Fear of the dark in children: is stationary night blindness the cause?

No abstract available

A study of the probability of depositing viable organisms on Mars during the Mariner 1964 mission

Probability of depositing viable organisms on Mars during 1964 Mariner missio

On Steering Swarms

The main contribution of this paper is a novel method allowing an external observer/controller to steer and guide swarms of identical and indistinguishable agents, in spite of the agents' lack of information on absolute location and orientation. Importantly, this is done via simple global broadcast signals, based on the observed average swarm location, with no need to send control signals to any specific agent in the swarm

Demographic growth and the distribution of language sizes

It is argued that the present log-normal distribution of language sizes is, to a large extent, a consequence of demographic dynamics within the population of speakers of each language. A two-parameter stochastic multiplicative process is proposed as a model for the population dynamics of individual languages, and applied over a period spanning the last ten centuries. The model disregards language birth and death. A straightforward fitting of the two parameters, which statistically characterize the population growth rate, predicts a distribution of language sizes in excellent agreement with empirical data. Numerical simulations, and the study of the size distribution within language families, validate the assumptions at the basis of the model.Comment: To appear in Int. J. Mod. Phys. C (2008

Cost effective flat plate photovoltaic modules using light trapping

Work in optical trapping in 'thick films' is described to form a design guide for photovoltaic engineers. A thick optical film can trap light by diffusive reflection and total internal reflection. Light can be propagated reasonably long distances compared with layer thicknesses by this technique. This makes it possible to conduct light from inter-cell and intra-cell areas now not used in photovoltaic modules onto active cell areas

Cluster analysis of midlatitude oceanic cloud regimes: mean properties and temperature sensitivity

Clouds play an important role in the climate system by reducing the amount of shortwave radiation reaching the surface and the amount of longwave radiation escaping to space. Accurate simulation of clouds in computer models remains elusive, however, pointing to a lack of understanding of the connection between large-scale dynamics and cloud properties. This study uses a k-means clustering algorithm to group 21 years of satellite cloud data over midlatitude oceans into seven clusters, and demonstrates that the cloud clusters are associated with distinct large-scale dynamical conditions. Three clusters correspond to low-level cloud regimes with different cloud fraction and cumuliform or stratiform characteristics, but all occur under large-scale descent and a relatively dry free troposphere. Three clusters correspond to vertically extensive cloud regimes with tops in the middle or upper troposphere, and they differ according to the strength of large-scale ascent and enhancement of tropospheric temperature and humidity. The final cluster is associated with a lower troposphere that is dry and an upper troposphere that is moist and experiencing weak ascent and horizontal moist advection. <br><br> Since the present balance of reflection of shortwave and absorption of longwave radiation by clouds could change as the atmosphere warms from increasing anthropogenic greenhouse gases, we must also better understand how increasing temperature modifies cloud and radiative properties. We therefore undertake an observational analysis of how midlatitude oceanic clouds change with temperature when dynamical processes are held constant (i.e., partial derivative with respect to temperature). For each of the seven cloud regimes, we examine the difference in cloud and radiative properties between warm and cold subsets. To avoid misinterpreting a cloud response to large-scale dynamical forcing as a cloud response to temperature, we require horizontal and vertical temperature advection in the warm and cold subsets to have near-median values in three layers of the troposphere. Across all of the seven clusters, we find that cloud fraction is smaller and cloud optical thickness is mostly larger for the warm subset. Cloud-top pressure is higher for the three low-level cloud regimes and lower for the cirrus regime. The net upwelling radiation flux at the top of the atmosphere is larger for the warm subset in every cluster except cirrus, and larger when averaged over all clusters. This implies that the direct response of midlatitude oceanic clouds to increasing temperature acts as a negative feedback on the climate system. Note that the cloud response to atmospheric dynamical changes produced by global warming, which we do not consider in this study, may differ, and the total cloud feedback may be positive

Mergers, Restructuring and the Boundaries of the Firm

Mergers and acquisitions are a fast way for a firm to acquire assets. Using plant-level data, we examine how firms redraw their boundaries after acquisitions. We find that there is a surprisingly substantial amount of restructuring in a short period after mergers are consummated. Acquirers sell 27 % and close 19 % of acquired plants within three years after completing an acquisition. Plants that belong to the target’s peripheral divisions, especially in industries in which asset values are increasing and in industries in which the acquirer does not have a comparative advantage, are more likely to be sold by the purchasing firm. Acquirers who exhibit skill in running their peripheral businesses tend to retain acquired plants. Plants retained by acquirers increase in productivity whereas sold plants do not. The extent of post-merger restructuring activities and their cross-sectional variation do not support an empire building explanation for mergers. Acquirers readjust their firm boundaries in ways that are consistent with the exploitation of their comparative advantage across industries

Analysis of referrals and triage patterns in a South African metropolitan adult intensive care service

Background. Intensive care unit (ICU) beds are scarce resources in low- and middle-income countries. Currently there is little literature that quantifies the extent of the demand placed on these resources or examines their allocation.Objectives. To analyse the number and nature of referrals to ICUs in the Pietermaritzburg metropolitan area, South Africa, over a 1-year period, to observe the triage process involved in selecting patients for admission.Methods. A retrospective review of the patients referred to ICUs at Grey’s and Edendale hospitals, Pietermaritzburg, was performed over a year. The spectrum of patients was evaluated with respect to various demographics, and the current triage process was observed.Results. The Pietermaritzburg Metropolitan Critical Care service (PMCCS) received 2 081 patient referrals, 53.4% (1 111/2 081) of males and 46.6% (970/2 081) of females, with a mean patient age of 32 years. The majority of referrals were of surgical patients (39.3%, 818/2 081), followed by medical (18.9%, 393/2 081), trauma (18.6%, 387/2 081) and obstetrics and gynaecology (11.7%, 244/2 081). The chief indications for referral were the need for cardiovascular and respiratory support. Of these referrals, 72.0% (1 499/2 081) were accepted and planned for admission and 28.0% (582/2 081) were refused ICU care. Of the patients accepted, 60.7% (910/1 499) experienced delays prior to admission and 37.4% (561/1 499) were never physically admitted to the units.Conclusions. The PMCCS receives a far greater number of patient referrals than it is able to accommodate, necessitating triage. Patient demographics reflect a young patient population referred with chiefly surgical pathology needing physiological support