Cyclic Oscillation Research Articles

PHOTOMETRIC PROPERTIES FOR SELECTED ALGOL-TYPE BINARIES. II. AO SERPENTIS AND V338 HERCULIS

We present the first multiband photometry for the semidetached eclipsing binary AO Serpentis, observed on seven nights between 2009 April and July at the Weihai Observatory of Shandong University. By using the 2003 version of the Wilson–Devinney code, the photometric solutions of AO Ser and a similar object V338 Her were (re)deduced. The spectral types and orbital periods are A2 and P = 0.8793 days for AO Ser, F1V and P = 1.3057 days for V338 Her. The results reveal that two binaries are low mass ratio systems, whose secondary components fill their Roche lobes. The fill-out factors of the primary components are f = 58.6% for AO Ser and f = 54.2% for V338 Her, respectively. From the O − C curves of AO Ser and V338 Her, it is discovered that secular period changes with cyclic variations exist. The periods and semiamplitudes are 17.32(±0.01) yr and 0.0051(±0.0001) days for AO Ser, 29.07(±0.04) yr and 0.0116(±0.0015) days for V338 Her, respectively. This kind of cyclic oscillation may be attributed to either the light-time effect via an assumed third body or perhaps cyclic magnetic activity on the secondary component. For AO Ser, the long-term period decreases at a rate of dP/dt = −5.35(±0.03) × 10−7 days yr-1, which may be caused by mass and angular momentum loss from the system. Considering the period decreasing, the fill-out factor of the primary for AO Ser will increase and it will finally fill its Roche lobe. Meanwhile, the secular period increase rate for V338 Her is dP/dt = +1.44(±0.24) × 10−7 days yr-1, indicating that mass transfers from the less massive component to the more massive component. This will also cause the fill-out factor of the primary to increase. When the primaries fill their Roche lobes, AO Ser and V338 Her may evolve into contact stars, as predicted by the theory of thermal relaxation oscillations.

Thermoelastic analysis of a copper-based monocristalline shape-memory alloy

The objective of this study is to observe the thermoelastic coupling effect in a monocrystalline Cu-Al-Be shape-memory alloy. The orientation of the austenite crystal is measured by Microfocus X-ray texture analysis. Uniaxial cyclic loading is applied to the specimen at room temperature. Infrared thermography is used to capture temperature fields on the specimen surface. The approach consists in analysing the cyclic temperature oscillation of points located on the surface of the specimen. The study highlights first the significant difference between the thermoelastic couplings in austenite and martensite. Second the anisotropy of both phases, especially the martensite, is evidenced.

ORBITAL PERIOD CHANGES AND THEIR EVOLUTIONARY STATUS FOR THE WEAK-CONTACT BINARIES. III. AO CAMELOPARDALIS AND AH TAURI

In this paper, we presented multicolor photometric observations for two eclipsing binaries, AO Camelopardalis and AH Tauri, obtained on 2008 December 16 and 17. Using the Wilson-Devinney Code, the photometric solution of AH Tau was determined from our new CCD data. The mass ratio and the fill-out factor are q = 0.503(±0.003) and f = 10.8%(±0.1%), respectively. This indicates that AH Tau is in weak contact. For the weak-contact binary AO Cam, BVI light curves clearly show a difference in the heights of the maxima (i.e., the O'Connell effect), which may be explained by spot activity. By analyzing the O – C curves for AO Cam and AH Tau, it is found that the orbital periods appear to show a secular period decrease with a cyclic variation. The observed period modulation is ΔP/P ~ 10–6. For AO Cam, the cyclic oscillation with a short period of 7.63(±0.07) yr and a low amplitude of 00019(±00003) may be preferably attributed to the cyclic magnetic activity. The period and amplitude of the cyclic variation for AH Tau are 45.8(±1.1) yr and 00171(±00005), which may more likely result from the light-time effect via a third body. The secular period decrease rates are dP/dt = –1.26(±0.04) × 10–7 days yr –1 for AO Cam and dP/dt = –6.98(±0.07) × 10–8 days yr –1 for AH Tau. This kind of period decrease can be plausibly explained by the mass transfer from the primary to the secondary, and may result in the system evolving into a deep contact configuration.

