Gravitational Lorentz force and the description of the gravitational interaction

In the context of a gauge theory for the translation group, we have obtained, for a spinless particle, a gravitational analogue of the Lorentz force. Then, we have shown that this force equation can be rewritten in terms of magnitudes related to either the teleparallel or the Riemannian structures induced in spacetime by the presence of the gravitational field. In the first case, it gives a force equation, with torsion playing the role of force. In the second, it gives the usual geodesic equation of general relativity. The main conclusion is that scalar matter is able to feel any one of the above spacetime geometries, the teleparallel and the metric ones. Furthermore, both descriptions are found to be completely equivalent in the sense that they give the same physical trajectory for a spinless particle in a gravitational field.

The anatomical connections of the macaque monkey orbitofrontal cortex. A review

The orbitofrontal cortex (OfC) is a heterogeneous prefrontal sector selectively connected with a wide constellation of other prefrontal, limbic, sensory and premotor areas. Among the limbic cortical connections, the ones with the bippocampus and parabippocampal cortex are particularly salient. Sensory cortices connected with the OfC include areas involved in olfactory, gustatory, somatosensory, auditory and visual processing. Subcortical structures with prominent OfC connections include the amygdala, numerous thalamic nuclei, the striatum, hypothalamus, periaqueductal gray matter, and biochemically specific cell groups in the basal forebrain and brainstem. Architectonic and connectional evidence supports parcellation of the OfC. The rostrally placed isocortical sector is mainly connected with isocortical areas, including sensory areas of the auditory, somatic and visual modalities, whereas the caudal non-isocortical sector is principally connected with non-isocortical areas, and, in the sensory domain, with olfactory and gustatory areas. The connections of the isocortical and non- isocortical orbital sectors with the amygdala, thalamus, striatum, hypotbalamus and periaqueductal gray matter are also specific. The medial sector of the OfC is selectively connected with the bippocampus, posterior parabippocampal cortex, posterior cingulate and retrosplenial areas, and area prostriata, while the lateral orbitofrontal sector is the most heavily connected with sensory areas of the gustatory, somatic and visual modalities, with premotor regions, and with the amygdala.

Interference phenomena, chiral bosons, and Lorentz invariance

We have studied the theory of gauged chiral bosons and proposed a general theory, a master action, that encompasses different kinds of gauge field couplings in chiral bosonized theories with first-class chiral constraints. We have fused opposite chiral aspects of this master action using the soldering formalism and applied the final action to several well-known models. The Lorentz rotation permitted us to fix conditions on the parameters of this general theory in order to preserve the relativistic invariance. We also have established some conditions on the arbitrary parameter concerned in a chiral Schwinger model with a generalized constraint, investigating both covariance and Lorentz invariance. The results obtained supplement the one that shows the soldering formalism as a new method of mass generation. ©2001 The American Physical Society.

Genetic interactions of yeast eukaryotic translation initiation factor 5a (eIF5A) reveal connections to poly(A)-binding protein and protein kinase C signaling

The highly conserved eukaryotic translation initiation factor eIF5A has been proposed to have various roles in the cell, from translation to mRNA decay to nuclear protein export. To further our understanding of this essential protein, three temperature-sensitive alleles of the yeast TIF51A gene have been characterized. Two mutant eIF5A proteins contain mutations in a proline residue at the junction between the two eIFSA domains and the third, strongest allele encodes a protein with a single mutation in each domain, both of which are required for the growth defect. The stronger tif51A alleles cause defects in degradation of short-lived mRNAs, supporting a role for this protein in mRNA decay. A multicopy suppressor screen revealed six genes, the overexpression of which allows growth of a tif51A-1 strain at high temperature; these genes include PAB1, PKC1, and PKC1 regulators WSC1, WSC2, and WSC3. Further results suggest that eIFSA may also be involved in ribosomal synthesis and the WSC/PKC1 signaling pathway for cell wall integrity or related processes.

Invariant conserved currents in gravity theories with local Lorentz and diffeomorphism symmetry

We discuss conservation laws for gravity theories invariant under general coordinate and local Lorentz transformations. We demonstrate the possibility to formulate these conservation laws in many covariant and noncovariant(ly looking) ways. An interesting mathematical fact underlies such a diversity: there is a certain ambiguity in a definition of the (Lorentz-) covariant generalization of the usual Lie derivative. Using this freedom, we develop a general approach to the construction of invariant conserved currents generated by an arbitrary vector field on the spacetime. This is done in any dimension, for any Lagrangian of the gravitational field and of a (minimally or nonminimally) coupled matter field. A development of the regularization via relocalization scheme is used to obtain finite conserved quantities for asymptotically nonflat solutions. We illustrate how our formalism works by some explicit examples. © 2006 The American Physical Society.

