Serial Mechanism Research Articles

Size Versus Truthfulness in the House Allocation Problem

We study the House Allocation problem (also known as the Assignment problem), i.e., the problem of allocating a set of objects among a set of agents, where each agent has ordinal preferences (possibly involving ties) over a subset of the objects. We focus on truthful mechanisms without monetary transfers for finding large Pareto optimal matchings. It is straightforward to show that no deterministic truthful mechanism can approximate a maximum cardinality Pareto optimal matching with ratio better than 2. We thus consider randomised mechanisms. We give a natural and explicit extension of the classical Random Serial Dictatorship Mechanism (RSDM) specifically for the House Allocation problem where preference lists can include ties. We thus obtain a universally truthful randomised mechanism for finding a Pareto optimal matching and show that it achieves an approximation ratio of frac{e}{e-1}. The same bound holds even when agents have priorities (weights) and our goal is to find a maximum weight (as opposed to maximum cardinality) Pareto optimal matching. On the other hand we give a lower bound of frac{18}{13} on the approximation ratio of any universally truthful Pareto optimal mechanism in settings with strict preferences. By using a characterisation result of Bade, we show that any randomised mechanism that is a symmetrisation of a truthful, non-bossy and Pareto optimal mechanism has an improved lower bound of frac{e}{e-1}. Since our new mechanism is a symmetrisation of RSDM for strict preferences, it follows that this lower bound is tight. We moreover interpret our problem in terms of the classical secretary problem and prove that our mechanism provides the best randomised strategy of the administrator who interviews the applicants.

Neural decoding with visual attention using sequential Monte Carlo for leaky integrate-and-fire neurons.

How the brain makes sense of a complicated environment is an important question, and a first step is to be able to reconstruct the stimulus that give rise to an observed brain response. Neural coding relates neurobiological observations to external stimuli using computational methods. Encoding refers to how a stimulus affects the neuronal output, and entails constructing a neural model and parameter estimation. Decoding refers to reconstruction of the stimulus that led to a given neuronal output. Existing decoding methods rarely explain neuronal responses to complicated stimuli in a principled way. Here we perform neural decoding for a mixture of multiple stimuli using the leaky integrate-and-fire model describing neural spike trains, under the visual attention hypothesis of probability mixing in which the neuron only attends to a single stimulus at any given time. We assume either a parallel or serial processing visual search mechanism when decoding multiple simultaneous neurons. We consider one or multiple stochastic stimuli following Ornstein-Uhlenbeck processes, and dynamic neuronal attention that switches following discrete Markov processes. To decode stimuli in such situations, we develop various sequential Monte Carlo particle methods in different settings. The likelihood of the observed spike trains is obtained through the first-passage time probabilities obtained by solving the Fokker-Planck equations. We show that the stochastic stimuli can be successfully decoded by sequential Monte Carlo, and different particle methods perform differently considering the number of observed spike trains, the number of stimuli, model complexity, etc. The proposed novel decoding methods, which analyze the neural data through psychological visual attention theories, provide new perspectives to understand the brain.

Size versus Truncation Robustness in the Assignment Problem

We study the size of matchings (expected number of agents matched to some objects) generated by random mechanisms in the assignment problem. We show that no mechanism that satisfies two weak axioms, weak truncation robustness and weak regularity, achieves an approximation ratio better than 1 - 1/e = 63.2%. This result indicates that it is impossible to achieve a matching size larger than 63.2% of the maximum feasible size in the worst case, as long as agents' preferences over objects are private information. Our result indicates that the random serial dictatorship mechanism and probabilistic serial mechanism (which indeed has an approximation ratio of 1 - 1/e) have the best approximation ratio among a broad class of mechanisms.