First orbital period analysis of the Algol-type eclipsing binary RZ Aurigae

A first analysis of the orbital period changes for the Algol-type eclipsing binary RZ Aur is presented, based on all available light minimum times. From the O − C curve, it is discovered that the orbital period appears to show a cyclic variation, which may be possibly attributed to the light-time effect via the presence of the third body. Due to smaller differences between the residuals from Eqs. (2) , (3) , those two equations may represent the orbital period changes of this binary. The periods and the semi-amplitudes of the cyclic oscillation are P 3 = 100.29 ( ± 1.57 ) yr and A = 0.0886 ( ± 0.0037 ) d from Eq. (2) , P 3 = 94.61 ( ± 2.74 ) yr and A = 0.0792 ( ± 0.0026 ) d from Eq. (3) , respectively. The lowest mass of the assumed third body is 2.39 ( ± 0.06 ) M ⊙ , which suggest that the unseen additional body may be a close binary. If it is true, RZ Aur may be a quadruple system. This kind of additional pair may remove angular momentum from the central system, which may play an important role for the formation and evolution of binary systems.

Period Changes of DF Hydrae: Evidence of Mass Transfer and the Presence of a Cool Tertiary Companion

Abstract Combining our six new determined times of light minimum obtained from 2001 to 2007 with others compiled from the literature, we investigated the period changes of DF Hydrae. The general trend of the $O-C$ curve based on all available data reveals that the period of the binary star is increasing continuously at a rate of $dP/dt$$=$$+$1.11($\pm$0.02) $\times$ 10$^{-7}$dyr$^{-1}$. After the long-term period increase was removed from the $O-C$ diagram, it was discovered that the residuals of the CCD and photoelectric observations suggest a small-amplitude cyclic oscillation with a period of 21.5 years. The continuous period increase can be explained by mass transfer from the secondary to the primary, indicating that DF Hydrae is on the TRO-controlled stage of the evolutionary scenario proposed by Qian. The cyclic period variation suggests that DF Hydrae is a triple system containing a cool tertiary component with a mass of $M_3$sin${i^{\prime}}$$=$ 0.21$M_{\odot}$ in a 21.5-year orbit. By removing angular momentum from the central binary system via Kozai oscillation or a combination of the Kozai cycle and tidal friction, the tertiary companion may play an important role for the formation and evolution of the contact system, which makes the eclipsing pair to have a short initial orbital period (i.e., $P$$\lt$ 5$^{\rm d}$). In that case, the detached progenitor of DF Hydrae evolves into the present contact configuration via a combination of magnetic braking and a case A mass transfer.

An Orbital Period Investigation of the Solar-Type Overcontact Binary V700 Cygni

Orbital period changes of the solar-type contact binary V700 Cyg were investigated based on one new eclipse time combined with the others collected from the literature. A cyclic oscillation, with a period of 39.1 yr and an amplitude of 0.$^{\rm d}$0197, was found to be superimposed on a secular period increase at a rate of $dP/dt$$=$$+$2.8 $\times$ 10$^{-8}{\rm d}$ yr$^{-1}$. Weak evidence indicates that there exists another small-amplitude period oscillation. The long-term period increase is in agreement with the conclusion that high-mass ratio W-type overcontact binaries usually show period increasing. This suggests that it may be in the stage controlled by thermal relaxation oscillations. Cyclic period oscillation can be explained as being the result of a light-travel time effect via the presence of an additional body. On the other hand, since both components of V700 Cyg are late-type stars, the period oscillation may be evidence of magnetic activity cycles of the two component stars.

On Period Variations of the K-Type Eclipsing Binary BM Ursae Majoris

Abstract From new CCD observations, 11 light minimum times are presented in this paper. The orbital period change of a W UMa-type eclipsing binary, BM Urase Majoris, was investigated, based on all available times of light minimum. It was discovered that the orbital period of the binary shows cyclic oscillation, superimposed on a secular period decrease. The amplitude and the period of the cyclic variation are $A$$=$ 0.0101($\pm$0.0004)d and $P_{3}$$=$ 30.8($\pm$0.2)yr, respectively. This kind of cyclic variation may be due to a light-time effect via an unseen third body. If the existence of an additional body is true, it may remove a great amount of angular momentum from the central system, and may play an important role in the formation of close binary. The orbital period continuously decreases at a rate of $dP/dt$$=$$-$7.49($\pm$0.16) $\times$ 10$^{-8}$dyr$^{-1}$, which may be due to mass transfer from the primary to the secondary, accompanying mass and angular-momentum loss from the binary system. The orbital period decrease, accompanying mass and angular momentum loss, would cause the contact degree to increase. Therefore, this binary will evolve into a deep contact configuration.

