Clathrin-mediated endocytosis (CME) involves nanoscale bending and inward budding of the plasma membrane, by which cells regulate both the distribution of membrane proteins and the entry of ...extracellular species. Extensive studies have shown that CME proteins actively modulate the plasma membrane curvature. However, the reciprocal regulation of how the plasma membrane curvature affects the activities of endocytic proteins is much less explored, despite studies suggesting that membrane curvature itself can trigger biochemical reactions. This gap in our understanding is largely due to technical challenges in precisely controlling the membrane curvature in live cells. In this work, we use patterned nanostructures to generate well-defined membrane curvatures ranging from +50 nm to -500 nm radius of curvature. We find that the positively curved membranes are CME hotspots, and that key CME proteins, clathrin and dynamin, show a strong preference towards positive membrane curvatures with a radius <200 nm. Of ten CME-related proteins we examined, all show preferences for positively curved membrane. In contrast, other membrane-associated proteins and non-CME endocytic protein caveolin1 show no such curvature preference. Therefore, nanostructured substrates constitute a novel tool for investigating curvature-dependent processes in live cells.
We experimentally study the motion of light-activated colloidal microswimmers in a viscoelastic fluid. We find that, in such a non-Newtonian environment, the active colloids undergo an unexpected ...transition from enhanced angular diffusion to persistent rotational motion above a critical propulsion speed, despite their spherical shape and stiffness. We observe that, in contrast to chiral asymmetric microswimmers, the resulting circular orbits can spontaneously reverse their sense of rotation and exhibit an angular velocity and a radius of curvature that nonlinearly depend on the propulsion speed. By means of a minimal non-Markovian Langevin model for active Brownian motion, we show that these nonequilibrium effects emerge from the delayed response of the fluid with respect to the self-propulsion of the particle without counterpart in Newtonian fluids.
Purpose
To evaluate changes in corrected distance visual acuity (CDVA), ratio of anterior and posterior corneal radii over the thinnest region of the cornea (ARC/PRC), and astigmatism after ...cross-linking (CXL) in keratoconus.
Methods
Subjective refraction and ARC/PRC (using Pentacam™) were monitored over 1 year in (I) keratoconus treated with routine CXL (
n
= 53), (II) relatively stable keratoconus (
n
= 23), and (III) age/gender matched controls (
n
= 24).
Results
CDVA (median, mode, interquartile range) improved significantly in group I, compared with groups II and III (
p
< 0.05), from 0.45 (0.60, 0.20–0.63) to 0.80 (0.95, 0.60–0.95); change in CDVA was associated with preop CDVA (
p
< 0.01 at all times postop). ARC/PRC (mean ± sd, 95% CI) changed from 1.362 (± 0.048, 1.347–1.377) to 1.425 (± 0.073, 1.401–1.449). CDVA and ARC/PRC remained stable in II and III. Significant relationships were revealed between logCDVA and ARC/PRC in I and II (at 12 months, I
r
s
= − 0.464, II
r
s
− 0.449) and logCDVA at postop(y), log CDVA at preop(x
1
), and ARC/PRC at preop(x
2
) in I (at 12 months,
y
= 0.356
x
1
− 1.312
x
2
+ 1.806,
r
2
1
= 0.494,
r
2
2
= 0.203). Astigmatic power (mean ± sd, 95% CI) improved from − 3.10DC (± 1.52, − 3.55 to − 2.66) to − 2.53DC (± 1.24, − 2.90 to − 2.17) in I, and worsened from − 1.27DC (± 1.32, − 1.81 to − 0.73) to − 1.61DC (± 1.28, − 2.13 to − 1.09) in II. Vector analysis revealed in group I (a) the power of the surgically induced astigmatism (SIA) was linked to astigmatic power at preop and (b) the difference between the axis of astigmatism at preop(ø) and the axis of the SIA was linked to ø.
