High Instrumental Resolution Research Articles

Parameter estimation from the Lyα forest in the Fourier space using an information-maximizing neural network

Our aim is to present a robust parameter estimation with simulated forest spectra from Sherwood-Relics simulations suite by using an information-maximizing neural network (IMNN) to extract maximal information from 1D-transmitted flux in the Fourier space. We performed 1D estimations using IMNN for intergalactic medium (IGM) thermal parameters $T_0$ and gamma at $z=2-4$, and cosmological parameters $ and s $ at $z=3-4$. We compared our results with estimates from the power spectrum using the posterior distribution from a Markov Chain Monte Carlo (MCMC). We then checked the robustness of IMNN estimates against deviation in spectral noise levels, continuum uncertainties, and instrumental smoothing effects. Using mock forest sightlines from the publicly available CAMELS project, we also checked the robustness of the trained IMNN on a different simulation. As a proof of concept, we demonstrated a 2D-parameter estimation for $T_0$ and photoionization rates, $ HI We obtain improved estimates of $T_0$ and gamma using IMNN over the standard MCMC approach. These estimates are also more robust against signal-to-noise deviations at $z=2$ and 3. At $z=4$, the sensitivity to noise deviations is on par with MCMC estimates. The IMNN also provides $T_0$ and gamma estimates that are robust against continuum uncertainties by extracting small-scale continuum-independent information from the Fourier domain. In the cases of $ and s $, the IMNN performs on par with MCMC but still offers a significant speed boost in estimating parameters from a new dataset. The improved estimates with IMNN are seen for high instrumental resolution (FWHM=6 At medium or low resolutions, the IMNN performs similarly to MCMC, suggesting an improved extraction of small-scale information with IMNN. We also find that IMNN estimates are robust against the choice of simulation. By performing a 2D-parameter estimation for $T_0$ and $ HI $, we also demonstrate how to take forward this approach observationally in the future.

Plasma Spectroscopy on an Aluminum-Pellet Ablation Cloud in an LHD Plasma with an Echelle Spectrometer

We developed an echelle spectrometer for the simultaneous observation of the whole visible range with a high instrumental resolution, for example, 0.055 nm (full width at the half maximum) at 400 nm and 0.10 nm at 750 nm. With the spectrometer, the emission from an ablation cloud of an aluminum pellet injected into a high-temperature plasma generated in the Large Helical Device (LHD) was measured. We separated the emission lines into Al I, II, III and IV groups, and estimated the electron temperature and density of the ablation cloud from the line intensity distribution and Stark broadening respectively, of each of the Al I, II and III groups. We also determined the Stark broadening coefficients of many Al II and III lines from the respective Stark widths with the estimated electron temperature and density.

Pushing data quality for laboratory pair distribution function experiments.

Over the last decade, some studies with laboratory pair distribution function (PDF) data emerged. Yet, limited Qmax or instrumental resolution impeded in-depth structural refinements. With more advanced detector technologies, the question arose how to design novel PDF equipment for laboratories that will allow decent PDF refinements over r = 1-70 Å. It is crucial to reflect the essential requirements, namely, monochromatic X-rays, suppression of air scattering, instrumental resolution, and overall measurement times. The result is a novel PDF setup based on a STOE STADI P powder diffractometer in transmission-/Debye-Scherrer geometry with monochromatic Ag Kα1 radiation, featuring a MYTHEN2 4K detector covering a Q range of 0.3-20.5 Å-1. PDF data are collected in a moving PDF mode within 6 h. Structural signatures of liquids can be satisfactorily resolved in the PDF as shown for the ionic liquid hmimPF6. The high instrumental resolution is mirrored in low qdamp values determined from LaB6 measurements. PDF data from a powder sample of ca. 7 nm TiO2 nanoparticles were successfully refined over up to 70 Å with goodness-of-fit values Rw < 0.22 (respectively Rw = 0.18 over 30 Å), thanks to the low background and high instrumental resolution, hereby enlarging the accessible r range by several tens of Angstroms compared to previous laboratory PDF studies.

