An a posteriori error-estimation framework is introduced to quantify and reduce modeling errors resulting from approximating complex mesoscale material behavior with a simpler macroscale model. Such errors may be prevalent when modeling welds and additively manufactured structures, where spatial variations and material textures may be present in the microstructure. We consider a case where a <100> fiber texture develops in the longitudinal scanning direction of a weld. Transversely isotropic elastic properties are obtained through homogenization of a microstructural model with this texture and are considered the reference weld properties within the error-estimation framework. Conversely, isotropic elastic properties are considered approximate weld properties since they contain no representation of texture. Errors introduced by using isotropic material properties to represent a weld are assessed through a quantified error bound in the elastic regime. An adaptive error reduction scheme is used to determine the optimal spatial variation of the isotropic weld properties to reduce the error bound.

We conducted the in-situ observations of the magnetic domain structure change inNd-Fe-B magnets at high temperature by transmission electron microscopy (TEM) /Lorentz microscopy with applying an external magnetic field. Prior toobservation, a thin foil was magnetized by an external magnetic field of 2.0 Tto almost saturation, then the magnetic domain structures were observed by theFresnel mode with in-situ heating. At 225°C, reverse magnetic domainswere found to generate in the thin foil sample without applying an externalmagnetic field. When we applied a magnetic field on the same direction to thepre-magnetization direction at 225°C, one magnetic domain wall waspinned by a grain boundary and the other magnetic domain wall moved. As theresults, the reverse magnetic domain shrank then annihilated. When we cut theapplied magnetic field, the reverse magnetic domain generated at almost the samelocation. On the other hand, when we applied a magnetic field to the foils inthe opposite direction, the reverse domain started to grow, i.e., magneticdomain walls started to move. The observation results of the shrink or growth ofthe reverse domain showed that the pinning effect of grain boundary againstdomain wall motion would be different depending on the applied magnetic fielddirection. Moreover, domain walls was observed to be pinned by grain boundariesat elevated temperature, so that the coercivity of Nd-Fe-B magnet would occur bypinning mechanism.

Magneto active elastomers (MAE), particulate filled magneto-sensitive composites,were made with increasing volume contents of 325 mesh M-type barium hexaferrite(BAM) particles within a silicone elastomer matrix. The volume contents of BAMranged from 10% to 35% v/v. Vibrating sample magnetometery measurements showedthat the remanence and saturation, both per unit magnetic material, increased by50% from 10%v/v to 20%v/v before slowing decreasing as v/v increased to 35%. Theresults clearly show in peak in the effectiveness of the embedded particles toproduce bulk magnetization near 20% v/v. One possible means for the increasestems from alignment of the magnetization of the particles and hence of themagnetic domains within particles. To assess this possible alignment, Gaussianprobability distribution of magnetization orientations was fit to theexperimental data to ascertain the change in the distribution as a function ofv/v. Results showed 20% v/v had the highest degree of alignment. The resultshighlight, at a bulk scale, the possible evolution of microstructure within thecomposite. Similar results have been seen in image analysis of physical particledistribution of other magneto-sensitive particulate composites. The resultssuggest that effective processing techniques can be used to greatly enhance thebulk magnetization of these and similar composites, paving the way fordecreasing required magnetic content to achieve target response specificationand possibly resulting miniaturization.

Metallographical examination of Uranium alloys can benefit from electron back scatter diffraction (EBSD) technique. Various methods of surface preparation for microstructural characterization are described and compared. The aim of the study was to optimize the preparation technique for surfaces of U alloy splats for EBSD mapping, particularly in the context of U1-x Mox alloys, as properties of γ-U surfaces (e.g. with more Mo) are very different than for mostly α-U type (low-alloyed U).

