Multiwavelength operation of erbium-doped fiber lasers by periodic filtering and phase modulation

This paper explains the principles behind multiwavelength operation of an erbium-doped fiber laser (EDFL) under the combined effect of cavity phase modulation and periodic wavelength filtering. A mathematical model is developed to simulate the behaviour of the multiwavelength EDFL, both in time and frequency domains. The effects of various parameters such as pump power, filter channel spacing, modulation index and frequency are observed and explained. An all-fiber EDFL was constructed, using a piezo-transducer-based phase modulator and a Sagnac loop periodic filter, to validate the theoretical results. The effects of pump power, modulation frequency and modulation index were monitored experimentally, justifying the theoretical explanation. The multiwavelength EDFL has several potential applications in fiber sensing due to its flexible all-fiber design

Assemblage of buried and seabed tunnel valleys in the central North Sea: from morphology to ice-sheet dynamics

Tunnel valleys are kilometre-scale, channel-like, incised subglacial landforms usually associated with glaciated lowlands (Ó Cofaigh 1996). Tunnel valleys related to the Pleistocene glaciations are present onshore and offshore of NW Europe (e.g. Huuse & Lykke-Andersen 2000; Van der Vegt et al. 2012). In the central North Sea, tunnel valleys are found buried in the Quaternary succession and as bathymetric deeps at the seabed. Three-dimensional (3D) seismic data from the central North Sea image extensive networks of buried tunnel valleys that consist of multiple generations of cross-cutting landforms (Stewart et al. 2013). Seabed tunnel valleys are identified in high-resolution bathymetric data, and form another set of younger glacial landforms. Morphological measurements of the buried and seabed tunnel valleys are compared to infer their relationship to past ice-margins and highlight the differences in ice-sheet configuration over time

The suitability of N2 to replace SF6 in a triggered spark-gap switch for pulsed power applications

The high dielectric strength of sulphur hexafluoride (SF6) when compared with other gases, coupled with safety benefits such as non-flammability and non-toxicity, has seen the widespread use of SF6 for the insulation of switching components. However, SF6 is now widely recognised as a highly damaging greenhouse gas, and investigations of the switching properties of alternative gases to replace SF6 within the bounds of existing system topologies are required. In the present paper, a comparative study has been carried out on a triggered spark-gap of type presently deployed in industrial pulsed-power machines, to determine the suitability of nitrogen (N2) to replace SF6 as the switching medium, without compromising on functionality. Experiments were performed with fast-rising trigger pulses to minimise the delay time to breakdown and jitter, and three distinct operational regimes have been identified for both gases as the pressure inside the switch is increased. The static breakdown characteristics and upper pressure boundaries of operation have been determined for both gases at a range of dc charging voltages. Measurements of the time to breakdown have shown jitters as low as 1.3 ns when operating in N2, highlighting the potential of N2 to replace SF6 without the need for re-design or replacement of the presently used switch

"And one lucky bastard who’s the artist" : V. I. Lenin and Oscar Wilde's ideologico-aesthetic debate in Tom Stoppard's Travesties

textTom Stoppard's play Travesties was revised considerably between its first edition of 1975 and the new edition of 1994, with the parts pertaining to V. I. Lenin and Marxism bearing the brunt of the cuts. The political fall of Marxism is not sufficient to account for these cuts since the play occurs in 1974 via the erratic memory of Henry Carr, a minor official at the British consulate in Zurich in 1917. The published textual history of Travesties is also insufficient to account for Lenin's diminishment. The archive of the play's composition at the Harry Ransom Center at the University of Texas at Austin provides a more detailed history of the play's debate over whether or not an artist can also be a revolutionary, suggesting that the debate can be reduced to two sides, one representing the subversive wit of Oscar Wilde via the intertext The Importance of Being Earnest and the other Leninist-Marxist functional-revolutionary aesthetics. The genius of Wilde functions like an ideologico-aesthetic edifice, manipulating the action to maintain its hegemonic position via theatrical devices in three main ways. Joyce, Tzara, and Carr are pitted against each other in order to split the Wildean aesthetic that makes a claim to the inextricable linkage of freedom and subversion in a sort of aesthetic Bunburyism, which displaces the terms of the debate from an ontology of the artist to the ethics of art. The 'time slip' device simultaneously lets us enjoy and neutralizes the obscene underside of Wildean subversive wit by allowing the play to go "off the rails" (12) and quickly rebound to a state of normalcy. These previous two features represent an effort to demonize Lenin by denying the subversive creativity he shows in the pursuit of his goals. Travesties, in its valorization of detached subversive wit, answers the question of whether an artist can simultaneously be a revolutionary with a dizzying 'no.'Englis

Modular Cosmology, Thermal Inflation, Baryogenesis and Predictions for Particle Accelerators

