Force mapping of an optical trap using an acousto-optical deflector in a time-sharing regime

We suggest and study experimentally a time-sharing protocol for acousto-optical deflectors (AODs) that permits one to map the radial optical trapping force of optical tweezers without using a controllable flux control or an additional beam. Variations of the trapping potential due to modifications of the optical system are easily detected in terms of the force map. The protocol can be used in optical tweezers that already include an AOD without adding new elements in the existing optical system.     

Temperature and velocity measurement fields of fluids using a schlieren system

This paper proposes a combined method for two-dimensional temperature and velocity measurements in liquid and gas flow using a schlieren system. Temperature measurements are made by relating the intensity level of each pixel in a schlieren image to the corresponding knife-edge position measured at the exit focal plane of the schlieren system. The same schlieren images were also used to measure the velocity of the fluid flow. The measurement is made by using particle image velocimetry (PIV). The PIV software used in this work analyzes motion between consecutive schlieren frames to obtain velocity fields. The proposed technique was applied to measure the temperature and velocity fields in the natural convection of water provoked by a heated rectangular plate.     

Diode-pumped 2 μm vibronic (Tm3+, Yb3+):KLu(WO4)2 laser

We report on laser operation in a (6 at. % Tm, 5 at. % Yb):KLu(WO4)2 codoped crystal. The vibrational frequencies of KLu(WO4)2 are coupled to the electronic transitions of Tm3+ at 1946 nm, creating virtual final laser levels at higher energy than the ground level 3H6 of Tm3+. The longest recorded laser wavelength was 2039 nm, which is longer than permitted by a pure electronic transition in Tm3+ ions in KLu(WO4)2. We show that every laser wavelength can be explained with the electron-phonon coupling effect, where the vibration frequencies were determined through Raman spectroscopy.     

Characterization of a SrF2 Scintillating Bolometer

We present the analysis of the data obtained with a 53?g SrF₂ scintillating bolometer operated at 20?mK. We have analyzed its heat and light response (time constants, linearity and energy resolution) and measured its scintillation relative efficiency factor for different particles (alpha, beta/gamma and neutrons). We have studied the spatial uniformity of the light output profiting from its internal contamination. The light amplitude of alphas from the delayed coincidence ²²⁴Ra→²²⁰Rn→²¹⁶Po (emitted from the same crystal position) shows a positive correlation, evidence of a non-uniformity that worsens the light signal energy resolution by more than?50%.     

Superplastic behavior of Zn–Al eutectoid alloy with 2?% Cu

The effects of deformation temperature and strain rate on the superplastic behavior of the Zn–21Al–2Cu alloy (Zinalco alloy) were investigated by uniaxial tensile tests. Results were compared with those of the Zn–22Al eutectoid alloy without Cu. It was observed that additions of 2 % Cu leads to a decrease of the maximum strain attainable from 2600 % to 1000 %. The maximum strain in Zinalco alloy is obtained at lower strain rates. The presence of Cu increases the values of flow stress up to 600 % compared with those reported in the Zn-22Al alloy. Grain size sensitivity (p), true activation energy (Q _t ), and constant A of the constitutive equation were not affected by presence of Cu unlike the stress exponent (n) which increased from 2.5 to 3.9. The main effect of Cu was to decrease the plastic flow stability of the Zn–22Al alloy. The results indicate that presence of Cu in the Zinalco alloy causes a hardening effect at low strain rates leading to a decrease in the strain rate sensitivity which promotes the formation and growth of sharp necks. Microstructural characterization suggests that the large deformations at necking could possibly be due to the substantial elongation capability of the Zn-rich phase (η).     

Compressive Viscoplastic Response of 6082‐T6 and 7075‐T6 Aluminium Alloys Under Wide Range of Strain Rate at Room Temperature: Experiments and Modelling

Abstract: In this work, the viscoplastic behaviour of 6082‐T6 and 7075‐T6 aluminium alloys is examined over a wide range of strain rates. Three different testing techniques were applied to this investigation: low‐rate experiments were performed using a regular servo‐hydraulic testing machine, high‐rate tests were conducted using a split Hopkinson bar apparatus and very‐high‐rate experiments were carried out using a miniaturised direct impact test arrangement. The latter testing set‐up allowed for the characterisation of material flow at strain rates up to . These experimental results showed a sharp increase in the rate sensitivity of the materials once a threshold loading rate of is exceeded. This behaviour may be attributed to the presence of viscous drag on high‐velocity dislocation motion. In addition, the thermo‐viscoplastic behaviour of the 6082‐T6 and 7075‐T6 aluminium alloys was analytically described using the extended Rusinek–Klepaczko model of viscous drag effects. Satisfactory correlation was observed between the experiments and the constitutive model results over the entire range of strain rates studied,      

Neutron diffraction and magnetic study of the low-temperature transitions in SrMo1−xFexO3−δ

SrMo_1?xFe_xO_3?δ (x = 0, 0.1, 0.2 and 0.3) perovskites have recently been described as performing anode materials in solid-oxide fuel cells. In this work, we describe the structural phase transitions they undergo below room-temperature (RT), studied “in-situ” from neutron powder diffraction data and DSC measurements. At RT all the studied compositions are cubic, space group Pm-3m, with unit-cell parameters that decrease with Fe doping. Upon cooling the samples, two structural phase transitions are identified: one to a tetragonal structure with I4/mcm space group (around T₁ = 240 K), and the second one to an orthorhombic Imma phase below T₂ = 100 K. The magnetic properties have also been evaluated; the Fe substitution drives an evolution from a Pauli-paramagnetic state (x = 0) to a weak ferromagnetic state combined with antiferromagnetic interactions; the susceptibility and the saturation magnetization increases monotonically with increasing the Fe-doping content.     

Electrodeposition of gold thin films with controlled morphologies and their applications in electrocatalysis and SERS

Here, an easy and effective electrochemical route towards the synthesis of gold thin films with well-controlled roughness, morphology and crystallographic orientation is reported. To control these different factors, the applied potential during deposition played a major role. A tentative nucleation and growth mechanism is demonstrated by means of electrochemical characterizations and a formation mechanism is proposed. Interestingly, the differences in geometry and orientation of the different gold deposits have shown a clear correlation with the electrocatalytical activity in the case of oxygen sensing. In addition, not only the electrocatalytical activity but also the surface-enhanced Raman scattering of the gold deposits have been found to depend both on the roughness and on the size of the surface nanostructures, allowing a fine tuning by controlling these two parameters during deposition.     

Chitosan/poly(dl,lactide-co-glycolide) scaffolds for tissue engineering

Chitosan/poly(dl-lactide-co-glycolide) (Ch/dl PLG) composite scaffolds were fabricated by freeze-drying lyophilization, and were evaluated and compared for use as a bone regeneration scaffold through measurements of the compression mechanical properties of the porous scaffolds. Also, In vitro cell culture of Sprague?CDawley rat??s osteoblasts were used to evaluate the phenotype expression of cells in the scaffolds, characterizing the cellular adhesion, proliferation and alkaline phosphatase activity. The gene expression of osteocalcin, sialoprotein, alkaline phosphatase, Type I collagen and TGF??1 were confirmed in the samples; moreover, it was confirmed, the mineralization by IR spectra and EDS analysis. Our results thus show that Ch/dl PLG scaffolds are suitable for biological applications.