118 research outputs found
Development of an oximeter for neurology
Cerebral desaturation can occur during surgery manipulation, whereas otherparameters vary insignificantly. Prolonged intervals of cerebral anoxia can cause seriousdamage to the nervous system. Commonly used method for measurement of cerebral bloodflow uses invasive catheters. Other techniques include single photon emission computedtomography (SPECT), positron emission tomography (PET), magnetic resonance imaging(MRI). Tomographic methods frequently use isotope administration, that may result inanaphylactic reactions to contrast media and associated nerve diseases. Moreover, the high costand the need for continuous monitoring make it difficult to apply these techniques in clinicalpractice. Cerebral oximetry is a method for measuring oxygen saturation using infraredspectrometry. Moreover reflection pulse oximetry can detect sudden changes in sympathetictone. For this purpose the reflectance pulse oximeter for use in neurology is developed.Reflectance oximeter has a definite advantage as it can be used to measure oxygen saturation inany part of the body. Preliminary results indicate that the device has a good resolution and highreliability. Modern applied schematics have improved device characteristics compared withexisting ones
Photoacoustic Sensing of Trapped Fluids in Nanoporous Thin Films: Device Engineering and Sensing Scheme
Accessing fluid infiltration in nanogranular coatings is an outstanding
challenge, of relevance for applications ranging from nanomedicine to
catalysis. A sensing platform, allowing to quantify the amount of fluid
infiltrated in a nanogranular ultrathin coating, with thickness in the 10 to 40
nm range, is here proposed and theoretically investigated by multiscale
modelling. The scheme relies on impulsive photoacoustic excitation of
hypersonic mechanical breathing modes in engineered gas-phase synthesised
nanogranular metallic ultathin films and time-resolved acousto-optical read-out
of the breathing modes frequency shift upon liquid infiltration. A superior
sensitivity, exceeding 26x103 cm^2/g, is predicted upon equivalent areal mass
loading of a few ng/mm^2. The capability of the present scheme to discriminate
among different infiltration patterns is discussed. The platform is an ideal
tool to investigate nano fluidics in granular materials and naturally serves as
a distributed nanogetter coating, integrating fluid sensing capabilities. The
proposed scheme is readily extendable to other nanoscale and mesoscale porous
materials.Comment: 14 pages, 4 figure
Thin film growth of semiconducting Mg2Si by codeposition
Includes bibliographical references (page 1088).Ultrahigh vacuum evaporation of magnesium onto a hot silicon substrate (⩾200 °C), with the intention of forming a Mg2Si thin film by reaction, does not result in any accumulation of magnesium or its silicide. On the other hand, codeposition of magnesium with silicon at 200 °C, using a magnesium-rich flux ratio, gives a stoichiometric Mg2Si film which can be grown several hundreds of nm thick. The number of magnesium atoms which condense is equal to twice the number of silicon atoms which were deposited; all the silicon condenses while the excess magnesium in the flux desorbs. The Mg2Si layers thus obtained are polycrystalline with a (111) texture. From the surface roughness analysis, a self-affine growth mode with a roughness exponent equal to 1 is deduced
Nanoengineered magnetic-field-induced superconductivity
The perpendicular critical fields of a superconducting film have been
strongly enhanced by using a nanoengineered lattice of magnetic dots (dipoles)
on top of the film. Magnetic-field-induced superconductivity is observed in
these hybrid superconductor / ferromagnet systems due to the compensation of
the applied field between the dots by the stray field of the dipole array. By
switching between different magnetic states of the nanoengineered field
compensator, the critical parameters of the superconductor can be effectively
controlled.Comment: 4 pages, 4 figure
Metastable states and hidden phase slips in nanobridge SQUIDs
We fabricated an asymmetric nanoscale SQUID consisting of one nanobridge weak
link and one Dayem bridge weak link. The current phase relation of these
particular weak links is characterized by multivaluedness and linearity. While
the latter is responsible for a particular magnetic field dependence of the
critical current (so-called vorticity diamonds), the former enables the
possibility of different vorticity states (phase winding numbers) existing at
one magnetic field value. In experiments the observed critical current value is
stochastic in nature, does not necessarily coincide with the current associated
with the lowest energy state and critically depends on the measurement
conditions. In this work, we unravel the origin of the observed metastability
as a result of the phase dynamics happening during the freezing process and
while sweeping the current. Moreover, we employ special measurement protocols
