Flow Till Research Articles

Subglacial evolution from distributed to channelized drainage: Evidence from the Lake Murtoo area in SW Finland

AbstractDuring the last millennia of the Weichselian glaciation (c. 11 700–14 000 cal BP) and the first millennium of the Holocene interglacial (c. 10 500–11 700 cal BP), melting of the ice sheet and subsequent subglacial drainage resulted in the formation of murtoos and murtoo‐related landforms in the Fennoscandian Ice Sheet area in Finland and Sweden. Murtoos are composed of clay‐poor diamictons produced by sediment‐concentrated creep and material sorting in a subglacial environment under effective pressure close to zero, and potentially represent a transition form from non‐channelized to channelized subglacial drainage networks. Here, we explore the geomorphology and substratum characteristics of the Lake Murtoo area, one of the locations where murtoos were initially found and described in SW Finland. Our interpretation suggests an interconnected development from inefficient distributed or semi‐distributed cavities (murtoos) to efficient channelized drainage (esker) via erosional escarpments, all displayed in the same region. In addition, our excavation into a murtoo‐related erosional escarpment (MRE) revealed subglacial erosional channels alongside MREs that were filled with fine‐grained finely laminated sediments. We suggest that these channel fill sediments were deposited subglacially, because they are covered by flow till and show spatial and lithological characteristics that deviate significantly from the proglacial basin fill clay (varve) sediments in the area. The appearance of rhythmically laminated silt and clay sediments indicates sedimentation in a suspension‐load‐dominated environment in shallow subglacial channels with relatively low (but repetitiously changing) water flow velocities, possibly reflecting disconnected spill‐over routes of subglacial drainage in small tributaries that were only periodically used due to water pressure changes in the up‐ice direction.

Onset Separation Aerodynamics of Crew Module from Crew Escape System

Aerodynamic characteristics of Crew Module (CM) during its separation from the Crew Escape System (CES) are essential to carry out separation dynamics analysis for confirming collision-free separation. As CM is at the base of CES, it has to clear the complex wake flow that prevails in the aft region. A 1 : 10-scale wind tunnel model is tested at 45 m/s freestream velocity in Indian Institute of Science, Bengaluru lowspeed tunnel. The interaction of CM with the base flows is studied for different attitude conditions in terms angle of attack, longitudinal and lateral movements. Results indicate that CM is recovered from forebody influence beyond X/D = 2, and it experiences reverse flow till it moves to X/D = 1.4D. Stability characteristics of CM are also analysed.

New evidence for the rank of the Wartanian cold period (Pleistocene, MIS 6): a case study from E Poland

In the stratigraphic division of the Saalian (Middle Pleistocene) in Europe, the Wartanian cold period has the rank of a stadial of the Odranian Glaciation, correlated with MIS 6. The authors demonstrate the higher rank of this cold period, on the basis of an analysis of the sedimentary succession in eastern Poland, at an exposure of the terminal moraine of the Wartanian ice sheet. At the Wólka Zagórna site, three stratigraphic units were distinguished: A (lower glacigenic deposits – glaciofluvial deposits and subglacial till), A/B (fossil soil of lessivé type), B and C (a periglacial horizon with deflation pavement, involutions, frost-wedge structures and upper glaciofluvial deposits and flow till, with ice-wedge casts). Two distinct periods of climatic cooling, associated with the youngest Saalian ice sheets, were recorded in this succession in E Poland: Odranian (unit A, an ice-sheet transgression marked by the deposition of glaciofluvial deposits dated as 365–226 ka, ending with the deposition of subglacial till), and Wartanian (units B and C, an ice sheet transgression marked by development of a periglacial zone, dated as 180–126 ka, and then deposition of glacigenic sediments at the front of the ice sheet and formation of a marginal moraine). Each of these periods of ice-sheet transgression occurred at a different time (in the MIS 8 and MIS 6 positions) and were separated by a warm period. It is documented by unit A/B – a fossil soil with a very well developed Bt horizon – which attests to its formation in an illuviation process beneath a complex of mixed forests during an interstadial warming that occurred in MIS 7. From this palaeoclimatic reconstruction, it is inferred that the Wartanian cold period should be viewed as a separate glaciation in MIS 6 and the Odranian period should be assigned to MIS 8 in the stratigraphic schema of the Quaternary.

