bluuebunny/crossref_metadata_2025 huggingface dataset:
Variants of Porphyromonas gingivalis lipopolysaccharide alter lipidation of autophagic protein, microtubule‐associated protein 1 light chain 3, LC3
Authors: Blasi I. , Korostoff J. , Dhingra A. , Reyes‐Reveles J. , Shenker B.J. , Shahabuddin N. , Alexander D. , Lally E.T. , Bragin A. , Boesze‐Battaglia K.
Published: October 2015

Porphyromonas gingivalis often subverts host cell autophagic processes for its own survival. Our previous studies document the association of the cargo sorting protein, melanoregulin (MREG), with its binding partner, the autophagic protein, microtubule‐associated protein 1 light chain 3 (LC3) in macrophages incubated with P. gingivalis (strain 33277). Differences in the lipid A moiety of lipopolysaccharide (LPS) affect the virulence of P. gingivalis; penta‐acylated LPS1690 is a weak Toll‐like receptor 4 agonist compared with Escherichia coli LPS, whereas tetra‐acylated LPS1435/1449 acts as an LPS1690 antagonist. To determine how P. gingivalis LPS1690 affects autophagy we assessed LC3‐dependent and MREG‐dependent processes in green fluorescent protein (GFP)‐LC3‐expressing Saos‐2 cells. LPS1690 stimulated the formation of very large LC3‐positive vacuoles and MREG puncta. This LPS1690‐mediated LC3 lipidation decreased in the presence of LPS1435/1449. When Saos‐2 cells were incubated with P. gingivalis the bacteria internalized but did not traffic to GFP‐LC3‐positive structures. Nevertheless, increases in LC3 lipidation and MREG puncta were observed. Collectively, these results suggest that P. gingivalis internalization is not necessary for LC3 lipidation. Primary human gingival epithelial cells isolated from patients with periodontitis showed both LC3II and MREG puncta whereas cells from disease‐free individuals exhibited little co‐localization of these two proteins. These results suggest that the prevalence of a particular LPS moiety may modulate the degradative capacity of host cells, so influencing bacterial survival.
Tobacco smoking: From ‘glamour’ to ‘stigma’. A comprehensive review
Authors: Castaldelli‐Maia João Mauricio , Ventriglio Antonio , Bhugra Dinesh
Published: October 2015

In this narrative review, we explore the history of tobacco smoking, its associations and portrayal of its use with luxury and glamour in the past, and intriguingly, its subsequent transformation into a mass consumption industrialized product encouraged by advertising and film. Then, we describe the next phase where tobacco in parts of the world has become an unwanted product. However, the number of smokers is still increasing, especially in new markets, and increasingly younger individuals are being attracted to it, despite the well‐known health consequences of tobacco use. We also explore current smoking behaviors, looking at trends in the prevalence of consumption throughout the world, discrimination against smokers, light and/or intermittent smokers, and the electronic cigarette (e‐cigarette). We place these changes in the context of neuroscience, which may help explain why the cognitive effects of smoking can be important reinforcers for its consumption despite strong anti‐smoking pressure in Western countries.
Factors associated with depression among elderly Koreans: the role of chronic illness, subjective health status, and cognitive impairment
Authors: Park Jong‐Il , Park Tae Won , Yang Jong‐Chul , Chung Sang‐Keun
Published: October 2015

Objectives

The objective of this cross‐sectional study was to investigate the relationship between depression in elderly individuals and chronic illness, subjective health status, and cognitive impairment.

Method

This study used the dataset of the Survey of Living Conditions and Welfare Needs of Korean Older Persons, which was conducted by the Korea Institute for Health and Social Affairs in 2011. Participants (n = 10 674) were randomly selected from a pool of individuals aged 65 years and older. Elderly depression was evaluated by the short version of the Geriatric Depression Scale. Multivariate logistic regression was used to investigate factors associated with depression in terms of their sociodemographic and health‐related characteristics.

Results

Our results revealed that chronic illness, subjective health status, and cognitive impairment were significant factors associated with depression. In particular, subjective health status showed the highest odds ratio (OR) (OR for bad subjective health status = 4.290, P < 0.001), followed by chronic illness (OR for three or more chronic illnesses = 1.403, P < 0.01) and cognitive impairment (OR = 1.347, P < 0.001) in the final model. Interestingly, the significant association between chronic illness and depression was attenuated (OR for three or more chronic illnesses = 1.403, P = 0.01) or even disappeared (OR for two chronic illnesses = 1.138, P = 0.274; OR for one chronic illnesses = 0.999, P = 0.996) after adjustment for subjective health status in the final model; this may be attributable to the close relationship among the variables studied: chronic illness, subjective health status, and depression.

