Near-spherical Shape Research Articles

Bottom-Up Design of Composite Supraparticles for Powder-Based Additive Manufacturing.

Additive manufacturing promises high flexibility and customized product design. Powder bed fusion processes use a laser to melt a polymer powder at predefined locations and iterate the scheme to build 3D objects. The design of flowable powders is a critical parameter for a successful fabrication process that currently limits the choice of available materials. Here, a bottom-up process is introduced to fabricate tailored polymer- and composite supraparticles for powder-based additive manufacturing processes by controlled aggregation of colloidal primary particles. These supraparticles exhibit a near-spherical shape and tailored composition, morphology, and surface roughness. These parameters can be precisely controlled by the mixing and size ratio of the primary particles. Polystyrene/silica composite particles are chosen as a model system to establish structure-property relations connecting shape, morphology, and surface roughness to the adhesion within the powder, which is accessed by tensile strength measurements. The adhesive properties are then connected to powder flowability and it is shown that the resulting powders allow the formation of dense powder films with uniform coverage. Finally, successful powder bed fusion is demonstrated by producing macroscopic single layer specimens with uniform distribution of nanoscale silica additives.

Mechanisms on inter-track void formation and phase transformation during laser Powder Bed Fusion of Ti-6Al-4V

The build quality of laser Powder Bed Fusion (PBF) components largely depends on printing issues such as inter-track voids and undesired microstructure. In this work, a comprehensive phenomenological model was developed to compute the complex transport phenomena during laser PBF of Ti-6Al-4V. The transient temperature and velocity fields during single-track and multi-track laser PBF were computed considering the melting and solidification of the powder feedstocks. Critical metallurgical variables including the molten pool characteristics and thermal cycles were obtained. The model was validated by comparing the computed results against corresponding experimental data. The formation and evolution of inter-track voids in different heat input conditions were studied. Two types of inter-track voids were specified considering their formation mechanisms. The first type appeared in irregular elongated shapes and was caused by the incomplete melting of the powder feedstocks. The second type appeared in near-spherical shapes and originated from the bubbles trapped in the overlap zone of adjacent tracks. Cooling rates were obtained to interpret the metallurgical conditions for the solid-state phase transformations. The novel findings from this research are helpful to the understanding of the formation and mitigation of inter-track voids, and the assessment of phase transformations during laser PBF of titanium alloys.

Synthesis of silver nanoparticles: double-green approach of using chitosan and microwave technique towards antimicrobial activity against pathogenic bacteria

A double green approach to the synthesis of silver nanoparticles using chitosan as a reducing agent and microwave radiation has been carried out in this study. Chitosan was extracted from marine crab carapace and the morphology of the produced chitosan was characterized using Scanning Electron Microscope (SEM). The production of silver nanoparticles (AgNPs) was monitored by the formation of surface plasmon resonance (SPR) at the λmax= 420 nm, indicates the reduction of the oxidation state of Ag+ to Ag0. The XRD data confirms the crystallinity nature of obtained AgNps, while the SEM and TEM revealed the formation of near-spherical shapes, polydisperse, heterogeneous distribution of AgNps with the size range between 7 to 25 nm. The antimicrobial activities of the AgNPs were investigated using The prepared AgNPs demonstrated dual mechanism action with chitosan, which acted as a stabilizer on the surface of AgNPs, and enhance the inhibition zone against E. tarda and E. coli. Therefore, the synthesized AgNPs in this study may have excellent potential for clinical application as it is green, low-cost and eco-friendly.

Formation of Al-based amorphous/nanocrystalline coatings by cold spraying

Al-based amorphous/nanocrystalline coatings were prepared by cold spraying. The microstructures and microhardness of the coatings were investigated. The single particle's deposition was prepared and the formation of coatings was discussed. The amorphous content decreased with increased preheating temperature. The main crystalline phase was α-Al at preheating temperatures below 400 °C, with the appearance of other crystalline phases at 440 °C. The porosity values remained in the 3–4% range at different preheating temperatures and the microhardness of coatings decreased as the amorphous content declined. Analysis of the single particle's morphology revealed no obvious jet splashing and some particles at the interface retained near-spherical shape due to inhomogeneous deformation. The interaction of particles with the deposited coatings revealed the importance of α-Al because the α-Al could promote deformation to some extent. Then three types of interactions of particles with the deposited coatings were put forward. The simulation results about the two particles' interaction confirmed the effect of α-Al phase on the coating formation.

