Collision of a sphere onto a wall coated with a liquid film

Particle-particle and particle-wall collisions occur in many natural and industrial applications such as sedimentation, agglomeration, and granular flows. To accurately predict the behavior of particulate flows, fundamental knowledge of the mechanisms of a single collision is required. In this fluid dynamics video, particle-wall collisions onto a wall coated with 1.5% poly(ethylene-oxide) (PEO) (viscoelastic liquid) and 80% Glycerol and water (Newtonian liquid) are shown.Comment: 1 page, no figure

On the mass distribution of neutron stars

The distribution of masses for neutron stars is analyzed using the Bayesian statistical inference, evaluating the likelihood of proposed gaussian peaks by using fifty-four measured points obtained in a variety of systems. The results strongly suggest the existence of a bimodal distribution of the masses, with the first peak around $1.37 {M_{\odot}}$, and a much wider second peak at $1.73 {M_{\odot}}$. The results support earlier views related to the different evolutionary histories of the members for the first two peaks, which produces a natural separation (even if no attempt to "label" the systems has been made here), and argues against the single-mass scale viewpoint. The bimodal distribution can also accommodate the recent findings of $\sim M_{\odot}$ masses quite naturally. Finally, we explore the existence of a subgroup around $1.25 {M_{\odot}}$, finding weak, if any, evidence for it. This recently claimed low-mass subgroup, possibly related to $O-Mg-Ne$ core collapse events, has a monotonically decreasing likelihood and does not stand out clearly from the rest of the sample.Comment: 11 pp., 3 figures, submitted to MNRAS Letter

The Variability of Seawater Carbonate Chemistry in two Florida Urban Mangrove Ecosystems

Anthropogenic carbon dioxide (CO2) emissions into the atmosphere are yielding serious impacts across the world’s ocean, including ocean acidification, sea level rise, and increasing seawater temperature. However, these changes are not occurring uniformly across all marine ecosystems. Coastal ecosystems, such as mangroves, already experience extreme and variable environmental conditions due to natural biogeochemical and physical processes. The goal of this study was to document small-scale variability in two urban mangrove ecosystems to gain insight into how ocean acidification will manifest within these systems. Using a stand-up paddleboard, a suite of sensors, and traditional bottle sampling techniques, we measured temperature, salinity, oxygen, and carbonate chemistry over short spatial distances (meters to kilometers) and timescales (minutes to days) in the surface waters of Whiskey Creek and West Lake (Fort Lauderdale, FL). While Whiskey Creek exhibited greater day-to-day variability in carbonate chemistry than spatial variability on any single day, the magnitude of spatial and temporal variability in West Lake was similar. Total alkalinity (TA) and dissolved inorganic carbon (DIC) were highly correlated in both systems, as is common for coastal ecosystems. Both sites showed a correlation between salinity and TA and DIC indicative of a freshwater source of both alkalinity and inorganic carbon. The ratio of TA:DIC changed from day-to-day in both systems based on mixing between fresh and salt water. Our results indicate that while a multitude of complex factors control the carbon chemistry of these two mangrove systems, buffering capacity (e.g., TA:DIC) is largely controlled by freshwater inputs. Further quantifying the drivers of seawater buffer capacity in coastal ecosystems could provide a way for managers and conservationists to locally manage the global trend of ocean acidification

Squeezing generation and revivals in a cavity-ion system in contact with a reservoir

We consider a system consisting of a single two-level ion in a harmonic trap, which is localized inside a non-ideal optical cavity at zero temperature and subjected to the action of two external lasers. We are able to obtain an analytical solution for the total density operator of the system and show that squeezing in the motion of the ion and in the cavity field is generated. We also show that complete revivals of the states of the motion of the ion and of the cavity field occur periodically.Comment: 9 pages, 3 figure