A Distributed Approach to Interference Alignment in OFDM-based Two-tiered Networks

In this contribution, we consider a two-tiered network and focus on the coexistence between the two tiers at physical layer. We target our efforts on a long term evolution advanced (LTE-A) orthogonal frequency division multiple access (OFDMA) macro-cell sharing the spectrum with a randomly deployed second tier of small-cells. In such networks, high levels of co-channel interference between the macro and small base stations (MBS/SBS) may largely limit the potential spectral efficiency gains provided by the frequency reuse 1. To address this issue, we propose a novel cognitive interference alignment based scheme to protect the macro-cell from the cross-tier interference, while mitigating the co-tier interference in the second tier. Remarkably, only local channel state information (CSI) and autonomous operations are required in the second tier, resulting in a completely self-organizing approach for the SBSs. The optimal precoder that maximizes the spectral efficiency of the link between each SBS and its served user equipment is found by means of a distributed one-shot strategy. Numerical findings reveal non-negligible spectral efficiency enhancements with respect to traditional time division multiple access approaches at any signal to noise (SNR) regime. Additionally, the proposed technique exhibits significant robustness to channel estimation errors, achieving remarkable results for the imperfect CSI case and yielding consistent performance enhancements to the network.Comment: 15 pages, 10 figures, accepted and to appear in IEEE Transactions on Vehicular Technology Special Section: Self-Organizing Radio Networks, 2013. Authors' final version. Copyright transferred to IEE

Cognitive Interference Alignment for OFDM Two-tiered Networks

In this contribution, we introduce an interference alignment scheme that allows the coexistence of an orthogonal frequency division multiplexing (OFDM) macro-cell and a cognitive small-cell, deployed in a two-tiered structure and transmitting over the same bandwidth. We derive the optimal linear strategy for the single antenna secondary base station, maximizing the spectral efficiency of the opportunistic link, accounting for both signal sub-space structure and power loading strategy. Our analytical and numerical findings prove that the precoder structure proposed is optimal for the considered scenario in the face of Rayleigh and exponential decaying channels.Comment: 5 pages, 4 figures. Accepted and presented at the IEEE 13th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2012. Authors' final version. Copyright transferred to IEE

Cognitive Orthogonal Precoder for Two-tiered Networks Deployment

In this work, the problem of cross-tier interference in a two-tiered (macro-cell and cognitive small-cells) network, under the complete spectrum sharing paradigm, is studied. A new orthogonal precoder transmit scheme for the small base stations, called multi-user Vandermonde-subspace frequency division multiplexing (MU-VFDM), is proposed. MU-VFDM allows several cognitive small base stations to coexist with legacy macro-cell receivers, by nulling the small- to macro-cell cross-tier interference, without any cooperation between the two tiers. This cleverly designed cascaded precoder structure, not only cancels the cross-tier interference, but avoids the co-tier interference for the small-cell network. The achievable sum-rate of the small-cell network, satisfying the interference cancelation requirements, is evaluated for perfect and imperfect channel state information at the transmitter. Simulation results for the cascaded MU-VFDM precoder show a comparable performance to that of state-of-the-art dirty paper coding technique, for the case of a dense cellular layout. Finally, a comparison between MU-VFDM and a standard complete spectrum separation strategy is proposed. Promising gains in terms of achievable sum-rate are shown for the two-tiered network w.r.t. the traditional bandwidth management approach.Comment: 11 pages, 9 figures, accepted and to appear in IEEE Journal on Selected Areas in Communications: Cognitive Radio Series, 2013. Copyright transferred to IEE

Local firms’ strategies and cluster coopetition in Tuscany: the case of “Toscana Promozione” Agency

