4,308 research outputs found
Virtual Testing of Experimental Continuation
We present a critical advance in experimental testing of nonlinear
structures. Traditional quasi-static experimental methods control the
displacement or force at one or more load-introduction points on a structure.
This approach is unable to traverse limit points in the control parameter, as
the immediate equilibrium beyond these points is statically unstable, causing
the structure to snap to another equilibrium. As a result, unstable
equilibria---observed numerically---are yet to be verified experimentally.
Based on previous experimental work, and a virtual testing environment
developed herein, we propose a new experimental continuation method that can
path-follow along unstable equilibria and traverse limit points. To support
these developments, we provide insightful analogies between a fundamental
building block of our technique---shape control---and analysis concepts such as
the principle of virtual work and Galerkin's method. The proposed testing
method will enable the validation of an emerging class of nonlinear structures
that exploit instabilities for novel functionality
A physics-based compact model of SiC power MOSFETs
The presented compact model of SiC power MOSFETs is based on a thorough consideration of the physical phenomena which are important for the device characteristics and its electrothermal behavior. The model includes descriptions of the dependence of channel charge and electron mobility on the charge of interface traps and a simple but effective calculation of the voltage-dependent drain resistance. Comparisons with both physical 2-D device simulations and experiments validate the correctness of the modeling approach and the accuracy of the results
Slow running of the Gradient Flow coupling from 200 MeV to 4 GeV in QCD
Using a finite volume Gradient Flow (GF) renormalization scheme with
Schr\"odinger Functional (SF) boundary conditions, we compute the
non-perturbative running coupling in the range . Careful continuum extrapolations turn out to
be crucial to reach our high accuracy. The running of the coupling is always
between one-loop and two-loop and very close to one-loop in the region of
. While there is no
convincing contact to two-loop running, we match non-perturbatively to the SF
coupling with background field. In this case we know the dependence up to
and can thus connect to the -parameter.Comment: 34 pages, LaTe
A status update on the determination of by the ALPHA collaboration
The ALPHA collaboration aims to determine with a total error
below the percent level. A further step towards this goal can be taken by
combining results from the recent simulations of 2+1-flavour QCD by the CLS
initiative with a number of tools developed over the years: renormalized
couplings in finite volume schemes, recursive finite size techniques, two-loop
renormalized perturbation theory and the (improved) gradient flow on the
lattice. We sketch the strategy, which involves both the standard SF coupling
in the high energy regime and a gradient flow coupling at low energies. This
implies the need for matching both schemes at an intermediate switching scale,
, which we choose roughly in the range 2-4 GeV. In this
contribution we present a preliminary result for this matching procedure, and
we then focus on our almost final results for the scale evolution of the SF
coupling from towards the perturbative regime, where we extract
the -parameter, , in units of . Connecting and
thus the -parameter to a hadronic scale such as requires 2
further ingredients: first, the connection of to
using a few steps with the step-scaling function of the gradient flow coupling,
and, second, the continuum extrapolation of .Comment: 7 pages, 4 figures, Proceedings of the 33rd International Symposium
on Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe, Japa
Building blocks that govern spontaneous and programmed pattern formation in pre-compressed bilayers
Engineering muscle networks in 3D gelatin methacryloyl hydrogels: influence of mechanical stiffness and geometrical confinement
In this work, the influence of mechanical stiffness and geometrical confinement on the 3D culture of myoblast-laden gelatin methacryloyl (GelMA) photo-crosslinkable hydrogels was evaluated in terms of in vitro myogenesis. We formulated a set of cell-laden GelMA hydrogels with a compressive modulus in the range 1Ă·17 kPa, obtained by varying GelMA concentration and degree of cross-linking. C2C12 myoblasts were chosen as the cell model, to investigate the supportiveness of different GelMA hydrogels on myotube formation up to 2 weeks. Results showed that the hydrogels with a stiffness in the range 1Ă·3 kPa provided enhanced support to C2C12 differentiation in terms of myotube number, rate of formation and space distribution. Finally, we studied the influence of geometrical confinement on myotube orientation by confining cells within thin hydrogel slabs having different cross-sections: i) 2000Ă2000 ïm, ii) 1000Ă1000 ïm and iii) 500Ă500 ïm. The obtained results showed that by reducing the cross-sectionâi.e., by increasing the level of confinementâmyotubes were more likely restrained and formed aligned myostructures that better mimicked the native morphology of skeletal muscle
Nudging axially compressed cylindrical panels towards imperfection insensitivity
Curved shell structures are known for their excellent load-carrying capability and are commonly used in thin-walled constructions. Although theoretically able to withstand greater buckling loads than flat structures, shell structures are notoriously sensitive to imperfections owing to their postbuckling behavior often being governed by subcritical bifurcations. Thus, shell structures often buckle at significantly lower loads than those predicted numerically and the ensuing dynamic snap to another equilibrium can lead to permanent damage. Furthermore, the strong sensitivity to initial imperfections, as well as their stochastic nature, limits the predictive capability of current stability analyses. Our objective here is to convert the subcritical nature of the buckling event to a supercritical one, thereby improving the reliability of numerical predictions and mitigating the possibility of catastrophic failure. We explore the elastically nonlinear postbuckling response of axially compressed cylindrical panels using numerical continuation techniques. These analyses show that axially compressed panels exhibit a highly nonlinear and complex postbuckling behavior with many entangled postbuckled equilibrium curves. We unveil isolated regions of stable equilibria in otherwise unstable postbuckled regimes, which often possess greater load-carrying capacity. By modifying the initial geometry of the panel in a targeted - rather than stochastic - and imperceptible manner, the postbuckling behavior of these shells can be tailored without a significant increase in mass. These findings provide new insight into the buckling and postbuckling behavior of shell structures and opportunities for modifying and controlling their postbuckling response for enhanced efficiency and functionality.</p
Experimental Path-Following of Equilibria Using Newton's Method, Part II:Applications and Outlook
- âŠ