Showing papers in "MRS Proceedings in 2014"
TL;DR: In this paper, a particular type of FO sensors, fiber Bragg grating (FBG) sensors, were externally attached to lithium ion pouch cells for monitoring additional informative cell parameter such as strain and temperature.
Abstract: The problems of using performance parameters such as voltage, current and temperature measured with electrical sensors in today’s battery management systems (BMS) are well known. These parameters can be weakly informative about cell state, particularly as cells age, and contribute to over-conservative utilization and oversizing of a battery pack. Fiber optic (FO) sensors can offer an interesting alternative to conventional electrical sensors, with several advantages such as high selective sensitivity to various parameters, light weight, robustness to EMI, and multiplexing capabilities. In this study, a particular type of FO sensors, fiber Bragg grating (FBG) sensors were externally attached to lithium ion pouch cells for monitoring additional informative cell parameter such as strain and temperature. Multiple charge and discharge cycle were performed to examine the qualification of these signals for cell state estimation in BMS. In comparison to corresponding measurements using conventional electrical sensors, the FBG signals showed very promising results for utilization in effective BMS.
27 citations
TL;DR: In this paper, the impact of the Schottky barrier height on the symmetry of Silicon nanowire RFET transfer characteristics and their performance within circuits is analyzed, showing that germanium-based RFETs of the same dimensions will show a distinctly increased performance, making them a promising material solution for future reconfigurable electronics.
Abstract: Reconfigurable nanowire transistors provide the operation of unipolar p-type and n-type FETs freely selectable within a single device. The enhanced functionality is enabled by controlling the currents through two individually gated Schottky junctions. Here we analyze the impact of the Schottky barrier height on the symmetry of Silicon nanowire RFET transfer characteristics and their performance within circuits. Prospective simulations are carried out, indicating that germanium nanowire based RFETs of the same dimensions will show a distinctly increased performance, making them a promising material solution for future reconfigurable electronics.
26 citations
TL;DR: In this paper, the authors highlight some of the advantages and challenges specific to the application of organic photovoltaic (OPV) in the field of building integration, including the ability to adapt semi-transparency, color and shape of the module.
Abstract: If a photovoltaic (PV) technology is assessed today in a technical framework, then efficiency is the most commonly addressed parameter, followed by service lifetime. Cost, as the third parameter of the “magic triangle”, is even less often reported. However, if a new technology is prepared to enter a market, other important parameters have to be considered, especially if non-standard PV applications are targeted. Organic photovoltaic (OPV) is a well known but young PV technology of the so called third generation, which offers unique advantages for integrated products such as building integrated photovoltaics (BIPV). In this contribution we would like to highlight some of the advantages and challenges which are specific to the application of OPV in the field of building integration. Architectural design features of OPV include the ability to adapt semi-transparency, color and shape of the module. Moreover, glass-laminated OPV modules are deemed suitable for BIPV because of their ease of integration, good fire resistance, high energy harvest per nominal watt-peak and long lifetimes.
24 citations
TL;DR: Spana as mentioned in this paper is a set of Java programs that can be used to draw chemical-equilibrium diagrams and perform radionuclide speciation and solubility calculations of minerals, including solubability calculations relevant for the performance assessment of a nuclear waste repository.
Abstract: A set of computer programs has been developed to draw chemical-equilibrium diagrams. This new software is the Java-language equivalent to the Medusa/Hydra software (developed some time ago in Visual basic at the Royal Institute of Technology, Stockholm, Sweden). The main program, now named “Spana” calls Java programs based on the HaltaFall algorithm. The equilibrium constants that are needed for the calculations may be retrieved from a database included in the software package (“Database” program). This new software is intended for undergraduate students as well as researchers and professionals. The “Spana” code can be easily applied to perform radionuclide speciation and solubility calculations of minerals, including solubility calculations relevant for the performance assessment of a nuclear waste repository. In order to handle ionic strength corrections in such calculations several approaches can be applied. The “Spana” code is able to perform calculations based on three models: the Davies equation; an approximation to the model by Helgeson et al. (HKF); and the Specific Ion-Interaction Theory (SIT). Default SIT-coefficients may be used, which widens the applicability of SIT significantly. A comparison is made here among the different ionic strength approaches used by “Spana” (Davies, HKF, SIT) when modelling the chemistry of radionuclides and minerals of interest under the conditions of a geological repository for nuclear waste. For this purpose, amorphous hydrous Thorium(IV) oxide (ThO2(am)), Gypsum (CaSO4·2H2O) and Portlandite (Ca(OH)2) solubility at high ionic strengths have been modelled and compared to experimental data from the literature. Results show a good fitting between the calculated values and the experimental data especially for the SIT approach in a wide range of ionic strengths (0-4 M).
