Tirole Research Articles

Chemical State, Distribution, and Role of Ti- and Nb-Based Additives on the Ca(BH4)2 System

Light metal tetrahydroborates are regarded as promising materials for solid state hydrogen storage. Due to both a high gravimetric hydrogen capacity of 11.5 wt % and an ideal dehydrogenation enthalpy of 32 kJ mol–1 H2, Ca(BH4)2 is considered to be one of the most interesting compounds in this class of materials. In this work, a comprehensive investigation of the effect of different selected additives (TiF4, NbF5, Ti-isopropoxide, and CaF2) on the reversible hydrogenation reaction of calcium borohydride is presented combining different investigation techniques. The chemical state of the Nb- and Ti-based additives is studied by X-ray absorption spectroscopy (e.g., XANES). Transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED) and energy-dispersive X-ray spectroscopy (EDX) was used to show the local structure, size, and distribution of the additive/catalyst. 11B{1H} solid state magic angle spinning-nuclear magnetic resonance (MAS NMR) was carried out to detect possible amorphous phases. The formation of TiB2 and NbB2 nanoparticles was observed after milling or upon sorption reactions of the Nb- and Ti-based Ca(BH4)2 doped systems. The formation of transition-metal boride nanoparticles is proposed to support the heterogeneous nucleation of CaB6. The {111}CaB6/{1011}NbB2, {111}CaB6/{1010}NbB2, as well as {111}CaB6/{1011}TiB2 plane pairs have the potential to be the matching planes because the d-value mismatch is well below the d-critical mismatch value (6%). Transition-metal boride nanoparticles act as heterogeneous nucleation sites for CaB6, refine the microstructure thus improving the sorption kinetics, and, as a consequence, lead to the reversible formation of Ca(BH4)2.

Role of Ti-based catalysts in the dehydrogenation mechanism of magnesium borohydride: A cluster approach

The role of Ti and Ti-based catalysts such as TiCl3 and TiF3 in the dehydrogenation of Mg(BH4)2 has been studied using a cluster approach and density functional theory. The optimized geometry of Mg(BH4)2 clusters mimics the structure it has in the crystalline form, but undergoes significant geometric distortion as well as changes in the natural bond orbital (NBO) charge after the addition of the catalysts. While all the catalysts lower the hydrogen desorption energy, elemental Ti appears to be the best catalyst followed by TiCl3 and TiF3. The lowering of the hydrogen desorption is shown to be due to the weakening of the BH bond which is caused by the interaction of Ti with H and Mg.

Role of Ti and N in line pipe steel welds

High strength line pipe steels exhibit a combination of excellent toughness and high strength achieved through microalloy additions and thermomechanical controlled processing. During welding, severe thermal cycles experienced by the heat affected zone (HAZ) result in precipitate coarsening/dissolution and subsequent grain growth. This significantly reduces toughness in this region. It is well known that small Ti additions are utilised to control grain growth in the HAZ through grain boundary pinning action of TiN precipitates. Because of a lack of systematic and controlled study, it has been difficult to quantify the effect of TiN in the variety of steels. Hence, the optimum levels proposed in the literature are inconsistent and even contradict each other when compared. This paper mainly reviews the effect of different levels of Ti, N and Ti/N ratios on steels and pipes manufactured using different processes, with particular focus on the HAZ toughness.

Role of Ti and Pt electrodes on resistance switching variability of HfO2-based Resistive Random Access Memory