X-ray backscattering study of crystal lattice distortion in hidden order of URu2Si2

We performed synchrotron X-ray diffraction measurements on a small single crystal of with approximate dimensions of . A backscattering diffraction set-up (2) in combination with a Si(6 6 0) monochromator ensures a high instrumental resolution of , where denotes a lattice-plane spacing and is its spread expressed as the full width at half maximum (FWHM). We carefully measured the (5 5 0) Bragg peak in the temperature range between 5 and 25 K, and found it to show no signature of broadening and splitting when “Hidden Order (HO)” sets in below 17.5 K. Temperature variation of the peak position closely follows the behaviour of the known linear thermal expansion coefficient. Detailed analysis of the peak width reveals that the tetragonal fourfold rotational symmetry of is conserved in HO within the experimental accuracy of the orthorhombicity of . We also found that the (5 5 0) peak profile exhibits a temperature-independent fine structure, which indicates that the tetragonal -axis lattice parameter of the used crystal is distributed with a FWHM of .

Improved energies for the 5.2 keV M1 and 42.0 keV M2 nuclear transitions in 83Rb

The low-energy electron spectrum following the decay of 83Sr was analysed at high instrumental resolution by an electrostatic spectrometer. Significantly improved energies of \( 5235.7\pm 0.8\) and \( 42078.0\pm 1.8\) eV were determined from the conversion electron spectra for the nuclear transitions depopulating the first 3/2- and the second \( 9/2^{+}\) excited states in 83Rb to the \( 5/2^{-}\) ground state, respectively. The M1 character for the 5.2keV nuclear transition was confirmed and the E2 admixture parameter \( \delta^{2}(E2/M1)=(2.6\pm 0.2)\times 10^{-5}\) was obtained. Values of \( 2.8\pm 0.2\), \( 3.8\pm 0.2\), \( 1.4\pm 0.3\), \( 1.4\pm 0.4\), and \( 4.1\pm 0.3\) eV were determined for the K, L1, L2, L3, and M1 natural atomic level widths of rubidium, respectively.

Inelastic x-ray scattering study of the collective dynamics in liquid sodium.

Inelastic x-ray scattering data have been collected for liquid sodium at T=390 K, i.e., slightly above the melting point. Owing to the very high instrumental resolution, pushed up to 1.5 meV, it has been possible to determine accurately the dynamic structure factor S(Q,omega) in a wide wave-vector range, 1.5-15 nm(-1), and to investigate on the dynamical processes underlying the collective dynamics. A detailed analysis of the line shape of S(Q,omega), similarly to other liquid metals, reveals the coexistence of two different relaxation processes with slow and fast characteristic time scales. The present data lead to the conclusion that (i) the picture of the relaxation mechanism based on a simple viscoelastic model fails and (ii) although the comparison with other liquid metals reveals similar behavior, the data do not exhibit an exact scaling law as the principle of the corresponding state would predict.

Collective dynamics of liquid aluminum probed by inelastic x-ray scattering

An inelastic x-ray scattering experiment has been performed in liquid aluminum for the purpose of studying the collective excitations at wave vectors below the first sharp diffraction peak. The high instrumental resolution (up to 1.5 meV) allows an accurate investigation of the dynamical processes in this liquid metal on the basis of a generalized hydrodynamics framework. The outcoming results confirm the presence of a viscosity relaxation scenario ruled by a two-time-scale mechanism, as recently found in liquid lithium.

Fluid phase structure of EPC and DMPC bilayers

X-ray diffraction data taken at high instrumental resolution were obtained for EPC and DMPC under various osmotic pressures, primarily at T=30°C. The headgroup thickness D HH was obtained from relative electron density profiles. By using volumetric results and by comparing to gel phase DPPC we obtain areas A EPC F =69.4±1.1 Å 2 and A DMPC F =59.7±0.2 Å 2. The analysis also gives estimates for the areal compressibility K A . The A F results lead to other structural results regarding membrane thickness and associated waters. Using the recently determined absolute electrons density profile of DPPC, the A F results also lead to absolute electron density profiles and absolute continuous transforms ∣ F( q)∣ for EPC and DMPC. Limited measurements of temperature dependence show directly that fluctuations increase with increasing temperature and that a small decrease in bending modulus K c accounts for the increased water spacing reported by Simon et al. (1995) Biophys. J. 69, 1473–1483.

