Teleparallel Theories of Gravity: Illuminating a Fully Invariant Approach

Teleparallel gravity and its popular generalization $f(T)$ gravity can be formulated as fully invariant (under both coordinate transformations and local Lorentz transformations) theories of gravity. Several misconceptions about teleparallel gravity and its generalizations can be found in the literature, especially regarding their local Lorentz invariance. We describe how these misunderstandings may have arisen and attempt to clarify the situation. In particular, the central point of confusion in the literature appears to be related to the inertial spin connection in teleparallel gravity models. While inertial spin connections are commonplace in special relativity, and not something inherent to teleparallel gravity, the role of the inertial spin connection in removing the spurious inertial effects within a given frame of reference is emphasized here. The careful consideration of the inertial spin connection leads to the construction of a fully invariant theory of teleparallel gravity and its generalizations. Indeed, it is the nature of the spin connection that differentiates the relationship between what have been called good tetrads and bad tetrads and clearly shows that, in principle, any tetrad can be utilized. The field equations for the fully invariant formulation of teleparallel gravity and its generalizations are presented and a number of examples using different assumptions on the frame and spin connection are displayed to illustrate the covariant procedure. Various modified teleparallel gravity models are also briefly reviewed.Comment: v2: 72 pages, revised version, references added, matches published versio

The RhoA transcriptional program in pre-T cells

The GTPase RhoA is essential for the development of pre-T cells in the thymus. To investigate the mechanisms used by RhoA to control thymocyte development we have used Affymetrix gene profiling to identify RhoA regulated genes in T cell progenitors. The data show that RhoA plays a specific and essential role in pre-T cells because it is required for the expression of transcription factors of the Egr-1 and AP-1 families that have critical functions in thymocyte development. Loss of RhoA function in T cell progenitors causes a developmental block that pheno-copies the consequence of losing pre-TCR expression in Recombinase gene 2 (Rag2) null mice. Transcriptional profiling reveals both common and unique gene targets for RhoA and the pre-TCR indicating that RhoA participates in the pre-TCR induced transcriptional program but also mediates pre-TCR independent gene transcription

Van diepe angst en stil genot: Louis Couperus

Modern and Contemporary Studie

Angular size test on the expansion of the Universe

Assuming the standard cosmological model as correct, the average linear size of galaxies with the same luminosity is six times smaller at z=3.2 than at z=0, and their average angular size for a given luminosity is approximately proportional to 1/z. Neither the hypothesis that galaxies which formed earlier have much higher densities nor their luminosity evolution, mergers ratio, or massive outflows due to a quasar feedback mechanism are enough to justify such a strong size evolution. Also, at high redshift, the intrinsic ultraviolet surface brightness would be prohibitively high with this evolution, and the velocity dispersion much higher than observed. We explore here another possibility to overcome this problem by considering different cosmological scenarios that might make the observed angular sizes compatible with a weaker evolution. One of the models explored, a very simple phenomenological extrapolation of the linear Hubble law in a Euclidean static universe, fits the angular size vs. redshift dependence quite well, which is also approximately proportional to 1/z with this cosmological model. There are no free parameters derived ad hoc, although the error bars allow a slight size/luminosity evolution. The type Ia supernovae Hubble diagram can also be explained in terms of this model with no ad hoc fitted parameter. WARNING: I do not argue here that the true Universe is static. My intention is just to discuss which theoretical models provide a better fit to the data of observational cosmology.Comment: 44 pages, accepted to be published in Int. J. Mod. Phys.

Oxygen saturation targets for children with respiratory distress:a systematic review

