bluuebunny/crossref_metadata_2025 huggingface dataset:
Holocene glacier chronology of Valenzuela Valley, Mendoza Andes, Argentina
Authors: Espizua Lydia E.
Published: October 2005

Glacial geologic evidence and radiocarbon-dated glacial deposits provide evidence of glacier fluctuations during the last 5 ka years in the Andes. Radiocarbon-dated moraines, morphological and stratigraphical studies permit the reconstruction of glacier fluctuations during the Holocene in the Valenzuela area of the Mendoza Andes valley located at 35S, in the upper Rio Grande basin. The Holocene record in this part of the Andes is mostly unknown, so this research is relevant for palaeoclimatic reconstructions in South America. In the Rio Valenzuela, glacier variations were dated in the El Azufre and El Pefión valleys. The first Neoglacial advance occurred at c. 5700 yr BP and a very close re-advance of similar magnitude occurred at 4700-4300 yr BP which formed well-preserved lateral-terminal moraines. The first Neoglacial advance occurred in the El Pefión valley at c. 4400 yr BP and a well-preserved terminal moraine is observed. A second Neoglacial advance reached its maxima at c. 2500-2200 yr BP in the El Azufre and El Pefión glaciers. A third, corresponding to the ‘Little Ice Age’, culminated at c. 400 yr BP (C. AD 1451-1641 cal. yr) and 350 +60 yr BP (c. AD 1460-1644 cal. yr) in the El Azufre valley. The third Neoglacial advance is distinguished in the El Pefión valley based on morphological characteristics, colour, freshness of the glacial deposits and the proximity to the active glacier. It is indicated by the Amarilla I, II, III lateral moraines. An estimation of the magnitude of snowline depression is obtained comparing the altitude of the present snowline with that of the reconstructed snow line for the first Neoglacial and ‘Little Ice Age’ advances.
Pervasive and long-term forcing of Holocene river instability and flooding in Great Britain by centennial-scale climate change
Authors: Macklin Mark G. , Johnstone Eric , Lewin John
Published: October 2005

This paper presents the first probability-based record of flooding in Europe that spans the entire Holocene. An analysis of 506 14C dated fluvial units collected across the whole of Great Britain provides a novel and robust methodology for improving flood risk assessment by geographically and temporally extending the record of extreme flood events. Sixteen episodes of increased flooding occurrence are identified, 12 of which (at c. 11 160, 5730, 4840, 4520, 3540, 2730, 2550, 2280, 1950, 1290, 660, 570, cal. BP) are recorded in most regions, whereas four phases (at c. 6820, 5540, 1650, 860 cal. BP) affected some parts of Great Britain more than others. In all regions large variations in flood frequency and magnitude occurred before forest clearance and indicate an underlying climatic control. During the mid-Holocene there is evidence for a hydroclimatic 'system switch', which in terms of catchment hydrology in Great Britain was marked by two sudden increases in both the frequency and severity of floods at c. 5000 cal. BP and, most notably, at c. 3000 cal. BP. The marked non-stationary behaviour of the British flood series at these times reflects a regional hydrologic response to large-scale ocean-atmospheric circulation changes superimposed on a pattern reflecting both long-term land-use change and the preferential preservation of later fluvial units. Centennial-scale variations in the occurrence of extreme flood events in Great Britain appear to be a sensitive indicator of past and present climate change in the North Atlantic region.
Archaeological evidence for the first Mesolithic occupation of the Western Isles of Scotland
Authors: Gregory Richard A. , Murphy Eileen M. , Church Mike J. , Edwards Kevin J. , Guttmann Erika B. , Simpson Derek D.A.
Published: October 2005

The examination of eroding coastal dunes at the prehistoric site of Northton, Harris, has produced the first archaeological evidence of Mesolithic activity in the Western Isles in the form of two midden-related deposits. The first phase of Mesolithic activity is dated to 7060-6650 cal. BC based on AMS dating of charred hazelnut shells. This discovery appears to validate the frequent pollen-based inferences of Mesolithic impact for the area and, as predicted, allows the Atlantic fringe of Scotland to become part of the European Mesolithic mainstream. A detailed pedological analysis also suggests that these early midden layers may have been amended during the Neolithic period as part of a possible phase of cultivation.
Holocene climate evolution in the high-latitude Southern Hemisphere simulated by a coupled atmosphere-sea ice-ocean-vegetation model
Authors: Renssen Hans , Goosse Hugues , Fichefet Thierry , Masson-Delmotte Valérie , Koç Nalan
Published: October 2005