The Properties of Memristive Structures Based on (Co40Fe40B20)x(LiNbO3)100 –x Nanocomposites Synthesized on SiO2/Si Substrates

The structural features and current–voltage curves of metal/nanocomposite/metal sandwiches based on (Co40Fe40B20)x(LiNbO3)100 –x nanocomposites synthesized on SiO2/Si substrates were studied. Samples were fabricated by ion-beam sputtering of a composite target, which provided an opportunity to produce nanocomposites with different compositions x = 5–48 at % in a single cycle. The results of electron microscopy analysis revealed that the obtained nanocomposites consisted of metallic granules in an amorphous nonstoichiometric matrix. These granules were ~2–3 nm in size and had a near-spherical (slightly elongated along the growth direction) shape. The local chemical composition of nanocomposite films was examined using X-ray photoelectron spectroscopy. The structures demonstrated resistive switching with the highest ratio of resistances in the low- and high-resistance states (~10) achieved at x ~ 13 at %. The number of write/erase cycles exceeded 104. The observed effect of resistive switching is attributable to the influence of oxygen vacancies on the tunneling conductivity of contacts of percolation granule chains with one of the electrodes of the structure, which is separated by a highly oxidized layer from the nanocomposite.

Plasma-assisted electrochemical synthesis of monodisperse Au and Au@Ag core–shell nanoparticles

The synthesis of well defined nanoparticles with green chemistry has been an area of intense investigation, but still requires development. In this study, we propose a novel approach for controlling the particle size and distribution through diffusion-controlled growth of plasma-assisted electrochemical synthesis. The continuous, controlled addition of an Au precursor with syringe pump successfully controls the particle size in the range of 50–300 nm with a monodisperse size distribution. Moreover, gold nanoparticles can be formed successfully without any stabilizer and reducing agent. Through optimization of the reaction parameters, including the reaction temperature, discharge current of the microplasma, pH, and concentration of D-(-)-fructose, we verify two distinct feature of diffusion-controlled growth that the particle growth is good agreement of theoretical growth rate (r ∼ t1/3) and the formed gold nanoparticles exhibit polyhedral or near-spherical shapes. This method has been applied to synthesize Au@Ag core–shell nanoparticles and control the Ag shell thickness.

Is Near-Spherical Shape “the New Black” for Smoke ?

We present smoke lidar measurements from the Canadian fires of 2017. The advected smoke layers over Europe are detected at both tropospheric and stratospheric heights, with the latter presenting non-typical values of the Particle Linear Depolarization Ratio (PLDR) with strong wavelength dependence from the UV to the Near-IR. Specifically, the PLDR values are of the order of 22, 18 and 4% at 355, 532 and 1064 nm respectively. In an attempt to interpret these results, we apply the hypothesis that smoke particles have near-spherical shapes. Scattering calculations with the T-matrix code support other findings in the literature ([1]- [2]), showing that the near-spherical shape (or closely similar shapes as in [2]), is the only shape that has been shown to reproduce the observed PLDR and Lidar Ratio (LR) values of the stratospheric smoke particles at the three measurement wavelengths.

Laser Plasma Induced Cu2O Nanoparticle Synthesis in Ethanol and Nanofluid Particle Characterization

