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Karin A. Hing - One of the best experts on this subject based on the ideXlab platform.
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Effects of serum protein on Ionic exchange between culture medium and microporous hydroxyapatite and Silicate-substituted hydroxyapatite
Journal of Materials Science: Materials in Medicine, 2011Co-Authors: Katharina Guth, Charlie Campion, Tom Buckland, Karin A. HingAbstract:It has been proposed that one of the underlying mechanisms contributing to the bioactivity of osteoinductive or osteoconductive calcium phosphates involves the rapid dissolutIon and net release of calcium and phosphate Ions from the matrix as alternatively a precursor to subsequent re-precipitatIon of a bone-like apatite at the surface and/or to facilitate Ion exchange in biochemical processes. In order to confirm and evaluate Ion release from sintered hydroxyapatite (HA) and to examine the effect of Silicate substitutIon into the HA lattice on Ion exchange under physiological conditIons we monitored Ca^2+, PO_4 ^3− and SiO_4 ^4− levels in Earl’s minimum essential medium (E-MEM) in the absence (serum-free medium, SFM) or presence (complete medium, C-MEM) of foetal calf serum (FCM), with both microporous HA or 2.6 wt% Silicate-substituted HA (SA) sintered discs under both static and semi-dynamic (SD) conditIons for up to 28 days. In SFM, variatIon in Ca^2+ Ion concentratIon was not observed with either disc chemistry or culture conditIons. In C-MEM, Ca^2+ Ions were released from SA under static and SD conditIons whereas with HA Ca^2+ was depleted under SD conditIons. PO_4 ^3− depletIon occurred in all cases, although it was greater in C-MEM, particularly under SD conditIons. SiO_4 ^4− release occurred from SA irrespective of medium or culture conditIons but a sustained release only occurred in C-MEM under SD conditIons. In conclusIon we showed that under physiological conditIons the reservoir of exchangeable Ions in both HA and SA in the absence of serum proteins is limited, but that the presence of serum proteins facilitated greater Ionic exchange, particularly with SA. These observatIons support the hypothesis that Silicate substitutIon into the HA lattice facilitates a number of Ionic interactIons between the material and the surrounding physiological environment, including but not limited to Silicate Ion release, which may play a key role in determining the overall bioactivity and osteoconductivity of the material. However, significant net release of Ca^2+ and PO_4 ^3− was not observed, thus rapid or significant net dissolutIon of the material is not necessarily a prerequisite for bioactivity in these materials.
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Effects of serum protein on Ionic exchange between culture medium and microporous hydroxyapatite and Silicate-substituted hydroxyapatite
Journal of Materials Science: Materials in Medicine, 2011Co-Authors: Katharina Guth, Charlie Campion, Tom Buckland, Karin A. HingAbstract:It has been proposed that one of the underlying mechanisms contributing to the bioactivity of osteoinductive or osteoconductive calcium phosphates involves the rapid dissolutIon and net release of calcium and phosphate Ions from the matrix as alternatively a precursor to subsequent re-precipitatIon of a bone-like apatite at the surface and/or to facilitate Ion exchange in biochemical processes. In order to confirm and evaluate Ion release from sintered hydroxyapatite (HA) and to examine the effect of Silicate substitutIon into the HA lattice on Ion exchange under physiological conditIons we monitored Ca^2+, PO_4 ^3− and SiO_4 ^4− levels in Earl’s minimum essential medium (E-MEM) in the absence (serum-free medium, SFM) or presence (complete medium, C-MEM) of foetal calf serum (FCM), with both microporous HA or 2.6 wt% Silicate-substituted HA (SA) sintered discs under both static and semi-dynamic (SD) conditIons for up to 28 days. In SFM, variatIon in Ca^2+ Ion concentratIon was not observed with either disc chemistry or culture conditIons. In C-MEM, Ca^2+ Ions were released from SA under static and SD conditIons whereas with HA Ca^2+ was depleted under SD conditIons. PO_4 ^3− depletIon occurred in all cases, although it was greater in C-MEM, particularly under SD conditIons. SiO_4 ^4− release occurred from SA irrespective of medium or culture conditIons but a sustained release only occurred in C-MEM under SD conditIons. In conclusIon we showed that under physiological conditIons the reservoir of exchangeable Ions in both HA and SA in the absence of serum proteins is limited, but that the presence of serum proteins facilitated greater Ionic exchange, particularly with SA. These observatIons support the hypothesis that Silicate substitutIon into the HA lattice facilitates a number of Ionic interactIons between the material and the surrounding physiological environment, including but not limited to Silicate Ion release, which may play a key role in determining the overall bioactivity and osteoconductivity of the material. However, significant net release of Ca^2+ and PO_4 ^3− was not observed, thus rapid or significant net dissolutIon of the material is not necessarily a prerequisite for bioactivity in these materials.
