bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculations of the Macroscopic Linear and Nonlinear Optical Properties of Nematic Liquid Crystals
Authors: Risser Steven M. , Ferris Kim F. , Exarhos Gregory J. , Morgan J. Corey 
Published: April 2011

AbstractMany studies have focused on the computation of the structural and electronic properties of liquid crystal molecules in a single static conformation. However, a complete and quantitatively accurate description of the macroscopic optical properties of liquid crystals must also include effects due to the long-range nematic order, the anisotropic local environment surrounding the molecules, and the dynamical fluctuations of the molecules. In this paper, we explore methods to simplify computation of the molecular average second hyperpolarizability of the nematogen 4-n-pentyl-4-cyanobiphenyl (5CB). The model we develop relates changes in the geometrical parameters of the molecule to corresponding changes in the hyperpolarizability. The model is first applied to a simple donor-acceptor substituted polyene, and then to 5CB. Use of a small set of geometrical variables results in a slight increase in the RMS deviation of the predicted hyperpolarizability over the deviation obtained from a complete set. We then discuss the importance of this work for the development of means to calculate macroscopic optical properties.
Ab Initio Design of Two-Photon Absorbing Materials
Authors: Day Paul N. , Nguyen Kiet A. , Pachter Ruth 
Published: April 2011

AbstractTwo-photon absorbing materials such as conjugated polyenes show promise as nonlinear optical materials. Prediction of two-photon absorption frequencies and cross-sections has been limited by the high level of ab initio calculations that must be carried out in order to accurately calculate excited state energies and transition dipole moments, by the size of many of the compounds of interest, and by the difficulty of handling condensed phase effects in the calculations. We have carried out geometry optimizations at the multi-configurational selfconsistent field level on a small polyene, hexatriene, both in the gas-phase and in solution, with the solvent effects being modeled by the effective fragment potential. The excited-state energies have been calculated by the multiconfigurational quasidegenerate perturbation theory. Transition dipole moment calculations have also been carried out, from which the two-photon absorption cross-section can be estimated. The results indicate that just one or two solvent molecules can have a large effect on the nonlinear optical properties of two-photon absorbing materials.
Surface Smoothing of Polycrystalline Si Waveguides With Gas-Cluster Ion Beams
Authors: Toyoda N. , Lee K. K. , Luan H-C. , Lim D. R. , Agarwal A. M. , Wada K. , Kimerling L. C. , Allen L. P. , Fenner D. B. , Kirkpatrick A. R. 
Published: April 2011

AbstractPolycrystalline Si (poly-Si) waveguides offer design flexibility and multilayered structures in Si-integrated photonic devices. However, as-deposited poly-Si surfaces are rough compared with single-crystalline Si, and a rough surface causes significant waveguide scattering loss at the surface. In this study, surface smoothing of poly-Si waveguides with a gas-cluster ion beam (GCIB) was demonstrated as a new smoothing technique. As the GCIB process is a directional ion-beam process, in principle it can be applied not only to plane surfaces but also to three-dimensional or non-flat structures, such as waveguide ridges.The initial average roughness of as-deposited poly-Si films (625°C, 1 μm thick) ranged from 15 nm to 22 nm, and the grain sizes were distributed from 0.2 to 0.4μm. This rough surface was dramatically smoothed to a roughness of 1.5 nm by Ar cluster ion irradiation. From the relation between the sputtered depth and the surface roughness, the sputtered depth must be greater than the height difference of the roughness (peak-to-valley) to obtain smooth surfaces. Optical transmission losses at λ =1.54 μm were measured using cutback measurement from samples before and after the smoothing by GCIB. After surface smoothing with GCIB, the optical loss decreased from 85 dB/cm to 54 dB/cm.
Two- and three-Dimensional Refractive Index Lattices Formed by Laterally Patterned Porous Silicon Layers
Authors: Uehara S. , Sasabu H. , Taira K , Hashimoto T. , Matsubara T. 
Published: April 2011

AbstractPorous silicon was used to fabricate refractive index lattices. Patterned n-doping and/ or substrate etching were used to introduce lateral periodicity. By anodizing p-type substrate with an n-doped area, we realized large refractive index contrast two-dimensional lattices with underlying cladding layer. The anodization process showed an effect specific to the small dimensional patterning and this effect has significant influence on the formed refractive index structure.
Polymeric Strip Waveguides and their Connection to Very Thin Ultrafast Metal-Semiconductor-Metal Detectors
Authors: Buchal Ch. , Roelofs A. , Siegert M. , Löken M. 
Published: April 2011