The Holocene climate is simulated in a 9000-yr-long transient experiment performed with the ECBilt-CLIO-VECODE coupled atmosphere-sea ice-ocean-vegetation model. This experiment is forced with annually varying orbital parameters and atmospheric concentrations of CO2 and CH4. The objective is to study the impact of these long-term forcings on the surface temperature evolution during different seasons in the high-latitude Southern Hemisphere. We find in summer a thermal optimum in the midHolocene (6-3 ka BP), with temperatures locally 3°C above the preindustrial mean. In autumn the temperatures experienced a long-term increase, particularly during the first few thousand years. The opposite trend was simulated for winter and spring, with a relatively warm Southern Ocean at 9 ka BP in winter (up to 3.5°C above the preindustrial mean) and a warm continent in spring (+3°C), followed by a gradual cooling towards the present. These long-term temperature trends can be explained by a combination of (1) a delayed response to orbital forcing, with temperatures lagging insolation by 1 to 2 months owing to the thermal inertia of the system, and (2) the long memory of the Southern Ocean. This long memory is related to the storage of the warm late winter-spring anomaly below the shallower summer mixed layer until next winter. Sea ice plays an important role as an amplifying factor through the ice-albedo and ice-insulation feedbacks. Our experiments can help to improve our understanding of the Holocene signal in proxies. For instance, the results suggest that, in contrast to recent propositions, teleconnections to the Northern Hemisphere appear not necessarily to explain the history of Southern Hemisphere temperature changes during the Holocene.
Phytolith assemblages as indicators of coastal environmental changes and hurricane overwash deposition
Authors: Lul Hou-Yuan , Liu Kam-Biu
Published: October 2005

We demonstrate that phytolith assemblages are a useful proxy for reconstructing coastal environmental changes and for validating the overwash origin of sand layers in palaeotempestology studies. Phytolith analysis was conducted on 50 topsoil or surface sediment samples collected from a variety of coastal plant communities or depositional environments in the southeastern USA. The data suggest that different coastal subenvironments can be distinguished by their modern phytolith assemblages. For example, coastal marsh samples contain a diverse phytolith assemblage dominated by smooth-elongate and square morpho-types and maritime forest samples are dominated by phytoliths from palms and broadleaf dicotyledonous plants. Remarkably, the phytolith assemblages from sand dunes are characterized by high percentages of two-horned-tower, flat-tower, spool/horned-tower and short-saddle types. Phytolith analysis of three prehistoric sand layers in a sediment core from Western Lake, northwestern Florida, shows that they contain a phytolith assemblage similar to those characteristic of sand dunes and interdune meadows. These observations are confirmed by the results of principal components analysis and discriminant analysis on the modern and fossil phytolith data sets. Our study results support the interpretation that the sand layers in Western Lake were indeed formed by the erosion of sand dunes during overwash processes caused by landfalling catastrophic hurricanes.
Aeolian sand depositional records from western Nebraska: landscape response to droughts in the past 1500 years
Authors: Forman S. L. , Marin L. , Pierson J. , Gomez J. , Miller G. H. , Webb R. S.
Published: October 2005

The Great Plains is dominated by presently stabilized dune fields that are indicators of extreme drought in the late Holocene. This study focused on deciphering the timing of reactivation of dunes in western Nebraska. Stratigraphy adjacent to dune-dammed lakes reveals aeolian sand separated by palaeosols, indicating mobilization of aeolian sand followed by landscape stability. The chronology of aeolian-sand depositional events is constrained using the luminescence-based, single aliquot regeneration method, providing resolution to relate dune movement to tree-ring and palaeolimnologic records of drought. There are at least a six aeolian depositional events in the past 1500 years, with apparent mean ages of 1390+130, 670 +70, 470 +40, 240 +40, 140 +20 and 70+10 yr. All study sites show evidence for aeolian accumulation in the twentieth century, potentially reflecting the 1930s drought. Significant aeolian activity is coincident with the tree-ring-identified sixteenth-century megadrought, indicating widespread landscape impacts.
Ice caves as an indicator of winter climate evolution: a case study from the Jura Mountains
Authors: Luetscher Marc , Jeannin Pierre-Yves , Haeberli Wilfried
Published: October 2005

Subsurface ice fillings were first described in the Jura Mountains at the end of the sixteenth century. In order to assess the impact of climate change on low-altitude cave ice a detailed inventory has been drawn up and more than 50 objects have been identified. Comparisons between older cave maps, photographic documents and present-day observations outline a negative trend in ice mass balances, a trend that increased at the end of the 1980s. As most of these ice caves act as cold air traps, this negative mass balance is mainly attributed to higher winter temperatures and to reduced snow precipitation at low altitudes. The equilibrium line altitude of ice caves is believed to have increased several hundred metres between AD 1978 and 2004. Photographic comparisons and proxy records in some of the caves studied provide evidence of a rapid mass turnover. Ice ages range between less than a few decades and a millennium. Climatic records in these ice fillings will therefore present only short time series compared with other cave sediments. However, indications of former ice fillings have been found in different caves of the Jura Mountains and outline their potential role as palaeoclimatic markers.
High-resolution reconstruction of a 1300 year old gully system in northern Bavaria, Germany: a basis for modelling long-term human-induced landscape evolution
Authors: Dotterweich Markus
Published: October 2005

