Experimental Configuration Research Articles

Euclid: The search for primordial features

Primordial features, in particular oscillatory signals, imprinted in the primordial power spectrum of density perturbations represent a clear window of opportunity for detecting new physics at high-energy scales. Future spectroscopic and photometric measurements from the Euclid space mission will provide unique constraints on the primordial power spectrum, thanks to the redshift coverage and high-accuracy measurement of nonlinear scales, thus allowing us to investigate deviations from the standard power-law primordial power spectrum. We consider two models with primordial undamped oscillations superimposed on the matter power spectrum described by 1 + 𝒜X sin (ωXΞX + 2 πϕX), one linearly spaced in k space with Ξlin ≡ k/k* where k* = 0.05 Mpc−1 and the other logarithmically spaced in k space with Ξlog ≡ ln(k/k*). We note that 𝒜X is the amplitude of the primordial feature, ωX is the dimensionless frequency, and ϕX is the normalised phase, where X = {lin, log}. We provide forecasts from spectroscopic and photometric primary Euclid probes on the standard cosmological parameters Ωm, 0, Ωb, 0, h, ns, and σ8, and the primordial feature parameters 𝒜X, ωX, and ϕX. We focus on the uncertainties of the primordial feature amplitude 𝒜X and on the capability of Euclid to detect primordial features at a given frequency. We also study a nonlinear density reconstruction method in order to retrieve the oscillatory signals in the primordial power spectrum, which are damped on small scales in the late-time Universe due to cosmic structure formation. Finally, we also include the expected measurements from Euclid’s galaxy-clustering bispectrum and from observations of the cosmic microwave background (CMB). We forecast uncertainties in estimated values of the cosmological parameters with a Fisher matrix method applied to spectroscopic galaxy clustering (GCsp), weak lensing (WL), photometric galaxy clustering (GCph), the cross correlation (XC) between GCph and WL, the spectroscopic galaxy clustering bispectrum, the CMB temperature and E-mode polarisation, the temperature-polarisation cross correlation, and CMB weak lensing. We consider two sets of specifications for the Euclid probes (pessimistic and optimistic) and three different CMB experiment configurations, that is, Planck, Simons Observatory (SO), and CMB Stage-4 (CMB-S4). We find the following percentage relative errors in the feature amplitude with Euclid primary probes: for the linear (logarithmic) feature model, with a fiducial value of 𝒜X = 0.01, ωX = 10, and ϕX = 0: 21% (22%) in the pessimistic settings and 18% (18%) in the optimistic settings at a 68.3% confidence level (CL) using GCsp+WL+GCph+XC. While the uncertainties on the feature amplitude are strongly dependent on the frequency value when single Euclid probes are considered, we find robust constraints on 𝒜X from the combination of spectroscopic and photometric measurements over the frequency range of (1, 102.1). Due to the inclusion of numerical reconstruction, the GCsp bispectrum, SO-like CMB reduces the uncertainty on the primordial feature amplitude by 32%–48%, 50%–65%, and 15%–50%, respectively. Combining all the sources of information explored expected from Euclid in combination with the future SO-like CMB experiment, we forecast 𝒜lin ≃ 0.010 ± 0.001 at a 68.3% CL and 𝒜log ≃ 0.010 ± 0.001 for GCsp(PS rec + BS)+WL+GCph+XC+SO-like for both the optimistic and pessimistic settings over the frequency range (1, 102.1).

Pairwise Tomlinson-Harashima precoding for multiple-lane IM-DD transmissions.

As for the photonic interconnection based on the multiple-lane intensity modulation direct detection (IM-DD) transmission, both intra-channel inter-symbol-interference (ISI) originating from bandwidth constraint, and inter-channel performance discrepancy emerging from inter-channel component differences are the major bottleneck for the throughput enhancement. Here, we propose a pairwise Tomlinson-Harshima precoding (P-THP) scheme, in order to simultaneously deal with both intra-channel ISI and inter-channel performance discrepancy. The effective function of the proposed P-THP scheme is experimentally evaluated by transmitting 4-channel 81-GBaud PAM4 signals over 2 km standard single-mode fiber (SSMF). Compared with the conventional scheme with only applying THP on individual wavelength channel, the required optical received power (ROP) under the back-to-back (B2B) transmission can be reduced by 0.75∼1 dB with the help of proposed P-THP in different experimental component configurations, at the 7% hard decision forward error correction (HD-FEC) threshold of BER = 3.8 × 10-3. After the 2 km SSMF transmission, only the use of proposed P-THP can guarantee to reach the designated HD-FEC threshold, leading to a net rate of >600 Gbit/s.

