bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of Hot Tearing of Cast Semi-Solid 206 Alloys
Authors: Lemieux Alain , Langlais Joseph , Chen X. Grant
Published: October 2012

The mechanical properties of 206 alloys are among the highest of aluminum alloys. However, these alloys are usually prone to hot tearing. It is known that the addition of silicon can reduce the hot tearing propensity and improve fluidity. However, the commercial 206 alloys used in conventional casting processes limit the silicon concentration ≤0.05 wt% to obtain good mechanical properties. However, the semi-solid forming offers a unique opportunity to increase the silicon content to improve the castability without compromise on mechanical properties. In the present paper, the development of modified 206 alloy compositions to minimize hot tearing during semi-solid forming while maintaining competitive mechanical properties is reported. The effect of high silicon contents with varying copper levels on hot tearing sensitivity is studied. The mechanical properties of a high Si 206 alloy with lowest hot tearing sensitivity are evaluated. It is found that increasing the silicon content in 206 alloys is beneficial to reduce hot tearing. The high Si 206 variants produced by the SEED rheocating process not only reduce significantly the hot tearing sensitivity but also attain superior mechanical properties.
Properties of Thixocast Spring Steel Ratchets
Authors: Bünck Matthias , Bührig-Polaczek Andreas
Published: October 2012

Forging is state of the art for the production of hand tools in industrial scales. Due to high demands on stiffness and fracture toughness high-strength forged steels are used to provide components with high mechanical load capacity. In spite of all advantages forging is restricted by some means like the freedom of scope. However, because of the extreme thermal load and the hardly avoidable casting defects, hand tools are nowadays not cast. By thixocasting steel technical difficulties can be reduced and new options are provided, which allow manufacturing of components with much higher complexity than forging. During this work ratchets were thixocast successfully using spring steel type 61SiCr7. Based on the STC-concept, a new method to prevent the shot sleeve from damage was tested. Dies made of hot forming tool steel X38CrMoV5 were optimized by simulation and coated by plasma chemical deposition of crystalline Al2O3 protective coatings. The cast parts were heat treated successfully to enhance the toughness, which was measured by tensile and Charpy impact tests.
The Influence of Reheating Profile on the Final Microstructure of the Semi-Solid S600 and K100 Tool Steels
Authors: Pouyafar Vahid , Sadough S.A. , Hosseini Farzad , Jabbari Amin
Published: October 2012

Semi-solid processing of steel alloys has attracted the attention of researchers recently. Many attempts have been carried out for the industrialization of the process. High temperature nature of the steel semi-solid processing compared to other semi-solid alloys has been a problem in studying different process parameters like reheating parameters and microstructures continuously and simultaneously. In this research in-process and final microstructures of semi-solid steel alloys M2 and K100 under different reheating cycles and different parameters have been studied. All experiments are carried out in a resistance furnace and in an argon controlled atmosphere to avoid any oxidation and decarburization. During the reheating cycle, surface and core temperature of the samples have been recorded and compared with the oven temperature. The result of such a comparison can be used in other experiments where there is no access to sample for its temperature control or it is very difficult to measure the sample temperature like in rheology tests. Partial reheating and quenching has been used to determine the in-process microstructure of the alloy. For each set of experiments particle shape factor has been derived and its relation to other parameters has been studied. Finally appropriate reheating cycle and parameters for each alloy has been determined.
Experimental and Simulation Study of Microstructure of the Aluminium Alloy 319s in Induction Reheating Process
Authors: Song Nan Nan , Zhang Fan , He You Feng , Zhu Qiang
Published: October 2012

Semi-solid processing of metallic alloys has been developing over the last 30 years. Millions of components are now manufactured by semi-solid processing. A semi-solid processing so called thixoforming requires reheating the feedstock to a semi-solid state in relatively short time interval with a uniform temperature distribution as well as an optimum liquid fraction. Microstructure, which makes significant impact on processing parameters and quality of the component, changes during the reheating process. The main objective of this study is to establish a quantitative relationship of the microstructure and the induction heating process parameters of the aluminum alloy 319s. This quantitative relationship is employed in the numerical simulation of calculating solid/liquid fraction changes during induction heating process. The simulation results are then successfully applied in aiding optimization of process parameters to make an automobile engine turbocharger compressor wheel, which has very complex geometry.
Rheological Properties and Microstructure of Hypereutectic Semi-Solid Al-Si-Mg Alloys Using Rheocasting Route
Authors: Tebib Mehand , Ajersch Frank , Chen X. Grant
Published: October 2012

