scholarly journals An enzyme-like imprinted-polymer reactor with segregated quantum confinements for a tandem catalyst

RSC Advances ◽  
2018 ◽  
Vol 8 (3) ◽  
pp. 1610-1620 ◽  
Author(s):  
Wenjing Wei ◽  
Tingting Zhou ◽  
Shuping Wu ◽  
Xiaojuan Shen ◽  
Maiyong Zhu ◽  
...  
Keyword(s):  
Imprinted Polymer ◽  
Precise Control ◽  
Catalytic Sites ◽  
Different Types ◽  
Quantum Confinements

This study was aimed at addressing the present challenge in tandem catalysts: how to furnish catalysts with tandem catalytic-ability without involving the precise control and man-made isolation of different types of catalytic sites.

scholarly journals Control of Differentiation of Human Mesenchymal Stem Cells by Altering the Geometry of Nanofibers

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Satoshi Fujita ◽  
Harue Shimizu ◽  
Shin-ichiro Suye
Keyword(s):  
Stem Cells ◽  
Mesenchymal Stem Cells ◽  
Human Mesenchymal Stem Cells ◽  
Clinical Applications ◽  
Soluble Factors ◽  
Precise Control ◽  
Mixed Medium ◽  
Aligned Nanofibers ◽  
Different Types ◽  
Msc Differentiation

Effective differentiation of mesenchymal stem cells (MSCs) is required for clinical applications. To control MSC differentiation, induction media containing different types of soluble factors have been used to date; however, it remains challenging to obtain a uniformly differentiated population of an appropriate quality for clinical application by this approach. We attempted to develop nanofiber scaffolds for effective MSC differentiation by mimicking anisotropy of the extracellular matrix structure, to assess whether differentiation of these cells can be controlled by using geometrically different scaffolds. We evaluated MSC differentiation on aligned and random nanofibers, fabricated by electrospinning. We found that induction of MSCs into adipocytes was markedly more inhibited on random nanofibers than on aligned nanofibers. In addition, adipoinduction on aligned nanofibers was also inhibited in the presence of mixed adipoinduction and osteoinduction medium, although osteoinduction was not affected by a change in scaffold geometry. Thus, we have achieved localized control over the direction of differentiation through changes in the alignment of the scaffold even in the presence of a mixed medium. These findings indicate that precise control of MSC differentiation can be attained by using scaffolds with different geometry, rather than by the conventional use of soluble factors in the medium.

scholarly journals Magnetic Functionalization of Scanning Probes by Focused Electron Beam Induced Deposition Technology

2021 ◽  
Vol 7 (10) ◽  
pp. 140
Author(s):  
Javier Pablo-Navarro ◽  
Soraya Sangiao ◽  
César Magén ◽  
José María de Teresa
Keyword(s):  
Electron Beam ◽  
High Resolution ◽  
Data Storage ◽  
Magnetic Nanostructures ◽  
Magnetic Sensing ◽  
Precise Control ◽  
Scanning Probes ◽  
Different Types ◽  
Electron Beam Induced Deposition ◽  
Deposition Technology

The fabrication of nanostructures with high resolution and precise control of the deposition site makes Focused Electron Beam Induced Deposition (FEBID) a unique nanolithography process. In the case of magnetic materials, apart from the FEBID potential in standard substrates for multiple applications in data storage and logic, the use of this technology for the growth of nanomagnets on different types of scanning probes opens new paths in magnetic sensing, becoming a benchmark for magnetic functionalization. This work reviews the recent advances in the integration of FEBID magnetic nanostructures onto cantilevers to produce advanced magnetic sensing devices with unprecedented performance.