The Nature and Origin of Inertia

This paper aims to present a new theory that explains the mechanism of inertia at providing a satisfying explanation for the yet unknown mechanism for inertia. By considering the vacuum as a liquid with a measurable density, hydrodynamics laws are used to describe the behaviour of the vacuum when it is dragged by moving body. The inertia is the result of the initial resistance between the moving bodies against the static vacuum. The moving body drags the resisting vacuum during acceleration, till the point that the vacuum travels with the moving body and has the same velocity. When the body decelerates, the vacuum continues to flow and to push the body at the same direction of the original flow till its complete stop. Formulations based on Planck theory derived to prove its equivalence to Newton inertia law. Formulation based on hydrodynamics is derived to confirm the theory that the force exerted by the vacuum on static body in gravity and on moving body in inertia is equivalent to Newton law. The strong equivalence principle is reaffirmed and, consequently, Einstein’s equations are preserved.

V06-04 NEW SURGICAL TECHNIQUE: INTRAURETHRAL TUBE IN TUBE PEDICLED PREPUTIAL FLAP FOR OBLITERATIVE STRICTURES

You have accessJournal of UrologyLower-Tract Reconstruction I: Sling/ Sphincter/ Penile & Urethral Reconstruction (V06)1 Apr 2020V06-04 NEW SURGICAL TECHNIQUE: INTRAURETHRAL TUBE IN TUBE PEDICLED PREPUTIAL FLAP FOR OBLITERATIVE STRICTURES Pankaj Joshi* and Sanjay Kulkarni Pankaj Joshi*Pankaj Joshi* More articles by this author and Sanjay KulkarniSanjay Kulkarni More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000885.04AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Management of Obliterative and recurrent long segment bulbar strictures is challenging. Few options exist such as double face urethroplasty or combined use of graft and flap. In majority of reported literature, the native urethra is excised and reconstruction is performed. This native urethra actually carries retrograde blood flow through bulbourethral arteries. We describe a new technique of preserving the native spongiosa and using it as cover for substitution decreasing the risk of diverticulum formation. METHODS: Ours is a tertiary care referral center for urethroplasty with experience of more than 4500 Urethroplasties in last 2 decades. This is a series of 3 patients operated between Jan 2019-March 2019.All had near Obliterative proximal bulbar stricture. Etiology was idiopathic in 1 patient and post TURP in 2 patients.2 patients had prior dorsal Onlay urethroplasties. RGU and MCU were performed. Perineal incision with ventral urethrotomy in proximal bulbar urethra was performed. The scarred urethral plate was excised. There was a gap of 3 cm between the healthy mucosal ends proximally and distally. Pedicled preputial flap was performed, transposed to perineum and tubularised over a 14 Fr Silicone catheter .The tube was anastomosed to the proximal urethral mucosa and then distally. The ventral urethrotomy which now had the spongiosa was closed over as a cover . RESULTS: Foleys catheter was kept for 6 weeks. On catheter removal, Uroflow was performed. Patients were followed up every 3 months with Uroflow, Ultrasound and urine culture .All 3 patients had good flow till last follow up.None of them developed infections.All complained of minimal post micturition dribbling. CONCLUSIONS: Obliterative redo urethral strictures merit reconstruction. Proximal post TURP strictures are not recommended to be treated with dorsal approach. Urethral substitution would require urethra transection, compromising the blood flow. This is a novel intraurethral tube in tube, flap technique which is vascular preserving and useful for management for such subset of patients. Source of Funding: none © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e557-e557 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Pankaj Joshi* More articles by this author Sanjay Kulkarni More articles by this author Expand All Advertisement PDF downloadLoading ...

