bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Phenomenological Combustion Simulation for a Dual Fuel Engine
Authors: Liu Yafeng , Bell Stuart R. , Midkiff K. Clark
Published: March 2020

A phenomenological cycle simulation for a dual fuel engine has been developed to mathematically simulate the significant processes of the engine cycle, to predict specific performance parameters for the engine, and to investigate approaches to improve performance and reduce emissions. The simulation employs two zones (crevice and unburned) during the processes of exhaust, intake, compression before fuel injection starts, and expansion after combustion ends. From the start of fuel injection to the end of combustion, several, zones are utilized to account for crevice flow, diesel fuel spray, air entrainment, diesel fuel droplet evaporation, ignition delay, flame propagation, and combustion quenching. The crevice zone absorbs charge gas from the cylinder as pressure increases, and releases mass back into the chamber as pressure decreases. Some crevice mass released during late combustion may not be oxidized, resulting in emissions of hydrocarbon and carbon monoxide. Quenching ahead of the flame front may leave additional charge unburned, yielding high methane emissions. Potential reduction of engine-out NOx emissions with natural gas fueling has also been investigated. The higher substitution of natural gas in the engine produces less engine-out NOx emissions. This paper presents the development of the model, baseline predictions, and comparisons to experimental measurements performed in a single-cylinder Caterpillar 3400 series engine.
A Stochastic Simulation of an HCCI Engine Using an Automatically Reduced Mechanism
Authors: Soyhan Hakan Serhad , Løvås Terese , Mauss Fabian
Published: March 2020

Homogeneous Charge Compression Ignition (HCCI) Engines are a promising alternative to the existing Spark Ignition Engines and Compression Ignition Engines. In an HCCI engine, the premixed fuel/air mixture ignites when sufficiently high temperature and pressure is reached. The entire bulk will auto-ignite at almost the same time because the physical conditions are similar throughout the combustion chamber. Therefore it is a justified assumption to consider the chemical reactions to be the rate-determining step for the ignition process. This gives us the opportunity to formulate a simple zero-dimensional model with detailed chemical kinetics for the calculations of the ignition process. Ignition calculations using this model have predicted a high sensitivity to fluctuations in temperature and fuel compositions. These predictions have later been confirmed by experiments.

Partially stirred plug flow reactor (PaSPFR) can be used to conquer the assumption of homogeneity. The assumption is replaced by that of statistical homogeneity and thus statistical fluctuations caused by inhomogeneities can be studied. However, the CPU-time needed for this approach is increased considerably and the usage of mechanism reduction becomes evident.

In this paper, we demonstrate how a reduced mechanism for natural gas as fuel is derived automatically. The original mechanism by Warnatz (589 reactions, 53 species) is first reduced to a skeletal mechanism (481 reactions, 43 species). By introduction of the quasi steady state assumption, the skeletal mechanism is reduced further to 23 species and 20 global reactions. The accuracy of the final mechanism is demonstrated using the stochastic reactor tool for an HCCI engine.
Hydrogen Peroxide Effect on HCCI Performance
Authors: Uykur Cüneyt , Zuccato Andrew L. , Reader Graham T. , Ting David S.-K.
Published: March 2020

Methane fueled Homogeneous Charged Compression Ignition (HCCI) combustion is investigated using detailed kinetic modeling. Control of heat release rate is identified as the biggest challenge against HCCI operation. A new control strategy, hydrogen peroxide (H2O2) addition, along with intake mixture preheating, is proposed to resolve this problem. A single-zone perfectly stirred reactor type formulation is employed with detailed chemical kinetic mechanism to predict homogeneous gas-phase chemical kinetics. The effects of H2O2 addition on the performance parameters of a methane-fueled HCCI engine are simulated. The results show that HCCI performance can be improved radically by the addition of H2O2 since it lowers the ignition delay time substantially. The resulting NOx concentration in high IMEP operating conditions is significantly less than that emitted from conventional internal combustion engines. Possibility of increasing NOx emissions with increasing initial temperature has been shown. Reduction in carbon monoxide emission is predicted with the addition of H2O2 via the increased hydroxyl chemistry. More flexible control of HCCI operation is possible by regulating the amount of H2O2 added.
Dynamic Response of Automotive Catalytic Converters to Variations in Air-Fuel Ratio
Authors: Shamim Tariq , Medisetty Vishnu C.
Published: March 2020

The automotive catalytic converters, which are employed to reduce engine exhaust emissions, operate in transient conditions under all modes of operation. The fluctuation in air-fuel ratio is a major contributor to these transients. The consideration of these transients is essential in accurate modeling of catalyst operation during actual driving conditions. In this work, a numerical investigation is carried out to comprehend the dynamic response of three-way catalytic converters subjected to changes in air-fuel ratio. The mathematical model considers the coupling effect of heat and mass transfer with the catalyst reactions as exhaust gases flow through the catalyst. The converter dynamic response is studied by considering a converter operating under steady conditions, which is suddenly subjected to air-fuel ratio variations. Two types of imposed fluctuations (sinusoidal and step changes) are considered. The catalyst response is predicted by using a detailed chemical mechanism. The paper elucidates the effect of air-fuel modulations on the catalyst HC, CO, and NO conversion efficiencies.
Development of an EGR Distribution Prediction Method Using Three-Dimensional Flow Analysis and its Application
Authors: Yoshizawa Koudai , Mori Kouji , Matayoshi Yutaka , Kimura Shuji
Published: March 2020

