Size Confinement Research Articles

Bedforms and sedimentary structures related to supercritical flows in glacigenic settings

AbstractUpper‐flow‐regime bedforms, including upper‐stage‐plane beds, antidunes, chutes‐and‐pools and cyclic steps, are ubiquitous in glacigenic depositional environments characterized by abundant meltwater discharge and sediment supply. In this study, the depositional record of Froude near‐critical and supercritical flows in glacigenic settings is reviewed, and similarities and differences between different depositional environments are discussed. Upper‐flow‐regime bedforms may occur in subglacial, subaerial and subaqueous environments, recording deposition by free‐surface flows and submerged density flows. Although individual bedform types are generally not indicative of any specific depositional environment, some observed trends are similar to those documented in non‐glacigenic settings. Important parameters for bedform evolution that differ between depositional environments include flow confinement, bed slope, aggradation rate and grain size. Cyclic‐step deposits are more common in confined settings, like channels or incised valleys, or steep slopes of coarse‐grained deltas. Antidune deposits prevail in unconfined settings and on more gentle slopes, like glacifluvial fans, sand‐rich delta slopes or subaqueous (ice‐contact) fans. At low aggradation rates, only the basal portions of bedforms are preserved, such as scour fills related to the hydraulic‐jump zone of cyclic steps or antidune‐wave breaking, which are common in glacifluvial systems and during glacial lake‐outburst floods and (related) lake‐level falls. Higher aggradation rates result in increased preservation potential, possibly leading to the preservation of complete bedforms. Such conditions are met in sediment‐laden jökulhlaups and subaqueous proglacial environments characterized by expanding density flows. Coarser‐grained sediment leads to steeper bedform profiles and highly scoured facies architectures, while finer‐grained deposits display less steep bedform architectures. Such differences are in part related to stronger flows, faster settling of coarse clasts, and more rapid breaking of antidune waves or hydraulic‐jump formation over hydraulically rough beds.

Turbulent flame propagation in corn dust clouds formed in confined and open spaces

Flame propagation stages in a corn dust cloud in a large room size confinement investigated. The clouds ignited by a weak heat source. The mass of the dust identified to be influenced the flame acceleration. Dust in the clouds burnt rapidly through several fluid dynamic mechanisms. Four types of instabilities contributed to fast flame development. Landau–Darrieus and Kelvin–Helmholtz instabilities increased the flame speed in the initial stages of the fireball. In the intermediate and final stages, corrugated and the wrinkled flame structure originated through Rayleigh–Taylor instabilities. In addition to flow aspects and instabilities, the shock waves also enhanced the flame speed. The shock overpressure measured with a dynamic pressure sensor. These shock waves induced Richtmyer–Meshkov instability in the fireball and developed turbulent flames. Density gradients across the fireball (due to higher temperature gradients) caused perturbations. Further, this gradient increased by the shock waves. The crosswind speed through the confinement windows was slower, therefore it has not enhanced the flame speed. Corn dust dispersed quickly to a wider area by the shock waves, established large dust clouds, and lead to explosions. The maximum surface temperature of the fireball predicted as 1384 K. The preheat zone around the fireball identified by an image processing tool. The turbulence parameters at the fireball obtained from qualitative and quantitative methods and analyzed. The clouds of a small quantity of corn dust lead to the formation of larger fireballs due to higher kinematic viscosity than the energy dissipation rate.

Crystalline Red Phosphorus Nanoribbons: Large‐Scale Synthesis and Electrochemical Nitrogen Fixation

AbstractTwo dimensional (2D) nanoribbons constitute an emerging nanoarchitecture for advanced microelectronics and energy conversion due to the stronger size confinement effects compared to traditional nanosheets. Triclinic crystalline red phosphorus (cRP) composed by a layered structure is a promising 2D phosphorus allotrope and the tube‐like substructure is beneficial to the construction of nanoribbons. In this work, few‐layer cRP nanoribbons are synthesized and the effectiveness in the electrochemical nitrogen reduction reaction (NRR) is investigated. An iodine‐assisted chemical vapor transport (CVT) method is developed to synthesize circa 10 g of bulk cRP lumps with a yield of over 99 %. With the aid of probe ultrasonic treatment, high‐quality cRP microcrystals are exfoliated into few‐layer nanoribbons (cRP NRs) with large aspect ratios. As non‐metallic materials, cRP NRs are suitable for the electrochemical nitrogen reduction reaction. The ammonia yield is 15.4 μg h−1 mgcat.−1 at −0.4 V vs. reversible hydrogen electrode in a neutral electrolyte under ambient conditions and the Faradaic efficiency is 9.4 % at −0.2 V. Not only is cRP a promising catalyst, but also the novel strategy expands the application of phosphorus‐based 2D structures beyond that of traditional nanosheets.

