bluuebunny/crossref_metadata_2025 huggingface dataset:
The advantages and limitations of geoelectrical methods in the foundation investigation of the tracked hovercraft experimental site in Cambridgeshire
Authors: McDowell Peter William
Published: September 2007

An electrical resistivity survey showed that the foundation conditions were more complicated than indicated by preliminary borehole information. The results of resistivity traversing, which was completed in a few days at comparatively little cost, clearly indicated that a sand and gravel layer, which had been proved at each borehole, was absent from at least one third of the site. Also, resistivity depth probes enabled the thickness of peat and soft clay, overlying the sand and gravel layer, to be calculated with remarkable accuracy. The problems of determining the thickness of the sand and gravel with suitable accuracy and of distinguishing silt from sand and gravel were unfortunately not resolved by these geoelectrical methods.
The influence of superficial deposits on groundwater quality in the Vale of York
Authors: Spears D. A. , Reeves M. J.
Published: September 2007

Borehole samples were obtained from the glacial, lacustrine and fluviatile sands and clays which overlie the Permo-Triassic sandstone aquifer in the Vale of York. Mineralogical and chemical analyses were undertaken for 26 samples from which pore water was also extracted and analysed. Ion concentrations in pore water were found to change as a function of depth and permeability. Most of the ions present in pore water are thought to be derived from the drift and the source minerals have been identified. The superficial deposits are thought to have an important influence on the chemistry of ground water in the underlying Permo-Triassic sandstones.

Comparison with ground water from similar aquifers, but drift free, indicates that in these cases the sandstone exerts an important influence on ground water chemistry.
Detection of clay filled sink-holes in the chalk by geophysical methods
Authors: McDowell P. W.
Published: September 2007

The significance of sink-holes in chalk to engineering structures is introduced and the available techniques for locating these features are briefly reviewed. Particular consideration is given to the rapid and relatively inexpensive geophysical techniques that are available.

The main text is concerned with clay-filled sink-holes, which are common in chalk areas, particularly in Southern England. The site of a large engineering structure, where drilling had indicated the presence of clay infilled sink-holes, has been used to compare the appropriate geophysical methods, and also to develop suitable field procedures. It was found that the magnetic method could locate and delimit the clay filled sink-holes very rapidly. The central electrode configuration was the most suitable for electrical resistivity traversing.

The cost and effectiveness of these geophysical methods, compared with conventional drilling, supports a combined approach to the site investigation.
A study of fresh water lens configuration in the Cayman Islands using resistivity methods
Authors: Bugg Stephen Fredrick , Lloyd John William
Published: September 2007

The problems of identifying the base of fresh water lenses in oceanic islands are discussed. A study carried out in the Cayman Islands is described in which the lens base is defined in relation to potable water standards and mapped using surface resistivity measurements with salinity profile controls in boreholes. Using depth-salinity ratios the piezometric surface is then determined. The technique is considered to provide a reliable cheap and rapid method of obtaining lens geometry in oceanic islands particularly where fairly homogeneous lithologies are present.
Threshold slopes in South Wales
Authors: Rouse W. Colin , Farhan Yahya I.
Published: September 2007

The uniformity of the valley-side slope, in the dissected landscape of South Wales, might be interpreted in terms of rapid mass movement. Many samples of the debris mantle were taken from the test area to establish the engineering properties. The residual strength (φ′
r
= 35.3°) and saturated unit weight (γ
s
= 17.4 kN/m
3
) were incorporated into a model of shallow sliding and gave threshold slopes of 35.3° (dry state) and 17.2° (saturated state). The slopes were randomly sampled to create a frequency distribution with a population mean for valley-side slope of 15.5° < μ < 17.8° equivalent to the limiting angle, so that rapid mass movement is important in interpreting valley side slope. The modes on the frequency distribution were also interpreted in terms of threshold values for mass movement processes and a comparison made with results from other environments. It is possible to interpret most of the British landscape as a relic feature of glacial, periglacial and mass movement processes superficially modified by current processes.
Some observations on surface instability associated with coal deposits in South Sumatra
Authors: Walton G. , Gunawan R.
Published: September 2007

Introduction

Recent exploration of Indonesian government coal concessions in South Sumatra by Shell Mijnbouw N.V. has revealed small-scale surface instability of recent origin, which could be important with respect to the construction of large spoil dumps.

The area of interest lies 145 km south-west of Palembang where Mio-Pliocene coals of the Muara Enim formation outcrop in country around Tanjung Enim. These coal seams and the related coal-bearing strata of claystones, siltstones, and sandstones are gently folded and faulted having dips in the range of 5°-30°. In places, the sediments are intruded by andesites which have locally upgraded the coal to anthracite or semi-anthracite, although away from the intrusions the coals have a semi-lignitic or sub-bituminous aspect.

