1,066 research outputs found
Tomographic inversion using -norm regularization of wavelet coefficients
We propose the use of regularization in a wavelet basis for the
solution of linearized seismic tomography problems , allowing for the
possibility of sharp discontinuities superimposed on a smoothly varying
background. An iterative method is used to find a sparse solution that
contains no more fine-scale structure than is necessary to fit the data to
within its assigned errors.Comment: 19 pages, 14 figures. Submitted to GJI July 2006. This preprint does
not use GJI style files (which gives wrong received/accepted dates).
Corrected typ
Additional symmetries of constrained CKP and BKP hierarchies
The additional symmetries of the constrained CKP (cCKP) and BKP (cBKP)
hierarchies are given by their actions on the Lax operators, and their actions
on the eigenfunction and adjoint eigenfunction are
presented explicitly. Furthermore, we show that acting on the space of the wave
operator, forms new centerless and
-subalgebra of centerless respectively. In
order to define above symmetry flows of the cCKP and cBKP
hierarchies, two vital operators are introduced to revise the additional
symmetry flows of the CKP and BKP hierarchies.Comment: 14 pages, accepted by SCIENCE CHINA Mathematics(2010
Some results on the eigenfunctions of the quantum trigonometric Calogero-Sutherland model related to the Lie algebra E6
The quantum trigonometric Calogero-Sutherland models related to Lie algebras
admit a parametrization in which the dynamical variables are the characters of
the fundamental representations of the algebra. We develop here this approach
for the case of the exceptional Lie algebra E6.Comment: 17 pages, no figure
Iterative algorithms for total variation-like reconstructions in seismic tomography
A qualitative comparison of total variation like penalties (total variation,
Huber variant of total variation, total generalized variation, ...) is made in
the context of global seismic tomography. Both penalized and constrained
formulations of seismic recovery problems are treated. A number of simple
iterative recovery algorithms applicable to these problems are described. The
convergence speed of these algorithms is compared numerically in this setting.
For the constrained formulation a new algorithm is proposed and its convergence
is proven.Comment: 28 pages, 8 figures. Corrected sign errors in formula (25
On the performance of algorithms for the minimization of -penalized functionals
The problem of assessing the performance of algorithms used for the
minimization of an -penalized least-squares functional, for a range of
penalty parameters, is investigated. A criterion that uses the idea of
`approximation isochrones' is introduced. Five different iterative minimization
algorithms are tested and compared, as well as two warm-start strategies. Both
well-conditioned and ill-conditioned problems are used in the comparison, and
the contrast between these two categories is highlighted.Comment: 18 pages, 10 figures; v3: expanded version with an additional
synthetic test problem
The Escherichia coli RnlA–RnlB toxin–antitoxin complex: production, characterization and crystallization
The Escherichia coli rnlAB operon encodes a toxin–antitoxin module that is involved in protection against infection by bacteriophage T4. The full-length RnlA–RnlB toxin–antitoxin complex as well as the toxin RnlA were purified to homogeneity and crystallized. When the affinity tag is placed on RnlA, RnlB is largely lost during purification and the resulting crystals exclusively comprise RnlA. A homogeneous preparation of RnlA–RnlB containing stoichiometric amounts of both proteins could only be obtained using a His tag placed C-terminal to RnlB. Native mass spectrometry and SAXS indicate a 1:1 stoichiometry for this RnlA–RnlB complex. Crystals of the RnlA–RnlB complex belonged to space group C2, with unit-cell parameters a = 243.32, b = 133.58, c = 55.64 Å, β = 95.11°, and diffracted to 2.6 Å resolution. The presence of both proteins in the crystals was confirmed and the asymmetric unit is likely to contain a heterotetramer with RnlA2:RnlB2 stoichiometry
Nuclear pores in the apoptotic cell.
During apoptosis, nuclear pores undergo strong modifications, which are described here in five different apoptotic models, Conventional electron microscopy, supported by freeze-fracture analysis, showed a constant migration of nuclear pores towards the diffuse chromatin areas, In contrast, dense chromatin areas appear pore-free and are frequently surrounded by strongly dilated cistemae, A possible functional significance of this pore behaviour during apoptosis is discussed
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"This culture is nurturing and caring" : ethnographic account of a campus climate from the perspective of African-American students
Different racial/ethnic groups often perceive the realities of the campus environment differently: This difference in perspective and the attendant reactions can be a factor in student satisfaction or dissatisfaction. A quantitative survey administered in 1996 and 1999 revealed that African-American students on the campus of a diverse two-year community college were less satisfied with aspects of the campus climate than other student groups. This study responded to those findings. The purpose of this study was to discover how African-American students perceive and describe their experiences on that campus. The researcher sought to discover the sectors of the campus environment that contributed to their satisfaction or dissatisfaction.
The qualitative research paradigm provided the framework for this study. Data was collected from six African-American students utilizing multiple, open-ended, individual interviews, a focus group, and a campus audit. The sample was small and purposefully selected in accordance with the purpose of the study. The individual interviews were spaced from three to seven days apart, which facilitated them placing their experiences in the context of their life histories.
The analysis of the data revealed that although the informants recounted some experiences that made them feel disconnected from the campus, their predominant perception of the campus climate was that it was caring and nurturing. The informants shared experiences that were consistent with the literature on commuter students and retention. Primarily, their transactions with faculty members shaped their perceptions and made their educational experiences meaningful. They perceived the faculty as authentic and available to them. Consequently, they utilized them as informal mentors, friends, and confidantes. Such an environment allowed these students to be fully present as learners
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