Performance of fluorene and terthiophene copolymer in bilayer photovoltaic devices: The role of the polymer conformations

We report experiments using fluorene and terthiophene copolymer as the active layer in bilayer devices with C₆₀. The highest short circuit current, open circuit voltage and power conversion efficiency upon AM1.5 illumination were 6.8 mA/cm², 0.68 V and 2.33%, respectively. Density functional theory analysis was used to identify the most stable configurations of the terthiophene moieties in the polymer: the most stable form has the thiophene rings in the alternate configuration (anti) and the second conformation has the thiophene rings pointing to the same direction (syn). Comparing theoretical results with measurements of absorbance, X-ray diffraction, and X-ray reflectometry experiments, we conclude that the annealing treatment produces conformational anti to syn transition along the backbone of poly[9,9′-n-dihexyl-2,7-fluorene-alt-2,5-terthiophene] (LaPPS45). The syn segments of the chain condensed then in a lamellar ordered structure which increases the degree of crystallinity of the annealed samples and improve the light harvest at long wavelengths. From absorption measurements of films submitted to different annealing temperatures and with the help of theoretical calculations we propose a “wave-like” aggregation pattern to the syn segments in those lamellas.     

Hydrothermal synthesis of cobalt-doped vanadium oxides: Antimicrobial activity study

Cobalt-doped vanadium oxide (CoVOx) nanocomposites were synthesized using facile hydrothermal sol-gel method. The final products were annealed at 500?°C in the furnace for 2?h under vacuum and air, which led to Co₃(VO₄)₂, CoV₂O₆ and pure V₂O₅ powders respectively. The nanoparticles (NPs) were characterized by X-ray Diffraction and Scanning Electron Microscopy (SEM). The magnetization behavior of the samples shows step–like increase for CoV₂O₆ material while the magnetic moment is quasi saturated at 2?T for Co₃(VO₄)_2.The antibacterial activity of CoVOx nanocomposites was tested against two gram negative and two gram positive bacterial isolates. The bacterial strains were treated with increasing concentrations of NPs (0–3.5?mg/ml) for 24?h. The cell viability was assessed using Alamar Blue assay to monitor the response and health of the cells in culture after treatment with various pathogens. Among the three NPs tested, Co₃(VO₄)₂ and CoV₂O₆ showed enhanced anti-bacterial activity on the four isolates compared to V₂O₅ which manifests an activity on E.coli at the highest dosage.     

Ultrasound evaluation of mechanical injury of bovine knee articular cartilage under arthroscopic control

A local cartilage injury can trigger development of posttraumatic osteoarthritis (OA). Surgical methods have been developed for repairing cartilage injuries. Objective and sensitive methods are needed for planning an optimal surgery as well as for monitoring the surgical outcome. In this laboratory study, the feasibility of an arthroscopic ultrasound technique for diagnosing cartilage injuries was investigated. In bovine knees (n = 7) articular cartilage in the central patella and femoral sulcus was mechanically degraded with a steel brush modified for use under arthroscopic control. Subsequently, mechanically degraded and intact adjacent tissue was imaged with a high frequency (40 MHz) intravascular ultrasound device operated under arthroscopic guidance. After opening the knee joint, mechanical indentation measurements were also conducted with an arthroscopic device at each predefined anatomical site. Finally, cylindrical osteochondral samples were extracted from the measurement sites and prepared for histological analysis. Quantitative parameters, i.e., reflection coefficient (R), integrated reflection coefficient (IRC), apparent integrated backscattering (AIB), and ultrasound roughness index (URI) were calculated from the ultrasound signals. The reproducibilities (sCV %) of the measurements of ultrasound parameters were variable (3.7% to 26.1%). Reflection and roughness parameters were significantly different between mechanically degraded and adjacent intact tissue (p < 0.05). Surface fibrillation of mechanically degraded tissue could be visualized in ultrasound images. Furthermore, R and IRC correlated significantly with the indentation stiffness. The present results are encouraging; however, further technical development of the arthroscopic ultrasound technique is needed for evaluation of the integrity of human articular cartilage in vivo.     

Measurement of swelling stresses in spruce (Picea abies) samples

Swelling stresses play a significant role in the efficient use of wood products in different applications such as paneling. The main objective of this study was to investigate development of swelling stresses in the tangential direction in spruce (Picea abies) as function of water soaking time in order to provide basic data. Experimental results were compared to the theoretical calculations obtained from different models. On the basis of the findings of this study it appears that the magnitude of the swelling stresses in spruce samples in the tangential direction was approximately 1.2 MPa.     

