3,663 research outputs found

    Some Properties of Noether Charge and a Proposal for Dynamical Black Hole Entropy

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    We consider a general, classical theory of gravity with arbitrary matter fields in nn dimensions, arising from a diffeomorphism invariant Lagrangian, \bL. We first show that \bL always can be written in a ``manifestly covariant" form. We then show that the symplectic potential current (n1)(n-1)-form, th\th, and the symplectic current (n1)(n-1)-form, \om, for the theory always can be globally defined in a covariant manner. Associated with any infinitesimal diffeomorphism is a Noether current (n1)(n-1)-form, \bJ, and corresponding Noether charge (n2)(n-2)-form, \bQ. We derive a general ``decomposition formula" for \bQ. Using this formula for the Noether charge, we prove that the first law of black hole mechanics holds for arbitrary perturbations of a stationary black hole. (For higher derivative theories, previous arguments had established this law only for stationary perturbations.) Finally, we propose a local, geometrical prescription for the entropy, SdynS_{dyn}, of a dynamical black hole. This prescription agrees with the Noether charge formula for stationary black holes and their perturbations, and is independent of all ambiguities associated with the choices of \bL, th\th, and \bQ. However, the issue of whether this dynamical entropy in general obeys a ``second law" of black hole mechanics remains open. In an appendix, we apply some of our results to theories with a nondynamical metric and also briefly develop the theory of stress-energy pseudotensors.Comment: 30 pages, LaTe

    Observational constraints on the neutron star mass distribution

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    Radio observations of neutron star binary pulsar systems have constrained strongly the masses of eight neutron stars. Assuming neutron star masses are uniformly distributed between lower and upper bounds mlm_l and mum_u, the observations determine with 95\% confidence that 1.01<ml/M<1.341.01 < m_l/\text{M}_\odot < 1.34 and 1.43<mu/M<1.641.43 < m_u/\text{M}_\odot < 1.64. These limits give observational support to neutron star formation scenarios that suggest that masses should fall predominantly in the range 1.3<m/M<1.61.3<m/\text{M}_\odot<1.6, and will also be important in the interpretation of binary inspiral observations by the Laser Interferometer Gravitational-wave Observatory.Comment: Postscript, 4 pages, NU-GR-

    IMPACT: Impersonation attack detection via edge computing using deep autoencoder and feature abstraction

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    An ever-increasing number of computing devices interconnected through wireless networks encapsulated in the cyber-physical-social systems and a significant amount of sensitive network data transmitted among them have raised security and privacy concerns. Intrusion detection system (IDS) is known as an effective defence mechanism and most recently machine learning (ML) methods are used for its development. However, Internet of Things (IoT) devices often have limited computational resources such as limited energy source, computational power and memory, thus, traditional ML-based IDS that require extensive computational resources are not suitable for running on such devices. This study thus is to design and develop a lightweight ML-based IDS tailored for the resource-constrained devices. Specifically, the study proposes a lightweight ML-based IDS model namely IMPACT (IMPersonation Attack deteCTion using deep auto-encoder and feature abstraction). This is based on deep feature learning with gradient-based linear Support Vector Machine (SVM) to deploy and run on resource-constrained devices by reducing the number of features through feature extraction and selection using a stacked autoencoder (SAE), mutual information (MI) and C4.8 wrapper. The IMPACT is trained on Aegean Wi-Fi Intrusion Dataset (AWID) to detect impersonation attack. Numerical results show that the proposed IMPACT achieved 98.22% accuracy with 97.64% detection rate and 1.20% false alarm rate and outperformed existing state-of-the-art benchmark models. Another key contribution of this study is the investigation of the features in AWID dataset for its usability for further development of IDS

