Discrete Slots Research Articles

Endwall film-cooling in a cascade with filleted vane, upstream discrete slots, and holes

ABSTRACT In vane cascades, large filleted vanes influence aerodynamics, while upstream endwall film-cooling arrangement impacts aero-thermal performance. This study explores experimental investigations on endwall flows and film-cooling effectiveness in a filleted vane cascade using discrete slots and holes. Two fillet profiles are examined covering the leading-edge area to either the throat or 62% of the axial chord. Film-cooling employs two slots and two rows of holes in the leading-edge region with inlet blowing ratios ranging from 1.0 to 2.8. Results show variations in total pressure loss and Nusselt number between filleted and un-filleted vanes, highlighting optimal film-cooling effectiveness with the smaller fillet profiles.

Exact and heuristic solution approaches for energy-efficient identical parallel machine scheduling with time-of-use costs

Nowadays, energy-efficient scheduling has assumed a key role in ensuring the sustainability of manufacturing processes. In this context, we focus on the bi-objective problem of scheduling a set of jobs on identical parallel machines to simultaneously minimize the maximum completion time and the total energy consumption over a time horizon partitioned into a set of discrete slots. The energy costs are determined by a time-of-use pricing scheme, which plays a crucial role in regulating energy demand and flattening its peaks. First, we uncover a symmetry-breaking property that characterizes the structure of the solution space of the problem. As a consequence, we provide a novel, compact mixed-integer linear programming formulation at the core of an efficient exact solution algorithm. A thorough experimental campaign shows that the use of the novel mathematical programming formulation enables the solution of larger-scale instances and entails a reduction in the computational times as compared to the formulation already available in the literature. Furthermore, we propose a new heuristic that improves the state-of-the-art in terms of required computational effort and quality of solutions. Such a heuristic outperforms the existing heuristics for the problem and is also capable of speeding up the exact solution algorithm when used for its initialization. Finally, we introduce a novel dynamic programming algorithm that is able to compute the optimal timing of the jobs scheduled on each machine to further improve the performance of the new heuristic.

Partial recall: Implications for the discrete slot limit of working memory capacity.

The nature of working memory capacity (WMC) has been a highly contested topic among cognitive scientists. Some advocate for the discrete nature of this construct, fixed to a set number of independent slots, each capable of storing a single chunk of bound information. Others advocate for a continuous limit, guided by a pool of immediately available resources spent across the to-be-remembered items. To understand the nature of WMC, it was first essential to separate capacity from other factors, such as performance consistency, which may impact overall WM performance. Recent work by Schor et al., (2020, Psychonomic Bulletin & Review, 27[5], 1006-1013) has provided a method for separating these constructs within a single visual array task. The present study used this statistical model to extract partial information, defined as accurate recall of a correct color, but not location, at a rate greater than expected through guessing. The successful memory of this information would demonstrate that capacity does not rely on the existence of empty slots, which discrete slot model advocates argue, are necessary for successful storage and recall of items. The present study found that participants were able to successfully recall partial information at a rate significantly greater than chance, but not beyond the individual working memory capacity limit. These findings help provide additional support for the discrete resource slot model, while simultaneously casting doubt on its strong object slot model alternative.

Characterization of Bond Fracture in Discrete Groove Wear of Cageless Ball Bearings.

Cageless ball bearings with discrete grooves in the outer raceway enable the dispersion of rolling elements. Once worn, the discrete groove can cause the rolling element to discretely fail. This paper presents the discrete element method to investigate the wear of discrete grooves in cageless bearings from the standpoint of bond fracture. In conjunction with the structural characteristics of bearing races with discrete slots, we propose a hexagonal close-spaced spherical particle arrangement, in which the discrete slots are discretized into particles of the same size that are connected by bonds. The contact model and contact force equation between the rolling elements and the aggregate elements are established, and the external force on the aggregate elements is calculated. Under the influence of an external force and the arrangement of particles in the aggregate element, the internal force transfer equation of different layers and different particles is derived, and the internal force of the particles in the aggregate unit is calculated. In accordance with Hertz–Mindline theory, the bonding model of discrete groove particles is established, the size of the particle shedding cohesive force during bond fracture is determined, and the wear degree of discrete grooves is characterized by comparing the cohesive force and internal force. Numerical solutions and wear tests are combined. Bond fracture can accurately characterize the wear of discrete grooves. This approach offers theoretical guidance for cageless bearing design.

