38 research outputs found
Bosonic Qiskit
The practical benefits of hybrid quantum information processing hardware that
contains continuous-variable objects (bosonic modes such as mechanical or
electromagnetic oscillators) in addition to traditional (discrete-variable)
qubits have recently been demonstrated by experiments with bosonic codes that
reach the break-even point for quantum error correction and by efficient
Gaussian boson sampling simulation of the Franck-Condon spectra of triatomic
molecules that is well beyond the capabilities of current qubit-only hardware.
The goal of this Co-design Center for Quantum Advantage (C2QA) project is to
develop an instruction set architecture (ISA) for hybrid qubit/bosonic mode
systems that contains an inventory of the fundamental operations and
measurements that are possible in such hardware. The corresponding abstract
machine model (AMM) would also contain a description of the appropriate error
models associated with the gates, measurements and time evolution of the
hardware. This information has been implemented as an extension of Qiskit.
Qiskit is an opensource software development toolkit (SDK) for simulating the
quantum state of a quantum circuit on a system with Python 3.7+ and for running
the same circuits on prototype hardware within the IBM Quantum Lab. We
introduce the Bosonic Qiskit software to enable the simulation of hybrid
qubit/bosonic systems using the existing Qiskit software development kit. This
implementation can be used for simulating new hybrid systems, verifying
proposed physical systems, and modeling systems larger than can currently be
constructed. We also cover tutorials and example use cases included within the
software to study Jaynes- Cummings models, bosonic Hubbard models, plotting
Wigner functions and animations, and calculating maximum likelihood estimations
using Wigner functions
An X-ray Mini-survey of Nearby Edge-on Starburst Galaxies II. The Question of Metal Abundance
(abbreviated) We have undertaken an X-ray survey of a far-infrared flux
limited sample of seven nearby edge-on starburst galaxies. Here, we examine the
two X-ray-brightest sample members NGC 253 and M 82 in a self-consistent
manner, taking account of the spatial distribution of the X-ray emission in
choosing our spectral models. There is significant X-ray absorption in the disk
of NGC 253. When this is accounted for we find that multi-temperature thermal
plasma models with significant underlying soft X-ray absorption are more
consistent with the imaging data than single-temperature models with highly
subsolar abundances or models with minimal absorption and non-equilibrium
thermal ionization conditions. Our models do not require absolute abundances
that are inconsistent with solar values or unusually supersolar ratios of the
alpha-burning elements with respect to Fe (as claimed previously). We conclude
that with current data, the technique of measuring abundances in starburst
galaxies via X-ray spectral modeling is highly uncertain.
Based on the point-like nature of much of the X-ray emission in the PSPC
hard-band image of NGC 253, we suggest that a significant fraction of the
``extended'' X-ray emission in the 3-10 keV band seen along the disk of the
galaxy with ASCA and BeppoSAX (Cappi et al.) is comprised of discrete sources
in the disk, as opposed to purely diffuse, hot gas. This could explain the low
Fe abundances of ~1/4 solar derived for pure thermal models.Comment: (accepted for publication in the Astrophysical Journal
Improved parametrization of Antarctic krill target strength models
Author Posting. © Acoustical Society of America, 2006. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 119 (2006): 232-242, doi:10.1121/1.2141229.There are historical discrepancies between empirical observations of Antarctic krill target strength and predictions using theoretical scattering models. These differences are addressed through improved understanding of key model parameters. The scattering process was modeled using the distorted-wave Born approximation, representing the shape of the animal as a bent and tapered cylinder. Recently published length-based regressions were used to constrain the sound speed and density contrasts between the animal and the surrounding seawater, rather than the earlier approach of using single values for all lengths. To constrain the parameter governing the orientation of the animal relative to the incident acoustic wave, direct measurements of the orientation of krill in situ were made with a video plankton recorder. In contrast to previous indirect and aquarium-based observations, krill were observed to orient themselves mostly horizontally. Averaging predicted scattering over the measured distribution of orientations resulted in predictions of target strength consistent with in situ measurements of target strength of large krill (mean length 40â43 mm) at four frequencies (43â420 kHz), but smaller than expected under the semi-empirical model traditionally used to estimate krill target strength.This project was
supported by NSF U.S. Antarctic Program Grant No. OPP-9910307. G. Lawson was supported by an Office of Naval
