Eigenstates of quasi-Keplerian self-gravitating particle discs

ABSTRACT Although quasi-Keplerian discs are among the most common astrophysical structures, computation of secular angular momentum transport within them routinely presents a considerable practical challenge. In this work, we investigate the secular small-inclination dynamics of a razor-thin particle disc as the continuum limit of a discrete Lagrange–Laplace secular perturbative theory and explore the analogy between the ensuing secular evolution – including non-local couplings of self-gravitating discs – and quantum mechanics. We find the ‘quantum’ Hamiltonian that describes the time evolution of the system and demonstrate the existence of a conserved inner product. The lowest-frequency normal modes are numerically approximated by performing a Wick rotation on the equations of motion. These modes are used to quantify the accuracy of a much simpler local-coupling model, revealing that it predicts the shape of the normal modes to a high degree of accuracy, especially in narrow annuli, even though it fails to predict their eigenfrequencies.

Description of Malenchus gilanensis n. sp. from Iran

Malenchus gilanensis n. sp. is described and illustrated from wood samples from Iran. Morphologically, this new species is characterized by very small body size, cuticle with narrow annuli (0.8–0.9 μm wide at mid-body), lateral field with two lines, originating at the level of the median pharyngeal bulb valve, straight amphidial apertures (similar to members of the subgenus Telomalenchus), sunken vulva with large lateral flaps, prophasmids located almost level with to 9 annuli posterior to the vulva in females, and undeveloped adanal bursa which can be considered as an outgrowth of the lateral field in males. Malenchus gilanensis n. sp. resembles members of subgenus Telomalenchus due to the straight amphidial apertures, prophasmid position and large lateral flaps, but it differs by having two lines in the lateral fields. This new species is morphologically similar to five known species of the subgenus Malenchus: M. acarayensis, M. bryanti, M. parvus, M. nanellus and M. truncatus. The new species can be distinguished from them and other species in the subgenus by having straight amphidial apertures, two lines in the lateral fields, position of prophasmids, and having a very small and undeveloped bursa.

Experimental and CFD Study of Circulation Efficiency in Simulated Irregular Annulus

Primary cementing is a critical well construction operation that should ensure annular zonal isolation over the life cycle of the oil well. Efficient conditioning and mobilisation of mud prior to cementing is important to ensure that residual mud, especially in washout zones, does not contaminate the cement slurry. Therefore, experiments are carried out to better understand the flow dynamics and associated phenomenon in irregular geometry. The narrow annulus between casing and formation is approximated by a rectangular slot, in order to aid instrumentation and data acquisition purposes. This methodology can be justified to reproduce flow in narrow annuli fairly well, and is considered a very useful technique for measurement in narrow geometries. Particle image velocimetry (PIV) is used to obtain the liquid velocity profiles in regular and irregular sections of the experimental setup. Analysis of velocity profiles and vector fields provides information on regions of flow in the vicinity of the irregularity, and this allows a systematic study on the effects of flow rate in regular and irregular wellbore geometries. Entry effects from regular to irregular section and the development of areas with recirculation zones are investigated in irregular section. This enables us to estimate variability of circulation efficiencies in the irregularity. The experimental results are compared with numerical simulations in corresponding irregular geometry.