Demonstration of particle tracking with scintillating fibres read out by a SPAD array sensor and application as a neutrino active target

Scintillating fibre detectors combine sub-mm resolution particle tracking, precise measurements of the particle stopping power and sub-ns time resolution. Typically, fibres are read out with silicon photomultipliers (SiPM). Hence, if fibres with a few hundred μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu $$\\end{document}m diameter are used, either they are grouped together and coupled with a single SiPM, losing spatial resolution, or a very large number of electronic channels is required. In this article we propose and provide a first demonstration of a novel configuration which allows each individual scintillating fibre to be read out regardless of the size of its diameter, by imaging them with Single-Photon Avalanche Diode (SPAD) array sensors. Differently from SiPMs, SPAD array sensors provide single-photon detection with single-pixel spatial resolution. In addition, O(us) or faster coincidence of detected photons allows to obtain noise-free images. Such a concept can be particularly advantageous if adopted as a neutrino active target, where scintillating fibres alternated along orthogonal directions can provide isotropic, high-resolution tracking in a dense material and reconstruct the kinematics of low-momentum protons (down to 150 MeV/c), crucial for an accurate characterisation of the neutrino-nucleus cross section. In this work the tracking capabilities of a bundle of scintillating fibres coupled to SwissSPAD2 is demonstrated. The impact of such detector configuration in GeV-neutrino experiments is studied with simulations and reported. Finally, future plans, including the development of a new SPAD array sensor optimised for neutrino detection, are discussed.

Simulation and experimental validation of the JCR-CNN model for hybrid modes recognition and decomposition in few-mode fibers

The issue of mode decomposition (MD) in optical fibers is regarded as a regression problem has been widely studied and applied, however, in contrast, the identification of different classes of hybrid modes groups when different modes are excited as a typical classification problem has rarely been studied, and the possibility of incorporating both tasks into a single neural network to be solved simultaneously is an important issue that deserves to be explored. Thus, a novel joint classification and regression task convolutional neural network (JCR-CNN) architecture is proposed, which can perform the discrimination of hybrid mode group categories in few-mode fibers (FMFs) and predict corresponding mode coefficients simultaneously. In addition, the introduction of the data augmentation (DA) technique establishes a tight link between experimental and synthetic simulation data, allowing the model trained only on simulation data to cope well with the acquisition errors in the experimental optical path configuration when making predictions based on experimental data. The quantitative results of both simulation and experimental data demonstrate the feasibility and validity of the proposed model and DA method. The mode classification accuracy and the Pearson coefficient of the image reached 99.71% and 98.81%, respectively. To the best of our knowledge, this work provides a new perspective for a more comprehensive characterization of hybrid modes in optical fibers, which is expected to have applications in various fields.

Numerical Investigation of an Experimental Setup for Thermoplastic Fuselage Panel Testing in Combined Loading

The main purpose of this study comprises the design and the development of a novel experimental configuration for carrying out tests on a full-scale stiffened panel manufactured of fiber-reinforced thermoplastic material. Two different test-bench design concepts were evaluated through a numerical modeling strategy, which will be validated at the next stage using a targeted series of mechanical tests. A baseline experimental setup was developed after a number of candidate configurations were numerically investigated. The supporting elements along with the load introduction systems were defined in such a way as to represent the stiffness of a fuselage barrel section and its representative loading scenarios. The test rig and the investigated thermoplastic panel were numerically simulated to acquire valuable data pertaining to deformations and stresses when subjected to different loading combinations. Two distinct load cases were numerically examined: the first case was the in-plane compression of the thermoplastic panel, while the second case consisted of an internally applied pressure load introduced via an inflatable airbag, installed under the panel. Both loading scenarios were recreated inside the numerical virtual environment in order to examine two distinct stiffening configurations as well as to determine the maximum/limit loads to be used in the planned future experimental campaign. It was concluded that the designed test rig could successfully be used for the structural evaluation of fuselage panels under representative loading conditions.

