bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixing and Combustion Characteristics of a Side Dump Combustor With Noncircular Fuel Injectors
Authors: Liou T. M. , Chen L.
Published: February 2015

A numerical study of the mixing and combustion characteristics of an axial jet issued from rectangular injectors of different aspect ratios (3 and 1/3) in a three-dimensional side-dump combustor is presented. The Reynolds number based on the bulk mean velocity and combustor duct height was 5.9×104 and the momentum ratio of the axial-fuel jet to the side-air jets was 0.2. A two equation k-ε turbulence model incorporating with a two-step finite-rate combustion model was adopted to simulate the nonreacting and reacting flows in a side-dump combustor. The computed nonreacting flow pattern was verified by the available experimental data. A comparison between the reacting and nonreacting flow patterns was made. The axis switching phenomenon previously observed for the unconfined or confined noncircular jets was examined in detail for the present side-dump combustor. It was found that the axis switching phenomenon was incomplete and that the aspect ratio had weak effects on the turbulent mixing and combustion in the ducted rocket combustor under the investigated conditions.
Effect of Axially Non-Uniform Rotor Tip Clearance on the Performance of a High Speed Axial Flow Compressor Stage
Authors: Mohan K. , Guruprasad S. A.
Published: February 2015

An axially non-uniform type of rotor tip clearance was conceived and tried on a single stage compressor. This concept is based on the advantages of a smaller tip clearance in the front portion of the blade and a larger clearance in the rear portion which allows a higher tip leakage flow to interact with the passage secondary flow, casing wall boundary layer, separated flow on the blade suction surface and the scraping vortex, which are more prominent at the rear portion of the blade. Experimental results indicated that an axially non-uniform clearance can provide improved performance of a compressor stage. Providing the tip clearance in the compressor casing instead of at the blade tip indicated certain advantages. An ‘optimum’ value of rotor tip clearance was noticed for this compressor stage, both for axially uniform and axially non-uniform clearance.
Evolution of Heavy-Duty Power Generation and Industrial Combustion Turbines in the United States
Authors: Scalzo A. J. , Bannister R. L. , DeCorso M. , Howard G. S.
Published: February 2015

This paper reviews the evolution of heavy-duty power generation and industrial combustion turbines in the United States from a Westinghouse Electric Corporation perspective. Westinghouse combustion turbine genealogy began in March of 1943 when the first wholly American designed and manufactured jet engine went on test in Philadelphia, and continues today in Orlando, Florida with the 160 MW, 501F Advanced Combustion Turbine. In this paper, advances in thermodynamics, materials, cooling, and unit size will be described. Many basic design features such as two-bearing rotor, cold-end drive, can-annular internal combustors, CURVIC2 clutched turbine discs, and tangential exhaust struts have endured successfully for over 40 years. Progress in turbine technology includes the clean coal technology and advanced turbine systems initiatives of the U.S. Department of Energy.
Conversion of T-100 MPSPU Technology
Authors: Thompson R. G. , Napier J. , Rodgers C.
Published: February 2015

Conversion of small tutbomachinery advanced technology from USA Department of Defense to commercial markets of opportunity is discussed in the light of recent development of the T-100 Multipurpose Small Power Unit (MPSPU) for the U.S. Army.

For the power class from 50 SHP to 75 SHP (37 KW to 56 KW), the small T-100 MPSPU Gas Turbine represents a milestone in achieved simple-cycle non-heat-exchanged thermal efficiency. Application of this turbomachinery technology, and in combination with heat recovery to compact turboalternator systems, is a prime candidate for conversion from airborne/defense use only to defense/commercial and airborne/ground implementation.

The T-100 MPSPU Test Program achievements are summarized in this paper. Also, preliminary design/off-design studies are presented for a turboalternator based on T-100 MPSPU components, and a scaled derivative that would achieve 60 KWe at modest turbine inlet temperature is presented. The turboalternator design objective is to provide a reliable compact source of electric power for military and commercial use in stationary, vehicular and aircraft applications that will run on most fuels, with low initial and operating costs, runs quietly, has low emissions and provides good to excellent specific fuel consumption.
GT Prime: Improvements to General Electric MS7001B Gas Turbines
Authors: Fuselier Edward M. , Prugger David K.
Published: February 2015

The eight General Electric MS7001B gas turbines in combined cycle service at the T.H. Wharton Station of Houston Lighting and Power currently have 85000 hours of operation with 2000 starts. The units are ready for their second major overhaul. A number of hot gas path components will require replacement at that time. Rather than replacing components one by one the user devised a Program for Reliability, Improved Maintenance and Efficiency (GT Prime) with an objective of achieving twenty additional years of trouble free service. Fortunately, the supplier had developed many improved parts for his newer units which could be applied to older machines with an attendant increase in component life, inspection intervals, system reliability, availability and performance. The significant impact on customer operating costs resulted in a very attractive payback period.

A contract for modification of all eight units was signed in December, 1991. Teardown of the first unit for modification started in November, 1992 with the rebuild and test completed in July, 1993.