Dynamic evolution of specific catalytic sites on Pt nanoparticles

2016 ◽  
Vol 6 (1) ◽  
pp. 144-151 ◽  
Author(s):  
Hector Barron ◽  
George Opletal ◽  
Richard D. Tilley ◽  
Amanda S. Barnard
Keyword(s):  
Surface Defects ◽  
Pt Nanoparticles ◽  
Catalytic Reactions ◽  
Dynamic Evolution ◽  
Stages Of Growth ◽  
Early Stages ◽  
Catalytic Sites ◽  
Different Types

Different types of surface defects are needed for specific types of catalytic reactions, and can be promoted or suppressed by varying the temperature and rates during the early stages of growth.

Nanoparticle Based Multilayers as Multifunctional Optical Coatings

2009 ◽  
Vol 1188 ◽  
Author(s):  
Silvia Colodrero ◽  
Mauricio E. Calvo ◽  
Olalla Sánchez Sobrado ◽  
Hernán Míguez
Keyword(s):  
Optical Coatings ◽  
Precise Control ◽  
Dye Sensitized ◽  
Base Materials ◽  
Optical Responses ◽  
Photovoltaic Materials ◽  
Technological Potential ◽  
Different Types ◽  
And Diffusion ◽  
Diffusion Properties

AbstractHerein we introduce nanoparticle based periodic multilayers as base materials to create different types of multifunctional coatings that combine optical, mechanical and diffusion properties. The technological potential of these versatile materials is demonstrated by showing applications in the fields of sensing and photovoltaic materials. Due to the porous nature of such structures, liquids and gases can infiltrate or condensate, respectively within the interstices, causing a variation of the refractive index (R.I.)of the layers. This gives rise to clear but gradual changes of the optical responses, either when liquids or the partial pressure of vapors are infiltrated in the structure. Also, photoconducting Bragg mirrors can be built by precise control of the spatial variation of the R.I. of the layers in a pure TiO2 multilayer. Rationally placed within a Dye Sensitized Solar Cell (DSSC), that gives rise to a significant enhancement of the solar to electric power conversion efficiency through the amplification of sunlight absorption. Direct observation of both optical absorption and photocurrent resonances can be seen.

scholarly journals Atomic Control of Active Site Ensembles in Ordered Alloys to Enhance Hydrogenation Selectivity

2021 ◽  
Author(s):  
Anish Dasgupta ◽  
Hoaran He ◽  
Rushi Gong ◽  
Shun-Li Shang ◽  
Eric Zimmerer ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Density Functional ◽  
Functional Theory ◽  
Ethane Conversion ◽  
Precise Control ◽  
Atom Manipulation ◽  
Catalytic Sites ◽  
Ordered Alloys ◽  
Ethylene Selectivity

Abstract Intermetallic compounds offer unique opportunities for atom-by-atom manipulation of catalytic ensembles through precise stoichiometric control. The [Pd, (M), Zn] γ-brass phase allows for controlled synthesis of Pd-M-Pd catalytic sites (M = Zn, Pd, Cu, Ag and Au) isolated in an inert Zn matrix. These multi-atom heteronuclear active sites are catalytically distinct from Pd single atoms and fully coordinated Pd. We quantify the unexpectedly large effect of active site composition (i.e., identity of M atom in Pd-M-Pd sites) on ethylene selectivity during acetylene semi-hydrogenation. Subtle stoichiometric control demonstrates Pd-Pd-Pd sites are active for ethylene hydrogenation, whereas Pd-Zn-Pd sites show no measurable ethylene to ethane conversion. Agreement between experimental and density functional theory predicted activities and selectivities demonstrates precise control of Pd-M-Pd active site composition. The diversity and well-defined structure of intermetallics can be utilized to design active sites assembled with atomic-level precision.

scholarly journals Non-catalytic binding sites induce weaker long-range evolutionary rate gradients than catalytic sites in enzymes

2019 ◽  
Author(s):  
Avital Sharir-Ivry ◽  
Yu Xia
Keyword(s):  
Ligand Binding ◽  
Long Range ◽  
Binding Sites ◽  
Evolutionary Rate ◽  
Functional Sites ◽  
Interaction Sites ◽  
Catalytic Sites ◽  
Ligand Binding Sites ◽  
Different Types ◽  
Rate Gradient

