bluuebunny/crossref_metadata_2025 huggingface dataset:
FROM SMILE ASYMPTOTICS TO MARKET RISK MEASURES
Authors: Sircar Ronnie , Sturm Stephan
Published: November 2012

The left tail of the implied volatility skew, coming from quotes on out‐of‐the‐money put options, can be thought to reflect the market's assessment of the risk of a huge drop in stock prices. We analyze how this market information can be integrated into the theoretical framework of convex monetary measures of risk. In particular, we make use of indifference pricing by dynamic convex risk measures, which are given as solutions of backward stochastic differential equations, to establish a link between these two approaches to risk measurement. We derive a characterization of the implied volatility in terms of the solution of a nonlinear partial differential equation and provide a small time‐to‐maturity expansion and numerical solutions. This procedure allows to choose convex risk measures in a conveniently parameterized class, distorted entropic dynamic risk measures, which we introduce here, such that the asymptotic volatility skew under indifference pricing can be matched with the market skew. We demonstrate this in a calibration exercise to market implied volatility data.
STATIC FUND SEPARATION OF LONG‐TERM INVESTMENTS
Authors: Guasoni Paolo , Robertson Scott
Published: November 2012

This paper proves a class of static fund separation theorems, valid for investors with a long horizon and constant relative risk aversion, and with stochastic investment opportunities. An optimal portfolio decomposes as a constant mix of a few preference‐free funds, which are common to all investors. The weight in each fund is a constant that may depend on an investor's risk aversion, but not on the state variable, which changes over time. Vice versa, the composition of each fund may depend on the state, but not on the risk aversion, since a fund appears in the portfolios of different investors. We prove these results for two classes of models with a single state variable, and several assets with constant correlations with the state. In the linear class, the state is an Ornstein–Uhlenbeck process, risk premia are affine in the state, while volatilities and the interest rate are constant. In the square root class, the state follows a square root diffusion, expected returns and the interest rate are affine in the state, while volatilities are linear in the square root of the state.
Cytoprotective Signaling and Gene Expression in Endothelial Cells and Macrophages—Lessons for Atherosclerosis
Authors: Haskard Dorian O. , Boyle Joseph J. , Evans Paul C. , Mason Justin. C. , Randi Anna M.
Published: November 2012

Atherosclerosis is a chronic inflammatory disease of the medium and large arteries driven in large part by the accumulation of oxidized low‐density lipoproteins and other debris at sites rendered susceptible because of the geometry of the arterial tree. As lesions develop, they acquire a pathologic microcirculation that perpetuates lesion progression, both by providing a means for further monocyte and T‐lymphocyte recruitment into the arterial wall and by the physical and chemical stresses caused by micro‐hemorrhage. This review summarizes work performed in our department investigating the roles of signaling pathways, alone and in combination, that lead to specific programs of gene expression in the atherosclerotic environment. Focusing particularly on cytoprotective responses that might be enhanced therapeutically, the work has encompassed the anti‐inflammatory effects of arterial laminar shear stress, mechanisms of induction of membrane inhibitors that prevent complement‐mediated injury, homeostatic macrophage responses to hemorrhage, and the transcriptional mechanisms that control the stability, survival, and quiescence of endothelial monolayers. Lastly, while the field has been dominated by investigation into the mechanisms of DNA transcription, we consider the importance of parallel post‐transcriptional regulatory mechanisms for fine‐tuning functional gene expression repertoires.
The recurrence of malignant pleural mesothelioma 14 years after extrapleural pneumonectomy: Possible histological transformation
Authors: Kinoshita Tomonari , Ishii Genichiro , Matsumura Yuki , Shiozawa Toshihiro , Aokage Keiju , Hishida Tomoyuki , Yoshida Junji , Nagai Kanji
Published: November 2012

A 56‐year‐old man underwent extrapleural pneumonectomy for malignant pleural mesothelioma (MPM). The histological diagnosis was epithelioid mesothelioma with T2N0M0, and no sarcomatoid component was observed. Subsequently, 14 years after complete resection, screening computed tomography detected a rapidly growing right thoracic mass, which was diagnosed as a recurrence of MPM on resection. However, it was composed of both epithelioid (50%) and sarcomatoid (50%) components, suggesting possible histological transformation. Although there have been some previous reports on the recurrence of MPM, to the best of our knowledge, this is the first clinical case which indicated that histological transformation of MPM might occur.
Redox status‐mediated regulation of gene expression and virulence in the brown rot pathogen Monilinia fructicola
Authors: Chiu C.‐M. , You B.‐J. , Chou C.‐M. , Yu P.‐L. , Yu F.‐Y. , Pan S.‐M. , Bostock R. M. , Chung K.‐R. , Lee M.‐H.
Published: November 2012