    Density-functional embedding using a plane-wave basis

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    The constrained electron density method of embedding a Kohn-Sham system in a substrate system (first described by P. Cortona, Phys. Rev. B {\bf 44}, 8454 (1991) and T.A. Wesolowski and A. Warshel, J. Phys. Chem {\bf 97}, 8050 (1993)) is applied with a plane-wave basis and both local and non-local pseudopotentials. This method divides the electron density of the system into substrate and embedded electron densities, the sum of which is the electron density of the system of interest. Coupling between the substrate and embedded systems is achieved via approximate kinetic energy functionals. Bulk aluminium is examined as a test case for which there is a strong interaction between the substrate and embedded systems. A number of approximations to the kinetic-energy functional, both semi-local and non-local, are investigated. It is found that Kohn-Sham results can be well reproduced using a non-local kinetic energy functional, with the total energy accurate to better than 0.1 eV per atom and good agreement between the electron densities.Comment: 11 pages, 4 figure

    On the positive mass theorem for manifolds with corners

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    We study the positive mass theorem for certain non-smooth metrics following P. Miao's work. Our approach is to smooth the metric using the Ricci flow. As well as improving some previous results on the behaviour of the ADM mass under the Ricci flow, we extend the analysis of the zero mass case to higher dimensions.Comment: 21 pages, incorporated referee's comment

    WISP genes are members of the connective tissue growth factor family that are up-regulated in Wnt-1-transformed cells and aberrantly expressed in human colon tumors

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    Wnt family members are critical to many developmental processes, and components of the Wnt signaling pathway have been linked to tumorigenesis in familial and sporadic colon carcinomas. Here we report the identification of two genes, WISP-1 and WISP-2, that are up-regulated in the mouse mammary epithelial cell line C57MG transformed by Wnt-1, but not by Wnt-4. Together with a third related gene, WISP-3, these proteins define a subfamily of the connective tissue growth factor family. Two distinct systems demonstrated WISP induction to be associated with the expression of Wnt-1. These included (i) C57MG cells infected with a Wnt-1 retroviral vector or expressing Wnt-1 under the control of a tetracyline repressible promoter, and (ii) Wnt-1 transgenic mice. The WISP-1 gene was localized to human chromosome 8q24.1-8q24.3. WISP-1 genomic DNA was amplified in colon cancer cell lines and in human colon tumors and its RNA overexpressed (2- to >30-fold) in 84% of the tumors examined compared with patient-matched normal mucosa. WISP-3 mapped to chromosome 6q22-6q23 and also was overexpressed (4- to >40-fold) in 63% of the colon tumors analyzed. In contrast, WISP-2 mapped to human chromosome 20q12-20q13 and its DNA was amplified, but RNA expression was reduced (2- to >30-fold) in 79% of the tumors. These results suggest that the WISP genes may be downstream of Wnt-1 signaling and that aberrant levels of WISP expression in colon cancer may play a role in colon tumorigenesis

    Conductance fluctuations in a quantum dot under almost periodic ac pumping

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    It is shown that the variance of the linear dc conductance fluctuations in an open quantum dot under a high-frequency ac pumping depends significantly on the spectral content of the ac field. For a sufficiently strong ac field γτϕ<<1\gamma\tau_{\phi}<< 1, where 1/τϕ1/\tau_{\phi} is the dephasing rate induced by ac noise and γ\gamma is the electron escape rate, the dc conductance fluctuations are much stronger for the harmonic pumping than in the case of the noise ac field of the same intensity. The reduction factor rr in a static magnetic field takes the universal value of 2 only for the white--noise pumping. For the strictly harmonic pumping A(t)=A0cosωtA(t)=A_{0}\cos\omega t of sufficiently large intensity the variance is almost insensitive to the static magnetic field r1=2τϕγ<<1r-1= 2\sqrt{\tau_{\phi}\gamma} << 1. For the quasi-periodic ac field of the form A(t)=A0[cos(ω1t)+cos(ω2t)]A(t)=A_{0} [\cos(\omega_{1} t)+\cos(\omega_{2} t)] with ω1,2>>γ\omega_{1,2} >> \gamma and γτϕ<<1\gamma\tau_{\phi} << 1 we predict the novel effect of enchancement of conductance fluctuations at commensurate frequencies ω2/ω1=P/Q\omega_{2}/\omega_{1}=P/Q.Comment: 4 pages RevTex, 4 eps figures; the final version to appear in Phys.Rev.
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