AbstractWe present data on the fabrication process of optical waveguides from four different polymers, which have been patterned either by standard lithographical masking and reactive ion beam etching (RIE) or by direct lithographical exposure of photosensitive material. Three of the resists were directly photosensitive, they could be exposed and developed. Thereafter they can be cured and remain stable. Waveguide losses of 3.5 dB/cm had to be accepted for the photosensitive materials, while the non-sensitive polymers formed very good guides (0.8 dB/cm), but were more difficult to process. We demonstrate the coupling of the strip waveguides to optical fibers on one side and to very thin metal-semiconductor-metal (MSM) photodetectors at the other side. A beam propagation method computer code has been used to evaluate the best coupling efficiencies between the guides and the detectors, which are ultrafast (3.5 ps FWHM) due to their very thin silicon slab design (Si thickness 400 nm, sandwiched between two Schottky contacts).
Hydroxyapatite Coating on Thermal Titanium Substrate in Aqueous Solution
Authors: Okido M. , Ichino R. , Kuroda K. , Ohsawa R. , Takai O. 
Published: April 2011

AbstractA hydroxyapatite, HAP, film was deposited on a titanium substrate in an aqueous solution, at an ambient temperature and ambient pressure. The solution included 3 mmoldm-3Ca(H2PO4)2and 7 mmol dm-3CaCl2at pH 5.5. The temperature of the substrate surface was controlled in both methods of applying alternative current through the Ti foil and high frequency induction heating using Ti ingot. In these methods, the substrate was heated up and the temperature gradient was formed between the substrate and the solution. The effects of surface temperature, fluoride ions, additive inhibitor and heating time on the morphology of HAP crystals formed on Ti substrate were investigated in various conditions. The morphology changed from compact layer to dendrite layer with the HAP growing time in AC current method and the HAP film with the thickness of 200 μm can be obtained on Ti foil with cross section of 30 μm × 2mm by heating for 20 min at 20 A-AC. On the other hand, the deposits consisted of algae-like whisker in the induction heating method. The HAP formation is found to take place only on the substrate surface by these substrate heating methods without HAP precipitation in aqueous solution
Calcium Phosphate Cements: Chemistry, Properties, and Applications
Authors: Chow Laurence C. 
Published: April 2011

AbstractThis paper reviews recent studies on self-setting calcium phosphate cements (CPC). Discussions are focused on the cement setting reactions, the products formed, those properties of the cements that contribute to their clinical efficacy, and areas of future improvements that could make CPC useful in a wider range of applications. The strengths of CPC are considerably lower than ceramic calcium phosphate biomaterials and are also lower than some of the dental cements. On the other hand, the combination of self-setting capability and high biocompatibility makes CPC a unique biomaterial. Near perfect adaptation of the cement to the tissue surfaces in a defect, and a gradual resorption followed by new bone formation are some of the distinctive advantages of CPC. In its present state CPC appears to be suitable for a number of applications. Much remains to be done to further improve its properties to meet the requirements for different applications.
Calcification Resistant Polyurethanes Modified with Geminal Bisphosphonate Groups
Authors: Alferiev I. S. , Vyavahare N. R. , Song C. X. , Levy R. J. 
Published: April 2011

AbstractNon-esterified geminal bisphosphonate groups (0.06–0.12 mmol/g) were covalently attached to elastomeric polyurethanes (PU) based on 4,4′-methylenebis(phenyl isocyanate) (MDI) and represented by a polyether-urethane (PEU), a polyurethane-urea (PUU), and a polycarbonate-urethane (PCU). Auxiliary 6-bromohexyl or carboxylic groups were attached to PU via base-induced N-alkylation of urethane NH sites either with 1,6-dibromohexane or with lithium salts of ω-bromocarboxylic acids. An alternative method to introduce carboxylic groups into the polymers via reactions of bromoalkylated PU with thiol-containing carboxylic acids was found to be more suitable than the direct carboxyalkylation. The subsequent reactions either of thiol-containing bisphosphonates with the attached 6-bromohexyl groups or of 3-amino-Ihydroxypropylidene-1,1-bisphosphonate (pamidronate) with N-hydroxysuccinimide-activated carboxylic groups of PU led to the bisphosphonate-modified PU. The polymers do not undergo a significant degradation in the course of the modification reactions, their mechanical properties and elasticity remain mostly unaffected. Water uptake of the bisphosphonate-modified PU increased up to 26% depending on the extent of modification. Bisphosphonate-modified PUU showed a significantly lower in vivo calcification compared to the non-modified polymer.
Mucin Coating on Hydrophobic Polymer Materials
Authors: Shi L. , Caldwell K. D. 
Published: April 2011

