H. Hauglin

Real-time magneto-optical imaging of vortices in superconducting NbSe2

We present here a new experimental tool for the direct observation of magnetic vortices in type-II superconductors. The magneto-optical imaging technique has been improved to enable single vortex observation at low flux densities. The main advantage of the new method is its high temporal resolution combined with the applicability to any superconducting sample with a flat surface. We give a short description of the experimental set-up and show examples of results obtained for a NbSe2 single crystal at 4.0 K.

Magneto-optical imaging setup for single vortex observation

A recently developed high-resolution magneto-optical imaging (MOI) setup is reviewed. It is the first MOI system capable of resolving the individual vortices in a type-II superconductor. We give a detailed description of the whole setup, and discuss its measured properties in terms of magnetic sensitivity and signal-noise characteristics. A simple model for the image intensity distribution due to a vortex lattice is developed, and for the intensity profile across a single vortex, we find good agreement between model calculations and experimental data. The minimum vortex spacing resolved experimentally is 1.3 μm. Our analysis shows that increased resolution can most easily be achieved by increasing the light input intensity, but maximum resolution is ultimately limited by the effective extinction ratio through the optical system and mechanical vibrations in the setup.

Manipulation of vortices by magnetic domain walls

In a type-II superconductor, the magnetic field penetrates in the form of thin filaments called vortices. The controlled behavior of these vortices may provide the basis for a new generation of nanodevices. We present here a series of experiments showing simultaneous manipulation and imaging of individual vortices in a NbSe2 single crystal. The magnetic field from a Bloch wall in a ferrite garnet film (FGF) is used to manipulate the vortices. High-resolution magneto-optical imaging enables real-time observation of the vortex positions using the Faraday effect in the same FGF. Depending on the thickness of the sample, the vortices are either swept away or merely bent with the Bloch wall.

Interaction between a magnetic domain wall and a superconductor

memory device based on active control of generation and annihilation of vortices by means of one or more domain walls. In recent years superconducting circuits based on single-flux-quantum pulses have been shown to provide a family of digital electronics with ultrahigh speed and very low-power dissipitation. At clock rates exceeding 10 GHz and an operation speed of many hundred GHz, these devices can in the future outrun any semiconductor device. 7 Using domain walls as active ‘‘vortex gates,’’ we may add an additional degree of freedom in these devices. It is known that bismuth-substituted ferrite garnet films with in-plane magnetization have domain walls with very low coercivity that can be moved without ambiguity at frequencies up to several GHz. 6 Furthermore, in such materials Bloch walls are easily formed by external magnetic fields or stress patterns, and these could be manipulated in numerous ways suitable for a memory device.

Cyclic AMP induces apoptosis in multiple myeloma cells and inhibits tumor development in a mouse myeloma model

BackgroundMultiple myeloma is an incurable disease requiring the development of effective therapies which can be used clinically. We have elucidated the potential for manipulating the cAMP signaling pathway as a target for inhibiting the growth of multiple myeloma cells.MethodsAs a model system, we primarily used the murine multiple myeloma cell line MOPC315 which can be grown both in vivo and in vitro. Human multiple myeloma cell lines U266, INA-6 and the B-cell precursor acute lymphoblastic leukemia cell line Reh were used only for in vitro studies. Cell death was assessed by flow cytometry and western blot analysis after treatment with cAMP elevating agents (forskolin, prostaglandin E2 and rolipram) and cAMP analogs. We followed tumor growth in vivo after forskolin treatment by imaging DsRed-labelled MOPC315 cells transplanted subcutaneously in BALB/c nude mice.ResultsIn contrast to the effect on Reh cells, 50 μM forskolin more than tripled the death of MOPC315 cells after 24 h in vitro. Forskolin induced cell death to a similar extent in the human myeloma cell lines U266 and INA-6. cAMP-mediated cell death had all the typical hallmarks of apoptosis, including changes in the mitochondrial membrane potential and cleavage of caspase 3, caspase 9 and PARP. Forskolin also inhibited the growth of multiple myeloma cells in a mouse model in vivo.ConclusionsElevation of intracellular levels of cAMP kills multiple myeloma cells in vitro and inhibits development of multiple myeloma in vivo. This strongly suggests that compounds activating the cAMP signaling pathway may be useful in the field of multiple myeloma.

Tracking Early Autoimmune Disease by Bioluminescent Imaging of NF-κB Activation Reveals Pathology in Multiple Organ Systems

It is desirable to have an early and sensitive detection marker of autoimmune disease in intact animals. Nuclear factor (NF)-kappaB is a transcription factor that is associated with inflammatory responses and immune disorders. Previously, we demonstrated that so-called idiotypic-driven T-B cell collaboration in mice doubly transgenic for paired immunoglobulin and T cell receptor transgenes resulted in a systemic autoimmune disease with systemic lupus erythematosus-like features. Here, we investigated NF-kappaB activation by including an NF-kappaB-responsive luciferase reporter transgene in this animal model. Triply transgenic mice developed bioluminescence signals from diseased organs before onset of clinical symptoms and autoantibody production, and light emissions correlated with disease progression. Signals were obtained from secondary lymphoid organs, inflamed intestines, skin lesions, and arthritic joints. Moreover, bioluminescence imaging and immunohistochemistry demonstrated that a minority of mice suffered from an autoimmune disease of the small intestine, in which light emissions correlated with antibodies against tissue transglutaminase and gliadin. Detection of luciferase by immunohistochemistry revealed NF-kappaB activation in collaborating B and T cells, as well as in macrophages. These results demonstrate that bioluminescent in vivo imaging of NF-kappaB activation can be used for early and sensitive detection of autoimmune disease in an experimental mouse model, offering new possibilities for the evaluation of anti-inflammatory drugs.

Single vortices observed as they enter NbSe2

We observe single vortices as they penetrate the edge of a superconductor using a high-sensitivity magneto-optical microscope. The vortices leap across a gap near the edge, a distance that decreases with increasing applied field and sample thickness. This behaviour can be explained by the combined effect of the geometrical barrier and bulk pinning.

Low-field vortex matter in YBa 2 Cu 3 O 7¿d : An atomic beam magnetic-resonance study

We report measurements of the low-field structure of the magnetic vortex lattice in an untwinned YBCO single-crystal platelet. Measurements were carried out using an atomic beam magnetic-resonance (ABMR) technique. For a 10.7 G field applied parallel to the c axis of the sample, we find a triangular lattice with orientational order extending across the entire sample. We find the triangular lattice to be weakly distorted by the a-b anisotropy of the material and measure a distortion factor. f=1.16. Model-experiment comparisons determine a penetration depth, λ a b = 140(′20) nm. The paper includes a detailed description of the ABMR technique. We discuss both technical details of the experiment and modeling used to interpret the measurements.

Magneto-optic study of spatial magnetic-field distribution relaxation in an HTSC film strip after transport current turn-on

The paper provides the first demonstration of the efficiency of applying the magneto-optic method to studies of the spatial and temporal magnetic-field relaxation in an YBa2Cu3O7 film strip after the transport current is switched on. It is shown that the evolution of magnetic flux distribution is adequately described in terms of a modified Bean model with time-dependent critical current. At a time 50 ms after the current is switched on, the critical current of the samples studied decreases by ≈15%. This proves the significance of thermally activated magnetic flux motion (creep) in the regime investigated. The magnetic vortex pinning energy has been estimated as U0≈20 kT.