bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Processing Methods for Silicon Nitride Ceramics
Authors: Natansohn S. , Pasto A. E.
Published: March 2015

This paper reviews the status of a program1 to develop silicon nitride ceramics of high strength and reliability, with the material performance goals being a tensile strength of 900 MPa at room temperature and 500 MPa at 1370°C, both with a Weibull modulus of 20. The selected process consists of injection molding and hot isostatic pressing of a silicon nitride formulation containing 6 w/o yttria as sintering aid. A comprehensive experimental approach has been adopted which consists of: a. complete characterization and subsequent modification of the starting silicon nitride powder in an attempt to correlate powder characteristics to ceramic properties; b. the design and fabrication of appropriate specimens for tensile strength testing; c. the implementation of alternate powder processing and shaping techniques, including the design of new compounding/molding equipment; and d. the expansion of non-destructive evaluation capabilities.
Development of Ceramic Components for a Power Generating Gas Turbine
Authors: Hara Y. , Tsuchiya T. , Maeda F. , Tsuji I. , Wada K.
Published: March 2015

Since 1984, TEPCO (Tokyo Electric Power Co., Inc.) has been conducting a cooperative research program to apply ceramics to power generating gas turbines with three Japanese gas turbine manufacturers (Toshiba Corporation, Mitsubishi Heavy Industries, Ltd., and Hitachi, Ltd.). The goal of the program is development of a 20MW class gas turbine with turbine inlet temperature of 1,300C (1,573K) to improve the efficiency of coal gasification combined cycle power generation.

Preliminary design of the gas turbine was conducted during 1984–1985 and basic design criteria, such as desired configuration and material properties, were established. Based on the results of the preliminary design, it was decided to apply ceramics to the liner and transition piece of the combustor, the 1st and 2nd stage nozzles and 1st stage rotor in a three stage turbine. As for the rotors, development efforts were also applied to thermal barrier coatings on conventional metal blades.

Parallel efforts have been conducted on the development of each ceramic component since 1986. This paper will review the design of ceramic components from structural and material standpoints, and present results obtained from tests conducted under various operational conditions.
A Bulk Flow Model of a Brush Seal System
Authors: Hendricks R. C. , Schlumberger S. , Braun M. J. , Choy F. , Mullen R. L.
Published: March 2015

Fibers such as fabric and bristles can be readily fabricated into a variety of seal configurations that are compliant and responsive to high speed or lightly loaded systems. A linear, circular, or contoured brush seal system is a contact seal consisting of the bristle pattern and hardened interface. When compared to a labyrinth seal the brush seal system is superior and features low leakage, dynamic stability, and permits compliant structures. But in turn the system usually requires a hardened smooth interface, permits only limited pressure drops. Wear life and wear debris for operations with static or dynamic excitation are largely undetermined. A seal system involves control of fluid within specific boundaries. The brush and rub ring (or rub surface) form a seal system. In this paper, design similitudes, a bulk flow model, and rub ring (interface) coatings are discussed. The bulk flow model calculations are based on flows in porous media and filters. The coatings work is based on our experience and expanded to include current practice.
Development of T-100 Multipurpose Small Power Unit
Authors: Napier James C.
Published: March 2015

The T-100 Multipurpose Small Power Unit (MPSPU) is a small gas turbine power unit technology demonstrator. Funding has been provided by the U. S. Army for development and test demonstration of this unit. The T-100 integrates emerging component technologies into a single power unit. The technology is targeted for use in airborne, vehicular, and ground auxiliary power applications. Three power levels will be demonstrated with a family of engines derived from the baseline 50-horsepower (HP) unit and include a modified 75-HP unit and two advanced technology versions of the Uprated 100-HP unit.

The T-100 MPSPU program approach was to develop advanced component concepts with analyses and rig tests to determine total system performance in the MPSPU power units. The results of this process are summarized here. Component rig tests included the inlet protection system, compressor stage, combustor, and turbine stage. These rig tests demonstrated advances in component capabilities for small turbomachinery. Power unit testing has demonstrated achievable levels in specific fuel consumption (SFC) and overall performance for a gas turbine power unit in this class.
Practical Experience in Achieving and Maintaining High Gas Turbine Availability
Authors: Gantenbein N. , Rohrer B.
Published: March 2015

This paper demonstrates and discusses the Reliability - Availability - Maintainability (RAM) topics of the first four ABB GT 8 gas turbines all of which have each reached over 40,000 full load operation hours in industrial service applications. The type 8 gas turbine is an advanced heavy duty industrial machine and in such applications has proven to be one of the worlds’ most reliable gas turbines, with a service factor of 94.7 per cent at an output factor of close to 93 per cent.
Design and Analysis of a High Pitch to Chord Ratio Cascade Representative of Ducted Propfans
Authors: Weber A. , Steinert W. , Starken H.
Published: March 2015

Efforts to reduce the specific fuel consumption of a modern aero engine focus in particular on increasing the by-pass ratio beyond the current level of around 5. One concept is the counterrotating shrouded propfan operating at low overall pressure ratio and having only very few fan blades of extremely high pitch/chord ratios. The relative inlet Mach numbers cover a range from 0.7 at the hub to 1.1 at the tip section of the first rotor.