Conclusions

Development and implementation of prevention strategies, including management of chronic illness, individual's perception of health status, and cognitive impairment, could possibly reduce the impact of depression.
Distinguishing Different Types of Coproduction: A Conceptual Analysis Based on the Classical Definitions
Authors: Brandsen Taco , Honingh Marlies
Published: October 2015

Coproduction of public services means that services are not only delivered by professional and managerial staff in public agencies but also coproduced by citizens and communities. Although recent research on this topic has advanced the debate considerably, there is still no consensus on precisely what coproduction means. This article argues that rather than trying to determine one encompassing definition of the concept, several different types of coproduction can be distinguished. Starting from the classical definitions of Elinor Ostrom and Roger Parks, the article draws on the literature on professionalism, volunteering, and public management to identify the distinctive nature of coproduction and identify basic dimensions on which a typology of coproduction can be constructed. Recognizing different types of coproduction more systematically is a critical step in making research on this phenomenon more comparable and more cumulative.
The Political Economy of Clientelism*
Authors: Robinson James A. , Verdier Thierry
Published: October 2015

In this paper, we argue that the political‐commitment problem provides an explanation for why much income redistribution takes an inefficient form, particularly employment in the public sector. A job is a credible way of redistributing when it provides rents (such as in situations with moral hazard), and employment is optimal ex post. Moreover, a job is selective and reversible, and thus ties the continuation utility of a voter to the political success of a particular politician. We show that the need to make offers of employment incentive‐compatible leads to inefficiencies in the supply of public goods. We also show that such inefficient redistribution becomes relatively attractive in situations with high inequality and low productivity. Inefficiency is increased when the stakes from politics are high, when inequality is high, and when money matters less than ideology in politics.
Macroeconomic Effects of Asset‐Price Shocks in a Globalized Financial Market
Authors: Quadrini Vincenzo
Published: October 2015

In this paper, I study a model in which shocks to asset prices affect the real sector of the economy through a credit channel. As financial markets become internationally integrated, the economy becomes less vulnerable to domestic asset‐price shocks, but more vulnerable to foreign asset‐price shocks. To the extent that monetary policy stabilization is feasible and desirable, the globalization of financial markets shifts the focus of monetary policy from domestic asset prices to worldwide asset prices.
“Large” versus “Small” Players: A Closer Look at the Dynamics of Speculative Attacks
Authors: Bjønnes Geir H. , Holden Steinar , Rime Dagfinn , Solheim Haakon O. Aa.
Published: October 2015

What is the role of “large players” (e.g., hedge funds) in speculative attacks? Recent work suggests that large players move early to induce smaller agents to attack. However, many observers argue that large players move late in order to benefit from interest‐rate differentials. We propose a model in which large players can do both. Using data on currency trading by foreign (large) and local (small) players, we find that foreign players moved last in three attacks on the Norwegian krone during the 1990s. During the attack on the Swedish krona after the Russian moratorium in 1998, foreign players moved early. Gains by delaying attack were small, however, because interest rates did not increase.
The Financial Resource Curse*
Authors: Benigno Gianluca , Fornaro Luca
Published: October 2015

In this paper, we present a model of the financial resource curse (i.e., episodes of abundant access to foreign capital coupled with weak productivity growth). We study a two‐sector (i.e., tradable and non‐tradable) small open economy. The tradable sector is the engine of growth, and productivity growth is increasing with the amount of labor employed by firms in the tradable sector. A period of large capital inflows, triggered by a fall in the interest rate, is associated with a consumption boom. While the increase in tradable consumption is financed through foreign borrowing, the increase in non‐tradable consumption requires a shift of productive resources toward the non‐tradable sector at the expenses of the tradable sector. The result is stagnant productivity growth. We show that capital controls can be welfare‐enhancing and can be used as a second‐best policy tool to mitigate the misallocation of resources during an episode of financial resource curse.
Heterogeneity in Consumer Demands and the Income Effect: Evidence from Panel Data
Authors: Christensen Mette
Published: October 2015

This paper uses unique Spanish panel data on household expenditures to test whether unobservable heterogeneity in household demands (taste, etc.) is correlated with total expenditures (income). The main finding is that tastes are indeed correlated with income for about half of the goods considered, implying that cross‐sectional estimates of income elasticities for these goods are biased. The goods are the following: food eaten outside home, alcohol and tobacco, transportation, and energy. The elasticity of alcohol and tobacco is more than halved when taking unobserved heterogeneity into account. For transportation, the bias is sufficiently large to misclassify the good as a luxury.
The Costs of Financial Crises: Resource Misallocation, Productivity, and Welfare in the 2001 Argentine Crisis
Authors: Sandleris Guido , Wright Mark L. J.
Published: October 2015

Financial crises in emerging market countries appear to be very costly: both output and a host of partial welfare indicators decline dramatically. The magnitude of these costs is puzzling both from an accounting perspective – factor usage does not decline as much as output, resulting in large falls in measured productivity – and from a theoretical perspective. With the aim of resolving this puzzle, we present a framework that allows us to do the following. First, we account for changes in a country's measured productivity during a financial crisis as the result of changes in the underlying technology of the economy, the efficiency with which resources are allocated across sectors, and the efficiency of the resource allocation within sectors, driven both by reallocation amongst existing plants and by entry and exit. Second, we measure the change in the country's welfare resulting from changes in productivity, government spending, the terms of trade, and a country's international investment position. We apply this framework to the Argentine crisis of 2001 using a unique establishment level dataset and we find that more than half of the, roughly, 10 percent decline in measured total factor productivity can be accounted for by deteriorations in the allocation of resources both across and within sectors. We measure the decline in welfare to be of the order of one‐quarter of one year's gross domestic product.
Optimal Retirement with Increasing Longevity
Authors: Bloom David E. , Canning David , Moore Michael
Published: October 2015

