bluuebunny/crossref_metadata_2025 huggingface dataset:
Constitutive changes in pigment concentrations: implications for estimating isoprene emissions using the photochemical reflectance index
Authors: Harris Angela , Owen Susan Margaret , Sleep Darren , Pereira Maria da Glória dos Santos
Published: August 2015

The photochemical reflectance index (PRI), through its relationship with light use efficiency (LUE) and xanthophyll cycle activity, has recently been shown to hold potential for tracking isoprene emissions from vegetation. However, both PRI and isoprene emissions can also be influenced by changes in carotenoid pigment concentrations. Xanthophyll cycle activity and changes in carotenoid concentrations operate over different timescales, but the importance of constitutive changes in pigment concentrations for accurately estimating isoprene emissions using PRI is unknown. To clarify the physiological mechanisms behind the PRI–isoprene relationship, the light environment of potted Salix viminalis (osier willow) trees was modified to induce acclimation in photosynthetic rates, phytopigments, isoprene emissions and PRI. Acclimation resulted in differences in pigment concentrations, isoprene emissions and PRI. Constitutive changes in carotenoid concentration were significantly correlated with both isoprene emissions and PRI, suggesting that the relationship between PRI and isoprene emissions is significantly influenced by constitutive pigment changes. Consequently knowledge regarding how isoprene emissions are affected by both longer term changes in total carotenoid concentrations and shorter term dynamic adjustments of LUE is required to facilitate interpretation of PRI for monitoring isoprene emissions.
Performance Management Routines That Work? An Early Assessment of the GPRA Modernization Act
Authors: Moynihan Donald P. , Kroll Alexander
Published: August 2015

The Government Performance and Results Act (GPRA) of 1993 provided a well‐studied framework for U.S. federal performance management initiatives. In the aftermath of the update of GPRA in 2010 with the GPRA Modernization Act, the authors offer the first systematic scholarly assessment of the new legislation. Managerial use of performance data was an explicit goal of the Modernization Act, an objective that eluded prior federal reforms. The Modernization Act established a new series of performance routines to encourage performance information use. The analysis shows that as federal managers experience those routines, they are more likely to report using performance data to make decisions. Specifically, routines centered on the pursuit of cross‐agency priority goals, the prioritization of a small number of agency goals, and data‐driven reviews are all associated with higher rates of performance information use. The authors also find that managers in better‐run data‐driven reviews report greater use of performance data.
Production goes global, compliance stays local: Private regulation in the global electronics industry
Authors: Distelhorst Greg , Locke Richard M. , Pal Timea , Samel Hiram
Published: August 2015

Poor working conditions in global supply chains have led to private initiatives that seek to regulate labor practices in developing countries. But how effective are these regulatory programs? We investigate the effects of transnational private regulation by studying Hewlett‐Packard's (HP) supplier responsibility program. Using analysis of factory audits, interviews with buyer and supplier management, and field research at production facilities across seven countries, we find that national context – not repeated audits, capability building, or supply chain power – is the key predictor of workplace compliance. Quantitative analysis shows that factories in China are markedly less compliant than those in countries with stronger civil society and regulatory institutions. Comparative field research then illustrates how these local institutions complement transnational private regulation. Although these findings imply limits to private regulation in institutionally poor settings, they also highlight opportunities for productive linkages between transnational actors and local state and society.
Temsirolimus targets multiple hallmarks of cancer to impede mesothelioma growth in vivo
Authors: Vazakidou Maria Eleni , Magkouta Sophia , Moschos Charalampos , Psallidas Ioannis , Pappas Apostolos , Psarra Katherina , Kalomenidis Ioannis
Published: August 2015

Background and objective

The mechanistic target of rapamycin (mTOR) promotes cancer cell proliferation and survival, transduces pro‐angiogenic signals and regulates immune cell differentiation and function. We hypothesized that temsirolimus, an mTOR inhibitor, would curtail experimental mesothelioma progression in vivo by limiting tumour cell growth, abrogating tumour angiogenesis and modulating immune/inflammatory tumour milieu.

Methods

We produced flank and pleural syngeneic murine mesotheliomas by delivering AE17 and AB1 murine mesothelioma cells into the right flank or the pleural space of C57BL/6 and BALB/c mice, respectively. Animals were given five times/week intraperitoneal injections of 20 mg/kg temsirolimus or vehicle and were sacrificed on day 26 (flank) or on day 15 (pleural) post‐tumour cell propagation.

Results

Temsirolimus limited mesothelioma growth in vivo by stimulating tumour cell apoptosis, inhibiting tumour angiogenesis, enhancing tumour lymphocyte abundance and blocking pro‐tumour myeloid cell recruitment. Pleural fluid accumulation was significantly mitigated in AE17 but not in AB1 mesotheliomas. In vitro, temsirolimus hindered mesothelioma cell growth, NF‐kappaB activation and macrophage migration.

