Thermal Oscillations Research Articles

An intense narrow equatorial jet in Jupiter’s lower stratosphere observed by JWST

The atmosphere of Jupiter has east–west zonal jets that alternate as a function of latitude as tracked by cloud motions at tropospheric levels. Above and below the cold tropopause at ~100 mbar, the equatorial atmosphere is covered by hazes at levels where thermal infrared observations used to characterize the dynamics of the stratosphere lose part of their sensitivity. James Webb Space Telescope observations of Jupiter in July 2022 show these hazes in higher detail than ever before and reveal the presence of an intense (140 m s−1) equatorial jet at 100–200 mbar (70 m s−1 faster than the zonal winds at the cloud level) that is confined to ±3° of the equator and is located below stratospheric thermal oscillations that extend at least from 0.1 to 40 mbar and repeat in multiyear cycles. This suggests that the new jet is a deep part of Jupiter’s Equatorial Stratospheric Oscillation and may therefore vary in strength over time.

Optical and X-Ray Studies of Marginal Contact Binary RW Dor Using TESS and XMM-Newton Observatories

Marginal short-period contact binaries are important to understand as they pose a different physical scenario than the predicted theoretical model based on the thermal relaxation oscillation mechanism due to their shallow degree of contact. Here we present the optical and X-ray studies of a contact binary source RW Dor using the Transiting Exoplanet Survey Satellite (TESS) and XMM-Newton telescopes. For the first time we report the varying O’Connell effect and explain the asymmetry with a spot model. Based on the new times of minima, we make a robust estimate of the orbital period of the third body at 47.01 ∼ 0.52 yr with an eccentricity e = 0.21. We show that the period-decreasing trend observed in O − C variation can be explained by both conservative mass transfer from primary to secondary and AML via stellar wind. The X-ray luminosity exhibited by RW Dor did not vary significantly on three different occasions and was found to be about 3.34 × 1029 erg s−1. Assuming that the quiescent X-ray emission is emitted from an undisturbed loop structure, the loop size is estimated to be 0.6–1 × 1010 cm which is ≤Alfvén radius r A ∼ 8 × 1010 cm.

The role of buoyancy and thermal acceleration in heat transfer deterioration and thermal oscillation for the CO2 around pseudo-critical region

Trans-critical CO2 Rankine cycle has great potential in converting low-grade heat into electricity, because of its good temperature glide matching between working medium and heat source. However, the drastic variation in thermo-physical properties of CO2 around the pseudo-critical region causes the abnormal flow and heat transfer behaviors. In this paper, the heat transfer deterioration and thermal oscillation in the heat addition of trans-critical CO2 cycle are investigated by experiments. The test section is heated uniformly by a DC power (0∼6 kW) and the minimum Reynolds number in the test section inlet is about 8000 (it is much larger than 2300) for the all cases. A shear stress reconstruction model is corrected by introducing the velocity profile of turbulence in the boundary layer to attempt to provide a quantitative criterion for deterioration and oscillation. The role of buoyancy and thermal acceleration in heat transfer deterioration and thermal oscillation is elucidated by connecting the shearing-stress reconstruction model and experimental results. It is found that, the thermal acceleration in the near-wall zone provides the key motivation to drive the heat transfer deterioration. The thermal oscillation is driven by the transition between partial and full re-laminarization flows in the local zone of heat transfer deterioration. When (Δτa/τw)<1&(Δτ/τw)tot>1 or 0.1<(Δτ/τw)tot<1, the turbulence is partially re-laminarized. When(Δτa/τw)>1&(Δτa/τw)>>(Δτbo/τw), the intense thermal acceleration causes the turbulence to be fully re-laminarized in the near-wall zone and it maintains the new laminar boundary . The turbulence is partially re-laminarized in the lower boundary and it is almost full re-laminarization in the upper boundary of the oscillation wall temperatures. The results confirm that the emergence of heat transfer deterioration and oscillation instability in mixed turbulent convective relate with the change of flow states caused by acceleration and buoyancy effects.

