143 research outputs found
An approximate dynamic programming approach to food security of communities following hazards
Food security can be threatened by extreme natural hazard events for
households of all social classes within a community. To address food security
issues following a natural disaster, the recovery of several elements of the
built environment within a community, including its building portfolio, must be
considered. Building portfolio restoration is one of the most challenging
elements of recovery owing to the complexity and dimensionality of the problem.
This study introduces a stochastic scheduling algorithm for the identification
of optimal building portfolio recovery strategies. The proposed approach
provides a computationally tractable formulation to manage multi-state,
large-scale infrastructure systems. A testbed community modeled after Gilroy,
California, is used to illustrate how the proposed approach can be implemented
efficiently and accurately to find the near-optimal decisions related to
building recovery following a severe earthquake.Comment: As opposed to the preemptive scheduling problem, which was addressed
in multiple works by us, we deal with a non-preemptive stochastic scheduling
problem in this work. Submitted to 13th International Conference on
Applications of Statistics and Probability in Civil Engineering, ICASP13
Seoul, South Korea, May 26-30, 201
Solving Markov decision processes for network-level post-hazard recovery via simulation optimization and rollout
Computation of optimal recovery decisions for community resilience assurance
post-hazard is a combinatorial decision-making problem under uncertainty. It
involves solving a large-scale optimization problem, which is significantly
aggravated by the introduction of uncertainty. In this paper, we draw upon
established tools from multiple research communities to provide an effective
solution to this challenging problem. We provide a stochastic model of damage
to the water network (WN) within a testbed community following a severe
earthquake and compute near-optimal recovery actions for restoration of the
water network. We formulate this stochastic decision-making problem as a Markov
Decision Process (MDP), and solve it using a popular class of heuristic
algorithms known as rollout. A simulation-based representation of MDPs is
utilized in conjunction with rollout and the Optimal Computing Budget
Allocation (OCBA) algorithm to address the resulting stochastic simulation
optimization problem. Our method employs non-myopic planning with efficient use
of simulation budget. We show, through simulation results, that rollout fused
with OCBA performs competitively with respect to rollout with total equal
allocation (TEA) at a meagre simulation budget of 5-10% of rollout with TEA,
which is a crucial step towards addressing large-scale community recovery
problems following natural disasters.Comment: Submitted to Simulation Optimization for Cyber Physical Energy
Systems (Special Session) in 14th IEEE International Conference on Automation
Science and Engineerin
Underground railroads: citizen entitlements and unauthorized mobility in the antebellum period and today
In recent years, some scholars and prominent political figures have advocated the deepening of North American integration on roughly the European Union model, including the creation of new political institutions and the free movement of workers across borders. The construction of such a North American Union, if it included even a very thin trans-state citizenship regime, could represent the most significant expansion of individual entitlements in the region since citizenship was extended to former slaves in the United States. With such a possibility as its starting point, this article explores some striking parallels between the mass, legally prohibited movement across boundaries by fugitive slaves in the pre-Civil War period, and that by current unauthorized migrants to the United States. Both were, or are, met on their journeys by historically parallel groups of would-be helpers and hinderers. Their unauthorized movements in both periods serve as important signals of incomplete entitlements or institutional protections. Most crucially, moral arguments for extending fuller entitlements to both groups are shown here to be less distinct than may be prima facie evident, reinforcing the case for expanding and deepening the regional membership regime
Influence of variability of material mechanical properties on seismic performance of steel and steel-concrete composite structures
Modern standards for constructions in seismic zones allow the construction of buildings able to dissipate the energy of the seismic input through an appropriate location of cyclic plastic deformations involving the largest possible number of structural elements, forming thus a global collapse mechanisms without failure and instability phenomena both at local and global level. The key instrument for this purpose is the capacity design approach, which requires an appropriate selection of the design forces and an accurate definition of structural details within the plastic hinges zones, prescribing at the same time the oversizing of non-dissipative elements that shall remain in the elastic field during the earthquake. However, the localization of plastic hinges and the development of the global collapse mechanism is strongly influenced by the mechanical properties of materials, which are characterized by an inherent randomness. This variability can alter the final structural behaviour not matching the expected performance. In the present paper, the influence of the variability of material mechanical properties on the structural behaviour of steel and steel/concrete composite buildings is analyzed, evaluating the efficiency of the capacity design approach as proposed by Eurocode 8 and the possibility of introducing an upper limitation to the nominal yielding strength adopted in the design
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Vulnerability assessment and feasibility analysis of seismic strengthening of school buildings
The majority of structures in seismic-prone areas worldwide are structures that have been designed either without seismic design considerations, or using codes of practice that are seriously inadequate in the light of current seismic design principles. In Cyprus, after a series of earthquakes that occurred between 1995 and 1999, it was decided to carry out an unprecedented internationally seismic retrofitting of all school buildings, taking into account the sensitivity of the society towards these structures. In this paper representative school buildings are analysed in both their pristine condition and after applying retrofitting schemes typical of those implemented in the aforementioned large-scale strengthening programme. Non-linear analysis is conducted on calibrated analytical models of the selected buildings and fragility curves are derived for typical reinforced concrete and unreinforced masonry structures. These curves are then used to carry out a feasibility study, including both benefit-cost and life-cycle analysis, and evaluate the effectiveness of the strengthening programme
Electron-beam Calibration of Aerogel Tiles for the HELIX RICH Detector
The HELIX cosmic-ray detector is a balloon-borne instrument designed to
measure the flux of light isotopes in the energy range from 0.2 GeV/n to beyond
3 GeV/n. It will rely on a ring-imaging Cherenkov (RICH) detector for particle
identification at energies greater than 1 GeV/n and will use aerogel tiles with
refractive index near 1.15 as the radiator. To achieve the performance goals of
the experiment it is necessary to know the refractive index and its position
dependence over the lateral extent of the tiles to a precision of O(10$^{-4}).
In this paper we describe the apparatus and methods developed to calibrate the
HELIX tiles in an electron beam, in order to meet this requirement.Comment: 27 pages and 16 figures. Accepted for publication in Nuclear
Instruments and Methods
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