Constant Space Research Articles

The effects of using intermittent metal part reinforcement and countersink on the strength of adhesively bonded joints

This study investigates the impact of two innovative methods, namely, intermittent metal part reinforcement and countersinking, on the strength of single lap joints (SLJs). In the former method, metal inserts are strategically integrated within the adhesive layer, while the latter involves the application of countersinks on the adherends to create conical depressions for adhesive application. The metal inserts and countersink samples were fabricated using a 5-axis CNC milling machine. Subsequently, the joints were produced by subjecting the samples to 0.15 MPa pressure and 70 °C temperature for 120 min with the aid of a hot press. Tensile tests were conducted on single lap joints (SLJs) featuring five different configurations of intermittent metal part reinforcement joints (IMRJs) with varying sizes and positions of reinforcements, as well as six countersunk reinforced joints (CRJs) with different orientations of countersinks, all while keeping the width and overlap length constant. A two-dimensional finite element (FE) model of the IMRJ was constructed using ABAQUS software, incorporating cohesive zone elements to simulate the behavior of the adhesive layer (DP 460). The model's accuracy was confirmed through experimental verification. Additionally, fractographic analysis of the failure surfaces of both types of joints was carried out. The inclusion of IMRJs and CRJs in the SLJs increased their load-carrying capacity by more than 10 % and 30 %, respectively.

Longitudinal Control for Cruise Control Features in Vehicle Automation

This research focuses on longitudinal control methods implemented in Cruise Control (CC) and Adaptive Cruise Control (ACC) systems, as well as the mechanism for switching between these two modes. Two primary longitudinal control methods are examined: Constant Space Headway Control, which maintains a constant distance between vehicles, and Constant Time Headway Control, which maintains a constant time gap between vehicles.
 The noteworthy feature of this research focuses on incorporating a switching mechanism between Cruise Control and Adaptive Cruise Control through the utilization of the virtual target method.

Reconstruction of neutron spectrum emitted by portable 14 MeV neutron generator by a combination of different methods

The presented paper is a continuation of the Tikhonov Regularisation, Minimum Fisher Information, Maximum Entropy, and Maximum Likelihood methods application to unfolding the neutron spectra emitted by the fusion devices from activation measurement. The aim of the analysis is the evaluation of the possible uncertainty improvement. The developed algorithms and methodology were validated with 14 MeV portable neutron generators before application to the analysis of the neutron spectrum emitted from tokamak. The analysis concerns plasma-target generator did not provide satisfactory uncertainty of the results. The modification of the irradiation foils’ set and the improvement in the activity measurement precision progress the results. The sealed tube portable neutron generator irradiated the Al, Fe, Ni, Zr, Au, Mg, and Nb foils. The HPGe spectrometer measured the induced activity with an uncertainty of about 10 %. The synthetic data analysis was made to establish the ratio between the error of the spectrum reconstruction and the discrepancy between the input data and activities reconstructed for this spectrum by the FISPACT-II inventory code. Two bin structures were considered. One was compatible with the FISPACT-II code, but the energy resolution was not regular. The second was characterised by constant bin spacing connected with the modification requirement before simulation and additional uncertainty of about 5 %. The best results were obtained by calculation of the mean value from all methods. The corresponding reconstruction uncertainty is equal to 11 %. The reconstructed spectrum has a dominant deuterium tritium peak slightly shifted to the higher energies due to the beam-target reaction kinematics. The evaluation of the impact of the deuterium-deuterium reaction due to the long-term operation was not reachable due to the measured high intensity from scattered neutrons.

Growth and characterization of organic 2-methylbenzimidazole 4-Aminobenzoate Single crystal for Opto-electronic device applications

A new organic material of 2-Methylbenzimidazole 4-Aminobenzoate (2MIAB) with a size of 5 × 4 × 3 mm3 was grown by solvent evaporation solution growth method. The SCXRD studies reveal that the 2MIAB crystal has a monoclinic crystal structure and belongs to the space group P21/nn number is 4 unit cell parameters are a=7.8319(3) Å, b=20.6465(8) Å, c=9.0432(3) Å, α =90°, β =90.4140°, γ =90°and V =1462.26(9) Å 3. The hkl planes are identified through Powder XRD analysis. The functional groups present in the 2MIAB crystal were determined from FTIR spectral analysis. The UV–Vis spectral analysis of 2MIAB shows a high transmittance range of 99% and a cut-off wavelength of approximately 315 nm. The surface morphology of the 2MIAB compound is examined through FE-SEM analysis. The thermal studies reveal that the grown crystal is stable up to 134 °C. dielectric constant in free space (ϵ0) and dielectric loss (tanδ) of 2MIAB crystal at varying temperatures (313 K, 323 K, 333 K) are recorded with a frequency range of 50 Hz to 5 MHz. The load-dependent hardness of the 2MIAB crystal was analyzed using Vicker’s microhardness test. The optical limiting was performed by Q-switch Nd: YAG laser with a wavelength of 532 nm and intensity of 2.46×1012 W/m2 (pulse rate of 9 ns and energy of 100 μJ ). We employed First-principles density functional theory and ab-initio molecular dynamics simulations to study the electronic and optical properties of the 2MIAB material. We demonstrate that this material is semiconductor in nature, with an energy band gap of 3.26 eV and significant absorption in the UV light range.

