澳大利亚旅华客源市场特征与拓展分析

2011年至2012年是澳大利亚首届“中国文化年”,研究澳大利亚旅华客源市场十分有现实意义。文章基于连续多年的大量统计资料,从历史发展阶段、人口统计学特征、入境方式、在华旅行方式、人均消费和平均停留时间、年内时间分布规律、空间分布规律等七方面分析了澳大利亚旅华客源市场特征,并得出与已有文献不同的研究结论。结合中澳两国的最新政策,文章最后从旅游领域交往、旅游宣传推广和旅游服务质量三方面提出了市场拓展建议。     

High-energy scalarons in R gravity as a model for Dark Matter in galaxies

We show that in the framework of R² gravity and in the linearized approach it is possible to obtain spherically symmetric stationary states that can be used as a model for galaxies. Such approach could represent a solution to the Dark Matter Problem. In fact, in the model, the Ricci curvature generates a high energy term that can in principle be identified as the dark matter field making up the galaxy. The model can also help to have a better understanding on the theoretical basis of Einstein-Vlasov systems. Specifically, we discuss, in the linearized R² gravity, the solutions of a Klein-Gordon equation for the spacetime curvature. Such solutions describe high energy scalarons, a field that in the context of galactic dynamics can be interpreted like the no-light-emitting galactic component. That is, these particles can be figured out like wave-packets showing stationary solutions in the Einstein-Vlasov system. In such approximation, the energy of the particles can be thought of as the galactic dark matter component that guarantees the galaxy equilibrium. Thus, because of the high energy of such particles the coupling constant of the R²-term in the gravitational action comes to be very small with respect to the linear term R. In this way, the deviation from standard General Relativity is very weak, and in principle the theory could pass the Solar System tests. As pertinent to the issue under analysis in this paper, we present an analysis on the gravitational lensing phenomena within this framework.Although the main goal of this paper is to give a potential solution to the Dark Matter Problem within galaxies, we add a section where we show that an important property of the Bullet Cluster can in principle be explained in the scenario introduced in this work.To the end, we discuss the generic prospective to give rise to the Dark Matter component of most galaxies within extended gravity.     

Novel technique for supernova detection with IceCube

The current supernova detection technique used in IceCube relies on the sudden deviation of the summed photomultiplier noise rate from its nominal value during the neutrino burst, making IceCube a ≈3 Megaton effective detection volume - class supernova detector. While galactic supernovae can be resolved with this technique, the supernova neutrino emission spectrum remains unconstrained and thus presents a limited potential for the topics related to supernova core collapse models.The paper elaborates analytically on the capabilities of IceCube to detect supernovae through the analysis of hits in the detector correlated in space and time. These arise from supernova neutrinos interacting in the instrumented detector volume along single strings. Although the effective detection volume for such coincident hits is much smaller (?35 kton, about the scale of SuperK), a wealth of information is obtained due to the comparatively low rate of coincident noise hits. We demonstrate that a neutrino flux from a core collapse supernova will produce a signature enabling the resolution of rough spectral features and, in the case of a strong signal, providing indication on its location.We further discuss the enhanced potential of a rather modest detector extension, a denser array in the center of IceCube, within our one dimensional analytic calculation framework. Such an extension would enable the exploration of the neutrino sky above a few GeV and the detection of supernovae up to a few 100’s of kilo parsec. However, a 3-4 Mpc detection distance, necessary for routine supernova detection, demands a significant increase of the effective detection volume and can be obtained only with a more ambitious instrument, particularly the boosting of sensor parameters such as the quantum efficiency and light collection area.     

Statistics of the Big Blue Bump Feature in a Low Redshift Sample of Active Galactic Nuclei

We present a statistical analysis of the big blue bump (BBB) feature for a large heterogeneous sample of 95 optically selected and soft X-ray bright, low redshift active galactic nuclei (AGNs). This sample covers a sufficiently broad luminosity range, allowing us to test the luminosity dependence of the spectral energy distribution in the BBB region. Following the works of Zheng et al., Laor et al. and Kriss et al., we introduce the broad band spectral index from 1050 Å to0.5 keV (α _UV-SX ), compare its distribution with that of the soft X-ray spectral index (α _SX ) obtained by ROSAT PSPC, and find that the two indices have equal average-values within 1 ～ 2σuncertainties, whether in the whole sample, in luminosity divisions or in subsamples. These equalities also have no obvious luminosity dependence. This indicates that a single power law can describe the overall UV toX-ray spectrum in a statistical sense, or the broad band UV to soft X-ray spectrum is the soft X-ray spectral extension on an average. Thus, our results support Laor et al.'s conjecture about the BBB peak aroundFUV 1050 Å from a statistical viewpoint. As we further test whether the equality holds for individual objects within measure errors, χ₂ test refuse to accept it. In addition, our statistical results, from the luminosity divisions and on the correlation of spectral indices with luminosity (M _B), imply that the luminosity dependence of α _UV and α _UV-SX is mainly due to absorption in low luminosity AGNs.     

