bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combinatorial Approaches to Peptide-Encapsulated CdS Nanoclusters
Authors: Spreitzer G. , Whitling J. M. , Wright D. W. 
Published: April 2011

AbstractAs many properties of group II-VI semiconductor nanocrystallites arise from their quantum confined nature, the synthesis of these clusters is of great interest. The challenge of synthesizing functional nanoclusters is, however, complicated by the limited stability of metalchalcogen surfaces under highly oxidizing conditions and Ostwald ripening. Our objectives are to develop methods for the synthesis of biogenic CdS semiconductor nanocrystallites that address the following issues: (1) What properties of the ligand peptide are important in stabilizing and producing CdS particles of any desired size? (2) Will hybrid peptides using nonnatural amino acids stabilize the nanoclusters while incorporating new surface functionality? (3) Is it possible to use novel peptides to modify the particle surface, thereby, controlling the photophysical properties of the CdS cluster? Our approach consists of parallel combinatorial techniques and computational methods for the discovery and optimization of peptide and peptidomimetic ligands to stabilize size-defined clusters of CdS. The effects of cysteine separation on CdS particle size by varying the number of bonds with rotational freedom within the spacer amino acids is examined. Furthermore, the properties of the resulting CdS nanoclusters are reported.
Hard Tissue Regeneration InStrombus Gigas, the Giant Queen Conch
Authors: Su X. , Heuer A. H. 
Published: April 2011

AbstractHard tissue regeneration (i.e. shell repair) is an important biomineralization process in mollusks. Rapid regeneration is important in avoiding loss of fluids and preventing attacks by predators. We have studied such tissue regeneration in the Queen conch (Strombus Gigas) by inserting an abiotic glass cover slide between the mantle tissue and the shell. The glass cover slides were removed after mineralization periods extending from 6 hours to 4 days, and the deposited materials on the glass substrates (“flat pearls”) analyzed by X-ray diffraction, and scanning and transmission electron microscopy.Although the CaCO3in native Queen conch shell is exclusively aragonite, calcite was detected in the regenerated materials grown on glass substrates. Calcite formation occurred only during the very early stage of mineralization and the initial minerals formed were soon overgrown by aragonite. The initial aragonite overgrowth had a spherulitic morphology, and was thus relatively poorly oriented; after this spherulitic transient, the microstructure was recognizable as the crossed-lamellar structure of the natural shell.Thus, shell regeneration on abiotic substrates differs from shell formation during growth of conchs only in the very early stage. Once the crossed-lamellar microstructure has formed, further hard tissue development is identical to that occurring during natural shell growth.
Three Dimentional Finite Element Modeling of Microstructural Development of Nacre in Seashells and Implication on Mineralization of CaCO3
Authors: Katti D. R. , Katti K. S. 
Published: April 2011

AbstractThree dimensional finite element models of nacre were constructed based on reported microstructural studies on the ‘brick and mortar’ micro-architecture of nacre. 3D eight noded isoparametric brick elements were used to design the microarchitecture of nacre. Tensile tests were simulated using this model at stresses of 2 MPa which occur well within the elastic regime of nacre and thus effects related to locus and extent of damage were ignored. The reported values of elastic moduli of organic (0.005 GPa) and aragonitic platelets (205 GPa) were used in our simulations and the resulting displacements were found to be extremely large and corresponding to a very low modulus of 0.011 GPa. The reported elastic modulus of nacre is of the order of 50 GPa. The large displacements can possibly result from two possibilities. Firstly. the organic layer due to its multilayered structure is possibly composed of distinct layers of different elastic moduli. A significantly higher modulus of the organic phase may be possible near the organic-inorganic interface. Simulations using variable elastic moduli for the organic phase suggest that an elastic modulus of 15 GPa is consistent with the observed elastic behavior of nacre. A second possibility for the observed higher elastic modulus may arise from localized platelet-platelet contact. Since the observed modulus of nacre lies within the above two extremes (i.e. 15 GPa and 205 GPa) it is suggested that a combination of the two, i.e. a higher modulus of the organic phase near the organic-inorganic interface and localized platelet-platelet contact can result in the observed elastic properties of nacre.
29Si NMR Chemical Shifts and Energetics of Silica-Serine and Silica-Polyalcohol Complexes as Indicators of Silica Biomineralization Mechanisms
Authors: Sahai N. , Tossell J. A. 
Published: April 2011

