Delayed adaptive antenna subset selection in measured wireless MIMO channels

Adaptive antenna subset selection can improve the expected theoretical capacity of a multiple-input, multiple-output (MIMO) wireless channel, whilst maintaining the tractable complexity of the lower order MIMO system. This paper seeks to explore the effects of delayed selection using measured indoor channel data at 5.2GHz, reflecting more accurately the situation facing a real-time system. Several selection schemes are considered and results show that delayed selection, while not as effective as instantaneous selection, can still improve the expected capacity by a significant margi

A collaborative approach to learning programming: a hybrid learning model

The use of cooperative working as a means of developing collaborative skills has been recognised as vital in programming education. This paper presents results obtained from preliminary work to investigate the effectiveness of Pair Programming as a collaborative learning strategy and also its value towards improving programming skills within the laboratory. The potential of Problem Based Learning as a means of further developing cooperative working skills along with problem solving skills is also examined and a hybrid model encompassing both strategies outlined

Robot navigation in dense human crowds: Statistical models and experimental studies of human–robot cooperation

We consider the problem of navigating a mobile robot through dense human crowds. We begin by exploring a fundamental impediment to classical motion planning algorithms called the “freezing robot problem”: once the environment surpasses a certain level of dynamic complexity, the planner decides that all forward paths are unsafe, and the robot freezes in place (or performs unnecessary maneuvers) to avoid collisions. We argue that this problem can be avoided if the robot anticipates human cooperation, and accordingly we develop interacting Gaussian processes, a prediction density that captures cooperative collision avoidance, and a “multiple goal” extension that models the goal-driven nature of human decision making. We validate this model with an empirical study of robot navigation in dense human crowds (488 runs), specifically testing how cooperation models effect navigation performance. The multiple goal interacting Gaussian processes algorithm performs comparably with human teleoperators in crowd densities nearing 0.8 humans/m^2, while a state-of-the-art non-cooperative planner exhibits unsafe behavior more than three times as often as the multiple goal extension, and twice as often as the basic interacting Gaussian process approach. Furthermore, a reactive planner based on the widely used dynamic window approach proves insufficient for crowd densities above 0.55 people/m^2. We also show that our non-cooperative planner or our reactive planner capture the salient characteristics of nearly any dynamic navigation algorithm. Based on these experimental results and theoretical observations, we conclude that a cooperation model is critical for safe and efficient robot navigation in dense human crowds

The Difficulty of Getting High Escape Fractions of Ionizing Photons from High-redshift Galaxies: a View from the FIRE Cosmological Simulations

We present a series of high-resolution (20-2000 Msun, 0.1-4 pc) cosmological zoom-in simulations at z~6 from the Feedback In Realistic Environment (FIRE) project. These simulations cover halo masses 10^9-10^11 Msun and rest-frame ultraviolet magnitude Muv = -9 to -19. These simulations include explicit models of the multi-phase ISM, star formation, and stellar feedback, which produce reasonable galaxy properties at z = 0-6. We post-process the snapshots with a radiative transfer code to evaluate the escape fraction (fesc) of hydrogen ionizing photons. We find that the instantaneous fesc has large time variability (0.01%-20%), while the time-averaged fesc over long time-scales generally remains ~5%, considerably lower than the estimate in many reionization models. We find no strong dependence of fesc on galaxy mass or redshift. In our simulations, the intrinsic ionizing photon budgets are dominated by stellar populations younger than 3 Myr, which tend to be buried in dense birth clouds. The escaping photons mostly come from populations between 3-10 Myr, whose birth clouds have been largely cleared by stellar feedback. However, these populations only contribute a small fraction of intrinsic ionizing photon budgets according to standard stellar population models. We show that fesc can be boosted to high values, if stellar populations older than 3 Myr produce more ionizing photons than standard stellar population models (as motivated by, e.g., models including binaries). By contrast, runaway stars with velocities suggested by observations can enhance fesc by only a small fraction. We show that "sub-grid" star formation models, which do not explicitly resolve star formation in dense clouds with n >> 1 cm^-3, will dramatically over-predict fesc.Comment: 17 pages, 16 figures, MNRAS in pres

Some mixed Hodge structure on l^2-cohomology of covering of K\"ahler manifolds

We give methods to compute l^2-cohomology groups of a covering manifolds obtained by removing pullback of a (normal crossing) divisor to a covering of a compact K\"ahler manifold. We prove that in suitable quotient categories, these groups admit natural mixed Hodge structure whose graded pieces are given by expected Gysin maps.Comment: 40 pages. This revised version will be published in Mathematische Annale

'It feels like being trapped in an abusive relationship': bullying prevalence and consequences in the New Zealand senior medical workforce: a cross-sectional study.

OBJECTIVES: To estimate prevalence of and factors contributing to bullying among senior doctors and dentists in New Zealand's public health system, to ascertain rates of reporting bullying behaviour, perceived barriers to reporting and the effects of bullying professionally and personally. DESIGN: Cross-sectional, mixed methods study. SETTING: New Zealand. PARTICIPANTS: Members of the Association of Salaried Medical Specialists (40.8% response rate). MAIN OUTCOME MEASURES: Prevalence of bullying was measured using the Negative Acts Questionnaire (revised) (NAQ-r). Workplace demands and level of peer and managerial support were measured with the Health and Safety Executive Management Standards Analysis tool. Categories of perpetrators for self-reported and witnessed bullying and barriers to reporting bullying were obtained and qualitative data detailing the consequence of bullying were analysed thematically. RESULTS: The overall prevalence of bullying, measured by the NAQ-r, was 38% (at least one negative act on a weekly or daily basis), 37.2% self-reported and 67.5% witnessed. There were significant differences in rates of bullying by specialty (P=0.001) with emergency medicine reporting the highest bullying prevalence (47.9%). The most commonly cited perpetrators were other senior medical or dental specialists. 69.6% declined to report their bullying. Bullying across all measures was significantly associated with increasing work demands and lower peer and managerial support (P=0.001). Consequences of bullying were wide ranging, affecting workplace environments, personal well-being and subjective quality of patient care. CONCLUSIONS: Bullying is prevalent in New Zealand's senior medical workforce and is associated with high workloads and low peer and managerial support. These findings help identify conditions and pressures that may encourage bullying and highlight the significant risk of bullying for individuals and their patients

