Search Results (3,506)

Fractional memory can substantially alter the period-doubling route to chaos, but the joint effects of fractional order q and memory length M on successive bifurcations in the finite-memory Grünwald–Letnikov (GL) fractional logistic map remain unclear. We formulate the period-doubling bifurcations of its exact periodic orbits as an exact Floquet problem. An algebraically equivalent periodic–antiperiodic phase reduction lowers the nonlinear system from $mM+M+1$ to $2m+1$ unknowns, making very long memory lengths computationally accessible. The reduced formulation reproduces an independently derived fixed-point bifurcation boundary with a maximum absolute discrepancy of $2.67\times {10}^{-15}$ and is further confirmed for successive doublings of period-4, period-8, and period-16 orbits. We compute the first seven cascade levels for orbit periods $m=1,2,4,8,16,32,64$ and memory lengths up to $M=2\times {10}^6$. Increasing M shifts these bifurcation points toward smaller values of the bifurcation parameter, with markedly stronger shifts at lower q. The dependence on q is nonmonotone: decreasing q first shifts the bifurcations toward smaller values and then reverses this trend. For $m=1,8,32$, the turnover locations move from $q\approx 0.46–0.49$ at $M=100$ to $q\approx 0.24–0.25$ at $M=2\times {10}^6$. The $O\left(M^{-q}\right)$ decay of the GL memory tail explains the stronger memory-length effect at low q, while the positive near-classical sensitivities and the fixed-memory $q\to 0^{+}$ limit explain the turnover. These results provide an exact and scalable framework for quantifying how finite fractional memory reorganizes the period-doubling cascade. Full article

A girth cycle refers to a cycle that has the minimum length within a graph. The graphs $D(k,q)$ form an important family of algebraically defined bipartite graphs over finite fields, and their short-cycle structure is closely related to questions in extremal graph theory and finite geometry. Motivated by the problem of determining the edge-girth-regular parameter of $D(k,q)$, we determine the exact number of girth cycles in $D(4,q)$ for every prime power q. Our proof uses a convenient isomorphic model $\Gamma (4,q)$ and edge-transitivity to reduce the global enumeration to counting the girth cycles containing one fixed edge. Specifically, we prove that when q is odd with $q>3$, the number of girth cycles in $D(4,q)$ is $q^5{(q-1)}^2(q-3)/8$. Moreover, when q is even, the number of girth cycles in $D(4,q)$ is $q^5{(q-1)}^2(2q-3)/8$. When $q=3$, the girth is 12 and the number of girth cycles is 729. Together, these results resolve the case $k=4$ of the problem posed in our earlier work. Full article

Per- and polyfluoroalkyl substances (PFASs) are persistent, surface-active contaminants for which soil represents the largest terrestrial reservoir. This review synthesizes a rapidly expanding but fragmented body of literature in order to reframe PFAS not merely as a groundwater transport problem but as a systemic stressor of soil health, drawing together their reported effects on the chemical, physical and biological properties of soils and giving particular attention to the calcareous, alkaline, carbon-poor and seasonally dry soils of the Mediterranean. The reviewed evidence suggests that, chemically, PFASs perturb the coupled carbon and nitrogen cycles rather than the bulk soil reaction, transiently stimulating and then depressing organic carbon turnover, drawing down the dissolved organic carbon pool and disturbing nitrification, while their retention and bioavailability are governed chiefly by organic carbon, chain length and pH. Physically, the surfactant character that defines these molecules lowers the surface tension of soil water and concentrates PFASs at the air–water interface, so that in unsaturated and drought-prone soils much of the burden is retained and then released episodically, most clearly on rewetting after dry periods. Biologically, the literature consistently reports dose-dependent declines in microbial viability, diversity and enzyme activity, alongside toxicity to earthworms and other soil fauna, with sensitivity strongly modulated by soil texture and organic matter. Across all three domains, the Mediterranean emerges as both potentially vulnerable and conspicuously understudied, the available data being clustered in a few western countries and effectively absent for much of the eastern and southern basin, so that the regional assessment offered here rests largely on mechanistic inference rather than on direct observation. The review argues that these coupled mechanistic and geographic gaps define an urgent, region-specific research agenda for the protection of soil health. Full article