Conclusion
CXL improved CDVA, increased the ARC/PRC ratio, and modified the association between CDVA and ARC/PRC. The change in CDVA was linked to preop CDVA and ARC/PRC values. The association between SIA and preop astigmatism implies there is not a simple cause and effect relationship with CXL.
The search for extra dimensions is a challenging endeavor to probe physics beyond the Standard Model. The joint detection of gravitational waves (GW) and electromagnetic (EM) signals from the merging ...of a binary system of compact objects like neutron stars can help constrain the geometry of extra dimensions beyond our 3+1 spacetime ones. A theoretically well-motivated possibility is that our observable Universe is a 3+1-dimensional hypersurface, or brane, embedded in a higher 4+1-dimensional anti–de Sitter (AdS5) spacetime, in which gravity is the only force which propagates through the infinite bulk space, while other forces are confined to the brane. In these types of brane-world models, GW and EM signals between two points on the brane would, in general, travel different paths. This would result in a time lag between the detection of GW and EM signals emitted simultaneously from the same source. We consider the recent near-simultaneous detection of the GW event GW170817 from the LIGO/Virgo collaboration, and its EM counterpart, the short gamma-ray burst GRB170817A detected by the Fermi Gamma-ray Burst Monitor and the International Gamma-Ray Astrophysics Laboratory Anti-Coincidence Shield spectrometer. Assuming the standard Λ-cold dark matter scenario and performing a likelihood analysis which takes into account astrophysical uncertainties associated to the measured time lag, we set an upper limit of ℓ≲0.535 Mpc at 68% confidence level on the AdS5 radius of curvature ℓ. Although the bound is not competitive with current Solar System constraints, it is the first time that data from a multimessenger GW-EM measurement is used to constrain extra-dimensional models. Thus, our work provides a proof of principle for the possibility of using multimessenger astronomy for probing the geometry of our space-time.
Superstrings on AdS3 at k = 1 Giribet, G.; Hull, C.; Kleban, M. ...
The journal of high energy physics,
08/2018, Letnik:
2018, Številka:
8
Journal Article
Recenzirano
Odprti dostop
A
bstract
We study superstring theory in three dimensional Anti-de Sitter spacetime with NS-NS flux, focusing on the case where the radius of curvature is equal to the string length. This corresponds ...to the critical level
k
= 1 in the formulation as a Wess-Zumino-Witten model. Previously, it was argued that a transition takes place at this special radius, from a phase dominated by black holes at larger radius to one dominated by long strings at smaller radius. We argue that the infinite tower of modes that become massless at
k
= 1 is a signal of this transition. We propose a simple two-dimensional conformal field theory as the holographic dual to superstring theory at
k
= 1. As evidence for our conjecture, we demonstrate that our putative dual exactly reproduces the full spectrum of the long strings of the weakly coupled string theory, including states unprotected by supersymmetry.
•Unshielded, conical, sharp W/WO2 ultramicroelectrodes are investigated.•Cyclic voltammetry shows higher electroactive/geometric area ratio at the apex.•Simulations show higher flux of species at the ...apex of conical ultramicroelectrodes.•The radius of curvature has a higher impact than the aspect ratio on the flow.
Ultramicroelectrodes (UMEs) have demonstrated their utility in different applications, ranging from probing chemistry to high-resolution electrochemical imaging. Conical UMEs with the apex in the nanometer range are of special interest because their geometrical features may allow the study of single/few nanoparticles, single entities, or electrochemical reactions occurring in the inner structures of living cells which are difficult to access with other types of UMEs. However, there is a lack of experimental studies with individual unshielded conical electrodes aiming at quantifying the impact of the geometry and dimensions on their electrochemical response. In this work, W / WO2 conical UMEs with aspect ratios ranging from 6.6 to 22 and apexes with nm-size dimensions were prepared by electrochemical etching of tungsten wires through an induced dynamic meniscus regime, and in one case followed by focused ion beam milling. The electrodes were characterized by scanning electron microscopy and by cyclic voltammetry in 5 mM Fe (CN)63− and 5 mM Fe (CN)64− in 0.5 M KCl as a function of the depth of the UME immersed in the electrolyte solution. Computational fluid dynamics simulations were used to investigate the mass transfer of the electroactive species at the vicinity of the electrodes. Analytical expressions to predict the steady-state current of conical electrodes with aspect ratios from 3 to 22 and radius of curvature below 110 nm were also derived. It was found that the ratio of the electrochemical surface area to the geometric one rapidly increases when the depth of the UME's in solution is lower than 15 µm, in agreement with a rapid increase of the magnitude of the total flux towards the UMEs apex. Both experimental and simulation studies point to the radius of curvature as the most important parameter determining the rate of the oxidation / reduction of the Fe (CN)63−/ Fe (CN)64− species at non-insulated conical UMEs with high aspect ratio.
