138 research outputs found
Growth mechanisms of perturbations in boundary layers over a compliant wall
The temporal modal and nonmodal growth of three-dimensional perturbations in
the boundary-layer flow over an infinite compliant flat wall is considered.
Using a wall-normal velocity/wall-normal vorticity formalism, the dynamic
boundary condition at the compliant wall admits a linear dependence on the
eigenvalue parameter, as compared to a quadratic one in the canonical
formulation of the problem. This greatly simplifies the accurate calculation of
the continuous spectrum by means of a spectral method, thereby yielding a very
effective filtering of the pseudospectra as well as a clear identification of
instability regions. The regime of global instability is found to be matching
the regime of the favorable phase of the forcing by the flow on the compliant
wall so as to enhance the amplitude of the wall. An energy-budget analysis for
the least-decaying hydroelastic (static-divergence, traveling-wave-flutter and
near-stationary transitional) and Tollmien--Schlichting modes in the parameter
space reveals the primary routes of energy flow. Moreover, the flow exhibits a
slower transient growth for the maximum growth rate of a superposition of
streamwise-independent modes due to a complex dependence of the wall-boundary
condition with the Reynolds number. The initial and optimal perturbations are
compared with the boundary-layer flow over a solid wall; differences and
similarities are discussed. Unlike the solid-wall case, viscosity plays a
pivotal role in the transient growth. A slowdown of the maximum growth rate
with the Reynolds number is uncovered and found to originate in the transition
of the fluid-solid interaction from a two-way to a one-way coupling. Finally, a
term-by-term energy budget analysis is performed to identify the key
contributors to the transient growth mechanism
Non-thermal emission from star-forming galaxies detected in gamma rays
Star-forming galaxies (SFGs) emit non-thermal radiation from radio to
gamma-rays. We aim to investigate the main mechanisms of global CR transport
and cooling in SFGs. The way they contribute in shaping the relations between
non-thermal luminosities and SFR could shed light onto their nature. We develop
a model to compute the CR populations of SFGs, taking into account their
production, transport, and cooling. The model is parameterised only through
global galaxy properties, and describes the non-thermal emission in both radio
and gamma-rays. We focus on the role of diffusive and advective transport by
galactic winds, either driven by turbulent or thermal instabilities. We compare
model predictions to observations, for which we compile a homogeneous set of
luminosities in these radio bands, and update those available in gamma-rays.
Our model reproduces reasonably well the observed relations between the
gamma-ray or 1.4 GHz radio luminosities and the SFR, assuming a single
power-law scaling of the magnetic field with the latter with index beta=0.3,
and winds blowing either at Alfvenic speeds or typical starburst wind
velocities. Escape of CR is negligible for > 30 Mo/yr. A constant ionisation
fraction of the interstellar medium fails to reproduce the 150 MHz radio
luminosity throughout the whole SFR range. Our results reinforce the idea that
galaxies with high SFR are CR calorimeters, and that the main mechanism driving
proton escape is diffusion, whereas electron escape also proceeds via wind
advection. They also suggest that these winds should be CR or thermally-driven
at low and intermediate SFR, respectively. Our results globally support that
magnetohydrodynamic turbulence is responsible for the dependence of the
magnetic field strength on the SFR and that the ionisation fraction is strongly
disfavoured to be constant throughout the whole SFR range.Comment: Submitted to Astronomy & Astrophysics (on 12/05/2021
Automated Code Generation For Safety-Related Applications: A Case Study
This paper addresses issues relating to the suitability of using automated code generation(ACG) technologies for the development of real-time, safety-critical systems. This researchexplored the characteristics of model-based software development methodologies and the automatedcode generation tools that support them. Specifically, data related to the engineeringchallenges, skills, and effort associated with ACG practices and technologies were collectedas part of a case study. Characteristics such as the generated code’s organization, size, readability,traceability to model, real-time constructs, and exception handling were identified. Inaddition, the case study involved software engineering practices that incorporate integratedanalysis and design iterations throughout a model-based development process. The researchinvestigated both the static and dynamic characteristics of the selected techniques and tools,identified characteristics of ACG tools with potential impact on safety, and considered thesemantic consistency between representations
