Optical properties of scandium films in the far and the extreme ultraviolet

The optical properties of thin Sc films deposited in ultrahigh-vacuum conditions have been investigated in the 6.7-174.4-nm spectral range. We measured transmittance and multiangle reflectance in situ in the 53.6-174.4 nm spectral range and used these measurements to obtain the complex refractive index of a Sc film at every individual wavelength investigated. Transmittance measurements were made of Sc samples that were deposited over grids coated with a support C film. The transmittance and the extinction coefficient of Sc films at wavelengths shorter than 30 nm were measured ex situ. The ex situ samples were protected with an additional top C film before their removal from vacuum. To our knowledge, these are the first optical measurements of Sc films reported in the spectral ranges cited.     

Surface treatments and roughness properties of Ti-based biomaterials

Nowadays, the use of implanted devices is a well-acknowledged practice in the field of orthopaedic and dental surgery. Scientific research and clinical experience suggest that the successful exploitation of these devices mainly depends on osseointegration, considered as both anatomical congruency and load-bearing capacity. Indeed, the osseointegration process is influenced by a wide range of factors: anatomical location, implant size and design, surgical procedure, loading effects, biological fluids, age and sex, and, in particular, surface characteristics. For this reason, several attempts have been aimed at modifying implant surface composition and morphology to optimise implant-to-bone contact and improve integration. Preliminary interactions between implanted materials and biological environment are deemed to be governed by the surface properties; they control the amount and quality of cell adhesion on the surface and, consequently, cell/tissue growth. Thus, surface properties govern new bone tissue formation and implant osseointegration. This paper reviews the state of art in the field of physical, chemical and biochemical treatments commonly used on Ti-based biomaterials for the production of biomedical devices. In particular, roughness characteristics due to physical and chemical techniques are investigated; the development of biologically active surfaces by means of biochemical functionalisation is also considered.     

Isotope and Impurity Content in Water Triple-Point Cells Manufactured at NMi VSL

The isotopic and impurity content of 15 water triple-point cells, manufactured at NMi VSL in the past three years, were investigated. The isotopic analyses were performed on water specimens sampled at three different stages of the manufacturing process. This allowed us to separate and quantify the influence of the source water and of the manufacturing process (distillation, degassing) on the final isotopic composition of the water in the cells. Inductively coupled plasma mass spectrometry (ICPMS) was conducted on selected water samples to investigate the potential contamination of the source water during the manufacturing process, and to evaluate the impact of impurities on the water triple-point temperature. The temperature differences among the manufactured cells were measured, and correlations between the observed differences and the results of isotope and chemical analysis were studied.     

Breakdown of the adiabatic Born-Oppenheimer approximation in graphene

The adiabatic Born-Oppenheimer approximation (ABO) has been the standard ansatz to describe the interaction between electrons and nuclei since the early days of quantum mechanics. ABO assumes that the lighter electrons adjust adiabatically to the motion of the heavier nuclei, remaining at any time in their instantaneous ground state. ABO is well justified when the energy gap between ground and excited electronic states is larger than the energy scale of the nuclear motion. In metals, the gap is zero and phenomena beyond ABO (such as phonon-mediated superconductivity or phonon-induced renormalization of the electronic properties) occur. The use of ABO to describe lattice motion in metals is, therefore, questionable. In spite of this, ABO has proved effective for the accurate determination of chemical reactions, molecular dynamics and phonon frequencies in a wide range of metallic systems. Here, we show that ABO fails in graphene. Graphene, recently discovered in the free state, is a zero-bandgap semiconductor that becomes a metal if the Fermi energy is tuned applying a gate voltage, Vg. This induces a stiffening of the Raman G peak that cannot be described within ABO.     

Experimental study of retrofit solutions for damaged concrete bridge slabs

Accurate information on the actual performance of the structural system after retrofit is an essential part of a cost-effective bridge management program. This paper summarizes the results of a thorough experimental program concerning the reinforced concrete deck of a real 40 year-old viaduct. The structure exhibited severe damage at the extrados mainly due to environmental agents, chemical attack and action of asphalt milling machines. Samples of the deck were cut and carried to the laboratory in order to assess the possibility of retrofit. The design of retrofit was aimed at increasing the load carrying capacity through replacement of the deteriorated concrete with a new concrete overlay and strengthening in flexure for both negative (hogging) and positive (sagging) bending moments. Experimental testing on small specimens and nondestructive techniques were carried out to identify the material properties and to evaluate the level of damage. The bonding between external reinforcement and the original or new (standard or polymer-modified) concrete was assessed through single-shear push–pull tests on 33 prismatic specimens of 100 × 200 × 500 mm³ strengthened with CFRP strips. The efficiency of the retrofit techniques was checked at the structural level through four-point bending tests on eight slabs of 500 × 200 × 2000 mm³. This research can contribute to guidelines for concrete patch repair of FRP-retrofitted concrete bridge decks, to ensure better long-term performance under service loads and environmental effects.     

