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1.
Mem Inst Oswaldo Cruz ; 114: e180556, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31241649

RESUMO

BACKGROUND: Angiostrongyliasis is caused by the nematode Angiostrongylus cantonensis and can lead to eosinophilic meningitis and meningoencephalitis in humans. The young adult worms play central pathogenic roles in the central nervous system (CNS); however, the underlying mechanism is unclear. Excretory-secretory products (ESPs) are good investigation targets for studying the relationship between a host and its parasite. OBJECTIVES: We aimed to profile, identify, and characterise the proteins in the ESPs of A. cantonensis young adults. METHODS: The ESPs of young adult worms were collected from culture medium after incubation ranging from 24 to 96 h. Proteomic and bioinformatics analyses were performed to characterise the ESPs. FINDINGS: A total of 51 spots were identified, and the highly expressed proteins included two protein disulphide isomerases, one calreticulin, and three uncharacterised proteins. Subsequently, approximately 254 proteins were identified in the ESPs of A. cantonensis young adults via liquid chromatography-mass spectrometry (LC-MS/MS) analysis, and these were further classified according to their characteristics and biological functions. Finally, we identified the immunoreactive proteins from a reference map of ESPs from A. cantonensis young adults. Approximately eight proteins were identified, including a protein disulphide isomerase, a putative aspartic protease, annexin, and five uncharacterised proteins. The study established and identified protein reference maps for the ESPs of A. cantonensis young adults. MAIN CONCLUSIONS: The identified proteins may be potential targets for the development of diagnostic or therapeutic agents for human angiostrongyliasis.


Assuntos
Angiostrongylus cantonensis/metabolismo , Proteínas de Helminto/análise , Proteômica , Animais , Western Blotting , Cromatografia Líquida/métodos , Eletroforese em Gel Bidimensional , Proteínas de Helminto/metabolismo , Espectrometria de Massas/métodos , Valores de Referência
2.
Mem. Inst. Oswaldo Cruz ; 114: e180556, 2019. tab, graf
Artigo em Inglês | LILACS | ID: biblio-1012674

RESUMO

BACKGROUND Angiostrongyliasis is caused by the nematode Angiostrongylus cantonensis and can lead to eosinophilic meningitis and meningoencephalitis in humans. The young adult worms play central pathogenic roles in the central nervous system (CNS); however, the underlying mechanism is unclear. Excretory-secretory products (ESPs) are good investigation targets for studying the relationship between a host and its parasite. OBJECTIVES We aimed to profile, identify, and characterise the proteins in the ESPs of A. cantonensis young adults. METHODS The ESPs of young adult worms were collected from culture medium after incubation ranging from 24 to 96 h. Proteomic and bioinformatics analyses were performed to characterise the ESPs. FINDINGS A total of 51 spots were identified, and the highly expressed proteins included two protein disulphide isomerases, one calreticulin, and three uncharacterised proteins. Subsequently, approximately 254 proteins were identified in the ESPs of A. cantonensis young adults via liquid chromatography-mass spectrometry (LC-MS/MS) analysis, and these were further classified according to their characteristics and biological functions. Finally, we identified the immunoreactive proteins from a reference map of ESPs from A. cantonensis young adults. Approximately eight proteins were identified, including a protein disulphide isomerase, a putative aspartic protease, annexin, and five uncharacterised proteins. The study established and identified protein reference maps for the ESPs of A. cantonensis young adults. MAIN CONCLUSIONS The identified proteins may be potential targets for the development of diagnostic or therapeutic agents for human angiostrongyliasis.


Assuntos
Humanos , Adolescente , Adulto , Contagem de Ovos de Parasitas , Angiostrongylus cantonensis/parasitologia , Fezes/parasitologia
3.
Artigo em Inglês | MEDLINE | ID: mdl-30600200

