218 research outputs found
On the Papapetrou field in vacuum
In this paper we study the electromagnetic fields generated by a Killing
vector field in vacuum space-times (Papapetrou fields). The motivation of this
work is to provide new tools for the resolution of Maxwell's equations as well
as for the search, characterization, and study of exact solutions of Einstein's
equations. The first part of this paper is devoted to an algebraic study in
which we give an explicit and covariant procedure to construct the principal
null directions of a Papapetrou field. In the second part, we focus on the main
differential properties of the principal directions, studying when they are
geodesic, and in that case we compute their associated optical scalars. With
this information we get the conditions that a principal direction of the
Papapetrou field must satisfy in order to be aligned with a multiple principal
direction of the Weyl tensor in the case of algebraically special vacuum
space-times. Finally, we illustrate this study using the Kerr, Kasner and pp
waves space-times.Comment: 24 pages, LaTeX2e, IOP style. To appear in Classical and Quantum
Gravit
Observation of magnetic circular dichroism in Fe L_{2,3} x-ray-fluorescence spectra
We report experiments demonstrating circular dichroism in the x-ray-fluorescence spectra of magnetic systems, as predicted by a recent theory. The data, on the L_{2,3} edges of ferromagnetic iron, are compared with fully relativistic local spin density functional calculations, and the relationship between the dichroic spectra and the spin-resolved local density of occupied states is discussed
Spinor classification of the Weyl tensor in five dimensions
We investigate the spinor classification of the Weyl tensor in five
dimensions due to De Smet. We show that a previously overlooked reality
condition reduces the number of possible types in the classification. We
classify all vacuum solutions belonging to the most special algebraic type. The
connection between this spinor and the tensor classification due to Coley,
Milson, Pravda and Pravdov\'a is investigated and the relation between most of
the types in each of the classifications is given. We show that the black ring
is algebraically general in the spinor classification.Comment: 40 page
General approach to the study of vacuum space-times with an isometry
In vacuum space-times the exterior derivative of a Killing vector field is a
2-form (named here as the Papapetrou field) that satisfies Maxwell's equations
without electromagnetic sources. In this paper, using the algebraic structure
of the Papapetrou field, we will set up a new formalism for the study of vacuum
space-times with an isometry, which is suitable to investigate the connections
between the isometry and the Petrov type of the space-time. This approach has
some advantages, among them, it leads to a new classification of these
space-times and the integrability conditions provide expressions that determine
completely the Weyl curvature. These facts make the formalism useful for
application to any problem or situation with an isometry and requiring the
knowledge of the curvature.Comment: 24 pages, LaTeX2e, IOP style. To appear in Classical and Quantum
Gravit
Consequences of a Killing symmetry in spacetime's local structure
In this paper we discuss the consequences of a Killing symmetry on the local
geometrical structure of four-dimensional spacetimes. We have adopted the point
of view introduced in recent works where the exterior derivative of the Killing
plays a fundamental role. Then, we study some issues related with this approach
and clarify why in many circumstances its use has advantages with respect to
other approaches. We also extend the formalism developed in the case of vacuum
spacetimes to the general case of an arbitrary energy-momentum content.
Finally, we illustrate our framework with the case of spacetimes with a
gravitating electromagnetic field.Comment: 20 pages, LaTeX2e, IOP style. Revised version accepted for
publication in Classical and Quantum Gravit
Myostatin inhibition in combination with antisense oligonucleotide therapy improves outcomes in spinal muscular atrophy
BACKGROUND
Spinal muscular atrophy (SMA) is caused by genetic defects in the survival motor neuron 1 (SMN1) gene that lead to SMN deficiency. Different SMN‐restoring therapies substantially prolong survival and function in transgenic mice of SMA. However, these therapies do not entirely prevent muscle atrophy and restore function completely. To further improve the outcome, we explored the potential of a combinatorial therapy by modulating SMN production and muscle‐enhancing approach as a novel therapeutic strategy for SMA.