AbstractIn this work, the adsorption isotherm and kinetics of bovine submaxillary gland mucin (BSM) onto a hydrophobic polystyrene surface were studied by the solution depletion method, in which mucin surface concentrations were analyzed by amino acid analysis. Using a Langmuir adsorption model and non-linear curve fitting, kinetics parameters, kon and koff were determined. The coating was found to be very stable with very limited desorption (less than 2%) from a long term observation. By measuring the water contact angles, the changes in surface hydrophobicity due to mucin coating were monitored on four polymer materials, namely polymethylmethacrylate (PMMA), polyurethane (PU), polystyrene (PS), and silicone. After coating, all the hydrophobic surfaces turned into very hydrophilic. A strict correlation between mucin surface concentration and surface wettability has been found.
Formation of Calcium Phosphate on Phosphorus-Containing Groups Introduced Substrate
Authors: Yokogawa Y. , Nishizawa K. , Nagata F. , Kameyama T. 
Published: April 2011

AbstractA calcium phosphate coating over chitin sample was produced by a process based on phosphorylation, Ca(OH)2 treatment and SBF immersion. Ca(OH)2 soaking of the fibers phosphorylated by urea/phosphorus acid (H3PO3) method is found to produce highly crystalline clusters lodged in the fibers which were calcium phosphite mono-hydrate (CaHPO3H2 O). CaHPO3H2O clusters were still present in chitin fibers even after 7 days of soaking, while after 17 days calcium phosphate was observed. While chitin fibers phosphorylated by urea and H3PO4 method and then soaked in saturated Ca(OH) 2 solution at ambient temperature, which lead to the formation of thin coatings formed by partial hydrolysis of PO4 functionalities which were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5×SBF solution for as little as 1 day. EDX analyses of the thin coating gave Ca/P ratio of 1.29, which is speculated to be OCP. The mechanism of formation of the coating is believed to involve dissolution of the CaHPO3 H2O clusters or the OCP upon introduction of the Ca(OH) 2- treated phosphorylated chitin fibers into the 1.5×SBF solution which elevates the Ca2+ ion concentration in the vicinity of the fibers so stimulating calcium phosphate formation from the soaking medium.
Effects of Growth Factor Presence on Mineralization of Porous Poly(Lactide-Co-Glycolide) Scaffolds In Vitro
Authors: Murphy William L. , Gilhool Katherine A. , Kohn David H. , Mooney David J. 
Published: April 2011

AbstractBasic design requirements of scaffolds for bone tissue engineering applications include biocompatibility, temporally controlled degradability, osteoconductivity, mechanical integrity, and mass transport capabilities. A recent study has attempted to meet design criteria via the growth of a carbonated apatite (bone-like) mineral on the inner pore surfaces of a highly porous 85:15 poly(lactide-co-glycolide) scaffold using a biomimetic process. It has also been recently demonstrated that the mineralization strategy can be combined with sustained growth factor delivery to induce vascular tissue ingrowth. The present study examines the effect of protein presence on the mineralization process by measuring the amount of protein incorporated into the scaffold during the process of mineral formation. Surprisingly, vascular endothelial growth factor incorporates more readily into control scaffolds than into scaffolds subjected to mineralization treatment. This finding suggests that there is little incorporation of protein into the growing mineral film, and offers insight into the mechanism for sustained drug delivery from the mineralized scaffolds.
Effect of Post-Treatment on Dissolution and Biomineralization on Surface of ha Coatings in Simulated Body Fluid (SBF)
Authors: Chen Jiyong , Weng Jie , Zhang Qiyi , Feng Jiaming , Cao Yang , Zhang Xingdong 
Published: April 2011

AbstractThe HA coatings were heated separately in vacuum, air and water vapor. The dissolution of the HA coatings was investigated by immersion in Tris buffer and SBF The dissolubility of HA coatings in the solutions decreased in this order: as-received, heated in vacuum, in air and in water vapor. The nucleation of bone-like apatite on the surfaces of HA coatings after immersing a period of 11 days in SBF was observed by SEM. The microenvironment with a sufficient supersaturation of Ca and P ions was crucial for the nucleation and growth of apatite in SBF. The dissolution of amorphous phase in coatings played an important part in establishing the supersaturation of Ca and P ions.
Structural and Chemical Analysis of Crystal Enamel Nucleation
Authors: Belío-Reyes I. A. , JimÉNez-García L. F. , Reyes-Gasga J. 
Published: April 2011