A propfan cascade was designed by taking into account two characteristic features of a propfan blade-blade section:

• a very high pitch/chord ratio of s/c = 2.25

• an inlet Mach number of M1 = 0.90 which leads to transonic flow conditions inside the blade passage

In the design process a profile generator and a quasi-3D Euler solver were used iteratively to optimize the profile Mach number distribution. Boundary layer behavior was checked with an integral boundary layer code. The cascade design was verified experimentally in the transonic cascade wind tunnel of DLR at Cologne. The extensive experimental results confirm the design goal of roughly 5 degree flow turning. A total pressure loss coefficient of less than 1.5% was measured at design conditions. This validates the very high efficiency level the propfan concept is calling for.

A 2D Navier-Stokes flow analysis code yields good results in comparison to the experimental ones.
Computations of Unsteady Multistage Compressor Flows in a Workstation Environment
Authors: Gundy-Burlet Karen L.
Published: March 2015

High-end graphics workstations are becoming a necessary tool in the Computational Fluid Dynamics (CFD) environment. In addition to their graphics capabilities, the latest generation of workstations have powerful floating point operation capabilities. As workstations become common, they could provide valuable computing time for applications, such as turbomachinery flow calculations. This paper discusses the issues involved in implementing an unsteady, viscous multistage turbomachinery code (STAGE-2) on workstations. The workstation version of STAGE-2 has then been used to study the effects of axial-gap spacing on the time-averaged and unsteady flow within a 2 1/2-stage compressor. Results include force polar plots, time-averaged pressure contours, standard deviation of pressure contours, time-averaged surface pressures and pressure amplitudes.
Gas Turbines Installations for EDF’s Island Grids
Authors: Cazemajou C. , Morzelle C.
Published: March 2015

EDF is responsible for the production and distribution of electricity on the French islands in Europe and overseas, such as:

- Corsica (in the Mediterranean),

- Martinique (in the Caribbean),

- Guadeloupe (in the Caribbean),

- Reunion (in the Indian Ocean),

- and French Guiana in South America.

Technical and economic studies revealed the viability in these regions of single cycle gas turbine technology for supplying peak demand requirements, or providing transitory means of production pending the installation of heavier production units (conventional thermal power plants, diesel generators or hydropower).

After consultations with the major European manufacturers, a list of machines with the capacity to meet the generation specifications, and their characteristics, was prepared.

On mainland France EDF had equipped its production units with 24 MW Alsthom MS 5000 and MS 5001 gas turbines. These were little used and studies showed the economic viability of transferring these units to island regions.

The program finally adopted was to install the following power generation facilities:

JARRY SUD (GUADELOUPE): 2 ALSTHOM MS 5001 – 20 MW – 40 MW

KOUROU (FRENCH GUIANA): 2 COOPER ROLLS – 13 MW – 26 MW; 1 ROLLS ROYCE – 11 MW – 11 MW

LUCCIANA (CORSICA): 2 ALSTHOM MS 5000 – 24 MW – 48 MW

LE PORT (REUNION): 2 ALSTHOM MS 5001 – 20 MW – 40 MW

POINTE DES CARRIERES (MARTINIQUE): 2 ALSTHOM MS 5001 – 20 MW – 40 MW

or total rated power of: 205 MW

The technical details, costs and scheduling of these works are described in the paper.

Finally, the authors describe the future development prospects for gas turbines in these regions, and especially certain combined cycle projects for Corsica coupled with a proposed Italy-Corsica-Sardinia natural gas link.
Numerical Study of Branched Turboprop Inlet Ducts Using a Multiple Block Grid Procedure
Authors: Tolpadi Anil K. , Braaten Mark E.
Published: March 2015

An important requirement in the design of an inlet duct of a turboprop engine is the ability to provide foreign object damage protection. A possible method for providing this protection is to include a bypass branch duct as an integral part of the main inlet duct. This arrangement would divert ingested debris away from the engine through the bypass. However, such an arrangement could raise the possibility of separated flow in the inlet, which in turn can increase pressure losses if not properly accounted for during the design.

A fully elliptic three-dimensional body-fitted computational fluid dynamics (CFD) code based on pressure correction techniques has been developed that has the capability of performing multiple block grid calculations compatible with present day turboshaft and turboprop branched inlet ducts. Calculations are iteratively performed between sets of overlapping grids with one grid representing the main duct and a second grid representing the branch duct. Both the grid generator and the flow solver have been suitably developed to achieve this capability. The code can handle multiple branches in the flow. Using the converged flow field from this code, another program was written to perform a particle trajectory analysis. Numerical solutions were obtained on a supercomputer for a typical branched duct for which experimental flow and pressure measurements were also made. The flow separation zones predicted by the calculations were found to be in good agreement with those observed in the experimental tests. The total pressure recovery factors measured in the experiments were also compared with those obtained numerically. Within the limits of the grid resolution and the turbulence model, the agreement was found to be fairly good. In order to simulate the path of debris entering the duct, the trajectories of spherical particles of different sizes introduced at the inlet were determined.
Optimization of Gas Turbine HRSG Cycles Some Concepts
Authors: Pasha Akber
Published: March 2015

Today the Heat Recovery Steam Generator (HRSG) has become an integral part of the combined cycle or Cogen plant because of its influence on other equipment. Therefore, the optimization of the HRSG has become one of the prime targets to improve the overall efficiency.

