The Superconductor-Insulator Transition in a Tunable Dissipative Environment

We study the influence of a tunable dissipative environment on the dynamics of Josephson junction arrays near the superconductor-insulator transition. The experimental realization of the environment is a two dimensional electron gas coupled capacitively to the array. This setup allows for the well-controlled tuning of the dissipation by changing the resistance of the two dimensional electron gas. The capacitive coupling cuts off the dissipation at low frequencies. We determine the phase diagram and calculate the temperature and dissipation dependence of the array conductivity. We find good agreement with recent experimental results.Comment: 4 pages, 4 .eps figures, revte

The Bose Metal: gauge field fluctuations and scaling for field tuned quantum phase transitions

In this paper, we extend our previous discussion of the Bose metal to the field tuned case. We point out that the recent observation of the metallic state as an intermediate phase between the superconductor and the insulator in the field tuned experiments on MoGe films is in perfect consistency with the Bose metal scenario. We establish a connection between general dissipation models and gauge field fluctuations and apply this to a discussion of scaling across the quantum phase boundaries of the Bose metallic state. Interestingly, we find that the Bose metal scenario implies a possible {\em two} parameter scaling for resistivity across the Bose metal-insulator transition, which is remarkably consistent with the MoGe data. Scaling at the superconductor-metal transition is also proposed, and a phenomenolgical model for the metallic state is discussed. The effective action of the Bose metal state is described and its low energy excitation spectrum is found to be $\omega \propto k^{3}$.Comment: 15 pages, 1 figur

Strongly correlated s-wave pairing in the n-type infinite-layer cuprate

Quasiparticle tunneling spectra of the electron-doped (n-type) infinite-layer cuprate Sr_{0.9}La_{0.1}CuO_2 reveal characteristics that counter a number of common phenomena in the hole-doped (p-type) cuprates. The optimally doped Sr_{0.9}La_{0.1}CuO_2 with T_c = 43 K exhibits a momentum-independent superconducting gap \Delta = 13.0 +- 1.0 meV that substantially exceeds the BCS value, and the spectral characteristics indicate insignificant quasiparticle damping by spin fluctuations and the absence of pseudogap. The response to quantum impurities in the Cu-sites also differs fundamentally from that of the p-type cuprates with d_{x^2-y^2}-wave pairing symmetry.Comment: 4 pages, 3 figures. Published in Physical Review Letter. Corresponding author: Nai-Chang Yeh (e-mail: [email protected]

Cuantificación del calcio mineral en la ateromatosis carotídea mediante angiografía por tomografía computarizada: perfil evolutivo y relación con la progresión del grado de estenosis volumétrica

