bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Systematic Approach to Estimate the Impact of the Aerodynamic Force Induced by Rotating Stall in a Vaneless Diffuser on the Rotordynamic Behavior of Centrifugal Compressors
Authors: Bianchini Alessandro , Biliotti Davide , Ferrara Giovanni , Ferrari Lorenzo , Belardini Elisabetta , Giachi Marco , Tapinassi Libero , Vannini Giuseppe 
Published: November 2013

One of the main challenges of the present industrial research on centrifugal compressors is the need of extending the left margin of the operating range of the machines. As a result, interest is being paid in accurately evaluating the amplitude of the pressure fluctuations caused by rotating stall, which usually occurs prior to surge. The related aerodynamic force acting on the rotor can produce subsynchronous vibrations, which can prevent the machine to further operate, in case their amplitude is too high. These vibrations are often contained thanks to the stiffness of the oil journals.
Centrifugal compressors design is, however, going towards alternative journal solutions having lower stiffness levels (e.g. Active Magnetic Bearings or Squeeze Film Dampers), which hence will be more sensitive to this kind of excitation: consequently, a more accurate estimation of the expected forces in presence of dynamic external forces like those connected to an aerodynamically unstable condition is needed to predict the vibration level and the compressor operability in similar conditions.
Within this scenario, experimental tests were carried out on an industrial impeller operating at high peripheral Mach number. The dedicated test rig was equipped with several dynamic pressure probes that were inserted in the gas flow path; moreover, the rotor vibrations were constantly monitored with typical vibration probes located near the journal bearings.
The pressure field induced by the rotating stall in the vaneless diffuser was reconstructed by means of an ensemble average approach, defining the amplitude and frequency of the external force acting on the impeller. The calculated force value was then included in the rotordynamic model of the test rig: the predicted vibrations on the bearings were compared with the measurements, showing satisfactory agreement.
Finally, the prospects of the proposed approach are discussed by investigating the response of a real machine in high-pressure functioning when different choices of journal bearings are made.
Speed Dependency of Coupled Rotor-Blade Torsional Natural Frequencies
Authors: Ehehalt Ulrich , Becs Balazs , Zhou Xiaoping , Güllenstern Stefan 
Published: November 2013

The natural frequencies of blades depend on the rotational speed of the rotor train as the stiffness changes with centrifugal loading. In the case of low pressure turbines with shrunk-on-disc design the coupled rotor-blade torsional natural frequencies can also show this property. For proper analysis of the speed dependency, a complete rotor-blade model which takes the elasticity of the blades into account is required.
In this paper the torsional natural frequencies calculated with a complete rotor-blade model are compared with those calculated with a model in which blade elasticity is not included. The analysis clearly demonstrates that calculations without blade elasticity lead to different natural frequencies. By modeling the complete rotor and taking blade elasticity into account, it is demonstrated that the torsional natural frequencies of a complete rotor-blade model can also become speed dependent. As a consequence, a distinction between the natural frequencies at nominal speed and natural frequency at critical speeds becomes necessary.
In the following, measured torsional natural frequencies at different rotating speeds of an individual low pressure rotor are presented. A comparison of the measured speed dependency of the torsional natural frequency with calculation results thereby taking the blade elasticity into account is conducted. The analysis shows that the measured speed dependency can be predicted with a high level of accuracy and can become important for modes which are dominated by the blades of the last stages.
As a consequence of this analysis, a clear distinction between natural frequency at nominal and at critical speed has to be made for certain rotor and blade designs. It is shown that the use of the Campbell diagram is highly beneficial for designing rotor trains with large blades with regard to their torsional vibration behavior.
Performance Improvements of Centrifugal Compressors Through Shroud Cavity Leakage Management
Authors: Basol A. M. , Abhari R. S. 
Published: November 2013

