Traversable wormholes in a string cloud

We study spherically symmetric thin-shell wormholes in a string cloud background in (3+1)-dimensional spacetime. The amount of exotic matter required for the construction, the traversability and the stability under radial perturbations, are analyzed as functions of the parameters of the model. Besides, in the Appendices a non perturbative approach to the dynamics and a possible extension of the analysis to a related model are briefly discussed.Comment: 21 pages, 10 figures; accepted for publication in Int. J. Mod. Phys.

Infrared radiation measurements of combustion gases third quarterly progress report, 1 jan. - 31 mar. 1965

Infrared absorption spectrum measurements of carbon monoxide - exhaust gase

Dilaton thin-shell wormholes supported by a generalized Chaplygin gas

In this article, we construct spherical thin-shell wormholes with charge in dilaton gravity. The exotic matter required for the construction is provided by a generalized Chaplygin gas. We study the stability under perturbations preserving the symmetry. We find that the increase of the coupling between the dilaton and the electromagnetic fields reduces the range of the parameters for which stable configurations are possible.Comment: 14 pages, 6 figures. v3: typos correcte

The study of base heating by radiation from exhaust gases final report, oct. 1, 1963 - sep. 30, 1964

Base heating by radiation from exhaust gase

Thin-shell wormholes with a generalized Chaplygin gas

In this article, spherically symmetric thin-shell wormholes supported by a generalized Chaplygin gas are constructed and their stability under perturbations preserving the symmetry is studied. Wormholes with charge and with a cosmological constant are analyzed and the results are compared with those obtained for the original Chaplygin gas, which was considered in a previous work. For some values of the parameters, one stable configuration is also present and a new extra unstable solution is found.Comment: 14 pages, 6 figures; v2: typos corrected and minor rewordin

Pola Kearifan Masyarakat Lokal dalam Sistem Sawah Surjan untuk Konservasi Ekosistem Pertanian

Tujuan penelitian ini adalah untuk mengetahui pola kearifan petani sawah surjan dalam mengkonservasi lahan pertanian dan hubungan pola kearifan petani sawah surjan dengan komponen-komponen ekosistem pertanian yang dapat dikonservasi. Metode penelitian yang digunakan adalah kuantitatif. Pengumpulan data dilakukan dengan menggunakan data sekunder dan angket. Data dianalisis secara deskriptif kuantitatif. Hasil penelitian dapat disimpulkan bahwa pola kearifan petani sawah surjan dalam mengkonservasi lahan pertanian adalah secara turun temurun, seringkali tanpa memahami makna atau tanpa sadar; dan hubungan pola kearifan petani sawah surjan dengan komponen-komponen ekosistem pertanian yang dapat dikonservasi adalah membantu menciptakan ekosistem pertanian yang lebih stabil dengan adanya keragaman tanaman yang ditanam, sehingga tidak mudah terserang hama dan dengan adanya diversifikasi hasil panen dapat memberikan keuntungan lebih bagi petan

Mate choice promotes inbreeding avoidance in the two-spotted spider mite

Since inbreeding in Tetranychus urticae can reduce offspring fitness, sexual selection may favour disassortative mate choice with respect to relatedness of the mating partners. We tested whether T. urticae shows this preference for mating with unrelated partners. We chose an experimental set-up with high potential for female choosiness, since females only mate once and are therefore expected to be the choosier gender. An adult virgin female was placed together with two adult males from the same population. One male was unrelated and the other male was related—a brother with whom she had grown up. Significantly more copulations (64%) took place with the unrelated male. Time to mating did not depend on the female-to-male relatedness. The remaining (non-copulating) male tried to interfere with the ongoing mating in the majority of cases, but this interference did not depend on the female-to-male relatedness. These results imply that T. urticae (a) can recognize kin (via genetic and/or environmental similarity) and (b) has the potential to avoid inbreeding through mate choice

Candle flames in microgravity

The candle flame in both normal and microgravity is non-propagating. In microgravity, however, the candle flame is also non-convective where (excepting Stefan flow) pure diffusion is the only transport mode. It also shares many characteristics with another classical problem, that of isolated droplet combustion. Given their qualitatively similar flame shapes and the required heat feedback to condensed-phase fuels, the gas-phase flow and temperature fields should be relatively similar for a droplet and a candle in reduced gravity. Unless the droplet diameter is maintained somehow through non-intrusive replenishment of fuel, the quasi-steady burning characteristics of a droplet can be maintained for only a few seconds. In contrast, the candle flame in microgravity may achieve a nearly steady state over a much longer time and is therefore ideal for examining a number of combustion-related phenomena. In this paper, we examine candle flame behavior in both short-duration and long-duration, quiescent, microgravity environments. Interest in this type of flame, especially 'candle flames in weightlessness', is demonstrated by very frequent public inquiries. The question is usually posed as 'will a candle flame burn in zero gravity', or, 'will a candle burn indefinitely (or steadily) in zero gravity in a large volume of quiescent air'. Intuitive speculation suggests to some that, in the absence of buoyancy, the accumulation of products in the vicinity of the flame will cause flame extinction. The classical theory for droplet combustion with its spherically-shaped diffusion flame, however, shows that steady combustion is possible in the absence of buoyancy if the chemical kinetics are fast enough. Previous experimental studies of candle flames in reduced and microgravity environments showed the flame could survive for at least 5 seconds, but did not reach a steady state in the available test time

Stability of Chaplygin gas thin-shell wormholes

In this paper we construct spherical thin-shell wormholes supported by a Chaplygin gas. For a rather general class of geometries we introduce a new approach for the stability analysis of static solutions under perturbations preserving the symmetry. We apply this to wormholes constructed from Schwarzschild, Schwarzschild-de Sitter, Schwarzschild-anti de Sitter and Reissner-Nordstrom metrics. In the last two cases, we find that there are values of the parameters for which stable static solutions exist.Comment: 14 pages, 5 figures; v2: minor changes and new references added. Accepted for publication in Physical Review