Measuring and testing the impact of interpersonal mentalizing skills on retail sales performance

The advancement of theory of mind in general, and development of interpersonal mentalizing (IM) skills measure in particular, has opened new avenues for sales research and practice. To further explore and validate this critical measure, we examine the impact of interpersonal mentalizing through the parallel as well as serial mechanisms of self-efficacy and adaptive selling. Modeling these constructs in an input-process-output framework as well as within the neurological brain network, we analyze sales data across two retail contexts. Interpersonal mentalizing skills not only directly increase performance in both the real estate and automobile sectors, but work indirectly through self-efficacy and adaptive selling. Our rival model uncovers a serial mediation from interpersonal mentalizing to self-efficacy to adaptive selling and, ultimately, to performance. Results further validate IM skills measure, bridge retail and neurology literature as an avenue of future research, and provide managers with a guide on how to transform salesperson traits into organizational outcomes.

Synthesis, Structural Characterization and Photodecarbonylation Study of a Dicarbonyl Ruthenium(II)-Bisquinoline Complex.

A photoactivatable ruthenium(II) carbonyl complex mer,cis‐[Ru(II)Cl(BisQ)(CO)2]PF6 2 was prepared using a tridentate bisquinoline ligand (BisQ=(2,6‐diquinolin‐2‐yl)pyridin). Compound 2 was thoroughly characterized by standard analytical methods and single crystal X‐ray diffraction. The crystal structure of the complex cation reveals a distorted octahedral geometry. The decarbonylation upon exposure to 350 and 420 nm light was monitored by UV/VIS absorbance and Fourier transform infrared spectroscopies in acetonitrile and 1 % (v/v) DMSO in water, respectively. The kinetic of the photodecarbonylation has been elucidated by multivariate curve resolution alternating least‐squares analysis. The stepwise decarbonylation follows a serial mechanism. The first decarbonylation occurs very quickly whereas the second decarbonylation step proceeds more slowly. Moreover, the second rate constant is lower in 1 % (v/v) DMSO in water than in acetonitrile. In comparison to 350 nm irradiation, exposure to 420 nm light in acetonitrile results in a lower second rate constant.

Short-term memory problems for phonemes’ serial order in adults with dyslexia: Evidence from a different analysis of the Nonword repetition task

AbstractMany studies show that poor readers make more errors in nonword repetition than better readers. Although this finding is generally linked to the lower quality of poor readers’ phonological representations in verbal short-term memory, the nature of this poor performance remains unclear. We addressed this issue by focusing on two types of phoneme-related performance in a nonword repetition task: (a) recall of phonemes irrespective of their serial order (phoneme identity) and (b) recall of correctly reproduced phonemes’ serial order (serial order). We tested 91 young adults with and without dyslexia. Generalized linear mixed-effects models demonstrated that controls outperformed individuals with dyslexia in the recall of phonemes’ serial order but failed to detect a difference in the recall of phonemes’ identity. These findings are discussed not only in terms of the nature of or access to phonological representations but also in terms of another concept that has recently been advanced in the literature: a specialized serial order mechanism in verbal short-term memory. We also consider the possibility that individuals with dyslexia may be less sensitive to phonotactic constraints.

Perceived CSR initiatives and intention to purchase game items

PurposeThe purpose of this paper is to investigate the effect of perceived corporate social responsibility (CSR) initiatives moderated by a user characteristic (heavy users) on game-item purchase intention and uniquely propose that this moderation is serially mediated by self-esteem and compassion.Design/methodology/approachA 2 (CSR initiatives: high vs low) by 2 (user characteristic: heavy vs non-heavy users) experimental design was employed to test the propositions in the context of an online mobile game.FindingsThe results demonstrate that heavy users with high-perceived CSR initiatives have a higher intention to purchase game items. The results also show that self-esteem and compassion fully and serially mediate the effect of moderation on the intention to purchase game items.Originality/valueThis serial mediation mechanism has rarely been proposed and tested in previous studies and may contribute to extending the literature.

