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Molecular anions are appealing targets for study because, compared with their neutral and cationic counterparts, they can be probed with conventional laboratory lasers without the need for multiphoton ionization schemes, and they provide spectroscopic details on the corresponding neutral molecules. Here, we describe a section of a modular instrument designed to perform high-throughput photoelectron and photodetachment spectroscopy of gas-phase anions, with future provision for time-resolved and isomer-selective spectroscopy. The instrument framework allows for the incorporation and adaptation of several ion sources, as demonstrated here with plasma (electric) discharge sources providing variable hard to soft ion generation conditions. The generated anions are separated according to their mass-to-charge ratio through time-of-flight mass spectrometry ( m / z Δ m / z = 500–600) and are focused into a set of perpendicular velocity-map imaging electrodes ( Δ E E ≈ 4 %), where mass-selected anions are probed using laser light and the ejected electrons are velocity-map imaged. Instrument performance is demonstrated through the acquisition of photodetachment and photoelectron spectra for CH2CN−, showing sharp resonances in the vicinity of the detachment threshold assigned to rovibrational states of a dipole-bound anion and broader lifetime-limited spectral features at photon energies well above the threshold assigned to prompt autodetachment from a temporary anion resonance. Similar measurements could be performed on any molecular anions generated in the sources. [ABSTRACT FROM AUTHOR]

Alternating current (ac) losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different ac loss components and provide approaches for reducing ac losses in cables. An FEA model based on the T-A formulation treats the cross section of thin superconducting layers as 1D lines and, therefore, only can predict the ac loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross section HTS tapes to provide the total ac losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. The 1D and 2D simulation models were validated by cross comparing the results from both models and by comparing sub-section and full cross section models. Subsequently, two models relate cable design and operational parameters to the surface and edge losses of a two-layer CORC cable by considering the (1) relative contributions of edge and surface losses to the overall ac losses; (2) effect of the current distribution between inner and outer HTS layers on ac losses; (3) impact of the tape alignment on ac losses in each HTS layer; (4) influence of the thickness of HTS layers on ac losses; (5) effect of size and number of inter-tape gaps on ac losses; and (6) contribution frequency on the ac losses. The research results given in this paper are therefore not only valuable to suggest strategies for reducing ac loss in multi-layer cables but also for developing more accurate and effective methods to calculate ac loss in CORC HTS cables. [ABSTRACT FROM AUTHOR]

This paper presents a study of the total ac loss characteristics of a rolling-assisted biaxially textured substrate (RABiTS) YBa2Cu3O7 (YBCO) sample exposed to a parallel ac magnetic field. The results have shown that, for a given applied magnetic field and transport current, a RABiTS YBCO tape can generate very different magnitudes of ac loss, depending on whether the transport current and applied field have the same phase or opposite phase. The results of this study are very important for the optimization of the design of a RABiTS YBCO cable because they can suggest an appropriate arrangement of RABiTS tapes in a cable to minimize the cable ac loss. In this study, both experimental and finite-element method simulation approaches were employed. A modeling model that takes the magnetic field dependent permeability and ferromagnetic loss of the substrate into account reproduced well the experimental data for both self-field and total ac losses. [ABSTRACT FROM AUTHOR]

In this paper we present a finite element model using the commercial COMSOL® software package for calculating the ac loss in bifilar stacks of high temperature superconducting tape. In the model, the current-voltage relationship characterizing the superconducting properties is assumed to follow a power law. The calculations were performed for infinite bifilar stacks with different values of layer-to-layer separation D. With appropriate settings for the boundary conditions, the numerical results agree well with the analytical data obtained from a recently proposed model [J. R. Clem, Phys. Rev. B 77, 134506 (2008)]. The numerical approach was also used to investigate the end effects in a bifilar stack to answer the following question: how many layers away from the end of a stack are required before the environment of a given layer is identical to that in an infinite stack? We find that the answer to this question depends strongly on the value of D. Based on this study, a model for calculating the ac loss in bifilar noninductively wound coils with a finite number of turns is proposed. [ABSTRACT FROM AUTHOR]

Yttrium barium copper oxide (YBCO) coated conductors are now the most promising high-temperature superconducting tapes in terms of current capacity and price. One form of these conductors utilizes YBCO films on Ni–W metallic tapes and is being considered for a number of power engineering applications. In these applications, the conductor will carry an ac current, leading to energy losses, which are the focus of significant technical and experimental efforts. Our measurements of the ac losses of YBCO/Ni–W conductors carrying ac currents in applied dc magnetic fields have revealed a complex interaction between the magnetic materials present, the geometry of the conductor, the ac and dc magnetic fields, and the electromagnetic “history” of the sample. The investigation of this interaction is the main subject of this paper. [ABSTRACT FROM AUTHOR]

