bluuebunny/crossref_metadata_2025 huggingface dataset:
Toward defining the preclinical stages of Alzheimer's disease: Recommendations from the National Institute on Aging‐Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease
Authors: Sperling Reisa A. , Aisen Paul S. , Beckett Laurel A. , Bennett David A. , Craft Suzanne , Fagan Anne M. , Iwatsubo Takeshi , Jack Clifford R. , Kaye Jeffrey , Montine Thomas J. , Park Denise C. , Reiman Eric M. , Rowe Christopher C. , Siemers Eric , Stern Yaakov , Yaffe Kristine , Carrillo Maria C. , Thies Bill , Morrison‐Bogorad Marcelle , Wagster Molly V. , Phelps Creighton H.
Published: April 2011

The pathophysiological process of Alzheimer's disease (AD) is thought to begin many years before the diagnosis of AD dementia. This long “preclinical” phase of AD would provide a critical opportunity for therapeutic intervention; however, we need to further elucidate the link between the pathological cascade of AD and the emergence of clinical symptoms. The National Institute on Aging and the Alzheimer's Association convened an international workgroup to review the biomarker, epidemiological, and neuropsychological evidence, and to develop recommendations to determine the factors which best predict the risk of progression from “normal” cognition to mild cognitive impairment and AD dementia. We propose a conceptual framework and operational research criteria, based on the prevailing scientific evidence to date, to test and refine these models with longitudinal clinical research studies. These recommendations are solely intended for research purposes and do not have any clinical implications at this time. It is hoped that these recommendations will provide a common rubric to advance the study of preclinical AD, and ultimately, aid the field in moving toward earlier intervention at a stage of AD when some disease‐modifying therapies may be most efficacious.
Performance characteristics of a combined hepatitis C virus core antigen and anti–hepatitis C virus antibody test in different patient groups
Authors: Yang Jeng‐Fu , Lin Ya‐Yun , Hsieh Meng‐Hsuan , Tsai Chiu‐Hung , Liu Shu‐Fen , Yu Ming‐Lung , Dai Chia‐Yen , Huang Jee‐Fu , Lin Wen‐Yi , Lin Zu‐Yau , Chen Shinn‐Chern , Chuang Wan‐Long
Published: April 2011

We evaluated the performance of a hepatitis C virus (HCV) antigen/antibody combination test [Murex HCV Antigen/Antibody Combination Test (Murex Ag/Ab test)] by comparing it with the current third‐generation HCV antibody enzyme immunoassay (anti‐HCV). A total of 403 serum samples were consecutively collected from four patient groups: healthy controls (n = 100); HCV‐infected patients (HCV group, n = 102); Human immunodeficiency virus (HIV)/HCV‐infected patients (HIV/HCV group, n = 100); and patients with uremia (uremia group, n = 101). Performances were evaluated for the Murex Ag/Ab, anti‐HCV, and HCV RNA in the HIV/HCV and uremia patient groups. In the HCV group, all 102 samples showed concordant positive and negative results for anti‐HCV, Murex Ag/Ab, and HCV RNA tests. In the HIV/HCV group, all 100 samples were positive for both anti‐HCV and Murex Ag/Ab tests, whereas 88 patients (88%) were HCV RNA positive. In the uremia group, 14 (69.0%) of the 23 anti‐HCV‐positive patients were HCV RNA positive, whereas 14 (77.8%) of the 18 Murex Ag/Ab–positive patients were HCV RNA positive. None of anti‐HCV‐negative or Murex Ag/Ab–negative patients were HCV RNA positive. Based on the HCV RNA assay, the sensitivities for both anti‐HCV and Murex Ag/Ab assays were 100%, whereas the specificities of these two assays were 89.7% and 95.4%, respectively. With good sensitivity and specificity, the Murex Ag/Ab assay could be a useful alternative diagnostic tool, especially in immunocompromised populations, such as patients with uremia or those infected with HIV.
Facial palsy as unusual complication of spontaneous intraparotid hematoma
Authors: Chen Chang‐Peng , Yang Miao‐Chun
Published: April 2011

A 55‐year‐old healthy female without trauma history visited our hospital for rapidly progressive enlarging right side painful neck mass within 5 days and also with comorbid House‐Brackmann Grade V facial palsy for 2 days. Magnetic resonance imaging showed heterogenous mass derived from parotid to parapharyngeal space. Much blood clot could be observed at exploratory operation. Only inflammatory change, but not tumor, was mentioned in pathology report. Facial palsy was kept stationary in Grade III from postoperative 6 months.
Anatomic and functional outcome after surgical removal of idiopathic macular epiretinal membrane
Authors: Lee Po‐Yen , Cheng Kai‐Chun , Wu Wen‐Chuan
Published: April 2011

