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1.
Insect Mol Biol ; 28(1): 86-98, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30126008

RESUMO

Eusocial insects have polyphenic caste systems in which each caste exhibits characteristic morphology and behaviour. In insects, caste systems arose independently in different lineages, such as Isoptera and Hymenoptera. Although partial molecular mechanisms for the development of eusociality in termites have been clarified by the functional analysis of genes and hormones, the contribution of microRNAs (miRNAs) to caste differentiation is unknown. To understand the role of miRNAs in termite caste polyphenism, we performed small RNA sequencing in a subterranean termite (Reticulitermes speratus) and identified the miRNAs that were specifically expressed in the soldier and worker castes. Of the 550 miRNAs annotated in the R. speratus genome, 74 were conserved in insects and 174 were conserved in other termite species. We found that eight miRNAs (mir-1, mir-125, mir-133, mir-2765, mir-87a and three termite-specific miRNAs) are differentially expressed (DE) in soldiers and workers of R. speratus. This differential expression was experimentally verified for five miRNAs by real-time quantitative PCR. Further, four of the eight DE miRNAs in soldier and worker termite castes were also differentially expressed in hymenopteran castes. The finding that Isoptera and Hymenoptera shared several DE miRNAs amongst castes suggests that these miRNAs evolved independently in these phylogenetically distinct lineages.


Assuntos
Hierarquia Social , Isópteros/metabolismo , MicroRNAs/metabolismo , Animais , Feminino , Masculino , Análise de Sequência de RNA
2.
Am J Transplant ; 18(6): 1328-1339, 2018 06.
Artigo em Inglês | MEDLINE | ID: mdl-29288556

RESUMO

Tolerance induction to prevent allograft rejection is a long-standing clinical goal. However, convincing and dependable tolerance identification remains elusive. Hypothesizing that intragraft RNA expression is informative in both rejection and tolerance, we profile intrarenal allograft RNA expression in a mixed chimerism renal allograft model of cynomolgus monkeys and identify biologically significant tolerance. Analysis of 67 genes identified 3 dominant factors, each with a different pattern of gene expressions, relating to T cell-mediated rejection (TCMR), chronic antibody-mediated rejection (CAMR), or Tolerance. Clustering these 3 factors created 9 groups. One of the 9 clustered groups, the Tolerance cluster, showed the lowest probability of terminal rejection, the longest duration of allograft survival, and the lowest relative risk of terminal rejection. The Tolerance factor consists of a novel set of gene expressions including cytokine and immunoregulatory genes adding mechanistic insights into tolerance. The Tolerance factor could not be identified within current pathologic diagnostic categories. The TCMR and CAMR factors are dominant to the Tolerance factor, causing rejection even if the Tolerance factor is present. These 3 factors determine the probability of terminal rejection or tolerance. This novel a posteriori approach permits identification of pathways of rejection, including tolerance.


Assuntos
Perfilação da Expressão Gênica , Rejeição de Enxerto/imunologia , Transplante de Rim , Primatas/imunologia , RNA/genética , Tolerância ao Transplante , Animais , Sobrevivência de Enxerto/imunologia , Imunossupressores/uso terapêutico , Macaca fascicularis
3.
Am J Transplant ; 18(6): 1340-1350, 2018 06.
Artigo em Inglês | MEDLINE | ID: mdl-29286578

RESUMO

RNA transcript expression estimates are a promising method to study the mechanisms and classification of renal allograft rejections. Here we use the Nanostring platform to profile RNA expression in renal allografts in a nonhuman primate (NHP), the Cynomolgus monkey. We analyzed protocol and indication 278 archival renal allograft samples, both protocol and indication from 76 animals with diagnoses of chronic antibody-mediated rejection (CAMR), acute cellular rejection (TCMR), and MIXED (both CAMR and TCMR), plus normals and samples with no pathological rejection using a Cynomolgus-specific probe set of 67 genes. Analysis identified RNA expression heterogeneity of endothelial and NK genes within CAMR and TCMR, including the stages of CAMR. Three factors were partitioned into additional groups. One group with the longest allograft survival time is pure CAMR without NK or CD3. Three mixed groups show variation in NK and CD3. TCMR was split into 2 groups with variation in NK genes. Additional validation of the complete gene-set correlated many of the genes with diagnoses of CAMR, MIXED, and TCMR rejections and with Banff histologic criteria defined in human subjects. These NHP data demonstrate the utility of RNA expression profiling to identify additional heterogeneity of endothelial and NK RNA gene expressions.