This study examines a new paradigm of coopetition strategy emerged in Tuscany, one of the most famous Italian area in the world for cultural and economic heritage. Nowadays, global success in business requires that firms implement both competitive and cooperative strategies (i.e. coopetition). This strategy, according to Ray Noorda (the founder of Novell – an American multinational software and services company headquartered in Provo, Utah), considers the advantages arising when both cooperation and competition coexist in the same domains. In the last twenty years, articles related to coopetition investigated several aspect of this strategy; in contrast, industry level coopetition has been investigated less than the other features (Rusko, 2011). Giving the literature review, there is a lack in knowledge regarding the benefits of coopetition fostered by local governments with foreign governments. This study presents a new approach of industry-level coopetition through the qualitative case study of the economic promotion agency in Tuscany, Toscana Promozione. The paper presents a new paradigm of coopetition strategy in where firms are in a coopetition relationship with foreign competitors (and governments) thanks to the support of local authorities. The main result of the research is that the boundary between institution and entrepreneur must be clear, government and local authorities must enforce competitiveness to improve the environment in which firms cooperate with the institution and compete each other with their own strategy. However during economic downturn periods, government and local authorities should, also, consider the possibility to become promoter, and supporter, of emerging entrepreneurship

Local firms’ strategies and cluster coopetition in Tuscany: the case of “Toscana Promozione” Agency

This study examines a new paradigm of coopetition strategy emerged in Tuscany, one of the most famous Italian area in the world for cultural and economic heritage. Nowadays, global success in business requires that firms implement both competitive and cooperative strategies (i.e. coopetition). This strategy, according to Ray Noorda (the founder of Novell – an American multinational software and services company headquartered in Provo, Utah), considers the advantages arising when both cooperation and competition coexist in the same domains. In the last twenty years, articles related to coopetition investigated several aspect of this strategy; in contrast, industry level coopetition has been investigated less than the other features (Rusko, 2011). Giving the literature review, there is a lack in knowledge regarding the benefits of coopetition fostered by local governments with foreign governments. This study presents a new approach of industry-level coopetition through the qualitative case study of the economic promotion agency in Tuscany, Toscana Promozione. The paper presents a new paradigm of coopetition strategy in where firms are in a coopetition relationship with foreign competitors (and governments) thanks to the support of local authorities. The main result of the research is that the boundary between institution and entrepreneur must be clear, government and local authorities must enforce competitiveness to improve the environment in which firms cooperate with the institution and compete each other with their own strategy. However during economic downturn periods, government and local authorities should, also, consider the possibility to become promoter, and supporter, of emerging entrepreneurship

Biochemical and spectroscopic analysis of two key proteins involved in FeS-clusters biogenesis

