La educación no formal de alumnos de primaria mediante la teoría de las situaciones didácticas : el caso del ludión

La teoría de situaciones didácticas de Guy Brousseau que se desarrolló en el área de las matemáticas ahora se está aplicando a todas las ciencias experimentales. Se presenta aquí su adaptación al programa de educación no formal «Niñ@s Talento» para alumnos de nivel primaria al emplear el experimento del ludión o buzo cartesiano. Una ventaja de esta teoría es que no exige llegar a los conocimientos científicos escolares (fase de institucionalización) para explicar diversos experimentos realizados. De esta manera los alumnos que participaron en esta actividad lúdica disfrutan realmente las situaciones didácticas y generan conocimiento que les permite explicar lo observado, a su nivel de conocimiento

Effect of Knife Wear on the Gluability of Planed Surfaces of Radiata Pine

The objectives of this study were to evaluate the effect of knife wear on the gluability of planed surfaces of radiata pine. A conventional process was used to plane samples to four lengths: 200; 10,000; 20,000; and 30,000 m. Cutting-edge recession was measured on the clearance surface of the planing knife for each length. The gluing properties of the planed surfaces were determined for each of the four levels of knife wear using polyvinyl acetate and emulsion polymer isocyanate adhesives. The results showed that the greatest amount of cutting-edge recession on the clearance surface was 65 μm after 30,000 m of planing. The tensile shear strength (TSS) of the lap-joint glue line decreased with knife wear from increased planing. However, TSS was generally greater than the minimum prescribed by the BS EN 204 standard. The effect of knife wear on TSS was more significant after accelerated aging of the glued samples

A User-Friendly Dynamic Reactor Simulator Built in Microsoft Excel

Computer plant simulation is being used in all aspects of engineering, through many simulation software packages. However, almost all of them require licenses that must be purchased by engineering colleges intending to use simulation in their teaching. As public educational institutions everywhere are facing a scarcity of economic resources, they can resort to a freeware steady-state plant simulator, however, there is no availability of reliable, free dynamic plant simulators. In addition, published experiences on developing dynamic simulators use programming languages requiring paid licenses (e.g. Matlab) and thus have limited relevancy to schools struggling to cut expenses. This article first uses a set of typical college objectives to discuss the advantages of building their own dynamic simulators, and then shows the development of a user-friendly dynamic simulator of a batch reactor constructed entirely within Microsoft Excel, which, in contrast to the programming languages used in related reports, is already widely used by universities around the world

Constitutive expression of selected genes from the pentose phosphate and aromatic pathways increases the shikimic acid yield in high-glucose batch cultures of an Escherichia coli strain lacking PTS and pykF

BACKGROUND: During the last two decades many efforts have been directed towards obtaining efficient microbial processes for the production of shikimic acid (SA); however, feeding high amounts of substrate to increase the titer of this compound has invariably rendered low conversion yields, leaving room for improvement of the producing strains. In this work we report an alternative platform to overproduce SA in a laboratory-evolved Escherichia coli strain, based on plasmid-driven constitutive expression of six genes selected from the pentose phosphate and aromatic amino acid pathways, artificially arranged as an operon. Production strains also carried inactivated genes coding for phosphotransferase system components (ptsHIcrr), shikimate kinases I and II (aroK and aroL), pyruvate kinase I (pykF) and the lactose operon repressor (lacI). RESULTS: The strong and constitutive expression of the constructed operon permitted SA production from the beginning of the cultures, as evidenced in 1 L batch-mode fermentors starting with high concentrations of glucose and yeast extract. Inactivation of the pykF gene improved SA production under the evaluated conditions by increasing the titer, yield and productivity of this metabolite compared to the isogenic pykF(+) strain. The best producing strain accumulated up to 43 g/L of SA in 30 h and relatively low concentrations of acetate and aromatic byproducts were detected, with SA accounting for 80% of the produced aromatic compounds. These results were consistent with high expression levels of the glycolytic pathway and synthetic operon genes from the beginning of fermentations, as revealed by transcriptomic analysis. Despite the consumption of 100 g/L of glucose, the yields on glucose of SA and of total aromatic compounds were about 50% and 60% of the theoretical maximum, respectively. The obtained yields and specific production and consumption rates proved to be constant with three different substrate concentrations. CONCLUSIONS: The developed production system allowed continuous SA accumulation until glucose exhaustion and eliminated the requirement for culture inducers. The obtained SA titers and yields represent the highest reported values for a high-substrate batch process, postulating the strategy described in this report as an interesting alternative to the traditionally employed fed-batch processes for SA production

Fast jitter tolerance testing for high-speed serial links in post-silicon validation