Gluon mass generation in the PT-BFM scheme

In this article we study the general structure and special properties of the Schwinger-Dyson equation for the gluon propagator constructed with the pinch technique, together with the question of how to obtain infrared finite solutions, associated with the generation of an effective gluon mass. Exploiting the known all-order correspondence between the pinch technique and the background field method, we demonstrate that, contrary to the standard formulation, the non-perturbative gluon self-energy is transverse order-by-order in the dressed loop expansion, and separately for gluonic and ghost contributions. We next present a comprehensive review of several subtle issues relevant to the search of infrared finite solutions, paying particular attention to the role of the seagull graph in enforcing transversality, the necessity of introducing massless poles in the three-gluon vertex, and the incorporation of the correct renormalization group properties. In addition, we present a method for regulating the seagull-type contributions based on dimensional regularization; its applicability depends crucially on the asymptotic behavior of the solutions in the deep ultraviolet, and in particular on the anomalous dimension of the dynamically generated gluon mass. A linearized version of the truncated Schwinger-Dyson equation is derived, using a vertex that satisfies the required Ward identity and contains massless poles belonging to different Lorentz structures. The resulting integral equation is then solved numerically, the infrared and ultraviolet properties of the obtained solutions are examined in detail, and the allowed range for the effective gluon mass is determined. Various open questions and possible connections with different approaches in the literature are discussed. © SISSA 2006.

Direct and indirect connections between cochlear root neurons and facial motor neurons: Pathways underlying the acoustic pinna reflex in the albino rat

Cochlear root neurons (CRNs) are involved in the acoustic startle reflex, which is widely used in behavioral models of sensorimotor integration. A short-latency component of this reflex, the auricular reflex, promotes pinna movements in response to unexpected loud sounds. However, the pathway involved in the auricular component of the startle reflex is not well understood. We hypothesized that the auricular reflex is mediated by direct and indirect inputs from CRNs to the motoneurons responsible for pinna movement, which are located in the medial subnucleus of the facial motor nucleus (Mot7). To assess whether there is a direct connection between CRNs and auricular motoneurons in the rat, two neuronal tracers were used in conjunction: biotinylated dextran amine, which was injected into the cochlear nerve root, and Fluoro-Gold, which was injected into the levator auris longus muscle. Under light microscopy, close appositions were observed between axon terminals of CRNs and auricular motoneurons. The presence of direct synaptic contact was confirmed at the ultrastructural level. To confirm the indirect connection, biotinylated dextran amine was injected into the auditory-responsive portion of the caudal pontine reticular nucleus, which receives direct input from CRNs. The results confirm that the caudal pontine reticular nucleus also targets the Mot7 and that its terminals are concentrated in the medial subnucleus. Therefore, it is likely that CRNs innervate auricular motoneurons both directly and indirectly, suggesting that these connections participate in the rapid auricular reflex that accompanies the acoustic startle reflex. © 2008 Wiley-Liss, Inc.

Optimization of multipulse converters with delta and Y-differential connections

This work presents a study regarding the optimization of multipulse converters. A general expression for the connection (Δ or Y) for both 12 and 18-pulses is obtained and describes the output voltages on the secondary windings, depending on the voltage reference from the primary. These generalized expressions allows choosing different ratios between input and output voltages and as result an optimum operation point for the converter can be calculated. Considering Δ-connected converters the optimum point occurs when the magnetic core of the autotransformer processes 18% and 17% of the output power for 12 and 18-pulses, respectively. For Y-connected converters the optimum point occurs when the kVA rating is 13% and 18% for 12 and 18-pulses, respectively. Based on these results magnetic elements can be calculated and designed leading to a great weight and volume reduction and also to lower costs and losses. Finally an analysis is made to improve the kVA rating of the transformers for 12 and 18 pulses converters. © 2009 IEEE.

