Space Constraints Research Articles

A Multi-Pointer Network for Multiple Agile Optical Satellite Scheduling Problem

With the rapid growth in space-imaging demands, the scheduling problem of multiple agile optical satellites has become a crucial problem in the field of on-orbit satellite applications. Because of the considerable solution space and complicated constraints, the existing methods suffer from a huge computation burden and a low solution quality. This paper establishes a mathematical model of this problem, which aims to maximize the observation profit rate and realize the load balance, and proposes a multi-pointer network to solve this problem, which adopts multiple attention layers as the pointers to construct observation action sequences for multiple satellites. In the proposed network, a local feature-enhancement strategy, a remaining time-based decoding sorting strategy, and a feasibility-based task selection strategy are developed to improve the solution quality. Finally, extensive experiments verify that the proposed network outperforms the comparison algorithms in terms of solution quality, computation efficiency, and generalization ability and that the proposed three strategies significantly improve the solving ability of the proposed network.

A Novel Topology of a 3 × 3 Series Phased Array Antenna with Aperture-Coupled Feeding.

This paper presents a novel 3 × 3 phased array antenna optimized for 4 GHz operation, achieving a realized gain of 13.2 dBi and enabling 30-degree beam steering with a minimal capacitance variation of 1.5 pF. The design features a series aperture-coupled feeding mechanism that not only reduces the antenna's size but also simplifies the fabrication process, making the device both cost-effective and compact. Integrating cost-efficient quadrature-hybrid phase shifters and novel power splitters with cascaded quadrature hybrids ensures uniform power distribution and precise beam steering. The innovative use of these components addresses common challenges in phased array systems, such as space constraints, high costs, and complex power distribution.

Evaluation of Solid Waste Produced in Garowe District Somalia

Historically, waste management in Garowe District was marked by traditional practices driven by necessity rather than environmental consciousness, the aim of the study was to evaluate solid waste produced in the district while the specific objectives were to identify the composition and quantity of biodegradable waste generated the Garowe District, to assess the types and quantities of non-biodegradable waste produced in Garowe District and also To evaluate the existing waste management practices in the district. The study employed mixed methods. Copies of questionnaires were administered to 388 households and interviews conducted with 5 key informants to assess solid waste composition, quantities, handling practices, and management gaps. The study found food scraps constitute the majority of biodegradable waste generated in households, while plastics dominate the non-biodegradable waste stream. On average, household waste generation exceeds 1 kg per day, and municipal collection services only reach a portion of district residence. Existing waste management efforts focus primarily on collection and disposal with minimal infrastructure for material recovery, recycling or composting. While most residents express willingness to separate organic waste, few households implement home composting due to knowledge gaps and space constraints. The findings reveal significant potential to improve waste management sustainability by reducing disposal volumes and introducing programs to divert organics and recyclables from dumping sites. Key recommendations include public education, expanding source segregation, constructing composting and recycling facilities, and better integrating the informal recycling sector. The study provides important baseline data to inform integrated municipal solid waste management planning aligned with local needs while minimizing environmental and public health impacts. KEYWORDS: Waste management, Garowe District, Municipal solid waste, Household waste, Somalia

A heuristic method for multi-objective hybrid flow shop scheduling problem with parent-child relationships and space constraints

ABSTRACT In modern ship manufacturing, a ship is divided into hundreds of blocks in the design stage, and the productivity of the block manufacturing process is vital to ship delivery. This paper investigates the production scheduling problem of ship blocks with the parent-child relationship; this relationship is characterised by the fact that sibling jobs at the same BOM layer must be processed on adjacent machines at their assembly stages. We formulate this problem as a multi-objective hybrid flow shop scheduling problem: the first objective is to minimise the total deviation from the target time of the jobs and the second one is to minimise the total processing time. To solve this problem, we propose a heuristic method based on the multi-objective genetic algorithm, in which an adjacent machine priority method is first proposed to generate feasible solutions that satisfy the space constraints. Then, we improve the individual quality in crossover and mutation of the algorithm via tabu search. We verify the performance of our algorithm by test instances generated from real manufacturing data of a shipbuilding company. Results show that the proposed method outperforms the existing algorithms when identifying the Pareto optimal solutions, especially for large-sized problems.