Crystalline Red Phosphorus Nanoribbons: Large-Scale Synthesis and Electrochemical Nitrogen Fixation.

Two dimensional (2D) nanoribbons constitute an emerging nanoarchitecture for advanced microelectronics and energy conversion due to the stronger size confinement effects compared to traditional nanosheets. Triclinic crystalline red phosphorus (cRP) composed by a layered structure is a promising 2D phosphorus allotrope and the tube-like substructure is beneficial to the construction of nanoribbons. In this work, few-layer cRP nanoribbons are synthesized and the effectiveness in the electrochemical nitrogen reduction reaction (NRR) is investigated. An iodine-assisted chemical vapor transport (CVT) method is developed to synthesize circa 10 g of bulk cRP lumps with a yield of over 99 %. With the aid of probe ultrasonic treatment, high-quality cRP microcrystals are exfoliated into few-layer nanoribbons (cRP NRs) with large aspect ratios. As non-metallic materials, cRP NRs are suitable for the electrochemical nitrogen reduction reaction. The ammonia yield is 15.4 μg h-1 mgcat. -1 at -0.4 V vs. reversible hydrogen electrode in a neutral electrolyte under ambient conditions and the Faradaic efficiency is 9.4 % at -0.2 V. Not only is cRP a promising catalyst, but also the novel strategy expands the application of phosphorus-based 2D structures beyond that of traditional nanosheets.

Direct formation of LaFeO3/MCM−41 nanocomposite catalysts and their catalytic reactivity for conversion of isopropanol

Direct formation of 3–30% (w/w) LaFeO3/MCM−41, nanocomposite catalysts were performed by a sol−gel process, followed by calcination at 550 and 750 °C. The nanocomposites were characterized through different techniques including LAXRD, WAXRD, EDX, simultaneous TG−DTA, ATR−FTIR, nitrogen adsorption/desorption, and TEM. The nanocomposites featured high surface areas (up to 1000 m2/g) and enhanced thermal stability. The direct formation method led to nanodispersion and size confinement of LaFeO3 in MCM−41 mesopores. The nanocomposites showed very high catalytic activity for isopropanol conversion, whereas their parent materials (blank MCM-41 or bulk LaFeO3) were totally inactive under the same reaction conditions. Thus, nanocomposite catalysts with low loading ratios and low calcination temperature produced pure dehydration product (propene) with very high conversion and total selectivity. Nanocomposite catalysts with high loading ratios and high calcination temperature produced an appreciable amount of the dehydrogenation product (acetone) as well as the dehydration products. Moreover, high loading ratios at high reaction temperatures in air atmosphere led to the formation of oxidation products. The different reactivities of the nanocomposite catalysts were discussed and correlated to their nanostructure, in terms of enhancing of the mesoporous textures with surface acidity, oxidation ability and thermal stability.

Synthesis of Metal Oxide/Carbon Nanofibers via Biostructure Confinement as High-Capacity Anode Materials.

For applications in energy storage and conversion, many metal oxide (MO)/C composite fibers have been synthesized using cellulose as the template. However, MO particles in carbon fibers usually experience anomalous growth to a size of >200 nm, which is detrimental to the overall performance of the composite. In this paper, we report the successful development of a generic approach to synthesize a fiber composite with highly dispersed MO nanoparticles (10-80 nm) via simple swelling, nitrogen doping, and carbonization of the cellulose microfibril. The growth of the MO nanoparticles is confined by the structure of the microfibrils. Density functional theory calculation further reveals that the doped N atoms supply ample nucleation sites for size confinement of the nanoparticles. The encapsulation structure of small MO nanoparticles in the conductive carbon matrix improves their electrochemical performance. For example, the formed SnOx/carbon nanocomposite exhibits high specific capacities of 1011.0 mA h g-1 at 0.5 A g-1 and 581.8 mA h g-1 at 5 A g-1. Moreover, the fiber-like nanocomposite can be combined with carbon nanotubes to form a flexible binder-free electrode with a capacity of ∼10 mA h cm-2, far beyond the commercial level. The process developed in this study offers an alternative approach to sophisticated electrospinning for the synthesis of other fiber-like MO/carbon nanocomposites for versatile applications.

