Index Rule Research Articles

Computing a Classic Index for Finite-Horizon Bandits

This paper considers the efficient exact computation of the counterpart of the Gittins index for a finite-horizon discrete-state bandit, which measures for each initial state the average productivity, given by the maximum ratio of expected total discounted reward earned to expected total discounted time expended that can be achieved through a number of successive plays stopping by the given horizon. Besides characterizing optimal policies for the finite-horizon one-armed bandit problem, such an index provides a suboptimal heuristic index rule for the intractable finite-horizon multiarmed bandit problem, which represents the natural extension of the Gittins index rule (optimal in the infinite-horizon case). Although such a finite-horizon index was introduced in classic work in the 1950s, investigation of its efficient exact computation has received scant attention. This paper introduces a recursive adaptive-greedy algorithm using only arithmetic operations that computes the index in (pseudo-)polynomial time in the problem parameters (number of project states and time horizon length). In the special case of a project with limited transitions per state, the complexity is either reduced or depends only on the length of the time horizon. The proposed algorithm is benchmarked in a computational study against the conventional calibration method.

Drinking behaviour, protective behavioural strategies and school performance of college students

Aims: Concepts that may be effective in alleviating negative alcohol-related consequences among college students are protective behavioural strategies (PBSs), such as alternating alcoholic and non-alcoholic drinks. Our study used an innovative hypothesis-testing statistical technique (structural equation modelling, SEM) to examine the relationship of PBSs, drinking behaviour and school performance among college student drinkers.Methods: We used confirmatory factor analysis and SEM to explore the relationship between drinking behaviour, PBSs and school performance among a sample of college students (N = 371) who reported drinking alcohol in the past 30 days.Findings: Results indicated that PBSs were positively associated with school performance and drinking behaviour mediated the relationship. Based on the combinatory rules for standardized root mean square residual (SRMR) and comparative fit index (CFI), this model represented a good fit to the data (χ2 = 34.4, df = 17, SRMR = 0.03 and CFI = 0.98).Conclusions: Our study extends the line of research examining the relationship between drinking behaviour, including PBSs, and academic performance of college students by showing the usefulness of an innovative hypothesis-testing statistical technique – SEM. Researchers might want to consider utilizing SEM when examining such relationships in the future. In addition, based on the results of our analyses, colleges and universities with an interest in the academic performance of their students may want to consider implementing and promoting programmes that concern increasing the awareness of PBSs.

Indexing and querying segmented web pages: the BlockWeb Model

We present in this paper a model for indexing and querying web pages, based on the hierarchical decomposition of pages into blocks. Splitting up a page into blocks has several advantages in terms of page design, indexing and querying such as (i) blocks of a page most similar to a query may be returned instead of the page as a whole (ii) the importance of a block can be taken into account, as well as (iii) the permeability of the blocks to neighbor blocks: a block b is said to be permeable to a block b? in the same page if b? content (text, image, etc.) can be (partially) inherited by b upon indexing. An engine implementing this model is described including: the transformation of web pages into blocks hierarchies, the definition of a dedicated language to express indexing rules and the storage of indexed blocks into an XML repository. The model is assessed on a dataset of electronic news, and a dataset drawn from web pages of the ImagEval campaign where it improves by 16% the mean average precision of the baseline.

Improvement of CRB-65 as a prognostic scoring system in adult patients with bacteraemic pneumococcal pneumonia

Community-acquired pneumonia (CAP) is the leading cause of hospitalization among infectious diseases, and is mainly caused by Streptococcus pneumoniae. Modifications were tested to improve the accuracy of CRB-65 as a simple but useful bedside scoring system, and to compare it with 3 established severity scoring systems (PSI, CURB-65 and CRB-65) to predict 30-day mortality in bacteraemic pneumococcal CAP. A retrospective analysis was performed on data from 375 adult patients with bacteraemic pneumococcal pneumonia. Mortality, sensitivity, specificity, positive predictive value, negative predictive value, and area under the receiver operating characteristic (ROC) curve were calculated for stratifications of the PSI, CURB-65 and CRB-65. The prognostic accuracy after addition of underlying disease and/or a peripheral oxygen saturation (SaO₂) < 90% was evaluated (DS CRB-65). The mean age of the patients was 61.5 y, and the 30-day mortality was 9%. Coexisting conditions defined according to the pneumonia severity index (PSI) rule (malignancy, liver, cerebrovascular, and renal disease and congestive heart failure, p = 0.006) and SaO₂ < 90% (p < 0.0001) were independently associated with mortality. By adding these variables, the area under the ROC curve of CRB-65 increased from 0.77 (95% confidence interval (CI) 0.66-0.84) to 0.83 (95% CI 0.73-0.89) (p = 0.01), similar to that of PSI (0.84) and CURB-65 (0.81). Modification of CRB-65 with the addition of 1 point for the presence of any underlying disease according to the PSI rule, and with 1 point if SaO₂ was < 90%, increased its prognostic accuracy in bacteraemic pneumococcal pneumonia with retained independence of laboratory data. The modified CRB-65 may have potential use in the assessment of prognosis in patients with CAP.

