Radiation Damping Effects in Two Level Maser Oscillators

Several experiments [1,2] have noted recently that when an inverted two-level spin system was permitted to radiate spontaneously, the resulting oscillation was characterized by an appreciable amplitude modulation. The phenomenon was first believed to be the result of interference of different spin packets in an inhomogeneously broadened spectrum [1]. A theoretical analysis (which will be reported separately) shows that this is not the case. The spins are not independent but are coupled together by means of their radiation field. This explanation has since been by its original authors

The Rapidly Fading Optical Afterglow of GRB 980519

GRB 980519 had the most rapidly fading of the well-documented GRB afterglows, consistent with t^{-2.05 +/- 0.04} in BVRI as well as in X-rays during the two days in which observations were made. We report VRI observations from the MDM 1.3m and WIYN 3.5m telescopes, and we synthesize an optical spectrum from all of the available photometry. The optical spectrum alone is well fitted by a power law of the form nu^{-1.20 +/- 0.25}, with some of the uncertainty due to the significant Galactic reddening in this direction. The optical and X-ray spectra together are adequately fitted by a single power law nu^{-1.05 +/- 0.10}. This combination of steep temporal decay and flat broad-band spectrum places a severe strain on the simplest afterglow models involving spherical blast waves in a homogeneous medium. Instead, the rapid observed temporal decay is more consistent with models of expansion into a medium of density n(r) proportional to r^{-2}, or with predictions of the evolution of a jet after it slows down and spreads laterally. The jet model would relax the energy requirements on some of the more extreme GRBs, of which GRB 980519 is likely to be an example because of its large gamma-ray fluence and faint host galaxy.Comment: 13 pages, submitted to ApJ Letter

Wall interference assessment and corrections

Wind tunnel wall interference assessment and correction (WIAC) concepts, applications, and typical results are discussed in terms of several nonlinear transonic codes and one panel method code developed for and being implemented at NASA-Langley. Contrasts between 2-D and 3-D transonic testing factors which affect WIAC procedures are illustrated using airfoil data from the 0.3 m Transonic Cryogenic Tunnel and Pathfinder 1 data from the National Transonic Facility. Initial results from the 3-D WIAC codes are encouraging; research on and implementation of WIAC concepts continue

The educational potential of the Harmony Project

This research, funded by Canterbury Christ Church University, involved semi-structured interviews with senior leaders from ten schools in England who are engaging with principles of Harmony. Interviews were conducted between May and July 2019 by research intern Julie Marshall and the project was led by Nicola Kemp and Alan Pagden. The aim was to explore the educational potential of the Harmony approach in different school contexts

Characterization of the human omega-oxidation pathway for omega-hydroxy-very-long-chain fatty acids

Very-long-chain fatty acids (VLCFAs) have long been known to be degraded exclusively in peroxisomes via beta-oxidation. A defect in peroxisomal beta-oxidation results in elevated levels of VLCFAs and is associated with the most frequent inherited disorder of the central nervous system white matter, X-linked adrenoleukodystrophy. Recently, we demonstrated that VLCFAs can also undergo omega-oxidation, which may provide an alternative route for the breakdown of VLCFAs. The omega-oxidation of VLCFA is initiated by CYP4F2 and CYP4F3B, which produce omega-hydroxy-VLCFAs. In this article, we characterized the enzymes involved in the formation of very-long-chain dicarboxylic acids from omega-hydroxy-VLCFAs. We demonstrate that very-long-chain dicarboxylic acids are produced via two independent pathways. The first is mediated by an as yet unidentified, microsomal NAD(+)-dependent alcohol dehydrogenase and fatty aldehyde dehydrogenase, which is encoded by the ALDH3A2 gene and is deficient in patients with Sjogren-Larsson syndrome. The second pathway involves the NADPH-dependent hydroxylation of omega-hydroxy-VLCFAs by CYP4F2, CYP4F3B, or CYP4F3A. Enzyme kinetic studies show that oxidation of omega-hydroxy-VLCFAs occurs predominantly via the NAD(+)-dependent route. Overall, our data demonstrate that in humans all enzymes are present for the complete conversion of VLCFAs to their corresponding very-long-chain dicarboxylic acids

