4,124 research outputs found
The stability of a rising droplet: an inertialess nonmodal growth mechanism
Prior modal stability analysis (Kojima et al., Phys. Fluids, vol. 27, 1984)
predicted that a rising or sedimenting droplet in a viscous fluid is stable in
the presence of surface tension no matter how small, in contrast to
experimental and numerical results. By performing a non-modal stability
analysis, we demonstrate the potential for transient growth of the interfacial
energy of a rising droplet in the limit of inertialess Stokes equations. The
predicted critical capillary numbers for transient growth agree well with those
for unstable shape evolution of droplets found in the direct numerical
simulations of Koh & Leal (Phys. Fluids, vol. 1, 1989). Boundary integral
simulations are used to delineate the critical amplitude of the most
destabilizing perturbations. The critical amplitude is negatively correlated
with the linear optimal energy growth, implying that the transient growth is
responsible for reducing the necessary perturbation amplitude required to
escape the basin of attraction of the spherical solution.Comment: 11pages, 7 figure
Conceptualizing a Knowledge Society in China: A Ubiquitous Network Perspective
Developing Ubiquitous Network Societies (UNS) has been a subject of investigation in last decade. Several policy and technological projects have been proposed and implemented at global level to promote ubiquitous network. This paper focuses on Chinaâs preparation towards UNS by analyzing and evaluating the prerequisite technological developments that enable the construction of UNS. The objective of this paper is to identify the notable features of UNS in context to China. Being the nascent area of study our research approach is from technological perspective
Bifurcation Dynamics of a Particle-Encapsulating Droplet in Shear Flow
To understand the behavior of composite fluid particles such as nucleated cells and double emulsions in flow, we study a finite-size particle encapsulated in a deforming droplet under shear flow as a model system. In addition to its concentric particle-droplet configuration, we numerically explore other eccentric and time-periodic equilibrium solutions, which emerge spontaneously via supercritical pitchfork and Hopf bifurcations. We present the loci of these solutions around the codimension-two point. We adopt a dynamic system approach to model and characterize the coupled behavior of the two bifurcations. By exploring the flow fields and hydrodynamic forces in detail, we identify the role of hydrodynamic particle-droplet interaction which gives rise to these bifurcations
SALSA VERDE: a machine learning attack on Learning With Errors with sparse small secrets
Learning with Errors (LWE) is a hard math problem used in post-quantum
cryptography. Homomorphic Encryption (HE) schemes rely on the hardness of the
LWE problem for their security, and two LWE-based cryptosystems were recently
standardized by NIST for digital signatures and key exchange (KEM). Thus, it is
critical to continue assessing the security of LWE and specific parameter
choices. For example, HE uses secrets with small entries, and the HE community
has considered standardizing small sparse secrets to improve efficiency and
functionality. However, prior work, SALSA and PICANTE, showed that ML attacks
can recover sparse binary secrets. Building on these, we propose VERDE, an
improved ML attack that can recover sparse binary, ternary, and narrow Gaussian
secrets. Using improved preprocessing and secret recovery techniques, VERDE can
attack LWE with larger dimensions () and smaller moduli (
for ), using less time and power. We propose novel architectures for
scaling. Finally, we develop a theory that explains the success of ML LWE
attacks.Comment: 18 pages, accepted to NeurIPS 202
Ground and excited state communication within a ruthenium containing benzimidazole metallopolymer
Emission spectroscopy and electrochemistry has been used to probe the electronic communication between adjacent metal centres and the conjugated backbone within a family of imidazole based metallopolymer, [Ru(bpy)2(PPyBBIM)n]2+, in the ground and excited states, bpy is 2,2â-bipyridyl, PPyBBIM is poly[2-(2-pyridyl)-bibenzimidazole] and n = 3, 10 or 20. Electronic communication in the excited state is not efficient and upon optical excitation dual emission is observed, i.e., both the polymer backbone and the metal centres emit. Coupling the ruthenium moiety to the imidazole backbone results in a red shift of approximately 50 nm in the emission spectrum. Luminescent lifetimes of up to 120 ns were also recorded. Cyclic voltammetry was also utilized to illustrate the distance dependence of the electron hopping rates between adjacent metal centres with ground state communication reduced by up to an order of magnitude compared to previously reported results when the metal to backbone ratio was not altered. DCT and De values of up to 3.96 x 10-10 and 5.32 x 10-10 cm2S-1 were observed with corresponding conductivity values of up to 2.34 x 10-8 Scm-1
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