Connection Length Research Articles

Prediction of temperature barriers in weakly collisional plasmas by a Lagrangian coherent structures computational tool

Analysis of Lagrangian Coherent Structures (LCSs) has been shown to be a valid mathematical approach to explain the formation of transport barriers in magnetized plasmas. Such LCSs, borrowed from fluid dynamics theory, can be considered as the hidden skeleton of the system and can be used for studying a wide spectrum of transport mechanisms, even in plasmas. An LCS can be considered as a generalization for a finite time interval and for a general dynamical system of what manifolds are for Hamiltonian systems. In this paper, we demonstrate that such structures can be particularly useful for underlying the hidden paths governing the motion of magnetic field lines in chaotic magnetic fields.To perform such an analysis, we developed a numerical tool able to detect LCSs for a general dynamical system. The tool is able to deal with general coordinate systems and it is shown to match with other techniques already used to analyse chaotic magnetic fields, e.g. connection length. After the description of the computational tool, we focus on the heat transport equation and the comparison between temperature profile and topology of the LCSs. We provide evidence that numerical simulations are able to reproduce the temperature profiles similar to those observed in reversed field pinch experiments and that our tool successfully predicts the location of temperature gradients. The results suggest that, inside the chaotic region, the field-lines motion is far from stochastic and that the presence of hidden patterns allows the development of high temperature gradients.

The operational space for divertor power exhaust in DEMO with a super-X divertor

SOLPS-ITER simulations of the European DEMO reactor with a Super-X divertor, which has larger major radius at the outer target and increased connection length, show an increased operational space for divertor power exhaust compared to the conventional single-null configuration. Using a multi-fluid approach with fluid neutrals and charge-state bundling of impurities, we assessed the existence and boundaries of the operational space in the single-null and Super-X configurations by carrying out fuelling, seeding and power scans. Compared to the conventional single-null divertor, the Super-X divertor offers lower impurity concentration (factor ∼2 lower) at the same main plasma density, and consistent with this, it has lower main plasma density at the same impurity concentration level. This observed difference is in line with the simple analytical Lengyel model predictions resulting from the increased connection length in the super-X configuration. DEMO with a Super-X divertor demonstrates remarkable robustness against increases in input power, and in this study is able to exhaust the maximum expected steady-state separatrix-crossing power of 300 MW while maintaining acceptable impurity concentration along the separatrix This is something that was not possible in the single-null configuration in this study. This robustness of the Super-X divertor lies mostly in its capability to sufficiently dissipate power in its divertor via argon (Ar) radiation at acceptable Ar concentration, which is related to two factors: long (with respect to single-null) parallel connection length from the upstream to the outer target and higher but tolerable extrinsic impurity concentration at higher input powers. Finally, consistent with neon-seeded simulations of ITER, it is observed in all our simulations that the plasma density drops with increasing Ar concentration given fixed power input. We find that as the Ar content increases, the accompanying enhancement of Ar radiation reduces the power available for deuterium (D) to be ionized, thus limiting the D ionization particle source, and consequently reducing the plasma density.

Calculating the linear critical gradient for the ion-temperature-gradient mode in magnetically confined plasmas

A first-principles method to calculate the critical temperature gradient for the onset of the ion-temperature-gradient mode (ITG) in linear gyrokinetics is presented. We find that conventional notions of the connection length previously invoked in tokamak research should be revised and replaced by a generalized correlation length to explain this onset in stellarators. Simple numerical experiments and gyrokinetic theory show that localized ‘spikes’ in shear, a hallmark of stellarator geometry, are generally insufficient to constrain the parallel correlation length of the mode. ITG modes that localize within bad drift curvature wells that have a critical gradient set by peak drift curvature are also observed. A case study of near-helical stellarators of increasing field period demonstrates that the critical gradient can indeed be controlled by manipulating the magnetic geometry, but underscores the need for a general framework to evaluate the critical gradient. We conclude that average curvature and global shear set the correlation length of resonant ITG modes near the absolute critical gradient, the physics of which is included through direct solution of the gyrokinetic equation. Our method, which handles the general geometry and is more efficient than conventional gyrokinetic solvers, could be applied to future studies of stellarator ITG turbulence optimization.

