3,820 research outputs found
The use of COSMIC NASTRAN in an integrated conceptual design environment
Changes in both software and hardware are rapidly bringing conceptual engineering tools like finite element analysis into mainstream mechanical design. Systems that integrate all phases of the manufacturing process provide the most cost benefits. The application of programming concepts like object oriented programming allow for the encapsulation of intelligent data within the design geometry. This combined with declining cost in per seat hardware bring new alternatives to the user
Quantum dynamics of thermalizing systems
We introduce a method "DMT" for approximating density operators of 1D systems
that, when combined with a standard framework for time evolution (TEBD), makes
possible simulation of the dynamics of strongly thermalizing systems to
arbitrary times. We demonstrate that the method performs well for both
near-equilibrium initial states (Gibbs states with spatially varying
temperatures) and far-from-equilibrium initial states, including quenches
across phase transitions and pure states
Combining galaxy and 21cm surveys
Acoustic waves traveling through the early Universe imprint a characteristic
scale in the clustering of galaxies, QSOs and inter-galactic gas. This scale
can be used as a standard ruler to map the expansion history of the Universe, a
technique known as Baryon Acoustic Oscillations (BAO). BAO offer a
high-precision, low-systematics means of constraining our cosmological model.
The statistical power of BAO measurements can be improved if the `smearing' of
the acoustic feature by non-linear structure formation is undone in a process
known as reconstruction. In this paper we use low-order Lagrangian perturbation
theory to study the ability of cm experiments to perform reconstruction
and how augmenting these surveys with galaxy redshift surveys at relatively low
number densities can improve performance. We find that the critical number
density which must be achieved in order to benefit cm surveys is set by
the linear theory power spectrum near its peak, and corresponds to densities
achievable by upcoming surveys of emission line galaxies such as eBOSS and
DESI. As part of this work we analyze reconstruction within the framework of
Lagrangian perturbation theory with local Lagrangian bias, redshift-space
distortions, -dependent noise and anisotropic filtering schemes.Comment: 10 pages, final version to appear in MNRAS, helpful suggestions from
referee and others include
Light converts endosymbiotic fungus to pathogen, influencing seedling survival and host tree recruitment
Endophytic fungi that asymptomatically colonize plants^1^ are diverse and abundant in tropical ecosystems^2^. These organisms can be weakly pathogenic^3^ and/or mutualistic, frequently enabling plants to adapt to extreme environments, alter competitive abilities of host individuals and improve host fitness under abiotic or biotic stresses^4,5,6^. _Diplodia mutila_ is a symbiotic endophyte/plant pathogenic fungus infecting the palm _Iriartea deltoidea_^7^, which dominates many wet lowland Neotropical forests. The fungus is an asymptomatic endophyte in mature plants, and disease and mortality are expressed in some seedlings, while others remain disease free. Here we show that seedlings bearing the endophyte show enhanced resistance to insect herbivory. However, high light availability triggers pathogenicity of the fungus, while low light favors endosymbiotic development, constraining recruitment of endophyte-infested seedlings to the shaded understory by limiting survival of seedlings in direct light. These results provide evidence that patterns of plant abundance and the mechanisms maintaining tropical forest biodiversity are the result of a more complex interplay between abiotic and biotic environments than previously thought
Quantum engine based on many-body localization
Many-body-localized (MBL) systems do not thermalize under their intrinsic dynamics. The athermality of MBL, we propose, can be harnessed for thermodynamic tasks. We illustrate this ability by formulating an Otto engine cycle for a quantum many-body system. The system is ramped between a strongly localized MBL regime and a thermal (or weakly localized) regime. The difference between the energy-level correlations of MBL systems and of thermal systems enables mesoscale engines to run in parallel in the thermodynamic limit, enhances the engine's reliability, and suppresses worst-case trials. We estimate analytically and calculate numerically the engine's efficiency and per-cycle power. The efficiency mirrors the efficiency of the conventional thermodynamic Otto engine. The per-cycle power scales linearly with the system size and inverse-exponentially with a localization length. This work introduces a thermodynamic lens onto MBL, which, having been studied much recently, can now be considered for use in thermodynamic tasks
Cosmology without cosmic variance
We examine the improvements in constraints on the linear growth factor G and
its derivative f=d ln G / dln a that are available from the combination of a
large-scale galaxy redshift survey with a weak gravitational lensing survey of
background sources. In the linear perturbation theory limit, the
bias-modulation method of McDonald & Seljak allows one to distinguish the
real-space galaxy clustering from the peculiar velocity signal in each Fourier
mode. The ratio of lensing signal to galaxy clustering in transverse modes
yields the bias factor b of each galaxy subset (as per Pen 2004), hence
calibrating the conversion from galaxy real-space density to matter density in
every mode. In combination these techniques permit measure of the growth rate f
in each Fourier mode. This yields a measure of the growth rate free of sample
variance, i.e. the uncertainty in f can be reduced without bound by increasing
the number of redshifts within a finite volume. In practice, the gain from the
absence of sample variance is bounded by the limited range of bias modulation
among dark-matter halos. Nonetheless, the addition of background weak lensing
data to a redshift survey increases information on G and f by an amount
equivalent to a 10-fold increase in the volume of a standard redshift-space
distortion measurement---if the lensing signal can be measured to sub-percent
accuracy. This argues that a combined lensing and redshift survey over a common
low-redshift volume is a more powerful test of general relativity than an
isolated redshift survey over larger volume at high redshift. An example case
is that a survey of ~10^6 redshifts over half the sky in the redshift range
can determine the growth exponent \gamma for the model
to an accuracy of , using only modes with
k<0.1h/Mpc, but only if a weak lensing survey is conducted in concert.
[Abridged]Comment: 9 pages, 3 figures, accepted by MNRAS, minor changes to match the
accepted versio
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