Aerodynamic characteristics of co-flow jet wing with simple high-lift devices

Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet (CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial parameters of CFJ wing, i.e., angle of attack, jet momentum and swept angle, are comprehensively examined. Additionally, the aerodynamic characteristics of two CFJ configurations, i.e., using open and discrete slots for injection, are compared. The results show that applying CFJ technique to a wing with simple high-lift device is able to generate more lift, reduce drag and enlarge stall margin with lower energy expenditure due to the super-circulation effect. Increasing the jet intensity can reduce the drag significantly, which is mainly contributed by the reaction jet force. The Oswald efficiency factor is, in some circumstances, larger than one, which indicates the potential of CFJ in reducing induced drag. Compared with clean wing configuration, using CFJ technique allows the aerodynamic force variation less sensitive to the swept angle, and such phenomenon is better observed for small swept angle region. Eventually, it is interesting to know that the discrete slotted CFJ configuration demonstrates a promising enhancement in aerodynamic performance in terms of high lift, low drag and efficiency.

Evolution of Hemodynamic Parameters Simulated by Means of Diffusion Models

Diffusion is a well-known physical phenomenon governing such processes as movement of particles or transportation of heat. In this paper, we prove that a close analogy to those processes exists in medical data behavior, and that changes in the values of medical parameters measured while treating patients may be described using diffusion models as well. The medical condition of a patient is usually described by a set of discrete values. The evolution of that condition and, consequently, of the disease has the form of a transition of that set of discrete values, which correspond to specific parameters. This is a typical medical diagnosis scheme. However, disease evolution is a phenomenon that is characterized by continuously varying, temporal characteristics. A mathematical disease evolution model is, in fact, a continuous diffusion process from one discrete slot of the diagnosed parameter value to another inside the mentioned set. The ability to predict such diffusion-related properties offer precious support in diagnostic decision-making. We have examined several hundred patients while conducting a medical research project. All patients were under treatment to stabilize their hemodynamic parameters. A diffusion model relied upon simulating the results of treatment is proposed here. Time evolution of thoraric fluid content (TFC) has been used as the illustrative example. The objective is to prove that diffusion models are a proper and convenient solution for predicting disease evolution processes. We applied the Fokker-Planck equation (FPE), considering it to be most adequate for examining the treatment results by means of diffusion. We confirmed that the phenomenon of diffusion explains the evolution of the heart disease parameters observed. The evolution of TFC has been chosen as an example of a hemodynamic parameter.

Effects of slot injection on detonation wavelet characteristics in a rotating detonation engine

Two-dimensional numerical simulations are performed to investigate the effects of spatially discrete slot injection of reactants on the features of detonation wavelets in a rotating detonation engine (RDE). The detonation dynamics is described by a model based on the reactive Euler equations coupled with two-step, induction-reaction kinetics. By varying injection conditions and the chemical sensitivity of the reactive mixture, a parametric study is carried out to examine the influence of the injection-slot area ratio α on the detonation wavelet patterns and different flow features inside an RDE combustion chamber. The simulation results demonstrate that the injection conditions, i.e., stagnation temperature and pressure, have a similar influence on slot-ozzle rotating detonation wavelets (RDWs) as compared with the mini-nozzle RDWs reported in a previous study. The corresponding mass flow rate and inhomogeneity generated due to the presence of slot injection, however, play a key factor in the self-sustained rotating detonation and its frontal structure.

