All-optical atom surface traps implemented with one-dimensional planar diffractive microstructures

We characterize the loading, containment and optical properties of all-optical atom traps implemented by diffractive focusing with one-dimensional (1D) microstructures milled on gold films. These on-chip Fresnel lenses with focal lengths of the order of a few hundred microns produce optical-gradient-dipole traps. Cold atoms are loaded from a mirror magneto-optical trap (MMOT) centered a few hundred microns above the gold mirror surface. Details of loading optimization are reported and perspectives for future development of these structures are discussed.Comment: 7 pages, 15 figure

Transient behavior of surface plasmon polaritons scattered at a subwavelength groove

We present a numerical study and analytical model of the optical near-field diffracted in the vicinity of subwavelength grooves milled in silver surfaces. The Green's tensor approach permits computation of the phase and amplitude dependence of the diffracted wave as a function of the groove geometry. It is shown that the field diffracted along the interface by the groove is equivalent to replacing the groove by an oscillating dipolar line source. An analytic expression is derived from the Green's function formalism, that reproduces well the asymptotic surface plasmon polariton (SPP) wave as well as the transient surface wave in the near-zone close to the groove. The agreement between this model and the full simulation is very good, showing that the transient "near-zone" regime does not depend on the precise shape of the groove. Finally, it is shown that a composite diffractive evanescent wave model that includes the asymptotic SPP can describe the wavelength evolution in this transient near-zone. Such a semi-analytical model may be useful for the design and optimization of more elaborate photonic circuits whose behavior in large part will be controlled by surface waves.Comment: 12 pages, 10 figure

Surface-wave interferometry on single subwavelength slit-groove structures fabricated on gold films

We apply the technique of far-field interferometry to measure the properties of surface waves generated by two-dimensional (2D) single subwavelength slit-groove structures on gold films. The effective surface index of refraction measured for the surface wave propagating over a distance of more than 12 microns is determined to be 1.016 with a measurement uncertainty of 0.004, to within experimental uncertainty of the expected bound surface plasmon-polariton (SPP) value for a Au/Air interface of 1.018. We compare these measurements to finite-difference-time-domain (FDTD) numerical simulations of the optical field transmission through these devices. We find excellent agreement between the measurements and the simulations for the surface index of refraction. The measurements also show that the surface wave propagation parameter exhibits transient behavior close to the slit, evolving smoothly from greater values asymptotically toward the value expected for the SPP over the first 2-3 microns of slit-groove distance. This behavior is confirmed by the FDTD simulations

The Bose-Einstein correlation function C2(Q)C_2(Q) from a Quantum Field Theory point of view

We show that a recently proposed derivation of Bose-Einstein correlations (BEC) by means of a specific version of thermal Quantum Field Theory (QFT), supplemented by operator-field evolution of the Langevin type, allows for a deeper understanding of the possible coherent behaviour of the emitting source and a clear identification of the origin of the observed shape of the BEC function $C_2(Q)$. Previous conjectures in this matter obtained by other approaches are confirmed and have received complementary explanation.Comment: Some misprints corrected. To be publishe in Phys. Rev.

Surface wave generation and propagation on metallic subwavelength structures measured by far-field interferometry

Transmission spectra of metallic films or membranes perforated by arrays of subwavelength slits or holes have been widely interpreted as resonance absorption by surface plasmon polaritons (SPPs). Alternative interpretations involving evanescent waves diffracted on the surface have also been proposed. These two approaches lead to divergent predictions for some surface wave properties. Using far-field interferometry, we have carried out a series of measurements on elementary one-dimensional (1-D) subwavelength structures with the aim of testing key properties of the surface waves and comparing them to predictions of these two points of view

Outcomes of an RCT of video‐conference vs. in‐person or in‐clinic nutrition and exercise in midlife adults with obesity

Objective New communication technologies have shown some promise in lifestyle weight loss interventions, but may be most effective when leveraging face‐to‐face communications. The study reported here sought to test whether weight loss program attendance and outcomes are greater when offered in‐person at community sites or remotely via videoconference versus in federally qualified health centers (FHQCs). In a three‐arm randomized trial among 150 FQHC adults, intervention delivery in community‐sites or via videoconference were tested against a clinic‐based lifestyle intervention (enhanced usual care [EUC]). Methods Twice weekly, a nutrition topic was reviewed, and exercise sessions were held in a 20‐week program delivered either in community settings or via videoconference. The primary outcome was the proportion of participants losing more than 2 kg at 6 (end of treatment) and 12 months in intent‐to‐treat analyses. Results Mean (SD) age was 53 (7) years, 82% were female, 65% were African‐American, 50% reported $18,000 or less household income, 49% tested low in health literacy, and mean (SD) body mass index was 39 (6) kg/m2. The proportion losing more than 2 kg of weight in the community site, videoconference, and EUC groups was 33%, 34%, and 24%, respectively at 6 months, and 29%, 34%, and 29% at 12 months. No differences reached significance. Attendance was poor in all groups; 45% of community site, 58% of videoconference, and 16% of EUC participants attended at least one session. Conclusion Videoconference and community‐based delivery were as effective as an FQHC‐based weight loss program

