Search results for "Note"

The role of surface diffusion in the growth mechanism of III-nitride nanowires and nanotubes.

2021

Abstract The spontaneous growth of GaN nanowires (NWs) in absence of catalyst is controlled by the Ga flux impinging both directly on the top and on the side walls and diffusing to the top. The presence of diffusion barriers on the top surface and at the frontier between the top and the sidewalls, however, causes an inhomogeneous distribution of Ga adatoms at the NW top surface resulting in a GaN accumulation in its periphery. The increased nucleation rate in the periphery promotes the spontaneous formation of superlattices in InGaN and AlGaN NWs. In the case of AlN NWs, the presence of Mg can enhance the otherwise short Al diffusion length along the sidewalls inducing the formation of AlN …

Enhanced Thermal Stability of Gold and Silver Nanorods by Thin Surface Layers

2007

Using in situ transmission electron microscopy, we find that a carbon shell governs the morphological transitions of gold and silver nanorods upon heating. Encapsulated Ag nanorods show a surprising nonuniform sublimation behavior starting from one side and leaving behind the shell. Uncovered gold nanorods transform their shape to spheres well below the bulk melting temperature through surface diffusion, which is prevented by a thin carbon shell.

Interface Diffusion Controlled Sintering of Atomically Clean Surfaces of Metals

2003

Competition between surface reaction and diffusion of gold deposited onto ZrTe3

2003

Abstract Surface reaction and diffusion of gold, deposited onto the (0 0 1) ZrTe 3 van der Waals (vdW) surface, is studied by transmission electron and scanning tunneling microscopy. It is shown that both processes compete at temperatures as low as room temperature. In case of diffusion the deposited gold mostly disappears from the surface and intercalates into the vdW gaps of the substrate. Residual unreacted gold agglomerates are rather mobile and are often displaced by the scanning tip along the [1 0 0] direction of the substrate. In case of reaction, which usually takes place at somewhat higher substrate temperatures, grains of Zr 3 Te 2 , AuTe 2 and/or Au 2 Te 3 are formed. Contrary to…

α-d-Glucopyranose Adsorption on a Pd30 Cluster Supported on Boron Nitride Nanotube

2016

Boron nitride nanotube (BNNT) as an innovative support for carbohydrate transformation processes was evaluated, using density functional theory. The α-d-glucopyranose adsorption on a Pd30 cluster, supported on BNNT, was used to check both the local activity of topologically different metallic sites and the effects of the proximity of the BNNT surface to the same metallic sites. Detailed geometrical and electronic analyses performed on Pd30/BNNT and α-d-glucopyranose/Pd30/BNNT systems were discussed. It was observed that the deposition of the Pd30 cluster onto the BNNT support gives rise to an electronic rearrangement, determining a charge transfer from the support to the adsorbed metal clus…

Dural splitting reconstruction in retethering after lipomeningocele repair: Technical note

2021

Background: Tethered spinal cord syndrome (TCS) can occur after the surgical repair of lipomeningoceles (LMCs). In these cases, the tethering results from postoperative adhesions between the spinal cord and the overlying repaired dura. A watertight dural closure using the residual dura and/or the surrounding tissues does not always provide enough space for the spinal cord and risks retethering. Here, we report a 16-year-old patient with secondary TCS following lipomeningocele repair who successfully underwent release of the tethered filum terminale utilizing a novel dural splitting reconstructive technique to attain a water-tight closure without the need for a duroplasty. Methods: A 16-yea…

Characterization of activated sludge settling properties with a sludge collapse-acceleration stage

2019

Abstract The sedimentability of the activated sludge can be affected by the presence of a large variety of coagulants and polymers from a previous physical-chemical process. In this paper, the activated sludge settling process in industrial wastewater treatment plants where the sludge does not settle in a conventional way is studied. The two observed constant hindered settling velocity stages and the instant the intermediate sludge acceleration period occurs are described. A variation of the Richardson and Zaki model is used to characterize the two stages of constant settling velocity. The concentration of suspended solids, where a sudden decrease of hindered settling velocity was observed,…

Metal–organic framework technologies for water remediation: towards a sustainable ecosystem

2018

Having access to clean water is a mandatory requirement for the proper development of living beings. So, addressing the removal of contaminants from aquatic systems should be a priority research topic in order to restore ecosystem balance and secure a more sustainable future. The fascinating structures and striking physical properties of metal–organic frameworks (MOFs) have revealed them as excellent platforms for the removal of harmful species from water. In this review, we have focused our attention on critically highlighting the latest developments achieved in the adsorptive removal of inorganic – metal cations, inorganic acids, oxyanions/cations, nuclear wastes and other inorganic anion…

The effect of chitosan on the bioaccessibility and intestinal permeability of acyclovir

2019

Chitosan is object of pharmaceutical research as a candidate permeability enhancer. However, chitosan was recently shown to reduce the oral bioavailability of acyclovir in humans. The effect of chitosan on two processes determining the oral bioavailability of acyclovir, bioaccessibility and intestinal absorption, was now investigated. Acyclovir's bioaccessibility was studied using the dynamic TNO gastro-Intestinal Model (TIM-1). Four epithelial models were used for permeability experiments: a Caco-2 cell model in absence and presence of mucus and both rat and porcine excised intestinal segments. Study concentrations of acyclovir (0.8 g/l) and chitosan (1.6 g/l and 4 g/l) were in line with t…

Gold nanoparticle interactions with endothelial cells cultured under physiological conditions

2017

PEGylated gold nanoparticles (AuNPs) have an extended circulation time after intravenous injection in vivo and exhibit favorable properties for biosensing, diagnostic imaging, and cancer treatment. No impact of PEGylated AuNPs on the barrier forming properties of endothelial cells (ECs) has been reported, but recent studies demonstrated that unexpected effects on erythrocytes are observed. Almost all studies to date have been with static-cultured ECs. Herein, ECs maintained under physiological cyclic stretch and flow conditions and used to generate a blood-brain barrier model were exposed to 20 nm PEGylated AuNPs. An evaluation of toxic effects, cell stress, the release profile of pro-infla…