bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns and Correlates of Tropical Dry Forest Structure and Composition in a Highly Replicated Chronosequence in Yucatan, Mexico
Authors: Dupuy Juan Manuel , Hernández‐Stefanoni José Luis , Hernández‐Juárez Rodrigo A. , Tetetla‐Rangel Erika , López‐Martínez Jorge Omar , Leyequién‐Abarca Eurídice , Tun‐Dzul Fernando J. , May‐Pat Filogonio
Published: May 2011

Research on tropical dry forest (TDF) succession i0s needed for effective conservation and management of this threatened and understudied ecosystem. We used a highly replicated chronosequence within a 37,242‐ha TDF landscape to investigate successional patterns by plant size class and to evaluate the influence of stand age, topographic position, soil properties and spatial autocorrelation on forest structure and composition. We used a SPOT5 satellite image to obtain a land‐cover thematic map, and sampled woody vegetation (adults: >5 cm diam; saplings: 1–5 cm) and soil properties in 168 plots distributed among four vegetation classes: VC1 (3–8‐yr‐old forest), VC2 (9–15‐yr‐old forest), VC3 (>15‐yr‐old forest on flat areas), VC4 (>15‐yr‐old forest on hills). Stem density decreased with stand age and was lowest in VC3, while height, basal area and species density increased with age and were higher in older than in younger forests. Topographic position also influenced forest structure and composition. Basal area and height were largely determined by stand age, whereas stem and species density, and composition were influenced mostly by soil variables associated with fertility, and by spatial autocorrelation. Adults and saplings showed contrasting patterns and correlates of community structure, but similar patterns and correlates of composition, possibly due to the prevalence of coppicing. Our results show that our sampling approach can overcome several limitations of chronosequence studies, and provide insights in the patterns and drivers of succession, as well as guidelines for forest management and conservation.

Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp.
Foraging Behavior and Coexistence of Two Sunbird Species in a Kenyan Woodland
Authors: Oyugi Joseph O. , Brown Joel S. , Whelan Christopher J.
Published: May 2011

We investigated the mechanism of coexistence of the rare Amani Sunbird (Hedydipna pallidigastra) and the widespread Collared Sunbird (H. collaris), within Brachystegia woodland in the Arabuko‐Sokoke Forest, Kenya. We compared how prey abundance and search strategies affect resource exploitation by the two species. We used foraging theory to direct our measures of feeding activities as influenced by sunbird species, tree species and foraging height. We evaluated invertebrate abundance among tree species at different heights within trees. The Collared Sunbird primarily used the understory, and the Amani Sunbird primarily used the upper‐canopy. Overall, the rate of prey attacks per flight of the Amani Sunbird was 2.8 times greater than that of the Collared Sunbird. The Amani Sunbird, however, used increased search and attack rates in the understory compared with the mid‐ and upper‐canopies, but the Collared Sunbird foraged similarly throughout all strata. We hypothesize that the increased foraging rate of the Amani in the understory reflects increased foraging costs due to interference from the Collared Sunbird in that stratum. Furthermore, the Collared Sunbird exploits rich patches by moving frequently from place to place. The Amani Sunbird forages slowly, with reduced travel rates, and with a greater number of prey captures within a patch. Arthropod density did not differ among the vegetative strata, but was higher in Brachystegia spiciformis and Hymenaea verrucosa than in six other tree species. We hypothesize that the Amani Sunbird appears dependent upon continued tall B. spiciformis trees within the canopy of the Arabuko‐Sokoke Forest.
Spatial kinematics of Brightest Cluster Galaxies and their close companions from Integral Field Unit spectroscopy
Authors: Brough S. , Tran K.-V. , Sharp R. G. , von der Linden A. , Couch Warrick J.
Published: May 2011

We present Integral Field Unit (IFU) spectroscopy of four brightest cluster galaxies (BCGs) at z ∼ 0.1. Three of the BCGs have close companions within a projected radius of 20 kpc and one has no companion within that radius. We calculate the dynamical masses of the BCGs and their companions to be 1.4 × 1011 < Mdyn(M⊙) < 1.5 × 1012. We estimate the probability that the companions of the BCGs are bound using the observed masses and velocity offsets. We show that the lowest mass companion (1:4) is not bound while the two nearly equal mass (1:1.45 and 1:1.25) companions are likely to merge with their host BCGs in 0.35 Gyr in major, dry mergers. We conclude that some BCGs continue to grow from major merging even at z ∼ 0. We analyse the stellar kinematics of these systems using the λR parameter developed by the SAURON team. This offers a new and unique means to measure the stellar angular momentum of BCGs and make a direct comparison to other early-type galaxies. The BCGs and their companions have similar ellipticities to those of other early-type galaxies but are more massive. We find that not all these massive galaxies have low λRe as one might expect. One of the four BCGs and the two massive companions are found to be fast-rotating galaxies with high angular momentum, thereby providing a new test for models of galaxy evolution and the formation of intracluster light.
A New Naturally Derived Photosensitizer and Its Phototoxicity on Head and Neck Cancer Cells
Authors: Lim Siang Hui , Lee Hong Boon , Ho Anthony Siong Hock
Published: May 2011

