2,515 research outputs found
Parameter Identification of Pressure Sensors by Static and Dynamic Measurements
Fast identification methods of pressure sensors are investigated. With regard
to a complete accurate sensor parameter identification two different
measurement methods are combined. The approach consists on one hand in
performing static measurements - an applied pressure results in a membrane
deformation measured interferometrically and the corresponding output voltage.
On the other hand optical measurements of the modal responses of the sensor
membranes are performed. This information is used in an inverse identification
algorithm to identify geometrical and material parameters based on a FE model.
The number of parameters to be identified is thereby generally limited only by
the number of measurable modal frequencies. A quantitative evaluation of the
identification results permits furthermore the classification of processing
errors like etching errors. Algorithms and identification results for membrane
thickness, intrinsic stress and output voltage will be discussed in this
contribution on the basis of the parameter identification of relative pressure
sensors.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Rheological Model for Wood
Wood as the most important natural and renewable building material plays an
important role in the construction sector. Nevertheless, its hygroscopic
character basically affects all related mechanical properties leading to
degradation of material stiffness and strength over the service life.
Accordingly, to attain reliable design of the timber structures, the influence
of moisture evolution and the role of time- and moisture-dependent behaviors
have to be taken into account. For this purpose, in the current study a 3D
orthotropic elasto-plastic, visco-elastic, mechano-sorptive constitutive model
for wood, with all material constants being defined as a function of moisture
content, is presented. The corresponding numerical integration approach, with
additive decomposition of the total strain is developed and implemented within
the framework of the finite element method (FEM). Moreover to preserve a
quadratic rate of asymptotic convergence the consistent tangent operator for
the whole model is derived.
Functionality and capability of the presented material model are evaluated by
performing several numerical verification simulations of wood components under
different combinations of mechanical loading and moisture variation.
Additionally, the flexibility and universality of the introduced model to
predict the mechanical behavior of different species are demonstrated by the
analysis of a hybrid wood element. Furthermore, the proposed numerical approach
is validated by comparisons of computational evaluations with experimental
results.Comment: 37 pages, 13 figures, 10 table
Functional renormalization group analysis of Dzyaloshinsky Moriya and Heisenberg spin interactions on the kagome lattice
We investigate the effects of Dzyaloshinsky-Moriya (DM) interactions on the
frustrated - kagome-Heisenberg model using the pseudo-fermion
functional-renormalization-group (PFFRG) technique. In order to treat the
off-diagonal nature of DM interactions, we develop an extended PFFRG scheme. We
benchmark this approach in parameter regimes that have previously been studied
with other methods and find good agreement of the magnetic phase diagram.
Particularly, finite DM interactions are found to stabilize all types of
non-collinear magnetic orders of the - Heisenberg model
(, , and cuboc orders) and shrink the
extents of magnetically disordered phases. We discuss our results in the light
of the mineral {\it herbertsmithite} which has been experimentally predicted to
host a quantum spin liquid at low temperatures. Our PFFRG data indicates that
this material lies in close proximity to a quantum critical point. In parts of
the experimentally relevant parameter regime for {\it herbertsmithite}, the
spin-correlation profile is found to be in good qualitative agreement with
recent inelastic-neutron-scattering data
Integration of new experiments into the reflood map
The reflood map, developed in the last decade, was designed as a tool to focus on preventive and mitigative measures to prevent severe core damage scenarios and to identify research areas. In the meanwhile, additional experiments were performed and their data are available, so that an update seems necessary. For homogeneous particulate debris configurations, several experimental programs shed light on coolability. For the transition from in-core early phase to in-core late phase i.e. the loss of the rod like geometry, experimental database is still rather scarce due to the difficulty to describe the state of the core components and the fluid adequately. According to the new insight, an update of the database and the reflood map is discussed, also with respect to assess available grace times
Characterization of quantum spin liquids and their spinon band structures via functional renormalization
We combine the pseudofermion functional renormalization group PFFRG method with a self consistent Fock like mean field scheme to calculate low energy effective theories for emergent spinon excitations in spin 1 2 quantum spin liquids. Using effective spin interactions from PFFRG as an input for the Fock equation and allowing for the most general types of free spinon Ansätze as classified by the projective symmetry group PSG method, we are able to systematically determine spinon band structures for spin liquid candidate systems beyond mean field theory. We apply this approach to the antiferromagnetic J1 amp; 8722;J2 Heisenberg model on the square lattice and to the antiferromagnetic nearest neighbor Heisenberg model on the kagome lattice. For the J1 amp; 8722;J2 model, we find that in the regime of maximal frustration a SU 2 pi flux state with Dirac spinons yields the largest mean field amplitudes. For the kagome model, we identify a gapless Z2 spin liquid with a small circular spinon Fermi surface and approximate Dirac cones at low but finite energie
Block-Transitive Designs in Affine Spaces
This paper deals with block-transitive - designs in affine
spaces for large , with a focus on the important index case. We
prove that there are no non-trivial 5- designs admitting a
block-transitive group of automorphisms that is of affine type. Moreover, we
show that the corresponding non-existence result holds for 4- designs,
except possibly when the group is one-dimensional affine. Our approach involves
a consideration of the finite 2-homogeneous affine permutation groups.Comment: 10 pages; to appear in: "Designs, Codes and Cryptography
Inhibition of Trophoblast-Induced Spiral Artery Remodeling Reduces Placental Perfusion in Rat Pregnancy.
Rats harboring the human angiotensinogen and human renin genes develop preeclamptic features in pregnancy. The preeclamptic rats exhibit a deeper trophoblast invasion associated with a reduced resistance index by uterine
Doppler. Doxycycline inhibits matrix metalloproteinase activity. We tested the hypothesis that matrix metalloproteinase inhibition reduces trophoblast invasion with subsequent changes in placental perfusion. Preeclamptic and pregnant control Sprague-Dawley rats were treated with doxycycline (30 mg/kg of body weight orally) from gestational day 12 until day 18. Placental perfusion was assessed using a micromarker contrast agent. The animals were euthanized on day 18 of pregnancy; biometric data were acquired, and trophoblast invasion was analyzed. Doxycycline resulted in intrauterine growth retardation and lighter placentas in both groups. Maternal body weight was not affected. As shown earlier, preeclamptic rats exhibited a deeper endovascular trophoblast invasion. However, doxycycline treatment reduced trophoblast invasion in the preeclamptic rats. The physiological spiral artery remodeling, as assessed by the deposition of fibrinoid and α-actin in the spiral artery contour, was significantly reduced by doxycycline. The vascularity index, as assessed by perfusion measurement of the placenta, was reduced after doxycycline treatment in preeclamptic rats. Thus, matrix metalloproteinase inhibition with doxycycline leads to reduced trophoblast invasion and associated reduced placental perfusion. These studies are the first to show that reducing trophoblast-induced vascular remodeling decreases subsequent placental perfusion. Our model allows the study of dysregulated trophoblast invasion and vascular remodeling in vivo to gain important insights into preeclampsia-related mechanisms
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