Spectral Analysis and the Dynamic Response of Complex Networks

The eigenvalues and eigenvectors of the connectivity matrix of complex networks contain information about its topology and its collective behavior. In particular, the spectral density $\rho(\lambda)$ of this matrix reveals important network characteristics: random networks follow Wigner's semicircular law whereas scale-free networks exhibit a triangular distribution. In this paper we show that the spectral density of hierarchical networks follow a very different pattern, which can be used as a fingerprint of modularity. Of particular importance is the value $\rho(0)$, related to the homeostatic response of the network: it is maximum for random and scale free networks but very small for hierarchical modular networks. It is also large for an actual biological protein-protein interaction network, demonstrating that the current leading model for such networks is not adequate.Comment: 4 pages 14 figure

Nondestructive Evaluation of Adhesive Bonds Using Leaky Lamb Waves

Adhesive bonding is a means for transferring load between structural components of an assembly. Proper transfer can be accomplished only through a continuous adhesive medium between the adherends. Furthermore, the adhesive must have sufficiently high strength to allow the structure to meet design requirements

Characterization of Adhesive Bonding Using Leaky Lamb Waves

The performance of adhesive bonds in primary structures strongly depends on the quality of adhesion. Many NDE methods are presently used to detect unbonded areas; however, these methods cannot be used to determine bond properties. In standard ultrasonic techniques, the velocity of bulk wave propagation through the specimen is measured by time-offlight. Unfortunately, the waves reflected from the bonded region cannot be easily identified or analyzed to determine the properties of the adhesive layer

Design Principles for Aqueous Interactive Materials: Lessons from Small Molecules and Stimuli-Responsive Systems.

Interactive materials are at the forefront of current materials research with few examples in the literature. Researchers are inspired by nature to develop materials that can modulate and adapt their behavior in accordance with their surroundings. Stimuli-responsive systems have been developed over the past decades which, although often described as "smart," lack the ability to act autonomously. Nevertheless, these systems attract attention on account of the resultant materials' ability to change their properties in a predicable manner. These materials find application in a plethora of areas including drug delivery, artificial muscles, etc. Stimuli-responsive materials are serving as the precursors for next-generation interactive materials. Interest in these systems has resulted in a library of well-developed chemical motifs; however, there is a fundamental gap between stimuli-responsive and interactive materials. In this perspective, current state-of-the-art stimuli-responsive materials are outlined with a specific emphasis on aqueous macroscopic interactive materials. Compartmentalization, critical for achieving interactivity, relies on hydrophobic, hydrophilic, supramolecular, and ionic interactions, which are commonly present in aqueous systems and enable complex self-assembly processes. Relevant examples of aqueous interactive materials that do exist are given, and design principles to realize the next generation of materials with embedded autonomous function are suggested.JAM thanks ESPRC for an IAA KTF M is grateful for a Newton International Fellowship OAS is thankful to ERC Consolidator Grant CAM-RI

Non-Inertial Quantum Clock Frames Lead to Non-Hermitian Dynamics

The operational approach to time is a cornerstone of relativistic theories, as evidenced by the notion of proper time. In standard quantum mechanics, however, time is an external parameter. Recently, many attempts have been made to extend the notion of proper time to quantum mechanics within a relational framework. Here, we use similar ideas combined with the relativistic mass-energy equivalence to study an accelerating massive quantum particle with an internal clock system. We show that the ensuing evolution from the perspective of the particle’s internal clock is non-Hermitian. This result does not rely on specific implementations of the clock. As a particular consequence, we prove that the effective Hamiltonian of two gravitationally interacting particles is non-Hermitian from the perspective of the clock of either particle