In our screening for photosensitizers from natural resources, 151‐hydroxypurpurin‐7‐lactone ethyl methyl diester (compound 1) was isolated for the first time from an Araceae plant. To evaluate the efficacy of compound 1 as a photosensitizer for head and neck cancers, compound 1 was studied in reference to a known photosensitizer pheophorbide‐a (Pha), in terms of photophysical properties, singlet oxygen generation and in in vitro experiments (intracellular uptake and phototoxicity assays) in two oral (HSC2 and HSC3) and two nasopharyngeal (HK1 and C666‐1) cancer cell lines. In this study, compound 1 exhibited higher intracellular uptake over 24 h compared with Pha in both HSC3 and HK1 cells. When activated by ≥4.8 J cm−2 of light, compound 1 was slightly more potent as a photosensitizer than Pha by consistently having marginally lower IC50 values across different cell lines. In flow cytometry experiments to study the mechanism of photoactivated cell death in HSC3, compound 1 was observed to induce more pronounced apoptosis compared with Pha, which may have been driven by the transient G2/M cell cycle block which was also observed. These promising results on compound 1 warrant its further investigation as a clinically useful photodynamic therapy agent for head and neck cancer.
Vitamin D Status of Adults from Tropical Australia Determined Using Two Different Laboratory Assays: Implications for Public Health Messages
Authors: Nowak Madeleine , Harrison Simone L. , Buettner Petra G. , Kimlin Michael , Porter David , Kennedy Lee , Speare Rick
Published: May 2011

We measured serum 25 hydroxyvitamin D [25(OH)D] levels of ambulatory adults in tropical Australia to determine whether it is appropriate to continue promoting sun‐safety in this population. In August 2006 (winter), self‐administered questionnaires were completed by 145 Meals‐on‐Wheels volunteers (49.3% male; mean age 57.8 ± 14.7 years; 76.6% response) from Townsville, Queensland (Latitude 19oS). Serum 25(OH)D was analyzed using two common assays. Mean levels were 68.3 (SD ± 18.7; range 26–142) by DiaSorin Radioimmunoassay and 83.0 (SD ± 30.8; range 30–184) by DiaSorin Liaison® one. No participants were 25(OH)D deficient (<25 nmol L−1). Nine participants (6.2%) had 25(OH)D levels between 25 and 50 nmol L−1 (insufficient), by both methods (seven with a BMI ≥ 25). Twenty‐eight participants (19.3%) had one result in the insufficient range and the other in the adequate range. Thus, almost all of these free‐living adults in tropical Australia had adequate vitamin D levels at the end of winter. There was poor agreement between the two 25(OH)D assays. These results suggest it is appropriate to continue promoting sun‐safe messages to the ambulatory Caucasian adult population of North Queensland, which has an extremely high incidence of skin cancer. The lack of agreement between the two assays is a concern. Few doctors are aware of this measurement issue.
“Deliberative Disagreement” in U.S. Health Policy Committee Hearings
Authors: ESTERLING KEVIN M.
Published: May 2011

The exchange of rationales among debate participants is necessary for legitimacy in a deliberative democracy. I show that witnesses in congressional committee hearings tend to use falsifiable rationales when they encounter moderate levels of disagreement and shift to nonfalsifiable rationales when they encounter extreme disagreement. I use data from a coding of hearings testimony on the Medicare program, held between 1990 and 2003, as well as from a survey of participating witnesses measuring their perceptions of disagreement at the hearing. The results identify conditions that enhance falsifiable discourse and help to establish the empirical grounding deliberative democratic theory.
The Effects of Uncontested Elections on Legislator Performance
Authors: KONISKY DAVID M. , UEDA MICHIKO
Published: May 2011

Political competition lies at the core of representative democracy. Yet, uncompetitive elections and uncontested races are widespread in the United States, particularly at the state level. In this article, we analyze the consequences of uncontested elections on lawmaking activity. Our primary hypothesis is that legislators who run unopposed are less active lawmakers than those who were selected through competitive elections. Studying roll‐call vote participation and bill introduction and enactment for most of the U.S. states for 1999–2000, we find that state legislators elected in unopposed elections perform more poorly compared to their colleagues elected in competitive contests.
Evidence of a Local Incumbency Advantage
Authors: TROUNSTINE JESSICA
Published: May 2011

Incumbents are highly likely to win reelection at all levels of government, but scholars continue to debate the extent to which serving in office has a causal effect on winning. For city council elections it is unclear whether or not we should predict a causal effect at all. City councilors may not regularly seek reelection, and any apparent advantage could be entirely attributable to preexisting qualities rather than incumbency. This article uses a regression discontinuity design to provide evidence that city council incumbents are more likely to run and win their next elections because they served a term in office.
Issue Voting and Partisan Defections in Congressional Elections
Authors: HERRNSON PAUL S. , CURRY JAMES M.
Published: May 2011

In every election cycle the fate of some candidates is determined by partisans who defect from their usual voting habits to cast a ballot for the candidate of the opposing party. Defections in congressional elections have been attributed to incumbency, presidential approval, partisan strength, and factors related to individual voters. Our systematic assessment of the impact of issues on voter defections shows that party‐owned issues and performance issues associated favorably with one party affect the likelihood of partisan defections. The results suggest that congressional candidates can use issues to draw supporters away from the opposing party and to keep partisan voters loyal.
Is Timing Everything? Retirement and Seat Maintenance in the U.S. House of Representatives
Authors: SWEARINGEN C. DOUGLAS , JATKOWSKI WALT
Published: May 2011

