Velocity Amplitude Research Articles

Numerical investigation on heat and mass transfer characteristics of ice slurry in pulsating flow

In this paper, the heat transfer enhancement of ice slurry in a horizontal pipe with constant heat flux has been investigated numerically. The model is validated with the experimental results from the literature. Then the axial distribution of the heat transfer coefficient, the bulk and wall temperature and the ice volume fraction are obtained. The factors that affect the heat transfer coefficient are analyzed. Furthermore, the heat transfer efficiency of ice slurry in pulsating flow is compared with that in steady state. It is found that the heat transfer efficiency of ice slurry can be significantly improved by pulsating flow. The maximum increment of cycle-averaged heat transfer coefficient reaches 34.32%. Moreover, the degrees of heat transfer enhancement increase with increasing pulsating frequency, relative amplitude of velocity, ice particle diameter and ice volume fraction, and decrease with increasing cycle-averaged velocity. And the heat transfer is more efficient to ice slurry with large particles and ice volume fraction under the pulsating flow conditions. The pulsating frequency is suggested to be not more than 10π Hz. Finally, the correlation for predicting cycle-averaged Nusselt number of ice slurry in pulsating flow is established, and obtaining the reasonably good prediction results.

Modulation of Gamma Spectral Amplitude and Connectivity During Reaching Predicts Peak Velocity and Movement Duration

Modulation of gamma oscillations recorded from the human motor cortex and basal ganglia appears to play a key role in movement execution. However, there are still major questions to be answered about the specific role of cortical gamma activity in both the planning and execution of movement features such as the scaling of peak velocity and movement time. In this study, we characterized movement-related gamma oscillatory dynamics and its relationship with kinematic parameters based on 256-channels EEG recordings in 64 healthy subjects while performing fast and uncorrected reaching movements to targets located at three distances. In keeping with previous studies, we found that movement-related gamma synchronization occurred during movement execution. As a new finding, we showed that gamma synchronization occurred also before movement onset, with planning and execution phases involving different gamma peak frequencies and topographies. Importantly, the amplitude of gamma synchronization in both planning and execution increased with target distance and predicted peak velocity and movement time. Additional analysis of phase coherence revealed a gamma-coordinated long-range network involving occipital, frontal and central regions during movement execution that was positively related to kinematic features. This is the first evidence in humans supporting the notion that gamma synchronization amplitude and phase coherence pattern can reliably predict peak velocity amplitude and movement time. Therefore, these findings suggest that cortical gamma oscillations have a crucial role for the selection, implementation and control of the appropriate kinematic parameters of goal-directed reaching movements.

A Multicomponent Temporal Coherence Model for 3-D Phase Unwrapping in Time-Series InSAR of Seasonal Deformation Areas

3-D phase unwrapping (PU) methods based on the 2-D linear temporal coherencemodel have been widely used in time-series interferometric synthetic aperture radar (TS-InSAR) for measuring topography and monitoring subtle deformation. However, the linear temporal coherencemodel can not characterize the coherence of highly coherent pixels accurately in seasonal deformation areas, where nonlinear deformation is deterministic and nonnegligible. Especially, for urban areas with groundwater or thermal dilation seasonal changes or permafrost regions, the nonlinear deformation is usually associated with periodic temperature changes. In this work, a general multi-component temporal coherence model, which considers multiple components including the seasonal deformation, is proposed for 3-D PU of seasonal deformation areas. Moreover, the uncertainty evaluation criterion, based on Cramér–Rao bound (CRB), is derived for TS-InSAR. The experimental results, obtained by applying the multi-component temporal coherence model to a data set acquired from January 2012 to February 2016 over the Beijing Capital International Airport area, confirm the effectiveness of the proposed method. High phase consistency, accurate corrected digital elevation model (DEM) and deformation information monitoring with high-density and high-coverage PS pixels are achieved. Under the same iterations and TS-InSAR procedure, the enhanced performance by the proposed model is illustrated by comparing with that of linear model in terms of phase consistency of 3-D phase unwrapping, PSCs selection at each step, and final results evaluation. In summary, the number of phase-consistency edges after 3-D PU is increased by about 15%, the number of final PS pixels selected with the same coherence threshold constraint is increased by about 10%, and more PS pixels provide a low uncertainty in residual topography, mean deformation velocity and seasonal amplitude estimation.