The paper presents recent developments and concepts used in HRSG design which improve either the efficiency or the range of performance or both. The paper discusses three major areas of a HRSG - Superheater/Reheater, Economizer, and LP Evaporator/Feedwater Preheater. Depending upon the requirement, the user can implement one or more of the concepts to improve the total performance and/or the reliability.
Future Chemical Energy Networks
Authors: Green Leon
Published: March 2015

Much speculation on the future nature of electic utilities has concerned transmission; e.g., complications from access by multiple generators and how to effect higher line loadings to accommodate them. This paper proposes an alternative concept: pipeline transmission of a liquid fuel produced from domestic coal by nuclear heat at centralized facilities to multiple, dispersed sites for local generation and distribution of power.
Visualization of Dome Region Mixing in a Quartz Combustor
Authors: Brady R. A. , Samuelsen G. S.
Published: March 2015

To improve the performance of gas turbine combustors (i.e. stability and emissions), the process of fuel-air mixing, within the dome region, must be better understood and enhanced. This paper takes a preliminary step by evaluating the influences of nozzle air/fuel ratio, swirl angle, and dome geometry on fuel-air mixing. A model combustor, fabricated from quartz and designed to utilize flow visualization as the primary diagnostic, was operated at atmospheric pressure with JP-4 injected through a twin-fluid (air-assist) atomizer. Photographs of the dome region were acquired for a variation in (1) nozzle air/fuel mass flow ratio from 2.0 to 4.0, (2) swirl angle from 45° to 60°, and (3) the shape of the dome from a dump to a 45° conical expansion configuration. The results show trends of improved mixing for higher nozzle air/fuel ratios as manifested by the improved homogeneity and reduced intermittency of the reaction structure. The effects of dome geometry and swirl strength also affect mixing, with the degree and direction of effect depending on the atomizer operating conditions.
Further Technical Aspects and Economics of a Utility-Size Kalina Bottoming Cycle
Authors: Kalina A. I. , Leibowitz H. M. , Markus D. W. , Pelletier R. I.
Published: March 2015

An 86 MW bottoming cycle has been designed based on the Kalina cycle principles previously reported by the authors. It is designated as Kalina Cycle System 6 (KCS6). It uses an ABB Type 13E gas turbine topping cycle to produce a 227 MW combined cycle having a heat rate (LHV) of 6460 Btu/kWh (52.8%). The working fluid is a 75% aqua ammonia mixture.

Equipment and installation costs were developed for KCS6 and a baseline two-pressure steam bottoming cycle. The KCS6 turbine was designed with input from ABB.

Compared to the two-pressure steam bottoming cycle, KCS6 provides an additional 12.1 MW (16.4%). The estimated cost of the bottoming cycle is $1,058/kW vs. $1,033/kW for the steam plant. The KCS6 heat acquisition equipment (boiler and recooler) and distillation/condensation subsystem represent the two major additions to cost over the steam plant. On the other hand, the turbine is less expensive, mostly due to the elimination of the large condensing stages.

An economic analysis of the KCS6 plant is presented using the value of the additional output as the decision-making economic variable. The analysis is based on a model which considers capital cost, heat rate and near-term world-wide fuel prices. At $4.25/106 Btu fuel, the KCS6 costs approximately $7 million less than the value of its output.
Advanced Turbine Technology Applications Project (ATTAP): Overview, and Ceramic Component Technology Status
Authors: Haley Philip J.
Published: March 2015

The automotive gas turbine’s (AGT) significant potential payoffs in fuel economy, emissions, and alternate fuels usage continue to motivate development activities worldwide. The U.S. Department of Energy-sponsored, NASA-managed Advanced Turbine Technology Applications Project (ATTAP) focuses on developing critical AGT structural ceramic component technologies. The area of greatest challenge is that of cost-effective, near-net-shape, high-volume, high-yield manufacturing processes. Process physics modeling and Taguchi analyses are affording substantial progress, and new processes are being explored. Laboratory characterization is building a shared materials data base among Allison, Garrett, Government labs, and ceramic manufacturers. General Motors (GM) has logged over 700 test hours with ceramic components in hot gasifier rigs during ATTAP. A key ATTAP milestone was addressed by successfully demonstrating full goal temperature and speed (2500°F rotor inlet at 100% shaft speed) with ceramic components.

Fast-fracture ceramic component design tools are well correlated. Although time-dependent data and mechanistic models exist, a validated design system for such phenomena does not, and is a pressing need. Damage tolerance and impact resistance have been substantially addressed through tailored component designs, tougher monolithic ceramics, and increased ceramic strengths. Ceramic turbine rotors are now continuing to run after various substantial impacts, and after chipping damage. Ceramic-ceramic and ceramic-metal interfacing is being addressed by minimizing components’ joints, and by other DOE-sponsored work on joining models, processes, and materials.