Irrespective of the degree of alteration, the coals are frequently more competent than the associated strata and outcrop as the cap rocks to escarpments and waterfalls. Preliminary sampling of three coal seams in one such setting took place along the valley of the Air Muara Tiga. A series of trenches up to 90 m long were dug down the valley slopes to depths of 3–6 m. The location of the coal seams, a generalized geological sequence, and the positions of the trenches referred to in this note (A and B) are shown in Fig. 1. The side slopes to this strike valley are convex with gradients increasing downwards from 3° to 45°, although much of the slope is inclined at 12° –16°. The local vegetation consists of secondary jungle, giving way to tropical grasses (alang
Rock grouting and water testing at Kielder Dam, Northumberland
Authors: Bruce Donald A. , Millmore James P.
Published: September 2007

A cement grout curtain has been formed in the North Abutment bedrock of Kielder Dam in Northumberland. In order to gauge the effectiveness of the grouting, a series of pre- and post-grouting Lugeon water tests were conducted in special control holes. This programme was executed according to proposals made in this journal on Lugeon testing (
Houlsby 1976
), which have now gained world-wide acclaim and acceptance. The paper demonstrates clearly both the practicality of the method and the usefulness of the results. Safe grouting pressures were selected following hydrofracture tests, again using similar methods. Data on curtain grouting design, execution and analysis are also provided, and fundamental observations made on the relationship of water takes and cement grout consumptions.
The hydrogeology of the Lee Valley and some effects of artificial recharge
Authors: Flavin R. J. , Joseph J. B.
Published: September 2007

The Chalk and overlying Tertiary sands of the London Basin comprise the aquifer system of a classical artesian basin, confined and underlain by the London Clay and the marls of the Lower Chalk, respectively. The piezometric surface was at or near ground level until extensive over-abstraction dewatered the aquifer system. Experimental artificial recharge has been carried out in the Lee Valley at three different periods since the 1890's, the most recent experiments leading directly to a full-scale operational recharge scheme.

Groundwater quality throughout the area shows considerable natural variation, closely related to the geology. The major dewatering and more recent refilling of the aquifer have led to various regional and local changes in groundwater quality, and these are discussed in relation to the hydrogeology of the system. The experimental and prototype recharge schemes have shown that large-scale, artificial recharge of this multiple aquifer system is a viable proposition; effects on groundwater quality are generally negligible except locally at two sites, where slight problems have been encountered, but these may only be temporary.
Applications of microcomputers in engineering geology: Introductory Note
Authors: Young R. Paul
Published: September 2007

1985 marks the tenth anniversary of the release of the first microcomputer in kit form in the USA. It is hard to believe that just over 40 years ago, the first computers were invented to crack secret message codes during the 2nd World War. These huge computers consisted of thousands of valves which essentially provided switches for on/off binary logic. The development of the transistor in 1948 led to the valve being replaced and started the miniaturization of computers. This miniaturization trend has continued since the 1950s, leading to the development of minicomputers in the 1970s and resulting today in a computer technology which allows over 100000 components to be etched onto a single chip of silicon less than l cm
2
. This is the microprocessor or computer on a chip and contains the equivalent of the many thousands of valves used in the earlier computers which occupied entire rooms. In a similar manner, the storage of digital information has undergone a revolution and it is common today to be able to store up to 1 Mbyte of information on one floppy disk. The advent of laser disks will, in the future, probably increase storage capacity by a factor of one million and the power of the new generation of super computers, such as the Cray, has led to problems being solved in microseconds rather than hours. These trends have resulted in faster precise processing of data and ready access to more reliable, smaller and cheaper computers with a greater capacity
Field measurements with microcomputers in soils and rocks
Authors: Coatsworth Andrew Michael , Corke David Julian , Finn Philip Stephen , Jones Alun Price
Published: September 2007

Four field applications of microcomputers are described: (i) a microcomputer system has been developed which allows inclinometer readings to be processed and plotted; (ii) system to monitor and analyse pressuremeter tests uses a microcomputer-based ‘autonomous data acquisition unit’ to log the data, which are simultaneously manipulated, and the results displayed on the graphics screen of a separate microcomputer without interfering with the data logging; (iii) seismic signals are logged by a microcomputer, on which the data can subsequently be processed; (iv) a data logging system has been developed for use with the CSIRO cell to carry out
in situ
measurements of rock stresses, with an on-site microcomputer plotting and analysing the strain measurements to give the complete stress tensor immediately following overcoring. By using microcomputers not only to collect but also to analyse data in the field, a programme of field tests and also the conduct of individual tests can be improved.
Microcomputers in laboratory testing and the assessment of site investigation data
Authors: Atkinson Michael Sidney , Coatsworth Andrew Michael , Eldred Peter John Lee
Published: September 2007

Microcomputers can be used in laboratory testing either for data logging alone or for both data logging and controlling a test. For such applications a microcomputer should possess a larger memory than may be envisaged at the planning stage and incorporate a real-time clock. A full range of interfaces and peripherals should be available. Consideration should be given to built-in obsolescence and the manufacturer's support of the microcomputer. Soil testing with the aid of a microcomputer is a real-time activity; a stable power supply, appropriate software and physical protection are essential.

