Chapter Managing Heat Transfer Issues in Thermoelectric Microgenerators

This chapter deals with heat transfer challenges in the microdomain. It focuses on practical issues regarding this matter when attempting the fabrication of small footprint thermoelectric generators (μTEGs). Thermoelectric devices are designed to bridge a heat source (e.g. hot surface) and a heat sink (e.g. ambient) assuring that a significant fraction of the available temperature difference is captured across the active thermoelectric materials. Coexistence of those contrasted temperatures in small devices is challenging. It requires careful decisions about the geometry and the intrinsic thermal properties of the materials involved. The geometrical challenges lead to micromachined architectures, which silicon technologies provide in a controlled way, but leading to fragile structures, too. In addition, extracting heat from small systems is problematic because of the high thermal resistance associated to heat exchanged by natural convection between the surrounding air and small bare surfaces. Forced convection or the application of a cold finger clearly shows the usefulness of assembling a heat exchanger in a way that is effective and compliant with the mechanical constraints of micromachined devices. Simulations and characterization of fabricated structures illustrate the effectiveness of this element integration and its impact on the trade-off between electrical and thermal behavior of the active materials in device performance

New evidence of dominant processing effects in standard and oxygenated silicon diodes after neutron irradiation

Abstract Silicon diodes processed on standard and oxygenated silicon substrates by three different manufacturers have been irradiated by neutrons in a nuclear reactor. The leakage current density ( J D ) increase is linear with the neutron fluence. J D and its annealing curve at 80°C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. The acceptor introduction rate ( β ) of the effective substrate doping concentration ( N eff ) is independent from the oxygen concentration when standard and oxygenated devices from the same manufacturer are considered. On the contrary, β significantly varies from one manufacturer to another showing that the β dependence on the particular process can be important, overtaking the small substrate oxygenation effect. Finally, the average saturation value of the N eff reverse annealing is slightly lower for the oxygenated samples, pointing out a positive effect of the substrate oxygenation even for devices irradiated by neutrons

Managing Heat Transfer Issues in Thermoelectric Microgenerators

This chapter deals with heat transfer challenges in the microdomain. It focuses on practical issues regarding this matter when attempting the fabrication of small footprint thermoelectric generators (μTEGs). Thermoelectric devices are designed to bridge a heat source (e.g. hot surface) and a heat sink (e.g. ambient) assuring that a significant fraction of the available temperature difference is captured across the active thermoelectric materials. Coexistence of those contrasted temperatures in small devices is challenging. It requires careful decisions about the geometry and the intrinsic thermal properties of the materials involved. The geometrical challenges lead to micromachined architectures, which silicon technologies provide in a controlled way, but leading to fragile structures, too. In addition, extracting heat from small systems is problematic because of the high thermal resistance associated to heat exchanged by natural convection between the surrounding air and small bare surfaces. Forced convection or the application of a cold finger clearly shows the usefulness of assembling a heat exchanger in a way that is effective and compliant with the mechanical constraints of micromachined devices. Simulations and characterization of fabricated structures illustrate the effectiveness of this element integration and its impact on the trade-off between electrical and thermal behavior of the active materials in device performance

Neuroprotective Natural Molecules, From Food to Brain

The prevalence of neurodegenerative disorders is increasing; however, an effective neuroprotective treatment is still remaining. Nutrition plays an important role in neuroprotection as recently shown by epidemiological and biochemical studies which identified food components as promising therapeutic agents. Neuroprotection includes mechanisms such as activation of specific receptors, changes in enzymatic neuronal activity, and synthesis and secretion of different bioactive molecules. All these mechanisms are focused on preventing neuronal damage and alleviating the consequences of massive cell loss. Some neuropathological disorders selectively affect to particular neuronal populations, thus is important to know their neurochemical and anatomical properties in order to design effective therapies. Although the design of such treatments would be specific to neuronal groups sensible to damage, the effect would have an impact in the whole nervous system. The difficult overcoming of the blood brain barrier has hampered the development of efficient therapies for prevention or protection. This structure is a physical, enzymatic, and influx barrier that efficiently protects the brain from exogenous molecules. Therefore, the development of new strategies, like nanocarriers, that help to promote the access of neuroprotective molecules to the brain, is needed for providing more effective therapies for the disorders of the central nervous system (CNS). In order both to trace the success of these nanoplatforms on the release of the bioactive cargo in the CNS and determinate the concentration at trace levels of targets biomolecules by analytical chemistry and concretely separation instrumental techniques, constitute an essential tool. Currently, these techniques are used for the determination and identification of natural neuroprotective molecules in complex matrixes at different concentration levels. Separation techniques such as chromatography and capillary electrophoresis (CE), using optical and/or mass spectrometry (MS) detectors, provide multiples combinations for the quantitative and qualitative analysis at basal levels or higher concentrations of bioactive analytes in biological samples. Bearing this in mind, the development of food neuroprotective molecules as brain therapeutic agents is a complex task that requires the intimate collaboration and engagement of different disciplines for a successful outcome. In this sense, this work reviews the new advances achieved in the area toward a better understanding of the current state of the art and highlights promising approaches for brain neuroprotection