A Randomized Greedy Heuristic for Steerable Wireless Backhaul Reconfiguration

In this paper, we consider the reconfiguration of wireless backhaul networks with mechanically steerable antennas in the presence of changing traffic demands. Reconfiguration requires the scheduling and coordination of several operations, including antenna alignment and link establishment/removal, with minimal disruption to existing user traffic. Previously, we proposed a Mixed Integer Linear Program (MILP) to orchestrate such reconfiguration with minimal packet loss. While the MILP solves the problem optimally for a limited number of discrete reconfiguration time slots, it does not scale well. In this paper, we propose an iterative randomized greedy algorithm to obtain suboptimal solutions in reduced time. The algorithm schedules the reconfiguration of wireless links by ranking them according to a set of attributes with associated weights and selecting them according to a randomized greedy function. Results on six different network scenarios indicate that the proposed algorithm can achieve good quality solutions in significantly less time. Furthermore, by extending the reconfiguration time beyond the maximum number of time slots solvable by the MILP, the proposed heuristic can obtain superior solutions for some problem instances. The number of iterations of the algorithm can be tuned for its applicability in both offline and online planning scenarios.

Evaluating and Optimizing Opportunity Fast-Charging Schedules in Transit Battery Electric Bus Networks

Public transport operators (PTOs) increasingly face a challenging problem in switching from conventional diesel to more sustainable battery electric buses (BEBs). In this study, we optimize the opportunity fast-charging schedule of transit BEB networks in order to minimize the charging costs and the impact on the grid. Two mixed-integer linear programming (MILP) formulations that use different discretization approaches are developed and compared. Discrete-Time Optimization (DTO) resembles a time-expanded network that discretizes the time and decisions to equal discrete slots. Discrete-Event Optimization (DEO) discretizes the time and decisions into nonuniform slots based on arrival and departure events in the network. In addition to the DEO’s higher practicability, the comparative computational study carried out on the transit-bus network in the city of Rotterdam, Netherlands, shows that the DEO is superior to the DTO in terms of computational performance. To show the potential benefits of the optimal schedule, it is compared with two reference common-sense greedy strategies: First-in-First-Served and Lowest-Charge-Highest-Priority.

Asynchronous Neighbor Discovery on Duty-Cycled Mobile Devices: Models and Schedules

Neighbor discovery is a fundamental problem in wireless networks. In this paper, we study asynchronous neighbor discovery on duty-cycled mobile devices. Most existing studies develop integer schedules where time proceeds in discrete slots and a node is awake or asleep for an entire slot duration. We show that integer schedules can lead to significant waste of resources, and develop a generalized non-integer model, where time is continuous and a node may become awake or asleep at any point of time (subject to a few constraints) so that the resultant schedules can be significantly more efficient than integer schedules. In addition, we provide a reduction that transforms any schedule in the integer model to a corresponding schedule in the generalized non-integer model while reducing the discovery latency by up to a factor of two. Applying this reduction, an optimal schedule in the integer model becomes an optimal schedule in the non-integer model. We further demonstrate the practicality of non-integer schedules in a testbed, and compare the worst-case discovery latency of several existing schemes under both integer and non-integer models. Last, we establish a family of lower bounds for the best achievable latency guarantee. These lower bounds are applicable to both integer and non-integer models, covering both symmetric and asymmetric settings, and encompassing the existing lower bounds that are only for a subset of settings as special cases.

Numerical investigation on a double layer combined cooling structure for aerodynamic heat control of hypersonic vehicle leading edge

A novel double layer combined cooling conception is suggested in this paper, i.e., an inner layer with discrete slots to allocate the coolant locally and an outer layer with homogeneous porous matrix to diffuse the coolant extensively. To investigate the cooling performances, mechanisms and improvements of the new structure, an entire-field-coupled numerical approach is established and validated by the experimental data obtained in an arc-heated wind tunnel under the supersonic conditions of Ma = 4.2, T0 = 2310 K and P0 = 1.33 MPa. Using the validated numerical approach, three interesting attempts are conducted: (1) The cooling characteristics of four slot-layouts (S1/S3/S5/S7) are systematically studied and compared at three coolant injection rates (30/40/50 g/s). (2) The comparison indicated that S3 can decrease the peak temperature most greatly even by 66.9% when Mc = 50 g/s, hence it’s chosen as the best design to investigate the cooling mechanisms in the entire region. (3) Based on the mechanism investigation, an improved design with a semi through-slot in the high temperature region is suggested, and the corresponding simulation predicated that this design can further reduce the coolant consumption by 20%. This work aims to provide the designers of future hypersonic vehicles with a valuable reference, to search for an active thermal management approach with high efficiency and low thermal stress.

