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

Sgr A* ``Visual Binaries'': A Direct Measurement of the Galactocentric Distance

We present a new geometrical method for measuring the distance to the Galactic center (R_0) by solving for the Keplerian orbit of individual stars bound to the black hole associated with the Sgr A* from radial velocity and proper motion measurements. We identify three stars to which the method may be applied, and show that 1-5 % accuracy of R_0 can be expected after 15 years of observing, and 0.5-2 % after 30 years of observing, depending on what the orbital parameters of these three stars turn out to be. Combining the measurements of the three stars with favorable orbital parameters leads to even more precise values. In the example that we present, such combined solution yields 4 % accuracy already by the year 2002. All these estimates assume that annual position measurements will continue to be made with the 2 mas precision recently reported by Ghez et al. The precision of the distance measurement is relatively insensitive to the radial velocity errors, provided that the latter are less than 50 km/s. Besides potentially giving an estimate of R_0 that is better than any currently in use, the greatest advantage of this method is that it is free from systematic errors.Comment: Submitted to ApJ, 14 pages, 8 figure

Peran Pelibatan Diri Siswa Sebagai Mediator Dalam Hubungan Antara Iklim Kelas Dengan Sikap Kreatif Siswa SD Sekolah Alam

The aim of this study is to measure the role of student‟s school engagement as mediator in relations between classroom climate with creative attitude in nature-based school. The background of this research is the needs of creative attitude to face the challenge in the future by create the classroom climate and make the children more involved in school activity. One of the ways to increase creative attitude and school engagement is by creating the classroom climate that support the student‟s need. Nature-based school is one of alternative schools in Indonesia that creates active learning in their classroom climate that encourage students to be more engage, so therefore the students can have creative attitude. This research is done with quantitative methods and non-probability sampling methods for elementary school students from grade 3 until 5 in one of Nature Based School in Jakarta, by giving them three self report questionnaires. This research use three measuring instruments, Inventory Classroom Environment, Creativity Attitude Survey, and School Engagement Measure. Thorugh regression analysis, the results showing the positive correlation between classroom climate and school engagement (r = .373; p = .006) and creative attitude (r = .217; p = .002). Through the mediation analysis, the results indicated that school engagement had a role as full mediator in relations between classroom climate with creative attitude in nature based school elementary students. This thing define that classroom climate in nature-based school will improve student‟s creative attitude when students involved emotionally, in cognitive and behavioral in school activity

A Compact Microchip-Based Atomic Clock Based on Ultracold Trapped Rb Atoms

We propose a compact atomic clock based on ultracold Rb atoms that are magnetically trapped near the surface of an atom microchip. An interrogation scheme that combines electromagnetically-induced transparency (EIT) with Ramsey's method of separated oscillatory fields can achieve atomic shot-noise level performance of 10^{-13}/sqrt(tau) for 10^6 atoms. The EIT signal can be detected with a heterodyne technique that provides noiseless gain; with this technique the optical phase shift of a 100 pW probe beam can be detected at the photon shot-noise level. Numerical calculations of the density matrix equations are used to identify realistic operating parameters at which AC Stark shifts are eliminated. By considering fluctuations in these parameters, we estimate that AC Stark shifts can be canceled to a level better than 2*10^{-14}. An overview of the apparatus is presented with estimates of duty cycle and power consumption.Comment: 15 pages, 11 figures, 5 table