"Physics behind music: an introduction" by Bryan H. Suits is a book that successfully combines physics and music. Unlike other books on the subject, Suits uses familiar aspects of music as a starting point to explain various physical principles. The book covers topics such as rates of processes, frequencies, pitch, auditory illusions, vibrating rods, wavepackets, non-linear physics, sound in pipes and tubes, room acoustics, electronic sound production, and more. Each chapter includes a summary, suggestions for additional reading, and problems with selected answers. The book is accessible to non-experts and is recommended for interested readers or as supplementary material for a physics course. [Extracted from the article]

By use of a free-jet expansion which incorporates a heated nozzle, we have recorded the laser excitation spectrum of the 460 nm band system of NiCl2 at rotational resolution. The rotational temperature in these recordings was about 12 K. Several bands have been recorded and analyzed for three isotopomers, 58Ni35Cl2, 60Ni35Cl2, and 58Ni35Cl37Cl in natural abundance. Spin components with Ω values of 0 and 1 have been identified in both the upper and lower states of the transition. Accurate values for all three vibrational intervals ν1, ν2, and ν3 have been determined for nickel dichloride in the upper state and for the bending wave number ν2 in the lower state. The results show that the molecule is linear in both states involved in the transition and that the lower (ground) state is 3Σ-g in character. Evidence is presented from the nickel isotope shifts to show that the transition is vibronically induced through the bending vibration and that the upper state is vibronically 3Πu in character; it probably derives from an electronic 3Δg state. The zero-point averaged bond lengths are determined for both states as r0′=0.209 435(13) nm and r0″=0.205 317(14) nm. The fine structure parameters for the X 3Σ-g state are interpreted in terms of low lying 1Σ+g and 3Πg states, which are shown to lie a few thousand reciprocal centimeters above the ground state. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Apart from one of the diagrams where "the ignorance is contained within the shaded blobs" the authors address ignorance head on. It is a perfect text for someone who has a background in physics but very little in particle physics, rather like me. It explains how the muddy footprints of particle physics turn up in the structures of galaxies and the cosmic microwave background, and how the physics of these can inform our theories, at the very least by helping to constrain them. [Extracted from the article]

This paper presents our new experimental facility and techniques to measure ac loss and current distribution between the layers for High Temperature Superconducting (HTS) cables. The facility is powered with a 45 kVA three-phase power supply which can provide three-phase currents up to 5 kA per phase via high current transformers. The system is suitable for measurements at any frequency between 20 and 500 Hz to better understand the ac loss mechanisms in HTS cables. In this paper, we will report techniques and results for ac loss measurements carried out on several HTS cables with and without an HTS shielding layer. For cables without a shielding layer, care must be taken to control the effect of the magnetic fields from return currents on loss measurements. The waveform of the axial magnetic field was also measured by a small pick-up coil placed inside a two-layer cable. The temporal current distribution between the layers can be calculated from the waveform of the axial field. [ABSTRACT FROM AUTHOR]

In I The Science of Learning Physics i , José Mestre and Jennifer Docktor have come to my rescue. I highly recommend this approachable and engaging text for any physics educator, and for anyone interested in pedagogical research in physics. The science of learning physics: by José P. Mestre and Jennifer L. Docktor, Singapore, World Scientific, 2021, 212 pp., £50.00 (hardback), ISBN 978-981-122-654-0. [Extracted from the article]

In superconducting coils tapes are often closely packed in a configuration similar to a ‘z-stack’, which strongly influences the AC losses with respect to when tapes can be considered as separate objects: losses are reduced in the presence of externally applied AC magnetic field, but are increased in the presence of AC transport current. In this paper, we quantify the magnitude of the tape interaction and the AC losses of these two cases, both experimentally and by means of finite-element method simulations. We also discuss the experimental issues arisen with the utilized AC loss measurement technique. [ABSTRACT FROM AUTHOR]

