Do proctored online University exams in Covid-19 era affect final grades respect face-to-face exams?

[EN] The Covid-19 pandemic forced universities to convert their traditional face-to-face exams to online exams with doubts as to whether student cheating or technical difficulties would affect their final grades. After taking three of these exams online, we considered comparing their grades with those of previous years on traditional exams. The average mark of the traditional exams before the pandemic was 6.95 over 10, while the average mark of the three exams carried out in the Covid-19 era is 6.64. The student's t test indicated that there are no significant differences between the two types of exams in the mean (p = 0.408), the median (p = 0.378), the range (p = 0.307), the minimum (p = 0.410) and the maximum (p = 0.072). Taking online exams did not modify the exam grades compared to previous years. There is a lot of variability in similar studies in the literature due to cheating that can be performed in online exams. A proctoring system, good question design, and limited exam time can minimize these differences.Alegre-Martínez, A.; Martinez-Martinez, MI.; Alfonso-Sanchez, JL. (2021). Do proctored online University exams in Covid-19 era affect final grades respect face-to-face exams?. En 7th International Conference on Higher Education Advances (HEAd'21). Editorial Universitat Politècnica de València. 727-734. https://doi.org/10.4995/HEAd21.2021.12701OCS72773

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Early development and reproductive lifespan of rabbit females: implications of growth rate, rearing diet and body condition at first mating

[EN] Factors influencing early development such as birth weight, nest competition, and the diet received during rearing have been proposed as elements conditioning the future reproductive performance of European rabbit (Oryctolagus cuniculus) females. To evaluate their effects, we followed the life of 1513 females from birth to time of death, culling or censoring (animals alive at a fixed date). Between 0 and 63 days of age 353 females died. From the remaining 1160 females, 864 were chosen based on their birth weight to be transferred from the selection to the production farm. At this farm, 431 females received the control diet (184g of CP, 381 g of NDF and 11.8 MJ of DE per kg DM), while the other 433 received the fibrous diet (134 g of CP, 436g of NDF and 10.0 MJ of DE per kg DM). Throughout the rearing period, we checked for the individual live weight and body condition (perirenal fat thickness) at first artificial insemination. Reproductive lifespan was defined as the number of days between the first parturition and the time of death, culling or censoring. Birth weight affected the survival of newborn females during lactation and the presence of a milk spot at birth (related to nest competition) increased the survivability of newborns weighing <45g (P <0.001). Rearing diet altered the growth curve of females and their body condition at first insemination. The diet also altered the relative risk of death during the rearing period, which was lower among females fed on the fibrous diet (-12.5%; P < 0.001). Therefore, a higher number of females fed with this diet reached their reproductive life, directly affecting the productivity measured per housed female. Fatter females at first insemination had smaller litter sizes and a higher risk of being culled than lean ones (P < 0.05). In general, the fibrous diet reduced the risk of leaving the herd at early rearing, and both birth weight and perirenal fat thickness affected female's reproductive lifespan. An excess of fat (positive change in one unit of perirenal fat) at their first insemination represented an increased the risk of death or elimination of 13%.The authors acknowledge Cesar Villalba (Fabara, Spain), Luis Eroles (Valderrobres, Spain) for the technical support in managing the animals and for kindly providing a space to conduct our study. They also thank the Commission for Science and Technology (CICYT) of the Spanish Government (AGL2014-53405-C2-1-P) for the economic support to carry out this study.Martinez-Paredes, E.; Ródenas Martínez, L.; Pascual Amorós, JJ.; Savietto, D. (2018). Early development and reproductive lifespan of rabbit females: implications of growth rate, rearing diet and body condition at first mating. animal. 12(11):2347-2355. https://doi.org/10.1017/S1751731118000162S23472355121

Nonlinear dynamic modeling and analysis of self-oscillating H-bridge parallel resonant converter under zero current switching control: unveiling coexistence of attractors