This study numerically investigated the effects of the geometry modifications in the vicinity of the shroud cavity area of a high flow coefficient, multi-stage, inline centrifugal compressor on its efficiency. The modifications in the shroud cavity area cover the lean of the seal teeth geometries and their streamwise positioning. The baseline four teeth seal geometry has been modified which resulted in 15 % reduction in the leakage mass flow and increased the compressor’s efficiency by 0.17 % by even reducing the number of the teeth to three.
Modifications in the radial inlet duct geometry aimed to reduce the pressure difference across the shroud cavity by providing further static pressure recovery at the shroud cavity outlet. The modified inlet duct design resulted in a further 0.13 % rise in efficiency in spite of the minor 4 % additional drop in the leakage mass flow. The modified inlet duct performed better only in presence of the shroud cavity leakage flow. Excluding the leakage the modified inlet duct resulted in a lower efficiency value compared to the efficiency value obtained with the existing inlet duct. These findings point out a possible reduction in the mixing loss between the main flow and the shroud cavity leakage flow with the modified inlet duct design which reduced the Mach number level close to the shroud side wall due to the increased static pressure. As the final conclusion on the design of the radial compressors this work shows the importance of considering the leakages at the early stages of the compressor design even deciding on the meridional flow path.
A Method of Map Extrapolation for Unequal and Partial Admission in a Double Entry Turbine
Authors: Newton Peter , Romagnoli Alessandro , Martinez-Botas Ricardo , Copeland Colin , Seiler Martin 
Published: November 2013

This paper presents a method for prediction of the unequal admission performance of a double entry turbine based on the full admission turbine maps and a minimal number of unequal admission points. The double entry turbine has two separate inlet ports which feed a single turbine wheel: this arrangement can be beneficial in a turbocharger application; however the additional entry does add complexity in producing a complete turbine map which includes unequal admission behaviour.
When a double entry turbine is operated under full admission conditions, with both entries feeding the turbine equally, this will act effectively as a single entry device and the turbine performance can be represented by a standard turbine map. In reality a multiple entry turbine will spend the majority of time operating under varying degrees of unequal admission, with each entry feeding the turbine different amounts; the extent of this inequality can have a considerable impact on turbine performance. In order to produce a full map which extends from full admission through to the partial admission case (where one inlet has no flow) a large number of unequal admission data points are required.
The paper starts by discussing previous attempts to describe the partial and unequal admission performance of a double entry turbine. The full unequal admission performance is then presented for a nozzled, double entry turbine. The impact of unequal admission on turbine performance is demonstrated. Under some conditions of operation, the turbine efficiency may be less than half that of the equivalent full admission case based on the average turbine velocity ratio. A method of using the steady, equal admission maps, with a limited number of unequal admission data points, to predict the full unequal admission behaviour is presented. A good agreement is found when the map extension method is validated against the full unequal admission turbine performance measured on a test stand. In the prediction of efficiency a mean error of approximately 0.39% is found between the test stand data and the proposed extrapolation method, with a standard deviation of 2.79%. A better agreement is generally found at conditions of higher power.
Estimation of Burner Can-Induced Excitation Levels in an Industrial Gas Turbine
Authors: Mayorca Maria A. , Bladh Ronnie , Ozturk Utkudeniz 
Published: November 2013

Burner cans lead to a flow field at the turbine inlet with higher temperature gradients than in annular combustors. The circumferential unevenness of the temperature can become a relevant source of harmonic excitation on the downstream rotor blades. The main purpose of this work is to estimate the forcing levels of the burner can excitations on blades through the entire turbine, i.e., not only the blades immediately downstream of the burners cans are of interest.
Both the compressor turbine and the power turbine are modeled in a unique setup using 3D unsteady flow simulations. Two relevant turbine inlet temperature distributions are considered. The high cycle fatigue risk due to the excitation from the burner can harmonics is assessed for the last stage rotor blade. The obtained results show that the hot streaks constitute an important source of excitation, but that the stress level of this blade can be expected to stay below the fatigue limit.
A further phenomenological study is conducted in order to understand the annular flow unevenness propagation along the stages. The hot streak-induced flow perturbations are found to vary considerably in both annular and span-wise directions. The blade force stimuli of the first burner can harmonic are found to remain on the same order through the turbine, while the second harmonic stimuli exhibit a one-order decay. The possibility to use simplified models to predict burner can excitation is discussed and found less promising.
The Staphylococcus aureus SrrAB Two-Component System Promotes Resistance to Nitrosative Stress and Hypoxia
Authors: Kinkel Traci L. , Roux Christelle M. , Dunman Paul M. , Fang Ferric C. 
Published: November 2013