Abstract: Iron dichloride, FeCl2, has been produced at low rotational and vibrational temperatures in the gas phase using a supersonic expansion. Laser-induced fluorescence from several vibronic bands in the 288nm band system has been dispersed to reveal extensive vibrational progressions. The symmetric stretching wavenumber, ν 1 is determined to be 352.39(13)cm−1 for Fe35Cl2 in the ground electronic state. The antisymmetric stretching wavenumber, ν 3 is found to be approximately 511cm−1. The evidence suggests that the molecule is linear in both the ground and excited electronic states. [Copyright &y& Elsevier]

We present high resolution, infrared laser absorption spectra of (DF)3 in a slit supersonic jet expansion. In contrast to previous structureless near IR spectra of (HF)3, the (DF)3 data reveal clear rotational structure characteristic of a cyclic, 6-membered ‘‘ring,’’ and therefore provide the first accurate experimental evidence for the equilibrium geometry of any hydrogen fluoride oligomer beyond the well-studied dimer. Furthermore, the spectra display homogeneous rotational fine structure 2–3 orders of magnitude in excess of what could be anticipated from a single vibrational band. Analysis of this fine structure elucidates a novel IVR mechanism which involves single hydrogen bond cleavage, and consequent opening of the (DF)3 ring on the 40 ps time scale. [ABSTRACT FROM AUTHOR]

Studies the structure of nickel dichloride. Energy levels and bonding in simple binary compounds of the d-block elements; Physical techniques use in the study of gas-phase molecule and the discrete species isolated in cryogenic matrices; Disadvantage of gas-phase studies under equilibrium conditions at the required high temperatures; Matrix effects; Isotope shift method.

This paper presents a new finite-element simulation model for computing the electromagnetic properties and AC losses in systems of YBCO (yttrium barium copper oxide) conductors on roll assisted biaxially textured substrates (RABiTS). In this model, the magnetic field dependent permeability and ferromagnetic loss of the substrates in RABiTS YBCO tapes are taken into account. The simulations were employed to simulate the AC loss in stacks of two parallel connected YBCO tapes. The simulation results are compared with the experimental data to check the validity of the simulation model. The result reveals an effective way of significantly reducing AC loss in YBCO tapes by stacking two RABiTS YBCO coated conductors with the appropriate relative tape orientation. [ABSTRACT FROM AUTHOR]

Abstract: The 288nm band system of FeCl2 has been recorded with a sample produced in a warmed, free-jet expansion at moderately high resolution (with a linewidth of 0.28cm−1). Under these conditions, several hot bands are observed involving excitation of the symmetric and anti-symmetric stretching vibrations. The wavenumbers determined as a result for FeCl2 in its ground 5Δg,4 state are and . No hot, sequence bands in the bending vibration were observed. The most likely explanation is that the wavenumber for ν 2 is essentially the same in both the electronic states involved (88cm−1). Additional strong hot bands are observed that are unrelated to the previously assigned electronic transitions; they appear to emanate from a low-lying electronic state of FeCl2. [Copyright &y& Elsevier]

Abstract: The laser excitation spectrum of the 288nm band system of FeCl2, formed in a free-jet expansion, has been recorded at a rotational temperature of approximately 10K. Vibronic transitions are observed from the ground state to two close-lying excited electronic states that differ in inversion (g, u) parity. Two extensive progressions in the symmetric stretching vibration have been identified, referred to as Progressions A and B. The main features of Progression A, which is based on the band, are allowed transitions to the excited electronic state of ungerade symmetry. Progression B is built on the band and consists of vibronically induced transitions to the gerade excited state. A substantial decrease in the symmetric stretching vibrational wavenumber is observed on excitation . Local perturbations are found to cause relative shifts between the different isotopomers. Several vibronic bands have been recorded and analysed at rotational resolution for the three isotopomers Fe35Cl2, Fe35Cl37Cl, and Fe37Cl2 in natural abundance. All bands show perpendicular rotational structure of a linear molecule, and have been unambiguously assigned to a Ω =5–4 transition, consistent with the inverted 5Δg ground state predicted by ab initio and DFT calculations. The zero-point averaged Feength is determined to be in the upper and lower electronic states. The results show that the molecule is linear in both states. [Copyright &y& Elsevier]

Sub-Doppler spectra of the A [SUP3]II-X[SUP3]∑ [SUP-](0,0) and (1,0) bands of the PH radical have been recorded using an injection seeded single mode optical parametric oscillator in a supersonic jet expansion. Most of the rotational lines in these laser-induced fluorescence spectra exhibit clear splittings or asymmetry due to hyperfine structure. An analysis of this structure is presented in terms of the electronic structure and bonding of the molecule. Comparisons are drawn with the corresponding A [SUP3]II state of the NH radical, and some shortcomings in the accepted methods for interpretation are highlighted and discussed. [ABSTRACT FROM AUTHOR]

