A VALIDATION STUDY OF THE ROBERTSON-BERGER METER

Abstract— An evaluation of the Robertson-Berger meter was done in order to address the question of whether instrumental and calibration factors can cause what might be interpreted as a change in the ground level solar ultraviolet-B (UV-B) flux. The evaluation consisted of reviewing information about the instrumentation and components in the published literature, a review of the records and procedures in both operations and calibrations, and examination of two instruments including temperature tests of them. It is shown that the instrument is basically stable and that the calibration procedures did not support data drift. There is a slight dependance of the two instruments upon temperature, 0.3°C/y and 0.6°C/y, which is not sufficient to lead to the reported UV-B trends of the order of 0.7 %/y. There is negligible temperature drift in the control electronics.     

A Weil–Petersson type metric on spaces of metric graphs

In this note, we discuss an analogue of the Weil–Petersson metric for spaces of metric graphs and some of its properties.     

Weil–Petersson metrics,Manhattan curves and Hausdorff dimension

Mathematische Zeitschrift -     

Closed Geodesics and Periods of Automorphic Forms

We study the detailed structure of the distribution of Eichler–Shimura periods of an automorphic form on a compact hyperbolic surface. We show that these periods do not cluster around the asymptotic period over a homology class discovered by Zelditch.     

Hydrodynamic and mass transfer studies in an external-loop air-lift bioreactor for immobilized animal cell culture

Air-lift bioreactors containing suspended or immobilized animal cells have been used for the production of a variety of high-value biologicals. In the bioprocessing industry, there is a need to study and quantify the relationships between bioreactor-system properties such as mixing, flow, mass transfer, and cell processes. In the present study, the performance of a 1-L external-loop air-lift bioreactor was investigated by studying gas-liquid oxygen transfer, mixing time, liquid velocity and gas hold-up at various aeration rates. These studies were performed over a range (0-25%) of loadings of small (500-800 μm) calcium alginate beads to investigate the effect of using various concentrations of cell immobilization matrices on the physical properties of the system. At an aeration rate of 0.5 vvm, the mixing time was decreased by 50%, from 75 s at 0% bead loading to 38 s at 10% bead loading. A minimum liquid velocity of 10 cm/s was required to keep the alginate beads in suspension. As bead loading increased, flow within the reactor went from turbulent conditions to the transition zone. At all bead loadings tested, the gas hold-up increased by only 2% with an increase in aeration rate from 0.1 to 1.0 vvm, regardless of whether the total reactor volume (i.e., liquid and beads) or the liquid volume was used in calculating the hold-up. A mathematical correlation was developed for expressing the dependence of the volumetric mass-transfer coefficient, k₁a, on aeration rate (vvm) and microbead loading. With this equation it was possible to predict, within 20%, the k₁a knowing the gas-flow rate and the volume percentage of microbeads present in the bioreactor. A theoretical study was also performed to calculate the oxygen transfer from the bulk liquid to the center of microcapsules containing animal cells using experimental k₁a data. The results suggest that whereas there is no oxygen limitation at 10 to 15% microcapsule loading, there is a potential mass-transfer problem at 25% loading if the bioreactor is operated at an aeration rate of less than 1.06 vvm.     

Electrochemical studies of complex fluorides in non-aqueous solvents

Electrochemical studies on hydrolytically unstable complex fluorides have been shown to be possible in highly purified acetonitrile. The techniques of study will be described briefly. A survey of the results obtained to date wille given.MoF₆ is a stronger oxidising agent than WF₆ by 1.06 volts. Neither |MoF₆|^? nor |WF₆|^? can be reduced below |MF₆|^? in acetonitrile. |UF₆|^? can be reduced to the transient species |UF₆|^2? which is unstable in solution. |OsF₆|^? undergoes successive reduction to |OsF₆|^2? and |OsF₆|^3?.|MF₆L|^? undergoes complex electrochemical behaviour involving reduction to |MF₆L|^2? with subsequent dissociation to |MF₆|^? and L^?. Reoxidation is in the presence of L^? and hence none of the redox steps are fu]ly reversible. The relation between the electrode potentials and the ligand L will be discussed.We thank NATO for a grant in support of this work.     

