Frequency-Dependent Attenuation Effects in Pulsed Doppler Ultrasound: Experimental Results

The quantitative capability of pulsed Doppler ultrasound in clinical practice is limited by the effects of frequency-dependent attenuation of ultrasound in tissue, as well as several other spectral-broadening mechanisms which distort the Doppler spectrum of an ultrasonic echo. In this communication, we present results of in vitro experiments which demonstrate the magnitude of the errors expected in clinical measurements of blood flow parameters when frequency-dependent attenuation Of ultrasound in biological tissue is ignored. It is shown that errors as large as 15 percent may occur in Doppler measurements of blood flow velocity through 7 cm of intervening tissue. A comparison is also made between experimental results and a theoretical model which includes the effects of scattering and attenuation.     

Reduction of Escherichia coli O157:H7 viability on leafy green vegetables by treatment with a bacteriophage mixture and trans-cinnamaldehyde

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 has been recognized as a major foodborne pathogen responsible for frequent gastroenteritis outbreaks. Phages and essential oils can be used as a natural antimicrobial method to reduce bacterial pathogens from the food supply. The objective of this study was to determine the effect of a bacteriophage cocktail, BEC8, alone and in combination with the essential oil trans-cinnameldehyde (TC) on the viability of a mixture of EHEC O157:H7 strains applied on whole baby romaine lettuce and baby spinach leaves. The EHEC O157:H7 strains used were Nal^R mutants of EK27, ATCC 43895, and 472. Exponentially growing cells from tryptic soy (TS) broth cultures were spot inoculated on leaves and dried. EHEC cells were placed at low, medium, and high inoculum levels (10⁴, 10⁵, and 10⁶ CFU/mL, respectively). Appropriate controls, BEC8 (approx. 10⁶ PFU/leaf), and TC (0.5% v/v) were applied on treated leaves. The leaves were incubated at 4, 8, 23, and 37 °C in Petri dishes with moistened filter papers. EHEC survival was determined using standard plate count on nalidixic acid (50 μg/mL) Sorbitol MacConkey agar. No survivors were detected when both leaves were treated with BEC8 or TC individually at low inoculum levels after 24 h at 23 and 37 °C. When the EHEC inoculum size increased and/or incubation temperature decreased, the efficacy of BEC8 and TC decreased. However, when the two treatments were combined, no survivors were detected after 10 min at all temperatures and inoculum levels on both leafy greens. These results indicated that the BEC8/TC combination was highly effective against EHEC on both leafy greens. This combination could potentially be used as an antimicrobial to inactivate EHEC O157:H7 and reduce their incidence in the food chain.     

Flexible organic P3HT:PCBM bulk-heterojunction modules with more than 1 year outdoor lifetime

Flexible organic solar cells and modules based on P3ht:PCBM bulk-heterojunctions were fabricated and their lifetime was investigated under laboratory and outdoor conditions. In the laboratory cells were exposed to 1 sun illumination at 65 °C in order to accelerate the degradation. The outdoor behavior of modules was investigated at the Konarka rooftop testing setup in Lowell, MA (USA). We show that these flexible polymer solar cells have a good light stability, passing 1000 h under accelerated light soaking conditions in the laboratory, and that flexible modules survived over 1 year of outdoor exposure without performance losses.     

Collapse of partially corroded or worn pipe under external pressure

This paper is concerned with the effect of internal corrosion or erosion defects on the collapse of pipelines under external pressure. Experiments are conducted on SS-304 tubes with D/t's of 21.0 and 18.7 with axially uniform grooves of several thicknesses and angular spans of 6–60°. All specimens exhibited the classical ovalization mode of collapse with the grooved side being more deformed. For groove angles between 6° and 20° the collapse pressure decreases as the angle increases but remains essentially constant for angles between 20° and 60°. The collapse pressure was found to decrease with groove depth, reducing by nearly 50% when the groove depth reached 50% of the pipe wall thickness. The experiments were simulated numerically using both the custom computer code BEPTICO as well as an axially uniform finite element model. The predictions were found to follow closely the trends of the experimental results. The three dimensionality of grooves was examined using appropriate finite element models. It was found that grooves shorter than about 8D constitute local imperfections and accurate prediction of their effect on collapse pressure requires fully 3-D modeling. By contrast, grooves 10D long or longer behave essentially as “long” grooves and can be analyzed using 2-D models.     

