Noise-resolution trade-off in projection algorithms for laser diffraction particle sizing

The size distribution of a particle suspension can be inferred from studying the diffracted light pattern produced by a laser beam that passes through the suspension. This involves solving an ill-posed linear system. Two previous versions of projection algorithms were tested by use of computer simulations and experiments. Both algorithms showed limitations in restoring the size distribution, because of either the shape of the size distribution or the presence of noise in the scattered light signal. The generalized projection algorithm presented in this work solves these difficulties by introducing a parameter that allows the user to adjust the noise-resolution trade-off, making it suitable for the analysis of natural suspensions.     

Linking quantitative exposure assessment and risk management using the food safety objective concept: an example with Listeria monocytogenes in different cross-contamination scenarios

A practical approach was used to achieve specified food safety objectives (FSOs) by incorporating risk assessment methodology. A series of cross-contamination scenarios at the retail level were evaluated in a spreadsheet and ranked according to their level of risk, and the degree to which they exceeded an FSO for Listeria monocytogenes (100 CFU/g) was determined. Percentiles and analyses of variance were used to identify which scenarios would be most likely not to achieve the FSO. It was also possible to incorporate into the model the effect of additional risk management interventions (e.g., hand washing method) by using "what if" scenarios analysis. The highest risk corresponded to the use of the same gloves to handle contaminated meat and then sliced ham compared with the safer method of using different gloves to handle each product. Nevertheless, in all scenarios bacterial concentrations could be higher than 10(8) CFU/g. A significant lack of knowledge regarding the transfer rates of L. monocytogenes was revealed, which provided the model with an important uncertainty component. The "what if" scenarios analysis based on the scenario representing handling food with bare hands followed by hand washing (scenario 2) revealed that the hand washing procedure had less impact than expected. This study illustrates the use of scenarios to model the most effective food processes and thus provide risk managers with appropriate information on which to base their decisions.     

Modelling the structure of latexin-carboxypeptidase A complex based on chemical cross-linking and molecular docking

We have determined the three-dimensional structure of the protein complex between latexin and carboxypeptidase A using a combination of chemical cross-linking, mass spectrometry and molecular docking. The locations of three intermolecular cross-links were identified using mass spectrometry and these constraints were used in combination with a speed-optimised docking algorithm allowing us to evaluate more than 3 x 10(11) possible conformations. While cross-links represent only limited structural constraints, the combination of only three experimental cross-links with very basic molecular docking was sufficient to determine the complex structure. The crystal structure of the complex between latexin and carboxypeptidase A4 determined recently allowed us to assess the success of this structure determination approach. Our structure was shown to be within 4 A r.m.s. deviation of Calpha atoms of the crystal structure. The study demonstrates that cross-linking in combination with mass spectrometry can lead to efficient and accurate structural modelling of protein complexes.     

High reliability outdoor sonar prototype based on efficient signal coding

Many mobile robots and autonomous vehicles designed for outdoor operation have incorporated ultrasonic sensors in their navigation systems, whose function is mainly to avoid possible collisions with very close obstacles. The use of these systems in more precise tasks requires signal encoding and the incorporation of pulse compression techniques that have already been used with success in the design of high-performance indoor sonars. However, the transmission of ultrasonic encoded signals outdoors entails a new challenge because of the effects of atmospheric turbulence. This phenomenon causes random fluctuations in the phase and amplitude of traveling acoustic waves, a fact that can make the encoded signal completely unrecognizable by its matched receiver. Atmospheric turbulence is investigated in this work, with the aim of determining the conditions under which it is possible to assure the reliable outdoor operation of an ultrasonic pulse compression system. As a result of this analysis, a novel sonar prototype based on complementary sequences coding is developed and experimentally tested. This encoding scheme provides the system with very useful additional features, namely, high robustness to noise, multi-mode operation capability (simultaneous emissions with minimum cross talk interference), and the possibility of applying an efficient detection algorithm that notably decreases the hardware resource requirements.     

Gauss-Legendre quadrature method used to evaluate the spatio-temporal intensity of ultrashort pulses in the focal region of lenses

We analyze the spatio-temporal intensity of sub-20 femtosecond pulses with a carrier wavelength of 810 nm along the optical axis of low numerical aperture achromatic and apochromatic doublets designed in the IR region by using the scalar diffraction theory. The diffraction integral is solved by expanding the wave number around the carrier frequency of the pulse in a Taylor series up to third order, and then the integral over the frequencies is solved by using the Gauss-Legendre quadrature method. The numerical errors in this method are negligible by taking 96 nodes and the computational time is reduced by 95% compared to the integration method by rectangles. We will show that the third-order group velocity dispersion (GVD) is not negligible for 10 fs pulses at 810 nm propagating through the low numerical aperture doublets, and its effect is more important than the propagation time difference (PTD). This last effect, however, is also significant. For sub-20 femtosecond pulses, these two effects make the use of a pulse shaper necessary to correct for second and higher-order GVD terms and also the use of apochromatic optics to correct the PTD effect. The design of an apochromatic doublet is presented in this paper and the spatio-temporal intensity of the pulse at the focal region of this doublet is compared to that given by the achromatic doublet.     