24 citations
TL;DR: In this paper, the authors describe methods to describe the evolution of dislocation systems in terms of a limited number of continuous field variables while correctly representing the kinematics of systems of flexible and connected lines.
Abstract: We discuss methods to describe the evolution of dislocation systems in terms of a limited number of continuous field variables while correctly representing the kinematics of systems of flexible and connected lines. We show that a satisfactory continuum representation may be obtained in terms of only four variables. We discuss the consequences of different approximations needed to formulate a closed set of equations for these variables and propose a benchmark problem to assess the performance of the resulting models. We demonstrate that best results are obtained by using the maximum entropy formalism to arrive at an optimal estimate for the dislocation orientation distribution based on its lowest-order angular moments.
24 citations
TL;DR: In this paper, the correlation of stress in Silicon Carbide (SiC) crystal and frequency shift in micro- Raman spectroscopy was determined by an experimental method, which revealed that the linearity coefficients between stress and Raman shift were -1.96 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (0001) face, -2.08 cm- 1 /GPa on FTO (2/ 4)E 2 on 4-H- SiC (11-20) face and -2
Abstract: The correlation of stress in Silicon Carbide (SiC) crystal and frequency shift in micro- Raman spectroscopy was determined by an experimental method. We applied uniaxial stress to 4H- and 6H-SiC single crystal square bar specimen shaped with (0001) and (11-20) faces by four point bending test, under measuring the frequency shift in micro-Raman spectroscopy. The results revealed that the linearity coefficients between stress and Raman shift were -1.96 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (0001) face, -2.08 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (11-20) face and -2.70 cm-1/GPa for FTO(2/6)E2 on 6H-SiC (0001) face. Determination of these coefficients has made it possible to evaluate the residual stress in SiC crystal quantitatively by micro-Raman spectroscopy. We evaluated the residual stress in SiC substrate that was grown in our laboratory by utilizing the results obtained in this study. The result of estimation indicated that the SiC substrate with a diameter of 6 inch remained residual stress as low as ±15 MPa.
23 citations
TL;DR: The magnetocaloric effect of chemically synthesized Mn0.3Zn0.7Fe2O4 superparamagnetic nanoparticles with average crystallite size of 11 nm is reported in this article.
Abstract: The magnetocaloric effect of chemically synthesized Mn0.3Zn0.7Fe2O4 superparamagnetic nanoparticles with average crystallite size of 11 nm is reported. The magnitude of the magnetic entropy change (ΔSm), calculated from magnetization isotherms in the temperature range of 30 K to 400 K, increases from - 0.16 J-kg−1K−1 for a field of 1 T to - 0.88 J-kg−1K−1 for 5 T at room temperature. Our results indicate that ΔSM values are much higher than primarily reported values for this class of nanoparticles. ΔSM is not limited to the ferromagnetic-paramagnetic transition temperature; instead, it occurs over a broad range of temperatures, resulting in high relative cooling power.
22 citations
TL;DR: In this paper, the synthesis and characterization of NixFe3-xO4 and CoxFe3XO4 redox nanomaterials using sol-gel method was reported.
Abstract: In this contribution, we report the synthesis and characterization of NixFe3-xO4 and CoxFe3-xO4 redox nanomaterials using sol-gel method. These materials will be used to produce solar fuels such as H2 or syngas from H2O and/or CO2 via solar thermochemical cycles (STCs). For the sol-gel synthesis of ferrites, the Ni, Co, Fe precursor salts were dissolved in ethanol and propylene oxide (PO) was added dropwise to the well mixed solution as a gelation agent to achieve gel formation. Freshly synthesized gels were aged, dried, and calcined by heating them to 600°C in air. The calcined powders were characterized by powder x-ray diffractometer (XRD), BET surface area, as well as scanning (SEM) and transmission (TEM) electron microscopy. Their suitability to be used in STCs for the production of solar fuels was assessed by performing several reduction/re-oxidation cycles using a thermogravimetric analyzer (TGA).
