Intercalated Rare-Earth Metals under Graphene on SiC

Intercalation of rare earth metals ($RE$ = Eu, Dy, and Gd) is achieved by depositing the $RE$ metal on graphene that is grown on silicon-carbide (SiC) and by subsequent annealing at high temperatures to promote intercalation. STM images of the films reveal that the graphene layer is defect free and that each of the intercalated metals has a distinct nucleation pattern. Intercalated Eu forms nano-clusters that are situated on the vertices of a Moir{\`e} pattern, while Dy and Gd form randomly distributed nano-clusters. X-ray magnetic circular dichroism (XMCD) measurements of intercalated films reveal the magnetic properties of these $RE$'s nano-clusters. Furthermore, field dependence and temperature dependence of the magnetic moments extracted from the XMCD show paramagnetic-like behaviors with moments that are generally smaller than those predicted by the Brillouin function. XMCD measurements of $RE$-oxides compared with those of the intercalated $RE$'s under graphene after exposure to air for months indicate that the graphene membranes protect these intercalants against oxidation.Comment: 9 pages, 7 figure

Intercalated europium metal in epitaxial graphene on SiC

X-ray magnetic circular dichroism (XMCD) reveal the magnetic properties of intercalated europium metal under graphene on SiC(0001). Intercalation of Eu nano-clusters (average size 2.5 nm) between graphene and SiC substate are formed by deposition of Eu on epitaxially grown graphene that is subsequently annealed at various temperatures while keeping the integrity of the graphene layer. Using sum-rules analysis of the XMCD of Eu M$_{4,5}$ edges at $T = 15$ K, our samples show paramagnetic-like behavior with distinct anomaly at T $\approx$ 90 K which may be related to the N{\`e}el transition, T$_N$ = 91 K, of bulk metal Eu. We find no evidence of ferromagnetism due to EuO or antiferromagnetism due to Eu$_2$O$_3$ indicating that the graphene layer protects the intercalated metallic Eu against oxidation over months of exposure to atmospheric environment.Comment: 6 pages, 5 figure

Intracerebral electroencephalography in targeting anterior thalamic nucleus for deep brain stimulation in refractory epilepsy

Background Results of DBS of ATN in refractory epilepsy depend on accuracy of the electrode's location. We searched for characteristic intraoperative, intracerebral EEG recording pattern from anterior thalamic nuclei (ATNs) as a biological marker for verifying the electrode's position. Methods There were six patients with refractory epilepsy scheduled for deep brain stimulation (DBS) procedure. At surgery, to map the target, we recorded EEG from each lead of DBS electrodes. One patient underwent a 24 hours EEG with continuous recording from both ATNs before internalization of stimulator units. Results In all patients we recorded spontaneous bioelectric activity of ATNs. The pattern of the recording from the ATN was similar in all cases. In the one patient where 24-hour recording was done with simultaneous scalp EEG, a complex partial seizure was captured. Conclusion This is the first report of using DBS electrode for intraoperative EEG recordings from the ATN in patients with refractory epilepsy. Since we managed to find the characteristic pattern of bioelectric activity of ATN, this technique seems to be a promising method for targeting this structure during the operation

Intracranial video-EEG monitoring in presurgical evaluation of patients with refractory epilepsy

Objective Reviewing our experience in intracranial video-EEG monitoring in the presurgical evaluation of patients with refractory epilepsy. Methods We report on 62 out of 202 (31%) patients with refractory epilepsy, who underwent a long term video-EEG monitoring (LTM). The epileptogenic zone (EZ) was localised either based on the results of LTM or after intracranial EEG recordings from depth, subdural or foramen ovale electrodes. The decision on the location of the electrodes was based upon semiology of the seizures, EEG findings and the lesions visualised in MRI brain scan. Intraoperative corticography was carried out before and right after the resection of the seizure onset zone. Results The video-EEG monitoring could localise EZ in 43 (69%) cases based. The remaining patients underwent invasive diagnostics: 10 (53%) had intracerebral depth electrodes, 6 (31%) depth and subdural and 3 (16%) foramen ovale electrodes. Intracranial video EEG recordings showed seizure focus in all the patients. Ten of them had EZ in mesial temporal structures, 4 in accessory motor area, 3 at the base of the frontal lobe and 2 in parietal lobe. There was one case of an asymptomatic intracerebral haematoma at the electrode. All patients were subsequently operated on. In 15 (79%) cases the seizures subsided (follow-up from 2 to 5 years), in 4 (21%) they decreased. Conclusions The intracranial EEG is required in all patients with normal MRI (so-called nonlesional cases) in whom EZ is suspected to be located in the hippocampus, insula or in the basal parts of the frontal lobe

Optimal time of duration of a long-term video-EEG monitoring in paroxysmal events – A retrospective analysis of 282 sessions in 202 patients

