Itinerant Ferromagnetism in the Periodic Anderson Model

We introduce a novel mechanism for itinerant ferromagnetism, based on a simple two-band model. The model includes an uncorrelated and dispersive band hybridized with a second band which is narrow and correlated. The simplest Hamiltonian containing these ingredients is the Periodic Anderson Model (PAM). Using quantum Monte Carlo and analytical methods, we show that the PAM and an extension of it contain the new mechanism and exhibit a non-saturated ferromagnetic ground state in the intermediate valence regime. We propose that the mechanism, which does not assume an intra atomic Hund's coupling, is present in both the iron group and in some f electron compounds like Ce(Rh_{1-x} Ru_x)_3 B_2, La_x Ce_{1-x} Rh_3 B_2 and the uranium monochalcogenides US, USe, and UTe

Para-infectious brain injury in COVID-19 persists at follow-up despite attenuated cytokine and autoantibody responses

To understand neurological complications of COVID-19 better both acutely and for recovery, we measured markers of brain injury, inflammatory mediators, and autoantibodies in 203 hospitalised participants; 111 with acute sera (1–11 days post-admission) and 92 convalescent sera (56 with COVID-19-associated neurological diagnoses). Here we show that compared to 60 uninfected controls, tTau, GFAP, NfL, and UCH-L1 are increased with COVID-19 infection at acute timepoints and NfL and GFAP are significantly higher in participants with neurological complications. Inflammatory mediators (IL-6, IL-12p40, HGF, M-CSF, CCL2, and IL-1RA) are associated with both altered consciousness and markers of brain injury. Autoantibodies are more common in COVID-19 than controls and some (including against MYL7, UCH-L1, and GRIN3B) are more frequent with altered consciousness. Additionally, convalescent participants with neurological complications show elevated GFAP and NfL, unrelated to attenuated systemic inflammatory mediators and to autoantibody responses. Overall, neurological complications of COVID-19 are associated with evidence of neuroglial injury in both acute and late disease and these correlate with dysregulated innate and adaptive immune responses acutely

Large-scale phenotyping of patients with long COVID post-hospitalization reveals mechanistic subtypes of disease

One in ten severe acute respiratory syndrome coronavirus 2 infections result in prolonged symptoms termed long coronavirus disease (COVID), yet disease phenotypes and mechanisms are poorly understood1. Here we profiled 368 plasma proteins in 657 participants ≥3 months following hospitalization. Of these, 426 had at least one long COVID symptom and 233 had fully recovered. Elevated markers of myeloid inflammation and complement activation were associated with long COVID. IL-1R2, MATN2 and COLEC12 were associated with cardiorespiratory symptoms, fatigue and anxiety/depression; MATN2, CSF3 and C1QA were elevated in gastrointestinal symptoms and C1QA was elevated in cognitive impairment. Additional markers of alterations in nerve tissue repair (SPON-1 and NFASC) were elevated in those with cognitive impairment and SCG3, suggestive of brain–gut axis disturbance, was elevated in gastrointestinal symptoms. Severe acute respiratory syndrome coronavirus 2-specific immunoglobulin G (IgG) was persistently elevated in some individuals with long COVID, but virus was not detected in sputum. Analysis of inflammatory markers in nasal fluids showed no association with symptoms. Our study aimed to understand inflammatory processes that underlie long COVID and was not designed for biomarker discovery. Our findings suggest that specific inflammatory pathways related to tissue damage are implicated in subtypes of long COVID, which might be targeted in future therapeutic trials

SARS-CoV-2-specific nasal IgA wanes 9 months after hospitalisation with COVID-19 and is not induced by subsequent vaccination

BACKGROUND: Most studies of immunity to SARS-CoV-2 focus on circulating antibody, giving limited insights into mucosal defences that prevent viral replication and onward transmission. We studied nasal and plasma antibody responses one year after hospitalisation for COVID-19, including a period when SARS-CoV-2 vaccination was introduced. METHODS: In this follow up study, plasma and nasosorption samples were prospectively collected from 446 adults hospitalised for COVID-19 between February 2020 and March 2021 via the ISARIC4C and PHOSP-COVID consortia. IgA and IgG responses to NP and S of ancestral SARS-CoV-2, Delta and Omicron (BA.1) variants were measured by electrochemiluminescence and compared with plasma neutralisation data. FINDINGS: Strong and consistent nasal anti-NP and anti-S IgA responses were demonstrated, which remained elevated for nine months (p < 0.0001). Nasal and plasma anti-S IgG remained elevated for at least 12 months (p < 0.0001) with plasma neutralising titres that were raised against all variants compared to controls (p < 0.0001). Of 323 with complete data, 307 were vaccinated between 6 and 12 months; coinciding with rises in nasal and plasma IgA and IgG anti-S titres for all SARS-CoV-2 variants, although the change in nasal IgA was minimal (1.46-fold change after 10 months, p = 0.011) and the median remained below the positive threshold determined by pre-pandemic controls. Samples 12 months after admission showed no association between nasal IgA and plasma IgG anti-S responses (R = 0.05, p = 0.18), indicating that nasal IgA responses are distinct from those in plasma and minimally boosted by vaccination. INTERPRETATION: The decline in nasal IgA responses 9 months after infection and minimal impact of subsequent vaccination may explain the lack of long-lasting nasal defence against reinfection and the limited effects of vaccination on transmission. These findings highlight the need to develop vaccines that enhance nasal immunity. FUNDING: This study has been supported by ISARIC4C and PHOSP-COVID consortia. ISARIC4C is supported by grants from the National Institute for Health and Care Research and the Medical Research Council. Liverpool Experimental Cancer Medicine Centre provided infrastructure support for this research. The PHOSP-COVD study is jointly funded by UK Research and Innovation and National Institute of Health and Care Research. The funders were not involved in the study design, interpretation of data or the writing of this manuscript