21 citations
TL;DR: In this article, the effects of process variation on the impedance characteristics of programmable metallization cells (PMC) in both HRS and LRS were examined through numerical simulation.
Abstract: Among the new non-volatile memories gaining attention as a potential replacement for flash technology is the programmable metallization cell (PMC) that works by creating and dissolving a conductive bridge across a solid electrolyte film. This enables switching between a high resistance state (HRS) and a low resistance state (LRS). The dominant mechanism for resistance switching is field dependent ion transport in the film. In this work, we examine, through numerical simulation, the effects of process variation on the impedance characteristics of the PMC in both HRS and LRS, by changing key parameters of the device. These parameters include the material bandgap, affinity and permittivity of each device layer. Finally, we show which parameters have the greatest effects on the impedance behavior.
20 citations
TL;DR: In this article, the authors investigated charge generation and transport in CH3NH3PbI3-xClx based mesostructured solar cells and proved the existence of oriented permanent dipoles, consistent with the hypothesis of an ordered perovskite layer close to the oxide surface.
Abstract: Charge generation and transport in CH3NH3PbI3-xClx based mesostructured solar cells are investigated. Time correlated single photon counting analysis proves highly efficient charge generation and provides insights on the structural properties of perovskite films. Photoinduced absorption and transient photovoltage analyses depict a double charge recombination dynamics suggesting the existence of two complementary paths for electron transport, involving either TiO2 and perovskite matrixes. Stark spectroscopy, a powerful tool allowing interface-sensitive analysis, is employed to prove the existence of oriented permanent dipoles, consistent with the hypothesis of an ordered perovskite layer close to the oxide surface. This evidence is also confirmed by first principle DFT calculations. The existence of a structural order, promoted by specific local interactions, could be one of the decisive reasons for highly efficient carriers transport within perovskite films.
18 citations
TL;DR: In this paper, the effect of coupling between nanotubes on the phonons was investigated in two model nano-systems: (i) a bundle of two non-identical SWNTs (inhomogeneous dimer), and (ii) double-walled carbon-nanotubes.
Abstract: Combining high resolution transmission electron spectroscopy, electron diffraction, and resonant Raman spectroscopy experiments on the same suspended (free-standing) individual carbon nanotubes is the ultimate approach to relate unambiguously the structure and the intrinsic phonon features of these nano-systems. By using this approach, the effect of coupling between nanotubes on the phonons is investigated in two model nano-systems: (i) a bundle of two non-identical SWNTs (inhomogeneous dimer), (ii) double-walled carbon nanotubes.
TL;DR: Coahuilite, a new variety of amber from the Late Cretaceous Olmos Formation (ca. 73 Ma), Coahuila, north of Mexico, is described in this article.
Abstract: Coahuilite, a new variety of amber is described from the Late Cretaceous Olmos Formation (ca. 73 Ma.), Coahuila, north of Mexico. This amber is totally distinct chemically and stratigraphically from the Miocene Chiapas amber (ca. 23-13 Ma.), Southern Mexico, which according to mineral nomenclature is currently known as Simojovelite var. nov. Additionally, an emended description of Bacalite is proposed, based on the physicochemical analysis and geological record of a fossil resin recently recovery from the Late Cretaceous El Gallo Formation (ca. 73 Ma.), Baja California, northwestern Mexico. The results are supported by characterization of such ambers using synchrotron-based Infrared (FTIR) microspectroscopy.
TL;DR: In this article, the authors developed efficient coarse-grained classical Monte Carlo (MC) methods to simulate the order of the molecular components in an organic nonlinear optical (ONLO) material in electro-optic modulators.
