Unemployment Duration: Competing and Defective Risks

This paper examines the determinants of unemployment duration in a competing risks framework with two destination states: inactivity and employment. The innovation is the recognition of defective risks. A polynomial hazard function is used to differentiate between two possible sources of infinite durations. The first is produced by a random process of unlucky draws, the second by workers rejecting a destination state. The evidence favors the mover-stayer model over the search model. Refinement of the former approach, using a more flexible baseline hazard function, produces a robust and more convincing explanation for positive and zero transition rates out of unemployment.

Secure Key Generation from OFDM Subcarriers’ Channel Response

The ability to exchange keys between users is vital in any wireless based security system. A key generation technique exploits the randomness of the wireless channel is a promising alternative to existing key distribution techniques, e.g., public key cryptography. In this paper a secure key generation scheme based on the subcarriers’ channel responses in orthogonal frequencydivision multiplexing (OFDM) systems is proposed. We first implement a time-variant multipath channel with its channel impulse response modelled as a wide sense stationary (WSS) uncorrelated scattering random process and demonstrate that each subcarrier’s channel response is also a WSS random process. We then define the X% coherence time as the time required to produce an X% correlation coefficient in the autocorrelation function (ACF) of each channel tap, and find that when all the channel taps have the same Doppler power spectrum, all subcarriers’ channel responses has the same ACF as the channel taps. The subcarrier’s channel response is then sampled every X% coherence time and quantized into key bits. All the key sequences’ randomness is tested using National Institute of Standards and Technology (NIST) statistical test suite and the results indicate that the commonly used sampling interval as 50% coherence time cannot guarantee the randomness of the key sequence.

Secure key generation from OFDM subcarriers' channel responses

The ability to exchange keys between users is vital in any wireless based security system. A key generation technique which exploits the randomness of the wireless channel is a promising alternative to existing key distribution techniques, e.g., public key cryptography. In this paper, a secure key generation scheme based on the subcarriers' channel responses in orthogonal frequency-division multiplexing (OFDM) systems is proposed. We first implement a time-variant multipath channel with its channel impulse response modelled as a wide sense stationary (WSS) uncorrelated scattering random process and demonstrate that each subcarrier's channel response is also a WSS random process. We then define the X% coherence time as the time required to produce an X% correlation coefficient in the autocorrelation function (ACF) of each channel tap, and find that when all the channel taps have the same Doppler power spectrum, all subcarriers' channel responses has the same ACF as the channel taps. The subcarrier's channel response is then sampled every X% coherence time and quantized into key bits. All the key sequences' randomness is tested using National Institute of Standards and Technology (NIST) statistical test suite and the results indicate that the commonly used sampling interval as 50% coherence time cannot guarantee the randomness of the key sequence.

Verification of Key Generation from Individual OFDM Subcarrier's Channel Response

This paper presents a key generation system derived from the channel response of individual subcarrier in orthogonal frequency-division multiplexing (OFDM) systems. Practical aspects of the security were investigated by implementing our key generation scheme on a wireless open-access research platform (WARP), which enables us to obtain channel estimation of individual OFDM subcarriers, a feature not currently available in most commercial wireless interface cards. Channel response of individual OFDM subcarrier is usually a wide sense stationary random process, which allows us to find the optimal probing period and maximize the key generation rate. The implementation requires cross layer design as it involves interaction between physical and MAC layer. We have experimentally verified the feasibility and principles of key generation, and also evaluated the performance of our system in terms of randomness, key generation rate and key disagreement rate, which proves that OFDM subcarrier's channel responses are valid for key generation.

An invasive-native mammalian species replacement process captured by camera trap survey random encounter models

Camera traps are used to estimate densities or abundances using capture-recapture and, more recently, random encounter models (REMs). We deploy REMs to describe an invasive-native species replacement process, and to demonstrate their wider application beyond abundance estimation. The Irish hare Lepus timidus hibernicus is a high priority endemic of conservation concern. It is threatened by an expanding population of non-native, European hares L. europaeus, an invasive species of global importance. Camera traps were deployed in thirteen 1 km squares, wherein the ratio of invader to native densities were corroborated by night-driven line transect distance sampling throughout the study area of 1652 km2. Spatial patterns of invasive and native densities between the invader’s core and peripheral ranges, and native allopatry, were comparable between methods. Native densities in the peripheral range were comparable to those in native allopatry using REM, or marginally depressed using Distance Sampling. Numbers of the invader were substantially higher than the native in the core range, irrespective of method, with a 5:1 invader-to-native ratio indicating species replacement. We also describe a post hoc optimization protocol for REM which will inform subsequent (re-)surveys, allowing survey effort (camera hours) to be reduced by up to 57% without compromising the width of confidence intervals associated with density estimates. This approach will form the basis of a more cost-effective means of surveillance and monitoring for both the endemic and invasive species. The European hare undoubtedly represents a significant threat to the endemic Irish hare.

