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Kurniawati H.,Queensland University of Technology | Bandyopadhyay T.,Singapore MIT Alliance for Research and Technology | Patrikalakis N.M.,Massachusetts Institute of Technology
Autonomous Robots | Year: 2012

Uncertainty in motion planning is often caused by three main sources: motion error, sensing error, and imperfect environment map. Despite the significant effect of all three sources of uncertainty to motion planning problems, most planners take into account only one or at most two of them. We propose a new motion planner, called Guided Cluster Sampling (GCS), that takes into account all three sources of uncertainty for robots with active sensing capabilities. GCS uses the Partially Observable Markov Decision Process (POMDP) framework and the point-based POMDP approach. Although point-based POMDPs have shown impressive progress over the past few years, it performs poorly when the environment map is imperfect. This poor performance is due to the extremely high dimensional state space, which translates to the extremely large belief space B. We alleviate this problem by constructing a more suitable sampling distribution based on the observations that when the robot has active sensing capability, B can be partitioned into a collection of much smaller sub-spaces, and an optimal policy can often be generated by sufficient sampling of a small subset of the collection. Utilizing these observations, GCS samples B in two-stages, a subspace is sampled from the collection and then a belief is sampled from the subspace. It uses information from the set of sampled sub-spaces and sampled beliefs to guide subsequent sampling. Simulation results on marine robotics scenarios suggest that GCS can generate reasonable policies for motion planning problems with uncertain motion, sensing, and environment map, that are unsolvable by the best point-based POMDPs today. Furthermore, GCS handles POMDPs with continuous state, action, and observation spaces. We show that for a class of POMDPs that often occur in robot motion planning, given enough time, GCS converges to the optimal policy. To the best of our knowledge, this is the first convergence result for point-based POMDPs with continuous action space. © 2012 Springer Science+Business Media, LLC. Source

Im E.-S.,Singapore MIT Alliance for Research and Technology | Gianotti R.L.,Massachusetts Institute of Technology | Eltahir E.A.B.,Massachusetts Institute of Technology
Journal of Climate | Year: 2014

This paper presents an evaluation of the performance of the Massachusetts Institute of Technology (MIT) regional climate model (MRCM) in simulating the West African monsoon. The MRCM is built on the Regional Climate Model, version 3 (RegCM3), but with several improvements, including coupling of Integrated Biosphere Simulator (IBIS) land surface scheme, a new surface albedo assignment method, new convective cloud and convective rainfall autoconversion schemes, and a modified scheme for simulating boundary layer height and boundary layer clouds. To investigate the impact of these more physically realistic representations when incorporated into MRCM, a series of experiments were carried out implementing two land surface schemes [IBIS with a new albedo assignment, and the Biosphere-Atmosphere Transfer Scheme (BATS)] and two convection schemes (Grell with the Fritsch-Chappell closure, and Emanuel in both the default form and modified with the new convective cloud cover and a rainfall autoconversion scheme). The analysis primarily focuses on comparing the rainfall characteristics, surface energy balance, and large-scale circulations against various observations. This work documents significant sensitivity in simulation of the West African monsoon to the choices of the land surface and convection schemes. Despite several deficiencies, the simulation with the combination of IBIS and the modified Emanuel scheme with the new convective cloud cover and a rainfall autoconversion scheme shows the best performance with respect to the spatial distribution of rainfall and the dynamics of the monsoon. The coupling of IBIS leads to representations of the surface energy balance and partitioning that show better agreement with observations compared to BATS. The IBIS simulations also reasonably reproduce the dynamical structures of the West African monsoon circulation. © 2014 American Meteorological Society. Source

Tan H.T.,National University of Singapore | Lee Y.H.,Singapore MIT Alliance for Research and Technology | Chung M.C.M.,National University of Singapore
Mass Spectrometry Reviews | Year: 2012

Cancer presents high mortality and morbidity globally, largely due to its complex and heterogenous nature, and lack of biomarkers for early diagnosis. A proteomics study of cancer aims to identify and characterize functional proteins that drive the transformation of malignancy, and to discover biomarkers to detect early-stage cancer, predict prognosis, determine therapy efficacy, identify novel drug targets, and ultimately develop personalized medicine. The various sources of human samples such as cell lines, tissues, and plasma/serum are probed by a plethora of proteomics tools to discover novel biomarkers and elucidate mechanisms of tumorigenesis. Innovative proteomics technologies and strategies have been designed for protein identification, quantitation, fractionation, and enrichment to delve deeper into the oncoproteome. In addition, there is the need for high-throughput methods for biomarker validation, and integration of the various platforms of oncoproteome data to fully comprehend cancer biology. © 2012 Wiley Periodicals, Inc. Mass Spec Rev 31:583-605, 2012 Copyright © 2012 Wiley Periodicals, Inc. Source

Li A.,Singapore MIT Alliance for Research and Technology
Methods in molecular biology (Clifton, N.J.) | Year: 2013

Atomic Force Microscopy (AFM) is a powerful tool for exploring the interaction between ligands and receptors, as well as their exact locations on the red cell surface. Here we discuss current and future applications for AFM based single-molecule force spectroscopy to study adhesion of Plasmodium-infected red blood cells. A protocol is provided for simultaneous topography and recognition imaging of the surface of Plasmodium falciparum-infected cells using CD36 functionalized tips. Source

Grandey B.S.,University of Oxford | Grandey B.S.,Singapore MIT Alliance for Research and Technology | Stier P.,University of Oxford | Wagner T.M.,University of Oxford
Atmospheric Chemistry and Physics | Year: 2013

Strong positive relationships between cloud fraction (fc) and aerosol optical depth (τ) have been reported. Data retrieved from the MODerate resolution Imaging Spectroradiometer (MODIS) instrument show positive fc-τ relationships across most of the globe. A global mean f c increase of approximately 0.2 between low and high τ conditions is found for both ocean and land. However, these relationships are not necessarily due to cloud-aerosol interactions. Using state-of-the-art Monitoring Atmospheric Composition and Climate (MACC) reanalysis-forecast τ data, which should be less affected by retrieval artefacts, it is demonstrated that a large part of the observed fc-τ signal may be due to cloud contamination of satellite-retrieved τ. For longer MACC forecast time steps of 24 h, which likely contain less cloud contamination, some negative f c-τ relationships are found. The global mean fc increase between low and high τ conditions is reduced to 0.1, suggesting that cloud contamination may account for approximately one half of the satellite retrieved increase in fc. ECHAM5-HAM general circulation model (GCM) simulations further demonstrate that positive fc-τ relationships may arise due to covariation with relative humidity. Widespread negative simulated fc-τ relationships in the tropics are shown to arise due to scavenging of aerosol by convective precipitation. Wet scavenging events are likely poorly sampled in satellite-retrieved data, because the properties of aerosol below clouds cannot be retrieved. Quantifying the role of wet scavenging, and assessing GCM representations of this important process, remains a challenge for future observational studies of aerosol-cloud-precipitation interactions. © Author(s) 2013. Source

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