A database program to aid the selection of design parameters is described; basic field and laboratory data can be stored and subjected to simple manipulations. Both the stored and manipulated data can be selectively plotted. An example of its use in assessing the undrained shear strength of a glacial clay is described. Single entry of the data and a less biased assessment based on all possibly useful data combinations are advantages of the microcomputer approach. Significant time and cost savings can result.
Fracture analysis from borehole geophysical techniques in crystalline rocks
Authors: McEwen T. J. , McCann D. M. , Shedlock S.
Published: September 2007

Geophysical borehole logging data from three 300 m boreholes in the Strath Halladale Granite in northeast Scotland have been analysed in terms of fracture delineation. The geophysical techniques which were found to be of most use in determining the location, nature and orientation of fractures are outlined, and the results used for defining fracture indices for the rock mass. A comparison is made between different fracture indices, and a simple geotechnical assessment of the rock mass is made using fracture measurements, on the complete core, and dynamic values of the bulk modules. Specific sections of the core material are compared with the responses of the geophysical sondes to illustrate the use of borehole geophysics in determining fracturing of the rock. Potential flow zones predicted from neutron and gamma-gamma logging are compared with those measured by temperature/conductivity logging, and are related to the fracturing of the rock and to its hydraulic conductivity.
Seismic spectroscopy in fracture characterization
Authors: Young R. P. , Hill J. J. , Bryan I. R. , Middleton R.
Published: September 2007

Characterization of fractures is an important factor in the assessment of the quality and strength of rock masses. Conventional seismic techniques of quantifying the broken-ness of rocks have concentrated on the use of velocity, but this has not resulted in unique interpretations. As part of a research project to assess fracturing in rock masses on opencast coal sites, empirical correlations are being developed which relate fracture characteristics to the attenuation of seismic signals.

An experimental programme into the design of efficient blasting/fragmentation systems in opencast mining is outlined. The programme involves the seismic assessment of rock brokenness before and after blasting, together with the associated ground vibrations and excavation process, in order to optimize blast fragmentation efficiency. The results show that the fragmentation efficiency of a mine blast can be quantified in terms of 3-D seismic attenuation spectra and polar anisotropy diagrams. These 3-D spectra and polar plots from a sequence of seismic experiments are then correlated with 3-D excavation efficiency profiles, blast and ground vibration spectral data in the optimization study. A data case study is given to highlight the scope of the data collected and the type of multivariate statistical analysis methods used.
Natural and artificial cavities as ground engineering hazards
Authors: Culshaw M. G. , Waltham A. C.
Published: September 2007

The occurrences of natural and artificial cavities are reviewed and their causes are assessed. Natural cavities are found principally in carbonate rocks and the processes of sinkhole formation are described. Solution cavities in non-carbonate rocks and cavities in insoluble rocks are also considered. Extraction methods for coal, metalliferous minerals and salts are described in relation to the creation of underground cavities. An outline procedure for locating cavities emphasizes the importance of the desk study in this type of investigation and the difficulty of proving the absence of cavities beneath a site.
Pile foundation problems in Kuala Lumpur Limestone, Malaysia
Authors: Bergado D. T. , Selvanayagam A. N.
Published: September 2007

The geology and karstic nature of the Kuala Lumpur (Malaysia) limestone are described in relation to pile foundation problems of heavily loaded structures. The presence of cavities, pinnacles, cantilever slabs, floating slabs and pockets of soft silty clay and loose sand in the underlying limestone bedrock presents formidable challenges to foundation engineers. Other problems include insufficient seating and damage to pile tips due to irregular and sloping bedrock surfaces. There is also the added difficulty of detecting the location and extent of cavities. Empirical design methods and local construction techniques have been successfully used such as: (i) bridging limestone cavities and slabs by filling with concrete, (ii) utilizing numerous small diameter high yield stress piles to distribute the loads and to withstand high driving stresses, (iii) filling cavities with concrete, and (iv) using micropiles to redistribute the loads. Two case histories are presented, consisting of an access ramp and a tall building. In each of these case histories, the soil investigation methods, the pile bearing capacity calculations, the selection of pile types, the pile load tests, the pile driving criteria, and construction problems are outlined and discussed. The pile foundation used consisted of H-section, high yield stress, 355 × 368 mm, driven steel piles with capacities of 750 kN to 1280 kN for the access ramp structures and the same H-section steel piles with pile capacities of 965 kN to 1070 kN for the tall building.
Karoo igneous activity, and the early stages of the break-up of Gondwanaland
Authors: Cox K. G.
Published: September 2007

The widespread early Jurassic Karoo vulcanism of southern Africa appears to have been generated from a large-scale mantle plume originating in the sub-lithospheric mantle, but with a considerable additional contribution in some areas of material from the lithosphere. Subduction-related vulcanism may also play a significant role, but the relationships of the two types of vulcanism, if indeed a clear distinction does exist, are at present uncertain. Continental break-up probably took place in two stages, the first of which, in the early Jurassic, was not accompanied by true seafloor spreading. In this stage, the reactivation of an ancient shear zone is thought to have resulted in the movement of Antarctica north-eastwards relative to Africa (in the present-day African reference frame), with the creation of a zone of thinned continental crust, or a mixed zone of oceanic and continental crust, in Mozambique. The second stage took place 10–30 Ma later as Antarctica and Madagascar moved southwards relative to Africa with the formation of the oldest-known oceanic crust of the Indian Ocean.
Jurassic magmatism and tectonism associated with Gondwanaland break-up: an Antarctic perspective
Authors: Elliot David H.
Published: September 2007

