709 research outputs found
Fragments of ML Decidable by Nested Data Class Memory Automata
The call-by-value language RML may be viewed as a canonical restriction of
Standard ML to ground-type references, augmented by a "bad variable" construct
in the sense of Reynolds. We consider the fragment of (finitary) RML terms of
order at most 1 with free variables of order at most 2, and identify two
subfragments of this for which we show observational equivalence to be
decidable. The first subfragment consists of those terms in which the
P-pointers in the game semantic representation are determined by the underlying
sequence of moves. The second subfragment consists of terms in which the
O-pointers of moves corresponding to free variables in the game semantic
representation are determined by the underlying moves. These results are shown
using a reduction to a form of automata over data words in which the data
values have a tree-structure, reflecting the tree-structure of the threads in
the game semantic plays. In addition we show that observational equivalence is
undecidable at every third- or higher-order type, every second-order type which
takes at least two first-order arguments, and every second-order type (of arity
greater than one) that has a first-order argument which is not the final
argument
Fast magnetoacoustic wave trains in magnetic funnels of the solar corona
Context: Fast magneto-acoustic waves are highly dispersive in waveguides, so they can generate quasi-periodic wave trains if a localised, impulsive driver is applied. Such wave trains have been observed in the solar corona and may be of use as a seismological tool since they depend upon the plasma structuring perpendicular to the direction of propagation.
Aims. We extend existing models of magnetoacoustic waveguides to consider the effects of an expanding magnetic field. The funnel geometry employed includes a field-aligned density structure.
Methods: We performed 2D numerical simulations of impulsively generated fast magneto-acoustic perturbations. The effects of the density contrast ratio, density stratification, and spectral profile of the driver upon the excited wave trains were investigated.
Results: The density structure acts as a dispersive waveguide for fast magneto-acoustic waves and generates a quasi-periodic wave train similar to previous models. The funnel geometry leads to generating additional wave trains that propagate outside the density structure. These newly discovered wave trains are formed by the leakage of transverse perturbations, but they propagate upwards owing to the refraction caused by the magnetic funnel.
Conclusions: The results of our funnel model may be applicable to wave trains observed propagating in the solar corona. They demonstrate similar properties to those found in our simulations
Three-dimensional numerical simulation of magnetohydrodynamic-gravity waves and vortices in the solar atmosphere
With the adaptation of the FLASH code we simulate magnetohydrodynamic-gravity
waves and vortices as well as their response in the magnetized
three-dimensional (3D) solar atmosphere at different heights to understand the
localized energy transport processes. In the solar atmosphere strongly
structured by gravitational and magnetic forces, we launch a localized velocity
pulse (in horizontal and vertical components) within a bottom layer of 3D solar
atmosphere modelled by initial VAL-IIIC conditions, which triggers waves and
vortices. The rotation direction of vortices depends on the orientation of an
initial perturbation. The vertical driver generates magnetoacoustic-gravity
waves which result in oscillations of the transition region, and it leads to
the eddies with their symmetry axis oriented vertically. The horizontal pulse
excites all magnetohydrodynamic-gravity waves and horizontally oriented eddies.
These waves propagate upwards, penetrate the transition region, and enter the
solar corona. In the high-beta plasma regions the magnetic field lines move
with the plasma and the temporal evolution show that they swirl with eddies. We
estimate the energy fluxes carried out by the waves in the magnetized solar
atmosphere and conclude that such wave dynamics and vortices may be significant
in transporting the energy to sufficiently balance the energy losses in the
localized corona. Moreover, the structure of the transition region highly
affects such energy transports, and causes the channelling of the propagating
waves into the inner corona.Comment: 11 Pages, 12 Figures, Accepted for the publication in MNRA
Numerical Simulations of Torsional Alfv\'en Waves in Axisymmetric Solar Magnetic Flux Tubes
We investigate numerically Alfv\'en waves propagating along an axisymmetric
and non-isothermal solar flux tube embedded in the solar atmosphere. The tube
magnetic field is current-free and diverges with height, and the waves are
excited by a periodic driver along the tube magnetic field lines. The main
results are that the two wave variables, the velocity and magnetic field
perturbations in the azimuthal direction, behave differently as a result of
gradients of physical parameters along the tube. To explain these differences
in the wave behavior, the time evolution of the wave variables and the
resulting cutoff period for each wave variable are calculated, and used to
determine regions in the solar chromosphere where strong wave reflection may
occur.Comment: Submitted to Solar Physics (accepted
Obstacles Faced by Latina Mothers of Children with Autism
The CDC’s most recent autism prevalence estimates document the continued trend of higher prevalence among non-Hispanic white children compared to Hispanic children. The disproportionate underrepresentation of Latino children in the health, education and service systems is measurable, disadvantaging the child and family. This quantitative study identifies support needs and obstacles experienced by 96 Latina mothers of children with autism, active in Spanish-language parent groups in California. Study measures included the Family Needs Survey and the Caring for My Child Survey. To determine the significance of the results on the Family Needs Survey, an item-by-item chi-square analysis compared results to those of to a similar population from a different study that used the same measure. A high proportion of mothers reported substantial levels of unmet needs in their role as primary caregiver using the Family Needs Survey: all 35 survey items were unmet for at least 50% of mothers; 28 items were common needs. The level and number of unmet needs of mothers in the present study in areas such as social support and care services were significantly greater than the comparison group. On the Caring for My Child Survey, mothers identified multiple barriers personally encountered in obtaining assistance for their children including psychosocial, economic, political, and healthcare factors. Findings are relevant to improve access for Latinos in the health, education and service systems, and to establish a baseline for comparison
Game semantic analysis of equivalence in IMJ
Using game semantics, we investigate the problem of verifying contextual equivalences in Interface Middleweight Java (IMJ), an imperative object calculus in which program phrases are typed using interfaces. Working in the setting where data types are non-recursive and restricted to finite domains, we identify the frontier between decidability and undecidability by reference to the structure of interfaces present in typing judgments. In particular, we show how to determine the decidability status of problem instances (over a fixed type signature) by examining the position of methods inside the term type and the types of its free identifiers. Our results build upon the recent fully abstract game semantics of IMJ. Decidability is proved by translation into visibly pushdown register automata over infinite alphabets with fresh-input recognition
- …