11,659 research outputs found
Mechanically-Induced Transport Switching Effect in Graphene-based Nanojunctions
We report a theoretical study suggesting a novel type of electronic switching
effect, driven by the geometrical reconstruction of nanoscale graphene-based
junctions. We considered junction struc- tures which have alternative
metastable configurations transformed by rotations of local carbon dimers. The
use of external mechanical strain allows a control of the energy barrier
heights of the potential profiles and also changes the reaction character from
endothermic to exothermic or vice-versa. The reshaping of the atomic details of
the junction encode binary electronic ON or OFF states, with ON/OFF
transmission ratio that can reach up to 10^4-10^5. Our results suggest the
possibility to design modern logical switching devices or mechanophore sensors,
monitored by mechanical strain and structural rearrangements.Comment: 10 pages, 4 figure
Modular termination verification for non-blocking concurrency
© Springer-Verlag Berlin Heidelberg 2016.We present Total-TaDA, a program logic for verifying the total correctness of concurrent programs: that such programs both terminate and produce the correct result. With Total-TaDA, we can specify constraints on a thread’s concurrent environment that are necessary to guarantee termination. This allows us to verify total correctness for nonblocking algorithms, e.g. a counter and a stack. Our specifications can express lock- and wait-freedom. More generally, they can express that one operation cannot impede the progress of another, a new non-blocking property we call non-impedance. Moreover, our approach is modular. We can verify the operations of a module independently, and build up modules on top of each other
Bloqueio Epidural Torácico em Cirurgia de Nuss: Caso de Sucesso
Os autores descrevem o caso c1ínico de um adolescente com o diagnóstico de pectus excavatum grave, submetido a cirurgia de Nuss sob controlo toracoscópico. Realizou-se anestesia combinada, com cateter epidural torácico que permitiu um periodo intra e pós-operatório estável, sem intercorrências e sem necessidade de suplementação analgésica
Rewriting Logic Semantics of a Plan Execution Language
The Plan Execution Interchange Language (PLEXIL) is a synchronous language
developed by NASA to support autonomous spacecraft operations. In this paper,
we propose a rewriting logic semantics of PLEXIL in Maude, a high-performance
logical engine. The rewriting logic semantics is by itself a formal interpreter
of the language and can be used as a semantic benchmark for the implementation
of PLEXIL executives. The implementation in Maude has the additional benefit of
making available to PLEXIL designers and developers all the formal analysis and
verification tools provided by Maude. The formalization of the PLEXIL semantics
in rewriting logic poses an interesting challenge due to the synchronous nature
of the language and the prioritized rules defining its semantics. To overcome
this difficulty, we propose a general procedure for simulating synchronous set
relations in rewriting logic that is sound and, for deterministic relations,
complete. We also report on two issues at the design level of the original
PLEXIL semantics that were identified with the help of the executable
specification in Maude
Evaporation of large black holes in AdS: greybody factor and decay rate
We consider a massless, minimally coupled scalar field propagating through
the geometry of a black 3-brane in an asymptotically space.
The wave equation for modes traveling purely in the holographic direction
reduces to a Heun equation and the corresponding greybody factor is obtained
numerically. Approximations valid in the low- and high-frequency regimes are
also obtained analytically. The greybody factor is then used to determine the
rate of evaporation of these large black holes in the context of the evaporon
model proposed in \cite{Rocha:2008fe}. This setting represents the evolution of
a black hole under Hawking evaporation with a known CFT dual description and is
therefore unitary. Information must then be preserved under this evaporation
process.Comment: 20 pages, 2 figures; v2: added references, published versio
Non-collinear coupling between magnetic adatoms in carbon nanotubes
The long range character of the exchange coupling between localized magnetic
moments indirectly mediated by the conduction electrons of metallic hosts often
plays a significant role in determining the magnetic order of low-dimensional
structures. In addition to this indirect coupling, here we show that the direct
exchange interaction that arises when the moments are not too far apart may
induce a non-collinear magnetic order that cannot be characterized by a
Heisenberg-like interaction between the magnetic moments. We argue that this
effect can be manipulated to control the magnetization alignment of magnetic
dimers adsorbed to the walls of carbon nanotubes.Comment: 13 pages, 5 figures, submitted to PR
Constraints on changes in fundamental constants from a cosmologically distant OH absorber/emitter
We have detected the four 18cm OH lines from the gravitational
lens toward PMN J0134-0931. The 1612 and 1720 MHz lines are in conjugate
absorption and emission, providing a laboratory to test the evolution of
fundamental constants over a large lookback time. We compare the HI and OH main
line absorption redshifts of the different components in the
absorber and the lens toward B0218+357 to place stringent
constraints on changes in . We obtain
,
consistent with no evolution over the redshift range . The
measurements have a sensitivity of or to fractional
changes in and over a period of Gyr, half the age of
the Universe. These are among the most sensitive current constraints on changes
in .Comment: 4 pages, 3 figures. Final version, with minor changes to match the
version in print in Phys. Rev. Let
Magnetic-field effects on transport in carbon nanotube junctions
Here we address a theoretical study on the behaviour of electronic states of
heterojunctions and quantum dots based on carbon nanotubes under magnetic
fields. Emphasis is put on the analysis of the local density of states, the
conductance, and on the characteristic curves of current versus voltage. The
heterostructures are modeled by joining zigzag tubes through single
pentagon-heptagon pair defects, and described within a simple tight binding
calculation. The conductance is calculated using the Landauer formula in the
Green functions formalism. The used theoretical approach incorporates the
atomic details of the topological defects by performing an energy relaxation
via Monte Carlo calculation. The effect of a magnetic field on the conductance
gap of the system is investigated and compared to those of isolated constituent
tubes. It is found that the conductance gap of the studied CNHs exhibits
oscillations as a function of the magnetic flux. However, unlike the pristine
tubes case, they are not Aharonov-Bohm periodic oscillations
Corioamnionite e Morbilidade Neonatal
CHORIOAMNIONITIS AND NEONATAL MORBIDITY
Introduction - Several studies highlight the association between perinatal infection/
inflammation and neonatal morbidity, mainly bronchopulmonary dysplasia and
periventricular leukomalacia.