Conventional flux-reversal permanent magnet motors have problems such as excessive torque ripple and rich harmonic content in direct drive applications such as oil exploration, which restrict their application in high-precision scenarios. To address this issue, this paper presents a hybrid excitation topology that integrates double-armature windings, stator Halbach hybrid permanent magnet arrays, rotor-staggered unequal-tooth and rotor-hybrid permanent magnets. Two-dimensional finite element analysis was conducted using ANSYS Maxwell 2023 R1 to evaluate electromagnetic performance under rated steady-state conditions, rated power 300 kW, rated speed 83 rpm, rated voltage 660 V, rated phase current 307 A, and axial core length 200 mm. The simulation results show that the proposed topology has an average output torque of 34.5 kN·m at rated conditions compared with the traditional flux-to-reverse permanent magnet motor of the same size, and the torque ripple rate is reduced from 27.5% to 17.4%, a relative reduction of 36.8%. The results are based only on numerical simulation and have not been verified by physical prototype experiments. Dynamic control strategies, multi-load transient responses and experimental verification will be carried out in subsequent work. Full article

IoT-connected healthcare sensor networks require authenticated and privacy-preserving data exchange among wearable sensors, mobile medical terminals, edge gateways, cloud servers, and medical institutions. Existing authentication schemes for healthcare IoT often bind signatures directly to user identities, exposing sensitive personal or institutional information and imposing heavy verification costs on resource-constrained sensing devices. To address this problem, we propose a fine-grained and flexible dual authentication scheme for healthcare sensor networks. In the proposed scheme, health data and diagnoses are signed with a fresh signing key and a fine-grained access control policy each time, so that the signer identity remains hidden while authorized entities can still modify permitted parts of signed data. No entity other than an authorized entity can trace a malicious signer or modify signed data without changing the data source. To support lightweight verification in sensor-edge-cloud deployments, we further present a verifiable outsourced authentication scheme that outsources time-consuming pairing operations to cloud servers; the online verification process then requires only six multiplication operations. As a fundamental technical component, we present a practical attribute-based sanitizable signature with shorter signature and key lengths and more efficient signing and signature-changing operations than the state-of-the-art policy-based sanitizable signature (P3S). Formal security analysis and experiments demonstrate the security and practicality of the proposed scheme for privacy-preserving healthcare sensing and medical data exchange. Full article

To address the issue of unbalanced path allocation in multi-UUV cooperative operations under inhomogeneous ocean environments during full-coverage search missions, this paper proposes a heterogeneous UUV path planning method that integrates a hybrid waypoint deployment strategy with a dual-chromosome co-evolutionary genetic algorithm. First, heterogeneous UUVs are adaptively assigned to sub-regions according to the search value of the sea area, and a combination of Poisson sampling and Voronoi iterative refinement is adopted to complete the layout of detection points. Subsequently, connectivity-constrained K-means clustering is introduced to decompose the multi-traveling salesman problem (MTSP) into several independent TSP sub-problems. Finally, a dual-chromosome encoding scheme for task sequences and split points is designed, and a penalty matrix is incorporated into the fitness function to account for obstacle avoidance constraints, thereby establishing an integrated genetic-algorithm-based solution framework that incorporates both decomposition and obstacle avoidance. Simulation results demonstrate that the proposed method reduces the number of planned detection points by 12.4%, 12.8%, and 9.3% compared with baseline methods in circular, rectangular, and irregular sea areas, respectively, while the optimal path lengths are shortened by 5.8%, 4.5%, and 5.9%. Moreover, the cooperative mission time with four UUVs is reduced by 73.9%, 72.7%, and 71.2% relative to a single UUV, demonstrating an approximately linear speedup relative to the number of UUVs. Convergence analysis and extended experiments on 15 instances further confirm the algorithm’s solution stability and robustness under varying regional scales, shapes, and obstacle configurations. These results validate that the proposed approach not only reduces the number of deployment points and path cost, but also effectively balances obstacle avoidance and multi-robot load distribution. Full article

This paper investigates the blind estimation problem of multiuser long-code Direct Sequence Spread Spectrum (DSSS) signals in non-cooperative reception scenarios. In a long-code DSSS system, the spreading-sequence length exceeds the spreading gain and is not an integer multiple of it, so each symbol interval contains only a fragment of the spreading sequence. Consequently, conventional short-code subspace methods cannot directly estimate the complete spreading-code subspace. To address this issue, a blind despreading method based on signal subspace reconstruction and iterative least-squares projection (ILSP) is proposed. First, symbol samples sharing identical spreading-sequence fragments are grouped, and subspace decomposition is applied to obtain multiple fragment subspace estimates. These fragment subspaces are then jointly combined through the periodic selection structure to reconstruct the complete spreading-code subspace. Finally, ILSP is employed to estimate the spreading sequences and recover the transmitted information sequences. Simulation results demonstrate that the proposed method remains effective under low signal-to-noise ratio (SNR) conditions and that its information-sequence bit error rate (BER) approaches that of cooperative reception as the SNR or sample size increases. Full article

