Identical Items Research Articles

Optimal service parts contract with multiple response times and on-site spare parts

This study examines user outsourcing of spare parts management to vendors through a service contract. The user’s selection of a fixed-price service parts contract is formulated as a stochastic integer programming model that decides multiple response times and on-site spare parts, while considering component breakdown with uncertain failure rates. We analytically derive the optimality conditions for the continuous case and subsequently design an efficient algorithm. Numerical illustrations and analyses are conducted to evaluate decisions under various scenarios. Our analysis shows that when both failure rate and expedited contract cost are high, coupled with low part cost, users would prefer the purchase of spare parts for all components to expedited contracts. A fixed-price expedited contract has a lower marginal cost with respect to failure rate than a fixed-price next day contract and a usage-based contract. We also examine inventory behaviour for a single part, multiple types of parts, and multiple groups of parts. It is shown that there is a cost-saving pooling effect in spare parts for identical items, which significantly raises the likelihood of having on-site stored parts. The problem becomes more complex for multiple items, reflecting bundling effects between items for a given contract.

A Stochastic Joint Replenishment Problem with Dissimilar Items

ABSTRACTThe classical stochastic joint replenishment problem (SJRP) often assumes uncapacitated batch size, and identical items. However, real problems encountered relate to the truck , or the container which has limited capacity. When the shipping capacity is limited, and the items are dissimilar in size, the problem becomes more challenging. By defining a class of order‐up‐to policies, we formulate the SJRP of this kind as a combinatorial optimization problem. To solve the problem, a data structure and an algorithm are developed. Based on the algorithm, we also suggest several heuristics including the (U, S) policy—a generalization of the well‐known (Q, S) policy for dissimilar items. The numerical study shows the (U, S) policy is robust and efficient. It performs well, especially when the items become more dissimilar, in terms of shipping size and inventory velocity.

Large neighborhood search for the bike request scheduling problem

AbstractThis paper introduces an efficient algorithm for the bike request scheduling problem (BRSP). The BRSP is built around the concept of request, defined as the pickup or dropoff of a number of identical items (bikes) at a specific station, within a certain time window, and with a certain priority. The aim of the BRSP is to sequence requests on (and hence determine the routes of) a set of vehicles, in such a way that the sum of the priorities of the executed requests is maximized, all time windows are respected, and the capacity of the vehicles is not exceeded. The generation of the set of requests is explicitly not a part of the problem definition of the BRSP. The primary application of the BRSP, from which it derives its name, is to determine the routes of a set of repositioning vehicles in a bike sharing system, although other applications exist. The algorithm introduced in this paper is based on a set of related greedy randomized adaptive search procedure followed by variable neighborhood descent (GRASP + VND) operators embedded in a large neighborhood search (LNS) framework. Since this paper presents the first heuristic for the BRSP, a computational comparison to existing approaches is not possible. We therefore compare the solutions found by our LNS heuristic to those found by an exact solver (Gurobi). These experiments confirm that the proposed algorithm scales to realistic dimensions and is able to find near‐optimal solutions in seconds.

Online Random Sampling for Budgeted Settings

We study online multi-unit auctions in which each agent’s private type consists of the agent’s arrival and departure times, valuation function and budget. Similarly to secretary settings, the different attributes of the agents’ types are determined by an adversary, but the arrival process is random. We establish a general framework for devising truthful random sampling mechanisms for online multi-unit settings with budgeted agents. We demonstrate the applicability of our framework by applying it to different objective functions (revenue and liquid welfare), and a range of assumptions about the agents’ valuations (additive or general) when selling identical divisible items. Our main result is the design of mechanisms for additive bidders with budget constraints that extract a constant fraction of the optimal revenue (under a standard large market assumption). We also show a mechanism that extracts a constant fraction of the optimal liquid welfare for general valuations.

