Phase Coordinates Research Articles

Performance and limits of a geotechnical centrifuge: DEM-LBM simulations of saturated granular column collapse

This study investigates the dynamics of granular flows in geotechnical centrifuge models, focusing on the effects of centrifugal and Coriolis accelerations. While conventional laboratory-scale investigations often rely on Froude scaling, geotechnical centrifuge modelling offers a unique advantage in incorporating stress-dependent processes that fundamentally shape flow rheology and dynamics. Using the Discrete Element Method (DEM) and the Lattice-Boltzmann Method (LBM), we simulate the collapse of a just-saturated granular column within a rotating reference frame. The model’s accuracy is validated against expected trends and physical experiments, demonstrating its strong performance in replicating idealised collapse behaviour. Acceleration effects on both macro- and grain-scale dynamics are examined through phase front and coordination number analysis, providing insight on how centrifugal and Coriolis accelerations influence flow structure and mobility. This work enhances our understanding of granular flow dynamics in geotechnical centrifuge models by introducing an interstitial pore fluid and considering multiple factors that influence flow behaviour over a wide parameter space.Graphical abstract

PHASE RELATIONS IN THE Bi2-Bi2Se3-Bi2Te3 SYSTEM AND CHARACTERIZATION OF SOLID SOLUTIONS

Phase relations in the Bi2–Bi2Se3–Bi2Te3 system were determined experimentally using differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Based on the experimental results, a solid-phase equilibria diagram at room temperature, a projection of the liquidus surface, and several polythermal sections of the phase diagram were constructed. The regions of primary crystallization and phase homogeneity, types, and coordinates of non- and monovariant equilibria were determined. Continuous solid solutions along the Bi8Se9–Bi8Te9, BiSe–BiTe, and Bi4Se3–Bi4Te3 sections, as well as wide areas of solid solutions based on other bismuth selenides and tellurides, were found. The established phase diagrams can be used for the synthesis of solid solutions of a given composition and the growth of their single crystals by directional crystallization from solution-melts

Changes in gait performances during walking with head movements in older adults with chronic neck pain.

Chronic neck pain (CNP) can lead to altered gait which is worse when combined with head movement. Gait parameters for indicating speed and symmetry have not been thoroughly investigated in older adults with CNP. This study aimed to compare gait performance in term of speed and symmetry in older adults with and without CNP during walking with head movement. Fifty young older adults, consisting of 36 healthy controls without neck pain (OLDs) and 14 older adults with CNP, participated in the study. Participants completed the Neck Disability Index and Activities-specific Balance Confidence Scale. The 10-Meter Walk Test (10MWT) was used to assess gait performance. Participants were instructed to walk at preferred speed under three different head movement patterns: no head movement (NM), horizontal head movement (HM), and vertical head movement (VM). The Inertial Measurement Unit was used to capture gait performance, and its software was used to analyze gait variables; gait speed, Locomotor Rehabilitation Index (LRI), gait asymmetry index, Phase Coordination Index (PCI). The CNP group reported moderate neck pain with mild disability in activities of daily living, and less balance confidence than the OLD group (p < 0.05). The CNP group showed significantly slower gait speed and lower LRI during walking with both the HM and VM (p < 0.05), which corresponded to lower stride length and cadence. The gait asymmetry index in the CNP group was significantly higher than the OLD group during walking with VM (p < 0.05), whereas the PCI was significantly higher than the OLD group during walking with both HM and VM (p < 0.05). Chronic neck pain affects both speed and symmetry when walking with head movement. Gait parameters in this study could be implemented to identify changes in speed and symmetry of gait in older adults with CNP who have mild disability and high physical functioning.

Mathematical model of a DC/DC converter based on SEPIC topology

Objectives. A DC/DC converter based on SEPIC topology is a unipolar electronic device which converts an input positive voltage into a stabilized output voltage of the same polarity. It also has the ability to regulate polarity both below and above the input voltage. The aim of the paper is to analyze the DC/DC converter in its both operation phases, as well as to draw up equivalent circuits and obtain characterizing differential equations using Kirchhoff’s rules for each phase. Each system of differential equations is reduced to Cauchy equations, in order to be further transformed into a limiting continuous mathematical model. Each system of equations is converted into a matrix form and subsequently combined into a single matrix system.Methods. The construction of a limiting continuous mathematical model was accomplished using Kirchhoff’s rules. Multisim software was used for the computer simulation, thus enabling the calculated results of direct currents and voltages to be compared to those of the simulation.Results. Results show that the phase coordinates of the mathematical model tend towards the values of real currents and voltages of the converter at a switching frequency higher than 200 kHz. Fairly good agreement is established between the calculated values of currents and voltages and the values obtained by simulation (with varying fill factor and switching frequency).Conclusions. The resulting limiting continuous mathematical model of the DC/DC converter based on SEPIC topology allows for an estimation of the dependence of the currents flowing through the inductor windings and the voltages across the capacitors on a number of parameters. The limiting continuous mathematical model of the DC/DC converter based on SEPIC topology is the basis for its circuit design and physical-and-mathematical analysis.

