bluuebunny/crossref_metadata_2025 huggingface dataset:
DETECTING COPY NUMBER VARIATIONS FROM ARRAY CGH DATA BASED ON A CONDITIONAL RANDOM FIELD MODEL
Authors: YIN XIAO-LIN , LI JING
Published: April 2010

Array comparative genomic hybridization (aCGH) allows identification of copy number alterations across genomes. The key computational challenge in analyzing copy number variations (CNVs) using aCGH data or other similar data generated by a variety of array technologies is the detection of segment boundaries of copy number changes and inference of the copy number state for each segment. We have developed a novel statistical model based on the framework of conditional random fields (CRFs) that can effectively combine data smoothing, segmentation and copy number state decoding into one unified framework. Our approach (termed CRF-CNV) provides great flexibilities in defining meaningful feature functions. Therefore, it can effectively integrate local spatial information of arbitrary sizes into the model. For model parameter estimations, we have adopted the conjugate gradient (CG) method for likelihood optimization and developed efficient forward/backward algorithms within the CG framework. The method is evaluated using real data with known copy numbers as well as simulated data with realistic assumptions, and compared with two popular publicly available programs. Experimental results have demonstrated that CRF-CNV outperforms a Bayesian Hidden Markov Model-based approach on both datasets in terms of copy number assignments. Comparing to a non-parametric approach, CRF-CNV has achieved much greater precision while maintaining the same level of recall on the real data, and their performance on the simulated data is comparable.
Disequilibrium textures versus equilibrium modelling: geochronology at the crossroads
Authors: Villa Igor M.
Published: April 2010

Submicroscopic microchemical disequilibrium in minerals is extremely widespread. Disequilibrium recrystallization is promoted by water in metamorphic terranes and near granites, contact aureoles, and faults. Recrystallization is energetically less costly at almost any temperature than diffusive re-equilibration.

Radiogenic isotopes (except
4
He) never diffusively re-equilibrate faster than major elements forming the mineral structure. Isotopic inheritance tied to relicts was demonstrated for zircon, monazite, amphibole, K-feldspar, biotite and muscovite.

The mechanism for resetting the isotope record in nature depends more on the availability of recrystallization-enhancing water than on reaching a preset temperature. Laboratory diffusion experiments on hydrous minerals were plagued, to a variable but always large extent, by dissolution–reprecipitation. Mineral geochronometers should be viewed as ‘geohygrometers’ that essentially date the fluid circulation episodes.

Thanks to submicroscopic petrology, isotopic disequilibria can be put into context with petrogenetic disequilibria. Analytical advances allow the successful dating of each mineral generation. This has opened up a much richer wealth of data on the
P
–
T
–
A
–
X
–
d
history of rocks, which in the long run will also improve our ability to develop credible numeric models.
Three-dimensional evaluation of fabric evolution and metamorphic reaction progress in polycyclic and polymetamorphic terrains: a case from the Central Italian Alps
Authors: Salvi Francesca , Spalla Maria Iole , Zucali Michele , Gosso Guido
Published: April 2010

The 3D reconstruction of geological bodies is an excellent tool for the representation of crustal structures and is applied here to understand related heterogeneities in the grain-scale fabrics; the western portion of the Languard–Tonale Alpine tectono-metamorphic unit (Austroalpine domain, Central Alps) allows evaluation of the per cent volume of textural reworking during polyphase pre-Alpine and Alpine deformations. The structural and metamorphic overprinting during the last deformation imprint involved less than 50% of rock volume; this estimate is obtained by discriminating domains that homogeneously recorded structural and metamorphic re-equilibration during crenulation–decrenulation cycles. These domains are reconstructed using a geograhpical information system (GIS) to manipulate field data and interpretative cross-sections as a means to constrain their 3D volumes. The degree of fabric evolution is integrated at the microscale with the estimate of the reactants/products ratio to infer the progress of metamorphic transformation related to advancing degree of mechanical reactivation. The correlation between degree of fabric evolution and progress of synkinematic metamorphic reactions shows that differences between pristine mineral assemblages v. pre-existing fabrics influence the rate of reaction accomplishment. Fabric evolution and degree of metamorphic transformation increase proportionally once above the threshold value of 60% of volume affected by fabric rejuvenation; metamorphic degree also influences the progress of metamorphic reactions.
Brittle
plus
plastic deformation of gypsum aggregates experimentally deformed in torsion to high strains: quantitative microstructural and texture analysis from optical and diffraction data
Authors: Zucali M. , Barberini V. , Chateigner D. , Ouladdiaf B. , Lutterotti L.
Published: April 2010

