13,139 research outputs found
Performance limits of graphene-ribbon-based field effect transistors
The performance of field effect transistors based on an single graphene
ribbon with a constriction and a single back gate are studied with the help of
atomistic models. It is shown how this scheme, unlike that of traditional
carbon-nanotube-based transistors, reduces the importance of the specifics of
the chemical bonding to the metallic electrodes in favor of the carbon-based
part of device. The ultimate performance limits are here studied for various
constriction and metal-ribbon contact models. In particular we show that, even
for poorly contacting metals, properly taylored constrictions can give
promising values for both the on-conductance and the subthreshold swing.Comment: 5 pages, 4 figure
Calculable inverse-seesaw neutrino masses in supersymmetry
We provide a scenario where naturally small and calculable neutrino masses
arise from a supersymmetry breaking renormalization-group-induced vacuum
expectation value. We adopt a minimal supergravity scenario without ad hoc
supersymmetric mass parameters. The lightest supersymmetric particle can be an
isosinglet scalar neutrino state, potentially viable as WIMP dark matter
through its Higgs new boson coupling. The scenario leads to a plethora of new
phenomenological implications at accelerators including the Large Hadron
Collider.Comment: LaTeX, 5 pages, 4 figures. Comments and references added. Final
version to appear in PR
Development of polymer network of phenolic and epoxies resins mixed with linseed oil: pilot study
Epoxy resin was mixed with phenolic resins in different percentages by weight. Composite 40/60 means the proportion by weight of epoxy resin is 40 percent. It was found that only composites 50/50 and 40/60 could be cured in ambient conditions. Dynamic mechanical analysis showed that only these two composites form interpenetrating polymer network. The addition of linseed oil to the two resins results also in the formation of interpenetrating network irrespective of proportion by weight of the resins; the mechanical properties will only be better when the percentage by weight of epoxy resin is higher; the aim of reducing cost and at the same time maintaining the mechanical properties cannot be fully achieved because epoxy resin is much more expensive than its counterpart
Dynamical phase coexistence: A simple solution to the "savanna problem"
We introduce the concept of 'dynamical phase coexistence' to provide a simple
solution for a long-standing problem in theoretical ecology, the so-called
"savanna problem". The challenge is to understand why in savanna ecosystems
trees and grasses coexist in a robust way with large spatio-temporal
variability. We propose a simple model, a variant of the Contact Process (CP),
which includes two key extra features: varying external
(environmental/rainfall) conditions and tree age. The system fluctuates locally
between a woodland and a grassland phase, corresponding to the active and
absorbing phases of the underlying pure contact process. This leads to a highly
variable stable phase characterized by patches of the woodland and grassland
phases coexisting dynamically. We show that the mean time to tree extinction
under this model increases as a power-law of system size and can be of the
order of 10,000,000 years in even moderately sized savannas. Finally, we
demonstrate that while local interactions among trees may influence tree
spatial distribution and the order of the transition between woodland and
grassland phases, they do not affect dynamical coexistence. We expect dynamical
coexistence to be relevant in other contexts in physics, biology or the social
sciences.Comment: 8 pages, 7 figures. Accepted for publication in Journal of
Theoretical Biolog
Efecto del origen de plantas y silvicultura de establecimiento en la inclinación de plantaciones jóvenes de Pinus radiata D. Don por efecto del viento
Gallegos, J. Forestal Mininco S.A., Los Ángeles, Chile.
Muñoz, F.;Cancino, J. Facultad de Ciencias Forestales, Universidad de Concepción. Casilla 160-C, Concepción, Chile.El fenómeno de pérdida de estabilidad por viento en árboles jóvenes de Pinus radiata D. Don, es una perturbación abiótica que se manifiesta en forma de inclinaciones anormales, derribamiento, formación de cuencas en la base del árbol y descalces. La investigación tiene como objetivo identificar el efecto del origen de la planta, control de malezas y fertilización en el daño por viento en plantaciones jóvenes de pino radiata.
El ensayo fue establecido en el año 2003 en predios ubicados en la Comuna de Cunco, IX Región. Se establecieron cuatro orígenes de plantas (estacas de huerto, estacas de setos juveniles, estacas de setos envejecidos y plantas provenientes de semilla), combinados con tres esquemas de control de malezas y dos de fertilización (total 24 tratamientos). La variable respuesta fue la inclinación expresada en porcentaje, previamente normalizada, la cual fue medida luego de los temporales de viento durante el invierno del año 2005.
