bluuebunny/crossref_metadata_2025 huggingface dataset:
Coordinating for Contingencies: Taking Stock of Post‐9/11 Homeland Security Reforms
Authors: Brattberg Erik
Published: March 2012

Over a decade after September 11, American citizens are still asking themselves: ‘how much safer are we today?’ This question is also pertinent for scholars seeking to understand the post‐September 11 homeland security reforms. This paper, drawing on the public administration literature and using Don Kettl's ‘contingent coordination’ framework, sets out to discuss how well these efforts have addressed the central coordination challenges posed by homeland security. In doing so, it makes two contributions: one methodological (e.g., operationalizing the contingent coordination framework) and one empirical (e.g., assessing the effectiveness of post‐9/11 homeland security reforms). The paper concludes with an overall assessment of how to find ways to further strengthen the capacity of the US homeland security system.
The magnitude of hydraulic redistribution by plant roots: a review and synthesis of empirical and modeling studies
Authors: Neumann Rebecca B. , Cardon Zoe G.
Published: March 2012

Hydraulic redistribution (HR) – the movement of water from moist to dry soil through plant roots – occurs worldwide within a range of different ecosystems and plant species. The proposed ecological and hydrologic impacts of HR include increasing dry‐season transpiration and photosynthetic rates, prolonging the life span of fine roots and maintaining root–soil contact in dry soils, and moving rainwater down into deeper soil layers where it does not evaporate. In this review, we compile estimates of the magnitude of HR from ecosystems around the world, using representative empirical and modeling studies from which we could extract amounts of water redistributed by plant root systems. The reported average magnitude of HR varies by nearly two orders of magnitude across ecosystems, from 0.04 to 1.3 mm H2O d−1in the empirical literature, and from 0.1 to 3.23 mm H2O d−1in the modeling literature. Using these synthesized data, along with other published studies, we examine this variation in the magnitude of upward and downward HR, considering effects of plant, soil and ecosystem characteristics, as well as effects of methodological details (in both empirical and modeling studies) on estimates of HR. We take both ecological and hydrologic perspectives.

ContentsSummary337I.Introduction337II.Synthesis of the magnitudes of HR across ecosystems338III.Hydraulic redistribution models339IV.Methodological considerations affecting the magnitude of HR344V.Site characteristics affecting the magnitude of HR346VI.Plant characteristics affecting the magnitude of HR347VII.Conclusions349Acknowledgements350References350
Recurrent delusional ideas due to left caudate head infarction, without dementia
Authors: MEGURO Kenichi , MEGURO Mitsue , AKANUMA Kyoko
Published: March 2012

Herein we report the case of a 77‐year‐old, right‐handed man, without dementia, who had a cerebral infarction in the left caudate head that manifested recurrent delusional ideas. He experienced three episodes of delusional ideas; the first two occurred after loss of consciousness and the third after delirium at night. MRI findings of left caudate head infarction were the same for all three episodes. An unstable cerebral perfusion may have caused problems in the cerebral network between the caudate head and cerebral cortex. Decreased cerebral blood flow in the frontal lobe was noted particularly in the second and third episodes, supporting the neurological background of disinhibition of emotional behaviour. Antipsychotic drugs and a small dose of risperidone were effective in controlling the patient's delusional ideas.
Learning from Positive and Negative Monetary Feedback in Patients with Alcohol Dependence
Authors: Rustemeier Martina , Römling Juliane , Czybulka Christine , Reymann Gerhard , Daum Irene , Bellebaum Christian
Published: March 2012

Background

Chronic and excessive consumption of alcohol is associated with structural, physiological, and functional changes in multiple regions of the human brain including the prefrontal cortex, the medial temporal lobe, and the structures of the reward system. The present study aimed to assess the ability of alcohol‐dependent patients (ADP) to learn probabilistic stimulus–reward contingencies and to transfer the acquired knowledge to new contexts. During transfer, the relative preference to learn from positive or negative feedback was also assessed.

Methods

Twenty‐four recently detoxified ADP and 20 healthy controls engaged in a feedback learning task with monetary rewards. The learning performance per se and transfer performance including positive versus negative learning were examined, as well as the relationship between different learning variables and variables comprising alcohol and nicotine consumption patterns, depression, and personality traits (harm avoidance and impulsivity).

Results

Patients did not show a significant general learning deficit in the acquisition of stimulus–response–outcome associations. Fifteen healthy subjects and 13 patients reached the transfer phase, in which ADP showed generally lower performance than healthy controls. There was no specific deficit with regard to learning from positive or negative feedback. The only near‐significant (negative) correlation between learning variables and drug consumption patterns, depression, and personality traits emerged for harm avoidance and positive learning in controls.