Abstract: The use of organic nonlinear optical (ONLO) materials in electro-optic (EO) modulators requires that the active molecular components (chromophores) be acentrically oriented. The fundamental molecular constituents are in a condensed, glassy phase. Molecular orientation in such systems is typically achieved by applying a DC poling field to the glassy material. We are developing efficient coarse-grained classical Monte Carlo (MC) methods to simulate the order of such systems. The most challenging aspects of these simulations are convergence to an experimentally relevant equilibrium ensemble and verification of simulation accuracy. We use a variety of molecular descriptions and a variety of MC methods to achieve proper order in the shortest number of computational cycles possible. Herein, we illustrate a few examples of the types of calculations and compare with experimental results with representative amorphous organic materials, including electro-optic chromophores.
TL;DR: In this paper, a novel matrix with increasing pore volume from one end to other, along the matrix length, was designed and developed to support osteochondral tissue engineering while forming a seamless interface between the cartilage and the bone matrix, where the microsphere and hydrogel phases co-exist with opposing gradients.
Abstract: Osteochondral (OC) tissue is comprised of articular cartilage, the subchondral bone and the central cartilage-bone interface. To facilitate proper regeneration, an equally complex and multiphasic matrix must be used. Although mono-phasic and bi-phasic matrices were previously applied, they failed to establish the OC interface upon regeneration. In this study, we designed and developed a novel matrix with increasing pore volume from one end to other, along the matrix length. For this matrix polylactide-co-glycolide (PLGA) 85:15 microspheres were combined with a water-soluble porogen in a layer-by-layer fashion and thermally sintered. The resulting matrix was then porogen-leached to form a gradiently-porous structured matrix. The formation of this gradient pore structure was established using Micro-Computed Tomography (μCT) scanning. A biodegradable hydrogel was infiltrated into the structure to form a unique OC matrix where the microsphere and hydrogel phases co-exist with opposing gradients. When the individual phases are associated with osteogenic and chondrogenic growth factors, the structureinduced factor delivery might provide the spatially controlled factor delivery necessary to regenerate osteochondral tissue structure. Overall, we designed a gradient matrix system that is expected to support osteochondral tissue engineering while forming a seamless interface between the cartilage and the bone matrix.
TL;DR: In this article, the electrical and optical properties of room temperature deposited zinc-tin oxide thin films are discussed and the resistivity has been controlled over seven orders of magnitude via the oxygen growth pressure.
Abstract: For a cost-efficient fabrication of homogeneous oxide thin films the usage of amorphous materials is favorable. They can be deposited at room temperature (RT) and represent an interesting alternative to amorphous silicon in electronics. Zinc-tin oxide is a promising n-type channel material for thin film transistors and consists of abundant elements, only, in contrast to the well-explored indium gallium zinc oxide. Here, the electrical and optical properties of room temperature deposited ZTO thin films are discussed. These films were fabricated via pulsed-laser deposition on glass substrates by ablating a ceramic target composed of ZnO and SnO2 in a 1:2 ratio. The resistivity has been controlled over seven orders of magnitude via the oxygen growth pressure. Further, the optical transmittance tends to be higher for higher oxygen growth pressures.
TL;DR: In this article, an oil-in-water (o/w) emulsion was prepared using starch molecules as the stabilizer/emulsifier, and the physical stability, oxygen permeability and release of curcumin from the starch Pickering emulsion in simulated saliva fluid (SSF) were determined.
Abstract: The goal of this study was to determine the potential use of starch Pickering emulsion as a vehicle to deliver a natural phenolic compound, curcumin in the oral cavity. To this end, an oil-in-water (o/w) emulsion was prepared using starch molecules as the stabilizer/emulsifier. The physical stability, oxygen permeability and release of curcumin from the starch Pickering emulsion in simulated saliva fluid (SSF) were determined. The results of this study showed that the starch stabilized o/w emulsions were stable for up to 2 weeks. The starch Pickering emulsion also provided better protection against oxidation than a surfactant-stabilized emulsion, and the digestion of the starch Pickering emulsion using amylase led to the complete disruption and phase separation of the emulsion.
TL;DR: In this article, contemporary methods for dispersion of carbon nanotubes in water and non-aqueous media are discussed, including ultrasonic, plasma and other physical techniques, as well as the use of surfactants, functionalizing and debundling agents.