Choon-hong Tan - One of the best experts on this subject based on the ideXlab platform.
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Enantioselective AdditIon-AlkylatIon of α,β-Unsaturated Carbonyls via Bisguanidinium Silicate Ion Pair Catalysis.
Journal of the American Chemical Society, 2020Co-Authors: Wenchao Chen, Esther Cai Xia Ang, Siu Min Tan, Zhijie Chua, Jingyun Ren, Ziqi Yang, Bo Teng, Richmond Lee, Choon-hong TanAbstract:Silicon hydrides, alkynylsilanes, and alkoxylsilanes were activated by fluoride in the presence of bisguanidinium catalyst to form hypervalent Silicate Ion pairs. These activated Silicates undergo 1,4-additIons with chromones, coumarins, and α-cyanocinnamic esters generating enolSilicate intermediates, for a consequent stereoselective alkylatIon reactIon. The reductIon-alkylatIon reactIon proceeded under mild conditIons using polymethylhydrosiloxane, a cheap and environmentally friendly hydride source. The additIon-alkylatIon reactIons with alkynylsilanes and alkoxylsilanes resulted in the constructIon of two vicinal chiral carbon centers with excellent enantioselectivities and diastereoselectivities (up to 99% ee, >99:1 dr). Density functIonal theory calculatIons and experimental NMR studies revealed that penta-coordinated Silicates are crucial intermediates.
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Enantioselective 1,2-AnIonotropic Rearrangement of Acylsilane through a Bisguanidinium Silicate Ion Pair
Journal of the American Chemical Society, 2018Co-Authors: Weidi Cao, Richmond Lee, Davin Tan, Choon-hong TanAbstract:Highly enantioselective bisguanidinium-catalyzed tandem rearrangements of acylsilanes are reported. The acylsilanes were activated via an additIon of fluoride on the silicon to form a penta-coordinate anIonic Silicate intermediate. The Silicate then underwent alkyl or aryl group migratIon from the silicon atom to the neighboring carbonyl carbon atom (1,2-anIonotropic rearrangement), followed by [1,2]-Brook rearrangement to provide the secondary alcohols in high yields with excellent enantioselectivities (up to 95% ee). The isolatIon of an α-silylcarbinol intermediate as well as DFT calculatIons revealed that the 1,2-anIonotropic rearrangement occurred via a bisguanidinium Silicate Ion pair, which is the stereodetermining step. The chiral center formed is then retained without inversIon through the subsequent [1,2]-Brook rearrangement. Crotyl acylsilanes were smoothly transformed into homoallylic linear crotyl alcohols with retentIon of E/Z geometry, and no branched alcohols were detected. This clearly sug...
Katharina Guth - One of the best experts on this subject based on the ideXlab platform.
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Effects of serum protein on Ionic exchange between culture medium and microporous hydroxyapatite and Silicate-substituted hydroxyapatite
Journal of Materials Science: Materials in Medicine, 2011Co-Authors: Katharina Guth, Charlie Campion, Tom Buckland, Karin A. HingAbstract:It has been proposed that one of the underlying mechanisms contributing to the bioactivity of osteoinductive or osteoconductive calcium phosphates involves the rapid dissolutIon and net release of calcium and phosphate Ions from the matrix as alternatively a precursor to subsequent re-precipitatIon of a bone-like apatite at the surface and/or to facilitate Ion exchange in biochemical processes. In order to confirm and evaluate Ion release from sintered hydroxyapatite (HA) and to examine the effect of Silicate substitutIon into the HA lattice on Ion exchange under physiological conditIons we monitored Ca^2+, PO_4 ^3− and SiO_4 ^4− levels in Earl’s minimum essential medium (E-MEM) in the absence (serum-free medium, SFM) or presence (complete medium, C-MEM) of foetal calf serum (FCM), with both microporous HA or 2.6 wt% Silicate-substituted HA (SA) sintered discs under both static and semi-dynamic (SD) conditIons for up to 28 days. In SFM, variatIon in Ca^2+ Ion concentratIon was not observed with either disc chemistry or culture conditIons. In C-MEM, Ca^2+ Ions were released from SA under static and SD conditIons whereas with HA Ca^2+ was depleted under SD conditIons. PO_4 ^3− depletIon occurred in all cases, although it was greater in C-MEM, particularly under SD conditIons. SiO_4 ^4− release occurred from SA irrespective of medium or culture conditIons but a sustained release only occurred in C-MEM under SD conditIons. In conclusIon we showed that under physiological conditIons the reservoir of exchangeable Ions in both HA and SA in the absence of serum proteins is limited, but that the presence of serum proteins facilitated greater Ionic exchange, particularly with SA. These observatIons support the hypothesis that Silicate substitutIon into the HA lattice facilitates a number of Ionic interactIons between the material and the surrounding physiological environment, including but not limited to Silicate Ion release, which may play a key role in determining the overall bioactivity and osteoconductivity of the material. However, significant net release of Ca^2+ and PO_4 ^3− was not observed, thus rapid or significant net dissolutIon of the material is not necessarily a prerequisite for bioactivity in these materials.
