bluuebunny/crossref_metadata_2025 huggingface dataset:
Postoperative washed red cell reinfusion reduces allogeneic transfusion requirements after total knee replacement
Authors: CARRERO ANTONIO , Del MONTE TRUJILLO MARIA , MUÑOZ MANUEL
Published: December 2006

In patients undergoing total knee replacement (TKR), most of blood loss occurs during the postoperative period and 30–50% of these patients receive allogeneic blood transfusion (ABT). For this reason, salvage and return of washed shed blood (WSB) from postoperative drainage may represent an alternative to ABT in these patients. We have, therefore, evaluated the clinical utility of WSB return in TKR patients. Data from 220 consecutive TKR patients were prospectively collected. WSB salvage and reinfusion (OrthoPAT, Haemonetics Corp., Braintree, MA, USA) were intended for 115 patients (reinfusion group), whereas the remaining 105 patients served as a control group. Patients received ABT if their hemoglobin concentration was lower than 8.0 g/dL or they showed clinical signs and symptoms of acute anemia. WSB return was possible in 97 patients who received a mean of 283 ± 180 mL of red cells (hematocrit, 66% ± 4%), without any clinically relevant incident. Return of WSB decreased both the ABT rate (50%vs. 19%, for control and reinfusion groups, respectively; P < 0.01) and the ABT index (0.86 ± 0.99 vs. 0.35 ± 0.83 units/patient, respectively; P < 0.01). In addition, when compared with those in the control group, patients in the reinfusion group had less postoperative infections (11.4%vs. 4.3%; P < 0.05), recovered the ability to walk 1 day earlier (P < 0.01), and had shorter hospital stay (P < 0.01). Return of WSB after TKR seems to effectively reduce postoperative requirements for ABT. However, for patients with preoperative hemoglobin concentrations below 13.0 g/dL, additional blood‐saving methods should be combined with WSB return.
An Experimental Investigation on the Effect of Post-Injection Strategies on Combustion and Emissions in the Low-Temperature Diesel Combustion Regime
Authors: Yun Hanho , Reitz Rolf D.
Published: December 2006

In order to meet future emissions regulations, new combustion concepts are being developed. Among them, the development of low-temperature diesel combustion systems has received considerable attention. Low NOx emissions are achieved through minimization of peak temperatures during the combustion process. Concurrently, soot formation is inhibited due to a combination of low combustion temperatures and extensive fuel-air premixing. In this study, the effect of late-cycle mixing enhancement by post-injection strategies on combustion and engine-out emissions in the low-temperature (low soot and NOx emissions) combustion regime was experimentally investigated. The baseline operating condition considered for low-temperature combustion was 1500rpm, 3bar IMEP with 50% EGR rate, and extension to high loads was considered by means of post injection. Post-injection strategies gave very favorable emission results in the low-temperature combustion regime at all loads tested in this study. Since post injection leads to late-cycle mixing improvement, further reductions in soot emissions were achieved without deteriorating the NOx emissions. With smaller fuel injected amounts for the second pulse, better soot emissions were found. However, the determination of the dwell between the injections was found to be very important for the emissions.
Effects of Bearing Stiffness Anisotropy on Hydrostatic Micro Gas Journal Bearing Dynamic Behavior
Authors: Liu L. X. , Spakovszky Z. S.
Published: December 2006

The high-speed microhydrostatic gas journal bearings used in the high-power density MIT microengines are of very low aspect ratio with an L∕D of less than 0.1 and are running at surface speeds of order 500m∕s. These ultra-short high-speed bearings exhibit whirl instability limits and a dynamic behavior much different from conventional hydrostatic gas bearings. The design space for stable high-speed operation is confined to a narrow region and involves singular behavior (Spakovszky and Liu, 2005, “Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings,” ASME J. Vibr. Acoust., 127(3), pp. 254–261). This together with the limits on achievable fabrication tolerance, which can be achieved in the silicon chip manufacturing technology, severely affects bearing operability and limits the maximum achievable speeds of the microturbomachinery. This paper introduces a novel variation of the axial-flow hydrostatic micro gas journal bearing concept, which yields anisotropy in bearing stiffness. By departing from axial symmetry and introducing biaxial symmetry in hydrostatic stiffness, the bearing's top speed is increased and fabrication tolerance requirements are substantially relieved making more feasible extended stable high-speed bearing operation. The objectives of this work are: (i) to characterize the underlying physical mechanisms and the dynamic behavior of this novel bearing concept and (ii) to report on the design, implementation, and test of this new microbearing technology. The technical approach involves the combination of numerical simulations, experiment, and simple, first-principles-based modeling of the gas bearing flow field and the rotordynamics. A simple description of the whirl instability threshold with stiffness anisotropy is derived explaining the instability mechanisms and linking the governing parameters to the whirl ratio and stability limit. An existing analytical hydrostatic gas bearing model is extended and modified to guide the bearing design with stiffness anisotropy. Numerical simulations of the full nonlinear governing equations are conducted to validate the theory and the novel bearing concept. Experimental results obtained from a microbearing test device are presented and show good agreement between the theory and the measurements. The theoretical increase in achievable bearing top speed and the relief in fabrication tolerance requirements due to stiffness anisotropy are quantified and important design implications and guidelines for micro gas journal bearings are discussed.
High-Pressure Turbine Deposition in Land-Based Gas Turbines From Various Synfuels
Authors: Bons Jeffrey P. , Crosby Jared , Wammack James E. , Bentley Brook I. , Fletcher Thomas H.
Published: December 2006