Curves constructed directly on point clouds are a core primitive in reverse engineering, product design, and point-based CAD; many workflows additionally require the curve to lie in a plane—e.g., as a section profile, inspection path, or design reference. This paper presents an algorithmic framework for computing free and plane-constrained geodesic curves directly on oriented point clouds, without any intermediate surface or mesh reconstruction. A geodesic-curvature-minimizing solver that combines a Newton/conjugate-gradient flow with directed projection, elliptic Gabriel neighborhoods, and Taubin smoothing forms the backbone; the plane-constrained problem is then reduced to a one-parameter pencil of planes through the endpoint chord and solved per plane by alternating projection onto the cloud and the plane, with a projection-only pre-lift and a penalized length objective that rejects sections floating off the cloud; the returned section is the best found over a sampled pencil of candidate planes. The returned sections are attached to the cloud within a small fraction of the mean sampling distance. All algorithms are given in pseudocode with convergence criteria and complexity estimates. Two parallel realizations of the plane search are developed and measured: a multithreaded CPU backend (about 3× over the serial scan) and a WebGPU backend that evaluates the whole plane pencil in a single compute dispatch. Accuracy is validated against the analytic conic sections of a cone and against cylinder and sphere benchmarks whose optimal plane is known in closed form; robustness is assessed under noise, non-uniform sampling, missing regions, outliers, and perturbed normals, and against both a slab-projection baseline and the conventional reconstruct-then-slice route. Five applications—shoe-last reverse engineering with a C² surface reconstruction, anthropometric girth measurement, medical transverse sectioning, dimensional metrology on industrial mold scans, and cleaning-path planning for a robotic surface-treatment task—demonstrate the plane-constrained geodesic curves in practice. Full article

The currently common procedures in orthognathic surgery are widely used. Different forms of skeletal malocclusion can be treated with great outcomes in terms of bite, bone harmony, function, improved mastication, esthetics, and even decreased problems with breathing. Each type and intensity of malocclusion may affect decision-making in terms of distraction, selection of osteotomy design, or even guide clinical and surgical decisions to use a less popular osteotomy protocol. CBCT (cone-beam computed tomography) is currently a milestone in the establishment of the condition of jaw bones, bone structure, temporomandibular joints, and central relation (CR), as well as the scope of maxilla–mandibular and tooth relations. When establishing all of the following in a clinical and radiological (CBCT-based) evaluation, it becomes possible to measure the occlusal plane, height, length, and three-dimensional position of each dental segment, as well as other dentoalveolar features. In the present case, CBCT helped distinguish a localized vertical anterior mandibular dentoalveolar discrepancy from generalized mandibular malposition and supported the planning of a mandibular anterior segmental subapical osteotomy (MASSO) by mapping the osteotomy corridor in relation to the dental roots, cortical bone, periapical bone height, and neurovascular structures. Significant therapeutic complexity emerges when severe skeletal Class III malocclusion (mandibular prognathism) is compounded by transverse maxillary discrepancies and a markedly elevated mandibular anterior segment. This constellation of deformities leads to profound disturbances in the anterior facial height, a disrupted maxillomandibular interincisal relationship, and the loss of a level occlusal plane. The presented case highlights how the patient’s clinical evaluation should be carefully compared with radiological data, status of both cortices in the mandible, the height of the mandibular anterior segment, presence of gum recessions and poor bone status that may affect healing, osteotomies, and occurrence of some unwanted events. Therefore, CBCT was useful not only for diagnosis and planning, but also for understanding the biological limits of movement and the risk of postoperative periodontal complications in this uncommon reversed Köle-type MASSO. Full article

