Deep Metric Learning and Image Classification with Nearest Neighbour Gaussian Kernels

We present a Gaussian kernel loss function and training algorithm for convolutional neural networks that can be directly applied to both distance metric learning and image classification problems. Our method treats all training features from a deep neural network as Gaussian kernel centres and computes loss by summing the influence of a feature's nearby centres in the feature embedding space. Our approach is made scalable by treating it as an approximate nearest neighbour search problem. We show how to make end-to-end learning feasible, resulting in a well formed embedding space, in which semantically related instances are likely to be located near one another, regardless of whether or not the network was trained on those classes. Our approach outperforms state-of-the-art deep metric learning approaches on embedding learning challenges, as well as conventional softmax classification on several datasets.Comment: Accepted in the International Conference on Image Processing (ICIP) 2018. Formerly titled Nearest Neighbour Radial Basis Function Solvers for Deep Neural Network

Constructing Kurdistan: Cross-Border Kurdish Relations and Ethnic Identity

This thesis examines the emergence and politicization of ethnic identity in the Kurdish populations of Turkey, Iraq, Iran, and Syria. Through a historical analysis of Kurdish revolts and nationalist movements the late imperial and colonial eras, it demonstrates that ‘Kurdishness’, or Kurdayetî, has been instrumentalized as ethnonationalism primarily in a defensive capacity, in response to external coercive pressures forcing the Kurds to ‘think like a state’ and view themselves in increasingly ethnopolitical terms. By illustrating the extent to which ethnonationalism was imposed upon the Kurdish people and the limited appeal it enjoyed in the first half of the twentieth century, I aim to repudiate a ‘cliched constructivism’ prevalent in explanatory international relations as problematized by Rogers Brubaker. While most contemporary scholars of nationalism acknowledge the artificiality of the state, many depict ‘ethnic ties’ as the ostensibly ancient and natural proclivities upon which modern political communities are constructed. An objective analysis of early Kurdish nationalism, however, will demonstrate that ethnic linkages had little relevance in the emergence of Kurdish political sentiments and that the retrospective misunderstanding of Kurdish separatism as naturally occurring is rooted in a groupist doxa upheld by the socialized reinforcement of the ethnonational state as the default unit of political organization. Building upon this historical analysis, the thesis will proceed to examine the emergence of contemporary Kurdish political parties and separatist movements, all the while placing them in the local and global political contexts that produce them. It will demonstrate that, despite a perception by governments and scholars alike that Kurds would form collaborative co-ethnic dyads when given the opportunity, disparate Kurdish political parties prioritize their own strategic interests over those of their ethnic brethren, even when doing so requires the subjugation or elimination of rival Kurdish forces. Ultimately, the project will conclude by applying the theoretical and historical frameworks discussed above to two transversal dyads impacting the ‘Kurdish question’ in the Middle East today. By evaluating the similarities between the KRG’s relationship with the PYD and KDP and previous instances of pan-Kurdish interaction, this thesis will provide insights into the future of Kurdish movements in the Modern Middle East, which are likely to be plagued by the same structural constraints and a lack of organic solidarity that has inhibited transversal collaboration between the Kurds for more than a century

A new representation of the Adler function for lattice QCD

We address several aspects of lattice QCD calculations of the hadronic vacuum polarization and the associated Adler function. We implement a representation derived previously which allows one to access these phenomenologically important functions for a continuous set of virtualities, irrespective of the flavor structure of the current. Secondly we present a theoretical analysis of the finite-size effects on our particular representation of the Adler function, based on the operator product expansion at large momenta and on the spectral representation of the Euclidean correlator at small momenta. Finally, an analysis of the flavor structure of the electromagnetic current correlator is performed, where a recent theoretical estimate of the Wick-disconnected diagram contributions is rederived independently and confirmed.Comment: 9 pages, 5 figure

Charge transport and vector meson dissociation across the thermal phase transition in lattice QCD with two light quark flavors

We compute and analyze correlation functions in the isovector vector channel at vanishing spatial momentum across the deconfinement phase transition in lattice QCD. The simulations are carried out at temperatures $T/T_c=0.156, 0.8, 1.0, 1.25$ and $1.67$ with $T_c\simeq203$MeV for two flavors of Wilson-Clover fermions with a zero-temperature pion mass of $\simeq270$MeV. Exploiting exact sum rules and applying a phenomenologically motivated ansatz allows us to determine the spectral function $\rho(\omega,T)$ via a fit to the lattice correlation function data. From these results we estimate the electrical conductivity across the deconfinement phase transition via a Kubo formula and find evidence for the dissociation of the $\rho$ meson by resolving its spectral weight at the available temperatures. We also apply the Backus-Gilbert method as a model-independent approach to this problem. At any given frequency, it yields a local weighted average of the true spectral function. We use this method to compare kinetic theory predictions and previously published phenomenological spectral functions to our lattice study.Comment: 28 pages, 6 figure