Growth of semiconducting GaN hollow spheres and nanotubes with very thin shells via a controllable liquid gallium-gas interface chemical reaction.

PubMed

Yin, Long-Wei; Bando, Yoshio; Li, Mu-Sen; Golberg, Dmitri

2005-11-01

An in situ liquid gallium-gas interface chemical reaction route has been developed to synthesize semiconducting hollow GaN nanospheres with very small shell size by carefully controlling the synthesis temperature and the ammonia reaction gas partial pressure. In this process the gallium droplet does not act as a catalyst but rather as a reactant and a template for the formation of hollow GaN structures. The diameter of the synthesized hollow GaN spheres is typically 20-25 nm and the shell thickness is 3.5-4.5 nm. The GaN nanotubes obtained at higher synthesis temperatures have a length of several hundreds of nanometers and a wall thickness of 3.5-5.0 nm. Both the hollow GaN spheres and nanotubes are polycrystalline and are composed of very fine GaN nanocrystalline particles with a diameter of 3.0-3.5 nm. The room-temperature photoluminescence (PL) spectra for the synthesized hollow GaN spheres and nanotubes, which have a narrow size distribution, display a sharp, blue-shifted band-edge emission peak at 3.52 eV (352 nm) due to quantum size effects.

Atomistic tight-binding computations of the structural and optical properties of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals

NASA Astrophysics Data System (ADS)

Sukkabot, Worasak

2018-05-01

A study of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals is carried out using atomistic tight-binding theory and the configuration interaction method to provide information for applications in bioimaging, biolabeling, display devices and near-infrared electronic instruments. The calculations yield the dependences of the internal and external passivated shells on the natural behaviours of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals. The reduction of the optical band gaps is observed with increasing numbers of monolayers in the external ZnS shell due to quantum confinement. Interestingly, the optical band gaps of CdTe/CdS/ZnS core/shell/shell nanocrystals are greater than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. In the presence of an external ZnS-coated shell, electron-hole wave function overlaps, oscillation strengths, ground-state exchange energies and Stokes shift are improved, whereas ground-state coulomb energies and fine-structure splitting are reduced. The oscillation strengths, Stokes shift and fine-structure splitting are reduced with the increase in external ZnS shell thickness. The oscillation strengths, Stokes shift and fine-structure splitting of CdTe/CdS/ZnS core/shell/shell nanocrystals are larger than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. Reduction of the atomistic electron-hole interactions is observed with increasing external ZnS shell size. The strong electron-hole interactions are more probed in CdTe/CdS/ZnS core/shell/shell nanocrystals than in CdTe/CdSe/ZnS core/shell/shell nanocrystals.

Chemical state analysis of Cl Kα and Kβ1,3 X-ray emission lines using polychromatic WDXRF spectrometer

NASA Astrophysics Data System (ADS)

Kainth, Harpreet Singh; Upmanyu, Arun; Sharma, Hitesh; Singh, Tejbir; Kumar, Sanjeev

2018-02-01

With the support of research projects focusing on sampling and data analysing of different varieties of chemical compounds, wavelength dispersive X-ray fluorescence (WDXRF) technique is commonly used in many research laboratories throughout the world wide to determine the elemental composition of various unknown samples. In the present study, first time we have employed polychromatic S8 TIGER WDXRF spectrometer to study the chemical state analysis in Cl Kα and Kβ1,3 X-ray emission lines. A Voigt function is used to determine the central peak position of the K shell emission lines in all samples. From the present measurements, it is seen that both positive and negative shifts have been observed in Cl Kα (2.622 keV) and Kβ1,3 (2.817 keV) emission peaks. It has been also seen that the effective charge, relative line-width and relative intensity ratio I(Kβ1,3/Kα) are found proportional with the chemical shift. Furthermore, a parabolic relation is also established between them.

Facile, one-pot and scalable synthesis of highly emissive aqueous-based Ag,Ni:ZnCdS/ZnS core/shell quantum dots with high chemical and optical stability

NASA Astrophysics Data System (ADS)

Sahraei, Reza; Soheyli, Ehsan; Faraji, Zahra; Soleiman-Beigi, Mohammad

2017-11-01

We report here on a one-pot, mild and low cost aqueous-based synthetic route for the preparation of colloidally stable and highly luminescent dual-doped Ag,Ni:ZnCdS/ZnS core/shell quantum dots (QDs). The pure dopant emission of the Ni-doped core/shell QDs was found to be highly affected by the presence of a second dopant ion (Ag+). Results showed that the PL emission intensity increases while its peak position experiences an obvious blue shift with an increase in the content of Ag+ ions. Regarding the optical observations, we provide a simple scheme for absorption-recombination processes of the carriers through impurity centers. To obtain optimum conditions with a better emission characteristic, we also study the effect of different reaction parameters, such as refluxing temperature, the pH of the core and shell solution, molar ratio of the dopant ions (Ni:(Zn+Cd) and Ag:(Zn+Cd)), and concentration of the core and shell precursors. Nonetheless, the most effective parameter is the presence of the ZnS shell in a suitable amount to eliminate surface trap states and enhance their emission intensity. It can also improve the bio-compatibility of the prepared QDs by restricting the Cd2+ toxic ions inside the core of the QDs. The present suggested route also revealed the remarkable optical and chemical stability of the colloidal QDs which establishes them as a decent kind of nano-scale structure for light emitting applications, especially in biological technologies. The suggested process also has the potential to be scaled-up while maintaining the emission characteristics and structural quality necessary for industrial applications in optoelectronic devices.

Shell morphology and Raman spectra of epitaxial Ge-SixGe1-x and Si-SixGe1-x core-shell nanowires

NASA Astrophysics Data System (ADS)

Wen, Feng; Dillen, David C.; Kim, Kyounghwan; Tutuc, Emanuel

2017-06-01

We investigate the shell morphology and Raman spectra of epitaxial Ge-SixGe1-x and Si-SixGe1-x core-shell nanowire heterostructures grown using a combination of a vapor-liquid-solid (VLS) growth mechanism for the core, followed by in-situ epitaxial shell growth using ultra-high vacuum chemical vapor deposition. Cross-sectional transmission electron microscopy reveals that the VLS growth yields cylindrical Ge, and Si nanowire cores grown along the ⟨111⟩, and ⟨110⟩ or ⟨112⟩ directions, respectively. A hexagonal cross-sectional morphology is observed for Ge-SixGe1-x core-shell nanowires terminated by six {112} facets. Two distinct morphologies are observed for Si-SixGe1-x core-shell nanowires that are either terminated by four {111} and two {100} planes associated with the ⟨110⟩ growth direction or four {113} and two {111} planes associated with the ⟨112⟩ growth direction. We show that the Raman spectra of Si- SixGe1-x are correlated with the shell morphology thanks to epitaxial growth-induced strain, with the core Si-Si mode showing a larger red shift in ⟨112⟩ core-shell nanowires compared to their ⟨110⟩ counterparts. We compare the Si-Si Raman mode value with calculations based on a continuum elasticity model coupled with the lattice dynamic theory.

Design, synthesis and applications of core-shell, hollow core, and nanorattle multifunctional nanostructures.

PubMed

El-Toni, Ahmed Mohamed; Habila, Mohamed A; Labis, Joselito Puzon; ALOthman, Zeid A; Alhoshan, Mansour; Elzatahry, Ahmed A; Zhang, Fan

2016-02-07

With the evolution of nanoscience and nanotechnology, studies have been focused on manipulating nanoparticle properties through the control of their size, composition, and morphology. As nanomaterial research has progressed, the foremost focus has gradually shifted from synthesis, morphology control, and characterization of properties to the investigation of function and the utility of integrating these materials and chemical sciences with the physical, biological, and medical fields, which therefore necessitates the development of novel materials that are capable of performing multiple tasks and functions. The construction of multifunctional nanomaterials that integrate two or more functions into a single geometry has been achieved through the surface-coating technique, which created a new class of substances designated as core-shell nanoparticles. Core-shell materials have growing and expanding applications due to the multifunctionality that is achieved through the formation of multiple shells as well as the manipulation of core/shell materials. Moreover, core removal from core-shell-based structures offers excellent opportunities to construct multifunctional hollow core architectures that possess huge storage capacities, low densities, and tunable optical properties. Furthermore, the fabrication of nanomaterials that have the combined properties of a core-shell structure with that of a hollow one has resulted in the creation of a new and important class of substances, known as the rattle core-shell nanoparticles, or nanorattles. The design strategies of these new multifunctional nanostructures (core-shell, hollow core, and nanorattle) are discussed in the first part of this review. In the second part, different synthesis and fabrication approaches for multifunctional core-shell, hollow core-shell and rattle core-shell architectures are highlighted. Finally, in the last part of the article, the versatile and diverse applications of these nanoarchitectures in catalysis, energy storage, sensing, and biomedicine are presented.

Interface formation during silica encapsulation of colloidal CdSe/CdS quantum dots observed by in situ Raman spectroscopy

NASA Astrophysics Data System (ADS)

Biermann, Amelie; Aubert, Tangi; Baumeister, Philipp; Drijvers, Emile; Hens, Zeger; Maultzsch, Janina

2017-04-01

We investigate the encapsulation of CdSe/CdS quantum dots (QDs) in a silica shell by in situ Raman spectroscopy and find a distinct shift of the CdS Raman signal during the first hours of the synthesis. This shift does not depend on the final silica shell thickness but on the properties of the initial core-shell QD. We find a correlation between the Raman shift rate and the speed of the silica formation and attribute this to the changing configuration of the outermost layers of the QD shell, where an interface to the newly formed silica is created. This dependence of Raman shift rate on the speed of silica formation process will give rise to many possible studies concerning the growth mechanism in the water-in-oil microemulsion, rendering in situ Raman a valuable instrument in monitoring this type of reaction.

Silicon K-edge XANES spectra of silicate minerals

NASA Astrophysics Data System (ADS)

Li, Dien; Bancroft, G. M.; Fleet, M. E.; Feng, X. H.

1995-03-01

Silicon K-edge x-ray absorption near-edge structure (XANES) spectra of a selection of silicate and aluminosilicate minerals have been measured using synchrotron radiation (SR). The spectra are qualitatively interpreted based on MO calculation of the tetrahedral SiO{4/4-}cluster. The Si K-edge generally shifts to higher energy with increased polymerization of silicates by about 1.3 eV, but with considerable overlap for silicates of different polymerization types. The substitution of Al for Si shifts the Si K-edge to lower energy. The chemical shift of Si K-edge is also sensitive to cations in more distant atom shells; for example, the Si K-edge shifts to lower energy with the substitution of Al for Mg in octahedral sites. The shifts of the Si K-edge show weak correlation with average Si-O bond distance (dSi-O), Si-O bond valence (sSi-O) and distortion of SiO4 tetrahedra, due to the crystal structure complexity of silicate minerals and multiple factors effecting the x-ray absorption processes.

Fabrication and investigation of effect of core size in heterostructure PbS/CdS core/shell nanoparticles

NASA Astrophysics Data System (ADS)

Das, D.; Hussain, A. M. P.

2018-04-01

PbS/CdS core/shell (CS) nanoparticles (NPs) were fabricated with three different concentrations of PbS core and CdS shell. Formation of core/shell heterostructure was confirmed from X-ray diffraction studies. The diffraction patterns exhibited formation of cubic phase and polycrystalline core/shell nanostructure. The crystalline sizes calculated from Williamson-Hall plot exhibited increase with molar concentration of precursors with decrease in strain. High resolution electron microscopy studies also confirm the formation of core/shell structure with particle size around 10 nm. A large blue-shift for PbS core compared to its bulk and small red-shift for the PbS/CdS core/shell as compared to the core is being observed in absorption spectra.

A broadening temperature sensitivity range with a core-shell YbEr@YbNd double ratiometric optical nanothermometer

NASA Astrophysics Data System (ADS)

Marciniak, L.; Prorok, K.; Francés-Soriano, L.; Pérez-Prieto, J.; Bednarkiewicz, A.

2016-02-01

The chemical architecture of lanthanide doped core-shell up-converting nanoparticles can be engineered to purposely design the properties of luminescent nanomaterials, which are typically inaccessible to their homogeneous counterparts. Such an approach allowed to shift the up-conversion excitation wavelength from ~980 to the more relevant ~808 nm or enable Tb or Eu up-conversion emission, which was previously impossible to obtain or inefficient. Here, we address the issue of limited temperature sensitivity range of optical lanthanide based nano-thermometers. By covering Yb-Er co-doped core nanoparticles with the Yb-Nd co-doped shell, we have intentionally combined temperature dependent Er up-conversion together with temperature dependent Nd --> Yb energy transfer, and thus have expanded the temperature response range ΔT of a single nanoparticle based optical nano-thermometer under single ~808 nm wavelength photo-excitation from around ΔT = 150 K to over ΔT = 300 K (150-450 K). Such engineered nanocrystals are suitable for remote optical temperature measurements in technology and biotechnology at the sub-micron scale.The chemical architecture of lanthanide doped core-shell up-converting nanoparticles can be engineered to purposely design the properties of luminescent nanomaterials, which are typically inaccessible to their homogeneous counterparts. Such an approach allowed to shift the up-conversion excitation wavelength from ~980 to the more relevant ~808 nm or enable Tb or Eu up-conversion emission, which was previously impossible to obtain or inefficient. Here, we address the issue of limited temperature sensitivity range of optical lanthanide based nano-thermometers. By covering Yb-Er co-doped core nanoparticles with the Yb-Nd co-doped shell, we have intentionally combined temperature dependent Er up-conversion together with temperature dependent Nd --> Yb energy transfer, and thus have expanded the temperature response range ΔT of a single nanoparticle based optical nano-thermometer under single ~808 nm wavelength photo-excitation from around ΔT = 150 K to over ΔT = 300 K (150-450 K). Such engineered nanocrystals are suitable for remote optical temperature measurements in technology and biotechnology at the sub-micron scale. Electronic supplementary information (ESI) available: Characterization, structural and morphological characterization of nanocrystals, the measurement setup. See DOI: 10.1039/c5nr08223d

75 FR 18239 - Notice of Proposed Consent Decree Under the Clean Air Act

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-09

... given that on March 31, 2010, two proposed Consent Decrees were lodged. United States et al. v. Shell... Southern District of Texas. United States v. Shell Chemical Yabucoa, Inc., Civil Action No. 3:10-cv-1268... in these Clean Air Act enforcement actions against Shell Chemical LP and Shell Chemical Yabucoa, Inc...

Enhance the photoluminescence and radioluminescence of La2Zr2O7:Eu3+ core nanoparticles by coating with a thin Y2O3 shell

NASA Astrophysics Data System (ADS)

Pokhrel, Madhab; Burger, Arnold; Groza, Michael; Mao, Yuanbing

2017-06-01

We report the generation of La2Zr2O7:5%Eu3+@Y2O3 (LZO5E@YO) core@shell crystalline inorganic-inorganic heterogeneous nanoparticles (NPs). The Y2O3 (YO) shell coating process based on a chemical sol-gel method led to the growth of a thin YO shell on the ordered pyrochlore La2Zr2O7:5%Eu3+ (LZO5E) core NPs. Photoluminescence (PL) analyses demonstrated a blue shift of 15 nm on charge transfer (CT) excitation band of the core@shell NPs from that of the core NPs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) along x-ray diffraction (XRD), Fourier-transform Infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) studies confirmed the formation of the thin YO layer over the LZO5E core NPs. The PL intensity of the LZO5E@YO core@shell NPs was enhanced by three fold compared to that of the LZO5E core NPs, and higher quantum yield (QY) was observed for the former compared to the original NPs by more than 70%. Higher radioluminescence (RL) emission was also observed for the core@shell NPs compared to the core NPs. Our ability of obtaining near-perfect core@shell heterostructure with enhanced luminescence performance opens the door for the development of efficient La2Zr2O7:5%Eu3+@Y2O3 NPs for both optical and x-ray scintillation applications.

LSPR Tuning from 470 to 800 nm and Improved Stability of Au-Ag Nanoparticles Formed by Gold Deposition and Rebuilding in the Presence of Poly(styrenesulfonate).

PubMed

Cathcart, Nicole; Chen, Jennifer I L; Kitaev, Vladimir

2018-01-16

Stability and precise control over functional properties of metal nanoparticles remain a challenge for the realization of prospective applications. Our described process of shell formation and rebuilding can address both these challenges. Template silver nanoparticles (AgNPs) stabilized by poly(styrenesulfonate) are first transformed with gold deposition, after which the resulting shell rebuilds with the replaced silver. The shell formation and rebuilding are accompanied by large shifts in localized surface plasmon resonance (LSPR) peak position, which enables LSPR tuning in a range from 470 to 800 nm. Furthermore, chemical stability of Au-AgNPs is significantly improved compared to AgNPs due to gold stability. Silver templates of different shapes and sizes were demonstrated to transform to AuAg composite NPs to further extend the accessible LSPR range tuning. Stabilization of template AgNPs with poly(styrenesulfonate), in contrast to commonly used poly(vinylpyrrolidone), was found to be a key factor for shell rebuilding. The developed Au-AgNPs were shown to be advantageous for surface plasmon resonance (SPR) detection and surface-enhanced Raman spectroscopy (SERS) owing to their tunable LSPR and enhanced stability.

Fractal dimension study of polaron effects in cylindrical GaAs/Al x Ga1- x As core-shell nanowires

NASA Astrophysics Data System (ADS)

Sun, Hui; Li, Hua; Tian, Qiang

2018-04-01

Polaron effects in cylindrical GaAs/Al x Ga1- x As core-shell nanowires are studied by applying the fractal dimension method. In this paper, the polaron properties of GaAs/Al x Ga1- x As core-shell nanowires with different core radii and aluminum concentrations are discussed. The polaron binding energy, polaron mass shift, and fractal dimension parameter are numerically determined as functions of shell width. The calculation results reveal that the binding energy and mass shift of the polaron first increase and then decrease as the shell width increases. A maximum value appears at a certain shell width for different aluminum concentrations and a given core radius. By using the fractal dimension method, polaron problems in cylindrical GaAs/Al x Ga1- x As core-shell nanowires are solved in a simple manner that avoids complex and lengthy calculations.

MR imaging of breast implants.

PubMed

Gorczyca, D P

1994-11-01

MR imaging has proved to be an excellent imaging modality in locating free silicone and evaluating an implant for rupture, with a sensitivity of approximately 94% and specificity of 97%. Silicone has a unique MR resonance frequency and long T1 and T2 relaxation times, which allows several MR sequences to provide excellent diagnostic images. The most commonly used sequences include T2-weighted, STIR, and chemical shift imaging (Figs. 3, 13, and 14). The T2-weighted and STIR sequences are often used in conjunction with chemical water suppression. The most reliable findings on MR images for detection of implant rupture include identification of the collapsed implant shell (linguine sign) and free silicone within the breast parenchyma.

Bandgap engineered reverse type-I CdTe/InP/ZnS core-shell nanocrystals for the near-infrared.

PubMed

Kim, Sunghoon; Shim, Wooyoung; Seo, Heonjin; Hyun Bae, Je; Sung, Jaeyoung; Choi, Seung Hong; Moon, Woo Kyung; Lee, Gwang; Lee, Bunyeoul; Kim, Sang-Wook

2009-03-14

New quantum dots were fabricated with a core/shell/shell structure consisting of CdTe core/InP shell/ZnS shell of which the InP shell causes a red-shift to the NIR region and the ZnS shell imparts photo-stability; toxicity tests on mammalian cells and NIR imaging of a mouse highlight their potential applications in biomedical imaging.

Chemical and thermal stability of core-shelled magnetite nanoparticles and solid silica

NASA Astrophysics Data System (ADS)

Cendrowski, Krzysztof; Sikora, Pawel; Zielinska, Beata; Horszczaruk, Elzbieta; Mijowska, Ewa

2017-06-01

Pristine nanoparticles of magnetite were coated by solid silica shell forming core/shell structure. 20 nm thick silica coating significantly enhanced the chemical and thermal stability of the iron oxide. Chemical and thermal stability of this structure has been compared to the magnetite coated by mesoporous shell and pristine magnetite nanoparticles. It is assumed that six-membered silica rings in a solid silica shell limit the rate of oxygen diffusion during thermal treatment in air and prevent the access of HCl molecules to the core during chemical etching. Therefore, the core/shell structure with a solid shell requires a longer time to induce the oxidation of iron oxide to a higher oxidation state and, basically, even strong concentrated acid such as HCl is not able to dissolve it totally in one month. This leads to the desired performance of the material in potential applications such as catalysis and environmental protection.

Improved nine-node shell element MITC9i with reduced distortion sensitivity

NASA Astrophysics Data System (ADS)

Wisniewski, K.; Turska, E.

2017-11-01

The 9-node quadrilateral shell element MITC9i is developed for the Reissner-Mindlin shell kinematics, the extended potential energy and Green strain. The following features of its formulation ensure an improved behavior: 1. The MITC technique is used to avoid locking, and we propose improved transformations for bending and transverse shear strains, which render that all patch tests are passed for the regular mesh, i.e. with straight element sides and middle positions of midside nodes and a central node. 2. To reduce shape distortion effects, the so-called corrected shape functions of Celia and Gray (Int J Numer Meth Eng 20:1447-1459, 1984) are extended to shells and used instead of the standard ones. In effect, all patch tests are passed additionally for shifts of the midside nodes along straight element sides and for arbitrary shifts of the central node. 3. Several extensions of the corrected shape functions are proposed to enable computations of non-flat shells. In particular, a criterion is put forward to determine the shift parameters associated with the central node for non-flat elements. Additionally, the method is presented to construct a parabolic side for a shifted midside node, which improves accuracy for symmetric curved edges. Drilling rotations are included by using the drilling Rotation Constraint equation, in a way consistent with the additive/multiplicative rotation update scheme for large rotations. We show that the corrected shape functions reduce the sensitivity of the solution to the regularization parameter γ of the penalty method for this constraint. The MITC9i shell element is subjected to a range of linear and non-linear tests to show passing the patch tests, the absence of locking, very good accuracy and insensitivity to node shifts. It favorably compares to several other tested 9-node elements.

Redox-Active Bis(phenolate) N-Heterocyclic Carbene [OCO] Pincer Ligands Support Cobalt Electron Transfer Series Spanning Four Oxidation States.

PubMed

Harris, Caleb F; Bayless, Michael B; van Leest, Nicolaas P; Bruch, Quinton J; Livesay, Brooke N; Bacsa, John; Hardcastle, Kenneth I; Shores, Matthew P; de Bruin, Bas; Soper, Jake D

2017-10-16

A new family of low-coordinate Co complexes supported by three redox-noninnocent tridentate [OCO] pincer-type bis(phenolate) N-heterocyclic carbene (NHC) ligands are described. Combined experimental and computational data suggest that the charge-neutral four-coordinate complexes are best formulated as Co(II) centers bound to closed-shell [OCO] 2- dianions, of the general formula [(OCO)Co II L] (where L is a solvent-derived MeCN or THF). Cyclic voltammograms of the [(OCO)Co II L] complexes reveal three oxidations accessible at potentials below 1.2 V vs Fc + /Fc, corresponding to generation of formally Co(V) species, but the true physical/spectroscopic oxidation states are much lower. Chemical oxidations afford the mono- and dications of the imidazoline NHC-derived complex, which were examined by computational and magnetic and spectroscopic methods, including single-crystal X-ray diffraction. The metal and ligand oxidation states of the monocationic complex are ambiguous; data are consistent with formulation as either [( S OCO)Co III (THF) 2 ] + containing a closed-shell [ S OCO] 2- diphenolate ligand bound to a S = 1 Co(III) center, or [( S OCO • )Co II (THF) 2 ] + with a low-spin Co(II) ion ferromagnetically coupled to monoanionic [ S OCO • ] - containing a single unpaired electron distributed across the [OCO] framework. The dication is best described as [( S OCO 0 )Co II (THF) 3 ] 2+ , with a single unpaired electron localized on the d 7 Co(II) center and a doubly oxidized, charge-neutral, closed-shell S OCO 0 ligand. The combined data provide for the first time unequivocal and structural evidence for [OCO] ligand redox activity. Notably, varying the degree of unsaturation in the NHC backbone shifts the ligand-based oxidation potentials by up to 400 mV. The possible chemical origins of this unexpected shift, along with the potential utility of the [OCO] pincer ligands for base-metal-mediated organometallic coupling catalysis, are discussed.

Tuning the field distribution and fabrication of an Al@ZnO core-shell nanostructure for a SPR-based fiber optic phenyl hydrazine sensor.

PubMed

Tabassum, Rana; Kaur, Parvinder; Gupta, Banshi D

2016-05-27

We report the fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic sensor that uses coatings of silver and aluminum (Al)-zinc oxide (ZnO) core-shell nanostructure (Al@ZnO) for the detection of phenyl hydrazine (Ph-Hyd). To optimize the volume fraction (f) of Al in ZnO and the thickness of the core-shell nanostructure layer (d), the electric field intensity along the normal to the multilayer system is simulated using the two-dimensional multilayer matrix method. The Al@ZnO core-shell nanostructure is prepared using the laser ablation technique. Various probes are fabricated with different values of f and an optimized thickness of core-shell nanostructure for the characterization of the Ph-Hyd sensor. The performance of the Ph-Hyd sensor is evaluated in terms of sensitivity. It is found that the Ag/Al@ZnO nanostructure core-shell-coated SPR probe with f = 0.25 and d = 0.040 μm possesses the maximum sensitivity towards Ph-Hyd. These results are in agreement with the simulated ones obtained using electric field intensity. In addition, the performance of the proposed probe is compared with that of probes coated with (i) Al@ZnO nanocomposite, (ii) Al nanoparticles and (iii) ZnO nanoparticles. It is found that the probe coated with an Al@ZnO core-shell nanostructure shows the largest resonance wavelength shift. The detailed mechanism of the sensing (involving chemical reactions) is presented. The sensor also manifests optimum performance at pH 7.

Chemical shift in Lα, Lβ1, Lβ3,4, Lβ2,15, Lγ1 and Lγ2,3 emission lines of 47Ag, 48Cd and 50Sn compounds

NASA Astrophysics Data System (ADS)

Singh Kainth, Harpreet; Singh, Ranjit; Singh, Gurjot; Mehta, D.

2018-01-01

Positive and negative shifts in L shell emission lines of 47Ag, 48Cd and 50Sn elements in different chemical compounds were determined from their recorded X-ray emission spectra in high resolution wavelength dispersive X-ray fluorescence (WDXRF) spectrometer. In 47Ag compounds, the measured energy shifts in Lα X-ray emission line were in the ranges from (0.12 to 0.40) eV, Lβ1 (0.27 to 0.36) eV, Lβ3,4 (1.10 to 4.89) eV, Lγ1 (-0.09 to 1.13) eV and Lγ2,3 (-2.08 to 0.59) eV. Likewise, for 48Cd compounds, the estimated shifts in Lα X-ray emission lines were in the range (-0.27 to 0.69) eV, Lβ1 (0.50 to 2.06) eV, Lβ2,15 (0.12 to 0.79), Lβ3,4 (-0.62 to 1.79) eV, Lγ1 (0.10 to 1.35) eV and Lγ2,3 (-0.73 to 1.75) eV, while for 50Sn compounds, the measured shifts in Lα X-ray emission lines were in the range of (0.02 to 1.81) eV, Lβ1 (0.11 to 0.78) eV, Lβ2,15 (0.15 to 1.40), Lβ3,4 (0.17 to 2.01) eV, Lγ1 (0.09 to 1.08) eV and Lγ2,3 (0.17 to 1.40) eV respectively. The effective charges (qP, qS, qL and qB) were calculated by four different theoretical methods (Pauling method, Suchet method, Levine method and Batsonav method) and found to be linear dependent with the chemical shift. Further, the measured chemical shifts were correlated with bond length, relative line-width (FWHM), effective charge, electronegativity, number of ligands and Coster-Kronig (CK) transition processes.

Estimation of sensing characteristics for refractory nitrides based gain assisted core-shell plasmonic nanoparticles

NASA Astrophysics Data System (ADS)

Shishodia, Manmohan Singh; Pathania, Pankaj

2018-04-01

Refractory transition metal nitrides such as zirconium nitride (ZrN), hafnium nitride (HfN) and titanium nitride (TiN) have emerged as viable alternatives to coinage metals based plasmonic materials, e.g., gold (Au) and silver (Ag). The present work assesses the suitability of gain assisted ZrN-, HfN- and TiN-based conventional core-shell nanoparticles (CCSNPs) and multilayered core-shell nanoparticles (MCSNPs) for refractive index sensing. We report that the optical gain incorporation in the dielectric layer leads to multifold enhancement of the scattering efficiency (Qsca), substantial reduction of the spectral full width at half maximum, and a higher figure of merit (FOM). In comparison with CCSNPs, the MCSNP system exhibits superior sensing characteristics such as higher FOM, ˜ 45% reduction in the critical optical gain, response shift towards the biological window, and higher degree of tunability. Inherent biocompatibility, growth compatibility, chemical stability and flexible spectral tuning of refractory nitrides augmented by superior sensing properties in the present work may pave the way for refractory nitrides based low cost sensing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, Stephanie B.; Harding, Eric C.; Knapp, Patrick F.

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated bymore » the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.« less

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

NASA Astrophysics Data System (ADS)

Hansen, S. B.; Harding, E. C.; Knapp, P. F.; Gomez, M. R.; Nagayama, T.; Bailey, J. E.

2018-05-01

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. We show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 1024 e/cm3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.

Investigation of novel inverted NiO@NixCo1-xO core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Hasan, Samiul; Mayanovic, R. A.; Benamara, Mourad

2018-05-01

Inverse core-shell nanoparticles, comprised of an antiferromagnetic (AFM) core covered by a ferromagnetic (FM) or ferrimagnetic (FiM) shell, are of current interest due to their different potential application and due to the tunability of their magnetic properties. The antiferromagnetic nature of NiO and high Néel temperature (523 K) makes this material well suited for inverse core-shell nanoparticle applications. Our primary objective in this project has been to synthesize and characterize inverted core-shell nanoparticles (CSNs) comprised of a NiO (AFM) core and a shell consisting of a NixCo1-xO (FiM) compound. The synthesis of the CSNs was made using a two-step process. The NiO nanoparticles were synthesized using a chemical reaction method. Subsequently, the NiO nanoparticles were used to grow the NiO@NixCo1-xO CSNs using our hydrothermal nano-phase epitaxy method. XRD structural characterization shows that the NiO@NixCo1-xO CSNs have the rock salt cubic crystal structure. SEM-EDS data indicates the presence of Co in the CSNs. Magnetic measurements show that the CSNs exhibit AFM/FiM characteristics with a small coercivity field of 30 Oe at 5 K. The field cooled vs zero field cooled hysteresis loop measurements show a magnetization axis shift which is attributed to the exchange bias effect between the AFM NiO core and an FiM NixCo1-xO shell of the CSNs. Our ab initio based calculations of the NixCo1-xO rock salt structure confirm a weak FiM character and a charge transfer insulator property of the compound.

X-ray absorption spectral studies of copper (II) mixed ligand complexes

NASA Astrophysics Data System (ADS)

Soni, B.; Dar, Davood Ah; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

2014-09-01

X-ray absorption spectra at the K-edge of copper have been studied in two copper mixed ligand complexes, one having tetramethyethylenediamine (tmen) and the other having tetraethyethylenediamine (teen) as one of the ligands. The spectra have been recorded at BL-8 dispersive extended X-ray absorption fine structure (EXAFS) beamline at the 2.5 GeV INDUS- 2 synchrotron, RRCAT, Indore, India. The data obtained has been processed using the data analysis program Athena. The energy of the K-absorption edge, chemical shift, edge-width and shift of the principal absorption maximum in the complexes have been determined and discussed. The values of these parameters have been found to be approximately the same in both the complexes indicating that the two complexes possess similar chemical environment around the copper metal atom. The chemical shift has been utilized to estimate effective nuclear charge on the absorbing atom. The normalized EXAFS spectra have been Fourier transformed. The position of the first peak in the Fourier transform gives the value of first shell bond length, which is shorter than the actual bond length because of energy dependence of the phase factors in the sine function of the EXAFS equation. This distance is thus the phase- uncorrected bond length. Bond length has also been determined by Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods. The results obtained from LSS and the Fourier transformation methods are comparable with each other, since both are phase uncorrected bond lengths.

The death assemblage as a marker for habitat and an indicator of climate change: Georges Bank, surfclams and ocean quahogs

NASA Astrophysics Data System (ADS)

Powell, Eric N.; Kuykendall, Kelsey M.; Moreno, Paula

2017-06-01

A comprehensive dataset for the Georges Bank region is used to directly compare the distribution of the death assemblage and the living community at large spatial scales and to assess the application of the death assemblage in tracking changes in species' distributional pattern as a consequence of climate change. Focus is placed on the biomass-dominant clam species of the northwest Atlantic continental shelf: the surfclam Spisula solidissima and the ocean quahog Arctica islandica, for which extensive datasets exist on the distributions of the living population and the death assemblage. For both surfclams and ocean quahogs, the distribution of dead shells, in the main, tracked the distribution of live animals relatively closely. Thus, for both species, the presence of dead shells was a positive indicator of present, recent, or past occupation by live animals. Shell dispersion within habitat was greater for surfclams than for ocean quahogs either due to spatial time averaging, animals not living in all habitable areas all of the time, or parautochthonous redistribution of shell. The regional distribution of dead shell differed from the distribution of live animals, for both species, in a systematic way indicative of range shifts due to climate change. In each case the differential distribution was consistent with warming of the northwest Atlantic. Present-day overlap of live surfclams with live ocean quahogs was consistent with the expectation that the surfclam's range is shifting into deeper water in response to the recent warming trend. The presence of locations devoid of dead shells where live surfclams nevertheless were collected measures the recentness of this event. The presence of dead ocean quahog shells at shallower depths than live ocean quahogs offers good evidence that a range shift has occurred in the past, but prior to the initiation of routine surveys in 1980. Possibly, this range shift tracks initial colonization at the end of the Little Ice Age.

Interplay between Surface Chemistry, Precursor Reactivity, and Temperature Determines Outcome of ZnS Shelling Reactions on CuInS2 Nanocrystals

PubMed Central

2018-01-01

ZnS shelling of I–III–VI2 nanocrystals (NCs) invariably leads to blue-shifts in both the absorption and photoluminescence spectra. These observations imply that the outcome of ZnS shelling reactions on I–III–VI2 colloidal NCs results from a complex interplay between several processes taking place in solution, at the surface of, and within the seed NC. However, a fundamental understanding of the factors determining the balance between these different processes is still lacking. In this work, we address this need by investigating the impact of precursor reactivity, reaction temperature, and surface chemistry (due to the washing procedure) on the outcome of ZnS shelling reactions on CuInS2 NCs using a seeded growth approach. We demonstrate that low reaction temperatures (150 °C) favor etching, cation exchange, and alloying regardless of the precursors used. Heteroepitaxial shell overgrowth becomes the dominant process only if reactive S- and Zn-precursors (S-ODE/OLAM and ZnI2) and high reaction temperatures (210 °C) are used, although a certain degree of heterointerfacial alloying still occurs. Remarkably, the presence of residual acetate at the surface of CIS seed NCs washed with ethanol is shown to facilitate heteroepitaxial shell overgrowth, yielding for the first time CIS/ZnS core/shell NCs displaying red-shifted absorption spectra, in agreement with the spectral shifts expected for a type-I band alignment. The insights provided by this work pave the way toward the design of improved synthesis strategies to CIS/ZnS core/shell and alloy NCs with tailored elemental distribution profiles, allowing precise tuning of the optoelectronic properties of the resulting materials. PMID:29657360

Band bending at the heterointerface of GaAs/InAs core/shell nanowires monitored by synchrotron X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Khanbabaee, B.; Bussone, G.; Knutsson, J. V.; Geijselaers, I.; Pryor, C. E.; Rieger, T.; Demarina, N.; Grützmacher, D.; Lepsa, M. I.; Timm, R.; Pietsch, U.

2016-10-01

Unique electronic properties of semiconductor heterostructured nanowires make them useful for future nano-electronic devices. Here, we present a study of the band bending effect at the heterointerface of GaAs/InAs core/shell nanowires by means of synchrotron based X-ray photoelectron spectroscopy. Different Ga, In, and As core-levels of the nanowire constituents have been monitored prior to and after cleaning from native oxides. The cleaning process mainly affected the As-oxides and was accompanied by an energy shift of the core-level spectra towards lower binding energy, suggesting that the As-oxides turn the nanowire surfaces to n-type. After cleaning, both As and Ga core-levels revealed an energy shift of about -0.3 eV for core/shell compared to core reference nanowires. With respect to depth dependence and in agreement with calculated strain distribution and electron quantum confinement, the observed energy shift is interpreted by band bending of core-levels at the heterointerface between the GaAs nanowire core and the InAs shell.

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

DOE PAGES

Hansen, Stephanie B.; Harding, Eric C.; Knapp, Patrick F.; ...

2018-03-07

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated bymore » the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.« less

Shell Chemical LP To Install $10 Million In Pollution Monitoring And Control Equipment At Norco Chemical Facility In Louisiana To Resolve Alleged Federal And State Clean Air Violations

EPA Pesticide Factsheets

EPA News Release: Shell Chemical LP To Install $10 Million In Pollution Monitoring And Control Equipment At Norco Chemical Facility In Louisiana To Resolve Alleged Federal And State Clean Air Violations

Shell Biorefinery: Dream or Reality?

PubMed

Chen, Xi; Yang, Huiying; Yan, Ning

2016-09-12

Shell biorefinery, referring to the fractionation of crustacean shells into their major components and the transformation of each component into value-added chemicals and materials, has attracted growing attention in recent years. Since the large quantities of waste shells remain underexploited, their valorization can potentially bring both ecological and economic benefits. This Review provides an overview of the current status of shell biorefinery. It first describes the structural features of crustacean shells, including their composition and their interactions. Then, various fractionation methods for the shells are introduced. The last section is dedicated to the valorization of chitin and its derivatives for chemicals, porous carbon materials and functional polymers. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structure and photoluminescence properties of TeO2-core/TiO2-shell nanowires

NASA Astrophysics Data System (ADS)

Park, Sunghoon; An, Soyeon; Lee, Chongmu

2013-12-01

TeO2-core/TiO2-shell nanowires were fabricated by thermal evaporation of Te powders and MOCVD of TiO2. The as-synthesized TeO2 nanowires showed a weak broad violet band centered at approximately 430 nm. The emission peak was shifted to a bluish violet region (∼455 nm) by the encapsulation of the nanowires with a TiO2 thin film. The intensity of the major emission from the core-shell nanowires showed strong dependence on the shell layer thickness. The strongest emission was obtained for the shell layer thickness of ∼15 nm and its intensity was approximately 80 times higher than that of the violet emission from the as-synthesized TeO2 nanowires. This enhancement in emission intensity is attributed to the subwavelength optical resonant cavity formation in the shell layer. The major emission intensity was enhanced further and blue-shifted by annealing, which might be attributed to the increase in the Ti interstitial and O vacancy concentrations in the TeO2 cores during annealing.

Effect of core-shell structure on optical properties of Au-Cu2O nanoparticles

NASA Astrophysics Data System (ADS)

Sai, Cong Doanh; Ngac, An Bang

2018-03-01

Solid Au-Cu2O core-shell nanoparticles were synthesized using gold nanoparticles of 16.6 nm in size as the core. The core-shell structure of the synthesized particles was confirmed and characterized by TEM and HRTEM images. Due to their similar crystal structure, the (111) planes of Cu2O are nucleated and grown epitaxially on the {111} facets of Au nanoparticles with the lattice mismatch of about 4.3% resulting in a polycrystallized Cu2O shell covering the Au nanocore. Due to the quantum confinement effect, the band gap energy Eg of the synthesized Cu2O shells is blue-shifted from 2.35 to 2.70 eV as the shell thickness decreases from of 24.6±3.6 to 9.0±1.7 nm. The localized SPR (Surface Plasmon Resonance) peak of the Au nanocore undergoes a large red shift of the order of a hundred of nm due to both the high refractive index and the increase of the thickness of Cu2O shell. Theoretical models within the Drude framework significantly underestimate the experimental data and predict a wrong rate of change of the SPR peak position with respect to the shell thickness.

Ag@ZnO core-shell nanoparticles study by first principle: The structural, magnetic and optical properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Hai-Xia; Wang, Xiao-Xu; Beijing Computing Center, Beijing 100094

Ag@ZnO core-shell nanoparticles of around 72 atoms have been investigated by the density functional theory, revealing proving for the first time that the core-shell structure exhibits a shrinkage phenomenon from outer shell in agreement with the other studies in literatures. Our calculations predict that the Ag@ZnO core-shell structure is a ferromagnetic spin polarized state, and the magnetism mainly stems from the spin splitting of 2p electrons of O atoms. In addition, the total and partial DOS of Ag@ZnO indicate that the nanostructure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. Furthermore, the optical properties calculations showmore » that the absorption edge of Ag@ZnO have a red shift and good photocatalysis compare to that of the bulk ZnO. These results of the Ag@ZnO core-shell structure obtain a well agreement with the experimental measurement. - Graphical abstract: Geometric structure of (a) Ag@ZnO core-shell nanostructure; (b) the core of Ag; (c) the shell of ZnO The core-shell nanoparticle Ag@ZnO contains Ag inner core of radius of 4 Å and ZnO outer shell with thickness of 2 Å. Ag@ZnO core-shell nanoparticles of around 72 atoms have been proved for the first time that the core-shell structure exhibit a shrinkage phenomenon from outer shell. Our calculations predict that the Ag@ZnO core-shell structure is a half-metallic nanoparticle and has the characters of the p-type semiconductor. The absorption edge of Ag@ZnO have a red shift and get good photo-catalysis compare to that of the bulk ZnO.« less

Diagenetic changes in Concholepas concholepas shells (Gastropoda, Muricidae) in the hyper-arid conditions of Northern Chile - implications for palaeoenvironmental reconstructions

NASA Astrophysics Data System (ADS)

Guzmán, N.; Dauphin, Y.; Cuif, J. P.; Denis, A.; Ortlieb, L.

2009-02-01

Variations in the chemical composition of fossil biogenic carbonates, and in particular of mollusc shells, have been used in a range of palaeoenvironmental reconstructions. It is of primary importance, therefore, to detect and understand the diagenetic processes that may modify the original chemical signature. This microstructural and biogeochemical study focuses on modern and fossil (Holocene and Pleistocene) shells of a littoral gastropod of Northern Chile, and on the characterization of mineral component transformations at the nanometric scale and concomitant intracrystalline organic compound modifications. The inner aragonite layer of the shell exhibits more complex deteriorations than the calcite layer. This preliminary study confirms that physical and chemical alterations of various components of mollusc shell biocrystals are complex and might manifest in different ways even within a single individual. The single criterion of determining the mineralogical composition to verify the conservation state of shell samples is insufficient.

Diagenetic changes in Concholepas concholepas shells (Gastropoda, Muricidae) in the hyper-arid conditions of Northern Chile - implications for palaeoenvironmental reconstructions

NASA Astrophysics Data System (ADS)

Guzman, N.; Dauphin, Y.; Cuif, J. P.; Denis, A.; Ortlieb, L.

2008-02-01

Variations on chemical composition in fossil biogenic carbonates, and in particular of mollusk shells, have been used in a range of palaeoenvironmental reconstructions. Therefore, it is of primary importance to detect and understand the diagenetic processes that may modify the original chemical signature. This microstructural and biogeochemical study focuses on modern and fossil (Pleistocene and Holocene) shells of a littoral gastropod of Northern Chile, and on the characterization of mineral component transformations at the nanometric scale and concomitant intracrystalline organic compound modifications. The inner aragonite layer of the shell exhibits more complex deteriorations than the calcite layer. This preliminary study confirms that physical and chemical alterations of various components of mollusk shell biocrystals are complex and might manifest in different ways even within a single individual. The single criterion of determining the mineralogical composition to attest shell sample conservation state should not be considered as sufficient.

Inner-shell chemistry under high pressure

NASA Astrophysics Data System (ADS)

Miao, Maosheng; Botana, Jorge; Pravica, Michael; Sneed, Daniel; Park, Changyong

2017-05-01

Chemistry at ambient conditions has implicit boundaries rooted in the atomic shell structure: the inner-shell electrons and the unoccupied outer-shell orbitals do not contribute as the major component to chemical reactions and in chemical bonds. These general rules govern our understanding of chemical structures and reactions. We review the recent progresses in high-pressure chemistry demonstrating that the above rules can be violated under extreme conditions. Using a first principles computation method and crystal structure search algorithm, we demonstrate that stable compounds involving inner shell electrons such as CsF3, CsF5, HgF3, and HgF4 can form under high external pressure and may present exotic properties. We also discuss experimental studies that have sought to confirm these predictions. Employing our recently developed hard X-ray photochemistry methods in a diamond anvil cell, we show promising early results toward realizing inner shell chemistry experimentally.

Direct mapping between exchange potentials of Hartree-Fock and Kohn-Sham schemes as origin of orbital proximity

NASA Astrophysics Data System (ADS)

Cinal, M.

2010-01-01

It is found that for closed-l-shell atoms, the exact local exchange potential vx(r) calculated in the exchange-only Kohn-Sham (KS) scheme of the density functional theory (DFT) is very well represented within the region of every atomic shell by each of the suitably shifted potentials obtained with the nonlocal Fock exchange operator for the individual Hartree-Fock (HF) orbitals belonging to this shell. This newly revealed property is not related to the well-known steplike shell structure in the response part of vx(r), but it results from specific relations satisfied by the HF orbital exchange potentials. These relations explain the outstanding proximity of the occupied HF and exchange-only KS orbitals as well as the high quality of the Krieger-Li-Iafrate and localized HF (or, equivalently, common-energy-denominator) approximations to the DFT exchange potential vx(r). Another highly accurate representation of vx(r) is given by the continuous piecewise function built of shell-specific exchange potentials, each defined as the weighted average of the shifted orbital exchange potentials corresponding to a given shell. The constant shifts added to the HF orbital exchange potentials, to map them onto vx(r), are nearly equal to the differences between the energies of the corresponding KS and HF orbitals. It is discussed why these differences are positive and grow when the respective orbital energies become lower for inner orbitals.

The microstructure and magnetic properties of Cu/CuO/Ni core/multi-shell nanowire arrays

NASA Astrophysics Data System (ADS)

Yang, Feng; Shi, Jie; Zhang, Xiaofeng; Hao, Shijie; Liu, Yinong; Feng, Chun; Cui, Lishan

2018-04-01

Multifunctional metal/oxide/metal core/multi-shell nanowire arrays were prepared mostly by physical or chemical vapor deposition. In our study, the Cu/CuO/Ni core/multi-shell nanowire arrays were prepared by AAO template-electrodeposition and oxidation processes. The Cu/Ni core/shell nanowire arrays were prepared by AAO template-electrodeposition method. The microstructure and chemical compositions of the core/multi-shell nanowires and core/shell nanowires have been characterized using transmission electron microscopy with HADDF-STEM and X-ray diffraction. Magnetization measurements revealed that the Cu/CuO/Ni and Cu/Ni nanowire arrays have high coercivity and remanence ratio.

Disorders of metal metabolism

PubMed Central

Ferreira, Carlos R.; Gahl, William A.

2017-01-01

Trace elements are chemical elements needed in minute amounts for normal physiology. Some of the physiologically relevant trace elements include iodine, copper, iron, manganese, zinc, selenium, cobalt and molybdenum. Of these, some are metals, and in particular, transition metals. The different electron shells of an atom carry different energy levels, with those closest to the nucleus being lowest in energy. The number of electrons in the outermost shell determines the reactivity of such an atom. The electron shells are divided in sub-shells, and in particular the third shell has s, p and d sub-shells. Transition metals are strictly defined as elements whose atom has an incomplete d sub-shell. This incomplete d sub-shell makes them prone to chemical reactions, particularly redox reactions. Transition metals of biologic importance include copper, iron, manganese, cobalt and molybdenum. Zinc is not a transition metal, since it has a complete d sub-shell. Selenium, on the other hand, is strictly speaking a nonmetal, although given its chemical properties between those of metals and nonmetals, it is sometimes considered a metalloid. In this review, we summarize the current knowledge on the inborn errors of metal and metalloid metabolism. PMID:29354481

Preliminary evaluation of physical and chemical characterization of waste palm oil shell as cool material replaced in asphaltic concrete as fine aggregate

NASA Astrophysics Data System (ADS)

Anuar, M. A. M.; Anting, N.; Shahidan, S.; Lee, Y. Y.; Din, M. F. Md; Khalid, F. S.; Nazri, W. M. H. W.

2017-11-01

Malaysia is one of the biggest producer of palm oil product and currently as main source of economy for the country. During the production of crude palm oil, a large amount of waste material is generated, such as palm oil fibres, palm oil shells and empty fruit bunches. Palm oil shell aggregate (POSA) is identified as a material that shows good potential to be used as a fine aggregate replacement in asphaltic concrete. On other hand, the chemical compound that exist in the Palm Oil Shell (POS) have shown a good potential as reflective component in cool-material. The purpose of this study is to obtain the physical and chemical properties of palm oil shell. The result shows the apparent particle density of Palm Oil Shell is 1.6 mg/m3. The specific gravity of palm oil shell was obtained with the value 1.6 and the water absorption amount of palm oil shell recorded from this study was 25.1%. The X-Ray Fluorescence study shows that palm oil shell contains the highest amount of SiO2 (46.412 wt%) and the second highest amount of Fe2O3 (34.016 wt%), both is the main output of relectivity compound. As a conclusion, waste palm oil shell has a potential to be used as alternative material for fine aggregate replacement. Besides that, the amount of chemical element that consist in palm oil shell which high in SiO2 and Fe2O3, promising the benefit to mitigate urban heat island as a cooling material agent.

Rhythmic patterns in ancient shells: Can we reconstruct sub-annual cyclicity in trace element and stable isotope profiles from rudist bivalves?

NASA Astrophysics Data System (ADS)

de Winter, N.; Sinnesael, M.; Vansteenberge, S.; Goderis, S.; Snoeck, C.; Van Malderen, S. J. M.; Vanhaecke, F. F.; Claeys, P.

2017-12-01

Well-preserved shells of Torreites rudists from the Late Campanian Saiwan Formation in Oman exhibit fine internal layering. These fine (±20 µm) laminae are rhythmically bundled (±400 µm) and subdivide the shells' larger scale annual lamination (±15 mm), suggesting the presence of several interfering cycles in shell growth rate. The aim of the present study is to determine the duration and chemical signature of these rhythmic variations in shell composition. To achieve this, a range of micro-analytical techniques is applied on cross sections through the shells. Firstly, microscopy-based layer counting and colorimetric analysis are carried out on thin sections of shell calcite. Secondly, X-Ray Fluorescence (XRF) and Fourier Transform InfraRed (FTIR) mapping of cross sections of the shells reveal chemical and structural differences between laminae in 2D. Thirdly, high-resolution XRF (25 µm) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS; 10 µm) trace element profiles are used to quantify variations in chemical composition between shell laminae. Fourthly, annual chronology is established based on micro-sampled stable carbon and oxygen stable isotope measurements (250 µm) along the growth axis of the shells. Finally, spectral analysis routines are applied to extract rhythmic patterns matched to the shell laminae from the structural, chemical and colorimetric data. Combining these methods allows for a full evaluation of the structural and chemical characteristics as well as the timing of sub-annual lamination in rudist shells. The results of this study shed light on the external factors that influenced growth rates in rudist bivalves. A better understanding of the timing of deposition of these laminae allows them to be used to improve age models of geochemical records in rudist shells. Characterization of small scale variations in shell composition will characterize the uncertainties contained within lower resolution proxy records from these fossil bivalves. Finally, the study of these laminae enables the reconstruction of sub-annual cyclicity in the environment of Late Cretaceous rudist bivalves. This may in turn shed light on the mechanics of climate in this shallow marine hothouse setting, which provide an analogue of future climate in the light of anthropogenic climate change.

Computer Technology for Industry

NASA Technical Reports Server (NTRS)

1982-01-01

Shell Oil Company used a COSMIC program, called VISCEL to insure the accuracy of the company's new computer code for analyzing polymers, and chemical compounds. Shell reported that there were no other programs available that could provide the necessary calculations. Shell produces chemicals for plastic products used in the manufacture of automobiles, housewares, appliances, film, textiles, electronic equipment and furniture.

X-Ray Absorption Microspectroscopy with Electrostatic Force Microscopy and its Application to Chemical States Mapping

NASA Astrophysics Data System (ADS)

Ishii, M.; Rigopoulos, N.; Poolton, N. R. J.; Hamilton, B.

2007-02-01

A new technique named X-EFM that measures the x-ray absorption fine structure (XAFS) of nanometer objects was developed. In X-EFM, electrostatic force microscopy (EFM) is used as an x-ray absorption detector, and photoionization induced by x-ray absorption of surface electron trapping sites is detected by EFM. An EFM signal with respect to x-ray photon energy provides the XAFS spectra of the trapping sites. We adopted X-EFM to observe Si oxide thin films. An edge jump shift intrinsic to the X-EFM spectrum was found, and it was explained with a model where an electric field between the trapping site and probe deepens the energy level of the inner-shell. A scanning probe under x-rays with fixed photon energy provided the chemical state mapping on the surface.

Core-shell SrTiO3/graphene structure by chemical vapor deposition for enhanced photocatalytic performance

NASA Astrophysics Data System (ADS)

He, Chenye; Bu, Xiuming; Yang, Siwei; He, Peng; Ding, Guqiao; Xie, Xiaoming

2018-04-01

Direct growth of high quality graphene on the surface of SrTiO3 (STO) was realized through chemical vapor deposition (CVD), to construct few-layer 'graphene shell' on every STO nanoparticle. The STO/graphene composite shows significantly enhanced UV light photocatalytic activity compared with the STO/rGO reference. Mechanism analysis confirms the role of special core-shell structure and chemical bond (Tisbnd C) for rapid interfacial electron transfer and effective electron-hole separation.

Introduction of biotin or folic acid into polypyrrole magnetite core-shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nan, Alexandrina; Turcu, Rodica; Liebscher, Jürgen

2013-11-13

In order to contribute to the trend in contemporary research to develop magnetic core shell nanoparticles with better properties (reduced toxicity, high colloidal and chemical stability, wide scope of application) in straightforward and reproducible methods new core shell magnetic nanoparticles were developed based on polypyrrole shells functionalized with biotin and folic acid. Magnetite nanoparticles stabilized by sebacic acid were used as magnetic cores. The morphology of magnetite was determined by transmission electron microscopy TEM, while the chemical structure investigated by FT-IR.

Off-shell amplitudes as boundary integrals of analytically continued Wilson line slope

NASA Astrophysics Data System (ADS)

Kotko, P.; Serino, M.; Stasto, A. M.

2016-08-01

One of the methods to calculate tree-level multi-gluon scattering amplitudes is to use the Berends-Giele recursion relation involving off-shell currents or off-shell amplitudes, if working in the light cone gauge. As shown in recent works using the light-front perturbation theory, solutions to these recursions naturally collapse into gauge invariant and gauge-dependent components, at least for some helicity configurations. In this work, we show that such structure is helicity independent and emerges from analytic properties of matrix elements of Wilson line operators, where the slope of the straight gauge path is shifted in a certain complex direction. This is similar to the procedure leading to the Britto-Cachazo-Feng-Witten (BCFW) recursion, however we apply a complex shift to the Wilson line slope instead of the external momenta. While in the original BCFW procedure the boundary integrals over the complex shift vanish for certain deformations, here they are non-zero and are equal to the off-shell amplitudes. The main result can thus be summarized as follows: we derive a decomposition of a helicity-fixed off-shell current into gauge invariant component given by a matrix element of a straight Wilson line plus a reminder given by a sum of products of gauge invariant and gauge dependent quantities. We give several examples realizing this relation, including the five-point next-to-MHV helicity configuration.

Chemical insights into the roles of nanowire cores on the growth and supercapacitor performances of Ni-Co-O/Ni(OH)2 core/shell electrodes

PubMed Central

Yin, Xuesong; Tang, Chunhua; Zhang, Liuyang; Yu, Zhi Gen; Gong, Hao

2016-01-01

Nanostructured core/shell electrodes have been experimentally demonstrated promising for high-performance electrochemical energy storage devices. However, chemical insights into the significant roles of nanowire cores on the growth of shells and their supercapacitor behaviors still remain as a research shortfall. In this work, by substituting 1/3 cobalt in the Co3O4 nanowire core with nickel, a 61% enhancement of the specific mass-loading of the Ni(OH)2 shell, a tremendous 93% increase of the volumetric capacitance and a superior cyclability were achieved in a novel NiCo2O4/Ni(OH)2 core/shell electrode in contrast to a Co3O4/Ni(OH)2 one. A comparative study suggested that not only the growth of Ni(OH)2 shells but also the contribution of cores were attributed to the overall performances. Importantly, their chemical origins were revealed through a theoretical simulation of the core/shell interfacial energy changes. Besides, asymmetric supercapacitor devices and applications were also explored. The scientific clues and practical potentials obtained in this work are helpful for the design and analysis of alternative core/shell electrode materials. PMID:26857606

Chemical insights into the roles of nanowire cores on the growth and supercapacitor performances of Ni-Co-O/Ni(OH)₂ core/shell electrodes.

PubMed

Yin, Xuesong; Tang, Chunhua; Zhang, Liuyang; Yu, Zhi Gen; Gong, Hao

2016-02-09

Nanostructured core/shell electrodes have been experimentally demonstrated promising for high-performance electrochemical energy storage devices. However, chemical insights into the significant roles of nanowire cores on the growth of shells and their supercapacitor behaviors still remain as a research shortfall. In this work, by substituting 1/3 cobalt in the Co3O4 nanowire core with nickel, a 61% enhancement of the specific mass-loading of the Ni(OH)2 shell, a tremendous 93% increase of the volumetric capacitance and a superior cyclability were achieved in a novel NiCo2O4/Ni(OH)2 core/shell electrode in contrast to a Co3O4/Ni(OH)2 one. A comparative study suggested that not only the growth of Ni(OH)2 shells but also the contribution of cores were attributed to the overall performances. Importantly, their chemical origins were revealed through a theoretical simulation of the core/shell interfacial energy changes. Besides, asymmetric supercapacitor devices and applications were also explored. The scientific clues and practical potentials obtained in this work are helpful for the design and analysis of alternative core/shell electrode materials.

Observations on ichnology, taphonomy and epibiota in the freshwater realm

NASA Astrophysics Data System (ADS)

Lawfield, Andrew Martin William

Ichnology concerns the study of interactions between organisms and both soft and hard substrates. Actualistic observation of a modern day river channel molluscan assemblage including unionid and sphaeriid bivalves and gastropods within the Saint John River, Fredericton, New Brunswick, Canada reveals their production of almond shaped Lockeia like resting traces, together with varied, horizontally aligned furrowed, meandering, looping and spiral plan view locomotion/grazing traces. These traces occur within a shifting sand softground substrate. An emersion event associated with a low water level allowed collection of unionid samples, amongst which Elliptio complanata predominates, alongside Lampsilis radiata and Anodonta implicata. Detailed analysis of shell material, with methodologies including scanning electron microscopy (SEM) reveals microboring, various taphonomic signatures and the development of biofilm and extracellular polymeric substances (EPS). These are often associated with one another and their location closely influenced by the shell structure. Taphonomic decay of the shells was noted, with the external periostracum and prismatic aragonite layers decaying, particularly in the umbonal region. Physical puncturing and tearing penetrate the periostracum. Exposed regions of nacreous aragonite are smoothed by a combination of chemical interaction with the water column and physical abrasion from agitated silt and sand sediments. Surface pitting and circular to ovoid penetrations with morphologies comparable to Oichnus borings are noted and their formation is tentatively attributed to bacterial decay processes. In marine settings, the outer protective periostracum of molluscs often possesses physical and chemical defence mechanisms intended to inhibit the attachment of epibiota. Our observations suggest their absence from unionids, with final instar larval or pupal stage Trichoptera, including Goera, Neophylax and Helicopsyche selectively attached to regions of intact periostracum in preference to exposed aragonite on dead shells. In addition, live unionids can display thick growths of cyanobacterial or cyanophyte dominated microbial mat. Biofilm and extracellular polymeric substances, with bacterial, diatomaceous and filamentous components are also observed, often displaying a close association with both microboring and the shells conchiolin layers. Several styles of microboring are noted, with predominantly surficial and both simple tubular and complex network penetrative styles observed. Microborings may be attributed to cyanobacterial, cyanophyte and fungal activity.

Composted oyster shell as lime fertilizer is more effective than fresh oyster shell.

PubMed

Lee, Young Han; Islam, Shah Md Asraful; Hong, Sun Joo; Cho, Kye Man; Math, Renukaradhya K; Heo, Jae Young; Kim, Hoon; Yun, Han Dae

2010-01-01

Physio-chemical changes in oyster shell were examined, and fresh and composted oyster shell meals were compared as lime fertilizers in soybean cultivation. Structural changes in oyster shell were observed by AFM and FE-SEM. We found that grains of the oyster shell surface became smoother and smaller over time. FT-IR analysis indicated the degradation of a chitin-like compound of oyster shell. In chemical analysis, pH (12.3+/-0.24), electrical conductivity (4.1+/-0.24 dS m(-1)), and alkaline powder (53.3+/-1.12%) were highest in commercial lime. Besides, pH was higher in composted oyster shell meal (9.9+/-0.53) than in fresh oyster shell meal (8.4+/-0.32). The highest organic matter (1.1+/-0.08%), NaCl (0.54+/-0.03%), and moisture (15.1+/-1.95%) contents were found in fresh oyster shell meal. A significant higher yield of soybean (1.33 t ha(-1)) was obtained by applying composted oyster shell meal (a 21% higher yield than with fresh oyster shell meal). Thus composting of oyster shell increases the utility of oyster shell as a liming material for crop cultivation.

Controlled synthesis of AlN/GaN multiple quantum well nanowire structures and their optical properties.

PubMed

Qian, Fang; Brewster, Megan; Lim, Sung K; Ling, Yichuan; Greene, Christopher; Laboutin, Oleg; Johnson, Jerry W; Gradečak, Silvija; Cao, Yu; Li, Yat

2012-06-13

We report the controlled synthesis of AlN/GaN multi-quantum well (MQW) radial nanowire heterostructures by metal-organic chemical vapor deposition. The structure consists of a single-crystal GaN nanowire core and an epitaxially grown (AlN/GaN)(m) (m = 3, 13) MQW shell. Optical excitation of individual MQW nanowires yielded strong, blue-shifted photoluminescence in the range 340-360 nm, with respect to the GaN near band-edge emission at 368.8 nm. Cathodoluminescence analysis on the cross-sectional MQW nanowire samples showed that the blue-shifted ultraviolet luminescence originated from the GaN quantum wells, while the defect-associated yellow luminescence was emitted from the GaN core. Computational simulation provided a quantitative analysis of the mini-band energies in the AlN/GaN superlattices and suggested the observed blue-shifted emission corresponds to the interband transitions between the second subbands of GaN, as a result of quantum confinement and strain effect in these AlN/GaN MQW nanowire structures.

A shell regeneration assay to identify biomineralization candidate genes in mytilid mussels.

PubMed

Hüning, Anne K; Lange, Skadi M; Ramesh, Kirti; Jacob, Dorrit E; Jackson, Daniel J; Panknin, Ulrike; Gutowska, Magdalena A; Philipp, Eva E R; Rosenstiel, Philip; Lucassen, Magnus; Melzner, Frank

2016-06-01

Biomineralization processes in bivalve molluscs are still poorly understood. Here we provide an analysis of specifically expressed sequences from a mantle transcriptome of the blue mussel, Mytilus edulis. We then developed a novel, integrative shell injury assay to test, whether biomineralization candidate genes highly expressed in marginal and pallial mantle could be induced in central mantle tissue underlying the damaged shell areas. This experimental approach makes it possible to identify gene products that control the chemical micro-environment during calcification as well as organic matrix components. This is unlike existing methodological approaches that work retroactively to characterize calcification relevant molecules and are just able to examine organic matrix components that are present in completed shells. In our assay an orthogonal array of nine 1mm holes was drilled into the left valve, and mussels were suspended in net cages for 20, 29 and 36days to regenerate. Structural observations using stereo-microscopy, SEM and Raman spectroscopy revealed organic sheet synthesis (day 20) as the first step of shell-repair followed by the deposition of calcite crystals (days 20 and 29) and aragonite tablets (day 36). The regeneration period was characterized by time-dependent shifts in gene expression in left central mantle tissue underlying the injured shell, (i) increased expression of two tyrosinase isoforms (TYR3: 29-fold and TYR6: 5-fold) at day 20 with a decline thereafter, (ii) an increase in expression of a gene encoding a nacrein-like protein (max. 100-fold) on day 29. The expression of an acidic Asp-Ser-rich protein was enhanced during the entire regeneration process. This proof-of-principle study demonstrates that genes that are specifically expressed in pallial and marginal mantle tissue can be induced (4 out of 10 genes) in central mantle following experimental injury of the overlying shell. Our findings suggest that regeneration assays can be used systematically to better characterize gene products that are essential for distinct phases of the shell formation process, particularly those that are not incorporated into the organic shell matrix. Copyright © 2016 Elsevier B.V. All rights reserved.

Energy transfer in aggregated CuInS2/ZnS core-shell quantum dots deposited as solid films

NASA Astrophysics Data System (ADS)

Gardelis, S.; Fakis, M.; Droseros, N.; Georgiadou, D.; Travlos, A.; Nassiopoulou, A. G.

2017-01-01

We report on the morphology and optical properties of CuInS2/ZnS core-shell quantum dots in solid films by means of AFM, SEM, HRTEM, steady state and time-resolved photoluminescence (PL) spectroscopy. The amount of aggregation of the CuInS2/ZnS QDs was controlled by changing the preparation conditions of the films. A red-shift of the PL spectrum of CuInS2/ZnS core-shell quantum dots, deposited as solid films on silicon substrates, is observed upon increasing the amount of aggregation. The presence of larger aggregates was found to lead to a larger PL red-shift. Besides, as the degree of aggregation increased, the PL decay became slower. We attribute the observed PL red-shift to energy transfer from the smaller to the larger dots within the aggregates, with the emission being realized via a long decay recombination mechanism (100-200 ns), the origin of which is discussed.

Activated coconut shell charcoal carbon using chemical-physical activation

NASA Astrophysics Data System (ADS)

Budi, Esmar; Umiatin, Nasbey, Hadi; Bintoro, Ridho Akbar; Wulandari, Futri; Erlina

2016-02-01

The use of activated carbon from natural material such as coconut shell charcoal as metal absorbance of the wastewater is a new trend. The activation of coconut shell charcoal carbon by using chemical-physical activation has been investigated. Coconut shell was pyrolized in kiln at temperature about 75 - 150 °C for about 6 hours in producing charcoal. The charcoal as the sample was shieved into milimeter sized granule particle and chemically activated by immersing in various concentration of HCl, H3PO4, KOH and NaOH solutions. The samples then was physically activated using horizontal furnace at 400°C for 1 hours in argon gas environment with flow rate of 200 kg/m3. The surface morphology and carbon content of activated carbon were characterized by using SEM/EDS. The result shows that the pores of activated carbon are openned wider as the chemical activator concentration is increased due to an excessive chemical attack. However, the pores tend to be closed as further increasing in chemical activator concentration due to carbon collapsing.

Surface-enhanced Raman spectroscopy of double-shell hollow nanoparticles: electromagnetic and chemical enhancements.

PubMed

Mahmoud, Mahmoud A

2013-05-28

Enhancements of the Raman signal by the newly prepared gold-palladium and gold-platinum double-shell hollow nanoparticles were examined and compared with those using gold nanocages (AuNCs). The surface-enhanced Raman spectra (SERS) of thiophenol adsorbed on the surface of AuNCs assembled into a Langmuir-Blodgett monolayer were 10-fold stronger than AuNCs with an inner Pt or Pd shell. The chemical and electromagnetic enhancement mechanisms for these hollow nanoparticles were further proved by comparing the Raman enhancement of nitrothiophenol and nitrotoulene. Nitrothiophenol binds to the surface of the nanoparticles by covalent interaction, and Raman enhancement by both the two mechanisms is possible, while nitrotoulene does not form any chemical bond with the surface of the nanoparticles and hence no chemical enhancement is expected. Based on discrete dipole approximation (DDA) calculations and the experimental SERS results, AuNCs introduced a high electromagnetic enhancement, while the nanocages with inner Pt or Pd shell have a strong chemical enhancement. The optical measurements of the localized surface plasmon resonance (LSPR) of the nanocages with an outer Au shell and an inner Pt or Pd shell were found, experimentally and theoretically, to be broad compared with AuNCs. The possible reason could be due to the decrease of the coherence time of Au oscillated free electrons and fast damping of the plasmon energy. This agreed well with the fact that a Pt or Pd inner nanoshell decreases the electromagnetic field of the outer Au nanoshell while increasing the SERS chemical enhancement.

Clam Shell Dredging in Lakes Pontchartrain and Maurepas, Louisiana. Volume 2. Public Comments.

DTIC Science & Technology

1987-11-01

levels and pattern of distribution of polycyclic aromatic hydrocarbons , is presented, despite the fact that these compounds are identified . . as the...DEIS. Moreover, the DEIS implies that the potential for bioaccumulation of the pollutants present in Lake Ponchartrain is low except for a small...CHEMICAL AIR PRODUCTS SHELL OIL CO SHELL CHEMICAL CIBA GEIGY CORPORATION UNION TEXAS PETROLEUM SAVOIE INDUSTRIES SUNLAND SERVICES VULCAN MATERIAL

Structure/Property Relations in "Giant" Semiconductor Nanocrystals: Opportunities in Photonics and Electronics.

PubMed

Navarro-Pardo, Fabiola; Zhao, Haiguang; Wang, Zhiming M; Rosei, Federico

2018-03-20

Semiconductor nanocrystals exhibit size-tunable absorption and emission ranging from the ultraviolet (UV) to the near-infrared (NIR) spectral range, high absorption coefficient, and high photoluminescence quantum yield. Effective surface passivation of these so-called quantum dots (QDs) may be achieved by growing a shell of another semiconductor material. The resulting core/shell QDs can be considered as a model system to study and optimize structure/property relations. A special case consists in growing thick shells (1.5 up to few tens of nanometers) to produce "giant" QDs (g-QDs). Tailoring the chemical composition and structure of CdSe/CdS and PbS/CdS g-QDs is a promising approach to widen the spectral separation of absorption and emission spectra (i.e., the Stokes shift), improve the isolation of photogenerated carriers from surface defects and enhance charge carrier lifetime and mobility. However, most stable systems are limited by a thick CdS shell, which strongly absorbs radiation below 500 nm, covering the UV and part of the visible range. Modification of the interfacial region between the core and shell of g-QDs or tuning their doping with narrow band gap semiconductors are effective approaches to circumvent this challenge. In addition, the synthesis of g-QDs composed of environmentally friendly elements (e.g., CuInSe 2 /CuInS 2 ) represents an alternative to extend their absorption into the NIR range. Additionally, the band gap and band alignment of g-QDs can be engineered by proper selection of the constituents according to their band edge positions and by tuning their stoichiometry during wet chemical synthesis. In most cases, the quasi-type II localization regime of electrons and holes is achieved. In this type of g-QDs, electrons can leak into the shell region, while the holes remain confined within the core region. This electron-hole spatial distribution is advantageous for optoelectronic devices, resulting in efficient electron-hole separation while maintaining good stability. This Account provides an overview of emerging engineering strategies that can be adopted to optimize structure/property relations in colloidal g-QDs for efficient photon management or charge separation/transfer. In particular, we focus on our recent contributions to this rapidly expanding field of research. We summarize the design and synthesis of a variety of colloidal g-QDs with the aim of tuning the optical properties, such as absorption/emission in a wide region of the solar spectrum, which allows enlargement of their Stokes shift. We also describe the band alignment within these systems, charge carrier dynamics, and charge transfer from g-QDs into semiconducting oxides. We show how these tailored g-QDs may be used as active components in luminescent solar concentrators, photoelectrochemical cells for hydrogen generation, QD-sensitized solar cells and optical nanothermometers. In each case, we aim at providing insights on structure/property relationships and on how to optimize them toward improving device performance. Finally, we describe perspectives for future work, sketching new directions and opportunities in this field of research at the intersection between chemistry, physics, materials science and engineering.

Wave Function Engineering in CdSe/PbS Core/Shell Quantum Dots.

PubMed

Wieliczka, Brian M; Kaledin, Alexey L; Buhro, William E; Loomis, Richard A

2018-05-25

The synthesis of epitaxial CdSe/PbS core/shell quantum dots (QDs) is reported. The PbS shell grows in a rock salt structure on the zinc blende CdSe core, thereby creating a crystal structure mismatch through additive growth. Absorption and photoluminescence (PL) band edge features shift to lower energies with increasing shell thickness, but remain above the CdSe bulk band gap. Nevertheless, the profiles of the absorption spectra vary with shell growth, indicating that the overlap of the electron and hole wave functions is changing significantly. This leads to over an order of magnitude reduction of absorption near the band gap and a large, tunable energy shift, of up to 550 meV, between the onset of strong absorption and the band edge PL. While the bulk valence and conduction bands adopt an inverse type-I alignment, the observed spectroscopic behavior is consistent with a transition between quasi-type-I and quasi-type-II behavior depending on shell thickness. Three effective mass approximation models support this hypothesis and suggest that the large difference in effective masses between the core and shell results in hole localization in the CdSe core and a delocalization of the electron across the entire QD. These results show the tuning of wave functions and transition energies in CdSe/PbS nanoheterostructures with prospects for use in optoelectronic devices for luminescent solar concentration or multiexciton generation.

Solar-thermal reaction processing

DOEpatents

Weimer, Alan W; Dahl, Jaimee K; Lewandowski, Allan A; Bingham, Carl; Raska Buechler, Karen J; Grothe, Willy

2014-03-18

In an embodiment, a method of conducting a high temperature chemical reaction that produces hydrogen or synthesis gas is described. The high temperature chemical reaction is conducted in a reactor having at least two reactor shells, including an inner shell and an outer shell. Heat absorbing particles are included in a gas stream flowing in the inner shell. The reactor is heated at least in part by a source of concentrated sunlight. The inner shell is heated by the concentrated sunlight. The inner shell re-radiates from the inner wall and heats the heat absorbing particles in the gas stream flowing through the inner shell, and heat transfers from the heat absorbing particles to the first gas stream, thereby heating the reactants in the gas stream to a sufficiently high temperature so that the first gas stream undergoes the desired reaction(s), thereby producing hydrogen or synthesis gas in the gas stream.

Effect of core quantum-dot size on power-conversion-efficiency for silicon solar-cells implementing energy-down-shift using CdSe/ZnS core/shell quantum dots.