Abstract: Contemporary methods for dispersion of carbon nanotubes in water and non-aqueous media are discussed. Main attention is paid to ultrasonic, plasma techniques and other physical techniques, as well as to the use of surfactants, functionalizing and debundling agents of distinct nature (elemental substances, metal and organic salts, mineral and organic acids, oxides, inorganic and organic peroxides, organic sulfonates, polymers, dyes, natural products, biomolecules, and coordination compounds).
TL;DR: In this article, the structural, optical, and electrical properties of thin film WSe2 grown via the selenization of sputter deposited tungsten films are presented. And the authors employ these results to numerically simulate solar cells based on this material, where they show efficiencies greater than 20% are possible.
Abstract: An excellent candidate for an earth abundant absorber material is WSe2 which can be directly grown as a p-type semiconductor with a band gap near 1.4 eV. In this work we present the structural, optical, and electrical properties of thin film WSe2 grown via the selenization of sputter deposited tungsten films. We will show that highly textured films with an optical band gap in range of 1.4 eV, and absorption coefficients greater than 105/cm across the visible spectrum can be easily achieved. In addition we will present Hall Effect and carrier density measurements as well, where will show densities in the 1017cm-3 range and p-type Hall mobilities greater than 10 cm2/V-s range can be obtained. We employ these results to numerically simulate solar cells based on this material, where we will show efficiencies greater than 20% are possible.
TL;DR: In this article, a critical discussion on four important parameters, including interface quality, material properties, deposition parameters, and residual stress, is given to predict the fatigue limit of a cold spray system as a function of residual stress.
Abstract: Cold spray is a novel and promising technology to obtain surface coating Notwithstanding the several technological advantages with respect to other processes, its diffusion is somewhat limited because of the limited knowledge on the mechanical properties of the cold sprayed materials and in particular, the fatigue behavior Moreover, the existing data concerning fatigue behavior of coated specimens are controversial and different material system shows different behaviors The aim of this study is to distinguish the involved parameters and their effect on fatigue behavior of cold sprayed systems A critical discussion on four important parameters ie interface quality, material properties, deposition parameters and residual stress is given The influential parameters are consolidated in one formula, which can predict the fatigue limit of cold spray system as a function of residual stress, coating hardness and stress gradient in the specimen
TL;DR: In this paper, a novel and simple technique is developed to characterize the behavior of an artificial lipid bilayer interface containing mechano-sensitive (MS) channels, and the results show that the response of channel activity to mechanical stimuli is voltage-dependent and highly related to the frequency and amplitude of oscillations.
Abstract: This paper presents the first attempts to study the large conductance mechano-sensitive channel (MscL) activity in an artificial droplet interface bilayer (DIB) system. A novel and simple technique is developed to characterize the behavior of an artificial lipid bilayer interface containing mechano-sensitive (MS) channels. The experimental setup is assembled on an inverted microscope and consists of two micropipettes filled with PEG-DMA hydrogel and containing Ag/AgCl wires, a cylindrical oil reservoir glued on top of a thin acrylic sheet, and a piezoelectric oscillator actuator. By using this technique, dynamic tension can be applied by oscillating axial motion of one droplet, producing deformation of both droplets and area changes of the DIB interface. The tension in the artificial membrane will cause the MS channels to gate, resulting in an increase in the conductance levels of the membrane. The results show that the MS channels are able to gate under an applied dynamic tension. Moreover, it can be concluded that the response of channel activity to mechanical stimuli is voltage-dependent and highly related to the frequency and amplitude of oscillations.
TL;DR: In this article, leaching tests were conducted using an irradiated Zry cladding tube from a boiling-water reactor (BWR) to obtain leaching data and to investigate the relationship between Zry metal corrosion and C-14 release behavior.
Abstract: C-14 contained in Hull waste is one of the most important radionuclides in the safety assessment of transuranic (TRU) waste disposal. For more realistic safety assessment, it is important to clarify the release mechanism and chemical species of C-14 from Hull waste. In this research, leaching tests were conducted using an irradiated Zry cladding tube from a boiling-water reactor (BWR) to obtain leaching data and to investigate the relationship between Zry metal corrosion and C-14 release behavior. Both organic and inorganic C-14 compounds existed in the the liquid phase, and some C-14 moved to the gaseous phase. The release rate of C-14 obtained from the BWR cladding tube after two-year leaching tests was lower than the release rate from a pressurize water reactor (PWR) cladding tube. It is considered that the BWR cladding tube used in this test did not easily corrode since it used a comparatively new material. The release rate of C-14 was slightly lower as compared with the corrosion rate of unirradiated Zry. This is thought to be the result of improved corrosion resistance conferred by neutron irradiation, which encouraged the dissolution of grain boundary precipitation elements, such as Fe, Cr, and Ni, into the crystal grains. The leaching tests will be continued for 10 years.
