Evaluating implicit feedback models using searcher simulations

In this article we describe an evaluation of relevance feedback (RF) algorithms using searcher simulations. Since these algorithms select additional terms for query modification based on inferences made from searcher interaction, not on relevance information searchers explicitly provide (as in traditional RF), we refer to them as implicit feedback models. We introduce six different models that base their decisions on the interactions of searchers and use different approaches to rank query modification terms. The aim of this article is to determine which of these models should be used to assist searchers in the systems we develop. To evaluate these models we used searcher simulations that afforded us more control over the experimental conditions than experiments with human subjects and allowed complex interaction to be modeled without the need for costly human experimentation. The simulation-based evaluation methodology measures how well the models learn the distribution of terms across relevant documents (i.e., learn what information is relevant) and how well they improve search effectiveness (i.e., create effective search queries). Our findings show that an implicit feedback model based on Jeffrey's rule of conditioning outperformed other models under investigation

Impurity in a Luttinger liquid away from half-filling: a numerical study

Conformal field theory gives quite detailed predictions for the low energy spectrum and scaling exponents of a massless Luttinger liquid at generic filling in the presence of an impurity. While these predictions were verified for half-filled systems, there was till now no analysis away from this particular filling. Here, we fill in this gap by numerically investigating a quarter-filled system using the density matrix renormalization group technique. Our results confirm conformal field theory predictions, and suggest that they are indeed valid for arbitrary fillings.Comment: 9 pages (include figures), one reference added in this new versio

Impurities in s=1s=1 Heisenberg Antiferromagnets

The $s=1$ Heisenberg Antiferromagnet is studied in the presence of two kinds of local impurities. First, a perturbed antiferromagnetic bond with $J'\ne J$ at the center of an even-length open chain is considered. Using the density matrix renormalization group method we find that, for sufficiently strong or weak $J'$, a bound state is localized at the impurity site, giving rise to an energy level in the Haldane gap. The energy of the bound state is in agreement with perturbative results, based on $s=1/2$ chain-end excitations, both in the weak and strong coupling limit. In a region around the uniform limit, $J'=J$, no states are found with energy below the Haldane gap. Secondly, a $s=1/2$ impurity at the center of an otherwise even-length open chain is considered. The coupling to the $s=1/2$ impurity is varied. Bound states in the Haldane gap are found {\it only} for sufficiently weak (antiferromagnetic) coupling. For a $s=1/2$ impurity coupled with a strong (antiferromagnetic) bond, {\it no} states are found in the Haldane. Our results are in good qualitative agreement with recent experiments on doped NENP and Y$_2$BaNiO$_5$.Comment: 29 pages, RevTeX 3.0, 12 uuencoded postscript figures include

S(k) for Haldane Gap Antiferromagnets: Large-scale Numerical Results vs. Field Theory and Experiment

The structure function, S(k), for the s=1, Haldane gap antiferromagnetic chain, is measured accurately using the recent density matrix renormalization group method, with chain-length 100. Excellent agreement with the nonlinear $\sigma$ model prediction is obtained, both at $k\approx \pi$ where a single magnon process dominates and at $k\approx 0$ where a two magnon process dominates. We repeat our calculation with crystal field anisotropy chosen to model NENP, obtaining good agreement with both field theory predictions and recent experiments. Correlation lengths, gaps and velocities are determined for both polarizations.Comment: 11 pages, 3 postscript figures included, REVTEX 3.0, UBCTP-93-02

Equal Time Correlations in Haldane Gap Antiferromagnets

The $S=1$ antiferromagnetic Heisenberg chain both with and without single ion anisotropy is studied. Using the recently proposed density matrix renormalization group technique we calculate the energy gaps as well as several different correlation functions. The two gaps, $\Delta_{||}, \Delta_\perp$, along with associated correlation lengths and velocities are determined. The numerical results are shown to be in good agreement with theoretical predictions derived from the nonlinear sigma model and a free boson model. We also study the $S=1/2$ excitations that occur at the ends of open chains; in particular we study the behavior associated with open boundary conditions, using a model of $S=1/2$ spins coupled to the free bosons.Comment: 32 pages, uufiles encoded REVTEX 3.0, 19 postscript figures included, UBCTP-93-02

The politics of evidence: methodologies for understanding the global land rush

Since the most recent ‘land rush’ precipitated by the convergent ‘crises’ of fuel, feed and food in 2007-08, the debate on the consequences of land investments has been massively heightened, with widespread media coverage, policy commentary and civil society engagement. The ‘land rush’ of recent years has been accompanied by a ‘literature rush’, with a fast-growing body of reports, articles, tables and books with varied purposes, metrics and methods. ‘Land grabbing’ is now a hot political topic around the world, discussed amongst the highest circles. This is why getting the facts right is really important, and having effective methodologies is crucial. Several global initiatives have set out to aggregate information on land deals, and to describe their scale, character and distribution. All have contributed to building a better picture of the phenomenon, but all have struggled with methodology. This JPS Forum identifies a profound uncertainty about what it is that is being counted, questions methods used to collate and aggregate ‘land grabs’, and calls for a second phase of land grab research which abandons the aim of deriving total numbers of hectares in favour of more specific, grounded and transparent methods.ESR