The Relationship of Nerve Conduction Velocity (NCV) Amplitude with Controlled and Uncontrolled Diabetes Mellitus based on HBA1C in Peripherals Polyneuropathy Patients in Sanglah Hospital

Background: Complications microangiopathy in the field of nerves resulting from diabetes mellitus is diabetic neuropathy. Patients with diabetes mellitus with blood glucose levels that are not regulated well have a 25.6% risk of developing neuropathy. Neuropathy can be diagnosed clinically, the presence of complaints such as numbness, tingling, or burning in the distal extremity, but almost half of patients are asymptomatic, other methods to determine the presence of neuropathy are questionnaires and electrodiagnostic examinations which are the gold standard. The purpose of this study was to find the relationship between the amplitude of nerve conduction velocity (NCV) with controlled and uncontrolled diabetes mellitus based on HBA1c in patients with peripheral diabetic polyneuropathy at Sanglah Hospital. Method: This study was conducted with a case-control analytic design at Sanglah Hospital by taking data retrospectively where patient data were directly taken from January 2021-October 31 2021 Results: There were 40 research subjects where 20 subjects with controlled DM and 20 subjects with uncontrolled DM, 62.5% men, with an age range of 50-60 years, BMI obesity, duration of diagnosis > 3 years where the results obtained were peripheral polyneuropathy conditions. with the results of NCV only found a significant difference in CMAP N Median with p 0.026 and in SNAP with p = 0.035 in SNAP Conclusion: All patients have the result of decreased function of NCV with the highest risk if it is not controlled with HBA1C levels < 7%, there will be the greatest decrease in NCV motor and sensory N. radialis. Keywords: diabetes mellitus, CMAP, HBA1C, NCV, SNAP.

Time periodic electroosmotic flow in a pH-regulated parallel-plate nanochannel

In this paper, the separation of variables method is applied to investigate the effects of solution pH, background salt concentration and AC electric field frequency on time periodic electroosmotic flow in a pH-regulated parallel-plate nanochannel. The surface charge is generated by the protonation and deprotonation of the functional group SiOH. The background salt is KCl. The pH value of the solution is adjusted by HCl and KOH. Analytical and semi-analytical solutions for electric potential and velocity distributions are obtained. The results show that the electric potential caused by the electric double layer depends greatly on the solution pH and background salt concentration. The amplitudes of the velocity and flow rate of the time periodic electroosmotic flow decrease with the background salt concentration and increase with the deviation of the solution pH from the isoelectric point. In a nanochannel having a height less than 100 nm, the electroosmotic velocity amplitude is not affected by the AC electric field frequency because the oscillating Reynolds number is much less than unity.

Drastic variations in estuarine morphodynamics in Southern Vietnam: Investigating riverbed sand mining impact through hydrodynamic modelling and field controls

Recent riverbed sand mining activities have modified estuarine morphology and sedimentation patterns in many Southeast Asian deltas. The Soai Rap Estuary along the Dong Nai River (one of the largest rivers in Southern Vietnam) is one of the most intensively mined areas in the region, where large-scale sand mining activities have started since the 1990′s. In this paper, we used hydrodynamic modelling (TELEMAC-2D) to investigate the estuarine morphological changes and sediment dynamics related to the intensive riverbed mining in the Soai Rap Estuary. After the hydraulic calibration and validation of the model, we simulate four scenarios: two with dredging, one with sand excavation, and a baseline condition. Our results show that dredging substantially changed the hydraulic regimes, morphological and sediment dynamics of the estuary. Compared to the baseline, dredging substantially influences flow velocity and tidal amplitude. These activities reduce the amount of sediment accumulating upstream by 18% to 36%, while increasing sediment deposition in the Soai Rap Estuary by 6% to 13%. Furthermore, sediment accumulation in the Ganh Rai Bay area decrease by 5% to 10% due to increased sediment transport from the sea to the estuary. Our modelled results also show that the mining pits (pockmarks) created by sand extractions efficiently trap sediment, causing discontinuities in the longitudinal transport of sediment and resulting morphological patterns. We conclude that the morphology and sediment transport regime of the Soai Rap estuary has been significantly altered by the river sand dredging. As such, we recommend that the local government put in place measures to ensure that sand extraction is carried out sustainably in the future, to minimise further alterations to the natural sedimentation patterns and geomorphology of this estuary.