Algorithm for the static balancing of serial and parallel mechanisms combining counterweights and springs: Generation, assessment and ranking of effective design variants

Static balancing through passive devices is a suitable strategy to reduce motor loads for numerous applications in the automation and robotics fields. Many known methods require initially defining which balancing elements to install, thus possibly limiting the compensation effectiveness, since potentially optimal solutions may be neglected. This work presents an approach to statically balance linkages characterized by open and/or closed kinematic chains. The proposed algorithm searches for possible balanced variants of the mechanism that can be arranged by installing combinations of counterweights and springs, without auxiliary linkages. If solutions are found, the corresponding balancing parameters are tuned for optimizing the mechanism energy consumption, by considering the mechanism dynamics when performing its operational tasks. Actual benefits and drawbacks of the variants are assessed through quantitative criteria. The corresponding performance indicators are proposed as a guideline for designers to identify the most convenient balancing solutions. The implemented procedure is general and suitable to study any mechanism admitting closed-form solutions for its forward kinematics. A case study concerning an industrial palletizing robot is reported as an example of application. Overload issues affecting the robot actuators are solved through gravity compensation. The results achieved for the industrial problem prove the procedure effectiveness.

A multi-unit serial inspection robot for power transmission lines

Purpose The purpose of this paper is to introduce a robot mechanism designed for power transmission line inspection. The focus for this design is on obstacle-crossing ability with a goal to create a robot moving and crossing obstacle on not only the straight line but also the steering line. Design/methodology/approach A novel four-unit tri-arm serial robot mechanism is proposed. Every novel unit designed for pitching motion is based on parallelogram structure, which is driven by cables and only one motor. There is gripper-wheel compounding mechanism mounted on the arm. The prototype and obstacle environments are established, and the obstacle-crossing experiments are conducted. Findings The novel unit mechanism and robot prototype have been tested in the lab. The prototype has demonstrated the obstacle-crossing ability when moving and crossing fundamental obstacles on the line. The experimental results show that the robot mechanism meets the obstacle-crossing requirements. Practical implications The novel robot technology can be used for defect inspection of power transmission line by power companies. Social implications It stands to lower the intense and risk of inspection works and reduce the costs related to inspection. Originality/value Innovative features include its architecture, mobility and driving method.

Optimization design for a compact redundant hybrid parallel kinematic machine

Abstract Designing a machine tool that simultaneously satisfies the requirements of high rigidity, large dexterous workspace and small footprint is challenging. This paper proposed a redundant hybrid manipulator as a machine tool with these features. The design attempted to integrate the advantages of a PKM (parallel kinematic mechanism), SKM (serial kinematic mechanism) and redundancy mechanism. The geometric parameters of the manipulator were elaborately tuned to overcome intrinsic and extrinsic singularities with an optimal machining plane. High-accuracy and complex-shape machine results have been experimentally verified. The advantage is the ability to shorten the required strokes of the linear actuators effectively. This change not only improves the performance in terms of rigidity, accuracy and dynamics of the entire mechanism but also reduces the cost of the materials and the performance ratio. The second is to decrease the overall machinery-footprint-to-workspace ratio and lower the manufacturing cost via occupied floor space reduction and layout flexibility of the production line.

On the validity of compliance-based matrix method in output compliance modeling of flexure-hinge mechanism

Compliance-based matrix method (CMM) has been regarded as an efficient technique for output compliance modeling of the flexure hinge-based compliant mechanism, owing to its simplicity and high accuracy. However, this study demonstrates that CMM is not always valid due to the intrinsic ill-condition of the compliance matrix of right circular flexure hinge (RCFH). Inversion of compliance matrix can result in numerical instability in the calculation of its stiffness matrix. It is shown in this study that CMM can be effectively applied to serial compliant mechanism, while its adoption in modeling parallel compliant mechanism needs to be carefully examined due to the matrix inversion involved. The validity of CMM is highly dependent on the spatial configuration, degree of freedom, and singularity of the parallel mechanism. The validity criteria of CMM are discussed in detail with exemplary configurations of 3RRR, 2RR, and bridge-type compliant mechanisms.