This contribution presents a quantitative microstructural analysis of a polycrystalline aggregate of gypsum, deformed in torsion (
T
=70–90 °C) at γ (shear strain) ranging from 0 to 4.82. Quantitative microstructural analysis is used to compare the evolution of microstructures observed by optical microscope with those obtained from analysis of X-ray and neutron diffraction data. This analysis shows that during experimental deformation, gypsum accommodated strain by brittle and plastic deformation mechanisms, developing Riedel-like microfaults with plastic foliations and crystallographic preferred orientation (CPO). The relations of microstructures show that with increasing strain, the Riedel systems start from
R
planes with an angle of ≈30° to the Imposed Shear Plane. This angle decreases (5°–15°) when strain increases, and
Y
planes develop. Quantitative texture analysis (QTA) shows that S-foliations start developing at low γ and maintain their orientation up to high γ, and that the most active slip system is the (010) along normal to (100) and the [001]-axis. Shape preferred orientation (SPO) of gypsum does not coincide with the theoretical orientation as it does not decrease with increasing strain. This discrepancy is explained by the role of the brittle shear planes that impose a back rotation to gypsum. No brittle to plastic transition occurs. But both plastic and brittle structures contemporaneously accommodate and localize strain.
Numerical modelling of spontaneous slab breakoff dynamics during continental collision
Authors: Baumann Cyrill , Gerya Taras V. , Connolly James A. D.
Published: April 2010

Slab detachment or breakoff is directly associated with phenomena like morphological orogenesis, occurrence of earthquakes and magmatism. At depth the detachment process is slow and characterized by viscous rheolgy, whereas closer to the surface the process is relatively fast and plastic. Using a 2D mantle model 1500 km deep and 4000 km wide we investigated, with finite-difference and marker-in-cell numerical techniques, the impact of slab age, convergence rate and phase transitions on the viscous mode of slab detachment. In contrast to previous studies exploring simplified breakoff models in which the blockage responsible for inducing breakoff is kinematically prescribed, we constructed a fully dynamic coupled petrological–thermomechanical model of viscous slab breakoff. In this model, forced subduction of a 700 km-long oceanic plate was followed by collision of two continental plates and spontaneous slab blocking resulting from the buoyancy of the continental crust once it had been subducted to a depth of 100–124 km. Typically, five phases of model development can be distinguished: (a) oceanic slab subduction and bending; (b) continental collision initiation followed by the spontaneous slab blocking, thermal relaxation and unbending – in experiments with old oceanic plates in this phase slab roll-back occurs; (c) slab stretching and necking; (d) slab breakoff and accelerated sinking; and (e) post-breakoff relaxation.

Our experiments confirm a correlation between slab age and the time of spontaneous viscous breakoff as previously identified in simplified breakoff models. The results also demonstrate a non-linear dependence of the duration of the breakoff event on slab age: a positive correlation being characteristic of young (<50 Ma) slabs while for older slabs the correlation is negative. The increasing duration of the breakoff with slab age in young slabs is attributed to the slab thermal thickness, which increases both the slab thermal relaxation time and duration of the necking process. In older slabs this tendency is counteracted by negative slab buoyancy, which generate higher stresses that facilitate slab necking and breakoff. A prediction from our breakoff models is that the olivine–wadsleyite transition plays an important role in localizing viscous slab breakoff at depths of 410–510 km due to the buoyancy effects of the transition.
Present-day vertical isostatic readjustment of the Western Alps revealed by numerical modelling and geodetic and seismotectonic data
Authors: Gardi Annalisa , Baize Stéphane , Scotti Oona
Published: April 2010

The active tectonics of the Western Alps reveals contrasting regimes: ongoing extension at the heart of the chain and transpression–compression at its external sectors. The active processes currently affecting this region are still a matter of debate. The classical models proposed in the literature invoke: Eurasia–Adria plate collision, counterclockwise motion of the Adria microplate, slab retreat of the subducted continental lithosphere and slab-detachment. More recently, several authors prefer the hypothesis of tectonics driven by isostasy–buoyancy forces. To better understand the influence of these processes on the velocity, strain and stress fields at the surface and in the crust, we developed 2D viscoelastic numerical models along a vertical cross-section perpendicular to the Western Alps. We run our models with different driving forces in order to investigate, one by one, the geodynamic processes proposed in the literature. Results are compared with available geodetic, geological and seismotectonic data. In order to bring into coincidence model predictions and observations, an important vertical isostatic readjustment must be included in the modelling, together with a slight horizontal compression (0.5 mm year
−1
), probably due to Africa–Eurasia convergence. We show that the subduction process in this Alpine region is likely to be dead and that buoyancy forces may be dominating the present-day tectonics.
Operation and data mapping for CGRAs with multi-bank memory
Authors: Kim Yongjoo , Lee Jongeun , Shrivastava Aviral , Paek Yunheung
Published: April 2010

Coarse Grain Reconfigurable Architectures (CGRAs) promise high performance at high power efficiency. They fulfil this promise by keeping the hardware extremely simple, and moving the complexity to application mapping. One major challenge comes in the form of data mapping. For reasons of power-efficiency and complexity, CGRAs use multi-bank local memory, and a row of PEs share memory access. In order for each row of the PEs to access any memory bank, there is a hardware arbiter between the memory requests generated by the PEs and the banks of the local memory. However, a fundamental restriction remains that a bank cannot be accessed by two different PEs at the same time. We propose to meet this challenge by mapping application operations onto PEs and data into memory banks in a way that avoids such conflicts. Our experimental results on kernels from multimedia benchmarks demonstrate that our local memory-aware compilation approach can generate mappings that are up to 40% better in performance (17.3% on average) compared to a memory-unaware scheduler.
Modeling structured event streams in system level performance analysis
Authors: Perathoner Simon , Rein Tobias , Thiele Lothar , Lampka Kai , Rox Jonas
Published: April 2010