Conclusions

Impaired transfer performance suggests that ADP had problems applying their acquired knowledge in a new context. Potential relations to dysfunctions of specific brain structures and implications of the finding for therapy are discussed.
Desplazamiento de trabajadores, ampliaciones de la Unión Europea y mundialización de los servicios
Authors: LALANNE Stéphane
Published: March 2012

Europa occidental es la región del mundo desarrollado más favorable a los desplazamientos de trabajadores, pues la liberalización de los mismos comenzó ya con la estrategia para el mercado interior de los servicios. Ahora bien, las ampliaciones de la Unión Europea hacia el este han ahondado las desigualdades salariales entre naciones y el peligro de dumpin social. Debido a la enérgica oposición manifestada por ciertos países, las autoridades comunitarias se vieron obligadas a mejorar la protección de estos trabajadores. El mercado interior europeo, laboratorio de la mundialización, demuestra que es necesario implantar salvaguardias como contrapartida de la liberalización de los desplazamientos.
Trabajo durante la primaria y aprovechamiento escolar en Chile, Colombia, Ecuador y Perú
Authors: POST David
Published: March 2012

En toda América Latina son muchos los estudiantes que hacen trabajo extraescolar durante sus estudios obligatorios, ya sea en su hogar o fuera de él. El autor usa modelos econométricos para averiguar la influencia del mismo en las puntuaciones de los estudiantes en matemáticas y en lectura al término de la enseñanza primaria. Incluso después de considerar el factor de que los alumnos que trabajan sean más numerosos en las escuelas peores, comprueba que el trabajo perjudica mucho el aprovechamiento escolar, sobre todo a los que lo desempeñan durante cuatro horas diarias o más.
Trabajo decente en las redes productivas mundiales. Marco del debate programático
Authors: BARRIENTOS Stephanie , MAYER Frederick , PICKLES John , POSTHUMA Anne
Published: March 2012

Los autores presentan esta sección monográfica de la Revista Internacional del Trabajo titulada «Trabajo decente en las redes productivas mundiales». Su objetivo es estudiar los retos que plantean estas redes que están transformando la estructura del comercio, la producción y el empleo en la economía globalizada actual. Los firmantes definen el concepto de progreso (y el de retroceso) en los ámbitos económico y social que se usan para investigar los efectos de las redes. Por último, estudian las iniciativas que han adoptado los Estados y otros agentes para subsanar el «déficit de gobernanza mundial» y el déficit consiguiente de trabajo decente que ha traído consigo la expansión de dichas redes.
La reglamentación de la jornada laboral en los Estados Unidos y Europa
Authors: Dembe Allard E.
Published: March 2012

El tiempo de trabajo se reglamentó por vez primera en la Inglaterra del siglo XIX debido a la situación que sufrían las mujeres y los niños empleados en las fábricas, y la normativa estadounidense surgió después como reacción al malestar social. A lo largo del siglo XX se sigue acortando la jornada laboral con el propósito de repartir mejor el empleo disponible a fin de atajar el desempleo. Durante los últimos veinte años se adopta la directiva europea al respecto y hay una presión política constante para reducir el desempleo y para que la seguridad en el trabajo abarque la ergonomía y las cuestiones de organización.
Plexiform melanocytic schwannoma: a mimic of melanoma
Authors: Yeh Iwei , Argenyi Zsolt , Vemula Swapna S. , Furmanczyk Paul S. , Bouffard Danielle , McCalmont Timothy H.
Published: March 2012

We present a unique dermal tumor for which we propose the term plexiform melanocytic schwanomma. The proliferation consisted of lobules of epithelioid and spindled cells with S100, Melan‐A and HMB‐45 positivity but without obvious melanin pigmentation. The nuclei were moderately pleomorphic in some areas, and in a few areas the mitotic index was elevated. Schwannian differentiation was inferred from the presence of areas with nuclear palisading resembling Verocay bodies, from plexiform architecture and from the presence of a thin rim of EMA positivity around the tumor. Array‐based comparative genomic hybridization showed genomic losses that overlap with those seen in sporadic schwanomma. The differential diagnosis included melanoma, melanotic schwannoma and cutaneous melanocytoneuroma, and we compare and contrast our case with these entities.

Yeh I, Argenyi Z, Vemula SS, Furmanczyk PS, Bouffard D, McCalmont TH. Plexiform melanocytic schwannoma: a mimic of melanoma.
The effect of strength training volume on satellite cells, myogenic regulatory factors, and growth factors
Authors: Hanssen K.E. , Kvamme N.H. , Nilsen T.S. , Rønnestad B. , Ambjørnsen I.K. , Norheim F. , Kadi F. , Hallèn J. , Drevon C.A. , Raastad T.
Published: March 2012

