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The upper critical field sets the thermodynamic limit to superconductivity. A big gap is present between the upper-critical-field values measured in MgB2 polycrystalline bulk superconductors and those of thin films, where values as high as ~ 50 T have been achieved at 4.2 K. Filling this gap would unlock the potential of MgB2 for magnet applications. This work presents the results of an extensive experimental campaign on MgB2 bulk samples, which has been guided by a Design of Experiment. We modeled the dependence of the upper critical field on the main synthesis parameters and established a new record (~ 35 T at 4.2 K) preparing C-doped bulk samples by a non-conventional rapid-synthesis route. This value appears to be an upper boundary for the upper critical field in bulk samples. Structural disorder in films seems to act selectively on one of the two bands where superconductivity in MgB2 takes place: this enhances the upper critical field while reducing the critical temperature only by few Kelvins. On the other hand, the critical temperature in bulk samples decreases monotonically when structural disorder increases, and this imposes a limit to the maximum achievable upper critical field. [ABSTRACT FROM AUTHOR]

Background: Surveillance for hepatocellular carcinoma (HCC) is recommended in patients with cirrhosis. As α-fetoprotein (AFP) is considered a poor surveillance test, we tested the performance of its changes over time.Methods: Eighty patients were diagnosed with HCC (cases) during semiannual surveillance with ultrasonography and AFP measurement were recruited and matched for age, gender, etiology and Child-Pugh class with 160 contemporary cancer-free controls undergoing the same surveillance training group (TG). As a validation group (VG) we considered 36 subsequent patients diagnosed with HCC, matched 1 : 3 with contemporary cancer-free controls. α-Fetoprotein values at the time of HCC diagnosis (T0) and its changes over the 12 (Δ12) and 6 months (Δ6) before cancer detection were considered.Results: In both TG and VG, >80% of HCCs were found at an early stage. In TG, AFP significantly increased over time only in cases. T0 AFP and a positive Δ6 were independently associated with HCC diagnosis (odds ratio: 1.031 and 2.402, respectively). The area under the curve of T0 AFP was 0.76 and its best cutoff (BC) was 10 ng ml(-1) (sensitivity 66.3%, specificity 80.6%). The combination of AFP >10 ng ml(-1) or a positive Δ6 composite α-fetoprotein index (CAI) increased the sensitivity to 80% with a negative predictive value (NPV) of 86.2%. Negative predictive value rose to 99%, considering a cancer prevalence of 3%. In the VG, the AFP-BC was again 10 ng ml(-1) (sensitivity 66.7%, specificity 88.9%), and CAI sensitivity was 80.6% with a NPV value of 90.5%.Conclusions: CAI achieves adequate sensitivity and NPV as a surveillance test for the early detection of HCC in cirrhosis. [ABSTRACT FROM AUTHOR]

Using electron spin resonance (ESR) technique we have obtained data evidencing the existence of magnetic vortices in high-temperature superconductors at temperatures above the critical one T. We have studied magnetic excitations in BiSrCaCuO single crystals above T with the method of surface spin decoration. The surface layer of diphenylpicrylhydrazyl was used as a sensitive probe of magnetic field distortions. The temperature dependence of the ESR signal parameters has indicated that far above T the magnetic flux of a sample is affected by the superconducting order parameter fluctuations while close to T its changes are due to vortex-type excitations. [ABSTRACT FROM AUTHOR]

Vortex excitations have been detected at temperatures both below and above the critical temperature when investigating local magnetic fields on the surface of a Bi2Sr2Ca2Cu3O10 single crystal by means of an electron paramagnetic resonance (EPR) probe. A thin layer of a diphenyl picrylhydrazyl organic radical deposited on the crystal surface is used as the EPR probe. A narrow EPR signal makes it possible to detect weak distortions of the magnetic field appearing at T ≿ Tc. The analysis of the temperature dependences of the resonance field and the EPR linewidth is thebasis of the assumption of the vortex nature of magnetic excitations in this temperature range. [ABSTRACT FROM AUTHOR]

