Proposals for new data quality objectives to underpin ambient air quality monitoring networks

The data completeness requirements for the production of defensible annual averages of air quality parameters are discussed. Data quality objectives concerning time coverage and data capture specified by current legislation are critically examined, and the improved, combined metric of data coverage is proposed. Best practice proposals to ensure the representativeness of air quality data across the calendar year are presented. These are based on minimising any bias between the annual average calculated using the data acquired and the annual average that would have been calculated if data coverage had been 100 %. In all cases, the optimum solution is for air quality network operators to aim for 100 % data coverage.     

Nonlinear mapping of massive data sets by fuzzy clustering and neural networks

Producing good low‐dimensional representations of high‐dimensional data is a common and important task in many data mining applications. Two methods that have been particularly useful in this regard are multidimensional scaling and nonlinear mapping. These methods attempt to visualize a set of objects described by means of a dissimilarity or distance matrix on a low‐dimensional display plane in a way that preserves the proximities of the objects to whatever extent is possible. Unfortunately, most known algorithms are of quadratic order, and their use has been limited to relatively small data sets. We recently demonstrated that nonlinear maps derived from a small random sample of a large data set exhibit the same structure and characteristics as that of the entire collection, and that this structure can be easily extracted by a neural network, making possible the scaling of data set orders of magnitude larger than those accessible with conventional methodologies. Here, we present a variant of this algorithm based on local learning. The method employs a fuzzy clustering methodology to partition the data space into a set of Voronoi polyhedra, and uses a separate neural network to perform the nonlinear mapping within each cell. We find that this local approach offers a number of advantages, and produces maps that are virtually indistinguishable from those derived with conventional algorithms. These advantages are discussed using examples from the fields of combinatorial chemistry and optical character recognition. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 373–386, 2001     

Raman spectrometry and neural networks for the classification of wood types. 2. Kohonen self-organizing maps

One- and two-dimensional Kohonen self-organizing maps (SOMs) were successfully used for the unsupervised differentiation of the Fourier transform Raman spectra of hardwoods from softwoods. The SOMs were also applied to differentiate temperate woods from tropical woods, and results showed that the two types of woods could only be partly differentiated. A semi-quantitative method that is based on the Euclidean distances of the weight matrix has been developed to assist the automatic clustering of the neurons in a two-dimensional SOM.     

3D mapping of the output laser beam from a PDLC sample

Self-transparency due to thermal non-linearities is presented as a basic switching effect in a thick polymer dispersed liquid crystal sample. For the first time a detailed 3D mapping of the output laser beam as a function of the x-y coordinates is presented: changes of the transmitted beam profile are recorded vs. both incident power and time. It is discussed how light intensity and temperature can be used as control parameters for the non-linear part of the refractive index. The experimental results confirm the existence of a threshold value of the incident light intensity at which the device switches from the scattering state to the transmissive state.     

3D mapping of the output laser beam from a PDLC sample

Self-transparency due to thermal non-linearities is presented as a basic switching effect in a thick polymer dispersed liquid crystal sample. For the first time a detailed 3D mapping of the output laser beam as a function of the x-y coordinates is presented: changes of the transmitted beam profile are recorded vs. both incident power and time. It is discussed how light intensity and temperature can be used as control parameters for the non-linear part of the refractive index. The experimental results confirm the existence of a threshold value of the incident light intensity at which the device switches from the scattering state to the transmissive state.     

Extraction of information from large data sets by pattern recognition

Summary Pattern recognition permits to extract information present in large data sets in an automatic way. Many scientists acknowledge this fact but are rebutted by the task of learning to use pattern recognition methods. Indeed, there are many methods available and for the newcomer it is extremely difficult to make a selection. For this reason, the paper starts by explaining the models used in pattern recognition. This is followed by a critical discussion of advantages and disadvantages of the methods and a selection of preferred methods.

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Gewinnung von Information aus großen Datenmengen mit Hilfe der Mustererkennung

Zusammenfassung Mit Hilfe der Mustererkennung können Informationen aus großen Datenmengen automatisch gewonnen werden. Obwohl man sich dessen allgemein bewußt ist, schreckt man doch gewöhnlich vor der Aufgabe zurück, sich mit den entsprechenden Methoden befassen zu müssen, denn es gibt sehr viele davon und eine geeignete Auswahl ist schwer zu treffen. Aus diesem Grund werden in dieser Arbeit die einzelnen Verfahren der Mustererkennung erklärt, deren Vor- und Nachteile diskutiert und eine entsprechende Auswahl geboten.

     

Extraction of information from large data sets by pattern recognition

The use of computers has made data collection much easier and analytical chemists increasingly wonder how to make use of all the data obtained. Pattern recognition permits to extract information present in large data sets in an automatic way.Many scientists acknowledge this fact but are rebutted by the task of learning to use pattern recognition methods. Indeed, there are many methods available and for the newcomer it is extremely difficult to make a selection. For this reason, the lecture will start by explaining the models used in pattern recognition. This will be followed by a critical discussion of advantages and disadvantages of the methods and a selection of preferred methods.

