3,034 research outputs found
Asymmetric dynamics and critical behavior in the Bak-Sneppen model
We investigate, using mean-field theory and simulation, the effect of
asymmetry on the critical behavior and probability density of Bak-Sneppen
models. Two kinds of anisotropy are investigated: (i) different numbers of
sites to the left and right of the central (minimum) site are updated and (ii)
sites to the left and right of the central site are renewed in different ways.
Of particular interest is the crossover from symmetric to asymmetric scaling
for weakly asymmetric dynamics, and the collapse of data with different numbers
of updated sites but the same degree of asymmetry. All non-symmetric rules
studied fall, independent of the degree of asymmetry, in the same universality
class. Conversely, symmetric variants reproduce the exponents of the original
model. Our results confirm the existence of two symmetry-based universality
classes for extremal dynamics.Comment: 14 pages, 8 figures, 1 tabl
Static Computation and Reflection
Thesis (PhD) - Indiana University, Computer Sciences, 2008Most programming languages do not allow programs to inspect their
static type information or perform computations on it. C++, however,
lets programmers write template metaprograms, which enable programs to
encode static information, perform compile-time computations,
and make static decisions about run-time behavior. Many C++ libraries
and applications use template metaprogramming to build specialized
abstraction mechanisms, implement domain-specific safety checks, and
improve run-time performance.
Template metaprogramming is an emergent capability of the C++ type
system, and the C++ language specification is informal and imprecise.
As a result, template metaprogramming often involves heroic
programming feats and often leads to code that is difficult to read and
maintain. Furthermore, many template-based code generation and
optimization techniques rely on particular compiler implementations,
rather than language semantics, for performance gains.
Motivated by the capabilities and techniques of C++ template
metaprogramming, this thesis documents some common programming patterns,
including static computation, type analysis, generative programming, and the
encoding of domain-specific static checks. It also documents notable
shortcomings to current practice, including limited support for reflection,
semantic ambiguity, and other issues that arise from the pioneering nature of
template metaprogramming. Finally, this thesis presents the design of a
foundational programming language, motivated by the analysis of template
metaprogramming, that allows programs to statically inspect type information,
perform computations, and generate code. The language is specified as a core
calculus and its capabilities are presented in an idealized setting
Interpolation and Approximation of Polynomials in Finite Fields over a Short Interval from Noisy Values
Motivated by a recently introduced HIMMO key distribution scheme, we consider
a modification of the noisy polynomial interpolation problem of recovering an
unknown polynomial from approximate values of the residues of
modulo a prime at polynomially many points taken from a short
interval
Implicit Cooperative Positioning in Vehicular Networks
Absolute positioning of vehicles is based on Global Navigation Satellite
Systems (GNSS) combined with on-board sensors and high-resolution maps. In
Cooperative Intelligent Transportation Systems (C-ITS), the positioning
performance can be augmented by means of vehicular networks that enable
vehicles to share location-related information. This paper presents an Implicit
Cooperative Positioning (ICP) algorithm that exploits the Vehicle-to-Vehicle
(V2V) connectivity in an innovative manner, avoiding the use of explicit V2V
measurements such as ranging. In the ICP approach, vehicles jointly localize
non-cooperative physical features (such as people, traffic lights or inactive
cars) in the surrounding areas, and use them as common noisy reference points
to refine their location estimates. Information on sensed features are fused
through V2V links by a consensus procedure, nested within a message passing
algorithm, to enhance the vehicle localization accuracy. As positioning does
not rely on explicit ranging information between vehicles, the proposed ICP
method is amenable to implementation with off-the-shelf vehicular communication
hardware. The localization algorithm is validated in different traffic
scenarios, including a crossroad area with heterogeneous conditions in terms of
feature density and V2V connectivity, as well as a real urban area by using
Simulation of Urban MObility (SUMO) for traffic data generation. Performance
results show that the proposed ICP method can significantly improve the vehicle
location accuracy compared to the stand-alone GNSS, especially in harsh
environments, such as in urban canyons, where the GNSS signal is highly
degraded or denied.Comment: 15 pages, 10 figures, in review, 201
Spectroscopy Of Short-lived Radioactive Molecules
Molecules containing heavy and octupole deformed radioactive nuclei are predicted to provide enhanced sensitivity to investigate the violation of fundamental symmetries and to search for physics beyond the Standard Model of particle physics. However, experimental measurements of such radioactive systems are scarce. Octupole deformed nuclei are very rare in nature or do not occur naturally. Thus, their study requires to overcome major experimental challenges. This contribution will discuss the recent achievements in laser spectroscopy of radioactive molecules at CRIS, ISOLDE-CERN. This talk will discuss recent spectroscopy measurements of short-lived radium fluoride molecules (RaF) alongside future perspectives in the study of other radioactive molecules. The impact of these developments in fundamental physics research will be discussed
