The spectrum of combustion-generated noise

A calculation of the energy release rate resulting from the combustion of propane-air mixtures is presented and the result is used to calculate the far field noise spectrum for an open flame by using appropriate Fourier transform techniques. The results illustrate the broad band nature of combustion noise and show that, for the range of parameters indicated, the peak frequency in the $\text{1}\text{3}$ octave band is in the range 400–1000 Hz. The results also indicate that the shape of spectrum is influenced by the time history of the heat release rate and the turbulence intensity and length scales; on the other hand, the peak frequency is a function of the heat release per unit mass of fuel which is essentially the same for hydrocarbon fuels.     

A NMR and theoretical study of the aggregates between alkyllithium and chiral lithium amides: control of the topology through a single asymmetric center

The complexes between methyllithium and chiral 3-aminopyrrolidine (3-AP) lithium amides bearing a second asymmetric center on their lateral amino group were studied using multinuclear ((1)H, (6)Li, (13)C, (15)N) low-temperature NMR spectroscopies in tetrahydrofuran-d(8). The results indicate that lithium chelation forces the pyrrolidine ring of the 3-AP to adopt a norbornyl-like conformation and that robust 1:1 noncovalent complexes between methyllithium and 3-AP lithium amides form in the medium. A set of (1)H-(1)H and (1)H-(6)Li NMR cross-coupling correlations shows that the binding of methyllithium can take place along the "exo" or the "endo" face of this puckered structure, depending on the relative configuration of the lateral chiral group. This aggregation step renders the nitrogen of the 3-amino group chiral, the "exo" and "endo" topologies corresponding to the (S) and (R) configurations, respectively, of this atom. Density functional theory calculations show that the "exo" and "endo" arrangements are, for both diastereomers, almost isoenergetic even when solvent is taken into account. This result suggests that the formation of the mixed aggregates is under strict kinetic control. A relationship between the topology of these complexes and the sense of induction in the enantioselective alkylation of aromatic aldehydes by alkyllithiums is proposed.     

Determination of endocrine-disrupting compounds in environmental samples using gas and liquid chromatography with mass spectrometry

This paper describes certain applications for endocrine-disrupting compounds determination. LC-MS was applied using an electrospray ionization (ESI) technique in positive mode for alcohol polyethoxylates and nonylphenol and octylphenol polyethoxylates (NPEOn and OPEOn), and in negative mode for 4-nonylphenol (4-NP) and 4-octylphenol (4-OP) to determine targeted compounds in wastewater and sludge. GC-MS and GC-MS-MS were used to determine 4-NP, 4-tert.-octylphenol (4-t-OP), bisphenol A, estradiol-17beta, estriol estrone, testosterone, 17alpha-ethynylestradioL cholesterol, coprostan-3-ol, coprostan and coprostan-3-one in both surface water and wastewater after derivatization with N,O-bis(trimethyl-silyl)trifluoroacetamide (BSTFA). Extraction from the water samples was by an SPE technique, using either a copolymeric (Oasis HLB) or C18 silica sorbents, depending on the target contaminants. Extraction from the sludge samples was by a Soxtec system using methanol. Percentage recoveries for most of the selected compounds, using either a copolymeric (Oasis HLB) or C18 silica sorbents, were satisfactory (>60%). Quantification limits for the target compounds were at ppb levels in both water and sludge samples when using LC-ESI-MS in both positive and negative modes. They reached ppt levels in water when using GC-MS (in large volume injection mode) and GC-MS-MS. The results revealed 4-NP, NPEOn and AEOs in sludge samples at a concentration range of 1.3-8.5 microg/g, and NPEOn, OPEOn and other compounds, such as coprostan and bisphenol A, in surface water and/or wastewater samples at concentrations ranging from the ppt to ppb levels.     

Autonomous Forms and Exact Solutions of Equations of Motion of Polytropic Gas

The system of motion of a polytropic gas can be reduced to an autonomous form by using group analysis. A new family of exact solutions are constructed.     

Modeling of Slurry Polymerization of Ethylene Using a Soluble Cp2ZrCl2/MAO Catalytic System

The slurry homopolymerization of ethylene catalyzed by a Cp₂ZrCl₂/MAO catalytic system was studied. A simple kinetic model including initiation, propagation, transfer to monomer and cocatalyst, spontaneous transfer and spontaneous deactivation was developed to predict dynamic yield of polymerization and molecular weight of final products. Kinetic constants were estimated by numerical solution of polymerization kinetic model, combined with Nelder‐Mead simplex method. The model predicts that the propagation reaction has the lower activation energy in relation to chain transfer reactions which leads to decrease of molecular weight at elevated temperatures. The initiation reaction has however, the highest activation energy that results in raising the peak of reaction rate at higher temperatures.

     

Convective heat transfer over two blocks arbitrary located in a 2D plane channel using a hybrid lattice Boltzmann-finite difference method

The present paper deals with the numerical investigation of a 2D laminar fluid flow and heat transfer in a plane channel with two square blocks located at arbitrary positions. The numerical model is based on a coupling between the multiple relaxation time-lattice Boltzmann equation and the finite difference method for incompressible flow. Both the horizontal and the vertical separation distances between the two blocks are varied. Particular attention was paid to the distribution patterns of the time averaged local Nusselt number on the top and bottom walls. Results obtained from the present study show a complex flow patterns developed in the channel due to the change of the square blocks positions.     

Magnetic Solid-Phase Extraction of Lawsone Using Polyphenol-Coated Magnetic Nanoparticles: Synthesis,Characterization and examination

Chromatographia - A novel polyphenol-coated CoFe2O4 system with sorption capacity of lawsone was synthesized as a magnetic sorbent by chemical oxidative polymerization process for magnetic...     

Simultaneous Filtration and Solid-Phase Extraction Combined with Large-Volume Injection in GC/MS for Ultra-Trace Analysis of Polar Pesticides in Surface Water

A method combining simultaneous filtration and solid-phase extraction (SPE) with large-volume injection (LVI) in gas chromatography/mass spectrometry (GC/MS) was developed to determine 13 polar pesticides in surface water. The selected pesticides - 4 organophosphorus, 7 organonitrogens and 2 triazine degradation products - were extracted from 0.5-L samples of filtered and raw water using cartridges filled with a silica-bonded material (1 g of ISOLUTE triazine, C-18) and a depth filter. No obstruction was observed during the extraction of raw water drawn from the St. Lawrence River (concentration of suspended particulate matter (SPM) ranging from 2 to 58 mg L^?1). Overall percent recoveries were satisfactory for all the target pesticides (>60%) except desisopropyl-atrazine (more polar), which varied from 29 to 46% according to sample pH. The coefficient of variation was below 10% for the majority of the target pesticides and detection limits ranged from 0.1 to 0.8 ng L^?1. Applied to real samples drawn from the St. Lawrence River, this method allowed for the detection of atrazine, cyanazine, desethyl-atrazine (DEA), desisopropyl-atrazine (DIA), metolachlor and simazine, at concentrations of 6 to 91 ng L^?1. Using atrazine and metolachlor as examples, the correlation between filtered and raw water samples was more significant for the former (r = 0.87) than for the latter (r = 0.67). Temporal variations in atrazine and metolachlor in filtered water drawn from the St. Lawrence River, for example, were similar whether using the established method, based on liquid-liquid large-volume extraction (LVE) combined with GC/NPD analysis, or the one proposed herein. The latter method, however, systematically found atrazine concentrations 62% higher than those obtained by the older one, applied to the same field samples. Thus, the switch to the new analytical method will require the application of a correction factor to the atrazine concentration time series acquired with the previously used method.