PubMed

Baek, Seung-Wook; Shim, Jae-Hyoung; Seung, Hyun-Min; Lee, Gon-Sub; Hong, Jin-Pyo; Lee, Kwang-Sup; Park, Jea-Gun

2014-11-07

Silicon solar cells mainly absorb visible light, although the sun emits ultraviolet (UV), visible, and infrared light. Because the surface reflectance of a textured surface with SiNX film on a silicon solar cell in the UV wavelength region (250-450 nm) is higher than ∼27%, silicon solar-cells cannot effectively convert UV light into photo-voltaic power. We implemented the concept of energy-down-shift using CdSe/ZnS core/shell quantum-dots (QDs) on p-type silicon solar-cells to absorb more UV light. CdSe/ZnS core/shell QDs demonstrated clear evidence of energy-down-shift, which absorbed UV light and emitted green-light photoluminescence signals at a wavelength of 542 nm. The implementation of 0.2 wt% (8.8 nm QDs layer) green-light emitting CdSe/ZnS core/shell QDs reduced the surface reflectance of the textured surface with SiNX film on a silicon solar-cell from 27% to 15% and enhanced the external quantum efficiency (EQE) of silicon solar-cells to around 30% in the UV wavelength region, thereby enhancing the power conversion efficiency (PCE) for p-type silicon solar-cells by 5.5%.

Enhanced cavitation and heating of flowing polymer- and lipid-shelled microbubbles and phase-shift nanodroplets during focused ultrasound exposures

NASA Astrophysics Data System (ADS)

Zhang, Siyuan; Cui, Zhiwei; Li, Chong; Zhou, Fanyu; Zong, Yujin; Wang, Supin; Wan, Mingxi

2017-03-01

Cavitation and heating are the primary mechanisms of numerous therapeutic applications of ultrasound. Various encapsulated microbubbles (MBs) and phase-shift nanodroplets (NDs) have been used to enhance local cavitation and heating, creating interests in developing ultrasound therapy using these encapsulated MBs and NDs. This work compared the efficiency of flowing polymer- and lipid-shelled MBs and phase-shift NDs in cavitation and heating during focused ultrasound (FUS) exposures. Cavitation activity and temperature were investigated when the solution of polymer- and lipid-shelled MBs and NDs flowed through the vessel in a tissue-mimicking phantom with varying flow velocities when exposed to FUS at various acoustic power levels. The inertial cavitation dose (ICD) for the encapsulated MBs and NDs were higher than those for the saline. Temperature initially increased with increasing flow velocities of the encapsulated MBs, followed by a decrease of the temperature with increasing flow velocities when the velocity was much higher. Meanwhile, ICD showed a trend of increases with increasing flow velocity. For the phase-shift NDs, ICD after the first FUS exposure was lower than those after the second FUS exposure. For the encapsulated MBs, ICD after the first FUS exposure was higher than those after the second FUS exposure. Further studies are necessary to investigate the treatment efficiency of different encapsulated MBs and phase-shift NDs in cavitation and heating.

Spherical silicon-shell photonic band gap structures fabricated by laser-assisted chemical vapor deposition

NASA Astrophysics Data System (ADS)

Wang, H.; Yang, Z. Y.; Lu, Y. F.

2007-02-01

Laser-assisted chemical vapor deposition was applied in fabricating three-dimensional (3D) spherical-shell photonic band gap (PBG) structures by depositing silicon shells covering silica particles, which had been self-assembled into 3D colloidal crystals. The colloidal crystals of self-assembled silica particles were formed on silicon substrates using the isothermal heating evaporation approach. A continuous wave Nd:YAG laser (1064nm wavelength) was used to deposit silicon shells by thermally decomposing disilane gas. Periodic silicon-shell/silica-particle PBG structures were obtained. By removing the silica particles enclosed in the silicon shells using hydrofluoric acid, hollow spherical silicon-shell arrays were produced. This technique is capable of fabricating structures with complete photonic band gaps, which is predicted by simulations with the plane wave method. The techniques developed in this study have the potential to flexibly engineer the positions of the PBGs by varying both the silica particle size and the silicon-shell thickness. Ellipsometry was used to investigate the specific photonic band gaps for both structures.

Microcapsule and methods of making and using microcapsules

DOEpatents

Okawa, David C.; Pastine, Stefan J.; Zettl, Alexander K.; Frechet, Jean M.J.

2014-09-02

An embodiment of a microcapsule includes a shell surrounding a space, a liquid within the shell, and a light absorbing material within the liquid. An embodiment of a method of making microcapsules includes forming a mixture of a light absorbing material and an organic solution. An emulsion of the mixture and an aqueous solution is then formed. A polymerization agent is added to the emulsion, which causes microcapsules to be formed. Each microcapsule includes a shell surrounding a space, a liquid within the shell, and light absorbing material within the liquid. An embodiment of a method of using microcapsules includes providing phototriggerable microcapsules within a bulk material. Each of the phototriggerable microcapsules includes a shell surrounding a space, a chemically reactive material within the shell, and a light absorbing material within the shell. At least some of the phototriggerable microcapsules are exposed to light, which causes the chemically reactive material to release from the shell and to come into contact with bulk material.

Synthesis and Luminescence Properties of Core/Shell ZnS:Mn/ZnO Nanoparticles.

PubMed

Jiang, Daixun; Cao, Lixin; Liu, Wei; Su, Ge; Qu, Hua; Sun, Yuanguang; Dong, Bohua

2009-01-01

In this paper the influence of ZnO shell thickness on the luminescence properties of Mn-doped ZnS nanoparticles is studied. Transmission electron microscopy (TEM) images showed that the average diameter of ZnS:Mn nanoparticles is around 14 nm. The formation of ZnO shells on the surface of ZnS:Mn nanoparticles was confirmed by X-ray diffraction (XRD) patterns, high-resolution TEM (HRTEM) images, and X-ray photoelectron spectroscopy (XPS) measurements. A strong increase followed by a gradual decline was observed in the room temperature photoluminescence (PL) spectra with the thickening of the ZnO shell. The photoluminescence excitation (PLE) spectra exhibited a blue shift in ZnO-coated ZnS:Mn nanoparticles compared with the uncoated ones. It is shown that the PL enhancement and the blue shift of optimum excitation wavelength are led by the ZnO-induced surface passivation and compressive stress on the ZnS:Mn cores.

Glycerol capped PbS/CdS core/shell nanoparticles at different molar ratio and its application in biosensors: An optical properties study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, D., E-mail: ddasphy014@gmail.com; Hussain, A. M. P.

2016-05-06

Glycerol capped PbS/CdS core/shell type nanoparticles fabricated with two different molar ratios are characterized for study of structural and optical properties. The X-ray diffraction (XRD) pattern exhibits cubic phased polycrystalline nanocrystals. The calculated grain sizes from Williamson-Hall plot were found to be around 6 nm with increased strain. HRTEM investigation confirms the formation of core/shell nanostructures and the sizes of the particles were found to be around 7 nm which is in good agreement with the results of the W-H plot. An increase of band gap with the decrease in precursor concentration is confirmed from the blue shift in the absorption spectramore » and also from Tauc plot. A clear blue shifted intense emission is observed in the photoluminescence spectra with decrease in particle size. Intense luminescence from the core/shell nanostructure may be applied in bio labelling and biosensors.« less

Role of 6-Mercaptopurine in the potential therapeutic targets DNA base pairs and G-quadruplex DNA: insights from quantum chemical and molecular dynamics simulations.

PubMed

Radhika, R; Shankar, R; Vijayakumar, S; Kolandaivel, P

2018-05-01

The theoretical studies on DNA with the anticancer drug 6-Mercaptopurine (6-MP) are investigated using theoretical methods to shed light on drug designing. Among the DNA base pairs considered, 6-MP is stacked with GC with the highest interaction energy of -46.19 kcal/mol. Structural parameters revealed that structure of the DNA base pairs is deviated from the planarity of the equilibrium position due to the formation of hydrogen bonds and stacking interactions with 6-MP. These deviations are verified through the systematic comparison between X-H bond contraction and elongation and the associated blue shift and red shift values by both NBO analysis and vibrational analysis. Bent's rule is verified for the C-H bond contraction in the 6-MP interacted base pairs. The AIM results disclose that the higher values of electron density (ρ) and Laplacian of electron density (∇ 2 ρ) indicate the increased overlap between the orbitals that represent the strong interaction and positive values of the total electron density show the closed-shell interaction. The relative sensitivity of the chemical shift values for the DNA base pairs with 6-MP is investigated to confirm the hydrogen bond strength. Molecular dynamics simulation studies of G-quadruplex DNA d(TGGGGT) 4 with 6-MP revealed that the incorporation of 6-MP appears to cause local distortions and destabilize the G-quadruplex DNA.

Chemical modification of the cocoa shell surface using diazonium salts.

PubMed

Fioresi, Flavia; Vieillard, Julien; Bargougui, Radhouane; Bouazizi, Nabil; Fotsing, Patrick Nkuigue; Woumfo, Emmanuel Djoufac; Brun, Nicolas; Mofaddel, Nadine; Le Derf, Franck

2017-05-15

The outer portion of the cocoa bean, also known as cocoa husk or cocoa shell (CS), is an agrowaste material from the cocoa industry. Even though raw CS is used as food additive, garden mulch, and soil conditioner or even burnt for fuel, this biomass material has hardly ever been investigated for further modification. This article proposes a strategy of chemical modification of cocoa shell to add value to this natural material. The study investigates the grafting of aryl diazonium salt on cocoa shell. Different diazonium salts were grafted on the shell surface and characterized by infrared spectroscopy and scanning electronic microscopy imaging. Strategies were developed to demonstrate the spontaneous grafting of aryl diazonium salt on cocoa shell and to elucidate that lignin is mainly involved in immobilizing the phenyl layer. Copyright © 2017 Elsevier Inc. All rights reserved.

Plasmonic Switches and Sensors Based on PANI-Coated Gold Nanostructures

NASA Astrophysics Data System (ADS)

Jiang, Nina

Gold nanostructures have been received intense and growing attention due to their unique properties associated with localized surface plasmon resonance (LSPR). The frequency and strength of the LSPR are highly dependent on the dielectric properties of the surrounding environment around gold nanostructures. Such dependence offers the essential basis for the achievement of plasmonic switching and sensing. While the plasmonic response of gold nanostructures is tuned by changing their dielectric environment, the external stimuli inducing the changes in the dielectric environment will be read out through the plasmonic response of gold nanostructures. As a consequence, plasmonic sensors and switches can be engineered by integrating active media that can respond to external stimuli with gold nanostructures. In this thesis research, I have achieved the coating of polyaniline (PANI) ' a conductive polymer, on gold nanostructures, and exploited the application of the core/shell nanostructures in plasmonic switching and sensing. Large modulation of the longitudinal plasmon resonance of single gold nanorods is achieved by coating PANI shell onto gold nanorods to produce colloidal plasmonic switches. The dielectric properties of PANI shell can be tuned by changing the proton-doping levels, which allows for the modulation of the plasmonic response of gold nanorods. The coated nanorods are sparsely housed in a simple microfluidic chamber. HCl and NaOH solutions are alternately pumped through the chamber for the realization of proton doping and dedoping. The plasmonic switching behavior is examined by monitoring the single-particle scattering spectra under the proton-doped and dedoped state of PANI. The coated nanorods exhibit a remarkable switching performance, with the modulation depth and scattering peak shift reaching 10 dB and 100 nm, respectively. Electrodynamic simulations are employed to confirm the plasmon switching behavior. I have further investigated the modulation of a macroscale array of PANI-coated gold nanorods immobilized on glass slides, whose performance is as good as that of the individual PANI-coated gold nanorods. With much smaller amounts of materials, my core/shell nanorod arrays show peak extinction values and maximal modulation depths that are comparable to those of PANI films with micrometer-scale thicknesses. Switching coupled surface plasmon relative to uncoupled one affords the possibility to achieve the modulation over a wide spectral band and with wealthy plasmonic responses. Thus, I have studied the active control of plasmon coupling in homodimers and homotrimers of PANI-coated gold nanospheres (PGNSs). The dimers and trimers are obtained by reducing the surfactant concentration in the polymerization process of PANI. The reversible proton-doping of PANI enables the control of plasmon coupling to succeed. When the plasmon coupling of the dimers is switched, the wavelength shift of the strongest scattering peak shows an exponential increase with the decrease of the interparticle gap distance. A giant wavelength shift of 231 nm is observed for the dimer with a shell thickness of 10 nm and a gap distance of 0.5 nm. Electrodynamic calculations ascertain that the wavelength shift of the strongest scattering peak originates from the tuning of the dipolar bonding plasmon resonance mode in the dimers. The quadrupolar bonding plasmon resonance mode is turned on and off by switching the doped and undoped state of the dimers with gap distances of less than 3 nm. The active tuning of plasmon coupling is further demonstrated with the trimers of PGNSs, which is sensitive to their configurations. In the triangular configuration, larger vertex angles lead to larger wavelength shifts for the plasmonic tuning. Another strategy for controlling the dielectric properties of PANI shell around gold nanostructures is to change its oxidation level. The variation of the oxidation state of PANI leads to the plasmonic peak wavelength shift. Based on this principle, I have fabricated (gold nanosphere core)/(oxidized PANI shell) plasmonic sensors. The sensors have great potential for sensing chemical and biological molecules with reducibility. By using ascorbic acid (AA) as a target analyte, the plasmonic sensor presents high sensing capability. The limit of detection is 0.5 muM, and the linear response range is from 0.5 muM to 10 muM. The limit of detection for my plasmonic sensor is lower than the lowest limit for AA sensors based on liquid chromatography, electrophoresis, and electrochemical method. The sensing performance of my plasmonic sensors is expected to be further improved by optimizing the amount of (gold nanosphere core)/(oxidized PANI shell) structures, or employing other gold nanostructures with higher refractive index sensitivities. I believe that the colloidal (metal core)/(PANI shell) nanostructures pave the way for the fabrication of high-performance, low-cost plasmonic switches as well as for the preparation of advanced, programmable chromic materials for a wide variety of applications, such as smart windows, military anti-counterfeiting and camouflage, environmental sensors and indicators. (Abstract shortened by UMI.).

Quantum mechanics/molecular mechanics modeling of photoelectron spectra: the carbon 1s core-electron binding energies of ethanol-water solutions.

PubMed

Löytynoja, T; Niskanen, J; Jänkälä, K; Vahtras, O; Rinkevicius, Z; Ågren, H

2014-11-20

Using ethanol-water solutions as illustration, we demonstrate the capability of the hybrid quantum mechanics/molecular mechanics (QM/MM) paradigm to simulate core photoelectron spectroscopy: the binding energies and the chemical shifts. An integrated approach with QM/MM binding energy calculations coupled to preceding molecular dynamics sampling is adopted to generate binding energies averaged over the solute-solvent configurations available at a particular temperature and pressure and thus allowing for a statistical assessment with confidence levels for the final binding energies. The results are analyzed in terms of the contributions in the molecular mechanics model-electrostatic, polarization, and van der Waals-with atom or bond granulation of the corresponding MM charge and polarizability force-fields. The role of extramolecular charge transfer screening of the core-hole and explicit hydrogen bonding is studied by extending the QM core to cover the first solvation shell. The results are compared to those obtained from pure electrostatic and polarizable continuum models. Particularly, the dependence of the carbon 1s binding energies with respect to the ethanol concentration is studied. Our results indicate that QM/MM can be used as an all-encompassing model to study photoelectron binding energies and chemical shifts in solvent environments.

Transition-Metal Nitride Core@Noble-Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

DOE PAGES

Garg, Aaron; Milina, Maria; Ball, Madelyn; ...

2017-05-25

Core–shell architectures offer an effective way to tune and enhance the properties of noble-metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. In conclusion, the ability to control shell coveragemore » and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.« less

Transition-Metal Nitride Core@Noble-Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garg, Aaron; Milina, Maria; Ball, Madelyn

Core–shell architectures offer an effective way to tune and enhance the properties of noble-metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. In conclusion, the ability to control shell coveragemore » and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.« less

Open-Shell-Character-Based Molecular Design Principles: Applications to Nonlinear Optics and Singlet Fission.

PubMed

Nakano, Masayoshi

2017-01-01

Open-shell character, e. g., diradical character, is a quantum chemically well-defined quantity in ground-state molecular systems, which is not an observable but can quantify the degree of effective bond weakness in the chemical sense or electron correlation strength in the physical sense. Because this quantity also correlates to specific excited states, physicochemical properties concerned with those states are expected to strongly correlate to the open-shell character. This feature enables us to open a new path to revealing the mechanism of these properties as well as to realizing new design principles for efficient functional molecular systems. This account explains the open-shell-character-based molecular design principles and introduces their applications to the rational design of highly efficient nonlinear optical and singlet fission molecular systems. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Connectivity clues from short-term variability in settlement and geochemical tags of mytilid mussels

NASA Astrophysics Data System (ADS)

Fodrie, F. Joel; Becker, Bonnie J.; Levin, Lisa A.; Gruenthal, Kristen; McMillan, Pat A.

2011-01-01

The use of geochemical tags in calcified structures of fish and invertebrates is an exciting tool for investigating larval population connectivity. Tag evaluation over relatively short intervals (weeks) may detect environmental and ecological variability at a temporal scale highly relevant to larval transport and settlement. We collected newly settled mussels ( Mytilus californianus and M. galloprovincialis) weekly during winter/spring of 2002 along the coast of San Diego, CA, USA, at sites on the exposed coast (SIO) and in a protected coastal bay (HI), to investigate temporal patterns of geochemical tags in mussel shells. Analyses of post-settlement shell via LA-ICP-MS revealed statistically significant temporal variability for all elements we examined (Mg, Mn, Cu, Sr, Cd, Ba, Pb and U). Despite this, our ability to distinguish multielemental signatures between sites was largely conserved. Throughout our 13-week study, SIO and HI mussels could be chemically distinguished from one another in 78-87% of all cases. Settlement varied between 2 and 27 settlers gram-byssus -1 week -1 at SIO and HI, and both sites were characterized by 2-3 weeks with "high" settlement. Geochemical tags recorded in early larval shell of newly settled mussels differed between "high" and "low" settlement weeks at both sites (MANOVA), driven by Mg and Sr at SIO (p = 0.013) and Sr, Cd, Ba and Pb at HI (p < 0.001). These data imply that shifts in larval sources or transport corridors were responsible for observed settlement variation, rather than increased larval production. In particular, increased settlement at HI was observed concurrent with the appearance of geochemical tags (e.g., elevated Cd), suggesting that those larvae were retained in upwelled water near the mouth of the bay. Such shifts may reflect short-term changes in connectivity among sites due to altered transport corridors, and influence the demography of local populations.

The long-range shelling of Paris and physical chemistry problems of extremely long-range firing

NASA Astrophysics Data System (ADS)

Stettbacher, A.

1986-04-01

The 128-km long-range artillery shelling of Paris is discussed considering its physical and chemical make-up from the vantage point of the technology in 1919. It compares this shelling with a hypothetical 240-km shelling and concludes that the most important influence on shelling range distance to be air resistance. The amount of air resistance and the resulting velocity deceleration depend on the air's density and the shell's velocity and configuration.

On the breakup of tectonic plates by polar wandering

NASA Technical Reports Server (NTRS)

Liu, H. S.

1973-01-01

The observed boundary system of the major tectonic plates on the surface of the earth lends fresh support to the hypothesis of polar wandering. A dynamic model of the outer shell of the earth under the influence of polar shift is developed. The analysis falls into two parts: (1) deriving equations for stresses caused by polar shifting; and (2) deducing the pattern according to which the fracture of the shell can be expected. For stress analysis, the theory of plates and shells is the dominant feature of this model. In order to determine the fracture pattern, the existence of a mathematical theorem of plasticity is recalled: it says that the plastic flow begins to occur when a function in terms of the differences of the three principal stresses surpasses a certain critical value. By introducing the figures for the geophysical constants, this model generates stresses which could produce an initial break in the lithosphere.

The Periodic Pyramid

ERIC Educational Resources Information Center

Hennigan, Jennifer N.; Grubbs, W. Tandy

2013-01-01

The chemical elements present in the modern periodic table are arranged in terms of atomic numbers and chemical periodicity. Periodicity arises from quantum mechanical limitations on how many electrons can occupy various shells and subshells of an atom. The shell model of the atom predicts that a maximum of 2, 8, 18, and 32 electrons can occupy…

Time-resolved inner-shell photoelectron spectroscopy: From a bound molecule to an isolated atom

NASA Astrophysics Data System (ADS)

Brauße, Felix; Goldsztejn, Gildas; Amini, Kasra; Boll, Rebecca; Bari, Sadia; Bomme, Cédric; Brouard, Mark; Burt, Michael; de Miranda, Barbara Cunha; Düsterer, Stefan; Erk, Benjamin; Géléoc, Marie; Geneaux, Romain; Gentleman, Alexander S.; Guillemin, Renaud; Ismail, Iyas; Johnsson, Per; Journel, Loïc; Kierspel, Thomas; Köckert, Hansjochen; Küpper, Jochen; Lablanquie, Pascal; Lahl, Jan; Lee, Jason W. L.; Mackenzie, Stuart R.; Maclot, Sylvain; Manschwetus, Bastian; Mereshchenko, Andrey S.; Mullins, Terence; Olshin, Pavel K.; Palaudoux, Jérôme; Patchkovskii, Serguei; Penent, Francis; Piancastelli, Maria Novella; Rompotis, Dimitrios; Ruchon, Thierry; Rudenko, Artem; Savelyev, Evgeny; Schirmel, Nora; Techert, Simone; Travnikova, Oksana; Trippel, Sebastian; Underwood, Jonathan G.; Vallance, Claire; Wiese, Joss; Simon, Marc; Holland, David M. P.; Marchenko, Tatiana; Rouzée, Arnaud; Rolles, Daniel

2018-04-01

Due to its element and site specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here, we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH3I ) is investigated by ionization above the iodine 4 d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal-field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules.

Nonplanar on-shell diagrams and leading singularities of scattering amplitudes

NASA Astrophysics Data System (ADS)

Chen, Baoyi; Chen, Gang; Cheung, Yeuk-Kwan E.; Li, Yunxuan; Xie, Ruofei; Xin, Yuan

2017-02-01

Bipartite on-shell diagrams are the latest tool in constructing scattering amplitudes. In this paper we prove that a Britto-Cachazo-Feng-Witten (BCFW) decomposable on-shell diagram process a rational top form if and only if the algebraic ideal comprised the geometrical constraints are shifted linearly during successive BCFW integrations. With a proper geometric interpretation of the constraints in the Grassmannian manifold, the rational top form integration contours can thus be obtained, and understood, in a straightforward way. All rational top form integrands of arbitrary higher loops leading singularities can therefore be derived recursively, as long as the corresponding on-shell diagram is BCFW decomposable.

Copper nanowire-graphene core-shell nanostructure for highly stable transparent conducting electrodes.

PubMed

Ahn, Yumi; Jeong, Youngjun; Lee, Donghwa; Lee, Youngu

2015-03-24

A copper nanowire-graphene (CuNW-G) core-shell nanostructure was successfully synthesized using a low-temperature plasma-enhanced chemical vapor deposition process at temperatures as low as 400 °C for the first time. The CuNW-G core-shell nanostructure was systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, and X-ray photoelectron spectroscopy measurements. A transparent conducting electrode (TCE) based on the CuNW-G core-shell nanostructure exhibited excellent optical and electrical properties compared to a conventional indium tin oxide TCE. Moreover, it showed remarkable thermal oxidation and chemical stability because of the tight encapsulation of the CuNW with gas-impermeable graphene shells. The potential suitability of CuNW-G TCE was demonstrated by fabricating bulk heterojunction polymer solar cells. We anticipate that the CuNW-G core-shell nanostructure can be used as an alternative to conventional TCE materials for emerging optoelectronic devices such as flexible solar cells, displays, and touch panels.

The effects of the chemical composition and strain on the electronic properties of GaSb/InAs core-shell nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ning, Feng; Wang, Dan; Tang, Li-Ming, E-mail: lmtang@hnu.edu.cn

2014-09-07

The effects of the chemical composition and strain on the electronic properties of [111] zinc-blende (ZB) and [0001] wurtzite (WZ) GaSb/InAs core-shell nanowires (NWs) with different core diameters and shell thicknesses are studied using first-principles methods. The band structures of the [111] ZB GaSb/InAs core-shell NWs underwent a noticeable type-I/II band alignment transition, associated with a direct-to-indirect band gap transition under a compressive uniaxial strain. The band structures of the [0001] WZ GaSb/InAs core-shell NWs preserved the direct band gap under either compressive or tensile uniaxial strains. In addition, the band gaps and the effective masses of the carriers couldmore » be tuned by their composition. For the core-shell NWs with a fixed GaSb-core size, the band gaps decreased linearly with an increasing InAs-shell thickness, caused by the significant downshift of the conduction bands. For the [111] ZB GaSb/InAs core-shell NWs, the calculated effective masses indicated that the transport properties could be changed from hole-dominated conduction to electron-dominated conduction by changing the InAs-shell thickness.« less

A Bottle-around-a-Ship Method To Generate Hollow Thin-Shelled Particles Containing Encapsulated Iron Species with Application to the Environmental Decontamination of Chlorinated Compounds.

PubMed

Su, Yang; Wang, Yingqing; Owoseni, Olasehinde; Zhang, Yueheng; Gamliel, David Pierce; Valla, Julia A; McPherson, Gary L; John, Vijay T

2018-04-25

Thin-shelled hollow silica particles are synthesized using an aerosol-based process where the concentration of a silica precursor tetraethyl orthosilicate (TEOS) determines the shell thickness. The synthesis involves a novel concept of the salt bridging of an iron salt, FeCl 3 , to a cationic surfactant, cetyltrimethylammonium bromide (CTAB), which modulates the templating effect of the surfactant on silica porosity. The salt bridging leads to a sequestration of the surfactant in the interior of the droplet with the formation of a dense silica shell around the organic material. Subsequent calcination consistently results in hollow particles with encapsulated iron oxides. Control of the TEOS levels leads to the generation of ultrathin-shelled (∼10 nm) particles which become susceptible to rupture upon exposure to ultrasound. The dense silica shell that is formed is impervious to entry of chemical species. Mesoporosity is restored to the shell through desilication and reassembly, again using CTAB as a template. The mesoporous-shelled hollow particles show good reactivity toward the reductive dichlorination of trichloroethylene (TCE), indicating access of TCE to the particle interior. The ordered mesoporous thin-shelled particles containing active iron species are viable systems for chemical reaction and catalysis.

Tropical sea snail shells: Possible exotic sources for ceramic biomaterial synthesis

NASA Astrophysics Data System (ADS)

Oktar, F. N.; Kiyici, I. A.; Gökçe, H.; Aǧaogulları, D.; Kayali, E. S.

2013-12-01

In this study, chemical and structural properties of sea snail shell based bioceramic materials (i.e. hydroxyapatite, whitlockite and other phases) are produced by using mechano-chemical (ultrasonic) conversion method. For this purpose, differential thermal and gravimetric analysis (DTA/TG), X-ray diffraction, infra-red (IR) and scanning electron microscope (SEM) studies are performed.

Physical defect formation in few layer graphene-like carbon on metals: influence of temperature, acidity, and chemical functionalization.

PubMed

Schumacher, Christoph M; Grass, Robert N; Rossier, Michael; Athanassiou, Evagelos K; Stark, Wendelin J

2012-03-06

A systematical examination of the chemical stability of cobalt metal nanomagnets with a graphene-like carbon coating is used to study the otherwise rather elusive formation of nanometer-sized physical defects in few layer graphene as a result of acid treatments. We therefore first exposed the core-shell nanomaterial to well-controlled solutions of altering acidity and temperature. The release of cobalt into these solutions over time offered a simple tool to monitor the progress of particle degradation. The results suggested that the oxidative damage of the graphene-like coatings was the rate-limiting step during particle degradation since only fully intact or entirely emptied carbon shells were found after the experiments. If ionic noble metal species were additionally present in the acidic solutions, the noble metal was found to reduce on the surface of specific, defective particles. The altered electrochemical gradients across the carbon shells were however not found to lead to a faster release of cobalt from the particles. The suggested mechanistic insight was further confirmed by the covalent chemical functionalization of the particle surface with chemically inert aryl species, which leads to an additional thickening of the shells. This leads to reduced cobalt release rates as well as slower noble metal reduction rates depending on the augmentation of the shell thickness.

A Chemical-Adsorption Strategy to Enhance the Reaction Kinetics of Lithium-Rich Layered Cathodes via Double-Shell Surface Modification.

PubMed

Guo, Lichao; Li, Jiajun; Cao, Tingting; Wang, Huayu; Zhao, Naiqin; He, Fang; Shi, Chunsheng; He, Chunnian; Liu, Enzuo

2016-09-21

Sluggish surface reaction kinetics hinders the power density of Li-ion battery. Thus, various surface modification techniques have been applied to enhance the electronic/ionic transfer kinetics. However, it is challenging to obtain a continuous and uniform surface modification layer on the prime particles with structure integration at the interface. Instead of classic physical-adsorption/deposition techniques, we propose a novel chemical-adsorption strategy to synthesize double-shell modified lithium-rich layered cathodes with enhanced mass transfer kinetics. On the basis of experimental measurement and first-principles calculation, MoO2S2 ions are proved to joint the layered phase via chemical bonding. Specifically, the Mo-O or Mo-S bonds can flexibly rotate to bond with the cations in the layered phase, leading to the good compatibility between the thiomolybdate adsorption layer and layered cathode. Followed by annealing treatment, the lithium-excess-spinel inner shell forms under the thiomolybdate adsorption layer and functions as favorable pathways for lithium and electron. Meanwhile, the nanothick MoO3-x(SO4)x outer shell protects the transition metal from dissolution and restrains electrolyte decomposition. The double-shell modified sample delivers an enhanced discharge capacity almost twice as much as that of the unmodified one at 1 A g(-1) after 100 cycles, demonstrating the superiority of the surface modification based on chemical adsorption.

Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

DOE PAGES

Hudry, Damien; Busko, Dmitry; Popescu, Radian; ...

2017-11-02

Core@shell design represents an important class of architectures because of its capability to dramatically increase the absolute upconversion quantum yield (UCQY) of upconverting nanocrystals (UCNCs) but also to tune energy migration pathways. A relatively new trend towards the use of very thick optically inert shells affording significantly higher absolute UCQYs raises the question of the crystallographic and chemical characteristics of such nanocrystals (NCs). In this article, local chemical analyses performed by scanning transmission electron microscopy (STEM) combined with energy dispersive x-ray spectroscopy (EDXS) and x-ray total scattering experiments together with pair distribution function (PDF) analyses were used to probe themore » local chemical and structural characteristics of hexagonal β-NaGd0.78Yb0.2Er0.02F4@NaYF4 core@shell UCNCs. The investigations lead to a new crystallochemical model to describe core@shell UCNCs that considerably digresses from the commonly accepted epitaxial growth concept with sharp interfaces. The results obtained on ultra-small (4.8 ± 0.5 nm) optically active cores (β-NaGd0.78Yb0.2Er0.02F4) surrounded by an optically inert shell (NaYF4) of tunable thickness (roughly 0, 1, 2, and 3.5 nm) clearly indicate the massive dissolution of the starting seeds and the inter-diffusion of the shell element (such as Y) into the Gd/Yb/Er-containing core giving rise to the formation of a non-homogeneous solid solution characterized by concentration gradients and the lack of sharp interfaces. Independently of the inert shell thickness, core/interface/shell architectures were observed for all synthesized UCNCs. The presented results constitute a significant step towards the comprehensive understanding of the “structure - property” relationship of upconverting core@shell architectures, which is of prime interest not only in the development of more efficient structures but also to provide new physical insights at the nanoscale to better explain upconversion (UC) properties alterations.« less

Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hudry, Damien; Busko, Dmitry; Popescu, Radian

Core@shell design represents an important class of architectures because of its capability to dramatically increase the absolute upconversion quantum yield (UCQY) of upconverting nanocrystals (UCNCs) but also to tune energy migration pathways. A relatively new trend towards the use of very thick optically inert shells affording significantly higher absolute UCQYs raises the question of the crystallographic and chemical characteristics of such nanocrystals (NCs). In this article, local chemical analyses performed by scanning transmission electron microscopy (STEM) combined with energy dispersive x-ray spectroscopy (EDXS) and x-ray total scattering experiments together with pair distribution function (PDF) analyses were used to probe themore » local chemical and structural characteristics of hexagonal β-NaGd0.78Yb0.2Er0.02F4@NaYF4 core@shell UCNCs. The investigations lead to a new crystallochemical model to describe core@shell UCNCs that considerably digresses from the commonly accepted epitaxial growth concept with sharp interfaces. The results obtained on ultra-small (4.8 ± 0.5 nm) optically active cores (β-NaGd0.78Yb0.2Er0.02F4) surrounded by an optically inert shell (NaYF4) of tunable thickness (roughly 0, 1, 2, and 3.5 nm) clearly indicate the massive dissolution of the starting seeds and the inter-diffusion of the shell element (such as Y) into the Gd/Yb/Er-containing core giving rise to the formation of a non-homogeneous solid solution characterized by concentration gradients and the lack of sharp interfaces. Independently of the inert shell thickness, core/interface/shell architectures were observed for all synthesized UCNCs. The presented results constitute a significant step towards the comprehensive understanding of the “structure - property” relationship of upconverting core@shell architectures, which is of prime interest not only in the development of more efficient structures but also to provide new physical insights at the nanoscale to better explain upconversion (UC) properties alterations.« less

Interfacial effect on the structural and optical properties of pure SnO2 and dual shells (ZnO; SiO2) coated SnO2 core-shell nanospheres for optoelectronic applications

NASA Astrophysics Data System (ADS)

Selvi, N.; Sankar, S.; Dinakaran, K.

2014-12-01

Nanocrystallites of SnO2 core and dual shells (ZnO, SiO2) coated SnO2 core-shell nanospheres were successfully synthesized by co-precipitation method. The as prepared and annealed samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), High resolution transmission electron microscopy (HRTEM) and UV-Vis analysis. XRD pattern confirms the obtained SnO2 core with tetragonal rutile crystalline structure and the shell ZnO with hexagonal structure. FTIR result shows the functional groups present in the samples. The spherical morphology and the formation of the core-shell structures have been confirmed by HRTEM measurements. The UV-Vis showed that band gap is red shifted for as-prepared and the shells coated core-shell samples. From this investigation it can be concluded that the surface modification with different metal and insulating oxides strongly influences the optical properties of the core-shell materials which enhance their potential applications towards optical devices fabrication.

Snoek Relaxation in Fe-Cr Alloys and Interstitial-Substitutional Interaction

NASA Astrophysics Data System (ADS)

Golovin, I. S.; Blanter, M. S.; Schaller, R.

1997-03-01

The internal friction (IF) spectra of -Fe, Fe-Cr ferritic alloys and Cr have been investigated in a frequency range of 0.01 to 10 Hz. A Snoek-type relaxation was found in all the investigated C doped Fe-Cr alloys, starting from pure Fe and finishing with pure Cr. The temperature location of the Snoek peak (Tmax) in -Fe was found to be 315 K (1 Hz). The activation energy deduced from the T - f shift was 0.81 eV. Tmax in Cr was 433 K with an activation energy of 1.11 eV. The Snoek-type peaks in Fe-Cr alloys are much wider than in pure Fe or pure Cr. The temperature location of the peak versus chromium content curve exhibits a maximum in the vicinity of 35 wt% Cr (Tmax was 573 to 578 K, f 1.2 Hz and the activation energy was about 1.45 eV). It is important that Cr atoms in α-Fe have a more pronounced influence on the temperature location of the peak than Fe atoms have in chromium. A new model based on the atomic interactions is proposed to explain the influence of composition on Snoek peak location. The internal friction has been simulated by a Monte Carlo method, using C-C and C-substitutional atom (s) interaction energies. A model of long-range strain-induced (elastic) interaction supplemented by the chemical interaction in the two nearest coordination shells around an immobile substitutional atom was used for the C-s interaction. The interatomic interaction was supposed to affect IF by changing both the carbon atom arrangement (short-range order) and the energy of C atoms in octahedral interstices, and therefore the activation energy of IF. The peak temperatue calculated coincides well with the experimental ones if the value for the chemical interaction in the first coordination shell (Hchem) for C-Cr in Fe is - 0.15 eV and for C-Fe in Cr +0.15 eV. The difference in the influence of Cr in α-Fe and Fe in Cr is accounted for by a difference in the elastic and chemical interaction both between the carbon atoms and the substitutional atoms. The relaxation process in chromium Fe-based alloys is due to the carbon atom diffusion under stress between octahedral interstices of first and second coordination shells around the Cr atoms, and in Cr-based alloys, between second and third shells around the Fe atoms.

Gold core@silver semishell Janus nanoparticles prepared by interfacial etching

NASA Astrophysics Data System (ADS)

Chen, Limei; Deming, Christopher P.; Peng, Yi; Hu, Peiguang; Stofan, Jake; Chen, Shaowei

2016-07-01

Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface.Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface. Electronic supplementary information (ESI) available: Additional TEM, UV-vis, XPS, and electrochemical data. See DOI: 10.1039/c6nr03368g

A Coulomb-Like Off-Shell T-Matrix with the Correct Coulomb Phase Shift

NASA Astrophysics Data System (ADS)

Oryu, Shinsho; Watanabe, Takashi; Hiratsuka, Yasuhisa; Togawa, Yoshio

2017-03-01

We confirm the reliability of the well-known Coulomb renormalization method (CRM). It is found that the CRM is only available for a very-long-range screened Coulomb potential (SCP). However, such an SCP calculation in momentum space is considerably difficult because of the cancelation of significant digits. In contrast to the CRM, we propose a new method by using an on-shell equivalent SCP and the rest term. The two-potential theory with r-space is introduced, which defines fully the off-shell Coulomb amplitude.

Second-Order Moller-Plesset Perturbation Theory for Molecular Dirac-Hartree-Fock Wave Functions

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.; Arnold, James O. (Technical Monitor)

1994-01-01

Moller-Plesset perturbation theory is developed to second order for a selection of Kramers restricted Dirac-Hartree-Fock closed and open-shell reference wave functions. The open-shell wave functions considered are limited to those with no more than two electrons in open shells, but include the case of a two-configuration SCF reference. Denominator shifts are included in the style of Davidson's OPT2 method. An implementation which uses unordered integrals with labels is presented, and results are given for a few test cases.

Decorating an individual living cell with a shell of controllable thickness by cytocompatible surface initiated graft polymerization.

PubMed

Wang, Guan; Zhang, Kai; Wang, Yindian; Zhao, Changwen; He, Bin; Ma, Yuhong; Yang, Wantai

2018-05-03

Surface engineering of individual living cells is a promising field for cell-based applications. However, engineering individual cells with controllable thickness by chemical methods has been rarely studied. This article describes the development of a new cytocompatible chemical strategy to decorate individual living cells. The thicknesses of the crosslinked shells could be conveniently controlled by the irradiation time, visible light intensity, or monomer concentration. Moreover, the lag phase of the yeast cell division was extended and their stability against lysis was improved, which could also be tuned by controlling the shell thickness.

Towards the Shell Biorefinery: Sustainable Synthesis of the Anticancer Alkaloid Proximicin A from Chitin.

PubMed

Sadiq, Alejandro D; Chen, Xi; Yan, Ning; Sperry, Jonathan

2018-02-09

A shell biorefinery would involve fractionation of crustacean shells and incorporation of the components into value-added products, particularly those that contain nitrogen. In a proof-of-concept study that validates this concept, the anticancer alkaloid proximicin A has been synthesized from the chitin-derived platform chemical 3-acetamido-5-acetylfuran (3A5AF). This study accentuates the leading role chitin is likely to play in the sustainable production of nitrogen-containing fine chemicals that are not directly attainable from lignocellulose. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen bonding in hydrates with one acetic acid molecule.

PubMed

Pu, Liang; Sun, Yueming; Zhang, Zhibing

2010-10-14

Hydrogen bonding (H-bond) interaction significantly influences the separation of acetic acid (HAc) from the HAc/H(2)O mixtures, especially the dilute solution, in distillation processes. It has been examined from the HAc mono-, di-, tri-, and tetrahydrates by analyzing the structures, binding energies, and infrared vibrational frequencies from quantum chemical calculations. For the first coordinate shell the 6-membered head-on ring is surely the most favorable structure because it has (1) the most favorable H-bonding parameters, (2) almost the largest binding energy per H-bond, (3) the biggest wavenumber shifts, and (4) the highest ring distribution (the AIMD simulations). Moreover, the comparison of the calculations with the experiments (the X-ray scattering data and IR frequencies) suggests that the possible structures in dilute aqueous solution are those involving two or more coordinate shells. The H-bonding in these water-surrounded HAc hydrates are the origin of the low-efficiency problem of isolating HAc from the dilute HAc/H(2)O mixtures. It is apparently a tougher work to break the H-bonds among HAc and the surrounded H(2)O molecules with respect to the case of more concentrated solutions, where the dominant structures are HAc or H(2)O aggregates.

Characterization of the phosphatic mineral of the barnacle Ibla cumingi at atomic level by solid-state nuclear magnetic resonance: comparison with other phosphatic biominerals

PubMed Central

Reid, David G.; Mason, Matthew J.; Chan, Benny K. K.; Duer, Melinda J.

2012-01-01

Ibliform barnacles are among the few invertebrate animals harnessing calcium phosphate to construct hard tissue. The 31P solid-state NMR (SSNMR) signal from the shell plates of Ibla cumingi (Iblidae) is broader than that of bone, and shifted by ca 1 ppm to low frequency. 1H–31P heteronuclear correlation (HETCOR) experiments show a continuum of different phosphorus/phosphate atomic environments, close to hydrogen populations with resonance frequencies between ca 10 and 20 ppm. Associated 1H and 31P chemical shifts argue the coexistence of weakly (high 31P frequency, low 1H frequency) to more strongly (lower 31P frequency, higher 1H frequency) hydrogen-bonded hydrogen phosphate-like molecular/ionic species. There is no resolved signal from discrete OH− ions. 13C SSNMR shows chitin, protein and other organic biomolecules but, unlike bone, there are no significant atomic scale organic matrix–mineral contacts. The poorly ordered hydrogen phosphate-like iblid mineral is strikingly different, structurally and compositionally, from both vertebrate bone mineral and the more crystalline fluoroapatite of the linguliform brachiopods. It probably represents a previously poorly characterized calcium phosphate biomineral, the evolution of which may have reflected either the chemical conditions of ancestral seas or the mechanical advantages of phosphatic biomineralization over a calcium carbonate equivalent. PMID:22298816

Cross-shell excitations from the f p shell: Lifetime measurements in 61Zn

NASA Astrophysics Data System (ADS)

Queiser, M.; Vogt, A.; Seidlitz, M.; Reiter, P.; Togashi, T.; Shimizu, N.; Utsuno, Y.; Otsuka, T.; Honma, M.; Petkov, P.; Arnswald, K.; Altenkirch, R.; Birkenbach, B.; Blazhev, A.; Braunroth, T.; Dewald, A.; Eberth, J.; Fransen, C.; Fu, B.; Hess, H.; Hetzenegger, R.; Hirsch, R.; Jolie, J.; Karayonchev, V.; Kaya, L.; Lewandowski, L.; Müller-Gatermann, C.; Régis, J.-M.; Rosiak, D.; Schneiders, D.; Siebeck, B.; Steinbach, T.; Wolf, K.; Zell, K.-O.

2017-10-01

Lifetimes of excited states in the neutron-deficient nucleus 61Zn were measured employing the recoil-distance Doppler-shift (RDDS) and the electronic fast-timing methods at the University of Cologne. The nucleus of interest was populated as an evaporation residue in 40Ca(24Mg,n 2 p )61Zn and 58Ni(α ,n )61Zn reactions at 67 and 19 MeV, respectively. Five lifetimes were measured for the first time, including the lifetime of the 5 /21- isomer at 124 keV. Short lifetimes from the RDDS analysis are corrected for Doppler-shift attenuation (DSA) in the target and stopper foils. Ambiguous observations in previous measurements were resolved. The obtained lifetimes are compared to predictions from different sets of shell-model calculations in the f p , f5 /2p g9 /2 , and multishell f p -g9 /2d5 /2 model spaces. The band built on the 9 /21+ state exhibits a prolate deformation with β ≈0.24 . Especially, the inclusion of cross-shell excitation into the 1 d5 /2 orbital is found to be decisive for the description of collectivity in the first excited positive-parity band.

Time-frequency analysis of the bistatic acoustic scattering from a spherical elastic shell.

PubMed

Anderson, Shaun D; Sabra, Karim G; Zakharia, Manell E; Sessarego, Jean-Pierre

2012-01-01

The development of low-frequency sonar systems, using, for instance, a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e., when the source and receiver are widely separated) allowing for multiple viewpoints of the target of interest. Time-frequency analysis, in particular, Wigner-Ville analysis, takes advantage of the evolution time dependent aspect of the echo spectrum to differentiate a man-made target, such as an elastic spherical shell, from a natural object of the similar shape. A key energetic feature of fluid-loaded and thin spherical shell is the coincidence pattern, also referred to as the mid-frequency enhancement (MFE), that results from antisymmetric Lamb-waves propagating around the circumference of the shell. This article investigates numerically the bistatic variations of the MFE with respect to the monostatic configuration using the Wigner-Ville analysis. The observed time-frequency shifts of the MFE are modeled using a previously derived quantitative ray theory by Zhang et al. [J. Acoust. Soc. Am. 91, 1862-1874 (1993)] for spherical shell's scattering. Additionally, the advantage of an optimal array beamformer, based on joint time delays and frequency shifts is illustrated for enhancing the detection of the MFE recorded across a bistatic receiver array when compared to a conventional time-delay beamformer. © 2012 Acoustical Society of America.

Multinuclear NMR studies of relaxor ferroelectrics

NASA Astrophysics Data System (ADS)

Zhou, Donghua

Multinuclear NMR of 93Nb, 45Sc, and 207Pb has been carried out to study the structure, disorder, and dynamics of a series of important solid solutions: perovskite relaxor ferroelectric materials (1-x) Pb(Mg1/3Nb 2/3)O3-x Pb(Sc1/2Nb1/2)O 3 (PMN-PSN). 93Nb NMR investigations of the local structure and cation order/disorder are presented as a function of PSN concentration, x. The superb fidelity and accuracy of 3QMAS allows us to make clear and consistent assignments of spectral intensities to the 28 possible nearest B-site neighbor (nBn) configurations, (NMg, NSc, NNb), where each number ranges from 0 to 6 and their sum is 6. For most of the 28 possible nBn configurations, isotropic chemical shifts and quadrupole product constants have been extracted from the data. The seven configurations with only larger cations, Mg 2+ and Sc3+ (and no Nb5+) are assigned to the seven observed narrow peaks, whose deconvoluted intensities facilitate quantitative evaluation of, and differentiation between, different models of B-site (chemical) disorder. The "completely random" model is ruled out and the "random site" model is shown to be in qualitative agreement with the NMR experiments. To obtain quantitative agreement with observed NMR intensities, the random site model is slightly modified by including unlike-pair interaction energies. To date, 45Sc studies have not been as fruitful as 93Nb NMR because the resolution is lower in the 45Sc spectra. The lower resolution of 45Sc spectra is due to a smaller span of isotropic chemical shift (40 ppm for 45Sc vs. 82 ppm for 93Nb) and to the lack of a fortuitous mechanism that simplifies the 93Nb spectra; for 93Nb the overlap of the isotropic chemical shifts of 6-Sc and 6-Nb configurations results in the alignment of all the 28 configurations along only seven quadrupole distribution axes. Finally we present variable temperature 207Pb static, MAS, and 2D-PASS NMR studies. Strong linear correlations between isotropic and anisotropic chemical shifts show that Pb-O bonds vary from more ionic to more covalent environments. Distributions of Pb-O bond lengthes are also quantitatively described. Such distributions are used to examine two competing models of Pb displacements; the shell model and the unique direction model. Only the latter model is able to reproduce the observed Pb-O distance distribution.

High-temperature stability of the hydrate shell of a Na+ cation in a flat nanopore with hydrophobic walls

NASA Astrophysics Data System (ADS)

Shevkunov, S. V.

2017-11-01

The effect of elevated temperature has on the hydrate shell of a singly charged sodium cation inside a flat nanopore with smooth walls is studied using the Monte Carlo method. The free energy and the entropy of vapor molecule attachment are calculated by means of a bicanonical statistical ensemble using a detailed model of interactions. The nanopore has a stabilizing effect on the hydrate shell with respect to fluctuations and a destabilizing effect with respect to complete evaporation. At the boiling point of water, behavior is observed that is qualitatively similar to behavior at room temperature, but with a substantial shift in the vapor pressure and shell size.

Chemical Mass Shifts in a Digital Linear Ion Trap as Analytical Identity of o-, m-, and p-Xylene.

PubMed

Sun, Lulu; Xue, Bing; Huang, Zhengxu; Cheng, Ping; Ma, Li; Ding, Li; Zhou, Zhen

2018-07-01

Chemical mass shifts between isomeric ions of o-, m-, and p-xylene were measured using a digital linear ion trap, and the directions and values of the shifts were found to be correlated to the collision cross sections of the isomers. Both forward and reverse scans were used and the chemical shifts for each pair of isomers in scans of opposite directions were in opposite signs. Using different voltage settings (namely the voltage dividing ratio-VDR) of the ion trap allows adding high order field components in the quadrupole field and results in larger chemical mass shifts. The differential chemical mass shift which combined the shifts from forward and reverse scans doubled the amount of chemical shift, e.g., 0.077 Th between o- and p-xylene, enough for identification of the type of isomer without using an additional ion mobility spectrometer. The feature of equal and opposite chemical mass shifts also allowed to null out the chemical mass shift by calculating the mean m/z value between the two opposite scans and remove or reduce the mass error caused by chemical mass shift. Graphical Abstract ᅟ.

Chemical Mass Shifts in a Digital Linear Ion Trap as Analytical Identity of o-, m-, and p-Xylene

NASA Astrophysics Data System (ADS)

Sun, Lulu; Xue, Bing; Huang, Zhengxu; Cheng, Ping; Ma, Li; Ding, Li; Zhou, Zhen

2018-04-01

Chemical mass shifts between isomeric ions of o-, m-, and p-xylene were measured using a digital linear ion trap, and the directions and values of the shifts were found to be correlated to the collision cross sections of the isomers. Both forward and reverse scans were used and the chemical shifts for each pair of isomers in scans of opposite directions were in opposite signs. Using different voltage settings (namely the voltage dividing ratio-VDR) of the ion trap allows adding high order field components in the quadrupole field and results in larger chemical mass shifts. The differential chemical mass shift which combined the shifts from forward and reverse scans doubled the amount of chemical shift, e.g., 0.077 Th between o- and p-xylene, enough for identification of the type of isomer without using an additional ion mobility spectrometer. The feature of equal and opposite chemical mass shifts also allowed to null out the chemical mass shift by calculating the mean m/z value between the two opposite scans and remove or reduce the mass error caused by chemical mass shift. [Figure not available: see fulltext.

[Spectroscopic Study of Salbutamol Molecularly Imprinted Polymers].

PubMed

Ren, Hui-peng; Guan, Yu-yu; Dai, Rong-hua; Liu, Guo-yan; Chai, Chun-yan

2016-02-01

In order to solve the problem of on-site rapid detection of salbutamol residues in feed and animal products, and develop a new method of fast detection of salbutamol on the basis of the molecular imprinting technology, this article uses the salbutamol (SAL) working as template molecule, methacrylic acid (MAA) working as functional monomer. On this basis, a new type of core-shell type salbutamol molecularly imprinted polymers were prepared with colloidal gold particles as triggering core. Superficial characteristics of the MIPs and the related compounds were investigated by ultraviolet (UV) spectra and infrared (IR) spectra, Raman spectra, Scanning electron microscopy (SEM) respectively. The results indicated that a stable hydrogen bonding complex has been formed between the carboxyl groups of SAL and MA with a matching ratio of 1:1. The complex can be easily eluted by the reagent containing hydrogen bonding. The chemical binding constant K reaches -0.245 x 10⁶ L² · mol⁻². The possible binding sites of the hydrogen bonding was formed between the hydrogen atoms of -COOH in MA and the oxygen atoms of C==O in SAL. IR and Raman spectrum showed that, compared with MA, a significant red shift of -OH absorption peak was manifested in MIPs, which proved that SAL as template molecule occurred a specific bond between MA. Red shift of stretching vibration absorption peak of C==O was also detected in the un-eluted MIPs and obvious energy loss happened, which demonstrated a possible binding sites is SAL intramolecular of C==O atom of oxygen. If the hydrogen atoms of -COOH in MA wanted to generate hydrogen bond. However, the shapes of absorption peak of other functional groups including C==C, C==O, and -OH were very similar both in MIPs and NIPs. Specific cavities were formed after the template molecules in MIPs were removed. It was proved by the adsorption experiment that the specific sites in these cavities highly match with the chemical and space structure of SAL. Besides, colloidal gold type core-shell molecularly imprinted polymers have looser surface, more cavities in the surface compared with ordinary molecularly imprinted polymers, which increased the effective area of adsorption to target molecules. So it have better performance in adsorption. Based on the principle that these cavities can specificly recognize and combine with target molecule in the test sample, and the excellent ability of colloidal gold core-shell molecularly imprinted polymers, the development of novel methods for fast determination of SAL based on the molecular imprinting technology can be expected in the near future.

Discovery of the Electronic Spectra of Hps and Dps

NASA Astrophysics Data System (ADS)

Grimminger, Robert A.; Wei, Jie; Ellis, Blaine; Clouthier, Dennis J.; Wang, Zhong; Sears, Trevor

2009-06-01

The hitherto unknown electronic spectrum of the closed shell transient molecule HPS has been observed in the 685 - 846 nm region by laser-induced fluorescence and single vibronic level emission techniques. HPS (and DPS) were produced in a pulsed electric discharge jet using a precursor mixture of 3% PH_3 and 1% H_2S (or PD_3 and D_2S) in high pressure argon. The weak set of observed bands are assigned to the à ^1A^''-X˜ ^1A^' electronic transition on the basis of chemical evidence, isotope shifts and the correspondence of the vibrational frequencies, excitation energy, and band contours with predictions based on our own high level ab initio calculations. Theory predicts that the HPS bond angle decreases on electronic excitation, contrary to expectations based on Walsh diagrams.

Temporal and local variations in biochemical composition of Crassostrea gigas shells

NASA Astrophysics Data System (ADS)

Almeida, Maria J.; Machado, Jorge; Moura, Gabriela; Azevedo, Manuela; Coimbra, João

1998-12-01

The objective of this work was to find relations between organic and inorganic shell components. Crassostrea gigas shells were analysed from live specimens collected at five different stations: the Lima estuary (1), the Ria de Aveiro (2, 3), and the Mondego estuary (4, 5), Portugal. About 30% of the oysters, from stations 1, 2 and 3 had shell-thickness-index values ≤10, indicating a severe thickening. Oysters from the Mondego estuary contained mud blisters due to Polydora infestations. Oysters from station 3 had thicker shells and showed a higher Pb content in shell and tissues than oysters from the other stations. Amino-acid composition changed mainly according to the modified protein (jelly-like substance) probably produced by the presence of TBT (tributyltin) in the water; in particular, we observed an increase in glutamic acid and threonine and a decrease in major amino acids such as aspartic acid, serine and glycine. Elemental shell composition was mainly associated with environmental conditions: shells from stations in open areas had higher Li, Cd, Cr and Ca and lower Mn levels than those from semi-enclosed areas (fish farms). Discriminant analyses against the three kinds of shell observed (normal, thick and infested), using chemical elements and amino acids as discriminant variables, showed the infested group to have the biggest differences. There was no correlation between amino-acid and chemical-element patterns in shell composition. Observed changes in amino-acid pattern, probably due to TBT, did not imply a simultaneous change of elemental composition.

Formation of Double-Shelled Zinc-Cobalt Sulfide Dodecahedral Cages from Bimetallic Zeolitic Imidazolate Frameworks for Hybrid Supercapacitors.

PubMed

Zhang, Peng; Guan, Bu Yuan; Yu, Le; Lou, Xiong Wen David

2017-06-12

Complex metal-organic frameworks used as precursors allow design and construction of various nanostructured functional materials which might not be accessible by other methods. Here, we develop a sequential chemical etching and sulfurization strategy to prepare well-defined double-shelled zinc-cobalt sulfide (Zn-Co-S) rhombic dodecahedral cages (RDCs). Yolk-shelled zinc/cobalt-based zeolitic imidazolate framework (Zn/Co-ZIF) RDCs are first synthesized by a controlled chemical etching process, followed by a hydrothermal sulfurization reaction to prepare double-shelled Zn-Co-S RDCs. Moreover, the strategy reported in this work enables easy control of the Zn/Co molar ratio in the obtained double-shelled Zn-Co-S RDCs. Owing to the structural and compositional benefits, the obtained double-shelled Zn-Co-S RDCs exhibit enhanced performance with high specific capacitance (1266 F g -1 at 1 A g -1 ), good rate capability and long-term cycling stability (91 % retention over 10,000 cycles) as a battery-type electrode material for hybrid supercapacitors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Isomer Shift and Magnetic Moment of the Long-Lived 1/2^{+} Isomer in _{30}^{79}Zn_{49}: Signature of Shape Coexistence near ^{78}Ni.

PubMed

Yang, X F; Wraith, C; Xie, L; Babcock, C; Billowes, J; Bissell, M L; Blaum, K; Cheal, B; Flanagan, K T; Garcia Ruiz, R F; Gins, W; Gorges, C; Grob, L K; Heylen, H; Kaufmann, S; Kowalska, M; Kraemer, J; Malbrunot-Ettenauer, S; Neugart, R; Neyens, G; Nörtershäuser, W; Papuga, J; Sánchez, R; Yordanov, D T

2016-05-06

Collinear laser spectroscopy is performed on the _{30}^{79}Zn_{49} isotope at ISOLDE-CERN. The existence of a long-lived isomer with a few hundred milliseconds half-life is confirmed, and the nuclear spins and moments of the ground and isomeric states in ^{79}Zn as well as the isomer shift are measured. From the observed hyperfine structures, spins I=9/2 and I=1/2 are firmly assigned to the ground and isomeric states. The magnetic moment μ (^{79}Zn)=-1.1866(10)μ_{N}, confirms the spin-parity 9/2^{+} with a νg_{9/2}^{-1} shell-model configuration, in excellent agreement with the prediction from large scale shell-model theories. The magnetic moment μ (^{79m}Zn)=-1.0180(12)μ_{N} supports a positive parity for the isomer, with a wave function dominated by a 2h-1p neutron excitation across the N=50 shell gap. The large isomer shift reveals an increase of the intruder isomer mean square charge radius with respect to that of the ground state, δ⟨r_{c}^{2}⟩^{79,79m}=+0.204(6)  fm^{2}, providing first evidence of shape coexistence.

Toxic chemical considerations for tank farm releases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Keuren, J.C.; Davis, J.S., Westinghouse Hanford

1996-08-01

This topical report contains technical information used to determine the accident consequences of releases of toxic chemical and gases for the Tank Farm Final Safety Analysis report (FSAR).It does not provide results for specific accident scenarios but does provide information for use in those calculations including chemicals to be considered, chemical concentrations, chemical limits and a method of summing the fractional contributions of each chemical. Tank farm composites evaluated were liquids and solids for double shell tanks, single shell tanks, all solids,all liquids, headspace gases, and 241-C-106 solids. Emergency response planning guidelines (ERPGs) were used as the limits.Where ERPGs weremore » not available for the chemicals of interest, surrogate ERPGs were developed. Revision 2 includes updated sample data, an executive summary, and some editorial revisions.« less

Probing silicon and aluminium chemical environments in silicate and aluminosilicate glasses by solid state NMR spectroscopy and accurate first-principles calculations

NASA Astrophysics Data System (ADS)

Gambuzzi, Elisa; Pedone, Alfonso; Menziani, Maria Cristina; Angeli, Frédéric; Caurant, Daniel; Charpentier, Thibault

2014-01-01

Silicon and aluminium chemical environments in silicate and aluminosilicate glasses with compositions 60SiO2·20Na2O·20CaO (CSN), 60SiO2·20Al2O3·20CaO (CAS), 78SiO2·11Al2O3·11Na2O (NAS) and 60SiO2·10Al2O3·10Na2O·20CaO (CASN) have been investigated by 27Al and 29Si solid state magic angle spinning (MAS) and multiple quantum MAS (MQMAS) nuclear magnetic resonance (NMR) experiments. To interpret the NMR data, first-principles calculations using density functional theory were performed on structural models of these glasses. These models were generated by Shell-model molecular dynamics (MD) simulations. The theoretical NMR parameters and spectra were computed using the gauge including projected augmented wave (GIPAW) method and spin-effective Hamiltonians, respectively. This synergetic computational-experimental approach offers a clear structural characterization of these glasses, particularly in terms of network polymerization, chemical disorder (i.e. Si and Al distribution in second coordination sphere) and modifier cation distributions. The relationships between the local structural environments and the 29Si and 27Al NMR parameters are highlighted, and show that: (i) the isotropic chemical shift of both 29Si and 27Al increases of about +5 ppm for each Al added in the second sphere and (ii) both the 27Al and 29Si isotropic chemical shifts linearly decrease with the reduction of the average Si/Al-O-T bond angle. Conversely, 27Al and 29Si NMR parameters are much less sensitive to the connectivity with triple bridging oxygen atoms, precluding their indirect detection from 27Al and 29Si NMR.

Using Micro CT Scanning to Assess Pteropod Shells in the Modern Ocean

NASA Astrophysics Data System (ADS)

Oakes, R. L.; Urbanski, J. M.; Bralower, T. J.

2016-02-01

Anthropogenic activities are causing fundamental changes to ocean chemistry. Calcareous plankton and nekton are predicted to be affected by these chemical changes, especially by ocean acidification. These groups are at the base of the marine food chain and therefore their demise will have a strong effect on the marine ecosystem as a whole. One challenge moving forward is to find a method to assess how chemical changes manifest themselves in plankton and nekton shells. Recent advancements in computed tomographic (CT) scanning technology allows for organisms to be imaged in three dimensions at micrometer resolution. CT data enables quantitative measurements of properties such as shell thickness, volume, and morphology. We apply this method to look at pteropods, nektonic molluscs which make their shells from the more soluble form of calcium carbonate, aragonite. Their shell mineralogy, and the fact that some groups live in polar and upwelling waters, place them at high risk for ocean acidification. We have scanned over 70 pteropods from 5 different locations globally. Analysis shows that there is a significant difference in pteropod shell thickness in different ocean basins with the thinnest shells being found off the coast of Washington. Changes in shell thickness may affect pteropod swimming efficiency, predation, and rate of sinking. Shell volume does not seem to vary with shell thickness suggesting that changes will impact pteropods at all ontogenetic stages. We are working towards a geometric morphometric analysis of these shells to see if the shape differs in areas with different ocean conditions. This initial set of CT scans of pteropods can be used as a baseline to which future changes can be compared. Furthermore, this technique has the potential to be easily transferred to other organisms as a method of assessing shell change in response to ocean acidification and associated factors.

Type I and II β-turns prediction using NMR chemical shifts.

PubMed

Wang, Ching-Cheng; Lai, Wen-Chung; Chuang, Woei-Jer

2014-07-01

A method for predicting type I and II β-turns using nuclear magnetic resonance (NMR) chemical shifts is proposed. Isolated β-turn chemical-shift data were collected from 1,798 protein chains. One-dimensional statistical analyses on chemical-shift data of three classes β-turn (type I, II, and VIII) showed different distributions at four positions, (i) to (i + 3). Considering the central two residues of type I β-turns, the mean values of Cο, Cα, H(N), and N(H) chemical shifts were generally (i + 1) > (i + 2). The mean values of Cβ and Hα chemical shifts were (i + 1) < (i + 2). The distributions of the central two residues in type II and VIII β-turns were also distinguishable by trends of chemical shift values. Two-dimensional cluster analyses on chemical-shift data show positional distributions more clearly. Based on these propensities of chemical shift classified as a function of position, rules were derived using scoring matrices for four consecutive residues to predict type I and II β-turns. The proposed method achieves an overall prediction accuracy of 83.2 and 84.2% with the Matthews correlation coefficient values of 0.317 and 0.632 for type I and II β-turns, indicating that its higher accuracy for type II turn prediction. The results show that it is feasible to use NMR chemical shifts to predict the β-turn types in proteins. The proposed method can be incorporated into other chemical-shift based protein secondary structure prediction methods.

Pecan shell-based granular activated carbon for treatment of chemical oxygen demand (COD) in municipal wastewater.

PubMed

Bansode, R R; Losso, J N; Marshall, W E; Rao, R M; Portier, R J

2004-09-01

The present investigation was undertaken to compare the adsorption efficiency of pecan shell-based granular activated carbon with the adsorption efficiency of the commercial carbon Filtrasorb 200 with respect to uptake of the organic components responsible for the chemical oxygen demand (COD) of municipal wastewater. Adsorption efficiencies for these two sets of carbons (experimental and commercial) were analyzed by the Freundlich adsorption model. The results indicate that steam-activated and acid-activated pecan shell-based carbons had higher adsorption for organic matter measured as COD, than carbon dioxide-activated pecan shell-based carbon or Filtrasorb 200 at all the carbon dosages used during the experiment. The higher adsorption may be related to surface area as the two carbons with the highest surface area also had the highest organic matter adsorption. These results show that granular activated carbons made from agricultural waste (pecan shells) can be used with greater effectiveness for organic matter removal from municipal wastewater than a coal-based commercial carbon. Copyright 2004 Elsevier Ltd.

Formation of grafted surface layers on silicon dioxide particles and their investigation by means of thermoprogrammed oxidation

NASA Astrophysics Data System (ADS)

Aleksandrova, E. O.; Novichkov, R. V.; Olenin, A. Yu.; Zuev, B. K.

2017-03-01

Silica nanoparticles are obtained according to the Stober-Fink-Bohn method, and their surfaces are chemically modified with 1H,1H,2H,2H-perfluorodecyltriethoxysilane. It is estimated that sols of porous silica nanoparticles (average sizes, 50-200 nm) form during primary chemical process; the average size of the particles can be increased to 400-500 nm by consecutive growth. Oxythermography (thermoprogrammed oxidation) measurements reveal a stepped dependence between the content of organic substance of nanoparticles and the duration of chemical modification reaction exists. It is concluded that this could be due to the formation of dense shell (or shells) as a result of sols aging between the cycles of growth; such shells impose diffusive restrictions when molecules penetrate into the pores of the internal volume of the particles.

Time averaging of NMR chemical shifts in the MLF peptide in the solid state.

PubMed

De Gortari, Itzam; Portella, Guillem; Salvatella, Xavier; Bajaj, Vikram S; van der Wel, Patrick C A; Yates, Jonathan R; Segall, Matthew D; Pickard, Chris J; Payne, Mike C; Vendruscolo, Michele

2010-05-05

Since experimental measurements of NMR chemical shifts provide time and ensemble averaged values, we investigated how these effects should be included when chemical shifts are computed using density functional theory (DFT). We measured the chemical shifts of the N-formyl-L-methionyl-L-leucyl-L-phenylalanine-OMe (MLF) peptide in the solid state, and then used the X-ray structure to calculate the (13)C chemical shifts using the gauge including projector augmented wave (GIPAW) method, which accounts for the periodic nature of the crystal structure, obtaining an overall accuracy of 4.2 ppm. In order to understand the origin of the difference between experimental and calculated chemical shifts, we carried out first-principles molecular dynamics simulations to characterize the molecular motion of the MLF peptide on the picosecond time scale. We found that (13)C chemical shifts experience very rapid fluctuations of more than 20 ppm that are averaged out over less than 200 fs. Taking account of these fluctuations in the calculation of the chemical shifts resulted in an accuracy of 3.3 ppm. To investigate the effects of averaging over longer time scales we sampled the rotameric states populated by the MLF peptides in the solid state by performing a total of 5 micros classical molecular dynamics simulations. By averaging the chemical shifts over these rotameric states, we increased the accuracy of the chemical shift calculations to 3.0 ppm, with less than 1 ppm error in 10 out of 22 cases. These results suggests that better DFT-based predictions of chemical shifts of peptides and proteins will be achieved by developing improved computational strategies capable of taking into account the averaging process up to the millisecond time scale on which the chemical shift measurements report.

Maria Goeppert Mayer, the Nuclear Shell Structure, and Magic Numbers

Science.gov Websites

dropdown arrow Site Map A-Z Index Menu Synopsis Maria Goeppert-Mayer, the Nuclear Shell Model, and Magic explanation of how neutrons and protons within atomic nuclei are structured. Called the "nuclear shell American husband, chemical physicist Joseph Mayer. At Argonne, Goeppert-Mayer learned most of her nuclear

Nanoreactors comprising a nanoreactor shell enveloping a space, and method of making

DOEpatents

Alivisatos, A Paul [Oakland, CA; Yin, Yadong [Moreno Valley, CA; Rioux, Robert M [Somerville, MA; Somorjai, Gabor A [Berkeley, CA

2011-01-25

Described herein are nanoreactors having various shapes that can be produced by a simple chemical process. The nanoreactors described herein may have a shell as thin as 0.5 nm and outside diameters that can be controlled by the process of making and have a nanoparticle enclosed therein. The nanoreactors have catalytic activity and may be used to catalyze a variety of chemical reactions.

Correlation of chemical shifts predicted by molecular dynamics simulations for partially disordered proteins.

PubMed

Karp, Jerome M; Eryilmaz, Ertan; Erylimaz, Ertan; Cowburn, David

2015-01-01

There has been a longstanding interest in being able to accurately predict NMR chemical shifts from structural data. Recent studies have focused on using molecular dynamics (MD) simulation data as input for improved prediction. Here we examine the accuracy of chemical shift prediction for intein systems, which have regions of intrinsic disorder. We find that using MD simulation data as input for chemical shift prediction does not consistently improve prediction accuracy over use of a static X-ray crystal structure. This appears to result from the complex conformational ensemble of the disordered protein segments. We show that using accelerated molecular dynamics (aMD) simulations improves chemical shift prediction, suggesting that methods which better sample the conformational ensemble like aMD are more appropriate tools for use in chemical shift prediction for proteins with disordered regions. Moreover, our study suggests that data accurately reflecting protein dynamics must be used as input for chemical shift prediction in order to correctly predict chemical shifts in systems with disorder.

Single-step generation of metal-plasma polymer multicore@shell nanoparticles from the gas phase.

PubMed

Solař, Pavel; Polonskyi, Oleksandr; Olbricht, Ansgar; Hinz, Alexander; Shelemin, Artem; Kylián, Ondřej; Choukourov, Andrei; Faupel, Franz; Biederman, Hynek

2017-08-17

Nanoparticles composed of multiple silver cores and a plasma polymer shell (multicore@shell) were prepared in a single step with a gas aggregation cluster source operating with Ar/hexamethyldisiloxane mixtures and optionally oxygen. The size distribution of the metal inclusions as well as the chemical composition and the thickness of the shells were found to be controlled by the composition of the working gas mixture. Shell matrices ranging from organosilicon plasma polymer to nearly stoichiometric SiO 2 were obtained. The method allows facile fabrication of multicore@shell nanoparticles with tailored functional properties, as demonstrated here with the optical response.

On the interplay of shell structure with low- and high-frequency mechanics of multifunctional magnetic microbubbles.

PubMed

Poehlmann, Melanie; Grishenkov, Dmitry; Kothapalli, Satya V V N; Härmark, Johan; Hebert, Hans; Philipp, Alexandra; Hoeller, Roland; Seuss, Maximilian; Kuttner, Christian; Margheritelli, Silvia; Paradossi, Gaio; Fery, Andreas

2014-01-07

Polymer-shelled magnetic microbubbles have great potential as hybrid contrast agents for ultrasound and magnetic resonance imaging. In this work, we studied US/MRI contrast agents based on air-filled poly(vinyl alcohol)-shelled microbubbles combined with superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs are integrated either physically or chemically into the polymeric shell of the microbubbles (MBs). As a result, two different designs of a hybrid contrast agent are obtained. With the physical approach, SPIONs are embedded inside the polymeric shell and with the chemical approach SPIONs are covalently linked to the shell surface. The structural design of hybrid probes is important, because it strongly determines the contrast agent's response in the considered imaging methods. In particular, we were interested how structural differences affect the shell's mechanical properties, which play a key role for the MBs' US imaging performance. Therefore, we thoroughly characterized the MBs' geometric features and investigated low-frequency mechanics by using atomic force microscopy (AFM) and high-frequency mechanics by using acoustic tests. Thus, we were able to quantify the impact of the used SPIONs integration method on the shell's elastic modulus, shear modulus and shear viscosity. In summary, the suggested approach contributes to an improved understanding of structure-property relations in US-active hybrid contrast agents and thus provides the basis for their sustainable development and optimization.

Chemical Structure, Ensemble and Single-Particle Spectroscopy of Thick-Shell InP-ZnSe Quantum Dots.

PubMed

Reid, Kemar R; McBride, James R; Freymeyer, Nathaniel J; Thal, Lucas B; Rosenthal, Sandra J

2018-02-14

Thick-shell (>5 nm) InP-ZnSe colloidal quantum dots (QDs) grown by a continuous-injection shell growth process are reported. The growth of a thick crystalline shell is attributed to the high temperature of the growth process and the relatively low lattice mismatch between the InP core and ZnSe shell. In addition to a narrow ensemble photoluminescence (PL) line-width (∼40 nm), ensemble and single-particle emission dynamics measurements indicate that blinking and Auger recombination are reduced in these heterostructures. More specifically, high single-dot ON-times (>95%) were obtained for the core-shell QDs, and measured ensemble biexciton lifetimes, τ 2x ∼ 540 ps, represent a 7-fold increase compared to InP-ZnS QDs. Further, high-resolution energy dispersive X-ray (EDX) chemical maps directly show for the first time significant incorporation of indium into the shell of the InP-ZnSe QDs. Examination of the atomic structure of the thick-shell QDs by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals structural defects in subpopulations of particles that may mitigate PL efficiencies (∼40% in ensemble), providing insight toward further synthetic refinement. These InP-ZnSe heterostructures represent progress toward fully cadmium-free QDs with superior photophysical properties important in biological labeling and other emission-based technologies.

Retrospective environmental biomonitoring - Mussel Watch expanded

NASA Astrophysics Data System (ADS)

Schöne, Bernd R.; Krause, Richard A.

2016-09-01

Monitoring bioavailable contaminants and determining baseline conditions in aquatic environments has become an important aspect of ecology and ecotoxicology. Since the mid-1970s and the initiation of the Mussel Watch program, this has been successfully accomplished with bivalve mollusks. These (mostly) sessile organisms reliably and proportionately record changes of a range of organic and inorganic pollutants occurring in the water, food or sediment. The great majority of studies have measured the concentration of pollutants in soft tissues and, to a much lesser extent, in whole shells or fractions thereof. Both approaches come with several drawbacks. Neither soft tissues nor whole shells can resolve temporal changes of the pollution history, except through the analysis of multiple specimens collected at different times. Soft tissues and shell fractions provide time-averaged data spanning months or years, and whole shells time-averaged data over the entire lifespan of the animal. Even with regular sampling of multiple specimens over long intervals of time, the resulting chronology may not faithfully resolve short-term changes of water quality. Compounding the problem, whole shell averages tend to be non-arithmetic and non-linear, because shell growth rate varies through seasons and lifetime, and different shell layers often vary ultrastructurally and can thus be chemically different from each other. Mussel Watch could greatly benefit from the potential of bivalve shells in providing high-resolution, temporally aligned archives of environmental variability. So far, only circa a dozen studies have demonstrated that the sclerochronological approach - i.e., combined growth pattern and high-resolution chemical analyses - can provide sub-seasonally to annually resolved time-series documenting the history of pollution over centuries and even millennia. On the other hand, the sclerochronological community has failed to fully appreciate that the formation of the shell and its chemical composition is controlled by the soft parts and that a robust interpretation of the shell record requires a detailed understanding of bivalve physiology, behavior and ecology. This review attempts to bring together the Mussel Watch and sclerochronology communities and lay the foundation of a new subdiscipline of the Mussel Watch: retrospective environmental biomonitoring. For this purpose, we provide an overview of seminal work from both fields and outline potential future research directions.

