bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and Evaluation of Silicon Nitride Components for Ceramic Gas Turbine
Authors: Hara Yasushi , Matsubara Katsura , Mizuno Ken-ichi , Shimamori Toru , Yoshida Hiro
Published: December 2014

NGK Spark Plug Co., Ltd. has been developing various silicon nitride materials, and the technology for fabricating components for ceramic gas turbines (CGT) using theses materials. We are supplying silicon nitride material components for the project to develop 300 kW class CGT for co-generation in Japan. EC-152 was developed for components that require high strength at high temperature, such as turbine blades and turbine nozzles.

In order to adapt the increasing of the turbine inlet temperature (TIT) up to 1350 °C in accordance with the project goals, we developed two silicon nitride materials with further improved properties: ST-1 and ST-2. ST-1 has a higher strength than EC-152 and is suitable for first stage turbine blades and power turbine blades. ST-2 has higher oxidation resistance than EC-152 and is suitable for power turbine nozzles.

On applying these silicon nitride ceramics to CGT engine, we evaluated various properties of silicon nitride materials considering the environment in CGT engine. Particle impact testing is one of those evaluations. Materials used in CGT engine are exposed in high speed gas flow, and impact damage of these materials is considered to be a concern. We tested ST-1 in the particle impact test. In this test, we observed fracture modes, and estimated the critical impact velocity.

This paper summarizes the development of silicon nitride components, and the result of evaluations of these silicon nitride materials.
Influence of Metal Temperature on Base Material and Coating Degradation of GTD-111 Buckets
Authors: Cheruvu N. S. , Leverant G. R.
Published: December 2014

The surface metal temperature on the first row cooled buckets varies along the height of a bucket and among the buckets in a row. Two first-row GT 29+ coated buckets, from the same turbine, have been investigated for in-service material and coating degradation variation. The results showed that the γ′ particles were coarser and the width of the interdiffusion zone below the CoCrAlY coating was wider in one bucket than the other, indicating that the former bucket had seen higher metal temperature than the latter. Fewer uncertainties are associated with interdiffusion zone width measurements, and the change in zone width can be used to develop a time-temperature correlation for the subject bucket material and coating system. The uncertainties associated with γ′ particle measurements for time temperature correlation are discussed.
Accuracy of the Riccati Transfer Matrix Method in Rotor Dynamic Analysis
Authors: Behzad M. , Mehri B.
Published: December 2014

This paper illustrates the theory behind the development of a General form of a numerically accurate and stable software for determining the lateral natural frequencies, mode shapes, stability and unbalance response of multi-shaft rotor bearing systems which may be gear coupled and supported on flexible anisotropic bearings, such as hydrodynamic bearings as well as rigid rolling elements. Gyroscopic effects, shear deformation and hysteretic damping are included in the analysis. To achieve the improved accuracy and numerical convergence to all relevant roots of the characteristic equations the Riccati transfer matrix is utilized rather than the traditional transfer matrix approach. This more accurate approach introduces poles into the characteristic equation. After cancellation of all poles, convergence to all relevant roots is guaranteed. In this study two different methods of handling in-span conditions are presented and it is proven that after elimination of poles the Riccati transfer matrix method and the transfer matrix method have the same characteristic equation. However with even 25% increase in average computation time, the Riccati transfer matrix method remains more accurate due to a different method of calculating the characteristic equation.
Predictions of Turbulent Flow in a Turbine Stator/Rotor Passage
Authors: Amano R. S. , Song B. , Sitarama S. , Lin B.
Published: December 2014

Numerical study on a three-dimensional turbulent flow in a turbine stator/rotor passage is presented in this paper. The standard k-ε model was used for the first phase of the turbulence computations. The computations were further extended by employing the full Reynolds-stress closure model (RSM). The computational results obtained using these models were compared in order to investigate the turbulence effect in the near-wall region. The governing equations in a generalized curvilinear coordinate system are discretized by using the SIMPLEC method with non-staggered grids. The oscillations in pressure and velocity due to non-staggered grids are eliminated by using a special interpolation method. The predicted midspan pressure coefficients using the k-ε model and the RSM are compared with the experimental data. It was shown that the present results obtained by using either model are fairly reasonable. Computations were then extended to cover the entire blade-to-blade flow passage, and the three-dimensional effects on pressure and turbulence kinetic energy were evaluated. It was observed that the two turbulence models predict different results for the turbulence kinetic energy. This variation was identified as being related to some non-isotropic turbulence occurring near the blade surface due to the severe acceleration of the flow. It was thus proven that the models based on the RSM give more realistic predictions for highly turbulent cascade flow computations than a Boussinesq viscosity model.
Ceramic Stationary Gas Turbine Development Program — Design and Test of a Ceramic Turbine Blade
Authors: Jimenez Oscar , McClain John , Edwards Bryan , Parthasarathy Vijay , Bagheri Hamid , Bolander Gary
Published: December 2014

The goal of the Ceramic Stationary Gas Turbine (CSGT) Development Program, under the sponsorship of the United States Department of Energy (DOE), Office of Industrial Technologies (OIT), is to improve the performance (fuel efficiency, output power, and exhaust emissions) of stationary gas turbines in cogeneration through the selective replacement of hot section components with ceramic parts. This program, which is headed by Solar Turbines Incorporated and supported by various suppliers, and national research institutes, includes detailed engine and component design, procurement, and field testing.