ABSTRACT

Staphylococcus aureus
is both a commensal and a pathogen of the human host. Survival in the host environment requires resistance to host-derived nitric oxide (NO·). However,
S. aureus
lacks the NO·-sensing transcriptional regulator NsrR that is used by many bacteria to sense and respond to NO·. In this study, we show that
S. aureus
is able to sense and respond to both NO· and hypoxia by means of the SrrAB two-component system (TCS). Analysis of the
S. aureus
transcriptome during nitrosative stress demonstrates the expression of SrrAB-dependent genes required for cytochrome biosynthesis and assembly (
qoxABCD
,
cydAB
,
hemABCX
), anaerobic metabolism (
pflAB
,
adhE
,
nrdDG
), iron-sulfur cluster repair (
scdA
), and NO· detoxification (
hmp
). Targeted mutations in SrrAB-regulated loci show that
hmp
and
qoxABCD
are required for NO· resistance, whereas
nrdDG
is specifically required for anaerobic growth. We also show that SrrAB is required for survival in static biofilms, most likely due to oxygen limitation. Activation by hypoxia, NO·, or a
qoxABCD
quinol oxidase mutation suggests that the SrrAB TCS senses impaired electron flow in the electron transport chain rather than directly interacting with NO· in the manner of NsrR. Nevertheless, like NsrR, SrrAB achieves the physiological goals of selectively expressing
hmp
in the presence of NO· and minimizing the potential for Fenton chemistry. Activation of the SrrAB regulon allows
S. aureus
to maintain energy production and essential biosynthetic processes, repair damage, and detoxify NO· in diverse host environments.

IMPORTANCE
The Hmp flavohemoglobin is required for nitric oxide resistance and is widely distributed in bacteria. Hmp expression must be tightly regulated, because expression under aerobic conditions in the absence of nitric oxide can exacerbate oxidative stress. In most organisms,
hmp
expression is controlled by the Fe-S cluster-containing repressor NsrR, but this transcriptional regulator is absent in the human pathogen
Staphylococcus aureus
. We show here that
S. aureus
achieves
hmp
regulation in response to nitric oxide and oxygen limitation by placing it under the control of the SrrAB two-component system, which senses reduced electron flow through the respiratory chain. This provides a striking example of convergent evolution, in which the common physiological goals of responding to nitrosative stress while minimizing Fenton chemistry are achieved by distinct regulatory mechanisms.
Overproduction of Flotillin Influences Cell Differentiation and Shape in Bacillus subtilis
Authors: Mielich-Süss Benjamin , Schneider Johannes , Lopez Daniel 
Published: November 2013

ABSTRACT

Bacteria organize many membrane-related signaling processes in functional microdomains that are structurally and functionally similar to the lipid rafts of eukaryotic cells. An important structural component of these microdomains is the protein flotillin, which seems to act as a chaperone in recruiting other proteins to lipid rafts to facilitate their interaction. In eukaryotic cells, the occurrence of severe diseases is often observed in combination with an overproduction of flotillin, but a functional link between these two phenomena is yet to be demonstrated. In this work, we used the bacterial model
Bacillus subtilis
as a tractable system to study the physiological alterations that occur in cells that overproduce flotillin. We discovered that an excess of flotillin altered specific signal transduction pathways that are associated with the membrane microdomains of bacteria. As a consequence of this, we detected significant defects in cell division and cell differentiation. These physiological alterations were in part caused by an unusual stabilization of the raft-associated protease FtsH. This report opens the possibility of using bacteria as a working model to better understand fundamental questions related to the functionality of lipid rafts.

