2,385 research outputs found
Composite infrared bolometers with Si_3N_4 micromesh absorbers
We report the design and performance of 300-mK composite bolometers that use micromesh absorbers and support structures patterned from thin films of low-stress silicon nitride. The small geometrical filling factor of the micromesh absorber provides 20× reduction in heat capacity and cosmic ray cross section relative to a solid absorber with no loss in IR-absorption efficiency. The support structure is mechanically robust and has a thermal conductance, G < 2 × 10^(−11) W/K, which is four times smaller than previously achieved at 300 mK. The temperature rise of the bolometer is measured with a neutron transmutation doped germanium thermistor attached to the absorbing mesh. The dispersion in electrical and thermal parameters of a sample of 12 bolometers optimized for the Sunyaev–Zel’dovich Infrared Experiment is ±7% in R (T), ±5% in optical efficiency, and ±4% in G
The plasticity of berry shrivelling in 'Shiraz': A vineyard survey
Berry water loss during late ripening is a cultivar dependent-trait and is accentuated in wine grape varieties such as 'Shiraz'. 'Shiraz' berry development was monitored in twelve vineyards over two seasons to characterise the extent of weight loss that can occur within a grape growing region. From veraison onwards, berry fresh mass was greatest in vineyards using excessive irrigation and least in vineyards using cautious irrigation strategies. In the first season, berry fresh mass increased, reached a maximum and subsequently declined. Conversely, in the second season, characterised by rain and high humidity, berry fresh mass increased, then stabilised without a consistent decline. In both seasons, berry sugar import rates were highest shortly after veraison but then declined gradually, terminating several weeks after the weight maximum. Notwithstanding that berries with large maximum weights tended to undergo greater rates of weight loss, these berries remained heavier at harvest compared to those berries that were smaller prior to the onset of weight loss. Canopy size, yield and crop load were not key determinants of berry weight loss rates. Berry anthocyanin and sugar accumulation were closely correlated during early ripening but anthocyanin degradation took place during the late weight loss phase
Vineyard and winery indicators of 'Shiraz' must fermentation behaviour
Nitrogen supply and rootstock have important consequences for the composition and quantity of nitrogenous compounds in the must, both of which impact on fermentation rate and wine quality. In the Sunraysia district (SE Australia), musts prepared from 'Shiraz' grapes from vines grafted onto three rootstocks and supplied with five different nitrogen (N) regimes were fermented to dryness. Leaf N at flowering and veraison, and berry and juice total N at harvest was influenced by N supply, but the juice total assimilable amino N pool was less sensitive. Consumption rate of soluble solids during fermentation was strongly and positively linearly related to %N in the petioles at veraison. The relationship described could be the basis of a tool to provide oenologists with timely data before harvest and receival on likely fermentation behaviour of specific parcels of grapes, and provide viticulturalists with another recognisable developmental stage to assess the efficacy of vineyard N management strategies within a season.
Doping and critical-temperature dependence of the energy gaps in Ba(Fe_{1-x}Co_x)_2As_2 thin films
The dependence of the superconducting gaps in epitaxial
Ba(Fe_{1-x}Co_{x})_2As_2 thin films on the nominal doping x (0.04 \leq x \leq
0.15) was studied by means of point-contact Andreev-reflection spectroscopy.
The normalized conductance curves were well fitted by using the 2D
Blonder-Tinkham-Klapwijk model with two nodeless, isotropic gaps -- although
the possible presence of gap anisotropies cannot be completely excluded. The
amplitudes of the two gaps \Delta_{S} and \Delta_{L} show similar monotonic
trends as a function of the local critical temperature T_{c}^{A} (measured in
the same point contacts) from 25 K down to 8 K. The dependence of the gaps on x
is well correlated to the trend of the critical temperature, i.e. to the shape
of the superconducting region in the phase diagram. When analyzed within a
simple three-band Eliashberg model, this trend turns out to be compatible with
a mechanism of superconducting coupling mediated by spin fluctuations, whose
characteristic energy scales with T_{c} according to the empirical law
\Omega_{0}= 4.65*k_{B}*T_{c}, and with a total electron-boson coupling strength
\lambda_{tot}= 2.22 for x \leq 0.10 (i.e. up to optimal doping) that slightly
decreases to \lambda_{tot}= 1.82 in the overdoped samples (x = 0.15).Comment: 8 pages, 5 color figure
Analytical and numerical analyses of the micromechanics of soft fibrous connective tissues
State of the art research and treatment of biological tissues require
accurate and efficient methods for describing their mechanical properties.
Indeed, micromechanics motivated approaches provide a systematic method for
elevating relevant data from the microscopic level to the macroscopic one. In
this work the mechanical responses of hyperelastic tissues with one and two
families of collagen fibers are analyzed by application of a new variational
estimate accounting for their histology and the behaviors of their
constituents. The resulting, close form expressions, are used to determine the
overall response of the wall of a healthy human coronary artery. To demonstrate
the accuracy of the proposed method these predictions are compared with
corresponding 3-D finite element simulations of a periodic unit cell of the
tissue with two families of fibers. Throughout, the analytical predictions for
the highly nonlinear and anisotropic tissue are in agreement with the numerical
simulations
Time-resolved spectroscopy of the primary photosynthetic processes of membrane-bound reaction centers from an antenna-deficient mutant of Rhodobacter capsulatus
The primary photosynthetic reactions in whole membranes of the antenna-deficient mutant strain U43 (pTXA6–10) of Rhodobacter capsulatus are studied by transient absorption and emission spectroscopy with subpicosecond time resolution. Extensive similarities between the transient absorption data on whole membranes and on isolated reaction centers support the idea that the primary processes in isolated reaction centers are not modified by the isolation procedure
BaFe_{1.8}Co_{0.2}As_2 thin film hybrid Josephson junctions
Josephson junctions with iron pnictides open the way for fundamental
experiments on superconductivity in these materials and their application in
superconducting devices. Here, we present hybrid Josephson junctions with a
BaFe_{1.8}Co_{0.2}As_2 thin film electrode, an Au barrier and a PbIn counter
electrode. The junctions show RSJ-like current-voltage characteristics up to
the critical temperature of the counter electrode of about 7.2K. The
temperature dependence of the critical current, IC, does not show an
Ambegaokar-Baratoff behavior. Well-pronounced Shapiro steps are observed at
microwave frequencies of 10-18GHz. Assuming an excess current, I_ex, of 200
{\mu}A at 4.2K we get an effective I_C R_N product of 6 {\mu}V.Comment: submitted to Appl. Phys. Let
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