bluuebunny/crossref_metadata_2025 huggingface dataset:
Autoregressive moving average modeling for spectral parameter estimation from a multigradient echo chemical shift acquisition
Authors: Taylor Brian A. , Hwang Ken‐Pin , Hazle John D. , Stafford R. Jason
Published: February 2009

The authors investigated the performance of the iterative Steiglitz–McBride (SM) algorithm on an autoregressive moving average (ARMA) model of signals from a fast, sparsely sampled, multiecho, chemical shift imaging (CSI) acquisition using simulation, phantom, ex vivo, and in vivo experiments with a focus on its potential usage in magnetic resonance (MR)‐guided interventions. The ARMA signal model facilitated a rapid calculation of the chemical shift, apparent spin‐spin relaxation time , and complex amplitudes of a multipeak system from a limited number of echoes . Numerical simulations of one‐ and two‐peak systems were used to assess the accuracy and uncertainty in the calculated spectral parameters as a function of acquisition and tissue parameters. The measured uncertainties from simulation were compared to the theoretical Cramer–Rao lower bound (CRLB) for the acquisition. Measurements made in phantoms were used to validate the estimates and to validate uncertainty estimates made from the CRLB. We demonstrated application to real‐time MR‐guided interventions ex vivo by using the technique to monitor a percutaneous ethanol injection into a bovine liver and in vivo to monitor a laser‐induced thermal therapy treatment in a canine brain. Simulation results showed that the chemical shift and amplitude uncertainties reached their respective CRLB at a signal‐to‐noise ratio for echo train lengths using a fixed echo spacing of 3.3 ms. estimates from the signal model possessed higher uncertainties but reached the CRLB at larger SNRs and/or ETLs. Highly accurate estimates for the chemical shift and amplitude were obtained with echoes and for with echoes. We conclude that, over a reasonable range of SNR, the SM algorithm is a robust estimator of spectral parameters from fast CSI acquisitions that acquire echoes for one‐ and two‐peak systems. Preliminary ex vivo and in vivo experiments corroborated the results from simulation experiments and further indicate the potential of this technique for MR‐guided interventional procedures with high spatiotemporal resolution in .
Design of optimal collimation for dedicated molecular breast imaging systems
Authors: Weinmann Amanda L. , Hruska Carrie B. , O'Connor Michael K.
Published: February 2009

Molecular breast imaging (MBI) is a functional imaging technique that uses specialized small field‐of‐view gamma cameras to detect the preferential uptake of a radiotracer in breast lesions. MBI has potential to be a useful adjunct method to screening mammography for the detection of occult breast cancer. However, a current limitation of MBI is the high radiation dose (a factor of 7–10 times that of screening mammography) associated with current technology. The purpose of this study was to optimize the gamma camera collimation with the aim of improving sensitivity while retaining adequate resolution for the detection of sub‐10‐mm lesions. Square‐hole collimators with holes matched to the pixilated cadmium zinc telluride detector elements of the MBI system were designed. Data from MBI patient studies and parameters of existing dual‐head MBI systems were used to guide the range of desired collimator resolutions, source‐to‐collimator distances, pixel sizes, and collimator materials that were examined. General equations describing collimator performance for a conventional gamma camera were used in the design process along with several important adjustments to account for the specialized imaging geometry of the MBI system. Both theoretical calculations and a Monte Carlo model were used to measure the geometric efficiency (or sensitivity) and resolution of each designed collimator. Results showed that through optimal collimation, collimator sensitivity could be improved by factors of 1.5–3.2, while maintaining a collimator resolution of either or at a distance of 3 cm from the collimator face. These gains in collimator sensitivity permit an inversely proportional drop in the required dose to perform MBI.
MRI endoscopy using intrinsically localized probes
Authors: Sathyanarayana Shashank , Bottomley Paul A.
Published: February 2009

Magnetic resonance imaging (MRI) is traditionally performed with fixed externally applied gradient magnetic fields and is hence intrinsically locked to the laboratory frame of reference (FoR). Here a method for high‐resolution MRI that employs active, catheter‐based, tiny internal probes that utilize the spatial properties of the probe itself for localization is proposed and demonstrated at 3 T. Because these properties are intrinsic to the probe, they move with it, transforming MRI from the laboratory FoR to the FoR of the device itself, analogous to an endoscope. The “MRI endoscope” can utilize loop coils and loopless antennas with modified sensitivity, in combination with adiabatic excitation by the device itself, to restrict the MRI sensitivity to a disk‐shaped plane a few mm thick. Excitation with the MRI endoscope limits the eddy currents induced in the sample to an excited volume whose size is orders of magnitude below that excited by a conventional body MRI coil. Heat testing shows maximum local temperature increases of during MRI, within regulatory guidelines. The method is demonstrated in a kiwifruit, in intact porcine and rabbit aortas, and in an atherosclerotic human iliac artery specimen, with in‐plane resolution as small as and 1.5–5 mm slice thickness.
A bone composition model for Monte Carlo x‐ray transport simulations
Authors: Zhou Hu , Keall Paul J. , Graves Edward E.
Published: February 2009