Abstract: Calix[4]arenes are unique macrocycles that through judicious functionalisation at the lower rim can be either fixed in one of four conformations or remain conformationally flexible. Introduction of propynyl or propenyl groups unexpectedly provides a new possibility; a unidirectional conformational switch, with the 1,3‐alternate and 1,2‐alternate conformers switching to the partial cone conformation, whilst the cone conformation is unchanged, under standard experimental conditions. Using 1H NMR kinetic studies, rates of switching have been shown to be dependent on the starting conformation, upper‐rim substituent, where reduction in bulk enables faster switching, solvent and temperature with 1,2‐alternate conformations switching fastest. Ab initio calculations (DFT) confirmed the relative stabilities of the conformations and point towards the partial cone conformer being the most stable of the four. The potential impact on synthesis through the “click” reaction has been investigated and found not to be significant. [ABSTRACT FROM AUTHOR]

Photophysical and photochemical measurements have been made on a series of novel alpha octa(alkyl-substituted) silicon, zinc and palladium phthalocyanines for which the synthesis is outlined. Fluorescence quantum yields and lifetimes, triplet quantum yields and lifetimes and singlet delta oxygen quantum yields were measured in 1% v/v pyridine in toluene. The effects of varying central atom and addition of alkyl substituents relative to unsubstituted parent molecules, zinc phthalocyanine (ZnPc) and silicon phthalocyanine (SiPc), are discussed. All phthalocyanines studied exhibit absorption and emission maxima in the region of 680–750 nm with molar absorptivity of the Q-band ∼105 M−1 cm−1. The series of compounds also exhibited triplet quantum yields of 0.65–0.95 and singlet oxygen quantum yields of 0.49–0.93. [ABSTRACT FROM AUTHOR]

Fourier transform spectra of collisionally induced fluorescence following isotopically selective laser excitation of NiH at ∼550 nm have located an excited Ω = 1/2 state of NiH lying 17900 cm−1 above the electronic ground state. This is identified as v = 0 of a 2Π1/2 state originating from an Ni+ 3d84s1 2F configuration. Emission from this Ω′ = 1/2 state occurs predominantly to v″ = 0 and 1 of the 2Σ+ and W2 2Π1/2 ligand field states, locating elusive f parity levels of W2 2Π1/2 up to 5600 cm−1 above the first rotational level of the electronic ground state, X 1 2Δ5/2. Collisionally induced fluorescence following laser excitation at lower energies has also been recorded in the presence of a magnetic field (0.7–1 T), at Doppler limited resolution. Effective Landé factors g J for rotational levels of the v = 0 and 1 levels of the low-lying Ω″ = 5/2 and 3/2 components of the 2Δ and 2Π states of NiH have been derived from partially resolved Zeeman patterns. About 1600 transitions recorded in field-free conditions have been reduced to term energies relative to the lowest level of the ground state. They confirm strong spin-orbit mixing between the low-lying ligand-field states. [ABSTRACT FROM PUBLISHER]

In this paper, we introduce a very fast method to compute the current distribution in helically wound thin conductors when one or many of them are arranged in a symmetrical manner to form a single-layer power cable. The method relies on two different approaches to find the magnetic vector potential due to helically wound current sheets. By invoking relevant symmetry arguments associated with the geometry of the problem and neglecting the thickness of the tape conductors, we show that this 3-D problem can be reduced to a computationally small 1-D problem whose domain lies along the half-width of any of the constituting conductor. As a consequence, the proposed method is very efficient in terms of computational time, and it is more accurate than many previous 2-D methods that cannot take into account the twist pitch. Since the nonlinear resistivity of the superconducting material can easily be treated with this method, it can be used to find current and field distributions, as well as ac losses in high-temperature superconductor coils and cables made of coated tapes. To verify the validity of the proposed method, we performed experimental measurements of ac losses in two configurations of solenoid-type cables made of a sample of YBCO-coated conductor tape. Excellent agreement was observed between the experimental data and the simulation results. [ABSTRACT FROM AUTHOR]

