Pseudo-contact angle due to superfluid vortices in 4^{4}He

We have investigated spreading of superfluid $^{4}$He on top of polished MgF$_2$ and evaporated SiO$_{2}$ substrates. Our results show strongly varying contact angles of 0 - 15 mrad on the evaporated layers. According to our theoretical calculations, these contact angles can be explained by a spatially varying distribution of vortex lines, the unpinning velocity of which is inversely proportional to the liquid depth.Comment: 10 pages, 4 figure

Ice-templated structures for biomedical tissue repair: From physics to final scaffolds

Ice-templating techniques, including freeze-drying and freeze casting, are extremely versatile and can be used with a variety of materials systems. The process relies on the freezing of a water based solution. During freezing, ice nucleates within the solution and concentrates the solute in the regions between the growing crystals. Once the ice is removed via sublimation, the solute remains in a porous structure, which is a negative of the ice. As the final structure of the ice relies on the freezing of the solution, the variables which influence ice nucleation and growth alter the structure of ice-templated scaffolds. Nucleation, the initial step of freezing, can be altered by the type and concentration of solutes within the solution, as well as the set cooling rate before freezing. After nucleation, crystal growth and annealing processes, such as Ostwald ripening, determine the features of the final scaffold. Both crystal growth and annealing are sensitive to many factors including the set freezing temperature and solutes. The porous structures created using ice-templating allow scaffolds to be used for many diverse applications, from microfluidics to biomedical tissue engineering. Within the field of tissue engineering, scaffold structure can influence cellular behavior, and is thus critical for determining the biological stimulus supplied by the scaffold. The research focusing on controlling the ice-templated structure serves as a model for how other ice-templating systems might be tailored, to expand the applications of ice-templated structures to their full potential.The authors gratefully acknowledge the financial support of the Gates Cambridge Trust, the Newton Trust, and ERC Advanced Grant No. 320598 3D-E. A.H. holds a Daphne Jackson Fellowship funded by the University of Cambridge.Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Reviews,1, 021301(2014) and may be found at: http://scitation.aip.org/content/aip/journal/apr2/1/2/10.1063/1.4871083

Информационная система образовательного отдела администрации города Юрги

Sintered targets of Al2O3 are removed by CO(2-) and excimer laser radiation and deposited as thin films onto steel and silicon substrates. Micro Raman spectroscopy and atomic force microscopy are used to characterize the morphological and structural properties of the films. Mechanical properties are investigated by nanoindentation measurements and a laser-acoustic method, optical properties are studied by ellipsometry. Al2O3 films deposited using CO2-laser radiation show an inhomogeneous surface structure with droplets embedded in a matrix, whereas the films deposited using excimer laser radiation are smooth, which is explained by different material removal mechanisms. The microhardness (i.e. ratio of indentation load to residual area of the indent) of the amorphous matrix structure is about 8 GPa, the crystalline droplets are softer at about 2 GPa. Varying the processing gas pressures in the range of 0.0 1 -0.6 mbar yields a change in the index of refraction of the films, which is clo se to the bulk value for gas pressures < 0.1 mbar. The decrease of the index of refraction is caused by a lowered film density, correlating with a lowered mean energy,of the particles impinging on the substrate, which is calculated. The results show the possibility of scaling-up the pulsed laser deposition process for industrial applications by use of C02-laser radiation

Understanding anisotropy and architecture in ice-templated biopolymer scaffolds.

Biopolymer scaffolds have great therapeutic potential within tissue engineering due to their large interconnected porosity and biocompatibility. Using an ice-templated technique, where collagen is concentrated into a porous network by ice nucleation and growth, scaffolds with anisotropic pore architecture can be created, mimicking natural tissues like cardiac muscle and bone. This paper describes a systematic set of experiments undertaken to understand the effect of local temperatures on architecture in ice-templated biopolymer scaffolds. The scaffolds within this study were at least 10mm in all dimensions, making them applicable to critical sized defects for biomedical applications. It was found that monitoring the local freezing behavior within the slurry was critical to predicting scaffold structure. Aligned porosity was produced only in parts of the slurry volume which were above the equilibrium freezing temperature (0°C) at the time when nucleation first occurs in the sample as a whole. Thus, to create anisotropic scaffolds, local slurry cooling rates must be sufficiently different to ensure that the equilibrium freezing temperature is not reached throughout the slurry at nucleation. This principal was valid over a range of collagen slurries, demonstrating that by monitoring the temperature within slurry during freezing, scaffold anisotropy with ice-templated scaffolds can be predicted.The authors gratefully acknowledge the financial supp ort of the Gates Cambridge Trust, the Newton Trust, and ERC Advanced Grant 320598 3D-E. A.H. holds a Daphne Jackson Fellowship funded by the University of Cambridge.This is a pre-print of an article which received final publication in Materials Science and Engineering: C Volume 37, 1 April 2014, Pages 141–147. The version offered here does not reflect changes resulting from peer-review. The version of record is available at http://www.sciencedirect.com/science/article/pii/S0928493114000101

Manipulating coincident charge and spin order with pressure and field in a doped manganite

The onset of charge order occurs simultaneously with the transition from ferromagnetic metal to antiferromagnetic insulator in Nd_(0.05)Sr_(0.5)MnO_3. The application of hydrostatic pressures P≥15 kbar removes the degeneracy, as recorded in both the electrical resistivity and the magnetic susceptibility. The charge-ordered state moves swiftly to higher temperature with increasing pressure at the expense of the ferromagnetic charge liquid, dominating the energetics. An applied magnetic field H suppresses both the pressure-split charge order and the antiferromagnetism, but charge order preferentially, so by H = 2 T the two transitions are reunited. Finally, depinning domains of charge order with electric field deep in the antiferromagnetic insulator permits us to monitor pressure-induced changes in the charge (poly)crystal

Ionic solutes impact collagen scaffold bioactivity.

The structure of ice-templated collagen scaffolds is sensitive to many factors. By adding 0.5 wt% of sodium chloride or sucrose to collagen slurries, scaffold structure could be tuned through changes in ice growth kinetics and interactions of the solute and collagen. With ionic solutes (sodium chloride) the entanglements of the collagen molecule decreased, leading to fibrous scaffolds with increased pore size and decreased attachment of chondrocytes. With non-ionic solutes (sucrose) ice growth was slowed, leading to significantly reduced pore size and up-regulated cell attachment. This highlights the large changes in structure and biological function stimulated by solutes in ice-templating systems.The authors gratefully acknowledge the financial support of the Gates Cambridge Trust, the Newton Trust, NIHR, and ERC Advanced Grant 320598 3D-E. A.H. holds a Daphne Jackson Fellowship funded by the University of Cambridge. Also, the authors thank Dr. S. Butler for help with the rheological measurements.This is the accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s10856-015-5457-8