Classical Bianchi type I cosmology in K-essence theory

We use one of the simplest forms of the K-essence theory and we apply it to the classical anisotropic Bianchi type I cosmological model, with a barotropic perfect fluid modeling the usual matter content and with cosmological constant. The classical solutions for any but the stiff fluid and without cosmological constant are found in closed form, using a time transformation. We also present the solution whith cosmological constant and some particular values of the barotropic parameter. We present the possible isotropization of the cosmological model, using the ratio between the anisotropic parameters and the volume of the universe and show that this tend to a constant or to zero for different cases. We include also a qualitative analysis of the analog of the Friedmann equation.Comment: 15 pages with one figure, accepted in Advances in High Energy Physic

Apparent first-order wetting and anomalous scaling in the two-dimensional Ising model

The global phase diagram of wetting in the two-dimensional (2d) Ising model is obtained through exact calculation of the surface excess free energy. Besides a surface field for inducing wetting, a surface-coupling enhancement is included. The wetting transition is critical (second order) for any finite ratio of surface coupling J_s to bulk coupling J, and turns first order in the limit J_s/J to infinity. However, for J_s/J much larger than 1 the critical region is exponentially small and practically invisible to numerical studies. A distinct pre-asymptotic regime exists in which the transition displays first-order character. Surprisingly, in this regime the surface susceptibility and surface specific heat develop a divergence and show anomalous scaling with an exponent equal to 3/2.Comment: This new version presents the exact solution and its properties whereas the older version was based on an approximate numerical study of the mode

Action at a distance in classical uniaxial ferromagnetic arrays

We examine in detail the theoretical foundations of striking long-range couplings emerging in arrays of fluid cells connected by narrow channels by using a lattice gas (Ising model) description of a system. We present a reexamination of the well known exact determination of the two-point correlation function along the edge of a channel using the transfer matrix technique and a new interpretation is provided. The explicit form of the correlation length is found to grow exponentially with the cross section of the channels at the bulk two-phase coexistence. The aforementioned result is recaptured by a refined version of the Fisher-Privman theory of first order phase transitions in which the Boltzmann factor for a domain wall is decorated with a contribution stemming from the point tension originated at its endpoints. The Boltzmann factor for a domain wall together with the point tension is then identified exactly thanks to two independent analytical techniques, providing a critical test of the Fisher-Privman theory. We then illustrate how to build up the network model from its elementary constituents, the cells and the channels. Moreover, we are able to extract the strength of the coupling between cells and express them in terms of the length and width and coarse grained quantities such as surface and point tensions. We then support our theoretical investigation with a series of corroborating results based on Monte Carlo simulations. We illustrate how the long range ordering occurs and how the latter is signaled by the thermodynamic quantities corresponding to both planar and three-dimensional Ising arrays.Comment: 36 pages, 19 figure

Polarization of the \lya Halos Around Sources Before Cosmological Reionization

In Loeb & Rybicki (1999; paper I) it was shown that before reionization, the scattering of \lya photons from a cosmological source might lead to a fairly compact ($\sim 15''$) \lya halo around the source. Observations of such halos could constrain the properties of the neutral intergalactic medium (IGM), and in particular yield the cosmological density parameters of baryons and matter on scales where the Hubble flow is unperturbed. Paper I did not treat the polarization of this scattered radiation, but did suggest that the degree of such polarization might be large. In this Letter we report on improved calculations for these \lya halos, now accounting for the polarization of the radiation field. The polarization is linear and is oriented tangentially to the projected displacement from the center of the source. The degree of polarization is found to be 14% at the core radius, where the intensity has fallen to half of the central value. It rises to 32% and 45% at the radii where the intensity has fallen to one-tenth and one-hundreth of the central intensity, respectively. At larger radii the degree of polarization rises further, asymptotically to 60%. Such high values of polarization should be easily observable and provide a clear signature of the phenomenon of \lya halos surrounding sources prior to reionization.Comment: 8 pages, 2 Postscript figures, accepted by Astrophysical Journal Letters; some typos corrected; added two paragraphs at the end of section 3 concerning detectability of Lyman alpha halo

The sources of knowledge of two medieval Jewish commentators in nature issues: The case of gathering the musk (Song of Songs 5:1)

