1,788 research outputs found
Toroidal Perturbations of Friedmann-Robertson-Walker Universes
Explicit expressions are found for the axisymmetric metric perturbations of
the closed, flat and open FRW universes caused by toroidal motions of the
cosmic fluid. The perturbations are decomposed in vector spherical harmonics on
2-spheres, but the radial dependence is left general. Solutions for general
odd-parity -pole perturbations are given for either angular velocities or
angular momenta prescribed. In particular, in case of closed universes the
solutions require a special treatment of the Legendre equation.Comment: 13 page
Marketing Tourism In The Galapagos Islands: Ecotourism Or Greenwashing?
Tourism accounts for approximately 7.5% - 15% of the world’s total employment and is the world’s most important service industry. In heavily frequented tourist destinations such as the Galapagos Islands in Ecuador, the importance is even higher. International travel is projected to double by 2020 with over 1.5 billion people traveling throughout the world. Within the tourism industry, ecotourism is the fastest growing sector, growing from 10 to 30 percent a year. While exact definitions of ecotourism vary, ecotourism is defined by the International Tourism Society (TIES) as “responsible travel to natural areas that conserves the environment and improves the welfare of local people.” A subset of sustainable tourism, ecotourism has a natural area focus, which benefits the environment and communities visited, fosters environmental and cultural understanding, appreciation and awareness. Because there is no universally adopted certification program for ecotourism, tourism operators may market their operations as “ecotourism” while in reality they are “greenwashing.” Greenwashers are dishonest tourism operators who embrace ecotourism as a new selling angle. To greenwash is to promote ecotourism while effectively doing the opposite. The Galapagos Islands is a popular destination for ecotourism. Beginning in the late 1960’s, the Galapagos tourism industry started with about 1,000 tourists per year and has boomed to 148,000 tourists in 2006. This has caused several problems: growing human population, introduction of alien and invasive species, and unwanted by-products from tourism. As a result, in 2007, the Galapagos Islands were placed on UNESCO’s list of World Heritage Sites in Danger. Because of the unique biodiversity of the Galapagos Islands, and the increase in tourism and its negative consequences, the Galapagos Islands presents an excellent example for a case study in marketing of ecotourism. Using the criteria established by the Mohonk Agreement for responsible ecotourism, this paper examines the websites of ecotourism operators in the Galapagos Islands to determine the extent to which they are “ecotours” or “greenwashed tours.” The implications for conservation of the islands and responsible marketing are discussed
Inertial frame rotation induced by rotating gravitational waves
We calculate the rotation of the inertial frames within an almost flat
cylindrical region surrounded by a pulse of non-axially-symmetric gravitational
waves that rotate about the axis of our cylindrical polar coordinates. Our
spacetime has only one Killing vector. It is along the z-axis and hypersurface
orthogonal. We solve the Einstein equations to first order in the wave
amplitude and superpose such linearized solutions to form a wave pulse. We then
solve the relevant Einstein equation to second order in the amplitude to find
the rotation of inertial frames produced by the pulse. The rotation is without
time delay. The influence of gravitational wave angular momentum on the
inertial frame demonstrates that Mach's principle can not be expressed in terms
of the influence of the stress-energy-momentum tensor alone but must involve
also influences of gravitational wave energy and angular momentum.Comment: Scheduled to appear in Class. and Quantum Grav. July 2008, "inertial"
added in titl
Do Rotations Beyond the Cosmological Horizon Affect the Local Inertial Frame?
If perturbations beyond the horizon have the velocities prescribed everywhere
then the dragging of inertial frames near the origin is suppressed by an
exponential factor. However if perturbations are prescribed in terms of their
angular momenta there is no such suppression.
We resolve this paradox and in doing so give new explicit results on the
dragging of inertial frames in closed, flat and open universe with and without
a cosmological constant.Comment: 12 page
Recommended from our members
Airborne gravity and precise positioning for geologic applications
Airborne gravimetry has become an important geophysical tool primarily because of advancements in methodology and instrumentation made in the past decade. Airborne gravity is especially useful when measured in conjunction with other geophysical data, such as magnetics, radar, and laser altimetry. The aerogeophysical survey over the West Antarctic ice sheet described in this paper is one such interdisciplinary study. This paper outlines in detail the instrumentation, survey and data processing methodology employed to perform airborne gravimetry from the multiinstrumented Twin Otter aircraft. Precise positioning from carrier-phase Global Positioning System (GPS) observations are combined with measurements of acceleration made by the gravity meter in the aircraft to obtain the free-air gravity anomaly measurement at aircraft altitude. GPS data are processed using the Kinematic and Rapid Static (KARS) software program, and aircraft vertical acceleration and corrections for gravity data reduction are calculated from the GPS position solution. Accuracies for the free-air anomaly are determined from crossover analysis after significant editing (2.98 mGal rms) and from a repeat track (1.39 mGal rms). The aerogeophysical survey covered a 300,000 km2 region in West Antarctica over the course of five field seasons. The gravity data from the West Antarctic survey reveal the major geologic structures of the West Antarctic rift system, including the Whitmore Mountains, the Byrd Subglacial Basin, the Sinuous Ridge, the Ross Embayment, and Siple Dome. These measurements, in conjunction with magnetics and ice-penetrating radar, provide the information required to reveal the tectonic fabric and history of this important region
Gravitational waves and dragging effects
Linear and rotational dragging effects of gravitational waves on local
inertial frames are studied in purely vacuum spacetimes. First the linear
dragging caused by a simple cylindrical pulse is investigated. Surprisingly
strong transversal effects of the pulse are exhibited. The angular momentum in
cylindrically symmetric spacetimes is then defined and confronted with some
results in literature. In the main part, the general procedure is developed for
studying weak gravitational waves with translational but not axial symmetry
which can carry angular momentum. After a suitable averaging the rotation of
local inertial frames due to such rotating waves can be calculated explicitly
and illustrated graphically. This is done in detail in the accompanying paper.