The aim of this work was to study the effect of training volume on activation of satellite cells. Healthy untrained men were randomly assigned into two groups. The 3L‐1UB group (n = 10) performed three‐set leg exercises and single‐set upper body exercises, and the 1L‐3UB group (n = 11) performed single‐set leg exercises and three‐set upper body exercises. Both groups performed three sessions (80–90 min) per week for 11 weeks. Biopsies were taken from m. vastus lateralis and m. trapezius. The number of satellite cells, satellite cells positive for myogenin and MyoD, and the number of myonuclei were counted. Homogenized muscle was analyzed for myogenin and MyoD, and extracted ribonucleic acid (RNA) was monitored for selected growth factor transcripts. Knee extensor strength increased more in the 3L‐1UB group than in the 1L‐3UB group (48 ± 4% vs 29 ± 4%), whereas the strength gain in shoulder press was similar in both training groups. The number of satellite cells in m. vastus lateralis increased more in the 3L‐1UB group than in the 1L‐3UB group. The number of myonuclei increased similarly in both groups. The messenger RNA expression of growth factors peaked after 2 weeks of training. In conclusion, increasing training volume enhanced satellite cell numbers in the leg muscle, but not in the upper body muscle.
Self‐reported and measured cardiorespiratory fitness similarly predict cardiovascular disease risk in young adults
Authors: Ortega F. B. , Sánchez‐López M. , Solera‐Martínez M. , Fernández‐Sánchez A. , Sjöström M. , Martínez‐Vizcaino V.
Published: March 2012

We aimed to (a) examine the validity and reliability of the International FItness Scale (IFIS) in Spanish young adults and (b) compare the capacity of self‐reported vs measured fitness to predict cardiovascular disease (CVD) risk. The study comprised 276 participants (18–30 years). Fitness level (overall and specific components) was both self‐reported (IFIS) and measured using standard fitness tests. Total and trunk fat was assessed by dual‐energy X‐ray absorptiometry. We computed a previously validated metabolic syndrome score. A separate sample of 181 of same age and characteristics fulfilled IFIS twice for reliability purposes. The results of the present study support the validity and reliability of self‐reported fitness, as measured by IFIS, in Spanish young adults. Our data also suggest that not only measured cardiorespiratory fitness but also self‐reported cardiorespiratory fitness predicts CVD risk, as assessed by adiposity and metabolic syndrome indicators. The associations for muscular fitness (both reported and measured) differed depending on how it was expressed (i.e., absolute vs relative terms). Self‐reported fitness, as assessed by IFIS, can be a good alternative when physical fitness cannot be measured in large surveys.
Retracted: Rehabilitation of the Atrophic Posterior Maxilla Using Short Implants or Sinus Augmentation with Simultaneous Standard‐Length Implant Placement: A 3‐Year Randomized Clinical Trial
Authors: Pieri Francesco , Aldini Nicolò Nicoli , Fini Milena , Marchetti Claudio , Corinaldesi Giuseppe
Published: March 2012

Retraction: The following article from Clinical Implant Dentistry and Related Research, “Rehabilitation of the Atrophic Posterior Maxilla Using Short Implants or Sinus Augmentation with Simultaneous Standard‐Length Implant Placement: A 3‐Year Randomized Clinical Trial”, by Francesco Pieri, Nicolò Nicoli Aldini, Milena Fini, Claudio Marchetti & Giuseppe Corinaldesi, published online on 15 March 2012 in Wiley Online Library (http://www.onlinelibrary.wiley.com), has been retracted by agreement between the journal Editors‐in‐Chief, William Becker and Lars Sennerby, and Wiley Periodicals, Inc. The retraction has been agreed due to the failure by the authors to respond to inquiries from the Editors‐in‐Chief regarding the provenance of the Astra implants prior to their release; approval of the study protocol; where the implants were placed; and the names and location of the patients who received the above implants.

REFERENCE

Francesco Pieri, Nicolò Nicoli Aldini, Milena Fini, Claudio Marchetti, Giuseppe Corinaldesi (2012) Rehabilitation of the atrophic posterior maxilla using short implants or sinus augmentation with simultaneous standard‐length implant placement: A 3‐year randomized clinical trial. Clinical Implant Dentistry and Related Research, doi: 10.1111/j.1708‐8208.2012.00451.x
Negative pressure wound therapy in acute, contaminated wounds: documenting its safety and efficacy to support current global practice
Authors: Shweiki Ehyal , Gallagher Kathy E
Published: March 2012

Negative pressure wound therapy (NPWT) is in widespread use and its role in wound care is expanding worldwide. It is estimated that 300 million acute wounds are treated globally each year. Currently, sporadic data exist to support NPWT in acutely contaminated wounds. Despite lack of data, use of negative pressure wound therapy in such cases is increasing across the globe. We retrospectively reviewed 86 consecutive patients, totalling 97 contaminated wounds. All wounds were Class IV based on US Center for Disease Control criteria. Sepsis criteria were present in 78/86 (91%) of patients. All patients were managed with NPWT. Wound type, degree of tissue destruction, presence of infection, wound dimension, timing of initial NPWT, type and timing of wound closure and patient comorbidities were recorded. Outcome endpoints included durability of wound closure and death. Wound location was 41/97 (42%) in the torso; 56/97 (58%) at the extremities. Tissue necrosis was present in 84/97 (87%) of wounds. Infection was present in 86/97 (89%) of wounds. Average wound size was 619 cm2 when square surface area measured; 786 cm3 when volume measurements taken. Mean time to wound closure was 17 days, median 10 days and mode 6 days. Durability of wound closure 73/79 (92%). Deaths were noted in 6/86 (7%) of patients. No deaths appeared related to NPWT. Contemporary NPWT related acute wound care is expanding empirically, in quantity and scope across the globe. However, several areas of concern are known regarding this contemporary use of NPWT in acute wounds. Thus, it is important to assess the safety and efficacy of such expanded empiric NPWT practice. Based on our findings with NPWT in the largest known patient cohort of this type, NPWT appears safe and effective in managing acute, contaminated wounds including patients meeting sepsis criteria. These findings provide evidence‐based support for current worldwide empiric NPWT‐related acute wound care.
Chinese firms in Vietnam: investment motives, institutional environment and human resource challenges
Authors: Cooke Fang Lee , Lin Zhaohong
Published: March 2012

