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Article ; Online: Determining Metastable Ion Lifetime and History through Wave-Particle Interaction.

Chu, F / Skiff, F

2019 Volume 122, Issue 7, Page(s) 75001

Abstract: Laser-induced fluorescence (LIF) performed on metastable ions is frequently used to probe the dynamics of ground-state ion motions in many laboratory plasmas. However, these measurements place restrictions on the metastable ion lifetime. Metastable ... ...

Abstract	Laser-induced fluorescence (LIF) performed on metastable ions is frequently used to probe the dynamics of ground-state ion motions in many laboratory plasmas. However, these measurements place restrictions on the metastable ion lifetime. Metastable states are produced from direct ionization of neutral atoms as well as ions in other electronic states, of which the former will only faithfully represent processes that act on the ion dynamics in a time shorter than the metastable lifetime. We present here the first experimental study of this type of systematic effect using wave-particle interaction in an argon multidipole plasma. The metastable lifetime and relative fraction of metastables produced from preexisting ions, necessary for correcting the LIF measurement errors, can be determined by fitting the experimental results with the theory we propose.
Language	English
Publishing date	2019-03-08
Publishing country	United States
Document type	Journal Article
ZDB-ID	208853-8
ISSN	1079-7114 ; 0031-9007
ISSN (online)	1079-7114
ISSN	0031-9007
DOI	10.1103/PhysRevLett.122.075001
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Article ; Online: FPGA based demodulation of laser induced fluorescence in plasmas.

Mattingly, Sean W / Skiff, Fred

The Review of scientific instruments

2018 Volume 89, Issue 4, Page(s) 43508

Abstract: We present a field programmable gate array (FPGA)-based system that counts photons from laser-induced fluorescence (LIF) on a laboratory plasma. This is accomplished with FPGA-based up/down counters that demodulate the data, giving a background- ... ...

Abstract	We present a field programmable gate array (FPGA)-based system that counts photons from laser-induced fluorescence (LIF) on a laboratory plasma. This is accomplished with FPGA-based up/down counters that demodulate the data, giving a background-subtracted LIF signal stream that is updated with a new point as each laser amplitude modulation cycle completes. We demonstrate using the FPGA to modulate a laser at 1 MHz and demodulate the resulting LIF data stream. This data stream is used to calculate an LIF-based measurement sampled at 1 MHz of a plasma ion fluctuation spectrum.
Language	English
Publishing date	2018-04
Publishing country	United States
Document type	Journal Article
ZDB-ID	209865-9
ISSN	1089-7623 ; 0034-6748
ISSN (online)	1089-7623
ISSN	0034-6748
DOI	10.1063/1.4995971
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Article ; Online: Laboratory measurements of the physics of auroral electron acceleration by Alfvén waves.

Schroeder, J W R / Howes, G G / Kletzing, C A / Skiff, F / Carter, T A / Vincena, S / Dorfman, S

Nature communications

2021 Volume 12, Issue 1, Page(s) 3103

Abstract: While the aurora has attracted attention for millennia, important questions remain unanswered. Foremost is how auroral electrons are accelerated before colliding with the ionosphere and producing auroral light. Powerful Alfvén waves are often found ... ...

Abstract	While the aurora has attracted attention for millennia, important questions remain unanswered. Foremost is how auroral electrons are accelerated before colliding with the ionosphere and producing auroral light. Powerful Alfvén waves are often found traveling Earthward above auroras with sufficient energy to generate auroras, but there has been no direct measurement of the processes by which Alfvén waves transfer their energy to auroral electrons. Here, we show laboratory measurements of the resonant transfer of energy from Alfvén waves to electrons under conditions relevant to the auroral zone. Experiments are performed by launching Alfvén waves and simultaneously recording the electron velocity distribution. Numerical simulations and analytical theory support that the measured energy transfer process produces accelerated electrons capable of reaching auroral energies. The experiments, theory, and simulations demonstrate a clear causal relationship between Alfvén waves and accelerated electrons that directly cause auroras.
Language	English
Publishing date	2021-06-07
Publishing country	England
Document type	Journal Article
ZDB-ID	2553671-0
ISSN	2041-1723 ; 2041-1723
ISSN (online)	2041-1723
ISSN	2041-1723
DOI	10.1038/s41467-021-23377-5
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Article ; Online: The Effect of Varying Dentin Chroma and Enamel Thickness on the Color of A2 Double-layered Resin Composite.