Bioinspired bilayer hydrogel-based actuator with rapidly bidirectional actuation, programmable deformation and devisable functionality

Smart hydrogel actuators which respond to external stimuli have attracted great attention and shown good application prospects in many fields as their simplicity and reliability, while the challenges remain in terms of the relatively low driving force, responsive velocity and deformation amplitude considering the structure-dependent actuation behavior. Here, we propose a thermosensitive hydrogel-based actuator with bioinspired bilayer structure by applying a textured airlaid paper to induce the formation of heterogeneous construction. This nature-inspired design benefits the hydrogel-based actuator rapidly bidirectional actuation, realizing excellent bending velocity (140.6° s−1 within first 5 s) and bending amplitude (850.0° within 30 s) in hot water, powerful recovery in cool water and remarkable reproducibility upon external environmental stimulus by optimizing the texture orientation and mechanical property of airlaid paper. The excellent bonding between airlaid paper and hydrogel also endows the actuator satisfactory stability for circularly operation under water environment for weeks. The programmable deformation and devisable functionality are further realized by propagable and elaborate design for architecture and component of responsive hydrogel, favoring the hydrogel-based actuator alterable ethanol-sensitive ability, photothermal drivability and regenerability. This bilayer hydrogel-based actuator provides promising potentials for the applications in soft robots, smart actuators, artificial muscles, and intelligent human-machine technologies.

Seismic monitoring of the STIMTEC hydraulic stimulation experiment in anisotropic metamorphic gneiss

Abstract. In 2018 and 2019, we performed STIMulation tests with characterising periodic pumping tests and high-resolution seismic monitoring for improving prognosis models and real-time monitoring TEChnologies for the creation of hydraulic conduits in crystalline rocks (STIMTEC). The STIMTEC underground research laboratory is located at 130 m depth in the Reiche Zeche mine in Freiberg, Germany. The experiment was designed to investigate the rock damage resulting from hydraulic stimulation and to link seismic activity and enhancement of hydraulic properties in strongly foliated metamorphic gneiss. We present results from active and passive seismic monitoring prior to and during hydraulic stimulations. We characterise the structural anisotropy and heterogeneity of the reservoir rocks at the STIMTEC site and the induced high-frequency (>1 kHz) acoustic emission (AE) activity, associated with brittle deformation at the centimetre-to-decimetre scale. We derived the best velocity model per recording station from over 300 active ultrasonic transmission measurements for high-accuracy AE event location. The average P-wave anisotropy is 12 %, in agreement with values derived from laboratory tests on core material. We use a 16-station seismic monitoring network comprising AE sensors, accelerometers, one broadband sensor and one AE hydrophone. All instrumentation was removable, providing us with the flexibility to use existing boreholes for multiple purposes. This approach also allowed for optimising the (near)-real-time passive monitoring system during the experiment. To locate AE events, we tested the effect of different velocity models and inferred their location accuracy. Based on the known active ultrasonic transmission measurement points, we obtained an average relocation error of 0.26±0.06 m where the AE events occurred using a transverse isotropic velocity model per station. The uncertainty resulting from using a simplified velocity model increased to 0.5–2.6 m, depending on whether anisotropy was considered or not. Structural heterogeneity overprints anisotropy of the host rock and has a significant influence on velocity and attenuation, with up to 4 % and up to 50 % decrease on velocity and wave amplitude, respectively. Significant variations in seismic responses to stimulation were observed ranging from abundant AE events (several thousand per stimulated interval) to no activity with breakdown pressure values ranging between 6.4 and 15.6 MPa. Low-frequency seismic signals with varying amplitudes were observed for all stimulated intervals that are more correlated with the injection flow rate rather than the pressure curve. We discuss the observations from STIMTEC in context of similar experiments performed in underground research facilities to highlight the effect of small-scale rock, stress and structural heterogeneity and/or anisotropy observed at the decametre scale. The reservoir complexity at this scale supports our conclusion that field-scale experiments benefit from high-sensitivity, wide-bandwidth instrumentation and flexible monitoring approaches to adapt to unexpected challenges during all stages of the experiment.