The extruded regenerator disk is a continuing goal which requires both forming process and materials technology development. Controlling turbine tip clearances and tolerating tip rubs are key technologies. GM has demonstrated clearance control schemes, as well as rotor survivability to high speed/temperature tip rubs. Several noteworthy ceramic materials reflect the rapid progress over the past decade of monolithic ceramics, especially the Si3N4 family. GM forecasts achieving ATTAP engine cyclic durability goals.
Marine Gas Turbine Condition Monitoring by Gas Path Electrostatic Detection Techniques
Authors: Cartwright R. A. , Fisher C.
Published: March 2015

It was discovered in 1970 that certain gas turbine failures are preceded by an increase in electrostatic activity in the exhaust gases. Joint research by the Royal Aerospace Establishment and Stewart Hughes Limited demonstrated that this characteristic could be used to provide an on-line monitor of the precursors to these failures. An extension of the research applied the theory to the detection of foreign objects ingested into engine inlets. The characteristics and performance of both the Ingested Debris Monitoring System (IDMS) and Engine Distress Monitoring System (EDMS) were examined during a recent 2000 hours endurance trial of a Rolls-Royce Marine Spey gas turbine.

The EDMS produced clear evidence of the minor combustor degradation that occurred steadily throughout the trial and also reflected the absence of other engine damage. IDMS data showed that few significant debris particles passed through the engine. Video endoscope and visual inspection confirmed these results. Debris seeding trials further explored the capability of the IDMS to identify the damaging nature of debris and to assess the EDMS signature of consequential engine damage.

The paper concludes that electrostatic monitoring at engine inlet and exhaust can identify the ingestion of debris, consequential engine damage and the onset of unexpected distresses caused by blade rubs or combustor degradation. The technique shows potential to provide early warning of certain types of engine damage to Engineer Officers at sea and development into a rugged gas path condition monitoring system continues.
Ceramic Candle Filter Performance at the Grimethorpe (UK) Pressurized Fluidized Bed Combustor
Authors: Stringer John , Leitch Alan J.
Published: March 2015

A pilot hot gas particulate removal system based on positive porous ceramic filters has been tested on the Grimethorpe Pressurized Fluidized Bed Combustor facility. The filters are in the form of closed ended tubes, 1.5 m long: these are generally called ‘candles’. The dust accumulates on the outside of the candles, and is periodically removed by a pulse of air into the candle interior, which then flows outwards through the candle wall in the reverse direction to the normal flow of the combustion gas. The EPRI system contained a maximum of 130 candles, which is approximately equivalent to the requirement for 7 MW(e) capacity, depending on the filter operating parameters. The filter unit operated for a total of 860 hours under PFBC conditions, of which 790 hours were at defined process conditions, typically 850°C and 10 bar.

The amount of gas flowing through each filter element was varied, and the time between cleaning pulses was also varied. The pressure drop through each filter element rose as the dust accumulated on the outer wall, and recovered after the cleaning pulse. However, the post-cleaning pressure drop does not recover to the original clean candle value, but increases with time. It is believed that a steady-state value is attained, but the exposure in the Grimethorpe test series was insufficient to establish this unequivocally.

During the test, five candles failed. This appears to have been due to mechanical shock, as a result of candles lifting because of excessive pressure differentials across their support plate, and dropping back. The failures are not believed to be intrinsic to the technology. However, in addition a reduction in the strength of the candles with time of exposure was observed. This might also attain a steady state value, but this too could not be established on the basis of the tests reported in this paper. This is clearly a matter of importance, and further work will be required to determine the suitability of the clay-bonded silicon carbide medium used in these tests for this application.

A number of deficiencies in the design of the unit emerged with the operating experience, and suggestions have been made for improvements. However, it is clear that further work on design optimization is required.

The pulse cleaning air usage in the tests was greater than would be economically acceptable in a practical system. Further work needs to be done to optimize the cleaning cycle.

Overall, the test was very successful, and when operating properly the filters removed essentially all of the dust in the gas exiting from the combustor. Apart from the issues with the candle strength and the pulse cleaning air usage, the other problems were not believed to be of major importance in the further development of the technology.

This paper will summarize the test results, emphasizing the problems of candle durability and the pulse cleaning system.
Two Step Simulation Method: A General Method for Establishing Gas Turbine’s Dynamic Model
Authors: Gong Yifang
Published: March 2015

A new approach is suggested to establish gas turbine’s dynamic model. The conventional approach of solving a nonlinear equation set is divided into the following two steps: 1) to establish a generalized steady-state model which is a set of explicit polynomial expressions; 2) to make the steady-state model applicable to the dynamic process by taking the major dynamic characteristics into account. Because all the parameters in the said model are explicitly expressed, the calculation load is cut by several hundred times, and can be estimated exactly. The model makes the real-time simulation become applicable on microcomputers. An example is discussed in detail to show the usage and advantages of this new method.
Propulsion Aspects of Hypersonic Turbo-Ramjet-Engines With Special Emphasis on Nozzle/Aftbody Integration
Authors: Herrmann H. , Rick H.
Published: March 2015

For hypersonic transport vehicles with combined turbo-ramjet engines operating in the Mach 0 to 6+ regime the exhaust nozzle/aftbody configuration is one of the most important areas. The variable and controllable hot gas single expansion ramp nozzles coupled with different bypass and boundary layer flows represent highly integrated propulsion/airframe-systems. These exhaust systems influence considerably the vectorial force and moment balance of the total aircraft.