The effect of procedural variables on TG,DTG and DTA curves of calcium carbonate

The effect of procedural variables, including sample mass, heating rate, particle size and partial pressure of carbon dioxide, on TG, DTG and DTA curves for the decomposition of A. R. calcium carbonate and limestone has been studied. Such variables have a marked effect, similar in magnitude for both DTG and DTA. The effect of sample mass, or depth of undiluted sample, is shown to be due to an increase in the partial pressure of carbon dioxide within the reacting powder and has been called the bed-depth effect. This effect is most pronounced in nitrogen but is much reduced in carbon dioxide. Inert diluents have little effect on the TG curves but changing the composition of the inert carrier gas causes variations which are correlated with the thermal conductivity of the gas. Water vapour causes a lowering of the DTG and DTA peak temperatures.

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Zusammenfassung Bei der Zersetzung von A.R. Calciumcarbonat bzw. Kalkstein wurde der Einflu\ der Versuchsparameter, einschlie\lich Probenmasse, Aufheizgeschwindigkeit, Partikelgrö\e und Partialdruck von CO₂ auf den Verlauf der TG-, DTG- und DTA-Kurven untersucht. Diese Parameter haben einen deutlichen Einflu\ auf DTG und DTA, der sich in beiden FÄllen im gleichen Ausma\ bemerkbar macht. Der Einflu\ der Masse bzw. Tiefe einer unverdünnten Probe Äu\ert sich in einem Ansteigen des Partialdruckes von Kohlendioxid innerhalb des reagierenden Pulvers und wird als Bett-Tiefen-Effekt bezeichnet. Dieser Effekt kommt in Stickstoff besonders zur Geltung und tritt in Kohlendioxid in den Hintergrund. Inerte Verdünnungsmittel haben einen nur geringen Effekt auf die TG-Kurve aber eine Änderung der Zusammensetzung des inerten TrÄgergases verursacht VerÄnderungen, die auf der WÄrmeleitfÄhigkeit des Gases begründet sind. Wasserdampf verursacht, da\ DTG- und DTA-Signale bei niedrigeren Temperaturen auftreten.

     

A two-component,non-aqueous route to silica gel

A new means for generating silica gel has been developed. Simple two component systems comprising tetraalkoxysilanes and strong carboxylic acids such as formic acid can react rapidly to give transparent monolithic gels. The acid serves as solvent, water source, and catalyst for both hydrolysis and condensation. Water need not be present as an initial reactant; it is generated in situ during the reaction. The gelation reaction is at least two orders of magnitude faster than those conducted in conventional acid-catalyzed aqueous systems at comparable pH*. Kinetic evidence indicates a lowering of the activation energy of condensation reactions, believed to be associated with reaction of silyl carboxylates and silanol groups. Physical properties of the dry gels such as bulk density more closely resemble conventional acid-catalyzed gels than those associated with other rapidly gelling systems. Dry gels often exhibit porosity so fine that nitrogen (at 77°K) is not absorbed at significant rates. Independent evidence of porosity arises from comparison of skeletal and bulk densities, sample immersion in water and adsorption isotherms of CO₂.     

Preference, Production and Performance in Data Envelopment Analysis

This paper attempts to provide a systematic approach to the DEA model building. To this end, we try to identify some essential aspects of DEA modelling. Three key building blocks in a DEA model are identified: they are preference order, production possibility set and performance measure. It is shown that the preferences and performance measurements used in the standard DEA models are only particular examples in this framework. It is also illustrated in this work that this methodology is useful in building new DEA models to handle nonstandard applications such as those involve non-Pareto preferences or undesirable inputs-outputs.