Underlying Processes Driving the Evolution of Nanoporous Silica in Water and Electrolyte Solutions

In this study, we related the alteration of mesoporous materials in aqueous solutions to the properties of confined water in the presence of ions, that is, its structure and its dynamics. To reach this goal, we have determined and quantified the evolution of the morphology of hexagonal mesoporous silica-based materials, that is, MCM-41 (mean pore size of 2.9 nm and dense pore wall) and SBA-15 (mean pore size of 6.8 nm and microporous pore wall), during their alteration in water and electrolyte solutions with ions presenting various kosmotropic properties ([XCl2] = 1 M and X = Ba, Ca, Mg) at 50 °C by in situ small and wide angle X-ray scattering. The experimental results and the calculated small-angle X-ray scattering spectra have demonstrated that the alteration behavior is strongly dependent on the type of silica and the water properties (water dynamics at a picosecond time scale and water structure) related to the confinement size, the nature of the cations, and their surface ion excesses. For MCM-41 silica, having reduced water dynamics, the alteration behavior is mainly driven by silica hydrolysis—recondensation/precipitation processes leading to a pore deformation and a possible precipitation of XCl2 metastable phases partially clogging the pores. In case of SBA-15, its alteration behavior in aqueous solutions starts with an initial increase of the pore size and the formation of an alteration layer within its microporosity which grows following a diffusive process of the solution. Inside the microporosity, similar alteration processes to MCM-41 silica occur. These recondensation/precipitation processes may continue until a thermodynamically stable silica phase is formed. The results obtained within the scope of this work revealed the importance of the influence of the dynamics and the structure of water in chemical reactions taking place in confined media filled with water and ions.

Anionic behavior and single-molecule crystal in fullerene confinements: A contribution from DFT energy decomposition and cooperativity analyses.

The recently proposed systems of various anions (A) confined inside C60 , A- @ C60 , which in turn behave as large and stable anions, (A @ C60 )- , can find potential applications in various fields. On the other hand, it has earlier been shown that from the dihalogens (X2 ) encapsulated C60 , X2 @ C60 , only F2 @ C60 can be introduced as a system in which the cage acts as a cation C60 + and interacts with an endohedral anion, F2 - , forming the F2 - @ C60 + as a single-molecule crystal compound. In this work, two density functional theory energy decomposition analysis (EDA) schemes, where in one of them the noninteracting kinetic, electrostatic, and exchange-correlation energies come into play while another scheme, called as EDA-SBL, includes the steric, electrostatic, and quantum effects as essential ingredients (S. Liu, J. Chem. Phys. 2007, 126, 244103), are utilized to find out what energetic components govern the unique characteristics of the (A @ C60 )- and X2 @ C60 confinements. It is shown that the noninteracting kinetic energy and steric energies have important contributions to the total interaction energies for the considered systems. However, there are other confinements for which the electrostatic and exchange-correlation contributions play also imperative roles. Furthermore, we find reasonable correlations between interaction energies and their components as well as the energetic components themselves, leading to an alternative EDA scheme including the noninteracting kinetic, steric, and electrostatic energies for investigations on other endohedral fullerenes. Extending our analyses to large size confinements, Cl- @ Cn with n up to 90 as illustrative examples, the quantitative cooperativity concept is also explored, where the positive and negative cooperativity profiles unveil a specific size of the anionic confinements to form the most stable large anion.

