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Curvature sensor for the measurement of the static corneal topography and the dynamic tear film topography in the human eye
A system to measure the topography of the first optical surface of the human eye noninvasively by using a curvature sensor is described. The static corneal topography and the dynamic topography of the tear film can both be measured, and the topographies obtained are presented. The system makes possible the study of the dynamic aberrations introduced by the tear film to determine their contribution to the overall ocular aberrations in healthy eyes, eyes with corneal pathologies, and eyes wearing contact lenses
Effect of many modes on self-polarization and photochemical suppression in cavities
The standard description of cavity-modified molecular reactions typically involves a single (resonant) mode, while in reality, the quantum cavity supports a range of photon modes. Here, we demonstrate that as more photon modes are accounted for, physicochemical phenomena can dramatically change, as illustrated by the cavity-induced suppression of the important and ubiquitous process of proton-coupled electron-transfer. Using a multi-trajectory Ehrenfest treatment for the photon-modes, we find that self-polarization effects become essential, and we introduce the concept of self-polarization-modified Born–Oppenheimer surfaces as a new construct to analyze dynamics. As the number of cavity photon modes increases, the increasing deviation of these surfaces from the cavity-free Born–Oppenheimer surfaces, together with the interplay between photon emission and absorption inside the widening bands of these surfaces, leads to enhanced suppression. The present findings are general and will have implications for the description and control of cavity-driven physical processes of molecules, nanostructures, and solids embedded in cavities
The role of the Roper resonance in n p --> d (pi pi)
In this work, a model for the n p --> d (pi pi) reaction is developed. It is
shown that the structure of the deuteron momentum spectra for a neutron beam
momentum of 1.46 GeV can be explained as a consequence of the interplay of two
mechanisms involving the excitation of the N^*(1440) resonance and its
subsequent decay into N (pi pi)^{T=0}_{S-wave} and Delta pi respectively. The
relevance of the present analysis for the study of the Roper excitation and
decay properties, as well as for the interpretation of other two-pion
production experiments is discussed.Comment: 13 pages, 6 ps figure
Application of Current Algebra in Three Pseudoscalar Meson Decays of Lepton
The decays of and
are calculated using the hard pion and kaon current algebra and assuming the
Axial-Vector meson dominance of the hadronic axial currents. Using the
experimental data on their masses and widths, the decay branching ratios
into these channels are calculated and found to be in a reasonable agreement
with the experimental data. In particular, using the available Aleph data on
the spectrum, we determine the parameters, ,
GeV; the hard current algebra calculation yields a
branching ratio of .Comment: 14 pages, Tex, 6 included figure
Fermi gamma-ray `bubbles' from stochastic acceleration of electrons
Gamma-ray data from Fermi-LAT reveal a bi-lobular structure extending up to
50 degrees above and below the galactic centre, which presumably originated in
some form of energy release there less than a few million years ago. It has
been argued that the gamma-rays arise from hadronic interactions of high energy
cosmic rays which are advected out by a strong wind, or from inverse-Compton
scattering of relativistic electrons accelerated at plasma shocks present in
the bubbles. We explore the alternative possibility that the relativistic
electrons are undergoing stochastic 2nd-order Fermi acceleration by plasma wave
turbulence through the entire volume of the bubbles. The observed gamma-ray
spectral shape is then explained naturally by the resulting hard electron
spectrum and inverse Compton losses. Rather than a constant volume emissivity
as in other models, we predict a nearly constant surface brightness, and
reproduce the observed sharp edges of the bubbles.Comment: 4 pages, 4 figures; REVTeX4-1; discussion amended and one figure
added; to appear in PR
Impact of the European Clinical Trials Directive on prospective academic clinical trials associated with BMT
The European Clinical Trials Directive (EU 2001; 2001/20/EC) was introduced to improve the efficiency of commercial and academic clinical trials. Concerns have been raised by interested organizations and institutions regarding the potential for negative impact of the Directive on non-commercial European clinical research. Interested researchers within the European Group for Blood and Marrow Transplantation (EBMT) were surveyed to determine whether researcher experiences confirmed this view. Following a pilot study, an internet-based questionnaire was distributed to individuals in key research positions in the European haemopoietic SCT community. Seventy-one usable questionnaires were returned from participants in different EU member states. The results indicate that the perceived impact of the European Clinical Trials Directive has been negative, at least in the research areas of interest to the EBMT
