AR Spectrum Research Articles

Bi-LSTM fault diagnosis method for rolling bearings based on segmented interception AR spectrum analysis and information fusion

The rolling bearing fault diagnosis is affected by industrial environmental noise and other factors, leading to the existence of some redundant components after signal decomposition. At the same time, the existence of the modal aliasing phenomenon in empirical mode decomposition (EMD) and the relevant improved algorithms also leads to the existence of many invalid features in the components. These phenomena have great influence on the bearing fault diagnosis. So a rolling bearing bidirectional-long short term memory (Bi-LSTM) fault diagnosis method was proposed based on segmented interception auto regressive (SIAR) spectrum analysis and information fusion. The ensemble empirical mode decomposition (EEMD), the complementary ensemble empirical mode decomposition (CEEMD) and the robust EMD (REMD) algorithms decompose the rolling bearing fault signals, and AR spectrum analysis is performed on the obtained components respectively. By comparing the AR spectra of the components corresponding to different fault locations, the effective AR spectral values are intercepted as the eigenvalues of the data, and finally all the eigenvalues are fused to achieve the purpose of screening effective features more efficiently so as to reduce the impact of feature redundancy caused by mode aliasing on neural network training. Then the Bi-LSTM neural network was used as a rolling bearing fault diagnosis classifier, and the simulation experiments were conducted based on the rolling bearing fault signal data from Case Western Reserve University to verify the effectiveness of the proposed feature extraction and fault diagnosis method.

Research on the Estimation Method of Target Motion Parameters Based on Ternary Array

The ternary array passive positioning technique performs the estimation of target distance and bearing by measuring the time delay difference between array elements. The estimates are limited by the geometric model and time delay measurement errors, and the positioning accuracy and reliability are poor. In this paper, we propose an orientation matching-based motion target localization model. By introducing the target motion model, and establish a matching objective function for the time delay difference obtained by calculating the predefined target motion trajectory and the actual received data of the ternary array separately. The matching objective function is optimally solved by using Burg algorithm in the AR spectrum estimation method, and a highly accurate and reliable target parameter estimation can be obtained in a short time. The results of computer simulation experiments verify the effectiveness of the method.

A Fault Diagnosis Method of Bogie Axle Box Bearing Based on Spectrum Whitening Demodulation.

The axle box bearing of bogie is one of the key components of the rail transit train, which can ensure the rotary motion of wheelsets and make the wheelsets adapt to the conditions of uneven railways. At the same time, the axle box bearing also exposes most of the load of the car body. Long-time high-speed rotation and heavy load make the axle box bearing prone to failure. If the bearing failure occurs, it will greatly affect the safety of the train. Therefore, it is extremely important to monitor the health status of the axle box bearing. At present, the health status of the axle box bearing is mainly monitored by vibration information and temperature information. Compared with the temperature data, the vibration data can more easily detect the early fault of the bearing, and early warning of the bearing state can avoid the occurrence of serious fault in time. Therefore, this paper is based on the vibration data of the axle box bearing to carry out adaptive fault diagnosis of bearing. First, the AR model predictive filter is used to denoise the vibration signal of the bearing, and then the signal is whitened in the frequency domain. Finally, the characteristic value of vibration data is extracted by energy operator demodulation, and the fault type is determined by comparing with the theoretical value. Through the analysis of the constructed simulation signal data, the characteristic parameters of the data can be effectively extracted. The experimental data collected from the bearing testbed of high-speed train are analyzed and verified, which further proves the effectiveness of the feature extraction method proposed in this paper. Compared with other axle box bearing fault diagnosis methods, the innovation of the proposed method is that the signal is denoised twice by using AR filter and spectrum whitening, and the adaptive extraction of fault features is realized by using energy operator. At the same time, the steps of setting parameters in the process of feature extraction are avoided in other feature extraction methods, which improves the diagnostic efficiency and is conducive to use in online monitoring system.

Increase of Power Efficiency in Coaxial Transmission Line Resonator by Using a Spacer to Compensate for Plasma Impedance

This article presents a method to improve the power efficiency of microwave plasma generators which have a resonator structure after plasma ignition. A coaxial transmission line resonator, one of the microwave plasma generators, was used to design to have an input impedance of 50 Ω in the absence of plasma. However, after plasma ignition, the plasma impedance affects the input impedance of the resonator, and the device efficiency decreases. The proposed resonator includes a spacer at the shorted end; the spacer has the necessary impedance to compensate for the plasma impedance. The spacer increased the device efficiency by up to 27.2% and increased the length of the plasma jet by 2.5 mm compared to the conventional one. Optical emission spectrum analysis confirmed that the intensities of Ar spectrum and reactive oxygen/nitrogen species spectra were also increased by 50% and 30% by using the spacer, respectively.