In the megavoltage energy range although the mass attenuation coefficients of different bones do not vary by more than 10%, it has been estimated that a simple tissue model containing a single‐bone composition could cause errors of up to 10% in the calculated dose distribution. In the kilovoltage energy range, the variation in mass attenuation coefficients of the bones is several times greater, and the expected error from applying this type of model could be as high as several hundred percent. Based on the observation that the calcium and phosphorus compositions of bones are strongly correlated with the bone density, the authors propose an analytical formulation of bone composition for Monte Carlo computations. Elemental compositions and densities of homogeneous adult human bones from the literature were used as references, from which the calcium and phosphorus compositions were fitted as polynomial functions of bone density and assigned to model bones together with the averaged compositions of other elements. To test this model using the Monte Carlo package DOSXYZnrc, a series of discrete model bones was generated from this formula and the radiation‐tissue interaction cross‐section data were calculated. The total energy released per unit mass of primary photons (terma) and Monte Carlo calculations performed using this model and the single‐bone model were compared, which demonstrated that at kilovoltage energies the discrepancy could be more than 100% in bony dose and 30% in soft tissue dose. Percentage terma computed with the model agrees with that calculated on the published compositions to within 2.2% for kV spectra and 1.5% for MV spectra studied. This new bone model for Monte Carlo dose calculation may be of particular importance for dosimetry of kilovoltage radiation beams as well as for dosimetry of pediatric or animal subjects whose bone composition may differ substantially from that of adult human bones.
Simulated scatter performance of an inverse‐geometry dedicated breast CT system
Authors: Bhagtani Reema , Schmidt Taly Gilat
Published: February 2009

The purpose of this work was to quantify the effects of scatter for inverse‐geometry dedicated breast CT compared to cone‐beam breast CT through simulations. The inverse geometry was previously proposed as an alternative to cone‐beam acquisition for volumetric CT. The inverse geometry consists of a large‐area scanned‐source opposite a detector array that is smaller in the transverse direction. While the gantry rotates, the x‐ray beam is rapidly sequenced through an array of positions, acquiring a truncated projection image at each position. Inverse‐geometry CT (IGCT) is expected to detect less scatter than cone‐beam methods because only a fraction of the object is irradiated at any time and the fast detector isolates the measurements from sequential x‐ray beams. An additional scatter benefit is the increased air gap due to the inverted geometry. In this study, we modeled inverse‐geometry and cone‐beam dedicated breast CT systems of equivalent resolution, field of view, and photon fluence. Monte Carlo simulations generated scatter and primary projections of three cylindrical phantoms of diameters 10, 14, and composed of 50% adipose/50% glandular tissue. The scatter‐to‐primary ratio (SPR) was calculated for each breast diameter. Monte Carlo simulations were combined with analytical simulations to generate inverse‐geometry and cone‐beam images of breast phantoms embedded with tumors. Noise representing the photon fluence of a realistic breast CT scan was added to the simulated projections. Cone‐beam data were reconstructed with and without an ideal scatter correction. The CNR between breast tumor and background was compared for the inverse and cone‐beam geometries for the three phantom diameters. Results demonstrated an order of magnitude reduction in SPR for the IGCT system compared to the cone‐beam system. For example, the peak IGCT SPRs were 0.05 and 0.09 for the 14 and phantoms, respectively, compared to 0.42 and 1 for the cone‐beam system. For both geometries, the effects of scatter on contrast‐to‐noise ratio (CNR) were small for the diameter phantom. The inverse‐geometry improved the CNR by factors of 1.16 for the phantom and 1.48 for the phantom compared to a cone‐beam acquisition without scatter correction. When an ideal scatter correction was applied to the cone‐beam acquisition, the IGCT CNR improvements were 1.03 and 1.25 for the 14 and phantoms. Overall, the results suggest that the inverse geometry may be advantageous for dedicated breast CT, an application that requires high‐contrast resolution, spatial resolution, and dose efficiency.
Image quality optimization and evaluation of linearly mixed images in dual‐source, dual‐energy CT
Authors: Yu Lifeng , Primak Andrew N. , Liu Xin , McCollough Cynthia H.
Published: February 2009