A multidimensional computational fluid dynamics (CED) method has been used to improve the exhaust gas recirculation (EGR) distribution in the intake manifold. Since gas flow in the intake system is affected by intake pulsation caused by the gas exchange process, a pulsation flow simulation is used. A one-dimensional gas exchange calculation is combined with three-dimensional intake gas flow to simulate pulsation flow. This pulsation flow simulation makes it possible to predict the EGR distribution. The gas flow in the intake system was analyzed in detail. It was found that a reverse flow region formed downstream of the throttle valve. The size and shape of the reverse flow region greatly depend on the engine operating conditions. With a conventional EGR system, it is difficult to distribute EGR uniformly under various engine operating conditions. A new EGR system that uses a spiral flow to mix the fresh air and EGR gas has been developed to obtain a uniform EGR distribution. As a result of adopting this system, a uniform EGR distribution is obtained regardless of the engine operating conditions. This spiral flow EGR system was applied to a low-emission vehicle (LEV) put on the Japanese market.
Inertial Impaction-Dominated Diesel Particle Collection in Filters With Rectangular Fibers
Authors: Chen S. , Cheung C. S. , Chan C. K. , Zhu C.
Published: March 2020

For the control of particulate emission from diesel engines, particulate filter is of great importance. Fibrous filter is one of the most common filters due to its simplicity in structure and low cost in manufacturing. In this paper, filters with rectangular fibers are studied numerically, in which the filter is simulated as a staggered array of parallel rectangular fibers placed transverse to the flow. Two-dimensional flow field is obtained by solving the Navier-Stokes equations with the finite volume method Particle trajectories are then calculated by solving the corresponding Lagrangian equation of motion to obtain the collection efficiency of filters. The simulation considers particle capture mechanisms of interception and inertial impaction. The effects of fiber aspect ratio, filter packing density, particulate size on the collection efficiency of a rectangular fiber are also numerically determined.
Using Co-Simulation Methods to Establish Variable Valve Actuation Hardware Specifications and Control Strategies
Authors: Burk Reinhard , Jacquelin Frederic , Wakeman Russell
Published: March 2020

With the increasing recognition that variable valve actuation (VVA) in its various forms is a powerful tool for optimizing the performance of internal combustion engines, more and more production systems are being designed and implemented throughout the industry. However, as these control systems become more capable of altering lift, timing, duration, and even the number of valve events, the complexity of designing algorithms and calibrating them becomes enormous. In addition, without prior knowledge of an engine’s response to these algorithms, designing a cost-effective mechanism which provides adequate but not over-reaching capability is difficult.

Ricardo has developed methodology for timestep coupled simulations which enables the use of one-dimensional (1-D) gas dynamics simulation of engine performance (WAVE™) coupled to a simulation of the valve actuation mechanism constructed in MATLAB® and AMESim®. This arrangement allows valve motion input to the 1-D code to be controlled either manually or by a VVA controller simulation, allowing such engine parameters as torque, fuel consumption, NVH, and EGR rates to be monitored as a function of valve timing strategy.

This method allows the examination of such engine development concerns as tolerances, valve velocities and accelerations, and interactions with other engine controls to be studied without the costs, leadtimes, or hardware reliability problems that are associated with prototyping a VVA system. In addition, the interfacing of the valve control/engine performance simulation combination with the Design of Experiments optimization software iSIGHT allows the control system space to be explored automatically, without the brute force numerical search required to examine all permutations of the control strategies. The output of this procedure is an array of requirements which can be quickly translated into a specification document which will guide hardware and controls design efforts.
Investigation of Acceleration of Turbocharged Diesel Engine
Authors: Hribernik Ales , Bombek Gorazd , Trenc Ferdinand
Published: March 2020

Acceleration of a 4-cylinder, 7-litre, turbocharged diesel engine has been investigated by the means of experimental and analytical procedure. The engine acceleration on a test stand has been tested using standard dynamometer which has been controlled by a computer. All measurements have been performed at the maximum fuel rack position, however the courses of engine load have been varied. Engine speed, dynamometer load, in-cylinder pressure and boost pressure-time history, have been measured during acceleration in order to acquire the data for validation of engine acceleration model. A non-linear, transient, multi-cylinder, turbocharged, diesel engine simulation has been developed for predictions of instantaneous engine and turbocharger speed and torque. The foundation of the model is a thermodynamic, steady state diesel engine simulation. The transient extension of the original model represents the diesel engine as a non-linear, dynamic system. The predictions of engine simulation model agree fairly well with experimental results and may be used for case studies of engine acceleration. As an example the model has been used to study the influence of manifold-pressure compensator (LDA-system) on the acceleration of turbocharged diesel engine. The original LDA-system has been modified and the comparison of the results predicted by the application of original and modified LDA system has been done.
Simulation of Cylinder Bore Surface Finish Parameters to Improve Laboratory-Scale Friction Tests in New and Used Diesel Oil
Authors: Blau Peter J.
Published: March 2020

