bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of gated cone‐beam CT to reduce respiratory motion blurring
Authors: Kincaid Russell E. , Yorke Ellen D. , Goodman Karyn A. , Rimner Andreas , Wu Abraham J. , Mageras Gig S.
Published: March 2013

Purpose:

Methods of reducing respiratory motion blurring in cone‐beam CT (CBCT) have been limited to lung where soft tissue contrast is large. Respiration‐correlated cone‐beam CT uses slow continuous gantry rotation but image quality is limited by uneven projection spacing. This study investigates the efficacy of a novel gated CBCT technique.

Methods:

In gated CBCT, the linac is programmed such that gantry rotation and kV image acquisition occur within a gate around end expiration and are triggered by an external respiratory monitor. Standard CBCT and gated CBCT scans are performed in 22 patients (11 thoracic, 11 abdominal) and a respiration‐correlated CT (RCCT) scan, acquired on a standard CT scanner, from the same day serves as a criterion standard. Image quality is compared by calculating contrast‐to‐noise ratios (CNR) for tumors in lung, gastroesophageal junction (GEJ) tissue, and pancreas tissue, relative to surrounding background tissue. Congruence between the object in the CBCT images and that in the RCCT is measured by calculating the optimized normalized cross‐correlation (NCC) following CBCT‐to‐RCCT rigid registrations.

Results:

Gated CBCT results in reduced motion artifacts relative to standard CBCT, with better visualization of tumors in lung, and of abdominal organs including GEJ, pancreas, and organs at risk. CNR of lung tumors is larger in gated CBCT in 6 of 11 cases relative to standard CBCT. A paired two‐tailedt‐test of lung patient mean CNR shows no statistical significance (p = 0.133). In 4 of 5 cases where CNR is not increased, lung tumor motion observed in RCCT is small (range 1.3–5.2 mm). CNR is increased and becomes statistically significant for 6 out of 7 lung patients with > 5 mm tumor motion (p = 0.044). CNR is larger in gated CBCT in 5 of 7 GEJ cases and 3 of 4 pancreas cases (p = 0.082 and 0.192). Gated CBCT yields improvement with lower NCC relative to standard CBCT in 10 of 11, 7 of 7, and 3 of 4 patients for lung, GEJ, and pancreas images, respectively (p = 0.0014, 0.0030, 0.165).

Conclusions:

Gated CBCT reduces image blurring caused by respiratory motion. The gated gantry rotation yields uniformly and closely spaced projections resulting in improved reconstructed image quality. The technique is shown to be applicable to abdominal sites, where image contrast of soft tissues is low.
Geometrical splitting technique to improve the computational efficiency in Monte Carlo calculations for proton therapy
Authors: Ramos‐Méndez José , Perl Joseph , Faddegon Bruce , Schümann Jan , Paganetti Harald
Published: March 2013

Purpose:

To present the implementation and validation of a geometrical based variance reduction technique for the calculation of phase space data for proton therapy dose calculation.

Methods:

The treatment heads at the Francis H Burr Proton Therapy Center were modeled with a new Monte Carlo tool (TOPAS based on Geant4). For variance reduction purposes, two particle‐splitting planes were implemented. First, the particles were split upstream of the second scatterer or at the second ionization chamber. Then, particles reaching another plane immediately upstream of the field specific aperture were split again. In each case, particles were split by a factor of 8. At the second ionization chamber and at the latter plane, the cylindrical symmetry of the proton beam was exploited to position the split particles at randomly spaced locations rotated around the beam axis. Phase space data in IAEA format were recorded at the treatment head exit and the computational efficiency was calculated. Depth–dose curves and beam profiles were analyzed. Dose distributions were compared for a voxelized water phantom for different treatment fields for both the reference and optimized simulations. In addition, dose in two patients was simulated with and without particle splitting to compare the efficiency and accuracy of the technique.

Results:

A normalized computational efficiency gain of a factor of 10–20.3 was reached for phase space calculations for the different treatment head options simulated. Depth–dose curves and beam profiles were in reasonable agreement with the simulation done without splitting: within 1% for depth–dose with an average difference of (0.2 ± 0.4)%, 1 standard deviation, and a 0.3% statistical uncertainty of the simulations in the high dose region; 1.6% for planar fluence with an average difference of (0.4 ± 0.5)% and a statistical uncertainty of 0.3% in the high fluence region. The percentage differences between dose distributions in water for simulations done with and without particle splitting were within the accepted clinical tolerance of 2%, with a 0.4% statistical uncertainty. For the two patient geometries considered, head and prostate, the efficiency gain was 20.9 and 14.7, respectively, with the percentages of voxels with gamma indices lower than unity 98.9% and 99.7%, respectively, using 2% and 2 mm criteria.

Conclusions:

The authors have implemented an efficient variance reduction technique with significant speed improvements for proton Monte Carlo simulations. The method can be transferred to other codes and other treatment heads.
Ovarian Stem Cells Find Their Niche
Authors: Oliver Trudy G.
Published: March 2013

A population of stem cells in the mouse hilum are prone to epithelial ovarian cancer.
High RANKs for Diabetes and Osteoporosis
Authors: Tirosh Amir
Published: March 2013

Blockade of RANKL signaling, a known approach for treating osteoporosis, may also improve liver insulin resistance and diabetes.
Influence of Acupuncture on the Outcomes of in Vitro Fertilisation When Embryo Implantation Has Failed: A Prospective Randomised Controlled Clinical Trial
Authors: di Villahermosa Daniela Isoyama Manca , dos Santos Lara Guercio , Nogueira Mariana Balthazar , Vilarino Fabia Lima , Barbosa Caio Parente
Published: March 2013

Objective

To evaluate the effectiveness of acupuncture and moxibustion as an adjuvant treatment in women undergoing in vitro fertilisation (IVF) when embryo implantation has failed.