Extant studies of HRM and industrial relations in multinational corporations (MNCs) have focused primarily on MNCs from developed economies. Few studies have examined the investment strategy and labour management practices of MNCs from emerging economies, such as China, in developing countries like Vietnam. Adopting a combined theoretical framework for analysis, this study fills the research gap by examining the investment motives, business strategy and management practices of three case study firms in the construction and light manufacturing industries. It compares and contrasts the institutional supports for and barriers to these state‐owned and privately owned firms from both home and host countries. The paper argues that the role of institutional actors differs across ownership forms and industrial sectors and that a multi‐theoretical perspective, including in particular the political economy perspective, is needed to study Chinese MNCs’ HRM practices in order to more fully understand how the practices are shaped and perceived.
Efectividad de las pensiones contributivas y financiadas con cargo a los impuestos de la seguridad social en América Central y efectos de la crisis mundial
Authors: Mesa‐Lago Carmelo
Published: March 2012

Durante los últimos treinta años, América Latina ha sido pionera en la realización de reformas estructurales de las pensiones. Este artículo se centra en una muestra regional representativa formada por siete países de América Central con diferentes niveles de desarrollo (Belice, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua y Panamá), y estudia las pensiones contributivas y financiadas con cargo a los impuestos, así como las recientes reformas de las pensiones. Evalúa de manera comparada la efectividad de los regímenes de pensión, basándose en los siguientes principios de la seguridad social: unidad, cobertura universal, adecuación de las prestaciones, igualdad de trato, solidaridad social e igualdad de género, y sostenibilidad financiera. Analiza también el efecto de la crisis mundial en los regímenes de pensiones de estos países, hace hincapié en las diferencias entre las pensiones públicas y privadas, y extrae enseñanzas y sugiere políticas para el futuro.
La eficacia del ingreso mínimo garantizado en Luxemburgo
Authors: Amétépé Fofo
Published: March 2012

A partir de los datos de 2007 este artículo analiza la eficacia del ingreso mínimo garantizado (IMG) en Luxemburgo. En primer lugar, examinamos la eficacia comparando la proporción de hogares elegibles según se apliquen los requisitos de 2007 o de 1986. Observamos que el 5,5 por ciento de los hogares son elegibles con los requisitos de 2007 y el 3,75 por ciento con los requisitos de 1986. Esto indica que la flexibilización de los requisitos permitió llegar a más hogares pobres. El artículo analiza luego la eficacia desde otra perspectiva, el índice de abstención en 2007. Dos tercios de los hogares elegibles no recurren al IMG. Los análisis de regresión de los potenciales determinantes de la abstención confirmaron las hipótesis que suele postular la bibliografía sobre el tema, en particular el factor pecuniario —el beneficio neto obtenido del IMG— y la estigmatización, que explican en gran parte la abstención del IMG.
Effect of Preconditioning and Stress Relaxation on Local Collagen Fiber Re-Alignment: Inhomogeneous Properties of Rat Supraspinatus Tendon
Authors: Miller Kristin S. , Edelstein Lena , Connizzo Brianne K. , Soslowsky Louis J.
Published: March 2012

Repeatedly and consistently measuring the mechanical properties of tendon is important but presents a challenge. Preconditioning can provide tendons with a consistent loading history to make comparisons between groups from mechanical testing experiments. However, the specific mechanisms occurring during preconditioning are unknown. Previous studies have suggested that microstructural changes, such as collagen fiber re-alignment, may be a result of preconditioning. Local collagen fiber re-alignment is quantified throughout tensile mechanical testing using a testing system integrated with a polarized light setup, consisting of a backlight, 90 deg-offset rotating polarizer sheets on each side of the test sample, and a digital camera, in a rat supraspinatus tendon model, and corresponding mechanical properties are measured. Local circular variance values are compared throughout the mechanical test to determine if and where collagen fiber re-alignment occurred. The inhomogeneity of the tendon is examined by comparing local circular variance values, optical moduli and optical transition strain values. Although the largest amount of collagen fiber re-alignment was found during preconditioning, significant re-alignment was also demonstrated in the toe and linear regions of the mechanical test. No significant changes in re-alignment were seen during stress relaxation. The insertion site of the supraspinatus tendon demonstrated a lower linear modulus and a more disorganized collagen fiber distribution throughout all mechanical testing points compared to the tendon midsubstance. This study identified a correlation between collagen fiber re-alignment and preconditioning and suggests that collagen fiber re-alignment may be a potential mechanism of preconditioning and merits further investigation. In particular, the conditions necessary for collagen fibers to re-orient away from the direction of loading and the dependency of collagen reorganization on its initial distribution must be examined.
Performance Analysis of Solar PV-Fuel Cell Integrated Floriculture Greenhouse
Authors: Ganguly A. , Ghosh S.
Published: March 2012

