175,784 research outputs found
Three-dimensionality in quasi-two dimensional flows: recirculations and barrel effects
A scenario is put forward for the appearance of three-dimensionality both in
quasi-2D rotating flows and quasi-2D magnetohydrodynamic (MHD) flows. We show
that 3D recirculating flows and currents originate in wall boundary layers and
that, unlike in ordinary hydrodynamic flows, they cannot be ignited by
confinement alone. They also induce a second form of three-dimensionality with
quadratic variations of velocities and current across the channel. This
scenario explains both the common tendency of these flows to two-dimensionality
and the mechanisms of the recirculations through a single formal analogy
covering a wide class of flow including rotating and MHD flows. These
trans-disciplinary effects are thus active in atmospheres, oceans or the
cooling blankets of nuclear fusion reactors.Comment: 6 pages, 1 Figur
Kilohertz QPOs in Neutron Star Binaries modeled as Keplerian Oscillations in a Rotating Frame of Reference
Since the discovery of kHz quasi-periodic oscillations (QPO) in neutron star
binaries, the difference between peak frequencies of two modes in the upper
part of the spectrum, i.e. Delta (omega)=omega_h-omega_K has been studied
extensively. The idea that the difference Delta(omega) is constant and (as a
beat frequency) is related to the rotational frequency of the neutron star has
been tested previously. The observed decrease of Delta(omega) when omega_h and
omega_k increase has weakened the beat frequency interpretation. We put forward
a different paradigm: a Keplerian oscillator under the influence of the
Coriolis force. For such an oscillator, omega_h and the assumed Keplerian
frequency omega_k hold an upper hybrid frequency relation:
omega^2_h-omega^2_K=4*Omega^2, where Omega is the rotational frequency of the
star's magnetosphere near the equatorial plane. For three sources (Sco X-1, 4U
1608-52 and 4U 1702-429), we demonstrate that the solid body rotation
Omega=Omega_0=const. is a good first order approximation. Within the second
order approximation, the slow variation of Omega as a function of omega_K
reveals the structure of the magnetospheric differential rotation. For Sco X-1,
the QPO have frequencies approximately 45 and 90 Hz which we interpret as the
1st and 2nd harmonics of the lower branch of the Keplerian oscillations for the
rotator with vector Omega not aligned with the normal of the disk: omega_L/2
pi=(Omega/pi)(omega_K/omega_h)sin(delta) where delta is the angle between
vector Omega and the vector normal to the disk.Comment: 13 pages, 3 figures, accepted for publications in ApJ Letter
A new invariant that's a lower bound of LS-category
Let be a simply connected CW-complex of finite type and any
field. A first known lower bound of LS-category is the Toomer
invariant (\cite{Too}). In 's F\'elix et al.
introduced the concept of {\it depth} in algebraic topology and proved the
depth theorem: .
In this paper, we use the Eilenberg-Moore spectral sequence of to
introduce a new numerical invariant, denoted by \textsc{r}(X, \mathbb{K}),
and show that it has the same properties as those of .
When the evaluation map (\cite{FHT88}) is non-trivial and
, we prove that \textsc{r}(X, \mathbb{K})
interpolates and .
Hence, we obtain an improvement of L. Bisiaux theorem (\cite{Bis99}) and then
of the depth theorem.
Motivated by these results, we associate to any commutative differential
graded algebra , a purely algebraic invariant \textsc{r}(A,d) and, via
the theory of minimal models, we relate it with our previous topological
results.
In particular, if is a Sullivan minimal algebra such that
and , a greater lower bound
is obtained, namely e_0(\Lambda V, d)\geq \textsc{r}(\Lambda V, d) + (k-2).Comment: 21 page
Inhibition of the Enzymatic Activity of Heme Oxygenases by Azole-Based Antifungal Drugs
ABSTRACT Ketoconazole (KTZ) and other azole antifungal agents are known to have a variety of actions beyond the inhibition of sterol synthesis in fungi. These drugs share structural features with a series of novel heme oxygenase (HO) inhibitors designed in our laboratory. Accordingly, we hypothesized that therapeutically used azole-based antifungal drugs are effective HO inhibitors. Using gas chromatography to quantify carbon monoxide formation in vitro and in vivo, we have shown that azole-containing antifungal drugs are potent HO inhibitors. Terconazole, sulconazole, and KTZ were the most potent drugs with IC 50 values of 0.41 Ϯ 0.01, 1.1 Ϯ 0.4, and 0.3 Ϯ 0.1 M for rat spleen microsomal HO activity, respectively. Kinetic characterization revealed that KTZ was a noncompetitive HO inhibitor. In the presence of KTZ (2.5 and 10 M), K m values for both rat spleen and brain microsomal HO were not altered; however, a significant decrease in the catalytic capacity (V max ) was observed (P Ͻ 0.005). KTZ was also found to weakly inhibit nitric-oxide synthase with an IC 50 of 177 Ϯ 2 M but had no effect on the enzymatic activity of NADPH cytochrome P450 reductase. Because these drugs were effective within the concentration range observed in humans, it is possible that inhibition of HO may play a role in some of the pharmacological actions of these antimycotic drugs
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