This paper deals with the role of platinum or titanium–titanium nitride electrodes on variability of resistive switching characteristics and electrical performances of HfO2-based memory elements. Capacitor-like Pt/HfO2 (10nm)/Pt and Ti/HfO2 (10nm)/TiN structures were fabricated on top of a tungsten pillar bottom electrode and integrated in-between two interconnect metal lines. First, quasi-static measurements were performed to apprehend the role of electrodes on electroforming, set and reset operations and their corresponding switching parameters. Memory elements with Pt as top and bottom electrodes exhibited a non-polar behavior with sharp decrease of current during reset operation while Ti/HfO2/TiN capacitors showed a bipolar switching behavior, with a gradual reset. In a second step, statistical distributions of switching parameters (voltage and resistance) were extracted from data obtained on few hundreds of capacitors. Even if the resistance in low resistive state and reset voltage was found to be comparable for both types of electrodes, the progressive reset operation observed on samples with Ti/TiN electrodes led to a lower variability of resistance in high resistive state and concomitantly of set voltage. In addition Ti–TiN electrodes enabled gaining: (i) lower forming and set voltages with significantly narrower capacitor-to-capacitor distributions; (ii) a better data retention capability (10years at 65°C instead of 10years at 50°C for Pt electrodes); (iii) satisfactory dynamic performances with lower set and reset voltages for ramp speed ranging from 10−2 to 107V/s. The significant improvement of switching behavior with Ti–TiN electrodes is mainly attributed to the formation of a native interface layer between HfO2 oxide and Ti top electrode.

Study of the series Ti1−yNbySnSb with 0 ≤ y ≤ 1 as anode material for Li-ion batteries

TiSnSb shows an excellent behavior as negative electrode for Li-ion batteries. However the role of Ti is still unclear in the mechanism. To better understand the role played by the transition metal on both the mechanism and the performance of TiSnSb, a progressive substitution of Ti by Nb has been achieved. A full study focuses on the electrochemical mechanisms of the Ti1−yNbySnSb system with 0 ≤ y ≤ 1 vs Li by combining in situ XRD and Mössbauer, and EXAFS analyses. The electrochemical mechanism is found to be a reversible conversion mechanism: MSnSb + 7Li ↔ Li3Sb + 1/2 Li7Sn2 + M0. The lithium is found to react simultaneously with both Sn and Sb. Nb-rich alloys have been found also to be very promising negative electrode demonstrating the versatility of the MSnSb electrode material family for Li-ion battery application. Using the appropriate electrode formulation, the good cycling life of TiSnSb is not affected by its substitution by Nb.

Book Reviews

Arvind Krishnamurthy of Kellogg School of Management, Northwestern University and NBER reviews “Inside and Outside Liquidity” by Bengt Holmstrom and Jean Tirole. The EconLit abstract of the reviewed work begins: Explores the demand for, and supply of, liquid assets from a modern corporate finance perspective. Discusses leverage; a simple model of liquidity demand; aggregate liquidity shortages and liquidity premia; a liquidity asset pricing model; public provision of liquidity in a closed economy; liquidity provision with access to global capital markets; financial muscle and overhoarding of liquidity; and specialized inputs and secondary markets. Holmstrom is Paul A. Samuelson Professor of Economics at the Massachusetts Institute of Technology. Tirole is Scientific Director of the Institut d'Economie Industrielle and Chairman of the Board of the Toulouse School of Economics. Bibliography; index.

The Possibilist Transactional Interpretation and Relativity

A recent ontological variant of Cramer's Transactional Interpretation, called "Possibilist Transactional Interpretation" or PTI, is extended to the relativistic domain. The present interpretation clarifies the concept of 'absorption,' which plays a crucial role in TI (and in PTI). In particular, in the relativistic domain, coupling amplitudes between fields are interpreted as amplitudes for the generation of confirmation waves (CW) by a potential absorber in response to offer waves (OW), whereas in the nonrelativistic context CW are taken as generated with certainty. It is pointed out that solving the measurement problem requires venturing into the relativistic domain in which emissions and absorptions take place; nonrelativistic quantum mechanics only applies to quanta considered as 'already in existence' (i.e., 'free quanta'), and therefore cannot fully account for the phenomenon of measurement, in which quanta are tied to sources and sinks.