Effect of plant spacing and sowing dates on the growth and yield of radish (Raphanus sativus) in Rupandehi district, Nepal

A field experiment was conducted from mid-April to mid-June 2022 in Rupandehi to evaluate the growth and yield of radish maintained in varied plant spacing at differed sowing dates. The study was aimed to compare the growth, production and economics of radish in Rupandehi district under different plant spacing and sowing dates and to evaluate the interaction between these two factors. Four plants spacing (10 cm, 20 cm, 30 cm and 40 cm) with constant row spacing was maintained at two sowing dates (Chaitra 29 and Baisakh 14). The treatments were arranged in two factorial Randomized Complete Block Design (RCBD) with 3 replications. The data were collected on 30 DAS and 45 DAS. The obtained data were recorded and analyzed using MS-Excel and R-studio, respectively. The results revealed that the highest yield was obtained from plant spacing of 20 cm (28.20 t/ha). However, individual plant weight was higher in wider spacing. Plant spacing of 20 cm showed significantly highest plant height (24.52 cm), number of leaves per plant (22.37) and leaf length (23.36 cm). Leaf blade width (10.67 cm) and petiole length (3.05 cm) was significantly highest in plant spacing of 30 cm. Early sowing date showed significantly better results for all growth and yield parameters and yield except leaf blade width. Higher gross return, net return and B:C ratio was observed in plant spacing of 20 cm and early sowing date. The study concluded that plant spacing of 20 cm and earlier sowing date was ideal for maximum growth and yield of radish in Rupandehi district.

Cosmological constant Petrov type-N space–time in Ricci-inverse gravity

Our focus is on a specific type-N space–time that exhibits closed time-like curves in general relativity theory within the framework of Ricci-inverse gravity model. The matter-energy content is solely composed of a pure radiation field, and it adheres to the energy conditions while featuring a negative cosmological constant. One of the key findings in this investigation is the non-zero determinant of the Ricci tensor (Rμν), which implies the existence of an anti-curvature tensor (Aμν) and, as a consequence, an anti-curvature scalar (A≠R−1). Furthermore, we establish that this type-N space–time serves as a solution within modified gravity theories via the Ricci-inverse model, which involves adjustments to the cosmological constant (Λ) and the energy density (ρ) of the radiation field expressed in terms of a coupling constant. As a result, our findings suggest that causality violations remain possible within the framework of this Ricci-inverse gravity model, alongside the predictions of general relativity.

Dynamical tunneling across the separatrix.

The strong enhancement of tunneling couplings typically observed in tunneling splittings in the quantum map is investigated. We show that the transition from instanton to noninstanton tunneling, which is known to occur in tunneling splittings in the space of the inverse Planck constant, takes place in a parameter space as well. By applying the absorbing perturbation technique, we find that the enhancement invoked as a result of local avoided crossings and that originating from globally spread interactions over many states should be distinguished and that the latter is responsible for the strong and persistent enhancement. We also provide evidence showing that the coupling across the separatrix in phase space is crucial in explaining the behavior of tunneling splittings by performing the wave-function-based observation. In the light of these findings, we examine the validity of the resonance-assisted tunneling theory.

Effect of CuAl2 on the Microstructure and Hardness of Al-Si-xCu Alloys Produced by Powder Metallurgy

Aluminum alloys are important in many industrial applications because of their light weight and good mechanical properties. In this study, the effect of copper addition with different percentages ( 0, 0.1, 0.2, 0.3wt. %) on the microstructure and mechanical strength of Al-Si alloy were studied using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and Vickers hardness (Hv) tests. XRD and SEM analyses showed that the Al-Si alloy consisted of α-Al and Si phases. The intermetallic compound (IMC) CuAl2 was detected with the addition of Cu. This IMC causes a change in the lattice constant and inter-atomic spacing (dhkl). The distortion and dense of the microstructure are considered indications of the enhancement in the hardness of alloys. The Vickers hardness (Hv) was measured for the samples before and after sintering. The highest value was 28.755 Hv with 0.2wt. % Cu after sintering, whereas the smallest value was 11.643 Hv without Cu content before sintering. This improvement in hardness is attributed to the temperature that promotes the diffusion of Cu atoms into theAl lattices.

