High Temperature Thermoelectric Device Concept Using Large Area PN Junction

Thermoelektrische Elemente können zur Erzeugung elektrischer Energie aus einer Temperaturdifferenz verwendet werden. Traditionell basieren thermoelektrische Generatoren auf komplementär dotierten Halbleitern, welche elektrisch in Serie und thermisch parallel verschaltet werden. Bei dem herkömmlichen Aufbau werden auf der Kalt- und auf der Heißseite sowohl elektrische als auch mechanische Kontakte auf einem Keramiksubstrat realisiert. In dieser Arbeit wird ein großflächiger pn-Übergang zur elektrischen Verbindung der komplementären Halbleiter auf der Heißseite verwendet. Damit erübrigt sich dort das verbindende Substrat, und dessen Verzicht führt zu einer Steigerung der Heißseitentemperatur. Darüberhinaus werden Probleme in Hinblick auf die Stabilität von elektro-mechanischem Kontakt sowie chemische Wechselwirkungen stark reduziert. Es zeigt sich, dass ein derartiges pn-Übergangs-Thermoelektrikelement ein zweidimensionales Transportverhalten aufweist, welches sich nicht durch das sonst übliche, eindimensionale „Constant property“-Modell beschreiben lässt. Hier wird nun ein grundsätzliches physikalisches Modell vorgeschlagen und mittels Simulationen auf Basis der Onsager-Theorie überprüft. Die simulierten thermischen und elektrischen Flüsse zeigen insbesondere auf, dass elektrische Verluste durch Kreisströme innerhalb des pn-Elementes hervorgerufen werden. Ferner geben die Simulationen Hinweise auf mögliche geometrische Optimierungen zur Reduzierung der Verluste, und eine entsprechende positive Wirkung konnte von uns tatsächlich experimentell nachgewiesen werden. Wir verwenden nanostrukturiertes Silizium aufgrund der im Vergleich zu kristallinem Material verringerten thermischen Leitfähigkeit. Die nanostrukturierten Proben wurden aus Nanopartikeln in der Gasphase hergestellt und durch ein „Spark-Plasma“-Sinterverfahren verdichtet. Zusätzlich zu den nanostrukturierten Siliziumproben wurden pn-Übergänge durch Lasersinterung von dotierten Nanopartikeln auf einem entgegengesetzt dotierten Siliziumwafer bzw. durch Verschweißen komplementärer Wafer hergestellt. Ein geeigneter Messplatz wurde entwickelt und eingerichtet, und es wurde gezeigt, dass die nanostrukturierten pn-Übergänge wiederholte Heizzyklen mit einer Heißseitentemperatur von 780°C überstehen. Somit wurde gezeigt, dass thermoelektrische Elemente auf Basis von pn-Übergängen bei höheren Temperaturen verwendet werden können als herkömmliche Generatoren. Und trotz der internen Verluste zeigen pn-Übergangselemente bei hohen Temperaturen vergleichbare Ausgangsleistungen wie die konventionellen Generatoren.Thermoelectric devices can be used to produce electricity given a temperature difference. Traditionally, thermoelectric devices are built by connecting complementary doped semiconductor materials electrically in series and thermally in parallel. In this architecture a ceramic substrate on both the cold and hot sides provides support for the electrical and mechanical connections. In this work, a large area pn junction is used to provide an electrical connection between the complementary semiconductors on the hot side. Having a pn junction means that the hot side electrical contacts are not required. The dismissal of the hot side substrate translates to higher hot side temperatures since problems associated with the stability of the electrical, mechanical and chemical properties on the hot side of the thermoelectric generator are largely reduced. A pn junction thermoelectric device is demonstrated to be a two dimensional transport device which cannot be described by the one dimensional constant property model commonly used in thermoelectrics theory. A basic working principle is proposed and further verified using simulations based on Onsager’s theory. The simulations describe the behavior of the pn junction device in terms of thermal and electrical fluxes and indicate that electrical losses arise due to internal current vortices within the pn thermoelectric device. The simulations also indicate that a geometrical optimization can be done to reduce such losses, and this we could verify experimentally. Nanostructured silicon is used as the primary material system due to its relatively low thermal conductivity with respect to crystalline silicon. The nanostructured samples are produced from nanoparticles produced from a gas phase, and densified by a spark plasma sintering method. In addition to the nanostructured silicon samples, pn junctions are produced by laser sintering of doped nanoparticles on a complementary doped silicon wafer, and by welding of complementary silicon wafers together. The metrology system is developed and it is shown that the nanostructured pn junctions can sustain repeated heating cycles with a hot side temperature of 780°C. It is shown that pn junction devices can be operated in higher temperatures than conventional devices and despite the internal losses of a pn junction device, it has comparable output power characteristic than a conventional device given high temperatures