This paper presents examples of some concept studies of generic nozzle configurations calculated by different computational fluid dynamic methods for selected flight regimes.

The following aspects are mainly discussed:

Bookkeeping system of the single expansion ramp nozzle and aircraft aftbody, the application of different CFD-codes, a critical comparison of typical examples and calculation methods and finally some considerations about future investigations and experimental correlation.
Two-Dimensional Inlet Temperature Profile Attenuation in a Turbine Stage
Authors: Dorney Daniel J. , Davis Roger L. , Sharma Om P.
Published: March 2015

Experimental evidence has shown that hot streaks which are emitted from the combustors of gas turbines are often largely responsible for the burning of first stage turbine blades. Designers have attempted to counteract the effects of these hot streaks through the use of complex internal and film cooling schemes. Unfortunately, due to the lack of accurate predictive tools which account for temperature non-uniformities in the gas path, as well as a lack of detailed understanding of the physical mechanisms which control the migration and accumulation of the hot streak gases, turbine blade “hot spots” still occasionally occur. In an effort to increase understanding of the interaction mechanisms between combustor hot streaks and turbine blade heat transfer, a numerical investigation has been conducted to determine if a two-dimensional solution procedure can accurately predict rotor airfoil surface heating for flows which include planar hot streaks. A two-dimensional Navier-Stokes analysis is used to predict unsteady viscous flow through a 1-stator/1-rotor configuration with a planar hot streak introduced at the stator inlet. Comparison of the predicted results with a new experimental data set demonstrates that the two-dimensional numerical procedure can be used to accurately predict time-averaged rotor pressure surface temperatures for flows which include planar hot streaks.
Propulsion System Evaluation for an Unmanned High Altitude Long Endurance RPV
Authors: Kowalski Edward J. , Baullinger Norman C. , Kolden Jennifer
Published: March 2015

Unmanned High-Altitude Long-Endurance (HALE) aircraft have been studied for several years. Reconnaissance, surveillance, search and rescue, drug interdiction, atmospheric sampling, etc. are a few of the potential missions for HALE aircraft. One of the pacing technology items for an aircraft of this type is the propulsion system. This paper will discuss three candidate propulsion systems: a turbocompounded spark ignition engine, a recuperative turboshaft engine and a turbocharged turbocompounded diesel-turbine. HALE mission requirements dictate that certain parameters influence the selection of the propulsion system: propulsion system weight per horsepower, brake specific fuel consumption (lb/hr/shp), and reliability.
Applying Auxiliary Power Unit Technology to Starting Ship’s Gas Turbines
Authors: Francis George W. , Saby Gordon W. , Goom Kevin A.
Published: March 2015

Large shipboard gas turbines are traditionally started by means of an air motor (starter). In the absence of bleed air from another operating gas turbine, the starters are driven by stored high pressure air. Onboard gas turbine powered compressors, auxiliary power units (APUs) would offer improvements over using stored high pressure air for starting. Certain APUs have demonstrated extreme reliability in aircraft applications. However, the concept of APU use has not come to fruition on a U.S. Navy surface combatant. The focus of this paper is on an APU test done at the Naval Ship Systems Engineering Station’s (NAVSSES’s) gas turbine test site for DDG-51 Class destroyers. Since starting scenarios are similar among the U.S. Navy’s gas turbine ships, a potentially broad base exists for this application.
Joining of ODS-Superalloys
Authors: Hedrich H. D. , Mayer H. G. , Haufler G. , Kopf M. , Reheis N.
Published: March 2015

A stable oxide dispersoid distribution in the metal matrix, a textured orientation and a coarse grain structure with high grain aspect ratio are characteristics of ODS-super-alloys. This grain structure is the reason for enhanced mechanical properties, oxidation and corrosion resistance at high temperature unobtainable in other superalloys. Therefore ODS-alloys are promising materials for advanced combustion engines and energy generation units. The ferritic ODS-alloy permits operating temperatures up to 1350°C.

In order to produce complex and high temperature resistant components suitable joining methods are technically and economically significant. This paper presents first results of investigations of joining the new iron-base-ODS-alloy PM 2000 developed by Metallwerk Plansee. The following joining techniques are under investigation: gas tungsten-arc welding, laser beam welding and electron beam welding as fusion welding techniques and diffusion bonding as a solid state joining technique. Joining is done in recrystallized and in unrecrystallized condition. Pre- and post-heat treatment procedures were applied and tested to improve the joint strength.
Constitutive equations for thixotropic fluids
Authors: Larson R. G.
Published: March 2015