Maximum Entropy Principle Underlies Wiring Length Distribution in Brain Networks.

A brain network comprises a substantial amount of short-range connections with an admixture of long-range connections. The portion of long-range connections in brain networks is observed to be quantitatively dissimilar across species. It is hypothesized that the length of connections is constrained by the spatial embedding of brain networks, yet fundamental principles that underlie the wiring length distribution remain unclear. By quantifying the structural diversity of a brain network using Shannon's entropy, here we show that the wiring length distribution across multiple species-including Drosophila, mouse, macaque, human, and C. elegans-follows the maximum entropy principle (MAP) under the constraints of limited wiring material and the spatial locations of brain areas or neurons. In addition, by considering stochastic axonal growth, we propose a network formation process capable of reproducing wiring length distributions of the 5 species, thereby implementing MAP in a biologically plausible manner. We further develop a generative model incorporating MAP, and show that, for the 5 species, the generated network exhibits high similarity to the real network. Our work indicates that the brain connectivity evolves to be structurally diversified by maximizing entropy to support efficient interareal communication, providing a potential organizational principle of brain networks.

The role of the orbitofrontal cortex and the nucleus accumbens for craving in alcohol use disorder

This study aimed to investigate structural and functional alterations of the reward system and the neurobiology of craving in alcohol use disorder (AUD). We hypothesized reduced volume of the nucleus accumbens (NAcc), reduced structural connectivity of the segment of the supero-lateral medial forebrain bundle connecting the orbitofrontal cortex (OFC) with the NAcc (OFC-NAcc), and reduced resting-state OFC-NAcc functional connectivity (FC). Furthermore, we hypothesized that craving is related to an increase of OFC-NAcc FC. Thirty-nine recently abstinent patients with AUD and 18 healthy controls (HC) underwent structural (T1w-MP2RAGE, diffusion-weighted imaging (DWI)) and functional (resting-state fMRI) MRI-scans. Gray matter volume of the NAcc, white matter microstructure (fractional anisotropy (FA)) and macrostructure (tract length) of the OFC-NAcc connection and OFC-NAcc FC were compared between AUD and HC using a mixed model MANCOVA controlling for age and gender. Craving was assessed using the thoughts subscale of the obsessive-compulsive drinking scale (OCDS) scale and was correlated with OFC-NAcc FC. There was a significant main effect of group. Results were driven by a volume reduction of bilateral NAcc, reduced FA in the left hemisphere, and reduced tract length of bilateral OFC-NAcc connections in AUD patients. OFC-NAcc FC did not differ between groups. Craving was associated with increased bilateral OFC-NAcc FC. In conclusion, reduced volume of the NAcc and reduced FA and tract length of the OFC-NAcc network suggest structural alterations of the reward network in AUD. Increased OFC-NAcc FC is associated with craving in AUD, and may contribute to situational alcohol-seeking behavior in AUD.

MRI network progression in mesial temporal lobe epilepsy related to healthy brain architecture.

We measured MRI network progression in mesial temporal lobe epilepsy (mTLE) patients as a function of healthy brain architecture. Resting-state functional MRI and diffusion-weighted MRI were acquired in 40 unilateral mTLE patients and 70 healthy controls. Data were used to construct region-to-region functional connectivity, structural connectivity, and streamline length connectomes per subject. Three models of distance from the presumed seizure focus in the anterior hippocampus in the healthy brain were computed using the average connectome across controls. A fourth model was defined using regions of transmodal (higher cognitive function) to unimodal (perceptual) networks across a published functional gradient in the healthy brain. These models were used to test whether network progression in patients increased when distance from the anterior hippocampus or along a functional gradient in the healthy brain decreases. Results showed that alterations of structural and functional networks in mTLE occur in greater magnitude in regions of the brain closer to the seizure focus based on healthy brain topology, and decrease as distance from the focus increases over duration of disease. Overall, this work provides evidence that changes across the brain in focal epilepsy occur along healthy brain architecture.

A novel methodology to describe neuronal networks activity reveals spatiotemporal recruitment dynamics of synchronous bursting states.