Legal Status Effects on Parent-Child Relationships and Parent Well-Being
Despite heightened levels of parenting stress and psychological distress experienced by many immigrant-origin families in the United States, little is known about the resiliency of Latinx families, particularly in today’s political climate. This research presents the results of a pilot study examining the effects of legal stressors on parent-child relationships and parent well-being in Latinx immigrant families. Taken from the Latinx Immigrant Family Stories and Strengths project, this mixed-methods study was informed by the integrative risk and resilience model for understanding the adaptation of immigrant-origin children and youth (Suarez-Orozco, Motti- Stefanidi, Marks, & Katsiaficas, 2018). The pilot included a sample of 30 adult parent participants with various legal statuses and migration experiences. Qualitatively, participants shared their experiences of legal vulnerability, fears or concerns of deportation, and coping mechanisms. Quantitatively, scores for parental stress, psychological distress, post-traumatic stress disorder (PTSD) symptoms, and resilience were collected. Following a, sequential explanatory design (Creswell et al., 2003), quantitative data were analyzed for relationships among study variables. A case-oriented research comparative strategy (Eckstein, 1975; Mahoney & Goertz, 2004; George & Bennett, 2005; Gerring, 2006) was then used to qualitatively examine the migration and resiliency experiences of the two cases with lowest and highest levels of resilience according to the Brief Resilience Scale (BRS; Smith et al., 2008) scores. Results suggest that, on average, parents experienced normal to high rates of parenting-related stress, low levels of psychological distress, moderate to severe symptoms of PTSD, and low to average levels of resiliency. Parents identifying as undocumented experienced higher rates of parental stress (r = 0.49, p\u3c.05) and psychological distress (r = 0.41, p\u3c.05) compared to their liminally
legal and documented peers. Although the trauma experienced by many immigrant-origin parents in the study was markedly high, resilience was fostered and expressed, and was exemplified through our high-resilience case analysis. Participants’ stories expressed throughout this study spoke volumes about the complex and often times traumatic lived experiences that many foreign- born parents face. Implications for comprehensive, detailed, and longitudinal future research is discussed.https://scholarscompass.vcu.edu/gradposters/1106/thumbnail.jp
Weak positive cloud-to-ground flashes in Northeastern Colorado
The frequency distributions of the peak magnetic field associated with the first detected return stroke of positive and negative cloud-to-ground (CG) flashes were studied using lightning data from northeastern Colorado. These data were obtained during 1985 with a medium-to-high gain network of three direction finders (DF's). The median signal strength of positive flashes was almost two times that of the negatives for flashes within 300 km of the DF's, which have an inherent detection-threshold bias that tends to discriminate against weak signals. This bias increases with range, and affects the detection of positive and negative flashes in different ways, because of the differing character of their distributions. Positive flashes appear to have a large percentage of signals clustered around very weak values that are lost to the medium-to-high gain Colorado Detection System very quickly with increasing range. The resulting median for positive signals could thus appear to be much larger than the median for negative signals, which are more clustered around intermediate values. When only flashes very close to the DF's are considered, however, the two distributions have almost identical medians. The large percentage of weak positive signals detected close to the DF's has not been explored previously. They have been suggested to come from intracloud discharges and thus are improperly classified as CG flashes. Evidence in hand, points to their being real positive, albeit weak CG flashes. Whether or not they are real positive ground flashes, it is important to be aware of their presence in data from magnetic DF networks
X-ray Reflection Spectroscopy of the Black Hole GX 339-4: Exploring the Hard State with Unprecedented Sensitivity
We analyze {\it simultaneously} six composite {\it RXTE} spectra of GX 339--4
in the hard state comprising 77 million counts collected over 196 ks. The
source spectra are ordered by luminosity and spanthe range 1.6\% to 17\% of the
Eddington luminosity. Crucially, using our new tool {\tt pcacorr}, we
re-calibrate the data to a precision of 0.1\%, an order of magnitude
improvement over all earlier work. Using our advanced reflection model {\tt
relxill}, we target the strong features in the component of emission reflected
from the disk, namely, the relativistically-broadened Fe K emission line, the
Fe K edge and the Compton hump. We report results for two joint fits to the six
spectra: For the first fit, we fix the spin parameter to its maximal value
() and allow the inner disk radius to vary. Results
include (i) precise measurements of , with evidence that the disk
becomes slightly truncated at a few percent of Eddington; and (ii) an
order-of-magnitude swing with luminosity in the high energy cutoff, which
reaches keV at our lowest luminosity. For the second fit, we make the
standard assumption in estimating spin that the inner edge of the accretion
disk is located at the innermost stable circular orbit () and find (90\% confidence,
statistical). For both fits, and at the same level of statistical confidence,
we estimate that the disk inclination is deg and that the Fe
abundance is super-solar, .Comment: Accepted for publication in ApJ, 20 pages, 13 figure
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