bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconfigurable modelling for drivetrain real-time simulation
Authors: Mason B A , Ebrahimi M , Farid M
Published: August 2009

This article discusses a body of ongoing work that seeks to reduce the time and effort required to create, reconfigure, and parameterize physically based models that are to be used as part of a model-based design (‘MBD’) process.

Initially a new modular approach for system model creation is presented. The method facilitates rapid creation of simulation models to be used within an MBD process making use of application-specific submodels. It is shown that through the use of the submodels created using Simulink configurable subsystems, the number of degrees of freedom and thus fidelity of a model may be altered by a simple parameter change.

The work continues, beyond the introduction of a number of plug-and-simulate drivetrain submodels, to investigate a means by which a model's parameters may be reduced to an absolute minimum. An algorithm capable of identifying parameters of potentially low significance to an output of interest is shown in the form of the parameter elimination and model evaluation algorithm (‘PEMEA’). Simulation results that make use of the PEMEA suggest that a number of parameters may be eliminated. The parameter eliminations, conducted in situ in Simulink models, are shown to have minimum effect on the model outputs-of-interest and marginally decrease the computational overhead of the model.
Impacting chatter and stick in a transmission system with two oscillators
Authors: Luo A C J , O'Connor D
Published: August 2009

In this article, an investigation on non-linear dynamical behaviours of a transmission system with a gear pair is conducted. The transmission system is described through an impact model with a possible stick between the two gears. From the theory of discontinuous dynamical systems, the motion mechanism of impacting chatter with stick is investigated. The onset and vanishing conditions for stick motions are developed, and the condition for maintaining stick motion is obtained as well. The corresponding physical interpretation is given for a better understanding of non-linear behaviours of gear transmission systems. A parameter map is presented to provide a global picture of the relationship between system parameters and corresponding motion. Grazing and stick conditions are utilized to determine the existence of periodic motions. Such periodic motions are predicted analytically through mapping structures, and the corresponding local stability and bifurcation analyses are carried out. Numerical simulations are performed to illustrate periodic motions and stick motion criteria. A better understanding of the motion mechanism between two gears may be helpful for improving the efficiency of gear transmission systems.
Polynomial chaos-based parameter estimation methods applied to a vehicle system
Authors: Blanchard E D , Sandu A , Sandu C
Published: August 2009

Parameter estimation for large systems is a difficult problem, and the solution approaches are computationally expensive. The polynomial chaos approach has been shown to be more efficient than Monte Carlo for quantifying the effects of uncertainties on the system response. This article compares two new computational approaches for parameter estimation based on the polynomial chaos theory for parameter estimation: a Bayesian approach, and an approach using an extended Kalman filter (EKF) to obtain the polynomial chaos representation of the uncertain states and the uncertain parameters. The two methods are applied to a non-linear four-degree-of-freedom roll plane model of a vehicle, in which an uncertain mass with an uncertain position is added on the roll bar. When using appropriate excitations, the results obtained with both approaches are close to the actual values of the parameters, and both approaches can work with noisy measurements. The EKF approach has an advantage over the Bayesian approach: the estimation comes in the form of a posteriori probability densities of the estimated parameters. However, it can yield poor estimations when dealing with non-identifiable systems, and it is recommended to repeat the estimation with different sampling rates in order to verify the coherence of the results with the EKF approach. The Bayesian approach is more robust, can recognize non-identifiability, and use regularization techniques if necessary.
Design concepts and analysis of a semi-active steering system for a passenger car
Authors: Baharom M B , Hussain K , Day A J
Published: August 2009

The fundamentals and preliminary analyses of an innovative future technology referred to as ‘semi-active steering’ (SAS) are presented in this article. The proposed steering system configuration is similar to a conventional electrical power-assisted steering with the replacement of the rigid steering shaft with a low stiffness resilient shaft (LSRS), the presence of which allows ‘active control’ to be performed on vehicles similar to the concept of full steer-by-wire (SBW). But, unlike SBW, the LSRS is an integral part of the system characteristics. The advantages of the semi-active system in comparison with SBW and other conventional systems are demonstrated. A mathematical model to predict the mechanical properties of the LSRS has been developed, and experiments were conducted on a medium-sized car fitted with an LSRS to verify that vehicle stability and drivability can be ensured in the event of active system failure. The results have indicated that the vehicle was stable and safe to be driven at low speeds, and is predicted to be driveable and safe at higher speeds. It is concluded that an SAS system of this type has the potential to improve the safety of SBW systems.
Direct eigenanalysis of constrained system dynamics
Authors: Masarati P
Published: August 2009

This work addresses the direct eigenanalysis of the problem that results from the linearization of the dynamics of constrained systems about arbitrary, problem-dependent steady solutions. The procedure is outlined; the expected properties of the eigensolution are illustrated; implementation issues, related to the application of the procedure to an existing multi-body formulation, are addressed. The soundness of the proposed approach is illustrated by a simple, yet exhaustive example, and by the analysis of a relatively detailed model of a flexible helicopter rotor blade.
A compound archery bow dynamic model, suggesting modifications to improve accuracy
Authors: Park J L
Published: August 2009

