Magnetic Nanoparticles for Power Absorption: optimizing size, shape and magnetic properties

We present a study on the magnetic properties of naked and silica-coated Fe3O4 nanoparticles with sizes between 5 and 110 nm. Their efficiency as heating agents was assessed through specific power absorption (SPA) measurements as a function of particle size and shape. The results show a strong dependence of the SPA with the particle size, with a maximum around 30 nm, as expected for a Neel relaxation mechanism in single-domain particles. The SiO2 shell thickness was found to play an important role in the SPA mechanism by hindering the heat outflow, thus decreasing the heating efficiency. It is concluded that a compromise between good heating efficiency and surface functionality for biomedical purposes can be attained by making the SiO2 functional coating as thin as possible.Comment: 15 pages, 7 figures, 2 table

Digital Quantum Simulation with Rydberg Atoms

We discuss in detail the implementation of an open-system quantum simulator with Rydberg states of neutral atoms held in an optical lattice. Our scheme allows one to realize both coherent as well as dissipative dynamics of complex spin models involving many-body interactions and constraints. The central building block of the simulation scheme is constituted by a mesoscopic Rydberg gate that permits the entanglement of several atoms in an efficient, robust and quick protocol. In addition, optical pumping on ancillary atoms provides the dissipative ingredient for engineering the coupling between the system and a tailored environment. As an illustration, we discuss how the simulator enables the simulation of coherent evolution of quantum spin models such as the two-dimensional Heisenberg model and Kitaev's toric code, which involves four-body spin interactions. We moreover show that in principle also the simulation of lattice fermions can be achieved. As an example for controlled dissipative dynamics, we discuss ground state cooling of frustration-free spin Hamiltonians.Comment: submitted to special issue "Quantum Information with Neutral Particles" of "Quantum Information Processing

Forage yield of Urochloa cultivars in a warm sub-humid environment

Objective: Evaluate for 10 weeks the growth of five Urochloa cultivars: Camello, Cobra, Cayman, Convert 330, Mavuno and Xaraés; during the Nortes (NS), Drought (DS) and Rainy (RS) seasons in a humid semi-warm environment. Design/methodology/approach: Variables were crop growth rate (CGR; kg ha-1 d-1) and total dry matter yield (TDM; t ha-1); which were analyzed under a completely randomized design (Tukey; p=0.05). Results: During NS, Mavuno and Xaraés presented, on average, the highest values ??of CGR (p<0.05), 23.7 and 19.4 kg ha-1 d-1, respectively. In DS the cultivars Xaraés, Convert 330, Mavuno and Cayman, presented the highest values, with 20.7 and 26.8 kg ha-1 d-1, in week 2 and 4, respectively. During RS, in the second and fourth week of regrowth, the Xaraés and Mavuno cultivars presented the highest CGR (p<0.05), 119.8 and 144.7 kg ha-1 d-1, on average. In the NS, the Mavuno hybrid presented the highest yields (p<0.05) of TDM, 0.886, 1.553 and 2.156 t ha-1 in week 6, 8 and 10, respectively. For RS, the cultivars Camello, Cayman, Mavuno and Xaraés presented similar yields of TDM; which, on average, were 4.652, 5.312 and 6.278 t ha-1, at 6, 8 and 10 weeks, respectively. Findings/conclusions: The cultivars Xaraés, Mavuno and Cayman presented good forage potential in a humid semi-warm environment; mainly for showing greater growth and accumulation of total dry matter.Objective: To evaluate for 10 weeks the growth of five Urochloa cultivars: Camello,Cobra, Cayman, Convert 330, Mavuno and Xaraés; during the North Winds (NS), Dry(DS) and Rainy (RS) seasons in a warm sub-humid environment. Design/Methodology/Approach: The variables were crop growth rate (CGR; kg ha-1 d-1 ) and total dry matter yield (TDM; t ha -1 ); which were analyzed under a completelyrandomized design (Tukey; p=0.05). Results: During NS, Mavuno and Xaraés presented, on average, the highest values ??ofCGR (p<0.05), 23.7 and 19.4 kg ha-1 d-1, respectively. In DS the cultivars Xaraés,2Convert 330, Mavuno, and Cayman presented the highest values, with 20.7 and 26.8 kgha-1 d-1 , in week 2 and 4, respectively. During RS, in the second and fourth week ofregrowth, the Xaraés and Mavuno cultivars presented the highest CGR (p<0.05), 119.8and 144.7 kg ha-1 d-1 , on average. In the NS, the Mavuno hybrid presented the highestyields (p<0.05) of TDM, 0.886, 1.553 and 2.156 t ha -1 in week 6, 8 and 10, respectively.For RS, the cultivars Camello, Cayman, Mavuno, and Xaraés presented similar yields ofTDM; which, on average, were 4.652, 5.312 and 6.278 t ha -1 , at 6, 8 and 10 weeks,respectively. Findings/Conclusions: The cultivars Xaraés, Mavuno and Cayman presented goodforage potential in a warm sub-humid environment; mainly for showing greater growthand accumulation of total dry matter

