Fermionic collective excitations in a lattice gas of Rydberg atoms

We investigate the many-body quantum states of a laser-driven gas of Rydberg atoms confined to a large spacing ring lattice. If the laser driving is much stronger than the van-der-Waals interaction among the Rydberg sates, these many-body states are collective fermionic excitations. The first excited state is a spin-wave that extends over the entire lattice. We demonstrate that our system permits to study fermions in the presence of disorder although no external atomic motion takes place. We analyze how this disorder influences the excitation properties of the fermionic states. Our work shows a route towards the creation of complex many-particle states with atoms in lattices

Creating collective many-body states with highly excited atoms

We study the collective excitation of a gas of highly excited atoms confined to a large spacing ring lattice, where the ground and the excited states are coupled resonantly via a laser field. Our attention is focused on the regime where the interaction between the highly excited atoms is very weak in comparison to the Rabi frequency of the laser. We demonstrate that in this case the many-body excitations of the system can be expressed in terms of free spinless fermions. The complex many-particle states arising in this regime are characterized and their properties, e.g. their correlation functions, are studied. In addition we investigate how one can actually experimentally access some of these many-particle states by a temporal variation of the laser parameters.Comment: 10 pages, 7 figure

Parâmetros de consistência dos solos: seu estudo e avaliação ao longo de perfis pedológicos para aplicação na engenharia rodoviária.

Foram estudados os limites de consistencia dos solos ao longo de perfis pedologicos para aplicacao na engenharia rodoviaria. As amostras foram coletadas de horizontes superficiais e subsuperficiais em dez perfis de diferentes classes de solos. As analises das amostras foram efetuadas em laboratorio seguindo a rotina usada em pedologia. Foram determinados tambem, para cada horizonte considerado, os limites de liquidez(LL), plasticidade(LP) e contracao(LC); o indice de plasticidade(IP), e o grau de contracao(GC). A analise dos dados de laboratorio, aliada as observacoes de campo, demonstrou haver uma correlacao empirica, entre as razoes "% de argila/IP" ou "IP//% de argila" e as propriedades dos solos considerados quanto a conservacao das estradas, no caso dossolos com mais de 35% de argila no horizonte B. Essas relacoes poderiam funcionar como indicadores das qualidades desses solos para a implantacao de rodovias. Obteve-se tambem uma certa evidencia neste sentido, para esses mesmos solos, atraves de graficos elaborados para cada perfil.bitstream/item/62536/1/CNPS-BOL.-PESQ.-13-82.pd

Universal time-evolution of a Rydberg lattice gas with perfect blockade

We investigate the dynamics of a strongly interacting spin system that is motivated by current experimental realizations of strongly interacting Rydberg gases in lattices. In particular we are interested in the temporal evolution of quantities such as the density of Rydberg atoms and density-density correlations when the system is initialized in a fully polarized state without Rydberg excitations. We show that in the thermodynamic limit the expectation values of these observables converge at least logarithmically to universal functions and outline a method to obtain these functions. We prove that a finite one-dimensional system follows this universal behavior up to a given time. The length of this universal time period depends on the actual system size. This shows that already the study of small systems allows to make precise predictions about the thermodynamic limit provided that the observation time is sufficiently short. We discuss this for various observables and for systems with different dimensions, interaction ranges and boundary conditions.Comment: 16 pages, 3 figure

In silico evaluation of a control system and algorithm for automated insulin infusion in the ICU setting

<p>Abstract</p> <p>Background</p> <p>It is known that tight control of glucose in the Intensive Care Unit reduces morbidity and mortality not only in diabetic patients but also in those non-diabetics who become transiently hyperglycemic. Taking advantage of a recently marketed subcutaneous glucose sensor we designed an <it>Automatic Insulin Infusion System </it>(AIIS) for inpatient treatment, and tested its stability under simulated clinical conditions.</p> <p>Methods</p> <p>The system included: reference glucose, glucose sensor, insulin and glucose infusion controllers and emergency infusion logic. We carried out computer simulations using Matlab/Simulink^®, in both common and worst-case conditions.</p> <p>Results</p> <p>The system was capable of controlling glucose levels without entering in a phase of catastrophic instability, even under severe simulated challenges. Care was taken to include in all simulations the 5-10 minute delay of the subcutaneous glucose signal when compared to the real-time serum glucose signal, a well-known characteristic of all subcutaneous glucose sensors.</p> <p>Conclusions</p> <p>When tested <it>in-Silico</it>, a commercially available subcutaneous glucose sensor allowed the stable functioning of a proportional-derivative Automatic Insulin Infusion System, which was able to maintain glucose within acceptable limits when using a well-established glucose response model simulating a patient. Testing of the system <it>in vivo </it>using animal models is now warranted.</p

Stability of relative equilibria with singular momentum values in simple mechanical systems

A method for testing $G_\mu$-stability of relative equilibria in Hamiltonian systems of the form "kinetic + potential energy" is presented. This method extends the Reduced Energy-Momentum Method of Simo et al. to the case of non-free group actions and singular momentum values. A normal form for the symplectic matrix at a relative equilibrium is also obtained.Comment: Partially rewritten. Some mistakes fixed. Exposition improve

Tailoring accidental double bound states in the continuum in all-dielectric metasurfaces

Bound states in the continuum (BICs) have been thoroughly investigated due to their formally divergent Q-factor, especially those emerging in all-dielectric, nanostructured metasurfaces from symmetry protection at the $\Gamma$ point (in-plane wavevector $k_{||}=0$). Less attention has been paid to accidental BICs that may appear at any other $k_{||}\not =0$ in the band structure of supported modes, being in turn difficult to predict. Here we make use of a coupled electric/magnetic dipole model to determine analytical conditions for the emergence of accidental BICs, valid for any planar array of meta-atoms that can be described by dipolar resonances, which is the case of many nanostructures in the optical domain. This is explored for all-dielectric nanospheres through explicit analytical conditions that allow us in turn to predict accidental BIC positions in the parameter space $(\omega,\bf{k_{||}}$). Finally, such conditions are exploited to determine not only single, but also double (for both linear polarizations) accidental BICs occurring at the same position in the dispersion relation $\omega-\bf{k_{||}}$ for realistic semiconductor nanodisk meta-atoms. This might pave the way to a variety of BIC-enhanced light-matter interaction phenomena at the nanoscale such as lasing or non-linear conversion, that benefit from emerging at wavevectors away from the $\Gamma$ point (off-normal incidence) overlapping for both linear polarizations.Comment: 18 pages, 7 figure

Photonic Integrated Circuits for mmW Systems

The bandwidth of wireless networks needs to grow exponentially over the next decade, due to an increasingly interconnected and smart environment. By 2020 there will be 50 billion devices connected to the internet. Low-cost, compact and broadband wireless transceivers will be required. The current WiFi frequency bands do not have enough capacity and wireless communication needs to move to the millimeter-wavelength or sub-terahertz range. The use of all-electronic solutions becomes increasingly prohibitive, though, at these higher frequencies. Microwave photonic technology o®ers the bandwidth and carrier frequencies required for high- capacity wireless networks and remote sensing applications. In this paper, we will introduce our e®orts to leverage the advantages of microwave photonics and photonic integrated circuits to de- velop low-cost and ubiquitous wireless technology enabled by silicon photonics based transceivers