This paper provides a static and dynamic mathematical model for a single cam compound archery bow. The static performance is that seen by the archer in drawing and aiming the bow. The dynamic performance is of importance in determining how the arrow is accelerated and exits the bow. Building on the work of Hickman, it is shown that in order to flatten the arrow acceleration profile during the power stroke it is important to select a limb profile that minimizes the limb's effective mass and to use a heavy arrow. To minimize the time the string and arrow spend in the vicinity of the archer's face it is necessary to minimize the inertia of the bow's cams. Various aspects of the model have been validated, showing a good fit with experimental data. The conclusions are applicable to other compound bow configurations.
Rhodium Catalysts Bearing Mixed Thioether–Phosphine Ligands for Carbonylation of Methanol
Authors: Sakakibara Ken , Nozaki Kyoko
Published: August 2009

Two kinds of thioether–trialkylphosphine ligands and their Rh complexes were synthesized and applied to the carbonylation of methanol to acetic acid to reveal that one of the two complexes showed higher activity compared to Rh catalyst without any ligands.
Copper-Catalyzed Arylation of Chlorosilanes with Grignard Reagents
Authors: Morita Eiji , Murakami Kei , Iwasaki Masayuki , Hirano Koji , Yorimitsu Hideki , Oshima Koichiro
Published: August 2009

Nucleophilic substitution reactions of chlorosilanes with aryl Grignard reagents take place efficiently in the presence of copper(I) iodide to afford tetraorganosilanes.
Active Mercury(II) Ion Removal: Stoichiometrically Controlled Thiol-Functionalized Mesoporous Silica by a Mass Production Spray Dry System
Authors: Yamauchi Yusuke , Suzuki Norihiro , Sato Keisuke , Fukata Naoki , Murakami Miwa , Shimizu Tadashi
Published: August 2009

Stoichiometrically controlled thiol-functionalized mesoporous silica particles are synthesized by a spray dry technique in one step. The EDS (energy dispersive X-ray spectrometer) mapping shows that thiol groups are well dispersed throughout the particles without phase separation at micrometer scale. From TEM (transmission electron microscope) observation, SAXS (small-angle X-ray scattering) measurements, and N2 adsorption–desorption isotherms, it is proven that the thiol groups can be successfully embedded in the frameworks up to 30% without any collapse of ordered mesoporous structures. The amount of the embedded thiol groups in the final products can be stoichiometrically controlled by changing the compositions of the initial precursor solutions, as is confirmed by 29Si NMR measurements. The total adsorption capacity of mercury(II) ions was increased in proportion to the amount of the thiol groups embedded in the frameworks.
Metal–Organic Framework (MOF) as a Precursor for Synthesis of Platinum Supporting Zinc Oxide Nanoparticles
Authors: Liu Bo , Han Song , Tanaka Koji , Shioyama Hiroshi , Xu Qiang
Published: August 2009

Nanocrystalline ZnO-supported platinum nanoparticles were synthesized by introducing inorganic platinum salt into the pores of MOF-5 ([Zn4O(bdc)]3; bdc = 1,4-benzenedicarboxylate) followed by heating in air at 600 °C. The Pt particle sizes can be controlled by adjusting Pt precursor concentration. The resultant Pt/ZnO samples displayed higher catalytic activity for CO oxidation than conventional Pt/ZnO catalyst.
Briaexcavatins V–Z, Discovery of New Briaranes from a Cultured Octocoral Briareum excavatum
Authors: Sung Ping-Jyun , Lin Mei-Ru , Chiang Michael Y , Hwang Tsong-Long
Published: August 2009

Five new briarane derivatives, briaexcavatins V–Z (1–5), have been isolated from a cultured octocoral Briareum excavatum. The structures of compounds 1–5 were established by spectroscopic methods. Single-crystal X-ray diffraction data for 2 confirmed the structure. Briarane 4 possesses an unprecedented 8,9-epoxy moiety. The relationships between 13C NMR chemical shifts and the conformations of briaranes possessing an 11,12-epoxy group are described. Briaranes 1, 3, and 4 have displayed weak inhibitory effects on superoxide anion generation by human neutrophils. Briarane 1 was found to show mild inhibitory effects on human neutrophil elastase release and 5 exhibited mild activity to enhance human neutrophil elastase release.
Metazoan stress granule assembly is mediated by P-eIF2α-dependent and -independent mechanisms
Authors: Farny Natalie G. , Kedersha Nancy L. , Silver Pamela A.
Published: August 2009

Stress granules (SGs) are cytoplasmic bodies wherein translationally silenced mRNAs are recruited for triage in response to environmental stress. We report that Drosophila cells form SGs in response to arsenite and heat shock. Drosophila SGs, like mammalian SGs, are distinct from but adjacent to processing bodies (PBs, sites of mRNA silencing and decay), require polysome disassembly, and are in dynamic equilibrium with polysomes. We further examine the role of the two Drosophila eIF2α kinases, PEK and GCN2, in regulating SG formation in response to heat and arsenite stress. While arsenite-induced SGs are dependent upon eIF2α phosphorylation, primarily via PEK, heat-induced SGs are phospho-eIF2α-independent. In contrast, heat-induced SGs require eIF2α phosphorylation in mammalian cells, as non-phosphorylatable eIF2α Ser51Ala mutant murine embryonic fibroblasts do not form SGs even after severe heat shock. These results suggest that mammals evolved alternative mechanisms for dealing with thermal stress.
Asymptotic Convergence of Optimal Policies for Resource Management with Application to Harvesting of Multiple Species Forest
Authors: Cominetti Roberto , Piazza Adriana
Published: August 2009