Damage to bile ducts in chronic hepatitis C is a characteristic histological lesion. Moreover, the presence of abnormal levels of gammaGT in these patients is also a common finding. Assessing whether the presence of bile duct lesions is indicated by biochemical abnormalities or whether virological characteristics can influence their development may help in the definition of clinical-histological relationships in chronic hepatitis C. In this study we evaluated the relationships among routine biochemical parameters, serum bile acids, and pi-class glutathione S-transferase levels, and the presence of bile duct lesions in 60 patients with chronic hepatitis C. Furthermore, we assessed whether the presence of bile duct lesion might be related to HCV genotype, HCV-RNA serum levels, and positivity for HGV-RNA. We found that gammaGT was the only parameter related to the presence of bile duct lesions. Although a trend towards higher serum bile acids and pi-class glutathione S-transferase levels was observed in patients with bile duct lesions, this trend did not reach statistical significance. Different HCV genotypes and RNA levels, and HGV-RNA positivity did not seem to influence the presence of bile duct damage. In conclusion we found that gammaGT levels point out the presence of bile duct lesions in patients with chronic hepatitis C. Since we observed a different pattern of alteration of gammaGT, serum bile acids, and pi-class glutathione S-transferase, we suggest that these various biochemical alterations reflect a more complex damage to bile duct structures, which is not likely represented by the common assessment of bile duct lesions. Viral factors such as HCV genotype and RNA levels as well as HGV-RNA positivity are probably not the main cause of this histological damage. [ABSTRACT FROM AUTHOR]

The ratio of serum aspartate aminotransferase to alanine aminotransferase (AST/ALT ratio) has been proposed as a noninvasive method of assessing liver fibrosis and cirrhosis. Our aims were to confirm the usefulness of the AST/ALT ratio in diagnosing cirrhosis noninvasively as well as to verify the existence of a relationship between the ratio and liver functional impairment. In all, 348 patients (177 with chronic hepatitis, 171 with cirrhosis) were retrospectively evaluated and the AST/ALT ratio was related to monoethyl glycine xylidide (MEGX) formation. Moreover, in a subgroup of 54 patients we analyzed the relationships among the AST/ALT ratio and indocyanine green clearance and half-life. The AST/ALT ratio was able to separate patients with mild fibrosis from those with severe fibrosis and cirrhosis. The AST/ALT ratio, MEGX, prothrombin activity, and platelet count were selected by multivariate analysis as variables associated with cirrhosis. The AST/ALT ratio showed significant correlations both with MEGX formation and with indocyanine green clearance and half-life. The alterations of indocyanine green kinetics, which depend upon liver blood flow and uptake, were likely due to progressive fibrosis. These findings might partially explain the increase in the AST/ALT ratio as disease progresses. [ABSTRACT FROM AUTHOR]

Despite questions regarding its validity as an estimator of inflammatory disease activity, monitoring of the erythrocyte sedimentation rate (ESR) continues to be routine practice among pediatric rheumatologists caring for children with juvenile rheumatoid arthritis (JRA). We studied a large group of patients with JRA in order to determine the degree of correlation between clinically apparent inflammation and the ESR. regression and correlation analyses and descriptive statistical techniques were used to establish the relationship between 1) the ESR and the amount of clinically apparent inflammation at a point in time, and 2) changes in the ESR and the corresponding changes in apparent inflammation. One hundred fifty-nine children with JRA who were participants in a double-blind, controlled trial of two antirheumatic drugs were assessed for clinical and laboratory evidence of inflammatory disease activity at an initial visit, and then periodically for the duration of the one year study. Results showed that, at the initial assessment, neither the total number of joints with active arthritis nor the severity score correlated well with the ESR (r=.196 and .245 respectively). These findings were independent of the course type of JRA and age of the child. Changes from baseline in inflammation showed little correlation (r<.25) with changes in the ESR. These findings suggest that the ESR is a relatively poor indicator of the amount of articular inflammation present, and that changes of disease activity are not reflected closely by changes in the ESR among children with JRA. [ABSTRACT FROM AUTHOR]

