658 research outputs found
Nucleation at the DNA supercoiling transition
Twisting DNA under a constant applied force reveals a thermally activated
transition into a state with a supercoiled structure known as a plectoneme.
Using transition state theory, we predict the rate of this plectoneme
nucleation to be of order 10^4 Hz. We reconcile this with experiments that have
measured hopping rates of order 10 Hz by noting that the viscosity of the bead
used to manipulate the DNA limits the measured rate. We find that the intrinsic
bending caused by disorder in the base-pair sequence is important for
understanding the free energy barrier that governs the transition. Both
analytic and numerical methods are used in the calculations. We provide
extensive details on the numerical methods for simulating the elastic rod model
with and without disorder.Comment: 18 pages, 15 figure
High-temperature-grown buffer layer boosts electron mobility in epitaxial La-doped BaSnO/SrZrO heterostructures
By inserting a SrZrO buffer layer between the film and the substrate, we
demonstrate a significant reduction of the threading dislocation density with
an associated improvement of the electron mobility in La:BaSnO films. A
room temperature mobility of 140 cm V is achieved for
25-nm-thick films without any post-growth treatment. The density of threading
dislocations is only cm for buffered films prepared
on (110) TbScO substrates by pulsed laser deposition.Comment: 5 pages, 4 figure
WSPEC: A waveguide filter-bank focal plane array spectrometer for millimeter wave astronomy and cosmology
Imaging and spectroscopy at (sub-)millimeter wavelengths are key frontiers in
astronomy and cosmology. Large area spectral surveys with moderate spectral
resolution (R=50-200) will be used to characterize large scale structure and
star formation through intensity mapping surveys in emission lines such as the
CO rotational transitions. Such surveys will also be used to study the SZ
effect, and will detect the emission lines and continuum spectrum of individual
objects. WSPEC is an instrument proposed to target these science goals. It is a
channelizing spectrometer realized in rectangular waveguide, fabricated using
conventional high-precision metal machining. Each spectrometer is coupled to
free space with a machined feed horn, and the devices are tiled into a 2D array
to fill the focal plane of the telescope. The detectors will be aluminum
Lumped-Element Kinetic Inductance Detectors (LEKIDs). To target the CO lines
and SZ effect, we will have bands at 135-175 GHz and 190-250 GHz, each
Nyquist-sampled at R~200 resolution. Here we discuss the instrument concept and
design, and successful initial testing of a WR10 (i.e. 90 GHz) prototype
spectrometer. We recently tested a WR5 (180 GHz) prototype to verify that the
concept works at higher frequencies, and also designed a resonant backshort
structure that may further increase the optical efficiency. We are making
progress towards integrating a spectrometer with a LEKID array and deploying a
prototype device to a telescope for first light.Comment: 7 pages, 4 figures, submitted to Journal of Low Temperature Physic
An Assessment of Climate Induced Increase in Soil Water Availability for Soil Bacterial Communities Exposed to Long-Term Differential Phosphorus Fertilization
The fate of future food productivity depends primarily upon the health of soil used for cultivation. For Atlantic Europe, increased precipitation is predicted during both winter and summer months. Interactions between climate change and the fertilization of land used for agriculture are therefore vital to understand. This is particularly relevant for inorganic phosphorus (P) fertilization, which already suffers from resource and sustainability issues. The soil microbiota are a key indicator of soil health and their functioning is critical to plant productivity, playing an important role in nutrient acquisition, particularly when plant available nutrients are limited. A multifactorial, mesocosm study was established to assess the effects of increased soil water availability and inorganic P fertilization, on spring wheat biomass, soil enzymatic activity (dehydrogenase and acid phosphomonoesterase) and soil bacterial community assemblages. Our results highlight the significance of the spring wheat rhizosphere in shaping soil bacterial community assemblages and specific taxa under a moderate soil water content (60%), which was diminished under a higher level of soil water availability (80%). In addition, an interaction between soil water availability and plant presence overrode a long-term bacterial sensitivity to inorganic P fertilization. Together this may have implications for developing sustainable P mobilization through the use of the soil microbiota in future. Spring wheat biomass grown under the higher soil water regime (80%) was reduced compared to the constant water regime (60%) and a reduction in yield could be exacerbated in the future when grown in cultivated soil that have been fertilized with inorganic P. The potential feedback mechanisms for this need now need exploration to understand how future management of crop productivity may be impacted.</p
A Titanium Nitride Absorber for Controlling Optical Crosstalk in Horn-Coupled Aluminum LEKID Arrays for Millimeter Wavelengths
We discuss the design and measured performance of a titanium nitride (TiN)
mesh absorber we are developing for controlling optical crosstalk in
horn-coupled lumped-element kinetic inductance detector arrays for
millimeter-wavelengths. This absorber was added to the fused silica
anti-reflection coating attached to previously-characterized, 20-element
prototype arrays of LEKIDs fabricated from thin-film aluminum on silicon
substrates. To test the TiN crosstalk absorber, we compared the measured
response and noise properties of LEKID arrays with and without the TiN mesh.
For this test, the LEKIDs were illuminated with an adjustable, incoherent
electronic millimeter-wave source. Our measurements show that the optical
crosstalk in the LEKID array with the TiN absorber is reduced by 66\% on
average, so the approach is effective and a viable candidate for future
kilo-pixel arrays.Comment: 7 pages, 5 figures, accepted for publication in the Journal of Low
Temperature Physic
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