Elementary excitations of single-photon emitters in hexagonal boron nitride.

Single-photon emitters serve as building blocks for many emerging concepts in quantum photonics. The recent identification of bright, tunable and stable emitters in hexagonal boron nitride (hBN) has opened the door to quantum platforms operating across the infrared to ultraviolet spectrum. Although it is widely acknowledged that defects are responsible for single-photon emitters in hBN, crucial details regarding their origin, electronic levels and orbital involvement remain unknown. Here we employ a combination of resonant inelastic X-ray scattering and photoluminescence spectroscopy in defective hBN, unveiling an elementary excitation at 285 meV that gives rise to a plethora of harmonics correlated with single-photon emitters. We discuss the importance of N π* anti-bonding orbitals in shaping the electronic states of the emitters. The discovery of elementary excitations in hBN provides fundamental insights into quantum emission in low-dimensional materials, paving the way for future investigations in other platforms.

Interaction-driven transport of dark excitons in 2D semiconductors with phonon-mediated optical readout.

The growing field of quantum information technology requires propagation of information over long distances with efficient readout mechanisms. Excitonic quantum fluids have emerged as a powerful platform for this task due to their straightforward electro-optical conversion. In two-dimensional transition metal dichalcogenides, the coupling between spin and valley provides exciting opportunities for harnessing, manipulating, and storing bits of information. However, the large inhomogeneity of single layers cannot be overcome by the properties of bright excitons, hindering spin-valley transport. Nonetheless, the rich band structure supports dark excitonic states with strong binding energy and longer lifetime, ideally suited for long-range transport. Here we show that dark excitons can diffuse over several micrometers and prove that this repulsion-driven propagation is robust across non-uniform samples. The long-range propagation of dark states with an optical readout mediated by chiral phonons provides a new concept of excitonic devices for applications in both classical and quantum information technology.

Visualization of Dark Excitons in Semiconductor Monolayers for High-Sensitivity Strain Sensing.

Transition-metal dichalcogenides (TMDs) are layered materials that have a semiconducting phase with many advantageous optoelectronic properties, including tightly bound excitons and spin-valley locking. In tungsten-based TMDs, spin- and momentum-forbidden transitions give rise to dark excitons that typically are optically inaccessible but represent the lowest excitonic states of the system. Dark excitons can deeply affect the transport, dynamics, and coherence of bright excitons, hampering device performance. Therefore, it is crucial to create conditions in which these excitonic states can be visualized and controlled. Here, we show that compressive strain in WS2 enables phonon scattering of photoexcited electrons between momentum valleys, enhancing the formation of dark intervalley excitons. We show that the emission and spectral properties of momentum-forbidden excitons are accessible and strongly depend on the local strain environment that modifies the band alignment. This mechanism is further exploited for strain sensing in two-dimensional semiconductors, revealing a gauge factor exceeding 104.

Diagnóstico ecográfico de la corionicidad y amnionicidad en el embarazo múltiple

La determinación ecográfica de la corionicidad y de la amnionicidad constituye la piedra angular en el manejo obstétrico del embarazo múltiple. Esta debe hacerse en el primer trimestre del embarazo, no solamente por la mayor facilidad diagnóstica sino sobretodo porque constituye el inicio de la ruta a seguir en el control de este tipo de gestaciones. Por lo mencionado anteriormente, el profesional que lidie con esta clase de ecografías debe disponer de los conocimientos necesarios para llegar a un diagnóstico certero de la corionicidad y amnionicidad por ultrasonido.

Determination of chorionicity and amnionicity by ultrasound is the most important step in the management of multiple pregnancies. This diagnosis should be done in the first trimester of pregnancy not only because less difficulty but because it constitutes the beginning ofvarious steps in the control of these types of pregnancies. It is highly recommended that professionals dealing with this kind of study have the knowledge to assess correctly and promptly chorionicity and amnionicity in multiple pregnancies.

[Arthroplasty after failed osteosynthesis in hip fractures]. / Reemplazo articular en osteosíntesis fallida de fracturas de cadera.

OBJECTIVE: To assess the functional status of patients with arthroplasty after failed osteosynthesis in hip fractures. MATERIAL AND METHODS: Prospective, descriptive, cohort of patients with primary failed osteosynthesis in hip fracture, who underwent total arthroplasty in the period 2002-2004, analyzed with the Harris functional scale. RESULTS: 26 patients: 17 women and 9 men, mean age of 74.8 years. Seventeen patients had loosening of dynamic hip screw, 5 of condylar screw 5 and 4 with cannulated screws. We made 12 hybrid, 10 cemented and 4 not cemented arthroplasties. Eighteen patients with good results, 7 with regular and 1 bad result. Patients with the highest rating were the youngest. DISCUSSION: Arthroplasty of the hip in a patient with failed osteosynthesis should be considered necessary. If we can improve pain of the hip, the patient will have less functional limitation and a better quality of life. This type of surgery requires high technical capability and experience by the orthopedic surgeon. CONCLUSIONS: Hip arthroplasty after failed osteosynthesis in hip fractures is a method that improves function and a gives a better life quality.

Comparación de la resistencia a la deformación de dos materiales no metálicos para estructuras de prótesis fija: evaluación por elementos finitos / A comparison of the resistance to deformation of two non-metallic materials for fixed prosthesis frameworks: an evaluation by finite elements

Antecedentes: las restauraciones en cavidad bucal han sido realizadas tradicionalmente en materiales metálicos, los cuales han cumplido con las exigencias mecánicas de forma excelente pero con esporádicos inconvenientes de bicompatibilidad y estética. Nuevos materiales se han desarrollado en la odontología, para soportar las necesidades estéticas y funcionales de las restauraciones parciales y fijas. Para tener un perfil completo, se realizan estudios complementarios con métodos físicos y numéricos en los cuales se evalúan las propiedades físicas y mecánicas con las cuales se puede crear un criterio para utilizar un material como restaurador definitivo. Objetivo: comparar dos materiales, Vectris(R) y Construct(R) en cuanto a resistencia a la deformación, por fuerzas longitudinales y cortantes, al soportar cargas ejercidas sobre una prótesis parcial fija de tres unidades, utilizando el método de elementos finitos. Métodos: se realizaron estructuras de prótesis fija de tres unidades con pilares en 35 y 37 y póntico del 36 con los materiales mencionados, los cuales fueron comparados con una estructura estándar de oro tipo IV. Se hicieron mediciones manuales con calibradores metálicos para obtener las dimensiones de estas estructuras. Se tomaron fotos digitalizadas estandarizadas y se realizaron cortes a las estructuras, para ser llevadas a un programa de graficación en computador (Autocad 2000, Autodesk(R), el cual desarrolló las geométricas a escala. Estas gráficas fueron importadas en el programa Cosmos/M(R), que es el programa de elementos finitos donde se analizaron las fuerzas longitudinales en todas las estructuras y las fuerzas cortantes en los pónticos, mostrando en una serie de tablas los resultados numéricos en Newtons y analizando por medio de distribución de colores los esfuerzos internos de las estructuras de estudio. Resultados: al analizar el comportamiento de flexión y torsión de las estructuras de fibras de vidrio, polietileno y oro tipo IV, se observó que la condición crítica que generó deformación plástica para los materiaoles de estudio, fue de una carga concéntrica de 970 N, 85.1 N, 298 N, respectivamente. Conclusiones: las fibras que mejor comportamiento presentaron frente a las cargas aplicadas y analizadas por elementos finitos fueron las de vidrio