Aggregate Implications of a Credit Crunch

We take an off-the-shelf model with financial frictions and heterogeneity, and study the mapping from a credit crunch, modeled as a shock to collateral constraints, to simple aggregate wedges. We study three variants of this model that only differ in the form of underlying heterogeneity. We find that in all three model variants a credit crunch shows up as a different wedge: efficiency, investment, and labor wedges. Furthermore, all three model variants have an undistorted Euler equation for the aggregate of firm owners. These results highlight the limitations of using representative agent models to identify sources of business cycle fluctuations.

Correction of High Vibration on a Vertical Turbine Deep Well Pump with a Dynamic Vibration Absorber

Case StudyA 100 horsepower, 180 foot deep vertical turbine pump called #12 Well Pump had a history of reoccurring high vibration despite multiple pump rebuilds and motor replacements. The problem was identified as a structural resonance of the motor and discharge head assembly. It was determined that a dynamic vibration absorber (DVA) would be the most effective solution. This case study presents the technique of diagnosing the resonance and the methodology of designing and calibrating a dynamic vibration absorber. Installation of the DVA reduced the overall vibration velocity amplitude by a factor of 16

Controlling a distribution of heterogeneous agents

Este artículo analiza el problema de un planificador benevolente que desea controlar una población de agentes heterogéneos sujetos a perturbaciones idiosincrásticas. Esto es equivalente a un problema de control determinista en el que la variable de estado pertinente es la distribución de agentes. Demostramos cómo, trabajando en tiempo continuo, este problema puede descomponerse en una ecuación de programación dinámica junto a la ley de movimiento de la distribución y presentamos un nuevo algoritmo para resolverlo numéricamente. Como aplicación, analizamos la solución eficiente-restringida de una economía à la Aiyagari con una distribución de la riqueza que replica la observada en los datos. Nuestros resultados indican que la solución óptima se caracteriza por un nivel de desigualdad de la riqueza mayor que el observado en el equilibrio competitivoThis paper analyzes the problem of a benevolent planner wishing to control a population of heterogeneous agents subject to idiosyncratic shocks. This is equivalent to a deterministic control problem in which the state variable is the cross-sectional distribution. We show how, in continuous time, this problem can be broken down into a dynamic programming equation plus the law of motion of the distribution, and we introduce a new numerical algorithm to solve it. As an application, we analyze the constrained-efficient allocation of an Aiyagari economy with a fat-tailed wealth distribution. We find that the constrained-efficient allocation features more wealth inequality than the competitive equilibriu

Knowledge Growth and the Allocation of Time

We analyze a model economy with many agents, each with a different productivity level. Agents divide their time between two activities: producing goods with the production-related knowledge they already have, and interacting with others in search of new, productivity-increasing ideas. These choices jointly determine the economy’s current production level and its rate of learning and real growth. Individuals’ time allocation decisions depend on the knowledge distribution because the productivity levels of others determine their own chances of improving their productivities through search. The time allocations of everyone in the economy in turn determine the evolution of its knowledge distribution. We construct the balanced growth path for this economy, thereby obtaining a theory of endogenous growth that captures in a tractable way the social nature of knowledge creation. We also study the allocation chosen by an idealized planner who takes into account and internalizes the external benefits of search, and tax structures that implement an optimal solution. Finally, we provide two examples of alternative learning technologies, as concrete illustrations of other directions that might be pursued.

Correction of High Vibration on a Vertical Turbine Deep Well Pump with a Dynamic Vibration Absorber

Case StudyA 100 horsepower, 180 foot deep vertical turbine pump called #12 Well Pump had a history of reoccurring high vibration despite multiple pump rebuilds and motor replacements. The problem was identified as a structural resonance of the motor and discharge head assembly. It was determined that a dynamic vibration absorber (DVA) would be the most effective solution. This case study presents the technique of diagnosing the resonance and the methodology of designing and calibrating a dynamic vibration absorber. Installation of the DVA reduced the overall vibration velocity amplitude by a factor of 16

