mi im - Academia.edu (original) (raw)

Papers by mi im

Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 1988

The synthesis of monofluerescein, monorhodamine, and mono-4-nitrobenz-2-oxa-l,3-diazule (NBD) der... more The synthesis of monofluerescein, monorhodamine, and mono-4-nitrobenz-2-oxa-l,3-diazule (NBD) derivafives of glucagon is reported. The fluorescent groups were introduced by conve~ng tryptophan-25 to 2.thloltryptophan using thiol-speeific fluorescent reagents. All derivatives retained the ability to activate adenylate cydase when compared to glucagon and thus were considered full agonists. ICs0 values of 6.8.10 -9, 1.7.10 -s, 1.8.10 -s and 5.4" 10 `-9 M were measured in rat liver membranes for NBD-, fluerescein-, rhedamine-TrpZS.glueagon and native glueagon, respeefivaly. From the ICs0 values Kd values of 2.16.10 -9, 4.10 -9, 2-10 -9 and 1.72.10 -9 M were calculated for the binding of NBD-, fluorescein-, rhodamlue-Ts~-glueagon and native glueagon, respectively. The highest quantum yield (0.18) of the monomer derivatives was obtained with fluorescein-TrpZS-glucagon in phosphate-buffered saline (pH 7.4). Difluerescein-glueagon was also prepared by reacting the amino groups of histidine-I and lysine-12 with fluorescein isothiocyanate and dimer derivatives were prepared using fluorescein-labelled 2-thiulTrp 2sglueagon. Difluorescein.glueagon bound only weakly to glucagon receptors and displayed antagonist properties, The dimer derivative formed from two difluorescoin.2-thlolTq~.glucagon molecules had similar poor binding qualities, whereas the dimer formed from dlfluorescein-2-thioiTrp~-glueagon and 2-thiolTrl~glueagon exhibited, at low concentrations, properties similar to monofluorescein-glucagon. Both dimer derivatives were only sparingly soluble in aqueous medium. Specific binding of fluorescein-Trp~-glueagon and difluores~in-glueagon to rat hepatueytes was followed using flow cytometry.

Korean Journal of Fisheries and Aquatic Sciences, 2013

Spectroscopy, Spectromicroscopy, and Scattering Techniques, 2010

Magnetic vortices in magnetic nanodots, which are characterized by an in-plane (chirality) and an... more Magnetic vortices in magnetic nanodots, which are characterized by an in-plane (chirality) and an out-of-plane (polarity) magnetizations, have been intensively attracted because of their high potential for technological application to data storage and memory scheme as well as their scientific interest for an understanding of fundamental physics in magnetic nanostructures. Complete understanding of the formation process of vortex state in

IEEE Photonics Journal, 2010

ABSTRACT Imaging nanoscale magnetic structures and their fast dynamics is scientifically interest... more ABSTRACT Imaging nanoscale magnetic structures and their fast dynamics is scientifically interesting and technologically of highest relevance. The combination of circularly polarized soft X-ray photons, which provide a strong X-ray magnetic circular dichroism effect at characteristic X-ray absorption edges, with a high-resolution soft X-ray microscope utilizing Fresnel zone plate optics allows, in a unique way, the study of the stochastical behavior in the magnetization reversal process of thin films and the ultrafast dynamics of magnetic vortices and domain walls in confined ferromagnetic structures. Future sources of femtosecond-short and highly intense soft X-ray photon pulses hold the promise of magnetic imaging down to fundamental magnetic length and time scales.

Physical Review Letters, 2009

The stochastic field-driven depinning of a domain wall pinned at a notch in a magnetic nanowire i... more The stochastic field-driven depinning of a domain wall pinned at a notch in a magnetic nanowire is directly observed using magnetic x-ray microscopy with high lateral resolution down to 15 nm. The depinning-field distribution in Ni80Fe20 nanowires considerably depends on the wire width and the notch depth. The difference in the multiplicity of domain-wall types generated in the vicinity of a notch is responsible for the observed dependence of the stochastic nature of the domain-wall depinning field on the wire width and the notch depth. Thus the random nature of the domain-wall depinning process is controllable by an appropriate design of the nanowire.