The Calculating Dynamics Erosion of Support Foundations of Ocean-Technical Installations

The article discusses an approach to calculating the characteristics of soil erosion near the support foundations of ocean-technical structures under the influence of wave and constant currents. Vertical supports in the form of a circular cylinder are considered a support base. An example of the choice of the initial and boundary conditions for the calculation is given. Simulation is carried out near the cylindrical support. The results obtained were compared with empirical data. Conclusions are drawn about the displacement of the zones of maximum and minimum velocities during wave movement. The spatial distribution of the amplitudes of the wave velocities was calculated. A decrease in the amplitude in the rear part of the cylinder and immediately in front of its frontal part was revealed, and it was also determined that the zone of an increase in the amplitude was formed near the lateral surfaces of the cylinder.

A multi-planetary system orbiting the early-M dwarf TOI-1238

Context. The number of super-Earth and Earth-mass planet discoveries has increased significantly in the last two decades thanks to the Doppler radial velocity and planetary transit observing techniques. Either technique can detect planet candidates on its own, but the power of a combined photometric and spectroscopic analysis is unique for an insightful characterization of the planets, which in turn has repercussions for our understanding of the architecture of planetary systems and, therefore, their formation and evolution. Aims. Two transiting planet candidates with super-Earth radii around the nearby (d = 70.64 ± 0.06 pc) K7–M0 dwarf star TOI-1238 were announced by NASA’s Transiting Exoplanet Survey Satellite (TESS), which observed the field of TOI-1238 in four different sectors. We aim to validate their planetary nature using precise radial velocities taken with the CARMENES spectrograph. Methods. We obtained 55 CARMENES radial velocity measurements that span the 11 months between 9 May 2020 and 5 April 2021. For a better characterization of the parent star’s activity, we also collected contemporaneous optical photometric observations at the Joan Oró and Sierra Nevada observatories and retrieved archival photometry from the literature. We performed a combined TESS+CARMENES photometric and spectroscopic analysis by including Gaussian processes and Keplerian orbits to account for the stellar activity and planetary signals simultaneously. Results. We estimate that TOI-1238 has a rotation period of 40 ± 5 d based on photometric and spectroscopic data. The combined analysis confirms the discovery of two transiting planets, TOI-1238 b and c, with orbital periods of 0.764597−0.000011+0.000013 d and 3.294736−0.000036+0.000034 d, masses of 3.76−1.07+1.15 M⊕ and 8.32−1.88+1.90 M⊕, and radii of 1.21−0.10+0.11 R⊕ and 2.11−0.14+0.14 R⊕. They orbit their parent star at semimajor axes of 0.0137 ± 0.0004 au and 0.036 ± 0.001 au, respectively.The two planets are placed on opposite sides of the radius valley for M dwarfs and lie between the star and the inner border of TOI-1238’s habitable zone. The inner super-Earth TOI-1238 b is one of the densest ultra-short-period planets ever discovered (ρ = 11.7−3.4+4.2 g cm−3). The CARMENES data also reveal the presence of an outer, non-transiting, more massive companion with an orbital period and radial velocity amplitude of ≥600 d and ≥70 m s−1, which implies a likely mass of M ≥ 2 √(1− e2) MJup and a separation ≥1.1 au from its parent star.