We develop an optimizing life‐cycle model of retirement with perfect capital markets. We show that longer healthy life expectancy usually leads to later retirement, but with an elasticity less than unity. We calibrate our model using data from the US and find that, over the last century, the effect of rising incomes, which promote early retirement, has dominated the effect of rising lifespans. Our model predicts continuing declines in the optimal retirement age, despite rising life expectancy, provided the rate of real wage growth remains as high as in the last century.
Tracking Can Be More Equitable Than Mixing
Authors: Hidalgo‐Hidalgo Marisa
Published: October 2015

Parents and policy‐makers often wonder whether and how the choice of a tracked or mixed educational system affects the equality of opportunity. I answer this question by analyzing the influence of peers on future educational results. I define an equal opportunity policy as one that maximizes the average lifetime income of the worst‐off type of individuals in society (i.e., students from disadvantaged backgrounds). I find that tracking maximizes average lifetime income if the opportunity cost of college attendance is sufficiently high.
Public Provision, Commodity Demand, and Hours of Work: An Empirical Analysis
Authors: Pirttilä Jukka , Suoniemi Ilpo
Published: October 2015

The theoretical analysis of optimal commodity taxation is advanced, but there is only limited empirical evidence to guide commodity tax policies. With this paper, we contribute to this body of literature by empirically examining, using Finnish consumption data, the relation between working hours, consumption demand, and the use of publicly provided day care. When labour income is controlled for in a non‐parametric way, we find that capital income and housing expenses are negatively associated with working hours, whereas the use of childcare is positively correlated with working hours. These results provide arguments for taxing capital income and housing, and for subsidizing day care.
Does Employee Body Weight Affect Employers' Behavior?
Authors: Kromann Lene
Published: October 2015

In this paper, we study the possible segregation of overweight individuals already established in the labor market when firms make decisions on hiring, firing, and promoting. Most existing studies use wage equations to document wage differences, but little is known about the reason for the differences and the sorting of workers. Using an equilibrium search model, search frictions are taken into account. Additionally, sorting is examined using a logit model. We find that wage differences between workers who have a normal weight and workers who are overweight or obese can be explained by differential firm behavior, with respect to both the job‐offer arrival rate and the probability of being promoted.
Welfare Magnet Hypothesis, Fiscal Burden, and Immigration Skill Selectivity
Authors: Razin Assaf , Wahba Jackline
Published: October 2015

In this paper, we investigate the effect of welfare state generosity on the difference between skilled and unskilled migration rates, and the role of mobility restriction in shaping this effect. We utilize the free labor movement within the European Union plus Norway and Switzerland (EUR) and the restricted movement from outside the EUR in order to compare the free‐migration regime to the restricted‐migration regime. We find strong support for the magnet hypothesis under the free‐migration regime, and the fiscal burden hypothesis under the restricted‐migration regime, even after controlling for differences in educational quality and returns to skills in source and host countries.
Formation of Migrant Networks
Authors: Comola Margherita , Mendola Mariapia
Published: October 2015

In this paper, we provide the first direct evidence on the internal structure of the migrant social network. By using a purposely designed survey on Sri Lankan immigrants living in Milan, we show that the pattern of within‐group link formation is heterogeneous across immigrants, and differentiated according to the network function (i.e., accommodation, credit, job‐finding). We find that migrants tend to interact with co‐nationals who come from nearby localities at origin, while the time of arrival has a U‐shaped effect. Once the link is formed, material support is provided mainly to relatives, while early migrant fellows are helpful for job‐finding.
United States Immigration Policy: The 1965 Act and its Consequences
Authors: Hatton Timothy J.
Published: October 2015

The United States Immigration Act of 1965 was followed by a steep upward trend in total immigration, and by a dramatic shift in the source‐country composition away from Europe and towards Asia and Latin America. In this paper I ask if and how the 1965 Act generated these unanticipated consequences. The result was partly because of the pre‐existing legislation and partly because of the admission of immigrants outside the terms of the Act. However, much of it was a result of the Act itself, and specifically because of family reunification effects that were larger, the poorer the source country.
Causal Effects of Paternity Leave on Children and Parents
Authors: Cools Sara , Fiva Jon H. , Kirkebøen Lars J.
Published: October 2015

Reserving a share of the parental leave period for fathers is considered necessary in order to induce fathers to take leave, and to increase men's participation in child‐rearing. We investigate how a parental leave reform directed towards fathers affected leave‐taking, and, in turn, children's and parents' long‐term outcomes. A paternal leave quota greatly increases the share of men taking paternity leave. We find evidence that children's school performance improves as a result, particularly in families where the father has higher education than the mother. We find no evidence that paternity leave counters the traditional allocation of parents' labor supply.
Social Preferences in the Lab: A Comparison of Students and a Representative Population
Authors: Cappelen Alexander W. , Nygaard Knut , Sørensen Erik Ø. , Tungodden Bertil
Published: October 2015