Numerical investigation of tangential blowing over the rudder of a vertical tailplane

Tangential blowing over the shoulder of a deflected rudder is applied on a vertical tailplane. For a large rudder deflection angle and without blowing the flow is mostly separated on the rudder. Three configurations are investigated in a numerical study with the aim to increase the side force coefficient. The first one is the baseline without blowing, the second one has a continuous full span slot and for the third one discrete slots are used. With sufficient blowing through the continuous slot the separation on the rudder can be removed completely while the separation extent is greatly reduced when using discrete slots. This is investigated for different sideslip angles. An approximately linear increase in the side force coefficient can be found until a sudden side force breakdown occurs. In a further study, the jet blowing velocity is varied. A smaller jet velocity leads to a smaller increase in the side force coefficient. Comparing the continuous and discrete slot configurations shows that for a similar increase in the side force coefficient a much smaller mass flow rate is needed for the discrete slots. However, for jet velocities below the sonic speed the increase in the side force coefficient is limited. It can only be increased by a larger slot extent in spanwise direction but this comes at the expense of an increase in the required mass flow rate.

The investigations of slot film outflow used on the laminated cooling configuration

The discrete film hole is the most common form of film cooling configurations in the turbine vane and blade. To enhance the film cooling effect, the improved hole, such as expanding-shape hole, is being used to replace the traditional cylindrical hole in the vane and blade cooling design. However the slot film outflow is been seen as the best form of film cooling when compared to the discrete holes. The slot film cooling configuration is usually used in the trailing edge of turbine vane and blade, but cannot be used in the mid-body of turbine vane and blade, with be drawback of lower mechanical strength. The present paper used the slot film outflow on the laminated cooling configuration. With the ribs in the laminated cooling configuration, the novel configuration can remarkably overcome the mechanical drawback of the simple slot film cooling, and can enhance the film cooling effect of the laminated cooling configuration. To investigate the cooling effect of laminated configuration with slot film outflow, four kinds of specimens are designed, including the traditional design with discrete film hole (baseline), the rearrangement design with discrete film hole (case A), the novel design with discrete slot (case B), and the novel design with continuous slot (case C). The Conjugate heat transfer (CHT) computations and the Pressure Sensitive Paint (PSP) test methods are used to assess the overall cooling performance (ηoverall) and the adiabatic film cooling effectiveness (ηfilm). The results show the two slot design cases (case B and case C) have higher film cooling effectiveness with more covered surface areas of film outflow, while performs lower flow resistance due to the lower flow velocity of the coolants in the slot. With the increase of Br, the film cooling effectiveness of two slot design cases (case B and case C) can keep increase, but the two hole design case (baseline and case A) cannot increase at area of Br > 0.55. At the blowing ratio near 0.96, for the baseline case, case A, case B, and case C, the area-averaged film cooling effectiveness is 0.26, 0.20, 0.68, and 0.50 respectively; and area-averaged the overall cooling effectiveness is 0.72, 0.81, 0.89, and 0.85 respectively; the flow frictions coefficients is 1.78, 2.15, 1.37, and 2.01 respectively.

