627 research outputs found
On a generalization of the binomial distribution and its Poisson-like limit
We examine a generalization of the binomial distribution associated with a
strictly increasing sequence of numbers and we prove its Poisson-like limit.
Such generalizations might be found in quantum optics with imperfect detection.
We discuss under which conditions this distribution can have a probabilistic
interpretation.Comment: 17 pages, 6 figure
Carbon nanotubes adhesion and nanomechanical behavior from peeling force spectroscopy
Applications based on Single Walled Carbon Nanotube (SWNT) are good example
of the great need to continuously develop metrology methods in the field of
nanotechnology. Contact and interface properties are key parameters that
determine the efficiency of SWNT functionalized nanomaterials and nanodevices.
In this work we have taken advantage of a good control of the SWNT growth
processes at an atomic force microscope (AFM) tip apex and the use of a low
noise (1E-13 m/rtHz) AFM to investigate the mechanical behavior of a SWNT
touching a surface. By simultaneously recording static and dynamic properties
of SWNT, we show that the contact corresponds to a peeling geometry, and
extract quantities such as adhesion energy per unit length, curvature and
bending rigidity of the nanotube. A complete picture of the local shape of the
SWNT and its mechanical behavior is provided
Arbitrary rotation and entanglement of flux SQUID qubits
We propose a new approach for the arbitrary rotation of a three-level SQUID
qubit and describe a new strategy for the creation of coherence transfer and
entangled states between two three-level SQUID qubits. The former is succeeded
by exploring the coupled-uncoupled states of the system when irradiated with
two microwave pulses, and the latter is succeeded by placing the SQUID qubits
into a microwave cavity and used adiabatic passage methods for their
manipulation.Comment: Accepted for publication in Phys. Rev.
Elastic modulus of multi-walled carbon nanotubes produced by catalytic chemical vapour deposition
Carbon nanotubes (CNTs) are ideal structures for use as reinforcement fibres in composite materials, due to their extraordinary mechanical properties, in particular high Young's modulus (E∼1TPa). Usually the high value of E is taken as granted for all types of carbon CNTs. Here we demonstrate that multi-walled carbon nanotubes (MWCNTs) produced by catalytic chemical vapour deposition (CCVD) have low moduli (E<100GPa) independently of their growth conditions. We attribute this to the presence of structural defects. Additional high-temperature annealing failed to improve the mechanical properties. This study urges a better control of the growth process in order to obtain high strength CCVD grown MWCNTs suitable for reinforcement in large-scale industrial application
Bundling up carbon nanotubes through Wigner defects
We show, using ab initio total energy density functional theory, that the
so-called Wigner defects, an interstitial carbon atom right besides a vacancy,
which are present in irradiated graphite can also exist in bundles of carbon
nanotubes. Due to the geometrical structure of a nanotube, however, this defect
has a rather low formation energy, lower than the vacancy itself, suggesting
that it may be one of the most important defects that are created after
electron or ion irradiation. Moreover, they form a strong link between the
nanotubes in bundles, increasing their shear modulus by a sizeable amount,
clearly indicating its importance for the mechanical properties of nanotube
bundles.Comment: 5 pages and 4 figure
Detecting the translocation of DNA through a nanopore using graphene nanoribbons
Solid-state nanopores can act as single-molecule sensors and could potentially be used to rapidly sequence DNA molecules. However, nanopores are typically fabricated in insulating membranes that are as thick as 15 bases, which makes it difficult for the devices to read individual bases. Graphene is only 0.335 nm thick (equivalent to the spacing between two bases in a DNA chain) and could therefore provide a suitable membrane for sequencing applications. Here, we show that a solid-state nanopore can be integrated with a graphene nanoribbon transistor to create a sensor for DNA translocation. As DNA molecules move through the pore, the device can simultaneously measure drops in ionic current and changes in local voltage in the transistor, which can both be used to detect the molecules. We examine the correlation between these two signals and use the ionic current measurements as a real-time control of the graphene-based sensing device
Direct sampling of exponential phase moments of smoothed Wigner functions
We investigate exponential phase moments of the s-parametrized
quasidistributions (smoothed Wigner functions). We show that the knowledge of
these moments as functions of s provides, together with photon-number
statistics, a complete description of the quantum state. We demonstrate that
the exponential phase moments can be directly sampled from the data recorded in
balanced homodyne detection and we present simple expressions for the sampling
kernels. The phase moments are Fourier coefficients of phase distributions
obtained from the quasidistributions via integration over the radial variable
in polar coordinates. We performed Monte Carlo simulations of the homodyne
detection and we demonstrate the feasibility of direct sampling of the moments
and subsequent reconstruction of the phase distribution.Comment: RevTeX, 8 pages, 6 figures, accepted Phys. Rev.