Physical Review B, 2005

The local coercivity distribution of CoCrPt alloy films prepared by dc magnetron sputtering has b... more The local coercivity distribution of CoCrPt alloy films prepared by dc magnetron sputtering has been investigated by means of magneto-optical microscope magnetometer, capable of simultaneously measuring the local magnetic properties on a submicrometer spatial resolution. We find that with increasing Pt concentration the local coercivity distribution becomes asymmetric and the average local coercivity as well as the width of the distribution increases. Transmission electron microscopy studies, together with a theoretical explanation, reveal that the results are closely correlated with the grain size distribution dependent on the Pt concentration.

Journal of Applied Physics, 2005

We report on the saturation magnetostriction coefficient of 500 Å ͑Co 82 Cr 18 ͒ 100−x Pt x and x... more We report on the saturation magnetostriction coefficient of 500 Å ͑Co 82 Cr 18 ͒ 100−x Pt x and x Å ͑Co 82 Cr 18 ͒ 79 Pt 21 alloy thin films with perpendicular magnetic anisotropy. The CoCrPt alloy films were prepared by dc magnetron sputtering and the magnetostriction coefficients were measured via a highly sensitive optical deflection-detecting system using a one-dimensional position sensitive detector. The saturation magnetostriction coefficient is increased from −7.23ϫ 10 −6 to 8.5ϫ 10 −6 and from −8 ϫ 10 −6 to 14ϫ 10 −6 with increasing the Pt concentration from 0 to 35 at. % and the film thickness from 400 to 800 Å, respectively. X-ray diffractometry study revealed that crystalline orientation in CoCrPt alloy film, which depends on the Pt concentration and the CoCrPt film thickness, strongly influences the evolution of saturation magnetostriction coefficient.

Journal of Applied Physics, 2006

Recent progress in x-ray optics has pushed the lateral resolution of soft x-ray magnetic microsco... more Recent progress in x-ray optics has pushed the lateral resolution of soft x-ray magnetic microscopy to below 15 nm. We have measured local magnetic hysteresis on a nanometer scale at the full-field x-ray microscope XM-1 at the Advanced Light Source in Berkeley, approaching fundamental length scales such as exchange lengths, Barkhausen lengths, and grain diameters. We have studied the evolution of magnetic domain patterns in a nanogranular CoCrPt film with a pronounced perpendicular magnetic anisotropy and revealed nanoscopic details associated with the granular film structure. From a quantitative analysis of the field-dependent magnetic domain patterns, we are able to generate local magnetic hysteresis map on a nanometer scale. Our findings indicate a significant variation of local coercive fields corresponding to the nanoscopic behavior of magnetic domains.

IEEE Transactions on Magnetics, 2000

We have used magnetic transmission X-ray microscopy (M-TXM) to image in-field magnetization confi... more We have used magnetic transmission X-ray microscopy (M-TXM) to image in-field magnetization configurations of patterned Ni8oFe2o domain wall 'injection pads' and attached planar nanowires. Comparison with micromagnetic simulations suggests that the evolution of magnetic domains in rectangular injection pads depends on the relative orientation of closure domains in the remanent state. The magnetization reversal pathway is also altered by the inclusion of transverse magnetic fields. These different modes explain previous results of domain wall injection into nanowires. Even more striking was the observation of domain walls injecting halfway across the width of wider (>400 nm wide) wires but over wire lengths of several micrometers. These extended Neel walls can interact with adjacent nanowires and cause a switching in the side of the wire undergoing reversal as the domain wall continues to expand.