Double serial adaptation mechanism for keystroke dynamics authentication based on a single password

Cyber-attacks have spread all over the world to steal information such as trade secrets, intellectual property and banking data. Facing the danger of the insecurity of saved data (personal, professional, official, etc.), keystroke dynamics was proposed as an interesting, non-intrusive, inexpensive, permanent and weakly constrained solution for users. Based on the typing rhythm of users, it improves logical access security. Nevertheless, it was demonstrated that such an authentication mechanism would need a larger number of samples to enroll the typing characteristics of users. Moreover, these registered characteristics generally undergo aging effects after a time span. Different solutions have been suggested to remedy these variability problems, including template adaptation. In this paper, we propose a double serial adaptation strategy that considers a single-capture-based enrollment process. When using the authentication system, the template of users and the decision/adaptation thresholds are updated. Experimental results on three public keystroke dynamics datasets show the benefits of the proposed method.

Switching attention from internal to external information processing: A review of the literature and empirical support of the resource sharing account.

Despite its everyday ubiquity, not much is currently known about cognitive processes involved in flexible shifts of attention between external and internal information. An important model in the task-switching literature, which can serve as a blueprint for attentional flexibility, states that switch costs correspond to the time needed for a serial control mechanism to reallocate a limited resource from the previous task context to the current one. To formulate predictions from this model when applied to a switch between perceptual attention (external component) and working memory (WM; internal component), we first need to determine whether a single, serial control mechanism is in place and, subsequently, whether a limited resource is shared between them. Following a review of the literature, we predicted that a between-domain switch cost should be observed, and its size should be either similar or reduced compared to the standard, within-domain, switch cost. These latter two predictions derive from a shared resource account between external and internal attention or partial independence among them, respectively. In a second phase, we put to the test these opposing predictions in four successive behavioral experiments by means of a new paradigm suited to compare directly between- (internal to external) and within- (external to external) domain switch costs. Across them, we demonstrated the existence of a reliable between-domain switch cost whose magnitude was similar to the within-domain one, thereby lending support to the resource-sharing account.

Geometry based synthesis of planar compliances with redundant mechanisms having five compliant components

In this paper, a geometric approach to the passive realization of any planar compliance with a redundant compliant mechanism is presented. The mechanisms considered are either simple serial mechanisms consisting of five elastic joints or simple parallel mechanisms consisting of five springs. For each type of mechanism, realization conditions to achieve a given compliance are derived. The physical significance of each condition is identified and graphically interpreted. Geometry based synthesis procedures to achieve any given compliance are developed for both types of mechanisms. Since each realization condition imposes restrictions solely on the mechanism geometry, the procedures allow one to choose the geometric properties of each component (from a set of admissible options) independently from the selection of the elastic properties of each component.

A Common Serial Order Mechanism for Verbal Working Memory and Language Production: Evidence from Aphasia

A Common Serial Order Mechanism for Verbal Working Memory and Language Production: Evidence from Aphasia

Compliance Analysis for Flow Effector Actuator Based on Serial Compliant Mechanism With Double Guide Ends

To promote the speed of the supersonic air-to-air missile response when the target moves rapidly, a serial compliant mechanism based on the traditional double-slider mechanism actuated by shape memory alloy (SMA) wire is proposed to adjust the protruding height of the flow effector (FE) from the projectile. The aim is to achieve the active disturbance control of the projectile flight attitude. The actuation displacement of the SMA wire is amplified in the output direction, and the FE actuator structure is more lightweight and compact. Based on strain energy, Castigliano's second displacement theorem, and the coordinate transformation method, a free-end displacement mathematical model for a single corner filleted flexure hinge with a single load is developed. For the serial compliant mechanism under single or multiple loads, displacements of the focus points on different rigid links are investigated under varying boundary conditions, such as one fixed end and the other free, double fixed ends, one fixed end and the other a guide end, and double guide ends. The input displacement, output displacement, and displacement amplification of the proposed FE actuator are provided based on the above-mentioned compliance model and verified by finite element analysis and experiments.