We study the long-term behavior of the optimal harvesting policies for a mixed forest composed by multiple species of different maturity ages. This model is a prototype for the exploitation of a finite resource such as land or space, which can be allocated to different activities that produce their revenue after certain delays at which the resource is liberated for reuse. We prove the existence and uniqueness of a sustainable state, and we discuss the conditions under which an optimal trajectory converges in the long run toward this state or toward the set of optimal periodic cycles. We also analyze different situations in which the convergence occurs in finite time.
Markov Decision Processes with Arbitrary Reward Processes
Authors: Yu Jia Yuan , Mannor Shie , Shimkin Nahum
Published: August 2009

We consider a learning problem where the decision maker interacts with a standard Markov decision process, with the exception that the reward functions vary arbitrarily over time. We show that, against every possible realization of the reward process, the agent can perform as well—in hindsight—as every stationary policy. This generalizes the classical no-regret result for repeated games. Specifically, we present an efficient online algorithm—in the spirit of reinforcement learning—that ensures that the agent's average performance loss vanishes over time, provided that the environment is oblivious to the agent's actions. Moreover, it is possible to modify the basic algorithm to cope with instances where reward observations are limited to the agent's trajectory. We present further modifications that reduce the computational cost by using function approximation and that track the optimal policy through infrequent changes.
Refined MDP-Based Branch-and-Fix Algorithm for the Hamiltonian Cycle Problem
Authors: Ejov Vladimir , Filar Jerzy A. , Haythorpe Michael , Nguyen Giang T.
Published: August 2009

We consider the famous Hamiltonian cycle problem (HCP) embedded in a Markov decision process (MDP). More specifically, we consider the HCP as an optimisation problem over the space of occupation measures induced by the MDP's stationary policies. In recent years, this approach to the HCP has led to a number of alternative formulations and algorithmic approaches. In this paper, we focus on a specific embedding, because of the work of Feinberg. We present a “branch-and-fix” type algorithm that solves the HCP. At each branch of the algorithm, only a linear program needs to be solved and the dimensions of the successive linear programs are shrinking rather than expanding. Because the nodes of the branch-and-fix tree correspond to specially structured 1-randomised policies, we characterise the latter. This characterisation indicates that the total number of such policies is significantly smaller than the subset of all 1-randomised policies. Finally, we present some numerical results.
A New Approach for Air Cargo Network Planning
Authors: Derigs Ulrich , Friederichs Stefan , Schäfer Simon
Published: August 2009

A central element of the air cargo planning process is the generation of optimal flight schedules. A flight schedule simultaneously defines the market potential of an airline and allocates its resources. The schedule design process is a difficult and time-consuming task that involves and affects virtually all business units. Because of its complexity, the process is traditionally decomposed into several steps that are executed in a sequential manner. In this paper, we present novel model formulations and solution procedures which have been developed in the course of a feasibility study for a decision support system (DSS) for a pragmatic approach to “freighter network planning” at one of the top international cargo carriers. We formulate two integrated models that combine the three planning steps: flight selection, aircraft rotation planning, and cargo routing. The aim of the schedule optimization is to maximize the network-wide profit by determining the best combination from a list of mandatory and optional flights, assigning the selected flights to aircrafts and identifying optimal cargo flows. Both model formulations are embedded in a solution procedure that builds on the column generation technique with shortest path algorithms for solving the subproblems. The applicability of the models in a DSS is demonstrated on realistic problem instances that match the requirements specified in the feasibility study.
Development of an Immunoassay for the Quantification of Soluble LR11, a Circulating Marker of Atherosclerosis
Authors: Matsuo Masanao , Ebinuma Hiroyuki , Fukamachi Isamu , Jiang Meizi , Bujo Hideaki , Saito Yasushi
Published: August 2009

Background: Vascular smooth muscle cells (SMCs) migrate from the arterial media to the intima in the progression of atherosclerosis, and dysfunction of SMCs leads to enhanced atherogenesis. A soluble form of the LDL receptor relative with 11 ligand-binding repeats (sLR11) is produced by the intimal SMCs, and the circulating concentrations of sLR11 likely reflect the pathophysiological condition of intimal SMCs. Furthermore, polymorphism of the LR11 gene has been found to be related to the onset of Alzheimer disease. This study describes the development of a sandwich immunoassay for quantifying sLR11 in human serum and cerebrospinal fluid.

Methods: We used synthetic peptides or DNA immunization to produce monoclonal antibodies (MAbs) A2-2–3, M3, and R14 against different epitopes of LR11.

Results: sLR11 was immunologically identified as a 250-kDa protein in human serum and cerebrospinal fluid by SDS-PAGE separation, and was purified from serum by use of a receptor-associated protein and MAb M3. An immunoassay for quantification of sLR11 with a working range of 0.25–4.0 μg/L was developed using the combination of MAbs M3 and R14. Treatment of serum with 5.25% n-nonanoyl-N-methyl-d-glucamine reduced the matrix effects of serum on the absorbance detection in the ELISA system. The linear dynamic range of the ELISA spanned the variation of circulating sLR11 concentrations in individuals with atherosclerosis.

Conclusions: A sandwich ELISA was established for quantifying sLR11 in serum and cerebrospinal fluid. This technique provides a novel means for assessing the pathophysiology of atherosclerosis, and possibly neurodegenerative diseases.
Lower serum testosterone is independently associated with insulin resistance in non-diabetic older men: the Health In Men Study
Authors: Yeap Bu B , Chubb S A Paul , Hyde Zoë , Jamrozik Konrad , Hankey Graeme J , Flicker Leon , Norman Paul E
Published: August 2009

Objective

Insulin resistance is associated with metabolic syndrome and type 2 diabetes, representing a risk factor for cardiovascular disease. This relationship may be modulated to some extent by age-related changes in sex hormone status. We examined whether lower testosterone or sex hormone-binding globulin (SHBG) levels in older men are associated with insulin resistance independently of measures of central obesity.