An integrated approach to a biophysiologically based classification of floating aquatic macrophytes

Globally, invasive species are identified as one of the most serious threats to ecological stability and biodiversity. Water hyacinth (Eichhornia crassipes), an aggressive invasive aquatic species, has caused severe economic and ecological impacts in the Sacramento-San Joaquin River Delta in California. In the Delta, water hyacinth co-occurs with native pennywort (Hydrocotyle umbellata L.) and non-native water primrose (Ludwigia spp.). All of the species express a wide range of phenotypic variability, making it difficult to map them with remote sensing techniques because their spectral response is highly variable. We present an integrated approach to mapping these floating species using a sequence of hyperspectral methods, such as spectral angle mapper (SAM), linear spectral unmixing (LSU), continuum removal and several indices in a decision tree format. The ensuing tree, based on biophysiological differences between the species, was robust and consistent across three separate years and over multiple flightlines each year, spread across an area of approximately 2500 km2. The most important inputs used to create the tree were reflectance in the short-wave infrared (SWIR), Red Edge Index, near-infrared (NIR) reflectance, LSU fractions and SAM rule values. The floating species were mapped with average accuracy of 88% for water hyacinth, 87% for pennywort and 71% for water primrose.

Ageing and the welfare state: securing sustainability

Over the next four decades, increasing old-age dependency ratios will exert an enormous upward pressure on welfare spending in most developed countries. As this is mainly due to existing unfunded public pension schemes, many countries have embarked on far-reaching reforms in this area, strengthening actuarial fairness, modifying indexation rules, adding elements of pre-funding, and, last but not least, attempting to extend the period of economic activity. Efforts to contain costs may also be relevant with regard to public expenditure on health and long-term care but, thus far, no country has started to really deal with these issues. Still, some countries have made substantial progress in securing the long-term sustainability of their welfare systems. What remains to be considered is re-constructing the system of intergenerational transactions as a potential way of removing disincentives to raise children and invest in their human capital in the long run.

Dividend-Yield Based Trading Rules: The Turkish Evidence

Recent research documents the superiority of dividend-yield based trading rules over a buy-and-hold strategy in the U.S. and Finland. We extend the international evidence on the superiority of dividend-yield based trading rules by examining whether the trading rules outperform a buy-and-hold strategy in Turkey. Specifically, we examine the returns of the ISE 30 index and trading rule portfolios that are components of the Istanbul Stock Exchange. Using a multiplicity of parametric and non-parametric tests, empirical results reveal that dynamic trading strategies do not outperform a passive strategy in Turkey.

Refractive Index of Liquid Mixtures: Theory and Experiment

An innovative approach is presented to interpret the refractive index of binary liquid mixtures. The concept of refractive index "before mixing" is introduced and shown to be given by the volume-fraction mixing rule of the pure-component refractive indices (Arago-Biot formula). The refractive index of thermodynamically ideal liquid mixtures is demonstrated to be given by the volume-fraction mixing rule of the pure-component squared refractive indices (Newton formula). This theoretical formulation entails a positive change of refractive index upon ideal mixing, which is interpreted in terms of dissimilar London dispersion forces centred in the dissimilar molecules making up the mixture. For real liquid mixtures, the refractive index of mixing and the excess refractive index are introduced in a thermodynamic manner. Examples of mixtures are cited for which excess refractive indices and excess molar volumes show all of the four possible sign combinations, a fact that jeopardises the finding of a general equation linking these two excess properties. Refractive indices of 69 mixtures of water with the amphiphile (R,S)-1-propoxypropan-2-ol are reported at five temperatures in the range 283-303 K. The ideal and real refractive properties of this binary system are discussed. Pear-shaped plots of excess refractive indices against excess molar volumes show that extreme positive values of excess refractive index occur at a substantially lower mole fraction of the amphiphile than extreme negative values of excess molar volume. Analysis of these plots provides insights into the mixing schemes that occur in different composition segments. A nearly linear variation is found when Balankina's ratios between excess and ideal values of refractive indices are plotted against ratios between excess and ideal values of molar volumes. It is concluded that, when coupled with volumetric properties, the new thermodynamic functions defined for the analysis of refractive indices of liquid mixtures give important complementary information on the mixing process over the whole composition range.