Methods

A prospective, randomised controlled clinical trial was conducted with 84 infertile patients who had had at least two unsuccessful attempts of IVF. The patients were randomised in three groups: control (n=28), sham (n=28) and acupuncture (n=28). The sample size was calculated by assuming a pregnancy rate of 10% when embryo implantation had failed. The pregnancy rates of the current IVF cycle were evaluated by measurement of blood β human chorionic gonadotrophin (βhCG) and subsequent transvaginal ultrasound. Acupuncture was performed on the first and seventh day of ovulation induction, on the day before ovarian puncture and on the day after embryo transfer. In the acupuncture group, patients were treated with moxibustion at nine acupuncture points (BL18, BL22, BL23, BL52, CV3, CV4, CV5, CV7, GV4) and needling at 12 points. In the sham group needles were inserted in eight areas that did not correspond to known acupuncture points.

Results

The clinical pregnancy rate in the acupuncture group was significantly higher than that in the control and sham groups (35.7% vs 7.1% vs 10.7%; p=0.0169).

Conclusions

In this study, acupuncture and moxibustion increased pregnancy rates when used as an adjuvant treatment in women undergoing IVF, when embryo implantation had failed.
Sports participation in non-compaction cardiomyopathy: a systematic review
Authors: Ganga Harsha V , Thompson Paul D
Published: March 2013

Non-compaction cardiomyopathy (NCCM) is typified by deep invaginations of the myocardium and is caused by an arrest of normal myocardial morphogenesis. NCCM was once considered rare, but is now widely recognised owing to frequent use of advanced imaging techniques. NCCM can also be detected when competitive athletes undergo preparticipation screening for cardiac disease or when being evaluated for cardiac symptoms. It is not clear how athletes with NCCM should be managed. We searched PubMed and Google for articles addressing the issue of NCCM and athletic participation. We were able to identify only 18 cases of NCCM described in the context of sports, athletics or exercise. We conclude that there are insufficient data to develop firm recommendations on how to manage vigorous activity in patients with NCCM and future registries of sudden death in athletes should include a careful search for cases of NCCM among the victims so that clinicians can develop more definitive recommendations for athletes with this condition.
Upper limb international spasticity study: rationale and protocol for a large, international, multicentre prospective cohort study investigating management and goal attainment following treatment with botulinum toxin A in real-life clinical practice
Authors: Turner-Stokes Lynne , Fheodoroff Klemens , Jacinto Jorge , Maisonobe Pascal , Zakine Benjamin
Published: March 2013

Objectives

This article provides an overview of the Upper Limb International Spasticity (ULIS) programme, which aims to develop a common core dataset for evaluation of real-life practice and outcomes in the treatment of upper-limb spasticity with botulinum toxin A (BoNT-A). Here we present the study protocol for ULIS-II, a large, international cohort study, to describe the rationale and steps to ensure the validity of goal attainment scaling (GAS) as the primary outcome measure.

Methods and analysis design

An international, multicentre, observational, prospective, before-and-after study, conducted at 84 centres in 22 countries across three continents.

Participants

468 adults presenting with poststroke upper limb spasticity in whom a decision had already been made to inject BoNT-A (5–12 consecutive participants recruited per centre).

Interventions

Physicians were free to choose targeted muscles, BoNT-A preparation, injected doses/technique and timing of follow-up in accordance with their usual practice and the goals for treatment. Primary outcome measure: GAS. Secondary outcomes: Measurements of spasticity, standardised outcome measures and global benefits. Steps to ensure validity included: (1) targeted training of all investigators in the use of GAS; (2) within-study validation of goal statements and (3) establishment of an electronic case report form with an in-built tracking facility for separation of baseline/follow-up data.

Analysis

Efficacy population: all participants who had (1) BoNT-A injection and (2) subsequent assessment of GAS. Primary efficacy variable: percentage (95% CI) achievement of the primary goal from GAS following one BoNT-A injection cycle.

Ethics and dissemination

This non-interventional study is conducted in compliance with guidelines for good pharmacoepidemiology practices. Appropriate ethical approvals were obtained according to local regulations. ULIS-II will provide important information regarding treatment and outcomes from BoNT-A in real-life upper limb spasticity management. The results will be published separately.

Registration

ClinicalTrials.gov identifier:NCT01020500.
Young adult women smokers’ response to using plain cigarette packaging: a naturalistic approach
Authors: Moodie Crawford S , Mackintosh Anne Marie
Published: March 2013

Objectives

To explore young adult women smokers’ cognitive and emotional response to using dark brown ‘plain’ cigarette packs in natural settings and whether plain packaging is associated with any short-term change in smoking behaviour.

Design

A naturalistic approach. Participants used plain cigarette packs provided to them for 1 week and for 1 week their own fully branded packs, but otherwise smoked and socialised as normal. Participants completed questionnaires twice a week.

Setting

The six most populated cities and towns in Scotland.

Participants

301 young women smokers were recruited, with a final sample of 187 (62.1%). To meet the inclusion criteria women had to be between the ages of 18 and 35, daily cigarette smokers and provide a breath sample to confirm smoking status.

Primary and secondary outcome measures

Pack perceptions and feelings, feelings about smoking, salience and perceptions of health warnings and avoidant and cessation behaviours.