Musk, which is produced from the glands of several species of deer, was a well-known perfume throughout the Mediterranean Basin in the Middle Ages. The current article examines the meaning of the gathering operation of myrrh mentioned in Song of Songs 5:1, according to R. Joseph Ibn Aknin and Naḥmanides. The two commentators argue that the phrase ariiti mori can be interpreted as the unique manner of gathering the perfume of the musk deer in its lands of origin in the Far East. They contend that harvesting the perfume refers to gathering the perfume that the deer spreads on the rocks naturally, which is a higher quality product. The two medieval rabbis were exposed to contemporary scholars or oral traditions on the way of gathering the musk. Ibn Aknin took the information from Arabic writings, such as of al-Sirāfī and al-Masʿūdī and Ibn JulJuly With regard to Naḥmanides, his source of information on gathering musk is not clear. Contribution: This article contributes to the understanding of the issue of the sources of knowledge of scholars in medieval times and how the achieved information influenced their commentaries on the Biblical Text. The current study expounds the commentators’ interpretations from a multidisplinary perspective, such as the medieval zoology and perfume industry

‘Ostrich is a Fowl for any Matter’: The ostrich as a ‘strange’ fowl in Jewish literature

The size, strange body shape and behaviour of the ostrich aroused the imagination of the ancients, Jews and non-Jews, and therefore beginning from the classical era until recent generations, various legends and beliefs were attached to it. The ancients deliberated whether the ostrich is a bird or it is a cross between a bird and a four-legged creature. In this case, Jewish writings reflected an advanced and sometimes independent conception that the ostrich is a bird. A belief that is indeed partially based on reality has to do with the food of the ostrich. In ancient sources, the ostrich is described as eating glass or metal, and according to some testimonies, this is a major component of its food. Medieval literature includes another common belief that the ostrich is gifted with miraculous powers of sight and it can use these powers to hatch the eggs by staring at them. The general impression formed from the study is that the Jews were aware of legends that existed among the nations, and even used them in their study halls for halakhic discussions and to enrich their spiritual world

He said that the manna is that called taranjebin’: Ibn Ezra against Hiwi al-Balkhi’s interpretation of the biblical story of the manna

The biblical story on the miracle of the manna in the Sinai Desert aroused many discussions and interpretations over the generations. The current study focuses on Ibn Ezra’s controversy with Hiwi al-Balkhi on the question of whether the manna was a natural or miraculous phenomenon. The article explores the claims of the two sides in light of the historical evidence and the literature describing the phenomenon of ‘falling manna’ in various areas of the Sinai Desert and Eastern countries. According to Hiwi, the manna that rained down on the Israelites is taranjebin, a semi-liquid resinous sweet secretion of insects (honeydew) that exudes onto plants. Ibn Ezra deals with Hiwi’s claims through a series of refutations and arguments. He argues that the characteristics of the taranjebin do not fit the description of the biblical manna. For example, it does not come down in the Sinai Desert, it appears during a limited season, does not melt in the sun and does not rot during the night, and serves as a medicine rather than as food. Contribution: This article contributes to the understanding of Hiwi al-Balkhi’s identification of the biblical manna as honeydew and Ibn Ezra’s claims against his thesis. It expounds the commentators’ interpretations from a multidisciplinary perspective, such as the reality of harvesting the taranjebin in Iran and North Africa and its uses as food and medicine in the medieval culture

Scattering statistics of rock outcrops: Model-data comparisons and Bayesian inference using mixture distributions

The probability density function of the acoustic field amplitude scattered by the seafloor was measured in a rocky environment off the coast of Norway using a synthetic aperture sonar system, and is reported here in terms of the probability of false alarm. Interpretation of the measurements focused on finding appropriate class of statistical models (single versus two-component mixture models), and on appropriate models within these two classes. It was found that two-component mixture models performed better than single models. The two mixture models that performed the best (and had a basis in the physics of scattering) were a mixture between two K distributions, and a mixture between a Rayleigh and generalized Pareto distribution. Bayes' theorem was used to estimate the probability density function of the mixture model parameters. It was found that the K-K mixture exhibits significant correlation between its parameters. The mixture between the Rayleigh and generalized Pareto distributions also had significant parameter correlation, but also contained multiple modes. We conclude that the mixture between two K distributions is the most applicable to this dataset.Comment: 15 pages, 7 figures, Accepted to the Journal of the Acoustical Society of Americ

Stripping the 21st Century Classroom Naked: Treachery or Technique?

Some things at a glance though not desirable could be tolerated and ignored in this 21st century regarding the outlook of a typical classroom but not a naked classroom The paradigm shift in the age of the technology driven instructional delivery is a classroom equipped with modern technological tools for enhancing teaching and learning The new age schools and educational institutions pride themselves as having learning delivered by state-of-the-art technology thus classrooms having the touch of information and communication technology equipment and teachers who are trained in the art students as digital natives etc Anyone who thinks otherwise stripping classroom naked must be living in the past would be the immediate response to such postulation This paper take a critical look at a naked classroom in bid to unravel whether so doing has any relevance a technique or a fallacy The paper makes conclusion and recommendations amongst others that our classrooms should be reserved for useful face-to-face discussions and engaging students by using technology outside the classroo