Research on FPC coils with limited turns in planar electromagnetic tomography

Electromagnetic tomography (EMT) is a non-destructive testing method that reconstructs electrical parameter distribution based on boundary electromagnetic measurement data along electromagnetic rotation projection. The coil is a critical component of the EMT system, used to excite and detect changing magnetic fields. The performance of excitation-detection with specific coils directly affects the quality of the reconstructed image. The traditional EMT coils are wound coils. The excitation-detection performance of the coils is enhanced by increasing the number of turns to obtain better imaging quality. A larger coil volume has better sensitivity, but it cannot meet the space constraints of many applications. To solve this problem, this paper proposes a method using extremely thin FPC coil arrays as EMT sensors. To verify the feasibility of FPC coil imaging with a limited number of turns, firstly, this article analyses the excitation-detection capabilities of FPC coil with 1 to 12 turns through a combination of simulation and experiment. Secondly, the impact of excitation-detection capability on the EMT sensitivity matrix was studied. Finally, a 4×4 8-Turns FPC coil sensor was designed for image reconstruction experiments. The experimental results show that FPC coils with limited turns can be used for image reconstruction and to solve the problem of planar nondestructive testing in a small space.

Quantum computing and tensor networks for laminate design: A novel approach to stacking sequence retrieval

As with many tasks in engineering, structural design frequently involves navigating complex and computationally expensive problems. A prime example is the weight optimization of laminated composite materials, which to this day remains a formidable task, due to an exponentially large configuration space and non-linear constraints. The rapidly developing field of quantum computation may offer novel approaches for addressing these intricate problems. However, before applying any quantum algorithm to a given problem, it must be translated into a form that is compatible with the underlying operations on a quantum computer. Our work specifically targets stacking sequence retrieval with lamination parameters, which is typically the second phase in a common bi-level optimization procedure for minimizing the weight of composite structures. To adapt stacking sequence retrieval for quantum computational methods, we map the possible stacking sequences onto a quantum state space. We further derive a linear operator, the Hamiltonian, within this state space that encapsulates the loss function inherent to the stacking sequence retrieval problem. Additionally, we demonstrate the incorporation of manufacturing constraints on stacking sequences as penalty terms in the Hamiltonian. This quantum representation is suitable for a variety of classical and quantum algorithms for finding the ground state of a quantum Hamiltonian. For a practical demonstration, we performed numerical state-vector simulations of two variational quantum algorithms and additionally chose a classical tensor network algorithm, the DMRG algorithm, to numerically validate our approach. For the DMRG algorithm, we derived a matrix product operator representation of the loss function Hamiltonian and the penalty terms. Although this work primarily concentrates on quantum computation, the application of tensor network algorithms presents a novel quantum-inspired approach for stacking sequence retrieval.

Using Remotely Operated Suction Irrigation System in da Vinci SP Submucosal Dissection.

Submucosal dissection using the da Vinci SP® system (Intuitive Surgical, Sunnyvale, CA, USA) is an emerging approach for treating premalignant lesions in the colon and rectum. The endoluminal space is tight and small, and during the procedure, this tight space is accessed by the 40 mm GelPOINT® Path transanal platform (Applied Medical, Rancho Santa Margarita, CA, USA). Most of the trocar space is occupied by the 25 mm port of the da Vinci SP® system. There is limited space for an additional trocar, and the full mobility of this trocar is restricted; hence there is a need for an effective suction irrigator during these procedures. Although the da Vinci SP® system has four instrument capabilities, it does not have a suction irrigation instrument. To address this issue, we tested a Remotely Operated Suction Irrigation System (ROSI™) (VTI, Nashua, NH, USA) in three patients undergoing da Vinci SP® submucosal dissection. The impact of innovation is the evaluation of a flexible suction irrigator during endorobotic submucosal dissection (ERSD), addressing space constraints and enhancing surgical precision. This was a single-center retrospective observational study involving three patients who underwent ERSD, between February 2023 and May 2023. ROSI™ was used selectively for rectal lesions. The first patient was a 67-year-old male with a 30 mm tubulovillous adenoma found in the rectum at 4 cm. The second patient was a 49-year-old female, referred after a screening colonoscopy, with a 40 mm rectal mass 12 cm from the anal verge. A biopsy revealed a tubular adenoma without dysplasia. The last patient was a 66-year-old male with a 25 mm tubulovillous adenoma with a focal high-grade dysplasia at 10 cm. There was no evidence of invasive carcinoma or lymph node metastasis on MRI in any of the patients. The patients were placed in a modified lithotomy position, and the GelPOINT® Path was inserted. A silk suture was attached at the proximal end of ROSI™ to facilitate tubing manipulation. ROSI™ was freely passed into the endoluminal space through the gel using a surgical clamp. Any bleeding during the operation was aspirated and irrigated using ROSI™ with the assistance of bipolar forceps. All surgeries were completed without complications and the patients were discharged on the same day. ROSI™ is a flexible foot pedal-controlled suction irrigator that can facilitate da Vinci SP® submucosal dissection. The flexibility and controllability of ROSI in the surgeon's hand may qualify it as an essential tool for performing ERSD and possibly other TAMIS procedures.

