8,054 research outputs found
Free-moving Quantitative Gamma-ray Imaging
The ability to map and estimate the activity of radiological source
distributions in unknown three-dimensional environments has applications in the
prevention and response to radiological accidents or threats as well as the
enforcement and verification of international nuclear non-proliferation
agreements. Such a capability requires well-characterized detector response
functions, accurate time-dependent detector position and orientation data, an
algorithmic understanding of the surrounding 3D environment, and appropriate
image reconstruction and uncertainty quantification methods. We have previously
demonstrated 3D mapping of gamma-ray emitters with free-moving detector systems
on a relative intensity scale using a technique called Scene Data Fusion (SDF).
Here we characterize the detector response of a multi-element gamma-ray imaging
system using experimentally benchmarked Monte Carlo simulations and perform 3D
mapping on an absolute intensity scale. We present experimental reconstruction
results from hand-carried and airborne measurements with point-like and
distributed sources in known configurations, demonstrating quantitative SDF in
complex 3D environments.Comment: 19 pages, 5 figures, 4 supplementary figures, submitted to Scientific
Reports - Natur
On page-based optimistic process checkpointing
Persistent object systems must provide some form of checkpointing to ensure that changes to persistent data are secured on non-volatile storage. When processes share or exchange modified data, mechanisms must be provided to ensure that they may be consistently checkpointed. This may be performed eagerly by synchronously checkpointing all dependent data. Alternatively, optimistic techniques may be used where processes are individually checkpointed and globally consistent states are found asynchronously. This paper examines two eager checkpointing techniques and describes a new optimistic technique. The technique is applicable in systems such as SASOS, where the notion of process and address space are decoupled.Othe
An Agent-Based Simulation API for Speculative PDES Runtime Environments
Agent-Based Modeling and Simulation (ABMS) is an effective paradigm to model systems exhibiting complex interactions, also with the goal of studying the emergent behavior of these systems. While ABMS has been effectively used in many disciplines, many successful models are still run only sequentially. Relying on simple and easy-to-use languages such as NetLogo limits the possibility to benefit from more effective runtime paradigms, such as speculative Parallel Discrete Event Simulation (PDES). In this paper, we discuss a semantically-rich API allowing to implement Agent-Based Models in a simple and effective way. We also describe the critical points which should be taken into account to implement this API in a speculative PDES environment, to scale up simulations on distributed massively-parallel clusters. We present an experimental assessment showing how our proposal allows to implement complicated interactions with a reduced complexity, while delivering a non-negligible performance increase
Collective motion of cells: from experiments to models
Swarming or collective motion of living entities is one of the most common
and spectacular manifestations of living systems having been extensively
studied in recent years. A number of general principles have been established.
The interactions at the level of cells are quite different from those among
individual animals therefore the study of collective motion of cells is likely
to reveal some specific important features which are overviewed in this paper.
In addition to presenting the most appealing results from the quickly growing
related literature we also deliver a critical discussion of the emerging
picture and summarize our present understanding of collective motion at the
cellular level. Collective motion of cells plays an essential role in a number
of experimental and real-life situations. In most cases the coordinated motion
is a helpful aspect of the given phenomenon and results in making a related
process more efficient (e.g., embryogenesis or wound healing), while in the
case of tumor cell invasion it appears to speed up the progression of the
disease. In these mechanisms cells both have to be motile and adhere to one
another, the adherence feature being the most specific to this sort of
collective behavior. One of the central aims of this review is both presenting
the related experimental observations and treating them in the light of a few
basic computational models so as to make an interpretation of the phenomena at
a quantitative level as well.Comment: 24 pages, 25 figures, 13 reference video link
An Agent Based Transaction Manager for Multidatabase Systems
A multidatabase system (MDBMS) is a facility that allows users to access data located in multiple autonomous database management systems (DBMSs) at different sites. To ensure global atomicity for multidatabase transactions, a reliable global atomic commitment protocol is a possible solution. In this protocol a centralized transaction manager (TM) receives global transactions, submits subtransactions to the appropriate sites via AGENTS. An AGENT is a component of MDBS that runs on each site; AGENTS after receiving subtransactions from the transaction manager perform the transaction and send the results back to TM. We have presented a unique proof-of-concept, a JAVA application for an Agent Based Transaction Manager that preserves global atomicity. It provides a user friendly interface through which reliable atomic commitment protocol for global transaction execution in multidatabase environment can be visualized. We demonstrated with three different test case scenarios how the protocol works. This is useful in further research in this area where atomicity of transactions can be verified for protocol correctness
Field-control, phase-transitions, and life's emergence
Instances of critical-like characteristics in living systems at each
organizational level as well as the spontaneous emergence of computation
(Langton), indicate the relevance of self-organized criticality (SOC). But
extrapolating complex bio-systems to life's origins, brings up a paradox: how
could simple organics--lacking the 'soft matter' response properties of today's
bio-molecules--have dissipated energy from primordial reactions in a controlled
manner for their 'ordering'? Nevertheless, a causal link of life's macroscopic
irreversible dynamics to the microscopic reversible laws of statistical
mechanics is indicated via the 'functional-takeover' of a soft magnetic
scaffold by organics (c.f. Cairns-Smith's 'crystal-scaffold'). A
field-controlled structure offers a mechanism for bootstrapping--bottom-up
assembly with top-down control: its super-paramagnetic components obey
reversible dynamics, but its dissipation of H-field energy for aggregation
breaks time-reversal symmetry. The responsive adjustments of the controlled
(host) mineral system to environmental changes would bring about mutual
coupling between random organic sets supported by it; here the generation of
long-range correlations within organic (guest) networks could include SOC-like
mechanisms. And, such cooperative adjustments enable the selection of the
functional configuration by altering the inorganic network's capacity to assist
a spontaneous process. A non-equilibrium dynamics could now drive the
kinetically-oriented system towards a series of phase-transitions with
appropriate organic replacements 'taking-over' its functions.Comment: 54 pages, pdf fil
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