24 research outputs found
Dynamic electromagnetic response of three-dimensional Josephson junction arrays
We present a theoretical study on the dynamical properties of
three-dimensional arrays of Josephson junctions. Our results indicate that such
superconducting networks represent highly sensitive 3D-SQUIDs having some major
advantages in comparison with conventional planar SQUIDs. The voltage response
function of 3D-SQUIDs is directly related to the vector-character of external
electromagnetic fields. The theory developed here allows the three-dimensional
reconstruction of a detected external field including phase information about
the field variables. Applications include the design of novel magnetometers,
gradiometers and particle detectors.Comment: 5 pages, 9 figures, submitted to Journal of Applied Physic
High performance magnetic field sensor based on Superconducting Quantum Interference Filters
We have developed an absolute magnetic field sensor using Superconducting
Quantum Interference Filter (SQIF) made of high-T_c grain boundary Josephson
junctions. The device shows the typical magnetic field dependent voltage
response V(B), which is sharp delta-like dip in the vicinity of zero magnetic
field. When the SQIF is cooled with magnetic shield, and then the shield is
removed, the presence of the ambient magnetic field induces a shift of the dip
position from B_0 ~ 0 to a value B ~ B_1, which is about the average value of
the earth magnetic field, at our latitude. When the SQIF is cooled in the
ambient field without shielding, the dip is first found at B ~ B_1, and the
further shielding of the SQIF results in a shift of the dip towards B_0 ~ 0.
The low hysteresis observed in the sequence of experiments (less than 5% of
B_1) makes SQIFs suitable for high precision measurements of the absolute
magnetic field. The experimental results are discussed in view of potential
applications of high-T_c SQIFs in magnetometry.Comment: 4 pages, 2 figure
Quadratic Mixing of Radio Frequency Signals using Superconducting Quantum Interference Filters
The authors demonstrate quadratic mixing of weak time harmonic
electromagnetic fields applied to Superconducting Quantum Interference Filters,
manufactured from high- grain boundary Josephson junctions and
operated in active microcooler. The authors use the parabolic shape of the dip
in the dc-voltage output around B=0 to mix \emph{quadratically} two external
rf-signals, at frequencies and well below the
Josephson frequency , and detect the corresponding mixing
signal at . Quadratic mixing takes also place when the SQIF
is operated without magnetic shield. The experimental results are well
described by a simple analytical model based on the adiabatic approximation.Comment: 3 pages, 3 figure
Effects of magnetic field on two-dimensional Superconducting Quantum Interference Filters
We present an experimental study of two-dimensional superconducting quantum
interference filters (2D-SQIFs) in the presence of a magnetic field B. The
dependences of the dc voltage on the applied magnetic field are characterized
by a unique delta-like dip at B=0, which depends on the distribution of the
areas of the individual loops, and on the bias current. The voltage span of the
dip scales proportional to the number of rows simultaneously operating at the
same working point. In addition, the voltage response of the 2D-SQIF is
sensitive to a field gradient generated by a control line and superimposed to
the homogeneous field coil. This feature opens the possibility to use 2D
superconducting quantum interference filters as highly sensitive detectors of
spatial gradients of magnetic field.Comment: 3 pages, 4 figures, submitted to AP
Intronic Cis-Regulatory Modules Mediate Tissue-Specific and Microbial Control of angptl4/fiaf Transcription
The intestinal microbiota enhances dietary energy harvest leading to increased fat storage in adipose tissues. This effect is caused in part by the microbial suppression of intestinal epithelial expression of a circulating inhibitor of lipoprotein lipase called Angiopoietin-like 4 (Angptl4/Fiaf). To define the cis-regulatory mechanisms underlying intestine-specific and microbial control of Angptl4 transcription, we utilized the zebrafish system in which host regulatory DNA can be rapidly analyzed in a live, transparent, and gnotobiotic vertebrate. We found that zebrafish angptl4 is transcribed in multiple tissues including the liver, pancreatic islet, and intestinal epithelium, which is similar to its mammalian homologs. Zebrafish angptl4 is also specifically suppressed in the intestinal epithelium upon colonization with a microbiota. In vivo transgenic reporter assays identified discrete tissue-specific regulatory modules within angptl4 intron 3 sufficient to drive expression in the liver, pancreatic islet Ξ²-cells, or intestinal enterocytes. Comparative sequence analyses and heterologous functional assays of angptl4 intron 3 sequences from 12 teleost fish species revealed differential evolution of the islet and intestinal regulatory modules. High-resolution functional mapping and site-directed mutagenesis defined the minimal set of regulatory sequences required for intestinal activity. Strikingly, the microbiota suppressed the transcriptional activity of the intestine-specific regulatory module similar to the endogenous angptl4 gene. These results suggest that the microbiota might regulate host intestinal Angptl4 protein expression and peripheral fat storage by suppressing the activity of an intestine-specific transcriptional enhancer. This study provides a useful paradigm for understanding how microbial signals interact with tissue-specific regulatory networks to control the activity and evolution of host gene transcription