203 research outputs found
Mechanical detection of carbon nanotube resonator vibrations
Bending-mode vibrations of carbon nanotube resonator devices were
mechanically detected in air at atmospheric pressure by means of a novel
scanning force microscopy method. The fundamental and higher order bending
eigenmodes were imaged at up to 3.1GHz with sub-nanometer resolution in
vibration amplitude. The resonance frequency and the eigenmode shape of
multi-wall nanotubes are consistent with the elastic beam theory for a doubly
clamped beam. For single-wall nanotubes, however, resonance frequencies are
significantly shifted, which is attributed to fabrication generating, for
example, slack. The effect of slack is studied by pulling down the tube with
the tip, which drastically reduces the resonance frequency
Lyapunov exponents for stochastic differential equations on semi-simple Lie groups
summary:With an intrinsic approach on semi-simple Lie groups we find a Furstenberg–Khasminskii type formula for the limit of the diagonal component in the Iwasawa decomposition. It is an integral formula with respect to the invariant measure in the maximal flag manifold of the group (i.e. the Furstenberg boundary ). Its integrand involves the Borel type Riemannian metric in the flag manifolds. When applied to linear stochastic systems which generate a semi-simple group the formula provides a diagonal matrix whose entries are the Lyapunov spectrum. Some Brownian motions on homogeneous spaces are discussed
Imaging mechanical vibrations in suspended graphene sheets
We carried out measurements on nanoelectromechanical systems based on
multilayer graphene sheets suspended over trenches in silicon oxide. The motion
of the suspended sheets was electrostatically driven at resonance using applied
radio-frequency voltages. The mechanical vibrations were detected using a novel
form of scanning probe microscopy, which allowed identification and spatial
imaging of the shape of the mechanical eigenmodes. In as many as half the
resonators measured, we observed a new class of exotic nanoscale vibration
eigenmodes not predicted by the elastic beam theory, where the amplitude of
vibration is maximum at the free edges. By modeling the suspended sheets with
the finite element method, these edge eigenmodes are shown to be the result of
non-uniform stress with remarkably large magnitudes (up to 1.5 GPa). This
non-uniform stress, which arises from the way graphene is prepared by pressing
or rubbing bulk graphite against another surface, should be taken into account
in future studies on electronic and mechanical properties of graphene
Mechano-Optical Analysis of Single Cells with Transparent Microcapillary Resonators
The study of biophysical properties of single cells is becoming increasingly relevant in cell biology and pathology. The measurement and tracking of magnitudes such as cell stiffness, morphology, and mass or refractive index have brought otherwise inaccessible knowledge about cell physiology, as well as innovative methods for high-throughput label-free cell classification. In this work, we present hollow resonator devices based on suspended glass microcapillaries for the simultaneous measurement of single-cell buoyant mass and reflectivity with a throughput of 300 cells/minute. In the experimental methodology presented here, both magnitudes are extracted from the devices' response to a single probe, a focused laser beam that enables simultaneous readout of changes in resonance frequency and reflected optical power of the devices as cells flow within them. Through its application to MCF-7 human breast adenocarcinoma cells and MCF-10A nontumorigenic cells, we demonstrate that this mechano-optical technique can successfully discriminate pathological from healthy cells of the same tissue type
Optomechanical devides for mechanobiological fingerprinting
Resumen del trabajo presentado en el Frontiers of Nanomechanical Systems (FSN2021), celebraod de forma virtual del 19 al 21 de enero de 2021Twenty years have passed since the first detection of biomolecular recognition using micromechanical systems[1]. In the last two decades, micro- nanomechanical systems have been refined to achieve amazing detection limits in force and mass that have enabled different schemes for ultrasensitive measurements of biological interactions as well as new ways of biological spectrometry. More recently, these figures of merit have been improved by coupling optical cavities to mechanical systems. In this talk, I will review the use of micro- nanomechanical systems for mechanobiological fingerprinting of biological entities, particularizing in the contributions of our group [2]. An essential core of this topic is the discussion about the mechanical coupling between a biological particle and a mechanical resonator, an issue that it is has been often oversimplified. We show that the biomechanical coupling that emerges between a bioparticle and a mechanical resonator is more complex than previously expect and it can give rise to different interaction regimes, in which the resonator response is dominated by different physical parameters of the analyte [3-4]. In particular, we will show experiments done with a variety of micro- nano- optomechanical systems using different measurement schemes where the mass, the stiffness and even the vibration modes of single biological entities can be measured with high sensitivity. It is now widely appreciated the essential role of mechanics in relevant biological processes and how disease can be revealed as changes in the mechanical properties of biological matter. I am pretty sure that future developments in optomechanical devices will contribute for major understanding of diseases as well as for new avenues in diagnosis and therapy