Conclusions

In conclusion, temsirolimus apart from inducing tumour cell apoptosis, targets tumour angiogenesis and influences inflammatory tumour microenvironment to halt experimental mesothelioma growth in vivo.
The Costs and Valuation of Health Impacts of Measles and Rubella Risk Management Policies
Authors: Thompson Kimberly M. , Odahowski Cassie L.
Published: August 2015

National and global health policymakers require good information about the costs and benefits of their investments in measles and rubella immunization programs. Building on our review of the existing measles and rubella health economics literature, we develop inputs for use in regional and global models of the expected future benefits and costs of vaccination, treatment, surveillance, and other global coordination activities. Given diversity in the world and limited data, we characterize the costs for countries according to the 2013 World Bank income levels using 2013 U.S. dollars (2013$US). We estimate that routine immunization and supplemental immunization activities will cost governments and donors over 2013$US 2.3 billion per year for the foreseeable future, with high‐income countries accounting for 55% of the costs, to vaccinate global birth cohorts of approximately 134 million surviving infants and to protect the global population of over 7 billion people. We find significantly higher costs and health consequences of measles or rubella disease than with vaccine use, with the expected disability‐adjusted life year (DALY) loss for case of disease generally at least 100 times the loss per vaccine dose. To support estimates of the economic benefits of investments in measles and/or rubella elimination or control, we characterize the probabilities of various sequelae of measles and rubella infections and vaccine adverse events, the DALY inputs for health outcomes, and the associated treatment costs. Managing measles and rubella to achieve the existing and future regional measles and rubella goals and the objectives of the Global Vaccine Action Plan will require an ongoing commitment of financial resources that will prevent adverse health outcomes and save the associated treatment costs.
Keep calm and have a good night: nurses' strategies to promote inpatients' sleep in the hospital environment
Authors: Salzmann‐Erikson Martin , Lagerqvist Linda , Pousette Sandra
Published: August 2015

Patients in the hospital environment are suffering from disrupted sleep, which adversely affects their recovery process, health and well‐being. The aim of this study was to explore nurses' experiences and their strategies to promote inpatients' sleep. An empirical qualitative design was applied. Eight nurses at a hospital in Sweden were purposefully selected to be included in semi‐structured interviews. Burnard's method for inductively analysing interview transcripts was applied. The findings are presented in four categories: (i) prevention and planning as a sleep‐promoting nursing strategy; (ii) adaptation of the environment as a sleep‐promoting nursing strategy; (iii) use of drugs as a sleep‐promoting nursing strategy; and (iv) caring conversation as a sleep‐promoting nursing strategy. Using strategies to promote sleep is important as it affects the recovery of the patients. We argue for the use of simple strategies of sensory reduction as cost‐effective sleep‐promoting measures that also reduce the use of sedative drugs.
Predictors of individual adaptation to high‐volume or high‐intensity endurance training in recreational endurance runners
Authors: Vesterinen V. , Häkkinen K. , Laine T. , Hynynen E. , Mikkola J. , Nummela A.
Published: August 2015

The aim of this study was to investigate factors that can predict individual adaptation to high‐volume or high‐intensity endurance training. After the first 8‐week preparation period, 37 recreational endurance runners were matched into the high‐volume training group (HVT) and high‐intensity training group (HIT). During the next 8‐week training period, HVT increased their running training volume and HIT increased training intensity. Endurance performance characteristics, heart rate variability (HRV), and serum hormone concentrations were measured before and after the training periods. While HIT improved peak treadmill running speed (RSpeak) 3.1 ± 2.8% (P < 0.001), no significant changes occurred in HVT (RSpeak: 0.5 ± 1.9%). However, large individual variation was found in the changes of RSpeak in both groups (HVT: −2.8 to 4.1%; HIT: 0–10.2%). A negative relationship was observed between baseline high‐frequency power of HRV (HFPnight) and the individual changes of RSpeak (r = −0.74, P = 0.006) in HVT and a positive relationship (r = 0.63, P = 0.039) in HIT. Individuals with lower HFP showed greater change of RSpeak in HVT, while individuals with higher HFP responded well in HIT. It is concluded that nocturnal HRV can be used to individualize endurance training in recreational runners.
Comparison of Outcome After Use of Extra‐Luminal Rings and Intra‐Luminal Stents for Treatment of Tracheal Collapse in Dogs
Authors: Tinga Selena , Thieman Mankin Kelley M. , Peycke Laura E. , Cohen Noah D.
Published: August 2015

Objective

To report short‐ and long‐term complications and outcomes of dogs treated for tracheal collapse secondary to chondromalacia with extra‐luminal rings (ELR) or intra‐luminal stents (ILS).

Study Design

Retrospective cohort.

Sample Population

Dogs with naturally occurring tracheal collapse (n = 103).

