Scale dependent dimension of luminous matter in the universe

We suggest a geometrical model for the distribution of luminous matter in the Universe, where the apparent dimension, D(l), increases linearly with the logarithm of the scale l. Beyond the correlation length, xi, the Universe is homogeneous, and D = 3. Comparison with data from the SARS redshift catalog, and the LEDA database provides a good fit with a correlation length xi approximately 300 Mpc. This type of scaling structure was recently discovered in a simple reaction-diffusion "forest-fire" model, indicating a broad class of scaling phenomena.     

Reflexionsversuche mit elektromagnetisch erzeugten Verdichtungsstößen hoher Mach-Zahlen

In a 80 cm long quartz-tube of 33 mm diameter plasma is generated by theta-pinch mechanism with conical coil and accelerated in the direction along the axis of the tube. A luminous front is observed and its velocity has been studied in, in dependence of coil distance and initial pressure. In Helium in a pressure range from 0·3 to 5 Torr it has been found by reflection experiments that before the luminous front a discontinuity in the pressure is moving ahead of the luminous front. The distanceΔx between this discontinuity and luminous front increases with increasing distance from the coil and with increasing initial pressure for instance up to 10 cm at a distance of about 50 cm and an initial pressure of 5 Torr. The results are compared to theoretical considerations.     

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研究了无汞等离子体平板荧光光源的气压、气隙、气体组成、光源结构及荧光粉加工对光源发光效率的影响。通过优化,光源的发光效率显著提高。实验结果表明,在450Torr、纯氙气、气体间隙0.7mm、前板玻璃厚为2.8mm,在前板采用60%浓度荧光粉图案印刷获得约20μm厚荧光粉层时,尺寸130mm×90mm的等离子体平板光源的发光效率和亮度超过40lm•w-1、11000cd•m-2,光通量超过500lm。通过优化,获得了较高的亮度和较高的发光效率,讨论了各影响因素引起光源发光效率变化的原因。     

Submillimeter galaxies

A cosmologically significant population of very luminous high-redshift galaxies has recently been discovered at submillimeter (submm) wavelengths. Advances in submm detector technologies have opened this new window on the distant Universe. Here we discuss the properties of the high-redshift submm galaxies, their significance for our understanding of the process of galaxy formation, and the selection effects that apply to deep submm surveys. The submm galaxies generate a significant fraction of the energy output of all the galaxies in the early Universe. We emphasize the importance of studying a complete sample of submm galaxies, and stress that because they are typically very faint in other wavebands, these follow-up observations are very challenging. Finally, we discuss the surveys that will be made using the next generation of submm-wave instruments under development.     

Apparent clustering of intermediate-redshift galaxies as a probe of dark energy

We show that the apparent redshift-space clustering of galaxies in the redshift range of 0.2-0.4 provides surprisingly useful constraints on dark-energy components in the Universe, because of the right balance between the density of objects and the survey depth. We apply Fisher matrix analysis to the luminous red galaxies in the Sloan Digital Sky Survey, as a concrete example. Possible degeneracies in the evolution of the equation of state and the other cosmological parameters are clarified.     

Living in a void: testing the Copernican principle with distant supernovae

We show that the local redshift dependence of the luminosity distance can be used to test the Copernican principle that we are not in a central or otherwise special region of the Universe. Future surveys of type Ia supernovae that focus on a redshift range of approximately 0.1-0.4 will be ideally suited to observationally determine the validity of the Copernican principle on new scales, as well as probing the degree to which dark energy must be considered a necessary ingredient in the Universe.     

A Unified Grand Tour of Theoretical Physics, 3rd edn., by Ian D. Lawrie

The emergence of the first black holes during the first billion years of cosmic history marks a key event in cosmology. Their formation is part of the overall process of ending the cosmic dark ages, when the first stars appeared in low-mass dark matter haloes about a few 100 million years after the Big Bang. The first stars, galaxies, and black holes transformed the Universe from its simple initial state into one of ever increasing complexity. We review recent progress on our emerging theoretical picture of how the first black holes appeared on the cosmic scene, and how they impacted the subsequent history of the Universe. Our focus is on supermassive black holes, in particular assessing possible pathways to the formation of the billion-solar-mass black holes inferred to power the luminous quasars at high redshifts. We conclude with a discussion of upcoming empirical probes, such as the James Webb Space Telescope (JWST), and the Laser Interferometer Space Antenna (LISA), further ahead in time.     

