Phonon-induced linewidths of graphene electronic states

The linewidths of the electronic bands originating from the electron-phonon coupling in graphene are analyzed based on model tight-binding calculations and experimental angle-resolved photoemission spectroscopy (ARPES) data. Our calculations confirm the prediction that the high-energy optical phonons provide the most essential contribution to the phonon-induced linewidth of the two upper occupied $\sigma$ bands near the $\bar{\Gamma}$-point. For larger binding energies of these bands, as well as for the $\pi$ band, we find evidence for a substantial lifetime broadening from interband scattering $\pi \rightarrow \sigma$ and $\sigma \rightarrow \pi$, respectively, driven by the out-of-plane ZA acoustic phonons. The essential features of the calculated $\sigma$ band linewidths are in agreement with recent published ARPES data [F. Mazzola et al., Phys.~Rev.~B. 95, 075430 (2017)] and of the $\pi$ band linewidth with ARPES data presented here.Comment: 7 pages, 4 figure

Nonlinear evolution of the magnetized Kelvin-Helmholtz instability: from fluid to kinetic modeling

The nonlinear evolution of collisionless plasmas is typically a multi-scale process where the energy is injected at large, fluid scales and dissipated at small, kinetic scales. Accurately modelling the global evolution requires to take into account the main micro-scale physical processes of interest. This is why comparison of different plasma models is today an imperative task aiming at understanding cross-scale processes in plasmas. We report here the first comparative study of the evolution of a magnetized shear flow, through a variety of different plasma models by using magnetohydrodynamic, Hall-MHD, two-fluid, hybrid kinetic and full kinetic codes. Kinetic relaxation effects are discussed to emphasize the need for kinetic equilibriums to study the dynamics of collisionless plasmas in non trivial configurations. Discrepancies between models are studied both in the linear and in the nonlinear regime of the magnetized Kelvin-Helmholtz instability, to highlight the effects of small scale processes on the nonlinear evolution of collisionless plasmas. We illustrate how the evolution of a magnetized shear flow depends on the relative orientation of the fluid vorticity with respect to the magnetic field direction during the linear evolution when kinetic effects are taken into account. Even if we found that small scale processes differ between the different models, we show that the feedback from small, kinetic scales to large, fluid scales is negligable in the nonlinear regime. This study show that the kinetic modeling validates the use of a fluid approach at large scales, which encourages the development and use of fluid codes to study the nonlinear evolution of magnetized fluid flows, even in the colisionless regime

Computational reconstruction and analysis of structural models of avian cryptochrome 4

A recent study by Xu et al. (Nature,2021, 594, 535−540) provided strongevidence that cryptochrome 4 (Cry4) is a key protein to endow migratory birds with the magneticcompass sense. The investigation compared the magneticfield response of Cry4 from migratoryand nonmigratory bird species and suggested that a difference in magnetic sensitivity could exist.Thisfinding prompted an in-depth investigation into Cry4 protein differences on the structuraland dynamic levels. In the present study, the pigeon Cry4 (ClCry4) crystal structure was used toreconstruct the missing avian Cry4 protein structures via homology modeling for carefullyselected bird species. The reconstructed Cry4 structure from European robin, Eurasian blackcap,zebrafinch, chicken, and pigeon were subsequently simulated dynamically and analyzed. Thestudied avian Cry4 structures showflexibility in analogous regions pointing to similar activationmechanisms and/or signaling interaction partners. It can be concluded that the experimentallyrecorded difference in the magneticfield sensitivity of Cry4 from different birds is unlikely to bedue to solely intrinsic dynamics of the proteins but requires additional factors that have not yet been identified

Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields

Plasma instabilities (e.g., Buneman, Weibel and other two-stream instabilities) excited in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a new 3-D relativistic particle-in-cell code, we have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. The simulation has been performed using a long simulation system in order to study the nonlinear stages of the Weibel instability, the particle acceleration mechanism, and the shock structure. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic (HD) like shock structure. In the leading shock, electron density increases by a factor of <_ 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. We discuss the possible implication of our simulation results within the AGN and GRB context. We have calculated the time evolution of the spectrum from two electrons propagating in a uniform parallel magnetic field to verify the technique. The same technique will be used to calculate radiation from accelerated electrons (positrons) in turbulent magnetic fields generated by Weibel instability

A search for new MRI criteria for dissemination in space in subjects with a clinically isolated syndrome

The International Panel on the Diagnosis of Multiple Sclerosis (MS) incorporated the Barkhof/Tintoré (B/T) magnetic resonance criteria into their diagnostic scheme to provide evidence of dissemination in space of central nervous system lesions, a prerequisite for diagnosing MS in patients who present with clinically isolated syndromes (CIS). Although specific for MS, the B/T criteria were criticised for their low sensitivity and relative complexity in clinical use. We used lesion characteristics at onset from 349 CIS patients in logistic regression and recursive partitioning modelling in a search for simpler and more sensitive criteria, while maintaining current specificity. The resulting models, all based on the presence of periventricular and deep white matter lesions, performed roughly in agreement with the B/T criteria, but were unable to provide higher diagnostic accuracy based on information from a single scan. Apparently, findings from contrast-enhanced and follow-up magnetic resonance scans are needed to improve the diagnostic algorithm

