The PL calibration for Milky Way Cepheids and its implications for the distance scale

The rationale behind recent calibrations of the Cepheid PL relation using the Wesenheit formulation is reviewed and reanalyzed, and it is shown that recent conclusions regarding a possible change in slope of the PL relation for short-period and long-period Cepheids are tied to a pathological distribution of HST calibrators within the instability strip. A recalibration of the period-luminosity relation is obtained using Galactic Cepheids in open clusters and groups, the resulting relationship, described by log L/L_sun = 2.415(+-0.035) + 1.148(+-0.044)log P, exhibiting only the moderate scatter expected from color spread within the instability strip. The relationship is confirmed by Cepheids with HST parallaxes, although without the need for Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos parallaxes, albeit with concerns about the cited precisions of the latter. A Wesenheit formulation of Wv = -2.259(+-0.083) - 4.185(+-0.103)log P for Galactic Cepheids is tested successfully using Cepheids in the inner regions of the galaxy NGC 4258, confirming the independent geometrical distance established for the galaxy from OH masers. Differences between the extinction properties of interstellar and extragalactic dust may yet play an important role in the further calibration of the Cepheid PL relation and its application to the extragalactic distance scale.Comment: Accepted for Publication (Astrophysics & Space Science

Linear Time LexDFS on Cocomparability Graphs

Lexicographic depth first search (LexDFS) is a graph search protocol which has already proved to be a powerful tool on cocomparability graphs. Cocomparability graphs have been well studied by investigating their complements (comparability graphs) and their corresponding posets. Recently however LexDFS has led to a number of elegant polynomial and near linear time algorithms on cocomparability graphs when used as a preprocessing step [2, 3, 11]. The nonlinear runtime of some of these results is a consequence of complexity of this preprocessing step. We present the first linear time algorithm to compute a LexDFS cocomparability ordering, therefore answering a problem raised in [2] and helping achieve the first linear time algorithms for the minimum path cover problem, and thus the Hamilton path problem, the maximum independent set problem and the minimum clique cover for this graph family

Mobile distributed authentication protocol

Networks access control is a crucial topic and authentication is a pre-requisite of that process. Most existing authentication protocols (for example that used in the GSM mobile network) are centralised. Depending on a single entity is undesirable as it has security, trust and availability issues. This paper proposes a new protocol, GSM-secure network access protocol (G-SNAP). In G-SNAP, the authentication procedure and network access control is handled by a quorum of authentication centres. The advantages of the novel protocol include increased security, availability and distributed trust

The adsorption of nitric oxide on a silicon (100) 2 × 1 surface studied with Auger electron spectroscopy

We present an Auger electron spectroscopy (AES) study of the adsorption of nitric oxide (NO) on a clean Si(100)2 × 1 surface at 300 and 550 K. Accurate measurement reeveal well resolved fine structure at Auger SiL2.3VV transitions at 62 and 83 eV. These peaks can be attributed to Si---O and Si---N bonds. Furthermore, it is argued that the broadening in the SiLi2.3VV Auger transition at 83 eV at 300 K may be composed of two nearby peaks, which could be attributed to two different kinds of chemical bonding, Si---N and Si---O. The absence of a peak at 69 eV at room temperature strongly suggests the NO adsorption on a Si(100)2 × 1 surface to be molecular. Dissociation of NO on the Si(100)2 × 1 surface is observed at 550 K

Dam Rain and Cumulative Gain

We consider a financial contract that delivers a single cash flow given by the terminal value of a cumulative gains process. The problem of modelling and pricing such an asset and associated derivatives is important, for example, in the determination of optimal insurance claims reserve policies, and in the pricing of reinsurance contracts. In the insurance setting, the aggregate claims play the role of the cumulative gains, and the terminal cash flow represents the totality of the claims payable for the given accounting period. A similar example arises when we consider the accumulation of losses in a credit portfolio, and value a contract that pays an amount equal to the totality of the losses over a given time interval. An explicit expression for the value process is obtained. The price of an Arrow-Debreu security on the cumulative gains process is determined, and is used to obtain a closed-form expression for the price of a European-style option on the value of the asset. The results obtained make use of various remarkable properties of the gamma bridge process, and are applicable to a wide variety of financial products based on cumulative gains processes such as aggregate claims, credit portfolio losses, defined-benefit pension schemes, emissions, and rainfall.Comment: 25 Pages, 1 Figur