A major challenge in the successful introduction of ceramic parts into a gas turbine is the design of the interface between the ceramic parts and metallic hardware. A turbine blade, which incorporated a dovetail root, was designed with such considerations. A relatively thin compliant layer between the ceramic-metallic loading surface was considered for equalizing pressure face load distributions.

Five monolithic siliocn nitride ceramic materials were considered: AS800 and GN10, AlliedSignal Ceramic Components; NT164, Norton Advanced Ceramics; SN281 and SN253, Kyocera Industrial Ceramics Corporation. The probability of survival using NASA/CARES for 30,000 hours of engine operation was calculated for each material. The blade frequencies, stresses, and temperatures were predicted. The influence of the dovetail angle was also analyzed to determine the most optimum configuration. Prior to engine installation all blades underwent extensive nondestructive evaluation and spin proof testing. This paper will review the design, life prediction, and testing of the first stage ceramic turbine blade for the Solar Turbines Centaur 5OS engine.
Total and Static Quantity Measurements in Unsteady Flow — Effect of Unsteadiness
Authors: Lou Weiliang , Aalburg Christian , Hourmouziadis Jean
Published: December 2014

The effects of unsteadiness both on high-response dynamic measurements and on time-averaged measurements with slow-response probes are analytically investigated separately from the response characteristics of the measuring system. The approach is based on physical similarity and dimensional analysis. The potential errors from flow unsteadiness and the major parameters which influence the measurement results are discussed. In the case of five sensor spherical probes a quantitative investigation for inviscid, incompressible, irrotational flow is carried out with the help of potential theory.
The Effect of Turbulence on the Heat Transfer in Closed Gas-Filled Rotating Annuli for Different Rayleigh Numbers
Authors: Bohn Dieter , Gier Jochen
Published: December 2014

Higher turbine inlet temperatures are a common method of increasing the thermal efficiency of modern gas turbines. This development not only generates the need for more efficient turbine blade cooling but also demands a more profound knowledge of the mechanically and thermally stressed parts of the rotor. In order to determine thermal stresses from the temperature distribution in the rotor of a gas turbine, one has to encounter the convective heat transfer in rotor cavities. In the special case of a completely closed gas-filled rotating annulus the convective flow is governed by strong natural convection.

As shown in a previous paper by the authors, and for example by Owen, the presence of turbulence and its inclusion in the modeling of the flow has been found to cause significant differences in the flow development in rotating annuli. This influence in the special case of a closed rotating annulus has been recently investigated by the authors for a moderately high Rayleigh-Number. Based on this work an investigation was undertaken focusing on the development of turbulence and turbulence related changes in the flow structure for increasing Rayleigh-Numbers.

The flow is investigated numerically using a three-dimensional Navier-Stokes solver, based on a pressure correction scheme. To account for the turbulence, a low-Reynolds-number k-ε-model is employed. This model is complemented by an additional term for turbulence production due to buoyancy. The results are compared with experiments performed at the Institute of Steam and Gas Turbines. The computations demonstrate the considerable influence on the overall heat transfer as well as on the local heat transfer distribution.
Manual GTAW of Superalloy Blade Materials Using High Strength Fillers
Authors: Greaves Wayne , van Esch Hans
Published: December 2014

Nickel-based superalloys are some of the most difficult materials to weld. Exceptional aging characteristics result in susceptibility to strain-age cracking in the heat affected zone and in the weld itself. To overcome the latter situation, filler alloys are commonly used which are much less strain sensitive than the base alloy. Mechanical strength is sacrificed for ductility with these materials thereby limiting the weldable areas of gas turbine components to regions of relatively low operating stresses. Sophisticated automated techniques have been developed to join superalloys using fillers having similar or identical chemistries to the base alloys. These welding methods are expensive compared to manual processes and are limited when the application involves localized repairs in varied locations. This study demonstrates the successful application of a specially developed process for the manual GTAW joining of precipitation-hardening alloys with filler materials of similar composition and properties.
ASTM Single Fiber Room Temperature Test Standard Development
Authors: Hurst Janet B. , Hong William S. , Gambone Mary L. , Porter John R.
Published: December 2014

Development of an updated single filament test standard for tensile strength determination has been undertaken by a joint government-industry task group under the auspices of the Subcommittee C28.07 of the American Society for Testing and Materials (ASTM). This update was initiated in response to a need expressed by people involved with fiber testing. A fiber testing workshop in 1991 attracted a wide range of attendees with concerns regarding the uniformity of testing methods and comparability of resulting data in the fiber literature. With the inception of a C28.07.07 Task Group for Ceramic Fibers, an effort to conduct round robin testing was begun among interested government and industrial test facilities. User surveys and discussion groups were also employed to determine areas of concern with the current standard test method, ASTM D 3379-75. Shortcomings in the current standard were identified and methods of addressing these areas were discussed with experts including fiber manufacturers, testing facilities and composite manufacturers. Among the main concerns was the method and application of fiber diameter measurements.
Life Prediction and Reliability Analysis of Ceramic Structures Under Combined Static and Cyclic Fatigue
Authors: Rahman Sharif , Nemeth Noel N. , Gyekenyesi John P.
Published: December 2014