IEEE Transactions on Magnetics, 2000

The local modification of magnetic properties by ion irradiation opens the possibility to create ... more The local modification of magnetic properties by ion irradiation opens the possibility to create pinning sites for domain walls in magnetic nanowires without geometric constrictions. Implantation of chromium ions into Ni 80 Fe 20 nanowires is used to cause a local reduction of the saturation magnetization and thus a decrease of the energy associated with the domain wall. Field-driven pinning and depinning of a domain wall at the here so-called magnetic soft spots is directly observed using magnetic transmission soft X-ray microscopy. The pinning rate and the depinning field considerably depend on the wire width and the chromium fluence.

IEEE Magnetics Letters, 2000

Ni81Fe19 microwires are investigated as the basis of a switchable template for positioning magnet... more Ni81Fe19 microwires are investigated as the basis of a switchable template for positioning magnetically-labeled neural Schwann cells. Magnetic transmission X-ray microscopy and micromagnetic modeling show that magnetic domain walls can be created or removed in zigzagged structures by an applied magnetic field. Schwann cells containing superparamagnetic beads are trapped by the field emanating from the domain walls. The design allows Schwann cells to be organized on a surface to form a connected network and then released from the surface if required. As aligned Schwann cells can guide nerve regeneration, this technique is of value for developing glial-neuronal co-culture models in the future treatment of peripheral nerve injuries.

ACS Nano, 2012

Logic operations based on coupled magnetic vortices were experimentally demonstrated. We utilized... more Logic operations based on coupled magnetic vortices were experimentally demonstrated. We utilized a simple chain structure consisting of three physically separated but dipolar-coupled vortex-state Permalloy disks as well as two electrodes for application of the logical inputs. We directly monitored the vortex gyrations in the middle disk, as the logical output, by timeresolved full-field soft X-ray microscopy measurements. By manipulating the relative polarization configurations of both end disks, two different logic operations are programmable: the XOR operation for the parallel polarization and the OR operation for the antiparallel polarization. This work paves the way for new-type programmable logic gates based on the coupled vortex-gyration dynamics achievable in vortex-state networks. The advantages are as follows: a low-power input signal by means of resonant vortex excitation, low-energy dissipation during signal transportation by selection of low-damping materials, and a simple patterned-array structure.

Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 1988

The synthesis of monofluerescein, monorhodamine, and mono-4-nitrobenz-2-oxa-l,3-diazule (NBD) der... more The synthesis of monofluerescein, monorhodamine, and mono-4-nitrobenz-2-oxa-l,3-diazule (NBD) derivafives of glucagon is reported. The fluorescent groups were introduced by conve~ng tryptophan-25 to 2.thloltryptophan using thiol-speeific fluorescent reagents. All derivatives retained the ability to activate adenylate cydase when compared to glucagon and thus were considered full agonists. ICs0 values of 6.8.10 -9, 1.7.10 -s, 1.8.10 -s and 5.4" 10 `-9 M were measured in rat liver membranes for NBD-, fluerescein-, rhedamine-TrpZS.glueagon and native glueagon, respeefivaly. From the ICs0 values Kd values of 2.16.10 -9, 4.10 -9, 2-10 -9 and 1.72.10 -9 M were calculated for the binding of NBD-, fluorescein-, rhodamlue-Ts~-glueagon and native glueagon, respectively. The highest quantum yield (0.18) of the monomer derivatives was obtained with fluorescein-TrpZS-glucagon in phosphate-buffered saline (pH 7.4). Difluerescein-glueagon was also prepared by reacting the amino groups of histidine-I and lysine-12 with fluorescein isothiocyanate and dimer derivatives were prepared using fluorescein-labelled 2-thiulTrp 2sglueagon. Difluorescein.glueagon bound only weakly to glucagon receptors and displayed antagonist properties, The dimer derivative formed from two difluorescoin.2-thlolTq~.glucagon molecules had similar poor binding qualities, whereas the dimer formed from dlfluorescein-2-thioiTrp~-glueagon and 2-thiolTrl~glueagon exhibited, at low concentrations, properties similar to monofluorescein-glucagon. Both dimer derivatives were only sparingly soluble in aqueous medium. Specific binding of fluorescein-Trp~-glueagon and difluores~in-glueagon to rat hepatueytes was followed using flow cytometry.

