Eastern tropical Pacific corals monitor low latitude climate of the past 400 years

EXTRACT (SEE PDF FOR FULL ABSTRACT): We have measured coral growth band thickness and skeletal stable isotopic composition through a 371-year transect (AD 1583-1954) from a massive specimen of Pavona clavus from the Galápagos Islands. ... We observe a general cooling trend during 1860-1954, corresponding to the end of the Little Ice Age, an interval characterized by general warming at many mid-latitude sites. Variance at sunspot cycle frequencies in growth rate, stable isotopic, and trace element composition implies a direct or indirect link between the solar cycle and climate modulation in the eastern Pacific.

Radiocarbon record of solar variability and Holocene climatic change in coastal southern California

EXTRACT (SEE PDF FOR FULL ABSTRACT): Pollen analysis and 5 radiocarbon dates for a 687-cm core provide a detailed chronology of environmental change for San Joaquin Marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea level rise during the mid-Holocene, but after 4500 years BP, sea water regularly reached the coring site, and salt marsh was the local vegetation. Brief periods of dominance by fresh-water vegetation 3800, 2800, 2300 and after 560 years BP correlate global cooling events and (except the 3800-year BP event) with carbon-14 production anomalies. The coincidence of climate change and carbon-14 anomalies support a causal connection with solar variability, but regardless of the causal mechanism(s) the delta-carbon-14 curves provide a chronology for global, high-frequency climatic change comparable to that of Milankovitch cyclicity for longer time scales.

Seasonal and spatial distribution of Chlorophyll a in the north Arabian Sea bordering Pakistan

The average integrated chlorophyll a values for a 30-m deep surface layer in the north Arabian Sea bordering Pakistan ranged from negligible amounts to as high as 0.53μg chl. a 1ˉ¹(15.9mg mˉ²) during the period January 20, 1977 to June 4, 1977. The values, in general, decreased offshore except for the westernmost part of the Makran shelf, where unexpectedly high values were recorded over deep water. Seasonal distribution showed very high values in January (northeast monsoon season) which, with a few exceptions, gradually decreased to very low values in May, and then increased in June. The January peak may be related to winter cooling of surface waters resulting in convection and the June peak to the onset of southwest monsoon season in May. Coastal water shallower than 30m showed no seasonality and were often sites of intense phytoplankton blooms.

Factors controlling drained weight in canned prawn

The paper gives an account of factors controlling the drained weight in canned prawn. The most important among them are concentration of brine used for blanching and blanching time which are found to be fixed and specific for different sizes of prawn irrespective of the quality of the material used. Other factors such as, acidity of brine used for filling the can, volume of brine, time of sterilization and time of cooling the blanched meat are also to some extent found responsible for fluctuations in drained weight.

Solid particle erosion of boronized steels

Boronizing is a thermochemical diffusion-based process for producing iron boride layers in the surface of steel components. The boride layer is wear resistant and is very hard. Large residual stresses are found to exist in the surface layers, which are a function of substrate steel composition and heat treatment. By slow cooling from the boronizing temperature (900°C), a large compressive stress is developed in the boride layer. Hardening the steel by rapid cooling, either directly from the boronizing treatment or after subsequent austenitizing, develops tension in the coating which causes it to fracture. Tempering of the martensite produces compression in the coating, closing but not welding the cracks. The results of solid particle erosion experiments using silicon carbide, quartz, and glass bead erodents on boronized steels are presented.

Magnetic field and current distributins in melt-textured YBa 2Cu 3O 7-x with an artificial grain boundary

Using a magneto-optical (MO) technique, magnetic field distributions have been measured in a melt-textured YBa 2Cu 3O 7-x bulk superconductor, joined to form an artificial grain boundary (GB), in an external magnetic field perpendicular to the sample surface. The magnetic field at a weak section of the GB shows different values between the field increasing up to 150mT and decreasing down to 0T after zero-field-cooling. Namely, the magnetic field in increasing field is higher than that in decreasing field, even in the same external field. This result supports a model in which such differences in magnetic field at the weak-link GB give rise to the hysteresis behavior in the field dependence of transport critical current density in polycrystalline samples. The field distributions across a well-joined region of the GB behave similarly to the adjoining bulk material and this result indicates the possibility of creating useful artifacts provided that the strongly coupled sections can be reproduced on a larger scale.

