Closed Time-like Curves and Inertial Frame Dragging: How to Time Travel via Spacetime Rotation

As the number of solutions to the Einstein equations with realistic matter sources that admit closed time-like curves (CTC's) has grown drastically, it has provoked some authors [10] to call for a physical interpretation of these seemingly exotic curves that could possibly allow for causality violations. A first step in drafting a physical interpretation would be to understand how CTC's are created because the recent work of [16] has suggested that, to follow a CTC, observers must counter-rotate with the rotating matter, contrary to the currently accepted explanation that it is due to inertial frame dragging that CTC's are created. The exact link between inertialframe dragging and CTC's is investigated by simulating particle geodesics and the precession of gyroscopes along CTC's and backward in time oriented circular orbits in the van Stockum metric, known to have CTC's that could be traversal, so the van Stockum cylinder could be exploited as a time machine. This study of gyroscopeprecession, in the van Stockum metric, supports the theory that CTC's are produced by inertial frame dragging due to rotating spacetime metrics.

Constraining the low-energy pion electromagnetic form factor with space-like and phase of time-like data

The Taylor coefficients c and d of the EM form factor of the pion are constrained using analyticity, knowledge of the phase of the form factor in the time-like region, 4m(pi)(2) <= t <= t(in) and its value at one space-like point, using as input the (g - 2) of the muon. This is achieved using the technique of Lagrange multipliers, which gives a transparent expression for the corresponding bounds. We present a detailed study of the sensitivity of the bounds to the choice of time-like phase and errors present in the space-like data, taken from recent experiments. We find that our results constrain c stringently. We compare our results with those in the literature and find agreement with the chiral perturbation-theory results for c. We obtain d similar to O(10) GeV-6 when c is set to the chiral perturbation-theory values.

Periodic geodesics and geometry of compact Lorentzian manifolds with a Killing vector field

We study the geometry and the periodic geodesics of a compact Lorentzian manifold that has a Killing vector field which is timelike somewhere. Using a compactness argument for subgroups of the isometry group, we prove the existence of one timelike non self-intersecting periodic geodesic. If the Killing vector field is nowhere vanishing, then there are at least two distinct periodic geodesics; as a special case, compact stationary manifolds have at least two periodic timelike geodesics. We also discuss some properties of the topology of such manifolds. In particular, we show that a compact manifold M admits a Lorentzian metric with a nowhere vanishing Killing vector field which is timelike somewhere if and only if M admits a smooth circle action without fixed points.

Electromagnetic form factor of the pion in the space- and time-like regions within the front-form dynamics

The pion electromagnetic form factor is calculated in the space- and time-like regions from -10 (GeV/c)2 up to 10 (GeV/c)2, within a front-form model. The dressed photon vertex where a photon decays in a quark-antiquark pair is depicted generalizing the vector meson dominance ansatz, by means of the vector meson vertex functions. An important feature of our model is the description of the on-mass-shell vertex functions in the valence sector, for the pion and the vector mesons, through the front-form wave functions obtained within a realistic quark model. The theoretical results show an excellent agreement with the data in the space-like region, while in the time-like region the description is quite encouraging. © 2003 Elsevier B.V. All rights reserved.

Time-like and space-like pion form factors within front-form dynamics

An approach for a unified description of the pion electromagnetic form factor in the space- and time-like regions, within a constituent quark model on the light front is briefly illustrated. Three main ingredients enter our approach: i) the on-shell quark-hadron vertex functions in the valence sector, ii) the dressed photon vertex where a photon decays in a quark-antiquark pair, and iii) the emission and absorption amplitudes of a pion by a quark. © 2005 American Institute of Physics.

Geometry of the de-Sitter universe

By making use of the fact that the de-Sitter metric corresponds to a hyperquadric in a five-dimensional flat space, it is shown that the three Robertson-Walker metrics for empty spacetime and positive cosmological constant, corresponding to 3-space of positive, negative and zero curvative, are geometrically equivalent. The 3-spaces correspond to intersections of the hyperquadric by hyperplanes, and the time-like geodesics perpendicular to them correspond to intersections by planes, in all three cases.

Generating string solutions in BTZ

Integrability of classical strings in the BTZ black hole enables the construction and study of classical string propagation in this background. We first apply the dressing method to obtain classical string solutions in the BTZ black hole. We dress time like geodesics in the BTZ black hole and obtain open string solutions which are pinned on the boundary at a single point and whose end points move on time like geodesics. These strings upon regularising their charge and spins have a dispersion relation similar to that of giant magnons. We then dress space like geodesics which start and end on the boundary of the BTZ black hole and obtain minimal surfaces which can penetrate the horizon of the black hole while being pinned at the boundary. Finally we embed the giant gluon solutions in the BTZ background in two different ways. They can be embedded as a spiral which contracts and expands touching the horizon or a spike which originates from the boundary and touches the horizon.