Antecedentes: La cuantificación y caracterización del calcio (Ca) mineral (hidroxiapatita) en la bifurcación carotídea con AngioTC, y su relación con la sintomatología neurológica, en un estudio preliminar de casos y controles (Miralles y cols. Eur J Vasc Endovasc Surg 2006), constituye la base conceptual del presente estudio. Sus resultados, al igual que los de otras publicaciones, sugerían un posible papel protector del calcio en el desarrollo de eventos neurológicos. Sin embargo, su relación con la progresión de la ateromatosis carotídea ha sido escasamente analizado. Objetivos: Principales: 1. Diseñar un método de medición volumétrica de la ateromatosis (AE) carotídea y contenido de Ca mediante AngioTC. 2. Analizar el grado de calcificación arterial y su relación con la progresión de la ateromatosis carotídea. Secundarios: 3. Evaluar la relación entre calcificación arterial carotídea y descalcificación ósea, así como su posible conexión a través de los factores humorales implicados en la regulación del metabolismo Ca-P. 4. Estudiar un posible mecanismo genético común: relación entre los polimorfismos del gen de la OPG y la progresión de la calcificación en la placa de ateroma. Pacientes y método: Diseño: Cohortes, medidas repetidas. Pacientes: 54 pacientes, neurológicamente asintomáticos con estenosis de la arteria carótida interna (ECI) >50% (eco-Doppler). Determinaciones: Medición del grado de ECI mediante eco-Doppler y proyecciones MIP 2D de AngioTC. Medición del Volumen del molde de contraste y contenido de Ca (AngioTC cuantitativa: Agatston score modificado: volumen de Ca (mm3) x densidad radiológica (unidades Hounsfield, UH) en reconstrucción volumétrica (volume rendering) de la bifurcación carotídea (volumen de contraste entre 2 cm por debajo y 1 cm por encima de la bifurcación [VBif] y su cociente con un segmento de 1 cm en carótida primitiva [VCP]) (n=45). En todos los pacientes se repitió la exploración a los 122 meses para valorar la variación en el contenido de Ca y en el grado de estenosis volumétrica de la bifurcación, como medición indirecta de la progresión/regresión de la AE carotídea. Densitometría ósea de columna y fémur (n=32), (basal y a los 122 meses). Bioquímica y metabolismo Ca-P (Ca, P, vit D, PTH). Determinación de osteopontina (OPN) y osteoprotegerina (OPG) sérica y distribución de 7 SNPs del gen de la OPG seleccionados sobre bases bibiliométricas (n=48). Análisis estadístico: descriptivo (media [DE]); concordancia intra e interobservador (gráficos de Bland-Altman) y coeficiente de correlación intraclase (CCI), precisión eco-Doppler/AngioTC y Volumetría 3D/MIP 2D: sensibilidad (Sens), especificidad (Esp), índice kappa, curvas operador receptor (COR), comparación de medias (prueba T), análisis de regresión uni y multivariable. Resultados: 1. La medición volumétrica de la bifurcación carotídea mostró una concordancia intra e interobservador con un CCI de 0,96 (IC 95%: 0,904-0,985) y 0,94 (IC 95%: 0,822-0,977), respectivamente. El VBif/VCP del grupo de ECI50% (p=0,001). El punto de corte óptimo de la relación VBif/VCP se identificó a partir de la curva COR en 4,1 (Sens=0,75; Esp=0,75, kappa=0,46). 2. La medición mediante AngioTC demostró, a los 12 meses, un aumento del volumen promedio de pared arterial (disminución del volumen de la columna de contraste), respecto al valor basal (475,45 [155,6] mm3xUH vs 501,3 [171,9] mm3xUH, p=0,04), así como un aumento del Ca intraplaca (56,8 [52,3] vs 64,58 [57,8] mm3xUH, p=0,002). El análisis univariable demostró una correlación inversa entre el contenido basal de Ca y progresión de estenosis volumétrica de la bifurcación (r=-0,481; p<0,001). El análisis de regresión múltiple permitió ajustar un modelo de regresión lineal entre la reducción del volumen de la bifurcación (progresión de AE carotídea) y el contenido basal de Ca intraplaca, ajustado por el índice de masa corporal (IMC). 3. Se observó una disminución estadísticamente significativa de la densidad ósea respecto a la determinación basal (2,08 [0,22] vs 2,06 [0,23] g/cm2; p=0,013), así como un aumento del Ca intraplaca respecto a los valores basales (79,2 [55] vs 64,58 [49,2] mm3xUH, p=0,12). Sin embargo, se identificó una correlación positiva entre la variación relativa del contenido de Ca y la variación relativa de la densidad ósea (r=0,574, p=0,003). En otras palabras, una mayor tendencia a la osteoporosis se asoció con una menor tendencia a la progresión del calcio intraplaca. Así mismo, se observó una relación entre los niveles plasmáticos de Vit D y la densitometría basal (r=-0,459, p=0,036) y entre los niveles plasmáticos de HDL-colesterol y la variación relativa, respecto a los valores basales, de la densidad ósea (r=-0,579, p=0,009). El análisis univariable demostró una correlación inversa entre el incremento del contenido de calcio intraplaca y los niveles plasmáticos de vit D (r=0,4; p=0,025) y score Z en fémur (r=0,378; p=0,047). Sólo la concentración de P en orina presentó una correlación positiva moderada con el aumento de Ca intraplaca (r=0,488, p=0,015). Ninguna otra variable, entre los parámetros del metabolismo Ca-P, mostró relación con la calcificación arterial. 4. No se observaron diferencias entre la distribución de los SNPs en los pacientes de la muestra del estudio y el grupo control. Tampoco se observó relación entre el genotipo (SNPs) y la concentración de OPG sérica. Conclusiones: 1. La medición volumétrica de la bifurcación carotídea supone un nuevo concepto basado en la valoración de la carga de placa más que en su efecto hemodinámico o estenosis máxima. Dada su precisión en la detección de variaciones pequeñas de la luz arterial, este método puede ser de especial utilidad en estudios de progresión de placa. 2. Los resultados de este estudio sugieren que un mayor contenido de Ca confiere mayor estabilidad frente a la progresión de la AE carotídea y, eventualmente, a su capacidad para generar sintomatología tromboembólica. 3. Encontramos una tendencia independiente a la progresiva calcificación arterial y descalcificación ósea. Sin embargo, los resultados sugieren una relación temporal directa en la evolución del depósito de calcio en ambas localizaciones, por lo que no es posible descartar que su modulación se rija por mecanismos similares. 