Dual Wavelength Optical System for Multiple Quantum Communication Transmitters in Cubesat Platform

Quantum Key Distribution systems will play an important role in future networks for secure data communication. In order to provide a global coverage of a future Quantum Key Distribution service, satellites will be needed to bridge large distances. These satellite systems must be cost efficient to facilitate deployment since many network nodes will be needed. The CubeSat standard is frequently used for New Space projects as a versatile platform for satellite payloads. It is also chosen as a baseline for the construction of the system described in this paper. The DLR Institute of Communications and Navigation develops optical free space communication systems for scientific research in classical and quantum communications. In the OSIRIS4CubeSat (Optical Opace Infrared Downlink System for CubeSats) project a 1/3 U CubeSat laser-communication terminal for up to 100 Mbit/s downlinks was developed.1 This developement is adapted to be used for quantum communications tests with multiple transmitters in the scope of the project QUBE.2 Since the OSIRIS4CubeSat terminal was designed for C- and L-band wavelengths, a redesign of the optical system is needed to achieve polychromatic performance for C- and L-band and 850 nm. The optical system consists of a fiber collimator, a fine pointing assembly and an afocal telescope. Most important requirement of the latter is a similar magnification for all wavelengths to ensure coaligned beams pointing to the optical ground station (OGS). As the afocal telescope is used bidirectionally, it also needs to be optimized for the incident wave-front of the beacon laser from the OGS with respect to the beam shape at the tracking sensor which is used in the fine pointing assembly. These parameters are important for a correct pointing control. In addition to the laser terminal, a fiber-based wavelength division multiplexer (WDM) was specified for combining signals from three sources into one output fiber. It is based on cascaded thin film interference filters which are coupled to the fibers. Especially the propagation of 850 nm and C/L-band signals in one single mode fiber is critical. Therefore the types of optical fibers were selected with respect to the bend loss, to single mode propagation behaviour, polarisation integrity and optimal cladding diameter for production

Cathepsin S and protease-activated receptor-2 drive alloimmunity and immune regulation in kidney allograft rejection

Alloantigen presentation is an essential process in acute allorejection. In this context, we speculated on a pathogenic role of cathepsin S (Cat-S), a cysteine protease known to promote antigenic peptide loading into MHC class II and to activate protease-activated receptor (PAR)-2 on intrarenal microvascular endothelial and tubular epithelial cells. Single-cell RNA sequencing and immunostaining of human kidney allografts confirmed Cat-S expression in intrarenal mononuclear phagocytes

Development of laser terminals for satellite-based QKD on CubeSat platforms

Satellite-based Quantum Key Distribution (QKD) plays an important role in future quantum safe networks to overcome the limited transmission range of fiber based QKD. Recent missions demonstrated the feasibility of this technique paving the way for future projects. CubeSats provide a cost-efficient way for testing new QKD technologies in space and pose a promising and scalable platform for future constellation. The DLR Institute of Communication and Navigation (DLR-KN) develops terminals for satellite QKD systems. Within the scope of the project QUBE, a 1/3U sized terminal is developed for space-to-ground QKD experiments. The terminal will set up a multi wavelength downlink, providing a classical synchronization and a quantum channel. Its functionality is verified in a ground-to-ground link and the launch of the 3U CubeSat is planned for 2024. During the mission, core technologies for future QKD technologies are tested in space. Follow up projects at DLR-KN aim at the development and integration of bigger telescopes in CubeSats leading to an increased antenna gain, enabling full QKD implementation. Based on the QUBE system, a terminal breadboard with an aperture diameter of 85mm is developed within the QuNET project. The paper presents an overview of the system concept, a detailed insight into the optics design, the concept for the optomechanics and the implementation of the pointing assembly. The parallel development of the subsequent QUBE-II terminal exploits the gathered experience and lessons learned from the QUBE mission and QuNET breadboard development. The QUBE-II terminal will enable full space-to-ground QKD implementation with a CubeSat and will additionally provide an optical data up- and downlink. QUBE-II will be launched at the end of 2025