2,103 research outputs found
Recommended from our members
Effect of stent position on flow characteristics in a cerebral aneurysm
The position of an intracranial stent in relation to the ostium of a cerebral aneurysm can
significantly affect the blood flow characteristics through the ostium and inside the aneurysm.
An idealised cerebral artery and aneurysm were simulated with a pulsatile flow. Simulation
results show that the effect on mass inflow between two stent positions is about 20%
whereas the difference in the porosity effect of the pattern at these two positions is around
3%. The remainder may be attributed to differences in flow velocity profile across the stent
into the aneurysm. The implications for clinical practice are an important consideration as the
surgeon may place the stent in any position between the two investigated and hence this will
lead to markedly different stent performance. Therefore, computational tools that take into
account the variability of stent placement will be valuable for assisting surgical planning
Large Firm Dynamics and the Business Cycle
Do large firm dynamics drive the business cycle? We answer this question by developing a quantitative theory of aggregate fluctuations caused by firm-level disturbances alone. We show that a standard heterogeneous firm dynamics setup already contains in it a theory of the business cycle,
without appealing to aggregate shocks. We offer an analytical characterization of the law of motion of the aggregate state in this class of models – the firm size distribution – and show that aggregate output and productivity dynamics display: (i) persistence, (ii) volatility and (iii) time-varying second moments. We explore the key role of moments of the firm size distribution – and, in particular, the role of large firm dynamics – in shaping aggregate fluctuations, theoretically, quantitatively and in the data.ERC, Keynes Fun
The use of histological analysis for the detection of somatic embryos in sugarcane
The aim of this study was to establish an in vitro system for the induction, maturation and regeneration of somatic embryo in sugarcane from buds of cultivar RB 867515. Embryogenic calluses were obtained on semi-solid MS medium supplemented with 4.42 mg L-1 2,4-D. After four weeks of culture of explants on the callus induction medium, globular structures were obtained. At the end of 20 days in maturation medium, somatic embryos were observed. Histological analysis showed somatic embryos with caulinarand root apex, protodermal tissue, and the vascular system, which apparently has no connection with the vascular tissue explant that gave rise to it confirming the presence of the somatic embryo. The embryos were transferred to regeneration medium containing 1 mg L-1 GA3 and BAP, and after 1 to 2 weeks of culture, green points were observed, indicating the beginning of the formation of shoots. Key words: Saccharum spp, bud culture, 2.4-D, morphogenetic pathway, embryogenesis, plant regeneration
Strained graphene structures: from valleytronics to pressure sensing
Due to its strong bonds graphene can stretch up to 25% of its original size
without breaking. Furthermore, mechanical deformations lead to the generation
of pseudo-magnetic fields (PMF) that can exceed 300 T. The generated PMF has
opposite direction for electrons originating from different valleys. We show
that valley-polarized currents can be generated by local straining of
multi-terminal graphene devices. The pseudo-magnetic field created by a
Gaussian-like deformation allows electrons from only one valley to transmit and
a current of electrons from a single valley is generated at the opposite side
of the locally strained region. Furthermore, applying a pressure difference
between the two sides of a graphene membrane causes it to bend/bulge resulting
in a resistance change. We find that the resistance changes linearly with
pressure for bubbles of small radius while the response becomes non-linear for
bubbles that stretch almost to the edges of the sample. This is explained as
due to the strong interference of propagating electronic modes inside the
bubble. Our calculations show that high gauge factors can be obtained in this
way which makes graphene a good candidate for pressure sensing.Comment: to appear in proceedings of the NATO Advanced Research Worksho
Realization of a Tunable Artificial Atom at a Supercritically Charged Vacancy in Graphene
The remarkable electronic properties of graphene have fueled the vision of a
graphene-based platform for lighter, faster and smarter electronics and
computing applications. One of the challenges is to devise ways to tailor its
electronic properties and to control its charge carriers. Here we show that a
single atom vacancy in graphene can stably host a local charge and that this
charge can be gradually built up by applying voltage pulses with the tip of a
scanning tunneling microscope (STM). The response of the conduction electrons
in graphene to the local charge is monitored with scanning tunneling and Landau
level spectroscopy, and compared to numerical simulations. As the charge is
increased, its interaction with the conduction electrons undergoes a transition
into a supercritical regime 6-11 where itinerant electrons are trapped in a
sequence of quasi-bound states which resemble an artificial atom. The
quasi-bound electron states are detected by a strong enhancement of the density
of states (DOS) within a disc centered on the vacancy site which is surrounded
by halo of hole states. We further show that the quasi-bound states at the
vacancy site are gate tunable and that the trapping mechanism can be turned on
and off, providing a new mechanism to control and guide electrons in grapheneComment: 18 pages and 5 figures plus 14 pages and 15 figures of supplementary
information. Nature Physics advance online publication, Feb 22 (2016
