983 research outputs found
On the formation of cyclones and anticyclones in a rotating fluid
It is commonly observed that the columnar vortices that dominate the large scales in homogeneous, rapidly rotating turbulence are predominantly cyclonic. This has prompted us to ask how this asymmetry arises. To provide a partial answer to this we look at the process of columnar vortex formation in a rotating fluid and, in particular, we examine how a localized region of swirl (an eddy) can convert itself into a columnar structure by inertial wave propagation. We show that, when the Rossby number (Ro) is small, the vortices evolve into columnar eddies through the radiation of linear inertial waves. When the Rossby number is large, on the other hand, no such column is formed. Rather, the eddy bursts radially outward under the action of the centrifugal force. There is no asymmetry between cyclonic and anticyclonic eddies for these two regimes. However, cyclones and anticyclones behave differently in the intermediate regime of Ro~1. Here we find that the transition from columnar vortex formation to radial bursting occurs at lower values of Ro for anticyclones, with the transition for anticyclones occurring at Ro~0.5, and that for cyclones at Ro~2. Thus, in a homogeneous turbulence experiment conducted at, say, Ro=1, we would expect to see more cyclones than anticyclones. The reason for this asymmetry at Ro~1 is explained
Hard x-ray photon-in-photon-out spectroscopy with lifetime resolution – of XAS, XES, RIXSS and HERFD
Spectroscopic techniques that aim to resolve the electronic configuration and local coordination of a central
atom by detecting inner-shell radiative decays following photoexcitation using hard X-rays are presented. The
experimental setup requires an X-ray spectrometer based on perfect crystal Bragg optics. The possibilities arising from
non-resonant (X-Ray Emission Spectroscopy - XES) and resonant excitation (Resonant Inelastic X-Ray Scattering
Spectroscopy – RIXSS, High-Energy-Resolution Fluorescence Detected (HERFD) XAS) are discussed when the
instrumental energy broadenings of the primary (beamline) monochromator and the crystal spectrometer for x-ray
emission detection are on the order of the core hole lifetimes of the intermediate and final electronic states. The small
energy bandwidth in the emission detection yields line-sharpened absorption features. In transition metal compounds,
electron-electron interactions as well as orbital splittings and fractional population can be revealed. Combination with
EXAFS spectroscopy enables to extent the k-range beyond unwanted absorption edges in the sample that limit the
EXAFS range in conventional absorption spectroscopy
The decay of Batchelor and Saffman rotating turbulence
The decay rate of isotropic and homogeneous turbulence is known to be
affected by the large-scale spectrum of the initial perturbations, associated
with at least two cannonical self-preserving solutions of the von
K\'arm\'an-Howarth equation: the so-called Batchelor and Saffman spectra. The
effect of long-range correlations in the decay of anisotropic flows is less
clear, and recently it has been proposed that the decay rate of rotating
turbulence may be independent of the large-scale spectrum of the initial
perturbations. We analyze numerical simulations of freely decaying rotating
turbulence with initial energy spectra (Batchelor turbulence) and
(Saffman turbulence) and show that, while a self-similar decay
cannot be identified for the total energy, the decay is indeed affected by
long-range correlations. The decay of two-dimensional and three-dimensional
modes follows distinct power laws in each case, which are consistent with
predictions derived from the anisotropic von K\'arm\'an-Howarth equation, and
with conservation of anisotropic integral quantities by the flow evolution
The decay of turbulence in rotating flows
We present a parametric space study of the decay of turbulence in rotating
flows combining direct numerical simulations, large eddy simulations, and
phenomenological theory. Several cases are considered: (1) the effect of
varying the characteristic scale of the initial conditions when compared with
the size of the box, to mimic "bounded" and "unbounded" flows; (2) the effect
of helicity (correlation between the velocity and vorticity); (3) the effect of
Rossby and Reynolds numbers; and (4) the effect of anisotropy in the initial
conditions. Initial conditions include the Taylor-Green vortex, the
Arn'old-Beltrami-Childress flow, and random flows with large-scale energy
spectrum proportional to . The decay laws obtained in the simulations for
the energy, helicity, and enstrophy in each case can be explained with
phenomenological arguments that separate the decay of two-dimensional from
three-dimensional modes, and that take into account the role of helicity and
rotation in slowing down the energy decay. The time evolution of the energy
spectrum and development of anisotropies in the simulations are also discussed.
Finally, the effect of rotation and helicity in the skewness and kurtosis of
the flow is considered.Comment: Sections reordered to address comments by referee
Identification of signaling pathways in early mammary gland development by mouse genetics
The mammary gland develops as an appendage of the ectoderm. The prenatal stage of mammary development is hormone independent and is regulated by sequential and reciprocal signaling between the epithelium and the mesenchyme. A number of recent studies using human and mouse genetics, in particular targeted gene deletion and transgenic expression, have identified some of the signals that control specific steps in development. This process involves cell specification and proliferation, reciprocal tissue interactions and cell migration. Since some of these events are recapitulated during tumorigenesis, an understanding of these signaling pathways may contribute to the development of targeted therapies and novel drugs
p16 mutations/deletions are not frequent events in prostate cancer.
Cyclin-dependent kinase-4 inhibitor gene (p16INK4) has recently been mapped to chromosome 9p21. Homozygous deletions of this gene have been found at high frequency in cell lines derived from different types of tumours. These findings suggested therefore, that p16INK4 is a tumour-suppressor gene involved in a wide variety of human cancers. To investigate the frequency of p16INK mutations/deletions in prostate cancer, we screened 20 primary prostate tumours and four established cell lines by polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP) analysis for exon 1 and exon 2. In contrast to most previous reports, no homozygous deletions were found in prostate cancer cell lines, but one cell line (DU145) has revealed to a mutation at codon 76. Only two SSCP shifts were detected in primary tumours: one of them corresponds to a mutation at codon 55 and the other one probably corresponds to a polymorphism. These data suggest that mutation of the p16INK4 gene is not a frequent genetic alteration implicated in prostate cancer development
- …