Magmatic and tectonic activity in Antarctica associated with the early stages of continental rifting and break-up of Gondwanaland culminated with tholeiitic magmatism at about 175–180 Ma. In the Ross Sea sector of the Transantarctic Mountains, Jurassic igneous rocks, comprising pyroclastic rocks and Ferrar Group tholeiitic basalts, overlie fluvial strata of the Permian-Upper Triassic Gondwana sequence. Petrological, structural and volcanological data suggest that the Jurassic pyroclastic rocks and overlying flood basalts were erupted into a volcano-tectonic rift system associated with lithospheric extension and decompression melting. Geochemically the Ferrar tholeiites form part of the Gondwana low-Ti province, but they exhibit marked differences in initial
87
Sr/
86
Sr ratios and in high field strength element abundances in comparison with other parts of the province.

Three Early to Middle Jurassic tectono-magmatic terrains were present in this part of Gondwanaland: a plate margin magmatic arc; a belt of silicic within-plate igneous rocks inboard of the arc; and a continental flood basalt province (the Gondwana low-Ti province). Silicic volcanism mainly preceeded emplacement of Ferrar tholeiites, whereas major silicic activity elsewhere either accompanied basaltic magmatism or, though spatially separated preceded it. Younger magmatic episodes have obscured much of the plate margin record. Lack of reliable age determinations makes details of relations between tectonism and magmatism difficult to assess.
Timing and duration of Early Tertiary volcanism in the North Atlantic: new evidence from West Greenland
Authors: Larsen Lotte M. , Pedersen Asger K. , Pedersen Gunver K. , Piasecki Stefan
Published: September 2007

Marine mudstones intercalated with Early Tertiary volcanic hyaloclastites in West Greenland contain dinoflagellate cyst assemblages corresponding to nanoplankton zones NP4-NP8 (Danian to Thanetian). Sediments correlated with NP3 are known from the bottom of the volcanic sequence, whereas the top of the sequence is non-marine. A horizon with normally-magnetized subaerial lavas correlates with hyaloclastites within the NP4 interval. This horizon must correspond to magnetic polarity zone 27N; the overlying reversely-magnetized lavas are assumed to belong to both polarity zones 26R and 25R. The main plateau-building volcanic phase in West Greenland is thereby constrained between ‘top polarity chron C28N’ and ‘top polarity chron C25R’, a time interval of 5–6 Ma.

In comparison with other parts of the North Atlantic Tertiary Igneous Province, the volcanism in West Greenland started at an early stage, and the main plateau-building phase was finished before the volcanism in East Greenland started in the NP9 interval (C24R). Sea-floor formation and onshore picrite volcanism started almost simultaneously within a region; first along the West Greenland margin and later along the East Greenland margin. In terms of an impinging mantle plume in the North Atlantic, the volcanism started over the peripheral parts and not over the central part. The differences in timing and character of the volcanic products in the North Atlantic indicate a considerable lithospheric control. The early, picrite-dominated volcanism in West Greenland may be caused by channelling of hot material from the axial part of the plume, impinging on a thick Archaean lithosphere beneath central to eastern Greenland, towards the west into a pre-existing lithospheric ‘thinspot’. The switch of the onshore volcanism from West to East Greenland may be caused by a concomitant switch of the hot axial plume flow from west to east because of the westwards drift of the plate over the plume.
Right place, wrong time: anomalous post-rift subsidence in sedimentary basins around the North Atlantic Ocean
Authors: Joy Aidan M.
Published: September 2007

The central and northern North Sea Basin was formed as a result of at least two extensional episodes, the latest of which took place during the Late Jurassic. During the Early Tertiary, some 80 Ma later, the basin experienced a dramatic acceleration in subsidence. Subsidence acceleration of Early Tertiary age has also been reported from a number of other extensional basins, on both sides of the North Atlantic, in which stretching had ceased several tens of millions of years previously. This phenomenon is not in agreement with the published models of extensional basin formation, which predict that the rate of thermal subsidence should progressively decline following extension. It is possible that the predicted pattern of thermal subsidence was obscured by the effects of a mantle hot spot beneath the North Atlantic lithosphere during the Cretaceous to Early Tertiary. However, it is difficult to explain the subsidence phenomena observed in basins around the North Atlantic Ocean using simple hot spot models. It is concluded that the relationships between hot spot activity, continental break-up and vertical crustal movements in the North Atlantic region are subtle and complex, but that subsidence history analysis can yield valuable insights into these relationships.
Geochronologies and environmental records of Quaternary fluvial sequences in the Guadalope basin, northeast Spain, based on luminescence dating
Authors: Fuller Ian C. , Macklin Mark G. , Passmore David G. , Brewer Paul A. , Lewin John , Wintle Ann G.
Published: September 2007

Geomorphological investigations of Quaternary fluvial deposits in the Guadalope basin, NE Spain, have revealed an extended record of river and drainage basin response to long term environmental change. Investigations have focused on a 13 km long reach centred on the town of Castelserás and a 4 km long reach at Mas de Las Matas. The study reach at Mas de Las Matas is located at the confluence of the Rio Guadalope and its principal tributary the Rio Bergantes. The Castelserás reach is situated 16 km downstream from the Bergantes confluence within a relatively narrow bedrock-confined valley.

