632 research outputs found
A technological acceptance of e-learning tools used in practical and laboratory teaching, according to the European higher education area
The application of scientific tools to analyse the use of Internet-based e-learning tools in academic settings is in
general an ignored area. E-learning tools are actually an emergent topic as a result of the new ideas introduced by the
European Higher Education Area. Lifelong learning, or the promotion of student initiative, is the new paradigm of a
learner-centred education. In this context, e-learning tools can represent an effective way of supporting this new
trend in education. Assuming the premise that successful use of these web-based tools depends primarily on a user’s
behaviour, the objective of this research is to examine the technology acceptance model (TAM) of web-based elearning
tools used in practical and laboratory teaching. The research hypotheses derived from this model have
empirically been validated using the responses to a survey on e-learning usage among 220 users. These responses
have been examined through partial least square. The obtained results strongly support the extended TAM in
predicting a student’s intention to use e-learning and define a set of external variables with a significant influence in
the original TAM variables. Surprisingly, perceived ease of use did not posit a significant impact on student attitude
or intention towards e-learning tool usage. Therefore, early evaluation of e-learning material is considered essential
to providing a framework for further improvements of the too
Simultaneous J-, H-, K- and L-band spectroscopic observations of galactic Be stars. I. IR atlas
It is already accepted that Be stars are surrounded by circumstellar
envelopes, which are mostly compatible with a disc geometry in Keplerian
rotation. We aim to obtain a more complete characterisation of the properties
of the circumstellar environment of Be stars that helps to constrain the
theoretical models of the Be phenomenon. We present near-infrared,
medium-resolution spectra of a sample of galactic Be stars with different
spectral subtypes and luminosity classes. We measure different parameters of
the hydrogen recombination lines from the Paschen, Brackett, Pfund, and
Humphreys series, and use them to diagnose physical conditions in the
circumstellar environment. We analysed the equivalent-width (EW) ratio between
Br and Br lines and different diagrams of flux ratios. We also
identify lines from He I, C I, N I, O I, Na I, Mg I, Mg II, Si I, Fe I, and Fe
II. Analysing the EW measurements of particular He I, Mg II, Fe I, Fe II and O
I lines, we find that for some lines they correlate with the spectral type of
the star. Particularly, the emission of the O I~m line
decreases towards the later spectral types. We present an atlas of 22 Be stars,
that covers a wide infrared (IR) spectral range with quasi-simultaneous
observations. From a detailed analysis, we define new complementary criteria to
Mennickent's classification of Be stars according to their disc opacity. Some
objects in our sample present compact thick envelopes, while in others the
envelope is extended and optically thin. The correlation between the full
widths at half maximum (FWHM) and the peak separation ()
versus for the Br10, Br, and Hu14 lines reveals that the
broadening mechanism is rotational. The Ly fluorescence is a key
mechanism to explain the intensity of the emission of Mg II and O I lines.Comment: 27 pages, 14 figures. Accepted for publication in A&
Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73
We aim to improve our knowledge on the structure and dynamics of the
circumstellar disk of the LMC B[e] supergiant LHA 120-S 73. High-resolution
optical and near-IR spectroscopic data were obtained over a period of 16 and 7
years, respectively. The spectra cover the diagnostic emission lines from
[CaII] and [OI], as well as the CO bands. These features trace the disk at
different distances from the star. We analyzed the kinematics of the individual
emission regions by modeling their emission profiles. A low-resolution
mid-infrared spectrum was obtained as well, which provides information on the
composition of the dusty disk. All diagnostic emission features display
double-peaked line profiles, which we interpret as due to Keplerian rotation.