Validity of British Thoracic Society guidance (the CRB-65 rule) for predicting the severity of pneumonia in general practice: systematic review and meta-analysis

The CRB-65 score is a clinical prediction rule that grades the severity of community-acquired pneumonia in terms of 30-day mortality. The study sought to validate CRB-65 and assess its clinical value in community and hospital settings. Systematic review and meta-analysis of validation studies of CRB-65. Medline (1966 to June 2009), Embase (1988 to November 2008), British Nursing Index (BNI) and PsychINFO were searched, using a diagnostic accuracy search filter combined with subject-specific terms. The derived (index) rule was used as a predictive model and applied to all validation studies. Comparison was made between the observed and predicted number of deaths stratified by risk group (low, intermediate, and high) and setting of care (community or hospital). Pooled results are presented as risk ratios (RRs) in terms of over-prediction (RR>1) or under-prediction (RR<1) of 30-day mortality. Fourteen validation studies totalling 397 875 patients are included. CRB-65 performs well in hospitalised patients, particularly in those classified as intermediate (RR 0.91, 95% confidence interval [CI] = 0.71 to 1.17) or high risk (RR 1.01, 95% CI = 0.87 to 1.16). In community settings, CRB-65 over-predicts the probability of 30-day mortality across all strata of predicted risk, low (RR 9.41, 95% CI = 1.75 to 50.66), intermediate (RR 4.84, 95% CI = 2.61 to 8.69), and high (RR 1.58, 95% CI = 0.59 to 4.19). CRB-65 performs well in stratifying severity of pneumonia and resultant 30-day mortality in hospital settings. In community settings, CRB-65 appears to over-predict the probability of 30-day mortality across all strata of predicted risk. Caution is needed when applying CRB-65 to patients in general practice.

The cμ/θ Rule for Many-Server Queues with Abandonment

We consider a multiclass queueing system with multiple homogeneous servers and customer abandonment. For each customer class i, the holding cost per unit time, the service rate, and the abandonment rate are denoted by ci, μi, and θi, respectively. We prove that under a many-server fluid scaling and overload conditions, a server-scheduling policy that assigns priority to classes according to their index ciμi/θi is asymptotically optimal for minimizing the overall long-run average holding cost. An additional penalty on customer abandonment is easily incorporated into this model and leads to a similar index rule.

X-RAY EMISSION FROM THE SOMBRERO GALAXY: DISCRETE SOURCES

We present a study of discrete X-ray sources in and around the bulge-dominated, massive Sa galaxy, Sombrero (M104), based on new and archival Chandra observations with a total exposure of ~200 ks. With a detection limit of L_X = 1E37 erg/s and a field of view covering a galactocentric radius of ~30 kpc (11.5 arcminute), 383 sources are detected. Cross-correlation with Spitler et al.'s catalogue of Sombrero globular clusters (GCs) identified from HST/ACS observations reveals 41 X-rays sources in GCs, presumably low-mass X-ray binaries (LMXBs). We quantify the differential luminosity functions (LFs) for both the detected GC and field LMXBs, whose power-low indices (~1.1 for the GC-LF and ~1.6 for field-LF) are consistent with previous studies for elliptical galaxies. With precise sky positions of the GCs without a detected X-ray source, we further quantify, through a fluctuation analysis, the GC LF at fainter luminosities down to 1E35 erg/s. The derived index rules out a faint-end slope flatter than 1.1 at a 2 sigma significance, contrary to recent findings in several elliptical galaxies and the bulge of M31. On the other hand, the 2-6 keV unresolved emission places a tight constraint on the field LF, implying a flattened index of ~1.0 below 1E37 erg/s. We also detect 101 sources in the halo of Sombrero. The presence of these sources cannot be interpreted as galactic LMXBs whose spatial distribution empirically follows the starlight. Their number is also higher than the expected number of cosmic AGNs (52+/-11 [1 sigma]) whose surface density is constrained by deep X-ray surveys. We suggest that either the cosmic X-ray background is unusually high in the direction of Sombrero, or a distinct population of X-ray sources is present in the halo of Sombrero.