Assuntos
Endotélio/metabolismo , Perfilação da Expressão Gênica , Transplante de Rim , Células Matadoras Naturais/metabolismo , Animais , Rejeição de Enxerto , Sobrevivência de Enxerto , Macaca fascicularis , Transplante Homólogo
4.
Nat Commun ; 8(1): 173, 2017 08 02.
Artigo em Inglês | MEDLINE | ID: mdl-28765525

RESUMO

The dynamic interaction between the traveling charges and the molecular vibrations is critical for the charge transport in organic semiconductors. However, a direct evidence of the expected impact of the charge-phonon coupling on the band dispersion of organic semiconductors is yet to be provided. Here, we report on the electronic properties of rubrene single crystal as investigated by angle resolved ultraviolet photoelectron spectroscopy. A gap opening and kink-like features in the rubrene electronic band dispersion are observed. In particular, the latter results in a large enhancement of the hole effective mass (> 1.4), well above the limit of the theoretical estimations. The results are consistent with the expected modifications of the band structures in organic semiconductors as introduced by hole-phonon coupling effects and represent an important experimental step toward the understanding of the charge localization phenomena in organic materials.The charge transport properties in organic semiconductors are affected by the impact of molecular vibrations, yet it has been challenging to quantify them to date. Here, Bussolotti et al. provide direct experimental evidence on the band dispersion modified by molecular vibrations in a rubrene single crystal.

5.
Am J Transplant ; 17(11): 2841-2850, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28444814

RESUMO

Molecular testing represents a promising adjunct for the diagnosis of antibody-mediated rejection (AMR). Here, we apply a novel gene expression platform in sequential formalin-fixed paraffin-embedded samples from nonhuman primate (NHP) renal transplants. We analyzed 34 previously described gene transcripts related to AMR in humans in 197 archival NHP samples, including 102 from recipients that developed chronic AMR, 80 from recipients without AMR, and 15 normal native nephrectomies. Three endothelial genes (VWF, DARC, and CAV1), derived from 10-fold cross-validation receiver operating characteristic curve analysis, demonstrated excellent discrimination between AMR and non-AMR samples (area under the curve = 0.92). This three-gene set correlated with classic features of AMR, including glomerulitis, capillaritis, glomerulopathy, C4d deposition, and DSAs (r = 0.39-0.63, p < 0.001). Principal component analysis confirmed the association between three-gene set expression and AMR and highlighted the ambiguity of v lesions and ptc lesions between AMR and T cell-mediated rejection (TCMR). Elevated three-gene set expression corresponded with the development of immunopathological evidence of rejection and often preceded it. Many recipients demonstrated mixed AMR and TCMR, suggesting that this represents the natural pattern of rejection. These data provide NHP animal model validation of recent updates to the Banff classification including the assessment of molecular markers for diagnosing AMR.


Assuntos
Rejeição de Enxerto/etiologia , Sobrevivência de Enxerto/imunologia , Isoanticorpos/efeitos adversos , Transplante de Rim/efeitos adversos , Aloenxertos , Animais , Biomarcadores/análise , Doença Crônica , Perfilação da Expressão Gênica , Rejeição de Enxerto/diagnóstico , Humanos , Macaca fascicularis , Fenótipo , Curva ROC , Estudos Retrospectivos
6.
Phys Rev Lett ; 117(5): 056403, 2016 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-27517783

RESUMO

We present an angle-resolved photoemission study of the electronic structure of the three-dimensional pyrochlore iridate Nd_{2}Ir_{2}O_{7} through its magnetic metal-insulator transition. Our data reveal that metallic Nd_{2}Ir_{2}O_{7} has a quadratic band, touching the Fermi level at the Γ point, similar to that of Pr_{2}Ir_{2}O_{7}. The Fermi node state is, therefore, a common feature of the metallic phase of the pyrochlore iridates. Upon cooling below the transition temperature, this compound exhibits a gap opening with an energy shift of quasiparticle peaks like a band gap insulator. The quasiparticle peaks are strongly suppressed, however, with further decrease of temperature, and eventually vanish at the lowest temperature, leaving a nondispersive flat band lacking long-lived electrons. We thereby identify a remarkable crossover from Slater to Mott insulators with decreasing temperature. These observations explain the puzzling absence of Weyl points in this material, despite its proximity to the zero temperature metal-insulator transition.