A significant reduction of ac losses in twisted Bi(2223) multifilamentary tapes with Ag sheaths has been achieved by using oxide (BaZrO3 and SrZrO3) barriers between filaments. These barriers have two important effects: they increase the transverse resistivity, which suppresses induced coupling currents, and they reduce filament bridging, which in pure Ag sheath tapes largely cancels the beneficial effect of filament twisting. The decoupling can be gauged by the frequency at which loss shows a maximum in a low-amplitude ac field applied perpendicular to the tape. So far, the frequency of the loss maximum, fm, in Ag-sheathed tapes has been enhanced from 5 Hz (untwisted) to 82 Hz (11 mm in twist pitch length). Different ways to introduce oxide barriers in tapes with 19–95 filaments are presented. The critical current density in the filaments varied between 10,000 and 20,000 A/cm2. Ac loss measurements as well as the electrical and mechanical characterization are discussed in detail. The variation of the critical current density with bending strain is shown to be similar to that of tapes without barriers. [ABSTRACT FROM AUTHOR]

The assessment of overall health status of a child with juvenile rheumatoid arthritis (JRA) is complex and multi-dimensional. The general physical examination is complemented by a rheumatological evaluation that includes determination of articular indices of inflammation and duration of inactivity stiffness. Laboratory assessment plays a critical role in monitoring side effects of pharmacologic management, but is limited in its ability to portray accurately the degree of active inflammation. Newly measureable indicators of inflammatory activity, such as serum cytokine and soluble cytokine receptors will likely become part of routine laboratory assessment in the future. Radiographs remain a useful tool for assessing disease progression, but may be replaced in the future by magnetic resonance imaging. In recent years, rheumatologists have realized that measurement of overall physical and psycho-social functional ability, quality of life, and pain are major descriptors to consider during routine follow-up. They are also critical in the assessment of long-term clinical effectiveness. The importance of nutritional assessment has also been realized. This section seeks to describe some of the methodologic approaches currently used to assess the variables mentioned above, and includes a brief discussion of the evolving instrumentation which attempts to measure variables of a more cognitive or subjective aspect. [ABSTRACT FROM AUTHOR]

We present paraconductivity measurements on YBCO thin films obtained by means of pulsed laser ablation in MBE condition. The films, grown in different oxygen pressure, exhibit critical temperatures ranging from 81 to 91K. The excess conductivity was analyzed in order to study critical phenomena. We observe the Lawrence-Doniach crossover and, at higher temperatures, the crossover related to the breakdown of the Ginzburg-Landau approximation, due to the importance of short wave fluctuations; the first crossover shifts to lower temperatures as the critical temperature of the film decreases, while the second occurs for all the samples roughly at the same reduced temperature, which proves the universality of the paraconductivity behaviour. [ABSTRACT FROM AUTHOR]

The recently discovered intermetallic superconducting compounds with the general formula REMBC (M 4 Pd, Ni, Pt and RE = Y + rare earths) present a record critical temperature for intermetallic compounds and other interesting properties related to the anisotropic layered structure and to an intriguing interplay between superconductivity and magnetism when RE is magnetic. Here we present the results of a wide collaboration between different groups of physicists and chemists that allowed the preparation of in situ thin films by two different techniques, namely the magnetron sputtering technique of nonmagnetic YNiBC and the high vacuum laser ablation for YNiBC and for magnetic ErNiBC and HoNiBC. The best results were obtained on MgO substrates, but superconducting films of lower quality were also obtained on sapphire and LaAlO3 substrates. [ABSTRACT FROM AUTHOR]

