Group Based Interference Alignment

In the $K$-user single-input single-output (SISO) frequency-selective fading interference channel, it is shown that the maximal achievable multiplexing gain is almost surely $K/2$ by using interference alignment (IA). However, when the signaling dimensions are limited, allocating all the resources to all users simultaneously is not optimal. So, a group based interference alignment (GIA) scheme is proposed, and it is formulated as an unbounded knapsack problem. Optimal and greedy search algorithms are proposed to obtain group patterns. Analysis and numerical results show that the GIA scheme can obtain a higher multiplexing gain when the resources are limited.Comment: 3 pages, 3 figures. resubmitted to IEEE Communications Letter

Dynamics and delocalisation transition for an interface driven by a uniform shear flow

We study the effect of a uniform shear flow on an interface separating the two broken-symmetry ordered phases of a two-dimensional system with nonconserved scalar order parameter. The interface, initially flat and perpendicular to the flow, is distorted by the shear flow. We show that there is a critical shear rate, \gamma_c, proportional to 1/L^2, (where L is the system width perpendicular to the flow) below which the interface can sustain the shear. In this regime the countermotion of the interface under its curvature balances the shear flow, and the stretched interface stabilizes into a time-independent shape whose form we determine analytically. For \gamma > \gamma_c, the interface acquires a non-zero velocity, whose profile is shown to reach a time-independent limit which we determine exactly. The analytical results are checked by numerical integration of the equations of motion.Comment: 5 page

Finding Action Tubes with a Sparse-to-Dense Framework

The task of spatial-temporal action detection has attracted increasing attention among researchers. Existing dominant methods solve this problem by relying on short-term information and dense serial-wise detection on each individual frames or clips. Despite their effectiveness, these methods showed inadequate use of long-term information and are prone to inefficiency. In this paper, we propose for the first time, an efficient framework that generates action tube proposals from video streams with a single forward pass in a sparse-to-dense manner. There are two key characteristics in this framework: (1) Both long-term and short-term sampled information are explicitly utilized in our spatiotemporal network, (2) A new dynamic feature sampling module (DTS) is designed to effectively approximate the tube output while keeping the system tractable. We evaluate the efficacy of our model on the UCF101-24, JHMDB-21 and UCFSports benchmark datasets, achieving promising results that are competitive to state-of-the-art methods. The proposed sparse-to-dense strategy rendered our framework about 7.6 times more efficient than the nearest competitor.Comment: 5 figures; AAAI 202

Stellar Coronal and Wind Models: Impact on Exoplanets

Surface magnetism is believed to be the main driver of coronal heating and stellar wind acceleration. Coronae are believed to be formed by plasma confined in closed magnetic coronal loops of the stars, with winds mainly originating in open magnetic field line regions. In this Chapter, we review some basic properties of stellar coronae and winds and present some existing models. In the last part of this Chapter, we discuss the effects of coronal winds on exoplanets.Comment: Chapter published in the "Handbook of Exoplanets", Editors in Chief: Juan Antonio Belmonte and Hans Deeg, Section Editor: Nuccio Lanza. Springer Reference Work

A crowdsourced global data set for validating built-up surface layers

Several global high-resolution built-up surface products have emerged over the last five years, taking full advantage of open sources of satellite data such as Landsat and Sentinel. However, these data sets require validation that is independent of the producers of these products. To fill this gap, we designed a validation sample set of 50 K locations using a stratified sampling approach independent of any existing global built-up surface products. We launched a crowdsourcing campaign using Geo-Wiki (https://www.geo-wiki.org/) to visually interpret this sample set for built-up surfaces using very high-resolution satellite images as a source of reference data for labelling the samples, with a minimum of five validations per sample location. Data were collected for 10 m sub-pixels in an 80 × 80 m grid to allow for geo-registration errors as well as the application of different validation modes including exact pixel matching to majority or percentage agreement. The data set presented in this paper is suitable for the validation and inter-comparison of multiple products of built-up areas

Real-time measurements of secondary organic aerosol formation and aging from ambient air in an oxidation flow reactor in the Los Angeles area

