Search

Since 2019, GRAVITY has provided direct observations of giant planets and brown dwarfs at separations of down to 95 mas from the host star. Some of these observations have provided the first direct confirmation of companions previously detected by indirect techniques (astrometry and radial velocities). We want to improve the observing strategy and data reduction in order to lower the inner working angle of GRAVITY in dual-field on-axis mode. We also want to determine the current limitations of the instrument when observing faint companions with separations in the 30-150 mas range. To improve the inner working angle, we propose a fiber off-pointing strategy during the observations to maximize the ratio of companion-light-to-star-light coupling in the science fiber. We also tested a lower-order model for speckles to decouple the companion light from the star light. We then evaluated the detection limits of GRAVITY using planet injection and retrieval in representative archival data. We compare our results to theoretical expectations. We validate our observing and data-reduction strategy with on-sky observations; first in the context of brown dwarf follow-up on the auxiliary telescopes with HD 984 B, and second with the first confirmation of a substellar candidate around the star Gaia DR3 2728129004119806464. With synthetic companion injection, we demonstrate that the instrument can detect companions down to a contrast of $8\times 10^{-4}$ ($\Delta \mathrm{K}= 7.7$ mag) at a separation of 35 mas, and a contrast of $3\times 10^{-5}$ ($\Delta \mathrm{K}= 11$ mag) at 100 mas from a bright primary (K<6.5), for 30 min exposure time. With its inner working angle and astrometric precision, GRAVITY has a unique reach in direct observation parameter space. This study demonstrates the promising synergies between GRAVITY and Gaia for the confirmation and characterization of substellar companions., Comment: 16 pages, 14 figures. Submitted to A&A

Recently Tsallis cosmology has been presented as a novel proposal for alleviating both $H_0$ and $\sigma_8$ tensions. Hence a universe filled with matter and radiation as perfect fluids and considering the Tsallis entropy is confronted using recent cosmological measurements coming from cosmic chronometers, type Ia supernovae, hydrogen II galaxies, quasars, and baryon acoustic oscillations. Following a Bayesian Monte Carlo Markov Chain analysis and combining the samples, we constrain the main characteristic parameters $\alpha = 1.031^{+0.054}_{-0.051}$ and $\delta = 1.005^{+0.001}_{-0.001}$ where the uncertainties are $1\sigma$ confidence level. Additionally, we estimate the current deceleration parameter $q_0=-0.530^{+0.018}_{-0.017}$, the deceleration-acceleration transition redshift $z_T=0.632^{+0.028}_{-0.028}$ and the age of the universe $\tau_U = 12.637^{+0.067}_{-0.066}\,\rm{Gyrs}$ which are in agreement with the standard cosmology ($\Lambda$CDM) within $1.5\sigma$. Furthermore, we find that the dark energy equation of state is consistent with both phantom and quintessence behaviors within $1\sigma$ in the past and converging to $\Lambda$CDM in the future. Additionally, we find agreement values of $H_0$ within $1\sigma$ with the SH0ES values when the CMB distance priors are added to the analysis, suggesting that $H_0$ tension could be alleviated. Finally, Tsallis cosmology is preferred over $\Lambda$CDM by the combined data that motives further studies at the perturbation level., Comment: 9 pages, 2 figures, 2 tables. Version accepted in EPJC

The open-source console MaRCoS, which stands for "Magnetic Resonance Control System", combines hardware, firmware and software elements for integral control of Magnetic Resonance Imaging (MRI) scanners. Previous developments have focused on making the system robust and reliable, rather than on users, who have been somewhat overlooked. This work describes a Graphical User Interface (GUI) designed for intuitive control of MaRCoS, as well as compatibility with clinical environments. The GUI is based on an uncomplicated set of panels and a renewed Application Program Interface (API). Compared to the previous versions, the MaRGA package ("MaRCoS Graphical Application") includes new functionalities such as the possibility to export images to standard DICOM formats, create and manage clinical protocols, or display and process image reconstructions, among other features conceived to simplify the operation of MRI scanners. All prototypes in our facilities are commanded by MaRCoS and operated with the new GUI. Here we report on its performance on an experimental 0.2 T scanner designed for hard-tissue imaging, as well as a 72~mT portable scanner presently installed in the radiology department of a large hospital. The possibility to customize, adapt and streamline processes has substantially improved our workflows and overall experience., Comment: 9 pages, 7 figures, download MaRGA package from https://github.com/yvives/PhysioMRI_GUI