AbstractSerine- and polysaccharide-enriched organic matrix is associated with biogenic silica such as diatom tests, sponge spicules, and phytoliths. We have used molecular orbital theory to determine the relative stability and 29Si NMR shifts of direct Si-O-C ester-like bonds versus hydrogen bonds between the monomeric silicic acid and the alcohol group on aliphatic organics such as serine and threitol (a polyacohol as proxy for polysaccharides). Preliminary results suggest that at neutral pHs, H-bonds and ester-bonds of four-fold coordinated silicon are of comparable stability. Formation of ester-like bonds with five-fold coordinated silicon is endothermic at neutral pHs but is stabilized at higher pHs. 29Si shifts of the H-bonded and ester-bonded complexes of four-fold coordinated silicon range from −55 to −73 ppm similar to monomeric inorganic silicic acid but far more positive than the −92, −102, and −110 ppm values observed experimentally in biogenic silicas. The five-coordinated silicon complexes yield shifts of −96 to −107 ppm. The latter range is within the range of inorganic, polymerized silica. If five-fold coordinated Si with direct Si-O-C bonds is present as a precursor or intermediate or stable species in biogenic silica, it could have escaped detection due to overlap with inorganic polymerized silica. Thus, 29Si NMR shifts are not necessarily diagnostic of the presence or absence of Si-O-C bonds in biogenic silica.
Effect of Calcification on The Fatigue Behavior of Fluorinated Polyurethanes
Authors: Benson R. S. , Kim H. J. 
Published: April 2011

AbstractThe present study compares the fatigue propagation behavior of a fluorinated and nonfluorinated polyurethane-calcium salt blends. The calcium salts used in this study are calcium chloride and hydroxyapatite (HAP). The fatigue crack propagation (FCP) behavior of the polyurethanes exhibited a dependence on the chemical composition of the polymer and calcium salt. The pure non-fluorinated PTMG2000 did no undergo crack propagation. While the fluorinated PTMG2003F exhibit a crack propagation rate of 7.8 × 10-6m/cycle at constant strain amplitude and tearing energy range. The incorporation of calcium chloride into PTMG2000 did not promote any changes in the FCP behavior; while the addition of HAP produced cracks with a growth rate of 3.33 × 10-6m/cycle. In the case of PTMG2003F, the addition of calcium chloride did not lead to formation of cracks; while HAP produced a material in which cracks propagated at a rate of 10.0 × 10-6m/cycle. The difference in the response the non-fluorinated and fluorinated polyurethane-calcium salt blends to cyclic loading can be attributed to molecular level variations such as domains disruption and changes in chain orientation at the crack tip.
Self-Assembled β-Sheet Architectures for Bone-Tissue Engineering
Authors: Spreitzer G. , Doctor J. , Wright D. W. 
Published: April 2011

AbstractAdvances in the understanding of biomineralization processes in a variety of organisms have revealed the critical role of three-dimensional scaffolding architectures to create a highly functionalized surface. These complex matrices function on a variety of length scales ranging from the macromolecular (10–100 nm) to the cellular (1–10mm) and larger. One dominant structural motif found in many of these architectures is macromolecules containing antiparallel β-pleated sheets. These “hints” from Nature have lead to the iterative design and development of a novel multipurpose platform technology based on a self-assembled periodic peptide architecture for use in bone-tissue engineering. Combining molecular modeling, structural biochemistry and synthetic techniques, we have produced a β-sheet hollow tube peptide nanoassembly. Such a synthetic approach allows for the template's designed parameters of electrostatic, geometric and stereochemical complimentarily to match those of the desired biomineral. Consequently, these templates readily nucleate calcite. Future studies will investigate the in vitro osteoconductive and osteogenic properties of these templates.
Comparison on Regulation of Calcium Phosphate by Organic Monolayer, Unilamellar Phospholipid Vesicles and Hydrothermal Self-Assembly
Authors: Cui F. Z. , Zhang Y. , Cai Q. 
Published: April 2011