BACKGROUND: In children with respiratory distress, supplemental oxygen is indicated at peripheral oxygen saturation ( S pO 2 ) thresholds of 90-94%. However, these thresholds are poorly studied. We conducted a systematic review to summarise the existing evidence for S pO 2 thresholds in children with respiratory distress. METHODS: Electronic databases and registries were searched for original articles published from 1 January 2010 to 7 January 2022 comparing two or more S pO 2 thresholds in children with respiratory distress. Primary outcomes were safety, including mortality, neurocognitive outcomes and readmissions, and effectiveness, including admission rate and length of hospital stay. Methodological appraisal was performed using the Cochrane Risk of Bias 2 (RoB-2) or Risk of Bias in Non-Randomized Studies - of Interventions (ROBINS-I) tools. Results were narratively synthesised. RESULTS: We retrieved 3384 results; seven studies were included. Lower thresholds ranged from 80% to 92% and were compared with higher thresholds ranging from 92% to 94%. Studies were highly heterogeneous in setting, design, population and outcomes. Risk of bias varied from low to high. Lower S pO 2 thresholds had equivalent mortality, neurocognitive outcomes and readmissions or re-attendance to healthcare to higher thresholds. Lower S pO 2 thresholds showed a significant decrease in admission rates by up to 40% and shortened hospitalisation duration by 10-18 h. CONCLUSIONS: The current S pO 2 thresholds of 90-94% in children with respiratory distress may be too high, which could lead to unnecessary hospitalisations and prolonged hospitalisation duration. S pO 2 thresholds as low as 88% are potentially safe in children with respiratory distress and may reduce hospitalisation rates and length of stay. However, high-quality evidence is needed to support this. </p

Regulatory T cell defects in rheumatoid arthritis

No abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55983/1/22415_ftp.pd

Are galaxies extending?

It is suggested that the recently observed size evolution of very massive compact galaxies in the early universe can be explained, if dark matter is in Bose Einstein condensate. In this model the size of the dark matter halos and galaxies depends on the correlation length of dark matter and, hence, on the the expansion of the universe. This theory predicts that the size of the galaxies increases as the Hubble radius of the universe even without merging, which agrees well with the recent observational data.Comment: 5 pages, 2figs, revtex,accepted version for PL

Guanine a-carboxy nucleoside phosphonate (G-a-CNP) shows a different inhibitory kinetic profile against the DNA polymerases of human immunodeficiency virus (HIV) and herpes viruses

α-Carboxy nucleoside phosphonates (α-CNPs) are modified nucleotides that represent a novel class of nucleotide-competing reverse transcriptase (RT) inhibitors (NcRTIs). They were designed to act directly against HIV-1 RT without the need for prior activation (phosphorylation). In this respect, they differ from the nucleoside or nucleotide RTIs [N(t)RTIs] that require conversion to their triphosphate forms before being inhibitory to HIV-1 RT. The guanine derivative (G-α-CNP) has now been synthesized and investigated for the first time. The (L)-(+)-enantiomer of G-α-CNP directly and competitively inhibits HIV-1 RT by interacting with the substrate active site of the enzyme. The (D)-(−)-enantiomer proved inactive against HIV-1 RT. In contrast, the (+)- and (−)-enantiomers of G-α-CNP inhibited herpes (i.e. HSV-1, HCMV) DNA polymerases in a non- or uncompetitive manner, strongly indicating interaction of the (L)-(+)- and the (D)-(−)-G-α-CNPs at a location different from the polymerase substrate active site of the herpes enzymes. Such entirely different inhibition profile of viral polymerases is unprecedented for a single antiviral drug molecule. Moreover, within the class of α-CNPs, subtle differences in their sensitivity to mutant HIV-1 RT enzymes were observed depending on the nature of the nucleobase in the α-CNP molecules. The unique properties of the α-CNPs make this class of compounds, including G-α-CNP, direct acting inhibitors of multiple viral DNA polymerases

Classical big-bounce cosmology: dynamical analysis of a homogeneous and irrotational Weyssenhoff fluid

A dynamical analysis of an effective homogeneous and irrotational Weyssenhoff fluid in general relativity is performed using the 1+3 covariant approach that enables the dynamics of the fluid to be determined without assuming any particular form for the space-time metric. The spin contributions to the field equations produce a bounce that averts an initial singularity, provided that the spin density exceeds the rate of shear. At later times, when the spin contribution can be neglected, a Weyssenhoff fluid reduces to a standard cosmological fluid in general relativity. Numerical solutions for the time evolution of the generalised scale factor in spatially-curved models are presented, some of which exhibit eternal oscillatory behaviour without any singularities. In spatially-flat models, analytical solutions for particular values of the equation-of-state parameter are derived. Although the scale factor of a Weyssenhoff fluid generically has a positive temporal curvature near a bounce, it requires unreasonable fine tuning of the equation-of-state parameter to produce a sufficiently extended period of inflation to fit the current observational data.Comment: 34 pages, 18 figure