Magnetic fields in galaxies

Summary Recent years have seen an amazing development in our knowledge of the magnetic fields in the universe. The last ten years were crucial in our realization of the importance of the magnetic fields in galaxies. While a lot of the earlier data on our Galaxy depended on optical observations, the bulk of the recent results depend on radio measurements. The radio Zeeman effect gave us new information on magnetic fields in molecular clouds. The mapping of galaxies at several radio frequencies resulted in new knowledge about the large-scale magnetic fields in these basic building blocks of the universe. These exciting observations have led to new theoretical developments. In particular, the dynamo theory of flat objects received much attention since the observed large-scale structures can best be explained through the action of the dynamo effect. This review will attempt to summarise the observational evidence and to give viable explanations for the magnetic fields in galaxies.     

The Sun's Distance from the Galactic Plane

Use is made of 93,106 parallaxes from the Hipparcos catalog, with a mixture of spectrum-luminosity classes, to derive the position of the Galactic plane. The reduction technique, mixed total least squares-least squares, takes into account the errors in the parallaxes, and the condition that the direction cosines of the Galactic pole have unit Euclidean norm is rigorously enforced. To obtain an acceptable solution it is necessary to eliminate the stars of classes O and B that belong to the Gould belt. The Sun is found to lie 34.56±0.56 pc above the plane. The coordinates of the Galactic pole, l _g , b _g, are found to be: l _g =0.°004±0.°039; b _g =89.°427±0.°035.This agrees well with what radio observations find and demonstrates that the IAU's recommendation in 1960 to use only radio observations to determine the Galactic pole, although correct at the time because of the paucity of optical observations, can no longer be justified given the plethora of observations contained in the Hipparcos catalog and an adequate reduction technique, unavailable in 1960. The reduction technique is also demonstrably superior to others because it involves fewer assumptions and calculates smaller mean errors. This revised version was published online in July 2006 with corrections to the Cover Date.     

The galactic evolution of the supernova rates

Supernova rates (hypernova, type II, type Ib/c and type Ia) in a particular galaxy depend on the metallicity (i.e. on the galaxy age), on the physics of star formation and on the binary population. In order to study the time evolution of the galactic supernova rates, we use our chemical evolutionary model that accounts in detail for the evolution of single stars and binaries. In particular, supernovae of type Ia are considered to arise from exploding white dwarfs in interacting binaries and we adopt the two most plausible physical models: the single degenerate model and the double degenerate model. Comparison between theoretical prediction and observations of supernova rates in different types of galaxies allows to put constraints on the population of intermediate mass and massive close binaries.

The temporal evolution of the absolute galactic rates of different types of supernovae (including the type Ia rate) is presented in such a way that the results can be directly implemented into a galactic chemical evolutionary model. Particularly for type Ia’s the inclusion of binary evolution leads to results considerably different from those in earlier population synthesis approaches, in which binary evolution was not included in detail.     

观测结果对三成分多分量星系化学演化模型的约束

本文是在银河系化学演化的基础上,利用银河系的三成分(threezone)(即晕、厚盘和薄盘)多相(multi phase)(气体,分子云,大、小质量恒星以及剩余物质)的化学演化的理论模型,讨论了以下观测约束:1、质量面密度、恒星形成率,各分区质量比;2、场星的年龄-金属丰度关系;3、α元素化学演化;4、太阳附近G矮星金属丰度分布;5、三成分金属丰度特征量;6、超新星爆发率;7、内落速率。结果表明,三成分多分量模型能够较好地满足观测约束,比较真实地反映星系演化过程。可以用该模型计算元素的星系化学演化。     

Cosmic and Galactic neutrino backgrounds from thermonuclear sources

We estimate energy spectra and fluxes at the Earth’s surface of the cosmic and Galactic neutrino backgrounds produced by thermonuclear reactions in stars. The extra-galactic component is obtained by combining the most recent estimates of the cosmic star formation history and the stellar initial mass function with accurate theoretical predictions of the neutrino yields all over the thermonuclear lifetime of stars of different masses. Models of the structure and evolution of the Milky Way are used to derive maps of the expected flux generated by Galactic sources as a function of sky direction. The predicted neutrino backgrounds depend only slightly on model parameters. In the relevant 50 keV–10 MeV window, the total flux of cosmic neutrinos ranges between 20 and 65 cm⁻² s⁻¹. Neutrinos reaching the Earth today have been typically emitted at redshift z2. Their energy spectrum peaks at E0.1–0.3 MeV. The energy and entropy densities of the cosmic background are negligible with respect to the thermal contribution of relic neutrinos originated in the early universe. In every sky direction, the cosmic background is outnumbered by the Galactic one, whose integrated flux amounts to 300–1000 cm⁻² s⁻¹. The emission from stars in the Galactic disk contributes more than 95% of the signal.