The MfCUT1 gene encoding the major cutinase of Monilinia fructicola, a causal agent of blossom blight and fruit rot of stone fruits, is a virulence factor of the pathogen. The pathogen remains quiescent on stage II fruit, which contain high levels of chlorogenic acid, a quinate ester of caffeic acid (CA). A medium shift system was established to show that MfCUT1 expression is down‐regulated by CA, consistent with previous findings in continuous culture, and by the antioxidants glutathione (GSH), N‐acetyl‐l‐cysteine and ascorbic acid. However, MfCUT1 expression is up‐regulated by the superoxide‐generating oxidant menadione and by the GSH synthesis inhibitor buthionine sulphoximine (BSO). The changes in MfCUT1 transcript levels induced by CA or BSO are related to the levels of intracellular GSH and H2O2. In addition, GSH reductase activity was increased by CA. Monilinia fructicola genes encoding enzymes that may contribute to redox homeostasis (GSH reductase and GSH peroxidase) were cloned and their expression was found to be slightly affected following exposure of cultures to CA. The hybrid tea rose cv. Flaming Peace was identified as an alternative host to complement pathogenicity assays of M. fructicola on stone fruits, which are seasonally restricted. Pathogenicity assays on detached peach fruit and rose petals revealed that CA suppresses and H2O2 enhances formation of brown rot lesions. The results indicate that changes in cellular redox status impact MfCUT1 expression and virulence in M. fructicola, and suggest that redox cycling of GSH is related to this regulation.
Biochemical responses to ultraviolet‐C radiation and methyl jasmonate in Pinus radiata seedlings that accompany induced resistance to Diplodia pinea
Authors: Reglinski T. , Taylor J. T. , Ah Chee A. , Northcott G. , Spiers M.
Published: November 2012

Irradiation of Pinus radiata seedlings with ultraviolet‐C (UV‐C) radiation or spray application of methyl jasmonate (MeJA) each resulted in induced resistance to subsequent wound inoculation with Diplodia pinea. Induced resistance was expressed by lower incidence of disease and by reduced size of stem lesions than in untreated seedlings. UV‐C was more effective than MeJA and the induced resistance was greatest in seedlings that were irradiated with UV‐C for 60 min, 1 week before pathogen inoculation. Induced resistance in the UV‐C treated stems was concomitant with increases in peroxidase (POX) and polyphenol oxidase (PPO) activity but showed no correlation with concentrations of α‐pinene and β‐pinene or total phenolics. Furthermore, POX induction in stem tissue was cumulative and was greatest after three repeat treatments with UV‐C at 6, 3 and 1 week before inoculation. In contrast to UV‐C, MeJA induced a significant increase in β‐pinene concentration in stem tissue but did not affect PPO activity. POX activity was induced by MeJA in stems, although to a lesser extent than by UV‐C, but was not affected in needles. This appears to be the first report demonstrating the use of UV‐C radiation to induce resistance to fungal infection in a coniferous species. The implications of the underlying differences between UV‐C‐ and MeJA‐mediated resistance to D. pinea are discussed.
Pretend play, deferred imitation and parent‐child interaction in speaking and non‐speaking children with autism
Authors: STRID KARIN , HEIMANN MIKAEL , TJUS TOMAS
Published: November 2012

Strid, K., Heimann, M. & Tjus T. (2013). Pretend play, deferred imitation and parent‐child interaction in speaking and non‐speaking children with autism. Scandinavian Journal of Psychology 54, 26–32.

This study investigates spontaneous pretend play during a parent‐child free play observation, and deferred imitation observed in an experimental setting in speaking and non‐speaking children with autism in comparison to children with typical development. Both groups of children with autism showed a reduced level of deferred imitation compared to the typically developing group, but only the non‐speaking children with autism spent significantly less time in pretend play compared to children with typical development. Deferred imitation was related to parents’ verbal interaction in both groups. An analysis of the parent‐child interaction revealed that parents of children with autism used less synchronized comments compared to parents of typically developing children. Parents of the speaking group with autism used more synchronized than unsynchronized comments, while parents of the non‐speaking group used the same amount of synchronized and unsynchronized comments. These findings are discussed in terms of how the developmental level affects behavior and interaction in autism.
Goals influence memory and imitation for dynamic human action in 36‐month‐old children
Authors: LOUCKS JEFF , MELTZOFF ANDREW N.
Published: November 2012

Loucks, J. & Meltoff, A. N. (2013). Goals influence memory and imitation for dynamic human action in 36‐month‐old children.Scandinavian Journal of Psychology54, 41–50.

Adults’ memory for action is organized according to a hierarchy of goals. Little previous research has examined whether goals also play a crucial role in young children’s memory for action, and particularly whether goal information is privileged over veridical sequential order information. The current experiment investigated 3‐year‐old children’s (N = 40) memory for naturally occurring interleaved action sequences: Sequences in which an actor switched back and forth between carrying out actions related to two distinct goals. Such sequences allowed a test of whether children’s action representations prioritize a goal interpretation over veridical sequential information. Children’s memory for the action events was assessed by deferred imitation, 5‐min after the demonstration had ceased. Results indicated that children’s memory prioritizes goals over veridical sequential order – even to the extent that the actual sequential order is distorted in memory. These findings deepen our understanding of action processing and memory with implications for social‐cognitive development.
Visual processing speed in old age
Authors: HABEKOST THOMAS , VOGEL ASMUS , ROSTRUP EGILL , BUNDESEN CLAUS , KYLLINGSBÆK SØREN , GARDE ELLEN , RYBERG CHARLOTTE , WALDEMAR GUNHILD
Published: November 2012

