97 research outputs found
Stray-fields-based magnetoresistance mechanism in Ni80Fe20-Nb-Ni80Fe20 trilayers
We report on the transport and magnetic properties of hybrid trilayers and
bilayers that consist of low spin-polarized Ni80Fe20 exhibiting in-plane but no
uniaxial anisotropy and low-Tc Nb. We reveal a magnetoresistance effect that is
pronounced. In our trilayers the magnetoresistance exhibits an increase of two
orders of magnitude when the superconducting state is reached: from the
conventional normal-state values 0.6 % it goes up to 1000 % for temperatures
below Tc. In contrast, in the bilayers the effect is only minor since from 3%
in the normal state increases only to 70 % for temperatures below Tc.
Magnetization data of both the longitudinal and transverse magnetic components
are presented. Most importantly, we present data not only for the normal state
of Nb but also in its superconducting state. Strikingly, these data show that
below its Tc SC the Nb interlayer under the influence of the outer Ni80Fe20
layers attains a magnetization component transverse to the external field. By
comparing the transport and magnetization data we propose a candidate mechanism
that could motivate the pronounced magnetoresistance effect observed in the
trilayers. Adequate magnetostatic coupling of the outer Ni80Fe20 layers is
motivated by stray fields that emerge naturally in their whole surface due to
the multidomain magnetic structure that they attain near coercivity. Atomic
force microscopy is employed in order to examine the possibility that such
magnetostatic coupling could be promoted by interface roughness. Referring to
the bilayers, although out-of-plane rotation of the magnetization of the single
Ni80Fe20 layer is still observed, in these structures magnetostatic coupling
does not occur due to the absence of a second Ni80Fe20 one so that the observed
magnetoresistance peaks are only modest.Comment: 9 pages, 7 figure
Crystal and magnetic structure of LaCaMnO compound $(0.11\leq x\leq 0.175
We studied the crystal and magnetic structure of the
LaCaMnO compound for using
stoichiometric samples. For the system's ground state is insulating
canted antiferromagnetic. For e below the Jahn Teller
transition temperature () the crystal structure undergoes a
monoclinic distortion. The crystal structure can be described with
space group which permits two Mn sites. The unit cell strain parameter
increases for , taking the maximum value at the
Curie point, and then decreases. Below K
abruptly changes slope and finally approaches T=0 K with nearly zero slope. The
change of at is connected to a characteristic feature
in the magnetic measurements. As increases towards the ferromagnetic
metallic boundary, although is reduced appreciably, the monoclinic
structure is preserved. The monoclinic structure is discussed with relation to
the orbital ordering, which can produce the ferromagnetic insulating ground
state. We also studied samples that were prepared in air atmosphere. This
category of samples shows ferromagnetic insulating behavior without following
the particular variation of the parameter. The crystal structure of these
samples is related to the so-called O () structure
Symmetries of Pairing Correlations in Superconductor-Ferromagnet Nanostructures
Using selection rules imposed by the Pauli principle, we classify pairing
correlations according to their symmetry properties with respect to spin,
momentum, and energy. We observe that inhomogeneity always leads to mixing of
even- and odd-energy pairing components. We investigate the superconducting
pairing correlations present near interfaces between superconductors and
ferromagnets, with focus on clean systems consisting of singlet superconductors
and either weak or half-metallic ferromagnets. Spin-active scattering in the
interface region induces all of the possible symmetry components. In
particular, the long-range equal-spin pairing correlations have odd-frequency
s-wave and even-frequency p-wave components of comparable magnitudes. We also
analyze the Josephson current through a half-metal. We find analytic
expressions and an interesting universality in the temperature dependence of
the critical current in the tunneling limit.Comment: 20 pages, 5 figures, added citations, corrected typo
Nucleation of superconductivity and vortex matter in superconductor - ferromagnet hybrids
The theoretical and experimental results concerning the thermodynamical and
low-frequency transport properties of hybrid structures, consisting of
spatially-separated conventional low-temperature superconductor (S) and
ferromagnet (F), is reviewed. Since the superconducting and ferromagnetic parts
are assumed to be electrically insulated, no proximity effect is present and
thus the interaction between both subsystems is through their respective
magnetic stray fields. Depending on the temperature range and the value of the
external field H_{ext}, different behavior of such S/F hybrids is anticipated.