Anthropogenic relief features in tropical northern Australia: a physical and chemical analysis of the Weipa shell mounds

NASA Astrophysics Data System (ADS)

Fanning, Patricia; Holdaway, Simon; Allely, Kasey; Larsen, Bernie; Petchey, Fiona

2017-04-01

Large mounded deposits of shell are prominent archaeological features across much of the north Australian tropical coast. Many of the shell mounds are composed almost entirely of the bivalve Anadara granosa (Linnaeus 1758), a food source for Aboriginal people in the past. They are identified in the field by their distinct mounded topographic form and the unique vegetation community growing on them. A relatively long history of inquiry into the nature and significance of the shell mounds has focused primarily on analysing the shell component as clues to Australian Aboriginal coastal economies in the past. This paper presents results of new analyses on the non-shell sediments of mounds located near Weipa in far north Queensland, examining the physical and chemical signatures of depositional and post-depositional processes with a view to obtaining insights into how the mounds formed and for what purposes, and how their morphology, structure and content may have changed since they ceased accumulating. We also consider how such changes might relate to past and present environmental conditions. The mounds we studied are primarily located on topographic high points, such as cliffs, hillslopes and beach ridges, though a proportion are located on estuarine floodplains at low elevations. Terrestrial Laser Scanning (TLS) of a sample of 51 shell mounds demonstrates substantial variation in mound size and shape, and suggests patterning in mound form related to age as well as position on the landscape. However, radiocarbon chronologies demonstrate that the mounds do not conform to a model of linear formation of a shell deposit, suggesting mound histories are variable in both the nature of shell deposition as well as post-depositional processes. Soil physical and chemical analyses indicate that post-depositional diagenetic alteration has strongly influenced the present day composition and form of the shell mounds, in particular the accession of carbon and silica to the mounds by environmental burning aided by strong leaching under seasonal high rainfall conditions. As such, mound chemistry is more likely to reflect modern environmental conditions rather than provide an archive of the past.

Mechanical ball-milling preparation of fullerene/cobalt core/shell nanocomposites with high electrochemical hydrogen storage ability.

PubMed

Bao, Di; Gao, Peng; Shen, Xiande; Chang, Cheng; Wang, Longqiang; Wang, Ying; Chen, Yujin; Zhou, Xiaoming; Sun, Shuchao; Li, Guobao; Yang, Piaoping

2014-02-26

The design and synthesis of new hydrogen storage nanomaterials with high capacity at low cost is extremely desirable but remains challenging for today's development of hydrogen economy. Because of the special honeycomb structures and excellent physical and chemical characters, fullerenes have been extensively considered as ideal materials for hydrogen storage materials. To take the most advantage of its distinctive symmetrical carbon cage structure, we have uniformly coated C60's surface with metal cobalt in nanoscale to form a core/shell structure through a simple ball-milling process in this work. The X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectra, high-solution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectrometry (EDX) elemental mappings, and X-ray photoelectron spectroscopy (XPS) measurements have been conducted to evaluate the size and the composition of the composites. In addition, the blue shift of C60 pentagonal pinch mode demonstrates the formation of Co-C chemical bond, and which enhances the stability of the as-obtained nanocomposites. And their electrochemical experimental results demonstrate that the as-obtained C60/Co composites have excellent electrochemical hydrogen storage cycle reversibility and considerably high hydrogen storage capacities of 907 mAh/g (3.32 wt % hydrogen) under room temperature and ambient pressure, which is very close to the theoretical hydrogen storage capacities of individual metal Co (3.33 wt % hydrogen). Furthermore, their hydrogen storage processes and the mechanism have also been investigated, in which the quasi-reversible C60/Co↔C60/Co-Hx reaction is the dominant cycle process.

Optical properties of core-shell and multi-shell nanorods

NASA Astrophysics Data System (ADS)

Mokkath, Junais Habeeb; Shehata, Nader

2018-05-01

We report a first-principles time dependent density functional theory study of the optical response modulations in bimetallic core-shell (Na@Al and Al@Na) and multi-shell (Al@Na@Al@Na and Na@Al@Na@Al: concentric shells of Al and Na alternate) nanorods. All of the core-shell and multi-shell configurations display highly enhanced absorption intensity with respect to the pure Al and Na nanorods, showing sensitivity to both composition and chemical ordering. Remarkably large spectral intensity enhancements were found in a couple of core-shell configurations, indicative that optical response averaging based on the individual components can not be considered as true as always in the case of bimetallic core-shell nanorods. We believe that our theoretical results would be useful in promising applications depending on Aluminum-based plasmonic materials such as solar cells and sensors.

Tuning the Pitch of a Wine Glass by Playing with the Liquid inside

ERIC Educational Resources Information Center

Courtois, Matthieu; Guirao, Boris; Fort, Emmanuel

2008-01-01

It is well known that the pitch of the sound produced by an excited glass shell can be tuned by adding some liquid in it. In this paper, it will be proved that the distribution of the liquid inside the shell plays a crucial role in this frequency shift. Thus it provides another way to tune the pitch of the sound by modifying the liquid…

Determination of trichloroethylene by using self-referenced SERS and gold-core/silver-shell nanoparticles.

PubMed

Yu, Zhao; Smith, Michael E; Zhang, Jinnan; Zhou, Yan; Zhang, Peng

2018-06-18

A surface-enhanced Raman scattering (SERS) method has been developed to determine the concentration of trichloroethylene (TCE) in environmental water. Au-core/Ag-shell nanoparticles containing 4-mercaptophenylboronic acid (4-MPBA) between the core and shell are used as the SERS substrate. 4-MPBA serves as an internal reference with a Raman shift at 534 cm -1 . TCE reacts with 4-mercaptopyridine (4-MPy) in a so-called Fujiwara reaction. With the presence of TCE in water, the consumption of 4-MPy results in a change in the intensity of its Raman signal at 1220 cm -1 . The ratio of the Raman shift at 1220 cm -1 and 534 cm -1 decreases linearly in the 0.2 to 1.0 μM TCE concentration range, and the detection limit of TCE is as low as 8 ppb (60 nM). The method has been successfully applied to the determination of TCE in spiked lake water. Graphical abstract Gold-core/silver-shell nanoparticles with internal reference embedded have been fabracated to improve the quantitative measurement of SERS. These nanoparticles as SERS substrates, are used to indirectly quantify the concentration of trichloroethylene (a typical halogenated organic compound) by the consumption of 4-mercaptopyridine through the Fujiwara reaction.

High Level ab initio Predictions of the Energetics of mCO2•(H2O)n (n = 1-3, m = 1-12) Clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thanthiriwatte, Sahan; Duke, Jessica R.; Jackson, Virgil E.

Electronic structure calculations at the correlated molecular orbital theory and density functional theory levels have been used to generate a reliable set of clustering energies for up to three water molecules in carbon dioxide clusters up to n = 12. The structures and energetics are dominated by Lewis acid-base interactions with hydrogen bonding interactions playing a lesser energetic role. The actual binding energies are somewhat larger than might be expected. The correlated molecular orbital MP2 method and density functional theory with the ωB97X exchange-correlation functional provide good results for the energetics of the clusters but the B3LYP and ωB97X-D functionalsmore » do not. Seven CO2 molecules form the first solvent shell about a single H2O with four CO2 molecules interacting with the H2O via Lewis acid-base interactions, two CO2 interacting with the H2O by hydrogen bonds, and the seventh CO2 completing the shell. The Lewis acid-base and weak hydrogen bond interactions between the water molecules and the CO2 molecules are strong enough to disrupt the trimer ring configuration for as few as seven CO2 molecules. Calculated 13C NMR chemical shifts for mCO2•(H2O)n show little change with respect to the number of H2O or CO2 molecules in the cluster. The O-H stretching frequencies do exhibit shifts that can provide information about the interactions between water and CO2 molecules.« less

The effects of staggered bandgap in the InP/CdSe and CdSe/InP core/shell quantum dots.

PubMed

Kim, Sunghoon; Park, Jaehyun; Kim, Sungwoo; Jung, Won; Sung, Jaeyoung; Kim, Sang-Wook

2010-06-15

New type-II structures of CdSe/InP and InP/CdSe core-shell nanocrystals which have staggered bandgap alignment were fabricated. Using a simple model for the wave function for electrons and holes in InP/CdSe and CdSe/InP core/shell nanocrystals showed the wave function of the electron and hole spread into the shell, respectively. The probability density of the InP/CdSe and CdSe/InP core/shell QDs also showed a similar tendency. As a result, the structure exhibits increased delocalization of electrons and holes, leading to a red-shift in absorption and emission. Quantum yield increased in the InP/CdSe, however decreased in the CdSe/InP. The reason may be due to the surface trap and high activation barrier for de-trapping in the InP shell. 2010 Elsevier Inc. All rights reserved.

Dye-Sensitized Core/Active Shell Upconversion Nanoparticles for Optogenetics and Bioimaging Applications

DOE PAGES

Wu, Xiang; Zhang, Yuanwei; Takle, Kendra; ...

2016-01-06

A near-infrared (NIR) dye-sensitized upconversion nanoparticles (UCNPs) can broaden the absorption range and boost upconversion efficiency of UCNPs. We achieved significantly enhanced upconversion luminescence in dye-sensitized core/active shell UCNPs via the doping of ytterbium ions (Yb 3+ ) in the UCNP shell, which bridged the energy transfer from the dye to the UCNP core. As a result, we synergized the two most practical upconversion booster effectors (dye-sensitizing and core/shell enhancement) to amplify upconversion efficiency. We also demonstrated two biomedical applications using these UCNPs. By using dye-sensitized core/active shell UCNP embedded poly(methyl methacrylate) polymer implantable systems, we successfully shifted the optogeneticmore » neuron excitation window to a biocompatible and deep tissue penetrable 800 nm wavelength. Furthermore, UCNPs were water-solubilized with Pluronic F127 with high upconversion efficiency and can be imaged in a mouse model.« less

Wide-range tuning of the surface plasmon resonance of silver/gold core shell and alloyed nanoparticles

NASA Astrophysics Data System (ADS)

Hubenthal, Frank; Ziegler, Torsten; Hendrich, Christian; Träger, Frank

2004-03-01

For many applications like surface enhanced Raman scattering in which the optical field enhancement associated with surface plasmon excitation is exploited, tunability of this collective resonance over a wide range is required. For this purpose we have prepared Ag/Au core shell and Ag/Au alloyed nanoparticles with different shell thicknesses and different percentages of the two metals. The nanoparticles were made by subsequent deposition of Ag and Au atoms on dielectric substrates followed by diffusion and nucleation or heat treatment. Depending on the Au shell thickness the plasmon frequency can be tuned, e.g. from 2.8 eV (442 nm) to 2.1 eV (590 nm). Annealing of the core-shell nanoparticles causes a shift of the resonance frequency to 2.6 eV. Theoretical modelling allows us to attribute this observation to the production of alloyed nanoparticles. Possible application of the Ag/Au nanoparticles will be discussed.

High spin structure and intruder configurations in 31P

NASA Astrophysics Data System (ADS)

Ionescu-Bujor, M.; Iordachescu, A.; Napoli, D. R.; Lenzi, S. M.; Mărginean, N.; Otsuka, T.; Utsuno, Y.; Ribas, R. V.; Axiotis, M.; Bazzacco, D.; Bizzeti-Sona, A. M.; Bizzeti, P. G.; Brandolini, F.; Bucurescu, D.; Cardona, M. A.; De Angelis, G.; De Poli, M.; Della Vedova, F.; Farnea, E.; Gadea, A.; Hojman, D.; Kalfas, C. A.; Kröll, Th.; Lunardi, S.; Martínez, T.; Mason, P.; Pavan, P.; Quintana, B.; Alvarez, C. Rossi; Ur, C. A.; Vlastou, R.; Zilio, S.

2006-02-01

The nucleus 31P has been studied in the 24Mg(16O,2αp) reaction with a 70-MeV 16O beam. A complex level scheme extended up to spins 17/2+ and 15/2-, on positive and negative parity, respectively, has been established. Lifetimes for the new states have been investigated by the Doppler shift attenuation method. Two shell-model calculations have been performed to describe the experimental data, one by using the code ANTOINE in a valence space restricted to the sd shell, and the other by applying the Monte Carlo shell model in a valence space including the sd-fp shells. The latter calculation indicates that intruder excitations, involving the promotion of a T=0 proton-neutron pair to the fp shell, play a dominant role in the structure of the positive-parity high-spin states of 31P.

Records of River Variation in the Shells of Freshwater Bivalves

NASA Astrophysics Data System (ADS)

Carroll, M.; Romanek, C.

2005-12-01

The skeletons of hard-shelled invertebrates such as corals and bivalves are commonly used in marine settings as archives of environmental information. They are less commonly used in freshwater settings where variability in water chemistry makes it more difficult to calibrate chemical proxies such as the Sr:Ca in a shell. Our objective is to evaluate whether trace element concentrations in freshwater bivalve shells contain information on environmental conditions. Multiple elements (Ba, Cu, Mn and Sr) were analyzed within the shells of modern bivalves from four streams on DOE's Savannah River Site in S.C. Laser Ablation ICP-MS was used to measure elemental concentrations across five aragonitic shells from each site. These elements were chosen because they are present in detectable concentrations (ppm) in the shell and they have been suggested as useful proxies for temperature, rainfall, productivity and pollution. Results were compared to historical monthly site records of water chemistry and chemical analyses of water samples collected from the streams where the clams were found. The average shell concentrations of Sr and Mn were significantly different between sites and increased proportionally to water concentration. This was not observed for Ba and Cu. For example, the Ba concentrations of shells collected at a site downstream of a lake were higher than those for shells from stream sites with significantly higher dissolved Ba concentrations. Copper was only detected at dark growth lines with the number of lines and shell material between them varying between shells within the same stream. Intrashell profiles of Ba, Sr and Mn concentrations exhibited cyclical variation. The magnitude of cyclical variation for Mn and Sr within a shell corresponds with the annual variation in monthly water sample concentrations. Again, this pattern was not observed for Ba, especially in shells from the site downstream of a lake. This supports suggestions that particulate organic matter, to which Ba preferentially partitions, plays a role in bivalve Ba uptake. Finally, variations in Ba, Cu, Mn and Sr profiles across shells are not in unison. The individual elemental responses to biological and physicochemical effects suggest that the elemental records in freshwater bivalve shells can be interpreted as environmental proxies.

Comparison of experimental and DFT-calculated NMR chemical shifts of 2-amino and 2-hydroxyl substituted phenyl benzimidazoles, benzoxazoles and benzothiazoles in four solvents using the IEF-PCM solvation model.

PubMed

Pierens, Gregory K; Venkatachalam, T K; Reutens, David C

2016-04-01

A comparative study of experimental and calculated NMR chemical shifts of six compounds comprising 2-amino and 2-hydroxy phenyl benzoxazoles/benzothiazoles/benzimidazoles in four solvents is reported. The benzimidazoles showed interesting spectral characteristics, which are discussed. The proton and carbon chemical shifts were similar for all solvents. The largest chemical shift deviations were observed in benzene. The chemical shifts were calculated with density functional theory using a suite of four functionals and basis set combinations. The calculated chemical shifts revealed a good match to the experimentally observed values in most of the solvents. The mean absolute error was used as the primary metric. The use of an additional metric is suggested, which is based on the order of chemical shifts. The DP4 probability measures were also used to compare the experimental and calculated chemical shifts for each compound in the four solvents. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

The role of radial nodes of atomic orbitals for chemical bonding and the periodic table.

PubMed

Kaupp, Martin

2007-01-15

The role of radial nodes, or of their absence, in valence orbitals for chemical bonding and periodic trends is discussed from a unified viewpoint. In particular, we emphasize the special role of the absence of a radial node whenever a shell with angular quantum number l is occupied for the first time (lack of "primogenic repulsion"), as with the 1s, 2p, 3d, and 4f shells. Although the consequences of the very compact 2p shell (e.g. good isovalent hybridization, multiple bonding, high electronegativity, lone-pair repulsion, octet rule) are relatively well known, it seems that some of the aspects of the very compact 3d shell in transition-metal chemistry are less well appreciated, e.g., the often weakened and stretched bonds at equilibrium structure, the frequently colored complexes, and the importance of nondynamical electron-correlation effects in bonding. Copyright (c) 2006 Wiley Periodicals, Inc.

Role of N-methyl-2-pyrrolidone for preparation of Fe3O4@SiO2 controlled the shell thickness

NASA Astrophysics Data System (ADS)

Wee, Sung-Bok; Oh, Hyeon-Cheol; Kim, Tae-Gyun; An, Gye-Seok; Choi, Sung-Churl

2017-04-01

We developed a simple and novel approach for the synthesis of Fe3O4@SiO2 nanoparticles with controlled shell thickness, and studied the mechanism. The introduction of N-methyl-2-pyrrolidone (NMP) led to trapping of monomer nuclei in single shell and controlled the shell thickness. Fe3O4@SiO2 controlled the shell thickness, showing a high magnetization value (64.47 emu/g). Our results reveal the role and change in the chemical structure of NMP during the core-shell synthesis process. NMP decomposed to 4-aminobutanoic acid in alkaline condition and decreased the hydrolysis rate of the silica coating process.

Shell effect on the electron and hole reorganization energy of core-shell II-VI nanoclusters

NASA Astrophysics Data System (ADS)

Cui, Xianhui; Wang, Xinqin; Yang, Fang; Cui, Yingqi; Yang, Mingli

2017-09-01

Density functional theory calculations were performed to study the effect of shell encapsulation on the geometrical and electronic properties of pure and hybrid core-shell CdSe nanoclusters. The CdSe cores are distorted by the shells, and the shells exhibit distinct surface activity from the cores, which leads to remarkable changes in their electron transition behaviors. Although the electron and hole reorganization energies, which are related to the formation and recombination of electron-hole pairs, vary in a complicated way, their itemized contributions, potentials of electron extraction, ionization and affinity, and hole extraction (HEP), are dependent on the cluster size, shell composition and/or solvent. Our calculations suggest that the behaviors of charge carriers, free electrons and holes, in the semiconductor core-shell nanoclusters can be modulated by selecting appropriate cluster size and controlling the chemical composition of the shells.

Nuclear magnetic resonance studies of the solvation structures of a high-performance nonaqueous redox flow electrolyte

NASA Astrophysics Data System (ADS)

Deng, Xuchu; Hu, Mary; Wei, Xiaoliang; Wang, Wei; Mueller, Karl T.; Chen, Zhong; Hu, Jian Zhi

2016-03-01

Understanding the solvation structures of electrolytes is important for developing nonaqueous redox flow batteries that hold considerable potential for future large scale energy storage systems. The utilization of an emerging ionic-derivatived ferrocene compound, ferrocenylmethyl dimethyl ethyl ammonium bis(trifluoromethanesulfonyl)imide (Fc1N112-TFSI), has recently overcome the issue of solubility in the supporting electrolyte. In this work, 13C, 1H and 17O NMR investigations were carried out using electrolyte solutions consisting of Fc1N112-TFSI as the solute and the mixed alkyl carbonate as the solvent. It was observed that the spectra of 13C experience changes of chemical shifts while those of 17O undergo linewidth broadening, indicating interactions between solute and solvent molecules. Quantum chemistry calculations of both molecular structures and chemical shifts (13C, 1H and 17O) are performed for interpreting experimental results and for understanding the detailed solvation structures. The results indicate that Fc1N112-TFSI is dissociated at varying degrees in mixed solvent depending on concentrations. At dilute solute concentrations, most Fc1N112+ and TFSI- are fully disassociated with their own solvation shells formed by solvent molecules. At saturated concentration, Fc1N112+-TFSI- contact ion pairs are formed and the solvent molecules are preferentially interacting with the Fc rings rather than interacting with the ionic pendant arm of Fc1N112-TFSI.

Protein structure refinement using a quantum mechanics-based chemical shielding predictor.

PubMed

Bratholm, Lars A; Jensen, Jan H

2017-03-01

The accurate prediction of protein chemical shifts using a quantum mechanics (QM)-based method has been the subject of intense research for more than 20 years but so far empirical methods for chemical shift prediction have proven more accurate. In this paper we show that a QM-based predictor of a protein backbone and CB chemical shifts (ProCS15, PeerJ , 2016, 3, e1344) is of comparable accuracy to empirical chemical shift predictors after chemical shift-based structural refinement that removes small structural errors. We present a method by which quantum chemistry based predictions of isotropic chemical shielding values (ProCS15) can be used to refine protein structures using Markov Chain Monte Carlo (MCMC) simulations, relating the chemical shielding values to the experimental chemical shifts probabilistically. Two kinds of MCMC structural refinement simulations were performed using force field geometry optimized X-ray structures as starting points: simulated annealing of the starting structure and constant temperature MCMC simulation followed by simulated annealing of a representative ensemble structure. Annealing of the CHARMM structure changes the CA-RMSD by an average of 0.4 Å but lowers the chemical shift RMSD by 1.0 and 0.7 ppm for CA and N. Conformational averaging has a relatively small effect (0.1-0.2 ppm) on the overall agreement with carbon chemical shifts but lowers the error for nitrogen chemical shifts by 0.4 ppm. If an amino acid specific offset is included the ProCS15 predicted chemical shifts have RMSD values relative to experiments that are comparable to popular empirical chemical shift predictors. The annealed representative ensemble structures differ in CA-RMSD relative to the initial structures by an average of 2.0 Å, with >2.0 Å difference for six proteins. In four of the cases, the largest structural differences arise in structurally flexible regions of the protein as determined by NMR, and in the remaining two cases, the large structural change may be due to force field deficiencies. The overall accuracy of the empirical methods are slightly improved by annealing the CHARMM structure with ProCS15, which may suggest that the minor structural changes introduced by ProCS15-based annealing improves the accuracy of the protein structures. Having established that QM-based chemical shift prediction can deliver the same accuracy as empirical shift predictors we hope this can help increase the accuracy of related approaches such as QM/MM or linear scaling approaches or interpreting protein structural dynamics from QM-derived chemical shift.

Chemical Component and Proteomic Study of the Amphibalanus (= Balanus) amphitrite Shell

PubMed Central

Zhang, Gen; He, Li-sheng; Wong, Yue-Him; Xu, Ying; Zhang, Yu; Qian, Pei-yuan

2015-01-01

As typical biofoulers, barnacles possess hard shells and cause serious biofouling problems. In this study, we analyzed the protein component of the barnacle Amphibalanus (= Balanus) amphitrite shell using gel-based proteomics. The results revealed 52 proteins in the A. Amphitrite shell. Among them, 40 proteins were categorized into 11 functional groups based on KOG database, and the remaining 12 proteins were unknown. Besides the known proteins in barnacle shell (SIPC, carbonic anhydrase and acidic acid matrix protein), we also identified chorion peroxidase, C-type lectin-like domains, serine proteases and proteinase inhibitor proteins in the A. Amphitrite shell. The sequences of these proteins were characterized and their potential functions were discussed. Histology and DAPI staining revealed living cells in the shell, which might secrete the shell proteins identified in this study. PMID:26222041

Developing core-shell upconversion nanoparticles for optical encoding

NASA Astrophysics Data System (ADS)

Huang, Kai

Lanthanide-doped upconversion nanoparticles (UCNPs) are an emerging class of luminescent materials that emit UV or visible light under near infra-red (NIR) excitations, thereby possessing a large anti-Stokes shift property. Also considering their sharp emission bands, excellent photo- and chemical stability, and almost zero auto-fluorescence of their NIR excitation, UCNPs are advantageous for optical encoding. Fabricating core-shell structured UCNPs provides a promising strategy to tune and enhance their upconverting luminescence. However, the energy transfer between core and shell had been rarely studied. Moreover, this strategy had been limited by the difficulty of coating thick shells onto the large cores of UCNPs. To overcome these constraints, the overall aim of this project is to study the inter-layers energy transfer in core-shell UCNPs and to develop an approach for coating thicker shell onto the core UCNPs, in order to fabricate UCNPs with enhanced and tunable luminescence for optical encoding. The strategy for encapsulating UCNPs into hydrogel droplet to fabricate multi-color bead barcodes has also been developed. Firstly, to study the inter-layers energy transfer between the core and shell of coreshell UCNPs, the activator and sensitizer ions were separately doped in the core or shell by fabricating NaYF4:Er NaYF4:Yb and NaYF4:Yb NaYF4:Er UCNPs. This eliminated the intra-layer energy transfer, resulting in a luminescence that is solely based on the energy transfer between layers, which facilitated the study of inter-layers energy transfer. The results demonstrated that the NaYF4:Yb NaYF4:Er structure, with sensitizer ions doped in the core, was preferable because of the strong luminescence, through minimizing the cross relaxations between Er3+ and Yb3+ and the surface quenching. Based on these information, a strategy of enhancing and tuning upconversion luminescence of core-shell UCNPs by accumulating sensitizer in the core has been developed. Next, a strategy of coating a thick shell by lutetium doping has been developed. With a smaller ion radius compared to Y3+, when Lu3+ partially replace Y3+ in the NaYF4 UCNPs during nanoparticle synthesis, nucleation process is suppressed and the growth process is promoted, which are favorable for increasing the nanoparticle size and coating a thicker shell onto the core UCNPs. Through the rational doping of Lu3+, core UCNPs with bigger sizes and enhanced luminescence were produced. Using NaLuF4 as the shell material, shells with tremendous thickness were coated onto core UCNPs, with the shell/core ratio of up to 10:1. This led to the fabrication of multi-color UCNPs with well-designed core-shell structures with multiple layers and controllable thicknesses. Finally, a strategy of encapsulating these UCNPs to produce optically encoded micro-beads through high-throughput microfluidics has been developed. The hydrophobic UCNPs were first modified with Pluronic F127 to render them hydrophilic and uniformly distributed in the poly (ethylene glycol) diacrylate (PEGDA) hydrogel precursor. Droplets of the hydrogel precursor were formed in a microfluidic device and cross-linked into micro-beads under UV irradiation. Through encapsulation of multi-color UCNPs and by controlling their ratio, optically encoded multi-color micro-beads have been easily fabricated. These multi-color UCNPs and micro-bead barcodes have great potential for use in multiplexed bioimaging and detection.

Linear and nonlinear magneto-optical properties of an off-center single dopant in a spherical core/shell quantum dot

NASA Astrophysics Data System (ADS)

Feddi, E.; Talbi, A.; Mora-Ramos, M. E.; El Haouari, M.; Dujardin, F.; Duque, C. A.

2017-11-01

Using the effective mass approximation and a variational procedure, we have investigated the nonlinear optical absorption coefficient and the relative refractive index changes associated to a single dopant confined in core/shell quantum dots considering the influences of the core/shell dimensions, externally applied magnetic field, and dielectric mismatch. The results show that the optical absorption coefficient and the coefficients of relative refractive index change depend strongly on the core/shell sizes and they are blue shifted when the spatial confinement increases so this effect is magnified by higher structural dimensions. Additionally, it is obtained that both studied optical properties are sensitive to the dielectric environment in such a way that their amplitudes are very affected by the local field corrections.

Electronic and Optical Properties of Core/Shell Pb16X16/Cd52X52 (X =S, Se, Te) Quantum Dots

NASA Astrophysics Data System (ADS)

Tamukong, Patrick; Mayo, Michael; Kilina, Svetlana

2015-03-01

The electronic and optoelectronic properties of semiconductor quantum dots (QDs) are mediated by surface defects due to the presence of dangling bonds producing trap states within the HOMO-LUMO energy gap, and contributing to fluorescence quenching. Surface capping ligands are generally used to alleviate this problem and increase the quantum yields of QDs. An alternative way is to synthesize core-shell QD structures; i.e., a QD core with a shell of another semiconductor material. We have investigated the effects of Cd52X52 shells on the photoexcited dynamics of Pb16X16 (X =S, Se, Te) QDs. The thin (~ 0.50 nm) shells were found to result largely in type I core/shell structures and a blue shift of the absorption spectra. Our studies revealed fairly strong core-shell hybridization in the electronic states close to the conduction band (CB) edge for Pb16S16andPb16Se16 cores, whereas for the Pb16Te16 core, such CB states were largely shell-like in nature. Nonadiabatic DFT-based dynamics, coupled with the surface hopping method, was used to study the effects of the core and shell compositions on energy relaxation rates in these systems.

Predator-induced morphological plasticity across local populations of a freshwater snail.

PubMed

Brönmark, Christer; Lakowitz, Thomas; Hollander, Johan

2011-01-01

The expression of anti-predator adaptations may vary on a spatial scale, favouring traits that are advantageous in a given predation regime. Besides, evolution of different developmental strategies depends to a large extent on the grain of the environment and may result in locally canalized adaptations or, alternatively, the evolution of phenotypic plasticity as different predation regimes may vary across habitats. We investigated the potential for predator-driven variability in shell morphology in a freshwater snail, Radix balthica, and whether found differences were a specialized ecotype adaptation or a result of phenotypic plasticity. Shell shape was quantified in snails from geographically separated pond populations with and without molluscivorous fish. Subsequently, in a common garden experiment we investigated reaction norms of snails from populations' with/without fish when exposed to chemical cues from tench (Tinca tinca), a molluscivorous fish. We found that snails from fish-free ponds had a narrow shell with a well developed spire, whereas snails that coexisted with fish had more rotund shells with a low spire, a shell morphology known to increase survival rate from shell-crushing predators. The common garden experiment mirrored the results from the field survey and showed that snails had similar reaction norms in response to chemical predator cues, i.e. the expression of shell shape was independent of population origin. Finally, we found significant differences for the trait means among populations, within each pond category (fish/fish free), suggesting a genetic component in the determination of shell morphology that has evolved independently across ponds.

Synthesis of fullerene@gold core-shell nanostructures.

PubMed

Ren, Yupeng; Paira, Priyankar; Nayak, Tapas Ranjan; Ang, Wee Han; Pastorin, Giorgia

2011-07-21

A "direct encapsulation" method was developed for the synthesis of highly stable water-soluble fullerene@gold core-shell nanostructures, with gold nanoshells showing either closed or porous morphology. This gold nano-shell coating formed a "nano-oven", capable of decomposing encapsulated fullerene molecules rapidly when irradiated by laser. We envisaged this being a useful tool for chemical reactions as well as a novel scaffold for nano-material synthesis.

Gold core@silver semishell Janus nanoparticles prepared by interfacial etching.

PubMed

Chen, Limei; Deming, Christopher P; Peng, Yi; Hu, Peiguang; Stofan, Jake; Chen, Shaowei

2016-08-14

Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface.

Thermal Expansion Measurements of Polymer Matrix Composites and Syntactics

DTIC Science & Technology

1992-04-01

828 (Shell Chemical) epoxy combined with 50.0 PBW EPON® V-40 polyamide curing agent (Shell Chemical) and Owens Corning (E-780) polyester combined 1...with 24 oz. woven roving with an Owens Corning 463 finish. " A 3 x 1, S-2 glass with 27 oz. woven roving with an Owens Corning 933 finish, nominally...wet polyester resin ( Owens Corning E-780) and subsequently processing the composites using the standard vacuum bag cure cycle for this polyester

Cretaceous honeycomb oysters (Pycnodonte vesicularis) as palaeoseasonality records: A multi-proxy study

NASA Astrophysics Data System (ADS)

de Winter, Niels J.; Vellekoop, Johan; Vorsselmans, Robin; Golreihan, Asefeh; Petersen, Sierra V.; Meyer, Kyle W.; Speijer, Robert P.; Claeys, Philippe

2017-04-01

Pycnodonte or "honeycomb-oysters" (Bivalvia: Gryphaeidea) is an extinct genus of calcite-producing bivalves which is found in abundance in Cretaceous to Pleistocene fossil beds worldwide. As such, Pycnodonte shells could be ideal tracers of palaeoclimate through time, with the capability to reconstruct sea water conditions and palaeotemperatures in a range of palaeoenvironmental settings. Only few studies have attempted to reconstruct palaeoclimate based on Pycnodonte shells and with variable degrees of success (e.g. Videt, 2003; Huyge et al., 2015). Our study investigates the shell growth, structure and chemical characteristics of Maastrichtian Pycnodonte vesicularis from Bajada de Jaguel in Argentina and aims to rigorously test the application of multiple palaeoenvironmental proxies on the shells of several Maastrichtian Pycnodonte oysters for palaeoclimate reconstruction. The preservation state of four calcite shells was assessed by fluorescence microscopy, cathodoluminescence and micro X-Ray Fluorescence (XRF) mapping. Their shell structure was investigated using a combination of XRF mapping, high-resolution color scanning and microCT scanning. Long integration time point-by-point XRF line scanning yielded high-resolution trace element profiles through the hinge of all shells. Microdrilled samples from the same locations on the shell were analyzed for trace element composition by ICP-MS and for stable carbon and oxygen isotopes by IRMS. Preservation of the calcite microstructure was found to be of sufficient quality to allow discussion of original shell porosity, annual growth increments and pristine chemical signatures of the bivalves. The combination of fluorescence and cathodoluminescence microscopy with XRF mapping and microCT scanning sheds light on the characteristic internal "honeycomb" structure of these extinct bivalves and allows comparison with that of the related extant Neopycnodonte bivalves (Wisshak et al., 2009). Furthermore, high resolution trace element and stable isotope records allow discussion of the degree to which Pycnodonte shells record their palaeoenvironment and can be used to reconstruct past sea water conditions. Preliminary results indicate that stable isotope and trace element ratios in Pynodonte shells record different seasonally changing sea water conditions in the Maastrichtian and reconstructed temperatures are consistent with results from clumped isotope analysis on the same shells and TEX86 analysis on the surrounding rocks. This multi-proxy study sheds light on the shell structure of Pycnodonte oysters, their chemical signature and growth pattern and investigates the expression of palaeoenvironmental proxies in the pristine shell calcite of these bivalves. This investigation shows the potential of using fossil Pycnodonte bivalves as a new archive for palaeoclimate reconstruction on a seasonal scale over a wide range of palaeolatitudes from the Cretaceous until the Pleistocene. References Huyghe et al. (2015) J. Geol Soc 172.5: 576-587. Videt (2003) Diss. Université Rennes 1. Wisshak, et al. (2009) Deep-Sea Res Pt I 56.3: 374-407.

State interference in resonance Auger and x-ray emission

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cesar, A.; Agren, H.

1992-03-01

Starting from a scattering-theory formulation, cross sections for Auger and x-ray decay from energetically shifted inner-shell states are derived. Two situations are studied: (i) when there are several close-lying intermediate core-hole states with no vibrational excitations, in which case a {ital state} {ital interference} effect is identified; and (ii) when there are several close-lying intermediate states with vibrational excitations, in which case a {ital vibronic} {ital interference} effect is identified. In the latter case, the present formalism is a many-state generalization of the {ital vibrational} {ital interference} {ital effects} derived from the same type of scattering formalism in our previousmore » paper (A. Cesar, H. Agren, and V. Carravetta, Phys. Rev. A 40, 187 (1989)). Applications are carried out for spectra of some few-state model systems. It is found that a conventional analysis in terms of discrete noninteracting (noninterfering) states, such as the one-center decomposition model, is only valid when the ratio ({ital R}) between energy shift and lifetime is sufficiently large. For states with small {ital R}, a more complete theoretical account must be undertaken, including, e.g., the calculation of phases of the respective transition moments. The presented formalism applies to resonance Auger or x-ray emission spectra, to Auger and x-ray emission from core-electron shake-up states, and also, under certain circumstances, to emission from chemically shifted core-hole states.« less

Enhanced NMR Discrimination of Pharmaceutically Relevant Molecular Crystal Forms through Fragment-Based Ab Initio Chemical Shift Predictions.

PubMed

Hartman, Joshua D; Day, Graeme M; Beran, Gregory J O

2016-11-02

Chemical shift prediction plays an important role in the determination or validation of crystal structures with solid-state nuclear magnetic resonance (NMR) spectroscopy. One of the fundamental theoretical challenges lies in discriminating variations in chemical shifts resulting from different crystallographic environments. Fragment-based electronic structure methods provide an alternative to the widely used plane wave gauge-including projector augmented wave (GIPAW) density functional technique for chemical shift prediction. Fragment methods allow hybrid density functionals to be employed routinely in chemical shift prediction, and we have recently demonstrated appreciable improvements in the accuracy of the predicted shifts when using the hybrid PBE0 functional instead of generalized gradient approximation (GGA) functionals like PBE. Here, we investigate the solid-state 13 C and 15 N NMR spectra for multiple crystal forms of acetaminophen, phenobarbital, and testosterone. We demonstrate that the use of the hybrid density functional instead of a GGA provides both higher accuracy in the chemical shifts and increased discrimination among the different crystallographic environments. Finally, these results also provide compelling evidence for the transferability of the linear regression parameters mapping predicted chemical shieldings to chemical shifts that were derived in an earlier study.

Enhanced NMR Discrimination of Pharmaceutically Relevant Molecular Crystal Forms through Fragment-Based Ab Initio Chemical Shift Predictions

PubMed Central

2016-01-01

Chemical shift prediction plays an important role in the determination or validation of crystal structures with solid-state nuclear magnetic resonance (NMR) spectroscopy. One of the fundamental theoretical challenges lies in discriminating variations in chemical shifts resulting from different crystallographic environments. Fragment-based electronic structure methods provide an alternative to the widely used plane wave gauge-including projector augmented wave (GIPAW) density functional technique for chemical shift prediction. Fragment methods allow hybrid density functionals to be employed routinely in chemical shift prediction, and we have recently demonstrated appreciable improvements in the accuracy of the predicted shifts when using the hybrid PBE0 functional instead of generalized gradient approximation (GGA) functionals like PBE. Here, we investigate the solid-state 13C and 15N NMR spectra for multiple crystal forms of acetaminophen, phenobarbital, and testosterone. We demonstrate that the use of the hybrid density functional instead of a GGA provides both higher accuracy in the chemical shifts and increased discrimination among the different crystallographic environments. Finally, these results also provide compelling evidence for the transferability of the linear regression parameters mapping predicted chemical shieldings to chemical shifts that were derived in an earlier study. PMID:27829821

Rapid and reliable protein structure determination via chemical shift threading.

PubMed

Hafsa, Noor E; Berjanskii, Mark V; Arndt, David; Wishart, David S

2018-01-01

Protein structure determination using nuclear magnetic resonance (NMR) spectroscopy can be both time-consuming and labor intensive. Here we demonstrate how chemical shift threading can permit rapid, robust, and accurate protein structure determination using only chemical shift data. Threading is a relatively old bioinformatics technique that uses a combination of sequence information and predicted (or experimentally acquired) low-resolution structural data to generate high-resolution 3D protein structures. The key motivations behind using NMR chemical shifts for protein threading lie in the fact that they are easy to measure, they are available prior to 3D structure determination, and they contain vital structural information. The method we have developed uses not only sequence and chemical shift similarity but also chemical shift-derived secondary structure, shift-derived super-secondary structure, and shift-derived accessible surface area to generate a high quality protein structure regardless of the sequence similarity (or lack thereof) to a known structure already in the PDB. The method (called E-Thrifty) was found to be very fast (often < 10 min/structure) and to significantly outperform other shift-based or threading-based structure determination methods (in terms of top template model accuracy)-with an average TM-score performance of 0.68 (vs. 0.50-0.62 for other methods). Coupled with recent developments in chemical shift refinement, these results suggest that protein structure determination, using only NMR chemical shifts, is becoming increasingly practical and reliable. E-Thrifty is available as a web server at http://ethrifty.ca .

Hazardous Waste Cleanup: Huntsman Corporation in West Deptford Township, New Jersey

EPA Pesticide Factsheets

Huntsman Corporation is located on Mantua Grove Road in West Deptford Township, New Jersey. The Shell Chemical Company manufactured polypropylene pellets at this facility since 1961. Shell stored waste oil and burned it in an on-site boiler.

Size-Dependent Specific Surface Area of Nanoporous Film Assembled by Core-Shell Iron Nanoclusters

DOE PAGES

Antony, Jiji; Nutting, Joseph; Baer, Donald R.; ...

2006-01-01

Nmore » anoporous films of core-shell iron nanoclusters have improved possibilities for remediation, chemical reactivity rate, and environmentally favorable reaction pathways. Conventional methods often have difficulties to yield stable monodispersed core-shell nanoparticles. We produced core-shell nanoclusters by a cluster source that utilizes combination of Fe target sputtering along with gas aggregations in an inert atmosphere at 7 ∘ C . Sizes of core-shell iron-iron oxide nanoclusters are observed with transmission electron microscopy (TEM). The specific surface areas of the porous films obtained from Brunauer-Emmett-Teller (BET) process are size-dependent and compared with the calculated data.« less

A Short History of Three Chemical Shifts

ERIC Educational Resources Information Center

Nagaoka, Shin-ichi

2007-01-01

A short history of chemical shifts in nuclear magnetic resonance (NMR), electron spectroscopy for chemical analysis (ESCA) and Mossbauer spectroscopy, which are useful for chemical studies, is described. The term chemical shift is shown to have originated in the mistaken assumption that nuclei of a given element would all undergo resonance at the…

Silica diatom shells tailored with Au nanoparticles enable sensitive analysis of molecules for biological, safety and environment applications.

PubMed

Onesto, V; Villani, M; Coluccio, M L; Majewska, R; Alabastri, A; Battista, E; Schirato, A; Calestani, D; Coppedé, N; Cesarelli, M; Amato, F; Di Fabrizio, E; Gentile, F

2018-04-10

Diatom shells are a natural, theoretically unlimited material composed of silicon dioxide, with regular patterns of pores penetrating through their surface. For their characteristics, diatom shells show promise to be used as low cost, highly efficient drug carriers, sensor devices or other micro-devices. Here, we demonstrate diatom shells functionalized with gold nanoparticles for the harvesting and detection of biological analytes (bovine serum albumin-BSA) and chemical pollutants (mineral oil) in low abundance ranges, for applications in bioengineering, medicine, safety, and pollution monitoring.

Conformationally selective multidimensional chemical shift ranges in proteins from a PACSY database purged using intrinsic quality criteria

PubMed Central

Hong, Mei

2016-01-01

We have determined refined multidimensional chemical shift ranges for intra-residue correlations (13C–13C, 15N–13C, etc.) in proteins, which can be used to gain type-assignment and/or secondary-structure information from experimental NMR spectra. The chemical-shift ranges are the result of a statistical analysis of the PACSY database of >3000 proteins with 3D structures (1,200,207 13C chemical shifts and >3 million chemical shifts in total); these data were originally derived from the Biological Magnetic Resonance Data Bank. Using relatively simple non-parametric statistics to find peak maxima in the distributions of helix, sheet, coil and turn chemical shifts, and without the use of limited “hand-picked” data sets, we show that ~94 % of the 13C NMR data and almost all 15N data are quite accurately referenced and assigned, with smaller standard deviations (0.2 and 0.8 ppm, respectively) than recognized previously. On the other hand, approximately 6 % of the 13C chemical shift data in the PACSY database are shown to be clearly misreferenced, mostly by ca. −2.4 ppm. The removal of the misreferenced data and other outliers by this purging by intrinsic quality criteria (PIQC) allows for reliable identification of secondary maxima in the two-dimensional chemical-shift distributions already pre-separated by secondary structure. We demonstrate that some of these correspond to specific regions in the Ramachandran plot, including left-handed helix dihedral angles, reflect unusual hydrogen bonding, or are due to the influence of a following proline residue. With appropriate smoothing, significantly more tightly defined chemical shift ranges are obtained for each amino acid type in the different secondary structures. These chemical shift ranges, which may be defined at any statistical threshold, can be used for amino-acid type assignment and secondary-structure analysis of chemical shifts from intra-residue cross peaks by inspection or by using a provided command-line Python script (PLUQin), which should be useful in protein structure determination. The refined chemical shift distributions are utilized in a simple quality test (SQAT) that should be applied to new protein NMR data before deposition in a databank, and they could benefit many other chemical-shift based tools. PMID:26787537

A general and high-yield galvanic displacement approach to Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells and enhanced electrocatalytic performances.

PubMed

Kuai, Long; Geng, Baoyou; Wang, Shaozhen; Sang, Yan

2012-07-23

In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au-Au, Au-Pd, and Au-Pt core-shell nanostructures with typical porous shells. Moreover, the Au-Au isomeric core-shell nanostructure is reported for the first time. The lower oxidation states of Au(I), Pd(II), and Pt(II) are supposed to contribute to the formation of porous core-shell nanostructures instead of yolk-shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au-Pd core-shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core-shell nanostructures. As expected, the Au-Pd core-shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44 mV and 32 mV), a much improved CO tolerance (I(f)/I(b) is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au-M (M = Au, Pd, and Pt) core-shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface-enhanced Raman scattering, and so forth. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Protein structure refinement using a quantum mechanics-based chemical shielding predictor† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc04344e Click here for additional data file.

PubMed Central

2017-01-01

The accurate prediction of protein chemical shifts using a quantum mechanics (QM)-based method has been the subject of intense research for more than 20 years but so far empirical methods for chemical shift prediction have proven more accurate. In this paper we show that a QM-based predictor of a protein backbone and CB chemical shifts (ProCS15, PeerJ, 2016, 3, e1344) is of comparable accuracy to empirical chemical shift predictors after chemical shift-based structural refinement that removes small structural errors. We present a method by which quantum chemistry based predictions of isotropic chemical shielding values (ProCS15) can be used to refine protein structures using Markov Chain Monte Carlo (MCMC) simulations, relating the chemical shielding values to the experimental chemical shifts probabilistically. Two kinds of MCMC structural refinement simulations were performed using force field geometry optimized X-ray structures as starting points: simulated annealing of the starting structure and constant temperature MCMC simulation followed by simulated annealing of a representative ensemble structure. Annealing of the CHARMM structure changes the CA-RMSD by an average of 0.4 Å but lowers the chemical shift RMSD by 1.0 and 0.7 ppm for CA and N. Conformational averaging has a relatively small effect (0.1–0.2 ppm) on the overall agreement with carbon chemical shifts but lowers the error for nitrogen chemical shifts by 0.4 ppm. If an amino acid specific offset is included the ProCS15 predicted chemical shifts have RMSD values relative to experiments that are comparable to popular empirical chemical shift predictors. The annealed representative ensemble structures differ in CA-RMSD relative to the initial structures by an average of 2.0 Å, with >2.0 Å difference for six proteins. In four of the cases, the largest structural differences arise in structurally flexible regions of the protein as determined by NMR, and in the remaining two cases, the large structural change may be due to force field deficiencies. The overall accuracy of the empirical methods are slightly improved by annealing the CHARMM structure with ProCS15, which may suggest that the minor structural changes introduced by ProCS15-based annealing improves the accuracy of the protein structures. Having established that QM-based chemical shift prediction can deliver the same accuracy as empirical shift predictors we hope this can help increase the accuracy of related approaches such as QM/MM or linear scaling approaches or interpreting protein structural dynamics from QM-derived chemical shift. PMID:28451325

Toxic-Waste Disposal by Combustion in Containers

NASA Technical Reports Server (NTRS)

Houseman, J.; Stephens, J. B.; Moynihan, P. I.; Compton, L. E.; Kalvinskas, J. J.

1986-01-01

Chemical wastes burned with minimal handling in storage containers. Technique for disposing of chemical munitions by burning them inside shells applies to disposal of toxic materials stored in drums. Fast, economical procedure overcomes heat-transfer limitations of conventional furnace designs by providing direct contact of oxygenrich combustion gases with toxic agent. No need to handle waste material, and container also decontaminated in process. Oxygen-rich torch flame cuts burster well and causes vaporization and combustion of toxic agent contained in shell.

Prediction of supercritical ethane bulk solvent densities for pyrazine solvation shell average occupancy by 1, 2, 3, and 4 ethanes: combined experimental and ab initio approach.

PubMed

Hrnjez, Bruce J; Sultan, Samuel T; Natanov, Georgiy R; Kastner, David B; Rosman, Michael R

2005-11-17

We introduce a method that addresses the elusive local density at the solute in the highly compressible regime of a supercritical fluid. Experimentally, the red shift of the pyrazine n-pi electronic transition was measured at infinite dilution in supercritical ethane as a function of pressure from 0 to about 3000 psia at two temperatures, one close (35.0 degrees C) to the critical temperature and the other remote (55.0 degrees C). Computationally, stationary points were located on the potential surfaces for pyrazine and one, two, three, and four ethanes at the MP2/6-311++G(d,p) level. The vertical n-pi ((1)B(3u)) transition energies were computed for each of these geometries with a TDDFT/B3LYP/6-311++G(d,p) method. The combination of experiment and computation allows prediction of supercritical ethane bulk densities at which the pyrazine primary solvation shell contains an average of one, two, three, and four ethane molecules. These density predictions were achieved by graphical superposition of calculated shifts on the experimental shift versus density curves for 35.0 and 55.0 degrees C. Predicted densities are 0.0635, 0.0875, and 0.0915 g cm(-3) for average pyrazine primary solvation shell occupancy by one, two, and three ethanes at both 35.0 and 55.0 degrees C. Predicted densities are 0.129 and 0.150 g cm(-3) for occupancy by four ethanes at 35.0 and 55.0 degrees C, respectively. An alternative approach, designed to "average out" geometry specific shifts, is based on the relationship Deltanu = -23.9n cm(-1), where n = ethane number. Graphical treatment gives alternative predicted densities of 0.0490, 0.0844, and 0.120 g cm(-3) for average pyrazine primary solvation shell occupancy by one, two, and three ethanes at both 35.0 and 55.0 degrees C, and densities of 0.148 and 0.174 g cm(-3) for occupancy by four ethanes at 35.0 and 55.0 degrees C, respectively.

ZnSe based semiconductor core-shell structures: From preparation to application

NASA Astrophysics Data System (ADS)

Sun, Chengcheng; Gu, Yarong; Wen, Weijia; Zhao, Lijuan

2018-07-01

Inorganic core-shell semiconductor materials have attracted increasing interest in recent years because of the unique structure, stable chemical properties and high performance in devices. With special properties such as a direct band-gap and excellent photoelectrical characteristics, ZnSe based semiconductor core-shell structures are promising materials for applications in such fields as photocatalysts, light-emitting diodes, solar cells, photodetectors, biomedical science and so on. However, few reviews on ZnSe based semiconductor core-shell structures have been reported so far. Therefore this manuscript mainly focuses on the research activities on ZnSe based semiconductor core-shell composites including various preparation methods and the applications of these core-shell structures, especially in photocatalysts, light emitting, solar cells and photodetectors. The possibilities and limitations of studies on ZnSe based semiconductor core-shell composites are also highlighted.

Redox-dependent structure change and hyperfine nuclear magnetic resonance shifts in cytochrome c

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Yiquing; Roder, H.; Englander, S.W.

1990-04-10

Proton nuclear magnetic resonance assignments for reduced and oxidized equine cytochrome c show that many individual protons exhibit different chemical shifts in the two protein forms, reflecting diamagnetic shift effects due to structure change, and in addition contact and pseudocontact shifts that occur only in the paramagnetic oxidized form. To evaluate the chemical shift differences for structure change, the authors removed the pseudocontact shift contribution by a calculation based on knowledge of the electron spin g tensor. The g-tensor calculation, when repeated using only 12 available C{sub {alpha}}H proton resonances for cytochrom c from tuna, proved to be remarkably stable.more » The derived g tensor was then used together with spatial coordinates for the oxidized form to calculate the pseudocontact shift contribution to proton resonances at 400 identifiable sites throughout the protein, so that the redox-dependent chemical shift discrepancy, could be evaluated. Large residual changes in chemical shift define the Fermi contact shifts, where are found as expected to be limited to the immediate covalent structure of the heme and its ligands and to be asymmetrically distributed over the heme. The chemical shift discrepancies observed appear in the main to reflect structure-dependent diamagnetic shifts rather than hyperfine effects due to displacements in the pseudocontact shift field. Although 51 protons in 29 different residues exhibit significant chemical shift changes, the general impressions one of small structural adjustments to redox-dependent strain rather than sizeable structural displacements or rearrangements.« less

Demonstration of a Three-dimensional Negative Index Medium Operated at Multiple-angle Incidences by Monolithic Metallic Hemispherical Shells

NASA Astrophysics Data System (ADS)

Yeh, Ting-Tso; Huang, Tsung-Yu; Tanaka, Takuo; Yen, Ta-Jen

2017-04-01

We design and construct a three-dimensional (3D) negative index medium (NIM) composed of gold hemispherical shells to supplant an integration of a split-ring resonator and a discrete plasmonic wire for both negative permeability and permittivity at THz gap. With the proposed highly symmetric gold hemispherical shells, the negative index is preserved at multiple incident angles ranging from 0° to 85° for both TE and TM waves, which is further evidenced by negative phase flows in animated field distributions and outweighs conventional fishnet structures with operating frequency shifts when varying incident angles. Finally, the fabrication of the gold hemispherical shells is facilitated via standard UV lithographic and isotropic wet etching processes and characterized by μ-FTIR. The measurement results agree the simulated ones very well.

A Glycoprotein in Shells of Conspecifics Induces Larval Settlement of the Pacific Oyster Crassostrea gigas

PubMed Central

Vasquez, Hebert Ely; Hashimoto, Kyotaro; Yoshida, Asami; Hara, Kenji; Imai, Chisato Chris; Kitamura, Hitoshi; Satuito, Cyril Glenn

2013-01-01

Settlement of larvae of Crassostrea gigas on shell chips (SC) prepared from shells of 11 different species of mollusks was investigated. Furthermore, the settlement inducing compound in the shell of C. gigas was extracted and subjected to various treatments to characterize the chemical cue. C. gigas larvae settled on SC of all species tested except on Patinopecten yessoensis and Atrina pinnata. In SC of species that induced C. gigas larvae to settle, settlement was proportionate to the amount of SC supplied to the larvae. When compared to C. gigas SC, all species except Crassostrea nippona showed lower settlement inducing activities, suggesting that the cue may be more abundant or in a more available form to the larvae in shells of conspecific and C. nippona than in other species. The settlement inducing activity of C. gigas SC remained intact after antibiotic treatment. Extraction of C. gigas SC with diethyl ether (Et2O-ex), ethanol (EtOH-ex), and water (Aq-ex) did not induce larval settlement of C. gigas larvae. However, extraction of C. gigas SC with 2N of hydrochloric acid (HCl-ex) induced larval settlement that was at the same level as the SC. The settlement inducing compound in the HCl-ex was stable at 100°C but was destroyed or degraded after pepsin, trypsin, PNGase F and trifluoromethanesulfonic acid treatments. This chemical cue eluted between the molecular mass range of 45 and 150 kDa after gel filtration and revealed a major band at 55 kDa on the SDS-PAGE gel after staining with Stains-all. Thus, a 55 kDa glycoprotein component in the organic matrix of C. gigas shells is hypothesized to be the chemical basis of larval settlement on conspecifics. PMID:24349261

Chemical Behavior of Sulfur in Minerals and Silicate Glasses Studied Using Inner Shell Spectroscopy

NASA Astrophysics Data System (ADS)

Alonso Mori, R.; Paris, E.; Glatzel, P.; Giuli, G.; Scaillet, B.

2008-12-01

Understanding the chemical behaviour of sulfur is of fundamental importance in explaining different geological mechanisms ranging from volcano-climatic interactions to the genesis of ore deposits. Understanding how sulphur behaves is also of great economic importance in industrial activities including glass-forming processes and the treatment of vitreous waste material from refuse incineration. The chemical behaviour of sulfur in minerals and glasses has been widely studied via X-ray absorption near edge structure (XANES) spectroscopy, which probes the unoccupied density of states and thus provides information on the oxidation state and local structure of the species under study. However, the XANES spectral shape is influenced by various effects, namely the local symmetry, the ligand type, even up to high coordination spheres, and the valence electron occupation, making it difficult to systematically analyze the different spectral contributions. We use X-ray emission spectroscopy (XES) as a complementary technique to avoid some of the inherent difficulties of XANES analysis, and to extract additional information on the electronic structure. The Kb lines, close to the K-edge, directly yield the p-density of occupied valence states, giving valuable information on the local coordination. We have compared XANES and Kb XES experimental data on sulfur- bearing minerals with ab initio quantum-chemical calculations based on density functional theory (DFT), in order to visualize the molecular orbitals and to extract information about the chemical bonding in these compounds. The S Ka emission lines, which arise from 2p to 1s transitions, are expected to be mostly free from chemical bond effects except for small energy shifts that reflect the valence orbital electron population via screening effects. S Ka shifts can be readily used to determine the speciation of sulfur in silicate glasses. The electronic configuration of the sulfur atoms is obtained by calculating the effective charge around the sulfur atom based on the Mulliken population analysis generated by DFT calculations, and then successfully correlated with the observed experimental shifts. In order to check these results using a theoretical framework other than DFT, we also performed calculations using a multiple scattering approach (FEFF8.4). X-ray absorption and emission spectroscopy has been applied to three series of peralkaline rhyolitic obsidians each with different alkali/alumina ratios ((Na2O + K2O)/Al2O3). The occurrence of sulfur was accurately determined by using the energy shift of the S Ka emission lines to make a quantitative analysis. We observe that we can follow the evolution of sulfur as a function of controlled formation conditions with respect to pressure, temperature or oxygen fugacity, and determine whether it is present as sulfate or sulfide. XANES and Kb emission lines also yield detailed information on the local chemistry and structure, and thus help us to understand the geochemical role of S in these systems.

A solar-thermal energy harvesting scheme: enhanced heat capacity of molten HITEC salt mixed with Sn/SiOx core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Lai, Chih-Chung; Chang, Wen-Chih; Hu, Wen-Liang; Wang, Zhiming M.; Lu, Ming-Chang; Chueh, Yu-Lun

2014-04-01

We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiOx core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiOx core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiOx core-shell NPs during cyclic heating processes. The latent heat of ~29 J g-1 for Sn/SiOx core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g-1 K-1 for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiOx core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants.We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiOx core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiOx core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiOx core-shell NPs during cyclic heating processes. The latent heat of ~29 J g-1 for Sn/SiOx core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g-1 K-1 for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiOx core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants. Electronic supplementary information (ESI) available: Detailed experimental results are included for the following: SEM images of the HITEC molten salt with and without a mixture of Sn/SiOx core-shell NPs; statistical diameter distribution of pure Sn and Sn/SiOx core-shell NPs; the HAADF image and EDS linescan profile of a Sn/SiOx core-shell NP; XRD analysis for Sn NPs annealing at different heating temperatures; the XRD spectra of Sn/SiOx core-shell NPs before and after RTA for the shell protection test. See DOI: 10.1039/c3nr06810b

Stereospecific assignment of the asparagine and glutamine sidechain amide protons in proteins from chemical shift analysis.

PubMed

Harsch, Tobias; Schneider, Philipp; Kieninger, Bärbel; Donaubauer, Harald; Kalbitzer, Hans Robert

2017-02-01

Side chain amide protons of asparagine and glutamine residues in random-coil peptides are characterized by large chemical shift differences and can be stereospecifically assigned on the basis of their chemical shift values only. The bimodal chemical shift distributions stored in the biological magnetic resonance data bank (BMRB) do not allow such an assignment. However, an analysis of the BMRB shows, that a substantial part of all stored stereospecific assignments is not correct. We show here that in most cases stereospecific assignment can also be done for folded proteins using an unbiased artificial chemical shift data base (UACSB). For a separation of the chemical shifts of the two amide resonance lines with differences ≥0.40 ppm for asparagine and differences ≥0.42 ppm for glutamine, the downfield shifted resonance lines can be assigned to H δ21 and H ε21 , respectively, at a confidence level >95%. A classifier derived from UASCB can also be used to correct the BMRB data. The program tool AssignmentChecker implemented in AUREMOL calculates the Bayesian probability for a given stereospecific assignment and automatically corrects the assignments for a given list of chemical shifts.

Biomineral shell formation under ocean acidification: a shift from order to chaos.

PubMed

Fitzer, Susan C; Chung, Peter; Maccherozzi, Francesco; Dhesi, Sarnjeet S; Kamenos, Nicholas A; Phoenix, Vernon R; Cusack, Maggie

2016-02-15

Biomineral production in marine organisms employs transient phases of amorphous calcium carbonate (ACC) in the construction of crystalline shells. Increasing seawater pCO2 leads to ocean acidification (OA) with a reduction in oceanic carbonate concentration which could have a negative impact on shell formation and therefore survival. We demonstrate significant changes in the hydrated and dehydrated forms of ACC in the aragonite and calcite layers of Mytilus edulis shells cultured under acidification conditions (1000 μatm pCO2) compared to present day conditions (380 μatm pCO2). In OA conditions, Mytilus edulis has more ACC at crystalisation sites. Here, we use the high-spatial resolution of synchrotron X-ray Photo Emission Electron Microscopy (XPEEM) combined with X-ray Absorption Spectroscopy (XAS) to investigate the influence of OA on the ACC formation in the shells of adult Mytilus edulis. Electron Backscatter Diffraction (EBSD) confirms that OA reduces crystallographic control of shell formation. The results demonstrate that OA induces more ACC formation and less crystallographic control in mussels suggesting that ACC is used as a repair mechanism to combat shell damage under OA. However, the resultant reduced crystallographic control in mussels raises concerns for shell protective function under predation and changing environments.

Biomineral shell formation under ocean acidification: a shift from order to chaos

PubMed Central

Fitzer, Susan C.; Chung, Peter; Maccherozzi, Francesco; Dhesi, Sarnjeet S.; Kamenos, Nicholas A.; Phoenix, Vernon R.; Cusack, Maggie

2016-01-01

Biomineral production in marine organisms employs transient phases of amorphous calcium carbonate (ACC) in the construction of crystalline shells. Increasing seawater pCO2 leads to ocean acidification (OA) with a reduction in oceanic carbonate concentration which could have a negative impact on shell formation and therefore survival. We demonstrate significant changes in the hydrated and dehydrated forms of ACC in the aragonite and calcite layers of Mytilus edulis shells cultured under acidification conditions (1000 μatm pCO2) compared to present day conditions (380 μatm pCO2). In OA conditions, Mytilus edulis has more ACC at crystalisation sites. Here, we use the high-spatial resolution of synchrotron X-ray Photo Emission Electron Microscopy (XPEEM) combined with X-ray Absorption Spectroscopy (XAS) to investigate the influence of OA on the ACC formation in the shells of adult Mytilus edulis. Electron Backscatter Diffraction (EBSD) confirms that OA reduces crystallographic control of shell formation. The results demonstrate that OA induces more ACC formation and less crystallographic control in mussels suggesting that ACC is used as a repair mechanism to combat shell damage under OA. However, the resultant reduced crystallographic control in mussels raises concerns for shell protective function under predation and changing environments. PMID:26876022

Biomineral shell formation under ocean acidification: a shift from order to chaos

NASA Astrophysics Data System (ADS)

Fitzer, Susan C.; Chung, Peter; Maccherozzi, Francesco; Dhesi, Sarnjeet S.; Kamenos, Nicholas A.; Phoenix, Vernon R.; Cusack, Maggie

2016-02-01

Biomineral production in marine organisms employs transient phases of amorphous calcium carbonate (ACC) in the construction of crystalline shells. Increasing seawater pCO2 leads to ocean acidification (OA) with a reduction in oceanic carbonate concentration which could have a negative impact on shell formation and therefore survival. We demonstrate significant changes in the hydrated and dehydrated forms of ACC in the aragonite and calcite layers of Mytilus edulis shells cultured under acidification conditions (1000 μatm pCO2) compared to present day conditions (380 μatm pCO2). In OA conditions, Mytilus edulis has more ACC at crystalisation sites. Here, we use the high-spatial resolution of synchrotron X-ray Photo Emission Electron Microscopy (XPEEM) combined with X-ray Absorption Spectroscopy (XAS) to investigate the influence of OA on the ACC formation in the shells of adult Mytilus edulis. Electron Backscatter Diffraction (EBSD) confirms that OA reduces crystallographic control of shell formation. The results demonstrate that OA induces more ACC formation and less crystallographic control in mussels suggesting that ACC is used as a repair mechanism to combat shell damage under OA. However, the resultant reduced crystallographic control in mussels raises concerns for shell protective function under predation and changing environments.

Ag@Ni core-shell nanowire network for robust transparent electrodes against oxidation and sulfurization.

PubMed

Eom, Hyeonjin; Lee, Jaemin; Pichitpajongkit, Aekachan; Amjadi, Morteza; Jeong, Jun-Ho; Lee, Eungsug; Lee, Jung-Yong; Park, Inkyu

2014-10-29

Silver nanowire (Ag NW) based transparent electrodes are inherently unstable to moist and chemically reactive environment. A remarkable stability improvement of the Ag NW network film against oxidizing and sulfurizing environment by local electrodeposition of Ni along Ag NWs is reported. The optical transmittance and electrical resistance of the Ni deposited Ag NW network film can be easily controlled by adjusting the morphology and thickness of the Ni shell layer. The electrical conductivity of the Ag NW network film is increased by the Ni coating via welding between Ag NWs as well as additional conductive area for the electron transport by electrodeposited Ni layer. Moreover, the chemical resistance of Ag NWs against oxidation and sulfurization can be dramatically enhanced by the Ni shell layer electrodeposited along the Ag NWs, which provides the physical barrier against chemical reaction and diffusion as well as the cathodic protection from galvanic corrosion. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shell and small particles; evaluation of new column technology.

PubMed

Fekete, Szabolcs; Fekete, Jeno; Ganzler, Katalin

2009-01-15

The performance of 5 cm long columns packed with shell particles was compared to totally porous sub-2 microm particles in gradient and isocratic elution separations of hormones (dienogest, finasteride, gestodene, levonorgestrel, estradiol, ethinylestradiol, noretistherone acetate, bicalutamide and tibolone). Peak capacities around 140-150 could be achieved in 25 min with the 5 cm long columns. The Ascentis Express column (packed with 2.7 microm shell particles) showed similar efficiency to sub-2 microm particles under gradient conditions. Applying isocratic separation, the column of 2.7 microm shell particles had a reduced plate height minimum of approximately h=1.6. It was much smaller than obtained with totally porous particles (h approximately = 2.8). The impedance time also proved more favorable with 2.7 microm shell particles than with totally porous particles. The influence of extra-column volume on column efficiency was investigated. The extra-column dispersion of the chromatographic system may cause a shift of the HETP curves.

Adsorption and Pore of Physical-Chemical Activated Coconut Shell Charcoal Carbon

NASA Astrophysics Data System (ADS)

Budi, E.; Umiatin, U.; Nasbey, H.; Bintoro, R. A.; Wulandari, Fi; Erlina, E.

2018-04-01

The adsorption of activated carbon of coconut shell charcoal on heavy metals (Cu and Fe) of the wastewater and its relation with the carbon pore structure was investigated. The coconut shell was pyrolized in kiln at temperature about 75 - 150 °C for about 6 hours to produce charcoal and then shieved into milimeter sized granule particles. Chemical activation was done by immersing the charcoal into chemical solution of KOH, NaOH, HCl and H3PO4, with various concentration. The activation was followed by physical activation using horizontal furnace at 400°C for 1 hours in argon gas environment with flow rate of 200 kg/m3. The surface morphology of activated carbon were characterized by using Scanning Electron Microscopy (SEM). Wastewater was made by dissolving CuSO4.5H2O and FeSO4.7H2O into aquades. The metal adsorption was analized by using Atomic Absorption Spectroscopy (AAS). The result shows that in general, the increase of chemical concentration cause the increase of pore number of activated carbon due to an excessive chemical attack and lead the increase of adsorption. However it tend to decrease as further increasing in chemical activator concentration due to carbon collapsing. In general, the adsorption of Cu and Fe metal from wastewater by activated carbon increased as the activator concentration was increased.

Net Reaction Rate and Neutrino Cooling Rate for the Urca Process in Departure from Chemical Equilibrium in the Crust of Fast-accreting Neutron Stars

NASA Astrophysics Data System (ADS)

Wang, Wei-Hua; Huang, Xi; Zheng, Xiao-Ping

We discuss the effect of compression on Urca shells in the ocean and crust of accreting neutron stars, especially in superbursting sources. We find that Urca shells may be deviated from chemical equilibrium in neutron stars which accrete at several tenths of the local Eddington accretion rate. The deviation depends on the energy threshold of the parent and daughter nuclei, the transition strength, the temperature, and the local accretion rate. In a typical crust model of accreting neutron stars, the chemical departures range from a few tenths of kBT to tens of kBT for various Urca pairs. If the Urca shell can exist in crusts of accreting neutron stars, compression may enhance the net neutrino cooling rate by a factor of about 1-2 relative to the neutrino emissivity in chemical equilibrium. For some cases, such as Urca pairs with small energy thresholds and/or weak transition strength, the large chemical departure may result in net heating rather than cooling, although the released heat can be small. Strong Urca pairs in the deep crust are hard to be deviated even in neutron stars accreting at the local Eddington accretion rate.

Microwave absorption properties of Ni/(C, silicides) nanocapsules

PubMed Central

2012-01-01

The microwave absorption properties of Ni/(C, silicides) nanocapsules prepared by an arc discharge method have been studied. The composition and the microstructure of the Ni/(C, silicides) nanocapsules were determined by means of X-ray diffraction, X-ray photoelectric spectroscopy, and transmission electron microscope observations. Silicides, in the forms of SiOx and SiC, mainly exist in the shells of the nanocapsules and result in a large amount of defects at the ‘core/shell’ interfaces as well as in the shells. The complex permittivity and microwave absorption properties of the Ni/(C, silicides) nanocapsules are improved by the doped silicides. Compared with those of Ni/C nanocapsules, the positions of maximum absorption peaks of the Ni/(C, silicides) nanocapsules exhibit large red shifts. An electric dipole model is proposed to explain this red shift phenomenon. PMID:22548846

ZnO/ZnSxSe1-x core/shell nanowire arrays as photoelectrodes with efficient visible light absorption

NASA Astrophysics Data System (ADS)

Wang, Zhenxing; Zhan, Xueying; Wang, Yajun; Safdar, Muhammad; Niu, Mutong; Zhang, Jinping; Huang, Ying; He, Jun

2012-08-01

ZnO/ZnSxSe1-x core/shell nanowires have been synthesized on n+-type silicon substrate via a two-step chemical vapor deposition method. Transmission electron microscopy reveals that ZnSxSe1-x can be deposited on the entire surface of ZnO nanowire, forming coaxial heterojunction along ZnO nanowire with very smooth shell surface and high shell thickness uniformity. The photoelectrode after deposition of the ternary alloy shell significantly improves visible light absorption efficiency. Electrochemical impedance spectroscopy results explicitly indicate that the introduction of ZnSxSe1-x shell to ZnO nanowires effectively improves the photogenerated charge separation process. Our finding opens up an efficient means for achieving high efficient energy conversion devices.

Preparation and Properties of Melamine Urea-Formaldehyde Microcapsules for Self-Healing of Cementitious Materials

PubMed Central

Li, Wenting; Zhu, Xujing; Zhao, Nan; Jiang, Zhengwu

2016-01-01

Self-healing microcapsules were synthesized by in situ polymerization with a melamine urea-formaldehyde resin shell and an epoxy resin adhesive. The effects of the key factors, i.e., core–wall ratio, reaction temperature, pH and stirring rate, were investigated by characterizing microcapsule morphology, shell thickness, particle size distribution, mechanical properties and chemical nature. Microcapsule healing mechanisms in cement paste were evaluated based on recovery strength and healing microstructure. The results showed that the encapsulation ability, the elasticity modulus and hardness of the capsule increased with an increase of the proportion of shell material. Increased polymerization temperatures were beneficial to the higher degree of shell condensation polymerization, higher resin particles deposition on microcapsule surfaces and enhanced mechanical properties. For relatively low pH values, the less porous three-dimensional structure led to the increased elastic modulus of shell and the more stable chemical structure. Optimized microcapsules were produced at a temperature of 60 °C, a core-wall ratio of 1:1, at pH 2~3 and at a stirring rate of 300~400 r/min. The best strength restoration was observed in the cement paste pre-damaged by 30% fmax and incorporating 4 wt % of capsules. PMID:28773280

MICROBIAL COMETABOLISM OF RECALCITRANT CHEMICALS IN CONTAMINATED AIR STREAMS

EPA Science Inventory

Chlorinated Solvents: The treatment system consists of a laboratory-scale hollow fiber membrane (HFM) module containing a center baffle and a radial cross-flow pattern on the shell side of the fibers. The shell and lumen fluids are contacting in a counter-current f...

Shell cracking strength in almond (Prunus dulcis [Mill.] D.A. Webb.) and its implication in uses as a value-added product.

PubMed

Ledbetter, C A

2008-09-01

Researchers are currently developing new value-added uses for almond shells, an abundant agricultural by-product. Almond varieties are distinguished by processors as being either hard or soft shelled, but these two broad classes of almond also exhibit varietal diversity in shell morphology and physical characters. By defining more precisely the physical and chemical characteristics of almond shells from different varieties, researchers will better understand which specific shell types are best suited for specific industrial processes. Eight diverse almond accessions were evaluated in two consecutive harvest seasons for nut and kernel weight, kernel percentage and shell cracking strength. Shell bulk density was evaluated in a separate year. Harvest year by almond accession interactions were highly significant (p0.01) for each of the analyzed variables. Significant (p0.01) correlations were noted for average nut weight with kernel weight, kernel percentage and shell cracking strength. A significant (p0.01) negative correlation for shell cracking strength with kernel percentage was noted. In some cases shell cracking strength was independent of the kernel percentage which suggests that either variety compositional differences or shell morphology affect the shell cracking strength. The varietal characterization of almond shell materials will assist in determining the best value-added uses for this abundant agricultural by-product.

Valley-orbit splitting in doped nanocrystalline silicon: k•p calculations

NASA Astrophysics Data System (ADS)

Belyakov, Vladimir A.; Burdov, Vladimir A.

2007-07-01

The valley-orbit splitting in silicon quantum dots with shallow donors has been theoretically studied. In particular, the chemical-shift calculation was carried out within the frames of k•p approximation for single- and many-donor cases. For both cases, the great value of the chemical shift has been obtained compared to its bulk value. Such increase of the chemical shift becomes possible due to the quantum confinement effect in a dot. It is shown for the single-donor case that the level splitting and chemical shift strongly depend on the dot radius and donor position inside the nanocrystal. In the many-donor case, the chemical shift is almost proportional to the number of donors.

