Competitive X-Ray and Optical Cooling in the Collisionless Shocks of WR 140

The long-period, highly eccentric Wolf-Rayet star binary system WR 140 has exceptionally well-determined orbital and stellar parameters. Bright, variable X-ray emission is generated in shocks produced by the collision of the winds of the WC7pd+O5.5fc component stars. We discuss the variations in the context of the colliding-wind model using broadband spectrometry from the RXTE, Swift, and NICER observatories obtained over 20 yr and nearly 1000 observations through three consecutive 7.94 yr orbits, including three periastron passages. The X-ray luminosity varies as expected with the inverse of the stellar separation over most of the orbit; departures near periastron are produced when cooling shifts to excess optical emission in C iii λ5696 in particular. We use X-ray absorption to estimate mass-loss rates for both stars and to constrain the system morphology. The absorption maximum coincides closely with the inferior conjunction of the WC star and provides evidence of the ion-reflection mechanism that underlies the formation of collisionless shocks governed by magnetic fields probably generated by the Weibel instability. Comparisons with K-band emission and He i λ10830 absorption show that both are correlated after periastron with the asymmetric X-ray absorption. Dust appears within a few days of periastron, suggesting formation within shocked gas near the stagnation point. The X-ray flares seen in η Car have not occurred in WR 140, suggesting the absence of large-scale wind inhomogeneities. Relatively constant soft emission revealed during the X-ray minimum is probably not from recombining plasma entrained in outflowing shocked gas.

Digital virus manipulation chip with a large array of all-dielectric nanocavities

Spatial manipulation of a precise number of viruses for host cell infection is essential for the study of virus pathogenesis and evolution. Albeit optical tweezers have been advanced to the atomic level via optical cooling, it remains a formidable challenge to efficiently trap and move viruses in an aqueous environment, being restricted by insufficient strength of optical forces and a lack of precise spatial manipulation techniques. Here, we demonstrate giant optical forces produced by the enhancement of light in engineered arrays of nanocavities for trapping and digitally moving viruses down to 40 nm in size. By employing the virus hopping and flexibility of moving the laser position, we demonstrate a digital virus manipulation chip with a large trapping area, enabling single or massive virus transporting, positioning, and concentrating. Our work paves the way to efficient and precise manipulation of either single viruses or their massive ensembles, opening a wide range of novel opportunities for virus pathogenesis, virus diagnostics, vaccine, and antiviral drug development, being also important to tackle the current COVID-19 outbreaks.

LiNbO3-Tm3+ Crystal. Material for Optical Cooling

The possibilities of LiNbO3-Tm3+ crystals for optical cooling based on anti-Stokes luminescence in the wavelength range of 1818–2200 nm are investigated. The concentration dependences of the final temperature of the crystal have been determined under continuous (CW) excitation at wavelengths of 1822–1977 nm with a pump intensity Fp=5×1021 cm−2s−1. It was shown that significant cooling with ∆T = 22 K, 19 K, and 16.4 K can be achieved, respectively, with excitation at wavelengths 1977, 1967, and 1948 nm.