This paper presents a computational methodology for life prediction and time-dependent reliability analysis of ceramic structures under combined effects of static and cyclic fatigue. It involves (1) a crack-growth equation representing damage contributions from both static and cyclic fatigue, (2) a multivariate nonlinear regression model for performing parameter estimation from fatigue data generated by small specimens, and (3) the Batdorf model for structural reliability analysis. A linear superposition of crack-growth rates obtained from the Power-law and Walker-law equations was used. The model assumes that the time-dependent and cycle-dependent crack growth formulation exponents are identical, and that loading frequency and amplitude do not vary over time. For the parameter estimation, the regression was performed using nonlinear least squares and a modified Levenberg-Marquardt algorithm. This methodology was implemented into the integrated design code named CARES/Life (Ceramics Analysis and Reliability Evaluation of Structures/Life). A numerical example is presented to illustrate the parameter estimation component of this methodology. The results suggest that the predicted stress-life curves based on the proposed model can correlate better with experimental data when compared with either Power-law or the Walker-law models individually.
A Design Method to Prevent Low Pressure Turbine Blade Flutter
Authors: Panovsky Josef , Kielb Robert E.
Published: December 2014

A design approach to avoid flutter of low pressure turbine blades in aircraft engines is described. A linearized Euler analysis, previously validated using experimental data, is used for a series of parameter studies. The influence of mode shape and reduced frequency are investigated. Mode shape is identified as the most important contributor to determining the stability of a blade design. A new stability parameter is introduced to gain additional insight into the key contributors to flutter. This stability parameter is derived from the influence coefficient representation of the cascade, and includes only contributions from the reference blade and its immediate neighbors. This has the effect of retaining the most important contributions to aerodynamic damping while filtering out terms of less significance. This parameter is utilized to develop a stability map, which provides the critical reduced frequency as a function of torsion axis location. Rules for preliminary design and procedures for detailed design analysis are defined.
Sweep in a Transonic Fan Rotor: Part 2 — CFD and Stress Analyses
Authors: Abdelhamid Hazem F. , Shreeve Raymond P. , Hobson Garth V.
Published: December 2014

Forward-swept and back-swept transonic rotor geometries were generated from a reference design using a new 3D surface representation for blade geometry. Flow fields and performance were calculated using a thin-layer Navier-Stokes code and rotational stresses were calculated using a finite-element code. Grid generation problems, due to interfacing with the new geometry package, were resolved to obtain a consistent data set that isolated the effect of sweep on rotor performance. The intent of the study was to exercise and demonstrate the new geometry package by introducing sweep into an existing rotor design. The package is intended for aero-structural-manufacturing optimization.
Investigation of the Thermoacoustic Characteristics of a Lean Premixed Gas Turbine Burner
Authors: Paschereit Christian Oliver , Polifke Wolfgang
Published: December 2014

To model thermoacoustic oscillations, a combustion system can be described as a network of acoustic elements, representing for example fuel and air supply, burner and flame, combustor, cooling channels, suitable terminations, etc. For most of these elements, simple analytical models provide an adequate description of their thermoacoustic properties. However, the complex response of burner and flame to acoustic perturbations has — at least in a first step — to be determined by experiment. In our approach, we describe the burner as an active acoustical two-port, where the state variables pressure and velocity at the inlet and the outlet are coupled via a four element transfer matrix. This approach is similar to the “black box” theory in communication engineering. To determine ail four coefficients, two independent test states have to be created. This is achieved by using acoustic sources upstream and downstream of the burner, respectively. In application to a full size gas turbine burner, the method’s accuracy was tested in a first step without combustion and the results were compared to an analytical model for the burner’s acoustic properties. Then the method was used to determine the burner transfer matrix with combustion and to investigate the influence of various parameters such as acoustic amplitude and equivalence ratio. The treatment of burners as acoustic two-port with feedback used to model the thermoacoustic behavior of combustion chambers and the experimental determination of the burner transfer matrix is novel.
Oxidation Characteristics of Nickel Based Superalloys in Steam
Authors: Desai Vimal H. , Tamboli Dnyanesh C. , Cheruvu N. S.
Published: December 2014

An improvement in the efficiency of land based gas turbines is sought by replacing air with steam for the internal cooling of hot gas path components. However, the degradation behavior and mechanisms associated with the interaction of superalloys with steam at high temperatures are unknown. This information is very crucial for the reliability as well as for useful life prediction of the gas turbine components. In this work, oxidation in steam has been studied for three nickel based superalloys commonly used in the gas turbines. These are IN 738, Inconel 617, and CMSX-4. The study was carried out at four different test temperatures in the range of 800° C to 950° C for times up to 1400 hours. The results indicated significantly different oxidation behavior in steam compared to air for all the alloys tested.
An Experimental Investigation of System Effects in Axial Flow Compressors
Authors: Silkowski Peter O. , Shin Hyoun-Woo
Published: December 2014