Braille readers break mirror invariance for both visual Braille and Latin letters

For this study, we started from the observation that the poor adequacy of a script to the requirements of the human visual system strongly impacts some aspects of reading expertise (e.g., fluent reading). Here we investigated another of these aspects, namely the ability to break mirror invariance, which makes it hard for readers to ignore the mirrored contrasts of letters even if this hinders performance. In particular, we hypothesized that this ability would be preserved for the visually presented letters of the Braille alphabet despite their poor fit to the constraints of the human visual system, as it did for congenital Braille readers when they explored the same letters through the tactile modality (de Heering, Collignon, & Kolinsky, 2018). To test so, we measured visual Braille readers’ mirror costs, indexing for their difficulty to consider mirrored items as identical compared to strictly identical items, for three materials: Braille letters, geometrical shapes and Latin letters, which invariant properties are typically considered as having been selected through cultural evolution because they match the requirements of the visual system. Contrary to people having never experienced Braille, Braille readers’ mirror cost was of the same magnitude for Latin letters and Braille letters and steadily increased the more they had experience with the latter material. Both these costs were also stronger than what was observed for geometrical shapes. Overall these results suggest that the poor adequacy of the Braille alphabet to the visual system does not impede Braille readers to break mirror invariance for the Braille material.

The German W-DEQ version B—Factor structure and prediction of posttraumatic stress symptoms six weeks and one year after childbirth

The Wijma Delivery Expectancy/Experience Questionnaire is a frequently used measure in the context of childbirth. There are two versions with identical items for use during pregnancy (version A, fear of childbirth) and postpartum (version B, subjective experience) respectively. The original authors report that the measure is unidimensional, but since, very different factor structures have been found with different language versions. In this study, I tested the previously found factor structures in a sample of 338 German new mothers with confirmatory factor analysis. As none showed an adequate fit, I conducted an exploratory factor analysis, which yielded six factors with satisfactory internal consistencies.

Considering “Sameness” of Monographic Holdings in Shared Print Retention Decisions

In addition to the pressure of operating in a steady state of insufficient funding, academic libraries face incessant pressure to use space differently. As a result, libraries are aggressively withdrawing materials to relieve cramped shelves and reduce overall collection footprints. Selection for withdrawal may be based on various factors, but of concern is the withdrawal of materials for which copies are currently held in shared print repositories. Recent publications point to the need for thoughtful and strategic evaluation of shared print for quality and completeness, plus the evaluation of copies considered for withdrawal to ensure the perseverance of our print heritage. This study focuses on the comparison of forty-seven monographic titles cataloged as identical items that show broadly varying differences in editions, printings, condition, and preservation and repair. Survey data collected includes information about bibliographic accuracy, printing and binding variances, completeness, physical damage, chemical deterioration, provenance, and presence in the HathiTrust. The results show wide variability in the accuracy of cataloging records, historical use, physical condition of the materials, and the ability for those materials to be successfully digitized in the future. These results are illustrative of the strong potential for variation in “identical” bibliographic holdings among the broader academic library community.

Predicting Search Performance in Heterogeneous Scenes: Quantifying the Impact of Homogeneity Effects in Efficient Search

Recently, Wang, Buetti and Lleras (2017) developed an equation to predict search performance in heterogeneous visual search scenes (i.e., multiple types of non-target objects simultaneously present) based on parameters observed when participants perform search in homogeneous scenes (i.e., when all non-target objects are identical to one another). The equation was based on a computational model where every item in the display is processed with unlimited capacity and independently of one another, with the goal of determining whether the item is likely to be a target or not. The model was tested in two experiments using real-world objects. Here, we extend those findings by testing the predictive power of the equation to simpler objects. Further, we compare the model’s performance under two stimulus arrangements: spatially-intermixed (items randomly placed around the scene) and spatially-segregated displays (identical items presented near each other). This comparison allowed us to isolate and quantify the facilitatory effect of processing displays that contain identical items (homogeneity facilitation), a factor that improves performance in visual search above-and-beyond target-distractor dissimilarity. The results suggest that homogeneity facilitation effects in search arise from local item-to-item interaction (rather than by rejecting items as “groups”) and that the strength of those interactions might be determined by stimulus complexity (with simpler stimuli producing stronger interactions and thus, stronger homogeneity facilitation effects).

