Reassessing the Source of Long-Period Comets

We present numerical simulations to model the production of observable long-period comets (LPCs) from the Oort Cloud, a vast reservoir of icy bodies surrounding the Sun. We show that inner Oort Cloud objects can penetrate Jupiter's orbit via a largely unexplored dynamical pathway, and they are an important, if not the dominant, source of known LPCs. We use this LPC production to place observationally motivated constraints on the population and mass of the inner Oort Cloud, which are consistent with giant planet formation theory. These constraints indicate that only one comet shower producing late Eocene bombardment levels has likely occurred since the Cambrian Explosion, making these phenomena an improbable cause of additional extinction events.Comment: Originally published in Science (9/4/09), 30 pages, 9 figures, main article and online material combine

The Formation of the Oort Cloud in Open Cluster Environments

We study the influence of an open cluster environment on the formation and current structure of the Oort cloud. To do this, we have run 19 different simulations of the formation of the Oort Cloud for 4.5 Gyrs. In each simulation, the solar system spends its first 100 Myrs in a different open cluster environment before transitioning to its current field environment. We find that, compared to forming in the field environment, the inner Oort Cloud is preferentially loaded with comets while the Sun resides in the open cluster and that most of this material remains locked in the interior of the cloud for the next 4.4 Gyrs. In addition, the outer Oort Cloud trapping efficiencies we observe in our simulations are lower than previous formation models by about a factor of 2, possibly implying an even more massive early planetesimal disk. Furthermore, some of our simulations reproduce the orbits of observed extended scattered disk objects, which may serve as an observational constraint on the Sun's early environment. Depending on the particular open cluster environment, the properties of the inner Oort Cloud and extended scattered disk can vary widely. On the other hand, the outer portions of the Oort Cloud in each of our simulations are all similar.Comment: 65 pages, 14 figures, 3 tables, Accepted to Icaru

Composite Fermions and the Fractional Quantum Hall Effect: Essential Role of the Pseudopotential

The mean field (MF) composite Fermion (CF) picture successfully predicts the band of low lying angular momentum multiplets of fractional quantum Hall systems for any value of the magnetic field. This success cannot be attributed to a cancellation between Coulomb and Chern--Simons interactions between fluctuations beyond the mean field. It results instead from the short range behavior of the Coulomb pseudopotential in the lowest Landau level (LL). The class of pseudopotentials for which the MFCF picture is successful can be defined, and used to explain the success or failure of the picture in different cases (e.g. excited LL's, charged magneto-excitons, and Laughlin quasiparticles in a CF hierarchy picture).Comment: 4 pages, 4 figures (RevTeX+epsf); talk at EP2DS-XII

New safety model for the commercial human spaceflight industry

The aviation and space domains have safety guidelines and recommended practices for Design Organisations (DOs) and Operators alike. In terms of Aerospace DOs there are certification criteria to meet and to demonstrate compliance there are Advisory Circulars or Acceptable Means of Compliance to follow. Additionally there are guidelines such as Aerospace Recommended Practices (ARP), Military Standards (MIL-STD 882 series) and System Safety Handbooks to follow in order to identify and manage failure conditions. In terms of Operators there are FAA guidelines and a useful ARP that details many tools and techniques in understanding Operator Safety Risks. However there is currently no methodology for linking the DO and Operator safety efforts. In the space domain NASA have provided safety standards and guidelines to follow and also within Europe there are European Co-operation of Space Standardization (ECSS) to follow. Within the emerging Commercial Human Spaceflight Industry, the FAA’s Office of Commercial Space Transportation has provided hazard analysis guidelines. However all of these space domain safety documents are based on the existing aerospace methodology and once again, there is no link between the DO and Operator’s safety effort. This paper addresses the problematic issue and presents a coherent methodology of joining up the System Safety effort of the DOs to the Operator Safety Risk Management such that a ‘Total System’ approach is adopted. Part of the rationale is that the correct mitigation (control) can be applied within the correct place in the accident sequence. Also this contiguous approach ensures that the Operator is fully aware of the safety risks (at the accident level) and therefore has an appreciation of the Total System Risk. The authors of this paper contend that it is better practice to have a fully integrated safety model as opposed to disparate requirements or guidelines. Our methodology is firstly to review ‘best practice’ approaches from the aviation and space industries, and then to integrate these approaches into a contiguous safety model for the commercial human spaceflight industry

What contributes to depression in Parkinson's disease?

Background: Depression is a common problem in patients with Parkinson's disease, but its mechanism is poorly understood. It is thought that neurochemical changes contribute to its occurrence, but it is unclear why some patients develop depression and others do not. Using a community-based sample of patients with Parkinson's disease, we investigated the contributions of impairment, disability and handicap to depression in Parkinson's disease. Methods: Ninety-seven patients seen in a population-based study on the prevalence of Parkinson's disease completed the Beck Depression Inventory (BDI). Clinical and historical information on symptoms and complications of Parkinson's disease were obtained from the patients by a neurologist. In addition, clinician and patient ratings of disability on the Schwab and England scale were obtained and a quality of life questionnaire was completed. Results: Moderate to severe depression (BDI [gt-or-equal, slanted] 18) was reported by 19·6% of the patients. Higher depression scores were associated with advancing disease severity, recent self-reported deterioration, higher akinesia scores, a mini-mental score of 50% of the variance of depression scores. Conclusions: Depression in patients with Parkinson's disease is associated with advancing disease severity, recent disease deterioration and occurrence of falls. Regression analysis suggests that depression in Parkinson's disease is more strongly influenced by the patients' perceptions of handicap than by actual disability. The treatment of depression should therefore be targeted independently of treatment of the motor symptoms of Parkinson's disease, and consider the patients' own perception of their disease

Making space for proactive adaptation of rapidly changing coasts: a windows of opportunity approach

Coastlines are very often places where the impacts of global change are felt most keenly, and they are also often sites of high values and intense use for industry, human habitation, nature conservation and recreation. In many countries, coastlines are a key contested territory for planning for climate change, and also locations where development and conservation conflicts play out. As a “test bed” for climate change adaptation, coastal regions provide valuable, but highly diverse experiences and lessons. This paper sets out to explore the lessons of coastal planning and development for the implementation of proactive adaptation, and the possibility to move from adaptation visions to actual adaptation governance and planning. Using qualitative analysis of interviews and workshops, we first examine what the barriers are to proactive adaptation at the coast, and how current policy and practice frames are leading to avoidable lock-ins and other maladaptive decisions that are narrowing our adaptation options. Using examples from UK, we then identify adaptation windows that can be opened, reframed or transformed to set the course for proactive adaptation which links high level top-down legislative requirements with local bottom-up actions. We explore how these windows can be harnessed so that space for proactive adaptation increases and maladaptive decisions are reduced