On the Collapsar Model of Long Gamma-Ray Bursts: Constraints from Cosmic Metallicity Evolution

We explore the consequences of new observational and theoretical evidence that long gamma-ray bursts prefer low metallicity environments. Using recently derived mass-metallicity correlations and the mass function from SDSS studies, and adopting an average cosmic metallicity evolution from \citet{kewley2005} and \citet{savaglio2005} we derive expressions for the the relative number of massive stars formed below a given fraction of solar metallicity, $\epsilon$, as function of redshift. We demonstrate that about 1/10th of all stars form with $\epsilon < 0.1$. Therefore, a picture where the majority of GRBs form with $\epsilon < 0.1$ is not inconsistent with an empirical global SN/GRB ratio of 1/1000. It implies that (1) GRB's peak at a significantly higher redshift than supernovae; (2) massive star evolution at low metallicity may be qualitatively different and; (3) the larger the low-metallicity bias of GRBs the less likely binary evolution channels can be significant GRB producers.Comment: 12 pages, 2 figures; accepted as ApJ Lette

The Strong Levinson Theorem for the Dirac Equation

We consider the Dirac equation in one space dimension in the presence of a symmetric potential well. We connect the scattering phase shifts at E=+m and E=-m to the number of states that have left the positive energy continuum or joined the negative energy continuum respectively as the potential is turned on from zero.Comment: Submitted to Physical Review Letter

Hot Spots on the Fermi Surface of Bi2212: Stripes versus Superstructure

In a recent paper Saini et al. have reported evidence for a pseudogap around (pi,0) at room temperature in the optimally doped superconductor Bi2212. This result is in contradiction with previous ARPES measurements. Furthermore they observed at certain points on the Fermi surface hot spots of high spectral intensity which they relate to the existence of stripes in the CuO planes. They also claim to have identified a new electronic band along Gamma-M1 whose one dimensional character provides further evidence for stripes. We demonstrate in this Comment that all the measured features can be simply understood by correctly considering the superstructure (umklapp) and shadow bands which occur in Bi2212.Comment: 1 page, revtex, 1 encapsulated postscript figure (color

Examining the Human Security Challenges Emanating from the Weaponisation of Women. A Case study of Boko Haram and the Islamic State 2001-2018

The post-cold war period has witnessed an evolution in the nature of conflict from the new wars of the 1990s to asymmetric conflicts involving the weaponisation of civilians. This has achieved the twin objective of operating within the ranks of the combatants (in the case of women) as wives and child-bearers of the fighters, and inflicting harm on adversaries through suicide attacks. The weaponisation of women in the case of the wars in Syria and Nigeria has therefore elicited both human security challenges for the communities being targeted, and for the weaponised women. The biggest dilemma facing states of origin has been whether to accept the weaponised women’s return and rehabilitate them or declare them stateless. There has been a clear tendency to securitise them, especially when internal political dynamics are factored in. This qualitative study uses a case study approach to delve into the human security challenges emanating from the weaponisation of women in the case of Boko Haram and the Islamic State between 2001 and 2018. The paper further relies on content analysis to delve deeper into the discourse on human security. Through the use of a human security conceptual framework and securitisation theory, the paper argues that although once weaponised, some women become human security threats to targeted communities, and also face human security challenges during and after the insurgency, there is a need to deal with the women on a case-by-case basis rather than pursuing a blanket policy of securitising them. States need to work with international organisations to action processes aimed at delivering justice, demobilisation, rehabilitation, and the reintegration of these women. This will uphold international law and respect for human rights.El período posterior a la guerra fría ha sido testigo de una evolución en la naturaleza de los conflictos, desde las nuevas guerras de los años noventa hasta los conflictos asimétricos que implican la militarización de los civiles. Con ello se ha logrado el doble objetivo de operar dentro de las filas de los combatientes (en el caso de las mujeres) como esposas e hijas de los combatientes, e infligir daño a los adversarios mediante ataques suicidas. Por consiguiente, la militarización de las mujeres en el caso de las guerras de Siria y Nigeria ha suscitado tanto problemas de seguridad humana para las comunidades contra las que se dirigen los ataques como para las mujeres armadas. El mayor dilema al que se han enfrentado los Estados de origen ha sido si aceptar el regreso de las mujeres armadas y rehabilitarlas o declararlas apátridas. Ha habido una clara tendencia a la «securitización » especialmente cuando se tiene en cuenta la dinámica política interna. Este estudio cualitativo utiliza un enfoque de estudio de casos para ahondar en los desafíos de seguridad humana que se derivan de la militarización de las mujeres en el caso de Boko Haram y el Estado Islámico entre 2001 y 2018. El documento se basa además en un análisis de contenido para profundizar en el discurso sobre la seguridad humana. Mediante el uso de un marco conceptual de seguridad humana y la teoría de la securitización, el documento sostiene que, aunque una vez convertidas en armas, algunas mujeres se convierten en amenazas para la seguridad humana de las comunidades objetivo, y también se enfrentan a desafíos de seguridad humana durante y después de la insurgencia, es necesario tratar con las mujeres caso por caso en lugar de seguir una política general de securitización. Los Estados deben colaborar con las organizaciones internacionales en los procesos de acción encaminados a impartir justicia, desmovilizar, rehabilitar y reintegrar a esas mujeres. De esta manera se respetará el derecho internacional y el respeto de los derechos humanos

Two controversies in classical electromagnetism

This paper examines two controversies arising within classical electromagnetism which are relevant to the optical trapping and micromanipulation community. First is the Abraham-Minkowski controversy, a debate relating to the form of the electromagnetic energy momentum tensor in dielectric materials, with implications for the momentum of a photon in dielectric media. A wide range of alternatives exist, and experiments are frequently proposed to attempt to discriminate between them. We explain the resolution of this controversy and show that regardless of the electromagnetic energy momentum tensor chosen, when material disturbances are also taken into account the predicted behaviour will always be the same. The second controversy, known as the plane wave angular momentum paradox, relates to the distribution of angular momentum within an electromagnetic wave. The two competing formulations are reviewed, and an experiment is discussed which is capable of distinguishing between the two

Physical dependencies in accident sequence analysis

Includes bibliographical references (leaves 25-26)Supported by the Office of Nuclear Regulatory Research, United States Nuclear Regulatory Commission. NRC-04-88-14

Temperature dependent characterization of optical fibres for distributed temperature sensing in hot geothermal wells

This study was performed in order to select a proper fibre for the application of a distributed temperature sensing system within a hot geothermal well in Iceland. Commercially available high temperature graded index fibres have been tested under in-situ temperature conditions. Experiments have been performed with four different polyimide coated fibres, a fibre with an aluminum coating and a fibre with a gold coating. To select a fibre, the relationship between attenuation, temperature, and time has been analyzed together with SEM micrographs. On the basis of these experiments, polyimide fibres have been chosen for utilisation. Further tests in ambient and inert atmosphere have been conducted with two polyimide coated fibres to set an operating temperature limit for these fibres. SEM micrographs, together with coating colour changes have been used to characterize the high temperature performance of the fibres. A novel cable design has been developed, a deployment strategy has been worked out and a suitable well for deployment has been selected.Comment: PACS: 42.81.Pa, 93.85.Fg, 47.80.Fg, 91.35.Dc, 07.20.Dt, 07.60.V