The Network Origins of Aggregate Fluctuations

This paper combines material from Carvalho’s Ph.D. dissertation at the University of Chicago (Carvalho, 2008) and Acemoglu, Ozdaglar, and Tahbaz-Salehi (2010). We thank the editor, Stephen Morris, and four anonymous referees for very helpful remarks and suggestions. We thank Stefana Stantcheva for excellent research assistance and Bill Kerr and Kaushik Ghosh for initial help with the NBER manufacturing productivity database. Carvalho thanks his advisor Lars Hansen and other members of his thesis committee, Robert Lucas and Timothy Conley. We are also grateful to John Fernald, Xavier Gabaix, Ali Jadbabaie, Alp Simsek, Hugo Sonnenschein, Jean Tirole, Jaume Ventura and numerous seminar and conference participants for useful feedback and suggestions. Carvalho acknowledges financial support from the Government of Catalonia (grant 2009SGR1157), the Spanish Ministry of Education and Science (grants Juan de la Cierva, JCI2009-04127, ECO2008-01665 and CSD2006-00016) and Barcelona GSE Research Network. Acemoglu, Ozdaglar and Tahbaz-Salehi acknowledge financial support from the Toulouse Network of Information Technology, National Science Foundation (Grant 0735956) and the Air Force Office of Scientific Research (Grant FA9550-09-1-0420).

Book Reviews

Matthew Richardson of New York University Stern School of Business reviews “Balancing the Banks: Global Lessons from the Financial Crisis” by Mathias Dewatripont, Jean-Charles Rochet, and Jean Tirole. The EconLit abstract of the reviewed work begins, “Three previously published papers explore what happened in the recent financial crisis and consider the lessons to be learned in order to avoid a repetition of the large-scale meltdown of financial markets, industrial recession, and public deficits. Papers discuss lessons from the crisis (Jean Tirole); the future of banking regulation (Jean-Charles Rochet); and the treatment of distressed banks (Mathias Dewatripont and Rochet). Dewatripoint is Professor of Economics at the Free University of Brussels, Annual Visiting Professor of Economics at the Massachusetts Institute of Technology, and Research Director of the Center for Economic Policy and Research. Rochet is Professor of Economics at the University of Toulouse I. Tirole is Chairman of the Foundation Jean-Jacques Laffont at the Toulouse School of Economics, Scientific Director of Toulouse's Industrial Economics Institute, and Annual Visiting Professor of Economics at the Massachusetts Institute of Technology. Index.”

Effect of Titanium Doping of Al(111) Surfaces on Alane Formation, Mobility, and Desorption

Alanes are critical intermediates in hydrogen storage reactions for mass transport during the formation of complex metal hydrides. Titanium has been shown to promote hydrogen desorption and hydrogenation, but its role as a catalyst is not clear. Combining surface infrared (IR) spectroscopy and density functional theory (DFT), the role of Ti is explored during the interaction of atomic hydrogen with Ti-doped Al(111) surfaces. Titanium is found to reduce the formation of large alanes, due to a decrease of hydrogen mobility and to trapping of small alanes on Ti sites, thus hindering oligomerization. For high doping levels ({approx}0.27 ML Ti) on Al(111), only chemisorbed AlH{sub 3} is observed on Ti sites, with no evidence for large alanes. Titanium also dramatically lowers the desorption temperature of large alanes from 290 to 190 K, due to a more restricted translational motion of these alanes.

Effect of titanium interlayer on the microstructure and electron emission characteristics of multiwalled carbon nanotubes

The influence of the titanium (Ti) interlayer thickness on the growth and electron emission characteristics of carbon nanotubes (CNTs) deposited on silicon (Si) coated with an iron (Fe) catalyst layer was investigated. Ti films 5 nm, 10 nm, and 15 nm in thickness were deposited beneath the Fe catalyst layers. Multiwalled carbon nanotubes (MWCNTs) were deposited via microwave plasma enhanced chemical vapor deposition. The Ti interlayer hinders the diffusion of Fe into the silicon substrate and thus helps in the growth of MWCNTs. In addition, the role of Ti as a sacrificial layer on the catalytic diffusion, surface morphology, microstructure, and, thus, the growth of MWCNTs was probed through scanning and high resolution transmission electron microscope studies. The enhanced electron emission mechanism as a result of the introduction of a Ti interlayer is explained on the basis of a double barrier model and the formation of a conducting channel between the substrate and the CNTs. The intensified micro-Raman characteristics of the MWCNTs were directly related with the thickness of the Ti interlayer in the three layered system (Ti/Fe/CNT) as compared to a two layer system (Fe/CNT) deposited on a Si substrate.