Water-stable CdSTe quantum dots were synthesized under microwave irradiation heating conditions. An aqueous telluride solution (produced by reducing metallic Te with NaBH4), cadmium sulphate and thioglycolic acid were mixed together in an oxygen-free atmosphere to prevent oxidation of the telluride species. The reaction temperature varied from 60° C to 180° C and was controlled by using a microwave reactor (1,000 W) to control nucleation rate and tune the size of the quantum dots. Photoluminescence analyses of resulting quantum dots evidenced a red shift (from 490 nm to 640 nm, using an excitation wavelength of 380 nm) when the reaction temperature was increased, which suggested crystal growth. The variation in size was also evidenced by the color of the quantum dot suspensions that changed from blue to red, when excited with a 405 nm, 5mW diode laser. The highest quantum yield was observed for quantum dots synthesized from 120° to 150° C. X-ray diffraction analyses suggested the formation of a solid solution of CdSTe with average crystallite size ranging from 1.4 nm to 3.2 nm. FT-IR spectroscopy evidenced the presence of residual thioglycolic functional groups onto the crystals surface, whereas HRTEM confirmed the nanometric size of the quantum dots.

Here we fabricated and characterized a CMOS compatible metal-insulator-semiconductor (MIS) plasmonic tunnel junction for Si-based photonic circuitry. A grating structure was realized on MIS plasmonic tunnel junction via focused-ion-beam milling (FIB) to increase the intensity of the light emission that occurs during inelastic electron tunneling. Approximately 65 times higher intensity of light emission is achieved with the grating structure during the measurements.

Detection of volatile organic compounds (VOCs) emitted from cancerous tumor cells in exhaled human breath allows for early diagnosis of various types of cancers. 3D graphene with a large surface area is considered a suitable material for creating novel sensitive VOCs sensors. In this study, 3D graphene and 3D graphene oxide were synthesized from graphene oxide suspension, hydroquinone and formaldehyde by employing polymerization and reduction. The capability of VOC gas sensing was evaluated by measuring the electrical current response in flowing N2 gas over a range of concentrations of acetone or 1-butanol at room temperature. It was observed that the device current correlated well with the VOC concentration. The adsorption of acetone decreased the current, but the adsorption of 1-butanol increased the current during sensing. 3D graphene oxide device was more sensitive than 3D graphene device because of the high concentration of oxygen-containing functional groups on the surface. These results indicated that 3D graphene and 3D graphene oxide may be the suitable materials for VOCs sensing devices.

This work presents a preliminary experimental study on the possibility toinitiate growth of whiskers on the surfaces of some technologically importantmetals utilizing the enhanced electric field of surface plasmon polaritons(SPPs). The results provide evidence that a relatively high concentration ofwhat appear to be whisker nuclei form in the region where SPPs were excited,whereas no such changes are observed on the untreated surface.

Polymer solar cell (PSC) has great spectrum matching with the room lights and PSChas great photovoltaic performance under the low to high illuminance compared toother types of solar cells. So, we fabricate the PSC module for the indoor useand investigate the electrical characteristics under the various light sources.The PSC photovoltaic performance is 43.5µW/cm2 under thefluorescent light 1000lux (0.1mW/cm2) and PCE=6.0% under thesunlight (1SUN-100mW/cm2).

This PSC module has practical durability and stability against the heat and lightexposure. So, PSC is used as the self-charging batteries for mobile devices andwireless sensor networks.

Due to injuries and disease, there is a great need for a robust, biocompatible, biodegradable, skin-like dermal substitute to repair and regenerate damaged or lost skin. A novel electrochemical process was used to fabricate planarly aligned, densely packed collagen-based sheet which closely mimics the major structure of collagen in skin. The collagen matrix was characterized by scanning electron microscopy (SEM), oxygen permeation, moisture vapor transmission rate (MVTR), and mechanical strength. The seeding and proliferation of adipose derived stem cells (ADSCs) on the matrix was also evaluated. The results indicate that electrochemically-aligned collagen matrix has good MVTR, superior oxygen permeability, and is robust and biocompatible. Thus, it will be evaluated in vivo in the near future as a dermal substitute material.