7.
Nat Commun ; 6: 10042, 2015 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-26640114

RESUMO

Strong spin-orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin-orbit and strong electron-electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour is predicted, for which we observe some evidence. Our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states.

8.
Phys Rev Lett ; 115(10): 106803, 2015 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-26382694

RESUMO

We performed high-resolution photon-energy and polarization-dependent ARPES measurements on ultrathin Bi(111) films [6-180 bilayers (BL), 2.5-70 nm thick] formed on Si(111). In addition to the extensively studied surface states (SSs), the edge of the bulk valence band was clearly measured by using S-polarized light. We found direct evidence that this valence band edge, which forms a hole pocket in the bulk Bi crystal, does not cross the Fermi level for the 180 BL thick film. This is consistent with the predicted semimetal-to-semiconductor transition due to the quantum-size effect [V.B. Sandomirskii, Sov. Phys. JETP 25, 101 (1967)]. However, it became metallic again when the film thickness was decreased (below 30 BL). A plausible explanation for this phenomenon is the modification of the charge neutrality condition due to the size effect of the SSs.

9.
Phys Rev Lett ; 115(25): 256405, 2015 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-26722935

RESUMO

We study the electronic structure of bulk single crystals and epitaxial films of Fe_{3}O_{4}. Fe 2p core level spectra show clear differences between hard x-ray (HAX) and soft x-ray photoemission spectroscopy (PES). The bulk-sensitive spectra exhibit temperature (T) dependence across the Verwey transition, which is missing in the surface-sensitive spectra. By using an extended impurity Anderson full-multiplet model-and in contrast to an earlier peak assignment-we show that the two distinct Fe species (A and B site) and the charge modulation at the B site are responsible for the newly found double peaks in the main peak above T_{V} and its T-dependent evolution. The Fe 2p HAXPES spectra show a clear magnetic circular dichroism (MCD) in the metallic phase of magnetized 100-nm-thick films. The model calculations also reproduce the MCD and identify the contributions from magnetically distinct A and B sites. Valence band HAXPES shows a finite density of states at E_{F} for the polaronic half metal with a remnant order above T_{V} and a clear gap formation below T_{V}. The results indicate that the Verwey transition is driven by changes in the strongly correlated and magnetically active B-site electronic states, consistent with resistivity and optical spectra.

10.
J Physiol Pharmacol ; 63(1): 61-8, 2012 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-22460462

RESUMO

Hydrogen sulfide (H(2)S) is generated from L-cysteine by certain enzymes including cystathionine-γ-lyase (CSE) and cystathionine-ß-synthase (CBS), and causes excitation of nociceptors mainly via activation of Ca(v)3.2 T-type Ca(2+) channels in the peripheral tissue, facilitating somatic and colonic pain. Here, we investigated whether sensory nerves and Ca(v)3.2 are involved in the H(2)S-induced mucosal cytoprotection against 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis in rats. Colitis was evaluated 3 days after intracolonic (i.c.) TNBS in the rat. Phosphorylation of ERK in the spinal dorsal horn was detected by immunohistochemistry. Protein expression of Ca(v)3.2 in the dorsal root ganglia (DRG) and of CSE and CBS in the colon was determined by Western blotting. Repeated i.c. NaHS significantly suppressed the TNBS-induced colitis in rats, an effect prevented by ablation of sensory nerves with repeated administration of capsaicin. Repeated pretreatment with T-type Ca(2+) channel blockers including ethosuximide significantly reduced the protective effects of repeated i.c. NaHS in the rats with TNBS-induced colitis. A single i.c. administration of NaHS induced ethosuximide-sensitive prompt phosphorylation of ERK in the spinal dorsal horn at T13 and L6-S1 levesl in the rats 1 day or 3 days after TNBS treatment, but not in naive rats. Ca(v)3.2 protein was upregulated in DRG 1 day after i.c. TNBS in rats, while CSE, but not CBS, protein was downregulated in the colon. Our findings suggest that luminal H(2)S causes excitation of sensory nerves most probably by activating Ca(v)3.2 T-type Ca(2+) channels that are upregulated in the early stage of colitis, leading to colonic mucosal cytoprotection in rats.