The development of alloys, coatings, surface treatments, and lubricants for improved cylinder liners and rings has historically included friction and wear testing. The correlation of results from motored engines or laboratory-scale tribotests with those from full-scale, fired engines remains a subject of contention. Attempts to develop valid engine wear simulators have met with varying degrees of success. Complexities in understanding and duplicating the relevant contact conditions in fired engines have challenged the designers of sub-scale, simulative laboratory tests. The current paper describes one aspect of this problem; namely, simulating the cylinder bore surface finish for use in bench tests. A rapid method to prepare cast iron test specimens that have similar surface roughness parameters to a production cast iron cylinder liner has been developed. To compare the sliding response of simulated liners with actual liners, cast iron specimens were friction-tested in both new and used 15W40 commercial diesel engine oil, in mineral oil, and without liquid lubrication. A reciprocating, ball-on-flat testing machine was used with test lengths that ranged from 100 to 20,000 cycles. Kinetic friction coefficient data compared favorably between the simulated cylinder liner specimens and actual cylinder liner segments. The friction coefficients obtained in tests with different lubricants on the simulated surfaces were related through a second-degree polynomial to the change in arithmetic average roughness that occurred during running-in. Additional elements of the fired engine environment will be added in the next stages of this research to determine the degree of complexity that is needed to obtain increasingly better simulations.
Engine Friction Characteristics Under Cold Start Conditions
Authors: Shayler Paul J. , Burrows John A. , Tindle Clive R. , Murphy Michael
Published: March 2020

Most studies of engine friction have been carried out at fully-warm operating conditions. Relatively little attention has been given to frictional losses when the engine is running cold, although these can be considerably higher and have a strong influence both on cold-start characteristics and fuel consumption during warm-up. The losses which effect the indicated load on the engine are rubbing losses and loads associated with driving auxiliaries. The equivalent frictional mean effective pressures (fmep) are generally highest during the first seconds of engine operation. These decay rapidly onto a characteristic variation which depends upon oil viscosity, and which fmep follows throughout the warm-up period. The oil viscosity can be evaluated at the bulk temperature of oil in the sump or main gallery.

Breakdown motoring tests have been carried out on a series of diesel engines to examine how the friction contribution of various sub-assemblies in the engine contribute to the total and how this varies with temperature and speed. Tests were carried out using a compact cold cell and engine motoring facility. The engine was cold soaked to a target test temperature and then motored to a target speed and the variation of motoring torque recorded. Sets of tests were carried out at several stages of breaking the engine down. This enables the contributions due to the valve train, piston and big end assembly, crankshaft, fuel injection pump, and auxiliary load to be determined.
Modeling of Axial and Circumferential Ring Pack Lubrication
Authors: Ejakov Mikhail A.
Published: March 2020

The ring-pack lubrication is a complicated physical process involving multiple physical phenomena. This paper presents an attempt to model the ring-pack lubrication in three-dimensional space, considering the ring-bore structure interaction, bore distortion, ring-twist, piston secondary motion, non-Newtonian lubricant behavior, and ring/bore asperity contacts.

The physics of the model includes the interface between the structure of the ring, oil lubricant, and the structure of the cylinder liner. The ring is modeled as a three-dimensional FEA model with the nodes along the ring circumference. The ring face orientation changes circumferentially depending on ring geometry as well as piston tilt angle and three-dimensional ring twist angle at every crank angle degree. The oil lubrication is modeled with the Reynolds equation with shear thinning and temperature dependent oil viscosity and with or without the flow factors. The cylinder liner description allows three-dimensional bore distortion and ring/liner asperity contact to be modelled. The key of the analysis is solving simultaneously at every crank angle increment a set of coupled linear and non-linear equations of ring structure, ring face lubrication, bore distortion, and asperity contact. The model predicts variations of the ring-pack lubrication in the axial and circumferential directions.

Using the hydrodynamic lubrication model coupled with the asperity contact model allows calculations of the friction forces due to asperity contact (boundary and mixed lubrication) and oil film interactions (hydrodynamic and mixed lubrication). The transition from hydrodynamic lubrication to boundary lubrication through mixed lubrication is determined interactively based on ring / liner surface properties, ring loads, and lubrication properties. The new friction sub-module calculates axial and circumferential variation of both types of friction forces as well as total friction. The asperity contact induced friction forces and asperity contact pressure can further be used for ring wear calculations.

The developed model has been applied to determine the performance of a production engine ring-pack. The influence of different phenomena affecting the ring-pack performance has been analyzed and compared.
Investigation of a In-Line Oil-Cleaning Device for 4-Stroke Locomotive Diesel Engine Use
Authors: Su Fan , Payne Malcolm , Vasquez Manuel , Taghizadeh Aref
Published: March 2020

Tests have been performed on a single-cylinder medium-speed diesel research engine (SCRE-251) to investigate the possibility of using an in-line oil-cleaning device (IOD) on diesel locomotive engines for improving engine performance and exhaust emissions. The engine was operated at full load for both the baseline and with IOD test. Engine fuel consumption and emission data were obtained at different engine operating time. The effects of the device on engine combustion process were determined by analyzing recorded engine cylinder pressure data. Oil samples were taken during the test to monitor changes in oil properties. The engine test results showed that the device reduced engine fuel consumption by up to 2% of the baseline results. Average CO and smoke of the device were lower and average NOx of the device was higher than that of baseline. The trends of changes of fuel consumption and emissions are consistent with Taylor’s [1] investigations. Engine oil analysis indicated that the viscosity, TAN and TBN data of the IOD test changed slightly with increasing oil-aging time.
Design and Construction of a Large Bore Engine Flow Bench to Experimentally Determine Port Discharge Coefficients for Better Prediction of Airflow
Authors: Chapman Kirby S. , Brentano Traci L. , Malicke Dustin , Brown Jacob
Published: March 2020