This paper extends the methodology of analytic real-time analysis of distributed embedded systems towards merging and extracting sub-streams based on event type information. For example, one may first merge a set of given event streams, then process them jointly and finally decompose them into separate streams again. In other words, data streams can be hierarchically composed into higher level event streams and decomposed later on again. The proposed technique is strictly compositional, hence highly suited for being embedded into well known performance evaluation frameworks such as Symta/S and MPA (Modular Performance Analysis). It is based on a novel characterization of structured event streams which we denote as Event Count Curves. They characterize the structure of event streams in which the individual events belong to a finite number of classes. This new concept avoids the explicit maintenance of stream-individual information when routing a composed stream through a network of system components. Nevertheless it allows an arbitrary composition and decomposition of sub-streams at any stage of the distributed event processing. For evaluating our approach we analyze a realistic case-study and compare the obtained results with other existing techniques.
Contracts for modular discrete controller synthesis
Authors: Delaval Gwenaël , Marchand Hervé , Rutten Eric
Published: April 2010

We describe the extension of a reactive programming language with a behavioral contract construct. It is dedicated to the programming of reactive control of applications in embedded systems, and involves principles of the supervisory control of discrete event systems. Our contribution is in a language approach where modular discrete controller synthesis (DCS) is integrated, and it is concretized in the encapsulation of DCS into a compilation process. From transition system specifications of possible behaviors, DCS automatically produces controllers that make the controlled system satisfy the property given as objective. Our language features and compiling technique provide correctness-by-construction in that sense, and enhance reliability and verifiability. Our application domain is adaptive and reconfigurable systems: closed-loop adaptation mechanisms enable flexible execution of functionalities w.r.t. changing resource and environment conditions. Our language can serve programming such adaption controllers. This paper particularly describes the compilation of the language. We present a method for the modular application of discrete controller synthesis on synchronous programs, and its integration in the BZR language. We consider structured programs, as a composition of nodes, and first apply DCS on particular nodes of the program, in order to reduce the complexity of the controller computation; then, we allow the abstraction of parts of the program for this computation; and finally, we show how to recompose the different controllers computed from different abstractions for their correct co-execution with the initial program. Our work is illustrated with examples, and we present quantitative results about its implementation.
Design exploration and automatic generation of MPSoC platform TLMs from Kahn Process Network applications
Authors: Viskic Ines , Yu Lochi , Gajski Daniel
Published: April 2010

With increasingly more complex Multi-Processor Systems on Chip (MPSoC) and shortening time-to-market projections, Transaction Level Modeling and Platform Aware Design are seen as promising >approaches to efficient MPSoC design.

In this paper, we present an automatized 3-phase process of Platform Aware Design and apply it to Kahn Process Networks (KPN) applications, a widely used model of computation for data-flow applications. We start with the KPN application and an abstract platform template and automatically generate an executable TLM with estimated timing that accurately reflects the system platform. We support homogeneous and heterogeneous multi-master platform models with shared memory or direct communication paradigm. The communication in heterogeneous platform modules is enabled with the transducer unit (TX) for protocol translation. TX units also act as message routers to support Network on Chip (NoC) communication.

We evaluate our approach with the case study of the H.264 Encoder design process, in which the specification compliant design was reached from the KPN application in less than 2 hours. The example demonstrates that automatic generation of platform aware TLMs enables a fast, efficient and error resilient design process.
Compiler directed network-on-chip reliability enhancement for chip multiprocessors
Authors: Ozturk Ozcan , Kandemir Mahmut , Irwin Mary J. , Narayanan Sri H.K.
Published: April 2010

Chip multiprocessors (CMPs) are expected to be the building blocks for future computer systems. While architecting these emerging CMPs is a challenging problem on its own, programming them is even more challenging. As the number of cores accommodated in chip multiprocessors increases, network-on-chip (NoC) type communication fabrics are expected to replace traditional point-to-point buses. Most of the prior software related work so far targeting CMPs focus on performance and power aspects. However, as technology scales, components of a CMP are being increasingly exposed to both transient and permanent hardware failures. This paper presents and evaluates a compiler-directed power-performance aware reliability enhancement scheme for network-on-chip (NoC) based chip multiprocessors (CMPs). The proposed scheme improves on-chip communication reliability by duplicating messages traveling across CMP nodes such that, for each original message, its duplicate uses a different set of communication links as much as possible (to satisfy performance constraint). In addition, our approach tries to reuse communication links across the different phases of the program to maximize link shutdown opportunities for the NoC (to satisfy power constraint). Our results show that the proposed approach is very effective in improving on-chip network reliability, without causing excessive power or performance degradation. In our experiments, we also evaluate the performance oriented and energy oriented versions of our compiler-directed reliability enhancement scheme, and compare it to two pure hardware based fault tolerant routing schemes.
Elastic computing
Authors: Wernsing John Robert , Stitt Greg
Published: April 2010