Assuntos
Canais de Cálcio Tipo T/metabolismo , Colo/efeitos dos fármacos , Citoproteção/efeitos dos fármacos , Sulfeto de Hidrogênio/farmacologia , Mucosa Intestinal/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Animais , Bloqueadores dos Canais de Cálcio/farmacologia , Capsaicina/farmacologia , Colite/induzido quimicamente , Colite/tratamento farmacológico , Colite/metabolismo , Colo/metabolismo , Cistationina beta-Sintase/metabolismo , Cistationina gama-Liase/metabolismo , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/metabolismo , Mucosa Intestinal/metabolismo , Masculino , Mucosa/efeitos dos fármacos , Mucosa/metabolismo , Neurônios/metabolismo , Nociceptores/efeitos dos fármacos , Nociceptores/metabolismo , Dor/tratamento farmacológico , Dor/metabolismo , Fosforilação/efeitos dos fármacos , Células do Corno Posterior/efeitos dos fármacos , Células do Corno Posterior/metabolismo , Ratos , Ratos Wistar , Células Receptoras Sensoriais/efeitos dos fármacos , Células Receptoras Sensoriais/metabolismo , Coluna Vertebral/efeitos dos fármacos , Coluna Vertebral/metabolismo , Ácido Trinitrobenzenossulfônico/efeitos adversos
11.
J Physiol Pharmacol ; 63(6): 571-6, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23388472

RESUMO

To clarify the relationship between Helicobacter pylori (H. pylori), a risk factor for gastritis, peptic ulcer and gastric cancer, and proteinase-activated receptors (PARs) that contribute to inflammatory responses, we determined and characterized the biological activity of H. pylori components in the mammalian cells that express PARs. The activity of H. pylori extracts was assessed in distinct cell lines with high expression of PAR1 (RGM1 cells), PAR2 (A549 cells), or PAR2 and PAR4 (HCT-15 cells). A PAR1-activating peptide (AP), but not H. pylori extracts, caused prostaglandin E2 (PGE2) release in RGM1 cells. On the other hand, H. pylori extracts produced release of PGE2 and interleukin-8 (IL-8) in A549 and HCT-15 cells, respectively, as a PAR2-AP did. The activity of H. pylori extracts in A549 cells was not affected by a proteinase inhibitor or exposure to boiling, but abolished by inhibitors of lipopolysaccharide (LPS), IRAK-1/4 or NF-κB. The activity of H. pylori extracts in HCT-15 cells was partially suppressed by boiling or the proteinase inhibitor. In rat platelets that express PAR4 and PAR3, like a PAR4-AP, H. pylori extracts induced aggregation when assessed in platelet rich plasma, an effect unaffected by the proteinase inhibitor, but did not cause aggregation of washed rat platelets that responded to the PAR4-AP or thrombin. The present study thus shows the biological activities of H. pylori extracts in A549 and HCT-15 cells or rat platelets, and suggests that they are not mediated by any PAR-activating proteinases, but may involve the other pathogenic factors including LPS.


Assuntos
Helicobacter pylori/metabolismo , Receptores Ativados por Proteinase/metabolismo , Animais , Proteínas de Bactérias/metabolismo , Plaquetas/metabolismo , Linhagem Celular Tumoral , Dinoprostona/metabolismo , Temperatura Alta , Humanos , Interleucina-8/metabolismo , Lipopolissacarídeos/metabolismo , Masculino , Oligopeptídeos/farmacologia , Agregação Plaquetária , Inibidores de Proteases/farmacologia , Desnaturação Proteica , Inibidores de Proteínas Quinases/farmacologia , Ratos , Ratos Wistar , Receptor PAR-1/metabolismo , Receptor PAR-2/metabolismo , Receptores Ativados por Proteinase/efeitos dos fármacos , Receptores de Trombina/metabolismo , Trombina/metabolismo
12.
Phys Rev Lett ; 109(22): 227401, 2012 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-23368158

RESUMO

We studied the atomic and electronic structures of ultrathin Bi(111) films grown on Bi(2)Te(3) by means of angle-resolved photoemission, first-principles calculations, and low-energy electron diffraction. These Bi films were found to be strained due to the influence of the substrate. Accordingly, the band structure is affected and Bi undergoes a topological phase transition; it is shown that the Z(2) topological invariant in three dimensions switches from +1 (trivial) to -1 (nontrivial or topological). This was clearly confirmed from the change in the surface-state dispersion near the Fermi level. Our discovery offers a method to produce novel topological systems from simple materials.

