bluuebunny/crossref_metadata_2025 huggingface dataset:
Last Improvements of the CALMOS Calorimeter Dedicated to Thermal Neutron Flux and Nuclear Heating Measurements inside the OSIRIS Reactor
Authors: Carcreff H. , Salmon L. , Lepeltier V. , Guyot J.M. , Bouard E.
Published: January 2018

Nuclear heating inside an MTR reactor needs to be known in order to design and to run irradiation experiments which have to fulfill target temperature constraints. To improve the nuclear heating knowledge, an innovative calorimetric system CALMOS has been studied, manufactured and tested for the 70MWth OSIRIS reactor operated by CEA. This device is based on a mobile calorimetric probe which can be inserted in any in-core experimental location and can be moved axially from the bottom of the core to 1000 mm above the core mid-plane. Obtained results and advantages brought by the first CALMOS-1 equipment have been already presented. However, some difficulties appeared with this first version. A thermal limitation in cells did not allow to monitor nuclear heating up to the 70 MW nominal power, and some significant discrepancies were observed at high heating rates between results deduced from the calibration and those obtained by the “zero method”. Taking this feedback into account, the new CALMOS-2 calorimeter has been designed both for extending the heating range up to 13W.g-1 and for improving the “zero method” measurement thanks to the implementation of a 4-wires technique. In addition, the new calorimeter has been designed as a real operational measurement system, well suited to characterize and to follow the radiation field evolution throughout the reactor cycle. To meet this requirement, a programmable system associated with a specific software allows automatic complete cell mobility in the core, the data acquisition and the measurements processing. This paper presents the analysis of results collected during the 2015 comprehensive measurement campaign. The 4-wires technique was tested up to around a 4 W.g-1 heating level and allowed to quantify discrepancies between “zero” and calibration methods. Thermal neutron flux and nuclear heating measurements from CALMOS-1 and CALMOS-2 are compared. Thermal neutron flux distributions, obtained with the Self-Power Neutron Detector suited to the CALMOS-2 calorimetric probe, are compared with those obtained with current devices. This campaign allowed to highlight advantages brought by the human machine interface automation, which deeply refined the profiles definition. Finally, the decay of the reactor residual power after shutdown could be performed after shutdown, demonstrating the ability of such type of calorimeter to follow the heating level whatever the thermohydraulic conditions, forced or natural convection regimes.
High temperature ultrasonic sensor for fission gas characterization in MTR harsh environment
Authors: Gatsa O. , Combette P. , Rozenkrantz E. , Fourmentel D. , Destouches C. , Ferrandis J.Y.
Published: January 2018

In the contemporary world, the measurements in hostile environment is one of the predominant necessity for automotive, aerospace, metallurgy and nuclear plant. The measurement of different parameters in experimental reactors is an important point in nuclear power strategy. In the near past, IES (Institut d’Électronique et des Systèmes) on collaboration with CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives) have developed the first ultrasonic sensor for the application of gas quantity determination that has been tested in a Materials Testing Reactor (MTR). Modern requirements state to labor with the materials that possess stability on its parameters around 350°C in operation temperature. Previous work on PZT components elaboration by screen printing method established the new basis in thick film fabrication and characterization in our laboratory. Our trials on Bismuth Titanate ceramics showed the difficulties related to high electrical conductivity of fabricated samples that postponed further research on this material. Among piezoceramics, the requirements on finding an alternative solution on ceramics that might be easily polarized and fabricated by screen printing approach were resolved by the fabrication of thick film from Sodium Bismuth Titanate (NBT) piezoelectric powder. This material exhibits high Curie temperature, relatively good piezoelectric and coupling coefficients, and it stands to be a good solution for the anticipated application.

In this paper, we present NBT thick film fabrication by screen printing, characterization of piezoelectric, dielectric properties and material parameters studies in dependence of temperature. Relatively high resistivity in the range of 1.1013 Ohm.cm for fabricated thick film is explained by Aurivillius structure in which a-and b-layers form perovskite structure between oxides of c-layer. Main results of this study are presented and discussed in terms of feasibility for an application to a new sensor device operating at high temperature level (400°). Piezoelectric parameters enhancement and loss reduction at elevated temperatures are envisaged to be optimized. Further sensor development and test in MTR are expected to be realized in the near future.
Innovative hybrid pile oscillator technique in the Minerve reactor: open loop vs. closed loop
Authors: Geslot Benoit , Gruel Adrien , Bréaud Stéphane , Leconte Pierre , Blaise Patrick
Published: January 2018

