Massively parallel single-molecule manipulation using centrifugal force

Precise manipulation of single molecules has already led to remarkable insights in physics, chemistry, biology and medicine. However, widespread adoption of single-molecule techniques has been impeded by equipment cost and the laborious nature of making measurements one molecule at a time. We have solved these issues with a new approach: massively parallel single-molecule force measurements using centrifugal force. This approach is realized in a novel instrument that we call the Centrifuge Force Microscope (CFM), in which objects in an orbiting sample are subjected to a calibration-free, macroscopically uniform force-field while their micro-to-nanoscopic motions are observed. We demonstrate high-throughput single-molecule force spectroscopy with this technique by performing thousands of rupture experiments in parallel, characterizing force-dependent unbinding kinetics of an antibody-antigen pair in minutes rather than days. Additionally, we verify the force accuracy of the instrument by measuring the well-established DNA overstretching transition at 66 $\pm$ 3 pN. With significant benefits in efficiency, cost, simplicity, and versatility, "single-molecule centrifugation" has the potential to revolutionize single-molecule experimentation, and open access to a wider range of researchers and experimental systems.Comment: 5 pages, 3 figure

Strengthening the global system of protected areas post-2020: A perspective from the IUCN World Commission on Protected Areas

Protected areas are the cornerstones of biodiversity conservation and have never been more relevant than at the present time when the world is facing both a biodiversity and a climate change crisis. The International Union for Conservation of Nature (IUCN) World Commission on Protected Areas (WCPA) has been helping to set global standards and best practice guidelines in protected area planning and management for 60 years. Following this guidance, many countries have made significant progress toward their Aichi Target 11 commitments under the Convention on Biological Diversity (CBD). The global community will be coming together at the 15th Conference of the Parties of the CBD to set new biodiversity conservation targets for the next decade, as milestones to 2050 and a vision of “a world living in harmony with nature.” This paper lays out the WCPA perspective on priorities for supporting effective protected and conserved areas for the post-2020 era

Quantifying the resolution of spatial and temporal representation in children with 22q11.2 deletion syndrome.

ObjectivesOur ability to generate mental representation of magnitude from sensory information affects how we perceive and experience the world. Reduced resolution of the mental representations formed from sensory inputs may generate impairment in the proximal and distal information processes that utilize these representations. Impairment of spatial and temporal information processing likely underpins the non-verbal cognitive impairments observed in 22q11.2 deletion syndrome (22q11DS). The present study builds on prior research by seeking to quantify the resolution of spatial and temporal representation in children with 22q11DS, sex chromosome aneuploidy (SCA), and a typically developing (TD) control group.Participants and methodsChildren (22q11DS = 70, SCA = 49, TD = 46) responded to visual or auditory stimuli with varying difference ratios. The participant's task was to identify which of two sequentially presented stimuli was of larger magnitude in terms of, size, duration, or auditory frequency. Detection threshold was calculated as the minimum difference ratio between the "standard" and the "target" stimuli required to achieve 75% accuracy in detecting that the two stimuli were different.ResultsChildren with 22q11DS required larger magnitude difference between spatial stimuli for accurate identification compared with both the SCA and TD groups (% difference from standard: 22q11DS = 14; SCA = 8; TD: 7; F  = 8.42, p < 0.001). Temporal detection threshold was also higher for the 22q11DS group to both visual (% difference from standard: 22q11DS = 14; SCA = 8; TD = 7; F  = 8.33, p < 0.001) and auditory (% difference from standard: 22q11DS = 23; SCA = 12; TD: 8; F  = 8.99, p < 0.001) stimuli compared with both the SCA and TD groups, while the SCA and TD groups displayed equivalent performance on these measures (p's > 0.05). Pitch detection threshold did not differ among the groups (p's > 0.05).ConclusionsThe observation of higher detection thresholds to spatial and temporal stimuli indicates further evidence for reduced resolution in both spatial and temporal magnitude representation in 22q11DS, that does not extend to frequency magnitude representation (pitch detection), and which is not explained by generalized cognitive impairment alone. These findings generate further support for the hypothesis that spatiotemporal hypergranularity of mental representations contributes to the non-verbal cognitive impairment seen in 22q11DS

Long-wavelength excitations in a Bose gas at zero temperature

The long-wavelength excitations in a simple model of a dilute Bose gas at zero temperature are investigated from a purely microscopic viewpoint. The role of the interaction and the effects of the condensate are emphasized in a dielectric formulation, in which the response functions are expressed in terms of regular functions that do not involve an isolated single-interaction line nor an isolated single-particle line. Local number conservation is incorporated into the formulation by the generalized Ward identities, which are used to express the regular functions involving the density in terms of regular functions involving the longitudinal current. A perturbation expansion is then developed for the regular functions, producing to a given order in the perturbation expansion an elementary excitation spectrum without a gap and simultaneously response functions that obey local number conservation and related sum rules.Explicit results to the first order beyond the Bogoliubov approximation in a simple one-parameter model are obtained for the elementary excitation spectrum [omega]k, the dynamic structure function (k, [omega]), the associated structure function m(k), and the one-particle spectral function (k, [omega]), as functions of the wavevector k and frequency [omega]. These results display the sharing of the gapless spectrum [omega]k by the various response functions and are used to confirm that the sum rules of interest are satisfied. It is shown that [omega]k and some of the m(k) are not analytic functions of k in the long wavelength limit. The dynamic structure function (k, [omega]) can be conveniently separated into three parts: a one-phonon term which exhausts the f sum rule, a backflow term, and a background term. The backflow contribution to the static structure function 0(k) leads to the breakdown of the one-phonon Feynman relation at order k3. Both (k, [omega]) and (k, [omega]) display broad backgrounds because of two-phonon excitations. Simple arguments are given to indicate that some of the qualitative features found for various physical quantities in the first-order model calculation might also be found in superfluid helium.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22380/1/0000829.pd

Structure functions in an interacting Boson system

A microscopic analysis of the dynamic structure factor in a simple interacting Boson system at T=0 shows that the coherent two-phonon backflow leads to the breakdown of the one-phonon Feynman relation for the statis structure factor at order k3.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34104/1/0000386.pd

Neoclassical tearing modes in DIII-D and calculations of the stabilizing effects of localized electron cyclotron current drive

Neoclassical tearing modes are found to limit the achievable beta in many high performance discharges in DIII-D. Electron cyclotron current drive within the magnetic islands formed as the tearing mode grows has been proposed as a means of stabilizing these modes or reducing their amplitude, thereby increasing the beta limit by a factor around 1.5. Some experimental success has been obtained previously on Asdex-U. Here the authors examine the parameter range in DIII-C in which this effect can best be studied