1,330 research outputs found
Turbine engine Hot Section Technology (HOST) project
The Hot Section Technology (HOST) Project is a NASA-sponsored endeavor to improve the durability of advanced gas turbine engines for commercial and military aircraft. Through improvements in the analytical models and life prediction systems, designs for future hot section components , the combustor and turbine, will be more accurately analyzed and will incorporate features required for longer life in the more hostile operating environment of high performance engines
Philosophy and the Integrity of the Person: The Phenomenology of Robert Sokolowski
This chapter offers an overview of the philosophy of Robert S. Sokolowski with a focus on his account of what philosophy is, how philosophy arises out of pre-philosophical life, and how it is related back to pre-philosophical life. It also situates Sokolowsk’s achievements in articulating the relationship between Husserlian phenomenology and modern and pre-modern styles of philosophizing
Extending the dynamic range of transcription factor action by translational regulation
A crucial step in the regulation of gene expression is binding of
transcription factor (TF) proteins to regulatory sites along the DNA. But
transcription factors act at nanomolar concentrations, and noise due to random
arrival of these molecules at their binding sites can severely limit the
precision of regulation. Recent work on the optimization of information flow
through regulatory networks indicates that the lower end of the dynamic range
of concentrations is simply inaccessible, overwhelmed by the impact of this
noise. Motivated by the behavior of homeodomain proteins, such as the maternal
morphogen Bicoid in the fruit fly embryo, we suggest a scheme in which
transcription factors also act as indirect translational regulators, binding to
the mRNA of other transcription factors. Intuitively, each mRNA molecule acts
as an independent sensor of the TF concentration, and averaging over these
multiple sensors reduces the noise. We analyze information flow through this
new scheme and identify conditions under which it outperforms direct
transcriptional regulation. Our results suggest that the dual role of
homeodomain proteins is not just a historical accident, but a solution to a
crucial physics problem in the regulation of gene expression.Comment: 14 pages, 5 figure
Large scale excitation of the ISM in NGC 1068
Researchers have shown that photoionization by the continuum of the hidden Seyfert I nucleus in NGC 1068 can have a significant effect on the ionization state and energetics of this disk's Interstellar Medium (ISM). Photoionization models with appropriate power law spectra can produce (NII) lambda lambda 6538, 6584/H alpha line ratios of 1.25 for ionization parameters Q approx. 10 (exp -12). However the data indicate large regions where the (NII)/H alpha ratio is 1 to 3. Since the abundances are known to be solar, there must be additional heating sources. Hardening of the incident radiation field by intervening absorption should be able to raise T sub e, thereby raising the (NII)/H alpha ratio. Heating with moderate efficiency by the intense starburst ring should also be a significant factor in raising the temperature of the ISM. The photoionization models with additional heating predict enhanced emission from other forbidden lines including (OII) lambda 3727 and (SII) lambda 6731
The dynamical equivalence of modified gravity revisited
We revisit the dynamical equivalence between different representations of
vacuum modified gravity models in view of Legendre transformations. The
equivalence is discussed for both bulk and boundary space, by including in our
analysis the relevant Gibbons-Hawking terms. In the f(R) case, the Legendre
transformed action coincides with the usual Einstein frame one. We then
re-express the R+f(G) action, where G is the Gauss-Bonnet term, as a second
order theory with a new set of field variables, four tensor fields and one
scalar and study its dynamics. For completeness, we also calculate the
conformal transformation of the full Jordan frame R+f(G) action. All the
appropriate Gibbons-Hawking terms are calculated explicitly.Comment: 17 pages; v3: Revised version. New comments added in Sections 3 & 5.
New results added in Section 6. Version to appear in Class. Quantum Gravit
A Tight Upper Bound on Mutual Information
We derive a tight lower bound on equivocation (conditional entropy), or
equivalently a tight upper bound on mutual information between a signal
variable and channel outputs. The bound is in terms of the joint distribution
of the signals and maximum a posteriori decodes (most probable signals given
channel output). As part of our derivation, we describe the key properties of
the distribution of signals, channel outputs and decodes, that minimizes
equivocation and maximizes mutual information. This work addresses a problem in
data analysis, where mutual information between signals and decodes is
sometimes used to lower bound the mutual information between signals and
channel outputs. Our result provides a corresponding upper bound.Comment: 6 pages, 3 figures; proof illustration adde
Are stealth scalar fields stable?
Non-gravitating (stealth) scalar fields associated with Minkowski space in
scalar-tensor gravity are examined. Analytical solutions for both non-minimally
coupled scalar field theory and for Brans-Dicke gravity are studied and their
stability with respect to tensor perturbations is assessed using a covariant
and gauge-invariant formalism developed for alternative gravity. For
Brans-Dicke solutions, the stability with respect to homogeneous perturbations
is also studied. There are regions of parameter space corresponding to
stability and other regions corresponding to instability.Comment: 10 pages, 1 table, no figures, to appear in Phys. Rev,
- …