We are developing a high-current cyclotron as a driver for the IsoDAR neutrino experiment. It accelerates 5 mA H2+ to 60 MeV/amu, after which the electron is removed to produce a 10 mA, 60 MeV proton beam. The enabling innovations that offset space-charge effects occur at injection and in the first few turns, allowing one to construct cyclotrons with energies ranging from below 5 MeV up to 60 MeV/amu, or possibly higher, with the same performance for accelerated ions with Q/A = 0.5 (H2+, D+, He++, ...). In this paper, we discuss the possible uses of such cyclotrons for isotope production, including production of long-lived generator parents (68Ga, 44Ti, 82Sr,...), as well as intense fast neutron beams from deuteron breakup for (n,2n) production of isotopes like 225Ac., Comment: 35 pages, 19 figures, paper submitted to the Journal of Radioanalytical and Nuclear Chemistry, as part of the Proceedings of the 11th International Conference on Isotopes, held in Saskatoon, Canada, July 2023. This version replies to further Referee comments from original submission

The definition of a consistent evolution equation for statistical hybrid quantum-classical systems is still an open problem. In this paper we analyze the case of Ehrenfest dynamics on systems defined by a probability density and identify the relations of the non-linearity of the dynamics with the obstructions to define a consistent dynamics for the first quantum moment of the distribution. This first quantum moment represents the physical states as a family of classically-parametrized density matrices $\hat \rho(\xi)$, for $\xi$ a classical point; and it is the most common representation of hybrid systems in the literature. Due to this obstruction, we consider higher order quantum moments, and argue that only a finite number of them are physically measurable. Because of this, we propose an effective solution for the hybrid dynamics problem based on approximating the distribution by those moments and representing the states by them., Comment: 21 pages. Minor correction in the list of affiliations

This paper presents the results of real-world testing of human-vehicle interactions with an autonomous vehicle equipped with internal and external Human Machine Interfaces (HMIs) in a crosswalk scenario. The internal and external HMIs were combined with implicit communication techniques using gentle and aggressive braking maneuvers in the crosswalk. Results have been collected in the form of questionnaires and measurable variables such as distance or speed when the pedestrian decides to cross. The questionnaires show that pedestrians feel safer when the external HMI or the gentle braking maneuver is used interchangeably, while the measured variables show that external HMI only helps in combination with the gentle braking maneuver. The questionnaires also show that internal HMI only improves passenger confidence in combination with the aggressive braking maneuver., Comment: 6 pages, 7 figures, 4 tables, conferecence paper

We study by numerical simulation the magnetic order in ensembles of randomly packed magnetic spherical particles which, induced by their uniaxial anisotropy in the strong coupling limit, behave as Ising dipoles. We explore the role of the frozen disorder in the positions of the particles assuming a common fixed direction for the easy axes of all spheres. We look at two types of spatially disordered configurations. In the first one we consider isotropic positional distributions which can be obtained from the liquid state of the hard sphere fluid. We derive the phase diagram in the $T$-$\Phi$ plane where $T$ is the temperature and $\Phi$ the volume fraction. This diagram exhibits long-range ferromagnetic order at low $T$ for volume fractions above the threshold $\Phi_{c} = 0.157$ predicted by mean-field calculations. For $\Phi \lesssim \Phi_{c}$ a spin-glass phase forms with the same marginal behavior found for other strongly disordered dipolar systems. The second type of spatial configurations we study are anisotropic distributions that can be obtained by freezing a dipolar hard sphere liquid in its polarized state at low temperature. This structural anisotropy enhances the ferromagnetic order present in isotropic hard sphere configurations., Comment: 10 pages, 13 figures

We generalize the Hamiltonian picture of General Relativity coupled to classical matter, known as geometrodynamics, to the case where such matter is described by a Quantum Field Theory in Curved Spacetime, but gravity is still described by a classical metric tensor field over a spatial hypersurface and its associated momentum. Thus, in our approach there is no non-dynamic background structure, apart from the manifold of events, and the gravitational and quantum degrees of freedom have their dynamics inextricably coupled. Given the Hamiltonian natureof the framework, we work with the generators of hypersurface deformations over the manifold of quantum states. The construction relies heavily on the differential geometry of a fibration of the set of quantum states over the set of gravitational variables. An important feature of this work is the use of Gaussian measures over the space of matter fields and of Hida distributions to define a common superspace to all possible Hilbert spaces with different measures, to properly characterize the Schrodinger wave functional picture of QFT in curved spacetime. This allows us to relate states within different Hilbert spaces in the case of vacuum states or measures that depend on the gravitational degrees of freedom, as the ones associated to Ashtekar's complex structure. This is achieved through the inclusion of a quantum Hermitian connection for the fibration, which will have profound physical implications. The most remarkable physical features of the construction are norm conservation of the quantum state (even if the total dynamics are non-unitary), the clear identification of the hybrid conserved quantities and the description of a dynamical backreaction of quantum matter on geometry and vice versa, which shall modify the physical properties the gravitational field would have in the absence of backreaction.

