1,849 research outputs found
Two phase detonation studies
An experimental study of the passage of a shock wave over a burning fuel drop is described. This includes high speed framing photographs of the interaction taken at 500,000 frames per second. A theoretical prediction of the ignition of a fuel drop by a shock wave is presented and the results compared with earlier experimental work. Experimental attempts to generate a detonation in a liquid fuel drop (kerosene)-liquid oxidizer drop (hydrogen peroxide)-inert gas-environment are described. An appendix is included which gives the analytical prediction of power requirements for the drop generator to produce certain size drops at a certain mass rate. A bibliography is also included which lists all of the publications resulting from this research grant
Theoretical analysis of magnetic coupling in sandwich clusters V_n(C_6H_6)_{n+1}
The mechanism of ferromagnetism stability in sandwich clusters
V(CH) has been studied by first-principles calculation and
model analysis. It is found that each of the three types of bonds between V and
benzene (Bz) plays different roles. V 3d orbital, extending along the
molecular axis, is weakly hybridized with Bz's HOMO-1 orbital to form the
-bond. It is quite localized and singly occupied, which contributes
1 to the magnetic moment but little to the magnetic coupling of
neighboring V magnetic moments. The in-plane d, d orbitals
are hybridized with the LUMO of Bz and constitute the -bond. This
hybridization is medium and crucial to the magnetic coupling though the
states have no net contribution to the total magnetic moment.
d, d and HOMO of Bz form a quite strong -bond to hold the
molecular structure but they are inactive in magnetism because their energy
levels are far away from the Fermi level. Based on the results of
first-principles calculation, we point out that the ferromagnetism stability is
closely related with the mechanism proposed by Kanamori and Terakura [J.
Kanamori and K. Terakura, J. Phys. Soc. Jpn. 70, 1433 (2001)]. However, the
presence of edge Bz's in the cluster introduces an important modification. A
simple model is constructed to explain the essence of the physical picture.Comment: 16 pages, 7 figure
Detection of Noble Gas Scintillation Light with Large Area Avalanche Photodiodes (LAAPDs)
Large Area Avalanche Photodiodes (LAAPDs) were used for a series of
systematic measurements of the scintillation light in Ar, Kr, and Xe gas.
Absolute quantum efficiencies are derived. Values for Xe and Kr are consistent
with those given by the manufacturer. For the first time we show that argon
scintillation (128 nm) can be detected at a quantum efficiency above 40%.
Low-pressure argon gas is shown to emit significant amounts of non-UV
radiation. The average energy expenditure for the creation of non-UV photons in
argon gas at this pressure is measured to be below 378 eV.Comment: 16 pages, 7 figure
Anomalous Hall voltage rectification and quantized spin-wave excitation induced by the simultaneous dc- and rf-current application in Ni81Fe19 wire
An anomalous Hall effect and rectification of a Hall voltage are observed by
applying a radio-frequency (rf) current through a single-layered ferromagnetic
wire located on a coplanar waveguide. The components of the magnetization
precession, both in and perpendicular to the plane, can be detected via the
Hall voltage rectification of the rf current by incorporating an additional
direct (dc) current. In this paper, we propose a phenomenological model, which
describes the time-dependent anisotropic magnetoresistance and time-dependent
planer Hall effect. The nonlinearity of the spin dynamics accompanied by
spin-waves as functions of rf and dc currents is also studied, as well as those
of the magnitude and orientation of the external magnetic field.Comment: 42 pages, 5 figures, submitte
Broadband ferromagnetic resonance of Ni81Fe19 wires using a rectifying effect
The broadband ferromagnetic resonance measurement using the rectifying effect
of Ni81Fe19 wire has been investigated. One wire is deposited on the center
strip line of the coplanar waveguide (CPW) and the other one deposited between
two strip lines of CPW. The method is based on the detection of the
magnetoresistance oscillation due to the magnetization dynamics induced by the
radio frequency field. The magnetic field dependences of the resonance
frequency and the rectification spectrum are presented and analytically
interpreted on the standpoint of a uniform magnetization precession model.Comment: 33pages, 8 figures. submitte
The Effect of Fe-Al Substitution on the Crystal Structure of MgSiO3 Bridgmanite
The crystal chemistry of ten well-characterized bridgmanite single-crystals with Fe and Al contents ranging from 0 to 0.40 atoms per two-cation formula units were investigated by single-crystal X-ray diffraction. Structural refinements indicate that Fe3+ and Al mainly occupy the Mg and Si sites, respectively, when present in similar proportions. Molar volumes of bridgmanite endmember components were refined using data from this and previous studies and found to decrease in the order Fe3+Fe3+O3 > MgFe3+O2.5 > Fe3+AlO3 > MgAlO2.5 > AlAlO3 > Fe2+SiO3 > MgSiO3. Fe3+AlO3 charge-coupled substitution leads to an anisotropic increase of B-O bond distances, resulting in more distorted octahedral B sites and in a more significant increase of the c-axis with respect to the a- and b-axes. Valence bond calculations indicate that the A site is more compressible than the B site for all bridgmanite samples studied, implying that octahedral tilting and distortion will dominate the bridgmanite compression mechanism. Guided by these crystal chemical observations, bulk moduli of bridgmanite endmember components were estimated using results of previous studies. The volume changes of equilibria controlling the speciation of bridgmanite components were then calculated at conditions relevant to the top of Earth's lower mantle. The proportion of oxygen vacancy components is predicted to decrease with pressure. While the stability of the bridgmanite Fe3+AlO3 component will drive charge disproportionation to produce iron metal at the top of the lower mantle, this appears to be much less favorable by 50 GPa. An increase in the proportion of the Fe3+Fe3+O3 bridgmanite component, however, may favor the formation of iron metal at higher pressures
Rectification of radio frequency current in ferromagnetic nanowire
We report the rectification of a constant wave radio frequency (RF) current
by using a single-layer magnetic nanowire; a direct-current voltage is
resonantly generated when the RF current flows through the nanowire. The
mechanism of the rectification is discussed in terms of the spin torque diode
effect reported for magnetic tunnel junction devices and the rectification is
shown to be direct attributable to resonant spin wave excitation by the RF
current.Comment: 20 Pages, 4 figures, submitte
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