This paper describes the design and preliminary construction of a large bore engine cylinder flow bench. The flow bench is designed to experimentally determine the discharge coefficients of large bore engine ports and valves. The discharge coefficients are an integral part in modeling and predicting the airflow through an engine system. This information can be used by designers to better match turbochargers and intercoolers to engines, and can also provide critical information to enhance the accuracy of the Turbocharger-Reciprocating Engine Computer Simulation (T-RECS) that is currently under development at Kansas State University (KSU).

Large bore engine cylinders are typically are 35–56 cm (14–22 in.) in diameter, and the engines they occupy have power outputs ranging 745–3730 kW (1000–6000 hp). In general, the majority of these engines were built in the 1940–1950’s. The importance of predicting the airflow rate through these engines has become paramount due to increasingly stringent EPA emission regulations.
Supercharging of SI Engines Using a New Kind of Screw-Type Supercharger
Authors: von Rueden K. , Pucher H. , Nickel J.
Published: March 2020

In result of the permanent endeavor to reduce fuel consumption of vehicle engines, nowadays the implementation of downsizing concepts is being enforced. Thereby the desired nominal engine power can be produced by an engine with lower displacement operating with correspondingly higher charging pressure. Mechanical supercharging as well as turbocharging can be considered as a suitable supercharging method.

This paper reports on experimental and simulation results regarding the stationary and transient operation of a four-stroke cycle SI passenger car engine supercharged by a new type of screw-type supercharger. In this manner the load control of the SI engine is performed by a supercharger internal slide valve system. Thus not only the throttling losses will be reduced noticeably, but also expansion work can be regained by this supercharger under certain operating conditions. The results obtained will be compared with those of the turbocharged reference engine.
Swirl Turbocharging Exhaust System and its Application Study
Authors: Liu Huimeng , Liu Yongchang , Cao Li
Published: March 2020

A novel modular single exhaust manifold called swirl turbocharging exhaust system is described. The flow field was modeled and compared with the flow behavior in MPC system. Numerical calculation results of the manifold flow show that its flow field characteristics were different from that of the MPC’s. To investigate the efficient two swirl turbocharging exhaust systems were designed and applied to two turbocharged diesel engines respectively. The test results reveal that both engines with the new type turbocharging system have promising performance.
Usefulness of real time elastography strain ratio in the assessment of cervical intraepithelial neoplasia and cervical cancer using a reference material
Authors: Dudea-Simon Marina , Dudea Sorin Marian , Burde Alexandru , Ciortea Razvan , Malutan Andrei , Mihu Dan
Published: March 2020

Aims: To assess the usefulness of real time elastography (RTE) strain ratio (SR) in diagnosing cervical cancer (CC) and cervical intraepithelial neoplasia (CIN), using a synthetic experimental device (ED) as reference material.Material and methods: Seventy-nine participants were enrolled, divided in three groups: Group 1 – benign cervix (n=39); Group 2 – CIN (n=32); Group 3 - CC (n=8). Transvaginal RTE was performed, with SR determination, as the ratio between the ED and the cervical tissue. Mean SR values of the groups were compared; diagnostic performance was assessed by tracing the receiver operating characteristic (ROC) curve. Area under the curve (AUC) was analyzed. Cut-off values were established. Pathological results were considered as reference for data interpretation.Results: SR means significantly differed in Group 1 as compared to Groups 2 and 3 (p=0.001). Excluding 2 aberrant values in Group 3, assigned to cases complicated by hemorrhagic necrosis, statistical difference was also noted between Groups 2 and 3 (p=0.02). For Groups 1 and 3, AUC was 0.966 with a 95%CI (0.914-1.000); the cut-off point of SR was 1.42, with a sensitivity of 100% and a specificity of 94.9%. AUC was 0.752 with a 95%CI (0.629-0.876) for Groups 1 and 2. For the cut-off value of 1.03, sensitivity and specificity were 75% and 74%, respectively.Conclusion: RTE SR, performed with a synthetic reference material, seems a reliable method for distinguishing between benign uterine cervix and malignancy, with promising results as a complementary investigation in diagnosing CIN. However, SR becomes inoperant in cases of cancer complicated with hemorrhagic necrosis.
Third-order shear deformation beam model for flexural waves and free vibration of pipes
Authors: Ma Wei-Li , Li Xian-Fang , Yong Lee Kang
Published: March 2020