A case study comparing seismic retrofitting techniques for a historically significant masonry building’s minaret

Historical masonry structures are extremely susceptible to earthquakes due to their characteristic features. Seismic performance and corresponding damage patterns vary between these buildings. Even though the main structure was undamaged, many minarets suffered damage or collapsed due to the transmission of large forces from the main mass to the minaret and the abrupt changes in cross-section due to the geometry of the minaret. This study uses an ancient masonry mosque as a case study, whose minaret and main building are constructed as a single structure. The mosque’s minaret under seismic excitation is the focus of this study. The adopted model is called Alaeddin Bey Mosque in Muş, Türkiye. The seismic performance assessment of the minaret, considering various retrofitting options, is mainly based on four critical parameters: base shear, acceleration, displacement, and maximum tensile forces in all three dimensions. The analyzed retrofitting methods include base isolation located in the basement of the mosque, viscous dampers placed only in the upper part of the minaret, Carbon Fiber-Reinforced Polymer fabric fitted to only the minaret, and steel plates applied to only the minaret. Representative structural models of the mosque have been modelled with SAP2000 software. The main novelty of this study is the use of viscous dampers in the minaret. It is the first time a design methodology has been introduced for viscous damper applications in minarets. This methodology aims to prevent local damage to the minaret due to the forces generated by the dampers, while also considering the constraints of limited internal space within the minaret. The finding of this study shows that viscous damper application yields significantly better results compared to the application of Carbon Fiber-Reinforced Polymer fabric and steel plates. However, although base isolation reduces the tensile stress values throughout the entire mosque to levels well below the material’s strength, viscous damper application in the minaret significantly reduces tensile stresses only in the minaret. As a result, viscous dampers are recommended for damage reduction in the minaret only. Otherwise, base isolation should be considered for reducing stress values throughout the entire mosque including the minaret. This study contributes towards the development of new seismic retrofitting methods for historic masonry buildings ‘minaret.

Clamping Force Control of Electromechanical Brake Actuator Considering Contact Point between Friction Lining and Brake Disc

Currently, most electromechanical brake (EMB) schemes are only suitable for passenger cars, and their maximum clamping force is insufficient to satisfy the braking demands of commercial vehicles. Additionally, previous studies on clamping force control are largely based on an EMB equipped with sensors. Due to constraints in installation space and cost, sensorless EMBs are gradually gaining attention. Furthermore, accurately identifying the contact point between the friction lining and the brake disc is the promise of clamping force control for sensorless EMBs. Hence, a sensorless EMB scheme suitable for commercial vehicles is proposed in this study. Secondly, a dynamics model of the EMB actuator is established. After a comprehensive analysis of the proposed EMB actuator, a clamping force control strategy considering the contact points between the friction lining and the brake disc is proposed. Finally, simulation analyses of the strategy are carried out. The results show that the axial length of the proposed EMB actuator is shortened by 17.6% compared with a mainstream pneumatic disc brake. Furthermore, the proposed method can accurately identify the contact points between the friction lining and the brake disc, and the proposed control strategy enables the EMB actuator to achieve the fast response, accurate tracking, and stable maintenance of the target clamping force.

Hydrogen-Bond-Repairing Solar Evaporator with Reconstructed Large-Width Channels for Durable Solarizing Seawater.

