Mechanism for Spontaneous Growth of Nanopillar Arrays in Ultrathin Films Subject to a Thermal Gradient

Several groups have reported spontaneous formation of periodic pillar-like arrays in molten polymer nanofilms confined within closely spaced substrates maintained at different temperatures. These formations have been attributed to a radiation pressure instability caused by acoustic phonons. In this work, we demonstrate how variations in the thermocapillary stress along the nanofilm interface can produce significant periodic protrusions in any viscous film no matter how small the initial transverse thermal gradient. The linear stability analysis of the interface evolution equation explores an extreme limit of B\'{e}nard-Marangoni flow peculiar to films of nanoscale dimensions in which hydrostatic forces are altogether absent and deformation amplitudes are small in comparison to the pillar spacing. Finite element simulations of the full nonlinear equation are also used to examine the array pitch and growth rates beyond the linear regime. Inspection of the Lyapunov free energy as a function of time confirms that in contrast to typical cellular instabilities in macroscopically thick films, pillar-like elongations are energetically preferred in nanofilms. Provided there occurs no dewetting during film deformation, it is shown that fluid elongations continue to grow until contact with the cooler substrate is achieved. Identification of the mechanism responsible for this phenomenon may facilitate fabrication of extended arrays for nanoscale optical, photonic and biological applications.Comment: 20 pages, 9 figure

Formation of Nanopillar Arrays in Ultrathin Viscous Films: The Critical Role of Thermocapillary Stresses

Experiments by several groups during the past decade have shown that a molten polymer nanofilm subject to a large transverse thermal gradient undergoes spontaneous formation of periodic nanopillar arrays. The prevailing explanation is that coherent reflections of acoustic phonons within the film cause a periodic modulation of the radiation pressure which enhances pillar growth. By exploring a deformational instability of particular relevance to nanofilms, we demonstrate that thermocapillary forces play a crucial role in the formation process. Analytic and numerical predictions show good agreement with the pillar spacings obtained in experiment. Simulations of the interface equation further determine the rate of pillar growth of importance to technological applications.Comment: 5 pages, 4 figure

Messung und Bestimmung von Determinanten der optischen Dichte des makulären Pigments (MPOD) mit der Zweiwellenlängen-Methode des Autofluoreszenz-Imaging: Untersuchungen im Rahmen der Münsteraner Altern und Retina Studie (MARS)

Man vermutet einen protektiven Effekt des makulären Pigments (MP), bestehend aus Lutein (L) und Zeaxanthin (Z), im Hinblick auf die Altersabhängige Makuladegeneration (AMD). In dieser Arbeit wurden die optische Dichte des MP (MPOD) mittels Zweiwellenlängen-Methode des Autofluoreszenz-Imaging bei Probanden von MARS, einer prospektiven Studie zur AMD-Progression, zentral (0,5°) und peripher (2,0°) gemessen und MPOD-Determinanten bestimmt (n=376). Untersucht wurden Zusammenhänge zwischen MPOD und Alter, Geschlecht, Rauchen, Blutdruck, Body-Mass-Index (BMI), Parametern von Lipidstoffwechsel und Inflammation, L- bzw. Z-Serumwerten, L-Supplementation sowie Vorliegen einer AMD. Alter, weibliches Geschlecht, systolischer Blutdruck, BMI und Rauchen wurden als unabhängige Determinanten der MPOD bei 0,5° bzw. 2,0° identifiziert. L- und Z-Serumspiegel und L-Supplementierung waren eng mit der MPOD verbunden. Der hypothetische, inverse Zusammenhang des MP mit der AMD wurde nicht bestätigt

Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures

Variations in barium (Ba) stable isotope abundances measured in low and high temperature environments have recently received increasing attention. The actual processes controlling Ba isotope fractionation, however, remain mostly elusive. In this study, we present the first experimental approach to quantity the contribution of diffusion and adsorption on mass-dependent Ba isotope fractionation during transport of aqueous Ba²+ ions through a porous medium. Experiments have been carried out in which a BaCl₂ solution of known isotopic composition diffused through u-shaped glass tubes filled with silica hydrogel at 10 °C and 25 °C for up to 201 days. The diffused Ba was highly fractionated by up to -2.15 ‰ in δ¹³⁷⁄¹³⁴Ba, despite its high atomic mass. The time-dependent isotope fractionation can be successfully reproduced by a diffusive transport model accounting for mass-dependent differences in the effective diffusivities of the Ba isotope species (D₁₃₇Ba ⁄D₁₃₄Ba =(m₁₃₄⁄m₁₃₇ )β ). Values of β extracted from the transport model were in the range of 0.010 to 0.011. Independently conducted batch experiments revealed that adsorption of Ba onto the surface of silica hydrogel favoured the heavier Ba isotopes (α = 1.00015 ± 0.00008). The contribution of adsorption on the overall isotope fractionation in the diffusion experiments, however, was found to be small. Our results contribute to the understanding of Ba isotope fractionation processes, which is crucial for interpreting natural isotope variations and the assessment of Ba isotope ratios as geochemical proxies

Geographical Distribution of Fungal Plant Pathogens in Dust Across the United States

As the world's population grows, global food production will need to increase. While food production efficiency has increased in recent decades through pathogen control, climate change poses new challenges in crop protection against pathogens. Understanding the natural geographical distribution and dispersal likelihood of fungal plant pathogens is essential for forecasting disease plant spread. Here we used cultivation-independent techniques to identify fungal plant pathogens in 1,289 near-surface dust samples collected across the United States. We found that overall fungal pathogen community composition is more related to environmental conditions (in particular soil pH, precipitation and frost) than to agricultural hosts and practices. We also delimited five susceptibility geographical areas in the United States where different sets of pathogens tend to occur.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Asymmetric nanofluidic grating detector for differential refractive index measurement and biosensing.

Measuring small changes in refractive index can provide both sensitive and contactless information on molecule concentration or process conditions for a wide range of applications. However, refractive index measurements are easily perturbed by non-specific background signals, such as temperature changes or non-specific binding. Here, we present an optofluidic device for measuring refractive index with direct background subtraction within a single measurement. The device is comprised of two interdigitated arrays of nanofluidic channels designed to form an optical grating. Optical path differences between the two sets of channels can be measured directly via an intensity ratio within the diffraction pattern that forms when the grating is illuminated by a collimated laser beam. Our results show that no calibration or biasing is required if the unit cell of the grating is designed with an appropriate built-in asymmetry. In proof-of-concept experiments we attained a noise level equivalent to ∼10(-5) refractive index units (30 Hz sampling rate, 4 min measurement interval). Furthermore, we show that the accumulation of biomolecules on the surface of the nanochannels can be measured in real-time. Because of its simplicity and robustness, we expect that this inherently differential measurement concept will find many applications in ultra-low volume analytical systems, biosensors, and portable devices