We propose a novel phase based analysis with the purpose of quantifying the periodic bursts of activity observed in various neuronal systems. The way bursts are intiated and propagate in a spatial network is still insufficiently characterized. In particular, we investigate here how these spatiotemporal dynamics depend on the mean connection length. We use a simplified description of a neuron's state as a time varying phase between firings. This leads to a definition of network bursts, that does not depend on the practitioner's individual judgment as the usage of subjective thresholds and time scales. This allows both an easy and objective characterization of the bursting dynamics, only depending on system's proper scales. Our approach thus ensures more reliable and reproducible measurements. We here use it to describe the spatiotemporal processes in networks of intrinsically oscillating neurons. The analysis rigorously reveals the role of the mean connectivity length in spatially embedded networks in determining the existence of "leader" neurons during burst initiation, a feature incompletely understood observed in several neuronal cultures experiments. The precise definition of a burst with our method allowed us to rigorously characterize the initiation dynamics of bursts and show how it depends on the mean connectivity length. Although presented with simulations, the methodology can be applied to other forms of neuronal spatiotemporal data. As shown in a preliminary study with MEA recordings, it is not limited to in silico modeling.

Layout optimization of stratospheric balloon solar array based on energy production

Solar array plays a decisive role in the energy system of stratospheric balloon. Optimizing the layout of solar array is beneficial to the improvement of energy production, but the research about this subject is rare. This paper established a theoretical model consisting of thermal and energy model, weight/lift equilibrium. A MATLAB computer program is developed to simulate the output power of solar array and the energy harvesting along with connection length and balloon diameter. Through comparative analysis, the theoretical model is proved to be feasible. Further, the effects of connection length, balloon diameter and the ratio of connection length to balloon diameter are discussed in detail. The results show that solar array total output power is sensitive to the variation of the connection length, balloon diameter and the ratio of connection length to balloon diameter. Moreover, the layout of solar array can be optimized though increasing the ratio of connection length to balloon diameter, however, the total output power would not increase when the ratio of connection length to balloon diameter is greater than 1.5. Therefore, Choosing the proper ratio of connection length to balloon diameter might be an effective approach for optimizing the stratospheric balloon energy system.

An enhanced design method for 3D contact surfaces on shaft–hub connections joined through lateral extrusion

A recently developed design method for circular shaft–hub connections joined using the cold-forming process of lateral extrusion allows predefined contact stress distributions to be generated on the contact surface by gradient-less shape optimization. Using contact stress results from elastic-plastic finite-element analyses and simplified rules derived from cylindrical interference fits, the contact surface of the hub is adapted locally to the shape of the formed shaft in an iterative process. In this paper, the design method is expanded from circular to non-circular profile shapes based on complex cycloids to create optimized, polygon shaft–hub connections, minimizing sliding and fretting fatigue under dynamic loads. To enable local adaptation of non-circular contact surfaces, we introduce a suitable definition for 3D profiles, which allows simultaneous variation of the profile mean radius and eccentricity. This allows designers to create contact surface designs with complex shapes that conform to predefined contact stress distributions along the connection length. The feasibility of the method is finally demonstrated by undertaking a design adaptation study on a sample non-circular shaft–hub connection and comparing the results to the initial design. While the contact stress results for the adapted design agree very well with the specified target curves, an overall more uniform stress distribution in the hub is also achieved. Due to its combined form and friction-fit properties with high residual contact pressure, the connection is predestined for use in novel electric and hybrid drive applications, where lightweight design as well as high power density and rotational speeds are required.