4. No se observó una relación estadísticamente significativa entre la distribución de los SNPs analizados y los niveles de la OPG o la calcificación intraplaca en los pacientes estudiados.Background: Quantification and characterization of mineral calcium (Ca) (hydroxyapatite) in the carotid bifurcation with AngioCT, and its relation with neurological symptomatology, in a preliminary case-control study (Miralles et al., Eur J Vasc Endovasc Surg 2006) Constitutes the conceptual basis of the present study. Their results, like those of other publications, suggested a possible protective role for calcium in the development of neurological events. However, its relationship with the progression of carotid atheromatosis has been scarcely analyzed. Objectives: Primary: 1. To design a method of volumetric measurement of carotid atheromatosis (AE) and Ca content by AngioCT. 2. To analyze the degree of arterial calcification and its relation with the progression of carotid atheromatosis. Secondary: 3. To evaluate the relationship between carotid artery calcification and bone decalcification, as well as its possible connection through humoral factors involved in the regulation of Ca-P metabolism. 4 To study a possible common genetic mechanism: relationship between polymorphisms of osteoprotegerin (OPG) gene and the progression of calcification in the atherosclerotic plaque. Patients and method: Design: Cohorts, repeated measures. Patients: 54 asymptomatic patients with internal carotid artery stenosis CAS>50% (duplex scanning). Determinations: Measurement of CAS grade with duplex scanning and MIP 2D projections of AngioCT. Volume measurement of contrast medium and Ca content (quantitative AngioCT: Agatston score: Ca volume (mm3) x radiological density (Hounsfield units, HU) in volume reconstruction of the carotid bifurcation [contrast volume between 2 cm below and 1 cm above the bifurcation (BifV) and its ratio with that from 1 cm segment in common carotid artery (CCV)] (n=45). In all patients, the scans was repeated at 12±2 months to assess the variation in Ca content and the degree of bifurcation volumetric stenosis as an indirect measure of carotid AE progression / regression. Bone and spine densitometry (n=32), where obtained at baseline and after 12±2 months, as well as Biochemistry and Ca-P metabolism parameters (Ca, P, vit D, PTH). Determination of plasma levels of osteopontin (OPN) and osteoprotegerin (OPG) where compared with the distribution of 7 SNPs of the OPG gene selected on bibiliometrics bases (n=48). Statistical analysis: descriptive [mean (SD)]; Intra and interobserver agreement (Bland-Altman plots and intraclass correlation coefficient (ICC), duplex scanning / AngioCT precision and 3D Volumetry / MIP 2D: Sensitivity (S), specificity (E), kappa index, ROC curves, means comparison (T test), univariate and multivariate regression analysis. Results: 1.The volumetric measurement of the carotid bifurcation showed intra and interobserver agreement with a ICC of 0.96 (95% CI: 0.904-0.985) and 0.94 (95% CI: 0.822-0.977), respectively. The BifV/CCV of the CAS > 50% group was 5.2±1.8 vs 3.8 ±1.3 in the CAS >50% group (p=0.001). The optimum cutoff point for the BifV/CCV relation was identified from the ROC curve at 4,1 (S=0.75, E=0.75, kappa=0.46). 2. AngioCT measurement showed, at 12 months, an increase in mean arterial wall volume (decrease in contrast column volume), compared to baseline (475.45 [155.6] mm3xHU vs 501.3 [171.9] mm3xHU, p=0.04), as well as an increase in intraplaque Ca (56.8 [52.3] vs 64.58 [57.8] mm3xHU, p=0.002). Univariate analysis showed an inverse correlation between basal Ca content and progression of bifurcation volumetric stenosis (r=-0.481; p<0.001). The multiple regression analysis allowed to fit a linear regression model between the reduction of bifurcation volume (carotid AE progression) and the baseline intraplaque content of Ca, adjusted for body mass index (BMI). 3. A statistically significant decrease in bone density was observed with respect to the baseline determination (2.08 [0.22] vs 2.06 [0.23] g/cm2, p=0.013), as well as increased intraplaque Ca as compared with baseline values (79.2 [55] vs 64.58 [49.2] mm3xHU, p=0.12). However, a positive correlation was identified between the relative variation of Ca content and the relative variation of bone density (r=0.574, p=0.003). In other words, a greater tendency to osteoporosis was associated with a lower tendency to progression of intraplaque calcium. Likewise, a relationship between Vit D plasma levels and baseline densitometry (r=-0.459, p=0.036) and between plasma HDL-cholesterol levels and the relative variation, relative to baseline values, were observed. Bone density (r=-0.579, p=0.009). The univariate analysis showed an inverse correlation between the basal Ca content and the progression of bifurcation volumetric stenosis (r=-0.481; p<0.001), as well as between the increase in the intra-plaque calcium content and plasma levels of vit D (R=0.4, p=0.025) and femur Z score (r=0.378, p=0.047). Only the urine P concentration presented a moderate positive correlation with the increase of intra-plaque Ca (r=0.488, p=0.015). No other variable, among Ca-P metabolism parameters, was related to arterial calcification. 4. There were no differences between the distribution of SNPs in patients and control group. There was also no relationship between genotype and serum OPG concentration. Conclusions: 1. The volumetric measurement of the carotid bifurcation is a new concept based on the assessment of the plaque load rather than on its hemodynamic effect or maximal stenosis. Given its accuracy in detecting small variations in arterial lumen, this method may be especially useful in plaque progression studies. 2. The results of this study suggest that a higher content of Ca confers greater stability against the progression of carotid AE and, eventually, its capacity to generate symptomatology. 3. We found an independent tendency to progressive arterial calcification and bone decalcification. However, the results suggest a direct temporal relationship in the evolution of the calcium deposit in both locations, so it is not possible to rule out that its modulation is controlled by similar mechanisms. 4. The results are inconclusive with regard to the role of OPG in AE plaque calcification. No significant relationship between the distribution of SNPs analyzed and OPG levels in the studied patients was observed