Purpose To find the optimal duration of the long-term video-EEG (LTM) and assess diagnostics utility of LTM in patients with epilepsy and other paroxysmal events in terms of future diagnosis and management. Methods Retrospective analysis of 282 LTMs performed in the last 5 years in our Epilepsy Monitoring Unit (EMU), in 202 consecutive patients. The analysis included demographic data, monitoring time, number and type of paroxysmal events, the time until their onset, influence of LTM result on the diagnosis and future management. Results There were 117 women and 85 men, mean age 34.2 years. Mean duration of LTM was 5 days (3–9), with 447 paroxysmal events recorded in 131 (65%) patients. Epileptic seizures were recorded in 82% cases (in 11% associated with PNES). The remaining 18% had either PNES (psychogenic non-epileptic seizures) – 11%, or parasomnias – 7%. Only 15% of epileptic seizures took place within the first 24h of the LTM (53% and 32% on the 2nd and 3rd day, respectively), whereas as many as 62% of PNES did (while only 28% and 10% on the 2nd and 3rd day, respectively). The LTM results changed the diagnosis in 36% of the patients, most frequently in PNES (from 2% to 14%). Altogether, it changed the management in 64% of the patients – particularly with PNES and those who underwent epilepsy surgery. Conclusions LTM should last at least 72h in patients with refractory epilepsy. Most of cases with PNES could be diagnosed after 48h

Femtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene

We show that strongly photoexcited graphene monolayers with 35 fs pulses quasi-instantaneously build up a broadband, inverted Dirac fermion population. Optical gain emerges and directly manifests itself via a negative conductivity at the near-infrared region for the first 200 fs, where stimulated emission completely compensates absorption loss in the graphene layer. Our experiment-theory comparison with two distinct electron and hole chemical potentials reproduce absorption saturation and gain at 40 fs, revealing, particularly, the evolution of the transient state from a hot classical gas to a dense quantum fluid with increasing the photoexcitation

Reverberação nas Salas do ISEP

Com o passar do tempo, a exigência sobre as construções foi se tornando cada vez maior no quesito da economia, conforto, desempenho, entre outros. É neste contexto que a acústica é inserida como uma necessidade a ser atendida pelas construções. Esta deve atender a diversos parâmetros para que seja considerada como satisfatória, sendo o tempo de reverberação – objeto de estudo deste trabalho – um deles. O tempo de reverberação está diretamente ligado ao entendimento das palavras dentro de um compartimento, ou seja, para que os ouvintes possam entender o locutor claramente, é necessário que o tempo de reverberação seja adequado. O ISEP – Instituto Superior de Engenharia do Porto – como instituição de ensino demanda de ambientes que contemplem um tempo de reverberação adequado para que a transmissão de toda a informação seja eficiente. Por isso, este trabalho tem por objetivo analisar o tempo de reverberação das salas do ISEP, comparando os valores ensaiados com os teóricos, observar a influência de variáveis cotidianas e sugerir possíveis melhorias para algumas salas. A fórmula utilizada foi a de Sabine, pois as salas se enquadrarem dentro de seus parâmetros de aplicação, e foram ensaiadas sete salas, sendo dois auditórios, uma sala de reuniões e quatro salas de aula, com o auxílio dos equipamentos Brüel & Kjaer. As variáveis analisadas foram as janelas, os estores, os blackouts e a presença de pessoas. Os resultados apresentados demonstram que a presença de pessoas é a variável que, dentro daquelas estudadas, mais diminui o tempo de reverberação e que nenhuma das salas abordadas se enquadram dentro da legislação estudada, sendo necessária a reforma das mesmas que pode contar com o uso de cadeiras de assento estofado e painéis perfurados.Over time, the demand on construction has been increasing in the economy, comfort, performance, among other aspects. Acoustics is inserted in this context as a necessity to be achieved by the constructions. This must comply with several parameters to be considered as satisfactory, being the reverberation time - object of study of this work - one of them. The reverberation time is directly linked to the understanding of the words within a compartment, in other words, to the listeners understand the speaker clearly it is necessary an adequate reverberation time. The ISEP - Instituto Superior de Engenharia do Porto - as an educational institution demands environments that contemplate a suitable reverberation time so that the transmission of all information is efficient. Therefore, this paper has the objective of analyzing the reverberation time of the ISEP rooms, comparing the values tested with the theoreticians, observing the influence of daily variables and suggest possible improvements for these rooms. To perform this work was used Sabine’s formula, since the rooms fit within their application parameters, and seven rooms were tested, being two auditoriums, a meeting room and four classrooms, with the help of Brüel & Kjaer equipment. The analyzed variables were the windows, the blinds, the blackouts and the presence of people. The results show that the presence of people is the variable that, among those studied, decreases the reverberation time. It was also noticed that none of the rooms comply with the legislation studied, being necessary the reform of them what can be done using upholstered seat chairs and perforated panels

Femtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene

We show that strongly photoexcited graphene monolayers with 35fs pulses quasi-instantaneously build up a broadband, inverted Dirac fermion population. Optical gain emerges and directly manifests itself via a negative optical conductivity for the first 200fs, where stimulated emission completely compensates absorption loss in the graphene layer. Our experiment-theory comparison with two distinct electron and hole chemical potentials reproduce absorption saturation and gain at 40fs, revealing, particularly, the evolution of the transient state from a hot classical gas to a dense quantum fluid with increasing the photoexcitation