Methods

Medical records (2002–2012) of dogs diagnosed with tracheal collapse that had treatment with ELR (n = 73) or ILS (30) were reviewed. Demographic information, procedural information, complications, survival time, and subjective outcomes were recorded. Follow‐up periods were defined as <730 days (short‐term) and>730 days (long‐term).

Results

Ninety‐two percent of dogs undergoing ELR and 100% of dogs undergoing ILS survived to hospital discharge. ELR dogs were significantly younger (P = .009) and significantly fewer had main‐stem bronchial collapse (P < .001). After accounting for effects of age and presence of main‐stem bronchial collapse, there was no significant difference in median survival time between groups. Dogs with main‐stem bronchial collapse (regardless of treatment type) had a shorter survival time than dogs without main‐stem bronchial collapse. Major complications occurred in ELR (42%) and ILS dogs (43%).

Conclusions

Both ELR and ILS are associated with high complication rates. Younger dogs and dogs without main‐stem bronchial collapse had a longer survival time, regardless of treatment.
Psychometric Evaluation of a Self‐Report Evidence‐Based Practice Tool Using Rasch Analysis
Authors: Blackman Ian R. , Giles Tracey
Published: August 2015

Aims

This paper reports if estimates of final year nursing students’ self‐rated abilities in responding to evidence‐based practice (EBP) issues is a psychometrically robust measure.

Background

EBP as it applies to nursing continues to be heralded as a method to improve clinical patient care. Health professionals such as nurses are well positioned to respond to this demand; however, evidence suggests they are not always able to embrace this important foundation of everyday nursing practice.

Design

Instrument development.

Methods

The study was a survey set in a large teaching university in Adelaide, South Australia. The evidence‐based practice survey was made available to a convenience sample of 471 final year nursing students, with a response rate of 79.6% (n = 375). Rasch analysis was used to critique and develop a scale for future learning based on the conjoint estimates of nursing students’ self‐efficacy estimates, when meeting the challenges of various EBP of differing complexities.

Results

Outcomes confirm that final year nursing students’ EBP ability measures can be reliably estimated and a hierarchical scale of learning can be developed for use by beginning registered nurses’ in their staff development.

Linking Evidence to Action

Although Australian health and nursing authorities acknowledge the desirability of the nursing workforce in adopting EBP for patient management, elements of this approach remains problematic for nurses. Measures to estimate EBP skills difficulty can be reliably generated to inform EBP education and skills development.
A Feynman integral via higher normal functions
Authors: Bloch Spencer , Kerr Matt , Vanhove Pierre
Published: August 2015

We study the Feynman integral for the three-banana graph defined as the scalar two-point self-energy at three-loop order. The Feynman integral is evaluated for all identical internal masses in two space-time dimensions. Two calculations are given for the Feynman integral: one based on an interpretation of the integral as an inhomogeneous solution of a classical Picard–Fuchs differential equation, and the other using arithmetic algebraic geometry, motivic cohomology, and Eisenstein series. Both methods use the rather special fact that the Feynman integral is a family of regulator periods associated to a family of$K3$surfaces. We show that the integral is given by a sum of elliptic trilogarithms evaluated at sixth roots of unity. This elliptic trilogarithm value is related to the regulator of a class in the motivic cohomology of the$K3$family. We prove a conjecture by David Broadhurst which states that at a special kinematical point the Feynman integral is given by a critical value of the Hasse–Weil$L$-function of the$K3$surface. This result is shown to be a particular case of Deligne’s conjectures relating values of$L$-functions inside the critical strip to periods.
Examples of CM curves of genus two defined over the reflex field
Authors: Bouyer Florian , Streng Marco
Published: August 2015

Van Wamelen [Math. Comp. 68 (1999) no. 225, 307–320] lists 19 curves of genus two over $\mathbf{Q}$ with complex multiplication (CM). However, for each curve, the CM-field turns out to be cyclic Galois over $\mathbf{Q}$, and the generic case of a non-Galois quartic CM-field did not feature in this list. The reason is that the field of definition in that case always contains the real quadratic subfield of the reflex field.

We extend Van Wamelen’s list to include curves of genus two defined over this real quadratic field. Our list therefore contains the smallest ‘generic’ examples of CM curves of genus two.

We explain our methods for obtaining this list, including a new height-reduction algorithm for arbitrary hyperelliptic curves over totally real number fields. Unlike Van Wamelen, we also give a proof of our list, which is made possible by our implementation of denominator bounds of Lauter and Viray for Igusa class polynomials.
Schubert presentation of the cohomology ring of flag manifolds
Authors: Duan Haibao , Zhao Xuezhi
Published: August 2015

Let $G$ be a compact connected Lie group with a maximal torus $T$. In the context of Schubert calculus we present the integral cohomology $H^{\ast }(G/T)$ by a minimal system of generators and relations.
Aeroelastic Instability in Transonic Fans
Authors: Vahdati Mehdi , Cumpsty Nick
Published: August 2015