Eulerian CFD modeling of nozzle geometry effects on ECN Sprays A and D: assessment and analysis

Diesel spray modeling is a multi-scale problem with complex interactions between different flow regions, that is, internal nozzle flow, near-nozzle region and developed spray, including evaporation and combustion. There are several modeling approaches that have proven particularly useful for some spray regions although they have struggled at other areas, while Eulerian modeling has shown promise in dealing with all characteristics at a reasonable computational effort for engineering calculations. In this work, the [Formula: see text]–Y single-fluid diffuse-interface model, based on scale separation assumptions at high Reynolds and Weber numbers, is used to simulate the engine combustion network Sprays A and D within a Reynolds-averaged Navier–Stokes turbulence modeling approach. The study is divided into two parts. First of all, the larger diameter Spray D is modeled from the nozzle flow till evaporative spray conditions, obtaining successful prediction of numerous spray metrics, paying special attention to the near-nozzle region where spray dispersion and interfacial surface area can be validated against measurements conducted at the Advanced Photon Source at Argonne National Laboratory, including both the ultra-small-angle X-ray scattering and the X-ray radiography. Afterwards, an analysis of the modeling predictions is made in comparison with previous results obtained for Spray A, considering the nozzle geometry effects in the modeling behavior.

Ice-marginal sedimentation and processes of diamicton deposition in large proglacial lakes, Lake Erie, Ontario, Canada

Detailed studies of coastal cliff exposures through two end moraines form the basis for a model of ice-marginal sedimentation in large ice-contact glacier-fed lakes. The input to the ice-marginal environment directly from the glacier included subglacial till and subaquatic flow tills. The subaquatic flow till (thinly bedded diamicton) was deposited in an apron (up to 1 km wide) along the ice margin. An upward gradient of pore-water pressure immediately beyond the ice margin, causing heaving and dilation of the sediments, initiated debris flows of glacially derived debris (subaquatic flow tills). Most of the stratified sediments in the ice-marginal zone entered the lake by way of a large proglacial stream. Sedimentation was dominated by quasi- or near-continuous density underflows that resulted in the deposition of a sequence of thick rhythmites. The glacier in the Lake Erie basin most likely behaved like an ice stream, with its movement controlled predominantly by a deforming bed of glacial debris, separating the glacier sole from underlying predeposited sediments. The deforming bed is preserved as a massive diamicton layer, interpreted here as subglacially deposited till.

Directional properties of glacial relief and sediments as an effect of multi-stage evolution: Case study of the Tczew Hump, northern Poland

This paper focuses on the upland territory south-west of the Gulf of Gdańsk characterized by the existence of numerous hills with distinct ordering of their crest-line orientation. Characteristic features of relief in the Tczew Hump were analysed using GIS-based tools. Directional properties and morphometric characteristics are not uniform throughout the study area. Therefore, subsequent detailed analyses were performed after dividing it into three zones: north-western (NW), central and south-eastern (SE). The highest hills are situated in the central part of the Hump. The landforms analysed are mostly elongated, but they show varying elongation ratios (1.0–4.05). In general a NE-SW orientation is observed, however, the azimuthal distribution of their crest-lines shows considerable variation (from N-S to E-W). Two main systems of the crest-line orientation are distinguished: System A (NNE-SSW) and System B (NE-SW/ENE-WSW).The landforms considered are covered with till consisting of two subunits, what reflects two subsequent ice-sheet movement periods in the Late Weichselian but without releasing the area from ice-sheet cover. The subunits can be identified by changes in their petrographic composition – up to ten times more erratics of local provenance in the upper one than in the lower one. Ice flow direction during deposition of both till subunits, based on the till fabric of each of the three analysed sections, coincides with System A of the crest-lines. However, most of the till-covered hills fit System B, which suggests that they retained their previous (older than Late Weichselian) orientation. The complex relief of the Tczew Hump has a palimpsest nature and its arrangement emerged in several stages: (1) formation of the primeval relief before the Late Weichselian (hills built of sediments of heterogeneous ages); (2) partial relief reshaping in subglacial conditions during the two, successive, ice-flow events in the Late Weichselian (till-covered hills, clear bipartition of the till); (3) development of additional landforms during deglaciation − typically not covered with till (or with flow till on the slopes only), showing an orientation determined by the crevasse system developed in the ice.