Over the past decade, system architectures have started on a clear trend towards increased parallelism and heterogeneity, often resulting in speedups of 10x to 100x. Despite numerous compiler and high-level synthesis studies, usage of such systems has largely been limited to device experts, due to significantly increased application design complexity. To reduce application design complexity, we introduce elastic computing - a framework that separates functionality from implementation details by enabling designers to use specialized functions, called elastic functions, which enable an optimization framework to explore thousands of possible implementations, even ones using different algorithms. Elastic functions allow designers to execute the same application code efficiently on potentially any architecture and for different runtime parameters such as input size, battery life, etc. In this paper, we present an initial elastic computing framework that transparently optimizes application code onto diverse systems, achieving significant speedups ranging from 1.3x to 46x on a hyper-threaded Xeon system with an FPGA accelerator, a 16-CPU Opteron system, and a quad-core Xeon system.
RNFTL
Authors: Wang Yi , Liu Duo , Wang Meng , Qin Zhiwei , Shao Zili , Guan Yong
Published: April 2010

In this paper, we propose a hybrid-level flash translation layer (FTL) called RNFTL (Reuse-Aware NFTL) to improve the endurance and space utilization of NAND flash memory. Our basic idea is to prevent a primary block with many free pages from being erased in a merge operation. The preserved primary blocks are further reused as replacement blocks. In such a way, the space utilization and the number of erase counts for each block in NAND flash can be enhanced. To the best of our knowledge, this is the first work to employ a reuse-aware strategy in FTL for improving the space utilization and endurance of NAND flash. We conduct experiments on a set of traces that collected from real workload in daily life. The experimental results show that our technique has significant improvement on space utilization, block lifetime and wear-leveling compared with the previous work.
(Invited) Novel Processing for Si-Nanocrystal Based Photonic Materials
Authors: Halsall Matthew P. , Crowe Iain Forbes , Hylton Nicholas , Hulko Oksana , Knights Andrew , Ruffell Simon , Gwilliam Russel , Wojdak Maciej , Kenyon Anthony
Published: April 2010

We report a study of novel processing approaches for the formation of silicon nanocrystals for photonic devices. A silicon rich oxide was formed using ion implantation into thermally grown oxides on Silicon and transparent sapphire substrates. These layers were then treated with rapid thermal processing to observe the formation of silicon nanocrystals on a one second to ten minute timescale. Transmission electron microscopy and Raman scattering were used to follow the evolution of the nanocrystal mean diameter with anneal time. Identical samples co-implanted with Erbium demonstrated the widely reported non-resonant energy transfer mechanism from the nanocrystals to the internal energy levels of the erbium. We quantified the sensitization efficiency, IEr/Inc as a function of the Si-NC size by correcting the relative visible and IR luminescence intensities for variations in the nanocrystal density and observed photoluminescence lifetime. We find that the sensitizing efficiency increases exponentially with decreasing Si-NC mean diameter.
Photoluminescence Efficiency of Ge Dots Self-Assembled on SiO2 and TiO2 Films
Authors: Lockwood D.J. , Rowell N.L. , Berbezier I. , Amiard G. , Favre L. , Ronda A. , Grosso D.
Published: April 2010

Self-assembled Ge nanodots were formed by in-situ thermal annealing of a thin amorphous Ge layer deposited by molecular beam epitaxy on a thin SiO2 or TiO2 layer on Si(001). The dot photoluminescence (PL) appeared primarily as a wide near-infrared band peaked near 800 meV. Using both the k•p and tight binding theoretical models, we have analyzed the PL spectrum in terms of the dot size distribution required to reproduce the observed asymmetric band shape. The peak energy of the PL band reflects the average dot size and its shape depends on the dot size distribution. The observed size distribution determined from transmission electron and atomic force microscopy allowed the determination of the nonlinear increase in the PL quantum efficiency with decreasing dot diameter. In addition, we show it is possible to evaluate the size distribution of Ge dots from their PL energy dependence.
Effect of Annealing Time on the Growth, Structure, and Luminescence of Nitride-Passivated Silicon Nanoclusters
Authors: Wilson Patrick R. , Roschuk Tyler , Dunn Kayne , Normand Elise , Chelomentsev Evgueni , Wojcik Jacek , Mascher P.
Published: April 2010

Rapid thermal annealing has been used to study the changes in luminescence and structure from silicon-rich silicon nitride films for annealing times ranging from 2 seconds to 1 hour at 600 and 800°C. Silicon nanoclusters formed within the silicon nitride host matrix provided the source of the luminescence in the films through quantum confinement effects. Room temperature photoluminescence spectra exhibited a large, abrupt red-shift in emission after only 2 seconds of annealing, indicating early formation and growth of the silicon nanoclusters occurs through a fast transient diffusion mechanism. This initial shift was followed by a slower but steady growth of the nanoclusters as the annealing time was increased further. X-ray absorption near edge structure at the Si K- and L3,2-edges supported the trends observed in the photoluminescence spectra, providing evidence of silicon nanocluster growth and restructuring of the silicon nitride host matrix over the course of annealing.
Electrical Properties of Silicon-Rich Silicon Carbide Films Prepared by Using Catalytic Chemical Vapor Deposition
Authors: Lee Kyoung-Min , Hwang Jae-Dam , Lee Youn-Jin , No Kil-Sun , Hong Wan-Shick
Published: April 2010

