7,363 research outputs found
Theoretical study on the protonation of AZA-aromatics
The protonation of azanaphthalenes and azabenzenes has been studied theoretically using CNDO/2 wavefunctions and perturbation theory in order to examine the correlation between pKa values and quantum-mechanical quantities
Diazanaphthalenes: A 13C NMR investigation on the site of protonation and pKa values
The pH dependence of the 13C chemical shifts (δ) of the diazanaphthalenes has been recorded. From this dependence the pKa values have been determined using the Henderson-Hasselbach equation. The change in 13C chemical shifts under the influence of nitrogen protonation (Δδ) has been predicted using the Δδ values of quinoline and isoquinoline. The correlation between observed and expected Δδ values of the symmetric diazanaphthalenes is very good. Assuming these changes in chemical shifts to be of general validity, the site of protonation in the asymmetric diazanaphthalenes has been determined by comparison of the expected Δδ values for α- and ß-nitrogen protonation with the observed ones. The site of protonation for 1,6- and 1,7-naphthyridine is the ß-nitrogen atom, whereas for cinnoline both monoprotonated species are present in a significant amount
Liquid-grain mixing suppresses droplet spreading and splashing during impact
Would a raindrop impacting on a coarse beach behave differently from that
impacting on a desert of fine sand? We study this question by a series of model
experiments, where the packing density of the granular target, the wettability
of individual grains, the grain size, the impacting liquid, and the impact
speed are varied. We find that by increasing the grain size and/or the
wettability of individual grains the maximum droplet spreading undergoes a
transition from a capillary regime towards a viscous regime, and splashing is
suppressed. The liquid-grain mixing is discovered to be the underlying
mechanism. An effective viscosity is defined accordingly to quantitatively
explain the observations
Crater formation during raindrop impact on sand
After a raindrop impacts on a granular bed, a crater is formed as both drop
and target deform. After an initial, transient, phase in which the maximum
crater depth is reached, the crater broadens outwards until a final steady
shape is attained. By varying the impact velocity of the drop and the packing
density of the bed, we find that avalanches of grains are important in the
second phase and hence, affect the final crater shape. In a previous paper, we
introduced an estimate of the impact energy going solely into sand deformation
and here we show that both the transient and final crater diameter collapse
with this quantity for various packing densities. The aspect ratio of the
transient crater is however altered by changes in the packing fraction.Comment: 9 pages, 9 figure
Exploring droplet impact near a millimetre-sized hole: comparing a closed pit with an open-ended pore
We investigate drop impact dynamics near both closed pits and open- ended
pores experimentally. The resulting impact phenomena differ greatly for a pit
or a pore. For the first, we observe three phenomena: a splash, a jet and an
air bubble, whose appearance depends on the distance between impact location
and pit. Furthermore, we found that splash velocities can reach up to seven
times the impact velocity. Drop impact near a pore, however, results solely in
splashing. Surprisingly, two distinct and disconnected splashing regimes occur,
with a region of plain spreading in-between. For pores, splashes are less
pronounced than in the pit case. We state that, for the pit case, the presence
of air inside the pit plays a crucial role: it promotes splashing and allows
for air bubbles to appear.Comment: 17 pages, 11 figures, 1 supplementary movie, submitted to JF
Dramatic effect of fluid chemistry on cornstarch suspensions: linking particle interactions to macroscopic rheology
Suspensions of cornstarch in water exhibit strong dynamic shear-thickening.
We show that partly replacing water by ethanol strongly alters the suspension
rheology. We perform steady and non-steady rheology measurements combined with
atomic force microscopy to investigate the role of fluid chemistry on the
macroscopic rheology of the suspensions and its link with the interactions
between cornstarch grains. Upon increasing the ethanol content, the suspension
goes through a yield-stress fluid state and ultimately becomes a shear-thinning
fluid. On the cornstarch grain scale, atomic force microscopy measurements
reveal the presence of polymers on the cornstarch surface, which exhibit a
co-solvency effect. At intermediate ethanol content, a maximum of polymer
solubility induces high microscopic adhesion which we relate to the macroscopic
yield stress
Inquiry into the diagnostic workup of patients with fever of unknown origin
Contains fulltext :
inqiinthd.pdf (publisher's version ) (Open Access
Einselection and Decoherence from an Information Theory Perspective
We introduce and investigate a simple model of conditional quantum dynamics.
It allows for a discussion of the information-theoretic aspects of quantum
measurements, decoherence, and environment-induced superselection
(einselection).Comment: Proceedings of the Planck constant centenary meeting. Uses
annalen.cls and fleqn.st
In vitro proliferation of mononuclear phagocytes from murine and human bone marrow
Contains fulltext :
4339.pdf (publisher's version ) (Open Access
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