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Effects of serum protein on Ionic exchange between culture medium and microporous hydroxyapatite and Silicate-substituted hydroxyapatite
Journal of Materials Science: Materials in Medicine, 2011Co-Authors: Katharina Guth, Charlie Campion, Tom Buckland, Karin A. HingAbstract:It has been proposed that one of the underlying mechanisms contributing to the bioactivity of osteoinductive or osteoconductive calcium phosphates involves the rapid dissolutIon and net release of calcium and phosphate Ions from the matrix as alternatively a precursor to subsequent re-precipitatIon of a bone-like apatite at the surface and/or to facilitate Ion exchange in biochemical processes. In order to confirm and evaluate Ion release from sintered hydroxyapatite (HA) and to examine the effect of Silicate substitutIon into the HA lattice on Ion exchange under physiological conditIons we monitored Ca^2+, PO_4 ^3− and SiO_4 ^4− levels in Earl’s minimum essential medium (E-MEM) in the absence (serum-free medium, SFM) or presence (complete medium, C-MEM) of foetal calf serum (FCM), with both microporous HA or 2.6 wt% Silicate-substituted HA (SA) sintered discs under both static and semi-dynamic (SD) conditIons for up to 28 days. In SFM, variatIon in Ca^2+ Ion concentratIon was not observed with either disc chemistry or culture conditIons. In C-MEM, Ca^2+ Ions were released from SA under static and SD conditIons whereas with HA Ca^2+ was depleted under SD conditIons. PO_4 ^3− depletIon occurred in all cases, although it was greater in C-MEM, particularly under SD conditIons. SiO_4 ^4− release occurred from SA irrespective of medium or culture conditIons but a sustained release only occurred in C-MEM under SD conditIons. In conclusIon we showed that under physiological conditIons the reservoir of exchangeable Ions in both HA and SA in the absence of serum proteins is limited, but that the presence of serum proteins facilitated greater Ionic exchange, particularly with SA. These observatIons support the hypothesis that Silicate substitutIon into the HA lattice facilitates a number of Ionic interactIons between the material and the surrounding physiological environment, including but not limited to Silicate Ion release, which may play a key role in determining the overall bioactivity and osteoconductivity of the material. However, significant net release of Ca^2+ and PO_4 ^3− was not observed, thus rapid or significant net dissolutIon of the material is not necessarily a prerequisite for bioactivity in these materials.
S A Shady - One of the best experts on this subject based on the ideXlab platform.
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chromatographic separatIon of sodium cobalt and europium on the particles of zirconium molybdate and zirconium Silicate Ion exchangers
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006Co-Authors: B Elgammal, S A ShadyAbstract:Abstract Zirconium molybdate and zirconium Silicate were prepared by applicatIon of the precipitatIon and sol–gel routes, respectively. The produced Ion exchange powders were physically characterized using X-ray diffractIon, infrared and differential thermal analysis. The obtained data revealed that they are thermally and chemically stable, having unique microstructure properties that permit their use in chromatographic separatIon of Na + , Co 2+ , and Eu 3+ from liquid waste streams. DistributIon coefficient studies have been conducted in parallel with the loading-elutIon column operatIons; both Ion exchangers showed the same order of selectivity towards the aforementIoned Ions and the K d values decreased in the order; Eu 3+ > Co 2+ > Na + . The capacities of the used exchangers differed with drying temperature; zirconium-Silicate possessed higher capacities than corresponding molybdate one. 22 Na, 60 Co and 152+154 Eu were separated from each other on the loaded columns using 0.1 M HNO 3 and 1 M HNO 3 .
P.k. Roy - One of the best experts on this subject based on the ideXlab platform.