Selecting creep models using Bayesian methods

The development of creep prediction models has been a field of extensive research and many different models have already been proposed. This paper presents an evaluation method of the prediction quality of creep models for specific experimental data. Within the scope of this paper, the model according to Bockhold and the model according to Heidolf are examined. First, the parameters of the models are identified with respect to existing experimental data. This is done using a sampling based approach of Bayesian updating developed by Ba?ant and Chern. In extension to the method by Ba?ant and Chern, the uncertainty coming from inaccurate measurement data is taken into account in the definition of the likelihood function within the updating algorithm. The more inaccurate the measurements are, the more uncertain the estimated model parameters and model prognoses become. The identification is performed for different short- and long-term creep tests. The intension is not to validate these models intensively, but to evaluate their prognoses for the individually tested creep behavior. The results show that the identifiability of the models?? parameters is different for both models and consequently the models prognoses differ in their uncertainties. Second, the models are evaluated using two different strategies: the stochastic model selection according to MacKay, Beck and Yuen based on the Ockham factor, and a comparison of the uncertainties taking into account parameter and model uncertainties. The results of the evaluation of the creep models differ for various experimental tests. Model Heidolf is more flexible and gives a better fit to the data, however, it fails to predict reliable long-term creep deformations using only short-term measurements compared to model Bockhold. Comparing the evaluation methods, the analysis of uncertainties of the creep prognosis proofs to be more stable than the evaluation using the stochastic model selection.     

High-rate quantum key distribution at short wavelength: Performance analysis and evaluation of silicon single photon avalanche diodes

Abstract

Experimental results obtained with silicon single photon avalanche diodes (SPADs) in quantum key distribution (QKD) at short wavelengths reveal remarkable potential for application in local area networks (LAN) and for free-space transmission at high rate. Actual application prospects, however, depend on the performance level and on the suitability of practical systems using the available silicon SPAD devices. They can be essentially divided in two groups: planar p-n junction structures with a thin depletion layer (typically 1 μm); and reach-through structures with a thick depletion layer (from 20 μm to 150μm). The physical mechanisms that control the device behaviour were investigated and the effect on the key parameters of the detector (quantum detection efficiency, dark counting rate, afterpulsing probability and photon-timing jitter) were thoroughly assessed. A quantitative analysis was made of the influence of such parameters on the quantum bit error rate (QBER). Actual parameters were measured and the attainable performance and system suitability of the two device types evaluated. Comparable performance is obtained, but from a system viewpoint thin SPADs appear inherently better suited to high-rate QKD applications, because of their faster response time, ruggedness, low voltage, low power dissipation and fabrication technology, which is simple, efficient, economical and compatible with monolithic integration of detector and associated circuits.     

Experimental realization of optical lumped nanocircuits at infrared wavelengths

The integration of radiofrequency electronic methodologies on micro- as well as nanoscale platforms is crucial for information processing and data-storage technologies. In electronics, radiofrequency signals are controlled and manipulated by 'lumped' circuit elements, such as resistors, inductors and capacitors. In earlier work, we theoretically proposed that optical nanostructures, when properly designed and judiciously arranged, could behave as nanoscale lumped circuit elements--but at optical frequencies. Here, for the first time we experimentally demonstrate a two-dimensional optical nanocircuit at mid-infrared wavelengths. With the guidance of circuit theory, we design and fabricate arrays of Si3N4 nanorods with specific deep subwavelength cross-sections, quantitatively evaluate their equivalent impedance as lumped circuit elements in the mid-infrared regime, and by Fourier transform infrared spectroscopy show that these nanostructures can indeed function as two-dimensional optical lumped circuit elements. We further show that the connections among nanocircuit elements, in particular whether they are in series or in parallel combination, can be controlled by the polarization of impinging optical signals, realizing the notion of 'stereo-circuitry' in metatronics-metamaterials-inspired optical circuitry.