Ash deposits from four candidate power turbine synfuels were studied in an accelerated deposition test facility. The facility matches the gas temperature and velocity of modern first-stage high-pressure turbine vanes. A natural gas combustor was seeded with finely ground fuel ash particulate from four different fuels: straw, sawdust, coal, and petroleum coke. The entrained ash particles were accelerated to a combustor exit flow Mach number of 0.31 before impinging on a thermal barrier coating (TBC) target coupon at 1150°C. Postexposure analyses included surface topography, scanning electron microscopy, and x-ray spectroscopy. Due to significant differences in the chemical composition of the various fuel ash samples, deposit thickness and structure vary considerably for each fuel. Biomass products (e.g., sawdust and straw) are significantly less prone to deposition than coal and petcoke for the same particle loading conditions. In a test simulating one turbine operating year at a moderate particulate loading of 0.02 parts per million by weight, deposit thickness from coal and petcoke ash exceeded 1 and 2mm, respectively. These large deposits from coal and petcoke were found to detach readily from the turbine material with thermal cycling and handling. The smaller biomass deposit samples showed greater tenacity in adhering to the TBC surface. In all cases, corrosive elements (e.g., Na, K, V, Cl, S) were found to penetrate the TBC layer during the accelerated deposition test. Implications for the power generation goal of fuel flexibility are discussed.
Ceramic Matrix Composite Combustor Liners: A Summary of Field Evaluations
Authors: van Roode Mark , Price Jeff , Kimmel Josh , Miriyala Naren , Leroux Don , Fahme Anthony , Smith Kenneth
Published: December 2006

Solar Turbines Incorporated, under U.S. government sponsored programs, has been evaluating ceramic matrix composite combustor liners in test rigs and Solar’s Centaur® 50S gas turbine engines since 1992. The objective is to evaluate and improve the performance and durability of CMCs as high-temperature materials for advanced low emissions combustors. Field testing of CMC combustor liners started in May of 1997 and by the end of 2004, over 67,000 operating hours had been accumulated on SiC∕SiC and oxide∕oxide CMC liners. NOx and CO emissions have been consistently <15ppmv and <10ppmv, respectively. Maximum test durations of 15,144h and 13,937h have been logged for SiC∕SiC liners with protective environmental barrier coatings. An oxide∕oxide CMC liner with a Friable Graded Insulation coating has been tested for 12,582h. EBCs significantly improve SiC∕SiC CMC liner life. The basic three-layer EBC consists of consecutive layers of Si, mullite, and BSAS. The durability of the baseline EBC can be improved by mixing BSAS with mullite in the intermediate coating layer. The efficacy of replacing BSAS with SAS has not been demonstrated yet. Heavy degradation was observed for two-layer Si∕BSAS and Si∕SAS EBCs, indicating that the elimination of the intermediate layer is detrimental to EBC durability. Equivalent performance was observed when the Hi-Nicalon fiber reinforcement was replaced with Tyranno ZM or ZMI fiber. Melt infiltrated SiC∕SiC CMCs have improved durability compared to SiC∕SiC CMCs fabricated by Chemical Vapor Infiltration of the matrix, in the absence of an EBC. However, the presence of an EBC results in roughly equivalent service life for MI and CVI CMCs. Results to date indicate that oxide∕oxide CMCs with protective FGI show minor degradation under Centaur® 50S gas turbine engine operating conditions. The results of, and lessons learned from CMC combustor liner engine field testing, conducted through 2004, have been summarized.
25

Years

of BBC/ABB/Alstom Lean Premix Combustion Technologies
Authors: Döbbeling Klaus , Hellat Jaan , Koch Hans
Published: December 2006

The paper will show the development of lean premix combustion technologies in BBC, ABB, and Alstom gas turbines. Different technologies have been developed and applied in Brown Boveri Company (BBC) before 1990. Considerable improvements with respect to NOx emissions as compared to gas turbines with a single combustor and a single diffusion burner for liquid and gaseous fuel have been achieved with burners with extended premixing sections and with multi-injection burners for annular combustors. Between 1990 and 2005, burners with short but effective premixing zones (EV burners: environmentally friendly V-shaped burners) have been implemented in all new gas turbines of the ABB (and later Alstom) fleet with NOx levels well below 25 vppmd (@15% O2). In addition to this, three variants of premix technologies have been successfully developed and deployed into Alstom GT engines: the sequential EV burners—a technology that allows premixing of natural gas and oil into a hot exhaust stream to reheat the exhaust gases of a first high-pressure turbine; the MBtu EV burners that are used to burn syngas in a premix flame with low NOx emissions; and the advanced EV burners (AEV) that are capable to prevaporize and premix liquid fuel prior to combustion and burn it with very low NOx emissions without water injection. The paper will give an overview of these technologies and their usage in Alstom gas turbines over the last 25years.
CO2 Sequestration From IGCC Power Plants by Means of Metallic Membranes
Authors: Chiesa Paolo , Kreutz Thomas G. , Lozza Giovanni G.
Published: December 2006

