297 research outputs found
Biomechanics of DNA structures visualized by 4D electron microscopy
We present a technique for in situ visualization of the biomechanics of DNA structural networks using 4D electron microscopy. Vibrational oscillations of the DNA structure are excited mechanically through a short burst of substrate vibrations triggered by a laser pulse. Subsequently, the motion is probed with electron pulses to observe the impulse response of the specimen in space and time.
From the frequency and amplitude of the observed oscillations, we determine the normal modes and eigenfrequencies of the structures involved. Moreover, by selective “nano-cutting” at a given point in the network, it was possible to obtain Young’s modulus, and hence the stiffness, of the DNA filament at that position. This
experimental approach enables nanoscale mechanics studies of
macromolecules and should find applications in other domains of biological networks such as origamis
Visualizing Nanoscale Dynamics with Time-resolved Electron Microscopy
The large number of interactions in nanoscale systems leads to the emergence of complex behavior. Understanding such complexity requires atomic-resolution observations with a time resolution that is high enough to match the characteristic timescale of the system. Our laboratory’s method of choice is time-resolved electron microscopy. In particular, we are interested in the development of novel methods and instrumentation for high-speed observations with atomic resolution. Here, we present an overview of the activities in our laboratory
Electron Diffraction of Water in No Man's Land
A generally accepted understanding of the anomalous properties of water will
only emerge if it becomes possible to systematically characterize water in the
deeply supercooled regime, from where the anomalies appear to emanate. This has
largely remained elusive because water crystallizes rapidly between 160 K and
232 K. Here, we present an experimental approach to rapidly prepare deeply
supercooled water at a well-defined temperature and probe it with electron
diffraction before crystallization occurs. We show that as water is cooled from
room temperature to cryogenic temperature, its structure evolves smoothly,
approaching that of amorphous ice just below 200 K. Our experiments narrow down
the range of possible explanations of the origin for the water anomalies and
open up new avenues for studying supercooled water
Observing liquid flow in nanotubes by 4D electron microscopy
Nanofluidics involves the study of fluid transport in nanometer-scale structures. We report the direct observation of fluid dynamics in a single zinc oxide nanotube with the high spatial and temporal resolution of four-dimensional (4D) electron microscopy. The
nanotube is filled with metallic lead, which we melt in situ with a temperature jump induced
by a heating laser pulse. We then use a short electron pulse to create an image of the
ensuing dynamics of the hot liquid. Single-shot images elucidate the mechanism of
irreversible processes, whereas stroboscopic diffraction patterns provide the heating and
cooling rates of single nanotubes. The temporal changes of the images enable studies of
the viscous friction involved in the flow of liquid within the nanotube, as well as studies
of mechanical processes such as those that result in the formation of extrusions
In Situ Melting and Revitrification as an Approach to Microsecond Time-Resolved Cryo-Electron Microscopy
Proteins typically undergo conformational dynamics on the microsecond to
millisecond timescale as they perform their function, which is much faster than
the time-resolution of cryo-electron microscopy and has thus prevented
real-time observations. Here, we propose a novel approach for microsecond
time-resolved cryo-electron microscopy that involves rapidly melting a cryo
specimen in situ with a laser beam. The sample remains liquid for the duration
of the laser pulse, offering a tunable time window in which the dynamics of
embedded particles can be induced in their native liquid environment. After the
laser pulse, the sample vitrifies in just a few microseconds, trapping
particles in their transient configurations, so that they can subsequently be
characterized with conventional cryo-electron microscopy. We demonstrate that
our melting and revitrification approach is viable and affords microsecond time
resolution. As a proof of principle, we study the disassembly of particles
after they incur structural damage and trap them in partially unraveled
configurations
Momentum dependence of orbital excitations in Mott-insulating titanates
High-resolution resonant inelastic x-ray scattering has been used to
determine the momentum dependence of orbital excitations in Mott-insulating
LaTiO and YTiO over a wide range of the Brillouin zone. The data are
compared to calculations in the framework of lattice-driven and
superexchange-driven orbital ordering models. A superexchange model in which
the experimentally observed modes are attributed to two-orbiton excitations
yields the best description of the data.Comment: to appear in PR
SBS 0335-052W - an Extremely Low Metallicity Dwarf Galaxy
We present Multiple Mirror Telescope (MMT) and Keck II telescope
spectrophotometry and 3.5m Calar Alto telescope R, I photometry of the western
component of the extremely low-metallicity blue compact galaxy SBS 0335-052.