Interfacial thermal conductance of multilayer graphene/MoS2 heterostructure

We investigated the Interfacial thermal conductance (ITC) with a heterogeneous structure of a bilayer of MoS2 embedded in the middle of four graphene layers by non-equilibrium molecular dynamics (NEMD). Surprisingly, the ITC of MoS2/MoS2 (M/M) is significantly higher than that of the graphene/MoS2 (G/M). Interestingly, changes in the cross-sectional dimensions do not affect the ITC of the G/M and M/M, as the constant interface spacing preserves their structural characteristics so that phonon mean free range remains unchanged. Intriguingly, the interfacial strain affects the ITC notably. A 10% compression strain increases the G/M ITC by 100%, while a 10% tension strain reduces it by 70%. Unexpectedly, increasing defect concentration near the G/M interface leads to a decrease in thermal conductance. We find that graphene plays a dominant role in heat conduction within the heterostructure, while defects primarily enhanced low-frequency phonon vibrations of graphene, with MoS2 vibrations remaining largely unaffected. Due to the increase in defect rate, the out-of-plane phonon coupling is weakened, thus leading to a decrease in G/M ITC. These findings provide concise insights into the heat conduction of G/M heterostructures.

Misfit and the mechanism of high temperature and low stress creep of Ni-base single crystal superalloys

The present work proposes a new elementary deformation mechanism which governs high temperature and low stress creep of single crystal superalloys (SXs), where the misfit between the γ- and the γ′-phase plays a central role. In the coherent two phase SX microstructure, there is a tendency to minimize the overall elastic strain energy. This is accomplished by the formation of dislocation networks in the γ-phase close to the γ/γ’-interfaces. The stress fields of the network dislocations and misfit stresses accommodate each other to keep the overall strain energy of the system at a minimum. Previous work has shown that dynamic recovery is associated with knitting-out reactions, where dislocations from the network shear the γ’-phase and annihilate with dislocations of opposite sign on the other side of the γ’-phase region. Due to the presence of the misfit this results in an increase of elastic strain energy which is counteracted by coupled knitting-in reactions where newly arriving γ-channel dislocations re-establish the minimum energy configuration. Here we provide microstructural evidence for knitting-out and knitting-in reactions and show that while these reactions clearly occur, dislocation network spacings stay constant. The misfit between the γ- and the γ′-phase accounts for a constant network spacing. Dislocation networks are not static but represent dynamic steady state equilibrium structures in an evolving microstructure. Knitting regular networks requires climb processes which are suggested to be rate controlling. This new view of high temperature and low stress creep mechanism of SXs allows to rationalize previous results published in the literature.

Why and when should organisms elongate their telomeres? Elaborations on the 'excess resources elongation' and 'last resort elongation' hypotheses.

Telomere length and telomere shortening are thought to be critical cellular attributes and processes that are related to an individual's life span and fitness. The general pattern across most taxa is that after birth telomere length gradually decreases with age. Telomere protection and restoration mechanisms are usually assumed to reduce the rate of shortening or at most keep telomere length constant. However, here we have compiled a list of 26 articles showing that there is an increasing number of studies reporting apparent elongation of telomeres (i.e., a net increase in TL from timet to timet+1) often in a considerable proportion of the individuals studied. Moreover, the few studies which have studied telomere elongation in detail show that increases in telomere length are unlikely to be due to measurement error alone. In this article, we argue that episodes of telomere elongation deserve more attention as they could reflect individual strategies to optimise life histories and maximise fitness, which may not be reflected in the overall telomere dynamics patterns. We propose that patterns of telomere (net) elongation may be partly determined by other factors than those causing telomere shortening, and therefore deserve analyses specifically targeted to investigate the occurrence of telomere elongation. We elaborate on two ecological hypotheses that have been proposed to explain patterns of telomere elongation (the 'excess resources elongation' and the 'last resort elongation' hypothesis) and we discuss the current evidence for (or against) these hypotheses and propose ways to test them.

Separation, compactness, and sobriety in the category of constant limit spaces

The objective of this article is to characterize each of compact, sober, and $T_{i}$ for $i=0,1,2$ constant limit spaces as well as to investigate the relationships between them. Finally, we compare our results in some topological categories.