We report from a lab experiment conducted with a sample of participants that is nationally representative for the adult population in Norway and two student samples (economics students and non‐economics students). The participants make choices both in a dictator game (a non‐strategic environment) and in a generalized trust game (a strategic environment). We find that the representative sample differs fundamentally from the student samples, both in the relative importance assigned to different moral motives (efficiency, equity, and reciprocity) and in the level of selfish behavior. It is also interesting to note that the gender effects observed in the student samples do not correspond to the gender effects observed in representative sample. Finally, whereas economics students behave less pro‐socially than non‐economics students, the two student groups are similar in the relative importance they assign to different moral motives.
Do Not Trash the Incentive! Monetary Incentives and Waste Sorting
Authors: Bucciol Alessandro , Montinari Natalia , Piovesan Marco
Published: October 2015

In this paper, we examine whether combining non‐monetary and monetary incentives increases municipal solid waste sorting. We empirically investigate this issue, exploiting the exogenous variation in waste management policies experienced during the years 1999–2008 by the 95 municipalities in the district of Treviso (Italy). Using a panel regression analysis, we estimate that pay‐as‐you‐throw (PAYT) incentive schemes increase the sorted‐to‐total waste ratio by 17 percent, and that their effect reinforces that of a door‐to‐door (DtD) collection system, which is equal to 15.7 percent. Moreover, the panel structure of our dataset allows us to find learning and spatial effects associated with both PAYT and DtD.
Peer Effects among Swimmers
Authors: Yamane Shoko , Hayashi Ryohei
Published: October 2015

We develop a novel identification strategy and examine various aspects of peer effects using swimming data. We find that the performance of adjacent competitors positively influences swimmers' performances. In particular, swimmers are influenced by slower‐lane peers, suggesting that being chased improves one's performance. We use absenteeism data to directly compare the performances of swimmers with and without peers. We have found that swimmers swim faster with peers swimming behind them than when swimming alone, but that they swim slower with peers swimming ahead. Finally, we find that observability is a key determinant of peer effects, by comparing freestyle and backstroke competitions.
Valuing School Quality via a School Choice Reform
Authors: Machin Stephen , Salvanes Kjell G.
Published: October 2015

Among policymakers, educators, and economists, there remains a strong debate on the extent to which good schools matter. In this paper, we estimate school quality valuations based upon house prices, by considering a policy reform regarding pupils' choices to attend high school. We exploit a change in school choice that occurred in Oslo county in 1997, where school authorities altered policy from one based on catchment zones to an open enrollment policy that allowed pupils to apply to any high school. Our estimates show that parents substantially value better performing schools because the sensitivity of housing valuations to school performance falls significantly (by over 50 percent) following the school choice reform that made the move to open enrollment.
Earnings Instability and Tenure
Authors: Cappellari Lorenzo , Leonardi Marco
Published: October 2015

We study the effect of tenure on earnings instability in Italy using the reforms of temporary employment contracts, which affected the average tenure of workers differentially across cohorts. We develop a model of earnings dynamics, and we exploit the variation of tenure and instability over time and across birth cohorts to estimate policy‐relevant parameters. Our results indicate that each year of tenure on the job reduces earnings instability by 11 percent; the drop is faster in the first three years of the match. Workers on a temporary contract have an earnings instability up to 100 percent higher than workers on a permanent contract.
How the Populist Radical Right Transformed Swiss Welfare Politics: From Compromises to Polarization
Authors: Afonso Alexandre , Papadopoulos Yannis
Published: October 2015

This paper shows how the rise of the Swiss People's Party (SVP) has affected welfare state reforms in Switzerland between the 1990s and the 2000s. In the 1990s, welfare state reforms drew on “modernizing” coalitions between FDP (Liberals), CVP (Christian Democrats) and SP (Social Democrats) combining retrenchment and “recalibration”. In the 2000s the FDP and CVP increasingly sided with the SVP in right‐wing coalitions pushing retrenchment alone. The article shows that changes in party competition have affected welfare schemes differently, with a policy gridlock in pension reforms, where voters of the SVP do not follow their elites, but unilateral retrenchment in unemployment insurance, where recipients can be portrayed as “underserving”.
Are rapidly mutating Y‐short tandem repeats useful to resolve a lineage? Expanding mutability data on distant male relationships
Authors: Turrina Stefania , Caratti Stefano , Ferrian Melissa , De Leo Domenico
Published: October 2015

BACKGROUND

Y‐chromosomal short tandem repeats (Y‐STRs) are essential to relate male lineages in forensic and evolutionary studies. Although large panels of Y‐STR markers are now available, none possess sufficient discrimination power to distinguish close male relatives. This limit may be overcome by the use of rapidly mutating Y‐STRs (RM Y‐STRs), characterized by mutation rates higher than common Y‐STRs. Recently, multicenter studies evaluated the ability of RM Y‐STRs to differentiate father–son pairs; however, more extensive data on distantly related males are needed.

STUDY DESIGN AND METHOD

A total of 157 male relative pairs separated by two to seven meiotic events, originating from Italy, were analyzed by 13 RM Y‐STRs and 23 Y‐STRs.

RESULTS

Overall, 154 mutational events were observed at RM Y‐STR loci and the estimated mutation rate was of 2.59 × 10−2 (95% confidence interval, 2.16 × 10−2−2.97 × 10−2). A total of 105 male relative pairs showed at least one mutation in at least one locus and differentiation rates increased from 52.8% to 88.9% from the second to the fourth generation, while 23 Y‐STRs provided much lower values, spanning from 10.1% to 29.6%.

