Compact and low power consumption tunable photonic crystal nanobeam cavity

A proof-of-concept for a new and entirely CMOS compatible tunable nanobeam cavity is demonstrated in this paper. Preliminary results show that a compact nanobeam cavity (~20 μm^2) with high Q-factor (~50,000) and integrated with a micro-heater atop, is able of tuning the resonant wavelength up to 15 nm with low power consumption (0.35nm/mW), and of attaining high modulation depth with only ~100 μW. Additionally, a tunable bi-stable behavior is reported

Study of the Fully Frustrated Clock Model using the Wang-Landau Algorithm

Monte Carlo simulations using the newly proposed Wang-Landau algorithm together with the broad histogram relation are performed to study the antiferromagnetic six-state clock model on the triangular lattice, which is fully frustrated. We confirm the existence of the magnetic ordering belonging to the Kosterlitz-Thouless (KT) type phase transition followed by the chiral ordering which occurs at slightly higher temperature. We also observe the lower temperature phase transition of KT type due to the discrete symmetry of the clock model. By using finite-size scaling analysis, the higher KT temperature $T_2$ and the chiral critical temperature $T_c$ are respectively estimated as $T_2=0.5154(8)$ and $T_c=0.5194(4)$. The results are in favor of the double transition scenario. The lower KT temperature is estimated as $T_1=0.496(2)$. Two decay exponents of KT transitions corresponding to higher and lower temperatures are respectively estimated as $\eta_2=0.25(1)$ and $\eta_1=0.13(1)$, which suggests that the exponents associated with the KT transitions are universal even for the frustrated model.Comment: 7 pages including 9 eps figures, RevTeX, to appear in J. Phys.

Metastable States in High Order Short-Range Spin Glasses

The mean number of metastable states in higher order short-range spin glasses is estimated analytically using a variational method introduced by Tanaka and Edwards for very large coordination numbers. For lattices with small connectivities, numerical simulations do not show any significant dependence on the relative positions of the interacting spins on the lattice, indicating thus that these systems can be described by a few macroscopic parameters. As an extremely anisotropic model we consider the low autocorrelated binary spin model and we show through numerical simulations that its landscape has an exceptionally large number of local optima

Self-avoiding fractional Brownian motion - The Edwards model

In this work we extend Varadhan's construction of the Edwards polymer model to the case of fractional Brownian motions in $\R^d$, for any dimension $d\geq 2$, with arbitrary Hurst parameters $H\leq 1/d$.Comment: 14 page

Biot-Savart-like law in electrostatics

The Biot-Savart law is a well-known and powerful theoretical tool used to calculate magnetic fields due to currents in magnetostatics. We extend the range of applicability and the formal structure of the Biot-Savart law to electrostatics by deriving a Biot-Savart-like law suitable for calculating electric fields. We show that, under certain circumstances, the traditional Dirichlet problem can be mapped onto a much simpler Biot-Savart-like problem. We find an integral expression for the electric field due to an arbitrarily shaped, planar region kept at a fixed electric potential, in an otherwise grounded plane. As a by-product we present a very simple formula to compute the field produced in the plane defined by such a region. We illustrate the usefulness of our approach by calculating the electric field produced by planar regions of a few nontrivial shapes.Comment: 14 pages, 6 figures, RevTex, accepted for publication in the European Journal of Physic

Landscape statistics of the low autocorrelated binary string problem

The statistical properties of the energy landscape of the low autocorrelated binary string problem (LABSP) are studied numerically and compared with those of several classic disordered models. Using two global measures of landscape structure which have been introduced in the Simulated Annealing literature, namely, depth and difficulty, we find that the landscape of LABSP, except perhaps for a very large degeneracy of the local minima energies, is qualitatively similar to some well-known landscapes such as that of the mean-field 2-spin glass model. Furthermore, we consider a mean-field approximation to the pure model proposed by Bouchaud and Mezard (1994, J. Physique I France 4 1109) and show both analytically and numerically that it describes extremely well the statistical properties of LABSP

Biosynthesis of Indole-3-Acetic Acid by New Klebsiella oxytoca Free and Immobilized Cells on Inorganic Matrices

While many natural and synthetic compounds exhibit auxin-like activity in bioassays, indole-3-acetic acid (IAA) is recognized as the key auxin in most plants. IAA has been implicated in almost all aspects of plant growth and development and a large array of bacteria have been reported to enhance plant growth. Cells of Klebsiella oxytoca isolated from the rhizosphere of Aspidosperma polyneuron and immobilized by adsorption on different inorganic matrices were used for IAA production. The matrices were prepared by the sol-gel method and the silica-titanium was the most suitable matrix for effective immobilization. In operational stability assays, IAA production was maintained after four cycles of production, obtaining 42.80 ± 2.03 μg mL−1 of IAA in the third cycle, which corresponds to a 54% increase in production in relation to the first cycle, whereas free cells began losing activity after the first cycle. After 90 days of storage at 4°C the immobilized cells showed the slight reduction of IAA production without significant loss of activity

