Dependence on ion temperature of shallow-angle magnetic presheaths with adiabatic electrons

The magnetic presheath is a boundary layer occurring when magnetized plasma is in contact with a wall and the angle α between the wall and the magnetic field B is oblique. Here, we consider the fusion-relevant case of a shallow-angle, α �1, electron-repelling sheath, with the electron density given by a Boltzmann distribution, valid for α/√τ + 1 �√me/mi, where me is the electron mass, mi is the ion mass, τ = Ti/ZTe,Te is the electron temperature, Ti is the ion temperature and Z is the ionic charge state. The thickness of the magnetic presheath is of the order of a few ion sound Larmor radii ρs = √mi(ZTe + Ti)/ZeB, where e is the proton charge and B = |B| is the magnitude of the magnetic field. We study the dependence on τ of the electrostatic potential and ion distribution function in the magnetic presheath by using a set of prescribed ion distribution functions at the magnetic presheath entrance, parameterized by τ . The kinetic model is shown to be asymptotically equivalent to Chodura’s fluid model at small ion temperature, τ � 1, for |ln α| > 3|ln τ | � 1. In this limit, despite the fact that fluid equations give a reasonable approximation to the potential, ion gyroorbits acquire a spatial extent that occupies a large portion of the magnetic presheath. At large ion temperature, τ � 1, relevant because Ti is measured to be a few times larger than Te near divertor targets of fusion devices, ions reach the Debye sheath entrance (and subsequently the wall) at a shallow angle whose size is given by √α or 1/√τ, depending on which is largest

Gyrokinetic treatment of a grazing angle magnetic field

>We develop a gyrokinetic treatment for ions in the magnetic presheath, close to the plasma-wall boundary. We focus on magnetic presheaths with a small magnetic field to wall angle, α ⟪ 1. Characteristic lengths perpendicular to the wall in such a magnetic presheath scale with the typical ion Larmor orbit size, pi. The smallest scale length associated with variations parallel to the wall is taken to be across the magnetic field, and ordered l = ρi/δ, where δ ⟪ 1 is assumed. The scale lengths along the magnetic field line are assumed so long that variations associated with this direction are neglected. These orderings are consistent with what we expect close to the divertor target of a tokamak. We allow for a strong electric field E in the direction normal to the electron repelling wall, with strong variation in the same direction. The large change of the electric field over an ion Larmor radius distorts the orbit so that it is not circular. We solve for the lowest order orbits by identifying coordinates, which consist of constants of integration, an adiabatic invariant and a gyrophase, associated with periodic ion motion in the system with α = δ = 0. By using these new coordinates as variables in the limit α ~ δ ⟪ 1, we obtain a generalized ion gyrokinetic equation. We find another quantity that is conserved to first order and use this to simplify the gyrokinetic equation, solving it in the case of a collisionless magnetic presheath. Assuming a Boltzmann response for the electrons, a form of the quasineutrality equation that exploits the change of variables is derived. The gyrokinetic and quasineutrality equations give the ion distribution function and electrostatic potential in the magnetic presheath if the entrance boundary condition is specified

Solution to a collisionless shallow-angle magnetic presheath with kinetic ions

Using a kinetic model for the ions and adiabatic electrons, we solve a steady state, electron-repelling magnetic presheath in which a uniform magnetic field makes a small angle $\alpha \ll 1$ (in radians) with the wall. The presheath characteristic thickness is the typical ion gyroradius ${\rho }_{{\rm{i}}}$. The Debye length ${\lambda }_{{\rm{D}}}$ and the collisional mean free path of an ion λ mfp satisfy the ordering λ D Lt ρ i Lt α λ mfp, so a quasineutral and collisionless model is used. We assume that the electrostatic potential is a function only of distance from the wall, and it varies over the scale ρ i. Using the expansion in α Lt 1, we derive an analytical expression for the ion density that only depends on the ion distribution function at the entrance of the magnetic presheath and the electrostatic potential profile. Importantly, we have added the crucial contribution of the orbits in the region near the wall. By imposing the quasineutrality equation, we derive a condition that the ion distribution function must satisfy at the magnetic presheath entrance—the kinetic equivalent of the Chodura condition. Using an ion distribution function at the entrance of the magnetic presheath that satisfies the kinetic Chodura condition, we find numerical solutions for the self-consistent electrostatic potential, ion density and flow across the magnetic presheath for several values of α. Our numerical results also include the distribution of ion velocities at the Debye sheath entrance. We find that at small values of α there are substantially fewer ions travelling with a large normal component of the velocity into the wall