Large Extra Dimensions from a Small Extra Dimension

Models with extra dimensions have changed our understanding of the hierarchy problem. In general, these models explain the weakness of gravity by diluting gravity in a large bulk volume, or by localizing the graviton away from the standard model. In this paper, we show that the warped geometries necessary for the latter scenario can naturally induce the large volumes necessary for the former. We present a model in which a large volume is stabilized without supersymmetry. We comment on the phenomenology of this scenario and generalizations to additional dimensions.Comment: Some formulae altered, conclusions unchange

Sympathetic cooling and collisional properties of a Rb-Cs mixture

We report on measurements of the collisional properties of a mixture of $^{133}$Cs and $^{87}$Rb atoms in a magnetic trap at $\mu\mathrm{K}$ temperatures. By selectively evaporating the Rb atoms using a radio-frequency field, we achieved sympathetic cooling of Cs down to a few $\mu\mathrm{K}$. The inter-species collisional cross-section was determined through rethermalization measurements, leading to an estimate of $a_s=595 a_0$ for the s-wave scattering length for Rb in the $|F=2, m_F=2>$ and Cs in the $|F=4, m_F=4>$ magnetic states. We briefly speculate on the prospects for reaching Bose-Einstein condensation of Cs inside a magnetic trap through sympathetic cooling

The molecular and dusty composition of Betelgeuse's inner circumstellar environment

The study of the atmosphere of red supergiant stars in general and of Betelgeuse (alpha Orionis) in particular is of prime importance to understand dust formation and how mass is lost to the interstellar medium in evolved massive stars. A molecular shell, the MOLsphere (Tsuji, 2000a), in the atmosphere of Betelgeuse has been proposed to account for the near- and mid-infrared spectroscopic observations of Betelgeuse. The goal is to further test this hypothesis and to identify some of the molecules in this MOLsphere. We report on measurements taken with the mid-infrared two-telescope beam combiner of the VLTI, MIDI, operated between 7.5 and 13.5 $\mu$m. The data are compared to a simple geometric model of a photosphere surrounded by a warm absorbing and emitting shell. Physical characteristics of the shell are derived: size, temperature and optical depth. The chemical constituents are determined with an analysis consistent with available infrared spectra and interferometric data. We are able to account for the measured optical depth of the shell in the N band, the ISO-SWS spectrum and K and L band interferometric data with a shell whose inner and outer radii are given by the above range and with the following species: H2O, SiO and Al2O3. These results confirm the MOLsphere model. We bring evidence for more constituents and for the presence of species participating in the formation of dust grains in the atmosphere of the star, i.e. well below the distance at which the dust shell is detected. We believe these results bring key elements to the understanding of mass loss in Betelgeuse and red supergiants in general and bring support to the dust-driven scenario.Comment: 11 pages, 10 figures, accepted for publication in A&

Trying to Make Ends Meet: Reconciling the Law and Practice of Human Rights Amnesties Symposium - Human Rights in the Americas - Commentary.

The problem of amnesty for widespread human rights violations in the Americas illustrates the credibility gap in public international law. This Commentary reviews applicable standards and attempts to identify a minimum state response to past human rights violations. It also examines the question of amnesties, offers certain legal interpretations, and presents some criteria for an amnesty framework which might be reconcilable with the state’s international obligations. This Commentary’s aim is not to suggest amnesties are a proper response to the problem of past human rights abuses, however, it does acknowledge amnesties have so far been the most common response. It further recognizes the international community becoming increasingly involved in brokering or monitoring terms of transition. Such laws may gain a dangerous imprimatur of inevitability if not of legitimacy. Therefore, this Commentary articulates a less stringent, but defensible, interpretation of legal norms which might be demanded from governments and international bodies. This Commentary concludes by suggesting minimum requirements. The investigation should be the core of the remedy at issue. There are three components. First, an affirmative inquiry into the facts by the relevant authorities. Second, an opportunity for victims to come forth and tell their stories. Third, an adjudication of sorts—a formal finding of the facts and conclusions of relevant law. Amnesties have typically foreclosed the possibility of prosecution and have precluded civil remedies. Although politics may ultimately provide the opportunity for the ambitious undertaking suggested herein, legal application has its relevance as well. Political factors may determine how much can be accomplished; however, what is ultimately of greatest importance is for political space to be exploited to support the rule of law, even as the state absolves the guilty