Asymptotic solutions of glass temperature profiles during steady optical fibre drawing

In this paper we derive realistic simplified models for the high-speed drawing of glass optical fibres via the downdraw method, that capture the fluid dynamics and heat transport in the fibre via conduction, convection and radiative heating. We exploit the small aspect ratio of the fibre and the relative orders of magnitude of the dimensionless parameters that characterize the heat transfer to reduce the problem to one- or two-dimensional systems via asymptotic analysis. The resulting equations may be readily solved numerically and in many cases admit exact analytic solutions. The systematic asymptotic breakdown presented is used to elucidate the relative importance of furnace temperature profile, convection, surface radiation and conduction in each portion of the furnace and the role of each in controlling the glass temperature.\ud \ud The models derived predict many of the qualitative features observed in the real industrial process, such as the glass temperature profile within the furnace and the sharp transition in fibre thickness. The models thus offer a desirable route to quick scenario testing, providing valuable practical information into the dependencies of the solution on the parameters and the dominant heat-transport mechanism

Towards a Bayesian evaluation of features in questioned handwritten signatures

In this work, we propose the construction of a evaluative framework for supporting experts in questioned signature examinations. Through the use of Bayesian networks, we envision to quantify the probative value of well defined measurements performed on questioned signatures, in a way that is both formalised and part of a coherent approach to evaluation. At the current stage, our project is explorative, focusing on the broad range of aspects that relate to comparative signature examinations. The goal is to identify writing features which are both highly discriminant, and easy for forensic examiners to detect. We also seek for a balance between case-specific features and characteristics which can be measured in the vast majority of signatures. Care is also taken at preserving the interpretability at every step of the reasoning process. This paves the way for future work, which will aim at merging the different contributions to a single probabilistic measure of strength of evidence using Bayesian networks

Estimating the quantity of transferred DNA in primary and secondary transfers.

We conducted experiments to characterize the quantity of DNA recovered on surfaces using 6 donors with a view to help assigning probabilities to the observation of given quantities of DNA under different transfer scenarios. The donors were asked to conduct a total of 120 simulations involving primary transfer on a knife handle. With 2 selected donors, 60 associated experiments involving secondary transfer were also carried out. DNA recovered on COPAN’s FLOQSwab™ was extracted, quantified and profiled using standard commercial kits. DNA mixtures were subsequently deconvoluted using STRmix™ to obtain the proportion corresponding to the person of interest (POI). The transfer proportion between the quantity of DNA on the bare hands and the amounts recovered on the touched surfaces was also measured and studied. For a given activity, each donor left varying amounts of DNA amounting to distributions that can be characterized by their means and standard deviations. The quantity of transferred DNA is dependent on the donor and on the type of transfer. Typically, our “best” donor left an average of 0.84ng (SD = 1.23) on a knife handle compared to a mean of 0.07ng (SD = 0.09) for the least “prone to leave DNA” donor. For secondary transfer, we recorded a mean of 0.04ng (SD = 0.11) for the first donor and of 0.002 (SD = 0.01, max = 0.04ng) for the second. Linked to the above is the observation that the transfer proportion (i.e. the ratio of the quantity of DNA on an hand to the amount of DNA recovered following a transfer) depends also on the donor and on the type of the transfer. Hence the amount of DNA obtained on a given touched surface cannot simply be deduced from the quantity of DNA available on a donor’s hand. Given these sources of variability, it is not advised to use a single and fixed label, such as “good “or “bad” regardless of the circumstances, to describe a donor’s ability to leave DNA. To properly evaluate the probability of finding a given quantity of DNA the whole variation of DNA quantity should be accounted for. This can be done by using or measuring empirically the appropriate underpinning distribution for that quantity. Note however that it will be conditioned upon the donor, the receiving surface and the transfer mechanism. We also explored the potential benefit of deconvoluting mixtures to better characterize the quantity of DNA left by the POI as opposed to the total quantity of DNA measured by quantification. Our results show that such deconvolution is beneficial when low quantities of POI’s DNA may be mixed with larger quantities such as in secondary transfer scenarios. For primary transfers on clean surfaces, the touching person will dominate in the recovered DNA and the deconvolution is not critical

Wetting Modification by Photocatalysis: A Hands-on Activity To Demonstrate Photoactivated Reactions at Semiconductor Surfaces