Knowledge of historical gullying and long-term processes of interactions between land use and gullying is still rather limited. Here, I review results from case studies in Germany and neighbouring countries and exmine the complex development of a gully system in northern Bavaria, integrating land-use changes and their interactions within a conceptual model. Reconstructions of gully development were made by identifying and dating sediment layers, artificial modifications and soil horizons at high spatial and temporal resolution, combined with analyses of historical documents. The case study in northern Bavaria shows that more than 150 colluvial layers found in a gully system revealed the detailed history of gully development during the last 1300 years. The first gullying took place in early Mediaeval times during several heavy rainfall events but the main phases of gullying took place between the fourteenth and the mid-eighteenth centuries. Occurrence of gullying was strongly linked to phases of high land-use intensity, which later changed the runoff pattern and enlarged the catchment area by 50%/o. Subsequently, overflowing field furrows led to the development of two gullies, up to 6 m deep, in late Mediaeval and early modern times. From the middle of the nineteenth century until today, only a little soil erosion has taken place and most of the catchment area has become grassland or forest. During the 1050 years from AD 800 to 1850, a soil volume of about 6430 m3 was eroded by gullying, destroying 15% of the arable land. The results provide a basis for modelling long-term human-induced landscape evolution.
Estimating relevant source area of pollen for small Danish lakes around AD 1800
Authors: Nielsen Anne Birgitte , Sugita Shinya
Published: October 2005

The aims of this study were to obtain estimates of the relevant source area of pollen (RSAP) that can be used to interpret fossil pollen diagrams from medium sized lakes, and to elucidate factors affecting RSAP for such lakes. A data set of sediment pollen assemblages dating from AD 1800 from 25 Danish lakes (3-27 ha) and land cover around the same lakes from historical maps was used. The plant abundance data were distance weighted using a species-specific model of pollen dispersal/deposition and other distance weighting functions (1, Ild and lId2). Extended R-value models were applied to evaluate the relationship between pollen and plant abundance and to estimate RSAP. The choice of distance weighting function influenced the RSAP estimates. When using the species-specific model, wind speed and species-specific properties of pollen dispersal had little effect on the RSAP estimates, which were approximately 1700 m in radius, when all lakes were analysed together. When the pollen types were classified into fewer groups, the RSAP estimate increased, probably because this procedure affected the spatial pattern of the plant abundance data by, in effect, increasing patch size. When the lakes were classified into two distinct groups (western Jutland and remaining sites) using a multivariate statistical technique (TWINSPAN), we obtained different RSAP estimates for each of the two groups. This result could be explained by a difference in average patch size of the land cover types between regions. A series of simulations supported our interpretation that the patch size was the main factor determining the size of the RSAP for the Danish lakes at AD 1800.
Vegetation changes during the past 1300 years in western equatorial Afnrca: a highresolution pollen record from Lake Kamalee, Lope Reserve, Central Gabon
Authors: Ngomanda Alfred , Chepstow-Lusty Alex , Makaya Mvoubou , Schevin Patrick , Maley Jean , Fontugne Michel , Oslisly Richard , Rabenkogo Nicaise , Jolly Dominique
Published: October 2005

Vegetation changes during the past 1300 years are reconstructed in western equatorial Africa using a high-resolution pollen record from Lake Kamalete This small marshy basin (c. 5-7 ha) is located in forest-savanna mosaic in Lope Reserve (043'S, 116'E), central Gabon. The Kamalete pollen data show the persistence over the past 1300 years of a relatively stable forest-savanna mosaic, associated with significant changes of the forest component. Three successive stages of forest dynamics occurred. First, at 1325 cal. BP, moist semi-evergreen rainforest existed around the catchment of Lake Kamalete. However, it appears from the consistent presence of > 70% Gramineae pollen that the site was always primarily in savanna. Secondly, from c. 1240 to 550 cal BP, a noticeable increase in shade-intolerant plant species indicate openings in the rainforest canopy. The persistence of gap-colonizer species, such as Macaranga, Tetrorchidium and Musanga for several centuries in the rainforest, is explained by recurring canopy disturbance associated with shifts in available moisture. These hydrological changes may be related to a succession of longer and more severe dry seasons than observed today. Thirdly, at 550 cal BP, mature forest was re-established, corresponding to progressive savanna colonization by forest pioneer species such as Aucoumea klaineana, Lophira alata and Fagara macrophylla. This new phase of forest expansion coincided with a marked lithological change, indicating an increase in lake-level. It is concluded that the major vegetation changes observed are due to climatic variability, and anthropogenic action had limited influence.
Soil erosion and sediment deposition in the Belgian oess belt during the Holocene: establishing a sediment budget for a small agricultural catchment
Authors: Rommens Tom , Verstraeten Gert , Lang Andreas , Poesen Jean , Govers Gerard , Van Rompaey Anton , Lang Andreas , Peeters Iris
Published: October 2005

A method to establish a Holocene sediment budget for a 103 ha agricultural catchment representative for the Belgian loess belt is presented. Soil erosion and sediment deposition were determined based on 185 coring locations and a large excavation in the valley bottom. Results were integrated in a GIS and interpolation techniques applied to derive spatial patterns of erosion and sedimentation. Total soil erosion, sediment deposition and sediment export were calculated and the results show that volumes are highly dependent on the interpolation technique used. Sediment delivery ratios between 20% and 42% are derived and are consistent with data reported in previous studies. This clearly shows that the majority of the sediments produced during the Holocene have been stored near their source area and have not been delivered to the downstream rivers. The spatial distribution of soil erosion and sediment deposition within the catchment is strongly dependent on slope gradient and position within the catchment, which suggests that, since human impact began, topography has been the main factor determining long-term soil erosion and sedimentation.
Late-Holocene environmental variability at Munsa archaeological site, Uganda: a multicore, multiproxy approach
Authors: Lejju B. J. , Taylorl D. , Robertshaw P.
Published: October 2005