In this paper, experimental results are presented which demonstrate the potential importance of component coupling and system effects on the pumping stability and performance of a rotor in an axial flow compressor. Three different configurations are presented: (1) series coupling, (2) parallel coupling, and (3) combined series/parallel coupling. In all three configurations the more stable component or region successfully stabilizes the entire compression system beyond the stability boundary of the less stable component or region. A novel method for assessing the relative stability of the different regions is employed. This method utilizes the small scale pre-stall disturbances of the compressor to probe the stability of the different regions. The role of length scales or domains of dependence in determining stability is consistently demonstrated. Specifically, the stability of small length scale disturbances is shown to be governed by the local environment while being relatively insensitive to other components. However, the stability of larger length scale phenomena is affected by the global environment created by considering all of the parts of the overall system. Consideration and knowledge of these results is important when modeling, analyzing, or designing a compression system. Furthermore, these results serve as a cautionary note when interpreting solutions from a simplified analytical/computational analysis.
Temperature effect on zinc oxysulfide-Zn(O,S) films synthesized by atomic layer deposition for Cu(In,Ga)Se2 solar cells
Authors: Bugot Cathy , Schneider Nathanaëlle , Jubault Marie , Lincot Daniel , Donsanti Frédérique
Published: December 2014

Thin films of Zn(O,S) were deposited by atomic layer deposition from diethylzinc, water (H2O), and hydrogen sulfide (H2S). First, a study on the influence of the H2S/(H2O+H2S) pulse ratio from pure ZnO to pure ZnS was performed at deposition temperature Tdep=120 and 200 °C. Zn(O,S) films had higher S content than expected, and this effect was stronger at Tdep=200 °C. Then, Zn(O,S) films have been synthesized over the range of temperature 120–220 °C at the constant H2S/(H2O+H2S) pulse ratio of 9%. For Tdep<180 °C, high and almost constant S content has been measured in the films. The significant increase of the S/(O+S) atomic ratio for Tdep>180 °C confirmed that exchange reactions occurred between the Zn(O,S) growing films and H2S. The grazing incidence x-ray diffraction patterns showed Zn(O,S) films with hexagonal wurtzite structures and with an optimum crystallization for temperatures Tdep=160–180 °C. Indeed, in this temperature range, well crystallized and large grains were obtained which was in good correlation with the film morphology determined by scanning electron microscope; and Hall effect measurements revealed low resistivities, high carrier concentrations (>1019 cm−3), and low mobilities. From these results, the authors propose the existence of a temperature range where the properties undergo significant changes while the atomic composition remains constant.
Aperture-time of oxygen-precursor for minimum silicon incorporation into the interface-layer in atomic layer deposition-grown HfO2/Si nanofilms
Authors: Mani-Gonzalez Pierre Giovanni , Vazquez-Lepe Milton Oswaldo , Herrera-Gomez Alberto
Published: December 2014

Hafnium oxide nanofilms were grown with atomic layer deposition on H-terminated Si (001) wafers employing tetrakis dimethyl amino hafnium (TDMA-Hf) and water as precursors. While the number of cycles (30) and the aperture-time for TDMA-Hf (0.08 s) were kept constant, the aperture-time (τH2O) for the oxidant-agent (H2O) was varied from 0 to 0.10 s. The structure of the films was characterized with robust analysis employing angle-resolved x-ray photoelectron spectroscopy. In addition to a ∼1 nm hafnium oxide layer, a hafnium silicate interface layer, also ∼1 nm thick, is formed for τH2O > 0. The incorporation degree of silicon into the interface layer (i.e., the value of 1 − x in HfxSi1−xOy) shows a minimum of 0.32 for τH2O = 0.04 s. By employing the simultaneous method during peak-fitting analysis, it was possible to clearly resolve the contribution from the silicate and from oxide to the O 1s spectra, allowing for the assessment of the oxygen composition of each layer as a function of oxidant aperture time. The uncertainties of the peak areas and on the thickness and composition of the layers were calculated employing a rigorous approach.
Photoemission properties of nanocrystalline diamond thin films on silicon
Authors: Mazellier Jean-Paul , Di Giola Cyril , Legagneux Pierre , Hébert Clément , Scorsone Emmanuel , Bergonzo Philippe , Saada Samuel
Published: December 2014

The authors have built up a dedicated ultrahigh vacuum setup to measure ultraviolet (266 nm photons) photoemission properties of nanocrystalline diamond thin films obtained by chemical vapor deposition on silicon substrates. The authors validated their setup by measuring polycrystalline copper quantum efficiency of ∼10−6, which is in good agreement with literature. The authors also measured quantum efficiency of bare silicon (highly p and n doped) and demonstrate strong influence of doping type. The authors then measured quantum efficiency of silicon samples coated with submicron (50 and 100 nm thick) nanocrystalline diamond layers. This coating reveals to have major influence on the photoemission properties when deposited on highly n-doped silicon samples. The authors obtain quantum yield as high as 1.60 × 10−5. The relatively high quantum efficiency of such structure associated with its high stability in air and easy processing make it a good candidate as fast electron source for electron gun based systems such as scanning/transmission electron microscopes or x-ray sources.
Atomic layer deposition grown MOx thin films for solar water splitting: Prospects and challenges
Authors: Singh Trilok , Lehnen Thomas , Leuning Tessa , Mathur Sanjay
Published: December 2014