TL;DR: In this paper, the (P/Pmax) - (Rh,th / Rc,th) relationship was analyzed for thermal energy recovery in a TE power generation system, and the non-dimensional functional relationships were defined for various electrical contact resistances, differing thermal loss factors, and at various hot side/cold side temperature conditions.
Abstract: Thermoelectric energy recovery is an important technology for recovering waste thermal energy in high-temperature industrial, transportation and military energy systems. Thermoelectric (TE) power systems in these applications require high performance hot-side and cold-side heat exchangers to provide the critical temperature differential and transfer the required thermal energy to create the power output. Hot-side and cold-side heat exchanger performance is typically characterized by hot-side and cold-side thermal resistances, Rh,th and Rc,th, respectively. Heat exchanger performance determines the hot-side temperature, Th, and cold-side temperature, Tc, conditions when operating in energy recovery environments with available temperature differentials characterized by exhaust temperatures, Texh, and ambient temperature, Tamb. This work analytically defined a crucially important design relationship between (P/Pmax) and (Rh,th / Rc,th) in TE power generation systems to determine the optimum ratio of (Rh,th / Rc,th) maximizing TE system power. A sophisticated integrated TE device / heat exchanger analysis was used, which simultaneously integrates hot- and cold-side heat exchanger models with TE device optimization models incorporating temperature-dependent TE material properties for p-type and n-type materials, thermal and electrical contact resistances, and hot side and cold side heat loss factors. This work examined the (P/Pmax) - (Rh,th / Rc,th) relationship for system designs employing single-material and segmented-material TE couple legs with various TE material combinations, including bismuth telluride alloys, skutterudite compounds, and skutterudite / bismuth telluride segmented combinations. This work defined the non-dimensional functional relationships and found the optimum thermal resistance condition: (Rh,th / Rc,th)opt > 10 to 30 created the maximum power output in TE optimized designs for various TE material combinations investigated. The non-dimensional relationships were investigated for various electrical contact resistances, differing thermal loss factors, and at various hot-side/cold-side temperature conditions. This work showed that the non-dimensional functional relationships were invariant under these differing conditions. It was determined that a condition of (Rh,th / Rc,th) = 1 creates power output far below maximum power conditions. The (P/Pmax) - (Rh,th / Rc,th) relationship also dictated certain temperature profile conditions, defined by the parameter, (Th – Tc) / (Texh – Tamb), which were directly associated with design points in this relationship including maximum power points. The value of (Th – Tc) / (Texh – Tamb) was generally less than 0.5 at maximum power conditions in TE energy recovery designs using TE materials investigated here. The wide-ranging ramifications on TE energy recovery systems and their design optimization for industrial and transportation-related applications are discussed.
TL;DR: In this article, the authors demonstrate a surface micromachined fabrication approach for integrated addressable metal electrodes within centimeter-long nanofluidic channels using a low-temperature, xenon diflouride dry-release method for novel biosensing applications.
Abstract: Electrokinetic based micro- and nanofluidic technologies provide revolutionary opportunities to separate, identify and analyze biomolecular species. Key to fully harnessing the power of such systems is the development of a robust method for integrated electrodes as well as a thorough understanding of the influence of the electrokinetic surface properties with and without different surface modifications. In this work, we demonstrate a surface micromachined fabrication approach for integrated addressable metal electrodes within centimeter-long nanofluidic channels using a low-temperature, xenon diflouride dry-release method for novel biosensing applications, as well as recent results from a joint theoretical and experimental study of electrokinetic surface properties in nano- and microfluidic channels fabricated with fused silica. The main contribution of this fabrication process involves the addition of addressable electrodes to a novel dry-release channel fabrication method, produced at <300°C, to be used in nanofluidic electronic sensing of biomolecules. Finally, we also show a novel method with which to coat our channels with silane based chemistries. Certain modifications are observed to show improved resistance to non-specific adhesion of both small molecules and proteins, indicating their further use as compatible surfaces in micro- and nanofluidic applications.