To distinguish it clearly from nonlinear viscoelasticity, we define “ideal thixotropy” as “a time-dependent viscous response to the history of the strain rate, with fading memory of that history,” endowing such fluids with memory but no elasticity. An “ideal thixotropic fluid” has instantaneous stress relaxation upon cessation of flow and no elastic recoil on removal of stress. We describe “nonideal thixotropic” fluids as those whose viscoelastic time scales governing stress relaxation are much shorter than those governing the thixotropic response. This ensures that a clear distinction can be maintained between “thixotropy” and “nonlinear viscoelasticity.” The stress tensor for an ideal thixotropic fluid can in general be expressed as a contraction product of a fourth rank viscosity tensor with the velocity gradient tensor, in which the viscosity tensor depends on the history of the flow. We show examples of constitutive equations that meet the definitions of ideal thixotropy or nonideal thixotropy. We also show examples of constitutive equations that have been designated as “thixotropic” by virtue of containing an equation for evolution of a “structure parameter,” but whose behavior is indistinguishable from that of ordinary nonlinear viscoelasticity, and so should not be considered thixotropic.
The Effect of Predeparture Training Loads on Posttour Physical Capacities in High-Performance Junior Tennis Players
Authors: Murphy Alistair P. , Duffield Rob , Kellett Aaron , Gescheit Dani , Reid Machar
Published: March 2015

Purpose:

Difficulties in preserving physical capacities while on tennis tours necessitate targeted training prescription. This study analyzed training and match loads performed before and on tour for their relationship with posttour physical-capacity changes. A secondary aim was to determine whether the presence of a strength and conditioning (S&C) coach affected the type and volume of on-tour training load.

Methods:

The training and match loads of 30 high-performance junior tennis players were recorded over 8 wk: 4 wk before and 4 wk during an international tour. Fitness tests were conducted pretour and posttour, including double and single-leg (dominant and nondominant) countermovement jump, speed (5, 10, and 20 m), modified 5-0-5 agility, 10 × 20-m repeated-sprint ability, and multistage fitness tests. Tour training and match loads were categorized according to whether S&C support was present or absent.

Results:

Total and tennis training loads were significantly greater on tour than pretour (P ≤ .05, d > 0.8). Increases in on-tour, on-court training loads were moderately correlated with decrements in speed and aerobic power (r = .31-.52). Finally, S&C presence on tour significantly increased total, on-court, and off-court training load completed (P ≤ .05, d > 0.8).

Conclusions:

Training loads should be carefully prescribed to ensure that sufficient total and tennis loads are completed pretour. Specifically, speed and aerobic capacities may regress with increased training on tour. Finally, a practical observation was that on-tour S&C support resulted in increased S&C training load (around match loads), potentially countering the observed regression of physical capacities. Such a finding has the capacity to alter current physical-preparation structures in high-performance tennis environments with finite resources.
Physiological Performance Determinants of a 22-km Handbiking Time Trial
Authors: Fischer Gabriela , Figueiredo Pedro , Ardigò Luca P.
Published: March 2015

Purpose:

To investigate physiological performance determinants of the partial laps and an overall 22-km handbiking (HB) time trial in athletes with high paraplegia.

Methods:

Seven male HB athletes with spinal cord injury (lesion levels thoracic 2-8) performed a laboratory maximal incremental test under cardiorespiratory-mechanical monitoring including respiratory-exchange ratio (RER), oxygen uptake (V̇O2), and mechanical power output (PO). Individual first and second ventilatory thresholds (V̇O2VT1 and V̇O2VT2), V̇O2peak, and POpeak were posteriorly identified. Athletes also performed a simulated HB time trial along a 4-lap bike circuit under cardiorespiratory measurement. Overall metabolic cost (C) and %V̇O2peak (ratio of V̇O2 to V̇O2peak) were calculated from race data. Race performance was defined as mean race velocity (v).

Results:

athletes completed the 22-km HB time trial in 45 ± 6 min, at 29.9 ± 3.6 km/h, with %V̇O2peak = 0.86 ± 0.10 and RER = 1.07 ± 0.17. V̇O2peak (r = .89, P = .01), POpeak (r = .85, P = .02), V̇O2VT1 (r = .96, P = .001), V̇O2VT2 (r = .92, P = .003), and C (2nd lap, r = .78; 3rd lap, r = .80; and 4th lap, r = .80) were significantly (P < .05) positively correlated with race performance. Within-subjects correlation coefficient revealed a large and significant (r = .68, P < .001) relationship between %V̇O2peak and v.

Conclusions:

V̇O2peak, POpeak, ventilatory thresholds, %V̇O2peak, and C appeared to be important physiological performance determinants of HB time trial.
Lack of Effect of Typical Rapid-Weight-Loss Practices on Balance and Anaerobic Performance in Apprentice Jockeys
Authors: Cullen SarahJane , Dolan Eimear , Brien Kate O , McGoldrick Adrian , Warrington Giles
Published: March 2015

Balance and anaerobic performance are key attributes related to horse-racing performance, but research on the impact of making weight for racing on these parameters remains unknown. The purpose of this study was to investigate the effects of rapid weight loss in preparation for racing on balance and anaerobic performance in a group of jockeys.

Methods:

Twelve apprentice male jockeys and 12 age- and gender-matched controls completed 2 trials separated by 48 h. In both trials, body mass, hydration status, balance, and anaerobic performance were assessed. Between the trials, the jockeys reduced body mass by 4% using weight-loss methods typically adopted in preparation for racing, while controls maintained body mass through typical daily dietary and physical activity habits.