Robust Two-Stage Packing into Designated and Multipurpose Bins

Abstract Multitype bin packing is a natural extension of the classical bin packing with applications to shipping using climate-controlled containers and plain dry containers. In transportation and other logistics applications there may be significant uncertainty with respect to the exact quantities of different variants of products (or item types) that may need to be shipped at the time when the containers and packaging are procured. In the current paper we model the problem as a robust two-stage two-item type bin packing problem. In the first stage bins of different types are acquired (e.g., reefer containers and dry containers). In the second stage the items are packed into bins. The bins that are secured in the first phase must allow for all of the items to be packed in the “worst-case” demand scenario. We first develop an algorithm for the robust two-stage two-item type bin packing problem with general item-number uncertainty sets and certain box uncertainty sets for item sizes (or equivalently two item sizes). We then consider the special case of identical (or unit) item sizes. In this special case we develop closed-form solutions for the optimal solution. Our closed-form solution reveals that it is optimal to use a number of multipurpose bins that is linear in the number of items. This is in contrast with solutions of the online and offline deterministic version of our problem that use at most one multipurpose bin. Finally, we consider computational methods that are efficient in practice for a generalization with unit item sizes but with an arbitrary number of item and bin types and arbitrary compatibility structures.

A Block Corner-Occupying Heuristic Algorithm for Constrained Two-Dimensional Guillotine Cutting Problem of Rectangular Items

Aiming at the constrained two-dimensional guillotine cutting problem of rectangular items, a heuristic algorithm with block corner-occupying pattern is presented in this paper. It can maximize the pattern value for the totally included items, but the occurring frequency of each item type doesn’t exceed its upper bound. Several rows and columns of identical items are packed at the left-bottom corner of the sheet, and the remaining part is divided into two sub-sheets. The sub-sheets are then packed and divided in the same way till no items can be packed. This upper bound and normal size methods applied in the algorithm will avoid the unnecessary calculation. The algorithm is compared with 9 literature algorithms with benchmark instances and random instances. Computational results show that, compared with the 8 heuristic algorithms, the pattern value of this algorithm is increased by 0.787% to 6.119% and the calculation time is reasonable. Compared with the exact algorithm, for large size instances the pattern value of this algorithm is 0.090% lower than it, but the calculation time is only 0.079% of it.

On social envy-freeness in multi-unit markets

We consider a market setting in which buyers are individuals of a population, whose relationships are represented by an underlying social graph. Given buyers' valuations for the items being sold, an outcome consists of a pricing of the objects and an allocation of bundles to the buyers. An outcome is social envy-free if no buyer strictly prefers the bundles of her neighbors in the social graph. We focus on the revenue maximization problem in multi-unit markets, in which there are multiple copies of the same item being sold, and each buyer is assigned a subset of identical items. We consider four different cases that arise when considering two different buyers valuations, i.e., single-minded or general, and by adopting two different forms of pricing, that is item- or bundle-pricing. For all the above cases we show the hardness of the revenue maximization problem and give corresponding approximation results. All our approximation bounds are optimal or nearly optimal. Moreover, under the assumption of social graphs of bounded treewidth, we provide an optimal allocation algorithm for general valuations with item-pricing. Finally, we determine optimal bounds on the corresponding price of envy-freeness, that is on the worst-case ratio between the maximum revenue that can be achieved without envy-freeness constraints, and the one obtainable in case of social relationships. Some of our results close hardness open questions or improve already known ones in the literature concerning the standard setting without sociality.

Efficient Computational Strategies for Dynamic Inventory Liquidation

We examine the dynamic inventory liquidation problem, in which a retailer liquidates a fixed number of identical items over a time period by strategically setting prices periodically according to knowledge about stochastic demand. We propose to solve the liquidation problem by deriving a deterministic representation of stochastic demand. Assuming that customer arrival and valuations follow known statistical distributions (e.g., estimated from past transaction data), the expected arrivals and expected order statistics of valuation distributions represent informative and advantageous approximations of demand. Under the deterministic demand representation, we develop a greedy heuristic for finding the optimal liquidation strategy that result in maximum total revenue. The heuristic approach is computationally highly efficient and provides optimal solutions under deterministic demand representation when customer valuation follows various typical statistical distributions. Compared with two simple and commonly used liquidation strategies (i.e., the fixed-price strategy and the fixed-quantity strategy), our heuristic yields higher liquidation revenue. Compared with sophisticated approaches that can find optimal liquidation strategies under stochastic demand (e.g., stochastic dynamic programming), our approach runs several magnitudes faster and still yields near optimal expected revenue. Therefore, the heuristic approach can serve as a useful tool for managers to make liquidation-related decisions in realistic, stochastic demand scenarios.