The goal of this work is to showcase the clinical value that portable MRI can provide in crowded events and major sports competitions. We temporarily installed a low-field and low-cost portable MRI system for extremity imaging in the medical facilities of the Ricardo Tormo Motor Racing Circuit during the four days of the Motorcycle Grand Prix held in Valencia (Spain), which closed the 2022 season of the MotoGP. During this time, we scanned 14 subjects, running a total of 21 protocols for wrist, knee and ankle imaging. Each protocol included a minimum of one T1-weighted 3D-RARE sequence for general anatomical information, and one 3D-STIR sequence to highlight fluid accumulation and inflammation. The circuit medical staff were able to visualize a number of lesions and conditions in the low-field reconstructions, including gonarthrosis, effusion, or Haglund's syndrome, as well as metallic implants and tissue changes due to surgical interventions. Out of eight low-field acquisitions on previously diagnosed lesions, only two (a meniscus tear and a Baker cyst) were not detected by the experts that evaluated our images. The main highlight was that a low-field MRI scan on a subject reporting pain in a wrist revealed a traumatic arthritis which an X-ray radiograph and visual inspection had missed. We have operated in a scenario where high-field MRI is unlikely to play a role but where a low-field system can lead to improved medical attention. In the case reported here, system transport, installation in the circuit facilities and calibration were all uncomplicated. The images presented to the medical staff were mostly unprocessed and there is thus room for improvement. In conclusion, this work supports the claim that low-field MRI can likely provide added value whenever concepts such as accessibility, portability and low-cost outweigh exquisite detail in images.

This letter is about confinement in QCD. At the moment we have pictures of confinement to complete our understanding of the physics of strongly interacting particles, interaction which asks for confinement. As it is said in [1] : " In principle it should be possible to derive the confinement hypothesis from the QCD Lagrangian. At this time, no rigorous derivation exists, so it is not absolutely clear that the confinement hypothesis is a bone fide prediction of QCD" . In this letter we show that a sufficient (of course not necessary) condition for confinement is that topological structure of vacuum in Nature does not correspond to the $\theta$-vacuum. Therefore, if different vacua with nontrivial winding number cannot be connected by tunneling, we obtain confinement as a consequence., Comment: 10 pages

In reactor-relevant plasmas, neoclassical transport drives an outward particle flux in the core of large stellarators and predicts strongly hollow density profiles. However, this theoretical prediction is contradicted by experiments. In particular, in Wendelstein 7-X, the first large optimized stellarator, flat or weakly peaked density profiles are generally measured, indicating that neoclassical theory is not sufficient and that an inward contribution to the particle flux is missing in the core. In this Research Letter, it is shown that the turbulent contribution to the particle flux can explain the difference between experimental measurements and neoclassical predictions. The results of this Research Letter also prove that theoretical and numerical tools are approaching the level of maturity needed for the prediction of equilibrium density profiles in stellarator plasmas, which is a fundamental requirement for the design of operation scenarios of present devices and future reactors., Comment: 8 pages, 6 figures, updated the title and incorporated the appendix into the main letter

The generation of shift and ballistic photocurrents in non-centrosymmetric materials represents a promising alternative mechanism for light energy harvesting. Many studies have focused on finding the best suited materials by maximizing the photocurrent magnitude, but estimating the actual efficiency requires knowledge of the light-induced DC photoconductivity and is rarely considered. Using the recently proposed jerk current as photoconductivity, in this work we show that only ballistic photocurrents have finite efficiency in the limit of large relaxation times $\tau$. Moreover, at zero temperature the only ballistic current which is finite for unpolarized light is the magnetic injection current, only present in magnetic materials. We present a band structure expression for the efficiency of such photocurrent, showing that it scales as $(\hbar \Omega-E_g)^2$ near the band edge, and we present its frequency dependence for a simple tight-binding model. Our work provides a new tool to guide the search for efficient energy harvesting based on the magnetic injection current., Comment: 10 pages, 3 figures

Purpose: To describe the current properties and capabilities of an open-source hardware and software package that is being developed by many sites internationally with the aim of providing an inexpensive yet flexible platform for low-cost MRI. Methods: This paper describes three different setups from 50 to 360 mT in different settings, all of which used the MaRCoS console for acquiring data, and different types of software interfaces (custom-built GUI or PulSeq overlay) to acquire the data. Results: Images are presented from both phantoms and in vivo from healthy volunteers to demonstrate the image quality that can be obtained from the MaRCoS hardware/software interfaced to different low-field magnets. Conclusions: The results presented here show that a number of different sequences commonly used in the clinic can be programmed into an open-source system relatively quickly and easily, and can produce good quality images even at this early stage of development. Both the hardware and software will continue to develop, and it is an aim of this paper to encourage other groups to join this international consortium., Comment: 9 pages, 10 figures, comments welcome

