Van der Waals Epitaxy of Weyl-Semimetal Td-WTe2.

Epitaxial growth of WTe2 offers significant advantages, including the production of high-quality films, possible long-range in-plane ordering, and precise control over layer thicknesses. However, the mean island size of WTe2 grown by molecular beam epitaxy (MBE) in the literature is only a few tens of nanometers, which is not suitable for the implementation of devices at large lateral scales. Here we report the growth of Td -WTe2 ultrathin films by MBE on monolayer (ML) graphene, reaching a mean flake size of ≃110 nm, which is, on overage, more than three times larger than previous results. WTe2 films thicker than 5 nm have been successfully synthesized and exhibit the expected Td phase atomic structure. We rationalize the epitaxial growth of Td-WTe2 and propose a simple model to estimate the mean flake size as a function of growth parameters that can be applied to other transition metal dichalcogenides (TMDCs). Based on nucleation theory and the Kolmogorov-Johnson-Meh-Avrami (KJMA) equation, our analytical model supports experimental data showing a critical coverage of 0.13 ML above which WTe2 nucleation becomes negligible. The quality of monolayer WTe2 films is demonstrated by electronic band structure analysis using angle-resolved photoemission spectroscopy (ARPES), which is in agreement with first-principles calculations performed on free-standing WTe2 and previous reports. We found electron pockets at the Fermi level, indicating a n-type doping of WTe2 with an electron density of n = 2.0 ± 0.5 × 1012 cm-2 for each electron pocket.

Influence of confinement on free radical chemistry in layered nanostructures.

The purpose of the present work was to study how chemical reactions and the electronic structure of atoms are affected by confinement at the sub-nanometer scale. To reach this goal, we studied the H atom in talc, a layered clay mineral. Talc is a highly 2D-confining material with the width of its interlayer space close to angstrom. We investigated talc with a particle accelerator-based spectroscopic method that uses elementary particles. This technique generates an exotic atom, muonium (Mu), which can be considered as an isotope of the H atom. Moreover, the technique allows us to probe a single atom (H atom) at any time and explore the effects of the layered clay on a single ion (proton) or atom. The cation/electron recombination happens in two time windows: one faster than a nanosecond and the other one at longer than microseconds. This result suggests that two types of electron transfer processes take place in these clay minerals. Calculations demonstrated that the interlayer space acts as a catalytic surface and is the primary location of cation/electron recombination in talc. Moreover, the studies of the temperature dependence of Mu decay rates, due to the formation of the surrogate of H2, is suggestive of an "H2" formation reaction that is thermally activated above 25 K, but governed by quantum diffusion below 25 K. The experimental and computational studies of the hyperfine coupling constant of Mu suggest that it is formed in the interlayer space of talc and that its electronic structure is extremely changed due to confinement. All these results imply that the chemistry could be strongly affected by confinement in the interlayer space of clays.

Gene expression profiling of patient-derived pancreatic cancer xenografts predicts sensitivity to the BET bromodomain inhibitor JQ1: implications for individualized medicine efforts.

c-MYC controls more than 15% of genes responsible for proliferation, differentiation, and cellular metabolism in pancreatic as well as other cancers making this transcription factor a prime target for treating patients. The transcriptome of 55 patient-derived xenografts show that 30% of them share an exacerbated expression profile of MYC transcriptional targets (MYC-high). This cohort is characterized by a high level of Ki67 staining, a lower differentiation state, and a shorter survival time compared to the MYC-low subgroup. To define classifier expression signature, we selected a group of 10 MYC target transcripts which expression is increased in the MYC-high group and six transcripts increased in the MYC-low group. We validated the ability of these markers panel to identify MYC-high patient-derived xenografts from both: discovery and validation cohorts as well as primary cell cultures from the same patients. We then showed that cells from MYC-high patients are more sensitive to JQ1 treatment compared to MYC-low cells, in monolayer, 3D cultured spheroids and in vivo xenografted tumors, due to cell cycle arrest followed by apoptosis. Therefore, these results provide new markers and potentially novel therapeutic modalities for distinct subgroups of pancreatic tumors and may find application to the future management of these patients within the setting of individualized medicine clinics.

Carcinoma metaplásico escamoso primario de mama: un subtipo infrecuente. A propósito de tres casos en el Hospital Universitario del Caribe / Primary breast squamous metaplastic squamous cell carcinoma of the breast: a rare subtype. Presentation of three cases in the Hospital Universitario del Caribe

De todas las neoplasias malignas de mama los carcinomas ductales son los más frecuentes. Menos del 5% son denaturaleza metaplásica y 0,04%-0,1% presentan diferenciación de células escamosas, subtipo que se considera más agresivo. Debido a los pocos casos en la literatura,no hay consenso sobre su diagnósticoy tratamiento. Presentamos tres casos con ese diagnóstico vistos entre 2014 y 2015 en nuestra institución y que corresponden a mujeres de 57, 49 y 65 años sin factores de riesgo y que presentaron cuadros clínicos similares consistentes con aparición de masa de crecimiento rápido. Dos de las pacientes se habían diagnosticado previamente con carcinoma ductal infiltrante de tipo no especial en biopsias por tru-cut con diagnóstico definitivo en la mastectomía radical que reportó en todos los casos carcinoma metaplásico escamoso confirmado por inmunohistoquímica.

