Eigenstate versus Zeeman-based approaches to the solid-effect

The solid effect is one of the simplest and most effective mechanisms for Dynamic Nuclear Polarization. It involves the exchange of polarization between one electron and one nuclear spin coupled via the hyperfine interaction. Even for such a small spin system, the theoretical understanding is complicated by the contact with the lattice and the microwave irradiation. Both being weak, they can be treated within perturbation theory. In this work, we analyze the two most popular perturbation schemes: the Zeeman and the eigenstate-based approaches which differ in the way the hyperfine interaction is treated. For both schemes, we derive from first principles an effective Liouville equation which describes the density matrix of the spin system; we then study numerically the behavior of the nuclear polarization for several values of the hyperfine coupling. In general, we obtain that the Zeeman-based approach underestimates the value of the nuclear polarization. By performing a projection onto the diagonal part of the spin-system density matrix, we are able to understand the origin of the discrepancy, which is due to the presence of parasite leakage transitions appearing whenever the Zeeman basis is employed.Comment: 9 pages, 4 figures, 7 pages of supplementary materia

Darcy law for yield stress fluid

Predicting the flow of non-Newtonian fluids in porous structure is still a challenging issue due to the interplay betwen the microscopic disorder and the non-linear rheology. In this letter, we study the case of an yield stress fluid in a two-dimensional structure. Thanks to a performant optimization algorithm, we show that the system undergoes a continuous phase transition in the behavior of the flow controlled by the applied pressure drop. In analogy with the studies of the plastic depinning of vortex lattices in high-$T_c$ superconductors we characterize the nonlinearity of the flow curve and relate it to the change in the geometry of the open channels. In particular, close to the transition, an universal scale free distribution of the channel length is observed and explained theoretically via a mapping to the KPZ equation.Comment: 5 pages, 4 figures + 1 Supplementary materia

Thermalization and many-body localization in systems under dynamic nuclear polarization

We study the role of dipolar interactions in the standard protocol used to achieve dynamic nuclear polarization (DNP). In the so-called spin-temperature regime, where the interactions establish an effective thermodynamic behavior in the out-of-equilibrium stationary state, we provide numerical predictions for the level of hyperpolarization. We show that nuclear spins equilibrate to the effective spin-temperature established among the electron spins of radicals, as expected from the quantum theory of thermalization. Moreover, we present an analytical technique to estimate the spin temperature, and thus, the nuclear hyperpolarization in the steady state, as a function of interaction strength and quenched disorder. This reproduces both our numerical data and experimental results. Our central finding is that the nuclear hyperpolarization increases steadily upon reducing the interaction strength (by diluting the radical density). Interestingly, the highest polarization is reached at a point where the establishment of a spin temperature is just about to break down due to the incipient many-body localization transition in the electron spin system.Comment: 12 pages (+ 3 pages of appendix), 8 figure

Evidences of spin-temperature in Dynamic Nuclear Polarization: an exact computation of the EPR spectrum

In dynamic nuclear polarization (DNP) experiments, the compound is driven out-of-equilibrium by microwave (MW) irradiation of the radical electron spins. Their stationary state has been recently probed via electron double resonance (ELDOR) techniques showing, at low temperature, a broad depolarization of the electron paramagnetic resonance (EPR) spectrum under microwave irradiation. In this theoretical manuscript, we develop a numerical method to compute exactly the EPR spectrum in presence of dipolar interactions. Our results reproduce the observed broad depolarisation and provide a microscopic justification for spectral diffusion mechanism. We show the validity of the spin-temperature approach for typical radical concentration used in dissolution DNP protocols. In particular once the interactions are properly taken into account, the spin-temperature is consistent with the non-monotonic behavior of the EPR spectrum with a wide minimum around the irradiated frequency.Comment: 8 pages, 7 figures. Title and abstract change

Poor weight control, alcoholic beverage consumption and sudden sleep onset at the wheel among Italian truck drivers: A preliminary pilot study.