Mechanism for Electrostatically Generated Magnetoresistance in Chiral Systems without Spin-Dependent Transport.

Significant attention has been drawn to electronic transport in chiral materials coupled to ferromagnets in the chirality-induced spin selectivity (CISS) effect. A large magnetoresistance (MR) is usually observed, which is widely interpreted to originate from spin (dependent) transport. However, there are severe discrepancies between the experimental results and the theoretical interpretations, most notably the apparent failure of the Onsager reciprocity relations in the linear response regime. We provide an alternative mechanism for the two terminal MR in chiral systems coupled to a ferromagnet. For this, we point out that it was observed experimentally that the electrostatic contact potential of chiral materials on a ferromagnet depends on the magnetization direction and chirality. The mechanism that we provide causes the transport barrier to be modified by the magnetization direction, already in equilibrium, in the absence of a bias current. This strongly alters the charge transport through and over the barrier, not requiring spin transport. This provides a mechanism that allows the linear response resistance to be sensitive to the magnetization direction and also explains the failure of the Onsager reciprocity relations. We propose experimental configurations to confirm our alternative mechanism for MR.

Conservation of a Spectral Asymmetry Invariant in Optical Fiber Four‐Wave Mixing

AbstractThe conservation of spectral asymmetry is a fundamental feature of the ideal four‐wave mixing process as it exists in a medium combining quadratic chromatic dispersion and third‐order nonlinearity. The robustness of this invariant in an experimental configuration where the excitation conditions of an optical fiber are sequentially updated, mimicking infinite propagation is tested in this paper. This theoretical and experimental study reveals the high sensitivity of the asymmetry to very slight deviations from the ideal case, and the idealized system behaves as an intermediate case between the ideal case of noncascaded four‐wave mixing and propagation in a system governed by the nonlinear Schrödinger equation is shown.

Complete and robust magnetic field confinement by superconductors in fusion magnets

The fusion created by magnetically confined plasma is a promising clean and essentially unlimited future energy source. However, there are important problems hindering controlled fusion like the imperfect magnetic confinement and the associated plasma instabilities. We theoretically demonstrate how to create a fully confined magnetic field with the precise three-dimensional shape required by fusion theory, using a bulk superconducting toroid with a toroidal cavity. The vacuum field in the cavity consists of nested flux surfaces. The coils creating the field, embedded in the superconducting bulk, can be chosen with very simple shapes, in contrast with the cumbersome arrangements in current experiments, and can be spared from large magnetic forces between them. Because of the superconductor properties, the system will tend to maintain the optimum field distribution in response to instabilities in the plasma. We numerically demonstrate how a fully-confined magnetic field with the three-dimensional spatial distribution required in two of the most advanced stellarators, Large Helical Device and Wendelstein 7-X, can be exactly generated, using simple round coils as magnetic sources. Current high-temperature superconductors can be employed to construct the bulk superconducting toroid. This can lead to optimized robust magnetic confinement and largely simplified configurations in future fusion experiments.

The effect of In(Ga)As/GaAs quantum dots on the optical loss of photonic crystal cavities

We present a systematic investigation of the optical losses in GaAs photonic crystal cavities with and without embedded self-assembled In(Ga)As quantum dots (QDs) to shed light on additional loss mechanisms related to the presence of the QDs. To clarify the role of the measurement method, we propose an experimental configuration where the optical properties can be evaluated simultaneously through reflection and photoluminescence measurements. Independently of the measurement method, we observe a reduced quality (Q) factor in cavities with embedded QDs when compared to the passive counterparts. Our analysis indicates that these additional losses—about 7 GHz—are unrelated to direct excitonic absorption for the investigated areal QD densities of 175 μm−2. We analyze several mechanisms which could explain our observations and suggest that a possible origin could be unsaturable absorption from midgap defects introduced by the QD growth.

Point projection radiography of electromagnetically accelerated flyer plates with an external X-pinch driver.

