5,915 research outputs found
Investigations of lubricant rheology as applied to elastohydrodynamic lubrication
The pressure viscometer was modified to permit the measurement of viscosity at elevated pressures and shear stresses up to 5 x 10 to the 6th power N/sq m (720 psi). This shear stress is within a factor of three of the shear stress occurring in a sliding ehd point contact such as occurs in the ehd simulator. Viscosity data were taken on five lubricant samples, and it was found that viscous heating effects on the viscosity were predominant and not non-Newtonian behavior at the high shear stresses. The development of the infrared temperature measuring technique for the ehd simulator was completed, and temperature data for a set of operating conditions and one lubricant are reported. The numerical analysis of the behavior of nonlinear lubricants in the lubrication of rollers is reported
Plant growth responses to elevated atmospheric CO2 are increased by phosphorus sufficiency but not by arbuscular mycorrhizas
Capturing the full growth potential in crops under future elevated CO₂ (eCO₂) concentrations would be facilitated by improved understanding of eCO₂ effects on uptake and use of mineral nutrients. This study investigates interactions of eCO₂, soil phosphorus (P), and arbuscular mycorrhizal (AM) symbiosis in Medicago truncatula and Brachypodium distachyon grown under the same conditions. The focus was on eCO₂ effects on vegetative growth, efficiency in acquisition and use of P, and expression of phosphate transporter (PT) genes. Growth responses to eCO₂ were positive at P sufficiency, but under low-P conditions they ranged from non-significant in M. truncatula to highly significant in B. distachyon Growth of M. truncatula was increased by AM at low P conditions at both CO₂ levels and eCO₂×AM interactions were sparse. Elevated CO₂ had small effects on P acquisition, but enhanced conversion of tissue P into biomass. Expression of PT genes was influenced by eCO₂, but effects were inconsistent across genes and species. The ability of eCO₂ to partly mitigate P limitation-induced growth reductions in B. distachyon was associated with enhanced P use efficiency, and requirements for P fertilizers may not increase in such species in future CO₂-rich climates.Iver Jakobsen, Sally E. Smith, F. Andrew Smith, Stephanie J. Watts-Williams, Signe S. Clausen and Mette Grønlun
Linear-Time Zero-Knowledge Proofs for Arithmetic Circuit Satisfiability
We give computationally efficient zero-knowledge proofs of knowledge for arithmetic circuit satisfiability over a large field. For a circuit with N addition and multiplication gates, the prover only uses O(N)O(N) multiplications and the verifier only uses O(N)O(N) additions in the field. If the commitments we use are statistically binding, our zero-knowledge proofs have unconditional soundness, while if the commitments are statistically hiding we get computational soundness. Our zero-knowledge proofs also have sub-linear communication if the commitment scheme is compact.
Our construction proceeds in three steps. First, we give a zero-knowledge proof for arithmetic circuit satisfiability in an ideal linear commitment model where the prover may commit to secret vectors of field elements, and the verifier can receive certified linear combinations of those vectors. Second, we show that the ideal linear commitment proof can be instantiated using error-correcting codes and non-interactive commitments. Finally, by choosing efficient instantiations of the primitives we obtain linear-time zero-knowledge proofs
Cosmological constant and the fate of the DDM theory
We investigate the impact of the non-zero cosmological constant on the
classical decaying dark matter theory developed by the late Dennis Sciama. In
particular, we concentrate on the change in relevant values of cosmological
parameters in comparison to the high-precision estimates given by Sciama
(1997). It is shown that the appropriate changes in resulting parameter values
are such to make the DDM concept less plausible. This is in complete agreement
with recently reported observational results detrimental to this theory.Comment: 4 pages, 2 eps figures, uses AA latex styl
Technical Note: Mesocosm approach to quantify dissolved inorganic carbon percolation fluxes
Dissolved inorganic carbon (DIC) fluxes across the vadose zone are
influenced by a complex interplay of biological, chemical and physical
factors. A novel soil mesocosm system was evaluated as a tool for providing
information on the mechanisms behind DIC percolation to the groundwater from
unplanted soil. Carbon dioxide partial pressure (<i>p</i>CO<sub>2</sub>), alkalinity, soil
moisture and temperature were measured with depth and time, and DIC in the
percolate was quantified using a sodium hydroxide trap. Results showed good
reproducibility between two replicate mesocosms. The <i>p</i>CO<sub>2</sub> varied between
0.2 and 1.1%, and the alkalinity was 0.1–0.6 meq L<sup>−1</sup>. The measured cumulative
effluent DIC flux over the 78-day experimental period was 185–196 mg L<sup>−1</sup> m<sup>−2</sup> and in the same range as estimates derived from
<i>p</i>CO<sub>2</sub> and alkalinity in samples extracted from the side of the mesocosm
column and the drainage flux. Our results indicate that the mesocosm system
is a promising tool for studying DIC percolation fluxes and other
biogeochemical transport processes in unsaturated environments
Metal enrichment and evolution in four z > 6.5 quasar sightlines observed with JWST/NIRSpec
We present JWST/NIRSpec R2700 spectra of four high-redshift quasars:
VDES J0020-3653 (z = 6.860), DELS J0411-0907(z = 6.825), UHS J0439+1634 (z =
6.519) and ULAS J1342+0928 (z = 7.535). The exquisite data quality,
signal-to-noise ratio of 50-200, and large spectral coverage allows us to identify between 13 and 17
intervening and proximate metal absorption line systems in each quasar
spectrum, with a total number of 61 absorption-line systems detected at
including the highest redshift intervening OI 1302 and
MgII systems at and . We investigate the evolution of the
metal enrichment in the epoch of reionization at and find: i) A continued
increase of the low-ionization OI, CII, and SiII incidence, ii) Decreasing
high-ionization CIV and SiIV incidence with a transition from predominantly
high- to low-ionization at , and iii) a constant MgII incidence
across all redshifts. The observations support a change in the ionization state
of the intergalactic medium in the EoR rather than a change in metallicity. The
abundance ratio of [Si/O] in five absorption systems show enrichment
signatures produced by low-mass Pop III pair instability supernovae, and
possibly Pop III hypernovae. In the Gunn-Peterson troughs we detect
transmission spikes where Ly photons can escape. From 22 absorption
systems at , only a single low-ionization system out of 13 lies within
2000 km s from a spike, while four high-ionization systems out of nine
lie within 2000 km s from a spike. This confirms that galaxies
responsible for the heavy elements that are transported into the circumgalactic
medium lie in predominantly in high-density, neutral environments, while lower
density environments are ionized without being polluted by metals at
6-7. [abridged]Comment: 50 pages including 30 pages of appendices. Submitted to A&
- …