Structural lightweight aggregates concrete

This paper addresses the development of a structural lightweight aggregates concrete (SLWAC), aiming at a good balance between a low specific density and thermal conductivity, and high mechanical properties. The mix design is performed by applying the modified Andreasen and Andersen model to secure a densely packed matrix, composed of a binder and lightweight aggregates. The water absorption of the applied lightweight aggregates, expanded clay, is studied and an effective water dosage is determined from the obtained results. The fresh behaviour test of the designed concrete shows an acceptable workability, under a water-cement dosage of 0.35. The developed SLWAC shows excellent thermal properties, with a low thermal conductivity of about 0.20 W/(m¿K); and moderate mechanical properties, with a 28-day compressive strength of about 34 MPa (class of LC30-33 according to EN 206-1), with an apparent density of about 1250 kg/m3. The significantly low thermal conductivity of the developed concrete under this strength class can find a wide application potential, both for structural and thermal insulating purposes

Mid-Infrared Plasmonic Platform Based on n-Doped Ge-on-Si: Molecular Sensing with Germanium Nano-Antennas on Si

CMOS-compatible, heavily-doped semiconductor films are very promising for applications in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate n-type doped germanium epilayers grown on Si substrates. We design and realize Ge nanoantennas on Si substrates demonstrating the presence of localized plasmon resonances, and exploit them for molecular sensing in the mid-infrared

A 750 mW, continuous-wave, solid-state laser source at 313 nm for cooling and manipulating trapped 9Be+ ions

We present a solid-state laser system that generates 750 mW of continuous-wave single-frequency output at 313 nm. Sum-frequency generation with fiber lasers at 1550 nm and 1051 nm produces up to 2 W at 626 nm. This visible light is then converted to UV by cavity-enhanced second-harmonic generation. The laser output can be tuned over a 495 GHz range, which includes the 9Be+ laser cooling and repumping transitions. This is the first report of a narrow-linewidth laser system with sufficient power to perform fault-tolerant quantum-gate operations with trapped 9Be+ ions by use of stimulated Raman transitions.Comment: 9 pages, 4 figure

Worst case and probabilistic analysis of the 2-Opt algorithm for the TSP

2-Opt is probably the most basic local search heuristic for the TSP. This heuristic achieves amazingly good results on “real world” Euclidean instances both with respect to running time and approximation ratio. There are numerous experimental studies on the performance of 2-Opt. However, the theoretical knowledge about this heuristic is still very limited. Not even its worst case running time on 2-dimensional Euclidean instances was known so far. We clarify this issue by presenting, for every p∈N , a family of L p instances on which 2-Opt can take an exponential number of steps. Previous probabilistic analyses were restricted to instances in which n points are placed uniformly at random in the unit square [0,1]2, where it was shown that the expected number of steps is bounded by O~(n10) for Euclidean instances. We consider a more advanced model of probabilistic instances in which the points can be placed independently according to general distributions on [0,1] d , for an arbitrary d≥2. In particular, we allow different distributions for different points. We study the expected number of local improvements in terms of the number n of points and the maximal density ϕ of the probability distributions. We show an upper bound on the expected length of any 2-Opt improvement path of O~(n4+1/3⋅ϕ8/3) . When starting with an initial tour computed by an insertion heuristic, the upper bound on the expected number of steps improves even to O~(n4+1/3−1/d⋅ϕ8/3) . If the distances are measured according to the Manhattan metric, then the expected number of steps is bounded by O~(n4−1/d⋅ϕ) . In addition, we prove an upper bound of O(ϕ√d) on the expected approximation factor with respect to all L p metrics. Let us remark that our probabilistic analysis covers as special cases the uniform input model with ϕ=1 and a smoothed analysis with Gaussian perturbations of standard deviation σ with ϕ∼1/σ d

Increasing alkyl chain length in a series of layered metal–organic frameworks aids ultrasonic exfoliation to form nanosheets