FeS clusters are ancient prosthetic groups, widely diffused in almost all living beings in which they are involved in several fundamental metabolic pathways, including redox reactions, electron transfer, enzyme catalysis and many other functions. This assortment is reflected in the presence of several FeS clusters with different structures, from the simple rhombic 2Fe2S and cubic 4Fe4S clusters, to the highly complex 2Fe[4Fe4S] H-cluster (metal cofactor of [FeFe]-hydrogenases). Distinct biosynthetic pathways for the assembly of different FeS clusters exist, in both prokaryotic and eukaryotic microorganisms. In general, these are rather complex processes carried out by many proteins interacting with each other. While keeping some key peculiarities, these systems are highly conserved in terms of action strategy, which can be generally divided in two main steps: the assembly of the metal cofactor on a scaffold protein, and the subsequent transfer of the de novo generated FeS cluster from the scaffold to the acceptor apoprotein, which is eventually converted into the mature active holoprotein. Both steps require key scaffold proteins, that must be able to dynamically interact with the biosynthetic partners as well as with a combination of several chaperones and co-chaperones which participate into the final transfer of the prosthetic group to the recipient FeS protein. Thus, the structural features of scaffold proteins allowing their interactions with all the functional partners are key points. However, for many of these fundamental proteins a clear structure-function relationship characterization is missing, and a complete characterization of the whole complex multistep molecular pathways in which they are functionally involved need a deeper investigation. In this PhD thesis, two different FeS clusters biosynthetic systems have been studied: in Chapter 1), the [FeFe]-hydrogenases maturation system and in Chapter 2), the human mitochondrial FeS clusters biosynthetic system. Chapter 1) [FeFe]-hydrogenases are FeS proteins that in several prokaryotes as well as in unicellular green algae catalyze the reversible reduction of protons to hydrogen gas. Thus, they received an increasing attention for potential technological applications in the field of biological production of clean and renewable fuel. A specific and highly conserved biosynthetic system is required to assemble the complex [FeFe]-hydrogenases FeS cluster, the so-called H-cluster, which is composed by a 4Fe4S center linked to a 2Fe subcluster coordinated by CO and CN- ligands as well as to a bridging dithiolate. Despite the high complexity of this cofactor, its biosynthesis and transfer is carried out by only three specific proteins, working in combination with the FeS cluster housekeeping biogenesis machinery: HydE and HydG assemble the H-cluster on the scaffold protein HydF, a small GTPase which also drives the delivery of the complete cluster to the target apohydrogenase. Thus, HydF plays a central double role of FeS cluster scaffold and carrier protein in [FeFe]-hydrogenases maturation. Although several molecular and functional data have been obtained since the discovery of the HydE/HydF/HydG machinery, the whole biosynthetic process is still not completely characterized. The crystal structure of a recombinant HydF apoprotein was solved in my laboratory and suggested useful molecular insights into the protein function. On the other hand, several open issues remained, including the specific role of the HydF GTPase domain, which is essential for the [FeFe]-hydrogenase maturation and activation. Chapter 2). In mammals, FeS clusters are mainly present and synthetized in mitochondria. Their assembly is performed by a complex and highly conserved system involving several proteins. Among them, ISCU is the scaffold upon which FeS clusters are assembled at the so called SDU, which also includes the desulfurase NFS1, the accessory protein ISD11, and frataxin (FXN). FXN is an iron-binding protein (Fe2+ and Fe3+) whose specific role in this biosynthetic pathway is still controversial, as it was first proposed to be the iron donor of the process, and then an allosteric activator of the SDU complex. In humans, defects of both ISCU or FXN lead to diseases with distinct clinical phenotypes but similar cellular and biochemical features. Decreased levels of ISCU mitochondrial isoform caused by a point mutation of the ISCU gene lead to a rare myopathy with lactic acidosis (ISCU myopathy); decreased levels of FXN, due to an abnormal expansion of GAA trinucleotide repeat in the FXN gene, cause Friedreich’s Ataxia (FRDA), a neurodegenerative disorder. Cellular hallmarks of both diseases are compromised respiration, mitochondrial iron overload and increased sensitivity to oxidative stress, and for both a specific therapy is still missing. This may be due, at least in part, to an incomplete characterization of the pathway(s) in which these proteins are involved, and in particular it is worth to note that FXN is a protein still looking for a function. Based on these premises, I focused the work of my PhD on these two open issues by taking advantage, in both cases, of a combination of biochemical and spectroscopic approaches to assess structural features of 1) HydF GTPase domain and 2) FXN, both alone and in binary complex with the scaffold ISCU. In particular, to explore the HydF protein and its structural response to GTP binding, in collaboration with Prof. Carbonera (Department of Chemical Sciences Padova, University of Padova), I exploited an advanced spectroscopic technique, EPR (Electron Paramagnetic Resonance), that is the ultimate technique for the study of FeS proteins; to characterize into detail the FXN-ISCU direct interaction, I applied the two-dimensional NMR (Nuclear Magnetic Resonance) technique, in collaboration with Prof. Bellanda (Department of Chemical Sciences, University of Padova). Chapter 1). I carried out in vitro spectroscopic studies to characterize the HydF GTPase domain. The obtained results allowed me to conclude that HydF can be considered as a novel member of the K+-dependent GTPases. Thus, these proteins may have a larger spread of functions than supposed before. HydF could be a molecular switch undergoing significant structural modifications upon GTP binding, as other members of the same family. Moreover, diffuse conformational changes due to GTP binding were detected, and this could be pivotal for dynamic structural and functional interactions with the other proteins involved in [FeFe]-hydrogenase maturation and activation. Starting from this discovery, it will be possible to model the GTP-bound state of HydF, an important structural information which was missing in the X-ray structure of the apoprotein previously solved in our laboratory. Chapter 2). I performed biochemical and spectroscopic analysis of human FXN, alone and in complex with ISCU, that allowed me to identify in FXN the residues involved in the binding of Fe3+/2+ and in its interaction with ISCU, which a confirmed to be iron-dependent. Then, since many FXN residues that I found to be involved in the direct interaction with ISCU are mutated in patients with variants of FRDA, I evaluated if and how these mutations can interfere with ISCU-FXN direct interaction and with its capability to bind iron. I found that FRDA-related frataxin variants in which mutations are located in ISCU-binding region do not affect frataxin iron-binding properties, while impairing both the interaction with ISCU and the ability to activate the SDU complex. Other FRDA related frataxin variants, instead, in which mutations are located in the iron-binding region or between the latter and ISCU-binding region, affect, as expected, the capability of FXN to bind iron while not completely impairing its interaction with ISCU. Moreover, these FXN variants keep a partial capability to activate SDU complex. Taken together, these results open new perspectives in the study of the mechanisms leading to FRDA variants, and give additional hints useful to clarify the physiological role of FXN as well as its contribution to the pathogenesis of Friedreich’s ataxia