Aim – To evaluate the role of histological chorioamnionitis on the overall morbidity of
preterm newborns.
Methods – A retrospective study on preterm newborns less than 34 weeks gestational
age at birth, and respective mothers, at three tertiary medical centers (Hospital de São
João, Maternidade Júlio Dinis and Centro Hospitalar de Vila Nova de Gaia) in the north
of Portugal, between January 2001 and December 2002.
We evaluated the association between histological chorioamnionitis and the overall
neonatal morbidity. The association between histological chorioamnionitis and acute
(respiratory distress syndrome) and chronic (bronchopulmonary dysplasia) lung
damage was also evaluated in the subgroup of less than 1000 g birthweight preterm
neonates.
Results – 452 [ M 253 / F 217; birthweight 1440 (515 – 2620) g; gestational age 31 (23 –
33) weeks] preterm newborns were included. The association between histological
chorioamnionitis and the overall neonatal morbidity was: respiratory distress syndrome
OR 1,5 (95% CI 0,94 – 2,31); bronchopulmonary dysplasia OR 2,6 (95% CI 1,16 – 6,03);
patent ductus arteriosus OR 2,5 (95% CI 1,17 – 5,44); sepsis OR 1,2 (95% CI 0,9 – 2,13);
necrotizing enterocolitis OR 1,4 (95% CI 0,9 – 1,76); intraventricular hemorrhage grades
III-IV OR 2,5 (1,20 – 5,11); cystic periventricular leukomalacia OR 3,0 (1,5 – 6,07);
retinopathy of prematurity OR 1,4 (95% CI 0,8 – 1,35). The association adjusted to
birthweight and gestational age was: bronchopulmonary dysplasia OR 1,2 (95% CI
0,51 – 2,95); patent ductus arteriosus OR 0,9 (95% CI 0,4 – 2,35); intraventricular
hemorrhage grades III-IV OR 0,9 (95% CI 0,39 – 2,28); cystic periventricular leukomalacia
OR 2,2 (95% CI 1,03 – 4,61). The association between histological chorioamnionitis
and lung damage in the subgroup of less than 1000 g birthweight preterm neonates
was: respiratory distress syndrome OR 0,23 (95% CI 0,01 – 2,51); bronchopulmonary
dysplasia OR 1,61 (95% CI 0,38 – 6,97).
Conclusion – This study confirms the association between histological chorioamnionitis
and cystic periventricular leukomalacia of the preterm newborn
Relativistic two-pion exchange nucleon-nucleon potential: configuration space
We have recently performed a relativistic chiral expansion of the
two-pion exchange potential, and here we explore its configuration space
content. Interactions are determined by three families of diagrams, two of
which involve just and , whereas the third one depends on
empirical coefficients fixed by subthreshold data. In this sense, the
calculation has no adjusted parameters and gives rise to predictions, which are
tested against phenomenological potentials. The dynamical structure of the
eight leading non-relativistic components of the interaction is investigated
and, in most cases, found to be clearly dominated by a well defined class of
diagrams. In particular, the central isovector and spin-orbit, spin-spin, and
tensor isoscalar terms are almost completely fixed by just and .
The convergence of the chiral series in powers of the ratio (pion mass/nucleon
mass) is studied as a function of the internucleon distance and, for 1 fm,
found to be adequate for most components of the potential. An important
exception is the dominant central isoscalar term, where the convergence is
evident only for 2.5 fm. Finally, we compare the spatial behavior of the
functions that enter the relativistic and heavy baryon formulations of the
interaction and find that, in the region of physical interest, they differ by
about 5%.Comment: 27 pages, 33 figure
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