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This study aims to reveal the room-temperature effect of a superconducting gravimeter prototype, which will guide its subsequent optimization to improve its gravimetric measurement accuracy.

Without leveling, the prototype output signal, tilt data and room temperature were measured under steady operating conditions. After analyzing the correlations of the three data sets, the residuals of the prototype’s output signal were compensated using the tilt data and the geodynamic effects (ocean tide loading, atmospheric loading and the gravitational effect of polar motion) were then corrected.

The remaining residuals after correction may be caused by small tilt variations that are due to the sensor chamber temperature and radiation shield temperature changes. These small tilt variations were submerged in the tilt signal noise. Although the peak-to-peak noise of the tiltmeter does not exceed 15 µrad, it can still produce gravimetric deviations above 60 µGal when the prototype is significantly tilted.

This study analyzes in detail the room-temperature effect of a superconducting gravimeter prototype, introduces the tilt effect of the relative gravimeters to compensate for the gravimetric deviations and emphasizes that the improvement of fine leveling and the accuracy of the tiltmeter are key requirements for the prototype to perform high-accuracy gravity measurement tasks.

The purpose of this paper is to examine the determinants of immigration from European Neighborhood (EN) and new member states to the EU core countries over the period 2000-2010. Apart from income differentials, unemployment rates and other standard variables hypothesized to determine immigration, the paper focusses attention on welfare-chasing as well as measures to enforce immigration policy. Using a variant of the gravity model, the paper investigates whether tests of these hypotheses are robust with respect to spatial misspecification.

The determinants of migration from the European Neighborhood and new member states to the EU core countries is estimated using a spatial variant of the gravity model. The methodology is used for both multilateral and spatial flows. Gravity model estimations are presented for immigration into the EU core destinations using standard, non-spatial econometrics, as well as spatial econometrics for single and double-spatial dynamics.

Immigration to EU core countries varies directly with the change in social spending per head in the destination. This result stands out in all the models, both OLS and spatial. Immigrants are attracted by economic inequality as measured by the Gini coefficient. However, in this case it is the level that matters rather than its change. No evidence is found that the threat of apprehension at the destination deters migrants from the European Neighborhood and other countries.

The authors assume multilateralism is spatial. This means that everything else given, destinations are closer substitutes the nearer they are, and that immigration shocks are likely to be more correlated among origins the closer they are. This implicit assumption is restrictive because multilateralism is just spatial.

While immigration to EU core countries varies directly with the change in (not level of) social spending per head. If a given country becomes more benevolent it attracts more immigration. The results suggest that if during 2000-2010 social spending per capita grew by 1 percent, the immigration rate increased by between 1 and 2 percentage points relative to the number of foreign-born in 2000. This is a large demographic effect.

Uniquely, this paper does not assume immigration flows are independent and stresses their spatial and multilateral nature. A series of new non-spatial and spatial (single and double-spatial lag) models are used to empirically test hypotheses about the determinants of immigration to the EU core countries.

Asymmetric rotating machinery supported by oil film bearings is relatively common in practical applications. The purpose of this study is to propose a method for estimating the oil film parameters of the bearings in an asymmetric rotor-bearing system.

The proposed method requires the finite element model and translational displacement responses at the center of mass and bearings locations to form a regression equation to estimate the unknown parameters. Due to the transverse stiffness of the asymmetric rotor is not symmetrical, the analysis and parameter estimation procedures are performed in a rotating coordinate. Numerical simulations were carried out to illustrate the vibration characteristics of the asymmetric rotor system. The proposed method is applied to the simulated responses to estimate the assumed oil film parameters. The influence of the estimated parameter deviations on the rotor dynamic characteristics is discussed.

The vibration characteristics of asymmetric rotors are different from those of symmetrical rotors. The bearing parameters estimated by the proposed method are close to the assumed values, within a maximum error of 9%. The deviations of the estimated parameters have little effect on the vibration characteristic of the rotor system.