Cosmological constant from gauge fields on extra dimensions

We present a new model of dark energy which could explain the observed accelerated expansion of our Universe. We show that a five-dimensional Einstein–Yang–Mills theory defined in a flat Friedmann–Robertson–Walker universe compactified on a circle possesses degenerate vacua in four dimensions. The present Universe could be trapped in one of these degenerate vacua. With the natural requirement that the size of the extra dimension could be of the GUT scale or smaller, the energy density difference between the degenerate vacua and the true ground state can provide us with just the right amount of dark energy to account for the observed expansion rate of our Universe.     

On dark energy and accelerated reference frames

The paper is devoted to an explanation of the accelerated rate of expansion of the Universe. Usually the acceleration of the Universe, which is described by FRW metric, is due to dark energy. It is shown that this effect may be considered as a manifestation of torsion tensor for a flat Universe in the realm of Teleparallel gravity. An observer with radial field velocity obey Hubble's Law. As a consequence it is established that this is radial acceleration in a flat Universe. In Eq. (35) the acceleration is written in terms of the deceleration parameter, the Hubble’s constant and the proper distance. This may be interpreted as an acceleration of the Universe.     

Where galaxies really come from

The fundamental paradox of the incompatibility of the observed large-scale uniformity of the Universe with the fact that the age of the Universe is finite is overcome by the introduction of an initial period of superluminal expansion of space, called cosmic inflation. Inflation can also produce the small deviations from uniformity needed for the formation of structures in the Universe such as galaxies. This is achieved by the conjunction of inflation with the quantum vacuum, through the so-called particle production process. This mechanism is explained and linked with Hawking radiation of black holes. The nature of the particles involved is discussed and the case of using massive vector boson fields instead of scalar fields is presented, with emphasis on its distinct observational signatures. Finally, a particular implementation of these ideas is included, which can link the formation of galaxies, the standard model vector bosons and the observed galactic magnetic fields.     

The prospects of using gravitational waves for constraining the anisotropy of the Universe

The observation of GW150914 gave a new independent measurement of the luminosity distance of a gravitational wave event. In this paper, we constrain the anisotropy of the Universe by using gravitational wave events.We simulate hundreds of events of binary neutron star merger that may be observed by the Einstein Telescope. Full simulation of the production process of gravitational wave data is employed. We find that 200 binary neutron star merging events with the redshift in (0,1) observed by the Einstein Telescope may constrain the anisotropy with an accuracy comparable to that from the Union2.1 supernovae. This result shows that gravitational waves can be a powerful tool for investigating cosmological anisotropy.     

The Antikythera mechanism and the mechanical universe

Astronomers have two approaches to trying to determine the age of the Universe. They can estimate the ages of individual objects in the Universe and specifically in our Galaxy. These estimates use either the observed properties of stars and theoretical ideas concerning stellar evolution or the abundances of long-lived radioactive isotopes and their decay products. Alternatively they can use cosmological theories and observations to try to determine the age of the entire Universe. Obviously the Universe must be older than its component parts but neither of the above methods is sufficiently reliable that this is true of the deduced ages. As a result, it is from time to time reported that some object in the Universe is older than the Universe itself. In this article we discuss the methods that are currently being used to determine the age and we emphasize the problems in obtaining reliable results. It is not at present possible to provide a definite value for the age of the Universe.     

Probing Physics at Extreme Energies with Cosmic Ultra-High Energy Radiation

The highest energy cosmic rays observed possess macroscopic energies and their origin is likely to be associated with the most energetic processes in the Universe. Their existence triggered a flurry of theoretical explanations ranging from conventional shock acceleration to particle physics beyond the Standard Model and processes taking place at the earliest moments of our Universe. Furthermore, many new experimental activities promise a strong increase of statistics at the highest energies and a combination with γ-ray and neutrino astrophysics will put strong constraints on these theoretical models. We give an overview over this quickly evolving research field with a focus on testing new particle physics.     