Sukcesja osadowa i etapy formowania ozu gostynińskiego, Równina Kutnowska, centralna Polska

Artykuł nie zawiera streszczenia w języku polski.

Evaluation of Groundwater Potential Zones Using Electrical Resistivity and GIS in Noyyal River Basin, Tamil Nadu

Abstract: The purpose of this study was to identify the groundwater potential zones in Noyyal river basin using GIS and electrical resistivity. River Noyyal was perennial with good flow till early seventies. In recent years, the scene has changed drastically and the river has become practically seasonal and receives copious water during northeast monsoon from September to November. The rest of the years it remains more or less dry. Since the surface water resources in the area are inadequate to meet the local needs it is necessary to explore groundwater resources which has not been done properly. Hence various thematic maps have been used for the preparation of groundwater prospective map by integrating geology, geomorphology, slope, drainage and lineament of the study area. Electrical resistivity survey was conducted at 52 locations by using Schlumberger configuration. From this weathered thickness and depth to basement have been taken and overlaid for identifying groundwater potential sites and finally this result was compared with yield data. The interpretation shows that the entire study area has moderate to good category of groundwater potential.

Discharge Modes Suggested by Emission Spectra of Nitrogen Dielectric Barrier Discharge with Wire-Cylinder Electrodes**supported by National Natural Science Foundation of China (Nos. 11475040, 11375041) and the Fundamental Research Funds for the Central Universities (No. DUT14ZD[G]04)

In this paper, nitrogen dielectric barrier discharge (DBD) plasma was generated in a quartz tube with coaxial wire-cylinder electrodes at atmospheric pressure. By varying the nitrogen gas flow (FN) in the range of 0-1 m3/h, the plasma optical emission spectra (OES) were measured and studied. The vibration (Tvib) and rotation temperature (Trot) of nitrogen were obtained, by fitting the rovibronic bands of N2(C3Πu – B3Πg, 0-1), and by the Boltzmann plot method for purposes of comparison. Tvib increased up to 2481 K with increasing nitrogen flow till 0.2 m3/h, and then decreased with further increasing FN, while Trot decreased monotonously and approached to ∼350 K for FN ≥ 0.6 m3/h. The intensity of N2(C3Πu – B3Πg, 0-0, 1-0, 0-3) and N2+ (B2Σu+ – X2 Σ+g, 0-0) exhibited similar evolution with increasing FN to those of the Tvib and Trot, respectively. The discharge photos revealed that the discharge filaments gradually decreased with increasing FN, and eventually disappeared, which implied that a discharge mode transition emerged with increasing FN. The possible mechanism for the discharge mode transition is studied in detail according to the vibration (Tvib) and rotation temperature (Trot) of nitrogen.

Evaluation of groundwater potential zones using GIS and remote sensing in Noyyal Basin, Tamil Nadu, India

Groundwater is a dynamic and replenishable natural resource but in hard rock terrain the availability of groundwater is of limited extent. The occurrence and movement of groundwater in an area is governed by several factors. It is therefore, necessary to integrate several factors on these terrain characteristics. This can be best achieved by geographical information system (GIS). River Noyyal was perennial with good flow till early 70s. In recent years, the scenario has changed drastically and the river has become practically seasonal. River Noyyal receives copious water during northeast monsoon from September to November. The rest of the year it remains more or less dry. While the surface water resources in the area are inadequate to meet the local needs and the groundwater resources also not properly explored. So, various thematic maps have been used for the preparation of groundwater prospective map by integrating geology, geomorphology, slope, drainage and lineament of the study area. The interpretation shows that the entire study area is predominant in moderate to good category for groundwater potential.