The purpose of this study is to investigate the functional and structural outcomes of surgical treatment of eyes with idiopathic macular epiretinal membrane (ERM). Clinical records of 21 patients (22 eyes) who underwent macular ERM removal with at least 6 months of postoperative follow‐up period were reviewed retrospectively. All patients were treated with pars plana vitrectomy and ERM peeling surgery. Fourteen patients also underwent cataract surgery at the same time. Pre‐ and postoperative visual acuity (VA), intraocular pressure (IOP), and macular thickness along with postoperative adverse events were all recorded. The mean follow‐up was 8.5 ± 3.2 months. Three eyes were pseudophakic and 19 eyes were phakic preoperatively. Five phakic eyes undergoing simple ERM peeling surgery had worsened cataracts, and vision was recovered after subsequent cataract extraction surgery. Mean preoperative IOP was 13.1 ± 4.2 mmHg, which did not differ significantly postoperatively (p = 0.228). One patient had increased IOP postoperatively and needed topical antiglaucoma treatment. Thirteen eyes showed visual improvement, and six eyes became worse during the follow‐up. Mean preoperative best‐corrected VA was 0.36 decimal equivalent, which was then converted to logarithm of the minimum angle of resolution (logMAR 0.502 ± 0.259) for statistical analysis; this had improved to a mean of 0.536 decimal equivalent (logMAR 0.38 ± 0.35) at the final follow‐up. Mean central macular thickness (CMT) also significantly declined (p < 0.0001). From an analysis of dividing patients into two subgroups according to clinical severity [macular pucker (MP) and cellophane maculopathy (CM)], measured mean CMT of both groups demonstrated significant reduction at final follow‐up (MP, p < 0.0001; CM, p = 0.005). Mean final best‐corrected VA also reached significant improvement in MP group (p = 0.008). However, in the CM group, no significant change in VA was observed (p = 0.52). Besides, VA measurements in the MP group had improved significantly to that of CM (p = 0.037). The measured CMTs of the MP group had also reduced significantly (p = 0.046) compared with those of the CM group. In conclusion, membrane peeling surgery can lead to a significant reduction of macular edema in patients with idiopathic macular ERM. The advantages of combined peeling and cataract surgery will achieve maximum positive visual outcome.
Physicochemical conditions for melting in the Earth’s mantle containing a C–O–H fluid (from experimental data)
Authors: Litasov K.D.
Published: April 2011

Experimental data on phase transformations and melting in peridotite and eclogite systems with a C–O–H fluid at 6–30 GPa have been analyzed with special attention to the influence of redox conditions. It has been found that melting in systems with H2O depends heavily on its total content and considerably on its solubility in nominally anhydrous rock-forming minerals. Partial melting occurs when the total H2O content of the system exceeds the H2O storage capacity in the rock under given physicochemical conditions. Melting in CO2-containing systems is determined by carbonate stability and the chemical composition of the system, mainly its Na2O and K2O contents, and, to a smaller extent, the content of CO2 itself. Studies of peridotite and eclogite systems containing H2O, CO2, H2O + CO2, and a reduced C–O–H fluid show that most solidi flatten out at pressures above 6–8 GPa when intersecting the geotherms of subduction and average mantle. Mantle melting at constant pressure in the presence of a C–O–H fluid depends not only on temperature but also on redox conditions. The oxidation of the system causes redox melting. The stability boundary of a Fe–Ni alloy (it may coincide with the lithosphere–asthenosphere boundary under cratons, 200–250 km) and the 410-km discontinuity are paramount to redox and decarbonation–dehydration melting. Also, the paper provides evidence that subducted carbonates play the leading role in the “big” mantle wedge model for stagnant slabs. Volatile-containing eclogite systems melt at lower temperatures than peridotite ones (the difference is up to 100–200 °C). This suggests that eclogites are of global importance in mantle melting, which agrees with modern geochemical models.
The tectonomagmatic evolution of structure-lithologic complexes in the Tannu-Ola zone, Tuva, in the Late Vendian–Early Cambrian (from geochemical, Nd isotope, and geochronological data)
Authors: Mongush A.A. , Lebedev V.I. , Kovach V.P. , Sal’nikova E.B. , Druzhkova E.K. , Yakovleva S.Z. , Plotkina Yu.V. , Zagornaya N.Yu. , Travin A.V. , Serov P.A.
Published: April 2011

In the Tannu-Ola zone, there are island-arc (Late Vendian) and subduction-accretionary (first half of the Early Cambrian) complexes whose mantle sources were generated from melts produced in suprasubduction conditions as a result of the melting of mantle wedge peridotites. The island arc, whose fragment is present in the Tannu-Ola zone, formed tentatively at 570 Ma and ceased as an individual structure at the Vendian–Cambrian boundary, though the subduction continued till the middle Early Cambrian. From the Vendian–Cambrian boundary to middle Early Cambrian, the accretion of island-arc, back-arc, oceanic, and metamorphic structure-lithologic complexes took place at this segment of the Central Asian Fold Belt. From middle to late Early Cambrian, the Tannu-Ola zone was an active continental margin, where basalts with island-arc characteristics, quartz microdiorites of adakite composition, basalts, dolerites, and quartz microdiorites of intraplate type, and diorite-tonalite-plagiogranite association of island-arc type formed. To explain the spatial and temporal conjugation of different magmatism manifestations on the active margin, we applied the slab–window model.
Trace-element composition and origin of granitoids from the Shakhtama complex and Kukul’bei rare-metal complex (Aga zone, Transbaikalia)
Authors: Kozlov V.D.
Published: April 2011