Solution to a collisionless shallow-angle magnetic presheath with kinetic ions

Using a kinetic model for the ions and adiabatic electrons, we solve a steady state, electron-repelling magnetic presheath in which a uniform magnetic field makes a small angle $\alpha \ll 1$ (in radians) with the wall. The presheath characteristic thickness is the typical ion gyroradius ${\rho }_{{\rm{i}}}$. The Debye length ${\lambda }_{{\rm{D}}}$ and the collisional mean free path of an ion λ mfp satisfy the ordering λ D Lt ρ i Lt α λ mfp, so a quasineutral and collisionless model is used. We assume that the electrostatic potential is a function only of distance from the wall, and it varies over the scale ρ i. Using the expansion in α Lt 1, we derive an analytical expression for the ion density that only depends on the ion distribution function at the entrance of the magnetic presheath and the electrostatic potential profile. Importantly, we have added the crucial contribution of the orbits in the region near the wall. By imposing the quasineutrality equation, we derive a condition that the ion distribution function must satisfy at the magnetic presheath entrance—the kinetic equivalent of the Chodura condition. Using an ion distribution function at the entrance of the magnetic presheath that satisfies the kinetic Chodura condition, we find numerical solutions for the self-consistent electrostatic potential, ion density and flow across the magnetic presheath for several values of α. Our numerical results also include the distribution of ion velocities at the Debye sheath entrance. We find that at small values of α there are substantially fewer ions travelling with a large normal component of the velocity into the wall

Gyrokinetic treatment of a grazing angle magnetic field

>We develop a gyrokinetic treatment for ions in the magnetic presheath, close to the plasma-wall boundary. We focus on magnetic presheaths with a small magnetic field to wall angle, α ⟪ 1. Characteristic lengths perpendicular to the wall in such a magnetic presheath scale with the typical ion Larmor orbit size, pi. The smallest scale length associated with variations parallel to the wall is taken to be across the magnetic field, and ordered l = ρi/δ, where δ ⟪ 1 is assumed. The scale lengths along the magnetic field line are assumed so long that variations associated with this direction are neglected. These orderings are consistent with what we expect close to the divertor target of a tokamak. We allow for a strong electric field E in the direction normal to the electron repelling wall, with strong variation in the same direction. The large change of the electric field over an ion Larmor radius distorts the orbit so that it is not circular. We solve for the lowest order orbits by identifying coordinates, which consist of constants of integration, an adiabatic invariant and a gyrophase, associated with periodic ion motion in the system with α = δ = 0. By using these new coordinates as variables in the limit α ~ δ ⟪ 1, we obtain a generalized ion gyrokinetic equation. We find another quantity that is conserved to first order and use this to simplify the gyrokinetic equation, solving it in the case of a collisionless magnetic presheath. Assuming a Boltzmann response for the electrons, a form of the quasineutrality equation that exploits the change of variables is derived. The gyrokinetic and quasineutrality equations give the ion distribution function and electrostatic potential in the magnetic presheath if the entrance boundary condition is specified

