Search results for " diffusion"

Germination Pattern of Chamaerops humilis Seed after Short-Time Storage

2015

Dwarf fan palm (Chamaerops humilis) plays an important ecological role in the thermo Mediterranean vegetation stage, both in woodlands, xerophitic shrub communities and degraded ecosystems. Dwarf fan palm is typically propagated from seeds. Whereas other palm species show reduced germination after few months of seed storage, no information is available on the effects of storage time on seed germinability . We examined the germination pattern of dwarf palm seeds aged after a storage of four, six or eight months in comparison to fresh seed (control). A covariance analysis was performed to test the effect of time within seed-storage treatment. The germination patterns were significantly fitted…

In-situ observation of β-ray induced optical absorption in a-SiO2: radiation darkening and room temperature recovery

2008

Social network analysis and political phenomena: a contribution to the small world theory

2014

Spectroscopic studies of semiconducting single-walled carbon nanotubes

2010

The unique nature of optical properties of single-walled carbon nanotubes (SWCNT), together with their promising potential applications, have created enormous interest towards the photophysics of SWCNT. Many aspects of carbon nanotubes originate from the electronic structure of carbon honeycomb lattice and one-dimensionality. SWCNTs exist in various chiral structures and diameters, which the optical and electrical properties are dependent on. It has been discovered that SWCNT excited states are excitonic with strong Coulomb interaction between the electron and the hole. However, many features of excitons are not yet well defined, such as absorption cross-sections, fluorescence quantum yield…

Reduced Order Models for Pricing European and American Options under Stochastic Volatility and Jump-Diffusion Models

2017

Abstract European options can be priced by solving parabolic partial(-integro) differential equations under stochastic volatility and jump-diffusion models like the Heston, Merton, and Bates models. American option prices can be obtained by solving linear complementary problems (LCPs) with the same operators. A finite difference discretization leads to a so-called full order model (FOM). Reduced order models (ROMs) are derived employing proper orthogonal decomposition (POD). The early exercise constraint of American options is enforced by a penalty on subset of grid points. The presented numerical experiments demonstrate that pricing with ROMs can be orders of magnitude faster within a give…

Reduced Order Models for Pricing American Options under Stochastic Volatility and Jump-diffusion Models

2016

American options can be priced by solving linear complementary problems (LCPs) with parabolic partial(-integro) differential operators under stochastic volatility and jump-diffusion models like Heston, Merton, and Bates models. These operators are discretized using finite difference methods leading to a so-called full order model (FOM). Here reduced order models (ROMs) are derived employing proper orthogonal decomposition (POD) and non negative matrix factorization (NNMF) in order to make pricing much faster within a given model parameter variation range. The numerical experiments demonstrate orders of magnitude faster pricing with ROMs. peerReviewed

IMEX schemes for pricing options under jump–diffusion models

2014

We propose families of IMEX time discretization schemes for the partial integro-differential equation derived for the pricing of options under a jump-diffusion process. The schemes include the families of IMEX-midpoint, IMEX-CNAB and IMEX-BDF2 schemes. Each family is defined by a convex combination parameter [email protected]?[0,1], which divides the zeroth-order term due to the jumps between the implicit and explicit parts in the time discretization. These IMEX schemes lead to tridiagonal systems, which can be solved extremely efficiently. The schemes are studied through Fourier stability analysis and numerical experiments. It is found that, under suitable assumptions and time step restric…

Digital generations, but not as we know them

2019

The aim of this article is to see whether or not adolescents were the real leaders of the digital ‘revolution’ in the 1990s and whether they have sustained or even improved their position in the 2000s. The analysis is based on two surveys carried out in Italy, France, the United Kingdom, Germany, and Spain in 1996 ( N = 6609) and in 2009 ( N = 7255). The results show that the adolescents belonging to the first digital generation in 1996 were the most equipped with new technologies, although not the most intensive users. In 2009, the adolescents lost their position as the leading adopters and lagged behind youth and young adults regarding the use of new technologies and computer skills.

Les sarcophages mérovingiens en trachyte. Des carrières aux lieux d'enfouissement (Massif central)

2018

A multi-disciplinary team is currently working on trachyte, a volcanic rock from the Chaîne des Puys (French massif central), within a research program supported by the French ministry of Culture. Although it has been known at least since the 19th century that this rock was used for construction and sculpture in antiquity, and in the making of sarcophagi in the middle ages, the systematisation of the research on trachyte, carried out since 2008, has enabled us to make significant advances in the knowledge of its exploitation and dissemination. Geologists have established a detailed identity card of the six volcanoes where massive lava is available, thereby allowing the classification of eac…

HIPPOCAMPAL REVERSIBLE LESIONS IN A CASE OF TRANSIENT GLOBAL AMNESIA

2013

PURPOSE: We present a case of transient global amnesia (TGA) onset in a 52-year-old male with a medical history of migraine. METHODS: Patient was taken to ER by his colleagues which reported that after an emotional stress he suddenly appeared perplexed and started asking repetitive questions. In ER a neurological examination excluded other neurological signs or symptoms and it was confirmed that cognitive impairment was limited to the amnesia domain; electroencephalography was unremarkable and he had no history of epileptic seizures or head trauma. At the neurologic examination Capland and Hodges criteria were fulfilled and the diagnostic hypothesis of TGA was placed. He underwent to a brai…