The paper gives major-element and extended trace-element descriptions of plutons from the Shakhtama complex in the Aga tectonic zone (Transbaikalia). They are composed of hornblende–biotite gabbrodiorites, monzonites, diorites, and granodiorites. It has been found that they were initially enriched in granitophile (including ore-forming) trace elements. This suggests consanguinity between the intrusions of the Shakhtama complex (J2–J3) and the ore-bearing Kukul’bei rare-metal complex of granites and leucogranites (J3) (Aga zone, Transbaikalia). Since granitophile elements are incompatible, their content in granitoids with an elevated mafic content from the Shakhtama complex is substantially less above the clarke than that in the rare-metal granites and leucogranites from the Kukul’bei complex, which ended postcollisional magmatism in the Aga zone. Analysis of normalized REE patterns for the granitoids from both complexes has revealed their magmatic heterogeneity. It has been demonstrated that the Kukul’bei granite and leucogranite intrusions in the western Aga zone are granitic differentiates of granitoid magma chambers associated with the Shakhtama complex, which were initially enriched in granitophile trace elements. The granites from the rare-metal intrusions of the Kukul’bei complex (in the eastern periphery of the Aga zone) are not directly related to the magma chambers of the Shakhtama complex. They are magmatic melts, which might result from the deep-level selective melting of metamorphosed rocks enriched in volatile trace elements. It has been confirmed that there is no direct genetic relation between the majorand trace-element compositions of the granitoids and their metallogeny and ore content.

The granitophile rare-metal specialization of the intrusions in Mesozoic Transbaikalian gabbrodiorite–monzonite–granodiorite and leucogranite complexes is the major evidence supporting the theory of the formation of late- and postcollisional magma chambers associated with deep faults, which were initially enriched in volatile and incompatible trace elements.
Simple models for dynamic hysteresis loop calculations of magnetic single-domain nanoparticles: Application to magnetic hyperthermia optimization
Authors: Carrey J. , Mehdaoui B. , Respaud M.
Published: April 2011

To optimize the heating properties of magnetic nanoparticles (MNPs) in magnetic hyperthermia applications, it is necessary to calculate the area of their hysteresis loops in an alternating magnetic field. The separation between “relaxation losses” and “hysteresis losses” presented in several articles is artificial and criticized here. The three types of theories suitable for describing hysteresis loops of MNPs are presented and compared to numerical simulations: equilibrium functions, Stoner–Wohlfarth model based theories (SWMBTs), and a linear response theory (LRT) using the Néel–Brown relaxation time. The configuration where the easy axis of the MNPs is aligned with respect to the magnetic field and the configuration of a random orientation of the easy axis are both studied. Suitable formulas to calculate the hysteresis areas of major cycles are deduced from SWMBTs and from numerical simulations; the domain of validity of the analytical formula is explicitly studied. In the case of minor cycles, the hysteresis area calculations are based on the LRT. A perfect agreement between the LRT and numerical simulations of hysteresis loops is obtained. The domain of validity of the LRT is explicitly studied. Formulas are proposed to calculate the hysteresis area at low field that are valid for any anisotropy of the MNP. The magnetic field dependence of the area is studied using numerical simulations: it follows power laws with a large range of exponents. Then analytical expressions derived from the LRT and SWMBTs are used in their domains of validity for a theoretical study of magnetic hyperthermia. It is shown that LRT is only pertinent for MNPs with strong anisotropy and that SWMBTs should be used for weakly anisotropic MNPs. The optimum volume of MNPs for magnetic hyperthermia is derived as a function of material and experimental parameters. Formulas are proposed to allow to the calculation of the optimum volume for any anisotropy. The maximum achievable specific absorption rate (SAR) is calculated as a function of the MNP anisotropy. It is shown that an optimum anisotropy increases the SAR and reduces the detrimental effects of the size distribution of the MNPs. The optimum anisotropy is simple to calculate; it depends only on the magnetic field used in the hyperthermia experiments and the MNP magnetization. The theoretical optimum parameters are compared to those of several magnetic materials. A brief review of experimental results as well as a method to analyze them is proposed. This study helps in the determination of suitable and unsuitable materials for magnetic hyperthermia and provides accurate formulas to analyze experimental data. It is also aimed at providing a better understanding of magnetic hyperthermia to researchers working on this subject.
Anomalously large bend elastic constant and faster electro-optic response in anisotropic gels formed by a dipeptide
Authors: Bhargavi R. , Nair Geetha G. , Prasad S. Krishna , Prabhu Rashmi , Yelamaggad C. V.
Published: April 2011

We report rheological, static, and dynamic Freedericksz transformation measurements on an anisotropic thermoreversible gel formed by gelation of a nematic liquid crystal (NLC) with a monodisperse dipeptide. The storage and loss modulii obtained from a low strain oscillatory shear experiment display that the material forms a weak anisotropic gel, and undergoes a sharp thermal transition to an anisotropic sol state. Freedericksz transformation studies employing an electric field for the reorientation of the molecules present a surprising result: the gel possesses a very large Frank bend elastic constant value, which is orders of magnitude higher than that for the high temperature sol state as well as that for the neat NLC used. On the other hand, the splay elastic constant shows relatively a small increase. Further, these elastic constants show systematic but nonlinear variation with the concentration of the gelator. Attractive features of the electro-optic switching when the sol transforms to the gel state are the vanishing of the undesirable backflow effect, and nearly an order of magnitude decrease in the switching speed. In both the gel and sol states the extracted rotational viscosities are comparable to the values of the neat NLC at corresponding temperatures. In contrast, the bulk dynamic viscosity is more than three orders of magnitude higher in the gel. The studies also demonstrate that the anisotropic gel to anisotropic sol transition seen in this weak gel can be tracked by simply monitoring the static or the dynamic Freedericksz transformation.
Finite element modeling of magnetic field sensors based on nonlinear magnetoelectric effect
Authors: Nguyen Thu Trang , Bouillault Frédéric , Daniel Laurent , Mininger Xavier
Published: April 2011