13.
Neuroscience ; 188: 148-56, 2011 Aug 11.
Artigo em Inglês | MEDLINE | ID: mdl-21596106

RESUMO

Hydrogen sulfide (H2S), a gasotransmitter, facilitates pain sensation by targeting Ca(v)3.2 T-type calcium channels. The H2S/Ca(v)3.2 pathway appears to play a role in the maintenance of surgically evoked neuropathic pain. Given evidence that chemotherapy-induced neuropathic pain is blocked by ethosuximide, known to block T-type calcium channels, we examined if more selective T-type calcium channel blockers and also inhibitors of cystathionine-γ-lyase (CSE), a major H2S-forming enzyme in the peripheral tissue, are capable of reversing the neuropathic pain evoked by paclitaxel, an anti-cancer drug. It was first demonstrated that T-type calcium channel blockers, NNC 55-0396, known to inhibit Ca(v)3.1, and mibefradil inhibited T-type currents in Ca(v)3.2-transfected HEK293 cells. Repeated systemic administration of paclitaxel caused delayed development of mechanical hyperalgesia, which was reversed by single intraplantar administration of NNC 55-0396 or mibefradil, and by silencing of Ca(v)3.2 by antisense oligodeoxynucleotides. Systemic administration of dl-propargylglycine and ß-cyanoalanine, irreversible and reversible inhibitors of CSE, respectively, also abolished the established neuropathic hyperalgesia. In the paclitaxel-treated rats, upregulation of Ca(v)3.2 and CSE at protein levels was not detected in the dorsal root ganglia (DRG), spinal cord or peripheral tissues including the hindpaws, whereas H(2)S content in hindpaw tissues was significantly elevated. Together, our study demonstrates the effectiveness of NNC 55-0396 in inhibiting Ca(v)3.2, and then suggests that paclitaxel-evoked neuropathic pain might involve the enhanced activity of T-type calcium channels and/or CSE in rats, but not upregulation of Ca(v)3.2 and CSE at protein levels, differing from the previous evidence for the neuropathic pain model induced by spinal nerve cutting in which Ca(v)3.2 was dramatically upregulated in DRG.


Assuntos
Antineoplásicos/toxicidade , Canais de Cálcio Tipo T/metabolismo , Sulfeto de Hidrogênio/metabolismo , Hiperalgesia/metabolismo , Neuralgia/metabolismo , Paclitaxel/toxicidade , Animais , Benzimidazóis/farmacologia , Western Blotting , Ciclopropanos/farmacologia , Inibidores Enzimáticos/farmacologia , Células HEK293 , Humanos , Hiperalgesia/induzido quimicamente , Masculino , Naftalenos/farmacologia , Neuralgia/induzido quimicamente , Técnicas de Patch-Clamp , Ratos , Ratos Wistar
14.
Nat Mater ; 10(4): 273-7, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-21358648

RESUMO

Pairing symmetry is a fundamental property that characterizes a superconductor. For the iron-based high-temperature superconductors, an s(±)-wave pairing symmetry has received increasing experimental and theoretical support. More specifically, the superconducting order parameter is an isotropic s-wave type around a particular Fermi surface, but it has opposite signs between the hole Fermi surfaces at the zone centre and the electron Fermi surfaces at the zone corners. Here we report the low-energy electronic structure of the newly discovered superconductors, A(x)Fe(2)Se(2) (A=K,Cs) with a superconducting transition temperature (Tc) of about 30 K. We found A(x)Fe(2)Se(2) (A=K,Cs) is the most heavily electron-doped among all iron-based superconductors. Large electron Fermi surfaces are observed around the zone corners, with an almost isotropic superconducting gap of ~10.3 meV, whereas there is no hole Fermi surface near the zone centre, which demonstrates that interband scattering or Fermi surface nesting is not a necessary ingredient for the unconventional superconductivity in iron-based superconductors. Thus, the sign change in the s(±) pairing symmetry driven by the interband scattering as suggested in many weak coupling theories becomes conceptually irrelevant in describing the superconducting state here. A more conventional s-wave pairing is probably a better description.