Mental speed is a common concept in theories of cognitive aging, but it is difficult to get measures of the speed of a particular psychological process that are not confounded by the speed of other processes. We used Bundesen’s (1990) Theory of Visual Attention (TVA) to obtain specific estimates of processing speed in the visual system controlled for the influence of response latency and individual variations of the perception threshold. A total of 33 non‐demented old people (69–87 years) were tested for the ability to recognize briefly presented letters. Performance was analyzed by the TVA model. Visual processing speed decreased approximately linearly with age and was on average halved from 70 to 85 years. Less dramatic aging effects were found for the perception threshold and the visual apprehension span. In the visual domain, cognitive aging seems to be most clearly related to reductions in processing speed.
Middle cerebral artery blood velocity during running
Authors: Lyngeraa T. S. , Pedersen L. M. , Mantoni T. , Belhage B. , Rasmussen L. S. , van Lieshout J. J. , Pott F. C.
Published: November 2012

Running induces characteristic fluctuations in blood pressure (BP) of unknown consequence for organ blood flow. We hypothesized that running‐induced BP oscillations are transferred to the cerebral vasculature. In 15 healthy volunteers, transcranial Doppler‐determined middle cerebral artery (MCA) blood flow velocity, photoplethysmographic finger BP, and step frequency were measured continuously during three consecutive 5‐min intervals of treadmill running at increasing running intensities. Data were analysed in the time and frequency domains. BP data for seven subjects and MCA velocity data for eight subjects, respectively, were excluded from analysis because of insufficient signal quality. Running increased mean arterial pressure and mean MCA velocity and induced rhythmic oscillations in BP and in MCA velocity corresponding to the difference between step rate and heart rate (HR) frequencies. During running, rhythmic oscillations in arterial BP induced by interference between HR and step frequency impact on cerebral blood velocity. For the exercise as a whole, average MCA velocity becomes elevated. These results suggest that running not only induces an increase in regional cerebral blood flow but also challenges cerebral autoregulation.
Fecal microbiota transplantation for fulminant Clostridium difficile infection in an allogeneic stem cell transplant patient
Authors: Neemann K. , Eichele D.D. , Smith P.W. , Bociek R. , Akhtari M. , Freifeld A.
Published: November 2012

We present a case of severe Clostridium difficile infection (CDI) in a non‐neutropenic allogeneic hematopoietic stem cell transplant recipient who was treated successfully with fecal microbiota therapy after standard pharmacologic therapy had failed. Following naso‐jejunal instillation of donor stool, the patient's symptoms resolved within 48 h. Bowel resection was averted. This is the first case in the literature, to our knowledge, to describe fecal microbiota therapy in a profoundly immunocompromised host with severe CDI. We propose that fecal microbiota therapy be considered as a therapeutic option in immunosuppressed patients with refractory severe CDI.
Conjugate vaccine introduction in the African meningitis belt: meeting surveillance objectives
Authors: Mueller Judith E.
Published: November 2012

The epidemiology of bacterial meningitis will change with introduction of meningococcal and pneumococcal conjugate vaccines in the African meningitis belt. The principal objectives of surveillance are to evaluate the impact of vaccination, to detect and investigate epidemics and provide material for research. The capacity of existing surveillance activities in the meningitis belt to meet these objectives varies due to infrastructural and financial constraints. Impact assessment of conjugate vaccine against meningococcal serogroup A will be limited to comparing incidence trends from a few surveillance sites with data obtained before vaccine introduction and to comparing trends in the incidence of suspected cases or localised epidemics in most other settings. The timeliness of detection of epidemics and identification of epidemic meningococcal serogroups could be improved in most countries by analysing suspected case data in health centre level resolution and by investigating outbreaks with mobile teams. For research and impact assessment of pneumococcal conjugate vaccines, several surveillance sites covering at least 0.5 million inhabitants should be maintained which undertake exhaustive case finding and systematic laboratory confirmation of meningitis and pneumonia. Molecular diagnostics will facilitate surveillance in remote areas, but the available techniques should be evaluated for diagnostic performance in the field and long‐term sustainability.
High‐resolution positron emission tomography/computed tomography imaging of the mouse heart
Authors: Greco Adelaide , Fiumara Giovanni , Gargiulo Sara , Gramanzini Matteo , Brunetti Arturo , Cuocolo Alberto
Published: November 2012

New Findings

What is the topic of this review?

To discuss the mouse models of myocardial ischaemia and infarction and the applications of dedicated hybrid positron emission tomography (PET)/computed tomography (CT) systems technology for small laboratory animals, including radiotracers and image postprocessing.

What advances does it highlight?

In a mouse model of coronary occlusion, non‐invasive measurement of infarct size with high‐resolution PET/CT systems has excellent reproducibility and high accuracy, supporting the use of this non‐invasive methodology in longitudinal studies to monitor cardiac biochemical parameters and to assess the effect of different interventions after acute myocardial ischaemia.

Different animal models have been used to reproduce coronary heart disease, but in recent years mice have become the animals of choice, because of their short life cycle and the possibility of genetic manipulation. Various techniques are currently used for cardiovascular imaging in mice, including high‐resolution ultrasound, X‐ray computed tomography (CT), magnetic resonance imaging and nuclear medicine procedures. In particular, molecular imaging with cardiac positron emission tomography (PET) allows non‐invasive evaluation of changes in myocardial perfusion, metabolism, apoptosis, inflammation and gene expression or measurement of changes in left ventricular functional parameters. With technological advances, dedicated small laboratory PET/CT imaging has emerged in cardiovascular research, providing in vivo a non‐invasive, serial and quantitative assessment of left ventricular function, myocardial perfusion and metabolism at a molecular level. This non‐invasive methodology might be useful in longitudinal studies to monitor cardiac biochemical parameters and might facilitate studies to assess the effect of different interventions after acute myocardial ischaemia.
The Effects of Ribs and Tip Wall Distance on Heat Transfer for a Varying Aspect Ratio Two-Pass Ribbed Internal Cooling Channel
Authors: Jenkins Sean C. , Zehnder Frank , Shevchuk Igor V. , von Wolfersdorf Jens , Weigand Bernhard , Schnieder Martin
Published: November 2012