Gas properties as a limit to gas turbine performance

Although increasing the turbine inlet temperature has traditionally proved the surest way to increase cycle efficiency, recent work suggests that the performance of future gas turbines may be limited by increased cooling flows and losses. Another limiting scenario concerns the effect on cycle performance of real gas properties at high temperatures. Cycle calculations of uncooled gas turbines show that when gas properties are modelled accurately, the variation of cycle efficiency with turbine inlet temperature at constant pressure ratio exhibits a maximum at temperatures well below the stoichiometric limit. Furthermore, the temperature at the maximum decreases with increasing compressor and turbine polytropic efficiency. This behaviour is examined in the context of a two-component model of the working fluid. The dominant influences come from the change of composition of the combustion products with varying air/fuel ratio (particularly the contribution from the water vapour) together with the temperature variation of the specific heat capacity of air. There are implications for future industrial development programmes, particularly in the context of advanced mixed gas-steam cycles.

The flexoelectric behaviour of a hypertwisted chiral nematic liquid crystal

The flexoelectric behaviour of a hypertwisted chiral nematic bimesogenic liquid crystal is presented. Through detailed electro-optic measurements, with particular emphasis on the switching properties, we demonstrate remarkably high optical axis tilt angles. The material studied possessed a room temperature nematic phase and aligned easily on cooling under the application of a moderate electric field. Switching times of the order of 500 μs and contrast ratios of 90:1 are readily achieved. The tilt angles, measured using the rotating analyser technique, were found to be practically temperature independent and linear with the applied field. Tilt angles of 22.5° were obtained with moderate applied fields of 9.4 V/μm whilst fields of 25 V/μm yielded tilt angles of 45°. We believe these are the highest tilt angles ever recorded for such fields. © 2001 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint, a member of the Taylor & Francis Group.

Heat transfer and aerodynamics of turbine blade tips in a linear cascade

Local measurements of the heat transfer coefficient and pressure coefficient were conducted on the tip and near tip region of a generic turbine blade in a five-blade linear cascade. Two tip clearance gaps were used: 1.6% and 2.8% chord. Data was obtained at a Reynolds number of 2.3 × 10 5 based on exit velocity and chord. Three different tip geometries were investigated: a flat (plain) tip, a suction-side squealer, and a cavity squealer. The experiments reveal that the flow through the plain gap is dominated by flow separation at the pressure-side edge and that the highest levels of heat transfer are located where the flow reattaches on the tip surface. High heat transfer is also measured at locations where the tip-leakage vortex has impinged onto the suction surface of the aerofoil. The experiments are supported by flow visualisation computed using the CFX CFD code which has provided insight into the fluid dynamics within the gap. The suction-side and cavity squealers are shown to reduce the heat transfer in the gap but high levels of heat transfer are associated with locations of impingement, identified using the flow visualisation and aerodynamic data. Film cooling is introduced on the plain tip at locations near the pressure-side edge within the separated region and a net heat flux reduction analysis is used to quantify the performance of the successful cooling design. copyright © 2005 by ASME.

Numerical simulations of unsteady wet steam flows with non-equilibrium condensation in the nozzle and the steam turbine

Numerical techniques for non-equilibrium condensing flows are presented. Conservation equations for homogeneous gas-liquid two-phase compressible flows are solved by using a finite volume method based on an approximate Riemann solver. The phase change consists of the homogeneous nucleation and growth of existing droplets. Nucleation is computed with the classical Volmer-Frenkel model, corrected for the influence of the droplet temperature being higher than the steam temperature due to latent heat release. For droplet growth, two types of heat transfer model between droplets and the surrounding steam are used: a free molecular flow model and a semi-empirical two-layer model which is deemed to be valid over a wide range of Knudsen number. The computed pressure distribution and Sauter mean droplet diameters in a convergent-divergent (Laval) nozzle are compared with experimental data. Both droplet growth models capture qualitatively the pressure increases due to sudden heat release by the non-equilibrium condensation. However the agreement between computed and experimental pressure distributions is better for the two-layer model. The droplet diameter calculated by this model also agrees well with the experimental value, whereas that predicted by the free molecular model is too small. Condensing flows in a steam turbine cascade are calculated at different Mach numbers and inlet superheat conditions and are compared with experiments. Static pressure traverses downstream from the blade and pressure distributions on the blade surface agree well with experimental results in all cases. Once again, droplet diameters computed with the two-layer model give best agreement with the experiments. Droplet sizes are found to vary across the blade pitch due to the significant variation in expansion rate. Flow patterns including oblique shock waves and condensation-induced pressure increases are also presented and are similar to those shown in the experimental Schlieren photographs. Finally, calculations are presented for periodically unsteady condensing flows in a low expansion rate, convergent-divergent (Laval) nozzle. Depending on the inlet stagnation subcooling, two types of self-excited oscillations appear: a symmetric mode at lower inlet subcooling and an asymmetric mode at higher subcooling. Plots of oscillation frequency versus inlet sub-cooling exhibit a hysteresis loop, in accord with observations made by other researchers for moist air flow. Copyright © 2006 by ASME.