The magnitude of energy challenge not only calls for efficient devices but also for abundant, inexpensive, and stable photoactive materials that can enable efficient light harvesting, charge separation and collection, as well as chemical transformations. Photoelectrochemical systems based on semiconductor materials have the possibility to transform solar energy directly into chemical energy the so-called “solar hydrogen.” The current challenge lies in the harvesting of a larger fraction of electromagnetic spectrum by enhancing the absorbance of electrode materials. In this context, atomically precise thin films of metal oxide semiconductors and their multilayered junctions are promising candidates to integrate high surface areas with well-defined electrode–substrate interface. Given its self-limited growth mechanism, the atomic layer deposition (ALD) technique offers a wide range of capabilities to deposit and modify materials at the nanoscale. In addition, it opens new frontiers for developing precursor chemistry that is inevitable to design new processes. Herein, the authors review the properties and potential of metal oxide thin films deposited by ALD for their application in photoelectrochemical water splitting application. The first part of the review covers the basics of ALD processes followed by a brief discussion on the electrochemistry of water splitting reaction. The second part focuses on different MOx films deposited by atomic layer deposition for water splitting applications; in this section, The authors discuss the most explored MOx semiconductors, namely, Fe2O3, TiO2, WO3, and ZnO, as active materials and refer to their application as protective coatings, conductive scaffolds, or in heterojunctions. The third part deals with the current challenges and future prospects of ALD processed MOx thin films for water splitting reactions.
Photosensitive field emission study of SnS2 nanosheets
Authors: Joshi Padmashree D. , Joag Dilip S. , Rout Chandra Shekhar , Late Dattatray J.
Published: December 2014

SnS2 nanosheets (SnS2NSs), synthesized by one-step hydrothermal reaction, are subjected to field emission (FE) studies. For synthesis, specific concentrations of Na2SnO3 and thioamide solutions are used. The FE study is carried out in a planar diode configuration at a base pressure of ∼10−8 mbar. The emission photosensitivity is also investigated by illuminating the specimen with a visible light source. In dark, the turn on field, the electric field required to obtain a current density of 1 μA/cm2, is found to be 5.9 V/μm. Upon illumination, the emitter with visible light, it is found to reduce to 5.0 V/μm. A significant change in the nature of the Fowler–Nordheim plot with light illumination is also observed and has been explained on the basis of photoconductivity. Repetitive switching ON and OFF the light source, at a fixed applied voltage, is found to generate current pulses. The photosensitivity is also studied with various color filters. With the photoswitching and the enhanced field emission properties, it is envisaged that SnS2NSs possess a potential for optoelectronic applications of field emitters.
The CNAO dose delivery system for modulated scanning ion beam radiotherapy
Authors: Giordanengo S. , Garella M. A. , Marchetto F. , Bourhaleb F. , Ciocca M. , Mirandola A. , Monaco V. , Hosseini M. A. , Peroni C. , Sacchi R. , Cirio R. , Donetti M.
Published: December 2014

Purpose:

This paper describes the system for the dose delivery currently used at the Centro Nazionale di Adroterapia Oncologica (CNAO) for ion beam modulated scanning radiotherapy.

Methods:

CNAO Foundation, Istituto Nazionale di Fisica Nucleare and University of Torino have designed, built, and commissioned a dose delivery system (DDS) to monitor and guide ion beams accelerated by a dedicated synchrotron and to distribute the dose with a full 3D scanning technique. Protons and carbon ions are provided for a wide range of energies in order to cover a sizable span of treatment depths. The target volume, segmented in several layers orthogonally to the beam direction, is irradiated by thousands of pencil beams which must be steered and held to the prescribed positions until the prescribed number of particles has been delivered. For the CNAO beam lines, these operations are performed by the DDS. The main components of this system are two independent beam monitoring detectors, called BOX1 and BOX2, interfaced with two control systems performing the tasks of real‐time fast and slow control, and connected to the scanning magnets and the beam chopper. As a reaction to any condition leading to a potential hazard, a DDS interlock signal is sent to the patient interlock system which immediately stops the irradiation. The essential tasks and operations performed by the DDS are described following the data flow from the treatment planning system through the end of the treatment delivery.

Results:

The ability of the DDS to guarantee a safe and accurate treatment was validated during the commissioning phase by means of checks of the charge collection efficiency, gain uniformity of the chambers, and 2D dose distribution homogeneity and stability. A high level of reliability and robustness has been proven by three years of system activity needing rarely more than regular maintenance and working with 100% uptime. Four identical and independent DDS devices have been tested showing comparable performances and are presently in use on the CNAO beam lines for clinical activity.