Internal cooling channels with differing aspect ratios are typically found in gas turbine blades due to the varying thickness of the blade from the leading to trailing edge. These serpentine passages often contain several 180 deg bends, which are sharp edged in the region of the blade tip. The 180 deg bend has a pronounced effect on the heat transfer characteristics in the outlet channel and tip wall, where a strong influence is seen due to the divider wall-to-tip wall distance in the bend. The present study investigates the effect of the divider wall-to-tip wall distance for a ribbed two-pass cooling channel with a 2:1 inlet and 1:1 outlet channel. Spatially resolved heat transfer measurements were made using the transient thermochromic liquid crystal technique for a smooth and a ribbed configuration using parallel 45 deg ribs. Effects of the 180 deg bend on heat transfer and rib-induced enhancements were identified separately and bend effects were found to dominate the heat transfer increase in the outlet channel near the bend. Pressure losses due to the bend and ribs were also independently evaluated for a range of tip wall distances. Results show that the smaller tip wall distances increase heat transfer on the tip wall and outlet channel but at the cost of an increased pressure loss. An optimum tip wall position is suggested, forming a compromise between heat transfer improvement and increased pressure losses.
Study of Unforced and Modulated Film-Cooling Jets Using Proper Orthogonal Decomposition—Part II: Forced Jets
Authors: Bidan Guillaume , Vézier Clementine , Nikitopoulos Dimitris E.
Published: November 2012

The effects of jet flow-rate modulation were investigated in the case of a 35 deg inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records, and large eddy simulations (LES). In forced experiments, average blowing ratios of 0.3 and 0.4 were investigated with a duty cycle of 50% and pulsing frequencies of St = 0.016 and 0.159. Time-resolved flow rate measurements during the experiments provided precise knowledge of the instantaneous jet blowing ratio and adequate inlet boundary conditions for large eddy simulations. The dynamics of the vortical structures generated during the transient parts of the forcing cycle as well as their impact on film cooling performance were investigated with respect of the forcing parameters. At the considered blowing ratios, a starting ring vortex was consistently generated at the transition from low to high blowing ratio. Ingestion of cross-flow fluid at the transition from high to low blowing ratio was also observed and had a negative impact on film cooling performance. All studied cases exhibited an overall decrease in coverage regardless of pulsing parameters over their corresponding steady jet cases at fixed mass flow rate. Comparisons between pulsed and steady jets at constant pressure supply (same high blowing ratio) did exhibit some film-cooling improvement with pulsing. 3D Proper orthogonal decomposition was performed on LES results at distinct forcing frequencies to provide an analysis of dominant modes in the velocity and temperature fields. Significantly different results were obtained depending on the forcing frequency.
Stability Improvement of High-Pressure-Ratio Turbocharger Centrifugal Compressor by Asymmetric Flow Control—Part I: Non-Axisymmetrical Flow in Centrifugal Compressor
Authors: Yang Mingyang , Zheng Xinqian , Zhang Yangjun , Bamba Takahiro , Tamaki Hideaki , Huenteler Joern , Li Zhigang
Published: November 2012

This is Part I of a two-part paper documenting the development of a novel asymmetric flow control method to improve the stability of a high-pressure-ratio turbocharger centrifugal compressor. Part I focuses on the nonaxisymmetrical flow in a centrifugal compressor induced by the nonaxisymmetrical geometry of the volute while Part II describes the development of an asymmetric flow control method to avoid the stall on the basis of the characteristic of nonaxisymmetrical flow. To understand the asymmetries, experimental measurements and corresponding numerical simulation were carried out. The static pressure was measured by probes at different circumferential and stream-wise positions to gain insights about the asymmetries. The experimental results show that there is an evident nonaxisymmetrical flow pattern throughout the compressor due to the asymmetric geometry of the overhung volute. The static pressure field in the diffuser is distorted at approximately 90 deg in the rotational direction of the volute tongue throughout the diffuser. The magnitude of this distortion slightly varies with the rotational speed. The magnitude of the static pressure distortion in the impeller is a function of the rotational speed. There is a significant phase shift between the static pressure distributions at the leading edge of the splitter blades and the impeller outlet. The numerical steady state simulation neglects the aforementioned unsteady effects found in the experiments and cannot predict the phase shift, however, a detailed asymmetric flow field structure is obviously obtained.
Validation of Numerical Simulation for Rotating Stall in a Transonic Fan
Authors: Choi Minsuk , Smith Nigel H. S. , Vahdati Mehdi
Published: November 2012

