145 research outputs found
El mundo y la tierra en “el obrero del vidrio analiza las condiciones objetivas del milagro de la copa” de Alberto Szpunberg
En todas las estrofas del poema de Alberto Szpunberg podemos ver como principioregulador, la interrogación sobre la realidad objetiva por medio de la cual se pretende interpelar a un “alguien” que no aparece mencionado en el poema. Ese “alguien” nos sirve como base para conjeturar sobre el sentido que reviste el poema. El lenguaje que adoptaremos para revisar lo cerrado y lo abierto (dos aspectos importantes que luego veremos) nos servirán de “orientación”, más que como una respuesta a la pregunta de qué es lo que se “cierra sobre sí mismo” y qué es la “apertura” en el poema
Homoallylic o-halobenzylamines: asymmetric diversity-oriented synthesis of benzo-fused cyclic amines
The presence of a halogen atom in the proximity of a homoallylic amine, obtained by asymmetric addition of allylzinc bromide to the corresponding tert-butyl sulfinimine, makes them versatile building blocks suitable to participate in several palladium-catalyzed processes, such as the intramolecular Heck reaction or the Sonogashira cross-coupling. The thus obtained orthoalkynyl derivatives display two unsaturated functional groups which may be further modified by means of the intramolecular Pauson–Khand reaction or the ring-closing enyne metathesis. In this way, a variety of benzo-fused amines can be obtained in 2–3 steps from readily available starting materials
Analysis and implementation of the Buck-Boost Modified Series Forward converter applied to photovoltaic systems
The mismatching phenomenon is one of the main issues in photovoltaic (PV)
applications. It could reduce the generated power of a string when a PV panel
has different performances from the other PV panels connected to the same
string. Distributed Maximum Power Point Tracking (DMPPT) architectures are one
of the most promising solutions to overcome the drawbacks associated with
mismatching phenomena in PV applications. In this kind of architectures, a
DC-DC module integrated converter (MIC) manages each PV panel, isolating it
from the rest of the PV panels, for harvesting the maximum available power from
the Sun. Due to the high number of DCDC converters used in a grid-tied PV
installation, the most desired MIC requirements are high efficiency, low cost
and the capability of voltage step-up and step-down. This paper proposes the
Buck-Boost Modified Forward (BBMSF) converter as a good candidate to be applied
in DMPPT architectures. A complete analysis of the BBMSF converter is carried
out, including the steady-state analysis as well as the small signal analysis
in continuous conduction mode. The main advantages of the BBMSF converter are
its step-up and step-down voltage transfer function; a higher simplicity, since
it only includes a single controlled switch; the soft switching characteristics
in all the diodes and MOSFET, reaching in some cases ZVS and ZCS, and yielding
high efficiencies; the use of an autotransformer, with better performances than
a typical Forward transformer; and the good dynamic performance, like the
Forward converter ones. The theoretical analyses are validated through the
experimental results in a 225 W BBMSF prototype designed and built under the
requirements of a 100 kW grid-tied PV installation, achieving an efficiency up
to 93.6%.Comment: This work has been supported by the Ministry of Economy and
Competitiveness and FEDER funds through the research project "Storage and
Energy Management for Hybrid Electric Vehicles based on Fuel Cell, Battery
and Supercapacitors" - ELECTRICAR-AG- (DPI2014-53685-C2-1-R
Difference in pulse arrival time at forehead and at finger as a surrogate of pulse transit time
Pulse transit time (PTT) difference (PTTD) to the forehead and finger dynamics are compared to pulse arrival time towards the finger (PATF) dynamics during a tilt table test. Two frequency bands, where different physiological information is expected, are analyzed: low frequency (LF) influenced by both sympathetic and parasympathetic activity, and high frequency (HF) influenced by parasympathetic activity. As PATF, PTTD is influenced by PTT, but in contrast to PATF, PTTD is not influenced by the pre-ejection period (PEP). This is advantaging in certain applications such as arterial stiffness assessment or blood pressure estimation. Results showed higher correlation between PTTD and PATF during rest stages than during tilt stage, when the PEP dynamics have stronger effect in PATF dynamics. This suggests that PTTD variability can potentially be a surrogate of PTT variability that is not influenced by PEP, which is advantaging in the previously mentioned applications. However, further studies must be elaborated in order to evaluate the potential of PTTD in such specific applications
Analysis, design, and implementation of the AFZ converter applied to photovoltaic systems
Grid-tied photovoltaic (PV) installations with Distributed Maximum Power
Point Tracking (DMPPT) architectures include a DC-DC Module Integrated
Converter (MIC) for managing each PV panel, isolating it from the others,
reducing the mismatching effect and maximizing the harvested power. In this
paper, the Autotransformer Forward converter with type-Zeta resonant reset
(AFZ) is proposed as a DMPPT architecture MIC candidate. The main
characteristics of the AFZ converter are the high versatility due to its
voltage step-up and step-down capability; the use of an optimized
autotransformer with only two windings, reducing the complexity and power
losses of this component; the good dynamic performances, like the Forward
converter ones; the low number of components and the simplicity and high
feasibility associated to the use of just one active switch. Besides, soft
switching transitions are achieved thanks to the autotransformer type-Zeta
resonant reset. The steady-state theoretical analysis, considering the effect
of the autotransformer leakage inductance, is presented. The converter is also
studied in the frequency domain, obtaining the small-signal transfer functions.