EVALUACIÓN DE LA CONCENTRACIÓN DE CADMIO EN EL SUELO Y FRUTOS DE UNA PLANTACIÓN DE CACAO (Theobroma cacao L.) EN AUCAYACU, DISTRITO DE JOSÉ CRESPO Y CASTILLO - HUÁNUCO 2020

Esta tesis titulada fue realizado con la finalidad de evaluar la concentración de cadmio en el suelo y frutos (granos de cacao) de una plantación de cacao, de la zona de Aucayacu; buscando a la vez demostrar la presencia de este metal pesado, en uno de los productos más importantes de la región Huánuco; y del Perú. Por lo que la presente investigación tuvo como objetivo general: Evaluar la concentración de cadmio en el suelo y frutos de una plantación de cacao (Theobroma cacao L.) en Aucayacu, distrito de José Crespo y Castillo - Huánuco 2020. Para esta investigación, se realizó el muestreo en la zona establecida, donde se recolectaron 5 muestras de suelo y de frutos en (mazorcas), las cuales fueron trasladadas al laboratorio de la UNAS, para sus respectivos análisis. Los resultados fueron; Para suelo: El suelo cacaotero, de la zona de Aucayacu presenta un pH, de 5.19, lo cual refiere que es muy acido, en cuanto a la concentración de cadmio en el suelo fue de 0.21 ppm, estos resultados fueron comparados con el ECA, indicando que no sobrepasa el ECA; para suelos agrícolas. Si bien no sobrepasan el ECA (1.4 ppm), respectivo; demuestra la presencia de Cd en el suelo del cultivo de cacao (Theobroma cacao L.). Para Fruto (granos de cacao): La concentración de cadmio disponible en los granos de cacao (Theobroma cacao L.), de una plantación de la zona de Aucayacu, fue de 0.638 ppm, estos resultados fueron comparados con el LMP, respectivo, indicando que sobrepasa el LMP (0.50 ppm).Tesi

La Alfabetización digital mediado web 2.0 para fortalecer las competencias de gestión educativa en directivos, Santiago de Chuco 2019

La presente investigación tiene como objetivo general determinar si el programa de alfabetización digital mediado Web 2.0 fortalece las Competencias de gestión educativa en directivos, Santiago de Chuco 2019. El fundamento se sustenta en las dimensiones, de la Gestión propuestas por Senge (2016) y Pozner (2014), Gestión institucional, Gestión pedagógica, Gestión administrativa y Gestión comunitaria. La metodología de investigación es de tipo aplicada, con un diseño es cuasiexperimental, tomándose una muestra no probabilística, a través de la técnica del muestreo por conveniencia. La muestra la conformaron 50 directivos entre los niveles de primaria y secundaria, distribuidos en 25 directivos para el grupo control y 25 directivos para el grupo experimental. Se utilizó el método hipotético deductivo, la técnica empleada fue la observación y el instrumento que se utilizó fue la Guía de observación para valorar la alfabetización digital mediado Web 2.0 en las competencias de Gestión Institucional, Pedagógica, Administrativa y Comunitaria. Este instrumento fue validado a través de juicio de expertos, para su confiabilidad se aplicó una prueba piloto a 23 directivos con la misma realidad y características, obteniendo una confiabilidad de 0,936 según el Alfa de Cronbach. El programa de Alfabetización digital se realizó en sesiones de aprendizaje. La evaluación del pre test y post en el grupo experimental en la variable Competencias de Gestión Educativa, se observó una media de 57,5 en el pre test a 65,5 en el post test lo que representa un aumento de 8 puntos. Por otro lado, en la prueba de hipótesis de “t” de Student los resultados se encuentran al 95% de confiabilidad, donde se obtuvo el grado de significancia de 0,01 con p < 0,05 en consecuencia se rechaza la hipótesis nula y se acepta la hipótesis de investigación. Es decir, se acepta que el programa de alfabetización digital mediado Web 2.0 fortalece significativamente las competencias de Gestión Educativa en los directivos, Santiago de Chuco, 2019

The incidence of some critical cognitive factors that prevent change of order in university students: uncertainty analysis