Magnetoelectric effect in composite materials results from the combination of piezoelectric and magnetostrictive effects. This paper focuses on the development of a harmonic finite element formulation for such coupled problems, taking into account the nonlinearity of magnetostrictive behavior. An application to a magnetic sensor operating under dynamic excitation is presented in order to illustrate the formulation. The enhancement of the magnetoelectric coefficient when a low amplitude harmonic field is superimposed to the static field to be measured is shown to be related to the nonlinearity of magnetic and magnetostrictive behavior.
Magnetic and structural properties of fcc/hcp bi-crystalline multilayer Co nanowire arrays prepared by controlled electroplating
Authors: Pirota K. R. , Béron F. , Zanchet D. , Rocha T. C. R. , Navas D. , Torrejón J. , Vazquez M. , Knobel M.
Published: April 2011

We report on the structural and magnetic properties of crystalline bi-phase Co nanowires, electrodeposited into the pores of anodized alumina membranes, as a function of their length. Co nanowires present two different coexistent crystalline structures (fcc and hcp) that can be controlled by the time of pulsed electrodeposition. The fcc crystalline phase grows at the early stage and is present at the bottom of all the nanowires, strongly influencing their magnetic behavior. Both structural and magnetic characterizations indicate that the length of the fcc phase is constant at around 260–270 nm. X-ray diffraction measurements revealed a strong preferential orientation (texture) in the (1 0–1 0) direction for the hcp phase, which increases the nanowire length as well as crystalline grain size, degree of orientation, and volume fraction of oriented material. The first-order reversal curve (FORC) method was used to infer both qualitatively and quantitatively the complex magnetization reversal of the nanowires. Under the application of a magnetic field parallel to the wires, the magnetization reversal of each region is clearly distinguishable; the fcc phase creates a high coercive contribution without an interaction field, while the hcp phase presents a smaller coercivity and undergoes a strong antiparallel interaction field from neighboring wires.
Nucleation and growth of Pt atomic layer deposition on Al2O3 substrates using (methylcyclopentadienyl)-trimethyl platinum and O2 plasma
Authors: Baker L. , Cavanagh A. S. , Seghete D. , George S. M. , Mackus A. J. M. , Kessels W. M. M. , Liu Z. Y. , Wagner F. T.
Published: April 2011

The nucleation and growth of Pt atomic layer deposition (ALD) on Al2O3 substrates was studied using (methylcyclopentadienyl)-trimethyl platinum (MeCpPtMe3) and O2 plasma as the reactants. The nucleation of Pt ALD was examined on Al2O3 ALD substrates at 300 °C using a variety of techniques including spectroscopic ellipsometry, x-ray reflectivity, x-ray photoelectron spectroscopy, and scanning electron microscopy. These techniques revealed that Pt ALD does not nucleate and grow immediately on the Al2O3 ALD substrates. There was negligible Pt ALD during the first 38 ALD cycles. The Pt ALD growth rate then increased substantially during the next 12 ALD cycles. Subsequently, the Pt ALD growth rate reached a steady state linear growth regime for >50 ALD cycles. These measurements suggest that the Pt ALD first forms a number of nanoclusters that grow slowly during the first 38 ALD cycles. These islands then merge during the next 12 cycles and yield a steady state Pt ALD growth rate of ∼0.05 nm/cycle for >50 ALD cycles. The Pt ALD film at the onset of the steady state linear growth regime was approximately 2–3 nm in thickness. However, the SEM images of these Pt ALD films appeared corrugated and wormlike. These films also had a density that was only 50–70% of bulk Pt. Film densities that were consistent with bulk Pt were not observed until after >100 ALD cycles when the Pt ALD films appeared much smoother and were 4–5 nm in thickness. The Pt ALD nucleation rate could be enhanced somewhat using different O2 plasma parameters.
Dynamics of vesicles in shear and rotational flows: Modal dynamics and phase diagram
Authors: Zabusky Norman J. , Segre Enrico , Deschamps Julien , Kantsler Vasiliy , Steinberg Victor
Published: April 2011

Despite the recent upsurge of theoretical reduced models for vesicle shape dynamics, comparisons with experiments have not been accomplished. We review the implications of some of the recently proposed models for vesicle dynamics, especially the tumbling-trembling domain regions of the phase plane, and show that they all fail to capture the essential behavior of real vesicles for excess areas Δ greater than 0.4. We emphasize new observations of shape harmonics and the role of thermal fluctuations.
Preliminary study on the matching characteristics between wind wheel and pump in a wind-powered water pumping system
Authors: Sun Xiaojing , Zhou Wanli , Huang Diangui , Wu Guoqing
Published: April 2011