Palaeoenvironmental data, in the form of 113 counts of pollen, fungal spores and charcoal abundances, 121 counts of phytoliths and 15 AMS 14C dates (11 macrofossil and 4 bulk sediment samples), have provided a means of reconstructing the late-Holocene environmental history of Munsa archaeological site, Uganda. The data were extracted from sediment cores from what is today a papyrus swamp, located within an area described by an outermost ring of earthworks at Munsa. Sediment core data indicate the general presence of forested conditions to C. AD 1100, although there is evidence for the local presence of food plants prior to this date. Deforestation from c. AD 1100 is marked in both the pollen and phytolith records, while fungal spores indicate the presence of increased numbers of herbivores post-deforestation. Indicators of deforestation and increased herbivore numbers broadly accord with the archaeological evidence for substantial occupation of the site at Munsa and the establishment of a mixed economy based on crops, cattle and iron working. Evidence for forest recovery and reduced herbivore numbers locally from C. AD 1780 could reflect abandonment of permanent settlement at the site, possibly during or following a period of drought and/or political upheaval in the region. Fungal spores and phytoliths provide evidence of agricultural activities at Munsa that have not left an imprint on pollen records, thus supporting the case for the use of multiproxies in palaeoenvironmental research, while intercore differences between the three sediment cores analysed, although relatively minor, confirm the benefits of a multicore approach. Tentative evidence for the very early presence of Musa (cultivated edible banana) is provided and warrants further study.
Vegetation and fire history since the Late Pleistocene from the Trinity Mountains, northwestern California, USA
Authors: Daniels Mark L. , Anderson Scott , Whitlock Cathy
Published: October 2005

A 267-cm sediment core spanning the past c. 15 200 cal. yr was recovered from Mumbo Lake, in the Trinity Mountains of northwestern California's Klamath Region. Plant macrofossils and pollen detail local and extra-local vegetation history, while high-resolution charcoal analysis provides details on local fire history. For the first c. 3000 years, climate was colder and drier than present, and supported an open, subalpine parkland vegetation, with low fire frequencies and fuel biomass. From c. 12 100 to 9800 cal. yr BP increasing moisture and soil development led to a woodland community with three new pine species invading the basin. Fire frequencies remained low, but individual fires may have been more intense because of increased fuel loads. Between c. 9800 and 7200 cal. yr BP, climate warmed and dried considerably, allowing for the expansion of oak and other chaparral species. Fire frequencies increased in the early Holocene, but low charcoal accumulation rates suggest a frequent, relatively low-intensity fire regime. From c. 7200 to 3800 cal. yr BP, the climate became cooler and moister again. Many conifer species appeared for the first time, although chaparral species maintained a strong presence. The fire record shows a dramatic increase in charcoal accumulation rates as well as an increase in fire frequency. From c. 3800 cal. yr BP to present, more conifer species enter the record, and abundance of chaparral species gradually diminishes to present levels.
Aeolian sand preserved in Silver Lake: a new signal of Holocene high stands of Lake Michigan
Authors: Fisher Timothy G. , Loope Walter L.
Published: October 2005

Aeolian sand within lake sediment from Silver Lake, Michigan can be used as a proxy for the timing of high lake levels of Lake Michigan. We demonstrate that the sand record from Silver Lake plotted as percent weight is in-phase with the elevation curve of Lake Michigan since the mid-Holocene Nipissing Phase. Because fluctuations in Lake Michigan's lake level are recorded in beach ridges, and are a response to climate change, the aeolian sand record within Silver Lake is also a proxy for climate change. It appears that increases in dune activity and lake sand are controlled by similar climatic shifts that drive fluctuations in lake level of Lake Michigan. High lake levels destabilize coastal bluffs that drive dune sand instability, and along with greater wintertime storminess, increase niveo-aeolian transport of sand across lake ice. The sand is introduced into the lake each spring as the ice cover melts.
Tephra-dated climate-and human-impact studies during the last 1500 years from a raised bog in central Ireland
Authors: Hall V. A. , Mauquoy Dmitri
Published: October 2005

Historic Icelandic tephrochronology constrains the time frame of a plant macrofossil and palynological study of ombrotrophic peat to evaluate the effects of climatic and human impact over the last 1500 years on the landscape at a large monastic site in the Irish Midlands. The plant macrofossil climate proxy record indicates maximum wetness during the sixth century AD. Decreasing wetness occurred from the late ninth century to the late thirteenth century. From c. AD 1290 to 1830, the plant macrofossils record a reduction in mire surface wetness and there is no evidence for ‘Little Ice Age’ climatic deteriorations. The pollen analytical evidence indicates an agricultural system dominated by pastoralism throughout the first millennium AD with arable agriculture increasing in the closing years of the first millennium and throughout the second millennium AD. From the eighteenth century onward, agricultural land use expands with a concomitant reduction in scrub.
An evaluation of multielement analysis of historic soil contamination to differentiate space use and former function in and around abandoned farms
Authors: Wilson Clare A. , Davidson Donald A. , Cresser Malcolm S.
Published: October 2005

