Comparing observed and modelled growth of larval herring (Clupea harengus): Testing individual-based model parameterisations

Experiments that directly test larval fish individual-based model (IBM) growth predictions are uncommon since it is difficult to simultaneously measure all relevant metabolic and behavioural attributes. We compared observed and modelled somatic growth of larval herring (Clupea harengus) in short-term (50 degree-day) laboratory trials conducted at 7 and 13°C in which larvae were either unfed or fed ad libitum on different prey sizes (~100 to 550 μm copepods, Acartia tonsa). The larval specific growth rate (SGR, % DW d-1) was generally overestimated by the model, especially for larvae foraging on large prey items. Model parameterisations were adjusted to explore the effect of 1) temporal variability in foraging of individuals, and 2) reduced assimilation efficiency due to rapid gut evacuation at high feeding rates. With these adjustments, the model described larval growth well across temperatures, prey sizes, and larval sizes. Although the experiments performed verified the growth model, variability in growth and foraging behaviour among larvae shows that it is necessary to measure both the physiology and feeding behaviour of the same individual. This is a challenge for experimentalists but will ultimately yield the most valuable data to adequately model environmental impacts on the survival and growth of marine fish early life stages. Comparación entre crecimiento observado y predicho de larvas de arenque (Clupea harengus): analizando parametrizaciones de modelos basados en individuos. – Los experimentos que analizan directamente las predicciones de crecimiento generadas por modelos basados en individuos (IBM) son poco comunes puesto que resulta difícil medir simultáneamente todos los atributos metabólicos y conductuales. En este estudio, comparamos el crecimiento somático observado y el estimado a partir de modelos de larvas de arenque (Clupea harengus) en experimentos de laboratorio a corto plazo (50 grados-día) a 7 y 13°en los que las larvas fueron mantenidas en condiciones de ayuno o recibieron alimentación ad libitum con diferentes tamaños de presa (copépodos, Acartia tonsa, de aproximadamente 100 a 500 μm). Las estimas de tasa específica de crecimiento (SGR, % de peso seco por día) fueron, en general, sobreestimadas por el modelo, especialmente para larvas que se alimentaron con presas grandes. estimas del modelo se ajustaron a dos escenarios para explorar el efecto de 1) variabilidad temporal en la alimentación de las larvas, y 2) disminución en la eficiencia de asimilación debida una rápida evacuación del tubo digestivo a tasas de alimentación altas. Con estos ajustes, el modelo describió bien el crecimiento larvario para temperaturas, tamaños de presa y edades de las larvas, indicando que las parametrizaciones metabólicas son robustas. Aunque los experimentos llevados a cabo con grupos de larvas verificaron los modelos de crecimiento, la variabilidad en el crecimiento y conducta de alimentación entre larvas sometidas a las mismas condiciones ambientales ponen de relieve la necesidad de que las medidas fisiológicas y de conducta vayan emparejadas y sean tomadas a nivel individual. Esto representa un reto para los experimentalistas, pero a largo plazo generará datos valiosos para los modeladores encargados de simular efectos ambientales sobre las tasas vitales de estadíos tempranos de desarrollo de peces marinos

Coexistence of multi-photon processes and longitudinal couplings in superconducting flux qubits

In contrast to natural atoms, the potential energies for superconducting flux qubit (SFQ) circuits can be artificially controlled. When the inversion symmetry of the potential energy is broken, we find that the multi-photon processes can coexist in the multi-level SFQ circuits. Moreover, there are not only transverse but also longitudinal couplings between the external magnetic fields and the SFQs when the inversion symmetry of potential energy is broken. The longitudinal coupling would induce some new phenomena in the SFQs. Here we will show how the longitudinal coupling can result in the coexistence of multi-photon processes in a two-level system formed by a SFQ circuit. We also show that the SFQs can become transparent to the transverse coupling fields when the longitudinal coupling fields satisfy the certain conditions. We further show that the quantum Zeno effect can also be induced by the longitudinal coupling in the SFQs. Finally we clarify why the longitudinal coupling can induce coexistence and disappearance of single- and two-photon processes for a driven SFQ, which is coupled to a single-mode quantized field.Comment: 11 pages, 6 figure

Temperature effects on vital rates of different life stages and implications for population growth of Baltic sprat