Spectral Analysis and New Visible and Ultraviolet Lines of Ar v

Abstract A capillary discharge tube was used to record the Ar spectrum in the region of 330–4400 Å. We analyzed a set of 109 lines of Ar v, with 10 of them being classified for the first time. Part of these newly identified lines (six in total) corresponds to electric dipole transitions in the visible and ultraviolet regions of the spectrum. We calculated weighted transition rates (gA) for all experimentally observed lines and the corresponding lifetimes using a relativistic Hartree–Fock method with configuration interaction. The equations were modified to consider core polarization (CP) effects. A study on the Si isoelectronic sequence found that considering CP effects is essential for the correct description of the Ar v structure.

Second-order autoregressive model-based Kalman filter for the estimation of a slow fading channel described by the Clarke model: Optimal tuning and interpretation

This paper treats the estimation of a flat fading Rayleigh channel with Jakes' Doppler spectrum model and slow fading variations. A common method is to use a Kalman filter (KF) based on an auto-regressive model of order p (AR(p)). The parameters of the AR model can be simply tuned by using the correlation matching (CM) criterion. However, the major drawback of this method is that high orders are required to approach the Bayesian Cramer–Rao lower bound. The choice of p together with the tuning of the model parameters is thus critical, and a tradeoff must be found between the numerical complexity and the performance. The reasonable tradeoff arising from setting p=2 has received much attention in the literature. However, the methods proposed for tuning the model parameters are either based on an extensive grid-search analysis or experimental results, which limits their applicability. A general solution for any scenario is simply missing for p=2 and this paper aims at filling this gap. We propose using a Minimization of Asymptotic Variance (MAV) criterion, for which a general closed-form formula has been derived for the optimal tuning of the model and the mean square error. This provides deeper insight into the behavior of the KF with respect to the channel state (Doppler frequency and signal to noise ratio). Moreover, the paper interprets the proposed solution, especially the dependence of the shape of the optimal AR(2) spectrum on the channel state. Analytic and numerical comparisons with first- and second-order algorithms in the literature are also performed. Simulation results show that the proposed AR(2)-MAV model performs better than the literature and similarly to AR(p)-CM models with p≥15.

Driven molecular dynamics studies of the shared proton motion in the H5O2+·Ar cluster: the effect of argon tagging and deuteration on vibrational spectra.

We report IR spectra of H5O2(+) and H5O2(+)·Ar and their deuterium isotopologues using ab initio molecular dynamics. The trajectories were propagated as microcanonical (NVE) ensembles at energies corresponding to temperatures 50 and 100 K. The potential energy surface is calculated on-the-fly at the MP2/aug-cc-pVDZ level of theory. The calculations show that adding an argon atom to H5O2(+) introduces symmetry breaking in the Zundel core ion, causes blueshift in the shared proton vibration by about 200 cm(-1), and leads to the splitting of the OH stretch vibrations into four bands. Driven molecular dynamics (DMD) method is used to assign the spectrum by coupling the dipole moment to an external electric field oscillating at frequency ω. The broad feature at 1100 cm(-1) in the H5O2(+)·Ar spectrum is ascribed to the large amplitude shared proton vibration coupled with torsion and wag modes. MD MP2 simulations predict the H/D redshift in the shared proton vibration and water bending vibration to be about 280 and 460 cm(-1), respectively, in good agreement with experimental observations.

Comparative and integrative study of Langmuir probe and optical emission spectroscopy in a variable magnetic field electron cyclotron resonance chemical vapor deposition process used for depositing hydrogenated amorphous silicon thin films