We studied electrical properties of the silicon rich silicon carbide (SRSC) films deposited by catalytic chemical vapor deposition (Cat-CVD) technique. A mixture of SiH4, CH4 and H2 gas was employed as the source gas in deposition process. Atomic composition of SRSC films and formation of Si QDs in SRSC films depended on control of CH4/SiH4 mixture ratios. The each different tunneling behavior was observed in current-voltage (I-V) curve of two samples prepared at different CH4/SiH4 mixture ratios. The PL spectra of two samples were also each different. These results were analyzed with relating formation of Si QDs in SRSC films.
(Invited) Photoluminescence Properties of Alkaline-Earth Oxide Nanoparticles
Authors: Sushko Peter V. , McKenna Keith , Muñoz Ramo D. , Shluger A. L. , Sternig Andreas , Stankic Slavica , Müller Markus , Diwald Oliver
Published: April 2010

Previous experiments have demonstrated that photoluminescence properties, both excitation and emission spectra, of powdered MgO depend strongly on the powder preparation and treatment. Similar dependencies have been found for CaO, SrO, and BaO powders. The observed broad photoemission bands have been attributed to the low-coordinated surface sites. Recent advances in nanoscale science and technology have made it possible to produce nearly monodispersed alkaline-earth oxide nanoparticles of very high surface area and investigate their optical properties in details. Here we present the results of our theoretical and experimental work in this area and present new results.
(Invited) Synthesis and Characterization of Photoluminescent Polymer Micro- and Nanopillar Arrays
Authors: Marsal Lluis F. , Palacios Raquel , Santos Abel , Formentín Pilar , Martinez-Ferrero Eugenia , Ferré-Borrull Josep , Pallarès Josep
Published: April 2010

Photoluminescent micro- and nanopillars are fabricated by replication from macroporous silicon and nanoporous anodic alumina via template wetting using different conducting polymers. The geometric features of the resulting structures are characterized through environmental scanning electron microscopy. The influence of the porous dimension in the photophysical properties of the polymeric structures is investigated by absorption and emission measurements. By means of micro-X-ray diffraction we analyze the amorphous-crystalline nature of the fabricated structures. These structures can be interesting as hole conducting donors in different applications such as nanostructured solar cells and polymer light emitting diodes.
Combustion Synthesis and Photoluminescence Characteristics of Y1-xCaAl3O7:xEu3+ Nanoparticles
Authors: Taxak Vinod B. , Khatkar Satyender P. , Kumar Mukesh , Han Sang-Do
Published: April 2010

Europium-activated CaYAlO4:Eu3+ nanocrystals were synthesized by combustion method using an aqueous concentrated paste of calculated amounts of metal nitrates and urea as organic fuel. Comparing with traditional material processing techniques, combustion method is relatively simple method. The nano crystals obtained through combustion method was characterized by using scanning electron microscopy (SEM), X-ray diffractions (XRD), and photoluminescence (PL) spectra. The photoluminescence (PL) spectra of the nano crystals prepared shows predominant red colour under an UV source which is attributed to the transitions [5D0 → 7F2] of Eu3+ ions at 612 nm .In addition, effect of heat treatment on the size of the nano crystals and the dependence of the luminescence intensity on the Eu3+ concentrations have also been discussed. The as-synthesized nanophosphors have a very small crystallite sizes range from 50 nm to 70 nm.
Synthesis and Photoluminescence Properties of Y2O3:Eu3+/SiO2 Core/Shell Phosphor Nanoparticles
Authors: Han Jinkyu , Talbot Jan , McKittrick Joanna
Published: April 2010

This paper reports on the fabrication and photoluminescence properties of Y2O3:Eu3+ core particles synthesized by a Pechini-type sol-gel process with SiO2 shells fabricated by the Stöber method. Various factors affecting the dispersion of the nanophosphors, such as calcination temperature, solvents and the ratio of metal ions to citric acid and ethylene glycol were examined. The morphology and particle size of the core-shell particles were studied by scanning electron microscopy. The particle size of the phosphor core varied from 25 to 40 nm and that of SiO2 shell was 100 to 350 nm, depending on the concentration of reactants. Photoluminescence measurements of the Y2O3Eu3+ particles showed strong red emission peaks at 611 nm (5D0→7F2) and the photoluminescence intensity of core/shell particles were more than 2 times higher than that of core only particles.
(Invited) Optical Response of II-VI ZnSe Nanowires
Authors: Ruda Harry E. , Philipose Usha , Saxena Ankur , De Souza Christina , Nair Selvakumar , Salfi Joseph , Shik A. , Othonos A. , Lioudakis E. , Tsokkou D. , Zhong L. , Fernandes Carlos
Published: April 2010

II-VI nanowires offer a unique combination of properties for developing blue/UV optoelectronic devices. Key to realizing this potential is managing the nanowire growth process to ensure appropriate properties are realized. Taking ZnSe as an example, we report on the influence of growth conditions (namely, growth temperature and constituent flux ratio) on optimizing the luminescence response. It is shown that native defects ultimately dictate properties including steady state photoluminescence, ultra-fast optical response and even nonlinear behavior. We demonstrate how careful control over materials can enable the realization of a state of the art photo-detector based on such nanowires.
(Invited) Surface Manipulation of the Magnetic Properties of CdSe Quantum Dots
Authors: Meulenberg Robert W. , Lee Jonathan , McCall Scott , Haskel Daniel , Lang Jonathan C. , Terminello Louis J. , Van Buuren Tony
Published: April 2010

