Optimal Time-Consistent Government Debt Maturity

Abstract: This paper develops a model of optimal debt maturity in which the government cannot issue statecontingent debt. As the literature has established, if the government can perfectly commit to fiscal policy, it fully insulates the economy against government spending shocks by purchasing short-term assets and issuing long-term debt. These positions are quantitatively very large relative to GDP and do not need to be actively managed by the government. Our main result is that these conclusions are not robust when lack of commitment is introduced. Under lack of commitment, large and tilted debt positions are very expensive to finance ex-ante since they ex-post exacerbate the government's problem stemming from a lack of commitment. In contrast, a flat maturity structure minimizes the cost entailed by a lack of commitment, though this structure also limits the ability to insure against shocks and increases the volatility of fiscal policy distortions. We show that the optimal time-consistent maturity structure is nearly flat because reducing average borrowing costs is quantitatively more important for welfare than reducing fiscal policy volatility. Thus, under lack of commitment, the government actively manages its debt positions and can approximate optimal policy by confining its debt instruments to consols

The Substrate-Bound Crystal Structure of a Baeyer–Villiger Monooxygenase Exhibits a Criegee-like Conformation

The Baeyer\u2013Villiger monooxygenases (BVMOs) are a family of bacterial flavoproteins that catalyze the synthetically useful Baeyer\u2013Villiger oxidation reaction. This involves the conversion of ketones into esters or cyclic ketones into lactones by introducing an oxygen atom adjacent to the carbonyl group. The BVMOs offer exquisite regio- and enantiospecificity while acting on a wide range of substrates. They use only NADPH and oxygen as cosubstrates, and produce only NADP+ and water as byproducts, making them environmentally attractive for industrial purposes. Here, we report the first crystal structure of a BVMO, cyclohexanone monooxygenase (CHMO) from Rhodococcus sp. HI-31 in complex with its substrate, cyclohexanone, as well as NADP+ and FAD, to 2.4 \uc5 resolution. This structure shows a drastic rotation of the NADP+ cofactor in comparison to previously reported NADP+-bound structures, as the nicotinamide moiety is no longer positioned above the flavin ring. Instead, the substrate, cyclohexanone, is found at this location, in an appropriate position for the formation of the Criegee intermediate. The rotation of NADP+ permits the substrate to gain access to the reactive flavin peroxyanion intermediate while preventing it from diffusing out of the active site. The structure thus reveals the conformation of the enzyme during the key catalytic step. CHMO is proposed to undergo a series of conformational changes to gradually move the substrate from the solvent, via binding in a solvent excluded pocket that dictates the enzyme\u2019s chemospecificity, to a location above the flavin\u2013peroxide adduct where catalysis occurs.Peer reviewed: YesNRC publication: Ye

Pilot in the Loop Aeroservoelastic Simulation in Support to the Conceptual Design of a Fly by Wire Airplane

This paper deals with the creation of a low-budget interdisciplinary simulation environment to support design and optimization of new generation aircraft with Fly-By-Wire (FBW) control systems technology. Such tool must be able to merge flight and structural dynamics, allowing flight simulation with pilot-in-the-loop for handling qualities evaluations and providing valuable information for the conceptual design loop. Accounting for aeroservoelastic phenomena from early stages of the design, time to market and development costs of new aircrafts should be reduced. Flight test campaign has been addressed to verify the existence of a Control Spillover or Pilot Induced Oscillation (PIO), and whether the Aeroservoelastic airplane is able to influence the piloting technique while also considering the effect of turbulence and FCS time delays

Parametric Formulation of the Floodable Length Curve: Application Case to Offshore Patrol Vessels

The residual buoyancy of vessels after damage has a fundamental role in their survivability and it is implemented through adequate ship internal subdivision. Traditionally the number and the position of transverse watertight bulkheads are selected for most ships early in the design phase by means of the \u201cfloodable length curve\u201d coupled with the concept of \u201cmargin line\u201d. However, for naval vessels, it is more and more common during the acquisition process to explore a wide domain of feasible ships, identified with the assistance of automated processes and assessed also in terms of capabilities, among which is survivability. The generation and the comparison of a considerable number of different ship configurations is very time consuming. Therefore recourse to a parametric expression of the floodable length curve is considered to be a very efficient approach and would thus enable characterisation of the ship, in terms of survivability performance. In this paper such an approach is presented, using an offshore patrol vessel (OPV) as the case study

Neuroleptic induced parkinsonism: MRI findings in relation to clinical course after withdrawal of neuroleptic drugs.

Parkinsonism is a common complication of neuroleptic drug use; however, the pathophysiology of the persistence of parkinsonian symptoms after withdrawal of neuroleptic drugs is poorly understood. Twenty patients with neuroleptic induced parkinsonism were studied by high field MRI. Persistence of symptoms was associated with different findings depending on the age of the patients--namely, putaminal hypointensity in young patients and striatal hyperintensities in old patients. High field MRI may be useful in identifying patients at higher risk for neuroleptic induced parkinsonism