Pile oscillator techniques are powerful methods to measure small reactivity worth of isotopes of interest for nuclear data improvement. This kind of experiments has long been implemented in the Mineve experimental reactor, operated by CEA Cadarache. A hybrid technique, mixing reactivity worth estimation and measurement of small changes around test samples is presented here. It was made possible after the development of high sensitivity miniature fission chambers introduced next to the irradiation channel. A test campaign, called MAESTRO-SL, took place in 2015. Its objective was to assess the feasibility of the hybrid method and investigate the possibility to separate mixed neutron effects, such as fission/capture or scattering/capture. Experimental results are presented and discussed in this paper, which focus on comparing two measurements setups, one using a power control system (closed loop) and another one where the power is free to drift (open loop). First, it is demonstrated that open loop is equivalent to closed loop. Uncertainty management and methods reproducibility are discussed. Second, results show that measuring the flux depression around oscillated samples provides valuable information regarding partial neutron cross sections. The technique is found to be very sensitive to the capture cross section at the expense of scattering, making it very useful to measure small capture effects of highly scattering samples.
Tests and foreseen developments of fibered-OSLD gamma heating measurements in low-power reactors
Authors: Gruel A. , Guillou M. Le , Blaise P. , Destouches C. , Magne S.
Published: January 2018

In this paper are presented test measurements of a fibered-OSLD system performed during a dedicated experimental phase in EOLE zero-power reactor. The measurement setup consists of an OSLD crystal connected onto the extremity of an optical fiber and a laser stimulation system, manufactured by the CEA/LIST in Saclay. The OSL sensor is remotely stimulated via an optical fiber using a diode-pumped solid-state laser. The OSL light is collected and guided back along the same fiber to a photomultiplier tube. Results obtained using this system are compared to usual gamma heating measurement protocol using OSLD pellets. The presence of induced radio-luminescence in the OSLD during the irradiation was also observed and could be used to monitor the gamma flux.

The feasibility of remote measurements is achieved, whereas further developments could be conducted to improve this technique since the readout procedure still requires to withdraw the OSLD off the gamma flux (hence from the core) on account of the dose rate (around a few Gy.h-1), and the readout time remains quite long for on-line applications. Several improvements are foreseen, and will be tested in the forthcoming years.
Study of the linearity of CABRI experimental ionization chambers during RIA transients
Authors: Lecerf J. , Garnier Y. , Hudelot JP. , Duc B. , Pantera L.
Published: January 2018

CABRI is an experimental pulse reactor operated by CEA at the Cadarache research center and funded by the French Nuclear Safety and Radioprotection Institute (IRSN).

For the purpose of the CABRI International Program (CIP), operated and managed by IRSN under an OECD/NEA framework it has been refurbished since 2003 to be able to provide experiments in prototypical PWR conditions (155 bar, 300 °C) in order to study the fuel behavior under Reactivity Initiated Accident (RIA) conditions.

This paper first reminds the objectives of the power commissioning tests performed on the CABRI facility. The design and location of the neutron detectors monitoring the core power are also presented.

Then it focuses on the different methodologies used to calibrate the detectors and check the consistency and co-linearity of the measurements.

Finally, it presents the methods used to check the linearity of the neutron detectors up to the high power levels (~20 GW) reached during power transients. Some results obtained during the power tests campaign are also presented.
Current Mode Neutron Noise Measurements in the Zero Power Reactor CROCUS
Authors: Pakari O. , Lamirand V. , Perret G. , Braun L. , Frajtag P. , Pautz A.
Published: January 2018

The present article is an overview of developments and results regarding neutron noise measurements in current mode at the CROCUS zero power facility. Neutron noise measurements offer a non-invasive method to determine kinetic reactor parameters such as the prompt decay constant at criticality α = βeff / λ, the effective delayed neutron fraction βeff, and the mean generation time λ for code validation efforts. At higher detection rates, i.e. above 2×104 cps in the used configuration at 0.1 W, the previously employed pulse charge amplification electronics with BF3 detectors yielded erroneous results due to dead time effects. Future experimental needs call for higher sensitivity in detectors, higher detection rates or higher reactor powers, and thus a generally more versatile measurement system. We, therefore, explored detectors operated with current mode acquisition electronics to accommodate the need. We approached the matter in two ways:

1) By using the two compensated 10B-coated ionization chambers available in CROCUS as operational monitors. The compensated current signal of these chambers was extracted from coremonitoring output channels.

2) By developing a new current mode amplification station to be used with other available detectors in core. Characteristics and first noise measurements of the new current system are presented. We implemented post-processing of the current signals from 1)and 2) with the APSD/CPSD method to determine α. At two critical states (0.5 and 1.5 W), using the 10B ionization chambers and their CPSD estimate, the prompt decay constant was measured after 1.5 hours to be α=(156.9 ± 4.3) s-1 (1σ). This result is within 1σ of statistical uncertainties of previous experiments and MCNPv5-1.6 predictions using the ENDF/B-7.1 library. The newsystem connected to a CFUL01 fission chamber using the APSDestimate at 100 mW after 33 min yielded α = (160.8 ± 6.3) s-1, also within 1σ agreement.