An innovative procedure for melt-texturing Nd Ba CuO(in7±δ) in Ar-1% O was developed. The precursor bars were allowed to crystallize from semisolid under the strong thermal gradient created by a moving thermal shield with micrometric displacement. The advantages are in the possibility of varying the thermal profile on the sample and processing long bars. The procedure allows to obtain large domains with a satisfactory control on the stoichiometry. The problems of bar deformation and reactivity with the support were definitely solved. Additional evidence of a spiral growth mechanism of the platelets stacked in the domains is shown. A.C. susceptibility measurements show T = 95.5 K and full diamagnetism below 88 K in 0.01 mT applied field. J value, determined from magnetization hysteresis loops by application of the standard critical state model, is: 6.5·10A/cm at 5 K and μH = 1T, revealing the strong pinning typical of textured materials. [ABSTRACT FROM AUTHOR]

Magnetic measurements on type-II superconducting thin films subjected to a transverse external field can be explained by a model that takes demagnetizing effects into account. We carried out measurements of magnetic flux distribution on the film surface by means of a self made apparatus, based on two Hall probes and a differential transformer and we tested the validity of a recent model presented in the literature. [ABSTRACT FROM AUTHOR]

In this paper we present magnetoresistivity and Hall effect measurements performed on a YBCO epitaxial film as a function of the angle θ between the external magnetic field and the a- b planes. The resistivity and Hall effect measurements are analyzed in term of the general scaling approach proposed by Blatter and coworkers; the Hall conductivity data are examined to separate the contributions due to vortices and quasi-particles. [ABSTRACT FROM AUTHOR]

Twisted and not twisted multifilamentary BSCCO (2223)-Ag tapes, prepared by the PIT technique, have been characterized by SQUID magnetometry with the magnetic field applied both parallel and perpendicular to the c-axis. From these measurements an estimation of the critical current densities J with Hext parallel to the c-axis, J with Hext parallel to the a- b planes and J is obtained. These values are in fairly good agreement with those obtained by transport measurements. The tapes turned out to be very homogeneous and practically no difference was found in the hysteresis loops of twisted and not twisted tapes, which suggests that the mean grain alignment is the same in the two types of samples and the current path probably follows the 'brick wall' model. [ABSTRACT FROM AUTHOR]

We report the synthesis procedure and the chemical-physical characterization of the YNiBC superconductor. From magnetic measurements we show that this material is a type-II superconductor. We evaluate the penetration depth, the coherence length and, thus, the Ginzburg-Landau parameter. Despite the low value of κ(12), a very large region of reversibility in the H-T plane is observed. [ABSTRACT FROM AUTHOR]

We report the influence on the superconducting critical temperature Tc in doped SrTiO3 of the substitution of the natural 16O atoms by the heavier isotope 18O. We observe that for a wide range of doping this substitution causes a strong (~50%) enhancement of Tc. Also the magnetic critical field Hc2 is increased by a factor ~2. Such a strong impact on Tc and Hc2, with a sign opposite to conventional superconductors, is unprecedented. The observed effect could be the consequence of strong coupling of the doped electrons to lattice vibrations (phonons), a notion which finds support in numerous optical and photo-emission studies. The unusually large size of the observed isotope effect supports a recent model for superconductivity in these materials based on strong coupling to the ferroelectric soft modes of SrTiO3. [ABSTRACT FROM AUTHOR]

We report the influence on the superconducting critical temperature Tc in doped SrTiO3 of the substitution of the natural 16O atoms by the heavier isotope 18O. We observe that for a wide range of doping this substitution causes a strong (~50%) enhancement of Tc. Also the magnetic critical field Hc2 is increased by a factor ~2. Such a strong impact on Tc and Hc2, with a sign opposite to conventional superconductors, is unprecedented. The observed effect could be the consequence of strong coupling of the doped electrons to lattice vibrations (phonons), a notion which finds support in numerous optical and photo-emission studies. The unusually large size of the observed isotope effect supports a recent model for superconductivity in these materials based on strong coupling to the ferroelectric soft modes of SrTiO3. [ABSTRACT FROM AUTHOR]