Variability, asymmetry and bilateral coordination of gait during single- and dual-task walking of patients with cerebral small vessel disease

Objective We investigated coefficient of variation (CV), gait asymmetry (GA) and phase coordination index (PCI) in cerebral small vessel disease (CSVD) patients during single-task walking (STW) and dual-task walking (DTW) and explored the relationship between above parameters with disease severity and cognitive function. Methods This cross-sectional study collected cognitive function indices and gait parameters from 23 healthy controls and 94 patients with CSVD during STW and DTW. According to the Fazekas scales, the severity of CSVD valued by white matter hyperintensity (WMH) were divided into control, mild, moderate, severe and control group. MRIs were analyzed for WMHs, CMB, lacunes, etc. Results The control group showed lower PCI than CSVD patients during STW; no differences were detected among the disease severity groups. During DTW, all four groups exhibited significant differences in PCI and CV. For the moderate and severe groups, coordination and variation significantly differed between the two walking methods. There were correlations between the PCI and GA in the moderate and severe groups (R = 0.376, R = 0.573 during DTW; R = 0.414, R = 0.643 during STW) and no correlations in the control group and mild CSVD group. Conclusion PCI and CV may be vital for detecting the symptoms in the early stage of CSVD disease. We also verified that the PCI could become the bridge across the cognition and motor disorder in CSVD, which was helpful for evaluating clinical symptoms comprehensively.

Method for Finding Solution to Nonsmooth Differential Inclusion of Special Structure

The paper explores the differential inclusion of a special form. It is supposed that the support function of the set in the right-hand side of an inclusion may contain the maximum of the finite number of continuously differentiable (in phase coordinates) functions. It is required to find a trajectory that would satisfy differential inclusion with the boundary conditions prescribed and simultaneously lie on the surface given. Such problems arise in practical modeling discontinuous systems and in other applied ones. The initial problem is reduced to a variational one. It is proved that the resulting functional to be minimized is superdifferentiable. The necessary minimum conditions in terms of superdifferential are formulated. The superdifferential (or the steepest) descent method in a classical form is then applied to find stationary points of this functional. Herewith, the functional is constructed in such a way that one can verify whether the stationary point constructed is indeed a global minimum point of the problem. The convergence of the method proposed is proved. The method constructed is illustrated by examples.

Determining the energy efficiency indicators of the diesel train DPKr-2 and the rail bus 620M based on traction calculations using the numerical method of solving the equation of train movement

The purpose of the article is to compare the technical and energy parameters of the diesel train DPKr-2 and the railbus 620M based on traction calculations using mathematical modeling when solving the train movement equation. The mathematical model of the train is adapted to determine the movement parameters of the specified rolling stock units according to different variable phase coordinates for different movement modes. To achieve this purpose, the authors used methods of system analysis, nonlinear programming, and numerical methods for solving differential equations. The accuracy of the calculations was verified using simulation modeling methods and compared with experimental data. To analyze the results, the obtained indicators of traction calculations – technical speed and specific consumption of diesel fuel – were compared. As a result of the comparison, the specific fuel consumption per ton-kilometer meter, a significant saving of energy resources is observed. Comparative specific fuel consumption per passenger-kilometer meter, on the contrary, indicates an increase in the consumption of energy resources. The mathematical model of the train is adapted to determine the movement parameters of diesel trains and rail buses according to different variable phase coordinates for different drive modes. The practical significance lies in determining the efficiency indicators of the use of different types of rolling stock on the railways of Ukraine, taking into account economic, social and migration factors.

