Adjoint computations by algorithmic differentiation of a parallel solver for time-dependent PDEs

A computational fluid dynamics code is differentiated using algorithmic differentiation (AD) in both tangent and adjoint modes. The two novelties of the present approach are 1) the adjoint code is obtained by letting the AD tool Tapenade invert the complete layer of message passing interface (MPI) communications, and 2) the adjoint code integrates time-dependent, non-linear and dissipative (hence physically irreversible) PDEs with an explicit time integration loop running for ca. $10^{6}$ time steps. The approach relies on using the Adjoinable MPI library to reverse the non-blocking communication patterns in the original code, and by controlling the memory overhead induced by the time-stepping loop with binomial checkpointing. A description of the necessary code modifications is provided along with the validation of the computed derivatives and a performance comparison of the tangent and adjoint codes.Comment: Submitted to Journal of Computational Scienc

Pulse Dynamics in a Chain of Granules With Friction

We study the dynamics of a pulse in a chain of granules with friction. We present theories for chains of cylindrical granules (Hertz potential with exponent $n=2$) and of granules with other geometries ($n>2$). Our results are supported via numerical simulations for cylindrical and for spherical granules ($n=5/2$).Comment: Submitted to PR

Evidence for a Photospheric Component in the Prompt Emission of the Short GRB120323A and its Effects on the GRB Hardness-Luminosity Relation

The short GRB 120323A had the highest flux ever detected with the Fermi/GBM. Here we study its remarkable spectral properties and their evolution using two spectral models: (i) a single emission component scenario, where the spectrum is modeled by the empirical Band function, and (ii) a two component scenario, where thermal (Planck-like) emission is observed simultaneously with a non-thermal component (a Band function). We find that the latter model fits the integrated burst spectrum significantly better than the former, and that their respective spectral parameters are dramatically different: when fit with a Band function only, the Epeak of the event is unusually soft for a short GRB, while adding a thermal component leads to more typical short GRB values. Our time-resolved spectral analysis produces similar results. We argue here that the two-component model is the preferred interpretation for GRB 120323A, based on: (i) the values and evolution of the Band function parameters of the two component scenario, which are more typical for a short GRB, and (ii) the appearance in the data of a significant hardness-intensity correlation, commonly found in GRBs, when we employee two-component model fits; the correlation is non-existent in the Band-only fits. GRB 110721A, a long burst with an intense photospheric emission, exhibits the exact same behavior. We conclude that GRB 120323A has a strong photospheric emission contribution, first time observed in a short GRB. Magnetic dissipation models are difficult to reconcile with these results, which instead favor photospheric thermal emission and fast cooling synchrotron radiation from internal shocks. Finally, we derive a possibly universal hardness-luminosity relation in the source frame using a larger set of GRBs L,i=(1.59+/-0.84).10^50 (Epeak,i)^(1.33+/-0.07) erg/s), which could be used as a possible redshift estimator for cosmology.Comment: 27 pages, 13 figures, Accepted by ApJ (April, 7th 2013

How universal is the fractional-quantum-Hall edge Luttinger liquid?

This article reports on our microscopic investigations of the edge of the fractional quantum Hall state at filling factor $\nu=1/3$. We show that the interaction dependence of the wave function is well described in an approximation that includes mixing with higher composite-fermion Landau levels in the lowest order. We then proceed to calculate the equal time edge Green function, which provides evidence that the Luttinger exponent characterizing the decay of the Green function at long distances is interaction dependent. The relevance of this result to tunneling experiments is discussed.Comment: 5 page

Development of Flutter Constraints for High-fidelity Aerostructural Optimization

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143080/1/6.2017-4455.pd

Infant exposure to Fluvoxamine through placenta and human milk: a case series - A contribution from the ConcePTION project [case report].

INTRODUCTION Fluvoxamine is widely used to treat depression during pregnancy and lactation. However, limited data are available on its transfer to the fetus or in human milk. This case series provides additional information on the infant exposure to fluvoxamine during pregnancy and lactation. CASE PRESENTATION Two women, aged 38 and 34 years, diagnosed with depression were treated with 50 mg fluvoxamine during pregnancy and lactation. At delivery a paired maternal and cord blood sample was collected for each woman. The first mother exclusively breastfed her child for 4 months and gave one foremilk and one hindmilk sample at 2 days and 4 weeks post-partum, whereas the second mother did not breastfeed. RESULTS The cord to plasma concentration ratios were 0.62 and 0.48, respectively. At 2 weeks post-partum, relative infant doses (RID) were 0.47 and 0.57% based on fluvoxamine concentrations in foremilk and hindmilk, respectively. At 4 weeks post-partum, the RIDs were 0.35 and 0.90%, respectively. The child from the first mother was born healthy and showed a normal development at the 6th, 18th and 36th month follow-ups. One of the twins from the second woman was hospitalized for hypoglycemia that was attributed to gestational diabetes and low birth weight. The second one was born healthy. CONCLUSION These results suggest a minimal exposure to fluvoxamine during lactation which is in accordance with previously published data. Larger clinical and pharmacokinetic studies assessing the long-term safety of this drug during lactation and the variability of its exposure through breastmilk are warranted

Aerostructural design optimization of a 100-passenger regional jet with surrogate-based mission analysis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106481/1/AIAA2013-4372.pd

LOW-Γ JETS from COMPACT STELLAR MERGERS: CANDIDATE ELECTROMAGNETIC COUNTERPARTS to GRAVITATIONAL WAVE SOURCES

The American Astronomical Society. All rights reserved.Short gamma-ray bursts (GRBs) are believed to be produced by relativistic jets from mergers of neutron stars (NSs) or NSs and black-holes (BHs). If the Lorentz-factors Γ of jets from compact stellar mergers follow a similar power-law distribution to those observed for other high-energy astrophysical phenomena (e.g., blazars, active galactic nuclei), the population of jets should be dominated by low-Γ outflows. These jets will not produce prompt gamma-rays, but jet energy will be released as X-ray/optical/radio transients when they collide with the ambient medium. Using Monte Carlo simulations, we study the properties of such transients. Approximately 78% of merger jets Mpc result in failed GRBs if the jet Γ follows a power-law distribution of index -1.75. X-ray/optical transients from failed GRBs will have broad distributions of their characteristics: light-curves peak tp ∼ 0.1-10 days after a merger; flux peaks for X-ray 10-6 mJy ≲ Fx ≲ 10-2 mJy; and optical flux peaks at 14 ≲ mg ≲ 22. X-ray transients are detectable by Swift XRT, and ∼85% of optical transients will be detectable by telescopes with limiting magnitude mg ≳ 21, for well localized sources on the sky. X-ray/optical transients are followed by radio transients with peak times narrowly clustered around tp ∼ 10 days, and peak flux of ∼10-100 mJy at 10 GHz and ∼0.1 mJy at 150 MHz. By considering the all-sky rate of short GRBs within the LIGO/Virgo range, the rate of on-axis orphan afterglows from failed GRBs should be 2.6(26) per year for NS-NS(NS-BH) mergers, respectively. Since merger jets from gravitational-wave (GW) trigger events tend to be directed to us, a significant fraction of GW events could be associated with the on-axis orphan afterglow