Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 35
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Intern Med ; 63(2): 309-313, 2024 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-37197954

RESUMO

A 57-year-old man whose mother had been pathologically diagnosed with Alexander disease (ALXDRD), presented with cerebellar ataxia, pyramidal signs, and mild dysarthria. Brain magnetic resonance imaging revealed typical ALXDRD alterations, such as atrophy of the medulla oblongata (MO) and cervical spinal cord, a reduced sagittal diameter of the MO, and garland-like hyperintensity signals along the lateral ventricular walls. A genetic analysis of GFAP by Sanger sequencing revealed a single heterozygous mutation of Glu to Lys at codon 332 (c.994G>A) in the GFAP gene. Our results newly confirmed that p.E332K alone is the pathogenic causative mutation for adult-onset ALXDRD.


Assuntos
Doença de Alexander , Humanos , Masculino , Pessoa de Meia-Idade , Doença de Alexander/diagnóstico por imagem , Doença de Alexander/genética , Códon/genética , Proteína Glial Fibrilar Ácida/genética , Imageamento por Ressonância Magnética/métodos , Bulbo/diagnóstico por imagem , Bulbo/patologia , Mutação
2.
Sci Rep ; 13(1): 21905, 2023 12 11.
Artigo em Inglês | MEDLINE | ID: mdl-38081947

RESUMO

Rheumatoid arthritis (RA) causes significant physical disability. We comprehensively investigated the relationship between RA disease activity (Disease Activity Score 28-C-reactive protein [DAS28-CRP], Simplified Disease Activity Index [SDAI], and Clinical Disease Activity Index [CDAI]), physical function (10-Meter Walk Test [10 MWT], Timed Up and Go test [TUG], Functional Reach Test [FRT], and Disabilities of the Arm, Shoulder, and Hand [DASH]), and quality of life (QOL) (Short-Form 36 [SF-36®]). We also investigated the relationship between van der Heijde's modified Total Sharp Score (mTSS), modified Health Assessment Questionnaire (mHAQ), and physical function and QOL assessments. Among 35 female patients with RA, DAS28-CRP correlated solely with DASH (r = 0.376), while SDAI and CDAI did not correlate with physical function. The mTSS-hand roentgenographic evaluation correlated with TUG (r = 0.359), FRT (r = - 0.415), and DASH (r = 0.533) among physical function assessments. The mHAQ correlated with 10 MWT (r = 0.347), TUG (r = 0.356), FRT (r = - 0.420), and DASH (r = 0.646). DAS28-CRP correlated with six of the eight subscales of SF-36®, and mTSS and mHAQ correlated with only one subscale. RA disease activity assessments may not reflect all physical functions and QOL domains of female patients with RA. Evaluating physical function and QOL in female patients with RA is essential.


Assuntos
Artrite Reumatoide , Qualidade de Vida , Humanos , Feminino , Equilíbrio Postural , Estudos de Tempo e Movimento , Exame Físico , Índice de Gravidade de Doença
3.
ACS Omega ; 8(28): 24875-24882, 2023 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-37483234

RESUMO

CoxFe3-xO4(CFO)/Pt bilayers prepared by molecular beam epitaxy were investigated for the anomalous Hall effect and X-ray magnetic circular dichroism (XMCD). We found that the anomalous Hall effect originates from a magnetic proximity effect at the CFO/Pt interface. The XMCD signal in the Pt L-edge was obtained only for the sample deposited at 600 °C, indicating that the magnetic proximity effect is sensitive to the interface structure. Transmission electron microscopy images of the CFO/Pt interface and XMCD measurements of Co and Fe L-edges do not provide direct evidence for interfacial atomic diffusion or alloying. In summary, these results suggest that the magnetic proximity effect is robust for transport properties, such as the anomalous Hall effect, while the induced magnetic moment depends on slight differences in the interfacial structure, such as the presence or absence of interfacial oxygen ions.