IsoDAR@Yemilab is a unique facility for underground neutrino physics. The system comprises an accelerator-driven $\bar{\nu}_e$ source located next to the Yemilab LSC 2.3 kt detector. Because this facility is first-of-its-kind, it opens new approaches to Beyond Standard Model (BSM) physics searches. The program is most well-known for its capability to perform searches for new oscillation signatures at high statistics in a model-agnostic manner. IsoDAR@Yemilab can definitively resolve the question of $\bar{\nu}_e$ disappearance at short baselines. Beyond this, IsoDAR offers a broad range of searches for new neutrino properties and new particles. The facility uses a state-of-the art cyclotron, that is now fully designed and is undergoing protoyping. Preliminary approval to run at Yemilab in South Korea has led to the completed excavation of caverns. While the accelerator is designed to run underground, IsoDAR accelerators can also be constructed on the surface, allowing this project to contribute to the opportunity for production of life-saving medical isotopes. The capabilites, technical elements, and deployment studies are well-documented in articles on arXiv, and appear in multiple Snowmass'21 whitepapers. Rather than repeat this text, this whitepaper provides a "table of contents" to these documents., Comment: contribution to Snowmass 2021

In recent times, large organic molecules of exceptional complexity have been found in diverse regions of the interstellar medium. In this context, we aim to provide accurate frequencies of the ground vibrational state of two key aliphatic aldehydes, n-butanal and its branched-chain isomer, i-butanal, to enable their eventual detection in the interstellar medium. We employ a frequency modulation millimeter-wave absorption spectrometer to measure the rotational features of n- and i-butanal. We use the spectral line survey ReMoCA performed with the Atacama Large Millimeter/submillimeter Array to search for n- and i-butanal toward the star-forming region Sgr B2(N). We also search for both aldehydes toward the molecular cloud G+0.693-0.027 with IRAM 30 m and Yebes 40 m observations. Several thousand rotational transitions belonging to the lowest-energy conformers have been assigned in the laboratory spectra up to 325 GHz. A precise set of the relevant rotational spectroscopic constants has been determined for each structure. We report non-detections of n- and i-butanal toward both sources, Sgr B2(N1S) and G+0.693-0.027. We find that n- and i-butanal are at least 2-6 and 6-18 times less abundant than acetaldehyde toward Sgr B2(N1S), respectively, and that n-butanal is at least 63 times less abundant than acetaldehyde toward G+0.693-0.027. Comparison with astrochemical models indicates good agreement between observed and simulated abundances (where available). Grain-surface chemistry appears sufficient to reproduce aldehyde ratios in G+0.693-0.027; gas-phase production may play a more active role in Sgr B2(N1S). Our astronomical results indicate that the family of interstellar aldehydes in the Galactic center region is characterized by a drop of one order of magnitude in abundance at each incrementation in the level of molecular complexity.

Mobile medical imaging devices are invaluable for clinical diagnostic purposes both in and outside healthcare institutions. Among the various imaging modalities, only a few are readily portable. Magnetic resonance imaging (MRI), the gold standard for numerous healthcare conditions, does not traditionally belong to this group. Recently, low-field MRI start-up companies have demonstrated the first decisive steps towards portability within medical facilities, but these are so far incompatible with more demanding use cases such as in remote and developing regions, sports facilities and events, medical and military camps, or home healthcare. Here we present in vivo images taken with a light, home-made, low-field extremity MRI scanner outside the controlled environment provided by medical facilities. To demonstrate the true portability of the system and benchmark its performance in various relevant scenarios, we have acquired images of a volunteer's knee in: i) an MRI physics laboratory; ii) an office room; iii) outside a campus building, connected to a nearby power outlet; iv) in open air, powered from a small fuel-based generator; and v) at the volunteer's home. All images have been acquired within clinically viable times, and signal-to-noise ratios (SNR) and tissue contrast suffice for 2D and 3D reconstructions with diagnostic value, with comparable overall image quality across all five situations. Furthermore, the volunteer carries a fixation metallic implant screwed to the femur, which leads to strong artifacts in standard clinical systems but appears sharp in our low-field acquisitions. Altogether, this work opens a path towards highly accessible MRI under circumstances previously unrealistic., Comment: 17 pages, 4 figures, comments welcome

Purpose: To expand the capabilities of Zero Echo Time (ZTE) pulse sequences with a slice selection method suitable for the shortest-lived tissues in the body. Methods: We introduce two new sequences that integrate spin-locking pulses into standard ZTE imaging to achieve slice selection: one for moderately short $T_2$ (DiSLoP), the other for ultra-short $T_2$ samples (PreSLoP). These methods exploit the slower signal decay (at $T_{1\rho}\gg T_2$) to retain the magnetization in the slices during the selection process, which is otherwise comparable to or even much longer than $T_2$. Results: We demonstrate control over the slice profiles and positions for 2D imaging. We measure magnetization decay times during spin-locking ($T_{1\rho}$) as a function of pulse amplitude, showing significant lifetime enhancement for amplitudes as low as 10 uT. We show imaging of slice-selected samples with $T_2$ characteristic times in the range of single milliseconds with DiSLoP and PreSLoP, and with the latter for sub-millisecond $T_2$ tissues. As compared to standard 3D ZTE sequences, PreSLoP achieves the same signal-to-noise ratio (SNR) in 2-5 times shorter scan times, and we argue that this is due to the filling scheme of the finite gap at the center of $k$-space unavoidable with ZTE sequences. Finally, we discuss a combination of DiSLoP with a dynamical decoupling sequence to avoid this central gap, leading to further scan time accelerations. Conclusions: The proposed sequences are capable of slice-selected 2D imaging of tissues with $T_2$ as low as 275 us with good SNR within clinically acceptable scan times., Comment: 12 pages, 14 figures, commments welcome