UAV-based plant height estimation of maize cultivated using different varieties and sowing spacing

This study aimed at estimating plant height of maize using low-cost unmanned aerial vehicle (UAV) based imagery. The experiment was laid out in a factorial arrangement in randomized complete block design. The factors were maize varieties (honampa, ahooden, ahoofe and abontem) and intra-row sowing spacing (20 cm, 30 cm and 40 cm). A constant inter-row spacing of 80 cm was used for all sub-plots. Data (both UAV-based imagery and manual data) were taken 21 days after sowing (DAS) -seedling/establishment stage-, 42 DAS (vegetative stage), 63 DAS (tasseling stage), and 84 DAS (physiological maturity stage). The results showed a high correlation between the UAV-based plant height and manual measurement with R2 (adjust) > 0.92 in all cases. For the intra-row sowing spacing, the 20 cm plant spacing was found to have had the best overall R2 (adjust) of 0.949, showing the strongest regression of UAV with the manual data among the treatments. Also, it was found that the best stage to estimate maize plant height is dependent on the variety being used since the honampa gave the best correlation coefficient (R = 0.85) at the tasseling stage while the ahooden, ahoofe and abontem gave optimum correlation coefficients (R) of 0.70, 0.90 and 0.69 respectively at the vegetative stage. Overall, the study shows potency of using UAV-based imagery for estimating plant height of maize. The findings of the study could be useful to agronomists and smallholder farmers in Ghana and other developing countries regarding the usefulness of the technology for in-field data collection and advisory services.

A compact high resolution semi-variable mesh exponential finite difference method for non-linear boundary value problems of elliptic nature

In this research an original exponential approximation of second accuracy in y- and third accuracy in x-axis employing full step discretization has been designed for solving 2D non-linear partial differential equation of elliptic nature in a rectangular domain. We adopted non-constant grid spacing in x -axis and constant grid spacing in y -axis in numerical computation of convection-diffusion equation where convection term dominates. An exhaustive error behaviour of the technique has been analysed. Non-linear elliptic equations are computed using this method. Lastly, proposed idea is scrutinized on simulations of physical repute with emphasis on convection-diffusion equation articulating the efficacy of the technique.

PEM-based random vibration analysis under service-braking conditions on an irregular track

PurposeAccording to relevant research, non-uniform speed has a significant impact on the vehicle-track systems. Up to now, research work on it is still very limited. In this paper, the PEM is adopted to further transform it into a deterministic process to solve the vehicle’s problem of running at a non-uniform speed.Design/methodology/approachThe multi-body vehicle model has 10 degrees of freedom and the track is regarded as a finite long beam supported by lumped sleepers and ballast blocks. They are connected via linear Hertz springs. The vertical track irregularity is a Gaussian stationary process in the space domain. It is transformed into a uniformly modulated nonstationary random process in the time domain with respect to the non-uniform vehicle speed. By solving the equation of motion of the coupled vehicle-track system with the pseudo-excitation method, the pseudo-response and consequently the power spectral density and the standard deviation of the structural response can be obtained.FindingsTwo kinds of vehicle braking programs are taken in the numerical example and some beneficial conclusions are drawn.Originality/valueThe pseudo-excitation method (PEM) was used to perform the random vibration analysis of a coupled non-uniform speed vehicle-track system. Transforming the track irregularity into a uniformly modulated nonstationary random process in time domain with respect to the non-uniform vehicle speed was undertaken. The pseudo-response of the coupled system is solved by applying the Newmark algorithm with constant space integral steps. The random vibration transfer mechanism of the coupled system is fully discussed.

Manifolds with harmonic Weyl tensor and nonnegative curvature operator of the second kind

We show that a compact manifold with harmonic Weyl tensor and nonnegative curvature operator of the second kind is globally conformally equivalent to a space of positive constant curvature or is isometric to a flat manifold. Moreover, we obtain that a compact manifold with harmonic curvature and nonnegative curvature operator of the second kind is isometric to a space of constant curvature. These improve Kashiwada's result that Riemannian manifolds with harmonic curvature tensor for which the curvature operator of the second kind is nonnegative and positive are locally symmetric spaces and constant curvature spaces, respectively.