Design

Cross-sectional analysis of 2470 community-dwelling non-diabetic men aged ≥70 years.

Methods

Age, body mass index (BMI) and waist circumference were measured. Early morning sera were assayed for total testosterone, SHBG, LH and insulin levels. Free testosterone was calculated using mass action equations, and insulin resistance was assessed using a homeostatic model (HOMA2-IR).

Results

Total testosterone, free testosterone and SHBG declined progressively across increasing quintiles of HOMA2-IR (all P<0.001) and correlated inversely with log HOMA2-IR (r=−0.27, −0.14 and −0.24 respectively, all P<0.001). After adjusting for age, BMI, waist circumference, high-density lipoprotein and triglyceride levels, total testosterone was independently associated with log HOMA2-IR (β=0.05, P<0.001), while SHBG was not. Serum total testosterone <8 nmol/l was associated with HOMA2-IR in the highest quintile (odds ratio (OR) 1.67, 95% confidence interval (CI) 1.02–2.73) as was total testosterone ≥8 and <15 nmol/l (OR 1.29, 95% CI 1.03–1.63).

Conclusions

In older men, lower total testosterone is associated with insulin resistance independently of measures of central obesity. This association is seen with testosterone levels in the low to normal range. Further studies are needed to evaluate interventions that raise testosterone levels in men with reduced insulin sensitivity.
Familial risks for hospitalized Graves' disease and goiter
Authors: Hemminki Kari , Shu Xiaochen , Li Xinjun , Ji Jianguang , Sundquist Kristina , Sundquist Jan
Published: August 2009

Objectives

Familial clustering of a disease is an indicator of a possible heritable cause, provided that environmental sharing can be excluded. Thus, data on familial risks are important for genetic studies and for clinical genetic counseling.

Design

We carried out a nationwide family study on nontoxic and toxic nodular goiters, and Graves' disease in order to search for familial clustering of these diseases at the population level.

Methods

The Swedish Multigeneration Register on 0–75 year old subjects was linked to the Hospital Discharge Register from years 1987 to 2007. Standardized incidence ratios (SIRs) were calculated for offspring of affected parents and for siblings by comparing to those whose relatives had no hospitalization for thyroid disease.

Results

The number of hospitalized patients in the offspring generations was 11 659 for nontoxic goiter, 9514 for Graves' disease, and 1728 for toxic nodular goiter. Familial cases accounted for 8.2, 5.2, and 2.1% of all patients respectively. The highest familial risk for offspring of affected parents was noted for Graves' disease (SIR 3.87), followed by toxic nodular goiter (3.37) and nontoxic goiter (3.15). Familial risks were higher for affected siblings: toxic nodular goiter (11.66), Graves' disease (5.51), and nontoxic goiter (5.40). Weaker familial associations were observed between the three diseases.

Conclusions

To our knowledge this is a first population-based family study on these thyroid diseases. The observed high familial aggregation for defined thyroid diseases cannot be explained by the known genetic basis, calling for further studies into genetic and environmental etiology of thyroid diseases.
Long term effect of external pituitary irradiation on IGF1 levels in patients with acromegaly free of adjunctive treatment
Authors: Mullan K , Sanabria C , Abram W P , McConnell E M , Courtney H C , Hunter S J , McCance D R , Leslie H , Sheridan B , Atkinson A B
Published: August 2009

Objective

It is established that external pituitary irradiation (EPI) effectively reduces serum GH levels in acromegaly. However, its effect in normalising serum IGF1 has been disputed. We looked at the number of our patients who achieved persistently normal IGF1 levels whilst free of adjunctive treatment for at least 1 year after EPI.

Patients and design

We identified 63 acromegalic patients between 1964 and 2004 who received EPI. Six were excluded: three had surgery after EPI, two had no medical records available, and one had a pituitary Yttrium implant.

Measurements

Patients received 4500–5000 cGy in fractionated doses. IGF1 levels were correlated with their respective age-related reference ranges.

Results

After EPI, the number of patients with normal IGF1 and free of adjunctive medical treatment for at least 1 year were four patients by 3 years, nine patients by 5 years and seventeen by 10 years, with the current number of 25/57 (44%). Concordance between IGF1 levels and random GH dropped from 90% at the time of EPI to 65% at 3 years, 66% at 5 years and 71% at 10 years.

Conclusions

We have demonstrated that, with time, EPI achieves a normal IGF1 in significant numbers of patients with acromegaly, thus obviating the need for life-long expensive medical therapy. For each patient this benefit has to be weighed against the possibility of new hypopituitarism as a result of the treatment. Any decision to use EPI is easier in the context of pre-existent hypopituitarism.
Ablation of idiopathic fascicular ventricular tachycardia
Authors: Gellér László , Szilágyi Szabolcs , Solymossy Katalin , Srej Marianna , Zima Endre , Tahin Tamás , Merkely Béla
Published: August 2009

