bluuebunny/crossref_metadata_2025 huggingface dataset:
The “van Zijl” Jurassic geomagnetic reversal revisited
Authors: Moulin Maud , Courtillot Vincent , Fluteau Frédéric , Valet Jean‐Pierre
Published: February 2012

We have collected two new detailed records of what could be the second oldest well documented reversal, the “van Zijl” Jurassic (∼180 Ma) reversal recorded in the thick basalt sequences of the Karoo large igneous province in Lesotho and South Africa. Sections yielded 10 and 8 independent transitional paleomagnetic directions respectively over two continuous 130 m and 160 m sequences. The corresponding VGP reversing paths share a number of consistent features and are integrated with a third record at Bushmen's Pass from Prévot et al. (2003) to yield a single reversal path with: 1‐ a large directional jump with no transitional poles between 45°S and 45°N in the first, main phase of the reversal, 2‐ a large elongated loop (multiple hairpin) to the SE with poles going down to ∼20° latitudes in the second phase of the reversal, and 3‐ a rebound before finally settling in normal polarity. We have measured relative paleo‐intensities on a set of carefully selected samples. Intensity was low prior to the directional changes and recovery to the following normal polarity was progressive. Transitional intensity is 80 to 90% lower than full polarity values. There is no significant increase in intensity at the time of transitional directional clusters. Our results are consistent with a weak non‐dipolar reversing field, with faster and larger directional secular variation as the equator is crossed by VGPs. They tend to vindicate the notion of a short duration of the directional reversal, though one cannot draw global conclusions from a record limited to essentially a single location.
Influence of atmospheric circulation on turbulent air‐sea heat fluxes over the Mediterranean Sea during winter
Authors: Papadopoulos Vassilis P. , Kontoyiannis Harilaos , Ruiz Simón , Zarokanellos Nikolaos
Published: February 2012

The influence of the winter atmospheric circulation on the turbulent variables of the air‐sea boundary layer in the Mediterranean Sea is investigated. We examine the effects of several climatic indices and the corresponding large scale atmospheric patterns on the above variables by using a correlation analysis. The spatial characteristics and the behavior of the turbulent variables are also examined based on standard deviation and EOF analysis. Two main types of response to the index‐specified atmospheric patterns have been identified: (1) A relatively uniform response of the entire basin associated with the influence of the East Atlantic pattern and (2) opposite responses in the western and eastern sub‐basins linked mainly to the intrabasin SLP. The latter is a combined effect of the first four modes of atmospheric variability in the North Atlantic/Eurasia region, the North Atlantic Oscillation (NAO), the East Atlantic Pattern (EA), the Scandinavian Pattern (SCAND), and the East Atlantic‐West Russia Pattern (EAWR). The two identified responses of the Mediterranean Sea to the atmospheric forcing are also in accordance with the primary modes of variability of the turbulent variables that result in the EOF analysis. All of the statistically independent indices (NAO, EA, SCAND, EAWR) have to be considered in order to fully account for the modulation of the turbulent variables in the Mediterranean Sea. As an example we refer to the mechanism through which, independent modes of atmospheric variability contributed to the Eastern Mediterranean Transient event between 1987 and 1995.
Comparison of methods to determine Tropical Tropopause Layer cirrus formation mechanisms
Authors: Riihimaki Laura D. , McFarlane Sally A. , Liang Calvin , Massie Steven T. , Beagley Nathaniel , Toth Travis D.
Published: February 2012

A new method of estimating Tropical Tropopause Layer Cirrus (TTLC) formation mechanism (object method) is compared to interpretations of formation from previous studies using back trajectory calculations matched to convection identified from satellites and statistical relationships of TTLC with temperature and water vapor. The object method groups neighboring Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) TTLC cloud profiles into cloud objects and classifies them as convective (35% of TTLC) if they are directly attached to a convective cloud along the CALIPSO track. The percentage of back trajectory calculations that intersect convection (39–95% of TTLC within 5 days) depends strongly on the spatial and temporal resolution of the convection data set, and the manner in which deep convection is identified. Using minimum brightness temperature in 3 hourly, 1° resolution grid boxes to define convection, 46% of non‐convective TTLC (37% of all TTLC) did not trace back to convection within 24 h. Back trajectory calculations of thin cirrus identified by the High Resolution Dynamics Limb Sounder (HIRDLS) gave similar results. Temperature is not a good proxy for formation mechanism as convective and non‐convective TTLC frequencies both increase monotonically with decreasing temperature at approximately the same rate. Non‐convective TTLC frequencies have a stronger relationship with relative humidity than convective TTLC frequencies, though are not sufficiently different to distinguish object method categories. A decrease in TTL cirrus frequency found at low temperatures in previous studies is caused by insufficient variability in reanalysis temperature data and is not indicative of TTLC formation mechanism.
Responses of trace gases to hydrologic pulses in desert floodplains
Authors: Harms Tamara K. , Grimm Nancy B.
Published: February 2012