Fabrication and characterization of optical sensors using metallic core-shell thin film nanoislands for ozone detection

NASA Astrophysics Data System (ADS)

Addanki, Satish; Nedumaran, D.

2017-07-01

Core-Shell nanostructures play a vital role in the sensor field owing to their performance improvements in sensing characteristics and well-established synthesis procedures. These nanostructures can be ingeniously tuned to achieve tailored properties for a particular application of interest. In this work, an Ag-Au core-shell thin film nanoislands with APTMS (3-Aminopropyl trimethoxysilane) and PVA (Polyvinyl alcohol) binding agents was modeled, synthesized and characterized. The simulation results were used to fabricate the sensor through chemical route. The results of this study confirmed that the APTMS based Ag-Au core-shell thin film nanoislands offered a better performance over the PVA based Ag-Au core-shell thin film nanoislands. Also, the APTMS based Ag-Au core-shell thin film nanoislands exhibited better sensitivity towards ozone sensing over the other types, viz., APTMS/PVA based Au-Ag core-shell and standalone Au/Ag thin film nanoislands.

Understanding to Hierarchical Microstructures of Crab (Chinese hairy) Shell as a Natural Architecture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chuanqiang, Zhou; Xiangxiang, Gong; School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou

This work was done to better understand the microstructures, composition and mechanical properties of Chinese hairy crab shell. For fully revealing its hierarchical microstructure, the crab shell was observed with electron microscope under different magnifications from different facets. XRD, EDS, FTIR and TGA techniques have been used to characterize the untreated and chemically-treated crab shells, which provided enough information to determine the species and relative content of components in this biomaterial. Combined the microstructures with constituents analysis, the structural principles of crab shell was detailedly realized from different structural levels beyond former reports. To explore the relationship between structure andmore » function, the mechanical properties of shell have been measured through performing tensile tests. The contributions of organics and minerals in shell to the mechanical properties were also discussed by measuring the tensile strength of de-calcification samples treated with HCl solution.« less

Determination of mustard and lewisite related compounds in abandoned chemical weapons (Yellow shells) from sources in China and Japan.

PubMed

Hanaoka, Shigeyuki; Nomura, Koji; Wada, Takeharu

2006-01-06

Knowledge of the states of the contents in chemical munitions that Japanese Imperial Forces abandoned at the end of World War II in Japan and China is gravely lacking. To unearth and recover these chemical weapons and detoxify the contents safely, it is essential to establish analytical procedures to definitely determine the CWA contents. We established such a procedure and applied it to the analysis of chemicals in the abandoned shells. Yellow shells are known to contain sulfur mustard, lewisite, or a mixture of both. Lewisite was analyzed without thiol derivatization, because it and its decomposition products yield the same substances in the derivatization. Analysis using our new procedure showed that both mustard and lewisite remained as the major components after the long abandonment of nearly 60 years. The content of mustard was 43% and that of lewisite 55%. The viscous material found was suggested to be mostly oligomers of mustard. Comparison of the components in the Yellow agents with mustard recovered in both Japan and China showed a difference in the impurities between the CWAs produced by the former Imperial navy and those by the former Imperial army.

Direct observation and analysis of york-shell materials using low-voltage high-resolution scanning electron microscopy: Nanometal-particles encapsulated in metal-oxide, carbon, and polymer

NASA Astrophysics Data System (ADS)

Asahina, Shunsuke; Suga, Mitsuo; Takahashi, Hideyuki; Young Jeong, Hu; Galeano, Carolina; Schüth, Ferdi; Terasaki, Osamu

2014-11-01

Nanometal particles show characteristic features in chemical and physical properties depending on their sizes and shapes. For keeping and further enhancing their features, the particles should be protected from coalescence or degradation. One approach is to encapsulate the nanometal particles inside pores with chemically inert or functional materials, such as carbon, polymer, and metal oxides, which contain mesopores to allow permeation of only chemicals not the nanometal particles. Recently developed low-voltage high-resolution scanning electron microscopy was applied to the study of structural, chemical, and electron state of both nanometal particles and encapsulating materials in yolk-shell materials of Au@C, Ru/Pt@C, Au@TiO2, and Pt@Polymer. Progresses in the following categories were shown for the yolk-shell materials: (i) resolution of topographic image contrast by secondary electrons, of atomic-number contrast by back-scattered electrons, and of elemental mapping by X-ray energy dispersive spectroscopy; (ii) sample preparation for observing internal structures; and (iii) X-ray spectroscopy such as soft X-ray emission spectroscopy. Transmission electron microscopy was also used for characterization of Au@C.

Characterization of the conformational equilibrium between the two major substates of RNase A using NMR chemical shifts.

PubMed

Camilloni, Carlo; Robustelli, Paul; De Simone, Alfonso; Cavalli, Andrea; Vendruscolo, Michele

2012-03-07

Following the recognition that NMR chemical shifts can be used for protein structure determination, rapid advances have recently been made in methods for extending this strategy for proteins and protein complexes of increasing size and complexity. A remaining major challenge is to develop approaches to exploit the information contained in the chemical shifts about conformational fluctuations in native states of proteins. In this work we show that it is possible to determine an ensemble of conformations representing the free energy surface of RNase A using chemical shifts as replica-averaged restraints in molecular dynamics simulations. Analysis of this surface indicates that chemical shifts can be used to characterize the conformational equilibrium between the two major substates of this protein. © 2012 American Chemical Society

Criteria to average out the chemical shift anisotropy in solid-state NMR when irradiated with BABA I, BABA II, and C7 radiofrequency pulse sequences.

PubMed

Stephane Mananga, Eugene

2013-01-01

Floquet-Magnus expansion is used to study the effect of chemical shift anisotropy in solid-state NMR of rotating solids. The chemical shift interaction is irradiated with two types of radiofrequency pulse sequences: BABA and C7. The criteria for the chemical shift anisotropy to be averaged out in each rotor period are obtained. Copyright © 2013 Elsevier Inc. All rights reserved.

Theories of Variable Mass Particles and Low Energy Nuclear Phenomena

NASA Astrophysics Data System (ADS)

Davidson, Mark

2014-02-01

Variable particle masses have sometimes been invoked to explain observed anomalies in low energy nuclear reactions (LENR). Such behavior has never been observed directly, and is not considered possible in theoretical nuclear physics. Nevertheless, there are covariant off-mass-shell theories of relativistic particle dynamics, based on works by Fock, Stueckelberg, Feynman, Greenberger, Horwitz, and others. We review some of these and we also consider virtual particles that arise in conventional Feynman diagrams in relativistic field theories. Effective Lagrangian models incorporating variable mass particle theories might be useful in describing anomalous nuclear reactions by combining mass shifts together with resonant tunneling and other effects. A detailed model for resonant fusion in a deuterium molecule with off-shell deuterons and electrons is presented as an example. Experimental means of observing such off-shell behavior directly, if it exists, is proposed and described. Brief explanations for elemental transmutation and formation of micro-craters are also given, and an alternative mechanism for the mass shift in the Widom-Larsen theory is presented. If variable mass theories were to find experimental support from LENR, then they would undoubtedly have important implications for the foundations of quantum mechanics, and practical applications may arise.

Proton chemical shift tensors determined by 3D ultrafast MAS double-quantum NMR spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Rongchun; Mroue, Kamal H.; Ramamoorthy, Ayyalusamy

2015-10-01

Proton NMR spectroscopy in the solid state has recently attracted much attention owing to the significant enhancement in spectral resolution afforded by the remarkable advances in ultrafast magic angle spinning (MAS) capabilities. In particular, proton chemical shift anisotropy (CSA) has become an important tool for obtaining specific insights into inter/intra-molecular hydrogen bonding. However, even at the highest currently feasible spinning frequencies (110-120 kHz), 1H MAS NMR spectra of rigid solids still suffer from poor resolution and severe peak overlap caused by the strong 1H-1H homonuclear dipolar couplings and narrow 1H chemical shift (CS) ranges, which render it difficult to determine the CSA of specific proton sites in the standard CSA/single-quantum (SQ) chemical shift correlation experiment. Herein, we propose a three-dimensional (3D) 1H double-quantum (DQ) chemical shift/CSA/SQ chemical shift correlation experiment to extract the CS tensors of proton sites whose signals are not well resolved along the single-quantum chemical shift dimension. As extracted from the 3D spectrum, the F1/F3 (DQ/SQ) projection provides valuable information about 1H-1H proximities, which might also reveal the hydrogen-bonding connectivities. In addition, the F2/F3 (CSA/SQ) correlation spectrum, which is similar to the regular 2D CSA/SQ correlation experiment, yields chemical shift anisotropic line shapes at different isotropic chemical shifts. More importantly, since the F2/F1 (CSA/DQ) spectrum correlates the CSA with the DQ signal induced by two neighboring proton sites, the CSA spectrum sliced at a specific DQ chemical shift position contains the CSA information of two neighboring spins indicated by the DQ chemical shift. If these two spins have different CS tensors, both tensors can be extracted by numerical fitting. We believe that this robust and elegant single-channel proton-based 3D experiment provides useful atomistic-level structural and dynamical information for a variety of solid systems that possess high proton density.

Proton chemical shift tensors determined by 3D ultrafast MAS double-quantum NMR spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Rongchun; Mroue, Kamal H.; Ramamoorthy, Ayyalusamy, E-mail: ramamoor@umich.edu

2015-10-14

Proton NMR spectroscopy in the solid state has recently attracted much attention owing to the significant enhancement in spectral resolution afforded by the remarkable advances in ultrafast magic angle spinning (MAS) capabilities. In particular, proton chemical shift anisotropy (CSA) has become an important tool for obtaining specific insights into inter/intra-molecular hydrogen bonding. However, even at the highest currently feasible spinning frequencies (110–120 kHz), {sup 1}H MAS NMR spectra of rigid solids still suffer from poor resolution and severe peak overlap caused by the strong {sup 1}H–{sup 1}H homonuclear dipolar couplings and narrow {sup 1}H chemical shift (CS) ranges, which rendermore » it difficult to determine the CSA of specific proton sites in the standard CSA/single-quantum (SQ) chemical shift correlation experiment. Herein, we propose a three-dimensional (3D) {sup 1}H double-quantum (DQ) chemical shift/CSA/SQ chemical shift correlation experiment to extract the CS tensors of proton sites whose signals are not well resolved along the single-quantum chemical shift dimension. As extracted from the 3D spectrum, the F1/F3 (DQ/SQ) projection provides valuable information about {sup 1}H–{sup 1}H proximities, which might also reveal the hydrogen-bonding connectivities. In addition, the F2/F3 (CSA/SQ) correlation spectrum, which is similar to the regular 2D CSA/SQ correlation experiment, yields chemical shift anisotropic line shapes at different isotropic chemical shifts. More importantly, since the F2/F1 (CSA/DQ) spectrum correlates the CSA with the DQ signal induced by two neighboring proton sites, the CSA spectrum sliced at a specific DQ chemical shift position contains the CSA information of two neighboring spins indicated by the DQ chemical shift. If these two spins have different CS tensors, both tensors can be extracted by numerical fitting. We believe that this robust and elegant single-channel proton-based 3D experiment provides useful atomistic-level structural and dynamical information for a variety of solid systems that possess high proton density.« less

O-H anharmonic vibrational motions in Cl(-)···(CH3OH)(1-2) ionic clusters. Combined IRPD experiments and AIMD simulations.

PubMed

Beck, Jordan P; Cimas, Alvaro; Lisy, James M; Gaigeot, Marie-Pierre

2014-02-05

The structures of Cl(-)-(Methanol)1,2 clusters have been unraveled combining Infrared Predissociation (IR-PD) experiments and DFT-based molecular dynamics simulations (DFT-MD) at 100 K. The dynamical IR spectra extracted from DFT-MD provide the initial 600 cm(-1) large anharmonic red-shift of the O-H stretch from uncomplexed methanol (3682 cm(-1)) to Cl(-)-(Methanol)1 complex (3085 cm(-1)) as observed in the IR-PD experiment, as well as the subtle supplementary blue- and red-shifts of the O-H stretch in Cl(-)-(Methanol)2 depending on the structure. The anharmonic vibrational calculations remarkably provide the 100 cm(-1) O-H blue-shift when the two methanol molecules are simultaneously organized in the anion first hydration shell (conformer 2A), while they provide the 240 cm(-1) O-H red-shift when the second methanol is in the second hydration shell of Cl(-) (conformer 2B). RRKM calculations have also shown that 2A/2B conformers interconvert on a nanosecond time-scale at the estimated 100 K temperature of the clusters formed by evaporative cooling of argon prior to the IR-PD process. Copyright © 2013 Elsevier B.V. All rights reserved.

A High-Performance Lithium-Ion Battery Anode Based on the Core-Shell Heterostructure of Silicon-Coated Vertically Aligned Carbon Nanofibers

DTIC Science & Technology

2013-01-01

nanotubes ( MWCNTs ) using chemical vapour deposition (CVD) to form a hybrid Si– MWCNT structure consisting of 54 to 57 wt% of Si.16 The initial specic...retained less than 70% aer 100 cycles.16 The wavy and partially entangled structure may still have prevented uniform Si deposition deep into the MWCNT ...silicon shells, as illustrated in Fig. 1. The VACNFs are a special type of MWCNTs which are grown with DC-biased plasma chemical vapour deposition (PECVD

Impact of pecan nut shell aqueous extract on the oxidative properties of margarines during storage.

PubMed

Engler Ribeiro, Paula Cristina; de Britto Policarpi, Priscila; Dal Bo, Andrea; Barbetta, Pedro Alberto; Block, Jane Mara

2017-07-01

The oxidative properties of margarines supplemented with pecan nut shell extract, rosemary extract and butylated hydroxytoluene (BHT) were investigated. The extracts of pecan nut shell and rosemary showed a high content of total phenolics and condensed tannins (93 and 102.9 mg GAE g -1 and 46 and 38.9 mg CE g -1 respectively) as well as a high antioxidant activity (1257 and 2306 µmol TEAC g -1 and 293 and 856 mg TEAC g -1 by ABTS and DPPH methods respectively). Gallic acid, chlorogenic acid, p-hydroxybenzoic acid, epicatechin and epicatechin gallate were identified in the pecan nut shell extract. Peroxide and p-anisidine values of 3.75-4.43 meq kg -1 and 1.22-2.73 respectively, Totox values of 9.88-10.8 and specific extinction values of 4.38-4.59 and 0.92-0.94 at 232 and 268 nm respectively were observed after 8 months of storage in the studied samples. Margarines supplemented with pecan nut shell extract, rosemary extract or BHT during prolonged storage were found to be of equal quality within the degree of confidence limits. The extract of pecan nut shell may be considered as a natural product replacement for the synthetic antioxidant BHT. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

High-performance heterostructured cathodes for lithium-ion batteries with a Ni-rich layered oxide core and a Li-rich layered oxide shell

DOE PAGES

Oh, Pilgun; Oh, Seung -Min; Li, Wangda; ...

2016-05-30

The Ni-rich layered oxides with a Ni content of >0.5 are drawing much attention recently to increase the energy density of lithium-ion batteries. However, the Ni-rich layered oxides suffer from aggressive reaction of the cathode surface with the organic electrolyte at the higher operating voltages, resulting in consequent impedance rise and capacity fade. To overcome this difficulty, we present here a heterostructure composed of a Ni-rich LiNi 0.7Co 0.15Mn 0.15O 2 core and a Li-rich Li 1.2-xNi 0.2Mn 0.6O 2 shell, incorporating the advantageous features of the structural stability of the core and chemical stability of the shell. With amore » unique chemical treatment for the activation of the Li 2MnO 3 phase of the shell, a high capacity is realized with the Li-rich shell material. Aberration-corrected scanning transmission electron microscopy (STEM) provides direct evidence for the formation of surface Li-rich shell layer. Finally, the heterostructure exhibits a high capacity retention of 98% and a discharge- voltage retention of 97% during 100 cycles with a discharge capacity of 190 mA h g -1 (at 2.0–4.5 V under C/3 rate, 1C = 200 mA g -1).« less

Enhanced collectivity along the N = Z line: Lifetime measurements in 44Ti, 48Cr, and 52Fe

NASA Astrophysics Data System (ADS)

Arnswald, K.; Braunroth, T.; Seidlitz, M.; Coraggio, L.; Reiter, P.; Birkenbach, B.; Blazhev, A.; Dewald, A.; Fransen, C.; Fu, B.; Gargano, A.; Hess, H.; Hirsch, R.; Itaco, N.; Lenzi, S. M.; Lewandowski, L.; Litzinger, J.; Müller-Gatermann, C.; Queiser, M.; Rosiak, D.; Schneiders, D.; Siebeck, B.; Steinbach, T.; Vogt, A.; Wolf, K.; Zell, K. O.

2017-09-01

Lifetimes of the 21+ states in 44Ti, 48,50Cr, and 52Fe were determined with high accuracy exploiting the recoil distance Doppler-shift method. The reduced E2 transition strengths of 44Ti and 52Fe differ considerably from previously known values. A systematic increase in collectivity is found for the N = Z nuclei compared to neighboring isotopes. The B (E2) values along the Ti, Cr, and Fe isotopic chains are compared to shell-model calculations employing established interactions for the 0 f 1 p shell, as well as a novel effective shell-model Hamiltonian starting from a realistic nucleon-nucleon potential. The theoretical approaches underestimate the B (E2) values for the lower-mass Ti isotopes. Strong indication is found for particle-hole cross-shell configurations, recently corroborated by similar results for the neighboring isotone 42Ca.

WE-D-210-04: Radiation-Induced Polymerization of Ultrasound Contrast Agents in View of Non-Invasive Dosimetry in External Beam Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Callens, M; Verboven, E; Van Den Abeele, K

2015-06-15

Purpose: Ultrasound contrast agents (UCA’s) based on gas-filled microbubbles encapsulated by an amphiphilic shell are well established as safe and effective echo-enhancers in diagnostic imaging. In view of an alternative application of UCA’s, we investigated the use of targeted microbubbles as radiation sensors for external beam radiation therapy. As radiation induces permanent changes in the microbubble’s physico-chemical properties, a robust measure of these changes can provide a direct or indirect estimate of the applied radiation dose. For instance, by analyzing the ultrasonic dispersion characteristics of microbubble distributions before and after radiation treatment, an estimate of the radiation dose at themore » location of the irradiated volume can be made. To increase the radiation sensitivity of microbubbles, polymerizable diacetylene molecules can be incorporated into the shell. This study focuses on characterizing the acoustic response and quantifying the chemical modifications as a function of radiation dose. Methods: Lipid/diacetylene microbubbles were irradiated with a 6 MV photon beam using dose levels in the range of 0–150 Gy. The acoustic response of the microbubbles was monitored by ultrasonic through-transmission measurements in the range of 500 kHz to 20 MHz, thereby providing the dispersion relations of the phase velocity, attenuation and nonlinear coefficient. In addition, the radiation-induced chemical modifications were quantified using UV-VIS spectroscopy. Results: UV-VIS spectroscopy measurements indicate that ionizing radiation induces the polymerization of diacetylenes incorporated in the microbubble shell. The polymer yield strongly depends on the shell composition and the radiation-dose. The acoustic response is inherently related to the visco-elastic properties of the shell and is strongly influenced by the shell composition and the physico-chemical changes in the environment. Conclusion: Diacetylene-containing microbubbles are polymerizable under influence of ionizing radiation and are a promising design concept within the development of a novel non-invasive in-vivo radiation dosimeter for external beam radiation therapy. This work was funded by the Research Foundation - Flanders (FWO)« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Xuchu; Hu, Mary Y.; Wei, Xiaoliang

Understanding the solvation structures of electrolytes should prove conducive for the development of nonaqueous redox flow batteries that hold considerable potential for future large scale energy storage systems. The utilization of an emerging ionic-derivatived ferrocene compound, ferrocenylmethyl dimethyl ethyl ammonium bis(trifluoromethanesulfonyl)imide (Fc1N112-TFSI), has recently overcome the issue of solubility in the supporting electrolyte. In this work, 13C, 1H and 17O NMR investigations were carried out using electrolyte solutions consisting of Fc1N112-TFSI as the solute and the mixed alkyl carbonate as the solvent. It was observed that the spectra of 13C experience changes of chemical shifts while those of 17O undergomore » linewidth broadening, indicating interactions between solute and solvent molecules. Quantum chemistry calculations of both molecular structures and chemical shifts (13C, 1H and 17O) are performed for interpreting experimental results and of understanding the detailed solvation structures and molecular dynamics. The results indicate that Fc1N112-TFSI is dissociated at varying degrees in mixed solvent depending on concentrations. Solvent molecules encircle Fc1N112 and TFSI respectively as solvation shells, rapidly exchanging with both bulk solvent and TFSI. Additionally, the solvent with high dielectric constant is more capable of dissociating Fc1N112-TFSI molecules compared with those with low dielectric constant. At saturated concentration, contact ion pairs are formed and the solvent molecules are interacting with the Fc rings rather than interacting with the ionic pendant arm of Fc1N112-TFSI. These studies will contribute to the development of nonaqueous electrolytes of storage systems.« less

Rates of morphological evolution, asymmetry and morphological integration of shell shape in scallops.

PubMed

Sherratt, Emma; Serb, Jeanne M; Adams, Dean C

2017-12-08

Rates of morphological evolution vary across different taxonomic groups, and this has been proposed as one of the main drivers for the great diversity of organisms on Earth. Of the extrinsic factors pertaining to this variation, ecological hypotheses feature prominently in observed differences in phenotypic evolutionary rates across lineages. But complex organisms are inherently modular, comprising distinct body parts that can be differentially affected by external selective pressures. Thus, the evolution of trait covariation and integration in modular systems may also play a prominent role in shaping patterns of phenotypic diversity. Here we investigate the role ecological diversity plays in morphological integration, and the tempo of shell shape evolution and of directional asymmetry in bivalved scallops. Overall, the shape of both valves and the magnitude of asymmetry of the whole shell (difference in shape between valves) are traits that are evolving fast in ecomorphs under strong selective pressures (gliders, recessers and nestling), compared to low rates observed in other ecomorphs (byssal-attaching, free-living and cementing). Given that different parts of an organism can be under different selective pressures from the environment, we also examined the degree of evolutionary integration between the valves as it relates to ecological shifts. We find that evolutionary morphological integration is consistent and surprisingly high across species, indicating that while the left and right valves of a scallop shell are diversifying in accordance with ecomorphology, they are doing so in a concerted fashion. Our study on scallops adds another strong piece of evidence that ecological shifts play an important role in the tempo and mode of morphological evolution. Strong selective pressures from the environment, inferred from the repeated evolution of distinct ecomorphs, have influenced the rate of morphological evolution in valve shape and the magnitude of asymmetry between valves. Our observation that morphological integration of the valves making up the shell is consistently strong suggests tight developmental pathways are responsible for the concerted evolution of these structures while environmental pressures are driving whole shell shape. Finally, our study shows that directional asymmetry in shell shape among species is an important aspect of scallop macroevolution.

Sum-over-states density functional perturbation theory: Prediction of reliable 13C, 15N, and 17O nuclear magnetic resonance chemical shifts

NASA Astrophysics Data System (ADS)

Olsson, Lars; Cremer, Dieter

1996-11-01

Sum-over-states density functional perturbation theory (SOS-DFPT) has been used to calculate 13C, 15N, and 17O NMR chemical shifts of 20 molecules, for which accurate experimental gas-phase values are available. Compared to Hartree-Fock (HF), SOS-DFPT leads to improved chemical shift values and approaches the degree of accuracy obtained with second order Møller-Plesset perturbation theory (MP2). This is particularly true in the case of 15N chemical shifts where SOS-DFPT performs even better than MP2. Additional improvements of SOS-DFPT chemical shifts can be obtained by empirically correcting diamagnetic and paramagnetic contributions to compensate for deficiencies which are typical of DFT.

Calculation of NMR chemical shifts in organic solids: accounting for motional effects.

PubMed

Dumez, Jean-Nicolas; Pickard, Chris J

2009-03-14

NMR chemical shifts were calculated from first principles for well defined crystalline organic solids. These density functional theory calculations were carried out within the plane-wave pseudopotential framework, in which truly extended systems are implicitly considered. The influence of motional effects was assessed by averaging over vibrational modes or over snapshots taken from ab initio molecular dynamics simulations. It is observed that the zero-point correction to chemical shifts can be significant, and that thermal effects are particularly noticeable for shielding anisotropies and for a temperature-dependent chemical shift. This study provides insight into the development of highly accurate first principles calculations of chemical shifts in solids, highlighting the role of motional effects on well defined systems.

Enhanced linear photonic nanojet generated by core-shell optical microfibers

NASA Astrophysics Data System (ADS)

Liu, Cheng-Yang; Yen, Tzu-Ping; Chen, Chien-Wen

2017-05-01

The generation of linear photonic nanojet using core-shell optical microfiber is demonstrated numerically and experimentally in the visible light region. The power flow patterns for the core-shell optical microfiber are calculated by using the finite-difference time-domain method. The focusing properties of linear photonic nanojet are evaluated in terms of length and width along propagation and transversal directions. In experiment, the silica optical fiber is etched chemically down to 6 μm diameter and coated with metallic thin film by using glancing angle deposition. We show that the linear photonic nanojet is enhanced clearly by metallic shell due to surface plasmon polaritons. The large-area superresolution imaging can be performed by using a core-shell optical microfiber in the far-field system. The potential applications of this core-shell optical microfiber include micro-fluidics and nano-structure measurements.

Laboratory measurements of the K-shell transition energies in L-shell ions of Si and S [Energy measurements of K-shell transitions in L-shell ions of Si and S

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hell, Natalie; Brown, G. V.; Wilms, J.

We have measured the energies of the strongest 1s–2more » $${\\ell }\\ ({\\ell }={\\rm{s}},{\\rm{p}})$$ transitions in He- through Ne-like silicon and sulfur ions to an accuracy of $$\\lt 1\\,\\mathrm{eV}$$ using the Lawrence Livermore National Laboratory's electron beam ion traps, EBIT-I and SuperEBIT, and the NASA/GSFC EBIT Calorimeter Spectrometer (ECS). We identify and measure the energies of 18 and 21 X-ray features from silicon and sulfur, respectively. The results are compared to new Flexible Atomic Code calculations and to semi-relativistic Hartree–Fock calculations by Palmeri et al. (2008). These results will be especially useful for wind diagnostics in high-mass X-ray binaries, such as Vela X-1 and Cygnus X-1, where high-resolution spectral measurements using Chandra's high-energy transmission grating has made it possible to measure Doppler shifts of $$100\\,\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$. The accuracy of our measurements is consistent with that needed to analyze Chandra observations, exceeding Chandra's $$100\\,\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$ limit. Hence, the results presented here not only provide benchmarks for theory, but also accurate rest energies that can be used to determine the bulk motion of material in astrophysical sources. Finally, we show the usefulness of our results by applying them to redetermine Doppler shifts from Chandra observations of Vela X-1.« less

Laboratory measurements of the K-shell transition energies in L-shell ions of Si and S [Energy measurements of K-shell transitions in L-shell ions of Si and S

DOE PAGES

Hell, Natalie; Brown, G. V.; Wilms, J.; ...

2016-10-04

We have measured the energies of the strongest 1s–2more » $${\\ell }\\ ({\\ell }={\\rm{s}},{\\rm{p}})$$ transitions in He- through Ne-like silicon and sulfur ions to an accuracy of $$\\lt 1\\,\\mathrm{eV}$$ using the Lawrence Livermore National Laboratory's electron beam ion traps, EBIT-I and SuperEBIT, and the NASA/GSFC EBIT Calorimeter Spectrometer (ECS). We identify and measure the energies of 18 and 21 X-ray features from silicon and sulfur, respectively. The results are compared to new Flexible Atomic Code calculations and to semi-relativistic Hartree–Fock calculations by Palmeri et al. (2008). These results will be especially useful for wind diagnostics in high-mass X-ray binaries, such as Vela X-1 and Cygnus X-1, where high-resolution spectral measurements using Chandra's high-energy transmission grating has made it possible to measure Doppler shifts of $$100\\,\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$. The accuracy of our measurements is consistent with that needed to analyze Chandra observations, exceeding Chandra's $$100\\,\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$ limit. Hence, the results presented here not only provide benchmarks for theory, but also accurate rest energies that can be used to determine the bulk motion of material in astrophysical sources. Finally, we show the usefulness of our results by applying them to redetermine Doppler shifts from Chandra observations of Vela X-1.« less

Relative Configuration of Natural Products Using NMR Chemical Shifts

USDA-ARS?s Scientific Manuscript database

By comparing calculated with experimental NMR chemical shifts, we were able to determine the relative configurations of three monoterpene diastereomers produced by the walkingstick Anisomorpha buprestoides. The combined RMSDs of both 1H and 13C quantum chemically calculated shifts were able to predi...

Towards better light harvesting capability for DSSC (dye sensitized solar cells) through addition of Au@SiO2 core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Fadhilah, Nur; Alhadi, Emha Riyadhul Jinan; Risanti, Doty Dewi

2018-04-01

The Au nanoparticles as core can increase the light harvesting due to the strong near-field effect LSPR (Localized Surface Plasmon Resonance), effectively minimized the electron recombination process and also can improve the optical absorption of the dye sensitized. Au@SiO2 core-shell nanoparticles were prepared using SiO2 extracted from Sidoarjo mud volcano. In this work investigated the influence of pH solution and silica shell volume fraction in Au@SiO2 nanoparticles core-shell structure on DSSC loaded with Ru-based dye. From XRD characterization it was found that core-shell contains SiO2, Au, γAl2O3 and traces NaCl. UV-Vis absorption spectra of core-shell showed the position of the surface plasmon AuNP band in the range of 500-600 nm. The Au@SiO2 core-shell with volume fraction of 30ml silica has the highest peak absorbance. The enhanced light absorption is primarily attributed to the LSPR effect of the Au core. Our results on incident photon-to-current conversion efficiency indicates that the presence of SiO2 depending on its volume fraction tends to shift to longer wavelength.

Quantum-mechanics-derived 13Cα chemical shift server (CheShift) for protein structure validation

PubMed Central

Vila, Jorge A.; Arnautova, Yelena A.; Martin, Osvaldo A.; Scheraga, Harold A.

2009-01-01

A server (CheShift) has been developed to predict 13Cα chemical shifts of protein structures. It is based on the generation of 696,916 conformations as a function of the φ, ψ, ω, χ1 and χ2 torsional angles for all 20 naturally occurring amino acids. Their 13Cα chemical shifts were computed at the DFT level of theory with a small basis set and extrapolated, with an empirically-determined linear regression formula, to reproduce the values obtained with a larger basis set. Analysis of the accuracy and sensitivity of the CheShift predictions, in terms of both the correlation coefficient R and the conformational-averaged rmsd between the observed and predicted 13Cα chemical shifts, was carried out for 3 sets of conformations: (i) 36 x-ray-derived protein structures solved at 2.3 Å or better resolution, for which sets of 13Cα chemical shifts were available; (ii) 15 pairs of x-ray and NMR-derived sets of protein conformations; and (iii) a set of decoys for 3 proteins showing an rmsd with respect to the x-ray structure from which they were derived of up to 3 Å. Comparative analysis carried out with 4 popular servers, namely SHIFTS, SHIFTX, SPARTA, and PROSHIFT, for these 3 sets of conformations demonstrated that CheShift is the most sensitive server with which to detect subtle differences between protein models and, hence, to validate protein structures determined by either x-ray or NMR methods, if the observed 13Cα chemical shifts are available. CheShift is available as a web server. PMID:19805131

Detection of CI line emission towards the oxygen-rich AGB star omi Ceti

NASA Astrophysics Data System (ADS)

Saberi, M.; Vlemmings, W. H. T.; De Beck, E.; Montez, R.; Ramstedt, S.

2018-05-01

We present the detection of neutral atomic carbon CI(3P1-3P0) line emission towards omi Cet. This is the first time that CI is detected in the envelope around an oxygen-rich M-type asymptotic giant branch (AGB) star. We also confirm the previously tentative CI detection around V Hya, a carbon-rich AGB star. As one of the main photodissociation products of parent species in the circumstellar envelope (CSE) around evolved stars, CI can be used to trace sources of ultraviolet (UV) radiation in CSEs. The observed flux density towards omi Cet can be reproduced by a shell with a peak atomic fractional abundance of 2.4 × 10-5 predicted based on a simple chemical model where CO is dissociated by the interstellar radiation field. However, the CI emission is shifted by 4 km s-1 from the stellar velocity. Based on this velocity shift, we suggest that the detected CI emission towards omi Cet potentially arises from a compact region near its hot binary companion. The velocity shift could, therefore, be the result of the orbital velocity of the binary companion around omi Cet. In this case, the CI column density is estimated to be 1.1 × 1019 cm-2. This would imply that strong UV radiation from the companion and/or accretion of matter between two stars is most likely the origin of the CI enhancement. However, this hypothesis can be confirmed by high-angular resolution observations.

The argonaut shell: gas-mediated buoyancy control in a pelagic octopus.

PubMed

Finn, Julian K; Norman, Mark D

2010-10-07

Argonauts (Cephalopoda: Argonautidae) are a group of rarely encountered open-ocean pelagic octopuses with benthic ancestry. Female argonauts inhabit a brittle 'paper nautilus' shell, the role of which has puzzled naturalists for millennia. The primary role attributed to the shell has been as a receptacle for egg deposition and brooding. Our observations of wild argonauts have revealed that the thin calcareous shell also functions as a hydrostatic structure, employed by the female argonaut to precisely control buoyancy at varying depths. Female argonauts use the shell to 'gulp' a measured volume of air at the sea surface, seal off the captured gas using flanged arms and forcefully dive to a depth where the compressed gas buoyancy counteracts body weight. This process allows the female argonaut to attain neutral buoyancy at depth and potentially adjust buoyancy to counter the increased (and significant) weight of eggs during reproductive periods. Evolution of this air-capture strategy enables this negatively buoyant octopus to survive free of the sea floor. This major shift in life mode from benthic to pelagic shows strong evolutionary parallels with the origins of all cephalopods, which attained gas-mediated buoyancy via the closed-chambered shells of the true nautiluses and their relatives.

Porogranular materials composed of elastic Helmholtz resonators for acoustic wave absorption.

PubMed

Griffiths, Stéphane; Nennig, Benoit; Job, Stéphane

2017-01-01

A theoretical and experimental study of the acoustic absorption of granular porous media made of non-cohesive piles of spherical shells is presented. These shells are either rigid or elastic, possibly drilled with a neck (Helmholtz resonators), and either porous or impervious. A description is given of acoustic propagation through these media using the effective medium models proposed by Johnson (rigid particles) and Boutin (rigid Helmholtz resonators), which are extended to the configurations studied in this work. A solution is given for the local equation of elasticity of a shell coupled to the viscous flow of air through the neck and the micropores. The models and the simulations are compared to absorption spectra measured in reflection in an impedance tube. The effective medium models and the measurements show excellent agreement for configurations made of rigid particles and rigid Helmholtz resonators that induce an additional peak of absorption at low frequency. A shift of the Helmholtz resonance toward low frequencies, due to the softness of the shells is revealed by the experiments for elastic shells made of soft elastomer and is well reproduced by the simulations. It is shown that microporous shells enhance and broaden acoustic absorption compared to stiff or elastic resonators.

Study of chemical shift in Kα, Kβ1,3 and Kβ// X-ray emission lines of 37Rb compounds with WDXRF

NASA Astrophysics Data System (ADS)

Kainth, Harpreet Singh; Singh, Ranjit; Singh, Tejbir; Mehta, D.; Shahi, J. S.; Kumar, Sanjeev

2018-05-01

The positive and negative chemical shifts in Kα, Kβ1,3 and Kβ// X-ray emission lines of rubidium compounds were measured with high resolution WDXRF spectrometer. The measured energy shifts in Kα emission lines ranges from -2.95 eV to -3.64 eV, Kβ1,3 emission lines ranges from 1.16 eV to 1.32 eV and Kβ// emission lines ranges from 1.31 eV to 4.36 eV respectively. In the present work, it has been found that chemical shift in Kβ// X-ray emission lines were found to be larger than Kα and Kβ1,3 X-ray emission lines. To find the cause of chemical shift, various factors like effective charge, line intensity ratio, bond length and electro-negativity were calculated and correlated with the chemical shift.

Data on the pozzolanic activity in coconut shell ash (CSA) for use in sustainable construction.

PubMed

Joshua, Opeyemi; Olusola, Kolapo O; Busari, Ayobami A; Omuh, Ignatius O; Ogunde, Ayodeji O; Amusan, Lekan M; Ezenduka, Chidiogo J

2018-06-01

The data presented herein are results of the research summary of the investigation for pozzolanic activity in coconut shell ash (CSA) towards a sustainable construction. The data article provides information on the properties of Coconut Shell Ash that are indicative of pozzolanic activity as stated in ASTM C618-15 (2015) [1], BS EN 197-1 (2011) [2] and Joshua et al. (2018) [3]. The data are the physical property of the sand used in determining the binder strengths and the chemical and physical properties (oxide composition and Strength Activity Indices respectively) of the pulverized, calcined and sieved Coconut Shell Ash.

One-pot production of chitin with high purity from lobster shells using choline chloride-malonic acid deep eutectic solvent.

PubMed

Zhu, Ping; Gu, Zhongji; Hong, Shu; Lian, Hailan

2017-12-01

For the first time in this study, chitin was solely extracted from lobster shells through a fast, easy and eco-friendly method using deep eutectic solvents (DESs), consisting of mixtures of choline chloride-thiourea (CCT), choline chloride-urea (CCU), choline chloride-glycerol (CCG) and choline chloride-malonic acid (CCMA). The physiochemical properties of the isolated chitins were compared with those of the chemically prepared one and commercial one from shrimp shells. Results showed that CCT, CCU and CCG DESs had no important effect on the elimination of proteins and minerals, while chitin obtained by CCMA DES showed a high purity. The yield (20.63±3.30%) of chitin isolated by CCMA DES was higher than that (16.53±2.35%) of the chemically prepared chitin. The chitin obtained by CCMA DES could be divided into two parts with different crystallinity (67.2% and 80.6%), which also had different thermal stability. Chitin from lobster shells showed porous structure, which is expected to be used for adsorption materials and tissue engineering. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fabrication of Yolk-Shell Cu@C Nanocomposites as High-Performance Catalysts in Oxidative Carbonylation of Methanol to Dimethyl Carbonate

NASA Astrophysics Data System (ADS)

Wang, Juan; Hao, Panpan; Shi, Ruina; Yang, Leilei; Liu, Shusen; Zhao, Jinxian; Ren, Jun; Li, Zhong

2017-08-01

A facile way was developed to fabricate yolk-shell composites with tunable Cu cores encapsulated within hollow carbon spheres (Cu@C) with an average diameter about 210 nm and cavity size about 80 nm. During pyrolysis, the confined nanospace of hollow cavity ensures that the nucleation-and-growth process of Cu nanocrystals take place exclusively inside the cavities. The size of Cu cores can be easily tuned from 30 to 55 nm by varying the copper salt concentration. By deliberately creating shell porosity through KOH chemical activation, at an optimized KOH/HCS mass ratio of 1/4, the catalytic performance for the oxidative carbonylation of methanol to dimethyl carbonate (DMC) of the activated sample is enhanced remarkably with TOF up to 8.6 h-1 at methanol conversion of 17.1%. The activated yolk-shell catalyst shows promising catalytic properties involving the reusability with slight loss of catalytic activity and negligible leaching of activated components even after seven recycles, which is beneficial to the implementation of clean production for the eco-friendly chemical DMC thoroughly.

Core/multishell nanowire heterostructures as multicolor, high-efficiency light-emitting diodes.

PubMed

Qian, Fang; Gradecak, Silvija; Li, Yat; Wen, Cheng-Yen; Lieber, Charles M

2005-11-01

We report the growth and characterization of core/multishell nanowire radial heterostructures, and their implementation as efficient and synthetically tunable multicolor nanophotonic sources. Core/multishell nanowires were prepared by metal-organic chemical vapor deposition with an n-GaN core and InxGa1-xN/GaN/p-AlGaN/p-GaN shells, where variation of indium mole fraction is used to tune emission wavelength. Cross-sectional transmission electron microscopy studies reveal that the core/multishell nanowires are dislocation-free single crystals with a triangular morphology. Energy-dispersive X-ray spectroscopy clearly shows shells with distinct chemical compositions, and quantitatively confirms that the thickness and composition of individual shells can be well controlled during synthesis. Electrical measurements show that the p-AlGaN/p-GaN shell structure yields reproducible hole conduction, and electroluminescence measurements demonstrate that in forward bias the core/multishell nanowires function as light-emitting diodes, with tunable emission from 365 to 600 nm and high quantum efficiencies. The ability to synthesize rationally III-nitride core/multishell nanowire heterostructures opens up significant potential for integrated nanoscale photonic systems, including multicolor lasers.

Hexakis(3,6-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)cyclohexane: Closed-shell [6]Radialene or Open-shell Hexa-radicaloid?

PubMed

Wu, Jishan; Feng, Jiaqi; Gopalakrishna, Tullimilli Y; Phan, Hoa

2018-04-19

We report a star-shaped hexaquinocyclohexane molecule 4c, which turns out to be a closed-shell extended [6]radialene with a twisted-boat conformation according to X-ray crystallographic analysis. It was formed by an unusually slow decay of its in situ generated open-shell valence isomer, the hexa-radicaloid 4o, with a half-life time of about 156 min at room temperature. Reaction progress kinetic analysis revealed a large energy barrier of about 95.5 ± 4.3 kJ/mol at room temperature from the hexa-radical form 4o to the contorted [6]radialene form 4c, because the transformation need overcome large steric repulsion between the neighbouring phenoxyl units. Compound 4c can be chemically reduced to radical anion and dianion, and the dianion is actually a diradical dianion, with a calculated diradical character of 71.9%. This study demonstrated the unique chemical bonding nature of contorted quinoidal π-conjugated molecules and a very unusual valence isomerization process. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analysis of the temperature and pressure dependence of the 129Xe NMR chemical shift and signal intensity for the derivation of basic parameters of adsorption as applied to zeolite ZSM-5.

PubMed

Kawata, Yoko; Adachi, Yuko; Haga, Saori; Fukutomi, Junko; Imai, Hirohiko; Kimura, Atsuomi; Fujiwara, Hideaki

2007-12-01

Temperature and pressure dependences of the 129Xe NMR chemical shift and the signal intensity have been investigated using ZSM-5 as an adsorbent under routine conditions without using any high-pressure or especially high-temperature facilities. The use of a rigorously shielded system and a calibration sample for the signal intensity was found to be valuable to obtain reliable data about the chemical shift and the signal intensity. The 129Xe NMR data obtained between 0.05 and 1.5 atm and from 24 to 80 degrees C were analyzed based on the Dubinin-Radushkevich equation as well as the Langmuir type equation. In both analyses, chemical shift data succeeded only partially in providing the profile of adsorption, such as energetic aspects, surface area, saturated amount of Xe adsorption and specific parameters of 129Xe chemical shift. It was shown that the reliable total analysis was achieved when the chemical shift data were used together with the intensity data. Such an analysis of the chemical shift data, aided by the intensity data, will be useful in performing nano-material analysis on 129Xe NMR without invoking the traditional methodology of gravimetric or volumetric adsorption experiments.

Tuning of shell thickness of solid lipid particles impacts the chemical stability of encapsulated ω-3 fish oil.

PubMed

Salminen, Hanna; Helgason, Thrandur; Kristinsson, Bjarki; Kristbergsson, Kristberg; Weiss, Jochen

2017-03-15

This study demonstrates that tuning the shell thickness of lipid particles can modulate their oxidative stability. We hypothesized that a thick crystallized shell around the incorporated fish oil would improve the oxidative stability due to the reduced diffusion of prooxidants and oxygen. We prepared solid lipid nanoparticles (5%w/w lipid phase, 1.5%w/w surfactant, pH 7) by using different ratios of tristearin as carrier lipid and ω-3 fish oil as incorporated liquid lipid stabilized by high- or low-melting lecithin. The physical, polymorphic and oxidative stability of the lipid particles was assessed. The high-melting lecithin was the key in inducing the formation of a solidified tristearin shell around the lipid particles by interfacial heterogeneous nucleation. Lipid particles containing a higher ratio of tristearin showed a better oxidative stability. The results revealed that a crystallized tristearin layer above 10nm was required to inhibit oxidation of the incorporated fish oil. This cut-off was shown for lipid particles containing 50-60% fish oil. This research gives important insights into understanding the relation between the thickness of the crystallized shell around the lipid particles and their chemical stability. Copyright © 2016 Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oh, Pilgun; Oh, Seung -Min; Li, Wangda

The Ni-rich layered oxides with a Ni content of >0.5 are drawing much attention recently to increase the energy density of lithium-ion batteries. However, the Ni-rich layered oxides suffer from aggressive reaction of the cathode surface with the organic electrolyte at the higher operating voltages, resulting in consequent impedance rise and capacity fade. To overcome this difficulty, we present here a heterostructure composed of a Ni-rich LiNi 0.7Co 0.15Mn 0.15O 2 core and a Li-rich Li 1.2-xNi 0.2Mn 0.6O 2 shell, incorporating the advantageous features of the structural stability of the core and chemical stability of the shell. With amore » unique chemical treatment for the activation of the Li 2MnO 3 phase of the shell, a high capacity is realized with the Li-rich shell material. Aberration-corrected scanning transmission electron microscopy (STEM) provides direct evidence for the formation of surface Li-rich shell layer. Finally, the heterostructure exhibits a high capacity retention of 98% and a discharge- voltage retention of 97% during 100 cycles with a discharge capacity of 190 mA h g -1 (at 2.0–4.5 V under C/3 rate, 1C = 200 mA g -1).« less

Liquid-liquid phase separation in aerosol particles: Imaging at the Nanometer Scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

O'Brien, Rachel; Wang, Bingbing; Kelly, Stephen T.

2015-04-21

Atmospheric aerosols can undergo phase transitions including liquid-liquid phase separation (LLPS) while responding to changes in the ambient relative humidity (RH). Here, we report results of chemical imaging experiments using environmental scanning electron microscopy (ESEM) and scanning transmission x-ray microscopy (STXM) to investigate the LLPS of micron sized particles undergoing a full hydration-dehydration cycle. Internally mixed particles composed of ammonium sulfate (AS) and either: limonene secondary organic carbon (LSOC), a, 4-dihydroxy-3-methoxybenzeneaceticacid (HMMA), or polyethylene glycol (PEG-400) were studied. Events of LLPS with apparent core-shell particle morphology were observed for all samples with both techniques. Chemical imaging with STXM showed thatmore » both LSOC/AS and HMMA/AS particles were never homogeneously mixed for all measured RH’s above the deliquescence point and that the majority of the organic component was located in the shell. The shell composition was estimated as 65:35 organic: inorganic in LSOC/AS and as 50:50 organic: inorganic for HMMA/AS. PEG-400/AS particles showed fully homogeneous mixtures at high RH and phase separated below 89-92% RH with an estimated 50:50% organic to inorganic mix in the shell. These two chemical imaging techniques are well suited for in-situ analysis of the hygroscopic behavior, phase separation, and surface composition of collected ambient aerosol particles.« less

Orexin in Rostral Hotspot of Nucleus Accumbens Enhances Sucrose ‘Liking' and Intake but Scopolamine in Caudal Shell Shifts ‘Liking' Toward ‘Disgust' and ‘Fear'

PubMed Central

Castro, Daniel C; Terry, Rachel A; Berridge, Kent C

2016-01-01

The nucleus accumbens (NAc) contains a hedonic hotspot in the rostral half of medial shell, where opioid agonist microinjections are known to enhance positive hedonic orofacial reactions to the taste of sucrose (‘liking' reactions). Within NAc shell, orexin/hypocretin also has been reported to stimulate food intake and is implicated in reward, whereas blockade of muscarinic acetylcholine receptors by scopolamine suppresses intake and may have anti-reward effects. Here, we show that NAc microinjection of orexin-A in medial shell amplifies the hedonic impact of sucrose taste, but only within the same anatomically rostral site, identical to the opioid hotspot. By comparison, at all sites throughout medial shell, orexin microinjections stimulated ‘wanting' to eat, as reflected by increases in intake of palatable sweet chocolates. At NAc shell sites outside the hotspot, orexin selectively enhanced ‘wanting' to eat without enhancing sweetness ‘liking' reactions. In contrast, microinjections of the antagonist scopolamine at all sites in NAc shell suppressed sucrose ‘liking' reactions as well as suppressing intake of palatable food. Conversely, scopolamine increased aversive ‘disgust' reactions elicited by bitter quinine at all NAc shell sites. Finally, scopolamine microinjections localized to the caudal half of medial shell additionally generated a fear-related anti-predator reaction of defensive treading and burying directed toward the corners of the transparent chamber. Together, these results confirm a rostral hotspot in NAc medial shell as a unique site for orexin induction of hedonic ‘liking' enhancement, similar to opioid enhancement. They also reveal distinct roles for orexin and acetylcholine signals in NAc shell for hedonic reactions and motivated behaviors. PMID:26787120

Exploring the Oxidation Chemistry of Enceladus' Ocean

NASA Astrophysics Data System (ADS)

Ray, C.; Glein, C. R.; Waite, J. H.; Teolis, B. D.

2018-05-01

We explore the various physical and chemical processes in Enceladus ice shell and ocean that affect the availability of oxidants, and constrain this availability to determine how much chemical energy may be available for possible life.

Chemical Shifts of the Carbohydrate Binding Domain of Galectin-3 from Magic Angle Spinning NMR and Hybrid Quantum Mechanics/Molecular Mechanics Calculations.

PubMed

Kraus, Jodi; Gupta, Rupal; Yehl, Jenna; Lu, Manman; Case, David A; Gronenborn, Angela M; Akke, Mikael; Polenova, Tatyana

2018-03-22

Magic angle spinning NMR spectroscopy is uniquely suited to probe the structure and dynamics of insoluble proteins and protein assemblies at atomic resolution, with NMR chemical shifts containing rich information about biomolecular structure. Access to this information, however, is problematic, since accurate quantum mechanical calculation of chemical shifts in proteins remains challenging, particularly for 15 N H . Here we report on isotropic chemical shift predictions for the carbohydrate recognition domain of microcrystalline galectin-3, obtained from using hybrid quantum mechanics/molecular mechanics (QM/MM) calculations, implemented using an automated fragmentation approach, and using very high resolution (0.86 Å lactose-bound and 1.25 Å apo form) X-ray crystal structures. The resolution of the X-ray crystal structure used as an input into the AF-NMR program did not affect the accuracy of the chemical shift calculations to any significant extent. Excellent agreement between experimental and computed shifts is obtained for 13 C α , while larger scatter is observed for 15 N H chemical shifts, which are influenced to a greater extent by electrostatic interactions, hydrogen bonding, and solvation.

Synthetical Analysis for Morphology, biological Species, and stable Isotopes (SAMSI) of single-cell planktonic foraminifer

NASA Astrophysics Data System (ADS)

Ujiie, Y.; Kimoto, K.; Ishimura, T.

2017-12-01

Planktonic foraminifers are widely used in the studies of paleontology and paleoceanography, because the morphology of their calcareous shells is enough highly variable to identify the morphospecies and the chemical composition of the shells reflect ambient seawater condition. Although the morphospecies were believed to represent environments associating with latitudinal temperature range of the world ocean, molecular phylogeographic studies have unveiled the presence of multiple biological species in a single morphospecies and their species-specific distributions. This implicates the actual complexity of planktonic foraminiferal ecology. Conversely, these biological species have a high potential for providing novel ecological and environmental information to us. In order to reassess the morphological and geochemical characters of biological species, the DNA extraction method with the guanidium isothiocyanate buffer was developed to preserve the calcareous shells. The present study carefully tested the physical and chemical damages of the DNA extraction process to the shells, by our novel approaches with geochemical analysis of the shells after non-destructive analysis for morphometrics on a same specimen. First, we checked the changes of the shell densities between pre- and post-DNA extraction by using the micro-focus X-ray CT (MXCT) scanning. Based on the simultaneous measurement of a sample and the standard material, we confirmed no significant changes to the shell densities through the DNA extraction process. As a next step, we compared stable oxygen and carbon isotopes among individuals of three sample sets: (1) no chemical and incubation as control, (2) incubation in the DNA extraction buffer at 65-70°C for 40 minutes as standard way, and (3) incubation in the DNA extraction buffer at 65-70°C for 120 minutes, by using the microscale isotopic analytical system (MICAL3c). Consequently, there were no significant differences among the three sample sets. These examinations clearly certified that we define morphological and geochemical features from same specimens after genetic identification. Thus, our novel approach (SAMSI) provides future studies to establish the accurate ecological and environmental proxies both in the modern and past oceans.

Synthesis of hollow silica spheres with hierarchical shell structure by the dual action of liquid indium microbeads in vapor-liquid-solid growth.

PubMed

Wang, Jian-Tao; Wang, Hui; Ou, Xue-Mei; Lee, Chun-Sing; Zhang, Xiao-Hong

2011-07-05

Geometry-based adhesion arising from hierarchical surface structure enables microspheres to adhere to cells strongly, which is essential for inorganic microcapsules that function as drug delivery or diagnostic imaging agents. However, constructing a hierarchical structure on the outer shell of the products via the current microcapsule synthesis method is difficult. This work presents a novel approach to fabricating hollow microspheres with a hierarchical shell structure through the vapor-liquid-solid (VLS) process in which liquid indium droplets act as both templates for the formation of silica capsules and catalysts for the growth of hierarchical shell structure. This hierarchical shell structure offers the hollow microsphere an enhanced geometry-based adhesion. The results provide a facile method for fabricating hollow spheres and enriching their function through tailoring the geometry of their outer shells. © 2011 American Chemical Society

Phenolic profile and antioxidant activity from non-toxic Mexican Jatropha curcas L. shell methanolic extracts.

PubMed

Perea-Domínguez, Xiomara Patricia; Espinosa-Alonso, Laura Gabriela; Hosseinian, Farah; HadiNezhad, Mehri; Valdez-Morales, Maribel; Medina-Godoy, Sergio

2017-03-01

Jatropha curcas seed shells are the by-product obtained during oil extraction process. Recently, its chemical composition has gained attention since its potential applications. The aim of this study was to identify phenolic compounds profile from a non-toxic J. curcas shell from Mexico, besides, evaluate J. curcas shell methanolic extract (JcSME) antioxidant activity. Free, conjugate and bound phenolics were fractionated and quantified (606.7, 193.32 and 909.59 μg/g shell, respectively) and 13 individual phenolic compounds were detected by HPLC. The radical-scavenging activity of JcSME was similar to Trolox and ascorbic acid by DPPH assay while by ABTS assay it was similar to BHT. Effective antioxidant capacity by ORAC was found (426.44 ± 53.39 μmol Trolox equivalents/g shell). The Mexican non-toxic J. curcas shell is rich in phenolic compounds with high antioxidant activity; hence, it could be considerate as a good source of natural antioxidants.

Polypropylenes foam consisting of thermally expandable microcapsule as blowing agent

NASA Astrophysics Data System (ADS)

Jeoung, Sun Kyung; Hwang, Ye Jin; Lee, Hyun Wook; Kwak, Sung Bok; Han, In-Soo; Ha, Jin Uk

2016-03-01

The structure of thermally expandable microcapsule (TEMs) is consisted of a thermoplastic shell which is filled with liquid hydrocarbon at core. The shell of TEMs becomes soft when the temperature is higher than boiling temperature of liquid hydrocarbon. The shell of TEMs is expanded under the high temperature because the inner pressure of TEMs is increased by vaporization of hydrocarbon core. Therefore, the TEMs are applicable for blowing agents and light weight fillers. In this research, we fabricated the polypropylene (PP) foam by using the TEMs and chemical blowing agents and compared to their physical properties. The density of the specimen was decreased when the contents of chemical blowing agents and TEMs were increased. In addition, the mechanical properties (i.e. tensile strength and impact strength) of specimens were deteriorated with increasing amount of chemical blowing agents and TEMs. However, PP foam produced with TEMs showed higher impact strength than the one with the chemical blowing agent. In order to clarify the dependence of impact strength of PP foam as the blowing agent, the morphology difference of the PP foams was investigated. Expanding properties of PP foams produced with TEMs was changed with TEMs content of PP foams. Processing conditions also influenced the mechanical properties of PP foam containing TEMs.

Error assessment in molecular dynamics trajectories using computed NMR chemical shifts.

PubMed

Koes, David R; Vries, John K

2017-01-01

Accurate chemical shifts for the atoms in molecular mechanics (MD) trajectories can be obtained from quantum mechanical (QM) calculations that depend solely on the coordinates of the atoms in the localized regions surrounding atoms of interest. If these coordinates are correct and the sample size is adequate, the ensemble average of these chemical shifts should be equal to the chemical shifts obtained from NMR spectroscopy. If this is not the case, the coordinates must be incorrect. We have utilized this fact to quantify the errors associated with the backbone atoms in MD simulations of proteins. A library of regional conformers containing 169,499 members was constructed from 6 model proteins. The chemical shifts associated with the backbone atoms in each of these conformers was obtained from QM calculations using density functional theory at the B3LYP level with a 6-311+G(2d,p) basis set. Chemical shifts were assigned to each backbone atom in each MD simulation frame using a template matching approach. The ensemble average of these chemical shifts was compared to chemical shifts from NMR spectroscopy. A large systematic error was identified that affected the 1 H atoms of the peptide bonds involved in hydrogen bonding with water molecules or peptide backbone atoms. This error was highly sensitive to changes in electrostatic parameters. Smaller errors affecting the 13 C a and 15 N atoms were also detected. We believe these errors could be useful as metrics for comparing the force-fields and parameter sets used in MD simulation because they are directly tied to errors in atomic coordinates.

Metathesis Activity Encoded in the Metallacyclobutane Carbon-13 NMR Chemical Shift Tensors

PubMed Central

2017-01-01

Metallacyclobutanes are an important class of organometallic intermediates, due to their role in olefin metathesis. They can have either planar or puckered rings associated with characteristic chemical and physical properties. Metathesis active metallacyclobutanes have short M–Cα/α′ and M···Cβ distances, long Cα/α′–Cβ bond length, and isotropic 13C chemical shifts for both early d0 and late d4 transition metal compounds for the α- and β-carbons appearing at ca. 100 and 0 ppm, respectively. Metallacyclobutanes that do not show metathesis activity have 13C chemical shifts of the α- and β-carbons at typically 40 and 30 ppm, respectively, for d0 systems, with upfield shifts to ca. −30 ppm for the α-carbon of metallacycles with higher dn electron counts (n = 2 and 6). Measurements of the chemical shift tensor by solid-state NMR combined with an orbital (natural chemical shift, NCS) analysis of its principal components (δ11 ≥ δ22 ≥ δ33) with two-component calculations show that the specific chemical shift of metathesis active metallacyclobutanes originates from a low-lying empty orbital lying in the plane of the metallacyclobutane with local π*(M–Cα/α′) character. Thus, in the metathesis active metallacyclobutanes, the α-carbons retain some residual alkylidene character, while their β-carbon is shielded, especially in the direction perpendicular to the ring. Overall, the chemical shift tensors directly provide information on the predictive value about the ability of metallacyclobutanes to be olefin metathesis intermediates. PMID:28776018

Errors in the Calculation of 27Al Nuclear Magnetic Resonance Chemical Shifts

PubMed Central

Wang, Xianlong; Wang, Chengfei; Zhao, Hui

2012-01-01

Computational chemistry is an important tool for signal assignment of 27Al nuclear magnetic resonance spectra in order to elucidate the species of aluminum(III) in aqueous solutions. The accuracy of the popular theoretical models for computing the 27Al chemical shifts was evaluated by comparing the calculated and experimental chemical shifts in more than one hundred aluminum(III) complexes. In order to differentiate the error due to the chemical shielding tensor calculation from that due to the inadequacy of the molecular geometry prediction, single-crystal X-ray diffraction determined structures were used to build the isolated molecule models for calculating the chemical shifts. The results were compared with those obtained using the calculated geometries at the B3LYP/6-31G(d) level. The isotropic chemical shielding constants computed at different levels have strong linear correlations even though the absolute values differ in tens of ppm. The root-mean-square difference between the experimental chemical shifts and the calculated values is approximately 5 ppm for the calculations based on the X-ray structures, but more than 10 ppm for the calculations based on the computed geometries. The result indicates that the popular theoretical models are adequate in calculating the chemical shifts while an accurate molecular geometry is more critical. PMID:23203134

Core-shell TiO2@ZnO nanorods for efficient ultraviolet photodetection

NASA Astrophysics Data System (ADS)

Panigrahi, Shrabani; Basak, Durga

2011-05-01

Core-shell TiO2@ZnO nanorods (NRs) have been fabricated by a simple two step method: growth of ZnO NRs' array by an aqueous chemical technique and then coating of the NRs with a solution of titanium isopropoxide [Ti(OC3H7)4] followed by a heating step to form the shell. The core-shell nanocomposites are composed of single-crystalline ZnO NRs, coated with a thin TiO2 shell layer obtained by varying the number of coatings (one, three and five times). The ultraviolet (UV) emission intensity of the nanocomposite is largely quenched due to an efficient electron-hole separation reducing the band-to-band recombinations. The UV photoconductivity of the core-shell structure with three times TiO2 coating has been largely enhanced due to photoelectron transfer between the core and the shell. The UV photosensitivity of the nanocomposite becomes four times larger while the photocurrent decay during steady UV illumination has been decreased almost by 7 times compared to the as-grown ZnO NRs indicating high efficiency of these core-shell structures as UV sensors.

Alternative Way of Shifting Mass to Move a Spherical Robot

NASA Technical Reports Server (NTRS)

Lux, James

2005-01-01

The method proposed calls for suspending a payload by use of four or more cables that would be anchored to the inner surface of the sphere. In this method, the anchor points would not be diametrically opposite points defining Cartesian axes. The payload, which includes the functional analog of the aforementioned control box, would contain winches that would shorten or lengthen the cables in a coordinated manner to shift the position of the payload within the shell.

Theoretical investigation of geometries, stabilities, electronic and optical properties for advanced Ag{sub n}@(ZnO){sub 42} (n=6-18) hetero-nanostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Hai-Xia; Department of Physics, National University of Singapore, 117542; Wang, Xiao-Xu

The structural properties of Ag{sub n}@(ZnO){sub 42} (n=6-18) core-shell nanoparticles have been investigated by the first principles calculations, and the core-shell nanostructure with n=13 is proved to be the most stable one for the first time. Ag{sub 13}@(ZnO){sub 42} core-shell nanostructure possesses higher chemistry activity and shows a red shift phenomenon in the light of the absorption spectrum compare to the (ZnO){sub 48}, this can be confirmed by the calculated electron structure. The visible-light could be absorbed by Ag{sub 13}@(ZnO){sub 42} to improve the photo-catalysis of (ZnO){sub 48} nanostructure. Our results show good agreement with experiments.

Unraveling the meaning of chemical shifts in protein NMR.

PubMed

Berjanskii, Mark V; Wishart, David S

2017-11-01

Chemical shifts are among the most informative parameters in protein NMR. They provide wealth of information about protein secondary and tertiary structure, protein flexibility, and protein-ligand binding. In this report, we review the progress in interpreting and utilizing protein chemical shifts that has occurred over the past 25years, with a particular focus on the large body of work arising from our group and other Canadian NMR laboratories. More specifically, this review focuses on describing, assessing, and providing some historical context for various chemical shift-based methods to: (1) determine protein secondary and super-secondary structure; (2) derive protein torsion angles; (3) assess protein flexibility; (4) predict residue accessible surface area; (5) refine 3D protein structures; (6) determine 3D protein structures and (7) characterize intrinsically disordered proteins. This review also briefly covers some of the methods that we previously developed to predict chemical shifts from 3D protein structures and/or protein sequence data. It is hoped that this review will help to increase awareness of the considerable utility of NMR chemical shifts in structural biology and facilitate more widespread adoption of chemical-shift based methods by the NMR spectroscopists, structural biologists, protein biophysicists, and biochemists worldwide. This article is part of a Special Issue entitled: Biophysics in Canada, edited by Lewis Kay, John Baenziger, Albert Berghuis and Peter Tieleman. Copyright © 2017 Elsevier B.V. All rights reserved.

Automated and assisted RNA resonance assignment using NMR chemical shift statistics

PubMed Central

Aeschbacher, Thomas; Schmidt, Elena; Blatter, Markus; Maris, Christophe; Duss, Olivier; Allain, Frédéric H.-T.; Güntert, Peter; Schubert, Mario

2013-01-01

The three-dimensional structure determination of RNAs by NMR spectroscopy relies on chemical shift assignment, which still constitutes a bottleneck. In order to develop more efficient assignment strategies, we analysed relationships between sequence and 1H and 13C chemical shifts. Statistics of resonances from regularly Watson–Crick base-paired RNA revealed highly characteristic chemical shift clusters. We developed two approaches using these statistics for chemical shift assignment of double-stranded RNA (dsRNA): a manual approach that yields starting points for resonance assignment and simplifies decision trees and an automated approach based on the recently introduced automated resonance assignment algorithm FLYA. Both strategies require only unlabeled RNAs and three 2D spectra for assigning the H2/C2, H5/C5, H6/C6, H8/C8 and H1′/C1′ chemical shifts. The manual approach proved to be efficient and robust when applied to the experimental data of RNAs with a size between 20 nt and 42 nt. The more advanced automated assignment approach was successfully applied to four stem-loop RNAs and a 42 nt siRNA, assigning 92–100% of the resonances from dsRNA regions correctly. This is the first automated approach for chemical shift assignment of non-exchangeable protons of RNA and their corresponding 13C resonances, which provides an important step toward automated structure determination of RNAs. PMID:23921634

Influence of the shell thickness and charge distribution on the effective interaction between two like-charged hollow spheres.

PubMed

Angelescu, Daniel G; Caragheorgheopol, Dan

2015-10-14

The mean-force and the potential of the mean force between two like-charged spherical shells were investigated in the salt-free limit using the primitive model and Monte Carlo simulations. Apart from an angular homogeneous distribution, a discrete charge distribution where point charges localized on the shell outer surface followed an icosahedral arrangement was considered. The electrostatic coupling of the model system was altered by the presence of mono-, trivalent counterions or small dendrimers, each one bearing a net charge of 9 e. We analyzed in detail how the shell thickness and the radial and angular distribution of the shell charges influenced the effective interaction between the shells. We found a sequence of the potential of the mean force similar to the like-charged filled spheres, ranging from long-range purely repulsive to short-range purely attractive as the electrostatic coupling increased. Both types of potentials were attenuated and an attractive-to-repulsive transition occurred in the presence of trivalent counterions as a result of (i) thinning the shell or (ii) shifting the shell charge from the outer towards the inner surface. The potential of the mean force became more attractive with the icosahedrally symmetric charge model, and additionally, at least one shell tended to line up with 5-fold symmetry axis along the longest axis of the simulation box at the maximum attraction. The results provided a basic framework of understanding the non-specific electrostatic origin of the agglomeration and long-range assembly of the viral nanoparticles.

Fabrication of diamond shells

DOEpatents

Hamza, Alex V.; Biener, Juergen; Wild, Christoph; Woerner, Eckhard

2016-11-01

A novel method for fabricating diamond shells is introduced. The fabrication of such shells is a multi-step process, which involves diamond chemical vapor deposition on predetermined mandrels followed by polishing, microfabrication of holes, and removal of the mandrel by an etch process. The resultant shells of the present invention can be configured with a surface roughness at the nanometer level (e.g., on the order of down to about 10 nm RMS) on a mm length scale, and exhibit excellent hardness/strength, and good transparency in the both the infra-red and visible. Specifically, a novel process is disclosed herein, which allows coating of spherical substrates with optical-quality diamond films or nanocrystalline diamond films.

Spectrophotometry of the shell around AG Carinae

NASA Technical Reports Server (NTRS)

Mitra, P. Mila; Dufour, Reginald J.

1990-01-01

Spatially-resolved long-slit spectrophotometry are presented for two regions of the shell nebula around the P-Cygni variable star AG Carinae. The spectra cover the 3700-6800 A wavelength range. Emission-line diagnostics are used to derive extinction, electron temperatures, and densities for various positions in the nebula. The chemical abundances and ionization structure are calculated and compared with other types of planetary nebulae and shells around other luminous stars. It is found that the N/O and N/S ratios of Ag Car are high compared to solar neighborhood ISM values. The O/H depletion found for the AG Car shell approaches that found in the condensations of the Eta Car system.

Synthesis and controllable oxidation of monodisperse cobalt-doped wüstite nanoparticles and their core-shell stability and exchange-bias stabilization.

PubMed

Chen, Chih-Jung; Chiang, Ray-Kuang; Kamali, Saeed; Wang, Sue-Lein

2015-09-14

Cobalt-doped wüstite (CWT), Co0.33Fe0.67O, nanoparticles were prepared via the thermal decomposition of CoFe2-oleate complexes in organic solvents. A controllable oxidation process was then performed to obtain Co0.33Fe0.67O/CoFe2O4 core-shell structures with different core-to-shell volume ratios and exchange bias properties. The oxidized core-shell samples with a ∼4 nm CoFe2O4 shell showed good resistance to oxygen transmission. Thus, it is inferred that the cobalt ferrite shell provides a better oxidation barrier performance than magnetite in the un-doped case. The hysteresis loops of the oxidized 19 nm samples exhibited a high exchange bias field (H(E)), an enhanced coercivity field (H(C)), and a pronounced vertical shift, thus indicating the presence of a strong exchange bias coupling effect. More importantly, the onset temperature of H(E) was found to be higher than 200 K, which suggests that cobalt doping increases the Néel temperature (T(N)) of the CWT core. In general, the results show that the homogeneous dispersion of Co in iron precursors improves the stability of the final CWT nanoparticles. Moreover, the CoFe2O4 shells formed following oxidation increase the oxidation resistance of the CWT cores and enhance their anisotropy energy.

Synthesis and Plasmonic Understanding of Core/Satellite and Core Shell Nanostructures

NASA Astrophysics Data System (ADS)

Ruan, Qifeng

Localized surface plasmon resonance, which stems from the collective oscillations of conduction-band electrons, endows Au nanocrystals with unique optical properties. Au nanocrystals possess extremely large scattering/absorption cross-sections and enhanced local electromagnetic field, both of which are synthetically tunable. Moreover, when Au nanocrystals are closely placed or hybridized with semiconductors, the coupling and interaction between the individual components bring about more fascinating phenomena and promising applications, including plasmon-enhanced spectroscopies, solar energy harvesting, and cancer therapy. The continuous development in the field of plasmonics calls for further advancements in the preparation of high-quality plasmonic nanocrystals, the facile construction of hybrid plasmonic nanostructures with desired functionalities, as well as deeper understanding and efficient utilization of the interaction between plasmonic nanocrystals and semiconductor components. In this thesis, I developed a seed-mediated growth method for producing size-controlled Au nanospheres with high monodispersity and assembled Au nanospheres of different sizes into core/satellite nanostructures for enhancing Raman signals. For investigating the interactions between Au nanocrystals and semiconductors, I first prepared (Au core) (TiO2 shell) nanostructures, and then studied their synthetically controlled plasmonic properties and light-harvesting applications. Au nanocrystals with spherical shapes are desirable in plasmon-coupled systems owing to their high geometrical symmetry, which facilitates the analysis of electrodynamic responses in a classical electromagnetic framework and the investigation of quantum tunneling and nonlocal effects. I prepared remarkably uniform Au nanospheres with diameters ranging from 20 nm to 220 nm using a simple seed-mediated growth method associated with mild oxidation. Core/satellite nanostructures were assembled out of differently sized Au nanospheres with molecular linkers. The plasmon resonances of the core/satellite nanostructures undergo red shifts in comparison to those of the sole Au cores, which is consistent with Mie theory analysis. As predicted by finite-difference time-domain simulations, the assembled core/satellite nanostructures exhibit large enhancements for Raman scattering. The facile growth of Au nanospheres and assembly of core/satellite nanostructures blaze a new way to the design of nanoarchitectures with desired plasmonic properties and functions. Coating semiconductors onto Au nanocrystals to form core shell configurations can increase the interactions between the two materials, benefiting from their large active interfacial area. The shell can also protect the Au nanocrystal core from aggregation, reshaping, and chemical corrosion. In this thesis, (Au nanocrystal core) (titania shell) nanostructures with tunable shell thicknesses were prepared by a facile wetchemistry method. Au nanocrystals with strong and tunable plasmon resonances in the visible and near-infrared regions can enhance and broaden the light utilization of TiO2 through the scattering/absorption enhancement, sensitization, and hot-electron injection. The integration of Au nanocrystals therefore hold the prospect of breaking the light-harvesting limit of TiO2 arising from its wide band gap. The resultant (Au core) (TiO2 shell) nanostructures were examined to be capable of efficiently generating reactive oxygen species under near-infrared resonant excitation. On the other hand, the transverse plasmon modes of Au nanorods, which are often too weak to be observed on scattering spectra, are enhanced by the TiO2 shell through energy transfer. With the increment of the shell thickness, the intensity of the transverse plasmon mode increases significantly and even becomes comparable with the longitudinal plasmon mode. Interestingly, both the transverse and longitudinal modes of the (Au core) (TiO2 shell) nanostructures exhibit asymmetric Fano line shapes. The Fano resonances result from the coupling between the core and shell, as understood by the mechanical oscillator model. Besides varying the shell thickness, the plasmonic bands of the core shell nanostructures can also be tailored by employing Au nanorods with different aspect ratios. The synthetically tunable plasmonic properties and synergistic interactions between the gold core and the titania shell make the hybrid nanostructure a multifunctional nanomaterial and ideal system for studying the plasmonic hybrid nanostructures.

Characterization of Nano-Hydroxyapatite Synthesized from Sea Shells Through Wet Chemical Method

NASA Astrophysics Data System (ADS)

Santhosh, S.; Prabu, S. Balasivanandha

2012-10-01

Nano-hydroxyapatite (HA) was synthesized by a wet chemical reaction using powdered sea shells (CaO) as starting material which was converted to calcium hydroxide (Ca(OH)2) and subsequently reacted with phosphoric acid (H3PO4). Initially raw sea shells (CaCO3) were thermally converted to amorphous calcium oxide by heat treatment. Two sets of experiments were done; in the first experiment, HA powder was dried in an electric furnace and in the second experiment, the reactants were irradiated in a domestic microwave oven followed by microwave drying. In each set of experiments, the concentrations of the reactants were decreased gradually. HA was synthesized by slow addition of phosphoric acid (H3PO4) in to calcium hydroxide (Ca(OH)2) maintaining the pH of the solution at 10 to avoid the formation of calcium deficient apatites. In both the experiments, Ca:P ratio of 1.67 was maintained for the reagents. The synthesized samples showed X-ray diffraction (XRD) patterns corresponding to hydroxyapatite. The wet chemical process with furnace drying resulted in HA particles of size 7-34 nm, whereas microwave irradiated process yielded HA particles of size 34-102 nm as evidenced from XRD analyses. The above experimental work done by wet chemical synthesis to produce HA powder from sea shells is a simple processing method at room temperature. Microwave irradiation leads to uniform crystallite sizes as evident from this study, at differing concentrations of the reactants and is a comparatively easy method to synthesize HA. The high resolution scanning electron microscopy (HRSEM)/transmission electron microscopic (TEM) analyses revealed the characteristic rod-shaped nanoparticles of HA for the present study.