Ismail, E H / Dawson, D V / Vidal, Cmp / Skiff, F N / Brogden, K / Maia, R R

Operative dentistry

2022

Abstract: Objectives: To evaluate chroma (C*) and overall color of double-layered (DL) resin composite (RC) restorations with various dentin shades and enamel thicknesses.: Methods: Enamel specimens were fabricated using custom-made molds to replicate VITA ... ...

Abstract	Objectives: To evaluate chroma (C) and overall color of double-layered (DL) resin composite (RC) restorations with various dentin shades and enamel thicknesses. Methods:* Enamel specimens were fabricated using custom-made molds to replicate VITA shade tabs with variant enamel thicknesses (0.5, 0.7, and 1.0 mm) (n=7) from two RC: Clearfil-Majesty (CM) shade (A2), and Vit-l-escence (VL), shade (pearl-neutral). Dentin specimens (shades A1, A2, and A3) were fabricated using custom molds corresponding to the enamel molds. Each enamel specimen was paired with three different dentin specimens. Lab* parameters were measured with VITA Easyshade-V. Color difference between DL specimens and the A2 VITA shade tab were calculated with the CIEDE2000 formula. Relationships among enamel thickness, ΔE00, C* of dentin layer, C* of DL, and change in chroma were assessed by Spearman rank correlations. ΔE00 was compared among groups using one-way analysis of variance with Tukey post-hoc adjustment for all possible pairwise group comparisons (experiment-wise α=0.05). Results: There was no statistical difference among C* of DL specimens (p=0.65, 0.53) for CM and VL, respectively. Combinations of enamel thickness/ dentin shade had a significant difference in ΔE00 (p>0.05). No significant correlation was observed among enamel thickness and C* of dentin, and C* of the DL (p>0.05). Significant correlations were observed between ΔE00 of the VL DL and C* DL (r=-0.8, p<0.001); and ΔE00 of CM DL and enamel thickness (r=0.5, p<0.001). Conclusions: Enamel thickness did not affect C* of the dentin layer. Unlike VL RC, variations in dentin shades with CM produced a closer match to the A2 shade tab. Enamel is recommended to be 0.7 mm or less.
Language	English
Publishing date	2022-12-15
Publishing country	United States
Document type	Journal Article
ZDB-ID	752995-8
ISSN	1559-2863 ; 0361-7734
ISSN (online)	1559-2863
ISSN	0361-7734
DOI	10.2341/21-138-L
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Article ; Online: Measurements of parallel electron velocity distributions using whistler wave absorption.

Thuecks, D J / Skiff, F / Kletzing, C A

The Review of scientific instruments

2012 Volume 83, Issue 8, Page(s) 83503

Abstract: We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense (ω(pe) > ω(ce)). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background ... ...

Abstract	We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense (ω(pe) > ω(ce)). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency ω(ce). As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation ω - k([parallel])v([parallel]) = ω(ce). The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow.
Language	English
Publishing date	2012-08
Publishing country	United States
Document type	Journal Article
ZDB-ID	209865-9
ISSN	1089-7623 ; 0034-6748
ISSN (online)	1089-7623
ISSN	0034-6748
DOI	10.1063/1.4742766
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Article: Comparison of light-transmittance in dental tissues and dental composite restorations using incremental layering build-up with varying enamel resin layer thickness.

Rocha Maia, Rodrigo / Oliveira, Dayane / D'Antonio, Tracy / Qian, Fang / Skiff, Frederick

Restorative dentistry & endodontics

2018 Volume 43, Issue 2, Page(s) e22

Abstract: Objectives: To evaluate and compare light-transmittance in dental tissues and dental composite restorations using the incremental double-layer technique with varying layer thickness.: Materials and methods: B1-colored natural teeth slabs were ... ...

