487 research outputs found
Influence of Line Tension on Spherical Colloidal Particles at Liquid-Vapor Interfaces
Atomic force microscopy (AFM) imaging of isolated submicron dodecyltrichlorosilane coated silica spheres, immobilized at the liquid polystyrene- (PS-) air interface at the PS glass transition temperature, Tg , allows for determination of the contact angle θ versus particle radius R . At Tg , all θ versus R measurements are well described by the modified Youngâs equation for a line tension Ď=0.93âânN . The AFM measurements are also consistent with a minimum contact angle θmin and minimum radius Rmin , below which single isolated silica spheres cannot exist at the PS-air interface
Improved In Situ Spring Constant Calibration for Colloidal Probe Atomic Force Microscopy
In colloidal probe atomic force microscopy (AFM) surface forces cannot be measured without an accurate determination of the cantilever spring constant. The effective spring constant k depends upon the cantilever geometry and therefore should be measured in situ; additionally, k may be coupled to other measurement parameters. For example, colloidal probe AFM is frequently used to measure the slip length b at solid/liquid boundaries by comparing the measured hydrodynamic force with Vinogradova slip theory (V-theory). However, in this measurement k and b are coupled, hence, b cannot be accurately determined without knowing k to high precision. In this paper, a new in situ spring constant calibration method based upon the residuals, namely, the difference between experimental force-distance data and V-theory is presented and contrasted with two other popular spring constant determination methods. In this residuals calibration method, V-theory is fitted to the experimental force-distance data for a range of systematically varied spring constants where the only adjustable parameter in V-theory is the slip length b. The optimal spring constant k is that value where the residuals are symmetrically displaced about zero for all colloidal probe separations. This residual spring constant calibration method is demonstrated by studying three different liquids (n-decanol, n-hexadecane, and n-octane) and two different silane coated colloidal probe-silicon wafer systems (n-hexadecyltrichlorosilane and n-dodecyltrichlorosilane)
Viscosity Dependent Liquid Slip at Molecularly Smooth Hydrophobic Surfaces
Colloidal probe atomic force microscopy is used to study the slip behavior of 18 Newtonian liquids from two homologous series, the n-alkanes and n-alcohols, at molecularly smooth hydrophobic n-hexadecyltrichlorosilane coated surfaces. We find that the slip behavior is governed by the bulk viscosity Ρ of the liquid, specifically, the slip length bâźÎˇx with xâź0.33. Additionally, the slip length was found to be shear rate independent, validating the use of Vinogradova slip theory in this work
Coexistence Curve Singularities at Critical End Points
We report an extensive Monte Carlo study of critical end point behaviour in a
symmetrical binary fluid mixture. On the basis of general scaling arguments,
singular behaviour is predicted in the diameter of the liquid-gas coexistence
curve as the critical end point is approached. The simulation results show
clear evidence for this singularity, as well as confirming a previously
predicted singularity in the coexistence chemical potential. Both singularities
should be detectable experimentally.Comment: 9 pages Revtex, 3 figures. To appear in Phys. Rev. Let
The infrared imaging spectrograph (IRIS) for TMT: the science case
The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument being
designed for the Thirty Meter Telescope (TMT). IRIS is a combination of an
imager that will cover a 16.4" field of view at the diffraction limit of TMT (4
mas sampling), and an integral field unit spectrograph that will sample objects
at 4-50 mas scales. IRIS will open up new areas of observational parameter
space, allowing major progress in diverse fields of astronomy. We present the
science case and resulting requirements for the performance of IRIS.
