Light and Period Variations in Two K-type Contact Binaries:HI Leo and V523 Cas

We presented a low-precision spectrum for HI Leo,Transiting Exoplanet Survey Satellite data for V523 Cas,and new photometry for both K-type contact binaries.Comparing their light curves on different observing dates,we found small intrinsic variabilities,such as variable amplitudes for HI Leo and the varying heights around the second maxima for V523 Cas.By the Wilson-Devinney Code,we deduced six photometric solutions.The dark spot of V523 Cas may appear on the surface of the more massive component on BJD 2458768,while it disappears on BJD 2458779.Our results indicate that the two binaries are W-type shallow-contact binaries(f≤10%).From the eclipse timing residuals,we found that the orbital periods may continuously increase,accompanied by one to two light-time effects due to additional bodies.The modulated periods and semi-amplitudes are P_(3)=25.8(±1.0)yr and A_(3)=0_·^(d)0066(6)for HI Leo,P_(3)=-14.8(±2.0)yr and A_(3)=0_·^(d)0448(12),P_(4)=18.89(±0.14)yr and A4=0_·^(d)0025(2)for V523 Cas,respectively.The orbital period secularly increases at a rate of dP/dt=2.86(±0.11)×10^(-7)day yr^(-1)for HI Leo and dP/dt=3.45(±0.07)×10^(-8)day yr^(-1)for V523 Cas,which may be attributed to mass transfer from the secondary to the primary.With mass transferring,the shallow-contact binaries,HI Leo and V523 Cas,will evolve into the broken-contact configurations.

Photometric and Spectroscopic Studies for Two Magnetic-activity Contact Binaries:V724 And and QR Com

We presented new CCD photometry for two contact binaries,V724 And and QR Com,which were observed during the 2020–2022 observing seasons.By using the Wilson–Devinney method,the photometric solutions were deduced from new observed data and TESS ones.Their asymmetric light curves were modeled by a dark spot on the more massive component.Results indicate that the starspot may immigrate or disappear on the surface of the active component.From the TESS observations of QR Com,it is discovered that the difference between light maxima exhibits a 29.5 day oscillation,which implies the continuous evolution of spot feathers on the timescale of several weeks.Their mass ratio and fill-out factor are q=2.308 and f=11.55% for V724 And,and q=0.624 and f=12.77% for QR Com,respectively.From the(O-C)curve,the orbital period secularly decrease at a rate of d P/dt=-1.66×10^(-7)day yr^(-1)for V724 And and d P/dt=-3.98×10^(-7)day yr^(-1)for QR Com,which was interpreted by mass transfer from the more massive component to the less massive one.With period decreasing,this kind of shallow-contact binaries,V724 And and QR Com,will evolve into the deep-contact configurations.

Coupling atom ensemble and electron transfer in PdCu for superior catalytic kinetics in hydrogen generation

The design of high-performance catalysts is the key to the efficient utilization of hydrogen energy.In this work,a PdCu nanoalloy was successfully anchored on TiO_(2)encapsulated with carbon to construct a catalyst.Outstanding kinetics of the hydrolysis of ammonia borane(turnover frequency of 279 mol·min^(-1·)mol_(Pd)^(-1))ranking the third place among Pd-based catalysts was achieved in the absence of alkali.Both experimental research and theoretical calculations reveal a lower activation energy of the B-H bond on the PdCu nanoalloy catalyst than that on pristine Pd and a lower activation energy of the O-H bond than that on pristine Cu.The redistribution of d electron and the shift of the d-band center play a critical role in increasing the electron density of Pd and improving the catalytic performances of Pd_(0.1)Cu_(0.9)/TiO_(2)-porous carbon(Pd_(0.1)Cu_(0.9)/T-PC).This work provides novel insights into highly dual-active alloys and sheds light on the mechanism of dual-active sites in promoting borohydride hydrolysis.

In-situ fabrication of PtSe2/GaN heterojunction for self-powered deep ultraviolet photodetector with ultrahigh current on/off ratio and detectivity

The research of ultraviolet photodetectors(UV PDs)have been attracting extensive attention,due to their important applications in many areas.In this study,PtSe2/GaN heterojunction is in-situ fabricated by synthesis of large-area vertically standing two-dimensional(2D)PtSe2 film on n-GaN substrate.The PtSe2/GaN heterojunction device demonstrates excellent photoresponse properties under illumination by deep UV light of 265 nm at zero bias voltage.Further analysis reveals that a high responsivity of 193 mA·W^-1,an ultrahigh specific detectivity of 3.8 × 10^14 Jones,linear dynamic range of 155d B and current on/off ratio of^10^8,as well as fast response speeds of 45/102μs were obtained at zero bias voltage.Moreover,this device response quickly to the pulse laser of 266 nm with a rise time of 172 ns.Such high-performanee PtSe2/GaN heteroj u nction UV PD demonstrated in this work is far superior to previously reported results,suggesting that it has great potential for deep UV detection.