Si2pphotoabsorption inSiH4andSiD4: Molecular distortion in core-excited silane

We report on a high-resolution photoabsorption study of ${\mathrm{SiH}}_{4}$ and ${\mathrm{SiD}}_{4}$ in the excitation region below the Si $2p$ threshold. The spectra can be separated into a lower region from valence excitations and an upper region from Rydberg excitations. In the valence region, intense excitations of vibrational bending modes were observed, reflecting a deviation of the core-excited molecules from the ${T}_{d}$ symmetry of ground-state silane. The derived geometry of the core- to -valence-excited molecules was found to be similar to that of the equivalent-cores molecule ${\mathrm{PH}}_{4}.$ For excitations to higher Rydberg states, symmetric-stretching vibrational modes were exclusively observed, while for the lowest Rydberg states, additional bending-mode vibrational excitations were found to contribute. The latter observation can be explained by a mixing of Rydberg and valence character, causing an increase of the deviation from ${T}_{d}$ symmetry with increasing valence character of the core-excited state. The spectral shape of the ${2p}_{3/2}^{\ensuremath{-}1}5s$ Rydberg state was analyzed by a four-mode Franck-Condon fit, providing insight into the structure of the core-excited molecule. The high instrumental resolution ($\ensuremath{\Delta}E=15\mathrm{meV}$ full width at half maximum) allowed the derivation of the natural widths \ensuremath{\Gamma} of the Rydberg states, which were found to be identical within the limits of error (with $\ensuremath{\Gamma}=50\ifmmode\pm\else\textpm\fi{}5\mathrm{meV}$).

Microstrain characterization of metals using high-resolution neutron diffraction

Two neutron diffraction arrangements were used for the investigation of residual microstrains in metals. A high instrumental resolution was reached exploiting the neutron-optical properties of bent perfect Si crystals; Δd/ d = 2.6 × 10 −3 for the three-axis arrangement and Δd/ d = 8 × 10 −4 in the case of energy-dispersive transmission diffraction geometry. Low-carbon steel subjected to small tensile prestrains was tested by using both instruments. Microstrain distribution was deduced from the width and shape of Bragg diffraction peaks and edges, respectively.

X-ray structure determination of fully hydrated L alpha phase dipalmitoylphosphatidylcholine bilayers

Bilayer form factors obtained from x-ray scattering data taken with high instrumental resolution are reported for multilamellar vesicles of L alpha phase lipid bilayers of dipalmitoylphosphatidylcholine at 50 degrees C under varying osmotic pressure. Artifacts in the magnitudes of the form factors due to liquid crystalline fluctuations have been eliminated by using modified Caillé theory. The Caillé fluctuation parameter eta 1 increases systematically with increasing lamellar D spacing and this explains why some higher order peaks are unobservable for the larger D spacings. The corrected form factors fall on one smooth continuous transform F(q); this shows that the bilayer does not change shape as D decreases from 67.2 A (fully hydrated) to 60.9 A. The distance between headgroup peaks is obtained from Fourier reconstruction of samples with four orders of diffraction and from electron density models that use 38 independent form factors. By combining these results with previous gel phase results, area AF per lipid molecule and other structural quantities are obtained for the fluid L alpha phase. Comparison with results that we derived from previous neutron diffraction data is excellent, and we conclude from diffraction studies that AF = 62.9 +/- 1.3 A2, which is in excellent agreement with a previous estimate from NMR data.

