149 research outputs found
Topology optimization of multiple anisotropic materials, with application to self-assembling diblock copolymers
We propose a solution strategy for a multimaterial minimum compliance
topology optimization problem, which consists in finding the optimal allocation
of a finite number of candidate (possibly anisotropic) materials inside a
reference domain, with the aim of maximizing the stiffness of the body. As a
relevant and novel application we consider the optimization of self-assembled
structures obtained by means of diblock copolymers. Such polymers are a class
of self-assembling materials which spontaneously synthesize periodic
microstructures at the nanoscale, whose anisotropic features can be exploited
to build structures with optimal elastic response, resembling biological
tissues exhibiting microstructures, such as bones and wood. For this purpose we
present a new generalization of the classical Optimality Criteria algorithm to
encompass a wider class of problems, where multiple candidate materials are
considered, the orientation of the anisotropic materials is optimized, and the
elastic properties of the materials are assumed to depend on a scalar
parameter, which is optimized simultaneously to the material allocation and
orientation. Well-posedness of the optimization problem and well-definition of
the presented algorithm are narrowly treated and proved. The capabilities of
the proposed method are assessed through several numerical tests
Trojans in Early Design Steps—An Emerging Threat
Hardware Trojans inserted by malicious foundries
during integrated circuit manufacturing have received substantial
attention in recent years. In this paper, we focus on a different
type of hardware Trojan threats: attacks in the early steps of
design process. We show that third-party intellectual property
cores and CAD tools constitute realistic attack surfaces and that
even system specification can be targeted by adversaries. We
discuss the devastating damage potential of such attacks, the
applicable countermeasures against them and their deficiencies
Exploring Energy Efficiency of Lightweight Block Ciphers
Abstract. In the last few years, the field of lightweight cryptography has seen an influx in the number of block ciphers and hash functions being proposed. One of the metrics that define a good lightweight design is the energy consumed per unit operation of the algorithm. For block ciphers, this operation is the encryption of one plaintext. By studying the energy consumption model of a CMOS gate, we arrive at the conclusion that the total energy consumed during the encryption operation of an r-round unrolled architecture of any block cipher is a quadratic function in r. We then apply our model to 9 well known lightweight block ciphers, and thereby try to predict the optimal value of r at which an r-round unrolled architecture for a cipher is likely to be most energy efficient. We also try to relate our results to some physical design parameters like the signal delay across a round and algorithmic parameters like the number of rounds taken to achieve full diffusion of a difference in the plaintext/key
An oscillation-free fully staggered algorithm for velocity-dependent active models of cardiac mechanics
In this paper we address an unresolved problem in the numerical modeling of cardiac electromechanics, that is the onset of numerical oscillations due to the dependence of force generation models on the fibers shortening velocity. A way to avoid numerical oscillations is to use monolithic schemes for the solution of the coupled problem of active-passive mechanics. However, staggered strategies, which foresee the sequential solution of the models of force generation and of tissue mechanics, are preferable, due to their reduced computational cost and low implementation effort. In this paper we propose a cure for this issue, by introducing, with respect to the standard staggered scheme, a numerically consistent stabilization term. This term is derived in virtue of the identification of the cause of instability in the mismatch between macroscopic and microscopic strains, inconsistently expressed in Lagrangian and Eulerian coordinates, respectively. By considering a model problem of active mechanics we prove that the proposed scheme is unconditionally absolutely stable (i.e. it is stable for any time step size), yet within a fully staggered framework. As such, the new scheme removes the non-physical oscillations, as we prove by applying it to three force generation models, namely the Niederer-Hunter-Smith model, the model by Land and coworkers, and the mean-field force generation model that we have recently proposed. (C) 2020 The Author(s). Published by Elsevier B.V
Preserving the positivity of the deformation gradient determinant in intergrid interpolation by combining RBFs and SVD: application to cardiac electromechanics
The accurate robust and efficient transfer of the deformation gradient tensor
between meshes of different resolution is crucial in cardiac electromechanics
simulations. We present a novel method that combines rescaled localized Radial
Basis Function (RBF) interpolation with Singular Value Decomposition (SVD) to
preserve the positivity of the determinant of the deformation gradient tensor.
The method involves decomposing the evaluations of the tensor at the quadrature
nodes of the source mesh into rotation matrices and diagonal matrices of
singular values; computing the RBF interpolation of the quaternion
representation of rotation matrices and the singular value logarithms;
reassembling the deformation gradient tensors at quadrature nodes of the
destination mesh, to be used in the assembly of the electrophysiology model
equations. The proposed method overcomes limitations of existing interpolation
methods, including nested intergrid interpolation and RBF interpolation of the
displacement field, that may lead to the loss of physical meaningfulness of the
mathematical formulation and then to solver failures at the algebraic level,
due to negative determinant values. The proposed method enables the transfer of
solution variables between finite element spaces of different degrees and
shapes and without stringent conformity requirements between different meshes,
enhancing the flexibility and accuracy of electromechanical simulations.
Numerical results confirm that the proposed method enables the transfer of the
deformation gradient tensor, allowing to successfully run simulations in cases
where existing methods fail. This work provides an efficient and robust method
for the intergrid transfer of the deformation gradient tensor, enabling
independent tailoring of mesh discretizations to the particular characteristics
of the physical components concurring to the of the multiphysics model.Comment: 24 pages; 11 figure
Atomic-AES v2.0
Very recently, the {\sf Atomic AES} architecture that provides dual functionality of the AES encryption and decryption module was proposed.
It was surprisingly compact and occupied only around 2605 GE of silicon area and took 226 cycles for both the encryption and decryption operations. In this work we further optimize the above architecture to provide the dual encryption/decryption functionality in only 2060 GE and latency of 246/326 cycles for the encryption and decryption operations respectively. We take advantage of
clock gating techniques to achieve Shiftrow and Inverse Shiftrow operations in 3 cycles instead of 1. This helps us replace many of the scan flip-flops in the design with ordinary flip-flops.
Furthermore we take advantage of the fact that the Inverse Mixcolumn matrix in AES is the cube of the forward Mixcolumn matrix. Thus by executing the forward Mixcolumn operation three times over the
state, one can achieve the functionality of Inverse Mixcolumn. This saves some more gate area as one is no longer required to have a combined implementation of the Forward and Inverse Mixcolumn circuit
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