The improvements to previous neutron noise measurementsinclude shorter measurement durations that can achievecomparable statistical uncertainties and measurements at higherdetection rates.
Stochastic approach for radionuclides quantification
Authors: Clement A. , Saurel N. , Perrin G.
Published: January 2018

Gamma spectrometry is a passive non-destructive assay used to quantify radionuclides present in more or less complex objects. Basic methods using empirical calibration with a standard in order to quantify the activity of nuclear materials by determining the calibration coefficient are useless on non-reproducible, complex and single nuclear objects such as waste packages. Package specifications as composition or geometry change from one package to another and involve a high variability of objects. Current quantification process uses numerical modelling of the measured scene with few available data such as geometry or composition. These data are density, material, screen, geometric shape, matrix composition, matrix and source distribution. Some of them are strongly dependent on package data knowledge and operator backgrounds. The French Commissariat à l’Energie Atomique (CEA) is developing a new methodology to quantify nuclear materials in waste packages and waste drums without operator adjustment and internal package configuration knowledge. This method suggests combining a global stochastic approach which uses, among others, surrogate models available to simulate the gamma attenuation behaviour, a Bayesian approach which considers conditional probability densities of problem inputs, and Markov Chains Monte Carlo algorithms (MCMC) which solve inverse problems, with gamma ray emission radionuclide spectrum, and outside dimensions of interest objects. The methodology is testing to quantify actinide activity in different kind of matrix, composition, and configuration of sources standard in terms of actinide masses, locations and distributions. Activity uncertainties are taken into account by this adjustment methodology.
Modeling Photo-multiplier Gain and Regenerating Pulse Height Data for Application Development
Authors: Aspinall Michael D. , Jones Ashley R.
Published: January 2018

Systems that adopt organic scintillation detector arrays often require a calibration process prior to the intended measurement campaign to correct for significant performance variances between detectors within the array. These differences exist because of low tolerances associated with photo-multiplier tube technology and environmental influences. Differences in detector response can be corrected for by adjusting the supplied photo-multiplier tube voltage to control its gain and the effect that this has on the pulse height spectra from a gamma-only calibration source with a defined photo-peak. Automated methods that analyze these spectra and adjust the photo-multiplier tube bias accordingly are emerging for hardware that integrate acquisition electronics and high voltage control. However, development of such algorithms require access to the hardware, multiple detectors and calibration source for prolonged periods, all with associated constraints and risks. In this work, we report on a software function and related models developed to rescale and regenerate pulse height data acquired from a single scintillation detector. Such a function could be used to generate significant and varied pulse height data that can be used to integration-test algorithms that are capable of automatically response matching multiple detectors using pulse height spectra analysis. Furthermore, a function of this sort removes the dependence on multiple detectors, digital analyzers and calibration source. Results show a good match between the real and regenerated pulse height data. The function has also been used successfully to develop auto-calibration algorithms.
Development of Neutron Energy Spectral Signatures for Passive Monitoring of Spent Nuclear Fuels in Dry Cask Storage
Authors: Harkness Ira , Zhu Ting , Liang Yinong , Rauch Eric , Enqvist Andreas , Jordan Kelly A.
Published: January 2018

Demand for spent nuclear fuel dry casks as an interim storage solution has increased globally and the IAEA has expressed a need for robust safeguards and verification technologies for ensuring the continuity of knowledge and the integrity of radioactive materials inside spent fuel casks. Existing research has been focusing on “fingerprinting” casks based on count rate statistics to represent radiation emission signatures. The current research aims to expand to include neutron energy spectral information as part of the fuel characteristics. First, spent fuel composition data are taken from the Next Generation Safeguards Initiative Spent Fuel Libraries, representative for Westinghouse 17ˣ17 PWR assemblies. The ORIGEN-S code then calculates the spontaneous fission and (α,n) emissions for individual fuel rods, followed by detailed MCNP simulations of neutrons transported through the fuel assemblies. A comprehensive database of neutron energy spectral profiles is to be constructed, with different enrichment, burn-up, and cooling time conditions. The end goal is to utilize the computational spent fuel library, predictive algorithm, and a pressurized 4He scintillator to verify the spent fuel assemblies inside a cask. This work identifies neutron spectral signatures that correlate with the cooling time of spent fuel. Both the total and relative contributions from spontaneous fission and (α,n) change noticeably with respect to cooling time, due to the relatively short half-life (18 years) of the major neutron source 244Cm. Identification of this and other neutron spectral signatures allows the characterization of spent nuclear fuels in dry cask storage.
Instrumentation effects on U and Pu CBNM standards spectra quality measured on a 500 mm3CdZnTe and a 2×2 inch LaBr3detectors
Authors: Meleshenkovskii I. , Borella A. , Van der Meer K. , Bruggeman M. , Pauly N. , Labeau P.E. , Schillebeeckx P.
Published: January 2018