Probing Short Range Nucleon Correlations in High Energy Hard Quasielastic pd Reactions
We show that the strong dependence of the amplitude for hard scattering
on the collision energy can be used to magnify the effects of short range
nucleon correlations in quasielastic scattering. Under specific
kinematical conditions the effect of initial and final state interactions can
be accounted for by rescaling the cross section calculated within the plane
wave impulse approximation. The feasibility to investigate the role of
relativistic effects in the deuteron wave function is demonstrated by comparing
the predictions of different formalisms. Binding effects due to short range
correlations in deuteron are discussed as well.Comment: 18 pages (LaTex) + 10 postscript figs (available on request
Magnetic field turbulence in the solar wind at sub-ion scales: in situ observations and numerical simulations
We investigate the transition of the solar wind turbulent cascade from MHD to
sub-ion range by means of a detail comparison between in situ observations and
hybrid numerical simulations. In particular we focus on the properties of the
magnetic field and its component anisotropy in Cluster measurements and hybrid
2D simulations. First, we address the angular distribution of wave-vectors in
the kinetic range between ion and electron scales by studying the variance
anisotropy of the magnetic field components. When taking into account the
single-direction sampling performed by spacecraft in the solar wind, the main
properties of the fluctuations observed in situ are also recovered in our
numerical description. This result confirms that solar wind turbulence in the
sub-ion range is characterized by a quasi-2D gyrotropic distribution of
k-vectors around the mean field. We then consider the magnetic compressibility
associated with the turbulent cascade and its evolution from large-MHD to
sub-ion scales. The ratio of field-aligned to perpendicular fluctuations,
typically low in the MHD inertial range, increases significantly when crossing
ion scales and its value in the sub-ion range is a function of the total plasma
beta only, as expected from theoretical predictions, with higher magnetic
compressibility for higher beta. Moreover, we observe that this increase has a
gradual trend from low to high beta values in the in situ data; this behaviour
is well captured by the numerical simulations. The level of magnetic field
compressibility that is observed in situ and in the simulations is in fairly
good agreement with theoretical predictions, especially at high beta,
suggesting that in the kinetic range explored the turbulence is supported by
low-frequency and highly-oblique fluctuations in pressure balance, like kinetic
Alfv\'en waves or other slowly evolving coherent structures.Comment: Manuscript submitted to Frontiers Astronomy and Space Sciences,
Research Topic: Improving the Understanding of Kinetic Processes in Solar
Wind and Magnetosphere: From CLUSTER to MM
A method for detection of structure
Context. In order to understand the evolution of molecular clouds it is
important to identify the departures from self-similarity associated with the
scales of self-gravity and the driving of turbulence.
Aims. A method is described based on structure functions for determining
whether a region of gas, such as a molecular cloud, is fractal or contains
structure with characteristic scale sizes.
Methods. Using artificial data containing structure it is shown that
derivatives of higher order structure functions provide a powerful way to
detect the presence of characteristic scales should any be present and to
estimate the size of such structures. The method is applied to observations of
hot H2 in the Kleinman-Low nebula, north of the Trapezium stars in the Orion
Molecular Cloud, including both brightness and velocity data. The method is
compared with other techniques such as Fourier transform and histogram
techniques.
Results. It is found that the density structure, represented by H2 emission
brightness in the K-band (2-2.5micron), exhibits mean characteristic sizes of
110, 550, 1700 and 2700AU. The velocity data show the presence of structure at
140, 1500 and 3500AU. Compared with other techniques such as Fourier transform
or histogram, the method appears both more sensitive to characteristic scales
and easier to interpret.Comment: Astronomy and Astrophysics, in pres
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