In dual‐source dual‐energy CT, the images reconstructed from the low‐ and high‐energy scans (typically at 80 and 140 kV, respectively) can be mixed together to provide a single set of non‐material‐specific images for the purpose of routine diagnostic interpretation. Different from the material‐specific information that may be obtained from the dual‐energy scan data, the mixed images are created with the purpose of providing the interpreting physician a single set of images that have an appearance similar to that in single‐energy images acquired at the same total radiation dose. In this work, the authors used a phantom study to evaluate the image quality of linearly mixed images in comparison to single‐energy CT images, assuming the same total radiation dose and taking into account the effect of patient size and the dose partitioning between the low‐and high‐energy scans. The authors first developed a method to optimize the quality of the linearly mixed images such that the single‐energy image quality was compared to the best‐case image quality of the dual‐energy mixed images. Compared to 80 kV single‐energy images for the same radiation dose, the iodine CNR in dual‐energy mixed images was worse for smaller phantom sizes. However, similar noise and similar or improved iodine CNR relative to 120 kV images could be achieved for dual‐energy mixed images using the same total radiation dose over a wide range of patient sizes (up to 45 cm lateral thorax dimension). Thus, for adult CT practices, which primarily use 120 kV scanning, the use of dual‐energy CT for the purpose of material‐specific imaging can also produce a set of non‐material‐specific images for routine diagnostic interpretation that are of similar or improved quality relative to single‐energy 120 kV scans.
Variability of surface and center position radiation dose in MDCT: Monte Carlo simulations using CTDI and anthropomorphic phantoms
Authors: Zhang Di , Savandi Ali S. , Demarco John J. , Cagnon Chris H. , Angel Erin , Turner Adam C. , Cody Dianna D. , Stevens Donna M. , Primak Andrew N. , McCollough Cynthia H. , McNitt‐Gray Michael F.
Published: February 2009

The larger coverage afforded by wider ‐axis beams in multidetector CT (MDCT) creates larger cone angles and greater beam divergence, which results in substantial surface dose variation for helical and contiguous axial scans. This study evaluates the variation of absorbed radiation dose in both cylindrical and anthropomorphic phantoms when performing helical or contiguous axial scans. The approach used here was to perform Monte Carlo simulations of a 64 slice MDCT. Simulations were performed with different radiation profiles (simulated beam widths) for a given collimation setting (nominal beam width) and for different pitch values and tube start angles. The magnitude of variation at the surface was evaluated under four different conditions: (a) a homogeneous CTDI phantom with different combinations of pitch and simulated beam widths, (b) a heterogeneous anthropomorphic phantom with one measured beam collimation and various pitch values, (c) a homogeneous CTDI phantom with fixed beam collimation and pitch, but with different tube start angles, and (d) pitch values that should minimize variations of surface dose—evaluated for both homogeneous and heterogeneous phantoms. For the CTDI phantom simulations, peripheral dose patterns showed variation with percent ripple as high as 65% when pitch is 1.5 and simulated beam width is equal to the nominal collimation. For the anterior surface dose on an anthropomorphic phantom, the percent ripple was as high as 40% when the pitch is 1.5 and simulated beam width is equal to the measured beam width. Low pitch values were shown to cause beam overlaps which created new peaks. Different x‐ray tube start angles create shifts of the peripheral dose profiles. The start angle simulations showed that for a given table position, the surface dose could vary dramatically with minimum values that were 40% of the peak when all conditions are held constant except for the start angle. The last group of simulations showed that an “ideal” pitch value can be determined which reduces surface dose variations, but this pitch value must take into account the measured beam width. These results reveal the complexity of estimating surface dose and demonstrate a range of dose variability at surface positions for both homogeneous cylindrical and heterogeneous anthropomorphic phantoms. These findings have potential implications for small‐sized dosimeter measurements in phantoms, such as with TLDs or small Farmer chambers.
Physics of Radiology 2nd ed.
Authors: Yester Michael
Published: February 2009

Physics of Radiology 2nd ed. Wolbarst Anthony B. Medical Physics Publishing, Madison, WI, 2005. Hardcover, 660 pp. Price: $110.90. ISBN: 9781930524224.
The Strategic Dialogue on Tobacco Harm Reduction: a vision and blueprint for action in the US
Authors: Zeller Mitchell , Hatsukami Dorothy
Published: February 2009

The issues related to tobacco harm reduction continue to challenge the tobacco control research and policy communities. The potential for combusting tobacco products to reduce exposure and risk remains largely unknown, but this has not stopped manufacturers from offering such products making these claims. The role of oral tobacco products in a harm reduction regimen has also been a source of dialogue and debate. Within the last few years, major cigarette manufacturing companies have begun selling smokeless products for the first time, claiming to target current cigarette smokers. Other cigarette manufacturers are also offering smokeless products in markets around the world. The harm reduction debate has at times been divisive. There has been no unifying set of principles or goals articulated to guide tobacco control efforts. In particular, the research needs are extraordinarily high in order to drive evidence-based policy in this area and avoid the mistakes made with “light” cigarettes. This paper discusses recommendations from a strategic dialogue held with key, mostly US-based tobacco control researchers and policy makers to develop a strategic vision and blueprint for research, policy and communications to reduce the harm from tobacco for the US. Short-term and long-term objectives are described.
Fungal parasites of rotifers: Harposporium
Authors: Barron G. L.
Published: February 2009

Two new species, Harposporium angularis and Harposporium cylindrosporum, are described as parasitic on a species of bdelloid rotifer belonging to the genus Adineta. In H. angularis the conidia are long, slender, bent at right angles and taper to an acutely pointed slightly curved apex. Infection is initiated by conidia lodging and germinating in the gullet of the host between the mouth and the mastax. In H. cylindrosporum the conidia are also ingested but apparently pass through the mastax to initiate infection in the lower gut.
Photoinduction des périthèces du Nectria galligena. II. Influence de la qualité de la lumière
Authors: Dehorter B. , Jacques R. , Lacoste L.
Published: February 2009