Business Cycles and Fiscal Policy in an Open Economy

Do business cycle fluctuations leave a role and a welfare case for an active stabilization policy by means of fiscal policy instruments? We address this issue in a two-sector open economy model with price-taking firms and imperfect competition in the labour market. Fiscal policies are shown to affect the equilibrium distribution of prices and hence output in the case of both supply (productivity) and demand (preferences) shocks.BUSINESS CYCLES ; FISCAL POLICY ; DEMAND ; SUPPLY

Magnetic inelastic scattering in uranium nitride

De tous les pnictures d'uranium de structure cubique, le nitrure d'uranium possède la plus petite distance U-U, le plus faible moment magnétique (0,75 µB) et la plus basse température de Néel (TN = 49,6 ± 0,3 K). Il est intéressant de connaître la nature des spectres d'excitation de UN pour la compréhension de la structure électronique de l'ion uranium comme des ions actinides en général. Des questions telles que le caractère localisé des électrons 5f dans les pnictures métalliques sont encore sans réponse. Nous présentons des mesures de diffusion inélastique des neutrons, effectuées à 4,2 K sur un monocristal de UN ; la diffusion magnétique est d'intensité faible et diffère en symétrie et nature des ondes de spin des composés 4f (étroites, à basse vitesse et principalement transverses). La réponse magnétique au point (110) du réseau réciproque présente une large distribution (FWHM = 5 ± 1 THz) centrée à 4,2 ± 0,5 THz. Des balayages à transfert de fréquence fixé pour des valeurs de ν comprises entre 2,5 et 8,0 THz conduisent à un pic unique centré sur le point (110). Les résultats indiquent que UN possède une branche d'excitations à forte montée et avec un gap d'anisotropie. Des mesures près de (330) où le facteur de forme est moitié de celui à (110) confirment le caractère magnétique de la diffusion. La symétrie de la réponse magnétique est essentiellement longitudinale. On a observé l'intensité là où une diffusion transverse était attendue, c.-à-d. près de (010), mais la diffusion était un peu plus étroite en fréquence et plus faible qu'en (110) de plus d'un facteur 2. La composante transverse à (110) est en conséquence inférieure au quart de la réponse observée. L'effet, sur la diffusion près de (110), de relever la température jusqu'à 0,8 TN est d'augmenter fortement la réponse basse fréquence (par un facteur de 4 à ν = 1,5 THz), ce qui conduit à une large distribution de la diffusion inélastique centrée à ν = 0. Aux hautes fréquences cette distribution présente une forme similaire à la partie haute fréquence de la distribution à 4,2 K. Les résultats fournissent la première évidence expérimentale directe d'excitations de spin longitudinales et de grande vitesse dans des composés ordonnés d'actinide, avec des conséquences importantes pour la théorie du magnétisme itinérant.Of the cubic uranium pnictides, uranium nitride has the smallest U-U separation, the smallest magnetic moment (0.75 µB) and the lowest Néel temperature (TN = 49.6 ± 0.3 K). It is of interest to know the nature of the excitation spectrum of UN to gain an understanding of the electronic structure of the uranium ion and of actinide ions in general. Such questions as whether the 5f electrons are localized or itinerant for the metallic pnictides have not yet been answered. We report neutron inelastic scattering measurements at 4.2 K from a single crystal of UN which reveal magnetic scattering that is weak in intensity and differs in symmetry and nature from the sharp, low-velocity, largely transverse spin waves of the 4f cubic compounds. The magnetic response at the (110) magnetic reciprocal lattice point is a broad (FWHM = 5 ± 1 THz) distribution of intensity peaked at 4.2 ± 0.5 THz. Constant-frequency-transfer scans for ν between 2.5 and 8.0 THz show a single peak centred on the (110) point. The results indicate that UN possesses a steeply rising branch of excitations with an anisotropy gap. Measurements near (330) where the form factor is half that at (110) confirmed the magnetic character of the scattering. The symmetry of the magnetic response is primarily longitudinal. Intensity was observed where transverse scattering is anticipated, i.e. near (010), but the scattering was somewhat sharper in frequency and more than a factor two weaker than at (110). The transverse component at (110) is therefore less than 25 % of the observed response. The effect on the scattering near (110) of raising the temperature to 0.8 TN is to enhance the low-frequency response strongly (by a factor of 4 at ν = 1.5 THz) so as to give a broad distribution of inelastic scattering centred on ν = 0. At high frequencies this distribution is similar in form to the high-frequency part of the 4.2 K distribution. The results provide the first direct experimental evidence for high-velocity longitudinal spin excitations in ordered actinide compounds, and have important consequences for the theory of itinerant magnetism