Task Persistence: A Potential Mediator of the Income-Achievement Gap

Background: The pervasive gap in achievement among impoverished children has been investigated primarily in terms of parental investments, specifically parent to child speech and other forms of cognitive stimulation (e.g., toys, print materials). This research extends that literature by considering the role of a non-cognitive factor, namely task persistence, in the income-achievement gap. Using task persistence as the hypothesized mediator, duration of childhood in poverty is used to predict two educational variables - perceived academic competence and educational attainment. Although bivariate relationships between each of the variables have been demonstrated in past research, a full model linking task persistence with the income-achievement gap has not been investigated thus far. Methods: Using multiple waves of longitudinal data, duration of childhood poverty (ages 0-9) is used to predict both perceived academic competence (age 17) and educational attainment (age 23) with task persistence (average of ages 9, 13, 17) as a mediator. Results: With task persistence included in each model, the relationships between duration of childhood in poverty and both perceived academic competence and educational attainment are significantly reduced, confirming a mediational influence of task persistence. Conclusions: As hypothesized, task persistence statistically mediates the relationship between duration of childhood in poverty and educational outcomes. The implications of these findings on school success and intergenerational poverty are addressed, as well as suggestions for future research

Indoor radio channel characterization and modeling for a 5.2-GHz bodyworn receiver

[Abstract]: Wireless local area network applications may include the use of bodyworn or handportable terminals. For the first time, this paper compares measurements and simulations of a narrowband 5.2-GHz radio channel incorporating a fixed transmitter and a mobile bodyworn receiver. Two indoor environments were considered, an 18-m long corridor and a 42-m2 office. The modeling technique was a site-specific ray-tracing simulator incorporating the radiation pattern of the bodyworn receiver. In the corridor, the measured body-shadowing effect was 5.4 dB, while it was 15.7 dB in the office. First- and second-order small-scale fading statistics for the measured and simulated results are presented and compared with theoretical Rayleigh and lognormal distributions. The root mean square error in the cumulative distributions for the simulated results was less than 0.74% for line-of-sight conditions and less than 1.4% for nonline-of-sight conditions

Microlensing Halo Models with Abundant Brown Dwarfs

All previous attempts to understand the microlensing results towards the Large Magellanic Cloud (LMC) have assumed homogeneous present day mass functions (PDMFs) for the lensing populations. Here, we present an investigation into the microlensing characteristics of haloes with spatially varying PDMFs and anisotropic velocity dispersion tensors. One attractive possibility -- suggested by baryonic dark cluster formation in pregalactic and protogalactic cooling flows -- is that the inner halo is dominated by stellar mass objects, whereas low mass brown dwarfs become more prevalent on moving outwards. The contribution to the microlensing rate must be dominated by dark remnants (of about 0.5 solar masses) to recover the observed timescales of the microlensing experiments. But, even though stellar remnants control the rate, they do not dominate the mass of the baryonic halo, and so the well-known enrichment and mass budget problems are much less severe. Using a simple ansatz for the spatial variation of the PDMF, models are constructed in which the contribution of brown dwarfs to the mass of the baryonic halo is 55 % and to the total halo is 30 %. An unusual property of the models is that they predict that the average timescale of events towards M31 is shorter than the average timescale towards the LMC. This is because the longer line of sight towards M31 probes more of the far halo where brown dwarfs are the most common constituent.Comment: 17 pages, 1 figure, in press at The Astrophysical Journal (Letters

Propagation modelling and measurements in a populated indoor environment at 5.2 GHz