Luminescence dating provides a geochronology indicating that deposits in both study reaches span the Mid-Pleistocene through to the historic period. The Mid-Pleistocene was characterized by large-scale (locally up to 40 m) aggradation and incision cycles associated with tributary stream and slope input of sediment. More gradual alluviation in oxygen isotope stages 4 and 5 was followed by renewed dissection and aggradation immediately preceding the Last Glacial Maximum. At least four river terraces were formed during this period, with heights above present river level of between 10 and 15 m. River instability continued after the glacial maximum and into the Holocene, when the most recent major alluvial unit was formed 3000 to 5000 years ago.

Progressive entrenchment of the Guadalope valley floor during the Pleistocene would appear to reflect long-term regional uplift with channel aggradation and dissection episodes linked to the climate changes shown by vegetation and oxygen isotope records. Rates of downcutting increased during oxygen isotope stages 2 and 3. This change probably occurred in response to a reduction of coarse sediment delivery to the main channel from tributary catchments, an increase in trunk stream competence and/or catchment uplift.
Magnitude and frequency of Holocene palaeofloods in the southwestern United States: A review and discussion of implications
Authors: Enzel Yehouda , Ely Lisa L. , House P. Kyle , Baker Victor R.
Published: September 2007

Data about the magnitude and time of occurrence of palaeofloods from the lower Colorado River basin enable us to test two long-standing hypotheses which have affected many studies and applications in the field of flood hydrology. The two hypotheses are (a) the existence of an upper boundary to flood magnitudes and whether there is a possibility of determining it from the existing data, and (b) the random occurrence versus clustering of the large floods through time.

Earlier observations on regional flood envelope curves indicated the existence of an upper limit for flood magnitudes, but these studies limited their conclusions because of the short length of the systematic gauged data. This limitation is overcome here because palaeoflood data cover a much longer period of observation. Palaeoflood studies provide information about the largest individual floods experienced in many rivers in a specific region occurring over the last millennia. In the southwestern US, this information demonstrates that, even when the length of observational data increases to centuries and millennia, there is no change in the stabilized, regional envelope curves constructed from gauged and historical flood records. This pattern supports the hypothesis of an upper limit to flood magnitudes and points to a method for testing this hypothesis in other regions. There are surprising similarities between the envelope curve of the palaeoflood data and the envelope curve for the gauged and historical data in the lower Colorado River basin. These similarities indicate that in regions of the world where flood data is sparse envelop curves based on palaeoflood studies can provide basic data for engineering design purposes and other hydrological applications.

The random occurrence of large floods in time is tested by constructing chronologies for the largest palaeofloods in several basins in the lower Colorado River basin. These chronologies indicate a clustering of the large floods in specific time periods. The similarity between the various time periods characterized by high- and low-flooding and other palaeoclimatic indicators from the southwestern United States seems best explained by a climatic control on flood frequency over the last 5000 years.
Late Quaternary intra-continental river palaeohydrology and polycyclic terrace formation: the example of south Siberian river valleys
Authors: Yamskikh A. F.
Published: September 2007

The subject of intra-continental river regime and related polycyclic terrace formation has been investigated in south and central Siberia. The intra-continental river regime in the past has differed from the regimes of regions with both marine dominated climates and marine/continental transitional climates. The main feature of the intra-continental paleohydrological river regime was extremely high increases in river level. These increases in level were caused by periodic increases of river discharge during the Pleistocene and Holocene which occurred during periods of valley relief instability caused by climate cooling. The simultaneous accumulation of alluvium on surfaces of different heights occurred during high floods and caused the formation of polycyclic terraces. These are the type terraces of the intra-continental regions.
River responses to decadal-scale changes in discharge regime: the Gila River, SE Arizona
Authors: Hooke J. M.
Published: September 2007

Rapid and large responses of semi-arid fluvial systems to alterations in discharge are well documented. Some of these changes have been sudden and have resulted in ‘metamorphosis’ of the channel. The Gila River in SE Arizona, USA, was identified as behaving in this way in the early twentieth century. Changes of the Gila River channel since 1920 have been investigated, and in particular, the last three relatively wet decades have been compared with the drier ones of the 1920s to 1950s. The research has shown that the morphological response to high flow events depends on sequences of events and critical combinations of conditions. Feedback effects of morphology can induce a ramped response and morphology can be further complicated by interactive effects with vegetation growth. Morphology may therefore not show a simple relationship to size of event or wetness of a period and therefore care should be taken when making palaeohydrological inferences from morphology.
Identifying Phanerozoic extinction controls: statistical considerations and preliminary results
Authors: Macleod N.
Published: September 2007