This paper will discuss turbine condition, differences between the old and new parts, improved performance and reduced emissions attained as a result of implementing the program.
Effects of high-temperature thermal annealing on the electronic properties of In-Ga-Zn oxide thin films
Authors: Li Qin , Song Zhong Xiao , Ma Fei , Li Yan Huai , Xu Ke Wei
Published: February 2015

Indium gallium zinc oxide (IGZO) thin films were deposited by radio-frequency magnetron sputtering at room-temperature. Then, thermal annealing was conducted to improve the structural ordering. X-ray diffraction and high-resolution transmission electron microscopy demonstrated that the as-deposited IGZO thin films were amorphous and crystallization occurred at 800 and 950 °C. As a result of crystallization at high temperature, the carrier concentration and the Hall mobility of IGZO thin films were sharply increased, which could be ascribed to the increased oxygen vacancies and improved structural ordering of the thin films.
The LHC's Next Big Mystery
Authors: Lincoln Don
Published: February 2015

When the sun rose over America on July 4, 2012, the world of science had radically changed. The Higgs boson had been discovered. Mind you, the press releases were more cautious than that, with “a new particle consistent with being the Higgs boson” being the carefully constructed phrase of the day. But, make no mistake, champagne corks were popped and backs were slapped. The data had spoken and a party was in order. Even if the observation turned out to be something other than the Higgs boson, the first big discovery from data taken at the Large Hadron Collider had been made.
Astronomy stories
Authors: Berenson Rhoda
Published: February 2015

For many years I have taught physics and astronomy courses to liberal arts students. I have found most of my students to be intelligent and diligent, but not anxious to study science. They typically take the class only because their degree requires a science course. Many arrive having already decided they will not be able to do the math or understand the scientific concepts, and have essentially built a wall between themselves and science. In the 1990s, in an effort to help break down that wall, as part of an NSF-supported course, “The Evolution of the Universe, Earth and Life,” I began using creative writing assignments.
Locus equations and coarticulation in three Australian languages
Authors: Graetzer Simone , Fletcher Janet , Hajek John
Published: February 2015

Locus equations were applied to F2 data for bilabial, alveolar, retroflex, palatal, and velar plosives in three Australian languages. In addition, F2 variance at the vowel-consonant boundary, and, by extension, consonantal coarticulatory sensitivity, was measured. The locus equation slopes revealed that there were place-dependent differences in the magnitude of vowel-to-consonant coarticulation. As in previous studies, the non-coronal (bilabial and velar) consonants tended to be associated with the highest slopes, palatal consonants tended to be associated with the lowest slopes, and alveolar and retroflex slopes tended to be low to intermediate. Similarly, F2 variance measurements indicated that non-coronals displayed greater coarticulatory sensitivity to adjacent vowels than did coronals. Thus, both the magnitude of vowel-to-consonant coarticulation and the magnitude of consonantal coarticulatory sensitivity were seen to vary inversely with the magnitude of consonantal articulatory constraint. The findings indicated that, unlike results reported previously for European languages such as English, anticipatory vowel-to-consonant coarticulation tends to exceed carryover coarticulation in these Australian languages. Accordingly, on the F2 variance measure, consonants tended to be more sensitive to the coarticulatory effects of the following vowel. Prosodic prominence of vowels was a less significant factor in general, although certain language-specific patterns were observed.
Blind phone segmentation based on spectral change detection using Legendre polynomial approximation
Authors: Hoang Dac-Thang , Wang Hsiao-Chuan
Published: February 2015

Phone segmentation involves partitioning a continuous speech signal into discrete phone units. In this paper, a method for automatic phone segmentation without prior knowledge of speech content is proposed. The signal spectrum was represented by band-energies. A segment of the band-energy curve was approximated using Legendre polynomial expansion, allowing Legendre polynomial coefficients to describe the properties of the segment. The spectral changes, which imply phone boundaries in the speech signal, were then detected by monitoring the variations of Legendre polynomial coefficients. A two-step algorithm for detecting phone boundaries was derived. The first step was to detect phone boundaries using first-order and second-order coefficients of the Legendre polynomial approximation. The second step was to locate slow spectral changes in the regions of concatenated voiced phones using zero-order coefficients of the Legendre polynomial approximation. This enabled the phone boundaries missed during the first step to be recovered. An evaluation using the TIMIT corpus indicated that the proposed method is comparable to or more accurate than previous methods.
Sound extinction by fish schools: Forward scattering theory and data analysis
Authors: Raveau M. , Feuillade C.
Published: February 2015

A model used previously to study collective back scattering from fish schools [Feuillade et al., J. Acoust. Soc. Am. 99(1), 196–208 (1996)], is used to analyze the forward scattering properties of these objects. There is an essential physical difference between back and forward scattering from fish schools. Strong frequency dependent interference effects, which affect the back scattered field amplitude, are absent in the forward scattering case. This is critically important for data analysis. There is interest in using back scattering and transmission data from fish schools to study their size, the species and abundance of fish, and fish behavior. Transmission data can be processed to determine the extinction of the field by a school. The extinction of sound depends on the forward scattering characteristics of the school, and data inversion to provide information about the fish should be based upon a forward scattering paradigm. Results are presented of an analysis of transmission data obtained in September 1995 during an experiment performed in the Gulf of Lion in the Mediterranean Sea [Diachok, J. Acoust. Soc. Am. 105(4), 2107–2128 (1999)]. The analysis shows that using forward scattering leads to significantly larger estimates of fish abundance than previous analysis based upon back scattering approaches.
Hearing frequency thresholds of harbor porpoises (Phocoena phocoena) temporarily affected by played back offshore pile driving sounds
Authors: Kastelein Ronald A. , Gransier Robin , Marijt Michelle A. T. , Hoek Lean
Published: February 2015

