426 research outputs found
The size effect in corrosion greatly influences the predicted life span of concrete infrastructures
Chloride-induced corrosion of reinforcing steel in concrete is the main cause for premature degradation of concrete infrastructures worldwide. Since mid of the last century, the conceptual approach to tackle this challenge in science and engineering is based on a threshold chloride concentration (Ccrit) for corrosion initiation. Here, we present an experiment that shows that Ccrit depends strongly on the exposed steel surface area. The smaller the tested specimen, the higher and the more variable becomes Ccrit. This size effect can be explained by the local conditions at the steel-concrete interface, which exhibit pronounced spatial variability. The size effect has major implications for the future use of the concept of Ccrit. It questions the reproducibility of typically small-scale laboratory testing and the applicability of laboratory results to engineering structures. We show that the weakest link theory is suitable to transform Ccrit from small to large dimensions, which lays the basis for taking into account the size effect in science and engineering of corrosion of infrastructures
Evidence for two distinct anisotropies in the oxypnictide superconductors SmFeAsO_(0.8)F_(0.2) and NdFeAsO_(0.8)F_(0.2)
Single crystals of the oxypnictide superconductors SmFeAsO_(0.8)F_(0.2) and
NdFeAsO_(0.8)F_(0.2) with T_c in the range of 44 K to 48 K were investigated by
torque magnetometry. An analysis of the data in terms of a recently proposed
model for the anisotropic magnetization in the superconducting state, treating
the penetration depth anisotropy differently than the upper critical field
anisotropy, provides evidence that in the oxypnictide superconductors two
distinct anisotropies are present. As a result the penetration depth anisotropy
differs significantly in magnitude and in temperature dependence from the upper
critical field anisotropy, analogous to MgB_2 but with a reversed sign of
slope. This scenario strongly suggests a new multi-band mechanism in the novel
class of oxypnictide high-temperature superconductors.Comment: published online in J. Supercond. Nov. Mag
Depression und SuizidalitÀt
Even if the freedom to suicide is part of our human existence, about 90% of all suicides occur in the context of psychiatric disorders and thus in states of limited power of judgment. Depressive disorders represent the most frequent cause for suicides. Thus, optimization of medical care for depressive patients is one of the most promising strategies to prevent suicides. In the context of the `Nuremberg Alliance Against Depression' it came to an obvious reduction of suicidal acts compared to a baseline year and compared to the control region of Wurzburg. The reduction could be reached by a cooperation with GPs, multipliers such as teachers, priests, geriatric caregivers and the media, through intensive public relations work and through support of self help activities. This approach is carried forward within the Germany-wide `Alliance Against Depression' and within the `European Alliance Against Depression' ( EAAD) which is funded by the European Commission. In the last part of the article the suicide- preventive, but also the possible suicide-inducing effect of antidepressants is discussed
MgB2 single crystals: high pressure growth and anisotropic properties
Single crystals of MgB2 with a size up to 1.5x0.9x0.2 mm3 have been grown
with a high pressure cubic anvil technique. The crystal growth process is very
peculiar and involves an intermediate nitride, namely MgNB9. Single crystals of
BN and MgB2 grow simultaneously by a peritectic decomposition of MgNB9.
Magnetic measurements in fields of 1-5 Oe show sharp transitions to the
superconducting state at 37-38.6 K with width of ~0.5 K. The high quality of
the crystals allowed the accurate determination of magnetic, transport and
optical properties as well as scanning tunnelling spectroscopy (STS) and
decoration studies. Investigations of crystals with torque magnetometry show
that Hc2//c is very low (24 kOe at 15 K), while Hc2//ab increases up to 140 kOe
at 15 K. The upper critical field anisotropy gamma = Hc2//ab/ Hc2//c was found
to be temperature dependent (decreasing from 6 at 15 K to 2.8 at 35 K). The
effective anisotropy gamma_eff, as calculated from reversible torque data near
Tc, is field dependent (increasing roughly linearly from 2 in zero field to 3.7
in 10 kOe). The temperature and field dependence of the anisotropy can be
related to the double gap structure of MgB2 with a large two-dimensional gap
and small three-dimensional gap, the latter being rapidly suppressed in a
magnetic field. Torque magnetometry investigations show a pronounced peak
effect, indicating an order-disorder transition of vortex matter. Decoration
experiments and STS visualise a hexagonal vortex lattice. STS spectra evidence
two gaps (3 meV/6 meV) with direction dependent weight. Magneto-optic
investigations with H//c show a clear signature of the smaller of the two gaps,
disappearing in fields higher than Hc2//c.Comment: 17 pages pdf only, 15 figures integrated (higher resolution
photographs available on request); submitted to Supercond. Sci. Technol.