Two prominent patterns have been recognized in Phanerozoic extinction data: (1) a quasi-periodic distribution of extinction-intensity peaks, and (2) a linear, declining background extinction intensity gradient. Characterization and interpretation of both patterns are necessary to understand Phanerozoic extinction controls. The extinction-intensity peak spectrum has been variously interpreted as a reflection of the time-series of major sea-level regressions, continental flood-basalt province (CFBP) eruptions, and bolide impacts. In order to evaluate the level of association between these time-series and the Phanerozoic marine invertebrate extinction record statistically, a new Monte Carlo simulation strategy is presented. Results of simulation-based tests suggest that the time-series of major, eustatic sea-level regressions and CFBP eruption events have a statistically significant (p≤ 0.05) association with Tatarian-Pliocene, stage-level, extinction intensity peaks. Associations between this peak series and the time-series of crater-producing bolide impacts do not appear significant at this level. A limited multicausal event scenario was also tested using the Monte Carlo method, and recognized the combination of sea-level regression and CFBP volcanism to be significantly associated with the largest extinction intensity peaks of the last 250 Ma. The background extinction-intensity gradient has been interpreted variously as: (1) an indicator of progressive improvement in extinction resistance through selection; (2) the by-product of an invasion of marginal (extinction-resistant) habitats; and (3) as a taxonomic-stratigraphical artefact. Results of subdivided linear trend analyses suggest that the background extinction-intensity gradient is largely confined to the Late Palaeozoic-Cenozoic interval. No statistically significant gradient is present in the most recent compilation of Early-Middle Palaeozoic data on marine, invertebrate extinctions. The timing of gradient initiation and extinction variance analyses suggest that reorganization of global carbon cycles and oceanographical circulation patterns in the Devonian-Early Carboniferous, and the evolutionary appearance of modern phytoplankton groups in the Late Triassic both had dramatic effects on the character of the extinction-intensity gradient.
Conodont sample-population approach to defining the base of the Changhsingian Stage, Lopingian Series, Upper Permian
Authors: Mei Shilong , Henderson Charles M. , Cao Changqun
Published: September 2007

Conodonts have been restudied in order to define the base of the Changhsingian Stage boundary at Meishan, Changxing County, Zhejiang Province, China. The Changhsingian represents the second and last stage of the Upper Permian, which is also known as the Lopingian Series. A sample-population based taxonomic approach has been used and described. This approach usually views the entire collection within a given sample as a population and recognizes the most consistent and stable characters within that ‘sample-population’ for identification. Three related conodont species,
Clarkina longicuspidata
Mei & Wardlaw
in
Mei
et al.
1994,
C. wangi
(Zhang 1987) and
C. subcarinata
(Sweet
in
Teichert
et al.
1973) have been redefined and redescribed using this new approach that recognizes carinal development as an apomorphic character for these taxa. A consistent change in denticulation has been observed between
Clarkina longicuspidata
and
Clarkina wangi
wherein
C. longicuspidata
has a prominent gap in front of the cusp, whereas
C. wangi
has a ‘wall’-like carina. The carinal change may have resulted from a heterochronic process involving acceleration, since juvenile descendants exhibit features of ancestral adults; the change may be related to the evolution of other biota that may represent potential food sources for the conodont animal, given the apparent importance of the conodont carina for food processing. It is suggested that the base of the Changhsingian Stage could be defined within the
C. longicuspidata-C. wangi
lineage, based on the newly refined taxonomy. This boundary occurs close to the flooding surface that represents at least the second parasequence within the Changxing Limestone. The proposed boundary is close to, but not identical with, the traditionally defined boundary.
Early-Middle Pleistocene deep circulation in the western subtropical Atlantic: southern hemisphere modulation of the North Atlantic Ocean
Authors: Ferretti P. , Shackleton N. J. , Rio D. , Hall M. A.
Published: September 2007

Early-Middle Pleistocene climate and deep ocean hydrography have been reconstructed using oxygen and carbon isotope ratio measurements in planktonic and benthic foraminifera from a high-deposition-rate sedimentary succession recovered at the Bermuda Rise, in the northern Sargasso Sea (Ocean Drilling Program Leg 172, Site 1063). The site’s water depth makes it sensitive to changes in the balance between North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) in the deep North Atlantic, allowing the evaluation of perturbations in deep water production at different timescales. Millennial-scale fluctuations, superimposed on the longer period oscillations of orbital origin, occurred during all the observed climate states. The highest amplitude sub-Milankovitch fluctuations were mainly associated with interglacials, particularly after the intensification of the glacial regime atc.900 ka. Using the benthic carbon isotope signal as a water mass tracer, and by comparing the δ13C record to a suite of drill sites in the North Atlantic and Pacific oceans, it has been possible to infer that the relative strength of AABW production varied through time, as did that of NADW. A scenario in which the two different source components of deep water can undergo dramatic changes in their circulation regime through time should be taken into consideration when evaluating the role of thermohaline circulation in global climate change.
The Genetic Reinscription of Race
Authors: El-Haj Nadia Abu
Published: September 2007