Conventional solarizing seawater suffers from inefficiency and space constraints. Interfacial solar vapor generation (ISVG) presents an energy-efficient alternative, yet the scalability, adaptability, and durability of a solar evaporator for practical use are remaining concerns. Herein, a hydrogen-bond-repairing solar evaporator featuring reconstructed large-width channels is proposed for ongoing solarization of seawater in ISVG. The polyacrylamide/trehalose/graphene hydrogel (PTGH) exhibits excellent mechanical properties and large-width salt discharge channels. PTGH achieves a notable water evaporation rate of 2.82 kg m-2 h-1 under 1 sun and remains effective even in low-temperature environments. The large-area PTGH is able to continuously operate for solarizing seawater under different conditions, until raw brine is highly concentrated, and eventually solid salt is separated from water. Compared to conventional solarizing seawater, PTGH can save 66.67%-75% of time or land to obtain the same amount of solid salt.

Recycling drop-off centre: can it have an effect?

Municipalities in Greece hold the responsibility for establishing and organizing Green Points (a type of recycling drop-off centre), as mandated by law to have at least one within their jurisdiction. The aim of this study was to assess the recycling habits and opinions of the residents of the city of Larissa, with a specific focus on the potential impact of introducing a Green Point within the municipality area. Finally, a comparison was carried out to examine the differing viewpoints of individuals who recycle and those who do not, as well as the potential effects of a Green Point on them. A web-based qualitative questionnaire with closed-ended questions was deployed for the analysis. The key questions in the survey were clearly answered by 213 participants, providing strong indications. The local community is actively involved in recycling efforts and is generally satisfied with the current related system, but they feel that changes must be made. Although almost all the participants held a positive opinion on the potential location of a Green Point in their city, the majority of them disagreed with a potential increase in the current waste charges to support the operation of the Green Point. Non-recyclers cited time and space constraints as the primary reasons for not participating. The general consensus among participants is that a financial reward and/or fine can serve as a viable motivator for recycling. The primary distinctions between recyclers and non-recyclers are reflected in their beliefs about how powerful these motivators can be and how much they would increase the travel distance for recycling in the case of their existence.

Fast generation of spectrally shaped disorder.

Media with correlated disorder display unexpected transport properties, but it is still a challenge to design structures with desired spectral features at scale. In this work, we introduce an optimal formulation of this inverse problem by means of the nonuniform fast Fourier transform, thus arriving at an algorithm capable of generating systems with arbitrary spectral properties, with a computational cost that scales O(NlogN) with system size. The method is extended to accommodate arbitrary real-space interactions, such as short-range repulsion, to simultaneously control short- and long-range correlations. We thus generate the largest-ever stealthy hyperuniform configurations in 2d (N=10^{9}) and 3d (N>10^{7}) and demonstrate the flexibility of the approach by generating structures with designed spectral features at scale. By an Ewald sphere construction we link the spectral and optical properties at the single-scattering level and show that stealthy hyperuniform structures generically display transmission gaps, providing a concrete example of fine-tuning of a physical property. We also show that large 3d power-law hyperuniformity in particle packings leads to single-scattering properties nearly identical to those of simple hard spheres. Finally, we demonstrate generalizations of the approach to impose features in either continuous or discrete real space, using constraints in either continuous or discrete reciprocal space. In particular, enforcing large spectral power at peaks with the right symmetry leads to the nondeterministic generation of quasicrystalline structures in 2d and 3d. This technique should become an essential tool to embed, and understand the role of, long-range correlations in disordered metamaterials.

Dual-Spatial Domain Generalization for Fundus Lesion Segmentation in Unseen Manufacturer's OCT Images.

Optical Coherence Tomography (OCT) images can provide non-invasive visualization of fundus lesions; however, scanners from different OCT manufacturers largely vary from each other, which often leads to model deterioration to unseen OCT scanners due to domain shift. To produce the T-styles of the potential target domain, an Orthogonal Style Space Reparameterization (OSSR) method is proposed to apply orthogonal constraints in the latent orthogonal style space to the sampled marginal styles. To leverage the high-level features of multi-source domains and potential T-styles in the graph semantic space, a Graph Adversarial Network (GAN) is constructed to align the generated samples with the source domain samples. To align features with the same label based on the semantic feature in the graph semantic space, Graph Semantic Alignment (GSA) is performed to focus on the shape and the morphological differences between the lesions and their surrounding regions. Comprehensive experiments have been performed on two OCT image datasets. Compared to state-of-the-art methods, the proposed method can achieve better segmentation. The proposed fundus lesion segmentation method can be trained with labeled OCT images from multiple manufacturers' scanners and be tested on an unseen manufacturer's scanner with better domain generalization. The proposed method can be used in routine clinical occasions when an unseen manufacturer's OCT image is available for a patient.