The influence of light quality on the sexual reproduction of Nectria galligena Bres. has been studied in three experimental series with progressive accuracy. The last one, as did the two previous experiments, showed that wavelengths of 320, 370, 420, 450 et 480 nm were the most effective for ascocarp production. The sexual induction stimulated by these five wavelengths has been demonstrated for an irradiation of 12 h, at 40 μW cm−2, applied on the 7th day of growth.The action spectrum of the photoinduced sexual stage and the absorption spectra of mycelia in vivo and aqueous acellular fungi extracts presented some similarities. The analysis of these results did not allow characterization of the nature of the photoreceptor molecule, but some hypotheses about mycosporine action are suggested by this work.
BREATHERS IN INHOMOGENEOUS NONLINEAR LATTICES: AN ANALYSIS VIA CENTER MANIFOLD REDUCTION
Authors: JAMES GUILLAUME , SÁNCHEZ-REY BERNARDO , CUEVAS JESÚS
Published: February 2009

We consider an infinite chain of particles linearly coupled to their nearest neighbors and subject to an anharmonic local potential. The chain is assumed weakly inhomogeneous, i.e. coupling constants, particle masses and on-site potentials can have small variations along the chain. We look for small amplitude and time-periodic solutions, and, in particular, spatially localized ones (discrete breathers). The problem is reformulated as a nonautonomous recurrence in a space of time-periodic functions, where the dynamics is considered along the discrete spatial coordinate. Generalizing to nonautonomous maps a center manifold theorem previously obtained for infinite-dimensional autonomous maps [44], we show that small amplitude oscillations are determined by finite-dimensional nonautonomous mappings, whose dimension depends on the solutions frequency. We consider the case of two-dimensional reduced mappings, which occur for frequencies close to the edges of the phonon band (computed for the unperturbed homogeneous chain). For an homogeneous chain, the reduced map is autonomous and reversible, and bifurcations of reversible homoclinic orbits or heteroclinic solutions are found for appropriate parameter values. These orbits correspond respectively to discrete breathers for the infinite chain, or "dark" breathers superposed on a spatially extended standing wave. Breather existence is shown in some cases for any value of the coupling constant, which generalizes (for small amplitude solutions) an existence result obtained by MacKay and Aubry at small coupling [57]. For an inhomogeneous chain, the study of the nonautonomous reduced map is in general far more involved. Here, the problem is considered when the chain presents a finite number of defects. For the principal part of the reduced recurrence, using the assumption of weak inhomogeneity, we show that homoclinics to 0 exist when the image of the unstable manifold under a linear transformation (depending on the defect sequence) intersects the stable manifold. This provides a geometrical understanding of tangent bifurcations of discrete breathers commonly observed in classes of systems with impurities as defect strengths are varied. The case of a mass impurity is studied in detail, and our geometrical analysis is successfully compared with direct numerical simulations. In addition, a class of homoclinic orbits is shown to persist for the full reduced mapping and yields a family of discrete breathers with maximal amplitude at the impurity site.
ON THE COMPLEXITY OF SOME MALTSEV CONDITIONS
Authors: FREESE RALPH , VALERIOTE MATTHEW A.
Published: February 2009

This paper studies the complexity of determining if a finite algebra generates a variety that satisfies various Maltsev conditions, such as congruence distributivity or modularity. For idempotent algebras we show that there are polynomial time algorithms to test for these conditions but that in general these problems are EXPTIME complete. In addition, we provide sharp bounds in terms of the size of two-generated free algebras on the number of terms needed to witness various Maltsev conditions, such as congruence distributivity.
ON MODULAR SYMBOLS AND THE COHOMOLOGY OF HECKE TRIANGLE SURFACES
Authors: WIESE GABOR
Published: February 2009

The aim of this article is to give a concise algebraic treatment of the modular symbols formalism, generalized from modular curves to Hecke triangle surfaces. A sketch is included of how the modular symbols formalism gives rise to the standard algorithms for the computation of holomorphic modular forms. Precise and explicit connections are established to the cohomology of Hecke triangle surfaces and group cohomology. A general commutative ring is used as coefficient ring in view of applications to the computation of modular forms over rings different from the complex numbers.
STATISTICS OF PRIME DIVISORS IN FUNCTION FIELDS
Authors: RHOADES ROBERT C.
Published: February 2009

We show that the prime divisors of a random polynomial in 𝔽q[t] are typically "Poisson distributed". This result is analogous to the result in ℤ of Granville [1]. Along the way, we use a sieve developed by Granville and Soundararajan [2] to give a simple proof of the Erdös–Kac theorem in the function field setting. This approach gives stronger results about the moments of the sequence {ω(f)}f∈𝔽q[t] than was previously known, where ω(f) is the number of prime divisors of f.
ON THE LINEAR INDEPENDENCE OF ROOTS
Authors: CARR RICHARD , O'SULLIVAN CORMAC
Published: February 2009

