294 research outputs found
Evidence of a new low field cross-over in the vortex critical velocity of type-II superconducting thin films
We measure current-voltage characteristics as function of magnetic field and
temperature in Nb strips of different thickness and width. The instability
voltage of the flux flow state related to the vortex critical velocity v* is
studied and compared with the Larkin-Ovchinnikov theory. Beside the usual
power-law dependence v* ~ B^-1/2, in the low field range a new cross-over
field, Bcr1, is observed below which v* decreases by further lowering the
external magnetic field B. We ascribe this unexpected cross-over to vortex
channeling due to a fan-like penetration of the applied magnetic field as
confirmed by magneto-optic imaging. The observation of Bcr1 becomes a direct
evidence of a general feature in type-II superconducting films at low fields,
that is a channel-like vortex motion induced by the inhomogeneous magnetic
state caused by the relatively strong pinning
A new apparatus for deep patterning of beam sensitive targets by means of high-energy ion beam
The paper reports on a high precision equipment designed to modify over
3-dimensions (3D) by means of high-energy gold ions the local properties of
thin and thick films. A target-moving system aimed at creating patterns across
the volume is driven by an x-y writing protocol that allows one to modify beam
sensitive samples over micrometer-size regions of whatever shape. The apparatus
has a mechanical resolution of 15 nm. The issue of the local fluence
measurement has been particularly addressed. The setup has been checked by
means of different geometries patterned on beam sensitive sheets as well as on
superconducting materials. In the last case the 3D modification consists of
amorphous nanostructures. The nanostructures create zones with different
dissipative properties with respect to the virgin regions. The main analysis
method consists of magneto-optical imaging that provides local information on
the electrodynamics of the modified zones. Features typical of non-linear
current flow hint at which pattern geometry is more functional to applications
in the framework of nanostructures across superconducting films.Comment: 7 page
Control of bulk superconductivity in a BCS superconductor by surface charge doping via electrochemical gating
The electrochemical gating technique is a powerful tool to tune the surface conduction properties
of various materials by means of pure charge doping, but its efficiency is thought to be hampered in
materials with a good electronic screening. We show that, if applied to a metallic superconductor
(NbN thin films), this approach allows observing reversible enhancements or suppressions of the bulk
superconducting transition temperature, which vary with the thickness of the films. These results
are interpreted in terms of proximity effect, and indicate that the effective screening length depends
on the induced charge density, becoming much larger than that predicted by standard screening
theory at very high electric fields
Magneto-plasmonic heterodimers: Evaluation of different synthesis approaches
Nanomedicine has gained huge attention in recent years with new approaches in medical diagnosis and therapy. Particular consideration has been devoted to the nanoparticles (NPs) in theranostic field with specific interest for magnetic and gold NPs (MNPs and GNPs) due to their peculiar properties under exposition to electromagnetic fields. In this paper, we aim to develop magneto-plasmonic heterodimer by combining MNPs and GNPs through a facile and reproducible synthesis and to investigate the influence of different synthesis parameters on their response to magnetic and optical stimuli. In particular, various syntheses were performed by changing the functionalization step and using or not a reducing agent to obtain stable NP suspensions with tailored properties. The obtained heterodimers were characterized through physical, chemical, optical, and magnetic analysis, in order to evaluate their size, shape, plasmonic properties, and superparamagnetic behavior. The results revealed that the shape and dimensions of the nanocomposites can be tuned by MNPs surface functionalization, as well as by the use of a reducing agent, giving rise to nanoplatform suitable for biomedical application, exploiting the gold absorbing peak in the specific gold absorbing range of GNPs, while maintaining the superparamagnetic behavior typical of the MNPs. The obtained nanocomposites can be proposed as potential candidates for cancer theranostics
Universal temperature scaling of flux line pinning in high-temperature superconducting thin films
Dissipation-free current transport in high-temperature superconductors is one
of the most crucial properties of this class of materials which is directly
related to the effective inhibition of flux line movement by defect structures.
In this respect epitaxially grown thin films of YBa2Cu3O7-d (YBCO) are proving
to be the strongest candidates for many widescale applications that are close
to realization. We show that the relation between different defect structures
and flux line pinning in these films exhibits universal features which are
clearly displayed in a detailed analysis of the temperature-dependent behaviour
of local critical currents. This allows us to identify different pinning
mechanisms at different temperatures to be responsible for the found critical
currents. Additionally, the presence of grain boundaries with very low
misorientation angles affects the temperature stability of the critical
currents which has important consequences for future applications.Comment: 5 pages, 4 figures To be published in Journal of Physics: Condensed
matte
Association between preoperative levels of 25-hydroxyvitamin D and hospital-acquired infections after hepatobiliary surgery: A prospective study in a third-level hospital
Introduction
Evidence implicates vitamin D deficiency in poorer outcomes and increased susceptibility to hospital-acquired infections (HAIs). This study examined the association between serum vitamin D levels and HAIs in a population of hepatobiliary surgery patients.