Shear Lag Effect in Welded Single Angle Tension Member

The typical failure of a welded single angle tension member is a gross section failure. The rupture strength of the single angle tension member is affected by the effect of shear lag. Full-scale tests on twenty-seven single angle specimens reported in this paper. Four different angle sections with four different section types were used in the test. The test parameter includes the steel's grade, length of the connection, the eccentricity of the connection, and balanced and unbalanced weld arrangement. Twenty-three specimens failed by fracture of the gross section area, one failed in mixed mode (angle tear and the weld failure), and the remaining three failed in the weld. To interpret the experimental results, finite element analysis was performed on the specimen’s model. The finite element model well represents the welded single-angle tension member's behaviour, and finite element results show exemplary test results. The ultimate strengths of the test specimens were also evaluated by using the current design standards (IS 800, AISC, CSA, AS 4100, and EC-3), the (1− x/L) rule, and Kulak and Wu’s equation. In general, IS 800 provides a good prediction of test results, AISC and AS 4100 provide a slightly conservative forecast; however, CSA and EC-3 provide a slightly un-conservative prediction. For a balanced weld arrangement, the specimen's ultimate strength increased with an increase in connection length; however, an increase in connection length does not increase the specimen's ultimate strength for an unbalanced weld arrangement. The angle specimen's efficiency decreased significantly with an increase in eccentricity. The rupture strength predicted by assuming the ultimate strength of the connected leg and the strength contributed by the outstanding leg at the critical section shows a good prediction of the strength over the (1− x/L) rule.

Study of the double null divertor configuration in DTT

• Defined Double Null plasma scenarios for the Divertor Test Tokamak facility (DTT). • Evaluated gas-puffing and particle flux from the core at maximum plasma current. • Analysed effect of pumping position in achieving detachment with neon seeding. • Analysed effect of gas puffing position in achieving detachment. • Shown easier detachment achievement pumping from bottom only. • Shown easier detachment achievement with gas puffing from the outer the mid-plane. On the way to the development of a fusion reactor based on the Tokamak configuration, the Divertor Test Tokamak facility (DTT) [1] in construction in Italy should provide useful information for the DEMO [2] reactor in the field of the power and particle exhaust. DTT is designed to accept the Single Null divertor (SND) and also divertors optimized for all the present more promising configurations like the Snowflake divertor (SFD), the X divertor (XD), the Super-X (SXD), the X-point target (XPD) and the double null (DND). The DND in particular has gained a new attention as a DEMO candidate considering its ability to reduce the peak heat flux at the divertor targets splitting the power on twice the surface, but this geometrical advantage can in principle be overcome on the physical side by the shorter connection length and the additional engineering complications and costs associated to the need of a double divertor with its pair pumping systems. In this paper we present the analysis carried out for the DND configuration in DTT to evaluate its advantages/disadvantage with respect to the SND one in terms of pumping system. To study the engineering requirements of DND its power exhaust handling capability has been analysed both in the optimal case of two exactly symmetric divertors (in terms of pumping and main specie/seeding gas puffing locations) than in the simpler case of a secondary divertor without pumping. In all cases full tungsten divertors and wall have been considered and neon gas has been used as seeding impurity, the analysis has been done at the maximum DTT heating power of P TOT = 45 MW which corresponds to a P SOL ≈32 MW and at separatrix density between n sep = 6∙10 19 and n sep = 10∙10 19 m −3 . In addition, the transport coefficients have been set up at the separatrix to provide an outer mid-plane heat flux decay length of 1.0 mm in SND, in agreement with the present Eich scaling [3] prediction at the previous DTT parameters. The SOLEDGE2D-EIRENE [4,5] edge code has been used for the analysis for its ability to deal with all configurations and to extend the fluid domain up to the first wall.

Relation between rich-club organization versus brain functions and functional recovery after acute ischemic stroke

Studies have shown the brain’s rich-club organization may underpin brain function and be associated with various brain disorders. In this study, we aimed to investigate the relation between poststroke brain functions and functional recovery versus the rich-club organization of the structural brain network of patients after first-time acute ischemic stroke. A cohort of 16 acute ischemic stroke patients (11 males) was recruited. Structural brain networks were measured using diffusion tensor imaging within 1 week and at 1, 3 and 6 months after stroke. Motor impairment was assessed using the Upper-Extremity Fugl-Meyer motor scale and activities of daily living using the Barthel Index at the same time points as MRI. The rich-club regions that were stable over the course of stroke recovery included the bilateral dorsolateral superior frontal gyri, right supplementary motor area, and left median cingulate and paracingulate gyri. The network properties that correlated with poststroke brain functions were mainly the ratio between communication cost ratio and density ratio of rich-club, feeder and local connections. The recovery of both motor functions and activities of daily living were correlated with higher normalized rich club coefficients and a shorter length of local connections within a week after stroke. The communication cost ratio of feeder connections, the length of rich-club and local connections, and normalized rich club coefficients were found to be potential prognostic indicators of stroke recovery. Our results provide additional support to the notion that different types of network connections play different roles in brain functions as well as functional recovery.