Lithostratigraphy, sedimentation and evolution of the Volta Basin in Ghana

We present a revised lithostratigraphy for the Voltaian Supergroup of Ghana, based on a review of existing literature, interpretations of remotely sensed data and reconnaissance field survey of the Volta Basin. These strata thicken eastwards, to a maximum of between 5 and 6 km adjacent to the Pan-African Dahomeyide orogen. They began to accumulate some time after about 1000 Ma, along the margin of an epicontinental sea. Initial sedimentation, comprising the age-equivalent Kwahu and Bombouaka Groups, shows a cyclical mode of deposition controlled by eustatic changes in sea-level that produced a range of nearshore marine, littoral and terrestrial environments. A major erosional interval was followed by deposition of the 3–4 km thick Oti-Pendjari Group. Basal tillites and associated sandy diamictons are correlated with the Marinoan (end-Cryogenian) glaciation, indicating a maximum depositional age of about 635 Ma. The overlying cap carbonates and tuffs were deposited within a shallow epeiric sea bordered by a volcanically active rift system. The main part of the group records the transition from a rifted passive margin to a fully developed foreland basin receiving marine flysch in the form of argillaceous strata interbedded with highly immature wacke-type sandstones and conglomerates. Maximum accommodation space was developed within a foredeep adjacent to the Dahomeyide belt. Towards the end of the orogenic phase, the foredeep succession became partially inverted and then was buried under coarse terrestrial, red-bed molasse of the Obosum Group

Description of larval instars of Mystrophorus formicaeformis Ruthe (Hymenoptera: Dryinidae).

The last immature stage and the mature larva of Mystrophorus formicaeformis Ruthe are described for the first time. The affinities of both immature and mature larvae of M. formicaeformis and corresponding instars of other subfamilies are respectively discussed

User evaluation of an interactive learning framework for single-arm and dual-arm robots

The final publication is available at link.springer.comSocial robots are expected to adapt to their users and, like their human counterparts, learn from the interaction. In our previous work, we proposed an interactive learning framework that enables a user to intervene and modify a segment of the robot arm trajectory. The framework uses gesture teleoperation and reinforcement learning to learn new motions. In the current work, we compared the user experience with the proposed framework implemented on the single-arm and dual-arm Barrett’s 7-DOF WAM robots equipped with a Microsoft Kinect camera for user tracking and gesture recognition. User performance and workload were measured in a series of trials with two groups of 6 participants using two robot settings in different order for counterbalancing. The experimental results showed that, for the same task, users required less time and produced shorter robot trajectories with the single-arm robot than with the dual-arm robot. The results also showed that the users who performed the task with the single-arm robot first experienced considerably less workload in performing the task with the dual-arm robot while achieving a higher task success rate in a shorter time.Peer ReviewedPostprint (author's final draft

XTE J2123-058: A New Neutron Star X-Ray Transient

We report on optical and RXTE observations of a new high-latitude bursting X-ray transient, XTE J2123-058. We identified the optical counterpart, measured the 5.9573 hr orbital period and constrained the binary inclination and the source distance. The distance lower limit indicates that the source is at least 2.6 kpc from the Galactic plane, which is unusual for an LMXB. RXTE observations were made between June and August 1998 during the first detected outburst from this source. We describe correlations between X-ray timing and spectral properties and discuss the possibility that the propeller mechanism turned on during the decay of the outburst. During one of the RXTE observations, we detect a pair of high frequency QPOs at 847.1 +/- 5.5 Hz and 1102 +/- 13 Hz simultaneously. According to the beat frequency model, the QPO separation implies a neutron star spin period near 3.9 ms. As the X-ray flux decreases at the end of the outburst, the amplitude of the optical modulation increases significantly. This behavior can be explained if the size of the accretion disk decreases during the decay of the outburst.Comment: 24 pages, 9 figures, accepted by Ap

miR-786 Regulation of a Fatty-Acid Elongase Contributes to Rhythmic Calcium-Wave Initiation in \u3cem\u3eC. elegans\u3c/em\u3e

Background: Rhythmic behaviors are ubiquitous phenomena in animals. In C. elegans, defecation is an ultradian rhythmic behavior: every ∼50 s a calcium wave initiating in the posterior intestinal cells triggers the defecation motor program that comprises three sequential muscle contractions. Oscillatory calcium signaling is central to the periodicity of defecation. The posteriormost intestinal cells function as the pacemaker for this rhythmic behavior, although it is unclear how the supremacy of these cells for calcium-wave initiation is controlled. Results: We describe how the loss of the mir-240/786 microRNA cluster, which results in arrhythmic defecation, causes ectopic intestinal calcium-wave initiation. mir-240/786 expression in the intestine is restricted to the posterior cells that function as the defecation pacemaker. Genetic data indicate that mir-240/786 functions upstream of the inositol 1,4,5-trisphosphate (IP3) receptor. Through rescue analysis, it was determined that miR-786 functions to regulate defecation. Furthermore, we identified elo-2, a fatty-acid elongase with a known role in defecation cycling, as a direct target for miR-786. We propose that the regulation of palmitate levels through repression of elo-2 activity is the likely mechanistic link to defecation. Conclusions: Together, these data indicate that miR-786 confers pacemaker status on posterior intestinal cells for the control of calcium-wave initiation through the regulation of elo-2 and, subsequently, palmitate levels. We propose that a difference in fatty-acid composition in the posterior intestinal cells may alter the activities of membrane proteins, such as IP3-receptor or TRPM channels, that control pacemaker activity in the C. elegans intestine