Az idiopathiás fascicularis kamrai tachycardia fontos és nem nagyon ritka szívritmuszavar specifikus EKG-jelekkel és terápiás lehetőségekkel. A kamrai tachycardia EKG-képe relatíve keskeny QRS-morfológiát mutat a jobb-Tawara-szár-blokk morfológiájával. A QRS-tengelyállás attól függ, hogy melyik fasciculus része a reentry körnek. Baltengely-deviáció van jelen bal posterior fascicularis tachycardia, jobbtengely-deviáció bal anterior fascicularis tachycardia esetén. Bal septalis fascicularis tachycardia együtt járhat normális tengelyállással is. A fascicularis tachycardiák általában strukturális szívbetegség nélkül alakulnak ki. A fascicularis tachycardiák egyik fontos ismérve, hogy verapamilkezelésre jól reagálnak. Néhány esetben intravénás adenozin is hatékony lehet a ritmuszavar terminálásában. A fascicularis tachycardiában szenvedő betegek nagy részében sinusrhythmusban és a kamrai tachycardia alatt is a QRS-t megelőző preszisztolés vagy diasztolés potenciál regisztrálható, amely feltehetően a Purkinje-rostokból ered. Ez az úgynevezett P-potenciál szolgál segítségül a leghatékonyabb terápia, a katéterablatio során. A ritmuszavar azonnali felismerése és megfelelő helyre történő irányítása azért fontos, mert a ritmuszavar kitűnően ablálható, és az ablatio kuratív. Áttekintésünkben három fiatal idiopathiás fascicularis tachycardiában szenvedő betegünk kórtörténetét és sikeres ablatióját írjuk le, és az esetek kapcsán foglaljuk össze a speciális ritmuszavarral kapcsolatos jelenlegi ismereteinket.
High performance polymer/BaTiO3 nanocomposites based on surface-modified metal oxide nanoparticles using functional phosphonic acids for electronic applications
Authors: Kim Philseok , Doss Natalie M. , Tillotson John P. , Zhang Xiao-Hong , Jones Simon C. , Hotchkiss Peter J. , Li Jiangyu , Calame Jeffrey P. , Domercq Benoit , Kippelen Bernard , Marder Seth R. , Perry Joseph W.
Published: August 2009

Polymer/ceramic nanocomposites provide a means of combining the high permittivities (εr) of metal oxide nanoparticles with the solution-processability and high dielectric strength of polymeric hosts. Simple mixing of nanoparticles and polymers generally results in poor quality nanocomposites due to the agglomeration of nanoparticles and poor miscibility of nanoparticles with host materials. We have shown that surface modification of metal oxide nanoparticles with phosphonic acid-based ligands affords robust surface modification and improves the processiblity and the quality of the resulting nanocomposites. We report on the use of phosphonic-acid modified barium titanate (BaTiO3, BT) nanoparticles in dielectric nanocomposites and their applications to high-energy-density capacitors and solution-processable high permittivity gate insulators in organic field-effect transistors (OFETs). Surface modification of BT nanoparticles enabled the formation of high quality nanocomposite thin films with ferroelectric polymer hosts such as poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-HFP), with large volume fractions (up to 50 vol. %), which are potentially useful materials for electrical energy storage. Similarly, the use of phosphonic acid-modified BT nanoparticles in cross-linked poly(4-vinylphenol) (PVP) allowed to form gate insulators for OFETs. High quality nanocomposite thin films at high nanoparticle volume fractions (up to 37 vol. %) with a large capacitance density (∼50 nF/cm2) and a low leakage current (10−8 A/cm2) were obtained. Pentacene-based p-type OFETs using these nanocomposites showed a large on/off current ratio (Ion/off 104 ∼ 106). We will also present the results from a recent experimental and theoretical study where the BT nanoparticle volume fraction was systematically varied in P(VDF-HFP) host, εr = 11, to find the optimum permittivity and dielectric strength, which provided a guideline for the optimization of the volume fraction for achieving maximum energy density.
Rapid Electrical Sintering of Nanoparticle Stuctures
Authors: Alastalo Ari T. , Mattila Tomi , Allen Mark L. , Aronniemi Mikko J. , Leppäniemi Jaakko H. , Ojanperä Kimmo A. , Suhonen Mika P. , Seppä Heikki
Published: August 2009

A method for rapid electrical sintering (RES) of nanoparticle structures on temperature-sensitive substrates is presented. For an inkjetted silver nanoparticle conductor, a conductance increase of five orders of magnitude is demonstrated to occur in a timescale that typically varies between a few and one hundred milliseconds depending on process parameters. Furthermore, most of the conductance change takes only a few microseconds. The achievable final conductivities are within a factor of two from the bulk silver conductivity, as calculated using the external geometric dimensions of the structure ignoring porosity. The method is also applicable to other inorganic conductors such as indium-tin-oxide (ITO). More generally, the method offers a versatile tool in nanotechnology for electrical functionalization of nanoparticle structures. The method is also potentially suited for mass production.
Binding Characteristics of Surface Ligands on PbSe QDs and Impact on Electrical Conductivity
Authors: Kim Won Jin , Kim Sung Jin , Seo Jangwon , Sahoo Y. , Cartwright A. N. , Lee Kwang-Sup , Prasad Paras N.
Published: August 2009

We report the binding and conductivity characteristics of PbSe nanocrystal quantum dots which have different ligands on the surface. The PbSe nanocrystal quantum dots were surface functionalized using chemical treatment. The results of post-treatment analysis show that the PbSe surface can be successfully functionalized with various ligands based on thiol- and amine-molecules (e.g., oleic acid, dodecanethiol and butylamine). Conductivity measurements performed using a metal-semiconductor-metal structure indicate that there is an increase of conductivity as the length of the ligand connecting the quantum dots is reduced.
Preparation of Smooth Zinc Oxide Thin Film via Liquid Phase Reaction with Cation Additives
Authors: Saito Takeyasu , Hirata Yoshihisa , Okamoto Naoki , Kondo Kazuo
Published: August 2009

