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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Characterization of Mid-Infrared Single Mode Fibers as Modal Filters

We present a technique for measuring the modal filtering ability of single mode fibers. The ideal modal filter rejects all input field components that have no overlap with the fundamental mode of the filter and does not attenuate the fundamental mode. We define the quality of a nonideal modal filter Q(sub f) as the ratio of transmittance for the fundamental mode to the transmittance for an input field that has no overlap with the fundamental mode. We demonstrate the technique on a 20 cm long mid-infrared fiber that was produced by the U.S. Naval Research Laboratory. The filter quality Q(sub f) for this fiber at 10.5 micron wavelength is 1000 +/- 300. The absorption and scattering losses in the fundamental mode are approximately 8 dB/m. The total transmittance for the fundamental mode, including Fresnel reflections, is 0.428 +/- 0.002. The application of interest is the search for extrasolar Earthlike planets using nulling interferometry. It requires high rejection ratios to suppress the light of a bright star, so that the faint planet becomes visible. The use of modal filters increases the rejection ratio (or, equivalently, relaxes requirements on the wavefront quality) by reducing the sensitivity to small wavefront errors. We show theoretically that, exclusive of coupling losses, the use of a modal filter leads to the improvement of the rejection ratio in a two-beam interferometer by a factor of Q(sub f).

single mode fibers↗
NASA NTRS2012

A Comparison of Filter-based Approaches for Model-based Prognostics

Model-based prognostics approaches use domain knowledge about a system and its failure modes through the use of physics-based models. Model-based prognosis is generally divided into two sequential problems: a joint state-parameter estimation problem, in which, using the model, the health of a system or component is determined based on the observations; and a prediction problem, in which, using the model, the stateparameter distribution is simulated forward in time to compute end of life and remaining useful life. The first problem is typically solved through the use of a state observer, or filter. The choice of filter depends on the assumptions that may be made about the system, and on the desired algorithm performance. In this paper, we review three separate filters for the solution to the first problem: the Daum filter, an exact nonlinear filter; the unscented Kalman filter, which approximates nonlinearities through the use of a deterministic sampling method known as the unscented transform; and the particle filter, which approximates the state distribution using a finite set of discrete, weighted samples, called particles. Using a centrifugal pump as a case study, we conduct a number of simulation-based experiments investigating the performance of the different algorithms as applied to prognostics.

prognostics↗
DOE OSTI2019

Towards Efficient Convolutional Neural Networks Through Low-Error Filter Saliency Estimation

Filter saliency based channel pruning is a state-of-the-art method for deep convolutional neural network compression and acceleration. This channel pruning method ranks the importance of individual filter by estimating its impact of each filter’s removal on the training loss, and then remove the least important filters and fine-tune the remnant network. In this work, we propose a systematic channel pruning method that significantly reduces the estimation error of filter saliency. Different from existing approaches, our method largely reduces the magnitude of parameters in a network by introducing alternating direction method of multipliers (ADMM) into the pre-training procedure. Therefore, the estimation of filter saliency based on Taylor expansion is significantly improved. Extensive experiments with various benchmark network architectures and datasets demonstrate that the proposed method has a much improved unimportant filter selection capability and outperform state-of-the-art channel pruning method.

Wang, Zi↗
DOE OSTI2019

Nuclear Factor-κB is Activated in Filter-Implanted Vena Cava

Background: Implantation of a retrievable vena cava filter (VCF) is an effective method for preventing pulmonary embolism. Retrieval of filters, however, may be difficult due to intimal hyperplasia and inflammation in the cava wall. The transcription factor nuclear factor-kappaB (NF-κB) plays an important role in regulation of numerous genes participating in the inflammatory and proliferative responses of cells. The present study was to determine whether VCF implantation resulted in activation of NF-κB in the venous neointima. Methods: Filters were placed in vena cava (VC) in four swine for 30 days and then removed. Intimal specimens adhering to the filter struts were analyzed with reference to normal VC tissues. Immunohistochemical analyses were used to assess the NF-κB subunits p65 and p50 and the phosphorylated inhibitor of κB-α (phosphor-IκB-α) in the tissues. NF-κB DNA-binding activity was measured with enzyme-linked immunosorbent assay. Results: As compared to normal VC tissues, the intimal tissues contained higher percentages of cell nucleus-located p65 and p50, and NF-κB DNA-binding activity. Elevated immunoreactivities of p65, p50 and phosphor-IκB-α were also present in the intima. Conclusion: The present study demonstrates for the first time that VCF implantation caused NF-κB activation in neointima. We further demonstrate the activation is at least partly due to phosphorylation of IκB-α. Our data suggest that NF-κB activation would significantly contribute to development of intimal hyperplasia and inflammation in filter-inserted vena cava walls. NF-κB might be a therapeutic target for inhibiting filter-induced neointima and improving filter retrieval.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Inferior Vena Cava Filters in Hemodynamically Unstable Patients with Acute Pulmonary Embolism: How Often are They Used? Data from Multicenter Prospective Registries on Acute Pulmonary Embolism

