Characteristic molecular properties of one-electron double quantum rings under magnetic fields

The molecular states of conduction electrons in laterally coupled quantum rings are investigated theoretically. The states are shown to have a distinct magnetic field dependence, which gives rise to periodic fluctuations of the tunnel splitting and ring angular momentum in the vicinity of the ground state crossings. The origin of these effects can be traced back to the Aharonov-Bohm oscillations of the energy levels, along with the quantum mechanical tunneling between the rings. We propose a setup using double quantum rings which shows that Aharonov-Bohm effects can be observed even if the net magnetic flux trapped by the carriers is zero.Comment: 16 pages (iopart format), 10 figures, accepted in J.Phys.Cond.Mat

Method for obtaining an enriched population of sirna-expressing cells

ReportProblems with transience of siRNA-mediated knock-down and transfection efficiency have limited the scope of RNAi-based experiments. The invention provides a tool for employing RNAi more efficiently and effectively by integrating RNAi expression with methods of cell enrichment

On the role of AGN feedback on the thermal and chemodynamical properties of the hot intra-cluster medium

We present an analysis of the properties of the ICM in an extended set of cosmological hydrodynamical simulations of galaxy clusters and groups performed with the TreePM+SPH GADGET-3 code. Besides a set of non-radiative simulations, we carried out two sets of simulations including radiative cooling, star formation, metal enrichment and feedback from supernovae, one of which also accounts for the effect of feedback from AGN resulting from gas accretion onto super-massive black holes. These simulations are analysed with the aim of studying the relative role played by SN and AGN feedback on the general properties of the diffuse hot baryons in galaxy clusters and groups: scaling relations, temperature, entropy and pressure radial profiles, and ICM chemical enrichment. We find that simulations including AGN feedback produce scaling relations that are in good agreement with X-ray observations at all mass scales. However, our simulations are not able to account for the observed diversity between CC and NCC clusters: unlike for observations, we find that temperature and entropy profiles of relaxed and unrelaxed clusters are quite similar and resemble more the observed behaviour of NCC clusters. As for the pattern of metal enrichment, we find that an enhanced level of iron abundance is produced by AGN feedback with respect to the case of purely SN feedback. As a result, while simulations including AGN produce values of iron abundance in groups in agreement with observations, they over-enrich the ICM in massive clusters. The efficiency of AGN feedback in displacing enriched gas from halos into the inter-galactic medium at high redshift also creates a widespread enrichment in the outskirts of clusters and produces profiles of iron abundance whose slope is in better agreement with observations.Comment: 23 pages, 14 figures, 1 table, accepted for publication in MNRA

Galaxy clusters with the square kilometer array

We review some science cases for galaxy clusters and the impact that the future SKA data will have in those analyses. We first describe how the search for galaxy clusters through radio-sources will be significantly improved through the detection of much fainter radiosources in a big volume. Secondly, we bring out the benefits of using very sensitive radio data to study the thermal and non-thermal component of clusters and disentangle the main processes happening in the physics of their plasma. Moreover, we discuss the possibility of using the high frequencies of the SKA to separate the thermal Sunyaev-Zeldovich (SZ) effect from the radio halo emission and use the former as a mass proxy for galaxy clusters. Finally, we investigate how the very high sensitivity and spatial resolution of SKA will result into a great improvement in the lensing treatment, underlining the lensing distribution of the 21-cm intensity from the reionization period. As a whole, SKA will become an impressive window covering a significant wider range in redshift to look at an unknown radio universe and set constraints on different mechanisms happening in clusters.This work has been supported by a grant funded by the “Consorzio per la Fisica di Trieste”. SP also acknowledges support by the PRIN-INAF09 project “Towards an Italian Network for Computational Cosmology”, by the PRIN-MIUR09 “Tracing the growth of structures in the Universe”, and by the PD51 INFN grant. Partial support is also provided by Spanish Ministerio de Ciencia e Innovación (AYA2010-21322-C03-02). JD acknowledges support from the Spanish Ministry of Economy and Competitiveness (MINECO) through grants AYA2010-21766-C03-02, AYA2012-30789, and the Consolider-Ingenio project CSD2010-00064 (EPI: Exploring the Physics of Inflation). YA is financially supported by the Spanish Ramón y Cajal programme (RyC-2011-09461) and grant AYA2013-47742-C4-3-P (MINECO), as well as the ‘Study of Emission-Line Galaxies with Integral-Field Spectroscopy’ (SELGIFS) exchange programme, funded by the EU through the IRSES scheme (FP7-PEOPLE-2013-IRSES-612701). BA acknowledges financial support for a postdoctoral fellowship from the Observatory of Paris.Peer reviewe

