Search results for "Matrix"

Lead speciation in rainwater samples by modified fused silica capillaries coupled to a direct injection nebulizer (DIN) for sample introduction in IC…

2001

Lead speciation using modified silica capillaries for the introduction of liquid samples to a direct injection nebulizer of an inductively coupled plasma quadrupole mass spectrometer is described and demonstrated. The fused silica capillaries were coated by covalently bonding a cation exchange active organic molecule to the activated capillary surface. The best results were obtained by introducing a bifunctional reagent in a prior step. In this case, a silane reagent was chosen which acted as a methacrylic acid group for further binding. The influence of the chemical modification of the surface of the sample capillary of the DIN on the selective retention of inorganic lead (Pb2+) and trieth…

Holographic properties of azobenzene oligomers with differently bonded chromophore groups

2007

Holographic properties of two types (I and II, specified in the text) of azobenzene oligomers (ABO) have been experimentally studied in the spectral region of low absorption at 633 nm. In the case of type I ABO the chromophore groups were covalently bonded to either tolyl-polyurethane or hexamethylene-polyurethane matrix. In the case of type II ABO azobenzene chromophores were dispersed in polystyrene matrix, and their concentration was varied from 0.005 to 0.200 mol/l. Samples were in the form of 10 µm thick films. In both cases the diffraction efficiency exposure time dependences were measured for the holographic grating period of 2 (m at 633 nm. The diffraction efficiency of more than 2%…

Über synthetische Matrizenreaktionen

2007

Molecularly homogeneous, polynuclear phenolic compounds were esterified with acrylic acid and methacrylic acid chlorides. The pcresyl esters of acrylic and methacrylic acid react in high dilution in boiling benzene with a large excess of radicals derived from AIBN in such manner that the growth step of the free-radical polymerization is prevented; this may be denoted a “suppressed” polymerization. The application of these conditions to the previously mentioned poly-nuclear esters results in the formation of molecularly homogeneous cyclooligomers (ladder oligomers). Alkaline hydrolysis of these oligomers permits recovery of the polynuclear phenols and yields molecularly homogeneous oligoacry…

Selective trace enrichment of chlorotriazine pesticides from natural waters and sediment samples using terbuthylazine molecularly imprinted polymers

2000

Two molecularly imprinted polymers were synthesized using either dichloromethane or toluene as the porogen and terbuthylazine as the template and were used as solid-phase extraction cartridges for the enrichment of six chlorotriazines (deisopropylatrazine, deethylatrazine, simazine, atrazine, propazine, and terbuthylazine) in natural water and sediment samples. The extracted samples were analyzed by liquid chromatography/diode array detection (LC/DAD). Several washing solvents, as well as different volumes, were tested for their ability to remove the matrix components nonspecifically adsorbed on the sorbents. This cleanup step was shown to be of prime importance to the successful extraction…

A New Reference Material and Safe Sampling of Terrorists Peroxide Explosives by a Non-Volatile Matrix

2015

Vibrational characterization of the 1:1 iodine-benzene complex isolated in solid krypton.

2008

The structure and properties of a 1:1 iodine-benzene complex isolated in an inert krypton matrix at low temperature have been studied with infrared and resonance Raman spectroscopy and with MP2 calculations. The structure of the ground-state complex is found to be unsymmetric, and the I-I vibrational frequency is found to be red-shifted by 3.94 cm(-1) upon complexation. The experimental data agree well with computational results, leading to the conclusion that the I2-Bz complex structure is not axial but of above-bond type, identically with other halogen-benzene complexes.

Molecular electric quadrupole moments calculated with matrix dressed SDCI

2002

Abstract We have calculated the molecular electric quadrupole moment (MEQM) for the set of molecules N 2 , C 2 H 2 , CO, CO 2 , CS 2 , HF, and BH. We have used SR-SDCI and (SC) 2 -SR-SDCI methods and we have compared our results with high-level theoretical ones, including FCI values for HF and BH, and with experimental values. The calculated MEQM provides a test of the effect that the energy converged (SC) 2 dressing method brings to the SDCI wavefunctions. The results suggest that the (SC) 2 -SR-SDCI method can be a cost-effective and quite accurate method for the calculation of post-SCF effects on electric quadrupole moments.

A coupled-cluster study of lanthanum trihalide structures

2002

Coupled-cluster calculations were carried at the CCSD(T)-level in order to determine the structures and vibrational spectra of the lanthanum trihalides LaF3 and LaCl3. Two different approaches were employed to describe scalar relativistic effects; the quasi-relativistic Effective Core Potential approach and the all-electron Douglas–Kroll approach. We find LaF3 to be of pyramidal structure and LaCl3 to be planar. The obtained vibrational frequencies accord well with experimental measurements except for the ν2 mode. This disagreement is attributed to the intrinsic uncertainty of harmonic frequencies of this fluxional mode as extracted from spectra which were obtained at high temperature and f…

Matrix Shuffle- Exchange Networks for Hard 2D Tasks

2021

Convolutional neural networks have become the main tools for processing two-dimensional data. They work well for images, yet convolutions have a limited receptive field that prevents its applications to more complex 2D tasks. We propose a new neural model, called Matrix Shuffle-Exchange network, that can efficiently exploit long-range dependencies in 2D data and has comparable speed to a convolutional neural network. It is derived from Neural Shuffle-Exchange network and has O(log N) layers and O(N ^ 2 log N) total time and O(N^2) space complexity for processing a NxN data matrix. We show that the Matrix Shuffle-Exchange network is well-suited for algorithmic and logical reasoning tasks on …

Calculating minimum discrepancy to assess the nestedness of species assemblages

2009

Nestedness is a pattern whereby species-poor assemblages are composed of subsets of the species occurring in richer assemblages. One of the most commonly used measures of the degree of nestedness for presence-absence matrices is the ‘discrepancy’ metric. A hitherto neglected property of that metric is that it may take several values for a given site-by-species matrix in the presence of ties in the marginal totals. This complicates the quantification of nestedness for the observed presence-absence matrix, as well as the assessment of statistical significance, which is typically achieved through Monte Carlo simulations. A solution to the problem is to calculate the minimum discrepancy using a…