Hydrofracturing in response to the development of an overpressurised subglacial meltwater system during drumlin formation: an example from Anglesey,NW Wales     

Emrys Phillips  Leanne Hughes 《Proceedings of the Geologists' Association. Geologists' Association》2014

This paper presents the results of a detailed study of a complex hydrofracture system and host diamictons exposed within a longitudinal section through an elongate drumlin located to the west of Cemlyn Bay, Anglesey, NW Wales. This complex, laterally extensive sand, silt and clay filled hydrofracture system was active over a prolonged period and is thought to have developed beneath the Late Devensian (Weichselian) Irish Sea Ice Stream as it overrode this part of NW Anglesey. The sediment-fill to the hydrofracture system is deformed with kinematic indicators (folds, thrusts, augen) recording a SW-directed sense of shear, consistent with the regional ice flow direction across this part of the island. The lack of any geomorphological evidence for active retreat of the Irish Sea ice across Anglesey has led to the conclusion that hydrofracturing at the Cemlyn Bay site occurred within the bed of the Irish Sea Ice Stream whilst this relatively faster flowing corridor of ice was actively overriding the island. Shear imposed by the overriding ice led to the development of a subglacial shear zone which facilitated the propagation of the hydrofracture system with the laterally extensive feeder sills occurring parallel to Y-type Riedel shears. Although a subglacial setting beneath the active Irish Sea Ice Stream can be argued for the Cemlyn Bay hydrofracture system, its relationship to the formation of the ‘host’ drumlin remains uncertain. However, evidence presented here suggests that hydrofracturing may have occurred during the later stages or post landform development in response to the migration of overpressurised meltwater within the bed of the Irish Sea ice; possibly accompanying the local thinning and shutdown of the Irish Sea Ice Stream on Anglesey.  相似文献   

Economic and subsistence values of the standing stocks of seagrass fisheries: Potential benefits of no-fishing marine protected area management     

Richard K.F. Unsworth  Leanne C. Cullen  Jules N. Pretty  David J. Smith  James J. Bell 《Ocean & Coastal Management》2010,53(5-6):218-224

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Whipple telescope observations of LS I +61 303: 2004–2006     

A. Smith  R. W. Atkins  S. Bradbury  O. Celik  Y. C. K. Chow  P. Cogan  C. Dowdall  S. J. Fegan  P. Fortin  D. Gall  G. H. Gillanders  J. Grube  K. J. Gutierrez  T. A. Hall  D. Hanna  J. Holder  D. Horan  S. B. Hughes  T. B. Humensky  I. Jung  P. Kaaret  G. Kenny  M. Kertzman  D. B. Kieda  A. Konopelko  H. Krawczynski  F. Krennrich  M. J. Lang  S. Le Bohec  G. Maier  J. Millis  P. Moriarty  R. A. Ong  J. S. Perkins  K. Ragan  G. H. Sembroski  J. A. Toner  L. Valcarcel  V. V. Vassiliev  R. G. Wagner  S. P. Wakely  T. C. Weekes  R. J. White  D. A. Williams 《Astrophysics and Space Science》2007,309(1-4):299-303

In this paper we present the results of the past two years observations on the galactic microquasar LS I +61 303 with the Whipple 10 m gamma-ray telescope. The recent MAGIC detection of the source between 200 GeV and 4 TeV suggests that the source is periodic with very high energy (VHE) gamma-ray emission linked to its orbital cycle. The entire 50-hour data set obtained with Whipple from 2004 to 2006 was analyzed with no reliable detection resulting. The upper limits obtained in the 2005–2006 season covered several of the same epochs as the MAGIC Telescope detections, albeit with lower sensitivity. Upper limits are placed on emission during the orbital phases of 0→0.1 and 0.8→1, phases which are not included in the MAGIC data set.   相似文献   

The magnitude distribution, perihelion distribution and flux of long-period comets     

David W. Hughes 《Monthly notices of the Royal Astronomical Society》2001,326(2):515-523

The mass distribution and perihelion distribution of long-period comets are re-assessed. The mass distribution index is found to be 1.598±0.016 , indicating that the distribution is somewhat steeper than was obtained by previous analyses of an amalgam of all the available historical data. The number of long-period comets that have orbital perihelion distances, q , that fall in a specific q to q +d q range is found to be independent of q . It is also noted that the flux of long-period comets to the inner Solar system has remained constant throughout recorded history.
The number of long-period comets, , per 1-au interval of perihelion distance, per year, brighter than H , entering the inner Solar system is found to be given by log₁₀ =−2.607+0.359 H . It is therefore estimated that, for example, about 0.5, 30 and 2000 long-period comets with absolute magnitudes brighter than 0, 5 and 10 respectively pass the Sun on orbits with perihelion distances less than 2.0 au, every century.  相似文献   

A submillimetre survey of the star formation history of radio galaxies   总被引：1，自引：0，他引：1  

