Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 40
Filtrar
Más filtros

Tipo del documento
Intervalo de año de publicación
1.
Phys Rev Lett ; 126(3): 037002, 2021 Jan 22.
Artículo en Inglés | MEDLINE | ID: mdl-33543973

RESUMEN

We report a comprehensive Cu L_{3}-edge resonant x-ray scattering (RXS) study of two- and three-dimensional (2D and 3D) incommensurate charge correlations in single crystals of the underdoped high-temperature superconductor YBa_{2}Cu_{3}O_{6.67} under uniaxial compression up to 1% along the two inequivalent Cu─O─Cu bond directions (a and b) in the CuO_{2} planes. We confirm the strong in-plane anisotropy of the 2D charge correlations and observe their symmetric response to pressure: pressure along a enhances correlations along b, and vice versa. Our results imply that the underlying order parameter is uniaxial. In contrast, 3D long-range charge order is only observed along b in response to compression along a. Spectroscopic RXS measurements show that the 3D charge order resides exclusively in the CuO_{2} planes and may thus be generic to the cuprates. We discuss implications of these results for models of electronic nematicity and for the interplay between charge order and superconductivity.

2.
Nature ; 516(7529): 71-3, 2014 Dec 04.
Artículo en Inglés | MEDLINE | ID: mdl-25471882

RESUMEN

Terahertz-frequency optical pulses can resonantly drive selected vibrational modes in solids and deform their crystal structures. In complex oxides, this method has been used to melt electronic order, drive insulator-to-metal transitions and induce superconductivity. Strikingly, coherent interlayer transport strongly reminiscent of superconductivity can be transiently induced up to room temperature (300 kelvin) in YBa2Cu3O6+x (refs 9, 10). Here we report the crystal structure of this exotic non-equilibrium state, determined by femtosecond X-ray diffraction and ab initio density functional theory calculations. We find that nonlinear lattice excitation in normal-state YBa2Cu3O6+x at above the transition temperature of 52 kelvin causes a simultaneous increase and decrease in the Cu-O2 intra-bilayer and, respectively, inter-bilayer distances, accompanied by anisotropic changes in the in-plane O-Cu-O bond buckling. Density functional theory calculations indicate that these motions cause drastic changes in the electronic structure. Among these, the enhancement in the character of the in-plane electronic structure is likely to favour superconductivity.

3.
Nat Mater ; 13(7): 705-11, 2014 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-24813422

RESUMEN

Nonlinear optical excitation of infrared active lattice vibrations has been shown to melt magnetic or orbital orders and to transform insulators into metals. In cuprates, this technique has been used to remove charge stripes and promote superconductivity, acting in a way opposite to static magnetic fields. Here, we show that excitation of large-amplitude apical oxygen distortions in the cuprate superconductor YBa2Cu3O6.5 promotes highly unconventional electronic properties. Below the superconducting transition temperature (Tc = 50 K) inter-bilayer coherence is transiently enhanced at the expense of intra-bilayer coupling. Strikingly, even above Tc a qualitatively similar effect is observed up to room temperature, with transient inter-bilayer coherence emerging from the incoherent ground state and similar transfer of spectral weight from high to low frequency. These observations are compatible with previous reports of an inhomogeneous normal state that retains important properties of a superconductor, in which light may be melting competing orders or dynamically synchronizing the interlayer phase. The transient redistribution of coherence discussed here could lead to new strategies to enhance superconductivity in steady state.

4.
Phys Rev Lett ; 114(21): 217003, 2015 May 29.
Artículo en Inglés | MEDLINE | ID: mdl-26066453

RESUMEN

We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor YBa_{2}Cu_{3}O_{6+x} over a wide range of doping levels (0.1≤x≤1). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x. These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically [Benjamin et al. Phys. Rev. Lett. 112, 247002 (2014)]. Implications for the theoretical description of the electron system in the cuprates are discussed.

6.
Phys Rev Lett ; 110(18): 187001, 2013 May 03.
Artículo en Inglés | MEDLINE | ID: mdl-23683237

RESUMEN

We use resonant x-ray scattering to determine the momentum-dependent charge correlations in YBa(2)Cu(3) O(6.55) samples with highly ordered chain arrays of oxygen acceptors (ortho-II structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments are carried out on a YBa(2)Cu(3)O(6.6) crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length are found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa(2)Cu(3)O(6+δ).