The application of greenhouse technology for cultivation of high value crops is rapidly expanding worldwide. But the requirement of electricity imposes a restriction on the emanation of this technology to areas which are remote. In a developing country like India, where a significant number of villages are yet to be connected to any national or regional grid, this restriction assumes considerable significance. The present paper has been divided into two parts: The first part dealing with the performance analysis of a floriculture greenhouse located in the plains of Indian subcontinent equipped with fan induced ventilation system and wet pad along with shading screens. The second part deals with the performance analysis of the greenhouse integrated power system comprising of solar photovoltaic array, electrolyser and fuel cell stacks. The hourly photovoltaic generation, load consumption, cumulative daylong hydrogen gas generation and consumption have been computed for various seasons of a climatic cycle and presented in this paper.
Maximizing the Usage of PCM Materials in Buildings
Authors: Aldoss Taha Khalil
Published: March 2012

The fundamentals of how PCM materials works need more consideration. It has been reported that using PCM materials may reduce the cooling/heating loads in buildings. PCM can only affect the fluctuation of the load and not the magnitude of the load. Thus PCM materials should be considered as an energy management tool only. For PCM to operate effectively the cycle of charging and discharging of PCM material should be completed over the period of the day, i.e. PCM must be melted and solidified over the 24 hrs of the day. Using the appropriate amount of the PCM will maximize its usage. Fewer amounts will show more fluctuation in the load and larger amount will be a waste without benefit. The appropriate amount for an application is found to be function of PCM properties, k, Cp, density and melting temperature. For PCM to complete the whole cycle in a day period melting temperature need to be near the average between the indoor and outdoor design temperature of the conditioned space. In this investigations a one dimensional model were investigated and solved numerically using finite difference technique. The effect of the amount of PCM material on load fluctuation is calculated and presented. Packing capsulated PCM material of linearly varying melting temperatures is found to maximize the effectiveness of the technique.
Energy Storage Via Electrochemical Conversion of CO2 Into Specialty Chemicals
Authors: Hill Davion , Zhai Yumei , Agarwal Arun , Rode Edward , Ayello Francois , Sridhar Narasi
Published: March 2012

There is significant interest in technologies that reduce or mitigate greenhouse gases in the atmosphere because of their contribution to climate change. In addition, concerns for energy security are linked to political, environmental, and economic factors that threaten supply of hydrocarbon sources for fuels and the petrochemical feedstock that support the production of plastics, fertilizers, and chemical supply chains. With these climate and energy security concerns, there is a need for technologies that can economically address both issues. In addition, with increased integration of renewable energy systems into the grid, there are major concerns about grid instability and the need for energy storage. Significant research is being done on both topics, but there is a need to more efficiently transmit and use energy (which is the focus of the Smart Grid initiatives) as well as store energy for future use. Electrochemical conversion of CO2 to useful products will be discussed including analyses of the energy and carbon balances required for the process, the value of the end use chemicals as energy storage media, and the energy density of the end use chemicals compared to other energy storage technologies.
Metal-Foam-Enhanced PCM Storage System: The Cylindrical Shell Geometry
Authors: Dukhan Nihad
Published: March 2012

Phase-change systems remain to be widely used for storage of thermal energy such as the energy harnessed by solar collectors. The major disadvantage of phase change materials (PCMs) is their low thermal conductivities, which drastically slows the phase change process and causes wide temperature variations within PCMs, while requiring heat transfer area. Metal foams are one class of porous media that possess thermal conductivities that are an order of magnitude higher than PCMs. When embedded in PCMs, the random internal structure and high porosity of metal foam enhance and accelerate the phase change process without significantly reducing PCMs’ heat storage capacity. Unlike traditional PCM systems, the distribution of the foam ligaments in PCMs makes the melting and solidification processes uniform and less dependent on location inside PCMs. This also leads to shorter charging and discharging times. The design, fabrication and characterization of a small PCM-metal-foam thermal storage system are described in this paper. The core of the system is a cylindrical shell composed of 90%-porous open-cell aluminum foam filled with Paraffin-based PCM. The foam occupies only 10% of the total volume. The shell walls were fabricated from copper. The system was tested in an open loop wind tunnel. Results for the convection heat transfer coefficient and the effect of volumetric flow rate on the system’s performance were obtained. The heat transfer rate from the system was computed and discussed.
Optimization of Equipment Control Parameters to Minimize HVAC Energy Consumption
Authors: Wemhoff Aaron P.
Published: March 2012

