18,274 research outputs found
Steady-state and transitional aerodynamic characteristics of a wing in simulated heavy rain
The steady-state and transient effects of simulated heavy rain on the subsonic aerodynamic characteristics of a wing model were determined in the Langley 14- by 22-Foot Subsonic Tunnel. The 1.29 foot chord wing was comprised of a NACA 23015 airfoil and had an aspect ratio of 6.10. Data were obtained while test variables of liquid water content, angle of attack, and trailing edge flap angle were parametrically varied at dynamic pressures of 10, 30, and 50 psf (i.e., Reynolds numbers of .76x10(6), 1.31x10(6), and 1.69x10(6)). The experimental results showed reductions in lift and increases in drag when in the simulated rain environment. Accompanying this was a reduction of the stall angle of attack by approximately 4 deg. The transient aerodynamic performance during transition from dry to wet steady-state conditions varied between a linear and a nonlinear transition
The Quantum McKay Correspondence for polyhedral singularities
Let G be a polyhedral group, namely a finite subgroup of SO(3). Nakamura's
G-Hilbert scheme provides a preferred Calabi-Yau resolution Y of the polyhedral
singularity C^3/G. The classical McKay correspondence describes the classical
geometry of Y in terms of the representation theory of G. In this paper we
describe the quantum geometry of Y in terms of R, an ADE root system associated
to G. Namely, we give an explicit formula for the Gromov-Witten partition
function of Y as a product over the positive roots of R. In terms of counts of
BPS states (Gopakumar-Vafa invariants), our result can be stated as a
correspondence: each positive root of R corresponds to one half of a genus zero
BPS state. As an application, we use the crepant resolution conjecture to
provide a full prediction for the orbifold Gromov-Witten invariants of [C^3/G].Comment: Introduction rewritten. Issue regarding non-uniqueness of conifold
resolution clarified. Version to appear in Inventione
The Diamine Cation Is Not a Chemical Example Where Density Functional Theory Fails
In a recent communication, Weber and co-workers presented a surprising study
on charge-localization effects in the N,N'-dimethylpiperazine (DMP+) diamine
cation to provide a stringent test of density functional theory (DFT) methods.
Within their study, the authors examined various DFT methods and concluded that
"all DFT functionals commonly used today, including hybrid functionals with
exact exchange, fail to predict a stable charge-localized state." This
surprising conclusion is based on the authors' use of a self-interaction
correction (namely, complex-valued Perdew-Zunger Self-Interaction Correction
(PZ-SIC)) to DFT, which appears to give excellent agreement with experiment and
other wavefunction-based benchmarks. Since the publication of this recent
communication, the same DMP+ molecule has been cited in numerous subsequent
studies as a prototypical example of the importance of self-interaction
corrections for accurately calculating other chemical systems. In this
correspondence, we have carried out new high-level CCSD(T) analyses on the DMP+
cation to show that DFT actually performs quite well for this system (in
contrast to their conclusion that all DFT functionals fail), whereas the PZ-SIC
approach used by Weber et al. is the outlier that is inconsistent with the
high-level CCSD(T) (coupled-cluster with single and double excitations and
perturbative triples) calculations. Our new findings and analysis for this
system are briefly discussed in this correspondence.Comment: Accepted by Nature Communication
The Lyman Alpha Forest in Hierarchical Cosmologies
The comparison of quasar absorption spectra with numerically simulated
spectra from hierarchical cosmological models of structure formation promises
to be a valuable tool to discriminate among these models. We present simulation
results for the column density, Doppler b parameter, and optical depth
probability distributions for five popular cosmological models.Comment: 4 pages, 3 figures, uses aipproc.sty, to appear in the Proceedings of
the 9th Annual October Astrophysics Conference in Maryland, "After the Dark
Ages: When Galaxies Were Young (the Universe at 2<z<5)", ed. S. S. Holt and
E. P. Smith, October 12-14, 199
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