Extremely large-angle beam deflection based on low-index sparse dielectric metagratings

Metasurfaces for beam engineering are usually implemented by using dense-plasmonic or high-contrast dielectric building blocks with deep-subwavelength feature size and strong field confinement. Here, we theoretically and experimentally demonstrate extremely large angle deflection with a very steep phase gradient based on low-contrast () metagratings composed of very sparse building blocks. Only two ridges are included in a 4π variation supercell, which diffracts the normal excitation to desired angles as large as 80° with a theoretical efficiency of more than 80%. Due to the limited beam radius relative to the metasurfaces, the angular distribution of the intensity is broadened with reduced peak intensity. Such metagratings are 3D-printed for 0.14 THz operation. The measured peak intensities are 57% of the theoretical ones due to material loss and fabrication errors. Repeatability, bandwidth and angular sensitivity are systematically studied, and the results pave the way towards using practical THz elements for large-gradient wavefront shaping.

Water in confinement of epoxy layer and hydroxylated (001) γ-alumina: An atomistic simulation view

Abstract In this work, we used atomistic level simulations to study water molecules confined between an epoxy layer and alumina substrate. Water is responsible for many complex reactions at the interface of substrate, which makes understanding characteristic properties of water at this particular confinement essential. Three different confinement sizes were selected. The substrate is hydroxylated gamma alumina and the organic coating layer is constructed with epoxy molecules. Different properties such as density, mobility and displacement, inter-molecular structures, power spectra, and hydrogen bond energy of water molecules were obtained. The results are studied in connection with the size of confinement. It is shown that the properties of water in this type of confinement are different from the bulk water and as the size of confinement decreases, some of the unique behaviors of water molecules are revealed.

Development and qualification of triple-GEM detector built with large size single mask foils produced in India

The Gas Electron Multiplier (GEM) is the new age detector for nuclear and particle physics experiments, which was first developed by the European Center for Nuclear Research (CERN). It is comprised of an excellent insulator (Kapton/Apical) having a thickness of 50 μm which is covered with 5 μm copper layer on both sides and pierced by a regular array of holes. From its invention, CERN has been the sole supplier of the GEM foils until recently when few private companies started manufacturing GEM foils under the transfer of technology (TOT) from CERN. However, it's a long process to validate the foils delivered by these companies to claim that the GEM detectors made from them are compatible with high scientific standards. Along these lines, an India based company Micropack Pvt. Ltd. began fabricating both double and single mask GEM foils; at first Micropack produced 10 × 10 cm2 double mask foils which were tested both at foil and detector level by University of Delhi (DU) and it was confirmed to satisfy the required standards. Because of the double mask technique, the size of the GEM foil was constantly constrained so to overcome the confinement in size of GEM foils the single mask technique was developed in 2010. Micropack produced the first batch of 30 × 30 cm2 single mask foils in a joint effort with DU. A triple-GEM detector was constructed using these foils to test the fundamental quality controls, which include effective gain measurement, energy spectrum, and gain uniformity. Along with this, we will also report on the few advance studies which include discharge probability, rate capability, and charging up for this detector and foils.

Investigation of the dimensionality using temperature-dependent decay times in InGaAs-coupled quantum well-quantum dots structures

The radiative temperature-dependent decay times were exploited to understand the confinement size analyzing the relaxation from thermally-excited states in InGaAs coupled quantum well (QW)–quantum dots (QDs) structures. We investigated the confinement size from coupled QW-QDs structures by measuring the decay time of radiative process from exciton states when the temperature is gradually increased. The photoluminescence (PL) decay time from the exciton states is amended with the PL intensity at low temperature (~5 K) to distinguish the radiative decay time. The zero-dimensional and the two-dimensional confinement size are obtained from the isolated QDs and QW. However, this assumption is no longer correct for optical coupling because of the direct tunneling when the distance between the QW and the QDs becomes less than 10 nm in the coupled QW-QDs structures. Below 6 nm between the QW and the QDs in the coupled QW-QDs structures, the power factor from the temperature variations increases from 0 to 0.3 (for QDs) and from 1 to 1.37 (for QW), which accords with a quasi-zero-dimensional density of states (~Tα=0.3) and a quasi-two-dimensional density of states (~Tα=1.37), respectively, because of the extended wave functions in the optical couplings and the existence of dark states in the coupled QW-QDs structures.