This paper investigates novel IGCC plants that employ hydrogen separation membranes in order to capture carbon dioxide for long-term storage. The thermodynamic performance of these membrane-based plants are compared with similar IGCCs that capture CO2 using conventional (i.e., solvent absorption) technology. The basic plant configuration employs an entrained-flow, oxygen-blown coal gasifier with quench cooling, followed by an adiabatic water gas shift (WGS) reactor that converts most of CO contained in the syngas into CO2 and H2. The syngas then enters a WGS membrane reactor where the syngas undergoes further shifting; simultaneously, H2 in the syngas permeates through the hydrogen-selective, dense metal membrane into a counter-current nitrogen “sweep” flow. The permeated H2, diluted by N2, constitutes a decarbonized fuel for the combined cycle power plant whose exhaust is CO2 free. Exiting the membrane reactor is a hot, high pressure “raffinate” stream composed primarily of CO2 and steam, but also containing “fuel species” such as H2S, unconverted CO, and unpermeated H2. Two different schemes (oxygen catalytic combustion and cryogenic separation) have been investigated to both exploit the heating value of the fuel species and produce a CO2-rich stream for long term storage. Our calculations indicate that, when 85vol% of the H2+CO in the original syngas is extracted as H2 by the membrane reactor, the membrane-based IGCC systems are more efficient by ∼1.7 percentage points than the reference IGCC with CO2 capture based on commercially ready technology.
Comparisons of Diesel PCCI Combustion Simulations Using a Representative Interactive Flamelet Model and Direct Integration of CFD With Detailed Chemistry
Authors: Kong Song-Charng , Kim Hoojoong , Reitz Rolf D. , Kim Yongmo
Published: December 2006

Diesel engine simulation results using two different combustion models are presented in this study, namely the representative interactive flamelet (RIF) model and the direct integration of computational fluid dynamics and CHEMKIN. Both models have been implemented into an improved version of the KIVA code. The KIVA/RIF model uses a single flamelet approach and also considers the effects of vaporization on turbulence-chemistry interactions. The KIVA/CHEMKIN model uses a direct integration approach that solves for the chemical reactions in each computational cell. The above two models are applied to simulate combustion and emissions in diesel engines with comparable results. Detailed comparisons of predicted heat release data and in-cylinder flows also indicate that both models predict very similar combustion characteristics. This is likely due to the fact that after ignition, combustion rates are mixing controlled rather than chemistry controlled under the diesel conditions studied.
Basic Limitations on the Performance of Stirling
Engines
Authors: de Boer P. C. T.
Published: December 2006

The performance of Stirling engines is subject to limitations resulting from power dissipation in the regenerator. The dissipation is caused by pressure gradients in the regenerator required to generate flow. Without this flow the power output would be zero. Hence the dissipation is an essential element of the operation of the engine. Using linearized theory, the pressure in the compression and expansion spaces is found as a function of the ratio of piston amplitudes and piston phase difference. The regenerator is taken to be thermally perfect. All variations are taken to be sinusoidal in time. Expressions are derived for the dimensionless power output and the thermal efficiency at a given amplitude of the compression piston. Upper bounds on the power output and the efficiency are found as function of frequency and of regenerator void volume. Special attention is given to the case of piston amplitude ratio equal to 1.
Effects of Multi-Injection Mode on Diesel Homogeneous Charge Compression Ignition Combustion
Authors: Su Wanhua , Liu Bin , Wang Hui , Huang Haozhong
Published: December 2006

Early injection, well before top dead center (TDC), has perhaps been the most commonly investigated approach to obtain homogeneous charge compression ignition (HCCI) combustion in a direct-injection (DI) diesel engine. However, wall wetting due to overpenetration of the fuel spray can lead to unacceptable amounts of unburned fuel and removal of lubrication oil. Another difficulty of diesel HCCI combustion is the control of combustion phasing. In order to overcome these difficulties, a multipulse fuel injection technology has been developed for the purpose of organizing diesel HCCI combustion, by which the injection width, injection number, and the dwell time between two neighboring pulse injections can be flexibly regulated. In present paper, the effects of a series of multipulse injection modes realized based on the prejudgment of combustion requirement, on engine emissions, thermal efficiency, and cycle fuel energy distribution of diesel HCCI combustion are studied. The designed injection modes include so-called even mode, hump mode, and progressive increase mode, and each mode with five and six pulses, respectively. Engine test was conducted with these modes. The experimental results show that diesel HCCI combustion is extremely sensitive to multipulse injection modes and that thermal efficiency can be improved with carefully modulated ones. There are many modes that can reach near zero NOx and smoke emissions, but it is significant to be aware that multipulse injection mode must be carefully designed for higher thermal efficiency.
Catalytic Combustion Systems for Microscale Gas Turbine Engines
Authors: Spadaccini C. M. , Peck J. , Waitz I. A.
Published: December 2006