Research of direct and inverse problems of sensitivity using methods of practical stability by direction

The general statements of the problems of construction of extreme ranges of tolerances on parameters for a linear system of differential equations in the presence of dynamic restrictions on the spread of the state vector are considered. It was found that such sensitivity problems are closely related to the problems of estimating the maximum area of stability in the corresponding function space. In order to obtain upper estimates of the sought values, the problem of estimating tolerances from the positions of stability in a single direction is formalized. The cases of linear and nonlinear restrictions on the spread of the phase coordinate vector with initial linear initial conditions relative to the vector of the system parameters are studied. Necessary and sufficient conditions are formulated in the form of criteria for estimating tolerances on parameters covering the case of fixed initial conditions. The tasks of estimating the maximum volume of the stability region with respect to the deviations of the state vectors and system parameters are considered. For the case of compatible admissible constraints, the paper gives the corresponding numerical calculations for the upper estimates. In particular, for fixed initial conditions, the maximum set of tolerances for system parameters with compatible dynamic restrictions on fluctuations of state vectors and parameters are determined according to these evaluation criteria. From the standpoint of practical stability in direction, direct sensitivity problems are investigated, numerical estimates of the spread of the phase coordinate vector of the system in the presence of linear and fixed initial conditions relative to the parameter vector are given. It has been demonstrated that in the given specification of the problem of maximum estimation of tolerances it is completely covered by problem statements of practical stability by direction. Thus, to calculate areas of guaranteed sensitivity, the concept of practical stability in a single direction is extended to the space of sensitivity functions at the initial moment of time. The above algorithms are used to estimate the range of tolerances for the adjustment parameters of the discrete model of the induction acceleration system with the given limitations on the spread of the quality criterion; the variation of the quality indicator within the tolerance field is presented in the form of a linear form relative to the spread of the parameter vector.

Biomechanical Effects of Dominant or Nondominant Limb on Asymmetry during Running Stance Phase

Purpose. This study explores lower limb joint displacement differences during the stance phase and to examine the effects of limb dominance on asymmetry. A total of 32 healthy male amateur marathon runners were recruited (age: 35.33 ± 6.90 years, height: 174.17 ± 3.34 cm, weight: 63.92 ± 4.53 kg). The experiment employed a Vicon eight‐camera motion capture system synchronized with an AMTI force plate to record the phase from heel strike to toe‐off. The continuous relative phase (CRP) between the dominant and nondominant limbs was assessed using of independent t‐test of SPM1d. Results. The hip–knee joint of the dominant limb had a larger maximum CRP (t = 1.104, p &gt; 0.05, effect size = 0.270), smaller minimum CRP (t = −2.672, p &lt; 0.05, effect size = 0.653), larger values of mean absolute relative phase (MARF) (t = 3.275, p &lt; 0.05, effect size = 0.122), and deviation phase (DP) (t = 7.582, p &lt; 0.001, effect size = 0.717) than that of the nondominant limb. Comparing the dominant limb of the knee–ankle joints with the nondominant, there are smaller maximum CRP (t = −0.422, p &gt; 0.05, effect size = 0.144), smaller DP (t = −7.237, p &lt; 0.001, effect size = 0.754), a larger minimum CRP (t = 7.909, p &lt; 0.001, effect size = 2.704), and larger MARF (t = 0.355, p &gt; 0.05, effect size = 0.801). Furthermore, during the stance phases, there are significant differences in coordination modes between the dominant limb and nondominant limb of intersegmental joints (p &lt; 0.05). Conclusion. Throughout different phases of the stance phase, asymmetry in the sagittal plane of lower limb joint displacement is evident. The dominant limb undergoes significant changes in joint leading phase coordination modes, with notably less in‐phase coordination compared to the nondominant limb. This predisposes muscles to overstretching, thereby increasing the risk of muscle strains, while the nondominant limb compensates for lower muscle strength. Recognizing and addressing such asymmetries is key to optimizing nondominant limb strength and minimizing muscle overstretching in the dominant limb, leading to improved stability and movement efficiency during marathon running. Consequently, when designing exercise programs or physical therapy, it is crucial to consider limb dominance‐related symmetry differences to mitigate the risk of injury resulting from interlimb disparities in motion.

Effects of Sport Participation on Gait Coordination, Symmetry, and Variability in Older Adults.

The aim of this study was to compare the interlimb coordination, asymmetry, and variability between older adults who participated in sports (n = 25; age = 72.6 ± 6.46years) and sedentary older adults (n = 20; age = 70.85 ± 3.82years). The sport participants were selected from tennis and badminton clubs, whereas the sedentary participants were recruited from local community centers. The participants walked at their preferred speed in a 10-m walkway for 2min. The interlimb coordination was measured by the phase coordination index. Other walking metrics were speed, cadence, swing time, stance time, double-support time, stride time, and swing time asymmetry. The results showed that the sport participants relative to the sedentary group had better interlimb coordination, higher walking speed and cadence, and less swing time variability. Young older adults also had a better interlimb coordination. In conclusion, the findings of this study showed that long-term participation in sports has some antiaging benefits on gait coordination and symmetry in older adults.