Fuzzy Non-Linear Programming for Fuzzy Inventory Model with Storage Space and Budget Constraint

Fuzzy Non-Linear Programming for Fuzzy Inventory Model with Storage Space and Budget Constraint

Aerodynamic Characterization of a Hypersonic Projectile Using Acceleration-Based Measurements and Numerical Methods

Armor-piercing fin-stabilized projectiles stand out by their exceptionally high slenderness ratios and ground-level flight at super- and hypersonic speeds. As space constraints limit the integration of measurement equipment into such slender test models, nonintrusive measurement techniques become favorable. The present analysis demonstrates a renewed approach to the free-flight technique, which sets models into unconstrained flight through the test section. It enabled the evaluation of the quasi-steady drag, lift, and pitching moment characteristics, and, to some extent, also the dynamic pitch damping characteristics. An alternative to the free-flight technique is the free-oscillation technique, which limits the motion to a rotation around the center of gravity. The free-oscillation technique allowed a higher-fidelity analysis of the static and dynamic pitching moments. Both methods were based on the analysis of the accelerations derived from trajectory tracking. This acceleration-based approach enabled the evaluation of the highly nonlinear characteristics. The high slenderness of the investigated projectile leads to a significant contribution of the viscous forces to the overall drag. These viscous forces are sensitive to the laminar-turbulent boundary-layer state, as well as the thermal boundary conditions. The application of a high-resolution schlieren system enabled the assessment of the local laminar-turbulent boundary-layer state, while the use of low- and high-enthalpy testing facilities enabled the assessment of the aerothermal influence. Steady-state Reynolds-averaged Navier–Stokes simulations, which included laminar-turbulent transition modeling, were employed to replicate the results of the experimental efforts.

Kinematics of rift linkage between the Eastern and Ethiopian rifts in the Turkana Depression, Africa

AbstractRift initiation within cold, thick, strong lithosphere and the evolving linkage to form a contiguous plate boundary remains debated in part owing to the lack of time–space constraints on kinematics of basement‐involved faults. Different rift sectors initiate diachronously and may eventually link to produce a jigsaw spatial pattern, as in the East African rift, and along the Atlantic Ocean margins. The space–time distribution of earthquakes illuminates the geometry and kinematics of fault zones within the crystalline crust, as well as areas with pressurized magma bodies. We use seismicity and Global Navigation System Satellites (GNSS) data from the Turkana Rift Array Investigating Lithospheric Structure (TRAILS) project in East Africa and a new digital compilation of faults and eruptive centres to evaluate models for the kinematic linkage of two initially separate rift sectors: the Main Ethiopian Rift (MER) and the Eastern rift (ER). The ca. 300 km wide zone of linkage includes failed basins and linkage zones; seismicity outlines active structures. Models of GNSS data indicate that the ca. 250 km‐wide zone of seismically active en echelon basins north of the Turkana Depression is a zone, or block, of distributed strain with small counterclockwise rotation that serves to connect the Main Ethiopian and Eastern rifts. Its western boundary is poorly defined owing to data gaps in South Sudan. Strain across the northern and southern boundaries of this block, and an ca. 50 km‐wide kink in the southern Turkana rift is accommodated by en echelon normal faults linked by short strike‐slip faults in crystalline basement, and relay ramps at the surface. Short segments of obliquely oriented basement structures facilitate across‐rift linkage of faults, but basement shear zones and Mesozoic rift faults are not actively straining. This configuration has existed for at least 2–5 My without the development of localized shear zones or transform faults, documenting the importance of distributed deformation in continental rift tectonics.

The Efficacy of a Novel Board Game to Teach Cable Properties to Introductory Neuroscience Undergraduate Students.