We find that LHA 120-S 73 is surrounded by at least four individual rings of
material with alternating densities (or by a disk with strongly non-monotonic
radial density distribution). Moreover, we find that the molecular ring must
have gaps or at least strong density inhomogeneities, or in other words, a
clumpy structure. The mid-infrared spectrum displays features of oxygen- and
carbon-rich grain species, which indicates a long-lived, stable dusty disk. We
cannot confirm the previously reported high value for the stellar rotation
velocity. The line profile of HeI 5876 A is strongly variable in both width and
shape and resembles of those seen in non-radially pulsating stars. A proper
determination of the real underlying stellar rotation velocity is hence not
possible. The existence of multiple stable and clumpy rings of alternating
density recalls ring structures around planets. Although there is currently
insufficient observational evidence, it is tempting to propose a scenario with
one (or more) minor bodies or planets revolving around LHA 120-S 73 and
stabilizing the ring system, in analogy to the shepherd moons in planetary
systems.Comment: 14 pages, 13 figure, accepted for pulication in A&
Machine Learning Models that Remember Too Much
Machine learning (ML) is becoming a commodity. Numerous ML frameworks and
services are available to data holders who are not ML experts but want to train
predictive models on their data. It is important that ML models trained on
sensitive inputs (e.g., personal images or documents) not leak too much
information about the training data.
We consider a malicious ML provider who supplies model-training code to the
data holder, does not observe the training, but then obtains white- or
black-box access to the resulting model. In this setting, we design and
implement practical algorithms, some of them very similar to standard ML
techniques such as regularization and data augmentation, that "memorize"
information about the training dataset in the model yet the model is as
accurate and predictive as a conventionally trained model. We then explain how
the adversary can extract memorized information from the model.
We evaluate our techniques on standard ML tasks for image classification
(CIFAR10), face recognition (LFW and FaceScrub), and text analysis (20
Newsgroups and IMDB). In all cases, we show how our algorithms create models
that have high predictive power yet allow accurate extraction of subsets of
their training data
Posibilidades de reproducción de Schinus johnstonii (Anacardiaceae), una especie nativa del Monte argentino
Schinus johnstonii F. A. Barkley (Anacardiaceae) es un arbusto nativo de la ProvinciaFitogeográfica del Monte, donde representa un importante componente del pastizal natural. Su tolerancia a la sequía, junto a la presencia de una floración abundante,la convierten en una buena opción para proyectos paisajísticos y de restauración de ambientes degradados y deforestados. Para tales fines es necesario contar con informaciónacerca de sus posibilidades de reproducción. Los objetivos de este trabajo fueron determinar los requerimientos básicos para la germinación de sus semillas(reproducción sexual), en condiciones de laboratorio, la viabilidad de las mismas y analizar la supervivencia de estacas (reproducción vegetativa), en condiciones controladasy bajo distintos tratamientos. Las semillas recolectadas se sometieron a seis tratamientos pre-germinativos: exocarpo intacto (control), remoción de exocarpo(desnudas), semillas desnudas con escarificación mecánica, semillas desnudas con escarificación química, semillas desnudas en remojo y semillas desnudas con exposicióna humo. Sólo se observó germinación en semillas sin exocarpo. Las semillas desnudas germinaron a partir de los 10 días, con un valor máximo del 38%, sinencontrarse diferencias entre los tratamientos. Se observó, además, una importanteproporción de semillas no viables o vacías (30-40%). El estudio de reproducciónvegetativa, con estacas recolectadas durante los estadios fenológicos vegetativo yreproductivo, con y sin hormona de enraizamiento, dio como resultado un porcentajebajo de rebrote (20%), sin diferencias entre tratamientos. Según los resultados,las semillas de S. johnstonii presentarían dormición física impuesta por la cubierta(superada por remoción del exocarpo). La reproducción de este arbusto no seríarecomendable por medio de estacas, aunque se sugiere realizar más estudios.Schinus johnstonii F. A. Barkley (Anacardiaceae) is a native shrub to the Monte Phytogeographic Province, where it represents an important component of rangelands.