High throughput chemical munitions treatment system

DOEpatents

Haroldsen, Brent L [Manteca, CA; Stofleth, Jerome H [Albuquerque, NM; Didlake, Jr., John E.; Wu, Benjamin C-P [San Ramon, CA

2011-11-01

A new High-Throughput Explosive Destruction System is disclosed. The new system is comprised of two side-by-side detonation containment vessels each comprising first and second halves that feed into a single agent treatment vessel. Both detonation containment vessels further comprise a surrounding ventilation facility. Moreover, the detonation containment vessels are designed to separate into two half-shells, wherein one shell can be moved axially away from the fixed, second half for ease of access and loading. The vessels are closed by means of a surrounding, clam-shell type locking seal mechanisms.

Synthesis of Au/TiO2 Core-Shell Nanoparticles from Titanium Isopropoxide and Thermal Resistance Effect of TiO2 Shell

NASA Astrophysics Data System (ADS)

Kwon, Hyun-Woo; Lim, Young-Min; Tripathy, Suraj Kumar; Kim, Byoung-Gyu; Lee, Min-Sang; Yu, Yeon-Tae

2007-04-01

On the synthesis of Au/TiO2 core-shell structure nanoparticles, the effect of the concentration of Ti4+ on the morphology and optical property of Au/TiO2 core-shell nanoparticles was examined. A gold colloid was prepared by mixing HAuCl4\\cdot4H2O and C6H5Na3\\cdot2H2O. Titanium stock solution was prepared by mixing solutions of titanium(IV) isopropoxide (TTIP) and triethanolamine (TEOA). The concentration of the Ti4+ stock solution was adjusted to 0.01-0.3 mM, and then the gold colloid was added to the Ti4+ stock solution. Au/TiO2 core-shell structure nanoparticles could be prepared by the hydrolysis of the Ti4+ stock solution at 80 °C. The size of the as-prepared Au nanoparticles was 15 nm. The thickness of the TiO2 shell on the surface of gold particles was about 10 nm. The absorption peak of the Au/TiO2 core-shell nanoparticles shifted towards the red end of the spectrum by about 3 nm because of the formation of the TiO2 shell on the surface of the gold particles. The crystal structure of the TiO2 shell showed an anatase phase. The increase in the Au crystallite size of the Au/TiO2 nanoparticles with increasing heat treatment temperature is smaller than that in the pure Au nanoparticles. This may be due to the encapsulation of Au particles with the TiO2 shell that prevents the growth of the nanoparticle nucleation.

NMR shielding calculations across the periodic table: diamagnetic uranium compounds. 2. Ligand and metal NMR.

PubMed

Schreckenbach, Georg

2002-12-16

In this and a previous article (J. Phys. Chem. A 2000, 104, 8244), the range of application for relativistic density functional theory (DFT) is extended to the calculation of nuclear magnetic resonance (NMR) shieldings and chemical shifts in diamagnetic actinide compounds. Two relativistic DFT methods are used, ZORA ("zeroth-order regular approximation") and the quasirelativistic (QR) method. In the given second paper, NMR shieldings and chemical shifts are calculated and discussed for a wide range of compounds. The molecules studied comprise uranyl complexes, [UO(2)L(n)](+/-)(q); UF(6); inorganic UF(6) derivatives, UF(6-n)Cl(n), n = 0-6; and organometallic UF(6) derivatives, UF(6-n)(OCH(3))(n), n = 0-5. Uranyl complexes include [UO(2)F(4)](2-), [UO(2)Cl(4)](2-), [UO(2)(OH)(4)](2-), [UO(2)(CO(3))(3)](4-), and [UO(2)(H(2)O)(5)](2+). For the ligand NMR, moderate (e.g., (19)F NMR chemical shifts in UF(6-n)Cl(n)) to excellent agreement [e.g., (19)F chemical shift tensor in UF(6) or (1)H NMR in UF(6-n)(OCH(3))(n)] has been found between theory and experiment. The methods have been used to calculate the experimentally unknown (235)U NMR chemical shifts. A large chemical shift range of at least 21,000 ppm has been predicted for the (235)U nucleus. ZORA spin-orbit appears to be the most accurate method for predicting actinide metal chemical shifts. Trends in the (235)U NMR chemical shifts of UF(6-n)L(n) molecules are analyzed and explained in terms of the calculated electronic structure. It is argued that the energy separation and interaction between occupied and virtual orbitals with f-character are the determining factors.

Enhanced collectivity along the N = Z line: lifetime measurements in 44Ti, 48Cr, and 52Fe

NASA Astrophysics Data System (ADS)

Arnswald, K.; Reiter, P.; Coraggio, L.; Birkenbach, B.; Blazhev, A.; Braunroth, T.; Dewald, A.; Fransen, C.; Fu, B.; Gargano, A.; Hess, H.; Hirsch, R.; Itaco, N.; Lenzi, S. M.; Lewandowski, L.; Litzinger, J.; Müller-Gatermann, C.; Queiser, M.; Rosiak, D.; Schneiders, D.; Seidlitz, M.; Siebeck, B.; Steinbach, T.; Vogt, A.; Wolf, K.; Zell, K. O.

2018-02-01

Lifetimes of the {2}1+ states in 44Ti, 48,50Cr, and 52Fe were determined with high accuracy exploiting the recoil distance Doppler-shift method. The reduced E2 transition strengths of 44Ti and 52 Fe differ considerably from previously known values. A systematic increase in collectivity is found for the N = Z nuclei compared to neighboring isotopes. The B(E2) values along the Ti, Cr, and Fe isotopic chains are compared to shell-model calculations employing established interactions for the 0f 1p shell, as well as a novel effective shell-model Hamiltonian starting from a realistic nucleon-nucleon potential. The theoretical approaches underestimate the B(E2) values for the lower-mass Ti isotopes. Strong indication is found for particle-hole cross-shell configurations, recently corroborated by similar results for the neighboring isotone 42 Ca. A detailed manuscript has meanwhile been published in Physics Letters B [1].

Effect of iron oxide loading on magnetoferritin structure in solution as revealed by SAXS and SANS.

PubMed

Melníková, L; Petrenko, V I; Avdeev, M V; Garamus, V M; Almásy, L; Ivankov, O I; Bulavin, L A; Mitróová, Z; Kopčanský, P

2014-11-01

Synthetic biological macromolecule of magnetoferritin containing an iron oxide core inside a protein shell (apoferritin) is prepared with different content of iron. Its structure in aqueous solution is analysed by small-angle synchrotron X-ray (SAXS) and neutron (SANS) scattering. The loading factor (LF) defined as the average number of iron atoms per protein is varied up to LF=800. With an increase of the LF, the scattering curves exhibit a relative increase in the total scattered intensity, a partial smearing and a shift of the match point in the SANS contrast variation data. The analysis shows an increase in the polydispersity of the proteins and a corresponding effective increase in the relative content of magnetic material against the protein moiety of the shell with the LF growth. At LFs above ∼150, the apoferritin shell undergoes structural changes, which is strongly indicative of the fact that the shell stability is affected by iron oxide presence. Copyright © 2014 Elsevier B.V. All rights reserved.

Production and decay of K -shell hollow krypton in collisions with 52-197-MeV/u bare xenon ions

NASA Astrophysics Data System (ADS)

Shao, Caojie; Yu, Deyang; Cai, Xiaohong; Chen, Xi; Ma, Kun; Evslin, Jarah; Xue, Yingli; Wang, Wei; Kozhedub, Yury S.; Lu, Rongchun; Song, Zhangyong; Zhang, Mingwu; Liu, Junliang; Yang, Bian; Guo, Yipan; Zhang, Jianming; Ruan, Fangfang; Wu, Yehong; Zhang, Yuezhao; Dong, Chenzhong; Chen, Ximeng; Yang, Zhihu

2017-07-01

X-ray spectra of K -shell hollow krypton atoms produced in single collisions with 52-197-MeV/u X e54 + ions are measured in a heavy-ion storage ring equipped with an internal gas-jet target. Energy shifts of the K α1,2 s , K α1,2 h ,s , and K β1,3 s transitions are obtained. Thus the average number of the spectator L vacancies presented during the x-ray emission is deduced. From the relative intensities of the K α1,2 s and K α1,2 h ,s transitions, the ratio of K -shell hollow krypton to singly K -shell ionized atoms is determined to be 14 %-24 % . In the considered collisions, the K vacancies are mainly created by the direct ionization which cannot be calculated within the perturbation descriptions. The experimental results are compared with a relativistic coupled-channel calculation performed within the independent particle approximation.

Visualising crystal packing interactions in solid-state NMR: Concepts and applications

NASA Astrophysics Data System (ADS)

Zilka, Miri; Sturniolo, Simone; Brown, Steven P.; Yates, Jonathan R.

2017-10-01

In this article, we introduce and apply a methodology, based on density functional theory and the gauge-including projector augmented wave approach, to explore the effects of packing interactions on solid-state nuclear magnetic resonance (NMR) parameters. A visual map derived from a so-termed "magnetic shielding contribution field" can be made of the contributions to the magnetic shielding of a specific site—partitioning the chemical shift to specific interactions. The relation to the established approaches of examining the molecule to crystal change in the chemical shift and the nuclear independent chemical shift is established. The results are applied to a large sample of 71 molecular crystals and three further specific examples from supermolecular chemistry and pharmaceuticals. This approach extends the NMR crystallography toolkit and provides insight into the development of both cluster based approaches to the predictions of chemical shifts and for empirical predictions of chemical shifts in solids.

Using NMR chemical shifts to calculate the propensity for structural order and disorder in proteins.

PubMed

Tamiola, Kamil; Mulder, Frans A A

2012-10-01

NMR spectroscopy offers the unique possibility to relate the structural propensities of disordered proteins and loop segments of folded peptides to biological function and aggregation behaviour. Backbone chemical shifts are ideally suited for this task, provided that appropriate reference data are available and idiosyncratic sensitivity of backbone chemical shifts to structural information is treated in a sensible manner. In the present paper, we describe methods to detect structural protein changes from chemical shifts, and present an online tool [ncSPC (neighbour-corrected Structural Propensity Calculator)], which unites aspects of several current approaches. Examples of structural propensity calculations are given for two well-characterized systems, namely the binding of α-synuclein to micelles and light activation of photoactive yellow protein. These examples spotlight the great power of NMR chemical shift analysis for the quantitative assessment of protein disorder at the atomic level, and further our understanding of biologically important problems.

Three Dimensional Characterization of Typical Urban and Desert Particles: Implications to Particle Optics

NASA Astrophysics Data System (ADS)

Goel, V.; Mishra, S.; Ahlawat, A. S.; Sharma, C.; Kotnala, R. K.

2017-12-01

Aerosol particles are generally considered as chemically homogeneous spheres in the retrieval techniques of ground and space borne observations which is not accurate approach and can lead to erroneous observations. For better simulation of optical and radiative properties of aerosols, a good knowledge of aerosol's morphology, chemical composition and internal structure is essential. Till date, many studies have reported the morphology and chemical composition of particles but very few of them provide internal structure and spatial distribution of different chemical species within the particle. The research on the effect of particle internal structure and its contribution to particle optics is extremely limited. In present work, we characterize the PM10 particles collected form typical arid (the Thar Desert, Rajasthan, India) and typical urban (New Delhi, India) environment using microscopic techniques. The particles were milled several times to investigate their internal structure. The EDS (Energy Dispersive X-ray Spectroscopy) spectra were recorded after each milling to check the variation in the chemical composition. In arid environment, Fe, Ca, C, Al, and Mg rich shell was observed over a Si rich particle whereas in urban environment, shell of Hg, Ag, C and N was observed over a Cu rich particle. Based on the observations, different model shapes [homogenous sphere and spheroid; heterogeneous sphere and spheroid; core shell] have been considered for assessing the associated uncertainties with the routine modeling of optical properties where volume equivalent homogeneous sphere approximation is considered. The details will be discussed during presentation.

Cell-in-Shell Hybrids: Chemical Nanoencapsulation of Individual Cells.

PubMed

Park, Ji Hun; Hong, Daewha; Lee, Juno; Choi, Insung S

2016-05-17

Nature has developed a fascinating strategy of cryptobiosis ("secret life") for counteracting the stressful, and often lethal, environmental conditions that fluctuate sporadically over time. For example, certain bacteria sporulate to transform from a metabolically active, vegetative state to an ametabolic endospore state. The bacterial endospores, encased within tough biomolecular shells, withstand the extremes of harmful stressors, such as radiation, desiccation, and malnutrition, for extended periods of time and return to a vegetative state by breaking their protective shells apart when their environment becomes hospitable for living. Certain ciliates and even higher organisms, for example, tardigrades, and others are also found to adopt a cryptobiotic strategy for survival. A common feature of cryptobiosis is the structural presence of tough sheaths on cellular structures. However, most cells and cellular assemblies are not "spore-forming" and are vulnerable to the outside threats. In particular, mammalian cells, enclosed with labile lipid bilayers, are highly susceptible to in vitro conditions in the laboratory and daily life settings, making manipulation and preservation difficult outside of specialized conditions. The instability of living cells has been a main bottleneck to the advanced development of cell-based applications, such as cell therapy and cell-based sensors. A judicious question arises: can cellular tolerance against harmful stresses be enhanced by simply forming cell-in-shell hybrid structures? Experimental results suggest that the answer is yes. A micrometer-sized "Iron Man" can be generated by chemically forming an ultrathin (<100 nm) but durable shell on a "non-spore-forming" cell. Since the report on silica nanoencapsulation of yeast cells, in which cytoprotective yeast-in-silica hybrids were formed, several synthetic strategies have been developed to encapsulate individual cells in a cytocompatible fashion, mimicking the cryptobiotic cell-in-shell structures found in nature, for example, bacterial endospores. Bioinspired silicification and phenolics-based coatings are, so far, the main approaches to the formation of cytoprotective cell-in-shell hybrids, because they ensure cell viability during encapsulations and also generate durable nanoshells on cell surfaces. The resulting cell-in-shell hybrids extrinsically possess enhanced resistance to external aggressors, and more intriguingly, the encapsulation alters their metabolic activity, exemplified by retarded or suppressed cell cycle progression. In addition, recent developments in the field have further advanced the synthetic tools available to the stage of chemical sporulation and germination of mammalian cells, where cytoprotective shells are formed on labile mammalian cells and broken apart on demand. For example, individual HeLa cells are coated with a metal-organic complex of ferric ion and tannic acid, and cellular adherence and proliferation are controlled by the programmed shell formation and degradation. Based on these demonstrations, the (degradable) cell-in-shell hybrids are anticipated to find their applications in various biomedical and bionanotechnological areas, such as cytotherapeutics, high-throughput screening, sensors, and biocatalysis, as well as providing a versatile research platform for single-cell biology.

The argonaut shell: gas-mediated buoyancy control in a pelagic octopus

PubMed Central

Finn, Julian K.; Norman, Mark D.

2010-01-01

Argonauts (Cephalopoda: Argonautidae) are a group of rarely encountered open-ocean pelagic octopuses with benthic ancestry. Female argonauts inhabit a brittle ‘paper nautilus’ shell, the role of which has puzzled naturalists for millennia. The primary role attributed to the shell has been as a receptacle for egg deposition and brooding. Our observations of wild argonauts have revealed that the thin calcareous shell also functions as a hydrostatic structure, employed by the female argonaut to precisely control buoyancy at varying depths. Female argonauts use the shell to ‘gulp’ a measured volume of air at the sea surface, seal off the captured gas using flanged arms and forcefully dive to a depth where the compressed gas buoyancy counteracts body weight. This process allows the female argonaut to attain neutral buoyancy at depth and potentially adjust buoyancy to counter the increased (and significant) weight of eggs during reproductive periods. Evolution of this air-capture strategy enables this negatively buoyant octopus to survive free of the sea floor. This major shift in life mode from benthic to pelagic shows strong evolutionary parallels with the origins of all cephalopods, which attained gas-mediated buoyancy via the closed-chambered shells of the true nautiluses and their relatives. PMID:20484241

Oxygen and carbon isotopes in terrestrial mollusk shells. From modern to fossil values, climatic impact on the mollusk diet.

NASA Astrophysics Data System (ADS)

Metref, S.; Labonne, M.; Rousseau, D.; Rousseau, D.; Bentaleb, I.; Vianey-Liaud, M.

2001-12-01

Stable isotope studies on fossil material as well as on sediment have been very successful these past years indicating such method a very promising Quaternary paleonvironmental index for continental studies. Although most of the studies on fossil material was related to modern material collected near the fossil record, no precise analysis of the impact of the diet and precipitation was carried out in order to justify the previous assumptions. Here we present the results of two sets of analysis from terrestrial mollusk shells, a particularly good climate indicator. On one hand, individuals from hatched eggs of raised Helix aspersa were fed with different plants characteristic of the two main photosynthetic pathways (C3 and C4), and waters of different isotopic values. The shells were analyzed in order to observe the impact of the food diet and of the precipitation on the isotope content of the shell carbonate. On the other hand, the study of fossil shells (Vertigo modesta) from the loess series of the Great Plains, an area where shifts in photosynthetic pathways where detected during the last isotopic stage 2 (24,000-12,000 yr B.P.), is carried out. The interpretation of the results is based on those of the study of modern shells

Highly Stretchable and Transparent Supercapacitor by Ag-Au Core-Shell Nanowire Network with High Electrochemical Stability.

PubMed

Lee, Habeom; Hong, Sukjoon; Lee, Jinhwan; Suh, Young Duk; Kwon, Jinhyeong; Moon, Hyunjin; Kim, Hyeonseok; Yeo, Junyeob; Ko, Seung Hwan

2016-06-22

Stretchable and transparent electronics have steadily attracted huge attention in wearable devices. Although Ag nanowire is the one of the most promising candidates for transparent and stretchable electronics, its electrochemical instability has forbidden its application to the development of electrochemical energy devices such as supercapacitors. Here, we introduce a highly stretchable and transparent supercapacitor based on electrochemically stable Ag-Au core-shell nanowire percolation network electrode. We developed a simple solution process to synthesize the Ag-Au core-shell nanowire with excellent electrical conductivity as well as greatly enhanced chemical and electrochemical stabilities compared to pristine Ag nanowire. The proposed core-shell nanowire-based supercapacitor still possesses fine optical transmittance and outstanding mechanical stability up to 60% strain. The Ag-Au core-shell nanowire can be a strong candidate for future wearable electrochemical energy devices.

Densification control and analysis of outer shell of new high-temperature vacuum insulated composite

NASA Astrophysics Data System (ADS)

Wang, Yang; Chen, Zhaofeng; Jiang, Yun; Yu, Shengjie; Xu, Tengzhou; Li, Binbin; Chen, Zhou

2017-11-01

A novel high temperature vacuum insulated composite with low thermal conductivity composed of SiC foam core material and sealing outer shell is discussed, which will have a great potential to be used as thermal protection system material. In this composite, the outer shell is the key to maintain its internal vacuum, which is consisted of 2.5D C/C and SiC coating. So the densification processes of outer shell, including 2.5D braiding process, chemical vapor infiltration (CVI) pyrolytic carbon (PyC) process, polymer infiltration and pyrolysis (PIP) glassy carbon (GC) process and chemical vapor deposition (CVD) SiC process, are focused in this paper. The measuring result of the gas transmission quantity of outer shell is only 0.14 cm3/m2 · d · Pa after 5 times CVD processes, which is two order of magnitude lower than that sample deposited one time. After 10 times thermal shock cycles, the gas transmission quantity increases to 1.2 cm3/m2 · d · Pa. The effective thermal conductivity of high temperature vacuum insulated composite ranged from 0.19 W m-1 K-1 to 0.747 W m-1 K-1 within the temperature from 20 °C to 900 °C. Even after 10 thermal shock cycles, the variation of the effective thermal conductivity is still consistent with that without treatments.

Fabrication of Hierarchical Layer-by-Layer Assembled Diamond-based Core-Shell Nanocomposites as Highly Efficient Dye Absorbents for Wastewater Treatment

NASA Astrophysics Data System (ADS)

Zhao, Xinna; Ma, Kai; Jiao, Tifeng; Xing, Ruirui; Ma, Xilong; Hu, Jie; Huang, Hao; Zhang, Lexin; Yan, Xuehai

2017-03-01

The effective chemical modification and self-assembly of diamond-based hierarchical composite materials are of key importance for a broad range of diamond applications. Herein, we report the preparation of novel core-shell diamond-based nanocomposites for dye adsorption toward wastewater treatment through a layer-by-layer (LbL) assembled strategy. The synthesis of the reported composites began with the carboxyl functionalization of microdiamond by the chemical modification of diamond@graphene oxide composite through the oxidation of diamond@graphite. The carboxyl-terminated microdiamond was then alternatively immersed in the aqueous solution of amine-containing polyethylenimine and carboxyl-containing poly acrylic acid, which led to the formation of adsorption layer on diamond surface. Alternating (self-limiting) immersions in the solutions of the amine-containing and carboxyl-containing polymers were continued until the desired number of shell layers were formed around the microdiamond. The obtained core-shell nanocomposites were successfully synthesized and characterized by morphological and spectral techniques, demonstrating higher surface areas and mesoporous structures for good dye adsorption capacities than nonporous solid diamond particles. The LbL-assembled core-shell nanocomposites thus obtained demonstrated great adsorption capacity by using two model dyes as pollutants for wastewater treatment. Therefore, the present work on LbL-assembled diamond-based composites provides new alternatives for developing diamond hybrids as well as nanomaterials towards wastewater treatment applications.

Protein Structure Validation and Refinement Using Amide Proton Chemical Shifts Derived from Quantum Mechanics

PubMed Central

Christensen, Anders S.; Linnet, Troels E.; Borg, Mikael; Boomsma, Wouter; Lindorff-Larsen, Kresten; Hamelryck, Thomas; Jensen, Jan H.

2013-01-01

We present the ProCS method for the rapid and accurate prediction of protein backbone amide proton chemical shifts - sensitive probes of the geometry of key hydrogen bonds that determine protein structure. ProCS is parameterized against quantum mechanical (QM) calculations and reproduces high level QM results obtained for a small protein with an RMSD of 0.25 ppm (r = 0.94). ProCS is interfaced with the PHAISTOS protein simulation program and is used to infer statistical protein ensembles that reflect experimentally measured amide proton chemical shift values. Such chemical shift-based structural refinements, starting from high-resolution X-ray structures of Protein G, ubiquitin, and SMN Tudor Domain, result in average chemical shifts, hydrogen bond geometries, and trans-hydrogen bond (h3 JNC') spin-spin coupling constants that are in excellent agreement with experiment. We show that the structural sensitivity of the QM-based amide proton chemical shift predictions is needed to obtain this agreement. The ProCS method thus offers a powerful new tool for refining the structures of hydrogen bonding networks to high accuracy with many potential applications such as protein flexibility in ligand binding. PMID:24391900

A Magic-Angle Spinning NMR Method for the Site-Specific Measurement of Proton Chemical-Shift Anisotropy in Biological and Organic Solids.

PubMed

Hou, Guangjin; Gupta, Rupal; Polenova, Tatyana; Vega, Alexander J

2014-02-01

Proton chemical shifts are a rich probe of structure and hydrogen bonding environments in organic and biological molecules. Until recently, measurements of 1 H chemical shift tensors have been restricted to either solid systems with sparse proton sites or were based on the indirect determination of anisotropic tensor components from cross-relaxation and liquid-crystal experiments. We have introduced an MAS approach that permits site-resolved determination of CSA tensors of protons forming chemical bonds with labeled spin-1/2 nuclei in fully protonated solids with multiple sites, including organic molecules and proteins. This approach, originally introduced for the measurements of chemical shift tensors of amide protons, is based on three RN -symmetry based experiments, from which the principal components of the 1 H CS tensor can be reliably extracted by simultaneous triple fit of the data. In this article, we expand our approach to a much more challenging system involving aliphatic and aromatic protons. We start with a review of the prior work on experimental-NMR and computational-quantum-chemical approaches for the measurements of 1 H chemical shift tensors and for relating these to the electronic structures. We then present our experimental results on U- 13 C, 15 N-labeled histdine demonstrating that 1 H chemical shift tensors can be reliably determined for the 1 H 15 N and 1 H 13 C spin pairs in cationic and neutral forms of histidine. Finally, we demonstrate that the experimental 1 H(C) and 1 H(N) chemical shift tensors are in agreement with Density Functional Theory calculations, therefore establishing the usefulness of our method for characterization of structure and hydrogen bonding environment in organic and biological solids.

Adsorption Studies of Chromium(VI) on Activated Carbon Derived from Mangifera indica (Mango) Seed Shell

NASA Astrophysics Data System (ADS)

Mise, Shashikant; Patil, Trupti Nagendra

2015-09-01

The removal of chromium(VI) from synthetic sample by adsorption on activated carbon prepared from Mangifera indica (mango) seed shell have been carried out at room temperature 32 ± 1 °C. The removal of chromium(VI) from synthetic sample by adsorption on two types of activated carbon, physical activation and chemical activation (Calcium chloride and Sodium chloride), Impregnation Ratio's (IR) 0.25, 0.50, 0.75 for optimum time, optimum dosages and variation of pH were studied. It is observed that contact time differs for different carbons i.e. for physically and chemically activated carbons. The contact time decreases for chemically activated carbon compared to the physically activated carbon. It was observed that as dosage increases the adsorption increased along with the increase in impregnation ratio. It was also noted that as I.R. increases the surface area of Mangifera indica shell carbon increased. These dosage data were considered in the construction of isotherms and it was found that adsorption obeys Freundlich Isotherm and does not obey Langmuir Isotherm. The maximum removal of chromium (VI) was obtained in highly acidic medium at a pH of 1.50.

Incorporation of Copper Enhances the Anti-Ageing Property of Flame-Sprayed High-Density Polyethylene Coatings

NASA Astrophysics Data System (ADS)

Jia, Zhengmei; Huang, Jing; Gong, Yongfeng; Jin, Peipeng; Suo, Xinkun; Li, Hua

2017-02-01

High-density polyethylene (HDPE)-copper (Cu) composite coatings were prepared through depositing HDPE-Cu core-shell particles by flame spraying. The HDPE-Cu composite coatings and the HDPE coatings were aged in xenon lamp ageing testing chamber. The variations of chemical compositions and surface morphology of the coatings before and after the ageing testing were analyzed using infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and ultraviolet-visible spectrophotometer. Results show that there is no chemical composition variation in the HDPE-Cu coatings. Cracks were found on the surfaces of the HDPE coatings, while the HDPE-Cu coating shows almost intact surface morphology. These results suggest that the HDPE-Cu coatings present better anti-ageing performances than the HDPE coatings. Further assessment of the function of Cu shells on the anti-ageing property reveals that Cu shells not only enhanced the absorption of the coatings to ultraviolet, but also increased their reflectivity to visible light. Additionally, the Cu shells enhanced the decomposition temperature and thermal stability of HDPE in the composite coatings. These results give bright insight into potential anti-ageing applications of the polymer-based structures.

Enhanced Performance of Photoelectrochemical Water Splitting with ITO@α-Fe2O3 Core-Shell Nanowire Array as Photoanode.

PubMed

Yang, Jie; Bao, Chunxiong; Yu, Tao; Hu, Yingfei; Luo, Wenjun; Zhu, Weidong; Fu, Gao; Li, Zhaosheng; Gao, Hao; Li, Faming; Zou, Zhigang

2015-12-09

Hematite (α-Fe2O3) is one of the most promising candidates for photoelectrodes in photoelectrochemical water splitting system. However, the low visible light absorption coefficient and short hole diffusion length of pure α-Fe2O3 limits the performance of α-Fe2O3 photoelectrodes in water splitting. Herein, to overcome these drawbacks, single-crystalline tin-doped indium oxide (ITO) nanowire core and α-Fe2O3 nanocrystal shell (ITO@α-Fe2O3) electrodes were fabricated by covering the chemical vapor deposited ITO nanowire array with compact thin α-Fe2O3 nanocrystal film using chemical bath deposition (CBD) method. The J-V curves and IPCE of ITO@α-Fe2O3 core-shell nanowire array electrode showed nearly twice as high performance as those of the α-Fe2O3 on planar Pt-coated silicon wafers (Pt/Si) and on planar ITO substrates, which was considered to be attributed to more efficient hole collection and more loading of α-Fe2O3 nanocrystals in the core-shell structure than planar structure. Electrochemical impedance spectra (EIS) characterization demonstrated a low interface resistance between α-Fe2O3 and ITO nanowire arrays, which benefits from the well contact between the core and shell. The stability test indicated that the prepared ITO@α-Fe2O3 core-shell nanowire array electrode was stable under AM1.5 illumination during the test period of 40,000 s.

Determination on the chemical composition of Ammonia beccarii shell using SEM and EDX: Preliminary study of benthic foraminifera capacity in response to anthropogenic metal contamination in coastal areas

NASA Astrophysics Data System (ADS)

Rositasari, R.; Suratno; Yogaswara, D.

2018-02-01

The use of single-celled and shelled biota, such as foraminifera that lives as benthic, in coastal environmental monitoring activity is very efficient. Several species of the Ammonia have been used as a proxy of various aquatic environmental monitoring activities. Chemical constituents screening in foraminiferal shell is a step ahead to identify the capacity of benthic foraminifera in responding to anthropogenic metal contamination in coastal water areas. The initial hypothesis of this study is the calcite test of Ammonia beccarii binds the anthropogenic metal in its shell structure and triggers the deformation test. The normal and abnormal shells of Ammonia specimens from Jakarta Bay and Batam waters are used in this study. The Ponar grab was used to sample surface sediment in Jakarta Bay and Batam waters in 2015, and the short core was used to acquire substratum sediment in Jakarta Bay in 2011.The Ammonia beccarii shell was analyzed using SEM and EDX detectors (Scanning Electron Microscope and Energy Dispersive X-ray). The shooting was performed three times in each test, i.e. in the first chamber (proloculus), the last chamber and the chamber between the two. The main building blocks of the foraminifera test are oxygen with an average weight range of 42.86 - 58.79% and carbon with an average weight range of 17.69 - 26.32%. There is a tendency for low levels of C and O elements in the abnormal tests.

NMR crystallography of campho[2,3-c]pyrazole (Z' = 6): combining high-resolution 1H-13C solid-state MAS NMR spectroscopy and GIPAW chemical-shift calculations.

PubMed

Webber, Amy L; Emsley, Lyndon; Claramunt, Rosa M; Brown, Steven P

2010-09-30

(1)H-(13)C two-dimensional magic-angle spinning (MAS) solid-state NMR correlation spectra, recorded with the MAS-J-HMQC experiment, are presented for campho[2,3-c]pyrazole. For each (13)C moiety, there are six resonances associated with the six distinct molecules in the asymmetric unit cell (Z' = 6). The one-bond C-H correlations observed in the 2D (1)H-(13)C MAS-J-HMQC spectra allow the experimental determination of the (1)H and (13)C chemical shifts associated with the separate CH, CH(2), and CH(3) groups. (1)H and (13)C chemical shifts calculated by using the GIPAW (Gauge Including Projector Augmented Waves) plane-wave pseudopotential approach are presented. Calculations for the whole unit cell (12 × 29 = 348 atoms, with geometry optimization of all atoms) allow the assignment of the experimental (1)H and (13)C chemical shifts to the six distinct molecules. The calculated chemical shifts for the full crystal structure are compared with those for isolated molecules as extracted from the geometry-optimized crystal structure. In this way, the effect of intermolecular interactions on the observed chemical shifts is quantified. In particular, the calculations are sufficiently precise to differentiate the small (<1 ppm) differences between the (1)H chemical shifts of the six resonances associated with each distinct CH or CH(2) moiety.

Effects of water, sodium hypochlorite, peroxyacetic acid, and acidified sodium chlorite on in-shell hazelnuts inoculated with Salmonella enterica serovar Panama.

PubMed

Weller, Lisa D; Daeschel, Mark A; Durham, Catherine A; Morrissey, Michael T

2013-12-01

Recent foodborne disease outbreaks involving minimally processed tree nuts have generated a need for improved sanitation procedures. Chemical sprays and dips have shown promise for reducing pathogens on fresh produce, but little research has been conducted for in-shell hazelnuts. This study analyzed the effectiveness of 3 chemical sanitizers for reducing Salmonella on in-shell hazelnuts. Treatments of water, sodium hypochlorite (NaOCl; 25 and 50 ppm), peroxyacetic acid (PAA; 80 and 120 ppm), and acidified sodium chlorite (ASC; 450, 830, and 1013 ppm) were sprayed onto hazelnut samples inoculated with Salmonella enterica serovar Panama. Hazelnut samples were immersed in liquid cultures of S. Panama for 24 h, air-dried, and then sprayed with water and chemical treatments. Inoculation achieved S. Panama populations of approximately 8.04 log CFU/hazelnut. Surviving S. panama populations were evaluated using a nonselective medium (tryptic soy agar), incubated 3 h, and then overlaid with selective media (xylose lysine deoxycholate agar). All of the chemical treatments significantly reduced S. Panama populations (P ≤ 0.0001). The most effective concentrations of ASC, PAA, and NaOCl treatments reduced populations by 2.65, 1.46, and 0.66 log units, respectively. ASC showed the greatest potential for use as a postharvest sanitation treatment. © 2013 Institute of Food Technologists®

Camellia oleifera shell as an alternative feedstock for furfural production using a high surface acidity solid acid catalyst.

PubMed

Zhang, Luxin; He, Yunfei; Zhu, Yujie; Liu, Yuting; Wang, Xiaochang

2018-02-01

This paper focuses on the high-value transformation of camellia oleifera shell, which is an agricultural waste enriched in hemicellulose. An efficient catalytic route employing sulfonated swelling mesoporous polydivinylbenzene (PDVB-SO 3 H) as catalyst in monophasic or biphasic solvents was developed for the conversion of raw camellia oleifera shell into furfural. The reaction parameters were evaluated and optimized for improving the furfural yield. It was found that the solvent greatly influenced the hydrolysis of camellia oleifera shells, and the highest furfural yield of 61.3% was obtained in "γ-butyrolactone + water" system when the feedstock-to-catalyst ratio was 2 for 30 min at 443 K. Camellia oleifera shell exhibited a high potential as feedstock to produce furfural in high yields. The outcome of this study provides an attractive utilization option to camellia oleifera shell, which is currently burned or discarded for producing a bio-based chemical. Copyright © 2017 Elsevier Ltd. All rights reserved.

A solar-thermal energy harvesting scheme: enhanced heat capacity of molten HITEC salt mixed with Sn/SiO(x) core-shell nanoparticles.

PubMed

Lai, Chih-Chung; Chang, Wen-Chih; Hu, Wen-Liang; Wang, Zhiming M; Lu, Ming-Chang; Chueh, Yu-Lun

2014-05-07

We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiO(x) core-shell nanoparticles (NPs) embedded in a eutectic salt. The microstructures and chemical compositions of Sn/SiO(x) core-shell NPs were characterized. In situ heating XRD provides dynamic crystalline information about the Sn/SiO(x) core-shell NPs during cyclic heating processes. The latent heat of ∼29 J g(-1) for Sn/SiO(x) core-shell NPs was measured, and 30% enhanced heat capacity was achieved from 1.57 to 2.03 J g(-1) K(-1) for the HITEC solar salt without and with, respectively, a mixture of 5% Sn/SiO(x) core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants.

ShellFit: Reconstruction in the MiniCLEAN Detector

NASA Astrophysics Data System (ADS)

Seibert, Stanley

2010-02-01

The MiniCLEAN dark matter experiment is an ultra-low background liquid cryogen detector with a fiducial volume of approximately 150 kg. Dark matter candidate events produce ultraviolet scintillation light in argon at 128 nm and in neon at 80 nm. In order to detect this scintillation light, the target volume is enclosed by acrylic plates forming a spherical shell upon which an organic fluor, tetraphenyl butadiene (TPB), has been applied. TPB absorbs UV light and reemits visible light isotropically which can be detected by photomultiplier tubes. Two significant sources of background events in MiniCLEAN are decays of radon daughters embedded in the acrylic surface and external sources of neutrons, such as the photomultiplier tubes themselves. Both of these backgrounds can be mitigated by reconstructing the origin of the scintillation light and cutting events beyond a particular radius. The scrambling of photon trajectories at the TPB surface makes this task very challenging. The ``ShellFit'' algorithm for reconstructing event position and energy in a detector with a spherical wavelength-shifting shell will be described. The performance of ShellFit will be demonstrated using Monte Carlo simulation of several event types in the MiniCLEAN detector. )

The role of interfacial metal silicates on the magnetism in FeCo/SiO 2 and Fe 49% Co 49% V 2% /SiO 2 core/shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desautels, R. D.; Freeland, J. W.; Rowe, M. P.

2015-05-07

We have investigated the role of spontaneously formed interfacial metal silicates on the magnetism of FeCo/SiO2 and Fe49%Co49%V2%/SiO2 core/shell nanoparticles. Element specific x-ray absorption and photoelectron spectroscopy experiments have identified the characteristic spectral features of metallic iron and cobalt from within the nanoparticle core. In addition, metal silicates of iron, cobalt, and vanadium were found to have formed spontaneously at the interface between the nanoparticle core and silica shell. X-ray magnetic circular dichroism experiments indicated that the elemental magnetism was a result of metallic iron and cobalt with small components from the iron, cobalt, and vanadium silicates. Magnetometry experiments havemore » shown that there was no exchange bias loop shift in the FeCo nanoparticles; however, exchange bias from antiferromagnetic vanadium oxide was measured in the V-doped nanoparticles. These results showed clearly that the interfacial metal silicates played a significant role in the magnetism of these core/shell nanoparticles, and that the vanadium percolated from the FeCo-cores into the SiO2-based interfacial shell.« less

PbSe-Based Colloidal Core/Shell Heterostructures for Optoelectronic Applications

PubMed Central

Zaiats, Gary; Yanover, Diana; Vaxenburg, Roman; Tilchin, Jenya; Sashchiuk, Aldona; Lifshitz, Efrat

2014-01-01

Lead-based (IV–VI) colloidal quantum dots (QDs) are of widespread scientific and technological interest owing to their size-tunable band-gap energy in the near-infrared optical region. This article reviews the synthesis of PbSe-based heterostructures and their structural and optical investigations at various temperatures. The review focuses on the structures consisting of a PbSe core coated with a PbSexS1–x (0 ≤ x ≤ 1) or CdSe shell. The former-type shells were epitaxially grown on the PbSe core, while the latter-type shells were synthesized using partial cation-exchange. The influence of the QD composition and the ambient conditions, i.e., exposure to oxygen, on the QD optical properties, such as radiative lifetime, Stokes shift, and other temperature-dependent characteristics, was investigated. The study revealed unique properties of core/shell heterostructures of various compositions, which offer the opportunity of fine-tuning the QD electronic structure by changing their architecture. A theoretical model of the QD electronic band structure was developed and correlated with the results of the optical studies. The review also outlines the challenges related to potential applications of colloidal PbSe-based heterostructures. PMID:28788244

7Li(d,p)8Li transfer reaction in the NCSM/RGM approach

NASA Astrophysics Data System (ADS)

Raimondi, F.; Hupin, G.; Navrátil, P.; Quaglioni, S.

2018-03-01

Recently, we applied an ab initio method, the no-core shell model combined with the resonating group method, to the transfer reactions with light p-shell nuclei as targets and deuteron as the projectile. In particular, we studied the elastic scattering of deuterium on 7Li and the 7Li(d,p)8Li transfer reaction starting from a realistic two-nucleon interaction. In this contribution, we review of our main results on the 7Li(d,p)8Li transfer reaction, and we extend the study of the relevant reaction channels, by showing the dominant resonant phase shifts of the scattering matrix. We assess also the impact of the polarization effects of the deuteron below the breakup on the positive-parity resonant states in the reaction. For this purpose, we perform an analysis of the convergence trend of the phase and eigenphase shifts, with respect to the number of deuteron pseudostates included in the model space.

Reduced Dirac equation and Lamb shift as off-mass-shell effect in quantum electrodynamics

NASA Astrophysics Data System (ADS)

Ni, Guang-Jiong; Xu, Jian-Jun; Lou, Sen-Yue

2011-02-01

Based on the accurate experimental data of energy-level differences in hydrogen-like atoms, especially the 1S—2S transitions of hydrogen and deuterium, the necessity of introducing a reduced Dirac equation with reduced mass as the substitution of original electron mass is stressed. Based on new cognition about the essence of special relativity, we provide a reasonable argument for the reduced Dirac equation to have two symmetries, the invariance under the (newly defined) space-time inversion and that under the pure space inversion, in a noninertial frame. By using the reduced Dirac equation and within the framework of quantum electrodynamics in covariant form, the Lamb shift can be evaluated (at one-loop level) as the radiative correction on a bound electron staying in an off-mass-shell state—-a new approach eliminating the infrared divergence. Hence the whole calculation, though with limited accuracy, is simplified, getting rid of all divergences and free of ambiguity.

Shifting baselines in Antarctic ecosystems; ecophysiological response to warming in Lissarca miliaris at Signy Island, Antarctica.

PubMed

Reed, Adam J; Thatje, Sven; Linse, Katrin

2012-01-01

The Antarctic Peninsula has experienced a rapid increase in atmospheric temperature over the last 50 years. Whether or not marine organisms thriving in this cold stenothermal environment are able to cope with warming is of concern. Here, we present changes to the growth and shell characteristics of the ecologically important, small and short lived brooding bivalve Lissarca miliaris from Signy Island, Antarctica. Using material collected from the 1970's to the present day, we show an increase in growth rate and adult shell deterioration accompanied by a decrease in offspring size, associated with an increase in annual average temperatures. Critical changes to the bivalve's ecology seen today evidence the problem of a shift in baseline since the onset of warming recorded in Antarctica. These small bivalves are demonstrating ecophysiological responses to subtle warming that, provided warming continues, could soon surpass a physiological tipping point, adding to warming associated threats such as increased predatory pressure and ocean acidification.

Shifting Baselines in Antarctic Ecosystems; Ecophysiological Response to Warming in Lissarca miliaris at Signy Island, Antarctica

PubMed Central

Reed, Adam J.; Thatje, Sven; Linse, Katrin

2012-01-01

The Antarctic Peninsula has experienced a rapid increase in atmospheric temperature over the last 50 years. Whether or not marine organisms thriving in this cold stenothermal environment are able to cope with warming is of concern. Here, we present changes to the growth and shell characteristics of the ecologically important, small and short lived brooding bivalve Lissarca miliaris from Signy Island, Antarctica. Using material collected from the 1970's to the present day, we show an increase in growth rate and adult shell deterioration accompanied by a decrease in offspring size, associated with an increase in annual average temperatures. Critical changes to the bivalve's ecology seen today evidence the problem of a shift in baseline since the onset of warming recorded in Antarctica. These small bivalves are demonstrating ecophysiological responses to subtle warming that, provided warming continues, could soon surpass a physiological tipping point, adding to warming associated threats such as increased predatory pressure and ocean acidification. PMID:23285298

Modelling studies in aqueous solution of lanthanide (III) chelates designed for nuclear magnetic resonance biomedical applications

NASA Astrophysics Data System (ADS)

Henriques, E. S.; Geraldes, C. F. G. C.; Ramos, M. J.

Molecular dynamics simulations and complementary modelling studies have been carried out for the [Gd(DOTA)·(H2O)]- and [Tm(DOTP)]5- chelates in aqueous media, to provide a better understanding of several structural and dynamical properties of these versatile nuclear magnetic resonance (NMR) probes, including coordination shells and corresponding water exchange mechanisms, and interactions of these complexes with alkali metal ions. This knowledge is of key importance in the areas of 1H relaxation and shift reagents for NMR applications in medical diagnosis. A new refinement of our own previously developed set of parameters for these Ln(III) chelates has been used, and is reported here. Calculations of water mean residence times suggest a reassessment of the characterization of the chelates' second coordination shell, one where the simple spherical distribution model is discarded in favour of a more detailed approach. Na+ probe interaction maps are in good agreement with the available site location predictions derived from 23Na NMR shifts.

Elemental compositions of crab and snail shells from the Kueishantao hydrothermal field in the southwestern Okinawa Trough

NASA Astrophysics Data System (ADS)

Zeng, Zhigang; Ma, Yao; Wang, Xiaoyuan; Chen, Chen-Tung Arthur; Yin, Xuebo; Zhang, Suping; Zhang, Junlong; Jiang, Wei

2018-04-01

To reveal differences in the behavior of benthic vent animals, and the sources and sinks of biogeochemical and fluid circulations, it is necessary to constrain the chemical characteristics of benthic animals from seafloor hydrothermal fields. We measured the abundances of 27 elements in shells of the crab Xenograpsus testudinatus and the snail Anachis sp., collected from the Kueishantao hydrothermal field (KHF) in the southwestern Okinawa Trough, with the aim of improving our understanding of the compositional variations between individual vent organisms, and the sources of the rare earth elements (REEs) in their shells. The Mn, Hg, and K concentrations in the male X. testudinatus shells are found to be higher than those in female crab shells, whereas the reverse is true for the accumulation of B, implying that the accumulation of K, Mn, Hg, and B in the crab shells is influenced by sex. This is inferred to be a result of the asynchronous molting of the male and female crab shells. Snail shells are found to have higher Ca, Al, Fe, Ni, and Co concentrations than crab shells. This may be attributed to different metal accumulation times. The majority of the light rare earth element (LREE) distribution patterns in the crab and snail shells are similar to those of Kueishantao vent fluids, with the crab and snail shells also exhibiting LREE enrichment, implying that the LREEs contained in crab and snail shells in the KHF are derived from vent fluids.

Water dynamics in protein hydration shells: the molecular origins of the dynamical perturbation.

PubMed

Fogarty, Aoife C; Laage, Damien

2014-07-17

Protein hydration shell dynamics play an important role in biochemical processes including protein folding, enzyme function, and molecular recognition. We present here a comparison of the reorientation dynamics of individual water molecules within the hydration shell of a series of globular proteins: acetylcholinesterase, subtilisin Carlsberg, lysozyme, and ubiquitin. Molecular dynamics simulations and analytical models are used to access site-resolved information on hydration shell dynamics and to elucidate the molecular origins of the dynamical perturbation of hydration shell water relative to bulk water. We show that all four proteins have very similar hydration shell dynamics, despite their wide range of sizes and functions, and differing secondary structures. We demonstrate that this arises from the similar local surface topology and surface chemical composition of the four proteins, and that such local factors alone are sufficient to rationalize the hydration shell dynamics. We propose that these conclusions can be generalized to a wide range of globular proteins. We also show that protein conformational fluctuations induce a dynamical heterogeneity within the hydration layer. We finally address the effect of confinement on hydration shell dynamics via a site-resolved analysis and connect our results to experiments via the calculation of two-dimensional infrared spectra.

Water Dynamics in Protein Hydration Shells: The Molecular Origins of the Dynamical Perturbation

PubMed Central

2014-01-01

Protein hydration shell dynamics play an important role in biochemical processes including protein folding, enzyme function, and molecular recognition. We present here a comparison of the reorientation dynamics of individual water molecules within the hydration shell of a series of globular proteins: acetylcholinesterase, subtilisin Carlsberg, lysozyme, and ubiquitin. Molecular dynamics simulations and analytical models are used to access site-resolved information on hydration shell dynamics and to elucidate the molecular origins of the dynamical perturbation of hydration shell water relative to bulk water. We show that all four proteins have very similar hydration shell dynamics, despite their wide range of sizes and functions, and differing secondary structures. We demonstrate that this arises from the similar local surface topology and surface chemical composition of the four proteins, and that such local factors alone are sufficient to rationalize the hydration shell dynamics. We propose that these conclusions can be generalized to a wide range of globular proteins. We also show that protein conformational fluctuations induce a dynamical heterogeneity within the hydration layer. We finally address the effect of confinement on hydration shell dynamics via a site-resolved analysis and connect our results to experiments via the calculation of two-dimensional infrared spectra. PMID:24479585

Core-shell TiO2@ZnO nanorods for efficient ultraviolet photodetection.

PubMed

Panigrahi, Shrabani; Basak, Durga

2011-05-01

Core-shell TiO(2)@ZnO nanorods (NRs) have been fabricated by a simple two step method: growth of ZnO NRs' array by an aqueous chemical technique and then coating of the NRs with a solution of titanium isopropoxide [Ti(OC(3)H(7))(4)] followed by a heating step to form the shell. The core-shell nanocomposites are composed of single-crystalline ZnO NRs, coated with a thin TiO(2) shell layer obtained by varying the number of coatings (one, three and five times). The ultraviolet (UV) emission intensity of the nanocomposite is largely quenched due to an efficient electron-hole separation reducing the band-to-band recombinations. The UV photoconductivity of the core-shell structure with three times TiO(2) coating has been largely enhanced due to photoelectron transfer between the core and the shell. The UV photosensitivity of the nanocomposite becomes four times larger while the photocurrent decay during steady UV illumination has been decreased almost by 7 times compared to the as-grown ZnO NRs indicating high efficiency of these core-shell structures as UV sensors. © The Royal Society of Chemistry 2011

Large-area super-resolution optical imaging by using core-shell microfibers

NASA Astrophysics Data System (ADS)

Liu, Cheng-Yang; Lo, Wei-Chieh

2017-09-01

We first numerically and experimentally report large-area super-resolution optical imaging achieved by using core-shell microfibers. The particular spatial electromagnetic waves for different core-shell microfibers are studied by using finite-difference time-domain and ray tracing calculations. The focusing properties of photonic nanojets are evaluated in terms of intensity profile and full width at half-maximum along propagation and transversal directions. In experiment, the general optical fiber is chemically etched down to 6 μm diameter and coated with different metallic thin films by using glancing angle deposition. The direct imaging of photonic nanojets for different core-shell microfibers is performed with a scanning optical microscope system. We show that the intensity distribution of a photonic nanojet is highly related to the metallic shell due to the surface plasmon polaritons. Furthermore, large-area super-resolution optical imaging is performed by using different core-shell microfibers placed over the nano-scale grating with 150 nm line width. The core-shell microfiber-assisted imaging is achieved with super-resolution and hundreds of times the field-of-view in contrast to microspheres. The possible applications of these core-shell optical microfibers include real-time large-area micro-fluidics and nano-structure inspections.

A colorimetric assay for measuring iodide using Au@Ag core-shell nanoparticles coupled with Cu(2+).

PubMed

Zeng, Jingbin; Cao, Yingying; Lu, Chun-Hua; Wang, Xu-Dong; Wang, Qianru; Wen, Cong-Ying; Qu, Jian-Bo; Yuan, Cunguang; Yan, Zi-Feng; Chen, Xi

2015-09-03

Au@Ag core-shell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu(2+)) for the colorimetric sensing of iodide ion (I(-)). This assay relies on the fact that the absorption spectra and the color of metallic core-shell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I(-) was added to the Au@Ag core-shell NPs-Cu(2+) system/solution, Cu(2+) can oxidize I(-) into iodine (I2), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core-shell NPs led to color changes from yellow to purple, which was utilized for the colorimetric sensing of I(-). The assay only took 10 min with a lowest detectable concentration of 0.5 μM, and it exhibited excellent selectivity for I(-) over other common anions tested. Furthermore, Au@Ag core-shell NPs-Cu(2+) was embedded into agarose gels as inexpensive and portable "test strips", which were successfully used for the semi-quantitation of I(-) in dried kelps. Copyright © 2015 Elsevier B.V. All rights reserved.

Radio observations of globulettes in the Carina nebula

NASA Astrophysics Data System (ADS)

Haikala, L. K.; Gahm, G. F.; Grenman, T.; Mäkelä, M. M.; Persson, C. M.

2017-06-01

Context. The Carina nebula hosts a large number of globulettes. An optical study of these tiny molecular clouds shows that the majority are of planetary mass, but there are also those with masses of several tens up to a few hundred Jupiter masses. Aims: We seek to search for, and hopefully detect, molecular line emission from some of the more massive objects; in case of successful detection we aim to map their motion in the Carina nebula complex and derive certain physical properties. Methods: We carried out radio observations of molecular line emission in 12CO and 13CO (2-1) and (3-2) of 12 globulettes in addition to positions in adjacent shell structures using APEX. Results: All selected objects were detected with radial velocities shifted relative to the emission from related shell structures and background molecular clouds. Globulettes along the western part of an extended dust shell show a small spread in velocity with small velocity shifts relative to the shell. This system of globulettes and shell structures in the foreground of the bright nebulosity surrounding the cluster Trumpler 14 is expanding with a few km s-1 relative to the cluster. A couple of isolated globulettes in the area move at similar speed. Compared to similar studies of the molecular line emission from globulettes in the Rosette nebula, we find that the integrated line intensity ratios and line widths are very different. The results show that the Carina objects have a different density/temperature structure than those in the Rosette nebula. In comparison the apparent size of the Carina globulettes is smaller, owing to the larger distance, and the corresponding beam filling factors are small. For this reason we were unable to carry out a more detailed modelling of the structure of the Carina objects in the way as performed for the Rosette objects. Conclusions: The Carina globulettes observed are compact and denser than objects of similar mass in the Rosette nebula. The distribution and velocities of these globulettes suggest that they have originated from eroding shells and elephant trunks. Some globulettes in the Trumpler 14 region are quite isolated and located far from any shell structures. These objects move at a similar speed as the globulettes along the shell, suggesting that they once formed from cloud fragments related to the same foreground shell. Based on observations collected with the Atacama Pathfinder Experiment (APEX), Llano Chajnantor, Chile (O-091.F-9316A and O-094.F-9312A).The final reduced radio data (FITS format) are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A61

Effects of gold diffusion on n-type doping of GaAs nanowires.

PubMed

Tambe, Michael J; Ren, Shenqiang; Gradecak, Silvija

2010-11-10

The deposition of n-GaAs shells is explored as a method of n-type doping in GaAs nanowires grown by the Au-mediated metal-organic chemical vapor deposition. Core-shell GaAs/n-GaAs nanowires exhibit an unintended rectifying behavior that is attributed to the Au diffusion during the shell deposition based on studies using energy dispersive X-ray spectroscopy, current-voltage, capacitance-voltage, and Kelvin probe force measurements. Removing the gold prior to n-type shell deposition results in the realization of n-type GaAs nanowires without rectification. We directly correlate the presence of gold impurities to nanowire electrical properties and provide an insight into the role of seed particles on the properties of nanowires and nanowire heterostructures.

On the possibility of room temperature ferromagnetism on chunk-shape BaSnO3/ZnO core/shell nanostructures

NASA Astrophysics Data System (ADS)

Rajamanickam, N.; Jayakumar, K.; Ramachandran, K.

2018-04-01

Core/shell BaSnO3/ZnO (BS-ZO) nanostructures were prepared by oxalate precipitation method and wet-chemical method. BaSnO3 (BSO) cubic perovskite structure and ZnO hexagonal wurtzite structure were confirmed by X-ray diffraction (XRD). The crystallite sizes is 23 nm, 29 nm and 27 nm for BSO, ZnO and BS-ZO, respectively. Chunk-shape and cuboids morphology observed from scanning electron microscopy (SEM) analysis. The magnetic properties were studied by VSM for bare and core-shell nano systems and the room temperature ferromagnetism observed for core-shell nanostructures. The BSO/ZnO shows enhanced coercivity and saturated magnetization as compared with BSO and ZnO nanostructures.

Tuning colloidal quantum dot band edge positions through solution-phase surface chemistry modification

DOE PAGES

Kroupa, Daniel M.; Vörös, Márton; Brawand, Nicholas P.; ...

2017-05-16

Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells and light emitting diodes. Here we show that band edge positions of lead sulfide (PbS) colloidal semiconductor nanocrystals, specifically quantum dots (QDs), can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control through the development of simple, robust and scalable solution-phase ligand exchange methods, which completely replace native ligands with functionalized cinnamate ligands, allowing for well-defined, highly tunable chemical systems. By combining experiments and ab initio simulations, we establish clear relationships between QD surface chemistry and the bandmore » edge positions of ligand/QD hybrid systems. We find that in addition to ligand dipole, inter-QD ligand shell inter-digitization contributes to the band edge shifts. As a result, we expect that our established relationships and principles can help guide future optimization of functional organic/inorganic hybrid nanostructures for diverse optoelectronic applications.« less

Tuning colloidal quantum dot band edge positions through solution-phase surface chemistry modification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kroupa, Daniel M.; Vörös, Márton; Brawand, Nicholas P.

Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells and light emitting diodes. Here we show that band edge positions of lead sulfide (PbS) colloidal semiconductor nanocrystals, specifically quantum dots (QDs), can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control through the development of simple, robust and scalable solution-phase ligand exchange methods, which completely replace native ligands with functionalized cinnamate ligands, allowing for well-defined, highly tunable chemical systems. By combining experiments and ab initio simulations, we establish clear relationships between QD surface chemistry and the bandmore » edge positions of ligand/QD hybrid systems. We find that in addition to ligand dipole, inter-QD ligand shell inter-digitization contributes to the band edge shifts. As a result, we expect that our established relationships and principles can help guide future optimization of functional organic/inorganic hybrid nanostructures for diverse optoelectronic applications.« less

Ocean acidification: the other CO2 problem.

PubMed

Doney, Scott C; Fabry, Victoria J; Feely, Richard A; Kleypas, Joan A

2009-01-01

Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Many calcifying species exhibit reduced calcification and growth rates in laboratory experiments under high-CO2 conditions. Ocean acidification also causes an increase in carbon fixation rates in some photosynthetic organisms (both calcifying and noncalcifying). The potential for marine organisms to adapt to increasing CO2 and broader implications for ocean ecosystems are not well known; both are high priorities for future research. Although ocean pH has varied in the geological past, paleo-events may be only imperfect analogs to current conditions.

Tuning colloidal quantum dot band edge positions through solution-phase surface chemistry modification

PubMed Central

Kroupa, Daniel M.; Vörös, Márton; Brawand, Nicholas P.; McNichols, Brett W.; Miller, Elisa M.; Gu, Jing; Nozik, Arthur J.; Sellinger, Alan; Galli, Giulia; Beard, Matthew C.

2017-01-01

Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells and light emitting diodes. Here we show that band edge positions of lead sulfide (PbS) colloidal semiconductor nanocrystals, specifically quantum dots (QDs), can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control through the development of simple, robust and scalable solution-phase ligand exchange methods, which completely replace native ligands with functionalized cinnamate ligands, allowing for well-defined, highly tunable chemical systems. By combining experiments and ab initio simulations, we establish clear relationships between QD surface chemistry and the band edge positions of ligand/QD hybrid systems. We find that in addition to ligand dipole, inter-QD ligand shell inter-digitization contributes to the band edge shifts. We expect that our established relationships and principles can help guide future optimization of functional organic/inorganic hybrid nanostructures for diverse optoelectronic applications. PMID:28508866

Spectroscopic study of the benchmark Mn+-H2 complex.

PubMed

Dryza, Viktoras; Poad, Berwyck L J; Bieske, Evan J

2009-05-28

We have recorded the rotationally resolved infrared spectrum of the weakly bound Mn+-H2 complex in the H-H stretch region (4022-4078 cm(-1)) by monitoring Mn+ photodissociation products. The band center of Mn+-H2, the H-H stretch transition, is shifted by -111.8 cm(-1) from the transition of the free H2 molecule. The spectroscopic data suggest that the Mn+-H2 complex consists of a slightly perturbed H2 molecule attached to the Mn+ ion in a T-shaped configuration with a vibrationally averaged intermolecular separation of 2.73 A. Together with the measured Mn+...H2 binding energy of 7.9 kJ/mol (Weis, P.; et al. J. Phys. Chem. A 1997, 101, 2809.), the spectroscopic parameters establish Mn+-H2 as the most thoroughly characterized transition-metal cation-dihydrogen complex and a benchmark for calibrating quantum chemical calculations on noncovalent systems involving open d-shell configurations. Such systems are of possible importance for hydrogen storage applications.

Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene: experiment and theory.

PubMed

Alagia, Michele; Baldacchini, Chiara; Betti, Maria Grazia; Bussolotti, Fabio; Carravetta, Vincenzo; Ekström, Ulf; Mariani, Carlo; Stranges, Stefano

2005-03-22

The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K-edge absorption spectrum present two main groups of discrete transitions between 283 and 288 eV photon energy, due to absorption to pi* virtual orbitals, and broader structures at higher energy, involving sigma* virtual orbitals. The sharp absorption structures to the pi* empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K-edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of pi* symmetry, from the six chemically shifted C 1s core orbitals.

Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene: Experiment and theory

NASA Astrophysics Data System (ADS)

Alagia, Michele; Baldacchini, Chiara; Betti, Maria Grazia; Bussolotti, Fabio; Carravetta, Vincenzo; Ekström, Ulf; Mariani, Carlo; Stranges, Stefano

2005-03-01

The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K-edge absorption spectrum present two main groups of discrete transitions between 283 and 288eV photon energy, due to absorption to π* virtual orbitals, and broader structures at higher energy, involving σ* virtual orbitals. The sharp absorption structures to the π* empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K-edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of π* symmetry, from the six chemically shifted C 1s core orbitals.

Tuning colloidal quantum dot band edge positions through solution-phase surface chemistry modification

NASA Astrophysics Data System (ADS)

Kroupa, Daniel M.; Vörös, Márton; Brawand, Nicholas P.; McNichols, Brett W.; Miller, Elisa M.; Gu, Jing; Nozik, Arthur J.; Sellinger, Alan; Galli, Giulia; Beard, Matthew C.

2017-05-01

Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells and light emitting diodes. Here we show that band edge positions of lead sulfide (PbS) colloidal semiconductor nanocrystals, specifically quantum dots (QDs), can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control through the development of simple, robust and scalable solution-phase ligand exchange methods, which completely replace native ligands with functionalized cinnamate ligands, allowing for well-defined, highly tunable chemical systems. By combining experiments and ab initio simulations, we establish clear relationships between QD surface chemistry and the band edge positions of ligand/QD hybrid systems. We find that in addition to ligand dipole, inter-QD ligand shell inter-digitization contributes to the band edge shifts. We expect that our established relationships and principles can help guide future optimization of functional organic/inorganic hybrid nanostructures for diverse optoelectronic applications.

Thermo-responsive plasmonic nanohybrids with tunable optical properties

NASA Astrophysics Data System (ADS)

Zhang, Lingyu; Song, Gang

2017-10-01

In this paper, we study the temperature-dependent optical properties of gold-silver core-shell (Au@Ag) nanorods coated by a thermo-responsive polymer poly (N-isopropylacrylamide) (PNIPAM). The wavelength of the plasmonic resonant absorption of the nanohybrids changes with temperature due to the combination effects of the plasmon resonance of the core and the thermal response of the shell. Using effective medium theory, we find that with increase of temperature, the absorption peak red-shifts due to the competition effects from the changes of the thickness and the effective refractive index of the polymer shell. The working wavelength can be tuned by the aspect ratio of nanorods. Moreover, the temperature sensitivity of plasmon resonance increases with the increase of the aspect ratio. Our studies provide a proof-of-concept design of thermal responsive plasmonic smart material.

Fragment-based 13C nuclear magnetic resonance chemical shift predictions in molecular crystals: An alternative to planewave methods

NASA Astrophysics Data System (ADS)

Hartman, Joshua D.; Monaco, Stephen; Schatschneider, Bohdan; Beran, Gregory J. O.

2015-09-01

We assess the quality of fragment-based ab initio isotropic 13C chemical shift predictions for a collection of 25 molecular crystals with eight different density functionals. We explore the relative performance of cluster, two-body fragment, combined cluster/fragment, and the planewave gauge-including projector augmented wave (GIPAW) models relative to experiment. When electrostatic embedding is employed to capture many-body polarization effects, the simple and computationally inexpensive two-body fragment model predicts both isotropic 13C chemical shifts and the chemical shielding tensors as well as both cluster models and the GIPAW approach. Unlike the GIPAW approach, hybrid density functionals can be used readily in a fragment model, and all four hybrid functionals tested here (PBE0, B3LYP, B3PW91, and B97-2) predict chemical shifts in noticeably better agreement with experiment than the four generalized gradient approximation (GGA) functionals considered (PBE, OPBE, BLYP, and BP86). A set of recommended linear regression parameters for mapping between calculated chemical shieldings and observed chemical shifts are provided based on these benchmark calculations. Statistical cross-validation procedures are used to demonstrate the robustness of these fits.

Fragment-based (13)C nuclear magnetic resonance chemical shift predictions in molecular crystals: An alternative to planewave methods.

PubMed

Hartman, Joshua D; Monaco, Stephen; Schatschneider, Bohdan; Beran, Gregory J O

2015-09-14

We assess the quality of fragment-based ab initio isotropic (13)C chemical shift predictions for a collection of 25 molecular crystals with eight different density functionals. We explore the relative performance of cluster, two-body fragment, combined cluster/fragment, and the planewave gauge-including projector augmented wave (GIPAW) models relative to experiment. When electrostatic embedding is employed to capture many-body polarization effects, the simple and computationally inexpensive two-body fragment model predicts both isotropic (13)C chemical shifts and the chemical shielding tensors as well as both cluster models and the GIPAW approach. Unlike the GIPAW approach, hybrid density functionals can be used readily in a fragment model, and all four hybrid functionals tested here (PBE0, B3LYP, B3PW91, and B97-2) predict chemical shifts in noticeably better agreement with experiment than the four generalized gradient approximation (GGA) functionals considered (PBE, OPBE, BLYP, and BP86). A set of recommended linear regression parameters for mapping between calculated chemical shieldings and observed chemical shifts are provided based on these benchmark calculations. Statistical cross-validation procedures are used to demonstrate the robustness of these fits.

Improved open-circuit voltage in polymer/oxide-nanoarray hybrid solar cells by formation of homogeneous metal oxide core/shell structures.

PubMed

Wu, Fan; Cui, Qi; Qiu, Zeliang; Liu, Changwen; Zhang, Hui; Shen, Wei; Wang, Mingtai

2013-04-24

Incorporation of vertically aligned nanorod/nanowire arrays of metal oxide (oxide-NAs) with a polymer can produce efficient hybrid solar cells with an ideal bulk-heterojunction architecture. However, polymer/oxide-NAs solar cells still suffer from a rather low (normally, < 0.4 V) open-circuit voltage (Voc). Here we demonstrate, for the first time, a novel strategy to improve the Voc in polymer/oxide-NAs solar cells by formation of homogeneous core/shell structures and reveal the intrinsic principles involved therein. A feasible hydrothermal-solvothermal combined method is developed for preparing homogeneous core/shell nanoarrays of metal oxides with a single-crystalline nanorod as core and the aggregation layer of corresponding metal oxide quantum dots (QDs) as shell, and the shell thickness (L) is easily controlled by the solvothermal reaction time for growing QDs on the nanorod. The core/shell formation dramatically improves the device Voc up to ca. 0.7-0.8 V depending on L. Based on steady-state and dynamic measurements, as well as modeling by space-charge-limited current method, it is found that the improved Voc originates from the up-shifted conduction band edge in the core by the interfacial dipole field resulting from the decreased mobility difference between photogenerated electrons and holes after the shell growth, which increases the energy difference between the quasi-Fermi levels of photogenerated electrons in the core and holes in the polymer for a higher Voc. Our results indicate that increasing Voc by the core/shell strategy seems not to be dependent on the kinds of metal oxides.

Synthesis and properties MFe2O4 (M = Fe, Co) nanoparticles and core-shell structures

NASA Astrophysics Data System (ADS)

Yelenich, O. V.; Solopan, S. O.; Greneche, J. M.; Belous, A. G.

2015-08-01

Individual Fe3-xO4 and CoFe2O4 nanoparticles, as well as Fe3-xO4/CoFe2O4 core/shell structures were synthesized by the method of co-precipitation from diethylene glycol solutions. Core/shell structure were synthesized with CoFe2O4-shell thickness of 1.0, 2.5 and 3.5 nm. X-ray diffraction patterns of individual nanoparticles and core/shell are similar and indicate that all synthesized samples have a cubic spinel structure. Compares Mössbauer studies of CoFe2O4, Fe3-xO4 nanoparticles indicate superparamagnetic properties at 300 K. It was shown that individual magnetite nanoparticles are transformed into maghemite through oxidation during the synthesis procedure, wherein the smallest nanoparticles are completely oxidized while a magnetite core does occur in the case of the largest nanoparticles. The Mössbauer spectra of core/shell nanoparticles with increasing CoFe2O4-shell thickness show a gradual decrease in the relative intensity of the quadrupole doublet and significant decrease of the mean isomer shift value at both RT and 77 K indicating a decrease of the superparamagnetic relaxation phenomena. Specific loss power for the prepared ferrofluids was experimentally calculated and it was determined that under influence of ac-magnetic field magnetic fluid based on individual CoFe2O4 and Fe3-xO4 particles are characterized by very low heating temperature, when magnetic fluids based on core/shell nanoparticles demonstrate higher heating effect.

First-principles calculations of Ti and O NMR chemical shift tensors in ferroelectric perovskites

NASA Astrophysics Data System (ADS)

Pechkis, Daniel; Walter, Eric; Krakauer, Henry

2011-03-01

Complementary chemical shift calculations were carried out with embedded clusters, using quantum chemistry methods, and with periodic boundary conditions, using the GIPAW approach within the Quantum Espresso package. Compared to oxygen chemical shifts, δ̂ (O), cluster calculations for δ̂ (Ti) were found to be more sensitive to size effects, termination, and choice of gaussian-type atomic basis set, while GIPAW results were found to be more sensitive to the pseudopotential construction. The two approaches complemented each other in optimizing these factors. We show that the two approaches yield comparable chemical shifts for suitably converged simulations, and results are compared with available experimental measurements. Supported by ONR.

13C and 15N—Chemical Shift Anisotropy of Ampicillin and Penicillin-V Studied by 2D-PASS and CP/MAS NMR

NASA Astrophysics Data System (ADS)

Antzutkin, Oleg N.; Lee, Young K.; Levitt, Malcolm H.

1998-11-01

The principal values of the chemical shift tensors of all13C and15N sites in two antibiotics, ampicillin and penicillin-V, were determined by 2-dimensionalphaseadjustedspinningsideband (2D-PASS) and conventional CP/MAS experiments. The13C and15N chemical shift anisotropies (CSA), and their confidence limits, were evaluated using a Mathematica program. The CSA values suggest a revised assignment of the 2-methyl13C sites in the case of ampicillin. We speculate on a relationship between the chemical shift principal values of many of the13C and15N sites and the β-lactam ring conformation.

Single and multi-layered core-shell structures based on ZnO nanorods obtained by aerosol assisted chemical vapor deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sáenz-Trevizo, A.; Amézaga-Madrid, P.; Pizá-Ruiz, P.

2015-07-15

Core–shell nanorod structures were prepared by a sequential synthesis using an aerosol assisted chemical vapor deposition technique. Several samples consisting of ZnO nanorods were initially grown over TiO{sub 2} film-coated borosilicate glass substrates, following the synthesis conditions reported elsewhere. Later on, a uniform layer consisting of individual Al, Ni, Ti or Fe oxides was grown onto ZnO nanorod samples forming the so-called single MO{sub x}/ZnO nanorod core–shell structures, where MO{sub x} was the metal oxide shell. Additionally, a three-layer core–shell sample was developed by growing Fe, Ti and Fe oxides alternately, onto the ZnO nanorods. The microstructure of the core–shellmore » materials was characterized by grazing incidence X-ray diffraction, scanning and transmission electron microscopy. Energy dispersive X-ray spectroscopy was employed to corroborate the formation of different metal oxides. X-ray diffraction outcomes for single core–shell structures showed solely the presence of ZnO as wurtzite and TiO{sub 2} as anatase. For the multi-layered shell sample, the existence of Fe{sub 2}O{sub 3} as hematite was also detected. Morphological observations suggested the existence of an outer material grown onto the nanorods and further microstructural analysis by HR-STEM confirmed the development of core–shell structures in all cases. These studies also showed that the individual Al, Fe, Ni and Ti oxide layers are amorphous; an observation that matched with X-ray diffraction analysis where no apparent extra oxides were detected. For the multi-layered sample, the development of a shell consisting of three different oxide layers onto the nanorods was found. Overall results showed that no alteration in the primary ZnO core was produced during the growth of the shells, indicating that the deposition technique used herein was and it is suitable for the synthesis of homogeneous and complex nanomaterials high in quality and purity. In addition, materials absorptance determined from the total transmittance and reflectance spectra revealed a broader absorption interval including visible light, indicating potential uses of these nanostructures on solar energy appliances. - Graphical abstract: Display Omitted - Highlights: • Uniform ZnO nanorods (core)–metal oxide (shell) were obtained sequentially by AACVD. • Shells were structured of homogeneous single or multi-layered non-mixed metal oxides. • ZnO nanorod core was preserved during the shell synthesis. • Optical absorptance revealed visible interval absorption for FeO{sub x} shell samples. • Materials can be suitable for photocatalytic or photovoltaic applications.« less

Effective Role of Magnetic Core-Shell Nanocomposites in Removing Organic and Inorganic Wastes from Water.

PubMed

Shah, Nasrullah; Claessyns, Frederick; Rimmer, Stephen; Arain, Muhammad Balal; Rehan, Touseef; Wazwaz, Aref; Ahmad, Mohammad Wasi; Ul-Islam, Mazhar

2016-01-01

Affordable and efficient water treatment process to produce water free from various contaminants is a big challenge. The presence of toxic heavy metals, dyes, hazardous chemicals and other toxins causes contamination of water sources and our food chain and make them hazardous to living organisms. The current water treatment processes are no longer sustainable due to high cost and low efficiency. Due to advantageous properties, nanotechnology based materials can play a great role in increasing the efficiency of water treatment processes. Magnetic nanocomposites use nano as well as magnetic properties and have the potential to provide a sophisticated system to overcome most of the impurities present in water. There is a diversity of magnetic nanocomposites, however presently we have focussed the core-shell magnetic nanocomposites because they have excellent magnetic and separation properties, stability, and good biocompatibility. We collected systematically the bibliographic data bases for peer-reviewed research literature focusing on the theme of our review. The quality of the included research papers are selected by standard tools. A conceptual frame work is designed to arrange the topics and extracted the interventions and findings of the included studies. The overall study was divided into sections and each section incorporated the most appropriate literature citation. Total one hundred and eight references were included of which 32 references were used for basic description/introduction of core-shell magnetic nanocomposites. One review paper containing the synthesis methods for core shell magnetic nanocomposites is included while majority (76) of the references are included for comprehensive description of applications of the core-shell nanocomposites among which 25 were for dyes removal, 27 for hazardous metals, 07 for hazardous chemicals, 12 for pesticides and biological contaminants removal and five other including patents were added as miscellaneous substances removal from water sources. This review identified the effective role of core-shell magnetic nanocomposites for environmental remediation in terms of removal of various hazardous substances from water resources. The outcome of the present review confirms that the magnetic core-shell nanocomposites provide a cost effective and efficient way for the removal of various toxic substances including dyes, heavy metals, toxic organic chemicals, pesticides and some biological contaminants from water sources.

Noise affects resource assessment in an invertebrate.