AbstractThe aim of the present study is to obtain structural and chemical information about nucleation and growth of dental enamel as a function of location in secretory mouse foetus enamel. Then enamel tissues were obtained from 19-days-mouse foetus. TEM images show that enamel crystallites had the well-documented thin ribbons, or needles. They were found in the outermost zone in the vicinity of ameloblasts. Chemical analysis by EDS showed that, besides the elements of hydroxyapatite, Na, Cl, Al and Mg are presents from the beginning of enamel mineralization. All of these elements will play an important role on the physics and chemical properties in mature enamel.
The Control of Mineralization on Natural and Implant Surfaces
Authors: Nancollas G. H. , Wu W. , Tang R. 
Published: April 2011

AbstractThe generation of minerals such as calcium phosphates on the surfaces of dental and joint replacement implants is beneficial since the facilitation of bone formation permits their fixation. In contrast, the prevention of crystallization is desired on other surfaces such as kidney and cardiac valve prostheses. A key to the development of successful biomaterials is therefore an understanding of the factors that control crystal nucleation, growth and dissolution in aqueous solution. The Constant Composition method was used to investigate the influence of factors such as solution composition, ionic strength, pH and temperature on the crystallization and dissolution of the calcium phosphates, brushite (DCPD), octacalcium phosphate (OCP), hydroxyapatite (HAP) and fluorapatite (FAP). In parallel with these studies, a contact angle method along with surface tension component theory was employed to investigate the roles of interfacial free energy in mineralization and demineralization. Values of the interfacial tensions, -4.2, 4.3, 10.4 and 18.5 mJm-2obtained from contact angle measurements for DCPD, OCP, HAP and FAP, respectively, compare well with those calculated from dissolution kinetics experiments and provide information concerning the growth and dissolution mechanisms. The exploitation of these approaches is illustrated in studies of the coating of specific calcium phosphate phases on titanium metal and alloy surfaces and nucleation and growth of OCP on polymer surfaces modified by silanization to produce amine- and carboxylterminated end groups. In all these reactions involving the calcium phosphates, concomitant dissolution reactions are often involved. Constant Composition kinetic studies have shown that the rate of these reactions decrease markedly with time despite a sustained driving force, and eventually, the rates approach zero even though crystals remain in the undersaturated solutions. Dissolution can be reinitiated by exposing the crystals to the solutions of different undersaturations. These results suggest that dislocation sizes play a significant role in the dissolution kinetic processes.
Charge Inhomogeneities in the Colossal Magnetoresistant Manganites From the Local Atomic Structure
Authors: Billinge S. J. L. , Petkov V. , Proffen Th. , Kwei G. H. , Sarrao J. L. , Shastri S. D. , Kycia S. 
Published: April 2011

AbstractWe have measured atomic pair distribution functions (PDF) of La1−xCaxMnO3 using high energy x-ray diffraction. This approach yields accurate PDFs with very high real-space resolution. It also avoids potential pitfalls from the more usual neutron measurements that magnetic scattering is present in the measurement, that the neutron scattering length of manganese is negative leading to partial cancellation of PDF peaks, and that inelasticity effects might distort the resulting PDF We have used this to address the following questions which do not have a satisfactory answer: (1) What are the amplitudes and natures of the local Jahn-Teller and polaronic distortions in the CMR region. (2) Is the ground-state of the ferromagnetic metallic phase delocalized or polaronic. (3) As one moves away from the ground-state, by raising temperature or decreasing doping, towards the metal insulator transition, how does the state of the material evolve?
New Magnetic and Ferroelectric Cubic Phase of Thin-Film Fe-Doped BaTiO3
Authors: Maier R. , Cohn J. L. , Neumeier J. J. , Bendersky L. A. 
Published: April 2011

AbstractThe properties of a new cubic perovskite phase of thin-film BaFexTi1−xO3 (0.5 ≤x≤0.75) are reported. This material is novel because the corresponding bulk compounds have hexagonal structure for comparable x. The films, grown by pulsed laser deposition on MgO and SrTiO3 substrates, are magnetic (ferro- or ferri-, with Tc > 500°C) and ferroelectric (Tc ∼ 200-300°C).
Is Magnetic Circular Dichroism Surface Sensitive in the Manganese Perovskites?
Authors: Borca C.N. , Cheng R.H. , Stadler Shane , Idzerda Y.U. , Choi Jaewu , Mcilroy D.N. , Xu Q.L. , Liou S.H. , Zhong Z.C. , Dowben P.A. 
Published: April 2011

