4,713 research outputs found
On weak and strong magnetohydrodynamic turbulence
Recent numerical and observational studies contain conflicting reports on the
spectrum of magnetohydrodynamic turbulence. In an attempt to clarify the issue
we investigate anisotropic incompressible magnetohydrodynamic turbulence with a
strong guide field . We perform numerical simulations of the reduced MHD
equations in a special setting that allows us to elucidate the transition
between weak and strong turbulent regimes. Denote ,
characteristic field-parallel and field-perpendicular wavenumbers of the
fluctuations, and the fluctuating field at the scale . We find that when the critical balance condition, , is satisfied, the turbulence is strong, and the energy
spectrum is . As the width of
the spectrum increases, the turbulence rapidly becomes weaker, and in the limit
, the spectrum approaches
. The observed sensitivity of the spectrum
to the balance of linear and nonlinear interactions may explain the conflicting
numerical and observational findings where this balance condition is not well
controlled.Comment: 4 pages, 2 figure
Protective factors for posttraumatic stress disorder among second generation combat veterans
Research has consistently examined the effects of intergenerational trauma among children of combat veterans and the negative impact this has on psychological functioning. The current study explored the relationship between attachment style, post-traumatic growth, and Post-traumatic stress disorder (PTSD) among second generation combat veterans. A sample of male combat veterans from Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF) were included in the study (n = 6). The was an exploratory study that utilized a mixed-methods approach to explore lived experiences. Descriptive statistics, as well as correlation analysis were conducted to examine associations among quantitative variables. Results from qualitative analysis revealed several themes on how relational patterns and combat experiences can serve as either risk factors or protective factors for PTSD. Quantitative analysis found that veterans with secure attachment style endorsed less psychological symptoms when compared to fellow veterans with anxious/avoidant attachment patterns. Veterans with anxious/avoidant attachment styles had higher post-traumatic growth scores, were more likely to misuse alcohol, and had a history of mental health treatment. The study lays the groundwork for future studies to explore protective factors among second generation combat veterans. It also highlights the importance of early attachment experiences and how these impact an individual’s ability to regulate future stress, such as combat
Multi-scale path planning for a planetary exploration vehicle with multiple locomotion modes
Planetary exploration vehicles (rovers) can encounter with a great variety of
situations. Most of them are related to the terrain, which can cause the end of
the mission if these vehicles are not able to traverse it. It was the case of Spirit
rover, which got stuck in loose sand, making it impossible to continue advancing.
A solution to this is to make rovers capable of modifying their locomotion to
traverse terrains with particular terramechanic parameters.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Strong magnetohydrodynamic turbulence with cross helicity
Magnetohydrodynamics (MHD) provides the simplest description of magnetic
plasma turbulence in a variety of astrophysical and laboratory systems. MHD
turbulence with nonzero cross helicity is often called imbalanced, as it
implies that the energies of Alfv\'en fluctuations propagating parallel and
anti-parallel the background field are not equal. Recent analytical and
numerical studies have revealed that at every scale, MHD turbulence consists of
regions of positive and negative cross helicity, indicating that such
turbulence is inherently locally imbalanced. In this paper, results from high
resolution numerical simulations of steady-state incompressible MHD turbulence,
with and without cross helicity are presented. It is argued that the inertial
range scaling of the energy spectra (E^+ and E^-) of fluctuations moving in
opposite directions is independent of the amount of cross-helicity. When cross
helicity is nonzero, E^+ and E^- maintain the same scaling, but have differing
amplitudes depending on the amount of cross-helicity.Comment: To appear in Physics of Plasma
Gapless Hamiltonians for the toric code using the PEPS formalism
We study Hamiltonians which have Kitaev's toric code as a ground state, and
show how to construct a Hamiltonian which shares the ground space of the toric
code, but which has gapless excitations with a continuous spectrum in the
thermodynamic limit. Our construction is based on the framework of Projected
Entangled Pair States (PEPS), and can be applied to a large class of
two-dimensional systems to obtain gapless "uncle Hamiltonians".Comment: 8 pages, 2 figure
Reproducibility of Pop-Ins in Laboratory Testing ofWelded Joints
The pop-in phenomenon, quite common in fracture mechanics tests of welded joints, corresponds to a brittle crack initiation grown from a local brittle zone (LBZ) that is arrested in reaching the higher toughness material that surrounds this LBZ.
A methodology to obtain a high percentage of pop-in occurrence in laboratory testing is necessary to study the pop-in significance. Such a method is introduced in this work and includes the consumable combination and welding procedures for the SMAW welding process to generate artificial LBZ.
In order to find out the influence of the loading state upon the pop-in phenomenon, laboratory CTOD tests were performed using two specimen configurations: some single edge-notched specimens were loaded on a three-point bending (SE(B)) fixture while others were tested in tensile load (SE(T)). A higher frequency of pop-in occurrence was observed in the SE(B) geometry
Role of cross helicity in magnetohydrodynamic turbulence
Strong incompressible three-dimensional magnetohydrodynamic turbulence is
investigated by means of high resolution direct numerical simulations. The
simulations show that the configuration space is characterized by regions of
positive and negative cross-helicity, corresponding to highly aligned or
anti-aligned velocity and magnetic field fluctuations, even when the average
cross-helicity is zero. To elucidate the role of cross-helicity, the spectra
and structure of turbulence are obtained in imbalanced regions where
cross-helicity is non-zero. When averaged over regions of positive and negative
cross-helicity, the result is consistent with the simulations of balanced
turbulence. An analytical explanation for the obtained results is proposed.Comment: 4 pages, 4 figure
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