In a wind-powered water pumping system, the water pump is driven directly by a wind wheel without any control system, other than a gear box. Thus, there exists a dynamic balance between the torque provided by the wind wheel and that accessed by the water pump. That is, the torque produced by the wind wheel will often be larger or smaller than that required by the pump. If so, the system will accelerate or decelerate, thus increasing or decreasing the torque provided by the wind wheel, which will then result in an increase or a decrease in that accessed by the pump until equilibrium is re-established. In addition, the amount of water that can be pumped corresponds directly to the effective power of the wind wheel, whereas the output torque and actual power from the wind wheel depend only on its rotation rate, which is a function of the wind speed. Hence, once a good match is obtained between the torque and the power provided by the wind wheel and those required by the pump, the entire system can operate most efficiently, maximizing the amount of water lifted by the pump. On the other hand, unlike steam or gas turbines, whose performance characteristics under different operating conditions have long been a popular subject for research, there are as yet very few studies of the characteristics of wind wheels under varying wind conditions, even though the wind changes continuously in speed and direction. Therefore, the primary purpose of this paper is to provide a preliminary investigation of wind wheel performance under time-varying wind conditions, while also studying the matching characteristics between a wind wheel and a water pump. The present paper is thus intended to help design and select a pump optimized for a wind-powered water pumping system, which could operate efficiently over a wide range of wind speeds.
Exchange-bias in amorphous ferromagnetic and polycrystalline antiferromagnetic bilayers: Structural study and micromagnetic modeling
Authors: Kohn A. , Dean J. , Kovacs A. , Zeltser A. , Carey M. J. , Geiger D. , Hrkac G. , Schrefl T. , Allwood D.
Published: April 2011

We study the role of the structure of antiferromagnetic polycrystalline metallic films in determining the magnetic properties of an exchange-coupled amorphous ferromagnetic layer. The bilayers are sputter-deposited, highly textured {111} Ir22Mn78 and Co65.5Fe14.5B20 thin films. We focus on structural characterization of Ir22Mn78 as a function of layer thickness in the range having the strongest influence over the exchange-bias field and training effect. We have used transmission electron microscopy to characterize defects in the form of interface steps and roughness, interdiffusion, twin- and grain-boundaries. Such defects can result in uncompensated magnetic spins in the antiferromagnet, which then contribute to exchange-bias. These experimental results form the basis of a general model, which uses finite element micromagnetic simulations. The model incorporates the experimental structural parameters of the bilayer by implementing a surface integral technique that allows numerical calculations to solve the transition from an amorphous to a granular structure. As a result, a detailed calculation of the underlying magnetic structure within the antiferromagnetic material is achieved. These calculations are in good agreement with micromagnetic imaging using Lorentz transmission electron microscopy and the macro-magnetic properties of these bilayers.
Annealing effects on structural and magnetic properties of Co implanted ZnO single crystals
Authors: Wikberg J. M. , Knut R. , Audren A. , Ottosson M. , Linnarsson M. K. , Karis O. , Hallén A. , Svedlindh P.
Published: April 2011

Single crystals of ZnO were implanted with 100 keV-Co ions at room temperature with a fluence of 4.8×1016cm−2 and subsequently annealed at different temperatures up to 800∘C. The samples were analyzed by Rutherford backscattering spectrometry, secondary ion mass spectrometry, X-ray diffraction, X-ray photoemission spectroscopy and magnetometry. The as-implanted Co:ZnO crystal shows a homogeneous distribution of Co in the near surface region of the crystal. Upon annealing, clear evidence of secondary phases is found. At the highest annealing temperature (800∘C) a ferromagnetic behavior is observed at room temperature with a coercive field of 120 Oe assigned mainly to metallic fcc Co nano-crystallites. We find that for the annealed samples, the temperature dependent magnetization cannot be explained within a model containing only a paramagnetic contribution due to well dispersed Co ions and a ferromagnetic contribution due to Co nano-crystallites, at least one more ferromagnetic contribution is needed for a consistent explanation of the experimental results.
Ferromagnetic resonance, magnetic susceptibility, and transformation of domain structure in CoFeB film with growth induced anisotropy
Authors: Manuilov S. A. , Grishin A. M. , Munakata M.
Published: April 2011

Field dependence of magnetic susceptibility in nanocrystalline CoFeB film was studied in a wide frequency range from 500 kHz to 15 GHz. Anomalies of the susceptibility were detected exciting CoFeB film with a solenoidal coil, microwave strip line, in the tunable microwave cavity as well as employing magneto-optical domains imaging. Critical spin fluctuations in the form of “soft” modes were observed in a whole range of orientations of magnetic field perpendicular to the “easy” magnetic axis. A sequence of domain structure transformations was extensively examined in a “hard” direction in in-plane magnetic field reduced below the field of uniaxial anisotropy Hp = 535 Oe. At first, uniformly magnetized state in CoFeB film transforms to stripe domains separated by low angle Néel domain walls (DWs) parallel to the “hard”-axis. Then, at critical field Hcr = 232 Oe, Néel DWs gradually convert to the“easy”-axis oriented Bloch DWs loaded with vertical Bloch lines (VBLs). After field reversal at H = −Hcr, backward conversion of VBL-loaded Bloch DWs to Néel DWs results in instantaneous energy release and sharp anomaly of magnetic susceptibility. Appearance of critical spin fluctuations accomplishes domains transformation to the uniformly magnetized state at H = −535 Oe.
On the uniformity of films fabricated by glancing angle deposition
Authors: Wakefield Nicholas G. , Sit Jeremy C.
Published: April 2011

