Local And Global Structure Of A Thick-domain-wall Space-time

The local and global properties of the Goetz thick plane domain-wall space-time are studied. It is found that when the surface energy of the wall is greater than a critical value c, the space-time will be closed by intermediate singularities at a finite proper distance. A model is presented in which these singularities will give rise to scalar ones when interacting with null fluids. The maximum extension of the space-time of the wall whose surface energy is less than c is presented. It is shown that for a certain choice of the free parameter the space-time has a black hole structure but plane symmetry. © 1995 The American Physical Society.5112R6612R661

Gravitational Collapse of Cylindrical Shells Made of Counter-Rotating Dust Particles

The general formulas of a non-rotating dynamic thin shell that connects two arbitrary cylindrical regions are given using Israel's method. As an application of them, the dynamics of a thin shell made of counter-rotating dust particles, which emits both gravitational waves and massless particles when it is expanding or collapsing, is studied. It is found that when the models represent a collapsing shell, in some cases the angular momentum of the dust particles is strong enough to halt the collapse, so that a spacetime singularity is prevented from forming, while in other cases it is not, and a line-like spacetime singularity is finally formed on the symmetry axis.Comment: To appear in Phys. Rev.

Domain Wall Spacetimes: Instability of Cosmological Event and Cauchy Horizons

The stability of cosmological event and Cauchy horizons of spacetimes associated with plane symmetric domain walls are studied. It is found that both horizons are not stable against perturbations of null fluids and massless scalar fields; they are turned into curvature singularities. These singularities are light-like and strong in the sense that both the tidal forces and distortions acting on test particles become unbounded when theses singularities are approached.Comment: Latex, 3 figures not included in the text but available upon reques

The Interaction Of Outgoing And Ingoing Spherically Symmetric Null Fluids

Using similarity methods, the Einstein field equations coupled to two oppositely directed null fluids for a spherically symmetric space-time are reduced to an autonomous system of three ordinary differential equations. The space of solutions is studied in some detail and solutions are found that represent: (i) the backscattering of an initially outgoing thick null fluid shell in a background gravitational field with a central naked singularity, (ii) the formation of strong space-time singularities by the interaction of thick null fluid shells, (iii) the interaction of a core of null radiation with an incoming shell of null fluid, and (iv) cosmological models of Kantowski-Sachs type with initial and final singularities clothed by apparent horizons. © 1995 American Institute of Physics.3673663367

Physiological Measurement on Students’ Engagement In a Distributed Learning Environment

Measuring students’ engagement in a distributed learning environment is a challenge. In particular, a teacher gives a lecture at one location, while at the same time the remote students watch the lecture through a display screen. In such situation, it is difficult for the teacher to know the reaction at the remote location. In this paper, we conducted a field study to measure students’ engagement by using galvanic skin response (GSR) sensors, where students simultaneously watched the lecture at the two locations. Our results showed the students’ GSR response was aligned with the surveys, which means that during a distributed learning environment, GSR sensors can be used as an indicator on students’ engagement. Furthermore, our user studies resulted in non-engaging student learning experiences that would be difficult obtained at a lab condition. Based on the findings, we found that the patterns of GSR readings were rather different when compared to the previous relevant studies, where users were engaged. In addition, we noticed that the density of GSR response at the remote location was higher when compared to the one at the lecture room. We believe that our studies are beneficial on physiological computing, as we first presented the patterns of GSR sensors on non-engaging user experiences. Moreover, as an alternative method, GSR sensors can be easily implemented in a distributed learning environment to provide feedback to teachers

Decentralised demand response market model based on reinforcement learning

A new decentralised demand response (DR) model relying on bi-directional communications is developed in this study. In this model, each user is considered as an agent that submits its bids according to the consumption urgency and a set of parameters defined by a reinforcement learning algorithm called Q-learning. The bids are sent to a local DR market, which is responsible for communicating all bids to the wholesale market and the system operator (SO), reporting to the customers after determining the local DR market clearing price. From local markets’ viewpoint, the goal is to maximise social welfare. Four DR levels are considered to evaluate the effect of different DR portions in the cost of the electricity purchase. The outcomes are compared with the ones achieved from a centralised approach (aggregation-based model) as well as an uncontrolled method. Numerical studies prove that the proposed decentralised model remarkably drops the electricity cost compare to the uncontrolled method, being nearly as optimal as a centralised approach.© 2020 The Institution of Engineering and Technology. This is an open access article published by the IET under the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/)fi=vertaisarvioitu|en=peerReviewed