Critics have debated for the past decade or more whether race is dead or alive in “the new genetics”: Is genomics opening up novel terrains for social identities or is it reauthorizing race? I explore the relationship between race and the new genetics by considering whether this “race” is the same scientific object as that produced by race science and whether these race-making practices are animated by similar social and political logics. I consider the styles of reasoning characteristic of the scientific work together with the economic and political rationalities of neo-liberalism, including identity politics as it meets biological citizenship. I seek to understand why and how group-based diversity emerges as an object of value—something to be studied and specified, something to be fought for and embraced, and something that is profitable—in the networks that sustain the world of (post)genomics today.
Metrology, Analysis and Characterization in Micro- and Nanotechnologies - A European Challenge
Authors: Pfitzner Lothar , Nutsch Andreas , Oechsner Richard , Pfeffer Markus , Don Eric , Wyon Christophe , Hurlebaus Matthias
Published: September 2007

Europe offers excellent expertise in the area of metrology, analysis and characterization in micro- and nanotechnologies. This exper-tise is borne through research institutes, academia, small/medium enterprises and industry. The European approach to develop syner-gies, enhance the existing technologies and to develop innovative methods is displayed by two projects named Analytical Network for Nanotech (ANNA) and Semiconductor Equipment Assessment for NanoElectronic Technologies (SEA-NET). ANNA is an infra-structure initiative focusing on the integration of independently op-erating laboratories. This multi-site laboratory forms a collabora-tive, synergistic network of analytical working scientists and pre-existing institutions. The objective of SEA-NET is to validate emerging semiconductor manufacturing equipment including me-trology tools for advanced process requirements for the next tech-nology nodes. The prototype equipment assessment is done in co-operation of tool suppliers with integrated device manufacturers and research institutes. Results of non-contact resistivity measure-ments, x-ray metrology platform and a gas detection system based on IMS technology are presented.
Structural and Analytical Characterization by Scanning Transmission Electron Microscopy of Silicon-based Nanostructures
Authors: Armigliato Aldo , Balboni Roberto , Parisini Andrea
Published: September 2007

A few recent applications of scanning transmission electron microscopy (STEM) methods to problems of interest for nanoelectronics are reported. They include nanometer-scaled dopant profiles by Z-contrast and strain mapping by convergent beam diffraction.
Detailed Photocurrent Analysis of Iron Contaminated Boron Doped Silicon by Comparison of Simulation and Measurement
Authors: Rommel Mathias , Bauer Anton , Ryssel Heiner
Published: September 2007

In this work, an extensive injection level dependent carrier lifetime study on intentionally iron contaminated boron-doped silicon has been performed by using the Elymat carrier lifetime method. The influence of both, iron and boron concentrations is investigated. Results from both Elymat measurement modes are considered and critically compared with simulations. The results clearly indicate that for low injection conditions, surface passivation with diluted HF is not sufficient whereas so-called electrostatic passivation allows for correct lifetime measurements. For the first time, results from both Elymat measurement modes are modeled consistently. The results prove that using optimized measurement and evaluation procedures the Elymat method is an appropriate technique for the quantitative determination of iron in case of iron being the relevant contaminant in boron doped silicon.
Mobility-Enhanced Device Technologies Using SiGe/Ge MOS Channels
Authors: Takagi Shinichi , Irisawa Toshifumi , Tezuka Tsutomu , Nakaharai Shu , Numata Toshinori , Hirashita Norio , Moriyama Yoshihiko , Usuda Koji , Dissanayake Sanjeewa , Takenaka Mitsuru , Sugahara Satoshi , Sugiyama Naoharu
Published: September 2007

Mobility enhancement technologies have currently been recognized as mandatory for future scaled MOSFETs. In this paper, we review our recent results on the development of mobility-enhanced CMOS device structures using strained-Si/SiGe/Ge MOS channels and the carrier transport properties in those channels. It is shown, particularly, that uniaxial compressive strain and Ge channels are quite effective in pMOS performance enhancement, while uniaxial tensile strain is effective in nMOS performance.
Fabrication of SiGe Virtual Substrates by Ion Implantation Technique
Authors: Sawano Kentarou , Shiraki Yasuhiro , Nakagawa Kiyokazu
Published: September 2007