Complex Period Variations of the Neglected W UMa-type Binary System NY Lyrae

AbstractOrbital-period variations of the neglected W UMa-type binary star, NY Lyr, were analyzed based on two newly determined eclipse times together with the others compiled from the literature. A cyclic oscillation with a period of 82.1 yr and an amplitude of 0.0247 d was discovered to be superimposed on a continuous period increase (dP/dt = +1.33 × 10−7 d yr−1). After the long-term period increase and the large-amplitude cyclic oscillation were removed from the O–C diagram, the residuals suggest that there is another small-amplitude period oscillation (A4 = 0.0053 d, P4 = 19.4 years) in the orbital period changes. As in the cases of AH Cnc and AD Cnc, both the continuous period increase and the two cyclic period oscillations make NY Lyr an interesting system to study in the future. In order to understand the evolutionary state of the binary system, new photometric and spectroscopic observations and a careful investigation on those data are needed.

POOL BOILING IN MICROGRAVITY AND IN THE PRESENCE OF ELECTRIC FIELD: EVALUATION OF THE VOID FRACTION IN THE ARIEL EXPERIMENT

The ARIEL experiment was flown aboard a Foton-M2 satellite and hosted in a FLUIDPAC facility, sharing its optical diagnostics and power systems. Its aim was to investigate boiling heat transfer in microgravity on a surface of industrial relevance, at high heat rates. The effect of an externally applied electrostatic field on boiling performance was also tested. The void fraction in microgravity was much larger than in normal gravity condition: the application of electric field was very effective in reducing it. In the absence of electric field, bubbles coalesced giving origin to a large mass of vapor residing near the surface. The application of reduced bubble coalescence and suppressed boiling heat transfer oscillations thus enhanced boiling performance in microgravity. In this paper, a quantitative evaluation of overall and near-wall void fraction was performed, based on the digital processing of the video images. The results showed that the cyclic oscillation of the near-wall void fraction was well correlated with temperature oscillations of the heated wall. Besides, the electric field was very effective in reducing overall void fraction even at low values of the applied voltage.

A NEW PHOTOMETRIC INVESTIGATION OF THE W UMA-TYPE BINARY BI CVn

New photometric observations and their investigation of the W UMa-type binary, BI CVn, are presented. The variations of the orbital period were analyzed based on 12 new determined times of light minimum together with the others compiled from the literature. It is discovered that the period of BI CVn shows a long-term period decrease at a rate of. (P) over dot = -1.51(+/- 0.12) x 10(-7) days year(-1) while it undergoes a cyclic variation with a period of 27.0 years and an amplitude of 0(d).0151. Photometric solutions determined with the Wilson-Devinney method suggest that BI CVn is a contact binary with a degree of contact of 18.0(+/- 1.7)%. The asymmetry of the light curves was interpreted by the presence of dark spots on both components, and absolute parameters were determined by combining the photometric elements with the spectroscopic solutions given by Lu. The observed period decrease can be plausibly explained by a combination of the mass transfer from the primary to the secondary and angular momentum loss via magnetic braking. The cyclic period oscillation suggests that BI CVn is a triple system containing a tertiary component with a mass no less than 0.58 M(circle dot) in a 27.0 year orbit. As in the cases of the other contact binaries (e. g., AH Cnc, AP Leo, AD Cnc, and UX Eri), it is possible that this tertiary companion played an important role for the formation and evolution of the contact system by removing angular momentum from the central system via Kozai oscillation or a combination of Kozai cycle and tidal friction, which causes the eclipsing pair to have a short initial orbital period (e. g., P < 5(d)). In that case, can the initially detached system evolve into the present contact configuration via a combination of magnetic torques from stellar winds and a case A mass transfer?

Evidence of a Massive Black Hole Companion in the Massive Eclipsing Binary V Puppis

Up to now, most stellar-mass black holes have been discovered in X-ray-emitting binaries, in which the black holes are formed through a common-envelope evolution. Here we give evidence for the presence of a massive black hole candidate as a tertiary companion in the massive eclipsing binary V Puppis. We found that the orbital period of this short-period binary ( P 1: 45 days) shows a periodic variation while it undergoes a long-term increase. The cyclic period oscillation can be interpreted by the light-travel time effect via the presence of a third body with a mass of no less than 10.4 M-circle dot.. However, no spectral lines of the third body were discovered, which indicates that it is a massive black hole candidate. The black hole candidate may correspond to the weak X-ray source close to V Pup, discovered by the Uhuru, Copernicus, and ROSAT satellites, produced by accreting materials from the massive binary via a stellar wind. The circumstellar matter with many heavy elements around this binary may have been formed by the supernova explosion of the progenitor of the massive black hole. All of the observations suggest that a massive black hole is orbiting the massive close binary V Pup with a period of 5.47 yr. Meanwhile, we found that the central close binary is undergoing a slow mass transfer from the secondary to the primary star on a nuclear timescale of the secondary component, revealing that the system has passed through a rapid mass transfer stage.