Numerical investigation of slot variations on the efficiency of tangential blowing at a vertical tailplane with infinite span

On a swept vertical tailplane with infinite span tangential blowing over the shoulder of a deflected rudder is applied. For large rudder deflection angles the flow on the rudder is separated without blowing. A numerical study is conducted with the aim to increase the side force coefficient. This could, for example, be required during take-off if the engine on one side fails, necessitating the compensation of a large yawing moment. If this criterion is critical for the sizing of the vertical tailplane, active flow control like tangential blowing could help to reduce the size of the vertical tailplane and thus save weight and fuel. With a continuous slot it is demonstrated that the separation on the rudder can be reduced or avoided. It is shown that using discrete slots this can be achieved with a smaller momentum coefficient. To analyze the effects of the discrete slots and their jets on each other and their effectivity with regard to the gain in side force coefficient a parameter study is conducted. The number of slots as well as the size of the slots in spanwise direction is varied and the impact of jet velocity changes is also studied. In comparing the results for a constant increase in side force and constant slot size in spanwise direction the configuration with the smaller number of slots but a higher jet velocity proved to be the most effective one.

Multifaceted pattern of neural efficiency in working memory capacity

The objective of the present study was to investigate whether neural efficiency can be observed in visual working memory performance. Thirty low- and thirty high-performers were selected from a larger cohort of students based on performance on a visual WM task. Electroencephalogram (EEG) data during performance on this task was analyzed with event-related desynchronization/synchronization (ERD/ERS) and event-related coherence (ErCoh) in individually determined theta, alpha, and gamma frequency bands. The results demonstrated that high-performers in comparison to low-performers showed significantly different brain oscillatory responses in all three cognitive processes identified in the WM task – encoding, maintenance and retrieval. High-performers displayed: (1) Increased alpha ERD during encoding and increased gamma ERD during encoding and maintenance, which did not depend on set size, as well as (2) increased theta band ErCoh in fronto-parietal networks during maintenance and retrieval. To some extent, neural efficiency was observed in the gamma frequency band (ERD) and in theta coherence (ErCoh). The results tentatively lend support to the continuous single resource model assuming that working memory capacity is a flexible resource that can be spread among all elements in the sensory input as opposed to the model of discrete slots.

A two-phase model of resource allocation in visual working memory.

Two broad theories of visual working memory (VWM) storage have emerged from current research, a discrete slot-based theory and a continuous resource theory. However, neither the discrete slot-based theory or continuous resource theory clearly stipulates how the mental commodity for VWM (discrete slot or continuous resource) is allocated. Allocation may be based on the number of items via stimulus-driven factors, or it may be based on task demands via voluntary control. Previous studies have obtained conflicting results regarding the automaticity versus controllability of such allocation. In the current study, we propose a two-phase allocation model, in which the mental commodity could be allocated only by stimulus-driven factors in the early consolidation phase. However, when there is sufficient time to complete the early phase, allocation can enter the late consolidation phase, where it can be flexibly and voluntarily controlled according to task demands. In an orientation recall task, we instructed participants to store either fewer items at high-precision or more items at low-precision. In 3 experiments, we systematically manipulated memory set size and exposure duration. We did not find an effect of task demands when the set size was high and exposure duration was short. However, when we either decreased the set size or increased the exposure duration, we found a trade-off between the number and precision of VWM representations. These results can be explained by a two-phase model, which can also account for previous conflicting findings in the literature. (PsycINFO Database Record

The number of objects determines visual working memory capacity allocation even for complex items

article i nfo Article history: The goal of the present study was to examine whether visual working memory (WM) capacity allocation is determined solely by complexity, with the number of objects being redundant, as suggested by flexible resource models. Participants performed the change detection task with random polygons as stimuli, while we monitored the contralateral delay activity (CDA), an electrophysiological marker whose amplitude rises as WM load increases. In Experiment 1, we compared the WM maintenance of one whole polygon to a single half of the polygon, equating the number of items but varying the complexity level. Additionally, we compared the whole polygon to two halves of a polygon, thus roughly equating perceptual complexity but manipulating the number of items. The results suggested that only thenumberof objectsdetermined WMcapacity allocation: theCDA was identicalwhen comparing one wholepolygonto onepolygon half,eventhoughtheseconditions differedincom- plexity. Furthermore, the CDA amplitude was lower in the whole polygon condition relative to the two halves condition, even though both contained roughly the same amount of information. Experiment 2 extended these results by showing that two polygon halves that moved separately but then met and moved together were gradually integrated to consume similar WM capacity as one polygon half. Additionally, in both experiments we found an object benefit in accuracy, corroborating the important role of objects in WM. Our results demon- strate that WM capacity allocation cannot be explained by complexity alone. Instead, it is highly sensitive to objecthood, as suggested by discrete slot models.