Budesonide orodispersible tablets maintain remission in a randomized, placebo-controlled trial of patients with eosinophilic esophagitis

Background & Aims: Eosinophilic esophagitis (EoE) is a chronic inflammatory disorder. Swallowed topical-acting corticosteroids are effective in bringing active EoE into remission. However, it is not clear whether these drugs are effective for long-term maintenance of remission. Methods: We performed a double-blind trial to compare the efficacy and safety of 2 dosages of a budesonide orodispersible tablet (BOT) vs placebo in maintaining remission of EoE. Maintenance of remission was defined as absence of clinical and histologic relapse and no premature withdrawal for any reason. Two hundred and four adults with EoE in clinical and histologic remission, from 29 European study sites, were randomly assigned to groups given BOT 0.5 mg twice daily (n = 68), BOT 1.0 mg twice daily (n = 68), or placebo twice daily (n = 68) for up to 48 weeks. Results: At end of treatment, 73.5% of patients receiving BOT 0.5 mg twice daily and 75% receiving BOT 1.0 mg twice daily were in persistent remission compared with 4.4% of patients in the placebo group (P < .001 for both comparisons of BOT with placebo). Median time to relapse in the placebo group was 87 days. The frequency of adverse events was similar in the BOT and placebo groups. Morning serum levels of cortisol were in the normal range at baseline and did not significantly change during treatment. Four patients receiving BOT developed asymptomatic, low serum levels of cortisol. Clinically manifested candidiasis was suspected in 16.2% of patients in the BOT 0.5 mg group and in 11.8% of patients in the BOT 1.0 mg group; all infections resolved with treatment. Conclusions: In a phase 3 trial, up to 48 weeks of treatment with BOT (0.5 mg or 1.0 mg twice daily) was superior to placebo in maintaining remission of EoE. Both dosages were equally effective and well tolerated. EudraCT number; 2014-001485-99; ClinicalTrials.gov number, NCT02434029

Biosynthetic studies on vitamin B₁₂

Typescript (photocopy).The role of folates in the enzymatic formation of the porphyrin macrocycles was investigated. Uroporphyrinogen III cosynthetase-free hydroxymethylbilane synthase from Rhodopseudomonas spheroides was incubated with the substrate PBG. In contrast to earlier findings with enzyme from rat liver, the presence of tetrahydrofolic acid, 5-methyl-tetrahydrofolic acid or N⁵,N¹⁰-methenyl-tetrahydrofolic acid showed no effect on the ratio of uro'gen III/uro'gen I produced. Several precursors of cobyrinic acid including ALA, PBG, uro'gen III and reduced factor III were used in cobalt-free feeding experiments with whole cells and cell-free preparations from Propionibacterium shermanii. In the absence of cobalt, no intermediates beyond factor III could be isolated. Sufficient factor II and factor III octamethylesters were isolated to allow acquisition of their natural abundance ¹³C NMR spectra and tentative assignments are presented. Reduction of these compounds afforded the corresponding dipyrrocorphins which were characterized both by ¹H and ¹³C NMR. The synthesis of [3-¹³C]ALA is described. High-field ¹³C NMR analyses of three isotopomers (derived from [3-¹³C]ALA, [4-¹³C]ALA and [5-¹³C]ALA) of two new tetramethylated tetrapyrroles permitted their structural characterization. Both compounds are derived from the symmetric uro'gen I and represent the first case of natural methylations on the type I isomer. Factor S₁ is methylated at the four acetate termini and Factor S₃ is methylated at three acetate termini and one α-pyrrolic position. Pulse labeling experiments with whole cells and cell-free preparations from P. shermanii using [¹³CH₃]methionine and [¹³CH₃]S-adenosylmethionine led to the definition of the sequence of methylations beyond the known trimethylated isobacteriochlorin, factor III. The fourth methylation site is C-17, followed by C-12, C-1 and finally C-15/C-5. ¹³C NMR analyses of the incubation products of [4-¹³C]ALA and [¹³CH₃]methionine with P. shermanii showed no formation of C-17 or C-1 methylated species, suggesting that cobalt may be inserted prior the formation of the C-17 methylated pyrrocorphin. A mechanistic scheme based on these results is proposed. [4-¹³C]ALA and [3-¹³C]ALA were fed to P. shermanii in a medium containing 50% D₂O. Analyses of the ¹³C NMR spectra of the cyanocobalamin specimens indicated that both C-18 and C-19 were deuterated. This finding ruled out the intermediacy of 18,19 unsaturated corrins setting further constraints on the possible mechanisms of the last steps of vitamin B₁₂ biosynthesis