Pulsed hydrologic inputs interact with antecedent moisture conditions to shape biogeochemical dynamics in many ecosystems, but the outcomes of these interactions remain difficult to predict. Hydrologic pulses may influence biogeochemical activity through several mechanisms: by providing water as a resource, providing limiting nutrients or substrates that fuel particular biogeochemical pathways, or determining redox conditions. Antecedent moisture conditions may modify the relative importance of each of these potential mechanisms, by influencing accumulation of labile carbon and nutrients, the severity of water limitation to biological processes, and longer‐term effects on abiotic conditions, including redox. We experimentally applied hydrologic pulses of different sizes (1‐cm and 20‐cm events) to soils of desert floodplains and assessed responses of trace gases (CO2, CH4, NO, and N2O) in dry and monsoon seasons to test these mechanisms. Size of the hydrologic pulse strongly interacted with antecedent soil‐moisture conditions to determine emissions of some trace gases. Following dry antecedent conditions, water addition stimulated emissions of CO2, CH4, and NO, but not N2O, and larger experimental pulses resulted in larger fluxes. In the monsoon season, responses to water addition were muted and size of the hydrologic pulse had no effect, except for CH4emission, which increased in response to the 20‐cm event. Seasonal contrasts indicated that antecedent moisture conditions constrain the effects of hydrologic pulses on biogeochemical processes, whereas contrasts among responses of different trace gases demonstrated that mechanisms controlling emissions of particular gases are water limitation (CO2), in situ production of nitrogen substrates (NO), or redox conditions (CH4). Strong and predictable interactive effects of water inputs and antecedent conditions indicate that extended droughts may cause elevated emissions of gaseous C and NO following the return of precipitation, whereas larger floods or longer wet seasons are expected to dampen gaseous fluxes, which may contribute to conserving soil C and nutrients within floodplains.
NASA technology development priorities outlined
Authors: Showstack Randy
Published: February 2012

NASA's technology development efforts should focus on 16 high‐priority technologies and their associated top technical challenges, according to a 1 February report by a committee of the U.S. National Research Council (NRC). The report grouped technology priorities within three objectives: extend and sustain human activities beyond low‐Earth orbit; explore the evolution of the solar system and the potential for life elsewhere; and expand our understanding of Earth and the universe in which we live. In pulling together its priority list, the committee boiled down priority technologies from a much longer list to “as short a list as is reasonable in the face of anticipated constrained budgets.” In addition, the committee also “assumes NASA will pursue enabling technology related to all three objectives in a balanced approach, and the committee does not advocate support for one objective over another.”
Love and Eos make the world go round
Authors: Nelson Deborah Imel
Published: February 2012

After 15 years of teaching environmental science, health, and safety at the College of Engineering, University of Oklahoma (not far from the Holocene Meers Fault), it was time for a change. I took a deep breath, gave up a tenured faculty position, and moved to Boulder, Colo., to work for a well‐known geological society, where my office looked out on steep slabs of Pennsylvanian sandstone at the edge of the Rocky Mountains. Seven months later, I realized there was a new neighbor next door—literally on the other side of the wall of my condo. Remembering my Oklahoma manners, I went next door to welcome the new neighbor. Alan Nelson answered the door and was momentarily speechless when I introduced myself as Deborah Nelson. He quickly recovered and invited me in. We began one of those halting conversations that proceeded until I spied a copy of Eos on the coffee table. “You must be a geologist!” I proudly exclaimed, since I knew that Eos is the weekly publication of AGU. Once again, Alan, who is indeed a geologist, was at a loss for words—but with this happy discovery, the conversation was off and running.
Estimating hyperconcentrated flow discharge
Authors: Balcerak Ernie
Published: February 2012

Determining flow discharge in torrential mountain floods can help in managing flood risk. However, standard methods of estimating discharge have significant uncertainties. To reduce these uncertainties, Bodoque et al. developed an iterative methodological approach to flow estimation based on a method known as the critical depth method along with paleoflood evidence. They applied the method to study a flash flood that occurred on 17 December 1997 in the Arroyo Cabrera catchment in central Spain. This large flow event, triggered by torrential rains, was complex and included hyperconcentrated flows, which are flows of water mixed with significant amounts of sediment.
Range of motion in intervertebral joints: why we don’t trust DinoMorph
Authors: Taylor Michael
Published: February 2012

Attempts to quantitatively reconstruct the range of motion of sauropod necks are intrinsically flawed because of ubiquitous distortion in preserved cervical vertebrae. This is true even for specimens that are usually considered particularly well preserved, such as the Carnegie Diplodocus and the Berlin Giraffatitan.
Gender‐Specific Effects of Early Nutritional Restriction on Adult Obesity Risk: Evidence From Quasi‐Experimental Studies
Authors: Robinson Whitney R.
Published: February 2012

In countries undergoing nutrition transition and historically poor minority groups in wealthy countries, obesity tends to be more common in women than men. A potential contributor to this female excess of obesity is a mismatch between perinatal nutritional restriction and a later calorie‐rich environment. Several epidemiologic and quasi‐experimental studies support a gender‐differential effect of early nutritional deprivation on adult obesity. The quasi‐experimental studies are of particular interest because results of quasi‐experimental studies are typically less vulnerable to confounding bias than observational studies. Four quasi‐experimental studies—exploiting 20th century famines that occurred in Europe, Africa, and Asia—provide evidence that perinatal nutritional restriction followed by relative caloric abundance may increase adult obesity risk to a greater extent in women than men. If the findings are accurate and generalizable to contemporary food environments, they suggest that the female offspring of poor, or otherwise nutritionally restricted, women in rapidly developing and wealthy countries may be at particularly high risk of adult obesity. Research into gender‐specific effects of early life nutritional deprivation and its interactions with later environmental exposures may provide insight into global gender differences in obesity prevalence.
Role and function of macrophages in the metabolic syndrome
Authors: Bhargava Prerna , Lee Chih-Hao
Published: February 2012