Dynamical 1/N approach to time-dependent currents through quantum dots

A systematic truncation of the many-body Hilbert space is implemented to study how electrons in a quantum dot attached to conducting leads respond to time-dependent biases. The method, which we call the dynamical 1/N approach, is first tested in the most unfavorable case, the case of spinless fermions (N=1). We recover the expected behavior, including transient ringing of the current in response to an abrupt change of bias. We then apply the approach to the physical case of spinning electrons, N=2, in the Kondo regime for the case of infinite intradot Coulomb repulsion. In agreement with previous calculations based on the non-crossing approximation (NCA), we find current oscillations associated with transitions between Kondo resonances situated at the Fermi levels of each lead. We show that this behavior persists for a more realistic model of semiconducting quantum dots in which the Coulomb repulsion is finite.Comment: 18 pages, 7 eps figures, discussion extended for spinless electrons and typo

Kondo effect in coupled quantum dots: a Non-crossing approximation study

The out-of-equilibrium transport properties of a double quantum dot system in the Kondo regime are studied theoretically by means of a two-impurity Anderson Hamiltonian with inter-impurity hopping. The Hamiltonian, formulated in slave-boson language, is solved by means of a generalization of the non-crossing approximation (NCA) to the present problem. We provide benchmark calculations of the predictions of the NCA for the linear and nonlinear transport properties of coupled quantum dots in the Kondo regime. We give a series of predictions that can be observed experimentally in linear and nonlinear transport measurements through coupled quantum dots. Importantly, it is demonstrated that measurements of the differential conductance ${\cal G}=dI/dV$, for the appropriate values of voltages and inter-dot tunneling couplings, can give a direct observation of the coherent superposition between the many-body Kondo states of each dot. This coherence can be also detected in the linear transport through the system: the curve linear conductance vs temperature is non-monotonic, with a maximum at a temperature $T^*$ characterizing quantum coherence between both Kondo states.Comment: 20 pages, 17 figure

Green function techniques in the treatment of quantum transport at the molecular scale

The theoretical investigation of charge (and spin) transport at nanometer length scales requires the use of advanced and powerful techniques able to deal with the dynamical properties of the relevant physical systems, to explicitly include out-of-equilibrium situations typical for electrical/heat transport as well as to take into account interaction effects in a systematic way. Equilibrium Green function techniques and their extension to non-equilibrium situations via the Keldysh formalism build one of the pillars of current state-of-the-art approaches to quantum transport which have been implemented in both model Hamiltonian formulations and first-principle methodologies. We offer a tutorial overview of the applications of Green functions to deal with some fundamental aspects of charge transport at the nanoscale, mainly focusing on applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references, submitted to Springer series "Lecture Notes in Physics

COVID-19 and stem cell transplantation; results from an EBMT and GETH multicenter prospective survey

Altres ajuts: British Society for Blood and Marrow Transplantation and Cellular Therapy (BSBMTCT); UK NIHR Imperial College Biomedical Research Centre.This study reports on 382 COVID-19 patients having undergone allogeneic (n = 236) or autologous (n = 146) hematopoietic cell transplantation (HCT) reported to the European Society for Blood and Marrow Transplantation (EBMT) or to the Spanish Group of Hematopoietic Stem Cell Transplantation (GETH). The median age was 54.1 years (1.0-80.3) for allogeneic, and 60.6 years (7.7-81.6) for autologous HCT patients. The median time from HCT to COVID-19 was 15.8 months (0.2-292.7) in allogeneic and 24.6 months (−0.9 to 350.3) in autologous recipients. 83.5% developed lower respiratory tract disease and 22.5% were admitted to an ICU. Overall survival at 6 weeks from diagnosis was 77.9% and 72.1% in allogeneic and autologous recipients, respectively. Children had a survival of 93.4%. In multivariate analysis, older age (p = 0.02), need for ICU (p < 0.0001) and moderate/high immunodeficiency index (p = 0.04) increased the risk while better performance status (p = 0.001) decreased the risk for mortality. Other factors such as underlying diagnosis, time from HCT, GVHD, or ongoing immunosuppression did not significantly impact overall survival. We conclude that HCT patients are at high risk of developing LRTD, require admission to ICU, and have increased mortality in COVID-19