Conclusions:

The dose delivery system described in this paper is one among the few worldwide existing systems to operate ion beam for modulated scanning radiotherapy. At the time of writing, it has been used to treat more than 350 patients and it has proven to guide and control the therapeutic pencil beams reaching performances well above clinical requirements. In particular, in terms of dose accuracy and stability, daily quality assurance measurements have shown dose deviations always lower than the acceptance threshold of 5% and 2.5%, respectively.
Problem roulette: Studying introductory physics in the cloud
Authors: Evrard August E. , Mills Michael , Winn David , Jones Kathryn , Tritz Jared , McKay Timothy A.
Published: December 2014

We introduce Problem Roulette (PR), a web-based study service at the University of Michigan that offers random-within-topic access to a large library of past exam problems in introductory physics courses. Built on public-private cloud infrastructure, PR served nearly 1000 students during Fall 2012 term, delivering more than 60,000 problem pages. The service complements that of commercial publishing houses by offering problems authored by local professors and by explicitly aligning topics with exam content. We describe the service architecture, including reporting and analytical capabilities, and present an initial evaluation of the impact of its use. Among roughly 500 students studying electromagnetism, we find that the 229 students who worked fifty or more problems over the term outperformed their complement by 0.40 grade points (on a 4.0 scale). This improvement partly reflects a selection bias that academically stronger students used the service more frequently. Adjusting for this selection bias, we find a grade point improvement of 0.22, significantly above the random noise level of 0.04. The simple message to students is that working five or more additional problems per week can lead to a quarter-letter grade improvement in introductory physics. Student comments emphasize the importance of randomness in helping them to synthesize concepts. The PR source code is publicly available.
Experimental determination of circuit equations
Authors: Shulman Jason , Malatino Frank , Widjaja Matthew , Gunaratne Gemunu H.
Published: December 2014

Kirchhoff's laws offer a general, straightforward approach to circuit analysis. Unfortunately, their application becomes impractical for all but the simplest of circuits. This work presents an alternative procedure, based on an approach developed to analyze complex networks, thus making it appropriate for use on large, complicated circuits. The procedure is unusual in that it is not an analytic method but is based on experiment. Yet, this approach produces the same circuit equations obtained by more traditional means.
Nonequivalence of equivalence principles
Authors: Di Casola Eolo , Liberati Stefano , Sonego Sebastiano
Published: December 2014

Equivalence principles played a central role in the development of general relativity. Furthermore, they have provided operative procedures for testing the validity of general relativity, or constraining competing theories of gravitation. This has led to a flourishing of different, and inequivalent, formulations of these principles, with the undesired consequence that often the same name, “equivalence principle,” is associated with statements having a quite different physical meaning. In this paper, we provide a precise formulation of the several incarnations of the equivalence principle, clarifying their uses and reciprocal relations. We also discuss their possible role as selecting principles in the design and classification of viable theories of gravitation.
Conical shape of frozen water droplets
Authors: Schetnikov Andrei , Matiunin Vitalii , Chernov Vyacheslav
Published: December 2014

When a small water droplet is deposited on a cold surface, the freezing process transforms the droplet so that its upper portion attains a conical shape. Such a transformation occurs because the density of ice is lower than the density of water. Here, we assume that the freezing process in its final stage becomes self-similar, so the freezing front has a concave spherical shape, with a center that coincides with the vertex of the forming cone. This assumption gives a vertex angle of 65°, corresponding to a density ratio of 0.917, in a good agreement with experimental data.
What is superresolution microscopy?
Authors: Bechhoefer John
Published: December 2014

In this paper, we discuss what is, what is not, and what is only sort of superresolution microscopy. We begin by considering optical resolution, first in terms of diffraction theory, then in terms of linear-systems theory, and finally in terms of techniques that use prior information, nonlinearity, and other tricks to improve resolution. This discussion reveals two classes of superresolution microscopy, “pseudo” and “true.” The former improves images up to the diffraction limit, whereas the latter allows for substantial improvements beyond the diffraction limit. The two classes are distinguished by their scaling of resolution with photon counts. Understanding the limits to imaging resolution involves concepts that pertain to almost any measurement problem, implying a framework with applications beyond optics.
Examining Elite Parasport Athletes With Sport Involvement and Sports Equipment
Authors: Hambrick Marion E. , Hums Mary A. , Bower Glenna G. , Wolff Eli A.
Published: December 2014

Elite athletes require the most advanced sports equipment to maintain their competitive edge, but manufacturers cannot always satisfy these athletes’ specific equipment needs. Sport involvement can influence sports-equipment selections and is described as the process by which individuals rely on attitudes and belief systems to make sports-related consumption decisions. This study involved semistructured interviews with 5 elite Parasport athletes to identify and analyze the role of sport involvement in their selection of sports equipment. The results revealed that the athletes identified product limitations, created a collaborative environment, and promoted a culture of innovation to develop new sports products and address existing limitations. Theoretical and practical implications are discussed.
For the Immune System, Silence Is Golden
Authors: Mueller Kristen L.
Published: December 2014

T
regs
silenced self-reactive T cells.
BAT Signal to the Liver
Authors: Wong Wei
Published: December 2014

Neuregulin 4 released by brown adipose tissue attenuates lipogenesis in the liver.
In Vitro
Susceptibility of Characterized β-Lactamase-Producing Strains Tested with Avibactam Combinations
Authors: Li Henry , Estabrook Mark , Jacoby George A. , Nichols Wright W. , Testa Raymond T. , Bush Karen
Published: December 2014

