Optimized time-dependent perturbation theory for pulse-driven quantum dynamics in atomic or molecular systems

We present a time-dependent perturbative approach adapted to the treatment of intense pulsed interactions. We show there is a freedom in choosing secular terms and use it to optimize the accuracy of the approximation. We apply this formulation to a unitary superconvergent technique and improve the accuracy by several orders of magnitude with respect to the Magnus expansion.Comment: 4 pages, 2 figure

Strong Coupling Theory of Two Level Atoms in Periodic Fields

We present a new convergent strong coupling expansion for two-level atoms in external periodic fields, free of secular terms. As a first application, we show that the coherent destruction of tunnelling is a third-order effect. We also present an exact treatment of the high-frequency region, and compare it with the theory of averaging. The qualitative frequency spectrum of the transition probability amplitude contains an effective Rabi frequency.Comment: 4 pages with 3 figure

Added value of bleach sedimentation microscopy for diagnosis of tuberculosis: a cost-effectiveness study.

SETTING: Bleach sedimentation is a method used to increase the diagnostic yield of sputum microscopy for countries with a high prevalence of human immunodeficiency virus (HIV) infection and limited resources. OBJECTIVES: To compare the relative cost-effectiveness of different microscopy approaches in diagnosing tuberculosis (TB) in Kenya. METHODS: An analytical decision tree model including cost and effectiveness measures of 10 combinations of direct (D) and overnight bleach (B) sedimentation microscopy was constructed. Data were drawn from the evaluation of the bleach sedimentation method on two specimens (first on the spot [1] and second morning [2]) from 644 TB suspects in a peripheral health clinic. Incremental cost per smear-positive detected case was measured. Costs included human resources and materials using a micro-costing evaluation. RESULTS: All bleach-based microscopy approaches detected significantly more cases (between 23.3% for B1 and 25.9% for B1+B2) than the conventional D1+D2 approach (21.0%). Cost per tested case ranged between respectively euro 2.7 and euro 4.5 for B1 and B1+D2+B2. B1 and B1+B2 were the most cost-effective approaches. D1+B2 and D1+B1 were good alternatives to avoid using approaches exclusively based on bleach sedimentation microscopy. CONCLUSIONS: Among several effective microscopy approaches used, including sodium hypochlorite sedimentation, only some resulted in a limited increase in the laboratory workload and would be most suitable for programmatic implementation

Time Minimal Trajectories for a Spin 1/2 Particle in a Magnetic Field

In this paper we consider the minimum time population transfer problem for the $z$-component of the spin of a (spin 1/2) particle driven by a magnetic field, controlled along the x axis, with bounded amplitude. On the Bloch sphere (i.e. after a suitable Hopf projection), this problem can be attacked with techniques of optimal syntheses on 2-D manifolds. Let $(-E,E)$ be the two energy levels, and $|\Omega(t)|\leq M$ the bound on the field amplitude. For each couple of values $E$ and $M$, we determine the time optimal synthesis starting from the level $-E$ and we provide the explicit expression of the time optimal trajectories steering the state one to the state two, in terms of a parameter that can be computed solving numerically a suitable equation. For $M/E<<1$, every time optimal trajectory is bang-bang and in particular the corresponding control is periodic with frequency of the order of the resonance frequency $\omega_R=2E$. On the other side, for $M/E>1$, the time optimal trajectory steering the state one to the state two is bang-bang with exactly one switching. Fixed $E$ we also prove that for $M\to\infty$ the time needed to reach the state two tends to zero. In the case $M/E>1$ there are time optimal trajectories containing a singular arc. Finally we compare these results with some known results of Khaneja, Brockett and Glaser and with those obtained by controlling the magnetic field both on the $x$ and $y$ directions (or with one external field, but in the rotating wave approximation). As byproduct we prove that the qualitative shape of the time optimal synthesis presents different patterns, that cyclically alternate as $M/E\to0$, giving a partial proof of a conjecture formulated in a previous paper.Comment: 31 pages, 10 figures, typos correcte

Pulse-driven quantum dynamics beyond the impulsive regime

We review various unitary time-dependent perturbation theories and compare them formally and numerically. We show that the Kolmogorov-Arnold-Moser technique performs better owing to both the superexponential character of correction terms and the possibility to optimize the accuracy of a given level of approximation which is explored in details here. As an illustration, we consider a two-level system driven by short pulses beyond the sudden limit.Comment: 15 pages, 5 color figure

Tribological properties of room temperature fluorinated graphite heat-treated under fluorine atmosphere

This work is concerned with the study of the tribologic properties of room temperature fluorinated graphite heat-treated under fluorine atmosphere. The fluorinated compounds all present good intrinsic friction properties (friction coefficient in the range 0.05–0.09). The tribologic performances are optimized if the materials present remaining graphitic domains (influenced by the presence of intercalated fluorinated species) whereas the perfluorinated compounds, where the fluorocarbon layers are corrugated (armchair configuration of the saturated carbon rings) present higher friction coefficients. Raman analyses reveal that the friction process induces severe changes in the materials structure especially the partial re-building of graphitic domains in the case of perfluorinated compounds which explains the improvement of μ during the friction tests for these last materials