A platform for flyer plate benchmarking experiments has been developed, with an external X-pinch driver for point projection radiography. The experiments were performed using CEPAGE, a low inductance pulsed power machine at First Light Fusion (2 MA, 1.4 µs), with a new vacuum transmission line and flyer load hardware designed specifically to give a line of sight for radiography. A broadband 10-20keV x-ray source was produced by a portable X-pinch driver (140kA, 350ns) [Strucka etal., Matter Radiat. Extremes 7, 016901 (2021)] and was used to image the flyer. Radiography compliments the pre-existing diagnostic suite, which consists of current probes, velocimetry, and side-on optical probing of the impact shock transmitted into a transparent sample. The platform allows for significant insights into the 2D and 3D nature of the flyer launch, such as deformation and instability formation. It was used to diagnose a 10 × 9 × 1mm3 aluminum flyer, which reached a peak velocity of 4.2 km s-1 before impact with a poly(methylmethacrylate) sample. The experimental configuration, on-shot source characterization, and the results from two flyer plate experiments on CEPAGE are discussed.

Synthetic Mirnov diagnostic for the validation of experimental observations.

A synthetic Mirnov diagnostic has been developed to investigate the capabilities and limitations of an arrangement of Mirnov coils in terms of a mode analysis. Eight test cases have been developed, with different coil arrangements and magnetic field configurations. Three of those cases are experimental configurations of the stellarator Wendelstein 7-X. It is observed that, for a high triangularity of the flux surfaces, the arrangement of the coils plays a significant role in the exact determination of the poloidal mode number. For the mode analysis, torus and magnetic coordinates have been used. In most cases, the reconstruction of the poloidal mode number of a prescribed mode was found to be more accurate in magnetic coordinates. As an application, the signal of an Alfvén eigenmode, which has been calculated with a three-dimensional magnetohydrodynamics code, is compared to experimental observations at Wendelstein 7-X. For the chosen example, the calculated and measured mode spectra agree very well and additional information on the toroidal mode number and localization of the mode has been inferred.

Head stabilization apparatus for high-resolution ophthalmic imaging.

Head movement must be stabilized to enable high-quality data collection from optical instrumentation such as eye trackers and ophthalmic imaging devices. Though critically important for imaging, head stabilization is often an afterthought in the design of advanced ophthalmic imaging systems, and experimental devices often adapt used and/or discarded equipment from clinical devices for this purpose. Alternatively, those seeking the most stable solution possible, including many users of adaptive optics ophthalmoscopy systems, utilize bite bars. Bite bars can provide excellent stability but are time consuming to fabricate, decreasing imaging efficiency, and uncomfortable for many patients, especially the elderly and/or those with prosthodontics such as dentures who may refuse participation in a study that requires one. No commercial vendors specifically offer head mount solutions for experimental ophthalmic imaging devices, resulting in nearly every custom device having a different solution for this commonly encountered problem. Parallelizing the head stabilization apparatus across different custom devices may improve standardization of experimental imaging systems for clinical trials and other multicenter investigations. Here we introduce a head mount design for ophthalmic imaging that is modular, adjustable, and customizable to the constraints of different experimental imaging configurations. The three points of head contact in our solution provide excellent stabilization across a range of head sizes and shapes from small children to adults, and the ease of adjustment afforded by our design minimizes the time to get participants stabilized and comfortable.

Design, implementation, and experimental validation of a new low-cost sensorless wind turbine emulator: Applications for small-scale turbines

Research and investigation into renewable energy sources is being sparked by the rapidly rising need for electricity, higher costs of fossil fuels, and increasing worries about the environment. Recent years have seen a tremendous increase in the use of wind energy (WE). In-depth study has been done to effectively produce power from WE. Nevertheless, it is exceedingly challenging and dangerous to set up wind turbines (WTs) for research and teaching uses due to constraints like space and upkeep. Numerous benefits come with a lab-scale WT emulator (WTE), such as freedom from space restrictions, an improved level of control, and independence from existing weather conditions. The design and execution of a low-power, lab-scale WTE are the focus of this study. The investigated experimental configuration is intended to precisely mimic the mechanical behavior of a real WT. Aerodynamics, blades, slow shafts, gearboxes, and controller elements, for example, are modeled in MATLAB/Simulink before they are assembled and implemented on a dSPACE 1104 board. A DC motor running under buck converter control is used to substitute the quick shaft. The WTE’s functionality is evaluated in various wind speed conditions. The findings of comparing the WTE’s dynamics with those offered by the manufacturer amply show the efficacy of the proposed WTE and its capacity to take the position of an actual WT. This paper will be a useful resource for investigators in helping them select the best WTE approach for their purposes.