As part of an ongoing effort to develop a microscale gas turbine engine for power generation and micropropulsion applications, this paper presents the design, modeling, and experimental assessment of a catalytic combustion system. Previous work has indicated that homogenous gas-phase microcombustors are severely limited by chemical reaction timescales. Storable hydrocarbon fuels, such as propane, have been shown to blow out well below the desired mass flow rate per unit volume. Heterogeneous catalytic combustion has been identified as a possible improvement. Surface catalysis can increase hydrocarbon-air reaction rates, improve ignition characteristics, and broaden stability limits. Several radial inflow combustors were micromachined from silicon wafers using deep reactive ion etching and aligned fusion wafer bonding. The 191mm3 combustion chambers were filled with platinum-coated foam materials of various porosity and surface area. For near stoichiometric propane-air mixtures, exit gas temperatures of 1100K were achieved at mass flow rates in excess of 0.35g∕s. This corresponds to a power density of ∼1200MW∕m3; an 8.5-fold increase over the maximum power density achieved for gas-phase propane-air combustion in a similar geometry. Low-order models, including time-scale analyses and a one-dimensional steady-state plug-flow reactor model, were developed to elucidate the underlying physics and to identify important design parameters. High power density catalytic microcombustors were found to be limited by the diffusion of fuel species to the active surface, while substrate porosity and surface area-to-volume ratio were the dominant design variables.
A Bulk Flow Model for Off-Centered Honeycomb Gas Seals
Authors: Soulas Thomas , Andres Luis San
Published: December 2006

A computational analysis for prediction of the static and dynamic forced performance of gas honeycomb seals at off-centered rotor conditions follows. The bulk-flow analysis, similar to the two-control volume flow model of Kleynhans and Childs (1997, “The Acoustic Influence of Cell Depth on the Rotordynamic Characteristics of Smooth-Rotor/Honeycomb-Stator Annular Gas Seals,” ASME J. Eng. Gas Turbines Power, 119, pp. 949–957), is brought without loss of generality into a single-control volume model, thus simplifying the computational process. The formulation accommodates the honeycomb effective cell depth, and existing software for annular pressure seals and is easily upgraded for damper seal analysis. An analytical perturbation method for derivation of zeroth- and first-order flow fields renders the seal equilibrium response and frequency-dependent dynamic force impedances, respectively. Numerical predictions for a centered straight-bore honeycomb gas seal shows good agreement with experimentally identified impedances, hence validating the model and confirming the paramount influence of excitation frequency on the rotordynamic force coefficients of honeycomb seals. The effect of rotor eccentricity on the static and dynamic forced response of a smooth annular seal and a honeycomb seal is evaluated for characteristic pressure differentials and rotor speeds. Leakage for the two seal types increases slightly as the rotor eccentricity increases. Rotor off-centering has a pronounced nonlinear effect on the predicted (and experimentally verified) dynamic force coefficients for smooth seals. However, in honeycomb gas seals, even large rotor center excursions do not sensibly affect the effective local film thickness, maintaining the flow azimuthal symmetry. The current model and predictions thus increase confidence in honeycomb seal design, operating performance, and reliability in actual applications.
Field Methods for Identification of Bearng Support Parameters—Part I: Identification From Transient Rotor Dynamic Response due to Impacts
Authors: De Santiago Oscar C. , Andrés Luis San
Published: December 2006

A simple procedure, with the potential as a field resource, for identification of a bearing support parameter from recorded transient rotor responses due to impact loads follows. The method is applied to a test rotor supported on a pair of mechanically complex bearing supports, each comprising a tilting pad bearing in series with an integral squeeze film damper. Identification of frequency dependent bearing force coefficients is good at a rotor speed of 2000 rpm. Stiffness coefficients are best identified in the low frequency range (below 25 Hz) while damping coefficients are best identified in the vicinity of the first natural frequency (48 Hz) of the rotor bearing system. The procedure shows that using multiple-impact frequency averaged rotor responses reduces the variability in the identified parameters. The identification of frequency-dependent force coefficients at a constant rotor speed is useful to assess rotor-bearing system stability.
Advancements in the Structural Stiffness and Damping of a Large Compliant Foil Journal Bearing: An Experimental Study
Authors: Salehi Mohsen , Heshmat Hooshang , Walton James F.
Published: December 2006

This paper presents the results of an experimental investigation into the dynamic structural stiffness and damping characteristics of a 21.6‐cm(8.5in.)-diameter compliant surface foil journal bearing. The goal of this development was to achieve high levels of damping without the use of oil, as is used in squeeze film dampers, while maintaining a nearly constant dynamic stiffness over a range of frequencies and amplitudes of motion. In the experimental work described herein, a full compliant foil bearing was designed, fabricated, and tested. The test facility included a non-rotating journal located inside the bearing. The journal was connected to an electrodynamic shaker so that dynamic forces simulating expected operating conditions could be applied to the structurally compliant bump foil elements. Excitation test frequencies to a maximum of 400Hz at amplitudes of motion between 25.4 and 102μm were applied to the damper assembly. During testing, both compressive preload and unidirectional static loads of up to 1335 and 445N, respectively, were applied to the damper assembly. The experimental data from these tests were analyzed using both a single degree of freedom model and an energy method. These methods of data analysis are reviewed here and results are compared. Excellent agreement in results obtained from the two methods was achieved. Equivalent viscous damping coefficients as high as 1050N.s∕cm(600lbf.s∕in) were obtained at low frequencies. Dynamic stiffness was shown to be fairly constant with frequency.
Development of an Improved High Cycle Fatigue Criterion
Authors: Scott-Emuakpor Onome , Shen M.-H. Herman , George Tommy , Cross Charles J. , Calcaterra Jeffrey
Published: December 2006