The SEED rheocasting process was used to produce semi-solid slurries of hypereutectic Al-17Si-4.5Cu (A390) and Al-15Si-10.5Mg-4Cu alloys respectively. The rheological properties of these alloys in the semi-solid state were characterized at different deformation rates and at variable solid fractions using the parallel plate compression viscometry. The viscosity at different shear rates was calculated using a Newtonian fluid model for increments of deformation during compression. Microstructures of both alloys, after partial solidification and compression, were examined in order to characterize the flow behavior during deformation. The comparison of the viscosity between the A390 and Al-15Si-10.5Mg-4Cu alloys indicated that the high Mg containing alloy possessed a higher viscosity for the range of shear rates and solid fractions investigated. Rheological results showed that at a given solid fraction, the viscosity of both alloys decreased significantly with increasing shear rates, indicating a shear thinning behavior. In addition, a separation of liquid and solid phases was also observed for both alloys in the microstructural study of compressed semi-solid billets.
Rheological Characterization of Semi-Solid A356 Aluminium Alloy
Authors: Das Prosenjit , Samanta Sudip K. , Chattaopadhyay Himadri , Dutta Pradip , Barman Nilkanta
Published: October 2012

Rheological behavior of semi-solid slurries forms the backbone of semi-solid processing of metallic alloys. In particular, the effects of several process and metallurgical parameters such as shear rate, shear time, temperature, rest time and size, distribution and morphology of the primary phase on the viscosity of the slurry needs in-depth characterization. In the present work, rheological behaviour of the semisolid aluminium alloy (A356) slurry is investigated by using a high temperature Searle type Rheometer using concentric cylinders. Three different types of experiment are carried out: isothermal test, continuous cooling test and steady state test. Continuous decrease in viscosity is observed with increasing shear rate at a fixed temperature (isothermal test). It is also found that the viscosity increases with decreasing temperature for a particular shear rate due to increasing solid fraction (continuous cooling test). Thixotropic nature of the slurry is confirmed from the hysteresis loops obtained during experimentation. Time dependence of slurry viscosity has been evaluated from the steady state tests. After a longer shearing time under isothermal conditions the starting dendritic structure of the said alloy is transformed into globular grains due to abrasion, agglomeration, welding and ripening.
New Developments with the SEED Technology
Authors: Côté Pascal , Larouche Marie Eve , Chen X. Grant
Published: October 2012

The SEED technology, a rheocasting process based on the slurry-on-demand approach, is an emerging technology that was developed in the mid-2000s. Many publications with regard to the process and to alloy development using this technology were made since, and several industrial units are operated worldwide. Moreover, the process is still actively developed and is fully supported by a team of scientists, engineers and technicians. With a global objective of addressing the user requirements and the industry needs, works were conducted toward optimization of the process and equipment. At first, the focus was on developing a simplified version of the SEED process to eliminate the so-called “drainage” phase while preserving the prime quality of the slurry produced. Improvement of some system components and integration of new features were also targeted to secure the overall equipment efficiency (OEE) and increase the process reliability. This work, backed with the optimization of process parameters and comprehensive techniques adapted for semi solid casting, led to the consolidation and even improvement of the properties of the parts produced for the common foundry alloys 356/357 and 319. Furthermore, the non-drained SEED version was applied to the validation of the process capabilities for uncommon cast alloys with works on 6061 wrought alloy, Duralcan metal matrix composite, and others. The results confirmed that the SEED process can efficiently be used in non-drained mode and achieve the same quality of slurry as the drained version originally developed. It is now proven in the industrial scale and actually integrated in the updated industrial equipment. Moreover, the capabilities of the process for special alloys and applications are still the subject of active development works.
Effect of the Parameters in Inverted Cone-Shaped Pouring Channel Process on the Microstructure of Semi-Solid 7075 Aluminum Alloy Slurry
Authors: Yang Bin , Mao W.M. , Zeng Jian Nan , Song Xiao Jun
Published: October 2012

The semi-solid slurry of 7075 aluminum alloy was prepared by using an innovative non-stirring technology that can be called inverted cone-shaped pouring channel process (ICSPC). The effect of pouring temperature and structural parameters of the channel on the microstructure of semi-solid 7075 aluminum alloy slurry was investigated. The experimental results reveal that when keeping the pouring temperature within some range, the slurry with spherical primary α(Al) grains can be prepared by ICSPC process, and with the decline of the pouring temperature, the microstructure of semi-solid 7075 aluminum alloy is more desirable under the same channel. The appropriate combination of channel length and interior surface slope can also give rise to a transition of the growth morphology of primary α(Al) from coarse dendritic to coarse particle-like and further to fine-globular at the same pouring temperature. In ICSPC process, numerous effective heterogeneous nucleation takes place in the melt as it flowed along the interior surface of the channel and the morphology of primary α(Al) grains is virtually determined by the degree of contact condition between the superheat melt and the interior surface of the channel. A better contact condition stands for a stronger heat extraction from the melt, and will finally appear as a remarkable increase of primary α(Al) grains survived in the melt, which will conspicuously promote the spherical growth of the primary α(Al) grains.
A357 Aluminium Cast Alloys for Extrusion Processes
Authors: Campillo Manel , Baile M. Teresa , Menargues Sergi , Martín Enric , Forn Antonio
Published: October 2012