School performance depends on cognitive impact while academic performance depends on how the qualitative and quantitative evaluation of students is carried out, which is open to a wide range of very complex criteria. Students’ emotional intelligence is put to the test by the intense and constant completion of tasks to achieve the required credits. However, students do not manage to adapt to this system, which causes rejection and procrastination in completing tasks, and is evident from their really bad state of mind and stress intolerance. These factors can be so strong that they prevent adequate development; school commitments and obligations are neglected, affecting academic performance, which remains in the first order. Consequently, we aim to identify the critical cognitive factors that prevent the change of order and process them through fuzzy cognitive maps. To do so, a survey of students and teachers from Spanish and Mexican universities was carried out. Through confirmatory factor analysis, the number of items to be analysed was reduced. The variance analysis detected significant differences between students’ attitude and what teachers thought, and an assignment matrix was obtained. Finally, by obtaining Hamming distance, the critical factors that prevent good academic performance could be found. The main result obtained is that the critical factors that prevent change of order in cognitive elements are mainly problem solving, stress tolerance, reality testing , empathy, self-concept and happiness

Violência física intra-familiar entre jovens mexicanos e egípcios

OBJECTIVE: To determine the prevalence of experiencing intra-familial violence among Mexican and Egyptian youth and to describe its associated risk factors. METHODS: Data from questionnaires applied to 12,862 Mexican and 5,662 Egyptian youth, aged 10 to 19, who attended public schools were analyzed. Biviarate and logistic regression analysis were used to determine the relationship between socio-demographics, the experience of intra-familial violence and violence perpetration. RESULTS: The prevalence of having experienced intra-familial violence was comparable across the Mexican and Egyptian populations (14% and 17%, respectively). In Mexico, young men were more likely to have experienced such violence (OR=2.36) than women, whereas in Egypt, young women were at slightly greater risk than young men (OR=1.25). Older age, male gender and urban residence were independent correlates of experiencing intra-familial violence among Mexican youth. For Egyptian adolescents, in contrast, younger age, female gender and having non-married parents were independent correlates of victimization. Intra-familial violence victims were also more likely than non-victims to perpetrate violence (Mexico: OR=13.13; Egypt: OR=6.58). CONCLUSIONS: Mexican and Egyptian youth experienced intra-familial violence at a relatively low prevalence when compared with youth of other countries. A strong association was found between experiencing intra-familial violence and perpetrating violence.OBJETIVO: Determinar a prevalência da violência intra-familiar sofrida por jovens mexicanos e egípcios, e descrever os fatores de risco associados. MÉTODOS: Os dados analisados foram obtidos de questionários aplicados a 12.862 mexicanos e 5.662 egípcios, jovens de 10 a 19 anos, que freqüentam escolas públicas. O relacionamento entre fatores sociodemográficos, a violência sofrida e sua perpetração foram investigados por meio de análise bivariada e regressão logística. RESULTADOS: A prevalência de violência intra-familiar foi comparável entre as populações mexicana e egípcia (14% e 17%, respectivamente). No México, essa violência foi muito mais provável entre os homens jovens do que entre mulheres (OR=2,36), enquanto que no Egito era mais provável entre as mulheres jovens do que homens (OR=1,25). Idade mais elevada, gênero masculino e residência urbana são fatores associados a violência intra-familiar entre jovens mexicanos. Entre jovens egípcios, a idade mais baixa,o gênero feminino e pais não casados foram fatores associados a essa violência. Foi mais provável a repetição da violência pelos jovens que eram vítimas da violência intra-familiar (México: OR=13,13; Egito: OR=6,58). CONCLUSÕES: A prevalência de experimentar a violência intra-familiar de jovens mexicanos e egípcios foi baixa em comparação com jovens em outros países. Houve forte associação entre vítimas de violência intra-familiar e a repetição da violência

Fatores de abuso sexual na infância e adolescência de estudantes de Morelos, México

