Returns to scale, productivity and efficiency in US banking (1989-2000): the neural distance function revisited

Productivity and efficiency analyses have been indispensable tools for evaluating firms’ performance in the banking sector. In this context, the use of Artificial Neural Networks (ANNs) has been recently proposed in order to obtain a globally flexible functional form which is capable of approximating any existing output distance function while enabling the a priori imposition of the theoretical properties dictated by production theory, globally. Previous work has proposed and estimated the so-called Neural Distance Function (NDF) which has numerous advantages when compared to widely adopted specifications. In this paper, we carefully refine some of the most critical characteristics of the NDF. First, we relax the simplistic assumption that each equation has the same number of nodes because it is not expected to approximate reality with any reasonable accuracy and different numbers of nodes are allowed for each equation of the system. Second, we use an activation function which is known to achieve faster convergence compared to the conventional NDF model. Third, we use a relevant approach for technical efficiency estimation based on the widely adopted literature. Fitting the model to a large panel data we illustrate our proposed approach and estimate the Returns to Scale, the Total Factor Productivity and the Technical Efficiency in US commercial banking (1989-2000). Our approach provides very satisfactory results compared to the conventional model, a fact which implies that the refined NDF model successfully expands and improves the conventional NDF approach.Output distance function; Neural networks; Technical efficiency; US banks

Coupled cluster benchmarks of water monomers and dimers extracted from DFT liquid water: the importance of monomer deformations

To understand the performance of popular density-functional theory (DFT) exchange-correlation (xc) functionals in simulations of liquid water, water monomers and dimers were extracted from a PBE simulation of liquid water and examined with coupled cluster with single and double excitations plus a perturbative correction for connected triples [CCSD(T)]. CCSD(T) reveals that most of the dimers are unbound compared to two gas phase equilibrium water monomers, largely because monomers within the liquid have distorted geometries. Of the three xc functionals tested, PBE and BLYP systematically underestimate the cost of the monomer deformations and consequently predict too large dissociation energies between monomers within the dimers. This is in marked contrast to how these functionals perform for an equilibrium water dimer and other small water clusters in the gas phase, which only have moderately deformed monomers. PBE0 reproduces the CCSD(T) monomer deformation energies very well and consequently the dimer dissociation energies much more accurately than PBE and BLYP. Although this study is limited to water monomers and dimers, the results reported here may provide an explanation for the overstructured radial distribution functions routinely observed in BLYP and PBE simulations of liquid water and are of relevance to water in other phases and to other associated molecular liquids.Comment: 10 pages, 8 figures, Submitted to Journal of Chemical Physics, Related information can be found in http://www.fhi-berlin.mpg.de/th

Technoeconomic study of engine deterioration and compressor washing for military gas turbine engines

Despite spending much of their operating life in clear air, aircraft gas turbine engines are naturally prone to deterioration as they are generally not fitted with air filters. Engines are particularly at risk during takeoff and landing, and whilst operating in areas of pollution, sand, dust storms, etc. The build-up of contaminants, especially on the compressor surfaces, leads to a dramatic reduction in compressor efficiency, which gives rise to a loss of available power, increased fuel consumption and increased exhaust gas temperature. These conditions can lead to flight delays, inspection failures, withdrawal from service, increased operating costs and safety compromises.With the growing interest in life cycle costs for gas turbine engines, both engine manufacturers and operators are investigating the tradeoffs between performance improvements and associated maintenance costs. This report introduces the problem of output and efficiency degradation in two aero gas turbine engines (the T56–A–15 and the F110–GE–129) caused by various deterioration factors. Their causes are broadly discussed and the effects on powerplant performance are simulated and analyzed. One of the key factors leading to performance losses during operation of these engines is compressor fouling. The fouling can come from a wide variety of sources; hydrocarbons from fuel and lubricating oils; volcanic ash; pollen; marine aerosols; dust; smoke; pollution, etc. The presence of these fouling sources acts as a bonding agent for the solid contaminants, ‘gluing’ them to the compressor surfaces. Thus, the aggravation in terms of power output, fuel consumption and additional time to carry out a typical mission will be assessed and an economic analysis will be attempted in order to quantify the effects of compressor fouling on the additional costs which arise, because of this specific deterioration. The effect of compressor fouling can be maintained by frequent cleaning to improve efficiency, resulting, hence, in improved power output, fuel savings and prolonged engine life. Compressor cleaning is thoroughly presented, and the implementation of on-wing off-line cleaning on the performance of the F110 engine was investigated from a technical and economical standpoint. Finally, according to the results obtained, the optimal frequency of compressor washing for the F110 engine is estimated, in order to eliminate safety compromises, improve performance and reduce the engine’s life cycle cost

On how good DFT exchange-correlation functionals are for H bonds in small water clusters: Benchmarks approaching the complete basis set limit

The ability of several density-functional theory (DFT) exchange-correlation functionals to describe hydrogen bonds in small water clusters (dimer to pentamer) in their global minimum energy structures is evaluated with reference to second order Moeller Plesset perturbation theory (MP2). Errors from basis set incompleteness have been minimized in both the MP2 reference data and the DFT calculations, thus enabling a consistent systematic evaluation of the true performance of the tested functionals. Among all the functionals considered, the hybrid X3LYP and PBE0 functionals offer the best performance and among the non-hybrid GGA functionals mPWLYP and PBE1W perform the best. The popular BLYP and B3LYP functionals consistently underbind and PBE and PW91 display rather variable performance with cluster size.Comment: 9 pages including 4 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

CPR flow to prime the ischemic heart during cardiac arrest?

Cardiac arrest is unique among cardiac ischemic syndromes in that all circulation must be generated external to the heart. Although, chest compressions deliver limited blood flow, it may be possible to take advantage of this cardiopulmonary resuscitation (CPR) low-flow state to “prime” the heart in advance of return of restoration of spontaneous circulation. Prior investigation has demonstrated improved cardiac function after perfusing the globally ischemic heart with a cardioprotective agent under low-flow perfusion conditions (modeling CPR flow). These results raise the question as to whether CPR-generated flow can be utilized to induce pharmacological post-conditioning in the arrested heart

Action Amplification: A New Approach To Scalable Administration

We present a systems-management approach that enables administrators to effectively handle the challenge of increasing numbers of hosts, routers, users, and services in the networks to manage. Our approach is to map the actions of an administrator on a single host (such as creating a new user account) to the network at large, while maintaining the exact same interface. Our system amplifies the administrator's actions appropriately throughout the network, and confirms the correct propagation of all configuration changes throughout the distributed system. We argue that this approach allows administrators to easily manage several aspects of a large domain, because it provides a familiar and intuitive interface. Such a system can be used as a front-end to any other automation system used to manage large domains. To determine the feasibility of our approach, we implemented it on the OpenBSD system. We discuss the prototype implementation, along with the limitations to our approach that it exposes