IsoDAR seeks to place a high-power-cyclotron and target combination, as an intense source of $\bar{\nu}_e$ at the level of $\sim 10^{23}$/year, close to a kiloton-scale neutrino detector in order to gain sensitivity to very short-baseline neutrino oscillations ($\bar{\nu}_e \rightarrow \bar{\nu}_{e}$) and perform precision tests of the weak interaction, among other physics opportunities. Recently, IsoDAR has received preliminary approval to be paired with the 2.26~kton target volume liquid scintillator detector at the Yemi Underground Laboratory (Yemilab) in Korea, at a 17~m center-to-center baseline, and cavern excavation for IsoDAR is now complete. In this paper, we present the physics capabilities of IsoDAR@Yemilab in terms of sensitivity to oscillations (via inverse beta decay, IBD; $\bar{\nu}_e+p \rightarrow e^+ + n$), including initial-state wavepacket effects, and the weak mixing angle (via elastic scattering off atomic electrons, $\bar{\nu}_e + e^- \rightarrow \bar{\nu}_e + e^-$). We also introduce a study of IsoDAR sensitivity to new particles, such as a light $X$ boson, produced in the target that decays to $\nu_e \bar \nu_e$., Comment: 17 pages, 16 figures; this version presents a number of new physics topics and studies

Context:Optical interferometry is at a key development stage. ESO's VLTI has established a stable, robust infrastructure for long-baseline interferometry for general astronomical observers. The present second-generation instruments offer a wide wavelength coverage and improved performance. Their sensitivity and measurement accuracy lead to data and images of high reliability. Aims:We have developed MATISSE, the Multi AperTure mid-Infrared SpectroScopic Experiment, to access high resolution imaging in a wide spectral domain and explore topics such: stellar activity and mass loss; planet formation and evolution in the gas and dust disks around young stars; accretion processes around super massive black holes in AGN. Methods:The instrument is a spectro-interferometric imager covering three atmospheric bands (L,M,N) from 2.8 to 13.0 mu, combining four optical beams from the VLTI's telscopes. Its concept, related observing procedure, data reduction and calibration approach are the product of 30 years of instrumental research. The instrument utilizes a multi-axial beam combination that delivers spectrally dispersed fringes. The signal provides the following quantities at several spectral resolutions: photometric flux, coherent fluxes, visibilities, closure phases, wavelength differential visibilities and phases, and aperture-synthesis imaging. Results:We provide an overview of the physical principle of the instrument and its functionalities, the characteristics of the delivered signal, a description of the observing modes and of their performance limits. An ensemble of data and reconstructed images are illustrating the first acquired key observations. Conclusion:The instrument has been in operation at Cerro Paranal, ESO, Chile since 2018, and has been open for science use by the international community since April 2019. The first scientific results are being published now., Comment: 24 pages, 26 figures, submitted to Astronomy & Astrophysics

Glycinamide is considered to be one of the possible precursors of the simplest amino acid glycine. Its only rotational spectrum reported so far has been in the cm-wave region. The aim of this work is to extend its laboratory spectrum into the mm wave region to support its searches in the ISM. Glycinamide was synthesised chemically and was studied with broadband rotational spectroscopy in the 90-329 GHz region. Tunneling across a low energy barrier between two symmetry equivalent configurations of the molecule resulted in splitting of each vibrational state and many perturbations in associated rotational energy levels, requiring careful coupled state fits for each vibrational doublet. We searched for emission of glycinamide in the imaging spectral line survey ReMoCA performed with ALMA toward Sgr B2(N). We report the first analysis of the mm-wave rotational spectrum of glycinamide, resulting in fitting to experimental measurement accuracy of over 1200 transition frequencies for the ground state tunneling doublet, of many lines for tunneling doublets for two singly excited vibrational states, and determination of precise vibrational separation in each doublet. We did not detect emission from glycinamide in the hot core Sgr B2(N1S). We found that glycinamide is at least seven times less abundant than aminoacetonitrile and 1.8 times less abundant than urea in this source. A comparison with results of astrochemical kinetics models for species related to glycinamide suggests that its abundance may be at least one order of magnitude below the upper limit obtained toward Sgr B2(N1S). This means that glycinamide emission in this source likely lies well below the spectral confusion limit in the frequency range covered by the ReMoCA survey. Targetting sources with a lower level of spectral confusion, such as the Galactic Center shocked region G+0.693-0.027, may be a promising avenue. [abridged], Comment: Accepted for publication in A&A

This Conceptual Design Report addresses the site-specific issues associated with the deployment of the IsoDAR experiment at the Yemilab site. IsoDAR@Yemilab pairs the IsoDAR cyclotron-driven $\bar{\nu}_e$ source with the proposed Liquid Scintillator Counter (LSC) 2.5 kton detector. This document describes the proposed siting: requirements for the caverns to house the cyclotron, beam transport line, and target systems; issues associated with transport and assembly of components on the site; electrical power, cooling and ventilation; as well as issues associated with radiation protection of the environment and staff of Yemilab who will be interfacing with IsoDAR during its operational phases. The onset of construction of the IsoDAR area at Yemilab, in tandem with the release of this design report, represents a key step forward in establishing IsoDAR@Yemilab.