PubMed

Walsh, Erin P; Arnott, Gareth; Kunc, Hansjoerg P

2017-04-01

Anthropogenic noise is a global pollutant, affecting animals across taxa. However, how noise pollution affects resource acquisition is unknown. Hermit crabs ( Pagurus bernhardus ) engage in detailed assessment and decision-making when selecting a critical resource, their shell; this is crucial as individuals in poor shells suffer lower reproductive success and higher mortality. We experimentally exposed hermit crabs to anthropogenic noise during shell selection. When exposed to noise, crabs approached the shell faster, spent less time investigating it, and entered it faster. Our results demonstrate that changes in the acoustic environment affect the behaviour of hermit crabs by modifying the selection process of a vital resource. This is all the more remarkable given that the known cues used in shell selection involve chemical, visual and tactile sensory channels. Thus, our study provides rare evidence for a cross-modal impact of noise pollution. © 2017 The Author(s).

Atomic level characterization of cadmium selenide nanocrystal systems using atomic number contrast scanning transmission electron microscopy and Rutherford backscattering spectroscopy

NASA Astrophysics Data System (ADS)

McBride, James R.

This project involved the characterization of CdSe nanocrystals. Through the use of Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-STEM) and Rutherford Backscattering Spectroscopy (RBS), atomic level structure and chemical information was obtained. Specifically, CdSe nanocrystals produced using a mixture of hexadecylamine (HDA) and trioctylphosphine oxide (TOPO) were determined to be spherical compared to nanocrystals produced in TOPO only, which had elongated (101) facets. Additionally, the first Z-STEM images of CdSe/ZnS core/shell nanocrystals were obtained. From these images, the growth mechanism of the ZnS shell was determined and the existence of non-fluorescent ZnS particles was confirmed. Through collaboration with Quantum Dot Corp., core/shell nanocrystals with near unity quantum yield were developed. These core/shell nanocrystals included a US intermediate layer to improve shell coverage.

Enhanced exchange bias and improved ferromagnetic properties in Permalloy-BiFe0.95Co0.05O3 core-shell nanostructures.

PubMed

Javed, K; Li, W J; Ali, S S; Shi, D W; Khan, U; Riaz, S; Han, X F

2015-12-14

Hybrid core-shell nanostructures consisting of permalloy (Ni80Fe20) and multiferroic(BiFeO3, BFO/BiFe0.95Co0.05O3, BFC) materials were synthesized by a two-step method, based on wet chemical impregnation and subsequent electrodeposition within porous alumina membranes. Structural and magnetic characterizations have been done to investigate doping effect on magnetic properties and exchange bias. The magnetometry analysis revealed significant enhancements of the exchange bias and coercivity in NiFe-BFC core-shell nanostructures as compared with NiFe-BFO core-shell nanostructures. The enhancements can be attributed to the effective reduction of ferromagnet domain sizes between adjacent layers of core-shell structure. It indicates that it is possible to improve properties of multiferroic composites by site-engineering method. Our approach opens a pathway to obtain optimized nanostructured multiferroic composites exhibiting tunable magnetic properties.

Enhanced exchange bias and improved ferromagnetic properties in Permalloy–BiFe0.95Co0.05O3 core–shell nanostructures

PubMed Central

Javed, K.; Li, W. J.; Ali, S. S.; Shi, D. W.; Khan, U.; Riaz, S.; Han, X. F.

2015-01-01

Hybrid core–shell nanostructures consisting of permalloy (Ni80Fe20) and multiferroic(BiFeO3, BFO/BiFe0.95Co0.05O3, BFC) materials were synthesized by a two-step method, based on wet chemical impregnation and subsequent electrodeposition within porous alumina membranes. Structural and magnetic characterizations have been done to investigate doping effect on magnetic properties and exchange bias. The magnetometry analysis revealed significant enhancements of the exchange bias and coercivity in NiFe-BFC core-shell nanostructures as compared with NiFe-BFO core-shell nanostructures. The enhancements can be attributed to the effective reduction of ferromagnet domain sizes between adjacent layers of core-shell structure. It indicates that it is possible to improve properties of multiferroic composites by site-engineering method. Our approach opens a pathway to obtain optimized nanostructured multiferroic composites exhibiting tunable magnetic properties. PMID:26658956

Ru-core/Cu-shell bimetallic nanoparticles with controlled size formed in one-pot synthesis.

PubMed

Helgadottir, I; Freychet, G; Arquillière, P; Maret, M; Gergaud, P; Haumesser, P H; Santini, C C

2014-12-21

Suspensions of bimetallic nanoparticles (NPs) of Ru and Cu have been synthesized by simultaneous decomposition of two organometallic compounds in an ionic liquid. These suspensions have been characterized by Anomalous Small-Angle X-ray Scattering (ASAXS) at energies slightly below the Ru K-edge. It is found that the NPs adopt a Ru-core, a Cu-shell structure, with a constant Ru core diameter of 1.9 nm for all Ru : Cu compositions, while the Cu shell thickness increases with Cu content up to 0.9 nm. The formation of RuCuNPs thus proceeds through rapid decomposition of the Ru precursor into RuNPs of constant size followed by the reaction of the Cu precursor and agglomeration as a Cu shell. Thus, the different decomposition kinetics of precursors make possible the elaboration of core-shell NPs composed of two metals without chemical affinity.

Field-assisted organization, substrate effects and magnetic behavior of Ag 30Co 70 core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Crisan, A. D.; Angelakeris, M.; Simeonidis, K.; Tsiaoussis, I.; Crisan, O.

2010-11-01

In core-shell systems with non-magnetic core and magnetic shell, the electron transport and magnetic properties are expected to show enhanced behavior due to the particular morpho-structural features of the conductive and magnetic regions. This may lead to novel advanced GMR materials and spin valves. This is the case of core-shell Ag-Co colloidal nanoscale particles that organize into regular arrays. An insight on the structure and morphology of the newly synthesized Ag-Co nanoparticles deposited on different substrates will be presented. The influence of the substrate on different morphologies and organization dynamics is discussed. It is shown that the magnetic behavior of the Ag-Co nanoparticles is highly influenced by the corona-like morphology of Co shell, chemical environment of the magnetic atoms and by the fact that they exhibit strongly reduced coordination due to the surface states.

Biofiltration of methanol in an organic biofilter using peanut shells as medium.

PubMed

Ramirez-Lopez, E M; Corona-Hernandez, J; Avelar-Gonzalez, F J; Omil, F; Thalasso, F

2010-01-01

Biofiltration consists of a filter-bed of organic matter serving both as carrier for the active biomass and as nutrient supply, through which the polluted gas passes. The selection of a suitable medium material is of major importance to ensure optimum biofilter efficiency. Peanut shells are an agricultural byproduct locally available in large quantities at a low price in most tropical and sub-tropical countries. A previous study showed that peanut shells are physically and chemically suitable for biofiltration. This paper presents the results obtained during a six month biofiltration experiment using peanut shells as medium and methanol as air pollutant. It is shown that peanut shells are potentially suitable as biofiltration medium, since degradation rates of up to 30 kg MeOH/m(3)d with an empty bed residence time of 19s was obtained. The biofilter showed a good resistance to shock load and no operational problems were observed.

Use of extracts from oyster shell and soil for cultivation of Spirulina maxima.

PubMed

Jung, Joo-Young; Kim, Sunmin; Lee, Hansol; Kim, Kyochan; Kim, Woong; Park, Min S; Kwon, Jong-Hee; Yang, Ji-Won

2014-12-01

Calcium ion and trace metals play important roles in various metabolisms of photosynthetic organisms. In this study, simple methods were developed to extract calcium ion and micronutrients from oyster shell and common soil, and the prepared extracts were tested as a replacement of the corresponding chemicals that are essential for growth of microalgae. The oyster shell and soil were treated with 0.1 M sodium hydroxide or with 10 % hydrogen peroxide, respectively. The potential application of these natural sources to cultivation was investigated with Spirulina maxima. When compared to standard Zarrouk medium, the Spirulina maxima cultivated in a modified Zarrouk media with elements from oyster shell and soil extract exhibited increases in biomass, chlorophyll, and phycocyanin by 17, 16, and 64 %, respectively. These results indicate that the extracts of oyster shell and soil provide sufficient amounts of calcium and trace metals for successful cultivation of Spirulina maxima.

Optimization of ultrasound extraction of phenolic compounds from coconut (Cocos nucifera) shell powder by response surface methodology.

PubMed

Rodrigues, Sueli; Pinto, Gustavo A S; Fernandes, Fabiano A N

2008-01-01

Coconut is a tropical fruit largely consumed in many countries. In some areas of the Brazilian coast, coconut shell represents more than 60% of the domestic waste volume. The coconut shell is composed mainly of lignin and cellulose, having a chemical composition very similar to wood and suitable for phenolic extraction. In this work, the use of ultrasound to extract phenolic compounds from coconut shell was evaluated. The effect of temperature, solution to solid ratio, pH and extraction time were evaluated through a 2(4) experimental planning. The extraction process was also optimized using surface response methodology. At the optimum operating condition (30 degrees C, solution to solid ratio of 50, 15 min of extraction and pH 6.5) the process yielded 22.44 mg of phenolic compounds per gram of coconut shell.

Synthesis of Co/MFe(2)O(4) (M = Fe, Mn) Core/Shell Nanocomposite Particles.

PubMed

Peng, Sheng; Xie, Jin; Sun, Shouheng

2008-01-01

Monodispersed cobalt nanoparticles (NPs) with controllable size (8-14 nm) have been synthesized using thermal decomposition of dicobaltoctacarbonyl in organic solvent. The as-synthesized high magnetic moment (125 emu/g) Co NPs are dispersible in various organic solvents, and can be easily transferred into aqueous phase by surface modification using phospholipids. However, the modified hydrophilic Co NPs are not stable as they are quickly oxidized, agglomerated in buffer. Co NPs are stabilized by coating the MFe(2)O(4) (M = Fe, Mn) ferrite shell. Core/shell structured bimagnetic Co/MFe(2)O(4) nanocomposites are prepared with tunable shell thickness (1-5 nm). The Co/MFe(2)O(4) nanocomposites retain the high magnetic moment density from the Co core, while gaining chemical and magnetic stability from the ferrite shell. Comparing to Co NPs, the nanocomposites show much enhanced stability in buffer solution at elevated temperatures, making them promising for biomedical applications.

Sensitivity of ab Initio vs Empirical Methods in Computing Structural Effects on NMR Chemical Shifts for the Example of Peptides.

PubMed

Sumowski, Chris Vanessa; Hanni, Matti; Schweizer, Sabine; Ochsenfeld, Christian

2014-01-14

The structural sensitivity of NMR chemical shifts as computed by quantum chemical methods is compared to a variety of empirical approaches for the example of a prototypical peptide, the 38-residue kaliotoxin KTX comprising 573 atoms. Despite the simplicity of empirical chemical shift prediction programs, the agreement with experimental results is rather good, underlining their usefulness. However, we show in our present work that they are highly insensitive to structural changes, which renders their use for validating predicted structures questionable. In contrast, quantum chemical methods show the expected high sensitivity to structural and electronic changes. This appears to be independent of the quantum chemical approach or the inclusion of solvent effects. For the latter, explicit solvent simulations with increasing number of snapshots were performed for two conformers of an eight amino acid sequence. In conclusion, the empirical approaches neither provide the expected magnitude nor the patterns of NMR chemical shifts determined by the clearly more costly ab initio methods upon structural changes. This restricts the use of empirical prediction programs in studies where peptide and protein structures are utilized for the NMR chemical shift evaluation such as in NMR refinement processes, structural model verifications, or calculations of NMR nuclear spin relaxation rates.

Lateral Earth Pressure at Rest and Shear Modulus Measurements on Hanford Sludge Simulants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wells, Beric E.; Jenks, Jeromy WJ; Boeringa, Gregory K.

2010-09-30

This report describes the equipment, techniques, and results of lateral earth pressure at rest and shear modulus measurements on kaolin clay as well as two chemical sludge simulants. The testing was performed in support of the problem of hydrogen gas retention and release encountered in the double- shell tanks (DSTs) at the Hanford Site near Richland, Washington. Wastes from single-shell tanks (SSTs) are being transferred to double-shell tanks (DSTs) for safety reasons (some SSTs are leaking or are in danger of leaking), but the available DST space is limited.

Facile synthesis and microwave absorbability of C@Ni–NiO core–shell hybrid solid sphere and multi-shelled NiO hollow sphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Hongjing, E-mail: wuhongjing@mail.nwpu.edu.cn; Wu, Guanglei, E-mail: wuguanglei@mail.xjtu.edu.cn; Wu, Qiaofeng

2014-11-15

We reported the preparation of C@Ni–NiO core–shell hybrid solid spheres or multi-shelled NiO hollow spheres by combining a facile hydrothermal route with a calcination process in H{sub 2} or air atmosphere, respectively. The synthesized C@Ni–NiO core–shell solid spheres with diameters of approximately 2–6 μm were in fact built from dense NiO nanoparticles coated by random two-dimensional metal Ni nanosheets without any visible pores. The multi-shelled NiO hollow spheres were built from particle-like ligaments and there are a lot of pores with size of several nanometers on the surface. Combined Raman spectra with X-ray photoelectron spectra (XPS), it suggested that themore » defects in the samples play a limited role in the dielectric loss. Compared with the other samples, the permeability of the samples calcined in H{sub 2} and air was increased slightly and the natural resonance frequency shifted to higher frequency (7, 11 and 14 GHz, respectively), leading to an enhancement of microwave absorption property. For the sample calcined in H{sub 2}, an optimal reflection loss less than − 10 was obtained at 7 GHz with a matching thickness of 5.0 mm. Our study demonstrated the potential application of C@Ni–NiO core–shell hybrid solid sphere or multi-shelled NiO hollow sphere as a more efficient electromagnetic (EM) wave absorber. - Highlights: • C@Ni–NiO core–shell hybrid solid sphere was synthesized by a facile method. • Multi-shelled NiO hollow sphere was synthesized by a facile method. • It suggested that the defects in the samples play a limited role in dielectric loss. • The permeability of the samples calcined in H{sub 2} and air was increased. • Microwave absorbability of C@Ni–NiO core–shell hybrid solid sphere was investigated.« less

Data on Molluscan Shells in parts of Nellore Coast, southeast coast of India.

PubMed

Lakshmanna, B; Jayaraju, N; Prasad, T Lakshmi; Sreenivasulu, G; Nagalakshmi, K; Kumar, M Pramod; Madakka, M

2018-02-01

X-ray diffraction (XRD), Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS), and Fourier Transform Infrared Spectroscopy (FT-IR), were applied to analyze the organic matrix of two Molluscan shells . The Mollusca shells are mineral structure and calcium carbonate crystallized as aragonite. The FT-IR spectra showed Alkyl Halide, Alkanes, Alcohols, Amides, Aromatic, and Hydroxyl groups in the organic matrix of the whole (organic and mineral) Molluscan shells. SEM images of particles of the two Molluscan shells at different magnifications were taken. The morphologies of the samples show a flake like structures with irregular grains, their sizes are at micrometric scale and the chemical analysis of EDS indicated that the major elements of Cardita and Gastropoda were C, O, and Ca, consistent with the results of XRD analysis. The results of the analysis of the EDS spectra of the shells showed that the content of most of the powder composition of shells is the element carbon, calcium oxygen, aluminium, and lead peaks that appear on the Cardita and Gastropoda and shells powders tap EDS spectra. The present work examined organic matrix of the selected shells of the heavily polluted and light polluted sites, along Nellore Coast, South East Coast of India. The heavily polluted sites have significantly thickened shells. The data demonstrated the sensitivity of this abundant and widely distributed intertidal fragile environment.

Fluidized bed calciner apparatus

DOEpatents

Owen, Thomas J.; Klem, Jr., Michael J.; Cash, Robert J.

1988-01-01

An apparatus for remotely calcining a slurry or solution feed stream of toxic or hazardous material, such as ammonium diurante slurry or uranyl nitrate solution, is disclosed. The calcining apparatus includes a vertical substantially cylindrical inner shell disposed in a vertical substantially cylindrical outer shell, in which inner shell is disposed a fluidized bed comprising the feed stream material to be calcined and spherical beads to aid in heat transfer. Extending through the outer and inner shells is a feed nozzle for delivering feed material or a cleaning chemical to the beads. Disposed in and extending across the lower portion of the inner shell and upstream of the fluidized bed is a support member for supporting the fluidized bed, the support member having uniform slots for directing uniform gas flow to the fluidized bed from a fluidizing gas orifice disposed upstream of the support member. Disposed in the lower portion of the inner shell are a plurality of internal electric resistance heaters for heating the fluidized bed. Disposed circumferentially about the outside length of the inner shell are a plurality of external heaters for heating the inner shell thereby heating the fluidized bed. Further, connected to the internal and external heaters is a means for maintaining the fluidized bed temperature to within plus or minus approximately 25.degree. C. of a predetermined bed temperature. Disposed about the external heaters is the outer shell for providing radiative heat reflection back to the inner shell.

Rational Construction of Uniform CoNi-Based Core-Shell Microspheres with Tunable Electromagnetic Wave Absorption Properties.

PubMed

Chen, Na; Jiang, Jian-Tang; Xu, Cheng-Yan; Yan, Shao-Jiu; Zhen, Liang

2018-02-16

Core-shell particles with integration of ferromagnetic core and dielectric shell are attracting extensive attention for promising microwave absorption applications. In this work, CoNi microspheres with conical bulges were synthesized by a simple and scalable liquid-phase reduction method. Subsequent coating of dielectric materials was conducted to acquire core-shell structured CoNi@TiO 2 composite particles, in which the thickness of TiO 2 is about 40 nm. The coating of TiO 2 enables the absorption band of CoNi to effectively shift from K u to S band, and endows CoNi@TiO 2 microspheres with outstanding electromagnetic wave absorption performance along with a maximum reflection loss of 76.6 dB at 3.3 GHz, much better than that of bare CoNi microspheres (54.4 dB at 17.8 GHz). The enhanced EMA performance is attributed to the unique core-shell structures, which can induce dipole polarization and interfacial polarization, and tune the dielectric properties to achieve good impedance matching. Impressively, TiO 2 coating endows the composites with better microwave absorption capability than CoNi@SiO 2 microspheres. Compared with SiO 2 , TiO 2 dielectric shells could protect CoNi microspheres from merger and agglomeration during annealed. These results indicate that CoNi@TiO 2 core-shell microspheres can serve as high-performance absorbers for electromagnetic wave absorbing application.

Relativistically corrected nuclear magnetic resonance chemical shifts calculated with the normalized elimination of the small component using an effective potential-NMR chemical shifts of molybdenum and tungsten

NASA Astrophysics Data System (ADS)

Filatov, Michael; Cremer, Dieter

2003-07-01

A new method for relativistically corrected nuclear magnetic resonance (NMR) chemical shifts is developed by combining the individual gauge for the localized orbital approach for density functional theory with the normalized elimination of a small component using an effective potential. The new method is used for the calculation of the NMR chemical shifts of 95Mo and 183W in various molybdenum and tungsten compounds. It is shown that quasirelativistic corrections lead to an average improvement of calculated NMR chemical shift values by 300 and 120 ppm in the case of 95Mo and 183W, respectively, which is mainly due to improvements in the paramagnetic contributions. The relationship between electronic structure of a molecule and the relativistic paramagnetic corrections is discussed. Relativistic effects for the diamagnetic part of the magnetic shielding caused by a relativistic contraction of the s,p orbitals in the core region concern only the shielding values, however, have little consequence for the shift values because of the large independence from electronic structure and a cancellation of these effects in the shift values. It is shown that the relativistic corrections can be improved by level shift operators and a B3LYP hybrid functional, for which Hartree-Fock exchange is reduced to 15%.

Electrowetting-on-dielectrics for manipulation of oil drops and gas bubbles in aqueous-shell compound drops.

PubMed

Li, Jiang; Wang, Yixuan; Chen, Haosheng; Wan, Jiandi

2014-11-21

We present the manipulation of oil, organic and gaseous chemicals by electrowetting-on-dielectric (EWOD) technology using aqueous-shell compound drops. We demonstrate that the transport and coalescence of viscous oil drops, the reaction of bromine with styrene in benzene solution, and the reaction of red blood cells with carbon monoxide bubbles can be accomplished using this method.

Benchmarking quantum mechanical calculations with experimental NMR chemical shifts of 2-HADNT

NASA Astrophysics Data System (ADS)

Liu, Yuemin; Junk, Thomas; Liu, Yucheng; Tzeng, Nianfeng; Perkins, Richard

2015-04-01

In this study, both GIAO-DFT and GIAO-MP2 calculations of nuclear magnetic resonance (NMR) spectra were benchmarked with experimental chemical shifts. The experimental chemical shifts were determined experimentally for carbon-13 (C-13) of seven carbon atoms for the TNT degradation product 2-hydroxylamino-4,6-dinitrotoluene (2-HADNT). Quantum mechanics GIAO calculations were implemented using Becke-3-Lee-Yang-Parr (B3LYP) and other six hybrid DFT methods (Becke-1-Lee-Yang-Parr (B1LYP), Becke-half-and-half-Lee-Yang-Parr (BH and HLYP), Cohen-Handy-3-Lee-Yang-Parr (O3LYP), Coulomb-attenuating-B3LYP (CAM-B3LYP), modified-Perdew-Wang-91-Lee-Yang-Parr (mPW1LYP), and Xu-3-Lee-Yang-Parr (X3LYP)) which use the same correlation functional LYP. Calculation results showed that the GIAO-MP2 method gives the most accurate chemical shift values, and O3LYP method provides the best prediction of chemical shifts among the B3LYP and other five DFT methods. Three types of atomic partial charges, Mulliken (MK), electrostatic potential (ESP), and natural bond orbital (NBO), were also calculated using MP2/aug-cc-pVDZ method. A reasonable correlation was discovered between NBO partial charges and experimental chemical shifts of carbon-13 (C-13).

Electronically excited and ionized states in condensed phase: Theory and applications

NASA Astrophysics Data System (ADS)

Sadybekov, Arman

Predictive modeling of chemical processes in silico is a goal of XXI century. While robust and accurate methods exist for ground-state properties, reliable methods for excited states are still lacking and require further development. Electronically exited states are formed by interactions of matter with light and are responsible for key processes in solar energy harvesting, vision, artificial sensors, and photovoltaic applications. The greatest challenge to overcome on our way to a quantitative description of light-induced processes is accurate inclusion of the effect of the environment on excited states. All above mentioned processes occur in solution or solid state. Yet, there are few methodologies to study excited states in condensed phase. Application of highly accurate and robust methods, such as equation-of-motion coupled-cluster theory EOM-CC, is limited by a high computational cost and scaling precluding full quantum mechanical treatment of the entire system. In this thesis we present successful application of the EOM-CC family of methods to studies of excited states in liquid phase and build hierarchy of models for inclusion of the solvent effects. In the first part of the thesis we show that a simple gasphase model is sufficient to quantitatively analyze excited states in liquid benzene, while the latter part emphasizes the importance of explicit treatment of the solvent molecules in the case of glycine in water solution. In chapter 2, we use a simple dimer model to describe exciton formation in liquid and solid benzene. We show that sampling of dimer structures extracted from the liquid benzene is sufficient to correctly predict exited-state properties of the liquid. Our calculations explain experimentally observed features, which helped to understand the mechanism of the excimer formation in liquid benzene. Furthermore, we shed light on the difference between dimer configurations in the first solvation shell of liquid benzene and in unit cell of solid benzene and discussed the impact of these differences on the formation of the excimer state. In chapter 3, we present a theoretical approach for calculating core-level states in condensed phase. The approach is based on EOM-CC and effective fragment potential (EFP) method. By introducing an approximate treatment of double excitations in the EOM-CCSD (EOM-CC with single and double substitutions) ansatz, we addressed poor convergence issues that are encountered for the core-level states and significantly reduced computational costs. While the approximations introduce relatively large errors in the absolute values of transition energies, the errors are systematic. Consequently, chemical shifts, changes in ionization energies relative to the reference systems, are reproduced reasonably well. By using different protonation forms of solvated glycine as a benchmark system, we showed that our protocol is capable of reproducing the experimental chemical shifts with a quantitative accuracy. The results demonstrate that chemical shifts are very sensitive to the solvent interactions and that explicit treatment of solvent, such as EFP, is essential for achieving quantitative accuracy. In chapter 4, we outline future directions and discuss possible applications of the developed computational protocol for prediction of core chemical shifts in larger systems.

1H NMR spectra part 31: 1H chemical shifts of amides in DMSO solvent.

PubMed

Abraham, Raymond J; Griffiths, Lee; Perez, Manuel

2014-07-01

The (1)H chemical shifts of 48 amides in DMSO solvent are assigned and presented. The solvent shifts Δδ (DMSO-CDCl3 ) are large (1-2 ppm) for the NH protons but smaller and negative (-0.1 to -0.2 ppm) for close range protons. A selection of the observed solvent shifts is compared with calculated shifts from the present model and from GIAO calculations. Those for the NH protons agree with both calculations, but other solvent shifts such as Δδ(CHO) are not well reproduced by the GIAO calculations. The (1)H chemical shifts of the amides in DMSO were analysed using a functional approach for near ( ≤ 3 bonds removed) protons and the electric field, magnetic anisotropy and steric effect of the amide group for more distant protons. The chemical shifts of the NH protons of acetanilide and benzamide vary linearly with the π density on the αN and βC atoms, respectively. The C=O anisotropy and steric effect are in general little changed from the values in CDCl3. The effects of substituents F, Cl, Me on the NH proton shifts are reproduced. The electric field coefficient for the protons in DMSO is 90% of that in CDCl3. There is no steric effect of the C=O oxygen on the NH proton in an NH…O=C hydrogen bond. The observed deshielding is due to the electric field effect. The calculated chemical shifts agree well with the observed shifts (RMS error of 0.106 ppm for the data set of 257 entries). Copyright © 2014 John Wiley & Sons, Ltd.

Distinct Contributions of Dopamine in the Dorsolateral Striatum and Nucleus Accumbens Shell to the Reinforcing Properties of Cocaine

PubMed Central

Veeneman, Maartje M J; Broekhoven, Mark H; Damsteegt, Ruth; Vanderschuren, Louk J M J

2012-01-01

Dopaminergic neurotransmission in the dorsal and ventral striatum is thought to be involved in distinct aspects of cocaine addiction. Ventral striatal dopamine mediates the acute reinforcing properties of cocaine, whereas dopamine in the dorsolateral striatum (DLS) is thought to become involved in later stages of the addiction process to mediate well-established cue-controlled drug seeking. However, it is unclear whether the DLS also has a role in the reinforcing properties of cocaine itself. Therefore, we systematically investigated the involvement of dopamine in dorsal and ventral striatal regions in cocaine self-administration, using various schedules of reinforcement in animals with limited drug taking experience. Intra-DLS infusion of the dopamine receptor antagonist α-flupenthixol did not affect the acquisition of cocaine self-administration, increased cocaine self-administration under a fixed ratio-1 (FR-1) schedule of reinforcement, caused a rightward and downward shift of the dose–response curve of cocaine under an FR-1 schedule of reinforcement and decreased responding for cocaine under a progressive ratio (PR) schedule of reinforcement. Infusion of α-flupenthixol into the ventral nucleus accumbens (NAcc) shell inhibited the acquisition of cocaine self-administration, reduced responding for the drug under FR-1 and PR schedules of reinforcement, and caused a downward shift of the dose–response curve of cocaine self-administration under an FR-1 schedule of reinforcement. These data show that dopamine in both the DLS and NAcc shell is involved in cocaine reinforcement. We suggest that the DLS and the NAcc shell mediate somewhat distinct facets of the reinforcing properties of cocaine, related to its rewarding and motivational aspects, respectively. PMID:21918505

Experimental and DFT evaluation of the 1H and 13C NMR chemical shifts for calix[4]arenes

NASA Astrophysics Data System (ADS)

Guzzo, Rodrigo N.; Rezende, Michelle Jakeline Cunha; Kartnaller, Vinicius; Carneiro, José Walkimar de M.; Stoyanov, Stanislav R.; Costa, Leonardo Moreira da

2018-04-01

The density functional theory is employed to determine the efficiency of 11 exchange-correlation (XC) functionals to compute the 1H and 13C NMR chemical shifts of p-tert-butylcalix[4]arene (ptcx4, R1 = C(CH3)3) and congeners using the 6-31G(d,p) basis set. The statistical analysis shows that B3LYP, B3PW91 and PBE1PBE are the best XC functionals for the calculation of 1H chemical shifts. Moreover, the best results for the 13C chemical shifts are obtained using the LC-WPBE, M06-2X and wB97X-D functionals. The performance of these XC functionals is tested for three other calix[4]arenes: p-sulfonic acid calix[4]arene (sfxcx4 - R1 = SO3H), p-nitro-calix[4]arene (ncx4, R1 = NO2) and calix[4]arene (cx4 - R1 = H). For 1H chemical shifts B3LYP, B3PW91 and PBE1PBE yield similar results, although B3PW91 shows more consistency in the calculated error for the different structures. For 13C NMR chemical shifts, the XC functional that stood out as best is LC-WPBE. Indeed, the three functionals selected for each of 1H and 13C show good accuracy and can be used in future studies involving the prediction of 1H and 13C chemical shifts for this type of compounds.

Time-Resolved K-shell Photoabsorption Edge Measurement in a Strongly Coupled Matter Driven by Laser-converted Radiation

NASA Astrophysics Data System (ADS)

Zhao, Yang; Yang, Jia-Min; Zhang, Ji-Yan; Yang, Guo-Hong; Xiong, Gang; Wei, Min-Xi; Song, Tian-Ming; Zhang, Zhi-Yu

2013-06-01

A time-resolved K edge absorption measurement of warm dense KCl was performed on Shenguang II laser facility. The x-ray radiation driven shocks were adopted to take colliding shocks compression. By using Dog bone hohlraum the CH/KCl/CH sample was shielded from the laser hitting point to suppress the M band preheating and enhance the compressibility. Thus, an unexplored and extreme region of the plasma state with the maximum 5 times solid density and temperature lower than 3 eV (with coupling constant Γii around 100) was first obtained. The photoabsorption spectra of chlorine near the K-shell edge have been measured with a crystal spectrometer using a short x-ray backlighter. The K edge red shift up to 11.7 eV and broadening of 15.2 eV were obtained for the maximum compression. The electron temperature, inferred by Fermi-Dirac fit of the measured K-edge broadening, was consistent with the hydrodynamic predictions. The comparison of the K edge shift with a plasma model, in which the ionization effect, continuum lowering and partial degeneracy are considered, shows that more improvements are desired to describe in details the variation of K edge shift. This work might extend future study of WDM in extreme conditions of high compression.

Alloy and heterostructure architectures as promising tools for controlling electronic properties of semiconductor quantum dots

NASA Astrophysics Data System (ADS)

Vaxenburg, Roman; Lifshitz, Efrat

2012-02-01

Tunability of energy levels and wavefunctions of carriers in colloidal quantum dots (CQDs) has a marked effect on numerous physical aspects, such as Coulomb interactions and charge separation, which in turn has a direct impact on the functioning of CQD-based opto-electronic devices. The electronic properties of CQDs are conventionally controlled by variation of their size. Here we demonstrate a theoretical approach to engineer the electronic properties of IV-VI CQDs by introducing an alloy composition in core and core/shell heterostructures, having the general chemical formula PbSexS1-x/PbSeyS1-y (0 ≤ x ≤ 1, 0 ≤ y ≤ 1), while maintaining a constant size. The theoretical model considered an effective mass anisotropy and smooth potential step at the core/shell interface. The model revealed the influence induced by variation of chemical composition and core-to-shell division on the band-gap energy, remote states’ density, internal charge separation, electron-hole Coulomb interaction, and optical transition oscillator strength.

Synthesis of green Fe3+/glucose/rGO electrode for supercapacitor application assisted by chemical exfoliation process from burning coconut shell

NASA Astrophysics Data System (ADS)

Putra, Gilang B. A.; Pradana, Herdy Y.; Soenaryo, Dimas E. T.; Baqiya, Malik A.; Darminto

2018-04-01

For the goal of large, environmental - friendly, renewable, and inexpensive energy storage, the development of supercapacitor electrodes is needed, by anchoring transition metal oxide (Fe3+ ion) as pseudo capacitor electrode material with reduced graphene oxide (rGO) from an old coconut shell as electrochemical double layer capacitor (EDLC). This porous electrode composite is prepared by sonication and chemical exfoliation assisted by acid. Synthesis of supercapacitor is also added by glucose, which acts as a spacer between layers of rGO to increase the capacitance, also as binder between the materials used. Combining Fe3+ with old coconut shell rGO give high specific capacitance of up to 99 F/g at a potential window of -1 V to 1 V. The Fe3+/glucose/rGO electrode has thickness of up to 57 nm (from PSA result) and give a uniform distribution from EDX mapping with disperse Fe domains and not bonding with rGO.

Single Domain SmCo5@Co Exchange-coupled Magnets Prepared from Core/shell Sm[Co(CN)6]·4H2O@GO Particles: A Novel Chemical Approach

PubMed Central

Yang, Ce; Jia, Lihui; Wang, Shouguo; Gao, Chen; Shi, Dawei; Hou, Yanglong; Gao, Song

2013-01-01

SmCo5 based magnets with smaller size and larger maximum energy product have been long desired in various fields such as renewable energy technology, electronic industry and aerospace science. However, conventional relatively rough synthetic strategies will lead to either diminished magnetic properties or irregular morphology, which hindered their wide applications. In this article, we present a facile chemical approach to prepare 200 nm single domain SmCo5@Co core/shell magnets with coercivity of 20.7 kOe and saturation magnetization of 82 emu/g. We found that the incorporation of GO sheets is responsible for the generation of the unique structure. The single domain SmCo5 core contributes to the large coercivity of the magnets and the exchange-coupled Co shell enhances the magnetization. This method can be further utilized in the synthesis other Sm-Co based exchange-coupled magnets. PMID:24356309

129 Xe chemical shift in human blood and pulmonary blood oxygenation measurement in humans using hyperpolarized 129 Xe NMR.

PubMed

Norquay, Graham; Leung, General; Stewart, Neil J; Wolber, Jan; Wild, Jim M

2017-04-01

To evaluate the dependency of the 129 Xe-red blood cell (RBC) chemical shift on blood oxygenation, and to use this relation for noninvasive measurement of pulmonary blood oxygenation in vivo with hyperpolarized 129 Xe NMR. Hyperpolarized 129 Xe was equilibrated with blood samples of varying oxygenation in vitro, and NMR was performed at 1.5 T and 3 T. Dynamic in vivo NMR during breath hold apnea was performed at 3 T on two healthy volunteers following inhalation of hyperpolarized 129 Xe. The 129 Xe chemical shift in RBCs was found to increase nonlinearly with blood oxygenation at 1.5 T and 3 T. During breath hold apnea, the 129 Xe chemical shift in RBCs exhibited a periodic time modulation and showed a net decrease in chemical shift of ∼1 ppm over a 35 s breath hold, corresponding to a decrease of 7-10 % in RBC oxygenation. The 129 Xe-RBC signal amplitude showed a modulation with the same frequency as the 129 Xe-RBC chemical shift. The feasibility of using the 129 Xe-RBC chemical shift to measure pulmonary blood oxygenation in vivo has been demonstrated. Correlation between 129 Xe-RBC signal and 129 Xe-RBC chemical shift modulations in the lung warrants further investigation, with the aim to better quantify temporal blood oxygenation changes in the cardiopulmonary vascular circuit. Magn Reson Med 77:1399-1408, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Theoretical and experimental NMR study of protopine hydrochloride isomers.

PubMed

Tousek, Jaromír; Malináková, Katerina; Dostál, Jirí; Marek, Radek

2005-07-01

The 1H and 13C NMR chemical shifts of cis- and trans-protopinium salts were measured and calculated. The calculations of the chemical shifts consisted of conformational analysis, geometry optimization (RHF/6-31G** method) and shielding constants calculations (B3LYP/6-31G** method). Based on the results of the quantum chemical calculations, two sets of experimental chemical shifts were assigned to the particular isomers. According to the experimental results, the trans-isomer is more stable and its population is approximately 68%. Copyright 2005 John Wiley & Sons, Ltd

Tandem Core–Shell Si–Ta 3N 5 Photoanodes for Photoelectrochemical Water Splitting

DOE PAGES

Narkeviciute, Ieva; Chakthranont, Pongkarn; Mackus, Adriaan J. M.; ...

2016-11-22

Here, nanostructured core–shell Si–Ta 3N 5 photoanodes were designed and synthesized to overcome charge transport limitations of Ta 3N 5 for photoelectrochemical water splitting. The core–shell devices were fabricated by atomic layer deposition of amorphous Ta 2O 5 onto nanostructured Si and subsequent nitridation to crystalline Ta 3N 5. Nanostructuring with a thin shell of Ta 3N 5 results in a 10-fold improvement in photocurrent compared to a planar device of the same thickness. In examining thickness dependence of the Ta 3N 5 shell from 10 to 70 nm, superior photocurrent and absorbed-photon-to-current efficiencies are obtained from the thinner Tamore » 3N 5 shells, indicating minority carrier diffusion lengths on the order of tens of nanometers. The fabrication of a heterostructure based on a semiconducting, n-type Si core produced a tandem photoanode with a photocurrent onset shifted to lower potentials by 200 mV. CoTiO x and NiO x water oxidation cocatalysts were deposited onto the Si–Ta 3N 5 to yield active photoanodes that with NiO x retained 50–60% of their maximum photocurrent after 24 h chronoamperometry experiments and are thus among the most stable Ta 3N 5 photoanodes reported to date.« less

Further conventions for NMR shielding and chemical shifts IUPAC recommendations 2008.

PubMed

Harris, Robin K; Becker, Edwin D; Cabral De Menezes, Sonia M; Granger, Pierre; Hoffman, Roy E; Zilm, Kurt W

2008-03-01

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the (1)H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS). This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating (13)C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids are reviewed in some detail, and recommendations are given for best practice.

Further conventions for NMR shielding and chemical shifts (IUPAC Recommendations 2008).

PubMed

Harris, Robin K; Becker, Edwin D; De Menezes, Sonia M Cabral; Granger, Pierre; Hoffman, Roy E; Zilm, Kurt W

2008-06-01

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the (1)H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS). This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating (13)C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids are reviewed in some detail, and recommendations are given for best practice. Copyright (c) 2008 John Wiley & Sons, Ltd

DOE Office of Scientific and Technical Information (OSTI.GOV)

Metaxas, Athena E.; Cort, John R.

The highly toxic plant alkaloid strychnine is often isolated in the form of the anion salt of its protonated tertiary amine. Here we characterize the relative influence of different counterions on 1H and 13C chemical shifts in several strychnine salts in D2O, methanol-d4 (CD3OD) and chloroform-d (CDCl3) solvents. In organic solvents, but not in water, substantial variation in chemical shifts of protons near the tertiary amine was observed among different salts. These secondary shifts reveal differences in the way each anion influences electronic structure within the protonated amine. The distributions of secondary shifts allow salts to be easily distinguished frommore » each other as well as from the free base form. The observed effects are much greater in organic solvents than in water. Slight concentration-dependence in chemical shifts of some protons near the amine was observed for two salts in CDCl3, but this effect is small compared to the influence of the counterion. Distinct chemical shifts in different salt forms of the same compound may be useful as chemical forensic signatures for source attribution and sample matching of alkaloids such as strychnine and possibly other organic acid and base salts.« less

The converse approach to NMR chemical shifts from first-principles: application to finite and infinite aromatic compounds

NASA Astrophysics Data System (ADS)

Thonhauser, T.; Ceresoli, D.; Marzari, N.

2009-03-01

We present first-principles, density-functional theory calculations of the NMR chemical shifts for polycyclic aromatic hydrocarbons, starting with benzene and increasing sizes up to the one- and two-dimensional infinite limits of graphene ribbons and sheets. Our calculations are performed using a combination of the recently developed theory of orbital magnetization in solids, and a novel approach to NMR calculations where chemical shifts are obtained from the derivative of the orbital magnetization with respect to a microscopic, localized magnetic dipole. Using these methods we study on equal footing the ^1H and ^13C shifts in benzene, pyrene, coronene, in naphthalene, anthracene, naphthacene, and pentacene, and finally in graphene, graphite, and an infinite graphene ribbon. Our results show very good agreement with experiments and allow us to characterize the trends for the chemical shifts as a function of system size.

Chemical potential shift in organic field-effect transistors identified by soft X-ray operando nano-spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nagamura, Naoka, E-mail: NAGAMURA.Naoka@nims.go.jp; Kitada, Yuta; Honma, Itaru

2015-06-22

A chemical potential shift in an organic field effect transistor (OFET) during operation has been revealed by soft X-ray operando nano-spectroscopy analysis performed using a three-dimensional nanoscale electron-spectroscopy chemical analysis system. OFETs were fabricated using ultrathin (3 ML or 12 nm) single-crystalline C10-DNBDT-NW films on SiO{sub 2} (200 nm)/Si substrates with a backgate electrode and top source/drain Au electrodes, and C 1s line profiles under biasing at the backgate and drain electrodes were measured. When applying −30 V to the backgate, there is C 1s core level shift of 0.1 eV; this shift can be attributed to a chemical potential shift correspondingmore » to band bending by the field effect, resulting in p-type doping.« less

Chemical (knight) shift distortions of quadrupole-split deuteron powder spectra in solids

NASA Astrophysics Data System (ADS)

Torgeson, D. R.; Schoenberger, R. J.; Barnes, R. G.

In strong magnetic fields (e.g., 8 Tesla) anisotropy of the shift tensor (chemical or Knight shift) can alter the spacings of the features of quadrupole-split deuteron spectra of polycrystalline samples. Analysis of powder spectra yields both correct quadrupole coupling and symmetry parameters and all the components of the shift tensor. Synthetic and experimental examples are given to illustrate such behavior.

Mg and 18O Variations in the Shell of the Chilean Gastropod Concholepas concholepas Reflect SST and Growth Rate variations

NASA Astrophysics Data System (ADS)

Guzman, N.; Lazareth, C. E.; Poitrasson, F.; Cuif, J.; Ortlieb, L.

2004-12-01

To validate the use of fossil mollusc shells as recorders of environmental conditions, a primary calibration study was carried out on modern shells of the Chilean gastropod Concholepas concholepas, the so-called southern hemisphere abalone which is particularly abundant in Holocene archaeological sites. Organisms were maintained in culture tanks and feed with live mytilids. The sea water temperature in the tank was recorded every half-an-hour by an automatic device. The experiment lasted several months. Periodical marking with calcein provided a precise chronological control of the shell growth. Thus, well-dated high resolution chemical profiles could be directly compared with temperatures during shell formation. Geochemical analyses of the calcite layers include Mg, Sr and 16O/18O composition. Trace elements were analysed using Laser Ablation ICP-MS and Electron Microprobe while stable isotopes were measured on a Secondary Ion Mass spectrometry (SIMS). The shell growth rate during two months of formation varied between 30 and 140 µm/day which allows us to reach a temporal resolution for chemical profiles between a few hours and three days. The growth rate variations do not seem to be related to temperature fluctuations. Only Mg content was analytically reproducible and showed significant variations across the shells. The Mg high-resolution profiles display a grossly sinusoidal shape. Shells from different sites along the coasts of Chile showed mean Mg contents of 300 ppm and 500 ppm for mean temperatures of 17 and 20° C, respectively. This suggests a gross correlation between Mg and temperature. However, high resolution Mg results do not show an exact fitting neither with temperature nor with growth rates. Other parameters, like shell ageing as suggested by an amplitude increase observed near the edge of one of the shells, or other complex biological factors, may influence Mg incorporation into the shell. \\delta 18O values of the calcite vary between -1,5 and 2,0 \\permil for a temperature range between 17 and 22° C. Growth rate variations seem to be an important factor affecting the oxygen isotopic ratio within shells. When growth rate variations are limited, \\delta 18O and temperature are well correlated. The study confirms that, like for all biogenic carbonates, elemental and isotopic composition of the calcite layer of this gastropod, should not be used in paleoenvironmental reconstructions without detailed calibration experiments, and must systematically include precise growth rate analyses. The growth rhythms, which vary under the double influence of environmental and biological factors, are of paramount importance in the relationship between environmental parameters and geochemical composition of the growth layers of the shells. Work supported by "CONCHAS" Project (PNEDC).

Study on River Snail Shells Unearthed from Laoniupo Shang Dynasty Site.

PubMed

Zhang, Rui; Yue, Lianjian; Yang, Junchang

2016-03-01

The samples of river snail shell pieces, unearthed from Laoniupo Shang dynasty site, were observed and characterized by SEM, Raman and IR to obtain the information about their chemical component and crystal structure. The uneven surface of the cuticle was covered with nanoparticles, which formed rough surface of the shells. The surface of pearl layer was combined with nano-sized flakes and kept smooth on the whole. The insection of shell was composed of three layers: the cuticle (100-120 μm in thickness), the prismatic layer (-130-140 μm in thickness), and the thickest pearl layer (280-300 μm in thickness). All layers had the component of calcium carbonate with aragonite structure and they were different in nanostructures because of different biomineralization processes.

Lithium sulfide compositions for battery electrolyte and battery electrode coatings

DOEpatents

Liang, Chengdu; Liu, Zengcai; Fu, Wunjun; Lin, Zhan; Dudney, Nancy J; Howe, Jane Y; Rondinone, Adam J

2013-12-03

Methods of forming lithium-containing electrolytes are provided using wet chemical synthesis. In some examples, the lithium containing electroytes are composed of .beta.-Li.sub.3PS.sub.4 or Li.sub.4P.sub.2S.sub.7. The solid electrolyte may be a core shell material. In one embodiment, the core shell material includes a core of lithium sulfide (Li.sub.2S), a first shell of .beta.-Li.sub.3PS.sub.4 or Li.sub.4P.sub.2S.sub.7, and a second shell including one or .beta.-Li.sub.3PS.sub.4 or Li.sub.4P.sub.2S.sub.7 and carbon. The lithium containing electrolytes may be incorporated into wet cell batteries or solid state batteries.

Lithium sulfide compositions for battery electrolyte and battery electrode coatings

DOEpatents

Liang, Chengdu; Liu, Zengcai; Fu, Wujun; Lin, Zhan; Dudney, Nancy J; Howe, Jane Y; Rondinone, Adam J

2014-10-28

Method of forming lithium-containing electrolytes are provided using wet chemical synthesis. In some examples, the lithium containing electrolytes are composed of .beta.-Li.sub.3PS.sub.4 or Li.sub.4P.sub.2S.sub.7. The solid electrolyte may be a core shell material. In one embodiment, the core shell material includes a core of lithium sulfide (Li.sub.2S), a first shell of .beta.-Li.sub.3PS.sub.4 or Li.sub.4P.sub.2S.sub.7, and a second shell including one of .beta.-Li.sub.3PS.sub.4 or Li.sub.4P.sub.2S.sub.7 and carbon. The lithium containing electrolytes may be incorporated into wet cell batteries or solid state batteries.

Electronic structure and mechanical properties of plasma nitrided ferrous alloys

NASA Astrophysics Data System (ADS)

Portolan, E.; Baumvol, I. J. R.; Figueroa, C. A.

2009-04-01

The electronic structures of the near-surface regions of two different nitrided steels (AISI 316 and 4140) were investigated using X-ray photoelectron spectroscopy. Photoelectron groups from all main chemical elements involved were addressed for steel samples with implanted-N concentrations in the range 16-32 at.%. As the implanted-N concentrations were increased, rather contrasting behaviors were observed for the two kinds of steel. The N1s photoelectrons had spectral shifts toward lower (nitrided AISI 316) or higher (nitrided AISI 4140) binding energies, whereas the Fe2p 3/2 photoelectron spectrum remains at a constant binding energy (nitrided AISI 316) or shifts toward higher binding energies (AISI 4140). These trends are discussed in terms of the metallic nitride formation and the overlapping of atomic orbitals. For nitrided AISI 316, a semi-classical approach of charge transfer between Cr and N is used to explain the experimental facts (formation of CrN), while for nitrided AISI 4140 we propose that the interaction between orbitals 4s from Fe and 2p from N promotes electrons to the conduction band increasing the electrical attraction of the N1s and Fe2p electrons in core shells (formation of FeN x). The increase in hardness of the steel upon N implantation is attributed to the localization of electrons in specific bonds, which diminishes the metallic bond character.

On the Mössbauer Effect and the Rigid Recoil Question

NASA Astrophysics Data System (ADS)

Davidson, Mark

2017-03-01

The rigid recoil of a crystal is the accepted mechanism for the Mössbauer effect. It's at odds with the special theory of relativity which does not allow perfectly rigid bodies. The standard model of particle physics which includes QED should not allow any signals to be transmitted faster than the speed of light. If perturbation theory can be used, then the X-ray emitted in a Mössbauer decay must come from a single nuclear decay vertex at which the 4-momentum is exactly conserved in a Feynman diagram. Then the 4-momentum of the final state Mössbauer nucleus must be slightly off the mass shell. This off-shell behavior would be followed by subsequent diffusion of momentum throughout the crystal to bring the nucleus back onto the mass shell and the crystal to a final relaxed state in which it moves rigidly with the appropriate recoil velocity. This mechanism explains the Mössbauer effect at the microscopic level and reconciles it with relativity. Because off-mass-shell quantum mechanics is required, the on-mass-shell theories developed originally for the Mössbauer effect are inadequate. Another possibility is that that the recoil response involves a non-perturbative effect in the standard model which could allow for a non-local instantaneous momentum transfer between the crystal and the decay (or absorption), as proposed for example by Preparata and others in super-radiance theory. The recoil time of the crystal is probably not instantaneous, and if it could be measured, one could distinguish between various theories. An experiment is proposed in this paper to measure this time. The idea is to measure the total energy radiated due to bremsstrahlung from a charged Mössbauer crystal which has experienced a recoil. Using Larmor's formula, along with corrections to it, allows one to design an experiment. The favored idea is to use many small nano-spheres of Mössbauer-active metals, whose outer surfaces are charged. The energy radiated then varies as the charge squared divided by the recoil time. This can then be measured with the extreme sensitivity available in Mössbauer experiments. If it turns out that experiments prove the need for off-mass-shell theory, then this would have profound implications for all of condensed matter physics. It would mean that an off-mass-shell theory like those considered by Stueckelberg, Horwitz, Piron, Greenberger, and many others are required to describe nature. The inclusion of these would be a major shift in the foundations. It would mean that there are new dynamic variables—the rest masses of particles. The ability to measure the diffusion relaxation time should prove useful also in chemical analysis, and provide a new class of analytical methods for material science. This problem is also interesting because the Mössbauer effect is a phenomenon where the solid-state environment dramatically and indisputably influences the probability of a nuclear process.

IODIDE AEROSOL SORBENTS FOR MERCURY CAPTURE IN COMBUSTION EXHAUSTS

EPA Science Inventory

Several sorbent processes are being studied for their feasibility for mercury capture. Mercury is different from the other heavy metals as it is not as chemically reactive (due to a filled outer electronic shell), thus making it difficult for sorbents to chemically trap it (a). ...

The role of radiative de-excitation in the neutralization process of highly charged ions interacting with a single layer of graphene

NASA Astrophysics Data System (ADS)

Schwestka, J.; Wilhelm, R. A.; Gruber, E.; Heller, R.; Kozubek, R.; Schleberger, M.; Facsko, S.; Aumayr, F.

2018-05-01

X-ray emission of slow (<1 a.u.) highly charged Argon and Xenon ions is measured for transmission through a freestanding single layer of graphene. To discriminate against X-ray emission originating from the graphene's support grid a coincidence technique is used. X-ray emission of 75 keV Ar17+ and Ar18+ ions with either one or two K-shell vacancies is recorded. Using a windowless Bruker XFlash detector allows us to measure additionally Ar KLL and KLM Auger electrons and determine the branching ratio of radiative vs. non-radiative decay of Ar K-shell holes. Furthermore, X-ray spectra for 100 keV Xe22+-Xe35+ ions are compared, showing a broad M-line peak for all cases, where M-shell vacancies are present. All these peaks are accompanied by emission lines at still higher energies indicating the presence of a hollow atom during X-ray decay. We report a linear shift of the main M-line peak to higher energies for increasing incident charge state, i.e. increasing number of M-shell holes.

Tuning the Magnetic Properties of Metal Oxide Nanocrystal Heterostructures by Cation Exchange

PubMed Central

2013-01-01

For three types of colloidal magnetic nanocrystals, we demonstrate that postsynthetic cation exchange enables tuning of the nanocrystal’s magnetic properties and achieving characteristics not obtainable by conventional synthetic routes. While the cation exchange procedure, performed in solution phase approach, was restricted so far to chalcogenide based semiconductor nanocrystals, here ferrite-based nanocrystals were subjected to a Fe2+ to Co2+ cation exchange procedure. This allows tracing of the compositional modifications by systematic and detailed magnetic characterization. In homogeneous magnetite nanocrystals and in gold/magnetite core shell nanocrystals the cation exchange increases the coercivity field, the remanence magnetization, as well as the superparamagnetic blocking temperature. For core/shell nanoheterostructures a selective doping of either the shell or predominantly of the core with Co2+ is demonstrated. By applying the cation exchange to FeO/CoFe2O4 core/shell nanocrystals the Neél temperature of the core material is increased and exchange-bias effects are enhanced so that vertical shifts of the hysteresis loops are obtained which are superior to those in any other system. PMID:23362940

Single-mode tunable laser emission in the single-exciton regime from colloidal nanocrystals

PubMed Central

Grivas, Christos; Li, Chunyong; Andreakou, Peristera; Wang, Pengfei; Ding, Ming; Brambilla, Gilberto; Manna, Liberato; Lagoudakis, Pavlos

2013-01-01

Whispering-gallery-mode resonators have been extensively used in conjunction with different materials for the development of a variety of photonic devices. Among the latter, hybrid structures, consisting of dielectric microspheres and colloidal core/shell semiconductor nanocrystals as gain media, have attracted interest for the development of microlasers and studies of cavity quantum electrodynamic effects. Here we demonstrate single-exciton, single-mode, spectrally tuned lasing from ensembles of optical antenna-designed, colloidal core/shell CdSe/CdS quantum rods deposited on silica microspheres. We obtain single-exciton emission by capitalizing on the band structure of the specific core/shell architecture that strongly localizes holes in the core, and the two-dimensional quantum confinement of electrons across the elongated shell. This creates a type-II conduction band alignment driven by coulombic repulsion that eliminates non-radiative multi-exciton Auger recombination processes, thereby inducing a large exciton–bi-exciton energy shift. Their ultra-low thresholds and single-mode, single-exciton emission make these hybrid lasers appealing for various applications, including quantum information processing. PMID:23974520

Fragment-based {sup 13}C nuclear magnetic resonance chemical shift predictions in molecular crystals: An alternative to planewave methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartman, Joshua D.; Beran, Gregory J. O., E-mail: gregory.beran@ucr.edu; Monaco, Stephen

2015-09-14

We assess the quality of fragment-based ab initio isotropic {sup 13}C chemical shift predictions for a collection of 25 molecular crystals with eight different density functionals. We explore the relative performance of cluster, two-body fragment, combined cluster/fragment, and the planewave gauge-including projector augmented wave (GIPAW) models relative to experiment. When electrostatic embedding is employed to capture many-body polarization effects, the simple and computationally inexpensive two-body fragment model predicts both isotropic {sup 13}C chemical shifts and the chemical shielding tensors as well as both cluster models and the GIPAW approach. Unlike the GIPAW approach, hybrid density functionals can be used readilymore » in a fragment model, and all four hybrid functionals tested here (PBE0, B3LYP, B3PW91, and B97-2) predict chemical shifts in noticeably better agreement with experiment than the four generalized gradient approximation (GGA) functionals considered (PBE, OPBE, BLYP, and BP86). A set of recommended linear regression parameters for mapping between calculated chemical shieldings and observed chemical shifts are provided based on these benchmark calculations. Statistical cross-validation procedures are used to demonstrate the robustness of these fits.« less

Ionic bonding of lanthanides, as influenced by d- and f-atomic orbitals, by core-shells and by relativity.

PubMed

Ji, Wen-Xin; Xu, Wei; Schwarz, W H Eugen; Wang, Shu-Guang

2015-03-15

Lanthanide trihalide molecules LnX3 (X = F, Cl, Br, I) were quantum chemically investigated, in particular detail for Ln = Lu (lutetium). We applied density functional theory (DFT) at the nonrelativistic and scalar and SO-coupled relativistic levels, and also the ab initio coupled cluster approach. The chemically active electron shells of the lanthanide atoms comprise the 5d and 6s (and 6p) valence atomic orbitals (AO) and also the filled inner 4f semivalence and outer 5p semicore shells. Four different frozen-core approximations for Lu were compared: the (1s(2) -4d(10) ) [Pd] medium core, the [Pd+5s(2) 5p(6) = Xe] and [Pd+4f(14) ] large cores, and the [Pd+4f(14) +5s(2) 5p(6) ] very large core. The errors of LuX bonding are more serious on freezing the 5p(6) shell than the 4f(14) shell, more serious upon core-freezing than on the effective-core-potential approximation. The LnX distances correlate linearly with the AO radii of the ionic outer shells, Ln(3+) -5p(6) and X(-) -np(6) , characteristic for dominantly ionic Ln(3+) -X(-) binding. The heavier halogen atoms also bind covalently with the Ln-5d shell. Scalar relativistic effects contract and destabilize the LuX bonds, spin orbit coupling hardly affects the geometries but the bond energies, owing to SO effects in the free atoms. The relativistic changes of bond energy BE, bond length Re , bond force k, and bond stretching frequency vs do not follow the simple rules of Badger and Gordy (Re ∼BE∼k∼vs ). The so-called degeneracy-driven covalence, meaning strong mixing of accidentally near-degenerate, nearly nonoverlapping AOs without BE contribution is critically discussed. © 2015 Wiley Periodicals, Inc.

Microcavity surface plasmon resonance bio-sensors

NASA Astrophysics Data System (ADS)

Mosavian, Nazanin

This work discusses a miniature surface plasmon biosensor which uses a dielectric sub- micron diameter core with gold spherical shell. The shell has a subwavelength nanoaperture believed to excite stationary plasmon resonances at the biosensor's surface. The sub-micron cavity enhances the measurement sensitivity of molecules binding to the sensor surface. We used visible-range optical spectroscopy to study the wavelength shift as bio-molecules absorbed-desorbed at the shell surface. We also used Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB) ablation to study the characteristics of microcavity surface plasmon resonance sensor (MSPRS) and the inner structure formed with metal deposition and its spectrum. We found that resonances at 580 nm and 670 nm responded to bound test agents and that Surface Plasmon Resonance (SPR) sensor intensity could be used to differentiate between D-glucose and L-glucose. The responsiveness of the system depended upon the mechanical integrity of the metallic surface coating.

Preparation of SiC/SiO2 core-shell nanowires via molten salt mediated carbothermal reduction route

NASA Astrophysics Data System (ADS)

Zhang, Ju; Yan, Shuai; Jia, Quanli; Huang, Juntong; Lin, Liangxu; Zhang, Shaowei

2016-06-01

The growth of silicon carbide (SiC) crystal generally requires a high temperature, especially when low quality industrial wastes are used as the starting raw materials. In this work, SiC/SiO2 core-shell nanowires (NWs) were synthesized from low cost silica fume and sucrose via a molten salt mediated carbothermal reduction (CR) route. The molten salt was found to be effective in promoting the SiC growth and lowering the synthesis temperature. The resultant NWs exhibited a heterostructure composed of a 3C-SiC core of 100 nm in diameter and a 5-10 nm thick amorphous SiO2 shell layer. The photoluminescence spectrum of the achieved SiC NWs displayed a significant blue shift (a dominant luminescence at round 422 nm), which suggested that they were high quality and could be a promising candidate material for future optoelectronic applications.

Synthesis of NiAu alloy and core-shell nanoparticles in water-in-oil microemulsions

NASA Astrophysics Data System (ADS)

Chiu, Hsin-Kai; Chiang, I.-Chen; Chen, Dong-Hwang

2009-07-01

NiAu alloy nanoparticles with various Ni/Au molar ratios were synthesized by the hydrazine reduction of nickel chloride and hydrogen tetrachloroaurate in the microemulsion system. They had a face-centered cubic structure and a mean diameter of 6-13 nm, decreasing with increasing Au content. As Au nanoparticles did, they showed a characteristic absorption peak at about 520 nm but the intensity decreased with increasing Ni content. Also, they were nearly superparamagnetic, although the magnetization decreased significantly with increasing Au content. Under an external magnetic field, they could be self-organized into the parallel lines. In addition, the core-shell nanoparticles, Ni3Au1@Au, were prepared by the Au coating on the surface of Ni3Au1 alloy nanoparticles. By increasing the hydrogen tetrachloroaurate concentration for Au coating, the thickness of Au shells could be raised and led to an enhanced and red-shifted surface plasmon absorption.

Counter Nuclear, Biological, and Chemical Operations, This document compliments JCS Pub 3-11

DTIC Science & Technology

2000-08-16

Successful German Chemical Attack The concept of creating a toxic gas cloud from chemical cylinders was credited to Fritz Haber of the Kaiser Wilhelm Physical...of considerations: The high caliber of German theoretical and experimental physicists like Otto Hahn, Paul Harteck, Werner Heisenberg, Fritz ...Institute of Berlin in late 1914. Owing to a shortage of artillery shells, Haber thought a chemical gas cloud would negate the enemy’s earthworks

Rubber Fruit Shell (Hevea brasiliensis) as bio sorbent to remove FFA (Free Fatty Acid) content in CPO (Crude Palm Oil)

NASA Astrophysics Data System (ADS)

Pandia, S.; Sinaga, M. S.; Masyithah, Z.; Husin, A.; Nurfadilla, S.; Fitriani; Sipahutar, B. K. S.

2018-02-01

This study aimed to discover the effectiveness of the shell of rubber fruit as bio sorbent for removing FFA (Free Fatty Acid) content in CPO (Crude Palm Oil). Methods used in this study were pretreatment, activation (carbonating and chemically) and adsorption process at room temperature. In the beginning, the shell of rubber fruit was cleaned and dried under the sun. Then the shell was cut for about 0.5 cm of length and carbonated in a furnace for 1h at 600°C. After that, they were crushed to pass through 140 meshes and activated using three variations of chemical such as 6 of HNO3, 6N of KOH and 6N of H3PO4 at certain ratio as 1:3, 1:4, and 1:5 (b/v). The adsorption process was carried out using bio sorbent with the highest iodine number in varying bio sorbent dosage and contact time. The highest iodine number was 913.680 mg/g and obtained at the ratio of bio sorbent to 6N of KOH as 1:5. The best removal of FFA content was 91.94% and at 1% bio sorbent dose and 30 min of contact time.

Novel Organically Modified Core-Shell Clay for Epoxy Composites-"SOBM Filler 1".

PubMed

Iheaturu, Nnamdi Chibuike; Madufor, Innocent Chimezie

2014-01-01

Preparation of a novel organically modified clay from spent oil base drilling mud (SOBM) that could serve as core-shell clay filler for polymers is herein reported. Due to the hydrophilic nature of clay, its compatibility with polymer matrix was made possible through modification of the surface of the core clay sample with 3-aminopropyltriethoxysilane (3-APTES) compound prior to its use. Fourier transform infrared (FT-IR) spectroscopy was used to characterize clay surface modification. Electron dispersive X-ray diffraction (EDX) and scanning electron microscopy (SEM) were used to expose filler chemical composition and morphology, while electrophoresis measurement was used to examine level of filler dispersion. Results show an agglomerated core clay powder after high temperature treatment, while EDX analysis shows that the organically modified clay is composed of chemical inhomogeneities, wherein elemental compositions in weight percent vary from one point to the other in a probe of two points. Micrographs of the 3-APTES coupled SOBM core-shell clay filler clearly show cloudy appearance, while FT-IR indicates 25% and 5% increases in fundamental vibrations band at 1014 cm(-1) and 1435 cm(-1), respectively. Furthermore, 3-APTES coupled core-shell clay was used to prepare epoxy composites and tested for mechanical properties.

Novel Organically Modified Core-Shell Clay for Epoxy Composites—“SOBM Filler 1”

PubMed Central

Iheaturu, Nnamdi Chibuike; Madufor, Innocent Chimezie

2014-01-01

Preparation of a novel organically modified clay from spent oil base drilling mud (SOBM) that could serve as core-shell clay filler for polymers is herein reported. Due to the hydrophilic nature of clay, its compatibility with polymer matrix was made possible through modification of the surface of the core clay sample with 3-aminopropyltriethoxysilane (3-APTES) compound prior to its use. Fourier transform infrared (FT-IR) spectroscopy was used to characterize clay surface modification. Electron dispersive X-ray diffraction (EDX) and scanning electron microscopy (SEM) were used to expose filler chemical composition and morphology, while electrophoresis measurement was used to examine level of filler dispersion. Results show an agglomerated core clay powder after high temperature treatment, while EDX analysis shows that the organically modified clay is composed of chemical inhomogeneities, wherein elemental compositions in weight percent vary from one point to the other in a probe of two points. Micrographs of the 3-APTES coupled SOBM core-shell clay filler clearly show cloudy appearance, while FT-IR indicates 25% and 5% increases in fundamental vibrations band at 1014 cm−1 and 1435 cm−1, respectively. Furthermore, 3-APTES coupled core-shell clay was used to prepare epoxy composites and tested for mechanical properties. PMID:27355022

The effect of temperature and dot size on the spectral properties of colloidal InP/ZnS core-shell quantum dots.

PubMed

Narayanaswamy, Arun; Feiner, L F; Meijerink, A; van der Zaag, P J

2009-09-22

Visual color changes between 300 and 510 K were observed in the photoluminescence (PL) of colloidal InP/ZnS core-shell nanocrystals. A subsequent study of PL spectra in the range 2-510 K and fitting the temperature dependent line shift and line width to theoretical models show that the dominant (dephasing) interaction is due to scattering by acoustic phonons of about 23 meV. Low temperature photoluminescence excitation measurements show that the excitonic band gap depends approximately inversely linearly on the quantum dot size d, which is distinctly weaker than the dependence predicted by current theories.

Dropping macadamia nuts-in-shell reduces kernel roasting quality.

PubMed

Walton, David A; Wallace, Helen M

2010-10-01

Macadamia nuts ('nuts-in-shell') are subjected to many impacts from dropping during postharvest handling, resulting in damage to the raw kernel. The effect of dropping on roasted kernel quality is unknown. Macadamia nuts-in-shell were dropped in various combinations of moisture content, number of drops and receiving surface in three experiments. After dropping, samples from each treatment and undropped controls were dry oven-roasted for 20 min at 130 °C, and kernels were assessed for colour, mottled colour and surface damage. Dropping nuts-in-shell onto a bed of nuts-in-shell at 3% moisture content or 20% moisture content increased the percentage of dark roasted kernels. Kernels from nuts dropped first at 20%, then 10% moisture content, onto a metal plate had increased mottled colour. Dropping nuts-in-shell at 3% moisture content onto nuts-in-shell significantly increased surface damage. Similarly, surface damage increased for kernels dropped onto a metal plate at 20%, then at 10% moisture content. Postharvest dropping of macadamia nuts-in-shell causes concealed cellular damage to kernels, the effects not evident until roasting. This damage provides the reagents needed for non-enzymatic browning reactions. Improvements in handling, such as reducing the number of drops and improving handling equipment, will reduce cellular damage and after-roast darkening. Copyright © 2010 Society of Chemical Industry.

Geoarchaeological approaches to understanding human-environment interactions in Australia's tropical north: the Weipa shell mounds revisited.

NASA Astrophysics Data System (ADS)

Fanning, P. C.; Holdaway, S. J.; Shiner, J.; Petchey, F.

2012-04-01

Western Cape York Peninsula, particularly the Weipa region, has seen sustained archaeological investigation since the 1960s. These studies primarily concentrated on the shell mounds associated with coastal environments first observed at the beginning of the 20th century. Despite claims that the shell mounds were of natural origin, archaeological investigations convincingly demonstrated that they are primarily cultural deposits. Geomorphological studies indicate that chenier (beach ridge) formation occurred after sea-level stabilisation in the mid- to late Holocene, and is connected to the formation of estuaries at the mouths of the Mission, Pine, Hey and Embley Rivers. Anadara shell bed formation is in turn connected with the evolution of the estuaries. However, the relationship between shell mound age and location relative to the coastline at Weipa is neither well defined, nor tested at multiple locations. Given that the coast is susceptible to the effects of sea-level fluctuations and environmental change, and the Anadara beds can become depleted as a result of environmental shifts, the shell mounds provide a datable record of human reaction to coastal landscape and environmental change. Here, we report preliminary results of a new investigation of the shell mounds of the Weipa region. Radiocarbon and OSL-based age determinations from samples of shell, charcoal and sediment collected from trenches excavated into shell mounds on the northern shore of the Embley River indicate a relationship between the time of initial accumulation of shell and the age of the landform features upon which they were built, which in turn are a result of coastline evolution during the mid to late Holocene. These mounds are the oldest yet recorded for the Weipa region, with accumulation in one case commencing around 3500 cal BP. Accumulation appears to be more or less continuous, and abruptly ceases after 400-650 yrs. We discuss implications for understanding human-environment interactions in the past, and our strategy for further research.

Adsorption of volatile organic compounds by pecan shell- and almond shell-based granular activated carbons.

PubMed

Bansode, R R; Losso, J N; Marshall, W E; Rao, R M; Portier, R J

2003-11-01

The objective of this research was to determine the effectiveness of using pecan and almond shell-based granular activated carbons (GACs) in the adsorption of volatile organic compounds (VOCs) of health concern and known toxic compounds (such as bromo-dichloromethane, benzene, carbon tetrachloride, 1,1,1-trichloromethane, chloroform, and 1,1-dichloromethane) compared to the adsorption efficiency of commercially used carbons (such as Filtrasorb 200, Calgon GRC-20, and Waterlinks 206C AW) in simulated test medium. The pecan shell-based GACs were activated using steam, carbon dioxide or phosphoric acid. An almond shell-based GAC was activated with phosphoric acid. Our results indicated that steam- or carbon dioxide-activated pecan shell carbons were superior in total VOC adsorption to phosphoric acid-activated pecan shell or almond shell carbons, inferring that the method of activation selected for the preparation of activated carbons affected the adsorption of VOCs and hence are factors to be considered in any adsorption process. The steam-activated, pecan shell carbon adsorbed more total VOCs than the other experimental carbons and had an adsorption profile similar to the two coconut shell-based commercial carbons, but had greater adsorption than the coal-based commercial carbon. All the carbons studied adsorbed benzene more effectively than the other organics. Pecan shell, steam-activated and acid-activated GACs showed higher adsorption of 1,1,1-trichloroethane than the other carbons studied. Multivariate analysis was conducted to group experimental carbons and commercial carbons based on their physical, chemical, and adsorptive properties. The results of the analysis conclude that steam-activated and acid-activated pecan shell carbons clustered together with coal-based and coconut shell-based commercial carbons, thus inferring that these experimental carbons could potentially be used as alternative sources for VOC adsorption in an aqueous environment.

A novel magnetic core-shell nanocomposite Fe3O4@chitosan@ZnO for the green synthesis of 2-benzimidazoles

NASA Astrophysics Data System (ADS)

Tian, Fei; Niu, Libo; Chen, Bo; Gao, Xuejia; Lan, Xingwang; Huo, Li; Bai, Guoyi

2017-10-01

A novel magnetic core-shell nanocomposite Fe3O4@Chitosan@ZnO was successfully prepared by in situ chemical precipitation method. It has a clear core-shell structure with magnetic Fe3O4 (about 160 nm in diameter) as core, chitosan as the inner shell, and ZnO as the outer shell, as demonstrated by the transmission electron microscopy and the related elemental mapping. Moreover, this nanocomposite has high magnetization (43.6 emu g-1) so that it can be easily separated from the reaction mixture within 4 s by an external magnetic field. The introduction of the natural chitosan shell, instead of the conventional SiO2 shell, and its combination with the active ZnO ensures this novel nanocomposite green character and good catalytic performance in the synthesis of 2-benzimidazoles with moderate to excellent isolated yields at room temperature. Notably, it can be recycled seven times without appreciable loss of its initial catalytic activity, demonstrating its good stability and making it an attractive candidate for the green synthesis of 2-benzimidazoles. [Figure not available: see fulltext.

Core@shell@shell structured carbon-based magnetic ternary nanohybrids: Synthesis and their enhanced microwave absorption properties

NASA Astrophysics Data System (ADS)

Yang, Erqi; Qi, Xiaosi; Xie, Ren; Bai, Zhongchen; Jiang, Yang; Qin, Shuijie; Zhong, Wei; Du, Youwei

2018-05-01

High encapsulation efficiency of core@shell@shell structured carbon-based magnetic ternary nanohybrids have been synthesized in high yield by chemical vapor deposition of acetylene directly over octahedral-shaped Fe2O3 nanoparticles. By controlling the pyrolysis temperature, Fe3O4@Fe3C@carbon nanotubes (CNTs) and Fe@Fe3C@CNTs ternary nanohybrids could be selectively produced. The optimal RL values for the as-prepared ternary nanohybrids could reach up to ca. -46.7, -52.7 and -29.5 dB, respectively. The excellent microwave absorption properties of the obtaiend ternary nanohybrids were proved to ascribe to the quarter-wavelength matching model. Moreover, the as-prepared Fe@Fe3C@CNTs ternary nanohybrids displayed remarkably enhanced EM wave absorption capabilities compared to Fe3O4@Fe3C@CNTs due to their excellent dielectric loss abilities, good complementarities between the dielectric loss and the magnetic loss, and high attenuation constant. Generally, this strategy can be extended to explore other categories of core@shell or core@shell@shell structured carbon-based nanohybrids, which is very beneficial to accelerate the advancements of high performance MAMs.

