The Causal Boundary of spacetimes revisited

We present a new development of the causal boundary of spacetimes, originally introduced by Geroch, Kronheimer and Penrose. Given a strongly causal spacetime (or, more generally, a chronological set), we reconsider the GKP ideas to construct a family of completions with a chronology and topology extending the original ones. Many of these completions present undesirable features, like those appeared in previous approaches by other authors. However, we show that all these deficiencies are due to the attachment of an ``excessively big'' boundary. In fact, a notion of ``completion with minimal boundary'' is then introduced in our family such that, when we restrict to these minimal completions, which always exist, all previous objections disappear. The optimal character of our construction is illustrated by a number of satisfactory properties and examples.Comment: 37 pages, 10 figures; Definition 6.1 slightly modified; multiple minor changes; one figure added and another replace

Feedback system for divertor impurity seeding based on real-time measurements of surface heat flux in the Alcator C-Mod tokamak

Mitigation of the intense heat flux to the divertor is one of the outstanding problems in fusion energy. One technique that has shown promise is impurity seeding, i.e., the injection of low-Z gaseous impurities (typically N2 or Ne) to radiate and dissipate the power before it arrives to the divertor target plate. To this end, the Alcator C-Mod team has created a first-of-its-kind feedback system to control the injection of seed gas based on real-time surface heat flux measurements. Surface thermocouples provide real-time measurements of the surface temperature response to the plasma heat flux. The surface temperature measurements are inputted into an analog computer that "solves" the 1-D heat transport equation to deliver accurate, real-time signals of the surface heat flux. The surface heat flux signals are sent to the C-Mod digital plasma control system, which uses a proportional-integral-derivative (PID) algorithm to control the duty cycle demand to a pulse width modulated piezo valve, which in turn controls the injection of gas into the private flux region of the C-Mod divertor. This paper presents the design and implementation of this new feedback system as well as initial results using it to control divertor heat flux

Understanding the newly observed Y(4008) by Belle

Very recently a new enhancement around 4.05 GeV was observed by Belle experiment. In this short note, we discuss some possible assignments for this enhancement, i.e. $\psi(3S)$ and $D^*\bar{D}^*$ molecular state. In these two assignments, Y(4008) can decay into $J/\psi\pi^0\pi^0$ with comparable branching ratio with that of $Y(4008)\to J/\psi\pi^+\pi^-$. Thus one suggests high energy experimentalists to look for Y(4008) in $J/\psi\pi^0\pi^0$ channel. Furthermore one proposes further experiments to search missing channel $D\bar{D}$, $D\bar{D}^*+h.c.$ and especially $\chi_{cJ}\pi^+\pi^-\pi^0$ and $\eta_c\pi^+\pi^-\pi^0$, which will be helpful to distinguish $\psi(3S)$ and $D^*\bar{D}^*$ molecular state assignments for this new enhancement.Comment: 4 pages, 5 figures. Typos correcte

Dynamics and Berry phase of two-species Bose-Einstein condensates

In terms of exact solutions of the time-dependent Schrodinger equation for an effective giant spin modeled from a coupled two-mode Bose-Einstein condensate (BEC) with adiabatic and cyclic time-varying Raman coupling between two hyperfine states of the BEC, we obtain analytic time-evolution formulas of the population imbalance and relative phase between two components with various initial states, especially the SU(2)coherent state. We find the Berry phase depending on the number parity of atoms, and particle number dependence of the collapse revival of population-imbalance oscillation. It is shown that self-trapping and phase locking can be achieved from initial SU(2) coherent states with proper parameters.Comment: 18 pages,5 figure

Exploring quantum criticality based on ultracold atoms in optical lattices

Critical behavior developed near a quantum phase transition, interesting in its own right, offers exciting opportunities to explore the universality of strongly-correlated systems near the ground state. Cold atoms in optical lattices, in particular, represent a paradigmatic system, for which the quantum phase transition between the superfluid and Mott insulator states can be externally induced by tuning the microscopic parameters. In this paper, we describe our approach to study quantum criticality of cesium atoms in a two-dimensional lattice based on in situ density measurements. Our research agenda involves testing critical scaling of thermodynamic observables and extracting transport properties in the quantum critical regime. We present and discuss experimental progress on both fronts. In particular, the thermodynamic measurement suggests that the equation of state near the critical point follows the predicted scaling law at low temperatures.Comment: 15 pages, 6 figure

