Eclipsing Binary Stars in Nearby Galaxies     

Ian Todd  Don Pollacco  Ian Skillen  D. M. Bramich  Steve Bell  Thomas Augusteijn 《Astrophysics and Space Science》2006,304(1-4):223-225

We briefly discuss the survey programme we are conducting to detect eclipsing binaries in local group galaxies. Some lightcurves from studies of M31, IC 1613 and NGC 6822 are presented along with details of future work.  相似文献   

The role of distance in peri-urban national park use: Who visits them and how far do they travel?     

《Applied geography (Sevenoaks, England)》2015

There is a sizable literature about the factors shaping park visitation and use – especially for urban parks, including (i) geographic (e.g. proximity), (ii) socio-cultural (e.g. population characteristics) and to a lesser extent, (iii) individual psychometric factors (e.g. attitudes and values). Yet comparatively little is known about how factors related to distance may affect peri-urban national park use, particularly outside the United States. This paper reports on research investigating distance-related factors affecting use of a peri-urban national park in Brisbane, Australia. This study found that older visitors live closer to the park while younger visitors travel further to use it. Surprisingly, travel distance did not vary with the type of recreational activities that users were conducting in the park. These results have implications for park planning and management including user demand for different recreational activities in peri-urban national parks. Results are useful for scholars using distance decay models to explain travel behaviour, evidencing the empirical veracity of the model in different places and across different service types. The findings are especially important for geographers because they demonstrate that assumptions about uniform park catchments may be unsupported and need to be empirically validated.  相似文献   

The role of morphology on the displacement of particles in a step–pool river system     

Hlne Lamarre  Andr G. Roy 《Geomorphology》2008,99(1-4):270-279

Although studies of sediment transport in steep and coarse-grained channels have been more numerous in recent years, the dynamics of sediment transport in step–pool river systems remain poorly understood. This paper investigates displacements of individual clasts through Spruce Creek (Québec, Canada), a classic step–pool channel, and the effects of the channel morphology on the path length of the clasts. Passive integrated transponder tags (PIT) were used to track the displacement of 196 individual particles over a range of discharges including the bankfull stage. Clasts were tracked after five sequences of flood events. The results showed that the distance distributions match a two-parameter Gamma model. Equal mobility transport occurs for the particle size investigated during each sequence of flood events. Mean travel distance of the clasts can be estimated from excess stream power, and the mobility of the clasts is more than an order of magnitude less than the model reported in riffle–pool channels. The dominant morphological length scale of the bed also controls the path length of the clasts. These results confirm some preliminary observations on sediment transport in step–pool channels.  相似文献   

The expansion field: the value of <Emphasis Type="Italic">H</Emphasis><Subscript>0</Subscript>     

G. A. Tammann  A. Sandage  B. Reindl 《Astronomy and Astrophysics Review》2008,15(4):289-331

Any calibration of the present value of the Hubble constant (H ₀) requires recession velocities and distances of galaxies. While the conversion of observed velocities into true recession velocities has only a small effect on the result, the derivation of unbiased distances which rest on a solid zero point and cover a useful range of about 4–30 Mpc is crucial. A list of 279 such galaxy distances within v < 2,000 km s⁻¹ is given which are derived from the tip of the red-giant branch (TRGB), from Cepheids, and/or from supernovae of type Ia (SNe Ia). Their random errors are not more than 0.15 mag as shown by intercomparison. They trace a linear expansion field within narrow margins, supported also by external evidence, from v = 250 to at least 2,000 km s⁻¹. Additional 62 distant SNe Ia confirm the linearity to at least 20,000 km s⁻¹. The dispersion about the Hubble line is dominated by random peculiar velocities, amounting locally to <100 km s⁻¹ but increasing outwards. Due to the linearity of the expansion field the Hubble constant H ₀ can be found at any distance >4.5 Mpc. RR Lyr star-calibrated TRGB distances of 78 galaxies above this limit give H ₀ = 63.0 ± 1.6 at an effective distance of 6 Mpc. They compensate the effect of peculiar motions by their large number. Support for this result comes from 28 independently calibrated Cepheids that give H ₀ = 63.4 ± 1.7 at 15 Mpc. This agrees also with the large-scale value of H ₀ = 61.2 ± 0.5 from the distant, Cepheid-calibrated SNe Ia. A mean value of H ₀ = 62.3 ± 1.3 is adopted. Because the value depends on two independent zero points of the distance scale its systematic error is estimated to be 6%. Other determinations of H ₀ are discussed. They either conform with the quoted value (e.g. line width data of spirals or the D _n −σ method of E galaxies) or are judged to be inconclusive. Typical errors of H ₀ come from the use of a universal, yet unjustified P–L relation of Cepheids, the neglect of selection bias in magnitude-limited samples, or they are inherent to the adopted models.  相似文献   

Isolation By Distance (IBD) signals in the deep-water rose shrimp Parapenaeus longirostris (Lucas, 1846) (Decapoda,Panaeidae) in the Mediterranean Sea     

