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Design Rules for Producing Cardiovascular Stents by Selective Laser Melting: Geometrical Constraints and Opportunities
摘要： Additive Manufacturing (AM) has risen great interest in biomedical applications, for its flexibility and the possibility of producing patient-customized devices. Customization has high importance to limit inflammation and rejection. Moreover, some occlusions may take place in bifurcation sites, which require the insertion of multiple stents, increasing the risk and complexity of the procedure. Selective Laser Melting (SLM) can be exploited to realize metallic stents with geometries not depending on tubular precursor, allowing the study of devices with new shapes, such as for occlusions in high-tortuosity vessels and in bifurcated arteries. The geometrical flexibility of SLM is largely exploited for large components, while for small implants such as cardiovascular stents it has not been studied in depth. Accordingly, this work analyses the geometrical requirements of cardiovascular stents starting from traditional meshes and identifies design rules for AM. Initially, traditional stent meshes are analysed to assess their feasibility in layer-by-layer production by SLM. An accurate investigation of the limitations imposed by the powder-bed process nature, the powder size and the laser spot diameter is performed, considering the relationship with stent dimensions, cell shape and strut inclinations. Finally, a set of design rules for SLM of stents are defined. These rules are used to design novel meshes producible with an industrial SLM system using cobalt-chromium powder. In particular, tubular stents are produced in expanded and semi-crimped configurations. Additionally, multi-branch stents were designed and produced to prove the capability of the process for bifurcation applications.
关键词： Cobalt-chromium alloy,Selective laser melting,Design for additive manufacturing,Additive manufacturing,Bifurcation
更新于2025-09-12 10:27:22
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An octahedral Cu <sub/>2</sub> O@AgNCs substrate in liquid-microextraction coupled chemometric algorithms for SERS sensing of chromium( <scp>iii</scp> & <scp>vi</scp> ) species
摘要： The current study assembles liquid-microextraction, surface enhanced Raman spectroscopy (SERS) and chemometric algorithms in one platform for chromium speciation using octahedral Cu2O@Ag nanocomposites (Cu2O@AgNCs) as a SERS substrate. The reaction between cationic dye rhodamine 6G (RG+) and the chlorochromate anion (CrO3Cl?) at pH < 1.0 has been exploited for chromium determination by the phenomenon of ion association. The conditions of microextraction were carefully recorded for suspension. The SERS intensity was followed by depositing the sediment organic phase on the ethanolic octahedral Cu2O@AgNCs, the complex ion associate (RG+$CrO3Cl?) versus a reagent blank. Chemometric algorithms such as partial least squares (PLS) and variable selection competitive adaptive reweighted sampling (CARS)-PLS were applied for masking redundancy in the SERS spectra of the complex ion associate (RG+$CrO3Cl?) formed in the sediment phase extract. Substrate characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), stoichiometry, analytical applications, selectivity and standard method validation was performed. The designed octahedral Cu2O@AgNCs/RG+/HCl probe displayed a detection limit of 0.028 mg L?1 for chromium(VI) under optimized chemometric modeling and microextraction conditions.
关键词： SERS,chemometric algorithms,liquid-microextraction,chromium speciation,octahedral Cu2O@Ag nanocomposites
更新于2025-09-12 10:27:22
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Investigation of the structure and optical absorption of silicon coated with a chromium film after femtosecond laser irradiation
摘要： Microstructured silicon (Si) doped with chromium (Cr) has been produced by femtosecond laser pulses. Microstructured surfaces were produced after laser irradiation at different fluence values. The dependence of its absorptance on laser fluence and thermal annealing were investigated. Microstructured Si that was fabricated at lower laser fluences exhibited perfect absorption below the Si bandgap as well as better thermal stability. The crystal structures of samples obtained before and after thermal annealing were characterized by Raman spectroscopy. The mechanism of absorption below the bandgap of Si is discussed in detail based on the results from Raman spectroscopy and optical absorption.