Macrophages are key innate immune effector cells best known for their role as professional phagocytes, which also include neutrophils and dendritic cells. Recent evidence indicates that macrophages are also key players in metabolic homoeostasis. Macrophages can be found in many tissues, where they respond to metabolic cues and produce pro- and/or anti-inflammatory mediators to modulate metabolite programmes. Certain metabolites, such as fatty acids, ceramides and cholesterol crystals, elicit inflammatory responses through pathogen-sensing signalling pathways, implicating a maladaptation of macrophages and the innate immune system to elevated metabolic stress associated with overnutrition in modern societies. The outcome of this maladaptation is a feedforward inflammatory response leading to a state of unresolved inflammation and a collection of metabolic pathologies, including insulin resistance, fatty liver, atherosclerosis and dyslipidaemia. The present review summarizes what is known about the contributions of macrophages to metabolic diseases and the signalling pathways that are involved in metabolic stress-induced macrophage activation. Understanding the role of macrophages in these processes will help us to develop therapies against detrimental effects of the metabolic syndrome.
A new extraction system for the Linac4 H−ion source
Authors: Midttun Ø. , Kalvas T. , Kronberger M. , Lettry J. , Pereira H. , Schmitzer C. , Scrivens R.
Published: February 2012

As part of the CERN accelerator complex upgrade, a new linear accelerator for H− (Linac4) is under construction. The ion source design is based on the non-caesiated DESY RF-driven ion source, with the goal of producing an H− beam of 80 mA beam current, 45 keV beam energy, 0.4 ms pulse length, and 2 Hz repetition rate. The source has been successfully commissioned for an extraction voltage of 35 kV, corresponding to the one used at DESY. Increasing the extraction voltage to 45 kV has resulted in frequent high voltage breakdowns in the extraction region caused by evaporating material from the electron dump, triggering a new design of the extraction and electron dumping system. Results of the ion source commissioning at 35 kV are presented as well as simulations of a new pulsed extraction system for beam extraction at 45 kV.
Numerical simulation of gridded electrostatic lens
Authors: Kropachev G. N. , Alexeev N. N. , Balabin A. I. , Kulevoy T. V. , Nikolaev V. I
Published: February 2012

Gridded electrostatic lenses are frequently used in extraction systems and low energy ion beam transport line. Typically, for numerical simulation the grid is treated as a metal plate transparent for beam particles. The influence of real grid geometry on the beam dynamics in the gridded lens has been investigated by KOBRA-3d code. Beam emittance growth for different lens parameters has been investigated. Approximating expressions for obtained results are presented. The grid geometry providing minimal beam distortions is proposed.
Development of a versatile multiaperture negative ion source
Authors: Cavenago M. , Kulevoy T. , Petrenko S. , Serianni G. , Antoni V. , Bigi M. , Fellin F. , Recchia M. , Veltri P.
Published: February 2012

A 60 kV ion source (9 beamlets of 15 mA each of H−) and plasma generators are being developed at Consorzio RFX and INFN-LNL, for their versatility in experimental campaigns and for training. Unlike most experimental sources, the design aimed at continuous operation. Magnetic configuration can achieve a minimum |B| trap, smoothly merged with the extraction filter. Modular design allows for quick substitution and upgrading of parts such as the extraction and postacceleration grids or the electrodes in contact with plasma. Experiments with a radio frequency plasma generator and Faraday cage inside the plasma are also described.
High-energy metal ion implantation for reduction of surface resistivity of alumina ceramic
Authors: Gushenets V. I. , Nikolaev A. G. , Oks E. M. , Savkin K. P. , Yushkov G. Yu. , Brown I. G.
Published: February 2012

In this work, the possibility to increase the surface conductivity of ceramic insulators through their treatment with accelerated metal ion beams produced by a MevvaV.Ru vacuum arc source is demonstrated. The increase in surface conductivity is made possible due to experimental conditions in which an insulated collector is charged by beam ions to a potential many times lower than the accelerating voltage, and hence, than the average beam ion energy. The observed effect of charge neutralization of the accelerated ion beam is presumably associated with electrons knocked out of the electrodes of the accelerating system of the source and of the walls of the vacuum chamber by the accelerated ions.
Magneto-optical cellular chip model for intracellular orientational-dynamic-activity detection
Authors: Miyashita Y. , Iwasaka M. , Kurita S. , Owada N.
Published: February 2012

In the present study, a magneto-optical cellular chip model (MoCCM) was developed to detect intracellular dynamics in macromolecules by using magneto-optical effects. For the purpose of cell-measurement under strong static magnetic fields of up to 10 T, we constructed a cellular chip model, which was a thin glass plate with a well for a cell culture. A cell line of osteoblast MC3T3-E1 was incubated in the glass well, and the well, 0.3 mm in depth, was sealed by a cover glass when the MoCCM was set in a fiber optic system. An initial intensity change of the polarized light transmission, which dispersed perpendicular to the cell’s attaching surface, was collected for 10 to 60 min, and then magnetic fields were applied parallel and perpendicular to the surface and light direction, respectively. The magnetic birefringence signals that originated from the magnetic orientation of intracellular molecules such as cytoskeletons apparently appeared when the magnetic fields were constant at 10 T. A statistical analysis with 15 experiments confirmed that the cellular components under 10 T magnetic fields caused a stronger alignment, which was transferred into polarizing light intensity that increased more than the case before exposure. Cellular conditions such as generation and cell density affected the magnetic birefringence signals.
The role of eddy currents and nanoparticle size on AC magnetic field–induced reflow in solder/magnetic nanocomposites
Authors: Habib A. H. , Xu S. , Walker E. , Ondeck M. , Swaminathan R. , McHenry M. E.
Published: February 2012