Historic and prehistoric human activity can cause accumulation of elements in the soil. Multielement soil analysis has been used extensively over the last two decades to study element patterns of historic soil enrichment as a means of prospecting for sites and as an aid to interpretation of space use within archaeological structures. However, there have been surprisingly few of studies designed to assist with the interpretation of the analytical results. In this investigation soils from six abandoned farms with a known history of spatial use were sampled to determine if similar patterns of trace element enhancement occur between different farms. The preliminary results show significant differences in soil elemental concentrations between the functional areas, and highlight similar patterns of element enhancement between the farms. Concentrations of Ca, P, Sr, Ba, Zn and Pb are elevated in the buildings and fields of all the farms and provide valuable information about past human activity.
Transforming Growth Factor-β1 to the Bone
Authors: Janssens Katrien , ten Dijke Peter , Janssens Sophie , Van Hul Wim
Published: October 2005

TGF-β1 is a ubiquitous growth factor that is implicated in the control of proliferation, migration, differentiation, and survival of many different cell types. It influences such diverse processes as embryogenesis, angiogenesis, inflammation, and wound healing. In skeletal tissue, TGF-β1 plays a major role in development and maintenance, affecting both cartilage and bone metabolism, the latter being the subject of this review. Because it affects both cells of the osteoblast and osteoclast lineage, TGF-β1 is one of the most important factors in the bone environment, helping to retain the balance between the dynamic processes of bone resorption and bone formation. Many seemingly contradictory reports have been published on the exact functioning of TGF-β1 in the bone milieu. This review provides an overall picture of the bone-specific actions of TGF-β1 and reconciles experimental discrepancies that have been reported for this multifunctional cytokine.
Insight into Graves’ Hyperthyroidism from Animal Models
Authors: McLachlan Sandra M. , Nagayama Yuji , Rapoport Basil
Published: October 2005

Graves’ hyperthyroidism can be induced in mice or hamsters by novel approaches, namely injecting cells expressing the TSH receptor (TSHR) or vaccination with TSHR-DNA in plasmid or adenoviral vectors. These models provide unique insight into several aspects of Graves’ disease: 1) manipulating immunity toward Th1 or Th2 cytokines enhances or suppresses hyperthyroidism in different models, perhaps reflecting human disease heterogeneity; 2) the role of TSHR cleavage and A subunit shedding in immunity leading to thyroid-stimulating antibodies (TSAbs); and 3) epitope spreading away from TSAbs and toward TSH-blocking antibodies in association with increased TSHR antibody titers (as in rare hypothyroid patients). Major developments from the models include the isolation of high-affinity monoclonal TSAbs and analysis of antigen presentation, T cells, and immune tolerance to the TSHR. Studies of inbred mouse strains emphasize the contribution of non-MHC vs. MHC genes, as in humans, supporting the relevance of the models to human disease. Moreover, other findings suggest that the development of Graves’ disease is affected by environmental factors, including infectious pathogens, regardless of modifications in the Th1/Th2 balance. Finally, developing immunospecific forms of therapy for Graves’ disease will require painstaking dissection of immune recognition and responses to the TSHR.
Respiratory syncytial virus infections: characteristics and treatment
Authors: Chidgey Sharon M , Broadley Kenneth J
Published: October 2005

In this review, we describe the history, epidemiology and clinical manifestations of infections attributed to respiratory syncytial virus (RSV) in children. At present, no cure exists for RSV infection but commonly employed palliative treatments include oxygen and inhaled β2-adrenoceptor agonists, such as salbutamol, to relieve the wheezing and increased bronchiolar smooth muscle constriction. Adrenaline (epinephrine) has been found to be superior to the selective β2-adrenoceptor agonists. Oral or inhaled corticosteroids should counteract the inflammatory response to RSV infection but their effectiveness is controversial. Inhaled ribavirin is the only licensed antiviral product approved for the treatment of RSV lower respiratory-tract infection in hospitalized children, although its use is now restricted to high-risk infants. Other treatments considered are nasopharyngeal suctioning, surfactant therapy, recombinant human deoxyribonuclease I, heliox (helium:oxygen) and inhaled nitric oxide. Prevention of infection by RSV antibodies is another strategy and, currently, palivizumab is the only safe, effective and convenient preventative treatment for RSV disease in high-risk populations of infants and young children. Its cost-effectiveness, however, has been questioned. Both live attenuated and subunit vaccines against RSV infection have been developed but so far there is no safe and effective vaccine available. Finding effective treatments and prophylactic measures remains a major challenge for the future.
Numerical study of the combustion mechanism of a homogeneous charge compression ignition engine fuelled with dimethyl ether and methane, with a detailed kinetics model
Authors: Yao M , Qin J , Zheng Z
Published: October 2005

