Model for resonant photon creation in a cavity with time dependent conductivity

In an electromagnetic cavity, photons can be created from the vacuum state by changing the cavity's properties with time. Using a simple model based on a massless scalar field, we analyze resonant photon creation induced by the time-dependent conductivity of a thin semiconductor film contained in the cavity. This time dependence may be achieved by irradiating periodically the film with short laser pulses. This setup offers several experimental advantages over the case of moving mirrors.Comment: 9 pages, 1 figure. Minor changes. Version to appear in Phys. Rev.

Encounter and its configurational logic: Understanding spatiotemporal co-presence with road network and social media check-in data

Public space facilitates the social interaction between people. It is widely accepted that the connection between spaces creates the possibility of the mutual visibility between people. The relationship between spatial configuration and the spatiotemporal encounters, however, has rarely been investigated explicitly in empirical cases. The focus of this study is two folded: firstly, it examines the way to measure spatiotemporal encounters between different groups of people based on their mobility records; secondly, it investigates how the design of the built environment contributes to physical co-presence on spatial and temporal dimensions. Using ubiquitous individual social media check-in data in Central Shanghai, China, this study proposes a framework for quantifying physical face-to-face co-presence patterns between the defined local random walkers and the remote visitors across time in every street. In the introduced People-Space-Time (PST) model, social capital is conceptualised as an integration among social difference, spatial distance (metric and geometrical distance) and time distance. The reliability of the applied data and the effectiveness of the introduced methods are validated by the investigations of the scaling nature of the extracted mobility patterns and the correlation between the outputs and surveyed data. The produced spatiotemporal patterns of face-toface co-presence reveal that city centres and the large-scale urban complexes (e.g., transport hubs, shopping malls, stadiums, etc.) are ideal places for people to encounter. The results of the regression analyses demonstrate that spatial and functional centrality measures are significant variables for predicting spatiotemporal co-presence in streets, but in which the functional centrality structures maintain a higher standard of explanatory power than the spatial network. The temporal complexity of the co-presence is revealed by the temporally shifting performance of the integrated regression models across time. The findings in this study yield that it is the spatio-functional interaction influencing spatiotemporal variation of the physical encounter between people, and reclaim the necessity of adding fine-scale land-use patterns in the traditional configurational analysis for deeply understanding the social processes with urban big data in the contemporary digitalised cities

Energy Approach for Liquefaction of Sandy and Clayey Silts

The liquefaction potential of sandy and clayey silts is assessed in this paper using an energy approach original developed for sand. Three series of laboratory tests were conducted to examine the liquefaction resistance of clean silt, sandy silt and clayey silt. The test results have been analyzed to establish a liquefaction failure criterion for silty soils. Based on this criterion, the case records of a new database have been studied and the results suggest that a single criterion can be used for sand, silt, sandy silt and clayey silt. For sandy or silty soils without clay content, the criterion is expressed in terms of the earthquake magnitude, hypocentral distance and the corrected standard penetration resistance. For clayey silt, the same criterion and parameters can be used except the standard penetration resistance has to be modified in terms of the clay content

The economic value of spatial network accessibility for UK cities: A comparative analysis using the hedonic price approach

Spatial network accessibility was found to be significant when associating with house prices using the hedonic price approach. These results suggest some individuals are willing to pay more for spatial isolation while some individuals will pay more for spatial co-presence. An obvious limitation of earlier research is a lack of comparative analysis between cities. Focusing on a single case study reduces the generalisability of the results and the extent to which different spatial contexts might value accessibility differently. The aim of this research was therefore to study the extent to which spatial network accessibility effects differ across cities in the UK. A hedonic price approach was used to explore the extent to which these differences are related to social-economic-mobility factors. Results show, both visually and quantitatively, the economic value of accessibility, measured using space syntax analysis, differs across geographical regions. The accessibility effect on house price ranges from strongly significant in London to insignificant in Birmingham. In general, the economic effect is weaker in smaller, more car dependent cities, with a greater proportion of the population employed in the manufacturing sector, and is stronger in cities that are denser, more walkable with greater productivity and a greater proportion of residents in the education sector. This exploration therefore suggests that the economic value placed upon urban accessibility may be related to a combination of mobility factors, its urban form and its economic profile. Finally, it appears that city productivity as measured by GVA is correlated with increased value placed upon accessibility

Natural orbits of atomic Cooper pairs in a nonuniform Fermi gas

We examine the basic mode structure of atomic Cooper pairs in an inhomogeneous Fermi gas. Based on the properties of Bogoliubov quasi-particle vacuum, the single particle density matrix and the anomalous density matrix share the same set of eigenfunctions. These eigenfunctions correspond to natural pairing orbits associated with the BCS ground state. We investigate these orbits for a Fermi gas in a spherical harmonic trap, and construct the wave function of a Cooper pair in the form of Schmidt decomposition. The issue of spatial quantum entanglement between constituent atoms in a pair is addressed.Comment: 14 pages, 4 figures, submitted to Phys. Rev.

Understanding Computer Forensics Requirements in China via the “Panda Burning Incense” Virus Case

In March 2012, Mainland China has amended its Criminal Procedure Law, which includes the introduction of a new type of evidence, i.e., digital evidence, to the court of law. To better understand the development of computer forensics and digital evidence in Mainland China, this paper discusses the Chinese legal system in relation to digital investigation and how the current legal requirements affect the existing legal and technical usage of digital evidence at legal proceedings. Through studying the famous “Panda Burning Incense (Worm.WhBoy.cw)” virus case that happened in 2007, this paper aims to provide a better understanding of how to properly conduct computer forensics examination and present digital evidence at court of law in Mainland China