This paper deals with the global dynamical analysis of an H-bridge parallel resonant converter under a zero current switching control. Due to the discontinuity of the vector field in this system, sliding dynamics may take place. Here, the sliding set is found to be an escaping region. Different tools are combined for studying the stability of oscillations of the system. The desired crossing limit cycles are computed by solving their initial value problem and their stability analysis is performed using Floquet theory. The resulting monodromy matrix reveals that these cycles are created according to a smooth cyclic-fold bifurcation. Under parameter variation, an unstable symmetric crossing limit cycle undergoes a crossing-sliding bifurcation leading to the creation of a symmetric unstable sliding limit cycle. Finally, this limit cycle undergoes a double homoclinic connection giving rise to two different unstable asymmetric sliding limit cycles. The analysis is performed using a piecewise-smooth dynamical model of a Filippov type. Sliding limit cycles divide the state plane in three basins of attraction, and hence, different steady-state solutions may coexist which may lead the system to start-up problems. Numerical simulations corroborate the theoretical predictions, which have been experimentally validated.Postprint (author's final draft

Suppression of undesired attractors in a self-oscillating H-bridge parallel resonant converters under zero current switching control

Resonant converters under zero current switching control strategy can exhibit coexistence of attractors, making it difficult the startup of the system from zero initial conditions. In this paper, the problem of multiple coexisting attractors in parallel resonant converters is addressed. Appropriate modifications of the switching decision with the aim of converting undesired attractors into virtual ones are proposed. A suitable control signal is generated from the state variables of the system and used to adjust the switching decision. Numerical simulations corroborate the proposed solutions and the simplest one was finally verified by measurements from a laboratory prototype.Postprint (author's final draft

Delay effects on the limit cycling behavior in an H-bridge resonant inverter with zero current switching control strategy

In this paper, bifurcations of limit cycles in a H-bridge LC resonant inverter under a zero current switching control strategy with delay in the switching action are analyzed. Mathematical analysis and numerical simulations show that the delay can degrade the quality of the oscillations and even inhibit them.Postprint (author's final draft

Effect of early development on semen parameters and lifespan of rabbit males selected by high growth rate

[EN] Life history theory suggests that different body development dynamics may influence survival and future reproductive performance of organisms. The present work studied how these dynamics could influence seminal traits and lifespan of rabbit males selected for growth rate and intended for Al. To achieve this goal, a total of 550 rabbit males were controlled from birth, evaluated both during the testing phase (four consecutive weeks after reaching 147 days of life) and the productive phase (377 of them from the end of the testing phase until 2 years of life). In order to obtain individuals with different body development dynamics, we pre-selected males based on their live weight (LW) at 0, 28, 63 and 147 days and on their average daily gain (ADG) between each period (0-28, 28-63 and 63-147 days). Libido and main seminal traits (semen volume, motility, concentration, and production, as well as normal apical ridge and abnormalities of spermatozoa) were controlled during the testing phase. Semen volume, motility and concentration were subsequently controlled during the productive phase, as well as the length of the male life, calculated as the number of days a rabbit was present at the farm between age 147 and day of death, culling or censoring; set to 2 years of life). The birth weight, the ADG between 0 and 28 days and between 28 and 63 days were positively related to some seminal parameters measured during the testing phase (semen volume, concentration, production and motility; P<0.05), while the ADG between 63 and 147 days was negatively related to the seminal productivity throughout the productive life of the males (an increment of 10 g per day on ADG reduced the number of profitable ejaculates by 4.9%; P<0.05). In addition, a higher growth between 0 and 28 and between 63 and 147 days increased the risk of death or culling of males during the productive phase (P < 0.05). In conclusion, an adequate body development early in life seems to have a positive effect on the degree of sexual maturity with which male rabbits begin their reproductive life, but reaching the reproduction onset with excessive weight can reduce their reproductive performance and lifespan. (C) 2019 Elsevier Inc. All rights reserved.The authors would like to thank Jose Manuel Arias, owner of the selection centre El Adil Redondo S.L., (Carrizo de la Ribera, Leon, Spain), and his team for their help, as without their collaboration this work could not have been carried out. This study was supported by the Interministerial Commission for Science and Technology (CICYT) of the Spanish Government (AGL2017-85162-C2-1-R).Martinez-Paredes, E.; Llorens, J.; Ródenas Martínez, L.; Savietto, D.; Pascual Amorós, JJ. (2019). Effect of early development on semen parameters and lifespan of rabbit males selected by high growth rate. Theriogenology. 139:72-80. https://doi.org/10.1016/j.theriogenology.2019.07.014S728013