Rather close to the superconducting phase transition line, when the
superconducting state is only weakly developed, the magnetization of the
ferromagnet is solely determined by the magnetic history of the system and it
is not influenced by the field generated by the supercurrents. In contrast to
that, the nonuniform magnetic field pattern, induced by the ferromagnet,
strongly affect the nucleation of superconductivity leading to an exotic
dependence of the critical temperature T_{c} on H_{ext}. Deeper in the
superconducting state the effect of the screening currents cannot be neglected
anymore. In this region of the phase diagram various aspects of the interaction
between vortices and magnetic inhomogeneities are discussed. In the last
section we briefly summarize the physics of S/F hybrids when the magnetization
of the ferromagnet is no longer fixed but can change under the influence of the
superconducting currents. As a consequence, the superconductor and ferromagnet
become truly coupled and the equilibrium configuration of this "soft" S/F
hybrids requires rearrangements of both, superconducting and ferromagnetic
characteristics, as compared with "hard" S/F structures.Comment: Topical review, submitted to Supercond. Sci. Tech., 67 pages, 33
figures, 439 reference
Intraperitoneal drain placement and outcomes after elective colorectal surgery: international matched, prospective, cohort study
Despite current guidelines, intraperitoneal drain placement after elective colorectal surgery remains widespread. Drains were not associated with earlier detection of intraperitoneal collections, but were associated with prolonged hospital stay and increased risk of surgical-site infections.Background Many surgeons routinely place intraperitoneal drains after elective colorectal surgery. However, enhanced recovery after surgery guidelines recommend against their routine use owing to a lack of clear clinical benefit. This study aimed to describe international variation in intraperitoneal drain placement and the safety of this practice. Methods COMPASS (COMPlicAted intra-abdominal collectionS after colorectal Surgery) was a prospective, international, cohort study which enrolled consecutive adults undergoing elective colorectal surgery (February to March 2020). The primary outcome was the rate of intraperitoneal drain placement. Secondary outcomes included: rate and time to diagnosis of postoperative intraperitoneal collections; rate of surgical site infections (SSIs); time to discharge; and 30-day major postoperative complications (Clavien-Dindo grade at least III). After propensity score matching, multivariable logistic regression and Cox proportional hazards regression were used to estimate the independent association of the secondary outcomes with drain placement. Results Overall, 1805 patients from 22 countries were included (798 women, 44.2 per cent; median age 67.0 years). The drain insertion rate was 51.9 per cent (937 patients). After matching, drains were not associated with reduced rates (odds ratio (OR) 1.33, 95 per cent c.i. 0.79 to 2.23; P = 0.287) or earlier detection (hazard ratio (HR) 0.87, 0.33 to 2.31; P = 0.780) of collections. Although not associated with worse major postoperative complications (OR 1.09, 0.68 to 1.75; P = 0.709), drains were associated with delayed hospital discharge (HR 0.58, 0.52 to 0.66; P < 0.001) and an increased risk of SSIs (OR 2.47, 1.50 to 4.05; P < 0.001). Conclusion Intraperitoneal drain placement after elective colorectal surgery is not associated with earlier detection of postoperative collections, but prolongs hospital stay and increases SSI risk
Comportamento de predação e conversão alimentar de Podisus nigrispinus sobre a traça-do-tomateiro
Sublethal effects of three essential oils on the development, longevity and fecundity of Acanthoscelides obtectus (say) (Coleoptera: Bruchidae)
Acanthoscelides obtectus larvae and pupae were exposed to three levels (LC10, LC40 and LC40) of lavender, rosemary and eucalyptus essential oil vapours. The exposure of larvae and pupae to sublethal doses of essential oil vapours resulted in increased larval and pupal developmental time and reduced longevity and fecundity of the emerged female adults. The observed Effects depended on the insect stage and sex as well as the essential oil tested. In all cases no delayed mortality was observed. © Benaki Phytopathological Institute
Fumigant toxicity of three essential oils on the eggs of Acanthoscelides obtectus (Say) (Coleoptera : Bruchidae)
Fumigant toxicity of the essential oils from Lavandula hybrida, Rosmarinus officinalis and Eucalyptus globulus against the eggs of Acanthoscelides obtectus was assessed. The essential oil vapours were toxic to eggs with LC50 values ranging between 1.3 and 35.1 mul/l air, depending on egg age and the essential oil. In all cases, the young eggs (less than or equal to 3-day old) were more tolerant to essential oil vapours than the older ones (greater than or equal to 4-day old). Apart from the inhibition of hatching, the exposure of eggs to essential oil vapours increased the subsequent mortality of hatched larvae. The influence of length of exposure to essential oil vapours on egg hatchability was also significant. (C) 2003 Elsevier Ltd. All rights reserved
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