AbstractEnzymes exhibit a strong long-range evolutionary constraint that extends from their catalytic site and affects even distant sites, where site-specific evolutionary rate increases monotonically with distance. While protein-protein sites in enzymes was previously shown to induce only a weak conservation gradient, a comprehensive relationship between different types of functional sites in proteins and the magnitude of evolutionary rate gradients they induce has yet to be established. Here, we systematically calculate the evolutionary rate (dN/dS) of sites as a function of distance from different types of binding sites on enzymes and other proteins: catalytic sites, non-catalytic ligand binding sites, allosteric binding sites, and protein-protein interaction sites. We show that catalytic binding sites indeed induce significantly stronger evolutionary rate gradient than all other types of non-catalytic binding sites. In addition, catalytic sites in enzymes with no known allosteric function still induce strong long-range conservation gradients. Notably, the weak long-range conservation gradients induced by non-catalytic binding sites on enzymes is nearly identical in magnitude to those induced by ligand binding sites on non-enzymes. Finally, we show that structural determinants such as local solvent exposure of sites cannot explain the observed difference between catalytic and non-catalytic functional sites. Our results suggest that enzymes and non-enzymes share similar evolutionary constraints only when examined from the perspective of non-catalytic functional sites. Hence, the unique evolutionary rate gradient from catalytic sites in enzymes is likely driven by the optimization of catalysis rather than ligand binding and allosteric functions.

scholarly journals Effect of Sharp Diameter Geometrical Modulation on the Magnetization Reversal of bi-Segmented FeNi Nanowires

2018 ◽  
Author(s):  
Miguel Méndez ◽  
Víctor Vega ◽  
Silvia González ◽  
Rafael Caballero-Flores ◽  
Javier García ◽  
...  
Keyword(s):  
Data Storage ◽  
Magnetization Reversal ◽  
Magnetic Nanostructures ◽  
Magnetic Behavior ◽  
Magnetic Data ◽  
Micromagnetic Simulations ◽  
Precise Control ◽  
Different Types ◽  
Magnetic Decoupling ◽  
Different Diameters

Controlling functional properties of matter and combine them for engineering a functional device is nowadays a common direction of scientific community. For instance, heterogeneous magnetic nanostructures can make use of different types of geometrical and compositional modulations to achieve the control of the magnetization reversal along with the nano-entities and thus enabling the fabrication of spintronic, magnetic data storage and sensing devices, among others. In this work, diameter modulated FeNi nanowires are fabricated paying special effort to obtain sharp transition regions between two segments of different diameters (from about 450 nm to 120 nm), enabling precise control over the magnetic behavior of the sample. Micromagnetic simulations performed on single bi-segmented nanowires predict a double step magnetization reversal where the wide segment magnetization switches near 200 Oe through a vortex domain wall, while at 500 Oe the magnetization of the narrow one is reversed through a corkscrew like mechanism. Finally, these results are confirmed with magneto-optic Kerr effect measurements at the transition of isolated bi-segmented nanowires. Furthermore, macroscopic vibrating sample magnetometry is used to demonstrate that the magnetic decoupling of nanowire segments is the main phenomenon occurring over the entire fabricated nanowires.

scholarly journals Tuning interactions between spins in a superconductor

2021 ◽  
Vol 118 (14) ◽  
pp. e2024837118
Author(s):  
Hao Ding ◽  
Yuwen Hu ◽  
Mallika T. Randeria ◽  
Silas Hoffman ◽  
Oindrila Deb ◽  
...  
Keyword(s):  
Band Structure ◽  
Scanning Tunneling ◽  
Energy Splitting ◽  
Many Body ◽  
Precise Control ◽  
Topological Superconductors ◽  
Spin Interactions ◽  
Different Types ◽  
Surface Magnetic Anisotropy ◽  
Millikelvin Temperatures