One Pot Aqueous Synthesis of L-Histidine Amino Acid Capped Mn: ZnS Quantum Dots for Dopamine Sensing

Background: Mn doped ZnS is selected as the right element which is prominent among quantum dot for its high luminescent and quantum yield property and also non toxicity while comparing with other organometallic quantum dot synthesized by using different capping agents. Methods: An interesting observation based on colorimetric sensing of dopamine using manganese doped zinc sulfide quantum dot is discussed in this study. Mn doped ZnS quantum dot surface passivated with capping agents such as L-histidine and also in polymers like chitosan, PVA and PVP were studied and compared. The tunable fluorescence effect was also observed in different polymers and amino acid as capping agents. Optical characterization studies like UV-Visible spectroscopy and PL spectroscopy have been carried out. The functional group modification of Quantum dot has been analyzed using FTIR and size and shape analysis was conducted by using HRTEM image. Result: The strong and broad peak of FTIR in the range of 3500-3300 cm-1 confirms the presence of O-H bond. It is also observed that quenching phenomena in the luminescent peak are due to weaker confinement effect. The average size of the particle is shown to be around 4-5 nm. Changes in color of the quantum dot solution from transparent to dark brown has been due to the interaction with dopamine. Conclusion: Finally, L-Histidine amino acid capped Mn:ZnS shows better results in luminescence and size confinement properties. Hence, it was chosen for dopamine sensing due to its colloidal nature and inborn affinity towards dopamine, a neurotransmitter which is essential for early diagnosis of neural diseases

Shape selectivity conversion of biomass derived glycerol to aromatics over hierarchical HZSM-5 zeolites prepared by successive steaming and alkaline leaching: Impact of acid properties and pore constraint

The selective production of light aromatics starting from biomass derived glycerol provides excellent prospect in reducing dependency on fossil resources and carbon dioxide emissions. The catalytic perfomances in glycerol to aromatics (GTA) procedure were systematically investigated for HZSM-5 catalysts with various porosity and acidic property, which were prepared by separate or multi-step treatments using NaOH and steaming on HZSM-5 zeolites. A consecutive steaming-alkali treatment of HZSM-5 zeolite enables the introduction of higher amounts of intra-mesoporosity with smaller-aperture (mainly at the range of 2–4 nm), which could be ascribed to the easier extraction of Si species in steaming treated HZSM-5 interior than that in steaming treated HZSM-5 outer surface. However, the combination of alkali-steaming treatment of HZSM-5 zeolite leads to a remarkable collapsion in the generated micro-mesopore hierarchical structure. Both the GTA reaction and coking process were varied with the HZSM-5 catalyst prepared by different post treatment means. Among all catalysts, 3 h 450 °C/0.3 M NaOH/HZSM-5 catalyst exhibited the highest BTX aroamtics yield, lowest coking rate and longest catalyst lifetime, which could be ascribed to the synergistic effect between the shape selectivity of micropores and size confinement of mesopores coupling with moderate acidity distribution in HZSM-5 crystals interior and surface for GTA process.

Phonon propagation scale and nanoscale order in vitreous silica from Raman spectroscopy

For nanoscale systems such as nanoparticles and 3D-bonded networks, the range of spatial coherence is well reflected in the Raman spectral pattern. For confined, or localized, phonons, the range of q-points contributing to the spectrum depends on the phonon confinement length, which makes it possible to derive size information from the spectra. In this work, the Raman spectrum of vitreous silica is described as localized phonons of an SiO2 network. The convergence of the spectral pattern with the confinement size is studied. It is shown that the phonon propagation scale in vitreous silica is within the 0.5–2 nm range.

Advances in polyaniline-based nanocomposites

In this review article, synthesis, properties and applications of polyaniline-based nanocomposites (PANI-NCs) have been described. Different methods (viz chemical, electrochemical, photochemical and mechano-chemical) and size confinement tools used for preparation of PANI-NC are described with their advantageous and disadvantageous features. On the basis of synergized electrical, magnetic, optical, mechanical and thermoelectric properties, PANI-NCs are used in development of sensors, support catalysts, water purifications, energy and biomedicals. Further, applications of PANI-NC are elaborated with suitable examples centring on the role of nano-confinements and chemical modification along with existing challenges for commercial uses.