We present a hands-on activity designed for advanced physical chemistry courses for Master\u2019s students on the application of photocatalysis to the modification of the surface properties of a semiconductor (titanium dioxide). The wetting properties of TiO2 films, deposited from commercial powders, are studied before and after UV irradiation. Irradiation-induced superhydrophilicity is exploited to provide antifogging properties. The TiO2 films are then functionalized with a perfluorinated alkylsilane to impart superhydrophobicity and subsequently lithographed by irradiation through a photomask: the photocatalytic degradation of the organic chains in the irradiated areas leads to a wetting contrast that can be revealed using dye solutions. This experience can be easily adapted to be suited for undergraduates or high-school students as well as to demonstrations for science festivals

Development and Persistence of 'Static' or 'Dead' Zones in Flows

Certain ceramic products are formed through extrusion processes, where a slurry is forced through small openings to form such products as filters. At the top is a large tank. The slurry is forced through the tank into an extrusion chamber, and then out through slots to form the finished product. [The slurry may be thought of as a mixture of clay (or other polymers), water, and other binders. There are many ways to model this mixture, some of which will be discussed in this report. For instance, the slurry can be modeled as a non-Newtonian fluid, a two-phase flow with liquid and solids, or a viscoelastic fluid. One can also model the mixture as an elongated particle suspension in water, where changes in the orientation of the particles could affect the flow.] After the extrusion process is complete, one finds that ‘dead zones’ of dry paste accumulate in two areas. Most prominently, they occur at the lower corners of the tank. They also occur on the floor of the extrusion chamber near the slots, both near and away from the walls. Since we will consider wall effects in the tank, for the extrusion chamber we consider only flow cells sufficiently far away from the walls. Then we may exploit the periodic nature of the device and consider only a single flow cell. The aim of this project is to determine the formation mechanisms of these dead zones, and see how they affect the overall flow

The salivary microbiome for differentiating individuals: proof of principle.

Human identification has played a prominent role in forensic science for the past two decades. Identification based on unique genetic traits is driving the field. However, this may have limitations, for instance, for twins. Moreover, high-throughput sequencing techniques are now available and may provide a high amount of data likely useful in forensic science. This study investigates the potential for bacteria found in the salivary microbiome to be used to differentiate individuals. Two different targets (16S rRNA and rpoB) were chosen to maximise coverage of the salivary microbiome and when combined, they increase the power of differentiation (identification). Paired-end Illumina high-throughput sequencing was used to analyse the bacterial composition of saliva from two different people at four different time points (t = 0 and t = 28 days and then one year later at t = 0 and t = 28 days). Five major phyla dominate the samples: Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes and Fusobacteria. Streptococcus, a Firmicutes, is one of the most abundant aerobic genera found in saliva and targeting Streptococcus rpoB has enabled a deeper characterisation of the different streptococci species, which cannot be differentiated using 16S rRNA alone. We have observed that samples from the same person group together regardless of time of sampling. The results indicate that it is possible to distinguish two people using the bacterial microbiota present in their saliva

Long Memory in Earthquake Time Series: The Case Study of the Geysers Geothermal Field.

The present study aims at proving the existence of long memory (or long-range dependence) in the earthquake process through the analysis of time series of induced seismicity. Specifically, we apply alternative statistical techniques borrowed from econometrics to the seismic catalog of The Geysers geothermal field (California), the world’s largest geothermal field. The choice of the study area is essentially guided by the completeness of the seismic catalog at smaller magnitudes (a drawback of conventional catalogs of natural seismicity). Contrary to previous studies, where the long-memory property was examined by using non-parametric approaches (e.g., rescaled range analysis), we assume a fractional integration model for which the degree of memory is defined by a real parameter d, which is related to the best known Hurst exponent. In particular, long-memory behavior is observed for d > 0. We estimate and test the value of d (i.e., the hypothesis of long memory) by applying parametric, semi-parametric, and non-parametric approaches to time series describing the daily number of earthquakes and the logarithm of the (total) seismic moment released per day. Attention is also paid to examining the sensitivity of the results to the uncertainty in the completeness magnitude of the catalog, and to investigating to what extent temporal fluctuations in seismic activity induced by injection operations affect the value of d. Temporal variations in the values of d are analyzed together with those of the b-value of the Gutenberg and Richter law. Our results indicate strong evidence of long memory, with d mostly constrained between 0 and 0.5. We observe that the value of d tends to decrease with increasing the magnitude completeness threshold, and therefore appears to be influenced by the number of information in the chain of intervening related events. Moreover, we find a moderate but significant negative correlation between d and the b-value. A negative, albeit weaker correlation is found between d and the fluid injection, as well as between d and the annual number of earthquakes.post-print4396 K