Novel many-body and topological electronic phases can be created in assemblies of interacting spins coupled to a superconductor, such as one-dimensional topological superconductors with Majorana zero modes (MZMs) at their ends. Understanding and controlling interactions between spins and the emergent band structure of the in-gap Yu–Shiba–Rusinov (YSR) states they induce in a superconductor are fundamental for engineering such phases. Here, by precisely positioning magnetic adatoms with a scanning tunneling microscope (STM), we demonstrate both the tunability of exchange interaction between spins and precise control of the hybridization of YSR states they induce on the surface of a bismuth (Bi) thin film that is made superconducting with the proximity effect. In this platform, depending on the separation of spins, the interplay among Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, spin–orbit coupling, and surface magnetic anisotropy stabilizes different types of spin alignments. Using high-resolution STM spectroscopy at millikelvin temperatures, we probe these spin alignments through monitoring the spin-induced YSR states and their energy splitting. Such measurements also reveal a quantum phase transition between the ground states with different electron number parity for a pair of spins in a superconductor tuned by their separation. Experiments on larger assemblies show that spin–spin interactions can be mediated in a superconductor over long distances. Our results show that controlling hybridization of the YSR states in this platform provides the possibility of engineering the band structure of such states for creating topological phases.

scholarly journals Effect of Sharp Diameter Geometrical Modulation on the Magnetization Reversal of Bi-Segmented FeNi Nanowires

Nanomaterials ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 595 ◽  
Author(s):  
Miguel Méndez ◽  
Víctor Vega ◽  
Silvia González ◽  
Rafael Caballero-Flores ◽  
Javier García ◽  
...  
Keyword(s):  
Data Storage ◽  
Magnetization Reversal ◽  
Magnetic Nanostructures ◽  
Magnetic Behavior ◽  
Magnetic Data ◽  
Micromagnetic Simulations ◽  
Precise Control ◽  
Different Types ◽  
Magnetic Decoupling ◽  
Different Diameters

Controlling functional properties of matter and combining them for engineering a functional device is, nowadays, a common direction of the scientific community. For instance, heterogeneous magnetic nanostructures can make use of different types of geometrical and compositional modulations to achieve the control of the magnetization reversal along with the nano-entities and, thus, enable the fabrication of spintronic, magnetic data storage, and sensing devices, among others. In this work, diameter-modulated FeNi nanowires are fabricated paying special effort to obtain sharp transition regions between two segments of different diameters (from about 450 nm to 120 nm), enabling precise control over the magnetic behavior of the sample. Micromagnetic simulations performed on single bi-segmented nanowires predict a double step magnetization reversal where the wide segment magnetization switches near 16 kA/m through a vortex domain wall, while at 40 kA/m the magnetization of the narrow segment is reversed through a corkscrew-like mechanism. Finally, these results are confirmed with magneto-optic Kerr effect measurements at the transition of isolated bi-segmented nanowires. Furthermore, macroscopic vibrating sample magnetometry is used to demonstrate that the magnetic decoupling of nanowire segments is the main phenomenon occurring over the entire fabricated nanowires.

The extinction time of a general birth and death process with catastrophes

1986 ◽  
Vol 23 (04) ◽  
pp. 851-858 ◽  
Author(s):  
P. J. Brockwell
Keyword(s):  
Laplace Transform ◽  
Size Distribution ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Death Process ◽  
Extinction Time ◽  
Birth And Death Process ◽  
Different Types ◽  
The Laplace Transform ◽  
Necessary And Sufficient

The Laplace transform of the extinction time is determined for a general birth and death process with arbitrary catastrophe rate and catastrophe size distribution. It is assumed only that the birth rates satisfyλ0= 0,λj> 0 for eachj> 0, and. Necessary and sufficient conditions for certain extinction of the population are derived. The results are applied to the linear birth and death process (λj=jλ, µj=jμ) with catastrophes of several different types.

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