Experimental and numerical studies of liquid dispersal from a soft projectile impacting a wall

A medium-scale IMPACT test programme is currently being implemented at the Technical Research Centre of Finland (VTT). In these tests, deformable cylindrical steel or aluminium projectiles impact a solid concrete wall or a steel force plate. One part of the test is conducted with a missile filled with liquid water to study liquid dispersal phenomena (i.e., wet missile tests).The fluid-filled missile ranged in length from 0.5 to 1.5 m, the water mass inside the missile from 15 to 68 kg, and the impact velocity of missile from 70 to 177 m/s.This paper describes the methods used to measure the liquid dispersal processes, and presents the main results for preliminary simulations of liquid spread. Because the IMPACT tests have focused on structural aspects, it was necessary to develop cost-effective methods for measuring liquid phenomena. The tests measured some important parameters associated with liquid: the discharge speed and direction of the liquid core released from the ruptured missile, propagation speed of the spray front, liquid pooling on the floor, extent of liquid dispersal away from the target, and the drop size of the liquid spray.The experimental findings indicate that the liquid release starts along the surface almost perpendicularly to the incoming direction of the missile and forms a fairly “flat” and uniform splash pattern around the missile. Although the discharge speed of the liquid core may be initially much higher than the impact velocity of the missile, the propagation speed of the spray front decreases rapidly with increasing distance from the source. Results of the preliminary simulations show that the Fire Dynamic Simulator (FDS) program is a usable tool for simulating two-phase flows involving high-speed droplets, provided that the initial conditions (angle and speed of liquid release, droplet size, and initial air speed) can be specified appropriately. Given these requirements, FDS can reasonably well predict the formation of the water spray cloud and final distribution of water.     

A continuum-based finite element formulation for the implicit solution of multibody,large deformation-frictional contact problems

In this paper, a formulation is presented for the finite element treatment of multibody, large deformation frictional contact problems. The term multibody is used to mean that when two bodies mechanically contact, both may be deformable. A novel aspect of the approach advocated is that the equations governing contact are developed in the continuum setting first, before deriving the corresponding finite element equations This feature distinguishes the current work from many earlier treatments of contact problems and renders it considerably more general. In particular, the approach yields a characterization of the frictional constraint (assuming a Coulomb law) suitable for arbitrary discretizations in either two or three dimensions. A geometric framework is constructed within which both frictionless and frictional response are naturally described, making subsequent finite element discretization a straightforward substitution of finite-dimensional solution spaces for their continuum counterparts. To our knowledge, this general formulation and implementation of the frictional contact problem in a finite element setting has not been reported previously in the literature. The development includes exact linearization of the statement of virtual work, which enables optimal convergence properties for Newton-Raphson solution strategies, and which appears to be highly desirable (if not essential) for the general robustness of implicit finite element techniques. Since the theory and subsequent linearization require no limitations on the amount of deformation or relative sliding that can occur, the resulting treatment of frictional contact is suitable for a wide range of examples displaying significant non-linear behaviour. This assertion is substantiated through presentation of a variety of examples in both two and three dimensions.     

Comparison of model-based flow rate estimation methods in frequency-converter-driven pumps and fans

Fluid handling systems such as pump and fan systems are found to have a significant potential for energy efficiency improvements. To determine the energy-saving potential, there is a need for easily implementable methods to monitor the system output. This essential information provides an opportunity to identify inefficient operation of the fluid handling system and to control the output of the pumping system according to process needs. Model-based pump or fan monitoring methods implemented in variable-speed drives have proven to be able to give information on the system output without additional metering; however, the present model-based methods may not be usable or sufficiently accurate in the whole operation range of the fluid handling device. To apply model-based system monitoring in a wider selection of systems and to improve the accuracy of the monitoring, this paper proposes a new method for pump and fan output monitoring with variable-speed drives. The method uses a combination of already known operating point estimation methods. Laboratory measurements are used to verify the benefits and applicability of the improved estimation method, and the new method is compared with five previously introduced model-based estimation methods. According to the laboratory measurements, the new estimation method is the most accurate and reliable of the model-based estimation methods.