Kinetic energy of a trapped Fermi gas interacting with a Bose-Einstein condensate

We study a confined mixture of bosons and fermions in the regime of quantal degeneracy, with particular attention to the effects of the interactions on the kinetic energy of the fermionic component. We are able to explore a wide region of system parameters by identifying two scaling variables which completely determine its state at low temperature. These are the ratio of the boson-fermion and boson-boson interaction strengths and the ratio of the radii of the two clouds. We find that the effect of the interactions can be sizeable for reasonable choices of the parameters and that its experimental study can be used to infer the sign of the boson-fermion scattering length. The interplay between interactions and thermal effects in the fermionic kinetic energy is also discussed.Comment: REVTEX, 8 pages, 6 figures included. Small corrections to text and figures, accepted for publication in EPJ

Temperature-dependent density profiles of trapped boson-fermion mixtures

We present a semiclassical three-fluid model for a Bose-condensed mixture of interacting Bose and Fermi gases confined in harmonic traps at finite temperature. The model is used to characterize the experimentally relevant behaviour of the equilibrium density profile of the fermions with varying composition and temperature across the onset of degeneracy, for coupling strengths relevant to a mixture of $^{39}$K and $^{40}$K atoms.Comment: 9 pages, 2 postscript figures, accepted for publication in Eur. Phys. Jour.

Conformal Field Theories in Fractional Dimensions

We study the conformal bootstrap in fractional space-time dimensions, obtaining rigorous bounds on operator dimensions. Our results show strong evidence that there is a family of unitary CFTs connecting the 2D Ising model, the 3D Ising model, and the free scalar theory in 4D. We give numerical predictions for the leading operator dimensions and central charge in this family at different values of D and compare these to calculations of phi^4 theory in the epsilon-expansion.Comment: 11 pages, 4 figures - references updated - one affiliation modifie

Skill assessment of the PELAGOS global ocean biogeochemistry model over the period 1980–2000

Global Ocean Biogeochemistry General Circulation Models are useful tools to study biogeochemical processes at global and large scales under current climate and future scenario conditions. The credibility of future estimates is however dependent on the model skill in capturing the observed multi-annual variability of firstly the mean bulk biogeochemical properties, and secondly the rates at which organic matter is processed within the food web. For this double purpose, the results of a multi-annual simulation of the global ocean biogeochemical model PELAGOS have been objectively compared with multi-variate observations from the last 20 years of the 20th century, both considering bulk variables and carbon production/consumption rates. Simulated net primary production (NPP) is comparable with satellite-derived estimates at the global scale and when compared with an independent data-set of in situ observations in the equatorial Pacific. The usage of objective skill indicators allowed us to demonstrate the importance of comparing like with like when considering carbon transformation processes. NPP scores improve substantially when in situ data are compared with modeled NPP which takes into account the excretion of freshly-produced dissolved organic carbon (DOC). It is thus recommended that DOC measurements be performed during in situ NPP measurements to quantify the actual production of organic carbon in the surface ocean. The chlorophyll bias in the Southern Ocean that affects this model as well as several others is linked to the inadequate representation of the mixed layer seasonal cycle in the region. A sensitivity experiment confirms that the artificial increase of mixed layer depths towards the observed values substantially reduces the bias. Our assessment results qualify the model for studies of carbon transformation in the surface ocean and metabolic balances. Within the limits of the model assumption and known biases, PELAGOS indicates a net heterotrophic balance especially in the more oligotrophic regions of the Atlantic during the boreal winter period. However, at the annual time scale and over the global ocean, the model suggests that the surface ocean is close to a weakly positive autotrophic balance in accordance with recent experimental findings and geochemical considerations

Universal constraints on conformal operator dimensions

We continue the study of model-independent constraints on the unitary conformal field theories (CFTs) in four dimensions, initiated in. Our main result is an improved upper bound on the dimension Δ of the leading scalar operator appearing in the operator product expansion (OPE) of two identical scalars of dimension d: φ d≠1+O δ+.... In the interval 1<1.7 this universal bound takes the form Δ≤2+0.7(d-1)1/2+2. 1(d-1)+0.43(d-1)3/2. The proof is based on prime principles of CFT: unitarity, crossing symmetry, OPE, and conformal block decomposition. We also discuss possible applications to particle phenomenology and, via a 2D analogue, to string theory. © 2009 The American Physical Society

A process-oriented model study of equatorial Pacific phytoplankton: the role of iron supply and tropical instability waves

The response of phytoplankton growth to iron supply and its modulation by large-scale circulation and tropical instability waves (TIWs) in the eastern equatorial Pacific has been investigated with an ocean biogeochemical model. This process study shows that iron can be efficiently advected from the New Guinea shelf through the Equatorial Undercurrent (EUC) to the eastern Pacific. The presence of a continental iron source is necessary for the maintenance of the observed subsurface iron maximum in the EUC core. In the eastern Pacific region, phytoplankton production is enhanced when additional iron is available in the EUC. Simulated phytoplankton variability is linked to TIWs activity, as revealed by a wavelet analysis of the total autotrophic carbon. The net local effect of the waves on phytoplankton can be either positive or negative depending on several factors. When the iron nutricline is sufficiently shallow to be reached by the wave vertical scale, the effect of the waves is to enhance iron availability in the euphotic zone leading to a net local increase of phytoplankton biomass. We therefore suggest that the local maxima of phytoplankton observed in moorings off the Equator in the eastern Pacific might be not only the result of concentration mechanisms, but also the result of an increase in local production sustained by advected iron

A process-oriented model study of equatorial Pacific phytoplankton: the role of iron supply and tropical instability waves