Magnetic nanoparticle (MNP)-based solder composites can facilitate solder reflow in AC magnetic fields. We compare power loss in a solder composite sample with MNP loading of different particle size distribution. Scaling of solder composite samples shows that, for smaller samples, power loss is not sufficient to realize solder reflow temperature. Additional heating can be derived from eddy current losses in Cu planes in the substrate board. Eddy current heating in Cu sheets of various thickness were evaluated to quantify their effect for low-temperature electronic assembly.
Magnetocaloric effect and refrigerant capacity in Sm1−xSrxMnO3 (x = 0.42, 0.44, 0.46) manganites
Authors: Bingham Nicholas S. , Lampen Paula J. , Phan The-Long , Phan Manh-Huong , Yu Seong-Cho , Srikanth Hariharan
Published: February 2012

Sm1−xSrxMnO3 (SSMO) with x ∼ 0.44 shows a multi-critical phase diagram which includes antiferromagnetic, charge ordering, and ferromagnetic transitions that give rise to large magnetoresistive and magnetocaloric effects. In this study, we systematically investigated the magnetic transitions, magnetocaloric effect (MCE), and refrigerant capacity (RC) in polycrystalline Sm1−xSrxMnO3 (x = 0.42, 0.44, 0.46) samples prepared by a standard ceramic method. Magnetization measurements and Arrott plot analyses reveal a first-order ferromagnetic transition for all samples investigated, with TC = 130 K, 134 K, and 133 K for x = 0.42, 0.44, and 0.46, respectively. The largest peak entropy change of −ΔSM = 4.61 J/kg K for a field change of μ0ΔH = 5 T is observed for the x = 0.44 composition around its Curie temperature of 134 K. After correcting for hysteretic losses of ∼15% – 30% engendered by the first order nature of the transition, sizable RC values of 151.42 J/kg, 140.15 J/kg, and 135.91 J/kg are still observed for x = 0.42, 0.44, and 0.46, respectively.
Observation and implications of magnetic domains in lateral spin valves
Authors: Mennig J. , Matthes F. , Bürgler D. E. , Schneider C. M.
Published: February 2012

Co/Cu/Co lateral spin valves (LSV), with Co being the topmost layer, are in situ prepared and measured under ultrahigh vacuum conditions. The clean process yields a non-local spin signal of 0.9 mΩ. Scanning electron microscopy with polarization analysis (SEMPA) reveals domain structures in both magnetic electrodes that depend on the LSV dimensions. The spin signal correlates to SEMPA images as well as the anisotropic magnetoresistance of both Co magnets, revealing a strong impact of multi-domain states on the spin signal.
Properties of NaZn13-type LaFe13−xSix (x=1.4, 1.5) compound with the first-order phase transition
Authors: Dong Q. Y. , Zhang H. W. , Shen J. , Chen J. , Sun J. R. , Shen B. G.
Published: February 2012

The investigations of dc magnetization, magnetic relaxation, specific heat, and electrical resistance for LaFe13−xSix (x = 1.4, 1.5) compounds have been carried out. Obvious thermal and magnetic hysteresis indicates that they experience a first-order phase transition. The phase transition temperature TC' is driven to high temperature with the increasing of field, which can be described by the relation TC'(H)2-TC'(0)2∝H. The large relaxation in magnetization around the field-induced metamagnetic transition field for LaFe13−xSix (x = 1.5) can be explained according to the thermal activation theory for the first-order phase transition and fitted by a logarithmic function M(t)M0=1±Sln(tt0+1), reflecting the distribution of energy barriers in this sample. The latent heat of LaFe13−xSix (x = 1.4) under zero field reaches to 1.8 kJ/kg. A good magnetic-thermal-resistive correspondence is also found in this compound.
Magnetovolume effect in Ho2Fe17-xMnx compounds
Authors: Wang J. L. , Studer A. J. , Kennedy S. J. , Zeng R. , Dou S. X. , Campbell S. J.
Published: February 2012

The structural and magnetic properties of seven compounds in the Ho2Fe17-xMnx series (x = 0-5) have been investigated. The spontaneous magnetization Ms at 10 K exhibits a minimum at x ≈ 3.8 while the 3d-sublattice magnetization MT is found to decrease at ∼ −3.4 μB/per Mn atom compared with the rate of ∼−2.0 μB/per Mn atom expected from a simple dilution model. All of the Ho2Fe17-xMnx compounds exhibit anisotropic thermal expansion below their Curie temperatures leading to the presence of strong magnetovolume effects and Invar-type behavior below TC. An approximately zero volume thermal expansion has been detected between 10 K and 270 K for Ho2Fe17. The maximum magnetic entropy changes for Ho2Fe17-xMnx with x = 0 and 2.0 are 3.2 J kg−1 K−1 around TC ∼ 336 K and 2.7 J kg−1 K−1 around TC ∼ 302 K, respectively, for magnetic field change of B = 0-5 T.
Magnetic properties and microstructure of Nd-Fe-B sintered magnets with DyHx addition
Authors: Liu Y. H. , Guo S. , Liu X. M. , Lee D. , Yan A. R.
Published: February 2012