The Theory of Corporate Finance, by Jean Tirole

The Theory of Corporate Finance, by Jean Tirole, 2006, Princeton, NJ: Princeton University Press, 644 pages. Jean Tirole has contributed to many aspects of economic theory, including industrial organization, public economics, contract theory, game theory, finance, and corporate governance. This book proposes an original contribution to the economics and finance literature by developing the foundations of corporate finance. It also covers in detail various corporate governance issues faced by organizations, including financial institutions such as banks and insurance companies. Although the emphasis is on theory, the book contains many examples and stylized facts that illustrate concepts of corporate finance theory, such as security design, incentives, and controls, which are the basis of modern corporate finance. The book consists of 16 chapters divided into six parts, a seventh part containing answers to selected exercises and review problems, a comprehensive list of references at the end of each chapter, and a subject index. Its content is devoted to positive and normative analyses of corporate finance and is directed at an authence interested in the theoretical foundations of corporate finance. The book is designed for professors and graduate students but can also be of interest to practitioners with a strong background in economics and finance. To my knowledge, no such text has been published before, and the book fills an important gap in the literature. It contains formal economic analyses (with equations and models) presented with exceptional intuition. The subjects covered are important for the understanding of almost all facets of corporate finance. At the end of the introduction, the author discusses omissions such as a detailed empirical analysis of the main theories developed in the book, taxes, bubbles, behavioral finance, and international finance. The book is an important input for the readers of The Journal of Risk and Insurance and remarkably supplements the empirical contributions on corporate governance in the insurance industry presented in this special issue of the Journal. The first two chapters introduce the reader to corporate finance by reviewing the main institutional features, empirical regularities, and policy issues discussed in the literature related to corporate governance and corporate financing. The goal of this section is to present an overview of corporate institutions in order to motivate the theoretical analyses presented in the next parts. It covers many subjects related to corporate governance, such as the separation between ownership and control, managerial incentives, and stakeholder society. It also presents stylized facts on corporate financing related to debt instruments, equity instruments, and financing patterns. The second part of the book starts the theoretical development of the microeconomics of corporate finance, which the author separates into several branches. The first branch, presented in this part, addresses the incentive problems of insiders. The chapters consider financial contracting with alternative assumptions regarding information asymmetries between insiders and outsiders. For example, Chapter 3 proposes a fixed-investment model with moral hazard and credit rationing, while Chapter 4 analyzes determinants of borrowing capacity. Chapter 5 extends the discussion to multiperiod financing, where liquidity management can become a complement to the standard solvency leverage requirement imposed by lenders. Chapter 6 introduces adverse selection at the financing stage, which increases the difficulty for insiders to raise project financing. Finally, Chapter 7 shows how product or market characteristics can affect financing choices. The next two parts treat situations where both insiders and outsiders are active, which may induce additional incentive problems. This is because outsiders can affect the distribution of events chosen by the insiders. …

Effect of Mo<sub>2</sub>C Content on Microstructure and Composition of Ti(C,N)-Based Cermets Mixing in Water

Element Mo plays a significant role in Ti(C,N)-based cermets. In this work, mixing was carried out in water and cermets with high mechanical properties were fabricated. The effect of Mo2C content on microstructure and composition was investigated by field emission scanning electron microscope (FSEM) and energy dispersive spectrometer (EDS). Results showed that microstructure becomes uniformly distributed, binder distribution becomes symmetrical and the particle size becomes small with increase of Mo2C content. The volume fraction of (outer + inner) rim structure increases, the volume fractions of core structure and binder phase decrease instead. It was found that Mo2C content in raw material affects compositions in phases. With the level of Mo2C content rising, the concentration of element Mo in rim structure increases, the concentration of element Ti in binder decreases.

