We propose an uplink massive MIMO system using an array of holographic metasurfaces as a sector antenna. The antenna consists of a set of rectangular waveguide-fed metasurfaces combined along the elevation direction into a planar aperture, each with
subwavelength-sized metamaterial elements as radiators. The metamaterial radiators are designed such that the waveguide-fed metasurface implements a holographic solution for the guided (or reference) mode, generating a fan beam towards a prescribed direction, thereby forming a multibeam antenna system. We demonstrate that a narrowband uplink massive MIMO system using the metasurfaces can achieve the sum capacity close to that offered by the Rayleigh channel at 3.5 GHz. We show that metasurfaces supporting multiple fan beams can achieve high spatial resolution in the azimuth directions in sub-6 GHz channels, and thereby form uncorrelated MIMO channels between the base station and users. Also, the proposed metasurface antenna is structurally simple, low-cost, and efficient, and thus is suitable to alleviate RF hardware issues common to massive MIMO systems equipped with a large antenna system.
The Reionization Era Bright Emission Line Survey (REBELS) is a cycle-7 ALMA Large Program (LP) that is identifying and performing a first characterization of many of the most luminous star-forming galaxies known in the z>6.5 universe. REBELS is provi
ding this probe by systematically scanning 40 of the brightest UV-selected (-23.0<M_{UV,AB}<-21.3) galaxies identified over a 7-deg**2 area (including the wide-area COSMOS/UltraVISTA, VIDEO/XMM-LSS, and UKIDSS/UDS fields) for bright 158-micron [CII] and 88-micron [OIII] lines and dust-continuum emission. Selection of the 40 REBELS targets was done by combining our own and other photometric selections, each of which is subject to extensive vetting using three completely independent sets of photometry and template-fitting codes. Building on the observational strategy deployed in two pilot programs, we are increasing the number of massive interstellar medium (ISM) reservoirs known at z>6.5 by ~4-5x to >30. In this manuscript, we motivate the observational strategy deployed in the REBELS program and present initial results. Based on the 60.6 hours of ALMA observations taken in the first year of the program (November 2019 to January 2020), 18 highly significant >~7sigma [CII] lines have already been discovered, the bulk of which (13/18) also show >~3 sigma dust-continuum emission. These newly discovered lines more than triple the number of bright ISM-cooling lines known in the z>6.5 universe, such that the number of ALMA-derived redshifts at z>6.5 already rival Lya redshift discoveries. An analysis of the completeness of our search results vs. star formation rate (SFR) suggests an ~81% efficiency in scanning for [CII] when the SFR(UV+IR) is in excess of 20 M_sol/yr. These new LP results further demonstrate ALMAs efficiency as a redshift machine, particularly in the epoch of reionization.
One of the key open questions in extragalactic astronomy is what stops star formation in galaxies. While it is clear that the cold gas reservoir, which fuels the formation of new stars, must be affected first, how this happens and what are the domina
nt physical mechanisms involved is still a matter of debate. At least for satellite galaxies, it is generally accepted that internal processes alone cannot be responsible for fully quenching their star formation, but that environment should play an important, if not dominant, role. In nearby clusters, we see examples of cold gas being removed from the star-forming disks of galaxies moving through the intracluster medium, but whether active stripping is widespread and/or necessary to halt star formation in satellites, or quenching is just a consequence of the inability of these galaxies to replenish their cold gas reservoirs, remains unclear. In this work, we review the current status of environmental studies of cold gas in star-forming satellites in the local Universe from an observational perspective, focusing on the evidence for a physical link between cold gas stripping and quenching of the star formation. We find that stripping of cold gas is ubiquitous in satellite galaxies in both group and cluster environments. While hydrodynamical mechanisms such as ram pressure are important, the emerging picture across the full range of dark matter halos and stellar masses is a complex one, where different physical mechanisms may act simultaneously and cannot always be easily separated. Most importantly, we show that stripping does not always lead to full quenching, as only a fraction of the cold gas reservoir might be affected at the first pericentre passage. We argue that this is a key point to reconcile apparent tensions between statistical and detailed analyses of satellite galaxies...(abridged)
We introduce an optimisation method for variational quantum algorithms and experimentally demonstrate a 100-fold improvement in efficiency compared to naive implementations. The effectiveness of our approach is shown by obtaining multi-dimensional en
ergy surfaces for small molecules and a spin model. Our method solves related variational problems in parallel by exploiting the global nature of Bayesian optimisation and sharing information between different optimisers. Parallelisation makes our method ideally suited to next generation of variational problems with many physical degrees of freedom. This addresses a key challenge in scaling-up quantum algorithms towards demonstrating quantum advantage for problems of real-world interest.