AbstractBiomineralization centers on the idea that organics control the nucleation, growth and final form of inorganics. The present studies investigated the deposition or precipitation of inorganics templated by organic monolayer films, unilamellar phospholipid vesicles, and selfassembled hexadecylamine, with the emphasis on the regulation of template on phase, orientation and microstructure of minerals. The obtained calcium phosphate varied from the thin layer precipitated on the organic monolayer to the confined particles formed inside the lipid vesicles to the mesolamellar structure self-organized in the precursor sol-gel. The typically regulated features of these three systems have been revealed. Consequently, the different phases of calcium phosphate can be obtained through variation of controllable parameters.
Modification of Assembled Structures of Steroids Adsorbed on Apatite Ceramic Surface by Electrical Poling
Authors: Nakamura S. , Obata A. , Yamashita K 
Published: April 2011

AbstractAggregate structures of steroids adsorbed on electrically-poled hydroxyapatite (HAp) ceramics were investigated by X-ray diffractometry (XRD) and scanning electron microscopy. Effectivity of the poled HAp on modification of the steroid assembly modes was discussed by the arrangement estimations of the steroid molecules. The dense HAp ceramics were obtained from the pelletized HAp powder precipitated from calcium hydroxide suspension and phosphoric acid using conventional sintering at 1250°C under the saturated water vapor pressure. The HAp ceramic blocks were poled in a DC electrical field of 1.0 kVcm-1 with being heated at 300°C. The HAp ceramics were immersed in ethanol solution of steroids at 37°C. The steroid crystals were overgrown onto the HAp substrates by recrystallization method. In the case of cholesterol, the tabular crystals of cholesterol monohydrate and the needle-like crystals of anhydrate were overgrown on all of the HAp ceramic surfaces. The thickness of the cholesterol layers on the positively (p) poled HAp surfaces was considerably less than those of the negatively (n) poled and non-poled (0) surfaces. The remanent chaige of the HAp ceramics altered the morphology of vitamin D3 crystals deposited on the HAp surfaces. It was revealed that the electrically-poled HAp ceramic surfaces changed the aggregate structures and the crystal growth rates of steroids.
Dip-Coating of Calcium Hydroxyapatite on Titanium Alloy (ti-6ai-4v) and Stainless Steel (316L) Substrates
Authors: Mavis B. , Tas A. C. 
Published: April 2011

AbstractTitanium alloy (Ti-6AI-4V) and stainless steel (316L) are two of the most commonly used materials in the manufacture of orthopaedic implants. To achieve better biocompatibility with bone, metal implants made of 316L or Ti-6Al-4V are often coated with calcium hydroxyapatite (HA) bioceramics. This paper is to describe a new dipping solution recipe used for HA coating. Sample characterization was performed by SEM and XRD.
Inhomogeneous Magnetic Structures of La0.7Ca0.3MnO3 Investigated by ESR and Magnetization Measurements
Authors: Joh Keon Woo , Lee Chang Hoon , Lee Cheol Eui , Jeong Yoon Hee , Hong C. S. , Hur Nam Hwi 
Published: April 2011

AbstractComprehensive measurements of electron spin resonance and magnetization of La0.7Ca0.3MnO3 in the ferromagnetic as well as paramagnetic phases were carried out. From the quantitative analysis of the ESR signal, attributed to itinerant spins and localized spins in the bottleneck regime, evidences for the inhomogeneous nature of both phases, consisting of clusters of one phase embedded in the other, were found. It is suggested that the microscopic local magnetic structures above and below Tc are qualitatively similar except that the phase below Tc carries long range order.
Substrate-Induced Anomalous Electrical Transport and Magnetic Transitions in Epitaxial La0.66Sr0.33MnO3 Films Grown on (001) BaTiO3 Substrates
Authors: Nath T.K. , Lee M.K. , Eom C.B. , Smoak M. , Ryan P.A. , Tsui F. 
Published: April 2011

AbstractEffects of drastic change of 3-dimensional films' lattice strain by substrate structural transformations on the transport and magnetic properties of tensile strained epitaxial La0.66Sr0.33MnO3 thin films were studied using (001) BaTiO3 as the templates. These films exhibit dramatic jumps in electrical resistance and magnetization at temperatures very close to different crystallographic structural change of BaTiO3 substrate. Application of high magnetic field (50 kOe) suppresses both the electrical transport and magnetization jumps. The observed low-field sharp transitions correspond sudden changes in magnetic anisotropy, caused by the structural transformation of the substrate. The magnetic easy axis lies in the film plane along [100] direction having a strong correlation with the substrate-induced 3-dimensional strain states as determined by the normal and grazing incidence x-ray diffraction. The sudden substrate structural transformations imposes an additional drastic sharp change of the film strain which is found to reorient the magnetic easy axis within the film plane.
Structural and Magnetic States in Layered Manganites: An Expanding View of the Phase Diagram
Authors: Mitchell J.F. , Millburn J.E. , Ling C. , Argyriou D.N. , Bordallo H. N. 
Published: April 2011