The use of inferior vena cava (IVC) filters is recommended in patients with acute pulmonary embolism (PE) who have absolute contraindications to anticoagulant drugs and/or in those subjects with recurrent PE despite treated with an adequate anticoagulant regimen. During the last 2 decades, some investigations have demonstrated that the use of IVC filters in high-risk PE patients, treated or not with systemic thrombolysis, was able to reduce the short-term mortality rate if inserted early after the acute event. The aim of the present review is to analyze the use of IVC filters in high-risk PE patients enrolled in prospective multicenter registries between 1990 and 2018. After screening 3542 article in PubMed, Scopus, Cochrane library and Goggle Scholar databases, we identified four registry studies meeting the inclusion criteria. In a prospective cohort of 39,056 patients, 1387 (3.5%) were hemodynamically unstable at admission. Among them, IVC filters were used only in 2.7% of cases. Conversely, IVC filters were inserted in 3.8% of hemodynamically stable patients. Over the years, a fluctuating trend in the use of IVC filters was observed. In the absence of randomized controlled trial on this issue, which would be difficult, if not impossible to realize, data obtained from the medical literature seem to suggest that IVC filters could represent a valid adjunctive therapy in hemodynamically unstable PE patients, able to prevent further hemodynamic deterioration. Further and larger subgroup analyses, obtained both by prospective and retrospective studies, are necessary to clarify this therapeutic approach.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Combined selective emitter and filter for high performance incandescent lighting

The efficiency of incandescent light bulbs (ILBs) is inherently low due to the dominant emission at infrared wavelengths, diminishing its popularity today. ILBs with cold-side filters that transmit visible light but reflect infrared radiation back to the filament can surpass the efficiency of state-of-the- art light-emitting diodes (LEDs). However, practical challenges such as imperfect geometrical alignment (view factor) between the filament and cold-side filters can limit the maximum achievable efficiency and make the use of cold-side filters ineffective. Here in this work, we show that by combining a cold-side optical filter with a selective emitter, the effect of the imperfect view factor between the filament and filter on the system efficiency can be minimized. We experimentally and theoretically demonstrate energy savings of up to 67% compared to a bare tungsten emitter at 2000 K, representing a 34% improvement over a bare tungsten filament with a filter. Our work suggests that this approach can be competitive with LEDs in both luminous efficiency and color rendering index (CRI) when using selective emitters and filters already demonstrated in the literature, thus paving the way for next-generation high-efficiency ILBs.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Enhancing Thomson scattering polychromator performance with multi-pass spectral filters

In photon-deficient, noncollective Thomson scattering diagnostics, filter polychromators are typically employed in the spectral analysis of Thomson-scattered signals to achieve acceptable signal-to-noise performance. Currently, the most common polychromator filter configuration employs a set of single-passband optical filters that define individual spectral channels. Here, we introduce a new spectral analysis method for Thomson scattering based on spectral filters with multiple passbands, referred to as Thomson scattering spectral multiplexing. Implementing multi-bandpass spectral filters on polychromators increases the achievable range of electron temperature measurement for a given number of filters employed. In addition, Thomson scattering spectral multiplexing reduces systematic measurement uncertainty, with fewer required spectral channels, thereby decreasing light loss from reduced optical element interactions. A multi-bandpass filter set, optimized by a genetic algorithm, has been successfully installed and tested on the Helically Symmetric eXperiment (HSX), demonstrating the benefits of the Thomson scattering spectral multiplexing method.

