Low-cost disordered carbons for Li/S batteries: A high-performance carbon with dual porosity derived from cherry pits

A micro- and mesoporous carbon obtained from cherry pit waste and activated with H₃PO₄ acid has been studied as the sulfur host for Li/S batteries. The carbon has a high specific surface area of 1,662 m²·g^–1 (SBET) and micropore and mesopore volumes of 0.57 and 0.40 cm³·g^–1, respectively. The S/C composite, with a sulfur content of 57% deposited by the disproportionate reaction of a S₂O₃ ^2? solution in an acid medium without an additional heating step above the S melting point, delivers an initial specific capacity of 1,148 mAh·g^–1 at a current of C/16. It also has a high capacity retention of 915 mAh·g^–1 after 100 cycles and a Coulombic efficiency close to 100%. The good performance of the composite was also observed under higher current rates and long-term cycling tests. The capacities delivered by the cell after 200 cycles were 707 and 410 mAh·g^–1 at C/2 and 1C (1C = 1,675 mA·g^–1), respectively, maintaining the high Coulombic efficiency. The overall electrochemical response of this carbon as the sulfur matrix is among the best reported so far among the other biomass-derived carbons, probably because of the micro- and mesopore system formed upon activation.

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Fractional Fourier transform optical system with programmable diffractive lenses

We present experimental results for a fractional Fourier transform (FRFT) system implemented with programmable lenses written onto a liquid-crystal spatial light modulator (LCSLM). Because the focal length can be changed, different orders of the FRFT can be obtained without changing the optical setup. The LCSLM can very easily implement more complicated operations, including the realization of simultaneous orders of the FRFT and anamorphic transforms.     

Surface analysis and electrochemical behavior of Ti–20Zr alloy in simulated physiological fluids

An advanced Ti–20Zr alloy was obtained by double vacuum melting in a semi-levitation furnace with cold crucible. The alloy shows fully lamellar α + β microstructure. Cyclic potentiodynamic polarization curves revealed that the alloy passivated easier, more rapid than Ti, having a more stable passive film in Ringer solutions of different pH values, simulating severe functional conditions of an implant. In neutral and alkaline Ringer solutions, the alloy passive film improved its properties in time (1500 h) by the deposition of protective hydroxyapatite, as was demonstrated by XPS, SEM, EDX, Raman and FT-IR measurements. Alloy presented lower corrosion rates and higher polarization resistances (from linear polarization measurements) than those of Ti (tens of times) proving a more resistant passive film. Alloy open circuit potentials had more electropositive values in comparison with Ti and tended to nobler values in time, which denote better passive state and its enhancement in time, due to the new depositions from the physiological solutions. Nyquist and Bode spectra depicted a more protective passive film on the alloy surface than on Ti surface. The passive film is formed by two layers: an inner barrier layer and an outer porous layer. An electric equivalent circuit with two time constants was modeled.     

An improved procedure for obtaining and maintaining well characterized partial water saturation states on concrete samples to be used for mass transport tests

A conditioning procedure is proposed allowing to install into the concrete specimens any selected value of water saturation degree with homogeneous moisture distribution. This is achieved within the least time and the minimum alteration of the concrete specimens. The protocol has the following steps: obtaining basic drying data at 50 °C (water absorption capacity and drying curves); unidirectional drying of the specimens at 50 °C until reaching the target saturation degree values; redistribution phase in closed containers at 50 °C (with measurement of the quasi-equilibrium relative humidities); storage into controlled environment chambers until and during mass transport tests, if necessary. A water transport model is used to derive transport parameters of the tested materials from the drying data, i.e., relative permeabilities and apparent water diffusion coefficients. The model also allows calculating moisture profiles during isothermal drying and redistribution phases, thus allowing optimization of the redistribution times for obtaining homogeneous moisture distributions.     

Minimum deviation angle in uniaxial prisms

Dispersion in a uniaxial prism provides an example of the application of the law of refraction for a uniaxial crystal. Formulas for the minimum deviation angle for the extraordinary ray are given when the crystal axis lies in the plane of incidence. Three particular cases for the crystal axis position are presented and are shown to have a behavior similar to that of an ordinary prism.     

Image segmentation through graph-based clustering from surface normals estimated by photometric stereo

A method for segmenting 2D images based on 3D shape information is proposed. First, a robust photometric stereo technique estimates the 3D normals of the objects present in the scene for every image pixel. Then, the image is segmented by grouping its pixels according to their estimated normals through graph-based clustering. Differently from other image segmentation algorithms based on intensity, colour or texture, the regions of which are determined by the visual appearance of the depicted objects, the regions obtained with the proposed technique only depend on the 3D shapes of those objects. This can be advantageous for higher level scene understanding algorithms. This technique is especially suited to poorly illuminated scenarios and utilises a conventional camera and six inexpensive strobe lights.     

A physically based C∞-continuous model forsmall-geometry MOSFET's

An explicit single-piece MOSFET model is derived from a surface potential formulation. The model covers small-geometry effects, like mobility reduction, channel-length modulation, carrier velocity saturation, and short- and narrow-channel effects. Good agreement has been found with measured characteristics. Furthermore, the DC current calculated using the new model shows smooth transitions through all regions of operation. Therefore the convergence when employed in circuit simulation will be improved     

New constructions of optimal cyclically permutable constant weightcodes

Three new constructions for families of cyclic constant weight codes are presented. All are asymptotically optimum in the sense that in each case, as the length of the sequences within the family approaches infinity, the ratio of family size to the maximum possible under the Johnson upper bound, approaches unity     

Brain maturation estimation using neural classifier

Quantitative electroencephalographic (EEG) signal analysis has revealed itself as an important diagnostic tool in the last few years. Through the use of signal processing techniques, new quantitative representations of EEG data are obtained. To automate the diagnosis, a problem of supervised classification must be solved on these. Artificial neural networks provide an alternative to more traditional classifier systems for this task. The authors perform a comparison between several classifiers in a particular problem, the brain maturation prediction. The data preprocessing/feature extraction process and the methodology for making the comparison are described. Performance of the methods is evaluated in terms of estimated percentage of correctly classified subjects     

Empirical study of a sequence of access to Internet use in Ecuador

Ecuador is a country that represents the efforts that a few countries in the Latin American and the Caribbean region are making on infrastructures, regulations and policies that are favorable towards the use of the Internet. However, although the digital divide in its most basic form (physical access and use) is closing with respect to developed countries, a new, more complex digital divide is moving forward, and is related to the socio-economic advantages of the Internet. This study, which used a random sample stratified by provinces and which comprised 3754 respondents representing the secondary school students in Ecuador, had as objectives: (a) to verify the relationship and sequence among the different levels to access the Internet found on secondary school students; and (b) to verify to what degree the student’s family status influenced the different levels of Internet access. Through the empirical analysis of a structural model, the results showed a sequence between the relationships found among the different levels of Internet access, as well as the cumulative effect of the technical resources and levels of digital literacy on the academic use of the Internet. Likewise, it was observed that the influence of the student’s family status lost strength as the level of Internet access increased.