The number of objects determines visual working memory capacity allocation for complex items

The goal of the present study was to examine whether visual working memory (WM) capacity allocation is determined solely by complexity, with the number of objects being redundant, as suggested by flexible resource models. Participants performed the change detection task with random polygons as stimuli, while we monitored the contralateral delay activity (CDA), an electrophysiological marker whose amplitude rises as WM load increases. In Experiment 1, we compared the WM maintenance of one whole polygon to a single half of the polygon, equating the number of items but varying the complexity level. Additionally, we compared the whole polygon to two halves of a polygon, thus roughly equating perceptual complexity but manipulating the number of items. The results suggested that only the number of objects determined WM capacity allocation: the CDA was identical when comparing one whole polygon to one polygon half, even though these conditions differed in complexity. Furthermore, the CDA amplitude was lower in the whole polygon condition relative to the two halves condition, even though both contained roughly the same amount of information. Experiment 2 extended these results by showing that two polygon halves that moved separately but then met and moved together were gradually integrated to consume similar WM capacity as one polygon half. Additionally, in both experiments we found an object benefit in accuracy, corroborating the important role of objects in WM. Our results demonstrate that WM capacity allocation cannot be explained by complexity alone. Instead, it is highly sensitive to objecthood, as suggested by discrete slot models.

The binding pool: A model of shared neural resources for distinct items in visual working memory

Visual working memory (VWM) refers to the ability to encode, store, and retrieve visual information. The two prevailing theories that describe VWM assume that information is stored either in discrete slots or within a shared pool of resources. However, there is not yet a good understanding of the neural mechanisms that would underlie such theories. To address this gap, we provide a computationally realized neural account that uses a pool of shared neurons to store information about one or more distinct stimuli. The binding pool model is a neural network that is essentially a hybrid of the slot and resource theories. It describes how information can be stored and retrieved from a pool of shared resources using a type/token architecture (Bowman & Wyble in Psychological Review 114(1), 38-70, 2007; Kanwisher in Cognition 27, 117-143, 1987; Mozer in Journal of Experimental Psychology: Human Perception and Performance 15(2), 287-303, 1989). The model can store multiple distinct objects, each containing binding links to one or more features. The binding links are stored in a pool of shared resources and, thus, produce mutual interference as memory load increases. Given a cue, the model retrieves a specific object and then reconstructs other features bound to that object, along with a confidence metric. The model can simulate data from continuous report and change detection paradigms and generates testable predictions about the interaction of report accuracy, confidence, and stimulus similarity. The testing of such predictions will help to identify the boundaries of shared resource theories, thereby providing insight into the roles of ensembles and context in explaining our ability to remember visual information.

Landscaping analyses of the ROC predictions of discrete-slots and signal-detection models of visual working memory

A fundamental issue concerning visual working memory is whether its capacity limits are better characterized in terms of a limited number of discrete slots (DSs) or a limited amount of a shared continuous resource. Rouder et al. (2008) found that a mixed-attention, fixed-capacity, DS model provided the best explanation of behavior in a change detection task, outperforming alternative continuous signal detection theory (SDT) models. Here, we extend their analysis in two ways: first, with experiments aimed at better distinguishing between the predictions of the DS and SDT models, and second, using a model-based analysis technique called landscaping, in which the functional-form complexity of the models is taken into account. We find that the balance of evidence supports a DS account of behavior in change detection tasks but that the SDT model is best when the visual displays always consist of the same number of items. In our General Discussion section, we outline, but ultimately reject, a number of potential explanations for the observed pattern of results. We finish by describing future research that is needed to pinpoint the basis for this observed pattern of results.