15.
Neuroscience ; 181: 257-64, 2011 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-21354272

RESUMO

Luminal hydrogen sulfide (H(2)S) causes colonic pain and referred hyperalgesia in mice through activation of T-type Ca(2+) channels. To test a hypothesis that H(2)S might chelate and remove endogenous Zn(2+) that inhibits the Ca(v)3.2 isoform of T-type Ca(2+) channels, facilitating visceral nociception, we asked if intracolonic (i.col.) administration of Zn(2+) chelators mimics H(2)S-induced visceral nociception. Visceral nociceptive behavior and referred abdominal allodynia/hyperalgesia were determined after i.col. administration of NaHS, a donor for H(2)S, or Zn(2+) chelators in mice. Phospholylation of extracellular signal-regulated protein kinase (ERK) in the spinal cord was analyzed by immunohistochemistry. The visceral nociceptive behavior and referred abdominal allodynia/hyperalgesia caused by i.col. NaHS in mice were abolished by i.col. preadministration of zinc chloride (ZnCl(2)), known to selectively inhibit Ca(v)3.2, but not Ca(v)3.1 or Ca(v)3.3, isoforms of T-type Ca(2+) channels, and by i.p. preadministration of mibefradil, a pan-T-type Ca(2+) channel blocker. Two distinct Zn(2+) chelators, N,N,N',N'-tetrakis(2-pyridylmethyl)ehylenediamine (TPEN) and dipicolinic acid, when administered i.col., mimicked the NaHS-evoked visceral nociceptive behavior and referred abdominal allodynia/hyperalgesia, which were inhibited by mibefradil and by NNC 55-0396, another T-type Ca(2+) channel blocker. Like i.col. NaHS, i.col. TPEN caused prompt phosphorylation of ERK in the spinal dorsal horn, an effect blocked by mibefradil. Removal of luminal Zn(2+) by H(2)S and other Zn(2+) chelators thus produces colonic pain through activation of T-type Ca(2+) channels, most probably of the Ca(v)3.2 isoform. Hence, endogenous Zn(2+) is considered to play a critical role in modulating visceral pain.


Assuntos
Dor Abdominal/induzido quimicamente , Canais de Cálcio Tipo T/efeitos dos fármacos , Quelantes/toxicidade , Colo/efeitos dos fármacos , Sulfeto de Hidrogênio/toxicidade , Zinco/deficiência , Dor Abdominal/enzimologia , Dor Abdominal/fisiopatologia , Animais , Canais de Cálcio Tipo T/fisiologia , Colo/inervação , Colo/fisiopatologia , Modelos Animais de Doenças , Masculino , Camundongos , Mimetismo Molecular/fisiologia
16.
Phys Rev Lett ; 106(4): 047602, 2011 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-21405362

RESUMO

We study the surface and bulk electronic structure of the room-temperature ferromagnet Co∶TiO(2) anatase films using soft- and hard-x-ray photoemission spectroscopy with probe sensitivities of ∼1 and ∼10 nm, respectively. We obtain direct evidence of metallic Ti(3+) states in the bulk, which get suppressed to give a surface semiconductor, thus indicating the difference in electronic structure between surface and bulk. X-ray absorption and resonant photoemission spectroscopy reveal Ti(3+) electrons at the Fermi level (E(F)) and high-spin Co(2+) electrons occurring away from E(F). The results show the importance of the charge neutrality condition: Co(2+)+V(O)(2-)+2Ti(4+)↔Co(2+)+2Ti(3+) (V(O) is oxygen vacancy), which gives rise to the elusive Ti 3d carriers mediating ferromagnetism via the Co 3d-O 2p-Ti 3d exchange interaction pathway of the occupied orbitals.