A Method for Analyzing Emergency Modes in Power Transmission Lines with a Complex Asymmetry of Parameters Using Phase Coordinates

A Method for Analyzing Emergency Modes in Power Transmission Lines with a Complex Asymmetry of Parameters Using Phase Coordinates

Gait Variability at Different Walking Speeds.

Gait variability (GV) is a crucial measure of inconsistency of muscular activities or body segmental movements during repeated tasks. Hence, GV might serve as a relevant and sensitive measure to quantify adjustments of walking control. However, it has not been clarified whether GV is associated with walking speed, a clarification needed to exploit effective better bilateral coordination level. For this aim, fourteen male students (age 22.4 ± 2.7 years, body mass 74.9 ± 6.8 kg, and body height 1.78 ± 0.05 m) took part in this study. After three days of walking 1 km each day at a self-selected speed (SS) on asphalt with an Apple Watch S. 7 (AppleTM, Cupertino, CA, USA), the participants were randomly evaluated on a treadmill at three different walking speed intensities for 10 min at each one, SS - 20%/SS + 20%/ SS, with 5 min of passive recovery in-between. Heart rate (HR) was monitored and normalized as %HRmax, while the rate of perceived exertion (RPE) (CR-10 scale) was asked after each trial. Kinematic analysis was performed, assessing the Contact Time (CT), Swing Time (ST), Stride Length (SL), Stride Cycle (SC), and Gait Variability as Phase Coordination Index (PCI). RPE and HR increased as the walking speed increased (p = 0.005 and p = 0.035, respectively). CT and SC decreased as the speed increased (p = 0.0001 and p = 0.013, respectively), while ST remained unchanged (p = 0.277). SL increased with higher walking speed (p = 0.0001). Conversely, PCI was 3.81 ± 0.88% (high variability) at 3.96 ± 0.47 km·h-1, 2.64 ± 0.75% (low variability) at SS (4.94 ± 0.58 km·h-1), and 3.36 ± 1.09% (high variability) at 5.94 ± 0.70 km·h-1 (p = 0.001). These results indicate that while the metabolic demand and kinematics variables change linearly with increasing speed, the most effective GV was observed at SS. Therefore, SS could be a new methodological approach to choose the individual walking speed, normalize the speed intensity, and avoid a gait pattern alteration.

Mathematical modeling of starting modes and static characteristics of a wound-rotor induction motor in phase coordinates

Mathematical modeling of starting modes and static characteristics of a wound-rotor induction motor in phase coordinates

Healthy Finland survey as the latest uptake for 50 years of population health monitoring in Finland

Abstract In Finland, population-based health examination surveys (HESs) have been conducted in regularly since early 1960's to obtain information on population health and health determinants. These surveys have covered adult population living in the mainland Finland. Surveys have always been conducted by specially trained personnel using international standardized protocols such as WHO MONICA protocol or EHES protocol. The latest HES, Healthy Finland, is ongoing and will run until June 2023. The Finnish Institute for Health and Welfare (THL) had the responsibility of the coordination of the preparation phase as well as conducting the survey. Survey planning was started already in early 2021 with a multidisciplinary group including representatives from different stakeholders. Survey sample includes 66.000 randomly selected adults aged 18+ years living in Finland. In the 1st phase, they receive a questionnaire to be filled in. Questionnaire covers topics such as quality of life, health, use of health care services, lifestyles, background information, work ability and functional capacity, wellbeing, accidents, and sexual and reproductive health. In the 2nd phase, 10.000 of those selected to the survey were invited to health examination including for example anthropometric measurements, blood pressure, spirometry test, collection of biological samples and sub-studies. This from these national HESs has been widely used for policy making, planning and evaluation of the prevention programmes, as epidemiological background for clinical treatment guidelines of several diseases, and for research. Information obtained from the Healthy Finland survey will be used for the evaluation of wellbeing service counties which are responsible for the organization of social and health care services in Finland. Survey will generate new information about health inequalities by providing information not only by age and sex but also by education and other socio-economic indicators.

Three-dimensional reconstruction of light field based on cubic B-spline curve fitting

Fringe projection profilometry has been widely used in three-dimensional (3D) reconstruction. In this paper, we replace the camera with a self-made light field camera to achieve structured light field 3D reconstruction. Our self-made light field camera boasts higher resolution and lower cost with the ability to adjust spatial and angular resolution as needed. A novel 3D reconstruction method based on cubic B-spline curve fitting is proposed to directly fit the relationship between phase and 3D coordinates, and the look up table method is utilized to accelerate the entire calculation process. The experimental results demonstrate that the proposed method can accomplish 3D reconstruction of the structured light field under various viewing angles. Specifically, it has respectively reduced the computation time for phase and modulation intensity by 64.03% and 41.43%, and the reconstruction time is decreased by 32.99% without compromising the reconstruction accuracy.

