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Due to their nature antiferromagnets are difficult to probe with conventional magnetometers. The Néel vector of a practically important antiferromagnet, CuMnAs, has now been determined by a femtosecond pump–probe magneto-optical experiment. Recent breakthroughs in the electrical detection and manipulation of antiferromagnets have opened a new avenue in the research of non-volatile spintronic devices 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 . Antiparallel spin sublattices in antiferromagnets, producing zero dipolar fields, lead to insensitivity to magnetic field perturbations, multi-level stability, ultrafast spin dynamics and other favourable characteristics, and may find utility in fields ranging from magnetic memories to optical signal processing. However, the absence of a net magnetic moment and ultrashort magnetization dynamics timescales make antiferromagnets notoriously difficult to study using common magnetometers or magnetic resonance techniques. Here, we demonstrate the experimental determination of the Néel vector in a thin film of antiferromagnetic CuMnAs (refs  9 , 10 ), a prominent material used in the first realization of antiferromagnetic memory chips 10 . We use a table-top femtosecond pump–probe magneto-optical experiment that is considerably more accessible than the traditionally employed large-scale-facility techniques such as neutron diffraction 11 and X-ray magnetic dichroism measurements 12 , 13 , 14 , 15 , 16 .

We report results of investigating carrier recombination in silicon nanocrystal/silicon dioxide superlattices. The superlattices prepared by nitrogen-free plasma enhanced chemical vapour deposition contained layers of silicon nanocrystals. Femtosecond transient transmission optical spectroscopy was used to monitor carrier mechanisms in the samples. The three-particle Auger recombination was observed in accord with previous reports. However, under high pump intensities (high photoexcited carrier densities) the bimolecular process dominated the recombination. Detailed analysis of measured data and fitting procedure made it possible to follow and quantify the interplay between the two recombination processes. The bimolecular recombination was interpreted in terms of the trap-assisted Auger recombination.

We review the theoretical background to diffusion tensor imaging (DTI) and some of its commoner clinical applications, such as cerebral ischemia, brain maturation and traumatic brain injury. We also review its potential use in diseases such as epilepsy, multiple sclerosis, and Alzheimer's disease. The value of DTI in the investigation of brain tumors and metabolic disorders is assessed.

The spin transfer torque is a phenomenon in which angular momentum of a spin polarized electrical current entering a ferromagnet is transferred to the magnetization. The effect has opened a new research field of electrically driven magnetization dynamics in magnetic nanostructures and plays an important role in the development of a new generation of memory devices and tunable oscillators. Optical excitations of magnetic systems by laser pulses have been a separate research field the aim of which is to explore magnetization dynamics at short timescales and enable ultrafast spintronic devices. We report the experimental observation of the optical spin transfer torque, predicted theoretically several years ago, building the bridge between these two fields of spintronics research. In a pump-and-probe optical experiment we measure coherent spin precession in a (Ga, Mn)As ferromagnetic semiconductor excited by circularly polarized laser pulses. During the pump pulse, the spin angular momentum of photo-carriers generated by the absorbed light is transferred to the collective magnetization of the ferromagnet. We analyse quantitatively the observed magnetization dynamics triggered by the optical spin transfer torque using independently determined micromagnetic parameters and magneto-optical coefficients of the studied (Ga, Mn)As. Spin transfer torque—the transfer of angular momentum from a spin-polarized current to a ferromagnet’s magnetization—has already found commercial application in memory devices, but the underlying physics is still not fully understood. Researchers now demonstrate the crucial role played by the polarization of the laser light that generates the current; a subtle effect only evident when isolated from other influences such as heating.

Electrical and optical control of magnetization are of central importance in the research and applications of spintronics. Non-relativistic angular momentum transfer or relativistic spin–orbit coupling provide efficient means by which electrical current driven through a ferromagnet can exert a torque on the magnetization. Ferromagnetic semiconductors like (Ga,Mn)As are suitable model systems with which to search for optical counterparts of these phenomena, where photocarriers excited by a laser pulse exert torque upon magnetization. Here, we report the observation of an optical spin–orbit torque (OSOT) in (Ga,Mn)As. The phenomenon originates from spin–orbit coupling of non-equilibrium photocarriers excitated by helicity-independent pump laser pulses, which do not impart angular momentum. In our measurements of the time-dependent magnetization trajectories, the signatures of OSOT are clearly distinct from the competing thermal excitation mechanism, and OSOT can even dominate in (Ga,Mn)As materials with appropriately controlled micromagnetic parameters. A novel non-thermal photomagnetic torque originating from spin–orbit coupling of non-equilibrium photocarriers excited by helicity-independent laser pulses is found in (Ga,Mn)As thin films. It differs fundamentally from optical spin–transfer torque. The possibility of studying spin–orbit torques on short timescales achievable by pump–probe magneto-optical measurements is demonstrated.

(Ga,Mn)As is at the forefront of spintronics research exploring the synergy of ferromagnetism with the physics and the technology of semiconductors. However, the electronic structure of this model spintronics material has been debated and the systematic and reproducible control of the basic micromagnetic parameters and semiconducting doping trends has not been established. Here we show that seemingly small departures from the individually optimized synthesis protocols yield non-systematic doping trends, extrinsic charge and moment compensation, and inhomogeneities that conceal intrinsic properties of (Ga,Mn)As. On the other hand, we demonstrate reproducible, well controlled and microscopically understood semiconducting doping trends and micromagnetic parameters in our series of carefully optimized epilayers. Hand-in-hand with the optimization of the material synthesis, we have developed experimental capabilities based on the magneto-optical pump-and-probe method that allowed us to simultaneously determine the magnetic anisotropy, Gilbert damping and spin stiffness constants from one consistent set of measured data. The electronic band structure of (Ga,Mn)As has been debated due to contrasting reports of experimental findings from samples differently synthesized. Nĕmec et al. show that a careful optimization of the synthesis protocol is necessary to evaluate the intrinsic semiconducting and magnetic properties of (Ga,Mn)As.