Modular cosmology is plagued by overproduction of unwanted relics, gravitinos and especially moduli, at relatively low energy scales. Thermal inflation provides a compelling solution to this moduli problem, but invalidates most baryogenesis scenarios. We propose a simple model in which the MSSM plus neutrino mass term $(LH_u)^2$ is supplemented by a minimal flaton sector to drive the thermal inflation, and make two crucial assumptions: the flaton vacuum expectation value generates the $\mu$-term of the MSSM and $m_L^2 + m_{H_u}^2 < 0$. The second assumption is particularly interesting in that it violates a well known constraint, implying that there exists a nearby deep non-MSSM vacuum, and provides a clear signature of our model which can be tested at future particle accelerators. We show that our model leads to thermal inflation followed by Affleck-Dine leptogenensis along the $LH_u$ flat direction. A key feature of our leptogenesis scenario is that the $H_uH_d$ flat direction is also induced to temporarily acquire a large value, playing a crucial role in the leptogenesis, as well as dynamically shielding the field configuration from the deep non-MSSM minimum, ensuring that the fields relax into our MSSM vacuum.Comment: v3; 19 pages, 3 figures; added a reference for section

Multiband superconductivity in NbSe_2 from heat transport

The thermal conductivity of the layered s-wave superconductor NbSe_2 was measured down to T_c/100 throughout the vortex state. With increasing field, we identify two regimes: one with localized states at fields very near H_c1 and one with highly delocalized quasiparticle excitations at higher fields. The two associated length scales are most naturally explained as multi-band superconductivity, with distinct small and large superconducting gaps on different sheets of the Fermi surface.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding

A summary of the methodology for the seismic stratigraphic interpretation for the 'GlaciStore' bid to IODP

This report summarises the methodology followed for the seismic interpretation of sedimentary strata that are the overburden sequence and the Palaeogene strata that are prospective CO2 storage formations, in the UK Central North Sea. The interpretation of selected 2D and 3D seismic reflection, well and borehole data in the UK North and Central North Sea is targeted to inform the preparation of the ‘GlaciStore’ proposal for scientific drilling submitted to the International Ocean Discovery Programme (IODP). Drilling sites proposed to IODP lie within the UK and Norwegian sectors of the North Sea. The methodology is described for the interpretation of seismic data for proposed sites within UK waters. The seismic interpretation was undertaken in collaboration with Norwegian members of the GlaciStore consortium. The seismic interpretation was divided into two teams according to depth, into ‘shallower and ‘deeper’ seismic interpretation activities, appropriate to the fields of expertise and experience of the interpreters. The ‘shallower seismic’ interpreters considered strata of latest Neogene and Quaternary age which were deposited during major glacial and interglacial cycles. The ‘deeper seismic’ interpreters considered slightly older strata of Mid Eocene to Quaternary in age. Seven potential UK drill sites were selected to address the scientific objectives in the proposal. 2D and 3D seismic, well, borehole and bathymetry data were used to map buried and open tunnel valleys and to identify any evidence for the presence of shallow gas in the ‘shallower seismic’ interpretation at each drill site. Only sites without any indication of shallow gas features were considered as these pose a serious hazard for drilling. 2D and 3D seismic and well datasets and existing interpretations were collated for the ‘deeper seismic’ interpretation. The hydrocarbon exploration well log data, which were found to be of variable quality, were used to identify and map a number of stratigraphical surfaces of Cenozoic age, and included Quaternary strata, around the grid of seismic lines. Maps from some of the key stratigraphical surfaces are presented, selected to inform the drilling proposal. A plot of acoustic velocity data was prepared to inform future conversion of the seismic interpretation to true vertical depth. Future work, based on the seismic interpretation undertaken to underpin the drilling proposal, is identified. Features observed within the ‘shallower’ and ‘deeper’ seismic interpretations that warrant further investigation are: a chaotic zone within the Quaternary sequence; prograding units within the Eocene Horda Formation; basin centre sandstone bodies as prospective CO2 storage strata within the Horda Formation; systematic mapping of cross-cutting, buried tunnel valleys in the Quaternary sequence from 3D seismic data

Purifying and Reversible Physical Processes

Starting from the observation that reversible processes cannot increase the purity of any input state, we study deterministic physical processes, which map a set of states to a set of pure states. Such a process must map any state to the same pure output, if purity is demanded for the input set of all states. But otherwise, when the input set is restricted, it is possible to find non-trivial purifying processes. For the most restricted case of only two input states, we completely characterize the output of any such map. We furthermore consider maps, which combine the property of purity and reversibility on a set of states, and we derive necessary and sufficient conditions on sets, which permit such processes.Comment: 5 pages, no figures, v2: only minimal change

Controls on the location of compressional deformation on the NW European margin

The distribution of Cenozoic compressional structures along the NW European margin has been compared with maps of the thickness of the crystalline crust derived from a compilation of seismic refraction interpretations and gravity modelling, and with the distribution of high-velocity lower crust and/or partially serpentinized upper mantle detected by seismic experiments. Only a subset of the mapped compressional structures coincide with areas susceptible to lithospheric weakening as a result of crustal hyperextension and partial serpentinization of the upper mantle. Notably, partially serpentinized upper mantle is well documented beneath the central part of the southern Rockall Basin, but compressional features are sparse in that area. Where compressional structures have formed but the upper mantle is not serpentinized, simple rheological modelling suggests an alternative weakening mechanism involving ductile lower crust and lithospheric decoupling. The presence of pre-existing weak zones (associated with the properties of the gouge and overpressure in fault zones) and local stress magnitude and orientation are important contributing factors