CONCLUSIONS

These findings confirmed the higher capability of RM Y‐STRs than conventional Y‐STRs to resolve male lineages, thus suggesting a possible future use for forensic male individual identification.
Survival after ultramassive transfusion: a review of 1360 cases
Authors: Dzik Walter Sunny , Ziman Alyssa , Cohen Claudia , Pai Menaka , Lozano Miguel , Kaufman Richard M. , Delaney Meghan , Selleng Kathleen , Murphy Michael F. , Hervig Tor , Yazer Mark ,   the Biomedical Excellence for Safer Transfusion Collaborative
Published: October 2015

BACKGROUND

Information about patient survival after transfusion of multiple blood volumes is limited, and most reports have focused on trauma patients.

STUDY DESIGN AND METHODS

Retrospective study of blood use and survival at 11 hospitals in six nations between 2009 and 2013. Ultramassive transfusion (UMT) was defined as transfusion of 20 or more red blood cell (RBC) units over the course of any 2 consecutive calendar days.

RESULTS

A total of 1975 patients received UMT and a representative sample of 1360 patients was studied in detail. Patients were grouped into seven diagnostic categories: solid organ transplantation (n = 411), cardiac or major vascular surgery (n = 317), general surgery (n = 228), trauma (n = 221), general medicine (n = 124), obstetrics (n = 23), and other (n = 36). During the 7 days after initiation of UMT, these patients used more than 120,000 blood components. The median (interquartile range) blood use was 35 (26‐50) RBC units, 30 (20‐47) plasma units, and 7 (4‐13) platelet doses. Five‐ and 30‐day survival significantly declined with increasing RBC use. Overall survivals of patients receiving UMT were 71% (5 day) and 60% (30 day), and in the subset of 165 patients receiving 60 or more RBC units over 2 consecutive days, 5‐day survival was 54% ranging from 17% (trauma) to 75% (solid organ transplant). The decline in survival with increasing RBC transfusions was minimal for patients undergoing solid organ transplantation and was most pronounced for trauma and nonsurgical bleeding patients.

CONCLUSION

Trauma was not the leading cause of UMT. Increasing RBC requirements were significantly associated with decreasing survival. However, survival was more strongly associated with diagnostic category than total RBCs transfused, with highest survival rates in solid organ transplant surgery.
Temporary Bonding/Debonding of Silicon Substrates Based on Propylene Carbonate
Authors: Zhu Zhiyuan , Yu Min , Liu Lisha , Jin Yufeng
Published: October 2015

This paper researches temporary bonding/debonding based on propylene carbonate (PPC). The highest shear strength of 4.1 MPa was achieved when pure PPC was used as bonding adhesive. Room temperature debonding methods were investigated and compared with thermal debonding. Chemical debonding at room temperature was realized for bonding with the pure PPC. Several different chemicals can be used for chemical debonding. A photo acid generator (PAG)-assisted debonding method was demonstrated at room temperature when PAG-loaded PPC (PAG-PPC) was used as bonding adhesive. The ultraviolet (UV) radiation was used to enhance the PAG-assisted debonding.
A Compact Experimentally Validated Model of Magnetorheological Fluids
Authors: Xu Fei-Hong , Xu Zhao-Dong , Zhang Xiang-Cheng , Guo Ying-Qing , Lu Yong
Published: October 2015

Magnetorheological (MR) dampers are one of the most promising devices for mitigation of vibration of engineering structures due to earthquakes and wind excitation. In this paper, a compact two-column model of an MR fluid is proposed in order to formulate a general solution for calculation of the yield shear stress of an MR fluid. The magnetic induction intensity in the damping gap, which is the key parameter of the compact two-column model, is determined through simulation of the magnetic circuit of the MR damper. To verify the effectiveness and significance of the proposed model, damping forces calculated based on the proposed model and the traditional single-chain model are compared with the experimental data. Results show that the proposed compact two-column model is more accurate and that it can describe the rheological properties of the MR fluids very well.
A Shape Memory Alloy-Based Morphing Axial Fan Blade—Part II: Blade Shape and Computational Fluid Dynamics Analyses
Authors: Suman Alessio , Fortini Annalisa , Aldi Nicola , Merlin Mattia , Pinelli Michele
Published: October 2015

The ability of a morphing blade to change its geometry according to the different operating conditions represents a challenging approach for the optimization of turbomachinery performance. In this paper, experimental and computational fluid dynamics (CFD) numerical analyses on a morphing blade for a heavy-duty automotive cooling axial fan are proposed. Starting from the experimental results proposed in the first part of this work, a morphing blade, made of shape memory alloy (SMA) strips embedded in a polymeric structure, was thoroughly tested. In order to assess the ability of the strips to reach a progressive and smooth shape changing evolution, several experiments were performed in a purpose-built wind tunnel. The morphing blade changed its shape as the strips were thermally activated by means of air stream flow. The bending deformation evolution with the increasing number of thermal cycles was evaluated by digital image analysis techniques. After the analyses in the wind tunnel, CFD numerical simulations of a partially shrouded fan composed of five morphing blades were performed in order to highlight the evolution of the fan performance according to air temperature conditions. In particular, the capability of the blade activation was evaluated by the comparison between the fan performance with nonactivated blades and with activated blades. The results show a progressive stabilization of the shape memory behavior after the first cycle. The blade deformation led to a significant improvement in the fan performance at a constant rotational velocity. The CFD numerical simulation points out the differences in the overall performance and of three-dimensional fluid dynamic behavior of the fan. This innovative concept is aimed at realizing a sensorless smart fan control, permitting (i) an energy saving that leads to fuel saving in the automotive application fields and (ii) an increase in engine life, thanks to a strong relationship between the engine thermal request and the cooling fan performance.
Flashback Propensity of Turbulent Hydrogen–Air Jet Flames at Gas Turbine Premixer Conditions
Authors: Kalantari Alireza , Sullivan-Lewis Elliot , McDonell Vincent
Published: October 2015