On a Gromoll-Meyer type theorem in globally hyperbolic stationary spacetimes

Following the lines of the celebrated Riemannian result of Gromoll and Meyer, we use infinite dimensional equivariant Morse theory to establish the existence of infinitely many geometrically distinct closed geodesics in a class of globally hyperbolic stationary Lorentzian manifolds.

Generating string solutions in BTZ

Integrability of classical strings in the BTZ black hole enables the construction and study of classical string propagation in this background. We first apply the dressing method to obtain classical string solutions in the BTZ black hole. We dress time like geodesics in the BTZ black hole and obtain open string solutions which are pinned on the boundary at a single point and whose end points move on time like geodesics. These strings upon regularising their charge and spins have a dispersion relation similar to that of giant magnons. We then dress space like geodesics which start and end on the boundary of the BTZ black hole and obtain minimal surfaces which can penetrate the horizon of the black hole while being pinned at the boundary. Finally we embed the giant gluon solutions in the BTZ background in two different ways. They can be embedded as a spiral which contracts and expands touching the horizon or a spike which originates from the boundary and touches the horizon. © 2013 SISSA, Trieste, Italy.

Wavelength/Time orthogonal codes with FEC offer dual advantage

To meet the growing demands of the high data rate applications, suitable asynchronous schemes such as Fiber-Optic Code Division Multiple Access (FO-CDMA) are required in the last mile. FO-CDMA scheme offers potential benefits and at the same time it faces many challenges. Wavelength/Time (W/T) 2-D codes for use in FO-CDMA, can be classified mainly into two types: 1) hybrid codes and 2) matrix codes, to reduce the 'time' like property, have been proposed. W/T single-pulse-per-row (SPR) are energy efficient codes as this family of codes have autocorrelation sidelobes of '0', which is unique to this family and the important feature of the W/T multiple-pulses-per-row (MPR) codes is that the aspect ratio can be varied by trade off between wavelength and temporal lengths. These W/T codes have improved cardinality and spectral efficiency over other W/T codes and at the same time have lowest crosscorrelation values. In this paper, we analyze the performances of the FO-CDMA networks using W/T SPR codes and W/T MPR codes, with and without forward error correction (FEC) coding and show that with FEC there is dual advantage of error correction and reduced spread sequence length.

Obtaining a light-like planar gauge

In the usual and current understanding of planar gauge choices for Abelian and non-Abelian gauge fields, the external defining vector n(mu), can either be space-like (n(2) < 0) or time-like (n(2) > 0) but not light-like (n(2) = 0). In this work we propose a light-like planar gauge that consists of defining a modified gauge-fixing term, L-GF, whose main characteristic is a two-degree violation of Lorentz covariance arising from the fact that four-dimensional space-time spanned entirely by null vectors as basis necessitates two light-like vectors, namely n(mu) and its dual m(mu), with n(2) = m(2) = 0, n . m not equal 0, say, e.g. normalized to n . m = 2.

Liberty

In terms of critical discourse, Liberty contributes to the ongoing aesthetic debate on ‘the sublime.’ Philosopher Immanuel Kant (1724–1804) defined the sublime as a failure of rationality in response to sensory overload: a state where the imagination is suspended, without definitive reference points—a state beyond unequivocal ‘knowing.’ I believe the events of September 11, 2001 eluded our understanding in much the same way, leaving us in a moment of suspension between awe and horror. It was an event that couldn’t be understood in terms of scope or scale. It was a moment of overload, which is so difficult to capture in art. With my work I attempt to rekindle that moment of suspension. Like the events of 9/11, Liberty defies definition. Its form is constantly changing; it is always presenting us with new layers of meaning. Nobody quite had a handle on the events that followed 9/11, because the implications were constantly shifting. In the same way, Liberty cannot be contained or defined at any moment in time. Like the events of 9/11, the full story cannot be told in a snapshot. One of the dictionary definitions for the word ‘sublime’ is the conversion of ‘a solid substance directly into a gas, without there being an intermediate liquid phase’. With this in mind, I would like to present Liberty as a work that is literally ‘sublime.’ But what’s really interesting to me about Liberty is that it presents the sublime on all levels: in its medium, in its subject matter (that moment of suspension), and in its formal (formless) presentation. On every level Liberty is sublime—subverting all tangible reference points and eluding capture entirely. Liberty is based on the Statue of Liberty in New York. However, unlike that statue which has stood in New York since 1886 and can be reasonably expected to stand for millennia, this work takes on diminishing proportions, carved as it is in carbon dioxide, a mysterious, previously unexplored medium—one which smokes, snows and dramatically vanishes into a harmless gas. Like the material this work is carved from, the civil liberties of the free world are diminishing fast, since 9/11 and before. This was my thought when I first conceived this work. Now it’s become evident that Liberty expresses a lot more than just this: it demonstrates the erosion of civil liberties, yes. However, it also presents the intangible, indefinable moments in the days and months that followed 9/11. The sculptural work will last for only a short time, and thereafter will exist only in documentation. During this time, the form is continually changing and self-refining, until it disappears entirely, to be inhaled, metabolised and literally taken to heart by viewers.