Intralipid in acute caffeine intoxication: a case report

Caffeine is arguably the most widely used stimulant drug in the world. Here we describe a suicide attempt involving caffeine overdose whereby the patient’s severe intoxication was successfully treated with the prompt infusion of Intralipid. A 19-year-old man was found in an agitated state at home by the volunteer emergency team about 1 h after the intentional ingestion of 40 g of caffeine (tablets). His consciousness decreased rapidly, followed quickly by seizures, and electrocardiographic monitoring showed ventricular fibrillation. Advanced life support maneuvers were started immediately, with the patient defibrillated 10 times and administered 5 mg epinephrine in total and 300 + 150 mg of amiodarone (as well as lidocaine and magnesium sulfate). The cardiac rhythm eventually evolved to asystole, necessitating the intravenous injection of epinephrine to achieve the return of spontaneous circulation. However, critical hemodynamic instability persisted, with the patient’s cardiac rhythm alternating between refractory irregular narrow complex tachycardia and wide complex tachycardia associated with hypotension. In an attempt to restore stability we administered three successive doses of Intralipid (120 + 250 + 100 mg), which successfully prevented a severe cardiovascular collapse due to a supra-lethal plasma caffeine level (>120 mg/L after lipid emulsion). The patient survived without any neurologic complications and was transferred to a psychiatric ward a few days later. The case emphasizes the efficacy of intravenous lipid emulsion in the resuscitation of patients from non-local anesthetic systemic toxicity. Intralipid appears to act initially as a vehicle that carries the stimulant drug away from heart and brain to less well-perfused organs (scavenging mechanism) and then, with a sufficient drop in the caffeine concentration, possibly as a tonic to the depressed heart

Inattentional blindness in anesthesiology: A gorilla is worth one thousand words

Introduction People are not able to anticipate unexpected events. Inattentional blindness is demonstrated to happen not only in naïve observers engaged in an unfamiliar task but also in field experts with years of training. Anaesthesia is the perfect example of a discipline which requires a high level of attention and our aim was to evaluate if inattentional blindness can affect anesthesiologists during their daily activities. Materials and methods An online survey was distributed on Facebook between May 1, 2021 and May 31, 2021. The survey consisted of five simulated cases with questions investigating the anesthetic management of day-case surgeries. Each case had an introduction, a chest radiography, an electrocardiogram, preoperative blood testing and the last case had a gorilla embedded in the chest radiography. Results In total 699 respondents from 17 different countries were finally included in the analysis. The main outcome was to assess the incidence of inattentional blindness. Only 34 (4.9%) respondents were able to spot the gorilla. No differences were found between anesthesiologists or residents, private or public hospitals, or between medical doctors with different experience. Discussion Our findings assess that inattentional blindness is common in anesthesia, and ever-growing attention is deemed necessary to improve patient safety; to achieve this objective several strategies should be adopted such as an increased use of standardized protocols, promoting automation based strategies to reduce human error when performing repetitive tasks and discouraging evaluation of multiple consecutive patients in the same work shifts independently of the associated complexity

Extensively drug-resistant and multidrug-resistant gram-negative pathogens in the neurocritical intensive care unit

Background: Abrupt increase of multidrug-resistant, extensively drug-resistant, and pandrug-resistant bacteria may complicate the course, management, and costs of neurocritical patients and is associated with high morbidity and mortality rates. No data exists regarding risk factors for colonization by gram-negative pathogens in neurocritical patients. The aim of the study was to identify risk factors associated with colonization by multidrug-resistant, extensively drug-resistant, and pandrug-resistant gram-negative bacteria in neurocritical patients. Methods: We conducted a retrospective cohort study in a neurointensive care unit over a period of 3\ua0years. We included adult neurocritical patients admitted for more than 48\ua0h. We analyzed several factors including both anamnestic factors and admission diagnosis. Results: Four hundred twenty neurocritical patients were retrospectively enrolled. Seventy-three patients developed colonization by multidrug-resistant and 53 by extensively drug-resistant gram negative pathogens. Logistic regression identified intensive care unit length of stay (LOS) as the strongest predictor for both multidrug-resistant (AUC 0.877; 95% CI 0.841\u20130.913) and extensively drug-resistant (AUC 0.839 0.787\u20130.892) gram negative pathogens. In addition, external ventricular drainage and intracerebral pressure monitoring catheter were risk factors for XDR. Survival analysis revealed that MDR bacteria colonization happens earlier (log-rank test p\ua0= 0.017). Conclusions: Optimization of healthcare strategies is required in order to reduce patients\u2019 length of stay to prevent multi- and extensively-drug gram-negative colonizations. Indeed, an early external ventricular drainage and intracerebral pressure monitoring catheter removal is deemed necessary as soon as clinically appropriate