The auto-ignition and combustion mechanisms of dimethyl ether (DME) in a fourstroke homogeneous charge compression ignition (HCCI) engine were investigated using a zero-dimensional thermodynamic model coupled with a detailed chemical kinetics model. The results indicate that DME displays two-stage auto-ignition, and heat release with a low-temperature reaction and a high-temperature reaction (HTR). Heat release with the HTR can be separated into two stages: blue flame and hot flame. HCCI ignition is controlled by hydrogen peroxide (H2O2) decomposition, and OH plays a very important role in HCCI combustion. Formaldehyde (CH2O) is the main source of H2O2. Based on the sensitivity analysis of chemical reactions, the major paths of the DME reaction occurring in the engine cylinder are clarified. The major paths of the DME reaction is H-atom abstraction from DME, followed by the first addition of O2 and second addition of O2, and then oxidation to formaldehyde (CH2O), the formyl radical (HCO), and finally carbon monoxide (CO). CO oxidation occurs at the hot flame by the elementary reaction CO + OH = CO2 + H. At leaner DME concentrations, CO cannot be completely converted to carbon dioxide (CO2), and the process will result in high CO emissions.
Numerical study of the combustion mechanism of a homogeneous charge compression ignition engine fuelled with dimethyl ether and methane, with a detailed kinetics model. Part 2: the reaction kinetics of dimethyl ether and methane dual-fuel
Authors: Yao M , Qin J , Zheng Z
Published: October 2005

A numerical study was carried out using a zero-dimensional detailed chemical kinetics model to investigate the chemical reaction phenomena encountered in the homogeneous charge compression ignition process of a dimethyl ether (DME) and methane dual-fuel mixture. The results show that the heat release of DME/methane dual-fuel combustion is a typical two-stage process: the first stage is mainly associated with DME oxidation, and the second is mainly the result of methane oxidation. The low-temperature reaction (LTR) of DME is inhibited, the second molecular oxygen addition of DME is restrained, and β-scission plays a dominant role in DME oxidation. Therefore, methane changes the paths of the LTR of DME. Most of the formaldehyde (CH2O) is produced from H abstraction of methoxy (CH3O) rather than from the LTR of the DME. The heat release by DME oxidation and the existence of H2O2 generated by DME oxidation make methane oxidation occur at a low initial temperature. However, methane oxidation also promotes hot flame reactions of DME. During the second stage of heat release, OH is produced in many different ways rather than only by way of H2O2 decomposing in neat DME oxidation; this results in higher OH mole fraction when dual fuel is used compared with DME alone. Finally, the major paths of the DME/methane HCCI reactions occurring in the engine cylinder are clarified.
Study on the effect of different combinations of engine coolant additives on the heat dissipation rate of radiators
Authors: Sathyanarayanan P L , Ramprabhu R
Published: October 2005

The performance, reliability, and life of a diesel engine largely depend on its efficiency to dispose waste heat under all weather conditions, especially at high ambient temperatures. The coolant of the engine plays a significant role in removing a major portion of this heat from the engine. Although pure water is the most efficient of all, it is essential to add certain additives to modify some of its deleterious actions on the engine and its components. For a given radiator configuration, the effectiveness of a coolant in dissipating heat is primarily governed by its composition and thereby its physical and chemical properties. Thus, a study on the effects of different combinations of engine coolant additives on the extent of heat dissipation was carried out. The study mainly concentrated on the use of cutting oil, ethylene glycol, and three-component additives (sodium nitrate, potassium dichromate, and trisodium phosphate), which were carefully analysed in a laboratory and compared on the basis of their respective performances.
Study of diesel-fuelled homogeneous charge compression ignition combustion by in-cylinder early fuel injection and negative valve overlap
Authors: Shi L , Deng K , Cui Y
Published: October 2005

This paper presents a scheme to achieve diesel-fuelled homogeneous charge compression ignition (HCCI) combustion, which is to inject diesel fuel directly into the cylinder at near intake top dead centre and adjust the valve overlap to obtain a higher internal exhaust gas recirculation (EGR) in the cylinder. The effects of the engine load, speed, inlet temperature, external EGR, and internal EGR on HCCI combustion and emission were studied. The combustion stability of HCCI combustion was also studied by statistics analysis. The results show the following: when the engine load or inlet temperature increases, which results in a higher in-cylinder temperature, the start of combustion (SOC) is advanced; the ignition time of HCCI relative to the engine crank angle is retarded when the engine speed increases; inert gases contained in the EGR can slow the chemical reaction rate, which can delay the auto ignition time; for the diesel-fuelled HCCI, increasing the negative valve overlap (NVO) makes the SOC advanced and makes the combustion stability better at low loads and worse at high loads. The emission results show that the nitrogen oxides (NOx) and smoke emissions are very low, and a large NVO can decrease the smoke emission but not benefit the NOx emission at high loads for diesel-fuelled HCCI combustion.
Computer simulation of driver working memory processing
Authors: Fansen Kong , Jie Sui
Published: October 2005