4.
Langmuir ; 39(14): 5137-5144, 2023 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-36995288

RESUMO

The relationship between the magnetorheology of bimodal magnetic elastomers with high concentrations (60 vol %) of plastic beads with diameters of 8 or 200 µm and the meso-structure of the particles was investigated. Dynamic viscoelasticity measurements revealed that the change in storage modulus of the bimodal elastomer with 200 µm beads was 2.8 × 105 Pa at a magnetic field of 370 mT. The change in the storage modulus for monomodal elastomer without beads was 4.9 × 104 Pa. The bimodal elastomer with 8 µm beads hardly responded to the magnetic field. In-situ observation for the particle morphology was performed using synchrotron X-ray CT. For the bimodal elastomer with 200 µm beads, a highly aligned structure of magnetic particles was observed in the gaps between the beads when the magnetic field was applied. On the other hand, for the bimodal elastomer with 8 µm beads, no chain structure of magnetic particles was observed. The orientation angle between the long axis of the aggregation of magnetic particles and the magnetic field direction was determined by an image analysis in three dimensions. The orientation angle varied from 56° to 11° for the bimodal elastomer with 200 µm beads and from 64° to 49° for that with 8 µm beads by applying the magnetic field. The orientation angle of the monomodal elastomer without beads changed from 63° to 21°. It was found that the addition of beads with a diameter of 200 µm linked the chains of magnetic particles, while beads with a diameter of 8 µm prevented the chain formation of the magnetic particles.

5.
Mol Ther ; 31(4): 1106-1122, 2023 04 05.
Artigo em Inglês | MEDLINE | ID: mdl-36694463

RESUMO

Antisense oligonucleotide (ASO) is a major tool used for silencing pathogenic genes. For stroke in the hyperacute stage, however, the ability of ASO to regulate genes is limited by its poor delivery to the ischemic brain owing to sudden occlusion of the supplying artery. Here we show that, in a mouse model of permanent ischemic stroke, lipid-ligand conjugated DNA/RNA heteroduplex oligonucleotide (lipid-HDO) was unexpectedly delivered 9.6 times more efficiently to the ischemic area of the brain than to the contralateral non-ischemic brain and achieved robust gene knockdown and change of stroke phenotype, despite a 90% decrease in cerebral blood flow in the 3 h after occlusion. This delivery to neurons was mediated via receptor-mediated transcytosis by lipoprotein receptors in brain endothelial cells, the expression of which was significantly upregulated after ischemia. This study provides proof-of-concept that lipid-HDO is a promising gene-silencing technology for stroke treatment in the hyperacute stage.


Assuntos
Isquemia Encefálica , Acidente Vascular Cerebral , Camundongos , Animais , Oligonucleotídeos , RNA , Células Endoteliais/metabolismo , Ligantes , Isquemia Encefálica/genética , Isquemia Encefálica/terapia , Oligonucleotídeos Antissenso/genética , Oligonucleotídeos Antissenso/metabolismo , Encéfalo/metabolismo , Isquemia , DNA , Lipídeos
6.
Langmuir ; 38(44): 13497-13505, 2022 Nov 08.
Artigo em Inglês | MEDLINE | ID: mdl-36288501

RESUMO

In situ observation of the migration and structure formation of magnetic particles in polyurethane elastomers was carried out by X-ray computed tomography using synchrotron radiation. The mean diameter of the magnetic particles was 7.0 µm, and the volume fraction was ϕ= 0.24 at its maximum. The exposure time was 100 ms/frame, and the pixel size was 0.458 µm/pixel. The orientation angle and the volume fraction of the maximum aggregate were analyzed using commercial software for image analysis. The orientation angle for magnetic elastomers with ϕ = 0.24 was approximately 55° at 0 mT and decreased remarkably with the magnetic field. At magnetic fields above 150 mT, the orientation angle gradually decreased with the field and showed a constant value of 38° at 300 mT, suggesting that magnetic particles move and form a chain-like structure although the chains do not align perfectly in the direction of the magnetic field. On the other hand, the volume fraction of the maximum aggregate was constant at magnetic fields below 100 mT, and it significantly increased with the field, indicating that magnetic particles were connected to each other and developed into a macroscopic structure with anisotropy. Dynamic viscoelastic measurements revealed that the storage modulus of the magnetic elastomers cannot be simply scaled by the orientation angle. It was also found that the volume fraction of the maximum aggregate is a good parameter for explaining the huge increase in the storage modulus. The dynamic movement of magnetic particles when a magnetic field of 300 mT was switched on and off was also successfully observed. When the field was switched on, magnetic particles connected instantly and their aggregates were rapidly elongated in the direction of the magnetic field. When the field was switched off, some of the connections between aggregates were broken; however, most of the aggregates did not return to the original position even 5 min after being switched off.