An integrated computational-experimental approach for prediction of total fatigue life applied to a uniaxial stress state is developed. The approach consists of the following elements: (1) development of a vibration based fatigue testing procedure to achieve low cost bending fatigue experiments and (2) development of a life prediction and estimation implementation scheme for calculating effective fatigue cycles. A series of fully reversed bending fatigue tests were carried out using a vibration-based testing procedure to investigate the effects of bending stress on fatigue limit. The results indicate that the fatigue limit for 6061-T6 aluminum is approximately 20% higher than the respective limit in fully reversed tension-compression (axial). To validate the experimental observations and further evaluate the possibility of prediction of fatigue life, an improved high cycle fatigue criterion has been developed, which allows one to systematically determine the fatigue life based on the amount of energy loss per fatigue cycle. A comparison between the prediction and the experimental results was conducted and shows that the criterion is capable of providing accurate fatigue life prediction.
Sensitivity Analysis of NOx Formation Kinetics in Pilot-Ignited Natural Gas Engines
Authors: Yang Huateng , Krishnan S. R. , Srinivasan K. K. , Midkiff K. C.
Published: December 2006

A sensitivity analysis of NOx formation in pilot-ignited natural gas dual fuel engines is performed based on a phenomenological combustion model. The NOx formation mechanism employed in this study incorporates a super-extended Zel’dovich mechanism (up to 43 reactions). The sensitivity analysis compares the contribution of each major reaction to NOx formation, and identifies the rate-controlling NOx formation reactions in different high-temperature regions—the burning pilot spray, the premixed flame associated with the gaseous fuel-air mixture, and the burned combustion products. The formation rates for reactions involving NOx are also investigated to reveal the primary NOx formation paths. Results show two main NOx formation paths both in the pilot spray (also called the packets zone) and the burned zone. The rate-limiting reactions for the packets zone are O+N2=NO+N and N2+HO2=NO+HNO. Rate-limiting reactions for the burned zone are N2O+M=N2+O+M and N2+HO2=NO+HNO. Since the aforementioned reactions significantly influence the net NOx prediction, it is important that the corresponding reaction rates be determined accurately. Finally, because the quasi-steady-state assumption is commonly used for certain species in NOx modeling, a transient relative error is estimated to evaluate the validity of the assumption. The relative error in NOx prediction with and without the use of the steady-state assumption is small, of the order of 2%. This work also confirms that sensitivity analysis can provide valuable insight into the possible NOx formation pathways in engines and improve the ability of current prediction tools to obtain more reliable predictions.
On-Line Measurements of Engine Oil Aeration by X-Ray Absorption
Authors: Manz Devon , Cheng Wai K.
Published: December 2006

The oil aeration in a V-6 spark-ignition passenger car engine under motoring condition was measured by the X-ray absorption method in the speed range of 2000–6000 rpm. Measurements were made at different locations in the sump representing the state of the oil at (1) the pump inlet, (2) the head return, and (3) the timing chain return. The aeration of the block return was estimated from these measurements. At a fixed engine speed, the aeration (in % volume of air) of the head return and the chain return were about the same, and they were approximately twice the value found in the block return. This distribution did not change with engine speed. When weighted by the flow rate, however, the block return contributed to 55% of the aeration at the pump inlet; the total contribution of the head return and the chain return was 45% (36% from head return and 9% from chain return). Further aeration observations were made by comparing the cases with and without the oil sump windage tray in place. When the tray was removed, aeration at the pump inlet was found to increase by less than 30% for all speeds.
Advancements in Gas Turbine Fuels From 1943 to 2005
Authors: Edwards Tim
Published: December 2006

The first provisional jet fuel specifications were published in 1943 in England (RDE/F/KER/210) and 1944 in the U.S. (AN-F-32a). Jet fuel has undergone many changes in subsequent years, with current specifications for JP-5 and JP-8 for the military in the U.S. and Jet A/Jet A-1 for commercial use worldwide. Jet fuel specifications are subject to constant tension between performance requirements and availability/cost considerations. In this paper we will discuss how jet fuels have evolved over the years from the first engines to current gas turbine engines. Jet fuels derived from nonpetroleum sources will also be discussed.
A Logarithmic Complexity Divide-and-Conquer Algorithm for Multi-flexible Articulated Body Dynamics
Authors: Mukherjee Rudranarayan M. , Anderson Kurt S.
Published: December 2006

This paper presents an efficient algorithm for the dynamics simulation and analysis of multi-flexible-body systems. This algorithm formulates and solves the nonlinear equations of motion for mechanical systems with interconnected flexible bodies subject to the limitations of modal superposition, and body substructuring, with arbitrarily large rotations and translations. The large rotations or translations are modelled as rigid body degrees of freedom associated with the interconnecting kinematic joint degrees of freedom. The elastic deformation of the component bodies is modelled through the use of modal coordinates and associated admissible shape functions. Apart from the approximation associated with the elastic deformations, this algorithm is exact, non-iterative, and applicable to generalized multi-flexible chain and tree topologies. In its basic form, the algorithm is both time and processor optimal in its treatment of the nb joint variables, providing O(log(nb)) turnaround time per temporal integration step, achieved with O(nb) processors. The actual cost associated with the parallel treatment of the nf flexible degrees of freedom depends on the specific parallel method chosen for dealing with the individual coefficient matrices which are associated locally with each flexible body.
Dynamics of Large Scale Mechanical Models Using Multilevel Substructuring
Authors: Papalukopoulos C. , Natsiavas S.
Published: December 2006