Study on transient heat transfer through multilayer thermal insulation: Numerical analysis and experimental investigation

This paper reports on a numerical and experimental study of heat transfer phenomena through two different multilayer fibrous insulations for building applications. The investigated samples were composed of different layers of fibrous materials and aluminium foils, placed between one or two air gaps in the vertical dimension. An experimental apparatus (a guarded hot box) has been used to measure heat transfer through the samples, while a finite volume numerical model combined radiation/conduction heat transfer was developed to predict the temperature distribution and heat transfer in such insulation systems comprised of the materials separated by multiple reflective foils. The model takes into account the coupling between the solid conduction of the fibrous system and the gaseous conduction and radiation. The radiation heat transfer through the insulation system has been modelled via the two flux approximation. The numerical results were compared with the experimental data from the guarded hot box for model validation, as well as to assess the effectiveness of the reflective foils in changing the resistance of the insulations. The comparative verification of the model showed that the numerical results were consistent with the experimental data through the environmental conditions under examination.     

Laser melting treatment by overlapping passes of preheated nickel electrodeposited coatings on Al−Si alloy

Microstructure improvements of a nickel electrodeposited Al−Si alloy were studied after high-power laser melting treatment through a single pass or partially overlapping successive adjacent passes. In some cases, laser melting treatment was preceded by a 5-hour heating of the specimens at 500°C in argon atmosphere furnace. Microstructure observations and microhardness measurements were carried out on the specimens before and after laser melting treatment with and without preheating. Best results concerning microhardness, microstructural homogeneity, and porosity elimination, as well as adhesion of the nickel coating on the Al−Si alloy, were achieved when the specimens were first subjected to heating at 500°C in an argon atmosphere furnace for 5 hours and then submitted to a laser melting treatment through successive adjacent laser passes with an overlapping rate of 70 pct. Microstructure studies were carried out employing X-ray diffraction analysis (XRD) and energy-dispersive spectrometry (EDS). AlNi and Al₃Ni phases were detected in the diffusion area which resulted from the 5-hour heating. AlNi, Al₃Ni, and Al₃Ni₂ phases were identified in the laser melted zones (LMZs). Each one of the above phase was found to be the main phase under different conditions.     

Statistical analysis of wind speed and direction in Cyprus

The aim of this study is to establish the meteorological basis for the assessment of wind energy resources in Cyprus and to provide suitable data for evaluating the potential wind power. For this purpose the mean values, the systematic daily and annual variations, the frequency distributions and the estimation of the extreme values are determined. Predictions were also obtained from the WAsP model and, finally, the Wind Atlas of the island, in the form of contours of constant wind speed, was produced.     

Reconstruction of large-scale flow structures in a stirred tank from limited sensor data

We combine reduced order modeling and system identification to reconstruct the temporal evolution of large-scale vortical structures behind the blades of a Rushton impeller. We performed direct numerical simulations at Reynolds number 600 and employed proper orthogonal decomposition (POD) to extract the dominant modes and their temporal coefficients. We then applied the identification algorithm, N4SID, to construct an estimator that captures the relation between the velocity signals at sensor points (input) and the POD coefficients (output). We show that the first pair of modes can be very well reconstructed using the velocity time signal from even a single sensor point. A larger number of points improves accuracy and robustness and also leads to better reconstruction for the second pair of POD modes. Application of the estimator derived at Re = 600 to the flows at Re = 500 and 700 shows that it is robust with respect to changes in operating conditions.