There are a number of significant radiowave propagation phenomena present in the populated indoor environment, including multipath fading and human body effects. The latter can be divided into shadowing and scattering caused by pedestrian movement, and antenna-body interaction with bodyworn or hand portable terminals [1]. Human occupants within indoor environments are not always stationary and their movement will lead to temporal channel variations that can strongly affect the quality of indoor wireless communication systems. Hence, populated environments remain a major challenge for wireless local area networks (WLAN) and other indoor communication systems. Therefore, it is important to develop an understanding of the potential and limitations of indoor radiowave propagation at key frequencies of interest, such as the 5.2 GHz band employed by commercial wireless LAN standards such as IEEE 802.11a and HiperLAN 2. Although several indoor wireless models have been proposed in the literature, these temporal variations have not yet been thoroughly investigated. Therefore, we have made an important contribution to the area by conducting a systematic study of the problem, including a propagation measurement campaign and statistical channel characterization of human body effects on line-of-sight indoor propagation at 5.2 GHz. Measurements were performed in the everyday environment of a 7.2 m wide University hallway to determine the statistical characteristics of the 5.2 GHz channel for a fixed, transverse line-of-sight (LOS) link perturbed by pedestrian movement. Data were acquired at hours of relatively high pedestrian activity, between 12.00 and 14.00. The location was chosen as a typical indoor wireless system environment that had sufficient channel variability to permit a valid statistical analysis. The paper compares the first and second order statistics of the empirical signals with the Gaussian-derived distributions commonly used in wireless communications. The analysis shows that, as the number of pedestrians within the measurement location increases, the Ricean K-factor that best fits the Cumulative Distribution Function (CDF) of the empirical data tends to decrease proportionally, ranging from K=7 with 1 pedestrian to K=0 with 4 pedestrians. These results are consistent with previous results obtained for controlled measurement scenarios using a fixed link at 5.2 GHz in [2], where the K factor reduced as the number of pedestrians within a controlled measurement area increased. Level crossing rate results were Rice distributed, considering a maximum Doppler frequency of 8.67 Hz. While average fade duration results were significantly higher than theoretically computed Rice and Rayleigh, due to the fades caused by pedestrians. A novel statistical model that accurately describes the 5.2 GHz channel in the considered indoor environment is proposed. For the first time, the received envelope CDF is explicitly described in terms of a quantitative measurement of pedestrian traffic within the indoor environment. The model provides an insight into the prediction of human body shadowing effects for indoor channels at 5.2 GHz

Role of Metastable States in Phase Ordering Dynamics

We show that the rate of separation of two phases of different densities (e.g. gas and solid) can be radically altered by the presence of a metastable intermediate phase (e.g. liquid). Within a Cahn-Hilliard theory we study the growth in one dimension of a solid droplet from a supersaturated gas. A moving interface between solid and gas phases (say) can, for sufficient (transient) supersaturation, unbind into two interfaces separated by a slab of metastable liquid phase. We investigate the criteria for unbinding, and show that it may strongly impede the growth of the solid phase.Comment: 4 pages, Latex, Revtex, epsf. Updated two reference

Numerical Evidence for Divergent Burnett Coefficients

In previous papers [Phys. Rev. A {\bf 41}, 4501 (1990), Phys. Rev. E {\bf 18}, 3178 (1993)], simple equilibrium expressions were obtained for nonlinear Burnett coefficients. A preliminary calculation of a 32 particle Lennard-Jones fluid was presented in the previous paper. Now, sufficient resources have become available to address the question of whether nonlinear Burnett coefficients are finite for soft spheres. The hard sphere case is known to have infinite nonlinear Burnett coefficients (ie a nonanalytic constitutive relation) from mode coupling theory. This paper reports a molecular dynamics caclulation of the third order nonlinear Burnett coefficient of a Lennard-Jones fluid undergoing colour flow, which indicates that this term is diverges in the thermodynamic limit.Comment: 12 pages, 9 figure

Diffusive Evolution of Stable and Metastable Phases II: Theory of Non-Equilibrium Behaviour in Colloid-Polymer Mixtures

By analytically solving some simple models of phase-ordering kinetics, we suggest a mechanism for the onset of non-equilibrium behaviour in colloid-polymer mixtures. These mixtures can function as models of atomic systems; their physics therefore impinges on many areas of thermodynamics and phase-ordering. An exact solution is found for the motion of a single, planar interface separating a growing phase of uniform high density from a supersaturated low density phase, whose diffusive depletion drives the interfacial motion. In addition, an approximate solution is found for the one-dimensional evolution of two interfaces, separated by a slab of a metastable phase at intermediate density. The theory predicts a critical supersaturation of the low-density phase, above which the two interfaces become unbound and the metastable phase grows ad infinitum. The growth of the stable phase is suppressed in this regime.Comment: 27 pages, Latex, eps

Ecosystem Approach to Small Scale Tropical Marine Fisheries

This is a 4-page brochure about a WorldFish led project. Throughout the world, poor fisheries management contributes to resource degradation, poverty, and food insecurity. This European Union project on an Ecosystem Approach to Small-scale Tropical Marine Fisheries is led by WorldFish and implemented in collaboration with national partners in Asia (Southeastern)-Indonesia; the Asia (Southeastern)-Philippines; the Solomon Islands and Tanzania. The overall objective is to use an ecosystem approach to fisheries management (EAFM) to improve governance of small-scale fisheries (SSF). The EAFM puts sustainability and equitability at the forefront of fisheries governance which enhances their contribution to poverty reduction.Specific objectives are to: 1. Assess existing institutional arrangements and identify opportunities for an EAFM to improve integrated SSF management; 2. Develop EAFM strategies and actions suitable for developing country contexts; 3. Strengthen the capacity of local fishery stakeholders and government agencies to collaborate and work within an EAFM. The project is taking a participatory and gender sensitive approach, both core philosophies of WorldFish. Representatives of all relevant stakeholder groups are involved in this action research project