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Lithium Ion sources
Nuclear Instruments and Methods in Physics Research Section A: Accelerators Spectrometers Detectors and Associated Equipment, 2014Co-Authors: P.k. Roy, Peter A. Seidl, Wayne G. Greenway, Joe W. Kwan, Steven Lidia, D.p. Grote, William L. WaldronAbstract:A 10.9 cm diameter lithium alumino-Silicate Ion source has been chosen as a source of �100 mA lithium Ion current for the Neutralized Drift CompressIon Experiment (NDCX-II) at LBNL. Research and development was carried out on lithium alumino-Silicate Ion sources prior to NDCX-II source fabricatIon. Space-chargelimited emissIon with the current density exceeding 1 mA/cm 2 was measured with 0.64 cm diameter lithium alumino-Silicate Ion sources at 1275 0 C. The beam current density is less for the first 10.9 cm diameter NDCX-II source, and it may be due to an issue of surface coverage. The lifetime of a thin coated (on a tungsten substrate) source is varied, roughly 40-50 hours, when pulsed at 0.05 Hz and with pulse length of 6 µs each, i.e., a duty factor of 3x10 -7 , at an operating temperature of 1250 to 1275 0 C. The 10.9 cm diameter source lifetime is likely the same as of a 0.64 cm source, but the lifetime of a source with a 2 mm diameter (without a tungsten substrate) is 10-15 hours with a duty factor of one (DC extractIon). The lifetime variatIon is dependent on the amount of depositIon of �-eucryptite mass, and the surface temperature. The amount of mass depositIon does not significantly alter the current density. More Ion source work is needed to improve the large source performance.
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CharacterizatIon of LI+ Alumino-Silicate Ion Source for Target Heating Experiments - eScholarship
2013Co-Authors: P.k. RoyAbstract:CHARACTERIZATIon OF LI + ALUMINO-Silicate Ion SOURCE FOR TARGET HEATING EXPERIMENTS ∗ P. K. Roy † , S. M. Lidia, W. G. Greenway, J. W. Kwan, P. A. Seidl, W. L. Waldron, and D. P. Grote Lawrence Berkeley NatIonal Laboratory, Berkeley, CA 94720, USA Abstract defined by the Child-Langmuir law: The Heavy Ion FusIon Sciences (HIFS) program at Lawrence Berkeley NatIonal Laboratory will carry out warm dense matter experiments using Li + Ion beam with energy 1.2 - 3 MeV to achieve uniform heating up to 0.1 - 1 eV. Experiments will be done using the Neutralized Drift CompressIon Experiment-II (NDCX-II) facility. The NDCX-II accelerator has been designed to use a large di- ameter (10.9 cm) Li + doped alumino-Silicate source to pro- duce short pulses of 93 mA beam current. FabricatIon of a lithium source is complex. It is necessary to apply a high temperature ( 1250 ◦ C) for thermIonic emissIon to achieve the required beam current density ∼1mA/cm 2 in the space-charge limited regime. The lifetime of this source is roughly 50 hours, when pulsed. CharacterizatIon of an operatIonal 10.9 cm diameter lithium alumino-Silicate Ion source is presented. INTRODUCTIon To heat targets to electron-volt temperatures for the study of warm dense matter [1] with intense Ion beams, low mass Ions, such as lithium, have an energy loss peak (dE/dx) at a suitable kinetic energy [2]. The accelerator physics design of Neutralized Drift CompressIon Experi- ment (NDCX-II) [3, 4] has a pulse length at the Ion source of about 0.5 µs [5, 6]. Thus for producing 50 nC of beam charge, the required beam current is about 100 mA. Focus- ability requires a normalized (edge) emittance ≤2 π-mm- mrad. Li + Ions have been produced by thermIonic emissIon from the alumino-Silicates compounds β-Spodumene and β-eucryptite [7, 8, 9]. In an Ion gun injector, a thermIonic source, may be heated by Ohmic heating, laser radiatIon, inductIon heating or other methods. The source surface temperature places a lower bound on the required input power, P = AσeT 4 ; where A is the cross sectIonal area πr 2 of the emissIon surface, σ is the Boltzmann con- stant, e is the emissivity of material and T is the source surface temperature. This is less than the required input power due to conductive and radiative heat loss from the sides and back of the source assembly. Once operating temperature is achieved, Ions are extracted by applying an electric field. The field between the source surface and the extractIon electrode controls the extracted current density. The space-charge limited current density of an Ion gun is ∗ This work was performed under the auspices of the U.S Department of Energy by LBNL under contract DE-AC02-05CH11231. † PKRoy@lbl.gov J (χ, V, d) = χ V 3/2 d 2 where, χ = 4e 9 0 2q m , d is the distance between source and extractIon electrode, V is the beam extractIon voltage, m is the mass of an Ion, and q is the Ion charge. The space- charge