Asunto(s)
Compuestos de Bario/química , Cobre/química , Óxidos/química , Itrio/química , Cristalización , Conductividad Eléctrica , Difracción de Rayos X
7.
Phys Rev Lett ; 111(18): 187001, 2013 Nov 01.
Artículo en Inglés | MEDLINE | ID: mdl-24237551

RESUMEN

We study the model high-temperature superconductor HgBa(2)CuO(4+δ) with electronic Raman scattering and optical ellipsometry over a wide doping range. The dependence of the resonant Raman cross section on the incident photon energy changes drastically as a function of doping, in a manner that corresponds to a rearrangement of the interband optical transitions seen with ellipsometry. This doping-dependent Raman resonance allows us to reconcile the apparent discrepancy between Raman and x-ray detection of magnetic fluctuations in superconducting cuprates. Intriguingly, the strongest variation occurs across the doping level where the antinodal superconducting gap appears to reach its maximum.

8.
Nat Genet ; 7(3): 440-7, 1994 07.
Artículo en Inglés | MEDLINE | ID: mdl-7920666

RESUMEN

To test the potential role of H19 as a tumour suppressor gene we have examined its expression and DNA methylation in Wilms' tumours (WTs). In most WTs (18/25), H19 RNA was reduced at least 20-fold from fetal kidney levels. Of the expression-negative tumours ten retained 11p15.5 heterozygosity: in nine of these, H19 DNA was biallelically hypermethylated and in two cases hypermethylation locally restricted to H19 sequences was also present in the non-neoplastic kidney parenchyma. IGF2 mRNA was expressed in most but not all WTs and expression patterns were consistent with IGF2/H19 enhancer competition without obligate inverse coupling. These observations implicate genetic and epigenetic inactivation of H19 in Wilms' tumorigenesis.


Asunto(s)
ADN de Neoplasias/genética , Regulación Neoplásica de la Expresión Génica , Genes Supresores de Tumor , Genes , Neoplasias Renales/genética , ARN Mensajero/genética , ARN Neoplásico/genética , Tumor de Wilms/genética , Alelos , ADN de Neoplasias/química , Elementos de Facilitación Genéticos , Femenino , Genes ras , Impresión Genómica , Genotipo , Humanos , Factor II del Crecimiento Similar a la Insulina/genética , Riñón/embriología , Riñón/metabolismo , Masculino , Metilación , Oncogenes , Secuencias Repetitivas de Ácidos Nucleicos , Transcripción Genética
9.
Laryngorhinootologie ; 90(8): 476-80, 2011 Aug.
Artículo en Alemán | MEDLINE | ID: mdl-21809232

RESUMEN

BACKGROUND: Aim of this study was to evaluate the perioperative level of pain and anxiety for endoscopic sinus surgery, and to compare 3 different types of nasal packing. MATERIAL AND METHODS: Prospective, controlled, randomized study comparing different types of nasal packing in regard to perioperative anxiety and pain. Patients suffered from chronic rhinosinusitis with nasal polyps involving all paranasal sinuses. Patients daily evaluated by standardized questionnaires (FPI-R, KASA, STAI) and also visual analog scale for pain on 5 consecutive days before and after endoscopic sinus surgery of all paranasal sinuses. Nasal packings were removed on 2(nd) postoperative day. RESULTS: A total of 73 patients (polyvinyl acetate packing N = 14, glove packing N = 37, glove packing with breathing tubes N = 22) completed the study. Female gender, bad preoperative mood and absence of pain were associated with increased preoperative state anxiety based on regression analysis. Also, preoperative gathering of additional information from relatives and friends was correlated with increased preoperative anxiety. Patients had significantly minor preoperative anxiety if they could expect use of nasal packings with breathing tubes. CONCLUSION: Female patients, who gathered information about the operation from friends or relatives or patient in worse preoperative mood are at risk for increased state anxiety and should be identified prior to rhinosurgical procedures. Use of nasal packing with at least partially preserved nasal breathing is recommended in clinically anxious patients.