The effects of DyHx addition on magnetic properties and microstructure of Nd-Fe-B sintered magnets were investigated. In order to obtain the best magnetic properties, the effects of sintering temperature and annealing time on magnetic properties were also investigated. The results shown that the addition of DyHx can affect the microstructure, increase the intrinsic coercivity (Hcj), and improve the thermal stability of sintered Nd-Fe-B magnets. The remanence (Br) and Hcj showed different variation trends as sintering temperature changes. Within a reasonable range, sintering at higher temperature can get higher Br but lower Hcj. The Hcj was further increased by heat treatment and annealing time was extended.
Investigation of a 7-pole/6-slot Halbach-magnetized permanent-magnet linear alternator used for free-piston stirling engines
Authors: Zheng Ping , Tong Chengde , Zhao Jing , Yu Bin , Li Lin , Bai Jingang , Zhang Lu
Published: February 2012

This paper investigates a 7-pole/6-slot Halbach-magnetized permanent-magnet linear alternator used for free piston Stirling engines (FPSEs). Taking the advantages of Halbach array, a 1 kW prototype alternator is designed. Considering the rms value of electromotive force (EMF) and harmonic distortion, the optimal length ratio of the axial- and radial-magnetized permanent magnets and thicknesses of the permanent magnets are optimized by 2D finite element method. The alternator detent force, which is an important factor for smooth operation of FPSEs, is studied by optimizing slot tip and end tooth. The load and thermal performances of the final design are simulated. A prototype alternator was designed, built and tested. Experimental data indicated satisfactory design.
Design and specifications of the diagnostics for the instrumented calorimeter of Source for the Production of Ions of Deuterium Extracted from Radio frequency plasma
Authors: De Muri M. , Dalla Palma M. , Fasolo D. , Pasqualotto R. , Pomaro N. , Rizzolo A. , Serianni G. , Tollin M.
Published: February 2012

In the development of the neutral beam injector for ITER experiment, the test facility SPIDER is going to be built. To measure the beam parameters, several diagnostics are used. One of them is the Short-Time Retractable Instrumented Kalorimeter Experiment (STRIKE) which measures beam uniformity, beamlet divergence, and stripping losses. This contribution gives an overview of the diagnostics dedicated to these measurements: thermal cameras, thermocouples, current sensors, and electrostatic sensors. The specifications of these diagnostics have been defined according to the results of electrostatic and thermal simulations. A failure modes and effects analysis has been performed during the design. Consequently the project of the STRIKE diagnostics has been optimized to reduce the possible failure risks.
First-order phase transitions in repulsive rigid k-mers on two-dimensional lattices
Authors: Pasinetti P. M. , Romá F. , Ramirez-Pastor A. J.
Published: February 2012

In a previous paper [F. Romá, A. J. Ramirez-Pastor, and J. L. Riccardo, Phys. Rev. B 72, 035444 (2005)], the critical behavior of repulsive rigid rods of length k (k-mers) on a square lattice at half coverage has been studied by using Monte Carlo (MC) simulations. The obtained results indicated that (1) the phase transition occurring in the system is a second-order phase transition for all adsorbate sizes k; and (2) the universality class of the transition changes from 2D Ising-type for monomers (k = 1) to an unknown universality class for k ≥ 2. In the present work, we revisit our previous results together with further numerical evidences, resulting from new extensive MC simulations based on an efficient exchange algorithm and using high-performance computational capabilities. In contrast to our previous conclusions (1) and (2), the new numerical calculations clearly support the occurrence of a first-order phase transition for k ≥ 2. In addition, a similar scenario was found for k-mers adsorbed on the triangular lattice at coverage k/(2k+1).
Organic photovoltaic cells with nano-fabric heterojunction structure
Authors: Hyoung Park June , Carter Austin R. , Mier Lynetta M. , Kao Chi-Yueh , Lewis Sharlene A. M. , Nandyala Raju P. , Min Yong , Epstein Arthur J.
Published: February 2012

Organic photovoltaic cells containing electron-transporting organic nanofibers in the form of “nanofabrics” are investigated. Nano-fabric heterojunctions of poly(3-hexylthiophene) and electron-transporting nanofibers significantly improve short-circuit current density in organic photovoltaic cells. The nanofibers and nanofabric are synthesized from organic electron-transporting material bis(octyl)-perylenediimide (PDI-C8). The PDI-C8 based nano-fabric’s electron mobility is measured to be 0.08 cm2/V s. The nanofabric improves charge collection by expanding the interfacial acceptor-donor area while simultaneously providing dedicated electron transport pathways to the LiF/Al electrodes. An increase in fill factor is observed for photovoltaic cells incorporating the nanofabric heterojunctions and is attributed to efficient removal of space charge.
Markov processes follow from the principle of maximum caliber
Authors: Ge Hao , Pressé Steve , Ghosh Kingshuk , Dill Ken A.
Published: February 2012

Markov models are widely used to describe stochastic dynamics. Here, we show that Markov models follow directly from the dynamical principle of maximum caliber (Max Cal). Max Cal is a method of deriving dynamical models based on maximizing the path entropy subject to dynamical constraints. We give three different cases. First, we show that if constraints (or data) are given in the form of singlet statistics (average occupation probabilities), then maximizing the caliber predicts a time-independent process that is modeled by identical, independently distributed random variables. Second, we show that if constraints are given in the form of sequential pairwise statistics, then maximizing the caliber dictates that the kinetic process will be Markovian with a uniform initial distribution. Third, if the initial distribution is known and is not uniform we show that the only process that maximizes the path entropy is still the Markov process. We give an example of how Max Cal can be used to discriminate between different dynamical models given data.
Observation and simulation of hard x ray photoelectron diffraction to determine polarity of polycrystalline zinc oxide films with rotation domains
Authors: Williams Jesse R. , Píš Igor , Kobata Masaaki , Winkelmann Aimo , Matsushita Tomohiro , Adachi Yutaka , Ohashi Naoki , Kobayashi Keisuke
Published: February 2012