Ultra intense lasers are a promising source of energetic ions for various applications. An interesting approach described in Ferri et al. 2019 argues from Particle-in-Cell simulations that using two laser pulses of half energy (half intensity) arrivi
ng with close to 45 degrees angle of incidence is more effective at accelerating ions than one pulse at full energy (full intensity). The authors describe this result as enhanced Target Normal Sheath Acceleration. For a variety of reasons, at the time of this writing there has not yet been a true experimental demonstration of this enhancement. In this paper we perform 2D Particle-in-Cell simulations to examine if a milliJoule class, 5 x 10^18 W cm^-2 peak intensity laser system could be used for such a demonstration experiment. Laser systems in this class can operate at a kHz rate which should be helpful for addressing some of the challenges of performing this experiment. Despite investigating a 3.5 times lower intensity than Ferri et al. 2019 did, we find that the double pulse approach enhances the peak proton energy and the energy conversion to protons by a factor of about three compared to a single laser pulse with the same total laser energy. We also comment on the nature of the enhancement and why the double pulse scheme is so efficient.
Cosmic Explorer (CE) is a next-generation ground-based gravitational-wave observatory concept, envisioned to begin operation in the 2030s, and expected to be capable of observing binary neutron star and black hole mergers back to the time of the firs
t stars. Cosmic Explorers sensitive band will extend below 10 Hz, where the design is predominantly limited by geophysical, thermal, and quantum noises. In this work, thermal, seismic, gravity-gradient, quantum, residual gas, scattered-light, and servo-control noises are analyzed in order to motivate facility and vacuum system design requirements, potential test mass suspensions, Newtonian noise reduction strategies, improved inertial sensors, and cryogenic control requirements. Our analysis shows that with improved technologies, Cosmic Explorer can deliver a strain sensitivity better than $10^{-23}/mathrm{Hz}^{1/2}$ down to 5 Hz. Our work refines and extends previous analysis of the Cosmic Explorer concept and outlines the key research areas needed to make this observatory a reality.
To increase the transmission distance of Wireless Power Transfer (WPT) systems, we provide guidelines on choosing the optimal location of an Intermediate Coil with respect to size within a standard five-coil axially aligned experimental setup. From o
ur results, for maximum magnitude of S21 at the resonant frequency we found the optimal location to exist where the coupling coefficient between the Transmitter and the Intermediate Coil and the coupling coefficient between the Receiver and the Intermediate Coil are identical. Additionally, the optimal outer diameter for the maximum magnitude of S21 at the resonant frequency of the Intermediate Coil in the given symmetric and asymmetric setup are found to be larger than both TX and RX.
Our present understanding of the structure of the Hoyle state in $^{12}$C and other near-threshold states in $alpha$-conjugate nuclei is reviewed in the framework of the $alpha$-condensate model. The $^{12}$C Hoyle state, in particular, is a candidat
e for $alpha$-condensation, due to its large radius and $alpha$-cluster structure. The predicted features of nuclear $alpha$-particle condensates are reviewed along with a discussion of their experimental indicators, with a focus on precision break-up measurements. Two experiments are discussed in detail, firstly concerning the break-up of $^{12}$C and then the decays of heavier nuclei. With more theoretical input, and increasingly complex detector setups, precision break-up measurements can, in principle, provide insight into the structures of states in $alpha$-conjugate nuclei. However, the commonly-held belief that the decay of a condensate state will result in $N$ $alpha$-particles is challenged. We further conclude that unambiguously characterising excited states built on $alpha$-condensates is difficult, despite improvements in detector technology.
We present an open source kinematic fitting routine designed for low-energy nuclear physics applications. Although kinematic fitting is commonly used in high-energy particle physics, it is rarely used in low-energy nuclear physics, despite its effect
iveness. A FORTRAN and ROOT C++ version of the FUNKI_FIT kinematic fitting code have been developed and published open access. The FUNKI_FIT code is universal in the sense that the constraint equations can be easily modified to suit different experimental set-ups and reactions. Two case studies for the use of this code, utilising experimental and Monte-Carlo data, are presented: (1) charged-particle spectroscopy using silicon-strip detectors; (2) charged-particle spectroscopy using active target detectors. The kinematic fitting routine provides an improvement in resolution in both cases, demonstrating, for the first time, the applicability of kinematic fitting across a range of nuclear physics applications. The ROOT macro has been developed in order to easily apply this technique in standard data analysis routines used by the nuclear physics community.
We study the anisotropic quantum Heisenberg antiferromagnet for spin-1/2 that interpolates smoothly between the one-dimensional (1D) and the two-dimensional (2D) limits. Using the spin Hartree-Fock approach we construct a quantitative theory of heat
capacity in the quasi-1D regime with a finite coupling between spin chains. This theory reproduces closely the exact result of Bethe Ansatz in the 1D limit and does not produces any spurious phase transitions for any anisotropy in the quasi-1D regime at finite temperatures in agreement with the Mermin-Wagner theorem. We study the static spin-spin correlation function in order to analyse the interplay of lattice geometry and anisotropy in these systems. We compare the square and triangular lattice. For the latter we find that there is a quantum transition point at an intermediate anisotropy of $sim0.6$. This quantum phase transition establishes that the quasi-1D regime extends upto a particular point in this geometry. For the square lattice the change from the 1D to 2D occurs smoothly as a function of anisotropy, i.e. it is of the crossover type. Comparing the newly developed theory to the available experimental data on the heat capacity of $rm{Cs}_2rm{CuBr}_4$ and $rm{Cs}_2rm{CuCl}_4$ we extract the microscopic constants of the exchange interaction that previously could only be measured using inelastic neutron scattering in high magnetic fields.