A set of real nth roots that is pairwise linearly independent over the rationals must also be linearly independent. We show how this result may be extended to more general fields.
Word sense disambiguation
Authors: Navigli Roberto
Published: February 2009

Word sense disambiguation (WSD) is the ability to identify the meaning of words in context in a computational manner. WSD is considered an AI-complete problem, that is, a task whose solution is at least as hard as the most difficult problems in artificial intelligence. We introduce the reader to the motivations for solving the ambiguity of words and provide a description of the task. We overview supervised, unsupervised, and knowledge-based approaches. The assessment of WSD systems is discussed in the context of the Senseval/Semeval campaigns, aiming at the objective evaluation of systems participating in several different disambiguation tasks. Finally, applications, open problems, and future directions are discussed.
Comments on temporal logics for real-time system specification
Authors: Furia Carlo A. , Pradella Matteo , Rossi Matteo
Published: February 2009

The article “Temporal Logics for Real-Time System Specification” surveys some of the relevant literature dealing with the use of temporal logics for the specification of real-time systems. Unfortunately, it introduces some imprecisions that might create some confusion in the reader. While a certain degree of informality is certainly useful when addressing a broad audience, imprecisions can negatively impact the legibility of the exposition. We clarify some of its remarks on a few topics, in an effort to contribute to the usefulness of the survey for the reader.
Flexible provisioning of web service workflows
Authors: Stein Sebastian , Payne Terry R. , Jennings Nicholas R.
Published: February 2009

Web services promise to revolutionize the way computational resources and business processes are offered and invoked in open, distributed systems, such as the Internet. These services are described using machine-readable metadata, which enables consumer applications to automatically discover and provision suitable services for their workflows at run-time. However, current approaches have typically assumed service descriptions are accurate and deterministic, and so have neglected to account for the fact that services in these open systems are inherently unreliable and uncertain. Specifically, network failures, software bugs and competition for services may regularly lead to execution delays or even service failures. To address this problem, the process of provisioning services needs to be performed in a more flexible manner than has so far been considered, in order to proactively deal with failures and to recover workflows that have partially failed. To this end, we devise and present a heuristic strategy that varies the provisioning of services according to their predicted performance. Using simulation, we then benchmark our algorithm and show that it leads to a 700% improvement in average utility, while successfully completing up to eight times as many workflows as approaches that do not consider service failures.
A model of process documentation to determine provenance in mash-ups
Authors: Groth Paul , Miles Simon , Moreau Luc
Published: February 2009

Through technologies such as RSS (Really Simple Syndication), Web Services, and AJAX (Asynchronous JavaScript and XML), the Internet has facilitated the emergence of applications that are composed from a variety of services and data sources. Through tools such as Yahoo Pipes, these “mash-ups” can be composed in a dynamic, just-in-time manner from components provided by multiple institutions (i.e., Google, Amazon, your neighbor). However, when using these applications, it is not apparent where data comes from or how it is processed. Thus, to inspire trust and confidence in mash-ups, it is critical to be able to analyze their processes after the fact. These
trailing analyses
, in particular the determination of the provenance of a result (i.e., the process that led to it), are enabled by
process documentation
, which is documentation of an application's past process created by the components of that application at execution time. In this article, we define a generic conceptual data model that supports the autonomous creation of attributable, factual process documentation for dynamic multi-institutional applications. The data model is instantiated using two Internet formats, OWL and XML, and is evaluated with respect to questions about the provenance of results generated by a complex bioinformatics mash-up.
A peer-to-peer recommender system based on spontaneous affinities
Authors: Ruffo Giancarlo , Schifanella Rossano
Published: February 2009

Network analysis has proved to be very useful in many social and natural sciences, and in particular Small World topologies have been exploited in many application fields. In this article, we focus on P2P file sharing applications, where spontaneous communities of users are studied and analyzed. We define a family of structures that we call “Affinity Networks” (or even Graphs) that show self-organized interest-based clusters. Empirical evidence proves that affinity networks are small worlds and shows scale-free features. The relevance of this finding is augmented with the introduction of a proactive recommendation scheme, namely
DeHinter
, that exploits this natural feature. The intuition behind this scheme is that a user would trust her network of “elective affinities” more than anonymous and generic suggestions made by impersonal entities. The accuracy of the recommendation is evaluated by way of a 10-fold cross validation, and a prototype has been implemented for further feedbacks from the users.
Expressive and modular predicate dispatch for Java
Authors: Millstein Todd , Frost Christopher , Ryder Jason , Warth Alessandro
Published: February 2009

Predicate dispatch
is an object-oriented (OO) language mechanism for determining the method implementation to be invoked upon a message send. With predicate dispatch, each method implementation includes a predicate guard specifying the conditions under which the method should be invoked, and logical implication of predicates determines the method overriding relation. Predicate dispatch naturally unifies and generalizes several common forms of dynamic dispatch, including traditional OO dispatch, multimethod dispatch, and functional-style pattern matching. Unfortunately, prior languages supporting predicate dispatch have had several deficiencies that limit the practical utility of this language feature.

