Blade Failures on an Axial Compressor by Unexpected Gas Compositions

Case StudiesA fifteen stage axial compressor including a bleed extraction was subject to a major overhaul after nearly 20 years of trouble free operation. Shortly after recommissioning and resumption of the production the compressor faced three major failures within two weeks. A root cause failure analysis was conducted and revealed that the process plant start-up procedures caused gas compositions which deviated strongly from the design conditions. The valve designs as well as the available control parameters were not able to protect the compressor from off-design operating conditions. For future compressor failure prevention, the process start-up procedures were adapted and the existing control parameters/logic was upgraded. The new control logic reacts to the transient process behaviours during start-up by continuous harmonization of the safety valves

The Impact of Social Media On Belief Formation

Social media are becoming increasingly important in our society and change the way people communicate, how they acquire information, and how they form beliefs. Experts are concerned that the rise of social media may make interaction and information exchange among like-minded individuals more pronounced and therefore lead to increased disagreement in a society. This paper analyzes a learning model with endogenous network formation in which people have different types and live in different regions. I show that when the importance of social media increases, the amount of disagreement in the society first decreases and then increases. Simultaneously people of the same type hold increasingly similar beliefs. Furthermore, people who find it hard to communicate with people in the same region may interact with similar people online and consequently hold extreme beliefs. Finally, I propose a simple way to model people who neglect a potential correlation of signals and show that these people may be made worse off by social media

Consumer Exploitation and Notice Periods

Firms often set long notice periods when consumers cancel a contract, and sometimes do so even when the costs of changing or canceling the contract are small. We investigate a model in which a firm offers a contract to consumers who may procrastinate canceling it due to naive present-bias. We show that the firm may set a long notice period to exploit naive consumers

The Timing of Choice-Enhancing Policies

Recent studies investigate policies motivating consumers to make an active choice as a way to protect unsophisticated consumers. We analyze the optimal timing of such choice-enhancing policies when a firm can strategically react to them. In our model, a firm provides a contract with automatic renewal. We show that a policy intending to enhance consumers choices when they choose a contract can be detrimental to welfare. By contrast, a choice-enhancing policy at the time of contract renewal increases welfare more robustly. Our results highlight that policies should be targeted in timing to the actual choice inefficiency

Reciprocal regulation of protein synthesis and carbon metabolism for thylakoid membrane biogenesis

Metabolic control of gene expression coordinates the levels of specific gene products to meet cellular demand for their activities. This control can be exerted by metabolites acting as regulatory signals and/or a class of metabolic enzymes with dual functions as regulators of gene expression. However, little is known about how metabolic signals affect the balance between enzymatic and regulatory roles of these dual functional proteins. We previously described the RNA binding activity of a 63 kDa chloroplast protein from Chlamydomonas reinhardtii, which has been implicated in expression of the psbA mRNA, encoding the D1 protein of photosystem II. Here, we identify this factor as dihydrolipoamide acetyltransferase (DLA2), a subunit of the chloroplast pyruvate dehydrogenase complex (cpPDC), which is known to provide acetyl-CoA for fatty acid synthesis. Analyses of RNAi lines revealed that DLA2 is involved in the synthesis of both D1 and acetyl-CoA. Gel filtration analyses demonstrated an RNP complex containing DLA2 and the chloroplast psbA mRNA specifically in cells metabolizing acetate. An intrinsic RNA binding activity of DLA2 was confirmed by in vitro RNA binding assays. Results of fluorescence microscopy and subcellular fractionation experiments support a role of DLA2 in acetate-dependent localization of the psbA mRNA to a translation zone within the chloroplast. Reciprocally, the activity of the cpPDC was specifically affected by binding of psbA mRNA. Beyond that, in silico analysis and in vitro RNA binding studies using recombinant proteins support the possibility that RNA binding is an ancient feature of dihydrolipoamide acetyltransferases. Our results suggest a regulatory function of DLA2 in response to growth on reduced carbon energy sources. This raises the intriguing possibility that this regulation functions to coordinate the synthesis of lipids and proteins for the biogenesis of photosynthetic membranes

A dynamic theory of regulatory capture

Firms often try to influence individuals that, like regulators, are tasked with advising or deciding on behalf of a third party. In a dynamic regulatory setting, we show that a firm may prefer to capture regulators through the promise of a lucrative future job opportunity (i.e., the revolving-door channel) than through a hidden payment (i.e., a bribe). This is because the revolving door publicly signals the firm's eagerness and commitment to rewarding lenient regulators, which facilitates collusive equilibria. We find that opening the revolving door conditional on the regulator's report is usually more efficient than a blanket ban on post-agency employment and may increase social welfare. This insight extends to a variety of applications and can also be used to determine the optimal length of cooling-off periods

Long-Term Employment Relations when Agents Are Present Biased

We analyze how agents' present bias affects optimal contracting in an infinite-horizon employment setting. The principal maximizes profits by offering a menu of contracts to naive agents: a virtual contract - which agents plan to choose in the future - and a real contract which they end up choosing. This virtual contract motivates the agent and allows the principal to keep the agent below his outside option. Moreover, under limited liability, implemented effort can be inefficiently high. With a finite time horizon, the degree of exploitation of agents decreases over the life-cycle. While the baseline model abstracts from moral hazard, we show that the result persists also when allowing for non-contractible effort

Blade Failures on an Axial Compressor by Unexpected Gas Compositions

Case StudiesA fifteen stage axial compressor including a bleed extraction was subject to a major overhaul after nearly 20 years of trouble free operation. Shortly after recommissioning and resumption of the production the compressor faced three major failures within two weeks. A root cause failure analysis was conducted and revealed that the process plant start-up procedures caused gas compositions which deviated strongly from the design conditions. The valve designs as well as the available control parameters were not able to protect the compressor from off-design operating conditions. For future compressor failure prevention, the process start-up procedures were adapted and the existing control parameters/logic was upgraded. The new control logic reacts to the transient process behaviours during start-up by continuous harmonization of the safety valves