The enhancement and suppression of immersion mode heterogeneous ice-nucleation by solutes

Heterogeneous nucleation of ice from aqueous solutions is an important yet poorly understood process in multiple fields, not least the atmospheric sciences where it impacts the formation and properties of clouds. In the atmosphere ice-nucleating particles are usually, if not always, mixed with soluble material. However, the impact of this soluble material on ice nucleation is poorly understood. In the atmospheric community the current paradigm for freezing under mixed phase cloud conditions is that dilute solutions will not influence heterogeneous freezing. By testing combinations of nucleators and solute molecules we have demonstrated that 0.015 M solutions (predicted melting point depression <0.1°C) of several ammonium salts can cause suspended particles of feldspars and quartz to nucleate ice up to around 3°C warmer than they do in pure water. In contrast, dilute solutions of certain alkali metal halides can dramatically depress freezing points for the same nucleators. At 0.015 M, solutes can enhance or deactivate the ice-nucleating ability of a microcline feldspar across a range of more than 10°C, which corresponds to a change in active site density of more than a factor of 105. This concentration was chosen for a survey across multiple solutes-nucleant combinations since it had a minimal colligative impact on freezing and is relevant for activating cloud droplets. Other nucleators, for instance a silica gel, are unaffected by these ‘solute effects’, to within experimental uncertainty. This split in response to the presence of solutes indicates that different mechanisms of ice nucleation occur on the different nucleators or that surface modification of relevance to ice nucleation proceeds in different ways for different nucleators. These solute effects on immersion mode ice nucleation may be of importance in the atmosphere as sea salt and ammonium sulphate are common cloud condensation nuclei (CCN) for cloud droplets and are internally mixed with ice-nucleating particles in mixed-phase clouds. In addition, we propose a pathway dependence where activation of CCN at low temperatures might lead to enhanced ice formation relative to pathways where CCN activation occurs at higher temperatures prior to cooling to nucleation temperature

Formation of Globular Cluster Candidates in Merging Proto-galaxies at High Redshift: A View from the FIRE Cosmological Simulations

Using a state-of-the-art cosmological simulation of merging proto-galaxies at high redshift from the FIRE project, with explicit treatments of star formation and stellar feedback in the interstellar medium, we investigate the formation of star clusters and examine one of the formation hypothesis of present-day metal-poor globular clusters. We find that frequent mergers in high-redshift proto-galaxies could provide a fertile environment to produce long-lasting bound star clusters. The violent merger event disturbs the gravitational potential and pushes a large gas mass of ~> 1e5-6 Msun collectively to high density, at which point it rapidly turns into stars before stellar feedback can stop star formation. The high dynamic range of the reported simulation is critical in realizing such dense star-forming clouds with a small dynamical timescale, t_ff <~ 3 Myr, shorter than most stellar feedback timescales. Our simulation then allows us to trace how clusters could become virialized and tightly-bound to survive for up to ~420 Myr till the end of the simulation. Because the cluster's tightly-bound core was formed in one short burst, and the nearby older stars originally grouped with the cluster tend to be preferentially removed, at the end of the simulation the cluster has a small age spread.Comment: 14 pages, 14 figures, Accepted for publication in the Monthly Notices of the Royal Astronomical Society, High-resolution version of this article also available at http://www.jihoonkim.org/index/research.html#g

The clinical utility of routine urinalysis in pregnancy: A prospective study

Objectives: To determine whether routine urinalysis in the antenatal period facilitates diagnosis of pre-eclampsia. Can routine urinalysis during pregnancy be discontinue in women with normal results of dipstick urinalysis and microscopy at the first antenatal visit? Design: Prospective observational study. Setting: A metropolitan public hospital and a private hospital in Sydney (NSW). Participants: One thousand women were enrolled at their first antenatal visit (March to November 1999), and 913 completed the study. Outcome measures: The primary outcome was a diagnosis of de novo hypertension (gestational hypertension, pre-eclampasia, or pre-eclampsia superimposed on chronic hypertension). Results: Thirty-five women had dipstick proteinuria at the first antenatal visit. In 25 (71%) of these women, further dipstick proteinuria was detected during pregnancy, and two (6%) were diagnosed with pre-eclampsia. Of the 867 without dipstick proteinuria at the first visit, 338 (39%) had dipstick proteinuria (> 1+) at some time during pregnancy. There were no statistically significant differences in the proportion of women with and without dipstick proteinuria at their first visit who developed hypertension during pregnancy. Only six women developed proteinuria before the onset of hypertension. Women who had an abnormal result of a midstream urine test at their first visit, compared with women with a normal result, were more likely to have a urinary tract infection diagnosed during pregnancy; however, the numbers were small. Conclusion: In the absence of hypertension, routine urinalysis during pregnancy is a poor predictor of pre-eclampsia. Therefore, after an initial screening urinalysis, routine urinalysis could be eliminated from antenatal care without adverse outcomes for women