Harbor porpoises may suffer hearing loss when exposed to intense sounds. After exposure to playbacks of broadband pile driving sounds for 60 min, the temporary hearing threshold shift (TTS) of a porpoise was quantified at 0.5, 1, 2, 4, 8, 16, 32, 63, and 125 kHz with a psychoacoustic technique. Details of the pile driving sounds were as follows: pulse duration 124 ms, rate 2760 strikes/h, inter-pulse interval 1.3 s, average received single strike unweighted sound exposure level (SEL) 146 dB re 1 μPa2 s (cumulative SEL: 180 dB re 1 μPa2 s). Statistically significant TTS only occurred at 4 and 8 kHz; mean TTS (1–4 min. after sound exposure stopped) was 2.3 dB at 4 kHz, and 3.6 dB at 8 kHz; recovery occurred within 48 min. This study shows that exposure to multiple impulsive sounds with most of their energy in the low frequencies can cause reduced hearing at higher frequencies in harbor porpoises. The porpoise's hearing threshold for the frequency in the range of its echolocation signals was not affected by the pile driving playback sounds.
Stabilizing the production of nonnative consonant clusters with acoustic variability
Authors: Davidson Lisa , Martin Sean , Wilson Colin
Published: February 2015

Previous research on the perception, recognition, and learning of sounds and words has identified diverse effects of phonetic variation. The present study examined how variation affects cross-language production of consonant clusters. American English speakers shadowed words beginning with nonnative clusters in low- and high-variability conditions. Shadowing responses in the low-variability condition were quite sensitive to fine-grained phonetic properties that were manipulated across the stimuli. Notably, longer stop bursts led to increased rates of epenthesis, lower burst amplitudes resulted in more feature change and deletion, and intense periods of voicing at cluster onset elicited prothetic responses. Sensitivity to the acoustic manipulations was substantially attenuated in the high-variability condition, which combined stimuli from the first condition with baseline productions of the same items from two additional talkers. Detailed analyses of the response patterns indicate that more stable production targets in the high-variability condition resulted from integration, or blending, of the multiple talker stimuli. Implications of these findings for language-specific speech processing and the role of phonetic variability in second language acquisition are discussed.
Regulation of glottal closure and airflow in a three-dimensional phonation model: Implications for vocal intensity control
Authors: Zhang Zhaoyan
Published: February 2015

Maintaining a small glottal opening across a large range of voice conditions is critical to normal voice production. This study investigated the effectiveness of vocal fold approximation and stiffening in regulating glottal opening and airflow during phonation, using a three-dimensional numerical model of phonation. The results showed that with increasing subglottal pressure the vocal folds were gradually pushed open, leading to increased mean glottal opening and flow rate. A small glottal opening and a mean glottal flow rate typical of human phonation can be maintained against increasing subglottal pressure by proportionally increasing the degree of vocal fold approximation for low to medium subglottal pressures and vocal fold stiffening at high subglottal pressures. Although sound intensity was primarily determined by the subglottal pressure, the results suggest that, to maintain small glottal opening as the sound intensity increases, one has to simultaneously tighten vocal fold approximation and/or stiffen the vocal folds, resulting in increased glottal resistance, vocal efficiency, and fundamental frequency.
The effect of spatial separation in distance on the intelligibility of speech in rooms
Authors: Westermann Adam , Buchholz Jörg M.
Published: February 2015

The influence of spatial separation in source distance on speech reception thresholds (SRTs) is investigated. In one scenario, the target was presented at 0.5 m distance, and the masker varied from 0.5 m distance up to 10 m. In a second scenario, the masker was presented at 0.5 m distance and the target distance varied. The stimuli were synthesized using convolution with binaural room impulse responses (BRIRs) measured on a dummy head in a reverberant auditorium, and were equalized to compensate for distance-dependent spectral and intensity changes. All sources were simulated directly in front of the listener. SRTs decreased monotonically when the target was at 0.5 m and the speech-masker was moved further away, resulting in a SRT improvement of up to 10 dB. When the speech masker was at 0.5 m and the target was moved away, a large variation across subjects was observed. Neither short-term signal-to-noise ratio (SNR) improvements nor cross-ear glimpsing could account for the observed improvement in intelligibility. However, the effect might be explained by an improvement in the SNR in the modulation domain and a decrease in informational masking. This study demonstrates that distance-related cues can play a significant role when listening in complex environments.
An approach to generating two zones of silence with application to personal sound systems
Authors: Poletti M. A. , Fazi F. M.
Published: February 2015

An application of current interest in sound reproduction systems is the creation of multizone sound fields which produce multiple independent sound fields for multiple listeners. The challenge in producing such sound fields is the avoidance of interference between sound zones, which is dependent on the geometry of the zone and the direction of arrival of the desired sound fields. This paper provides a theoretical basis for the generation of two zones based on the creation of sound fields with nulls and the positioning of those nulls at arbitrary positions. The nulls are created by suppressing low-order mode terms in the sound field expansion. Simulations are presented for the two-dimensional case which shows that suppression of interference is possible across a broad frequency audio range.
Evolution of the average steepening factor for nonlinearly propagating waves
Authors: Muhlestein Michael B. , Gee Kent L. , Neilsen Tracianne B. , Thomas Derek C.
Published: February 2015