A spectroscopic and thermal investigation into the relationship between composition, secondary structure and physical characteristics of electrospun zein nanofibers

Electrospun zein nanofibers have attracted interest as drug delivery systems due to their propensity for controlled drug release, flexible structure and low toxicity. However, comparatively little is known regarding the relationship between production method and fiber characteristics, both in terms of fiber architecture and protein structure. Here we use a range of imaging and spectroscopic techniques to elucidate the effects of solvent composition on zein secondary structure, fiber diameter and fiber integrity, plus we utilize the new technique of transition temperature microscopy to examine the thermal properties of the fibers. Zein nanofibers were prepared using ethanol, acetic acid and water mixes as solvents, alone and with plasticizers (polyethylene glycol, glycerol) and casein. Electrospinning was performed under controlled conditions and the products characterized using scanning electron microscopy (SEM), attenuated total reflection Fourier Transform infrared spectrometry (ATR - FTIR) and transition temperature microscopy (TTM). The choice of solvent, concentration and voltage, alongside the presence of additives (plasticizers and casein) were noted to influence both the diameter of the fibers and the tendency for bead formation. A relationship was noted between protein secondary structure and fiber architecture, with an enhanced β-sheet content, enhanced by the inclusion of casein, being associated with higher beading. In addition, thermal imaging of electrospun zein fiber mats was successfully achieved using TTM via two dimensional mapping of the softening temperatures across the spun samples, in particular demonstrating the plasticizing effects of the polyethylene glycol and glycerol

Some Bianchi Type III String Cosmological Models with Bulk Viscosity

We investigate the integrability of cosmic strings in Bianchi III space-time in presence of a bulk viscous fluid by applying a new technique. The behaviour of the model is reduced to the solution of a single second order nonlinear differential equation. We show that this equation admits an infinite family of solutions. Some physical consequences from these results are also discussed.Comment: 12 pages, no figure. To appear in Int. J. Theor. Phy

Solving 2D-pattern matching with networks of picture processors

We propose a solution based on networks of picture processors to the problem of picture pattern matching. The network solving the problem can be informally described as follows: it consists of two subnetworks, one of them extracts simultaneously all subpictures of the same size from the input picture and sends them to the second subnetwork. The second subnetwork checks whether any of the received pictures is identical to the pattern. We present an efficient solution based on networks with evolutionary processors only, for patterns with at most three rows or columns. Afterwards, we present a solution based on networks containing both evolutionary and hiding processors running in O(n+m+kl+k) computational (processing and communication) steps, where the input picture and the pattern are of size (n,m) and (k,l), respectively

Solar Capability Building Programme for Public Housing

AbstractExpanding the use of renewable energy such as solar photovoltaics (PV) is part of the Housing and Development Board's ongoing efforts to promote sustainable development and is in line with the second thrust of HDB's Roadmap for Better Living – to develop ‘Sustainable Towns’. Recognising the unique resource constraints of Singapore, HDB has looked towards solar PV. The Solar Capability Building Programme for public housing involves a wide-scale solar PV test-bedding in both new and existing towns. This paper documents the unique challenges that HDB faced (and still faces) in its drive towards sustainability, a key feature of which is the introduction of solar PV to public housing. The main sections covered are:•HDB's main objectives of starting the Solar Capability Building Programme,•The journey since 2008 till now,•HDB's vision of turning Punggol into a zero-energy (for common services) town,•Various challenges faced and how they were overcome,•Findings from the systems installed so far, and•The future direction HDB is headed in.The focus of the paper is on how HDB is working towards achieving its aims for the Solar Capability Building Programme despite the high solar PV system cost, small number of industry players and lack of grid parity or tariffs. It is an in-depth look into the ways in which HDB has chosen to push forward for solar PV despite the odds. Other governments and companies facing the same challenges can adopt similar methods to overcome them