Understanding the cooperative NHC/LA catalysis for stereoselective annulation reactions with homoenolates. A DFT study

The role of Ti(Oi-Pr)(4) Lewis acid (LA) in the cooperative N-heterocyclic carbene (NHC)/LA catalyzed addition of enals to enones to yield cis-cyclopentenes has been investigated using DFT methods at the B3LYP/6-31G** computational level. Ti(IV) effectively catalyzes the reaction by formation of a complex with cinnamaldehyde 1, which favors the nucleophilic attack of NHC 5 on 1, and the subsequent proton abstraction to yield the extended Ti(IV)-Breslow intermediate 21. The nature of the metal involved in the LA catalyst plays a relevant role due to the more basic character of NHCs than aldehydes. Thus, strong LAs, such as Zn(OTf)(2), prevent the catalytic behavior of NHCs to form a very stable complex. The subsequent formation of a complex between chalcone 2 and the extended Ti(IV)-Breslow intermediate 21 favors the cis stereoselective C-C bond-formation. Analysis of the structures of Ti(IV)-complex precursors for the cis and trans C-C bond-formation steps allows for an explanation of the unexpected cis stereoselectivity.

Role of Ti 4+ and Sn 4+ ions in spinel formation and reactive sintering of magnesia-rich ceramics

The solid solubility of magnesia in magnesium aluminate spinel and magnesium aluminate spinel in magnesia does not change with temperature thus not creating bonds or precipitation over periclase grains in a single stage sintering process. In comparison, the precipitated spinels in magnesia-chromia refractories form complex spinel due to inversion in the position of bivalent and trivalent cations within the structure, making them more stable at high temperature than either normal or inverse spinel. Additives form low-temperature compounds that diffuse into the spinel structure and create defects that change the properties of spinel solid solution. In the present study, magnesia and alumina powders along with tetravalent oxide additives were analyzed for their role in reactive densification of spinel in a single stage firing process in order to achieve a better binding system for magnesia-based refractories. These tetravalent oxides on reaction with magnesia form spinel solid solution with MgAl 2O 4 as they have similar crystal structure. The spinel solid solution formed using oxide additives is expected to have higher solubility in magnesia than magnesium aluminate spinel, resulting in improvement of the bonding during sintering through increased in solid solubility at elevated temperatures followed by precipitation of secondary spinel phases, similar to the complex spinel in magnesia-chrome refractories. The formation of spinel during firing remains as a second phase that retards the grain growth of periclase. The changes in unit cell dimensions with temperature and amount of additive were analyzed using Reitveld method and correlated with the densification behaviour at different temperatures.

A Price Theory of Multi-Sided Platforms

I develop a general theory of monopoly pricing of networks. Platforms use insulating tariffs to avoid coordination failure, implementing any desired allocation. Profit maximization distorts in the spirit of A. Michael Spence (1975) by internalizing only network externalities to marginal users. Thus the empirical and prescriptive content of the popular Jean-Charles Rochet and Jean Tirole (2006) model of two-sided markets turns on the nature of user heterogeneity. I propose a more plausible, yet equally tractable, model of heterogeneity in which users differ in their income or scale. My approach provides a general measure of market power and helps predict the effects of price regulation and mergers. (JEL D42, D85, L14)

Structural fluctuations and role of Ti as nucleating agent in an aluminosilicate glass

Nucleation is the initiating event for the formation of any crystal from undercooled melt. Although the classical nucleation theory describes qualitatively many aspects of the crystallization process, the mechanisms favoring the first steps of nucleation are still unknown and required the full identification of the catalytic sites. In this work, we report a structural investigation of the system 2MgO–2Al 2O 3–5SiO 2 + TiO 2, a major glass–ceramic for scientific and industrial interest, in order to understand the structural influence of Ti as a nucleating agent. X-ray scattering and 27Al Nuclear Magnetic Resonance studies were carried out on 2MgO–2Al 2O 3–5SiO 2 + xTiO 2 glasses, with 0 mol% ≤ x ≤ 15.5 mol%. No evidence of phase separation can be detected in the initial glasses by Transmission Electron Microscopy at nanoscale and Ti atoms appear to be homogeneously distributed within the glassy structure. We explain that the presence of TiO 2 favors nucleation by the formation in the initial glass of high-coordinated Al species and the presence of structural fluctuations that mimic the initial crystalline phase precipitating in the glass. The understanding of the parent glass structure appears as a critical constraint to understand the pathways promoting nucleation.