Asunto(s)
Ansiedad/diagnóstico , Ansiedad/psicología , Endoscopía/psicología , Pólipos Nasales/psicología , Pólipos Nasales/cirugía , Dolor Postoperatorio/diagnóstico , Dolor Postoperatorio/psicología , Enfermedades de los Senos Paranasales/psicología , Enfermedades de los Senos Paranasales/cirugía , Sinusitis/psicología , Sinusitis/cirugía , Tampones Quirúrgicos , Adulto , Afecto , Anciano , Enfermedad Crónica , Cultura , Femenino , Alemania , Humanos , Masculino , Persona de Mediana Edad , Dimensión del Dolor , Estudios Prospectivos , Factores de Riesgo , Factores Sexuales , Encuestas y Cuestionarios
10.
Psychother Psychosom ; 78(4): 233-9, 2009.
Artículo en Inglés | MEDLINE | ID: mdl-19401624

RESUMEN

BACKGROUND: Asthma is a frequently disabling and almost invariably distressing disease that has a high overall prevalence. Although relaxation techniques and hypnotherapeutic interventions have proven their effectiveness in numerous trials, relaxation therapies are still not recommended in treatment guidelines due to a lack of methodological quality in many of the trials. Therefore, this study aims to investigate the efficacy of the brief relaxation technique of functional relaxation (FR) and guided imagery (GI) in adult asthmatics in a randomized controlled trial. METHODS: 64 patients with extrinsic bronchial asthma were treated over a 4-week period and assessed at baseline, after treatment and after 4 months, for follow-up. 16 patients completed FR, 14 GI, 15 both FR and GI (FR/GI) and 13 received a placebo relaxation technique as the control intervention (CI). The forced expiratory volume in the first second (FEV(1)) as well as the specific airway resistance (sR(aw)) were employed as primary outcome measures. RESULTS: Participation in FR, GI and FR/GI led to increases in FEV(1) (% predicted) of 7.6 +/- 13.2, 3.3 +/- 9.8, and 8.3 +/- 21.0, respectively, as compared to -1.8 +/- 11.1 in the CI group at the end of the therapy. After follow-up, the increases in FEV(1) were 6.9 +/- 10.3 in the FR group, 4.4 +/- 7.3 in the GI and 4.5 +/- 8.1 in the FR/GI, compared to -2.8 +/- 9.2 in the CI. Improvements in sR(aw) (% predicted) were in keeping with the changes in FEV(1) in all groups. CONCLUSIONS: Our study confirms a positive effect of FR on respiratory parameters and suggests a clinically relevant long-term benefit from FR as a nonpharmacological and complementary therapy treatment option.


Asunto(s)
Asma/terapia , Terapias Complementarias , Imágenes en Psicoterapia , Terapia por Relajación , Hipersensibilidad Respiratoria/terapia , Adulto , Resistencia de las Vías Respiratorias , Animales , Asma/psicología , Terapia Combinada , Femenino , Estudios de Seguimiento , Volumen Espiratorio Forzado , Humanos , Masculino , Persona de Mediana Edad , Pletismografía Total , Pyroglyphidae , Hipersensibilidad Respiratoria/psicología , Rinitis Alérgica Perenne/psicología , Rinitis Alérgica Perenne/terapia , Espirometría , Resultado del Tratamiento
11.
Rev Sci Instrum ; 79(2 Pt 2): 02C710, 2008 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-18315263

RESUMEN

The next generation, superconducting electron cyclotron resonance (ECR) ion source VENUS (versatile ECR ion source for nuclear science) started operation with 28 GHz microwave heating in 2004. Since then it has produced world record ion beam intensities. For example, 2850 e microA of O(6+), 200 e microA of U(33+) or U(34+), and in respect to high charge state ions, 1 e microA of Ar(18+), 270 e microA of Ar(16+), 28 e microA of Xe(35+), and 4.9 e microA of U(47+) have been produced. A brief overview of the latest developments leading to these record intensities is given and the production of high intensity uranium beams is discussed in more detail.

12.
Science ; 362(6418): 1040-1044, 2018 11 30.
Artículo en Inglés | MEDLINE | ID: mdl-30498124

RESUMEN

Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa2Cu3O6.67 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the a axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials.