METHODS
The experiments were performed in a mouse model of severe SMA. A previously reported 25‐mer morpholino antisense oligomer PMO25 was used to restore SMN expression. The adeno‐associated virus‐mediated expression of myostatin propeptide was used to block the myostatin pathway. Newborn SMA mice were treated with a single subcutaneous injection of 40 μg/g (therapeutic dose) or 10 μg/g (low‐dose) PMO25 on its own or together with systemic delivery of a single dose of adeno‐associated virus‐mediated expression of myostatin propeptide. The multiple effects of myostatin inhibition on survival, skeletal muscle phenotype, motor function, neuromuscular junction maturation, and proprioceptive afferences were evaluated.
RESULTS
We show that myostatin inhibition acts synergistically with SMN‐restoring antisense therapy in SMA mice treated with the higher therapeutic dose PMO25 (40 μg/g), by increasing not only body weight (21% increase in male mice at Day 40), muscle mass (38% increase), and fibre size (35% increase in tibialis anterior muscle in 3 month female SMA mice), but also motor function and physical performance as measured in hanging wire test (two‐fold increase in time score) and treadmill exercise test (two‐fold increase in running distance). In SMA mice treated with low‐dose PMO25 (10 μg/g), the early application of myostatin inhibition prolongs survival (40% increase), improves neuromuscular junction maturation (50% increase) and innervation (30% increase), and increases both the size of sensory neurons in dorsal root ganglia (60% increase) and the preservation of proprioceptive synapses in the spinal cord (30% increase).
CONCLUSIONS
These data suggest that myostatin inhibition, in addition to the well‐known effect on muscle mass, can also positively influence the sensory neural circuits that may enhance motor neurons function. While the availability of the antisense drug Spinraza for SMA and other SMN‐enhancing therapies has provided unprecedented improvement in SMA patients, there are still unmet needs in these patients. Our study provides further rationale for considering myostatin inhibitors as a therapeutic intervention in SMA patients, in combination with SMN‐restoring drugs
Zoneamento agroclimático do arroz irrigado por épocas de semeadura no estado do Rio Grande do Sul (versão 4).
bitstream/CPACT/10487/1/documento_199.pd
Pamidronic acid and cabergoline as effective long-term therapy in a 12-year-old girl with extended facial polyostotic fibrous dysplasia, prolactinoma and acromegaly in McCune-Albright syndrome: a case report
<p>Abstract</p> <p>Introduction</p> <p>McCune-Albright syndrome is a complex inborn disorder due to early embryonal postzygotic somatic activating mutations in the <it>GNAS</it>1 gene. The phenotype is very heterogeneous and includes polyostotic fibrous dysplasia, typically involving the facial skull, numerous café-au-lait spots and autonomous hyperfunctions of several endocrine systems, leading to hyperthyroidism, hypercortisolism, precocious puberty and acromegaly.</p> <p>Case presentation</p> <p>Here, we describe a 12-year-old Caucasian girl with severe facial involvement of fibrous dysplasia, along with massive acromegaly due to growth hormone excess and precocious puberty, with a prolactinoma. Our patient was treated with a bisphosphonate and the prolactin antagonist, cabergoline, resulting in the inhibition of fibrous dysplasia and involution of both the prolactinoma and growth hormone excess. During a follow-up of more than two years, no severe side effects were noted.</p> <p>Conclusion</p> <p>Treatment with bisphosphonates in combination with cabergoline is a suitable option in patients with McCune-Albright syndrome, especially in order to circumvent surgical interventions in patients suffering from polyostotic fibrous dysplasia involving the skull base.</p
Constructing TI-Friendly Substitution Boxes Using Shift-Invariant Permutations
The threat posed by side channels requires ciphers that can be efficiently protected in both software and hardware against such attacks. In this paper, we proposed a novel Sbox construction based on iterations of shift-invariant quadratic permutations and linear diffusions. Owing to the selected quadratic permutations, all of our Sboxes enable uniform 3-share threshold implementations, which provide first order SCA protections without any fresh randomness. More importantly, because of the shift-invariant property, there are ample implementation trade-offs available, in software as well as hardware. We provide implementation results (software and hardware) for a four-bit and an eight-bit Sbox, which confirm that our constructions are competitive and can be easily adapted to various platforms as claimed. We have successfully verified their resistance to first order attacks based on real acquisitions. Because there are very few studies focusing on software-based threshold implementations, our software implementations might be of independent interest in this regard
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