Difficulties arise in attempting to discern the effects of nonlinearity in near-field jet-noise measurements due to the complicated source structure of high-velocity jets. This article describes a measure that may be used to help quantify the effects of nonlinearity on waveform propagation. This measure, called the average steepening factor (ASF), is the ratio of the average positive slope in a time waveform to the average negative slope. The ASF is the inverse of the wave steepening factor defined originally by Gallagher [AIAA Paper No. 82-0416 (1982)]. An analytical description of the ASF evolution is given for benchmark cases—initially sinusoidal plane waves propagating through lossless and thermoviscous media. The effects of finite sampling rates and measurement noise on ASF estimation from measured waveforms are discussed. The evolution of initially broadband Gaussian noise and signals propagating in media with realistic absorption are described using numerical and experimental methods. The ASF is found to be relatively sensitive to measurement noise but is a relatively robust measure for limited sampling rates. The ASF is found to increase more slowly for initially Gaussian noise signals than for initially sinusoidal signals of the same level, indicating the average distortion within noise waveforms occur more slowly.
Multisource statistically optimized near-field acoustical holography
Authors: Wall Alan T. , Gee Kent L. , Neilsen Tracianne B.
Published: February 2015

This paper presents a reduced-order approach to near-field acoustical holography (NAH) that allows the user to account for sound fields generated by multiple spatially separated sources. In this method, an equivalent wave model (EWM) of a given field is formulated to include combinations of planar, cylindrical, spherical, or other elementary wave functions in contrast to an EWM restricted to a single separable coordinate system. This can alleviate the need for higher-order functions, reduce the number of measurements, and decrease error. The statistically optimized near-field acoustical holography (SONAH) algorithm is utilized to perform the NAH projection after the formulation of the multisource EWM. The combined process is called multisource statistically optimized near-field acoustical holography (M-SONAH). This method is used to reconstruct simulated sound fields generated by combinations of a vibrating piston in a sphere and linear arrays of monopole sources. It is shown that M-SONAH can reconstruct near-field pressures in multisource environments with lower errors and fewer measurements than a strictly plane or cylindrical-wave formulation using the same simulated measurement.
Modeling of transient wave propagation in a heterogeneous solid layer coupled with fluid: Application to long bones
Authors: Naili Salah , Nguyen Vu-Hieu , Vu Mai-Ba , Desceliers Christophe , Soize Christian
Published: February 2015

The aim of this work is to evaluate the effects of the heterogeneity and anisotropy of material properties of cortical bone on its ultrasonic response obtained by using axial transmission method. The heterogeneity and anisotropy of material properties are introduced by using a parametric probabilistic model. The geometrical configuration of the tested sample is described by a tri-layer medium composed of a heterogeneous and anisotropic solid layer sandwiched between two acoustic fluid layers of which one of these layers is excited by an acoustic linear source. The numerical results focus on studying of an interest quantity, called velocity of the first arriving signal, showing that it strongly depends on the dispersion induced by statistical fluctuations of stochastic elasticity field.
Implementation of a virtual laboratory for training on sound insulation testing and uncertainty calculations in acoustic tests
Authors: Asensio C. , Gasco L. , Ruiz M. , Recuero M.
Published: February 2015

This paper describes a methodology and case study for the implementation of educational virtual laboratories for practice training on acoustic tests according to international standards. The objectives of this activity are (a) to help the students understand and apply the procedures described in the standards and (b) to familiarize the students with the uncertainty in measurement and its estimation in acoustics. The virtual laboratory will not focus on the handling and set-up of real acoustic equipment but rather on procedures and uncertainty. The case study focuses on the application of the virtual laboratory for facade sound insulation tests according to ISO 140-5:1998 (International Organization for Standardization, Geneva, Switzerland, 1998), and the paper describes the causal and stochastic models and the constraints applied in the virtual environment under consideration. With a simple user interface, the laboratory will provide measurement data that the students will have to process to report the insulation results that must converge with the “virtual true values” in the laboratory. The main advantage of the virtual laboratory is derived from the customization of factors in which the student will be instructed or examined (for instance, background noise correction, the detection of sporadic corrupted observations, and the effect of instrument precision).
Major League Baseball and Twitter Usage: The Economics of Social Media Use
Authors: Watanabe Nicholas , Yan Grace , Soebbing Brian P.
Published: February 2015

From the perspective of economic demand theory, this study examines the factors that determine daily changes in Twitter following of Major League Baseball teams as a form of derived demand for a sport product. Specifically, a linear regression model is constructed by taking consideration of factors relevant to fan interest: team performance, market characteristics, scheduling, and so on. The results reveal specific determinants that have significant relationship with Twitter following. From a team management perspective, factors such as the content of social media messages, certain calendar events, and postseason appearances can be used to enhance fan interest on social media. In so doing, it brings together communication inquiries and economic literature by delineating a comprehensive and nuanced account of interpreting sport social media from a consumer demand perspective.
Assessment of SYBR Green I Dye-Based Fluorescence Assay for Screening Antimalarial Activity of Cationic Peptides and DNA Intercalating Agents
Authors: Bhatia Rakesh , Gautam Ankur , Gautam Shailendra K. , Mehta Divya , Kumar Vinod , Raghava Gajendra P. S. , Varshney Grish C.
Published: February 2015