limited beam current, or Child-Langmuir current is I E = P V 3/2 , where, P = χ πr is the gun perveance which charac- d 2 terizes the geometry, charge state, and Ion mass of the in- jector. Thus, in the space-charge limited regime, the beam current is determined by the Ion mass and the geometry of the Ion gun, and is proportIonal to V 3/2 . A space- charge-limited beam with current densities (J) exceed- ing 1 mA/cm 2 have been measured [10, 11] from lithium alumino-Silicate Ion sources at a temperature of ∼1275 ◦ C. At higher extractIon voltages, the source appears to become emissIon limited with J ≥ 1.5 mA/cm 2 , and J increases weakly with the applied voltage. In order to operate a source with uniform extractIon, it is preferable to operate a source with low enough V to obtain space-charge limited extractIon. The space-charge limit effectively smoothes out spatial variatIon in emissIon. NDCX-II BEAM INJECTOR AND DIAGNOSTICS There are several steps to prepare a lithium alumino- Silicate source: (1) produce the chemical compound, (2) grind the compound into powder, (3) apply a “green coat- ing”, (4) sinter the material to form a hard surface layer. The lithium alumino-Silicate source fabricatIon process, source emissIon density and lifetime have been charac- terized in a recent publicatIon [12] by these authors for 0.64 mm diameter sources. Here we demonstrate a 10.9 cm diameter source performance. Figure 1 shows a sketch of NDCX-II injector with 10.9 cm diameter Li + Ion source, and a picture of the injector with a diagnostics statIon. A computer code simulatIon (WARP) has been used to ad- dress geometrical parameters of diagnostics. The diagnos- tics are-Faraday cup to measure beam current signal, and a gated camera with scintillator to determine beam images. Figure 2 shows simulated beam profile for current densities of (a) J=0.5 mA/cm 2 , and (b) J=1 mA/cm 2 .
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CHARACTERIZATIon OF LI + ALUMINO-Silicate Ion SOURCE FOR TARGET HEATING EXPERIMENTS ∗
2012Co-Authors: P.k. Roy, W.l. Waldron, Peter A. Seidl, Wayne G. Greenway, Joe W. Kwan, Steven Lidia, D.p. GroteAbstract:The Heavy Ion FusIon Sciences (HIFS) program at Lawrence Berkeley NatIonal Laboratory will carry out warm dense matter experiments using Li Ion beam with energy 1.2 3 MeV to achieve uniform heating up to 0.1 1 eV. Experiments will be done using the Neutralized Drift CompressIon Experiment-II (NDCX-II) facility. The NDCX-II accelerator has been designed to use a large diameter (10.9 cm) Li doped alumino-Silicate source to produce short pulses of 93 mA beam current. FabricatIon of a lithium source is complex. It is necessary to apply a high temperature ( 1250◦ C) for thermIonic emissIon to achieve the required beam current density ∼1mA/cm in the space-charge limited regime. The lifetime of this source is roughly 50 hours, when pulsed. CharacterizatIon of an operatIonal 10.9 cm diameter lithium alumino-Silicate Ion source is presented.
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Li+ alumino-Silicate Ion source development for the Neutralized Drift CompressIon Experiment (NDCX-II)
Lawrence Berkeley National Laboratory, 2011Co-Authors: P.k. RoyAbstract:HIFAN 1794 LBNL-3748E Li+ alumino-Silicate Ion source development for the Neutralized Drift CompressIon Experiment (NDCX-II) by P.K. Roy, W. Greenway, J.W. Kwan, P.A. Seidl, W. Waldron from Lawrence Berkeley NatIonal Laboratory (on behalf of U.S. HIFS-VNL) 1 Cyclotron Road, Berkeley, CA 94720 Accelerator FusIon Research DivisIon University of California Berkeley, California 94720 August 2010 This work was supported by the Director, Office of Science, Office of FusIon Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
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Li+ alumino-Silicate Ion source development for the neutralized drift compressIon experiment
The Review of scientific instruments, 2011Co-Authors: P.k. Roy, Peter A. Seidl, Wayne G. Greenway, Joe W. Kwan, William L. WaldronAbstract:We report results on lithium alumino-Silicate Ion source development in preparatIon for warm dense matter heating experiments on the new neutralized drift compressIon experiment II. The practical limit to the current density for a lithium alumino-Silicate source is determined by the maximum operating temperature that the Ion source can withstand before running into problems of heat transfer, melting of the alumino-Silicate material, and emissIon lifetime. Using small prototype emitters, at a temperature of ≈1275 °C, a space-charge limited Li+ beam current density of J ≈1 mA/cm2 was obtained. The lifetime of the Ion source was ≈50 h while pulsing at a rate of 0.033 Hz with a pulse duratIon of 5–6 μs.