Research Graduate Traineeship Award in Ocean Acoustics (Grant No. N000 14-03-1-0212), a Fulbright Scholarship, a
Natural Sciences and Engineering Research Council of Canada Post-Graduate Scholarship, and the Woods Hole
Oceanographic Institution Academic Programs Office
Interdisciplinary study of warm core ring physics, chemistry, and biology
We are conducting an interdisciplinary study of the structure and
dynamics of Gulf Stream \Warm Core Rings by a time series investigation of
selected rings. This program consists of highly integrated components
which include physical, chemical, and biological investigation and
modeling studies. These components are designed to provide information
on the structure of rings and exchange mechanisms at ring boundaries, on their marine chemistry, and on the environmental controls of biological
activity of selected constituents associated with Warm Core Rings. This
research is being conducted by approximately two dozen investigators from
thirteen marine institutions. An interdisciplinary program of the scope
proposed is required in order to understand the interdependence among
biological, chemical, and physical processes in the ocean. This study of
the structure and evolution of Warm Core Rings will enhance the understanding
of fundamental oceanic processes and the role of rings in the
region where they occur
Sound scattering by several zooplankton groups. II. Scattering models
Author Posting. © Acoustical Society of America, 1998. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 103 (1998): 236-253, doi:10.1121/1.421110.Mathematical scattering models are derived and compared with data from zooplankton from several gross anatomical groupsâfluidlike, elastic shelled, and gas bearing. The models are based upon the acoustically inferred boundary conditions determined from laboratory backscattering data presented in part I of this series [Stanton et al., J. Acoust. Soc. Am. 103, 225â235 (1998)]. The models use a combination of ray theory, modal-series solution, and distorted wave Born approximation (DWBA). The formulations, which are inherently approximate, are designed to include only the dominant scattering mechanisms as determined from the experiments. The models for the fluidlike animals (euphausiids in this case) ranged from the simplest case involving two rays, which could qualitatively describe the structure of target strength versus frequency for single pings, to the most complex case involving a rough inhomogeneous asymmetrically tapered bent cylinder using the DWBA-based formulation which could predict echo levels over all angles of incidence (including the difficult region of end-on incidence). The model for the elastic shelled body (gastropods in this case) involved development of an analytical model which takes into account irregularities and discontinuities of the shell. The model for gas-bearing animals (siphonophores) is a hybrid model which is composed of the summation of the exact solution to the gas sphere and the approximate DWBA-based formulation for arbitrarily shaped fluidlike bodies. There is also a simplified ray-based model for the siphonophore. The models are applied to data involving single pings, ping-to-ping variability, and echoes averaged over many pings. There is reasonable qualitative agreement between the predictions and single ping data, and reasonable quantitative agreement between the predictions and variability and averages of echo data.This
work was supported by the National Science Foundation
Grant No. OCE-9201264, the U.S. Office of Naval Research
Grant Nos. N00014-89-J-1729, N00014-95-1-0287, and
N00014-94-1-0452, and the MIT/WHOI Joint Graduate Education
Program
Tracing river chemistry in space and time : dissolved inorganic constituents of the Fraser River, Canada
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 124 (2014): 283-308, doi:10.1016/j.gca.2013.09.006.The Fraser River basin in southwestern Canada bears unique geologic and climatic features which make it an ideal setting for investigating the origins, transformations and delivery to the coast of dissolved riverine loads under relatively pristine conditions. We present results from sampling campaigns over three years which demonstrate the lithologic and hydrologic controls on fluxes and isotope compositions of major dissolved inorganic runoff constituents (dissolved nutrients, major and trace elements, 87Sr/86Sr, ÎŽD). A time series record near the Fraser mouth allows us to generate new estimates of discharge-weighted concentrations and fluxes, and an overall chemical weathering rate of 32 t km-2 y-1. The seasonal variations in dissolved inorganic species are driven by changes in hydrology, which vary in timing across the basin. The time series record of dissolved 87Sr/86Sr is of particular interest, as a consistent shift between higher (âmore radiogenicâ) values during spring and summer and less radiogenic values in fall and winter demonstrates the seasonal variability in source contributions throughout the basin. This seasonal shift is also quite large (0.709 â 0.714), with a discharge-weighted annual average of 0.7120 (2 s.d. = 0.0003). We present a mixing model which predicts the seasonal evolution of dissolved 87Sr/86Sr based on tributary compositions and water discharge. This model highlights the importance of chemical weathering fluxes from the old sedimentary bedrock of headwater drainage regions, despite their relatively small contribution to the total water flux.This work was supported by the WHOI Academic Programs Office and MIT PAOC Houghton Fund to BMV, a WHOI Arctic Research Initiative grant to ZAW, NSF-ETBC grant OCE-0851015 to BPE and TIE, and NSF grant EAR-1226818 to BPE
