Inference in Probabilistic Logic Programs with Continuous Random Variables

Probabilistic Logic Programming (PLP), exemplified by Sato and Kameya's PRISM, Poole's ICL, Raedt et al's ProbLog and Vennekens et al's LPAD, is aimed at combining statistical and logical knowledge representation and inference. A key characteristic of PLP frameworks is that they are conservative extensions to non-probabilistic logic programs which have been widely used for knowledge representation. PLP frameworks extend traditional logic programming semantics to a distribution semantics, where the semantics of a probabilistic logic program is given in terms of a distribution over possible models of the program. However, the inference techniques used in these works rely on enumerating sets of explanations for a query answer. Consequently, these languages permit very limited use of random variables with continuous distributions. In this paper, we present a symbolic inference procedure that uses constraints and represents sets of explanations without enumeration. This permits us to reason over PLPs with Gaussian or Gamma-distributed random variables (in addition to discrete-valued random variables) and linear equality constraints over reals. We develop the inference procedure in the context of PRISM; however the procedure's core ideas can be easily applied to other PLP languages as well. An interesting aspect of our inference procedure is that PRISM's query evaluation process becomes a special case in the absence of any continuous random variables in the program. The symbolic inference procedure enables us to reason over complex probabilistic models such as Kalman filters and a large subclass of Hybrid Bayesian networks that were hitherto not possible in PLP frameworks. (To appear in Theory and Practice of Logic Programming).Comment: 12 pages. arXiv admin note: substantial text overlap with arXiv:1203.428

Modeling and Analysis of Interactions in Virtual Enterprises

Advances in computer networking technology and open system standards are making the creation and management of virtual enterprises feasible. A virtual enterprise is a temporary consortium of autonomous, diverse, and possibly geographically dispersed organizations that pool their resources to meet short-term objectives and exploit fastchanging market trends. For a virtual enterprise to succeed, its business processes must be automated, and its startup costs must be minimized. In this paper we describe a formal framework for modeling and reasoning about interactions in a virtual enterprise. Such a framework will form the basis for tools that provide automated support for creation and operation of virtual enterprises. 1

Zero Temperature Insulator-Metal Transition in Doped Manganites

We study the transition at T=0 from a ferromagnetic insulating to a ferromagnetic metallic phase in manganites as a function of hole doping using an effective low-energy model Hamiltonian proposed by us recently. The model incorporates the quantum nature of the dynamic Jahn-Teller(JT) phonons strongly coupled to orbitally degenerate electrons as well as strong Coulomb correlation effects and leads naturally to the coexistence of localized (JT polaronic) and band-like electronic states. We study the insulator-metal transition as a function of doping as well as of the correlation strength U and JT gain in energy E_{JT}, and find, for realistic values of parameters, a ground state phase diagram in agreement with experiments. We also discuss how several other features of manganites as well as differences in behaviour among manganites can be understood in terms of our model.Comment: To be published in Europhysics Letter

Graphical technique for identifying a monotonic variance stabilizing transformation for absolute gene intensity signals

BACKGROUND: The usefulness of log(2 )transformation for cDNA microarray data has led to its widespread application to Affymetrix data. For Affymetrix data, where absolute intensities are indicative of number of transcripts, there is a systematic relationship between variance and magnitude of measurements. Application of the log(2 )transformation expands the scale of genes with low intensities while compressing the scale of genes with higher intensities thus reversing the mean by variance relationship. The usefulness of these transformations needs to be examined. RESULTS: Using an Affymetrix GeneChip(® )dataset, problems associated with applying the log(2 )transformation to absolute intensity data are demonstrated. Use of the spread-versus-level plot to identify an appropriate variance stabilizing transformation is presented. For the data presented, the spread-versus-level plot identified a power transformation that successfully stabilized the variance of probe set summaries. CONCLUSION: The spread-versus-level plot is helpful to identify transformations for variance stabilization. This is robust against outliers and avoids assumption of models and maximizations

Vitamins and Perinatal Outcomes Among HIV-Negative Women in Tanzania.