Results

In comparison to fully branded packaging, plain packaging was associated with more negative perceptions and feelings about the pack and about smoking (p<0.001). No significant overall differences in salience, seriousness or believability of health warnings were found between the pack types, but participants reported looking more closely at the warnings on plain packs and also thinking more about what the warnings were telling them (p<0.001). Participants reported being more likely to engage in avoidant behaviours, such as hiding or covering the pack (p<0.001), and cessation behaviours, such as foregoing cigarettes (p<0.05), smoking less around others (p<0.001), thinking about quitting (p<0.001) and reduced consumption (p<0.05), while using the plain packs. Results did not differ by dependence level or socioeconomic status.

Conclusions

No research design can capture the true impacts of plain packaging prior to its introduction, but this study suggests that plain packaging may help reduce cigarette consumption and encourage cessation in the short term.
Co-ACT—a framework for observing coordination behaviour in acute care teams
Authors: Kolbe Michaela , Burtscher Michael Josef , Manser Tanja
Published: March 2013

Background

Acute care teams (ACTs) represent action teams, that is, teams in which members with specialised roles must coordinate their actions during intense situations, often under high time pressure and with unstable team membership. Using behaviour observation, patient safety research has been focusing on defining teamwork behaviours—particularly coordination—that are critical for patient safety during these intense situations. As one result of this divergent research landscape, the number, scope and variety of applied behaviour observation taxonomies are growing, making comparison and convergent integration of research findings difficult.

Aim

To facilitate future ACT research by presenting a framework that provides a shared language of teamwork behaviours, allows for comparing previous and future ACT research and offers a measurement tool for ACT observation.

Method

Based on teamwork theory and empirical evidence, we developed Co-ACT—the Framework for Observing Coordination Behaviour in ACT. Integrating two previous, extensive taxonomies into Co-ACT, we also suggested 12 behavioural codes for which we determined inter-rater reliability by analysing the teamwork of videotaped anaesthesia teams in the clinical setting.

Results

The Co-ACT framework consists of four quadrants organised along two dimensions (explicit vs implicit coordination; action vs information coordination). Each quadrant provides three categories for which Cohen's κ overall value was substantial; but values for single categories varied considerably.

Conclusions

Co-ACT provides a framework for organising behaviour codes and offers respective categories for succinctly measuring teamwork in ACTs. Furthermore, it has the potential to allow for guiding and comparing ACTs study results. Future work using Co-ACT in different research and training settings will show how well it can generally be applied across ACTs.
Changes to the cardiac biomarkers of non-elite athletes completing the 2009 London Marathon
Authors: Baker Polly , Davies Sarah Louise , Larkin Joanne , Moult Daniel , Benton Sally , Roberts Andrew , Harris Timothy
Published: March 2013

Introduction

Many studies have demonstrated a rise in troponin and brain natriuretic peptide (BNP) levels following prolonged and/or strenuous exercise. Only one study looked at athletes who collapse and this showed no difference in cardiac biomarkers between those who collapsed and those who completed without requiring medical attention. We set out to describe and quantify the changes in troponin and BNP in three groups of non-elite runners at the 2009 London marathon: those with and without known structural heart disease (SHD) and those who collapsed on completion.

Methods

The first group (recruited group, RG) was recruited at the prerace exhibition. This group had two subsets, runners with SHD and without (non-SHD). A second group was recruited from those who collapsed (collapsed group, CG). Blood was taken for troponin I (TnI), troponin T (TnT), high sensitivity TnT (HSTnT) and BNP.

Results

Cardiac biomarker levels increased in all groups following the marathon. No statistically significant difference was seen between the SHD and non-SHD subgroups. When comparing the RG and CG the number and degree of rise was greater in those who collapsed. A trend for the degree of rise of HSTnT was demonstrated.

Discussion

We identified runners with troponin levels that, in other circumstances, would raise concern for myocardial necrosis. However absence of adverse clinical sequelae would suggest this rise is physiological. The cause and clinical significance of the increased HSTnT levels seen in those that collapsed is yet to be fully elucidated.
Buried pipeline responses to ground displacements induced by adjacent static pipe bursting
Authors: Shi Jiangwei , Wang Yu , Ng Charles W.W.
Published: March 2013

To minimize disruptions of economic and social activities on the ground surface in urban areas, trenchless techniques such as pipe bursting are often considered for underground pipeline construction, rehabilitation, and renewal of existing utility services. Pipe bursting, however, inevitably induces outward displacements of surrounding soil, and subsequently leads to potential damages to adjacent structures and utilities. This paper carries out finite element (FE) analyses to investigate effects of the static pipe bursting–induced ground displacements on adjacent pipelines. In total 760 FE parametric studies are performed to encompass various combinations of ground settlement profiles, pipe dimensions, material properties, and soil properties that are typical of utility pipelines and pipe bursting in urban areas. The FE parametric results are summarized in a dimensionless plot of relative pipe–soil stiffness versus ratio of maximum pipe curvature to maximum ground curvature, which can be used to directly estimate the maximum pipe bending strain and (or) directly evaluate pipeline responses to adjacent pipe bursting. A worked example is provided to illustrate usage of the dimensionless plot. It is further found that the pipe–soil interaction is similar for pipe bursting and tunneling, and the effects of both pipe bursting and tunneling on adjacent pipelines can be assessed using a unified dimensionless plot. Effects of the intersection angle between the pipe bursting centerline and adjacent pipeline are explored. The pipe responses are shown to be underestimated or unconservative when only the perpendicular case is considered in the analysis.
Application of variance decomposition approach in the uncertainty analysis of a hydrological model
Authors: Datta Arpana Rani , Bolisetti Tirupati
Published: March 2013