7.
Sci Rep ; 11(1): 14237, 2021 07 09.
Artigo em Inglês | MEDLINE | ID: mdl-34244578

RESUMO

Brain endothelial cells (BECs) are involved in the pathogenesis of ischemic stroke. Recently, several microRNAs (miRNAs) in BECs were reported to regulate the endothelial function in ischemic brain. Therefore, modulation of miRNAs in BECs by a therapeutic oligonucleotide to inhibit miRNA (antimiR) could be a useful strategy for treating ischemic stroke. However, few attempts have been made to achieve this strategy via systemic route due to lack of efficient delivery-method toward BECs. Here, we have developed a new technology for delivering an antimiR into BECs and silencing miRNAs in BECs, using a mouse ischemic stroke model. We designed a heteroduplex oligonucleotide, comprising an antimiR against miRNA-126 (miR-126) known as the endothelial-specific miRNA and its complementary RNA, conjugated to α-tocopherol as a delivery ligand (Toc-HDO targeting miR-126). Intravenous administration of Toc-HDO targeting miR-126 remarkably suppressed miR-126 expression in ischemic brain of the model mice. In addition, we showed that Toc-HDO targeting miR-126 was delivered into BECs more efficiently than the parent antimiR in ischemic brain, and that it was delivered more effectively in ischemic brain than non-ischemic brain of this model mice. Our study highlights the potential of this technology as a new clinical therapeutic option for ischemic stroke.


Assuntos
MicroRNAs/genética , Oligonucleotídeos/química , Oligonucleotídeos/uso terapêutico , alfa-Tocoferol/química , Animais , Encéfalo/metabolismo , Linhagem Celular , Imuno-Histoquímica , AVC Isquêmico/tratamento farmacológico , AVC Isquêmico/genética , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Reação em Cadeia da Polimerase Via Transcriptase Reversa
8.
Sci Rep ; 11(1): 4097, 2021 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-33674698

RESUMO

The dynamic properties of crystalline materials are important for understanding their local environment or individual single-grain motions. A new time-resolved observation method is required for use in many fields of investigation. Here, we developed in situ diffracted X-ray blinking to monitor high-resolution diffraction patterns from single-crystal grains with a 50 ms time resolution. The diffraction spots of single grains of silver halides and silver moved in the θ and χ directions during the photolysis chemical reaction. The movements of the spots represent tilting and rotational motions. The time trajectory of the diffraction intensity reflecting those motions was analysed by using single-pixel autocorrelation function (sp-ACF). Single-pixel ACF analysis revealed significant differences in the distributions of the ACF decay constants between silver halides, suggesting that the motions of single grains are different between them. The rotational diffusion coefficients for silver halides were estimated to be accurate at the level of approximately 0.1 to 0.3 pm2/s. Furthermore, newly formed silver grains on silver halides correlated with their ACF decay constants. Our high-resolution atomic scale measurement-sp-ACF analysis of diffraction patterns of individual grains-is useful for evaluating physical properties that are broadly applicable in physics, chemistry, and materials science.

9.
Mod Rheumatol ; 31(2): 312-318, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-32530346

RESUMO

OBJECTIVES: A pain-free stable wrist is a prerequisite for patients with rheumatoid arthritis to improve their activity of daily life. The present study investigated whether or not radiocarpal arthrodesis yielded good results for more than 20 years. METHODS: A retrospective study was performed on 20 unstable wrists in 17 patients with rheumatoid arthritis. Radiocarpal arthrodesis combined with synovectomy and the Darrach procedure was performed. Wrist pain, grip power, the range of motion, pharmacotherapy, ESR, CRP, and serial radiographs were investigated at the baseline and 20 years after the operation. Patient-reported outcomes using the mHAQ, DASH and patient's satisfaction level were investigated at the final follow-up. RESULTS: Pain had disappeared completely in all patients at 20 years after the operation. The average grip power increased in 16 wrists (80%) and decreased in 4 wrists (20%). Wrist extension and flexion significantly decreased, and supination and pronation remained within the functional range. Radiographically, ulnar shift and palmar subluxation initially improved and remained unchanged for a long time. Fourteen patients (82.4%) with 17 wrists were satisfied with this operation. CONCLUSION: Radiocarpal arthrodesis for rheumatoid wrists provided painless stability for a long period for 20 years or more.