AbstractColossal magnetoresistive (CMR) manganites display a spectacular range of structural, magnetic, and electronic phases as a function of hole concentration, temperature, magnetic field, etc. Although the bulk of research has concentrated on the 3-D perovskite manganites, the ability to study anisotropic magnetic and electronic interactions made available in reduced dimensions has accelerated interest in the layered Ruddlesden-Popper (R-P) phases of the manganite class. The quest for understanding the coupling among lattice, spin, and electronic degrees of freedom (and dimensionality) is driven by the availability of high quality materials. In this talk, we will present recent results on synthesis and magnetic properties of layered manganites from the La2−2xSr1+2xMn2O7 series in the Mn4+-rich regime x > 0.5. This region of the composition diagram is populated by antiferromagnetic structures that evolve from the A-type layered order to G-type “rocksalt” order as x increases. Between these two regimes is a wide region (0.7 < x < 0.9) where an incommensurate magnetic structure is observed. The IC structure joins spin canting and phase separation as a mode for mixed-valent manganites to accommodate FM/AF competition. Transport in these materials is dominated by highly insulating behavior, although a region close to x = 0.5 exhibits metal-nonmetal transitions and an extreme sensitivity to oxygen content. We suggest two possible explanations for this transport behavior at doping just above x=0.5: localization by oxygen defects or charge ordering of Mn3+/Mn4+ sites.
Cation Ordering Structure in La0.8Ca0.2MnO3 Thin Films by Pulsed Laser Deposition
Authors: Li Y. H. , Rajeswari M. , Biswasl A. , Kang D. J. , Sehmen C. , Salamanca-Riba L. , Ramesh R. , Venkatesan T. 
Published: April 2011

AbstractA careful analysis of high-resolution transmission electron microscopy images from La0.8Ca0.2MnO3 thin films indicates that the images can not explained based on either the classical Pnma structure or its monoclinic distortion. A cation ordered structure is proposed which could be responsible for the significantly higher Tc of the film (298K) compared with the bulk material of the same composition (190K).
Magnetotransport in Epitaxial Trilayer Junctions Fabricated from 90° Off-Axis Sputtered Manganite Films
Authors: Noh J. S. , Nath T. K. , Sun J. Z. , Eom C. B. 
Published: April 2011

AbstractWe report studies on La1−xSrxMnO3 /SrTiO3/ La1−xSrxMnO3 (x=0.33) trilayer junctions made using 90° off-axis sputtering. Both (110) NdGaO3 and (001) (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) are used for substrates. Optical lithography is used for junction formation. These sputtered trilayers show improved junction resistance uniformity over trilayers made using laser ablation. A magnetoresistance of ∼100% is observed for junctions on LSAT with 30 Å barrier at 13 K and around 100 Oe. The shape of junction magnetoresistance vs. field depends both on barrier thickness and on substrate type, suggesting that both inter-layer coupling and substrateinduced-strain play a role in determining the junction's micromagnetic state. These results indicate better junction interfaces can be obtained for manganite trilayer junctions by 90° off-axis sputtering.
30 GHz Electronically Steerable Antennas Using BaxSr1−xTiO3-Based Room-Temperature Phase Shifters
Authors: Carlson C. M. , Rivkin T. V. , Parilla P. A. , Perkins J. D. , Ginley D. S. , Kozyrev A. B. , Oshadchy V. N. , Pavlov A. S. , Golovkov A. , Sugak M. , Kalinikos D. , Sengupta L. C. , Chiu L. , Zhang X. , Zhu Y. , Sengupta S. 
Published: April 2011