Decomposition of uncertainty into individual sources is important for understanding the risks of decisions made under the modelling uncertainty. This paper has applied the predictive uncertainty analysis and variance decomposition (VD) approach for quantifying hydrological modelling uncertainty. The VD analysis is used for quantifying the contribution of various sources of uncertainty to total modelling uncertainty. The goal is to increase the reliability of predictive uncertainty analysis by the inclusion of the results of VD analysis. The approach is evaluated by analyzing uncertainty of the Soil and Water Assessment Tool (SWAT) model for a watershed of Southwestern Ontario, Canada. Three uncertainty analyzing frameworks are employed for quantifying modelling uncertainty by both predictive uncertainty analysis and VD approach. The contribution of parameter uncertainty to total error variance is expressed by the percentage of total variance explained by parameter uncertainty and this contribution is quantified for three uncertainty analyzing frameworks. The contributions of other uncertainties excluding model parameters and precipitation uncertainties to total error variance are quantified by applying the VD approach. The results obtained from predictive uncertainty and VD analyses are observed to be consistent. The underlying hypotheses of each uncertainty framework are also verified for the reliability of the uncertainty analysis.
The persistence and stability of fish assemblages within eelgrass meadows (Zostera marina) on the Pacific coast of Canada
Authors: Robinson Clifford L.K. , Yakimishyn Jennifer
Published: March 2013

The persistence and stability of fish assemblages found in 34 eelgrass (Zostera marina) meadows along the British Columbia coast was examined from 2004 to 2011. Assemblage persistence (nontrending species composition) and assemblage stability (constancy in abundance over time) were assessed using a time-lag regression method that tests for temporal turnover within short time series. Overall, 85% of the fish assemblages persisted, and 80% of the assemblages exhibited stability in abundance over the 8-year study. Environmental conditions in 33 of 34 meadows did not change substantially over the 8 years, and the low interannual variability may have contributed to the high persistence and stability of the fish assemblages. The lack of temporal turnover in relatively undisturbed eelgrass fish assemblage properties is a critical element for effective monitoring of coastal ecosystem integrity.
Comparative analysis of induction of osmotic-stress-dependent genes in Vibrio vulnificus exposed to hyper- and hypo-osmotic stress
Authors: Rao Namrata V. , Shashidhar Ravindranath , Bandekar Jayant R.
Published: March 2013

Vibrio vulnificus, a halophilic pathogenic bacterium of marine environments, encounters changes in salinity in its natural habitat and in the food-processing environment. The comparative response of V. vulnificus to hyperosmotic and hypoosmotic stress in terms of gene expression was investigated. Genes belonging to the proU operon for transport of compatible solutes and compatible solute synthesis were significantly upregulated (3- to 4.7-fold) under hyperosmotic stress. Under hypoosmotic stress, upregulation of genes coding for mechanosensitive channels of small conductance (mscS) was not observed. In hyperosmotic conditions a 2.3-fold decrease in the expression of aqpZ was observed. A 2-fold induction in gyrA was observed in V. vulnificus cells on exposure to hyperosmotic stress. groEL genes, VVA1659 (1.6-fold), and VV3106 (1-fold) were induced in hypoosmotic condition. Results of this study indicate that to manage hyperosmotic stress, V. vulnificus accumulated osmoprotectants through uptake or through endogenous synthesis of compatible solutes. Expression of mscS may not be necessary for immediate protection in cells exposed to hyper- and hypo-osmotic stress. Comparative analysis of important osmotic-stress-related genes showed up- or down-regulation of 14 genes in hyperosmotic stress as compared with up- or down-regulation of only 7 genes in hypoosmotic stress, indicating that the cells respond asymmetrically to hyper- and hypo-osmotic stress.
THE CRITICAL EXPONENT IS COMPUTABLE FOR AUTOMATIC SEQUENCES
Authors: SCHAEFFER LUKE , SHALLIT JEFFREY
Published: March 2013

The critical exponent of an infinite word is defined to be the supremum of the exponent of each of its factors. For k-automatic sequences, we show that this critical exponent is always either a rational number or infinite, and its value is computable. Our results also apply to variants of the critical exponent, such as the initial critical exponent of Berthé, Holton, and Zamboni and the Diophantine exponent of Adamczewski and Bugeaud. Our work generalizes or recovers previous results of Krieger and others, and is applicable to other situations; e.g., the computation of the optimal recurrence constant for a linearly recurrent k-automatic sequence.
AKSZ CONSTRUCTION OF TOPOLOGICAL OPEN p-BRANE ACTION AND NAMBU BRACKETS
Authors: BOUWKNEGT PETER , JURČO BRANISLAV
Published: March 2013

We review the AKSZ construction as applied to the topological open membranes and Poisson sigma models. We describe a generalization to open topological p-branes. Also, we propose a related (not necessarily BV) Nambu–Poisson sigma model.
ORBIFOLD ELLIPTIC GENERA OF QUOTIENTS OF COMPLETE INTERSECTIONS IN WEIGHTED PROJECTIVE SPACES
Authors: GUO SHUAI , ZHOU JIAN
Published: March 2013