Nowadays, there is interest in developing gamma-ray measuring devices based on the room temperature operated medium resolution detectors such as semiconductor detectors of the CdZnTe type and scintillators of the LaBr3type. This is true also for safeguards applications and the International Atomic Energy Agency (IAEA) has launched a project devoted to the assessment of medium resolution gamma-ray spectroscopy for the verification of the isotopic composition of U and Pu bearing samples. This project is carried out within the Non-Destructive Assay Working Group of the European Safeguards Research and Development Association (ESARDA). In this study we analyze medium resolution spectra of U and Pu standards with the aim to develop an isotopic composition determination algorithm, particularly suited for these types of detectors. We show how the peak shape of a CdZnTe detector is influenced by the instrumentation parameters. The experimental setup consisted of a 500 mm3CdZnTe detector, a 2×2 inch LaBr3detector, two types of measurement instrumentation – an analogue one and a digital one, and a set of certified samples – a207Bi point source and U and Pu CBNM standards. The results of our measurements indicate that the lowest contribution to the peak asymmetry and thus the smallest impact on the resolution of the 500 mm3 CdZnTe detector was achieved with the digital MCA. Analysis of acquired spectra allowed to reject poor quality measurement runs and produce summed spectra files with the least impact of instrumentation instabilities. This work is preliminary to further studies concerning the development of an isotopic composition determination algorithm particularly suited for CZT and LaBr3 detectors for safeguards applications.
New perspectives for undoped CaF2 scintillator as a threshold activation neutron detector
Authors: Sibczynski Pawel , Dziedzic Andrzej , Grodzicki Krystian , Iwanowska-Hanke Joanna , Moszyński Marek , Swiderski Lukasz , Syntfeld-Każuch Agnieszka , Wolski Dariusz , Carrel Frédérick , Grabowski Amélie , Hamel Matthieu , Laine Frederic , Sari Adrien , Iovene Alessandro , Tintori Carlo , Fontana Cristiano , Pino Felix
Published: January 2018

In this paper we present the prompt photofission neutron detection performance of undoped CaF2 scintillator using Threshold Activation Detection (TAD). The study is carried out in the frame of C-BORD Horizon 2020 project, during which an efficient toolbox for high volume freight non-intrusive inspection (NII) is under development. Technologies for radiation monitoring are the part of the project. Particularly, detection of various radiological threats on country borders plays an important significant role in Homeland Security applications. Detection of illegal transfer of Special Nuclear Material (SNM) - 235U, 233U and 239Pu - is particular due to the potential use for production of nuclear weapon as well as radiological dispersal device (RDD) V known also as a “dirty bomb”. This technique relies on activation of 19F nuclei in the scintillator medium by fast neutrons and registration of high-energy β particles and γ-rays from the decay of reaction products. The radiation from SNM is detected after irradiation in order to avoid detector blinding. Despite the low 19F(n,α)16N or 19F(n,p)19O reaction cross-section, the method could be a good solution for detection of shielded nuclear material. Results obtained with the CaF2 detector were compared with the previous study done for BaF2 and 3He detector. These experimental results were obtained using 252Cf source and 9 MeV Varian Linatron M9 linear accelerator (LINAC). Finally, performance of the prompt neutron detection system based on CaF2 will be validated at Rotterdam Seaport during field trails in 2018.
Educating Architects in Turkish Culture, Gains and Loses: A Historical Perspective
Authors: Numan Ibrahim , Budi Santosa Revianto
Published: January 2018

Ottoman and Turkish architecture have exhibited a constancy and change in the course of history. Nevertheless these changes can only be understood by taking architectural education into account. Here it will be tried to discuss the gains and losses between the increase in the degree of architectural education/specialized knowledge and the blindness to the value judgements of the society and their reflection on the Turkish architecture. The edifice can not be separated from the architect, architect from the society; society and education from the idea. An architect is educated by society. Architect in turn is the product of the common idea of the civilisation he or she is affiliated to. Even a small diversity in the depth of belief or change in the approach in life style brings a deviation in the understanding of arts and architecture consequently architectural education also experience gains and losses along with it.
Using City Branding as the Part of the Intersection Point of Modernization and Tradition. Case Study: Surakarta City (Solo), Indonesia
Authors: Nursanty Eko , Alie Syahbana Joesron , Suprapti Atik
Published: January 2018

To recognize a city is part of a city branding effort. By recognizing the dwelling, the city's inhabitants are able to create a spatial space in accordance with their easily recognizable cultural identity. In city branding, the memory of a city space is often the main ingredient in strengthening the identity. The efforts to use place making forces at this time are often used to solve the failures in multi-cultural spaces. Evolution in history is part of dynamic space planning as part of the identity of a city.The purpose of this research is to reveal the relationship between the formation of tradition spaces that are able to function in a modern way. The pattern of this relationship will produce spatial planning patterns with special characters as well. Humans as space users play a very big role as a space builder, where the decisions they make are often based on the tradition they have used for generations.The methods used in this study are qualitative, deductive using the theories that have been there before. Field research is used as empirical data in the form of interviews, photographs and field observations was conducted in various existing city spaces in Solo with the purpose to discover the existence of distinctive spatial patterns based on the typical behavior that has been passed down continuously as a result of the cultural process. The resulting discovery is a significant pattern of relationships between humans and their decision-making abilities in city space. This decision is based on self-awareness as part of the space they occupy. In a group, this awareness is part of the tradition's heritage that continues to develop in accordance with the human intellectual development.
Parametric Design in Timber Gridshell Tectonics
Authors: Ismailiyah Al Athas Syarifah
Published: January 2018