Photon Acceleration by Superluminal Ionization Fronts

This paper explores the use of superluminal ionization fronts to accelerate and amplify electromagnetic radiation. These fronts are defined as optical boundaries between two regions of a gas, the neutral region and the plasma region, characterized by two different values of the refractive index. For that reason, the front velocity is not necessarily related to the motion of material particles, such as neutral atoms, ions and electrons, which can stay at rest. The fronts can therefore become superluminal without violating causality. In recent years, different experimental configurations, such as the flying focus, showed that it is possible to create superluminal fronts in the laboratory. These fronts can easily be described theoretically in a special reference frame, called the time frame, which is used here. In this frame, superluminal fronts reduce to time refraction, a process that is symmetrical to the well-known optical refraction. It is shown that propagation through such fronts can lead to considerable frequency shifts and energy amplification of probe laser beams. This could eventually be used to develop new sources of tunable radiation.

Analysis of Local Track Discontinuities and Defects in Railway Switches Based on Track-Side Accelerations.

Switches are an essential, safety-critical part of the railway infrastructure. Compared to open tracks, their complex geometry leads to increased dynamic loading on the track superstructure from passing trains, resulting in high maintenance costs. To increase efficiency, condition monitoring methods specific to railway switches are required. A common approach to track superstructure monitoring is to measure the acceleration caused by vehicle track interaction. Local interruptions in the wheel-rail contact, caused for example by local defects or track discontinuities, appear in the data as transient impact events. In this paper, such transient events are investigated in an experimental setup of a railway switch with track-side acceleration sensors, using frequency and waveform analysis. The aim is to understand if and how the origins of these impact events can be distinguished in the data of this experiment, and what the implications for condition monitoring of local track discontinuities and defects with wayside acceleration sensors are in practice. For the same experimental configuration, individual impact events are shown to be reproducible in waveform and frequency content. Nevertheless, with this track-side sensor setup, the different types of track discontinuities and defects (squats, joints, crossing) could not be clearly distinguished using characteristic frequencies or waveforms. Other factors, such as the location of impact event origin relative to the sensor, are shown to have a much stronger influence. The experimental data suggest that filtering the data to narrow frequency bands around certain natural track frequencies could be beneficial for impact event detection in practice, but differentiating between individual impact event origins requires broadband signals. A multi-sensor setup with time-synchronized acceleration sensors distributed over the switch is recommended.

Process parameter effects estimation and surface quality prediction for selective laser melting empowered by Bayes optimized soft attention mechanism-enhanced transfer learning

Additive Manufacturing (AM), particularly Selective Laser Melting (SLM), has revolutionized the industrial manufacturing sector owing to its remarkable design flexibility and precision. However, it is well known that slight changes in SLM process parameters may highly affect the surface quality of the as-built product. In this paper, we investigate the influence of SLM printing parameters (laser power, laser scanning speed, layer thickness, and hatch distance) on surface quality and develop a predictive model for surface quality based on the given printing parameters. The developed model is constructed by a Bayesian Optimization and soft Attention mechanism-enhanced Transfer learning (BOAT) framework with superior domain adaptability and generalization capability. Through experimental validation, the effectiveness of the BOAT approach in estimating printing parameters and correlating them with surface quality has been verified. The comprehensive methodology, experimental configurations, prediction results, and ensuing discussions are all presented. This study contributes to providing valuable insights and practical implications for improving the competitiveness and impact of SLM in advanced manufacturing by accurately predicting surface quality with specified printing parameters.

Assessment of stone ablation rate using the Moses technology modes with different energy and pulse settings: An experimental study

