708 research outputs found
Object Recognition By Alignment Using Invariant Projections of Planar Surfaces
In order to recognize an object in an image, we must determine the best transformation from object model to the image. In this paper, we show that for features from coplanar surfaces which undergo linear transformations in space, there exist projections invariant to the surface motions up to rotations in the image field. To use this property, we propose a new alignment approach to object recognition based on centroid alignment of corresponding feature groups. This method uses only a single pair of 2D model and data. Experimental results show the robustness of the proposed method against perturbations of feature positions
Construction of Dependent Dirichlet Processes Based on Poisson Processes
We present a method for constructing dependent Dirichlet processes. The new approach
exploits the intrinsic relationship between Dirichlet and Poisson processes
in order to create a Markov chain of Dirichlet processes suitable for use as a prior
over evolving mixture models. The method allows for the creation, removal, and
location variation of component models over time while maintaining the property
that the random measures are marginally DP distributed. Additionally, we derive
a Gibbs sampling algorithm for model inference and test it on both synthetic and
real data. Empirical results demonstrate that the approach is effective in estimating
dynamically varying mixture models
Weak seed-pairing stability and high target-site abundance decrease the proficiency of lsy-6 and other microRNAs
Most metazoan microRNAs (miRNAs) target many genes for repression, but the nematode lsy-6 miRNA is much less proficient. Here we show that the low proficiency of lsy-6 can be recapitulated in HeLa cells and that miR-23, a mammalian miRNA, also has low proficiency in these cells. Reporter results and array data indicate two properties of these miRNAs that impart low proficiency: their weak predicted seed-pairing stability (SPS) and their high target-site abundance (TA). These two properties also explain differential propensities of small interfering RNAs (siRNAs) to repress unintended targets. Using these insights, we expand the TargetScan tool for quantitatively predicting miRNA regulation (and siRNA off-targeting) to model differential miRNA (and siRNA) proficiencies, thereby improving prediction performance. We propose that siRNAs designed to have both weaker SPS and higher TA will have fewer off-targets without compromised on-target activity.National Institutes of Health (U.S.) (grant GM067031)Seoul National University (Research Settlement Fund)Howard Hughes Medical Institute (Investigator
Probabilistic Search for Object Segmentation and Recognition
The problem of searching for a model-based scene interpretation is analyzed
within a probabilistic framework. Object models are formulated as generative
models for range data of the scene. A new statistical criterion, the truncated
object probability, is introduced to infer an optimal sequence of object
hypotheses to be evaluated for their match to the data. The truncated
probability is partly determined by prior knowledge of the objects and partly
learned from data. Some experiments on sequence quality and object segmentation
and recognition from stereo data are presented. The article recovers classic
concepts from object recognition (grouping, geometric hashing, alignment) from
the probabilistic perspective and adds insight into the optimal ordering of
object hypotheses for evaluation. Moreover, it introduces point-relation
densities, a key component of the truncated probability, as statistical models
of local surface shape.Comment: 18 pages, 5 figure
Effective Interactions and Volume Energies in Charge-Stabilized Colloidal Suspensions
Charge-stabilized colloidal suspensions can be conveniently described by
formally reducing the macroion-microion mixture to an equivalent one-component
system of pseudo-particles. Within this scheme, the utility of a linear
response approximation for deriving effective interparticle interactions has
been demonstrated [M. J. Grimson and M. Silbert, Mol. Phys. 74, 397 (1991)].