Lack of association between hyperglycaemia at arrival and clinical outcomes in acute stroke patients treated with tissue plasminogen activator

Hyperglycaemia is associated with adverse outcomes in some studies of acute ischaemic stroke.We hypothesised that in thrombolytic-treated stroke patients, hyperglycaemia would be independently associated with haemorrhagic transformation and unfavourable outcome.Consecutive rt-PA-treated acute ischaemic stroke patients presenting to four emergency departments were analysed. Associations of initial blood glucose and survival to hospital discharge, symptomatic intracerebral haemorrhage, any form of intracerebral haemorrhage, and disability at hospital discharge were determined. Potentially confounding factors of age, National Institutes of Health Stroke Scale, and smoking were analysed by univariate logistic regression and those with P <0·3 included in the multivariate model.In 268 patients, initial glucose values ranged from 62 to 507 mg/dl (mean 131). Elevated glucose at arrival was not significantly associated with any adverse clinical outcomes. A trend towards higher mortality in hyperglycaemic patients (odds ratio 1·71 per 100 mg/dl increase in glucose, 95% confidence interval 0·92–3·13, P =0·08) was seen, but is of unclear significance, and was not corroborated by effects on discharge disability, symptomatic intracerebral haemorrhage or intracerebral haemorrhage.Thrombolytic-treated stroke patients with hyperglycaemia at presentation did not have significantly worse outcomes than others in this cohort. These data fail to confirm previously described associations seen in similarly sized studies. Further study of these associations and their magnitude are necessary to better define the relationship between serum glucose and outcome in thrombolytic-treated acute ischaemic stroke.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79242/1/j.1747-4949.2010.00425.x.pd

Atypical idiopathic inflammatory demyelinating lesions: prognostic implications and relation to multiple sclerosis

Atypical lesions of a presumably idiopathic inflammatory demyelinating origin present quite variably and may pose diagnostic problems. The subsequent clinical course is also uncertain. We, therefore, wanted to clarify if atypical idiopathic inflammatory demyelinating lesions (AIIDLs) can be classified according to previously suggested radiologic characteristics and how this classification relates to prognosis. Searching the databases of eight tertiary referral centres we identified 90 adult patients (61 women, 29 men; mean age 34 years) with ≥ 1 AIIDL. We collected their demographic, clinical and magnetic resonance imaging data and obtained follow-up (FU) information on 77 of these patients over a mean duration of 4 years. The AIIDLs presented as a single lesion in 72 (80 %) patients and exhibited an infiltrative (n = 35), megacystic (n = 16), Baló (n = 10) or ring-like (n = 16) lesion appearance in 77 (86 %) patients. Additional multiple sclerosis (MS)-typical lesions existed in 48 (53 %) patients. During FU, a further clinical attack occurred rarely (23-35 % of patients) except for patients with ring-like AIIDLs (62 %). Further attacks were also significantly more often in patients with coexisting MS-typical lesions (41 vs. 10 %, p &lt; 0.005). New AIIDLs developed in six (7 %), and new MS-typical lesions in 29 (42 %) patients. Our findings confirm the previously reported subtypes of AIIDLs. Most types confer a relatively low risk of further clinical attacks, except for ring-like lesions and the combination with MS-typical lesions

Resource utilization and outcome at a university versus a community teaching hospital in tPA treated stroke patients: a retrospective cohort study

<p>Abstract</p> <p>Background</p> <p>Comparing patterns of resource utilization between hospitals is often complicated by biases in community and patient populations. Stroke patients treated with tissue plasminogen activator (tPA) provide a particularly homogenous population for comparison because of strict eligibility criteria for treatment. We tested whether resource utilization would be similar in this homogenous population between two hospitals located in a single Midwestern US community by comparing use of diagnostic testing and associated outcomes following treatment with t-PA.</p> <p>Methods</p> <p>Medical records from 206 consecutive intravenous t-PA-treated stroke patients from two teaching hospitals (one university, one community-based) were reviewed. Patient demographics, clinical characteristics and outcome were analyzed, as were the frequency of use of CT, MRI, MRA, echocardiography, angiography, and EEG.</p> <p>Results</p> <p>Seventy-nine and 127 stroke patients received t-PA at the university and community hospitals, respectively. The two patient populations were demographically similar. There were no differences in stroke severity. All outcomes were similar at both hospitals. Utilization of CT scans, and non-invasive carotid and cardiac imaging studies were similar at both hospitals; however, brain MR, TEE, and catheter angiography were used more frequently at the university hospital. EEG was obtained more often at the community hospital.</p> <p>Conclusions</p> <p>Utilization of advanced brain imaging and invasive diagnostic testing was greater at the university hospital, but was not associated with improved clinical outcomes. This could not be explained on the basis of stroke severity or patient characteristics. This variation of practice suggests substantial opportunities exist to reduce costs and improve efficiency of diagnostic resource use as well as reduce patient exposure to risk from diagnostic procedures.</p