Assuntos
Artrite Reumatoide/cirurgia , Artrodese/efeitos adversos , Luxações Articulares/epidemiologia , Dor/epidemiologia , Complicações Pós-Operatórias/epidemiologia , Sinovectomia/efeitos adversos , Articulação do Punho/cirurgia , Adulto , Idoso , Artrodese/métodos , Feminino , Força da Mão , Humanos , Masculino , Pessoa de Meia-Idade , Satisfação do Paciente , Amplitude de Movimento Articular
10.
Immunol Med ; 42(1): 29-38, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31067155

RESUMO

The aim of this study was to assess abatacept in rheumatoid arthritis (RA) patient. Patients (20 men, 89 women, aged 61.9 ± 10.4 y) who responded inadequately to conventional synthetic disease-modifying anti-rheumatic drug were treated with abatacept for 24-months. Disease activity score in 28 joints (DAS28-CRP) was evaluated. Of 109 patients, 82 (75.2%) were on methotrexate (MTX; mean dosage 9.0 ± 2.7 mg/week); 48 (44.0%) were naive to biologics and 61 (56.0%) had failed biologics. The 1- and 2-year retention rates were 77% and 53%, respectively. At 24-months, the DAS28-CRP remission rates were 54.5% in the biologic-naïve patients, and 28.2% in the biologic-failure patients (p < .01), while the structural remission rates were 83.9% and 73.1%, respectively (p = .461). Abatacept was equally effective in RA patients who were and were not on concomitant MTX. Biologic-naïve was associated with better clinical outcome. Abatacept was effective in patients who showed decreasing anti-CCP antibody titers or serum MMP-3 levels during treatment. Infection was the most frequent adverse effect of abatacept therapy. In conclusion, abatacept is more effective in biologic-naïve than in biologic-failure RA patients with or without concomitant use of MTX. Abatacept is more effective in RA patients with than without decreasing serum MMP-3 or anti-CCP antibody titers during treatment.


Assuntos
Abatacepte/administração & dosagem , Antirreumáticos/administração & dosagem , Artrite Reumatoide/tratamento farmacológico , Imunossupressores/administração & dosagem , Adulto , Idoso , Idoso de 80 Anos ou mais , Anticorpos Antiproteína Citrulinada/sangue , Artrite Reumatoide/diagnóstico , Povo Asiático , Biomarcadores/sangue , Relação Dose-Resposta a Droga , Feminino , Humanos , Masculino , Metaloproteinase 3 da Matriz , Metotrexato/administração & dosagem , Pessoa de Meia-Idade , Indução de Remissão , Resultado do Tratamento
11.
Clin Biochem ; 69: 8-14, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31077643

RESUMO

BACKGROUND: This study aimed to evaluate the relationships between concomitant biologic disease-modifying anti-rheumatic drugs (DMARDs) and prednisolone administration and blood tacrolimus exposure or serum CYP3A4/5-related markers in rheumatoid arthritis (RA) patients without severe disease activity. METHODS: Forty-six RA patients treated with oral tacrolimus once daily for maintenance of clinical remission to moderate disease activity were enrolled. The blood concentrations of tacrolimus and its major metabolite were determined at 12 h after the evening dosing. Blood samples for determination of serum markers including 4ß-hydroxycholesterol (4ß-OHC), 25-hydroxyvitamin D (25-OHD) and interleukin-6 (IL-6), and CYP3A5 genotype were collected. RESULTS: Most enrolled patients had RA with clinical remission to mild disease activity. Concomitant tocilizumab or low-dose prednisolone administration did not alter the blood tacrolimus exposure. Serum 4ß-OHC level was lower in tocilizumab co-treated patients than in the biologic DMARD non-treated patients. The blood tacrolimus concentration was inversely correlated with the serum level of 25-OHD, but not 4ß-OHC and IL-6. The serum level of 4ß-OHC was positively associated with that of 25-OHD. No correlations were observed between the serum levels of CYP3A4/5 activity markers and IL-6. The patients with the homozygous CYP3A5*3 had the higher blood tacrolimus concentration, while CYP3A5*3 allele was not associated with the serum levels of 4ß-OHC and 25-OHD. CONCLUSIONS: Concomitant use of tocilizumab or low-dose prednisolone had no effect on the pharmacokinetics of tacrolimus, while tocilizumab lowered serum 4ß-OHC. Blood tacrolimus exposure was negatively associated with serum 25-OHD in RA patients with clinical remission to moderate disease activity.