Instruments & Instrumentation↗
DOE OSTI2019

Protein interactions central to stabilizing the K[superscript +] channel selectivity filter in a four-sited configuration for selective K[superscript +] permeation

The structural and functional conversion of the nonselective NaK channel to a K{sup +} selective channel (NaK2K) allows us to identify two key residues, Tyr and Asp in the filter sequence of TVGYGD, that participate in interactions central to stabilizing the K{sup +} channel selectivity filter. By using protein crystallography and channel electrophysiology, we demonstrate that the K{sup +} channel filter exists as an energetically strained structure and requires these key protein interactions working in concert to hold the filter in the precisely defined four-sited configuration that is essential for selective K{sup +} permeation. Disruption of either interaction, as tested on both the NaK2K and eukaryotic K{sub v}1.6 channels, can reduce or completely abolish K{sup +} selectivity and in some cases may also lead to channel inactivation due to conformational changes at the filter. Additionally, on the scaffold of NaK we recapitulate the protein interactions found in the filter of the Kir channel family, which uses a distinct interaction network to achieve similar stabilization of the filter.

Sauer, David B.↗
DOE OSTI2022

Implementation and optimization of the PTOLEMY transverse drift electromagnetic filter

The PTOLEMY transverse drift filter is a new concept to enable precision analysis of the energy spectrum of electrons near the tritium β-decay endpoint. Here, we detail the implementation and optimization methods for successful operation of the filter for electrons with a known pitch angle. We present the first demonstrator that produces the required magnetic field properties with an iron return-flux magnet. Two methods for the setting of filter electrode voltages are detailed. The challenges of low-energy electron transport in cases of low field are discussed, such as the growth of the cyclotron radius with decreasing magnetic field, which puts a ceiling on filter performance relative to fixed filter dimensions. Additionally, low pitch angle trajectories are dominated by motion parallel to the magnetic field lines and introduce non-adiabatic conditions and curvature drift. To minimize these effects and maximize electron acceptance into the filter, we present a three-potential-well design to simultaneously drain the parallel and transverse kinetic energies throughout the length of the filter. These optimizations are shown, in simulation, to achieve low-energy electron transport from a 1 T iron core (or 3 T superconducting) starting field with initial kinetic energy of 18.6 keV drained to < 10 eV (< 1 eV) in about 80 cm. This result for low field operation paves the way for the first demonstrator of the PTOLEMY spectrometer for measurement of electrons near the tritium endpoint to be constructed at the Gran Sasso National Laboratory (LNGS) in Italy.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

SU-E-T-525: Ionization Chamber Perturbation in Flattening Filter Free Beams

Purpose: Changing the characteristic of a photon beam by mechanically removing the flattening filter may impact the dose response of ionization chambers. Thus, perturbation factors of cylindrical ionization chambers in conventional and flattening filter free photon beams were calculated by Monte Carlo simulations. Methods: The EGSnrc/BEAMnrc code system was used for all Monte Carlo calculations. BEAMnrc models of nine different linear accelerators with and without flattening filter were used to create realistic photon sources. Monte Carlo based calculations to determine the fluence perturbations due to the presens of the chambers components, the different material of the sensitive volume (air instead of water) as well as the volume effect were performed by the user code egs-chamber. Results: Stem, central electrode, wall, density and volume perturbation factors for linear accelerators with and without flattening filter were calculated as a function of the beam quality specifier TPR{sub 20/10}. A bias between the perturbation factors as a function of TPR{sub 20/10} for flattening filter free beams and conventional linear accelerators could not be observed for the perturbations caused by the components of the ionization chamber and the sensitive volume. Conclusion: The results indicate that the well-known small bias between the beam quality correction factor as a function of TPR20/10 for the flattening filter free and conventional linear accelerators is not caused by the geometry of the detector but rather by the material of the sensitive volume. This suggest that the bias for flattening filter free photon fields is only caused by the different material of the sensitive volume (air instead of water)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Filter Aerosol Measurements for ARM