The A357 Al-Si-Mg cast alloy is commonly used for cast production of automotive components in conventional HPDC and in semi-solid processes. The aim of this work is to study the application of A357 cast alloy in thixoextrusion processes. This technology offers new possibilities of application for cast alloys and several advantages in from of conventional processes of hot-extrusion: lower pressure, minor friction forces, higher material fluidity and longer tool life. The thixoextrusion was experimented in a pilot plant, at different speeds and temperatures, with an induction furnace and a 400 Tn press. With ingots of A357 as cast, a tool with a ratio of 8.5 and with temperatures of extrusion around 560 °C, it is possible to obtain extrusion speeds more than 3 m•s-1. In all cases, when the speed of extrusion increases, the press of extrusion decreases. The effect of heat treatments and extrusion speed in the microstructure of the extruded product is evaluated.
Improvement of Free Solidified Surface of Strip Cast Using a Single Roll Caster by Scribing Semisolid Layer
Authors: Haga Toshio , Akitsu Kazuya
Published: October 2012

AA5182 alloy was cast using the single roll caster equipped with the scraper. Improvement of flatness of the free solidified surface of the strip cast by a single roll caster was tried by scribing of semisolid layer using a scraper. The semisolid layer could be scribed and be made flat by the scraper. The scribing force was controlled by a dead weight. Defects which occurred on the scribed surface were investigated. The property of the free solidified surface (scribed surface) was compared with roll contact surface by the deep drawing test. The property of the scribed surface was almost as same as that of the roll contact surface. Mechanical property was investigated by the tension test.
Mini-Thixoforming of a Steel Produced by Powder Metallurgy
Authors: Jirková Hana , Aišman David , Sen Indrani , Wagner Martin F.X. , Behúlová Mária , Kusý Martin , Mašek Bohuslav
Published: October 2012

Semi-solid processing is complicated by various inherent technical problems. However, once these problems are solved, thixoforming allows intricately shaped components to be manufactured very effectively – often with microstructures that cannot be produced by any other techniques. The recently introduced mini-thixoforming method is an example of such a novel technique for semi-solid processing of steel. The wall thicknesses of resulting parts are about 1 mm. Microstructures of semi-solid-processed steels typically consist of a high proportion of globular particles of metastable austenite embedded in a carbide network, the latter being much harder and more brittle. This paper illustrates that mini-thixoforming allows inverting that microstructural configuration. As an experimental material, powder steel with increased content of vanadium and chromium was used. The post-thixoforming microstructure consisted of a dispersion of carbides and high-vanadium and high-chromium eutectic in an austenitic matrix. Applying optimised processing parameters, complex-shaped parts could be produced. According to the high hardness of resulting microstructural components, the new materials are likely to exhibit extraordinary strength and wear resistance.
Production of Titanium Alloy Components by Semi-Solid Forming
Authors: Kertesz Levente , Liewald Mathias
Published: October 2012

The relatively high costs of processing titanium alloys and the high variability in the products' quality currently represent the major economic obstacles to using such materials in either production or medical engineering. For this reason, new research and development work at the Institute for Metal Forming Technology of the University of Stuttgart is pursuing the objective of improving and enhancing pre-existing processes for these types of materials. In doing this, aspects are considered which specify definite mechanical properties during and after the forming process as well as reduce the costs by means of cutting the manufacturing times, increase the use of semi-finished products and minimise finishing operations.
Industrial Heat Treatment of R-HPDC A356 Automotive Brake Callipers
Authors: Chauke Levy , Möller Heinrich , Curle Ulyate Andries , Govender Gonasagren
Published: October 2012

Heat treatment of rheo-high pressure die cast (R-HPDC) A356 brake callipers has produced good mechanical properties on the laboratory scale. An industrial heat treatment is required to evaluate the applicability and conformance of the R-HPDC A356 brake callipers to the automotive industry. This research studied A356 brake callipers heat treated on the industrial scale with particular emphasis on the resulting microstructure, hardness and tensile properties. The eutectic Si-particle spheroidisation after solution heat treatment was achieved and observed with optical microscopy. A hardness increase from 64 to 100 Vickers was achieved from the as-cast condition to the industrially heat treated T6 condition. The heat treatment caused no significant variation in hardness and tensile properties from brake callipers within the same batch or from different batches. The yield and ultimate strengths of the industrial heat treated brake callipers were lower compared to the laboratory scale heat treatment properties, while the ductility increased, mainly due to quenching effects. Even though the industrial heat treated A356 brake callipers resulted in yield and ultimate tensile strengths lower than those achieved on a laboratory scale, they still exceeded the minimum specifications for gravity die cast A356 brake callipers.
Semisolid Processing of Al-Sn-Cu Alloys for Bearing Applications
Authors: Pola Annalisa , Montesano Lorenzo , Gelfi Marcello , Roberti Roberto
Published: October 2012

The aim of this work was to evaluate the advantages in using semisolid processing of Al-Sn alloys in order to improve microstructural homogeneity and, consequently, wear resistance. Different tests were performed on an Al3Sn4Cu by using ultrasound treatments during solidification to obtain an almost globular microstructure. Metallurgical characterizations and pin on disk wear tests were carried out on semisolid as well as on conventionally cast samples in order to assess the benefit of the treatment.
Semi-Solid High Pressure Die Casting of Metal Matrix Composites Produced by Liquid State Processing
Authors: Ivanchev Lilian , Camagu Sigqibo Templeton , Govender Gonasagren
Published: October 2012