We provide conclusive evidence that organic ligands used to coat CdSe quantum dots (QDs) have a fundamentally important effect upon their magnetic properties. Using x-ray absorption spectroscopy, magnetometry and x-ray magnetic circular dichroism, we demonstrate that the choice of organic ligand can be used to tune the magnetic properties. Moreover, our results suggest that a π-backbonding mechanism between the surface Cd atoms and the organic surfactants is responsible for the magnetic behavior of the QDs and that, contrary to previous reports, they exhibit paramagnetic and not ferromagnetic behavior. The potential impact of this research in the field is considerable with the possibility of the development of new and exciting magneto-optic luminescent nanostructures.
MOCVD Preparation and Photoluminescence of ZnS Nanowires
Authors: Juarez Jose. M. , Juarez Fernando
Published: April 2010

An original MOCVD reactor was developed to grow zinc sulphide nanowires. The design of a heater system to have an improved control of the process and to obtain homogenous deposition was performed. ZnS nanowires were successfully synthesized by simple metal-organic chemical vapor deposition technique from ZnS powders onto silicon substrates [111]. Substrates were carried out to a process of cleaning and impregnated with gold clusters from a colloidal solution. Field emission scanning electron microscope (FESEM) observations show that the ZnS nanowires have diameters about 10-20 nm and lengths up to several micrometers. Photoluminescence (PL) properties of these synthesized single-crystal ZnS nanowires have been presented. Finally PL detects peaks related to the nanosize effects of the ZnS nanowires.
(Invited) Doped Nanoparticles for Optoelectronics Applications
Authors: Godlewski Marek
Published: April 2010

Nanoparticles can be applied in biology and medicine as fluorescence labels and in optoelectronics as efficient phosphors. Arguments are presented why phosphors of nanosizes may emit light more efficiently than conventional phosphor materials. First, enhanced impurity-free carriers interactions result in more effective emission excitation and in brighter emission. Second, superradiance is likely more efficient than in bulk-like samples.
(Invited) Nanostructuring the Er3+ and Si Nanoparticle Distributions to Enhance the 1.5 μm Emission in Codoped Al2O3 Thin Films
Authors: Serna Rosalia , Núñez-Sánchez Sara , Roque Pablo
Published: April 2010

Nanostructured amorphous aluminum oxide (Al2O3) thin films codoped with Erbium ions (Er3+) and Si nanoparticles (Si NPs) are prepared by pulsed laser deposition. The doping structure can be controlled in such a way that Er3+ and Si NP concentrations are optimized independently, the Si NP sizes are selected and the Er3+ and Si NPs distances are varied to achieve a close contact below the nanometer scale. The optimized as-grown films show an enhanced photoluminescence performance at 1.5 μm which is related to an efficient Si NPs to Er3+ energy transfer. Upon low temperature thermal annealing it is found a further enhancement of the photoluminescence intensity which is due both to a decrease of the number of non-radiative defects in the film and to an increase the fraction of excitable Er3+ ions through Si NPs. The origin of the loss of the Si NPs-Er energy transfer upon high temperature annealing is discussed.
(Invited) Investigation into the Photophysics and Diffusion Properties of Water Soluble Quantum Dots Using Fluorescence Correlation Spectroscopy
Authors: Peters Robert , Goh J. B. , Dinglasan J. , Thakur A. , Shehata Shyemaa , Anderson D. J. , Fradin Cécile
Published: April 2010

Because of their superior photostability and fluorescence quantum yield, quantum dots are of great interest for biological applications. Unfortunately, most commercial quantum dots require a surfactant solubilizing layer to disperse in aqueous media. This significantly increases their effective diameter and limits their appeal for single molecule studies. Thus Carboxylate capped CdTe nanoparticles, which are water soluble, represent an attractive solution. We used fluorescence correlation spectroscopy to characterize the properties of these quantum dots. Our study confirms that they have small ~ 10 nm hydrodynamic radii. It also confirms that they undergo an excitation intensity dependent blinking process characterized by a power law distribution of "on" and "off" dwell times. This power law breaks down at dwell times on the order of ~10 μs.
(Invited) Emission Quenching of Semiconductor Quantum Dots and its Application to Biosensing
Authors: Kuwabata Susumu , Uematsu Taro , Torimoto Tsukasa
Published: April 2010

Emission quenching of semiconductor nanocrystals by redox molecules been studied using CdTe and ZnS-AgInS2 solid solution (ZAIS) nanocrystals. The quench behavior was investigated in terms of electric charge and electron transfer reaction. Regarding CdTe nanocrystals, it was found that charges of CdTe and redox species largely influenced the PL quench. Similar quenching behavior was also observed for ZAIS nanocrystals, and some quenchers showed different quench ability between their redox states. Furthermore, the combination of redox-responsive quenching with an enzymatic reaction allows fabrication of optical biosensor which increases their PL intensity with the addition of glucose.
(Invited) Si Nanocrystal MOSLEDs: From Materials to Transistors
Authors: Garrido Blas , Perálvarez Mariano , Berencén Yonder , Carreras Josep , Jambois Oliver
Published: April 2010