This paper begins with a simple proposition: rather than mimicking the geometric structures found in nature, perhaps the most effective modes of sustainable fabrication can be found throughunderstanding the nature of materials themselves. The material becomes a design parameter through the constraints of fabrication tools, limitations of material size, and most importantly the productivecapacity of material resistance a given material’s capacity and tendencies to take shape, rather than cutting shape out of material. Gridshell structures provide an intriguing case study to pursue this proposition. Not only is there clear precedent in the form finding experiments of frei Otto and the institute for lightweight structures, but also the very nurbs based tools of current design practices developed from the ability of wood to bend. Taking the bent wood spline quite literally, gridshells provide a means that is at once formally expressive, structurally optimized, materially efficient, and quite simply a delight to experience. The the larger motivation of this work anticipates a parametric system linking the intrinsic material values of the gridshell tectonic with extrinsic criteria such as programmatic needs and environmental response. Through an applied case study of gridshells, the play between form and material is tested out through the author’s own experimentation with gridshells and the pedagogical results of two gridshell studios.The goal of this research is to establish a give and take relationship between top down formal emphasis and a bottom-up material influence.
Eartquake Vulnerability Level of Reconstructed Houses, Lesson Learned after Ten Years Java Eartquake 2006
Authors: Cholis Idham Noor , Mohd Munther
Published: January 2018

Ten years after devastating earthquake May 27 th, 2006, housing reconstruction in the affected area has been done and development is still undergoing. Since then, houses are constructed in various forms and quality. Unrestrained housing development contributes uncertain quality of the buildings in term of building safety. This study examines the level of earthquake vulnerability on the reconstruction houses in the area according to the structural firmness. The method used is by assessing the structural completeness, especially the upper part of building elements, synchronized by the five damages classification for grouping the building affected by the quake. This method is aimed to predict damage level for the future similar earthquake. The outcome of this study shows the level of earthquake vulnerability in the every sub-district. It does also compare the level of building safety differences
The Techniques of Participatory Design for Inclusive Public Space Provision in Kampung Kota of Surakarta
Authors: N.H Kusumaningdyah , Sparingga Purnamasari Lia
Published: January 2018

The technique of participatory design is essential for the future development knowledge of architecture to inform the improvement of architectural education and practice in Asia. Therefore to provide of inclusive public spaces for the community, this research article presents a field study of the usage of community participation design method in design and planning to provide inclusive public spaces within the kampung (settlements) in Surakarta, Indonesia. Surakarta has a problem to provide inclusive public space for its dense organic-informal kampung’s for the vulnerable populations such as children. Multi dimensional complexities of the kampung’s often challenge the notion of public space provision. Community participation approach arises as one of the preferred alternative methods to solve the problems with its basic community-based foundation. This research chose Sangkrah and Gandekan sub-districts as research locations both of the areas represent kampung’s characteristics and inhabited by many children population. Steps toward the goal of the study are; (1) field observation of the implementation of a community participation design through participatory place making project, and (2) examining typology assessment perspective, and (3) clarify participation techniques. This research used: (1) descriptive analysis for the project implementation, and (2) qualitative analysis for examining community’s perspectives. Through this multi-perspective analysis, this research presents the an alternative framework for implementing techniques community participation methods in design and planning to provide inclusive public spaces especially for children in Indonesia and other developing countries.
Interface spacing, stability, band offsets, and electronic properties on a (001) SrHfO3/GaAs interface: First-principles calculations
Authors: Shi Li-Bin , Li Ming-Biao , Xiu Xiao-Ming , Liu Xu-Yang , Zhang Kai-Cheng , Liu Yu-Hui , Li Chun-Ran , Dong Hai-Kuan
Published: January 2018

SrHfO3 is a potential dielectric material for metal–oxide–semiconductor devices. The SrHfO3/GaAs interface has attracted attention because of its unique properties. In this paper, the interface properties of (001) SrHfO3/GaAs are investigated by first-principles calculations based on density functional theory. First, the adsorption behavior of Sr, Hf, and O atoms on the GaAs surface is investigated. An O atom has a lower adsorption energy on a Ga surface than on an As surface. Then, some possible (001) SrHfO3/GaAs configurations are considered to analyze the interface spacing, stability, band offsets, and charge transfer. The SrO/Ga(1) and HfO2/Ga(2) configurations are lower in binding energy than other interface configurations, indicating that they are more stable. Finally, we study the electronic properties of the SrO/Ga(1) and HfO2/Ga(2) configurations. The electronic density of states suggests that these systems exhibit metallic behavior. The band offset and charge transfer are related to the interface spacing. The valence band offset and charge transfer decrease with increasing interface spacing.
Quantum and FLR effects on the Rayleigh Taylor instability of stratified plasmas
Authors: Tiwari Anita , Argal Shraddha , Khan Nusrat , Sharma P. K.
Published: January 2018