RESUMO

BACKGROUND: Angiostrongylus cantonensis is an important etiologic agent of eosinophilic meningitis and/or eosinophilic meningoencephalitis in humans. Th2 responses have been considered to be predominant in non-permissive hosts. However, changes of cytokines in the central nervous system of the host remain unclear. The present study was conducted to determine the temporal-spatial expressions of IL-4, IL-10, and IL-13 in the brains of infected C57BL/6 and BALB/c mice by immunohistochemistry. METHODS: After infecting each mouse with 25 third-stage larvae (L3), brain specimens were collected on day 7 and day 28 post-infection. Each specimen was cut into five sections and stained with corresponding antibodies of the three cytokines. RESULTS: In infected C57BL/6 mice, high IL-4 expressions were found in the isocortex, IL-10 in the isocortex, olfactory area, hippocampus, cerebral nuclei, hypothalamus, cerebellum nuclei, and medulla, and IL-13 in the isocortex and cerebellum. In infected BALB/c mice, IL-4 and IL-10 were highly expressed in the isocortex, olfactory areas, cerebral nuclei, hypothalamus, and cerebellum nuclei and IL-13 in the thalamus and hypothalamus. High levels of the cytokines were usually detected in on day 7 in BALB/c mice and day 28 in C57BL/6 mice. CONCLUSION: The special temporal-spatial expression changes of these three cytokines in the infected mouse brain may explain the differences in the survival and the time of occurrence of immune responses in the hosts after A. cantonensis infection.

4.
J Microbiol Immunol Infect ; 51(4): 559-564, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28690027

RESUMO

BACKGROUND: The prevalence of pinworm infection is extremely low in Taipei, Taiwan. This population study was designed to determine the current status and the associated risk factors of this infection among pre-school children. METHODS: Perianal swab specimens were obtained from the parents or guardians using a two-consecutive-day adhesive cellophane perianal swab kit. Information of family background, personal hygiene, and household sanitary conditions were collected by asking the parents or guardians to complete a questionnaire. RESULTS: Of 44,163 children, 0.21% was found to infect with pinworm. The positive rate was highest in Datong (0.59%) and Nangang (0.58%) Districts and lowest in Neihu District (0.02%). There was no significant difference in the rates by gender (boys 0.24% and girls 0.19%) or school (kindergartens 0.25% and nurseries 0.17%). Significantly higher positive rates were found in children having parent with lower educational level and elder brother(s)/sister(s). Children taking bath by themselves and those sleeping in bed with matting had significantly higher positive rates. Five significant independent predictors of pinworm infection were determined by multivariate analysis: having elder brother(s), having elder sister(s), infrequent washing hands after using toilet facilities, bathing without the help of family members, and sleeping on bed with matting. CONCLUSION: The prevalence of pinworm infection in the pre-school children of Taipei is extremely low and decreasing. Good hand washing habit should be an important preventive measure. Transmission of this infection in pre-school children may occur in the family through their school-age siblings.


Assuntos
Enterobíase/epidemiologia , Enterobius/isolamento & purificação , Animais , Pré-Escolar , Transmissão de Doença Infecciosa/prevenção & controle , Feminino , Higiene das Mãos/métodos , Humanos , Lactente , Controle de Infecções/métodos , Masculino , Prevalência , Fatores de Risco , Instituições Acadêmicas , Estudantes , Inquéritos e Questionários , Taiwan/epidemiologia
5.
Korean J Parasitol ; 55(4): 425-428, 2017 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28877575

RESUMO

Human diphyllobothriasis is a parasitic disease caused by ingestion of larvae (plerocercoids) in raw or undercooked fish and commonly found in temperate areas. Rare cases were reported in tropical or subtropical areas especially in children. The first documented case of pediatric diphyllobothriasis in Taiwan had been reported 11 years ago. Here, we report another 8-year-old girl case who presented with a live noodle-like worm hanging down from her anus, with no other detectable symptoms. We pulled the worm out and found the strobila being 260 cm in length. Examination of gravid proglottids showed that they were wider than their lengths, containing an ovoid cirrus sac in the anterior side and the rosette-shaped uterus. Eggs extracted from the uterus were ovoid and operculated. Diphyllobothrium latum was confirmed by molecular analysis of the mitochondrial DNA cytochrome c oxidase subunit 1 (cox1) gene. The girl was treated with a single oral dose of praziquantel, and no eggs or proglottids were observed from her stool in the subsequent 3 months. The reemergence of human diphyllobothriasis in non-endemic countries is probably due to prevalent habit of eating imported raw fish from endemic areas. This pediatric case raised our concern that human diphyllobothriasis is likely underestimated because of unremarkable symptoms.