In general, using simulations to solve problems of human behaviour, as is done in engineering, is particularly difficult. Making use of research into motor vehicle manoeuvrability, this article studies, from the engineering perspective, a computer simulation of working memory processing disabilities of automobile drivers. Firstly, utilizing theories drawn from cognitive psychology, motor vehicle manoeuvrability dynamics, and fuzzy control theory, a driver working memory simulation model is advanced. The model integrates working memory, which is a critical factor in predicting complex cognitive manipulation activities. Secondly, the driver's working memory processing is simulated using the model, and its effects on motor vehicle manoeuvrability and stability are assessed. The test result shows that there is an optimal range of processing time for driving. The lower limit of the range is limited by human physiological limits. The upper limit is defined by the task's complexity. The task could not be finished if the information processing time for finishing the complex task is greater than the upper limit.
Investigation of diesel engine operating and injection system parameters for low noise, emissions, and fuel consumption using Taguchi methods
Authors: Win Z , Gakkhar R P , Jain S C , Bhattacharya M
Published: October 2005

In order to optimize the performance of a small direct injection (DI) diesel engine with respect to noise, emissions, and fuel economy, an experimental investigation was undertaken using Taguchi methods. A single-cylinder 3.5 kW diesel engine was selected for performance tests at different levels of two operating parameters (speed and load) and six injection parameters of the engine (static injection timing, plunger diameter, nozzle valve opening pressure, nozzle hole diameter, number of nozzle holes, and nozzle tip protrusion). These controlled parameters were varied at two levels, and the resulting changes in responses were investigated, namely engine noise, combustion noise, smoke, brake specific fuel consumption (b.s.f.c.), and emissions of unburned hydrocarbons (HC), oxides of nitrogen (NO x), and carbon monoxide (CO) were investigated. The optimum values of engine noise, combustion noise, smoke, emissions, and b.s.f.c. could be predicted using signal-noise ( S/N) ratios, and a relevant combination of controlled input parameters was specified. Results of confirmation runs of the engine showed good agreement with the predicted quantities of interest based on Taguchi analysis. The relative importance of the controlled parameters to the above responses was evaluated in terms of the percentage contributions of the parameters using analysis of variance (ANOVA). The Taguchi method of experimental design was found to be robust and more cost effective for understanding the relationship between diesel engine parameters and noise, emissions, and b.s.f.c. than full factorial design.
Non-linear modelling of a novel gas strut
Authors: Gao B , Darling J , Tilley D G , Williams R A , Bean A , Donahue J
Published: October 2005

The strut is one of the most important components in a vehicle suspension system; however, it is also one of the most difficult elements to model owing to its highly nonlinear characteristics. In this paper a non-linear gas strut model built in the software package Bath fp is presented. Both analytical and parametric modelling methods were used in the representation of different components in the strut. Simulations at various frequencies showed good agreement with experimental results. A sensitivity analysis of strut performance is presented at the end of the paper. It was found that the damper valve characteristics, the rod diameter, the temperature, and the user-defined polytropic index significantly affect the strut performance.
Development of a pre-ignition submodel for hydrogen engines
Authors: Sadiq Al-Baghdadi M A R
Published: October 2005

In hydrogen-fuelled spark ignition engine applications, the onset of pre-ignition remains one of the prime limitations that needs to be addressed to avoid its incidence and achieve superior performance. This paper describes a new pre-ignition submodel for engine modelling codes. The effects of changes in key operating variables, such as compression ratio, spark timing, intake pressure, and temperature on pre-ignition limiting equivalence ratios are established both analytically and experimentally. With the established pre-ignition model, it is possible not only to investigate whether pre-ignition is observed with changing operating and design parameters, but also to evaluate those parameters' effects on the maximum possible pre-ignition intensity.
Use of numerical optimization to determine the effect of the roll stiffness distribution on race car performance
Authors: Brayshaw D L , Harrison M F
Published: October 2005

The use of active systems for controlling suspensions has been used before in Formula One and other open wheel racing series but at present this form of active control is not allowed by Formula One regulations. The roll stiffness distribution is a key element of suspension design and it has an influence on the dynamic weight transfer of the vehicle. In this paper, the roll stiffness distribution has been optimized during a calculation process to simulate and quantify the possible benefits of controlling the distribution of roll stiffness between the front and rear axles of an open wheel race car. The roll axis concept has been used to provide the roll component to the lateral load transfer evaluation. The benefits shown by the optimization of the roll stiffness distribution have created a mean handling performance improvement over the base vehicle of over 10 per cent, which on the lap of the Barcelona Grand Prix circuit yielded a lap time improvement of 2.71 s, using a quasi-steady-state calculation method. Additionally, it has been shown how this improvement has been realized in terms of the change in vehicle dynamics. This research also shows that circuit dependent analysis is possible to exploit the value of the static setting of the roll stiffness distribution. Further work and validation are required to explore this avenue of vehicle set-up optimization, but it does appear that the optimized calculation approach offers a way of helping to make an objective choice of a static roll stiffness distribution setting for particular circuits.
Parameter optimization of a diesel engine to reduce noise, fuel consumption, and exhaust emissions using response surface methodology
Authors: Win Z , Gakkhar R P , Jain S C , Bhattacharya M
Published: October 2005