Blackbox between job crafting and job embeddedness of immigrant hotel employees: a serial mediation model

This study explores the influence of job crafting (JC) on migrant employees’ and its sensitivities on job embeddedness (JE) with the application of a serial mediation mechanism which takes into consideration the psychological capital and their work engagement as mediators. The data for this study was collected from immigrant employees in the hotel sector in North Cyprus. Both convenience and judgmental sampling techniques made up of 572 dyads were used. The findings of this study reveal that immigrant employees’ psychological capital and their work engagement has a mediating effect on the relationships between organizational crafting and the perceptions of employees’ job embeddedness. This study will serve as a substantial research evidence and tool for managers/owners in the hospitality industry for the purpose of retaining, engaging and embedding immigrant employees. The novelty of this study is the fact that it analyzes the work environment and conditions where organizational job crafting affects job embeddedness to determine the perceptions of immigrant employees using a serial mediation model.

Three hierarchical porous magnesium borate microspheres: a serial preparation strategy, growth mechanism and excellent adsorption behavior for Congo red.

The 3D hierarchical porous 7MgO·2B2O3·7H2O (MBH) microspheres were prepared by a phase transformation of chloropinnoite firstly, and anhydrous α-3MgO·B2O3 (MBA) microspheres were obtained by thermal conversion of 7MgO·2B2O3·7H2O, and then β-3MgO·B2O3 (MBB) microspheres were obtained by phase conversion of α-3MgO·B2O3. All samples were characterized by XRD, FT-IR, TG and SEM. The microsphere nanostructures with a hierarchical porous structure were assembled by nanosheets with a thickness of 20–30 nm, and the growth mechanisms were also proposed. By using N2 adsorption–desorption, the specific surface areas were measured as 103.62 m2 g−1 for MBH and 46.10 m2 g−1 for MBA. They exhibited excellent selective adsorption performance for Congo red (CR) with maximum adsorption capacities of 202.84 and 170.07 mg g−1 respectively, and the corresponding adsorption mechanisms were also investigated. The adsorption processes were well fitted with the pseudo-second-order rate equation and Langmuir adsorption model. In addition, the corresponding adsorption thermodynamic parameters were also calculated. It is necessary to highlight that the hierarchical porous microspheres could be considered as promising candidates for removal of CR dye pollutants.

Efficient and fair assignment mechanisms are strongly group manipulable

We study the assignment of indivisible objects to agents without using monetary transfers. We prove that, regardless of whether the number of objects is sufficient, a mechanism that satisfies ex-post Pareto efficiency, equal treatment of equals, equal total assignment (ETA), and uniform-head fairness (UHF) must be strongly manipulable by a group of agents. In other words, by misreporting their preferences, all group members can obtain lotteries that strictly first-order stochastically dominate the lotteries they would have obtained by reporting their true preferences. ETA requires that agents obtain equal total probability shares of objects. UHF requires that if all agents have equal preferences over a subset of objects and prefer the objects in that subset to the remaining objects, then they obtain equal probability shares of the objects in that subset. The random priority and probabilistic serial mechanisms satisfy our axioms.

Design, stiffness analysis and experimental study of a cable-driven parallel 3D printer

Although additive manufacturing (AM) has been developed rapidly and become an absolutely necessary tool for reducing the cycle and cost of new product development, the mechanical structures of most 3D printers based on Fused Deposition Modeling (FDM) technology are still traditional serial or parallel mechanisms with rigid components. In this paper, a novel cable-driven parallel 3D printer (CDPP) is developed. Compared with the traditional rigid mechanisms, CDPP has the advantages of larger workspace, higher payload-to-weight ratio, easier modularity and reconfigurability. A cable-driven module with three translational degrees of freedom and a follow-up tensioning module with a spring are adopted for positioning. Firstly, the inverse kinematics of the CDPP is derived considering the cable length constraint. The inverse dynamics model of the CDPP is established based on the Newton–Euler equation and the kinematics. Secondly, the system stiffness of the CDPP and stiffness along three coordinate axes are derived, respectively. The system static stiffness with respect to the stiffness constant of the spring and the coordinates of the moving platform are obtained. Finally, the experiments are performed based on numerical simulation. The results of experiments without executing extrusion demonstrate the simulation results about the static stiffness. The feasibility of the CDPP is verified via the experiments while executing extrusion.