Assuntos
Difilobotríase/diagnóstico por imagem , Difilobotríase/parasitologia , Diphyllobothrium/genética , Diphyllobothrium/isolamento & purificação , Técnicas de Diagnóstico Molecular , Administração Oral , Animais , Anti-Helmínticos/administração & dosagem , Criança , DNA de Helmintos/genética , DNA Mitocondrial/genética , Difilobotríase/tratamento farmacológico , Diphyllobothrium/anatomia & histologia , Complexo IV da Cadeia de Transporte de Elétrons/genética , Feminino , Interações Hospedeiro-Parasita , Humanos , Espécies Introduzidas , Contagem de Ovos de Parasitas , Praziquantel/administração & dosagem , Taiwan
6.
Parasit Vectors ; 10(1): 445, 2017 Sep 26.
Artigo em Inglês | MEDLINE | ID: mdl-28950910

RESUMO

BACKGROUND: Angiostrongylus cantonensis is an important causative agent of eosinophilic meningitis and eosinophilic meningoencephalitis in humans. Previous studies have shown that the Sonic hedgehog (Shh) signaling pathway may reduce cell apoptosis by inhibiting oxidative stress in A. cantonensis infection. In this study, we investigated the relationship between cytokine secretion and Shh pathway activation after treatment with excretory/secretory products (ESP) of fifth-stage larval A. cantonensis (L5). RESULTS: The results showed that IL-1ß and IL-6 levels in mouse astrocytes were increased. Moreover, ESP stimulated the protein expression of Shh pathway molecules, including Shh, Ptch, Smo and Gli-1, and induced IL-1ß and IL-6 secretion. The transcription factor nuclear factor-κB (NF-κB) plays an important role in inflammation, and it regulates the expression of proinflammatory genes, including cytokines and chemokines, such as IL-1ß and TNF-α. After ESP treatment, NF-κB induced IL-1ß and IL-6 secretion in astrocytes by activating the Shh signaling pathway. CONCLUSIONS: Overall, the data presented in this study showed that ESP of fifth-stage larval A. cantonensis stimulates astrocyte activation and cytokine generation through NF-κB and the Shh signaling pathway.


Assuntos
Angiostrongylus cantonensis/metabolismo , Astrócitos/metabolismo , Proteínas Hedgehog/metabolismo , Proteínas de Helminto/metabolismo , Interleucina-18/metabolismo , Interleucina-6/metabolismo , NF-kappa B/metabolismo , Infecções por Strongylida/parasitologia , Angiostrongylus cantonensis/química , Angiostrongylus cantonensis/crescimento & desenvolvimento , Animais , Astrócitos/parasitologia , Feminino , Proteínas Hedgehog/genética , Interações Hospedeiro-Parasita , Humanos , Interleucina-18/genética , Interleucina-6/genética , Larva/química , Larva/crescimento & desenvolvimento , Larva/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos BALB C , NF-kappa B/genética , Ratos , Ratos Sprague-Dawley , Transdução de Sinais , Infecções por Strongylida/genética , Infecções por Strongylida/metabolismo
7.
Sci Rep ; 7: 41574, 2017 02 07.
Artigo em Inglês | MEDLINE | ID: mdl-28169282

RESUMO

Angiostrongylus cantonensis, the rat lungworm, is an important aetiologic agent of eosinophilic meningitis and meningoencephalitis in humans. Co-culturing astrocytes with soluble antigens of A. cantonensis activated the Sonic hedgehog (Shh) signalling pathway and inhibited the apoptosis of astrocytes via the activation of Bcl-2. This study was conducted to determine the roles of the Shh signalling pathway, apoptosis, and oxidative stress in astrocytes after treatment with excretory-secretory products (ESP) from A. cantonensis fifth-stage larvae. Although astrocyte viability was significantly decreased after ESP treatment, the expression of Shh signalling pathway related proteins (Shh, Ptch-1 and Gli-1) was significantly increased. However, apoptosis in astrocytes was significantly decreased after activation of the Shh signalling pathway. Moreover, superoxide and hydrogen superoxide levels in astrocytes were significantly reduced after the activation of Shh pathway signalling due to increasing levels of the antioxidants catalase and superoxide dismutase. These findings indicate that the anti-apoptotic effects of the Shh signalling pathway in the astrocytes of mice infected with A. cantonensis are due to reduced levels of oxidative stress caused by the activation of antioxidants.