A randomized prospective study of desflurane versus isoflurane in minimal flow anesthesia using "equilibration time" as the change-over point to minimal flow

Background:In the administration of minimal flow anesthesia, traditionally a fixed time period of high flow has been used before changing over to minimal flow. However, newer studies have used “equilibration time” of a volatile anesthetic agent as the change-over point.Materials and Methods:A randomized prospective study was conducted on 60 patients, who were divided into two groups of 30 patients each. Two volatile inhalational anesthetic agents were compared. Group I received desflurane (n = 30) and group II isoflurane (n = 30). Both the groups received an initial high flow till equilibration between inspired (Fi) and expired (Fe) agent concentration were achieved, which was defined as Fe/Fi = 0.8. The mean (SD) equilibration time was obtained for both the agent. Then, a drift in end-tidal agent concentration during the minimal flow anesthesia and recovery profile was noted.Results:The mean equilibration time obtained for desflurane and isoflurane were 4.96 ± 1.60 and 16.96 ± 9.64 min (P < 0.001). The drift in end-tidal agent concentration over time was minimal in the desflurane group (P = 0.065). Recovery time was 5.70 ± 2.78 min in the desflurane group and 8.06 ± 31 min in the isoflurane group (P = 0.004).Conclusion:Use of equilibration time of the volatile anesthetic agent as a change-over point, from high flow to minimal flow, can help us use minimal flow anesthesia, in a more efficient way.

Social &amp; Idea Plasmas from Social &amp; Idea Fusions — Replicating Silicon Valley in China Using 45 Models of Innovation

China is establishing new industrial pars ata rate greater than ever seen before in history. China is also revisiting extant industrial parks to upgrade their performance and increase their innovativity. China is also washing over both new and established such parks, a sequence of upgrades to basic urban and technical infrastructures. Study of failed replications of Silicon Valley dynamics in industrial parks in Europe and the USA are being used by China's leadership to design and install robust edge-of-field measure of what they judge to be the key forces that push ordinary industrial concentrations into FUSION states — where ideas, technologies, people, funds, and ventures flow till all good ones find homes that love them. The formula that is emerging, from a series of interviews conducted bia Skype across China in 2011, is — pulsed systems, tech infrastructure upgrade rhythms, social-idea density, radical outsourced agile venture forms, measures for impact of tactics on: social index levels, flow rates, density of interaction, and finally decade-long steady defense technology demand. Parks are to be managed towards Social-Idea Fusion points, where Social-Idea Plasma states lead to radically intense, fast, dense flows that spawn globally competitive venture and technology formation rates. Finally, each of 45 models of innovation are being measured and designed into new parks, then balances among them tweaked to optimize density of idea and person measures. This paper reports the leading edge practices of the leading park founders and managers to date. These constitute an emerging new model of techno-park structure, functioning, and goal.

Late Pleistocene glaciolacustrine sedimentation and paleogeography of southeastern Michigan, USA