Conceptual design study for heat exhaust management in the ARC fusion pilot plant

The ARC pilot plant conceptual design study has been extended beyond its initial scope [B. N. Sorbom et al., FED 100 (2015) 378] to explore options for managing ~525 MW of fusion power generated in a compact, high field (B_0 = 9.2 T) tokamak that is approximately the size of JET (R_0 = 3.3 m). Taking advantage of ARC's novel design - demountable high temperature superconductor toroidal field (TF) magnets, poloidal magnetic field coils located inside the TF, and vacuum vessel (VV) immersed in molten salt FLiBe blanket - this follow-on study has identified innovative and potentially robust power exhaust management solutions.Comment: Accepted by Fusion Engineering and Desig

Level of risk management practice in Malaysia construction industry from a knowledge-based perspective

The construction industry is a competitive high-risk industry with unprecedented uncertainties in technology, budget and development processes. The need then evolved to develop a frame work for project performance in Malaysia construction company. This study investigated the associated problem in the management of risks in Malaysian construction projects using the knowledge-based approach. This perspective proposed a methodology based on a one-fold arrangement involving the application of risk management modelling function, evaluation of the comparative effectiveness and desired quality with the availability of a best practices model. The preliminary conclusion from these findings revealed that risk management in Malaysian construction projects is ineffective and still at a developmental stage. The applications of a knowledge-based framework, therefore, allow clients, contractors and consultants to develop a project’s risk management function based on best practices. The implementation of knowledge management will, therefore, avoid the organization the cost of repeating the same mistakes.This will invariably lead to improvement in the performance of construction work in Malaysia when incorporated as part of the organizational strategic plan

Government policy as a key moderator to contractors’ risk attitudes among Malaysian construction companies

Purpose: The main parties in construction projects are the engineers, clients, architects, contractors, material suppliers, and consultants such as the project managers. They play the most important roles in implementing construction projects, and their activities have a significant impact on their risk attitudes during the execution of projects. Because each participant has their particular interests, by proprietary information, each participant is driven to achieve maximum benefit, which can result in improper behaviour concerning each other. The risk in this situation is that there would be a moral hazard and adverse selection based on information asymmetry among principal construction participants especially contractors; this outcome is called risk attitudes. Behaviour is affected by various risk factors and the successful implementation of construction projects depends on effective management of the key risk factors part of which is a personal factor. The purpose of this paper is to identify the critical factors affecting contractors’ risk attitudes among Malaysian construction companies with the moderating role of government policy. Organizational control theory and expected utility theory were used to develop the theoretical framework. The study investigated G7 contractors in the Malaysian construction industry. Data were collected through the use of a questionnaire. Design/methodology/approach: The research analysis was based on structural equation modelling (SEM), and the research model was ascertained through the Smart PLS 3.0 software (Ringle et al., 2012). Partial least square-SEM is an appropriate analysis that was used to assess the results in the current research because its algorithm permits the unrestricted computation of cause-effect relationship models that use both reflective and formative measurement models. This study uses the quantitative method to identify the individual factors influencing contractors’ risk attitude and the moderating role of government policy among construction companies in Malaysia. This study also focussed on the G7 contractors operating in the Malaysia construction industry that specializes in building, bridge and road construction projects. The duration of the data collection was between two and three weeks. The questionnaire was prepared both in Malay and English languages to allow the respondents to respond most conveniently. Before the copies of the questionnaire were distributed, the selected contractors’ committees were duly informed about the details of the survey procedures. The adopted Likert scale was originally a five-point scale that ranges from “very low” to “very high” with “low or high” in between. Findings: The result of this study moderately supports the hypothesized relationships proposed in the theoretical model. In particular, the results recommended that personal factors that affect risk attitudes (working experience, emotional intelligence, professional competence and physical health) have a significant relation with contractors’ risk attitudes in the construction companies in Malaysia. Also, it has been found that government policy (rules and regulations) are important determinants of risk attitudes. Research limitations/implications: The study focussed on individual factors affecting contractors’ risk attitudes in the construction company’s in Malaysia. Therefore, the dimensions of factors affecting risk attitudes can be used in another aspect of construction projects such as management factors, economic factors and technical factors. Therefore, further research might investigate other grades of Malaysian construction companies apart from Grade 7 contractors to know if there is a similarity in the results; other grades of the contractors might have potential positive contributions to the construction industry as well. Practical implications: With consider to the practical, the current research findings have several contributions for the contractors and project managers. The research results demonstrate that government policy plays an important role in the construction industry and organizational support will also help contractors to control their attitudes in working place. Individual factor has a direct relationship with contractor risk attitudes (CRA), project managers must ensure that the government policy has an impact in all their workers and offered is competitive, fair and by their employees’ contribution. Apart from that managers should also focus on organizational goals especially in managing professional and skilled contractors in the companies. Employees who perceived their employers as uncaring or not supporting their needs and well-being may not be happy working with the organization and the tendency for them to change their attitudes towards risk will be high. Social implications: This study also contributes knowledge by lending empirical support to the organizational control theory and expected utility theory system’s effect on CRA and confirming that changing one individual attitude will change the whole equilibrium. This is useful to aid in further synthesis of organizational control theory and expected utility theory in construction companies. Originality/value: This study is the first attempt at evaluating the direct and moderating effect relationships among individual factor affecting risk attitudes, government policy and CRA in Malaysian construction companies. These findings also prop up the applicability of the organizational control theory and expected utility theory within the context of construction companies in Malaysia. Also, this study contributed to the literature on psychology by subjective (psychological) measures of individuals’ behaviour and decisions. In the CRA literature, there has been much discussion on personal characteristics to understand behaviours such as attitudes of a contractor towards risk and morals