Advantage of superconducting bearing in a commercial flywheel system

The use of a superconducting magnetic bearing in an Urenco Power Technologies (UPT) 100kW flywheel is being studied. The dynamics of a conventional flywheel energy storage system have been studied at low frequencies. We show that the main design consideration is overcoming drag friction losses and parasitic resonances. We propose an original superconducting magnetic bearing design and improved cryogenic motor cooling to increase stability and decrease energy losses in the system. © 2008 IOP Publishing Ltd.

Thin film shape memory alloys and microactuators

For Micro-electro-mechanical System (MEMS) applications, TiNi-based thin film Shape Memory Alloys (SMAs) possess many desirable properties, such as high power density, large transformation stress and strain upon heating and cooling, superelasticity and biocompatibility. In this paper, recent development in TiNi-based thin film SMA and microactuator applications is discussed. The topics related to film deposition and characterisation is mainly focused on crystal nucleation and growth during annealing, film thickness effect, film texture, stress induced surface relief, wrinkling and trenches as well as Temperature Memory Effect (TME). The microactuator applications are mainly focused on microvalve and microcage for biological applications, micromirror for optical applications and data storage using nanoindentation method. Copyright © 2009, Inderscience Publishers.

Hot streak and vane coolant migration in a downstream rotor

This paper describes a method of improving the cooling of the hub region of high-pressure turbine (HPT) rotor by making better use of the unsteady coolant flows originating from the upstream vane. The study was performed computationally on an engine HPT stage with representative inlet hot streak and vane coolant conditions. An experimental validation study of hot streak migration was undertaken on two low-speed test facilities. The unsteady mechanisms that transport hot and cold fluid within the rotor hub region are first examined. It was found that vortex-blade interaction dominated the unsteady transport of hot and cold fluid in the rotor hub region. This resulted in the transport of hot fluid onto the rotor hub and pressure surface, causing a peak in the surface gas temperatures. The vane film coolant was found to have only a limited effect in cooling this region. A new cooling configuration was thus examined which exploits the unsteadiness in rotor hub to aid transport of coolant towards regions of high rotor surface temperatures. The new coolant was introduced from a slot upstream of the vane. This resulted in the feed of slot coolant at a different phase and location relative to the vane film coolant within the rotor. The slot coolant was entrained into the unsteady rotor secondary flows and transported towards the rotor hub-pressure surface region. The slot coolant reduced the peak time-averaged rotor temperatures by a similar amount as the vane film coolant despite having only a sixth of the coolant mass flow. Copyright © 2008 by ASME.

Effect of thermal pollution on the hydrological parameters of River Jhelum (J & K)

The Buniyar hydroelectric project and the lower Jhelum Barrier at Gantamulla constructed across river Jhelum are in operation from several years. The two power stations have changed the hydrological features of the area where dam is situated. Therefore, the impact of hydroelectric projects on fishery resources of river Jhelum is a matter of great concern. The treated water from the power house is released through turbines, having cooling effect on them. The change in the hydrological parameters such as increase in temperature, depletion of oxygen etc. might have brought fishes under stress which is the main cause in decreased population of finfishes from site to site. The golden mahseer, Tor putitora which was once an abundant species in river Jhelum has disappeared due to human intervention. The prevailing water quality around hydroelectric projects is unsuitable for finfishes of river Jhelum.

Modeling evaporation effects in conditional moment closure for spray autoignition

Simulations of an n-heptane spray autoigniting under conditions relevant to a diesel engine are performed using two-dimensional, first-order conditional moment closure (CMC) with full treatment of spray terms in the mixture fraction variance and CMC equations. The conditional evaporation term in the CMC equations is closed assuming interphase exchange to occur at the droplet saturation mixture fraction values only. Modeling of the unclosed terms in themixture fraction variance equation is done accordingly. Comparison with experimental data for a range of ambient oxygen concentrations shows that the ignition delay is overpredicted. The trend of increasing ignition delay with decreasing oxygen concentration, however, is correctly captured. Good agreement is found between the computed and measured flame lift-off height for all conditions investigated. Analysis of source terms in the CMC temperature equation reveals that a convective-reactive balance sets in at the flame base, with spatial diffusion terms being important, but not as important as in lifted jet flames in cold air. Inclusion of droplet terms in the governing equations is found to affect the mixture fraction variance field in the region where evaporation is the strongest, and to slightly increase the ignition delay time due to the cooling associated with the evaporation. Both flame propagation and stabilization mechanisms, however, remain unaffected. © 2011 Taylor & Francis.