Pulse-driven near-resonant quantum adiabatic dynamics: lifting of quasi-degeneracy

We study the quantum dynamics of a two-level system driven by a pulse that starts near-resonant for small amplitudes, yielding nonadiabatic evolution, and induces an adiabatic evolution for larger amplitudes. This problem is analyzed in terms of lifting of degeneracy for rising amplitudes. It is solved exactly for the case of linear and exponential rising. Approximate solutions are given in the case of power law rising. This allows us to determine approximative formulas for the lineshape of resonant excitation by various forms of pulses such as truncated trig-pulses. We also analyze and explain the various superpositions of states that can be obtained by the Half Stark Chirped Rapid Adiabatic Passage (Half-SCRAP) process.Comment: 21 pages, 12 figure

Homelessness among older people: Assessing strategies and frameworks across Canada

Homelessness among older people is expected to rise as a result of unmet need and demographic change. Yet, strategies and responses to homelessness across Canada tend to focus on younger groups, overlooking the circumstances and needs of older people (i.e., age 50+). This article reports the results of a content analysis of government planning documents on homelessness conducted in 2014. A total of 42 local, provincial, and federal strategies were reviewed to assess the extent to which they recognized and targeted the needs of older people. Our review resulted in three categories of documents: 1) documents with no discussion of homelessness among older people (n=16; 38%); 2) documents with a minimal discussion of homelessness among older people (n=22; 55%); and 3) documents with a significant discussion of homelessness among older people (n=4; 7%). Results indicate that while many strategies are beginning to consider older people as a subgroup with unique needs, little action has been taken to develop comprehensive services and supports for this group. We conclude with a call to integrate the needs of diverse groups of older people into strategies to end homelessness and to develop programs and responses that are suitable for older people. L’itinérance parmi les personnes âgées: Évaluations des stratégies et des structures à travers le Canada RésuméIl est prévu que l’itinérance chez les personnes âgées augmentera au cours des prochaines années, en raison des changements démographiques et des besoins non comblés que l’on observe actuellement.  Malgré cela, les stratégies et les réponses à l’itinérance au Canada tendent à être centrées sur les populations plus jeunes, ignorant les besoins et réalités des personnes âgées. Cet article présente les résultats d’une analyse de contenu des stratégies canadiennes sur l’itinérance effectuée en 2014. 42 stratégies ont été recensées afin d’évaluer dans quelle mesure elles reconnaissaient et ciblaient les besoins des personnes âgées. Notre analyse regroupe en trois catégories les documents recensés : 1) les documents qui n’abordent pas l’itinérance chez les personnes âgées (n=16; 38 pour cent); 2) les documents  abordent très brièvement l’itinérance des personnes âgées (n=22; 55 pour cent); 3) les documents abordant de façon substantielle l’itinérance des personnes âgées (n=4; 7 pour cent). Les résultats indiquent que bien que plusieurs stratégies commencent à prendre en considération le fait que les personnes âgées constituent un sous-groupe qui présente des besoins particuliers, peu d’actions ont été entreprises afin de  développer des services et un soutien adaptés à leur réalité. Nous concluons en rappelant l’importance d’intégrer les besoins de différents groupes de personnes âgées aux stratégies qui visent à mettre fin à  l’itinérance et de développer des programmes et réponses qui sont adaptées à une population âgée. Mots Clefs : politique; pratique; vieillissement; exclusion sociale; pauvreté; logemen

Euclidean matrix theory of random lasing in a cloud of cold atoms

We develop an ab initio analytic theory of random lasing in an ensemble of atoms that both scatter and amplify light. The theory applies all the way from low to high density of atoms. The properties of the random laser are controlled by an Euclidean matrix with elements equal to the Green's function of the Helmholtz equation between pairs of atoms in the system. Lasing threshold and the intensity of laser emission are calculated in the semiclassical approximation. The results are compared to the outcome of the diffusion theory of random lasing.Comment: 6 pages, 4 figure

Time-dependent unitary perturbation theory for intense laser driven molecular orientation

We apply a time-dependent perturbation theory based on unitary transformations combined with averaging techniques, on molecular orientation dynamics by ultrashort pulses. We test the validity and the accuracy of this approach on LiCl described within a rigid-rotor model and find that it is more accurate than other approximations. Furthermore, it is shown that a noticeable orientation can be achieved for experimentally standard short laser pulses of zero time average. In this case, we determine the dynamically relevant parameters by using the perturbative propagator, that is derived from this scheme, and we investigate the temperature effects on the molecular orientation dynamics.Comment: 16 pages, 6 figure