Persistent luminescence in rare earth ion-doped gadolinium oxysulfide phosphors

A series of rare-earth ion-doped gadolinium oxysulfide phosphors Gd 2O 2S:RE 3+, Ti, Mg (RE = Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb) were synthesized by solid-state reaction. The excitation and photoluminescence spectra, afterglow spectra, afterglow decay curves and thermoluminescence spectra of the phosphors were examined. According to the afterglow spectra, gadolinium oxysulfide doped with rare-earth ions were classified into three groups. When rare earth ions such as Eu 3+, Sm 3+, Dy 3+, Ho 3+, Er 3+ and Tm 3+ were introduced into the Gd 2O 2S host, their characteristic emission as well as that from Gd 2O 2S:Ti, Mg were observed. In case of Yb 3+ and Nd 3+, only the broadband luminescence of Gd 2O 2S:Ti, Mg was obtained. Gadolinium oxysulfide doped with Pr 3+, Tb 3+ and Ce 3+ did not show afterglow emission. The calculated trap energy levels of the samples were compared. The role of Ti and Mg ions and a potential mechanism for persistent luminescence in the samples were discussed.

First-principles study on the catalytic role of Ti in the hydrogenation of Al(110) surfaces

First-principles calculation is used to study the hydrogen molecule adsorbed on Ti-doped Al(110) surface and pure Al(110) surface separately. We find an adsorption path of hydrogen molecule for decomposing hydrogen atoms and forming TiH2 with Ti atoms on top site. Afterwards, the TiH2 molecule moves to hollow site and approaches to the Al(110) surface. The analyses of density of state and Milliken overlap population show that there is covalence interaction between hydrogen atoms and Al atoms of surface, which gives rise to the formation of Al-H, Na3AlH6 and NaAlH4. Hydrogen molecule is unable to decompose hydrogen atoms on pure Al(110) surface.These results contribute further towards the understanding of the improved observation in recycling of hydrogen with Ti-doped NaAlH4.

Role of Ti−O Bonds in Phase Transitions of TiO2

A phase transition was achieved from TiO2 particles to titanate nanotubes by the breakage of Ti-O bonds without using expensive precursors, high temperatures, high chemical concentrations of alkaline solutions, and long synthesis times. The controlled preparation of one-dimensional nanostructures of titanates (H2Ti4O9.nH2O) has been conducted at a very low concentration of alkaline solution (1 M NaOH), and in a very short time (12 h) using TiO2 anatase and TiO2 P-25 (precursors) and a microwave enhanced soft chemical process. Temperature was used as a variable, and only low process temperatures (100-110 degrees C) were used. A combination of anatase nanoparticles/hydrogen tetratitanate nanotubes was synthesized using TiO2 (anatase) and a temperature of only 100 degrees C. When TiO2 (P-25) was used with the same concentration of alkaline solution (1 M NaOH), the same processing time of 12 h, and a higher temperature at 110 degrees C, only hydrogen tetratitanate nanotubes were observed. The linkages of "Ti-O" play a very important role in the structural features of different phases. X-ray diffraction (XRD) showed two crystalline phases (tetragonal and monoclinic) in the case of TiO2 (anatase) and one crystalline phase (monoclinic) for products of TiO2 (P-25). The role of Ti-O linkages is obvious in the Raman spectra as revealed by a shift in peak positions for a layered structure of the hydrogen tetratitanate and a nanosphere structure of the resulting TiO2. An X-ray photoelectron spectroscopy (XPS) study showed a shift to a lower binding energy of the 2p peaks (2p1/2, 3/2) in the Ti region for titanate and confirmed the formation of titanate nanostructures. Transmission electron microscopy (TEM) revealed nanotubes of hydrogen tetratitanates (H2Ti4O9.nH2O) in the form of bundles. High-resolution TEM (HRTEM) data supported findings of X-ray diffraction results of the products of TiO2 (anatase) and TiO2 (P-25).