Union Decline in Britain, CEP Discussion Paper No. 864

This paper investigates the demise of unionisation in British private sector workplaces over the last quarter century. We show that dramatic union decline has occurred across all types of workplace. Although the union wage premium persists it is quite small in 2004. Negative union effects on employment growth and financial performance are largely confined to the 1980s. Managerial perceptions of the climate of relations between managers and workers has deteriorated since the early 1980s across the whole private sector, whether the workplace is unionised or not

Changes over time in union relative wage effects in the UK and the US Revisited

This paper examines the impact of trade unions in the US and the UK and elsewhere. In both the US and the UK, despite declining membership numbers, unions are able to raise wages substantially over the equivalent non-union wage. Unions in other countries, such as Australia, Austria, Brazil, Canada, Chile, Cyprus, Denmark, Japan, New Zealand, Norway, Portugal and Spain, are also able to raise wages by significant amounts. In countries where union wage settlements frequently spill over into the non-union sector (e.g. France, Germany, Italy, the Netherlands and Sweden) there is no significant union wage differential. The estimates from the seventeen countries we examined averages out at 12 per cent. Time series evidence from both the US and the UK suggests three interesting findings. First, the union differential in the US is higher on average than that found in the UK (18 per cent compared with 10 per cent). Second, the union wage premium in both countries was untrended in the years up to the mid-1990s. Third, in both countries the wage premium has fallen in the boom years since 1994/95. It is too early to tell whether the onset of a downturn in 2002 will cause the differential to rise again or whether there is a trend change in the impact of unions. It is our view that most likely what has happened is that the tightening of the labor market has resulted in a temporary decline in the size of the union wage premium. Time will tell whether the current loosening of the labor market, that is occurring in both countries, will return the union wage premium to its long run values of 10 per cent in the case of the UK and 18 per cent in the case of the US. On the basis of past experience it seems likely that they will

Union Decline in Britain, IZA Discussion Paper No. 3436

This paper investigates the demise of unionisation in British private sector workplaces over the last quarter century. We show that dramatic union decline has occurred across all types of workplace. Although the union wage premium persists it is quite small in 2004. Negative union effects on employment growth and financial performance are largely confined to the 1980s. Managerial perceptions of the climate of relations between managers and workers have deteriorated since the early 1980s across the whole private sector, whether the workplace is unionised or not

The Union Wage Premium in the US and the UK

This paper presents evidence of both counter-cyclical and secular decline in the union membership wage premiu m in the US and the UK over the last couple of decades. The premium has fallen for most groups of workers, the main exception being public sector workers in the US. By the beginning of the 21st Century the premium remained substantial in the US but there was no premium for many workers in the UK. Industry, state and occupation-level analyses for the US identify upward as well as downward movement in the premium characterized by regression to the mean. Using linked employer-employee data for Britain we show estimates of the membership premium tend to be upwardly biased where rich employer data are absent and that OLS estimates are higher than those obtained with propensity score matching

Exploration for volcanogenic sulphide mineralisation at Benglog, north Wales

Exploration for volcanogenic sulphide mineralisation around Benglog is one of three investigations designed to assess the metallogenic potential of the Ordovician Aran Volcanic Group. Detailed geological mapping in the Benglog area enabled an interpretation of the volcanic environment, critical to such an assessment, to be made. The eruptive rocks are acid and basic in composition; the acid rocks are mostly ash-flow tuffs derived from outside the area, whereas the basic rocks have a local derivation. They are all interbedded with dark grey or black silty mudstone and were probably erupted in a submarine environment. Contemporaneous dolerite sills were intruded into wet sediment. This environment was suitable for volcanogenic exhalative sulphide deposits to form and indications of a metallogenic horizon were found at the top of the Y Fron Formation in the form of abundant pyrite, minor pyrrhotite and minor base metal enrichment. Soil samples, analysed for copper, lead and zinc, were collected and geophysical surveys were carried out along eleven east-west trending traverse lines 300 m apart across the volcanic succession. Indications were found of minor vein mineralisation at dolerite intrusion margins and locally along faults. Very high chargeability and low resistivity anomalies over mudstones did not spatially coincide with geochemical anomalies in soil, but the secondary redistribution of metals in soils and variable thickness of overburden precluded confident interpretation of the source of many soil anomalies. Geochemical drainage data, in conjunction with rock analyses, show strong barium enrichment in mudstones which could be volcanogenic in origin but related to two separate eruptive episodes. The findings of the survey were inconclusive. An environment suitable for the formation of volcanogenic exhalative sulphide deposits was established, but the geochemical and geophysical surveys located only minor vein mineralisation and tenuous indications of other styles of mineralisation. Recommendations are made for further work