Calculation of clearances in twin screw compressors

Clearances between rotating and stationary parts in a screw compressor are set to ensure the efficient operation and allow for thermal deformation without unwanted contacts. The change in clearances is caused by both pressure and temperature changes within the machine. If clearances are too large, the increased leakage flows will reduce efficiency. However, if the nominal clearances are too small, contacts between the rotating and stationary parts can occur as a consequence of rotor and casing deformations. In order to determine the operational clearances, a numerical analysis of deformation of screw compressor rotors and casing has to be performed. This paper discusses how the temperature of rotor and casing surfaces calculated from the one-dimensional chamber model in the SCORG could be used as a boundary conditions for a steady state thermal and structural analysis of a screw compressor solid parts. Deformations of rotors and casing under temperature load were calculated using a commercial Finite Element Analysis code ANSYS. Operational clearance are estimated from these deformations and some recommendations for further work are proposed

Dominant Role of the pi Framework in Cyclobutadiene

The extrinsic antiaromaticity of archetypal cyclobutadiene (CBD) is addressed with particular emphasis on the sigma-pi separability problem. The destabilization energy E(d)(CBD) of CBD is obtained by appropriate homodesmotic reactions involving the open chain zigzag, polyene(s). It is shown that E(d)(CBD) does not depend on the electron correlation and the zero-point vibrational energy contributions, since they are small and of the opposite sign. Consequently, they cancel in the first approximation. Further, it turns out that E(d)(CBD) can be estimated accurately enough with a very modest cc-pVDZ basis set at the Hartree-Fock (HF) level. The extrinsic antiaromatic destabilization E(ean)(CBD) of CBD is deduced after extracting the angular strain energy estimated to be 32 kcal/mol. The resulting E(ean)(CBD) value of 52 kcal/mol is in excellent agreement with the experimental thermodynamic data. If the E(ean)(CBD) is estimated relative to two isolated C=C double bonds, then it assumes 38 kcal/mol, which is roughly 10 kcal/mol per one pi electron. It is, therefore, safe to state that extrinsic antiaromaticity of CBD is larger than its angular strain. Although the sigma and pi electrons are coupled by a mutual Coulomb interaction V-ee(sigmapi), several attempts of their decoupling is made by using three partitioning schemes: stockholder, equipartition, and standard pi-electron theory recipe. The latter allocates the V-nn and V-ee(sigmapi) terms to the sigma- and pi-electron frameworks, respectively. The nuclear repulsion term V-nn is dissected into sigma and pi components in the former two partitioning schemes by using stockholder criterion. It appears that the extrinsic antiaromatic destabilization E(ean)(CBD) is determined by the pi-electron framework according to all three partitioning models

The PULSE@Parkes project: A new observing technique for long-term pulsar monitoring

The PULSE@Parkes project has been designed to monitor the rotation of radio pulsars over time spans of days to years. The observations are obtained using the Parkes 64-m and 12-m radio telescopes by Australian and international high school students. These students learn the basis of radio astronomy and undertake small projects with their observations. The data are fully calibrated and obtained with the state-of-the-art pulsar hardware available at Parkes. The final data sets are archived and are currently being used to carry out studies of 1) pulsar glitches, 2) timing noise, 3) pulse profile stability over long time scales and 4) the extreme nulling phenomenon. The data are also included in other projects such as gamma-ray observatory support and for the Parkes Pulsar Timing Array project. In this paper we describe the current status of the project and present the first scientific results from the Parkes 12-m radio telescope. We emphasise that this project offers a straightforward means to enthuse high school students and the general public about radio astronomy while obtaining scientifically valuable data sets.Comment: accepted for publication by PAS

Long-term palliation of right-sided congestive heart failure after stenting a recurrent cor triatriatum dexter in a 10½-year-old pug.

A 10½-year-old, male neutered, pug presented with increasing ascites over two months. Echocardiography revealed cor triatriatum dexter with no concurrent cardiovascular anomalies, subsequently confirmed by computed tomography angiography. Balloon dilation of the perforated intra-atrial membrane under fluoroscopic guidance resulted in the transient resolution of all clinical abnormalities, but six months later stenosis and ascites recurred. After repeated balloon dilation, a stent was placed across the membrane. The dog remains asymptomatic fourteen months after the second procedure. One noteworthy feature of this case is the onset of congestive heart failure due to a congenital defect only at more than 10 years of age

Dynamic adsorption characteristics of thin layered activated charcoal materials used in chemical protective overgarments

The efficiency of a thin layered activated charcoal material used in chemical protective overgarments has been evaluated. The study has been conducted with the aim to obtain protective materials with best characteristics considering resistance to benzene effect under dynamic conditions and to create a new filtration protection device. In order to evaluate dynamic adsorption characteristics of thin layered sorption materials, sophisticated dynamic gas chromatography method is used. The curves of benzene penetration are determined for sandwich materials, and sorption layers used in filtrating protective clothing shows that thin layered carbon sorption materials (type M00) have good protective properties as compared to other similar materials. The findings will help to create conditions for developing a functional model for producing a new protective overgarment in the near future

Near-Infrared Mapping and Physical Properties of the Dwarf-Planet Ceres

We study the physical characteristics (shape, dimensions, spin axis direction, albedo maps, mineralogy) of the dwarf-planet Ceres based on high-angular resolution near-infrared observations. We analyze adaptive optics J/H/K imaging observations of Ceres performed at Keck II Observatory in September 2002 with an equivalent spatial resolution of ~50 km. The spectral behavior of the main geological features present on Ceres is compared with laboratory samples. Ceres' shape can be described by an oblate spheroid (a = b = 479.7 +/- 2.3 km, c = 444.4 +/- 2.1 km) with EQJ2000.0 spin vector coordinates RA = 288 +/- 5 deg. and DEC = +66 +/- 5 deg. Ceres sidereal period is measured to be 9.0741 +/- 0.0001 h. We image surface features with diameters in the 50-180 km range and an albedo contrast of ~6% with respect to the average Ceres albedo. The spectral behavior of the brightest regions on Ceres is consistent with phyllosilicates and carbonate compounds. Darker isolated regions could be related to the presence of frost.Comment: 11 pages, 8 Postscript figures, Accepted for publication in A&