1,093 research outputs found
Nanoscale precision of 3D polymerisation via polarisation control
A systematic analysis of polarization effects in a direct write femtosecond
laser 3D lithography is presented. It is newly shown that coupling between
linear polarization of the writing light electric field and temperature
gradient can be used to fine-tune feature sizes in structuring of photoresists
at a nanoscale. The vectorial Debye focusing is used to simulate polarization
effects and a controlled variation up to 20% in the linewidth is shown
experimentally for the identical axial extent of the polymerised features. The
revealed mechanisms are relevant for a wide range of phenomena of light-matter
interaction at tight focusing in laser-tweezers and in plasmonic or dielectric
sub-wavelength focusing where strong light intensity and thermal gradients
coexist.Comment: 15 pages, 3 figure
Myosin II filament dynamics in actin networks revealed with interferometric scattering microscopy
The plasma membrane and the underlying cytoskeletal cortex constitute active platforms for a variety of cellular processes. Recent work has shown that the remodeling acto-myosin network modifies local membrane organization, but the molecular details are only partly understood due to difficulties with experimentally accessing the relevant time and length scales. Here, we use interferometric scattering (iSCAT) microscopy to investigate a minimal acto-myosin network linked to a supported lipid bilayer membrane. Using the magnitude of the interferometric contrast, which is proportional to molecular mass, and fast acquisition rates, we detect, and image individual membrane attached actin filaments diffusing within the acto-myosin network and follow individual myosin II filament dynamics. We quantify myosin II filament dwell times and processivity as functions of ATP concentration, providing experimental evidence for the predicted ensemble behavior of myosin head domains. Our results show how decreasing ATP concentrations lead to both increasing dwell times of individual myosin II filaments and a global change from a remodeling to a contractile state of the acto-myosin network
A Low Temperature Nonlinear Optical Rotational Anisotropy Spectrometer for the Determination of Crystallographic and Electronic Symmetries
Nonlinear optical generation from a crystalline material can reveal the
symmetries of both its lattice structure and underlying ordered electronic
phases and can therefore be exploited as a complementary technique to
diffraction based scattering probes. Although this technique has been
successfully used to study the lattice and magnetic structures of systems such
as semiconductor surfaces, multiferroic crystals, magnetic thin films and
multilayers, challenging technical requirements have prevented its application
to the plethora of complex electronic phases found in strongly correlated
electron systems. These requirements include an ability to probe small bulk
single crystals at the micron length scale, a need for sensitivity to the
entire nonlinear optical susceptibility tensor, oblique light incidence
reflection geometry and incident light frequency tunability among others. These
measurements are further complicated by the need for extreme sample
environments such as ultra low temperatures, high magnetic fields or high
pressures. In this review we present a novel experimental construction using a
rotating light scattering plane that meets all the aforementioned requirements.
We demonstrate the efficacy of our scheme by making symmetry measurements on a
micron scale facet of a small bulk single crystal of SrIrO using
optical second and third harmonic generation.Comment: 8 pages, 5 figure
Band-dependent Quasiparticle Dynamics in Single Crystals of the BaKFeAs Superconductor Revealed by Pump-Probe Spectroscopy
We report on band-dependent quasiparticle dynamics in
BaKFeAs () measured using ultrafast
pump-probe spectroscopy. In the superconducting state, we observe two distinct
relaxation processes: a fast component whose decay rate increases linearly with
excitation density and a slow component with an excitation density independent
decay rate. We argue that these two components reflect the recombination of
quasiparticles in the two hole bands through intraband and interband processes.
We also find that the thermal recombination rate of quasiparticles increases
quadratically with temperature. The temperature and excitation density
dependence of the decays indicates fully gapped hole bands and nodal or very
anisotropic electron bands.Comment: 4 pages, 4 figure
Physical Fitness Training in Patients with Subacute Stroke (PHYS-STROKE): multicentre, randomised controlled, endpoint blinded trial
OBJECTIVE:
To determine the safety and efficacy of aerobic exercise on activities of daily living in the subacute phase after stroke.
DESIGN:
Multicentre, randomised controlled, endpoint blinded trial.
SETTING:
Seven inpatient rehabilitation sites in Germany (2013-17).
PARTICIPANTS:
200 adults with subacute stroke (days 5-45 after stroke) with a median National Institutes of Health stroke scale (NIHSS, range 0-42 points, higher values indicating more severe strokes) score of 8 (interquartile range 5-12) were randomly assigned (1:1) to aerobic physical fitness training (n=105) or relaxation sessions (n=95, control group) in addition to standard care.
INTERVENTION:
Participants received either aerobic, bodyweight supported, treadmill based physical fitness training or relaxation sessions, each for 25 minutes, five times weekly for four weeks, in addition to standard rehabilitation therapy. Investigators and endpoint assessors were masked to treatment assignment.
MAIN OUTCOME MEASURES:
The primary outcomes were change in maximal walking speed (m/s) in the 10 m walking test and change in Barthel index scores (range 0-100 points, higher scores indicating less disability) three months after stroke compared with baseline. Safety outcomes were recurrent cardiovascular events, including stroke, hospital readmissions, and death within three months after stroke. Efficacy was tested with analysis of covariance for each primary outcome in the full analysis set. Multiple imputation was used to account for missing values.
RESULTS:
Compared with relaxation, aerobic physical fitness training did not result in a significantly higher mean change in maximal walking speed (adjusted treatment effect 0.1 m/s (95% confidence interval 0.0 to 0.2 m/s), P=0.23) or mean change in Barthel index score (0 (-5 to 5), P=0.99) at three months after stroke. A higher rate of serious adverse events was observed in the aerobic group compared with relaxation group (incidence rate ratio 1.81, 95% confidence interval 0.97 to 3.36).
CONCLUSIONS:
Among moderately to severely affected adults with subacute stroke, aerobic bodyweight supported, treadmill based physical fitness training was not superior to relaxation sessions for maximal walking speed and Barthel index score but did suggest higher rates of adverse events. These results do not appear to support the use of aerobic bodyweight supported fitness training in people with subacute stroke to improve activities of daily living or maximal walking speed and should be considered in future guidelines.
TRIAL REGISTRATION:
ClinicalTrials.gov NCT01953549
Transport and cooling of singly-charged noble gas ion beams
The transport and cooling of noble gas singly-charged ion beams by means of a
Radio Frequency Quadrupole Cooler Buncher (RFQCB) have been studied at the
LIMBE low energy beam line of the GANIL facility. Ions as light as
have been cooled and stored before their extraction in bunches using as
buffer gas. Bunches characteristics have been studied as a function of the
parameters of the device. Sizeable transmissions of up to 10 have been
obtained. A detailed study of the lifetime of ions inside the buncher has been
performed giving an estimate of the charge exchange cross-section. Results of a
microscopic Monte-Carlo transport code show reasonable agreement with
experimental data.Comment: 13 figure
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