1,295 research outputs found
Characterization of nickel-cadmium electrodes final report, 1 jul. 1963 - 31 dec. 1964
Characterization of electrodes in nickel-cadmium spacecraft batteries prior to and after cyclic testin
A Bayesian Networks Approach to Operational Risk
A system for Operational Risk management based on the computational paradigm
of Bayesian Networks is presented. The algorithm allows the construction of a
Bayesian Network targeted for each bank using only internal loss data, and
takes into account in a simple and realistic way the correlations among
different processes of the bank. The internal losses are averaged over a
variable time horizon, so that the correlations at different times are removed,
while the correlations at the same time are kept: the averaged losses are thus
suitable to perform the learning of the network topology and parameters. The
algorithm has been validated on synthetic time series. It should be stressed
that the practical implementation of the proposed algorithm has a small impact
on the organizational structure of a bank and requires an investment in human
resources limited to the computational area
Towards a Functionally-Formed Air Traffic System-of-Systems
Incremental improvements to the national aviation infrastructure have not resulted in sufficient increases in capacity and flexibility to meet emerging demand. Unfortunately, revolutionary changes capable of substantial and rapid increases in capacity have proven elusive. Moreover, significant changes have been difficult to implement, and the operational consequences of such change, difficult to predict due to the system s complexity. Some research suggests redistributing air traffic control functions through the system, but this work has largely been dismissed out of hand, accused of being impractical. However, the case for functionally-based reorganization of form can be made from a theoretical, systems perspective. This paper investigates Air Traffic Management functions and their intrinsic biases towards centralized/distributed operations, grounded in systems engineering and information technology theories. Application of these concepts to a small airport operations design is discussed. From this groundwork, a robust, scalable system transformation plan may be made in light of uncertain demand
Effects of Acute Cadmium Exposure on the Pituitary Gland of Podarcis sicula
Reptiles are rarely used in studies on the possible toxic effects of heavy metals even if they are susceptible to
the accumulation of persistent pollution due also to their presence in a variety of habitats. Cadmium is a heavy metal, a
significant environmental pollutant and an endocrine disruptor. Therefore the aim of this study was to analyze the
cytotoxic effects of cadmium on the pituitary gland of the lizard Podarcis sicula after an acute exposure to this metal. The
analysis were carried out after 2, 7 and 16 days following the intraperitoneal injection of a single and massive dose of
cadmium chloride. The pituitary glands were analyzed by histological and immuhistochemical stains. Besides cadmium
accumulation in brain was measured by atomic absorption spectrometry. Cadmium concentration increased in lizard brain
lightly after 2 days and widely after 16 days. The tissue of the pituitary gland appeared slightly atrophied in a few areas
only at 7 and 16 days after treatment. Moreover an increase in intensity of immunostaining and occurrence of some
adenohypophyseal cells was revealed respect to control lizards. This evidence suggests an inhibitory effect of cadmium on
the normal hormonal secretion. Evidently an acute cadmium exposure in P. sicula involves the accumulation of this metal
in the brain but also the alteration of the normal endocrine function of the pituitary gland
Integration of Weather Avoidance and Traffic Separation
This paper describes a dynamic convective weather avoidance concept that compensates for weather motion uncertainties; the integration of this weather avoidance concept into a prototype 4-D trajectory-based Airborne Separation Assurance System (ASAS) application; and test results from a batch (non-piloted) simulation of the integrated application with high traffic densities and a dynamic convective weather model. The weather model can simulate a number of pseudo-random hazardous weather patterns, such as slow- or fast-moving cells and opening or closing weather gaps, and also allows for modeling of onboard weather radar limitations in range and azimuth. The weather avoidance concept employs nested "core" and "avoid" polygons around convective weather cells, and the simulations assess the effectiveness of various avoid polygon sizes in the presence of different weather patterns, using traffic scenarios representing approximately two times the current traffic density in en-route airspace. Results from the simulation experiment show that the weather avoidance concept is effective over a wide range of weather patterns and cell speeds. Avoid polygons that are only 2-3 miles larger than their core polygons are sufficient to account for weather uncertainties in almost all cases, and traffic separation performance does not appear to degrade with the addition of weather polygon avoidance. Additional "lessons learned" from the batch simulation study are discussed in the paper, along with insights for improving the weather avoidance concept. Introductio
On the Number of Cosmic Strings
The number of cosmic strings in the observable universe is relevant in
determining the probability of detecting such cosmic defects through their
gravitational signatures. In particular, we refer to the observation of
gravitational lensing events and anisotropy in the CMB radiation induced by
cosmic strings. In this paper, a simple method is adopted to obtain an
approximate estimate of the number of segments of cosmic strings, crossing the
particle horizon, which fall inside the observed part of the universe. We show
that there is an appreciable difference in the expected number of segments
which differentiates cosmic strings arising in Abelian Higgs and Nambu-Goto
models, and that a different choice of setting for the cosmological model can
lead to significant differences in the expected number of cosmic string
segments. Of this number, the fraction realistically detectable may be
considerably smaller.Comment: LaTex2e, 15 pages, 1 figure, 5 tables. Subject extended to other
cosmological scenarios from Sect. 3 on hence, it follows a modification in
the title; three tables and references added. Version to appear in MNRA
Human in the Loop Simulation Measures of Pilot Response Delay in a Self-Separation Concept of Operations
A human-in-the-loop (HITL) simulation experiment was conducted by the National Aeronautics and Space Administration (NASA) to assess airline transport pilots performance and reported acceptance of the use of procedures relying on airborne separation assistance and trajectory management tools. This study was part of a larger effort involving two NASA centers that includes multiple HITL experiments planned over the next few years to evaluate the use of automated separation assurance (SA) tools by both air traffic controllers and pilots. This paper presents results of measured pilot response delay that subject pilots incurred when interacting with cockpit tools for SA and discusses possible implications for future concept and procedures design
Scaling relation for determining the critical threshold for continuum percolation of overlapping discs of two sizes
We study continuum percolation of overlapping circular discs of two sizes. We
propose a phenomenological scaling equation for the increase in the effective
size of the larger discs due to the presence of the smaller discs. The critical
percolation threshold as a function of the ratio of sizes of discs, for
different values of the relative areal densities of two discs, can be described
in terms of a scaling function of only one variable. The recent accurate Monte
Carlo estimates of critical threshold by Quintanilla and Ziff [Phys. Rev. E, 76
051115 (2007)] are in very good agreement with the proposed scaling relation.Comment: 4 pages, 3 figure
UAS in the NAS Air Traffic Controller Acceptability Study-1: The Effects of Horizontal Miss Distances on Simulated UAS and Manned Aircraft Encounters
This study examined air traffic controller acceptability ratings based on the effects of differing horizontal miss distances (HMDs) for encounters between UAS and manned aircraft. In a simulation of the Dallas/Fort Worth (DFW) East-side airspace, the CAS-1 experiment at NASA Langley Research Center enlisted fourteen recently retired DFW air traffic controllers to rate well-clear volumes based on differing HMDs that ranged from 0.5 NM to 3.0 NM. The controllers were tasked with rating these HMDs from "too small" to "too excessive" on a defined, 1-5, scale and whether these distances caused any disruptions to the controller and/or to the surrounding traffic flow. Results of the study indicated a clear favoring towards a particular HMD range. Controller workload was also measured. Data from this experiment and subsequent experiments will play a crucial role in the FAA's establishment of rules, regulations, and procedures to safely and efficiently integrate UAS into the NAS
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