The proposed method does not require changing the rotational speed or applying additional excitation force to the rotor, which is suitable for the field test.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2023-0111/

In large-scale environments and unstructured scenarios, the accuracy and robustness of traditional light detection and ranging (LiDAR) simultaneous localization and mapping (SLAM) algorithms are reduced, and the algorithms might even be completely ineffective. To overcome these problems, this study aims to propose a 3D LiDAR SLAM method for ground-based mobile robots, which uses a 3D LiDAR fusion inertial measurement unit (IMU) to establish an environment map and realize real-time localization.

First, we use a normal distributions transform (NDT) algorithm based on a local map with a corresponding motion prediction model for point cloud registration in the front-end. Next, point cloud features are tightly coupled with IMU angle constraints, ground constraints and gravity constraints for graph-based optimization in the back-end. Subsequently, the cumulative error is reduced by adding loop closure detection.

The algorithm is tested using a public data set containing indoor and outdoor scenarios. The results confirm that the proposed algorithm has high accuracy and robustness.

To improve the accuracy and robustness of SLAM, this method proposed in the paper introduced the NDT algorithm in the front-end and designed ground constraints and gravity constraints in the back-end. The proposed method has a satisfactory performance when applied to ground-based mobile robots in complex environments experiments.

The quality of crystals grown in space can be diversely affected by the melt flows induced by g‐jitter associated with a space vehicle. This paper presents a full three‐dimensional (3D) transient finite element analysis of the complex fluid flow and heat and mass transfer phenomena in a simplified Bridgman crystal growth configuration under the influence of g‐jitter perturbations and magnetic fields.

The model development is based on the Galerkin finite element solution of the magnetohydrodynamic governing equations describing the thermal convection and heat and mass transfer in the melt. A physics‐based re‐numbering algorithm is used to make the formidable 3D simulations computationally feasible. Simulations are made using steady microgravity, synthetic and real g‐jitter data taken during a space flight.

Numerical results show that g‐jitter drives a complex, 3D, time dependent thermal convection and that velocity spikes in response to real g‐jitter disturbances in space flights, resulting in irregular solute concentration distributions. An applied magnetic field provides an effective means to suppress the deleterious convection effects caused by g‐jitter. Based on the simulations with applied magnetic fields of various strengths and orientations, the magnetic field aligned with the thermal gradient provides an optimal damping effect, and the stronger magnetic field is more effective in suppressing the g‐jitter induced convection. While the convective flows and solute transport are complex and truly 3D, those in the symmetry plane parallel to the direction of g‐jitter are essentially two‐dimensional (2D), which may be approximated well by the widely used 2D models.

The physics‐based re‐numbering algorithm has made possible the large scale finite element computations for 3D g‐jitter flows in a magnetic field. The results indicate that an applied magnetic field can be effective in suppressing the g‐jitter driven flows and thus enhance the quality of crystals grown in space.

This study aims to consider how migrants may act as channel of diffusion of knowledge which contributes to the dynamics of trade and comparative advantages of EU and MENA countries for the period 1990–2015.

Adopting an IV approach and a gravity framework to instrument for migration, the authors document how variations in stocks of migrants coming from (in) countries that are already competitive exporters of a given product impact on the probability that the destination (home) country starts to export competitively new products or succeed in exporting more intensively.

Controlling for potential confounding factors which can be correlated to knowledge flows and productivity shifts, the authors find trade-promoting effects via migration flows (mostly immigration) between the two areas, testing our hypotheses by different technology classes of products and different specifications.

The contribution of this work to the literature is threefold. First, by providing evidence on international knowledge diffusion induced by migration flows between MENA and EU regions, like no other work before, the authors document the effects of migration on trade and comparative advantages. Second, unlike standard literature on migration-trade link, the authors focus more on long-term structural changes in comparative advantages than on trade volumes. Third, we exploit how the effect of migration on margins of trade varies according to different types of goods, classified by technological level.

The purpose of this paper is the dynamic analysis and seismic damage assessment of steel sheet pile quay wall with inelastic behavior underground motions using several accelerograms.

