1,366 research outputs found
Non-gaussian probability distribution functions in two dimensional Magnetohydrodynamic turbulence
Intermittency in MHD turbulence has been analyzed using high resolution 2D
numerical simulations. We show that the Probability Distribution Functions
(PDFs) of the fluctuations of the Elsasser fields, magnetic field and velocity
field depend on the scale at hand, that is they are self-affine. The departure
of the PDFs from a Gaussian function can be described through the scaling
behavior of a single parameter lambda_r^2 obtained by fitting the PDFs with a
given curve stemming from the analysis of a multiplicative model by Castaing et
al. (1990). The scaling behavior of the parameter lambda_r^2 can be used to
extract informations about the intermittency. A comparison of intermittency
properties in different MHD turbulent flows is also performed.Comment: 7 pages, with 5 figure
The role of surface chemical reactivity in the stability of electronic nanodevices based on two-dimensional materials "beyond graphene" and topological insulators
Here, we examine the influence of surface chemical reactivity toward ambient
gases on the performance of nanodevices based on two-dimensional materials
"beyond graphene" and novel topological phases of matter. While surface
oxidation in ambient conditions was observed for silicene and phosphorene with
subsequent reduction of the mobility of charge carriers, nanodevices with
active channels of indium selenide, bismuth chalcogenides and transition-metal
dichalcogenides are stable in air. However, air-exposed indium selenide suffers
of p-type doping due to water decomposition on Se vacancies, whereas the low
mobility of charge carriers in transition-metal dichalcogenides increases the
response time of nanodevices. Conversely, bismuth chalcogenides require a
control of crystalline quality, which could represent a serious hurdle for up
scaling
Scaling properties of three-dimensional magnetohydrodynamic turbulence
The scaling properties of three-dimensional magnetohydrodynamic turbulence
are obtained from direct numerical simulations of decaying turbulence using
modes. The results indicate that the turbulence does not follow the
Iroshnikov-Kraichnan phenomenology.In the case of hyperresistivity, the
structure functions exhibit a clear scaling range yielding absolute values of
the scaling exponents . The scaling exponents agree with a modified
She-Leveque model , corresponding to Kolmogorov
scaling but sheet-like geometry of the dissipative structures
Analysis of cancellation in two-dimensional magnetohydrodynamic turbulence
A signed measure analysis of two-dimensional intermittent magnetohydrodynamic
turbulence is presented. This kind of analysis is performed to characterize the
scaling behavior of the sign-oscillating flow structures, and their geometrical
properties. In particular, it is observed that cancellations between positive
and negative contributions of the field inside structures, are inhibited for
scales smaller than the Taylor microscale, and stop near the dissipative scale.
Moreover, from a simple geometrical argument, the relationship between the
cancellation exponent and the typical fractal dimension of the structures in
the flow is obtained.Comment: 21 pages, 5 figures (3 .jpg not included in the latex file
The lack of the Celf2a splicing factor converts a Duchenne genotype into a Becker phenotype
Substitutions, deletions and duplications in the dystrophin gene lead to either the severe Duchenne muscular dystrophy (DMD) or mild Becker muscular dystrophy depending on whether out-of-frame or in-frame transcripts are produced. We identified a DMD case (GSΔ44) where the correlation between genotype and phenotype is not respected, even if carrying a typical Duchenne mutation (exon 44 deletion) a Becker-like phenotype was observed. Here we report that in this patient, partial restoration of an in-frame transcript occurs by natural skipping of exon 45 and that this is due to the lack of Celf2a, a splicing factor that interacts with exon 45 in the dystrophin pre-mRNA. Several experiments are presented that demonstrate the central role of Celf2a in controlling exon 45 splicing; our data point to this factor as a potential target for the improvement of those DMD therapeutic treatments, which requires exon 45 skipping
Dynamo action at low magnetic Prandtl numbers: mean flow vs. fully turbulent motion
We compute numerically the threshold for dynamo action in Taylor-Green
swirling flows. Kinematic calculations, for which the flow field is fixed to
its time averaged profile, are compared to dynamical runs for which both the
Navier-Stokes and the induction equations are jointly solved. The kinematic
instability is found to have two branches, for all explored Reynolds numbers.
The dynamical dynamo threshold follows these branches: at low Reynolds number
it lies within the low branch while at high kinetic Reynolds number it is close
to the high branch.Comment: 4 pages, 4 figure
Dynamical constraints on some orbital and physical properties of the WD0137-349 A/B binary system
In this paper I deal with the WD0137-349 binary system consisting of a white
dwarf (WD) and a brown dwarf (BD) in a close circular orbit of about 116 min.
I, first, constrain the admissible range of values for the inclination i by
noting that, from looking for deviations from the third Kepler law, the
quadrupole mass moment Q would assume unlikely large values, incompatible with
zero at more than 1-sigma level for i 43 deg. Then, by
conservatively assuming that the most likely values for i are those that
prevent such an anomalous behavior of Q, i.e. those for which the third Kepler
law is an adequate modeling of the orbital period, I obtain i=39 +/- 2 deg.
Such a result is incompatible with the value i=35 deg quoted in literature by
more than 2 sigma. Conversely, it is shown that the white dwarf's mass range
obtained from spectroscopic measurements is compatible with my experimental
range, but not for i=35 deg. As a consequence, my estimate of yields an
orbital separation of a=(0.59 +/- 0.05)R_Sun and an equilibrium temperature of
BD of T_eq=(2087 +/- 154)K which differ by 10% and 4%, respectively, from the
corresponding values for i=35 deg.Comment: LaTex2e, 11 pages, 3 figures, no tables. It refers to gr-qc/0611126
and better clarify the result obtained there. Accepted by Astrophysics and
Space Scienc
The Role of Physical and Numerical Modeling in Design Development of the Priest Rapids Fish Bypass
This paper describes a number of years of physical and numerical modelling that were instrumental in the development of the final fish bypass design at Priest Rapids Dam. Three physical models and multiple numerical models were used to guide the design of the fish bypass including its location on the dam, impact on forebay and tailrace flow patterns, intake configuration, design flow rates, flow control scheme, tailrace egress, potential for scour near the dam, potential impacts on total dissolved gas (TDG), impacts on spillway and powerhouse operation, and overall fish friendliness of the bypass.
Throughout those years of design work, results from actively tagged salmonid smolt studies were used to guide and validate each step of the design process. In 2011, a construction contract was awarded and the Priest Rapids Fish Bypass facility was completed in the early spring of 2014. Final validation of this newly constructed facility came in the spring of 2014 with a survival and behavior study conducted using acoustic tagged yearling Chinook and juvenile steelhead smolts to evaluate the salmonid smolt survival rate through the bypass along with the fish passage efficiency (FPE) of the bypass facility.
This paper discusses the physical models plus CFD models used to support the design development of a non-turbine fish bypass and presents the results of the survival and behaviour studies conducted after the fish bypass was installed at Priest Rapids Dam
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