X ray photoelectron diffraction (XPD) patterns of polar zinc oxide (ZnO) surfaces were investigated experimentally using hard x rays and monochromatized Cr Kα radiation and theoretically using a cluster model approach and a dynamical Bloch wave approach. We focused on photoelectrons emitted from the Zn 2p3/2 and O 1s orbitals in the analysis. The obtained XPD patterns for the (0001) and (0001¯) surfaces of a ZnO single crystal were distinct for a given emitter and polarity. Polarity determination of c-axis-textured polycrystalline ZnO thin films was also achieved with the concept of XPD, even though the in-plane orientation of the columnar ZnO grains was random.
Study on the effect of pressure on the properties of intrinsic point defects in monoclinic zirconia: Ab initio calculations
Authors: Zhao Shijun , Xue Jianming , Wang Yugang , Yan Sha
Published: February 2012

First-principles calculations were performed to investigate the effects of external pressure on the properties of intrinsic point defects in monoclinic zirconia. Our results show that when the applied external pressure increases from atmospheric pressure to 14.9 GPa, the formation energies of oxygen vacancies decrease with increasing pressure, while the formation energies of the cation and anion interstitials increase all over the pressure regime investigated. Among them the most remarkable change occurs in neutral zirconium interstitial with an increase of 2.21 eV. In particular, the formation energy of zirconium vacancy depends strongly on its charge state. For all the chemical potential and Fermi level considered, the cation and anion vacancies are the most stable defects in all cases. The present calculations also reveal that the formation energies of Frenkel defects could be raised by external pressures, while the energetics of Schottky defects are not much affected. Moreover, the charge state transition of defects is found to be greatly influenced by the external pressures, and thus the stability diagram of defects in ZrO2 is strongly dependent on external pressures. Our findings suggest that external pressures should raise the concentration of oxygen vacancies significantly.
B(1)1Π state of KCs: High-resolution spectroscopy and description of low-lying energy levels
Authors: Birzniece I. , Nikolayeva O. , Tamanis M. , Ferber R.
Published: February 2012

The diode laser induced B(1)1Π → X1Σ+ fluorescence spectra of the KCs molecule were recorded by Fourier-transform spectrometer with resolution of 0.03 cm−1. Buffer gas Ar was used to facilitate appearance of rotation relaxation lines in the spectra, thus enlarging the B(1)1Π dataset, allowing one to determine the Λ-splitting constants and to reveal numerous local perturbations. A dataset was systematically obtained for B(1)1Π vibrational levels v′ ∈ [0; 5] nonuniformly covering rotational levels with J′ ∈ [7; 233]. For v′ ∈ [0; 3], the less-perturbed data of f-components were included in the fit. A pointwise potential energy curve (PEC) based on the inverted perturbation approach, as well as the Dunham coefficients, was obtained and compared with ab initio calculations; in particular, the energy of the PEC's minimum Te = 14 044.918(6) cm−1 was determined. Both approaches allowed us to reproduce the vast majority of data used in the fit with accuracy of 0.02 cm−1. Tentative molecular constants for several vibrational levels of the near lying C(3)1Σ+ state were estimated.
Total destruction of invariant tori for the generalized Frenkel–Kontorova model
Authors: Su Xifeng , Wang Lin
Published: February 2012

We consider generalized Frenkel–Kontorova models on higher dimensional lattices. We show that the invariant tori which are parameterized by continuous hull functions can be destroyed by small perturbations in the Cr topology with r < 1.
Quartz crystal microbalance based on passive frequency to voltage converter
Authors: Burda Ioan , Tunyagi Arthur
Published: February 2012

In dynamics of evaporation or drying of microdrops from a solid surface, a faster and precise quartz crystal microbalance (QCM) is needed. The fast QCM based on frequency to voltage converter is an attractive and powerful tool in the investigation of the dynamic regime of evaporation to translate the frequency shift in terms of a continuous voltage change. The frequency shift monitoring in fast QCM applications is a real challenge for electronic processing interface. Originally developed as a frequency shift processing interface, this novel passive frequency to voltage converter can produce faster, stable, and accurate results in regard to the QCM sensor behavior. In this article, the concept and circuit of passive frequency to voltage converter will be explained followed by static and dynamic characterization. Experimental results of microdrops evaporation will be given.
Vibronic coupling simulations for linear and nonlinear optical processes: Simulation results
Authors: Silverstein Daniel W. , Jensen Lasse
Published: February 2012

A vibronic coupling model based on time-dependent wavepacket approach is applied to simulate linear optical processes, such as one-photon absorbance and resonance Raman scattering, and nonlinear optical processes, such as two-photon absorbance and resonance hyper-Raman scattering, on a series of small molecules. Simulations employing both the long-range corrected approach in density functional theory and coupled cluster are compared and also examined based on available experimental data. Although many of the small molecules are prone to anharmonicity in their potential energy surfaces, the harmonic approach performs adequately. A detailed discussion of the non-Condon effects is illustrated by the molecules presented in this work. Linear and nonlinear Raman scattering simulations allow for the quantification of interference between the Franck-Condon and Herzberg-Teller terms for different molecules.
Modeling of the microstructure of carbon nanotube with two nonlocal elasticity theories
Authors: Jafari S. Basir , Malekfar R. , Khadem S. E.
Published: February 2012

