Aptek (United States)

How should one select the best detector and the best spectrometer configuration for a particular measurement in X‐ray spectroscopy? The end user is typically interested in obtaining the best precision, accuracy, and detection limit but these are indirectly related to the typical spectrometer specifications, such as energy resolution measured with 55Fe, maximum count rate, or detector area. In this article, we will quantify how the measurement uncertainty (precision, accuracy, and detection limit) are related to spectrometer parameters. We will derive the relationships for common measurement cases, will show data validating these relationships, and will indicate how this information can be used to select the optimum detector and spectrometer configuration for specific applications.

Project success depends on the ability to respond to risks and make correct decisions in a timely manner. The project approach provides a better framework for implementing a new management system into the company’s business processes. The risk management framework developed by the company comprises a risk management infrastructure, a set of standards, human resources, and a risk management information system. To improve staff compliance, it is necessary to provide training and to communicate the goals of the project effectively. It is also important to develop a motivation system because well trained and motivated staff are able to work more efficiently.

Sequence-to-sequence attention-based models on subword units allow simple open-vocabulary end-to-end speech recognition. In this work, we show that such models can achieve competitive results on the Switchboard 300h and LibriSpeech 1000h tasks. In particular, we report the state-of-the-art word error rates (WER) of 3.54% on the dev-clean and 3.82% on the test-clean evaluation subsets of LibriSpeech. We introduce a new pretraining scheme by starting with a high time reduction factor and lowering it during training, which is crucial both for convergence and final performance. In some experiments, we also use an auxiliary CTC loss function to help the convergence. In addition, we train long short-term memory (LSTM) language models on subword units. By shallow fusion, we report up to 27% relative improvements in WER over the attention baseline without a language model.

When an uncollimated radioactive X-ray source illuminates a silicon PIN sensor, some ionizing events are generated in the nonimplanted gap between the active area of the sensor and the guard rings (GRs). Carriers can be collected by floating electrodes, i.e., electron accumulation layers at the silicon/oxide interface, and floating GRs. The crosstalk signals generated by these events create spurious peaks, replicas of the main peaks at either lower amplitude or of opposite polarity. We explain this phenomenon as crosstalk caused by charge collected on these floating electrodes, which can be analyzed by means of an extension of Ramo theorem.

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We have developed a new compact thermal ion sensor suitable for spaceflight or laboratory applications. The device is highly sensitive and has a wide dynamic range due to its use of a microchannel plate charge multiplier. It allows spatial variations in velocity and anisotropic temperatures to be measured in a flowing plasma stream using a segmented anode. It has a high rejection to solar UV due to the trajectories of the particles within the device. The device has been flight tested as part of the Charging Hazards and Wake Studies flight experiment and sample data from the flight are presented. We discuss interpretation of the output of the device including extracting the parallel and perpendicular temperatures and the flow energy of a plasma stream.

In helping Los Alamos to understand the vessel response of explosive confinement vessels, APTEK has provided analysis of a 6 foot diameter vessel subjected to a spherical explosive blast. Correlations between analysis and test were very good except at the bottom of the vessel. A beating response was seen in the tests which reinforced the primary response mode at the bottom of the vessel, possibly to the extent of causing local yielding at the bottom. The authors did not predict the beating response and could not explain its origin. Since both APTEK and LANL felt that understanding these strains was important, they investigated the nature and possible origins of the response. They began a systematic study of the effects of various parameters of the problem. In separate analyses, they added boundary conditions, increased the mass of the ports by 10%, and included a row of 10% stiffer material to represent the weld. Of these, only the added boundary condition had a significant effect, and the boundary condition applied (vertical fixity at the bottom of two opposite ports to simulate the slings used) caused the strains at the bottom to decrease. They also made a less refined quarter-symmetric model with three elements through the thickness to perform a modal analysis. They found mode shapes similar in character to the deformed shapes obtained from the dynamic response. They theorized that the pressure reflections in the vessel were exciting one of these modes in the test but not in the analysis. They changed the timing of the pressure reflections to coincide with the suspected secondary response mode. For a 15% change in the timing of the pressure pulses, and with no change in the magnitude of the pressure, they obtained an increase in vessel strains at the bottom of over 40%.

A space qualified 260° spherical plate electrostatic analyzer has been developed as a plasma diagnostic tool. The use of nested spheres and unusually shaped microchannel plates has resulted in a sensor capable of measuring simultaneously the three-dimensional populations of ions and electrons in a plasma. High-current microchannel plates and a new packaging of a hybrid preamplifier discriminator are combined with an uncommon high-voltage circuit. The combination of these features yields an analyzer that is compact and lightweight, efficient in its power consumption, and has a broad dynamic range.

Abstract A closed‐form analysis for elastic—plastic response of a circular hole in an infinite Mohr—Coulomb medium under axisymmetric loading shows the effect of repeated loading on the stress and displacement fields around the hole. Examples show how repeat‐load closure increment is affected by working load, internal pressure, material compressive strength and internal friction. The solution is used to predict results of a laboratory test performed on a rock simulant specimen that contained a reinforced hole. Analytical and laboratory results are similar: at small closures (a few per cent, but well into the plastic response range), the closure increment from an unload—reload cycle is small compared with the initial closure. Closure increments for each of several cycles are comparable and cumulative.