50,828 research outputs found
Estimating Fiscal Multipliers: News From A Non-linear World
open4siCaggiano acknowledges the financial support received by the Visiting Research Scholar programme offered by the University of MelbourneWe estimate non-linear VARs to assess to what extent fiscal spending multipliers are countercyclical in the US. We deal with the issue of non-fundamentalness due to fiscal foresight by appealing to sums of revisions of expectations of fiscal expenditures. This measure of anticipated fiscal shocks is shown to carry valuable information about future dynamics of public spending. Results based on generalised impulse responses suggest that fiscal spending multipliers in recessions are greater than one, but not statistically larger than those in expansions. However, non-linearities arise when focusing on 'extreme' events, that is, deep recessions versus strong expansionary periods.openCaggiano, Giovanni; Castelnuovo, Efrem; Colombo, Valentina; Nodari, GabrielaCaggiano, Giovanni; Castelnuovo, Efrem; Colombo, Valentina; Nodari, Gabriel
Assessment of thermal instabilities and oscillations in multifinger heterojunction bipolar transistors through a harmonic-balance-based CAD-oriented dynamic stability analysis technique
We present a novel analysis of thermal instabilities and oscillations in multifinger heterojunction bipolar transistors (HBTs), based on a harmonic-balance computer-aided-design (CAD)-oriented approach to the dynamic stability assessment. The stability analysis is carried out in time-periodic dynamic conditions by calculating the Floquet multipliers of the limit cycle representing the HBT working point. Such a computation is performed directly in the frequency domain, on the basis of the Jacobian of the harmonic-balance problem yielding the limit cycle. The corresponding stability assessment is rigorous, and the efficient calculation method makes it readily implementable in CAD tools, thus allowing for circuit and device optimization. Results on three- and four-finger layouts are presented, including closed-form oscillation criteria for two-finger device
Scale Dependence of Multiplier Distributions for Particle Concentration, Enstrophy and Dissipation in the Inertial Range of Homogeneous Turbulence
Turbulent flows preferentially concentrate inertial particles depending on
their stopping time or Stokes number, which can lead to significant spatial
variations in the particle concentration. Cascade models are one way to
describe this process in statistical terms. Here, we use a direct numerical
simulation (DNS) dataset of homogeneous, isotropic turbulence to determine
probability distribution functions (PDFs) for cascade multipliers, which
determine the ratio by which a property is partitioned into sub-volumes as an
eddy is envisioned to decay into smaller eddies. We present a technique for
correcting effects of small particle numbers in the statistics. We determine
multiplier PDFs for particle number, flow dissipation, and enstrophy, all of
which are shown to be scale dependent. However, the particle multiplier PDFs
collapse when scaled with an appropriately defined local Stokes number. As
anticipated from earlier works, dissipation and enstrophy multiplier PDFs reach
an asymptote for sufficiently small spatial scales. From the DNS measurements,
we derive a cascade model that is used it to make predictions for the radial
distribution function (RDF) for arbitrarily high Reynolds numbers, ,
finding good agreement with the asymptotic, infinite inertial range theory
of Zaichik and Alipchenkov [New Journal of Physics 11, 103018 (2009)]. We
discuss implications of these results for the statistical modeling of the
turbulent clustering process in the inertial range for high Reynolds numbers
inaccessible to numerical simulations.Comment: 21 pages, 14 figures, accepted for publication in Physical Review
A Scalable Correlator Architecture Based on Modular FPGA Hardware, Reuseable Gateware, and Data Packetization
A new generation of radio telescopes is achieving unprecedented levels of
sensitivity and resolution, as well as increased agility and field-of-view, by
employing high-performance digital signal processing hardware to phase and
correlate large numbers of antennas. The computational demands of these imaging
systems scale in proportion to BMN^2, where B is the signal bandwidth, M is the
number of independent beams, and N is the number of antennas. The
specifications of many new arrays lead to demands in excess of tens of PetaOps
per second.
To meet this challenge, we have developed a general purpose correlator
architecture using standard 10-Gbit Ethernet switches to pass data between
flexible hardware modules containing Field Programmable Gate Array (FPGA)
chips. These chips are programmed using open-source signal processing libraries
we have developed to be flexible, scalable, and chip-independent. This work
reduces the time and cost of implementing a wide range of signal processing
systems, with correlators foremost among them,and facilitates upgrading to new
generations of processing technology. We present several correlator
deployments, including a 16-antenna, 200-MHz bandwidth, 4-bit, full Stokes
parameter application deployed on the Precision Array for Probing the Epoch of
Reionization.Comment: Accepted to Publications of the Astronomy Society of the Pacific. 31
pages. v2: corrected typo, v3: corrected Fig. 1
Integrated structural analysis tool using linear matching method part 1 : Software development
A number of direct methods based upon the Linear Matching Method (LMM) framework have been developed to address structural integrity issues for components subjected to cyclic thermal and mechanical load conditions. This paper presents a new integrated structural analysis tool using the LMM framework for the assessment of load carrying capacity, shakedown limit, ratchet limit and steady state cyclic response of structures. First, the development of the LMM for the evaluation of design limits in plasticity is introduced. Second, preliminary considerations for the development of the LMM into a tool which can be used on a regular basis by engineers are discussed. After the re-structuring of the LMM subroutines for multiple CPU solution, the LMM software tool for the assessment of design limits in plasticity is implemented by developing an Abaqus CAE plug-Âin with graphical user interfaces. Further demonstration of this new LMM analysis tool including practical application and verification is presented in an accompanying paper
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