Abstract	Objectives: To evaluate and compare light-transmittance in dental tissues and dental composite restorations using the incremental double-layer technique with varying layer thickness. Materials and methods: B1-colored natural teeth slabs were compared to dental restoration build-ups with A2D and B1E-colored nanofilled, supra-nanofilled, microfilled, and microhybrid composites. The enamel layer varied from 0.3, 0.5, or 1.2 mm thick, and the dentin layer was varied to provide a standardized 3.7 mm overall sample thickness ( Results: Mean light-transmittance observed at thicker final layers of enamel were significantly lower than those observed at thinner final layers. Within 1.2 mm final enamel resin layer (FERL) thickness, all composites were similar to the dental tissues, with exception of the nanofilled composite. However, within 0.5 mm FERL thickness, only the supra-nanofilled composite showed no difference from the dental tissues. Within 0.3 mm FERL thickness, none of the composites were similar to the dental tissues. Conclusions: The supra-nanofilled composite had the most similar light-transmittance pattern when compared to the natural teeth. However, for other composites, thicker FERL have a greater chance to match the light-transmittance of natural dental tissues.
Language	English
Publishing date	2018-04-16
Publishing country	Korea (South)
Document type	Journal Article
ZDB-ID	2715357-5
ISSN	2234-7666 ; 2234-7658
ISSN (online)	2234-7666
ISSN	2234-7658
DOI	10.5395/rde.2018.43.e22
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Article: Double-layer build-up technique: laser evaluation of light propagation in dental substrates and dental composites.

Maia, Rodrigo Rocha / Oliveira, Dayane / D'Antonio, Tracy / Qian, Fang / Skiff, Frederick

The international journal of esthetic dentistry

2018 Volume 13, Issue 4, Page(s) 538–549

Abstract: Purpose: To evaluate and compare light propagation in dental tissues and dental composite restorations using a double-layer build-up technique.: Materials and methods: Natural teeth slabs and dental restoration buildups with A2D and B1E-colored ... ...

Abstract	Purpose: To evaluate and compare light propagation in dental tissues and dental composite restorations using a double-layer build-up technique. Materials and methods: Natural teeth slabs and dental restoration buildups with A2D and B1E-colored nanofilled, supra-nanofilled, and microhybrid composites were randomized and equally distributed into four experimental groups (n = 10). Using a spectrophotometer, the samples were irradiated by three wavelengths of lasers: red, green, and blue. A voltmeter recorded the light output signal, and the following optical constants were calculated: absorption (A), transmittance (T), and attenuation (K). The data were analyzed using one-way analysis of variance (ANOVA), followed by post hoc Tukey's test (α = 0.05). Results: Absorption results varied according to the laser color and different composites tested. Regardless of the laser wavelength, the supra-nanofilled composite showed greater light transmittance and lower light attenuation compared with the dental tissues, which was the opposite of the nanofilled composite. The microhybrid composite showed no difference in light transmittance or light attenuation compared with the dental tissues. Conclusion: Within the limitations of this observational in vitro study, the microhybrid dental composite group had the most similar light propagation pattern compared with natural teeth when using the double-layer build-up technique.
MeSH term(s)	Composite Resins/chemistry ; Curing Lights, Dental ; Dental Materials/chemistry ; Dental Restoration, Permanent/methods ; Humans ; In Vitro Techniques ; Lasers ; Spectrophotometry/methods
Chemical Substances	Composite Resins ; Dental Materials
Language	English
Publishing date	2018-10-09
Publishing country	Germany
Document type	Journal Article
ISSN	2198-591X
ISSN	2198-591X
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Article ; Online: Comparison of light propagation in dental tissues and nano-filled resin-based composite.

Elgendy, Hanan / Maia, Rodrigo Rocha / Skiff, Fredrick / Denehy, Gerald / Qian, Fang

Clinical oral investigations

2018 Volume 23, Issue 1, Page(s) 423–433

Abstract: Objective: This study used three LASERs (red, green, and blue) with a spectrophotometer to compare the light propagation for the following: absorption (A), transmittance (T), attenuation (K), and scattering anisotropy coefficient (g) in dental tissues ... ...