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We propose a universal and analytic step-by-step method to calculate the optimal 90° and 180° waveguide bends (L-bends and U-bends) in silicon-on-insulator photonics platform. This approach consists ...of first building an analytic model of loss per unit length as a function of radius of curvature and then using a variational optimization of the bending loss. It is shown that the shape of the optimal bends is ultimately determined either by the radiation loss of tight bends if the curvature of the bend is set to eliminate mode-mismatch losses or by the sidewall roughness loss if the radius of curvature is large. Numerical results from full wave simulations and comparison of the optimal bend with the Bezier, Euler, and Hybrid Euler-Circular bend are also provided to show the validity of our approach.
Flexible and stretchable antennas are important for wireless communication using wearable and implantable devices to address mechanical mismatch at the tissue–device interface. Emerging technologies ...of liquid‐metal‐based stretchable electronics are promising approaches to improve the flexibility and stretchability of conventional metal‐based antennas. However, existing methods to encapsulate liquid metals require monolithically thick (at least 100 µm) substrates, and the resulting devices are limited in deformability and tissue‐adhesiveness. To overcome this limitation, fabrication of microchannels by direct ink writing on a 7 µm‐thick elastomeric substrate is demonstrated, to obtain liquid metal microfluidic antennas with unprecedented deformability. The fabricated wireless light‐emitting device is powered by a standard near‐field‐communication system (13.56 MHz, 1 W) and retained a consistent operation under deformations including stretching (>200% uniaxial strain), twisting (180° twist), and bending (3.0 mm radius of curvature) while maintaining a high quality factor (q > 20). Suture‐free conformal adhesion of the polydopamine‐coated device to ex vivo animal tissues under mechanical deformations is also demonstrated. This technology offers a new capability for the design and fabrication of wireless biomedical devices requiring conformable tissue‐device integration toward minimally invasive, imperceptible medical treatments.
Fabrication of unprecedentedly deformable liquid metal antennas by direct ink writing of silicone microchannels on a 7 µm‐thick elastomeric substrate is demonstrated. Suture‐free conformal adhesion of the polydopamine‐coated thin‐film antenna to ex vivo animal tissues and reliable wireless operations under mechanical deformations are also demonstrated.
Biological and morphological response of single cells are typically regulated by external physical stimuli such as substrate topographical dimension scale and pattern shape, etc. Different sizes of ...microstructures exhibit diverse regulation on cell behaviors such as proliferation, migration, and differentiation. However, the effects of cell-scale curvatures on cell differentiation and the underlying mechanism are yet to be understood. Here, we prepared microgrooves and microwells with different radii of curvatures and systematically analyzed the cell behaviors and functions on these structures. Interestingly, we found that microstructures with the cell scale curvature radii (50 µm) could provide maximum acting forces to cells and thus improve cell spreading and promote osteoblast differentiation of MC3T3-E1 cells. Additionally, the osteogenesis of MC3T3-E1 cells onto the microgroove outperformed these onto other microstructures, which may be attributed to the two-dimensional force generated by narrow continuous curvatures. This study presents an overview of cell differentiation induced by cell-scale microstructures, which may aid in the design of next-generation bone tissue engineering scaffolds.
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