Objectives: The aim of this study was to investigate the prevalence of obesity, alcoholic beverage consumption, unhealthy alcohol use and sudden sleep onset at the wheel among Italian truck drivers. In addition to prevalence rates, this study also aimed at investigating potential predictors for sudden-onset sleepiness and obesity. Material and Methods: A sample of truck drivers was extracted from the database of the High Risk Professional Driver Study. Data concerning demographics, anthropometry, medical information and working conditions were collected using anonymous questionnaires. Logistic regression analyses were performed to assess the association of the reported body mass index (BMI), alcohol consumption and sudden sleep onset with working conditions and general lifestyle factors. Results: Three hundred and thirty-five questionnaires were collected. According to their BMI, 45% of the participants were overweight and 21.4% of them were obese. Twenty-four point two percent declared they drank alcoholic beverages during working hours or work breaks and 21.3% of the drivers had an Alcohol Use Disorders Identyfication Test Consumption (AUDIT C) score ≥ 5 (the threshold value for unhealthy alcohol use). Forty-one point six percent of the interviewees experienced one episode of sudden sleep onset at the wheel per month (5.5% per week and 0.9% daily). Predictive factors for obesity were: length of service (odds ratio (OR) = 1.09, confidence interval (95% CI): 1.04–1.15, p 55 years old (OR = 5.22, 95% CI: 1.29–21.1, p = 0.020), driving more than 50 000 km per year (OR = 2.89, 95% CI: 1.37–6.11, p = 0.006) and the Chalder Fatigue Questionnaire (CFQ) score > 11 (adjusted OR = 2.97, 95% CI: 1.22–7.21, p = 0.016). Conclusions: This study strongly emphasizes the need for intervention in order to reduce and prevent important risk factors for the sake of road safety and truck drivers' health

The challenge of posttraumatic thrombus embolization from abdominal aortic aneurysm causing acute limb ischemia

We report the first documented case of distal thromboembolism originating from an abdominal aortic aneurysm (AAA) after a blunt trauma. A 72-year-old man with a known 6.2 cm AAA was brought to our emergency department with signs of bilateral acute limb ischemia developing immediately after an accidental fall. The occlusion was confirmed at computed tomographic angiography, and the aneurysm showed a fragmentated/ulcerated mural thrombus, morphologically different as compared to the previous computed tomography (CT). A thromboembolectomy was performed and, after treatment of the ischemic complications, the aneurysm was repaired by open surgery. Embolization from aneurysms in the setting of a trauma is a challenge for the vascular surgeon, also because of its rare occurrence. We describe the management and discuss the operative strategy we opted for in this patient

Quantification and characterization of additives, plasticizers, and small microplastics (5-100 μm) in highway stormwater runoff

Highway stormwater (HSW) runoff is a significant pathway for transferring microplastics from land-based sources to the other surrounding environmental compartments. Small microplastics (SMPs, 5-100 μm), additives, plasticizers, natural, and nonplastic synthetic fibers, together with other components of micro-litter (APFs), were assessed in HSW samples via Micro-FTIR; oleo-extraction and purification procedures previously developed were optimized to accomplish this goal. The distribution of SMPs and APFs observed in distinct HSW runoff varied significantly since rainfall events may play a crucial role in the concentration and distribution of these pollutants. The SMPs' abundance varied from 11932 ± 151 to 18966 ± 191 SMPs/L. The dominating polymers were vinyl ester (VE), polyamide 6 (PA6), fluorocarbon, and polyester (PES). The APFs' concentrations ranged from 12825 ± 157 to 96425 ± 430 APFs/L. Most APFs originated from vehicle and tire wear (e.g., Dioctyl adipate or 5-Methyl-1H-benzotriazole). Other sources of these pollutants might be pipes, highway signs, packaging from garbage debris, road marking paints, atmospheric deposition, and other inputs. Assessing SMPs in HSW runoff can help evaluating the potential threat they may represent to receiving water bodies and air compartments. Besides, APFs in HSW runoff may be efficient proxies of macro- and microplastic pollution