12,922 research outputs found
Shallow grooves in journal improve air bearing performance
Bearing designs, which shape the surface to create artificial fluid-film wedges in the absence of any applied radial load, generate radial restoring forces to keep journals from whirling. Helical- or herringbone-grooved journals or rotors show most promise of stable operation, with no sacrifice in load capacity
Do Natural Disasters Affect Trust/Trustworthiness? Evidence from the 2010 Chilean Earthquake
A series of trust games were conducted in Chile to analyze whether the past 2010 earthquake affected trust and trustworthiness in rural communities. Results show that trust levels are invariant between villages affected by the earthquake and villages not affected by this shock (control group). However, we find statistical evidence that trustworthiness has diminished in areas affected by the earthquake. Results are relevant for policy regarding aid and recovery of communities affected by these types of disasters.Trust games, natural disasters, trustworthiness, Community/Rural/Urban Development, International Development, C93, O13,
Experimental dynamic stiffness and damping of externally pressurized gas-lubricated journal bearings
A rigid vertical shaft was operated with known amounts of unbalance at speeds to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. The measured stiffness was proportional to the supply pressure, while damping was little affected by supply pressure. Damping dropped rapidly as the fractional frequency whirl threshold was approached. A small-eccentricity analysis overpredicted the stiffness by 20 to 70 percent. Predicted damping was lower than measured at low speeds but higher at high speeds
Experiments on rotating externally pressurized air journal bearings. Part 2 - Attitude angle and air flow
Air flow and attitude angle compared with theory for rotating externally pressurized air journal bearing
Imaging analysis of LDEF craters
Two small craters in Al from the Long Duration Exposure Facility (LDEF) experiment tray A11E00F (no. 74, 119 micron diameter and no. 31, 158 micron diameter) were analyzed using Auger electron spectroscopy (AES), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), low voltage scanning electron microscopy (LVSEM), and SEM energy dispersive spectroscopy (EDS). High resolution images and sensitive elemental and molecular analysis were obtained with this combined approach. The result of these analyses are presented
An Algorithm to Generate Deep-Layer Temperatures from Microwave Satellite Observations for the Purpose of Monitoring Climate Change
An algorithm for generating deep-layer mean temperatures from satellite-observed microwave observations is presented. Unlike traditional temperature retrieval methods, this algorithm does not require a first guess temperature of the ambient atmosphere. By eliminating the first guess a potentially systematic source of error has been removed. The algorithm is expected to yield long-term records that are suitable for detecting small changes in climate. The atmospheric contribution to the deep-layer mean temperature is given by the averaging kernel. The algorithm computes the coefficients that will best approximate a desired averaging kernel from a linear combination of the satellite radiometer's weighting functions. The coefficients are then applied to the measurements to yield the deep-layer mean temperature. Three constraints were used in deriving the algorithm: (1) the sum of the coefficients must be one, (2) the noise of the product is minimized, and (3) the shape of the approximated averaging kernel is well-behaved. Note that a trade-off between constraints 2 and 3 is unavoidable. The algorithm can also be used to combine measurements from a future sensor (i.e., the 20-channel Advanced Microwave Sounding Unit (AMSU)) to yield the same averaging kernel as that based on an earlier sensor (i.e., the 4-channel Microwave Sounding Unit (MSU)). This will allow a time series of deep-layer mean temperatures based on MSU measurements to be continued with AMSU measurements. The AMSU is expected to replace the MSU in 1996
Non-local quantum correlations and detection processes in QFT
Quantum detection processes in QFT must play a key role in the description of
quantum field correlations, such as the appearance of entanglement, and of
causal effects. We consider the detection in the case of a simple QFT model
with a suitable interaction to exact treatment, consisting of a quantum scalar
field coupled linearly to a classical scalar source. We then evaluate the
response function to the field quanta of two-level point-like quantum model
detectors, and analyze the effects of the approximation adopted in standard
detection theory. We show that the use of the RWA, that characterizes the
Glauber detection model, leads in the detector response to non-local terms
corresponding to an instantaneously spreading of source effects over the whole
space. Other detector models, obtained with non-standard or the no-application
of RWA, give instead local responses to field quanta, apart from source
independent vacuum contribution linked to preexisting correlations of
zero-point field.Comment: 23 page
The [4+2]âCycloaddition of αâNitrosoalkenes with Thiochalcones as a Prototype of Periselective HeteroâDielsâAlder ReactionsâExperimental and Computational Studies
The [4+2]âcycloadditions of αânitrosoalkenes with thiochalcones occur with high selectivity at the thioketone moiety of the dienophile providing styrylâsubstituted 4Hâ1,5,2âoxathiazines in moderate to good yields. Of the eight conceivable heteroâDielsâAlder adducts only this isomer was observed, thus a prototype of a highly periselective and regioselective cycloaddition has been identified. Analysis of crude product mixtures revealed that the αânitrosoalkene also adds competitively to the thioketone moiety of the thiochalcone dimer affording bisâheterocyclic [4+2]âcycloadducts. The experiments are supported by highâlevel DFT calculations that were also extended to related heteroâDielsâAlder reactions of other nitroso compounds and thioketones. These calculations reveal that the title cycloadditions are kinetically controlled processes confirming the role of thioketones as superdienophiles. The computational study was also applied to the experimentally studied thiochalcone dimerization, and showed that the 1,2âdithiin and 2Hâthiopyran isomers are in equilibrium with the monomer. Again, the DFT calculations indicate kinetic control of this process
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