Assuntos
Antirreumáticos/uso terapêutico , Artrite Reumatoide/sangue , Artrite Reumatoide/tratamento farmacológico , Citocromo P-450 CYP3A/sangue , Imunossupressores/uso terapêutico , Prednisolona/uso terapêutico , Tacrolimo/uso terapêutico , Idoso , Antirreumáticos/administração & dosagem , Artrite Reumatoide/enzimologia , Biomarcadores/sangue , Feminino , Humanos , Hidroxicolesteróis/sangue , Imunossupressores/sangue , Limite de Detecção , Masculino , Pessoa de Meia-Idade , Prednisolona/administração & dosagem , Tacrolimo/administração & dosagem , Vitamina D/análogos & derivados , Vitamina D/sangue
12.
Nat Commun ; 9(1): 1648, 2018 04 25.
Artigo em Inglês | MEDLINE | ID: mdl-29695776

RESUMO

Chiral spin textures of a ferromagnetic layer in contact to a heavy non-magnetic metal, such as Néel-type domain walls and skyrmions, have been studied intensively because of their potential for future nanomagnetic devices. The Dyzaloshinskii-Moriya interaction (DMI) is an essential phenomenon for the formation of such chiral spin textures. In spite of recent theoretical progress aiming at understanding the microscopic origin of the DMI, an experimental investigation unravelling the physics at stake is still required. Here we experimentally demonstrate the close correlation of the DMI with the anisotropy of the orbital magnetic moment and with the magnetic dipole moment of the ferromagnetic metal in addition to Heisenberg exchange. The density functional theory and the tight-binding model calculations reveal that inversion symmetry breaking with spin-orbit coupling gives rise to the orbital-related correlation. Our study provides the experimental connection between the orbital physics and the spin-orbit-related phenomena, such as DMI.

13.
Medicine (Baltimore) ; 97(10): e0082, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29517672

RESUMO

RATIONALE: OSAM is a rare ventriculoperitoneal (VP) shunt complication where cervical spinal cord compression by epidural venous plexus engorgement is caused by cerebrospinal fluid (CSF) overdrainage. Symmetrically indented deformity of the upper cervical spinal cord and surrounding epidural venous engorgement are characteristic radiological findings. Both of them are typically detected on magnetic resonance imaging (MRI) and enhanced computed tomography (CT). PATIENT CONCERNS: The 77-year-old man who underwent the placement of a VP shunt without an antisiphon device to treat post-subarachnoid hemorrhage (SAH) hydrocephalus presented with progressive quadriplegia 10 years postoperatively. DIAGNOSIS: MRI revealed a symmetrically indented spinal cord from the craniocervical junction (CCJ) to the C2 level and enhanced CT showed the epidural venous engorgement, which were characteristic radiological findings of overshunting-associated myelopathy (OSAM). However, MRI atypically failed to detect the engorged epidural vein and showed no compressive lesion around the spinal cord. INTERVENTION: In order to reveal how the cervical spinal cord was deformed and compressed by engorged epidural vein, CT myelography was performed. OUTCOMES: CT myelography proved that the epidural vein dynamically engorged and compressed the cervical spinal cord immediately after rotation and extension of the neck. LESSONS: CT myelography combined with neck rotation and extension revealed the dynamic change of the epidural venous engorgement, and is useful for evaluation and diagnosis of OSAM especially when epidural venous engorgement was not detectable on MRI.


Assuntos
Mielografia/métodos , Compressão da Medula Espinal/etiologia , Doenças da Medula Espinal/complicações , Tomografia Computadorizada por Raios X/métodos , Derivação Ventriculoperitoneal/efeitos adversos , Idoso , Medula Cervical/diagnóstico por imagem , Humanos , Imageamento por Ressonância Magnética , Masculino , Compressão da Medula Espinal/diagnóstico por imagem , Doenças da Medula Espinal/diagnóstico por imagem
14.
J Stroke Cerebrovasc Dis ; 27(5): 1237-1251, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29337049