Abstract The geomorphic, stratigraphic and sedimentological characteristics of glaciolacustrine sediments in the metropolitan Detroit, Michigan area were studied to determine environments of deposition and make paleogeographic reconstructions. Nine lithofacies were identified and paleoenvironments interpreted based on their morphostratigraphic relationships with relict landforms. The sediments studied are found southeast of the Defiance and Birmingham moraines lying beneath a lowland characterized by a low morainal swell (Detroit moraine) and a series of lacustrine terraces that descend progressively in elevation southeastward. The glaciolacustrine sediments were deposited approximately 14.3–12.4 kA BP during the Port Bruce and Port Huron glacial phases of late Wisconsinan time, and are related to proglacial paleolakes Maumee, Arkona, Whittlesey, Warren, Wayne, Grassmere, Lundy and Rouge. The glaciolacustrine section is typically 2–4 m thick and consists of a basal unit of wavy-bedded clayey diamicton overlain by a surficial deposit of stratified and cross-stratified sand and gravel. The basal unit is comprised of subaqueous debris flow deposits that accumulated as subaqueous moraine in paleolake Maumee along the retreating front of the Huron lobe. The surficial deposits of sand and gravel were formed by traction, resulting from lacustrine wave activity and fluvial processes, in lakebed plain, beach ridge and deltaic depositional settings. Much of the lake-margin sand and gravel was derived from clayey diamicton by lacustrine wave action and winnowing, and that associated with paleolakes of the Port Huron phase is largely reworked Port Bruce sediment. Paleogeographic reconstructions show that the Defiance, Birmingham and Detroit moraines, Defiance and Rochester channels, and the Rochester delta, were deposited penecontemporaneously as paleolake Maumee expanded northward across the map area. A unique type of wavy bedform is characteristic of clayey diamicton deposited by subaqueous mass flow in the study area that is useful for differentiating sediment: 1) deposited by mass flow in subaqueous vs. subaerial settings, and 2) deposited by subaqueous mass flow vs. basal till. These bedforms are a useful tool for identifying subglacial meltwater deposits, and facilitate the mapping and correlation of glacial sediments based on till sheets. The map area provides a continental record of ice sheet dynamics along the southern margin of the Laurentide ice sheet during Heinrich event H-1. The record reveals rapid glacial retreat (∼ 0.8 km/yr) contemporaneous with the discharge of a large volume of meltwater. Evidence in the study area for subglacial meltwater is problematic, but indications that periglacial conditions persisted in the map area until ∼ 12.7 kA BP, and extended for 200 km or more south of the ice front suggest that a frozen substrate may have contributed to instability of the LIS.

Using multi-beam RADARSAT-1 imagery to augment mapping surficial geology in northwest Alberta, Canada

This paper evaluates the applicability of multi-beam RADARSAT-1 satellite imagery for mapping surficial sediments in northwest Alberta, Canada, using simple arithmetic algorithms. The goal is to make the RADARSAT-1 imagery acquired by the Alberta Geological Survey (AGS) usable to common users who have no access to complex image classification software and (or) expertise. Unlike the Canadian Shield, northern Alberta is mantled with much thicker glacial deposits that are covered by the Northern Boreal Forest. This limits the use of conventional image classification techniques, as there is not a one-to-one relationship between vegetation and the underlying surficial sediments. The RADARSAT-1 data utilized consists of RADARSAT-1 imagery acquired using Standard Beam 1 and 7 in both ascending and descending passes. Moisture and surface roughness information can be extracted by applying algorithms that calculate the differences between images acquired from different incidence angles and look directions (ascending versus descending looks). The image created using different incidence angles highlights flat surfaces, including wetlands, agricultural areas, and forest fire scars. The image generated using opposing look directions enhances geomorphologic features, including ice flow features, meltwater channels, till hummocks, and sand dune ridges. In addition, the enhanced RADARSAT-1 imagery (includes integration of topographic information provided by a digital elevation model (DEM)) provides an additional level of confidence to the air photo interpretation conducted in regions with little or no ground access and also provides a regional perspective on large-scale subtle surface morphological elements (e.g., ice flow patterns) that might be overlooked in individual aerial photographs.

End moraine stratigraphy and formation in the southwestern Pyhä-Luosto fell area, northern Finland

The morphology, stratigraphy and composition of the small end moraine ridges were studied in the Pyhä-Luosto fell area, northern Finland. The ridges occur in a restricted area and are formed of unique formations, in groups of ridges with intervals of tens of metres, with the chains of ridges being several kilometres in length. The ridges are composed of two to three till units of which the middle one exhibits shear, thrust and push structures, and sandy or gravelly layers and lenses. Massive boulder-rich flow till units and stratified sediments relating to ice-marginal deposition are also observed. Based on the stratigraphical studies, the formation of the end moraines is due to oscillation of the ice margin in the supra-aquatic environment during the retreat phase of the Late Weichselian Ice Age. The end moraine ridge observations in the Pyhä-Luosto fell area are remarkable because these kinds of moraine deposits are rare in Finland, in the central part of the Last Scandinavian Ice Sheet.