ZnO thin films were deposited in a solution with Zn(NO3)2 and DMAB from 60 to 80°C. The effects of cation additives such as Mg, Ga and Al in a aqueous solution were investigated on surface morphology, crystallographic structure and growth rate. By adding 1E−4 mol/l of Ga or Al, the growth rate was enhanced from 0.13 m/h to 0.35-0.38 m/h. In addition, the surface morphology became flat in the case of Al addition.
Nanostructured Metal Oxide and Composite Electrodes for Use in Ultracapacitors
Authors: Brumbach Michael T. , Alam Todd M. , Kotula Paul G. , McKenzie Bonnie B. , Bunker Bruce C.
Published: August 2009

Maximizing power and energy densities of ultracapacitors requires configuring redox-active materials in specific architectures that: 1) maximize electrolyte-electrode contact area, 2) minimize transport distances for both electrons and charge compensating species, and 3) minimize transport barriers. We have developed a simple solution-based method, using an organic template, that enables us to introduce hierarchical porosity in ruthenium oxide down to the nano-scale by controlling the oxidative crystal growth of RuO2. The high capacitances of the resulting nanostructured electrodes were found to be comparable to hydrous ruthenium oxide formed under dramatically different conditions. Materials characterization reveals that the organic template directs structure formation and promotes hydroxyl retention.
Ultrasonic spray assisted Mist-CVD method for high-quality crystalline and amorphous oxide semiconductors growth
Authors: Nishinaka Hiroyuki , Kamada Yudai , Kiba Keiji , Kameyama Naoki , Fujita Shizuo
Published: August 2009

The growth of high-quality crystalline ZnO thin films on ZnO bulk substrates and of amorphous In-Ga-O and Ga-Al-O thin films has been demonstrated by using the solution-based cost-effective and environmental friendly ultrasonic spray assisted mist-CVD method. The homoepitaxial ZnO thin films with atomically flat surfaces were successfully grown on Zn-polar ZnO substrates via a step-flow growth mode, in spite of different miscut angles of the substrate, at the furnace temperature of 1000°C. The compositions and optical absorption edges of the amorphous In-Ga-O and Ga-Al-O thin films were controlled by means of the concentration ratios of [In]/([In]+[Ga]) and [Al]/([Al]+[Ga]) in the starting solutions.
Preparation and Characterization of Tin-doped Indium (ITO) Film by Photo Reaction of Nano-Particle (PRNP) Using Excimer Laser
Authors: Tsuchiya T. , Yamaguchi F. , Morimoto I. , Nakajima T. , Kumagai T.
Published: August 2009

An ITO film on an SiO2 substrate was prepared from spin-coated nano-particles using a simple thermal process and photo irradiation process. The effects of the excimer lamp and excimer laser on the resistivity of the film were investigated. When the film is 40 nm thick, the combined two-step irradiation by an excimer lamp and laser in N2 is effective for the preparation of the ITO film with a lower resistivity. Using the two-step irradiation and one-step KrF irradiation in N2 at room temperature, the resistivity of the ITO film was 5.94×10−4Ωcm. On the other hand, when using the thermal process, the resistivity of the film sintered at 500 °C in N2 was 4.10×10−3Ωcm. The differences in resistivity are discussed on the basis of the microstructure using SEM, XRD and Hall measurements.
Low-Temperature Processing of Sol-Gel Derived Metal Oxide Thin Films using Supercritical Carbon Dioxide Fluid
Authors: Uchida Hiroshi , Fujioka Kaori , Koda Seiichiro
Published: August 2009

We demonstrate a novel technique using supercritical carbon dioxide (scCO2) fluid for lowering processing temperature of sol-gel-derived metal oxide thin films. The film processing was performed in a hot-wall closed vessel filled with scCO2 fluid. The effects of fluid temperature and additives on the sol-gel synthesis reaction under scCO2 fluid were also investigated. Precursor films of titanium dioxide (TiO2) prepared on silicon wafer and silica glass by sol-gel coating using Ti-alkoxide were converted to crystalline TiO2 (anatase) films successfully by treatment in scCO2 without additive agent at a fluid pressure of 15 MPa and at a substrate temperature of above 250°C, which is significantly lower than the processing temperature of conventional sol-gel deposition. Furthermore, additive agents such as water (H2O) and nitrogen-oxygen mixture (N2-O2) promoted the decomposition and crystallization of precursor films in scCO2 fluid to form the crystalline TiO2 (anatase) films at a substrate temperature at as low as 200°C although it also produced surface absorbates consisted of hydroxides on the film surface. The experimental results suggested that the hydrolysis and polymerization reactions of Ti-alkoxide in the precursor films were proceeded by the scCO2 processing to form titanium-oxygen (Ti-O) networks and that byproducts such as alcohols were removed from the resulting films.
Electrochemical Co-deposition of In-Se and Ga-Se Thin Films for Preparation of CIGS Solar Cells
Authors: Aksu Serdar , Wang Jiaxiong , Basol Bulent M.
Published: August 2009