Nanofluids with nanoscale colloidal suspensions having condensed nanomaterials have been found to show highly-enhanced physical, chemical, thermal and transport properties and signifies great potential in many fields. In this article, laser induced plasmas at liquid-metal phase boundaries is investigated for copper oxide (Cu2O) nanoparticle synthesis in ethanol without any surfactants. The nanoparticles are generated using 1064 nm NdYAG laser ablation in a water confined plasma with 1.5 J laser energy pulsed at 10 Hz for 4 minutes, which resulted in narrow size distribution of nanoparticles of size ranging from 2 to 12 nm dispersed in ethanol sans surfactant. The synthesized Cu2O nanoparticles in ethanol are characterized for their sizes, surface morphology, crystalline structures and elemental compositions etc. The dynamic light scattering (DLS) measurements show Cu2O nanoparticles synthesized have an average size of 4.5 nm. The scanning electron microscope (SEM) measurements show Cu2O nanoparticles exhibit isolated and agglomerated nanoparticles with near-spherical and irregular surface morphologies. Transmission electron microscopy (TEM) measurements show Cu2O nanoparticles with near-spherical and irregular shapes, and the average size of the nanoparticles is ˜4.5 nm. Selected area electron diffraction (SAED) measurements show poly crystalline structure present in the Cu2O nanoparticles. The energy-dispersive X-ray spectroscopy (EDX) measurements show the purity of Cu2O nanoparticles with identification of significant Cu and O elements. X-ray diffraction (XRD) measurements confirm that the Cu2O nanoparticles are polycrystalline in nature and confirmed the presence of single phase of Cu2O nanoparticles.

Morphological prediction of glaucoma by quantitative analyses of ocular shape and volume using 3-dimensional T2-weighted MR images

Elongated axial length of the eye increases the morbidity of glaucoma. Myopia also associates with elongated axial length, and such ellipsoid shape of the eyeball strongly contributes its pathogenesis. Morphological features of the eyeballs, which could be important factors for developing glaucoma, have not been well described. The aim of this study was to investigate the three-dimensional (3D) topographic features of glaucomatous eyeballs with/without myopia to evaluate the potential of those features for predicting glaucoma. Using a 3.0-tesla MRI, volume-isotropic turbo-spin-echo acquisition T2-weighted images were obtained from 55 patients with glaucoma and 22 controls to delineate the eyeballs. Eyeball volumes, axial lengths and transverse lengths were semi-automatically calculated and compared between four groups: normal, myopia, glaucoma, and glaucoma with myopia. Both glaucoma and myopia increased the eyeball volume compared to the normal eyes. An increased anisotropy ratio (axial/transversus length) was observed in myopic eyes compared to normal, whereas in the glaucomatous eyes, with or without myopia, no increase in anisotropy ratio was observed. Increasing volume of eyes can be caused by myopia and glaucoma. Myopic eyes were ellipsoid in shape, but there was less anisotropy and a near-spherical shape in glaucomatous eyes, even in glaucomatous myopic eyes.

The Fall Speed Variability of Similarly Sized Ice Particle Aggregates

AbstractThe terminal velocity (Vt) of ice hydrometeors is of high importance to atmospheric modeling. Vt is governed by the physical characteristics of a hydrometeor, including mass and projected area, as well as environmental conditions. When liquid hydrometeors coalesce to form larger hydrometeors, the resulting hydrometeor can readily be characterized by its spherical or near-spherical shape. For ice hydrometeors, it is more complicated because of the variability of ice shapes possible in the atmosphere as well as the inherent randomness in the aggregation process, which leads to highly variable characteristics. The abundance of atmospheric processes affecting ice particle dimensional characteristics creates potential for highly variable Vt for ice particles that are predicted or measured to be of the “same size.” In this article we explore the variability of ice hydrometeor Vt both theoretically and through the use of experimental observations. Theoretically, the variability in Vt is investigated by analyzing the microphysical characteristics of randomly aggregated hexagonal shapes. The modeled dimensional characteristics are then compared to aircraft probe measurements to constrain the variability in atmospheric ice hydrometeor Vt. Results show that the spread in Vt can be represented with Gaussian distributions relative to a mean. Variability expressed as the full width at half maximum of the normalized Gaussian probability distribution function is around 20%, with somewhat higher values associated with larger particle sizes and warmer temperatures. Field campaigns where mostly convective clouds were sampled displayed low variability, while Arctic and midlatitude winter campaigns showed broader Vt spectra.

Geometrical model description of shape coexistence in Se isotopes

The coexistence and mixing between near-spherical and well-deformed shapes in 72,74,76Se nuclei is studied with a phenomenological exactly separable Bohr model employing a potential with two competing minima in the axial deformation. The dynamical evolution of the nuclear shapes and the emergence of shape mixing effects is investigated for the collective low-lying states by means of the corresponding effective potentials and the deformation probability distribution. The experimental energy levels and the electromagnetic properties of the considered nuclei are found to be in agreement with the proposed behavior of the shape dynamics.