We model the vacuum as a discrete face-centered-cubic ($K=12$) tensor network with Bell-pair bonds and use it to predict a two-step quantum-to-classical threshold for macroscopic center-of-mass superpositions. A reversible dispersive deformation of the center-of-mass mode sets in at $m_{\mathrm{soft}}\approx 13.1$$\mu$g, and coherence becomes geometrically unsustainable at $m_{\mathrm{hard}}\approx 22.6\mu$g. The two scales are separated by the exact, parameter-free ratio $\sqrt{3}$, fixed by the edge-to-circumradius ratio of the cuboctahedral triangular face. Gravitational-collapse models predict a single scale of the same order, so the distinctive, falsifiable content is the two-step structure and the exact $\sqrt{3}$ separation, testable by a mass scan across the window; the recent $16.2\mu$g cat-state oscillator of Bild et al. falls between the thresholds, where coherence is not ruled out. The absolute window depends on the bond length $L=\sqrt{4ln2}{\mathsf{\ell }}_P\approx 1.665{\mathsf{\ell }}_P$, fixed by one calibration against the Bekenstein–Hawking area law. This calibration and the Compton representability hypothesis—that a mass excitation remains coherent only while its reduced Compton wavelength is resolvable by the lattice—are stated model inputs rather than derivations, motivated by the Compton frequency internal clock of massive excitations, the mass cutoff generic to lattice-regularized field theories, and the total-mass dependence observed in composite-object interferometry. Open problems are stated explicitly. Full article

Borescope inspection is essential for assessing the airworthiness of aircraft gas turbines. Yet, current procedures remain highly manual, operator-dependent, and inconsistent, which limits the reliability of subsequent image-based damage analysis. This paper introduces a systematic design approach for an ultra-slender continuum robot (CR) tailored to the geometric and operational constraints of aero-engine inspection. We formalize the design space, compare actuation concepts, and select a tendon-driven architecture based on a structured evaluation. Dimensional synthesis is formulated as an optimization problem that maximizes the visible blade surface, yielding segment lengths that ensure high inspection coverage. We detail design, material, and cable choices, the actuation unit, and two variants of the manipulator: A fully actuated (FA) version and a hybrid version with a passive carrier (PC). Evaluation in a high-pressure compressor mock-up reveals distinct strengths in stiffness, controllability, friction, pose observability, and system complexity between the two systems. Based on these findings, future work should focus on advancing a hybrid solution that combines the benefits of both approaches. Moreover, the presented methodology is not limited to high-pressure compressor inspection but can be applied to any section of the engine, significantly broadening its scope of application. Full article

This paper proposes a spectral-grid method based on Chebyshev polynomials of the first kind for the numerical solution of second-order singularly perturbed boundary value problems containing two boundary layers. The proposed method possesses several important advantages, including high numerical accuracy, computational efficiency in terms of the number of arithmetic operations, reduced memory requirements, accurate localization and resolution of boundary layers, and applicability to singularly perturbed boundary value problems containing one, two, or multiple boundary layers. In the proposed approach, the computational domain is partitioned into several grid elements, and the solution on each element is approximated by a truncated series of Chebyshev polynomials. Continuity conditions for the solution and its derivatives are imposed at the interfaces between adjacent elements, resulting in a system of algebraic equations for the unknown expansion coefficients. The principal advantage of the method lies in its ability to accurately localize boundary layers by appropriately selecting the lengths of the grid elements and the degrees of the approximation polynomials. Numerical experiments for a wide range of perturbation parameters are presented in the form of tables and graphical illustrations and are compared with existing results available in the literature. The obtained results demonstrate that the proposed spectral-grid method provides highly accurate numerical solutions even for very small values of the perturbation parameter while significantly reducing the maximum absolute error. The convergence of the proposed method has been theoretically established, and its convergence rate has been analyzed. The numerical results confirm the accuracy, computational efficiency, robustness, and reliability of the proposed method for solving singularly perturbed boundary value problems. Full article

