Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles (MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses (2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction (MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications.</jats:p>

<jats:p>The pulsation and translation of two cavitation bubbles are studied numerically in sound field. The results show that bubbles’ pulsation driven by the sound makes them translate. Different pulsations lead to different translations. Two bubbles will be mutually attractive to each other if they pulsate in phase, while they will be repulsive if out of phase. Furthermore, the secondary Bjerknes force for small phase difference is attractive, and it becomes repulsive for other phase differences up to <jats:italic>π</jats:italic> phase difference due to the nonlinear effect, although the attractive strength between two bubbles is much larger than the repulsive strength. Finally, one bubble pulsation and the other bubble stationary make the bubbles repel each other.</jats:p>

<jats:p>We investigate the beam focusing technology of shear-vertical (SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.</jats:p>

<jats:p>Both ionic solutions under an external applied static electric field <jats:italic>E</jats:italic> and glassy-forming liquids under undercooled state are in non-equilibrium state. In this work, molecular dynamics (MD) simulations with three aqueous alkali ion chloride (NaCl, KCl, and RbCl) ionic solutions are performed to exploit whether the glass-forming liquid analogous fractional variant of the Stokes–Einstein relation also exists in ionic solutions under <jats:italic>E</jats:italic>. Our results indicate that the diffusion constant decouples from the structural relaxation time under <jats:italic>E</jats:italic>, and a fractional variant of the Stokes–Einstein relation is observed as well as a crossover analogous to the glass-forming liquids under cooling. The fractional variant of the Stokes–Einstein relation is attributed to the <jats:italic>E</jats:italic> introduced deviations from Gaussian and the nonlinear effect.</jats:p>

<jats:p>A new compound with one-dimensional spin chains, Ba<jats:sub>9</jats:sub>Co<jats:sub>3</jats:sub>Se<jats:sub>15</jats:sub>, was synthesized under high pressure and high temperature conditions and systematically characterized via structural, transport and magnetic measurements. Ba<jats:sub>9</jats:sub>Co<jats:sub>3</jats:sub>Se<jats:sub>15</jats:sub> crystallizes in a hexagonal structure with the space group <jats:italic>P</jats:italic>-6<jats:italic>c</jats:italic>2 (No. 188) and lattice constants of <jats:italic>a</jats:italic> = <jats:italic>b</jats:italic> = 9.6765 Å and <jats:italic>c</jats:italic> = 18.9562 Å. The structure consists of trimeric face-sharing octahedral CoSe<jats:sub>6</jats:sub> chains, which are arranged in a triangular lattice in the <jats:italic>ab</jats:italic>-plane and separated by Ba atoms. The distance of the nearest neighbor of CoSe<jats:sub>6</jats:sub> chains is very large, given by the lattice constant <jats:italic>a</jats:italic> = 9.6765 Å. The Weiss temperature <jats:italic>T<jats:sub>θ</jats:sub> </jats:italic> associated with the intra-chain coupling strength is about −346 K. However, no long-range magnetic order but a spin glass transition at ∼ 3 K has been observed. Our results indicate that the spin glass behavior in Ba<jats:sub>9</jats:sub>Co<jats:sub>3</jats:sub>Se<jats:sub>15</jats:sub> mainly arises from the magnetic frustration due to the geometrically frustrated triangular lattice.</jats:p>

<jats:p>For B2 NiAl and NiTi intermetallic compounds, the ideal stress–strain image is lack from the perspective of elastic constants. We use first-principles calculation to investigate the ideal strength and elastic behavior under the tensile and shear loads. The relation between the ideal strength and elastic constants is found. The uniaxial tension of NiAl and NiTi along <jats:inline-formula> <jats:tex-math> <?CDATA $\langle 001\rangle $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:mn>001</mml:mn> <mml:mo stretchy="false">〉</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_3_036201_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> crystal direction leads to the change from tetragonal path to orthogonal path, which is driven by the vanishing of the shear constant <jats:italic>C</jats:italic> <jats:sub>66</jats:sub>. The shear failure under {110}<jats:inline-formula> <jats:tex-math> <?CDATA $\langle 111\rangle $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:mn>111</mml:mn> <mml:mo stretchy="false">〉</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_29_3_036201_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> shear deformation occurring in process of tension may result in a small ideal tensile strength (∼2 GPa) for NiTi. The unlikeness in the ideal strength of NiAl and NiTi alloys is discussed based on the charge density difference.</jats:p>

