310 research outputs found
CFD investigation of airflow on a model radio control race car
The modern day design of vehicles, especially in the racing industry involve a great deal of air flow study. This study shows that drag force adversely affects the forward motion of the car and that there is a difference in the pressure between the air flowing above and below the car. This produces forces along the vertical axis. Aerodynamic forces acting on a car greatly reduces its efficiency. If the car is redesigned to optimise these forces it could produce better results. This paper discusses various techniques that have been used to redesign and optimise the aerodynamics of a model radio control race car
Connecting the one-band and three-band Hubbard models of cuprates via spectroscopy and scattering experiments
The one-band and three-band Hubbard models which describe the electronic
structure of cuprates indicate very different values of effective electronic
parameters (EPs), such as the Cu on-site Coulomb energy and the Cu-O
hybridization strength. In contrast, a comparison of EPs of several cuprates
with corresponding values from spectroscopy and scattering experiments
indicates similar values in the three-band model and cluster model calculations
used to simulate experimental results. To explore this relation in detail, a
CuO cluster model calculation was carried out to obtain an expression for
the Heisenberg exchange coupling between Cu sites using a downfolding
method, taking into account Cu and O on-site correlations ( and ),
the charge-transfer energy and the hopping between Cu and O sites.
A quantitative analysis provides a consistent description of from neutron
scattering experiments, using the three-band model and spectroscopic EPs. In
addition, can be expressed in the one-band Hubbard model form with
and , which denote renormalized and using
and , and their values indicate a large , in
agreement with reported values. The large arising from a
combination of , and is thus hidden in the effective
one-band Hubbard model. The ground-state singlet weights obtained from an exact
diagonalization show the importance of the Cu-O Zhang-Rice singlet in the
effective one-band Hubbard model. The results provide a consistent method to
connect EPs obtained from spectroscopy and the three-band model with values of
obtained from scattering experiments, band dispersion measurements and the
effective one-band Hubbard model.Comment: 9 pages, 2 figures (submitted to Physical Review B
Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films
Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in
contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane and
out-of-plane Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films
using energy dependent soft x-ray momentum-resolved photoemission spectroscopy.
We show that the SS originates in nested regions confined to out-of-plane FSs,
which are drastically modified compared to in-plane FSs. From precise
reciprocal space maps in successive zones, we obtain the associated real space
compressive strain of 1.5+-0.5% along c-axis. An autocorrelation analysis
quantifies the incommensurate ordering vector q=(2pi/a)(0,0,~0.86), favoring a
SS and consistent with magneto-optic Kerr effect experiments. The results
reveal the importance of in-plane and out-of-plane FS mapping for ultrathin
films.Comment: 4 pages, 3 figure
Disorder effects in electronic structure of substituted transition metal compounds
Investigating LaNi(1-x)M(x)O3 (M = Mn and Fe), we identify a characteristic
evolution of the spectral function with increasing disorder in presence of
strong interaction effects across the metal-insulator transition. We discuss
these results vis-a-vis existing theories of electronic structure in
simultaneous presence of disorder and interaction.Comment: Revtex, 4 pages, 3 postscript figures (To appear in Phys. Rev. Lett
Collapse of the charge ordering gap of Nd_{0.5}Sr_{0.5}MnO_{3} in an applied magnetic field
We report results of tunneling studies on the charge ordering compound
Nd_{0.5}Sr_{0.5}MnO_{3} in a magnetic field up to 6T and for temperature down
to 25K.We show that a gap (2\Delta_{CO} \approx 0.5eV opens up in the density
of state (DOS) at the Fermilevel (E_F) on charge ordering (T_{CO}=150K) which
collapses in an applied magnetic field when the charge ordered state melts.
There is a clear correspondence between the behavior of the resistivity and the
gap formation and its collapse in an applied magnetic field. We conclude that a
gap in the DOS at E_F is necessary for the stability of the charge ordered
state.Comment: 4 pages REVTeX, 5 postscript figures included, submitted to Phys.
Rev. Let
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