Methods
Participants in this prospective analytical observational study were patients who underwent hepatobiliary surgery in a tertiary hospital in Aragon, Spain, between February 2018 and March 2019. Vitamin D concentrations were measured at admission and all nosocomial infections during hospitalization and after discharge were recorded.
Results
The mean 25-hydroxyvitamin D concentration of the study population (n = 301) was 38.56 nmol/L, which corresponds to vitamin D deficiency. Higher vitamin D concentrations were associated with a decreased likelihood of developing a HAI in general (p = 0.014), and in particularly surgical site infection (p = 0.026). The risk of HAI decreased by 34% with each 26.2-nmol/L increase in serum vitamin D levels.
Conclusions
Vitamin D levels may constitute a modifiable risk factor for postoperative nosocomial infections in hepatobiliary surgery patients
Effective gap at microwave frequencies in MgB2 thin films with strong interband scattering
The microwave properties of polycrystalline MgB2 thin films prepared by the
so-called in-situ method are investigated. The characterization of the films at
microwave frequencies was obtained by a coplanar resonator technique. The
analysis of the experimental data results in the determination of penetration
depth, surface impedance and complex conductivity. The aim of this work is to
set the experimental results in a consistent framework, involving the two-band
model in the presence of impurity scattering. The energy gaps are calculated
and the contribution of intra- and inter-band scattering is considered. From
the comparison between the calculated gap values and the experimental data it
turns out that the temperature dependence of the penetration depth can be
accounted for by an effective mean energy gap, in agreement with the
predictions of Kogan et al. [Phys. Rev. B 69, 132506 (2004)]. On the other
hand, the temperature dependence of the real part of the microwave conductivity
and of the surface resistance is accounted for by the single smaller gap, in
agreement with the work of Jin et al. [Phys. Rev. Lett. 91, 127006 (2003)].
Since these findings rely on the same calculated gap structure, the required
consistency is fulfilled.Comment: 24 pages, 9 figures. Phys. Rev. B, in pres
Evidences of vortex curvature and anisotropic pinning in superconducting films by quantitative magneto-optics
We present the experimental observation of magnetic field line curvature at
the surface of a superconducting film by local quantitative magneto-optics. In
addition to the knowledge of the full induction field at the superconductor
surface yielding the quantitative observation of the flux line curvature, our
analysis method allows also local value measurements of the electrical current
density inside the sample. Thus, we study the interplay between the
electrodynamic constraints dictated by the film geometry and the pinning
properties of the superconductor. In particular, we investigate the anisotropic
vortex-pinning, due to columnar defects introduced by heavy ion irradiation, as
revealed in the local current density dependence on the vortex curvature during
magnetic flux diffusion inside the superconducting film.Comment: 12 pages, 11 figures, to be submitted to Phys. Rev.
Mapping ongoing nutrition intervention trials in muscle, sarcopenia, and cachexia: a scoping review of future research
Muscle loss alone, or in the context of sarcopenia or cachexia, is a prevalent condition and a predictor of negative outcomes in aging and disease. As adequate nutrition is essential for muscle maintenance, a growing number of studies has been conducted to explore the role of specific nutrients on muscle mass or function. Nonetheless, more research is needed to guide evidence-based recommendations. This scoping review aimed to compile and document ongoing clinical trials investigating nutrition interventions as a strategy to prevent or treat low muscle mass or function (strength and physical performance), sarcopenia, or cachexia. ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform were searched up to 21 April 2021 for planned and ongoing trials. Randomized controlled trials with ≥20 participants per arm were included based on intent to explore the effects of nutrition interventions on muscle-related outcomes (i.e. muscle mass or strength, physical performance, or muscle synthesis rate) in both clinical and non-clinical conditions (i.e. aging). Two reviewers independently screened records for eligibility, and a descriptive synthesis of trials characteristics was conducted. A total of 113 trials were included in the review. Most trials (69.0%) enroll adults with clinical conditions, such as cancer (19.5%), obesity and metabolic diseases (16.8%), and musculoskeletal diseases (10.7%). The effects of nutrition interventions on age-related muscle loss are explored in 31% of trials. Although nutrition interventions of varied types were identified, food supplements alone (48.7%) or combined with dietary advice (11.5%) are most frequently reported. Protein (17.7%), amino acids (10.6%), and β-hydroxy-β-methylbutyrate (HMB, 6.2%) are the top three food supplements' nutrients under investigation. Primary outcome of most trials (54.9%) consists of measures of muscle mass alone or in combination with muscle strength and/or performance (as either primary or secondary outcomes). Muscle strength and physical performance are primary outcomes of 38% and 31.9% of the trials, respectively. These measurements were obtained using a variety of techniques. Only a few trials evaluate muscle synthesis rate either as a primary or secondary outcome (5.3%). Several nutrition studies focusing on muscle, sarcopenia, and cachexia are underway and can inform future research in this area. Although many trials have similar type of interventions, methodological heterogeneity may challenge study comparisons, and future meta-analyses aiming to provide evidence-based recommendations. Upcoming research in this area may benefit from guidelines for the assessment of therapeutic effects of nutrition interventions
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