Electric coupling to the magnetic resonance of split ring resonators

We study both theoretically and experimentally the transmission properties of a lattice of split ring resonators (SRRs) for different electromagnetic (EM) field polarizations and propagation directions. We find unexpectedly that the incident electric field E couples to the magnetic resonance of the SRR when the EM waves propagate perpendicular to the SRR plane and the incident E is parallel to the gap-bearing sides of the SRR. This is manifested by a dip in the transmission spectrum. A simple analytic model is introduced to explain this interesting behavior.Comment: 4 pages, 4 figure

Invalidation-based protocols for replicated datastores

Distributed in-memory datastores underpin cloud applications that run within a datacenter and demand high performance, strong consistency, and availability. A key feature of datastores is data replication. The data are replicated across servers because a single server often cannot handle the request load. Replication is also necessary to guarantee that a server or link failure does not render a portion of the dataset inaccessible. A replication protocol is responsible for ensuring strong consistency between the replicas of a datastore, even when faults occur, by determining the actions necessary to access and manipulate the data. Consequently, a replication protocol also drives the datastore's performance. Existing strongly consistent replication protocols deliver fault tolerance but fall short in terms of performance. Meanwhile, the opposite occurs in the world of multiprocessors, where data are replicated across the private caches of different cores. The multiprocessor regime uses invalidations to afford strongly consistent replication with high performance but neglects fault tolerance. Although handling failures in the datacenter is critical for data availability, we observe that the common operation is fault-free and far exceeds the operation during faults. In other words, the common operating environment inside a datacenter closely resembles that of a multiprocessor. Based on this insight, we draw inspiration from the multiprocessor for high-performance, strongly consistent replication in the datacenter. The primary contribution of this thesis is in adapting invalidating protocols to the nuances of replicated datastores, which include skewed data accesses, fault tolerance, and distributed transactions

Some approximation results for Bayesian inverse problems

The current thesis consists of two results obtained during my PhD, both related to approximations of high/infinite-dimensional measures emerging from the Bayesian approach to inverse problems. In the first part, we study a technique for the reduction of the dimension in the finite but high-dimensional case when the prior is 1-exponentially distributed. In Chapter 4, this is done in a way that the approximated posterior measure minimises the distance to the posterior by using an appropriate metric. In the second part, we consider the problem of estimating the drift and diffusion coefficient of a stochastic differential equation using noisy measurements on a single path. There, we use a perturbation technique on the solution of the SDE to obtain an approximated posterior; in Chapter 5, we study the convergence properties of this approximation

Electrochemical Properties of APCVD alpha-Fe2O3 Nanoparticles at 300 degrees C

The growth of hematite (FeIII oxide) by atmospheric pressure chemical vapor deposition was possible at 300 oC by controlling the nitrogen flow rate through the iron precursor bubbler. An increase of crystallinity along with the presence of compact interconnected nanoparticles was observed upon increasing the nitrogen flow rate. The amount of incorporated charge was the highest for the 0.6 L min−1 coating presenting reversibility after a period of 1400 s as obtained from chronoamperometry measurements. Additionally, the charge transfer of lithium‐ions across the FeIII oxide / electrolyte interface was easier enhancing its performance presenting capacitance retention of 94 % after 500 scans. The importance of nitrogen flow rate towards the deposition of an anode with good stability and effective electrochemical behavior is highlighted

Magnetic metamaterials at telecommunication and visible frequencies

Arrays of gold split-rings with 50-nm minimum feature size and with an LC resonance at 200-THz frequency (1500-nm wavelength) are fabricated. For normal incidence conditions, they exhibit a pronounced fundamental magnetic mode, arising from a coupling via the electric component of the incident light. For oblique incidence, a coupling via the magnetic component is demonstrated as well. Moreover, we identify a novel higher-order magnetic resonance at around 370 THz (800-nm wavelength) that evolves out of the Mie resonance for oblique incidence. Comparison with theory delivers good agreement and also shows that the structures allow for a negative magnetic permeability.Comment: 4 pages, 3 figure