关键词： femtosecond laser,microstructured silicon,chromium doping,infrared absorption
更新于2025-09-11 14:15:04
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Single-step formation of Cr 2 N nanoparticles by pulsed laser irradiation
摘要： Chromium nitride nanoparticles with mean diameter distribution between 0.8 nm and 30 nm were produced by laser irradiation of a chromium target immersed in liquid nitrogen. Cr was directly converted to chromium nitride nanoparticles according to selected-area electron diffraction analyses using the transmission electron microscopy technique. Crystalline nanoparticles mostly consist of Cr2N, which is commonly reported together with the conversion of Cr2N to CrN and the mixture of chromium oxides. In addition, there is no evidence of oxidation by storage or photodegradation of the nanoparticles in isopropyl alcohol suspensions. The intensity profile of small-angle X-ray scattering indicates that the geometrical shape of the nanoparticles is not spherical but cylindrical with aspect ratio (height-to-radius) of 0:35–0:05. UV-Vis absorption spectroscopy reveals the presence of surface plasmon absorption at the ultraviolet region at wavelengths of 350, 372, and 397 nm. First-principles calculations of density of states, dielectric function, and optical conductivity performed within the theoretical framework of density functional theory for Cr2N with a hexagonal structure corroborate the formation of surface plasmons.
关键词： transmission electron microscopy,liquid nitrogen,chromium nitride nanoparticles,density functional theory,laser irradiation,UV-Vis absorption spectroscopy
更新于2025-09-11 14:15:04
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Vortex patterns in rotating dipolar Bose-Einstein condensate mixtures with squared optical lattices
摘要： Vortex lattice patterns with transitions from regular to other variety vortex shapes are predicted in rotating binary mixtures of dipolar Bose-Einstein condensates loaded in squared optical lattice. We focus our investigation in the experimentally accessible dipolar isotopes of dysprosium (162,164Dy), erbium (168Er), chromium (52Cr), and rubidium (87Rb), by considering the binary mixtures (164Dy-162Dy, 168Er-164Dy, 164Dy-52Cr and 164Dy-87Rb), which are con?ned in strong pancake-shaped trap and loaded in squared two-dimensional optical lattices, where we vary the polarization angle of dipoles, the inter-species contact interactions and the rotation frequency. The ratio between inter- to intra-species contact interaction is used for altering the miscibility properties; with the polarization of the dipolar species used for tuning to repulsive or attractive the dipole-dipole interactions. For enough higher rotation, of particular interest is the regime when the inter- to intra-species scattering in which a richer variety of vortex-lattice patterns are length is larger than one, predicted, including vortex sheets and two-dimensional rotating droplet formations. The patterns can be controlled by changing the optical lattice parameters, as shown for the symmetric 164Dy-162Dy dipolar mixture. For mixtures with stronger di?erences in the dipole moments, as 164Dy-52Cr and 164Dy-87Rb, only half quantum vortices and circular ones have been observed, which will depend on the dipole orientations.
关键词： rotating mixtures,rubidium,Vortex patterns,erbium,optical lattices,dipolar Bose-Einstein condensate,chromium,dysprosium
更新于2025-09-10 09:29:36
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Structural, optical and electrical properties of reactively sputtered CrxNy films: Nitrogen influence on the phase formation
摘要： The properties of various CrxNy films grown by direct current (DC) reactive sputtering process with different values of nitrogen partial pressures (0, 2×10-4, 3.5×10-4 and 5×10-4 mbar) were studied. The structural analysis of the samples was performed by using X-ray diffraction and transmission electron microscopy (TEM), while an elemental analysis was realized by means of Rutherford backscattering spectrometry. By varying nitrogen partial pressure the pure Cr layer, mixture of Cr, Cr2N and CrN phases, or single-phase CrN was produced. TEM analysis showed that at pN2 = 2×10-4 mbar the layer has dense microstructure. On the other hand, the layer deposited at the highest nitrogen partial pressure exhibits pronounced columnar structure. The optical properties of CrxNy films were evaluated from spectroscopic ellipsometry data by the Drude or combined Drude and Tauc-Lorentz model. It was found that both refractive index and extinction coefficient are strongly dependent on the dominant phase formation (Cr, Cr2N, CrN) during the deposition process. Finally, the electrical studies indicated the metallic character of Cr2N phase and semiconducting behaviour of CrN.