Field studies in polluted areas over the last decade have observed large formation of secondary organic aerosol (SOA) that is often poorly captured by models. The study of SOA formation using ambient data is often confounded by the effects of advection, vertical mixing, emissions, and variable degrees of photochemical aging. An oxidation flow reactor (OFR) was deployed to study SOA formation in real-time during the California Research at the Nexus of Air Quality and Climate Change (CalNex) campaign in Pasadena, CA, in 2010. A high-resolution aerosol mass spectrometer (AMS) and a scanning mobility particle sizer (SMPS) alternated sampling ambient and reactor-aged air. The reactor produced OH concentrations up to 4 orders of magnitude higher than in ambient air. OH radical concentration was continuously stepped, achieving equivalent atmospheric aging of 0.8 days-6.4 weeks in 3aEuro-min of processing every 2aEuro-h. Enhancement of organic aerosol (OA) from aging showed a maximum net SOA production between 0.8-6 days of aging with net OA mass loss beyond 2aEuro-weeks. Reactor SOA mass peaked at night, in the absence of ambient photochemistry and correlated with trimethylbenzene concentrations. Reactor SOA formation was inversely correlated with ambient SOA and O-x, which along with the short-lived volatile organic compound correlation, indicates the importance of very reactive (tau(OH)aEuro- aEuro-0.3 day) SOA precursors (most likely semivolatile and intermediate volatility species, S/IVOCs) in the Greater Los Angeles Area. Evolution of the elemental composition in the reactor was similar to trends observed in the atmosphere (OaEuro-:aEuro-C vs. HaEuro-:aEuro-C slope aEuro--0.65). Oxidation state of carbon (OSc) in reactor SOA increased steeply with age and remained elevated (OS(C)aEuro- aEuro-2) at the highest photochemical ages probed. The ratio of OA in the reactor output to excess CO (Delta CO, ambient CO above regional background) vs. photochemical age is similar to previous studies at low to moderate ages and also extends to higher ages where OA loss dominates. The mass added at low-to-intermediate ages is due primarily to condensation of oxidized species, not heterogeneous oxidation. The OA decrease at high photochemical ages is dominated by heterogeneous oxidation followed by fragmentation/evaporation. A comparison of urban SOA formation in this study with a similar study of vehicle SOA in a tunnel suggests the importance of vehicle emissions for urban SOA. Pre-2007 SOA models underpredict SOA formation by an order of magnitude, while a more recent model performs better but overpredicts at higher ages. These results demonstrate the value of the reactor as a tool for in situ evaluation of the SOA formation potential and OA evolution from ambient air

Dreaming in sleep disorders: a comparative analysis of REM and NREM parasomnias

Parasomnias are abnormal behaviours emanating from or associated with sleep and dreaming. By studying the dream content and observing the isomorphism in these parasomnias, in which dreams are translated into simple/complex behaviours, it provides a valuable window to the underlying cognitive mechanisms during REM and NREM sleep. The aim of this study was to quantify the differences between RBD and NREMP patients in terms of their sleep physiology and dream mentation. This was achieved by exploring their dream content and structure using the Orlinski scale, Hall and Van de Castle analysis and speech graph analysis. RBD patients were found to experience significantly higher dream recall/complexity and displayed fight behaviour in a fight-or-flight response. The novel use of speech graphs on dream reports were also found to be useful in differentiating between RBD and NREMP patients, in which RBD patients showed a pattern of linearity while NREMP patients exhibited convolution. This uncovers the potential of using speech graph analysis as a cost- efficient, fast and complementary tool in the differential diagnosis of these two parasomnias and in tracking disease progression. This allows for early intervention to introduce neuroprotective agents that may mitigate the progression of Parkinson’s and other neurodegenerative diseases.Bachelor of Science in Biological Science

TRANSITING FROM CLASSICAL TO QUANTUM MECHANICS: RELATIONSHIPS BETWEEN SOLUTIONS OF HAMILTON-JACOBI EQUATION AND SCHRODINGER EQUATION

Bachelor'sBACHELOR OF SCIENCE (HONOURS

How fragmentation affects insect predation rate : a Singapore case study

Over the last 150 years, the tropical forests in Singapore have been rapidly fragmented and urbanised but the effects of fragmentation remain poorly understood. In this study, I sought to understand how fragmentation may impact forest functioning and health through studying insect predation rate by using artificial caterpillars. I measured how fragment edge effects and forest patch size affected insect predation rate by using three separate forest fragments which differed in size and shape. Insect predation rate was found to increase with increasing distance away from the forest edge, although the relationship between edge effects and insect predation rate was very weak. Forest patch size was found to have no effect. This study highlights the importance in studying fragmentation effects on insect activity and response, especially in a highly urbanised setting such as Singapore where most forests have been heavily degraded and reduced to isolated patches.Bachelor of Science in Environmental Earth Systems Scienc