We compute the orbifold elliptic genera of quotients of smooth complete intersections in weighted projective spaces by the method of [X. Ma and J. Zhou, Elliptic genera of complete intersections, Internat. J. Math.16 (2005) 1131–1155]. This establishes a version of CY/LG correspondence for orbifold elliptic genera of global quotients.
SPREAD SPECTRUM COMMUNICATION SYSTEM WITH SEQUENCE SYNCHRONIZATION UNIT USING CHAOTIC SYMBOLIC DYNAMICS MODULATION
Authors: KADDOUM GEORGES , GAGNON GHYSLAIN , GAGNON FRANCOIS
Published: March 2013

In this paper, we propose a new asynchronous multiuser communication system based on spread spectrum and chaotic symbolic dynamics modulation. By combining spread spectrum and chaotic modulation, the proposed system provides increased security by reducing the probability of detection while allowing multiuser transmissions. The sequence synchronization of chaos communication system is studied. A time acquisition technique based on serial search is proposed to achieve synchronization. An analysis is carried out to determine the probability of detection, the probability of false alarm and the bit error rate of the system. Simulation results show that the proposed system can achieve sequence synchronization under low signal-to-noise ratios, and also confirm our analytically computed expressions.
ON HOPF BIFURCATION OF A DELAYED PREDATOR–PREY SYSTEM WITH DIFFUSION
Authors: LIU JIANXIN , WEI JUNJIE
Published: March 2013

A delayed predator–prey system with diffusion and Dirichlet boundary conditions is considered. By regarding the growth rate a of prey as a main bifurcation parameter, we show that Hopf bifurcation occurs when the parameter a is varied. Then, by using the center manifold theory and normal form method, an explicit algorithm for determining the direction of the Hopf bifurcations and stability of the bifurcating periodic solutions is derived.
ON THE NUMBER OF LIMIT CYCLES FOR DISCONTINUOUS PIECEWISE LINEAR DIFFERENTIAL SYSTEMS IN ℝ2n WITH TWO ZONES
Authors: LLIBRE JAUME , RONG FENG
Published: March 2013

We study the number of limit cycles of the discontinuous piecewise linear differential systems in ℝ2n with two zones separated by a hyperplane. Our main result shows that at most (8n - 6)n-1 limit cycles can bifurcate up to first-order expansion of the displacement function with respect to a small parameter. For proving this result, we use the averaging theory in a form where the differentiability of the system is not necessary.
THE STABILITY OF SOME KINDS OF GENERALIZED HOMOCLINIC LOOPS IN PLANAR PIECEWISE SMOOTH SYSTEMS
Authors: LIANG FENG , HAN MAOAN
Published: March 2013

In this paper, we present some kinds of generalized homoclinic loops in planar piecewise smooth systems. By establishing Poincaré map, we study the stability of generalized homoclinic loops for each case. Some criteria are given for their stability, respectively. As applications, several concrete piecewise systems are considered.
SCALE-FREE UNIVERSAL SPECTRUM FOR ATMOSPHERIC AEROSOL SIZE DISTRIBUTION FOR DAVOS, MAUNA LOA AND IZANA
Authors: SELVAM A. M.
Published: March 2013

Atmospheric flows exhibit fractal fluctuations and inverse power law for power spectra indicates an eddy continuum structure for the self-similar fluctuations. A general systems theory for aerosol size distribution based on fractal fluctuations is proposed. The model predicts universal (scale-free) inverse power law for fractal fluctuations expressed in terms of the golden mean. Atmospheric particulates are held in suspension in the fractal fluctuations of vertical wind velocity. The mass or radius (size) distribution for homogeneous suspended atmospheric particulates is expressed as a universal scale-independent function of the golden mean, the total number concentration and the mean volume radius. Model predicted spectrum is compared with the total averaged radius size spectra for the AERONET (aerosol inversions) stations Davos and Mauna Loa for the year 2010 and Izana for the year 2009. There is close agreement between the model predicted and the observed aerosol spectra. The proposed model for universal aerosol size spectrum will have applications in computations of radiation balance of earth–atmosphere system in climate models.
STABILITY OF NEARLY-INTEGRABLE SYSTEMS WITH DISSIPATION
Authors: LHOTKA CHRISTOPH , CELLETTI ALESSANDRA
Published: March 2013

We study the stability of a vector field associated to a nearly-integrable Hamiltonian dynamical system to which a dissipation is added. Such a system is governed by two parameters, namely the perturbing and dissipative parameters, and it depends on a drift function. Assuming that the frequency of motion satisfies some resonance assumption, we investigate the stability of the dynamics, and precisely the variation of the action variables associated to the conservative model. According to the structure of the vector field, one can find linear and long-term stability times, which are established under smallness conditions of the parameters. We also provide some applications to concrete examples, which exhibit a linear or long-term stability behavior.
High Frequency GaN-based Integrated Point-of-Load Converters
Authors: Lee Fred C. , Reusch David , Ji Shu , Su Yipeng , Li Qiang
Published: March 2013

High density integrated Point-of-Load (POL) converter is today's industry trend for portable electronic applications. In the past 10 years, Center for Power Electronics Systems (CPES) has successfully demonstrated a three-dimension (3D) integration method using magnetic as a substrate to achieve a very high power density. Recently, the Gallium Nitride (GaN) transistor has emerged as a possible candidate to replace Silicon MOSFET due to its faster switching speed, which gives the opportunity to push switching frequency to several MHz. This paper gives an overview of CPES' recent research efforts on high frequency 3D integrated POL converters with GaN transistors. A 5MHz 20A integrated POL converter with GaN transistors was demonstrated with power density as high as 1100W/in3, which is a factor of 10 improvements compared to industry products.
Managing Basal Plane Dislocations in SiC: Perspective and Prospects
Authors: Myers-Ward Rachael , Gaskill D. Kurt , Stahlbush R.S. , Mahadik N.A. , Wheeler Virginia , Nyakiti Luke O , Eddy C.R.
Published: March 2013