Parallel convection and E × B drifts in the TCV snowflake divertor and their effects on target heat-fluxes

Parallel convection and E × B drifts act together to redistribute heat between the strike-points in the low field side snowflake minus (LFS SF−). The cumulative heat convection from both mechanisms is enhanced near the secondary X-point and is shown to dominate over heat conduction, partly explaining why the LFS SF− distributes power more evenly than the single null (SN) or other snowflake (SF) configurations. Pressure profiles at the entrance of the divertor are strongly affected by the position of the secondary X-point and magnetic field direction indicating the importance of E × B drifts. Pressure drops of up to 50% appear between the outer-midplane (OMP) and the divertor entrance enhancing the role of parallel heat convection. The electron temperature and density profiles and the radial turbulent fluxes measured at the OMP are largely unaffected by the changes in divertor geometry, even on flux surfaces where the connection length is infinite.

Estimating effective permeability using connectivity and branch length distribution of fracture network

In this study, a new approach to estimate the effective permeability of the fracture network is proposed. New functional expressions are derived considering laminar fluid flow through fracture networks. Effective permeability of the fracture network is expressed as a function of topological connectivity, statistical branch segment length distributions, maximum, and minimum branch segment lengths. It is observed that the statistical cumulative branch segment length distribution of fracture networks can follow both fractal and multi-fractal patterns. Hence, analytical expressions of effective permeability are proposed considering both fractal and multi-fractal distribution of branch segment lengths. Obtained expressions are validated using numerical simulation results from past studies. It is observed from derived expressions that, effective permeability of fracture networks increases non-linearly with increasing topological connectivity and fractal dimensions of statistical branch segment length distributions. However, the non-linearity in the relationship is mainly governed by the scaling exponent and scaling coefficient of the fracture network. With increasing scaling exponent and scaling coefficient, non-linearity in the relation between effective permeability and topological connectivity increases. It is observed from the derived relation that, effective permeability of a fracture network is more sensitive to longer branch segments compared to the shorter branch segments. Effective permeability of fracture networks increases rapidly with increase in length of the branch segments. Hence it is interpreted, longer branch segments in fracture networks play a critical role in determining the effective permeability of the fractured reservoir.

Suppression of first-wall interaction in negative triangularity plasmas on TCV

Magnetically confined fusion plasmas with negative triangularity (δ) exhibit greater L-mode confinement than with positive δ. Recent experiments in the TCV and DIII-D tokamaks have correlated the confinement improvement to a reduction of fluctuations within the plasma core. We report on fluctuation measurements in the scrape-off layer (SOL) for −0.61 < δ < +0.64 in limited and diverted ohmic L-mode plasmas; these reveal a strong reduction in SOL fluctuation amplitudes at δ ≲ −0.25, and, surprisingly, an almost full suppression of plasma interaction with the main-chamber first-wall, which could have important implications for the prospects of using negative δ plasmas as a reactor solution. An exploration of several physical mechanisms suggests that a reduced connection length—intrinsic to negative δ plasmas—plays a critical role in the origin of this phenomenon.

Investigation on cavitating flow and parameter effects in a control valve with a perforated cage

Valve is widely used in the various industry areas to adjust and control the flow. Cavitation frequently takes place and sometimes is inevitable in various types of valve to cause the erosion damage. Therefore, how to control and minimize the effect of cavitation is still an important topic. This study numerically investigates the cavitating flow in a control valve with a perforated cage. The effects of some parameters on the cavitation are discussed. It also discusses to use the throttling steps to govern the cavitating flow. The results show that the opening degree of valve and the length of downstream divergent connection both influence the cavitation. The increase of the divergent length reinforces the cavitation. And the larger the opening of valve is, the intenser the cavitation is and the more vapor is present. The more throttling steps are helpful to decrease the cavitation.