Assuntos
Angiostrongylus cantonensis/metabolismo , Antígenos de Helmintos/metabolismo , Apoptose , Astrócitos/metabolismo , Proteínas Hedgehog/metabolismo , Estresse Oxidativo , Transdução de Sinais , Angiostrongylus cantonensis/imunologia , Animais , Antígenos de Helmintos/imunologia , Técnicas de Cocultura , Interações Hospedeiro-Parasita , Larva , Camundongos , Ratos , Espécies Reativas de Oxigênio/metabolismo , Superóxido Dismutase/metabolismo
8.
Exp Parasitol ; 157: 177-84, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26299243

RESUMO

Human cerebral angiostrongyliasis becomes an emerging disease in many parts of the world. By postmortem examination, Angiostrongylus cantonensis have been reported to cause severe pathological changes in the central nervous system. The present study was designed to determine the temporal-spatial pathological changes through experimental infections and histopathological examination of permissive (SD rats) and non-permissive (ICR mice) hosts. After infecting SD rats with 25, 50, or 100 third-stage larvae (L3) and ICR mice with 25 L3, one animal from each group was sacrificed daily from day 1 to day 30 post-infection. Each rat brain was cut into six sections and mouse brain into five sections. These sections were stained with haematoxylin and eosin and examined microscopically. Eosinophilic meningitis was found to be the most commonly pathological change and occurred on day 17 post-infection in rats with 25 L3, day 9 in the 50- or 100-L3 groups, and day 12 in infected mice. Thickness of the meninges increased 9-24 folds in infected rats and 89 folds in an infected mouse on day 28. Encephalitis, congestion, perivascular cuffing, and haemorrhage were revealed in infected mice and rats with 100 L3. Fifth-stage larvae were frequently observed in the meninges but occasionally in the parenchyma. Significant correlations between meningitis and presence of larvae in the meninges were found in the three infected rat groups but not in the infected mice. The results indicate that the clinical course of A. cantonensis infection is not self-limited but becomes more severe with the intensity of infection.


Assuntos
Angiostrongylus cantonensis/patogenicidade , Encéfalo/patologia , Meningite/parasitologia , Infecções por Strongylida/patologia , Animais , Cerebelo/patologia , Cérebro/patologia , Masculino , Meninges/parasitologia , Meninges/patologia , Camundongos , Camundongos Endogâmicos ICR , Ratos , Ratos Sprague-Dawley , Análise Espaço-Temporal
9.
Biomed Res Int ; 2015: 674371, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25961032

RESUMO

Angiostrongylus cantonensis infection may cause elevation of ROS and antioxidants in the CSF of infected mice. Astrocytes may protect the surrounding neurons from oxidative stress-induced cell death by secreting Sonic hedgehog (Shh) via the PI3-K/AKT/Bcl-2 pathway. This study was conducted to determine the role of the Shh signaling pathway in A. cantonensis-infected BABL/c mice by coculturing astrocytes with living fifth-stage larvae or soluble antigens. The Shh pathway was activated with corresponding increases in the level of the Shh. Glial fibrillary acidic protein (GFAP) and Shh were increased in astrocyte cocultured with living fifth-stage larvae or soluble antigens. The survival of astrocytes pretreated with Shh was significantly elevated in cocultures with the antigens but reduced by its inhibitor cyclopamine. The expression of GRP78 and Bcl-2 was significantly higher in astrocytes pretreated with recombinant Shh. These findings suggest that the expression of Shh may inhibit cell death by activating Bcl-2 through a GRP78-dependent pathway.


Assuntos
Proteínas de Choque Térmico/biossíntese , Proteínas Hedgehog/genética , Proteínas do Tecido Nervoso/biossíntese , Proteínas Proto-Oncogênicas c-bcl-2/biossíntese , Angiostrongylus cantonensis/patogenicidade , Animais , Apoptose/genética , Astrócitos/metabolismo , Astrócitos/microbiologia , Astrócitos/patologia , Regulação da Expressão Gênica , Proteína Glial Fibrilar Ácida , Proteínas de Choque Térmico/genética , Proteínas Hedgehog/administração & dosagem , Proteínas Hedgehog/metabolismo , Humanos , Camundongos , Proteínas do Tecido Nervoso/genética , Neurônios/metabolismo , Neurônios/microbiologia , Neurônios/patologia , Proteínas Proto-Oncogênicas c-bcl-2/genética , Transdução de Sinais/genética
10.
Parasitol Res ; 113(10): 3591-600, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-25028210