IMPORTANCE
The identification of signaling platforms in the membrane of bacteria that are functionally and structurally equivalent to eukaryotic lipid rafts reveals a level of sophistication in signal transduction and membrane organization unexpected in bacteria. It opens new and promising venues to address intricate questions related to the functionality of lipid rafts by using bacteria as a more tractable system. This is the first report that uses bacteria as a working model to investigate a fundamental question that was previously raised while studying the role of eukaryotic lipid rafts. It also provides evidence of the critical role of these signaling platforms in orchestrating diverse physiological processes in prokaryotic cells.
Genome-Wide Effects of Selenium and Translational Uncoupling on Transcription in the Termite Gut Symbiont Treponema primitia
Authors: Matson Eric G. , Rosenthal Adam Z. , Zhang Xinning , Leadbetter Jared R. 
Published: November 2013

ABSTRACTWhen prokaryotic cells acquire mutations, encounter translation-inhibiting substances, or experience adverse environmental conditions that limit their ability to synthesize proteins, transcription can become uncoupled from translation. Such uncoupling is known to suppress transcription of protein-encoding genes in bacteria. Here we show that the trace element selenium controls transcription of the gene for the selenocysteine-utilizing enzyme formate dehydrogenase (fdhFSec) through a translation-coupled mechanism in the termite gut symbiontTreponema primitia, a member of the bacterial phylumSpirochaetes. We also evaluated changes in genome-wide transcriptional patterns caused by selenium limitation and by generally uncoupling translation from transcription via antibiotic-mediated inhibition of protein synthesis. We observed that inhibiting protein synthesis inT. primitiainfluences transcriptional patterns in unexpected ways. In addition to suppressing transcription of certain genes, the expected consequence of inhibiting protein synthesis, we found numerous examples in which transcription of genes and operons is truncated far downstream from putative promoters, is unchanged, or is even stimulated overall. These results indicate that gene regulation in bacteria allows for specific post-initiation transcriptional responses during periods of limited protein synthesis, which may depend both on translational coupling and on unclassified intrinsic elements of protein-encoding genes.IMPORTANCEA large body of literature demonstrates that the coupling of transcription and translation is a general and essential method by which bacteria regulate gene expression levels. However, the potential role of noncanonical amino acids in regulating transcriptional output via translational control remains, for the most part, undefined. Furthermore, the genome-wide transcriptional state in response to translational decoupling is not well quantified. The results presented here suggest that the noncanonical amino acid selenocysteine is able to tune transcription of an important metabolic gene via translational coupling. Furthermore, a genome-wide analysis reveals that transcriptional decoupling produces a wide-ranging effect and that this effect is not uniform. These results exemplify how growth conditions that impact translational processivity can rapidly feed back on transcriptional productivity of prespecified groups of genes, providing bacteria with an efficient response to environmental changes.
A combination of anatomical and functional evaluations improves the prediction of cardiac event in patients with coronary artery bypass
Authors: Kawai Hideki , Sarai Masayoshi , Motoyama Sadako , Ito Hajime , Takada Kayoko , Harigaya Hiroto , Takahashi Hiroshi , Hashimoto Shuji , Takagi Yasushi , Ando Motomi , Anno Hirofumi , Ishii Junichi , Murohara Toyoaki , Ozaki Yukio 
Published: November 2013

ObjectiveTo study the usefulness of combined risk stratification of coronary CT angiography (CTA) and myocardial perfusion imaging (MPI) in patients with previous coronary-artery-bypass grafting (CABG).DesignA retrospective, observational, single centre study.Setting and patients204 patients (84.3% men, mean age 68.7±7.6) undergoing CTA and MPI.Main outcome measuresCTA defined unprotected coronary territories (UCT; 0, 1, 2 or 3) by evaluating the number of significant stenoses which were defined as the left main trunk ≥50% diameter stenosis, other native vessel stenosis ≥70% or graft stenosis ≥70%. Using a cut-off value with receiver-operating characteristics analysis, all patients were divided into four groups: group A (UCT=0, summed stress score (SSS)<4), group B (UCT≥1, SSS<4), group C (UCT=0, SSS≥4) and group D (UCT≥1, SSS≥4).ResultsCardiac events, as a composite end point including cardiac death, non-fatal myocardial infarction, unstable angina requiring revascularisation and heart-failure hospitalisation, were observed in 27 patients for a median follow-up of 27.5 months. The annual event rates were 1.1%, 2%, 5.7% and 12.9% of patients in groups A, B, C and D, respectively (log rank p value <0.0001). Adding UCT or SSS to a model with significant clinical factors including left ventricular ejection fraction, time since CABG and Euro SCORE II improved the prediction of events, while adding UCT and SSS to the model improved it greatly with increasing C-index, net reclassification improvement and integrated discrimination improvement.ConclusionsThe combination of anatomical and functional evaluations non-invasively enhances the predictive accuracy of cardiac events in patients with CABG.
Check It, Change It
Authors: Shah Bimal R. , Thomas Kevin L. , Elliot-Bynum Sharon , Thomas Kristin , Damon Katrina , Allen LaPointe Nancy , Calhoun Sarah A. , Thomas Laine , Mathews Robin , Califf Robert M. , Peterson Eric D. 
Published: November 2013