Finite element analysis is conducted using the Plaxis 2D software to generate the numerical model of quay wall. The extension of berth 25 at the port of Bejaia, located in northeastern Algeria, represents a case study. Incremental dynamic analyses are carried out to examine variation of the main response parameters under seismic excitations with increasing Peak ground acceleration (PGA) levels. Two global damage indices based on the safety factor and bending moment are introduced to assess the relationship between PGA and the damage levels.

The results obtained indicate that the sheet pile quay wall can safely withstand seismic loads up to PGAs of 0.35 g and that above 0.45 g, care should be taken with the risk of reaching the ultimate moment capacity of the steel sheet pile. However, for PGAs greater than 0.5 g, it was clearly demonstrated that the excessive deformations with material are likely to occur in the soil layers and in the structural elements.

The main contribution of the present work is a new double seismic damage index for a steel sheet pile supported quay wharf. The numerical modeling is first validated in the static case. Then, the results obtained by performing several incremental dynamic analyses are exploited to evaluate the degradation of the soil safety factor and the seismic capacity of the pile sheet wall. Computed values of the proposed damage indices of the considered quay wharf are a practical helping tool for decision-making regarding the seismic safety of the structure.

The purpose of this paper is to study the influence of friction on static and dynamic characteristics, as well as the strength and lifetime of a flexible three-axes computer numerical control (CNC) machine tool.

The machine tool is first modeled by using finite element method to analyze static structure with frictionless surface-to-surface contact type. Because the machine tool structure is becoming more and more sophisticated over time, the significant influence of contact conditions between structural elements on the dynamic characteristics of the whole structure must be considered. To examine the dynamic effects caused by inertia forces and displacement of moving bodies on contact stress, the coefficient of friction between two contact bodies is added to perform dynamic simulation and compare the results with the static analysis results.

Distribution of stress and contact forces in solid-flexible contact is also studied by using the fundamental dynamic characteristics of a bushing joint.

Finally, the influence of dynamic structure, cutting conditions and material properties on the strength and lifetime of the CNC machine tool is discussed by using fatigue analysis. Consequently, this research can be used for efficient simulation of structural dynamics, lifetime assessment and interactions of the real CNC machine with the machine tool structure in a virtual environment.

The purpose of this paper is to analyze and compare the similarities in the foreign trade patterns of China and the other BRICS (Brazil, Russia, India, China and South Africa) members.

Three panel data estimations, namely, fixed effect, random effect and fully modified ordinary least squares, have been conducted in this paper based on the gravitational model of international trade for bilateral trade of each BRICS member with five United Nations (UN) regional groups from 2001 to 2015.

The results revealed that Russia has a dissimilar trade pattern, based on the Heckscher–Ohlin (H-O) framework, with these five regional groups, while the other BRICS members follow the Linder hypothesis. Furthermore, it was found that China has a faster pace of globalization, while the rest of the BRICS members have experienced regionalization rather than globalization. In addition, geographical distance, as a proxy for transportation cost, has a weaker negative effect on the trade patterns of China and India, which makes the trade patterns of BRICS members dissimilar.

To the best of the authors’ knowledge, this paper is the first attempt to examine and compare the BRICS member countries’ foreign trade pattern through a gravity trade approach.

To demonstrate, through numerical models, that it is possible to simulated low‐gravity phase change (melting), of an electrically conducting material (gallium), in terrestrial conditions via the application of electromagnetic fields.

A complete three‐dimensional mathematical formulation governing a phase change process in the presence of an electromagnetic field has been developed. In addition a comprehensive parametric study has been completed to study the various effects of gravity, Stefan number, Hartmann number and electromagnetic pressure number upon the phase change process.

The results show that the application of an electromagnetic filed can be used to simulate key melting characteristics found for actual low‐gravity. However, the resulting three‐dimensional flow field in the melted region differs from actual low‐gravity. The application of an electromagnetic field creates a flow phenomenon not found in actual low‐gravity or previously seen in two‐dimensional problems.

Future work may include the use of oscillating electromagnetic fields to enhance convection in energy storage systems in a low‐gravity environment.

The ability to suppress unwanted convective flows in a phase change process without the high magnetic fields necessary in magnetic field only suppression systems.

This work fills a void in the literature related to conducting fluids and the effects of magnetic and electromagnetic fields.