6,456 research outputs found
Estudio de propuestas alternativas en la enseñanza de la termodinåmica båsica
We report in this work a research on an approach to Basic Thermodynamics teaching at secondary level. The results of four grups of students in different cities are discussed from qualitative and global quantitative perspectives in a complementary way. We suggest, in the light of the real implementation of that curricular proposal, some didactic recommendations for better adequacy to different contexts
Electronic heat current rectification in hybrid superconducting devices
In this work, we review and expand recent theoretical proposals for the
realization of electronic thermal diodes based on tunnel-junctions of normal
metal and superconducting thin films. Starting from the basic rectifying
properties of a single hybrid tunnel junction, we will show how the
rectification efficiency can be largely increased by combining multiple
junctions in an asymmetric chain of tunnel-coupled islands. We propose three
different designs, analyzing their performance and their potential advantages.
Besides being relevant from a fundamental physics point of view, this kind of
devices might find important technological application as fundamental building
blocks in solid-state thermal nanocircuits and in general-purpose cryogenic
electronic applications requiring energy management.Comment: 9 pages, 5 color figure
NanoSQUID magnetometry of individual cobalt nanoparticles grown by focused electron beam induced deposition
We demonstrate the operation of low-noise nano superconducting quantum
interference devices (SQUIDs) based on the high critical field and high
critical temperature superconductor YBaCuO (YBCO) as
ultra-sensitive magnetometers for single magnetic nanoparticles (MNPs). The
nanoSQUIDs exploit the Josephson behavior of YBCO grain boundaries and have
been patterned by focused ion beam milling. This allows to precisely define the
lateral dimensions of the SQUIDs so as to achieve large magnetic coupling
between the nanoloop and individual MNPs. By means of focused electron beam
induced deposition, cobalt MNPs with typical size of several tens of nm have
been grown directly on the surface of the sensors with nanometric spatial
resolution. Remarkably, the nanoSQUIDs are operative over extremely broad
ranges of applied magnetic field (-1 T 1 T) and temperature (0.3
K 80 K). All these features together have allowed us to perform
magnetization measurements under different ambient conditions and to detect the
magnetization reversal of individual Co MNPs with magnetic moments (1 - 30)
. Depending on the dimensions and shape of the
particles we have distinguished between two different magnetic states yielding
different reversal mechanisms. The magnetization reversal is thermally
activated over an energy barrier, which has been quantified for the (quasi)
single-domain particles. Our measurements serve to show not only the high
sensitivity achievable with YBCO nanoSQUIDs, but also demonstrate that these
sensors are exceptional magnetometers for the investigation of the properties
of individual nanomagnets
Rectification of electronic heat current by a hybrid thermal diode
We report the realization of an ultra-efficient low-temperature hybrid heat
current rectifier, thermal counterpart of the well-known electric diode. Our
design is based on a tunnel junction between two different elements: a normal
metal and a superconducting island. Electronic heat current asymmetry in the
structure arises from large mismatch between the thermal properties of these
two. We demonstrate experimentally temperature differences exceeding mK
between the forward and reverse thermal bias configurations. Our device offers
a remarkably large heat rectification ratio up to and allows its
prompt implementation in true solid-state thermal nanocircuits and
general-purpose electronic applications requiring energy harvesting or thermal
management and isolation at the nanoscale.Comment: 8 pages, 6 color figure
Recent Approaches for the Manufacturing of Polymeric Cranial Prostheses by Incremental Sheet Forming
This paper presents recent research experiences developed with the aim of manufacturing cranial prostheses in polymeric sheet using Incremental Sheet Forming (ISF) technologies. With this purpose, different approaches have been carried out in Single-Point Incremental Forming (SPIF) and Two-Point Incremental Forming (TPIF) in order to produce customized cranial implants using different polymeric materials. In this context, this research work provides a methodology to design and manufacture polymer customized cranial prostheses using the ISF technologies starting from a patientâs computerized tomography (CT). The results demonstrate the potential of manufacturing polymeric cranial prostheses by ISF in terms of the high formability achievable and show the appropriate geometrical accuracy at affordable manufacturing costs provided by these processes.Ministerio de EconomĂa y Competitividad DPI2015-64047-
Improving randomness characterization through Bayesian model selection
Nowadays random number generation plays an essential role in technology with
important applications in areas ranging from cryptography, which lies at the
core of current communication protocols, to Monte Carlo methods, and other
probabilistic algorithms. In this context, a crucial scientific endeavour is to
develop effective methods that allow the characterization of random number
generators. However, commonly employed methods either lack formality (e.g. the
NIST test suite), or are inapplicable in principle (e.g. the characterization
derived from the Algorithmic Theory of Information (ATI)). In this letter we
present a novel method based on Bayesian model selection, which is both
rigorous and effective, for characterizing randomness in a bit sequence. We
derive analytic expressions for a model's likelihood which is then used to
compute its posterior probability distribution. Our method proves to be more
rigorous than NIST's suite and the Borel-Normality criterion and its
implementation is straightforward. We have applied our method to an
experimental device based on the process of spontaneous parametric
downconversion, implemented in our laboratory, to confirm that it behaves as a
genuine quantum random number generator (QRNG). As our approach relies on
Bayesian inference, which entails model generalizability, our scheme transcends
individual sequence analysis, leading to a characterization of the source of
the random sequences itself.Comment: 25 page
Nanostructures with Group IV nanocrystals obtained by LPCVD and thermal annealing of SiGeO layers
Nanocrystals embedded in an oxide matrix have been fabricated by annealing SiGeO films deposited by LPCVD. The composition of the oxide layers and its evolution after annealing as well as the presence and nature of nanocrystals in the films have been studied by several experimental techniques. The results are analyzed and discussed in terms of the main deposition parameters and the annealing temperature
A CMOS self-contained quadrature signal generator for soc impedance spectroscopy
This paper presents a low-power fully integrated quadrature signal generator for system-on-chip (SoC) impedance spectroscopy applications. It has been designed in a 0.18 ”m-1.8 V CMOS technology as a self-contained oscillator, without the need for an external reference clock. The frequency can be digitally tuned from 10 to 345 kHz with 12-bit accuracy and a relative mean error below 1.7%, thus supporting a wide range of impedance sensing applications. The proposal is experimentally validated in two impedance spectrometry examples, achieving good magnitude and phase recovery results compared to the results obtained using a commercial LCR-meter. Besides the wide frequency tuning range, the proposed programmable oscillator features a total power consumption lower than 0.77 mW and an active area of 0.129 mm2, thus constituting a highly suitable choice as stimulation module for instrument-on-a-chip devices
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