Literature on open‐seat elections has focused on the individual attributes of a candidate and/or institutional arrangements. When a seat becomes an open contest could be a significant indicator as to how likely the incumbent party is able to maintain the seat. Examining data on open U.S. House seats from 1996 to 2008, we use OLS regression and logistic regression analysis, finding that time is a significant predictor for incumbent party fund‐raising and seat maintenance. We conclude that political parties have an interest in encouraging members of Congress to announce their retirement early in the election cycle.
A Teacher's Journey with a New Generation Handheld: Decisions, Struggles, and Accomplishments
Authors: Özgün‐Koca S. Aslı , Meagher Michael , Edwards Michael Todd
Published: May 2011

In this technology‐oriented age, teachers face daily decisions regarding the use of advanced digital technologies—graphing calculators, dynamic geometry software, blogs, wikis, podcasts and the like—to enhance student mathematical understanding in their classrooms. In this case study, the authors use the Technological, Pedagogical, and Content Knowledge (TPACK) model in conjunction with a five‐stage developmental model, which can be used to describe growth in TPACK to describe the initial attempts of a teacher, Jane, to develop TPACK as she learns and attempts to integrate an advanced teaching technology into her classroom, namely the TI‐Nspire graphing calculator. The study tracks her struggles to reconcile some traditional beliefs about how students learn with her desire to be responsive to what she perceives as affordances of advanced digital technologies. Main data collection methods were journal writing, observations, document analysis, and interviews. Using the five‐stage developmental model, we saw that this experience helped Jane to move among different stages. This study showed that the TPACK model with the five‐stage developmental model can be a beneficial tool for researchers to study teachers' professional growth and is also a valuable tool for teachers to reflect on their own growth.
Content Knowledge, Attitudes, and Self‐Efficacy in the Mathematics New York City Teaching Fellows (NYCTF) Program
Authors: Evans Brian R.
Published: May 2011

The purpose of this study was to understand the mathematical content knowledge new teachers have both before and after taking a mathematics methods course in the NYCTF program. Further, the purpose was to understand the attitudes toward mathematics and concepts of self‐efficacy that Teaching Fellows had over the course of the semester. The sample included 42 new Teaching Fellows who were given a mathematics content test, attitudes toward mathematics questionnaire, and teaching self‐efficacy questionnaire at the beginning and end of the semester. Further, the teachers kept teaching and learning journals. Findings revealed a significant increase in both mathematical content knowledge and positive attitudes toward mathematics. Additionally, Teaching Fellows were found to have positive attitudes and high self‐efficacy at the end of the semester, and relationships were found between attitudes and self‐efficacy. Finally, Teaching Fellows generally found that classroom management was the biggest issue in their teaching, and that problem solving and numeracy were the most important topics addressed in their learning. Future studies should address self‐efficacy differences between preservice and in‐service teachers and the effects of alternative certification teacher knowledge, attitudes toward mathematics, and self‐efficacy on students in the classroom.
Preservice Teachers' Beliefs and Attitude About Teaching and Learning Mathematics Through Music: An Intervention Study
Authors: An Song A. , Ma Tingting , Capraro Mary Margaret
Published: May 2011

This article presents exploratory research investigating the integration of music and a mathematics lesson as an intervention to promote preservice teachers' attitude and confidence and to extend their beliefs toward teaching mathematics integrated with music. Thirty students were randomly selected from 64 preservice teachers in a southern university. A 90‐minute mathematics lesson integrated with a music composition activity was taught by the first author. Pre‐ and postquestionnaires were provided to evaluate the change in preservice teachers' attitude and beliefs toward mathematics. The results demonstrated that the mathematics lesson integrated with music had a positive effect on preservice teachers' attitude and beliefs toward mathematics teaching and learning.
Inward and Outward Diffusion of Modifying Ions and its Impact on the Properties of Glasses and Glass–Ceramics
Authors: Smedskjaer Morten M. , Yue Yuanzheng
Published: May 2011

In this paper, we review our recent findings about both the cationic inward and outward diffusion processes in glasses and glass–ceramics caused by redox reactions. We provide new insights into these findings by mapping the diffusion depth, the thermal reduction temperature, and time in a three dimensional diagram and by looking into the correlation among the glass composition, structure, topology, and the diffusion process in the polyvalent elements containing glasses. We illustrate the link between glassy dynamics (via the liquid fragility index m) and activation energy of diffusion. Furthermore, the inward diffusion approach is used to study percolation phenomena in glass–ceramics. Finally, we show that the diffusion approaches are potential tools for tailoring the surface performances of bulk glasses and glass fibers.
Homogeneity of Inorganic Glasses: Quantification and Ranking
Authors: Jensen Martin , Zhang Long , Keding Ralf , Yue Yuanzheng
Published: May 2011