Finally, the rotational dragging is given for strong cylindrical waves
interacting with a rotating cosmic string with a small angular momentum.Comment: Scheduled to appear in Class. Quantum Grav. July 200
Centrifugal force induced by relativistically rotating spheroids and cylinders
Starting from the gravitational potential of a Newtonian spheroidal shell we
discuss electrically charged rotating prolate spheroidal shells in the Maxwell
theory. In particular we consider two confocal charged shells which rotate
oppositely in such a way that there is no magnetic field outside the outer
shell. In the Einstein theory we solve the Ernst equations in the region where
the long prolate spheroids are almost cylindrical; in equatorial regions the
exact Lewis "rotating cylindrical" solution is so derived by a limiting
procedure from a spatially bound system. In the second part we analyze two
cylindrical shells rotating in opposite directions in such a way that the
static Levi-Civita metric is produced outside and no angular momentum flux
escapes to infinity. The rotation of the local inertial frames in flat space
inside the inner cylinder is thus exhibited without any approximation or
interpretational difficulties within this model.
A test particle within the inner cylinder kept at rest with respect to axes
that do not rotate as seen from infinity experiences a centrifugal force.
Although the spacetime there is Minkowskian out to the inner cylinder
nevertheless that space has been induced to rotate, so relative to the local
inertial frame the particle is traversing a circular orbit.Comment: 12 pages, 2 figure
Comparative evaluation of plastic design methods for fatigue assessment of a nuclear class 1 piping nozzle
Design-by-analysis (DBA) procedures for Nuclear Class 1 pressure vessels such as those prescribed within ASME Boiler and Pressure Vessel Code (BPVC) Section III, provide rules to demonstrate assurance against fatigue failure. Two general assessment routes exist, linear finite element analysis (FEA) with stress categorization and elastic-plastic penalty factors, or nonlinear FEA with direct multiaxial strain evaluation. Whilst the elastic design route possesses many practical advantages, it is widely acknowledged to be very conservative, sometimes unacceptably so. At the cost of additional analysis effort, plastic design methods can provide a more appropriate evaluation of fatigue usage, potentially avoiding unnecessary design modifications and reducing the burden of in-service inspection requirements. This paper presents and compares various strain measures proposed for ASME III plastic fatigue analysis within the technical literature. A case study of a typical pressurized water reactor (PWR) main coolant line (MCL) piping nozzle subjected to pressure and thermal loads is presented. The influence of strain measure selection on the FE-derived strain concentration (Ke) factors is examined. Some important considerations for calculation of realistic Ke factors in ASME III are further discussed
Critical review of ASME III plasticity correction factors for fatigue design-by-analysis of nuclear power plant components
Abstract Despite significant technological progress in recent years, elastic–plastic fatigue analysis of pressure-retaining components remains a time-consuming venture. Accordingly, nuclear pressure vessel design codes such as ASME Section III provide simplified elastic–plastic analysis procedures as a practical alternative. This approach can be excessively conservative under certain conditions due to the bounding nature of the applied plasticity correction factor, Ke. While this over conservatism was tolerable in the past, recent technical challenges arising due to consideration of environmentally assisted fatigue and design for long-term operation have posed difficulty in achieving acceptable fatigue usage based on extant Code assessment procedures for certain components. The incorporation of more accurate Ke factors has since been identified as a nuclear industry priority. This paper presents a critical review of Ke factors within ASME Section III, with particular attention given to an approach proposed by Ranganath, which has recently been approved for publication as an ASME Section III Code Case. Correction factors adopted within other nuclear and nonnuclear codes and standards (C&S) were also considered. The code-based Ke factors were compared with Ke factors obtained directly from various elastic–plastic finite element (FE) models of representative plant components. The results revealed a considerable difference in conservatism between the code-based methods. Based on the elastic–plastic finite element analysis (FEA) results, an alternative improved plasticity correction method is proposed in this paper. The need for a harmonized approach to determining Ke based on elastic–plastic FE analysis and further development of efficient plasticity correction methods for total life assessment are highlighted as desirable industry objectives
Toroidal metrics: gravitational solenoids and static shells
In electromagnetism a current along a wire tightly wound on a torus makes a
solenoid whose magnetic field is confined within the torus. In Einstein's
gravity we give a corresponding solution in which a current of matter moves up
on the inside of a toroidal shell and down on the outside, rolling around the
torus by the short way. The metric is static outside the torus but stationary
inside with the gravomagnetic field confined inside the torus, running around
it by the long way. This exact solution of Einstein's equations is found by
fitting Bonnor's solution for the metric of a light beam, which gives the
required toroidal gravomagnetic field inside the torus, to the general Weyl
static external metric in toroidal coordinates, which we develop. We deduce the
matter tensor on the torus and find when it obeys the energy conditions. We
also give the equipotential shells that generate the simple Bach-Weyl metric
externally and find which shells obey the energy conditions.Comment: To appear in Class. Quantum Gra
- …