The SYBR green I (SG) dye-based fluorescence assay for screening antimalarial compounds is based on direct quantitation of parasite DNA. We show that DNA-interacting cationic cell-penetrating peptides (CPPs) and intercalating agents compete with SG dye to bind to DNA. Therefore, readouts of this assay, unlike those of the [
3
H]hypoxanthine incorporation assay, for the antimalarial activity of the above DNA binding agents may be erroneous. In the case of CPPs, false readouts can be improved by the removal of excess peptides.
Comparison of Antimicrobial Susceptibilities of Pharyngeal, Rectal, and Urethral Neisseria gonorrhoeae Isolates among Men Who Have Sex with Men
Authors: Kidd Sarah , Zaidi Akbar , Asbel Lenore , Baldwin Tamara , Gratzer Beau , Guerry Sarah , Kerani Roxanne P. , Pathela Preeti , Pettus Kevin , Soge Olusegun O. , Stirland Ali , Weinstock Hillard S.
Published: February 2015

U.S. surveillance for
Neisseria gonorrhoeae
antimicrobial susceptibilities is based exclusively on male urethral isolates. These data inform gonorrhea treatment guidelines, including recommendations for the treatment of extragenital infections, but data on the susceptibilities of extragenital isolates are limited. We compared the antimicrobial susceptibilities of pharyngeal, rectal, and urethral gonococcal isolates collected from men who have sex with men (MSM), at five sentinel sites throughout the United States. MICs were determined by the agar dilution method. Generalized linear models were used to compare (i) the proportions of isolates with elevated MICs and (ii) geometric mean MICs according to anatomic site, adjusted for city. In December 2011 to September 2013, totals of 205 pharyngeal, 261 rectal, and 976 urethral isolates were obtained. The proportions of isolates with elevated ceftriaxone MICs (≥0.125 μg/ml) did not differ according to anatomic site (0.5% of pharyngeal isolates, 1.5% of rectal isolates, and 1.7% of urethral isolates, with a city-adjusted odds ratio [aOR] of 0.4 [95% confidence interval {CI}, 0.0 to 3.9] for pharyngeal versus urethral isolates and an aOR of 0.9 [95% CI, 0.2 to 4.2] for rectal versus urethral isolates). The city-adjusted geometric mean ceftriaxone MICs of pharyngeal (0.0153 μg/ml) and rectal (0.0157 μg/ml) isolates did not differ from that of urethral isolates (0.0150 μg/ml) (ratios of geometric mean MICs of 1.02 [95% CI, 0.90 to 1.17] and 1.05 [95% CI, 0.93 to 1.19], respectively). Similar results were observed for other antimicrobials, including cefixime and azithromycin. These findings suggest that, at the population level, gonococcal antimicrobial susceptibility surveillance based on urethral isolates from MSM adequately reflects the susceptibilities of
N. gonorrhoeae
strains circulating among MSM.
Raltegravir Permeability across Blood-Tissue Barriers and the Potential Role of Drug Efflux Transporters
Authors: Hoque M. Tozammel , Kis Olena , De Rosa María F. , Bendayan Reina
Published: February 2015

The objectives of this study were to investigate raltegravir transport across several blood-tissue barrier models and the potential interactions with drug efflux transporters. Raltegravir uptake, accumulation, and permeability were evaluated
in vitro
in (i) P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), multidrug resistance-associated protein 1 (MRP1), or MRP4-overexpressing MDA-MDR1 (P-gp), HEK-ABCG2, HeLa-MRP1, or HEK-MRP4 cells, respectively; (ii) cell culture systems of the human blood-brain (hCMEC/D3), mouse blood-testicular (TM4), and human blood-intestinal (Caco-2) barriers; and (iii) rat jejunum and ileum segments using an
in situ
single-pass intestinal perfusion model. [
3
H]Raltegravir accumulation by MDA-MDR1 (P-gp) and HEK-ABCG2-overexpressing cells was significantly enhanced in the presence of PSC833 {6-[(2
S
,4
R
,6
E
)-4-methyl-2-(methylamino)-3-oxo-6-octenoic acid]-7-
l
-valine-cyclosporine}, a P-gp inhibitor, or Ko143 [(3
S
,6
S
,12
aS
)-1,2,3,4,6,7,12,12
a
-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-dioxopyrazino[1′,2′:1,6]pyrido[3,4-
b
]indole-3-propanoic acid 1,1-dimethylethyl ester], a BCRP inhibitor, suggesting the inhibition of a P-gp- or BCRP-mediated efflux process, respectively. Furthermore, [
3
H]raltegravir accumulation by human cerebral microvessel endothelial hCMEC/D3 and mouse Sertoli TM4 cells was significantly increased by PSC833 and Ko143. In human intestinal Caco-2 cells grown on Transwell filters, PSC833, but not Ko143, significantly decreased the [
3
H]raltegravir efflux ratios. In rat intestinal segments, [
3
H]raltegravir
in situ
permeability was significantly enhanced by the concurrent administration of PSC833 and Ko143. In contrast, in the transporter inhibition assays, raltegravir (10 to 500 μM) did not increase the accumulation of substrate for P-gp (rhodamine-6G), BCRP ([
3
H]mitoxantrone), or MRP1 [2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)] by MDA-MDR1 (P-gp)-, HEK-ABCG2-, or HeLa-MRP1-overexpressing cells, respectively. Our data suggest that raltegravir is a substrate but not an inhibitor of the drug efflux transporters P-gp and BCRP. These transporters might play a role in the restriction of raltegravir permeability across the blood-brain, blood-testicular, and blood-intestinal barriers, potentially contributing to its low tissue concentrations and/or low oral bioavailability observed in the clinic setting.
Emergence of KPC-2-Producing Pseudomonas aeruginosa Sequence Type 463 Isolates in Hangzhou, China
Authors: Hu Yan-yan , Gu Dan-xia , Cai Jia-chang , Zhou Hong-wei , Zhang Rong
Published: February 2015

