Numerical renormalization group calculation of impurity internal energy and specific heat of quantum impurity models

We introduce a method to obtain the specific heat of quantum impurity models via a direct calculation of the impurity internal energy requiring only the evaluation of local quantities within a single numerical renormalization group (NRG) calculation for the total system. For the Anderson impurity model, we show that the impurity internal energy can be expressed as a sum of purely local static correlation functions and a term that involves also the impurity Green function. The temperature dependence of the latter can be neglected in many cases, thereby allowing the impurity specific heat, $C_{\rm imp}$, to be calculated accurately from local static correlation functions; specifically via $C_{\rm imp}=\frac{\partial E_{\rm ionic}}{\partial T} + 1/2\frac{\partial E_{\rm hyb}}{\partial T}$, where $E_{\rm ionic}$ and $E_{\rm hyb}$ are the energies of the (embedded) impurity and the hybridization energy, respectively. The term involving the Green function can also be evaluated in cases where its temperature dependence is non-negligible, adding an extra term to $C_{\rm imp}$. For the non-degenerate Anderson impurity model, we show by comparison with exact Bethe ansatz calculations that the results recover accurately both the Kondo induced peak in the specific heat at low temperatures as well as the high temperature peak due to the resonant level. The approach applies to multiorbital and multichannel Anderson impurity models with arbitrary local Coulomb interactions. An application to the Ohmic two state system and the anisotropic Kondo model is also given, with comparisons to Bethe ansatz calculations. The new approach could also be of interest within other impurity solvers, e.g., within quantum Monte Carlo techniques.Comment: 16 pages, 15 figures, published versio

Atmospheric neutrons

Contributions to fast neutron measurements in the atmosphere are outlined. The results of a calculation to determine the production, distribution and final disappearance of atmospheric neutrons over the entire spectrum are presented. An attempt is made to answer questions that relate to processes such as neutron escape from the atmosphere and C-14 production. In addition, since variations of secondary neutrons can be related to variations in the primary radiation, comment on the modulation of both radiation components is made

Living IoT: A Flying Wireless Platform on Live Insects

Sensor networks with devices capable of moving could enable applications ranging from precision irrigation to environmental sensing. Using mechanical drones to move sensors, however, severely limits operation time since flight time is limited by the energy density of current battery technology. We explore an alternative, biology-based solution: integrate sensing, computing and communication functionalities onto live flying insects to create a mobile IoT platform. Such an approach takes advantage of these tiny, highly efficient biological insects which are ubiquitous in many outdoor ecosystems, to essentially provide mobility for free. Doing so however requires addressing key technical challenges of power, size, weight and self-localization in order for the insects to perform location-dependent sensing operations as they carry our IoT payload through the environment. We develop and deploy our platform on bumblebees which includes backscatter communication, low-power self-localization hardware, sensors, and a power source. We show that our platform is capable of sensing, backscattering data at 1 kbps when the insects are back at the hive, and localizing itself up to distances of 80 m from the access points, all within a total weight budget of 102 mg.Comment: Co-primary authors: Vikram Iyer, Rajalakshmi Nandakumar, Anran Wang, In Proceedings of Mobicom. ACM, New York, NY, USA, 15 pages, 201

A Neuropsychoanalytical approach to the hard problem of consciousness

A neuropsychoanalytical approach to the ‘hard problem’ of consciousness revolves around the distinction between the subject and objects of consciousness. In contrast to the mainstream of cognitive science, neuropsychoanalysis prioritises the subject. The subject of consciousness is the indispensable page upon which its objects are inscribed. This has implications for our conception of the mental. The subjective being of consciousness is not registered in the classical exteroceptive modalities; it is not a cognitive representation, not a memory trace. Cognitive representations are ‘mental solids,’ embedded within subjective consciousness, and their tangible and visible (etc.) properties are projected onto reality. It is important to recognise that mental solids (e.g. the body-as-object) are no more real than the subjective being they are represented in (the body-as-subject). Moreover, pure subjectivity is not without content or quality. This aspect of consciousness is conventionally described quantitatively as the level of consciousness, ‘wakefulness’. But it feels like something to be awake. The primary modality of this aspect of consciousness is affect. Some implications of this frame of reference are discussed here, in broad brush strokes. This is an electronic version of an article published as Journal of Integrative Neuroscience, Volume 13, Issue 2, 2014, pp. 173-185. DOI: http://dx.doi.org/10.1142/S0219635214400032, © World Scientific Publishing Company, http://www.worldscientific.com/worldscinet/jin

Svep1 stabilizes developmental vascular anastomosis in reduced flow conditions

We report the discovery that flow and Svep1 are modulator of vessel anastomosis during developmental angiogenesis in zebrafish embryos. We show that loss of Svep1 and blood flow reduction both contribute to defective anastomosis of intersegmental vessels. We show that this defect in primary angiogenic sprouts is associated with an expansion of Apelin-positive tip cells and with reduced formation and lumenisation of the dorsal longitudinal anastomotic vessel. Mechanistically, our results suggest that flow and Svep1 act synergistically to modulate vascular network formation in the zebrafish trunk

Svep1 stabilises developmental vascular anastomosis in reduced flow conditions

Molecular mechanisms controlling the formation, stabilization and maintenance of blood vessel connections remain poorly defined. Here we identify blood flow and the large extracellular protein Svep1 as co-modulators of vessel anastomosis during developmental angiogenesis in zebrafish embryos. Both loss of Svep1 and blood flow reduction contribute to defective anastomosis of intersegmental vessels. The reduced formation and lumenisation of the dorsal longitudinal anastomotic vessel (DLAV) is associated with a compensatory increase in Vegfa/Vegfr pERK signalling, concomittant expansion of apelin-positive tip cells, but reduced expression of klf2. Experimentally, further increasing Vegfa/Vegfr signalling can rescue the DLAV formation and lumenisation defects, while its inhibition dramatically exacerbates the loss of connectivity. Mechanistically, our results suggest that flow and Svep1 co-regulate the stabilization of vascular connections, in part by modulating the Vegfa/Vegfr signalling pathway

Explicit differential characterization of the Newtonian free particle system in m > 1 dependent variables

In 1883, as an early result, Sophus Lie established an explicit necessary and sufficient condition for an analytic second order ordinary differential equation y_xx = F(x,y,y_x) to be equivalent, through a point transformation (x,y) --> (X(x,y), Y(x,y)), to the Newtonian free particle equation Y_XX = 0. This result, preliminary to the deep group-theoretic classification of second order analytic ordinary differential equations, was parachieved later in 1896 by Arthur Tresse, a French student of S. Lie. In the present paper, following closely the original strategy of proof of S. Lie, which we firstly expose and restitute in length, we generalize this explicit characterization to the case of several second order ordinary differential equations. Let K=R or C, or more generally any field of characteristic zero equipped with a valuation, so that K-analytic functions make sense. Let x in K, let m > 1, let y := (y^1, ..., y^m) in K^m and let y_xx^j = F^j(x,y,y_x^l), j = 1,...,m be a collection of m analytic second order ordinary differential equations, in general nonlinear. We provide an explicit necessary and sufficient condition in order that this system is equivalent, under a point transformation (x, y^1, ..., y^m) --> (X(x,y), Y^1(x,y),..., Y^m(x, y)), to the Newtonian free particle system Y_XX^1 = ... = Y_XX^m = 0. Strikingly, the (complicated) differential system that we obtain is of first order in the case m > 1, whereas it is of second order in S. Lie's original case m = 1.Comment: 76 pages, no figur