Hereditary spastic paraplegia (HSP) is a genetically heterogeneous group of neurodegenerative disorders characterized by progressive lower extremity weakness and spasticity. HSP pathology involves axonal degeneration that is most pronounced in the terminal segments of the longest descending (pyramidal) and ascending (dorsal columns) tracts. In this study, we compared spinal cord magnetic resonance imaging (MRI) in 13 HSP patients with four different types of autosomal dominant hereditary spastic paraplegia (SPG3A, SPG4, SPG6, and SPG8) with age-matched control subjects. The cross-section area of HSP subjects at cervical level C2 was 59.42 +/- 12.57 mm2 and at thoracic level T9 was 28.58 +/- 5.25 mm2. Both of these values were less than in the healthy controls (p < 0.001). The degree of cord atrophy was more prominent in patients with SPG6 and SPG8 who had signs of severe cord atrophy (47.60 +/- 6.58 mm2 at C2, 21.40 +/- 2.4 mm2 at T9) than in subjects with SPG3 and SPG4 (66.0 +/- 8.94 mm2 at C2, p < 0.02; 31.75 +/- 2.76 mm2 at T9, p < 0.001). These observations indicate that spinal cord atrophy is a common finding in the four genetic types of HSP. Spinal cord atrophy was more severe in SPG6 and SPG8 HSP subjects than in other types of HSP we studied. This may suggest a different disease mechanism with more prominent axonal degeneration in these two types of HSP when compared with HSP due to spastin and atlastin mutations.

This work describes creation of FE model of clinched joint and brings information about its verification with help of experiment. Also the sensitivity of the simulation model to the selected parameters (size of the model and coefficient of friction) and boundary conditions is studied so that the model is close to the reality. Deformation and uniaxial stress near the joint obtained with help of strain gauge is the output from the unidirectional, nondestructive test. Comparison of two values of stress in the chosen place obtained by experiment and FE simulation is the principle for verification of FE model and its adjustment. Based on the results it can be said that the FE model corresponds with the reality with the desired accuracy.

Our objective was to review the frequency and pattern of signal abnormalities seen on conventional MRI in patients with suspected neuropsychiatric systemic lupus erythematosus (NP-SLE). We reviewed 116 MRI examinations of the brain performed on 85 patients with SLE, (81 women, four men, aged 21-78 years, mean 40.6 years) presenting with neurological disturbances. MRI was normal or nearly normal in 34%. In 60% high-signal lesions were observed on T2-weighted images, frequently in the frontal and parietal subcortical white matter. Infarct-like lesions involving gray and white matter were demonstrated in 21 of cases. Areas of restricted diffusion were seen in 12 of the 67 patients who underwent diffusion-weighted imaging. Other abnormalities included loss of brain volume, hemorrhage, meningeal enhancement, and bilateral high signal in occipital white-matter. The MRI findings alone did not allow us to distinguish between thromboembolic and inflammatory events in many patients. Some patients with normal MRI improved clinically while on immunosuppressive therapy. More sensitive and/or specific imaging methods, such as spectroscopy and perfusion-weighted imaging, should be investigated in these subgroups of patients with suspected NP-SLE.

MRI and 2D-CSI spectroscopy were performed in eight patients with systemic lupus erythematosus who presented with acute onset of neuropsychiatric lupus (NP-SLE), and in seven normal controls to evaluate for differences in metabolic peaks and metabolic ratios between the two groups. Also, the interval change of the metabolic peaks and their ratios during treatment in the NP-SLE patient group was evaluated. Metabolic peaks for N-acetyl-aspartate (NAA), choline (Cho), creatine (Cr), and lactate/lipids (LL) and their ratios (NAA/Cr, NAA/Cho, Cho/Cr, LL/Cr) were determined at initial presentation and 3 and 6 months later. In the eight lupus patients compared to the seven normal controls, NAA/Cho ratios were lower at presentation (1.05 vs 1.25; p = 0.004) and decreased even further at the three month follow-up (0.92 vs 1.05; p = 0.008). In contrast, both Cho/Cr (1.42 vs 1.26; p = 0.026) and LL/Cr ratios (0.26 vs 0.19; p = 0.002) were higher in the lupus patients at presentation compared to the controls and did not significantly change at three and six months follow-up. The NAA/Cr ratios were lower in the lupus patients compared to the controls at presentation but the difference was not statistically significant. However, the mean NAA/Cr significantly decreased from the initial examination to the three month follow-up (1.42 vs 1.32; p = 0.049) but did not significantly change from the three to the six month follow-up examinations. The NAA/Cr, Cho/Cr, and NAA/Cho ratios varied significantly (p < 0.05, p < 0.05, p < 0.05, respectively) between the 17 different locations measured in the brain in all eight patients and seven controls. Both the NAA/Cr ratios and the Cho/Cr ratios were also significantly lower in the gray matter than in the white matter (p < 0.0001) in both patients and controls, whereas the LL/Cr and NAA/Cho ratios were not significantly different. In conclusion, 2D-CSI MR spectroscopy may be useful in the early detection of metabolic CNS changes in NP-SLE patients with acute onset of new neurological symptoms as well as in the follow-up after treatment to assess presence and changes in metabolic brain injury. However, although there are detectable differences between normal individuals and lupus patients it is currently unclear whether these relate to the acute episode. Future studies are needed comparing NP-SLE patients with active CNS involvement with those inactive disease.