The combined effects of quantum corrections and finite Larmor radius (FLR) have been investigated on the linear hydrodynamic Rayleigh-Taylor (RT) instability of an incompressible stratified plasma. The basic quantum magnetohydrodynamic equations incorporating quantum and FLR effects are constructed and linearized under the small amplitude approximation. The general dispersion relation is derived considering appropriate magnetic field and density profiles using the normal mode analysis. It is analyzed numerically to study the effects of quantum and FLR corrections on the growth rate of RT instability in the stratified hydrodynamic fluids. It is found that the cut-off wavenumber (kmax) and critical wavenumber (kc) determining the growth rate of RT instability are modified due to the presence of FLR corrections and quantum effects. The FLR and quantum corrections have a stabilizing effect on the growth rate of RT instability of a stratified plasma.
Diffusion of a particle in the spatially correlated exponential random energy landscape: Transition from normal to anomalous diffusion
Authors: Novikov S. V.
Published: January 2018

Diffusive transport of a particle in a spatially correlated random energy landscape having exponential density of states has been considered. We exactly calculate the diffusivity in the nondispersive quasi-equilibrium transport regime for the 1D transport model and found that for slow decaying correlation functions the diffusivity becomes singular at some particular temperature higher than the temperature of the transition to the true non-equilibrium dispersive transport regime. It means that the diffusion becomes anomalous and does not follow the usual ∝ t1/2 law. In such situation, the fully developed non-equilibrium regime emerges in two stages: first, at some temperature there is the transition from the normal to anomalous diffusion, and then at lower temperature the average velocity for the infinite medium goes to zero, thus indicating the development of the true dispersive regime. Validity of the Einstein relation is discussed for the situation where the diffusivity does exist. We provide also some arguments in favor of conservation of the major features of the new transition scenario in higher dimensions.
Prediction and generation of binary Markov processes: Can a finite-state fox catch a Markov mouse?
Authors: Ruebeck Joshua B. , James Ryan G. , Mahoney John R. , Crutchfield James P.
Published: January 2018

Understanding the generative mechanism of a natural system is a vital component of the scientific method. Here, we investigate one of the fundamental steps toward this goal by presenting the minimal generator of an arbitrary binary Markov process. This is a class of processes whose predictive model is well known. Surprisingly, the generative model requires three distinct topologies for different regions of parameter space. We show that a previously proposed generator for a particular set of binary Markov processes is, in fact, not minimal. Our results shed the first quantitative light on the relative (minimal) costs of prediction and generation. We find, for instance, that the difference between prediction and generation is maximized when the process is approximately independently, identically distributed.
Mechanism of Na accumulation at extended defects in Si from first-principles
Authors: Park Ji-Sang , Chan Maria K. Y.
Published: January 2018

Sodium (Na) impurities in silicon solar cells are considered to play an important role in potential-induced degradation (PID), a significant cause of solar cell degradation and failure. Shorting due to Na accumulation at extended defects has been suggested as a culprit for PID. However, it is not clear how the extended defects are decorated by Na impurities. Using first-principles density functional theory calculations, we find that Na impurities segregate from the bulk into extended defects such as intrinsic stacking faults and Σ3 (111) grain boundaries. The energy barrier required for Na to escape from the extended defects is substantial and similar to the sum of the barrier energy in bulk Si (1.1–1.2 eV) and the segregation energy to the stacking fault (∼0.7 eV). Surprisingly, the migration barrier for Na diffusion within the extended defects is even higher than the energy barrier for escaping. The results suggest that the extended defects likely accumulate Na as the impurities segregate to the defects from the bulk, rather than because of migration through the extended defects.
Influence of N-type μc-SiOx:H intermediate reflector and top cell material properties on the electrical performance of “micromorph” tandem solar cells
Authors: Chatterjee P. , Roca i Cabarrocas P.
Published: January 2018

Amorphous silicon (a-Si:H) / micro-crystalline silicon (μc-Si:H), "micromorph" tandem solar cells have been investigated using a detailed electrical - optical model. Although such a tandem has good light absorption over the entire visible spectrum, the a-Si:H top cell suffers from strong light-induced degradation (LID). To improve matters, we have replaced a-Si:H by hydrogenated polymorphous silicon (pm-Si:H), a nano-structured silicon thin film with lower LID than a-Si:H. But the latter’s low current carrying capacity necessitates a thicker top cell for current-matching, again leading to LID problems. The solution is to introduce a suitable intermediate reflector (IR) at the junction between the sub-cells, to concentrate light of the shorter visible wavelengths into the top cell. Here we assess the suitability of N-type micro-crystalline silicon oxide (μc-SiOx:H) as an IR. The sensitivity of the solar cell performance to the complex refractive index, thickness and texture of such a reflector is studied. We conclude that N-μc-SiOx:H does concentrate light into the top sub-cell, thus reducing its required thickness for current-matching. However the IR also reflects light right out of the device; so that the initial efficiency suffers. The advantage of such an IR is ultimately seen in the stabilized state since the LID of a thin top cell is low. We also find that for high stabilized efficiencies, the IR should be flat (having no texture of its own). Our study indicates that we may expect to reach 15% stable tandem micromorph efficiency.
Molecular dynamics simulation of continuous nanoflow transport through the uneven wettability channel
Authors: Zhang Kai , Wang Feng-hui , Lu Yong-jun
Published: January 2018