This paper addresses a comparison of numerical stall simulations with experimental data at 60% (subsonic) and 95% (supersonic) of the design speed in a modern transonic fan rig. The unsteady static pressures were obtained with high frequency Kulite transducers mounted on the casing upstream and downstream of the fan. The casing pressure variation was clearly visible in the measurements when a stall cell passed below the transducers. Numerical stall simulations were conducted using an implicit, time-accurate, 3D compressible Reynolds-averaged Navier-Stokes (RANS) solver. The comparisons between the experiment and simulation mainly cover performance curves and time-domain pressure traces of Kulites during rotating stall. At two different fan speeds, the stall characteristics such as the number and rotating speed of the stall cells were well-matched to the experimental values. The mass flow rate and the loading parameter under the fully-developed rotating stall also showed good agreement with the experiment. In both the numerical and experimental results, a large stall cell was eventually formed after stall inception regardless of the fan speed. Based on the validation, the detailed flow has been evaluated to understand rotating stall in a transonic fan. In addition, it was found that the mass flow measurement using casing static pressure might be wrong during transient flow if the Kulites were mounted too close to the fan blade.
Three-Dimensional RANS Prediction of Gas-Side Heat Transfer Coefficients on Turbine Blade and Endwall
Authors: Luo Jiang , Razinsky Eli H. , Moon Hee-Koo
Published: November 2012

This paper presents a study using 3D computational fluid dynamics (CFD) based on Reynolds-averaged Navier-Stokes (RANS) equations to predict turbine gas-side heat transfer coefficients (HTC) on the entire airfoil and endwall. The CFD results at different spanwise sections and endwall have been compared with the flat-plate turbulent boundary layer correlation and with the data in a NASA turbine rotor passage with strong secondary flows, under three different flow conditions. The enhancement effects of secondary flow vortices on the blade surface and endwall heat transfer rate have been examined in detail. Analyses were conducted for the impact of Reynolds number and exit Mach number on heat transfer. The SST, k-ɛ, V2F, and realizable k-ɛ turbulence models have been assessed. The classical log-law wall-functions have been found to be comparable to the wall-integration methods but with much reduced sensitivity to inlet turbulence conditions. The migration of hot gas was simulated with a radial profile of inlet temperature. CFD results for mid-span HTCs of two other airfoils were also compared with test data. Overall, results are encouraging and indicate improved HTC and temperature predictions from 3D CFD could help optimize the design of turbine cooling schemes.
Robust Analysis of Design in Vibration of Turbomachines
Authors: Mbaye Moustapha , Soize Christian , Ousty Jean-Philippe , Capiez-Lernout Evangeline
Published: November 2012

In the context of turbomachinery design, a small variation in the blade characteristics due to manufacturing tolerances can affect the structural symmetry creating mistuning which increases the forced response. However, it is possible to detune the mistuned system in order to reduce the forced response amplification. The main technological methods to introduce detuning are based on modifying either the blade material properties, either the interface between blades and disk, or the blade shapes. This paper presents a robustness analysis of mistuning for a given detuning in blade geometry. Detuning is performed by modifying blade shapes. The different types of blades, obtained by those modifications, are then distributed on the disk circumference. A new reduced-order model of the detuned disk is introduced. It is based on the use of the cyclic modes of the different sectors which can be obtained from a usual cyclic symmetry modal analysis. Finally, the robustness of the computational model responses with respect to uncertainties, is performed with a stochastic analysis using a nonparametric probabilistic approach of uncertainties which allows both the system-parameter uncertainties and the modeling errors to be taken into account.
Three-Dimensional Simulation of Cross-Flow Microfilter Fouling in Tortuous Pore Profiles With Semisynthetic Metalworking Fluids
Authors: Yu Bingyi , Kapoor Shiv G. , DeVor Richard E.
Published: November 2012

Fouling mechanisms and models for flux decline are investigated with a three-dimensional simulation of the tortuous, verisimilar geometry of an α-alumina microfilter. Reconstruction of the three-dimensional geometry was accomplished from two-dimensional cross-sectional cuts. A wall collision model and a particle trapping model are developed for the investigation of fouling mechanisms. The reconstructed geometry and the two models were used in computational fluid dynamics to simulate metalworking colloidal particles travelling through and becoming trapped in the tortuous pore paths of a microfilter. Results reveal sharp flux decline initiating from partial pore blocking and subdued flux decline transitioning to cake layer development with steady-state flow. This flow behavior is in agreement with experimental data from earlier studies. The inclusion of the wall collision model and particle trapping model enabled the revelation of cake layer development as a fouling mechanism. Additional simulations of microfilters at different particle size distributions were conducted and discussed.
Discrete-Time Prediction of Chatter Stability, Cutting Forces, and Surface Location Errors in Flexible Milling Systems
Authors: Eksioglu C. , Kilic Z. M. , Altintas Y.
Published: November 2012

This paper presents a discrete-time modeling of dynamic milling systems. End mills with arbitrary geometry are divided into differential elements along the cutter axis. Variable pitch and helix angles, as well as run-outs can be assigned to cutting edges. The structural dynamics of the slender end mills and thin-walled parts are also considered at each differential element at the tool-part contact zone. The cutting forces include static chip removal, ploughing, regenerative vibrations, and process damping components. The dynamic milling system is modeled by a matrix of delay differential equations with periodic coefficients, and solved with an improved semidiscrete-time domain method in modal space. The chatter stability of the system is predicted by checking the eigenvalues of the time-dependent transition matrix which covers the tooth period for regular or spindle periods for variable pitch cutters, respectively. The same equation is also used to predict the process states such as cutting forces, vibrations, and dimensional surface errors at discrete-time domain intervals analytically. The proposed model is experimentally validated in down milling of a workpiece with 5% radial immersion and 30 mm axial depth of cut with a four fluted helical end mill.
Rotary Ultrasonic Machining of Alumina Dental Ceramics: A Preliminary Experimental Study on Surface and Subsurface Damages
Authors: Ahmed Yasser , Cong W. L. , Stanco Matthew R. , Xu Z. G. , Pei Z. J. , Treadwell C. , Zhu Y. L. , Li Z. C.
Published: November 2012