An appropriate substructuring methodology is applied in order to study the dynamic response of very large scale mechanical systems. The emphasis is put on enabling a systematic study of dynamical systems with nonlinear characteristics, but the method is equally applicable to systems possessing linear properties. The accuracy and effectiveness of the methodology are illustrated by numerical results obtained for example vehicle models, having a total number of degrees of freedom lying in the order of a million or even bigger. First, the equations of motion of each component are set up by applying the finite element method. The order of the resulting models is so high that the classical substructuring methodologies become numerically ineffective or practically impossible to apply. However, the method developed overcomes these difficulties by imposing a further, multilevel substructuring of each component, based on the sparsity pattern of the stiffness matrix. In this way, the number of the equations of motion of the complete system is substantially reduced. Consequently, the numerical results presented demonstrate that besides the direct computational savings, this reduction in the dimensions enables the application of numerical codes, which capture response characteristics of dynamical systems sufficiently accurate up to a prespecified level of forcing frequencies. The study concludes by investigating biodynamic response of passenger-seat subsystem models coupled with complex mechanical models of ground vehicles resulting from deterministic or random road excitation.
On an Implementation of the Hilber-Hughes-Taylor Method in the Context of Index 3 Differential-Algebraic Equations of Multibody Dynamics (DETC2005-85096)
Authors: Negrut Dan , Rampalli Rajiv , Ottarsson Gisli , Sajdak Anthony
Published: December 2006

The paper presents theoretical and implementation aspects related to a numerical integrator used for the simulation of large mechanical systems with flexible bodies and contact/impact. The proposed algorithm is based on the Hilber-Hughes-Taylor (HHT) implicit method and is tailored to answer the challenges posed by the numerical solution of index 3 differential-algebraic equations that govern the time evolution of a multibody system. One of the salient attributes of the algorithm is the good conditioning of the Jacobian matrix associated with the implicit integrator. Error estimation, integration step-size control, and nonlinear system stopping criteria are discussed in detail. Simulations using the proposed algorithm of an engine model, a model with contacts, and a model with flexible bodies indicate a 2 to 3 speedup factor when compared against benchmark MSC.ADAMS runs. The proposed HHT-based algorithm has been released in the 2005 version of the MSC.ADAMS/Solver.
Rigid Body Impact Modeling Using Integral Formulation
Authors: Zhang Yuning , Sharf Inna
Published: December 2006

A three-dimensional single-point impact solution has been developed based on the original work of Keller. The formulation involves an integrated form of Keller’s equations and leads to a different numerical procedure to solve for the after-impact velocities. In this integral formulation, the kinetic and static friction coefficients are differentiated and any of the three hypotheses of the coefficient of restitution can be employed. Furthermore, a singularity problem that may occur in Keller’s solution is avoided with the integral formulation. Numerical examples are given to illustrate the features of the integral formulation and the differences between the two formulations.
Transient Dynamics of the Metal V-Belt CVT: Effects of Pulley Flexibility and Friction Characteristic
Authors: Srivastava Nilabh , Haque Imtiaz
Published: December 2006

A continuously variable transmission (CVT) offers a continuum of gear ratios between desired limits. The present research focuses on developing a continuous one-dimensional model of the metal V-belt CVT in order to understand the influence of pulley flexibility and friction characteristics on its dynamic performance. A metal V-belt CVT falls under the category of friction-limited drives as its performance and torque capacity rely significantly on the friction characteristic of the contact patch between the belt element and the pulley. Since the friction characteristic of the contact patch may vary in accordance with the loading and design configurations, it is important to study the influence of the friction characteristic on the performance of a CVT. Friction between the belt and the pulley sheaves is modeled using different mathematical models which account for varying loading scenarios. Simple trigonometric functions are introduced to capture the effects of pulley deformation on the thrust ratio and slip behavior of the CVT. Moreover, since a number of models mentioned in the literature neglect the inertial coupling between the belt and the pulley, a considerable amount of effort in this paper is dedicated towards modeling the inertial coupling between the belt and the pulley and studying its influence on the dynamic performance of a CVT. The results discuss the influence of friction characteristics and pulley flexibility on the dynamic performance, the axial force requirements, and the torque transmitting capacity of a metal V-belt CVT drive.
Ancient Noncoding Elements Conserved in the Human Genome
Authors: Venkatesh Byrappa , Kirkness Ewen F. , Loh Yong-Hwee , Halpern Aaron L. , Lee Alison P. , Johnson Justin , Dandona Nidhi , Viswanathan Lakshmi D. , Tay Alice , Venter J. Craig , Strausberg Robert L. , Brenner Sydney
Published: December 2006

Cartilaginous fishes represent the living group of jawed vertebrates that diverged from the common ancestor of human and teleost fish lineages about 530 million years ago. We generated ~1.4× genome sequence coverage for a cartilaginous fish, the elephant shark (
Callorhinchus milii
), and compared this genome with the human genome to identify conserved noncoding elements (CNEs). The elephant shark sequence revealed twice as many CNEs as were identified by whole-genome comparisons between teleost fishes and human. The ancient vertebrate-specific CNEs in the elephant shark and human genomes are likely to play key regulatory roles in vertebrate gene expression.
Characterizing a Mammalian Circannual Pacemaker
Authors: Lincoln Gerald A. , Clarke Iain J. , Hut Roelof A. , Hazlerigg David G.
Published: December 2006