Numerical simulation of diverging plasma magneto-hydrodynamic acceleration channels

This paper presents a numerical study of plasma flow in a magneto-hydrodynamic acceleration channel. The results show that in the channel with equal electrode pair spacing, increasing the magnetic field strength reduces the Joule heat dissipation and the temperature. Increasing the applied voltage increases the external energy input, increasing both the exit Mach number and the internal temperature. Reducing the electrical conductivity achieves a balance between acceleration and temperature rise. For acceleration channels of different shapes, a constant cross section channel can only accelerate the fluid to near sonic speeds, whereas a diverging channel can achieve supersonic speeds. In addition, maintaining constant electrode spacing in the diverging channel effectively prevents fluid deceleration at the rear of the acceleration channel caused by the reverse Lorentz force under high magnetic field strength.

Control of Propagation of Salt Wedge by using Roughness Blocks having Different Inclination

The hydraulic conditions of a flow previously proved to be changed when placing large-scale geometric roughness elements on the bed of an open channel. These elements impose more resistance to the flow. The geometry of the roughness elements, the numbers used, and the configuration are parameters that can affect the hydraulic flow characteristics. The target is to use inclined block elements to control the salt wedge propagation pointed in most estuaries to prevent its negative effects. The Computational Fluid Dynamics CFD Software was used to simulate the two-phase flow in an estuary model. In this model, the used block elements are 2 cm by 3 cm cross-sections with an inclined face in the flow direction, with a length of their sides 2 and 3 cm. These elements were placed with a constant spacing in two rows at a distance from two sides of the bed of the channel model. Six simulation runs were conducted with two different discharges and three different inclinations of the centerline of the element concerning the flow direction. The applied discharges are 30 and 45.3 l/min, and the inclination of roughness elements are 15o, 30o, and 45o. The spacing between elements in each row is kept at 3cm. The results showed that when no roughness elements were used, the propagation of the salt wedge extended to 3.9m and 3.1m at a discharge of 30 l/min and 45.31/min, respectively. The propagation of the salt wedge was reduced when using the inclined blocks roughness element. This reduction depends on the applied discharge and the angle of inclination. At the minimum applied discharge of 30 l/min, the propagation of the salt wedge was reduced by 74% at 45o inclination. In contrast, it was 69% at 30o and 64% at 15o inclination at the same discharge. When the discharge is 45.3 l/min, the propagation of the salt wedge was reduced by 85% at 45o inclinations of roughness, 84% at 30o. It was 70% at 15o inclinations. The roughness elements improve the flow turbulence that disperses and slows the salt wedge propagation beneath the fresh water.

Effect of Si3N4 nanowires doping on microstructure and properties of Sn58Bi solder for Cu bonding

PurposeThe purpose of this study is to delve into the mechanism of Si3N4 nanowires (NWs) in Sn-based solder, thereby furnishing a theoretical foundation for the expeditious design and practical implementation of innovative lead-free solder materials in the electronic packaging industry.Design/methodology/approachThis study investigates the effect of adding Si3N4 NWs to Sn58Bi solder in various mass fractions (0, 0.1, 0.2, 0.4, 0.6 and 0.8 Wt.%) for modifying the solder and joining the Cu substrate. Meanwhile, the melting characteristics and wettability of solder, as well as the microstructure, interfacial intermetallic compound (IMC) and mechanical properties of joint were evaluated.FindingsThe crystal plane spacing and lattice constant of Sn and Bi phase increase slightly. A minor variation in the Sn58Bi solder melting point was caused, while it does not impact its functionality. An appropriate Si3N4 NWs content (0.2∼0.4 Wt.%) significantly improves its wettability, and modifies the microstructure and interfacial IMC layer. The shear strength increases by up to 10.74% when adding 0.4 Wt.% Si3N4 NWs, and the failure mode observed is brittle fracture mainly. However, excessive Si3N4 will cause aggregation at the junction between the solder matrix and IMC layer, this will be detrimental to the joint.Originality/valueThe Si3N4 NWs were first used for the modification of lead-free solder materials. The relative properties of composite solder and joints were evaluated from different aspects, and the optimal ratio was obtained.

Strip-saturation model for arbitrary polarized electro-elastic material weakened by an eccentrically situated anti-plane semi-permeable crack

A strip-saturation model is studied to observe the effect of changing polarization axis on an electro-elastic strip, weakened by an eccentrically situated anti-plane semipermeable crack. The model is modified by considering that the saturated limit of electric displacement over rims of the saturation zone is quadratic interpolating polynomial times. The proposed model is formulated and then solved by using the Fourier integral transform technique and integral equations method. Closed-form analytic expressions are derived for developed saturation zone and fracture parameters viz. electric crack condition parameter, crack-sliding displacement, crack-opening potential drop, field intensity factors, energy release rate, etc. The influence of poling angle, prescribed electro-mechanical loadings, crack length, and material constants on fracture parameters are presented and analyzed graphically.