On the origin of comets

Physico-chemical processes leading to the dynamic formation and physical evolution of comets are reviewed in relationship to the various theories that propose solar origins, protoplanetary origins, planetary origins and interstellar origins. Evidence points to the origins of comets by the growth and agglomeration of small particles from gas and dust at very low temperatures at undetermined regions in space

Gender and Disability Inclusion in Post-Disaster Rebuilding ‘Build Back Better’ Programmes in Sri Lanka: A Literature Review

In the last decade, many South Asian developing countries have suffered natural dis-asters. Severe disaster destruction results in an overwhelming need to rebuild hous-ing and infrastructure within a brief amount of time. United Nation Development Programme has sought to make this reconstruction program a "Build Back Better (BBB)" opportunity, hence gender inequality and marginalisation of people with disa-bilities remain a problem in many countries. Although the international community has sought to promote this resilience and inclusion, the Post-Disaster Rebuilding (PDR) process still overlooks these sectors of society and their needs. Therefore, this paper aims to bring in literature synthesis addressing gender and disability inclusion in PDR ‘BBB’ programmes in Sri Lanka. Besides, involvement in the mitigation of vulnerability and community resilience to disaster risks and relocation was found to play a significant role. Vulnerability and the risk of disasters can be dramatically re-duced by ensuring a culture of disaster prevention and resilience for all segments of populations, particularly rural areas, girls and women, and the disabled. All aspects of socially inclusive, formal, and non-formal commitments are important to take their desires and requirement into consideration

The solar wind interaction with comets: A post encounter view

The recent spacecraft encounters with comets Giacobini-Zinner and Halley have led to an enormous increase in our knowledge of comets, including their dust, neutral gas, plasma, and magnetic field environments. The latter has in turn led to better understanding of the nature of the solar wind interaction with the well developed atmosphere of a comet. The post-encounter understanding of this interaction is reviewed, underscoring the differences with pre-encounter reasoning. The problems outstanding in this area are emphasized

Effect of motor control training on hip muscles in elite football players with and without low back pain

Objectives: Previous research has shown that motor control training improved size and function of trunk muscles in elite football players with and without low back pain (LBP). Imbalances in hip muscles have been found in athletes with LBP and it is not known if motor control training can change these muscles. This study investigated if a motor control intervention program affected hip muscle size in elite football players with and without LBP. Design: Panel-randomised intervention design. Methods: Forty-six players from one club in the Australian Football League (AFL) participated in a motor control training program delivered across the season as a stepped-wedge intervention design with 3 treatment arms: 15 weeks intervention, 8 weeks intervention and a wait-list control who received 7 weeks intervention toward the end of the playing season. Presence of LBP was assessed by interview and physical examination. Cross-sectional areas of iliacus, psoas, iliopsoas, sartorius, gluteus minimus, and gluteus medius muscles were measured from magnetic resonance images taken at 3 time points during the season. Results: Iliopsoas, sartorius and gluteus medius muscle size increased for players who received intervention (p < 0.05). For players with current LBP, sartorius and gluteus medius muscle size increased for those who received motor control training (p < 0.05). Conclusions: Motor control training programs aimed at the lumbo-pelvic region also benefit the hip muscles. For players with current LBP, the intervention mitigated sartorius muscle atrophy and increased gluteus medius muscle size. These findings may help guide the management of LBP in elite football players

Plasma Interaction With Microbes

The germicidal effects of a non-equilibrium atmospheric pressure plasma generated by a novel resistive barrier discharge on representatives of the two classes of bacteria (Gram-negative and Gram-positive) are discussed. The plasma exposure, while being lethal to both bacterial classes, also produced gross structural damage in the Gram-negative E. coli while none was observed in the more structurally robust Gram-positive Bacillus subtilis. An electrophysical process involving the role of the electrostatic tension on a charged body in a plasma is invoked to explain both observations. Since the efficacy of this electrophysical process depends not only on the tensile strength of the bacterial cell wall but also on its shape and texture, the need for more experimental studies, using a wide range of bacteria belonging to various morphological groups, is suggested. Ways to further test the validity of this electrophysical lysis mechanism for Gram-negative bacteria on one hand, and also to extend its operation to the more robust Gram-positive bacteria on the other, are suggested

