5,929 research outputs found
Halving the Casimir force with conductive oxides
The possibility to modify the strength of the Casimir effect by tailoring the
dielectric functions of the interacting surfaces is regarded as a unique
opportunity in the development of Micro- and NanoElectroMechanical Systems. In
air, however, one expects that, unless noble metals are used, the electrostatic
force arising from trapped charges overcomes the Casimir attraction, leaving no
room for exploitation of Casimir force engineering at ambient conditions. Here
we show that, in the presence of a conductive oxide, the Casimir force can be
the dominant interaction even in air, and that the use of conductive oxides
allows one to reduce the Casimir force up to a factor of 2 when compared to
noble metals.Comment: modified version, accepted for publication in Phys Rev Let
Fiber-top atomic force microscope
We present the implementation of an atomic force microscope (AFM) based on fiber-top design. Our results demonstrate that the performances of fiber-top AFMs in contact mode are comparable to those of similar commercially available instruments. Our device thus represents an interesting\ud
alternative to existing AFMs, particularly for applications outside specialized research laboratories, where a compact, user-friendly, and versatile tool might often be preferred
Coherent Optomechanical State Transfer between Disparate Mechanical Resonators
Hybrid quantum systems have been developed with various mechanical, optical
and microwave harmonic oscillators. The coupling produces a rich library of
interactions including two mode squeezing, swapping interactions, back-action
evasion and thermal control. In a multimode mechanical system, coupling
resonators of different scales (both in frequency and mass) leverages the
advantages of each resonance. For example: a high frequency, easily manipulated
resonator could be entangled with a low frequency massive object for tests of
gravitational decoherence. Here we demonstrate coherent optomechanical state
swapping between two spatially and frequency separated resonators with a mass
ratio of 4. We find that, by using two laser beams far detuned from an optical
cavity resonance, efficient state transfer is possible through a process very
similar to STIRAP (Stimulated Raman Adiabatic Passage) in atomic physics.
Although the demonstration is classical, the same technique can be used to
generate entanglement between oscillators in the quantum regime
Experimental exploration of the optomechanical attractor diagram and its dynamics
We demonstrate experimental exploration of the attractor diagram of an
optomechanical system where the optical forces compensate for the mechanical
losses. In this case stable self-induced oscillations occur but only for
specific mirror amplitudes and laser detunings. We demonstrate that we can
amplify the mechanical mode to an amplitude 500 times larger than the thermal
amplitude at 300K. The lack of unstable or chaotic motion allows us to
manipulate our system into a non-trivial steady state and explore the dynamics
of self-induced oscillations in great detail.Comment: 6 pages, 4 figure
Interplay between antiferromagnetic order and spin polarization in ferromagnetic metal/electron-doped cuprate superconductor junctions
Recently we proposed a theory of point-contact spectroscopy and argued that
the splitting of zero-bias conductance peak (ZBCP) in electron-doped cuprate
superconductor point-contact spectroscopy is due to the coexistence of
antiferromagnetic (AF) and d-wave superconducting orders [Phys. Rev. B {\bf
76}, 220504(R) (2007)]. Here we extend the theory to study the tunneling in the
ferromagnetic metal/electron-doped cuprate superconductor (FM/EDSC) junctions.
In addition to the AF order, the effects of spin polarization, Fermi-wave
vector mismatch (FWM) between the FM and EDSC regions, and effective barrier
are investigated. It is shown that there exits midgap surface state (MSS)
contribution to the conductance to which Andreev reflections are largely
modified due to the interplay between the exchange field of ferromagnetic metal
and the AF order in EDSC. Low-energy anomalous conductance enhancement can
occur which could further test the existence of AF order in EDSC. Finally, we
propose a more accurate formula in determining the spin polarization value in
combination with the point-contact conductance data.Comment: 9 pages, 8 figure
Adsorption of Externally Stretched Two-Dimensional Flexible and Semi-flexible Polymers near an Attractive Wall
We study analytically a model of a two dimensional, partially directed,
flexible or semiflexible polymer, attached to an attractive wall which is
perpendicular to the preferred direction. In addition, the polymer is stretched
by an externally applied force. We find that the wall has a dramatic effect on
the polymer. For wall attraction smaller than the non-sequential nearest
neighbor attraction, the fraction of monomers at the wall is zero and the model
is the same as that of a polymer without a wall. However, for greater than, the
fraction of monomers at the wall undergoes a first order transition from unity
at low temperature and small force, to zero at higher temperatures and forces.
We present phase diagram for this transition. Our results are confirmed by
Monte-Carlo simulations.Comment: 15 pages, 6 figure
High-Q nested resonator in an actively stabilized optomechanical cavity
Experiments involving micro- and nanomechanical resonators need to be
carefully designed to reduce mechanical environmental noise. A small scale
on-chip approach is to add an additional resonator to the system as a
mechanical low-pass filter. Unfortunately, the inherent low frequency of the
low-pass filter causes the system to be easily excited mechanically. Fixating
the additional resonator ensures that the resonator itself can not be excited
by the environment. This, however, negates the purpose of the low-pass filter.
We solve this apparent paradox by applying active feedback to the resonator,
thereby minimizing the motion with respect the front mirror of an
optomechanical cavity. Not only does this method actively stabilize the cavity
length, but it also retains the on-chip vibration isolation.Comment: Minor adjustments mad
LIGHT AND ELECTRON MICROSCOPIC RADIOAUTOGRAPHY OF HEPATIC CELL NUCLEOLI IN MICE TREATED WITH ACTINOMYCIN D
Nucleolar partition induced by actinomycin D was used to demonstrate some aspects of nucleolar RNA synthesis and release in mouse hepatic cells, with light and electron microscopic radioautography. The effect of the drug on RNA synthesis and nucleolar morphology was studied when actinomycin D treatment preceded labeling with tritiated orotic acid. Nucleolar partition, consisting of a segegration into granular and fibrillar parts was visible if a dosage of 25 µg of actinomycin D was used, but nucleolar RNA was still synthesized. After a dosage of 400 µg of actinomycin D, nucleolar RNA synthesis was completely stopped If labeling with tritiated orotic acid preceded treatment with 400 µg of actinomycin D, labeled nucleolar RNA was present 15 min after actinomycin D treatment while high resolution radioautography showed an association of silver grains with the granular component. At 30 min after actinomicyn D treatment all labeling was lost. Since labeling was associated with the granular component the progressive loss of label as a result of actinomycin D treatment indicated a release of nucleolar granules. The correlation between this release and the loss of 28S RNA from actinomycin D treated nucleoli as described in the literature is discussed
Omineca Herald, July, 10, 1914
Patients admitted to an intensive care unit after cardiac arrest often suffer from severe brain injury. This injury worsens further after restoration of circulation due to the cascade of reactions in the brain. Neuroprotective therapies aim to diminish this secondary brain injury, thereby targeting at a better outcome. Several new large international studies will start soon, next to two smaller national phase II studies. In this paper we describe the new studies and invite Dutch intensive care units to join
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