Homogeneity of glasses is a key factor determining their physical and chemical properties and overall quality. However, quantification of the homogeneity of a variety of glasses is still a challenge for glass scientists and technologists. Here, we show a simple approach by which the homogeneity of different glass products can be quantified and ranked. This approach is based on determination of both the optical intensity and dimension of the striations in glasses. These two characteristic values are obtained using the image processing method established recently. The logarithmic ratio between the dimension and the intensity is used to quantify and rank the homogeneity of glass products. Compared with the refractive index method, the image processing method has a wider detection range and a lower statistical uncertainty.
Demonstration of a Palm-Sized 30 W Air-to-Power Turbine Generator
Authors: Sato S. , Jovanovic S. , Lang J. , Spakovszky Z.
Published: May 2011

A compact, high power density turbo-generator system was conceived, designed, and experimentally tested. The air-to-power (A2P) device with a nominal design point of 50 W electric power output operates on high pressure air such as from a plant pneumatic system or from a portable bottle of pressurized air. A concept design study was first carried out to explore the design space for a range of output power at cost efficiency levels specified in collaboration with industry. The cost efficiency is defined as the cost of electrical power over the cost of pressurized air. The key challenge in the design is the relatively low power demand of 50 W while operating at high supply pressures of nominally 5–6 bars. To meet the cost efficiency goal under these conditions, a high-speed turbine and generator (∼450,000 rpm) are required with small blade span (∼200 μm), minimizing the mass flow while achieving the highest possible turbine performance. Since turbines with such small turbomachinery blading are not commercially available, a silicon-based micro electro mechanical systems (MEMS) turbine was designed using 2D and 3D computational fluid dynamics (CFD) computations. To reduce the development time, existing and previously demonstrated custom-made generator and ceramic ball bearing technology were used, resulting in a compact A2P proof-of-concept demonstration. The cylindrical device of 35 mm diameter resembles a tube fitting with a standard M24 adapter. Without load, a top turbine speed of 475,000 rpm was demonstrated, exceeding the design specification. Using load resistors, the proof-of-concept A2P device achieved 30 W of electrical power at 360,000 rpm and a turbine efficiency of 47%, meeting the cost efficiency goal. Higher speeds under load could not be achieved due to thrust load limitations of the off-shelf ball bearings. The demonstrated performance is in good agreement with the projected CFD based predictions. To the authors’ knowledge, this is the first successful demonstration of a self-contained, 50 W class turbo-generator of hybrid architecture where a MEMS turbine disk is joined with a precision machined titanium shaft and aluminum housing.
Gas Turbine Gas Fuel Composition Performance Correction Using Wobbe Index
Authors: Li Bryan , Gross Mike J. , Schmitt Thomas P.
Published: May 2011

Gas turbine thermal performance is dependent on many external conditions, including fuel gas composition. Measured performance must be corrected to specified reference conditions prior to comparison against performance specifications. A performance correction for fuel composition is thus required. One current method of correction commonly used is to characterize fuel composition effects as a function of heating value and hydrogen to carbon ratio. This method has been used in the past within a limited range of fuel composition variation around the expected composition, yielding relatively small correction factors on the order of ±0.1%. With industry trends suggesting continued exposure of gas turbines to a broader range of fuels such as liquefied natural gas and synthesized low BTU fuel, the corresponding performance effects will be much larger. As a result, a more comprehensive correction methodology is required to encompass a broader range of fuel constituents encountered. Analytical studies have been completed with the aid of thermodynamic models to identify the extent to which the Wobbe index can be used to correlate the response of gas turbine performance parameters to fuel gas composition. Results suggest that improved performance test accuracy can be achieved by using the Wobbe index compared with the aforementioned conventional fuel characteristics. This proposed method remains compliant with intent of internationally accepted test codes such as ASME PTC-22, ASME PTC-46, and ISO 2314.
Optical Measurement of Thermal Conductivity Using Fiber Aligned Frequency Domain Thermoreflectance
Authors: Malen Jonathan A. , Baheti Kanhayalal , Tong Tao , Zhao Yang , Hudgings Janice A. , Majumdar Arun
Published: May 2011

Fiber aligned frequency domain thermoreflectance (FAFDTR) is a simple noncontact optical technique for accurately measuring the thermal conductivity of thin films and bulk samples for a wide range of materials, including electrically conducting samples. FAFDTR is a single-sided measurement that requires minimal sample preparation and no microfabrication. Like existing thermoreflectance techniques, a modulated pump laser heats the sample surface, and a probe laser monitors the resultant thermal wave via the temperature dependent reflectance of the surface. Via the use of inexpensive fiber coupled diode lasers and common mode rejection, FAFDTR addresses three challenges of existing optical methods: complexity in setup, uncertainty in pump-probe alignment, and noise in the probe laser. FAFDTR was validated for thermal conductivities spanning three orders of magnitude (0.1–100 W/m K), and thin film thermal conductances greater than 10 W/m2 K. Uncertainties of 10–15% were typical, and were dominated by uncertainties in the laser spot size. A parametric study of sensitivity for thin film samples shows that high thermal conductivity contrast between film and substrate is essential for making accurate measurements.
Thermal
and Hydraulic Performance of Counterflow Microchannel Heat Exchangers With and Without
Nanofluids
Authors: Seyf Hamid
Reza , Keshavarz
Mohammadian Shahabeddin
Published: May 2011

