Image segmentation using fuzzy LVQ clustering networks

In this note we formulate image segmentation as a clustering problem. Feature vectors extracted from a raw image are clustered into subregions, thereby segmenting the image. A fuzzy generalization of a Kohonen learning vector quantization (LVQ) which integrates the Fuzzy c-Means (FCM) model with the learning rate and updating strategies of the LVQ is used for this task. This network, which segments images in an unsupervised manner, is thus related to the FCM optimization problem. Numerical examples on photographic and magnetic resonance images are given to illustrate this approach to image segmentation

Financial Crises and Macro-Prudential Policies

Stochastic general equilibrium models of small open economies with occasionally binding financial frictions are capable of mimicking both the business cycles and the crisis events associated with the sudden stop in access to credit markets (Mendoza, 2010). In this paper we study the inefficiencies associated with borrowing decisions in a two-sector small open production economy. We find that this economy is much more likely to display "under-borrowing" rather than "over-borrowing" in normal times. As a result, macro-prudential policies (i.e. Tobin taxes or economy-wide controls on capital inflows) are costly in welfare terms in our economy. Moreover, we show that macro-prudential policies aimed at minimizing the probability of the crisis event might be welfare-reducing in production economies. Our analysis shows that there is a much larger scope for welfare gains from policy interventions during financial crises. That is to say that, within our modeling approach, ex post or crisis-management policies dominate ex ante or macro-prudential ones.Capital controls, crises, financial frictions, macro prudential policies, bailouts,overborrowing

Revisiting Overborrowing and its Policy Implications

This paper analyzes quantitatively the extent to which there is overborrowing (i.e., inefficient borrowing) in a business cycle model for emerging market economies with production and an occasionally binding credit constraint. The main finding of the analysis is that overborrowing is not a robust feature of this class of model economies: it depends on the structure of the economy and its parametrization. Specifically, we find underborrowing in a production economy with our baseline calibration, but overborrowing with more impatient agents and more volatile shocks. Endowment economies display overborrowing regardless of parameter values, but they do not allow for policy intervention when the constraint binds (in crisis times). Quantitatively, the welfare gains from implementing the constrained efficient allocation are always larger near crisis times than in normal

Structural Properties of the Caenorhabditis elegans Neuronal Network

Despite recent interest in reconstructing neuronal networks, complete wiring diagrams on the level of individual synapses remain scarce and the insights into function they can provide remain unclear. Even for Caenorhabditis elegans, whose neuronal network is relatively small and stereotypical from animal to animal, published wiring diagrams are neither accurate nor complete and self-consistent. Using materials from White et al. and new electron micrographs we assemble whole, self-consistent gap junction and chemical synapse networks of hermaphrodite C. elegans. We propose a method to visualize the wiring diagram, which reflects network signal flow. We calculate statistical and topological properties of the network, such as degree distributions, synaptic multiplicities, and small-world properties, that help in understanding network signal propagation. We identify neurons that may play central roles in information processing and network motifs that could serve as functional modules of the network. We explore propagation of neuronal activity in response to sensory or artificial stimulation using linear systems theory and find several activity patterns that could serve as substrates of previously described behaviors. Finally, we analyze the interaction between the gap junction and the chemical synapse networks. Since several statistical properties of the C. elegans network, such as multiplicity and motif distributions are similar to those found in mammalian neocortex, they likely point to general principles of neuronal networks. The wiring diagram reported here can help in understanding the mechanistic basis of behavior by generating predictions about future experiments involving genetic perturbations, laser ablations, or monitoring propagation of neuronal activity in response to stimulation

Molecular ion trap-depletion spectroscopy of BaCl+^+

We demonstrate a simple technique for molecular ion spectroscopy. BaCl$^+$ molecular ions are trapped in a linear Paul trap in the presence of a room-temperature He buffer gas and photodissociated by driving an electronic transition from the ground X$^1\Sigma^+$ state to the repulsive wall of the A$^1\Pi$ state. The photodissociation spectrum is recorded by monitoring the induced trap loss of BaCl$^+$ ions as a function of excitation wavelength. Accurate molecular potentials and spectroscopic constants are determined. Comparison of the theoretical photodissociation cross-sections with the measurement shows excellent agreement. This study represents the first spectroscopic data for BaCl$^+$ and an important step towards the production of ultracold ground-state molecular ions.Comment: 5 pages, 5 figure