Experimental creep data for a built-up aluminum/titanium structure subjected to heating and loading

Experimental creep, temperature, and strain data resulting from a laboratory experiment on a built-up aluminum/titanium structure are presented. The structure and the experiment are described in detail. A heating and loading experiment lasting approximately six hours is conducted on a test structure. Considerable creep strain resulted from compressive stresses in the heated skin. Large residual stresses were found after the experiment was completed. The residual stresses in the substructure frames were large enough to preclude further cycles of creep experiments with this built-up structure because of concern that the frame webs would buckle

Long-range correlations and trends in Colombian seismic time series

We study long-range correlations and trends in time series extracted from the data of seismic events occurred from 1973 to 2011 in a rectangular region that contains mainly all the continental part of Colombia. The long-range correlations are detected by the calculation of the Hurst exponents for the time series of interevent intervals, separation distances, depth differences and magnitude differences. By using a modification of the classical $R/S$ method that has been developed to detect short-range correlations in time series, we find the existence of persistence for all the time series considered except for magnitude differences. We find also, by using the $DFA$ until the third order, that the studied time series are not influenced by trends. Additionally, an analysis of the Hurst exponent as a function of the number of events in the time and the maximum window size is presented.Comment: 21 pages, 6 figures, 2 figures added, types corrected, accepted to be published in Physica

Systems development of a stall/spin research facility using remotely controlled/augmented aircraft models. Volume 1: Systems overview

A ground based, general purpose, real time, digital control system simulator (CSS) is specified, developed, and integrated with the existing instrumentation van of the testing facility. This CSS is built around a PDP-11/55, and its operational software was developed to meet the dual goal of providing the immediate capability to represent the F-18 drop model control laws and the flexibility for expansion to represent more complex control laws typical of control configured vehicles. Overviews of the two CSS's developed are reviewed as well as the overall system after their integration with the existing facility. Also the latest version of the F-18 drop model control laws (REV D) is described and the changes needed for its incorporation in the digital and analog CSS's are discussed

Efficient Algorithms for Asymptotic Bounds on Termination Time in VASS

Vector Addition Systems with States (VASS) provide a well-known and fundamental model for the analysis of concurrent processes, parameterized systems, and are also used as abstract models of programs in resource bound analysis. In this paper we study the problem of obtaining asymptotic bounds on the termination time of a given VASS. In particular, we focus on the practically important case of obtaining polynomial bounds on termination time. Our main contributions are as follows: First, we present a polynomial-time algorithm for deciding whether a given VASS has a linear asymptotic complexity. We also show that if the complexity of a VASS is not linear, it is at least quadratic. Second, we classify VASS according to quantitative properties of their cycles. We show that certain singularities in these properties are the key reason for non-polynomial asymptotic complexity of VASS. In absence of singularities, we show that the asymptotic complexity is always polynomial and of the form $\Theta(n^k)$, for some integer $k\leq d$, where $d$ is the dimension of the VASS. We present a polynomial-time algorithm computing the optimal $k$. For general VASS, the same algorithm, which is based on a complete technique for the construction of ranking functions in VASS, produces a valid lower bound, i.e., a $k$ such that the termination complexity is $\Omega(n^k)$. Our results are based on new insights into the geometry of VASS dynamics, which hold the potential for further applicability to VASS analysis.Comment: arXiv admin note: text overlap with arXiv:1708.0925

Restructurable Controls

Restructurable control system theory, robust reconfiguration for high reliability and survivability for advanced aircraft, restructurable controls problem definition and research, experimentation, system identification methods applied to aircraft, a self-repairing digital flight control system, and state-of-the-art theory application are addressed

Evaluación de las condiciones de mezcla y su influencia sobre el cloro residual entanques de compensación de un sistema de distribución de agua potable

We performed a real scale evaluation of mixing conditions and its influence on water quality in a compensation tank of drinking-water distribution system located in the city of Cali, Colombia. The hydrodynamic study with continuous injection of tracer, and temperature and free chlorine measurements for identifying the mixing regime in the tank’s interior, residence time, thermal stratification, and chlorine variations in the stored water showed the typical characteristics of a compensation tank. We concluded that water recirculation, inadequate water exchange, low moment fluxes associated with low velocity flows, and punctual thermal stratification could lead to high water age, high residence times in the tank, inadequate mixing, and important loss of free residual chlorine. The methodology developed is suitable for evaluation and optimization of compensation tanks of drinking water distribution systems.Realizamos una evaluación a escala real de las condiciones de mezcla y su influencia en la calidad del agua en un tanque de compensación del sistema de distribución de agua potable ubicado en la ciudad de Cali, Colombia. El estudio hidrodinámico con inyección continua de marcador y mediciones de temperatura y cloro libre para identificar el régimen de mezcla en el interior del tanque, el tiempo de residencia, la estratificación térmica y las variaciones de cloro en el agua almacenada mostraron las características típicas de un tanque de compensación. Llegamos a la conclusión de que la recirculación de agua, el intercambio de agua inadecuado, los flujos de momento bajos asociados con los flujos de baja velocidad y la estratificación térmica puntual podrían conducir a una alta edad del agua, tiempos de residencia elevados en el tanque, mezcla inadecuada y pérdida importante de cloro residual libre. La metodología desarrollada es adecuada para la evaluación y optimización de tanques de compensación de sistemas de distribución de agua potable

Synthesizing Skyrmion Molecules in Fe-Gd Thin Films

We show that properly engineered amorphous Fe-Gd alloy thin films with perpendicular magnetic anisotropy exhibit room-temperature skyrmion molecules, or a pair of like-polarity, opposite-helicity skyrmions. Magnetic mirror symmetry planes present in the stripe phase, instead of chiral exchange, determine the internal skyrmion structure and the net achirality of the skyrmion phase. Our study shows that stripe domain engineering in amorphous alloy thin films may enable the creation of skyrmion phases with technologically desirable properties.Comment: 15 pages, 6 figures. Accepted for publication in Applied Physics Letter

Status of Superconducting RF Linac Development for APT

This paper describes the development progress of high current superconducting RF linacs in Los Alamos, performed to support a design of the linac for the APT (Accelerator Production of Tritium) Project. The APT linac design includes a CW superconducting RF high energy section, spanning an energy range of 211 to 1030 MeV, and operating at a frequency of 700 MHz with two constant beta sections (beta of 0.64 and 0.82). In the last two years, we have progressed towards build a cryomodule with beta of 0.64. We completed the designs of the 5 cell superconducting cavities and the 210 kW power couplers. We are scheduled to begin assembly of the cryomodule in September 2000. In this paper, we present an overview of the status of our development efforts and a report on the results of the cavity and coupler test program.Comment: LINAC2000 THD1