Si nanocrystals or nanoclusters (Si-nc) either intrinsic or doped (C, Er, Yb,...) and embedded in dielectrics (silicon oxide or nitride) are used as gate materials for integrated Si LEDs. This is becoming the material system of choice of silicon photonics to devise light emitters integrated with CMOS technology. MOSLEDs and eventually MOSLASERs are the key for a number of Si-based platforms like optical interconnects, optical processing and optical sensing. Moreover, MOS light emitters bring about the possibility of adding new functionalities to electronic components and the ultimate merging of electronics and photonics in the same chip. This work is an overview of the last accomplishments of the Silicon Electro-Photonics group of the University of Barcelona with regards to the materials and devices for MOSLEDs.
(Invited) Electroluminescence in Metal-Oxide-Semiconductor Tunnel Diodes with a Silicon Nanolayer
Authors: Morita Mizuho , Matsumura Kei , Yamada Ryuta , Uchikoshi Junichi , Arima Kenta
Published: April 2010

Electroluminescence characteristics of metal-oxide-semiconductor tunnel diodes with a silicon nano-layer on silicon-on-insulator substrates have been studied. Peaks in the spectrum from the diode have been observed at ~1030 nm (~1.20 eV), ~950 nm (~1.31 eV), ~910 nm (~1.36 eV) and ~620 nm (~2.00 eV). It is suggested that the electroluminescence at ~620 nm is due to transitions between ultrathin silicon subbands.
(Invited) Coupling Silicon Nanocrystal Fluorescence to Optical Bottle Resonators
Authors: Bianucci P. , Veinot J. G. C. , Meldrum A.
Published: April 2010

We study the fluorescence of silicon-nanocrystal coated optical bottle resonators. The photoluminescence spectrum shows whispering gallery mode peaks with Q-factors close to 2,500, which evanescent coupling transmission measurements resolve into many modes with Q-factors up to 106. The mode structure is sensitive to both the position and polarization of the collected light. Time resolved photoluminescence measurements indicate the resonator is influencing the nanocrystal emission dynamics.
Surface Forces Measured Between Xanthate-Coated Gold Surfaces
Authors: Wang Jialin , Yoon Roe-Hoan
Published: April 2010

Direct force measurements were conducted between macroscopic gold surfaces using an atomic force microscope (AFM). The gold surfaces were hydrophobized in potassium amyl xanthate (KAX) and potassium ethyl xanthate (KEX) solutions at open circuit potentials. The force vs. distance curves obtained in the xanthate solutions showed the presence of long-range hydrophobic forces, without evidence for nanobubbles causing the attraction. In general, the hydrophobic force increased with xanthate concentration, immersion time, and contact angle. It was found also that hydrophobic force becomes considerably weaker after longer immersion times, which can be attributed to multi-layer formation. Further, the hydrophobic force became substantially stronger when a xanthate solution was replaced by deionized water, indicating that hydrophobic force becomes the strongest in pure water. The results obtained in the present work may be useful for improving flotation practice and shed lights to better understanding the origin of the hydrophobic force.
A SERS Study of the Interaction of n-Octanohydroxamate with a Copper Electrode
Authors: Hope Gregory A. , Woods Ronald , Parker Gretel K.
Published: April 2010

SERS spectroelectrochemical investigations have demonstrated that the flotation collector n-octanohydroxamate specifically adsorbs on copper surfaces in the region of thermodynamic stability of the metal and, at low ionic strength, this gives rise to a contact angle of ~ 70{degree sign}. The contact angle fell to zero when Cu2O was formed on the copper surface and increased again to ~ 70{degree sign} when the potential was increased further. Voltammetry established that, in 0.01 M KOH, the presence of hydroxamate in concentrations of 10-3 M and above retards the rate of formation of Cu2O and indicates that a stability zone of copper n octanohydroxamate replaces that of hydrated CuO. It is concluded that the development of a copper n octanohydroxamate layer is responsible for the copper oxide surface being rendered hydrophobic at high potentials. SERS investigations of the copper/hydroxamate system is considered not to be an appropriate model for advancing understanding of the interaction of this collector with oxidized mineral surfaces.
A Raman Spectroscopic Investigation of Pyrite Oxidation and Flotation Reagent Interaction
Authors: Parker Gretel K. , Hope Gregory A.
Published: April 2010

The oxidation of pyrite and the interaction of xanthate or hydroxamate flotation collectors with the pyrite surface were investigated via normal and surface-enhanced Raman scattering (SERS) techniques. SERS was facilitated via vapour deposition of a discontinuous gold island film or through the application of silver colloids to the pyrite surface. The oxidation of pyrite produced a Raman-inactive solid phase, in addition to octasulfur. 442 nm irradiation could induce the formation of polymeric sulfur from the pyrite oxidation products. Dixanthogen was the major species present on pyrite conditioned with xanthate solutions under oxidizing conditions, although a bound xanthate species was also evident, particularly at reducing potentials. The interaction of hydroxamate with pyrite under oxidizing conditions produced a ferric hydroxamate compound.
Surface Oxidation of Cuprite
Authors: Woods Ronald , Fleming Barry D. , Buckley Alan N. , Gong Bill
Published: April 2010