A third-order shear deformation beam model is proposed to analyze dynamic behavior of straight hollow cylinders of annular cross-section, in which shear stress vanishes on the inner and outer surfaces of the pipe. Shear deformation, warping, and rotational inertia of cross-section are all considered, and the shear correction factor is not needed. A single governing differential equation is derived for analyzing flexural wave propagation and free vibration of straight pipe-beams. The phase and group speeds of flexural waves propagating in pipes are determined for acoustic and optical modes. The dispersion of flexural waves is analyzed. The frequency equations are obtained explicitly for pipe-beams with ten typical boundary conditions including clamped, pinned, guided, and free ends. The natural frequencies of clamped-free, clamped-clamped, and pinned-pinned pipe-beams are evaluated for the first four vibration modes. A comparison of this paper's numerical results of the natural frequencies with the previous ones is made and turns out the effectiveness of the suggested method. The influences of the pipe's thickness and length on the natural frequencies and mode shapes for a cantilever pipe are presented.
The importance of processing resolution in “ideal time-frequency segregation” of masked speech and the implications for predicting speech intelligibility
Authors: Conroy Christopher , Best Virginia , Jennings Todd R. , Kidd Gerald
Published: March 2020

Ideal time-frequency segregation (ITFS) is a signal processing technique that may be used to estimate the energetic and informational components of speech-on-speech masking. A core assumption of ITFS is that it roughly emulates the effects of energetic masking (EM) in a speech mixture. Thus, when speech identification thresholds are measured for ITFS-processed stimuli and compared to thresholds for unprocessed stimuli, the difference can be attributed to informational masking (IM). Interpreting this difference as a direct metric of IM, however, is complicated by the fine time-frequency (T-F) resolution typically used during ITFS, which may yield target “glimpses” that are too narrow/brief to be resolved by the ear in the mixture. Estimates of IM, therefore, may be inflated because the full effects of EM are not accounted for. Here, T-F resolution was varied during ITFS to determine if/how estimates of IM depend on processing resolution. Speech identification thresholds were measured for speech and noise maskers after ITFS. Reduced frequency resolution yielded poorer thresholds for both masker types. Reduced temporal resolution did so for noise maskers only. Results suggest that processing resolution strongly influences estimates of IM and implies that current approaches to predicting masked speech intelligibility should be modified to account for IM.
Effect of Sildenafil Citrate on Exercise Capacity in Athletes With Spinal Cord Injury
Authors: Perret Claudio , Van Biesen Debbie , Strupler Matthias , Pit-Grosheide Pia , Vanlandewijck Yves
Published: March 2020

Purpose: Ingestion of sildenafil citrate has performance-enhancing effects at high altitudes above 3800 m in able-bodied individuals. It is unknown whether it can improve the performance of athletes with spinal cord injury (SCI) at moderate altitudes (<2200 m), relevant to Paralympic competitions. As most men with SCI suffer from erectile dysfunction of neurologic origin and use sildenafil on a regular basis, it seems important to study the impact of sildenafil on exercise capacity. The outcome of this study is also relevant to the antidoping community. Methods: Twenty-seven healthy male wheelchair athletes with a motor-complete SCI participated in this prospective double-blind, randomized, placebo-controlled study. The participants performed arm cranking exercise to exhaustion at sea level and moderate altitude (2200 m) after ingestion of 50 mg sildenafil citrate or a placebo. Peak power output, peak oxygen uptake, peak heart rate, rating of perceived exertion, oxygen saturation, and lactate concentrations at exhaustion were measured. Results: Friedman analysis showed that peak power output at sea level was significantly higher (P = .004) under placebo treatment (median [minimum; maximum]: 120 W [35; 170]) compared with sildenafil (115 W [40; 165]). Blood oxygen saturation under sildenafil treatment at sea level (98% [81; 100]) was significantly higher (P = .006) compared with sildenafil treatment at moderate altitude (94% [85; 100]). All other parameters revealed no impact of sildenafil or altitude. Conclusions: In this study, the ingestion of sildenafil citrate in athletes with SCI demonstrated no positive effects on peak arm-cranking-exercise capacity compared with placebo either at sea level or at moderate altitude.
Determination of Submaximal and Maximal Training Zones From a 3-Stage, Variable-Duration, Perceptually Regulated Track Test
Authors: Molinari Claire A. , Palacin Florent , Poinsard Luc , Billat Véronique L.
Published: March 2020

Purpose: To validate a new perceptually regulated, self-paced maximal oxygen consumption field test (the Running Advisor Billat Training [RABIT] test) that can be used by recreational runners to define personalized training zones. Design: In a cross-sectional study, male and female recreational runners (N = 12; mean [SD] age = 43 [8] y) completed 3 maximal exercise tests (2 RABIT tests and a University of Montreal Track Test), with a 48-hour interval between tests. Methods: The University of Montreal Track Test was a continuous, incremental track test with a 0.5-km·h−1 increment every minute until exhaustion. The RABIT tests were conducted at intensities of 11, 14, and 17 on the rating of perceived exertion (RPE) scale for 10, 5, and 3 minutes, respectively, with a 1-minute rest between efforts. Results: The 2 RABIT tests and the University of Montreal Track Test gave similar mean (SD) maximal oxygen consumption values (53.9 [6.4], 56.4 [9.1], and 55.4 [7.6] mL·kg−1·min−1, respectively, P = .722). The cardiorespiratory and speed responses were reliable as a function of the running intensity (RPE: 11, 14, and 17) and the relative time point for each RPE stage. Indeed, the oxygen consumption, heart rate, ventilation, and speed values did not differ significantly when the running time was expressed as a relative duration of 30%, 60%, or 90% (ie, at 3, 6, and 9 min of a 10-min effort at RPE 11; P = .997). Conclusions: The results demonstrate that the RABIT test is a valid method for defining submaximal and maximal training zones in recreational runners.
Efficacy of Antibiotic Combinations against Multidrug-Resistant Pseudomonas aeruginosa in Automated Time-Lapse Microscopy and Static Time-Kill Experiments
Authors: Olsson Anna , Wistrand-Yuen Pikkei , Nielsen Elisabet I. , Friberg Lena E. , Sandegren Linus , Lagerbäck Pernilla , Tängdén Thomas
Published: March 2020