Results:

Apprentice jockeys decreased mean body mass by 4.2% ± 0.3% (P < .001) with a subsequent increase in dehydration (P < .001). The controls maintained body mass and a euhydrated state. No differences in balance, on the left or right side, or in peak power, mean power, or fatigue index were reported between the trials in either group.

Conclusion:

Results from this study indicate that a 4% reduction in body mass in 48 h through the typical methods employed for racing, in association with an increase in dehydration, resulted in no impairments in balance or anaerobic performance. Further research is required to evaluate performance in a sport-specific setting and to investigate the specific physiological mechanisms involved.
Conformational activation of visual rhodopsin in native disc membranes
Authors: Malmerberg Erik , M. Bovee-Geurts Petra H. , Katona Gergely , Deupi Xavier , Arnlund David , Wickstrand Cecilia , Johansson Linda C. , Westenhoff Sebastian , Nazarenko Elena , X. Schertler Gebhard F. , Menzel Andreas , de Grip Willem J. , Neutze Richard
Published: March 2015

Structural analysis with TR-WAXS reveals a light-activated conformational change in rhodopsin in native membranes.
Science Signaling
Podcast: 10 March 2015
Authors: Neutze Richard , VanHook Annalisa M.
Published: March 2015

Structural analysis of rhodopsin in native membranes shows real-time conformational changes induced by light.
From signaling knowledge to personalized therapy
Authors: Gough Nancy R.
Published: March 2015

Understanding the regulation of apoptosis enables prediction of the most effective combination therapies.
Paving the way for intratumoral T cells
Authors: Nusinovich Yevgeniya
Published: March 2015

Respiratory hyperoxia stimulates lung tumor regression by promoting T cell infiltration into the tumors and decreasing immunosuppression.
Taking antidepressants to heart
Authors: Colmone Angela
Published: March 2015

GRK2 inhibition with paroxetine improves cardiac function independent of its central nervous system effects.
Association between Vancomycin Day 1 Exposure Profile and Outcomes among Patients with Methicillin-Resistant Staphylococcus aureus Infective Endocarditis
Authors: Casapao Anthony M. , Lodise Thomas P. , Davis Susan L. , Claeys Kimberly C. , Kullar Ravina , Levine Donald P. , Rybak Michael J.
Published: March 2015

Given the critical importance of early appropriate therapy, a retrospective cohort (2002 to 2013) was performed at the Detroit Medical Center to evaluate the association between the day 1 vancomycin exposure profile and outcomes among patients with MRSA infective endocarditis (IE). The day 1 vancomycin area under the concentration-time curve (AUC
0–24
) and the minimum concentration at 24 h (
C
min 24
) was estimated for each patient using the Bayesian procedure in ADAPT 5, an approach shown to accurately predict the vancomycin exposure with low bias and high precision with limited pharmacokinetic sampling. Initial MRSA isolates were collected and vancomycin MIC was determined by broth microdilution (BMD) and Etest. The primary outcome was failure, defined as persistent bacteremia (≥7 days) or 30-day attributable mortality. Classification and regression tree analysis (CART) was used to determine the vancomycin exposure variables associated with an increased probability of failure. In total, 139 patients met study criteria; 76.3% had right-sided IE, 16.5% had left-sided IE, and 7.2% had both left and right-sided IE. A total of 89/139 (64%) experienced failure by composite definition. In the CART analysis, failure was more pronounced in patients with an AUC
0–24
/MIC as determined by BMD of ≤600 relative to those with AUC
0–24
/MIC as determined by BMD of >600 (69.8% versus 54.7%, respectively,
P
= 0.073). In the logistic regression analysis, an AUC/MIC as determined by BMD of ≤600 (adjusted odds ratio, 2.3; 95% confidence interval, 1.01 to 5.37;
P
= 0.047) was independently associated with failure. Given the retrospective nature of the present study, further prospective studies are required but these data suggest that patients with an AUC
0–24
/MIC as determined by BMD of ≤600 present an increased risk of failure.
Influence of Renal Function Estimation on Pharmacokinetic Modeling of Vancomycin in Elderly Patients
Authors: Glatard Anaïs , Bourguignon Laurent , Jelliffe Roger W. , Maire Pascal , Neely Michael N. , Goutelle Sylvain
Published: March 2015

Vancomycin is a renally excreted drug, and its body clearance correlates with creatinine clearance. However, the renal function estimation equation that best predicts vancomycin clearance has not been established yet. The objective of this study was to compare the abilities of different renal function estimation equations to describe vancomycin pharmacokinetics in elderly patients. The NPAG algorithm was used to perform population pharmacokinetic analysis of vancomycin concentrations in 78 elderly patients. Six pharmacokinetic models of vancomycin clearance were built, based on the following equations: Cockcroft-Gault (CG), Jelliffe (JEL), Modification of Diet in Renal Disease (MDRD), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) (both in milliliters per minute per 1.73 m
2
), and modified MDRD and CKD-EPI equations (both in milliliters per minute). Goodness-of-fit and predictive performances of the six PK models were compared in a learning set (58 subjects) and a validation set (20 patients). Final analysis was performed to estimate population parameters in the entire population. In the learning step, the MDRD-based model best described the data, but the CG- and JEL-based models were the least biased. The mean weighted errors of prediction were significantly different between the six models (
P
= 0.0071). In the validation group, predictive performances were not significantly different. However, the use of a renal function estimation equation different from that used in the model building could significantly alter predictive performance. The final analysis showed important differences in parameter distributions and AUC estimation across the six models. This study shows that methods used to estimate renal function should not be considered interchangeable for pharmacokinetic modeling and model-based estimation of vancomycin concentrations in elderly patients.
Population Pharmacokinetics and Monte Carlo Dosing Simulations of Meropenem during the Early Phase of Severe Sepsis and Septic Shock in Critically Ill Patients in Intensive Care Units
Authors: Jaruratanasirikul Sutep , Thengyai Suriyan , Wongpoowarak Wibul , Wattanavijitkul Thitima , Tangkitwanitjaroen Kanyawisa , Sukarnjanaset Waroonrat , Jullangkoon Monchana , Samaeng Maseetoh
Published: March 2015