Small-angle x-ray scattering from lipid bilayers is well described by modified Caillé theory but not by paracrystalline theory

X-ray scattering data at high instrumental resolution are reported for multilamellar vesicles of L alpha phase lipid bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine at 50 degrees C under varying osmotic pressure. The data are fitted to two theories that account for noncrystalline disorder, paracrystalline theory (PT) and modified Caillé theory (MCT). The MCT provides good fits to the data, much better than the PT fits. The particularly important characteristic of MCT is the long power law tails in the scattering. PT fits (as well as ordinary integration with no attempt to account for the noncrystalline disorder) increasingly underestimate this scattering intensity as the order h increases, thereby underestimating the form factors used to obtain electron density profiles.

Three-crystal spectrometer for 150-keV synchrotron radiation

A triple-axis spectrometer for high-energy (≳150 keV) synchrotron radiation has been constructed and characterized. The reciprocal space resolution function of this instrument has been measured using perfect silicon crystals as monochromator, sample, and analyzer. It was found to have dimensions of 1.0×10−5 Å−1 and 2.3×10−4 Å−1 in the directions perpendicular and parallel to the momentum transfer Q, respectively, comparable to those achievable using standard 8-keV triple-axis instruments. The large penetration depths of high-energy x-ray photons, combined with the high instrumental resolution, opens new possibilities in the study of truly bulk condensed matter systems.

L beta 2,15 x-ray spectra of elements between 41Nb and 51Sb.

The L${\ensuremath{\beta}}_{2}$,15 spectra of elements between $_{41}\mathrm{Nb}$ and $_{51}\mathrm{Sb}$ have been measured at high instrumental resolution from solid samples. The satellite structure on the high-energy side of L${\ensuremath{\beta}}_{2}$,15 was resolved and the natural widths of diagram lines were determined. Two different satellite groups due to LM and LN double-hole states were clearly seen. The relative intensity of satellites was examined and it was noticed that the Coster-Kronig channels which create extra holes in the M shell are closed at $_{51}\mathrm{Sb}$. A faint structure was observed between the two main groups of satellites after $_{48}\mathrm{Cd}$. The ${L}_{3}$${O}_{1}$ transition falls in this region but it may also be partly the result of triple-hole states.

Electric Field Induced Splitting of the Stretching Vibration Lines of SH−, SeH−, and TeH− Centres in Alkali Halides

AbstractThe stretching vibration lines of SH−, SeH−, and TeH− centres in various alkali halides are split into several components by an external electric field. No similar effects are observed yet for other centres. The splitting patterns are measured with high instrumental resolution for various directions of field and light polarization. From the number of componental lines the orientations turn out to be 〈111〉 for all investigated centres. Possible reasons for the splitting are discussed. Paraelectric alignment, however, well known for the homologeous OH− centres, is not observed.

Inelastic neutron scattering study of one-dimensional inorganic conductors

We report on lattice dynamical studies in the one-dimensional conductirs NbSe 3 and (TaSe 4) 2I. The sample of NbSe 3 used in the present investigations consists of a large number of needles assembled with a common b -axis and random orientation around it. Satellite reflections induced by the charge density wave transition which occurs at T 1 = 145 K have been observed at (1, 2±2k F, 0). Besides the longitudinal acoustic mode, we have detected one transverse acoustic mode by multiple scattering processes. We have studied the long-wavelength lattice dynamics of (TaSe 4) 2I in connection with the Peierls instability at T = 263 K under high instrumental resolution conditions.

Structure and depolarization properties in the Raman spectra of superfluid 4He.

Raman spectra of superfluid $^{4}\mathrm{He}$ under saturated vapor pressure are measured at 1.37 K. Distinct changes in the slope ${\mathrm{dI}}_{R}$/dE are confirmed at several energy values in the plot of Raman intensity (${I}_{R}$) as a function of the energy shift (E) for a measurement with relatively high instrumental resolution. Depolarization ratios are determined up to the energy shift at 420 K. Existence of s partial-wave scattering is confirmed.