<jats:p>We have successfully grown an arsenopyrite marcasite type RhSb<jats:sub>2</jats:sub> single crystal, and systematically investigated its crystal structure, electrical transport, magnetic susceptibility, heat capacity, and thermodynamic properties. We found that the temperature-dependent resistivity exhibits a bad metal behavior with a board peak around 200 K. The magnetic susceptibility of RhSb<jats:sub>2</jats:sub> shows diamagnetism from 300 K to 2 K. The low-temperature specific heat shows a metallic behavior with a quite small electronic specific-heat coefficient. No phase transition is observed in both specific heat and magnetic susceptibility data. The Hall resistivity measurements show that the conduction carriers are dominated by electrons with <jats:italic>n</jats:italic> <jats:sub>e</jats:sub> = 8.62 × 10<jats:sup>18</jats:sup> cm<jats:sup>−3</jats:sup> at 2 K, and the electron carrier density increases rapidly above 200 K without change sign. Combining with <jats:italic>ab-initio</jats:italic> band structure calculations, we showed that the unusual peak around 200 K in resistivity is related to the distinct electronic structure of RhSb<jats:sub>2</jats:sub>. In addition, a large thermopower <jats:italic>S</jats:italic>(<jats:italic>T</jats:italic>) about –140 μV/K is observed around 200 K, which might be useful for future thermoelectric applications.</jats:p>

<jats:p>We investigate the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons (APNRs) containing atomic vacancies with different distributions and concentrations using <jats:italic>ab initio</jats:italic> density functional calculations. It is found that the atomic vacancies are easier to form and detain at the edge region rather than a random distribution through analyzing formation energy and diffusion barrier. The highly local defect states are generated at the vicinity of the Fermi level, and emerge a deep-to-shallow transformation as the width increases after introducing vacancies in APNRs. Moreover, the electrical transport of APNRs with vacancies is enhanced compared to that of the perfect counterparts. Our results provide a theoretical guidance for the further research and applications of PNRs through defect engineering.</jats:p>

<jats:p>Using <jats:italic>ab initio</jats:italic> density functional theory calculations, we explore the three most stable structural phases, namely, <jats:italic>α</jats:italic>, <jats:italic>β</jats:italic>, and cubic (c) phases, of two-dimensional (2D) antimonene, as well as its isoelectronic counterparts SnTe and InI. We find that the band gap increases monotonically from Sb to SnTe to InI along with an increase in ionicity, independent of the structural phases. The band gaps of this material family cover the entire visible-light energy spectrum, ranging from 0.26 eV to 3.37 eV, rendering them promising candidates for optoelectronic applications. Meanwhile, band-edge positions of these materials are explored and all three types of band alignments can be achieved through properly combining antimonene with its isoelectronic counterparts to form heterostructures. The richness in electronic properties for this isoelectronic material family sheds light on possibilities to tailor the fundamental band gap of antimonene via lateral alloying or forming vertical heterostructures.</jats:p>

<jats:p>We propose general principles to construct two-dimensional (2D) single-atom-thick carbon allotropes. They can be viewed as the generalization of patterning Stone–Walse defects (SWDs) by manipulating bond rotation and of patterning inverse SWDs by adding (or removing) carbon pairs on the pristine graphene, respectively. With these principles, numerous 2D allotropes of carbon can be systematically constructed. Using 20 constructed 2D allotropes as prototypical and benchmark examples, besides nicely reproducing all well-known ones, such as pentaheptites, T-graphene, OPGs, etc, we still discover 13 new allotropes. Their structural, thermodynamic, dynamical, and electronic properties are calculated by means of first-principles calculations. All these allotropes are metastable in energy compared with that of graphene and, except for OPG-A and C3-10-H allotropes, the other phonon spectra of 18 selected allotropes are dynamically stable. In particular, the proposed C3-11 allotrope is energetically favorable than graphene when the temperature is increased up to 1043 K according to the derived free energies. The electronic band structures demonstrate that (i) the C3-8 allotrope is a semiconductor with an indirect DFT band gap of 1.04 eV, (ii) another unusual allotrope is C3-12 which exhibits a highly flat band just crossing the Fermi level, (iii) four allotropes are Dirac semimetals with the appearance of Dirac cones at the Fermi level in the lattices without hexagonal symmetry, and (vi) without the spin–orbit coupling (SOC) effect, the hexagonal C3-11 allotrope exhibits two Dirac cones at <jats:italic>K</jats:italic> and <jats:italic>K</jats:italic> <jats:sup>′</jats:sup> points in its Brillouin zone in similarity with graphene.</jats:p>