The flashback propensity of a premixed jet flame has been studied experimentally. Boundary layer flashback has been investigated under turbulent flow conditions at elevated pressures and temperatures (i.e., 3–8 atm and 300–500 K). The data presented in this study are for hydrogen fuel at various Reynolds numbers, which are representative of practical gas turbine premixer conditions, and are significantly higher than results currently available in the literature. Three burner heads constructed of different materials (stainless steel, copper, and zirconia ceramic) were used to evaluate the effect of tip temperature, a parameter found previously to be an important factor in triggering flashback. This study characterizes flashback systematically by developing a comprehensive nondimensional model which takes into account all effective parameters in boundary layer flashback propensity. The model was optimized for new data and captures the behavior of the new results well. Further, comparison of the model with the single existing study of high-pressure jet flame flashback also indicates good agreement. For a given equivalence ratio, the critical velocity gradient and bulk velocity at flashback vary exponentially with pressure. The pressure exponent of the critical velocity gradient was found to be close to 1.1 at fuel-lean conditions and becomes higher as equivalence ratio is increased. The developed dimensionless correlation is Da=Const·Le1.68·Pef1.91·(Tu/T0)2.57·(Ttip/To)−0.49·(Pu/P0)−2.1, which can be used to predict the boundary layer flashback propensity for given parameters.
A minimum spanning forest based classification method for dedicated breast CT images
Authors: Pike Robert , Sechopoulos Ioannis , Fei Baowei
Published: October 2015

Purpose:

To develop and test an automated algorithm to classify different types of tissue in dedicated breast CT images.

Methods:

Images of a single breast of five different patients were acquired with a dedicated breast CT clinical prototype. The breast CT images were processed by a multiscale bilateral filter to reduce noise while keeping edge information and were corrected to overcome cupping artifacts. As skin and glandular tissue have similar CT values on breast CT images, morphologic processing is used to identify the skin based on its position information. A support vector machine (SVM) is trained and the resulting model used to create a pixelwise classification map of fat and glandular tissue. By combining the results of the skin mask with the SVM results, the breast tissue is classified as skin, fat, and glandular tissue. This map is then used to identify markers for a minimum spanning forest that is grown to segment the image using spatial and intensity information. To evaluate the authors’ classification method, they use DICE overlap ratios to compare the results of the automated classification to those obtained by manual segmentation on five patient images.

Results:

Comparison between the automatic and the manual segmentation shows that the minimum spanning forest based classification method was able to successfully classify dedicated breast CT image with average DICE ratios of 96.9%, 89.8%, and 89.5% for fat, glandular, and skin tissue, respectively.

Conclusions:

A 2D minimum spanning forest based classification method was proposed and evaluated for classifying the fat, skin, and glandular tissue in dedicated breast CT images. The classification method can be used for dense breast tissue quantification, radiation dose assessment, and other applications in breast imaging.
Direct measurement of electron beam quality conversion factors using water calorimetry
Authors: Renaud James , Sarfehnia Arman , Marchant Kristin , McEwen Malcolm , Ross Carl , Seuntjens Jan
Published: October 2015

Purpose:

In this work, the authors describe an electron sealed water calorimeter (ESWcal) designed to directly measure absorbed dose to water in clinical electron beams and its use to derive electron beam quality conversion factors for two ionization chamber types.

Methods:

A functioning calorimeter prototype was constructed in‐house and used to obtain reproducible measurements in clinical accelerator‐based 6, 9, 12, 16, and 20 MeV electron beams. Corrections for the radiation field perturbation due to the presence of the glass calorimeter vessel were calculated using Monte Carlo (MC) simulations. The conductive heat transfer due to dose gradients and nonwater materials was also accounted for using a commercial finite element method software package.

Results:

The relative combined standard uncertainty on the ESWcal dose was estimated to be 0.50% for the 9–20 MeV beams and 1.00% for the 6 MeV beam, demonstrating that the development of a water calorimeter‐based standard for electron beams over such a wide range of clinically relevant energies is feasible. The largest contributor to the uncertainty was the positioning (Type A, 0.10%–0.40%) and its influence on the perturbation correction (Type B, 0.10%–0.60%). As a preliminary validation, measurements performed with the ESWcal in a 6 MV photon beam were directly compared to results derived from the National Research Council of Canada (NRC) photon beam standard water calorimeter. These two independent devices were shown to agree well within the 0.43% combined relative uncertainty of the ESWcal for this beam type and quality. Absorbed dose electron beam quality conversion factors were measured using the ESWcal for the Exradin A12 and PTW Roos ionization chambers. The photon‐electron conversion factor, kecal, for the A12 was also experimentally determined. Nonstatistically significant differences of up to 0.7% were found when compared to the calculation‐based factors listed in the AAPM's TG‐51 protocol. General agreement between the relative electron energy dependence of the PTW Roos data measured in this work and a recent MC‐based study are also shown.