Implementing REDD through community-based forest management: lessons from Tanzania

REDD (reduced emissions from deforestation and degradation) aims to slow carbon releases caused by forest disturbance by making payments conditional on forest quality over time. Like earlier policies to slow deforestation, REDD must change the behaviour of forest degrading actors. Broadly, it can be implemented with payments to forest users in exchange for improved forest management, thus creating incentives; through payments for enforcement, thus creating disincentives; or through addressing external drivers such as urban charcoal demand. In Tanzania, community-based forest management (CBFM), a form of participatory forest management, was chosen by the Tanzania Forest Conservation Group, a local NGO, as a model for implementing REDD pilot programmes. Payments are made to villages that have the rights to forest carbon. In exchange, the villages must demonstrably reduce deforestation at the village level. In this paper, using this pilot programme as a case study, combined with a review of the literature, we provide insights for REDD implementation in sub-Saharan Africa. We pay particular attention to leakage, monitoring and enforcement. We suggest that implementing REDD through CBFM-type structures can create appropriate incentives and behaviour change when the recipients of the REDD funds are also the key drivers of forest change. When external forces drive forest change, however, REDD through CBFM-type structures becomes an enforcement programme with local communities rather than government agencies being responsible for the enforcement. That structure imposes costs on local communities, whose local authority limits the ability to address leakage outside the particular REDD village.

Representações sociais de discentes sobre universidade: um estudo psicossocial entre ingressantes do vestibular e da seleção ProUni

Demand for access to higher education to put in test the education Brazilian system in view of the surplus of selective processes of public universities, people without option to pay their studies at this education level. In this context, it has arisen the University for All(Universidade para Todos)Program, the ProUni, from Ministry of Education - MEC, created by the Federal Government in 2004, and that it aims the granting of full and partial scholarships in private higher education institutions, graduate courses in sequential specific training, low-income Brazilians students who do not have higher-level degree. Created by the Provisional Measure No 213/2004 and institutionalized by Law No. 11096 of January 13, 2005, the ProUni offers, however, the exemption of some taxes to those institutions that join the program. This is one of the privileged time for the study of Social Representations by offering the researcher, a living laboratory, natural environment, the confrontation between the established and new. In time like this people are challenged to incorporate the new system to the pre-existing one, aiming it through a strangeness of what was so familiar. It is through this game of social forces that we developed the present study with 196 entering higher education, of these are 116 of selective vestibular system and 80 of the ProUni selective system. We opt by the procedures for data collection in order to have access to the circulating senses, in addition to the streamlined responses. With foundation in Abric, we perform the test the Free Association of Words, then analysed by the software and by EVOC Content of the type theme as Bardin. Besides, we require of the subjects, a writing on the study object university later analysed by the software ALCESTE. The results point out to a representation strongly rooted in social factors such as more traditional socio-cultural elements: the beliefs, values, the symbols. It is unique in both groups of subjects: among those entering by the selective ProUni system, there was a stronger anchor in that it does not make inquiries about the program. At the same time, there is a stronger presence of objectivation, entering the selective vestibular system in order that they explained with a value judgement on the programme. It is suggested further studies considering the embryonic state of social representation, as recent as the social purpose that triggered. It would be relevant even the replication of the same research with other people in order to strengthen the power of the theorising of empiria available

Variação da qualidade da água de chuva no início da precipitação

One of the most evident and actual concern, not only in the scientific means, but also of the public knowledge in general, is the lack problem of the potable water, that come increasing more each time, motivated mainly for the po llution of the sources, the bad use of the water and the increase of the population. In such a way, the necessity of looking for new water sources and the development of techniques to use sources minus explored is becoming even more important and urgent. T he rainwater comes being used since a long time like a supplying source, but, due the few knowledge of its characteristics, the generated preconception and the discrimination around its consumption and to the bad use of the technique of collection and stor age, it comes being little used, wasting consequently a significant parcel of this source. Trying to develop the knowing of some characteristics of the rainwater, the present work looks for to define the curve of variation of the quality of the rainwater i n three points with distinct characteristics of the city of Natal -RN, in the course of the precipitation, in some situations of time and space. For describe the curve of variation of the water s quality, some variables must be analyzed, and to be identifie d when they modify themselves in the endurance of rain, showing in which moment the purification of the water is more or less quickly. The pH, the Turbidity and the Electric Conductivity can be related with a big part of the physicist -chemistries variables found in the water and, like its analyses don't spend any material, they have easy access and measurement. The present work analyzes the curves of decline of these three variables, in three points with distinct characteristics in the city of Natal -RN, being these points: one next to the sea, another one in region with great buildings concentration and the last point in a less polluted area. For the studied region, it was during the five first millimeters of rain that occurs the biggest reduction of the exi sting impurities in the atmosphere, mainly between the first and the second millimeter, and after the five first millimeters the values of the variables stabilize. With exception of the University Campus, where initially the rainwater already has very good quality, the values of Turbidity and Electric Conductivity suffer a brusque reduction after the first millimeter of rain