Pelvic fin locomotor function in fishes: three-dimensional kinematics in rainbow trout (Oncorhynchus mykiss)

The paired pelvic fins in fishes have been the subject of few studies. Early work that amputated pelvic fins concluded that these fins had very limited, and mainly passive, stabilizing function during locomotion. This paper is the first to use three-dimensional kinematic analysis of paired pelvic fins to formulate hypotheses of pelvic fin function. Rainbow trout (Oncorhynchus mykiss) were filmed swimming steadily at slow speeds (0.13-1.36 BL s(-1)) and during manoeuvres (0.21-0.84 BL s(-1)) in a variable speed flow tank. Two high-speed cameras filmed ventral and lateral views simultaneously, enabling three-dimensional analysis of fin motion. During steady swimming, pelvic fins oscillate in a regular contralateral cycle. This cyclic oscillation appears to have active and passive components, and may function to dampen body oscillation and stabilize body position. During manoeuvres, pelvic fins move variably but appear to act as trimming foils, helping to stabilize and return the body to a steady swimming posture after a manoeuvre has been initiated. Fins on the inside of the turn move differently from those on the outside of the turn, creating an asymmetric motion. This paper challenges the understanding that pelvic fins have a limited and passive function by proposing three new hypotheses. First, pelvic fins in rainbow trout have complex three-dimensional kinematics during slow-speed steady swimming and manoeuvres. Second, pelvic fins are moved actively against imposed hydrodynamic loads. Third, pelvic fins appear to produce powered correction forces during steady swimming and trim correction forces during manoeuvres.

Stable Stochastic Dynamics in Yeast Cell Cycle

Chemical reactions in cells are subject to intense stochastic fluctuations. An important question is how the fundamental physiological behavior of the cell is kept stable against those noisy perturbations. In this study, a stochastic model of the cell cycle of budding yeast was constructed to analyze the effects of noise on the cell-cycle oscillation. The model predicts intense noise in levels of mRNAs and proteins, and the simulated protein levels explain the observed statistical tendency of noise in populations of synchronous and asynchronous cells. Despite intense noise in levels of proteins and mRNAs, the cell cycle is stable enough to bring the largely perturbed cells back to the physiological cyclic oscillation. The model shows that consecutively appearing fixed points are the origin of this stability of the cell cycle.

Nonlinear Phenomena at Mercury Hg Electrode/Room-Temperature Ionic Liquid (RTIL) Interfaces: Polarographic Streaming Maxima and Current Oscillation

The polarographic streaming maxima and cyclic voltammetric anodic current oscillation (CVACO) at a hanging mercury drop electrode (HMDE) in room-temperature ionic liquid (RTIL) have been studied for the first time using cyclic voltammetric, potential step chronoamperometric and pulse voltammetric techniques. The reversible redox reaction of the 2,1,3-benzothiadiazole (BTD)/BTD*- (an anion radical of BTD) couple with a formal potential (E0') of -1.36 V versus Ag/AgCl/NaCl(saturated) in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) RTIL was typically employed for this purpose. A maximum was observed at the rising part of the normal pulse voltammogram for the reduction of BTD to BTD*- as well as of the reversed pulse voltammogram for the reoxidation of BTD*- to BTD at the HMDE. The conditions of the initiation and control of the CVACO at the HMDE in EMIBF4 were extensively investigated. Generally, the CVACO was enhanced by increasing the concentration of BTD at a given potential scan rate (upsilon) and was attenuated by increasing upsilon. An electrocapillary curve was measured using a dropping mercury electrode in EMIBF4, and the potential of zero charge was determined to be -0.23 V. On the basis of the modern theory of the polarographic streaming maxima of the first kind, the observed streaming maxima and CVACO phenomena are successfully explained to originate from the macroscopic instability at the electrode/solution interface wherein the oscillating mode creates the CVACO.