Internalization and viability studies of suspended nanowire silicon chips in HeLa Cells
Micrometer-sized silicon chips have been demonstrated to be cell-internalizable, offering the possibility of introducing in cells even smaller nanoelements for intracellular applications. On the other hand, silicon nanowires on extracellular devices have been widely studied as biosensors or drug delivery systems. Here, we propose the integration of silicon nanowires on cell-internalizable chips in order to combine the functional features of both approaches for advanced intracellular applications. As an initial fundamental study, the cellular uptake in HeLa cells of silicon 3 m 3 m nanowire-based chips with two different morphologies was investigated, and the results were compared with those of non-nanostructured silicon chips. Chip internalization without affecting cell viability was achieved in all cases; however, important cell behavior differences were observed. In particular, the first stage of cell internalization was favored by silicon nanowire interfaces with respect to bulk silicon. In addition, chips were found inside membrane vesicles, and some nanowires seemed to penetrate the cytosol, which opens the door to the development of silicon nanowire chips as future intracellular sensors and drug delivery systems
Interaction imaging with amplitude-dependence force spectroscopy
Knowledge of surface forces is the key to understanding a large number of
processes in fields ranging from physics to material science and biology. The
most common method to study surfaces is dynamic atomic force microscopy (AFM).
Dynamic AFM has been enormously successful in imaging surface topography, even
to atomic resolution, but the force between the AFM tip and the surface remains
unknown during imaging. Here, we present a new approach that combines high
accuracy force measurements and high resolution scanning. The method, called
amplitude-dependence force spectroscopy (ADFS) is based on the
amplitude-dependence of the cantilever's response near resonance and allows for
separate determination of both conservative and dissipative tip-surface
interactions. We use ADFS to quantitatively study and map the nano-mechanical
interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is
compatible with commercial atomic force microscopes and we anticipate its
wide-spread use in taking AFM toward quantitative microscopy
Design and analysis of cross vaults along history
The history of cross vaults began almost 2,000 years ago with a widespread use during the Middle Ages and Renaissance, becoming nowadays one of the most diffused and fascinating structural typologies of the European building cultural heritage. However, conversely to the undeniable excellence achieved by the ancient masons, the structural behavior of these elements is still at the center of the scientific debate. In this regard, with the aim of reviewing the knowledge on this subject as a concise and valuable support for researchers involved in conservation of historical buildings, with a focus on design rules and structural analysis, the present study firstly introduces the cross vaults from a historical perspective, by describing the evolution of the main geometrical shapes together with basic practical rules used to size them. Then, the article deals with the subsequent advancements in structural analysis methods of vaults, until the development of modern limit analysis.This work was partially carried out under the program "Dipartimento di Protezione Civile - Consorzio RELUIS", signed on 2013-12-27.info:eu-repo/semantics/publishedVersio
Temperature and force dependence of nanoscale electron transport via the Cu protein Azurin
The mechanisms of solid-state electron transport (ETp) via a monolayer of
immobilized Azurin (Az) was examined by conducting probe atomic force
microscopy (CP-AFM), both as function of temperature (248 - 373K) and of
applied tip force (6-12 nN). By varying both temperature and force in CP-AFM,
we find that the ETp mechanism can alter with a change in the force applied via
the tip to the proteins. As the applied force increases, ETp via Az changes
from temperature-independent to thermally activated at high temperatures. This
is in contrast to the Cu-depleted form of Az (apo-Az), where increasing the
applied force causes only small quantitative effects, that fit with a decrease
in electrode spacing. At low force ETp via holo-Az is temperature-independent
and thermally activated via apo-Az. This observation agrees with
macroscopic-scale measurements, thus confirming that the difference in ETp
dependence on temperature between holo- and apo-Az is an inherent one that may
reflect a difference in rigidity between the two forms. An important
implication of these results, which depend on CP-AFM measurements over a
significant temperature range, is that for ETp measurements on floppy systems,
such as proteins, the stress applied to the sample should be kept constant or,
at least controlled during measurement.Comment: 24 pages, 6 figures, plus Supporting Information with 4 pages and 2
figure
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