Its tolerance to drought and abundant flowering, render it a good option for landscaping and land restoration projects on degraded and deforested areas. For such purposes, information about its reproductive possibilities is needed. The objectives of this work were to determine the basic requirements for seed germination (sexual reproduction) under laboratory conditions, viability and to analyze the survival of cuttings (vegetative reproduction), under controlled conditions and different treatments. The collected seeds were subjected to six pre-germination treatments: intact exocarp (control), exocarp removal (bare), bare seeds with mechanical scarification, bare seeds with chemical scarification, bare seeds with soaking and bare seeds with exposure to smoke. Germination was only observed in seeds without exocarp. Bare seeds germinated after 10 days, with a maximum value of 38%, with no differences between treatments. In addition, a significant proportion of non-viable or empty seeds (30-40%) was observed. The vegetative reproductive study, with cuttings collected during the vegetative and reproductive phenological stages, with and without rooting hormone, resulted in a low percentage of regrowth (20%), with no differences between treatments. According to these results, seeds of S. johnstonii would present physical dormancy imposed by the seed coat (overcome by the removal of the exocarp). The reproduction of this shrub by cuttings is not recommended, although further studies are suggested
In vitro and in vivo leishmanicidal studies of Peperomia galioides (Piperaceae)
Petroleum ether and methylene chloride extracts of #Peperomia galioides and three phenylated diphenols, grifolic acid, grifolin and piperogalin exhibited in vitro antileishmanial activity. During the course of infection of BALB/c mice with #Leishmania amazonensis, the treatments with each of these compounds did not influence the progression of the disease. (Résumé d'auteur
A first--order irreversible thermodynamic approach to a simple energy converter
Several authors have shown that dissipative thermal cycle models based on
Finite-Time Thermodynamics exhibit loop-shaped curves of power output versus
efficiency, such as it occurs with actual dissipative thermal engines. Within
the context of First-Order Irreversible Thermodynamics (FOIT), in this work we
show that for an energy converter consisting of two coupled fluxes it is also
possible to find loop-shaped curves of both power output and the so-called
ecological function against efficiency. In a previous work Stucki [J.W. Stucki,
Eur. J. Biochem. vol. 109, 269 (1980)] used a FOIT-approach to describe the
modes of thermodynamic performance of oxidative phosphorylation involved in
ATP-synthesis within mithochondrias. In that work the author did not use the
mentioned loop-shaped curves and he proposed that oxidative phosphorylation
operates in a steady state simultaneously at minimum entropy production and
maximum efficiency, by means of a conductance matching condition between
extreme states of zero and infinite conductances respectively. In the present
work we show that all Stucki's results about the oxidative phosphorylation
energetics can be obtained without the so-called conductance matching
condition. On the other hand, we also show that the minimum entropy production
state implies both null power output and efficiency and therefore this state is
not fulfilled by the oxidative phosphorylation performance. Our results suggest
that actual efficiency values of oxidative phosphorylation performance are
better described by a mode of operation consisting in the simultaneous
maximization of the so-called ecological function and the efficiency.Comment: 20 pages, 7 figures, submitted to Phys. Rev.
Valorization of Rice Straw into Cellulose Microfibers for the Reinforcement of Thermoplastic Corn Starch Films
[EN] In the present study, agro-food waste derived rice straw (RS) was valorized into cellulose microfi-bers (CMFs) using a green process of combined ultrasound and heating treatments and were, thereafter, used to improve the physical properties of thermoplastic starch films (TPS). Mechanical defibrillation of the fibers gave rise to CMFs with cumulative frequencies of length and diameters below 200 and 5¿15 µm, respectively. The resultant CMFs were successfully incorporated by melt mixing into TPS and also starch subjected to dry heating (DH) modification to yield TPS modified by dry heating (TPSDH) by thermo-compression and characterized. It was observed that both DH modification and fiber incorporation at 3 and 5 wt% loadings interfered with the starch gelatini-zation, leading to non-gelatinized starch granules in the biopolymer matrix. Thermo-compressed films prepared with both types of starches that wereand reinforced with 3 wt% CMF were more rigid (percentages increases of ~215% for TPS and ~207% for the TPSDH), more resistant to break (~100% for TPS and ~60% for TPSDH), but also less extensible (~53% for TPS and ~78% for TPSDH). The incorporation of CMFs into the TPS matrix at both contents also promoted a de-crease in water vapor (~15%) and oxygen permeabilities (~30%). Finally, the TPS composite films showed low changes in terms of optical properties and equilibrium moisture, being less soluble in water than the TPSDH films.This research was funded by Spanish Ministry of Science and Innovation (MICI), grant number PID2019-105207RB-I00.Vieira-De Freitas, PA.; La Fuente Arias, CI.; Torres-Giner, S.; González Martínez, MC.; Chiralt Boix, MA. (2021). Valorization of Rice Straw into Cellulose Microfibers for the Reinforcement of Thermoplastic Corn Starch Films. Applied Sciences. 11(18):1-20. https://doi.org/10.3390/app11188433S120111
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