Journal Bearing “Morton Effect” Cause of Cyclic Vibration in Compressors

A tilting pad bearing supporting an integrally geared compressor in an air separation service had gradually developed symptoms of very consistent cycling of high synchronous vibration levels. The vibration envelope increased and decreased over a roughly six-minute period. There was a difference in the phasing of vibration increase at one end of the rotor versus the other such that the two ends were not in phase but not 180 degrees out of phase either. Intensive site testing determined that no rotor critical speeds were close to the running speed of the pinion or of the bull gear shaft. However, it was observed with infrared thermography that the temperatures of the bearing pedestals were also cyclic with the same period as the vibration, as were the bearing pad and exit oil temperatures. The temperature cycle peaks were not in phase with each other or with the vibration. Various process parameters were changed on an experimental basis, indicating that the main parametric influence was bearing oil inlet temperature. If the oil temperature was optimized in a certain range, the cycling stopped. The conclusion was that the cyclic vibration behavior was a form of “Morton effect,” as discussed in recent research papers. The worn bearing clearances and shaft straightness were being changed by the bearing oil film temperature, which in turn was being affected by the vibration level, which was in turn affected by the instantaneous clearances and the degree of the instantaneous shaft bow. This chain of events, together with the significant time lag associated with transient thermal conduction, led to the cyclic but stable oscillation of the envelope of the amplitude of synchronous vibration. In a double overhung rotor such as the one involved here, this effect was found to happen with a peak cycle amplitude at each end occurring at different times, and with the apparent phase angle shift of the “hot spot” being limited in a deceiving, but ultimately explainable, manner. Field testing showed that maintaining an oil inlet temperature above a practical threshold temperature minimized viscous shearing forces in the bearing film enough to prevent the thermal cycling from occurring. Another option for eliminating the problem would be a bearing re-design to reduce the hot spot temperature severity and sensitivity. Review led by Gordon Kirk

Laminar convective heat transfer in chaotic configuration

The convective heat transfer in chaotic configuration of circular cross-section under laminar flow regime at different values of Dean number and Prandtl number is investigated numerically. The chaotic configuration is the combination of 90° bends and coils. The insertion of equidistant 90° bends between the two consecutive coil produces the phenomenon of flow inversion. The hydrodynamics and heat transfer under laminar flow conditions in the chaotic configuration with constant wall flux as a boundary condition is studied. The control-volume finite difference method with second-order accuracy is used. The chaotic configuration shows a 25–36% enhancement in the heat transfer due to chaotic mixing while relative pressure drop is 5–6%. The effect of Prandtl number on fully developed heat transfer coefficient is also reported. It is observed that heat transfer increases with increase in Prandtl number. The stretching and folding phenomenon in chaotic configuration is observed and discussed for heat transfer coefficient and pressure drop in the chaotic configuration. The cyclic oscillation behavior in the heat transfer coefficient with downstream distance in the chaotic configuration and coiled tube is also observed and discussed. It appeared that heat transfer is strongly influenced by flow inversion. The effect of boundary conditions on heat transfer performance in the chaotic configuration as well as in the coiled tube is also carried out. The study is further extended to predict hydrodynamics and heat transfer with temperature-dependent viscosity in the chaotic configuration. A comparative study for heat transfer and friction factor is also carried out for constant and temperature-dependent viscosity in coiled tube and chaotic configuration. It was observed that the heat transfer under heating condition with temperature-dependent viscosity is higher as compared to the constant viscosity result while friction factor shows the reverse phenomenon in the chaotic configuration.

A New CCD Photometric Investigation of the Short-Period Close Binary AP Leonis

New CCD photometric light curves in the B, V, and R bands of the short-period close binary AP Leonis are presented. A photometric analysis with our symmetric light curves suggests that AP Leo is an overcontact binary with a degree of overcontact of 24.9%. Since the O - C values of photographic and visual times of light minimum showed a large scatter (up to 0.06 days), all of the period changes proposed for the eclipsing binary by previous investigators are not reliable. In this paper the orbital period changes of AP Leo are analyzed based on all published CCD and photoelectric eclipse times. A small-amplitude cyclic oscillation, with a period of 22.4 yr and an amplitude of 0.0049 days, is discovered to be superposed on a secular period decrease at a rate of dP/dt = - 1:08; 10(-7) days yr(-1). The continuous period decrease may be caused by angular momentum loss or a combination of the mass transfer from the primary to the secondary and angular momentum loss. The cyclic period change may indicate that AP Leo is a triple system containing a cool dwarf third component. If this is true, it is possible that this third component plays an important role in the origin and evolution of the overcontact system by removing angular momentum from the central system, and that it makes the eclipsing pair have a low angular momentum and a short initial orbital period ( e. g., P < 5 days). In that case, the initially detached system evolves into an overcontact configuration via magnetic torques from stellar winds. On the other hand, the rapid rotation of the solar-type components (spectral type G0) and the variations of the light curve indicate a high degree of magnetic activity from the spin-up of the components. Both the long-term period decrease and the oscillation can plausibly be interpreted by magnetic activity (i.e., enhanced magnetic stellar wind and activity cycles).