We have developed a new SiGe virtual substrate fabrication technique where pre-ion-implantation is employed. In this method, prior to growth of SiGe layers, defects are intentionally introduced in the vicinity of Si substrate surfaces via implantation of relatively heavy ions, such as Ar+, Si+ and Ge+. Thin SiGe layers are grown on the ion-implanted Si substrates and the subsequent annealing considerably enhances the strain relaxation of the SiGe layers due to implantation-induced defects working as dislocation generation sources. As a result, extremely thin (100 nm) and largely-relaxed SiGe layers with atomically flat surfaces and very uniform strain distribution are obtained. These thin SiGe virtual substrates can be applied to the fabrication of strained-Si nMOSFETs and the significant mobility enhancement over the bulk Si device is obtained. These results clearly indicate that the ion implantation technique is very promising for realization of high-performance Si/Ge heterodevices based on SiGe virtual substrates.
Fabrication of Hole Resonant Tunneling Diodes with Nanometer Order Heterostructures of Si/Strained Si1-xGex Epitaxially Grown on Si(100)
Authors: Sakuraba Masao , Ito Ryota , Seo Takahiro , Murota Junichi
Published: September 2007

Hole resonant tunneling diodes with Si/strained Si1-xGex heterostructures epitaxially grown on Si(100) were fabricated and improvement of the negative differential conductance characteristics was explored by reducing thickness of Si barriers and Si1-xGex quantum well into a few nanometer order. It was clearly shown that, by reducing the Si barrier thickness down to 2 nm, high peak current density above a few kA/cm2 can be obtained under a peak-to-valley ratio of about 2 at 11 K. From the temperature dependence of the peak and valley currents, it is suggested that local introduction of higher Ge fraction effectively suppresses increase of valley current at higher temperatures.
Breakdown Characteristics of High-k Gate Dielectrics with Metal Gates
Authors: Misra D. , Chowdhury Naser , Bersuker Gennadi , Young Chadwin D. , Choi Rino
Published: September 2007

This work examines the inherent asymmetry on breakdown characteristics of interfacial layer (IL) and high-k layer in the overall gate stacks breakdown. Ramped and constant voltage stresses were applied on atomic layer deposited TiN/HfO2/SiO2 gate stacks. Under ramped stress when a thin high-k layer ({less than or equal to} 3.3 nm) is used, IL is responsible for the overall gate stack breakdown otherwise the breakdown is initiated by the high-k layer. Under constant voltage stress the gate stack went through many degradation mechanisms such as charge trapping and defect generation, soft breakdown, progressive breakdown and finally hard breakdown. When the breakdown field of ILs, grown on various process conditions is compared, it was observed that for a fixed IL thickness, breakdown field does not depend on pre-deposition surface treatment rather as a function of the quality of IL. Stress-induced leakage current was also studied to correlate with that of the breakdown behavior.
Silicide and Germanide Technology for Contacts and Metal Gates in MOSFET Applications
Authors: Zaima Shigeaki , Nakatsuka Osamu , Kondo Hiroki , Sakashita Mitsuo , Sakai Akira , Ogawa Masaki
Published: September 2007

We report silicide and germanide technology for ohmic contacts and metal gates of MOSFET applications. We have investigated control of crystalline and electrical properties of NiSi/Si contacts by the incorporation of third elements. Thermal stability and electrical properties of NiSi/Si contacts are effectively controlled by the incorporation of Ge and C. We have also systematically investigated the work function and the resistivity of various Ni and Pt germanides as metal gate materials. The low resistivity and tunable work function of these germanides and silcides are desirable for future CMOS devices.
Characterization of Electronic Charged States of Si-Based Quantum Dots for Floating Gate Application
Authors: Miyazaki Seiichi , Ikeda Mitsuhisa , Makihara Katsunori
Published: September 2007

Discrete charged states of individual Si quantum dots (QDs) with and without Ge core have been studied. When Si-QDs are charged with a few electrons or holes, surface potential images showing a characteristic potential profile with a dimple around the center of the charged dots are observable because of the Coulomb repulsion among the charges retained in the dot. By an introduction of a Ge core in the Si-QD, electrons are retained in the Si clad and holes in the Ge core reflecting the energy band discontinuity at the Si-clad/Ge-core interface. The ionized impurity doping into the dots enables us to manage the bias conditions for stable charged states. For the Si-QDs floating gate in MOS capacitors and n-MOSFETs, discrete charged states are also confirmed from multiple-step charging and discharging characteristics associated with collective motion of electrons regulated by Coulombic interaction between electrons in dots and in the inversion layer.
Integration Issues in Metallic Source/Drain Nanoscale CMOS
Authors: Tao M. , Ali M. Y. , Song G.
Published: September 2007

The performance of Schotky source/drain nanoscale CMOS is critically dependent on a low barrier between metal and Si. Low Schottky barriers have been recently realized with various metals on selenium or sulfur passivated Si(100) surface, with a ~0-eV barrier height for electrons and a ~0.17-eV barrier height for holes demonstrated. Several issues need to be addressed for integration of these low Schottky barriers into Schottky source/drain CMOS. This paper reports our recent results on low Schottky barriers on n-type and p-type Si(100) surface, thermal stability of these low Schottky barriers upon annealing, and self-aligned integration of these low-barrier metallic source/drain into nanoscale CMOS. Electrical characterization suggests that these low Schottky barriers are thermally stable to ~400 C. A self-aligned fabrication process involving chemical mechanical polishing is proposed for these metallic source/drain CMOS devices.