106 research outputs found
Герменевтика іконографічної програми ранньобарокових священних євлогіїв у контексті євхаристійної еклезіології (на прикладі «могилянської» євхаристійної чаші)
We report a numerical study on the phase behaviour of a ‘patch–anti-patch’ model for particles with tetrahedrally arranged attractive spots. In particular, we compute the phase equilibria between the fluid and a low density diamond cubic (DC) crystal for different realizations of the patch–anti-patch interaction. By increasing the ‘specificity’ of the patches, i.e. lowering the number of corresponding attractive ‘anti-patches’ to a given patch, we find that the metastability gap between the DC freezing boundary and the liquid–gas critical point widens considerably. We argue that this effect of interaction specificity is relevant for the description of protein phase diagrams, as patch–anti-patch interactions can stabilise relatively open, ordered structures
Morphometric versus densitometric assessment of coronary vasomotor tone-an overview
The main advantage of the morphometric approach is that the spatial orientation of the vessel with respect to the image intensifier is not very important. Its most severe limitations are that reasonable accuracy can only be obtained with circular lumina, and that accuracy decreases rapidly with the vessel diameter. The densitometric approach is much less dependent on the shape of the lumen and on the correct identification of the vessel wall in the image. A further essential advantage is that one measures directly the cross-sectional area of the vessel instead of a ‘diameter' of low haemodynamic relevance. Severe requirements must however be met if the potential accuracy of densitometry is to be fully exploited. The morphometric approach seems thus preferable for absolute or relative diameter measurements on intact vessels, while densitometry is superior in case of irregular or small lumina. Morphometric calibration using the injection catheter can induce non-negligible errors in both approaches. Grid calibration is probably more accurate, but also more tedious. In the densitometric approach, ‘3D-calibration' by help of a cube of known size allows also determination of the spatial orientation of the vessel in space. This solution requires however biplane imagin
Cavitation Bubble Dynamics inside Liquid Drops in Microgravity
We studied spark-generated cavitation bubbles inside water drops produced in microgravity. High-speed visualizations disclosed unique effects of the spherical and nearly isolated liquid volume. In particular, (1) toroidally collapsing bubbles generate two liquid jets escaping from the drop, and the "splash jet" discloses a remarkable broadening. (2) Shockwaves induce a strong form of secondary cavitation due to the particular shockwave confinement. This feature offers a novel way to estimate integral shockwave energies in isolated volumes. (3) Bubble lifetimes in drops are shorter than in extended volumes in remarkable agreement with herein derived corrective terms for the Rayleigh-Plesset equation
New insight into cataract formation -- enhanced stability through mutual attraction
Small-angle neutron scattering experiments and molecular dynamics simulations
combined with an application of concepts from soft matter physics to complex
protein mixtures provide new insight into the stability of eye lens protein
mixtures. Exploring this colloid-protein analogy we demonstrate that weak
attractions between unlike proteins help to maintain lens transparency in an
extremely sensitive and non-monotonic manner. These results not only represent
an important step towards a better understanding of protein condensation
diseases such as cataract formation, but provide general guidelines for tuning
the stability of colloid mixtures, a topic relevant for soft matter physics and
industrial applications.Comment: 4 pages, 4 figures. Accepted for publication on Phys. Rev. Let
INTERACTION OF A CAVITATION BUBBLE WITH A SPHERICAL FREE SURFACE
The dynamic of a cavitation bubble inside a water drop is investigated in microgravity in order to analyze the interaction between the collapsing bubble and a quasispherical free surface. Tests are carried in the frame of the 42nd parabolic flight campaign organized by the European Space Agency (ESA). High-speed visualization revealed a significant influence of isolated, finite liquid volumes and spherical free surfaces on the bubble growth and collapse In particular; collapsing bubbles eject two liquid jets escaping from the drop in antipodal directions. The bubble lifetime is significantly shortened in good accordance with a herein derived analog of the Rayleigh- Plesset equation for bubbles in water drops. The spherical free surface leads to a broader counter jet than previously studied for flat free surfaces. The shock waves generated at the bubble collapse are spatially confined, which leads to the formation of a large number of transient micro bubbles. This phenomenon is hardly visible in the ground based experiments when bubbles are collapsing near a flat free surface within a large liquid volume