Prematurity and low birth weight are associated with high perinatal and infant mortality, especially in developing countries. Maternal micronutrient deficiencies may contribute to these adverse outcomes. In a double-blind trial in Dar es Salaam, Tanzania, we randomly assigned 8468 pregnant women (gestational age of fetus, 12 to 27 weeks) who were negative for human immunodeficiency virus infection to receive daily multivitamins (including multiples of the recommended dietary allowance) or placebo. All the women received prenatal supplemental iron and folic acid. The primary outcomes were low birth weight (<2500 g), prematurity, and fetal death. The incidence of low birth weight was 7.8% among the infants in the multivitamin group and 9.4% among those in the placebo group (relative risk, 0.82; 95% confidence interval [CI], 0.70 to 0.95; P=0.01). The mean difference in birth weight between the groups was modest (67 g, P<0.001). The rates of prematurity were 16.9% in the multivitamin group and 16.7% in the placebo group (relative risk, 1.01; 95% CI, 0.91 to 1.11; P=0.87), and the rates of fetal death were 4.3% and 5.0%, respectively (relative risk, 0.87; 95% CI, 0.72 to 1.05; P=0.15). Supplementation reduced both the risk of a birth size that was small for gestational age (<10th percentile; 10.7% in the multivitamin group vs. 13.6% in the placebo group; relative risk, 0.77; 95% CI, 0.68 to 0.87; P<0.001) and the risk of maternal anemia (hemoglobin level, <11 g per deciliter; relative risk, 0.88; 95% CI, 0.80 to 0.97; P=0.01), although the difference in the mean hemoglobin levels between the groups was small (0.2 g per deciliter, P<0.001). Multivitamin supplementation reduced the incidence of low birth weight and small-for-gestational-age births but had no significant effects on prematurity or fetal death. Multivitamins should be considered for all pregnant women in developing countries. (ClinicalTrials.gov number, NCT00197548 [ClinicalTrials.gov].)

Preliminary results of subintimal angioplasty for limb salvage in lower extremities with severe chronic ischemia and limb-threatening ischemia

ObjectiveThis study examined the hypothesis that superficial femoral artery (SFA) subintimal angioplasty (SI-PTA) can maintain limb salvage with minimal complications in patients with symptomatic occlusive arterial disease.MethodsFrom March 1, 2004, until April 28, 2006, 78 patients with rest pain (62.2%), gangrene (25.6%), or severe progressive claudication (12.2%) were treated consecutively with 82 SFA SI-PTAs (4 bilateral). The mean age was 59 ± 1.2 years, and 21 (27%) of the patients were female. All patients were treated in the operating room under local anesthesia by using fluoroscopic guidance, and the percentage SFA that was occluded was measured during the diagnostic portion of the procedure. Selective stent placement was performed after successful recanalization of the occluded arterial segments. Patients were treated with chronic aspirin and clopidogrel bisulfate for 3 months and followed up at 30 days and then every 3 months with physical examination and arterial duplex scan.ResultsOf the 82 SFA SI-PTA attempts, 76 (92%) were initially successful, with an increase in the ankle-brachial index from 0.46 ± 0.02 to 0.88 ± 0.01 (P < .001). Five of the six patients with a failed SFA SI-PTA were female, two of the six had had previous bypass attempts, and one of the six had had a previous SFA SI-PTA attempt by another physician. Forty-nine (64%) of the 76 initially successful SFA SI-PTAs required placement of a stent, and 43 (56.5%) of the successful 76 SFA SI-PTAs required additional PTA of 1 or more arterial segments. The group treated with a successful SFA SI-PTA had 42.5% ± 3.5% SFA occlusion, compared with 82% ± 10% (P < .05) in the group with a failed attempt at SFA SI-PTA. Two of the six patients with initial SI-PTA failure underwent leg amputation within 30 days, three were treated with successful leg bypass surgery, and one was lost to follow-up. Of the 76 successful SFA SI-PTAs, 5 (6.5%) failed within 90 days, and the patients were treated successfully with leg bypass surgery. Of the 71 limbs with patent SI-PTAs at 90 days, 68 have remained patent with a mean follow-up 10.4 ± 0.7 months (range, 2-24 months). Three of the 71 SFA SI-PTAs failed between 4 and 7 months (mean, 5 ± 0.7 months): 1 patient was treated with successful bypass surgery, 1 patient is currently considering further intervention, and 1 patient was treated with amputation. Ten (14%) of the 71 successful SFA SI-PTAs required limited PTA for asymptomatic restenosis, as identified by the arterial duplex scan (7.4 ± 1.4 months; range, 2-16 months). There were no perioperative deaths, and three patients have died during follow-up with patent SFA SI-PTAs (9.3 ± 1.4 months).ConclusionsThese data suggest that SFA SI-PTA can be successfully used for limb salvage with minimal morbidity and mortality in a group of patients with severe lower extremity occlusive vascular disease

Personalisation and recommender systems in digital libraries

Widespread use of the Internet has resulted in digital libraries that are increasingly used by diverse communities of users for diverse purposes and in which sharing and collaboration have become important social elements. As such libraries become commonplace, as their contents and services become more varied, and as their patrons become more experienced with computer technology, users will expect more sophisticated services from these libraries. A simple search function, normally an integral part of any digital library, increasingly leads to user frustration as user needs become more complex and as the volume of managed information increases. Proactive digital libraries, where the library evolves from being passive and untailored, are seen as offering great potential for addressing and overcoming these issues and include techniques such as personalisation and recommender systems. In this paper, following on from the DELOS/NSF Working Group on Personalisation and Recommender Systems for Digital Libraries, which met and reported during 2003, we present some background material on the scope of personalisation and recommender systems in digital libraries. We then outline the working group’s vision for the evolution of digital libraries and the role that personalisation and recommender systems will play, and we present a series of research challenges and specific recommendations and research priorities for the field