AbstractWe report the performance of 16-element phased array antennas operating at 30 GHz and ambient temperature. These antennas use BaxSr1−xTiO3(BST)-based phase shifters to produce the beam steering. Ferroelectric phase shifters offer advantages over current semiconductor and ferrite devices including faster switching speeds and lower costs. Also, ferroelectric phase shifters offer higher power handling capability than semiconductor devices and also have high radiation resistance. We made phase shifters from laser-ablated epitaxial BST films as well as from polycrystalline BST-oxide composite films. Although neither the devices nor the materials themselves are fully optimized, phase shifters have shown > 360° of phase shift with < 350 V DC bias (E < 9 V/µm) and ∼8 dB insertion loss. With ferroelectric phase shifters incorporated, antennas show radiation patterns with central-lobe half-power widths of ∼13° and side lobe intensities down by more than 10 dB. Using the phase shifters, the central lobe can be shifted, or “steered,” by ±18° in either direction. These results demonstrate a first step toward a prototype steerable antenna for 20–30 GHz satellite communications as well as other applications.
Near-Field Imaging of the Microwave Dielectric Properties of Single-Crystal PbTiO3 and Thin-Film Sr1−xBxTiO3
Authors: Wang Y.G. , Reeves M.E. , Chang W. , Horwitz J.S. , Kim W. 
Published: April 2011

AbstractA PbTiO3 crystal and Sr1−xBaxTiO3 films have been studied by near-field scanning microwave microscopy (SMM). In the PbTiO3 crystal, dielectric properties and topography are obtained simultaneously. In Sr1−xBaxTiO3 films, local variations and sample-to-sample differences are observed. To quantitatively determine local dielectric permittivity and loss, we also carry out theoretical calculations on dependence of resonant frequency and quality factor on dielectric constants of bulk samples and thin films. Good agreements between experimental and theoretical results are obtained.
Tunable Dielectric Thin Films for HTS Microwave Applications
Authors: Moeckly B. H. , Zhang Y. M. 
Published: April 2011

AbstractSrTiO3 (STO) thin films are promising for a variety of applications requiring tunability. We describe the growth and characterization of STO thin films including their dielectric properties. We also present attempts at reducing the loss tangent of these films, and we discuss their integration with high-temperature superconductor (HTS) microwave filters for trimming purposes.
Ferrites for Tunable RF and Microwave Devices
Authors: Dionne Gerald F. 
Published: April 2011

AbstractMicrowave systems for communications and radar require control of propagation of the rf signal. Devices that accomplish this function include phase shifters, isolators and circulators, and tunable filters. In many instances, these devices are magnetic and are based on the variable permeability of electrically insulating ferrimagnetic oxides (ferrites). Recent advances in microwave ferrite devices have featured superconductor circuitry that promises to virtually eliminate insertion losses due to rf surface resistance. Lower conduction losses allow the use of small lightweight microstrip configurations in place of traditional bulky waveguide structures. For operation at cryogenic temperatures ferrimagnetic spinels and garnets will require chemical alteration to realize the full potential of these devices. Challenges include the reduction of magnetocrystalline anisotropy to optimize switching energies and speeds, and the elimination of fast-relaxing impurities in the magnetic garnets that can increase magnetic losses and degrade resonator Q factors at low temperatures.
The Influence of the Initial Supersaturation of Si Interstitial Atoms on the Relative Thermal Stability of Dislocation Loops in Silicon
Authors: Cristiano F. , Colombeau B. , Mauduit B. de , Giles F. , Omri M. , Claverie A. 
Published: April 2011

AbstractIn this work, we have studied the relative stability of perfect (PDLs) and faulted (FDLs) dislocation loops formed during annealing of preamorphised silicon. In particular, we have investigated the effect of the initial supersaturation of Si interstitial atoms (Si(int)s) created by the implantation process on their thermal evolution. Transmission Electron Microscopy analysis shows that in samples with a low Si interstitial supersaturation, FDLs are the dominant defects while PDLs appear as the most stable defects in highly supersaturated samples. We have calculated the formation energies of both types of dislocation loops and found that, for defects of the same size, FDLs are more energetically stable than PDLs, if their diameter is smaller than 80 nm and viceversa. The application of these calculations to the samples studied in this work indicates that a direct correspondence exists between the formation energy of the two defect families and the number of atoms bound to them. Moreover, we have shown that the relative stability of FDLs and PDLs depends on the initial supersaturation of Si(int)s created during the implantation process.