Post-silicon electrical validation of high-speed input/output (HSIO) links is a critical process for product qualification schedules of high-performance computer platforms under current aggressive time-to-market (TTM) commitments. Improvements in signaling methods, circuits, and process technologies have allowed HSIO data rates to scale well beyond 10 Gb/s. Noise and EM effects can create multiple signal integrity problems, which are aggravated by continuously faster bus technologies. The goal of post-silicon validation for HSIO links is to ensure design robustness of both receiver (Rx) and transmitter (Tx) circuitry in real system environments. One of the most common ways to evaluate the performance of a HSIO link is to characterize the Rx jitter tolerance (JTOL) performance by measuring the bit error rate (BER) of the link under worst stressing conditions. However, JTOL testing is extremely time-consuming when executed at specification BER considering manufacturing process, voltage, and temperature (PVT) test coverage. In order to significantly accelerate this process, we propose a novel approach for JTOL testing based on an efficient direct search optimization methodology. Our approach exploits the fast execution of a modified golden section search with a high BER, while overcoming the lack of correlation between different BERs by performing a downward linear search at the actual target BER until no errors are found. Our proposed methodology is validated in a realistic industrial server post-silicon validation platform for three different computer HSIO links: SATA, USB3, and PCIe3.ITESO, A.C

Metabolic engineering for improving anthranilate synthesis from glucose in Escherichia coli

© 2009 Balderas-Hernández et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

Quantification of glycated hemoglobin and glucose in vivo using Raman spectroscopy and artificial neural networks

Undiagnosed type 2 diabetes (T2D) remains a major public health concern. The global estimation of undiagnosed diabetes is about 46%, being this situation more critical in developing countries. Therefore, we proposed a non-invasive method to quantify glycated hemoglobin (HbA1c) and glucose in vivo. We developed a technique based on Raman spectroscopy, RReliefF as a feature selection method, and regression based on feed-forward artificial neural networks (FFNN). The spectra were obtained from the forearm, wrist, and index finger of 46 individuals. The use of FFNN allowed us to achieve an error in the predictive model of 0.69% for HbA1c and 30.12 mg/dL for glucose. Patients were classified according to HbA1c values into three categories: healthy, prediabetes, and T2D. The proposed method obtained a specificity and sensitivity of 87.50% and 80.77%, respectively. This work demonstrates the benefit of using artificial neural networks and feature selection techniques to enhance Raman spectra processing to determine glycated hemoglobin and glucose in patients with undiagnosed T2D

PCIe Gen5 Physical Layer Equalization Tuning by Using K-means Clustering and Gaussian Process Regression Modeling in Industrial Post-silicon Validation

Peripheral component interconnect express (PCIe) is a high-performance interconnect architecture widely adopted in the computer industry. The continuously increasing bandwidth demand from new applications has led to the development of the PCIe Gen5, reaching data rates of 32 GT/s. To mitigate undesired channel effects due to such high-speed, the PCIe specification defines an equalization process at the transmitter (Tx) and the receiver (Rx). Current post-silicon validation practices consist of finding an optimal subset of Tx and Rx coefficients by measuring the eye diagrams across different channels. However, these experiments are very time consuming since they require massive lab measurements. In this paper, we use a K-means approach to cluster all available post-silicon data from different channels and feed those clusters to a Gaussian process regression (GPR)-based metamodel for each channel. We then perform a surrogate-based optimization to obtain the optimal tuning settings for the specific channels. Our methodology is validated by measurements of the functional eye diagram of an industrial computer platform.ITESO, A.C

Free energy of colloidal particles at the surface of sessile drops

The influence of finite system size on the free energy of a spherical particle floating at the surface of a sessile droplet is studied both analytically and numerically. In the special case that the contact angle at the substrate equals $\pi/2$ a capillary analogue of the method of images is applied in order to calculate small deformations of the droplet shape if an external force is applied to the particle. The type of boundary conditions for the droplet shape at the substrate determines the sign of the capillary monopole associated with the image particle. Therefore, the free energy of the particle, which is proportional to the interaction energy of the original particle with its image, can be of either sign, too. The analytic solutions, given by the Green's function of the capillary equation, are constructed such that the condition of the forces acting on the droplet being balanced and of the volume constraint are fulfilled. Besides the known phenomena of attraction of a particle to a free contact line and repulsion from a pinned one, we observe a local free energy minimum for the particle being located at the drop apex or at an intermediate angle, respectively. This peculiarity can be traced back to a non-monotonic behavior of the Green's function, which reflects the interplay between the deformations of the droplet shape and the volume constraint.Comment: 24 pages, 19 figure

System Margining Surrogate-Based Optimization in Post-Silicon Validation

There is an increasingly higher number of mixed-signal circuits within microprocessors. A significant portion of them corresponds to high-speed input/output (HSIO) links. Post-silicon validation of HSIO links is critical to provide a release qualification decision. One of the major challenges in HSIO electrical validation is the physical layer (PHY) tuning process, where equalization techniques are typically used to cancel any undesired effect. Current industrial practices for PHY tuning in HSIO links are very time consuming since they require massive lab measurements. On the other hand, surrogate modeling techniques allow to develop an approximation of a system response within a design space of interest. In this paper, we analyze several surrogate modeling methods and design of experiments techniques to identify the best approach to efficiently optimize a receiver equalizer. We evaluate the models performance by comparing with actual measured responses on a real server HSIO link. We then perform a surrogate-based optimization on the best model to obtain the optimal PHY tuning settings of a HSIO link. Our methodology is validated by measuring the real functional eye diagram of the physical system using the optimal surrogate model solution