This paper describes stall flutter, which can occur at part speed operating conditions near the stall boundary. Although it is called stall flutter, this phenomenon does not require the stalling of the fan blade in the sense that it can occur when the slope of the pressure rise characteristic is still negative. This type of flutter occurs with low nodal diameter forward traveling waves and it occurs for the first flap (1F) mode of blade vibration. For this paper, a computational fluid dynamics (CFD) code has been applied to a real fan of contemporary design; the code has been found to be reliable in predicting mean flow and aeroelastic behavior. When the mass flow is reduced, the flow becomes unstable, resulting in flutter or in stall (the stall perhaps leading to surge). When the relative tip speed into the fan rotor is close to sonic, it is found (by measurement and by computation) that the instability for the fan blade considered in this work results in flutter. The CFD has been used like an experimental technique, varying parameters to understand what controls the instability behavior. It is found that the flutter for this fan requires a separated region on the suction surface. It is also found that the acoustic pressure field associated with the blade vibration must be cut-on upstream of the rotor and cut-off downstream of the rotor if flutter instability is to occur. The difference in cut off conditions upstream and downstream is largely produced by the mean swirl velocity introduced by the fan rotor in imparting work and pressure rise to the air. The conditions for instability therefore require a three-dimensional geometric description and blades with finite mean loading. The third parameter that governs the flutter stability of the blade is the ratio of the twisting motion to the plunging motion of the 1F mode shape, which determines the ratio of leading edge (LE) displacement to the trailing edge (TE) displacement. It will be shown that as this ratio increases the onset of flutter moves to a lower mass flow.
Computational Study of Saturated Flow Boiling Within a Microchannel in the Slug Flow Regime
Authors: Magnini Mirco , Thome John R.
Published: August 2015

This paper presents a fundamental study of the flow dynamics and heat transfer induced by a slug flow under saturated flow boiling in a circular microchannel. Numerical simulations are carried out by utilizing the commercial CFD solver ansys fluent v. 14.5, with its built-in volume of fluid (VOF) method to advect the interface, which was improved here by implementing self-developed functions to model the phase change and the surface tension force. A continuous stream of bubbles is generated (by additional user-defined functions) by patching vapor bubbles at the channel upstream with a constant generation frequency. This modeling framework can capture the essential features of heat transfer in slug flows for a continuous stream of bubbles which are here investigated in detail, e.g., the mutual influence among the growing bubbles, the fluid mechanics in the liquid slug trapped between two consecutive bubbles, the effect of bubble acceleration on the thickness of the thin liquid film trapped against the channel wall and on other bubbles, and the transient growth of the heat transfer coefficient and then its periodic variation at the terminal steady-periodic regime, which is reached after the transit of a few bubble–liquid slug pairs. Furthermore, the results for a continuous stream of bubbles are found to be quite different than that of a single bubble, emphasizing the importance of modeling multiple bubbles to study this process. Finally, the outcomes of this analysis are utilized to advance a theoretical model for heat transfer in microchannel slug flow that best reproduces the present simulation data.
Orbit-Model Force Coefficients for Fluid Film Bearings: A Step Beyond Linearization
Authors: San Andrés Luis , Jeung Sung-Hwa
Published: August 2015

High-performance turbomachinery demands high shaft speeds, increased rotor flexibility, tighter clearances in the flow passages, advanced materials, and increased tolerance to imbalances. Operation at high speeds induces severe dynamic loading with large amplitude shaft motions at the bearing supports. Typical rotordynamic models rely on linearized force coefficients (stiffness K, damping C, and inertia M) to model the reaction forces from fluid film bearings and seal elements. These true linear force coefficients are derived from infinitesimally small amplitude motions about an equilibrium position. Often, however, a rotor–bearing system does not reach an equilibrium position and displaces with motions amounting to a sizable portion of the film clearance; the most notable example being a squeeze film damper (SFD). Clearly, linearized force coefficients cannot be used in situations exceeding its basic formulation. Conversely, the current speed of computing permits to evaluate fluid film element reaction forces in real time for ready numerical integration of the transient response of complex rotor–bearing systems. This approach albeit fast does not help to gauge the importance of individual effects on system response. Presently, an orbit analysis method estimates force coefficients from numerical simulations of specified journal motions and predicted fluid film reaction forces. For identical operating conditions in static eccentricity and whirl amplitude and frequency as those in measurements, the computational physics model calculates instantaneous damper reaction forces during one full period of motion and performs a Fourier analysis to characterize the fundamental components of the dynamic forces. The procedure is repeated over a range of frequencies to accumulate sets of forces and displacements building mechanical transfer functions from which force coefficients are identified. These coefficients thus represent best fits to the motion over a frequency range and dissipate the same mechanical energy as the nonlinear mechanical element. More accurate than the true linearized coefficients, force coefficients from the orbit analysis correlate best with SFD test data, in particular for large amplitude motions, statically off-centered. The comparisons also reveal the fallacy in representing nonlinear systems as simple K–C–M models impervious to the kinematics of motion.
Interaction of Flame Flashback Mechanisms in Premixed Hydrogen–Air Swirl Flames
Authors: Sattelmayer Thomas , Mayer Christoph , Sangl Janine
Published: August 2015