RESUMO

Angiostrongylus cantonensis is an important zoonotic parasite causing eosinophilic meningitis and eosinophilic meningoencephalitis in humans. In this study, the protein expression profiles of the infective third- and pathogenic fifth-stage larvae (L3 and L5) of this parasite were compared by proteomic techniques. Isolated protein samples were separated by two-dimensional gel electrophoresis (2-DE), stained with silver nitrate, and analyzed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS). Proteins from L5 were mainly at pH 5-7 and with molecular weight (MW) 40-100 kDa, whereas those from L3 were at pH 5-6 and with 5-35 kDa. Of 100 protein spots identified, 33 were from L3 whereas 67 from L5 and 63 had known identities, whereas 37 were hypothetical proteins. There were 15 spots of stress proteins, and HSP60 was the most frequently found heat stress proteins in L5. More binding and protein transport-related proteins were found in L5 including peptidylprolyl isomerase (cyclophilin)-like 2, serum albumin, preproalbumin precursor, and dilute class unconventional myosin. L3 had a higher expression of cytoskeleton and membrane proteins than L5. In addition, four protein spots were identified in the sera of the rat host by Western blot analysis. The present proteomic study revealed different protein expression profiles in L3 and L5 of A. cantonensis. These changes may reflect the development of L3 from the poikilothermic snails to L5 in the homoeothemic rats. This information may be useful for the finding of stage-specific proteins and biomarker for diagnosis of angiostrongyliasis.


Assuntos
Angiostrongylus cantonensis/metabolismo , Meningite/parasitologia , Proteoma , Proteômica , Infecções por Strongylida/parasitologia , Animais , Biomphalaria/parasitologia , Eletroforese em Gel Bidimensional , Feminino , Humanos , Concentração de Íons de Hidrogênio , Larva , Masculino , Meningoencefalite/parasitologia , Peso Molecular , Proteínas/metabolismo , Ratos , Ratos Sprague-Dawley , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz
11.
Parasitol Res ; 113(6): 2143-52, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24696276

RESUMO

Asparaginyl endopeptidase, also known as legumain, is a family of cysteine proteases in many organisms. In this study, an asparaginyl endopeptidase (Ac-AEP) was identified from the cDNA library of Angiostrongylus cantonensis. The full-length of Ac-AEP was determined to be 1,472 bp with an open reading frame of 1,341 bp encoding a putative protein with 446 amino acids. This putative protein was determined to have 37-65% identity in the amino acid sequences of the asparaginyl endopeptidases of other parasitic helminths. By real-time quantitative PCR analysis, Ac-AEP was revealed to be more abundantly expressed in the female adult worms than in other development stages. A recombinant asparaginyl endopeptidase (rAc-AEP) was then produced by a Pichia pastoris expression system. Posttranslational modification was shown to occur via N-linked glycosylation in this recombinant enzyme. The proteolytic activity of rAc-AEP was inhibited by iodoacetamide but not affected by E64, pepatain A, AEBSF, and EDTA. Moreover, the purified rAc-AEP was recognized by IgG in serum samples from BALB/c or ICR mice with A. cantonensis infection and patients with eosinophilic meningitis. These findings indicate that the rAc-AEP may have the potential for detecting A. cantonensis infection.


Assuntos
Angiostrongylus cantonensis/enzimologia , Cisteína Endopeptidases/metabolismo , Sequência de Aminoácidos , Angiostrongylus cantonensis/genética , Animais , Anticorpos Anti-Helmínticos , Especificidade de Anticorpos , Composição de Bases , Clonagem Molecular , Cisteína Endopeptidases/química , Cisteína Endopeptidases/genética , Feminino , Regulação Enzimológica da Expressão Gênica , Biblioteca Gênica , Humanos , Imunoglobulina G/sangue , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos ICR , Dados de Sequência Molecular , Pichia/genética , Pichia/metabolismo , Infecções por Strongylida
12.
ACS Nano ; 8(1): 443-8, 2014 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-24359599

RESUMO

Graphene is expected to enable superior corrosion protection due to its impermeability and chemical inertness. Previous reports, however, demonstrate limited corrosion inhibition and even corrosion enhancement of graphene on metal surfaces. To enable the reliable and complete passivation, the origin of the low inhibition efficiency of graphene was investigated. Combining electrochemical and morphological characterization techniques, nanometer-sized structural defects in chemical vapor deposition grown graphene were found to be the cause for the limited passivation effect. Extremely fast mass transport on the order of meters per second both across and parallel to graphene layers results in an inhibition efficiency of only ∼50% for Cu covered with up to three graphene layers. Through selective passivation of the defects by atomic layer deposition (ALD) an enhanced corrosion protection of more than 99% was achieved, which compares favorably with commercial corrosion protection methods.