Customizations, collections and corporations: Mass production and self-expression

Collecting and customizing highlight the interrelation of fan works and fan practices with corporate counterparts. Neither can be neatly isolated from the other. Corporations appropriate multiple aspects of material fan practices to encourage consumption, framing choice as customization and mass-produced merchandise as rare collectibles. Meanwhile, fans practice mini-mass-production, making multiple versions of fan works for sale or trade. Moving beyond an artificial value-laden binary opposition between fan customizations and collections or corporate versions, it would be more productive to focus on how both satisfy human urges for control and self-expression via one’s own creations and possessions. The personal investment of time and effort offers an expression and extension of self. Fans use toys, shoes, phone cases and other merchandise as raw materials for their creations. What varies is the amount of time, energy, skill or material resources individuals are able or willing to invest. Thus multiple supposedly distinct fan practices interconnect: customizers modifying or creating beloved fan objects; customers selecting from predetermined options to make their own variations on shoes, phone cases and other merchandise; shoppers seeking slight variations in seemingly identical items or collectors assembling work created by corporations or other customizers to display their own creations. Even if corporations monetize some forms of self-expression, collecting or customizing such items should be recognized as a form of fan activity instead of dismissed as mere consumerism.

Encoding strategies in self-initiated visual working memory.

During a typical day, visual working memory (VWM) is recruited to temporarily maintain visual information. Although individuals often memorize external visual information provided to them, on many other occasions they memorize information they have constructed themselves. The latter aspect of memory, which we term self-initiated WM, is prevalent in everyday behavior but has largely been overlooked in the research literature. In the present study we employed a modified change detection task in which participants constructed the displays they memorized, by selecting three or four abstract shapes or real-world objects and placing them at three or four locations in a circular display of eight locations. Half of the trials included identical targets that participants could select. The results demonstrated consistent strategies across participants. To enhance memory performance, participants reported selecting abstract shapes they could verbalize, but they preferred real-world objects with distinct visual features. Furthermore, participants constructed structured memory displays, most frequently based on the Gestalt organization cue of symmetry, and to a lesser extent on cues of proximity and similarity. When identical items were selected, participants mostly placed them in close proximity, demonstrating the construction of configurations based on the interaction between several Gestalt cues. The present results are consistent with recent findings in VWM, showing that memory for visual displays based on Gestalt organization cues can benefit VWM, suggesting that individuals have access to metacognitive knowledge on the benefit of structure in VWM. More generally, this study demonstrates how individuals interact with the world by actively structuring their surroundings to enhance performance.

Evaluating the Efficiency of CPUs, GPUs and FPGAs on a Near-Duplicate Document Detection Via OpenCL

Discovering identical or near-identical items is urgently important in many applications such as Web crawling since it drastically reduces the text processing costs. Simhash is a widely used technique, able to attribute a bit-string identity to a text, such that similar texts have similar identities. In this study, a real-time solution for a simhash calculation in OpenCL is presented. We also show how it can be utilized by multi-CPUs, GPUs and FPGAs. As a result we indicate that the bottom line computation realized on the FPGA through OpenCL provides significant power advantages.

On Social Envy-Freeness in Multi-Unit Markets

We consider a market setting in which buyers are individuals of a population, whose relationships are represented by an underlying social graph. Given buyers valuations for the items being sold, an outcome consists of a pricing of the objects and an allocation of bundles to the buyers. An outcome is social envy-free if no buyer strictly prefers the bundles of her neighbors in the social graph. We focus on the revenue maximization problem in multi-unit markets, in which there are multiple copies of a same item being sold and each buyer is assigned a set of identical items. We consider the four different cases arising by considering different buyers valuations, i.e., single-minded or general, and by adopting different forms of pricing, that is item- or bundle-pricing. For all the above cases we show the hardness of the revenue maximization problem and give corresponding approximation results. All our approximation bounds are optimal or nearly optimal. Moreover, we provide an optimal allocation algorithm for general valuations with item-pricing, under the assumption of social graphs of bounded treewidth. Finally, we determine optimal bounds on the corresponding price of envy-freeness, that is on the worst case ratio between the maximum revenue that can be achieved without envy-freeness constraints, and the one obtainable in case of social relationships. Some of our results close hardness open questions or improve already known ones in the literature concerning the classical setting without sociality.