13.
Int J Impot Res ; 19(1): 104-7, 2007.
Artículo en Inglés | MEDLINE | ID: mdl-16728967

RESUMEN

The effectiveness of cabergoline in 50 men with psychogenic erectile dysfunction was investigated in a 4-month, randomized, placebo-controlled, double-blind study with validated psychological tests, and prolactin, follicle-stimulating hormone, luteinizing hormone and testosterone serum levels. Cabergoline treatment was well-tolerated and resulted in normalization of hormone levels in most cases. In the cabergoline-treated group, significant interactions between prolactin and testosterone serum concentrations were observed. Erectile function improved significantly. Sexual desire, orgasmic function, and the patient's and his partner's sexual satisfaction were also enhanced. Cabergoline may be an effective and safe alternative agent for men with psychogenic ED.


Asunto(s)
Agonistas de Dopamina/uso terapéutico , Disfunción Eréctil/tratamiento farmacológico , Disfunción Eréctil/psicología , Ergolinas/uso terapéutico , Adulto , Cabergolina , Método Doble Ciego , Disfunción Eréctil/sangre , Hormona Folículo Estimulante/sangre , Humanos , Libido , Hormona Luteinizante/sangre , Masculino , Persona de Mediana Edad , Orgasmo , Satisfacción del Paciente , Placebos , Prolactina/sangre , Testosterona/sangre
14.
Struct Dyn ; 4(4): 044007, 2017 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-28345009

RESUMEN

Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO2 planes. The empty chain Cu dy2-z2 orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. Femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions.

15.
Rev Sci Instrum ; 87(2): 02A702, 2016 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-26931920

RESUMEN

To demonstrate a Mixed Axial and Radial field System (MARS) as the best magnet scheme for future ECRISs, MARS-D, a demonstrative ECRIS using a NbTi MARS magnet is progressing at Lawrence Berkeley National Laboratory. An optimized MARS design can use either NbTi or Nb3Sn coils with reduced engineering complexities to construct the needed high-field magnets. The optimized magnet design could enhance MARS-D to a next generation ECRIS by producing minimum-B field maxima of 5.6 T axially and 3.2 T radially for operating frequencies up to 45 GHz. In-progress test winding has achieved a milestone demonstrating the fabrication feasibility of a MARS closed-loop coil.

16.
Psychopharmacology (Berl) ; 126(1): 91-4, 1996 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-8853222

RESUMEN

Ten unmedicated and ten medicated patients with major depression and ten controls were investigated with IBZM-SPECT. The ten unmedicated patients were reinvestigated after treatment with tricyclic antidepressants. Dopamine D2 receptor occupancy was not different between patients and controls, or medicated and unmedicated patients. IBZM binding was increased in four patients with psychomotor retardation. Antidepressant therapy led to a decrease in IBZM binding in the five improved patients. Dopamine D2 receptor binding remained unchanged in nonresponders. It is concluded that striatal dopamine D2 receptor binding is not changed in depression or by tricyclic antidepressants; however, it is affected by psychomotor activity. The changes observed might be the result of increased tonic dopamine release in the basal ganglia, but several other explanations exist.


Asunto(s)
Benzamidas/metabolismo , Trastorno Depresivo/tratamiento farmacológico , Trastorno Depresivo/metabolismo , Antagonistas de Dopamina/metabolismo , Pirrolidinas/metabolismo , Receptores Dopaminérgicos/metabolismo , Medios de Contraste , Trastorno Depresivo/diagnóstico por imagen , Humanos , Masculino , Tomografía Computarizada de Emisión de Fotón Único/métodos
17.
Hematol Oncol Clin North Am ; 5(3): 557-69, 1991 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-1864823

RESUMEN

Cooley's anemia patients, treated with a combined regimen of blood transfusions and chelation therapy, can look forward today to near-normal survival and excellent quality of life. Transfusion therapy should be directed at maintaining a hemoglobin baseline (greater than or equal to 10 g/dL) adequate to prevent hypoxia and its consequences: bone marrow expansion and cardiomegaly. Chelation therapy should aim at a very reduced Fe overload, to be monitored by the serum ferritin level. Several oral Fe chelating drugs currently being developed appear promising; none, however, is ready for general use as yet. Transplantation of bone marrow from a compatible sibling can cure Cooley's anemia; however, this therapy is currently only applicable to a small percentage of patients.