In this paper, a detailed theoretical study on the dispersion of waves in carbon nanotubes (CNTs) is presented. For this purpose, CNTs are considered as nonlocal elastic thin cylindrical shells. The Eringen’s nonlocal elasticity theory is used for modeling the microstructure of CNT such that the proximity of the mathematical model to the actual atomic structure of CNT is retained. The results are compared with the results that are obtained based on the second-order strain-gradient elasticity (SG) theory. It has been shown that the SG theory is the first approximation of nonlocal continuum elasticity (NC) theory, which is used in the present paper. Also, it has been shown that the bending rigidity has important effect in the dispersion of waves in CNTs.
Deep ultraviolet and visible crystalloluminescence of sodium chloride
Authors: Alexander Andrew J.
Published: February 2012

A protocol has been developed for production of intense crystalloluminescence (XTL) from sodium chloride in aqueous solution by selective doping with transition metal salts (Ag+, Cu2+, and Dy3+). The method was used to record complete, fully dispersed deep UV–visible (200–650 nm) XTL spectra of sodium chloride for the first time. The results show conclusively that the emissions are due to dopant cations in the NaCl lattice, with no evidence for emission directly from NaCl, e.g., by triboluminescence resulting from crystalline fracture. The UV components of the XTL spectrum are attributed to single cation substituents (Ag+ and Cu+), and a strong visible component (∼415 nm) of the XTL is attributed to emission from silver-pair centers, (Ag+)2. The nature of the electronic transitions of the dopant cations is discussed. The results suggest that the timescale for transformation of a cluster to the crystalline phase is rapid, with efficient relaxation to the lowest excited electronic states of the dopant cation. This transformation is followed by photoemission of the cation in the nascent crystal.
Non-Hermitian exciton dynamics in a photosynthetic unit system
Authors: Thilagam A.
Published: February 2012

The non-Hermitian quantum dynamics of excitonic energy transfer in photosynthetic systems is investigated using a dissipative two-level dimer model. The approach is based on Green's function formalism which permits consideration of decoherence and intersite transfer processes on comparable terms. The results indicate a combination of coherent and incoherent behavior at higher temperatures with the possibility of exceptional points occurring at the coherent-incoherent crossover regime at critical temperatures. When each dimer site is coupled equally to the environmental sources of dissipation, the excitonic wavepacket evolves with time with a coherent component, which can be attributed to the indistinguishability of the sources of dissipation. The time evolution characteristics of the B850 Bchls dimer system is analysed using typical parameter estimates in photosynthetic systems, and the quantum brachistochrone passage times are obtained for a range of parameters.
Electron mobility determination of efficient phosphorescent iridium complexes with tetraphenylimidodiphosphinate ligand via transient electroluminescence method
Authors: Teng Ming-Yu , Zhang Song , Jiang Sheng-Wei , Yang Xu , Lin Chen , Zheng You-Xuan , Wang Leyong , Wu Di , Zuo Jing-Lin , You Xiao-Zeng
Published: February 2012

The electron mobility of Alq3 and iridium complexes was determined via transient electroluminescence (EL) method based on ITO (indium tin oxide)/di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane/complex/LiF/Al with short and rectangular driving voltage pulses. Apparent values of the electron mobility (μe) in complexes have been investigated from their onset of EL upon different driving voltages. The result reveals that the μe, 4.31 × 10−6 cm2/V·s, of the efficient phosphorescent material Ir(tfmppy)2(tpip) [1, tfmppy = 4-trifluoromethylphenylpyridine, tpip = tetraphenylimido-diphosphinate] under electric field of 1300 (V/cm)1/2 is as high as that of Alq3, which indicates that the good device performances of 1 are partly due to its high electron mobility.
Enhancing magnetic vacancies in semiconductors by strain
Authors: Kan Erjun , Wu Fang , Zhang Yuemei , Xiang Hongjun , Lu Ruifeng , Xiao Chuanyun , Deng Kaiming , Su Haibin
Published: February 2012

Although cation-vacancies can induce localized magnetic moments in semiconductors, the collective magnetism is impeded by low vacancy concentration. To improve the vacancy concentration, we study the effect of external hydrostatic strain on the vacancy formation energy. Our first-principles calculations discover that vacancy formation energy is significantly reduced in ionic semiconductors with the monotonic volume contraction, while only slightly decreased in covalent semiconductors. Especially for ZnO, the equilibrium concentration of cation-vacancies has been improved by 109 times. We predicted that strain can be used to produce “d0 magnetism” in ionic semiconductors much easier in experiments.
Electron stimulated desorption of anions from native and brominated single stranded oligonucleotide trimers
Authors: Polska Katarzyna , Rak Janusz , Bass Andrew D. , Cloutier Pierre , Sanche Léon
Published: February 2012

