Multiphase phenomena in Diesel fuel injection systems

Fuel Injection Equipment (FIE) are an integral component of modern Internal Combustion Engines (ICE), since they play a crucial role in the fuel atomization process and in the formation of a fuel/air combustible mixture, consequently affecting efficiency and pollutant formation. Advancements and improvements of FIE systems are determined by the complexity of the physical mechanisms taking place; the spatial scales are in the order of millimetres, flow may become locally highly supersonic, leading to very small temporal scales of microseconds or less. The operation of these devices is highly unsteady, involving moving geometries such as needle valves. Additionally, extreme pressure changes imply that many assumptions of traditional fluid mechanics, such as incompressibility, are no longer valid. Furthermore, the description of the fuel properties becomes an issue, since fuel databases are scarce or limited to pure components, whereas actual fuels are commonly hydrocarbon mixtures. Last but not least, complicated phenomena such as phase change or transition from subcritical to transcritical/supercritical state of matter further pose complications in the understanding of the operation of these devices

The Overlap of Small Molecule and Protein Binding Sites within Families of Protein Structures

Protein–protein interactions are challenging targets for modulation by small molecules. Here, we propose an approach that harnesses the increasing structural coverage of protein complexes to identify small molecules that may target protein interactions. Specifically, we identify ligand and protein binding sites that overlap upon alignment of homologous proteins. Of the 2,619 protein structure families observed to bind proteins, 1,028 also bind small molecules (250–1000 Da), and 197 exhibit a statistically significant (p<0.01) overlap between ligand and protein binding positions. These “bi-functional positions”, which bind both ligands and proteins, are particularly enriched in tyrosine and tryptophan residues, similar to “energetic hotspots” described previously, and are significantly less conserved than mono-functional and solvent exposed positions. Homology transfer identifies ligands whose binding sites overlap at least 20% of the protein interface for 35% of domain–domain and 45% of domain–peptide mediated interactions. The analysis recovered known small-molecule modulators of protein interactions as well as predicted new interaction targets based on the sequence similarity of ligand binding sites. We illustrate the predictive utility of the method by suggesting structural mechanisms for the effects of sanglifehrin A on HIV virion production, bepridil on the cellular entry of anthrax edema factor, and fusicoccin on vertebrate developmental pathways. The results, available at http://pibase.janelia.org, represent a comprehensive collection of structurally characterized modulators of protein interactions, and suggest that homologous structures are a useful resource for the rational design of interaction modulators

Evaluation of the light emission efficiency of LYSO:Ce scintillator under X-ray excitation for possible applications in medical imaging

Lutetium-yttrium-based scintillators, such as LYSO:Ce, have a high effective atomic number, are non-hygroscopic, fast emitting materials, and promising candidates for use in positron emission imagers. The present study investigates the light emission characteristics of (Lu, Y)2SiO5:Ce (LYSO:Ce) single-crystal scintillator under X-ray imaging conditions. Also, the parameters related to the luminescence emission spectrum and emission efficiency were studied using experimental methods. Various X-ray tube voltages currently employed in X-ray imaging techniques were used. Measurements were performed using an experimental set-up based on a photomultiplier coupled to an integration sphere. In addition, the emission spectrum under UV and X-ray excitation was measured using an optical grating monochromator to determine the spectral compatibility of optical photon detectors incorporated in medical imaging systems. The absolute efficiency of LYSO:Ce was found to increase with increasing X-ray tube voltage (from 2.2 EU at 22 kVp to 22.4 EU at 140 kVp), while its spectrum, peaking at about 430 nm, was found compatible with most optical detectors (photodiodes, photocathodes, charge coupled devices, etc.). The matching factor was estimated to range from 0.76 to 0.92 (for a silicon photodiode and for a GaAsP photocathode, respectively). © 2006 Elsevier B.V. All rights reserved

Evaluation of the light emission efficiency of LYSO:Ce scintillator under X-ray excitation for possible applications in medical imaging

Lutetium-yttrium-based scintillators, such as LYSO:Ce, have a high effective atomic number, are non-hygroscopic, fast emitting materials, and promising candidates for use in positron emission imagers. The present study investigates the light emission characteristics of (Lu, Y)2SiO5:Ce (LYSO:Ce) single-crystal scintillator under X-ray imaging conditions. Also, the parameters related to the luminescence emission spectrum and emission efficiency were studied using experimental methods. Various X-ray tube voltages currently employed in X-ray imaging techniques were used. Measurements were performed using an experimental set-up based on a photomultiplier coupled to an integration sphere. In addition, the emission spectrum under UV and X-ray excitation was measured using an optical grating monochromator to determine the spectral compatibility of optical photon detectors incorporated in medical imaging systems. The absolute efficiency of LYSO:Ce was found to increase with increasing X-ray tube voltage (from 2.2 EU at 22 kVp to 22.4 EU at 140 kVp), while its spectrum, peaking at about 430 nm, was found compatible with most optical detectors (photodiodes, photocathodes, charge coupled devices, etc.). The matching factor was estimated to range from 0.76 to 0.92 (for a silicon photodiode and for a GaAsP photocathode, respectively). © 2006 Elsevier B.V. All rights reserved

Imaging properties of cerium doped Yttrium Aluminum Oxide (YAP:Ce) powder scintillating screens under X-ray excitation

The aim of the present study was to evaluate the imaging performance of YAP:Ce powder scintillating screens under exposure conditions employed in diagnostic radiology (50-140 kV). Various screens were prepared in our laboratory from YAP: Ce powder (Phosphor Technology, Ltd.), with coating thickness ranging from 53 to 110 mg/cm2. The imaging performance of the screens was assessed by experimental determination of the modulation transfer function (MTF) and the noise transfer function (NTF). MTF was determined by the edge spread function (ESF) method while NTF was estimated by noise power spectrum (NPS) measurements after uniform screen irradiation. In addition, parameters related to overall image quality, such as the signal-to-noise ratio transfer (MTF/NTF), were estimated. MTF curves were affected by the beam hardening effects caused by the patient simulating 20 mm thick aluminum phantom. Under these conditions MTF values were found to increase with the mean X-ray photon energy. A similar effect was observed for NTF curves. Results were compared with data obtained on CsI:Tl scintillator. Taking into consideration the very fast response of YAP:Ce, these data may be of interest in designing X-ray imaging detectors. © 2006 Elsevier B.V. All rights reserved

Imaging properties of cerium doped Yttrium Aluminum Oxide (YAP:Ce) powder scintillating screens under X-ray excitation

The aim of the present study was to evaluate the imaging performance of YAP:Ce powder scintillating screens under exposure conditions employed in diagnostic radiology (50-140 kV). Various screens were prepared in our laboratory from YAP: Ce powder (Phosphor Technology, Ltd.), with coating thickness ranging from 53 to 110 mg/cm2. The imaging performance of the screens was assessed by experimental determination of the modulation transfer function (MTF) and the noise transfer function (NTF). MTF was determined by the edge spread function (ESF) method while NTF was estimated by noise power spectrum (NPS) measurements after uniform screen irradiation. In addition, parameters related to overall image quality, such as the signal-to-noise ratio transfer (MTF/NTF), were estimated. MTF curves were affected by the beam hardening effects caused by the patient simulating 20 mm thick aluminum phantom. Under these conditions MTF values were found to increase with the mean X-ray photon energy. A similar effect was observed for NTF curves. Results were compared with data obtained on CsI:Tl scintillator. Taking into consideration the very fast response of YAP:Ce, these data may be of interest in designing X-ray imaging detectors. © 2006 Elsevier B.V. All rights reserved