Korean Journal of Fisheries and Aquatic Sciences, 2013

Spectroscopy, Spectromicroscopy, and Scattering Techniques, 2010

Magnetic vortices in magnetic nanodots, which are characterized by an in-plane (chirality) and an... more Magnetic vortices in magnetic nanodots, which are characterized by an in-plane (chirality) and an out-of-plane (polarity) magnetizations, have been intensively attracted because of their high potential for technological application to data storage and memory scheme as well as their scientific interest for an understanding of fundamental physics in magnetic nanostructures. Complete understanding of the formation process of vortex state in

IEEE Photonics Journal, 2010

ABSTRACT Imaging nanoscale magnetic structures and their fast dynamics is scientifically interest... more ABSTRACT Imaging nanoscale magnetic structures and their fast dynamics is scientifically interesting and technologically of highest relevance. The combination of circularly polarized soft X-ray photons, which provide a strong X-ray magnetic circular dichroism effect at characteristic X-ray absorption edges, with a high-resolution soft X-ray microscope utilizing Fresnel zone plate optics allows, in a unique way, the study of the stochastical behavior in the magnetization reversal process of thin films and the ultrafast dynamics of magnetic vortices and domain walls in confined ferromagnetic structures. Future sources of femtosecond-short and highly intense soft X-ray photon pulses hold the promise of magnetic imaging down to fundamental magnetic length and time scales.

Physical Review Letters, 2009

The stochastic field-driven depinning of a domain wall pinned at a notch in a magnetic nanowire i... more The stochastic field-driven depinning of a domain wall pinned at a notch in a magnetic nanowire is directly observed using magnetic x-ray microscopy with high lateral resolution down to 15 nm. The depinning-field distribution in Ni80Fe20 nanowires considerably depends on the wire width and the notch depth. The difference in the multiplicity of domain-wall types generated in the vicinity of a notch is responsible for the observed dependence of the stochastic nature of the domain-wall depinning field on the wire width and the notch depth. Thus the random nature of the domain-wall depinning process is controllable by an appropriate design of the nanowire.

Physical Review B, 2005

The local coercivity distribution of CoCrPt alloy films prepared by dc magnetron sputtering has b... more The local coercivity distribution of CoCrPt alloy films prepared by dc magnetron sputtering has been investigated by means of magneto-optical microscope magnetometer, capable of simultaneously measuring the local magnetic properties on a submicrometer spatial resolution. We find that with increasing Pt concentration the local coercivity distribution becomes asymmetric and the average local coercivity as well as the width of the distribution increases. Transmission electron microscopy studies, together with a theoretical explanation, reveal that the results are closely correlated with the grain size distribution dependent on the Pt concentration.

Journal of Applied Physics, 2005

We report on the saturation magnetostriction coefficient of 500 Å ͑Co 82 Cr 18 ͒ 100−x Pt x and x... more We report on the saturation magnetostriction coefficient of 500 Å ͑Co 82 Cr 18 ͒ 100−x Pt x and x Å ͑Co 82 Cr 18 ͒ 79 Pt 21 alloy thin films with perpendicular magnetic anisotropy. The CoCrPt alloy films were prepared by dc magnetron sputtering and the magnetostriction coefficients were measured via a highly sensitive optical deflection-detecting system using a one-dimensional position sensitive detector. The saturation magnetostriction coefficient is increased from −7.23ϫ 10 −6 to 8.5ϫ 10 −6 and from −8 ϫ 10 −6 to 14ϫ 10 −6 with increasing the Pt concentration from 0 to 35 at. % and the film thickness from 400 to 800 Å, respectively. X-ray diffractometry study revealed that crystalline orientation in CoCrPt alloy film, which depends on the Pt concentration and the CoCrPt film thickness, strongly influences the evolution of saturation magnetostriction coefficient.