Background—
Despite the widespread availability of effective and affordable therapies, hypertension remains this country’s most significant modifiable cardiovascular risk factor. Approximately 30% to 50% of individuals with hypertension currently fail to reach guideline-recommended target blood pressure (BP) goals. Although multiple interventions have been proposed to affect better hypertension control, the integration of multiple elements in a community-based program has not been evaluated to date.

Methods and Results—
We created a broadly inclusive community-based initiative to control hypertension called Check It, Change It: The Durham Blood Pressure Challenge (CICI). We enrolled ≈2000 participants with hypertension in 8 ambulatory clinics across Durham County, NC. The CICI program engaged individuals by providing them with tools for self-monitoring and tied this information to their caregivers via a web-based portal (the American Heart Association’s Heart360, a remote BP monitoring system). Additionally, the CICI facilitated clinical intervention of high-risk individuals using physician assistants and community health coaches. The primary outcome will be a change in BP during the 6 months postenrollment in the program, which will be compared with concurrent and historical control populations of nonparticipants.

Conclusions—
We think that this integrated and tiered approach will lead to improved BP control within 6 months. If successful, the CICI program has the potential to enhance community-level BP control.
Schwann cell-free adult canine olfactory ensheathing cell preparations from olfactory bulb and mucosa display differential migratory and neurite growth-promoting properties in vitro
Authors: Roloff Frank , Ziege Susanne , Baumgärtner Wolfgang , Wewetzer Konstantin , Bicker Gerd 
Published: November 2013

Abstract

Background
Transplantation of olfactory ensheathing cells (OEC) and Schwann cells (SC) is a promising therapeutic strategy to promote axonal growth and remyelination after spinal cord injury. Previous studies mainly focused on the rat model though results from primate and porcine models differed from those in the rat model. Interestingly, canine OECs show primate-like in vitro characteristics, such as absence of early senescence and abundance of stable p75NTR expression indicating that this species represents a valuable translational species for further studies. So far, few investigations have tested different glial cell types within the same study under identical conditions. This makes it very difficult to evaluate contradictory or confirmatory findings reported in various studies. Moreover, potential contamination of OEC preparations with Schwann cells was difficult to exclude. Thus, it remains rather controversial whether the different glial types display distinct cellular properties.

Results
Here, we established cultures of Schwann cell-free OECs from olfactory bulb (OB-OECs) and mucosa (OM-OECs) and compared them in assays to Schwann cells. These glial cultures were obtained from a canine large animal model and used for monitoring migration, phagocytosis and the effects on in vitro neurite growth. OB-OECs and Schwann cells migrated faster than OM-OECs in a scratch wound assay. Glial cell migration was not modulated by cGMP and cAMP signaling, but activating protein kinase C enhanced motility. All three glial cell types displayed phagocytic activity in a microbead assay. In co-cultures with of human model (NT2) neurons neurite growth was maximal on OB-OECs.

Conclusions
These data provide evidence that OB- and OM-OECs display distinct migratory behavior and interaction with neurites. OB-OECs migrate faster and enhance neurite growth of human model neurons better than Schwann cells, suggesting distinct and inherent properties of these closely-related cell types. Future studies will have to address whether, and how, these cellular properties correlate with the in vivo behavior after transplantation.