Conclusions:

This is the first time that water calorimetry has been successfully used to measure electron beam quality conversion factors for energies as low as 6 MeV (R50 = 2.25 cm).
Analysis of the track‐ and dose‐averaged LET and LET spectra in proton therapy using the geant4 Monte Carlo code
Authors: Guan Fada , Peeler Christopher , Bronk Lawrence , Geng Changran , Taleei Reza , Randeniya Sharmalee , Ge Shuaiping , Mirkovic Dragan , Grosshans David , Mohan Radhe , Titt Uwe
Published: October 2015

Purpose:

The motivation of this study was to find and eliminate the cause of errors in dose‐averaged linear energy transfer (LET) calculations from therapeutic protons in small targets, such as biological cell layers, calculated using the geant 4 Monte Carlo code. Furthermore, the purpose was also to provide a recommendation to select an appropriate LET quantity from geant 4 simulations to correlate with biological effectiveness of therapeutic protons.

Methods:

The authors developed a particle tracking step based strategy to calculate the average LET quantities (track‐averaged LET, LETt and dose‐averaged LET, LETd) using geant 4 for different tracking step size limits. A step size limit refers to the maximally allowable tracking step length. The authors investigated how the tracking step size limit influenced the calculated LETt and LETd of protons with six different step limits ranging from 1 to 500 μm in a water phantom irradiated by a 79.7‐MeV clinical proton beam. In addition, the authors analyzed the detailed stochastic energy deposition information including fluence spectra and dose spectra of the energy‐deposition‐per‐step of protons. As a reference, the authors also calculated the averaged LET and analyzed the LET spectra combining the Monte Carlo method and the deterministic method. Relative biological effectiveness (RBE) calculations were performed to illustrate the impact of different LET calculation methods on the RBE‐weighted dose.

Results:

Simulation results showed that the step limit effect was small for LETt but significant for LETd. This resulted from differences in the energy‐deposition‐per‐step between the fluence spectra and dose spectra at different depths in the phantom. Using the Monte Carlo particle tracking method in geant 4 can result in incorrect LETd calculation results in the dose plateau region for small step limits. The erroneous LETd results can be attributed to the algorithm to determine fluctuations in energy deposition along the tracking step in geant 4. The incorrect LETd values lead to substantial differences in the calculated RBE.

Conclusions:

When the geant 4 particle tracking method is used to calculate the average LET values within targets with a small step limit, such as smaller than 500 μm, the authors recommend the use of LETt in the dose plateau region and LETd around the Bragg peak. For a large step limit, i.e., 500 μm, LETd is recommended along the whole Bragg curve. The transition point depends on beam parameters and can be found by determining the location where the gradient of the ratio of LETd and LETt becomes positive.
Adult abdomen–pelvis CT: Does equilibrium dose‐pitch product better account for the kVp dependence of organ dose than conventional CTDI?
Authors: Li Xiang , Morgan Ashraf G. , Liptak Christopher L. , Muryn John S. , Dong Frank F. , Primak Andrew N. , Segars W. Paul
Published: October 2015

Purpose:

In CT imaging, a desirable quality assurance dose quantity should account for the dose variability across scan parameters and scanner models. Recently, AAPM Task Group 111 proposed to use equilibrium dose‐pitch product , in place of CT dose index (CTDI100), for scan modes involving table translation. The purpose of this work is to investigate whether this new concept better accounts for the tube voltage (kVp) dependence of organ dose than the conventional CTDI100.

Methods:

Three extended cardiac‐torso patient models were included in this study. They represented normal‐weight, overweight, and obese patients with abdomen–pelvis diameters ranging between 23 and 36 cm and body mass indices ranging between 20 and 42. A Monte Carlo program developed and validated for a 128‐slice CT system was used to simulate organ dose for abdomen–pelvis scans at five tube voltages (70, 80, 100, 120, 140 kVp) with a pitch of 0.8 and a collimation of 38.4 mm. The same Monte Carlo program was also used to obtain CTDI100 and as well as their volume‐averaged values, CTDIvol and .

Results:

With other scan parameters kept constant, organ dose itself depended strongly on kVp. For the normal‐weight patient model, the coefficient of variation (COV) across the five kVp values ranged between 72% and 75% for nine organs (liver, spleen, stomach, pancreas, kidneys, colon, small intestine, bladder, and ovaries) fully encompassed by the primary radiation beam. The COV generally increased with increasing patient size, ranging between 72%–77% and 76%–81% for the overweight and obese patient models, respectively. One‐way analysis of variance for the effect of kVp was highly significant for all patient models (p < 2 × 10−26). When organ dose was normalized by CTDIvol, the COV across kVps reduced to 5%–11%, 6%–15%, 12%–22% for the normal‐weight, overweight, and obese patients, respectively. The effect of kVp was still highly significant (p = 0.0001–0.004). When organ dose was normalized by , the COV further reduced to 1%–8%, 3%–11%, 9%–19%, respectively. The effect of kVp was still significant for the obese patient model (p = 0.004), but no longer significant for the normal‐weight and overweight patient models (p = 0.4 and 0.09, respectively). Finally, if organ dose conversion factors obtained at 120 kVp were used to approximate the values at 70 and 80 kVp, the resulting errors in the estimated organ dose were significantly reduced when the conversion factors were based on instead of CTDIvol.