Abstract	Objective: This study used three LASERs (red, green, and blue) with a spectrophotometer to compare the light propagation for the following: absorption (A), transmittance (T), attenuation (K), and scattering anisotropy coefficient (g) in dental tissues and nano-filled resin-based composites. This study used three distinct incremental build-up techniques, which included one shade (body), two shades (enamel and dentin), and three shades (enamel, transparent, and dentin). Methods: Twenty human, un-erupted, recently extracted third molars (shade B1) were used to obtain 40 tooth slabs. The samples were randomized and equally distributed into four experimental groups. The Positive Control Group included dental tissues with enamel, dento-enamel junction DEJ, and dentin; the Technique 1 group (T1) included one shade tissues, B1B; the Technique 2 group (T2) included two-shades tissues, A2Dentin and B1Enamel; and the Technique 3 group (T3) included three shade tissues, A2Dentin, Transparent, and B1Enamel. Cavity preparation was standardized, and, using the spectrophotometer, each specimen was irradiated by three LASERs. A voltmeter recorded the light-output signal, and from this raw data, the following optical constants (A, T, K, g) were calculated. Results: ANOVA, followed by a post hoc Tukey's test (p < 0.05), revealed that absorption and transmittance in dental tissues were significantly different when comparing the three build-up technique groups. However, when examining attenuation coefficient, there was no significant difference in dental tissues for T2 and T3 as analyzed by blue and red lasers. There was also no significant difference among the three lasers for T2 and T3. There was also no significant effect of the types of experiments on the value of scattering anisotropy factor g for blue laser among the four experimental groups. Conclusion: Within the limitations of this study, none of the build-up techniques were able to reproduce the dental tissues optical properties, and T2 and T3 resulted in a similar pattern of light propagation. Clinical significance: The clinical success of restorative procedures depends on selecting materials and techniques that emulate the natural tooth and provide long-term stability in color and optical properties.
MeSH term(s)	Color ; Composite Resins/chemistry ; Dental Materials/chemistry ; Humans ; In Vitro Techniques ; Lasers ; Materials Testing ; Molar, Third ; Optical Phenomena
Chemical Substances	Composite Resins ; Dental Materials
Language	English
Publishing date	2018-04-30
Publishing country	Germany
Document type	Comparative Study ; Journal Article
ZDB-ID	1364490-7
ISSN	1436-3771 ; 1432-6981
ISSN (online)	1436-3771
ISSN	1432-6981
DOI	10.1007/s00784-018-2451-9
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Article: Bispectral analysis of nonlinear compressional waves in a two-dimensional dusty plasma crystal.

Nosenko, V / Goree, J / Skiff, F

Physical review. E, Statistical, nonlinear, and soft matter physics

2006 Volume 73, Issue 1 Pt 2, Page(s) 16401

Abstract: Bispectral analysis was used to study the nonlinear interaction of compressional waves in a two-dimensional strongly coupled dusty plasma. A monolayer of highly charged polymer microspheres was suspended in a plasma sheath. The microspheres interacted ... ...

Abstract	Bispectral analysis was used to study the nonlinear interaction of compressional waves in a two-dimensional strongly coupled dusty plasma. A monolayer of highly charged polymer microspheres was suspended in a plasma sheath. The microspheres interacted with a Yukawa potential and formed a triangular lattice. Two sinusoidal pump waves with different frequencies were excited in the lattice by pushing the particles with modulated Ar+ laser beams. Coherent nonlinear interaction of the pump waves was shown to be the mechanism of generating waves at the sum, difference, and other combination frequencies. However, coherent nonlinear interaction was ruled out for certain combination frequencies, in particular, for the difference frequency below an excitation-power threshold, as predicted by theory.
Language	English
Publishing date	2006-01
Publishing country	United States
Document type	Journal Article
ISSN	1539-3755
ISSN	1539-3755
DOI	10.1103/PhysRevE.73.016401
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Article ; Online: Design and use of an Elsässer probe for analysis of Alfvén wave fields according to wave direction.

Drake, D J / Kletzing, C A / Skiff, F / Howes, G G / Vincena, S

The Review of scientific instruments

2011 Volume 82, Issue 10, Page(s) 103505

Abstract: We have designed an electric and magnetic field probe which simultaneously measure both quantities in the directions perpendicular to the background magnetic field for application to Alfvén wave experiments in the Large Plasma Device at UCLA. This new ... ...

Abstract	We have designed an electric and magnetic field probe which simultaneously measure both quantities in the directions perpendicular to the background magnetic field for application to Alfvén wave experiments in the Large Plasma Device at UCLA. This new probe allows for the projection of measured wave fields onto generalized Elsässer variables. Experiments were conducted in a singly ionized He plasma at 1850 G in which propagation of Alfvén waves was observed using this new probe. We demonstrate that a clear separation of transmitted and reflected signals and determination of Poynting flux and Elsässer variables can be achieved.
Language	English
Publishing date	2011-10
Publishing country	United States
Document type	Journal Article
ZDB-ID	209865-9
ISSN	1089-7623 ; 0034-6748
ISSN (online)	1089-7623
ISSN	0034-6748
DOI	10.1063/1.3649950
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