OBJECTIVE: To estimate the prevalence and factors associated with sexual abuse in childhood and adolescence. METHODS: Study conducted in a sample of students in the state of Morelos, Mexico, in 2004-2005. Participants (n=1730) were drawn from a cohort of 13,293 students aged 12 to 24 years. Data were collected by means of a questionnaire comprising parts of validated scales. The variables studied were: sociodemographic (gender, living area, socioeconomic status), family (parental education, parental addictions, violence between parents), individual psychological factors (self-esteem assessed using the Coopersmith Self-Esteem Inventory, depression, alcohol consumption), intrafamily violence (assessed through Strauss Scale) and sexual abuse. Multiple logistic regression assessed the risk factors associated. Odds ratios (OR) with 95% confidence intervals were estimated. RESULTS: Of all students studied, 4.7% (n=80) reported attempted sexual abuse and 2.9% (n=50) were victims of consummated sexual abuse. Women had higher prevalence of attempted (6.1%) abuse; 3.6% of females and 1.9% of men were sexually abused. Main perpetrators were boyfriends in women and a stranger in men. Mean age was 12.02 years old among females and 11.71 years old among men. Factors found to be associated with abuse: high parental alcohol consumption (OR = 3.37, 95% CI 1.40;8.07), violence toward the mother (OR = 4.49, 95% CI 1.54;13.10), female gender (OR = 2.47, 95% CI 1.17;5.24), being a victim of great domestic violence (OR = 3.58, 95% CI 1.32;9.67). High self-esteem was a protective factor (OR = 0.27, 95% CI 0.09;0.75). CONCLUSIONS: Overall sexual abuse occurs at the age of 12 in both males and females, and it is more frequent among females. Most victims do not report abuse.OBJETIVO: Estimar la prevalencia y los factores asociados al abuso sexual en niñez y adolescencia. MÉTODOS: Estudio realizado en una muestra de estudiantes del estado de Morelos, México, en 2004-2005. Los participantes (n=1730) pertenecen a una cohorte de 13.293 estudiantes de 12 a 24 años. Los datos fueron colectados mediante la aplicación de un cuestionario conteniendo secciones de escalas validadas. Las variables analizadas fueron: factores sociodemográficos (sexo, zona de habitación, nivel socioeconómico); familiares (educación de los padres, adicciones de los padres, violencia entre padres); psicológicos individuales (autoestima - Inventario de Autoestima de Coopersmith, depresión, consumo de alcohol); violencia intrafamiliar (Escala de Strauss); y abuso sexual. Mediante regresión logística múltiple se evaluaron los factores asociados. Se obtuvieron Razones de Momios (RM) con intervalos de confianza al 95%. RESULTADOS: El 4.7% (n=80) de los (as) estudiantes presentaron intento de abuso y el 2.9% (n=50) fueron víctimas de abuso sexual consumado. Las mujeres tuvieron mayor prevalencia de intento (6.1%). El 3.6% de las mujeres y el 1.9% de los hombres fueron abusados sexualmente. Principal agresor en mujeres fue el novio y en hombres una persona desconocida. Edad promedio de 12.02 años en mujeres y 11.71 en hombres. Factores asociados al abuso: mayor consumo de alcohol padres (RM = 3.37; IC 95% 1.40;8.07); violencia hacia madre (RM=4.49; IC 95%1.54;13.10); ser mujer (RM = 2.47; IC 95%1.17;5.24); ser víctima de violencia intrafamiliar alta (RM=3.58; IC 95%1.32;9.67). Autoestima alta fue un factor protector (RM=0.27; IC 95% 0.09;0.75). CONCLUSIONES: En promedio el abuso sexual se presenta a los 12 años de edad en ambos sexos, siendo más frecuente en el sexo femenino. La mayoría de víctimas no lo denuncia.OBJETIVO: Estimar a prevalência e fatores associados ao abuso sexual infantil e na adolescência. MÉTODOS: Estudo realizado em amostra de estudantes do estado de Morelos, México, entre 2004 e 2005. Os participantes (n=1730) pertencem a uma coorte de 13.293 estudantes de 12 a 24 anos. Os dados foram coletados por meio de questionário formado por partes de escalas validadas. As variáveis analisadas foram: fatores sociodemográficos (sexo, zona de residência, nível socioeconômico); familiares (educação dos pais, vícios dos pai, violência entre pais); psicológicos individuais (autoestima- Inventario de Autoestima de Coopersmith, depressão, consumo de álcool); violência intrafamiliar (Escala de Strauss); e abuso sexual. As variáveis dependentes analisadas foram a intenção e o abuso sexual consumado. Os fatores associados foram analisados por meio de regressão logística múltipla, com odds ratios e respectivos intervalos de 95% de confiança (IC 95%). RESULTADOS: Do total, 4,7% (n=80) dos alunos reportaram terem sofrido intenção de abuso e 2,9% foram vítimas de abuso sexual consumado. As mulheres relataram maior prevalência de intenção (6,1%). Foram abusados sexualmente 3,6% das mulheres e 1,9% dos homens. O principal agressor das mulheres foi o namorado e dos homens, uma pessoa desconhecida. A idade do abuso foi de 12,02 anos para mulheres e 11,71 para os homens. Os fatores associados ao abuso foi o maior consumo de álcool pelos pais (RM = 3.37; IC 95% 1.40;8.07); violência contra a mãe (OR=4.49; IC 95%1.54;13.10); ser mulher (OR= 2.47; IC 95%1.17;5.24); ser vítima de violência intrafamiliar alta (OR=3.58; IC 95%1.32;9.67). Autoestima alta foi um fator protetor (RM=0.27; IC 95% 0.09;0.75). CONCLUSÕES: A média de idade do abuso sexual foi de 12 anos em ambos os sexos, sendo mais freqüente entre as do sexo feminino. A maioria das vítimas não denuncia o abuso