Is there a Phase Transition to the Flux Lattice State?

The sharp drops in the resistance and magnetization which are usually attributed to a phase transition from the vortex liquid state to a crystal state are explained instead as a crossover between three and two dimensional behavior, which occurs when the phase coherence length in the liquid becomes comparable to the sample thickness. Estimates of the width of the crossover region and the phase coherence length scales are in agreement with experiment.Comment: 4 pages, RevTe

Electron transport across a quantum wire in the presence of electron leakage to a substrate

We investigate electron transport through a mono-atomic wire which is tunnel coupled to two electrodes and also to the underlying substrate. The setup is modeled by a tight-binding Hamiltonian and can be realized with a scanning tunnel microscope (STM). The transmission of the wire is obtained from the corresponding Green's function. If the wire is scanned by the contacting STM tip, the conductance as a function of the tip position exhibits oscillations which may change significantly upon increasing the number of wire atoms. Our numerical studies reveal that the conductance depends strongly on whether or not the substrate electrons are localized. As a further ubiquitous feature, we observe the formation of charge oscillations.Comment: 7 pages, 7 figure

Evidence of Vortices on the Insulating Side of the Superconductor-Insulator Transition

The magnetoresistance of ultrathin insulating films of Bi has been studied with magnetic fields applied parallel and perpendicular to the plane of the sample. Deep in the strongly localized regime, the magnetoresistance is negative and independent of field orientation. As film thicknesses increase, the magnetoresistance becomes positive, and a difference between values measured in perpendicular and parallel fields appears, which is a linear function of the magnetic field and is positive. This is not consistent with the quantum interference picture. We suggest that it is due to vortices present on the insulating side of the superconductor-insulator transition.Comment: 4 pages, 3 figure

Landslide Risk Assessment by Using a New Combination Model Based on a Fuzzy Inference System Method

Landslides are one of the most dangerous phenomena that pose widespread damage to property and human lives. Over the recent decades, a large number of models have been developed for landslide risk assessment to prevent the natural hazards. These models provide a systematic approach to assess the risk value of a typical landslide. However, often models only utilize the numerical data to formulate a problem of landslide risk assessment and neglect the valuable information provided by experts’ opinion. This leads to an inherent uncertainty in the process of modelling. On the other hand, fuzzy inference systems are among the most powerful techniques in handling the inherent uncertainty. This paper develops a powerful model based on fuzzy inference system that uses both numerical data and subjective information to formulate the landslide risk more reliable and accurate. The results show that the proposed model is capable of assessing the landslide risk index. Likewise, the performance of the proposed model is better in comparison with that of the conventional techniques