This paper analyzes the thermal and hydraulic performance of a counterflow microchannel heat exchanger (CFMCHE) with and without nanofluid as working fluid. A 3D conjugate heat transfer simulation is carried out using a finite volume approach to evaluate the effects of inlet Reynolds number, Brownian motion, and volume fraction of nanoparticles on the pumping power, effectiveness, and performance index of CFMCHE. The accuracy of the code has been verified by comparing the results with those available in the literature. A single phase approach is used for the nanofluid modeling. The base fluid used in the analyses as a basis for comparison was pure water. Two types of nanofluids, namely, water-Al2O3 with a mean diameter of 47 nm and water-CuO with a mean diameter of 29 nm, each one with three different volume fractions, are utilized. In addition, two temperature dependent models for the thermal conductivity and viscosity of nanofluids that account for the fundamental role of Brownian motion are used. Calculated results demonstrate that the effectiveness and performance index of CFMCHE decrease with increasing Reynolds number. Moreover, it is observed that the relative enhancements in the pumping power become more prominent for higher values of Reynolds numbers. It was also found that the performance index and pumping power are not sensitive to volume fraction at higher and lower Reynolds numbers, respectively.
Modified Elliptical Machine Motor-Drive Design for Assistive Gait Rehabilitation
Authors: Nelson Carl A. , Burnfield Judith M. , Shu Yu , Buster Thad W. , Taylor Adam P. , Graham Andrew
Published: May 2011

Current gait rehabilitation systems have limited use in community and home settings due to issues of design, cost, and demands on clinical staff. To overcome these challenges, a new gait rehabilitation machine was designed and developed by modifying an existing elliptical trainer. The Intelligently Controlled Assistive Rehabilitation Elliptical (ICARE) provides answers to design limitations that occur in partial-bodyweight-support treadmill systems and other robotic systems by providing a simulated gait motion without the financial and human resource challenges. The ICARE system integrates ergonomic, comfort and safety enhancements with a motor-drive system to optimize usability by individuals with physical disabilities in hospitals, homes, and fitness settings. The affordable new design provides a complete system that reduces physical demands on clinical staff without compromising patient safety. Development and preliminary testing of the ICARE’s motor-drive system are detailed.
Modeling and Validating the Transient Behavior of Flat Miniature Heat Pipes Manufactured in Multilayer Printed Circuit Board Technology
Authors: Wits Wessel W. , Kok Jim B. W.
Published: May 2011

A novel, integrated approach in thermal management of electronic products, based on two-phase cooling, is presented. A flat miniature heat pipe, integrated inside the laminated structure of a printed circuit board (PCB), has been developed, based on mainstream PCB multilayer technology. To accurately predict the thermal performance of this two-phase heat transport device and to establish the operational limitations, a numerical model based on control volume elements is discussed. The advantage of this modular approach, compared with, e.g., finite element models, is that the model can be expanded with additional components (e.g., multiple evaporators) very easily. Actual PCBs with several hot spots cooled by flat miniature heat pipes and their parameter effects can be analyzed very quickly, without the necessity of complex and time-consuming finite element analyses. Experimental verification has shown a good comparison with model predictions. Time evolution analyses show that the developed control volume model is well capable of describing the heat pipe transient behavior.
Constructal Design of Complex Assembly of Fins
Authors: Lorenzini Giulio , Corrêa Roberta Lima , Domingues dos Santos Elizaldo , Rocha Luiz Alberto Oliveira
Published: May 2011

Constructal design is a method that conducts the designer toward flow (e.g., heat flux) architectures that have greater global performance. This numerical work uses this method to seek for the best geometry of a complex assembly of fins, i.e., an assembly where there is a cavity between the two branches of the T-Y-assembly of fins and two additional extended surfaces. The global thermal resistance of the assembly is minimized four times by geometric optimization subject to the following constraints: the total volume, the volume of fin material, the volume of the cavity, and the volume of the two additional extended surfaces. Larger amount of fin material improves the performance of the assembly of fins. The three times optimized global thermal resistance of the complex assembly of fins performs 32% better than the best T-Y-configuration under the same thermal and geometric conditions. The three times minimized global thermal resistance of the complex assembly of fins was correlated by power laws as a function of its corresponding optimal configurations.
Cl
2
/
BCl
3
/
Ar
plasma etching and in situ oxygen plasma treatment for leakage current suppression in AlGaN/GaN high-electron mobility transistors
Authors: Kim Hyeongnam , Schuette Michael L. , Lu Wu
Published: May 2011

An effective mesa-isolation process using Cl-based gas chemistry and oxygen plasma post-treatment is investigated to minimize the effect of plasma-induced damage on AlGaN/GaN high-electron mobility transistor (HEMT) performance. Plasma-induced dc bias of the dry etching of AlGaN/GaN heterostructures is optimized using Cl2/BCl3/Ar gases by monitoring leakage current between adjacent mesas and etch profiles near mesa edges. A dc bias of ∼100 V leads to a smoother etched surface and mesa surface near mesa edge and a lower leakage current than dc bias of 260 V. AlGaN/GaN HEMTs fabricated under a dc bias of 100 V show a reasonable pinch-off performance but still high drain leakage current level (tens of microamperes). Oxygen plasma treatment after dry etching is introduced for further reduction in the leakage current. In situ oxygen plasma treatment more effectively improves the leakage current/breakdown performance than ex situ oxygen plasma treatment after the HEMTs are exposed to air. Combination of low-bias Cl-based dry etching and in situ plasma treatment leads to a breakdown voltage higher than 90 V and a drain leakage current of a few nanoamperes at (VDS,VGS)=(5 V,<VT). It is suggested that in situ oxygen treatment, together with low-bias dry etching, passivates the plasma-induced surface damage and results in good pinch-off/breakdown characteristics in AlGaN/GaN HEMTs.
Increasing the speed of solid-state nanopores
Authors: Waggoner Philip S. , Kuan Aaron T. , Polonsky Stas , Peng Hongbo , Rossnagel Stephen M.
Published: May 2011