The presence of impurities in solids is a source of many interesting effects, particularly relevant in the conductivity, optical properties and specific heat. For instance, in nano-electronics these effects could be useful to develop molecular devices such as novel computer architectures, chemical and biomedical sensors. However, the inclusion of impurities breaks the translational symmetry, restricting the systems that can be addressed theoretically in an exact way to those of few atoms. In this work, we present an alternative way to study the electrical conductance in real-space by means of a renormalization plus convolution method applied on the Kubo-Greenwood formula for multidimensional systems of macroscopic size with site and bond impurities. The results show that the spectral average of conductivity depends strongly on the location of site and bond impurities in periodic chains. Particularly, when the distance between impurities follows the Fibonacci sequence, we find that the spectral average falls following a power law as the number of atoms in the system grows. Finally, we analyze the impurity effects on the conductance spectra of periodic core-shell nanowires with a macroscopic length and periodic and quasiperiodically located impurities.

Phase transformation enthalpies are determined using the recently developedmeasurement technique Thin-Film Calorimetry (TFC), which is based onpiezoelectric resonators vibrating in thickness shear mode. They are applicableup to at least 1000 °C. To the best of our knowledge, no comparable TFCsystems for such high temperatures exist.

The experimental part is divided into two subsections. The first is addressed toa thermodynamic investigation on piezoelectric langasite crystals (LGS,La3Ga5SiO14) which are the key component ofthe TFC system. The specific heat capacity is measured on LGS crystals of threedifferent manufacturers. It ranges from about 0.45 J g-1K-1 at 40 °C to about 0.60 J g-1 K-1at 1000 °C. Thereby, deviations of up to 5 % between the differentcrystals are detected. Thermal diffusivity data for Y-cut LGS crystals aredetermined as well. Here, a constant decrease with temperature is detectedranging from 0.48 mm2 s-1 at room temperature to 0.38mm2 s-1 at 700 °C.

The second part presents thin-film calorimetric investigation on thin films ofthe family Li-Ni-Mn-Co-Al-Oxide (NMC/NMCA). These cathode materials areinvestigated and compared when annealed in ambient air or 0.5 % H2/Arup to 860 °C. Three stoichiometries are chosen:Li(Ni1/3Mn1/3Co1/3)O2,Li(Ni0.6Mn0.2Co0.2)O2, andLi(Ni0.6Mn0.2Co0.15Al0.05)O2.The samples show three or four phase transformations. In air, the samplescrystallize in the range of 250-350 °C. In 0.5 % H2/Ar, thetransformations occur at higher temperatures. Especially in air, stoichiometricNMC crystallizes at lower temperatures compared to Ni-rich compositions.Additional doping with Al enhances the thermal stability which shifts all phasetransformations to higher temperatures in both atmospheres.

Diamond-based rectifiers are promising devices for the development of next-generation power electronics. However, presented device structures limit current operation as low as tens A, which hampers diamond from real industrial applications. One of the critical issues is poor availability of conductive (low-resistivity) substrates which can be used for vertical-type devices for high-output operations. Recently, we have successfully fabricated heavily boron-doped (p+) low-resistivity diamond by hot-filament chemical vapor deposition (HFCVD). Resistivity was monotonically decreased to 1.2 mΩcm with amount of doped boron. In this study, to further investigate potentials for electric applications, contact resistance between metal/p+ diamond was evaluated by transmission line model (TLM). From the current-voltage characteristics, low specific contact resistance of ∼10−7 Ωcm2 was demonstrated.