Multi-particle states of semiconductor hexagonal rings: Artificial benzene

We present a theoretical and numerical investigation of correlated multi-electron states of hexagonal semiconductor rings. Both single-particle and correlated states show localization patterns in the six corners and energy spectra degeneracies corresponding to a hexagonal benzene ring. Thus, our results can aid the interpretation of energy-loss or near-field experiments that, in turn, shed light on the nature of molecular few-particle orbitals of artificial benzene. Surprisingly, we find that charges get more localized in the corners as the number of electrons increases, up to six, this indicating the deficiency of a picture based on orbitals delocalized on the whole ring. We also expose the presence of several spin-correlated states and the effect of an asymmetry of the syste

Cool Core Clusters from Cosmological Simulations

We present results obtained from a set of cosmological hydrodynamic simulations of galaxy clusters, aimed at comparing predictions with observational data on the diversity between cool-core (CC) and non-cool-core (NCC) clusters. Our simulations include the effects of stellar and AGN feedback and are based on an improved version of the smoothed particle hydrodynamics code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical instabilities by including a suitable artificial thermal diffusion. In this Letter, we focus our analysis on the entropy profiles, the primary diagnostic we used to classify the degree of cool-coreness of clusters, and on the iron profiles. In keeping with observations, our simulated clusters display a variety of behaviors in entropy profiles: they range from steadily decreasing profiles at small radii, characteristic of cool-core systems, to nearly flat core isentropic profiles, characteristic of non-cool-core systems. Using observational criteria to distinguish between the two classes of objects, we find that they occur in similar proportions in both simulations and in observations. Furthermore, we also find that simulated cool-core clusters have profiles of iron abundance that are steeper than those of NCC clusters, which is also in agreement with observational results. We show that the capability of our simulations to generate a realistic cool-core structure in the cluster population is due to AGN feedback and artificial thermal diffusion: their combined action allows us to naturally distribute the energy extracted from super-massive black holes and to compensate for the radiative losses of low-entropy gas with short cooling time residing in the cluster core.Comment: 6 pages, 4 figures, accepted in ApJL, v2 contains some modifications on the text (results unchanged

An improved SPH scheme for cosmological simulations

We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for simulations of galaxies and the large-scale structure. In particular, we combine, implement, modify and test a vast majority of SPH improvement techniques in the latest instalment of the GADGET code. We use the Wendland kernel functions, a particle wake-up time-step limiting mechanism and a time-dependent scheme for artificial viscosity, which includes a high-order gradient computation and shear flow limiter. Additionally, we include a novel prescription for time-dependent artificial conduction, which corrects for gravitationally induced pressure gradients and largely improves the SPH performance in capturing the development of gas-dynamical instabilities. We extensively test our new implementation in a wide range of hydrodynamical standard tests including weak and strong shocks as well as shear flows, turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas clouds. We jointly employ all modifications; however, when necessary we study the performance of individual code modules. We approximate hydrodynamical states more accurately and with significantly less noise than standard SPH. Furthermore, the new implementation promotes the mixing of entropy between different fluid phases, also within cosmological simulations. Finally, we study the performance of the hydrodynamical solver in the context of radiative galaxy formation and non-radiative galaxy cluster formation. We find galactic disks to be colder, thinner and more extended and our results on galaxy clusters show entropy cores instead of steadily declining entropy profiles. In summary, we demonstrate that our improved SPH implementation overcomes most of the undesirable limitations of standard SPH, thus becoming the core of an efficient code for large cosmological simulations.Comment: 21 figures, 2 tables, accepted to MNRA

Isospin phases of vertically coupled double quantum rings under the influence of perpendicular magnetic fields

Vertically coupled double quantum rings submitted to a perpendicular magnetic field $B$ are addressed within the local spin-density functional theory. We describe the structure of quantum ring molecules containing up to 40 electrons considering different inter-ring distances and intensities of the applied magnetic field. When the rings are quantum mechanically strongly coupled, only bonding states are occupied and the addition spectrum of the artificial molecules resembles that of a single quantum ring, with some small differences appearing as an effect of the magnetic field. Despite the latter has the tendency to flatten the spectra, in the strong coupling limit some clear peaks are still found even when $B\neq 0$ that can be interpretated from the single-particle energy levels analogously as at zero applied field, namely in terms of closed-shell and Hund's-rule configurations. Increasing the inter-ring distance, the occupation of the first antibonding orbitals washes out such structures and the addition spectra become flatter and irregular. In the weak coupling regime, numerous isospin oscillations are found as a function of $B$.Comment: 27 pages, 11 figures. To be published in Phys. Rev.