The Decomposition of YBa₂Cu₃O₇₋δ Doped into Ba₂YRuO₆
One of the persistent criticisms of claims for observation of superconductivity in Ba2YRu1−uCuuO6 (O6) is that the diamagnetism is actually due to the decomposition of the material into YBa2Cu3O7−delta and other phases. We report a series of experiments in which YBa2Cu3O7−delta is doped into Ba2YRuO6 and carried through a series of sintering steps which were followed by magnetization, neutron diffraction, and scanning electron microscopy/microprobe measurements. It was found that the dopant YBa2Cu3O7−delta decomposed and failed to reform with cooling. It is concluded that the O6 phase is the stable high-temperature phase. The Cu released from the Y123 decomposition doped the host Ba2YRuO6, in partial substitution for Ru. This doping resulted in a small diamagnetic response with an onset temperature of ~84 K
Capabilities of infrared weld monitor
A non-obtrusive pre-aligned, solid-state device has been developed to monitor the primary infrared emissions during laser welding. The weld monitor output is a 100-1000 mV signal that depends on the beam power and weld characteristics. The DC level of this signal is related to weld penetration, while AC portions of the output can be correlated with surface irregularities and part misalignment or contamination. Changes in DC behavior are also noted for both full and deep penetration welds. Full penetration welds are signified by an abrupt reduction in the weld monitor output. Bead on plate welds were made on steel, aluminum, and magnesium with both a CW CO{sub 2} laser and a pulsed Nd:YAG laser to explore the relationships between the weld characteristics and the weld monitor output
Stimulatory antibody-induced activation and selective translocation of protein kinase C isoenzymes in human platelets
Green and animal manure use in organic field crop systems
Dual-use cover/green manure (CGM) crops and animal manure are used to supply nitrogen (N) and phosphorus (P) to organically grown field crops. A comprehensive review of previous research was conducted to identify how CGM crops and animal manure have been used to meet N and P needs of organic field crops, and to identify knowledge gaps to direct future research efforts. Results indicate that: (a) CGM crops are used to provide N to subsequent cash crops in rotations; (b) CGM-supplied N generally can meet field crop needs in warm, humid regions but is insufficient for organic grain crops grown in cool and sub-humid regions; (c) adoption of conservation tillage practices can create or exacerbate N deficiencies; (d) excess N and P can result where animal manures are accessible if application rates are not carefully managed; and (e) integrating animal grazing into organic field crop systems has potential benefits but is generally not practiced. Work is needed to better understand the mechanisms governing the release of N by CGM crops to subsequent cash crops, and the legacy effects of animal manure applications in cool and sub-humid regions. The benefits and synergies that can occur by combining targeted animal grazing and CGMs on soil N, P, and other nutrients should be investigated. Improved communication and networking among researchers can aid efforts to solve soil fertility challenges faced by organic farmers when growing field crops in North America and elsewhere
Rh-POP Pincer Xantphos Complexes for C-S and C-H Activation. Implications for Carbothiolation Catalysis
The neutral RhÂ(I)–Xantphos
complex [RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)ÂCl]<sub><i>n</i></sub>, <b>4</b>, and cationic RhÂ(III) [RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)Â(H)<sub>2</sub>]Â[BAr<sup>F</sup><sub>4</sub>], <b>2a</b>, and [RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos-3,5-C<sub>6</sub>H<sub>3</sub>(CF<sub>3</sub>)<sub>2</sub>)Â(H)<sub>2</sub>]Â[BAr<sup>F</sup><sub>4</sub>], <b>2b</b>, are described [Ar<sup>F</sup> = 3,5-(CF<sub>3</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>; Xantphos
= 4,5-bisÂ(diphenylphosphino)-9,9-dimethylxanthene; Xantphos-3,5-C<sub>6</sub>H<sub>3</sub>(CF<sub>3</sub>)<sub>2</sub> = 9,9-dimethylxanthene-4,5-bisÂ(bisÂ(3,5-bisÂ(trifluoromethyl)Âphenyl)Âphosphine].
A solid-state structure of <b>2b</b> isolated from C<sub>6</sub>H<sub>5</sub>Cl solution shows a κ<sup>1</sup>-chlorobenzene
adduct, [RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos-3,5-C<sub>6</sub>H<sub>3</sub>(CF<sub>3</sub>)<sub>2</sub>)Â(H)<sub>2</sub>(κ<sup>1</sup>-ClC<sub>6</sub>H<sub>5</sub>)]Â[BAr<sup>F</sup><sub>4</sub>], <b>3</b>. Addition of H<sub>2</sub> to <b>4</b> affords,
crystallographically characterized, [RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)Â(H)<sub>2</sub>Cl], <b>5</b>. Addition of diphenyl
acetylene to <b>2a</b> results in the formation of the C–H
activated metallacyclopentadiene [RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)Â(ClCH<sub>2</sub>Cl)Â(σ,σ-(C<sub>6</sub>H<sub>4</sub>)ÂCÂ(H)î—»CPh)]Â[BAr<sup>F</sup><sub>4</sub>], <b>7</b>, a rare example of a crystallographically characterized Rh–dichloromethane
complex, alongside the RhÂ(I) complex <i>mer</i>-[RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)Â(η<sup>2</sup>-PhCCPh)]Â[BAr<sup>F</sup><sub>4</sub>], <b>6</b>. Halide abstraction from [RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)ÂCl]<sub><i>n</i></sub> in the presence of diphenylacetylene affords <b>6</b> as the
only product, which in the solid state shows that the alkyne binds
perpendicular to the κ<sup>3</sup>-POP Xantphos ligand plane.
This complex acts as a latent source of the [RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)]<sup>+</sup> fragment and facilitates
<i>ortho</i>-directed C–S activation in a number
of 2-arylsulfides to give <i>mer</i>-[RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)Â(σ,κ<sup>1</sup>-Ar)Â(SMe)]Â[BAr<sup>F</sup><sub>4</sub>] (Ar = C<sub>6</sub>H<sub>4</sub>COMe, <b>8</b>; C<sub>6</sub>H<sub>4</sub>(CO)ÂOMe, <b>9</b>; C<sub>6</sub>H<sub>4</sub>NO<sub>2</sub>, <b>10</b>; C<sub>6</sub>H<sub>4</sub>CNCH<sub>2</sub>CH<sub>2</sub>O, <b>11</b>; C<sub>6</sub>H<sub>4</sub>C<sub>5</sub>H<sub>4</sub>N, <b>12</b>).
Similar C–S bond cleavage is observed with allyl sulfide,
to give <i>fac</i>-[RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)Â(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)Â(SPh)]Â[BAr<sup>F</sup><sub>4</sub>], <b>13</b>. These products of C–S
activation have been crystallographically characterized. For <b>8</b> in situ monitoring of the reaction by NMR spectroscopy reveals
the initial formation of <i>fac</i>-κ<sup>3</sup>-<b>8</b>, which then proceeds to isomerize to the <i>mer</i>-isomer. With the <i>para</i>-ketone aryl sulfide, 4-SMeC <sub>6</sub>H<sub>4</sub>COMe, C–H activation <i>ortho</i> to the ketone occurs to give <i>mer</i>-[RhÂ(κ<sup>3</sup>-<sub>P,O,P</sub>-Xantphos)Â(σ,κ<sup>1</sup>-4-(COMe)ÂC<sub>6</sub>H<sub>3</sub>SMe)Â(H)]Â[BAr<sup>F</sup><sub>4</sub>], <b>14</b>. The temporal evolution of carbothiolation catalysis using <i>mer</i>-κ<sup>3</sup>-<b>8</b>, and phenyl acetylene
and 2-(methylthio)Âacetophenone substrates shows initial fast catalysis
and then a considerably slower evolution of the product. We suggest
that the initially formed <i>fac</i>-isomer of the C–S
activation product is considerably more active than the <i>mer</i>-isomer (i.e., <i>mer</i>-<b>8</b>), the latter of
which is formed rapidly by isomerization, and this accounts for the
observed difference in rates. A likely mechanism is proposed based
upon these data
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