Prepolarized Magnetic Resonance Imaging (PMRI) is a long-established technique conceived to counteract the loss in signal-to-noise ratio (SNR) inherent to low-field MRI systems. When it comes to hard biological tissues and solid-state matter, PMRI is severely restricted by their ultra-short characteristic relaxation times. Here we demonstrate that efficient hard tissue prepolarization is within reach with a special-purpose 0.26 T scanner designed for dental MRI and equipped with suitable high-power electronics. We have characterized the performance of a 0.5 T prepolarizer module which can be switched on and off in just 200 us. To that end, we have used resin, dental and bone samples, all with T1 times in the order of 20 ms at our field strength. The measured SNR enhancement is in good agreement with a simple theoretical model, and small deviations in extreme regimes can be attributed to mechanical vibrations due to the magnetic interaction between the prepolarization and main magnets. Finally, we argue that these results can be applied to clinical dental imaging, opening the door to replacing hazardous X-ray systems with low-field PMRI scanners., Comment: 8 pages, 8 figures. Some numbers in Sec. VI have been revised in v2

A recent characterization of core turbulence carried out with a Doppler reflectometer in the optimized stellarator Wendelstein 7-X (W7-X) found that discharges achieving high ion temperatures at the core featured an ITG-like suppression of density fluctuations driven by a reduction of the gradient ratio $\eta_i = L_n/L_{T_i}$ [D. Carralero et al., Nucl. Fusion, 2021]. In order to confirm the role of ITG turbulence in this process, we set out to establish experimentally the relation between core density fluctuations, turbulent heat flux and global confinement. With this aim, we consider the scenarios found in the previous work and carry out power balance analysis for a number of representative ones, including some featuring high ion temperature. As well, we evaluate the global energy confinement time and discuss it in the context of the ISS04 inter-stellarator scaling. We find that, when turbulence is suppressed as a result of a reduction of $\eta_i$, there is a reduction of ion turbulent transport, and global performance is improved as a result. This is consistent with ITG turbulence limiting the ion temperature at the core of W7-X. In contrast, when turbulence is reduced following a decrease in collisionality, no changes are observed in transport or confinement. This could be explained by ITG modes being combined with TEM turbulence when the later is destabilized at low collisionalities., Comment: Submitted to PPCF, 47th EPS special issue

The ongoing development of electromagnets based on High Temperature Superconductors has led to the conceptual exploration of high-magnetic-field fusion reactors of the tokamak type, operating at on-axis fields above 10 T. In this work we explore the consequences of the potential future availability of high-field three-dimensional electromagnets on the physics design point of a stellarator reactor. We find that, when an increase in the magnetic field strength $B$ is used to maximally reduce the device linear size $R\sim B^{-4/3}$ (with otherwise fixed magnetic geometry), the physics design point is largely independent of the chosen field strength/device size. A similar degree of optimization is to be imposed on the magnetohydrodynamic, transport and fast ion confinement properties of the magnetic configuration of that family of reactor design points. Additionally, we show that the family shares an invariant operation map of fusion power output as a function of the auxiliary power and relative density variation. The effects of magnetic field over-engineering and the $R(B)$ scaling of design points with constant neutron wall loading are also inspected. In this study we use geometric parameters characteristic of the helias reactor, but most results apply to other stellarator configurations

Galaxy evolution is generally affected by tidal interactions. Firstly, in this series, we reported several effects which suggest that tidal interactions contribute to regulating star formation (SF). To confirm that so, we now compare stellar mass assembly histories and SF look-back time annular profiles between CALIFA survey tidally and non-tidally perturbed galaxies. We pair their respective star-forming regions at the closest stellar mass surface densities to reduce the influence of stellar mass. The assembly histories and annular profiles show statistically significant differences so that higher star formation rates characterize regions in tidally perturbed galaxies. These regions underwent a more intense (re)activation of SF in the last 1 Gyr. Varying shapes of the annular profiles also reflect fluctuations between suppression and (re)activation of SF. Since gas-phase abundances use to be lower in more actively than in less actively star-forming galaxies, we further explore the plausible presence of metal-poor gas inflows able to dilute such abundances. The resolved relations of oxygen (O) abundance, with stellar mass density and with total gas fraction, show slightly lower O abundances for regions in tidally perturbed galaxies. The single distributions of O abundances statistically validate that so. Moreover, from a metallicity model based on stellar feedback, the mass rate differentials (inflows$-$outflows) show statistically valid higher values for regions in tidally perturbed galaxies. These differentials, and the metal fractions from the population synthesis, suggest dominant gas inflows in these galaxies. This dominance, and the differences in SF through time, confirm the previously reported effects of tidal interactions on SF., Comment: 32 pages, 13 figures

