Exact 1-D Model for Coherent Synchrotron Radiation with Shielding and Bunch Compression

Coherent Synchrotron Radiation has been studied effectively using a 1-dimensional model for the charge distribution in the realm of small angle approximations and high energies. Here we use Jefimenko's form of Maxwell's equations, without such approximations, to calculate the exact wake-fields due to this effect in multiple bends and drifts. It has been shown before that the influence of a drift can propagate well into a subsequent bend. We show, for reasonable parameters, that the influence of a previous bend can also propagate well into a subsequent bend, and that this is especially important at the beginning of a bend. Shielding by conducting parallel plates is simulated using the image charge method. We extend the formalism to situations with compressing and decompressing distributions, and conclude that simpler approximations to bunch compression usually overestimates the effect. Additionally, an exact formula for the coherent power radiated by a Gaussian bunch is derived by considering the coherent synchrotron radiation spectrum, and is used to check the accuracy of wake-field calculations

Deconstructing Superconductivity

We present a dimensionally deconstructed model of an s-wave holographic superconductor. The 2+1 dimensional model includes multiple charged Cooper pair fields and neutral exciton fields that have interactions governed by hidden local symmetries. We derive AdS/CFT-like relations for the current and charge density in the model, and we analyze properties of the Cooper pair condensates and the complex conductivity.Comment: 24 pages, 10 eps figures. v2: Sign conventions clarified, references adde

Extended 1D Method for Coherent Synchrotron Radiation including Shielding

Coherent Synchrotron Radiation can severely limit the performance of accelerators designed for high brightness and short bunch length. Examples include light sources based on ERLs or FELs, and bunch compressors for linear colliders. In order to better simulate Coherent Synchrotron Radiation, the established 1-dimensional formalism is extended to work at lower energies, at shorter bunch lengths, and for an arbitrary configuration of multiple bends. Wide vacuum chambers are simulated by means of vertical image charges. This formalism has been implemented in the general beam dynamics code "Bmad" and its results are here compared to analytical approximations, to numerical solutions of the Maxwell equations, and to the simulation code "elegant"

The food safety culture in a large South African food service complex: Perspectives on a case study

Published ArticleThe purpose of this paper is to assess elements of food safety management and food safety culture within a prominent South African entertainment, hotel and food service complex. Design/methodology/approach In this paper a qualitative case study approach was used. Following a comprehensive literature review, based on factors known to be important in developing a food safety culture, in combination with national and international food safety standards, an interview guide was constructed and utilised in a series of semi-structured interviews. The interviewees represented different management levels involved in food delivery but did not include board level managers. Findings Many of the factors considered important in good food safety management, including the presence of a formal food safety policy and the creation and maintenance of a positive food safety culture, were absent. Although a formal system of internal hygiene auditing existed and food safety training was provided to food handlers they were not integrated into a comprehensive approach to food safety management. Food safety leadership, communication and support were considered deficient with little motivation for staff to practise good hygiene. Originality/value Food safety culture is increasingly recognised as a contributory factor in foodborne disease outbreaks and is the focus of increasing research. However, although every food business has a unique food safety culture there are relatively few published papers concerning its analysis, application and use within specific businesses. This case study has identified food safety culture shortcomings within a large food service facility suggesting there was a potentially significant food safety risk and indicates ways in which food safety could be improved and the risk reduced. The results also suggest further work is needed in the subject of food safety culture and its potential for reducing foodborne disease

Seasonal and interannual behaviour of groundwater catchment boundaries in a Chalk aquifer

Groundwater catchment boundaries and their associated groundwater catchment areas are typically assumed to be fixed on a seasonal basis. We investigated whether this was true for a highly permeable carbonate aquifer in England, the Berkshire and Marlborough Downs Chalk aquifer, using both borehole hydrograph data and a physics-based distributed regional groundwater model. Borehole hydrograph data time series were used to construct a monthly interpolated water table surface, from which was then derived a monthly groundwater catchment boundary. Results from field data showed that the mean annual variation in groundwater catchment area was about 20% of the mean groundwater catchment area, but interannual variation can be very large, with the largest estimated catchment size being approximately 80% greater than the smallest. The flow in the river was also dependent on the groundwater catchment area. Model results corroborated those based on field data. These findings have significant implications for issues such as definition of source protection zones, recharge estimates based on water balance calculations and integrated conceptual modelling of surface water and groundwater system

Design and characterization of optical-THz phase-matched traveling-wave photomixers

Design and characterization of optical-THz phase-matched traveling-wave photomixers for difference-frequency generation of THz waves are presented. A de-biased coplanar stripline fabricated on low-temperature-grown GaAs is illuminated by two non-collinear laser beams which generate moving interference fringes that are accompanied by THz waves. By tuning the offset angle between the two laser beams, the velocity of the interference fringe can be matched to the phase velocity of the THz wave in the coplanar stripline. The generated THz waves are radiated into free space by the antenna at the termination of the stripline. Enhancement of the output power was clearly observed when the phase-matching condition was satisfied. The output power spectrum has a 3-dB bandwidth of 2 THz and rolls off as ~9 dB/Oct which is determined by the frequency dependent attenuation in the stripline, while the bandwidth of conventional photomixer design has the limitation by the RC time constant due to the electrode capacitance. The device can handle the laser power of over 380 mW, which is 5 times higher than the maximum power handring capability of conventional small area devices. The results show that the traveling-wave photomixers have the potential to surpass small area designs, especially at higher frequencies over I THz, owing to their great thermal dissipation capability and capacitance-free wide bandwidth

A traveling-wave THz photomixer based on angle-tuned phase matching

A traveling-wave THz photomixer based on a free-space optical-THz phase-matching scheme is proposed. A dc-biased coplanar strip line fabricated on low-temperature-grown GaAs serves as the active area of the device, and is illuminated by two noncollinear laser beams which generate interference fringes that are accompanied by THz waves. The device with the laser-power-handling capability over 300 mW and a 3-dB bandwidth of 1.8 THz was experimentally demonstrated. The results show that traveling-wave photomixers have the potential to surpass small-area designs

UC-408 Web Hardening

Our project focuses on ethical hacking and defending in the form of a red/blue team. Our project was broken into 3 phases. In Phase one we were given a server stack and told to do what we could in order to analyze weak points. In phase 2 we were told to bolster the defenses of those weak points. Lastly, in phase 3 were we given an IP address of an opposing team to attack while defending against another teams advances