Conclusions:

In adult abdomen–pelvis CT, equilibrium dose‐pitch product better accounts for the kVp dependence of organ dose than CTDI100.
Large area CMOS active pixel sensor x‐ray imager for digital breast tomosynthesis: Analysis, modeling, and characterization
Authors: Zhao Chumin , Kanicki Jerzy , Konstantinidis Anastasios C. , Patel Tushita
Published: October 2015

Purpose:

Large area x‐ray imagers based on complementary metal‐oxide‐semiconductor (CMOS) active pixel sensor (APS) technology have been proposed for various medical imaging applications including digital breast tomosynthesis (DBT). The low electronic noise (50–300 e−) of CMOS APS x‐ray imagers provides a possible route to shrink the pixel pitch to smaller than 75 μm for microcalcification detection and possible reduction of the DBT mean glandular dose (MGD).

Methods:

In this study, imaging performance of a large area (29 × 23 cm2) CMOS APS x‐ray imager [Dexela 2923 MAM (PerkinElmer, London)] with a pixel pitch of 75 μm was characterized and modeled. The authors developed a cascaded system model for CMOS APS x‐ray imagers using both a broadband x‐ray radiation and monochromatic synchrotron radiation. The experimental data including modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE) were theoretically described using the proposed cascaded system model with satisfactory consistency to experimental results. Both high full well and low full well (LFW) modes of the Dexela 2923 MAM CMOS APS x‐ray imager were characterized and modeled. The cascaded system analysis results were further used to extract the contrast‐to‐noise ratio (CNR) for microcalcifications with sizes of 165–400 μm at various MGDs. The impact of electronic noise on CNR was also evaluated.

Results:

The LFW mode shows better DQE at low air kerma (Ka < 10 μGy) and should be used for DBT. At current DBT applications, air kerma (Ka ∼ 10 μGy, broadband radiation of 28 kVp), DQE of more than 0.7 and ∼0.3 was achieved using the LFW mode at spatial frequency of 0.5 line pairs per millimeter (lp/mm) and Nyquist frequency ∼6.7 lp/mm, respectively. It is shown that microcalcifications of 165–400 μm in size can be resolved using a MGD range of 0.3–1 mGy, respectively. In comparison to a General Electric GEN2 prototype DBT system (at MGD of 2.5 mGy), an increased CNR (by ∼10) for microcalcifications was observed using the Dexela 2923 MAM CMOS APS x‐ray imager at a lower MGD (2.0 mGy).

Conclusions:

The Dexela 2923 MAM CMOS APS x‐ray imager is capable to achieve a high imaging performance at spatial frequencies up to 6.7 lp/mm. Microcalcifications of 165 μm are distinguishable based on reported data and their modeling results due to the small pixel pitch of 75 μm. At the same time, potential dose reduction is expected using the studied CMOS APS x‐ray imager.
Modeling explosion generated Scholte waves in sandy sediments with power law dependent shear wave speed
Authors: Soloway Alexander G. , Dahl Peter H. , Odom Robert I.
Published: October 2015

Experimental measurements of Scholte waves from underwater explosions collected off the coast of Virginia Beach, VA in shallow water are presented. It is shown here that the dispersion of these explosion-generated Scholte waves traveling in the sandy seabed can be modeled using a power-law dependent shear wave speed profile and an empirical source model that determines the pressure time-series at 1 m from the source as a function of TNT-equivalent charge weight.
Running Mechanics During the World’s Most Challenging Mountain Ultramarathon
Authors: Degache Francis , Morin Jean-Benoît , Oehen Lukas , Guex Kenny , Giardini Guido , Schena Federico , Millet Guillaume Y. , Millet Grégoire P.
Published: October 2015

The aim of study was to examine the effects of the world’s most challenging mountain ultramarathon (Tor des Géants [TdG]) on running mechanics. Mechanical measurements were undertaken in male runners (n = 16) and a control group (n = 8) before (PRE), during (MID), and after (POST) the TdG. Contact (tc) and aerial (ta) times, step frequency (f), and running velocity (v) were sampled. Spring-mass parameters of peak vertical ground-reaction force (Fmax), vertical downward displacement of the center of mass (Δz), leg-length change (ΔL), and vertical (kvert) and leg (kleg) stiffness were computed. Significant decreases were observed in runners between PRE and MID for ta (P < .001), Fmax (P < .001), Δz (P < .05), and kleg (P < .01). In contrast, f significantly increased (P < .05) between PRE and MID-TdG. No further changes were observed at POST for any of those variables, with the exception of kleg, which went back to PRE. During the TdG, experienced runners modified their running pattern and spring-mass behavior mainly during the first half. The current results suggest that these mechanical changes aim at minimizing the pain occurring in lower limbs mainly during the eccentric phases. One cannot rule out that this switch to a “safer” technique may also aim to anticipate further damages.