A hybrid cementitious based-G/CFRP sandwich panel: concept, design and initial outcomes

Nowadays, the advantages of using fibre-reinforced polymers (FRP) in Civil Engineering structures are very well-known. In comparison to other materials, the FRPs show high strength-to-weight and stiffness-to-weight ratios, as well as high corrosion resistance [1]. Moreover, they can be easily moulded into complex shapes during the manufacturing process. Due to the slenderness of the cross section components and systems [2], and their significant initial cost [3], the FRPs are typically used along with other materials in composite structural elements. In the recent years, the FRPs have been increasingly used in composite sandwich panels designed for the building and housing industry [4]. However, in terms of flooring solutions, the sandwich panels still reveal some limitations for the most typical values of spans and loads in buildings [5]. In order to overcome the aforementioned drawbacks, the EasyFloor project was launched to develop enhanced composite sandwich panels for rehabilitation of floors in buildings. One of the important innovations included in the project relies on the use of both glass and carbon fibre roving (G/CFRP). This hybrid solution aims at improving significantly both the strength and stiffness. Furthermore, the top face of the panel is made of steel fibre reinforced self-compacting micro concrete (SFRSCMC), instead of the usual FRP compressive face, aiming to overcome face wrinkling issues. Additionally, this solution can provide higher ductility, fire endurance and impact resistance [6]. Furthermore, polycianurate (PIR) closed-cell foam is used as core material of the panel. Proper adhesion between G/CFRP and SFRSCMC is developed in order to obtain the full bending capacity of the composite solution. Finally, the FRP component is produced by pultrusion, taking all the advantages of this manufacturing process. The final proposal for the hybrid sandwich panel was obtained through the use of genetic algorithms in the design, which consisted in optimizing the geometric and the mechanical properties of the panel, taking into account the following features: (i) structural and energy efficiency; (ii) durability, versatility of use, ease of handling, quick assembly and production; (iii) low maintenance needs and aesthetics. The present work describes the design solution that resulted from the optimization procedure and subsequently presents initial experimental results regarding the mechanical characterization of the different materials, as well as the FRP/SFRSCMC interface. The experimental program comprised: (i) tensile and flexural tests on both the bottom and external ribs of the C/GFRP laminate skins; (ii) tensile, compressive and direct shear tests on both foam core materials (PIR); (iii) compressive and flexural tests on the SFRSCMC top face, and; (iv) pull-off tests for the characterization of the connection between the SFRSCMC and FRP using different types of adhesives.This work is part of the research project “EasyFloor – Development of composite sandwich panels for rehabilitation of floor buildings”, involving the company ALTO – Perfis Pultrudidos, Lda., CERis/Instituto Superior Técnico and ISISE/University of Minho, supported by FEDER funds through the Operational Program for Operational Program for Competitiveness and Internationalization (POCI) and the Portuguese National Innovation Agency (ANI) - project no. 3480 (POCI-01-0247-FEDER-003480). The authors would like to thanks the following companies for suppling the adhesives: KERAKOLL, MAPEI and SIKADUR.info:eu-repo/semantics/publishedVersio

Biotransformation of digitoxigenin by Cochliobolus lunatus

The biotransformation of digitoxigenin (1) by Cochliobolus lunatus was investigated. The biotransformation reaction was carried out in a 4-day process, resulting in the isolation of four products, whose structures were elucidated as 1beta-hydroxydigitoxigenin (2), 7beta-hydroxydigitoxigenin (3), 8beta-hydroxydigitoxigenin (4) and digitoxigenone (5). The production of these derivatives under the employed conditions has never been described so far. This is also the first report on the production of compound 4 by a biotransformation reaction

Experimental demonstration of a unidirectional reflectionless parity-time metamaterial at optical frequencies

Invisibility by metamaterials is of great interest, where optical properties are manipulated in the real permittivity– permeability plane. However, the most effective approach to achieving invisibility in various military applications is to absorb the electromagnetic waves emitted from radar to minimize the corresponding reflection and scattering, such that no signal gets bounced back. Here, we show the experimental realization of chip-scale unidirectional reflectionless optical metamaterials near the spontaneous parity-time symmetry phase transition point where reflection from one side is significantly suppressed. This is enabled by engineering the corresponding optical properties of the designed paritytime metamaterial in the complex dielectric permittivity plane. Numerical simulations and experimental verification consistently exhibit asymmetric reflection with high contrast ratios around a wavelength of of 1,550 nm. The demonstrated unidirectional phenomenon at the corresponding parity-time exceptional point on-a-chip confirms the feasibility of creating complicated on-chip parity-time metamaterials and optical devices based on their properties