There are two main technologies for manufacturing of particulate reinforced metal matrix composites (MMC), solid state and liquid state processing. The great challenge of producing cast metal matrix composites is to prevent agglomeration of particulates. This tendency is more pronounced with decreasing the particulate size to fine micro- and nano size. A method for producing MMC was successfully implemented for mixing hybrid, nano and low micron sized, reinforcing particles in an aluminium alloy matrix. The hybrid SiC particles were produced by milling 3µm to 5µm SiC particles to a particle size range between 2.5µm and 150 nm. The hybrid particles were mixed with A356 aluminium alloy under combined magneto-hydrodynamic (MHD) and mechanical stirring. The composite was then transferred to a High Pressure Die Casting (HPDC) machine in the semi-solid state. The micron size particles were found to be predominantly in the intergranular eutectic while the nano-particles were predominantly in the primary α-Al grains. Increased ultimate tensile strength, yield strength and hardness were achieved for the new cast metal matrix hybrid component (MMHC) alloy.
Contribution of Pulmonary KLRG1high and KLRG1low CD8 T Cells to Effector and Memory Responses during Influenza Virus Infection
Authors: Ye Fang , Turner Joanne , Flaño Emilio
Published: October 2012

In response to pathogen insult, CD8 T cells undergo expansion and a dynamic differentiation process into functionally different subpopulations. In this study, we show that during the effector response to influenza virus infection lung CD8 T cell subsets expressing killer cell lectin-like receptor G1 (KLRG1)high or KLRG1low had similar effector functions and immediate recall efficacy. The KLRG1 expression profile of lung CD8 T cells was not permanent after adoptive transfer and recall. Airway CD8 T cells exhibited a unique phenotype expressing low levels of KLRG1 together with high levels of markers of cellular activation. We investigated the functional characteristics of these cells by analyzing their capacity to survive and to respond to a secondary challenge outside of the airway environment. KLRG1high CD8 T cells isolated from the lung during the peak of the effector T cell response could survive for more than a month in the absence of cognate viral Ags after systemic adoptive transfer, and these “rested” CD8 T cells proliferated and participated in a recall response to influenza virus infection. These data highlight the unique phenotype and plasticity of effector CD8 T cell responses in the lung.
GM-CSF and IL-4 Stimulate Antibody Responses in Humanized Mice by Promoting T, B, and Dendritic Cell Maturation
Authors: Chen Qingfeng , He Fang , Kwang Jimmy , Chan Jerry K. Y. , Chen Jianzhu
Published: October 2012

Engraftment of human hematopoietic stem cells into immunodeficient mice that lack T cells, B cells, and NK cells results in reconstitution of human blood lineage cells, especially B cells, in the recipient mice. However, these humanized mice do not make any significant level of IgG Ab in response to Ag stimulation. In this study, we show that in humanized mice, B cells are immature, and there is a complete deficiency of CD209+ (DC-SIGN) human dendritic cells. These defects can be corrected by expression of human GM-CSF and IL-4 in humanized mice. As a result, these cytokine-treated humanized mice produced significant levels of Ag-specific IgG after immunization, including the production of neutralizing Abs specific for H5N1 avian influenza virus. A significant level of Ag-specific CD4 T cell response was also induced. Thus, we have identified defects in humanized mice and devised approaches to correct these defects such that the platform can be used for studying Ab responses and to generate novel human Abs against virulent pathogens and other clinically relevant targets.
Academic Wage Structure by Gender: The Roles of Peer Review, Performance, and Market Forces
Authors: Carlin Paul S. , Kidd Michael P. , Rooney Patrick M. , Denton Brian
Published: October 2012

We focus on understanding the role of productivity in determining wage structure differences between men and women in academia. The data arise from a pay equity study carried out in a single midwestern U.S. university over the 1996–1997 academic year. Econometric results confirm that external market forces exert influence over both male and female salary. But peer review ratings play a significant role in male but not female earnings determination, with similar results for objective measures of research, teaching, and service.
Sectoral Effects of Monetary Policy: The Evidence from Publicly Traded Firms
Authors: Jansen Dennis W. , Kishan Ruby P. , Vacaflores Diego E.
Published: October 2012

This article examines the impact of monetary policy on net sales of publicly traded firms in various sectors of the U.S. economy. We find that monetary policy has a heterogeneous effect on firms in different industries, with the strongest effect on firms in Retail and Wholesaling. Balance sheet characteristics, especially size, influence the impact of policy. Larger firms in several industries are able to mitigate the effect of policy. We find mixed results for firms' working capital, short‐term debt ratio, and leverage ratio with respect to the operation of the credit channel of monetary transmission mechanism.
The Timing of Redistribution
Authors: Glomm Gerhard , Jung Juergen
Published: October 2012

