Molecular Dissociation in Presence of a Catalyst II: The bond breaking role of the transition from virtual to localized states

We address a molecular dissociation mechanism that is known to occur when a H 2 molecule approaches a catalyst with its molecular axis parallel to the surface. It is found that molecular dissociation is a form of quantum dynamical phase transition associated to an ana- lytic discontinuity of quite unusual nature: the molecule is destabilized by the transition from non-physical virtual states into actual local- ized states. Current description complements our recent results for a molecule approaching the catalyst with its molecular axis perpendicu- lar to the surface. Also, such a description can be seen as a further successful implementation of a non-Hermitian Hamiltonian in a well defined model

Decentralized Control of Voltage Source Converters in Microgrids based on the Application of Instantaneous Power Theory

International audienceIn this paper, a new strategy to control microgrids highly penetrated by Voltage Source Converters (VSC) is proposed. The strategy is based on instantaneous measurements and calculations of voltages and currents and the application of Instantaneous Power Theory. This approach employs each VSC along with an LC filter as a current source. The grid parameters are not known to the controller, only the filter inductance and capacitance. The approach characterizes a theoretical methodology to define a grid status parameter that provides multiple alternatives to operate the VSC autonomously. Besides, one of those alternatives is sharing load among VSCs by regulating voltage of the local connection bus. This grid status parameter is an external voltage contribution vector defined by the operation of the other VSCs in the microgrid. Because of the definition of this parameter, frequency manipulation is not employed as a communication link between VSCs, avoiding perturbation to the grid stability. The approach provides an approximation of the equivalent impedance of the system seen from the filter output. The load sharing scheme under the proposed strategy is fully described. An experimental validation is performed in order to test the proposed approach for load sharing between three VSCs and the inclusion of nonlinear load

Results of emergency Hartmann's operation for obstructive or perforated left-sided colorectal cancer

<p>Abstract</p> <p>Background</p> <p>Up to 15% of colorectal cancer (CRC) patients present with obstructive or perforated tumours, and require emergency surgery. The Hartmann's procedure (HP) provides the opportunity to achieve a potentially curative (R0) resection, while minimizing surgical trauma in poor-risk patients. The aim of this study was to assess the surgical (operative mortality), and oncological (long-term survival after curative resection) results of emergency HP for obstructive or perforated left-sided CRC.</p> <p>Methods</p> <p>A retrospective review of 50 patients who underwent emergency HP for perforated/obstructive CRC in our institution between 1995 and 2006.</p> <p>Results</p> <p>Median age of patients was 75 (range 22–95) years and the indications for HP were obstruction (32) and perforation (18 patients). Operative mortality and morbidity were 8% and 26% respectively. 35 patients (70%) were operated with a curative intent; in this group, overall 1-, 3- and 5-year survival rates were 80%, 54% and 40%. In univariate analysis, the presence of lymph node metastases was associated with poor 5-year survival (62% [Stage II] vs. 27% [Stage III], log-rank test, p = 0.02). Eleven patients (22%) had their operation reversed with a median delay of 225 (range 94–390) days. In this subgroup, two patients died from distant metastases, but there were no instances of loco-regional recurrence.</p> <p>Conclusion</p> <p>Hartmann's operation remains a good option to palliate symptoms in 30% of patients with left-sided CRC who are not candidates to a curative resection. For those who have a curative resection, the oncological outcome is acceptable, especially stage II patients, who appear to benefit the most from this surgical strategy.</p

Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau

Classical T Tauri stars (CTTSs) are young stellar objects that accrete materials from their accretion disc influenced by their strong magnetic field. The magnetic pressure truncates the disc at a few stellar radii and forces the material to leave the disc plane and fall onto the stellar surface by following the magnetic field lines. However, this global scheme may be disturbed by the presence of a companion interacting gravitationally with the accreting component. This work is aiming to study the accretion and the magnetic field of the tight eccentric binary DQ Tau, composed of two equal-mass ($\sim$ 0.6 \msun ) CTTSs interacting at different orbital phases. We investigated the variability of the system using a high-resolution spectroscopic and spectropolarimetric monitoring performed with ESPaDOnS at the CFHT. We provide the first ever magnetic field analysis of this system, the Zeeman-Doppler imaging revealed a stronger magnetic field for the secondary than the primary (1.2 kG and 0.5 kG, respectively), but the small-scale fields analysed through Zeeman intensification yielded similar strengths (about 2.5 kG). The magnetic field topology and strengths are compatible with the accretion processes on CTTSs. Both components of this system are accreting, with a change of the main accretor during the orbital motion. In addition, the system displays a strong enhancement of the mass accretion rate at periastron and apastron. We also discovered, for the first time in this system, the apsidal motion of the orbital ellipse.Comment: 18 pages, 20 figures. Accepted for publication in MNRA

Molecular dissociation in the presence of catalysts: Interpreting bond breaking as a quantum dynamical phase transition

In this work we show that molecular chemical bond formation and dissociation in the presence of the d-band of a metal catalyst can be described as a quantum dynamical phase transition (QDPT). This agrees with DFT calculations that predict sudden jumps in some observables as the molecule breaks. According to our model this phenomenon emerges because the catalyst provides for a non-Hermitian Hamiltonian. We show that when the molecule approaches the surface, as occurs in the Heyrovsky reaction of H2, the bonding H2 orbital has a smooth crossover into a bonding molecular orbital built with the closest H orbital and the surface metal d-states. The same occurs for the antibonding state. Meanwhile, two resonances appear within the continuous spectrum of the d-band, which are associated with bonding and antibonding orbitals between the furthest H atom and the d-states at the second metallic layer. These move toward the band center, where they collapse into a pure metallic resonance and an almost isolated H orbital. This phenomenon constitutes a striking example of the non-trivial physics enabled when one deals with non-Hermitian Hamiltonian beyond the usual wide band approximation.Fil: Ruderman, Andres. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Dente, Axel Damián. Invap S. E.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Pastawski, Horacio Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Characterization of tissue engineered endothelial cell networks in composite collagen-agarose hydrogels

Scaffolds constitute an important element in vascularized tissues and are therefore investigated for providing the desired mechanical stability and enabling vasculogenesis and angiogenesis. In this study, supplementation of hydrogels containing either Matrigel™ and rat tail collagen I (Matrigel™/rCOL) or human collagen (hCOL) with SeaPlaque™ agarose were analyzed with regard to construct thickness and formation and characteristics of endothelial cell (EC) networks compared to constructs without agarose. Additionally, the effect of increased rCOL content in Matrigel™/rCOL constructs was studied. An increase of rCOL content from 1 mg/mL to 3 mg/mL resulted in an increase of construct thickness by approximately 160%. The high rCOL content, however, impaired the formation of an EC network. The supplementation of Matrigel™/rCOL with agarose increased the thickness of the hydrogel construct by approximately 100% while supporting the formation of a stable EC network. The use of hCOL/agarose composite hydrogels led to a slight increase in the thickness of the 3D hydrogel construct and supported the formation of a multi-layered EC network compared to control constructs. Our findings suggest that agarose/collagen-based composite hydrogels are promising candidates for tissue engineering of vascularized constructs as cell viability is maintained and the formation of a stable and multi-layered EC network is supported. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Three-dimensional trapping of light with light in semiconductor planar microcavities

