Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.

The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ionization energy loss, as well as identification of photon conversions, nuclear interactions, and heavy-flavour decays.

Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at √ s = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 ± 0.01 (stat.) ± 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 ± 0.01 (stat.) ± 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between −2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN ch /dη| |η|<0.5 , are 3.48 ± 0.02 (stat.) ± 0.13 (syst.) and 4.47 ± 0.04 (stat.) ± 0.16 (syst.), respectively. The results at 0.9 TeV are in agreement with previous measurements and confirm the expectation of near equal hadron production in pp and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date.

Evaporation is a ubiquitous phenomenon in the natural environment and a dominant form of energy transfer in the Earth's climate. Engineered systems rarely, if ever, use evaporation as a source of energy, despite myriad examples of such adaptations in the biological world. Here, we report evaporation-driven engines that can power common tasks like locomotion and electricity generation. These engines start and run autonomously when placed at air–water interfaces. They generate rotary and piston-like linear motion using specially designed, biologically based artificial muscles responsive to moisture fluctuations. Using these engines, we demonstrate an electricity generator that rests on water while harvesting its evaporation to power a light source, and a miniature car (weighing 0.1 kg) that moves forward as the water in the car evaporates. Evaporation-driven engines may find applications in powering robotic systems, sensors, devices and machinery that function in the natural environment.

Materials that respond mechanically to external chemical stimuli have wide--ranging applications in biomedical devices, adaptive architectural systems, robotics, and energy harvesting 1 . Synthesis and design principles inspired by biological systems have led to materials with capabilities for highly controlled and complex shape change 2 , oscillations 3 , fluid transport 4 , and homeostasis 5 . Despite the enhanced control over material behavior, the effectiveness of synthetic stimuli--responsive materials in generating work has been limited when compared to mechanical actuators 6 . Biological organisms with structures responsive to water gradients could potentially offer a solution for the limited work density of stimuli--responsive materials. Because water--responsive biological structures accomplish vital tasks like ascent of sap 7,8 , dispersal and self--burial of seeds 9,10 , they could possibly exhibit high energy densities and serve as building blocks of stimuli--responsive materials effective in generating work. Furthermore, biological nature of these materials offers the possibility of improving their characteristics through genetic mutations 11,12 . Here we report the discovery that the response of the spores of Bacillus to water potential gradients exhibit energy densities more than 10 MJ/m 3 , exceeding best synthetic water--responsive materials by 1000--fold 13,14 . We also identified a mutant spore form that nearly doubles the energy density relative to its wild type, highlighting the possibility for further improvements with genetic engineering of spores. We found that spores can self--assemble into dense, submicron--thick monolayers on substrates like silicon microcantilevers and elastomer sheets, creating bio--hybrid hygromorph actuators 15 . The spore monolayers forming these hygromorphs exhibited high--energy density and rapid response to changing water potentials. As an application of the strong mechanical response of spores, we have built an energy harvesting device that can remotely generate electrical power from an evaporating body of water. These results demonstrate that spores have a significant potential as building blocks of stimuli--responsive materials with dramatically enhanced capabilities for energy harvesting, storage, and actuation of robotic devices.Bacillus spores are dormant cells that can withstand harsh environmental conditions for long periods of time and still maintain biological functionality 16 (Fig. 1a,b). Despite their dormancy, spores are dynamic structures. For example, Bacillus spores respond to changes in relative humidity (RH) by expanding and shrinking and changing their diameter by as much as 12% 17--19 . We have used an atomic force microscope (AFM) based experiment (Fig. 2c) to determine the energy density of individual spores as they respond to changes in RH. By adjusting force and RH, we have created a thermodynamic cycle, in which individual spores go through four stages illustrated in Fig. 1d. In stage I, the spores rest at low RH (~20%). In stage II,...

Proteins are dynamic molecular machines having structural flexibility that allows conformational changes. Current methods for the determination of protein flexibility rely mainly on the measurement of thermal fluctuations and disorder in protein conformations and tend to be experimentally challenging. Moreover, they reflect atomic fluctuations on picosecond timescales, whereas the large conformational changes in proteins typically happen on micro- to millisecond timescales. Here, we directly determine the flexibility of bacteriorhodopsin -- a protein that uses the energy in light to move protons across cell membranes -- at the microsecond timescale by monitoring force-induced deformations across the protein structure with a technique based on atomic force microscopy. In contrast to existing methods, the deformations we measure involve a collective response of protein residues and operate under physiologically relevant conditions with native proteins.

Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at square root of s = 7  TeV are measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield is obtained by counting the number of reconstructed hits, hit pairs, and fully reconstructed charged-particle tracks. The combination of the three methods gives a charged-particle multiplicity per unit of pseudorapidity dN(ch)/dη|(|η|<0.5) = 5.78 ± 0.01(stat) ± 0.23(syst) for non-single-diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from square root of s = 0.9 to 7 TeV is [66.1 ± 1.0(stat) ± 4.2(syst)]%. The mean transverse momentum is measured to be 0.545 ± 0.005(stat) ± 0.015(syst)  GeV/c. The results are compared with similar measurements at lower energies.

Techniques to detect and quantify DNA and RNA molecules in biological samples have played a central role in genomics research1–3. Over the past decade, several techniques have been developed to improve detection performance and reduce the cost of genetic analysis4–10. In particular, dramatic advances in label-free methods have been reported11–17. Yet, detection of DNA molecules at concentrations below femtomolar level requires amplified detection schemes1,8. Here we report a unique nanomechanical response of hybridized DNA and RNA molecules that serves as an intrinsic molecular label. Nanomechanical measurements on a microarray surface exhibit excellent background signal rejection that allows direct detection and counting of hybridized molecules. The digital response of the sensor provides a large dynamic range that is critical for gene expression profiling. We have measured differential expressions of miRNAs in tumor samples, which has been shown to help discriminate tissue origins of metastatic tumors18. 200 picograms of total RNA is found to be sufficient for this analysis. In addition, the limit of detection in pure samples is found to be 1 attomolar. These results suggest that nanomechanical readout of microarrays promises attomolar level sensitivity and large dynamic range for the analysis of gene expression, while eliminating biochemical manipulations, amplification, and labeling.