E. N. Archibald  J. S. Dunlop  D. H. Hughes  S. Rawlings  S. A. Eales  R. J. Ivison 《Monthly notices of the Royal Astronomical Society》2001,323(2):417-444

We present the results of the first major systematic submillimetre survey of radio galaxies spanning the redshift range 1< z <5. The primary aim of this work is to elucidate the star formation history of this sub class of elliptical galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the JCMT, we have obtained 850-μm photometry of 47 radio galaxies to a consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The radio galaxy targets have been selected from a series of low-frequency radio surveys of increasing depth (3CRR, 6CE, etc.), in order to allow us to separate the effects of increasing redshift and increasing radio power on submillimetre luminosity. Although the dynamic range of our study is inevitably small, we find clear evidence that the typical submillimetre luminosity (and hence dust mass) of a powerful radio galaxy is a strongly increasing function of redshift; the detection rate rises from ≃15 per cent at z <2.5 to ≳75 per cent at z >2.5, and the average submillimetre luminosity rises at a rate ∝(1+ z )³ out to z ≃4. Moreover, our extensive sample allows us to argue that this behaviour is not driven by underlying correlations with other radio galaxy properties such as radio power, radio spectral index, or radio source size/age. Although radio selection may introduce other more subtle biases, the redshift distribution of our detected objects is in fact consistent with the most recent estimates of the redshift distribution of comparably bright submillimetre sources discovered in blank field surveys. The evolution of submillimetre luminosity found here for radio galaxies may thus be representative of massive ellipticals in general.  相似文献   

The status of measurement of the Mediterranean mean dynamic topography by geodetic techniques   总被引：1，自引：1，他引：0  

Philip L. Woodworth  Médéric Gravelle  Marta Marcos  Guy Wöppelmann  Chris W. Hughes 《Journal of Geodesy》2015,89(8):811-827

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Quaternary glacial records in mountain regions：A formal stratigraphical approach     

P.D.Hughes P.L.Gibbard J.C.Woodward 《《幕》》2005,28(2):85-92

Glacial deposits in locally-glaciated mountain regions are often expressed through their surface form and the study of these deposits constitutes a major branch of geomorphology. Studies of glacial depositional records in mountain areas have often neglected formal stratigraphical procedure resulting in an ad hoc development of quasi-stratigraphical nomenclature. Here, a formal stratigraphical procedure is recommended, since this enables a systematic approach to the subdivision of glacial deposits in mountain regions. Moreover, such an approach facilitates, in some instances, the development of a formal chronostratigraphy that can be compared to regional and global geological time scales. This is important in locally-glaciated mountain regions where glacial deposits represent one of the most important records of cold stage environments. Given that glacial landforms represent a key component of the Quaternary record, maintaining a formal link between geomorphological and geological stratigraphical procedure is a fundamental requirement of a consistent and comparable stratigraphical framework.  相似文献   

Estimating evapotranspiration for a temperate salt marsh,Newcastle, Australia     

C. E. Hughes  J. D. Kalma  P. Binning  G. R. Willgoose  M. Vertzonis 《水文研究》2001,15(6):957-975

Evapotranspiration was studied at a salt marsh site in the Hunter River estuary, NSW, Australia, during 1996–8. Estimates of actual evapotranspiration (E_a) were obtained for three sites using the eddy correlation method. These values were compared with results obtained with the Penman and Penman–Monteith equations, and with pan evaporation. The Penman–Monteith method was found to be most reliable in estimating daily and hourly evapotranspiration. Surface resistance values averaging 12 s m^?1 were derived from the eddy correlation estimates. Recent tidal flooding and rainfall were found to decrease surface resistance and increase E_a/E_p ratios. Estimates of evapotranspiration obtained using the Penman–Monteith method were shown to be sensitive to changes in surface resistance, canopy height and the method used to estimate net radiation from incoming solar radiation. These results underline the importance of accurately estimating such parameters based on site‐specific data rather than relying on empirical equations, which are derived primarily for crops and forests. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

The SCUBA 8-mJy survey – I. Submillimetre maps, sources and number counts     

S. E.Scott  M. J.Fox  J. S.Dunlop  S.Serjeant  J. A.Peacock  R. J.Ivison  S.Oliver  R. G.Mann  A.Lawrence  A.Efstathiou  M.Rowan-Robinson  D. H.Hughes  E. N.Archibald  A.Blain  M.Longair 《Monthly notices of the Royal Astronomical Society》2002,331(4):817-838

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VLF waves in the magnetosphere     

A. R. W. Hughes 《Astrophysics and Space Science》1995,230(1-2):431-438

The study of VLF waves at ground based stations is an important source of information on particles trapped in the magnetosphere. By various techniques it is also possible to measure plasma densities, electric fields and monitor energetic particle injection. By studying the propagation of waves beneath the ionosphere it is possible to study particle precipitation from the magnetosphere. In this paper we summarise some of the techniques and results obtained from the study of VLF waves at the South African research station in Antarctica.  相似文献