Dynamical Horizons: Energy, Angular Momentum, Fluxes and Balance Laws

Dynamical horizons are considered in full, non-linear general relativity. Expressions of fluxes of energy and angular momentum carried by gravitational waves across these horizons are obtained. Fluxes are local, the energy flux is positive and change in the horizon area is related to these fluxes. The flux formulae also give rise to balance laws analogous to the ones obtained by Bondi and Sachs at null infinity and provide generalizations of the first and second laws of black hole mechanics.Comment: 4 pages, RevTeX4. Minor typos corrected. To appear in Phys.Rev.Let

Pembangunan Pedesaan Berbasis Teknologi Informasi Dan Komunikasi (Studi Pada Gerakan Desa Membangun)

Pembangunan pedesaan mengalami Perubahan signifikan sejak digitalisasi Teknologi Informasi dan Komunikasi (TIK). Teknologi media hibrida terbukti mempermudah desa-desa inovatif membangun jejaring dan memberdayakan komunitasnya guna mempersempit kesenjangan TIK, salah satunya adalah melalui Gerakan Desa Membangun (GDM). Penulisan artikel ini bertujuan untuk: (1) Mengetahui profil dan program Gerakan Desa Membangun (GDM); (2) Mengetahui paradigma pembangunan pedesaan berbasis TIK yang dijalankan GDM; (3) Mengetahui masalah dan strategi pengembangan TIK di pedesaan; (4) Mengetahui pengembangan media komunikasi pedesaan berbasis TIK. Penelitian ini menggunakan metode studi kepustakaan, dengan menganalisis konten website GDM (http://desamembangun.or.id/) dan konten website desa berbasis desa.id yang berafiliasi dan dikembangkan oleh GDM. Hasil penelitian menunjukkan bahwa: (1) GDM lahir sebagai kritik atas praktik pembangunan perdesaan yang cenderung top down dengan program pelayanan publik, pengelolaan sumber daya, penerapan teknologi tepat guna serta perlindungan warga desa; (2) Paradigma pembangunan pedesaan yang dijalankan GDM berbasis TIK dengan mengoptimalkan aplikasi sistem informasi desa dan internet pedesaan; (3) Permasalahan pengembangan TIK berkaitan dengan rendahnya infrastruktur TIK di pedesaan dan kapasitas masyarakat dalam pembangunan yang diselesaikan dengan strategi pelatihan dan pendampingan; (4) Media komunikasi pedesaan yang dikembangkan adalah website desa dengan domain desa.id, pengembangan aplikasi open source, dan interkoneksi desa

Quasi-Local Linear Momentum in Black-Hole Binaries

We propose a quasi-local formula for the linear momentum of black-hole horizons inspired by the formalism of quasi-local horizons. We test this formula using two complementary configurations: (i) by calculating the large orbital linear momentum of the two black holes in an unequal-mass, zero-spin, quasi-circular binary and (ii) by calculating the very small recoil momentum imparted to the remnant of the head-on collision of an equal-mass, anti-aligned-spin binary. We obtain results consistent with the horizon trajectory in the orbiting case, and consistent with the net radiated linear momentum for the much smaller head-on recoil velocity.Comment: 5 pages, 3 figures, revtex

Does Internet Harms Music Sales? a Constructive Perspective

The main issue brought by this study is whether internet as medium and their users as actors behind the fall of music industry\u27s revenue during these years – many people stand on this point of view - or could be the facilitator of music purchasing. This study used data panel from 16 countries ranging from 1999 to 2004 to prove whether internet and their users harm the revenue of music industry, and employs four dummy variables, including piracy rates, economic development, market size, and individualism/collectivism. The results indicated that internet through their users in the USA does not harm as much as industry claimed before, only 2.1 percent. Furthermore, the panel data results indicate that level of piracy rates released by IFPI in 2001 partially supported, and surprisingly, the internet positively significant influences on the music sales for country\u27s with piracy level in the range of 25 to 50 percent. Moreover, the internet users interact with economic development and individualism/collectivism, and it has shown that internet users have positively significant impacts on the music sales. However, market size does not support the model developed in this study. The managerial implications, limitations of the study and directions for further research are also presented. Keywords: internet, piracy, music sales, piracy rates, economic development, market size, individualism/collectivism

The role of concurrent sexual relationships in the spread of sexually transmitted infections in young South Africans

We still do not know why the HIV prevalence in southern and eastern Africa is an order of magnitude higher than anywhere else in the world. An article in this journal in 2007 argued that a key determinant was not so much the lifetime numbers of sexual partnerships, but rather the high proportion of these partnerships that are arranged concurrently. Concurrency has been associated with elevated rates of sexually transmitted infections (STIs) elsewhere, but this relationship has never been demonstrated in an African setting, where its effect is proposed to be greatest. We conducted a secondary data analysis from a representative survey of 14 - 25-year-olds living in Cape Town to test the hypothesis that concurrency is associated with self-reported symptoms of an STI. On logistic multiple regression analysis we found a modest but statistically significant relationship between self-reported STI symptoms and having had a partner who engaged in concurrency