We investigate whether late redistribution programs that can be targeted toward low income families, but that may distort savings decisions, can “dominate” early redistribution programs that cannot be targeted as a result of information constraints. We use simple two‐period overlapping generations models with heterogeneous agents under six policy regimes: a model calibrated to the U.S. economy (benchmark), two early redistribution (lump sum) regimes, two (targeted) late redistribution regimes, and finally a model without taxes and redistribution. Redistribution programs are financed by a labor tax on the young generation and a capital tax on the old generation. We argue that if the programs are small in size, late redistribution can dominate early redistribution in terms of welfare but not in terms of real output. Better targeting of low income households cannot completely offset savings distortions. In addition, we find that the optimal transfer and tax policy implies a capital tax of 100% and transfers exclusively to the young generation.
Consumer Rationing and Cournot Outcomes: Experimental Evidence
Authors: Lepore Jason J. , Shafran Aric P.
Published: October 2012

We report the results of duopoly market experiments where firms first commit to capacities and then compete in prices. The theoretical literature pertaining to these duopoly models suggests that the way residual demand is rationed is fundamental to the character of equilibrium outcomes when capacity costs are sufficiently low. The experiments test this prediction by varying capacity cost and demand‐rationing schemes. We find that residual demand rationing does not significantly impact the capacity choices of experimental subjects, although it does affect pricing. Regardless of rationing scheme, the Cournot outcome is common with high capacity costs and rare with low capacity costs.
Quantifying diatom aspirations: Mechanical properties of chain‐forming species
Authors: Young A. M. , Karp-Boss L. , Jumars P. A. , Landis E. N.
Published: October 2012

Diatoms developed a variety of mechanisms to form chain‐like colonies, resulting in diverse morphologies and bulk mechanical properties. These properties affect translation, rotation, and deformation of colonies in ambient flows as well as their susceptibility to breakage by flow‐ and grazer‐induced forces. Morphological characteristics of diatom chains have been extensively studied, yet no studies have examined their mechanical properties. We studied the flexibility of four morphologically distinct species (Lithodesmium undulatum, Stephanopyxis turris, Lauderia annulata, and Guinardia delicatula) by measuring their deflections when held across a capillary tip in developing pipe flow and applying simple beam theory and a finite‐difference analysis of curvature to calculate flexural stiffness. Flexural stiffness varies greatly, with at least four orders of magnitude difference among the examined species (from 1.7 × 10−13 N m2, the most rigid, to 1.3 × 10−17 N m2, the most flexible), but two other species (Melosira nummuloides and a Thalassiosira sp.) were too flexible to measure with our apparatus. Vulnerability to breakage by flow also varied between species and, for species with heavily silicified joints between cells, was enhanced under nutrient depletion. These results highlight yet another attribute underlying the biodiversity of diatoms and their potential for utilizing highly differentiated ecological niches. Quantitative information from this study can now be used in the design of more mechanically realistic models that capture the dynamic coupling between elastic particles and flow to study diatom–flow interactions and their effects on nutrient acquisition, encounter with grazers, aggregate formation, and settling.
Organics in environmental ices: sources, chemistry, and impacts
Authors: McNeill V. F. , Grannas A. M. , Abbatt J. P. D. , Ammann M. , Ariya P. , Bartels-Rausch T. , Domine F. , Donaldson D. J. , Guzman M. I. , Heger D. , Kahan T. F. , Klán P. , Masclin S. , Toubin C. , Voisin D.
Published: October 2012

Abstract. The physical, chemical, and biological processes involving organics in ice in the environment impact a number of atmospheric and biogeochemical cycles. Organic material in snow or ice may be biological in origin, deposited from aerosols or atmospheric gases, or formed chemically in situ. In this manuscript, we review the current state of knowledge regarding the sources, properties, and chemistry of organic materials in environmental ices. Several outstanding questions remain to be resolved and fundamental data gathered before an accurate model of transformations and transport of organic species in the cryosphere will be possible. For example, more information is needed regarding the quantitative impacts of chemical and biological processes, ice morphology, and snow formation on the fate of organic material in cold regions. Interdisciplinary work at the interfaces of chemistry, physics and biology is needed in order to fully characterize the nature and evolution of organics in the cryosphere and predict the effects of climate change on the Earth's carbon cycle.
Impacts of the mountain-plains solenoid and cold pool dynamics on the diurnal variation of precipitation over Northern China
Authors:   Xinghua Bao,   Fuqing Zhang
Published: October 2012

Abstract. Convection-permitting numerical experiments using the Weather Research and Forecasting (WRF) model are performed to examine the impact of a thermally-driven Mountain-Plains Solenoid (MPS) on the diurnal variation of warm-season precipitation over Northern China. The focus of the analyses is a 15-day simulation that uses the 8-day average of the NCEP GFS gridded analyses at 00:00 UT between 17 and 24 June 2004 for the initial conditions and the 8-day averages at 00:00, 06:00, 12:00, and 18:00 UT for the lateral boundary conditions. Despite differences in rainfall intensity and location, the control experiment captures the essence of the observed diurnal variation of warm-season precipitation in North China. Consistent with observations, the simulated local precipitation peak initiates in the afternoon on the eastern edge and the immediate lee of the mountain ranges due to the upward branch of the MPS. The peak subsequently propagates downslope and southeastward along the steering-level mean flow, reaching the Central North China Plains around midnight and early morning hours resulting in a broad area of nocturnal precipitation maxima over the Central plains. Sensitivity experiments show that besides the impact of the MPS, cold pool dynamics play an essential role in the propagation and maintenance of the precipitation peak over the plains.
Temperature-dependent accumulation mode particle and cloud nuclei concentrations from biogenic sources during WACS 2010
Authors: Ahlm L. , Shakya K. M. , Russel L. M. , Schroder J. C. , Wong J. P. S. , Sjostedt S. J. , Hayden K. L. , Liggio J. , Wentzell J. J. B. , Wiebe H. A. , Mihele C. , Leaitch W. R. , Macdonald A. M.
Published: October 2012