It is necessary to understand and predict the behavior of continuous nanoflow, especially inside the nanochannel with uneven wettability. Because the properties of fluid confined in the nanochannel are different from the macroscopic fluid, molecular level understanding is critical for future applications. In this work, a series of molecular dynamics simulations were executed to investigate the effect of the wettability gradient on the continuous nanofluid. In the simulations, different osmotic pressures were applied to make the water transport through different nanochannels. Simulation data was analyzed to obtain water flow rate, shear viscosity, capillary force, density distributions along the height directions of channel and apparent friction factor. Results show that the uneven wettability has a significant effect on the transportation of confined water only under the proper applied osmotic pressure and the height of channel. Under the appropriate conditions, the uneven wettability has a promotion on the transportation of water when it is at the exit of channel. When the uneven wettability locates in the entrance and middle of the channel, the uneven wettability will hinder the transportation of water. Especially, it is worth mentioning that there is a special phenomenon when the height of the nanochannel becomes 0.8 nm. Depending on the applied osmotic pressure, the uneven wettability has a double-sided effect on the confined fluid inside the channel with H = 0.8 nm. Our work may contribute to the design of nanochannels.
Magneto-optical properties of BaTiO3/La0.76Sr0.24MnO3/BaTiO3 heterostructures
Authors: Moog M. , Singamaneni S. R. , Prater J. T. , Biegalski M. D. , Tsui F.
Published: January 2018

The magnetic properties of epitaxial BaTiO3/La0.76Sr0.24MnO3/BaTiO3 (BTO/LSMO/BTO) heterostructures have been studied using magneto-optic Kerr effect (MOKE) technique. Both longitudinal and polar MOKE were probed as a function of magnetic field and temperature (in the range between 80 and 320 K) for epitaxial films of BTO/LSMO/BTO and LSMO grown on TiO2-terminated SrTiO3 (001) substrates by pulsed laser deposition technique. The LSMO film without the BTO layers exhibits nearly square field-dependent MOKE hysteresis loops with low saturation fields below a bulk-like Curie temperature (TC) of ∼ 350K. In contrast, the film with the BTO layers exhibits a significantly suppressed TC of 155 K, accompanied by significantly enhanced coercive fields and perpendicular magnetic anisotropy.
The ferromagnetic resonance in WxMo1−x/YIG heterostructures
Authors: Ma L. , Lang L. L. , Zhou H. A. , Fan X. L. , Shi Z. , Fu H. R. , You C. Y. , Tian N.
Published: January 2018

The effective spin mixing conductance Gmixeff in WxMo1−x (WMo)/Y3Fe5O12 (YIG) heterostructure has been studied by the measurements of electron spin resonance and spin pumping technique which are based on the ferromagnetic resonance (FMR). It is interesting to find that the FMR linewidth for both YIG single layer and WMo/YIG heterostructures shows twofold and fourfold symmetry contributions although Gmixeff exhibits isotropic feature. The Gmixeff and resistivity ρ present a maximum and minimum value at x = 0.42 for WxMo1−x/YIG heterostructures, respectively, which could be ascribed to the complex phase constituents of the alloy films. This work emphasized that the consistent measurement orientation of YIG single layer and WMo/YIG heterostructures should be strictly obeyed to get the accurate Gmixeff owing to the anisotropic feature of in-plane FMR linewidth, which has always been ignored. Proper alloyed Mo could adjust the spin current related phenomenon of W based alloys, to achieve the high efficiency of spin current production from the large effective spin mixing conductance.
Non-reciprocal wave propagation in one-dimensional nonlinear periodic structures
Authors: Luo Benbiao , Gao Sha , Liu Jiehui , Mao Yiwei , Li Yifeng , Liu Xiaozhou
Published: January 2018

We study a one-dimensional nonlinear periodic structure which contains two different spring stiffness and an identical mass in each period. The linear dispersion relationship we obtain indicates that our periodic structure has obvious advantages compared to other kinds of periodic structures (i.e. those with the same spring stiffness but two different mass), including its increased flexibility for manipulating the band gap. Theoretically, the optical cutoff frequency remains unchanged while the acoustic cutoff frequency shifts to a lower or higher frequency. A numerical simulation verifies the dispersion relationship and the effect of the amplitude-dependent signal filter. Based upon this, we design a device which contains both a linear periodic structure and a nonlinear periodic structure. When incident waves with the same, large amplitude pass through it from opposite directions, the output amplitude of the forward input is one order magnitude larger than that of the reverse input. Our devised, non-reciprocal device can potentially act as an acoustic diode (AD) without an electrical circuit and frequency shifting. Our result represents a significant step forwards in the research of non-reciprocal wave manipulation.
Cu gettering by phosphorus-doped emitters in p-type silicon: Effect on light-induced degradation
Authors: Inglese Alessandro , Laine Hannu S. , Vähänissi Ville , Savin Hele
Published: January 2018