Does Disaster Risk Relate to Banks’ Loan Loss Provisions?

We examine the relation between disaster risk and banks’ loan loss provisions (LLP). We propose a disaster risk measure based on the natural disasters declared as major disasters by the Federal Emergency Management Agency over a 15-year span. We theoretically support and empirically validate our measure using three different approaches, including the UN Sendai Framework for disaster risk reduction, which relates disaster risk to natural hazard exposure, vulnerability and capacity, and hazard characteristics. Using more than 445,000 bank-quarter observations, we document that banks located in U.S. counties with higher disaster risk recognize larger LLP after controlling for other bank-level factors related to LLP. We employ several techniques to ensure the robustness of our findings, including difference-in-differences estimation and matched samples. In additional analysis, we explore the characteristics that better enable banks to recognize disaster risk in their LLP, and investigate the consequences of managing disaster risk through LLP. Our results are important, especially because of the increasing concern about disaster risk and because they inform the growing debate on the economic consequences of disaster risk and the ability of the banking system to proactively manage the resulting credit risk through LLP

Identifying conformational changes with site-directed spin labeling reveals that the GTPase domain of HydF is a molecular switch

[FeFe]-hydrogenases catalyse the reduction of protons to hydrogen at a complex 2Fe[4Fe4S] center called H-cluster. The assembly of this active site is a multistep process involving three proteins, HydE, HydF and HydG. According to the current models, HydF has the key double role of scaffold, upon which the final H-cluster precursor is assembled, and carrier to transfer it to the target hydrogenase. The X-ray structure of HydF indicates that the protein is a homodimer with both monomers carrying two functional domains: a C-terminal FeS cluster-binding domain, where the precursor is assembled, and a N-terminal GTPase domain, whose exact contribution to cluster biogenesis and hydrogenase activation is still elusive. We previously obtained several hints suggesting that the binding of GTP to HydF could be involved in the interactions of this scaffold protein with the other maturases and with the hydrogenase itself. In this work, by means of site directed spin labeling coupled to EPR/PELDOR spectroscopy, we explored the conformational changes induced in a recombinant HydF protein by GTP binding, and provide the first clue that the HydF GTPase domain could be involved in the H-cluster assembly working as a molecular switch similarly to other known small GTPases