Abstract. Submicron aerosol particles collected simultaneously at the mountain peak (2182 m a.s.l.) and at a forested mid-mountain site (1300 m a.s.l.) on Whistler Mountain, British Columbia, Canada, during June and July 2010 were analyzed by Fourier transform infrared (FTIR) spectroscopy for quantification of organic functional groups. Positive matrix factorization (PMF) was applied to the FTIR spectra. Three PMF factors associated with (1) combustion, (2) biogenics, and (3) vegetative detritus, were identified at both sites. The biogenic factor was correlated with both temperature and several volatile organic compounds (VOCs). The combustion factor dominated the submicron particle mass during the beginning of the campaign when the temperature was lower and advection was from the Vancouver area, but as the temperature started to rise in early July the biogenic factor came to dominate as a result of increased emissions of biogenic VOCs and thereby increased formation of secondary organic aerosol (SOA). On average, the biogenic factor represented 69% and 49% of the submicron organic particle mass at Whistler Peak and at the mid-mountain site, respectively. The lower fraction at the mid-mountain site was a result of more vegetative detritus there, and also higher influence from local combustion sources. The biogenic factor was strongly correlated (r ~ 0.9) to number concentration of particles with diameter (Dp)> 100 nm, whereas the combustion factor was better correlated to number concentration of particles with Dp < 100 nm (r~ 0.4). The number concentration of cloud condensation nuclei (CCN) was correlated (r ~ 0.7) to the biogenic factor for supersaturations (S) of 0.2% or higher, which indicates that particle condensational growth from biogenic vapors was an important factor in controlling the CCN concentration for clouds where S≥0.2%. Both the number concentration of particles with Dp > 100 nm and numbers of CCN for S≥0.2% were correlated to temperature. Considering the biogenic influence, these results indicate that temperature was a primary factor controlling these CCN concentrations at 0.2% supersaturation.
Secondary organic aerosol formation from gasoline vehicle emissions in a new mobile environmental reaction chamber
Authors: Platt S. M. , El Haddad I. , Zardini A. A. , Clairotte M. , Astorga C. , Wolf R. , Slowik J. G. , Temime-Roussel B. , Marchand N. , Ježek I. , Drinovec L. , Močnik G. , Möhler O. , Richter R. , Barmet P. , Bianchi F. , Baltensperger U. , Prévôt A. S. H.
Published: October 2012

Abstract. We present a new mobile environmental reaction chamber for the simulation of the atmospheric aging of aerosols from different emissions sources without limitation from the instruments or facilities available at any single site. The chamber can be mounted on a trailer for transport to host facilities or for mobile measurements. Photochemistry is simulated using a set of 40 UV lights (total power 4 KW). Characterisation of the emission spectrum of these lights shows that atmospheric photochemistry can be accurately simulated over a range of temperatures from −7–25 °C. A photolysis rate of NO2, JNO2, of (8.0 ± 0.7) × 10−3 molecules cm−3 s−1 was determined at 25 °C. Further, we present the first application of the mobile chamber and demonstrate its utility by quantifying primary organic aerosol (POA) emission and secondary organic aerosol (SOA) production from a Euro 5 light duty gasoline vehicle. Exhaust emissions were sampled during the New European Driving Cycle (NEDC), the standard driving cycle for European regulatory purposes, and injected into the chamber. The relative concentrations of oxides of nitrogen (NOx) and total hydrocarbon (THC) during the aging of emissions inside the chamber were controlled using an injection system developed as a part of the new mobile chamber set up. Total OA (POA + SOA) emission factors of (370 ± 18) × 10−3 g kg−1 fuel, or (14.6 ± 0.8) × 10−3 g km−1, after aging, were calculated from concentrations measured inside the smog chamber during two experiments. The average SOA/POA ratio for the two experiments was 15.1, a much larger increase than has previously been seen for diesel vehicles, where smog chamber studies have found SOA/POA ratios of 1.3–1.7. Due to this SOA formation, carbonaceous particulate matter (PM) emissions from a gasoline vehicle may approach those of a diesel vehicle of the same class. Furthermore, with the advent of emission controls requiring the use of diesel particle filters, gasoline vehicle emissions could become a far larger source of ambient PM than diesel vehicles. Therefore this large increase in the PM mass of gasoline vehicle aerosol emissions due to SOA formation has significant implications for our understanding of the contribution of on-road vehicles to ambient aerosols and merits further study.
On the efficient treatment of temperature profiles for the estimation of atmospheric transmittance under scattering conditions
Authors: Lindstrot R. , Preusker R.
Published: October 2012

