22,167 research outputs found
Volterra Series Approximation for Multi-Degree of Freedom, Multi-Input, Multi-Output, Aircraft Dynamics
An analytical model of a second order system is extended from a single-axis framework, to a multi-axis, multi-degree of freedom framework for a multiple input, multiple output system. This mathematical model is built from the variational approach of the Volterra series representation of nonlinear systems. The new representation describes the second order, oscillatory natural modes of a system, and shows how to organize the Volterra terms in intuitive ways. The constructed mathematical model aims to establish an organization of the Volterra kernels to allow for analytical cause and effect type analysis on system behavior.
To demonstrate the accuracy of the developed Volterra model, the model is applied to atmospheric flight dynamics. A numerical simulation of an F-16 aircraft was developed based on the experimental data collected at NASA Langley and is compared to the Volterra model. Both longitudinal and latitudinal aircraft dynamics are analyzed, and the results show that the Volterra model effectively tracks the numerical simulations and has less error than a more conventional linearized system. The results show that weak nonlinearities of a system are predicted based on this new model. The construction of the model allows for a more effective analysis to the cause and effect of the response. Individual responses of each nonlinear component are separated for analysis, and each component’s effects on the total system response are observed
Power Corrections to the Universal Heavy WIMP-Nucleon Cross Section
WIMP-nucleon scattering is analyzed at order in Heavy WIMP Effective
Theory. The power corrections, where is the WIMP mass,
distinguish between different underlying UV models with the same universal
limit and their impact on direct detection rates can be enhanced relative to
naive expectations due to generic amplitude-level cancellations at leading
order. The necessary one- and two-loop matching calculations onto the
low-energy effective theory for WIMP interactions with Standard Model quarks
and gluons are performed for the case of an electroweak SU(2) triplet WIMP,
considering both the cases of elementary fermions and composite scalars. The
low-velocity WIMP-nucleon scattering cross section is evaluated and compared
with current experimental limits and projected future sensitivities. Our
results provide the most robust prediction for electroweak triplet Majorana
fermion dark matter direct detection rates; for this case, a cancellation
between two sources of power corrections yields a small total correction,
and a total cross section close to the universal limit for . For the SU(2) composite scalar, the corrections
introduce dependence on underlying strong dynamics. Using a leading chiral
logarithm evaluation, the total correction has a larger magnitude and
uncertainty than in the fermionic case, with a sign that further suppresses the
total cross section. These examples provide definite targets for future direct
detection experiments and motivate large scale detectors capable of probing to
the neutrino floor in the TeV mass regime.Comment: 12 pages, 4 figures; references added, XENONnT projection included,
version to appear in Physics Letters
Fully anharmonic infrared cascade spectra of polycyclic aromatic hydrocarbons
The infrared (IR) emission of polycyclic aromatic hydrocarbons (PAHs)
permeates our universe; astronomers have detected the IR signatures of PAHs
around many interstellar objects. The IR emission of interstellar PAHs differs
from their emission as seen under conditions on Earth, as they emit through a
collisionless cascade down through their excited vibrational states from high
internal energies. The difficulty in reproducing interstellar conditions in the
laboratory results in a reliance on theoretical techniques. However, the size
and complexity of PAHs requires careful consideration when producing the
theoretical spectra. In this work we outline the theoretical methods necessary
to lead to a fully theoretical IR cascade spectra of PAHs including: an
anharmonic second order vibrational perturbation theory (VPT2) treatment; the
inclusion of Fermi resonances through polyads; and the calculation of
anharmonic temperature band shifts and broadenings (including resonances)
through a Wang--Landau approach. We also suggest a simplified scheme to
calculate vibrational emission spectra that retains the essential
characteristics of the full IR cascade treatment and can directly transform low
temperature absorption spectra in IR cascade spectra. Additionally we show that
past astronomical models were in error in assuming a 15 cm correction
was needed to account for anharmonic emission effects
Low-energy Population III supernovae and the origin of extremely metal-poor stars
Some ancient, dim, metal-poor stars may have formed in the ashes of the first
supernovae (SNe). If their chemical abundances can be reconciled with the
elemental yields of specific Population III (Pop III) explosions, they could
reveal the properties of primordial stars. But multidimensional simulations of
such explosions are required to predict their yields because dynamical
instabilities can dredge material up from deep in the ejecta that would
otherwise be predicted to fall back on to the central remnant and be lost in
one-dimensional (1D) models. We have performed two-dimensional (2D) numerical
simulations of two low-energy Pop III SNe, a 12.4 Msun explosion and a 60 Msun
explosion, and find that they produce elemental yields that are a good fit to
those measured in the most iron-poor star discovered to date, SMSS
J031300.36-670839.3 (J031300). Fallback on to the compact remnant in these weak
explosions accounts for the lack of measurable iron in J031300 and its low
iron-group abundances in general. Our 2D explosions produce higher abundances
of heavy elements (atomic number Z > 20) than their 1D counterparts due to
dredge-up by fluid instabilities. Since almost no Ni is ejected by these weak
SNe, their low luminosities will prevent their detection in the near-infrared
with the James Webb Space Telescope and future 30-m telescopes on the ground.