The presence of copper (Cu) contamination is known to cause relevant light-induced degradation (Cu-LID) effects in p-type silicon. Due to its high diffusivity, Cu is generally regarded as a relatively benign impurity, which can be readily relocated during device fabrication from the wafer bulk, i.e. the region affected by Cu-LID, to the surface phosphorus-doped emitter. This contribution examines in detail the impact of gettering by industrially relevant phosphorus layers on the strength of Cu-LID effects. We find that phosphorus gettering does not always prevent the occurrence of Cu-LID. Specifically, air-cooling after an isothermal anneal at 800°C results in only weak impurity segregation to the phosphorus-doped layer, which turns out to be insufficient for effectively mitigating Cu-LID effects. Furthermore, we show that the gettering efficiency can be enhanced through the addition of a slow cooling ramp (-4°C/min) between 800°C and 600°C, resulting in the nearly complete disappearance of Cu-LID effects.
Investigation of femtosecond laser induced ripple formation on copper for varying incident angle
Authors: Zuhlke Craig A. , Tsibidis George D. , Anderson Troy , Stratakis Emmanuel , Gogos George , Alexander Dennis R.
Published: January 2018

The hydrodynamic mechanisms associated with the formation of femtosecond laser induced ripples on copper for two angles of incidence are reported. Laser pulse length used for this work is 35 fs. A revised two-temperature model is presented that comprises transient changes of optical characteristics during the irradiation with femtosecond pulses to model relaxation processes and thermal response in bulk copper. The theoretical model takes into account the fluid flow dynamics that result in ripple periods shorter than the wavelength of the surface plasmon polaritons. Theoretical and experimental results are reported for incident angles of 0° and 45° relative to the surface normal. There is agreement between the experimentally measured and the theoretically predicted ripple periodicity for 50 pulses at 0° incidence. By contrast, for 100 pulses at 0° incidence, and 50 and 100 pulses at 45° incidence, the experimentally measured ripples have a larger period than the one predicted by the model while the trends in period with increased incident angle, and increased fluence are in agreement between the experimental and the theoretical results.
Nonsensing residues in S3–S4 linker’s C terminus affect the voltage sensor set point in K+ channels
Authors: Carvalho-de-Souza Joao L. , Bezanilla Francisco
Published: January 2018

Voltage sensitivity in ion channels is a function of highly conserved arginine residues in their voltage-sensing domains (VSDs), but this conservation does not explain the diversity in voltage dependence among different K+ channels. Here we study the non–voltage-sensing residues 353 to 361 in Shaker K+ channels and find that residues 358 and 361 strongly modulate the voltage dependence of the channel. We mutate these two residues into all possible remaining amino acids (AAs) and obtain Q-V and G-V curves. We introduced the nonconducting W434F mutation to record sensing currents in all mutants except L361R, which requires K+ depletion because it is affected by W434F. By fitting Q-Vs with a sequential three-state model for two voltage dependence–related parameters (V0, the voltage-dependent transition from the resting to intermediate state and V1, from the latter to the active state) and G-Vs with a two-state model for the voltage dependence of the pore domain parameter (V1/2), Spearman’s coefficients denoting variable relationships with hydrophobicity, available area, length, width, and volume of the AAs in 358 and 361 positions could be calculated. We find that mutations in residue 358 shift Q-Vs and G-Vs along the voltage axis by affecting V0, V1, and V1/2 according to the hydrophobicity of the AA. Mutations in residue 361 also shift both curves, but V0 is affected by the hydrophobicity of the AA in position 361, whereas V1 and V1/2 are affected by size-related AA indices. Small-to-tiny AAs have opposite effects on V1 and V1/2 in position 358 compared with 361. We hypothesize possible coordination points in the protein that residues 358 and 361 would temporarily and differently interact with in an intermediate state of VSD activation. Our data contribute to the accumulating knowledge of voltage-dependent ion channel activation by adding functional information about the effects of so-called non–voltage-sensing residues on VSD dynamics.
The Kurdyka–Łojasiewicz–Simon inequality and stabilisation in nonsmooth infinite-dimensional gradient systems
Authors: Chill Ralph , Mildner Sebastian
Published: January 2018

We state and reprove a stabilisation result for solutions of abstract gradient systems associated with nonsmooth energy functions on infinite- dimensional Hilbert spaces. The main feature is the introduction of a convenient topology on the effective domain of the energy function, and that in this general setting the usual assumption on the relative compactness of the range of the solution in the energy space can be considerably relaxed to relative compactness of the range in the ambient Hilbert space. This simplifies the applicability of the stabilisation result even in the case of smooth energies.
A Jensen–Rohrlich type formula for the hyperbolic 3-space
Authors: Herrero S. , Imamoḡlu Ö. , von Pippich A.-M. , Tóth Á.
Published: January 2018

We give a Jensen–Rohrlich type formula for a certain class of automorphic functions on the hyperbolic 3-space for the group

P
S
L

2

(

O

K

)

\mathrm {PSL}_2(\mathcal {O}_K)

.