In this work, the authors studied the time response of solid-state nanopores to the applied potentials and the corresponding capacitances. They primarily examined the effect of the doping of the silicon substrates as well as the addition of dielectrics above and below the device membrane. For simple silicon nitride membranes on a moderately doped Si, the measured RC time constants in 1M KCl are on the order of hundreds of microseconds or larger. The authors found that the silicon substrate’s doping level has a significant effect on the equivalent circuit of the device and the use of a more lightly doped Si significantly speeds up the device response. They attributed this effect to the reduction of depletion layer capacitance at the Si-electrolyte interfaces. In the best device structure tested, time constants of ∼425 ns were observed in 1M KCl, which is much faster than most DNA translocation times and on the same order of magnitude as the transit time of each base through typical nanopores.
MICRODYNAMICS OF MAGNETIC PARTICLES DISPERSED IN COMPLEX MEDIA
Authors: BOSSIS G. , LÓPEZ-LÓPEZ MODESTO T. , ZUBAREV A.
Published: May 2011

The aggregation of magnetic particles in the presence of a magnetic field is the basic phenomenon which underlies all the physics of magnetorheological (MR) fluids. Although these interactions are well understood when the suspending fluid is a simple liquid, new MR fluids based on dispersion of magnetic microparticles in a ferrofluid or MR elastomers based on dispersion of magnetic particles in a rubber matrix, present some unusual properties which are not well described by conventional theories. We analyze in this work the motion of magnetic particles dispersed in a ferrofluid and submitted to a magnetic field and discuss the possible applications.
ENHANCING MAGNETORHEOLOGY
Authors: KLINGENBERG D. J. , ULICNY J. C.
Published: May 2011

Experimental and simulation results are presented that illustrate how the addition of nonmagnetizable particles to a magnetorheological (MR) fluid can enhance the field-induced yield stress. Efforts to understand the underlying mechanisms are described.
FRACTAL GEOMETRY OF THE WAKE SHED BY A FLAPPING FILAMENT IN FLOWING SOAP-FILM
Authors: PORTARO ROCCO , FAYED MOHAMED , GUNTER AMY-LEE , ABDERRAHMANE HAMID AIT , NG HOI DICK
Published: May 2011

In this study, we illustrate the fractal nature of the wake shed by a periodically flapping filament. Such wake structure is a combination of primary vortex shedding resulting in the von Kármán vortex street, a series of concentrated vortex dipoles formed when the trailing edges of filaments reach their maximum amplitudes and small eddies form along the shear layer connected with the concentrated vortices due to the shear layer instability. The vortex dynamics of the flapping filament are visualized and imaged experimentally using a soap-film flow tunnel with a high-speed camera and a low pressure sodium lamp as a light source. The wake fractal geometry is measured using the standard box-counting method and it is shown that the fractal dimension of the soap pattern boundaries in the wake is D = 1.38 ± 0.05, which agrees well with those measured for fully developed turbulences and other shear flow phenomena. The invariant of the fractality in the wake induced by the flapping filament thus provides another illustration of the geometrical self-similarity and nonlinear dynamics of chaotic fluid flows.
CALCULUS ON FRACTAL SUBSETS OF REAL LINE — II: CONJUGACY WITH ORDINARY CALCULUS
Authors: PARVATE ABHAY , GANGAL A. D.
Published: May 2011

Calculus on fractals, or Fα-calculus, developed in a previous paper, is a calculus based fractals F ⊂ R, and involves Fα-integral and Fα-derivative of orders α, 0 < α ≤ 1, where α is the dimension of F. The Fα-integral is suitable for integrating functions with fractal support of dimension α, while the Fα-derivative enables us to differentiate functions like the Cantor staircase. Several results in Fα-calculus are analogous to corresponding results in ordinary calculus, such as the Leibniz rule, fundamental theorems, etc. The functions like the Cantor staircase function occur naturally as solutions of Fα-differential equations. Hence the latter can be used to model processes involving fractal space or time, which in particular include a class of dynamical systems exhibiting sublinear behaviour.

In this paper we show that, as operators, the Fα-integral and Fα-derivative are conjugate to the Riemann integral and ordinary derivative respectively. This is accomplished by constructing a map ψ which takes Fα-integrable functions to Riemann integrable functions, such that the corresponding integrals on appropriate intervals have equal values. Under suitable conditions, a restriction of ψ also takes Fα-differentiable functions to ordinarily differentiable functions such that their values at appropriate points are equal. Further, this conjugacy is generalized to one between Sobolev spaces in ordinary calculus and Fα-calculus.