The conflicting effects of the operating parameters and the injection parameter (injection timing) on engine performance and environmental pollution factors is studied in this paper. As an optimization objective, a 3.5 kW small direct injection diesel engine was used as the test engine, and its speed, load, and static injection timing were varied as per 4 × 4 × 3 full factorial design array. Radiated engine noise, smoke level, brake specific fuel consumption, and emissions of unburned hydrocarbons and nitrogen oxides were captured for all test runs. Objective functions relating input and output parameters were obtained using response surface methodology (RSM). Parameter optimization was carried out to control output responses under their mean limit using multi-objective goal programming and minimax programming optimization techniques.
Modelling of ignition mechanisms and pollutant formation in direct-injection diesel engines with multiple injections
Authors: Hasse C , Peters N
Published: October 2005

Multiple injections are an important aspect in modern direct-injection diesel engine development. The representative interactive flamelet (RIF) model, which was successfully used previously for simulations of diesel engine combustion, was recently extended to model multiple injections. In this paper this new RIF model is applied to model ignition and combustion with a pilot and a main injection with various dwell times, start of injection timings, and loads. Special emphasis is placed on the ignition of the main injection. It is shown that, for the investigated cases, the main injection does not auto-ignite but it is ignited by a strained premixed flame that propagates from the pilot injection to the mixture field of the main injection. The structure of that flame and the influence of the scalar dissipation rate on the propagation speed are investigated in detail. In addition to pressure curves, modelling results for NOx and soot emissions are compared with experimental data, showing good agreement.
Parametric study of combustion characteristics in a direct-injection diesel homogeneous charge compression ignition engine with a low-pressurefuel injector
Authors: Ra Y , Hruby E J , Reitz R D
Published: October 2005

Homogeneous charge compression ignition (HCCI) combustion is an alternative to current engine combustion systems and is used as a method to reduce emissions. It has the potential nearly to eliminate engine-out NOx emissions while producing diesel-like engine efficiencies, when a premixture of gas-phase fuel and air is burned spontaneously and entirely by an autoignition process. However, when direct injection is used for diesel fuel mixture preparation in engines, the complex in-cylinder flow field and limited mixing times may result in inhomogeneity of the charge. Thus, in order to minimize non-uniformity of the charge, early injection of the fuel is desirable. However, when fuel is injected during the intake or early compression stroke, the use of high-pressure injection is limited by the relatively low in-cylinder gas pressure because of spray impingement on the cylinder walls. Thus, it is also of interest to consider low-pressure injectors as an alternative. In the present paper, the parametric behaviour of the combustion characteristics in an HCCI engine operated with a low-pressure fuel injector were investigated through numerical simulations and engine experiments. Parameters including the start-of-injection (SOI) timing and exhaust gas recirculation were considered, and diesel and n-heptane fuels were used. The results show good agreement of behaviour trends between the experiments and the numerical simulations. With its lower vaporization rates, significant effects of the SOI timing and intake gas temperature were seen for diesel fuel due to the formation of wall films. The modelling results also explained the origin of high-temperature NO x-producing regions due to the effect of the gas density on the spray.
Effect of the hydrocarbon molecular structure in diesel fuel on the in-cylinder soot formation and exhaust emissions
Authors: Nakakita K , Akihama K , Weissman W , Farrell J T
Published: October 2005

Evaluations of diesel fuel effects on combustion and exhaust emissions in single-cylinder direct-injection diesel engines led to the unexpected result that a Swedish ‘class 1’ fuel generated more particulate matter (PM) than a fuel denoted ‘improved’, even though ‘class 1’ fuel had much lower distillation temperatures, aromatic concentration, sulphur level, and density than the ‘improved’ fuel. Little differences were observed in the combustion characteristics between these fuels, but detailed compositional analyses showed that ‘class 1’ fuel contains higher levels of cyclic and/or branched paraffins. Subsequent investigations in a laboratory flow reactor showed that ‘class 1’ fuel produces more soot precursors such as benzene and acetylene than the ‘improved’ fuel. In addition, experiments in a low-pressure laminar flame apparatus and shock tube with model (single-molecule) paraffin fuels showed that isoparaffins and cycloparaffins generate more soot precursors and soot than n-paraffins do. These results strongly suggested that the effect of molecular structure on exhaust PM formation should be more carefully examined. Therefore, a new series of investigations were performed to examine exhaust emissions and combustion characteristics in single-cylinder engines, with well-characterized test fuels having carefully controlled molecular composition and conventional distillation characteristics and cetane numbers (CNs). These investigations revealed the following. Firstly, under low and medium loads, cycloparaffins (naphthenes) have a higher PM formation tendency than isoparaffins and n-paraffins. Under high-load conditions, however, the paraffin molecular structure has a very small effect. Secondly, a highly n-paraffinic fuel does not yield PM reductions as high as expected, due to its high CN and corresponding shorter ignition lag, which initiates combustion under a state of insufficient fuel-air mixing. This finding was corroborated by laser-induced incandescence analyses. Thirdly, the lowest PM emissions were observed with a paraffinic fuel containing 55 per cent isoparaffins and 39 per cent n-paraffins. Fourthly, aromatics give higher soot and PM levels than paraffins do at high and medium load conditions. Smaller differences are observed at lower speeds and loads. Fifthly, the best fit to the PM emissions was obtained with an equation containing the regression variables CN, aromatic rings, and naphthene rings. This expression of the fuel effects in chemical terms allows well-to-wheel analyses of refining and vehicle impacts resulting from molecularly based fuel changes.