly perturbed of order one, with respect to the norm of C([0,T];H)$C([0,T];H)$. However, the boundary layer of order one is not visible through the norm of L²(0,T;H)$L^2(0,T;H)$.     

Direct determination of cadmium in calcium drug samples using electrothermal atomic absorption spectrometry with a metal tube atomizer and thiourea as a matrix modifier

A laboratory constructed molybdenum tube atomizer was used for direct determination of trace cadmium in drug samples by the electrothermal atomic absorption spectrometric (ETAAS) method. An ultrasonic agitation method for a solution including the sample powder was used. A calibration curve was constructed with a cadmium standard solution including matrix. To eliminate interference from other matrix elements, a chemical modifier thiourea, was used. The detection limit were 17 pg ml(-1) (3 S/N), and the RSD of the direct analysis was 5-17%. The results for cadmium in the four drug samples analysed by the direct ETAAS method matched well with those obtained with nitric acid digested samples. The recovery of added cadmium was 103-106%. An accurate method is elaborated for the determination of cadmium in drug samples by direct ETAAS techniques. The merits of this method are rapid calibration, simplicity, fast analysis, and low cost.     

Synthesis of Ferrocene-based Esters as Burning Rate Catalysts and their Anti-migration Study

Ferrocene-based (Fc-based) burning rate catalysts (BRCs) play an essential role in the solid rocket propellants. However, the migration problem during curing and storage limits their applications. To retard the migration problems of Fc-based BRCs and to increase the burning rate (BR) of AP-based propellants, Fc-based esters compounds (Es-Fcs) were synthesized. The synthesized Es-Fcs were characterized by X-ray diffraction, proton nuclear magnetic resonance (¹H NMR),¹³C NMR and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical behaviors of Es-Fcs were investigated by cyclic voltammetry (CV). The BR catalytic activity of Es-Fcs on thermal decomposition of AP were examined by thermogravimetry (TG). Thermal analysis results showed that these Es-Fcs had good BR catalytic effects on thermal decomposition of AP. It was found that the anti-migration performance of Es-Fcs were better than catocene and Fc.     

Applied Thermodynamics for Process Modeling in Catalytic Gas Phase Olefin Polymerization Reactors

The Sanchez–Lacombe Equation of State (SL EoS) is used to model the solubility of different industrial alkane penetrants in polyethylene to explain the importance of considering different diluents for different processes, and the impact that this choice can have on operating conditions, especially for the production of linear low density polyethylene (LLDPE). Extension of this approach to ternary (ethylene/penetrant/LLDPE) systems shows the effect of composition of penetrant/ethylene mixtures on the solubility of such mixtures in LLDPE and swelling of the polymer phase at conditions of industrial relevance. This analysis reveals that using a constant polymer density instead of that predicted by the SL EoS can result in erroneous calculations of the particle size distribution developments in an olefin polymerization reactor.     

Optimization along families of periodic and quasiperiodic orbits in dynamical systems with delay

Nonlinear Dynamics - This paper generalizes a previously conceived, continuation-based optimization technique for scalar objective functions on constraint manifolds to cases of periodic and...     

Cu3(HHTP)2 c-MOF/ZnO Ultrafast Ultraviolet Photodetector for Wearable Optoelectronics

Two-dimensional conductive metal–organic frameworks (2D c-MOFs) are a family of highly tunable and electrically conducting materials that can be utilized in optoelectronics. A major issue of 2D c-MOFs for photodetection is their poor charge separation and recombination dynamics upon illumination. This study demonstrates a Cu₃(HHTP)₂/ZnO type-II heterojunction ultraviolet (UV) photodetector fabricated by layer-by-layer (LbL) deposition, in which the charge separation of photogenerated carriers is enhanced. At optimized MOF layer cycles, the device achieves a responsivity of 78.2 A/W and detectivity of 3.8×10⁹ Jones at 1 V. Particularly, the device can be operated in the self-powered mode with an ultrafast response time of 70 μs, which is the record value for MOF-based photodetectors. In addition, even after 1000-time bending of 180°, the flexible device maintains stable performance. This flexible MOF-based UV photodetector with anti-fatigue and anti-bending properties provides strong implication to wearable optoelectronics.