The response of phytoplankton growth to iron supply and its modulation by large scale circulation and tropical instability waves (TIWs) in the eastern equatorial Pacific has been investigated with an ocean biogeochemistry model. This process study shows that iron can be efficiently advected from the New Guinea shelf through the Equatorial Undercurrent (EUC) to the eastern Pacific. In this region phytoplankton production is enhanced when an additional source of iron is applied in the New Guinea shelf and advected in the model by the EUC. In the eastern Pacific, phytoplankton variability is linked to TIWs activity, as revealed by a wavelet analysis of the total autotrophic carbon. The net local effect of the waves on phytoplankton can be either positive or negative depending on several fac- tors. In some cases the effect of the waves is to enhance iron availability in the euphotic zone leading to a net local increase of phytoplankton biomass, provided that the iron nu- tricline is sufficiently shallow to be reached by the wave vertical scale. In these cases it is also suggested that local maxima of phytoplankton observed in moorings off equator are sustained by advected iron and subsequent local production instead of being the result of concentration mechanisms

A generalized model of pelagic biogeochemistry for the global ocean ecosystem. Part I: theory

The set of equations for global ocean biogeochemistry deterministic models have been for-mulated in a comprehensive and unified form in order to use them in numerical simulations of the marine ecosystem for climate change studies (PELAGOS, PELAgic biogeochemistry for Global Ocean Simulations). The fundamental approach stems from the representation of marine trophic interactions and major biogeochemical cycles introduced in the European Regional Seas Ecosystem Model (ERSEM). Our theoretical formulation revisits and generalizes the stoichiometric approach of ERSEM by defining the state variables as Chemical Functional Families (CFF). CFFs are further subdivided into living, non-living and inorganic components. Living CFFs are the basis for the definition of Living Functional Groups, the biomass-based functional prototype of the real organisms. Both CFFs and LFGs are theoretical constructs which allow us to relate measurable properties of marine biogeochemistry to the state variables used in deterministic models. This approach is sufficiently generic that may be used to describe other existing biomass-based ecosystem model

A generalized model of pelagic biogeochemistry for the global ocean ecosystem. Part II: numerical simulations.

This paper presents a global ocean implementation of a multi-component model of marine pelagic biogeochemistry coupled on-line with an ocean general circulation model forced with climatological surface fields (PELAgic biogeochemistry for Global Ocean Simulations, PELAGOS). The final objective is the inclusion of this model as a component in an Earth System model for climate studies. The pelagic model is based on a functional stoichiometric representation of marine biogeochemical cycles and allows simulating the dynamics of C, N, P, Si, O and Fe taking into account the variation of their elemental ratios in the functional groups. The model also includes a parameterization of variable chlorophyll:carbon ratio in phytoplankton, carrying chl as a prognostic variable. The first part of the paper analyzes the contribution of non-local advective-diffusive terms and local vertical processes to the simulated chl distributions. The comparison of the three experiments shows that the mean chl distribution at higher latitudes is largely determined by mixing processes, while vertical advection dominates the distribution in the equatorial upwelling regions. Horizontal advective and diffusive processes are necessary mechanisms for the shape of chl distribution in the sub-tropical Pacific. In the second part, the results have been compared with existing datasets of satellite-derived chlorophyll, surface nutrients, estimates of phytoplankton community composition and primary production data. The agreement is reasonable both in terms of the spatial distribution of annual means and seasonal variability in different dynamical oceanographic regions. Results indicate that some of the model biases in chl and surface nutrients distributions can be related to deficiencies in the simulation of physical processes such as advection and mixing. Other discrepancies are attributed to inadequate parameterizations of phytoplankton functional groups. The model has skill in reproducing the overall distribution of large and small phytoplankton but tends to underestimate diatoms in the northern higher latitudes and overestimate nanophytoplankton with respect to picoautotrophs in oligotrophic regions. The performance of the model is discussed in the context of its use in climate studies and an approach for improving the parameterization of functional groups in deterministic models is outlined

I Annual Workshop INSA-UB "The Universe of the Olive Oil" held in the Food and Nutrition Torribera Campus of the University of Barcelona, Spain, 11th November 2015

The Institute for Research on Nutrition and Food Safety (INSA-UB) was formed by research groups belonging to the Faculties of Pharmacy, Biology, Chemistry and Geography and History, as well as other UB-affiliated centers and hospitals. INSA-UB was created to meet the current society's needs for research, training and service provision in sectors related to the agro-food industry. Due to its nutritional, gastronomic, cultural and economic value, olive oil is a product of particular importance within the Mediterranean region. In order to disseminate the latest findings on different analytical and legal regulation aspects, as well as on the healthy properties of extra virgin olive oil, INSA-UB organized the workshop "The Universe of Olive Oil". Researchers from universities, hospitals and research centres, as well as a wide range of representatives of the Catalan administration, olive oil costumers and olive oil industry were brought together with the aim of strengthening the knowledge and cooperation, and to favor the interaction between the main stakeholders to promote actions for the valorization, innovation and development in this strategic area. About 100 representatives of the above mentioned sectors attended the Workshop, which was supported by the International Olive Council (IOC), the Faculty of Pharmacy of the University of Barcelona, and by the five Catalan Protected Designations of Origin of virgin olive oil. Experts from different research centers, together with promoters and representatives of the local government, presented their recent results and current trends about olive oil. The Workshop was organized into different sessions, focused on different topics: olive oil quality, authenticity and control, healthy effects and the role played within the 'Mediterranean culture gastronomy' understanding that the best option to face the key challenges of the sector is a comprehensive approach in which subject areas and all stakeholders can complement and enhance themselves