Antibiotic combination therapy is used for severe infections caused by multidrug-resistant (MDR) Gram-negative bacteria, yet data regarding which combinations are most effective are lacking. This study aimed to evaluate the
in vitro
efficacy of polymyxin B in combination with 13 other antibiotics against four clinical strains of MDR
Pseudomonas aeruginosa
. We evaluated the interactions of polymyxin B in combination with amikacin, aztreonam, cefepime, chloramphenicol, ciprofloxacin, fosfomycin, linezolid, meropenem, minocycline, rifampin, temocillin, thiamphenicol, or trimethoprim by automated time-lapse microscopy using predefined cutoff values indicating inhibition of growth (≤10
6
CFU/ml) at 24 h.
Stp1 Loss of Function Promotes β-Lactam Resistance in Staphylococcus aureus That Is Independent of Classical Genes
Authors: Chatterjee Aditi , Poon Raymond , Chatterjee Som S.
Published: March 2020

β-Lactam resistance in
Staphylococcus aureus
limits treatment options. Stp1 and Stk1, a serine-threonine phosphatase and kinase, respectively, mediate serine-threonine kinase (STK) signaling. Loss-of-function point mutations in
stp1
were detected among laboratory-passaged β-lactam-resistant
S. aureus
strains lacking
mecA
and
blaZ
, the major determinants of β-lactam resistance in the bacteria.
Gamma Interferon Is Required forChlamydiaClearance but Is Dispensable for T Cell Homing to the Genital Tract
Authors: Helble Jennifer D. , Gonzalez Rodrigo J. , von Andrian Ulrich H. , Starnbach Michael N.
Published: March 2020

Chlamydia trachomatisis an important mucosal pathogen that is the leading cause of sexually transmitted bacterial infections in the United States. Despite this, there is no vaccine currently available. In order to develop such a vaccine, it is necessary to understand the components of the immune response that can lead to protection against this pathogen. It is well known that antigen-specific CD4+T cells are critical forChlamydiaclearance, but the contexts in which they are protective or not protective are unknown. Here, we aimed to characterize the importance of gamma interferon production and sensing by T cells and the effects on the immune response toC. trachomatis. Our work here helps to define the contexts in which antigen-specific T cells can be protective, which is critical to our ability to design an effective and protective vaccine againstC. trachomatis.
Structural Basis of Ca
2+
-Dependent Self-Processing Activity of Repeat-in-Toxin Proteins
Authors: Kuban Vojtech , Macek Pavel , Hritz Jozef , Nechvatalova Katerina , Nedbalcova Katerina , Faldyna Martin , Sebo Peter , Zidek Lukas , Bumba Ladislav
Published: March 2020

The Ca
2+
-dependent clip-and-link activity of large repeat-in-toxin (RTX) proteins is an exceptional posttranslational process in which an internal domain called a self-processing module (SPM) mediates Ca
2+
-dependent processing of a highly specific aspartate-proline (Asp-Pro) peptide bond and covalent linkage of the released aspartyl to an adjacent lysine residue through an isopeptide bond. Here, we report the solution structures of the Ca
2+
-loaded SPM (Ca-SPM) defining the mechanism of the autocatalytic cleavage of the Asp414-Pro415 peptide bond of the
Neisseria meningitidis
FrpC exoprotein. Moreover, deletion of the SPM domain in the ApxIVA protein, the FrpC homolog of
Actinobacillus pleuropneumoniae
, resulted in attenuation of virulence of the bacterium in a pig infection model, indicating that the Ca
2+
-dependent clip-and-link activity plays a role in the virulence of Gram-negative pathogens.
The Mitochondrial Calcium Uniporter Interacts with Subunit c of the ATP Synthase of Trypanosomes and Humans
Authors: Huang Guozhong , Docampo Roberto
Published: March 2020

The mitochondrial calcium uniporter (MCU) is essential for the regulation of oxidative phosphorylation in mammalian cells, and we have shown that in
Trypanosoma brucei
, the etiologic agent of sleeping sickness, this channel is essential for its survival and infectivity. Here we reveal that that
Trypanosoma brucei
MCU subunits interact with subunit c of the mitochondrial ATP synthase (ATPc). Interestingly, the direct physical MCU-ATPc interaction is conserved in
T. cruzi
and human cells.
Contextual Flexibility in Pseudomonas aeruginosa Central Carbon Metabolism during Growth in Single Carbon Sources
Authors: Dolan Stephen K. , Kohlstedt Michael , Trigg Stephen , Vallejo Ramirez Pedro , Kaminski Clemens F. , Wittmann Christoph , Welch Martin
Published: March 2020