Como resultado se determinó que el origen de planta desde estacas de huerto en combinación con control de malezas en tazas en el primer año de establecido y sin fertilización, presenta la mejor resistencia al daño por viento. El tratamiento con peor resistencia al daño de viento, esta formado por estacas de setos juveniles, control de malezas en banda durante los 2 primeros años y sin fertilización. Se determinó que la edad del material fisiológico es determinante en el daño por efecto del viento en plantaciones jóvenes de Pinus radiata D. Don
Geometric Hamilton-Jacobi Theory
The Hamilton-Jacobi problem is revisited bearing in mind the consequences
arising from a possible bi-Hamiltonian structure. The problem is formulated on
the tangent bundle for Lagrangian systems in order to avoid the bias of the
existence of a natural symplectic structure on the cotangent bundle. First it
is developed for systems described by regular Lagrangians and then extended to
systems described by singular Lagrangians with no secondary constraints. We
also consider the example of the free relativistic particle, the rigid body and
the electron-monopole system.Comment: 40 page
Sense and sensitivity of double beta decay experiments
The search for neutrinoless double beta decay is a very active field in which
the number of proposals for next-generation experiments has proliferated. In
this paper we attempt to address both the sense and the sensitivity of such
proposals. Sensitivity comes first, by means of proposing a simple and
unambiguous statistical recipe to derive the sensitivity to a putative Majorana
neutrino mass, m_bb. In order to make sense of how the different experimental
approaches compare, we apply this recipe to a selection of proposals, comparing
the resulting sensitivities. We also propose a "physics-motivated range" (PMR)
of the nuclear matrix elements as a unifying criterium between the different
nuclear models. The expected performance of the proposals is parametrized in
terms of only four numbers: energy resolution, background rate (per unit time,
isotope mass and energy), detection efficiency, and bb isotope mass. For each
proposal, both a reference and an optimistic scenario for the experimental
performance are studied. In the reference scenario we find that all the
proposals will be able to partially explore the degenerate spectrum, without
fully covering it, although four of them (KamLAND-Zen, CUORE, NEXT and EXO)
will approach the 50 meV boundary. In the optimistic scenario, we find that
CUORE and the xenon-based proposals (KamLAND-Zen, EXO and NEXT) will explore a
significant fraction of the inverse hierarchy, with NEXT covering it almost
fully. For the long term future, we argue that Xe-based experiments may provide
the best case for a 1-ton scale experiment, given the potentially very low
backgrounds achievable and the expected scalability to large isotope masses.Comment: 30 pages, 12 figures, 6 table
A Novel Low-Cost Sensor Prototype for Nocturia Monitoring in Older People
Indexación: Scopus.This work was supported in part by CORFO - CENS 16CTTS-66390 through the National Center on Health Information Systems, in part by the National Commission for Scientific and Technological Research (CONICYT) through the program STIC-AMSUD 17STIC-03: ‘‘e-MONITOR âĂŞ Chronic Disease: Ambient Assisted Living and vital teleMONOTORing for e-health,’’ FONDEF ID16I10449 ‘‘Sistema inteligente para la gestión y análisis de la dotación de camas en la red asistencial del sector público,’’ and MEC80170097 ‘‘Red de colaboración científica entre universidades nacionales e internacionales para la estructuración del doctorado y magister en informática médica en la Universidad de Valparaíso.’’ The work of V. H. C. de Albuquerque was supported by the Brazilian National Council for Research and Development (CNPq) under Grant #304315/2017-6.Nocturia is frequently defined as the necessity to get out of bed at least one time during the night to urinate, with each of these episodes being preceded and continued by sleep. Several studies suggest that an increase of nocturia is seen with the onset of age, occurring in around 70% of adults over the age of 70. Its appearance is associated with detrimental quality of life for those who present nocturia, since it leads to daytime sleepiness, cognitive dysfunction, among others. Currently, a voiding diary is necessary for nocturia assessment; these are prone to bias due to their inherent subjectivity. In this paper, we present the design of a low-cost device that automatically detects micturition events. The device obtained 73% in sensibility and 81% in specificity; these results show that systems such as the proposed one can be a valuable tool for the medical team when evaluating nocturia. © 2013 IEEE.https://ieeexplore.ieee.org/document/845445
A novel monitoring system for fall detection in older people
Indexación: Scopus.This work was supported in part by CORFO - CENS 16CTTS-66390 through the National Center on Health Information Systems, in part by the National Commission for Scientific and Technological Research (CONICYT) through the Program STIC-AMSUD 17STIC-03: ‘‘MONITORing for ehealth," FONDEF ID16I10449 ‘‘Sistema inteligente para la gestión y análisis de la dotación de camas en la red asistencial del sector público’’, and in part by MEC80170097 ‘‘Red de colaboración científica entre universidades nacionales e internacionales para la estructuración del doctorado y magister en informática médica en la Universidad de Valparaíso’’. The work of V. H. C. De Albuquerque was supported by the Brazilian National Council for Research and Development (CNPq), under Grant 304315/2017-6.Each year, more than 30% of people over 65 years-old suffer some fall. Unfortunately, this can generate physical and psychological damage, especially if they live alone and they are unable to get help. In this field, several studies have been performed aiming to alert potential falls of the older people by using different types of sensors and algorithms. In this paper, we present a novel non-invasive monitoring system for fall detection in older people who live alone. Our proposal is using very-low-resolution thermal sensors for classifying a fall and then alerting to the care staff. Also, we analyze the performance of three recurrent neural networks for fall detections: Long short-term memory (LSTM), gated recurrent unit, and Bi-LSTM. As many learning algorithms, we have performed a training phase using different test subjects. After several tests, we can observe that the Bi-LSTM approach overcome the others techniques reaching a 93% of accuracy in fall detection. We believe that the bidirectional way of the Bi-LSTM algorithm gives excellent results because the use of their data is influenced by prior and new information, which compares to LSTM and GRU. Information obtained using this system did not compromise the user's privacy, which constitutes an additional advantage of this alternative. © 2013 IEEE.https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=842305
- …