Pathophysiological changes during the early phase of severe sepsis and septic shock in critically ill patients, resulting in altered pharmacokinetic (PK) patterns for antibiotics, are important factors influencing therapeutic success. The aims of this study were (i) to reveal the population PK parameters and (ii) to assess the probability of target attainment (PTA) for meropenem. The PK studies were carried out following administration of 1 g of meropenem every 8 h during the first 24 h of severe sepsis and septic shock in nine patients, and a Monte Carlo simulation was performed to determine the PTA of achieving 40% exposure time during which the free plasma drug concentration remains above the MIC (
fT
>MIC
) and 80%
fT
>MIC
. The volume of distribution (
V
) and total clearance (CL) of meropenem in these patients were 23.7 liters and 7.82 liters/h, respectively. For pathogens with MICs of 4 μg/ml, the PTAs of 40%
fT
>MIC
following administration of meropenem as a 1-h infusion of 1 g every 8 h and a 4-h infusion of 0.5 g every 8 h were 92.52% and 90.29%, respectively. For pathogens with MICs of 2 μg/ml in immunocompromised hosts, the PTAs of 80%
fT
>MIC
following administration of 1-h and 4-h infusions of 2 g of meropenem every 8 h were 84.32% and 94.72%, respectively. These findings indicated that the
V
of meropenem was greater and the CL of meropenem was lower than the values obtained in a previous study with healthy subjects. The maximum recommended dose, i.e., 2 g of meropenem every 8 h, may be required for treatment of life-threatening infections in this patient population.
Bactericidal Efficiency and Modes of Action of the Novel Antimicrobial Peptide T9W against Pseudomonas aeruginosa
Authors: Zhu Xin , Shan Anshan , Ma Zhi , Xu Wei , Wang Jiajun , Chou Shuli , Cheng Baojing
Published: March 2015

The antipseudomonal efficiency and mechanism of action of a novel engineered antimicrobial peptide, T9W, were evaluated in this study. T9W displayed high activity, with a lethal concentration (LC) of 1 to 4 μM against
Pseudomonas aeruginosa
, including against ciprofloxacin-, gentamicin-, and ceftazidime-resistant strains, even in the presence of 50 to 300 mM NaCl, 1 to 5 mM Ca
2+
, or 0.5 to 2 mM Mg
2+
. The time-kill curve (TKC) analysis demonstrated concentration-dependent activity, with T9W achieving complete killing in less than 30 min at 1× LC and in less than 5 min at 4× LC. Combination TKC analyses additionally demonstrated a synergistic effect with ciprofloxacin and gentamicin. The selectivity of T9W was further supported by its ability to specifically eliminate
P. aeruginosa
in a coculture with macrophages without toxicity to the mammalian cells. The results from fluorescent measurement indicated that T9W bound to lipopolysaccharide (LPS) and induced
P. aeruginosa
membrane depolarization, and microscopic observations and flow cytometry further indicated that T9W targeted the
P. aeruginosa
cell membrane and disrupted cytoplasmic membrane integrity, thereby causing cellular content release leading to cell death. This study revealed the potential usefulness of T9W as a novel antimicrobial agent against
P. aeruginosa
.
Structural Characterization of an Alternative Mode of Tigecycline Binding to the Bacterial Ribosome
Authors: Schedlbauer Andreas , Kaminishi Tatsuya , Ochoa-Lizarralde Borja , Dhimole Neha , Zhou Shu , López-Alonso Jorge P. , Connell Sean R. , Fucini Paola
Published: March 2015

Although both tetracycline and tigecycline inhibit protein synthesis by sterically hindering the binding of tRNA to the ribosomal A site, tigecycline shows increased efficacy in both
in vitro
and
in vivo
activity assays and escapes the most common resistance mechanisms associated with the tetracycline class of antibiotics. These differences in activities are attributed to the
tert
-butyl-glycylamido side chain found in tigecycline. Our structural analysis by X-ray crystallography shows that tigecycline binds the bacterial 30S ribosomal subunit with its tail in an extended conformation and makes extensive interactions with the 16S rRNA nucleotide C1054. These interactions restrict the mobility of C1054 and contribute to the antimicrobial activity of tigecycline, including its resistance to the ribosomal protection proteins.