Thirty-nine
Klebsiella pneumoniae
carbapenemase (KPC)-producing
Pseudomonas aeruginosa
isolates, all exhibiting high-level resistance to carbapenems and other β-lactam antibiotics, were isolated in Hangzhou, China. Molecular epidemiology analysis indicated the presence of two dominant clones, namely, clones A and B, both of which belong to sequence type 463 (ST463). A genetic environment analysis demonstrated that both clones harbor an IS
Kpn8
transposase,
bla
KPC-2
, and an IS
Kpn6
-like transposase. These findings depict the features of clonal expansion and transmission of KPC-2-producing
P. aeruginosa
strains in Hangzhou, China.
Polymyxin Resistance Caused by
mgrB
Inactivation Is Not Associated with Significant Biological Cost in Klebsiella pneumoniae
Authors: Cannatelli Antonio , Santos-Lopez Alfonso , Giani Tommaso , Gonzalez-Zorn Bruno , Rossolini Gian Maria
Published: February 2015

The inactivation of the
mgrB
gene, which encodes a negative-feedback regulator of the PhoPQ signaling system, was recently shown to be a common mutational mechanism responsible for acquired polymyxin resistance among carbapenemase-producing
Klebsiella pneumoniae
strains from clinical sources. In this work, we show that
mgrB
mutants can easily be selected
in vitro
from different
K. pneumoniae
lineages, and
mgrB
inactivation is not associated with a significant biological cost.
Pharmacological Activation of Rap1 Antagonizes the Endothelial Barrier Disruption Induced by Exotoxins ExoS and ExoT of Pseudomonas aeruginosa
Authors: Bouillot Stéphanie , Attrée Ina , Huber Philippe
Published: February 2015

Most clinical strains of
Pseudomonas aeruginosa
, a leading agent of nosocomial infections, are multiresistant to antibiotherapy. Because of the paucity of new available antibiotics, the investigation of strategies aimed at limiting the action of its major virulence factors has gained much interest. The type 3 secretion system of
P. aeruginosa
and its effectors are known to be major determinants of toxicity and are required for bacterial dissemination in the host. Bacterial transmigration across the vascular wall is considered to be an important step in the infectious process. Using human endothelial primary cells, we demonstrate that forskolin (FSK), a drug inducing cyclic AMP (cAMP) elevation in eukaryotic cells, strikingly reduced the cell retraction provoked by two type 3 toxins, ExoS and ExoT, found in the majority of clinical strains. Conversely, cytotoxicity of a strain carrying the type 3 effector ExoU was unaffected by FSK. In addition, FSK altered the capacity of two ExoS/ExoT strains to transmigrate across cell monolayers. In agreement with these findings, other drugs and a cytokine inducing the increase of cAMP intracellular levels have also protected cells from retraction. cAMP is an activator of both protein kinase A and EPAC, a GTPase exchange factor of Rap1. Using activators or inhibitors of either pathway, we show that the beneficial effect of FSK is exerted by the activation of the EPAC/Rap1 axis, suggesting that its protective effect is mediated by reinforcing cell-cell and cell-substrate adhesion.
Genome-Wide Transposon Mutagenesis Indicates that Mycobacterium marinum Customizes Its Virulence Mechanisms for Survival and Replication in Different Hosts
Authors: Weerdenburg Eveline M. , Abdallah Abdallah M. , Rangkuti Farania , Abd El Ghany Moataz , Otto Thomas D. , Adroub Sabir A. , Molenaar Douwe , Ummels Roy , ter Veen Kars , van Stempvoort Gunny , van der Sar Astrid M. , Ali Shahjahan , Langridge Gemma C. , Thomson Nicholas R. , Pain Arnab , Bitter Wilbert
Published: February 2015