We describe JPred, a backward-compatible extension to Java supporting predicate dispatch. While prior languages with predicate dispatch have been extensions to toy or nonmainstream languages, we show how predicate dispatch can be naturally added to a traditional OO language. While prior languages with predicate dispatch have required the whole program to be available for typechecking and compilation, JPred retains Java's modular typechecking and compilation strategies. While prior languages with predicate dispatch have included special-purpose algorithms for reasoning about predicates, JPred employs general-purpose, off-the-shelf decision procedures. As a result, JPred's type system is more flexible, allowing several useful programming idioms that are spuriously rejected by those other languages. After describing the JPred language informally, we present an extension to Featherweight Java that formalizes the language and its modular type system, which we have proven sound. Finally, we discuss two case studies that illustrate the practical utility of JPred, including its use in the detection of several errors.
Probabilistic bisimulation as a congruence
Authors: Lanotte Ruggero , Tini Simone
Published: February 2009

We propose both an SOS transition rule format for the generative model of probabilistic processes, and an SOS transition rule format for the reactive model of the probabilistic processes. Our rule formats guarantee that probabilistic bisimulation is a congruence with respect to process algebra operations. Moreover, our rule format for generative process algebras guarantees that the probability of the moves of a given process, if there are any, sum up to 1, and the rule format for reactive process algebras guarantees that the probability of the moves of a given process labeled with the same action, if there are any, sum up to 1. We show that most operations of the probabilistic process algebras studied in the literature are captured by our formats, which, therefore, have practical applications.
Termination of rewriting under strategies
Authors: Gnaedig Isabelle , Kirchner Hélène
Published: February 2009

A termination proof method for rewriting under strategies, based on an explicit induction on the termination property, is presented and instantiated for the innermost, outermost, and local strategies. Rewriting trees are simulated by proof trees generated with an abstraction mechanism, narrowing and constraints representing sets of ground terms. Abstraction introduces variables to represent normal forms without computing them and to control the narrowing mechanism, well known to easily diverge. The induction ordering is not given a priori, but defined with ordering constraints, incrementally set during the proof. It is established that termination under strategy is equivalent to the construction of finite proof trees schematizing terminating rewriting trees. Sufficient effective conditions to ensure finiteness are studied and the method is illustrated on several examples for each specific strategy.
A compositional semantics for CHR
Authors: Gabbrielli Maurizio , Meo Maria Chiara
Published: February 2009

Constraint Handling Rules (CHR) is a committed-choice declarative language which has been designed for writing constraint solvers. A CHR program consists of multiheaded guarded rules which allow to rewrite constraints into simpler ones until a solved form is reached.

CHR has received considerable attention, both from the practical and from the theoretical side. Nevertheless, due the use of multiheaded clauses, there are several aspects of the CHR semantics which have not been clarified yet. In particular, no compositional semantics for CHR has been defined so far.

In this article we introduce a fix-point semantics which characterizes the input/output behavior of a CHR program and which is and-compositional, that is, which allows to retrieve the semantics of a conjunctive query from the semantics of its components. Such a semantics can be used as a basis to define incremental and modular analysis and verification tools.
PSPACE bounds for rank-1 modal logics
Authors: Schröder LUTZ , Pattinson Dirk
Published: February 2009

For lack of general algorithmic methods that apply to wide classes of logics, establishing a complexity bound for a given modal logic is often a laborious task. The present work is a step towards a general theory of the complexity of modal logics. Our main result is that all rank-1 logics enjoy a shallow model property and thus are, under mild assumptions on the format of their axiomatisation, in
PSPACE
. This leads to a unified derivation of tight
PSPACE
-bounds for a number of logics, including
K
,
KD
, coalition logic, graded modal logic, majority logic, and probabilistic modal logic. Our generic algorithm moreover finds tableau proofs that witness pleasant proof-theoretic properties including a weak subformula property. This generality is made possible by a coalgebraic semantics, which conveniently abstracts from the details of a given model class and thus allows covering a broad range of logics in a uniform way.
ViewpointYour students are your legacy
Authors: Patterson David A.
Published: February 2009

This Viewpoint boils down into a few magazine pages what I've learned in my 32 years of mentoring Ph.D. students.
Reflecting human values in the digital age
Authors: Sellen Abigail , Rogers Yvonne , Harper Richard , Rodden Tom
Published: February 2009

HCI experts must broaden the field's scope and adopt new methods to be useful in 21st-century sociotechnical environments.
Probabilistically checkable proofs
Authors: Sudan Madhu
Published: February 2009

Can a proof be checked without reading it?
Future Tense: Radical evolution
Authors: Garreau Joel
Published: February 2009