Pullout behavior of lap splice connections between double-steel-plate composite walls and RC raft foundation in nuclear engineering

Considering the flexibility of construction and convenience of transportation, the lap splice connection using dowel or lapped bars between double-steel-plate composite (DSC) walls and reinforced concrete (RC) raft foundation is becoming increasingly popular in nuclear engineering. Because the anchorage of dowel or lapped bars in RC members has already been stipulated by many codes, this study mainly focus on the portion in DSC wall of this connection. Eight 1/2 scaled DSC wall – RC foundation connection specimens were tested with monotonic tensile loading to study the pullout mechanism of this connection and provide solid basis for design. The investigated variables are the locations of lapped bars and tie configuration including the spacing and diameter of tie bars. A new tie form using internal steel webs instead of tie bars is also proposed. The test results are analyzed and discussed in terms of crack pattern, load-displacement relations, strains of key components including steel faceplates, tie bars and lapped bars. Based on the experimental findings and previous research, five possible failure modes are concluded and the steel faceplates yielding is regarded as the design target. To avoid the other failure modes, design recommendations on tie bars, lapped bars and shear studs are given. Particularly, a new formula is proposed to design the tie bars to avoid splitting failure based on the nonlinear strain distribution along the length of connection. In addition, the internal steel webs are recommended as a promising alternative forms of tie bars, which has shown better mechanical performance as well as more convenient construction process.

DETERMINANTS OF NON-REVENUE WATER

Water is one of the most essential needs in human daily life. Water losses or Non-Revenue Water (NRW) refers to the treated water that has been produced from water plant which did not reach to the customer. This waste of water has caused the company to suffer losses and hence, burdens the people with increasing water tariff. Moreover, it becomes one of the challenges for commercial water system management because the water company must fulfil the demand from the society which keep increasing day by day. In addition, the demand for water is increasing, as the population is growing. Despite having the rainfall throughout the year in Malaysia, many cities are experiencing water shortage and frequent water supply disruptions. Therefore, efficient management of water distribution is required to minimise the water losses and to make sure the sustainability of water reserve for a long period. This study focuses on identifying the significant factors that influence the Non-Revenue Water and modelling the data using Multiple Linear Regression Model. The sample size used in this study were 212 observations and the variables involved were Length of Connection, Number of Connection, Production Quantity, Consumption Quantity and Non-Revenue Water. It is found that the variables of Number of Connection, Consumption Quantity and Production Quantity were significant to Non-Revenue Water whereas the variable of Length of Connection was not significant. It is hoped that the result from this study can be used by the water authority company in improving the water distribution and thus reduce water losses and cost.

Optimization of microfluidic layouts as a wired packing problem

Abstract This paper presents a methodology to optimize the physical layout of microfluidic components, a key step in the design of custom microfluidic instruments that can be used in various process applications. A mathematical formulation is proposed under the form of a Mixed Integer Linear Problem allowing to treat non overlapping constraints for the multi-objective optimization of layout footprint and connectivity lengths. The method is numerically tested using randomly generated scenarios. Then, a real testcase serves as illustration.

Non-linear FEA of mechanical properties of modular prefabricated steel-concrete composite joints

This paper study the seismic performance of modular prefabricated SRC column to steel beam composite joint (MPCJ) under static loading. Numerical modeling of MPCJs with three different beam-end connections was carried out in ABAQUS. Results of the numerical calculation were compared with existing quasi-static test results to verify the feasibility of the numerical model. The model was then used to analyze changes in the moment-rotation relation, failure mode, ductility, stiffness, and bolt stress in the joint between the column and joint module. Besides, stress distributions in the joints were analyzed along different stress paths. Under monotonic loading, the mechanical performance of the MPCJ is significantly affected by the beam end connection mode. Failure of the MPCJ mainly occurs at the beam end connection, thus, the aim of keeping the plastic hinge away from the joint core and preventing shear failure is achieved. Furthermore, the maximum story drift ratio is 3.9–5 times greater than the recommended limit, which indicates good ductility and deformation performance. The MPCJ of the three-beam end connection methods is all semi-rigid connections. The beam end structure will have a large influence on the bolt tension and stress distribution. According to the test research results, a nonlinear model with three parameters including joint cover plate cantilever section length, flange connecting plate thickness and flange connecting plate weld length was established. The theoretical calculation results was consistent with the results of the numerical simulation. MPCJs can be designed based on the proposed theoretical calculation formula.