RESUMO

BACKGROUND: Development of collateral circulation after acute ischemic stroke is triggered by shear stress that occurs in pre-existing arterioles. Recently, sphingosine-1-phosphate receptor 1 (S1P1) on endothelial cells was reported to sense shear stress and transduce its signaling pathways. METHODS: BALB/c mice (n = 118) were subjected to permanent middle cerebral artery occlusion (pMCAO) or sham operation. We investigated the effect of an S1P1-selective agonist SEW2871 on leptomeningeal collateral arteries and neurological outcome after pMCAO. RESULTS: Immunohistochemistry showed that without treatment, the expression of S1P1 on endothelial cells of leptomeningeal arteries and capillaries increased early after pMCAO, peaking at 6 hours, whereas a significant increase in the expression of S1P1 in neurons was seen from 24 hours later. After intraperitoneal administration of SEW2871 for 7 days after pMCAO, the number of leptomeningeal collateral arteries was significantly increased, cerebral blood flow improved, infarct volume was decreased, and neurological outcome improved compared with the controls. Significantly increased phosphorylation of endothelial nitric oxide synthase (eNOS) as early as 6 hours after pMCAO and higher expression of tight junction proteins at postoperative day 3 were observed with SEW2871 treatment as assessed by Western blot. Daily administration of SEW2871 also increased capillary density in peri-infarct regions and promoted monocyte/macrophage mobilization to the surface of ischemic cortex at 7 days after pMCAO. CONCLUSIONS: An S1P1-selective agonist enhanced leptomeningeal collateral circulation via eNOS phosphorylation and promoted postischemic angiogenesis with reinforced blood-brain barrier integrity in a mouse model of acute ischemic stroke, leading to smaller infarct volume and better neurological outcome.


Assuntos
Circulação Cerebrovascular/efeitos dos fármacos , Circulação Colateral/efeitos dos fármacos , Infarto da Artéria Cerebral Média/tratamento farmacológico , Meninges/irrigação sanguínea , Meninges/efeitos dos fármacos , Neovascularização Fisiológica/efeitos dos fármacos , Oxidiazóis/farmacologia , Receptores de Lisoesfingolipídeo/agonistas , Tiofenos/farmacologia , Animais , Barreira Hematoencefálica/efeitos dos fármacos , Barreira Hematoencefálica/metabolismo , Barreira Hematoencefálica/patologia , Linhagem Celular , Modelos Animais de Doenças , Células Endoteliais/efeitos dos fármacos , Células Endoteliais/metabolismo , Células Endoteliais/patologia , Infarto da Artéria Cerebral Média/metabolismo , Infarto da Artéria Cerebral Média/patologia , Infarto da Artéria Cerebral Média/fisiopatologia , Macrófagos/efeitos dos fármacos , Macrófagos/metabolismo , Masculino , Meninges/metabolismo , Meninges/patologia , Camundongos Endogâmicos BALB C , Monócitos/efeitos dos fármacos , Monócitos/metabolismo , Óxido Nítrico Sintase Tipo III/metabolismo , Fosforilação , Receptores de Lisoesfingolipídeo/metabolismo , Recuperação de Função Fisiológica , Transdução de Sinais/efeitos dos fármacos , Receptores de Esfingosina-1-Fosfato , Proteínas de Junções Íntimas/metabolismo , Fatores de Tempo
15.
Nat Commun ; 8: 15848, 2017 06 23.
Artigo em Inglês | MEDLINE | ID: mdl-28643780

RESUMO

Electric fields at interfaces exhibit useful phenomena, such as switching functions in transistors, through electron accumulations and/or electric dipole inductions. We find one potentially unique situation in a metal-dielectric interface in which the electric field is atomically inhomogeneous because of the strong electrostatic screening effect in metals. Such electric fields enable us to access electric quadrupoles of the electron shell. Here we show, by synchrotron X-ray absorption spectroscopy, electric field induction of magnetic dipole moments in a platinum monatomic layer placed on ferromagnetic iron. Our theoretical analysis indicates that electric quadrupole induction produces magnetic dipole moments and provides a large magnetic anisotropy change. In contrast with the inability of current designs to offer ultrahigh-density memory devices using electric-field-induced spin control, our findings enable a material design showing more than ten times larger anisotropy energy change for such a use and highlight a path in electric-field control of condensed matter.

