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61.
Simon S Pierrard X Sjöblom J Sørland GH 《Journal of colloid and interface science》2011,356(1):352-361
The application range and validity of two new NMR sequences (hereafter called sequence 1 and sequence 2) for the study of water-in-oil emulsions (w/o) has been assessed using model emulsions and comparison with results obtained by a commercial apparatus (Turbiscan). These new NMR sequences allow to determine the brine profile i.e. the vertical variations of the dispersed phase content (brine) in the NMR tube. Measuring these parameters as a function of time allows to monitor the separation (sedimentation and coalescence rate) between oil and water. The results obtained on model water-in-oil emulsions with both NMR sequences are consistent and meaningful for both stable and coalescing emulsions and are similar, even if not strictly identical, to the ones obtained with the Turbiscan. It also appears that the second NMR sequence is faster (30s to obtain a profile compared with 3 min for the 1st one in the conditions used in this article) and has a broader application range. Indeed, for these two methods, the oil phase must have a viscosity higher or equal than values which is around 5 mPas for the sequence 2 and 20-25 mPas for the method 1. 相似文献
62.
Geir Agnarsson 《代数通讯》2013,41(9):4071-4087
Let R be an algebra over a field k. We say that an ideal I of R is co-generated by a set F of k-linear functionals R → k if I is the largest ideal of R that is contained in the kernels of all the functionals in F;. We will state sufficient conditions for an ideal of a free k-algebra to be co-generated by finitely many functionals. We then get as a corollary that every ideal of the polynomial algebra over a field in finitely many variables is finitely co-generated. This is a known result, but the way we construct the co-generators in the general case, leads to that we get a tight bound on how many co-generators are needed for such ideals. 相似文献
63.
Let Qk denote the k-dimensional hypercube on 2k vertices. A vertex in a subgraph of Qk is full if its degree is k. We apply the Kruskal–Katona Theorem to compute the maximum number of full vertices an induced subgraph on n≤2k vertices of Qk can have, as a function of k and n. This is then used to determine min(max(|V(H1)|,|V(H2)|)) where (i) H1 and H2 are induced subgraphs of Qk, and (ii) together they cover all the edges of Qk, that is E(H1)∪E(H2)=E(Qk). 相似文献
64.
Petrov OV Ersland G Balcom BJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,209(1):39-46
Two 1-D phase-encode sequences for T? mapping, namely CPMG-prepared SPRITE and spin-echo SPI, are presented and compared in terms of image quality, accuracy of T? measurements and the measurement time. The sequences implement two different approaches to acquiring T?-weighted images: in the CPMG-prepared SPRITE, the T?-weighting of magnetization precedes the spatial encoding, while in the spin-echo SPI, the T?-weighting follows the spatial encoding. The sequences are intended primarily for T? mapping of fluids in porous solids, where using frequency encode techniques may be problematic either due to local gradient distortions or too short T?. Their possible applications include monitoring fluid-flow processes in rocks, cement paste hydration, curing of rubber, filtering paramagnetic impurities and other processes accomplished by changing site-specific T?. 相似文献
65.
Geir Dahl 《Discrete Applied Mathematics》2009,157(8):1702-1710
We consider a combinatorial problem motivated by a special simplified timetabling problem for subway networks. Mathematically the problem is to find (pairwise) disjoint congruence classes modulo certain given integers; each such class corresponds to the arrival times of a subway line of a given frequency. For a large class of instances we characterize when such disjoint congruence classes exist and how they may be determined. We also study a generalization involving a minimum distance requirement between congruence classes, and a comparison of different frequency families in terms of their “efficiency”. Finally, a general method based on integer programming is also discussed. 相似文献
66.
The paper considers finite subsets Zd which possess the extensionproperty, namely that every collection {ck}k of complexnumbers which is positive definite with respect to is the restrictionof the Fourier coefficients of some positive measure on Td.All finite subsets of Z2 which possess the extension propertyare described. 相似文献
67.
68.
The collection of 10 DOP droplets from an aerosol flow around an array of five circular cylinders in a turbulent air stream was measured. Axial and angled alignments of the target array, normal to the flow, were examined. Cylinder Reynolds numbers ranged from 1,300 to 5,100, and effective Stokes numbers from 0.50 to 1.58. A continuous line source turbulent diffusion model was used with the centerline velocity and concentration distributions to derive the eddy diffusion coefficients for momentum and particle concentration in the near wake of the cyinders. Angled collection results showed an optimal target alignment at the edge of the momentum wake of the lead cylinder. Further examination with an LDA system suggests the peak in collection is due to a particle velocity surplus in the wake.List of symbols
A
k
projected area of cylinder k
-
A
t
cross sectional area of flow
-
b
wake width
-
C
particle concentration
-
C
1
concentration deficit
-
C
D.n
drag coefficient of nth cylinder
-
d
diameter
-
vortex shedding frequency
-
L
c
length of cylinder
-
n
cylinder rank
-
Q
strength of line source
-
R
L
Lagrangian time autocorrelation coefficient
-
Re
Reynolds number (U d/)
-
T
L
Lagrangian integral time scale
-
U
x-directed velocity
-
U
1
velocity deficit
-
u
fluctuating axial velocity component
-
v
fluctuating lateral velocity component
-
V
drop volume
-
x
intercylinder spacing
-
y
lateral displacement
-
mixing length proportionality constant
-
A
measured droplet diameter
-
eddy diffusivity
-
*
corrected collection efficiency
-
contact angle of droplet on surface
-
viscosity of air
-
density
-
time
-
non-Stokesian drag correction factor
-
c
cylinder
-
g
gas
-
M
momentum
-
p
particles
-
theoretical (Stokes efficiency)
- aneth
freestream value
- 1, n
cylinder rank 1 or n 相似文献
69.
Ona E Godø OR Handegard NO Hjellvik V Patel R Pedersen G 《The Journal of the Acoustical Society of America》2007,121(4):EL145-EL150
Behavior of herring (Clupea harengus) is stimulated by two ocean-going research vessels; respectively designed with and without regard to radiated-noise-standards. Both vessels generate a reaction pattern, but, contrary to expectations, the reaction initiated by the silent vessel is stronger and more prolonged than the one initiated by the conventional vessel. The recommendations from the scientific community on noise-reduced designs were motivated by the expectation of minimizing bias on survey results caused by vessel-induced fish behavior. In conclusion, the candidate stimuli for vessel avoidance remain obscure. Noise reduction might be necessary but is insufficient to obtain stealth vessel assets during surveys. 相似文献
70.
Andrei M Bjørnstad V Langli G Rømming C Klaveness J Taskén K Undheim K 《Organic & biomolecular chemistry》2007,5(13):2070-2080
Cyclic adenosine monophosphate (cAMP) has been converted into its 8-bromo derivative and 2'O-TBDMS protected before activation of the phosphoric acid moiety with a reagent generated in situ from oxalyl chloride and DMF. Further reactions with primary amines furnished corresponding phosphoramidates with high stereoselectivity at the phosphorus atom. Cross-coupling reactions with the 8-bromopurine yielded 8-hetaryl derivatives. X-Ray analyses showed the amidates to possess the (S(P))-configuration. Carbon disulfide effected thiylation under strongly basic conditions stereospecifically provided the (R(P))-phosphorothioic acids. 相似文献