Particle resolved numerical modeling of unsteady forced convection of nanofluid around a porous cuboid with sinusoidal inlet velocity

Abstract In this research, the laminar, incompressible, unsteady oscillatory flow and convective heat transfer of nanofluid around a porous cuboid were studied two-dimensionally using particle resolved calculations. Several cuboids of different sizes and porosities and with a constant temperature were subjected to a nanofluid flow with a sinusoidal velocity profile. The effects of the Reynolds number (Re = 100–900), the volume fraction of nanoparticles, the aspect ratio of the porous cuboid, the Darcy number and the amplitude and frequency of the inlet velocity on the flow field and heat transfer were investigated. To evaluate the system’s optimal performance, performance evaluation criteria (PEC) were also investigated. The results showed that increasing the Reynolds number improved thermal performance. Increasing the volume fraction of nanoparticles increased the Nusselt number; however, the pressure drop coefficient increased more strongly. The heat transfer and pressure drop coefficient increased in line with the growth of the porous cuboid aspect ratio. When the Darcy number was increased, the Nusselt number first increased and then decreased and the pressure drop coefficient continuously decreased. A higher amplitude of the inlet velocity profile augmented the heat transfer and pressure drop coefficient. An increase in the amplitude and frequency of the inlet velocity profile widened the range of drag and lift coefficients. Furthermore, flow at different inlet velocity frequencies (f * = 0–10) behaved differently; as a result, the maximum rate of heat transfer and pressure drop was obtained at f *=5. However, considering the ratio of the Nusselt number to the pressure drop coefficient and PEC parameter, the optimum frequency was f *=9.

Numerical simulation of tidal hydrodynamics in the Arabian Gulf

A vertically 2-D numerical model based on the Delft3D modelling system is set up, calibrated, and validated to simulate the tidal hydrodynamics in the Arabian Gulf. The model is a barotropic solution, controlled by 13 tidal components at open boundaries. The performance of the numerical model was evaluated using the hourly water level observations and the TOPEX/Poseidon altimetry data. Statistical analysis showed a good agreement between the simulated and observed water levels. RMS error was found to be ranged from 0.07 to 0.23 m, with maximum discrepancies observed at Ras Tanura and Mina Sulman stations. However, the IOA between the simulated and observed water levels was significant (0.95–0.99). On average, the errors for the tidal constituents considered in the analysis are in the order of <0.02 m (4%). The M2, S2, K1 and O1 tidal waves represent the largest among other constituents, where the amplitude of S2 represents almost 30% of the M2, and the O1 tidal wave represents about 50% of the K1 tide. The co-tidal charts of the semidiurnal tides show the existence of two anticlockwise amphidromic systems in the north and south ends (centred around 28.25° and 24.5°N respectively) close to the western side, while the diurnal constituents form only a single amphidromic point in the central part, centred around 26.8°N (North Bahrain). On the other hand, the velocity amplitudes of the U and V components of the numerical model were compared with a previous observational study and found to be agreed well.

Structural Vibration Analysis of Historical Drum Tower Structure Caused by Underground Train Running

The vibration induced by underground metro operation could have significant impacts on the safety of building structures. In this study, the dynamic response of the Nanjing Drum Tower affected by the metro line four operation was investigated by a three-dimensional FEM coupling train-track-tunnel-foundation-soil-basement–Drum Tower model performed on a 64 CPU parallel computing cluster platform. The results show that the vertical vibration caused by the subway operation has a more serious impact on the historical structure of the Drum Tower than the horizontal vibration. The vertical vibration attenuates rapidly from the basement bottom to the top of the tower. The horizontal vibration amplifies along the height of the historical building. The truss roof significantly weakens the vibration. As the speed of the train increases, the amplitude of horizontal and vertical vibration increases gradually from the bottom to the roof of the Drum Tower despite a relatively smaller increase for the horizontal vibration. As for the double-track operation case, the vertical vibration amplitude is much greater than that for the single-track operation, and no significant difference is observed in the horizontal direction. The amplitudes of horizontal vibration velocity for the basement and Drum Tower are 0.131 and 0.060 mm/s, respectively.