Ductal carcinomas are the most common of all breast malignancies, less than 5% are of metaplastic nature, and 0.04% to 0.1% have squamous cell differentiation. These special subtypes are considered more aggressive. Due to the few cases in the literature, there is no consensus about its diagnosis and treatment. Three cases are presented with this diagnosis, seen in our institution between 2014 and 2015. They were women of 57, 49, and 65 years old with no risk factors, and who presented with similar clinical features, consisting of the appearance of a rapid growing mass. Two of the patients had been previously diagnosed with infiltrating ductal carcinoma of no special type by core needle biopsy, with a definitive diagnosis in radical mastectomy, which reported squamous metaplastic carcinoma confirmed by immunohistochemistry.

Síndrome de Hamman / Hamman syndrome

Resumen Se conoce como Síndrome de Hamman al neumomediastino espontáneo. Condición considerada benigna, autolimitada y poco reportada en la literatura nacional e internacional. Es probable que exista un subregistro o no se dé a conocer lo suficiente. Debe tenerse en cuenta en todo paciente joven que ingrese a los servicios de urgencias por dolor torácico, disnea y enfisema subcutáneo. El diagnóstico se realiza por sospecha clínica y se confirma con los rayos x de tórax. El tratamiento es netamente conservador. Presentamos un caso ilustrativo de esta condición que se presentó en un joven después de un episodio paroxístico de tos ocasionado por contacto con gasolina. Su condición previa era completamente normal. (Acta Med Colomb 2016; 41: 206-210).

Abstract Spontaneous pneumomediastinum is known as Hamman's syndrome. This condition is considered benign, self-limited and is little reported in the national and international literature. It is probably underreported or is not enough publicized. It must be considered in every young patient admitted to the emergency department with chest pain, dyspnea and subcutaneous emphysema. The diagnosis is made by clinical suspicion and is confirmed by chest X-rays. The treatment is clearly conservative. An illustrative case of this condition that occurred in a young man after a paroxysmal coughing episode caused by contact with gasoline is presented. Its previous condition was completely normal. (Acta Med Colomb 2016; 41: 206-210).

Cement As a Waste Form for Nuclear Fission Products: The Case of (90)Sr and Its Daughters.

One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of (90)Sr insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its ß-decay on the cement paste structure. We show that (90)Sr is stable when it substitutes the Ca(2+) ions in C-S-H, and so is its daughter nucleus (90)Y after ß-decay. Interestingly, (90)Zr, daughter of (90)Y and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for (90)Sr storage.

Magnetic nanopantograph in the SrCu2(BO3)2 Shastry-Sutherland lattice.

Magnetic materials having competing, i.e., frustrated, interactions can display magnetism prolific in intricate structures, discrete jumps, plateaus, and exotic spin states with increasing applied magnetic fields. When the associated elastic energy cost is not too expensive, this high potential can be enhanced by the existence of an omnipresent magnetoelastic coupling. Here we report experimental and theoretical evidence of a nonnegligible magnetoelastic coupling in one of these fascinating materials, SrCu2(BO3)2 (SCBO). First, using pulsed-field transversal and longitudinal magnetostriction measurements we show that its physical dimensions, indeed, mimic closely its unusually rich field-induced magnetism. Second, using density functional-based calculations we find that the driving force behind the magnetoelastic coupling is the CuOCu superexchange angle that, due to the orthogonal Cu(2+) dimers acting as pantographs, can shrink significantly (0.44%) with minute (0.01%) variations in the lattice parameters. With this original approach we also find a reduction of ∼ 10% in the intradimer exchange integral J, enough to make predictions for the highly magnetized states and the effects of applied pressure on SCBO.

Conductance fluctuations in gold point contacts: an atomistic picture.

This paper concerns an experimental and theoretical study of the transition between two consecutive conductance plateaus as obtained in breaking gold contact experiments. The experimental measurements performed at 100 K with a scanning tunneling microscope and variable elongation speeds show that the transitions between consecutive plateaus can appear in the conductance traces as an abrupt conductance step, a smooth quasicontinuous change or as large amplitude conductance fluctuations. The theoretical calculations based on a non-orthogonal tight-binding Hamiltonian have shown that for a given deformation there are several structures having close and competing energies.We discuss the relation between the temperature, sampling frequency, stretching speed and energy barriers which can explain the conditions for the observation of the three kinds of conductance traces.

Are conductance plateaus independent events in atomic point contact measurements? A statistical approach.

Conductance-elongation curves of gold atomic wires are measured using a scanning tunneling microscope break junction technique at room temperature. Landauer's conductance plateaus are individually identified and statistically analyzed. Both the probabilities to observe and the lengths of the two last plateaus (at conductance values close to 2e(2)/h and 4e(2)/h) are studied. All results converge to show that the occurrences of these two conductance plateaus on a conductance-elongation curve are statistically independent events.

Scanning tunneling microscopy chemical signature of point defects on the MoS2(0001) surface.

Using ab initio calculations, we have studied the modification of the electronic structure of the MoS2(0001) surface by several point defects: a surface S vacancy and different transition metal atoms substituting a S atom (Pd, Au, Fe, and V). With a S vacancy, a gap state appears with weight mostly on the Mo and S atoms surrounding the vacancy. The substitutional atoms of complete d band (Pd and Au) do not present magnetic polarization and slightly modify the DOS near the Fermi energy. On the other hand, the incomplete d band atoms (Fe and V) present spin polarization and modify significantly the states near the band edges. From calculated STM images and STS curves, we show that this chemical signature can be measured and used to characterize the surface defects of the substrate which are suitable nucleation centers for nanocluster growth.