The interaction of environmental bacteria with unicellular eukaryotes is generally considered a major driving force for the evolution of intracellular pathogens, allowing them to survive and replicate in phagocytic cells of vertebrate hosts. To test this hypothesis on a genome-wide level, we determined for the intracellular pathogen
Mycobacterium marinum
whether it uses conserved strategies to exploit host cells from both protozoan and vertebrate origin. Using transposon-directed insertion site sequencing (TraDIS), we determined differences in genetic requirements for survival and replication in phagocytic cells of organisms from different kingdoms. In line with the general hypothesis, we identified a number of general virulence mechanisms, including the type VII protein secretion system ESX-1, biosynthesis of polyketide lipids, and utilization of sterols. However, we were also able to show that
M. marinum
contains an even larger set of host-specific virulence determinants, including proteins involved in the modification of surface glycolipids and, surprisingly, the auxiliary proteins of the ESX-1 system. Several of these factors were in fact counterproductive in other hosts. Therefore,
M. marinum
contains different sets of virulence factors that are tailored for specific hosts. Our data imply that although amoebae could function as a training ground for intracellular pathogens, they do not fully prepare pathogens for crossing species barriers.
The Quorum Sensing Regulator CinR Hierarchically Regulates Two Other Quorum Sensing Pathways in Ligand-Dependent and -Independent Fashions in Rhizobium etli
Authors: Zheng Huiming , Mao Yiling , Zhu Qingcheng , Ling Jun , Zhang Na , Naseer Nawar , Zhong Zengtao , Zhu Jun
Published: February 2015

Many rhizobial species use complexN-acyl-homoserine lactone (AHL)-based quorum sensing (QS) systems to monitor their population density and regulate their symbiotic interactions with their plant hosts. There are at least three LuxRI-type regulatory systems inRhizobium etliCFN42: CinRI, RaiRI, and TraRI. In this study, we show that CinI, RaiI, and TraI are responsible for synthesizing all AHLs under the tested conditions. The activation of these AHL synthase genes requires their corresponding LuxR-type counterparts. We further demonstrate that CinRI is at the top of the regulatory cascade that activates RaiRI and TraRI QS systems. Moreover, we discovered that CinR possesses a specific affinity to bindcinIpromoter in the absence of its cognate AHL ligand, thereby activatingcinItranscription. Addition of AHLs leads to improved binding to thecinIpromoter and enhancedcinIexpression. Furthermore, we found that compared to the wild type, thecinRmutation displayed reduced nodule formation, andcinR,raiR, andtraImutants show significantly lower levels of nitrogen fixation activity than the wild type. These results suggest that the complex QS regulatory systems inR. etliplay an important role in its symbiosis with legume hosts.

IMPORTANCEMany bacteria use quorum sensing (QS) to monitor their cell densities and coordinately regulate a number of physiological functions. Rhizobia often have diverse and complex LuxR/LuxI-type quorum sensing systems that may be involved in symbiosis and N2fixation. In this study, we identified three LuxR/LuxI-type QS systems inRhizobium etliCFN42: CinRI, RaiRI, and TraRI. We established a complex network of regulation between these QS components and found that these QS systems played important roles in symbiosis processes.
An Escherichia coli Mutant That Makes Exceptionally Long Cells
Authors: El-Hajj Ziad W. , Newman Elaine B.
Published: February 2015

Although
Escherichia coli
is a very small (1- to 2-μm) rod-shaped cell, here we describe an
E. coli
mutant that forms enormously long cells in rich media such as Luria broth, as long indeed as 750 μm. These
e
xtremely
el
ongated (eel) cells are as long as the longest bacteria known and have no internal subdivisions. They are metabolically competent, elongate rapidly, synthesize DNA, and distribute cell contents along this length. They lack only the ability to divide. The concentration of the essential cell division protein FtsZ is reduced in these eel cells, and increasing this concentration restores division.

IMPORTANCE
Escherichia coli
is usually a very small bacterium, 1 to 2 μm long. We have isolated a mutant that forms enormously long cells, 700 times longer than the usual
E. coli
cell.
E. coli
filaments that form under other conditions usually die within a few hours, whereas our mutant is fully viable even when it reaches such lengths. This mutant provides a useful tool for the study of aspects of
E. coli
physiology that are difficult to investigate with small cells.
A Single Serine Residue Determines Selectivity to Monovalent Metal Ions in Metalloregulators of the MerR Family
Authors: Ibáñez María M. , Checa Susana K. , Soncini Fernando C.
Published: February 2015

MerR metalloregulators alleviate toxicity caused by an excess of metal ions, such as copper, zinc, mercury, lead, cadmium, silver, or gold, by triggering the expression of specific efflux or detoxification systems upon metal detection. The sensor protein binds the inducer metal ion by using two conserved cysteine residues at the C-terminal metal-binding loop (MBL). Divalent metal ion sensors, such as MerR and ZntR, require a third cysteine residue, located at the beginning of the dimerization (α5) helix, for metal coordination, while monovalent metal ion sensors, such as CueR and GolS, have a serine residue at this position. This serine residue was proposed to provide hydrophobic and steric restrictions to privilege the binding of monovalent metal ions. Here we show that the presence of alanine at this position does not modify the activation pattern of monovalent metal sensors. In contrast, GolS or CueR mutant sensors with a substitution of cysteine for the serine residue respond to monovalent metal ions or Hg(II) with high sensitivities. Furthermore, in a mutant deleted of the Zn(II) exporter ZntA, they also trigger the expression of their target genes in response to either Zn(II), Cd(II), Pb(II), or Co(II).