Asunto(s)
Talasemia/terapia , Transfusión Sanguínea , Trasplante de Médula Ósea , Terapia por Quelación , Deferoxamina/uso terapéutico , Humanos , Hierro
18.
J Psychosom Res ; 42(5): 495-8, 1997 May.
Artículo en Inglés | MEDLINE | ID: mdl-9194024

RESUMEN

Psychogenic pain, disturbances of gait and stance, sensory symptoms, dizziness, and psychogenic seizures have been found to be the most common conversion symptoms in neurology clinics. A retrospective analysis of 18 patients suffering from pseudoseizure "status" is presented in this study. All of the patients fulfilled the DSM-III-R criteria of conversion disorder. However, 5 of them had concomitant major depression, 6 suffered from bulimia nervosa, and 7 met the criteria for substance abuse. On Axis II, 10 cases of borderline personality disorder, 2 cases of antisocial personality disorder, and 3 cases of histrionic personality disorder were diagnosed. The majority of the patients had attempted suicide and other forms of self-destructive behavior. The findings suggest that patients with pseudoseizure "status" suffer from severe affective imbalances and disturbed impulse control.


Asunto(s)
Trastornos de Conversión/psicología , Estado Epiléptico/psicología , Adolescente , Adulto , Trastornos de Conversión/complicaciones , Depresión/complicaciones , Epilepsia/complicaciones , Epilepsia/psicología , Femenino , Humanos , Conducta Impulsiva/complicaciones , Masculino , Trastornos de la Personalidad/complicaciones , Conducta Autodestructiva/complicaciones , Estado Epiléptico/diagnóstico
19.
Altern Ther Health Med ; 6(6): 70-5, 2000 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-11076449

RESUMEN

CONTEXT: Functional relaxation is based on concentration on body perception while moving the joints of the skeleton smoothly and simultaneously breathing out. Case reports have shown that patients with headaches can profit from functional relaxation. OBJECTIVE: To examine whether patients with chronic tension headaches (International Headache Society diagnosis) who use functional relaxation as a complementary treatment will report less pain than before they learned this technique. DESIGN: Randomized, prospective, single-blind, controlled trial. Standardized elements of functional relaxation were compared to a placebo-relaxation technique, a simple isotomic exercise of the hand. SETTING: Primary care, ambulatory private practice. PARTICIPANTS: Twelve matched pairs were chosen according to age, sex, and initial pain intensity. This poststratification was performed on patients, who kept a complete pain diary covering 60 days before and 60 days after the introduction to the therapy. After a 45-minute introduction in small groups, the patients were told to do the exercises as often as possible for the following 2 months. MAIN OUTCOME MEASURES: Pain diary. RESULTS: In the functional-relaxation group, a significant reduction was found in the sum of total pain hours and in high- and medium-intensive pain (Wilcoxon signed rank test). CONCLUSIONS: This study supports the concept that this psychosomatic therapy can bring relief from tension headaches. This procedure can be viewed as an easy-to-learn relaxation technique to be used either prophylactic or complementary to pharmaceutical treatment.


Asunto(s)
Terapia por Relajación , Cefalea de Tipo Tensional/terapia , Adulto , Enfermedad Crónica , Femenino , Humanos , Masculino , Persona de Mediana Edad , Dimensión del Dolor , Estudios Prospectivos , Psicofisiología/métodos , Método Simple Ciego , Resultado del Tratamiento
20.
Med Klin (Munich) ; 91(5): 272-6, 1996 May 15.
Artículo en Alemán | MEDLINE | ID: mdl-8709904

RESUMEN

BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives.


Asunto(s)
Síndrome de Inmunodeficiencia Adquirida/psicología , Actitud del Personal de Salud , Infecciones por VIH/psicología , Síndrome de Inmunodeficiencia Adquirida/prevención & control , Síndrome de Inmunodeficiencia Adquirida/transmisión , Adulto , Estudios Transversales , Femenino , Alemania , Infecciones por VIH/prevención & control , Infecciones por VIH/transmisión , Conocimientos, Actitudes y Práctica en Salud , Humanos , Transmisión de Enfermedad Infecciosa de Paciente a Profesional , Masculino , Persona de Mediana Edad , Factores de Riesgo , Muestreo
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA