829 research outputs found
Subband population in a single-wall carbon nanotube diode
We observe current rectification in a molecular diode consisting of a
semiconducting single-wall carbon nanotube and an impurity. One half of the
nanotube has no impurity, and it has a current-voltage (I-V) charcteristic of a
typical semiconducting nanotube. The other half of the nanotube has the
impurity on it, and its I-V characteristic is that of a diode. Current in the
nanotube diode is carried by holes transported through the molecule's
one-dimensional subbands. At 77 Kelvin we observe a step-wise increase in the
current through the diode as a function of gate voltage, showing that we can
control the number of occupied one-dimensional subbands through electrostatic
doping.Comment: to appear in Physical Review Letters. 4 pages & 3 figure
Universality of electron correlations in conducting carbon nanotubes
Effective low-energy Hamiltonian of interacting electrons in conducting
single-wall carbon nanotubes with arbitrary chirality is derived from the
microscopic lattice model. The parameters of the Hamiltonian show very weak
dependence on the chiral angle, which makes the low energy properties of
conducting chiral nanotubes universal. The strongest Mott-like electron
instability at half filling is investigated within the self-consistent harmonic
approximation. The energy gaps occur in all modes of elementary excitations and
estimate at eV.Comment: 4 pages, 2 figure
Bandgap Change of Carbon Nanotubes: Effect of Small Tensile and Torsional Strain
We use a simple picture based on the electron approximation to study
the bandgap variation of carbon nanotubes with uniaxial and torsional strain.
We find (i) that the magnitude of slope of bandgap versus strain has an almost
universal behaviour that depends on the chiral angle, (ii) that the sign of
slope depends on the value of and (iii) a novel change in sign
of the slope of bandgap versus uniaxial strain arising from a change in the
value of the quantum number corresponding to the minimum bandgap. Four orbital
calculations are also presented to show that the orbital results are
valid.Comment: Revised. Method explained in detai
Electronic Structure of Carbon Nanotube Ropes
We present a tight binding theory to analyze the motion of electrons between
carbon nanotubes bundled into a carbon nanotube rope. The theory is developed
starting from a description of the propagating Bloch waves on ideal tubes, and
the effects of intertube motion are treated perturbatively in this basis.
Expressions for the interwall tunneling amplitudes between states on
neighboring tubes are derived which show the dependence on chiral angles and
intratube crystal momenta. We find that conservation of crystal momentum along
the tube direction suppresses interwall coherence in a carbon nanorope
containing tubes with random chiralities. Numerical calculations are presented
which indicate that electronic states in a rope are localized in the transverse
direction with a coherence length corresponding to a tube diameter.Comment: 15 pages, 10 eps figure
Gravitational ultrarelativistic spin-orbit interaction and the weak equivalence principle
It is shown that the gravitational ultrarelativistic spin-orbit interaction
violates the weak equivalence principle in the traditional sense. This fact is
a direct consequence of the Mathisson-Papapetrou equations in the frame of
reference comoving with a spinning test particle. The widely held assumption
that the deviation of a spinning test body from a geodesic trajectory is caused
by tidal forces is not correctComment: 12 page
Andreev-Tunneling, Coulomb Blockade, and Resonant Transport of Non-Local Spin-Entangled Electrons
We propose and analyze a spin-entangler for electrons based on an s-wave
superconductor coupled to two quantum dots each of which is tunnel-coupled to
normal Fermi leads. We show that in the presence of a voltage bias and in the
Coulomb blockade regime two correlated electrons provided by the Andreev
process can coherently tunnel from the superconductor via different dots into
different leads. The spin-singlet coming from the Cooper pair remains preserved
in this process, and the setup provides a source of mobile and nonlocal
spin-entangled electrons. The transport current is calculated and shown to be
dominated by a two-particle Breit-Wigner resonance which allows the injection
of two spin-entangled electrons into different leads at exactly the same
orbital energy, which is a crucial requirement for the detection of spin
entanglement via noise measurements. The coherent tunneling of both electrons
into the same lead is suppressed by the on-site Coulomb repulsion and/or the
superconducting gap, while the tunneling into different leads is suppressed
through the initial separation of the tunneling electrons. In the regime of
interest the particle-hole excitations of the leads are shown to be negligible.
The Aharonov-Bohm oscillations in the current are shown to contain single- and
two-electron periods with amplitudes that both vanish with increasing Coulomb
repulsion albeit differently fast.Comment: 11 double-column pages, 2 figures, REVTeX, minor revision
Patient and physician satisfaction in an observational study with methyl aminolevulinate daylight-photodynamic therapy in the treatment of multiple actinic keratoses of the face and scalp in 6 European countries
BACKGROUND
Guidelines recommend treating actinic keratoses (AKs) as they are recognized as precursors of invasive squamous cell carcinoma.
OBJECTIVE
The objective of this study was to collect real-world clinical data on the use of methyl aminolevulinate daylight photodynamic therapy (MAL DL-PDT) for the treatment of face and scalp AK in Europe.
METHODS
A prospective, multicenter, non-interventional study was conducted in six European countries in patients receiving a single treatment of MAL DL-PDT for face and/or scalp AK. Patient-reported outcomes were assessed by patient questionnaires at baseline and at 3 months after treatment, efficacy was assessed at 3 months using a 6-point global improvement scale, and adverse events (AE) were recorded at each visit.
RESULTS
Overall, 325 patients were enrolled from 52 investigational centres, 314 of whom attended the 3-month visit. Most patients had multiple lesions (58.4% had >10 lesions) with lesions mainly located on the scalp (60.0%) and/or forehead (54.2%). AKs were predominantly grade I (39.4%) or grade II (33.2%), and 10.5% of patients had grade III lesions. The proportions of patients and physicians that were overall satisfied to very satisfied with the MAL DL-PDT treatment were 80.4% and 90.3%, respectively. The vast majority of patients (90.0%) would consider using MAL DL-PDT again if needed. Physician-assessed efficacy at 3 months was at least much improved in 83.5% of patients, with 45.9% of patients requiring no retreatment. Related AEs were reported in 15% of patients.
CONCLUSION
Use of MAL DL-PDT for multiple face and/or scalp AKs resulted in high levels of patient and physician satisfaction in clinical practice in Europe, reflecting the good efficacy and high tolerability of this convenient procedure
Superconductivity in Ropes of Single-Walled Carbon Nanotubes
We report measurements on ropes of Single Walled Carbon Nanotubes (SWNT) in
low-resistance contact to non-superconducting (normal) metallic pads, at low
voltage and at temperatures down to 70 mK. In one sample, we find a two order
of magnitude resistance drop below 0.55 K, which is destroyed by a magnetic
field of the order of 1T, or by a d.c. current greater than 2.5 microA. These
features strongly suggest the existence of superconductivity in ropes of SWNT.Comment: Accepted for publication in Phys. Rev. Let
Nonlinear surface waves in left-handed materials
We study both linear and nonlinear surface waves localized at the interface
separating a left-handed medium (i.e. the medium with both negative dielectric
permittivity and negative magnetic permeability) and a conventional (or
right-handed) dielectric medium. We demonstrate that the interface can support
both TE- and TM-polarized surface waves - surface polaritons, and we study
their properties. We describe the intensity-dependent properties of nonlinear
surface waves in three different cases, i.e. when both the LH and RH media are
nonlinear and when either of the media is nonlinear. In the case when both
media are nonlinear, we find two types of nonlinear surface waves, one with the
maximum amplitude at the interface, and the other one with two humps. In the
case when one medium is nonlinear, only one type of surface wave exists, which
has the maximum electric field at the interface, unlike waves in right-handed
materials where the surface-wave maximum is usually shifted into a
self-focussing nonlinear medium. We discus the possibility of tuning the wave
group velocity in both the linear and nonlinear cases, and show that
group-velocity dispersion, which leads to pulse broadening, can be balanced by
the nonlinearity of the media, so resulting in soliton propagation.Comment: 9 pages, 10 figure
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