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen–air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed (HS) particle image velocimetry (PIV)/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures, the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approximately 1/3 of the typical flow velocities in gas turbine burners. In that range, the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approximately 0.45 and delivers NOx emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.
Isothermal and Cyclic Oxidation Performance of Vertically Cracked and Columnar Thermal Barrier Coating Structures Produced Using Axial Suspension Plasma Spraying Process
Authors: Li Xiaolong , Huang Xiao , Yang Qi , Tang Zhaolin
Published: August 2015

Oxidation performance of thermal barrier coatings (TBCs) deposited by the axial suspension plasma spraying (ASPS) method was evaluated under isothermal and cyclic conditions with a peak temperature of 1080 °C. The TBC systems are based on two nickel-based superalloy substrates (CMSX-4 and IN738LC), platinum aluminide bond coat (BC), and yttria-stabilized zirconia (8YSZ) top coat (TC) of either vertically cracked (VC) or columnar structure. Samples with IN738LC substrate exhibited longer isothermal oxidation lives whereas the ones with CMSX-4 substrate showed greater cyclic oxidation lives. Outward diffusion of W and Ta in TBC systems containing CMSX-4 was found to have progressed to the interface between thermally grown oxide (TGO) and TC; this has contributed to the reduced isothermal oxidation life. The longer cyclic oxidation lives of TBC systems with CMSX-4 were attributed to less coefficient and thermal expansion (CTE) mismatch between coating layers (reduced strain energy) and better creep resistance of diffusional BC on CMSX-4, hence less TGO rumpling. TBC systems with columnar YSZ had longer isothermal oxidation lives while those with VC YSZ seemed to result in longer cyclic lives.
Tensile Stress-Driven Surface Wrinkles on Cylindrical Core–Shell Soft Solids
Authors: Tang Shan , Li Ying , Kam Liu Wing , Hu Ning , He Peng Xiang , Guo Zaoyang
Published: August 2015

It has been experimentally observed that wrinkles formed on the surface of electrospun polymer nanofibers when they are under uniaxial tension (Appl. Phys. Lett., 91, p. 151901 (2007)). Molecular dynamics (MD) simulations, finite element analyses (FEA), and continuum theory calculations have been performed to understand this interesting phenomenon. The surface wrinkles are found to be induced by the cylindrical core–shell microstructure of polymer nanofibers, especially the mismatch of Poisson's ratio between the core and shell layers. Through the MD simulations, the polymer nanofiber is found to be composed of a glassy core embedded into a rubbery shell. The Poisson's ratios of the core and shell layers are close to that of the compressible (0.2) and incompressible (0.5) polymers, respectively. The core is twice stiffer than the shell, due to its highly packed polymer chains and large entanglement density. Based on this observation, a FEA model has been built to study surface instability of the cylindrical core–shell soft solids under uniaxial tension. The “polarization” mechanism at the interphase between the core and shell layers, induced by the mismatch of their Poisson's ratios, is identified as the key element to drive the surface wrinkles during the instability analysis. Through postbuckling analysis, the plastic deformation is also found to play an important role in this process. Without the plastic deformation, the initial imperfection cannot lead to surface wrinkles. The FEA model shows that the yielding stress (or strain rate) can greatly affect the onset and modes of surface wrinkles, which are in good agreement with experimental observations on electrospun polymer nanofibers. The deformation mechanism and critical condition for the surface wrinkles are further clarified through a simplified continuum theory. This study provides a new way to understand and control the surface morphology of cylindrical core–shell materials.
Asynchronous Vibration Response Characteristics of Aero-Engine With Support Looseness Fault
Authors: Wang H. F. , Chen G. , Song P. P.
Published: August 2015

In this paper, the mechanism of the asynchronous vibration response phenomenon caused by the looseness fault in the aero-engine whole vibration system is investigated by numerical integration methods. A single degree-of-freedom (DOF) lumped mass model and a rotor-casing whole vibration model of a real engine are established, and two looseness fault models are introduced. The response of these two systems is obtained by numerical integration methods, and the asynchronous response characteristics are analyzed. By comparing the response of a single DOF lumped mass model with the response of multiple DOF model, the reason leading to the asynchronous response characteristics is the relationship between the changing period of stiffness and the changing period of the rotational speed. When the changing period of stiffness is equivalent to the changing period of the rotational speed, frequency multiplication will appear and the natural frequency will be excited at specific speeds. When the changing period of stiffness is equivalent to n (n = 2, 3,…) times the changing period of the rotating speed, 1/n (n = 2, 3,…) frequency division and frequency multiplication will appear and the natural frequency will be excited at specific speeds.
Analysis of Cohesive Microsized Particle Packing Structure Using History-Dependent Contact Models
Authors: Tayeb Raihan , Dou Xin , Mao Yijin , Zhang Yuwen
Published: August 2015