Metal–organic framework nanosheets (MONs) are attracting increasing attention as a diverse class of two-dimensional materials derived from metal–organic frameworks (MOFs). The principles behind the design of layered MOFs that can readily be exfoliated to form nanosheets, however, remain poorly understood. Here we systematically investigate an isoreticular series of layered MOFs functionalized with alkoxy substituents in order to understand the effect of substituent alkyl chain length on the structure and properties of the resulting nanosheets. A series of 2,5-alkoxybenzene-1,4-dicarboxylate ligands (O2CC6H2(OR)2CO2, R = methyl–pentyl, 1–5, respectively) was used to synthesize copper paddle-wheel MOFs. Rietveld and Pawley fitting of powder diffraction patterns for compounds Cu(3–5)(DMF) showed they adopt an isoreticular series with two-dimensional connectivity in which the interlayer distance increases from 8.68 Å (R = propyl) to 10.03 Å (R = pentyl). Adsorption of CO2 by the MOFs was found to increase from 27.2 to 40.2 cm3 g–1 with increasing chain length, which we attribute to the increasing accessible volume associated with increasing unit-cell volume. Ultrasound was used to exfoliate the layered MOFs to form MONs, with shorter alkyl chains resulting in higher concentrations of exfoliated material in suspension. The average height of MONs was investigated by AFM and found to decrease from 35 ± 26 to 20 ± 12 nm with increasing chain length, with the thinnest MONs observed being only 5 nm, corresponding to five framework layers. These results indicate that careful choice of ligand functionalities can be used to tune nanosheet structure and properties, enabling optimization for a variety of applications

Ground-state energy and entropy of the two-dimensional Edwards-Anderson spin-glass model with different bond distributions

We study the two-dimensional Edwards-Anderson spin-glass model using a parallel tempering Monte Carlo algorithm. The ground-state energy and entropy are calculated for different bond distributions. In particular, the entropy is obtained by using a thermodynamic integration technique and an appropriate reference state, which is determined with the method of high-temperature expansion. This strategy provide accurate values of this quantity for finite-size lattices. By extrapolating to the thermodynamic limit, the ground-state energy and entropy of the different versions of the spin-glass model are determined.Comment: 18 pages, 5 figure

Effective nonlinear optical properties of composite media of graded spherical particles

We have developed a nonlinear differential effective dipole approximation (NDEDA), in an attempt to investigate the effective linear and third-order nonlinear susceptibility of composite media in which graded spherical inclusions with weak nonlinearity are randomly embedded in a linear host medium. Alternatively, based on a first-principles approach, we derived exactly the linear local field inside the graded particles having power-law dielectric gradation profiles. As a result, we obtain also the effective linear dielectric constant and third-order nonlinear susceptibility. Excellent agreement between the two methods is numerically demonstrated. As an application, we apply the NDEDA to investigate the surface plasma resonant effect on the optical absorption, optical nonlinearity enhancement, and figure of merit of metal-dielectric composites. It is found that the presence of gradation in metal particles yields a broad resonant band in the optical region, and further enhances the figure of merit.Comment: 20 pages, 5 figure

On the Nature of the Phase Transition in SU(N), Sp(2) and E(7) Yang-Mills theory

We study the nature of the confinement phase transition in d=3+1 dimensions in various non-abelian gauge theories with the approach put forward in [1]. We compute an order-parameter potential associated with the Polyakov loop from the knowledge of full 2-point correlation functions. For SU(N) with N=3,...,12 and Sp(2) we find a first-order phase transition in agreement with general expectations. Moreover our study suggests that the phase transition in E(7) Yang-Mills theory also is of first order. We find that it is weaker than for SU(N). We show that this can be understood in terms of the eigenvalue distribution of the order parameter potential close to the phase transition.Comment: 15 page

Statistical mechanics of image restoration and error-correcting codes

We develop a statistical-mechanical formulation for image restoration and error-correcting codes. These problems are shown to be equivalent to the Ising spin glass with ferromagnetic bias under random external fields. We prove that the quality of restoration/decoding is maximized at a specific set of parameter values determined by the source and channel properties. For image restoration in mean-field system a line of optimal performance is shown to exist in the parameter space. These results are illustrated by solving exactly the infinite-range model. The solutions enable us to determine how precisely one should estimate unknown parameters. Monte Carlo simulations are carried out to see how far the conclusions from the infinite-range model are applicable to the more realistic two-dimensional case in image restoration.Comment: 20 pages, 9 figures, ReVTe