243 research outputs found
Investigating the effect of a stress-based uniaxial anisotropy on the magnetic behaviour of La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> elements
We investigate the interplay between shape anisotropy and a stress-based uniaxial anisotropy on the magnetic domain structure of La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> nanoelements as a function of aspect ratio, using micromagnetic simulations. We show that a direct competition between the anisotropies gives rise to high energy multi-domain flux closure configurations, whilst an alignment of the anisotropies can modify the effective element dimensions and act to stabilise a single domain configuration. Our results demonstrate the ability to control the spin state of La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> elements in addition to tailoring the domain wall width by controlling the anisotropy of the material, which is key for spintronic applications that require a high spin-polarization and stable magnetic configurations
Nanocharacterisation of precipitates in austenite high manganese steels with advanced techniques: HRSTEM and DualEELS mapping
To achieve optimal mechanical properties in high manganese steels, the precipitation of nanoprecipitates of vanadium and niobium carbides is under investigation. It is shown that under controlled heat treatments between 850°C and 950°C following hot deformation, few-nanometre precipitates of either carbide can be produced in test steels with suitable contents of vanadium or niobium. The structure and chemistry of these precipitates are examined in detail with a spatial resolution down to better than 1 nm using a newly commissioned scanning transmission electron microscope. In particular, it is shown that the nucleation of vanadium carbide precipitates often occurs at pre-existing titanium carbide precipitates which formed from titanium impurities in the bulk steel. This work will also highlight the links between the nanocharacterisation and changes in the bulk properties on annealing
Engineering magnetic domain-wall structure in permalloy nanowires
Using Lorentz transmission electron microscopy we investigate the behavior of
domain walls pinned at non-topographic defects in Cr(3 nm)/Permalloy(10
nm)/Cr(5 nm) nanowires of width 500 nm. The pinning sites consist of linear
defects where magnetic properties are modified by a Ga ion probe with diameter
~ 10 nm using a focused ion beam microscope. We study the detailed change of
the modified region (which is on the scale of the focused ion spot) using
electron energy loss spectroscopy and differential phase contrast imaging on an
aberration (Cs) corrected scanning transmission electron microscope. The signal
variation observed indicates that the region modified by the irradiation
corresponds to ~ 40-50 nm despite the ion probe size of only 10 nm. Employing
the Fresnel mode of Lorentz transmission electron microscopy, we show that it
is possible to control the domain wall structure and its depinning strength not
only via the irradiation dose but also the line orientation.Comment: Accepted for publication in Physical Review Applie
The anatomy and function of Cleland's ligaments
The cutaneous ligaments of the digits have been recognized by anatomists for several centuries, but the best known description is that of John Cleland. Subsequent varying descriptions of their morphology have resulted in the surgical community having an imprecise view of their structure and dynamic function. We micro-dissected 24 fresh frozen fingers to analyze the individual components of Cleland's ligamentous system. Arising from the proximal interphalangeal (PIP) joint, proximal, and sometimes middle phalanx, we found strong ligaments that ran proximally (PIP-P) and distally (PIP-D). On each side of each finger there was a PIP-P ligament present, which passed obliquely from the lateral side of the proximal and sometimes middle phalanx towards its insertion into the skin at the level of the proximal phalanx. The distal (PIP-D) ligaments were found to pass obliquely distally on the radial and ulnar aspects of the digit towards cutaneous insertions around the middle phalanx. A similar arrangement exists more distally with fibres originating from the DIP joint and middle phalanx (the DIP-P pass obliquely proximally, and the DIP-D, distally). Each individual PIP ligament consisted of three different layers originating from fibres overlying the flexor tendon sheath, periosteum or joint capsule, and extensor expansion. Ligaments arising at the DIP joint had two layers equivalent to the anterior two layers of the proximal ligaments. Cleland's ligaments act as skin anchors maintaining the skin in a fixed relationship to the underlying skeleton during motion and functional tasks. They also prevent the skin from 'bagging', protect the neurovascular bundle, and create a gliding path for the lateral slips of the extensor tendon
Characterisation of the Medipix3 detector for 60 and 80 keV electrons
In this paper we report quantitative measurements of the imaging performance for the current generation of hybrid pixel detector, Medipix3, used as a direct electron detector. We have measured the modulation transfer function and detective quantum efficiency at beam energies of 60 and 80 keV. In single pixel mode, energy threshold values can be chosen to maximize either the modulation transfer function or the detective quantum efficiency, obtaining values near to, or exceeding those for a theoretical detector with square pixels. The Medipix3 charge summing mode delivers simultaneous, high values of both modulation transfer function and detective quantum efficiency. We have also characterized the detector response to single electron events and describe an empirical model that predicts the detector modulation transfer function and detective quantum efficiency based on energy threshold. Exemplifying our findings we demonstrate the Medipix3 imaging performance recording a fully exposed electron diffraction pattern at 24-bit depth together with images in single pixel and charge summing modes. Our findings highlight that for transmission electron microscopy performed at low energies (energies <100 keV) thick hybrid pixel detectors provide an advantageous architecture for direct electron imaging
Medipix3 Demonstration and understanding of near ideal detector performance for 60 & 80 keV electrons
In our article we report first quantitative measurements of imaging
performance for the current generation of hybrid pixel detector, Medipix3, as
direct electron detector. Utilising beam energies of 60 & 80 keV, measurements
of modulation transfer function (MTF) and detective quantum efficiency (DQE)
have revealed that, in single pixel mode (SPM), energy threshold values can be
chosen to maximize either the MTF or DQE, obtaining values near to, or even