MODIFIED STEFAN CONDITION IN STEFAN PROBLEM

The two-phase one-dimensional Stefan problem (SP) with the boundary between the phases moving with time is considered. The position of the boundary is determined by the modified Stefan condition (MSC), which is obtained from the original nonlinear diffusion equation by integrating over a thin transition layer, and by tending its thickness to zero. Upon receipt of the MSC, the diffusion coefficient is represented by the sum of the Heaviside step functions. It is shown that the MSC differs from the standard one in that in the latter, the derivatives of the concentrations with respect to the phase coordinates are interchanged. An expression for the displacement of the interphase boundary is obtained, which, as in the standard SP, is proportional to the square root of time. The results of using the MSC are confirmed by experimental data on the displacement of the Cu/Sn interface during diffusion bonding during isothermal annealing.

Research and calculation of the levels of higher harmonics of rotary electric machines in active-adaptive networks

In the materials of the article, the parameters of the higher harmonics of the groove frequency are analyzed, which affect the reliability of the operation of electrical equipment and the loss of electrical energy in active-adaptive networks. The influence of higher harmonics of rotary electric machines on the modes of operation of active-adaptive networks and their power equipment is considered. It was established that this influence depends on the energy level of higher harmonics and the modes of operation of active-adaptive networks. A technique is proposed that allows determining the levels of groove harmonic components in the phase windings of electric machines. The calculation of the energy level of higher harmonics was carried out taking into account the electromagnetic asymmetry of rotating electric machines and asymmetric modes of operation of three-phase electric networks using the method of phase coordinates. The obtained results are based on theoretical and experimental studies of the influence of higher harmonics of rotating electric machines on the modes of operation of electrical networks and power energy equipment.

ω-Limit Sets of Impulsive Semigroups for Hyperbolic Equations

In this paper, we investigate the qualitative behavior of an evolutionary problem consisting of a hyperbolic dissipative equation whose trajectories undergo instantaneous impulsive discontinuities at the moments when the energy functional reaches a certain threshold value. The novelty of the current study is that we consider the case in which the entire infinite-dimensional phase vector undergoes an impulsive disturbance. This substantially broadens the existing results, which admit discontinuities for only a finite subset of phase coordinates. Under fairly general conditions on the system parameters, we prove that such a problem generates an impulsive dynamical system in the natural phase space, and its trajectories have nonempty compact ω-limit sets.

Quality Assurance Scheme of Undergraduate Medical Education in Medical Colleges of Bangladesh: Past, Present and Future

Improving quality of medical education is a key contributing factor to improving the quality of healthcare. The rapid increase in number of medical colleges in Bangladesh, especially in the private sector, makes its vital to have effective quality assurance system in place. Quality assurance resembles a state in which medical colleges take on challenges to address different aspects of quality in undergraduate medical education through check and balance in a methodical approach. In 1998, the World Health Organization (WHO) supported the Center for Medical Education (CME) and the Directorate General of Health Service (DGHS) to develop and publish the National Guidelines &amp; Tools for the Quality Assurance Scheme (QAS) for medical colleges in Bangladesh. Since then that guideline has been serving as resource material and guide for institutionalization of the QAS based on the three principles of accountability, self-evaluation, and external peer review, with the latest revision done in 2012. At the institutional level, the scheme was proposed to be managed by the Academic Council, Academic Coordination Committee, the four (previously three) Phase Coordination Groups, Subject Coordinators, and Faculty Review &amp; Development Committee. The operational framework is based on course appraisal, faculty development and review scheme and external review. A model of “pair of medical colleges” was also proposed as to oversee the QAS activities of each other and report to the National Quality Assurance Body (NQAB). This review paper aims to highlight the history of QAS in our medical colleges, their achievements to date and challenges as well as scopes for future improvement to enhance the quality of medical education in Bangladesh. Mugda Med Coll J. 2022; 5(2): 104-109

Fractal Characterization of Particle Size and Coordinate Distribution of Dispersed Phase in the Steelmaking Process of Combined Blowing Conversion

A two-dimensional water model was used to simulate the process of combined blowing. The effect of boundary conditions on the size and coordinate distribution of the dispersed phase was investigated. The results showed that the frequency of the dispersed phase at a certain size level is proportional to its size; the coordinates of the dispersed phase can be expressed in a dimensionless form that shows its uniformity of distribution. An empirical equation for the influence of the boundary conditions on the size and coordinate distribution of the dispersed phase in combined blowing process is also presented.