The only evidence that they ever occurred will be in the fossil abundance
record.Comment: Accepted to MNRA
Thermal noise of whispering gallery resonators
By direct application of the fluctuation-dissipation theorem, we numerically
calculate the fundamental dimensional fluctuations of crystalline CaF2
whispering gallery resonators in the case of structural damping, and the limit
that this noise imposes on the frequency stability of such resonators at both
room and cryogenic temperatures. We analyze elasto-optic noise - the effect of
Brownian dimensional fluctuation on frequency via the strain-dependence of the
refractive index - a noise term that has so far not been considered for
whispering-gallery resonators. We find that dimensional fluctuation sets a
lower limit of 1E-16 to the Allan deviation for a 10-millimeter-radius sphere
at 5 K, predominantly via induced fluctuation of the refractive index.Comment: 7 pages, 3 figure
Laminations and 2-filling rays on infinite type surfaces
The loop graph of an infinite type surface is an infinite diameter hyperbolic
graph first studied in detail by Juliette Bavard. An important open problem in
the study of infinite type surfaces is to describe the boundary of the loop
graph as a space of geodesic laminations. We approach this problem by
constructing the first examples of 2-filling rays on infinite type surfaces.
Such rays accumulate onto geodesic laminations which are in some sense filling,
but without strong enough properties to correspond to points in the boundary of
the loop graph. We give multiple constructions using both a hands-on
combinatorial approach and an approach using train tracks and automorphisms of
flat surfaces. In addition, our approaches are sufficiently robust to describe
all 2-filling rays with certain other basic properties as well as to produce
uncountably many distinct mapping class group orbits.Comment: v2: minor update, 44 pages, 37 figure
Magnetic properties of iron pnictides from spin-spiral calculations
The wave-vector (q) and doping dependences of the magnetic energy, iron
moment, and effective exchange interactions in LaFeAsO, BaFe2As2, and SrFe2As2\
are studied by self-consistent LSDA calculations for co-planar spin spirals.
For the undoped compounds, the calculated total energy, E(q), reaches its
minimum at q corresponding to stripe anti-ferromagnetic order. In LaFeAsO, this
minimum becomes flat already at low levels of electron-doping and shifts to an
incommensurate q at delta=0.2, where delta is the number of additional
electrons (delta>0) or holes (delta<0) per Fe. In BaFe2As2 and SrFe2As2, stripe
order remains stable for hole doping down to delta=-0.3. Under electron doping,
on the other hand, the E(q) minimum shifts to incommensurate q already at
delta=0.1.Comment: 4 pages, 2 figures, International Conference on Magnetism, Karlsruhe,
July 26 - 31, 200
A Language and Hardware Independent Approach to Quantum-Classical Computing
Heterogeneous high-performance computing (HPC) systems offer novel
architectures which accelerate specific workloads through judicious use of
specialized coprocessors. A promising architectural approach for future
scientific computations is provided by heterogeneous HPC systems integrating
quantum processing units (QPUs). To this end, we present XACC (eXtreme-scale
ACCelerator) --- a programming model and software framework that enables
quantum acceleration within standard or HPC software workflows. XACC follows a
coprocessor machine model that is independent of the underlying quantum
computing hardware, thereby enabling quantum programs to be defined and
executed on a variety of QPUs types through a unified application programming
interface. Moreover, XACC defines a polymorphic low-level intermediate
representation, and an extensible compiler frontend that enables language
independent quantum programming, thus promoting integration and
interoperability across the quantum programming landscape. In this work we
define the software architecture enabling our hardware and language independent
approach, and demonstrate its usefulness across a range of quantum computing
models through illustrative examples involving the compilation and execution of
gate and annealing-based quantum programs
- …