Ultratrace arsenic determination through hydride trapping on oxidized multiwall carbon nanotubes coupled to electrothermal atomic absorption spectrometry

Arsenic determination in natural waters is an issue of current research. This article reports a novel hydride generation (HG) approach developed for As determination with electrothermal atomic absorption spectrometry (ETAAS) detection. The HG process was interfaced with ETAAS through hydride trapping onto a carbon nanotubes microcolumn. To this end a homemade gas-liquid separator was used, allowing arsine formation and its flow throughout the CNT microcolumn. The retention process involved thus a solid phase extraction from the gas phase to the solid support. Once arsine generation was completed, the elution was carried out with nitric acid directly onto the dosing hole of the graphite furnace. Outstanding sensitivity with detection limit of 1 ng L-1, quantification limit of 5 ng L-1 and the characteristic mass, 5.8 ± 0.4 pg could be achieved. A satisfactory correlation between concentration of As and absorbance (R = 0.9993) from the limit of quantification up to 500 ng L-1, with a relative standard deviation of 6.3% were obtained. A sensitive enhancement factor of 38 was reached when 2 mL of sample were processed and 50 μL of HNO3 were used as eluent. The system was successfully applied to the analysis of a standard reference material, QC LL2 metals in natural waters. In addition tap water analysis provided an As concentration of 0.29±0.03 μg L-1.Fil: Maratta Martínez, Sergio Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Química de San Luis; ArgentinaFil: Acosta, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Química de San Luis; ArgentinaFil: Martinez, Luis Dante. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Química de San Luis; ArgentinaFil: Pacheco, Pablo Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Química de San Luis; ArgentinaFil: Gil, Raul Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Química de San Luis; Argentin

On the Whitham hierarchy: dressing scheme, string equations and additional symmetrie

A new description of the universal Whitham hierarchy in terms of a factorization problem in the Lie group of canonical transformations is provided. This scheme allows us to give a natural description of dressing transformations, string equations and additional symmetries for the Whitham hierarchy. We show how to dress any given solution and prove that any solution of the hierarchy may be undressed, and therefore comes from a factorization of a canonical transformation. A particulary important function, related to the $\tau$-function, appears as a potential of the hierarchy. We introduce a class of string equations which extends and contains previous classes of string equations considered by Krichever and by Takasaki and Takebe. The scheme is also applied for an convenient derivation of additional symmetries. Moreover, new functional symmetries of the Zakharov extension of the Benney gas equations are given and the action of additional symmetries over the potential in terms of linear PDEs is characterized

On the Whitham hierarchy: dressing scheme, string equations and additional symmetrie

A new description of the universal Whitham hierarchy in terms of a factorization problem in the Lie group of canonical transformations is provided. This scheme allows us to give a natural description of dressing transformations, string equations and additional symmetries for the Whitham hierarchy. We show how to dress any given solution and prove that any solution of the hierarchy may be undressed, and therefore comes from a factorization of a canonical transformation. A particulary important function, related to the $\tau$-function, appears as a potential of the hierarchy. We introduce a class of string equations which extends and contains previous classes of string equations considered by Krichever and by Takasaki and Takebe. The scheme is also applied for an convenient derivation of additional symmetries. Moreover, new functional symmetries of the Zakharov extension of the Benney gas equations are given and the action of additional symmetries over the potential in terms of linear PDEs is characterized