6,327 research outputs found
Sensitivity of the Atlantic meridional overturning circulation to South Atlantic freshwater anomalies
The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to changes in basin integrated net evaporation is highly dependent on the zonal salinity contrast at the southern border of the Atlantic. Biases in the freshwater budget strongly affect the stability of the AMOC in numerical models. The impact of these biases is investigated, by adding local anomaly patterns in the South Atlantic to the freshwater fluxes at the surface. These anomalies impact the freshwater and salt transport by the different components of the ocean circulation, in particular the basin-scale salt-advection feedback, completely changing the response of the AMOC to arbitrary perturbations. It is found that an appropriate dipole anomaly pattern at the southern border of the Atlantic Ocean can collapse the AMOC entirely even without a further hosing. The results suggest a new view on the stability of the AMOC, controlled by processes in the South Atlantic. <br/
Single copy shRNA configuration for ubiquitous gene knockdown in mice
RNA interference through the expression of small hairpin RNA (shRNA) molecules has become a very promising tool in reverse mouse genetics as it may allow inexpensive and rapid gene function analysis in vivo. However, the prerequisites for ubiquitous and reproducible shRNA expression are not well defined. Here we show that a single copy shRNA-transgene can mediate body-wide gene silencing in mice when inserted in a defined locus of the genome. The most commonly used promoters for shRNA expression, H1 and U6, showed a comparably broad activity in this configuration. Taken together, the results define a novel approach for efficient interference with expression of defined genes in vivo. Moreover, we provide a rapid strategy for the production of gene knockdown mice combining recombinase mediated cassette exchange and tetraploid blastocyst complementation approaches
Observation and Control of Laser-Enabled Auger Decay
Single photon laser enabled Auger decay (spLEAD) has been redicted
theoretically [Phys. Rev. Lett. 111, 083004 (2013)] and here we report its
first experimental observation in neon. Using coherent, bichromatic
free-electron laser pulses, we have detected the process and coherently
controlled the angular distribution of the emitted electrons by varying the
phase difference between the two laser fields. Since spLEAD is highly sensitive
to electron correlation, this is a promising method for probing both
correlation and ultrafast hole migration in more complex systems.Comment: 5 pages, 3 figure
DECam integration tests on telescope simulator
The Dark Energy Survey (DES) is a next generation optical survey aimed at
measuring the expansion history of the universe using four probes: weak
gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and
Type Ia supernovae. To perform the survey, the DES Collaboration is building
the Dark Energy Camera (DECam), a 3 square degree, 570 Megapixel CCD camera
which will be mounted at the Blanco 4-meter telescope at the Cerro Tololo
Inter- American Observatory. DES will survey 5000 square degrees of the
southern galactic cap in 5 filters (g, r, i, z, Y). DECam will be comprised of
74 250 micron thick fully depleted CCDs: 62 2k x 4k CCDs for imaging and 12 2k
x 2k CCDs for guiding and focus. Construction of DECam is nearing completion.
In order to verify that the camera meets technical specifications for DES and
to reduce the time required to commission the instrument, we have constructed a
full sized telescope simulator and performed full system testing and
integration prior to shipping. To complete this comprehensive test phase we
have simulated a DES observing run in which we have collected 4 nights worth of
data. We report on the results of these unique tests performed for the DECam
and its impact on the experiments progress.Comment: Proceedings of the 2nd International Conference on Technology and
Instrumentation in Particle Physics (TIPP 2011). To appear in Physics
Procedia. 8 pages, 3 figure
Scaling of Saddle-Node Bifurcations: Degeneracies and Rapid Quantitative Changes
The scaling of the time delay near a "bottleneck" of a generic saddle-node
bifurcation is well-known to be given by an inverse square-root law. We extend
the analysis to several non-generic cases for smooth vector fields. We proceed
to investigate vector fields. Our main result is a new phenomenon in
two-parameter families having a saddle-node bifurcation upon changing the first
parameter. We find distinct scalings for different values of the second
parameter ranging from power laws with exponents in (0,1) to scalings given by
O(1). We illustrate this rapid quantitative change of the scaling law by a an
overdamped pendulum with varying length.Comment: preprint version - for final version see journal referenc
Magnetic Resonance Force Microscopy of paramagnetic electron spins at millikelvin temperatures
Magnetic Resonance Force Microscopy (MRFM) is a powerful technique to detect
a small number of spins that relies on force-detection by an ultrasoft
magnetically tipped cantilever and selective magnetic resonance manipulation of
the spins. MRFM would greatly benefit from ultralow temperature operation,
because of lower thermomechanical noise and increased thermal spin
polarization. Here, we demonstrate MRFM operation at temperatures as low as 30
mK, thanks to a recently developed SQUID-based cantilever detection technique
which avoids cantilever overheating. In our experiment, we detect dangling bond
paramagnetic centers on a silicon surface down to millikelvin temperatures.
Fluctuations of such kind of defects are supposedly linked to 1/f magnetic
noise and decoherence in SQUIDs as well as in several superconducting and
single spin qubits. We find evidence that spin diffusion plays a key role in
the low temperature spin dynamics.Comment: 7 pages, 5 figure
The structure of the PapD-PapGII pilin complex reveals an open and flexible P5 pocket
P pili are hairlike polymeric structures that mediate binding of uropathogenic Escherichia coli to the surface of the kidney via the PapG adhesin at their tips. PapG is composed of two domains: a lectin domain at the tip of the pilus followed by a pilin domain that comprises the initial polymerizing subunit of the 1,000-plus-subunit heteropolymeric pilus fiber. Prior to assembly, periplasmic pilin domains bind to a chaperone, PapD. PapD mediates donor strand complementation, in which a beta strand of PapD temporarily completes the pilin domain's fold, preventing premature, nonproductive interactions with other pilin subunits and facilitating subunit folding. Chaperone-subunit complexes are delivered to the outer membrane usher where donor strand exchange (DSE) replaces PapD's donated beta strand with an amino-terminal extension on the next incoming pilin subunit. This occurs via a zip-in-zip-out mechanism that initiates at a relatively accessible hydrophobic space termed the P5 pocket on the terminally incorporated pilus subunit. Here, we solve the structure of PapD in complex with the pilin domain of isoform II of PapG (PapGIIp). Our data revealed that PapGIIp adopts an immunoglobulin fold with a missing seventh strand, complemented in parallel by the G1 PapD strand, typical of pilin subunits. Comparisons with other chaperone-pilin complexes indicated that the interactive surfaces are highly conserved. Interestingly, the PapGIIp P5 pocket was in an open conformation, which, as molecular dynamics simulations revealed, switches between an open and a closed conformation due to the flexibility of the surrounding loops. Our study reveals the structural details of the DSE mechanism
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