Pengaruh Solvabilitas dan Ukuran Perusahaan terhadap Nilai Perusahaan pada Perusahaan Restaurant, Hotel & Tourism Yang terdaftar di Bursa Efek Indonesia Tahun 2015-2017

Penelitian ini bertujuan untuk mengetahui pengaruh solvabilitas dan ukuran perusahaan terhadap nilai perusahaan, metodeyang digunakan penelitian sensus, yakni memasukkan semua perusahaan restaurant, hotel & tourism yang terdaftar di Bursa Efek Indonesia yang telah memenuhi kriteria ke dalam data pengamatan.Periode pengamatan data mulai tahun 2015 s.d 2017, berjumlah 66 perusahaan.Metode analisis data yang digunakan adalah regresi berganda linear.Hasil penelitian ini menyatakan bahwa solvabilitas dan ukuran perusahaan berpengaruh terhadap nilai perusahaan, baik secara individu (parsial) maupun bersama-sama (simultan)

Dogs Detecting COVID-19 From Sweat and Saliva of Positive People : A Field Experience in Mexico

ContextMolecular tests are useful in detecting COVID-19, but they are expensive in developing countries. COVID-19-sniffing dogs are an alternative due to their reported sensitivity (>80%) and specificity (>90%). However, most of the published evidence is experimental, and there is a need to determine the performance of the dogs in field conditions. Hence, we aimed to test the sensitivity and specificity of COVID-19-sniffing dogs in the field. MethodsWe trained four dogs with sweat and three dogs with saliva of COVID-19-positive patients, respectively, for 4.5 months. The samples were obtained from a health center in Hermosillo, Sonora, with the restriction to spend 5 min per patient. We calculated sensitivity, specificity, and their 95% confidence intervals (CI). ResultsTwo sweat-sniffing dogs reached 76 and 80% sensitivity, with the 95% CI not overlapping the random value of 50%, and 75 and 88% specificity, with the 95% CI not overlapping the 50% value. The 95% CI of the sensitivity and specificity of the other two sweat dogs overlapped the 50% value. Two saliva-sniffing dogs had 70 and 78% sensitivity, and the 95% CI of their sensitivity and specificity did not overlap the 50% value. The 95% CI of the third dog's sensitivity and specificity overlapped the 50% value. ConclusionFour of the six dogs were able to detect positive samples of patients with COVID-19, with sensitivity and specificity values significantly different from random in the field. We considered the performance of the dogs promising because it is reasonable to expect that with gauze exposed for a longer time to sweat and saliva of people with COVID-19, their detection capacity would improve. The target is to reach the sensitivity range requested by the World Health Organization for the performance of an antigen test (>= 80% sensitivity, >= 97% specificity). If so, dogs could become important allies for the control of the COVID-19 pandemic, especially in developing countries.Peer reviewe

Efficient p-n junction-based thermoelectric generator that can operate at extreme temperature conditions

In many industrial processes, a large proportion of energy is lost in the form of heat. Thermoelectric generators can convert this waste heat into electricity by means of the Seebeck effect. However, the use of thermoelectric generators in practical applications on an industrial scale is limited in part because electrical, thermal, and mechanical bonding contacts between the semiconductor materials and the metal electrodes in current designs are not capable of withstanding thermal-mechanical stress and alloying of the metal-semiconductor interface when exposed to the high temperatures occurring in many real-world applications. Here we demonstrate a concept for thermoelectric generators that can address this issue by replacing the metallization and electrode bonding on the hot side of the device by a p-n junction between the two semiconductor materials, making the device robust against temperature induced failure. In our proof-of-principle demonstration, a p-n junction device made from nanocrystalline silicon is at least comparable in its efficiency and power output to conventional devices of the same material and fabrication process, but with the advantage of sustaining high hot side temperatures and oxidative atmosphere