The components, separated by 22 kpc, appear to be members of a unique,
physically connected system. It is shown that SBS 0335-052W consists of at
least three stellar clusters and has the same redshift as SBS 0335-052. The
oxygen abundance in its two brightest knots is extremely low, 12+log(O/H)=
7.22+/-0.03 and 7.13+/-0.08, respectively. These values are lower than in SBS
0335-052 and are nearly the same as those in I Zw 18. The (R-I) color profiles
are very blue in both galaxies due to the combined effects of ionized gas and a
young stellar population emission. We argue that SBS 0335-052W is likely to be
a nearby, young dwarf galaxy.Comment: 18 pages, 4 EPS figures, to appear in ApJ, 1 July 199
4D Cryo-Electron Microscopy of Proteins
Cryo-electron microscopy is a form of
transmission electron microscopy that has been used to
determine the 3D structure of biological specimens in the
hydrated state and with high resolution. We report the
development of 4D cryo-electron microscopy by integrating
the fourth dimension, time, into this powerful
technique. From time-resolved diffraction of amyloid
fibrils in a thin layer of vitrified water at cryogenic
temperatures, we were able to detect picometer movements
of protein molecules on a nanosecond time scale.
Potential future applications of 4D cryo-electron microscopy
are numerous, and some are discussed here
Mobile Data Collection of Cognitive-Behavioral Tasks in Substance Use Disorders: Where Are We Now?
INTRODUCTION: Over the last decades, our understanding of the cognitive, motivational, and neural processes involved in addictive behavior has increased enormously. A plethora of laboratory-based and cross-sectional studies has linked cognitive-behavioral measures to between-subject differences in drinking behavior. However, such laboratory-based studies inevitably suffer from small sample sizes and the inability to link temporal fluctuations in task measures to fluctuations in real-life substance use. To overcome these problems, several existing behavioral tasks have been transferred to smartphones to allow studying cognition in the field. METHOD: In this narrative review, we first summarize studies that used existing behavioral tasks in the laboratory and self-reports of substance use with ecological momentary assessment (EMA) in the field. Next, we review studies on psychometric properties of smartphone-based behavioral tasks. Finally, we review studies that used both smartphone-based tasks and self-reports with EMA in the field. RESULTS: Overall, studies were scarce and heterogenous both in tasks and in study outcomes. Nevertheless, existing findings are promising and point toward several methodological recommendations: concerning psychometrics, studies show that - although more systematic studies are necessary - task validity and reliability can be improved, for example, by analyzing several measurement sessions at once rather than analyzing sessions separately. Studies that use tasks in the field, moreover, show that power can be improved by choosing sampling schemes that combine time-based with event-based sampling, rather than relying on time-based sampling alone. Increasing sampling frequency can further increase power. However, as this also increases the burden to participants, more research is necessary to determine the ideal sampling frequency for each task. CONCLUSION: Although more research is necessary to systematically study both the psychometrics of smartphone-based tasks and the frequency at which task measures fluctuate, existing studies are promising and reveal important methodological recommendations useful for researchers interested in implementing behavioral tasks in EMA studies
Mobile Data Collection of Cognitive-Behavioral Tasks in Substance Use Disorders: Where Are We Now?
Introduction: Over the last decades, our understanding of the cognitive, motivational, and neural processes involved in addictive behavior has increased enormously. A plethora of laboratory-based and cross-sectional studies has linked cognitive-behavioral measures to between-subject differences in drinking behavior. However, such laboratory-based studies inevitably suffer from small sample sizes and the inability to link temporal fluctuations in task measures to fluctuations in real-life substance use. To overcome these problems, several existing behavioral tasks have been transferred to smartphones to allow studying cognition in the field. Method: In this narrative review, we first summarize studies that used existing behavioral tasks in the laboratory and self-reports of substance use with ecological momentary assessment (EMA) in the field. Next, we review studies on psychometric properties of smartphone-based behavioral tasks. Finally, we review studies that used both smartphone-based tasks and self-reports with EMA in the field. Results: Overall, studies were scarce and heterogenous both in tasks and in study outcomes. Nevertheless, existing findings are promising and point toward several methodological recommendations: concerning psychometrics, studies show that – although more systematic studies are necessary – task validity and reliability can be improved, for example, by analyzing several measurement sessions at once rather than analyzing sessions separately. Studies that use tasks in the field, moreover, show that power can be improved by choosing sampling schemes that combine time-based with event-based sampling, rather than relying on time-based sampling alone. Increasing sampling frequency can further increase power. However, as this also increases the burden to participants, more research is necessary to determine the ideal sampling frequency for each task. Conclusion: Although more research is necessary to systematically study both the psychometrics of smartphone-based tasks and the frequency at which task measures fluctuate, existing studies are promising and reveal important methodological recommendations useful for researchers interested in implementing behavioral tasks in EMA studies
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