Granular packing structures of cohesive microsized particles with different sizes and size distributions, including monosized, uniform, and Gaussian distribution, are investigated by using two different history dependent contact models with discrete element method (DEM). The simulation is carried out in the framework of liggghts, which is a DEM simulation package extended based on branch of granular package of widely used open-source code LAMMPS. Contact force caused by translation and rotation, frictional and damping forces due to collision with other particles or container boundaries, cohesive force, van der Waals force, and gravity is considered. The radial distribution functions (RDFs), force distributions, porosities, and coordination numbers under cohesive and noncohesive conditions are reported. The results indicate that particle size and size distributions have great influences on the packing density for particle packing under cohesive effect: particles with Gaussian distribution have the lowest packing density, followed by the particles with uniform distribution; the particles with monosized distribution have the highest packing density. It is also found that cohesive effect to the system does not significantly affect the coordination number that mainly depends on the particle size and size distribution. Although the magnitude of net force distribution is different, the results for porosity, coordination number, and mean value of magnitude of net force do not vary significantly between the two contact models.
Toward 2D and 3D imaging of magnetic nanoparticles using EPR measurements
Authors: Coene A. , Crevecoeur G. , Leliaert J. , Dupré L.
Published: August 2015

Purpose:

Magnetic nanoparticles (MNPs) are an important asset in many biomedical applications. An effective working of these applications requires an accurate knowledge of the spatial MNP distribution. A promising, noninvasive, and sensitive technique to visualize MNP distributions in vivo is electron paramagnetic resonance (EPR). Currently only 1D MNP distributions can be reconstructed. In this paper, the authors propose extending 1D EPR toward 2D and 3D using computer simulations to allow accurate imaging of MNP distributions.

Methods:

To find the MNP distribution belonging to EPR measurements, an inverse problem needs to be solved. The solution of this inverse problem highly depends on the stability of the inverse problem. The authors adapt 1D EPR imaging to realize the imaging of multidimensional MNP distributions. Furthermore, the authors introduce partial volume excitation in which only parts of the volume are imaged to increase stability of the inverse solution and to speed up the measurements. The authors simulate EPR measurements of different 2D and 3D MNP distributions and solve the inverse problem. The stability is evaluated by calculating the condition measure and by comparing the actual MNP distribution to the reconstructed MNP distribution. Based on these simulations, the authors define requirements for the EPR system to cope with the added dimensions. Moreover, the authors investigate how EPR measurements should be conducted to improve the stability of the associated inverse problem and to increase reconstruction quality.

Results:

The approach used in 1D EPR can only be employed for the reconstruction of small volumes in 2D and 3D EPRs due to numerical instability of the inverse solution. The authors performed EPR measurements of increasing cylindrical volumes and evaluated the condition measure. This showed that a reduction of the inherent symmetry in the EPR methodology is necessary. By reducing the symmetry of the EPR setup, quantitative images of larger volumes can be obtained. The authors found that, by selectively exciting parts of the volume, the authors could increase the reconstruction quality even further while reducing the amount of measurements. Additionally, the inverse solution of this activation method degrades slower for increasing volumes. Finally, the methodology was applied to noisy EPR measurements: using the reduced EPR setup's symmetry and the partial activation method, an increase in reconstruction quality of ≈80% can be seen with a speedup of the measurements with 10%.

Conclusions:

Applying the aforementioned requirements to the EPR setup and stabilizing the EPR measurements showed a tremendous increase in noise robustness, thereby making EPR a valuable method for quantitative imaging of multidimensional MNP distributions.
Automated pericardium delineation and epicardial fat volume quantification from noncontrast CT
Authors: Ding Xiaowei , Terzopoulos Demetri , Diaz‐Zamudio Mariana , Berman Daniel S. , Slomka Piotr J. , Dey Damini
Published: August 2015

Purpose:

The authors aimed to develop and validate an automated algorithm for epicardial fat volume (EFV) quantification from noncontrast CT.

Methods:

The authors developed a hybrid algorithm based on initial segmentation with a multiple‐patient CT atlas, followed by automated pericardium delineation using geodesic active contours. A coregistered segmented CT atlas was created from manually segmented CT data and stored offline. The heart and pericardium in test CT data are first initialized by image registration to the CT atlas. The pericardium is then detected by a knowledge‐based algorithm, which extracts only the membrane representing the pericardium. From its initial atlas position, the pericardium is modeled by geodesic active contours, which iteratively deform and lock onto the detected pericardium. EFV is automatically computed using standard fat attenuation range.