Journal of Applied Physics, 2006

Recent progress in x-ray optics has pushed the lateral resolution of soft x-ray magnetic microsco... more Recent progress in x-ray optics has pushed the lateral resolution of soft x-ray magnetic microscopy to below 15 nm. We have measured local magnetic hysteresis on a nanometer scale at the full-field x-ray microscope XM-1 at the Advanced Light Source in Berkeley, approaching fundamental length scales such as exchange lengths, Barkhausen lengths, and grain diameters. We have studied the evolution of magnetic domain patterns in a nanogranular CoCrPt film with a pronounced perpendicular magnetic anisotropy and revealed nanoscopic details associated with the granular film structure. From a quantitative analysis of the field-dependent magnetic domain patterns, we are able to generate local magnetic hysteresis map on a nanometer scale. Our findings indicate a significant variation of local coercive fields corresponding to the nanoscopic behavior of magnetic domains.

IEEE Transactions on Magnetics, 2000

We have used magnetic transmission X-ray microscopy (M-TXM) to image in-field magnetization confi... more We have used magnetic transmission X-ray microscopy (M-TXM) to image in-field magnetization configurations of patterned Ni8oFe2o domain wall 'injection pads' and attached planar nanowires. Comparison with micromagnetic simulations suggests that the evolution of magnetic domains in rectangular injection pads depends on the relative orientation of closure domains in the remanent state. The magnetization reversal pathway is also altered by the inclusion of transverse magnetic fields. These different modes explain previous results of domain wall injection into nanowires. Even more striking was the observation of domain walls injecting halfway across the width of wider (>400 nm wide) wires but over wire lengths of several micrometers. These extended Neel walls can interact with adjacent nanowires and cause a switching in the side of the wire undergoing reversal as the domain wall continues to expand.

IEEE Transactions on Magnetics, 2000

The local modification of magnetic properties by ion irradiation opens the possibility to create ... more The local modification of magnetic properties by ion irradiation opens the possibility to create pinning sites for domain walls in magnetic nanowires without geometric constrictions. Implantation of chromium ions into Ni 80 Fe 20 nanowires is used to cause a local reduction of the saturation magnetization and thus a decrease of the energy associated with the domain wall. Field-driven pinning and depinning of a domain wall at the here so-called magnetic soft spots is directly observed using magnetic transmission soft X-ray microscopy. The pinning rate and the depinning field considerably depend on the wire width and the chromium fluence.

IEEE Magnetics Letters, 2000

Ni81Fe19 microwires are investigated as the basis of a switchable template for positioning magnet... more Ni81Fe19 microwires are investigated as the basis of a switchable template for positioning magnetically-labeled neural Schwann cells. Magnetic transmission X-ray microscopy and micromagnetic modeling show that magnetic domain walls can be created or removed in zigzagged structures by an applied magnetic field. Schwann cells containing superparamagnetic beads are trapped by the field emanating from the domain walls. The design allows Schwann cells to be organized on a surface to form a connected network and then released from the surface if required. As aligned Schwann cells can guide nerve regeneration, this technique is of value for developing glial-neuronal co-culture models in the future treatment of peripheral nerve injuries.

ACS Nano, 2012

Logic operations based on coupled magnetic vortices were experimentally demonstrated. We utilized... more Logic operations based on coupled magnetic vortices were experimentally demonstrated. We utilized a simple chain structure consisting of three physically separated but dipolar-coupled vortex-state Permalloy disks as well as two electrodes for application of the logical inputs. We directly monitored the vortex gyrations in the middle disk, as the logical output, by timeresolved full-field soft X-ray microscopy measurements. By manipulating the relative polarization configurations of both end disks, two different logic operations are programmable: the XOR operation for the parallel polarization and the OR operation for the antiparallel polarization. This work paves the way for new-type programmable logic gates based on the coupled vortex-gyration dynamics achievable in vortex-state networks. The advantages are as follows: a low-power input signal by means of resonant vortex excitation, low-energy dissipation during signal transportation by selection of low-damping materials, and a simple patterned-array structure.