13.
Parasitol Res ; 112(9): 3193-202, 2013 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-23828188

RESUMO

Angiostrongylus cantonensis is an important zoonotic nematode. It is the causative agent of eosinophilic meningitis and eosinophilic meningoencephalitis in humans. However, information of this parasite at the genomic level is very limited. In the present study, the transcriptomic profiles of the fifth-stage larvae (L5) of A. cantonensis were investigated by next-generation sequencing (NGS). In the NGS database established from the larvae isolated from the brain of Sprague-Dawley rats, 31,487 unique genes with a mean length of 617 nucleotides were assembled. These genes were found to have a 46.08% significant similarity to Caenorhabditis elegans by BLASTx. They were then compared with the expressed sequence tags of 18 other nematodes, and significant matches of 36.09-59.12% were found. Among these genes, 3,338 were found to participate in 124 Kyoto Encyclopedia of Genes and Genomes pathways. These pathways included 1,514 metabolisms, 846 genetic information processing, 358 environmental information processing, 264 cellular processes, and 91 organismal systems. Analysis of 30,816 sequences with the gene ontology database indicated that their annotations included 5,656 biological processes (3,364 cellular processes, 3,061 developmental processes, and 3,191 multicellular organismal processes), 7,218 molecular functions (4,597 binding and 3,084 catalytic activities), and 4,719 cellular components (4,459 cell parts and 4,466 cells). Moreover, stress-related genes (112 heat stress and 33 oxidation stress) and genes for proteases (159) were not uncommon. This study is the first NGS-based study to set up a transcriptomic database of A. cantonensis L5. The results provide new insights into the survival, development, and host-parasite interactions of this blood-feeding nematode.


Assuntos
Angiostrongylus cantonensis/genética , Meningoencefalite/parasitologia , Infecções por Strongylida/parasitologia , Transcriptoma/genética , Angiostrongylus cantonensis/citologia , Angiostrongylus cantonensis/crescimento & desenvolvimento , Animais , DNA Complementar/química , DNA Complementar/genética , DNA de Helmintos/genética , Etiquetas de Sequências Expressas , Feminino , Perfilação da Expressão Gênica , Sequenciamento de Nucleotídeos em Larga Escala , Interações Hospedeiro-Parasita , Humanos , Larva , Masculino , Anotação de Sequência Molecular , RNA de Helmintos/genética , Ratos , Ratos Sprague-Dawley , Análise de Sequência de DNA , Homologia de Sequência , Zoonoses
14.
Sci Rep ; 3: 2274, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23881449

RESUMO

We have studied a hybrid nanoelectronic system which consists of an AlGaAs/GaAs two-dimensional electron gas (2DEG) in close proximity (~70 nm) to an Al superconducting nanofilm. By tuning the current through the Al film, we can change the conductance of the 2DEG and furthermore vary the effective disorder in the Al superconducting film in a controllable way. When a high current is injected into the film, screening which couples the Al film and the 2DEG results in a collapse of anti-symmetric behavior in the current-voltage characteristics, V(I) ~ -V(-I), which holds true in a conventional superconductor. Our results may open a new avenue of experimentally realizing a superconducting diode.

15.
Nanoscale Res Lett ; 6(1): 139, 2011 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-21711656

RESUMO

A delta-doped quantum well with additional modulation doping may have potential applications. Utilizing such a hybrid system, it is possible to experimentally realize an extremely high two-dimensional electron gas (2DEG) density without suffering inter-electronic-subband scattering. In this article, the authors report on transport measurements on a delta-doped quantum well system with extra modulation doping. We have observed a 0-10 direct insulator-quantum Hall (I-QH) transition where the numbers 0 and 10 correspond to the insulator and Landau level filling factor ν = 10 QH state, respectively. In situ titled-magnetic field measurements reveal that the observed direct I-QH transition depends on the magnetic component perpendicular to the quantum well, and the electron system within this structure is 2D in nature. Furthermore, transport measurements on the 2DEG of this study show that carrier density, resistance and mobility are approximately temperature (T)-independent over a wide range of T. Such results could be an advantage for applications in T-insensitive devices.

16.
Nanoscale Res Lett ; 6(1): 102, 2011 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-24576326

RESUMO

Magnetotransport measurements are performed on an aluminum thin film grown on a GaAs substrate. A crossover from electron- to hole-dominant transport can be inferred from both longitudinal resistivity and Hall resistivity with increasing the perpendicular magnetic field B. Also, phenomena of localization effects can be seen at low B. By analyzing the zero-field resistivity as a function of temperature T, we show the importance of surface scattering in such a nanoscale film.

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