Baltic sprat (Sprattus sprattus balticus S.) is a key species in the pelagic ecosystem of the Baltic Sea. Most stocks of small pelagic species are characterized by natural, fishery-independent fluctuations, which make it difficult to predict stock development. Baltic sprat recruitment is highly variable, which can partly be related to climate-driven variability in hydrographic conditions. Results from experimental studies and field observations demonstrate that a number of important life history traits of sprat are affected by temperature, especially the survival and growth of early life stages. Projected climate-driven warming may impact important processes affecting various life stages of sprat, from survival and development during the egg and larval phases to the reproductive output of adults. This study presents a stage-based matrix model approach to simulate sprat population dynamics in relation to different climate change scenarios. Data obtained from experimental studies and field observations were used to estimate and incorporate stage-specific growth and survival rates into the model. Model-based estimates of population growth rate were affected most by changes in the transition probability of the feeding larval stage at all temperatures (+0, +2, +4, +6 °C). The maximum increase in population growth rate was expected when ambient temperature was elevated by 4 °C. Coupling our stage-based model and more complex, biophysical individual-based models may reveal the processes driving these expected climate-driven changes in Baltic Sea sprat population dynamics

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

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

Two-photon cooling of a nonlinear quantum oscillator

The cooling effects of a nonlinear quantum oscillator via its interaction with an artificial atom (qubit) are investigated. The quantum dissipations through the environmental reservoir of the nonlinear oscillator are included, taking into account the nonlinearity of the qubit-oscillator interaction. For appropriate bath temperatures and the resonator's quality factors, we demonstrate effective cooling below the thermal background. As the photon coherence functions behave differently for even and odd photon number states, we describe a mechanism distinguishing those states. The analytical formalism developed is general and can be applied to a wide range of systems.Comment: 11 pages, 2 figure

Hidden biosphere in an oxygen-deficient Atlantic open ocean eddy: future implications of ocean deoxygenation on primary production in the eastern tropical North Atlantic

The eastern tropical North Atlantic (ETNA) is characterized by a highly productive coastal upwelling system and a moderate oxygen minimum zone with lowest open ocean oxygen (O2) concentrations of around 40 μmol kg−1. Only recently, the discovery of re-occurring mesoscale eddies with sometimes close to anoxic O2 concentrations (<1 μmol kg−1) and located just below the mixed layer challenged our understanding of O2 distribution and biogeochemical processes in this area. Here, we present the first metagenomic dataset from a deoxygenated anticyclonic modewater eddy in the open waters of the ETNA. In the eddy, we observed a significantly lower bacterial diversity compared to surrounding waters, along with a significant community shift. We detected enhanced primary productivity in the surface layer of the eddy indicated by elevated chlorophyll concentrations and increased carbon uptake rates up to three times as high as in surrounding waters. Carbon uptake below the euphotic zone correlated to the presence of a specific high-light ecotype of Prochlorococcus, which is usually underrepresented in the ETNA. Our combined data indicate that high primary production in the eddy fuels export production and the presence of a specific microbial community responsible for enhanced respiration at shallow depths, below the mixed layer base. Progressively decreasing O2 concentrations in the eddy were found to promote transcription of the key gene for denitrification, nirS, in the O2-depleted core waters. This process is usually absent from the open ETNA waters. In the light of future ocean deoxygenation our results show exemplarily that even distinct events of anoxia have the potential to alter microbial community structures and with that critically impact primary productivity and biogeochemical processes of oceanic water bodies

Sisyphus cooling and amplification by a superconducting qubit

Laser cooling of the atomic motion paved the way for remarkable achievements in the fields of quantum optics and atomic physics, including Bose-Einstein condensation and the trapping of atoms in optical lattices. More recently superconducting qubits were shown to act as artificial two-level atoms, displaying Rabi oscillations, Ramsey fringes, and further quantum effects. Coupling such qubits to resonators brought the superconducting circuits into the realm of quantum electrodynamics (circuit QED). It opened the perspective to use superconducting qubits as micro-coolers or to create a population inversion in the qubit to induce lasing behavior of the resonator. Furthering these analogies between quantum optical and superconducting systems we demonstrate here Sisyphus cooling of a low frequency LC oscillator coupled to a near-resonantly driven superconducting qubit. In the quantum optics setup the mechanical degrees of freedom of an atom are cooled by laser driving the atom's electronic degrees of freedom. Here the roles of the two degrees of freedom are played by the LC circuit and the qubit's levels, respectively. We also demonstrate the counterpart of the Sisyphus cooling, namely Sisyphus amplification. Parallel to the experimental demonstration we analyze the system theoretically and find quantitative agreement, which supports the interpretation and allows us to estimate system parameters.Comment: 7 pages, 4 figure