An electron cyclotron resonance chemical vapor deposition (ECR-CVD) system applied in a hydrogenated amorphous silicon (a-Si:H) thin-film deposition process was diagnosed in-situ by using optical emission spectroscopy (OES) and a Langmuir probe. The optical actinometry technique was used to obtain the ratio of species concentration to the concentration of a trace gas (Ar). The electron temperature (Teoes) was estimated according to the spectrum intensity ratio of Hβ to Hα or that of Si* to SiH*, and the two estimation approaches were evaluated by comparing the results (TeLP) of Langmuir probe measurement. The probe surface contaminants (a-Si:H) produced during in-situ measurement created errors in the measurement of parameters such as the electron temperature and density (Ne). The results indicated that, when a-Si:H was coated on the probe at thicknesses less than 150nm, the errors were negligible. OES and Langmuir probe measurement were integrated and used to determine the dependence of the processing pressure and resonance magnetic field configuration on the properties of an a-Si:H film grown using ECR-CVD. When the process pressure was increased, the Ne, Teoes and TeLP decreased; moreover, the Fourier-transform infrared spectroscopy results indicated that structure factor (R*) increased, and both the photosensitivity and hydrogen content (CH) decreased. An analysis conducted using OES and Langmuir probe measurement revealed, that the decreased concentration of the H radical reduced the passivation effect, and surface diffusion decreased. Furthermore, the gas partial pressure exerted a substantial influence on OES measurement. The volatility of the Ar spectrum intensity equaled the product of the volatility of Ne and TeLP when the partial pressure effect is eliminated. Regarding the resonance magnetic field, the effects of plasma resonance position on film characteristics were substantial. The Ne decreased greatly when the distance between quartz and the resonance zone was increased.

Electronic absorptions of the benzylium cation

The electronic transitions of the benzylium cation (Bz(+)) are investigated over the 250-550 nm range by monitoring the photodissociation of mass-selected C(7)H(7)(+)-Ar(n) (n = 1, 2) complexes in a tandem mass spectrometer. The Bz(+)-Ar spectrum displays two distinct band systems, the S(1)←S(0) band system extending from 370 to 530 nm with an origin at 19,067 ± 15 cm(-1), and a much stronger S(3)←S(0) band system extending from 270 to 320 nm with an origin at 32,035 ± 15 cm(-1). Whereas the S(1)←S(0) absorption exhibits well resolved vibrational progressions, the S(3)←S(0) absorption is broad and relatively structureless. Vibronic structure of the S(1)←S(0) system, which is interpreted with the aid of time-dependent density functional theory and Franck-Condon simulations, reflects the activity of four totally symmetric ring deformation modes (ν(5), ν(6), ν(9), ν(13)). We find no evidence for the ultraviolet absorption of the tropylium cation, which according to the neon matrix spectrum should occur over the 260 - 275 nm range [A. Nagy, J. Fulara, I. Garkusha, and J. Maier, Angew. Chem., Int. Ed. 50, 3022 (2011)].

Spectral analysis of unevenly spaced climatological time series

Spectral analysis is often based on the periodogram and on fitting a first-order autoregressive [AR(1)] process to data as climatological time series generally exhibit red noise spectra that can be well approximated by AR(1) models. When the periodogram exceeds some threshold at a frequency, the spectrum is said to differ from the AR(1) spectrum, and the frequency is generally taken as a member of the discrete spectrum. This traditional technique, however, must not be used without modifications for unevenly spaced data. Our purpose is to provide an AR(1) modeling tool that is more accurate than the TAUEST procedure commonly used for unevenly spaced paleoclimatical records. A periodogram based on an entire least square fit to unevenly spaced data is also introduced instead of the well-known Lomb–Scargle periodogram. The methodology is applied to two paleoclimatological records. Our results compared to those of a frequently used procedure (consisting of TAUEST and Lomb–Scargle periodogram) show some interesting differences.

Measurement of extreme ultraviolet light and electron temperature for a dense plasmas from hypocycloidal pinch device

We have generated Ar plasma in dense plasma focus (DPF) of hypocycloidal pinch (HCP) for extreme ultraviolet (EUV) lithography and investigated an emitted visible light for electro-optical plasma diagnostics. We have applied an input voltage 4.5 kV to the capacitor bank of 1.53 uF, and Ar gas has been filled into a diode chamber. The EUV emission signal whose wavelength is about 6–16 nm has been detected by using a photo-detector (AXUV-100 Zr/C, IRD). It has been found that the EUV intensity was decreased as the Ar pressure was increased. For measurement of the electron temperature in plasma pinch for HCP, we have measured the Ar spectrum lines for various Ar pressures with spectrometer (HR4000CG, Ocean Optics). If we assumed that the focused plasma regions satisfy the local thermodynamic equilibrium (LTE) conditions, the electron temperature of the hypocycloidal pinch could be obtained by Boltzmann plot method of optical emission spectroscopy (OES). The electron temperature has been approximately observed to be 2.6 eV at the Ar pressure 1 mTorr. The electron temperature and EUV intensity have been measured in accordance with the Ar pressures. It has been shown that the optimized Ar gas pressure is at 1 mTorr for the intensive focused plasma.