Heating, Ventilating, and Air Conditioning Systems (HVAC) consume nearly one-third of household energy in the United States. The optimization of the control parameters in HVAC equipment allows for a reduction in energy consumption. In this study, a supervisory control method is applied to a lumped parameter model of an HVAC system of interest containing a chiller and three dampers. The method determines the choice of control parameters that minimize the energy consumption for 1000 sampled steady-state loads. An energy savings of 39% was achieved using the method in this study compared to the base case.
Optimal Placement of Horizontal- and Vertical-Axis Wind Turbines in a Wind Farm for Maximum Power Generation Using a Genetic Algorithm
Authors: Chen Xiaomin , Agarwal Ramesh
Published: March 2012

In this paper, we consider the Wind Farm layout optimization problem using a genetic algorithm. Both the Horizontal–Axis Wind Turbines (HAWT) and Vertical-Axis Wind Turbines (VAWT) are considered. The goal of the optimization problem is to optimally place the turbines within the wind farm such that the wake effects are minimized and the power production is maximized. The reasonably accurate modeling of the turbine wake is critical in determination of the optimal layout of the turbines and the power generated. For HAWT, two wake models are considered; both are found to give similar answers. For VAWT, a very simple wake model is employed.
An Integrated Model of Global Warming and Policy Making
Authors: Zhang Zheming , Agarwal Ramesh
Published: March 2012

This paper describes a simple integrated model of global warming due to anthropogenic CO2 emissions, which can help the policy makers in considering various CO2 mitigation strategies. First, the constant airborne fraction model is generalized to establish relationship between CO2 emissions and CO2 concentration in the atmosphere which is then used to determine the global average surface temperature using the Oglesby and Saltzman’s general circulation model. Using these simple relationships, the forecast for CO2 emissions, CO2 concentration and average global surface temperature is made for years 2030 and 2050 under Business as Usual (BAU) scenario. In order to achieve an acceptable target increase in global average surface temperature, several simple CO2 mitigation approaches, proposed by Socolow and Lam, are included in the integrated model.
Flow Control for Wind Turbine Airfoil
Authors: Gross Andreas , Fasel Hermann F.
Published: March 2012

The flow over a NREL S822 wind turbine airfoil was simulated for a chord Reynolds number of 100,000 and an angle of attack of 5deg. These conditions approximately match the blade element conditions at 80% radius of a 2m diameter turbine operating at 300rpm. A simulation of the uncontrolled flow with steady approach flow conditions shows boundary layer separation on the suction side which is consistent with University of Illinois at Urbana-Champaign experimental data. Active flow control has the potential to locally (and on demand) reduce the unsteady loads on individual turbine blades during non-nominal operation, thereby increasing turbine life. In addition, flow control may help lower the cut-in wind speed. Unsteady flow control for reducing the suction side separation using pulsed vortex generator jets, flip-flop jets, and plasma actuators were evaluated. It was found that very low actuation amplitudes were already sufficient for eliminating the suction side separation. The high effectiveness and efficiency is traced back to hydrodynamic instabilities that lead to a downstream growth of the forced disturbances. Too high actuator amplitudes resulted in early disturbance saturation which made the control inefficient.
On the Analysis of Two-Phase Channel Flow With Flow Regime Transitions for Energy System
Authors: Chung Moon-Sun , Jung Youn-Gyu , Yi Sung-Jae
Published: March 2012

Numerical test and eigenvalue analysis for a two-phase channel flows for energy conversion systems like fuel cells or water electrolysers with flow regime transitions are performed by using the well-posed system of equation that takes into account the pressure jump at the phasic interface. The interfacial pressure jump terms derived from the definition of surface tension which is based on the surface physics make the conventional two-fluid model hyperbolic without any additive terms, i.e., virtual mass or artificial viscosity terms. The four-equation system has three sets of eigenvalues; each of them has an analytical form of real eigenvalues relevant to the sonic speeds with phasic velocities of three typical flow regimes such as dispersed, slug, and separated flows. Further, the eigenvalues for the flow transition regions can also be obtained numerically for smooth calculation of flow regime transitions. The sonic speeds agree well not only with the earlier experimental data but also with those of an analytical model. Owing to the hyperbolicity of this model, we can adopt an upwind method, which is one of the well-known Godunov type upwind methods. A typical example of two-phase flows shows that the present model can simulate the phase separation caused by density difference of two-phase fluids.
ReflecTech® Polymer Mirror Film Advancements in Technology and Durability Testing
Authors: DiGrazia Michael J. , Jorgensen Gary , Gee Randy , Bingham Carl , Loux Christa
Published: March 2012