关键词： spectroscopic ellipsometry,thin films,chromium nitrides,electrical properties,microstructure
更新于2025-09-09 09:28:46
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Effect of thickness of Cr layer on Ag cocatalyst surface for highly selective photocatalytic conversion of CO <sub/>2</sub> by H <sub/>2</sub> O
摘要： In this study, we developed a Ag–Cr core–shell-structured (Ag@Cr) cocatalyst that modified the surface of the Ga2O3 photocatalyst. Compared to results provided by modifications with Ag cocatalysts and M–Cr dual cocatalysts (M = Au, Cu, Pd, and Pt), this change significantly improved the formation rate of CO and selectivity toward CO evolution in the photocatalytic conversion of CO2 by the electron donor H2O. As a result of this modification, the Cr(OH)3?xH2O shell changed to Cr(OH)x(CO3)y during the photocatalytic conversion. Furthermore, the thickness of the Cr(OH)3?xH2O shell was found to influence the photocatalytic performance. More specifically, Cr(OH)3?xH2O shells that were too thick or too thin were not beneficial to the CO evolution and suppression of H2 evolution. Notably, the highest photocatalytic activity (525.3 μmol h?1), selectivity toward CO evolution (85.2 %), and turnover number of CO to Ag (167) was achieved over 0.25 mol% (Ag@Cr)/Ga2O3. In addition to Ga2O3, the Ag@Cr cocatalyst modification strategy can also be applied to other photocatalyst materials such as NaTaO3, ZnGa2O4, and ZnGa2O4/Ga2O3 for the highly effective photocatalytic conversion of CO2 to CO when using H2O as an electron donor.
关键词： carbon dioxide,chromium hydroxide,Photocatalysis,core–shell structure,Ag cocatalyst
更新于2025-09-09 09:28:46
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Analytical fitting of temperature-dependent spin-flip transitions in absorption spectra of Cr3+-doped silicate glasses
摘要： Temperature-dependent optical absorption spectra have been recorded for Cr3+ doped silicate glasses between 10 K and 773 K. Due to the intermediate ligand field strength of the Cr3+ coordination environment, overlap of the lowest-energy spin-allowed 4A2 → 4T2 band and the two spin-forbidden transitions to the 2E and 2T1 states at approximately 650 nm results in interference dips. An analytical model equation is fitted to the spectra and electronic structure parameters extracted. This represents the first time that variations of these parameters with temperature are obtained over a large temperature range, revealing characteristics of all three overlapping d-d transitions.
关键词： Chromium(III) doped glasses,absorption spectra,spectra calculations,interference dips,temperature
更新于2025-09-04 15:30:14
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Synthesis of Highly Sensitive and Selective Probe for Fluorescent Detection of Chromium(III)
摘要： A new fluorescent probe capable of sensing Cr3+ has been synthesized. Complexing with Cr3+ triggers the formation of a highly fluorescent ring-open form which is pink in colour. The probe shows extremely high fluorescence enhancement upon complexation with Cr3+ and it can be used as a ‘naked eye’ probe.
关键词： Fluorescent,Chromium(III),Rhodamine B,Probe
更新于2025-09-04 15:30:14
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Photoelectron Spectroscopy and Theoretical Study of Cr <sub/><i>n</i> </sub> Si <sub/> 15– <i>n</i> </sub><sup>–</sup> ( <i>n</i> = 1–3): Effects of Doping Cr Atoms on the Structural and Magnetic Properties
摘要： CrnSi15?n? (n = 1?3) clusters were investigated by using size-selected anion photoelectron spectroscopy combined with density functional theory calculations. The results show that the most stable structure of CrSi14? is of C2v symmetry with the Cr atom encapsulated in a Si14 cage which can be viewed as a boat-shaped Si10 unit capped by four additional silicon atoms. A large HOMO?LUMO gap of neutral CrSi14 is confirmed based on the photoelectron spectrum of CrSi14?. Cr2Si13? has two isomers nearly degenerate in energy: one can be characterized as one Si atom interacting with a Cr2Si12 hexagonal prism while the other can be viewed as one Si atom capping a distorted Cr2Si12 hexagonal antiprism. Cr3Si12? has a D6d symmetric wheel structure in which three Cr atoms form an axle surrounded by 12 Si atoms. The magnetic moments of CrSi14?, Cr2Si13?, and Cr3Si12? increase from 1 to 3 μB and then to 7 μB with the increasing number of Cr atoms in the clusters. The magnetic moments of Cr2Si13? and Cr3Si12? are mainly contributed by the surface Cr atoms.
关键词： Photoelectron spectroscopy,Silicon clusters,Chromium doping,Density functional theory,Magnetic properties
更新于2025-09-04 15:30:14