Abstract. The vertical temperature profile of the atmosphere has an influence on the width and intensity of gaseous absorption lines. In the visible and near infrared part of the spectrum, this poses a problem for the fast forward simulation of the radiative transfer, needed in algorithms for the retrieval of any atmospheric or surface-related parameter from satellite measurements. We show that the main part of the global variability of temperature profiles can be described by their first 2 to 6 eigenvectors, depending on the accuracy requirement, by performing a Principal Component Analysis (PCA) on a global set of temperature profiles from the Global Forecast System (GFS). Furthermore, we demonstrate the possibility to approximate the atmospheric transmittance in the O2 A band for any temperature profile with almost perfect accuracy by a linear combination of the transmittances attributed to each of the significant temperature eigenvectors. For the retrieval of surface pressure from O2 A band measurements, this reduces the global root mean square error from >30 hPa to better than 1 hPa by strongly reducing the regional bias of surface pressure, retrieved on the assumption of an average temperature profile. The technique can be applied under scattering conditions to eliminate temperature-induced errors in, e.g., simulated radiances. In principal, the method can be useful for any problem including gaseous absorption or emission with a significant influence of the temperature profile, such as the retrieval of total water vapour content or sea surface temperature.
Radar diagnosis of the subglacial conditions in Dronning Maud Land, East Antarctica
Authors: Fujita S. , Holmlund P. , Matsuoka K. , Enomoto H. , Fukui K. , Nakazawa F. , Sugiyama S. , Surdyk S.
Published: October 2012

Abstract. In order to better understand the spatial distribution of subglacial environments, ground-based radar profiling data were analyzed for a total distance of ~ 3300 km across Dronning Maud Land, East Antarctica. The relationship between geometrically corrected bed returned power [Pcbed]dB in decibels and ice thickness H was examined. When H is smaller than a~critical value that varies according to location, [Pcbed]dB tends to decrease relatively smoothly with increasing H, which is explicable primarily by the cumulative effect of dielectric attenuation within the ice. However, at locations where H is larger than the critical H values, anomalous increases and fluctuations in [Pcbed]dB were observed, regardless of the choice of radar frequency or radar-pulse width. In addition, the amplitude of the fluctuations often range 10 ~ 20 dB. We argue that the anomalous increases are caused by higher bed reflectivity associated with the existence of subglacial water. We used these features to delineate frozen and temperate beds. Approximately two-thirds of the investigated area was found to have a temperate bed. The beds of the inland part of the ice sheet tend to be temperate, with the exception of subglacial high mountains. In contrast, the beds of coastal areas tend to be frozen, with the exception of fast-flowing ice on the subglacial lowland or troughs. We argue that this new analytical method can be applied to other regions.
Prosthetic Joint Infections due to Staphylococcus Aureus and Coagulase-Negative Staphylococci
Authors: Tornero Eduard , García-Oltra Ester , García-Ramiro Sebastían , Martínez-Pastor Juan C. , Bosch Jordi , Climent Consuelo , Morata Laura , Camacho Pilar , Mensa Josep , Soriano Alex
Published: October 2012

Purposes

To evaluate the specific characteristics, outcome, and predictors of failure of prosthetic joint infections (PJI) due to S. aureus and coagulase-negative staphylococci (CNS) treated with open debridement and retention of the implant.

Methods

PJI due to S. aureus or CNS prospectively registered in a database from 1999 to 2009 were retrospectively reviewed. During the study period, 106 patients met the inclusion criteria. The mean follow-up period was 3.8 years and for at least 2 years in all patients. The failure rate was 23.6% (25 out of 106). The only variable significantly associated with failure in the global cohort was polymicrobial infection (38.7% vs. 17.3%, p = 0.024). Fifty-seven (53.8%) patients had an infection due to S. aureus and 49 (46.2%) due to CNS. Among S. aureus infections, 95% corresponded to primary arthroplasties while 98% of PJIs due to CNS were after revision arthroplasties (p<0.001). C-reactive protein was significantly higher in PJI due to S. aureus (9.5 mg/dl vs. 4.9 mg/dl, p = 0.007). The rate of methicillin-resistance (8.8% vs. 59.2%, p<0.001) and fluoroquinolone-resistance (15.8% vs. 34.7%, p = 0.005) was significantly higher in CNS infections. The global failure rate was higher in S. aureus infections (28% vs. 18.3. p = 0.26). In S. aureus infections, patients diagnosed within the first 15 days after joint arthroplasty (p = 0.031) and with bacteremia (p = 0.046) had poor prognosis. In CNS infections only the location of the prosthesis (knee 27.6% vs. hip 5%, p = 0.045) was associated with failure.