Future Tense, one of the revolving features on this page, presents stories from the intersection of computational science and technological speculation, their boundaries limited only by our ability to imagine what will and could be.
Designing universally accessible games
Authors: Grammenos Dimitris , Savidis Anthony , Stephanidis Constantine
Published: February 2009

Today, computer games are one of the major sources of entertainment. Computer games are usually far more demanding than typical interactive applications in terms of motor and sensory skills needed for interaction control, due to special-purpose input devices, complicated interaction techniques, and the primary emphasis on visual control and attention. This renders computer games inaccessible to a large percentage of people with disabilities. This article introduces the concept of
universally accessible games
, that is, games proactively designed to optimally fit and adapt to individual gamer characteristics and to be concurrently played among people with diverse abilities, without requiring particular adjustments or modifications. The concept is elaborated and tested through four case studies: a web-based chess game (
UA-Chess
), an action game (
Access Invaders
), a universally inaccessible game (
Game Over
!) used as an interactive educational tool, and an improved version of
Access Invaders
(
Terrestrial Invaders
). For all cases, key design and evaluation findings are discussed, reporting consolidated know-how and experience. Finally, the research challenge of creating multiplayer universally accessible games is further elaborated, proposing the novel concept of
Parallel Game Universes
as a potential solution.
Requirements analysis of presence
Authors: Bostan Barbaros
Published: February 2009

Virtual worlds are computer-based simulations intended to give its users the impression of being in another place.
Presence
, or the sense of “being there,” is a major design requirement for virtual environments where users inhabit an artificial reality in the form of two or three-dimensional graphical representations. Promoting this subjective experience has always been one of the major concerns of designers, but this complex and difficult task requires the awareness of other design requirements and their effects on presence. This article aims to define various psychological and technological aspects of presence based on virtual environment design requirements defined by Stuart [2001].

Previous research tried to define hypothesized factors of presence by using subjective user responses obtained from questionnaires. This study incorporates a different approach to define potential components of presence, specifying the individual design requirements for virtual worlds based on the conceptual framework designed by Stuart. This framework has not been applied to the analysis of the concept of presence before, and it defines possible factors that contribute to a sense of presence, some of which have not been included in previous work. In order to decompose presence into its components, researchers should also be aware of the design requirements delineated in this framework.

Detailed analysis of design requirements will focus on a computer role-playing game (RPG), giving examples from one of the best titles in the genre. Since role-playing games are social and interactive worlds where players assume the role of a virtual character that can be subjectively defined as a second-self, they are highly relevant to presence research. Thus, selected design requirements will be discussed from a computer-gaming perspective by defining how each relevant requirement is addressed on the selected RPG, and how they should be addressed by game designers.
Robot Arena
Authors: Calife Daniel , Bernardes João Luiz , Tori Romero
Published: February 2009

Nowadays electronic games are of great importance to the economic sector, to computing, and to academic research, and not are limited to entertainment applications only. Augmented reality is one of the new frontiers to be explored in the search for innovation in gameplay and in interactive interfaces of electronic games. This article presents the research, development, and testing of an infrastructure, called Robot Arena, for the development of innovative games using the spatial augmented reality and new interfaces that this technology brings. Based on horizontal interfaces with elements of hardware and software, Robot ARena has a flexible architecture that enables different ways of interaction and visualization. Another aspect planned for this project is the control and communication of robots, which can be used as avatars in games. A Robot ARena prototype was implemented, tested, and used in the development of two game prototypes,
FootBot ARena
and
TanSpace
, which bring new challenges to the infrastructure, such as exploration of the influence of virtual objects on real objects and the application of tangible interfaces.
Exploring virtual environments in a decentralized lab
Authors: Li Peng
Published: February 2009

Virtualization technology has been used in a decentralized manner to deliver hands-on labs in an intrusion detection course in the past three years. The availability of free virtualization software and low-cost but high-performance personal computers made it possible for students to run virtual machines and perform lab exercises on their own computers. Different virtualization options including VMware, Sun xVM VirtualBox and Virtual Computing Lab (VCL) were explored. Both VMware and VirtualBox were proven to be effective tools for lab purposes. The decentralized virtual lab approach and the centralized remote lab approach (ex. VCL) can be complementary.
Tissue kallikrein deficiency and renovascular hypertension in the mouse
Authors: Griol-Charhbili Violaine , Sabbah Laurent , Colucci Juliana , Vincent Marie-Pascale , Baudrie Véronique , Laude Dominique , Elghozi Jean-Luc , Bruneval Patrick , Picard Nicolas , Meneton Pierre , Alhenc-Gelas François , Richer Christine
Published: February 2009