Defects, Dopants and Lithium Mobility in Li ₉ v ₃ (P ₂ O ₇ ) ₃ (PO ₄ ) ₂

Layered Li9V3(P2O7)3(PO4)2 has attracted considerable interest as a novel cathode material for potential use in rechargeable lithium batteries. The defect chemistry, doping behavior and lithium diffusion paths in Li9V3(P2O7)3(PO4)2 are investigated using atomistic scale simulations. Here we show that the activation energy for Li migration via the vacancy mechanism is 0.72 eV along the c-axis. Additionally, the most favourable intrinsic defect type is Li Frenkel (0.44 eV/defect) ensuring the formation of Li vacancies that are required for Li diffusion via the vacancy mechanism. The only other intrinsic defect mechanism that is close in energy is the formation of anti-site defect, in which Li and V ions exchange their positions (1.02 eV/defect) and this can play a role at higher temperatures. Considering the solution of tetravalent dopants it is calculated that they require considerable solution energies, however, the solution of GeO2 will reduce the activation energy of migration to 0.66 eV

Group Fisher Pruning for Practical Network Compression

Network compression has been widely studied since it is able to reduce the memory and computation cost during inference. However, previous methods seldom deal with complicated structures like residual connections, group/depth-wise convolution and feature pyramid network, where channels of multiple layers are coupled and need to be pruned simultaneously. In this paper, we present a general channel pruning approach that can be applied to various complicated structures. Particularly, we propose a layer grouping algorithm to find coupled channels automatically. Then we derive a unified metric based on Fisher information to evaluate the importance of a single channel and coupled channels. Moreover, we find that inference speedup on GPUs is more correlated with the reduction of memory rather than FLOPs, and thus we employ the memory reduction of each channel to normalize the importance. Our method can be used to prune any structures including those with coupled channels. We conduct extensive experiments on various backbones, including the classic ResNet and ResNeXt, mobile-friendly MobileNetV2, and the NAS-based RegNet, both on image classification and object detection which is under-explored. Experimental results validate that our method can effectively prune sophisticated networks, boosting inference speed without sacrificing accuracy