Relationship among Apis mellifera L. stings, swarming and climate conditions in the city of Rio Claro, SP, Brazil
The presence of bees (Apis mellifera L.) in urban areas has increased in recent years due to environmental disturbances caused by humans. Bee migration to cities may provoke serious accidents, since some people present allergic reactions to their venoms. In Rio Claro city, São Paulo state, Brazil, the number of calls to the fire brigade for removal of bee swarms, and the number admissions in local hospitals due to bee stings were investigated during 2002 and 2003, and a correlation between these data and the average temperature, rainfall and relative humidity was found. The study period was divided into three phases according to the number of times that the fire brigade was called to remove swarms (263 times): January to July 2002 - 51 calls (19.39%); August 2002 to July 2003 - 140 calls (53.23%); and August to December 2003 - 72 calls (27.38%). A significant correlation among the number of calls, the local temperature and rainfall was detected. The number of accidents was not associated with environmental variables. Based on the current results, public activities for prevention of bee attacks may be developed to avoid unwanted contact between humans and these insects, and/or provide the appropriate management of the colonies
Gate-Controlled Ionization and Screening of Cobalt Adatoms on a Graphene Surface
We describe scanning tunneling spectroscopy (STS) measurements performed on
individual cobalt (Co) atoms deposited onto backgated graphene devices. We find
that Co adatoms on graphene can be ionized by either the application of a
global backgate voltage or by the application of a local electric field from a
scanning tunneling microscope (STM) tip. Large screening clouds are observed to
form around Co adatoms ionized in this way, and we observe that some intrinsic
graphene defects display a similar behavior. Our results provide new insight
into charged impurity scattering in graphene, as well as the possibility of
using graphene devices as chemical sensors.Comment: 19 pages, 4 figure
Terrestrial impact structures as geoheritage: an assessment method of their scientific value and its application to Brazil
Terrestrial impact structures are geological and geomorphological features with particular importance to understand the history and evolution of the planet. Impact structures are scattered around the world but in many countries these features are under threat, essentially due to anthropic factors. Impact structures with higher scienti c value should be considered as geological heritage and, consequently, be subjected to geoconservation strategies. In order to select the most important impact structures to be properly conserved and managed, this paper proposes a quantitative assessment method of the scienti c value of these structures. The eight Brazilian impact structures were used to test this method that has the potential to be applied to any geological context in any country. The structures known as Araguainha Dome-MT and Serra da Cangalha-TO reached a higher scienti c value, which justi es the need to develop geoconservation strategies and a proper management.The Conselho Nacional de Pesquisa e
Desenvolvimento (CNPq / National Council for
Research and Development) and the Programa
Ciências sem Fronteiras / Science Without Borders
Programme are acknowledged for the support
of the postdoctoral grant No 233209/2013-1 of
the 1st author. The work was co-funded by the
European Union through the European Regional
Development Fund, based on COMPETE 2020
(Programa Operacional da Competitividade
e Internacionalização), project ICT (UID/
GEO/04683/2013) with reference POCI-01-0145-
FEDER-007690 and Portuguese funds provided by
Fundação para a Ciência e Tecnologia.info:eu-repo/semantics/publishedVersio
Strain- and Adsorption-Dependent Electronic States and Transport or Localization in Graphene
The chapter generalizes results on influence of uniaxial strain and
adsorption on the electron states and charge transport or localization in
graphene with different configurations of imperfections (point defects):
resonant (neutral) adsorbed atoms either oxygen- or hydrogen-containing
molecules or functional groups, vacancies or substitutional atoms, charged
impurity atoms or molecules, and distortions. To observe electronic properties
of graphene-admolecules system, we applied electron paramagnetic resonance
technique in a broad temperature range for graphene oxides as a good basis for
understanding the electrotransport properties of other active carbons. Applied
technique allowed observation of possible metal-insulator transition and
sorption pumping effect as well as discussion of results in relation to the
granular metal model. The electronic and transport properties are calculated
within the framework of the tight-binding model along with the Kubo-Greenwood
quantum-mechanical formalism. Depending on electron density and type of the
sites, the conductivity for correlated and ordered adsorbates is found to be
enhanced in dozens of times as compared to the cases of their random
distribution. In case of the uniaxially strained graphene, the presence of
point defects counteracts against or contributes to the band-gap opening
according to their configurations. The band-gap behaviour is found to be
nonmonotonic with strain in case of a simultaneous action of defect ordering
and zigzag deformation. The amount of localized charge carriers (spins) is
found to be correlated with the content of adsorbed centres responsible for the
formation of potential barriers and, in turn, for the localization effects.
Physical and chemical states of graphene edges, especially at a uniaxial strain
along one of them, play a crucial role in electrical transport phenomena in
graphene-based materials.Comment: 16 pages, 10 figure
- …