In this paper we present a new model for computing the current density and field distributions in superconductors by means of a finite element (FE) periodic space-time (PST) formulation. By considering the time as a space dimension, and considering periodic excitations for the applied field or transport current, we can use a static model to solve this time dependent problem. This approach has the potential to overcome one of the major problems of FE modeling of superconductors: the length of simulations, even for relatively simple cases. In this paper we show our first results for different cases of superconductors with AC magnetic fields and currents. Results are compared with those of standard time-dependent methods and analytical solutions. [ABSTRACT FROM AUTHOR]

In this paper we present a new model to compute the current density distribution and the AC losses in multiple YBCO coated conductors by means of coupled integral equations implemented in a finite-element (FE) environment. The model considers the superconducting tapes as 1D objects and allows overcoming the problem of the mesh of conductors of large aspect ratio, typical of 2D implementations; as a result, it is also much faster. The interaction between the different conductors is taken into account by means of a coupling of the electromagnetic variables. The magnetic field distribution in the space between the conductors is computed by coupling the 1D model with a standard 2D magnetic model, which uses the computed current density distributions as sources for the magnetic field. Results are compared with those obtained with standard 2D implementations and with experimental results. [ABSTRACT FROM AUTHOR]

All over the world there is a growing need for current limiting devices in electrical networks with steadily increasing power demands and fault currents. Production of YBCO coated conductors (CCs) paves the way for the economic viability of superconducting fault current limiters (FCLs) both in power distribution and transmission networks. In a cooperation between AMSC and Siemens the limiting capability of YBCO CCs has been investigated and was demonstrated in a successful laboratory test of a 2.2 MVA medium voltage FCL. This device is based on bifilar coils as switching elements and corresponds to one phase of a 3-phase FCL designed for the 13kV-class distribution voltage level. In more than 40 switching tests at voltages up to 7.7 kV the device showed excellent limiting performance. Presently this cooperation has entered a new DOE funded joint project that encompasses the design, construction and test of a 115 kV FCL for power transmission within a time frame of 4-5 years and additional partners. AMSC as the project leader is responsible for wire manufacturing, system integration and cryogenics. Siemens' main task is switching modules development, Nexans contributes the high voltage terminations and Los Alamos National Lab investigates AC losses. Installation and testing are planned for a Southern California Edison substation. A project overview and progress under the first phase will be reported. [ABSTRACT FROM AUTHOR]

In this paper we present initial results on growing YBCO/IBAD-MgO/YBCO stacks. Amorphous Y2O3 layers, deposited by sol-gel, are used to level the YBCO surface. Since the YRCO films prepared by pulsed laser deposition are relatively rough, preparing a smooth surface on top of YBCO for IBAD texturing is a major challenge for this structure. For all substrates studied-polished and unpolished metal tape and YBCO—we were able to reduce the roughness of the substrate using the sol-gel layer, with multiple coatings being more effective. First it is demonstrated that high quality YBCO films can be deposited on sol-gel-Y2 O3/IBAD-MgO templates. Second it is shown that the sol-gel and the IBAD process do not affect the superconducting properties of the underlying YBCO film. Finally, a superconducting YBCO bilayer stack is demonstrated. Improvements in the properties of the top YBCO layer is expected when the surface roughness is reduced further for deposition of subsequent IBAD-textured layers. This new technology should enable novel designs of coated conductors for reduced AC losses and increased Je. [ABSTRACT FROM AUTHOR]

We describe the construction of an all solid-state, narrow bandwidth, pulsed optical parametric oscillator (OPO) based on β-barium borate nonlinear crystals. The OPO was injection seeded by an external cavity diode laser in the range 755–855 nm to generate high power narrow bandwidth tunable light in this range and simultaneously at 606–669 nm. The bandwidth of the visible light was ∼130 MHz, and after frequency doubling or sum frequency mixing with the second harmonic of the pump Nd:YAG laser, sub-Doppler spectra with an overall resolution of 450 MHz were taken in the UV. The system is demonstrated by taking high-resolution spectra of the v[sup ′]=2–3 and 5–7 bands of the A [sup 3]Π–X [sup 3]Σ[sup -](v[sup ′],0) progression and the v[sup ′]=4–v[sup ″]=0 band of the d [sup 1]Π–a [sup 1]Δ transition in PF. These spectra show clear hyperfine structure, and an analysis of this structure is presented and interpreted in terms of the electronic structure of the molecule. As a prelude to this high-resolution study, the first ten members of the A–X band system and the first five members of the d–a band system were recorded at the moderate resolution provided by a pulsed dye laser. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]