Electrochemical co-depositions of indium (In) with selenium (Se) and gallium (Ga) with selenium were carried out to obtain high-quality In-Se and Ga-Se films. The approach utilized full potential of complexation for the first time by using aqueous electroplating solutions containing complexing agents at alkaline regime. Complexing agents were employed to solubilize In and Ga ions at high pH and to bring their reduction potentials down, closer to that of Se. Since no appreciable complexation occurred between Se and the complexing agents, Se reduction potential could be independently controlled by the amount of dissolved Se. Tartrate and citrate were determined to be suitable complexing agents for In and Ga. By optimizing the concentrations of the metal salts, the complexing agents, the selenium source, pH and the electrodeposition current density, it was possible to obtain adherent and smooth In-Se and Ga-Se films with high repeatability and controllable In/Se and Ga/Se molar ratios.
Synthesis of InGaZnO4 Colloids and Its Application in a TFT Device
Authors: Kao Chen-Yu , Chou Kan-Sen , Yang Y.H. , Yang S.S.
Published: August 2009

The deposition of amorphous InGaZnO4 (a-IGZO) semiconductor film, via a sputtering process, has been demonstrated in the literature. In this paper, we present a solution method as an alternative to obtain this semiconducting film. The dispersible IGZO colloids is formed first by co-precipitation of precursors, followed by hydrothermal treatment at 200°C for 1 hour and using CMC as the dispersion agent. The crystalline colloid would become amorphous when it was heated at above 250°C. The TFT structure was made by growing a dielectric silica layer using the CVD method, a metal layer using the sputtering method, and an active IGZO layer using the solution method. This device exhibits low operating voltage, the mobility is about 2cm2V−1s−1 and the Ion/Ioff ratio is 104. Further improvement in processing is needed.
Field Induced Crystal Nucleation in Chalcogenide Phase Change Memory
Authors: Nardone Marco , Karpov Victor G. , Mitra Mukut , Karpov Ilya V.
Published: August 2009

A summary is presented of our theoretical and experimental work over more than two years related to switching in chalcogenide glass phase change memory. As a significant addition to the well known experiments, we have studied switching under considerably lower voltages and elevated temperatures, as well as the statistics of switching events and relaxation oscillations. Our analytical theory, based on field induced crystal nucleation, predicts all of our observed features and their dependencies on material parameters.
Evidence of Magnetoelectric Coupling in Pb(Fe0.5Nb0.5)O3 Ceramics Through Impedance Spectroscopy and Electromechanical Resonance Measurements
Authors: Raymond Oscar , Font Reinaldo , Almodovar Nelson S. , Portelles Jorge J. , Siqueiros Jesús M
Published: August 2009

Multifunctional materials such as the single phase compound Pb(Fe0.5Nb0.5)O3 (PFN), where ferroelectric and antiferromagnetic order coexist, are very promising and have great interest from the academic and technological points of view. In this work, coupling of the ferroelectric and magnetic ordering has been observed. For this study, a combination of the small signal response using the impedance spectroscopy technique and the electromechanical resonance method with the large signal response through standard ferroelectric measurement, has been used with and without an applied magnetic field. The measurements to determine the electrical properties of the ceramic were performed as functions of the bias and poling electric fields. A simultaneous analysis of the complex dielectric constant , impedance , electric modulus , and the electromechanical coupling factors is presented. The results are correlated with a previous study of structural, morphological, small signal dielectric frequency-temperature response, and the ferroelectric hysteretic, magnetic and magnetodielectric behaviors. The observed shifts of the resonance and antiresonance frequency values can be associated with change of the domain size favored by the readjustment of the oxygen octahedron when the magnetic field is applied.From P-E hysteresis loops obtained without and with an external applied magnetic field a maximum value of dc magnetoelectric coefficient αME = 4 kV/cm T (400 mV/cm Oe) was obtained.
Flexible Ceramic-Polymer Composite Substrates with Spatially Variable Dielectrics for Miniaturized RF Applications
Authors: Tasdemir Zuhal , Kiziltas Gullu
Published: August 2009

The goal of this research is to develop a process suitable for producing monolithic conformal substrates with a spatial arrangement of material cells according to a particular design creating novel material systems, useful for many multi- functional electronic and Radio Frequency devices. In this study, MCT ceramics (Mg-Ca-Ti-O systems) and organic binders (polymer solution) are mixed and fabricated as films through a process called tape casting to compromise between high dielectric constant and flexibility. Prior to optimizing the process, several characterization studies are carried out: Commercial spray dried MCT powders (Transtech Inc.) with dielectric constant k=70 and k=20 were analyzed as pressed and produced into tape cast films. Dielectric properties are then measured by an Agilent 16451B material analysis kit and their microscopic behavior is examined by scanning electron microscopy. Results show that flexible composite films show a maximum dielectric constant of ε∼22 unlike their powder pressed form with ε ∼16 but their loss behavior deteriorates when compared with their sintered form and a loss tangent factor of 0.001. The difference is attributed to the air content vs. polymer presence of the material in powder pressed form. Also, these substrates naturally are no longer flexible; hence studies are focused on their tape cast form. The potential of these dielectric shades to serve as candidate constituents for producing monolithic textured polymer-ceramic-composites with controllable loss is studied further. Four properties are of prime importance: tunability of dielectric constants to achieve miniaturization, flexibility via low temperature processing of polymers and loss controllability.
Characterisation of Secondary Phases in Cu Poor CuInSe2: Surface and in-depth resolved Raman scattering analysis of polycrystalline layers
Authors: Izquierdo-Roca Victor , Fontané Xavier , Calvo-Barrio Lorenzo , Álvarez-García Jacobo , Pérez-Rodríguez Alejandro , Morante Joan Ramón , Witte Wolfram , Klenk Reiner
Published: August 2009