Here the response approach is extended to suspensions of finite-sized macroions
and used to derive explicit expressions for (1) an effective electrostatic pair
interaction between pseudo-macroions and (2) an associated volume energy that
contributes to the total free energy. The derivation recovers precisely the
form of the DLVO screened-Coulomb effective pair interaction for spherical
macroions and makes manifest the important influence of the volume energy on
thermodynamic properties of deionized suspensions. Excluded volume corrections
are implicitly incorporated through a natural modification of the inverse
screening length. By including nonlinear response of counterions to macroions,
the theory may be generalized to systematically investigate effective many-body
interactions.Comment: 13 pages (J. Phys.: Condensed Matter, in press
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Detection and analysis of statistical differences in anatomical shape
We present a computational framework for image-based analysis and interpretation of statistical differences in anatomical shape between populations. Applications of such analysis include understanding developmental and anatomical aspects of disorders when comparing patients vs. normal controls, studying morphological changes caused by aging, or even differences in normal anatomy, for example, differences between genders. Once a quantitative description of organ shape is extracted from input images, the problem of identifying differences between the two groups can be reduced to one of the classical questions in machine learning of constructing a classifier function for assigning new examples to one of the two groups while making as few misclassifications as possible. The resulting classifier must be interpreted in terms of shape differences between the two groups back in the image domain. We demonstrate a novel approach to such interpretation that allows us to argue about the identified shape differences in anatomically meaningful terms of organ deformation. Given a classifier function in the feature space, we derive a deformation that corresponds to the differences between the two classes while ignoring shape variability within each class. Based on this approach, we present a system for statistical shape analysis using distance transforms for shape representation and the Support Vector Machines learning algorithm for the optimal classifier estimation and demonstrate it on artificially generated data sets, as well as real medical studies
Hysteresis and the dynamic phase transition in thin ferromagnetic films
Hysteresis and the non-equilibrium dynamic phase transition in thin magnetic
films subject to an oscillatory external field have been studied by Monte Carlo
simulation. The model under investigation is a classical Heisenberg spin system
with a bilinear exchange anisotropy in a planar thin film geometry with
competing surface fields. The film exhibits a non-equilibrium phase transition
between dynamically ordered and dynamically disordered phases characterized by
a critical temperature Tcd, whose location of is determined by the amplitude H0
and frequency w of the applied oscillatory field. In the presence of competing
surface fields the critical temperature of the ferromagnetic-paramagnetic
transition for the film is suppressed from the bulk system value, Tc, to the
interface localization-delocalization temperature Tci. The simulations show
that in general Tcd < Tci for the model film. The profile of the time-dependent
layer magnetization across the film shows that the dynamically ordered and
dynamically disordered phases coexist within the film for T < Tcd. In the
presence of competing surface fields, the dynamically ordered phase is
localized at one surface of the film.Comment: PDF file, 21 pages including 8 figure pages; added references,typos
added; to be published in PR
Stability of Colloidal Quasicrystals
Freezing of charge-stabilized colloidal suspensions and relative stabilities
of crystals and quasicrystals are studied using thermodynamic perturbation
theory. Macroion interactions are modelled by effective pair potentials
combining electrostatic repulsion with polymer-depletion or van der Waals
attraction. Comparing free energies -- counterion terms included -- for
elementary crystals and rational approximants to icosahedral quasicrystals,
parameters are identified for which one-component quasicrystals are stabilized
by a compromise between packing entropy and cohesive energy.Comment: 6 pages, 4 figure
Business in Engineering Education: Issues, Identities, Hybrids, and Limits
This chapter explores how engineering students are broadened in their education through the teaching of non-engineering subjects, such as business subjects, in order to develop critical thinking skills and self-knowledge of what it means to be an engineer. The goal of the chapter is to provide a commentary on the level of interaction, from design of courses to design of curricula, between business faculty and engineering faculty, and the results of that interaction. This chapter sets out to (i) explore whether there appears to be a place in engineering education curricula for reflective critique of assumptions related to business thinking, and why; (ii) discover what kinds of business issues are reflected in engineering education curricula, and for what purpose; (iii) explore the degree of business hybridization in engineering degree programs; (iv) ask who teaches business issues within engineering education? To this end a taxonomy of engineering enlightenment is proposed, and this is used to discuss evidence of broadening with engineering curricula. The approach adopted is to describe all relevant engineering degree programs in Ireland, based on their publicly available program information; examine the accreditation reports for these same programs; and then survey deans from colleges or schools of business to examine whether the business college/school is involved in the education of engineering students in the institution or university. If yes, how the business college or relevant business faculty are engaged in the design of engineering curricula. In order to enable a comparative discussion, the chapter will focus on Irish engineering programs that seek accreditation from Engineers Ireland for professional engineering. A number of hybrid engineering programs of study are also explored, and their apparent strengths discussed, including hybridity limits
Effective Interactions and Volume Energies in Charged Colloids: Linear Response Theory
Interparticle interactions in charge-stabilized colloidal suspensions, of
arbitrary salt concentration, are described at the level of effective
interactions in an equivalent one-component system. Integrating out from the
partition function the degrees of freedom of all microions, and assuming linear
response to the macroion charges, general expressions are obtained for both an
effective electrostatic pair interaction and an associated microion volume
energy. For macroions with hard-sphere cores, the effective interaction is of
the DLVO screened-Coulomb form, but with a modified screening constant that
incorporates excluded volume effects. The volume energy -- a natural
consequence of the one-component reduction -- contributes to the total free
energy and can significantly influence thermodynamic properties in the limit of
low-salt concentration. As illustrations, the osmotic pressure and bulk modulus
are computed and compared with recent experimental measurements for deionized
suspensions. For macroions of sufficient charge and concentration, it is shown
that the counterions can act to soften or destabilize colloidal crystals.Comment: 14 pages, including 3 figure
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