Ultra high energy cosmic rays

The current status of Ultra High Energy Cosmic Rays (UHECR) is reviewed, with emphasis given to theoretical interpretation of the observed events. The galactic and extragalactic origin, in case of astrophysical sources of UHE particles, have the problems either with acceleration to the observed energies or with the fluxes and spectra. Topological defects can naturally produce particles with energies as observed and much higher, but in most cases fail to produce the observed fluxes. Cosmic necklaces and monopole-antimonopole pairs are identified as most plausible sources, which can provide the observed flux and spectrum. The relic superheavy particles are shown to be clustering in the Galactic halo, producing UHECR without Greisen-Zatsepin-Kuzmin cutoff. The Lightest Supersymmetric Particles are discussed as UHE carriers in the Universe.     

Cosmic inhomogeneities and averaged cosmological dynamics

If general relativity (GR) describes the expansion of the Universe, the observed cosmic acceleration implies the existence of a "dark energy." However, while the Universe is on average homogeneous on large scales, it is inhomogeneous on smaller scales. While GR governs the dynamics of the inhomogeneous Universe, the averaged homogeneous Universe obeys modified Einstein equations. Can such modifications alone explain the acceleration? For a simple generic model with realistic initial conditions, we show the answer to be "no." Averaging effects negligibly influence the cosmological dynamics.     

Instabilities and Annihilation Blockade of Macrospheres in the Gravitationally Neutral Universe Model

Corrections to the spectra describing Jeans instability and acoustic vibrations due to the consideration of annihilation processes in the hydrodynamic model of the gravitationally neutral Universe are obtained. The problem of annihilation of galactic clusters and anticlusters arising at the stages of the formation of massive gravitational clusters in the period following recombination of charged particles of the early Universe is also discussed. By the example of spherical macroscopic objects, it is shown that gravitational repulsion between cluster and anticluster results in the impossibility of their annihilation due to the existence of the finite closest approach distance if the latter exceeds the distance between macrosphere centers.     

Model for a Universe described by a non-minimally coupled scalar field and interacting dark matter

In this work the evolution of a Universe model is investigated where a scalar field, non-minimally coupled to space-time curvature, plays the role of quintessence and drives the Universe to a present accelerated expansion. A non-relativistic dark matter constituent that interacts directly with dark energy is also considered, where the dark matter particle mass is assumed to be proportional to the value of the scalar field. Two models for dark matter pressure are considered: the usual one, pressureless, and another that comes from a thermodynamic theory and relates the pressure with the coupling between the scalar field and the curvature scalar. Although the model has a strong dependence on the initial conditions, it is shown that the mixture consisted of dark components plus baryonic matter and radiation can reproduce the expected red-shift behavior of the deceleration parameter, density parameters and luminosity distance.     

海洋发光细菌的发光及其应用

海洋发光细菌是一类在正常的生理条件下能够发射可见光的异养细菌,其发光特性与细菌体内的物质结构、海洋环境要素、水中污染物等多种因素有关。通过对海洋发光细菌发光特性及其应用可能性的论述,如利用发光细菌的发光强度与水中毒物的浓度、毒性的关系检测污染物;利用潜艇航行时激发的生物发光勾画出潜艇涡动的光尾流可跟踪探测潜艇;海洋发光细菌的发光特性还可用以改进水下光通讯与探测、海洋水色遥感、海洋发光细菌分类、发光免疫和抗菌素浓度测定等方面。阐明海洋发光细菌发光特性的重要研究意义并为进一步开展应用研究提供借鉴。     

Essay review: Count Rumford-a forgotten genius

The search for a theory that explains the origin of galaxies and large-scale structure in the Universe is at an exciting stage. Observational advances, including measurements of the anisotropy in the cosmic microwave background and systematic surveys of galaxy redshifts, are confronting theoretical calculations of the distribution of matter produced by the action of gravity on small initial density fluctuations in the expanding Universe. Although the basic idea behind most theoretical models is simple, the details are complicated and there are many unknown parameters, such as the quantity and type of dark matter forming the bulk of the mass of the Universe. Consequently, at present, there are a number of contenders for a theory of structure formation but no single model can fit all the observational data completely satisfactorily.