Weichselian red tills in the Gardno Phase End Moraine (Dębina Cliff) – criteria for distinction, origin and stratigraphic position, and implications for the origin and course of the Baltic Ice Stream

Abstract. The paper presents the results of investigations of red tills from the South Baltic Middle Sea-Coast recorded in cliff exposures of Gardno Phase End Moraine. Distinctive features of these tills are: high percentage of Aland granitoids and porphyries identified in the 16-32 mm fraction, and large amounts of non-carbonate rocks, mostly red feldspars in relation to quartz, in the sandy fractions of 0,5-0,8 mm and 2-4 mm. Based on structural-textural features, the red till has been classified as flow till of local origin. The ice dynamism during Gardno Phase can be correlated with the Young Baltic Advance and most probably with the Belt Sea advance. On the basis of the petrographic properties of the Gardno red till and the results of radiocarbon dating, a new hypothesis regarding the origin, chronology and rate of flow of the Baltic Ice Stream is developed.

Structural and depositional evidence for repeated ice-marginal oscillation along the eastern margin of the Late Devensian Irish Sea Ice Stream

Late Devensian glacigenic sediments and landforms along the north-west coast of Wales document the advance and subsequent retreat of the eastern margin of an Irish Sea Ice Stream that met, coalesced and ultimately uncoupled from ice radiating outwards from the adjacent Welsh Ice Cap centred over Snowdonia. Across the boundary between the two former ice masses is a set of sediment–landform assemblages that reflect rapidly changing erosional and depositional conditions during ice interaction. From the inner part of the ice-stream the assemblages range outwards, from a subglacial depositional assemblage, characterised by drumlin swarms; through a subglacial erosional assemblage, marked by prominent bedrock scours and large subglacial rock channels; through an ice-marginal assemblage, identified by closely spaced, glaciotectonised push moraines and intervening marginal sandur troughs; into a freely expanding proglacial sandur and lacustrine delta assemblage. The ice-marginal assemblage provides evidence for numerous oscillatory episodes during retreat and at least 20 ice-marginal limits can be identified. At least 11 of these display multiple criteria for identifying readvance and, in the ideal case, is characterised by a moraine form built by localised tectonic stacking of diamict to the rear, fronted by a clastic wedge of ice-front alluvial fan gravel and intercalated flow till. The distribution of sediment–landform assemblages suggests a highly dynamic, convergent ice-stream flow pattern, with high ice velocity, a sharply delineated lateral shear margin, pervasive ice-marginal glaciotectonic deformation and a tightly focused ice-marginal sediment delivery system; all signature characteristics of contemporary ice streams.

Experimental studies on the effect of impeller width on centrifugal compressor stage performance with low solidity vaned diffusers

In an effort to improve the performance of centrifugal compressors, detailed studies were carried out on three different impeller-diffuser configurations covering a wide range of design flow coefficients. These were two-dimensional impellers chosen from a multi-stage compressor series with identical blade geometry. The impeller exit widths covered were 24.5, 18.5, and 11.5 mm, respectively. Extensive experimental studies have been carried out on the chosen stage configurations with parallel walled vaneless diffusers (VLDs) as well as low solidity vaned diffuser (LSD). For all the tested configurations, the aerofoil shape of the diffuser vanes remained same while the diffuser width, setting angle, and solidity were chosen as variables. The performance for each of the stages with LSDs was compared with that of the corresponding VLD. Significant improvement in performance in terms of polytropic efficiency, head coefficient, and static pressure recovery coefficient was observed with LSD vanes as compared with the VLD. Significant improvement in performance was noticed from low flow till design point for all the tested cases. The study revealed that among the tested configurations, there is an optimum width at impeller exit and diffuser for which the performance of the stage was the best. Performance in terms of static pressure recovery coefficient was also evaluated for all the tested configurations and compared. All the studies were conducted for solidity ratio of 0.81. The effect of setting angle on wall static pressure coefficient was also studied at 24° and 28° for the flow coefficients corresponding to 80, 100, and 120 per cent of design flow. Flow surveys at impeller exit for the three cases covering impellers/parallel walled diffusers of different widths have also been carried out to know the flow behaviour in the passage between the impeller and the diffuser.