Transient analysis and safety-oriented process optimization during electrolysis–fuel cell transition of a novel reversible solid oxide cell system

The reversible solid oxide cell (rSOC) is an emerging solution for power-gas conversion in renewable energy networks owing to its high efficiency and bi-directional operation. However, there are still many unidentified safety issues endangering the stability and lifespan of rSOC that need to be addressed before its widespread commercialization. In this paper, a novel one-dimensional rSOC stack model incorporating peripheral auxiliary components is introduced to investigate the transient behavior of the co-flow rSOC stack during electrolysis–fuel cell transition and to develop a safety-oriented optimization strategy for the switching process. This is the first comprehensive study of thermal−material safety hazards for rSOC in the system environment and the first proposal of a dual-model predictive control strategy to avoid nonlinearities in global predictive control during cross-mode switching. It is found that localized extreme temperature gradients, fuel starvation and thermal oscillations are the main safety issues faced by rSOC in switching transients. The conclusion that the current stride and the rate of current change are key factors in guaranteeing the transient safety of rSOC is obtained by evaluating targeted dispatch currents. On this basis, the constraint of current-change rate of 7 A s−1 is incorporated into the controller design, further results indicated that the proposed cooperative control strategy effectively prevents the reactant crisis with smoother thermodynamic responses, which are all within the safety threshold.

Study on Power Frequency Breakdown Characteristics of Nano-TiO2 Modified Transformer Oil under Severe Cold Conditions

With 45# transformer oil as the base fluid, different concentrations of TiO2 nanomodified transformer oil were prepared via the thermal oscillation method. Nanomodified transformer oil with a concentration of 0.01 g/L was selected for evaluation via the breakdown test. Then, 0.01 g/L nanomodified transformer oil and ordinary 45# transformer oil were subjected to the variable control of different moisture contents and different temperatures, and breakdown tests under different types of electrodes were performed within the temperature range of −30 °C to 30 °C. The test results showed the following: Under severe cold conditions, the improvement effect of the breakdown voltage in different temperature ranges was different. Within the temperature range of −30 °C to −10 °C, the enhancement effect could reach 13% to 15%. Within the temperature range of −10 °C to 0 °C, the enhancement effect could reach 8% to 9%. Within the temperature range of 0 °C to 30 °C, the enhancement effect could reach 18% to 21%. Compared with the test results at high water contents, the improvement in the breakdown voltage amplitude of transformer oil by nanomaterials was more obvious at low water contents. In addition, nanomaterials could reduce the dispersion of the breakdown voltage to make the breakdown voltage more stable. Lastly, COMSOL was used to simulate the polarization process of nanoparticles under a uniform electric field and the influence of the trajectory of charged particles in the oil to further analyze the mechanism of the influence of nanoparticles in oil on the breakdown voltage of the oil gap. The simulation results showed that, when the particles were accelerated by the electric field, they moved irregularly. After adding nanoparticles, the charged particles were adsorbed by the nanoparticles when passing through the nanoparticles, which reduced the migration rate of charged particles in the oil. The breakdown voltage of the oil gap increased.

A new look at the YY CrB binary system

This study presented a new analysis for the TESS-observed W Ursae Majoris (W UMa) binary star YY Coronea Borealis (YY CrB). The light curve was analyzed by the PHysics Of Eclipsing BinariEs (PHOEBE) Python version together with the Markov chain Monte Carlo (MCMC) method. The light curve solutions required a hot spot and l3. New eclipse times from the TESS observations were extracted, and the O-C curve of primary and secondary minima showed an anti-correlated manner. In order to study the O-C curve of minima, minima times between 1991 and 2023 were collected. This investigation reported a new linear ephemeris and by fitting a quadratic function to the O-C curve of minima, calculated the orbital period rate of Ṗ≈5.786×10−8dayyear. Assuming mass conservation, a mass exchange rate of Ṁ2=2.472×10−8 calculated from the more massive component to the less massive one. Then, by using the light travel time function, the possible third body was determined in the binary and derived the mass of the third body as 0.498M⊙ with a period of ≃7351.018 days. The O-C curve analysis and the quantity of mass indicate that the presence of a third body is unlikely. This binary is expected to evolve into a broken-contact phase and is a good case to support the thermal relaxation oscillation model.

Spur Pruning Leaving One Bud is an Interesting Viticultural Strategy to Control Bud Acrotony in Bolivian Vineyards

Bolivian viticulture is mostly found in the Central Valley of Tarija, which is characterised by a subtropical climate with high thermal oscillation in winter that results in low accumulation of chilling units. Such climatic conditions accentuate acrotony in vines, which affect budburst uniformity and, consequently, yield and bunch quality at harvest. The aim of this study was to evaluate the effect of different spur pruning strategies on the percentage of budburst and fertility of buds located in different nodal positions in both wine and table grape varieties growing in the Central Valley of Tarija. The results show that allocating spurs with fewer buds improved the budding of most of the distal buds studied. This was noted in both the wine and table grape cultivars, but mostly in the latter. Spur pruning leaving one bud improved the percentage of budburst and the fertility of the distal buds in Cabernet Sauvignon, Cardinal and Ribier, thereby preventing bud acrotony, compared to spur pruning leaving two buds. Spur pruning leaving two buds improved the budburst of latent buds in Cabernet Sauvignon. Therefore, to avoid acrotony patterns, viticulturists should perform pruning leaving one bud.