A design procedure based on the requirements of a 100 kW grid-tied photovoltaic
installation is described, yielding in a 225 W prototype with efficiencies up
to 95.6 %. Experimental results validate the theoretical analysis.Comment: This work was supported in part by the Spanish Ministry of Economy
and Competitiveness and FEDER funds through the research project: Modeling
and Control Strategies for the Stabilization of the Interconnection of Power
Electronic Converters CONEXPOT under Grant DPI2017-84572-C2-2-R. copyright:
2020 IEE
Signal peptide homology between the sweet protein thaumatin II and unrelated cereal α-amylase/trypsin inhibitors
A cDNA clone (pUP-23) corresponding to a member of a protein family that includes inhibitors of trypsin and of heterologous α-amylases has been selected from a library derived from developing barley endosperm and its sequence has been determined. A stretch of 95 nucleotides that included the signal peptide and the first 8 residues of the mature protein was found to be homologous to an exactly equivalent region of the nucleotide sequence encoding the sweet protein thaumatin II. Evolutionary implications of this finding are discussed
Learning an Effective Evolution Equation for Particle-Mesh Simulations Across Cosmologies
Particle-mesh simulations trade small-scale accuracy for speed compared to
traditional, computationally expensive N-body codes in cosmological
simulations. In this work, we show how a data-driven model could be used to
learn an effective evolution equation for the particles, by correcting the
errors of the particle-mesh potential incurred on small scales during
simulations. We find that our learnt correction yields evolution equations that
generalize well to new, unseen initial conditions and cosmologies. We further
demonstrate that the resulting corrected maps can be used in a simulation-based
inference framework to yield an unbiased inference of cosmological parameters.
The model, a network implemented in Fourier space, is exclusively trained on
the particle positions and velocities.Comment: 7 pages, 4 figures, Machine Learning and the Physical Sciences
Workshop, NeurIPS 202
Extension of the Injected-Absorbed-Current Method applied to DC-DC Converters with Input Filter, Output Post-filter and Feedforward Compensations
In railway applications, it is common to use an LC filter connected between
the catenary and the input port of the main converter of the auxiliary and
traction systems. In addition, in the auxiliary systems, there is a converter
operating as a battery charger, which requires a very low ripple in the output
current and output voltage, so a postfilter may be placed at the output port of
the converter. This article proposes a step-by-step methodology to extend the
injected-absorbed-current (IAC) method in order to obtain transfer functions
that consider the effects of the input filter, output postfilter, and some
feedforward compensations. The proposed methodology allows reusing the
characteristic coefficients of the DC-DC converter model derived from the
existing IAC method. One of the advantages of the proposed methodology is that
the transfer functions obtained in this article are valid for cases where both,
one or none of the filters, are implemented. Finally, for the experimental
validation of the proposed methodology, the phase-shifted full-bridge converter
was selected as a convenient example. Furthermore, the experimental
measurements have been performed on two prototypes.Comment: This work was supported in part by the European Regional Development
Fund (FEDER), in part by the Ministry of Science, Innovation and
Universities, and in part by the State Research Agency through the Research
Project: Modeling and Control Strategies for the Stabilization of the
Interconnection of Power Electronic Converters CONEXPOT-2 under Grant
DPI2017-84572-C2-2-R (AEI/FEDER, UE
Electrocardiogram Derived Respiration for Tracking Changes in Tidal Volume from a Wearable Armband
A pilot study on tracking changes in tidal volume (TV) using ECG signals acquired by a wearable armband is presented. The wearable armband provides three ECG channels by using three pairs of dry electrodes, resulting in a device that is convenient for long-term daily monitoring. An additional ECG channel was derived by computing the first principal component of the three original channels (by means of principal component analysis). Armband and spirometer signals were simultaneously recorded from five healthy subjects who were instructed to breathe with varying TV. Three electrocardiogram derived respiration (EDR) methods based on QRS complex morphology were studied: the QRS slopes range (SR), the R-wave angle (), and the R-S amplitude (RS). The peak-to-peak amplitudes of these EDR signals were estimated as surrogates for TV, and their correlations with the reference TV (estimated from the spirometer signal) were computed. In addition, a multiple linear regression model was calculated for each subject, using the peak-to-peak amplitudes from the three EDR methods from the four ECG channels. Obtained correlations between TV and EDR peak-to-peak amplitude ranged from 0.0448 up to 0.8491. For every subject, a moderate correlation (>0.5) was obtained for at least one EDR method. Furthermore, the correlations obtained for the subject-specific multiple linear regression model ranged from 0.8234 up to 0.9154, and the goodness of fit was 0.73±0.07 (median ± standard deviation). These results suggest that the peak-to-peak amplitudes of the EDR methods are linearly related to the TV. opening the possibility of estimating TV directly from an armband ECG device.Clinical Relevance - This opens the door to possible continuous monitoring of TV from the armband by using EDR
Venous Thromboembolism in Neonates, Children and Patients with Chronic Renal Disease – Special Considerations
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