Pseudomonas aeruginosa
is an opportunistic human pathogen that is well known for causing infections in the airways of people with cystic fibrosis. Although it is clear that
P. aeruginosa
is metabolically well adapted to life in the CF lung, little is currently known about how the organism metabolizes the nutrients available in the airways. In this work, we used a combination of gene expression and isotope tracer (“fluxomic”) analyses to find out exactly where the input carbon goes during growth on two CF-relevant carbon sources, acetate and glycerol (derived from the breakdown of lung surfactant). We found that carbon is routed (“fluxed”) through very different pathways during growth on these substrates and that this is accompanied by an unexpected remodeling of the cell’s electron transfer pathways. Having access to this “blueprint” is important because the metabolism of
P. aeruginosa
is increasingly being recognized as a target for the development of much-needed antimicrobial agents.
Sulfamoyl Heteroarylcarboxylic Acids as Promising Metallo-β-Lactamase Inhibitors for Controlling Bacterial Carbapenem Resistance
Authors: Wachino Jun-ichi , Jin Wanchun , Kimura Kouji , Kurosaki Hiromasa , Sato Ayato , Arakawa Yoshichika
Published: March 2020

Carbapenem antibiotics are the last resort for control of severe infectious diseases, bloodstream infections, and pneumonia caused by Gram-negative bacteria, including
Enterobacteriaceae
. However, carbapenem-resistant
Enterobacteriaceae
(CRE) strains have spread globally and are a critical concern in clinical settings because CRE infections are recognized as a leading cause of increased mortality among hospitalized patients. Most CRE produce certain kinds of serine carbapenemases (e.g., KPC- and GES-type β-lactamases) or metallo-β-lactamases (MBLs), which can hydrolyze carbapenems. Although effective MBL inhibitors are expected to restore carbapenem efficacy against MBL-producing CRE, no MBL inhibitor is currently clinically available. Here, we synthesized 2,5-diethyl-1-methyl-4-sulfamoylpyrrole-3-carboxylic acid (SPC), which is a potent inhibitor of MBLs. SPC is a remarkable lead compound for clinically useful MBL inhibitors and can potentially provide a considerable benefit to patients receiving treatment for lethal infectious diseases caused by MBL-producing CRE.
Phosphoric Metabolites Link Phosphate Import and Polysaccharide Biosynthesis for Candida albicans Cell Wall Maintenance
Authors: Liu Ning-Ning , Acosta-Zaldívar Maikel , Qi Wanjun , Diray-Arce Joann , Walker Louise A. , Kottom Theodore J. , Kelly Rachel , Yuan Min , Asara John M. , Lasky-Su Jessica Ann , Levy Ofer , Limper Andrew H. , Gow Neil A. R. , Köhler Julia R.
Published: March 2020

Candida
species cause hundreds of thousands of invasive infections with high mortality each year. Developing novel antifungal agents is challenging due to the many similarities between fungal and human cells. Maintaining phosphate balance is essential for all organisms but is achieved completely differently by fungi and humans. A protein that imports phosphate into fungal cells, Pho84, is not present in humans and is required for normal cell wall stress resistance and cell wall integrity signaling in
C. albicans
. Nucleotide sugars, which are phosphate-containing building block molecules for construction of the cell wall, are diminished in cells lacking Pho84. Cell wall-constructing enzymes may be slowed by lack of these building blocks, in addition to being inhibited by drugs. Combined targeting of Pho84 and cell wall-constructing enzymes may provide a strategy for antifungal therapy by which two sequential steps of cell wall maintenance are blocked for greater potency.
Multiple-Disease Detection and Classification across Cohorts via Microbiome Search
Authors: Su Xiaoquan , Jing Gongchao , Sun Zheng , Liu Lu , Xu Zhenjiang , McDonald Daniel , Wang Zengbin , Wang Honglei , Gonzalez Antonio , Zhang Yufeng , Huang Shi , Huttley Gavin , Knight Rob , Xu Jian
Published: March 2020

Here, we present a search-based strategy for disease detection and classification, which detects diseased samples via their outlier novelty versus a database of samples from healthy subjects and then compares them to databases of samples from patients. This approach enables the identification of microbiome states associated with disease even in the presence of different cohorts, multiple sequencing platforms, or significant contamination.
The Gut Microbiota in Camellia Weevils Are Influenced by Plant Secondary Metabolites and Contribute to Saponin Degradation
Authors: Zhang Shouke , Shu Jinping , Xue Huaijun , Zhang Wei , Zhang Yabo , Liu Yaning , Fang Linxin , Wang Yangdong , Wang Haojie
Published: March 2020

The gut microbiome may play an important role in insect-plant interactions mediated by plant secondary metabolites, but the microbial communities and functions of toxic plant feeders are still poorly characterized. In the present study, we provide the first metagenome of gut bacterial communities associated with a specialist weevil feeding on saponin-rich and saponin-low camellia seeds, and the results reveal the correlation between bacterial diversity and plant allelochemicals. We also used cultured microbes to establish their saponin-degradative capacity outside the insect. Our results provide new experimental context to better understand how gut microbial communities are influenced by plant secondary metabolites and how the resistance mechanisms involving microbes have evolved to deal with the chemical defenses of plants.
Has working-age morbidity been declining? Changes over time in survey measures of general health, chronic diseases, symptoms and biomarkers in England 1994–2014
Authors: Geiger Ben Baumberg
Published: March 2020

Objectives

As life expectancy has increased in high-income countries, there has been a global debate about whether additional years of life are free from ill-health/disability. However, little attention has been given to changes over time in morbidity in theworking-agepopulation, particularly outside the USA, despite its importance for health monitoring and social policy. This study therefore asks: what are the changes over time in working-age morbidity in England over two decades?