Conversion of basal plane dislocations (BPDs) to threading edge dislocations in 8 and 4{degree sign} offcut SiC material has been studied in order to eliminate the nucleation source of Shockley-type stacking faults in the active region of bipolar devices. Ex situ and in situ growth interrupts were used to convert BPDs in the 8{degree sign} material, where conversion rates up to 98% were achieved for in situ interrupts in epilayers with doping < 1x1016 cm-3. Complete spontaneous conversion of BPDs was found to be possible in 4{degree sign} offcut material after ~ 20 µm of epitaxial growth for both intentionally and unintentionally doped films.
GaN-on-Si for Power Technology
Authors: Visalli Domenica , Derluyn Joff , Sijmus Bram , Degroote Stefan , Germain Marianne
Published: March 2013

The optimization of the crystal growth of the GaN buffer, and more in general of the III-nitride epilayers, cannot be exclusively done at material level through crystalline measurements. As a matter of fact, device parameters such as current density, breakdown voltage, threshold voltage, gate capacitance, switching charges etc.. are ultimately resulting from the material properties themselves and from the design of the epilayer stack. In this manuscript we study the impact of uniform, crack-free and high-quality Gallium Nitride epilayer grown on Si substrate on device performance.
Angle-Resolved PES Studies on Transition Layers at SiO2/SiC Interfaces
Authors: Okada Hazuki , Komatsu Arata , Watanabe Masato , Izumi Yudai , Muro Takayuki , Nohira Hiroshi
Published: March 2013

We investigated on the chemical bonding states of thermally oxidized SiO2/SiC in detail by the angle-resolved X-ray photoemission spectroscopy (AR-XPS). Analyses of Si 2p, C 1s and O1s spectra show that the signal arising from sub-oxide is detected, and that the signals related carbon in SiO2 and C-C in SiC are detected. We also characterized SiO2/4H-SiC by Hard X-ray photoemission spectroscopy (HAX-PES) in order to check the depth profile of carbon in oxide in detail.
POCl3 Annealing as a New Method for Improving 4H-SiC MOS Device Performance
Authors: Yano Hiroshi , Hatayama Tomoaki , Fuyuki Takashi
Published: March 2013

Effects of POCl3 annealing on the electrical properties of metal-oxide-semiconductor (MOS) devices on 4H-SiC were investigated. Comparative results of non-annealed, NO-annealed, and POCl3-annealed MOS devices are shown. POCl3 annealing is more effective to reduce interface state density and improve channel mobility than conventional NO annealing. Breakdown characteristics and reliability of annealed oxides were also investigated. POCl3 annealing did not deteriorate oxide breakdown field very much. Time-dependent dielectric breakdown characteristics indicated different behavior due to enhanced electron trapping in the oxide. It is related with uniformly distributed phosphorus in the oxide. Flat-band voltage shift due to interface traps and near-interface traps in the oxide was very small at low oxide fields (< 3 MV/cm), whereas injected electrons were easily trapped in the POCl3 annealed oxide at high oxide fields (> 5 MV/cm). By combination of NO and POCl3 annealing, relatively high channel mobility and stabilized characteristics against electron injection were achieved.
Simple and Accurate Physics-Based Compact Circuit Simulation Models for Depletion-Mode Gallium Nitride(GaN) RF Power Transistors
Authors: Shenai K. , Leong S. K.
Published: March 2013

Gallium Nitride (GaN) power transistors are fast-emerging as viable candidates for efficient electrical power amplification. Two simple and reasonably accurate circuit simulation models are presented for GaN RF depletion-mode power transistors. In the first model, a SPICE LEVEL-1 MOS transistor is used to model the intrinsic transistor, and bias-dependent inter-electrode capacitances are modeled as simple diode junction capacitances; the series resistance between the drain and source electrodes is attached externally to the intrinsic transistor. In the second model, the GaN depletion-mode RF transistor is modeled using two SPICE LEVEL-2 MESFETs where the second MESFET is used in series with the drain of the first MESFET to model the gain compression at high values of drain currents; constant values of inter electrode capacitances are used. Both circuit simulation models are validated for DC and S-parameter performance from 100 MHz - 3 GHz.
Electro-Thermal Scaling Constraints in Chip-Scale Power Inductors
Authors: Shenai K. , Wu Jayne , Cui Haochen
Published: March 2013

Two-dimensional (2-D) full-wave finite-element (FE) solution of Maxwell's equations including thermal heating and diffusion in micro-fabricated power inductors suggests significant heating caused by increased AC resistance and eddy current losses, especially at increased power switching frequencies when conducting large currents. The simulation results indicate that severe thermal constraints arise when sourcing currents in excess of 5 amps in DC-DC power converters switching at frequencies in excess of 5 MHz. A simple circuit model is presented to evaluate the effect of frequency-dependence in power inductors on the efficiency and load regulation of point-of-load (POL) DC-DC power converters that utilize advanced silicon power MOSFETs and Gallium Nitride (GaN) power transistors.
Towards Very High Voltage SiC Power Devices
Authors: Planson Dominique , Brosselard Pierre , Tournier Dominique , Phung Luong Viet , Brykinski Christian
Published: March 2013