A haplotype map of allohexaploid wheat reveals distinct patterns of selection on homoeologous genomes
BACKGROUND: Bread wheat is an allopolyploid species with a large, highly repetitive genome. To investigate the impact of selection on variants distributed among homoeologous wheat genomes and to build a foundation for understanding genotype-phenotype relationships, we performed population-scale re-sequencing of a diverse panel of wheat lines. RESULTS: A sample of 62 diverse lines was re-sequenced using the whole exome capture and genotyping-by-sequencing approaches. We describe the allele frequency, functional significance, and chromosomal distribution of 1.57 million single nucleotide polymorphisms and 161,719 small indels. Our results suggest that duplicated homoeologous genes are under purifying selection. We find contrasting patterns of variation and inter-variant associations among wheat genomes; this, in addition to demographic factors, could be explained by differences in the effect of directional selection on duplicated homoeologs. Only a small fraction of the homoeologous regions harboring selected variants overlapped among the wheat genomes in any given wheat line. These selected regions are enriched for loci associated with agronomic traits detected in genome-wide association studies. CONCLUSIONS: Evidence suggests that directional selection in allopolyploids rarely acted on multiple parallel advantageous mutations across homoeologous regions, likely indicating that a fitness benefit could be obtained by a mutation at any one of the homoeologs. Additional advantageous variants in other homoelogs probably either contributed little benefit, or were unavailable in populations subjected to directional selection. We hypothesize that allopolyploidy may have increased the likelihood of beneficial allele recovery by broadening the set of possible selection targets
Sustainable and Equitable Increases in Fruit and Vegetable Productivity and Consumption are Needed to Achieve Global Nutrition Security
Increased intake of fruits and vegetables (F&V) is recommended for most populations across the globe. However, the current state of global and regional food systems is such that F&V availability, the production required to sustain them, and consumer food choices are all severely deficient to meet this need. Given the critical state of public health and nutrition worldwide, as well as the fragility of the ecological systems and resources on which they rely, there is a great need for research, investment, and innovation in F&V systems to nourish our global population. Here, we review the challenges that must be addressed in order to expand production and consumption of F&V sustainably and on a global scale. At the conclusion of the workshop, the gathered participants drafted the âAspen/Keystone Declarationâ (see below), which announces the formation of a new âCommunity of Practice,â whose area of work is described in this position paper. The need for this work is based on a series of premises discussed in detail at the workshop and summarized herein. To surmount these challenges, opportunities are presented for growth and innovation in F&V food systems. The paper is organized into five sections based on primary points of intervention in global F&V systems: (1) research and development, (2) information needs to better inform policy & investment, (3) production (farmers, farming practices, and supply), (4) consumption (availability, access, and demand), and (5) sustainable & equitable F&V food systems and supply chains
Behavior of Weak Polyelectrolyte Brushes in Mixed Salt Solutions
Hydrophilic
and hydrophobic weak polybasic brushes immersed in
aqueous solutions of mixed salt counterions are considered using a
mean-field numerical self-consistent field approach. On top of the
solvent quality of the polymer, the counterionâsolvent interactions
are accounted for by implementing FloryâHuggins interaction
parameters. We show that ion specificity within the brush can bring
about large changes in conformation. It is found that the collapse
transition of hydrophobic, weak polyelectrolyte brushes features an
intermediate two-phase state wherein a subset of chains are collapsed
in a dense layer at the substrate, while the remainder of chains are
well-solvated and strongly stretched away from the it. Besides pH
and ionic strength, solvent quality of counterions and the composition
of ions in the solvent are important control parameters for the behavior
of polyelectrolyte brushes. Increasingly hydrophobic counterions penetrate
deeper within the brush and stabilize the collapsed region, while
hydrophilic counterions do the opposite