The goal of this study was to determine the best filter media for use in ARM PSAPs following the manufacturer discontinuation of the current filter media. The study comprised by multiple experiments to assess four potential replacement filter medium relative to the Pallflex E-70, which is being discontinued, and is documented in ARM ServiceNow under ENG0003846. The experiments laid out in the document ‘180504 Filter Aerosol Measurements for ARM.docx’ and several subsequent tests suggest that the Pallflex Emfab media is the best candidate for ongoing ARM filter-based absorbance measurements. Other media were ruled out based on particle-capture efficiency for small particles. In tests with Nigrosin, EMFAB exceeded all other media. Tests were done measuring reported absorbance for all media in Particle Soot Absorption Photometers (PSAPs) operated in parallel sampling under several conditions: ambient air, 3 sizes of black-dyed PSL (Poly Styrene Latex) spheres, and Nigrosin particles. These tests indicate a different factor of reported absorbance for each media relative to the original Pallflex E70 filter. The factor for the Azumi media was consistent with unpublished work by Ogren (NOAA). The tests described here were not exhaustive and were complicated by time-varying differences among the PSAPs used. However, it is concluded that they are sufficient to justify ARM switching to Emfab filter media for future ARM PSAP measurements. The remaining store of E70 will be reserved to quantitatively characterize differences between Emfab and E70 (and Azumi?) in both laboratory and field side-by-side tests as put forth in a succeeding ENG. This future work will empirically identify correction factors applicable to Emfab and quantify the uncertainty in comparing the historical E70 measurements with ongoing Emfab measurements. Comparison of PSAP measurements with an independent absolute ‘reference’ for aerosol absorbance, i.e., PhotoThermal Interferometry or difference measurements of Cavity Attenuated Phase Shift extinction (CAPS) minus Nephelometry scattering would be valuable but exceed the scope of ARM Infrastructure. While the characterization of correction factors is required for maintaining and improving accuracy in future absorption measurements, it was beyond the scope of the current study.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Filter Aerosol Measurements for ARM

The goal of this study was to determine the best filter media for use in Atmospheric Radiation Measurement (ARM) particle soot absorption photometers (PSAPs) following the manufacturer discontinuation of the current filter media. The study comprised multiple experiments to assess four potential replacement filter medium relative to the Pallflex E-70, which is being discontinued, and is documented in ARM’s ServiceNow system under ENG0003846. The experiments laid out in the document ‘180504 Filter Aerosol Measurements for ARM.docx’ and several subsequent tests suggest that the Pallflex Emfab media is the best candidate for ongoing ARM filter-based absorbance measurements. Other media were ruled out based on particle capture efficiency for small particles. In tests with Nigrosin, Emfab exceeded all other media. Tests were done measuring reported absorbance for all media in PSAPs operated in parallel sampling under several conditions: ambient air, three sizes of black-dyed PSL (polystyrene latex) spheres, and Nigrosin particles. These tests indicate a different factor of reported absorbance for each media relative to the original Pallflex E70 filter. The factor for the Azumi media was consistent with unpublished work by Ogren (National Oceanic and Atmospheric Administration [NOAA]). The tests described here were not exhaustive and were complicated by time-varying differences among the PSAPs used. However, it is concluded that they are sufficient to justify ARM switching to Emfab filter media for future ARM PSAP measurements. The remaining store of E70 will be reserved to quantitatively characterize differences between Emfab and E70 (and Azumi?) in both laboratory and field side-by-side tests as put forth in a succeeding ENG. This future work will empirically identify correction factors applicable to Emfab and quantify the uncertainty in comparing the historical E70 measurements with ongoing Emfab measurements. Comparison of PSAP measurements with an independent absolute ‘reference’ for aerosol absorbance, i.e., photo thermal interferometry or difference measurements of cavity attenuated phase shift extinction (CAPS) minus nephelometry scattering, would be valuable but exceed the scope of ARM Infrastructure. While the characterization of correction factors is required for maintaining and improving accuracy in future absorption measurements, it was beyond the scope of the current study.

aerosol observing system↗
DOE OSTI2021

Collective Analysis of Alpha Particle Losses Due to Self-Absorption by Mass Loading on Radioactive Particulate Glass Fiber Filters

In this study, we derived a relationship between filter mass loading and the percent loss during analysis using the mass loading data collected from six previous studies of self-absorption. Components of mass loading include particulate dust, radioactive particulates, and filter material. In a research report published in 1984, Higby calculated a minimum burial depth for an alpha particle to be lost due to absorption (100% loss) of about 3.7 mg/cm 2 based on calculations for the range of 239-Pu alpha particles in glass fiber filters. From there, Higby concluded that a correction factor of 0.85 assumes approximately 15% losses in the count rate of both alpha and beta particles. In 2000, Luetzelschwab et al. recommended assuming a 40% loss at a loading of 3.3 mg/cm 2 and a 28% loss for a loading of 2.3 mg/cm 2 which included the frontal face mass of the filter. More recently, the 100% losses due to absorption were reported to be in the 10 mg/cm 2 range. Presented here is a trinomial relationship method of relating percent loss due to self-absorption to filter mass loading, based on data reported by Higby, Luetzelschwab et al., Huang et al., Barnett et al., Smith et al., and Hogue et al. Under normal operating conditions at the stacks monitored by Effluent Management, the mass loading of sample filters averages 0.09 ± 0.12 (2s) mg/cm 2 (excluding negative values and outliers) and ranges from 0 mg/cm 2 to 0.24 mg/cm 2 . Based on current mass loading results for Effluent Management stack sample filters, the forced-zero trinomial relationship method estimated self-absorption losses of less than 5%. Because American National Standards Institute/Health Physics Society N13.1-2011 guidelines indicate a correction factor should be used when the penetration of radioactive material into the collection media or self-absorption of radiation by the material collected would reduce the count rate by more than 5%, it is possible continued application of a correction factor to the Effluent Management stack samples is no longer necessary. Nevertheless, continuing to assign a correction factor at the 5% threshold (i.e., 0.95) would be a conservative approach.

