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Register a new userX-Ray Kinematography of Temperature-Jump Relaxation Probes the Elastic Properties of Fluid Bilayers
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The response kinetics of liquid crystalline phosphatidylcholine bilayer stacks to rapid, IR-laser induced temperature jumps has been studied by millisecond time-resolved x-ray diffraction. The system reacts on the fast temperature change by a discrete bilayer compression normal to its surface and a lateral bilayer expansion. Since water cannot diffuse from the excess phase into the interbilayer water region within the 2 ms duration of the laser pulse, the water layer has to follow the bilayer expansion, by an anomalous thinning. Structural analysis of a 20 ms diffraction pattern from the intermediate phase indicates that the bilayer thickness remains within the limits of isothermal equilibrium values. Both, the intermediate structure and its relaxation into the original equilibrium L_(alpha)-phase, depend on the visco-elastic properties of the bilayer/water system. We present an analysis of the relaxation process by an overdamped one-dimensional oscillation model revealing the concepts of Hookes law for phospholipid bilayers on a supramolecular basis. The results yield a constant bilayer repulsion and viscosity within Hookes regime suggesting that the hydrocarbon chains act as a buffer for the supplied thermal energy. The bilayer compression is a function of the initial temperature and the temperature amplitude, but is independent of the chain length.
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Optical bio-markers have been used extensively for intracellular imaging with high spatial and temporal resolution. Extending the modality of these probes is a key driver in cell biology. In recent years, the NV centre in nanodiamond has emerged as a promising candidate for bio-imaging and bio-sensing with low cytotoxicity and stable photoluminescence. Here we study the electrophysiological effects of this quantum probe in primary cortical neurons. Multi-electrode array (MEA) recordings across five replicate studies showed no statistically significant difference in 25 network parameters when nanodiamonds are added at varying concentrations over various time periods 12-36 hr. The physiological validation motivates the second part of the study which demonstrates how the quantum properties of these biomarkers can be used to report intracellular information beyond their location and movement. Using the optically detected magnetic resonance from the nitrogen vacancy defects within the nanodiamonds we demonstrate enhanced signal-to-noise imaging and temperature mapping from thousands of nanodiamond probes simultaneously. This work establishes nanodiamonds as viable multi-functional intraneuronal sensors with nanoscale resolution, that may ultimately be used to detect magnetic and electrical activity at the membrane level in excitable cellular systems.
The recent detection of the primordial gravitational waves from the BICEP2 observation seems to be in tension with the upper bound on the amplitude of tensor perturbations from the PLANCK data. We consider a phenomenological model of inflation in which the microscopical properties of the inflationary fluid such as the equation of state $w$ or the sound speed $c_s$ jump in a sharp manner. We show that the amplitude of the scalar perturbations is controlled by a non-trivial combination of $w$ and $c_s$ before and after the phase transition while the tensor perturbations remains nearly intact. With an appropriate choice of the fluid parameters $w$ and $c_s$ one can suppress the scalar perturbation power spectrum on large scales to accommodate a large tensor amplitude with $r=0.2$ as observed by BICEP2 observation.
This paper presents results of a spectroscopic analysis of the X-CLASS-redMaPPer (XC1-RM) galaxy cluster sample. X-CLASS is a serendipitous search for clusters in the X-ray wavebands based on the XMM-Newton archive, whereas redMaPPer is an optical cluster catalogue derived from the Sloan Digital Sky Survey (SDSS). The present sample comprises 92 X-ray extended sources identified in optical images within 1arcmin~separation. The area covered by the cluster sample is $sim$ 27 deg$^{2}$. The clusters span a wide redshift range (0.05 < z < 0.6) and 88 clusters benefit from spectrosopically confirmed redshifts using data from SDSS Data Release 14. We present an automated pipeline to derive the X-ray properties of the clusters in three distinct apertures: Rtextsubscript{500} (at fixed mass overdensity), Rtextsubscript{fit} (at fixed signal-to-noise ratio), Rtextsubscript{300kpc} (fixed physical radius). The sample extends over wide temperature and luminosity ranges: from 1 to 10 keV and from 6$times$10$^{42}$ to 11$times$10$^{44}$ erg,s$^{-1}$, respectively. We investigate the luminosity-temperature (L-T) relation of the XC1-RM sample and find a slope equals to 3.03 $pm$ 0.26. It is steeper than predicted by self-similar assumptions, in agreement with independent studies. A simplified approach is developed to estimate the amount and impact of selection biases which might be affecting our recovered L-T parameters. The result of this simulation process suggests that the measured L-T relation is biased to a steeper slope and higher normalization.
Lipid bilayers composed of non-alpha hydroxy sphingosine ceramide (CER NS), cholesterol (CHOL), and free fatty acids (FFA), which are components of the human skin barrier, are studied via molecular dynamics simulations. Since mixtures of these lipids exist in dense gel phases with little molecular mobility at physiological conditions, care must be taken to ensure that the simulations become decorrelated from the initial conditions. Thus, we propose and validate an equilibration protocol based on simulated tempering in which the simulation takes a random walk through temperature space, allowing the system to break out of metastable configurations and hence become decorrelated form its initial configuration. After validating the equilibration protocol, the effects of the lipid composition and ceramide tail length on bilayer properties are studied. Systems containing pure CER NS, CER NS + CHOL, and CER NS + CHOL + FFA, with the CER fatty acid tail length varied within each CER NS-CHOL-FFA composition, are simulated. The bilayer thickness is found to depend on the structure of the center of the bilayer, which arises as a result of the tail length asymmetry between the lipids studied. The hydrogen bonding between the lipid headgroups and with water is found to change with the overall lipid composition, but is mostly independent of the CER fatty acid tail length. Subtle differences in the lateral packing of the lipid tails are also found as a function of CER tail length. Overall, these results provide insight into the experimentally observed trend of altered barrier properties in skin systems where there are more ceramides with shorter tails present.
The coalescence in dense arrays of spontaneously formed GaN nanowires proceeds by bundling: adjacent nanowires bend and merge at their top, thus reducing their surface energy at the expense of the elastic energy of bending. We give a theoretical description of the energetics of this bundling process. The bending energy is shown to be substantially reduced by the creation of dislocations at the coalescence joints. A comparison of experimental and calculated x-ray diffraction profiles from ensembles of bundled nanowires demonstrates that a large part of the bending energy is indeed relaxed by plastic deformation. The residual bending manifests itself by extended tails of the diffraction profiles.
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