Electrophotoluminescence and the electrical properties of the photosynthetic membrane. I. Initial kinetics and the charging capacitance of the membrane

Preilluminated chloroplast membranes, and particularly hypotonically swollen vesicles (blebs), give rise to a strong characteristic luminescence (electrophotoluminescence, EPL; Ellenson and Sauer, 1976, Photochem. Photobiol., 23:113-123; Arnold and Azzi, 1971, Photochem. Photobiol., 14:233-240) during the application of a strong external electric field. A detailed kinetic study of EPL was carried out and the initial kinetics from the field onset are reported here. The fast rise time (less than 0.2 mus) of the applied external electric field together with a high instrumental time resolution allowed the observation of a characteristic delay (lag time) between the field onset and the appearance of the induced emission. The lag time decreased with increase in the applied field strength and/or the conductivity of the suspension and is interpreted to be a consequence of (a) the necessity to reach a threshold electrical potential difference in the bleb membrane, below which no emission can be triggered, and (b) the finite time required to attain such a transmembranal field during the charging process of the membrane. A quantitative analysis, connecting the lag time, the controllable experimental parameters, and the membrane electrical characteristics is presented. Its verification was carried out in both size-selected and heterogeneous bleb populations. In the latter, experiments were consistent with the assumption that the lag time reflects the charging of the largest blebs. The results indicate (a) the possibility of directly measuring the specific membrane capacitance, yielding an estimate of Cm = 1.2 +/- 0.3 microF/cm2 (the precision being particle size-homogeneity dependent); (b) A minimal transmembranal potential difference (of approximately 240 mV) is necessary to induce electrophotoluminescence; and (c) the lag duration depends on the time elapsed between the preillumination and the external field application. Correlated with the study of ionophore effects on the lag time, this suggests additivity of the light- and field-induced transmembrane potentials in attaining the threshold for emission.

Observation of algebraic decay of positional order in a smectic liquid crystal

A smectic-$A$ liquid crystal in three dimensions has been predicted to exhibit algebraic decay of the layer correlations rather than true long-range order. As a consequence, the smectic Bragg peaks are expected to be power-law singularities of the form ${q}_{\ensuremath{\parallel}}^{\ensuremath{-}2+\ensuremath{\eta}}$ and ${q}_{\ensuremath{\perp}}^{\ensuremath{-}4+2\ensuremath{\eta}}$, where $\ensuremath{\parallel}(\ensuremath{\perp})$ is along (perpendicular to) the smectic density wave vector direction, rather than $\ensuremath{\delta}$ function peaks. Observation of these phenomena requires very high instrumental resolution together with a resolution function with wings which drop off much more rapidly than ${q}_{\ensuremath{\parallel}}^{\ensuremath{-}2}({q}_{\ensuremath{\perp}}^{\ensuremath{-}4})$. We show that these requirements may be met by using a three crystal x-ray spectrometer with multiple-reflection channel cut crystals as monochromator and analyzer. We find that the smectic-$A$ Bragg peaks observed in the liquid-crystal octyloxy-cyanobiphenyl are indeed consistent with the predicted power-law singularity form. Furthermore, the explicit values of $\ensuremath{\eta}$ required to describe the measured profiles are in accordance with calculations of $\ensuremath{\eta}$ using the harmonic approximation with empirically determined splay and layer compressibility elastic constants.

Lαx-ray spectra of elements betweenZr40andCd48

The $L\ensuremath{\alpha}$ spectra for elements between $_{40}\mathrm{Zr}$ and $_{48}\mathrm{Cd}$ have been measured at high instrumental resolution. The natural widths of the diagram $L{\ensuremath{\alpha}}_{1}$ line (${L}_{3}\ensuremath{-}{M}_{5}$ transitions) of these elements are determined. The observed linewidths from Mo to Ag are systematically narrower than those predicted by theory. We suggest that a reason for this disagreement are too large theoretical Auger transition rates assumed for the ${M}_{4,5}$ shells of Mo to Ag. Owing to high resolution, characteristic features of satellites of $L{\ensuremath{\alpha}}_{1,2}$ diagram lines are revealed.