One of the most promising developments for lowering the cost of utility scale concentrating solar power (CSP) is the emergence of durable reflective polymer films as an alternative to conventional curved glass mirrors. The broad adoption of wide web polymer film reflectors has been slowed by the lack of long-term weathering data. With the advent of the Ultra Accelerated Weathering System (UAWS), testing and development can proceed at a faster pace, and ReflecTech® Mirror Film has recently exceeded the equivalent terrestrial UV cumulative dosage of 25 years. ReflecTech® Mirror Film was developed through earlier collaborations between ReflecTech, Inc. (a subsidiary of SkyFuel, Inc.) and the National Renewable Energy Laboratory (NREL). More recently, through a Cooperative Research and Development Agreement (CRADA), ReflecTech, Inc. and NREL have developed an abrasion resistant coating (ARC) appropriate for application to polymer based mirror film. This hardcoat was developed to address the need for reflectors that are low in cost, high in performance and durable to mechanical cleaning methods sometimes used in the CSP environment. The combined impact of these two developments has the potential to significantly change the preferred supply choice for solar reflectors in new utility scale CSP projects. ReflecTech® Mirror Film samples prepared with and without the ARC hardcoat were subjected to accelerated exposure conditions more extreme than actual conditions. Both the uncoated and ARC films exhibit excellent weatherability with no loss in reflectance after highly accelerated exposure of over 25 years equivalent terrestrial UV. The ARC coated samples also exhibited outstanding initial abrasion resistance and adhesion to ReflecTech® Mirror Film, properties that were retained after exposure to various accelerated stress conditions including condensation cycling, thermal cycling, water immersion, and accelerated exposure to UV light. ReflecTech® Mirror Film is a commercially available product. The ARC-coated ReflecTech® Mirror Film has been successfully manufactured as a 1.5 m (5 ft) wide roll-to-roll construction in a commercial production environment and after further testing is expected to be commercially available in late 2011.
Two Types of Calorimeters for Assessing Fresnel Lens Performance in Concentrating Solar Systems
Authors: Sahm Aaron , Boehm Robert , Agyenim-Boateng Kwame , Hynes Ken , Hammer Kim , Roberts Tommy , Stone Ken
Published: March 2012

Concentrating solar energy systems can use either refractive or reflective approaches to achieve the desired concentration ratio. However this is done, there is always a question about what the flux might actually be incident on the target of interest after the concentration process. Assessing the losses due to the concentration process is quite important in understanding the overall performance of the solar concentrating system. An issue that impacts this measurement is the type of system being evaluated, as the total flux at the focal point could be quite large. We have been working with concentrating PV units that utilize acrylic Fresnel lenses to achieve the necessary concentration on a single multi-junction cell. The magnitude of the losses associated with these types of lenses was desired. We developed two calorimeters for the purpose of evaluating the optical efficiency of Fresnel lenses utilized in various point focus concentrating systems. The first calorimeter developed utilizes a transient technique whereby a time-measured pulse of the beam is directed to a mass of material in a cavity form. The material has a high conductivity, so the lumped mass approximation can be used for the analysis of the energy absorbed if the temperature rise of the material is measured. The other calorimeter developed was a steady-state type that employs a technique commonly known as flow calorimetry. In this approach, the concentrated flux is beamed into the core of the calorimeter which is cooled to some steady-state value of temperature with a liquid (water near the ambient temperature was used in our tests). Knowing the liquid flow rate and temperature rise of the fluid allows the total heat input to be assessed. This paper discusses the development, testing, and comparison of the two calorimeters. Results are given for the evaluation of several types of commercial acrylic Fresnel lenses having different characteristics such as groove density and focal length.
Maximum Net Power Output of the Recuperative Open and Direct Solar Thermal Brayton Cycle
Authors: Le Roux W. G. , Bello-Ochende T. , Meyer J. P.
Published: March 2012

The small-scale open and direct solar thermal Brayton cycle with recuperator has several advantages. These include low operation and maintenance costs and high recommendation. The main disadvantages of this cycle are the pressure losses in the recuperator and receiver, turbo-machine efficiencies and recuperator effectiveness, which limit the net power output of such a system. Thermodynamic optimization can be applied to address these disadvantages in order optimize the receiver and recuperator and to maximize the net power output of the system at any steady-state condition. The dynamic trajectory optimization method is applied to maximize the net power output of the system by optimizing the geometries of the receiver and recuperator, limited to various constraints. Standard micro-turbines and parabolic dish concentrator diameters of six to eighteen meters are considered. An optimum system geometry and maximum net power output can be generated for each operating condition of each micro-turbine and concentrator combination. The results show how the irreversibilities are spread throughout the system optimally, in order for the system to produce its maximum net power output. It indicates that the optimum operating point of a micro-turbine is at the point where the internal irreversibilities are approximately three times larger than the external irreversibilities.
Investigations of the Regeneration Step of a Thermochemical Cycle Using Mixed Iron Oxides Coated on SiSiC Substrates
Authors: Neises Martina , Simon Heike , Roeb Martin , Schmu¨cker Martin , Sattler Christian , Pitz-Paal Robert
Published: March 2012

A two-step thermochemical cycle for hydrogen production using mixed iron oxides coated on silicon carbide substrates has been investigated. The water-splitting step proceeds at temperatures between 800 and 1000 °C while for the regeneration step temperatures around 1200 °C are needed. A deactivation of the material resulting in a decrease of the hydrogen production within the first couple of cycles was observed in preceding tests. For detailed investigations of the system composed of the redox-material and the substrate small scale samples were tested in a laboratory test-rig. For identification of material changes the samples were investigated via XRD and SEM-EDS analysis. The analysis revealed the reasons for the deactivation of the redox-material. Through parametric studies the influence of the regeneration parameters, namely regeneration temperature and time on the hydrogen production was analysed. A model for the regeneration step was developed describing the performance of the regeneration step as a function of temperature and time and additionally as a function of total regeneration time, i.e. the cumulated time the sample has been regenerated.
Computational and Experimental Investigation of Bubble Circulation Patterns Within a Column Photobioreactor
Authors: Mortuza S. M. , Kommareddy Anil , Gent Stephen P. , Anderson Gary A.
Published: March 2012