Long-Time Dynamics of Selected Molecular-Motor Components Using a Physics-Based Coarse-Grained Approach.

Molecular motors are essential for the movement and transportation of macromolecules in living organisms. Among them, rotatory motors are particularly efficient. In this study, we investigated the long-term dynamics of the designed left-handed alpha/alpha toroid (PDB: 4YY2), the RBM2 flagellum protein ring from Salmonella (PDB: 6SD5), and the V-type Na+-ATPase rotor in Enterococcus hirae (PDB: 2BL2) using microcanonical and canonical molecular dynamics simulations with the coarse-grained UNRES force field, including a lipid-membrane model, on a millisecond laboratory time scale. Our results demonstrate that rotational motion can occur with zero total angular momentum in the microcanonical regime and that thermal motions can be converted into net rotation in the canonical regime, as previously observed in simulations of smaller cyclic molecules. For 6SD5 and 2BL2, net rotation (with a ratcheting pattern) occurring only about the pivot of the respective system was observed in canonical simulations. The extent and direction of the rotation depended on the initial conditions. This result suggests that rotatory molecular motors can convert thermal oscillations into net rotational motion. The energy from ATP hydrolysis is required probably to set the direction and extent of rotation. Our findings highlight the importance of molecular-motor structures in facilitating movement and transportation within living organisms.

Unsteady Carbon Nanotubes Nanofluid Flow due to a Moving Cylinder with Thermal Radiation and Temperature Oscillation Effects

This paper discusses transient two-dimensional boundary layer laminar viscous incompressible free convective flow of nanofluids containing carbon nanotubes (SWCNTs and MWCNTs) over a moving vertical cylinder in the presence of thermal radiation and temperature oscillation. The governing boundary layer equations are converted to a dimensionless form and then solved using the Crank Nicolson type’s unconditionally stable and convergent implicit finite difference method. With diverse parameters such as Grashof number (Gr), volume fraction (Φ), phase angle (ωt), and thermal radiation parameter (N), numerical results are achieved for velocity and temperature profiles along with Nusselt number and skin friction coefficients. The numerical results are analysed in detail using graphs for both water-based nanofluid and kerosene-based nanofluids with single and multi-wall carbon nanotubes as the nanomaterials. It has been found that CNTs Water-based nanofluid has higher temperatures, velocities, skin friction coefficient values for all Gr, N, Φ, and ωt when compared to kerosene-based nanofluid with CNTs. But, Kerosene-based CNTs nanofluid has a higher Nusselt number coefficient values concerning all Gr, N, Φ, and ωt than water-based CNTs nanofluid.

CFD analysis of heat transfer enhancement by wall mounted flexible flow modulators in a channel with pulsatile flow

The aim of the present study is to explore heat transfer and pressure drop characteristics in a pulsating channel flow due to wall-mounted flexible flow modulators (FFM). Cold air in pulsating fashion is forced to enter through the channel having isothermally heated top and bottom walls with one/multiple FFMs mounted on them. The dynamic conditions of pulsating inflow are characterized by Reynolds number, non-dimensional pulsation frequency and amplitude. Applying the Galerkin finite element method in an Arbitrary Lagrangian-Eulerian (ALE) framework, the present unsteady problem has been solved. Flexibility (10−4 ≤ Ca ≤ 10−7), orientation angle (60° ≤ θ ≤ 120°), and location of FFM(s) have been considered in this study to find out the best-case scenario for heat transfer enhancement. The system characteristics have been analyzed by vorticity contours and isotherms. Heat transfer performance has been evaluated in terms of Nusselt number variations and pressure drop across the channel. Besides, power spectrum analysis of thermal field oscillation along with that of the FFM’s motion induced by pulsating inflow has been performed. The present study reveals that single FFM having flexibility of Ca = 10−5 and an orientation angle of θ = 90° offers the best-case scenario for heat transfer enhancement.