AbstractWe compare the magnetization versus temperature, determined by magnetic circular dichroism, with bulk magnetization determined by SQUID magnetometry. The results for two different manganese perovskites, La0.65A0.35MnO3 systems (A=Pb, Sr), epitaxially grown on LaAlO3 substrates compared. The results suggest that the magnetic circular dichroism results may not be representative of the bulk magnetization. Similar materials, but with a different secondary electron mean free path lengths or different surface compositions, may thus be expected to have different behavior in MCD or MXLD that depends on a photoyield for detection.
Polarization Dynamics in La5/3Sr1/3NiO4
Authors: Hakim N. , Zhai Z. , Kusko C. , Parimi P.V. , Cheong S-W. , Sridhar S. 
Published: April 2011

AbstractDynamic susceptibility measurements at microwave frequencies (2 – 10GHz) are a sensitive probe of charge dynamcis in La5/3Sr1/3NiO4. Below the charge ordering temperature of 240K, a dielectric loss peak due to a relaxation mode with a large dielectric susceptibility is observed, and is associated with charge stripe formation. The dielectric response for Hω∥b (Eω ⊥ b) is well represented by ε(T) = εo/(1 – iωτ(T)), with εo, ∼ 50, and τ(T) = 2 × 10−9(sec) exp(−T/37K). Parallel conductivity σ(T) contributions dominate at higher temperatures and for Hω∥c (Eω ⊥ c). The dielectric loss peak observed indicates that the charge relaxation rates lie in the GHz frequency ranges.
High Pressure Measurements on TI2Mn2O7
Authors: Núñez-Regueiro M. , Senis R. , Cheikh-Rouhou W. , Strobel P. , Bordet P. , Pernet M. , Hanfland M. , Martinez B. , Fontcuberta J. 
Published: April 2011

AbstractTransport and structural properties of the colossal magnetoresistance pyrochlore TI2Mn2O7 are studied as a function of applied pressure up to ∼20GPa. This allows us to probe the effect of structural changes on the ferromagnetic transition and the transport properties. We observe a non-monotonous pressure dependence of the ferromagnetic transition temperature. We correlate this unusual variation with the structural parameters that, according to electronic band calculations, are key in controlling the properties of these materials.
The role of strain in low-field magnetotransport properties of manganite thin films
Authors: Hu Y. F. , Wang H. S. , Wertz E. , Li Qi 
Published: April 2011

AbstractStrain-induced large low-field magnetoresistance has been observed in very thin Pr0.67Sr0.33MnO3 films1. To better understand the role of strain in the low-field magnetotransport properties of manganite thin films, we have studied and compared very thin (3-20 nm) Pr0.67Sr0.33MnO3 (PSMO), La0.67Ba0.33MnO3 (LBMO), La0.67Sr 0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) films grown on different substrates, such as LaAlO3(001) (LAO), NdGaO3(110) (NGO), and SrTiO3(001) (STO). Due to the lattice mismatch between the films and the substrates ranging from -2.6% to +1%, different strains can be imposed to the films. We have found that: (1) large low-field magnetoresistance(LFMR) behaviors are observed in PSMO, LCMO and LSMO thin films on LAO substrates when a magnetic field is applied perpendicular to the film plane, but the maximum LFMR is the largest in PSMO and LCMO samples; (2) most of the films grown on STO substrates show positive MR when a magnetic field is applied perpendicular to the film plane, and when the field is parallel to the film plane all films show negative MR regardless of the substrates; (3) the large low-field MR is strongly dependent on the film thickness and the composition of the manganites. The anomalous low-field MR effect will be discussed based on strain-induced magnetic anisotropy and domain rotation and movement.
Large Magnetoresistance Anisotropy in Strained Pr0.67Sr0.33MnO3 Thin Films
Authors: Wang H. S. , Hu Y. F. , Wertz E. , Li Qi 
Published: April 2011

AbstractWe have studied the anisotropic magnetoresistance (AMR) of strained Pr0.67Sr0.33MnO3 thin films by measuring the MR as a function of the angle between the magnetic field direction and the substrate normal (out-of-plane). The results show that the compressive- and tensile-strained ultrathin films (5-15 nm) grown on LaAlO3 (001) (LAO) and SrTiO3 (001) (STO) substrates show unusually large out-of-plane AMR, but with opposite signs. In contrast, the almost strainfree films on the NdGaO3 (110) substrates show much smaller AMR over all the temperature and field ranges studied. Thick films on LAO and STO substrates also show much smaller AMR.