Conventional spoon-type seed-metering devices have fixed spoon-cavity geometry, which makes it difficult to achieve both stable sowing of small-sized seeds and precise seeding-rate regulation. To address this problem, a coordinated variable-volume adjustment method based on an adjustment ring-seed-picking spoon structure was proposed, and a variable-rate spoon-type millet seed-metering device was designed. Through circumferential rotation of the adjustment ring, the effective volume of the scooping spoon and the length of the transition groove were synchronously adjusted, enabling precise regulation of the number of seeds per hill without replacing components. The zoning characteristics of seed-population flow in the seed-metering chamber and the effects of operating speed on seed-filling mechanical behaviour were investigated through theoretical analysis and discrete element simulation. The seed-filling and seed-clearing processes were clarified, and key parameter ranges were determined. Through response surface methodology (RSM) experiments, the optimal parameter combination was determined as an operating speed of 3.43 km∙h⁻¹, a scooping-spoon inclination angle of 35.25° and a transition-groove inclination angle of 62.47°. Under these conditions, the qualified rate of seeds per hill was 93.11%, the average number of seeds per hill was 5.51 seeds and the coefficient of variation in seeds per hill was 23.71%. When the seeding-rate adjustment ring was adjusted within 0–10°, the average number of seeds per hill increased from 5.7 to 11.2 seeds, while the coefficient of variation decreased from 22.71% to 19.97%. The device can adapt to differences in grain shape among different millet varieties and to seeding-rate adjustment requirements under varying soil fertility conditions across different fields, achieving precise seeding-rate regulation and uniform seed metering. This study provides a reference for improving the variable-rate operating precision of precision hill-drop seeding devices for small-sized seeds. Full article

The bent sub is a main deflection component in the near-bit assembly of small-diameter push-the-bit guided coring tools, and its parameters affect build-up capability and local structural response. Existing studies mainly focus on conventional rotary steerable drilling systems, whereas slim-hole constraints, including narrow annular clearance and cross-sectional weakening induced by internal coring channels, remain insufficiently considered. To address this problem, a static bending model of the near-bit section was established based on Euler–Bernoulli beam theory. Channel-induced cross-sectional weakening was represented using the actual concentric annular geometry of the primary load-bearing outer tube, and the bent-sub initial curvature, dual push-the-bit loads, axial weight on bit, and borehole-wall contact and friction effects were incorporated. The build-up rate (BUR), maximum equivalent stress, and maximum curvature served as response indicators. A control-variable approach was used to analyze the bent-sub length L_b, bend angle γ, and distance from the bit D_b. The results showed that D_b had the strongest effect on BUR, and all parameters exhibited a trade-off between steering performance and structural safety. Increasing L_b from 0.30 m to 0.80 m reduced BUR from 12.65°/30 m to 9.79°/30 m, whereas increasing γ from 0.5° to 2.5° increased BUR from 4.12°/30 m to 10.70°/30 m. Considering structural constraints and normalized BUR retention, the recommended engineering ranges are L_b = 0.65–0.80 m, γ = 1.3°–1.9°, and D_b = 0.50–0.70 m. Full article

To address the problems of the Electromagnetic Wave Propagation Algorithm (EMWPA)—insufficient initial-population coverage, an imbalance between exploration and exploitation, and a tendency to fall into local optima—in high-dimensional complex optimization problems, this paper proposes a boosted electromagnetic wave propagation optimization algorithm, BEMWPA. First, a cubic chaotic map is introduced in the population-initialization stage to enhance the uniformity of the initial-solution distribution and the search-space coverage. Second, nonlinear phase modulation is applied to the electric- and magnetic-field driving terms, and a differentiated probabilistic switching mechanism is constructed to improve the dynamic coordination between global exploration and local exploitation. Furthermore, a Beta-distribution opposition-based learning strategy is introduced to enhance the algorithm’s ability to escape local optima by generating high-quality opposite candidate solutions. To verify the effectiveness of the proposed algorithm, systematic comparative experiments are conducted on the CEC2017 benchmark function set, and BEMWPA is combined with rapidly-exploring random tree (RRT) and applied to path planning of a welding manipulator in complex multi-workpiece scenarios. For a three-dimensional welding scenario containing 12 workpieces, 12 closed weld seams, and multiple obstacle constraints, BEMWPA-RRT reduces the initial inter-seam transfer path length of RRT from 586.00 mm to 479.11 mm, representing a relative reduction of 18.24%, and the complete end-effector path length is reduced from 2974.00 mm to 2867.11 mm, representing a relative reduction of 3.59%. Meanwhile, the optimized transfer path length is only 1.59 mm longer than the obstacle-free ideal transfer length of 477.52 mm, indicating that the proposed method can approach the geometric lower bound of this scenario while satisfying the obstacle-avoidance constraints. Kinematic verification on a seven-degrees-of-freedom welding manipulator further shows that the optimized Cartesian-space path can be converted into a continuously executable joint-space trajectory, providing an effective method for offline welding path planning of complex multi-workpiece tasks. Full article