TL;DR: In this article, a biodegradable foams were produced using cellulose nanofibrils (CNFs) and starch (S) in a freeze-drying process with CNF/S water suspensions ranging from 1 to 7.5 wt.
Abstract: In this study, biodegradable foams were produced using cellulose nanofibrils (CNFs) and starch (S). The availability of high volumes of CNFs at lower costs is rapidly progressing with advances in pilot-scale and commercial facilities. The foams were produced using a freeze-drying process with CNF/S water suspensions ranging from 1 to 7.5 wt. % solids content. Microscopic evaluation showed that the foams have a microcellular structure and that the foam walls are covered with CNF’s. The CNF’s had diameters ranging from 30 nm to 100 nm. Pore sizes within the foam walls ranged from 20 nm to 100 nm. The materials’ densities ranging from 0.012 to 0.082 g/cm3 with corresponding porosities between 93.46% and 99.10%. Thermal conductivity ranged from 0.041 to 0.054 W/m-K. The mechanical performance of the foams produced from the starch control was extremely low and the material was very friable. The addition of CNF’s to starch was required to produce foams, which exhibited structural integrity. The mechanical properties of materials were positively correlated with solids content and CNF/S ratios. The mechanical and thermal properties for the foams produced in this study appear promising for applications such as insulation and packaging.
TL;DR: The role of glissile junctions forming during plastic deformation under various loading scenarios is in the center of interest in this article, where the activity of these naturally forming dislocation sources is followed in detail.
Abstract: The plasticity of micro-pillar deformation has widely been studied by discrete dislocation dynamics simulations to explain the so-called size effect. In this study the role of glissile junctions forming during plastic deformation under various loading scenarios is in the center of interest. The activity of these naturally forming dislocation sources is followed in detail. Surprisingly these junctions are rather active sources and not just another obstacle as often assumed. Their relative contribution to the overall dislocation density for the simulated specimens reaches often values of 20% or even more. The formation of such a glissile junction is often correlated to stress drops or the end of a stress drop. It is therefore suggested – at least for the sample sizes considered – that this dislocation multiplication mechanism should be take into account in continuum models such as crystal plasticity of higher order dislocation continuum theories.
TL;DR: In this article, a drift-diffusion simulation of the time evolution of the oxygen vacancy distribution in the virtual cathode (VC) was performed to identify the influence of process driving parameters on the evolution of VC region.
Abstract: Resistively switching devices have attracted great attention for potential use in future nonvolatile information storage. Among various oxide materials that show resistive switching (RS) behavior, SrTiO3 (STO) is regarded as a model material to study the effect of valence changes accompanying RS in the oxide [1]. In this class of materials, the RS effect is attributed to rely on the migration of oxygen vacancies and an associated valence change in the cation sublattice. To achieve a switchable state, an initial electroforming step is typically required, which is believed to create conductive regions in the insulating material [2]. Under high electrical stress, an oxygen-deficient region, often referred to as the virtual cathode (VC), is formed [3]. The RS occurs across a very short distance between the VC and the anode, allowing for very short switching times. As the electroforming step greatly impacts the device performance and switching variability, its understanding is essential for device optimization. Electroforming is affected by multiple parameters, e.g. voltage, current, temperature, dopant and defect concentrations, ambient gas atmosphere and time. Distinguishing the influence of the particular parameters is a desirable aim and challenging task. Electrocoloration of Fe-doped STO single crystals has proven a valuable means to visualize valence changes of the Fe ions and is thus suitable to study the formation of the VC. Therefore, we performed electrocoloration experiments and used high resolution transmission light optical microscopy to make the redoxprocesses during electroforming visible. The influence of process driving parameters on the evolution of the VC region is studied. The evolution of the VC is interpreted by drift-diffusion simulation of the time evolution of the oxygen vacancy distribution.
TL;DR: In this paper, the authors modify the evolution equations of the simplified continuum dislocation dynamics theory presented in [T. Hochrainer, S. Sandfeld, M. Zaiser, P. Gumbsch] to account for the nature of the curvature density as a conserved quantity.
