92,422 research outputs found
Backscattering and secondary-electron emission from metal targets of various thicknesses
Backscattering and secondary electron emission from metal targets of various thicknesse
Empirical equations for electron backscattering coefficients
Empirical equations for electron backscattering coefficient
Cramer-Rao Lower Bound for Point Based Image Registration with Heteroscedastic Error Model for Application in Single Molecule Microscopy
The Cramer-Rao lower bound for the estimation of the affine transformation
parameters in a multivariate heteroscedastic errors-in-variables model is
derived. The model is suitable for feature-based image registration in which
both sets of control points are localized with errors whose covariance matrices
vary from point to point. With focus given to the registration of fluorescence
microscopy images, the Cramer-Rao lower bound for the estimation of a feature's
position (e.g. of a single molecule) in a registered image is also derived. In
the particular case where all covariance matrices for the localization errors
are scalar multiples of a common positive definite matrix (e.g. the identity
matrix), as can be assumed in fluorescence microscopy, then simplified
expressions for the Cramer-Rao lower bound are given. Under certain simplifying
assumptions these expressions are shown to match asymptotic distributions for a
previously presented set of estimators. Theoretical results are verified with
simulations and experimental data
The Masers Towards IRAS 20126+4104
We present MERLIN observations of OH, water and methanol masers towards the
young high mass stellar object IRAS 20126+4104. Emission from the 1665-MHz OH,
22-GHz H_2O and 6.7-GHz CH_3OH masers is detected and all originates very close
to the central source. The OH and methanol masers appear to trace part of the
circumstellar disk around the central source. The positions and velocities of
the OH and methanol masers are consistent with Keplerian rotation around a
central mass of ~ 5 Msun. The water masers are offset from the OH and methanol
masers and have significantly changed since they were last observed, but still
appear to be associated to the outflow from the source. All the OH masers
components are circularly polarised, in some cases reaching 100 percent while
some OH components also have linear polarisation. We identify one Zeeman pair
of OH masers and the splitting of this pair indicates a magnetic field of
strength ~ 11 mG within ~ 0.5" (850 AU) of the central source. The OH and
methanol maser emission suggest that the disk material is dense, n > 10^6
cm^-3, and warm, T > 125 K and the high abundance of methanol required by the
maser emission is consistent with the evaporation of the mantles on dust grains
in the disk as a result of heating or shocking of the disk materialComment: 9 pages, 7 figures and 6 table
<i>âWeâre Seeking Relevanceâ</i>: Qualitative Perspectives on the Impact of Learning Analytics on Teaching and Learning
Whilst a significant body of learning analytics research tends to focus on impact from the perspective of usability or improved learning outcomes, this paper proposes an approach based on Affordance Theory to describe awareness and intention as a bridge between usability and impact. 10 educators at 3 European institutions participated in detailed interviews on the affordances they perceive in using learning analytics to support practice in education. Evidence illuminates connections between an educatorâs epistemic beliefs about learning and the purpose of education, their perception of threats or resources in delivering a successful learning experience, and the types of data they would consider as evidence in recognising or regulating learning. This evidence can support the learning analytics community in considering the proximity to the student, the role of the educator, and their personal belief structure in developing robust analytics tools that educators may be more likely to use
Measurement of the ac Stark shift with a guided matter-wave interferometer
We demonstrate the effectiveness of a guided-wave Bose-Einstein condensate
interferometer for practical measurements. Taking advantage of the large arm
separations obtainable in our interferometer, the energy levels of the 87Rb
atoms in one arm of the interferometer are shifted by a calibrated laser beam.
The resulting phase shifts are used to determine the ac polarizability at a
range of frequencies near and at the atomic resonance. The measured values are
in good agreement with theoretical expectations. However, we observe a
broadening of the transition near the resonance, an indication of collective
light scattering effects. This nonlinearity may prove useful for the production
and control of squeezed quantum states.Comment: 5 pages, three figure
Experimental determination of dipole moments for molecular ions: Improved measurements for ArH^+
An improved value for the dipole moment of ArH^+ has been obtained from new measurements of the rotational g factors of ArH^+ and ArD^+ made with tunable farâIR laser spectroscopy. Systematic errors present in earlier measurements have been eliminated. The new result (ÎŒ=3.0±0.6 D) is slightly higher than the ab initio value of Rosmus (2.2 D) at the 2Ï limits of precision
Deconfinement in the Quark Meson Coupling Model
The Quark Meson Coupling Model which describes nuclear matter as a collection
of non-overlapping MIT bags interacting by the self-consistent exchange of
scalar and vector mesons is used to study nuclear matter at finite temperature.
In its modified version, the density dependence of the bag constant is
introduced by a direct coupling between the bag constant and the scalar mean
field. In the present work, the coupling of the scalar mean field with the
constituent quarks is considered exactly through the solution of the Dirac
equation. Our results show that a phase transition takes place at a critical
temperature around 200 MeV in which the scalar mean field takes a nonzero value
at zero baryon density. Furthermore it is found that the bag constant decreases
significantly when the temperature increases above this critical temperature
indicating the onset of quark deconfinement.Comment: LaTeX/TeX 15 pages (zk2.tex)+ 6 figures in TeX forma
Does Being Attractive Always Help? Positive and Negative Effects of Attractiveness on Social Decision Making
Previous studies of organizational decision making demonstrate an abundance of positive biases directed toward highly attractive individuals. The current research, in contrast, suggests that when the person being evaluated is of the same sex as the evaluator, attractiveness hurts, rather than helps. Three experiments assessing evaluations of potential job candidates (Studies 1 and 3) and university applicants (Study 2) demonstrated positive biases toward highly attractive other-sex targets but negative biases toward highly attractive same-sex targets. This pattern was mediated by variability in participantsâ desire to interact with versus avoid the target individual (Studies 1 and 2) and was moderated by participantsâ level of self-esteem (Study 3); the derogation of attractive same-sex targets was not observed among people with high self-esteem. Findings demonstrate an important exception to the positive effects of attractiveness in organizational settings and suggest that negative responses to attractive same-sex targets stem from perceptions of self-threat
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