This conjugacy is useful, among other things, to find solutions to Fα-differential equations: they can be mapped to ordinary differential equations, and the solutions of the latter can be transformed back to get those of the former. This is illustrated with a few examples.
PRICES OF BARRIER AND FIRST-TOUCH DIGITAL OPTIONS IN LÉVY-DRIVEN MODELS, NEAR BARRIER
Authors: BOYARCHENKO MITYA , DE INNOCENTIS MARCO , LEVENDORSKIĬ SERGEI
Published: May 2011

We calculate the leading term of asymptotics of the prices of barrier options and first-touch digitals near the barrier for wide classes of Lévy processes with exponential jump densities, including the Variance Gamma model, the KoBoL (a.k.a. CGMY) model and Normal Inverse Gaussian processes. In the case of processes of infinite activity and finite variation, with the drift pointing from the barrier, we prove that the price is discontinuous at the boundary. This observation can serve as the basis for a simple robust test of the type of processes observed in real financial markets. In many cases, we calculate the second term of asymptotics as well. By comparing the exact asymptotic results for prices with those of Carr's randomization approximation, we conclude that the latter is very accurate near the barrier. We illustrate this by including numerical results for several types of Lévy processes commonly used in option pricing.
METHOD OF MOMENTS APPROACH TO PRICING DOUBLE BARRIER CONTRACTS IN POLYNOMIAL JUMP-DIFFUSION MODELS
Authors: ERIKSSON BJORN , PISTORIUS MARTIJN
Published: May 2011

We present a method of moments approach to pricing double barrier contracts when the underlying is modelled by a polynomial jump-diffusion. By general principles the price is linked to certain infinite dimensional linear programming problems. Subsequently approximating these by finite dimensional linear programming problems, upper and lower bounds for the prices of such options are found. We derive theoretical convergence results for this algorithm, and provide numerical illustrations by applying the method to the valuation of several double barrier-type contracts (double barrier knock-out call, American corridor and double-no-touch options) under a number of different models, also allowing for a deterministic short rate.
ON THE SPECTRAL MEASURES OF SOME WEAKLY STATIONARY SEQUENCES INVOLVING RANDOMLY SPACED OBSERVATIONS
Authors: BRADLEY RICHARD C.
Published: May 2011

In an earlier paper by the author, as part of a construction of a counterexample to the central limit theorem under certain strong mixing conditions, a formula is given that shows, for strictly stationary sequences with mean zero and finite second moments and a continuous spectral density function, how that spectral density function changes if the observations in that strictly stationary sequence are "randomly spread out" in a particular way, with independent "nonnegative geometric" numbers of zeros inserted in between. In this paper, that formula will be generalized to the class of weakly stationary, mean zero, complex-valued random sequences, with arbitrary spectral measure.
ALMOST SURE ASYMPTOTIC STABILITY OF SCALAR STOCHASTIC DELAY EQUATIONS: FINITE STATE MARKOV PROCESS
Authors: SRI NAMACHCHIVAYA N. , WIHSTUTZ VOLKER
Published: May 2011

In this paper, we study the almost-sure asymptotic stability of scalar delay differential equations with random parametric fluctuations which are modeled by a Markov process with finitely many states. The techniques developed for the determination of almost-sure asymptotic stability of finite dimensional stochastic differential equations will be extended to delay differential equations with random parametric fluctuations. For small intensity noise, we construct an asymptotic expansion for the exponential growth rate (the maximal Lyapunov exponent), which determines the almost-sure stability of the stochastic system.
Differential effects of diet-induced obesity on BKCa β1-subunit expression and function in rat skeletal muscle arterioles and small cerebral arteries
Authors: Howitt Lauren , Sandow Shaun L. , Grayson T. Hilton , Ellis Zoe E. , Morris Margaret J. , Murphy Timothy V.
Published: May 2011

Mechanisms underlying obesity-related vascular dysfunction are unclear. This study examined the effect of diet-induced obesity on expression and function of large conductance Ca2+-activated potassium channel (BKCa) in rat pressurized small resistance vessels with myogenic tone. Male Sprague-Dawley rats fed a cafeteria-style high fat diet (HFD; ∼30% energy from fat) for 16–20 wk were ∼30% heavier than controls fed standard chow (∼13% fat). Obesity did not alter BKCa α-subunit function or α-subunit protein or mRNA expression in vessels isolated from the cremaster muscle or middle-cerebral circulations. In contrast, BKCa β1-subunit protein expression and function were significantly reduced in cremaster muscle arterioles but increased in middle-cerebral arteries from obese animals. Immunohistochemistry showed α- and β1-subunits were present exclusively in the smooth muscle of both vessels. Cremaster muscle arterioles from obese animals showed significantly increased medial thickness, and media-to-lumen ratio and pressurized arterioles showed increased myogenic tone at 30 mmHg, but not at 50–120 mmHg. Myogenic tone was not affected by obesity in middle-cerebral arteries. The BKCa antagonist iberiotoxin constricted both cremaster muscle and middle-cerebral arterioles from control rats; this effect of iberiotoxin was abolished in cremaster muscle arteries only from obese rats. Diet-induced obesity has contrasting effects on BKCa function in different vascular beds, through differential effects on β1-subunit expression. However, these alterations in BKCa function had little effect on overall myogenic tone, suggesting that the mechanisms controlling myogenic tone can be altered and compensate for altered BKCa expression and function.
Prostaglandins do not contribute to the nitric oxide-mediated compensatory vasodilation in hypoperfused exercising muscle
Authors: Casey Darren P. , Joyner Michael J.
Published: May 2011