Optimization of a vertical axis wind turbine with a deflector under unsteady wind conditions via Taguchi and neural network applications

Vertical axis wind turbines (VAWTs), so named because of their vertical axis of rotation, are a sustainable, opportune, and versatile means of producing energy. Their operation is not dependent on wind direction, making them suitable for use in settings with turbulent and inconsistent winds (e.g., urban locations), and they can be installed at the bottom of towers for easier installation and maintenance. However, unsteady wind may cause a vertical axis wind turbine (VAWT) to operate under drag-controlled conditions and reduce its performance. The power coefficient of a VAWT under unsteady wind conditions is heavily impacted by the tip speed ratio (TSR). Understanding and optimizing TSR is critical to making VAWTs a more viable and attractive option for sustainable energy production. Deflectors have been shown to improve the aerodynamic performance of wind turbines. In the present study, the Taguchi method is used in the experimental design, and a high-fitting neural network (NN) model based on computational fluid dynamics (CFD) data is adopted to predict the optimal mean TSR for a VAWT operation with a deflector. The amplitude and frequency fluctuations of the mean inlet velocity are used to specify the unsteady wind conditions. The results show that the imposed unsteady wind reduces the average power coefficient (Cp-) of the VAWT. By applying the Taguchi method and NN analysis to the impact of unsteady wind conditions, it is found that the mean TSR (TSRmean) is the factor producing the greatest impact on Cp-. The optimal TSRmean is evaluated by the NN model. In light of the recommendation from the NN predictions, the Cp- value from CFD can be improved by up to 3.58 folds under the optimal TSRmean. Furthermore, the relative errors of predicted Cp- values between the NN and CFD simulation are less than 4%, showing the reliability of predictions of the developed NN model in efficiently calculating the optimal operation for a VAWT.

Postural Control in Unipedal Quiet Stance in Young Female Gymnasts and the Effects of Training with Consideration of Transient Behavior of Postural Sway.

The purpose of this study was twofold: (a) to compare postural control between a group of young female gymnasts (n = 15; age: 11.2 ± 1.9 years) and non-trained peers (n = 15; age: 10.9 ± 2.0 years), and (b) to investigate the effect of an 8-week whole body exercise intervention program on postural control in young female gymnasts. Postural control was assessed by recording center of pressure (CoP) movements during unipedal quiet stance. Velocity and amplitude of CoP movement in anterior-posterior (AP) and medial-lateral (ML) directions were considered. In addition to common trial-averaged CoP outcomes, we also considered the transient behavior of CoP movements, by calculating relative differences between the 1st and 2nd, and the 1st and 3rd 10-s intervals within the whole trial (DIF_21 and DIF_31, respectively). The gymnast group had lower total CoP velocity (Cohen’s d = 0.97) and AP amplitude (Cohen’s d = 0.85), compared to their non-trained peers. The gymnasts also had lower CoP AP amplitude DIF21 (Cohen’s d = 0.73), with almost constant values across all intervals. After the training ML CoP velocity was reduced for 13.12% (Cohen’s d = 0.60), while ML CoP amplitude increased (Cohen’s d = −0.89).

Using supervised learning techniques to automatically classify vortex-induced vibration in long-span bridges

Owing to a capacity for high flexibility and low damping, long-span bridges are subjected to vortex-induced vibrations (VIVs) under operational conditions. Long-term monitoring data with machine-learning algorithms indicate the potential for automating the VIV assessment of long-span bridges. These methods require a significant amount of labeled data, whereas obtaining such data is normally not feasible owing to the limited availability of VIV datasets. This study leverages supervised learning techniques to develop an automatic classification method for VIVs. To address manual data labeling and develop an optimum model, a three-stage strategy is presented: 1) Semi-supervised labeling, 2) deep neural network (DNN) training, and 3) identification of an optimum parameter range. First, semi-supervised labeling is employed to automatically label the dataset into either VIV or non-VIV classes. Second, a DNN model is trained using the wind and vibrational features of labeled data. Finally, the optimum parameter range is determined by analyzing the peak factor distribution, confusion matrix, and corresponding velocity–amplitude curve of the classified test datasets. An application of the model to a long-span, cable-stayed bridge is illustrated to assess the classification performance based on actual monitoring data. The DNN with the suggested labeling process demonstrates consistent and accurate detection of VIVs.