Synthesis of Pd(0) Nanoparticles in TiO2–SiO2 Xerogel

Pd/TiO2–SiO2 xerogels containing 0.15–0.75 wt % palladium are prepared from Pd(NO3)2 · 2H2O solutions in a mixture of tetrabutoxytitanium (TBT) and tetraethoxysilane (TEOS) in a desiccator under acetic acid–water vapors in the batch mode at 20°С followed by drying and calcination of the material at 850°С. IR spectroscopy showed that the presence of Pd(NO3)2 · 2H2O has no effect on the amount of newly formed Ti–O–Si bonds in the double oxide TiO2–SiO2 over the range of salt concentrations studied. X-ray powder diffraction showed that palladium present in the xerogel calcined at 850°С is in the form of Pd(0) nanoparticles. The electron-microscopic morphology study showed that the items prepared (Pd(0) nanoparticles) had near-spherical shapes; their sizes fell in the range 20–230 nm. A means for varying Pd(0) nanoparticle size in the material is to vary the palladium(II) salt concentration at the dissolution stage.

A novel gemcitabine derivative-loaded liposome with great pancreas-targeting ability.

Gemcitabine (Gem) is a standard first-line treatment for pancreatic cancer (PC). However, its chemotherapeutic efficacy is hampered by various limitations such as short half-life, metabolic inactivation, and lack of tumor localizing. We previously synthesized a lipophilic Gem derivative (Gem formyl hexadecyl ester, GemC16) that exhibited improved antitumor activity in vitro. In this study, a target ligand N,N-dimethyl-1,3-propanediamine was conjugated to 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[hydroxyl succinimidyl (polyethylene glycol-2000)] (DSPE-PEG-NHS) to form DSPE-PEG-2N. Then, pancreas-targeting liposomes (2N-LPs) were prepared using the film dispersion-ultrasonic method. GemC16-loaded 2N-LPs displayed near-spherical shapes with an average size distribution of 157.2 nm (polydispersity index (PDI) = 0.201). The encapsulation efficiency of GemC16 was up to 97.3% with a loading capacity of 8.9%. In human PC cell line (BxPC-3) and rat pancreatic acinar cell line (AR42J), cellular uptake of 2N-LPs was significantly enhanced compared with that of unmodified PEG-LPs. 2N-LPs exhibited more potent in vitro cytotoxicity against BxPC-3 and AR42J cell lines than PEG-LPs. After systemic administration in mice, 2N-LPs remarkably increased drug distribution in the pancreas. In an orthotopic tumor mouse model of PC, GemC16-bearing liposomes were more effective in preventing tumor growth than free GemC16. Among these treatments, 2N-LPs showed the best curative effect. Together, 2N-LPs represent a promising nanocarrier to achieve pancreas-targeting drug delivery, and this work would provide new ideas for the chemotherapy of PC.

Nanostructures, Faceting, and Splitting in Nanoliter to Yoctoliter Liquid Droplets.

Contrary to everyday experience, where all liquid droplets assume rounded, near-spherical shapes, the temperature-tuning of liquid droplets to faceted polyhedral shapes and to spontaneous splitting has been recently demonstrated in oil-in-water emulsions. However, the elucidation of the mechanism driving these surprising effects, as well as their many potential applications, ranging from faceted nanoparticle synthesis through new industrial emulsification routes to controlled-release drug delivery within the human body, have been severely hampered by the micron-scale resolution of the light microscopy employed to date in all in situ studies. Thus, the thickness of the interfacially frozen crystalline monolayer, suggested to drive these effects, could not be directly measured, and the low limit on the droplet size still showing these effects remained unknown. In this study, we employ a combination of super-resolution stimulated emission depletion microscopy, cryogenic transmission and freeze-fracture electron microscopy, to study these effects well into the nanometer length scale. We demonstrate the occurrence of the faceting transition in droplets spanning an incredible 12 decades in volume from nanoliters to yoctoliters and directly visualize the interfacially frozen, few nanometer thick, crystalline monolayer suggested to drive these effects. Furthermore, our measurements allow placing an upper-limit estimate on the two-dimensional Young modulus of the interfacial nanometer-thick surface crystal in the smallest droplets, providing insights into the virtually unexplored domain of nanoelasticity.