Green function for the diffusion limit of one-dimensional continuous time random walks

It is shown how the fractional probability density diffusion equation for the diffusion limit of one-dimensional continuous time random walks may be derived from a generalized Markovian Chapman-Kolmogorov equation. The non-Markovian behaviour is incorporated into the Markovian Chapman-Kolmogorov equation by postulating a Levy like distribution of waiting times as a kernel. The Chapman-Kolmogorov equation so generalised then takes on the form of a convolution integral. The dependence on the initial conditions typical of a non-Markovian process is treated by adding a time dependent term involving the survival probability to the convolution integral. In the diffusion limit these two assumptions about the past history of the process are sufficient to reproduce anomalous diffusion and relaxation behaviour of the Cole-Cole type. The Green function in the diffusion limit is calculated using the fact that the characteristic function is the Mittag-Leffler function. Fourier inversion of the characteristic function yields the Green function in terms of a Wright function. The moments of the distribution function are evaluated from the Mittag-Leffler function using the properties of characteristic functions and a relation between the powers of the second moment and higher order even moments is derived. (C) 2004 Elsevier B.V. All rights reserved.

Liquid source misted chemical deposition process of three-dimensional nano-ferroelectrics with substrate heating

A modification of liquid source misted chemical deposition process (LSMCD) with heating mist and substrate has developed, and this enabled to control mist penetrability and fluidity on sidewalls of three-dimensional structures and ensure step coverage. A modified LSMCD process allowed a combinatorial approach of Pb(Zr,Ti)O-3 (PZT) thin films and carbon nanotubes (CNTs) toward ultrahigh integration density of ferroelectric random access memories (FeRAMs). The CNTs templates were survived during the crystallization process of deposited PZT film onto CNTs annealed at 650 degrees C in oxygen ambient due to a matter of minute process, so that the thermal budget is quite small. The modified LSMCD process opens up the possibility to realize the nanoscale capacitor structure of ferroelectric PZT film with CNTs electrodes toward ultrahigh integration density FeRAMs.

Structural change in multipartite entanglement sharing: A random matrix approach

We study the typical entanglement properties of a system comprising two independent qubit environments interacting via a shuttling ancilla. The initial preparation of the environments is modeled using random matrix techniques. The entanglement measure used in our study is then averaged over many histories of randomly prepared environmental states. Under a Heisenberg interaction model, the average entanglement between the ancilla and one of the environments remains constant, regardless of the preparation of the latter and the details of the interaction. We also show that, upon suitable kinematic and dynamical changes in the ancillaenvironment subsystems, the entanglement-sharing structure undergoes abrupt modifications associated with a change in the multipartite entanglement class of the overall system's state. These results are invariant with respect to the randomized initial state of the environments.

Random particle motion in magnetized plasma

A multivariate Fokker-Planck-type kinetic equation modeling a test - panicle weakly interacting with an electrostatic plasma. in the presence of a magnetic field B . is analytically solved in an Ornstein - Uhlenbeck - type approximation. A new set of analytic expressions are obtained for variable moments and panicle density as a function of time. The process is diffusive.

Outcomes and process in reading tutoring

Background: Large-scale randomised controlled trials are relatively rare in education. The present study approximates to, but is not exactly, a randomised controlled trial. It was an attempt to scale up previous small peer tutoring projects, while investing only modestly in continuing professional development for teachers.Purpose: A two-year study of peer tutoring in reading was undertaken in one local education authority in Scotland. The relative effectiveness of cross-age versus same-age tutoring, light versus intensive intervention, and reading versus reading and mathematics tutoring were investigated.Programme description (if relevant): The intervention was Paired Reading, a freely available cross-ability tutoring method applied to books of the pupils' choice but above the tutee's independent readability level. It involves Reading Together and Reading Alone, and switching from one to the other according to need.Sample: Eighty-seven primary schools of overall average socio-economic status, ability and gender in one council in Scotland. There were few ethnic minority students. Proportions of students with special needs were low. Children were eight and 10 years old as the intervention started. Macro-evaluation n = 3520. Micro-evaluation Year 1 15 schools n = 592, Year 2 a different 15 schools n = 591, compared with a comparison group of five schools n = 240.Design and methods: Almost all the primary schools in the local authority participated and were randomly allocated to condition. A macro-evaluation tested and retested over a two-year period using Performance Indicators in Primary Schools. A micro-evaluation tested and retested within each year using norm-referenced tests of reading comprehension. Macro-evaluation was with multi-level modelling, micro-evaluation with descriptive statistics and effect sizes, analysis of variance (ANOVA) and multivariate analysis of variance (MANOVA).Results: Macro-evaluation yielded significant pre-post gains in reading attainment for cross-age tutoring over both years. No other differences were significant. Micro-evaluation yielded pre-post changes in Year 1 (selected) and Year 2 (random) greater than controls, with no difference between same-age and cross-age tutoring. Light and intensive tutoring were equally effective. Tutoring reading and mathematics together was more effective than only tutoring reading. Lower socio-economic and lower reading ability students did better. Girls did better than boys. Regarding observed implementation quality, some factors were high and others low. Few implementation variables correlated with attainment gain.Conclusions: Paired Reading tutoring does lead to better reading attainment compared with students not participating. This is true in the long term (macro-evaluation) for cross-age tutoring, and in the short term (micro-evaluation) for both cross-age and same-age tutoring. Tutors and tutees benefited. Intensity had no effect but dual tutoring did have an effect. Low-socio-economic status, low-ability and female students did better. The results of the different forms of evaluation were indeed different. There are implications for practice and for future research. © 2012 Copyright Taylor and Francis Group, LLC.