The kallikrein kinin system (KKS) is involved in arterial and renal functions. It may have an antihypertensive effect in both essential and secondary forms of hypertension. The role of the KKS in the development of two-kidneys, one-clip (2K1C) hypertension, a high-renin model, was investigated in mice rendered deficient in tissue kallikrein (TK) and kinins by TK gene inactivation (TK−/−) and in their wild-type littermates (TK+/+). Four weeks after clipping the renal artery, blood flow was reduced in the clipped kidney (2K1C-TK+/+: −90%, 2K1C-TK−/−: −93% vs. sham-operated mice), and the kidney mass had also decreased (2K1C-TK+/+: −65%, 2K1C-TK−/−: −66%), whereas in the unclipped kidney, blood flow (2K1C-TK+/+: +19%, 2K1C-TK−/−: +17%) and kidney mass (2K1C-TK+/+: +32%, 2K1C-TK−/−: +30%) had both increased. The plasma renin concentration (2K1C-TK+/+: +78%, 2K1C-TK−/−: +65%) and renal renin content of the clipped kidney (2K1C-TK+/+: +58%, 2K1C-TK−/−: +65%) had increased significantly. There was no difference for these parameters between 2K1C-TK+/+ and 2K1C-TK−/− mice. Blood pressure monitored by telemetry and by plethysmography, rose immediately after clipping in both genotypes, and reached similar levels (2K1C-TK+/+: +24%, 2K1C-TK−/−: +21%). 2K1C-TK+/+ and 2K1C-TK−/− mice developed similar concentric left ventricular hypertrophy (+24% and +17%, respectively) with normal cardiac function. These findings suggest that in the context of chronic unilateral reduction in renal blood flow, TK and kinins do not influence the trophicity of kidneys, the synthesis and secretion of renin, blood pressure increase, and cardiac remodeling due to renin angiotensin system activation.
Correlation Between BOLD fMRI and Theta-Band Local Field Potentials in the Human Hippocampal Area
Authors: Ekstrom Arne , Suthana Nanthia , Millett David , Fried Itzhak , Bookheimer Susan
Published: February 2009

The relation between the blood-oxygen-level-dependent (BOLD) signal, which forms the basis of functional magnetic resonance imaging (fMRI), and underlying neural activity is not well understood. We performed high-resolution fMRI in patients scheduled for implantation with depth electrodes for seizure monitoring while they navigated a virtual environment. We then recorded local field potentials (LFPs) and neural firing rate directly from the hippocampal area of the same subjects during the same task. Comparing BOLD signal changes with 396 LFP and 185 neuron recordings in the hippocampal area, we found that BOLD signal changes correlated positively with LFP power changes in the theta-band (4–8 Hz). This correlation, however, was largely present for parahippocampal BOLD signal changes; BOLD changes in the hippocampus correlated weakly or not at all with LFP power changes. We did not find a significant relationship between BOLD activity and neural firing rate in either region, which could not be accounted for by a lesser tendency for neurons to respond or a greater tendency for neurons to habituate to the task. Strengthening the idea of a dissociation between LFP power and neural firing rate in their relation to the BOLD signal, simultaneously recorded LFP power and neural firing rate changes were uncorrelated across electrodes. Together, our results suggest that the BOLD signal in the human hippocampal area has a more heterogenous relationship with underlying neural activity than has been described previously in other brain regions.
Neuromorphic Configurable Architecture for Robust Motion Estimation
Authors: Botella Guillermo , Rodríguez Manuel , García Antonio , Ros Eduardo
Published: February 2009

The robustness of the human visual system recovering motion estimation in almost any visual situation is enviable, performing enormous calculation tasks continuously, robustly, efficiently, and effortlessly. There is obviously a great deal we can learn from our own visual system. Currently, there are several optical flow algorithms, although none of them deals efficiently with noise, illumination changes, second-order motion, occlusions, and so on. The main contribution of this work is the efficient implementation of a biologically inspired motion algorithm that borrows nature templates as inspiration in the design of architectures and makes use of a specific model of human visual motion perception: Multichannel Gradient Model (McGM). This novel customizable architecture of a neuromorphic robust optical flow can be constructed with FPGA or ASIC device using properties of the cortical motion pathway, constituting a useful framework for building future complex bioinspired systems running in real time with high computational complexity. This work includes the resource usage and performance data, and the comparison with actual systems. This hardware has many application fields like object recognition, navigation, or tracking in difficult environments due to its bioinspired and robustness properties.
About Robust Stability of Dynamic Systems with Time Delays through Fixed Point Theory
Authors: De la Sen M.
Published: February 2009

This paper investigates the global asymptotic stability independent of the sizes of the delays of linear time-varying systems with internal point delays which possess a limiting equation via fixed point theory. The error equation between the solutions of the limiting equation and that of the current one is considered as a perturbation equation in the fixed- point and stability analyses. The existence of a unique fixed point which is later proved to be an asymptotically stable equilibrium point is investigated. The stability conditions are basically concerned with the matrix measure of the delay-free matrix of dynamics to be negative and to have a modulus larger than the contribution of the error dynamics with respect to the limiting one. Alternative conditions are obtained concerned with the matrix dynamics for zero delay to be negative and to have a modulus larger than an appropriate contributions of the error dynamics of the current dynamics with respect to the limiting one. Since global stability is guaranteed under some deviation of the current solution related to the limiting one, which is considered as nominal, the stability is robust against such errors for certain tolerance margins.