Engagement activities in large classrooms (>100 students) are difficult due to space constraints, number of participants, and overall noise. Additionally, electrophysiological concepts in foundational neuroscience courses can be confusing and lack excitement. Providing students an opportunity to further engage in the material they are learning and apply their knowledge promotes community in the classroom, a deeper understanding of the topic, and an overall increase in retention. Game-based learning has been used in education across all levels and disciplines to provide students with this opportunity. You're Getting on my Nerves is a board game created to offer students a fun way to learn and apply cable properties of action potential propagation. This game allows students to practice vocabulary terms, apply their knowledge of changes in the cell that impact the speed of an action potential, and develop comradery with their classmates. In this article, we have assessed the board game for its efficacy in teaching concepts of cable properties, its ability to promote engagement in a large classroom, its feasibility and timing with a large class, and its potential to elicit comparable formative assessment scores to students who learned these concepts through didactic lecture. Overall, the board game was feasible for a large class to complete within the class period. The results showed an increase in understanding and retention of the material in addition to preference over didactic lectures with students reporting higher engagement, interaction with their peers, and enjoyment in the activity.

Dynamic switched crowding-based multi-objective particle swarm optimization algorithm for solving multi-objective AC-DC optimal power flow problem

In this paper, the multi-objective AC-DC optimal power flow (MO/AC-DC OPF) problem in the presence of renewable energy sources (RESs), flexible AC transmission system (FACTS) devices and multi-terminal direct current (MTDC) systems is introduced for the first time. Conflicting objective functions and the high complexity of the objective and constraint spaces are the main challenges in finding optimal solutions for MO/AC-DC OPF. To overcome these challenges, twelve different versions of the dynamic switched crowding-based multi-objective particle swarm optimization (DSC-MOPSO) algorithm are introduced in this paper. Studies on multimodal optimization problems have shown that all DSC-MOPSO versions have better performance metrics than the MOPSO algorithm. Using the developed DSC-MOPSO and its strong competitors, the Pareto-optimal solution sets of the MO/AC-DC OPF problem are investigated. In these investigations, the performances of the algorithms are tested for the minimization of dual and triple objectives such as fuel cost, voltage level deviation, emission and power loss in a modified IEEE 30-bus power grid. According to the simulation results, the proposed DSC-MOPSO achieved an improvement in fuel cost between 0.02 % and 5.05 % and a reduction in active power loss between 0.44 % and 30.74 % compared to its competitors. The Hypervolume (HV) performance metric was used to evaluate the Pareto-front coverage performance of DSC-MOPSO and other optimizers. The results from nine case studies of the MO/AC-DC OPF were statistically analyzed by the Friedman test according to the 1/HV metric. According to the Friedman test results, the rankings of DSC-MOPSO and MOMA are 1.984 and 3.079, respectively, ranking first and second among all competitors. Finally, in this study, feasible solutions for MO/AC-DC OPF problem are identified for the first time and the stability of competitive algorithms in finding these solutions is analyzed for the first time. The success rates and search times of DSC-MOPSO and MOMA algorithms in finding feasible solutions for MO/AC-DC OPF are 91.01 % (30.641 s) and 82.01 % (46.038 s), respectively.

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Experimental analysis of irregularly shaped octagonal on-chip inductors for improving area-efficiency in CMOS RFICs for millimeter wave applications

This article deals with the analysis of irregularly shaped single turn octagonal spiral inductors for millimeter-wave and sub-THz CMOS IC designs. Simulations and experimental results, along with theoretical formulations, are used to characterize these irregular structures. This article proposes a novel approach for efficient use of silicon chip area by reshaping the on-chip inductors used in millimeter wave (mm-wave) applications without compromising the performance of the inductors. Especially in CMOS RFICs when a space constraint exists in either X- or Y-direction in their layout, such reshaping can be attempted. Moreover, two novel methods of reshaping the inductors are proposed and studied thoroughly. The study of these irregular shapes has interesting conclusions, which are validated through on-wafer measurements. Certain methods of reshaping result in inductors which do not have degradation in their quality factors (Q), while other approaches degrade the Q. Based on these insights, a design methodology is proposed for designers who need to reshape their inductors to irregular structures while not compromising on the quality factor. The measurement results agree with the simulations and prove that the proposed reshaping is practically possible.