Abstract: In the current paper we modify the evolution equations of the simplified continuum dislocation dynamics theory presented in [T. Hochrainer, S. Sandfeld, M. Zaiser, P. Gumbsch, Continuum dislocation dynamics: Towards a physical theory of crystal plasticity. J. Mech. Phys. Solids. (in print)] to account for the nature of the so-called curvature density as a conserved quantity. The derived evolution equations define a dislocation flux based crystal plasticity law, which we present in a fully three-dimensional form. Because the total curvature is a conserved quantity in the theory the time integration of the equations benefit from using conservative numerical schemes. We present a discontinuous Galerkin implementation for integrating the time evolution of the dislocation state and show that this allows simulating the evolution of a single dislocation loop as well as of a distributed loop density on different slip systems.
TL;DR: In this article, a detailed group theoretical analysis demonstrates that point defects reduce the local symmetry, lift the Raman selection rules, and thus diminish the distinction between Raman allowed and Raman forbidden lattice vibrations.
Abstract: The semiconductor cuprous oxide crystallizes in a simple cubic structure and reveals outstanding characteristics: Independent of the method and conditions of the synthesis of crystalline Cu2O its Raman spectra are dominated by infrared active, silent, and defect modes rather than by Raman allowed phonon modes only. A detailed group theoretical analysis demonstrates that point defects reduce the local symmetry, lift the Raman selection rules, and thus diminish the distinction between Raman allowed and Raman forbidden lattice vibrations. Of all intrinsic defects only the presence of the copper vacancy in the so called split configuration introduces possible Raman activity for all Cu2O extended phonon modes observed in experiment.
TL;DR: In this paper, the strong exothermic reaction of lithium with carbon dioxide (CO2) yields thermal energy directly comparable to the combustion of coal or methane in an oxygen containing atmosphere.
Abstract: In this work, electrochemically recyclable lithium is analyzed as high energy density, large scale storage material for stranded renewable energy in a closed loop. The strongly exothermic reaction of lithium with carbon dioxide (CO2) yields thermal energy directly comparable to the combustion of coal or methane in an oxygen containing atmosphere. The thermal level of the reaction is sufficient for re-electrification in a thermal power plant compatible process. The reaction of single lithium particles, avoiding particle-particle interactions, is compared to the combustion of atomized lithium spray in a CO2 containing atmosphere. Particle temperatures of up to 4000K were found for the reaction of single lithium particles in a CO2, nitrogen (N2), oxygen (O2) and steam gas mixture. Furthermore the combustion of atomized lithium spray in both dry CO2 atmosphere and CO2/steam gas mixture was analyzed. The identified solid reaction products are lithium carbonate, lithium oxide and lithium hydroxide. The formation of carbon monoxide (CO) as gaseous reaction product is demonstrated. Carbon monoxide is a valuable by-product, which could be converted to methanol or gasoline using hydrogen.
TL;DR: The Crystallography Open Database (COD) as mentioned in this paper is an open-access source for the structures of small molecules and small to medium-sized unit cell crystals, and it has been used extensively in interdisciplinary education.
Abstract: Complementing a multitude of activities around the International Year of Crystallography, we report here on a few resources that are helpful for integrating basic crystallography into interdisciplinary college education. We concentrate on four resources with which we are directly involved. The Crystallography Open Database (COD) features currently more than 295,000 entries and has over the last decade developed into the world’s premier open-access source for the structures of small molecules and small to medium sized unit cell crystals. ‘Educational offshoots’ of the COD with approximately a thousand entries combined provide structural information on small molecules, selected macromolecules, crystal structures, grain boundaries, and crystal morphologies in the well documented Crystallographic Information Framework (CIF) file format. This information can be displayed interactively on the website http://nanocrystallography.research.pdx.edu and freely downloaded. Files that allow for the printing of selected database entries on any 3D printer have been added to this site and are also freely downloadable. These files were created with the programs Cif2VRML and WinXMorph that convert CIF files directly into 3D printing files. Interested college educators are invited to visit our open access crystallography resource portal and suggest other resources that should receive wider exposure over this portal.