3,564 research outputs found
Pre-peak ram pressure stripping in the Virgo cluster spiral galaxy NGC 4501
VIVA HI observations of the Virgo spiral galaxy NGC 4501 are presented. The
HI disk is sharply truncated to the southwest, well within the stellar disk. A
region of low surface-density gas, which is more extended than the main HI
disk, is discovered northeast of the galaxy center. These data are compared to
existing 6cm polarized radio continuum emission, Halpha, and optical broad band
images. We observe a coincidence between the western HI and polarized emission
edges, on the one hand, and a faint Halpha emission ridge, on the other. The
polarized emission maxima are located within the gaps between the spiral arms
and the faint Halpha ridge. Based on the comparison of these observations with
a sample of dynamical simulations with different values for maximum ram
pressure and different inclination angles between the disk and the orbital
plane,we conclude that ram pressure stripping can account for the main observed
characteristics. NGC 4501 is stripped nearly edge-on, is heading southwest, and
is ~200-300 Myr before peak ram pressure, i.e. its closest approach to M87. The
southwestern ridge of enhanced gas surface density and enhanced polarized
radio-continuum emission is due to ram pressure compression. It is argued that
the faint western Halpha emission ridge is induced by nearly edge-on ram
pressure stripping. NGC 4501 represents an especially clear example of early
stage ram pressure stripping of a large cluster-spiral galaxy.Comment: 22 pages, 25 figures, accepted for publication in A&
Fermi acceleration and suppression of Fermi acceleration in a time-dependent Lorentz Gas
We study some dynamical properties of a Lorentz gas. We have considered both
the static and time dependent boundary. For the static case we have shown that
the system has a chaotic component characterized with a positive Lyapunov
Exponent. For the time-dependent perturbation we describe the model using a
four-dimensional nonlinear map. The behaviour of the average velocity is
considered in two situations (i) non-dissipative and (ii) dissipative. Our
results show that the unlimited energy growth is observed for the
non-dissipative case. However, when dissipation, via damping coefficients, is
introduced the senary changes and the unlimited engergy growth is suppressed.
The behaviour of the average velocity is described using scaling approach
Competitiveness – A Comparison of China and Mexico
Latin American countries have lost competitiveness in world markets in comparison to China over the last two decades. The main purpose of this study is to examine the causes of this development. To this end an augmented Ricardian model is estimated using panel data. The explanatory variables considered are productivity, unit labor costs, unit values, trade costs, price levels (in PPP), and real exchange rates in relative terms. Due to data restrictions, China’s relative exports (to the US, Argentina, Japan, Korea, UK, Germany, and Spain) will be compared to Mexico’s exports for a number of sectors over a period of eleven years. Panel and pooled estimation techniques (SUR-estimation, panel Feasible Generalized Least Squares (panel/pooled FGLS)) will be utilized to better control for country-specific effects (differences between American, Argentinian, Japanese, Korean, German, British, and Spanish markets), cross-section specific (sector-specific) effects, and correlation over time.Ricardian model of trade, panel data models, panel Feasible Generalized Least Squares, Seemingly Unrelated (SUR) estimation
Label-free optical detection of single enzyme-reactant reactions and associated conformational changes
Monitoring the kinetics and conformational dynamics of single enzymes is
crucial in order to better understand their biological functions as these
motions and structural dynamics are usually unsynchronized among the molecules.
Detecting the enzyme-reactant interactions and associated conformational
changes of the enzyme on a single molecule basis, however, remain as a
challenge with established optical techniques due to the commonly required
labeling of the reactants or the enzyme itself. The labeling process is usually
non-trivial and the labels themselves might skew the physical properties of the
enzyme. Here we demonstrate an optical, label-free method capable of observing
enzymatic interactions and the associated conformational changes on the single
molecule level. We monitor polymerase/DNA interactions via the strong
near-field enhancement provided by plasmonic nanorods resonantly coupled to
whispering gallery modes in microcavities. Specifically, we employ two
different recognition schemes: one in which the kinetics of polymerase/DNA
interactions are probed in the vicinity of DNA-functionalized nanorods, and the
other in which these interactions are probed via the magnitude of
conformational changes in the polymerase molecules immobilized on nanorods. In
both approaches we find that low and high polymerase activities can be clearly
discerned via their characteristic signal amplitude and signal length
distributions. Furthermore, the thermodynamic study of the monitored
interactions suggests the occurrence of DNA polymerization. This work
constitutes a proof-of-concept study of enzymatic activities via plasmonically
enhanced microcavities and establishes an alternative and label-free method
capable of investigating structural changes in single molecules
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