On noncommutative Nahm transform

Motivated by the recently observed relation between the physics of $D$-branes in the background of $B$-field and the noncommutative geometry we study the analogue of Nahm transform for the instantons on the noncommutative torus.Comment: Latex, 22 p

Icebergs boost phytoplankton growth in the Southern Ocean

Icebergs which calve from the Antarctic ice shelves and drift in the Southern Ocean deliver fresh water, dust and minerogenic particles to the surface ocean along the iceberg's path. Each of these components may have an effect on growth conditions for phytoplankton, as might the mechanical effects of the iceberg keel disturbing the water. Although anecdotal evidence and small-scale surveys suggest that drifting icebergs increase local primary production, no large-scale studies have reported on this possibility in detail. A combination of satellite and automated iceberg tracking data presented here shows that the probability of increased surface phytoplankton biomass was two-fold higher in the wake of a tracked iceberg compared to background biomass fluctuations. Only during the month of February were the effects of icebergs on surface biomass likely to be negative. These results confirm icebergs as a factor affecting phytoplankton in the Southern Ocean and highlight the need for detailed process studies so that responses to future changes in the Antarctic ice sheets may be predicted

Power spectra from an inflaton coupled to the Gauss-Bonnet term

We consider power-law inflation with a Gauss-Bonnet correction inspired by string theory. We analyze the stability of cosmological perturbations and obtain the allowed parameter space. We find that for GB-dominated inflation ultra-violet instabilities of either scalar or tensor perturbations show up on small scales. The Gauss-Bonnet correction with a positive (or negative) coupling may lead to a reduction (or enhancement) of the tensor-to-scalar ratio in the potential-dominated case. We place tight constraints on the model parameters by making use of the WMAP 5-year data.Comment: 5 pages, 4 figures, RevTeX, references added, published versio

Solomon Islands: Malaita Hub scoping report

The CGIAR Research Program (CRP) Aquatic Agricultural Systems (AAS) will target five countries, including Solomon Islands. The proposed hubs for Solomon Islands were to cover most provinces, referencing the Western, Central and Eastern regions. Scoping of the initial ‘Central’ hub was undertaken in Guadalcanal, Malaita and Central Islands provinces and this report details findings from all three. As scoping progressed however, it was agreed that, based on the AAS context and priority needs of each province and the Program’s capacity for full implementation, the Central Hub would be restricted to Malaita Province only and renamed “Malaita Hub”. Consistent in each AAS country, there are four steps in the program rollout: planning, scoping, diagnosis and design. Rollout of the Program in Solomon Islands began with a five month planning phase between August and December 2011, and scoping of the first hub began in January 2012. This report, the second to be produced during rollout, describes the findings from the scoping process between January and June 2012. This report marks the transition from the scoping phase to the diagnosis phase in which output from scoping was used to develop a hub level theory of change for identifying research opportunities. Subsequent reports detail in-depth analyses of gender, governance, nutrition and partner activities and discuss Program engagement with community members to identify grass-roots demand for research

Supersymmetry and localization

We study conditions under which an odd symmetry of the integrand leads to localization of the corresponding integral over a (super)manifold. We also show that in many cases these conditions guarantee exactness of the stationary phase approximation of such integrals.Comment: 16 pages, LATE

Energy efficiency of mmWave massive MIMO precoding with low-resolution DACs

With the congestion of the sub-6 GHz spectrum, the interest in massive multiple-input multiple-output (MIMO) systems operating on millimeter wave spectrum grows. In order to reduce the power consumption of such massive MIMO systems, hybrid analog/digital transceivers and application of low-resolution digital-to-analog/analog-to-digital converters have been recently proposed. In this work, we investigate the energy efficiency of quantized hybrid transmitters equipped with a fully/partially-connected phase-shifting network composed of active/passive phase-shifters and compare it to that of quantized digital precoders. We introduce a quantized single-user MIMO system model based on an additive quantization noise approximation considering realistic power consumption and loss models to evaluate the spectral and energy efficiencies of the transmit precoding methods. Simulation results show that partially-connected hybrid precoders can be more energy-efficient compared to digital precoders, while fully-connected hybrid precoders exhibit poor energy efficiency in general. Also, the topology of phase-shifting components offers an energy-spectral efficiency trade-off: active phase-shifters provide higher data rates, while passive phase-shifters maintain better energy efficiency.Comment: Published in IEEE Journal of Selected Topics in Signal Processin

Neuroendrines in pericardial organs of the crab, Cancer

Thesis (M.A.)--Boston UniversityThe pericardial organs are neurosecretory structures situated within the pericardial cavity of stomatopod and decapod crustaceans. Their location in the pericardium is such that blood approaching the heart must flow directly over them. This arrangement facilitates the distribution of pericardial organ secretions to all parts of the organism. It is not known how many different neurohormones are secreted by the pericardial organs, but at least one of these has been shown to act as a strong cardioexcitor. Electron microscopy of pericardial organs has revealed the presence of membrane-bounded granules, approximately 1500 A in diameter, which are believed to contain the neurosecretory material. An attempt was made here to isolate the cardiaexcitor by means of differential centrifugation of crude 0.9 M sucrose homogenates of pericardial organs from two species of Cancer. Live Homarus heart served as bioassay material. Cardioexci tatory effects were found in material which sedimented below 17,000 x g. On two occasions another active sediment was found at 71,000 x g. The present data is in agreement with the hypothesis that the cardioexcitor is contained within neurosecretory granules. However, a definitive statement to this effect cannot be made, as sediments were not checked microscopically. Presumptive evidence is offered for the existence of a second type of neurosecretory granule