arXiv subjects

3

Publications and source records attributed to 3.

7 recordsLinked to original sources

arXiv2024

comparison of two models to predict vertebral failure loads on the same experimental dataset

Clinical use of finite element analysis requires validation and reproducibility studies. The current study compared two models of vertebral bodies including endplates, on the same experimental dataset and evaluated the influence of the operator on the failure load. Models used were strongly correlated (R2=0.91). The intra-operator reproducibility was 6.4% and 3.5 % for each model. Both simulated results were close to experimental results. The differences in performance could be associated to the differences in segmentation process, mesh (hexahedral vs tetrahedral), material representation and failure criteria. Linear analysis did not decrease model accuracy. Comparison with literature for accuracy and precision shows a wide range of values partly related to the different experimental datasets and the different modelling approaches. Models benchmark using the same experimental dataset are needed to go towards clinical applications.

math.NA↗

arXiv2021

Goldilocks mixing in oceanic shear-induced turbulent overturns

We present a new physically-motivated parameterization, based on the ratio of Thorpe and Ozmidov scales, for the irreversible turbulent flux coefficient $\Gamma_{\mathcal M}= {\mathcal M}/\epsilon$, i.e. the ratio of the irreversible rate ${\mathcal M}$ at which the background potential energy increases in a stratified flow due to macroscopic motions to the dissipation rate of turbulent kinetic energy. Our parameterization covers all three key phases (crucially, in time) of a shear-induced stratified turbulence life cycle: the initial, `hot' growing phase, the intermediate energetically forced phase, and the final `cold' fossilization decaying phase. Covering all three phases allows us to highlight the importance of the intermediate one, to which we refer as the `Goldilocks' phase due to its apparently optimal (and so neither too hot nor too cold, but just right) balance, in which energy transfer from background shear to the turbulent mixing is most efficient. $\Gamma_{\mathcal M}$ is close to 1/3 during this phase, which we demonstrate appears to be related to an adjustment towards a critical or marginal Richardson number for sustained turbulence $\sim 0.2-0.25$.

physics.flu-dyn↗

arXiv2020

Evidence for the Alternating Next-Nearest Neighbor model in the dynamic behavior of a frustrated antiferromagnet

X-ray photon correlation spectroscopy (XPCS) enables us to study dynamics of antiferromagnets. Using coherent soft X-ray diffraction, we resonantly probe Mn and Co Bragg peaks in the frustrated magnetic chain compound Lu2CoMnO6 significantly below the Neel temperature. Bragg peaks of incommensurate order slide towards commensurate 'up up down down' order with decreasing temperature. Antiferromagnetic inhomogeneities produce speckle within the Bragg peaks, whose dynamics are probed by XPCS and compared to the classic Axial Next-Nearest Neighbor Interaction model of frustration. The data supports a novel model prediction: with decreasing temperature the dynamics become faster.

cond-mat.str-el↗

arXiv2017

Exclusive photoproduction of $\pi^0$ up to large values of Mandelstam variables $s, t$ and $u$ with CLAS

Exclusive photoproduction cross sections have been measured for the process $\gamma p \rightarrow p\pi^0(e^+e^-(\gamma))$ with the Dalitz decay final state using tagged photon energies in the range of $E_{\gamma} = 1.275-5.425$ GeV. The complete angular distribution of the final state $\pi^0$, for the entire photon energy range up to large values of $t$ and $u$, has been measured for the first time. The data obtained show that the cross section $d\sigma/dt$, at mid to large angles, decreases with energy as $s^{-6.89\pm 0.26} $. This is in agreement with the perturbative QCD quark counting rule prediction of $s^{-7} $. Paradoxically, the size of angular distribution of measured cross sections is greatly underestimated by the QCD based Generalized Parton Distribution mechanism at highest available invariant energy $s=11$ GeV$^2$. At the same time, the Regge exchange based models for $\pi^0$ photoproduction are more consistent with experimental data.

hep-ex↗

arXiv2015

A recent change in the optical and {\gamma}-ray polarization of the Crab nebula and pulsar

We report on observations of the polarization of optical and {\gamma}-ray photons from the Crab nebula and pulsar system using the Galway Astronomical Stokes Polarimeter (GASP), the Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) and the International Gamma-Ray Astrophysics Laboratory satellite (Integral). These, when combined with other optical polarization observations, suggest that the polarized optical emission and {\gamma}-ray polarization changes in a similar manner. A change in the optical polarization angle has been observed by this work, from 109.5 \pm 0.7\deg in 2005 to 85.3 \pm 1.4 \deg in 2012. On the other hand, the {\gamma}-ray polarization angle changed from 115 \pm 11 \deg in 2003-2007 to 80 \pm 12 \deg in 2012-2014. Strong flaring activities have been detected in the Crab nebula over the past few years by the high energy {\gamma}-ray missions Agile and Fermi, and magnetic reconnection processes have been suggested to explain these observations. The change in the polarized optical and {\gamma}-ray emission of the Crab nebula/pulsar as observed, for the first time, by GASP and Integral may indicate that reconnection is possibly at work in the Crab nebula. We also report, for the first time, a non-zero measure of the optical circular polarization from the Crab pulsar+knot system.

astro-ph.HE↗

arXiv2013

Two-dimensional magnetic interactions in LaFeAsO

Inelastic neutron scattering measurements demonstrate that the magnetic interactions in antiferromagnetic LaFeAsO are two-dimensional. Spin wave velocities within the Fe layer and the magnitude of the spin gap are similar to the \textit{A}Fe$_2$As$_2$ based materials. However, the ratio of interlayer and intralayer exchange is found to be less than $\sim 10^{-4}$ in LaFeAsO, very similar to the cuprates, and $\sim$ 100 times smaller than that found in \textit{A}Fe$_2$As$_2$ compounds. The results suggest that the effective dimensionality of the magnetic system is highly variable in the parent compounds of the iron arsenides and weak 3-D interactions may limit the maximum attainable superconducting $T_{c}$.

cond-mat.supr-con↗

arXiv2010

Room Temperature Coherent and Voltage Tunable Terahertz Emission from Nanometer-Sized Field Effect Transistors

We report on reflective electro-optic sampling measurements of TeraHertz emission from nanometer-gate-length InGaAs-based high electron mobility transistors. The room temperature coherent gate-voltage tunable emission is demonstrated. We establish that the physical mechanism of the coherent TeraHertz emission is related to the plasma waves driven by simultaneous current and optical excitation. A significant shift of the plasma frequency and the narrowing of the emission with increasing channel's current are observed and explained as due to the increase of the carriers density and drift velocity.

cond-mat.mes-hall↗