36 MATERIALS SCIENCE↗
NASA NTRS1972

The compensated Kalman filter.

This paper introduces the compensated Kalman filter, a suboptimal state estimator which can be used to eliminate steady-state bias errors when it is used in conjunction with the mismatched steady-state (asymptotic) time-invariant Kalman-Bucy filter. The uncompensated mismatched steady state Kalman-Bucy filter exhibits bias errors whenever the nominal plant parameters used in the filter design are different from the actual plant parameters. The approach used relies on the utilization of the residual (innovations) process of the mismatched filter to estimate, via a Kalman-Bucy filter, the state estimation errors and subsequent improvements of the state estimate. The compensated Kalman filter augments the mismatched steady state Kalman-Bucy filrby the introduction of additional dynamics and feedforward integral compensation channels.

Athans, M.↗
NASA NTRS1972

A biased filter for linear discrete dynamic systems.

A recursive estimator, the ridge filter, was developed for the linear discrete dynamic estimation problem. Theorems were established to show that the ridge filter can be, on the average, closer to the expected value of the system state than the Kalman filter. On the other hand, Kalman filter, on the average, is closer to the instantaneous system state than the ridge filter. The ridge filter has been formulated in such a way that the computational features of the Kalman filter are preserved.

Chang, J. W.↗
NASA NTRS1970

Effect of filtering on noise and timing in nuclear particle detection

The relations between signal shaping, noise, and timing resolution in nuclear particle detection systems are examined in this paper. Mathematical analysis of five commonly used types of filters leads to numerical results for system noise components arising from sources in the preamplifier, detector, and bias resistors. These results are presented in the form of design curves for the various filters, showing the dependence of each output noise component on both the magnitude of the noise sources and the filter time constants. Three of the filters considered are simple RC types; the remaining two are combinations of delay lines and RC elements. The quantitative calculations specifically assume a silicon detector and a field-effect-transistor preamplifier. Those filters that exhibit bipolar step response are analyzed in terms of crossover timing resolution, based on the earlier noise calculations. Again, the results are summarized in sets of design curves for each filter. Finally, the comparative performance of the various filter types is discussed, and specific examples are given.

Gary, S. A.↗
NASA NTRS1972

Fourier plane filters

An electrically addressed liquid crystal Fourier plane filter capable of real time optical image processing is described. The filter consists of two parts: a wedge filter having forty 9 deg segments and a ring filter having twenty concentric rings in a one inch diameter active area. Transmission of the filter in the off (transparent) state exceeds fifty percent. By using polarizing optics, contrast as high as 10,000:1 can be achieved at voltages compatible with FET switching technology. A phenomenological model for the dynamic scattering is presented for this special case. The filter is designed to be operated from a computer and is addressed by a seven bit binary word which includes an on or off command and selects any one of the twenty rings or twenty wedge pairs. The overall system uses addressable latches so that once an element is in a specified state, it will remain there until a change of state command is received. The drive for the liquid crystal filter is ? 30 V peak at 30 Hz to 70 Hz. These parameters give a rise time for the scattering of 20 msec and a decay time of 80 to 100 msec.

Oliver, D. S.↗
NASA NTRS1976

The Lockheed alternate partial polarizer universal filter

A tunable birefringent filter using an alternate partial polarizer design has been built. The filter has a transmission of 38% in polarized light. Its full width at half maximum is .09A at 5500A. It is tunable from 4500 to 8500A by means of stepping motor actuated rotating half wave plates and polarizers. Wave length commands and thermal compensation commands are generated by a PPD 11/10 minicomputer. The alternate partial polarizer universal filter is compared with the universal birefringent filter and the design techniques, construction methods, and filter performance are discussed in some detail. Based on the experience of this filter some conclusions regarding the future of birefringent filters are elaborated.

Title, A. M.↗