Cosmic 21-cm Fluctuations as a Probe of Fundamental Physics

Fluctuations in high-redshift cosmic 21-cm radiation provide a new window for observing unconventional effects of high-energy physics in the primordial spectrum of density perturbations. In scenarios for which the initial state prior to inflation is modified at short distances, or for which deviations from scale invariance arise during the course of inflation, the cosmic 21-cm power spectrum can in principle provide more precise measurements of exotic effects on fundamentally different scales than corresponding observations of cosmic microwave background anisotropies.Comment: 8 pages, 2 figure

Randomized Trial-PrEscription of intraDialytic exercise to improve quAlity of Life in Patients Receiving Hemodialysis

Introduction: Whether clinically implementable exercise interventions in people receiving hemodialysis (HD) therapy improve health-related quality of life (HRQoL) remains unknown. The PrEscription of intraDialytic exercise to improve quAlity of Life PEDAL) study evaluated the clinical benefit and cost-effectiveness of a 6-month intradialytic exercise program. Methods: In a multicenter, single-blinded, randomized, controlled trial, people receiving HD were randomly assigned to (i) intradialytic exercise training (exercise intervention group [EX]) and (ii) usual care (control group [CON]). Primary outcome was change in Kidney Disease Quality of Life Short-Form Physical Component Summary (KDQOL-SF 1.3 PCS) from baseline to 6 months. Cost-effectiveness was determined using health economic analysis; physiological impairment was evaluated by peak oxygen uptake; and harms were recorded. Results: We randomized 379 participants; 335 and 243 patients (EX  = 127; CON  = 116) completed baseline and 6-month assessments, respectively. Mean difference in change PCS from baseline to 6 months between EX and CON was 2.4 (95% confidence interval [CI]: -0.1 to 4.8) arbitrary units ( = 0.055); no improvements were observed in peak oxygen uptake or secondary outcome measures. Participants in the intervention group had poor compliance (47%) and poor adherence (18%) to the exercise prescription. Cost of delivering intervention ranged from US$598 to US$1092 per participant per year. The number of participants with harms was similar between EX ( = 69) and CON ( = 56). A primary limitation was the lack of an attention CON. Many patients also withdrew from the study or were too unwell to complete all physiological outcome assessments. Conclusions: A 6-month intradialytic aerobic exercise program was not clinically beneficial in improving HRQoL as delivered to this cohort of deconditioned patients on HD

The PrEscription of intraDialytic exercise to improve quAlity of Life in patients with chronic kidney disease trial:study design and baseline data for a multicentre randomized controlled trial

Background: Exercise interventions designed to improve physical function and reduce sedentary behaviour in haemodialysis (HD) patients might improve exercise capacity, reduce fatigue and lead to improved quality of life (QOL). The PEDAL study aimed to evaluate the effectiveness of a 6-month intradialytic exercise programme on quality of life (QOL) and physical function, compared to usual care for patients on HD in the UK.Methods: We conducted a prospective, pragmatic multicentre randomised controlled trial (RCT) in 335 HD patients and randomly (1:1) assigned them to either, i) intradialytic exercise training plus usual care maintenance HD, or ii) usual care maintenance HD. The primary outcome of the study was the change in Kidney Disease Quality of Life (KDQOL-SF 1.3) Physical Component Score between baseline and 6 months. Additional secondary outcomes included changes in: peak aerobic capacity, physical fitness, habitual physical activity levels and falls (International Physical Activity Questionnaire, Duke’s Activity Status Index and Tinetti Falls Efficacy Scale), quality of life and symptom burden assessments (EQ5D), arterial stiffness (pulse wave velocity), anthropometric measures, resting blood pressure, clinical chemistry, safety and harms associated with the intervention, hospitalisations, and cost-effectiveness. A nested qualitative study investigated the experience and acceptability of the intervention for both participants and members of the renal healthcare team.Results: At baseline assessment, 62.4% of the randomised cohort were male, the median age was 59.3 years, and 50.4% were White. Prior cerebrovascular events and myocardial infarction (MI) were present in 8 and 12% of the cohort, respectively, 77.9% of patients had 3hypertension and 39.4% had diabetes. Baseline clinical characteristic and laboratory data for the randomised cohort were generally concordant with data from the UK Renal Registry.Conclusion: The results from this study will address a significant knowledge gap in the prescription of exercise interventions for patients receiving maintenance HD therapy and inform the development of intradialytic exercise programmes both nationally and internationally.Trial Registration: ISRCTN N83508514; registered on 17th December 2014.</p

Statistical Characterization of the Chandra Source Catalog

The first release of the Chandra Source Catalog (CSC) contains ~95,000 X-ray sources in a total area of ~0.75% of the entire sky, using data from ~3,900 separate ACIS observations of a multitude of different types of X-ray sources. In order to maximize the scientific benefit of such a large, heterogeneous data-set, careful characterization of the statistical properties of the catalog, i.e., completeness, sensitivity, false source rate, and accuracy of source properties, is required. Characterization efforts of other, large Chandra catalogs, such as the ChaMP Point Source Catalog (Kim et al. 2007) or the 2 Mega-second Deep Field Surveys (Alexander et al. 2003), while informative, cannot serve this purpose, since the CSC analysis procedures are significantly different and the range of allowable data is much less restrictive. We describe here the characterization process for the CSC. This process includes both a comparison of real CSC results with those of other, deeper Chandra catalogs of the same targets and extensive simulations of blank-sky and point source populations.Comment: To be published in the Astrophysical Journal Supplement Series (Fig. 52 replaced with a version which astro-ph can convert to PDF without issues.