Many species express endogenous cycles in physiology and behavior that allow anticipation of the seasons. The anatomical and cellular bases of these circannual rhythms have not been defined. Here, we provide strong evidence using an in vivo Soay sheep model that the circannual regulation of prolactin secretion, and its associated biology, derive from a pituitary-based timing mechanism. Circannual rhythm generation is seen as the product of the interaction between melatonin-regulated timer cells and adjacent prolactin-secreting cells, which together function as an intrapituitary “pacemaker-slave” timer system. These new insights open the way for a molecular analysis of long-term timing mechanisms.
Lineages of Acidophilic Archaea Revealed by Community Genomic Analysis
Authors: Baker Brett J. , Tyson Gene W. , Webb Richard I. , Flanagan Judith , Hugenholtz Philip , Allen Eric E. , Banfield Jillian F.
Published: December 2006

Novel, low-abundance microbial species can be easily overlooked in standard polymerase chain reaction (PCR)–based surveys. We used community genomic data obtained without PCR or cultivation to reconstruct DNA fragments bearing unusual 16
S
ribosomal RNA (rRNA) and protein-coding genes from organisms belonging to novel archaeal lineages. The organisms are minor components of all biofilms growing in pH 0.5 to 1.5 solutions within the Richmond Mine, California. Probes specific for 16
S
rRNA showed that the fraction less than 0.45 micrometers in diameter is dominated by these organisms. Transmission electron microscope images revealed that the cells are pleomorphic with unusual folded membrane protrusions and have apparent volumes of <0.006 cubic micrometer.
Epochal Evolution Shapes the Phylodynamics of Interpandemic Influenza A (H3N2) in Humans
Authors: Koelle Katia , Cobey Sarah , Grenfell Bryan , Pascual Mercedes
Published: December 2006

Human influenza A (subtype H3N2) is characterized genetically by the limited standing diversity of its hemagglutinin and antigenically by clusters that emerge and replace each other within 2 to 8 years. By introducing an epidemiological model that allows for differences between the genetic and antigenic properties of the virus's hemagglutinin, we show that these patterns can arise from cluster-specific immunity alone. Central to the formulation is a genotype-to-phenotype mapping, based on neutral networks, with antigenic phenotypes, not genotypes, determining the degree of strain cross-immunity. The model parsimoniously explains well-known, as well as previously unremarked, features of interpandemic influenza dynamics and evolution. It captures the observed boom-and-bust pattern of viral evolution, with periods of antigenic stasis during which genetic diversity grows, and with episodic contraction of this diversity during cluster transitions.
Anticipatory Reproduction and Population Growth in Seed Predators
Authors: Boutin Stan , Wauters Lucas A. , McAdam Andrew G. , Humphries Murray M. , Tosi Guido , Dhondt André A.
Published: December 2006

Mast seeding, the intermittent, synchronous production of large seed crops by a population of plants, is a well-known example of resource pulses that create lagged responses in successive trophic levels of ecological communities. These lags arise because seed predators are thought capable of increasing reproduction and population size only after the resource pulse is available for consumption. The resulting satiation of predators is a widely cited explanation for the evolution of masting. Our study shows that both American and Eurasian tree squirrels anticipate resource pulses and increase reproductive output before a masting event, thereby increasing population size in synchrony with the resource pulse and eliminating the population lag thought to be universal in resource pulse systems.
HEALTH, GENES, & ENVIRONMENT: Prosperous People, Penurious Genes
Authors: Jones Steve
Published: December 2006

Mismatch
. Why Our World No Longer Fits Our Bodies.
By Peter Gluckman and Mark Hanson
. Oxford University Press, Oxford, 2006. 297 pp. $29.95, £16.99. ISBN 0-19-280683-1.

Exploring the interplay between genes and the environment, the author discusses the consequences of human behavior having "outstripped classical Darwinian processes."
Dose-Dependent Immune Response toMycobacterium bovisBCG Vaccination in Neonates
Authors: Davids Virginia , Hanekom Willem , Gelderbloem Sebastian J. , Hawkridge Anthony , Hussey Gregory , Sheperd Ronel , Workman Lesley , Soler Jorge , Murray Rose Ann , Ress Stanley R. , Kaplan Gilla
Published: December 2006

In 10-week-old infants vaccinated at birth with JapaneseMycobacterium bovisBCG, the number of dermal needle penetrations correlated positively with frequency of proliferating CD4+T cells in whole blood following BCG stimulation for 6 days but did not correlate with secreted cytokine levels after 7 h or interferon CD4+T-cell frequency after 12 h of BCG stimulation.
Development of Serological Assays for Thottapalayam Virus, an Insectivore-Borne Hantavirus
Authors: Okumura Megumi , Yoshimatsu Kumiko , Kumperasart Sanit , Nakamura Ichiro , Ogino Michiko , Taruishi Midori , Sungdee Araya , Pattamadilok Sirima , Ibrahim Ima Nurisa , Erlina Sri , Agui Takashi , Yanagihara Richard , Arikawa Jiro
Published: December 2006