Laser additive manufacturing of nano-TiC reinforced Ni-based nanocomposites with tailored microstructure and performance

Laser additive manufacturing has demonstrated a promising capability in the simultaneous formation of high-performance nanocomposites with unique microstructure characteristics. The present work studied the densification, microstructure and mechanical properties of nano-TiC reinforced Inconel 718 composites processed by selective laser melting (SLM) with variation of laser energy linear density (E). It revealed that a fully dense TiC/Inconel 718 part was fabricated at a proper E of 300 J/m. On increasing E from 225 to 300 J/m, the nano-TiC reinforcement experienced severe agglomeration to uniform distribution along the grain boundaries and inside the grains of matrix. The morphologies of nano-particles transferred from irregular polygonal to near-spherical shape. The presence of nano-TiC could also accelerate the refinement of columnar dendrites spacing of γ matrix. A high nanohardness of 4.48 GPa, a low coefficient of friction of 0.36 and resultant low wear rate of 3.83 × 10−4 mm3/N⋅m were obtained at E of 300 J/m, showing a significantly improved mechanical performance compared to the SLM-processed unreinforced nickel-based alloys.

Synthesis of nickel nanopowders in water/ethylene glycol solutions. The influence of precursor concentration and temperature on the particles’ size

Heterogeneous reaction of reduction of freshly prepared nickel hydroxide by hydrazine hydrate in water/ethylene glycol solutions have been investigated. The effect of the initial concentration of nickel hydroxide and temperature on duration of induction period and the total duration of the reaction and zero formal orders of nucleation and growth processes for nickel hydroxide were found as well as were observed that the activation energies of these processes are close. The size and composition of the formed nickel nanoparticles have been investigated using scanning electron microscopy. It was found that the obtained nickel particles are characterized by near-spherical shape and an average diameter of 120–140 nm and narrow size distribution. With the use of powder diffraction method it was found that obtained nickel nanopowders does not contain nickel oxide or hydroxide and consist of crystallites with a size 10–14 nm. Using Uv-vis spectroscopy the dissolution of nickel hydroxide and formation of complex [Ni(N 2 H 4 ) 3 ](OH) 2 in reaction mixture after adding of hydrazine was observed and the dependence of its solubility on ethylene glycol concentration in reaction mixture was investigated. Tentative multistage scheme of formation of nickel nanoparticles at heterogeneous conditions in water/ethylene glycol media was proposed. This scheme include 1) partial dissolution of nickel hydroxide and formation of nickel-hydrazine complex; 2) the decay of formed nickel-hydrazine complex on the nickel hydroxide surface and formation of nuclei of nickel nanoparticles; 3) growth of nickel nuclei via the reaction with dissolved nickel-hydrazine complex; 4) coagulation of small nickel particles; 5) growth of nickel nanoparticles from the surface. Keywords: nickel nanopowders, ethylene glycol, hydrazine, kinetics.

Laser Plasma Induced TiO2 Nanoparticle Synthesis in Water and Particle Characterization

Nanofluids with nanoscale colloidal suspensions having condensed nanomaterials have been found to show highly enhanced physical, chemical, thermal, and transport properties and signify great potential in many fields. In this paper, laser-induced plasmas at liquid-metal phase boundaries are investigated for titanium oxide (TiO2) nanoparticle synthesis in water without any surfactants. The nanoparticles are generated using 1064 nm NdYAG laser ablation in a water confined plasma with 1.5 J laser energy pulsed at 10 Hz for 4 min, which resulted in nanoparticles of size ranging from 5 to 35 nm. The synthesized TiO2 nanoparticles in water are characterized for their sizes, surface morphology, crystalline structures, and elemental compositions. The dynamic light scattering (DLS) measurements show the synthesized TiO2 nanoparticles have an average size of 18 nm. The scanning electron microscopy (SEM) measurements show TiO2 nanoparticles exhibit isolated and agglomerated nanoparticles with near-spherical and irregular surface morphologies. The Transmission electron microscopy (TEM) measurements show TiO2 nanoparticles with near-spherical and irregular shapes, and the average size of the nanoparticles is ~17 nm. The selected area electron diffraction (SAED) measurements show single and poly crystalline structures present in the TiO2 nanoparticles. The energy-dispersive X-ray spectroscopy (EDX) measurements show the purity of TiO2 nanoparticles with identification of Ti and O elements. The X-ray diffraction (XRD) measurements confirm that the TiO2 nanoparticles are crystalline in nature and confirmed the presence and coexistence of two crystal phases of TiO2 nanoparticles, such as anatase and rutile phases, and estimated nanoparticle size in the range between 11 and 31 nm.