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Gewinnung von Information aus großen Datenmengen mit Hilfe der Strukturerkennung

     

Mechanical exfoliation of large area 2D materials from vdW crystals

Monolayer two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides (TMDCs), provide a versatile platform for exploring novel physical phenomena at the 2D limit, and show great promise for next-generation electronic, optoelectronic, and quantum devices. To overcome the weak van der Waals interaction in the bulk layered crystal and achieve high quality single-crystal monolayers is a crucial task in top-down mechanical exfoliation. Tape exfoliation has long been the dominant approach to obtain single-crystal monolayers with high quality. More recently, there has been a fast development of using metals as an intermediate to enhance monolayer area and exfoliation yield. This review will provide a survey of mechanical exfoliation strategies of tape and metal-assisted exfoliations, particularly for the most popular graphene and TMDC materials. The interfacial interaction and lateral strain between monolayer and other materials such as oxides and metals play a crucial role in monolayer selectivity and yield. The challenges and opportunities will be highlighted for future development of exfoliating procedures to achieve large-area and high-quality 2D material monolayers and artificial stacks.     

Predicting hexadecane–air equilibrium partition coefficients (L) using a group contribution approach constructed from high quality data

A group contribution-based quantitative structure–property relationship (QSPR) for the hexadecane–air equilibrium partition coefficients (L) of organic chemicals is developed using the iterative fragment selection (IFS) approach. This new QSPR includes in its training and external validation data sets L values for a large number of structurally complex chemicals measured by the same group using consistent methods. The resulting QSPR has better predictive power than other prediction methods trained primarily using data for chemicals of simpler structures, and measurements of L values from diverse sources. For a subset of chemicals in which the L values have non-additive effects caused by intramolecular hydrogen bonds, the new QSPR gives much better performance in comparison to the most commonly used prediction method.     

2D hydrogen-bonded square-grid coordination networks with a substitution-active metal site

Reported here is the preparation and property of 2D coordination networks composed of rodlike ligands with ethylene glycol side chains (1). Two 2D coordination networks, [[Co(1)2(H2O)2](NO3)2.1.5H2O]n and [[Ni(1)2(H(2)O)2](NO3)2.1.5H2O]n, have been synthesized and characterized by single-crystal X-ray diffraction, TG, DSC, UV-vis spectroscopy, and magnetic measurements. The structural analyses clarified that infinite 1D hydrogen-bond arrays composed of ethylene glycol chains contribute to the stabilization of 2D coordination frameworks, keeping the environment of substitution-active metal sites unchanged. They are more stable than a similar square-grid coordination network that does not possess an ethylene glycol chain on the ligand. We also succeeded in the direct observation of a reversible apical-ligand-exchange reaction at the cobalt(II) and nickel(II) ions in a single-crystal-to-single-crystal fashion because of the considerable stability as well as moderate flexibility of the framework. The cobalt-containing coordination network crystal showed chromic behavior depending on temperatures. Crystallographic and spectroscopic studies revealed that the color change of the crystal was attributed to the ligand-exchange process between H2O and a NO3 anion on the cobalt metal. Magnetic measurements indicated weak antiferromagnetic nearest-neighbor spin coupling between cobalt(II) ions.     

Improved accuracy and robustness of NAA results in a large throughput laboratory by systematic evaluation of internal quality control data

The laboratory for INAA in Delft processes several thousands of samples per year for multielement determinations in a variety of matrices. Samples are measured on different spectrometers (using well-type and coaxial detectors), by different persons and using many different analytical protocols. All these results should be consistent with each other with respect to the degree of accuracy, i.e., the combination of trueness and precision. A rigorous internal quality control program has been implemented with automatic on-line evaluation. Annually an additional evaluation of the internal quality control results is carried out using statistical techniques. The Naji-plot approach has proven to be an important graphical tool since it provides direct insight in both trueness and precision. It is demonstrated that the degree of accuracy of the results obtained under the large variety of operational parameters is under constant improvement.     

Distinguishing the formation of C2D+4 ions from C2D+6 (by D2 loss) and from C2D5H+ (by HD loss) in a Reflectron spectrometer

The D₂ loss from C₂D⁺₆ ions and the HD loss from C₂D₅H⁺ ions has been investigated in a photoelectron photoion coincidence experiment employing a reflecting ion time of a flight mass spectrometer (Reflectron). The experiment is able to distinguish the metastable formation of C₂D⁺₄ ions (m/z = 32) from C₂D⁺₆ ions by D₂ loss and from C₂D₅H⁺ ions by HD loss simultaneously in a mixture of deuterated ethanes. The breakdown curves of the title reactions are presented and compared to the H₂ loss from C₂H⁺₆ ions. The HD loss from C₂D₅H⁺ is shifted by 67 meV and the D₂ loss from C₂D⁺₆ is shifted by 108 meV with respect to the H₂ loss from C₂H⁺₆. This shift reflects a strong kinetic isotope effect which is most likely due to tunneling of H/D atoms through a barrier.     