16.
Sci Rep ; 7: 46132, 2017 04 13.
Artigo em Inglês | MEDLINE | ID: mdl-28406236

RESUMO

We used x-ray absorption spectroscopy and x-ray magnetic circular dichroism to investigate the effects of inserting Cu into Co/Pt interfaces, and found that a 0.4-nm-thick inserted Cu layer showed perpendicularly magnetized properties induced by the proximity effect through the Co and Pt layers. The dependence of the magnetic properties on the thickness of the Cu layers showed that the proximity effects between Co and Pt with perpendicular magnetic anisotropy can be prevented by the insertion of a Cu layer with a nominal threshold thickness of 0.7 nm. Element-specific magnetization curves were also obtained, demonstrating that the out-of-plane magnetization is induced in the Cu layers of the Co/Cu/Pt structures.

18.
Microscopy (Oxf) ; 63 Suppl 1: i14, 2014 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-25359804

RESUMO

X-ray measurement offers several useful features that are unavailable from other microscopic means including electron-based techniques. By using X-rays, one can observe the internal parts of a thick sample. This technique basically requires no high vacuum environment such that measurements are feasible for wet specimens as well as under strong electric and magnetic fields and even at a high pressure. X-ray spectroscopy using core excitation provides element-selectivity with significant sensitivities to the chemical states and atomic magnetic moments in the matter. Synchrotron radiation sources produce a small and low-divergent X-ray beam, which can be converged to a spot with the size of a micrometer or less using X-ray focusing optics. The recent development in the focusing optics has been driving X-ray microscopy, which has already gone into the era of X-ray nanoscopy. With the use of the most sophisticated focusing devices, an X-ray beam of 7-nm size has successfully been achieved [1]. X-ray microscopy maintains above-mentioned unique features of X-ray technique, being a perfect complement to electron microscopy.In this paper, we present recent studies on magnetic microscopy and local magnetic analysis using hard X-rays. The relevant instrumentation developments are also described. The X-ray nanospectroscopy station of BL39XU at SPring-8 is equipped with a focusing optics consisting of two elliptic mirrors, and a focused X-ray beam with the size of 100 × 100 nm(2) is available [2]. Researchers can perform X-ray absorption spectroscopy: nano-XAFS (X-ray absorption fine structure) using the X-ray beam as small as 100 nm. The available X-ray energy is from 5 to 16 keV, which allows nano-XAFS study at the K edges of 3d transition metals, L edges of rare-earth elements and 5d noble metals. Another useful capability of the nanoprobe is X-ray polarization tunability, enabling magnetic circular dichroism (XMCD) spectroscopy with a sub-micrometer resolution. Scanning XMCD imaging, XMCD measurement in local areas, and element-specific magnetometry for magnetic particles/magnetic devices as small as 100 nm can be performed. Nano-XAFS application includes visualization of the chemical state in a particle catalyst [3] and phase-change memory devices [4]. For magnetic microscopic study, magnetization reversal processes of an individual magnetic CoPt dot in bit-patterned media have directly been observed [2]. Imaging of the chemical distribution and magnetic domain evolution in a Nd-Fe-B sintered magnet in demagnetization processes is presented.

19.
Angew Chem Int Ed Engl ; 53(51): 14110-4, 2014 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-25338523

RESUMO

There is limited information on the mechanism for platinum oxidation and dissolution in Pt/C cathode catalyst layers of polymer electrolyte fuel cells (PEFCs) under the operating conditions though these issues should be uncovered for the development of next-generation PEFCs. Pt species in Pt/C cathode catalyst layers are mapped by a XAFS (X-ray absorption fine structure) method and by a quick-XAFS(QXAFS) method. Information on the site-preferential oxidation and leaching of Pt cathode nanoparticles around the cathode boundary and the micro-crack in degraded PEFCs is provided, which is relevant to the origin and mechanism of PEFC degradation.

20.
J Synchrotron Radiat ; 21(Pt 3): 466-72, 2014 May.
Artigo em Inglês | MEDLINE | ID: mdl-24763633

RESUMO

A diamond phase retarder was applied to control the polarization states of a hard X-ray free-electron laser (XFEL) in the photon energy range 5-20 keV. The horizontal polarization of the XFEL beam generated from the planar undulators of the SPring-8 Angstrom Compact Free-Electron Laser (SACLA) was converted into vertical or circular polarization of either helicity by adjusting the angular offset of the diamond crystal from the exact Bragg condition. Using a 1.5 mm-thick crystal, a high degree of circular polarization, 97%, was obtained for 11.56 keV monochromatic X-rays, whereas the degree of vertical polarization was 67%, both of which agreed with the estimations including the energy bandwidth of the Si 111 beamline monochromator.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...