ABSTRACT Objectives To compare lithotripsy ablation rate with the Moses modes versus conventional pulse modes when using the Holmium:Yttrium–Aluminum–Garnet (Ho:YAG) laser. Methods The Lumenis® Pulse P120H Holmium Laser System and a 365 μm Moses D/F/L fiber were used to assess stone ablation rate in conventional Short and Long Pulse as well as Moses Contact and Distance at 10 W (0.5Jx20Hz and 2Jx5Hz) and 60 W (1Jx60Hz and 2Jx30Hz). Hard and soft phantom stones were formed, and all tests were conducted in a custom experimental configuration installed in a saline-filled bath. The laser was delivered up to 3 kJ of total energy. The fragmentation pattern was assessed via photographs in each cohort. Results The time to reach the target energy was 5 min and 50 s in all 10 W and 60 W trials, respectively. In both stone types, ablation was more effective when high-power, high-energy and Moses Distance was utilized. In soft stones, the lowest ablation rate was detected in the Long Pulse modality in all power, energy and frequency settings. Overall, when dusting settings (high-frequency, low-energy) were used, a deeper single cavitation was observed rather than small cavitations. Conclusions The most effective pulse modality as evaluated via stone ablation rate depends on the stone hardness as well as energy and frequency settings. In both hard and soft stones, ablation is more effective when 60 W (2Jx30Hz) power settings and Moses Distance are used. Tailored laser settings in terms of energy and frequency could be set for each case scenario.

Two-fold symmetric superconductivity in the Kagome superconductor RbV3Sb5

The recently discovered kagome superconductors offer a promising platform for investigating intertwined orders and novel states, including topology, superconductivity, charge density waves, and more. The interplay among these orders can spontaneously break rotational symmetry, giving rise to exotic phenomena such as nematicity or even nematic superconductivity. Here we present our findings on the two-fold symmetric superconductivity in thin-flake RbV3Sb5 in response to direction-dependent in-plane magnetic fields, in contrast to the inherent six-fold structural symmetry of the crystal lattice. The two-fold symmetry was evidenced through a combination of magnetoresistance transport experiments, critical magnetic field measurements, and observations of anisotropic superconducting gaps. Additionally, by altering the experimental configuration, we also detected the presence of six-fold symmetric components superimposed on the two-fold symmetry at the boundary between normal and superconducting states. Our results underscore the correlation-driven symmetry-breaking phenomena and emphasize the potential of this correlated kagome family as a promising platform for investigating intertwined orders, including unconventional superconductivity.

Operating Policies With Temporally and Spatially Varied Parameters in Station-Based Carsharing Services

This study investigates two operating policies with temporally and spatially varied parameters in station-based carsharing services, which are becoming a popular traffic mode. One is the so-called free-reservation policy, in which a user can reserve a car freely before his/her trip. The other is the extra-parking policy, in which a user can return a car to a station without valid parking slots but with a fixed extra-parking fee paid. A scheme with temporally and spatially varied parameters is proposed to maximize the total operational profit, where key service parameters in the two policies are varied with stations and periods. The strategic behavior of users is considered which involves the choices of both transportation modes and carsharing stations. A simulation-based optimization solution method is developed to optimize the key parameters in the policies, where the solution space is reduced. Extensive numerical experiments validate the solution method and the scheme with varied parameters. The results indicate that the scheme with varied parameters increases the total profit by approximately 20% compared to the scheme with unified parameters in the configuration of experiments. Several managerial implications are also proposed to help carsharing platforms utilize resources efficiently.

ASSESSING FUEL FRAGMENTATION IN AN OXIDIZING ATMOSPHERE FOR HYBRID ROCKET PROPELLANT SAFETY COMPREHENSION

Although hybrid rockets are considered safe, when solid fuel forms dust during impact and mixes with leaked oxidizer, a combustible gas mixture might form and burn rapidly. Therefore, to ascertain whether or not solid fuels burn by fragmentation in an oxidizing atmosphere, efforts are being made to fragment microcrystalline wax, which tends to generate dust among solid fuels under air and oxygen atmospheres. Earlier test results showed differences between results obtained in oxygen and air; however, the influence of experimental configurations cannot be ruled out. Therefore, experiments were conducted again with the air and oxygen experimental configurations combined. A transparent balloon was filled with a specimen and air or oxygen. A detonator and explosives were used to fragment the specimen. Then, the fragmentation was observed and a pressure-time history around the specimen was obtained. In all, nine experiments were conducted while varying the atmosphere, explosive mass, and presence of specimens. In all of the experiments, the pressure-time history comparisons under oxygen showed the same or higher peak overpressure and impulse compared to air. Furthermore, movies taken of experiments under an oxygen atmosphere showed strong luminescence, indicating clearly that combustion occurred in the oxygen atmosphere. The impulse values were highest in the oxygen atmosphere where the specimen was present, suggesting that the specimen burned.