89 research outputs found
Formal Abstraction of General Stochastic Systems via Noise Partitioning
Verifying the performance of safety-critical, stochastic systems with complex
noise distributions is difficult. We introduce a general procedure for the
finite abstraction of nonlinear stochastic systems with non-standard (e.g.,
non-affine, non-symmetric, non-unimodal) noise distributions for verification
purposes. The method uses a finite partitioning of the noise domain to
construct an interval Markov chain (IMC) abstraction of the system via
transition probability intervals. Noise partitioning allows for a general class
of distributions and structures, including multiplicative and mixture models,
and admits both known and data-driven systems. The partitions required for
optimal transition bounds are specified for systems that are monotonic with
respect to the noise, and explicit partitions are provided for affine and
multiplicative structures. By the soundness of the abstraction procedure,
verification on the IMC provides guarantees on the stochastic system against a
temporal logic specification. In addition, we present a novel refinement-free
algorithm that improves the verification results. Case studies on linear and
nonlinear systems with non-Gaussian noise, including a data-driven example,
demonstrate the generality and effectiveness of the method without introducing
excessive conservatism.Comment: 6 pages, 6 figures, submitted jointly to IEEE Control Systems Letters
and 2024 AC
Path Planning in 3D with Motion Primitives for Wind Energy-Harvesting Fixed-Wing Aircraft
In this work, a set of motion primitives is defined for use in an
energy-aware motion planning problem. The motion primitives are defined as
sequences of control inputs to a simplified four-DOF dynamics model and are
used to replace the traditional continuous control space used in many
sampling-based motion planners. The primitives are implemented in a Stable
Sparse Rapidly Exploring Random Tree (SST) motion planner and compared to an
identical planner using a continuous control space. The planner using
primitives was found to run 11.0\% faster but yielded solution paths that were
on average worse with higher variance. Also, the solution path travel time is
improved by about 50\%. Using motion primitives for sampling spaces in SST can
effectively reduce the run time of the algorithm, although at the cost of
solution quality.Comment: 4 page
A role of diffusion tensor imaging in movement disorder surgery
The safe and reversible nature of deep brain stimulation (DBS) has allowed movement disorder neurosurgery to become commonplace throughout the world. Fundamental understanding of individual patientās anatomy is critical for optimizing the effects and side effects of DBS surgery. Three patients undergoing stereotactic surgery for movement disorders, at the institutionās intraoperative magnetic resonance imaging operating suite, were studied with fiber tractography. Stereotactic targets and fiber tractography were determined on preoperative magnetic resonance imagings using the SchaltenbrandāWahren atlas for definition in the BrainLab iPlan software (BrainLAB Inc., Feldkirchen, Germany). Subthalamic nucleus, globus pallidus interna, and ventral intermediate nucleus targets were studied. Diffusion tensor imaging parameters used ranged from 2 to 8Ā mm for volume of interest in the x/y/z planes, fiber length was kept constant at 30Ā mm, and fractional anisotropy threshold varied from 0.20 to 0.45. Diffusion tensor imaging tractography allowed reliable and reproducible visualization and correlation between frontal eye field, premotor, primary motor, and primary sensory cortices via corticospinal tracts and corticopontocerebellar tracts. There is an apparent increase in the number of cortical regions targeted by the fiber tracts as the region of interest is enlarged. This represents a possible mechanism of the increased effects and side effects observed with higher stimulation voltages. Currently available diffusion tensor imaging techniques allow potential methods to characterize the effects and side effects of DBS. This technology has the potential of being a powerful tool to optimize DBS neurosurgery
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Malaria Control in South Africa 2000ā2010: Beyond MDG6