Results:

The authors applied their algorithm on 50 patients undergoing routine coronary calcium assessment by CT. Measurement time was 60 s per‐patient. EFV quantified by the algorithm (83.60 ± 32.89 cm3) and expert readers (81.85 ± 34.28 cm3) showed excellent correlation (r = 0.97, p < 0.0001), with no significant differences by comparison of individual data points (p = 0.15). Voxel overlap by Dice coefficient between the algorithm and expert readers was 0.92 (range 0.88–0.95). The mean surface distance and Hausdorff distance in millimeter between manually drawn contours and the automatically obtained contours were 0.6 ± 0.9 mm and 3.9 ± 1.7 mm, respectively. Mean difference between the algorithm and experts was 9.7% ± 7.4%, similar to interobserver variability between 2 readers (8.0% ± 5.3%, p = 0.3).

Conclusions:

The authors’ novel automated method based on atlas‐initialized active contours accurately and rapidly quantifies EFV from noncontrast CT.
Validation of clinical acceptability of an atlas‐based segmentation algorithm for the delineation of organs at risk in head and neck cancer
Authors: Hoang Duc Albert K. , Eminowicz Gemma , Mendes Ruheena , Wong Swee‐Ling , McClelland Jamie , Modat Marc , Cardoso M. Jorge , Mendelson Alex F. , Veiga Catarina , Kadir Timor , D'souza Derek , Ourselin Sebastien
Published: August 2015

Purpose:

The aim of this study was to assess whether clinically acceptable segmentations of organs at risk (OARs) in head and neck cancer can be obtained automatically and efficiently using the novel “similarity and truth estimation for propagated segmentations” (STEPS) compared to the traditional “simultaneous truth and performance level estimation” (STAPLE) algorithm.

Methods:

First, 6 OARs were contoured by 2 radiation oncologists in a dataset of 100 patients with head and neck cancer on planning computed tomography images. Each image in the dataset was then automatically segmented with STAPLE and STEPS using those manual contours. Dice similarity coefficient (DSC) was then used to compare the accuracy of these automatic methods. Second, in a blind experiment, three separate and distinct trained physicians graded manual and automatic segmentations into one of the following three grades: clinically acceptable as determined by universal delineation guidelines (grade A), reasonably acceptable for clinical practice upon manual editing (grade B), and not acceptable (grade C). Finally, STEPS segmentations graded B were selected and one of the physicians manually edited them to grade A. Editing time was recorded.

Results:

Significant improvements in DSC can be seen when using the STEPS algorithm on large structures such as the brainstem, spinal canal, and left/right parotid compared to the STAPLE algorithm (all p < 0.001). In addition, across all three trained physicians, manual and STEPS segmentation grades were not significantly different for the brainstem, spinal canal, parotid (right/left), and optic chiasm (all p > 0.100). In contrast, STEPS segmentation grades were lower for the eyes (p < 0.001). Across all OARs and all physicians, STEPS produced segmentations graded as well as manual contouring at a rate of 83%, giving a lower bound on this rate of 80% with 95% confidence. Reduction in manual interaction time was on average 61% and 93% when automatic segmentations did and did not, respectively, require manual editing.

Conclusions:

The STEPS algorithm showed better performance than the STAPLE algorithm in segmenting OARs for radiotherapy of the head and neck. It can automatically produce clinically acceptable segmentation of OARs, with results as relevant as manual contouring for the brainstem, spinal canal, the parotids (left/right), and optic chiasm. A substantial reduction in manual labor was achieved when using STEPS even when manual editing was necessary.
Evaluation of a synthetic single‐crystal diamond detector for relative dosimetry on the Leksell Gamma Knife Perfexion radiosurgery system
Authors: Mancosu Pietro , Reggiori Giacomo , Stravato Antonella , Gaudino Anna , Lobefalo Francesca , Palumbo Valentina , Navarria Piera , Ascolese Anna , Picozzi Piero , Marinelli Marco , Verona‐Rinati Gianluca , Tomatis Stefano , Scorsetti Marta
Published: August 2015

Purpose:

To evaluate the new commercial PTW‐60019 synthetic single‐crystal microDiamond detector (PTW, Freiburg, Germany) for relative dosimetry measurements on a clinical Leksell Gamma Knife Perfexion radiosurgery system.

Methods:

Detector output ratios (DORs) for 4 and 8 mm beams were measured using a microDiamond (PTW‐60019), a stereotactic unshielded diode [IBA stereotactic field detector (SFD)], a shielded diode (IBA photon field detector), and GafChromic EBT3 films. Both parallel and transversal acquisition directions were considered for PTW‐60019 measurements. Measured DORs were compared to the new output factor reference values for Gamma Knife Perfexion (0.814 and 0.900 for 4 and 8 mm, respectively). Profiles in the three directions were also measured for the 4 mm beam to evaluate full width at half maximum (FWHM) and penumbra and to compare them with the corresponding Leksell GammaPlan profiles.