Conclusions

PJIs due to S. aureus were mainly in primary arthroplasties; they had a higher inflammatory response; and the strains were more susceptible to fluoroquinolones and methicillin than CNS infections. S. aureus infections had a higher failure rate than CNS infections, however, the difference was not statistically significant. There were few factors associated with failure and they were different in S. aureus and CNS infections.
Trait-based surveillance of flood channel effects on the River Thames
Authors: Ruse Leslie Patrick
Published: October 2012

An artificial anabranch was opened to the main River Thames by the end of 2001. Chironomid pupal exuviae have been sampled from sites along the main river since 1977 including sites above and below the anabranch. Two sites on the anabranch have also been surveyed since its opening. Long-term surveillance of the chironomid assemblage prior to construction of the anabranch provided a reference state by which its impact could be assessed. Feeding and habitat preferences were attributed to chironomid taxa while additional environmental -tolerance traits were derived from the long-term data of the Thames. Canonical Correspondence Analysis, with spatial variation partialled out, was used to select temporal environmental variables explaining chironomid taxa distribution. Taxa with significant t-values in the regression with selected environmental variables were then included in the subsequent analysis of variance of traits by General Linear Modelling. From 1977 up to 2001 lower Thames sites, above and below the anabranch, showed no significant changes in any of the traits investigated. Four surveys from 2002 to 2009 have revealed some significant changes downstream of the anabranch, both in comparison with before-construction and between sites. These changes suggest the anabranch is providing a sink for poor-quality sediments. Immediately downstream of the anabranch fine sediment-dwelling chironomids have declined within the Thames, chironomids sensitive to ammonia have increased while chironomids tolerant of organic pollution have decreased.doi: 10.5324/fn.v31i0.1360.Published online: 17 October 2012.
Long-term patterns of chironomid assemblages in a high elevation stream/lake network (Switzerland) – Implications to global change
Authors: Lods-Crozet Brigitte , Oertli Beat , Robinson Christopher T
Published: October 2012

A long-term monitoring program was initiated in 2002 on running and standing waters in a high elevation cirque landscape (Macun) in the Swiss National Park. The region comprises contrasting basins with different water sources, a glacier-fed basin and two precipitation-fed basins. Sampling of 26 permanent and temporary ponds (or small lakes) and of interconnecting streams (10 sites) was conducted from 2002 to 2010. Pond macroinvertebrate assemblages were dominated by chironomids with 42 taxa. The Orthocladiinae were the dominant subfamily in richness and abundance with 22 taxa. The greatest diversity was found in ponds located in the south and outlet basins. The inter-year variability for the same pond is high, but no clear temporal trend was noticed in ponds frequently monitored ponds. The Orthocladiinae subfamily was also the richest in the stream sites where 33 taxa were collected. The north and south basins were separated on the basis of chironomid assemblages. The chironomid assemblages in the stream network shows a temporal trend from 2002 but it cannot be linked to any clear change at the community structure level. The higher richness and abundance in stream sites and ponds of the south basin could be related to a greater heterogeneity in water physico-chemistry and substrata, and by the presence of Bryophyta. The understanding of the environmental factors that influence faunal assemblages is crucial for the protection of this sensitive alpine pond network where a relatively high overall regional diversity (49 taxa) is detected. From the literature, temperature is recognized as the driving force on changes in chironomid assemblages in alpine systems. Our results support the use of chironomids as flagship indicators in the assessment of climatic change in alpine landscapes.doi: 10.5324/fn.v31i0.1361.Published online: 17 October 2012.
A benthic quality index for European alpine lakes
Authors: Rossaro Bruno , Boggero Angela , Lods-Crozet Brigitte , Free Gary , Lencioni Valeria , Marziali Laura , Wolfram Georg
Published: October 2012

The development of benthic quality indices for European lakes is hindered by the lack of information concerning many national lake types and pressures. Most information is from north European lakes stressed by acidification and from deep lakes subjected to eutrophication; for other lake types (the ones included in the Mediterranean areas for example) and for other pressures (hydro-morphological alteration, toxic stress) there is practically no information about the response of benthic macro-invertebrates; this hinders the possibility of an intercalibration of the indices among the member states (MS) in the EU. In the present communication three benthic quality indices are proposed considering the littoral, sublittoral and profundal zone in 5 reference and 7 non reference lakes from the Alpine region in response to eutrophication. The sensitivity values of the 177 species found in these lakes were calculated taking a weighted average of the values of environmental variables from lakes in which the species were present. The indicator taxa which prevailed in these lakes were Chironomids and Oligochaetes. A coinertia analysis emphasized the importance of trophic variables (transparency, nitrates, total phosphorous) in explaining the species distribution, but geographic (altitude) and morphometric (depth, volume) variables were also important. The indices enabeled a separation of reference from non-reference lakes and to assign the non-reference lakes to different quality classes in agreement with the Water Framework Directive.doi: 10.5324/fn.v31i0.1364.Published online: 17 October 2012.
Additions and corrections to Part 1 of ‘A World Catalogue of Chironomidae (Diptera)’
Authors: Ashe Patrick , O'Connor James P
Published: October 2012

An update of the more significant changes affecting Part 1 of ‘A World Catalogue of Chironomidae (Diptera)’ is provided. These concern new taxon names, new combinations and new synonymies that were proposed, as well as omissions and errors detected, since the publication of the Catalogue at the end of 2009.doi: 10.5324/fn.v31i0.1366.Published online: 17 October 2012.