A population study of type II bursts in the Rapid Burster

Type II bursts are thought to arise from instabilities in the accretion flow onto a neutron star in an X-ray binary. Despite having been known for almost 40 years, no model can yet satisfactorily account for all their properties. To shed light on the nature of this phenomenon and provide a reference for future theoretical work, we study the entire sample of Rossi X-ray Timing Explorer data of type II bursts from the Rapid Burster (MXB 1730-335). We find that type II bursts are Eddington-limited in flux, that a larger amount of energy goes in the bursts than in the persistent emission, that type II bursts can be as short as 0.130 s, and that the distribution of recurrence times drops abruptly below 15-18 s. We highlight the complicated feedback between type II bursts and the NS surface thermonuclear explosions known as type I bursts, and between type II bursts and the persistent emission. We review a number of models for type II bursts. While no model can reproduce all the observed burst properties and explain the source uniqueness, models involving a gating role for the magnetic field come closest to matching the properties of our sample. The uniqueness of the source may be explained by a special combination of magnetic field strength, stellar spin period and alignment between the magnetic field and the spin axis.Comment: Accepted 2015 February 12. Received 2015 February 10; in original form 2014 December 1

Nested-grid calculations of disk-planet interaction

We study the evolution of embedded protoplanets in a protostellar disk using very high resolution nested-grid computations. This method allows us to perform global simulations of planets orbiting in disks and, at the same time, to resolve in detail the dynamics of the flow inside the Roche lobe of the planet. The primary interest of this work lies in the analysis of the gravitational torque balance acting on the planet. For this purpose we study planets of different masses, ranging from one Earth-mass up to one Jupiter-mass, assuming typical parameters of the protostellar disk. The high resolution of the method allows a precise determination of the mass flow onto the planet and the resulting torques. The obtained migration time scales are in the range from few times 10^4 years, for intermediate mass planets, to 10^6 years, for very low and high mass planets. Typical growth time scales depend strongly on the planetary mass, ranging from a few hundred years, in the case of Earth-type planets, to several ten thousand years, in the case of Jupiter-type planets

Effect of multimode entanglement on lossy optical quantum metrology

In optical interferometry multimode entanglement is often assumed to be the driving force behind quantum enhanced measurements. Recent work has shown this assumption to be false: single-mode quantum states perform just as well as their multimode entangled counterparts. We go beyond this to show that when photon losses occur, an inevitability in any realistic system, multimode entanglement is actually detrimental to obtaining quantum enhanced measurements. We specifically apply this idea to a superposition of coherent states, demonstrating that these states show a robustness to loss that allows them to significantly outperform their competitors in realistic systems. A practically viable measurement scheme is then presented that allows measurements close to the theoretical bound, even with loss. These results promote an alternate way of approaching optical quantum metrology using single-mode states that we expect to have great implications for the future

Wetting and contact-line effects for spherical and cylindrical droplets on graphene layers: A comparative molecular-dynamics investigation

In Molecular Dynamics (MD) simulations, interactions between water molecules and graphitic surfaces are often modeled as a simple Lennard-Jones potential between oxygen and carbon atoms. A possible method for tuning this parameter consists of simulating a water nanodroplet on a flat graphitic surface, measuring the equilibrium contact angle, extrapolating it to the limit of a macroscopic droplet and finally matching this quantity to experimental results. Considering recent evidence demonstrating that the contact angle of water on a graphitic plane is much higher than what was previously reported, we estimate the oxygen-carbon interaction for the recent SPC/Fwwater model. Results indicate a value of about 0.2 kJ/mol, much lower than previous estimations. We then perform simulations of cylindrical water filaments on graphitic surfaces, in order to compare and correlate contact angles resulting from these two different systems. Results suggest that modified Young's equation does not describe the relation between contact angle and drop size in the case of extremely small systems and that contributions different from the one deriving from contact line tension should be taken into account.Comment: To be published on Physical Review E (http://pre.aps.org/

The changing Chinese community in London: new migration, new needs.

London’s Chinese population in London is one of the most rapidly growing of any national group and is becoming increasingly diverse as new forms of migration develop and people arrive from regions of China which have previously seen little emigration. These developments are a product of political and economic changes in both China and in Britain. The ending of restrictions on travel within China and its growing participation in the global economy have opened up new opportunities for internal and international migration. These new migrants include the most privileged - students, the highly skilled with established jobs in London - as well as those for whom China’s transformation to a market economy has meant dispossession and loss of livelihood. Many have been forced to emigrate for survival, often leaving family in China. Britain, with other European countries, has become increasingly dependent on migrant labour but immigration policies are increasingly selective, welcoming those with recognised skills while restricting entry to those deemed unskilled. Many of the new thus migrants find themselves forced to rely on ‘agents’ to enter the country and their insecure status means they have limited rights once they have arrived and are vulnerable to exploitation. The deaths of 20 Chinese cockle pickers in Morecambe Bay in 2004 drew attention to the ‘hidden’ population of new Chinese migrants. Many new migrants prosper and are able to take advantage of the opportunities which migration brings, but others, especially those with insecure legal and economic status, may struggle, often over a protracted period, to gain a foothold in British society. They may speak little English, have limited knowledge of British society and are poorly prepared to settle and find adequate work. They need support in order to access services, but many have little information about how to go about this and limited social networks to help them. Most of the established Chinese population in London migrated to Britain from Hong Kong and speak Cantonese, unlike the predominantly Mandarin-speaking new migrants. They have established a range of community, business and cultural organisations but these mainly cater for earlier generations. Some have struggled to respond to the new needs which these new migrants bring, but they often lack the necessary knowledge, language and resources. This report is based on research which focused on the experiences of this new population and ways in which service providers could support them in order to promote their inclusion. Although we focus on new migrants, we acknowledge that there is widespread poverty, exclusion and isolation among older generations of Chinese people, particularly as they reach retirement age. The research included all those identifying their ethnic origin as Chinese, including people from Hong Kong, Taiwan, Thailand and Vietnam. The majority of participants, however, came from mainland China. The study was based in London which has the largest and most diverse Chinese population in Britain and many Chinese organisations. We hope, however, that its findings and recommendations will also be relevant to the Chinese population across Britain. The research was carried out by researchers based at Middlesex University and working with Chinese community organisations in London. We are grateful to the Big Lottery Fund for their financial support and to the School of Health and Social Science at Middlesex University whose contribution ensured that the project was completed. We also wish to thank the informants from Chinese community organisations and the individuals interviewed for the research who have contributed generously with their time and ideas

Current status of laboratory and imaging diagnosis of neonatal necrotizing enterocolitis

Necrotizing enterocolitis continues to be a devastating disease process for very low birth weight infants in Neonatal Intensive Care Units. The aetiology and pathogenesis of necrotizing enterocolitis are not definitively understood. It is known that necrotizing enterocolitis is secondary to a complex interaction of multiple factors that results in mucosal damage, which leads to intestinal ischemia and necrosis. Advances in neonatal care, including resuscitation and ventilation support technology, have seen increased survival rates among premature neonates and a concomitant detection in the incidence of this intestinal disease.Diagnosis can be difficult, and identifying infants at the onset of disease remains a challenge. Early diagnosis, which relies on imaging findings, and initiation of prompt therapy are essential to limit morbidity and mortality. Moreover, early management is critical and life-saving.This review summarizes what is known on the laboratory and instrumental diagnostic strategies needed to improve neonatal outcomes and, possibily, to prevent the onset of an overt necrotizing enterocolitis