The effects of competitive reserve prices in online auctions

PurposeThis paper aims to investigate how competition among online auction sellers influences the setting of both open and secret reserve prices, thereby affecting auction outcome.Design/methodology/approachUsing a data set collected from eBay consisting of 787 identical product auctions, three empirical models have been proposed. Model 1 simultaneously estimates the effects of auction competition on a seller’s own open and secret reserve price strategies; Model 2 estimates the effects of auction competition on bidder participation; and Model 3 estimates the direct and indirect effects of auction competition on selling price.FindingsCompetition among sellers is central to shaping sellers’ reserve price strategies. When there are more concurrent auctions for identical items, sellers tend to specify a low open reserve and are less likely to set a secret reserve. Sellers are strongly influenced by competitors’ reserve price strategies, and tend to follow competition. Finally, auction competition and competitive reserve price strategies influence both bidder entry and selling prices.Practical implicationsThis study has important implications for both sellers and bidders. It highlights the importance for sellers to adapt their reserve price strategies in light of their competitors’ reserve price strategies and offers implications for bidders regarding auction selection. An auction with low starting bid does not necessarily lead to a lower selling price as it attracts more bidders.Originality/valueThis paper focuses on competition among auction sellers, whereas previous literature has focused on competition among bidders. This paper is the first to study the impact of competing reserve prices in auctions.

Psychopathological Symptoms and Satisfaction with Mental Health in Patients with Schizophrenia

Background: The patient’s view of their mental health is a central aspect in research and practice. Yet, little is known about which psychopathological symptoms are linked with patients’ satisfaction with their mental health. We aimed to identify these symptoms in patients with schizophrenia. Methods: An individual patient data meta-analysis was conducted with data from 2,488 patients from 8 independent studies. Satisfaction with mental health was rated on a 7-point scale, and symptoms were observer-rated using identical items from the Brief Psychiatric Rating Scale and the Positive and Negative Symptom Scale. Mixed multilevel univariate followed by multivariate regression models were used to identify symptoms associated with satisfaction with mental health. Results: In univariate regressions, all subscales – not age and gender – were associated with mental health satisfaction. In the multivariate regression, only affective and negative symptoms were significantly associated with a lower satisfaction with mental health, explaining 22.5% of the variance. Conclusions: Observer-rated psychopathological symptoms are linked to patients’ mental health satisfaction. In addition to affective symptoms – which are commonly negatively linked with satisfaction ratings – a higher level of negative symptoms makes patients less satisfied with their mental health, whilst positive and other symptoms do not influence mental health satisfaction.

Full‐order sliding mode control for finite‐time attitude tracking of rigid spacecraft

This study addresses an attitude tracking problem for a rigid spacecraft with bounded external disturbances. Attitude dynamics of the rigid spacecraft is modelled by a unit quaternion for global representation. Based on this representation, a novel continuous controller is proposed based on the full-order terminal sliding mode method. The finite-time stability of the closed-loop system is assured by Lyapunov and homogeneous finite-time stability theorems. Moreover, the singularity term in the terminal sliding surface is compensated by an identical item in the feedback control law, and this makes the closed-loop system trajectories converge to the equilibrium in finite-time, and hence a high precision is obtained. Finally, simulation results are presented to illustrate the effectiveness of the proposed controller.

Change in HIV-related stigma in South Africa between 2004 and 2016: a cross-sectional community study

ABSTRACTA critical component of an AIDS-free generation is to reduce HIV-related stigma. Previous research predicted that stigma would decline over time with increased contact with PLWH, understanding of the disease and availability of treatment. The aim of the research was to explore change in stigma over a 12-year period, by comparing data collected from two large cross-sectional samples from South African communities in 2004 (before the roll-out of antiretroviral treatment (ART)) and in 2016. Students recruited respondents according to criteria related to age, gender, race and area of living. A survey assessing moral judgement and interpersonal distance was used to assess personal and perceived community stigma. Responses to ten identical items used in the 2004 and 2016 data collection were compared. Personal stigma attached to HIV decreased significantly over time, except in respect of having close contact with PLWH, such as dating and befriending. Perceived community stigma remained high in all subgroups. It is argued that perceived community stigma contributes to high levels of internalised stigma among PLWH. Interventions should focus on helping PLWH to cope with perceived stigma and strategies to address stereotyping, which contributes to perceived community stigma.