3,746 research outputs found
Recommended from our members
The other side of critical psychology? A review of the utility of Lacanian psychoanalysis with a focus on the theory of the Four Discourses
Recommended from our members
How should we supervise qualitative projects?
There is a âshortfall in numbers of highly skilled qualitative researchersâ says the Economic and Social Research Council (2004). What is psychology doing about it? The Societyâs revised syllabus (BPS, 2002) states that students should be able to collect and analyse qualitative (non-numerical) data. The Quality Assessment Agency (QAA, 2002) also specifies that psychology should cover qualitative methods. Therefore, in time, psychology graduates should have the expertise the ESRC needs
Probing Solar Convection
In the solar convection zone acoustic waves are scattered by turbulent sound
speed fluctuations. In this paper the scattering of waves by convective cells
is treated using Rytov's technique. Particular care is taken to include
diffraction effects which are important especially for high-degree modes that
are confined to the surface layers of the Sun. The scattering leads to damping
of the waves and causes a phase shift. Damping manifests itself in the width of
the spectral peak of p-mode eigenfrequencies. The contribution of scattering to
the line widths is estimated and the sensitivity of the results on the assumed
spectrum of the turbulence is studied. Finally the theoretical predictions are
compared with recently measured line widths of high-degree modes.Comment: 26 pages, 7 figures, accepted by MNRA
Contemplations on Dirac's equation in quaternionic coordinates
A formulation of Dirac's equation using complex-quaternionic coordinates
appears to yield an enormous gain in formal elegance, as there is no longer any
need to invoke Dirac matrices. This formulation, however, entails several
peculiarities, which we investigate and attempt to interpret
Gravitational Helioseismology?
The magnitudes of the external gravitational perturbations associated with
the normal modes of the Sun are evaluated to determine whether these solar
oscillations could be observed with the proposed Laser Interferometer Space
Antenna (LISA), a network of satellites designed to detect gravitational
radiation. The modes of relevance to LISA---the , low-order , and
-modes---have not been conclusively observed to date. We find that the
energy in these modes must be greater than about in order
to be observable above the LISA detector noise. These mode energies are larger
than generally expected, but are much smaller than the current observational
upper limits. LISA may be confusion-limited at the relevant frequencies due to
the galactic background from short-period white dwarf binaries. Present
estimates of the number of these binaries would require the solar modes to have
energies above about to be observable by LISA.Comment: 8 pages; prepared with REVTEX 3.0 LaTeX macro
Errors in quantum optimal control and strategy for the search of easily implementable control pulses
We introduce a new approach to assess the error of control problems we aim to
optimize. The method offers a strategy to define new control pulses that are
not necessarily optimal but still able to yield an error not larger than some
fixed a priori threshold, and therefore provide control pulses that might be
more amenable for an experimental implementation. The formalism is applied to
an exactly solvable model and to the Landau-Zener model, whose optimal control
problem is solvable only numerically. The presented method is of importance for
applications where a high degree of controllability of the dynamics of quantum
systems is required.Comment: 13 pages, 3 figure
B and D Meson Decay Constants in Lattice QCD
We have calculated the decay constants of B and mesons with lattice QCD.
We use an improved action that takes light quark actions as a starting
point, tuned so that it can be directly applied at the physical masses of the
and quarks. Our results are f_B = 164 \err{+14}{-11} \pm 8 MeV,
f_{B_s} = 185 \err{+13}{-8} \pm 9 MeV, f_D = 194 \err{+14}{-10} \pm 10 MeV,
and f_{D_s} = 213 \err{+14}{-11} \pm 11 MeV in the quenched approximation.
The first error in each case is statistical, and the second is from
perturbation theory. We show that discretization errors are under control in
our approach, and smaller than our statistical errors. The effects of the
quenched approximation may raise our quenched result by up to 10%.Comment: 21 pages, 6 figure
Hierarchy and Feedback in the Evolution of the E. coli Transcription Network
The E.coli transcription network has an essentially feedforward structure,
with, however, abundant feedback at the level of self-regulations. Here, we
investigate how these properties emerged during evolution. An assessment of the
role of gene duplication based on protein domain architecture shows that (i)
transcriptional autoregulators have mostly arisen through duplication, while
(ii) the expected feedback loops stemming from their initial cross-regulation
are strongly selected against. This requires a divergent coevolution of the
transcription factor DNA-binding sites and their respective DNA cis-regulatory
regions. Moreover, we find that the network tends to grow by expansion of the
existing hierarchical layers of computation, rather than by addition of new
layers. We also argue that rewiring of regulatory links due to
mutation/selection of novel transcription factor/DNA binding interactions
appears not to significantly affect the network global hierarchy, and that
horizontally transferred genes are mainly added at the bottom, as new target
nodes. These findings highlight the important evolutionary roles of both
duplication and selective deletion of crosstalks between autoregulators in the
emergence of the hierarchical transcription network of E.coli.Comment: to appear in PNA
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