647 research outputs found
Turnstile behaviour of the Cooper-pair pump
We have experimentally studied the behaviour of the so-called Cooper pair
pump (CPP) with three Josephson junctions, in the limit of small Josephson
coupling EJ < EC. These experiments show that the CPP can be operated as a
traditional turnstile device yielding a gate-induced current 2ef in the
direction of the bias voltage, by applying an RF-signal with frequency f to the
two gates in phase, while residing at the degeneracy node of the gate plane.
Accuracy of the CPP during this kind of operation was about 3% and the
fundamental Landau-Zener limit was observed to lie above 20 MHz. We have also
measured the current pumped through the array by rotating around the degeneracy
node in the gate plane. We show that this reproduces the turnstile-kind of
behavior. To overcome the contradiction between the obtained e-periodic
DC-modulation and a pure 2e-behaviour in the RF-measurements, we base our
observations on a general principle that the system always minimises its
energy. It suggests that if the excess quasiparticles in the system have a
freedom to tunnel, they will organize themselves to the configuration yielding
the highest current.Comment: 29 pages, 16 figures, uses REVTeX and graphicx-packag
Molecular coupling of light with plasmonic waveguides
We use molecules to couple light into and out of microscale plasmonic
waveguides. Energy transfer, mediated by surface plasmons, from donor molecules
to acceptor molecules over ten micrometer distances is demonstrated. Also
surface plasmon coupled emission from the donor molecules is observed at
similar distances away from the excitation spot. The lithographic fabrication
method we use for positioning the dye molecules allows scaling to nanometer
dimensions. The use of molecules as couplers between far-field and near-field
light offers the advantages that no special excitation geometry is needed, any
light source can be used to excite plasmons and the excitation can be localized
below the diffraction limit. Moreover, the use of molecules has the potential
for integration with molecular electronics and for the use of molecular
self-assembly in fabrication. Our results constitute a proof-of-principle
demonstration of a plasmonic waveguide where signal in- and outcoupling is done
by molecules.Comment: 9 pages, 5 figure
Method for finding the critical temperature of the island in a SET structure
We present a method to measure the critical temperature of the island of a
superconducting single electron transistor. The method is based on a sharp
change in the slope of the zero-bias conductance as a function of temperature.
We have used this method to determine the superconducting phase transition
temperature of the Nb island of an superconducting single electron transistor
with Al leads. We obtain as high as 8.5 K and gap
energies up to meV. By looking at the zero bias
conductance as a function of magnetic field instead of temperature, also the
critical field of the island can be determined. Using the orthodox theory, we
have performed extensive numerical simulations of charge transport properties
in the SET at temperatures comparable to the gap, which match very well the
data, therefore providing a solid theoretical basis for our method.Comment: 4 pages, 2 figure
High-Yield of Memory Elements from Carbon Nanotube Field-Effect Transistors with Atomic Layer Deposited Gate Dielectric
Carbon nanotube field-effect transistors (CNT FETs) have been proposed as
possible building blocks for future nano-electronics. But a challenge with CNT
FETs is that they appear to randomly display varying amounts of hysteresis in
their transfer characteristics. The hysteresis is often attributed to charge
trapping in the dielectric layer between the nanotube and the gate. This study
includes 94 CNT FET samples, providing an unprecedented basis for statistics on
the hysteresis seen in five different CNT-gate configurations. We find that the
memory effect can be controlled by carefully designing the gate dielectric in
nm-thin layers. By using atomic layer depositions (ALD) of HfO and
TiO in a triple-layer configuration, we achieve the first CNT FETs with
consistent and narrowly distributed memory effects in their transfer
characteristics.Comment: 6 pages, 3 figures; added one reference, text reformatted with
smaller addition
Cooper-pair resonances and subgap Coulomb blockade in a superconducting single-electron transistor
We have fabricated and measured superconducting single-electron transistors
with Al leads and Nb islands. At bias voltages below the gap of Nb we observe
clear signatures of resonant tunneling of Cooper pairs, and of Coulomb blockade
of the subgap currents due to linewidth broadening of the energy levels in the
superconducting density of states of Nb. The experimental results are in good
agreement with numerical simulations.Comment: 4 pages, 3 figure
MYC is not detected in highly proliferating normal spermatogonia but is coupled with CIP2A in testicular cancers
High MYC expression is linked to proliferative activity in most normal
tissues and in cancer. MYC also supports self-renewal and proliferation
of many types of tissue progenitor cells. Cancerous inhibitor of PP2A
(CIP2A) promotes MYC phosphorylation and activity during intestinal
crypt regeneration in vivo and in various cancers. CIP2A also supports male germ cell proliferation in vivo.
However, the role of MYC in normal germ cell proliferation and
spermatogonial progenitor self-renewal is currently unclear. Here, we
demonstrate that male germ cells are CIP2A-positive but lack detectable
levels of MYC protein; whereas MYC is highly expressed in Leydig cells
and peritubular myoid cells contributing thereby to the testicular stem
cell niche. On the other hand, MYC was co-expressed with CIP2A in
testicular cancers. These results demonstrate that CIP2A and MYC are
spatially uncoupled in the regulation of spermatogenesis, but functional
relationship between these two human oncoproteins is established during
testicular cancer transformation. We propose that further analysis of
mechanisms of MYC silencing in spermatogonial progenitors may reveal
novel fundamental information relevant to understanding of MYC
expression in cancer. </p
Trapping of 27 bp - 8 kbp DNA and immobilization of thiol-modified DNA using dielectrophoresis
Dielectrophoretic trapping of six different DNA fragments, sizes varying from
the 27 to 8416 bp, has been studied using confocal microscopy. The effect of
the DNA length and the size of the constriction between nanoscale fingertip
electrodes on the trapping efficiency have been investigated. Using finite
element method simulations in conjunction with the analysis of the experimental
data, the polarizabilities of the different size DNA fragments have been
calculated for different frequencies. Also the immobilization of trapped
hexanethiol- and DTPA-modified 140 nm long DNA to the end of gold
nanoelectrodes was experimentally quantified and the observations were
supported by density functional theory calculations.Comment: 17 pages (1 column version), 8 figure
Onset and progression of puberty in Klinefelter syndrome
Objective: Klinefelter syndrome (KS) (47,XXY and variants, KS) is the most common sex chromosome disorder in humans. However, little is known about the onset and progression of puberty in patients with KS. In this study, we describe the onset and progression of puberty in a large series of boys with KS in a single tertiary centre. Design and Patients: Retrospective data (Tanner stages, testicular length, testosterone supplementation, levels of luteinizing hormone [LH] and testosterone) before possible testosterone treatment on 72 KS patients with 47,XXY karyotype were reviewed, and G (n = 59 patients) and P (n = 56 patients) stages were plotted on puberty nomograms. Measurements and Results: One boy had a delayed onset of puberty, as he was at the G1 stage at the age of 13.8 years (-2.2 SDs). No observations of delay were made of boys at Stage G2. The progression of G stages was within normal limits in the majority of patients; only few boys were late at G3 (4.1%; 1 out of 24) and G4 (7.4%; 2 out of 27). Testosterone supplementation was started at the average age of 15.5 years to 35 boys (47%), 2 of whom were over 18 years old. LH level was on average 18.2 IU/L (SD: 6.3 IU/L) and testosterone 9.1 nmol/L (SD: 3.1 nmol/L) when testosterone supplementation was started. Conclusions: Our results suggest that puberty starts within the normal age limits in boys with KS, and testosterone supplementation is not needed for the initial pubertal progression in the majority of patients.Peer reviewe
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