9,499 research outputs found
Embryo impacts and gas giant mergers II: Diversity of Hot Jupiters' internal structure
We consider the origin of compact, short-period, Jupiter-mass planets. We
propose that their diverse structure is caused by giant impacts of embryos and
super-Earths or mergers with other gas giants during the formation and
evolution of these hot Jupiters. Through a series of numerical simulations, we
show that typical head-on collisions generally lead to total coalescence of
impinging gas giants. Although extremely energetic collisions can disintegrate
the envelope of gas giants, these events seldom occur. During oblique and
moderately energetic collisions, the merger products retain higher fraction of
the colliders' cores than their envelopes. They can also deposit considerable
amount of spin angular momentum to the gas giants and desynchronize their spins
from their orbital mean motion. We find that the oblateness of gas giants can
be used to infer the impact history. Subsequent dissipation of stellar tide
inside the planets' envelope can lead to runaway inflation and potentially a
substantial loss of gas through Roche-lobe overflow. The impact of super-Earths
on parabolic orbits can also enlarge gas giant planets' envelope and elevates
their tidal dissipation rate over 100 Myr time scale. Since giant
impacts occur stochastically with a range of impactor sizes and energies, their
diverse outcomes may account for the dispersion in the mass-radius relationship
of hot Jupiters.Comment: 19 pages, 7 figures, 7 tables. Accepted for publication in MNRA
Time-frequency feature extraction from multiple impulse source signal of reciprocating compressor based on local frequency
Vibration signals generated by reciprocating compressor present a multiple impulse source property, which is typical non-stationary. For this kind of signal, time-frequency analysis techniques, such as STFT, WVT, WT and HHT, represent some limitations. To alleviate this problem, a novel concept of local frequency (LF) is proposed in the paper. Based on the concept, a time-frequency distribution algorithm is established. Some non-stationary simulation signals, including multi-harmonic signal, FM signal and multiple impulse source signal, are investigated to identify the feasibility and effectiveness of the novel time-frequency analysis technique. Compared with WVT, WT and HHT, time-frequency analysis based on LF represents a higher resolution and more useful information. Moreover, the proposed approach is applied to the fault feature extraction of reciprocating compressor gas valve vibration signal in normal valve state and gap valve state. The results indicate the superiority of proposed approach in extracting time-frequency features from multiple impulse source signal of reciprocating compressor, which obtains a more precise result than WVT, WT and HHT. So it can provide an effective basis to fault diagnosis of reciprocating compressor
Development of rheometer for semi-solid highmelting point alloys
A rheometer for semi-solid high-melting point alloys was developed based on the principle of a double-bucket rheometer, with which the solidifying of semi-solid high-melting point alloy melt could be effectively controlled by the control of temperature and the outer force-field; and different microstructures have also been obtained. This rheometer can be used to investigate the rheological behavior under different conditions by changing the Theological parameters. By way of full-duplex communication between the computer and each sensor, automatic control of the test equipment and real- timemeasurement of rheological parameters were realized. Finally, the influencing factors on torque are also quantitatively analyzed
Modified Kedem-Katchalsky equations for osmosis through nano-pore
This work presents a modified Kedem-Katchalsky equations for osmosis through
nano-pore. osmotic reflection coefficient of a solute was found to be chiefly
affected by the entrance of the pore while filtration reflection coefficient
can be affected by both the entrance and the internal structure of the pore.
Using an analytical method, we get the quantitative relationship between
osmotic reflection coefficient and the molecule size. The model is verified by
comparing the theoretical results with the reported experimental data of
aquaporin osmosis. Our work is expected to pave the way for a better
understanding of osmosis in bio-system and to give us new ideas in designing
new membranes with better performance.Comment: 19 pages, 4 figure
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