2,068 research outputs found
Dichroic atomic vapor laser lock with multi-gigahertz stabilization range
A dichroic atomic vapor laser lock (DAVLL) system exploiting
buffer-gas-filled millimeter-scale vapor cells is presented. This system offers
similar stability as achievable with conventional DAVLL system using bulk vapor
cells, but has several important advantages. In addition to its compactness, it
may provide continuous stabilization in a multi-gigahertz range around the
optical transition. This range may be controlled either by changing the
temperature of the vapor or by application of a buffer gas under an appropriate
pressure. In particular, we experimentally demonstrate the ability of the
system to lock the laser frequency between two hyperfine components of the
Rb ground state or as far as 16 GHz away from the closest optical
transition.Comment: 11 pages, 7 figures. Published in Review of Scientific Instruments
201
Two tone response of radiofrequency signals using the voltage output of a Superconducting Quantum Interference Filter
In the presence of weak time harmonic electromagnetic fields, Superconducting
Quantum Interference Filters (SQIFs) show the typical behavior of non linear
mixers. The SQIFs are manufactured from high-T_c grain boundary Josephson
junctions and operated in active microcooler. The dependence of dc voltage
output V_dc vs. static external magnetic field B is non-periodic and consists
of a well pronounced unique dip at zero field, with marginal side modulations
at higher fields. We have successfully exploited the parabolic shape of the
voltage dip around B=0 to mix quadratically two external time harmonic
rf-signals, at frequencies f_1 and f_2 below the Josephson frequency f_J, and
detect the corresponding mixing signal at f_1-f_2. When the mixing takes place
on the SQIF current-voltage characteristics the component at 2f_2 - f_1 is
present. The experiments suggest potential applications of a SQIF as a
non-linear mixing device, capable to operate at frequencies from dc to few GHz
with a large dynamic range.Comment: 10 pages, 3 Figures, submitted to J. Supercond. (as proceeding of the
HTSHFF Symposium, June 2006, Cardiff
Voltage-current and voltage-flux characteristics of asymmetric high TC DC SQUIDs
We report measurements of transfer functions and flux shifts of 20 on-chip
high T DC SQUIDs half of which were made purposely geometrically
asymmetric. All of these SQUIDs were fabricated using standard high T thin
film technology and they were single layer ones, having 140 nm thickness of
YBaCuO film deposited by laser ablation onto MgO bicrystal
substrates with 24 misorientation angle. For every SQUID the parameters of
its intrinsic asymmetry, i. e., the density of critical current and resistivity
of every junction, were measured directly and independently. We showed that the
main reason for the on-chip spreading of SQUIDs' voltage-current and
voltage-flux characteristics was the intrinsic asymmetry. We found that for
SQUIDs with a relative large inductance ( pH) both the voltage
modulation and the transfer function were not very sensitive to the junctions
asymmetry, whereas SQUIDs with smaller inductance ( pH) were
more sensitive. The results obtained in the paper are important for the
implementation in the sensitive instruments based on high T SQUID arrays
and gratings.Comment: 11 pages, 4 tables, 17 figures This version is substantially
modified. The Introduction and Section 2 are completely rewritten, while
experimental part is mainly the same as in previous versio
STABILITY OF DNA IN PURKINJE CELL NUCLEI OF THE MOUSE : An Autoradiographic Study
Neurons of the mouse were labeled with [3H]thymidine during their prenatal period of proliferation. The 3H activity of the Purkinje cell nuclei was then studied autoradiographically 8, 25, 55, and 90 days after birth. The measured grain number per nucleus decreased by about 14% between the 8th and 25th postnatal days and then remained constant up to 90 days. There was no significant decrease of the 3H activity of the Purkinje cell nuclei after correction of the measured grain number per nucleus for increasing nuclear volume of the growing Purkinje cells and for the influence of [3H]β self-absorption in the material of the sections. Injection of a high dose of [3H]thymidine into young adult mice did not result in 3H labeling of either Purkinje or other neurons in other brain regions. The results agree with the concept of metabolic stability of nuclear DNA. "Metabolic" DNA could not be observed in these experiments
Automated quantitative analysis of single and double label autoradiographs
A method for the analysis of silver grain content in both single and double label autoradiographs is presented. The total grain area is calculated by counting the number of pixels at which the recorded light intensity in transmission dark field illumination exceeds a selected threshold. The calibration tests included autoradiographs with low (3H- thymidin) and high (3H-desoxyuridin) silver grain density. The results are proportional to the customary visual grain count. For the range of visibly countable grain densities in single labeled specimens, the correlation coefficient between the computed values and the visual grain counts is better than 0.96. In the first emulsion of the two emulsion layer autoradiographs of double labeled specimens (3H-14C- thymidin) the correlation coefficient is 0.919 and 0.906. The method provides a statistical correction for the background grains not due to the isotope. The possibility to record 14C tracks by shifting the focus through the second emulsion of the double labeled specimens is also demonstrated. The reported technique is essentially independent of size, shape and density of the grains
The Influence of the Second Harmonic in the Current-Phase Relation on the Voltage-Current Characteristic of high TC DC SQUID
A theory for the voltage-current characteristic in high TC DC SQUIDs, which
accounts for a second harmonic in the junction current-phase relation, is
developed. The comparison with experiment is performed. It is shown that if the
second harmonic is prevailed, the theory can explain the large deviations of
the experimental voltage modulation from theoretical predictions and computer
simulations based on conventional sinusoidal current-phase relation.Comment: Eq. 13 is correcte
Two-phonon scattering of magnetorotons in fractional quantum Hall liquids
We study the phonon-assisted process of dissociation of a magnetoroton, in a
fractional quantum Hall liquid, into an unbound pair of quasiparticles. Whilst
the dissociation is forbidden to first order in the electron-phonon
interaction, it can occur as a two-phonon process. Depending on the value of
final separation between the quasiparticles, the dissociation is either a
single event involving absorption of one phonon and emission of another phonon
of similar energy, or a two-phonon diffusion of a quasiexciton in momentum
space. The dependence of the magnetoroton dissociation time on the filling
factor of the incompressible liquid is found.Comment: 4 pages, no figure
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