Avibactam, a broad-spectrum β-lactamase inhibitor, was tested with ceftazidime, ceftaroline, or aztreonam against 57 well-characterized Gram-negative strains producing β-lactamases from all molecular classes. Most strains were nonsusceptible to the β-lactams alone. Against AmpC-, extended-spectrum β-lactamase (ESBL)-, and KPC-producing
Enterobacteriaceae
or
Pseudomonas aeruginosa
, avibactam lowered ceftazidime, ceftaroline, or aztreonam MICs up to 2,048-fold, to ≤4 μg/ml. Aztreonam-avibactam MICs against a VIM-1 metallo-β-lactamase-producing
Enterobacter cloacae
and a VIM-1/KPC-3-producing
Escherichia coli
isolate were 0.12 and 8 μg/ml, respectively.
Multicenter, Randomized Clinical Trial To Compare the Safety and Efficacy of LFF571 and Vancomycin for Clostridium difficile Infections
Authors: Mullane Kathleen , Lee Christine , Bressler Adam , Buitrago Martha , Weiss Karl , Dabovic Kristina , Praestgaard Jens , Leeds Jennifer A. , Blais Johanne , Pertel Peter
Published: December 2014

Clostridium difficile
infection causes serious diarrheal disease. Although several drugs are available for treatment, including vancomycin, recurrences remain a problem. LFF571 is a semisynthetic thiopeptide with potency against
C. difficile
in vitro
. In this phase 2 exploratory study, we compared the safety and efficacy (based on a noninferiority analysis) of LFF571 to those of vancomycin used in adults with primary episodes or first recurrences of moderate
C. difficile
infection. Patients were randomized to receive 200 mg of LFF571 or 125 mg of vancomycin four times daily for 10 days. The primary endpoint was the proportion of clinical cures at the end of therapy in the per-protocol population. Secondary endpoints included clinical cures at the end of therapy in the modified intent-to-treat (mITT) population, the time to diarrhea resolution, and the recurrence rate. Seventy-two patients were randomized, with 46 assigned to receive LFF571. Based on the protocol-specified definition, the rate of clinical cure for LFF571 (90.6%) was noninferior to that of vancomycin (78.3%). The 30-day sustained cure rates for LFF571 and vancomycin were 56.7% and 65.0%, respectively, in the per-protocol population and 58.7% and 60.0%, respectively, in the modified intent-to-treat population. Using toxin-confirmed cases only, the recurrence rates were lower for LFF571 (19% versus 25% for vancomycin in the per-protocol population). LFF571 was generally safe and well tolerated. The incidence of adverse events (AEs) was higher for LFF571 (76.1% versus 69.2% for vancomycin), although more AEs in the vancomycin group were suspected to be related to the study drug (38.5% versus 32.6% for LFF571). One patient receiving LFF571 discontinued the study due to an AE. (This study has been registered at ClinicalTrials.gov under registration no. NCT01232595.)
Fidaxomicin Therapy in Critically Ill Patients with Clostridium difficile Infection
Authors: Penziner Samuel , Dubrovskaya Yanina , Press Robert , Safdar Amar
Published: December 2014

Fidaxomicin use to treat proven
Clostridium difficile
infection (CDI) was compared between 20 patients receiving care in critical care units (CCUs) and 30 patients treated on general medical floors. At baseline, the CCU patients had more initial CDI episodes, more severe and complicated disease, and more concurrent broad-spectrum antibiotic coverage. On multivariate analysis, the response to fidaxomicin therapy among the critically ill patients was comparable to that among patients in the general medical wards.
Antisecretory Factor Peptide AF-16 Inhibits the Secreted Autotransporter Toxin-Stimulated Transcellular and Paracellular Passages of Fluid in Cultured Human Enterocyte-Like Cells
Authors: Nicolas Valérie , Liévin-Le Moal Vanessa
Published: December 2014

Both the endogenous antisecretory factor (AF) protein and peptide AF-16, which has a sequence that matches that of the active N-terminal region of AF, inhibit the increase in the epithelial transport of fluid and electrolytes induced by bacterial toxins in animal and
ex vivo
models. We conducted a study to investigate the inhibitory effect of peptide AF-16 against the increase of transcellular passage and paracellular permeability promoted by the
s
ecreted
a
utotransporter
t
oxin (Sat) in a cultured cellular model of the human intestinal epithelial barrier. Peptide AF-16 produced a concentration-dependent inhibition of the Sat-induced increase in the formation of fluid domes, in the mucosal-to-serosal passage of
d
-[1-
14
C]mannitol, and in the rearrangements in the distribution and protein expression of the tight junction (TJ)-associated proteins ZO-1 and occludin in cultured human enterocyte-like Caco-2/TC7 cell monolayers. In addition, we show that peptide AF-16 also inhibits the cholera toxin-induced increase of transcellular passage and the
Clostridium difficile
toxin-induced effects on paracellular permeability and TJ protein organization in Caco-2/TC7 cell monolayers. Treatment of cell monolayers by the lipid raft disorganizer methyl-β-cyclodextrin abolished the inhibitory activity of peptide AF-16 at the transcellular passage level and did not modify the effect of the peptide at the paracellular level.
Enterohemorrhagic Escherichia coli Colonization of Human Colonic Epithelium
In Vitro
and
Ex Vivo
Authors: Lewis Steven B. , Cook Vivienne , Tighe Richard , Schüller Stephanie
Published: December 2014