17.
Phys Rev Lett ; 104(23): 236404, 2010 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-20867257

RESUMO

We investigate the electronic structure of chromium nitride (CrN) across the first-order magnetostructural transition at T(N)∼286 K. Resonant photoemission spectroscopy (PES) shows a gap in the 3d partial density of states at the Fermi level and an on-site Coulomb energy U∼4.5 eV, indicating strong electron-electron correlations. Bulk-sensitive high-resolution (6 meV) laser PES reveals a clear Fermi edge indicating an antiferromagnetic metal below T(N). Hard x-ray Cr 2p core-level PES shows T-dependent changes across T(N) which originate from screening due to coherent states as substantiated by cluster model calculations using the experimentally observed U. Electrical resistivity confirms an insulator above T(N) (E(g)∼70 meV) becoming a disordered metal below T(N). Thus, CrN transforms from a correlated insulator to an antiferromagnetic metal, coupled to the magnetostructural transition.

18.
Phys Rev Lett ; 104(24): 247201, 2010 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-20867330

RESUMO

Electronic structures of the quantum critical superconductor ß-YbAlB4 and its polymorph α-YbAlB4 are investigated by using bulk-sensitive hard x-ray photoemission spectroscopy. From the Yb 3d core level spectra, the values of the Yb valence are estimated to be ∼2.73 and ∼2.75 for α- and ß-YbAlB4, respectively, thus providing clear evidence for valence fluctuations. The valence band spectra of these compounds also show Yb2+ peaks at the Fermi level. These observations establish an unambiguous case of a strong mixed valence at quantum criticality for the first time among heavy fermion systems, calling for a novel scheme for a quantum critical model beyond the conventional Doniach picture in ß-YbAlB4.

19.
Phys Rev Lett ; 104(10): 106401, 2010 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-20366439

RESUMO

The Magnéli phase Ti(4)O(7) exhibits two sharp jumps in resistivity with coupled structural transitions as a function of temperature at T(c1) approximately 142 K and T(c2) = 154 K. We have studied electronic structure changes across the two transitions using 7 eV laser, soft x-ray, and hard x-ray (HX) photoemission spectroscopy (PES). Ti 2p-3d resonant PES and HX PES show a clear metallic Fermi edge and mixed valency above T(c2). The low temperature phase below T(c1) shows a clear insulating gap of approximately 100 meV. The intermediate phase between T(c1) and T(c2) indicates a pseudogap coexisting with remnant coherent states. HX PES and complementary calculations have confirmed the coherent screening in the strongly correlated intermediate phase. The results suggest the existence of a highly anomalous state sandwiched between the mixed-valent Fermi liquid and charge ordered Mott-insulating phase in Ti(4)O(7).

20.
J Phys Condens Matter ; 22(9): 095502, 2010 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-21389417

RESUMO

CeOs(4)Sb(12) and CeFe(4)P(12) are classified as Kondo semiconductors, which show coupled changes in electrical transport, thermodynamic and magnetic properties with a low-temperature semiconductor-like electrical resistivity. We have carried out core level and valence band photoemission spectroscopy on single crystal CeOs(4)Sb(12) and CeFe(4)P(12) to study their electronic structure and the evolution of states at the Fermi level as a function of temperature (∼10-300 K). The Ce 3d core level spectra show the presence of f(0), f(1) and f(2) final states with very different relative intensities in the two compounds. Single-impurity Anderson model calculations provide f electron counts of n(f) = 0.97 and 0.86 per Ce atom, suggestive of a low- and high-T(K) (= single ion Kondo temperature) for CeOs(4)Sb(12) and CeFe(4)P(12), respectively. The high-resolution temperature-dependent near-Fermi level spectra show pseudogaps of energy ∼ 50 meV and ∼ 110 meV in the valence band density of states (DOS) of CeOs(4)Sb(12) and CeFe(4)P(12), respectively. The temperature dependence of the DOS at the Fermi level follows the change in effective magnetic moment estimated from magnetic susceptibility for both materials, confirming the Kondo nature of the pseudogap in CeOs(4)Sb(12) and CeFe(4)P(12). A compilation of measured pseudogaps using photoemission and optical spectroscopy identifies the charge gaps Δ(C) for Ce-based Kondo semiconductors and provides a direct relation with T(K) given by Δ(C) ∼ 2k(B)T(K). In conjunction with the known behaviour of the spin gaps Δ(S) ∼ k(B)T(K), the results establish the coupled energy scaling of the spin and charge gaps in Kondo semiconductors.

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