A modeling framework for optimizing the flow-level scheduling with time-varying channels

We introduce a comprehensive modeling framework for the problem of scheduling a finite number of finite-length jobs where the available service rate is time-varying. The main motivation comes from wireless data networks where the service rate of each user varies randomly due to fading. We employ recent advances on the restless bandit problem that allow us to obtain an opportunistic scheduling rule for the system without arrivals. When the objective is to minimize the mean number of users in the system or to minimize the mean waiting time, we obtain a priority-based policy which we call the “Potential Improvement” (PI) rule, since the priority index equals the ratio between the current available service rate and the expected potential improvement of the service rate. We also show that for certain objective functions, the index rule takes the form of known opportunistic scheduling rules like “Relatively Best” (RB) or “Proportionally Best” (PB). Thus our model provides a formal justification for the deployment of opportunistic scheduling rules in order to improve the flow-level performance in the presence of time-varying capacities. We further analyze the performance of the PI rule in the presence of randomly arriving users. When the service rates are constant, PI is equivalent to the c μ -rule, which is known to be optimal with any distribution of arrivals. Using a recent characterization for the stability region of flow-level scheduling rules under random arrivals, we show that PI achieves the maximum stability region. We perform numerical experiments in a wide range of scenarios and compare the performance of PI with other popular disciplines like RB, PB, Score-Based (SB) and the c μ -rule. Our results show that RB, PB, SB or the c μ -rule might outperform the others depending on the scenario, but regardless of this, the performance of PI is always superior or equivalent to the best of these opportunistic rules.

The political and institutional determinants of fiscal adjustment: Entering and exiting fiscal distress

The literature on fiscal adjustment focuses on the determinants of “successful” adjustment episodes that generate desirable outcomes (such as lower debt levels), but it generally ignores whether an adjustment is needed or not. This paper introduces the notion of adjustment need, which is a period of severe fiscal distress that signals a clear need for consolidation. This new concept allows the author to empirically investigate the role of political and institutional factors in determining why countries get into fiscal distress, why some are able to fiscally consolidate when required, and why others are unable to adjust despite an evident need to do so. For developing economies, strong scores for broad measures of institutional quality (e.g. rule of law indices) are found to help avoid situations of fiscal distress, but weaker scores characterize those countries that actually manage to make large adjustments. For advanced countries, the results highlight the importance of budgetary institutions: fiscal rules contribute to avoiding situations of fiscal distress, and fiscal performance management systems improve the odds of implementing adjustments.

Ageing and the Welfare State: Securing Sustainability

Over the next four decades, increasing old-age dependency ratios exert an enormous upward pressure on welfare spending in most developed countries. As this is mainly due to existing unfunded public pension schemes, many countries have embarked on far-reaching reforms in this area, strengthening actuarial fairness, modifying indexation rules, adding elements of prefunding and, last but not least, attempting to extend the period of economic activity. Efforts to contain costs may also be relevant with regard to public expenditure on health and long-term care but, thus far, no country has started to really deal with these issues. Still, some countries have made substantial progress in securing the long-term sustainability of their welfare systems. What remains to be considered is re-constructing the system of intergenerational transactions as a potential way of removing disincentives to raise children and invest in their human capital in the long run.

Computational Design of Highly Selective Antimicrobial Peptides

We have created a structure-selectivity database (AMPad) of frog-derived, helical antimicrobial peptides (AMPs), in which the selectivity was determined as a therapeutic index (TI), and then used the novel concept of sequence moments to study the lengthwise asymmetry of physicochemical peptide properties. We found that the cosine of the angle between two sequence moments obtained with different hydrophobicity scales, defined as the D-descriptor, identifies highly selective peptide antibiotics. We could then use this descriptor to predict TI changes after point mutations in known AMPs, and to aid the prediction of TI for de novo designed AMPs. In combination with an amino acid selectivity index, a motif regularity index and other statistical rules extracted from AMPad, the D-descriptor enabled construction of the AMP-Designer algorithm. A 23 residue, glycine-rich, peptide suggested by the algorithm was synthesized and the activity and selectivity tested. This peptide, adepantin 1, is less than 50% identical to any other AMP, has a potent antibacterial activity against the reference organism, E. coli, and has a significantly greater selectivity (TI > 200) than the best AMP present in the AMPad database (TI = 125).