This paper presents a preliminary study about effects of ultrasonic vibration on machined surface and subsurface damages in rotary ultrasonic machining (RUM). The surface and subsurface damages are compared for machining of dental ceramics (Al2O3) with and without ultrasonic vibration. The surface chippings are evaluated and the subsurface cracks are observed under scanning electron microscope (SEM).
Self-Expanding Stent and Delivery System for Aortic Valve Replacement
Authors: Mazilu Dumitru , Li Ming , Kocaturk Ozgur , Horvath Keith A.
Published: November 2012

Currently, aortic valve replacement procedures require a sternotomy and use of cardiopulmonary bypass (CPB) to arrest the heart and provide a bloodless field in which to operate. A less invasive alternative to open heart surgery is transapical or transcatheter aortic valve replacement (TAVR), already emerging as a feasible treatment for patients with high surgical risk. The bioprosthetic valves are delivered via catheters using transarterial or transapical approaches and are implanted within diseased aortic valves. This paper reports the development of a new self-expanding stent for minimally invasive aortic valve replacement and its delivery device for the transapical approach under real-time magnetic resonance imaging (MRI) guidance. Made of nitinol, the new stent is designed to implant and embed a commercially available bioprosthetic aortic valve in aortic root. An MRI passive marker was affixed onto the stent and an MRI active marker to the delivery device. These capabilities were tested in ex vivo and in vivo experiments. Radial resistive force, chronic outward force, and the integrity of bioprosthesis on stent were measured through custom design dedicated test equipment. In vivo experimental evaluation was done using a porcine large animal model. Both ex vivo and in vivo experiment results indicate that the self-expanding stent provides adequate reinforcement of the bioprosthetic aortic valve and it is easier to implant the valve in the correct position. The orientation and positioning of the implanted valve is more precise and predictable with the help of the passive marker on stent and the active marker on delivery device. The new self-expanding nitinol stent was designed to exert a constant radial force and, therefore, a better fixation of the prosthesis in the aorta, which would result in better preservation of long-term heart function. The passive marker affixed on the stent and active marker embedded in the delivery devices helps to achieve precise orientation and positioning of the stent under MRI guidance. The design allows the stent to be retracted in the delivery device with a snaring catheter if necessary. Histopathology reports reveal that the stent is biocompatible and fully functional. All the stented bioprosthesis appeared to be properly seated in the aortic root.
The Time-Variant Degradation of a Photovoltaic System
Authors: Charki A. , Laronde R. , Bigaud D.
Published: November 2012

This article presents a method developed for carrying out the energy production estimation considering the energy losses in different components of a photovoltaic (PV) system and its downtime effect. The studied system is a grid-connected photovoltaic system including PV modules, wires, and inverter. PV systems are sensitive to environmental conditions (UV radiation, temperature, humidity) and all components are subjected to electrical losses. The proposed method allows obtaining the production of photovoltaic system and its availability during a specified period using meteorological data. The calculation of the production takes into account the downtime periods when no energy is delivered in the grid during this period. The time-to-failure and the time-to-repair of photovoltaic system are considered following a Weibull distribution. This method permits to have a best estimation of the production throughout the lifetime of the photovoltaic system.
Arrays of topographically and peptide-functionalized hydrogels for analysis of biomimetic extracellular matrix properties
Authors: Wilson Michelle J. , Jiang Yaming , Yañez-Soto Bernardo , Liliensiek Sara , Murphy William L. , Nealey Paul F.
Published: November 2012

Epithelial cells reside on specialized extracellular matrices that provide instructive cues to regulate and support cell function. The authors have previously demonstrated that substrate topography with dimensions similar to the native extracellular matrix (submicrometer and nanoscale features) significantly impacts corneal epithelial proliferation and migration. In this work, synthetic hydrogels were modified with both topographic and biochemical cues, where specified peptide ligands were immobilized within nanopatterned hydrogels. The efficient, systematic study of multiple instructive cues (peptide, peptide concentration, topographic dimensions), however, is contingent on the development of higher throughput platforms. Toward this goal, the authors developed a hydrogel array platform to systematically and rapidly evaluate combinations of two different peptide motifs and a range of nanoscale topographic dimensions. Specifically, distinct functional pegylated peptide ligands, RGD (GGGRGDSP) and AG73 (GRKRLQVQLSIRT), were synthesized for incorporation into an inert hydrogel network. Elastomeric stencils with arrays of millimeter-scale regions were used to spatially confine hydrogel precursor solutions on elastomeric stamps with nanoscale patterns generated by soft lithography. The resulting topographically and peptide-functionalized hydrogel arrays were used to characterize single cell migration. Epithelial cell migration speed and persistence were governed by both the biochemical and topographical cues of the underlying substrate.
HfxZr1−xO2 compositional control using co-injection atomic layer deposition
Authors: Consiglio Steven , Tapily Kandabara , Clark Robert D. , Nakamura Genji , Wajda Cory S. , Leusink Gert J.
Published: November 2012