Multi-range silicon micromachined flow sensor

A new approach of enlarging the measurement range of a thermal calorimetric flow sensor is presented. It is based on the fact that the response of these kind of sensors tends to saturate at a certain flow ratio, so the widening of the flow range can be achieved by increasing the number of sensing elements of the sensor. This implies only a redesign of the flow sensor device, which is fabricated with an existing standard low cost technology. This approach has been implemented achieving measurement ranges from 0.1 up to 8SLM by placing three different pairs of sensing resistors on the same membrane. Characterisation results and a simulation-based procedure to design flow sensors according to specific applications are included. © 2003 Elsevier B.V. All rights reserved.Peer reviewe

Tolerant Chalcogenide Cathodes of Membraneless Micro Fuel Cells.

International audienceThe most critical issues to overcome in micro direct methanol fuel cells (μDMFCs) are the lack of tolerance of the platinum cathode and fuel crossover through the polymer membrane. Thus, two novel tolerant cathodes of a membraneless microlaminar-flow fuel cell (μLFFC), Pt(x) S(y) and CoSe(2) , were developed. The multichannel structure of the system was microfabricated in SU-8 polymer. A commercial platinum cathode served for comparison. When using 5 M CH(3) OH as the fuel, maximum power densities of 6.5, 4, and 0.23 mW cm(-2) were achieved for the μLFFC with Pt, Pt(x) S(y) , and CoSe(2) cathodes, respectively. The Pt(x) S(y) cathode outperformed Pt in the same fuel cell when using CH(3) OH at concentrations above 10 M. In a situation where fuel crossover is 100 %, that is, mixing the fuel with the reactant, the maximum power density of the micro fuel cell with Pt decreased by 80 %. However, for Pt(x) S(y) this decrease corresponded to 35 % and for CoSe(2) there was no change in performance. This result is the consequence of the high tolerance of the chalcogenide-based cathodes. When using 10 M HCOOH and a palladium-based anode, the μLFFC with a CoSe(2) cathode achieved a maxiumum power density of 1.04 mW cm(-2) . This micro fuel cell does not contain either Nafion membrane or platinum. We report, for the first time, the evaluation of Pt(x) S(y) - and CoSe(2) -based cathodes in membraneless micro fuel cells. The results suggest the development of a novel system that is not size restricted and its operation is mainly based on the selectivity of its electrodes

VALIDEZ DE INSTRUMENTO CALA PARA EVALUAR ASESORÍAS ACADÉMICAS VIRTUALES.

This article shown the validity and reliability of instrument to measure the quality of academic assessment CALA, using dimensions of servqual, quality service model. Objective is the evaluation of perception about the quality of academic assessment through a virtual platform in elementary school institutions. The methodology follows validation of descriptive studio of multidimensional scales, design quasi experimental, factorial analysis technique. Sample was constituted by 1117 students of elementary school institution with mean age of 9.6 years old. Results: 24 indicators in satisfaction dimensions in availability of contents – didactic resources, feedback-follow-up, accessibility, comfort, proper internal consistency α=0.9 (Conbrach, 1951), global intra class correlation coefficient 0.8 (IC of 95%, 0.78 0.82) and Kappa indexes (Cohen, 1960) superiors to 0.78, shown a highly concordance between experts.El artículo presenta la validez y fiabilidad del instrumento CALA utilizando dimensiones del modelo de calidad de servicio servqual. Su objetivo es evaluar la percepción de la calidad de asesorías académicas a través de plataforma virtual en instituciones de educación básica. La metodología sigue estudio descriptivo de validación de escalas multidimensionales, diseño cuasi-experimental, técnica análisis factorial. La muestra estuvo constituida por 1117 estudiantes de instituciones de educación básica del Departamento Norte de Santander, con edad promedio de 9,6 años con una DT de 1,47 años. Resultados: 24 indicadores en dimensiones satisfacción en disponibilidad de contenidos-recursos didácticos, seguimiento-retroalimentación, accesibilidad, comodidad-confort, consistencia interna adecuada (alfa de cronbach 0,9), coeficiente de correlación intraclase global 0,8 (IC del 95%, 0,78-0,82) e índices de Kappa superiores a 0,78, muestra alto acuerdo entre expertos. Conclusión: CALA, es un instrumento válido y confiable para identificar la percepción de la calidad de la asesoría académica