A Universal Scaling Law for Jets of Collapsing Bubbles
Cavitation bubbles collapsing and rebounding in a pressure gradient grad(p)
form a "micro-jet" enveloped by a "vapor jet". This letter presents
unprecedented observations of the vapor jets formed in a uniform
gravity-induced grad(p), modulated aboard parabolic flights. The data uncovers
that the normalized jet volume is independent of the liquid density and
viscosity and proportional to zeta=grad(p)*R0/p, where R0 is the maximal bubble
radius and p is the driving pressure. A derivation inspired by "Kelvin-Blake"
considerations confirms this law and reveals its negligible dependence of
surface tension. We further conjecture that the jet only pierces the bubble
boundary if zeta>0.0004.Comment: 4 page letter, 4 figure
Colloidal characterization and thermodynamic stability of binary eye lens protein mixtures
We present a study of binary mixtures of eye lens crystallin proteins. A coarse-grained model of aqueous α- and γ-crystallin mixtures based on molecular dynamics simulations and SANS experiments is proposed. Thermodynamic perturbation theory is implemented to obtain the stability boundaries, or spinodal surface, of the binary mixture in the full parameter space. The stability of these high-concentration crystallin mixtures was found to depend on the α−γ attraction in a manner that is both extremely sensitive and nonmonotonic; stronger or weaker attraction resulted in a spectacularly enhanced instability. The relevance of these mechanisms as possible sources of the alteration of the spatial distribution of the lens proteins encountered in cataract disease is discussed
Identification and Mode of Action of a Plant Natural Product Targeting Human Fungal Pathogens.
<i>Candida albicans</i> is a major cause of fungal diseases in humans, and its resistance to available drugs is of concern. In an attempt to identify novel antifungal agents, we initiated a small-scale screening of a library of 199 natural plant compounds (i.e., natural products [NPs]). <i>In vitro</i> susceptibility profiling experiments identified 33 NPs with activity against <i>C. albicans</i> (MIC <sub>50</sub> s ≤ 32 μg/ml). Among the selected NPs, the sterol alkaloid tomatidine was further investigated. Tomatidine originates from the tomato ( <i>Solanum lycopersicum</i> ) and exhibited high levels of fungistatic activity against <i>Candida</i> species (MIC <sub>50</sub> s ≤ 1 μg/ml) but no cytotoxicity against mammalian cells. Genome-wide transcriptional analysis of tomatidine-treated <i>C. albicans</i> cells revealed a major alteration (upregulation) in the expression of ergosterol genes, suggesting that the ergosterol pathway is targeted by this NP. Consistent with this transcriptional response, analysis of the sterol content of tomatidine-treated cells showed not only inhibition of Erg6 (C-24 sterol methyltransferase) activity but also of Erg4 (C-24 sterol reductase) activity. A forward genetic approach in <i>Saccharomyces cerevisiae</i> coupled with whole-genome sequencing identified 2 nonsynonymous mutations in <i>ERG6</i> (amino acids D249G and G132D) responsible for tomatidine resistance. Our results therefore unambiguously identified Erg6, a C-24 sterol methyltransferase absent in mammals, to be the main direct target of tomatidine. We tested the <i>in vivo</i> efficacy of tomatidine in a mouse model of <i>C. albicans</i> systemic infection. Treatment with a nanocrystal pharmacological formulation successfully decreased the fungal burden in infected kidneys compared to the fungal burden achieved by the use of placebo and thus confirmed the potential of tomatidine as a therapeutic agent
Microcavity-integrated graphene photodetector
The monolithic integration of novel nanomaterials with mature and established
technologies has considerably widened the scope and potential of nanophotonics.
For example, the integration of single semiconductor quantum dots into photonic
crystals has enabled highly efficient single-photon sources. Recently, there
has also been an increasing interest in using graphene - a single atomic layer
of carbon - for optoelectronic devices. However, being an inherently weak
optical absorber (only 2.3 % absorption), graphene has to be incorporated into
a high-performance optical resonator or waveguide to increase the absorption
and take full advantage of its unique optical properties. Here, we demonstrate
that by monolithically integrating graphene with a Fabry-Perot microcavity, the
optical absorption is 26-fold enhanced, reaching values >60 %. We present a
graphene-based microcavity photodetector with record responsivity of 21 mA/W.
Our approach can be applied to a variety of other graphene devices, such as
electro-absorption modulators, variable optical attenuators, or light emitters,
and provides a new route to graphene photonics with the potential for
applications in communications, security, sensing and spectroscopy.Comment: 19 pages, 4 figure
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