Ultimately, the spectrograph will enable very well-resolved and sensitive
studies of the kinematics and internal chemical abundances of high-redshift
galaxies, shedding light on many scenarios for the evolution of galaxies at
early times. With unprecedented imaging and spectroscopy of exoplanets, IRIS
will allow detailed exploration of a range of planetary systems that are
inaccessible with current technology. By revealing details about resolved
stellar populations in nearby galaxies, it will directly probe the formation of
systems like our own Milky Way. Because it will be possible to directly
characterize the stellar initial mass function in many environments and in
galaxies outside of the the Milky Way, IRIS will enable a greater understanding
of whether stars form differently in diverse conditions. IRIS will reveal
detailed kinematics in the centers of low-mass galaxies, allowing a test of
black hole formation scenarios. Finally, it will revolutionize the
characterization of reionization and the first galaxies to form in the
universe.Comment: to appear in Proc. SPIE 773
Forces at Individual Pseudopod-Filament Adhesive Contacts
On-chip cellular force sensors are fabricated from cantilever poly(3,4-ethylene dioxythiophene) filaments that visibly deflect under forces exerted at individual pseudopod-filament adhesive contacts. The shape of the deflected filaments and their âź3 nN/Îźm spring constants are predicted by cantilever rod theory. Pulling forces exerted by Dictyostelium discoideumcells at these contacts are observed to reach âź20 nN without breaking the contact
Rapid, efficient functional characterization and recovery of HIV-specific human CD8+ T cells using microengraving
The nature of certain clinical samples (tissue biopsies, fluids) or the subjects themselves (pediatric subjects, neonates) often constrain the number of cells available to evaluate the breadth of functional T-cell responses to infections or therapeutic interventions. The methods most commonly used to assess this functional diversity ex vivo and to recover specific cells to expand in vitro usually require more than 106 cells. Here we present a process to identify antigen-specific responses efficiently ex vivo from 104â105 single cells from blood or mucosal tissues using dense arrays of subnanoliter wells. The approach combines on-chip imaging cytometry with a technique for capturing secreted proteinsâcalled âmicroengravingââto enumerate antigenspecific responses by single T cells in a manner comparable to conventional assays such as ELISpot and intracellular cytokine staining. Unlike those assays, however, the individual cells identified can be recovered readily by micromanipulation for further characterization in vitro. Applying this method to assess HIV-specific T cell responses demonstrates that it is possible to establish clonal CD8+ T-cell lines that represent the most abundant specificities present in circulation using 100- to 1,000-fold fewer cells than traditional approaches require and without extensive genotypic analysis a priori. This rapid (<24 h), efficient, and inexpensive process should improve the comparative study of human T-cell immunology across ages and anatomic compartments
The purpose of mess in action research: building rigour though a messy turn
Mess and rigour might appear to be strange bedfellows. This paper argues that the purpose of mess is to facilitate a turn towards new constructions of knowing that lead to transformation in practice (an action turn). Engaging in action research - research that can disturb both individual and communally held notions of knowledge for practice - will be messy. Investigations into the 'messy area', the interface between the known and the nearly known, between knowledge in use and tacit knowledge as yet to be useful, reveal the 'messy area' as a vital element for seeing, disrupting, analysing, learning, knowing and changing. It is the place where long-held views shaped by professional knowledge, practical judgement, experience and intuition are seen through other lenses. It is here that reframing takes place and new knowing, which has both theoretical and practical significance, arises: a 'messy turn' takes place
Fluctuation - induced forces in critical fluids
The current knowledge about fluctuation - induced long - ranged forces is
summarized. Reference is made in particular to fluids near critical points, for
which some new insight has been obtained recently. Where appropiate, results of
analytic theory are compared with computer simulations and experiments.Comment: Topical review, 24 pages RevTeX, 6 figure
The properties of (sub)millimetre-selected galaxies as revealed by CANDELS HST WFC3/IR imaging in GOODS-South
We have exploited the HST CANDELS WFC3/IR imaging to study the properties of
(sub-)mm galaxies in GOODS-South. After using the deep radio and Spitzer
imaging to identify galaxy counterparts for the (sub-)mm sources, we have used
the new CANDELS data in two ways. First, we have derived improved photometric
redshifts and stellar masses, confirming that the (sub-)mm galaxies are massive
(=2.2x10^11 M_solar) galaxies at z=1-3. Second, we have exploited the depth
and resolution of the WFC3/IR imaging to determine the sizes and morphologies
of the galaxies at rest-frame optical wavelengths, fitting two-dimensional
axi-symmetric Sersic models. Crucially, the WFC3/IR H-band imaging enables
modelling of the mass-dominant galaxy, rather than the blue high-surface
brightness features which often dominate optical (rest-frame UV) images of
(sub-)mm galaxies, and can confuse visual morphological classification. As a
result of this analysis we find that >95% of the rest-frame optical light in
almost all of the (sub-)mm galaxies is well-described by either a single
exponential disk, or a multiple-component system in which the dominant
constituent is disk-like. We demonstrate that this conclusion is consistent
with the results of high-quality ground-based K-band imaging, and explain why.
The massive disk galaxies which host luminous (sub-)mm emission are reasonably
extended (r_e=4 kpc), consistent with the sizes of other massive star-forming
disks at z~2. In many cases we find evidence of blue clumps within the sources,
with the mass-dominant disk becoming more significant at longer wavelengths.
Finally, only a minority of the sources show evidence for a major galaxy-galaxy
interaction. Taken together, these results support the view that most (sub-)mm
galaxies at z~2 are simply the most extreme examples of normal star-forming
galaxies at that era.Comment: 30 pages, 9 figure
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