Experimental investigation and analysis of two-phase flow instability of flow boiling in a mini-channel heat sink

High heat flux and good axial temperature uniformity of channel flow boiling demonstrate that it is ideally suited for next-generation cooling systems. Such systems, however, are hampered by undesirable flow fluctuations, making channel flow boiling ineffective due to the rapid bubble growth within the channels. Furthermore, especially in the mini-channel heat sink, the interactions between multiple parallel channels and inlet/outlet plenum induce complex hydraulic and thermal oscillations. Therefore, lots of consistent and detailed experimental data are still needed to design a reliable flow boiling system. However, only limited studies have examined the effects of channel interaction on flow boiling instability. Thus, to provide a better understanding of the flow boiling instabilities, a mini-channel heat sink was tested with near-saturated inlet conditions using FC-72 as the working fluid. The mini-channel heat sink consisted of a 150 mm long and 70.4 mm wide base area, having 22 identical rectangular channels measuring 1.6 × 4.8 mm2. The flow instabilities were analyzed by observing the vapor backflow and flow fluctuation in mini-channels with variations in the mass velocity, pressure, and heat fluxes. The analysis is based on the detailed flow visualization in the parallel channels and inlet plenum. It was found that the rapid bubble generation in individual channels promotes vapor backflow and hydraulic oscillations. Further observation of the high-speed camera images shows that the vapor crossing over between parallel channels through the inlet plenum led to the synchronization of vapor oscillations, which is responsible for the parallel channel flow instability. This visualization study revealed six dominant flow patterns showing multi-channel flow instability. Based on the classification of dominant flow patterns, a better understanding of the operating conditions for stable flow boiling was obtained.

Numerical analysis of combustion process and pressure oscillation phenomena in low-pressure injection natural gas/diesel dual fuel low speed marine engine

Dual fuel strategy is a promising way to achieve low-carbon emission for marine engines, but engine knock restricts the compression ratio and engine thermal efficiency by adopting premixed combustion mode. Engine knock of natural gas/diesel dual fuel low speed marine engine is not well understood under high compression ratio. The characteristics of combustion process and pressure oscillation phenomena were investigated by varying compression ratio, pre-chamber number, energy proportion of pilot diesel with a single-cylinder engine model with numerical simulation. The results show that, with increase in pre-chamber number using the same energy proportion of pilot diesel under compression ratio of 16, the maximum amplitude of pressure oscillation can be significantly reduced from 0.62 MPa to 0.23 MPa in main chamber, while both resonance modes follow (1,0) mode. With double pre-chamber, when the energy proportion of pilot diesel increases from 0.6% to 1.2%, due to the stronger intensity of jet flame, the heat release rate is accelerated as well as the accumulation of H2O2 radical become less before high speed spontaneous combustion, resulting in lower amplitude of pressure oscillation. When the energy proportion of pilot diesel increases from 1.2% to 3.0%, excessive amount of pilot diesel cannot strengthen the jet flame obviously while the amplitude of pressure oscillation increases slightly. These results suggest that about 1.0% in energy proportion of pilot diesel should be optimal by considering the thermal efficiency, pressure oscillation and NOx emission together.

Novel Control System Strategy for the Catalytic Oxidation of VOCs with Heat Recovery

A theoretical study of the dynamic closed-loop behaviour of a reactor/feed-effluent heat exchanger (FEHE)/furnace system for the catalytic combustion of volatile organic compounds (VOCs) is presented. A 1D pseudohomogeneous plug-flow model is proposed to simulate the non-steady-state operation of the monolith reactor and the FEHE, while the furnace behaviour is described by means of a heterogeneous model of lumped parameters. Positive energy feedback is a source of instability that leads to strong thermal oscillations (limit cycles) and may cause damage to the equipment and sintering of the catalyst. The design of a robust and flexible control system and an efficient control strategy are, therefore, required to ensure safe and stable operation. The response of the system under three different control strategies to the most frequent disturbance variables—the feed flowrate (FV0) and feed concentration of VOCs (C0Et)—was evaluated. One of the control strategies consisted of a single-loop feedback system with servomechanism changes in the reactor inlet temperature (T0) that manipulated the bypass valve and, sequentially, the natural gas flowrate in the furnace (FNG). This approach made it possible to meet the control objective (reducing VOCs) without losing controllability and while minimizing the use of external fuel.