Results:

FWHM and penumbra for PTW‐60019 differed from the calculated values by less than 0.2 and 0.3 mm, for the parallel and transversal acquisitions, respectively. GafChromic films showed FWHM and penumbra within 0.1 mm. The output ratio obtained with the PTW‐60019 for the 4 mm field was 1.6% greater in transverse direction compared to the nominal value. Comparable differences up to 0.8% and 1.0% for, respectively, GafChromic films and SFD were found.

Conclusions:

The microDiamond PTW‐60019 is a suitable detector for commissioning and routine use of Gamma Knife with good agreement of both DORs and profiles in the three directions.
Hybrid detection of lung nodules on CT scan images
Authors: Lu Lin , Tan Yongqiang , Schwartz Lawrence H. , Zhao Binsheng
Published: August 2015

Purpose:

The diversity of lung nodules poses difficulty for the current computer‐aided diagnostic (CAD) schemes for lung nodule detection on computed tomography (CT) scan images, especially in large‐scale CT screening studies. We proposed a novel CAD scheme based on a hybrid method to address the challenges of detection in diverse lung nodules.

Methods:

The hybrid method proposed in this paper integrates several existing and widely used algorithms in the field of nodule detection, including morphological operation, dot‐enhancement based on Hessian matrix, fuzzy connectedness segmentation, local density maximum algorithm, geodesic distance map, and regression tree classification. All of the adopted algorithms were organized into tree structures with multi‐nodes. Each node in the tree structure aimed to deal with one type of lung nodule.

Results:

The method has been evaluated on 294 CT scans from the Lung Image Database Consortium (LIDC) dataset. The CT scans were randomly divided into two independent subsets: a training set (196 scans) and a test set (98 scans). In total, the 294 CT scans contained 631 lung nodules, which were annotated by at least two radiologists participating in the LIDC project. The sensitivity and false positive per scan for the training set were 87% and 2.61%. The sensitivity and false positive per scan for the testing set were 85.2% and 3.13%.

Conclusions:

The proposed hybrid method yielded high performance on the evaluation dataset and exhibits advantages over existing CAD schemes. We believe that the present method would be useful for a wide variety of CT imaging protocols used in both routine diagnosis and screening studies.
Technical Note: Estimation of lung tumor thickness from planar dual‐energy kV images
Authors: Jung Frederick , Patel Rakesh , Campana Maria , Panfil Joshua , Pankuch Mark , Roeske John C.
Published: August 2015

Purpose:

Dual‐energy (DE) imaging is a method that suppresses bony anatomy on planar kV images while enhancing soft tissue contrast. This technique has been used specifically in the chest to improve the visualization of small lung tumors. However, DE imaging may also provide quantitative information that has not been previously investigated. In this study, the aim was to establish a theoretical relationship between DE image contrast and tumor thickness and to observe this trend in phantom experiments.

Methods:

A phantom consisting cork (used to simulate lung), tissue‐equivalent material, and pork ribs was constructed to test for a relationship between DE image contrast and simulated tumor thickness. Fifteen phantom setups were used with various thicknesses of cork and tissue‐equivalent material. For each setup, high (120 kVp) and low (60 kVp) energy planar images were acquired and DE images were produced. The image contrast between the simulated tumor and surrounding tissue was then plotted against the known thicknesses and a linear regression was performed.

Results:

A linear regression of the contrast data vs simulated tumor thickness resulted in a slope of −0.0454 with an R2 = 0.9904. The expected uncertainty in the thickness measurements using the regression parameters and DE contrast standard deviation was 0.13 cm.

Conclusions:

Phantom data exhibited a linear relationship between DE image contrast and simulated tumor thickness. Future studies will investigate patient‐specific parameters so that this method can be used clinically to evaluate tumor thickness from planar kV images. Such an approach may have benefits for both adaptive and heavy ion therapies.
Kinematic and Kinetic Indicators of Sit-to-Stand
Authors: Stevermer Catherine A. , Gillette Jason C.
Published: August 2015

Variation in the timing indicators separating sit-to-stand (STS) into movement phases complicates both research comparisons and clinical applications. The purpose of this study was to use kinetic reference standards to identify accurate kinematic and kinetic indicators for STS movement analysis such that consistent indicators might be used for STS from varied initial postures. Healthy adults performed STS using 4 foot placements: foot-neutral, foot-back, right-staggered, and left-staggered. Kinetic and kinematic data were collected from force platforms and an 8-camera video system. Initiation, seat-off, vertical posture, and termination were detected with 5% start and 7.5% end thresholds for changes in kinetic and kinematic STS indicators. Timing differences between kinetic and kinematic indicator time points and the reference vertical seated reaction force end point (seatoff) were determined. Kinematic indicators were compared with selected kinetic indicators using timing differences, statistical similarity, and internal consistency measures. Our results suggest that a single force platform system measuring vertical GRF or a simple camera system to evaluate the shoulder marker position and velocity can accurately and consistently detect STS initiation, seat-off, and vertical posture. In addition, these suggested STS indicators for initiation, seat-off, and vertical posture were not dependent upon foot placement.