exceeding, those for an ideal detector. We have demonstrated that the Medipix3
charge summing mode (CSM) can deliver simultaneous, near ideal values of both
MTF and DQE. To understand direct detection performance further we have
characterized the detector response to single electron events, building an
empirical model which can predict detector MTF and DQE performance based on
energy threshold. Exemplifying our findings we demonstrate the Medipix3 imaging
performance, recording a fully exposed electron diffraction pattern at 24-bit
depth and images in SPM and CSM modes. Taken together our findings highlight
that for transmission electron microscopy performed at low energies (energies
<100 keV) thick hybrid pixel detectors provide an advantageous and alternative
architecture for direct electron imagin
DMI meter: Measuring the Dzyaloshinskii-Moriya interaction inversion in Pt/Co/Ir/Pt multilayers
We describe a field-driven domain wall creep-based method for the
quantification of interfacial Dzyaloshinskii-Moriya interactions (DMI) in
perpendicularly magnetized thin films. The use of only magnetic fields to drive
wall motion removes the possibility of mixing with current-related effects such
as spin Hall effect or Rashba field, as well as the complexity arising from
lithographic patterning. We demonstrate this method on sputtered Pt/Co/Ir/Pt
multilayers with a variable Ir layer thickness. By inserting an ultrathin layer
of Ir at the Co/Pt interface we can reverse the sign of the effective DMI
acting on the sandwiched Co layer, and therefore continuously change the domain
wall (DW) structure from right- to the left-handed N\'{e}el wall. We also show
that the DMI shows exquisite sensitivity to the exact details of the atomic
structure at the film interfaces by comparison with a symmetric epitaxial
Pt/Co/Pt multilayer
A transmission electron microscope study of N\'eel skyrmion magnetic textures in multilayer thin film systems with large interfacial chiral interaction
Skyrmions in ultrathin ferromagnetic metal (FM)/heavy metal (HM) multilayer
systems produced by conventional sputtering methods have recently generated
huge interest due to their applications in the field of spintronics. The
sandwich structure with two correctly-chosen heavy metal layers provides an
additive interfacial exchange interaction which promotes domain wall or
skyrmion spin textures that are N\'eel in character and with a fixed chirality.
Lorentz transmission electron microscopy (TEM) is a high resolution method
ideally suited to quantitatively image such chiral magnetic configurations.
When allied with physical and chemical TEM analysis of both planar and
cross-sectional samples, key length scales such as grain size and the chiral
variation of the magnetisation variation have been identified and measured. We
present data showing the importance of the grain size (mostly < 10nm) measured
from direct imaging and its potential role in describing observed behaviour of
isolated skyrmions (diameter < 100nm). In the latter the region in which the
magnetization rotates is measured to be around 30 nm. Such quantitative
information on the multiscale magnetisation variations in the system is key to
understanding and exploiting the behaviour of skyrmions for future device
applications.Comment: 11 pages , 6 figures, journal articl
From attosecond to zeptosecond coherent control of free-electron wave functions using semi-infinite light fields
Light-electron interaction in empty space is the seminal ingredient for
free-electron lasers and also for controlling electron beams to dynamically
investigate materials and molecules. Pushing the coherent control of free
electrons by light to unexplored timescales, below the attosecond, would enable
unprecedented applications in light-assisted electron quantum circuits and
diagnostics at extremely small timescales, such as those governing
intramolecular electronic motion and nuclear phenomena. We experimentally
demonstrate attosecond coherent manipulation of the electron wave function in a
transmission electron microscope, and show that it can be pushed down to the
zeptosecond regime with existing technology. We make a relativistic pulsed
electron beam interact in free space with an appropriately synthesized
semi-infinite light field generated by two femtosecond laser pulses reflected
at the surface of a mirror and delayed by fractions of the optical cycle. The
amplitude and phase of the resulting coherent oscillations of the electron
states in energymomentum space are mapped via momentum-resolved ultrafast
electron energy-loss spectroscopy. The experimental results are in full
agreement with our theoretical framework for light-electron interaction, which
predicts access to the zeptosecond timescale by combining semi-infinite X-ray
fields with free electrons.Comment: 22 pages, 6 figure
An abnormality in glucocorticoid receptor expression differentiates steroid responders from nonresponders in keloid disease
Background: Glucocorticoids (GCs) are first-line treatment for keloid disease (KD) but are limited by high incidence of resistance, recurrence and undesirable sideeffects. Identifying patient responsiveness early could guide therapy. Methods: Nineteen patients with KD were recruited at week 0 (before treatment) and received intralesional steroids. At weeks 0, 2 and 4, noninvasive imaging and biopsies were performed. Responsiveness was determined by clinical response and a significant reduction in vascular perfusion following steroid treatment, using full-field laser perfusion imaging (FLPI). Responsiveness was also evaluated using (i) spectrophotometric intracutaneous analysis to quantify changes in collagen and melanin and (ii) histology to identify changes in epidermal thickness and glycosaminoglycan (GAG) expression. Biopsies were used to quantify changes in glucocorticoid receptor (GR) expression using quantitative reverse transcriptase polymerase chain reaction, immunoblotting and immunohistochemistry. Results: At week 2, the FLPI was used to separate patients into steroid responsive (n = 12) and nonresponsive groups (n = 7). All patients demonstrated a signifccant decrease in GAG at week 2 (P < 0 05). At week 4, responsive patients exhibited significant reduction in melanin, GAG, epidermal thickness (all P < 0 05) and a continued reduction in perfusion (P < 0 001) compared with nonresponders. Steroid-responsive patients had increased GR expression at baseline and showed autoregulation of GR compared with nonresponders, who showed no change in GR transcription or protein. Conclusions: This is the first demonstration that keloid response to steroids can be measured objectively using noninvasive imaging. FLPI is a potentially reliable tool to stratify KD responsiveness. Altered GR expression may be the mechanism gating therapeutic response
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