Braking the Gas in the beta Pictoris Disk

(Abridged) The main sequence star beta Pictoris hosts the best studied circumstellar disk to date. Nonetheless, a long-standing puzzle has been around since the detection of metallic gas in the disk: radiation pressure from the star should blow the gas away, yet the observed motion is consistent with Keplerian rotation. In this work we search for braking mechanisms that can resolve this discrepancy. We find that all species affected by radiation force are heavily ionized and dynamically coupled into a single fluid by Coulomb collisions, reducing the radiation force on species feeling the strongest acceleration. For a gas of solar composition, the resulting total radiation force still exceeds gravity, while a gas of enhanced carbon abundance could be self-braking. We also explore two other braking agents: collisions with dust grains and neutral gas. Grains surrounding beta Pic are photoelectrically charged to a positive electrostatic potential. If a significant fraction of the grains are carbonaceous (10% in the midplane and larger at higher altitudes), ions can be slowed down to satisfy the observed velocity constraints. For neutral gas to brake the coupled ion fluid, we find the minimum required mass to be $\approx$ 0.03 M_\earth, consistent with observed upper limits of the hydrogen column density, and substantially reduced relative to previous estimates. Our results favor a scenario in which metallic gas is generated by grain evaporation in the disk, perhaps during grain-grain collisions. We exclude a primordial origin for the gas, but cannot rule out the possibility of its production by falling evaporating bodies near the star. We discuss the implications of this work for observations of gas in other debris disks.Comment: 19 pages, 12 figures, emulateapj. Accepted for publication in Ap

The composition of heavy molecular ions inside the ionopause of Comet Halley

The RPA2-PICCA instrument aboard the Giotto spacecraft obtained 10-210 amu mass spectral of cold thermal molecular ions in the coma of Comet Halley. The dissociation products of the long chain formaldehyde polymer polyoxymethylene (POM) have recently been proposed as the dominant complex molecules in the coma of Comet Halley; however, POM alone cannot account for all of the features of the high resolution spectrum. An important component of the dust at Comet Halley is particles highly enriched in carbon, hydrogen, oxygen, and nitrogen relative to the composition of carbonaceous chondrites. Since this dust could be a source for the heavy molecules observed by PICCA, a search was conducted for other chemical species by determining all the molecules with mass between 20 and 120 amu which can be made from the relatively abundant C, H, O, and N, without regard to chemical structure

Video head impulse testing: Pitfalls in neurological patients

The video head impulse test (vHIT) assesses the vestibulo-ocular reflex (VOR) during a rapid high-velocity low amplitude (10°–20°) head rotation. Patients with peripheral vestibulopathy have a reduced VOR gain with corrective catch-up saccades during the head turn. There are several pitfalls, mainly technical, which may interfere with interpretation of vHIT data. In addition, intrusive eye movement disorders such as spontaneous nystagmus that affect normal eye position and tracking can affect the vHIT results. To date there has been little study of neurological saccadic eye movements that may interfere with the interpretation of vHIT data. Here, in ten patients with a range of central neurological disorders, we describe oculomotor abnormalities on vHIT in the presence of normal range VOR gain values, recorded at a tertiary vestibular neurology service

Design and fabrication of a SIO2/ST-cut quartz love mode surface acoustic wave transducer for operation in liquid media

Love mode surface acoustic wave (SAW) transducers were designed and fabricated by depositing silicon dioxide on a ST-cut quartz crystal wafer using r.f. magnetron sputtering. Two different propagation directions have been investigated by aligning the SAW finger pattern along the x-axis propagation direction and the direction orthogonal to the x-axis of the ST-cut quartz crystal. The latter, in which the propagation mode is dominantly the Love mode, shows promising characteristics for use as a high frequency SAW transducer because of high acoustic wave propagation velocity and electromechanical coupling coefficient. Phase and group velocity, capacitance per unit length of electrodes, insertion loss and input admittance, of two transducers, with different alignments, have been measured and compared