to prepare the desired vorticity state and identify the (hidden) phase slip
dynamics ruling the detected state of these nanodevices. In order to gain
insights into the dynamics of the condensate and, more specifically the hidden
phase slips, we performed time-dependent Ginzburg-Landau simulations.Comment: 10 pages, 4 figures, 1 supplementary vide
Enhanced Magnetoelectric Coupling in BaTiO3-BiFeO3 Multilayers—An Interface Effect
Combining various (multi-)ferroic materials into heterostructures is a promising route to enhance their inherent properties, such as the magnetoelectric coupling in BiFeO3 thin films. We have previously reported on the up-to-tenfold increase of the magnetoelectric voltage coefficient αME in BaTiO3-BiFeO3 multilayers relative to BiFeO3 single layers. Unraveling the origin and mechanism of this enhanced effect is a prerequisite to designing new materials for the application of magnetoelectric devices. By careful variations in the multilayer design we now present an evaluation of the influences of the BaTiO3-BiFeO3 thickness ratio, oxygen pressure during deposition, and double layer thickness. Our findings suggest an interface driven effect at the core of the magnetoelectric coupling effect in our multilayers superimposed on the inherent magnetoelectric coupling of BiFeO3 thin films, which leads to a giant αME coefficient of 480 Vcm−1 Oe−1 for a 16×(BaTiO3-BiFeO3) superlattice with a 4.8 nm double layer periodicity
Flux pinning by regular arrays of ferromagnetic dots
The pinning of flux lines by two different types of regular arrays of
submicron magnetic dots is studied in superconducting Pb films; rectangular Co
dots with in-plane magnetization are used as pinning centers to investigate the
influence of the magnetic stray field of the dots on the pinning phenomena,
whereas multilayered Co/Pt dots with out-of-plane magnetization are used to
study the magnetic interaction between the flux lines and the magnetic moment
of the dots. For both types of pinning arrays, matching anomalies are observed
in the magnetization curves versus perpendicular applied field at integer and
rational multiples of the first matching field, which correspond to stable flux
configurations in the artificially created pinning potential. By varying the
magnetic domain structure of the Co dots with in-plane magnetization, a clear
influence of the stray field of the dots on the pinning efficiency is found.
For the Co/Pt dots with out-of-plane magnetization, a pronounced field
asymmetry is observed in the magnetization curves when the dots are magnetized
in a perpendicular field prior to the measurement. This asymmetry can be
attributed to the interaction of the out-of-plane magnetic moment of the Co/Pt
dots with the local field of the flux lines and indicates that flux pinning is
stronger when the magnetic moment of the dot and the field of the flux line
have the same polarity.Comment: 7 pages including figures; submitted for publication in Physica C
(Proceedings ESF-Vortex Conference, 18-24 Sept. 1999, Crete, Greece
Interface induced out-of-plane magnetic anisotropy in magnetoelectric BiFeO3-BaTiO3 superlattices
Room temperature magnetoelectric BiFeO3-BaTiO3 superlattices with strong out-of-plane
magnetic anisotropy have been prepared by pulsed laser deposition. We show that the out-ofplane
magnetization component increases with the increasing number of double layers.
Moreover, the magnetoelectric voltage coefficient can be tuned by varying the number of
interfaces, reaching a maximum value of 29 V/cmOe for the20×BiFeO3-BaTiO3 superlattice.
This enhancement is accompanied by a high degree of perpendicular magnetic anisotropy,
making the latter an ideal candidate for the next generation of data storage devices
Exploring the optical and morphological properties of ag and Ag/TiO2nanocomposites grown by supersonic cluster beam deposition
Nanocomposite systems and nanoparticle (NP) films are crucial for many applications and research fields. The structure-properties correlation raises complex questions due to the collective structure of these systems, often granular and porous, a crucial factor impacting their effectiveness and performance. In this framework, we investigate the optical and morphological properties of Ag nanoparticles (NPs) films and of Ag NPs/TiO2porous matrix films, one-step grown by supersonic cluster beam deposition. Morphology and structure of the Ag NPs film and of the Ag/TiO2(Ag/Ti 50-50) nanocomposite are related to the optical properties of the film employing spectroscopic ellipsometry (SE). We employ a simple Bruggeman effective medium approximation model, corrected by finite size effects of the nano-objects in the film structure to gather information on the structure and morphology of the nanocomposites, in particular porosity and average NPs size for the Ag/TiO2NP film. Our results suggest that SE is a simple, quick and effective method to measure porosity of nanoscale films and systems, where standard methods for measuring pore sizes might not be applicable
- …