4,854 research outputs found
Validation and Benchmarking of a Practical Free Magnetic Energy and Relative Magnetic Helicity Budget Calculation in Solar Magnetic Structures
In earlier works we introduced and tested a nonlinear force-free (NLFF)
method designed to self-consistently calculate the free magnetic energy and the
relative magnetic helicity budgets of the corona of observed solar magnetic
structures. The method requires, in principle, only a single, photospheric or
low-chromospheric, vector magnetogram of a quiet-Sun patch or an active region
and performs calculations in the absence of three-dimensional magnetic and
velocity-field information. In this work we strictly validate this method using
three-dimensional coronal magnetic fields. Benchmarking employs both synthetic,
three-dimensional magnetohydrodynamic simulations and nonlinear force-free
field extrapolations of the active-region solar corona. We find that our
time-efficient NLFF method provides budgets that differ from those of more
demanding semi-analytical methods by a factor of ~3, at most. This difference
is expected from the physical concept and the construction of the method.
Temporal correlations show more discrepancies that, however, are soundly
improved for more complex, massive active regions, reaching correlation
coefficients of the order of, or exceeding, 0.9. In conclusion, we argue that
our NLFF method can be reliably used for a routine and fast calculation of free
magnetic energy and relative magnetic helicity budgets in targeted parts of the
solar magnetized corona. As explained here and in previous works, this is an
asset that can lead to valuable insight into the physics and the triggering of
solar eruptions.Comment: 32 pages, 14 figures, accepted by Solar Physic
Hypernuclear No-Core Shell Model
We extend the No-Core Shell Model (NCSM) methodology to incorporate
strangeness degrees of freedom and apply it to single- hypernuclei.
After discussing the transformation of the hyperon-nucleon (YN) interaction
into Harmonic-Oscillator (HO) basis and the Similarity Renormalization Group
transformation applied to it to improve model-space convergence, we present two
complementary formulations of the NCSM, one that uses relative Jacobi
coordinates and symmetry-adapted basis states to fully exploit the symmetries
of the hypernuclear Hamiltonian, and one working in a Slater determinant basis
of HO states where antisymmetrization and computation of matrix elements is
simple and to which an importance-truncation scheme can be applied. For the
Jacobi-coordinate formulation, we give an iterative procedure for the
construction of the antisymmetric basis for arbitrary particle number and
present the formulae used to embed two- and three-baryon interactions into the
many-body space. For the Slater-determinant formulation, we discuss the
conversion of the YN interaction matrix elements from relative to
single-particle coordinates, the importance-truncation scheme that tailors the
model space to the description of the low-lying spectrum, and the role of the
redundant center-of-mass degrees of freedom. We conclude with a validation of
both formulations in the four-body system, giving converged ground-state
energies for a chiral Hamiltonian, and present a short survey of the
hyper-helium isotopes.Comment: 17 pages, 8 figures; accepted versio
Agent-based modeling: a systematic assessment of use cases and requirements for enhancing pharmaceutical research and development productivity.
A crisis continues to brew within the pharmaceutical research and development (R&D) enterprise: productivity continues declining as costs rise, despite ongoing, often dramatic scientific and technical advances. To reverse this trend, we offer various suggestions for both the expansion and broader adoption of modeling and simulation (M&S) methods. We suggest strategies and scenarios intended to enable new M&S use cases that directly engage R&D knowledge generation and build actionable mechanistic insight, thereby opening the door to enhanced productivity. What M&S requirements must be satisfied to access and open the door, and begin reversing the productivity decline? Can current methods and tools fulfill the requirements, or are new methods necessary? We draw on the relevant, recent literature to provide and explore answers. In so doing, we identify essential, key roles for agent-based and other methods. We assemble a list of requirements necessary for M&S to meet the diverse needs distilled from a collection of research, review, and opinion articles. We argue that to realize its full potential, M&S should be actualized within a larger information technology framework--a dynamic knowledge repository--wherein models of various types execute, evolve, and increase in accuracy over time. We offer some details of the issues that must be addressed for such a repository to accrue the capabilities needed to reverse the productivity decline
Validating Animal Models
This paper responds to a recent challenge for the validity of extrapolation of neurobiological knowledge from laboratory animals to humans. According to this challenge, experimental neurobiology, and thus neuroscience, is in a state of crisis because the knowledge produced in different laboratories hardly generalizes from one laboratory to another. Presumably, this is so because neurobiological laboratories use simplified animal models of human conditions that differ across laboratories. By contrast, I argue that maintaining a multiplicity of experimental protocols and simple models is well justified. It fosters rather than precludes the validity of extrapolation of neurobiological knowledge. The discipline is thriving
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