When light is confined in all three directions and in dimensions of the order of the light wavelength, discretization of the photon spectra and distinctive phenomena occur, the Purcell effect and the inhibition of emission of atoms being two paradigmatic examples. Diverse solid-state devices that confine light in all three dimensions have been developed and applied. Typically the confinement volume, operating wavelength, and quality factor of these resonators are set by construction, and small variations of these characteristics with external perturbations are targeted for applications including light modulation and control. Here we describe full three-dimensional light trapping, that is set and tuned by laser excitation in an all-optical scheme. The proposed device is based on a planar distributed Bragg reflector GaAs semiconductor microcavity operated at room temperature. Lateral confinement is generated by an in-plane gradient in the refractive index of the structure's materials due to localized heating, which is in turn induced by carriers photoexcited by a focused laser. Strong three-dimensional trapping of light is evidenced by the laser-induced changes on the spectral, spatial, and k-space distribution of the emission. The dynamics of the laser-induced photonic potential is studied using modulated optical excitation, highlighting the central role of thermal effects at the origin of the observed phenomena.Fil: Anguiano, Sebastian. Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología; ArgentinaFil: Reynoso, Andres Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Bruchhausen, Axel Emerico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Lemaître, A.. Centre National de la Recherche Scientifique; FranciaFil: Bloch, J.. Centre de Nanosciences et de Nanotechnologies; FranciaFil: Fainstein, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin

Neoadjuvant Chemotherapy in Patients with Stage IV Colorectal Cancer: A Comparison of Histological Response in Liver Metastases, Primary Tumors, and Regional Lymph Nodes

Background: We report the histopathological results of a novel "inversed” strategy designed to manage patients with colorectal cancer (CRC) who have synchronous liver metastases by using chemotherapy first, liver surgery second, and resection of the primary tumor as a final step. This study was designed to compare the response to chemotherapy in liver metastases, primary tumors, and locoregional lymph nodes. Methods: Twenty-nine patients with stage IV CRC received a combination of oxaliplatin, irinotecan, 5-fluorouracil, and leucovorin (OCFL) for 3-4months. Histological response to chemotherapy was assessed by using a tumor regression grading (TRG) score based on presence of residual tumor cells and extent of fibrosis. Results: Median age of patients was 56 (range, 37-69) years. Primary tumor location was right colon (n=5), left colon (n=7), and rectum (n=17 patients). TRG scores correlated across disease sites (Spearman correlation coefficients for TRG in the primary tumor and lymph nodes was 0.59 [P=0.005]; for the primary tumor and metastases 0.44 [P=0.021]; and for lymph nodes and metastases 0.58 [P=0.006]). Complete absence or poor tumor response (TRG4/5) was significantly more frequent in primary tumors (35.7%) and locoregional lymph nodes (38%) than in liver metastases (6.9%; McNemar test, P=0.02). Two patients had a complete pathologic response (pT0N0M0). Conclusions: In patients with stage IV colorectal cancer, liver metastases exhibit a better histological response than primary tumors to OCFL neoadjuvant chemotherap

Systematic review and meta-analysis of fibrin sealants for patients undergoing pancreatic resection

AbstractIntroductionPost-operative pancreatic fistula (POPF) is a common complication after partial pancreatic resection, and is associated with increased rates of sepsis, mortality and costs. The role of fibrin sealants in decreasing the risk of POPF remains debatable. The aim of this study was to evaluate the literature regarding the effectiveness of fibrin sealants in pancreatic surgery.MethodsA comprehensive database search was conducted. Only randomized controlled trials comparing fibrin sealants with standard care were included. A meta-analysis regarding POPF, intra-abdominal collections, post-operative haemorrhage, pancreatitis and wound infections was performed according to the recommendations of the Cochrane collaboration.ResultsSeven studies were included, accounting for 897 patients. Compared with controls, patients receiving fibrin sealants had a pooled odds ratio (OR) of developing a POPF of 0.83 [95% confidence interval (CI): 0.6–1.14], P = 0.245. There was a trend towards a reduction in post-operative haemorrhage (OR = 0.43 (95%CI: 0.18–1.0), P = 0.05) and intra-abdominal collections (OR = 0.52 (95%CI: 0.25–1.06), P = 0.073) in those patients receiving fibrin sealants. No difference was observed in terms of mortality, wound infections, re-interventions or hospital stay.ConclusionOn the basis of these results, fibrin sealants cannot be recommended for routine clinical use in the setting of pancreatic resection