As a replacement for SiO2 based gate dielectrics, HfO2 with an admixture of ZrO2 has the potential to provide a higher dielectric constant than pure HfO2 by means of stabilization of higher-k phases. Accordingly, in this study the authors have pursued a means to control composition of HfxZr1−xO2 films grown by atomic layer deposition by simultaneously flowing Hf and Zr metal precursors during the precursor exposure step and varying the molar flow ratio. Using the tetrakis(ethylmethylamino) Hf and Zr precursors, TEMAH and TEMAZ, with either H2O or O3 co-reactants, the co-injection approach for HfxZr1−xO2 was compared with alternating HfO2 and ZrO2 growth cycles and was observed to allow uniform and tunable composition control. For the co-injection process, deviation from the cycle ratio trendline suggests more efficient chemisorption of TEMAZ compared to TEMAH. The authors have also evaluated these films in metal–oxide–semiconductor capacitor structures and verified the electrical equivalence and similar within-wafer distributions of Hf0.2Zr0.8O2 obtained from both processing schemes.
Comparison of beryllium oxide and pyrolytic graphite crucibles for boron doped silicon epitaxy
Authors: Ali Dyan , Richardson Christopher J. K.
Published: November 2012

This article reports on the comparison of beryllium oxide and pyrolytic graphite as crucible liners in a high-temperature effusion cell used for boron doping in silicon grown by molecular beam epitaxy. Secondary ion mass spectroscopy analysis indicates decomposition of the beryllium oxide liner, leading to significant incorporation of beryllium and oxygen in the grown films. The resulting films are of poor crystal quality with rough surfaces and broad x-ray diffraction peaks. Alternatively, the use of pyrolytic graphite crucible liners results in higher quality films.
Eutectic alloy electrode for rigid and low resistance carbon nanotube contact
Authors: Park Daehyun , Jeon Dongryul
Published: November 2012

The authors propose to use an Au–Al eutectic alloy to form rigid and low resistance contact to carbon nanotubes (CNTs). After depositing CNTs by dielectrophoresis to bridge the two Au/Al electrodes patterned on the SiO2/Si substrate, the authors annealed the substrate in air to induce eutectic melting. As proposed, the CNT contact was able to tolerate the ultrasonic washing for 90 s, and the contact resistance was lowered by a factor of as much as 10. Moreover, such a contact was demonstrated to be mechanically stable as it gave reproducible sensing properties after an ultrasonic washing process and it allowed to build a CNT cross-junction by using standard lithography and an electrophoresis step.
Atomic layer deposition of anatase TiO2 on porous electrodes for dye-sensitized solar cells
Authors: Dirnstorfer Ingo , Mähne Hannes , Mikolajick Thomas , Knaut Martin , Albert Matthias , Dubnack Kristina
Published: November 2012

Thin TiO2 films were grown by atomic layer deposition on planar and porous substrates and characterized by Raman spectroscopy, x-ray diffraction, high resolution transmission electron microscopy, and spectroscopic ellipsometry. The growth conditions of anatase TiO2 are investigated, motivated by the application in dye-sensitized solar cells, where best results are achieved with electrodes based on anatase TiO2. To enforce an anatase TiO2 growth on substrates stimulating rutile growth, a symmetry breaking ultra thin buffer layer of five cycles Al2O3 was introduced. With this buffer layer anatase TiO2 deposition was demonstrated on planar rutile TiO2 substrates. However, it was found that the necessity of the buffer layer depends on the substrate structure. On porous TiO2 electrodes containing a mixture of anatase and rutile TiO2 domains, a direct anatase TiO2 growth was possible even without a buffer layer.
A fully 3D approach for metal artifact reduction in computed tomography
Authors: Kratz Bärbel , Weyers Imke , Buzug Thorsten M.
Published: November 2012

Purpose:

In computed tomography imaging metal objects in the region of interest introduce inconsistencies during data acquisition. Reconstructing these data leads to an image in spatial domain including star‐shaped or stripe‐like artifacts. In order to enhance the quality of the resulting image the influence of the metal objects can be reduced. Here, a metal artifact reduction (MAR) approach is proposed that is based on a recomputation of the inconsistent projection data using a fully three‐dimensional Fourier‐based interpolation. The success of the projection space restoration depends sensitively on a sensible continuation of neighboring structures into the recomputed area. Fortunately, structural information of the entire data is inherently included in the Fourier space of the data. This can be used for a reasonable recomputation of the inconsistent projection data.

Methods:

The key step of the proposed MAR strategy is the recomputation of the inconsistent projection data based on an interpolation using nonequispaced fast Fourier transforms (NFFT). The NFFT interpolation can be applied in arbitrary dimension. The approach overcomes the problem of adequate neighborhood definitions on irregular grids, since this is inherently given through the usage of higher dimensional Fourier transforms. Here, applications up to the third interpolation dimension are presented and validated. Furthermore, prior knowledge may be included by an appropriate damping of the transform during the interpolation step. This MAR method is applicable on each angular view of a detector row, on two‐dimensional projection data as well as on three‐dimensional projection data, e.g., a set of sequential acquisitions at different spatial positions, projection data of a spiral acquisition, or cone‐beam projection data.

Results:

Results of the novel MAR scheme based on one‐, two‐, and three‐dimensional NFFT interpolations are presented. All results are compared in projection data space and spatial domain with the well‐known one‐dimensional linear interpolation strategy.