Objective and Subjective Components of the First-Night Effect in Young Nightmare Sufferers and Healthy Participants
The first-night effect—marked differences between the first- and the second-night sleep spent in a
laboratory—is a widely known phenomenon that accounts for the common practice of excluding
the first-night sleep from any polysomnographic analysis. The extent to which the first-night effect
is present in a participant, as well as its duration (1 or more nights), might have diagnostic value
and should account for different protocols used for distinct patient groups. This study investigated
the first-night effect on nightmare sufferers (NM; N D 12) and healthy controls .N D 15/ using
both objective (2-night-long polysomnography) and subjective (Groningen Sleep Quality Scale
for the 2 nights spent in the laboratory and 1 regular night spent at home) methods. Differences
were found in both the objective (sleep efficiency, wakefulness after sleep onset, sleep latency,
Stage-1 duration, Stage-2 duration, slow-wave sleep duration, and REM duration) and subjective
(self-rating) variables between the 2 nights and the 2 groups, with a more pronounced first-night
effect in the case of the NM group. Furthermore, subjective sleep quality was strongly related to
polysomnographic variables and did not differ among 1 regular night spent at home and the second
night spent in the laboratory. The importance of these results is discussed from a diagnostic point
of view
PPAR? Downregulation by TGF in Fibroblast and Impaired Expression and Function in Systemic Sclerosis: A Novel Mechanism for Progressive Fibrogenesis
The nuclear orphan receptor peroxisome proliferator-activated receptor-gamma (PPAR-γ) is expressed in multiple cell types in addition to adipocytes. Upon its activation by natural ligands such as fatty acids and eicosanoids, or by synthetic agonists such as rosiglitazone, PPAR-γ regulates adipogenesis, glucose uptake and inflammatory responses. Recent studies establish a novel role for PPAR-γ signaling as an endogenous mechanism for regulating transforming growth factor-ß (TGF-ß)- dependent fibrogenesis. Here, we sought to characterize PPAR-γ function in the prototypic fibrosing disorder systemic sclerosis (SSc), and delineate the factors governing PPAR-γ expression. We report that PPAR-γ levels were markedly diminished in skin and lung biopsies from patients with SSc, and in fibroblasts explanted from the lesional skin. In normal fibroblasts, treatment with TGF-ß resulted in a time- and dose-dependent down-regulation of PPAR-γ expression. Inhibition occurred at the transcriptional level and was mediated via canonical Smad signal transduction. Genome-wide expression profiling of SSc skin biopsies revealed a marked attenuation of PPAR-γ levels and transcriptional activity in a subset of patients with diffuse cutaneous SSc, which was correlated with the presence of a ''TGF-ß responsive gene signature'' in these biopsies. Together, these results demonstrate that the expression and function of PPAR-γ are impaired in SSc, and reveal the existence of a reciprocal inhibitory cross-talk between TGF-ß activation and PPAR-γ signaling in the context of fibrogenesis. In light of the potent anti-fibrotic effects attributed to PPAR-γ, these observations lead us to propose that excessive TGF-ß activity in SSc accounts for impaired PPAR-γ function, which in turn contributes to unchecked fibroblast activation and progressive fibrosis. © 2010 Wei et al
- …