4,502 research outputs found
Gravitational Effects of Rotating Bodies
We study two type effects of gravitational field on mechanical gyroscopes
(i.e. rotating extended bodies). The first depends on special relativity and
equivalence principle. The second is related to the coupling (i.e. a new force)
between the spins of mechanical gyroscopes, which would violate the equivalent
principle. In order to give a theoretical prediction to the second we suggest a
spin-spin coupling model for two mechanical gyroscopes. An upper limit on the
coupling strength is then determined by using the observed perihelion
precession of the planet's orbits in solar system. We also give predictions
violating the equivalence principle for free-fall gyroscopes .Comment: LaTex, 6 page
Filament L1482 in the California molecular cloud
Aims. The process of gravitational fragmentation in the L1482 molecular
filament of the California molecular cloud is studied by combining several
complementary observations and physical estimates. We investigate the kinematic
and dynamical states of this molecular filament and physical properties of
several dozens of dense molecular clumps embedded therein.
Methods. We present and compare molecular line emission observations of the
J=2--1 and J=3--2 transitions of 12CO in this molecular complex, using the
KOSMA 3-meter telescope. These observations are complemented with archival data
observations and analyses of the 13CO J=1--0 emission obtained at the Purple
Mountain Observatory 13.7-meter radio telescope at Delingha Station in QingHai
Province of west China, as well as infrared emission maps from the Herschel
Space Telescope online archive, obtained with the SPIRE and PACS cameras.
Comparison of these complementary datasets allow for a comprehensive
multi-wavelength analysis of the L1482 molecular filament.
Results. We have identified 23 clumps along the molecular filament L1482 in
the California molecular cloud. All these molecular clumps show supersonic
non-thermal gas motions. While surprisingly similar in mass and size to the
much better known Orion molecular cloud, the formation rate of high-mass stars
appears to be suppressed in the California molecular cloud relative to that in
the Orion molecular cloud based on the mass-radius threshold derived from the
static Bonnor Ebert sphere. Our analysis suggests that these molecular
filaments are thermally supercritical and molecular clumps may form by
gravitational fragmentation along the filament. Instead of being static, these
molecular clumps are most likely in processes of dynamic evolution.Comment: 10 pages, 9 figures, 2 tables, accepted to Astronomy and Astrophysic
Lead Iodide Perovskite Light-Emitting Field-Effect Transistor
Despite the widespread use of solution-processable hybrid organic-inorganic
perovskites in photovoltaic and light-emitting applications, determination of
their intrinsic charge transport parameters has been elusive due to the
variability of film preparation and history-dependent device performance. Here
we show that screening effects associated to ionic transport can be effectively
eliminated by lowering the operating temperature of methylammonium lead iodide
perovskite (CH3NH3PbI3) field-effect transistors (FETs). Field-effect carrier
mobility is found to increase by almost two orders of magnitude below 200 K,
consistent with phonon scattering limited transport. Under balanced ambipolar
carrier injection, gate-dependent electroluminescence is also observed from the
transistor channel, with spectra revealing the tetragonal to orthorhombic phase
transition. This first demonstration of CH3NH3PbI3 light-emitting FETs provides
intrinsic transport parameters to guide materials and solar cell optimization,
and will drive the development of new electro-optic device concepts, such as
gated light emitting diodes and lasers operating at room temperature
Number-resolved master equation approach to quantum transport under the self-consistent Born approximation
We construct a particle-number(n)-resolved master equation (ME) approach
under the self-consistent Born approximation (SCBA) for quantum transport
through mesoscopic systems. The formulation is essentially non-Markovian and
incorporates the interlay of the multi-tunneling processes and many-body
correlations. The proposed n-SCBA-ME goes completely beyond the scope of the
Born-Markov master equation, being applicable to transport under small bias
voltage, in non-Markovian regime and with strong Coulomb correlations. For
steady state, it can recover not only the exact result of noninteracting
transport under arbitrary voltages, but also the challenging nonequilibrium
Kondo effect. Moreover, the n-SCBA-ME approach is efficient for the study of
shot noise.We demonstrate the application by a couple of representative
examples, including particularly the nonequilibrium Kondo system.Comment: arXiv admin note: substantial text overlap with arXiv:1302.638
An experimental and numerical study on structural dynamic stress of a landing gear
This paper concerns the main landing gear of certain light aircraft, and the dynamic stress on the main landing gear during the landing process is analyzed. A complete dynamic drop test is developed for the landing gear of light aircraft on the main landing gear, and the changes of dynamic strain exerted on the strut in the process of drop are measured. Simultaneously, the simulation software LMS Virtual.Lab Motion is used to build the rigid-flexible coupling dynamic model and simulate the process of drop and the results of the dynamic stress is obtained by means of computer simulation. Afterwards, the results of the dynamic stress between simulation and test are contrasted, and the sources of data error are analyzed. To sum up, the study shows that the dynamic stress in the flexible part of landing gear possesses a high accuracy through combining the analysis results of simulation and test, which meets the safety design criteria of the landing gear. Moreover, the method used to build the rigid-flexible coupling model is an available and reliable way for the simulation of drop test, which can provide a deep basis for future research
- …