Single-qubit lasing and cooling at the Rabi frequency

For a superconducting qubit driven to perform Rabi oscillations and coupled to a slow electromagnetic or nano-mechanical oscillator we describe previously unexplored quantum optics effects. When the Rabi frequency is tuned to resonance with the oscillator the latter can be driven far from equilibrium. Blue detuned driving leads to a population inversion in the qubit and a bi-stability with lasing behavior of the oscillator; for red detuning the qubit cools the oscillator. This behavior persists at the symmetry point where the qubit-oscillator coupling is quadratic and decoherence effects are minimized. There the system realizes a "single-atom-two-photon laser".Comment: Replaced with final published version, fig. 2 compresse

Autoinsertion of soluble oligomers of Alzheimer's Aβ(1–42) peptide into cholesterol-containing membranes is accompanied by relocation of the sterol towards the bilayer surface

BACKGROUND: Soluble Alzheimer's Aβ oligomers autoinsert into neuronal cell membranes, contributing to the pathology of Alzheimer's Disease (AD), and elevated serum cholesterol is a risk factor for AD, but the reason is unknown. We investigated potential connections between these two observations at the membrane level by testing the hypothesis that Aβ(1–42) relocates membrane cholesterol. RESULTS: Oligomers of Aβ(1–42), but not the monomeric peptide, inserted into cholesterol-containing phosphatidylcholine monolayers with an anomalously low molecular insertion area, suggesting concurrent lipid rearrangement. Membrane neutron diffraction, including isomorphous replacement of specific lipid hydrogens with highly-scattering deuterium, showed that Aβ(1–42) insertion was accompanied by outward displacement of membrane cholesterol, towards the polar surfaces of the bilayer. Changes in the generalised polarisation of laurdan confirmed that the structural changes were associated with a functional alteration in membrane lipid order. CONCLUSION: Cholesterol is known to regulate membrane lipid order, and this can affect a wide range of membrane mechanisms, including intercellular signalling. Previously unrecognised Aβ-dependent rearrangement of the membrane sterol could have an important role in AD

Design of a unmanned aerial vehicle

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998.Includes bibliographical references.by Jean-Marc C. Hauss.M.Eng

Photon creation from vacuum and interactions engineering in nonstationary circuit QED

We study theoretically the nonstationary circuit QED system in which the artificial atom transition frequency, or the atom-cavity coupling, have a small periodic time modulation, prescribed externally. The system formed by the atom coupled to a single cavity mode is described by the Rabi Hamiltonian. We show that, in the dispersive regime, when the modulation periodicity is tuned to the `resonances', the system dynamics presents the dynamical Casimir effect, resonant Jaynes-Cummings or resonant Anti-Jaynes-Cummings behaviors, and it can be described by the corresponding effective Hamiltonians. In the resonant atom-cavity regime and under the resonant modulation, the dynamics is similar to the one occurring for a stationary two-level atom in a vibrating cavity, and an entangled state with two photons can be created from vacuum. Moreover, we consider the situation in which the atom-cavity coupling, the atomic frequency, or both have a small nonperiodic time modulation, and show that photons can be created from vacuum in the dispersive regime. Therefore, an analog of the dynamical Casimir effect can be simulated in circuit QED, and several photons, as well as entangled states, can be generated from vacuum due to the anti-rotating term in the Rabi Hamiltonian.Comment: 14 pages, 6 figures. Talk presented at the International Workshop "60 Years of Casimir Effect", 23 - 27 June, 2008, Brasili

Changing nutrient stoichiometry affects phytoplankton production, DOP accumulation and dinitrogen fixation – a mesocosm experiment in the eastern tropical North Atlantic

Ocean deoxygenation due to climate change may alter redox-sensitive nutrient cycles in the marine environment. The productive eastern tropical North Atlantic (ETNA) upwelling region may be particularly affected when the relatively moderate oxygen minimum zone (OMZ) deoxygenates further and microbially driven nitrogen (N) loss processes are promoted. Consequently, water masses with a low nitrogen to phosphorus (N : P) ratio could reach the euphotic layer, possibly influencing primary production in those waters. Previous mesocosm studies in the oligotrophic Atlantic Ocean identified nitrate availability as a control of primary production, while a possible co-limitation of nitrate and phosphate could not be ruled out. To better understand the impact of changing N : P ratios on primary production and N2 fixation in the ETNA surface ocean, we conducted land-based mesocosm experiments with natural plankton communities and applied a broad range of N : P ratios (2.67–48). Silicic acid was supplied at 15 µmol L−1 in all mesocosms. We monitored nutrient drawdown, biomass accumulation and nitrogen fixation in response to variable nutrient stoichiometry. Our results confirmed nitrate to be the key factor determining primary production. We found that excess phosphate was channeled through particulate organic matter (POP) into the dissolved organic matter (DOP) pool. In mesocosms with low inorganic phosphate availability, DOP was utilized while N2 fixation increased, suggesting a link between those two processes. Interestingly this observation was most pronounced in mesocosms where nitrate was still available, indicating that bioavailable N does not necessarily suppress N2 fixation. We observed a shift from a mixed cyanobacteria–proteobacteria dominated active diazotrophic community towards a diatom-diazotrophic association of the Richelia-Rhizosolenia symbiosis. We hypothesize that a potential change in nutrient stoichiometry in the ETNA might lead to a general shift within the diazotrophic community, potentially influencing primary productivity and carbon export

Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific Oceans

Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs). There are numerous feedbacks between oxygen concentrations, nutrient cycling and biological productivity; however, existing knowledge is insufficient to understand physical, chemical and biological interactions in order to adequately assess past and potential future changes. We investigated the pelagic biogeochemistry of OMZs in the eastern tropical North Atlantic and eastern tropical South Pacific during a series of cruise expeditions and mesocosm studies. The following summarizes the current state of research on the influence of low environmental oxygen conditions on marine biota, viruses, organic matter formation and remineralization with a particular focus on the nitrogen cycle in OMZ regions. The impact of sulfidic events on water column biogeochemistry, originating from a specific microbial community capable of highly efficient carbon fixation, nitrogen turnover and N2O production is further discussed. Based on our findings, an important role of sinking particulate organic matter in controlling the nutrient stochiometry of the water column is suggested. These particles can enhance degradation processes in OMZ waters by acting as microniches, with sharp gradients enabling different processes to happen in close vicinity, thus altering the interpretation of oxic and anoxic environments

Cortes comerciales y característica de la canal de borregos y cabritos suplementados con bloques multinutricionales

 Objective. Aimed to identify the weight and yield of the commercial cuts, muscularity, and adiposity in the carcasses of sheep and goats grazing in the Caatinga supplemented with different sources of supplementations; these include feed-blocks. Material and methods. Sixty non-castrated males an initial average body weight of 18.63 ± 1.93 kg were used: 30 goats and 30 sheep all animals did not have a defined breed standard (WDBS). The experimental design used was entirely randomized (DIC), in factorial scheme 3x2 (three types of supplementation: mineral salt, MBs and MBs + buffel hay, and two species: sheep and goats) and 10 replications. Animals were raised in a rangeland grazing system in an area with vegetation characteristic of Caatinga ecosystem under three types of supplementation: 1: only mineral salt; 2: Feed blocks (MBs); and 3: MBs + buffel hay There were measured the weight, yield and the components of left half-part of carcass of lambs and kids. Results. The sheep were superior to goats in carcass conformation, loin-eye area, index of muscularity of the leg and compactness index of the leg while the goats were superior to sheep in leg muscles weight. Conclusions. Sheep and Goats, when fed with supplementation of pasture feeding blocks in the Caatinga ecosystem; Supplementation with mineral salt and Multinutritional Blocks with and without Buffel can be used to improve herds in the caatinga, with similar results among the three. Sheep show more adiposity of meat than goats, in contrast, goats have higher musculature than sheep when fed with feed blocks.Objetivo. Con el objetivo de identificar el peso y rendimiento de los cortes comerciales, musculatura y adiposidad en las canales de borregos y cabritos pastando en la Caatinga suplementado con diferentes fuentes de suplementos; Estos incluyen bloques de alimentación. Material y métodos. Se utilizaron 60 machos no castrados con un peso corporal medio inicial de 18,63 ± 1,93 kg: 30 borregos y 30 cabritos, todos los animales no tenían un estándar de raza definido (WDBS). El diseño experimental utilizado fue totalmente al azar (DIC), en esquema factorial 3x2 (tres tipos de suplementación: sal mineral, MBs y MBs + heno buffel, y dos especies: borregos y cabritos) y 10 repeticiones. Los animales fueron criados en un sistema de pastoreo de pastizales en un área con vegetación característica del ecosistema de Caatinga bajo tres tipos de suplementación: 1: sal mineral solamente; 2: Bloques de alimentación (MBs); Y 3: MBs + heno buffel Se midió el peso, el rendimiento y los componentes de la mitad izquierda de la carcasa de corderos y cabritos. Resultados. Las cordeiros fueron superiores a las cabritos en conformación de carcasas, área de lomo, índice de musculatura de la pierna y índice de compacidad de la pierna mientras que las cabritos fueron superiores a las cordeiros en el peso de los músculos de las piernas. Conclusión. Cordeiros y cabritos, cuando se alimentan con suplementos de bloques de alimentación de pasto en el ecosistema de Caatinga; La suplementación con sal mineral y Bloques Multinutritivos con y sin Buffel puede ser utilizada para mejorar los rebaños en la caatinga, con resultados similares entre los tres. Las cordeiros muestran más adiposidad de carne que las cabritos, en contraste, las cabritos tienen mayor musculatura que las cordeiros cuando se alimentan con bloques de alimentación