Picophotonic localization metrology beyond thermal fluctuations

Despite recent tremendous progress in optical imaging and metrology1–6, there remains a substantial resolution gap between atomic-scale transmission electron microscopy and optical techniques. Is optical imaging and metrology of nanostructures exhibiting Brownian motion possible with such resolution, beyond thermal fluctuations? Here we report on an experiment in which the average position of a nanowire with a thermal oscillation amplitude of ∼150 pm is resolved in single-shot measurements with subatomic precision of 92 pm, using light at a wavelength of λ = 488 nm, providing an example of such sub-Brownian metrology with ∼λ/5,300 precision. To localize the nanowire, we employ a deep-learning analysis of the scattering of topologically structured light, which is highly sensitive to the nanowire’s position. This non-invasive metrology with absolute errors down to a fraction of the typical size of an atom, opens a range of opportunities to study picometre-scale phenomena with light.

Evidence of a Third Body and Photometric Solutions of a High Temperature Marginal Contact Binary CW Aqr

Marginal contact binary systems are an important class of binary systems in exploited by astronomers to understand various astrophysical phenomena as they bridge both semi-detached and overcontact stages. We studied the photometric data of CW Aqr using the JCB 1.3 m telescope (JCBT), Kepler, and TESS to understand the period variations and constrain the light curve solutions. We noted that the period of CW Aqr is increasing with a mass transfer rate of = 7.53 × 10−8 M ⊙ yr−1 from the secondary to the primary component. We also ascertained cyclic deviations along with a parabolic trend in the O − C diagram. The residuals displayed a sinusoidal trend which was fitted with an LTTE, indicating the presence of a third body with an orbital period of P 3 ∼10 yr and e = 0.10. We fitted the JCBT, Kepler, and TESS photometric normalized light curves and noted the mass ratio to be q ∼ 0.32 for both contact and semi-detached configurations. We identified a temperature difference between the primary and secondary components of ∼2500 K. No activity signatures were found in the observed light curves which were also evident from the Hα line studies where the filled-in effect was not seen. Overall our study suggests that CW Aqr is a marginal contact binary with a low mass ratio evolving toward a semi-detached configuration. However, it may merge if the period increases due to ongoing mass transfer accompanied by a lowering in the mass ratio and later oscillate back to the period-decreasing trend due to angular momentum loss over a few cycles of thermal relaxation oscillations followed by instability.

OT UMa and 2MASS J09251388+6424488: Two active contact eclipsing binary systems

In this paper, new photometric light curves (LCs) of OT UMa and 2MASS J09251388+6424488 (=NSVS 2497620, hereafter NSVS 2497) in BVRcIc-bands are presented and analyzed by using the 2015 version of the Wilson–Devinney (W–D) code. We found that both of them are active contact eclipsing binaries (CEBs) . At the same time, we estimated masses and radii of OT UMa and NSVS 2497 by using our photometric parameters. Then, we also studied the orbital period changes of them by using the O−C method via collecting all available times of light minimum for the first time, and new linear ephemerides are obtained. Besides, the formation and evolution of these two targets are discussed, and we thought that OT UMa could be undergoing thermal relaxation oscillations.

Mass-ratio distribution of contact binary stars

The mass ratio q of a contact binary star evolves through mass transfer, magnetic braking, and thermal relaxation oscillations to low values until it crosses a critical threshold qmin. When this occurs, the binary undergoes the tidal Darwin instability, leading to a rapid coalescence of the components and to an observable brightening of the system. The distribution of q has not been measured on a sufficiently large population of contact binary stars so far because determining q for a single contact binary usually requires spectroscopy. As was shown previously, however, it is possible to infer the mass-ratio distribution of the entire population of contact binaries from the observed distribution of their light-curve amplitudes. Employing Bayesian inference, we obtained a sample of contact binary candidates from the Kepler Eclipsing Binary Catalog combined with data from Gaia and estimates of effective temperatures. We assigned a probability of being a contact binary of either late or early type to each candidate. Overall, our sample includes about 300 late-type and 200 early-type contact binary candidates. We modeled the amplitude distribution assuming that mass ratios are described by a power law with an exponent b and a cutoff at qmin. We find qmin = 0.087−0.015+0.024 for late-type contact binaries with periods longer than 0.3 days. For late-type binaries with shorter periods, we find qmin = 0.246−0.046+0.029, but the sample is small. For early-type contact binary stars with periods shorter than one day, we obtain qmin = 0.030−0.022+0.018. These results indicate a dependence of qmin on the structure of the components, and they are broadly compatible with previous theoretical predictions. We do not find any clear trends in b. Our method can easily be extended to large samples of contact binaries from TESS and other space-based surveys.

