2,852 research outputs found
Potential of Interplanetary Torques and Solar Modulation for Triggering Terrestrial Atmospheric and Lithospheric Events
The Sun is forced into an orbit around the barycenter of the solar system
because of the changing mass distribution of the planets. Solar-planetary-lunar
dynamic relationships may form a new basis for understanding and predicting
cyclic solar forcing functions on the Earth's climate.Comment: Invited Paper at the Fourth UN/ESA Workshop on Basic Space Science,
Cairo, Egypt, July 1994. 7 pages LaTeX. Accepted for publication in the
journal Earth, Moon, and Planet
Experimental investigation of elastic mode control on a model of a transport aircraft
A 4.5 percent DC-10 derivative flexible model with active controls is fabricated, developed, and tested to investigate the ability to suppress flutter and reduce gust loads with active controlled surfaces. The model is analyzed and tested in both semispan and complete model configuration. Analytical methods are refined and control laws are developed and successfully tested on both versions of the model. A 15 to 25 percent increase in flutter speed due to the active system is demonstrated. The capability of an active control system to significantly reduce wing bending moments due to turbulence is demonstrated. Good correlation is obtained between test and analytical prediction
Violation of particle number conservation in the it GW approximation
We present a nontrivial model system of interacting electrons that can be solved analytically in the GW approximation. We obtain the particle number from the GW Green's function strictly analytically, and prove that there is a genuine violation of particle number conservation if the self-energy is calculated non-self-consistently from a zeroth order Green's function, as done in virtually all practical implementations. We also show that a simple shift of the self-energy that partially restores self-consistency reduces the numerical deviation significantly
The effects of bell vibrations on the sound of the modern trumpet
The acoustic spectrum of a modern trumpet with the bell section heavily damped has been compared to the spectrum of the same instrument with the bell section left free to vibrate. Measurements of the amplitude of vibration indicate that the damping significantly reduces the movement of the metal, and a corresponding change in the acoustic spectrum between the two cases is found. It is shown that the relative power in the fundamental may change by more than 3 dB when the vibrations in the bell section are damped. Two possible causes for the effects are considered: a change in input impedance, and the transfer of mechanical vibrations through the instrument to the lips. Results of modelling and experiments are presented that indicate the latter is the more plausible explanation; however, the etiology of the effect is still unknown
Multiple Core-Hole Coherence in X-Ray Four-Wave-Mixing Spectroscopies
Correlation-function expressions are derived for the coherent nonlinear
response of molecules to three resonant ultrafast pulses in the x-ray regime.
The ability to create two-core-hole states with controlled attosecond timing in
four-wave-mixing and pump probe techniques should open up new windows into the
response of valence electrons, which are not available from incoherent x-ray
Raman and fluorescence techniques. Closed expressions for the necessary
four-point correlation functions are derived for the electron-boson model by
using the second order cumulant expansion to describe the fluctuating
potentials. The information obtained from multidimensional nonlinear techniques
could be used to test and refine this model, and establish an anharmonic
oscillator picture for electronic excitations
Effect of high pressure on multiferroic BiFeO3
We report experimental evidence for pressure instabilities in the model
multiferroic BiFeO3 and namely reveal two structural phase transitions around 3
GPa and 10 GPa by using diffraction and far-infrared spectroscopy at a
synchrotron source. The intermediate phase from 3 to 9 GPa crystallizes in a
monoclinic space group, with octahedra tilts and small cation displacements.
When the pressure is further increased the cation displacements (and thus the
polar character) of BiFeO3 is suppressed above 10 GPa. The above 10 GPa
observed non-polar orthorhombic Pnma structure is in agreement with recent
theoretical ab-initio prediction, while the intermediate monoclinic phase was
not predicted theoretically.Comment: new version, accepted for publication in Phys. Rev.
Archaeal abundance in post-mortem ruminal digesta may help predict methane emissions from beef cattle
The Rowett Institute of Nutrition and Health and SRUC are funded by the Rural and Environment Science and Analytical Services Division (RESAS) of the Scottish Government. The project was supported by DEFRA and DA funded Agricultural Greenhouse Gas Inventory Research Platform. Our thanks are due to the excellent support staff at the SRUC Beef Research Centre, Edinburgh, also to Graham Horgan of BioSS, Aberdeen, for conducting multivariate analysis.Peer reviewedPublisher PD
Measuring and Correcting Wind-Induced Pointing Errors of the Green Bank Telescope Using an Optical Quadrant Detector
Wind-induced pointing errors are a serious concern for large-aperture
high-frequency radio telescopes. In this paper, we describe the implementation
of an optical quadrant detector instrument that can detect and provide a
correction signal for wind-induced pointing errors on the 100m diameter Green
Bank Telescope (GBT). The instrument was calibrated using a combination of
astronomical measurements and metrology. We find that the main wind-induced
pointing errors on time scales of minutes are caused by the feedarm being blown
along the direction of the wind vector. We also find that wind-induced
structural excitation is virtually non-existent. We have implemented offline
software to apply pointing corrections to the data from imaging instruments
such as the MUSTANG 3.3 mm bolometer array, which can recover ~70% of
sensitivity lost due to wind-induced pointing errors. We have also performed
preliminary tests that show great promise for correcting these pointing errors
in real-time using the telescope's subreflector servo system in combination
with the quadrant detector signal.Comment: 17 pages, 11 figures; accepted for publication in PAS
Energetic and spatial bonding properties from angular distributions of ultraviolet photoelectrons: application to the GaAs(110) surface
Angle-resolved ultraviolet photoemission spectra are interpreted by combining
the energetics and spatial properties of the contributing states. One-step
calculations are in excellent agreement with new azimuthal experimental data
for GaAs(110). Strong variations caused by the dispersion of the surface bands
permit an accurate mapping of the electronic structure. The delocalization of
the valence states is discussed analogous to photoelectron diffraction. The
spatial origin of the electrons is determined, and found to be strongly energy
dependent, with uv excitation probing the bonding region.Comment: 5 pages, 3 figures, submitted for publicatio
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