Dialysis is the process by which an artificial kidney device removes waste and excess water from a patient. An outstanding problem with dialysis is that the body has a remarkable immune function where proteins and antigens mark foreign objects as possible threats despite the biocompatibility of the material. Upon adhesion to polymeric materials used currently in dialysis, proteins are lost. In this study, polytetrafluoroethylene (PTFE) is investigated as a potential replacement material for dialysis tubing because of its unreactive nature. The focus is to determine if PTFE will prove a viable material in minimizing protein adhesion and further reducing antibody loss of the patient. Protein loss as a function of filtration time was measured. PVC and PTFE materials were investigated following the same battery of testing where the protein concentrations in the blood were characterized using UV Visible spectrophotometry. Results demonstrate a loss of nearly 12 percent of blood proteins to the PVC material over the course of a typical dialysis treatment. Conversely, the protein loss due to adhesion to PTFE was less than two percent.

The photo-structural changes in a 2 μm thick amorphous selenium (a-Se) thin film, thermally evaporated on Si substrate, have been studied by micro-Raman spectrometer with 532 nm laser at different laser power densities (1 to 64 W/mm2) and exposure times (15 – 60 s). In addition, the nanoscale photo-structural changes/photo-thermodynamic phase changes are examined on 90 nm a-Se film coated on SiO2 cladding of the optical Fiber Bragg Grating (FBG) sensor on prolonged exposure to a low power (1 mW/mm2, 10 mW/mm2) 532 nm laser, which is measured by means of photo-striction (light induced strain) in the material.

Duel p-block element doped carbon nanomaterial is a new kind of metal-freebifunctional catalysts for fuel cells and metal-air batteries because of theirlow-cost and high efficiency compared to traditional noble metals and theiralloys. To optimize co-doped catalysts, we studied the interactions of dopantson the doped graphene and their effect on oxygen reduction reaction (ORR) andoxygen evolution reaction (OER). It is found that the interactions between N andX (P, B, S) occur within a distance of ∼0.5 nm, and beyond thedistance their interactions are limited while the interactions between N and Cltake places beyond the distance of ∼0.5 nm.

The synthesis of gold nanoparticles (AuNPs) displaying pH and salt resistantactivity has been a challenging tasks. The use of aminopropyltrimethoxysilane(3-APTMS) as one of the reagent during the synthesis of AuNPs may control suchactivity due to its micellar behavior. The AuNPs made from 3-APTMS capped goldions in the presence of formaldehyde are found insensitive to pH- and salt. Themajor findings on 3-APTMS and formaldehyde mediated synthesis of AuNPs revealthe following: (1) 3-APTMS being amphiphilic, dispersibility of as preparedAuNPs largely depends on the organic reducing agents. (2) An increase in thehydrocarbon content of the reducing agent facilitate the dispersibility of AuNPsin organic solvent whereas decrease of the same increases the dispersibility inwater, (3) AuNPs made through aldehydic reducing agents (formaldehyde andacetaldehyde) have relatively better salt and pH tolerance as compared toketonic reducing agents (acetone, t-butyl dimethyl ketone), and (4) an increasein 3-APTMS concentrations enables salt- and pH- resistant property to AuNPsirrespective of organic reducing agents.

The migration behavior of the long-lived actinides was studied under the conditions of the deep disposal of the acidic liquid nuclear waste (LNW). Composition of LNW varies significantly including acidic technological wastes (pH ∼2.4), which consist of sodium nitrate, acetic acid, corrosion products (Fe, Cr, Mn, Ni, Al), fission products and actinides. Corrosion products tend to precipitate under the LNW disposal conditions that favor forming of the phases with high sorption capacity towards actinides. Sands of reservoir bed have their own initial sorbent surfaces besides new secondary phases that have formed as a result of interaction with acidic LNW. The nearest to the injection well conditions are gradually changing from pH ∼2.4 till neutral values due to the dilution by groundwater with formation of new precipitated phases of corrosion products. The solid phases characterization is a necessary step on the path of knowledge of migration behavior of actinides. The secondary phases of both corrosion products and sands of reservoir bed under LNW disposal conditions were characterized using XRD, SEM and Mössbauer spectroscopy. The recent results of the analyses of the behavior of actinides (Pu. U, Np, Am) under the conditions of the injection of the acid LNW are presented in the paper.