Films fabricated using the glancing angle deposition technique are subject to significant variations in several important film parameters across a sample due to geometric conditions that are not uniform across the substrate. This paper presents a method to quantify the non-uniformities in these quantities, starting from a generalized geometric framework, for low-pressure, physical vapor deposition of thin films on substrates of arbitrary size and position. This method is applicable to any glancing angle deposition setup including substrate tilt and rotation but focuses on the case of constant deposition angle and arbitrary azimuthal rotation. While some quantities, such as the effective deposition angle and the deposited mass per unit area at any given point on the substrate can be determined purely from the geometry of the deposition setup, obtaining further quantities, such as the film density and thickness, requires additional, material-specific information that is easily measured.
Random barrier double-well model for resistive switching in tunnel barriers
Authors: Bertin Eric , Halley David , Henry Yves , Najjari Nabil , Majjad Hicham , Bowen Martin , DaCosta Victor , Arabski Jacek , Doudin Bernard
Published: April 2011

The resistive switching phenomenon in MgO-based tunnel junctions is attributed to the effect of charged defects inside the barrier. The presence of electron traps in the MgO barrier, which can be filled and emptied, locally modifies the conductance of the barrier and leads to the resistive switching effects. A double-well model for trapped electrons in MgO is introduced to theoretically describe this phenomenon. Including the statistical distribution of potential barrier heights for these traps leads to a power-law dependence of the resistance as a function of time, under a constant bias voltage. This model also predicts a power-law relation of the hysteresis as a function of the voltage sweep frequency. Experimental transport results strongly support this model and in particular confirm the expected power laws dependencies of resistance. They moreover indicate that the exponent of these power laws varies with temperature as theoretically predicted.
Magnetism of Zn0.75Cr0.25S with ordered doping configurations predicted by generalized gradient approximation plus Hubbard U
Authors: Sun Lang , Li Guangshe , Guan Xiangfeng , Li Liping , Wu Liming
Published: April 2011

We applied the first-principles method with empirical Hubbard U parameters to study the magnetism of Zn0.75Cr0.25S with the varied doping configurations. Depending on the doping configurations, calculations using generalized gradient approximation (GGA) methods with and without U were compared to study the electronic structure and magnetic properties of Zn0.75Cr0.25S. Simulation with GGA method confirms the presence of ferromagnetic ordering in Zn0.75Cr0.25S as is theoretically concluded by previous literature work, while calculations with GGA+U methods predict either antiferromagnetic or ferromagnetic ordering depending on the doping configurations. The appearance of magnetic ordering is rationalized in terms of the coupling between two adjacent doping Cr atoms that primarily governs the magnetic ordering. Therefore, changing the coupling chains in the Cr-containing semiconductors may provide an alternative route to tune the magnetic properties.
Requirements for graphoepitaxial alignment through solid-state dewetting of Au films
Authors: Giermann A. L. , Thompson C. V.
Published: April 2011

Graphoepitaxial alignment of Au particles through solid-state dewetting of gold films on substrates patterned with topographic features has been demonstrated. Gold films were dewetted on surfaces with a diperiodic array of pits with inverted pyramidal shapes. Under specific conditions, films dewet to form a periodic array of monodisperse particles in the pits. Thick films pull out of the pits rather than dewet into the pits. While particles that form on flat surfaces or between the pits have a (111) out-of-plane texture and random in-plane orientation, particles in pits have (100) out-of plane texture and in-plane alignments such that Au (111) planes are parallel with the facets of the pits. Requirements for relative geometric characteristics of the pits and the film thickness, and requirements on surface-energy anisotropy, are defined for formation of monodisperse graphoepitaxially-aligned particles.
High confinement/high radiated power H-mode experiments in Alcator C-Mod and consequences for International Thermonuclear Experimental Reactor (ITER) QDT = 10 operation
Authors: Loarte A. , Hughes J. W. , Reinke M. L. , Terry J. L. , LaBombard B. , Brunner D. , Greenwald M. , Lipschultz B. , Ma Y. , Wukitch S. , Wolfe S.
Published: April 2011

Experiments in Alcator C-Mod in (Enhanced D-alpha) EDA H-modes with extrinsic impurity seeding (N2, Ne, and Ar) have demonstrated a direct correlation between plasma energy confinement and edge power flow, achieving values of H98 ≥ 1 for edge power flows only marginally exceeding the scaled power for access to H-mode confinement in these conditions. For lower Z impurity seeding (N2 and Ne), plasmas with high energy confinement are obtained with a radiative power fraction of 85% or larger and a reduction of the peak heat flux at the divertor by more than a factor of 5 compared to similar attached conditions. The H-mode plasmas thus achieved in Alcator C-Mod meet or exceed the requirements both in terms of divertor heat flux handling and energy confinement for ITER QDT = 10 operation and with an edge power flow only marginally above the H-mode threshold power (by 1.0–1.4) as expected in ITER.
Longitudinal variations in the Poisson’s ratio of collagen fibrils
Authors: Wenger Marco P. E. , Mesquida Patrick
Published: April 2011

Atomic force microscopy imaging was used to determine the behavior of the D-banding geometry of collagen fibrils upon stretching in air under ambient conditions. The fibrils were strained by attaching them on a stretchable foil, the strain being monitored by the D-banding spacing and height. It was found that stretching fibrils increases the D-banding spacing and decreases the D-banding height. A simple, continuum mechanics model based on classical elasticity theory suggests that the gap has a smaller Poisson’s ratio than the overlap region.
Small-sized dichroic atomic vapor laser lock
Authors: Lee Changmin , Iwata G. Z. , Corsini E. , Higbie J. M. , Knappe S. , Ledbetter M. P. , Budker D.
Published: April 2011