Generation of Bessel beam arrays through Dammann gratings

In this work we apply the Dammann grating concept to generate an equal-intensity square array of Bessel quasi-free diffraction beams that diverge from a common center. We generate a binary phase mask that combines the axicon phase with the phase of a Dammann grating. The procedure can be extended to include vortex spiral phases that generate an array of optical pipes. Experimental results are provided by means of a twisted nematic liquid crystal display operating as a binary π phase spatial light modulator.     

Characterization of a SrF2 Scintillating Bolometer

We present the analysis of the data obtained with a 53?g SrF₂ scintillating bolometer operated at 20?mK. We have analyzed its heat and light response (time constants, linearity and energy resolution) and measured its scintillation relative efficiency factor for different particles (alpha, beta/gamma and neutrons). We have studied the spatial uniformity of the light output profiting from its internal contamination. The light amplitude of alphas from the delayed coincidence ²²⁴Ra→²²⁰Rn→²¹⁶Po (emitted from the same crystal position) shows a positive correlation, evidence of a non-uniformity that worsens the light signal energy resolution by more than?50%.     

Environmental and economic feasibility of sugarcane ethanol for the Mexican transport sector

This study analyzes the environmental and economic feasibility of ethanol produced from sugarcane for use as a potential gasoline substitute in the Mexican transport sector from 2010 to 2030. One scenario was created by projecting the historical trend of energy demand assuming that a fraction of this demand is satisfied with ethanol produced from the cultivation of 2.9 million hectares of sugarcane. A life cycle study was performed according to the recommendations from the European Union Directive on Renewable Energies (that include direct land use change emissions) and was used to estimate life cycle Greenhouse gas (GHG) emissions. The method used by Fingerman et al. (2010) was adopted to estimate the water consumption. In the economic analysis, the production cost of ethanol was calculated, and a mitigation cost for carbon dioxide equivalent emissions was estimated. The potential for employment generation was also estimated. The results demonstrate that water use increases by 29.4 times and that the costs increase by 10,706 million USD with the alternative scenario. This scenario, however, has the potential to create 560,619 direct jobs. Furthermore, GHG mitigation is confirmed since the reference scenario resulted in GHG gasoline life cycle emissions of 78.7 kgCO_2e/GJ while the alternative scenario resulted in Ethanol GHG emissions in the life cycle of 57.52 kgCO_2e/GJ.     

Surface and structural characterisation of coprecipitated CexZr1?xO2 (0?≤?x?≤?1) mixed oxides

Ce _x Zr_1−x O₂-mixed oxides with three different Ce/Zr ratios (Ce_0.8Zr_0.2O₂, Ce_0.5Zr_0.5O₂ and Ce_0.2Zr_0.8O₂) along with pure cerium and zirconium oxides were prepared by coprecipitation of the metal hydroxides in alkali media and subsequent calcinations at 500 °C, using two different cerium precursors (Ce(NO₃)₃·6H₂O or (NH₄)₂Ce(NO₃)₆). These samples were characterised by N₂ adsorption at −196 °C, XRD, Raman spectroscopy, XPS and H₂-temperature programmed reduction. Besides, the two mixed oxides with higher cerium content were calcined at higher temperature (1000 °C) with the additional purpose of studying their thermal stability and phase homogeneity. XRD and Raman spectroscopy confirm a significant improvement in the insertion of zirconium cations into the ceria lattice when the samples Ce_0.8Zr_0.2O₂ and Ce_0.5Zr_0.5O₂ are synthesised with (NH₄)₂Ce(NO₃)₆ instead of Ce(NO₃)₃·6H₂O. This is attributed to a more homogeneous coprecipitation of cerium and zirconium hydroxides, leading to mixed oxides with better bulk oxygen mobility and smaller lattice parameter. Moreover, the mixed oxides prepared with the (NH₄)₂Ce(NO₃)₆ precursor and calcined at 1000 °C exhibit a single phase whereas phase segregation occurs in the counterpart mixed oxides prepared with the Ce(NO₃)₃·6H₂O precursor. XPS analysis reveal correlations among O/(Ce + Zr) surface atomic ratio and total cerium content for both cerium precursors. Among the samples calcined at 1000 °C, Ce_0.8Zr_0.2O₂ synthesised with Ce(NO₃)₃·6H₂O is the only one that preserves the low-temperature surface reduction peak, and also shows a BET surface area slightly higher than those of the rest of samples calcined at high temperature.     

Thermal Characterization, Using the Photopyroelectric Technique, of Liquids Used in the Automobile Industry

Thermal properties of liquids used in the automobile industry such as engine oil, antifreeze, and a liquid for windshield wipers were obtained using the photopyroelectric (PPE) technique. The inverse PPE configuration was used in order to obtain the thermal effusivity of the liquid samples. The theoretical equation for the PPE signal in this configuration, as a function of the incident light modulation frequency, was fitted to the experimental data in order to obtain the thermal effusivity of these samples. Also, the back PPE configuration was used to obtain the thermal diffusivity of these liquids; this thermal parameter was obtained by fitting the theoretical equation for this configuration, as a function of the sample thickness (called the thermal wave resonator cavity), to the experimental data. All measurements were done at room temperature. A complete thermal characterization of these liquids used in the automobile industry was achieved by the relationship between the obtained thermal diffusivities and thermal effusivities with their thermal conductivities and volumetric heat capacities. The obtained results are compared with the thermal properties of similar liquids.