Laser-assisted-autoionization dynamics of helium resonances with single attosecond pulses

The strong coupling between two autoionizing states in helium is studied theoretically with the pump-probe scheme. An isolated 100-as XUV pulse is used to excite helium near the 2s2p(1P) resonance state in the presence of an intense infrared (IR) laser. The laser field introduces strong coupling between 2s2p(1P) and 2p^2(1S) states. The IR also can ionize helium from both autoionizing states. By changing the time delay between the XUV and the IR pulses, we investigated the photoelectron spectra near the two resonances. The results are used to explain the recent experiment by Gilbertson et al. [Phys. Rev. Lett. 105, 263003 (2010)]. Using the same isolated attosecond pulse and a 540-nm laser, we also investigate the strong coupling between 2s2p(1P) and 2s^2(1S) by examining how the photoelectron spectra are modified versus the time delay and the possibility of observing Autler-Townes doublet in such experiments.Comment: 12 pages, 12 figure

Energy-Efficient Non-Orthogonal Transmission under Reliability and Finite Blocklength Constraints

This paper investigates an energy-efficient non-orthogonal transmission design problem for two downlink receivers that have strict reliability and finite blocklength (latency) constraints. The Shannon capacity formula widely used in traditional designs needs the assumption of infinite blocklength and thus is no longer appropriate. We adopt the newly finite blocklength coding capacity formula for explicitly specifying the trade-off between reliability and code blocklength. However, conventional successive interference cancellation (SIC) may become infeasible due to heterogeneous blocklengths. We thus consider several scenarios with different channel conditions and with/without SIC. By carefully examining the problem structure, we present in closed-form the optimal power and code blocklength for energy-efficient transmissions. Simulation results provide interesting insights into conditions for which non-orthogonal transmission is more energy efficient than the orthogonal transmission such as TDMA.Comment: accepted by IEEE GlobeCom workshop on URLLC, 201

Structure and formation of anticyclonic eddies in the Iceland Basin

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of [publisher] for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 5341-5359, doi:10.1029/2018JC013886.The Iceland Basin has the most energetic eddy activities in the subpolar North Atlantic. This study documents the structure for an anticyclonic eddy in the Iceland Basin using high‐resolution hydrographic and velocity observations. The eddy core waters have lens‐like structure with warm and salty features in the upper 1,000 m. The eddy distorts the density surface by doming the upper isopycnals and deepening the ones near the permanent pycnocline. The eddy has a diameter of about 120 km with substantial barotropic component in the velocity profiles. One branch of the North Atlantic Current in the central Iceland Basin is superimposed onto the eddy, leading to asymmetric velocity structure. Satellite maps show that eddy first shows up over the western slope of the Hatton Bank and moves westward to the central Iceland Basin. The waters enclosed in the eddy core share the same properties with Subpolar Mode Waters. Similar anticyclonic eddies are also found in high‐resolution numerical model simulations, which is used to explore eddy formation. The model results reveal that the potential vorticity gradient prior to the eddy event change signs in both horizontal and vertical directions. This potential vorticity gradient structure meets the necessary condition for the barotropic and baroclinic instabilities. Further calculation of the energy conversions suggests that eddies extract mean potential energy from the large‐scale isopycnal slope and gain the mean kinetic energy in the upper ocean. Therefore, both barotropic and baroclinic instabilities are involved to support the eddy growth.Fundamental Research Funds for the Central Universities Grant Numbers: 201362048, 201424001; China's National Key Research and Development Projects Grant Number: 2016YFA0601803; U.S. NSF Grant Numbers: OCE‐1634886, OCE‐1258823; Ocean University of China; Woods Hole Oceanographic Institution (WHOI)2019-02-0