Optimization of the design of air quality monitoring networks and its application to NO2 and O3 in Jaen,Spain

The assessment of air quality is necessary in order to control and reduce pollution to levels which minimise harmful effects on human health and the environment. This paper describes a method to design air quality monitoring networks for nitrogen dioxide and ozone and its application in Jaen (southern Spain). A fibre-glass filter impregnated with triethanolamine was used in diffusive sampling badges for NO₂ determination. For O₃ analysis, sodium nitrite was selected and nitrate, a product of the reaction of ozone and nitrite, was used to assess the ozone concentrations. Sampling campaigns with passive diffusion samplers at 62 sites were then carried out to obtain information on the pollution emissions in Jaen. The sampling campaigns in 2001–2002 revealed an average concentration of 10.4 μg/m³ NO₂ with maximum values up to 22.5 μg/m³ in Jaen City centre. The average ozone concentrations were recorded downwind from the emission source, reaching 96.2 μg/m³; the average ozone value in Jaen was 72.0 μg/m³. After spatial interpolation of the obtained values with Geographical Information Systems, a selection of the best locations for the monitoring stations was made, in line with the macro- and microscale siting requirements of the European Directive 2008/50/EC on ambient air quality and cleaner air for Europe. A second sampling campaign with diffusive samplers was carried out in 2005–2006 to control if the locations of the air quality assessment stations were still representative for their zone.     

2D warp-and-woof interwoven networks constructed by helical chains with different chirality

Two unprecedented 2D entangled layers of warp-and-woof threads interwoven by left- and right-handed helical chains, {[Mn(salen)Au(CN)2]4(H2O)}n (salen = N,N'-ethylenebis(salicylideneaminato)) and {Mn(acacen)Ag(CN)2}n (acacen = N,N'-ethylenebis(acetylacetonylideneiminate)) 2, have been synthesized and characterized.     

TOF-2: a large 1D channel thorium organic framework

A new neutral 1D channel thorium organic framework material (TOF-2) has been synthesized under hydrothermal conditions. TOF-2 exhibits a hexagonal channel structure consisting of eight-coordinate ThO6F2 polyhedra and 1,3,5-benzentricarboxylate ligands. The channels run along the c-axis and are approximately 13 A in diameter. The single-crystal X-ray structure suggests that the amount of void space is 41%. The structure is stable to ca. 400 degrees C. Gas adsorption measurements show deferential gas uptake behavior.     

Dynamics of D2 released from the dissociation of D2O on a zirconium surface

Hydrogen is efficiently released during water dissociation on zirconium (Zr), while even very rapid temperature programmed heating of a hydrogen covered Zr surface predominantly leads to dissolution (approximately 99% dissolution). To help resolve these apparently contradictory observations, we have studied the dynamics of water (D2O) dissociation on a crystalline Zr surface by probing the rotational and vibrational energy distributions of the D2 produced using resonant enhanced multiphoton ionization spectroscopy. The internal-state energy distribution of the D2 product was found to be rotationally cold and vibrationally hot with respect to the temperature of the surface. The rotational distribution shows slight deviations from Boltzmann's law, with a mean rotational temperature of 426 K while the surface is at 800 K. The population of the nu"=1 vibration is at least four times higher than a 800 K temperature would allow, this corresponding to a vibrational temperature of 1100 K. Information on the translational energy of the D2 product have also been obtained by time-of-flight spectroscopy and it is found to be nearly thermally equilibrated with the surface temperature. Similar results were obtained from studies of D2 scattered from a clean Zr surface, and of D2 released by a slow thermal desorption process which involves dissolved hydrogen as the source. The reconciliation of the present results with those for thermal desorption of preadsorbed hydrogen implies a role for both surface and subsurface adsorption sites on the Zr surface and clearly demonstrates that at high temperatures, the release of D2 arises from the recombinative desorption of adsorbed hydrogen formed by the complete dissociation of D2O.     

CO2 isotope analyses using large air samples collected on intercontinental flights by the CARIBIC Boeing 767

Analytical details for ¹³C and ¹⁸O isotope analyses of atmospheric CO₂ in large air samples are given. The large air samples of nominally 300 L were collected during the passenger aircraft‐based atmospheric chemistry research project CARIBIC and analyzed for a large number of trace gases and isotopic composition. In the laboratory, an ultra‐pure and high efficiency extraction system and high‐quality isotope ratio mass spectrometry were used. Because direct comparison with other laboratories was practically impossible, the extraction and measurement procedures were tested in considerable detail. Extracted CO₂ was measured twice vs. two different working reference CO₂ gases of different isotopic composition. The two data sets agree well and their distributions can be used to evaluate analytical errors due to isotope measurement, ion corrections, internal calibration consistency, etc. The calibration itself is based on NBS‐19 and also verified using isotope analyses on pure CO₂ gases (NIST Reference Materials (RMs) and NARCIS CO₂ gases). The major problem encountered could be attributed to CO₂‐water exchange in the air sampling cylinders. This exchange decreased over the years. To exclude artefacts due to such isotopic exchange, the data were filtered to reject negative δ¹⁸O(CO₂) values. Examples of the results are given. Copyright © 2009 John Wiley & Sons, Ltd.