Transient magnetic gratings on the nanometer scale

Laser-driven non-local electron dynamics in ultrathin magnetic samples on a sub-10 nm length scale is a key process in ultrafast magnetism. However, the experimental access has been challenging due to the nanoscopic and femtosecond nature of such transport processes. Here, we present a scattering-based experiment relying on a laser-induced electro- and magneto-optical grating in a Co/Pd ferromagnetic multilayer as a new technique to investigate non-local magnetization dynamics on nanometer length and femtosecond timescales. We induce a spatially modulated excitation pattern using tailored Al near-field masks with varying periodicities on a nanometer length scale and measure the first four diffraction orders in an x-ray scattering experiment with magnetic circular dichroism contrast at the free-electron laser facility FERMI, Trieste. The design of the periodic excitation mask leads to a strongly enhanced and characteristic transient scattering response allowing for sub-wavelength in-plane sensitivity for magnetic structures. In conjunction with scattering simulations, the experiment allows us to infer that a potential ultrafast lateral expansion of the initially excited regions of the magnetic film mediated by hot-electron transport and spin transport remains confined to below three nanometers

Constructing Exactly Solvable Pseudo-hermitian Many-particle Quantum Systems by Isospectral Deformation

A class of non-Dirac-hermitian many-particle quantum systems admitting entirely real spectra and unitary time-evolution is presented. These quantum models are isospectral with Dirac-hermitian systems and are exactly solvable. The general method involves a realization of the basic canonical commutation relations defining the quantum system in terms of operators those are hermitian with respect to a pre-determined positive definite metric in the Hilbert space. Appropriate combinations of these operators result in a large number of pseudo-hermitian quantum systems admitting entirely real spectra and unitary time evolution. Examples of a pseudo-hermitian rational Calogero model and XXZ spin-chain are considered.Comment: To appear in the Special Issue PHHQP 2010, International Journal of Theoretical Physics; 16 pages, LateX, no figur

Avancées thérapeutiques dans les epilepsies réfractaires de l'enfant [Therapeutic advances in refractory epilepsies in children].

Epilepsy concerns several thousands of children in Switzerland, and is refractory to classic antiepileptic drugs in an important proportion of cases. This percentage has remained stable, despite a constant production of new antiepileptic molecules. To alleviate this problem, several alternative approaches have been developed these last years. In this article, we present three children who suffer from different forms of pharmacoresistant epilepsy, managed with immunomodulatory or neurosurgical treatments, and we summarize the current knowledge about these therapeutic options

Isolated absence of optic chiasm revealed by congenital nystagmus, MRI and VEPs.

Congenital nystagmus is a rare condition mainly characterised by rhythmic, conjugate, and horizontal oscillations of both eyes that persist in the vertical gaze. This disorder is usually noticed in the neonatal period and persists throughout life. It can be of sensory origin, associated with low visual acuity of various causes, or of motor origin, caused by a defect in the slow eye movement system. The former can be genetically determined. It can also be associated with several conditions, the most frequent being albinism. The achiasma syndrome has recently been recognized in two patients as an autosomal recessive inherited cause of congenital nystagmus. We report the case of the so far youngest reported baby having been diagnosed with the isolated achiasmatic condition, which presented with congenital nystagmus and see-saw nystagmus, and discuss its clinical findings and 18 months follow-up. The achiasmatic syndrome should be included in the differential diagnosis of congenital nystagmus, as all the described cases presented like that. Complete investigations should be performed to allow the best evolution and follow-up of these children

Alexander disease: Early presence of cerebral MRI criteria

Alexander disease is a rare neurodegenerative disorder. Its most frequent subtype, the infantile form, is characterized by an early onset and a rapid neurological deterioration during the first months of life. Since the publication of cerebral radiological criteria in 2001, the disease has often been recognized by magnetic resonance imaging (MRI) findings. We report the case of a girl who at the age of 3 months presented with partial seizures and a normal neurological examination. MRI revealed the presence of a periventricular rim, extensive frontal white matter abnormalities, abnormalities of the basal ganglia and thalami and contrast enhancement involving optic chiasm, fornix, hypothalamus and mamillary bodies, corresponding to four of the five reported MRI criteria for Alexander disease. Additional MRI abnormalities not described so far were also observed. The diagnosis was confirmed by genetic analysis. This case illustrates that diagnostic MRI abnormalities of Alexander disease may be present at a very young age, long before the appearance of characteristic clinical signs. Early diagnosis by MRI allows prompt counselling of families