We measured the low energy electron stimulated desorption (ESD) of anions from thin films of native (TXT) and bromine monosubstituted (TBrXT) oligonucleotide trimers deposited on a gold surface (T = thymidine, X = T, deoxycytidine (C), deoxyadenosine (A) or deoxyguanosine (G), Br = bromine). The desorption of H−, CH3−/NH−, O−/NH2−, OH−, CN−, and Br− was induced by 0 to 20 eV electrons. Dissociative electron attachment, below 12 eV, and dipolar dissociation, above 12 eV, are responsible for the formation of these anions. The comparison of the results obtained for the native and brominated trimers suggests that the main pathways of TBrXT degradation correspond to the release of the hydride and bromide anions. Significantly, the presence of bromine in oligonucleotide trimers blocks the electron-induced degradation of nuclobases as evidenced by a dramatic decrease in CN− desorption. An increase in the yields of OH− is also observed. The debromination yield of particular oligonucleotides diminishes in the following order: BrdU > BrdA > BrdG > BrdC. Based on these results, 5-bromo-2′-deoxyuridine appears to be the best radiosensitizer among the studied bromonucleosides.
Multi-splitting and self-similarity of band gap structures in quasi-periodic plates of Cantor series
Authors: Ding Hong-Xing , Shen Zhong-Hua , Ni Xiao-Wu , Zhu Xue-Feng
Published: February 2012

The authors have demonstrated the multi-splitting and self-similarity of the band gap structures in quasi-periodic plates of Cantor series. The splitting peaks give the regularity of tri-branching. A semi-quantitative explanation is proposed in which the inherent cavity-like structure is proven to play the essential role in the phenomena of multi-splitting and self-similarity, which gives a reliable way to predict where and how the band gap is splitting in the quasi-periodic systems. Possible applications are discussed.
Stabilized hot electron bolometer heterodyne receiver at 2.5 THz
Authors: Hayton D. J. , Gao J. R. , Kooi J. W. , Ren Y. , Zhang W. , de Lange G.
Published: February 2012

We report on a method to stabilize a hot electron bolometer (HEB) mixer at 2.5 THz. The technique utilizes feedback control of the local oscillator (LO) laser power by means of a swing-arm actuator placed in the optical beam path. We demonstrate that this technique yields a factor of 50 improvement in the spectroscopic Allan variance time which is shown to be over 30 s in a 12 MHz noise fluctuation bandwidth. Furthermore, broadband signal direct detection effects may be minimized by this technique. The technique is versatile and can be applied to practically any local oscillator at any frequency.
Bending of metal-filled carbon nanotube under electron beam irradiation
Authors: Misra Abha
Published: February 2012

Electron beam irradiation induced, bending of Iron filled, multiwalled carbon nanotubes is reported. Bending of both the carbon nanotube and the Iron contained within the core was achieved using two approaches with the aid of a high resolution electron microscope (HRTEM). In the first approach, bending of the nanotube structure results in response to the irradiation of a pristine kink defect site, while in the second approach, disordered sites induce bending by focusing the electron beam on the graphite walls. The HRTEM based in situ observations demonstrate the potential for using electron beam irradiation to investigate and manipulate the physical properties of confined nanoscale structures.
Direct measurements and numerical simulations of gas charging in microelectromechanical system capacitive switches
Authors: Venkattraman A. , Garg A. , Peroulis D. , Alexeenko A. A.
Published: February 2012

Gas breakdown in microelectromechanical system capacitive switches is demonstrated using high resolution current measurements and by particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. Measurements show an electric current through a 3 μm air gap increasing exponentially with voltage, starting at 60 V. PIC/MCC simulations with Fowler-Nordheim [Proc. R. Soc. London, Ser. A 119, 173 (1928)] field emission reveal self-sustained discharges with significant ion enhancement and a positive space charge. The effective ion-enhanced field emission coefficient increases with voltage up to about 0.3 with an electron avalanche occurring at 159 V. The measurements and simulations demonstrate a charging mechanism for microswitches consistent with earlier observations of gas pressure and composition effects on lifetime.
Strong vortex pinning in FeSe0.5Te0.5 epitaxial thin film
Authors: Bellingeri E. , Kawale S. , Pallecchi I. , Gerbi A. , Buzio R. , Braccini V. , Palenzona A. , Putti M. , Adamo M. , Sarnelli E. , Ferdeghini C.
Published: February 2012

We report on the magnetic field and angular dependence of the critical current density of epitaxial FeTe0.5Se0.5 thin films. The films exhibit high critical current values and weak dependence on the applied magnetic field. The Jc is larger for field parallel to the c-axis, which is the opposite behavior of what expected from the critical field anisotropy. The analysis of the activation energy for vortex motion indicates that the single pinning regime holds up to 9 T, suggesting that correlated pinning centers are more effective than the vortex-vortex interaction even at the largest applied fields. Scanning tunneling microscope analysis indicates threading dislocations as possible pinning centers.
Prediction of the CEC to clay ratio using mid-infrared spectroscopy
Authors: Bloesch Philip M.
Published: February 2012

The ratio of cation exchange capacity to clay (CCR) has been used as an index of clay mineralogy in subsoils low in organic matter in place of the standard X-ray diffraction measurement. Laboratory determination of this ratio is time-consuming and expensive and involves two analyses. In this paper, the CCR has been successfully predicted from mid-infrared diffuse reflectance spectra using partial least-squares regression (PLSR) with a square-root transformation of the CCR values (R2 = 0.860; root mean squared error of prediction = 0.089; relative per cent deviation = 2.660 for an independent validation set). The most important wavelengths used in the PLSR calibration were identified. The prediction of CCR using mid-infrared spectroscopy provides a cheaper and faster alternative to laboratory determination.