Conclusions:

In conclusion, it is recommended to include as much spatial information into the recomputation step as possible. This is realized by increasing the dimension of the NFFT. The resulting image quality can be enhanced considerably.
Characterization of lung tumors motion baseline using cone‐beam computed tomography
Authors: Gauthier Jean‐François , Varfalvy Nicolas , Tremblay Daniel , Cyr Marc‐François , Archambault Louis
Published: November 2012

Purpose:

To characterize the interfractional variability in lung tumor volume, position, and tumor boundaries.

Methods:

Cone‐beam computed tomography (CBCT) scans were acquired weekly during the course of treatment for 34 lung cancer patients (1–20 scans) with large tumors. Spatial registration based on bones was performed between contoured planning CT and CBCT. Gross tumor volume (GTV) on each CBCT was then contoured. Tumor volume, centroid, and boundaries variability were quantified. A commercial deformable registration software was tested and results were compared to manual contours.

Results:

Mean volume reduction was 41 ± 32% (p < 0.001) after an average time of 51 days. Tumor centroid drifts were 0.03, 0.14, and −0.13 cm in right–left (RL), anterior–posterior (AP), and superior–inferior (SI) directions with standard deviations of 0.55, 0.50, and 0.51 cm. GTV boundaries displacements were −0.27, −0.14, and −0.16 cm with standard deviations of 0.64, 0.57, and 0.59 cm in RL, AP, and SI directions. Relative error between deformed and manual contours with the commercial deformable registration software rose up exponentially with the GTV decrease.

Conclusions:

GTV size changes for large lung tumors are similar to those for standard tumors. Magnitude absolute values of displacement vector for centroid and boundaries shifts show that there is not a preferred direction for the drifts but shrinkage.
The Imprint of the Extragalactic Background Light in the Gamma-Ray Spectra of Blazars
Authors: Ackermann M. , Ajello M. , Allafort A. , Schady P. , Baldini L. , Ballet J. , Barbiellini G. , Bastieri D. , Bellazzini R. , Blandford R. D. , Bloom E. D. , Borgland A. W. , Bottacini E. , Bouvier A. , Bregeon J. , Brigida M. , Bruel P. , Buehler R. , Buson S. , Caliandro G. A. , Cameron R. A. , Caraveo P. A. , Cavazzuti E. , Cecchi C. , Charles E. , Chaves R. C. G. , Chekhtman A. , Cheung C. C. , Chiang J. , Chiaro G. , Ciprini S. , Claus R. , Cohen-Tanugi J. , Conrad J. , Cutini S. , D’Ammando F. , de Palma F. , Dermer C. D. , Digel S. W. , do Couto e Silva E. , Domínguez A. , Drell P. S. , Drlica-Wagner A. , Favuzzi C. , Fegan S. J. , Focke W. B. , Franckowiak A. , Fukazawa Y. , Funk S. , Fusco P. , Gargano F. , Gasparrini D. , Gehrels N. , Germani S. , Giglietto N. , Giordano F. , Giroletti M. , Glanzman T. , Godfrey G. , Grenier I. A. , Grove J. E. , Guiriec S. , Gustafsson M. , Hadasch D. , Hayashida M. , Hays E. , Jackson M. S. , Jogler T. , Kataoka J. , Knödlseder J. , Kuss M. , Lande J. , Larsson S. , Latronico L. , Longo F. , Loparco F. , Lovellette M. N. , Lubrano P. , Mazziotta M. N. , McEnery J. E. , Mehault J. , Michelson P. F. , Mizuno T. , Monte C. , Monzani M. E. , Morselli A. , Moskalenko I. V. , Murgia S. , Tramacere A. , Nuss E. , Greiner J. , Ohno M. , Ohsugi T. , Omodei N. , Orienti M. , Orlando E. , Ormes J. F. , Paneque D. , Perkins J. S. , Pesce-Rollins M. , Piron F. , Pivato G. , Porter T. A. , Rainò S. , Rando R. , Razzano M. , Razzaque S. , Reimer A. , Reimer O. , Reyes L. C. , Ritz S. , Rau A. , Romoli C. , Roth M. , Sánchez-Conde M. , Sanchez D. A. , Scargle J. D. , Sgrò C. , Siskind E. J. , Spandre G. , Spinelli P. , Stawarz Łukasz , Suson D. J. , Takahashi H. , Tanaka T. , Thayer J. G. , Thompson D. J. , Tibaldo L. , Tinivella M. , Torres D. F. , Tosti G. , Troja E. , Usher T. L. , Vandenbroucke J. , Vasileiou V. , Vianello G. , Vitale V. , Waite A. P. , Winer B. L. , Wood K. S. , Wood M.
Published: November 2012

Glow from the Past

Extragalactic background light (EBL) is the integrated radiation from all extragalactic sources in the universe. Foreground emission from our solar system and galaxy makes direct detection of the EBL very difficult. However, it is possible to measure EBL from gamma-ray spectra of distant sources, because gamma-ray photons from these sources interact with the EBL.

Ackermann
et al.

(p.
1190
, published online 1 November; see the Perspective by

Bromm

) report a measurement of the EBL based on an attenuation feature seen in the combined spectra of distant active galaxies detected by the Fermi Gamma-Ray Space Telescope. The result puts constraints on the cosmic history of star formation.