This research project investigates bubble and liquid circulation patterns in a vertical column photobioreactor (PBR) both experimentally as well as computationally using Computational Fluid Dynamics (CFD). Dispersed gas–liquid flow in the rectangular bubble column PBR are modeled using Eulerian–Lagrangian approach. A low Reynolds number k–ε CFD model is used to describe the flow pattern near the wall. Bubble size distribution measurements are carried out using a high-speed digital camera. A flat surface bubble column PBR is used to achieve sufficient light penetration into the system. Carbon dioxide, which is necessary for photosynthetic microalgae growth, is added to the sparged air. The results are validated with experimental data and from current literature. Design parameters, bubble flow pattern and internal hydrodynamics of a bubble column reactor were studied and the numerical simulations presented for the hydrodynamics in a bubble column PBR account for bubble phenomena that have not been sufficiently accounted for in previous research. Bubble size and shape affect the hydrodynamics as does bubble interaction with other bubbles (multiple bubbles in a flow versus single bubbles and wall effects on bubble(s) which are not symmetrical or bubbles not centered on the reactor cross-section). Understanding the bubble movement patterns will aid in predicting other design parameters like mass transfer (bubble to liquid and liquid to bubble), heat transfer (within the PBR and between the PBR and environment surrounding the PBR), and interaction forces inside the PBR.
Dynamic Simulation of a Test Rig for Organic Vapours
Authors: Pini M. , Spinelli A. , Dossena V. , Gaetani P. , Casella F.
Published: March 2012

A blow-down facility for experimental analysis of real gases is under construction at Politecnico di Milano (Italy), in collaboration with Turboden s.r.l. and in the frame of the research project named Solar. Experiments are meant to characterize flow fields representative of expansions taking place in Organic Rankine Cycle (ORC) turbine passages. Indeed, ORC power plants represent a viable technology to exploit clean energy sources, but ORC turbines design tools still require accurate experimental data for validation. A significant improvement of turbine efficiency is expected from detailed investigations on vapour streams; in fact, ORC turbines design tools still require accurate experimental data for validation. The facility is equipped with a straight axis supersonic nozzle as a test section and a batch-closed loop plant has been designed in order to reduce investment and operational costs. Due to the batch operation, the evaluation of the time evolution of main processes involved in the cycle is of great importance. To this purpose a dynamic simulation of the test rig has been carried out using a dynamic simulator based on an object-oriented modeling language, Modelica, allowing an easy development of component models structured with a hierarchical approach. Models include control loop devices, strongly influencing processes duration. This paper presents how the test rig has been modelled, with particular emphasis on the models framework and on simulation procedure; the calculation results are finally discussed. With a lumped parameter approach, a first scheme of the facility has been built by modelling each of the three main plant section (heating, test, condensation) using components included in a self-made library. Several models, not embedded in the Modelica standard libraries, have been created using Modelica code; among them the most important has been the supersonic nozzle. In order to better describe the facility behaviour and the thermal losses, a plant calculation refinement has been carried out by the development of finite volume based one-dimensional models of ducts and reservoirs, either in radial or axial direction; in particular, a novel distributed-parameters model has been built for the heating section. All simulations have been performed using Siloxane MDM and Hydrofluorocarbon R245fa as reference fluids and FluidProp® to calculate thermodynamic properties. A quasi 1-D steady nozzle flow calculation has also been carried out by implementing FluidProp® routines in a dedicated Fortran software. Since the unsteady nozzle expansion is well approximated by a sequence of steady states, the computation provides all thermodynamic properties and velocity along the nozzle axis as a function of time. Simulation results have given a fundamental support to both plant and experiments design.
Hybrid Distributed Power Generation for an Isolated Rural Settlement in Masirah Island, Oman
Authors: Al Saadi Saleh , Krarti Moncef
Published: March 2012

This paper summarizes the findings from a feasibility study of using renewable energy sources in combination with conventional power systems to meet the electrical requirements for an isolated island of Masirah in Oman. The study has been conducted to determine the best hybrid system to generate electrical energy needed for a small community of 500 residential buildings. A series of a simulation analyses have been carried out to evaluate and optimize different distribution technologies including photovolatics, wind and diesel for electrical generation in combination with storage batteries. It was found that the cost of energy could be reduced by as much as 48% compared to the cost for the baseline generation system currently used in the Masirah Island (i.e. diesel-driven generators). In particular, it was found that wind turbines in combination with storage batteries have a great impact in reducing the cost of generating electrical energy for the residential community. Moreover, solar PV panels were found unattractive under the current diesel price rates but could potentially become viable if the diesel prices increase. The paper outlines an optimal design for generating electricity for the community at lowest cost while minimizing carbon emissions.