The development of high voltage devices is a great challenge. At least, railway and high voltage distribution network are example of applications requiring high voltage devices. SiC power devices and technology seems to be mature enough to give a short term solution. Indeed, silicon carbide devices appear to be the semiconductor of choice for high voltage (> 6.5 kV) applications compared to Gallium Nitride and Diamond. For high voltage devices, periphery protection is mandatory in order to reduce the well-known electric field crowding taking place at the junction edge. Some details are given about the different periphery technics (JTE, guard rings, MESA) applied to SiC devices, before combining some of them to reach higher and higher breakdown voltages. Some works remaining to be done are given as a conclusion of this paper.
Dielectric and Magnetic Properties of Pb(Fe0.5Nb0.5)O3 - Ni0.65Zn0.35Fe2O4 Composites
Authors: Pradhan Dhiren Kumar , Barik Sujit Kumar , Puli Venkata S , Sahoo Satyaprakash , Katiyar Ram S.
Published: March 2013

We report Raman spectra, magnetic, ferroelectric, and dielectric properties of (1-x)Pb(Fe0.5Nb0.5)O3 -xNi0.65Zn0.35Fe2O4 (x = 0.1-0.4) (PFN-NZFO) composites. Raman spectra reveal that the magnetic coupling strength increases with increasing NZFO concentration, which is well supported by the magnetization data. However, the saturation polarization and the maximum dielectric constant decrease with increasing NZFO concentration. The tan δ is found to be very small (< 0.2) for x = 0.2 and it increases with increasing x. Our results suggest that, the x = 0.2 composite shows significantly large saturation magnetization and polarization, large dielectric constant, and very low dielectric loss at room temperature, which makes it an excellent multiferroic material at room temperature and hence it is a promising candidate for practical applications.
Remote Scavenging Technology Using Ti/TiN Capping Layer Interposed in a Metal/High-k Gate Stack
Authors: Ma Xueli , Wang Xiaolei , Han Kai , Wang Wenwu , Yang Hong , Zhao Chao , Chen Dapeng , Ye Tianchun
Published: March 2013

High permittivity materials have been required to replace traditional SiO2 to be gate dielectric to extend Moore's law. However, growth of a thin SiO2-like interfacial layer (IL) is almost unavoidable during the deposition or subsequent high temperature anneal. This limits the scaling benefits of incorporating high-k dielectrics into transistors. In this work, a promising approach, in which O-scavenging metal layer and a barrier layer preventing scavenging metal diffusing into high-k gate dielectric are used to engineer the thickness of the IL, is reported. Using a Ti scavenging layer and TiN barrier layer on HfO2 dielectric, the effective removal of interfacial layer (IL) and almost no Ti diffusing into HfO2, have been confirmed by high resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS).
The Electrochemical Kinetics of Selectively Corroding Poly-Silicon in Generating Lonely Crater-Defects
Authors: Sheng Lieyi , Porath Paul , Glines Eddie
Published: March 2013

The electrochemical kinetics of selectively corroding poly-silicon has been elucidated for the first time in generating lonely crater-defects into the unnoticeable spots of damage due to the intermittent micro-arcing events during implantation. By largely shunting the electrochemical corrosion process in a weak electrolyte (HF), the crater-defects in poly-silicon have been eliminated for significantly improving the gate oxide integrity.
Process to Etch Ni and Pt Residues during Silicide Contact Electrode Processing Using Low Temperature Aqueous Solutions
Authors: Duong Anh Ngoc , Fitz Clemens , Metzger Sven , Karlsson Olov , Foster John Clayton , Nowling Greg , Sih Vincent , Besser Paul
Published: March 2013

During NiPtSi contact electrode processing and after the first thermal treatment to form Ni rich silicide, excessive Ni is removed by a strong acid mixture such as piranha (mixture of sulfuric acid and hydrogen peroxide. The post salicidation clean process has to be selective to all exposed materials: Si3N4, SiO2, NiPtSi, and NiPtSiGe (contact electrodes of source/drain for strain applications)). Performing a partition process with RTA1 (rapid thermal annealing) followed by Ni strip, followed by RTA2, and then with Pt strip is one method to check for NiPt removal. The Ni strip was performed using dilute nitric acid (20:1) and dilute aqua regia (1:5:4) and showed completed NiPt removal. A queue time study was also investigated after the Ni strip and after RTA2 for defect formation. Also, Pt removal using aqua regia solutions of various shelf-lives were tested. The result led to the conclusion that solutions of aqua regia with longer shelf-lives were also shown to be less effective in Pt residue removal. Using a High Productivity Combinatorial materials/process screening technique to reduce the number of product wafers used for evaluation process development, the etch rates of all the materials of interest were tested on blanket wafers. The chemistry consists of varying acid and base types and the relative combinations of these chemistries. Process conditions that consisted of various process chemistries, process temperatures, and degrees of fluid agitation (e.g. stirrer speed) were done on the same substrate.
Chemical Vapor Deposition of Silicon by the Reaction of Bromosilanes and Hydrogen
Authors: Tomono Kazuaki , Furuya Hirotoshi , Miyamoto Seiji , Ogawa Takuro , Okamura Yuki , Komatsu Ryuichi , Nakayama Masaharu
Published: March 2013