Electrokinetic energy conversion through cylindrical microannulus with periodic heterogeneous wall potentials

In microfluidic electrokinetic flows, heterogeneous wall potentials are often required to fulfill some functions, such as increasing dispersion and mixing efficiency. In this paper, we study the pressure-driven electrokinetic flow through microannulus with heterogeneous wall potentials in circumferential direction. The streaming potential induced by the ions accumulating in downstream of the microannulus is considered and the electrokinetic energy conversion (EKEC) efficiency is further investigated. Interestingly, based on the method of Fourier expansion, the analytical solutions of fluid velocity, streaming potential and energy conversion efficiency are derived for arbitrary peripheral distribution of the small wall potential for the first time. Four specific patterned modes of the heterogeneous wall potential, i.e. constant, step, sinusoid with period 2π and sinusoid with period π/2 are represented. The distributions of the electric potential and the velocity for four different modes are depicted graphically. Furthermore, the variations of the streaming potential and the EKEC conversion efficiency with related parameters are also discussed. Results show that when these integral values from −π to π associated with the wall potentials are identical, the streaming potential and the EKEC efficiency corresponding to different modes are the same. Additionally, the amplitude of fluid velocity peripherally reduces with the increase of the wavenumber of wall potential distribution in θ-direction.

Velocity monitoring of γ Cas stars reveals their binarity status

ABSTRACT The binary status of γ Cas stars has been discussed while theoretically examining the origin of their peculiar X-ray emission. However, except in two cases, no systematic radial velocity monitoring of these stars had been undertaken yet to clarify their status. We now fill this gap using TIGRE, CARMENES, and UVES high-resolution spectroscopy. Velocities were determined for 16 stars, revealing shifts and/or changes in line profiles. The orbit of six new binaries could be determined: the long periods (80–120 d) and small velocity amplitudes (5–7 km s−1) suggest low mass companions (0.6–1 M⊙). The properties of the known γ Cas binaries appear similar to those of other Be systems, with no clear-cut separation between them. One of the new systems is a candidate for a rare case of quadruple system involving a Be star. Five additional γ Cas stars display velocity variations compatible with the presence of companions, but no orbital solution could yet be formally established for them hence they only receive the status of ‘binary candidate’.

自動車エンジン排気系流動場を想定した脈動気流における矩形管壁面熱伝達の研究

The airflow in the exhaust pipe of an automobile engine fluctuates periodically in terms of flow velocity and gas temperature, and understanding the complex flow and heat transfer characteristics is extremely important for improving the performance of exhaust systems. In this study, using a horizontal rectangular pipe with a rectangular cross section, we experimentally obtained the time-averaged temperature in the cross section measured by thermocouples and the wall temperature by thermography on the outer wall of the pipe under the pulsation conditions assumed in the actual system, and investigated the effects on the heat transfer characteristics. The influence of flow characteristics on heat transfer characteristics was also investigated by using PIV. The results showed that the heat transfer coefficient peaked at a pulsation frequency of 25 Hz. At higher frequencies, the decrease in velocity amplitude was considered to be responsible for the decrease in heat transfer coefficient. At lower frequencies, the decrease in turbulent energy in the area close to the inner wall was considered to be the cause.

Influence of non-stationary river discharge on the quality of water withdrawal in the presence of density stratification

The paper presents the results of field measurements and numerical modeling of different aspects of water quality in the Kama River (Kama reservoir), which is the source of technical water supply of industrial enterprises of the city of Berezniki. During the summer season, there are significant risks related to sustainability of water supply. It is traditionally believed that, over the winter period of low water, these risks increase manyfold. However, the results of departmental monitoring and field studies performed in winter provide evidence of the performance stability of technical water intakes from the Kama river. It was found that, in summer, when this part of the Kama river is located in the backwater zone of the Kama hydroelectric power station and, respectively, the flow velocity decreases, vertical stratification of water masses is formed, which significantly reduces the stability of water use from the near-bottom area. In winter, with a decrease in the water level in the Kama reservoir, the typical river conditions characterized by increased flow velocities occur. Under these conditions, the intense vertical mixing of water masses is implemented, which improves the consumer properties of water for sustainable water supply. The numerical simulations carried out within the framework of a three-dimensional model confirmed this conclusion. It is shown that if the amplitude of the flow velocity at a point changes with time according to a harmonic law, then the value of the salt concentration at this point also changes harmonically, but in antiphase with the velocity.