Weyl Geometry as Characterization of Space-Time

Motivated by an axiomatic approach to characterize space-time it is investigated a reformulation of Einstein's gravity where the pseudo-riemannian geometry is substituted by a Weyl one. It is presented the main properties of the Weyl geometry and it is shown that it gives extra contributions to the trajectories of test particles, serving as one more motivation to study general relativity in Weyl geometry. It is introduced its variational formalism and it is established the coupling with other physical fields in such a way that the theory acquires a gauge symmetry for the geometrical fields. It is shown that this symmetry is still present for the red-shift and it is concluded that for cosmological models it opens the possibility that observations can be fully described by the new geometrical scalar field. It is concluded then that this reformulation, although representing a theoretical advance, still needs a complete description of their objects.Comment: 12 page

Nonlinear electrodynamics and the gravitational redshift of highly magnetised neutron stars

The idea that the nonlinear electromagnetic interaction, i. e., light propagation in vacuum, can be geometrized was developed by Novello et al. (2000) and Novello & Salim (2001). Since then a number of physical consequences for the dynamics of a variety of systems have been explored. In a recent paper Mosquera Cuesta & Salim (2003) presented the first astrophysical study where such nonlinear electrodynamics (NLEDs) effects were accounted for in the case of a highly magnetized neutron star or pulsar. In that paper the NLEDs was invoked {\it a l\`a} Euler-Heisenberg, which is an infinite series expansion of which only the first term was used for the analisys. The immediate consequence of that study was an overall modification of the space-time geometry around the pulsar, which is ``perceived'', in principle, only by light propagating out of the star. This translates into an significant change in the surface redshift, as inferred from absorption (emission) lines observed from a super magnetized pulsar. The result proves to be even more dramatic for the so-called magnetars, pulsars endowed with magnetic ($B$) fields higher then the Schafroth quantum electrodynamics critical $B$-field. Here we demonstrate that the same effect still appears if one calls for the NLEDs in the form of the one rigorously derived by Born & Infeld (1934) based on the special relativistic limit for the velocity of approaching of an elementary particle to a pointlike electron [From the mathematical point of view, the Born & Infeld (1934) NLEDs is described by an exact Lagrangean, whose dynamics has been successfully studied in a wide set of physical systems.].Comment: Accepted for publication in Month. Not. Roy. Ast. Soc. latex file, mn-1.4.sty, 5 pages, 2 figure

Capacity and Security of Heterogeneous Distributed Storage Systems

We study the capacity of heterogeneous distributed storage systems under repair dynamics. Examples of these systems include peer-to-peer storage clouds, wireless, and Internet caching systems. Nodes in a heterogeneous system can have different storage capacities and different repair bandwidths. We give lower and upper bounds on the system capacity. These bounds depend on either the average resources per node, or on a detailed knowledge of the node characteristics. Moreover, we study the case in which nodes may be compromised by an eavesdropper, and give bounds on the system secrecy capacity. One implication of our results is that symmetric repair maximizes the capacity of a homogeneous system, which justifies the model widely used in the literature.Comment: 7 pages, 2 figure

Analisis Pengaruh Manajemen Laba Terhadap Profitabilitas Perusahaan Dengan Good Corporate Governance Sebagai Variabel Moderasi: Studi Pada Perusahaan Manufaktur Yang Terdaftar Di Bursa Efek Indonesia Periode 2010-2012

The aims of this study is to analyze the effect of earning management on the profitability of the company moderated by good corporate governance. The measurement method of earning management employed is discretionary revenue approach that applies the method of conditional revenue developed by Stubben (2010). Good corporate governance is measured by frequency of audit committee meetings. Company's profitability is measured by using Return on Assets ratio (ROA). The total sample for this study are 70 manufacturing firms listed in Indonesia Stock Exchange from 2010-2012. The method used for data analysis is multiple regression. The result of this study shows that earning management influences company's profitability. Moreover, good corporate governance is the moderator of the relationship between earning management and company's profitability

Stimulated quantum phase slips from weak electromagnetic radiations in superconducting nanowires

We study the rate of quantum phase slips in an ultranarrow superconducting nanowire exposed to weak electromagnetic radiations. The superconductor is in the dirty limit close to the superconducting-insulating transition, where fluxoids move in strong dissipation. We use a semiclassical approach and show that external radiation stimulates a significant enhancement in the probability of quantum phase slips. This can help to outline a new type of detector for microwave to submillimetre radiations based on stimulated quantum phase slip phenomenon.Comment: 10 pages, 9 figure

Aspek Keselamatan pada Aplikasi Reaktor Nuklir Suhu Tinggi untuk Proses Steam Reforming Gas Alam

ASPEK KESELAMATAN PADA APLIKASI REAKTOR NUKLIR SUHU TINGGI UNTUK PROSES STEAM REFORMING GAS ALAM. Telah dilakukan pengkajian aspek keselamatan pada aplikasi reaktor nuklir suhu tinggi untuk proses steam reforming gas alam. Aspek keselamatan dasar pada kopel reaktor nuklir dengan proses kimia adalah mencegah kemungkinan lepasnya bahan-bahan radioaktif ke lingkungan dan atau ke zona proses kimia. Pada kopel nuklir untuk proses kimia, digunakan penukar panas intermediate (IHX) sebagai interface yang memisahkan antara zona nuklir dengan zona proses kimia. IHX adalah penukar panas helium-helium, dimana helium primer (905oC) mampu memindahkan panasnya ke helium sekunder (890oC). Untuk menjaga agar tidak terjadi lepasan bahan-bahan radioaktif dari zona nuklir, diterapkan sistem keseimbangan tekanan, yaitu tekanan proses kimia (4,5 MPa) dirancang lebih besar dari tekanan helium sekunder (4,1 MPa) maupun helium primer (4,0 MPa). Rancangan ini mengakibatkan kondisi operasi panas proses yang mampu disediakan oleh reaktor nuklir menjadi tidak optimal yaitu hanya mencapai sekitar 800oC pada daerah tabung katalisator. Kondisi ini mengakibatkan efisiensi termal steam reforming gas alam dengan panas nuklir hanya mencapai 50%, jauh di bawah proses dengan sumber panas bahan bakar fosil (80-85%). Sejumlah modifikasi desain operasi, seperti memanfaatkan reformer tipe bayonet yang dilengkapi dengan orifice baffle, dan peningkatan efektivitas pemanfaatan panas, mampu meningkatkan efisiensi termal steam reforming gas alam dengan panas nuklir menjadi sekitar 78%