The role of ion exchange in the passivation of In(Zn)P nanocrystals with ZnS

PubMed Central

Cho, Deok-Yong; Xi, Lifei; Boothroyd, Chris; Kardynal, Beata; Lam, Yeng Ming

2016-01-01

We have investigated the chemical state of In(Zn)P/ZnS core/shell nanocrystals (NCs) for color conversion applications using hard X-ray absorption spectroscopy (XAS) and photoluminescence excitation (PLE). Analyses of the edge energies as well as the X-ray absorption fine structure (XAFS) reveal that the Zn2+ ions from ZnS remain in the shell while the S2− ions penetrate into the core at an early stage of the ZnS deposition. It is further demonstrated that for short growth times, the ZnS shell coverage on the core was incomplete, whereas the coverage improved gradually as the shell deposition time increased. Together with evidence from PLE spectra, where there is a strong indication of the presence of P vacancies, this suggests that the core-shell interface in the In(Zn)P/ZnS NCs are subject to substantial atomic exchanges and detailed models for the shell structure beyond simple layer coverage are needed. This substantial atomic exchange is very likely to be the reason for the improved photoluminescence behavior of the core-shell particles compare to In(Zn)P-only NCs as S can passivate the NCs surfaces. PMID:26972936

Use of Walnut Shell Powder to Inhibit Expression of Fe2+-Oxidizing Genes of Acidithiobacillus Ferrooxidans

PubMed Central

Li, Yuhui; Liu, Yehao; Tan, Huifang; Zhang, Yifeng; Yue, Mei

2016-01-01

Acidithiobacillus ferrooxidans is a Gram-negative bacterium that obtains energy by oxidizing Fe2+ or reduced sulfur compounds. This bacterium contributes to the formation of acid mine drainage (AMD). This study determined whether walnut shell powder inhibits the growth of A. ferrooxidans. First, the effects of walnut shell powder on Fe2+ oxidization and H+ production were evaluated. Second, the chemical constituents of walnut shell were isolated to determine the active ingredient(s). Third, the expression of Fe2+-oxidizing genes and rus operon genes was investigated using real-time polymerase chain reaction. Finally, growth curves were plotted, and a bioleaching experiment was performed to confirm the active ingredient(s) in walnut shells. The results indicated that both walnut shell powder and the phenolic fraction exert high inhibitory effects on Fe2+ oxidation and H+ production by A. ferrooxidans cultured in standard 9K medium. The phenolic components exert their inhibitory effects by down-regulating the expression of Fe2+-oxidizing genes and rus operon genes, which significantly decreased the growth of A. ferrooxidans. This study revealed walnut shell powder to be a promising substance for controlling AMD. PMID:27144574

Molecular dynamics averaging of Xe chemical shifts in liquids.

PubMed

Jameson, Cynthia J; Sears, Devin N; Murad, Sohail

2004-11-15

The Xe nuclear magnetic resonance chemical shift differences that afford the discrimination between various biological environments are of current interest for biosensor applications and medical diagnostic purposes. In many such environments the Xe signal appears close to that in water. We calculate average Xe chemical shifts (relative to the free Xe atom) in solution in eleven liquids: water, isobutane, perfluoro-isobutane, n-butane, n-pentane, neopentane, perfluoroneopentane, n-hexane, n-octane, n-perfluorooctane, and perfluorooctyl bromide. The latter is a liquid used for intravenous Xe delivery. We calculate quantum mechanically the Xe shielding response in Xe-molecule van der Waals complexes, from which calculations we develop Xe (atomic site) interpolating functions that reproduce the ab initio Xe shielding response in the complex. By assuming additivity, these Xe-site shielding functions can be used to calculate the shielding for any configuration of such molecules around Xe. The averaging over configurations is done via molecular dynamics (MD). The simulations were carried out using a MD technique that one of us had developed previously for the simulation of Henry's constants of gases dissolved in liquids. It is based on separating a gaseous compartment in the MD system from the solvent using a semipermeable membrane that is permeable only to the gas molecules. We reproduce the experimental trends in the Xe chemical shifts in n-alkanes with increasing number of carbons and the large chemical shift difference between Xe in water and in perfluorooctyl bromide. We also reproduce the trend for a given solvent of decreasing Xe chemical shift with increasing temperature. We predict chemical shift differences between Xe in alkanes vs their perfluoro counterparts.

The chemical composition of the egg shells of the potato cyst-nematode, Heterodera rostochiensis Woll

PubMed Central

Clarke, A. J.; Cox, Patricia M.; Shepherd, Audrey M.

1967-01-01

1. Eggs of the potato cyst-nematode (Heterodera rostochiensis Woll.) were isolated by sieving a suspension of crushed cysts. Eggs were broken open by ultrasonic vibration and the egg shells separated from the released larvae by centrifuging in a potassium tartrate density gradient. About 1 mg. of dried egg shells was obtained from 1000 cysts. 2. The major constituent of the egg shells was protein (59%, calculated from nitrogen content). About 80% of the egg shells went into solution on acid hydrolysis. Of the 18 amino acids determined with the Technicon Auto-Analyser, proline was most abundant and, with aspartic acid, glycine and serine, made up about 64% by weight of the total amino acids. The small amounts of aromatic and sulphur-containing amino acids, and the presence of hydroxy-proline, indicate a collagen-like protein. 3. The egg shells gave a positive van Wisselingh colour test for chitin, and glucosamine was detected in their acid hydrolysate by chromatography. The glucosamine content of the egg shells, determined by the Elson–Morgan colorimetric method, was 7%, corresponding to about 9% chitin. 4. Dried egg shells contained about 7% of lipid, 6% of carbohydrate and 3% of ash. Polyphenols (3% by weight of the egg shells) were detected in the acid hydrolysates. 5. Neither the collagen nor the chitin showed evidence of crystallinity when examined by X-ray diffraction. PMID:6069200

Mussel Shell Evaluation as Bioindicator For Heavy Metals

NASA Astrophysics Data System (ADS)

Andrello, Avacir Casanova; Lopes, Fábio; Galvão, Tiago Dutra

2010-05-01

Recently, in Brazil, it has appeared a new and unusual "plague" in lazer and commercial fishing. It is caused by the parasitic larval phase of certain native bivalve mollusks of fresh water known as "Naiades" and its involves the presence of big bivalve of fresh water, mainly Anodontites trapesialis, in the tanks and dams of the fish creation. These bivalve mollusks belong to the Unionoida Order, Mycetopodidae Family. The objective of the present work was to analyze the shells of these mollusks to verify the possibility of use as bioindicators for heavy metals in freshwater. The mollusks shells were collected in a commercial fishing at Londrina-PR. A qualitative analysis was made to determine the chemical composition of the shells and verify a possible correlation with existent heavy metals in the aquatic environment. In the inner part of the shells were identified the elements Ca, P, Fe, Mn and Sr and in the outer part were identified Ca, P, Fe, Mn, Sr and Cu. The Ca ratio of the outer part by inner part of the analyzed shells is around of 1, as expected, because Ca is the main compound of mollusks shells. The ratio of P, Fe, Mn, and Sr to the Ca were constant in all analyzed shells, being close to 0.015. The ratio Cu/Ca varied among the shells, showing that this mollusk is sensitive to concentration of this element in the aquatic environment.

NMRDSP: an accurate prediction of protein shape strings from NMR chemical shifts and sequence data.

PubMed

Mao, Wusong; Cong, Peisheng; Wang, Zhiheng; Lu, Longjian; Zhu, Zhongliang; Li, Tonghua

2013-01-01

Shape string is structural sequence and is an extremely important structure representation of protein backbone conformations. Nuclear magnetic resonance chemical shifts give a strong correlation with the local protein structure, and are exploited to predict protein structures in conjunction with computational approaches. Here we demonstrate a novel approach, NMRDSP, which can accurately predict the protein shape string based on nuclear magnetic resonance chemical shifts and structural profiles obtained from sequence data. The NMRDSP uses six chemical shifts (HA, H, N, CA, CB and C) and eight elements of structure profiles as features, a non-redundant set (1,003 entries) as the training set, and a conditional random field as a classification algorithm. For an independent testing set (203 entries), we achieved an accuracy of 75.8% for S8 (the eight states accuracy) and 87.8% for S3 (the three states accuracy). This is higher than only using chemical shifts or sequence data, and confirms that the chemical shift and the structure profile are significant features for shape string prediction and their combination prominently improves the accuracy of the predictor. We have constructed the NMRDSP web server and believe it could be employed to provide a solid platform to predict other protein structures and functions. The NMRDSP web server is freely available at http://cal.tongji.edu.cn/NMRDSP/index.jsp.

Handling the influence of chemical shift in amplitude-modulated heteronuclear dipolar recoupling solid-state NMR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basse, Kristoffer; Shankar, Ravi; Bjerring, Morten

We present a theoretical analysis of the influence of chemical shifts on amplitude-modulated heteronuclear dipolar recoupling experiments in solid-state NMR spectroscopy. The method is demonstrated using the Rotor Echo Short Pulse IRrAdiaTION mediated Cross-Polarization ({sup RESPIRATION}CP) experiment as an example. By going into the pulse sequence rf interaction frame and employing a quintuple-mode operator-based Floquet approach, we describe how chemical shift offset and anisotropic chemical shift affect the efficiency of heteronuclear polarization transfer. In this description, it becomes transparent that the main attribute leading to non-ideal performance is a fictitious field along the rf field axis, which is generated frommore » second-order cross terms arising mainly between chemical shift tensors and themselves. This insight is useful for the development of improved recoupling experiments. We discuss the validity of this approach and present quaternion calculations to determine the effective resonance conditions in a combined rf field and chemical shift offset interaction frame transformation. Based on this, we derive a broad-banded version of the {sup RESPIRATION}CP experiment. The new sequence is experimentally verified using SNNFGAILSS amyloid fibrils where simultaneous {sup 15}N → {sup 13}CO and {sup 15}N → {sup 13}C{sub α} coherence transfer is demonstrated on high-field NMR instrumentation, requiring great offset stability.« less

Density functional study of the 13C NMR chemical shifts in small-to-medium-diameter infinite single-walled carbon nanotubes.

PubMed

Zurek, Eva; Pickard, Chris J; Walczak, Brian; Autschbach, Jochen

2006-11-02

NMR chemical shifts were calculated for semiconducting (n,0) single-walled carbon nanotubes (SWNTs) with n ranging from 7 to 17. Infinite isolated SWNTs were calculated using a gauge-including projector-augmented plane-wave (GIPAW) approach with periodic boundary conditions and density functional theory (DFT). In order to minimize intertube interactions in the GIPAW computations, an intertube distance of 8 A was chosen. For the infinite tubes, we found a chemical shift range of over 20 ppm for the systems considered here. The SWNT family with lambda = mod(n, 3) = 0 has much smaller chemical shifts compared to the other two families with lambda = 1 and lambda = 2. For all three families, the chemical shifts decrease roughly inversely proportional to the tube's diameter. The results were compared to calculations of finite capped SWNT fragments using a gauge-including atomic orbital (GIAO) basis. Direct comparison of the two types of calculations could be made if benzene was used as the internal (computational) reference. The NMR chemical shifts of finite SWNTs were found to converge very slowly, if at all, to the infinite limit, indicating that capping has a strong effect (at least for the (9,0) tubes) on the calculated properties. Our results suggest that (13)C NMR has the potential for becoming a useful tool in characterizing SWNT samples.

Synthesis of Ag@TiO2 core-shells using a rapid microwave irradiation and study of their nonlinear optical properties

NASA Astrophysics Data System (ADS)

Karimipour, M.; Ebrahimi, M.; Abafat, Z.; Molaei, M.

2016-07-01

Ag@TiO2 core-shells were synthesized by employing oleylamine as capping agent and using a rapid microwave method. The shell growth was optimized first based on the variation of oleylamine content in the reaction solution. Thereafter the shell thickness was varied just by varying titanium isopropoxide (TiTP) with 25, 50, 100 and 200 μl as TiO2 precursor. The prepared core-shells were characterized by means of XRD, FTIR spectroscopy, transmission electron microscopy, and UV-Vis spectroscopy. XRD analysis revealed a cubic crystal structure for Ag and Anatase phase for TiO2. TEM images clearly indicated that the size of Ag core is roughly 15 nm and with the increase of TiTP, the shell thickness increases and varies between 5 nm and 15 nm. UV-Vis spectroscopy indicated that the plasmon resonance of Ag nanoparticles shifts from 407 nm up to 454 nm with the increase of TiTP precursor. Using a low power laser diode at a 532 nm wavelength, the magnitude and the sign of the nonlinear refractive index were determined by the Z-scan technique and Sheik-Bahae model. The results show that the enhancement of nonlinear optical properties originates from the quality of TiO2 shell growth. The highest nonlinearity belongs to the sample synthesized with 100 μlit TiTP. Generally all the prepared Ag@TiO2 core-shells show both saturable and reverse saturable absorption. They exhibit also a considerable nonlinear absorption and nonlinear refractive index ranging from -4.21 × 10-7 to -3.51 × 10-6 which are comparable to the sole Ag and TiO2 nanoparticles.

Study of CNSL Processing Plants Located in Cuddalore District of Tamil Nadu, India

NASA Astrophysics Data System (ADS)

Bhaskaran, E.

2017-06-01

Basic chemicals and their related products like petrochemicals, fertilisers, paints, varnishes, glass, perfumes, toiletries, pharmaceuticals, etc. form a very significant part of the Indian economy and account for about 3% of India's GDP. Among the most diversified industrial sectors, it covers an array of more than 70,000 commercial products. The chemicals sector accounts for about 14% in overall index of industrial production, 11% of total exports and about 7.2% of total imports. The total Foreign Direct Investment in Chemicals (excluding fertilizers) was US 7252 million from April 2011 to March 2012. For inclusive growth and sustainable development most of the Chemical manufacturers should adopt the Cluster Development Approach. The objective is to Study the Occupational Hazards in Cashew Nut Shell Liquid (CNSL) Oil Processing Industries in Panruti Block of Cuddalore District. The methodology adopted is collection of primary processing data during November 2012 from 14 CNSL Processing Industries in Panruti Block of Cuddalore District. Majority of Industries has not processed the CNSL oil as per standards and there is much scope for occupational hazards. In two processes the CNSL oil is let out in the tank constructed equal to ground height where there is possibility of workers getting trapped inside the high temperature CNSL oil. The electric motor is also placed in the ground so that there is possibility of current passing in the ground which leads to occupational hazards for the workers. To conclude, Cashew Shell Oil Processing Industries in Panruti Block of Cuddalore District needs is re-engineering in design and operation starting from Cashew Shell storage, extraction of shell oil from expeller, processing and packaging of CNSL in barrels for better safety from occupational hazards and Cyclones. Moreover for sustainable development, they should adopt cluster development approach, so that infrastructure interrelationships, technology interrelationships, procurement interrelationships, production interrelationships and marketing interrelationships will take place among CNSL manufacturers to decrease cost, increase quality, productivity and efficiency to compete in the world market.

NMR Mapping of Protein Conformational Landscapes using Coordinated Behavior of Chemical Shifts upon Ligand Binding

PubMed Central

Cembran, Alessandro; Kim, Jonggul; Gao, Jiali; Veglia, Gianluigi

2014-01-01

Proteins exist as an ensemble of conformers that are distributed on free energy landscapes resembling folding funnels. While the most stable conformers populate low energy basins, protein function is often carried out through low-populated conformational states that occupy high energy basins. Ligand binding shifts the populations of these states, changing the distribution of these conformers. Understanding how the equilibrium among the states is altered upon ligand binding, interaction with other binding partners, and/or mutations and post-translational modifications is of critical importance for explaining allosteric signaling in proteins. Here, we propose a statistical analysis of the chemical shifts (CONCISE, COordiNated ChemIcal Shifts bEhavior) for the interpretation of protein conformational equilibria following linear trajectories of NMR chemical shifts. CONCISE enables one to quantitatively measure the population shifts associated with ligand titrations and estimate the degree of collectiveness of the protein residues’ response to ligand binding, giving a concise view of the structural transitions. The combination of CONCISE with thermocalorimetric and kinetic data allows one to depict a protein’s approximate conformational energy landscape. We tested this method with the catalytic subunit of cAMP-dependent protein kinase A, a ubiquitous enzyme that undergoes conformational transitions upon both nucleotide and pseudo-substrate binding. When complemented with chemical shift covariance analysis (CHESCA), this new method offers both collective response and residue-specific correlations for ligand binding to proteins. PMID:24604024

Correction of erroneously packed protein's side chains in the NMR structure based on ab initio chemical shift calculations.

PubMed

Zhu, Tong; Zhang, John Z H; He, Xiao

2014-09-14

In this work, protein side chain (1)H chemical shifts are used as probes to detect and correct side-chain packing errors in protein's NMR structures through structural refinement. By applying the automated fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) method for ab initio calculation of chemical shifts, incorrect side chain packing was detected in the NMR structures of the Pin1 WW domain. The NMR structure is then refined by using molecular dynamics simulation and the polarized protein-specific charge (PPC) model. The computationally refined structure of the Pin1 WW domain is in excellent agreement with the corresponding X-ray structure. In particular, the use of the PPC model yields a more accurate structure than that using the standard (nonpolarizable) force field. For comparison, some of the widely used empirical models for chemical shift calculations are unable to correctly describe the relationship between the particular proton chemical shift and protein structures. The AF-QM/MM method can be used as a powerful tool for protein NMR structure validation and structural flaw detection.

The role of interfacial metal silicates on the magnetism in FeCo/SiO{sub 2} and Fe{sub 49%}Co{sub 49%}V{sub 2%}/SiO{sub 2} core/shell nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desautels, R. D., E-mail: rddesautels@physics.umanitoba.ca; Toyota Research Institute of North America, Ann Arbor, Michigan 48169; Freeland, J. W.

2015-05-07

We have investigated the role of spontaneously formed interfacial metal silicates on the magnetism of FeCo/SiO{sub 2} and Fe{sub 49%}Co{sub 49%}V{sub 2%}/SiO{sub 2} core/shell nanoparticles. Element specific x-ray absorption and photoelectron spectroscopy experiments have identified the characteristic spectral features of metallic iron and cobalt from within the nanoparticle core. In addition, metal silicates of iron, cobalt, and vanadium were found to have formed spontaneously at the interface between the nanoparticle core and silica shell. X-ray magnetic circular dichroism experiments indicated that the elemental magnetism was a result of metallic iron and cobalt with small components from the iron, cobalt, andmore » vanadium silicates. Magnetometry experiments have shown that there was no exchange bias loop shift in the FeCo nanoparticles; however, exchange bias from antiferromagnetic vanadium oxide was measured in the V-doped nanoparticles. These results showed clearly that the interfacial metal silicates played a significant role in the magnetism of these core/shell nanoparticles, and that the vanadium percolated from the FeCo-cores into the SiO{sub 2}-based interfacial shell.« less

Development of silane grafted ZnO core shell nanoparticles loaded diglycidyl epoxy nanocomposites film for antimicrobial applications.

PubMed

Suresh, S; Saravanan, P; Jayamoorthy, K; Ananda Kumar, S; Karthikeyan, S

2016-07-01

In this article a series of epoxy nanocomposites film were developed using amine functionalized (ZnO-APTES) core shell nanoparticles as the dispersed phase and a commercially available epoxy resin as the matrix phase. The functional group of the samples was characterized using FT-IR spectra. The most prominent peaks of epoxy resin were found in bare epoxy and in all the functionalized ZnO dispersed epoxy nanocomposites (ZnO-APTES-DGEBA). The XRD analysis of all the samples exhibits considerable shift in 2θ, intensity and d-spacing values but the best and optimum concentration is found to be 3% ZnO-APTES core shell nanoparticles loaded epoxy nanocomposites supported by FT-IR results. From TGA measurements, 100wt% residue is obtained in bare ZnO nanoparticles whereas in ZnO core shell nanoparticles grafted DGEBA residue percentages are 37, 41, 45, 46 and 52% for 0, 1, 3, 5 and 7% ZnO-APTES-DGEBA respectively, which is confirmed with ICP-OES analysis. From antimicrobial activity test, it was notable that antimicrobial activity of 7% ZnO-APTES core shell nanoparticles loaded epoxy nanocomposite film has best inhibition zone effect against all pathogens under study. Copyright © 2016 Elsevier B.V. All rights reserved.

Luminescence emission from nonpolar Al0.3Ga0.7N/GaN core-shell and core-multi-shell nanowires

NASA Astrophysics Data System (ADS)

Namvari, E.; Shojaei, S.; Asgari, A.

2017-12-01

In the present work, we theoretically study the possibility of luminescence emission from two systems of nonpolar Al0.3Ga0.7N/GaN Core-shell and core-multi-shell c-axis oriented nanowires with hexagonal cross section. To obtain energy levels and wave functions through the solution of Schrodinger-Poisson equations, numerical Self-consistent procedure has been employed. N-type doping has been considered to investigate the two-dimensional electron gas formation and its effect on luminescence. The detailed analysis of the results as a function of the various structural parameters has been carried out. The results presents an examination of the band to band luminescence feature and its changes with involved parameters. We found that the size of the system determines the feature of luminescence emission. As main finding, our calculations show that the intensity of luminescence spectrum in facet to facet route of NW cross section is significant than that of corner to corner route. In addition, no shift of the peak position is observed with changing the amount of doping. Our numerical calculations give more insights into the luminescence emission of nonpolar GaN/AlGaN core/shell nanowire and have many implications in experiment.

Modeling 15N NMR chemical shift changes in protein backbone with pressure

NASA Astrophysics Data System (ADS)

La Penna, Giovanni; Mori, Yoshiharu; Kitahara, Ryo; Akasaka, Kazuyuki; Okamoto, Yuko

2016-08-01

Nitrogen chemical shift is a useful parameter for determining the backbone three-dimensional structure of proteins. Empirical models for fast calculation of N chemical shift are improving their reliability, but there are subtle effects that cannot be easily interpreted. Among these, the effects of slight changes in hydrogen bonds, both intramolecular and with water molecules in the solvent, are particularly difficult to predict. On the other hand, these hydrogen bonds are sensitive to changes in protein environment. In this work, the change of N chemical shift with pressure for backbone segments in the protein ubiquitin is correlated with the change in the population of hydrogen bonds involving the backbone amide group. The different extent of interaction of protein backbone with the water molecules in the solvent is put in evidence.

Factors affecting the use of 13Cα chemical shifts to determine, refine, and validate protein structures

PubMed Central

Vila, Jorge A.; Scheraga, Harold A.

2008-01-01

Interest centers here on the analysis of two different, but related, phenomena that affect side-chain conformations and consequently 13Cα chemical shifts and their applications to determine, refine, and validate protein structures. The first is whether 13Cα chemical shifts, computed at the DFT level of approximation with charged residues is a better approximation of observed 13Cα chemical shifts than those computed with neutral residues for proteins in solution. Accurate computation of 13Cα chemical shifts requires a proper representation of the charges, which might not take on integral values. For this analysis, the charges for 139 conformations of the protein ubiquitin were determined by explicit consideration of protein binding equilibria, at a given pH, that is, by exploring the 2ξ possible ionization states of the whole molecule, with ξ being the number of ionizable groups. The results of this analysis, as revealed by the shielding/deshield-ing of the 13Cα nucleus, indicated that: (i) there is a significant difference in the computed 13Cα chemical shifts, between basic and acidic groups, as a function of the degree of charge of the side chain; (ii) this difference is attributed to the distance between the ionizable groups and the 13Cα nucleus, which is shorter for the acidic Asp and Glu groups as compared with that for the basic Lys and Arg groups; and (iii) the use of neutral, rather than charged, basic and acidic groups is a better approximation of the observed 13Cα chemical shifts of a protein in solution. The second is how side-chain flexibility influences computed 13Cα chemical shifts in an additional set of ubiquitin conformations, in which the side chains are generated from an NMR-derived structure with the backbone conformation assumed to be fixed. The 13Cα chemical shift of a given amino acid residue in a protein is determined, mainly, by its own backbone and side-chain torsional angles, independent of the neighboring residues; the conformation of a given residue itself, however, depends on the environment of this residue and, hence, on the whole protein structure. As a consequence, this analysis reveals the role and impact of an accurate side-chain computation in the determination and refinement of protein conformation. The results of this analysis are: (i) a lower error between computed and observed 13Cα chemical shifts (by up to 3.7 ppm), was found for ~68% and ~63% of all ionizable residues and all non-Ala/Pro/Gly residues, respectively, in the additional set of conformations, compared with results for the model from which the set was derived; and (ii) all the additional conformations exhibit a lower root-mean-square-deviation (1.97 ppm ≤ rmsd ≤ 2.13 ppm), between computed and observed 13Cα chemical shifts, than the rmsd (2.32 ppm) computed for the starting conformation from which this additional set was derived. As a validation test, an analysis of the additional set of ubiquitin conformations, comparing computed and observed values of both 13Cα chemical shifts and χ1 torsional angles (given by the vicinal coupling constants, 3JN–Cγ and 3JC′–Cγ, is discussed. PMID:17975838

Optical and Electrical Characterization of Single Semiconductor Nanowires

NASA Astrophysics Data System (ADS)

Wickramasuriya, Nadeeka Thejanie

Strain distribution in the core and the shell of a semiconductor nanowire (NW) and its effect on band structures including carrier recombination dynamics of individual Wurtzite (WZ) In1- xGxAs/InP and Zincblende (ZB) GaAs1-xSbx/InP strained core-shell NWs are investigated using room temperature Raman scattering and transient Rayleigh scattering (TRS) optical spectroscopy techniques. In addition, the electrical transport properties of individual ZB InP NWs are explored using gate-dependent current-voltage (I-V) measurements. Micro-Raman scattering from individual In1-xGaxAs NWs show InAs like TO and GaAs like TO modes with frequencies which are consistent with the 35% Ga concentration determined from the growth parameters. Calculations showed that the In0.65Ga0.35As core is under compressive strain of 0.26% while the InP shell is in tensile strain of 0.42% in In 0.65Ga0.35As/InP NWs. TRS measurements of single NWs show clear evidence for a strong band resonance in the WZ In0.65Ga 0.35As NW at 0.819 eV which is estimated to be a 186 meV blue-shift with respect to bulk ZB In0.65Ga0.35As. Furthermore, both Raman scattering and TRS measurements are on excellent agreement with the band gap shift of In0.65Ga0.35As/InP core-shell NWs with respect to the core only NW by 46 48 meV which experimentally confirmed the InP shell induced compression of the core. The time decays of the resonance are observed to be long ( 125 ps) for core-shell NWs while it is short ( 31 ps) for core only NWs consistent with a larger nonradiative recombination rate. Optical phonon modes of GaAs1-xSbx are observed to be red-shifted with increasing Antimony fraction in GaAs1-xSb x NWs which can be expected in an alloy with increasing concentration of a heavier atom in the lattice. Using TRS measurements, the GaAs0.71 Sb0.29 band gap for the coreshell NW is observed to be reduced by 0.04 eV with respect to the core only NW because of the tensile strain in the core. Raman experiments show a blue-shift of the InP phonons and a redshift of the GaAs1-xSbx phonons in individual GaAs 0.71Sb0.29/InP NWs, which is consistent with the tensile core strain inferred from TRS results. The recombination life times in GaAs 0.71Sb0.29, GaAs0.71Sb0.29/InP NWs are found to be 31 ps and 127 ps respectively reflecting the effectiveness of the InP shell surface passivation. Individual InP NW field effect transistors are fabricated using photolithography to investigate the electrical transport properties of InP NWs. Gate-dependent I-V plots showed that the InP NWs are n-type and displayed typical non-Ohmic behavior due to the contact resistance between NW and metal electrodes. Carrier mobility determined for the InP NWs is as high as 655 cm2/(V.s) for the carrier density of 4.08 x 1017 cm-3 which is comparable to n-type InP thin film materials with similar carrier densities and thus demonstrates the high quality of the NWs. An equivalent circuit model of the metal-semiconductor-metal structure is used to extract the carrier density and mobility of the NW as 1.00 x 1017 cm -3 and 511 cm2/(V.s), This model makes it possible to determine the barrier heights of the NW device while providing a good agreement with the experimental results.

pH-Dependent spin state population and 19F NMR chemical shift via remote ligand protonation in an iron(ii) complex.

PubMed

Gaudette, Alexandra I; Thorarinsdottir, Agnes E; Harris, T David

2017-11-30

An Fe II complex that features a pH-dependent spin state population, by virtue of a variable ligand protonation state, is described. This behavior leads to a highly pH-dependent 19 F NMR chemical shift with a sensitivity of 13.9(5) ppm per pH unit at 37 °C, thereby demonstrating the potential utility of the complex as a 19 F chemical shift-based pH sensor.

A detailed view of the gas shell around R Sculptoris with ALMA

NASA Astrophysics Data System (ADS)

Maercker, M.; Vlemmings, W. H. T.; Brunner, M.; De Beck, E.; Humphreys, E. M.; Kerschbaum, F.; Lindqvist, M.; Olofsson, H.; Ramstedt, S.

2016-02-01

Context. During the asymptotic giant branch (AGB) phase, stars undergo thermal pulses - short-lived phases of explosive helium burning in a shell around the stellar core. Thermal pulses lead to the formation and mixing-up of new elements to the stellar surface. They are hence fundamental to the chemical evolution of the star and its circumstellar envelope. A further consequence of thermal pulses is the formation of detached shells of gas and dust around the star, several of which have been observed around carbon-rich AGB stars. Aims: We aim to determine the physical properties of the detached gas shell around R Sculptoris, in particular the shell mass and temperature, and to constrain the evolution of the mass-loss rate during and after a thermal pulse. Methods: We analyse 12CO(1-0), 12CO(2-1), and 12CO(3-2) emission, observed with the Atacama Large Millimeter/submillimeter Array (ALMA) during Cycle 0 and complemented by single-dish observations. The spatial resolution of the ALMA data allows us to separate the detached shell emission from the extended emission inside the shell. We perform radiative transfer modelling of both components to determine the shell properties and the post-pulse mass-loss properties. Results: The ALMA data show a gas shell with a radius of 19.̋5 expanding at 14.3 km s-1. The different scales probed by the ALMA Cycle 0 array show that the shell must be entirely filled with gas, contrary to the idea of a detached shell. The comparison to single-dish spectra and radiative transfer modelling confirms this. We derive a shell mass of 4.5 × 10-3 M⊙ with a temperature of 50 K. Typical timescales for thermal pulses imply a pulse mass-loss rate of 2.3 × 10-5 M⊙ yr-1. For the post-pulse mass-loss rate, we find evidence for a gradual decline of the mass-loss rate, with an average value of 1.6 × 10-5 M⊙ yr-1. The total amount of mass lost since the last thermal pulse is 0.03 M⊙, a factor four higher compared to classical models, with a sharp decline in mass-loss rate immediately after the pulse. Conclusions: We find that the mass-loss rate after a thermal pulse has to decline more slowly than generally expected from models of thermal pulses. This may cause the star to lose significantly more mass during a thermal pulse cycle, which affects the lifetime on the AGB and the chemical evolution of the star, its circumstellar envelope, and the interstellar medium.

On the thermo-chemical origin of the stratified region at the top of the Earth's core

NASA Astrophysics Data System (ADS)

Nakagawa, Takashi

2018-03-01

I developed a combined model of the thermal and chemical evolution of the Earth's core and investigated its influence on a thermochemically stable region beneath the core-mantle boundary (CMB). The chemical effects of the growing stable region are caused by the equilibrium chemical reaction between silicate and the metallic core. The thermal effects can be characterized by the growth of the sub-isentropic shell, which may have a rapid growth rate compared to that of the chemically stable region. When the present-day CMB heat flow was varied, the origin of the stable region changed from chemical to thermochemical to purely thermal because the rapid growth of the sub-isentropic shell can replace the chemically stable region. Physically reasonable values of the present-day CMB heat flow that can maintain the geodynamo action over 4 billion years should be between 8 and 11 TW. To constrain the thickness of the thermochemically stable region beneath the CMB, the chemical diffusivity is important and should be ∼O(10-8) m2/s to obtain a thickness of the thermochemically stable region beneath the CMB consistent with that inferred from geomagnetic secular variations (140 km). However, the strength of the stable region found in this study is too high to be consistent with the constraint on the stability of the stable region inferred from geomagnetic secular variations.

Modified ferrite core-shell nanoparticles magneto-structural characterization

NASA Astrophysics Data System (ADS)

Klekotka, Urszula; Piotrowska, Beata; Satuła, Dariusz; Kalska-Szostko, Beata

2018-06-01

In this study, ferrite nanoparticles with core-shell structures and different chemical compositions of both the core and shell were prepared with success. Proposed nanoparticles have in the first and second series magnetite core, and the shell is composed of a mixture of ferrites with Fe3+, Fe2+ and M ions (where M = Co2+, Mn2+ or Ni2+) with a general composition of M0.5Fe2.5O4. In the third series, the composition is inverted, the core is composed of a mixture of ferrites and as a shell magnetite is placed. Morphology and structural characterization of nanoparticles were done using Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), and Infrared spectroscopy (IR). While room temperature magnetic properties were measured using Mössbauer spectroscopy (MS). It is seen from Mössbauer measurements that Co always increases hyperfine magnetic field on Fe atoms at RT, while Ni and Mn have opposite influences in comparison to pure Fe ferrite, regardless of the nanoparticles structure.

Confidence Testing of Shell 405 and S-405 Catalysts in a Monopropellant Hydrazine Thruster

NASA Technical Reports Server (NTRS)

McRight, Patrick; Popp, Chris; Pierce, Charles; Turpin, Alicia; Urbanchock, Walter; Wilson, Mike

2005-01-01

As part of the transfer of catalyst manufacturing technology from Shell Chemical Company (Shell 405 catalyst manufactured in Houston, Texas) to Aerojet (S-405 manufactured in Redmond, Washington), Aerojet demonstrated the equivalence of S-405 and Shell 405 at beginning of life. Some US aerospace users expressed a desire to conduct a preliminary confidence test to assess end-of-life characteristics for S-405. NASA Marshall Space Flight Center (MSFC) and Aerojet entered a contractual agreement in 2004 to conduct a confidence test using a pair of 0.2-lbf MR-103G monopropellant hydrazine thrusters, comparing S-405 and Shell 405 side by side. This paper summarizes the formulation of this test program, explains the test matrix, describes the progress of the test, and analyzes the test results. This paper also includes a discussion of the limitations of this test and the ramifications of the test results for assessing the need for future qualification testing in particular hydrazine thruster applications.

A thermoresponsive nanorattle containing two different catalysts for controllable one-pot tandem catalysis

NASA Astrophysics Data System (ADS)

Niu, Chengrong; Hu, Jie; Li, Yinfeng; Leng, Jinghang; Li, Songjun

2018-03-01

In the present work, a thermoresponsive nanorattle with a Ag nanoparticle (NP) core (one catalyst in the nanorattle), and a poly(N-isopropylacrylamide) shell was developed. An imidazole group was grafted on the polymer shell by copolymerization as the other catalyst. Owing to the catalytic activities of the imidazole group and Ag NP with regards to hydrolysis and reduction, respectively, this nanorattle exhibited tandem-reaction catalytic abilities. In addition, because of the shrinkage of the poly(N-isopropylacrylamide) shell at high temperatures, the tandem reaction could be controlled to stop at the first reaction step. That is to say, only the hydrolysis reaction was catalyzed by the imidazole group being grafted on the surface of the shell. The reduction step in the tandem reaction catalyzed by the Ag particle, however, was switched off by the shrinkage of the poly(N-isopropylacrylamide) shell. This protocol opens up an opportunity to develop controllable catalysts for complicated chemical processes.

The Study of Blocking Agent on Lengkeng (Euphoria Logan Lour) Fruit Shell and Seed for Adsorption of Pb (II) from Aqueous Solution

NASA Astrophysics Data System (ADS)

Kurniawati, D.; Zein, R.; Chaidir, Z.; Aziz, H.

2018-04-01

The study focuses on the roles played by mayor functional groups(carboxyl) in the lengkeng shell for sorption of Pb (II). The biosorbent was characterized by FTIR and elemental analyses. The parameters such as pH, initial concentration, particle sizes, adsorbent dose and flow rate were also studied. The results showed that the optimum condition was at pH = 3, concentration 400 mg/l, 250 μm particle sizes, adsorbent dose 0,5 g and 2 ml/min flow rate with adsorption capacity 4,8933 mg/g(shell) and 5,2720 mg/g(seed). It is show that ion exchange play as a more important role in the sorption of Pb (II) on lengkeng shell and seed. Blocking of COOH groups by chemical esterification resulted in Pb important reduction in metal binding.The result showed that adsorption capacity of lengkeng shell uncreases until 63.67 % and lengkeng seed uncreases 98.70%.

Controlled Growth of Ordered III-Nitride Core-Shell Nanostructure Arrays for Visible Optoelectronic Devices

DOE PAGES

Rishinaramangalam, Ashwin K.; Mishkat Ul Masabih, Saadat; Fairchild, Michael N.; ...

2014-10-21

In our paper, we demonstrate the growth of ordered arrays of nonpolar {101 ¯ 0} core–shell nanowalls and semipolar {101 ¯ 1} core–shell pyramidal nanostripes on c-plane (0001) sapphire substrates using selective-area epitaxy and metal organic chemical vapor deposition. The nanostructure arrays are controllably patterned into LED mesa regions, demonstrating a technique to impart secondary lithography features into the arrays. Moreover, we study the dependence of the nanostructure cores on the epitaxial growth conditions and show that the geometry and morphology are strongly influenced by growth temperature, V/III ratio, and pulse interruption time. We also demonstrate the growth of InGaNmore » quantum well shells on the nanostructures and characterize the structures by using micro-photoluminescence and cross-section scanning tunneling electron microscopy.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

SAMS TL; GUILLOT S

Scoping laboratory scale tests were performed at the Chemical Engineering Department of the Georgia Institute of Technology (Georgia Tech), and the Hanford 222-S Laboratory, involving double-shell tank (DST) and single-shell tank (SST) Hanford waste simulants. These tests established the viability of the Lithium Hydrotalcite precipitation process as a solution to remove aluminum and recycle sodium hydroxide from the Hanford tank waste, and set the basis of a validation test campaign to demonstrate a Technology Readiness Level of 3.

Room-temperature synthesis of core-shell structured magnetic covalent organic frameworks for efficient enrichment of peptides and simultaneous exclusion of proteins.

PubMed

Lin, Guo; Gao, Chaohong; Zheng, Qiong; Lei, Zhixian; Geng, Huijuan; Lin, Zian; Yang, Huanghao; Cai, Zongwei

2017-03-28

Core-shell structured magnetic covalent organic frameworks (Fe 3 O 4 @COFs) were synthesized via a facile approach at room temperature. Combining the advantages of high porosity, magnetic responsiveness, chemical stability and selectivity, Fe 3 O 4 @COFs can serve as an ideal absorbent for the highly efficient enrichment of peptides and the simultaneous exclusion of proteins from complex biological samples.

Investigation of DOTA-Metal Chelation Effects on the Chemical Shift of 129 Xe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, Keunhong; Slack, Clancy C.; Vassiliou, Christophoros C.

2015-09-17

Recent work has shown that xenon chemical shifts in cryptophane-cage sensors are affected when tethered chelators bind to metals. Here in this paper, we explore the xenon shifts in response to a wide range of metal ions binding to diastereomeric forms of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) linked to cryptophane-A. The shifts induced by the binding of Ca 2+, Cu 2+, Ce 3+, Zn 2+, Cd 2+, Ni 2+, Co 2+, Cr 2+, Fe 3+, and Hg 2+ are distinct. In addition, the different responses of the diastereomers for the same metal ion indicate that shifts are affected by partial folding withmore » a correlation between the expected coordination number of the metal in the DOTA complex and the chemical shift of 129Xe. Lastly, these sensors may be used to detect and quantify many important metal ions, and a better understanding of the basis for the induced shifts could enhance future designs.« less

Volatile components and continental material of planets

NASA Technical Reports Server (NTRS)

Florenskiy, K. P.; Nikolayeva, O. V.

1986-01-01

It is shown that the continental material of the terrestrial planets varies in composition from planet to planet according to the abundances and composition of true volatiles (H20, CO2, etc.) in the outer shells of the planets. The formation of these shells occurs very early in a planet's evolution when the role of endogenous processes is indistinct and continental materials are subject to melting and vaporizing in the absence of an atmosphere. As a result, the chemical properties of continental materials are related not only to fractionation processes but also to meltability and volatility. For planets retaining a certain quantity of true volatile components, the chemical transformation of continental material is characterized by a close interaction between impact melting vaporization and endogeneous geological processes.

Dynamics and transformations of radionuclides in soils and ecosystem health

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fellows, Robert J.; Ainsworth, Calvin C.; Driver, Crystal J.

1998-12-01

The chemical behavior of radionuclides can vary widely in soil and sediment environments. Equally important, for a given radionuclide the physico-chemical properties of the solids and aqueous phase can greatly influence a radionuclides behavior. Radionuclides can conceivably occur in soils as soluble-free, inorganic-soluble-complexed, organic-soluble, complexed, adsorbed, precipitated, coprecipitated, or solid structural species. While it is clear that an assessment of a radionuclide?s soil chemistry and potential shifts in speciation will yield a considerable understanding of its behavior in the natural environment, it does not directly translate to bioavailability or its impact on ecosystems health. The soil chemical factors have tomore » be linked to food chain considerations and other ecological parameters that directly tie to an analysis of ecosystem health. In general, the movement of radionuclides from lower to higher trophic levels diminishes with each trophic level in both aqua tic and terrestrial systems. In some cases, transfer is limited because of low absorption/assimilation by successive trophic organisms (Pu, U); for other radionuclides (Tc, H) assimilation may be high but rapid metabolic turnover and low retention greatly reduce tissue concentrations available to predator species. Still others are chemical analogs of essential elements whose concentrations are maintained under strict metabolic control in tissues (Cs) or are stored in tissues seldom consumed by other organisms (Sr storage in exoskeleton, shells, and bone). Therefore, the organisms that receive the greatest ingestion exposures are those in lower trophic positions or are in higher trophic levels but within simple, short food chains. Food source, behavior, and habitat influence the accumulation of radionuclides in animals.« less

Development of multicomponent hybrid density functional theory with polarizable continuum model for the analysis of nuclear quantum effect and solvent effect on NMR chemical shift.

PubMed

Kanematsu, Yusuke; Tachikawa, Masanori

2014-04-28

We have developed the multicomponent hybrid density functional theory [MC_(HF+DFT)] method with polarizable continuum model (PCM) for the analysis of molecular properties including both nuclear quantum effect and solvent effect. The chemical shifts and H/D isotope shifts of the picolinic acid N-oxide (PANO) molecule in chloroform and acetonitrile solvents are applied by B3LYP electron exchange-correlation functional for our MC_(HF+DFT) method with PCM (MC_B3LYP/PCM). Our MC_B3LYP/PCM results for PANO are in reasonable agreement with the corresponding experimental chemical shifts and isotope shifts. We further investigated the applicability of our method for acetylacetone in several solvents.

Prevalence of Pathogens Associated with Eggs and the Environment of Conventional Cage and Free Range Egg Production

USDA-ARS?s Scientific Manuscript database

Alternative egg production methods are becoming more popular with US consumers. As the drive to expand the retail shell egg market to accommodate consumer shifts proceeds, a need arises for additional information to ensure processing methodologies result in safe eggs from all egg sources. A study ...

The consequences of human-driven ocean acidification for marine life.

PubMed

Doney, Scott

2009-05-08

Rising atmospheric carbon dioxide is causing a wholesale shift in surface seawater chemistry, potentially threatening many marine organisms that form shells and skeletons from calcium carbonate. Recent papers suggest that the biological consequences of ocean acidification already may be underway and may be more complex, nuanced and widespread than previously thought.

Protein Structural Information Derived from NMR Chemical Shift with the Neural Network Program TALOS-N

PubMed Central

Shen, Yang; Bax, Ad

2015-01-01

Summary Chemical shifts are obtained at the first stage of any protein structural study by NMR spectroscopy. Chemical shifts are known to be impacted by a wide range of structural factors and the artificial neural network based TALOS-N program has been trained to extract backbone and sidechain torsion angles from 1H, 15N and 13C shifts. The program is quite robust, and typically yields backbone torsion angles for more than 90% of the residues, and sidechain χ1 rotamer information for about half of these, in addition to reliably predicting secondary structure. The use of TALOS-N is illustrated for the protein DinI, and torsion angles obtained by TALOS-N analysis from the measured chemical shifts of its backbone and 13Cβ nuclei are compared to those seen in a prior, experimentally determined structure. The program is also particularly useful for generating torsion angle restraints, which then can be used during standard NMR protein structure calculations. PMID:25502373

Calculation of 125Te NMR Chemical Shifts at the Full Four-Component Relativistic Level with Taking into Account Solvent and Vibrational Corrections: A Gateway to Better Agreement with Experiment.

PubMed

Rusakova, Irina L; Rusakov, Yuriy Yu; Krivdin, Leonid B

2017-06-29

Four-component relativistic calculations of 125 Te NMR chemical shifts were performed in the series of 13 organotellurium compounds, potential precursors of the biologically active species, at the density functional theory level under the nonrelativistic and four-component fully relativistic conditions using locally dense basis set scheme derived from relativistic Dyall's basis sets. The relativistic effects in tellurium chemical shifts were found to be of as much as 20-25% of the total calculated values. The vibrational and solvent corrections to 125 Te NMR chemical shifts are about, accordingly, 6 and 8% of their total values. The PBE0 exchange-correlation functional turned out to give the best agreement of calculated tellurium shifts with their experimental values giving the mean absolute percentage error of 4% in the range of ∼1000 ppm, provided all corrections are taken into account.

Human health risks related to the consumption of foodstuffs of plant and animal origin produced on a site polluted by chemical munitions of the First World War.

PubMed

Gorecki, Sébastien; Nesslany, Fabrice; Hubé, Daniel; Mullot, Jean-Ulrich; Vasseur, Paule; Marchioni, Eric; Camel, Valérie; Noël, Laurent; Le Bizec, Bruno; Guérin, Thierry; Feidt, Cyril; Archer, Xavier; Mahe, Aurélie; Rivière, Gilles

2017-12-01

Shells fired during World War I exhibited different explosive compounds and some of these weapons also contained a wide variety of chemical warfare agents. At the end of the war, for safety purposes, the large quantity of weapons remaining on the former front needed to be dismantled and destroyed. A large amount of the remaining shells was destroyed in specific sites which led to the contamination of the surroundings in Belgium and France. In the 1920s, 1.5 million chemical shells and 30,000 explosive shells were destroyed in a place close to the city of Verdun, in the East of France. In this paper, the risk for human health related to the consumption of foodstuffs produced on this site was assessed. To this end, food products of plant and animal origin were sampled in 2015-2016 and contaminant analyses were conducted. Human exposure was assessed using a specifically built methodology. The contaminants considered in this study were trace elements (TEs - primarily Zn, As, Pb and Cd), nitroaromatic explosives (trinitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2-amino-4,6-dinitroluene and 4-amino-2,6-dinitrotoluene), phenylarsenic compounds including diphenylarsinic acid and triphenylarsine, perchlorate, tetrabromoethane and vinyl bromide. Depending on the compound, different approaches were used to assess the risk for both adults and children. Exposure to these contaminants through the consumption of foodstuffs produced locally on the considered site was unlikely to be a health concern. However, as for inorganic arsenic, given the presence of highly contaminated zones, it was suggested that cereals should not be grown on certain plots. Copyright © 2017 Elsevier B.V. All rights reserved.

Impact of prehistoric cooking practices on paleoenvironmental proxies in shell midden constituents

NASA Astrophysics Data System (ADS)

Müller, Peter; Staudigel, Philip; Murray, Sean T.; Westphal, Hildegard; Swart, Peter K.

2016-04-01

Paleoenvironmental proxy records such as oxygen isotopes of calcareous skeletal structures like fish otoliths or mollusk shells provide highest-resolution information about environmental conditions experienced by the organism. Accumulations of such skeletal structures by ancient coastal populations in so called "shell midden" deposits provide us with sub-seasonally resolved paleoclimate records covering time spans up to several millennia. Given their high temporal resolution, these deposits are increasingly used for paleoclimate reconstructions and complement our understanding of ancient climate changes. However, gathered as comestibles, most of these skeletal remains were subject to prehistoric cooking methods prior to deposition. The associated alteration of the chemical proxy signatures as well as the subsequent error for paleoenvironmental reconstructions remained almost entirely neglected so far. Here, we present clumped isotope, conventional oxygen and carbon isotopes as well as element:Ca ratios measured in modern bivalve shells after exposing them to different prehistoric cooking methods. Our data show that most cooking methods considerably alter commonly used paleoclimate proxy systems which can lead to substantial misinterpretations of ancient climate conditions. Since the magnitude of chemical alteration is not distinguishable from natural temperature variability in most coastal settings, the alteration of shell midden constituents by prehistoric cooking remains likely unnoticed in most cases. Thus, depending on the cooking method, pre-depositional heating might have introduced considerable errors into previous paleoclimate studies. However, our data also show that clumped isotope thermometry represents a suitable diagnostic tool to detect such pre-depositional cooking events and also allows differentiating between the most commonly applied prehistoric cooking methods.

[Mustard gas bombs found astray in the Faxaflói bay. Mustard gas: usage and poisonings].

PubMed

Kristinsson, Jakop; Jóhannesson, Thorkell

2009-05-01

The finding in 1972 of two World War II mustard gas artillery shells in crushed shell sediment dredged in the Faxaflói Bay and transported as raw material for cement production at Akranes (Western Iceland) is reported. One of the shells was wedged in a stone crusher in the raw material processing line and was ruptured. As a result dark fluid with a garlic like smell seeped out from the metal canister. The attending employees believed the metal object to be inert and tried to cut it out with a blow torch. This resulted in the explosion of the shell charge and in the exposure of four employees to mustard gas. All suffered burns on their hands and two of them in the eyes also. The second shell was detonated in the open at a distance from the factory. Emphasis is given to the fact that instant, or at least as soon as possible, cleansing and washing is the most efficient measure to be taken against the debilitating effects of mustard gas. It is also pointed out that the active principle in mustard gas (dichlorodiethyl sulphide) can easily be synthesized and none of the precursor substances are subjected to any restrictions of use. The authors conclude that mustard gas bombs may still be found in the arsenals of some military powers in spite of an international convention that prohibits the production, stockpiling and the use of chemical weapons. Terrorist groups have also seemingly tried to aquire mustard gas bombs and other chemical weapons. Therefore cases of mustard gas poisoning might still occur.

Chemical-mechanical stability of the hierarchical structure of shell nacre

NASA Astrophysics Data System (ADS)

Sun, Jinmei; Guo, Wanlin

2010-02-01

The hierarchical structure and mechanical property of shell nacre are experimentally investigated from the new aspects of chemical stability and chemistry-mechanics coupling. Through chemical deproteinization or demineralization methods together with characterization techniques at micro/nano scales, it is found that the nacre of abalone, haliotis discus hannai, contains a hierarchical structure stacked with irregular aragonite platelets and interplatelet organic matrix thin layers. Yet the aragonite platelet itself is a nanocomposite consisting of nanoparticles and intraplatelet organic matrix framework. The mean diameter of the nanoparticles and the distribution of framework are quite different for different platelets. Though the interplatelet and intraplatelet organic matrix can be both decomposed by sodium hydroxide solution, the chemical stability of individual aragonite platelets is much higher than that of the microstructure stacked with them. Further, macroscopic bending test or nanoindentation experiment is performed on the micro/nanostructure of nacre after sodium hydroxide treatment. It is found that the Young’s modulus of both the stacked microstructure and nanocomposite platelet reduced. The reduction of the microstructure is more remark than that of the platelet. Therefore the chemical-mechanical stability of the nanocomposite platelet itself is much higher than that of the stacked microstructure of nacre.

Reconstructing early 17th century estuarine drought conditions from Jamestown oysters.

PubMed

Harding, Juliana M; Spero, Howard J; Mann, Roger; Herbert, Gregory S; Sliko, Jennifer L

2010-06-08

Oysters (Crassostrea virginica) were a central component of the Chesapeake Bay ecosystem in 1607 when European settlers established Jamestown, VA, the first permanent English settlement in North America. These estuarine bivalves were an important food resource during the early years of the James Fort (Jamestown) settlement while the colonists were struggling to survive in the face of inadequate supplies and a severe regional drought. Although oyster shells were discarded as trash after the oysters were eaten, the environmental and ecological data recorded in the bivalve geochemistry during shell deposition remain intact over centuries, thereby providing a unique window into conditions during the earliest Jamestown years. We compare oxygen isotope data from these 17th century oyster shells with modern shells to quantify and contrast estuarine salinity, season of oyster collection, and shell provenance during Jamestown colonization (1609-1616) and the 21st century. Data show that oysters were collected during an extended drought between fall 1611 and summer 1612. The drought shifted the 14 psu isohaline above Jamestown Island, facilitating individual oyster growth and extension of oyster habitat upriver toward the colony, thereby enhancing local oyster food resources. Data from distinct well layers suggest that the colonists also obtained oysters from reefs near Chesapeake Bay to augment oyster resources near Jamestown Island. The oyster shell season of harvest reconstructions suggest that these data come from either a 1611 well with a very short useful period or an undocumented older well abandoned by late 1611.

Planetary Ice-Oceans: Numerical Modeling Study of Ice-Shell Growth in Convecting Two-Phase Systems

NASA Astrophysics Data System (ADS)

Allu Peddinti, Divya; McNamara, Allen

2017-04-01

Several icy bodies in the Solar system such as the icy moons Europa and Enceladus exhibit signs of subsurface oceans underneath an ice-shell. For Europa, the geologically young surface, the presence of surface features and the aligned surface chemistry pose interesting questions about formation of the ice-shell and its interaction with the ocean below. This also ties in with its astrobiological potential and implications for similar ice-ocean systems elsewhere in the cosmos. The overall thickness of the H2O layer on Europa is estimated to be 100-150 km while the thickness of the ice-shell is debated. Additionally, Europa is subject to tidal heating due to interaction with Jupiter's immense gravity field. It is of interest to understand how the ice-shell thickness varies in the presence of tidal internal heating and the localization of heating in different regions of the ice-shell. Thus this study aims to determine the effect of tidal internal heating on the growth rate of the ice-shell over time. We perform geodynamic modeling of the ice-ocean system in order to understand how the ice-shell thickness changes with time. The convection code employs the ice Ih-water phase diagram in order to model the two-phase convecting ice-ocean system. All the models begin from an initial warm thick ocean that cools from the top. The numerical experiments analyze three cases: case 1 with no tidal internal heating in the system, case 2 with constant tidal internal heating in the ice and case 3 with viscosity-dependent tidal internal heating in the ice. We track the ice-shell thickness as a function of time as the system cools. Modeling results so far have identified that the shell growth rate changes substantially at a point in time that coincides with a change in the planform of ice-convection cells. Additionally, the velocity vs depth plots indicate a shift from a conduction dominant to a convection dominant ice regime. We compare the three different cases to provide a comprehensive understanding of the temporal variation in the ice-shell thickness due to the addition of heating in the ice.

Dissecting ion-specific dielectric spectra of sodium-halide solutions into solvation water and ionic contributions.

PubMed

Rinne, Klaus F; Gekle, Stephan; Netz, Roland R

2014-12-07

Using extensive equilibrium molecular dynamics simulations we determine the dielectric spectra of aqueous solutions of NaF, NaCl, NaBr, and NaI. The ion-specific and concentration-dependent shifts of the static dielectric constants and the dielectric relaxation times match experimental results very well, which serves as a validation of the classical and non-polarizable ionic force fields used. The purely ionic contribution to the dielectric response is negligible, but determines the conductivity of the salt solutions. The ion-water cross correlation contribution is negative and reduces the total dielectric response by about 5%-10% for 1 M solutions. The dominating water dielectric response is decomposed into different water solvation shells and ion-pair configurations, by this the spectral blue shift and the dielectric decrement of salt solutions with increasing salt concentration is demonstrated to be primarily caused by first-solvation shell water. With rising salt concentration the simulated spectra show more pronounced deviations from a single-Debye form and can be well described by a Cole-Cole fit, in quantitative agreement with experiments. Our spectral decomposition into ionic and different water solvation shell contributions does not render the individual contributions more Debye-like, this suggests the non-Debye-like character of the dielectric spectra of salt solutions not to be due to the superposition of different elementary relaxation processes with different relaxation times. Rather, the non-Debye-like character is likely to be an inherent spectral signature of solvation water around ions.

Spin-echo based diagonal peak suppression in solid-state MAS NMR homonuclear chemical shift correlation spectra

NASA Astrophysics Data System (ADS)

Wang, Kaiyu; Zhang, Zhiyong; Ding, Xiaoyan; Tian, Fang; Huang, Yuqing; Chen, Zhong; Fu, Riqiang

2018-02-01

The feasibility of using the spin-echo based diagonal peak suppression method in solid-state MAS NMR homonuclear chemical shift correlation experiments is demonstrated. A complete phase cycling is designed in such a way that in the indirect dimension only the spin diffused signals are evolved, while all signals not involved in polarization transfer are refocused for cancellation. A data processing procedure is further introduced to reconstruct this acquired spectrum into a conventional two-dimensional homonuclear chemical shift correlation spectrum. A uniformly 13C, 15N labeled Fmoc-valine sample and the transmembrane domain of a human protein, LR11 (sorLA), in native Escherichia coli membranes have been used to illustrate the capability of the proposed method in comparison with standard 13C-13C chemical shift correlation experiments.

Modeling {sup 15}N NMR chemical shift changes in protein backbone with pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

La Penna, Giovanni, E-mail: glapenna@iccom.cnr.it; Mori, Yoshiharu, E-mail: ymori@ims.ac.jp; Kitahara, Ryo, E-mail: ryo@ph.ritsumei.ac.jp

2016-08-28

Nitrogen chemical shift is a useful parameter for determining the backbone three-dimensional structure of proteins. Empirical models for fast calculation of N chemical shift are improving their reliability, but there are subtle effects that cannot be easily interpreted. Among these, the effects of slight changes in hydrogen bonds, both intramolecular and with water molecules in the solvent, are particularly difficult to predict. On the other hand, these hydrogen bonds are sensitive to changes in protein environment. In this work, the change of N chemical shift with pressure for backbone segments in the protein ubiquitin is correlated with the change inmore » the population of hydrogen bonds involving the backbone amide group. The different extent of interaction of protein backbone with the water molecules in the solvent is put in evidence.« less

Equilibrium simulations of proteins using molecular fragment replacement and NMR chemical shifts.

PubMed

Boomsma, Wouter; Tian, Pengfei; Frellsen, Jes; Ferkinghoff-Borg, Jesper; Hamelryck, Thomas; Lindorff-Larsen, Kresten; Vendruscolo, Michele

2014-09-23

Methods of protein structure determination based on NMR chemical shifts are becoming increasingly common. The most widely used approaches adopt the molecular fragment replacement strategy, in which structural fragments are repeatedly reassembled into different complete conformations in molecular simulations. Although these approaches are effective in generating individual structures consistent with the chemical shift data, they do not enable the sampling of the conformational space of proteins with correct statistical weights. Here, we present a method of molecular fragment replacement that makes it possible to perform equilibrium simulations of proteins, and hence to determine their free energy landscapes. This strategy is based on the encoding of the chemical shift information in a probabilistic model in Markov chain Monte Carlo simulations. First, we demonstrate that with this approach it is possible to fold proteins to their native states starting from extended structures. Second, we show that the method satisfies the detailed balance condition and hence it can be used to carry out an equilibrium sampling from the Boltzmann distribution corresponding to the force field used in the simulations. Third, by comparing the results of simulations carried out with and without chemical shift restraints we describe quantitatively the effects that these restraints have on the free energy landscapes of proteins. Taken together, these results demonstrate that the molecular fragment replacement strategy can be used in combination with chemical shift information to characterize not only the native structures of proteins but also their conformational fluctuations.

The environmental impacts of oil platforms in the Persian (Arabian) Gulf: the conservation paleobiology approach

NASA Astrophysics Data System (ADS)

Albano, Paolo G.; Tomašových, Adam; Kaufman, Darrell; Stachowitsch, Michael; Zuschin, Martin

2016-04-01

The Persian (Arabian) Gulf is a semi-enclosed basin that currently hosts the highest concentration of infrastructures for oil and gas extraction in the world. Moreover, major oil spills have occurred here due to accidents and conflicts. The disjunction between recent environmental monitoring programmes and industry-scale oil exploration and extraction dating back to the mid-20th century means a lack of data on pre-impact ecosystem conditions. This shortcoming hampers quantifying disturbance and ecosystem shifts and calls for novel approaches to reconstruct baselines. Conservation palaeobiology is such a new research field. It uses the accumulations of hard skeletal parts left by organisms in the sediments after death (e.g., mollusk shells) to gain information on past community states. These so-called "death assemblages" contain skeletons produced over tens to thousands of years and change very slowly in comparison to living assemblages. Accordingly, under anthropogenic pressures, living assemblages change their structure and composition faster than their corresponding death assemblages. This increases the differences between the two beyond those caused by purely natural processes. When coupled with dating of dead shells (using radiocarbon calibrated amino acid racemization), such live-dead comparisons help assess the magnitude and timing of environmental impacts and ecosystem change when baseline data are not available. We applied these approaches to two major oil platforms off the United Arab Emirates coastline. We found a mismatch between living and death assemblages, with death assemblages dominated by a single bivalve species, the semelid Ervilia purpurea. However, the frequency distributions of post-mortem shell ages of this bivalve show that the mismatch can be mainly attributed to natural extreme demographic fluctuations in its population. We conclude that, at the field scale, decadal and century-level changes in the molluscan community composition were weak or too brief to leave any signatures in the death assemblages. At the regional scale, there was a weak shift towards trophic groups more tolerant to eutrophic conditions. Shell age dating is crucial in understanding the sources of the live-dead mismatch and enables exploring bivalve population dynamics in the past. Combining live-dead comparison with geochronology can shed light on community shifts in other oilfields and more broadly in areas where disturbance-related changes are expected and pre-impact conditions need to be reconstructed.

DEPENDENCY OF POLYCHLORINATED BIPHENYL AND POLYCYCLIC AROMATIC HYDROCARBON BIOACCUMULATION IN MYA ARENARIA ON BOTH WATER COLUMN AND SEDIMENT BED CHEMICAL ACTIVITIES

EPA Science Inventory

The bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) by the filter-feeding soft-shell clam Mya arenaria was evaluated at three sites near Boston (MA, USA) by assessing the chemical activities of those hydrophobic organic compounds (H...

Modeling Chemistry for Effective Chemical Education: An Interview with Ronald J. Gillespie

ERIC Educational Resources Information Center

Cardellini, Liberato

2010-01-01

Ronald J. Gillespie, the inventor of the Valence Shell Electron Pair Repulsion (VSEPR) model, relates how his career as researcher in Christopher Ingold's laboratories started. Gillespie developed a passion for chemistry and chemical education, searching for more appropriate and interesting ways to transmit the essential knowledge and enthusiasm…

Ab initio/GIAO-CCSD(T) (13)C NMR study of the rearrangement and dynamic aspects of rapidly equilibrating tertiary carbocations, C6H13(+) and C7H15(+).

PubMed

Olah, George A; Prakash, G K Surya; Rasul, Golam

2016-01-05

The rearrangement pathways of the equilibrating tertiary carbocations, 2,3-dimethyl-2-butyl cation (C6H13(+), 1), 2,3,3-trimethyl-2-butyl cation (C7H15(+), 5) and 2,3-dimethyl-2-pentyl cation (C7H15(+), 8 and 9) were investigated using the ab initio/GIAO-CCSD(T) (13)C NMR method. Comparing the calculated and experimental (13)C NMR chemical shifts of a series of carbocations indicates that excellent prediction of δ(13)C could be achieved through scaling. In the case of symmetrical equilibrating cations (1 and 5) the Wagner-Meerwein 1,2-hydride and 1,2-methide shifts, respectively, produce the same structure. This indicates that the overall (13)C NMR chemical shifts are conserved and independent of temperature. However, in the case of unsymmetrical equilibrating cations (8 and 9) the Wagner-Meerwein shift produces different tertiary structures, which have slightly different thermodynamic stabilities and, thus, different spectra. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level structure 8 is only 90 calories/mol more stable than structure 9. Based on computed (13)C NMR chemical shift calculations, mole fractions of these isomers were determined by assuming the observed chemical shifts are due to the weighted average of the chemical shifts of the static ions. © 2015 Wiley Periodicals, Inc.

Chemical shift-based identification of monosaccharide spin-systems with NMR spectroscopy to complement untargeted glycomics.

PubMed

Klukowski, Piotr; Schubert, Mario

2018-06-15

A better understanding of oligosaccharides and their wide-ranging functions in almost every aspect of biology and medicine promises to uncover hidden layers of biology and will support the development of better therapies. Elucidating the chemical structure of an unknown oligosaccharide is still a challenge. Efficient tools are required for non-targeted glycomics. Chemical shifts are a rich source of information about the topology and configuration of biomolecules, whose potential is however not fully explored for oligosaccharides. We hypothesize that the chemical shifts of each monosaccharide are unique for each saccharide type with a certain linkage pattern, so that correlated data measured by NMR spectroscopy can be used to identify the chemical nature of a carbohydrate. We present here an efficient search algorithm, GlycoNMRSearch, that matches either a subset or the entire set of chemical shifts of an unidentified monosaccharide spin system to all spin systems in an NMR database. The search output is much more precise than earlier search functions and highly similar matches suggest the chemical structure of the spin system within the oligosaccharide. Thus searching for connected chemical shift correlations within all electronically available NMR data of oligosaccharides is a very efficient way of identifying the chemical structure of unknown oligosaccharides. With an improved database in the future, GlycoNMRSearch will be even more efficient deducing chemical structures of oligosaccharides and there is a high chance that it becomes an indispensable technique for glycomics. The search algorithm presented here, together with a graphical user interface, is available at http://glyconmrsearch.santos.pwr.edu.pl. Supplementary data are available at Bioinformatics online.

Transmission electron microscopy of unstained hybrid Au nanoparticles capped with PPAA (plasma-poly-allylamine): structure and electron irradiation effects.

PubMed

Gontard, Lionel C; Fernández, Asunción; Dunin-Borkowski, Rafal E; Kasama, Takeshi; Lozano-Pérez, Sergio; Lucas, Stéphane

2014-12-01

Hybrid (organic shell-inorganic core) nanoparticles have important applications in nanomedicine. Although the inorganic components of hybrid nanoparticles can be characterized readily using conventional transmission electron microscopy (TEM) techniques, the structural and chemical arrangement of the organic molecular components remains largely unknown. Here, we apply TEM to the physico-chemical characterization of Au nanoparticles that are coated with plasma-polymerized-allylamine, an organic compound with the formula C3H5NH2. We discuss the use of energy-filtered TEM in the low-energy-loss range as a contrast enhancement mechanism for imaging the organic shells of such particles. We also study electron-beam-induced crystallization and amorphization of the shells and the formation of graphitic-like layers that contain both C and N. The resistance of the samples to irradiation by high-energy electrons, which is relevant for optical tuning and for understanding the degree to which such hybrid nanostructures are stable in the presence of biomedical radiation, is also discussed. Copyright © 2014 Elsevier Ltd. All rights reserved.

Homogeneous Nanodiamonds Are Different in Reality

NASA Astrophysics Data System (ADS)

Wu, Chi-Chin; Gottfried, Jennifer; Pesce-Rodriguez, Rose; Advanced Energetic Materials Team

Commercial detonation nanodiamonds (ND) have been investigated for many applications. They consist of carbon nanoparticles with diamond cores surrounded by onion-like graphitic shells. Unfortunately, variations in the purity and carbon structure between commercial ND samples due to variations in synthesis and purification conditions is an ongoing issue, since these differences can affect the resulting application-dependent ND behavior. Via characterization with transmission electron microscopy, this work investigates the structural and chemical differences among nominally homologous commercial detonation ND sold by a single vendor under the same item number. Significant discrepancies in the carbon structure and crystallinity between different batches with similar sizes and shapes were identified. The ND containing more non-carbon entities as impurities and oxygen-containing surface functional groups were found to possess thicker graphitic shells surrounding an unstable diamond core which quickly transforms to graphite under electron beam irradiation. However, the structure of ND with higher purities and thin onion shells remain unchanged over extended exposure to electron beams. This study demonstrates the structural and chemical differences between nominally identical commercial detonation ND samples and reveals their influence on the decomposition behavior of the particles.

Controlling energy flow in multimetallic nanostructures for plasmonic catalysis

NASA Astrophysics Data System (ADS)

Aslam, Umar; Chavez, Steven; Linic, Suljo

2017-10-01

It has been shown that photoexcitation of plasmonic metal nanoparticles (Ag, Au and Cu) can induce direct photochemical reactions. However, the widespread application of this technology in catalysis has been limited by the relatively poor chemical reactivity of noble metal surfaces. Despite efforts to combine plasmonic and catalytic metals, the physical mechanisms that govern energy transfer from plasmonic metals to catalytic metals remain unclear. Here we show that hybrid core-shell nanostructures in which a core plasmonic metal harvests visible-light photons can selectively channel that energy into catalytically active centres on the nanostructure shell. To accomplish this, we developed a synthetic protocol to deposit a few monolayers of Pt onto Ag nanocubes. This model system allows us to conclusively separate the optical and catalytic functions of the hybrid nanomaterial and determine that the flow of energy is strongly biased towards the excitation of energetic charge carriers in the Pt shell. We demonstrate the utility of these nanostructures for photocatalytic chemical reactions in the preferential oxidation of CO in excess H2. Our data demonstrate that the reaction occurs exclusively on the Pt surface.

Multi-methodological investigation of the variability of the microstructure of HPMC hard capsules.

PubMed

Faulhammer, E; Kovalcik, A; Wahl, V; Markl, D; Stelzer, F; Lawrence, S; Khinast, J G; Paudel, A

2016-09-25

The objective of this study was to analyze differences in the subtle microstructure of three different grades of HMPC hard capsule shells using mechanical, spectroscopic, microscopic and tomographic approaches. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), vibrational spectroscopic, X-Ray scattering techniques as well as environmental scanning electron microscopy (ESEM) and optical coherence tomography (OCT) were used. Two HPMC capsules manufactured via chemical gelling, one capsule shell manufactured via thermal gelling and one thermally gelled transparent capsule were included. Characteristic micro-structural alterations (associated manufacturing processes) such as mechanical and physical properties relevant to capsule performance and processability were thoroughly elucidated with the integration of data obtained from multi-methodological investigations. The physico-chemical and physico-mechanical data obtained from a gamut of techniques implied that thermally gelled HPMC hard capsule shells could offer an advantage in terms of machinability during capsule filling, owing to their superior micro- and macroscopic structure as well as specifically the mechanical stability under dry or humid conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

Hierarchical inorganic-organic multi-shell nanospheres for intervention and treatment of lead-contaminated blood

NASA Astrophysics Data System (ADS)

Khairy, Mohamed; El-Safty, Sherif A.; Shenashen, Mohamed. A.; Elshehy, Emad A.

2013-08-01

The highly toxic properties, bioavailability, and adverse effects of Pb2+ species on the environment and living organisms necessitate periodic monitoring and removal whenever possible of Pb2+ concentrations in the environment. In this study, we designed a novel optical multi-shell nanosphere sensor that enables selective recognition, unrestrained accessibility, continuous monitoring, and efficient removal (on the order of minutes) of Pb2+ ions from water and human blood, i.e., red blood cells (RBCs). The consequent decoration of the mesoporous core/double-shell silica nanospheres through a chemically responsive azo-chromophore with a long hydrophobic tail enabled us to create a unique hierarchical multi-shell sensor. We examined the efficiency of the multi-shell sensor in removing lead ions from the blood to ascertain the potential use of the sensor in medical applications. The lead-induced hemolysis of RBCs in the sensing/capture assay was inhibited by the ability of the hierarchical sensor to remove lead ions from blood. The results suggest the higher flux and diffusion of Pb2+ ions into the mesopores of the core/multi-shell sensor than into the RBC membranes. These findings indicate that the sensor could be used in the prevention of health risks associated with elevated blood lead levels such as anemia.The highly toxic properties, bioavailability, and adverse effects of Pb2+ species on the environment and living organisms necessitate periodic monitoring and removal whenever possible of Pb2+ concentrations in the environment. In this study, we designed a novel optical multi-shell nanosphere sensor that enables selective recognition, unrestrained accessibility, continuous monitoring, and efficient removal (on the order of minutes) of Pb2+ ions from water and human blood, i.e., red blood cells (RBCs). The consequent decoration of the mesoporous core/double-shell silica nanospheres through a chemically responsive azo-chromophore with a long hydrophobic tail enabled us to create a unique hierarchical multi-shell sensor. We examined the efficiency of the multi-shell sensor in removing lead ions from the blood to ascertain the potential use of the sensor in medical applications. The lead-induced hemolysis of RBCs in the sensing/capture assay was inhibited by the ability of the hierarchical sensor to remove lead ions from blood. The results suggest the higher flux and diffusion of Pb2+ ions into the mesopores of the core/multi-shell sensor than into the RBC membranes. These findings indicate that the sensor could be used in the prevention of health risks associated with elevated blood lead levels such as anemia. Electronic supplementary information (ESI) available: The experimental procedures for synthesis of AC-LHT, mesoporous core/double shell silica, and optical core/multi-shell sensors. The adsorption capacity, optical recognition of Pb ions, colorimetric response of Pb ions in ethanol medium, Langmuir adsorption isotherm and reusability of captor are addressed. See DOI: 10.1039/c3nr02403b

Enhancing absorption in coated semiconductor nanowire/nanorod core-shell arrays using active host matrices

NASA Astrophysics Data System (ADS)

Jule, Leta; Dejene, Francis; Roro, Kittessa

2016-12-01

In the present work, we investigated theoretically and experimentally the interaction of radiation field phenomena interacting with arrays of nanowire/nanorod core-shell embedded in active host matrices. The optical properties of composites are explored including the case when the absorption of propagating wave by dissipative component is completely compensated by amplification in active (lasing) medium. On the basis of more elaborated modeling approach and extended effective medium theory, the effective polarizability and the refractive index of electromagnetic mode dispersion of the core-shell nanowire arrays are derived. ZnS(shell)-coated by sulphidation process on ZnO(shell) nanorod arrays grown on (100) silicon substrate by chemical bath deposition (CBD) has been used for theoretical comparison. Compared with the bare ZnO nanorods, ZnS-coated core/shell nanorods exhibit a strongly reduced ultraviolet (UV) emission and a dramatically enhanced deep level (DL) emission. Obviously, the UV and DL emission peaks are attributed to the emissions of ZnO nanorods within ZnO/ZnS core/shell nanorods. The reduction of UV emission after ZnS coating seems to agree with the charge separation mechanism of type-II band alignment that holes transfer from the core to shell, which would quench the UV emission to a certain extent. Our theoretical calculations and numerical simulation demonstrate that the use of active host (amplifying) medium to compensate absorption at metallic inclusions. Moreover the core-shell nanorod/nanowire arrays create the opportunity for broad band absorption and light harvesting applications.

Shell thickness-dependent microwave absorption of core-shell Fe3O4@C composites.

PubMed

Du, Yunchen; Liu, Wenwen; Qiang, Rong; Wang, Ying; Han, Xijiang; Ma, Jun; Xu, Ping

2014-08-13

Core-shell composites, Fe3O4@C, with 500 nm Fe3O4 microspheres as cores have been successfully prepared through in situ polymerization of phenolic resin on the Fe3O4 surface and subsequent high-temperature carbonization. The thickness of carbon shell, from 20 to 70 nm, can be well controlled by modulating the weight ratio of resorcinol and Fe3O4 microspheres. Carbothermic reduction has not been triggered at present conditions, thus the crystalline phase and magnetic property of Fe3O4 micropsheres can be well preserved during the carbonization process. Although carbon shells display amorphous nature, Raman spectra reveal that the presence of Fe3O4 micropsheres can promote their graphitization degree to a certain extent. Coating Fe3O4 microspheres with carbon shells will not only increase the complex permittivity but also improve characteristic impedance, leading to multiple relaxation processes in these composites, thus the microwave absorption properties of these composites are greatly enhanced. Very interestingly, a critical thickness of carbon shells leads to an unusual dielectric behavior of the core-shell structure, which endows these composites with strong reflection loss, especially in the high frequency range. By considering good chemical homogeneity and microwave absorption, we believe the as-fabricated Fe3O4@C composites can be promising candidates as highly effective microwave absorbers.