IMPORTANCESpecificity in a stressor's recognition is essential for mounting an appropriate response. MerR metalloregulators trigger the expression of specific resistance systems upon detection of heavy metal ions. Two groups of these metalloregulators can be distinguished, recognizing either +1 or +2 metal ions, depending on the presence of a conserved serine in the former or a cysteine in the latter. Here we demonstrate that the serine residue in monovalent metal ion sensors excludes divalent metal ion detection, as its replacement by cysteine renders a pan-metal ion sensor. Our results indicate that the spectrum of signals detected by these sensors is determined not only by the metal-binding ligand availability but also by the metal-binding cavity flexibility.
Genetic Basis for Metabolism of Methylated Sulfur Compounds in Methanosarcina Species
Authors: Fu He , Metcalf William W.
Published: February 2015

Methanosarcina acetivorans
uses a variety of methylated sulfur compounds as carbon and energy sources. Previous studies implicated the
mtsD
,
mtsF
, and
mtsH
genes in catabolism of dimethylsulfide, but the genes required for use of other methylsulfides have yet to be established. Here, we show that a four-gene locus, designated
mtpCAP-msrH
, is specifically required for growth on methylmercaptopropionate (MMPA). The
mtpC
,
mtpA
, and
mtpP
genes encode a putative corrinoid protein, a coenzyme M (CoM) methyltransferase, and a
m
ajor
f
acilitator
s
uperfamily (MFS) transporter, respectively, while
msrH
encodes a putative transcriptional regulator. Mutants lacking
mtpC
or
mtpA
display a severe growth defect in MMPA medium but are unimpaired during growth on other substrates. The
mtpCAP
genes comprise a transcriptional unit that is highly and specifically upregulated during growth on MMPA, whereas
msrH
is monocistronic and constitutively expressed. Mutants lacking
msrH
fail to transcribe
mtpCAP
and grow poorly in MMPA medium, consistent with the assignment of its product as a transcriptional activator. The
mtpCAP-msrH
locus is conserved in numerous marine methanogens, including eight
Methanosarcina
species that we showed are capable of growth on MMPA. Mutants lacking the
mtsD
,
mtsF
, and
mtsH
genes display a 30% reduction in growth yield when grown on MMPA, suggesting that these genes play an auxiliary role in MMPA catabolism. A quadruple Δ
mtpCAP
Δ
mtsD
Δ
mtsF
Δ
mtsH
mutant strain was incapable of growth on MMPA. Reanalysis of
mtsD
,
mtsF
, and
mtsH
mutants suggests that the preferred substrate for MtsD is dimethylsulfide, while the preferred substrate for MtsF is methanethiol.

IMPORTANCE
Methylated sulfur compounds play pivotal roles in the global sulfur and carbon cycles and contribute to global temperature homeostasis. Although the degradation of these molecules by aerobic bacteria has been well studied, relatively little is known regarding their fate in anaerobic ecosystems. In this study, we identify the genetic basis for metabolism of methylmercaptopropionate, dimethylsulfide, and methanethiol by strictly anaerobic methanogens of the genus
Methanosarcina
. These data will aid the development of predictive sulfur cycle models and enable molecular ecological approaches for the study of methylated sulfur metabolism in anaerobic ecosystems.
Structural Basis of Functional Diversification of the HD-GYP Domain Revealed by the Pseudomonas aeruginosa PA4781 Protein, Which Displays an Unselective Bimetallic Binding Site
Authors: Rinaldo Serena , Paiardini Alessandro , Stelitano Valentina , Brunotti Paolo , Cervoni Laura , Fernicola Silvia , Protano Carmela , Vitali Matteo , Cutruzzolà Francesca , Giardina Giorgio
Published: February 2015

The intracellular level of the bacterial secondary messenger cyclic di-3′,5′-GMP (c-di-GMP) is determined by a balance between its biosynthesis and degradation, the latter achieved via dedicated phosphodiesterases (PDEs) bearing a characteristic EAL or HD-GYP domain. We here report the crystal structure of PA4781, one of the three
Pseudomonas aeruginosa
HD-GYP proteins, which we have previously characterized
in vitro
. The structure shows a bimetallic active site whose metal binding mode is different from those of both HD-GYP PDEs characterized so far. Purified PA4781 does not contain iron in the active site as for other HD-GYPs, and we show that it binds to a wide range of transition metals with similar affinities. Moreover, the structural features of PA4781 indicate that this is preferentially a pGpG binding protein, as we previously suggested. Our results point out that the structural features of HD-GYPs are more complex than predicted so far and identify the HD-GYP domain as a conserved scaffold which has evolved to preferentially interact with a partner GGDEF but which harbors different functions obtained through diversification of the active site.

IMPORTANCE
In bacteria, the capability to form biofilms, responsible for increased pathogenicity and antibiotic resistance, is almost universally stimulated by the second messenger cyclic di-GMP (c-di-GMP). To design successful strategies for targeting biofilm formation, a detailed characterization of the enzymes involved in c-di-GMP metabolism is crucial. We solved the structure of the HD-GYP domain of PA4781 from
Pseudomonas aeruginosa
, involved in c-di-GMP degradation. This is the third structure of this class of phosphodiesterases to be solved, and with respect to its homologues, it shows significant differences both in the nature and in the binding mode of the coordinated metals, indicating that HD-GYP proteins are able to fine-tune their function, thereby increasing the chances of the microorganism to adapt to different environmental needs.