First results from the optimized helias Wendelstein 7-X stellarator (W7-X) have shown that core transport is no longer mostly neoclassical, as is the case in previous kinds of stellarators. Instead, turbulent transport poses a serious limitation to the global performance of the machine. Several studies have found this particularly relevant for ion transport, with core ion temperatures becoming clamped at relatively low values of $T_{i} \simeq 1.7$ keV, except in the few scenarios in which turbulence can be suppressed. In order to understand turbulent mechanisms at play, it is important to have a clear understanding of the parametric dependencies of turbulent fluctuations, and the relation between them and turbulent transport. In this work we use Doppler reflectometry measurements carried out during a number of relevant operational scenarios to provide a systematic characterization of ion-scale ($k_\perp\rho_i\simeq 1$) density fluctuations in the core of W7-X. Then, we study the relation between fluctuation amplitude and plasma profiles and show how distinct regimes can be defined for the former, depending on normalized gradients $a/L_{ne}$ and $a/L_{Ti}$. Furthermore, we discuss the importance of other potentially relevant parameters such as $T_e/T_i$, $E_r$ or collisionality. Comparing the different regimes, we find that turbulence amplitude depends generally on the gradient ratio $\eta_i=L_{ne}/L_{Ti}$, as would be expected for ITG modes, with the exception of a range of discharges, for which turbulence suppression may be better explained by an ITG to TEM transition triggered by a drop in collisionality. Finally, we show a number of scenarios under which $T_{i,core} > 1.7$ keV is achieved and how core fluctuations are suppressed in all of them, thus providing experimental evidence of microturbulence being the main responsible for the limited ion confinement in W7-X., Comment: Manuscript submitted to Nuclear Fusion in May 2021

Molecular or condensed matter systems are often well approximated by hybrid quantum-classical models: the electrons retain their quantum character, whereas the ions are considered to be classical particles. We discuss various alternative approaches for the computation of equilibrium (canonical) ensemble averages for observables of these hybrid quantum-classical systems through the use of molecular dynamics (MD), i.e. by performing dynamics in the presence of a thermostat and computing time averages over the trajectories. Often, in classical or ab initio MD, the temperature of the electrons is ignored and they are assumed to remain at the instantaneous ground state given by each ionic configuration during the evolution. Here, however, we discuss the general case that considers both classical and quantum subsystems at finite temperature canonical equilibrium. Inspired by a recent formal derivation for the canonical ensemble for quantum classical hybrids, we discuss previous approaches found in the literature, and provide some new formulas., Comment: This is the version of the article before peer review or editing, as submitted by an author to New Journal of Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1367-2630/abf9b3

The nature of circumstellar envelopes (CSE) around Cepheids is still a matter of debate. The physical origin of their infrared (IR) excess could be either a shell of ionized gas, or a dust envelope, or both. This study aims at constraining the geometry and the IR excess of the environment of the long-period Cepheid $\ell$ Car (P=35.5 days) at mid-IR wavelengths to understand its physical nature. We first use photometric observations in various bands and Spitzer Space Telescope spectroscopy to constrain the IR excess of $\ell$ Car. Then, we analyze the VLTI/MATISSE measurements at a specific phase of observation, in order to determine the flux contribution, the size and shape of the environment of the star in the L band. We finally test the hypothesis of a shell of ionized gas in order to model the IR excess. We report the first detection in the L band of a centro-symmetric extended emission around l Car, of about 1.7$R_\star$ in FWHM, producing an excess of about 7.0\% in this band. In the N band, there is no clear evidence for dust emission from VLTI/MATISSE correlated flux and Spitzer data. On the other side, the modeled shell of ionized gas implies a more compact CSE ($1.13\pm0.02\,R_\star$) and fainter (IR excess of 1\% in the L band). We provide new evidences for a compact CSE of $\ell$ Car and we demonstrate the capabilities of VLTI/MATISSE for determining common properties of CSEs. While the compact CSE of $\ell$ Car is probably of gaseous nature, the tested model of a shell of ionized gas is not able to simultaneously reproduce the IR excess and the interferometric observations. Further Galactic Cepheids observations with VLTI/MATISSE are necessary for determining the properties of CSEs, which may also depend on both the pulsation period and the evolutionary state of the stars., Comment: 13 pages, 8 figures, accepted in Astronomy and Astrophysics