Spherical spindle shape promotes perpendicular cortical orientation by preventing isometric cortical pulling on both spindle poles during C. elegans female meiosis.

Meiotic spindles are positioned perpendicular to the oocyte cortex to facilitate segregation of chromosomes into a large egg and a tiny polar body. In C. elegans, spindles are initially ellipsoid and parallel to the cortex before shortening to a near-spherical shape with flattened poles and then rotating to the perpendicular orientation by dynein-driven cortical pulling. The mechanistic connection between spindle shape and rotation has remained elusive. Here, we have used three different genetic backgrounds to manipulate spindle shape without eliminating dynein-dependent movement or dynein localization. Ellipsoid spindles with flattened or pointed poles became trapped in either a diagonal or a parallel orientation. Mathematical models that recapitulated the shape dependence of rotation indicated that the lower viscous drag experienced by spherical spindles prevented recapture of the cortex by astral microtubules emanating from the pole pivoting away from the cortex. In addition, maximizing contact between pole dynein and cortical dynein stabilizes flattened poles in a perpendicular orientation, and spindle rigidity prevents spindle bending that can lock both poles at the cortex. Spindle shape can thus promote perpendicular orientation by three distinct mechanisms.

Earth’s Energy Imbalance Measured From Space

The direct measurement of earth’s energy imbalance (EEI) is one of the greatest challenges in climate research. The global mean EEI represents the integrated value of global warming and is tightly linked to changes in hydrological cycle and the habitability of our planet. Current space-born radiometers measure the individual radiative components of the energy balance with unprecedented stability, but with calibration errors too large to determine the absolute magnitude of global mean EEI as the components’ residual. Best estimates of the long-term EEI are currently derived from temporal changes in ocean heat content at ~0.7 Wm−2. To monitor EEI directly from space, we propose an independent approach based on accelerometry that measures nongravitational forces, such as radiation pressure, acting on earth-orbiting spacecrafts. The concept of deriving EEI from radiation pressure has been considered in the past, and we provide analysis that shows today’s capabilities are sufficiently accurate to answer the question: At what rate is our planet warming? To measure global mean EEI to within at least ±0.3 Wm−2 requires spacecraft(s) of near-spherical shape and well-characterized surface properties to reduce confounding effects. The proposed concept may provide the basis for a data record of global and zonal mean EEI on annual and potentially monthly timescales. It is not meant to replace the existing concepts designed to measure energy balance components or ocean heat storage, but to complement these by providing an independent estimate of EEI for comparison and to anchor data products and climate models that lack energy balance closure.

A Study of the Mechanical and Thermal Characteristics of an Al-Si-Fe Alloy Fabricated by Rolling and Heat Treatment

The effects of a rolling process and heat treatment on the mechanical and thermal properties of an Al-Si-Fe alloy were studied. The achieved thermal conductivity of the as-rolled alloy treated by a T6 heat treatment was 188.22 W/(m·K), which is as good as that of the as-cast alloy treated by the T6 heat treatment directly, mostly because of changes in the silicon morphology. The results also revealed that the lower quantity of precipitated Al8Fe2Si and Mg2Si phases had no obvious effect on the thermal properties of the material because the interphase spaces between precipitated phases were larger than the mean free path of electrons. However, the precipitated second phases influenced the elongation. The best mechanical properties of the Al-Si-Fe alloy were obtained by rolling and T6 treatment. The corresponding best tensile strength, yield strength, and elongation were 244 MPa, 295 MPa, and 9.56%, respectively, which are attributed to the near-spherical shape, small size, homogeneous distribution of the Si particles, and the precipitation strengthening of Mg2Si.