Feature Extraction Using Auto-Regression Spectral Analysis for Fabric Defect Detection

A new feature extraction method for fabric defect detection is proposed, which is based on one-dimensional projection series of fabric images. By using horizontal projection and vertical projection of the image, the characteristics of periodicity and orientation of fabric texture can be fully utilized. In terms of detection defects, it helps acquire information at most, and the computational complexity can also be greatly decreased with one-dimensional projection series. The proposed new method, named Auto-Regressive spectral analysis (AR), is a kind of modern spectral analysis method which is very suitable for analyzing short data with a high spectral resolution. The Burg algorithm is applied to estimate the AR spectrum. Finally, t-test is applied to verify the effectiveness of AR spectral features. This approach has been applied to various cases of defect detections with satisfactory results.

Compact fractal antenna with self-complementary hilbert-curves for WLAN dual-band and circular polarization applications

The authors propose a compact fractal antenna consisted of a Hilbert-curve and self-complementary configuration with dual-band and circular polarization characteristics. This design merges the inductively loaded monopole antenna and the self-complementary antenna to obtain a new monopole antenna. The self-complementary Hilbert-curve monopole antenna presents the desired bands of 2.43 GHz with bandwidth (BW) = 70 MHz (2.88%) and 5.35 GHz with BW = 550 MHz (10.36%). The circular polarizations for dual-band are demonstrated with AR spectrum and orthogonal modes. The proposed antenna is successfully simulated and measured with frequency responses, radiation patterns, current distributions, and electric field intensities. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2535–2539, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25528

Pattern Recognition for Control Charts Using AR Spectrum and Fuzzy ARTMAP Neural Network

The control charts pattern recognition can detect the unnatural fluctuation of the machining process and enhance the automation level of quality management, so it is important for manufacturing enterprise to implement the automatic pattern recognition of control charts. In this paper the quality data generated by Mote-Carlo simulation are preprocessed through AR spectrum analysis and the characteristic quantity are picked up in frequency domain. This approach decreases the complexity of characteristic quantity compared with traditional encoded mode. Then Fuzzy ARTMAP neural network which has incremental learning ability compared with traditional BP neural network is presented to recognize the control chart patterns. The recognition result indicates that the introduced method in this paper has advantage of traditional methods.

Penning ionization and ion fragmentation of formamide HCONH2 by He∗, Ne∗, and Ar∗ in molecular beams

Mass spectra from Penning ionization by metastable atom bombardment (MAB) in the title system at kinetic energies near 1 kcal/mol are reported. The experiments employ a supersonic excited noble gas beam crossing an effusive beam of formamide vapor. Product ions are extracted perpendicular to the plane of the beams, analyzed by a quadrupole mass filter, and counted by a scintillation-type ion counter. Relative to 70 eV electron impact, the He(*) and Ne(*) spectra show more extensive breakage of C-N and C-H bonds despite the smaller available energy, while the Ar(*) spectrum shows only the molecular ion (m/z 45), H atom elimination (44), and the decarbonylation products CO+NH(3)(+) (17). Fragmentation in the latter system has been analyzed using a combination of ab initio calculations and Rice-Ramsperger-Kassel-Marcus theory with tunneling correction; good agreement with the experimental 45/44/17 intensity ratio 100/6.8+/-0.7/6.2+/-1.7 is obtained. 15% of m/z 17 and 50% of m/z 44 is attributed to tunneling. The ab initio decarbonylation reaction path yields a hydrogen bonded H(2)N-HCO(+) transition state, which transfers a proton while proceeding downhill to the observed products, while both the path and the energetics support the earlier conclusion that the lowest lying electronically excited state of the ion (2pi or 2a(")) crosses the ground state early along the reaction path, thereby dominating the dynamics of decarbonylation.