Analytical analysis of the Pennes bioheat transfer equation with sinusoidal heat flux condition on skin surface

This study focuses on the effect of the temperature response of a semi-infinite biological tissue due to a sinusoidal heat flux at the skin. The Pennes bioheat transfer equation such as ρ t c t(∂ T/∂ t) + W b c b( T − T a) = k∂ 2 T/∂ x 2 with the oscillatory heat flux boundary condition such as q(0, t) = q 0e i ωt was investigated. By using the Laplace transform, the analytical solution of the Pennes bioheat transfer equation with surface sinusoidal heating condition is found. This analytical expression is suitable for describing the transient temperature response of tissue for the whole time domain from the starting periodic oscillation to the final steady periodic oscillation. The results show that the temperature oscillation due to the sinusoidal heating on the skin surface is unstable in the initial period. Further, it is unavailable to predict the blood perfusion rate via the phase shifting between the surface heat flux and the surface temperature. Moreover, the lower frequency of sinusoidal heat flux on the skin surface induces a more sensitive phase shift response to the blood perfusion rate change, but extends the beginning time of sampling because of the avoidance of the unavailable first cyclic oscillation.

Interfacial sticking and slipping in the friction stir welding process

In friction stir welding (FSW), a rotating threaded weld tool is inserted into a weld seam and literally stirs the edges of the seam together. To determine optimal processing parameters for producing a defect free weld, a physical understanding of the resulting metal deformation flow path is required. Marker studies are the principal method of studying the metal deformation flow path around the FSW weld tool. In our study, we have used a lead wire embedded in the weld seam as a tracer. At the welding temperature of aluminum, the lead becomes molten and is continuously carried with the macro-flow of the weld metal. A through thickness flow of metal was revealed in the X-ray imaging of the lead tracer in addition to revealing a cyclic oscillation in the plasticized metal affected by the process.

Orbital period investigations of two short-period early-type overcontact binaries BH Cen and V701 Sco in two extremely young galactic clusters IC 2944 and NGC 6383

Both V701 Sco and BH Cen are two early-type short-period overcontact systems ( P = 0. d 762 and P = 0. d 792, respectively). V701 Sco is a member of the young galactic cluster NGC 6383, while BH Cen is a component of a younger galactic cluster IC 2944 where star formation is in process. They provide good opportunity to understand the formation and evolution of binary stars. In the present paper, orbital period changes of the two binaries are investigated. It is discovered that the orbital period of BH Cen shows a long-term increase with a rate of d P/d t = +1.70(±0.39) × 10 −7 days/year while it undergoes a cyclic oscillation with a period of 44.6 years and an amplitude of A 3 = 0. d 0216. For V701 Sco, its O-C curve reveals a periodic change with a period of 41.2 years and amplitude of A 3 = 0. d 0158. The mass ratio of BH Cen is 0.84, but V701 Sco contains twin B1-1.5V type stars with a mass ratio of unit. The continuous period increase of BH Cen is caused by the mass transfer from the less massive component to the more massive one at a rate of d M 2/d t = 3.5 × 10 −6 days/year. The cyclic period changes of both systems can be plausibly explained as the results of light-travel time effects suggesting that they are triple systems. The astrophysical parameters of the unseen tertiary components in the two systems have been determined. We think that the invisible tertiary components in both binaries played an important role in the formations and evolutions of the overcontact configurations by bringing angular momentum out from the central systems. For BH Cen, this process created the initial short period and will support its evolution into an overcontact configuration via a Case A mass transfer within the life time of the extremely young cluster IC 2944. For V701 Sco, two identical zero-age main-sequence components in an overcontact configuration suggest that it may have been formed by fission, possibly by the fission of the third body. The fact that no long-term continuous period variations were found for V701 Sco may suggest that an overcontact binary with the mass ratio of unity can be in an equilibrium revealing that the original configuration of the binary was overcontact as is its present state. It has been reported that faint stars in the two extremely young clusters are relatively scare. From the present study, it is shown that faint stars in young clusters are usually formed as companions of OB stars (including binaries). It is very difficult to detect them because of their low luminosity when compared with the more luminous OB stars.