Oxidation of crystalline mineral cuprite in air under ambient conditions, and in alkaline aqueous solution, has been studied by means of potentiometry, voltammetry and X-ray photoelectron spectroscopy. The rest potential of cuprite in pH 9.2 solution in equilibrium with air was at the cuprite/hydrated CuO reversible value. Both electrochemical and spectroscopic data confirmed that cuprite surfaces oxidise under these conditions to form a surface layer of hydrated cupric oxide. Voltammetry shows the coverage of cupric oxide at pH 9.2 to be less than a monolayer under conditions equivalent to a 200 s exposure to solution in equilibrium with air. The low reactivity of natural crystals of cuprite is considered to be the cause of the low extent of reaction with thiols on abraded and fracture surfaces observed in previous research. The electron spectra showed that in air, a thin surface layer consisting of unhydrated and hydrated cupric oxide was formed.
Ex Situ Surface Chemical Characterization in Minerals Processing Research: The Effect of Hydrophilic Organic Solvents on Sulfide Mineral Surfaces
Authors: Buckley Alan N. , Goh Siew Wei , Fan Liang-Jen
Published: April 2010

The effect on abraded surfaces of chalcocite, covellite and chalcopyrite of their immersion in ethanol, propan-2-ol or acetone has been determined by synchrotron X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. It was confirmed that the extent of surface oxidation while immersed in these organic solvents can be greater than that from air exposure alone, possibly because of carboxylic acid formation at the solid/liquid interface. In all cases investigated, the surface layer was chemically altered following the immersion, even when primary oxidation products were removed by dissolution in the organic liquid. It is clear that the use of alcohols or ketones should be avoided in the preparation of sulfide surfaces for ex situ chemical characterisation in minerals processing research.
Fine Structure in XPS and XANES Spectra Acquired from a Series of Sphalerite Samples
Authors: Pratt Allen
Published: April 2010

The fine structure of high resolution XPS and XANES S L3,2-edge spectra collected from a series of high quality sphalerite samples are examined and discussed. Each of the sphalerite samples had a characteristic iron concentration and the range was from <0.01 wt % Fe to 14.79 wt% Fe. XPS spectra acquired from sphalerite surfaces leached in ferric sulphate-sulphuric acid media are presented and discussed. XANES near-edge spectra were evaluated by comparing S L3,2 -edge spectra acquired from unreacted sphalerite samples. The XPS data show that the sphalerite dissolution proceeds via the formation of a metal deficient sulphide that evolves into a surface dominated by polysulphide species. The XANES data show that S 2p electron transitions to empty S 3s and S 3d states occur across an energy range above the absorption edge. A chemical shift associated with iron to sulphur bonds is identified and a pre-edge feature associated with S - Fe bonding in sphalerite is identified.
Electrochemical and Spectroscopic Analysis of the Arsenopyrite (FeAsS) Oxidation under Calcareous Soil Conditions
Authors: Lara-Castro Rene H. , Briones Roberto , Monroy Marcos , Dossot M. , Mullet Martine , Cruz Roel
Published: April 2010

Electrochemical and spectroscopic studies of arsenopyrite samples were carried out under calcareous soil weathering conditions. Electrochemical study consisted of cyclic voltammetry using carbon paste electrodes with embedded FeAsS particles (CPE-FeAsS) in order to evaluate the oxidation process and the effect of the oxidation products on global reactivity. Leaching procedure consisted of mineral alteration by humid and aeration stages under calcareous conditions. Leached samples were characterized by cyclic voltammetry, SEM-EDS, Raman spectroscopy and XPS. Chemical analysis of leachates provided understanding of the extent of the mineral weathering process. The results indicated the formation of non-stoichiometric layers with variable composition (NL, e.g., Fe1-xAs1-yS) at all stages and the formation of α,β,δ-FeOOH compounds. Arsenic species were retained in this phases. A cyclic dissolution process of arsenopyrite was identified that seems to be influenced by NL composition. On the experimental basis, a dissolution process of arsenopyrite under calcareous soil weathering conditions is proposed.
Electrochemical Analysis of Highly Reactive Pyrite
Authors: Watling Kym M. , Burton Edward D. , Johnston Max , Bush Richard T. , Sullivan Leigh A.
Published: April 2010

Samples of highly reactive pyritic material, exposed during the construction of the Pennsylvania Interstate Highway 99 (I-99) has been characterized by X-ray diffraction, Raman microprobe spectroscopy, electron microscopy and electrochemical methods. Mineral standards of marcasite, arsenopyrite and pyrite were compared in order to determine the cause of rapid generation of acid and liberation of dissolved metals observed in the exposed pyritic material. Linear sweep voltammetry found no significant differences in the electrochemical activity, however, a significantly lower open circuit potential was found in the reactive pyrite material than in the pyrite or marcasite standards. A high concentration of zinc and aluminium impurities was observed in Energy Dispersive X-ray analysis of the finest iron sulfide crystals found in the reactive pyritic material.
Influence of Surfactant Adsorption on the Leaching of Copper Sulfides
Authors: Nowak Pawel
Published: April 2010

Electrochemical impedance spectroscopy was used to investigate the adsorption of several surface active substances at the surface of copper sulfides and the influence of that adsorption on the reaction of exchange of copper ions between crystal lattice of the sulfide and the solution of copper (II) ions. Simultaneously the influence of several possible inhibitors on the leaching rate of non-stoichiometric copper sulfide was investigated. Among all investigate compounds the strongest inhibiting effect showed sodium oleate. However that compound does not adsorb at the surface of copper sulfide, and the inhibition is due to the precipitation of the insoluble copper oleate at the surface of the sulfide.