214 research outputs found
On the self-similarity of line segments in decaying homogeneous isotropic turbulence
The self-similarity of a passive scalar in homogeneous isotropic decaying
turbulence is investigated by the method of line segments (M. Gauding et al.,
Physics of Fluids 27.9 (2015): 095102). The analysis is based on a highly
resolved direct numerical simulation of decaying turbulence. The method of line
segments is used to perform a decomposition of the scalar field into smaller
sub-units based on the extremal points of the scalar along a straight line.
These sub-units (the so-called line segments) are parameterized by their length
and the difference of the scalar field between the ending
points. Line segments can be understood as thin local convective-diffusive
structures in which diffusive processes are enhanced by compressive strain.
From DNS, it is shown that the marginal distribution function of the
length~ assumes complete self-similarity when re-scaled by the mean
length . The joint statistics of and , from which
the local gradient can be defined, play an important role
in understanding the turbulence mixing and flow structure. Large values of
occur at a small but finite length scale. Statistics of are characterized
by rare but strong deviations that exceed the standard deviation by more than
one order of magnitude. It is shown that these events break complete
self-similarity of line segments, which confirms the standard paradigm of
turbulence that intense events (which are known as internal intermittency) are
not self-similar
Coexistence of charge and ferromagnetic order in fcc Fe
Phase coexistence phenomena have been intensively studied in strongly
correlated materials where several ordered states simultaneously occur or
compete. Material properties critically depend on external parameters and
boundary conditions, where tiny changes result in qualitatively different
ground states. However, up to date, phase coexistence phenomena have
exclusively been reported for complex compounds composed of multiple elements.
Here we show that charge- and magnetically ordered states coexist in
double-layer Fe on Rh(001). Scanning tunneling microscopy and spectroscopy
measurements reveal periodic charge order stripes below a temperature of 130 K.
Close to liquid helium temperature, they are superimposed by ferromagnetic
domains as observed by spin-polarized scanning tunneling microscopy.
Temperature-dependent measurements reveal a pronounced cross-talk between
charge and spin order at the ferromagnetic ordering temperature about 70 K,
which is successfully modeled within an effective Landau theory including
sixth-order terms. Our results show that subtle balance between structural
modifications can lead to competing ordering phenomena
The Minimum of the Maximum Rectilinear Crossing Numbers of Small Cubic Graphs
Here we consider the minimum of the maximum rectilinear crossing numbers for all d-regular graphs of order n. The case of connected graphs only is investigated also. For d = 3 exact values are determined for n are less than or equal to 12 and some estimations are given in general
Gameboard Ramsey Numbers
Sequences Bn(p,q) of connected parts of Euclidean and hyperbolic (p,q)-mosaic graphs are considered. The smallest n such that any 2-coloring of the edges of Bn( p,q) contains a given monochromatic graph G is introduced as gameboard Ramsey number rp,q(G). For p ≥ 4 it is proved that these Ramsey numbers exist for finitely many graphs only. For p = 3 there exist infinitely many numbers r3,q(G). For p ≥ 6 all gameboard Ramsey numbers are determined
Reversible magnetic switching of high-spin molecules on a giant Rashba surface
The quantum mechanical screening of a spin via conduction electrons depends
sensitively on the environment seen by the magnetic impurity. A high degree of
responsiveness can be obtained with metal complexes, as the embedding of a
metal ion into an organic molecule prevents intercalation or alloying and
allows for a good control by an appropriate choice of the ligands. There are
therefore hopes to reach an "on demand" control of the spin state of single
molecules adsorbed on substrates. Hitherto one route was to rely on
"switchable" molecules with intrinsic bistabilities triggered by external
stimuli, such as temperature or light, or on the controlled dosing of chemicals
to form reversible bonds. However, these methods constrain the functionality to
switchable molecules or depend on access to atoms or molecules. Here, we
present a way to induce bistability also in a planar molecule by making use of
the environment. We found that the particular "habitat" offered by an antiphase
boundary of the Rashba system BiAg stabilizes a second structure for
manganese phthalocyanine molecules, in which the central Mn ion moves out of
the molecular plane. This corresponds to the formation of a large magnetic
moment and a concomitant change of the ground state with respect to the
conventional adsorption site. The reversible spin switch found here shows how
we can not only rearrange electronic levels or lift orbital degeneracies via
the substrate, but even sway the effects of many-body interactions in single
molecules by acting on their surrounding.Comment: Main text, 7 pages, 6 figures. Supplementary material available at
https://www.nature.com/articles/s41535-018-0126-
Transient Dynamic System Behavior of Pressure Actuated Cellular Structures in a Morphing Wing
High aspect ratio aircraft have a significantly reduced induced drag, but have only limited installation space for control surfaces near the wingtip. This paper describes a multidisciplinary design methodology for a morphing aileron that is based on pressure-actuated cellular structures (PACS). The focus of this work is on the transient dynamic system behavior of the multi-functional aileron. Decisive design aspects are the actuation speed, the resistance against external loads, and constraints preparing for a future wind tunnel test. The structural stiffness under varying aerodynamic loads is examined while using a reduced-order truss model and a high-fidelity finite element analysis. The simulations of the internal flow investigate the transient pressurization process that limits the dynamic actuator response. The authors present a reduced-order model based on the Pseudo Bond Graph methodology enabling time-efficient flow simulation and compare the results to computational fluid dynamic simulations. The findings of this work demonstrate high structural resistance against external forces and the feasibility of high actuation speeds over the entire operating envelope. Future research will incorporate the fluid–structure interaction and the assessment of load alleviation capability
Methodology of assessment of population satisfaction with the quality of medical service based on the adaptive polling technologyn
This article covers the problem of assessment of patient satisfaction as a parameter of the quality of medical service. The existing methods of assessment of patients' attitude to a medical institution, their benefits and disadvantages are considered. The methodology for the calculation of the satisfaction coefficient is proposed, which can be the basis for the application of the technology (depending on the type and amount of medical care received by the patient) of adaptive polling and analysis of the information received
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