《Marine environmental research》2013

The identification of boundaries of genetic demes is one of the major goals for fishery management, and few Mediterranean commercial species have not been studied from a genetic point of view yet. The deep-water rose shrimp Parapenaeus longirostris (Lucas, 1846) is one of the most important components of commercial landings in Mediterranean, its fishery aspects have received much attention, regrettably without any concern for the genetic architecture of its populations. The population structure in the central and eastern Mediterranean Sea (captures from six Italian and two Greek landings) has been analysed on the basis of surveys carried out with mitochondrial and AFLP markers. Data revealed the presence of a gradual discrepancy along a west–east axis. This species, occurring mainly at a depth of between 100 and 400 m, is not strongly confined in isolated demes, but it demonstrates an ‘Isolation By Distance’ model, within the Mediterranean Sea, which includes geographical areas with a some degree of isolation. The role of hydrodynamic forces, such as currents, water fronts, is discussed; and a further evidence of the ‘Levantine isolation’ within Mediterranean basin is shown.  相似文献   

Representing Spatial Uncertainty Using Distances and Kernels   总被引：8，自引：7，他引：1  

Céline Scheidt  Jef Caers 《Mathematical Geosciences》2009,41(4):397-419

Assessing uncertainty of a spatial phenomenon requires the analysis of a large number of parameters which must be processed by a transfer function. To capture the possibly of a wide range of uncertainty in the transfer function response, a large set of geostatistical model realizations needs to be processed. Stochastic spatial simulation can rapidly provide multiple, equally probable realizations. However, since the transfer function is often computationally demanding, only a small number of models can be evaluated in practice, and are usually selected through a ranking procedure. Traditional ranking techniques for selection of probabilistic ranges of response (P10, P50 and P90) are highly dependent on the static property used. In this paper, we propose to parameterize the spatial uncertainty represented by a large set of geostatistical realizations through a distance function measuring “dissimilarity” between any two geostatistical realizations. The distance function allows a mapping of the space of uncertainty. The distance can be tailored to the particular problem. The multi-dimensional space of uncertainty can be modeled using kernel techniques, such as kernel principal component analysis (KPCA) or kernel clustering. These tools allow for the selection of a subset of representative realizations containing similar properties to the larger set. Without losing accuracy, decisions and strategies can then be performed applying a transfer function on the subset without the need to exhaustively evaluate each realization. This method is applied to a synthetic oil reservoir, where spatial uncertainty of channel facies is modeled through multiple realizations generated using a multi-point geostatistical algorithm and several training images.  相似文献   

集值随机过程的样本函数连续性     

代宁  归庆明 《测绘学院学报》1999,(2)

讨论了集值随机过程Ｘ 的样本函数在闭收敛拓扑意义下的连续性,建立了此类性质与Ｘ 产生的实值随机过程ｄ（ｘ ,Ｘ） ,（ ｘ ∈Ｒｍ） 及其ＡＱＣａｓｔｉｎｇ 选择形成的向量值随机过程ｆｋ（ ｋ ≥１） 的样本函数连续性的等价关系。  相似文献   

基于概率分析的暴雨事件快速评估模型   总被引：7，自引：0，他引：7       下载免费PDF全文

陈艳秋  袁子鹏  盛永  戴廷仁 《气象与环境学报》2006,22(5):62-65

通过对区域性暴雨事件历史资料的统计分析,利用平均降水量、降水强度和覆盖范围3个指标,建立了基于距离函数的暴雨事件快速评估模型。在建模过程中,对每个指标进行了正态化转化和正态性检验,并利用正态分布概率密度函数确立了各指标数年一遇的等级标准。采用定义域平移的办法,对模型中各指标的权重系数进行了调整。另外,应用此模型对2005年汛期3次区域性暴雨灾害进行了评估应用,结果表明,决策服务效果较好。  相似文献   

Cycling willingness: Investigating distance as a dependent variable in cycling behavior among college students     

《Applied geography (Sevenoaks, England)》2015

We present a novel approach to understanding distance as a barrier to cycling and its use as a dependent variable in multinomial logistic regression. In doing so, this study explores distances in relation to spatially and relevant human factors such as gender and propensity to cycle among college students. College students (N = 949) participated in a health survey and stated possible predictors of cycling based on their cycle usage and preferences in the previous 30 days. While utilizing GIS in a bicycle-friendly network, we created geo-statistical GIS-groupings and performed multinomial logistic regression analysis. We examined college students to discover how their demographic and personal characteristics may mediate the deterrent properties of distance when considered as a dependent variable in cycling to a college campus. Age and propensity for cycling for transportation mediate the negative effect of distance on the likelihood of cycling. The findings also suggest that infrastructure improvements could lessen the impact of distance as a barrier to cycling and increase the likelihood of cycling for commuting.  相似文献   

Some studies of galactic and extragalactic distance scales     

Michael Feast 《Astrophysics and Space Science》1995,230(1-2):195-203

A review is given of some aspects of work in South Africa on the establishment, calibration and use of galactic and extragalactic distance indicators.  相似文献