Complex-valued Time Series Modeling for Improved Activation Detection in fMRI Studies

A complex-valued data-based model with th order autoregressive errors and general real/imaginary error covariance structure is proposed as an alternative to the commonly used magnitude-only data-based autoregressive model for fMRI time series. Likelihood-ratio-test-based activation statistics are derived for both models and compared for experimental and simulated data. For a dataset from a right-hand finger-tapping experiment, the activation map obtained using complex-valued modeling more clearly identifies the primary activation region (left functional central sulcus) than the magnitude-only model. Such improved accuracy in mapping the left functional central sulcus has important implications in neurosurgical planning for tumor and epilepsy patients. Additionally, we develop magnitude and phase detrending procedures for complex-valued time series and examine the effect of spatial smoothing. These methods improve the power of complex-valued data-based activation statistics. Our results advocate for the use of the complex-valued data and the modeling of its dependence structures as a more efficient and reliable tool in fMRI experiments over the current practice of using only magnitude-valued datasets

Particle-Hole Symmetry and the Bose Glass to Superfluid Transition

The generic Hamiltonian describing the zero temperature transition between the insulating Bose glass phase and the superfluid phase lacks particle-hole symmetry, but a statistical version of this symmetry is believed to be restored at the critical point. We show that the renormalization group relevance of particle-hole asymmetry may be explored in a controlled fashion only for small time dimensions, ετ≪1, where we find a stable particle-hole asymmetric and an unstable particle-hole symmetric fixed point, but we provide evidence that the two merge for some finite ετ≈2/3, which tends to confirm symmetry restoration at the physical ετ = 1

Integrals of motion for one-dimensional Anderson localized systems

Anderson localization is known to be inevitable in one dimension for generic disordered models. Since localization leads to Poissonian energy level statistics, we ask if localized systems possess "additional" integrals of motion as well, so as to enhance the analogy with quantum integrable systems. We answer this in the affirmative in the present work. We construct a set of nontrivial integrals of motion for Anderson localized models, in terms of the original creation and annihilation operators. These are found as a power series in the hopping parameter. The recently found Type-1 Hamiltonians, which are known to be quantum integrable in a precise sense, motivate our construction. We note that these models can be viewed as disordered electron models with infinite-range hopping, where a similar series truncates at the linear order. We show that despite the infinite range hopping, all states but one are localized. We also study the conservation laws for the disorder free Aubry-Andre model, where the states are either localized or extended, depending on the strength of a coupling constant. We formulate a specific procedure for averaging over disorder, in order to examine the convergence of the power series. Using this procedure in the Aubry-Andre model, we show that integrals of motion given by our construction are well-defined in localized phase, but not so in the extended phase. Finally, we also obtain the integrals of motion for a model with interactions to lowest order in the interaction.Comment: 23 pages, 5 figure

Stability of Bloch Oscillations in two coupled Bose-Einstein condensates

We investigate analytically, the stability of Bloch waves at the boundary of the first Brillouin zone in two coupled Bose-Einstein condensates confined in an optical lattice. Contrary to the single component case, we find here two critical density regimes which determine the stability of the Bloch waves. Breakdown of Bloch oscillations appear when n1/n2Nc2, here Nc1 and Nc2 are some critical values of n1/n2. There is an intermediate regime between Nc1 and Nc2 where the Bloch oscillations are stable and the condensates behave like single particles

Neutrinos in IceCube/KM3NeT as probes of Dark Matter Substructures in Galaxy Clusters

Galaxy clusters are one of the most promising candidate sites for dark matter annihilation. We focus on dark matter with mass in the range 10 GeV - 100 TeV annihilating to muon pairs, neutrino pairs, top pairs, or two neutrino pairs, and forecast the expected sensitivity to the annihilation cross section into these channels by observing galaxy clusters at IceCube/KM3NeT. Optimistically, the presence of dark matter substructures in galaxy clusters is predicted to enhance the signal by 2-3 orders of magnitude over the contribution from the smooth component of the dark matter distribution. Optimizing for the angular size of the region of interest for galaxy clusters, the sensitivity to the annihilation cross section of heavy DM with mass in the range 300 GeV - 100 TeV will be of the order of 10^{-24} cm^3 s^{-1}, for full IceCube/KM3NeT live time of 10 years, which is about one order of magnitude better than the best limit that can be obtained by observing the Milky Way halo. We find that neutrinos from cosmic ray interactions in the galaxy cluster, in addition to the atmospheric neutrinos, are a source of background. We show that significant improvement in the experimental sensitivity can be achieved for lower DM masses in the range 10 GeV - 300 GeV if neutrino-induced cascades can be reconstructed to approximately 5 degrees accuracy, as may be possible in KM3NeT. We therefore propose that a low-energy extension "KM3NeT-Core", similar to DeepCore in IceCube, be considered for an extended reach at low DM masses.Comment: v2: 17 pages, 5 figures. Neutrino spectra corrected, dependence on dark matter substructure model included, references added. Results unchanged. Accepted in PR

The Costs of Ecosystem Adaptation: Methodology and Estimates for Indian Forests

This paper presents a detailed methodology for estimating the cost of adaptation to climate change impacts on ecosystems. Up to date estimates are built-up following national investments in measures such as protected areas, with inaccurate estimates of the adaptation level needed. Here we propose a new methodology which identifies vulnerable areas due to climate impacts and the specific adaptation options feasible for these regions. An illustration of the methodology for shifts in forest ecosystems in India is presented. Advantages and future requirements for this methodology are finally discussed.Climate change, adaptation costs, forest ecosystems, India

Different aspects of cage culture management for sustainable fish production

A technological intervention has been the major impetus for the rapid development of cage farming of marine fishes across the world. In spite of the various technologies available for the fulfilment of high production and proper installation of the cages, it is necessary to optimise the many factors periodically to avoid the adverse impact of environmental and ecological factors for long maintenance of cages and also to maintain the healthy animals in the cage. In this context, monitoring plays vital role in any type of mariculture activity. Therefore, a well conceived and designed monitoring programme is needed to promote good growth of fishes and to obtain optimal production in a sustainable manner from cages. Cage monitoring is an integral part of the cage culture and it should be continued starting from the installation of the cage to till harvesting the fishes. The following are the major aspects where the cage monitoring is essential and it includes maintenance of cage and its accessories, stocking of the fish, feeding, fish husbandry, health management, water quality and harvesting