Thottapalayam virus (TPMV), a member of the genus
Hantavirus
in the family
Bunyaviridae
, was isolated from an insectivore,
Suncus murinus
(musk shrew), captured in southern India in 1964. While the isolation of TPMV predates the discovery of the prototype Hantaan virus, little is known about its genetics and biology. To date, preliminary evidence suggests that TPMV differs significantly, both antigenically and genetically, from all known rodent-borne hantaviruses. However, since detailed epizootiological studies have not been conducted, it is unclear if TPMV is naturally harbored by an insectivore host or if TPMV represents a “spillover” from its natural rodent reservoir host. Moreover, to what extent TPMV causes infection and/or disease in humans is not known. To address these issues, we first studied the antigenic profile of TPMV using monoclonal antibodies against Hantaan and Seoul viruses and polyclonal immune sera against Puumala virus and TPMV. Armed with this newfound information, we developed an enzyme-linked immunosorbent assay system for the diagnosis of TPMV infections in shrews and humans, using a recombinant TPMV N antigen manipulated to have an E5/G6 epitope to be captured by monoclonal antibody clone E5/G6. Using this assay, we found anti-TPMV antibodies in sera from a patient with high fever of unknown etiology in Thailand and from two shrews captured in Indonesia. Seropositivity was verified by the indirect immunofluorescence antibody test, Western blotting analysis, and focus reduction neutralization test. Collectively, our data indicate that TPMV is harbored by
Suncus murinus
as its host in nature and is capable of infecting humans.
Comparison of Cepheid's Analyte-Specific Reagents with BD Directigen for Detection of Respiratory Syncytial Virus
Authors: Goodrich Jennifer S. , Miller Melissa B.
Published: December 2006

For detection of respiratory syncytial virus (RSV), the BD Directigen RSV rapid antigen assay was compared to Cepheid's real-time reverse transcriptase PCR RSV analyte-specific reagents. The Directigen RSV assay resulted in a 23% false-negative rate, using PCR and chart review as the gold standard, indicating that rapid RSV PCR results would be advantageous.
The C-Terminal Portion of the Hrs Protein Interacts with Tsg101 and Interferes with Human Immunodeficiency Virus Type 1 Gag Particle Production
Authors: Bouamr Fadila , Houck-Loomis Brian R. , De Los Santos Martha , Casaday Rebecca J. , Johnson Marc C. , Goff Stephen P.
Published: December 2006

The human immunodeficiency virus type 1 (HIV-1) Gag protein recruits Tsg101 to facilitate HIV-1 particle budding and release. In uninfected cells, the Hrs protein recruits the ESCRT-I complex to the endosome, also through an interaction with Tsg101, to promote the sorting of host proteins into endosomal vesicles and multivesicular bodies. Here, we show that the overexpression of the C-terminal fragment of Hrs (residues 391 to 777) or Hrs mutants lacking either the N-terminal FYVE domain (mutant dFYVE) or the PSAP (residues 348 to 351) motif (mutant ASAA) all efficiently inhibit HIV-1 Gag particle production. Expression of the dFYVE or ASAA mutants of Hrs had no effect on the release of Moloney murine leukemia virus. Coimmunoprecipitation analysis showed that the expression of Hrs mutant dFYVE or ASAA significantly reduced or abolished the HIV-1 Gag-Tsg101 interaction. Yeast-two hybrid assays were used to identify two new and independent Tsg101 binding sites, one in the Hrs coiled-coil domain and one in the proline/glutamic acid-rich domain. Scanning electron microscopy of HeLa cells expressing HIV-1 Gag and the Hrs ASAA mutant showed viral particles arrested in “lump-like” structures that remained attached to the cell surface. Together, these data indicate that fragments of Hrs containing the C-terminal portion of the protein can potently inhibit HIV-1 particle release by efficiently sequestering Tsg101 away from the Gag polyprotein.
Inhibition of Filovirus Replication by the Zinc Finger Antiviral Protein
Authors: Müller Stefanie , Möller Peggy , Bick Matthew J. , Wurr Stephanie , Becker Stephan , Günther Stephan , Kümmerer Beate M.
Published: December 2006

The
zinc finger antiviral protein (ZAP) was recently shown to inhibit
Moloney murine leukemia virus and Sindbis virus replication. We tested
whether ZAP also acts against Ebola virus (EBOV) and Marburg virus
(MARV). Antiviral effects were observed after infection of cells
expressing the N-terminal part of ZAP fused to the product of the
zeocin resistance gene (NZAP-Zeo) as well as after infection of cells
inducibly expressing full-length ZAP. EBOV was inhibited by up to 4 log
units, whereas MARV was inhibited between 1 to 2 log units. The
activity of ZAP was dependent on the integrity of the second and fourth
zinc finger motif, as tested with cell lines expressing NZAP-Zeo
mutants. Heterologous expression of EBOV- and MARV-specific sequences
fused to a reporter gene suggest that ZAP specifically targets L gene
sequences. The activity of NZAP-Zeo in this assay was also dependent on
the integrity of the second and fourth zinc finger motif. Time-course
experiments with infectious EBOV showed that ZAP reduces the level of L
mRNA before the level of genomic or antigenomic RNA is affected.
Transient expression of ZAP decreased the activity of an EBOV replicon
system by up to 95%. This inhibitory effect could be partially
compensated for by overexpression of L protein. In conclusion, the data
demonstrate that ZAP exhibits antiviral activity against filoviruses,
presumably by decreasing the level of viral
mRNA.