Two, lightweight diode laser frequency stabilization systems designed for experiments in the field are described. A significant reduction in size and weight in both models supports the further miniaturization of measurement devices in the field. Similar to a previous design, magnetic field lines are contained within a magnetic shield enclosing permanent magnets and a Rb cell, so that these dichroic atomic vapor laser lock (DAVLL) systems may be used for magnetically sensitive instruments. The mini-DAVLL system (49 mm long) uses a vapor cell (20 mm long) and does not require cell heaters. An even smaller micro-DAVLL system (9 mm long) uses a microfabricated cell (3 mm square) and requires heaters. These new systems show no degradation in performance with regard to previous designs while considerably reducing dimensions.
Self-consistent particle modeling of radio frequency discharge in Ar/O2 mixtures: Effects of crossed electric and magnetic fields and partial pressure
Authors: Benyoucef Djilali , Yousfi Mohammed , Belmadani Bachir
Published: April 2011

A particle-in-cell/Monte Carlo model is developed to study and analyze the electrical characteristics of the nonequilibrium plasma created by radio frequency (RF) discharge in Ar/O2 mixtures in the presence of crossed electric and magnetic fields. The method of collision treatment is based on an optimized estimation of the free time flight. The needed basic data—more specifically, the ion–neutral cross sections—are determined first. The simulation conditions are 50 mTorr for the total gas pressure and 200 V for the peak of the RF voltage at a frequency of 13.56 MHz. The magnetic field is varied from 0 to 50 G. The effect of the partial pressure ratio of O2 in the mixture and the effect of the magnitude of the magnetic field are discussed. In particular, the results show an increase of the plasma density that is ten times higher in the presence of a magnetic field.
First-principles analysis of ZrN/ScN metal/semiconductor superlattices for thermoelectric energy conversion
Authors: Saha Bivas , Sands Timothy D. , Waghmare Umesh V.
Published: April 2011

We present a first-principles density functional theory-based analysis of the electronic structure, vibrational spectra, and transport properties of ZrN/ScN metal/semiconductor superlattices aiming to understand its potential and suitability for thermoelectric applications. We demonstrate (a) the presence of Schottky barriers of 0.34 eV at the metal/semiconductor interface and (b) a large asymmetry in the electronic densities of states and flattening of electronic bands along the cross-plane directions near the Fermi energy of these superlattices, desirable for high Seebeck coefficient. The vibrational spectra of these superlattices show softening of transverse acoustic phonon modes along the growth direction and localization of ScN phonons in the vibrational energy gap between metal and semiconductor layers. Boltzmann transport theory-based analysis suggests a reduction of lattice thermal conductivity by an order of magnitude compared to its individual bulk components, which makes these materials suitable for thermoelectric applications.
Impact of strain on deep ultraviolet nitride laser and light-emitting diodes
Authors: Sharma T. K. , Towe E.
Published: April 2011

To date, the shortest wavelength of an ultraviolet current-injection nitride laser has been limited to ∼340 nm. This begs the question of whether there is a fundamental limitation that restricts the realization of injection lasers below this wavelength. This letter investigates this issue. We find that, apart from being the decisive factor for the crystalline quality of nitride epitaxial layers, residual strain plays yet another crucial role in modifying the band structure of (Al,Ga)N quantum wells. A critical analysis of quantum-confinement effects, strain, and the polarization properties of strained (Al,Ga)N layers is essential for the realization of deep ultraviolet laser diodes.
The effect of Si-nanocrystal size distribution on Raman spectrum
Authors: Ke Weiwei , Feng Xue , Huang Yidong
Published: April 2011

The effect of Si-nanocrystal (Si-nc) size distribution on Raman spectrum is studied in detail within the framework of a phonon confinement model. It is found that size distribution has little effect on Raman frequency shift, but greatly affects the width and shape of Raman spectrum. Si-nc Raman spectrum can be well explained by considering the size distribution. Furthermore, a set of simple relationships between Raman frequency shift/full width at half maximum (FWHM) and size distribution is set up based on the framework of a modified phonon confinement model, which can be applied to calculate Si-nc size distribution from the Raman spectrum.
Rotation and alignment of rods in two-dimensional chaotic flow
Authors: Parsa Shima , Guasto Jeffrey S. , Kishore Monica , Ouellette Nicholas T. , Gollub J. P. , Voth Greg A.
Published: April 2011

We study the dynamics of rod shaped particles in two-dimensional electromagnetically driven fluid flows. Two separate types of flows that exhibit chaotic mixing are compared: one with time-periodic flow and the other with constant forcing but nonperiodic flow. Video particle tracking is used to make accurate simultaneous measurements of the motion and orientation of rods along with the carrier fluid velocity field. These measurements allow a detailed comparison of the motion and orientation of rods with properties of the carrier flow. Measured rod rotation rates are in agreement with predictions for ellipsoidal particles based on the measured velocity gradients at the center of the rods. There is little dependence on length for the rods we studied (up to 53% of the length scale of the forcing). Rods are found to align weakly with the extensional direction of the strain-rate tensor. However, the alignment is much stronger with the direction of Lagrangian stretching defined by the eigenvectors of the Cauchy–Green deformation tensor. A simple model of the stretching process predicts the degree of alignment of rods with the stretching direction.
First-order finite-Larmor-radius effects on magnetic tearing in pinch configurations
Authors: King J. R. , Sovinec C. R. , Mirnov V. V.
Published: April 2011