Chemical processes occurring in the vapor deposition of silicon from a mixture of bromosilanes (SiHBr3:SiBr4 = 1:4) with hydrogen gas have been monitored by means of online gas chromatography, and the obtained deposits were characterized by XRD, SEM, and EDX techniques. The deposition of silicon occurred at 900 ºC, accompanied by the larger consumption of SiBr4 than SiHBr3. The numerous rugged rod-like deposits of poly-silicon were grown appearing the crystal diffractions of (111), (220), (311), and (331) planes. The diameter of deposits mainly ranged from 2 to 4 um and their lengths extended to about 10 um.
Comparison of the Impact of Thermal Treatments on the Second and on the Millisecond Scales on the Precipitation of Interstitial Oxygen
Authors: Kissinger Gudrun , Kot Dawid , von Ammon Wilfried
Published: March 2013

The precipitation of oxygen was investigated after rapid thermal annealing pre-treatments for 30 s in the range 1100-1250 {degree sign}C and after flash lamp annealing for 3 ms and 20ms with different irradiances up to melting of the wafer surface. The difference between thermal processing on the second and on the millisecond scales is based on the temperature profiles generated by the different types of processing. These profiles influence the shrinking of grown-in oxide precipitate nuclei and the generation, diffusion, and annihilation of intrinsic point defects and thus the oxygen precipitation during further processing. Oxygen precipitation can be suppressed by flash anneals or bulk defect zones and defect denuded zones for internal gettering can be created both depending on the flash duration and energy density.
(Invited) Transistor-Based Extraction of Carrier Lifetime and Interface Traps Densities in Silicon-on-Insulator Materials
Authors: Martino Joao Antonio , Sonnenberg Victor , Galeti Milene , Aoulaiche Marc , Simoen Eddy , Claeys C.
Published: March 2013

This paper presents the main transistor-based extraction methods for the carrier lifetime and the interface trap density in Silicon-On-Insulator materials. The device/technology under analysis begins with the partially-depleted SOI MOSFET, following by the fully depleted SOI with ultra-thin buried oxide (UTBOX)devices. The results show that the major part of the method may be extended but requires some careful analysis/interpretation and sometime a correction factor.
Fin Width and Gate Length Dependences of Charge Pumping and DCIV Currents in Floating-Body SOI MOSFETs
Authors: Zhang Enxia , Fleetwood Dan M , Duan Guo Xing , Zhang C. X. , Schrimpf Ron D. , Simoen Eddy , Linten Dmitri
Published: March 2013

We have evaluated the effects of device geometry and frequency on DCIV and ACIV (charge pumping) currents in development-stage SOI finFETs with floating bodies that are built in two process technologies. Both the DCIV and ACIV currents are much smaller in devices for which the gate length exceeds ~100 nm or the fin width exceeds ~70 nm. ACIV currents are approximately linear with frequency up to ~300 kHz for the devices and measurement conditions used in this study. ACIV estimates of effective interface-trap densities for relatively short-channel, narrow-fin devices in each technology are ~4 × 1011 cm-2.
Epitaxial Growth of Iron-Silicide Nanodots on Si Substrates Using Ultrathin SiO2 Film Technique and Their Physical Properties
Authors: Nakamura Yoshiaki , Ichikawa Masakazu
Published: March 2013

We developed a formation technique for iron silicide nanodots (NDs) on Si substrates using ultrathin SiO2 film technique. In this technique, the NDs were epitaxially grown on Si substrates with ultrahigh density (>1012 cm-2). Furthermore, the crystal structures in formed NDs are controllable even though iron silicide has complicated phase diagram. The optical properties of semiconductor β-FeSi2 NDs were measured on nanometer scale, which clarified their optical absorption band edges. Magnetic properties of formed Fe3Si NDs were investigated, which indicated the magnetic dipole interactions in ultrahigh density ND system. This strongly depended on ND morphology demonstrating magnetic properties could be controlled by manipulating ND formation.
DC and RF Characteristics of Ga2O3/GaN Single Nanowire MOSFET
Authors: Yu Jeng-wei , Li Chi-kang , Yeh Po-Chun , Wu Yuh-Renn , Peng Lung-han
Published: March 2013

We reported transport characterization on [11-20] GaN single nanowire (SNW)-MOSFET laterally- and directionally- grown on c-plane sapphire substrates. The 60nm-dia. Ga2O3/GaN SNW-MOSFET of 50 nm gate length was shown to exhibit a high saturation current of 130μA, transconductance of 64μS, and unity current gain bandwidth fT at 150GHz. From a 3D diffusion and drift model analysis, it is shown that a polarization induced 2D electron gas (2DEG) density of 7×10^12 /cm2 with mobility of 1000cm2/V-sec confined at the interface of semi-polar {1-10-1} GaN/Ga2O3 was responsible for the high-speed transport characteristics.
Necessity of Epitaxial Growth of β-FeSi2 Thin Films in Formation of n-Type β-FeSi2/p-Type Si Heterojunction Photodiodes
Authors: Iwasaki Ryuhei , Promros Nathaporn , Yamashita Kyohei , Izumi Shota , Funasaki Suguru , Shaban Mahnoud , Yoshitake Tsuyoshi
Published: March 2013

n-Type β-FeSi2 thin films were epitaxially and non-epitaxially grown on p-type Si(111) substrates by facing-targets direct-current sputtering (FTDCS) at a substrate temperature of 600{degree sign}C. Whereas the n-type epitaxial β-FeSi2/p-type Si heterojunctions exhibited a typical rectifying behavior with a rectification ratio of more than two orders of magnitude at bias voltages between {plus minus}1 V, the heterojunctions comprising non-epitaxial β-FeSi2 films rarely exhibited rectifying action. The epitaxial growth of β-FeSi2 is an significant factor for forming the heterojunction diodes.