1,841 research outputs found
Quasinormal Modes Beyond Kerr
The quasinormal modes (QNMs) of a black hole spacetime are the free, decaying
oscillations of the spacetime, and are well understood in the case of Kerr
black holes. We discuss a method for computing the QNMs of spacetimes which are
slightly deformed from Kerr. We mention two example applications: the
parametric, turbulent instability of scalar fields on a background which
includes a gravitational QNM, and the shifts to the QNM frequencies of Kerr
when the black hole is weakly charged. This method may be of use in studies of
black holes which are deformed by external fields or are solutions to
alternative theories of gravity.Comment: Proceedings of the Sant Cugat Forum on Astrophysics (2014). Session
on 'Gravitational Wave Astrophysics.' 7 page
A Non-Relativistic Weyl Anomaly
We examine the Weyl anomaly for a four-dimensional z=3 Lifshitz scalar
coupled to Horava's theory of anisotropic gravity. We find a one-loop
break-down of scale-invariance at second order in the gravitational background.Comment: LaTeX, 23 pages, no figures, JHEP style; v2: typos fixed to match the
published versio
Restoring Speech Following Total Removal of the Larynx
By speech articulator movement and training a transformation to audio we can restore the power of speech to someone who has lost their larynx. We sense changes in magnetic field caused by movements of small magnets attached to the lips and tongue. The sensor transformation uses recurrent neural networks
Can a pseudo-symmetry solve the cosmological constant problem?
A general no-go theorem dampens hope that the cosmological constant problem
can be solved by a local symmetry mechanism. The possibility is considered here
that this no-go theorem can be avoided by a pseudo-symmetry. A simple
macroscopic effective field theory is constructed which admits an enhanced
pseudo-symmetry in the absence of a cosmological term. It is pointed out that
this pseudo-symmetry is an exact classical invariance of superstrings. The
conjecture that this pseudo-symmetry survives in the quantum theory has several
interesting consequences.Comment: Changes in language (including new title), and assorted perestroika.
One new consequence of conjecture. 10 pages, uuencoded Postscript file. To
appear in Phys.Lett.
Could Fermion Masses Play a Role in the Stabilization of the Dilaton in Cosmology?
We study the possibility that the Dilaton is stabilized by the contribution
of fermion masses to its effective potential. We consider the Dilaton gravity
action in four dimensions to which we add a mass term for a Dirac fermion. Such
an action describes the interaction of the Dilaton with the fermions in the
Yang-Mills sector of the coupled supergravity/super-Yang-Mills action which
emerges as the low energy effective action of superstring theory after the
extra spatial dimensions have been fixed. The Dilaton couples to the Fermion
mass term via the usual exponential factor of this field which multiplies the
non-kinetic terms of the matter Lagrangian, if we work in the Einstein frame.
In the kinetic part of the Fermion action in the Einstein frame the Dilaton
does not enter. Such masses can be generated in several ways: they can arise as
a consequence of flux about internal spatial dimensions, they may arise as
thermal fermion masses in a quasi-static phase in the early universe, and they
will arise after the breaking of supersymmetry at late times. The vacuum
contribution to the potential for the Dilaton is evaluated up to two loops. The
result shows a minimum which could stabilize the Dilaton for reasonable ranges
of parameter values.Comment: 11 pages, 1 figure; shortened versio
Direct Speech Reconstruction From Articulatory Sensor Data by Machine Learning
This paper describes a technique that generates speech acoustics from articulator movements. Our motivation is to help people who can no longer speak following laryngectomy, a procedure that is carried out tens of thousands of times per year in the Western world. Our method for sensing articulator movement, permanent magnetic articulography, relies on small, unobtrusive magnets attached to the lips and tongue. Changes in magnetic field caused by magnet movements are sensed and form the input to a process that is trained to estimate speech acoustics. In the experiments reported here this “Direct Synthesis” technique is developed for normal speakers, with glued-on magnets, allowing us to train with parallel sensor and acoustic data. We describe three machine learning techniques for this task, based on Gaussian mixture models, deep neural networks, and recurrent neural networks (RNNs). We evaluate our techniques with objective acoustic distortion measures and subjective listening tests over spoken sentences read from novels (the CMU Arctic corpus). Our results show that the best performing technique is a bidirectional RNN (BiRNN), which employs both past and future contexts to predict the acoustics from the sensor data. BiRNNs are not suitable for synthesis in real time but fixed-lag RNNs give similar results and, because they only look a little way into the future, overcome this problem. Listening tests show that the speech produced by this method has a natural quality that preserves the identity of the speaker. Furthermore, we obtain up to 92% intelligibility on the challenging CMU Arctic material. To our knowledge, these are the best results obtained for a silent-speech system without a restricted vocabulary and with an unobtrusive device that delivers audio in close to real time. This work promises to lead to a technology that truly will give people whose larynx has been removed their voices back
Characterization of active and total fungal communities in the atmosphere over the Amazon rainforest
Fungi are ubiquitous in the atmosphere and may play an important role in atmospheric processes. We investigated the composition and diversity of fungal communities over the Amazon rainforest canopy and compared these communities to fungal communities 5 found in terrestrial environments. We characterized the total fungal community and the metabolically active portion of the community using high-throughout DNA and RNA sequencing and compared these data to predictions generated by a mass-balance model. We found that the total community was primarily comprised of fungi from the phylum Basidiomycota. In contrast, the active community was primarily composed of 10 members of the phylum Ascomycota and included a high relative abundance of lichen fungi, which were not detected in the total community. The relative abundance of Basidiomycota and Ascomycota in the total and active communities was consistent with our model predictions, suggesting that this result was driven by the relative size and number of spores produced by these groups. When compared to other environments, 15 fungal communities in the atmosphere were most similar to communities found in tropical soils and leaf surfaces, suggesting that inputs of fungi to the atmosphere are from local, rather than distant, sources. Our results demonstrate that there are significant differences in the composition of the total and active fungal communities in the atmosphere, and that lichen fungi, which have been shown to be efficient ice nucleators, 20 may be abundant members of active atmospheric fungal communities over the forest canopy
The Effective Action For Brane Localized Gauge Fields
The low energy effective action including gauge field degrees of freedom on a
non-BPS p=2 brane embedded in a N=1, D=4 target superspace is obtained through
the method of nonlinear realizations of the associated super-Poincare
symmetries. The invariant interactions of the gauge fields and the brane
excitation modes corresponding to the Nambu-Goldstone degrees of freedom
resulting from the broken space translational symmetry and the target space
supersymmetries are determined. Brane localized matter field interactions with
the gauge fields are obtained through the construction of the combined gauge
and super-Poincare covariant derivatives for the matter fields.Comment: 12 pages, no figure
- …