Enterohemorrhagic
Escherichia coli
(EHEC) is an important foodborne pathogen causing gastroenteritis and more severe complications, such as hemorrhagic colitis and hemolytic uremic syndrome. Pathology is most pronounced in the colon, but to date there is no direct clinical evidence showing EHEC binding to the colonic epithelium in patients. In this study, we investigated EHEC adherence to the human colon by using
in vitro
organ culture (IVOC) of colonic biopsy samples and polarized T84 colon carcinoma cells. We show for the first time that EHEC colonizes human colonic biopsy samples by forming typical attaching and effacing (A/E) lesions which are dependent on EHEC type III secretion (T3S) and binding of the outer membrane protein intimin to the translocated intimin receptor (Tir). A/E lesion formation was dependent on oxygen levels and suppressed under oxygen-rich culture conditions routinely used for IVOC. In contrast, EHEC adherence to polarized T84 cells occurred independently of T3S and intimin and did not involve Tir translocation into the host cell membrane. Colonization of neither biopsy samples nor T84 cells was significantly affected by expression of Shiga toxins. Our study suggests that EHEC colonizes and forms stable A/E lesions on the human colon, which are likely to contribute to intestinal pathology during infection. Furthermore, care needs to be taken when using cell culture models, as they might not reflect the
in vivo
situation.
Activation of the σ
E
-Dependent Stress Pathway by Conjugative TraR May Anticipate Conjugational Stress
Authors: Grace Elicia D. , Gopalkrishnan Saumya , Girard Mary E. , Blankschien Matthew D. , Ross Wilma , Gourse Richard L. , Herman Christophe
Published: December 2014

Horizontal gene transfer by conjugation plays a major role in bacterial evolution, allowing the acquisition of new traits, such as virulence and resistance to antibacterial agents. With the increased antibiotic resistance in bacterial pathogens, a better understanding of how bacteria modulate conjugation under changing environments and the genetic factors involved is needed. Despite the evolutionary advantages conjugation may confer, the process can be quite stressful for the donor cell. Here, we characterize the ability of TraR, encoded on the episomal F′ plasmid, to upregulate the σ
E
extracytoplasmic stress pathway in
Escherichia coli
. TraR, a DksA homolog, modulates transcription initiation through the secondary channel of RNA polymerase. We show here that TraR activates transcription directly; however, unlike DksA, it does so without using ppGpp as a cofactor. TraR expression can stimulate the σ
E
extracytoplasmic stress response independently of the DegS/RseA signal transduction cascade. In the absence of TraR, bacteria carrying conjugative plasmids become more susceptible to external stress. We propose that TraR increases the concentrations of periplasmic chaperones and proteases by directly activating the transcription of σ
E
-dependent promoters; this increased protein folding capacity may prepare the bacterium to endure the periplasmic stress of sex pilus biosynthesis during mating.
Transcriptional Regulation of the Vanillate Utilization Genes (
vanABK
Operon) of Corynebacterium glutamicum by VanR, a PadR-Like Repressor
Authors: Morabbi Heravi Kambiz , Lange Julian , Watzlawick Hildegard , Kalinowski Jörn , Altenbuchner Josef
Published: December 2014

Corynebacterium glutamicum
is able to utilize vanillate, the product of lignin degradation, as the sole carbon source. The vanillate utilization components are encoded by the
vanABK
operon. The
vanA
and
vanB
genes encode the subunits of vanillate
O
-demethylase, converting vanillate to protocatechuate, while VanK is the specific vanillate transporter. The
vanABK
operon is regulated by a PadR-type repressor, VanR. Heterologous gene expression and variations of the
vanR
open reading frame revealed that the functional VanR contains 192 residues (21 kDa) and forms a dimer, as analyzed by size exclusion chromatography.
In vivo
, ferulate, vanillin, and vanillate induced P

vanABK

in
C. glutamicum
, while only vanillate induced the activity of P

vanABK

in
Escherichia coli
lacking the ferulate catabolic system. Differential scanning fluorimetry verified that vanillate is the only effector of VanR. Interaction between the P

vanABK

DNA fragment and the VanR protein had an equilibrium dissociation constant (

K
D

) of 15.1 ± 1.7 nM. The VanR-DNA complex had a dissociation rate constant (

K
d

) of (267 ± 23) × 10
−6
s
−1
, with a half-life of 43.5 ± 3.6 min. DNase I footprinting localized the VanR binding site at P

vanABK

, extending from +9 to +45 on the coding strand. Deletion of the nucleotides +18 to +27 inside the VanR binding site rendered P

vanABK

constitutive. Fusion of the T7 promoter and the wild-type VanR operator, as well as its shortened versions, indicated that the inverted repeat AACTAACTAA(N
4
)TTAGGTATTT is the specific VanR binding site. It is proposed that the VanR-DNA complex contains two VanR dimers at the VanR operator.