Structural characterization of (C2H2)1–6+ cluster ions by vibrational predissociation spectroscopy

Vibrational predissociation spectra are reported for the cationic acetylene clusters, (C(2)H(2))(n) (+), n=1-6, in the region of the C-H stretching fundamentals. For n=1 and 2, predissociation could only be observed for the Ar-tagged clusters. These were prepared by charge-transfer collisions of Ar(k) (+) with C(2)H(2) to create C(2)H(2) (+)Ar(m) clusters, which were then converted into larger members of the (C(2)H(2))(n) (+)Ar series by sequential addition of acetylene molecules. The (C(2)H(2))(2) (+)Ar spectrum indicates that this species is predominantly present as the cyclobutadiene cation. Although mobility measurements on the electron-impact-generated (C(2)H(2))(3) (+) ion indicated that it primarily occurs as the benzene cation, [P. O. Momoh, J. Am. Chem. Soc. 128, 12408 (2006)] photofragmentation of (C(2)H(2))(3) (+)Ar in the C-H stretching region is dominated by the loss of C(2)H(2) in addition to the weakly bound Ar atom. This suggests that the dominant n=3 species formed by sequential addition of C(2)H(2) is based on a covalently bound C(4)H(4) (+) core ion. Interestingly, the spectrum of this core C(4)H(4) (+) species is different from that found for the cyclobutadiene cation, displaying instead a new band pattern that is retained in the higher (C(2)H(2))(3-6) (+) clusters. Multiple isomers are clearly involved, as yet another pattern of bands is recovered when the (C(2)H(2))(3) (+)Ar action spectrum is recorded in the (minor) Ar loss fragmentation channel. One of these features does appear in the location of the single band characteristic of the Ar-tagged benzene cation reported earlier [Phys. Chem. Chem. Phys. 4, 24 (2002)], supporting a scenario where the benzene cation is one of the isomers present. We then compare the Ar predissociation results with (C(2)H(2))(n) (+) spectra obtained when the ions are prepared by electron impact ionization of neutral acetylene clusters. The photofragmentation behavior and vibrational spectra indicate that the dominant species formed in this way also occur with a covalently bound C(4)H(4) (+) core. There are absorptions, however, which are consistent with a minor contribution from (C(2)H(2))(n) (+) clusters based on the benzene cation.

Evidence for an Alleghanian (Early Carboniferous to Late Permian) tectonothermal event in the New Jersey Coastal Plain basement from 40Ar/39Ar biotite data, geochemistry and gravity modeling

40 Ar/ 39 Ar dating of biotite from felsic orthogneiss recovered from the −3890-foot level of the Island Beach State Park (IBSP) well beneath the outer New Jersey Coastal Plain was accomplished using CO 2 laser incremental-heating techniques. Over 75% of the Ar released from the incremental-heating experiment form a well-behaved plateau with a calculated age of 243.98 ± 0.10 Ma. The new 244 Ma biotite age reported here is a cooling age younger than the metamorphic event that crystallized or reheated the biotite. We consider reheating of older biotite to be unlikely because the concordant 40 Ar/ 39 Ar spectrum upon repeated incremental laser heating showed a well-developed plateau. Thus, biotites from the IBSP gneiss are interpreted as having crystallized during a single thermal event, followed by cooling to below 300 °C. The IBSP well falls on a structural and geophysical anomaly trend that is along strike with rocks of the Bronson Hill anticlinorium to the north of the IBSP gneiss. Locally graphitic metasedimentary schists and gneisses recovered from New Jersey wells inboard of the IBSP well gneiss correlate to similar lithologies of the Connecticut Valley synclinorium west of the Hartford basin. Our reinterpretation of the IBSP gneiss as metamorphosed dacite or dacitic tuff is consistent with a correlation to some rocks of the Bronson Hill magmatic arc east of the Hartford basin. If correct, this would imply a Late Ordovician age for the protolith of the IBSP gneiss. Reported 40 Ar/ 39 Ar biotite ages of 235–253 Ma from southwestern Rhode Island, and of 238–247 Ma from southeastern Connecticut, are interpreted as cooling ages following a tectonothermal event associated with the Alleghanian orogeny (Early Carboniferous to Late Permian). Cooling ages of Alleghanian age (Early Carboniferous to Late Permian) are not recognized west of the Bronson Hill volcanic arc in either central Connecticut or in Massachusetts. Therefore, the 244 Ma cooling age presented here, and the geochemical affinity of the IBSP gneiss to some orthogneisses of the Bronson Hill arc, support an interpretation of the IBSP well as representing the southern continuation of the Bronson Hill arc into New Jersey. Moreover, it documents the presence of rocks beneath the outer New Jersey Coastal Plain that experienced a Permian Alleghanian metamorphism.

