23,398 research outputs found
Ratchet effect in dc SQUIDs
We analyzed voltage rectification for dc SQUIDs biased with ac current with
zero mean value. We demonstrate that the reflection symmetry in the
2-dimensional SQUID potential is broken by an applied flux and with appropriate
asymmetries in the dc SQUID. Depending on the type of asymmetry, we obtain a
rocking or a simultaneously rocking and flashing ratchet, the latter showing
multiple sign reversals in the mean voltage with increasing amplitude of the ac
current. Our experimental results are in agreement with numerical solutions of
the Langevin equations for the asymmetric dc SQUID.Comment: 10 pages including 5 Postscript figure
Human complement factor H
We isolated cDNA clones coding for the functionally important tryptic N-terminal38-
kDa fragment of human complement control protein factor H using polyclonal and
monoclonal antibodies to screen a human liver cDNA library cloned in a bacterial
expression vector, PEX-1. By testing the reactivity of antibodies specific for the
recombinant proteins produced by individual clones with proteolytic fragments of
serum H the exact position of these cDNA clones within H was mapped. One clone,
H-19, coding for the 38-kDa fragment of H was sequenced and found to code for 289
amino acids derived from the 38-kDa N-terminal fragment as well as for the first 108
amino acids belonging to the complementary 142-kDa tryptic fragment. The derived
protein sequence could be arranged in 6 highly homologous repeats of about 60 amino
acids each, the homology between the repeats being determined by the characteristic
position of cysteine, proline, glycine, tyrosine and tryptophane residues. The region
coding for the epitope recognized by one of our monoclonal antibodies was localized
by subcloning restriction fragments of H-19 into the expression plasmid and testing
for the expression of this epitope
Deformation of grain boundaries in polar ice
The ice microstructure (grain boundaries) is a key feature used to study ice
evolution and to investigate past climatic changes. We studied a deep ice core,
in Dome Concordia, Antarctica, which records past mechanical deformations. We
measured a "texture tensor" which characterizes the pattern geometry and
reveals local heterogeneities of deformation along the core. These results
question key assumptions of the current models used for dating
Decoherence of a two-qubit system with a variable bath coupling operator
We examine the decoherence of an asymmetric two-qubit system that is coupled
via a tunable interaction term to a common bath or two individual baths of
harmonic oscillators. The dissipative dynamics are evaluated using the
Bloch-Redfield formalism. It is shown that the behaviour of the decoherence
effects is affected mostly by different symmetries between the qubit operator
which is coupled to the environment and temperature, whereas the differences
between the two bath configurations are very small. Moreover, it is elaborated
that small imperfections of the qubit parameters do not lead to a drastic
enhancement of the decoherence rates.Comment: 10 pages, 5 figure
Laser Interferometric Detectors of Gravitational Waves
A laser interferometric detector of gravitational waves is studied and a
complete solution (to first order in the metric perturbation) of the coupled
Einstein-Maxwell equations with appropriate boundary conditions for the light
beams is determined. The phase shift, the light deflection and the rotation of
the polarization axis induced by gravitational waves are computed. The results
are compared with previous literature, and are shown to hold also for detectors
which are large in comparison with the gravitational wavelength.Comment: 13 pages, LaTe
New insights on the dense molecular gas in NGC253 as traced by HCN and HCO+
We have imaged the central ~1kpc of the circumnuclear starburst disk in the
galaxy NGC253 in the HCN(1-0), HCO+(1-0), and CO(1-0) transitions at 60pc
resolution using the Owens Valley Radio Observatory Millimeter-Wavelength Array
(OVRO). We have also obtained Atacama Pathfinder Experiment (APEX) observations
of the HCN(4-3) and the HCO+(4-3) lines of the starburst disk. We find that the
emission from the HCN(1-0) and HCO+(1-0) transitions, both indicators of dense
molecular gas, trace regions which are non-distinguishable within the
uncertainties of our observations. Even though the continuum flux varies by
more than a factor 10 across the starburst disk, the HCN/HCO+ ratio is constant
throughout the disk, and we derive an average ratio of 1.1+/-0.2. From an
excitation analysis we find that all lines from both molecules are subthermally
excited and that they are optically thick. This subthermal excitation implies
that the observed HCN/HCO+ line ratio is sensitive to the underlying chemistry.
The constant line ratio thus implies that there are no strong abundance
gradients across the starburst disk of NGC253. This finding may also explain
the variations in L'(HCN)/L'(HCO+) between different star forming galaxies both
nearby and at high redshifts.Comment: 9 pages, 12 figures, ApJ in press (volume 666 September
Quantum nondemolition-like, fast measurement scheme for a superconducting qubit
We present a measurement protocol for a flux qubit coupled to a
dc-Superconducting QUantum Interference Device (SQUID), representative of any
two-state system with a controllable coupling to an harmonic oscillator
quadrature, which consists of two steps. First, the qubit state is imprinted
onto the SQUID via a very short and strong interaction. We show that at the end
of this step the qubit dephases completely, although the perturbation of the
measured qubit observable during this step is weak. In the second step,
information about the qubit is extracted by measuring the SQUID. This step can
have arbitrarily long duration, since it no longer induces qubit errors.Comment: published version, minor correction
Harmonic Love wave devices for biosensing applications
Simultaneous operation of a Love wave biosensor at the fundamental frequency and third harmonic, including the optimisation of IDT metallisation thickness, has been investigated. Data is presented showing a sequence of deposition and removal of a model mass layer of palmitoyl-oleoyl-sn-glycerophosphocholine (POPC) vesicles while frequency hopping between 110 and 330 MH
Entanglement and bifurcations in Jahn-Teller models
We compare and contrast the entanglement in the ground state of two
Jahn-Teller models. The system models the coupling of a
two-level electronic system, or qubit, to a single oscillator mode, while the
models the qubit coupled to two independent, degenerate
oscillator modes. In the absence of a transverse magnetic field applied to the
qubit, both systems exhibit a degenerate ground state. Whereas there always
exists a completely separable ground state in the system, the
ground states of the model always exhibit entanglement. For
the case we aim to clarify results from previous work, alluding
to a link between the ground state entanglement characteristics and a
bifurcation of a fixed point in the classical analogue. In the
case we make use of an ansatz for the ground state. We
compare this ansatz to exact numerical calculations and use it to investigate
how the entanglement is shared between the three system degrees of freedom.Comment: 11 pages, 9 figures, comments welcome; 2 references adde
- …