A DSC study of the phase transformations of ammonium nitrate

A literature survey has been made of heat capacity and transition enthalpy values for ammonium nitrate. New DSC experiments lead to Δ H⁰ values for the IV å III, III å II and II å I transitions in good agreement with older data, and to a new value for the enthalpy of fusion. The effect of thermal history and moisture content is discussed.     

Computer screen photo-excited surface plasmon resonance imaging

Angle and spectra resolved surface plasmon resonance (SPR) images of gold and silver thin films with protein deposits is demonstrated using a regular computer screen as light source and a web camera as detector. The screen provides multiple-angle illumination, p-polarized light and controlled spectral radiances to excite surface plasmons in a Kretchmann configuration. A model of the SPR reflectances incorporating the particularities of the source and detector explain the observed signals and the generation of distinctive SPR landscapes is demonstrated. The sensitivity and resolution of the method, determined in air and solution, are 0.145 nm pixel⁻¹, 0.523 nm, 5.13 × 10⁻³ RIU degree⁻¹ and 6.014 × 10⁻⁴ RIU, respectively, encouraging results at this proof of concept stage and considering the ubiquity of the instrumentation.     

Laser-induced fluorescence of formaldehyde in combustion using third harmonic Nd:YAG laser excitation

Formaldehyde (CH2O) is an important intermediate species in combustion processes and it can through laser-induced fluorescence measurements be used for instantaneous flame front detection. The present study has focussed on the use of the third harmonic of a Nd:YAG laser at 355 nm as excitation wavelength for formaldehyde, and different dimethyl ether (C2H6O) flames were used as sources of formaldehyde in the experiments. The investigations included studies of the overlap between the laser profile and the absorption lines of formaldehyde, saturation effects and the potential occurrence of laser-induced photochemistry. The technique was applied for detection of formaldehyde in an internal combustion engine operated both as a spark ignition engine and as a homogenous charge compression ignition engine.     

Data processing for image-based chemical sensors: unsupervised region of interest selection and background noise compensation

Natural olfaction suggests that numerous replicas of small sensors can achieve large sensitivity. This concept of sensor redundancy can be exploited by use of optical chemical sensors whose use of image sensors enables the simultaneous measurement of several spatially distributed indicators. Digital image sensors split the framed scene into hundreds of thousands of pixels each corresponding to a portion of the sensing layer. The signal from each pixel can be regarded as an independent sensor, which leads to a highly redundant sensor array. Such redundancy can eventually be exploited to increase the signal-to-noise ratio. In this paper we report an algorithm for reduction of the noise of pixel signals. For this purpose, the algorithm processes the output of groups of pixels whose signals share the same time behavior, as is the case for signals related to the same indicator. To define these groups of pixels, unsupervised clustering, based on classification of the indicator colors, is proposed here. This approach to signal processing is tested in experiments on the chemical sensitivity of replicas of eight indicators spotted on to a plastic substrate. Results show that the groups of pixels can be defined independently of the geometrical arrangement of the sensing spots, and substantial improvement of the signal-to-noise ratio is obtained, enabling the detection of volatile compounds at any location on the distributed sensing layer.     

Alpha scattering by heavy nuclei

We develop an approximation scheme to calculate the Glauber amplitude for elastic and inelastic alpha-nucleus scattering. It is rapidly converging and works for any nuclear density. The α-particle density is assumed Gaussian.     

Eine Mikromethode zur Bestimmung von organisch gebundenem Kohlenstoff in Seewasser

Zusammenfassung Die organische Substanz in natürlichen Wässern wird durch kontinuierliches Einengen im Vakuum in einem Spezialkolben bei Anwesenheit von wenig Phosphorsäure konzentriert. Das Konzentrat wird sodann im selben Kolben mit einer flüssigen Oxidationsmischung verascht, das Kohlendioxyd im Vakuum von einer Barytlösung absorbiert und die Carbonatmenge zwischen ph 10 und 4 titriert. Die Apparatur ist einfach und die Methode arbeitet mit einer Genauigkeit von 1% für eine Probenmenge mit 2 mg organischem Kohlenstoff. Die Ausführung einer Analyse nimmt 1 1/4 Stunden in Anspruch.Die Verteilung von gelöster und suspendierter Substanz in einem See wurde vorläufig untersucht.

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Summary The organic material in natural waters was concentrated by continuous evaporation in vacuo in a special flask and in the presence of phosphoric acid. The concentrate was then ashed in the same flask by means of a liquid oxydizing mixture and the carbon dioxide absorbed in vacuo in a solution of barium hydroxide. The resulting carbonate was titrated between ph 10 and 4. The apparatus is simple, the method yields an accuracy of 1% with samples containing 2 mg organic matter. The analysis requires 75 minutes. — The distribution of dissolved and suspended substance in lake water was tentatively determined.

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Résumé Les matières organiques des eaux naturelles sont concentrées par evaporation continue sous vide, dans un récipient spécial, en présence, d'acide phosphorique. Le produit de la concentration est alors minéralisé dans le récipient même à l'aide d'un mélange liquide oxydant et le gaz carbonique absorbé sous vide dans une solution de baryte. Le carbonate formé est titré entre ph 10 et 4. L'appareil est simple, la méthode conduit àune précision de 1% avec des échantillons contenant 2 mg de matière organique. L'analyse demande 75 minutes. On a déterminé la distribution de substances dissoutes ou en suspension dans les eaux d'un lac.