We tested the hypothesis that 1) prostaglandins (PGs) contribute to compensatory vasodilation in contracting human forearm subjected to acute hypoperfusion, and 2) the combined inhibition of PGs and nitric oxide would attenuate the compensatory vasodilation more than PG inhibition alone. In separate protocols, subjects performed forearm exercise (20% of maximum) during hypoperfusion evoked by intra-arterial balloon inflation. Each trial included baseline, exercise before inflation, exercise with inflation, and exercise after deflation. Forearm blood flow (FBF; ultrasound) and local (brachial artery) and systemic arterial pressure [mean arterial pressure (MAP); Finometer] were measured. In protocol 1 ( n = 8), exercise was repeated during cyclooxygenase (COX) inhibition (Ketorolac) alone and during Ketorolac-NOS inhibition [ NG-monomethyl-l-arginine (l-NMMA)]. In protocol 2 ( n = 8), exercise was repeated during l-NMMA alone and during l-NMMA-Ketorolac. Forearm vascular conductance (FVC; ml·min−1·100 mmHg−1) was calculated from FBF (ml/min) and local MAP (mmHg). The percent recovery in FVC during inflation was calculated as (steady-state inflation + exercise value − nadir)/[steady-state exercise (control) value − nadir] × 100. In protocol 1, COX inhibition alone did not reduce the %FVC recovery compared with the control (no drug) trial (92 ± 11 vs. 100 ± 10%, P = 0.83). However, combined COX-nitric oxide synthase (NOS) inhibition caused a substantial reduction in %FVC recovery (54 ± 8%, P < 0.05 vs. Ketorolac alone). In protocol 2, the percent recovery in FVC was attenuated with NOS inhibition alone (69 ± 9 vs. 107 ± 10%, P < 0.01) but not attenuated further during combined NOS-COX inhibition (62 ± 10%, P = 0.74 vs. l-NMMA alone). Our data indicate that PGs are not obligatory to the compensatory dilation observed during forearm exercise with hypoperfusion.
Elastic Moduli of Carbon Nanohorns
Authors: Kumar Dinesh , Verma Veena , Bhatti H. S. , Dharamvir Keya
Published: May 2011

Carbon nanotube is a special case of carbon nanohorns or carbon nanocones with zero apex angle. Research into carbon nanohorns started almost at the same time as the discovery of nanotubes in 1991. Most researchers focused on the investigation of nanotubes, and the exploration of nanohorns attracted little attention. To model the carbon nanohorns, we make use of a more reliable second-generation reactive empirical bond-order potential by Brenner and coworkers. We investigate the elastic moduli and conclude that these nanohorns are equally strong and require in-depth investigation. The values of Young's and Shear moduli decrease with apex angle.
Scalp Angiosarcoma Remission with Bevacizumab and Radiotherapy without Surgery: A Case Report and Review of the Literature
Authors: De Yao Jocelyn T. , Sun Danyu , Powell Angela T. , Rehmus Esther H.
Published: May 2011

Angiosarcoma (AS) is a rare and aggressive vascular neoplasm with very poor prognosis. Patients with extensive cutaneous AS who are not surgical candidates have very limited options since there is no standard treatment. Treatment options include radiation, chemotherapy, and angiogenesis inhibitor with varying success rates. Here, we report a case an 88 year old patient with extensive scalp angiosarcoma having biopsy proven remission with bevacizumab and radiotherapy without undergoing surgery.
Numerical Computation and Investigation of the Characteristics of Microscale Synthetic Jets
Authors: Lee Ann , Yeoh Guan H. , Timchenko Victoria , Reizes John
Published: May 2011

A synthetic jet results from periodic oscillations of a membrane in a cavity. Jet is formed when fluid is alternately sucked into and ejected from a small cavity by the motion of membrane bounding the cavity. A novel moving mesh algorithm to simulate the formation of jet is presented. The governing equations are transformed into the curvilinear coordinate system in which the grid velocities evaluated are then fed into the computation of the flow in the cavity domain thus allowing the conservation equations of mass and momentum to be solved within the stationary computational domain. Numerical solution generated using this moving mesh approach is compared with an experimental result measuring the instantaneous velocity fields obtained by μPIV measurements in the vicinity of synthetic jet orifice 241 μm in diameter issuing into confined geometry. Comparisons between experimental and numerical results on the streamwise component of velocity profiles at the orifice exit and along the centerline of the pulsating jet in microchannel as well as the location of vortex core indicate that there is good agreement, thereby demonstrating that the moving mesh algorithm developed is valid.
Results for Twin Singular Nonlinear Problems with Damping Term
Authors: Zhang Youwei
Published: May 2011

By using the functional type cone expansion and compression fixed‐point theorem in cones, some new and general results on the existence of positive solution for twin singular boundary value problems with damping term are obtained. An example is given to illustrate our results.