(Proceedings of Boromag conference
Reversible magnetization of MgB2 single crystals with a two-gap nature
We present reversible magnetization measurements on MgB2 single crystals in
magnetic fields up to 2.5 T applied parallel to the crystal's c-axis. This
magnetization is analyzed in terms of the Hao-Clem model, and various
superconducting parameters, such as the critical fields [Hc(0) and Hc2(0)], the
characteristic lengths [xi(0) and lambda(0)], and the Ginzburg-Landau
parameter, kappa, are derived. The temperature dependence of the magnetic
penetration depth, lambda(T), obtained from the Hao-Clem analysis could not be
explained by theories assuming a single gap. Our data are well described by
using a two-gap model.Comment: 20 pages, 1 table, 4 figures, will be published in Phys. Rev.
Coherence lengths and anisotropy in MgB2 superconductor
Field and temperature microwave measurements have been carried out on MgB2
thin film grown on Al2O3 substrate. The analysis reveals the mean field
coherence length xi_{MF} in the mixed state and a temperature independent
anisotropy ratio gamma_{MF} = xi_{MF}^{ab} / xi_{MF}^c approximately 2. At the
superconducting transition, the scaling of the fluctuation conductivity yields
the Ginzburg-Landau coherence length with a different anisotropy ratio
gamma_{GL} = 2.8, also temperature independent.Comment: submitted to PR
Multimorbidity in bipolar disorder and under-treatment of cardiovascular disease: a cross sectional study
Background: Individuals with serious mental disorders experience poor physical health, especially increased rates of cardiometabolic morbidity and premature morbidity. Recent evidence suggests that individuals with schizophrenia have numerous comorbid physical conditions which may be under-recorded and under-treated but to date very few studies have explored this issue for bipolar disorder.
Methods:We conducted a cross-sectional analysis of a dataset of 1,751,841 registered patients within 314 primary-care practices in Scotland, U.K. Bipolar disorder was identified using Read Codes recorded within electronic medical records. Data on 32 common chronic physical conditions were also assessed. Potential prescribing inequalities were evaluated by analyzing prescribing data for coronary heart disease (CHD) and hypertension.
Results: Compared to controls, individuals with bipolar disorder were significantly less likely to have no recorded physical conditions (OR 0.59, 95% CI 0.54-0.63) and significantly more likely to have one physical condition (OR 1.27, 95% CI 1.16-1.39), two physical conditions (OR 1.45, 95% CI 1.30-1.62) and three or more physical conditions (OR 1.44, 95% CI 1.30-1.64). People with bipolar disorder also had higher rates of thyroid disorders, chronic kidney disease, chronic pain, chronic obstructive airways disease and diabetes but, surprisingly, lower recorded rates of hypertension and atrial fibrillation. People with bipolar disorder and comorbid CHD or hypertension were significantly more likely to be prescribed no antihypertensive or cholesterol-lowering medications compared to controls, and bipolar individuals with CHD or hypertension were significantly less likely to be on 2 or more antihypertensive agents.
Conclusions: Individuals with bipolar disorder are similar to individuals with schizophrenia in having a wide range of comorbid and multiple physical health conditions. They are also less likely than controls to have a primary-care record of cardiovascular conditions such as hypertension and atrial fibrillation. Those with a recorded diagnosis of CHD or hypertension were less likely to be treated with cardiovascular medications and were treated less intensively. This study highlights the high physical healthcare needs of people with bipolar disorder, and provides evidence for a systematic under-recognition and under-treatment of cardiovascular disease in this group
Anisotropy of the Upper Critical Field and Critical Current in Single Crystal MgB
We report on specific heat, high magnetic field transport and
susceptibility measurements on magnesium diboride single crystals. The
upper critical field for magnetic fields perpendicular and parallel to
the Mg and B planes is presented for the first time in the entire temperature
range. A very different temperature dependence has been observed in the two
directions which yields to a temperature dependent anisotropy with 5 at low temperatures and about 2 near . A peak effect is observed
in susceptibility measurements for 2 T parallel to the axis and
the critical current density presnts a sharp maximum for parallel to the
ab-plane.Comment: 6 pages, 5 figure
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