Hierarchical Mesoporous Organosilica-Silica Core-Shell Nanoparticles Capable of Controlled Fungicide Release.

PubMed

Luo, Leilei; Liang, Yucang; Erichsen, Egil Severin; Anwander, Reiner

2018-05-17

A new class of hierarchically structured mesoporous silica core-shell nanoparticles (HSMSCSNs) with a periodic mesoporous organosilica (PMO) core and a mesoporous silica (MS) shell is reported. The applied one-pot, two-step strategy allows rational control over the core/shell chemical composition, topology, and pore/particle size, simply by adjusting the reaction conditions in the presence of cetyltrimethylammonium bromide (CTAB) as structure-directing agent under basic conditions. The spherical, ethylene- or methylene-bridged PMO cores feature hexagonal (p6mm) or cage-like cubic symmetry (Pm3‾ n) depending on the organosilica precursor. The hexagonal MS shell was obtained by n-hexane-induced controlled hydrolysis of TEOS followed by directional co-assembly/condensation of silicate/CTAB composites at the PMO cores. The HSMSCSNs feature a hierarchical pore structure with pore diameters of about 2.7 and 5.6 nm in the core and shell domains, respectively. The core sizes and shell thicknesses are adjustable in the ranges of 90-275 and 15-50 nm, respectively, and the surface areas (max. 1300 m 2  g -1 ) and pore volumes (max. 1.83 cm 3  g -1 ) are among the highest reported for core-shell nanoparticles. The adsorption and controlled release of the fungicide propiconazole by the HSMSCSNs showed a three-stage release profile. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

13C and (15)N chemical shift tensors in adenosine, guanosine dihydrate, 2'-deoxythymidine, and cytidine.

PubMed

Stueber, Dirk; Grant, David M

2002-09-04

The (13)C and (15)N chemical shift tensor principal values for adenosine, guanosine dihydrate, 2'-deoxythymidine, and cytidine are measured on natural abundance samples. Additionally, the (13)C and (15)N chemical shielding tensor principal values in these four nucleosides are calculated utilizing various theoretical approaches. Embedded ion method (EIM) calculations improve significantly the precision with which the experimental principal values are reproduced over calculations on the corresponding isolated molecules with proton-optimized geometries. The (13)C and (15)N chemical shift tensor orientations are reliably assigned in the molecular frames of the nucleosides based upon chemical shielding tensor calculations employing the EIM. The differences between principal values obtained in EIM calculations and in calculations on isolated molecules with proton positions optimized inside a point charge array are used to estimate the contributions to chemical shielding arising from intermolecular interactions. Moreover, the (13)C and (15)N chemical shift tensor orientations and principal values correlate with the molecular structure and the crystallographic environment for the nucleosides and agree with data obtained previously for related compounds. The effects of variations in certain EIM parameters on the accuracy of the shielding tensor calculations are investigated.

Saturated amine oxides: Part 8. Hydroacridines: Part 27. Effects of N-oxidation and of N-quaternization on the 15N NMR chemical shifts of N-methylpiperidine-derived mono-, bi-, and tricycloaliphatic tertiary amines.

PubMed

Potmischil, Francisc; Duddeck, Helmut; Nicolescu, Alina; Deleanu, Calin

2007-03-01

The (15)N chemical shifts of 13 N-methylpiperidine-derived mono-, bi- and tricycloaliphatic tertiary amines, their methiodides and their N-epimeric pairs of N-oxides were measured, and the contributions of specific structural parameters to the chemical shifts were determined by multilinear regression analysis. Within the examined compounds, the effects of N-oxidation upon the (15)N chemical shifts of the amines vary from +56 ppm to +90 ppm (deshielding), of which approx. +67.7 ppm is due to the inductive effect of the incoming N(+)--O(-) oxygen atom, whereas the rest is due to the additive shift effects of the various C-alkyl substituents of the piperidine ring. The effects of quaternization vary from -3.1 ppm to +29.3 ppm, of which approx. +8.9 ppm is due to the inductive effect of the incoming N(+)--CH(3) methyl group, and the rest is due to the additive shift effects of the various C-alkyl substituents of the piperidine ring. The shift effects of the C-alkyl substituents in the amines, the N-oxides and the methiodides are discussed. Copyright (c) 2007 John Wiley & Sons, Ltd.

Impact of hydrostatic pressure on an intrinsically disordered protein: a high-pressure NMR study of α-synuclein.

PubMed

Roche, Julien; Ying, Jinfa; Maltsev, Alexander S; Bax, Ad

2013-09-23

The impact of pressure on the backbone (15) N, (1) H and (13) C chemical shifts in N-terminally acetylated α-synuclein has been evaluated over a pressure range 1-2500 bar. Even while the chemical shifts fall very close to random coil values, as expected for an intrinsically disordered protein, substantial deviations in the pressure dependence of the chemical shifts are seen relative to those in short model peptides. In particular, the nonlinear pressure response of the (1) H(N) chemical shifts, which commonly is associated with the presence of low-lying "excited states", is much larger in α-synuclein than in model peptides. The linear pressure response of (1) H(N) chemical shift, commonly linked to H-bond length change, correlates well with those in short model peptides, and is found to be anticorrelated with its temperature dependence. The pressure dependence of (13) C chemical shifts shows remarkably large variations, even when accounting for residue type, and do not point to a clear shift in population between different regions of the Ramachandran map. However, a nearly universal decrease in (3) JHN-Hα by 0.22 ± 0.05 Hz suggests a slight increase in population of the polyproline II region at 2500 bar. The first six residues of N-terminally acetylated synuclein show a transient of approximately 15% population of α-helix, which slightly diminishes at 2500 bar. The backbone dynamics of the protein is not visibly affected beyond the effect of slight increase in water viscosity at 2500 bar. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Solution and solid-state effects on NMR chemical shifts in sesquiterpene lactones: NMR, X-ray, and theoretical methods.

PubMed

Dračínský, Martin; Buděšínský, Miloš; Warżajtis, Beata; Rychlewska, Urszula

2012-01-12

Selected guaianolide type sesquiterpene lactones were studied combining solution and solid-state NMR spectroscopy with theoretical calculations of the chemical shifts in both environments and with the X-ray data. The experimental (1)H and (13)C chemical shifts in solution were successfully reproduced by theoretical calculations (with the GIAO method and DFT B3LYP 6-31++G**) after geometry optimization (DFT B3LYP 6-31 G**) in vacuum. The GIPAW method was used for calculations of solid-state (13)C chemical shifts. The studied cases involved two polymorphs of helenalin, two pseudopolymorphs of 6α-hydroxydihydro-aromaticin and two cases of multiple asymmetric units in crystals: one in which the symmetry-independent molecules were connected by a series of hydrogen bonds (geigerinin) and the other in which the symmetry-independent molecules, deprived of any specific intermolecular interactions, differed in the conformation of the side chain (badkhysin). Geometrically different molecules present in the crystal lattices could be easily distinguished in the solid-state NMR spectra. Moreover, the experimental differences in the (13)C chemical shifts corresponding to nuclei in different polymorphs or in geometrically different molecules were nicely reproduced with the GIPAW calculations.

(3, 2)D 1H, 13C BIRDr,X-HSQC-TOCSY for NMR structure elucidation of mixtures: application to complex carbohydrates.

PubMed

Brodaczewska, Natalia; Košťálová, Zuzana; Uhrín, Dušan

2018-02-01

Overlap of NMR signals is the major cause of difficulties associated with NMR structure elucidation of molecules contained in complex mixtures. A 2D homonuclear correlation spectroscopy in particular suffers from low dispersion of 1 H chemical shifts; larger dispersion of 13 C chemical shifts is often used to reduce this overlap, while still providing the proton-proton correlation information e.g. in the form of a 2D 1 H, 13 C HSQC-TOCSY experiment. For this methodology to work, 13 C chemical shift must be resolved. In case of 13 C chemical shifts overlap, 1 H chemical shifts can be used to achieve the desired resolution. The proposed (3, 2)D 1 H, 13 C BIRD r,X -HSQC-TOCSY experiment achieves this while preserving singlet character of cross peaks in the F 1 dimension. The required high-resolution in the 13 C dimension is thus retained, while the cross peak overlap occurring in a regular HSQC-TOCSY experiment is eliminated. The method is illustrated on the analysis of a complex carbohydrate mixture obtained by depolymerisation of a fucosylated chondroitin sulfate isolated from the body wall of the sea cucumber Holothuria forskali.

Analysis of the contributions of ring current and electric field effects to the chemical shifts of RNA bases.

PubMed

Sahakyan, Aleksandr B; Vendruscolo, Michele

2013-02-21

Ring current and electric field effects can considerably influence NMR chemical shifts in biomolecules. Understanding such effects is particularly important for the development of accurate mappings between chemical shifts and the structures of nucleic acids. In this work, we first analyzed the Pople and the Haigh-Mallion models in terms of their ability to describe nitrogen base conjugated ring effects. We then created a database (DiBaseRNA) of three-dimensional arrangements of RNA base pairs from X-ray structures, calculated the corresponding chemical shifts via a hybrid density functional theory approach and used the results to parametrize the ring current and electric field effects in RNA bases. Next, we studied the coupling of the electric field and ring current effects for different inter-ring arrangements found in RNA bases using linear model fitting, with joint electric field and ring current, as well as only electric field and only ring current approximations. Taken together, our results provide a characterization of the interdependence of ring current and electric field geometric factors, which is shown to be especially important for the chemical shifts of non-hydrogen atoms in RNA bases.

Highly efficient near-infrared light-emitting diodes by using type-II CdTe/CdSe core/shell quantum dots as a phosphor

NASA Astrophysics Data System (ADS)

Shen, Huaibin; Zheng, Ying; Wang, Hongzhe; Xu, Weiwei; Qian, Lei; Yang, Yixing; Titov, Alexandre; Hyvonen, Jake; Li, Lin Song

2013-11-01

In this paper, we present an innovative method for the synthesis of CdTe/CdSe type-II core/shell structure quantum dots (QDs) using ‘greener’ chemicals. The PL of CdTe/CdSe type-II core/shell structure QDs ranges from 600 to 820 nm, and the as-synthesized core/shell structures show narrow size distributions and stable and high quantum yields (50-75%). Highly efficient near-infrared light-emitting diodes (LEDs) have been demonstrated by employing the CdTe/CdSe type-II core/shell QDs as emitters. The devices fabricated based on these type-II core/shell QDs show color-saturated near-infrared emission from the QD layers, a low turn-on voltage of 1.55 V, an external quantum efficiency (EQE) of 1.59%, and a current density and maximum radiant emittance of 2.1 × 103 mA cm-2 and 17.7 mW cm-2 at 8 V it is the first report to use type-II core/shell QDs as near-infrared emitters and these results may offer a practicable platform for the realization of near-infrared QD-based light-emitting diodes, night-vision-readable displays, and friend/foe identification system.

Core-shell designed scaffolds for drug delivery and tissue engineering.

PubMed

Perez, Roman A; Kim, Hae-Won

2015-07-01

Scaffolds that secure and deliver therapeutic ingredients like signaling molecules and stem cells hold great promise for drug delivery and tissue engineering. Employing a core-shell design for scaffolds provides a promising solution. Some unique methods, such as co-concentric nozzle extrusion, microfluidics generation, and chemical confinement reactions, have been successful in producing core-shelled nano/microfibers and nano/microspheres. Signaling molecules and drugs, spatially allocated to the core and/or shell part, can be delivered in a controllable and sequential manner for optimal therapeutic effects. Stem cells can be loaded within the core part on-demand, safely protected from the environments, which ultimately affords ex vivo culture and in vivo tissue engineering. The encapsulated cells experience three-dimensional tissue-mimic microenvironments in which therapeutic molecules are secreted to the surrounding tissues through the semi-permeable shell. Tuning the material properties of the core and shell, changing the geometrical parameters, and shaping them into proper forms significantly influence the release behaviors of biomolecules and the fate of the cells. This topical issue highlights the immense usefulness of core-shell designs for the therapeutic actions of scaffolds in the delivery of signaling molecules and stem cells for tissue regeneration and disease treatment. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Enhancing the methanol tolerance of platinum nanoparticles for the cathode reaction of direct methanol fuel cells through a geometric design.

PubMed

Feng, Yan; Ye, Feng; Liu, Hui; Yang, Jun

2015-11-18

Mastery over the structure of nanoparticles might be an effective way to enhance their performance for a given application. Herein we demonstrate the design of cage-bell nanostructures to enhance the methanol tolerance of platinum (Pt) nanoparticles while remaining their catalytic activity for oxygen reduction reaction. This strategy starts with the synthesis of core-shell-shell nanoparticles with Pt and silver (Ag) residing respectively in the core and inner shell regions, which are then agitated with saturated sodium chloride (NaCl) solution to eliminate the Ag component from the inner shell region, leading to the formation of bimetallic nanoparticles with a cage-bell structure, defined as a movable Pt core enclosed by a metal shell with nano-channels, which exhibit superior methanol-tolerant property in catalyzing oxygen reduction reaction due to the different diffusion behaviour of methanol and oxygen in the porous metal shell of cage-bell structured nanoparticles. In particular, the use of remarkably inexpensive chemical agent (NaCl) to promote the formation of cage-bell structured particles containing a wide spectrum of metal shells highlights its engineering merit to produce highly selective electrocatalysts on a large scale for the cathode reaction of direct methanol fuel cells.

Fabrication and characterization of ZnS/ZnO core shell nanostructures on silver wires

NASA Astrophysics Data System (ADS)

Kao, Chyuan Haur; Su, Wei Ming; Li, Cheng Yuan; Weng, Wei Chih; Weng, Chen Yuan; Cheng, Chin-Chi; Lin, Yung-Sen; Lin, Chia Feng; Chen, Hsiang

2018-06-01

In this research, ZnS nanoparticles were synthesized on ZnO/silver wires to form ZnS/ZnO core shell structures. Various outward appearance and colors could be observed by different ZnO growth and sulfurization conditions. To evaluate the properties of these nanostructures, optical properties and chemical bindings were analyzed by photoluminescence, Raman analysis, and X-ray photoelectron spectroscopy. Furthermore, material characterizations including transmission electron microscopy and X-ray diffraction confirmed that cubic ZnS (311)/ZnO nanostructures were grown on silver wires for the first time. ZnS/ZnO core shell structures on silver wires are promising for future optoelectronic and biomedical applications.

Spectrum of Slow and Super-Slow (Picosecond to Nanosecond) Water Dynamics around Organic and Biological Solutes.

PubMed

Ramakrishnan, Gopakumar; González-Jiménez, Mario; Lapthorn, Adrian J; Wynne, Klaas

2017-07-06

Water dynamics in the solvation shell of solutes plays a very important role in the interaction of biomolecules and in chemical reaction dynamics. However, a selective spectroscopic study of the solvation shell is difficult because of the interference of the solute dynamics. Here we report on the observation of heavily slowed down water dynamics in the solvation shell of different solutes by measuring the low-frequency spectrum of solvation water, free from the contribution of the solute. A slowdown factor of ∼50 is observed even for relatively low concentrations of the solute. We go on to show that the effect can be generalized to different solutes including proteins.

Novel core-shell (TiO2@Silica) nanoparticles for scattering medium in a random laser: higher efficiency, lower laser threshold and lower photodegradation.

PubMed

Jimenez-Villar, Ernesto; Mestre, Valdeci; de Oliveira, Paulo C; de Sá, Gilberto F

2013-12-21

There has been growing interest in scattering media in recent years, due to their potential applications as solar collectors, photocatalyzers, random lasers and other novel optical devices. Here, we have introduced a novel core-shell scattering medium for a random laser composed of TiO2@Silica nanoparticles. Higher efficiency, lower laser threshold and long photobleaching lifetime in random lasers were demonstrated. This has introduced a new method or parameter (fraction of absorbed pumping), which opens a new avenue to characterize and study the scattering media. Optical chemical and colloidal stabilities were combined by coating a suitable silica shell onto TiO2 nanoparticles.

Electroless nickel – phosphorus coating on crab shell particles and its characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arulvel, S., E-mail: gs.arulvel.research@gmail.com; Elayaperumal, A.; Jagatheeshwaran, M.S.

Being hydrophilic material, crab shell particles have only a limited number of applications. It is, therefore, necessary to modify the surface of the crab shell particles. To make them useful ever for the applications, the main theme we proposed in this article is to utilize crab shell particles (CSP) with the core coated with nickel phosphorus (NiP) as a shell using the electroless coating process. For dealing with serious environmental problems, utilization of waste bio-shells is always an important factor to be considered. Chelating ability of crab shell particles eliminates the surface activation in this work proceeding to the coatingmore » process. The functional group, phase structure, microstructure, chemical composition and thermal analysis of CSP and NiP/CSP were characterized using Fourier transform infra-red spectroscopy (FTIR), x-ray diffraction analyzer (XRD), scanning electron microscope (SEM), energy-dispersive x-ray spectroscopy (EDS), and thermogravimetric analysis (TGA). The combination of an amorphous and crystalline structure was exhibited by CSP and NiP/CSP. NiP/CSP has shown a better thermal stability when compared to uncoated CSP. Stability test, adsorption test, and conductivity test were conducted for the study of adsorption behavior and conductivity of the particles. CSP presented a hydrophilic property in contrast to hydrophobic NiP/CSP. NiP/CSP presented a conductivity of about 44% greater compared to the CSP without any fluctuations. - Highlights: • Utilization of crab shell waste is focused on. • NiP coating on crab shell particle is fabricated using electroless process. • Thermal analysis, stability test, adsorption test and conductivity test were done. • Organic matrix of crab shell particle favors the coating process. • Results demonstrate the characterization of CSP core – NiP shell structure.« less

On the breakup of tectonic plates by polar wandering

NASA Technical Reports Server (NTRS)

Liu, H.-S.

1974-01-01

The equations for the stresses in a homogeneous shell of uniform thickness caused by a shift of the axis of rotation are derived. The magnitude of these stresses reaches a maximum value of the order of 10 to the 9th power dyn/sq cm, which is sufficient for explaining a tectonic breakup. In order to deduce the fracture pattern according to which the breakup of tectonic plates can be expected the theory of plastic deformation of shells is applied. The analysis of this pattern gives an explanation of the existing boundary systems of the major tectonic plates as described by Morgan (1968), LePichon (1968) and Isacks et al. (1968).

Measurement of wavelengths and lamb shifts for inner-shell transitions in Fe XVIII-XXIV. [from solar flare X-ray spectra

NASA Technical Reports Server (NTRS)

Seely, J. F.; Feldman, U.; Safronova, U. I.

1986-01-01

The wavelengths of inner-shell 1s-2p transitions in the ions Fe XVIII-XXIV have been measured in solar flare spectra recorded by the Naval Research Laboratory crystal spectrometer (SOLFLEX) on the Air Force P78-1 spacecraft. The measurements are compared with previous measurements and with recently calculated wavelengths. It is found that the measured wavelengths are systematically larger than the wavelengths calculated using the Z-expansion method by up to 0.65 mA. For the more highly charged ions, these differences can be attributed to the QED contributions to the transition energies that are not included in the Z-expansion calculations.

Production of Chitosan from Amusium sp Scallop Shell Waste

NASA Astrophysics Data System (ADS)

Rokhati, Nur; Istirokhatun, Titik; Titik Apriyanti, Dwi; Susanto, Heru

2017-02-01

Chitosan is one of the natural polysaccharides, which is produced from chitin by deacetylation process. In this study, chitosan was produced from Amusium sp scallop shell waste. First, chitin was isolated by extraction via deproteinization using alkaline solution followed by demineralization using acid solution. Thereafter, chitosan was resulted from deacetylation of chitin using a high concentration of alkaline solution. The chemical structure of chitin and chitosan products was characterized using fourier transform infrared spectroscopy (FTIR).

Supercritical fluid technology of nanoparticle coating for new ceramic materials.

PubMed

Aymonier, Cyril; Elissalde, Catherine; Reveron, Helen; Weill, François; Maglione, Mario; Cansell, François

2005-06-01

This work highlights, for the first time, the coating of ferroelectric nanoparticles with a chemical fluid deposition process in supercritical fluids. BaTiO3 nanoparticles of about 50 nm are coated with a shell of a few nanometers of amorphous alumina and can be recovered as a dry powder for processing. The sintering of these core-shell nanoparticles gives access to a ceramic material with very interesting ferroelectric properties, in particular, dielectric losses below 1%.

NMR shifts for polycyclic aromatic hydrocarbons from first-principles

NASA Astrophysics Data System (ADS)

Thonhauser, T.; Ceresoli, Davide; Marzari, Nicola

We present first-principles, density-functional theory calculations of the NMR chemical shifts for polycyclic aromatic hydrocarbons, starting with benzene and increasing sizes up to the one- and two-dimensional infinite limits of graphene ribbons and sheets. Our calculations are performed using a combination of the recently developed theory of orbital magnetization in solids, and a novel approach to NMR calculations where chemical shifts are obtained from the derivative of the orbital magnetization with respect to a microscopic, localized magnetic dipole. Using these methods we study on equal footing the 1H and 13 shifts in benzene, pyrene, coronene, in naphthalene, anthracene, naphthacene, and pentacene, and finally in graphene, graphite, and an infinite graphene ribbon. Our results show very good agreement with experiments and allow us to characterize the trends for the chemical shifts as a function of system size.

General route for the assembly of functional inorganic capsules.

PubMed

Akartuna, Ilke; Tervoort, Elena; Studart, André R; Gauckler, Ludwig J

2009-11-03

Semipermeable, hollow capsules are attractive materials for the encapsulation and delivery of active agents in food processing, pharmaceutical and agricultural industries, and biomedicine. These capsules can be produced by forming a solid shell of close packed colloidal particles, typically polymeric particles, at the surface of emulsion droplets. However, current methods to prepare such capsules may involve multistep chemical procedures to tailor the surface chemistry of particles or are limited to particles that exhibit inherently the right hydrophobic-hydrophilic balance to adsorb around emulsion droplets. In this work, we describe a general and simple method to fabricate semipermeable, inorganic capsules from emulsion droplets stabilized by a wide variety of colloidal metal oxide particles. The assembly of particles at the oil-water interface is induced by the in situ hydrophobization of the particle surface through the adsorption of short amphiphilic molecules. The adsorption of particles at the interface leads to stable capsules comprising a single layer of particles in the outer shell. Such capsules can be used in the wet state or can be further processed into dry capsules. The permeability of the capsules can be modified by filling the interstices between the shell particles with polymeric or inorganic species. Functional capsules with biocompatible, bioresorbable, heat-resistant, chemical-resistant, and magnetic properties were prepared using alumina, silica, iron oxide, or tricalcium phosphate as particles in the shell.

Size-controlled synthesis of superparamagnetic iron oxide nanoparticles and their surface coating by gold for biomedical applications

NASA Astrophysics Data System (ADS)

Maleki, H.; Simchi, A.; Imani, M.; Costa, B. F. O.

2012-11-01

The size mono-dispersity, saturation magnetization, and surface chemistry of magnetic nanoparticles (NPs) are recognized as critical factors for efficient biomedical applications. Here, we performed modified water-in-oil inverse nano-emulsion procedure for preparation of stable colloidal superparamagnetic iron oxide NPs (SPIONs) with high saturation magnetization. To achieve mono-dispersed SPIONs, optimization process was probed on several important factors including molar ratio of iron salts [Fe3+ and Fe2+], the concentration of ammonium hydroxide as reducing agent, and molar ratio of water to surfactant. The biocompatibility of the obtained NPs, at various concentrations, was evaluated via MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay and the results showed that the NPs were non-toxic at concentrations <0.1 mg/mL. Surface functionalization was performed by conformal coating of the NPs with a thin shell of gold (˜4 nm) through chemical reduction of attached gold salts at the surface of the SPIONs. The Fe3O4 core/Au shell particles demonstrate strong plasmon resonance absorption and can be separated from solution using an external magnetic field. Experimental data from both physical and chemical determinations of the changes in particle size, surface plasmon resonance optical band, phase components, core-shell surface composition, and magnetic properties have confirmed the formation of the mono-dispersed core-shell nanostructure.

Quantum-Chemical Approach to NMR Chemical Shifts in Paramagnetic Solids Applied to LiFePO4 and LiCoPO4.

PubMed

Mondal, Arobendo; Kaupp, Martin

2018-04-05

A novel protocol to compute and analyze NMR chemical shifts for extended paramagnetic solids, accounting comprehensively for Fermi-contact (FC), pseudocontact (PC), and orbital shifts, is reported and applied to the important lithium ion battery cathode materials LiFePO 4 and LiCoPO 4 . Using an EPR-parameter-based ansatz, the approach combines periodic (hybrid) DFT computation of hyperfine and orbital-shielding tensors with an incremental cluster model for g- and zero-field-splitting (ZFS) D-tensors. The cluster model allows the use of advanced multireference wave function methods (such as CASSCF or NEVPT2). Application of this protocol shows that the 7 Li shifts in the high-voltage cathode material LiCoPO 4 are dominated by spin-orbit-induced PC contributions, in contrast with previous assumptions, fundamentally changing interpretations of the shifts in terms of covalency. PC contributions are smaller for the 7 Li shifts of the related LiFePO 4 , where FC and orbital shifts dominate. The 31 P shifts of both materials finally are almost pure FC shifts. Nevertheless, large ZFS contributions can give rise to non-Curie temperature dependences for both 7 Li and 31 P shifts.

Growth control, structure, chemical state, and photoresponse of CuO-CdS core-shell heterostructure nanowires.

PubMed

El Mel, A A; Buffière, M; Bouts, N; Gautron, E; Tessier, P Y; Henzler, K; Guttmann, P; Konstantinidis, S; Bittencourt, C; Snyders, R

2013-07-05

The growth of single-crystal CuO nanowires by thermal annealing of copper thin films in air is studied. We show that the density, length, and diameter of the nanowires can be controlled by tuning the morphology and structure of the copper thin films deposited by DC magnetron sputtering. After identifying the optimal conditions for the growth of CuO nanowires, chemical bath deposition is employed to coat the CuO nanowires with CdS in order to form p-n nanojunction arrays. As revealed by high-resolution TEM analysis, the thickness of the polycrystalline CdS shell increases when decreasing the diameter of the CuO core for a given time of CdS deposition. Near-edge x-ray absorption fine-structure spectroscopy combined with transmission x-ray microscopy allows the chemical analysis of isolated nanowires. The absence of modification in the spectra at the Cu L and O K edges after the deposition of CdS on the CuO nanowires indicates that neither Cd nor S diffuse into the CuO phase. We further demonstrate that the core-shell nanowires exhibit the I-V characteristic of a resistor instead of a diode. The electrical behavior of the device was found to be photosensitive, since increasing the incident light intensity induces an increase in the collected electrical current.

On the supersymmetrization of Galileon theories in four dimensions

NASA Astrophysics Data System (ADS)

Elvang, Henriette; Hadjiantonis, Marios; Jones, Callum R. T.; Paranjape, Shruti

2018-06-01

We use on-shell amplitude techniques to study the possible N = 1 supersymmetrizations of Galileon theories in 3 + 1 dimensions, both in the limit of decoupling from DBI and without. Our results are that (1) the quartic Galileon has a supersymmetrization compatible with Galileon shift symmetry (ϕ → ϕ + c +bμxμ) for the scalar sector and a constant shift symmetry (ψ → ψ + ξ) for the fermion sector, and it is unique at least at 6th order in fields, but possibly not beyond; (2) the enhanced "special Galileon" symmetry is incompatible with supersymmetry; (3) there exists a quintic Galileon with a complex scalar preserving Galileon shift symmetry; (4) one cannot supersymmetrize the cubic and quintic Galileon while preserving the Galileon shift symmetry for the complex scalar; and (5) for the quartic and quintic Galileon, we present evidence for a supersymmetrization in which the real Galileon scalar is partnered with an R-axion to form a complex scalar which only has an ordinary shift symmetry.

Design of multi-shell Fe2O3@MnOx@CNTs for the selective catalytic reduction of NO with NH3: improvement of catalytic activity and SO2 tolerance

NASA Astrophysics Data System (ADS)

Cai, Sixiang; Hu, Hang; Li, Hongrui; Shi, Liyi; Zhang, Dengsong

2016-02-01

Manganese based catalysts are highly active in the NH3-SCR reaction for NOx removal. Unfortunately, manganese oxides can be easily deactivated by sulfur dioxide in the flow gas, which has become the main obstacle for their practical applications. To address this problem, we presented a green and facile method for the synthesis of multi-shell Fe2O3@MnOx@CNTs. The morphology and structural properties of the catalysts were systematically investigated. The results revealed that the MnOx@CNT core-shell structure was formed during the chemical bath deposition, while the outermost MnOx species were transformed to Fe2O3 after the galvanic replacement reaction. The formation of the multi-shell structure induced the enhancement of the active oxygen species, reducible species as well as adsorption of the reactants, which brought about excellent de-NOx performance. Moreover, the Fe2O3 shell could effectively suppress the formation of the surface sulfate species, leading to the desirable SO2 resistance to the multi-shell catalyst. Hence, the synthesis protocol could provide guidance for the preparation and elevation of manganese based catalysts.Manganese based catalysts are highly active in the NH3-SCR reaction for NOx removal. Unfortunately, manganese oxides can be easily deactivated by sulfur dioxide in the flow gas, which has become the main obstacle for their practical applications. To address this problem, we presented a green and facile method for the synthesis of multi-shell Fe2O3@MnOx@CNTs. The morphology and structural properties of the catalysts were systematically investigated. The results revealed that the MnOx@CNT core-shell structure was formed during the chemical bath deposition, while the outermost MnOx species were transformed to Fe2O3 after the galvanic replacement reaction. The formation of the multi-shell structure induced the enhancement of the active oxygen species, reducible species as well as adsorption of the reactants, which brought about excellent de-NOx performance. Moreover, the Fe2O3 shell could effectively suppress the formation of the surface sulfate species, leading to the desirable SO2 resistance to the multi-shell catalyst. Hence, the synthesis protocol could provide guidance for the preparation and elevation of manganese based catalysts. Electronic supplementary information (ESI) available: Experimental details and catalytic performance of the Fe-Mn@CNTs IM, TEM images of Fe@Mn CNTs, stability and H2O resistance studies of the catalysts. See DOI: 10.1039/c5nr08701e

Reaction monitoring using hyperpolarized NMR with scaling of heteronuclear couplings by optimal tracking

NASA Astrophysics Data System (ADS)

Zhang, Guannan; Schilling, Franz; Glaser, Steffen J.; Hilty, Christian

2016-11-01

Off-resonance decoupling using the method of Scaling of Heteronuclear Couplings by Optimal Tracking (SHOT) enables determination of heteronuclear correlations of chemical shifts in single scan NMR spectra. Through modulation of J-coupling evolution by shaped radio frequency pulses, off resonance decoupling using SHOT pulses causes a user-defined dependence of the observed J-splitting, such as the splitting of 13C peaks, on the chemical shift offset of coupled nuclei, such as 1H. Because a decoupling experiment requires only a single scan, this method is suitable for characterizing on-going chemical reactions using hyperpolarization by dissolution dynamic nuclear polarization (D-DNP). We demonstrate the calculation of [13C, 1H] chemical shift correlations of the carbanionic active sites from hyperpolarized styrene polymerized using sodium naphthalene as an initiator. While off resonance decoupling by SHOT pulses does not enhance the resolution in the same way as a 2D NMR spectrum would, the ability to obtain the correlations in single scans makes this method ideal for determination of chemical shifts in on-going reactions on the second time scale. In addition, we present a novel SHOT pulse that allows to scale J-splittings 50% larger than the respective J-coupling constant. This feature can be used to enhance the resolution of the indirectly detected chemical shift and reduce peak overlap, as demonstrated in a model reaction between p-anisaldehyde and isobutylamine. For both pulses, the accuracy is evaluated under changing signal-to-noise ratios (SNR) of the peaks from reactants and reaction products, with an overall standard deviation of chemical shift differences compared to reference spectra of 0.02 ppm when measured on a 400 MHz NMR spectrometer. Notably, the appearance of decoupling side-bands, which scale with peak intensity, appears to be of secondary importance.

A Chemical View on X-ray Photoelectron Spectroscopy: the ESCA Molecule and Surface-to-Bulk XPS Shifts.

PubMed

Delesma, Francisco A; Van den Bossche, Maxime; Grönbeck, Henrik; Calaminici, Patrizia; Köster, Andreas M; Pettersson, Lars G M

2018-01-19

In this paper we remind the reader of a simple, intuitive picture of chemical shifts in X-ray photoelectron spectroscopy (XPS) as the difference in chemical bonding between the probed atom and its neighbor to the right in the periodic table, the so called Z+1 approximation. We use the classical ESCA molecule, ethyl trifluoroacetate, and 4d-transition metals to explicitly demonstrate agreement between core-level shifts computed as differences between final core-hole states and the approach where each core-ionized atom is replaced by a Z+1 atom. In this final state, or total energy picture, the XPS shift arises due to the more or less unfavorable chemical bonding of the effective nitrogen in the carbon geometry for the ESCA molecule. Surface core level shifts in metals are determined by whether the Z+1 atom as an alloy segregates to the surface or is more soluble in the bulk. As further illustration of this more chemical picture, we compare the geometry of C 1s and O 1s core-ionized CO with that of, respectively, NO + and CF + . The scope is not to propose a new method to compute XPS shifts but rather to stress the validity of this simple interpretation. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nuclear magnetic resonance shielding constants and chemical shifts in linear 199Hg compounds: a comparison of three relativistic computational methods.

PubMed

Arcisauskaite, Vaida; Melo, Juan I; Hemmingsen, Lars; Sauer, Stephan P A

2011-07-28

We investigate the importance of relativistic effects on NMR shielding constants and chemical shifts of linear HgL(2) (L = Cl, Br, I, CH(3)) compounds using three different relativistic methods: the fully relativistic four-component approach and the two-component approximations, linear response elimination of small component (LR-ESC) and zeroth-order regular approximation (ZORA). LR-ESC reproduces successfully the four-component results for the C shielding constant in Hg(CH(3))(2) within 6 ppm, but fails to reproduce the Hg shielding constants and chemical shifts. The latter is mainly due to an underestimation of the change in spin-orbit contribution. Even though ZORA underestimates the absolute Hg NMR shielding constants by ∼2100 ppm, the differences between Hg chemical shift values obtained using ZORA and the four-component approach without spin-density contribution to the exchange-correlation (XC) kernel are less than 60 ppm for all compounds using three different functionals, BP86, B3LYP, and PBE0. However, larger deviations (up to 366 ppm) occur for Hg chemical shifts in HgBr(2) and HgI(2) when ZORA results are compared with four-component calculations with non-collinear spin-density contribution to the XC kernel. For the ZORA calculations it is necessary to use large basis sets (QZ4P) and the TZ2P basis set may give errors of ∼500 ppm for the Hg chemical shifts, despite deceivingly good agreement with experimental data. A Gaussian nucleus model for the Coulomb potential reduces the Hg shielding constants by ∼100-500 ppm and the Hg chemical shifts by 1-143 ppm compared to the point nucleus model depending on the atomic number Z of the coordinating atom and the level of theory. The effect on the shielding constants of the lighter nuclei (C, Cl, Br, I) is, however, negligible. © 2011 American Institute of Physics

Palladium-platinum core-shell electrocatalysts for oxygen reduction reaction prepared with the assistance of citric acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Lulu; Su, Dong; Zhu, Shangqian

Core–shell structure is a promising alternative to solid platinum (Pt) nanoparticles as electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). A simple method of preparing palladium (Pd)–platinum (Pt) core–shell catalysts (Pd@Pt/C) in a gram-batch was developed with the assistance of citric acid. The Pt shell deposition involves three different pathways: galvanic displacement reaction between Pd atoms and Pt cations, chemical reduction by citric acid, and reduction by negative charges on Pd surfaces. The uniform ultrathin (~0.4 nm) Pt shell was characterized by in situ X-ray diffraction (XRD) and high-angle annular dark-field scanning transmission electron microscopymore » (HAADF-STEM) images combined with electron energy loss spectroscopy (EELS). Compared with state-of-the-art Pt/C, the Pd@Pt/C core–shell catalyst showed 4 times higher Pt mass activity and much better durability upon potential cycling. As a result, both the mass activity and durability were comparable to that of Pd@Pt/C synthesized by a Cu-mediated-Pt-displacement method, which is more complicated and difficult for mass production.« less

Super-tough, ultra-stretchable and strongly compressive hydrogels with core-shell latex particles inducing efficient aggregation of hydrophobic chains.

PubMed

Ren, Xiuyan; Huang, Chang; Duan, Lijie; Liu, Baijun; Bu, Lvjun; Guan, Shuang; Hou, Jiliang; Zhang, Huixuan; Gao, Guanghui

2017-05-14

Toughness, strechability and compressibility for hydrogels were ordinarily balanced for their use as mechanically responsive materials. For example, macromolecular microsphere composite hydrogels with chemical crosslinking exhibited excellent compression strength and strechability, but poor tensile stress. Here, a novel strategy for the preparation of a super-tough, ultra-stretchable and strongly compressive hydrogel was proposed by introducing core-shell latex particles (LPs) as crosslinking centers for inducing efficient aggregation of hydrophobic chains. The core-shell LPs always maintained a spherical shape due to the presence of a hard core even by an external force and the soft shell could interact with hydrophobic chains due to hydrophobic interactions. As a result, the hydrogels reinforced by core-shell LPs exhibited not only a high tensile strength of 1.8 MPa and dramatic elongation of over 20 times, but also an excellent compressive performance of 13.5 MPa at a strain of 90%. The Mullins effect was verified for the validity of core-shell LP-reinforced hydrogels by inducing aggregation of hydrophobic chains. The novel strategy strives to provide a better avenue for designing and developing a new generation of hydrophobic association tough hydrogels with excellent mechanical properties.

Characterization of preservative and pesticide as potential of bio oil compound from pyrolisis of cocoa shell using gas chromatography

NASA Astrophysics Data System (ADS)

Mashuni, Jahiding, M.; Kurniasih, I.; Zulkaidah

2017-03-01

Cocoa shell is one of the plant waste that has not been widely used. Cocoa shell is potential as a producer of bio oil because it contains lignocellulose. The bio oil of Liquid volatile matter (LVM) is the products of smoke condensation from the pyrolysis reactor. The bio oil of cocoa shell from pyrolysis process can be made as raw materials for the application of pesticide and preservative. The aims of this research were to produce bio oil from cocoa shell by pyrolysis and analyzing the content using Gas Chromatography (GC). Bio oil production was done by pyrolysis with variations of temperature, i.e. 400, 500, 600 and 700 °C. Pyrolysis reaction generates three products: gas, liquid and solid. The yield of bio oil with variations of pyrolisis temperature, i.e. 400, 500, 600 and 700 °C were obtained i.e. 46, 45, 44 and 40% (v/w), respectively. The chromatogram results showed the chemical components of bio oil from the cocoa shell were ammonia, hexane, alcohol, ketone, acid and phenolic compounds which can be used as material of preservative and pesticide.

Hybrid nanomaterial for stabilizing the antibiofilm activity of Eugenia carryophyllata essential oil.

PubMed

Grumezescu, Alexandru Mihai; Chifiriuc, Mariana Carmen; Saviuc, Crina; Grumezescu, Valentina; Hristu, Radu; Mihaiescu, Dan Eduard; Stanciu, George A; Andronescu, Ecaterina

2012-12-01

The aim of the present study was to demonstrate that Fe(3)O(4)/oleic acid core/shell nanostructures could be used as systems for stabilizing the Eugenia carryophyllata essential oil (EO) on catheter surface pellicles, in order to improve their resistance to fungal colonization. EO microwave assisted extraction was performed in a Neo-Clevenger (related) device and its chemical composition was settled by GC-MS analysis. Fe(3)O(4)/oleic acid-core/shell nanoparticles (NP) were obtained by a precipitation method under microwave condition. High resolution transmission electron microscopy (HR-TEM) was used as a primary characterization method. The NPs were processed to achieve a core/shell/EO coated-shell nanosystem further used for coating the inner surface of central venous catheter samples. The tested fungal strains have been recently isolated from different clinical specimens. The biofilm architecture was assessed by confocal laser scanning microscopy (CLSM). Our results claim the usage of hybrid nanomaterial (core/shell/coated-shell) for the stabilization of E. carryophyllata EO, which prevented or inhibited the fungal biofilm development on the functionalized catheter, highlighting the opportunity of using these nanosystems to obtain improved, anti-biofilm coatings for biomedical applications.

Electrospun core-shell fibers for robust silicon nanoparticle-based lithium ion battery anodes.

PubMed

Hwang, Tae Hoon; Lee, Yong Min; Kong, Byung-Seon; Seo, Jin-Seok; Choi, Jang Wook

2012-02-08

Because of its unprecedented theoretical capacity near 4000 mAh/g, which is approximately 10-fold larger compared to those of the current commercial graphite anodes, silicon has been the most promising anode for lithium ion batteries, particularly targeting large-scale energy storage applications including electrical vehicles and utility grids. Nevertheless, Si suffers from its short cycle life as well as the limitation for scalable electrode fabrication. Herein, we develop an electrospinning process to produce core-shell fiber electrodes using a dual nozzle in a scalable manner. In the core-shell fibers, commercially available nanoparticles in the core are wrapped by the carbon shell. The unique core-shell structure resolves various issues of Si anode operations, such as pulverization, vulnerable contacts between Si and carbon conductors, and an unstable sold-electrolyte interphase, thereby exhibiting outstanding cell performance: a gravimetric capacity as high as 1384 mAh/g, a 5 min discharging rate capability while retaining 721 mAh/g, and cycle life of 300 cycles with almost no capacity loss. The electrospun core-shell one-dimensional fibers suggest a new design principle for robust and scalable lithium battery electrodes suffering from volume expansion. © 2011 American Chemical Society

Palladium-platinum core-shell electrocatalysts for oxygen reduction reaction prepared with the assistance of citric acid

DOE PAGES

Zhang, Lulu; Su, Dong; Zhu, Shangqian; ...

2016-04-26

Core–shell structure is a promising alternative to solid platinum (Pt) nanoparticles as electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). A simple method of preparing palladium (Pd)–platinum (Pt) core–shell catalysts (Pd@Pt/C) in a gram-batch was developed with the assistance of citric acid. The Pt shell deposition involves three different pathways: galvanic displacement reaction between Pd atoms and Pt cations, chemical reduction by citric acid, and reduction by negative charges on Pd surfaces. The uniform ultrathin (~0.4 nm) Pt shell was characterized by in situ X-ray diffraction (XRD) and high-angle annular dark-field scanning transmission electron microscopymore » (HAADF-STEM) images combined with electron energy loss spectroscopy (EELS). Compared with state-of-the-art Pt/C, the Pd@Pt/C core–shell catalyst showed 4 times higher Pt mass activity and much better durability upon potential cycling. As a result, both the mass activity and durability were comparable to that of Pd@Pt/C synthesized by a Cu-mediated-Pt-displacement method, which is more complicated and difficult for mass production.« less

Structural and electronic properties of CdSe/ZnS and ZnS/CdSe core/shell nanowires via first principles study

NASA Astrophysics Data System (ADS)

Rehman, Shafiq Ur; Li, H. M.; Ding, Z. J.

2018-05-01

First principles calculations have been performed to predict the structural stability and electronic structures of hydrogen passivated wurtzite CdSe/ZnS and ZnS/CdSe core/shell nanowires (CSNWs) in the [0001] direction. The calculated binding energy shows that ZnS/CdSe CSNWs are more stable than CdSe/ZnS CSNWs and the stability of ZnS/CdSe CSNWs increases with increasing the thickness of ZnS shell. The modulated electronic band gap demonstrates an increase when the size of both CSNWs is reduced, as a result of the quantum confinement effect. The core-to-shell chemical composition of atoms shows that a strong composition effect also exists in these CSNWs, which in turn affects their electronic properties. Our simulated results show that the photoemission spectra of the CSNWs can be significantly improved by tuning the energy gap of CSNWs.

Cellulose nanofibers reinforced sodium alginate-polyvinyl alcohol hydrogels: Core-shell structure formation and property characterization.

PubMed

Yue, Yiying; Han, Jingquan; Han, Guangping; French, Alfred D; Qi, Yadong; Wu, Qinglin

2016-08-20

Core-shell structured hydrogels consisting of a flexible interpenetrating polymer network (IPN) core and a rigid semi-IPN shell were prepared through chemical crosslinking of polyvinyl alcohol (PVA) and sodium alginate (SA) with Ca(2+) and glutaraldehyde. Short cellulose nanofibers (CNFs) extracted from energycane bagasse were incorporated in the hydrogel. The shell was micro-porous and the core was macro-porous. The hydrogels could be used in multiple adsorption-desorption cycles for dyes, and the maximum methyl blue adsorption capacity had a 10% increase after incorporating CNFs. The homogeneous distribution of CNFs in PVA-SA matrix generated additional hydrogen bonds among the polymer molecular chains, resulting in enhanced density, viscoelasticity, and mechanical strength for the hydrogel. Specifically, the compressive strength of the hydrogel reached 79.5kPa, 3.2 times higher than that of the neat hydrogel. Copyright © 2016 Elsevier Ltd. All rights reserved.

Properties and potential environmental applications of carbon adsorbents from waste tire rubber

USGS Publications Warehouse

Lehmann, C.M.B.; Rameriz, D.; Rood, M.J.; Rostam-Abadi, M.

2000-01-01

The properties of tire-derived carbon adsorbents (TDCA) produced from select tire chars were compared with those derived from an Illinois coal and pistachio nut shells. Chemical analyses of the TDCA indicated that these materials contain metallic elements not present in coal-and nut shell-derived carbons. These metals, introduced during the production of tire rubber, potentially catalyze steam gasification reactions of tire char. TDCA carbons contained larger meso-and macopore volumes than their counterparts derived from coal and nut shell (on the moisture-and ash-free-basis). Adsorptive properties of the tire-derived adsorbent carbons for air separation, gas storage, and gas clean up were also evaluated and compared with those of the coal-and nut shell derived carbons as well as a commercial activated carbon. The results revealed that TDCA carbons are suitable adsorbents for removing vapor-phase mercury from combustion flue gases and hazardous organic compounds from industrial gas streams.

Encapsulation of superparamagnetic Fe 3 O 4 @SiO 2 core/shell nanoparticles in MnO 2 microflowers with high surface areas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Yu-Gang; Truong, Tu T.; Liu, Yu-Zi

2015-02-01

Microflowers made of interconnected MnO2 nanosheets have been successfully synthesized in a microwave reactor through a hydrothermal reduction of KMnO4 with aqueous HCl at elevated temperatures in the presence of superparamagnetic Fe3O4@SiO2 core-shell nanoparticles. Due to the chemical compatibility between SiO2 and MnO2, the heterogeneous reaction leads to the spontaneous encapsulation of the Fe3O4@SiO2 core-shell nanoparticles in the MnO2 microflowers. The resulting hybrid particles exhibit multiple properties including high surface area associated with the MnO2 nanosheets and superparamagnetism originated from the Fe3O4@SiO2 core-shell nanoparticles, which are beneficial for applications requiring both high surface area and magnetic separation. (C) 2014 Yu-Gangmore » Sun.« less

Hydrazine Catalyst Production: Sustaining S-405 Technology

NASA Technical Reports Server (NTRS)

Wucherer, E. J.; Cook, Timothy; Stiefel, Mark; Humphries, Randy, Jr.; Parker, Janet

2003-01-01

The development of the iridium-based Shell 405 catalyst for spontaneous decomposition of hydrazine was one of the key enabling technologies for today's spacecraft and launch vehicles. To ensure that this crucial technology was not lost when Shell elected to exit the business, Aerojet, supported by NASA, has developed a dedicated catalyst production facility that will supply catalyst for future spacecraft and launch vehicle requirements. We have undertaken a program to transfer catalyst production from Shell Chemical USA (Houston, TX) to Aerojet's Redmond, WA location. This technology transition was aided by Aerojet's 30 years of catalyst manufacturing experience and NASA diligence and support in sustaining essential technologies. The facility has produced and tested S-405 catalyst to existing Shell 405 specifications and standards. Our presentation will describe the technology transition effort including development of the manufacturing facility, capture of the manufacturing process, test equipment validation, initial batch build and final testing.

Helmet of a laminate construction of polycarbonate and polysulfone polymeric material

NASA Technical Reports Server (NTRS)

Kosmo, Joseph J. (Inventor); Dawn, Frederic S. (Inventor)

1991-01-01

An article of laminate construction is disclosed which is comprised of an underlayer of polycarbonate polymer material to which is applied a chemically resistant outer layer of polysulfone. The layers which are joined by compression-heat molding, are molded to form the shape of a body protective shell such as a space helmet comprising a shell of polycarbonate, polysulfone laminate construction attached at its open end to a sealing ring adapted for connection to a space suit. The front portion of the shell provides a transparent visor for the helmet. An outer visor of polycarbonate polysulfone laminate construction is pivotally mounted to the sealing ring for covering the transparent visor portion of the shell during extravehicular activities. The polycarbonate under layer of the outer visor is coated on its inner surface with a vacuum deposit of gold to provide additional thermal radiation resistance.

Reassigning the Structures of Natural Products Using NMR Chemical Shifts Computed with Quantum Mechanics: A Laboratory Exercise

ERIC Educational Resources Information Center

Palazzo, Teresa A.; Truong, Tiana T.; Wong, Shirley M. T.; Mack, Emma T.; Lodewyk, Michael W.; Harrison, Jason G.; Gamage, R. Alan; Siegel, Justin B.; Kurth, Mark J.; Tantillo, Dean J.

2015-01-01

An applied computational chemistry laboratory exercise is described in which students use modern quantum chemical calculations of chemical shifts to assign the structure of a recently isolated natural product. A pre/post assessment was used to measure student learning gains and verify that students demonstrated proficiency of key learning…

Lifetime Measurement of Nickel-58 Using RDM with GRETINA

NASA Astrophysics Data System (ADS)

Loelius, Charles

2014-09-01

The structure of nuclei near the doubly magic 56Ni has provided a sensitive probe of configuration mixing across the N=Z=28 shell gap. The shell model description of nuclei in this region is well established, with the gxpf1 interaction accurately reproducing the energy levels and transition strengths of Nuclei in the vicinity of 56Ni. However, there remain open questions as to the effects of higher lying orbitals beyond the pf shell. These can be addressed by a study of the B(E2)'s of nuclei in near the shell gap, particularly the B(E2;4+ -->2+) where effects of high l orbitals may be enhanced. 58Ni provides a strong candidate for study, as the only previous B(E2;4+ -->2+) measurement using the Doppler Shift Attenuation Method resulted in a B(E2) three times larger than that predicted by theory. In order to determine the possible effects of higher lying orbitals, a second measurement of the lifetime of 58Ni was undertaken at the National Superconducting Cyclotron Laboratory using the the Gamma-Ray Energy Tracking in Beam Nuclear Array (GRETINA) and the Recoil Distance Method (RDM). Preliminary results of this measurement will be presented.

Swelling and Softening of the Cowpea Chlorotic Mottle Virus in Response to pH Shifts

PubMed Central

Wilts, Bodo D.; Schaap, Iwan A.T.; Schmidt, Christoph F.

2015-01-01

Cowpea chlorotic mottle virus (CCMV) forms highly elastic icosahedral protein capsids that undergo a characteristic swelling transition when the pH is raised from 5 to 7. Here, we performed nano-indentation experiments using an atomic force microscope to track capsid swelling and measure the shells’ Young’s modulus at the same time. When we chelated Ca2+ ions and raised the pH, we observed a gradual swelling of the RNA-filled capsids accompanied by a softening of the shell. Control experiments with empty wild-type virus and a salt-stable mutant revealed that the softening was not strictly coupled to the swelling of the protein shells. Our data suggest that a pH increase and Ca2+ chelation lead primarily to a loosening of contacts within the protein shell, resulting in a softening of the capsid. This appears to render the shell metastable and make swelling possible when repulsive forces among the capsid proteins become large enough, which is known to be followed by capsid disassembly at even higher pH. Thus, softening and swelling are likely to play a role during inoculation. PMID:25992732

Coulomb Excitation of the 64Ni Nucleus and Application of Inverse Kinematics

NASA Astrophysics Data System (ADS)

Greaves, Beau; Muecher, Dennis; Ali, Fuad A.; Drake, Tom; Bildstein, Vinzenz; Berner, Christian; Gernhaeuser, Roman; Nowak, K.; Hellgartner, S.; Lutter, R.; Reichert, S.

2017-09-01

In this contribution, we present new data on the semi-magic 64Ni nucleus, close to the N =40 harmonic oscillator shell gap. Recent studies suggest a complicated existence of shape coexistence in 68Ni, likely caused by type-II shell evolutions. The region studied here thus might define the ``shore'' of the region of more deformed nuclei in the Island of Inversion below 68Ni. At the Maier-Leibnitz-Laboratory (MLL) in Munich, a beam of 64Ni was excited using Coulomb excitation. The high-granularity MINIBALL HPGe array and a segmented silicon strip detector were used to identify gamma decays in 64Ni. Doppler-shifted attenuation method (DSAM) analysis was applied to the experimental data acquired to resolve the low-lying excited states and acquire a lifetime measurement based on Geant4 simulations of the first excited 2 + state, clarifying the previously conflicting results. Furthermore, we show DSAM data following transfer reactions in inverse kinematics. This new method has the potential to provide insight into tests of ab-initio shell model calculations in the sd-pf shell and for the study of nuclear reaction rates. Supported under NSERC SAPIN-2016-00030.

Seasonal oxygen and carbon isotope variability in euthecosomatous pteropods from the Sargasso Sea

NASA Astrophysics Data System (ADS)

Juranek, L. W.; Russell, A. D.; Spero, H. J.

2003-02-01

We examine seasonal variations in the stable carbon and oxygen isotopic composition of individual shells of the pteropods Limacina inflata and Styliola subula, collected from Oceanic Flux Program sediment traps (at 500 m depth) near Bermuda in the western Sargasso Sea. Calcification depths estimated from L. inflata δ18O vary between 200 and 650 m in late winter and spring, and between 50 and 250 m in late summer and fall. S. subula shows similar seasonal variability with calcification depths between 250 and 600 m in late winter and spring and 50-400 m in late summer and fall. These results suggest that both species calcify across a greater range of depths than indicated by previous geochemical studies. Furthermore, the data indicate that these species change their calcification depth in conjunction with changes in thermal stratification of the water column. Pteropod shell δ13C values vary inversely with δ13C DIC but show a positive correlation with seawater [CO 32-] and temperature after depth differences in δ13C DIC are accounted for. We hypothesize that either the influence of temperature on metabolic CO 2 incorporation during shell growth and/or the influence of ambient [CO 32-] on shell geochemistry can explain these relationships. Taken together, the individual shell δ18O and δ13C data suggest that shell calcification, and by inference the life cycle, of these pteropods is several months or less. Individual pteropod shell analyses have potential for contributing to our understanding of the environmental parameters that play a role in seasonal calcification depth shifts, as well as to our knowledge of past upper ocean thermal structure.

Bifunctional catalyst of graphite-encapsulated iron compound nanoparticle for magnetic carbon nanotubes growth by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Saraswati, Teguh Endah; Prasiwi, Oktaviana Dewi Indah; Masykur, Abu; Anwar, Miftahul

2017-01-01

The carbon nanotube has widely taken great attractive in carbon nanomaterial research and application. One of its preparation methods is catalytic chemical vapor deposition (CCVD) using catalyst i.e. iron, nickel, etc. Generally, except the catalyst, carbon source gasses as the precursor are still required. Here, we report the use of the bifunctional material of Fe3O4/C which has an incorporated core/shell structures of carbon-encapsulated iron compound nanoparticles. The bifunctional catalyst was prepared by submerged arc discharge that simply performed using carbon and carbon/iron oxide electrodes in ethanol 50%. The prepared material was then used as a catalyst in thermal chemical vapor deposition at 800°C flown with ethanol vapor as the primer carbon source in a low-pressure condition. This catalyst might play a dual role as a catalyst and secondary carbon source for growing carbon nanotubes at the time. The synthesized products were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The successful formation of carbon nanotubes was assigned by the shifted X-ray diffracted peak of carbon C(002), the iron oxides of Fe3O4 and γ-Fe2O3, and the other peaks which were highly considered to the other carbon allotropes with sp2 hybridization structures. The other assignment was studied by electron microscopy which successfully observed the presence of single-wall carbon nanotubes. In addition, the as-prepared carbon nanotubes have a magnetic property which was induced by the remaining of metal catalyst inside the CNT.

Freshwater mussel shells as environmental chronicles: Geochemical and taphonomic signatures of mercury-related extirpations in the North Fork Holston River, Virginia

USGS Publications Warehouse

Brown, M.E.; Kowalewski, M.; Neves, R.J.; Cherry, D.S.; Schreiber, M.E.

2005-01-01

This study utilized freshwater mussel shells to assess mercury (Hg) contamination in the North Fork Holston River that extirpated (caused local extinctions of) a diverse mussel fauna. Shells (n = 366) were collected from five sites situated upstream (two sites), just below (one site), and downstream (two sites) of the town of Saltville, Virginia, where Hg was used to produce chlorine and caustic soda from 1950 to 1972. Shell samples were used to test the (1) utility of geochemical signatures of shells for assessing the spatial variation in Hg levels in the river relative to the contamination source and (2) value of taphonomy (postmortem shell alteration) for distinguishing sites that differ in extirpation histories. Geochemical signatures of 40 shells, analyzed using atomic absorption spectroscopy, indicated a strong longitudinal pattern. All shells from the two upstream sites had low Hg concentrations (<5-31 ??g/kg), shells directly below Saltville had variable, but dramatically higher concentrations (23-4637 ??g/kg), and shells from the two downstream sites displayed intermediate Hg levels (<5-115 ??g/kg) that declined with distance from Saltville. Two pre-industrial shells, collected at Saltville in 1917, yielded very low Hg estimates (5-6 ??g/kg). Hg signatures were consistent among mussel species, suggesting that Hg concentrations were invariant to species type; most likely, highly variable Hg levels, both across sites and through time, overwhelmed any interspecific differences in Hg acquisition. Also, a notable postmortem incorporation of Hg in mussel shells seemed unlikely, as the Hg content was not correlated with shell taphonomy (r = 0.18; p = 0.28). The taphonomic analysis (n = 366) showed that the degree of shell alteration reliably distinguished sites with different extirpation histories. At Saltville, where live mussels have been absent for at least 30 years, shells were most heavily altered and fragmented. Conversely, fresh-looking shells abounded upstream, where reproducing mussel populations are still present. In summary, relic shells offered valuable spatiotemporal data on Hg concentrations in a polluted ecosystem, and shell taphonomic signatures discriminated sites with different extirpation histories. The shell-based strategies exemplified here do not require sampling live specimens and may augment more standard strategies applied to environmental monitoring. The approach should prove especially useful in areas with unknown extirpation and pollution histories. ?? 2005 American Chemical Society.

Anomalous center of mass shift: gravitational dipole moment.

NASA Astrophysics Data System (ADS)

Jeong, Eue Jin

1997-02-01

The anomalous, energy dependent shift of the center of mass of an idealized, perfectly rigid, uniformly rotating hemispherical shell which is caused by the relativistic mass increase effect is investigated in detail. It is shown that a classical object on impact which has the harmonic binding force between the adjacent constituent particles has the similar effect of the energy dependent, anomalous shift of the center of mass. From these observations, the general mode of the linear acceleration is suggested to be caused by the anomalous center of mass shift whether it's due to classical or relativistic origin. The effect of the energy dependent center of mass shift perpendicular to the plane of rotation of a rotating hemisphere appears as the non zero gravitational dipole moment in general relativity. Controlled experiment for the measurement of the gravitational dipole field and its possible links to the cylindrical type line formation of a worm hole in the extreme case are suggested. The jets from the black hole accretion disc and the observed anomalous red shift from far away galaxies are considered to be the consequences of the two different aspects of the dipole gravity.

46 CFR 38.05-10 - Installation of cargo tanks-general-TB/ALL.

Code of Federal Regulations, 2011 CFR

2011-10-01

... prevent the tanks from shifting when subjected to external forces. Each tank shall be so supported as to prevent the concentration of excessive loads on the supporting portions of the shell or head as prescribed... consider the resonance of the cargo tank, or parts thereof, and the vibratory forces, found in the tank...

46 CFR 38.05-10 - Installation of cargo tanks-general-TB/ALL.

Code of Federal Regulations, 2012 CFR

2012-10-01

... prevent the tanks from shifting when subjected to external forces. Each tank shall be so supported as to prevent the concentration of excessive loads on the supporting portions of the shell or head as prescribed... consider the resonance of the cargo tank, or parts thereof, and the vibratory forces, found in the tank...

46 CFR 38.05-10 - Installation of cargo tanks-general-TB/ALL.

Code of Federal Regulations, 2014 CFR

2014-10-01

... prevent the tanks from shifting when subjected to external forces. Each tank shall be so supported as to prevent the concentration of excessive loads on the supporting portions of the shell or head as prescribed... consider the resonance of the cargo tank, or parts thereof, and the vibratory forces, found in the tank...

46 CFR 38.05-10 - Installation of cargo tanks-general-TB/ALL.

Code of Federal Regulations, 2010 CFR

2010-10-01

... prevent the tanks from shifting when subjected to external forces. Each tank shall be so supported as to prevent the concentration of excessive loads on the supporting portions of the shell or head as prescribed... consider the resonance of the cargo tank, or parts thereof, and the vibratory forces, found in the tank...

46 CFR 38.05-10 - Installation of cargo tanks-general-TB/ALL.

Code of Federal Regulations, 2013 CFR

2013-10-01

... prevent the tanks from shifting when subjected to external forces. Each tank shall be so supported as to prevent the concentration of excessive loads on the supporting portions of the shell or head as prescribed... consider the resonance of the cargo tank, or parts thereof, and the vibratory forces, found in the tank...

Tunable Narrow Band Emissions from Dye-Sensitized Core/Shell/Shell Nanocrystals in the Second Near-Infrared Biological Window

PubMed Central

Shao, Wei; Chen, Guanying; Kuzmin, Andrey; Kutscher, Hilliard L.; Pliss, Artem; Ohulchanskyy, Tymish Y.; Prasad, Paras N.

2017-01-01

We introduce a hybrid organic–inorganic system consisting of epitaxial NaYF4:Yb3+/X3+@NaYbF4@NaYF4:Nd3+ (X = null, Er, Ho, Tm, or Pr) core/shell/shell (CSS) nanocrystal with organic dye, indocyanine green (ICG) on the nanocrystal surface. This system is able to produce a set of narrow band emissions with a large Stokes-shift (>200 nm) in the second biological window of optical transparency (NIR-II, 1000–1700 nm), by directional energy transfer from light-harvesting surface ICG, via lanthanide ions in the shells, to the emitter X3+ in the core. Surface ICG not only increases the NIR-II emission intensity of inorganic CSS nanocrystals by ~4-fold but also provides a broadly excitable spectral range (700–860 nm) that facilitates their use in bioapplications. We show that the NIR-II emission from ICG-sensitized Er3+-doped CSS nanocrystals allows clear observation of a sharp image through 9 mm thick chicken breast tissue, and emission signal detection through 22 mm thick tissue yielding a better imaging profile than from typically used Yb/Tm-codoped upconverting nanocrystals imaged in the NIR-I region (700–950 nm). Our result on in vivo imaging suggests that these ICG-sensitized CSS nanocrystals are suitable for deep optical imaging in the NIR-II region. PMID:27935695

Fabrication of a transparent ultraviolet detector by using n-type Ga2O3 and p-type Ga-doped SnO2 core-shell nanowires.

PubMed

Hsu, Cheng-Liang; Lu, Ying-Ching

2012-09-21

This study investigates the feasibility of synthesizing high-density transparent Ga(2)O(3)/SnO(2):Ga core-shell nanowires on a sapphire substrate at 1000 °C by VLS. The doping Ga concentrations are 0.46, 1.07, 2.30 and 17.53 atomic%. The XRD spectrum and HR-TEM reveal Ga(2)O(3) and SnO(2) as having monoclinic and tetragonal rutile structures, respectively. Experimental results indicate that the XRD peak shift of SnO(2) to a larger angle increases with the increasing amount of Ga doping. According to the CL spectrum, SnO(2) and Ga(2)O(3) peak at approximately 528-568 nm and 422-424 nm, respectively. The maximum quantum efficiency of Ga(2)O(3)/SnO(2):Ga core-shell nanowires is around 0.362%. The UV light on-off current contrast ratio of Ga(2)O(3)/SnO(2):Ga core-shell nanowires is around 1066.7 at a bias of 5 V. Moreover, the dynamic response of Ga(2)O(3)/SnO(2):Ga core-shell nanowires has an on-off current contrast ratio of around 16. Furthermore, the Ga(2)O(3) region functions similar to a capacitor and continues to accumulate SnO(2):Ga excited electrons under UV light exposure.

Environmental salinity modulates the effects of elevated CO2 levels on juvenile hard-shell clams, Mercenaria mercenaria.

PubMed

Dickinson, Gary H; Matoo, Omera B; Tourek, Robert T; Sokolova, Inna M; Beniash, Elia

2013-07-15

Ocean acidification due to increasing atmospheric CO2 concentrations results in a decrease in seawater pH and shifts in the carbonate chemistry that can negatively affect marine organisms. Marine bivalves such as the hard-shell clam, Mercenaria mercenaria, serve as ecosystem engineers in estuaries and coastal zones of the western Atlantic and, as for many marine calcifiers, are sensitive to the impacts of ocean acidification. In estuaries, the effects of ocean acidification can be exacerbated by low buffering capacity of brackish waters, acidic inputs from freshwaters and land, and/or the negative effects of salinity on the physiology of organisms. We determined the interactive effects of 21 weeks of exposure to different levels of CO2 (~395, 800 and 1500 μatm corresponding to pH of 8.2, 8.1 and 7.7, respectively) and salinity (32 versus 16) on biomineralization, shell properties and energy metabolism of juvenile hard-shell clams. Low salinity had profound effects on survival, energy metabolism and biomineralization of hard-shell clams and modulated their responses to elevated PCO2. Negative effects of low salinity in juvenile clams were mostly due to the strongly elevated basal energy demand, indicating energy deficiency, that led to reduced growth, elevated mortality and impaired shell maintenance (evidenced by the extensive damage to the periostracum). The effects of elevated PCO2 on physiology and biomineralization of hard-shell clams were more complex. Elevated PCO2 (~800-1500 μatm) had no significant effects on standard metabolic rates (indicative of the basal energy demand), but affected growth and shell mechanical properties in juvenile clams. Moderate hypercapnia (~800 μatm PCO2) increased shell and tissue growth and reduced mortality of juvenile clams in high salinity exposures; however, these effects were abolished under the low salinity conditions or at high PCO2 (~1500 μatm). Mechanical properties of the shell (measured as microhardness and fracture toughness of the shells) were negatively affected by elevated CO2 alone or in combination with low salinity, which may have important implications for protection against predators or environmental stressors. Our data indicate that environmental salinity can strongly modulate responses to ocean acidification in hard-shell clams and thus should be taken into account when predicting the effects of ocean acidification on estuarine bivalves.

Ab initio/GIAO-CCSD(T) study of structures, energies, and 13C NMR chemical shifts of C4H7(+) and C5H9(+) ions: relative stability and dynamic aspects of the cyclopropylcarbinyl vs bicyclobutonium ions.

PubMed

Olah, George A; Surya Prakash, G K; Rasul, Golam

2008-07-16

The structures and energies of the carbocations C 4H 7 (+) and C 5H 9 (+) were calculated using the ab initio method. The (13)C NMR chemical shifts of the carbocations were calculated using the GIAO-CCSD(T) method. The pisigma-delocalized bisected cyclopropylcarbinyl cation, 1 and nonclassical bicyclobutonium ion, 2 were found to be the minima for C 4H 7 (+) at the MP2/cc-pVTZ level. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level the structure 2 is 0.4 kcal/mol more stable than the structure 1. The (13)C NMR chemical shifts of 1 and 2 were calculated by the GIAO-CCSD(T) method. Based on relative energies and (13)C NMR chemical shift calculations, an equilibrium involving the 1 and 2 in superacid solutions is most likely responsible for the experimentally observed (13)C NMR chemical shifts, with the latter as the predominant equilibrating species. The alpha-methylcyclopropylcarbinyl cation, 4, and nonclassical bicyclobutonium ion, 5, were found to be the minima for C 5H 9 (+) at the MP2/cc-pVTZ level. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level ion 5 is 5.9 kcal/mol more stable than the structure 4. The calculated (13)C NMR chemical shifts of 5 agree rather well with the experimental values of C 5H 9 (+).

Investigating the Vanadium Environments in Hydroxylamido V(V) Dipicolinate Complexes Using 51V NMR Spectroscopy and Density Functional Theory

PubMed Central

Ooms, Kristopher J.; Bolte, Stephanie E.; Smee, Jason J.; Baruah, Bharat; Crans, Debbie C.; Polenova, Tatyana

2014-01-01

Using 51V magic angle spinning solid-state NMR, SSNMR, spectroscopy and quantum chemical DFT calculations we have characterized the chemical shift and quadrupolar coupling parameters of a series of 8 hydroxylamido vanadium(V) dipicolinate complexes of the general formula VO(dipic)(ONR1R2)(H2O) where R1 and R2 can be H, CH3, or CH2CH3. This class of vanadium compounds was chosen for investigation because of their seven coordinate vanadium atom, a geometry for which there is limited 51V SSNMR data. Furthermore, a systematic series of compounds with different electronic properties are available and allows for the effects of ligand substitution on the NMR parameters to be studied. The quadrupolar coupling constants, CQ, are small, 3.0 to 3.9 MHz, but exhibit variations as a function of the ligand substitution. The chemical shift tensors in the solid state are sensitive to changes in both the hydroxylamide substituent and the dipic ligand, a sensitivity which is not observed for isotropic chemical shifts in solution. The chemical shift tensors span approximately 1000 ppm, and are nearly axially symmetric. Based on DFT calculations of the chemical shift tensors, one of the largest contributors to the magnetic shielding anisotropy is an occupied molecular orbital with significant vanadium dz2 character along the V=O bond. PMID:17902653

Improved Electrostatic Embedding for Fragment-Based Chemical Shift Calculations in Molecular Crystals.

PubMed

Hartman, Joshua D; Balaji, Ashwin; Beran, Gregory J O

2017-12-12

Fragment-based methods predict nuclear magnetic resonance (NMR) chemical shielding tensors in molecular crystals with high accuracy and computational efficiency. Such methods typically employ electrostatic embedding to mimic the crystalline environment, and the quality of the results can be sensitive to the embedding treatment. To improve the quality of this embedding environment for fragment-based molecular crystal property calculations, we borrow ideas from the embedded ion method to incorporate self-consistently polarized Madelung field effects. The self-consistent reproduction of the Madelung potential (SCRMP) model developed here constructs an array of point charges that incorporates self-consistent lattice polarization and which reproduces the Madelung potential at all atomic sites involved in the quantum mechanical region of the system. The performance of fragment- and cluster-based 1 H, 13 C, 14 N, and 17 O chemical shift predictions using SCRMP and density functionals like PBE and PBE0 are assessed. The improved embedding model results in substantial improvements in the predicted 17 O chemical shifts and modest improvements in the 15 N ones. Finally, the performance of the model is demonstrated by examining the assignment of the two oxygen chemical shifts in the challenging γ-polymorph of glycine. Overall, the SCRMP-embedded NMR chemical shift predictions are on par with or more accurate than those obtained with the widely used gauge-including projector augmented wave (GIPAW) model.

An investigation into the effective surface passivation of quantum dots by a photo-assisted chemical method

NASA Astrophysics Data System (ADS)

Joo, So-Yeong; Park, Hyun-Su; Kim, Do-yeon; Kim, Bum-Sung; Lee, Chan Gi; Kim, Woo-Byoung

2018-01-01

In this study, we have developed an effective amino passivation process for quantum dots (QDs) at room temperature and have investigated a passivation mechanism using a photo-assisted chemical method. As a result of the reverse reaction of the H2O molecules, the etching kinetics of the photo-assisted chemical method increased upon increasing the 3-amino-1-propanol (APOL)/H2O ratio of the etching solution. Photon-excited electron-hole pairs lead to strong bonding between the organic and surface atoms of the QDs, and results in an increase of the quantum yield (QY%). This passivation method is also applicable to CdSe/ZnSe core/shell structures of QDs, due to the passivation of mid-gap defects states at the interface. The QY% of the as-synthesized CdSe QDs is dramatically enhanced by the amino passivation from 37% to 75% and the QY% of the CdSe/ZnSe core/shell QDs is also improved by ˜28%.

Chemical defence in mussels: antifouling effect of crude extracts of the periostracum of the blue mussel Mytilus edulis.

PubMed

Bers, A Valeria; D'Souza, Fraddry; Klijnstra, Job W; Willemsen, Peter R; Wahl, Martin

2006-01-01

Shells of the blue mussel Mytilus edulis remain free of fouling organisms as long as they possess an intact periostracum, and a multiple antifouling defence that comprises a ripple-like microtopography and the production of chemical antifouling compounds has been suggested previously. This study investigates the chemical defence strategy of blue mussels for the first time. Six crude extracts of the periostracum of intact shells were made using solvents of increasing polarity. These extracts were tested against common fouling organisms in laboratory based bioassays. Non-polar and moderately polar fractions showed the highest activities: the diethyl ether fraction strongly inhibited attachment of Balanus amphitrite cyprids and the marine bacteria Cobetia marina and Marinobacter hydrocarbonoclasticus. Attachment of the benthic diatom Amphora coffeaeformis was significantly reduced by the dichloromethane extract, whereas both ethyl acetate and diethyl ether fractions slowed diatom growth. These results provide the first evidence of surface bound compounds that may moderate surface colonisation.

Ultrafast hydrogen bond dynamics and partial electron transfer after photoexcitation of diethyl ester of 7-(diethylamino)-coumarin-3-phosphonic acid and its benzoxaphosphorin analog.

PubMed

Wagner, M S; Ilieva, E D; Petkov, P St; Nikolova, R D; Kienberger, R; Iglev, H

2015-04-21

The solvation dynamics after optical excitation of two phosphono-substituted coumarin derivatives dissolved in various solutions are studied by fluorescence up-conversion spectroscopy and quantum chemical simulations. The Kamlet-Taft analysis of the conventional absorption and emission spectra suggests weakening of the solvent-solute H-bonds upon optical excitation, which is in contrast to the results gained by the quantum simulations and earlier studies reported for coumarin derivatives without phosphono groups. The simulations give evidence that the solvent reorganisation around the excited fluorophore leads to partial electron transfer to the first solvation shell. The process occurs on a timescale between 1 and 10 ps depending on the solvent polarity and leads to a fast decay of the time-resolved emission signal. Using the ultrafast spectral shift of the time-dependent fluorescence we estimated the relaxation time of the H-bonds in the electronically excited state to be about 0.6 ps in water, 1.5 ps in ethanol and 2.8 ps in formamide.