We present a magnet and high power electronics for Prepolarized Magnetic Resonance Imaging (PMRI) in a home-made, special-purpose preclinical system designed for simultaneous visualization of hard and soft biological tissues. PMRI boosts the signal-to-noise ratio (SNR) by means of a long and strong magnetic pulse which must be rapidly switched off prior to the imaging pulse sequence, in timescales shorter than the spin relaxation (or T1) time of the sample. We have operated the prepolarizer at up to 0.5 T and demonstrated enhanced magnetization, image SNR and tissue contrast with PMRI of tap water, an ex vivo mouse brain and food samples. These have T1 times ranging from hundreds of milli-seconds to single seconds, while the preliminary high-power electronics setup employed in this work can switch off the prepolarization field in tens of milli-seconds. In order to make this system suitable for solid-state matter and hard tissues, which feature T1 times as short as 10 ms, we are developing new electronics which can cut switching times to ~300 us. This does not require changes in the prepolarizer module, opening the door to the first experimental demonstration of PMRI on hard biological tissues., Comment: 8 pages, 10 figures, 2 tables, comments welcome

For all the amides detected in the interstellar medium (ISM), the corresponding nitriles or isonitriles have also been detected in the ISM, some of which have relatively high abundances. Among the abundant nitriles for which the corresponding amide has not yet been detected is cyanoacetylene (HCCCN), whose amide counterpart is propiolamide (HCCC(O)NH$_2$). With the aim of supporting searches for this amide in the ISM, we provide a complete rotational study of propiolamide from 6 GHz to 440 GHz using rotational spectroscopic techniques in the frequency and time domain. We identified and measured more than 5500 distinct frequency lines of propiolamide and obtained accurate sets of spectroscopic parameters for the ground state and the three low-lying excited vibrational states. We used the ReMoCA spectral line survey performed with the Atacama Large Millimeter/submillimeter Array toward the star-forming region Sgr B2(N) to search for propiolamide. We report the nondetection of propiolamide toward the hot cores Sgr B2(N1S) and Sgr B2(N2). We find that propiolamide is at least 50 and 13 times less abundant than acetamide in Sgr B2(N1S) and Sgr B2(N2), respectively, indicating that the abundance difference between both amides is more pronounced by at least a factor of 8 and 2, respectively, than for their corresponding nitriles. Although propiolamide has yet to be included in astrochemical modeling networks, the observed upper limit to the ratio of propiolamide to acetamide seems consistent with the ratios of related species as determined from past simulations., Comment: The article will be published as a regular paper in Astronomy and Astrophysics

NGC 7469 is a well known Luminous IR Galaxy, with a circumnuclear star formation ring ($\sim 830$ pc radius) surrounding a Seyfert 1 AGN. Nuclear unresolved winds were previously detected in X-rays and UV, as well as an extended biconical outflow in IR coronal lines. We search for extended outflows by measuring the kinematics of the $\mathrm{H\beta}$ and [O III] $\lambda 5007$ optical emission lines, in data of the VLT/MUSE integral field spectrograph. We find evidence of two outflow kinematic regimes: one slower regime extending across most of the star formation ring -- possibly driven by the massive star formation -- and a faster regime (with a maximum velocity of $-715 \ \mathrm{km \ s^{-1}}$), only observed in [O III], in the western region between the AGN and the massive star forming regions of the ring, likely AGN-driven. This work shows a case where combined AGN/star-formation feedback can be effectively spatially-resolved, opening up a promising path toward a deeper understanding of feedback processes in the central kiloparsec of AGN., Comment: 10 pages, 5 figures. Accepted for publication in The Astrophysical Journal Letters

Peripheral Nerve Stimulation (PNS) constrains the clinical performance of Magnetic Resonance and Particle Imaging (MRI and MPI) systems. Extensive magneto-stimulation studies have been carried out recently in the field of MPI, where typical operation frequencies range from single to tens of kilo-hertz. PNS literature is scarce for MRI in this regime, where the resonant character of MPI coils prevents studies of broad-band excitation pulses. We have constructed an apparatus for PNS threshold determination on a subject's limb, capable of narrow and broad-band magnetic excitation with pulse characteristic times down to 40 us. From a first set of measurements on 51 volunteers, we observe that PNS limits coincide for sinusoidal (biphasic narrow-band) and triangular (biphasic broad-band) excitations, and are slightly lower for trapezoidal (monophasic broad-band) pulses. We have also measured statistically significant correlations of PNS sensitivity with arm size and body weight, and no correlation with height or gender. As opposed to resonant systems, our setup allows the execution of arbitrarily short pulse trains. We have confirmed thresholds increase significantly as trains transition from tens to a few pulses also in these fast timescales. By changing the polarity of the coils in our setup, we also looked at the influence of the spatial distribution of magnetic field strength on PNS effects. We find that thresholds are higher in an approximately linearly inhomogeneous field (relevant to MRI) than in a rather homogeneous distribution (as in MPI). Finally, given the large intersubject variability of PNS sensitivity, we propose employing a versatile low-cost system (such as presented here) for fast offline determination of a subject's limits prior to medical scanning, and then using this information to boost clinical imaging while preserving the patient's safety., Comment: 8 pages, 9 figures, comments welcome