A ABORDAGEM MICROECONOMICA DA INDEXAÇÃO SALARIAL: TEORIA E EVIDÊNCIA

Este artigo apresenta, tanto em nível teórico quanto empírico, os principais resultados da abordagem macroeconômica da indexação salarial. O objetivo de tal abordagem é o de procurar explicar uma série de características referentes à incidência das cláusulas de irulexação salarial nos acordos coletivos de trabalho firmados principalmente entre as empresas e os sindicatos.

On the Gittins index in the M/G/1 queue

For an M/G/1 queue with the objective of minimizing the mean number of jobs in the system, the Gittins index rule is known to be optimal among the set of non-anticipating policies. We develop properties of the Gittins index. For a single-class queue it is known that when the service time distribution is of type Decreasing Hazard Rate (New Better than Used in Expectation), the Foreground---Background (First-Come-First-Served) discipline is optimal. By utilizing the Gittins index approach, we show that in fact, Foreground---Background and First-Come-First-Served are optimal if and only if the service time distribution is of type Decreasing Hazard Rate and New Better than Used in Expectation, respectively. For the multi-class case, where jobs of different classes have different service distributions, we obtain new results that characterize the optimal policy under various assumptions on the service time distributions. We also investigate distributions whose hazard rate and mean residual lifetime are not monotonic.

Investigating the Scheduling Sensitivity of P2P Video Streaming: An Experimental Study

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Peer-to-peer (P2P) technology has recently been employed to deliver large scale video multicast services on the Internet. Considerable efforts have been made by both academia and industry on P2P streaming design. While academia mostly focus on exploring design space to approach the theoretical performance bounds, our recent measurement study on several commercial P2P streaming systems indicates that they are able to deliver good user quality of experience with seemingly simple designs. One intriguing question remains: <emphasis emphasistype="boldital">how elaborate should a good P2P video streaming design be?</emphasis> Towards answering this question, we developed and implemented several representative P2P streaming designs, ranging from theoretically proved optimal designs to straightforward “naive” designs. Through an extensive comparison study on PlanetLab, we unveil several key factors contributing to the successes of simple P2P streaming designs, including system resource index, server capacity and chunk scheduling rule, peer download buffering and peering degree. We also identify regions where naive designs are inadequate and more elaborate designs can improve things considerably. Our study not only brings us better understandings and more insights into the operation of existing systems, it also sheds lights on the design of future systems that can achieve a good balance between the performance and the complexity. </para>

Opportunistic spectrum access based on a constrained multi-armed bandit formulation

Tracking and exploiting instantaneous spectrum opportunities are fundamental challenges in opportunistic spectrum access (OSA) in presence of the bursty traffic of primary users and the limited spectrum sensing capability of secondary users. In order to take advantage of the history of spectrum sensing and access decisions, a sequential decision framework is widely used to design optimal policies. However, many existing schemes, based on a partially observed Markov decision process (POMDP) framework, reveal that optimal policies are non-stationary in nature which renders them difficult to calculate and implement. Therefore, this work pursues stationary OSA policies, which are thereby efficient yet low-complexity, while still incorporating many practical factors, such as spectrum sensing errors and a priori unknown statistical spectrum knowledge. First, with an approximation on channel evolution, OSA is formulated in a multi-armed bandit (MAB) framework. As a result, the optimal policy is specified by the well-known Gittins index rule, where the channel with the largest Gittins index is always selected. Then, closed-form formulas are derived for the Gittins indices with tunable approximation, and the design of a reinforcement learning algorithm is presented for calculating the Gittins indices, depending on whether the Markovian channel parameters are available a priori or not. Finally, the superiority of the scheme is presented via extensive experiments compared to other existing schemes in terms of the quality of policies and optimality.

The Medical Library Association Essential Guide to Becoming an Expert Searcher: Proven Techniques, Strategies, and Tips for Finding Health Information

The Medical Library Association Essential Guide to Becoming an Expert Searcher: Proven Techniques, Strategies, and Tips for Finding Health Information