Phase transitions for Quantum Markov Chains associated with Ising type models on a Cayley tree

The main aim of the present paper is to prove the existence of a phase transition in quantum Markov chain (QMC) scheme for the Ising type models on a Cayley tree. Note that this kind of models do not have one-dimensional analogous, i.e. the considered model persists only on trees. In this paper, we provide a more general construction of forward QMC. In that construction, a QMC is defined as a weak limit of finite volume states with boundary conditions, i.e. QMC depends on the boundary conditions. Our main result states the existence of a phase transition for the Ising model with competing interactions on a Cayley tree of order two. By the phase transition we mean the existence of two distinct QMC which are not quasi-equivalent and their supports do not overlap. We also study some algebraic property of the disordered phase of the model, which is a new phenomena even in a classical setting.Comment: 24 pages. arXiv admin note: text overlap with arXiv:1011.225

Secure Silicon: Towards Virtual Prototyping

Evaluating security vulnerabilities of software implementations at design step is of primary importance for applications developers, while it has received litte attention from scientific communauty. In this paper, we describe virtual prototyping of an implementation of Elliptic curve cryptography (ECC), aiming to make it secure against first-order horizontal and vertical side-channel attacks (SCAs). Reproducing information leakage as close to reality as possible requires bit- and clock-cycle accuracy, we got with Mentor Graphics Modelsim tool, simulating the execution of the ECC software implementations on PULPino, an open-source 32-bit microcontroller based on the recently released RISC-V instruction set architecture. For each clock cycle, we compute the number of bit toggles into microcontroller's registers, an image of the power consumption, and watch the program counter to identify the assembly instruction executed, then the corresponding C function. We first start with a naive double-and-add implementation relying on cryptographic primitives of the mbed TLS library, formerly PolarSSL before acquisition by ARM. The virtual analysis pinpoints differences in the way the double function on one side and the add function on the other side manage variables and internal operations, which can be used for horizontal SCAs. We propose some modifications of the C code, hence independent of the considered microcontroller, with an overhead extremely small compared to that of the double-and-add-always countermeasure. Then, we reiterate analyses, still for the mbed TLS library, but using the regular Montgomery ladder version, most used in practice as more efficient

Macroprudential Regulation and Systemic Capital Requirements

In the aftermath of the financial crisis, there is interest in reforming bank regulation such that capital requirements are more closely linked to a bank's contribution to the overall risk of the financial system. In our paper we compare alternative mechanisms for allocating the overall risk of a banking system to its member banks. Overall risk is estimated using a model that explicitly incorporates contagion externalities present in the financial system. We have access to a unique data set of the Canadian banking system, which includes individual banks' risk exposures as well as detailed information on interbank linkages including OTC derivatives. We find that systemic capital allocations can differ by as much as 50% from 2008Q2 capital levels and are not related in a simple way to bank size or individual bank default probability. Systemic capital allocation mechanisms reduce default probabilities of individual banks as well as the probability of a systemic crisis by about 25%. Our results suggest that financial stability can be enhanced substantially by implementing a systemic perspective on bank regulation.Financial stability

Understanding Systemic Risk: The Trade-Offs between Capital, Short-Term Funding and Liquid Asset Holdings

We offer a multi-period systemic risk assessment framework with which to assess recent liquidity and capital regulatory requirement proposals in a holistic way. Following Morris and Shin (2009), we introduce funding liquidity risk as an endogenous outcome of the interaction between market liquidity risk, solvency risk, and the funding structure of banks. To assess the overall impact of different mix of capital and liquidity, we simulate the framework under a severe but plausible macro scenario for different balance-sheet structures. Of particular interest, we find that (1) capital has a decreasing marginal effect on systemic risk, (2) increasing capital alone is much less effective in reducing liquidity risk than solvency risk, (3) high liquid asset holdings reduce the marginal effect of increasing short term liability on systemic risk, and (4) changing liquid asset holdings has little effect on systemic risk when short term liability is sufficiently low.Financial stability; Financial system regulation and policies

The Emergent Writes Back: Emergent Ethnic Self-History Recasting Dominant Ethnohistory in Khaled Hosseini’s Fiction

“Anglophone,” “Postcolonial,” Diasporic,” “Transnational,” “Ethnic,” “Multicultural,” “Cosmopolitan,” and “Emergent” are all umbrella terms that are used to lump together writers who write from the fringes of the Western center. Such writers, however various and different their literary productions are, create worlds in their stories and populate them with characters that defy and counteract many Western essentialist misconceptions about their homelands. In this context, and resonating with Salman Rushdie’s seminal statement— “the empire writes back to the center”—and Smaro Kamboureli’s “the diaspora writes back home” (30), I argue that “the emergent” also writes back as a response to the dominant mainstream discourse. This paper seeks to read Khaled Hosseini’s fiction as an exemplar of an emergent narrative that deals with Afghanistan’s ethnic self-history and voices the gory details that can only be perceived and mirrored through the lenses of an insider. Being a diasporic ethnic writer, Hosseini’s fiction discredits the Western ethnohistory that mainly offers an essentialist depiction of the writer’s homeland, typifying, thereby, the colonial discourse as dominant.