Generalization of Wye and Delta auto-connections: Analysis of voltages and currents

Multipulse rectifier topologies based on autoconnections, or differential connections, are more and more applied as interface stages between the mains and power converters. These topologies mitigate many low-order current harmonics in the utility, reducing the THD (total harmonic distortion) and increasing the power factor. This paper presents a mathematical model based on phasor diagrams, that results in a single expression able to unify all differential topologies connections (Delta and Wye), for both step-up or step-down autotransformers, for 12 and 18-pulse AC-DC converters. The proposed family of converters can be designed for any relationship between the input voltage and the load voltage. An immediate application would be the retrofit, i.e. to replace a conventional rectifier with poor quality of the processed energy by the 12 or 18 pulses rectifier with Wye or Delta-differential connection. The design procedure, simple and fast, is developed and tested for a prototype rating 6 kW and 250 V on the DC load © 2010 IEEE.

Search for violation of Lorentz invariance in top quark pair production and decay

Using data collected with the D0 detector at the Fermilab Tevatron Collider, corresponding to 5.3fb -1 of integrated luminosity, we search for violation of Lorentz invariance by examining the tt̄ production cross section in lepton+jets final states. We quantify this violation using the standard-model extension framework, which predicts a dependence of the tt̄ production cross section on sidereal time as the orientation of the detector changes with the rotation of the Earth. Within this framework, we measure components of the matrices (c Q) μν33 and (c U) μν33 containing coefficients used to parametrize violation of Lorentz invariance in the top quark sector. Within uncertainties, these coefficients are found to be consistent with zero. © 2012 American Physical Society.

Reliability and failure modes of internal conical dental implant connections

Objective: Biological and mechanical implant-abutment connection complications and failures are still present in clinical practice, frequently compromising oral function. The purpose of this study was to evaluate the reliability and failure modes of anterior single-unit restorations in internal conical interface (ICI) implants using step-stress accelerated life testing (SSALT). Materials and methods: Forty-two ICI implants were distributed in two groups (n = 21 each): group AT-OsseoSpeed™ TX (Astra Tech, Waltham, MA, USA); group SV-Duocon System Line, Morse Taper (Signo Vinces Ltda., Campo Largo, PR, Brazil). The corresponding abutments were screwed to the implants and standardized maxillary central incisor metal crowns were cemented and subjected to SSALT in water. Use-level probability Weibull curves and reliability for a mission of 50,000 cycles at 200 N were calculated. Differences between groups were assessed by Kruskal-Wallis along with Bonferroni's post-hoc tests. Polarized-light and scanning electron microscopes were used for failure analyses. Results: The Beta (β) value derived from use level probability Weibull calculation was 1.62 (1.01-2.58) for group AT and 2.56 (1.76-3.74) for group SV, indicating that fatigue was an accelerating factor for failure of both groups. The reliability for group AT was 0.95 and for group SV was 0.88. Kruskal-Wallis along with Bonferroni's post-hoc tests showed no significant difference between the groups tested (P > 0.27). In all specimens of both groups, the chief failure mode was abutment fracture at the conical joint region and screw fracture at neck's region. Conclusions: Reliability was not different between investigated ICI connections supporting maxillary incisor crowns. Failure modes were similar. © 2012 John Wiley & Sons A/S.

Stress distribution in implant-supported prosthesis with external and internal implant-abutment connections

Objective. This study aimed to investigate the stress distribution in screwed implant-supported prostheses with different implant-abutment connections by using a photoelastic analysis. Materials and methods. Four photoelastic models were fabricated in PL-2 resin and divided according to the implant-abutment connection (external hexagon (EH) and Morse taper (MT) implants (3.75 × 11.5 mm)) and the number crowns (single and 3-unit piece). Models were positioned in a circular polariscope and 100-N axial and oblique (45) loading were applied in the occlusal surface of the crowns by using a universal testing machine. The stresses were photographically recorded and qualitatively analyzed using software (Adobe Photoshop). Results. Under axial loading, the MT implants exhibited a lower number of fringes for single-unit crowns than EH implants, whereas for a 3-unit piece the MT implants showed a higher number of fringes vs EH implants. The oblique loading increased the number of fringes for all groups. Conclusion. In conclusion, the MT implant-abutment connection reduced the amount of stress in single-unit crowns, for 3-unit piece crowns the amount of stress was lower using an external hexagon connection. The stress pattern was similar for all groups. Oblique loading promoted a higher stress concentration than axial loading. © Informa Healthcare.

The Lorentz transformation on the light front, is it possible?

Lorentz transformations are key to relativistic particles. In this work, we construct the Lorentz transformations in the coordinates of the light front, and we will derive from them the well-known time dilation and space contraction in these coordinates, with surprising novel factors. © 2013 American Institute of Physics.