Fractal monopole‐like antenna with series Hilbert‐curves for WLAN dual‐band and circular polarization applications

AbstractA novel design of fractal monopole‐like antenna with series Hilbert‐curve configuration is proposed for 2.45/5.35 GHz dual‐band and circular polarization applications in this article. The compact fractal antenna consists of five series Hilbert‐curve and the monopole couplings, and exhibits the desired dual‐band 2.45 GHz (BW = 85 MHz, 3.45%) and 5.35 GHz (BW = 240 MHz, 4.46%), respectively, for IEEE 802.11a/b/g WLAN applications. The circular polarizations for dual‐band are demonstrated with AR spectrum and electric field intensities. Results included with frequency responses, radiation patterns, and electric field intensities are presented and discussed. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 876–880, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24204

Ionization-induced switch in aromatic molecule–nonpolar ligand recognition: Acidity of 1-naphthol+(1-Np+) rotamers probed by IR spectra of 1-Np+–Lncomplexes (L = Ar/N2, n ≤ 5)

The interaction of the trans (t) and cis (c) rotamers of the 1-naphthol cation (1-C10H8O+ = 1-Np+ = 1-hydroxynaphthalene+) with nonpolar ligands in the ground electronic state is characterized by IR photodissociation spectra of isolated 1-Np+–Ln complexes (L = Ar/N2) and density functional calculations at the UB3LYP/6-311G(2df,2pd) level. Size-dependent frequency shifts of the O–H stretch vibration (Δν1) and photofragmentation branching ratios provide information about the stepwise microsolvation of both 1-Np+ rotamers in a nonpolar hydrophobic environment, including the formation of structural isomers, the competition between H-bonding and π-bonding, the estimation of ligand binding energies, and the acidity of t/c-1-Np+. t-1-Np+ is predicted to be more stable than c-1-Np+ by 9 kJ mol−1, with an isomerization barrier of 38 kJ mol−1. The OH group in t-1-Np+ is slightly more acidic than in c-1-Np+ leading to stronger intermolecular H-bonds. Both 1-Np+ rotamers are considerably less acidic than the phenol cation because of enhanced charge delocalization. The 1-Np+−Ar spectrum displays ν1 bands of the more stable H-bound and the less stable π-bound t-1-Np+–Ar isomers. Only the more stable H-bound dimers are identified for t/c-1-Np+–L2. Analysis of the Δν1 shifts of the H-bound dimers yields a first experimental estimate for the proton affinity of the t-1-naphthoxy radical (∼908 ± 30 kJ mol−1). The Δν1 shifts of 1-Np+–Ln (n ≤ 2 for Ar, n ≤ 5 for N2) suggest that the preferred microsolvation path begins with the formation of H-bound 1-Np+–L, which is further solvated by (n−1) π-bound ligands. Ionization of 1-Np−Ln drastically changes the topology of the intermolecular interaction potential and thus the preferred aromatic substrate–nonpolar ligand recognition pattern.

Dynamic hohlraum driven inertial fusion capsules

A dynamic hohlraum is formed when an imploding annular cylindrical Z-pinch driven plasma collides with an internal low density convertor. This collision generates an inward traveling shock wave that emits x rays, which are trapped by the optically thick Z-pinch plasma and can be used to drive an inertial fusion capsule embedded in the convertor. This scheme has the potential to efficiently drive high yield capsules due to the close coupling between the intense radiation generation and the capsule. In prior dynamic hohlraum experiments [J. E. Bailey et al., Phys. Rev Lett. 89, 095004 (2002)] the convertor shock wave has been imaged with gated x-ray pinhole cameras. The shock emission was observed to be very circular and to be quite narrow in the radial direction. This implies that there is minimal Rayleigh–Taylor imprinting on the shock wave. Thus, the dominant source of radiation asymmetry is not random and in principle could be significantly decreased by proper design. Due to the closed geometry of the dynamic hohlraum, the most convenient way to diagnose the radiation symmetry is to image the x rays from the core of an imploded capsule. However, the core temperatures in the prior experiments were not high enough to obtain images. Using numerical simulations we have redesigned the dynamic hohlraum to obtain higher capsule core temperatures. This has enabled us to obtain x-ray pinhole images and Ar K-shell spectra from the imploded cores of 1.7–2.0 mm diameter CH-wall capsules filled with either D2 or CD4 and doped with a small amount of Ar. These capsules absorbed approximately 20 kJ of x-ray energy from the radiation drive, which peaked at a temperature of about 200 eV. Core temperatures of approximately 1 keV were inferred from the Ar spectrum. Our present understanding of the physics of dynamic hohlraums is presented along with our plans to improve this system.