Anatomy, drying behaviour and mechanical properties of lesser used wood species from Mozambique

The study provides an overview of Mozambique timber sector, descriptive and comparative wood anatomy, drying experiments and interrelationships between mechanics, density and anatomical features of lesser used species from Mozambique. Exhaustive literature review described the timber sector as dominated by few hardwood species selectively harvested from a forest containing 118 potential wood species. The survey discussed the need to revert the current situation by proposing studies on lesser used timbers to enlarge the resource base and ensure sustainable logging practices. Afterwards, based on growing stock reported in the forest inventory, three lesser used timbers namely ntholo (Pseudolachnostylis maprounaefolia Pax), metil (Sterculia appendiculata K. Schum) and muanga (Pericopsis angolensis Meeuwen) were selected and subjected to descriptive and comparative wood anatomical studies aiming to understand their structure with regard to prospective end uses. Classical methods of wood sectioning and both light microscopy (LM) and scanning electron microscopy (SEM) were used. The results showed that ntholo and muanga are characterized by diffuse porosity, indistinct growth rings, 18 vessel/mm2, extractives in heartwood vessels, ray width (1-3 cells), % fibre proportion (ntholo 57%; muanga 58%). This set of anatomical features typifies dense timbers with recognized strength and good natural durability. Metil has shown wood structure characterized by very wide vessels without extractives recorded in low density (< 5 vessels/mm2), ground tissues dominated by thin-walled axial parenchyma (50-61%) and fibre proportion (17-27%). Metil wood anatomy is typical for light timbers with poor natural durability. Nevertheless, metil timber seems easy to impregnate with wood preservatives as demonstrated by the high uptake of 463 kg/m3. In addition, the study carried out drying experiments on ntholo boards aimed to assign adequate drying schedule. The experiment was conducted in two stages, i.e. non-symmetrical drying tests (NSD) and laboratory batch kiln drying (LBK). NSD was intended to select provisional schedule and LBK to test the performance of the selected schedule based on European standards. The results from NSD assigned provisional schedule (T6-D2) corresponding to other tropical timbers with similar drying behaviour. The LBK lasted 266 h and ensured standard quality drying described by 8.9% final moisture content, a gradient of 1.2% and 1.2 mm of casehardening. Minor deformations were recorded and twist was the largest with an average of 3.4 mm. However, in general, the drying experiment can be regarded as successful since it provided background for industrial drying. Finally, the study determined ntholo timber mechanics and thereafter examined interrelationships with density and anatomical features of ntholo through correlation and regression analysis. The results show that ntholo is a very dense timber with high mechanical strength in comparison to well known timbers. Correlation analysis revealed fibre length as the only anatomical feature significantly correlated to density and all tested mechanical properties of ntholo. The number of vessels/mm2 and %vessels were not significantly correlated to any of the measured properties but appeared to be key anatomical features for predictions under regression analysis. All tested properties of ntholo sapwood seemed to be influenced mainly by ground tissue proportions, while heartwood properties were described by more leveled anatomical predictors. The regression analyses show that both ntholo sapwood and heartwood densities are poor predictors for the tested mechanical properties, although may provide rough indication of tested properties given the observed correlations. The integrated analysis of results from the timber sector review, wood anatomy, drying behaviour and mechanical properties are expected to form a reliable background for a successful utilization of the relatively lesser explored timbers from Mozambique

Privacy Tradeoffs in Predictive Analytics

Online services routinely mine user data to predict user preferences, make recommendations, and place targeted ads. Recent research has demonstrated that several private user attributes (such as political affiliation, sexual orientation, and gender) can be inferred from such data. Can a privacy-conscious user benefit from personalization while simultaneously protecting her private attributes? We study this question in the context of a rating prediction service based on matrix factorization. We construct a protocol of interactions between the service and users that has remarkable optimality properties: it is privacy-preserving, in that no inference algorithm can succeed in inferring a user's private attribute with a probability better than random guessing; it has maximal accuracy, in that no other privacy-preserving protocol improves rating prediction; and, finally, it involves a minimal disclosure, as the prediction accuracy strictly decreases when the service reveals less information. We extensively evaluate our protocol using several rating datasets, demonstrating that it successfully blocks the inference of gender, age and political affiliation, while incurring less than 5% decrease in the accuracy of rating prediction.Comment: Extended version of the paper appearing in SIGMETRICS 201

Quality control procedures for GNSS precise point positioning in the presence of time correlated residuals

PhD ThesisPrecise point positioning (PPP) is a technique for processing Global Navi- gation Satellite Systems (GNSS) data, often using recursive estimation methods e.g. a Kalman Filter, that can achieve centimetric accuracies using a single receiver. PPP is now the dominant real-time application in o shore marine positioning industry. For high precision real-time applications it is necessary to use high rate orbit and clock corrections in addition to high rate observations. As Kalman filters require input of process and measurement noise statistics, not precisely known in practice, the filter is non-optimal. Geodetic quality control procedures as developed by Baarda in the 1960s are well established and their extension to GNSS is mature. This methodology, largely unchanged since the 1990s, is now being applied to processing techniques that estimate more parameters and utilise many more observations at higher rates. \Detection, Identification and Adaption" (DIA), developed from an optimal filter perspective and utilising Baarda's methodology, is a widely adopted GNSS quality control procedure. DIA utilises various test statistics, which require observation residuals and their variances. Correct derivation of the local test statistic requires residuals at a given epoch to be uncorrelated with those from previous epochs. It is shown that for a non-optimal filter the autocorrelations between observations at successive epochs are non-zero which has implications for proper application of DIA. Whilst less problematic for longer data sampling periods, high rate data using real-time PPP results in significant time correlations between residuals over short periods. It is possible to model time correlations in the residuals as an autoregressive process. Using the autoregressive parameters, the effect of time correlation in the residuals can be removed, creating so-called whitened residuals and their variances. Thus a whitened test statistic can be formed, that satisfies the preferred assumption of uncorrelated residuals over time. The effectiveness of this whitened test statistic and its impact on quality control is evaluated.Fugro Intersite B.V.: The Natural Environment Research Council