Background: Malaria is one of the key targets within Goal 6 of the Millennium Development Goals (MDGs), whereby the disease needs to be halted and reversed by the year 2015. Several other international targets have been set, however the MDGs are universally accepted, hence it is the focus of this manuscript. Methods: An assessment was undertaken to determine the progress South Africa has made against the malaria target of MDG Goal 6. Data were analyzed for the period 2000 until 2010 and verified after municipal boundary changes in some of South Africaās districts and subsequent to verifying actual residence of malaria positive cases. Results: South Africa has made significant progress in controlling malaria transmission over the past decade; malaria cases declined by 89.41% (63663 in 2000 vs 6741 in 2010) and deaths decreased by 85.4% (453 vs 66) in the year 2000 compared to the year 2010. Coupled with this, malaria cases among children under five years of age have also declined by 93% (6791 in 2000 vs 451 in 2010). This has resulted in South Africa achieving and exceeding the malaria target of the MDGs. A series of interventions have attributed to this decrease, these include: drug policy change from monotherapy to artemisinin combination therapy, insecticide change from pyrethroids back to DDT; cross border collaboration (South Africa with Mozambique and Swaziland through the Lubombo Spatial Development Initiativeā LSDI) and financial investment in malaria control. The KwaZulu-Natal Province has seen the largest reduction in malaria cases and deaths (99.1% cases- 41786 vs 380; and 98.5% deaths 340 vs 5), when comparing the year 2000 with 2010. The Limpopo Province recorded the lowest reduction in malaria cases compared to the other malaria endemic provinces (56.1% reduction- 9487 vs 4174; when comparing 2000 to 2010). Conclusions: South Africa is well positioned to move beyond the malaria target of the MDGs and progress towards elimination. However, in addition to its existing interventions, the country will need to sustain its financing for malaria control and support programmed reorientation towards elimination and scale up active surveillance coupled with treatment at the community level. Moreover cross-border malaria collaboration needs to be sustained and scaled up to prevent the re-introduction of malaria into the country
Improving wind power market value with various aspects of diversification
The wind generation share in many European bidding zones is now large enough to affect the market value of wind power, and wind energy is getting less-than-average market price in day-ahead markets. As alternatives to investing in dedicated energy storage, there are two main ways to mitigate the decreasing market value trend. The first is employing different diversification measures (geographical spread, alternative wind turbine technologies, integration with solar). The second is implementing demand flexibility measures. Examples of these measures from some European and USA studies are given in this article, which stems from the international collaboration under IEA Wind TCP Tasks 25 and 53.Improving wind power market value with various aspects of diversificationacceptedVersio
Flexible Supervised Autonomy for Exploration in Subterranean Environments
While the capabilities of autonomous systems have been steadily improving in
recent years, these systems still struggle to rapidly explore previously
unknown environments without the aid of GPS-assisted navigation. The DARPA
Subterranean (SubT) Challenge aimed to fast track the development of autonomous
exploration systems by evaluating their performance in real-world underground
search-and-rescue scenarios. Subterranean environments present a plethora of
challenges for robotic systems, such as limited communications, complex
topology, visually-degraded sensing, and harsh terrain. The presented solution
enables long-term autonomy with minimal human supervision by combining a
powerful and independent single-agent autonomy stack, with higher level mission
management operating over a flexible mesh network. The autonomy suite deployed
on quadruped and wheeled robots was fully independent, freeing the human
supervision to loosely supervise the mission and make high-impact strategic
decisions. We also discuss lessons learned from fielding our system at the SubT
Final Event, relating to vehicle versatility, system adaptability, and
re-configurable communications.Comment: Field Robotics special issue: DARPA Subterranean Challenge,
Advancement and Lessons Learned from the Final
The First Provenance Challenge
The first Provenance Challenge was set up in order to provide a forum for the community to help understand the capabilities of different provenance systems and the expressiveness of their provenance representations. To this end, a Functional Magnetic Resonance Imaging workflow was defined, which participants had to either simulate or run in order to produce some provenance representation, from which a set of identified queries had to be implemented and executed. Sixteen teams responded to the challenge, and submitted their inputs. In this paper, we present the challenge workflow and queries, and summarise the participants contributions
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