44 research outputs found
An off-board quantum point contact as a sensitive detector of cantilever motion
Recent advances in the fabrication of microelectromechanical systems (MEMS)
and their evolution into nanoelectromechanical systems (NEMS) have allowed
researchers to measure extremely small forces, masses, and displacements. In
particular, researchers have developed position transducers with resolution
approaching the uncertainty limit set by quantum mechanics. The achievement of
such resolution has implications not only for the detection of quantum behavior
in mechanical systems, but also for a variety of other precision experiments
including the bounding of deviations from Newtonian gravity at short distances
and the measurement of single spins. Here we demonstrate the use of a quantum
point contact (QPC) as a sensitive displacement detector capable of sensing the
low-temperature thermal motion of a nearby micromechanical cantilever.
Advantages of this approach include versatility due to its off-board design,
compatibility with nanoscale oscillators, and, with further development, the
potential to achieve quantum limited displacement detection.Comment: 5 pages, 5 figure
A picogram and nanometer scale photonic crystal opto-mechanical cavity
We describe the design, fabrication, and measurement of a cavity
opto-mechanical system consisting of two nanobeams of silicon nitride in the
near-field of each other, forming a so-called "zipper" cavity. A photonic
crystal patterning is applied to the nanobeams to localize optical and
mechanical energy to the same cubic-micron-scale volume. The picrogram-scale
mass of the structure, along with the strong per-photon optical gradient force,
results in a giant optical spring effect. In addition, a novel damping regime
is explored in which the small heat capacity of the zipper cavity results in
blue-detuned opto-mechanical damping.Comment: 15 pages, 4 figure
Frequency stabilization in nonlinear micromechanical oscillators
Mechanical oscillators are present in almost every electronic device. They mainly consist of a resonating element providing an oscillating output with a specific frequency. Their ability to maintain a determined frequency in a specified period of time is the most important parameter limiting their implementation. Historically, quartz crystals have almost exclusively been used as the resonating element, but micromechanical resonators are increasingly being considered to replace them. These resonators are easier to miniaturize and allow for monolithic integration with electronics. However, as their dimensions shrink to the microscale, most mechanical resonators exhibit nonlinearities that considerably degrade the frequency stability of the oscillator. Here we demonstrate that, by coupling two different vibrational modes through an internal resonance, it is possible to stabilize the oscillation frequency of nonlinear self-sustaining micromechanical resonators. Our findings provide a new strategy for engineering low-frequency noise oscillators capitalizing on the intrinsic nonlinear phenomena of micromechanical resonators.Fil: Antonio, Dario. Argonne National Laboratory. Center for Nanoscale Materials; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zanette, Damian Horacio. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: López, Daniel . Argonne National Laboratory. Center for Nanoscale Materials; Estados Unido
Ultrasensitive force detection with a nanotube mechanical resonator
Since the advent of atomic force microscopy, mechanical resonators have been
used to study a wide variety of phenomena, such as the dynamics of individual
electron spins, persistent currents in normal metal rings, and the Casimir
force. Key to these experiments is the ability to measure weak forces. Here, we
report on force sensing experiments with a sensitivity of 12 zN Hz^(-1/2) at a
temperature of 1.2 K using a resonator made of a carbon nanotube. An
ultra-sensitive method based on cross-correlated electrical noise measurements,
in combination with parametric downconversion, is used to detect the
low-amplitude vibrations of the nanotube induced by weak forces. The force
sensitivity is quantified by applying a known capacitive force. This detection
method also allows us to measure the Brownian vibrations of the nanotube down
to cryogenic temperatures. Force sensing with nanotube resonators offers new
opportunities for detecting and manipulating individual nuclear spins as well
as for magnetometry measurements.Comment: Early version. To be published in Nature Nanotechnolog
Actuation of Micro-Optomechanical Systems Via Cavity-Enhanced Optical Dipole Forces
We demonstrate a new type of optomechanical system employing a movable,
micron-scale waveguide evanescently-coupled to a high-Q optical microresonator.