Design, setting and participants

We use a high-quality annual cross-sectional survey, the Health Survey for England (HSE) 1994–2014. HSE uses a random sample of the English household population, with a combined sample size of over 140 000 people. We produce a newly harmonised version of HSE that maximises comparability over time, including new non-response weights. While HSE is used for monitoring population health, it has hitherto not used for investigating morbidity as a whole.

Outcome measures

We analyse all 39 measures that are fully comparable over time—including chronic disease diagnoses, symptomatology and a number of biomarkers—adjusting for gender and age.

Results

We find a mixed picture: we see improving cardiovascular and respiratory health, but deteriorations in obesity, diabetes, some biomarkers and feelings of extreme anxiety/depression, alongside stability in moderate mental ill-health and musculoskeletal-related health. In several domains we also see stable or rising chronic diseasediagnoseseven wheresymptomatologyhas declined. While data limitations make it challenging to combine these measures into a single morbidity index, there is little systematic trend for declining morbidity to be seen in the measures that predict self-reported health most strongly.

Conclusions

Despite considerable falls in working-age mortality—and the assumptions of many policy-makers that morbidity will follow mortality – there is no systematic improvement in overall working-age morbidity in England from 1994 to 2014.
Pediatric Adenotonsillectomy Trial for Snoring (PATS): protocol for a randomised controlled trial to evaluate the effect of adenotonsillectomy in treating mild obstructive sleep-disordered breathing
Authors: Wang Rui , Bakker Jessie P. , Chervin Ronald D. , Garetz Susan L. , Hassan Fauziya , Ishman Stacey L. , Mitchell Ron B. , Morrical Michael G. , Naqvi Syed K. , Radcliffe Jerilynn , Riggan Emily I. , Rosen Carol L. , Ross Kristie , Rueschman Michael , Tapia Ignacio E. , Taylor H. Gerry , Zopf David A. , Redline Susan
Published: March 2020

Introduction

Mild obstructive sleep-disordered breathing (oSDB), characterised by habitual snoring without frequent apnoeas and hypopnoeas on polysomnography, is prevalent in children and commonly treated with adenotonsillectomy (AT). However, the absence of high-level evidence addressing the role of AT in improving health and behavioural outcomes has contributed to significant geographical variations in care and potential for surgery to be both overused and underused.

Methods and analysis

The Pediatric Adenotonsillectomy Trial for Snoring (PATS) is a single-blinded, multicentre randomised controlled trial designed to evaluate the effect of AT in treating mild oSDB. Four hundred sixty eligible children, aged 3.0–12.9 years old, will be randomised to either early adenotonsillectomy or to watchful waiting with supportive care (WWSC) with a 1:1 ratio. The study’s coprimary endpoints are (1) change from baseline in executive behaviour relating to self-regulation and organisation skills as measured by the Behavioural Rating Inventory of Executive Function (BRIEF) Global Composite Score (GEC); and (2) change from baseline in vigilance as measured on the Go-No-Go (GNG) signal detection parameter (d-prime). A mixed effects model will be used to compare changes in the BRIEF GEC score and GNG score at 6 and 12 months from baseline between the AT arm and the WWSC arm.

Ethics and dissemination

The study protocol was approved by the institutional review board (IRB) at Children’s Hospital of Philadelphia (CHOP) on 3 October 2014 (14–0 11 214). The approval of CHOP as the central IRB of record was granted on 29 February 2016. The results will be published in peer-reviewed journals and presented at academic conferences. The data collected from the PATS study will be deposited in a repository (National Sleep Research Resource, sleepdata.org) after completion of the study to maximise use by the scientific community.

Trial registration number

NCT02562040; Pre-results.
Spotlight on the fetus: how physical activity during pregnancy influences fetal health: a narrative review
Authors: Bauer Ilena , Hartkopf Julia , Kullmann Stephanie , Schleger Franziska , Hallschmid Manfred , Pauluschke-Fröhlich Jan , Fritsche Andreas , Preissl Hubert
Published: March 2020

Before and during pregnancy, women often aim to improve their lifestyle so as to provide a healthier environment for their developing child. It remains unresolved, however, as to whether physical activity (PA) during pregnancy poses a possible risk or whether it might even have beneficial effects on the developing child. There is increasing evidence that PA during pregnancy is indeed beneficial to maternal physiological and psychological health and that it is generally not detrimental to the fetal cardiovascular system and neuronal function in the developing child. This also led to international recommendations for PAs during pregnancy. In the current review, we aimed to comprehensively assess the evidence of beneficial and harmful effects of maternal PA, including high-performance sports, on fetal development. The different mental and body-based relaxation techniques presented here are frequently performed during pregnancy. We found a considerable number of studies addressing these issues. In general, neither low key, moderate maternal PA nor relaxation techniques were observed to have a harmful effect on the developing child. However, we identified some forms of PA which could have at least a transient unfavourable effect. Notably, the literature currently available does not provide enough evidence to enable us to make a general conclusive statement on this subject. This is due to the lack of longitudinal studies on the metabolic and cognitive effects of regular PA during pregnancy and the wide diversity of methods used. In particular, the kind of PA investigated in each study differed from study to study.