Strain evolution in GaN Nanowires: from free-surface objects to coalesced templates

Top-down fabricated GaN nanowires, 250 nm in diameter and with various heights, have been used to experimentally determine the evolution of strain along the vertical direction of 1-dimensional objects. X-ray diffraction and photoluminescence techniques have been used to obtain the strain profile inside the nanowires from their base to their top facet for both initial compressive and tensile strains. The relaxation behaviors derived from optical and structural characterizations perfectly match the numerical results of calculations based on a continuous media approach. By monitoring the elastic relaxation enabled by the lateral free-surfaces, the height from which the nanowires can be considered strain-free has been estimated. Based on this result, NWs sufficiently high to be strain-free have been coalesced to form a continuous GaN layer. X-ray diffraction, photoluminescence and cathodoluminescence clearly show that despite the initial strain-free nanowires template, the final GaN layer is strained

Vertical and adiabatic excitations in anthracene from quantum Monte Carlo: Constrained energy minimization for structural and electronic excited-state properties in the JAGP ansatz

We study the ionization energy, electron affinity, and the \u3c0 \u2192 \u3c0- (1La) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO \u2192 LUMO one, which underlies the 1La excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in \u3c0-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral 1La excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account. \ua9 2015 AIP Publishing LLC

Role of phase nanosegregation in the photoluminescence spectra of halide perovskites

The study of MAPbI3 phase transitions based on temperature-dependent optical spectroscopy has recently gained a huge attention. Photoluminescence (PL) investigations of the tetragonal-orthorhombic transition suggest that tetragonal nanodomains are present below the transition temperature and signatures associated with tetragonal segregations are observed. We have studied the impact of phase nanosegregation across the orthorhombic-tetragonal phase transition of MAPbI3 on the system's properties employing a tight binding (TB) approach. The particle swarm optimization has been used to obtain a consistent set of TB parameters, where the target properties of the system have been derived by first-principles calculations. The theoretical results have been compared with the measured PL spectra for a temperature range going from 10 to 100 K. Our model effectively captures the carriers' localization phenomenon induced by the presence of residual tetragonal nanodomains and demonstrates that the assumption of phase nanosegregation can explain the low-energy features in the PL spectra of MAPbI3

Impact of time to surgery after neoadjuvant chemotherapy in patients with operable breast cancer.

Background: Some studies of adjuvant chemotherapy (CT) suggested that a shorter interval before the start of therapies may improve survival outcomes in many groups of patients. Time to surgery (TTS) after neoadjuvant CT and survival outcomes have not been established yet. The aim of this study is to evaluate the impact of TTS after neoadjuvant CT in terms of Overall Survival (OS) and Disease Free Survival (DFS). Patients and Methods: A retrospective analysis was conducted in 295 patients receiving neoadjuvant CT for stage I-IIIc breast cancer between 1991 and 2013. 56 pts underwent surgery within 21 days (group A) from last CT cycle, 148 pts within 22-35 days (group B) and 91 pts after 36 days (group C). The majority were infiltrating ductal carcinoma, stage IIA (37.6%) and IIB (33.9%), with nodal involvement in 51.6% of the cases. LumA 18.3%, LumB/HER2- 28.2%, LumB/Her2+ 20.7%, HER2+ 9.8%, TNBC 21%. All patients were treated with neoadjuvant CT: 70.5% with anthra-taxanes based regimen, 18% with anthra- alone, 10.9% with taxanes alone, 0.3% with CMF; plus Trastuzumab in 70% of HER2+ diseases. Results: After a median follow up of 4.6 years, it was observed that patients in group A showed a significant better OS than group B (HR 4.22; 95% CI, 1.27 \u2013 14.00, p=0.018) and group C (HR 3.61; 95% CI, 1.01 \u2013 12.86, p=0.048). Moreover group A showed a significant better DFS than group B (HR 3.41; 95% CI 1.34 to 8.65, p=0.010) and group C (HR 3.77; 95% CI 1.42 to 9.95, p=0.007). No correlations with OS were found in pts who achieved pCR (20.7%); pCR was predictive of better 5- and 10-years DFS independently from TTS (95.4% in the pCR-group vs 75.4% of non-pCR group, HR 0.16; 95% CI 0.04 to 0.66, p=0.011). TTS may influence DFS in non-pCR group: indeed 5-years DFS is 97.3% in group A, 72.7% in group B (HR 2.89; 95% CI 1.14 to 7.36, p=0.026), and 68.5% in group C (HR 3.44; 95% CI 1.3 to 9.1, p=0.013). No significant correlations with regard of stage at diagnosis or molecular subtypes were found. Conclusions: These results suggest that TTS after primary CT may influence patients' survival, regardless of stage at diagnosis and tumor subtype, so that a shorter interval between that last cycle of neoadjuvant chemotherapy and breast surgery should be addressed whenever possible