A Liquid Mirror Resonator.

We present the first experimental demonstration of a Fabry‒Perot resonator that utilizes total internal reflection from a liquid-gas interface. Our hybrid resonator hosts both optical and capillary waves that mutually interact. Except for the almost perfect reflection by the oil-air interface at incident angles smaller than the critical angle, reflections from the liquid-phase boundary permit optically examining thermal fluctuations and capillary waves at the oil surface. Characterizing our optocapillary Fabry‒Perot reveals optical modes with transverse cross-sectional areas of various shapes and longitudinal modes that are separated by the free spectral range. The optical finesse of our hybrid optocapillary resonator is Fo = 60, the optical quality factor is Qo = 20 million, and the capillary quality factor is Qc = 6. By adjusting the wavelength of our laser near the optical resonance wavelength, we measure the liquid's Brownian fluctuations. As expected, the low-viscosity liquid exhibits a distinct frequency of capillary oscillation, indicating operation in the underdamped regime. Conversely, going to the overdamped regime reveals no such distinct capillary frequency. Our optocapillary resonator might impact fundamental studies and applications in surface science by enabling optical interrogation, excitation, and cooling of capillary waves residing in a plane. Moreover, our optocapillary Fabry‒Perot might permit photographing thermal capillary oscillation, which the current state-of-the-art techniques do not support.

Different types of criteria for dealing with anomalous noise events in urban environments under stable road traffic flow conditions

The management of anomalous noise events in the assessment of environmental noise of specific sources is an important issue for determining the actual exposure of the population to noise pollution. Of all the sources currently considered in the European Noise Directive, road traffic is the most important in cities, both in terms of its temporal and spatial presence, as it is generally maintained 24 h a day and affects almost all streets in urban environments. This paper proposes two types of criteria for dealing with these events in urban environments under stable vehicle flow conditions. The results show the convenience of using each type of the suggested criteria for the elimination of anomalous noise events depending on the objective of the research. Those exclusion criteria based on applying a threshold to the average sound level, may be considered the best among the proposed options to study the variation of the annual average LAeq,1h. However, to study the relation between road traffic noise and temperature, a novel proposal for anomalous event elimination criteria based on dividing the full temperature range into small intervals may be a relevant approach. Overall increases of 8 %, respectively, 14 %, in the explanation of variability were found for the criteria C6 (successive application of the thresholds ±10 dB, ±6 dB and ±3 dB at each temperature interval of 3 °C) with respect to the cases where anomalous sound events were not excluded, respectively, using criteria C1 from the scientific literature. The application of this type of criteria for the management of anomalous noise events could also be useful for the study of the relation between road traffic noise and other objective and subjective variables in cities, especially in those areas with a greater daily thermal oscillation.

The First Photometric and Spectroscopic Study of Contact Binary V2840 Cygni

The first photometric, spectroscopic and period variation studies of neglected short-period eclipsing binary V2840 Cygni are presented. High mass ratio contact binaries (HMRCBs), especially those in the weak-contact configuration, are vital when probing the evolutionary models of contact binaries (CBs) using stellar parameters. The photometric solutions reveal the weak-contact nature of V2840 Cygni with a high mass ratio (∼1.36), motivating us to investigate the nature of such binaries. The period variation study of V2840 Cygni spanning 15 yr shows a secular period decrease at a rate of ∼5.5 × 10−7 day yr−1, indicating mass transfer between the components. The superimposed cyclic variation provides a basic understanding of the possible third body (P 3 ∼ 8 yr, m 3 ∼ 0.51 M ⊙). Following the derived parameters, the evolution of the system is discussed based on the thermal relaxation oscillation (TRO) model. It is found that V2840 Cygni falls in a special category of HMRCBs, which validates TRO. To characterize the nature of HMRCBs, a catalog of 59 CBs with high mass ratios has been compiled along with their derived parameters from the literature. For all the HMRCBs in the study, a possible correlation between their contact configuration and observed period variations for relative log J rel is discussed. The spectroscopic study of V2840 Cygni provides evidence of the presence of magnetic activity in the system and the existence of ongoing mass transfer which is additionally deduced from the period variation study. The LAMOST spectra of 17 HMRCBs are collected to interpret the stellar magnetic activity in such systems.