The linear and nonlinear evolution of a single-helicity tearing mode in a cylindrical, force-free pinch are investigated using a fluid model with first-order finite-Larmor-radius corrections. Linear results computed with the nimrod [nonideal magnetohydrodynamics (MHD) with rotation, open discussion] code [Sovinec et al., J. Comput. Phys. 195, 355 (2004)] produce a regime at small ρs where the growth rate is reduced relative to resistive MHD, though the Hall term is not significant. The leading order contributions from ion gyroviscosity may be expressed as a drift associated with ∇B0 and poloidal curvature for experimentally relevant β=0.1, S~105-106 force-free equilibria. The heuristic analytical dispersion relation, γ4(γ-iω*gv)=γMHD5 where ω*gv is the gyroviscous drift frequency, confirms numerical results. The behavior of our cylindrical computations at large ρs corroborates previous analytic slab studies where an enhanced growth rate and radially localized Hall dynamo are predicted. Similar to previous drift-tearing results, nonlinear computations with cold ions demonstrate that the Hall dynamo is small when the island width is large in comparison with the scale for electron–ion coupling. The saturation is then determined by the resistive MHD physics. However, with warm ions the gyroviscous stress supplements the nonlinear Lorentz force, and the saturated island width is reduced.
Range, resolution and power of THz systems for remote detection of concealed radioactive materials
Authors: Nusinovich G. S. , Sprangle P. , Romero-Talamas C. A. , Granatstein V. L.
Published: April 2011

This paper analyzes parameters required for realizing remote detection of a concealed source of ionizing radiation by observing the occurrence of breakdown in air by a focused wave beam. Production of free electrons and the free electron density in the absence/presence of additional sources of ionization are analyzed. The maximum electron density in the discharge and the time required for this density to return after the discharge back to its stationary level, are estimated. The optimal excess of the power density and the corresponding power level as the function of frequency are determined. It is shown that the optimal frequency of such systems ranges from 0.3 up to 0.8 THz. The paper also determines the range of such systems as the function of the source frequency and power and contains a brief analysis of available sources of microwave, millimeter-wave and THz radiation.
Extrinsic origins of the apparent relaxorlike behavior in CaCu3Ti4O12 ceramics at high temperatures: A cautionary tale
Authors: Li Ming , Sinclair Derek C. , West Anthony R.
Published: April 2011

Although the origins of the high effective permittivity observed in CaCu3Ti4O12 (CCTO) ceramics and single crystals at ∼100–400 K have been resolved, the relaxorlike temperature- and frequency-dependence of permittivity obtained from fixed frequency capacitance measurements at higher temperatures reported in the literature remains unexplained, especially as CCTO adopts a centrosymmetric cubic crystal structure in the range of ∼35–1273 K. Impedance spectroscopy studies reveal that this type of relaxorlike behavior is an artifact induced mainly by a nonohmic sample-electrode contact impedance. In addition, an instrument-related parasitic series inductance and resistance effect modifies the measured capacitance values as the sample resistance decreases with increasing temperature. This can lead to an underestimation of the sample capacitance and, in extreme cases, to so-called ‘negative capacitance.’ Such a relaxorlike artifact and negative capacitance behavior are not unique to CCTO and may be expected in other leaky dielectrics whose resistance is low.
Investigation of modified p-n junctions in crystalline silicon on glass solar cells
Authors: Lausch D. , Werner M. , Naumann V. , Schneider J. , Hagendorf C.
Published: April 2011

In this paper various methods for studying p-n junctions in thin film solar cells are applied with the aim to localize and investigate defects on a microscopic scale. Different electron and ion beam characterization methods are introduced to determine the p-n junction position using two different examples from crystalline silicon on glass thin film technology. In a first example, planview and cross section electron beam induced current measurements revealed that oxygen rich columnar growth at textured substrates strongly disturbs the p-n junction. In a second example, diffusion from glass substrate is identified by ToF-SIMS to influence the electrical and structural characteristics of the thin Si layer resulting in a modified p-n junction. A model describing the formation of both defect structures is introduced.
Observation of femtosecond laser-induced nanostructure-covered large scale waves on metals
Authors: Hwang Taek Yong , Guo Chunlei
Published: April 2011

Following femtosecond (fs) laser pulse irradiation, we produce a type of periodic surface structure with a period tens of times greater than the laser wavelength and densely covered by an iterating pattern that consists of stripes of nanostructures and microscale cellular structures. The morphology of this large scale wave pattern crucially depends on laser fluence and the number of laser pulses, but not on the laser wavelength. Our study suggests that this large scale wave is initiated by fs laser induced surface unevenness followed by periodically distributed nonuniform surface heating from fs pulse irradiation.
VLS growth of SiOx nanowires with a stepwise nonuniformity in diameter
Authors: Huang Shengli , Wu Yan , Zhu Xianfang , Li Lunxiong , Wang Zhanguo , Wang Lianzhou , Lu Gaoqing
Published: April 2011

With a precise control of temperature, gas flow, and pressure and with sequentially increased durations for reactions, the detailed processes of catalyzing, nucleation, and growth of the SiOx nanowires were successfully traced. Especially a stepwise nonuniformity in diameter of nanowire during the growth was for the first time detected. With analysis of these detailed processes via nanocurvature and nano ripening effects, a further understanding of the vapor-liquid-solid mechanism was achieved and a novel mechanism for formation of the stepwise nonuniformity in diameter of nanowire was particularly proposed. All these will be the crucial basis for the further, accurately controlled growth of SiOx nanowires and the relevant applications.