Micron-scale displacements of the waveguide are observed for
milliwatt(mW)-level optical input powers. Measurement of the spatial variation
of the force on the waveguide indicates that it arises from a cavity-enhanced
optical dipole force due to the stored optical field of the resonator. This
force is used to realize an all-optical tunable filter operating with sub-mW
control power. A theoretical model of the system shows the maximum achievable
force to be independent of the intrinsic Q of the optical resonator and to
scale inversely with the cavity mode volume, suggesting that such forces may
become even more effective as devices approach the nanoscale.Comment: 4 pages, 5 figures. High resolution version available at
(http://copilot.caltech.edu/publications/CEODF_hires.pdf). For associated
movie, see (http://copilot.caltech.edu/research/optical_forces/index.htm
A tunable carbon nanotube electromechanical oscillator
Nanoelectromechanical systems (NEMs) hold promise for a number of scientific
and technological applications. In particular, NEMs oscillators have been
proposed for use in ultrasensitive mass detection, radio-frequency signal
processing, and as a model system for exploring quantum phenomena in
macroscopic systems. Perhaps the ultimate material for these applications is a
carbon nanotube. They are the stiffest material known, have low density,
ultrasmall cross-sections and can be defect-free. Equally important, a nanotube
can act as a transistor and thus may be able to sense its own motion. In spite
of this great promise, a room-temperature, self-detecting nanotube oscillator
has not been realized, although some progress has been made. Here we report the
electrical actuation and detection of the guitar-string-like oscillation modes
of doubly clamped nanotube oscillators. We show that the resonance frequency
can be widely tuned and that the devices can be used to transduce very small
forces.Comment: 9 pages, 3 figure
The Effects of Age on Inflammatory and Coagulation-Fibrinolysis Response in Patients Hospitalized for Pneumonia
Objective: To determine whether inflammatory and hemostasis response in patients hospitalized for pneumonia varies by age and whether these differences explain higher mortality in the elderly. Methods: In an observational cohort of subjects with community-acquired pneumonia (CAP) recruited from emergency departments (ED) in 28 hospitals, we divided subjects into 5 age groups (85% subjects, older subjects had modestly increased hemostasis markers and IL-6 levels (p,0.01). Conclusions: Modest age-related increases in coagulation response occur during hospitalization for CAP; however these differences do not explain the large differences in mortality. Despite clinical recovery, immune resolution may be delayed in older adults at discharge. © 2010 Kale et al
Innate Immune Responses of Drosophila melanogaster Are Altered by Spaceflight
Alterations and impairment of immune responses in humans present a health risk for space exploration missions. The molecular mechanisms underpinning innate immune defense can be confounded by the complexity of the acquired immune system of humans. Drosophila (fruit fly) innate immunity is simpler, and shares many similarities with human innate immunity at the level of molecular and genetic pathways. The goals of this study were to elucidate fundamental immune processes in Drosophila affected by spaceflight and to measure host-pathogen responses post-flight. Five containers, each containing ten female and five male fruit flies, were housed and bred on the space shuttle (average orbit altitude of 330.35 km) for 12 days and 18.5 hours. A new generation of flies was reared in microgravity. In larvae, the immune system was examined by analyzing plasmatocyte number and activity in culture. In adults, the induced immune responses were analyzed by bacterial clearance and quantitative real-time polymerase chain reaction (qPCR) of selected genes following infection with E. coli. The RNA levels of relevant immune pathway genes were determined in both larvae and adults by microarray analysis. The ability of larval plasmatocytes to phagocytose E. coli in culture was attenuated following spaceflight, and in parallel, the expression of genes involved in cell maturation was downregulated. In addition, the level of constitutive expression of pattern recognition receptors and opsonins that specifically recognize bacteria, and of lysozymes, antimicrobial peptide (AMP) pathway and immune stress genes, hallmarks of humoral immunity, were also reduced in larvae. In adults, the efficiency of bacterial clearance measured in vivo following a systemic infection with E. coli post-flight, remained robust. We show that spaceflight altered both cellular and humoral immune responses in Drosophila and that the disruption occurs at multiple interacting pathways
“Es fundamental que la información que se transmita sea confiable”
El flamante Doctor Honoris Causa de la UNLP, Emilio Luque Fadón, de la Universidad Autónoma de Barcelona, fue uno de los conferencistas de CACIC 2017. Durante su estadía por la ciudad de La Plata, el español habló acerca de las nuevas tecnologías, su tolerancia a los fallos y el consumo energético.Facultad de Informátic