This work reports the surface and in-depth resolved Raman scattering analysis of polycrystalline CuInSe2 layers grown with different chemical composition, as function of the Cu to In content ratio (0.48 ≤ × ≤ 1.14). Measurements performed at the surface of the Cu-poor layers corroborate the formation of both Cu-poor Ordered Vacancy Compound (OVC) and CuAu ordered CuInSe2 phases for compositions corresponding to x ≤ 0.82 (OCV) and x ≤ 0.66 (CuAu), respectively. In-depth resolved measurements performed on the layers with lower Cu content have allowed observing a strong decrease with the depth of the intensity of the Raman peak from the chalcopyrite ordered CuInSe2 phase. This suggests a preferential formation of both OVC and CuAu ordered phases at the region close to the interface with the back Mo layer. On the other hand, the comparison between the spectra directly measured on the front and back surfaces of the layers -after removal of the layers from the Mo coated glass substrates- suggests also a worsening of the crystalline quality at the back region of the layers in the whole range of compositions.
Crystalline Perfection of Epitaxial Structure: Correlations with Composition, Thickness, and Elastic Strain of Epitaxial Layers
Authors: Jampana Balakrishnam R , Faleev Nikolai N , Ferguson Ian T , Opila Robert L , Honsberg Christiana B
Published: August 2009

Crystalline perfection of InGaN epi-layers is the missing design parameter for InGaN solar cells. Structural deterioration of InGaN epi-layers depends on the thickness, composition and growth conditions as well. Increasing the InGaN epi-layer thickness beyond a critical point introduces extended crystalline defects that hinder the optical absorption and electrical properties. Increasing the InGaN composition further reduces this critical layer thickness. The optical absorption band edge is sharp for III-nitride direct band gap materials. The band edge profile is deteriorated by creation of extended crystalline defects in the InGaN epitaxial material. The design of InGaN solar cells requires the growth of epi-layers where a trade off between crystalline perfection and optical absorption properties is reached.
Electron Microscopy Characterization of Low-Temperature Growth Zn-doped TiO2 Nanowires
Authors: Eastman Micah , Li Haiyan , Jiao Jun
Published: August 2009

We report the synthesis of Zn-doped TiO2 nanowires by a solution-based process. The synthesis takes place at 200°C in an alkali solution and results in both nanowire and nanoparticle precipitates. Several transmission electron microscopy techniques were used to characterize the resulting precipitates: diffraction patterns and high resolution phase contrast images provided identification of the crystalline phase of the material as well as insights into the resulting lattice parameters, energy dispersive x-ray spectroscopy allowed identification of constituent elements, and electron energy loss spectroscopy permitted quantification of relative concentrations of hydroxyl and lattice-type oxygen bonding. In addition, scanning electron microscope images provide overall perspective of the growth uniformity and morphology.
ZnO nano-pillar Resonators with Coaxial Bragg-Reflectors
Authors: Schmidt-Grund Rudiger , Hinkel Annekatrin , Hilmer Helena , Zúñiga-Pérez Jesus , Sturm Chris , Rheinländer Bernd , Grundmann Marius
Published: August 2009

We demonstrate the growth of lateral concentric BR on ZnO nano-pillars. It opens the opportunity to be used for (i) the enhancement of the lateral confinement in classical pillar-resonators in order to increase the emission rates in the regime of weak exciton-photon coupling (Purcell-effect), (ii) to enhance the exciton-polariton coupling strength in the strong-coupling regime, and (iii) to be used for two-dimensional confinement in free-standing photonic wire resonators. Spatially resolved PL experiments in dependence on the pillar diameter and on the temperature provide strong hints for the ZnO nano-pillar resonator being in the strong-coupling regime. The coupling strength can be estimated to be V = 80 meV.
Laser Micro-machining of Three-Dimensional Microstructures in Optical Materials
Authors: Wang Xianghua , Lai Pui To , Choi Anthony H.W.
Published: August 2009

We demostrate an advanced precision cutting tool using a 349 nm nanosecond-pulsed UV laser micromachining setup. After expansion and collimation, the laser beam is directed vertically and focused with a high performance triplet lens. With an Al mirror inserted in the path of the convergent beam, the beam can be focused on a horizontal machining plane at any desired tilting angles. Microstructures of a wide range of geometries on hard materials can be formed using this custom machining method. Conventional linear and rotary machining on sapphire materials have been demonstrated.
Fidelity of Holographic Lithography for Fabrication of 3D SU-8 Photonic Structures and How to Minimize Distortion by Optical Design
Authors: Zhu Xuelian , Xu Yongan , Cheng Shih-Chieh , Yang Shu
Published: August 2009

Theoretical analysis can impart great benefits on the rationale design of 3D photonic structures by revealing the underlying mechanisms of structural distortion during each processing step. In this report, we quantitatively study the distortion of a three-term diamond-like structure fabricated in SU-8 polymer by four-beam interference lithography, which can be attributed to refraction at the air-film interface, and resist film shrinkage during lithographic process. In study of photonic bandgap (PBG) properties of Si photonic crystals templated by the SU-8 structures, we find that the distortion has degraded the quality of PBGs. Furthermore, we theoretically design new optical setups to fabricate three-term diamond-like structure with minimal deformation. Instead of single exposure of four beams, we use triple exposure of two beams, one from the central beam and the other from the side beam each time. A set of new linear polarization vectors is suggested to enhance the contrast between the minimal and maximal intensities of interference pattern.