Ligand induced anomalous emission shift of size-controlled CsPbBr3 nanocrystals

CsPbX3 perovskite nanocrystals (NCs) have attracted much attention from researchers because of their excellent photoelectric properties like high quantum yield, large absorption cross section, and simple preparation process. The addition of ligands in the synthesis process has a significant effect on the microstructure and photophysical properties of solution-processed NCs, which needs further extensive studies. In this Letter, the effects of ligand electronegativity on the size and photoluminescence (PL) properties of CsPbBr3 NCs were reported. One is typical oleic acid with weak electronegativity, and another is 2-acrylamide-2-methylpropionic sulfonic acid with strong electronegativity. The third is their typical mixture with a molar ratio of 1:1. With the increase in ligand electronegativity, the size of CsPbBr3 NCs increases significantly. However, in contrast to the traditional quantum size confinement effect, the PL peak exhibits an abnormal blue shift gradually and the ligand passivation effect on NC surface defects also becomes more significant. The physical mechanism of this anomalous PL shift phenomena of CsPbBr3 NCs was investigated using the time-resolved PL spectrum and transient absorption spectrum.

Intrinsic photoluminescence of amine-functionalized graphene derivatives for bioimaging applications

Photoluminescent graphene-based materials have enormous application potential in cell imaging, display technologies, biomedicine and biosensing. Therefore, their development represents a principal yet highly challenging task for graphene chemistry. Up to now, strategies based on the size confinement in graphene/graphene oxide (GO) quantum dots, non-covalent chemistry combining GO with photoluminescence species, and GO chemistry enabling band gap tuning have been reported. Here, we introduce a simple approach to intrinsically photoluminescent graphene derivatives via one-step fluorographene chemistry enabling controlled surface engineering/chemical reduction by amines. Specifically, the reaction of fluorographene with dodecylamine and hexamethylenediamine results in organophilic and hydrophilic graphene derivatives, respectively, exhibiting intrinsic fluorescence. Both density functional theory calculations and experimental data show that the emission properties occur because of the energy gaps engineered by the choice of amine. Cytotoxicity measurements on NIH/3T3 and HeLa cells demonstrated high biocompatibility for the hydrophilic amine-functionalized derivative. Due to the intrinsic fluorescence, quantification of the uptake by cells and localization of graphene-based sheets in cells can be performed directly using a flow cytometry technique and fluorescence microscopy imaging. These findings pave the way for a new class of functional photoluminescent graphene derivatives with high application potential in fields like biosensing, biomedicine and bioimaging.

Persuasive Evidence for Electron-Nuclear Coupling in Diluted Magnetic Colloidal Nanoplatelets Using Optically Detected Magnetic Resonance Spectroscopy.

The incorporation of magnetic impurities into semiconductor nanocrystals with size confinement promotes enhanced spin exchange interaction between photogenerated carriers and the guest spins. This interaction stimulates new magneto-optical properties with significant advantages for emerging spin-based technologies. Here we observe and elaborate on carrier-guest interactions in magnetically doped colloidal nanoplatelets with the chemical formula CdSe/Cd1-xMnxS, explored by optically detected magnetic resonance and magneto-photoluminescence spectroscopy. The host matrix, with a quasi-type II electronic configuration, introduces a dominant interaction between a photogenerated electron and a magnetic dopant. Furthermore, the data convincingly presents the interaction between an electron and nuclear spins of the doped ions located at neighboring surroundings, with consequent influence on the carrier's spin relaxation time. The nuclear spin contribution by the magnetic dopants in colloidal nanoplatelets is considered here for the first time.

Dynamic instability and migration modes of collective cells in channels.

Migrating cells constantly experience geometrical confinements in vivo, as exemplified by cancer invasion and embryo development. In this paper, we investigate how intrinsic cellular properties and extrinsic channel confinements jointly regulate the two-dimensional migratory dynamics of collective cells. We find that besides external confinement, active cell motility and cell crowdedness also shape the migration modes of collective cells. Furthermore, the effects of active cell motility, cell crowdedness and confinement size on collective cell migration can be integrated into a unified dimensionless parameter, defined as the cellular motility number (CMN), which mirrors the competition between active motile force and passive elastic restoring force of cells. A low CMN favours laminar-like cell flows, while a high CMN destabilizes cell motions, resulting in a series of mode transitions from a laminar phase to an ordered vortex chain, and further to a mesoscale turbulent phase. These findings not only explain recent experiments but also predict dynamic behaviours of cell collectives, such as the existence of an ordered vortex chain mode and the mode selection under non-straight confinements, which are experimentally testable across different epithelial cell lines.