Holographically aided iterative phase retrieval

Fourier transform holography FTH is a noise resistant imaging technique which allows for nanometer spatial resolution x ray imaging, where the inclusion of a small reference scattering object provides the otherwise missing phase information. With FTH, one normally requires a considerable distance between the sample and the reference to ensure spatial separation of the reconstruction and its autocorrelation. We demonstrate however that this requirement can be omitted at the small cost of iteratively separating the reconstruction and autocorrelation. In doing so, the photon efficiency of FTH can be increased due to a smaller illumination area, and we show how the presence of the reference prevents the non uniqueness problems often encountered with plane wave iterative phase retrieval. The method was tested on a cobalt platinum multilayer exhibiting out of plane magnetized domains, where the magnetic circular dichroism effect was used to image the magnetic domains at the cobalt L3 edge at 780e

When is a child with status epilepticus likely to have Dravet syndrome?

PURPOSE: To identify clinical risk factors for Dravet syndrome (DS) in a population of children with status epilepticus (SE). MATERIAL AND METHODS: Children aged between 1 month and 16 years with at least one episode of SE were referred from 6 pediatric neurology centers in Switzerland. SE was defined as a clinical seizure lasting for more than 30min without recovery of normal consciousness. The diagnosis of DS was considered likely in previously healthy patients with seizures of multiple types starting before 1 year and developmental delay on follow-up. The presence of a SCN1A mutation was considered confirmatory for the diagnosis. Data such as gender, age at SE, SE clinical presentation and recurrence, additional seizure types and epilepsy diagnosis were collected. SCN1A analyses were performed in all patients, initially with High Resolution Melting Curve Analysis (HRMCA) and then by direct sequencing on selected samples with an abnormal HRMCA. Clinical and genetic findings were compared between children with DS and those with another diagnosis, and statistical methods were applied for significance analysis. RESULTS: 71 children with SE were included. Ten children had DS, and 61 had another diagnosis. SCN1A mutations were found in 12 of the 71 patients (16.9%; ten with DS, and two with seizures in a Generalized Epilepsy with Febrile Seizures+(GEFS+) context). The median age at first SE was 8 months in patients with DS, and 41 months in those with another epilepsy syndrome (p<0.001). Nine of the 10 DS patients had their initial SE before 18 months. Among the 26 patients aged 18 months or less at initial SE, the risk of DS was significantly increased for patients with two or more episodes (56.3%), as compared with those who had only one episode (0.0%) (p=0.005). CONCLUSION: In a population of children with SE, patients most likely to have DS are those who present their initial SE episode before 18 months, and who present with recurrent SE episodes

When should clinicians search for GLUT1 deficiency syndrome in childhood generalized epilepsies?

UNLABELLED: GLUT1 deficiency (GLUT1D) has recently been identified as an important cause of generalized epilepsies in childhood. As it is a treatable condition, it is crucial to determine which patients should be investigated. METHODS: We analyzed SLC2A1 for mutations in a group of 93 unrelated children with generalized epilepsies. Fasting lumbar puncture was performed following the identification of a mutation. We compared our results with a systematic review of 7 publications of series of patients with generalized epilepsies screened for SLC2A1 mutations. RESULTS: We found 2/93 (2.1%) patients with a SLC2A1 mutation. One, carrying a novel de novo deletion had epilepsy with myoclonic-atonic seizures (MAE), mild slowing of head growth, choreiform movements and developmental delay. The other, with a paternally inherited missense mutation, had childhood absence epilepsy with atypical EEG features and paroxysmal exercise-induced dyskinesia (PED) initially misdiagnosed as myoclonic seizures. Out of a total of 1110 screened patients with generalized epilepsies from 7 studies, 2.4% (29/1110) had GLUT1D. This rate was higher (5.6%) among 303 patients with early onset absence epilepsy (EOAE) from 4 studies. About 50% of GLUT1D patients had abnormal movements and 41% a family history of seizures, abnormal movements or both. CONCLUSION: GLUT1D is most likely to be found in MAE and in EOAE. The probability of finding GLUT1D in the classical idiopathic generalized epilepsies is very low. Pointers to GLUT1D include an increase in seizures before meals, cognitive impairment, or PED which can easily be overlooked