1,810 research outputs found
Rotational Invariance in the M(atrix) Formulation of Type IIB Theory
The matrix model formulation of M-theory can be generalized by
compactification to ten-dimensional type II string theory, formulated in the
infinite momentum frame. Both the type IIA and IIB string theories can be
formulated in this way. In the M-theory and type IIA cases, the transverse
rotational invariance is manifest, but in the IIB case, one of the transverse
dimensions materializes in a completely different way from the other seven. The
full O(8) rotational symmetry then follows in a surprising way from the
electric-magnetic duality of supersymmetric Yang-Mills field theory.Comment: 7 pages, harvmac; references adde
Desarrollo de conductas antisociales y funcionamiento familiar en estudiantes de nivel secundaria de instituciones educativas públicas de Comas, 2019
La presente investigación titulada Desarrollo de conductas antisociales y funcionamiento
familiar en estudiantes de nivel secundario de instituciones educativas públicas de Comas,
2019, tuvo como objetivo, determinar la relación existente entre el desarrollo de conductas
antisociales y el funcionamiento familiar, a través de una muestra conformada por 343
estudiantes de ambos sexos, con edades oscilantes entre los 11 y 17 años de edad,
pertenecientes a 4 instituciones educativas públicas de nivel secundario, del distrito
mencionado. Se aplicaron instrumentos como el Cuestionario de Conducta Antisocial (CCA) y la Escala de Cohesión y Adaptabilidad Familiar (FACES III). Asimismo, la presente
investigación fue de tipo descriptivo y correlacional, de enfoque cuantitativo, de tipo básica
y de diseño no experimental, dentro de los resultados obtenidos, gracias a la prueba de
normalidad Shapiro - Wilk, se determinó que en la mayoría de los casos, nuestra muestra no
se ajustó a una distribución normal de los datos, motivo por el cual se trabajaron las
correlaciones, mediante el coeficiente de correlación Rho de Spearman, igualmente, los
resultados demostraron que el desarrollo de conductas antisociales se correlaciona de manera
inversa y significativa con el funcionamiento familiar, concluyendo que aquellos individuos
que presenten mayores índices para el desarrollo de conductas antisociales, se encontrarían
vivenciando un funcionamiento familiar que denote disfunción familiar
Spectropolarimetry of Supernovae
Overwhelming evidence has accumulated in recent years that supernova
explosions are intrinsically 3-dimensional phenomena with significant
departures from spherical symmetry. We review the evidence derived from
spectropolarimetry that has established several key results: virtually all
supernovae are significantly aspherical near maximum light; core-collapse
supernovae behave differently than thermonuclear (Type Ia) supernovae; the
asphericity of core-collapse supernovae is stronger in the inner layers showing
that the explosion process itself is strongly aspherical; core-collapse
supernovae tend to establish a preferred direction of asymmetry; the
asphericity is stronger in the outer layers of thermonuclear supernovae
providing constraints on the burning process. We emphasize the utility of the
Q/U plane as a diagnostic tool and revisit SN 1987A and SN 1993J in a
contemporary context. An axially-symmetric geometry can explain many basic
features of core-collapse supernovae, but significant departures from axial
symmetry are needed to explain most events. We introduce a spectropolarimetry
type to classify the range of behavior observed in polarized supernovae.
Understanding asymmetries in supernovae is important for phenomena as diverse
as the origins of gamma-ray bursts and the cosmological applications of Type Ia
supernovae in studies of the dark energy content of the universe.Comment: Draft of Annual Review article prior to final copy editing; 85 pages,
13 figures, 1 tabl
Reverse Biomimetic’ Synthesis of L-Arogenate and its Stabilized Analogues from L-Tyrosine
l-Arogenate (also known as l-pretyrosine) is a primary metabolite on a branch of the shikimate biosynthetic pathway to aromatic amino acids. It plays a key role in the synthesis of plant secondary metabolites including alkaloids and the phenylpropanoids that are the key to carbon fixation. Yet understanding the control of arogenate metabolism has been hampered by its extreme instability and the lack of a versatile synthetic route to arogenate and its analogues. We now report a practical synthesis of l-arogenate in seven steps from O-benzyl l-tyrosine methyl ester in an overall yield of 20%. The synthetic route also delivers the fungal metabolite spiroarogenate, as well as a range of stable saturated and substituted analogues of arogenate. The key step in the synthesis is a carboxylative dearomatization by intramolecular electrophilic capture of tyrosine's phenolic ring using an N-chloroformylimidazolidinone moiety, generating a versatile, functionalizable spirodienone intermediate
A new fractionation assay, based on the size of formaldehyde-crosslinked, mildly sheared chromatin, delineates the chromatin structure at promoter regions
To explore the higher order structure of transcribable chromatin in vivo, its local configuration was assessed through the accessibility of the chromatin to crosslinking with formaldehyde. The application of crosslinked and mildly sheared chromatin to sedimentation velocity centrifugation followed by size-fractionation of the DNA enabled us to biochemically distinguish between chromatin with heavily versus sparsely crosslinkable structures. The separated fractions showed a good correlation with gene expression profiles. Genes with poor crosslinking around the promoter region were actively transcribed, while transcripts were hardly detected from genes with extensive crosslinking in their promoter regions. For the inducible gene, Il2, the distribution of the promoter shifted in the gradient following T-cell receptor stimulation, consistent with a change in structure at this locus during activation. The kinetics of this switch preceded the chromatin change observed in a DNase I accessibility assay. Thus, this new chromatin fractionation technique has revealed a change in chromatin structure that has not been previously characterized
Comparing different models of aftershock rate decay: the role of catalog incompleteness in the first times after main shock
We evaluated the efficiency of various models in describing the time decay of
aftershock rate of 47 simple sequences occurred in California (37) from 1933 to
2004 and in Italy (10) from 1976 to 2004. We compared the models by the
corrected Akaike Information Criterion (AICc) and the Bayesian Information
Criterion (BIC), both based on the log-likelihood function but also including a
penalty term that takes into account the number of independent observations and
of free parameters of each model. We compared the performance of different
models by varying the starting time Ts and the minimum magnitude threshold Mmin
for each sequence. We found that Omori-type models including parameter c are
preferable to those not including it, only for short Ts and low Mmin while the
latters generally perform better than the formers for Ts longer than a few
hours and Mmin larger than the main shock magnitude Mm minus 3 units. This
clearly indicates that a value of parameter c different from zero does not
represent a general property of aftershock sequences in California and Italy
but it is very likely induced in most cases by catalog incompleteness in the
first times after the main shock. We also considered other models of aftershock
decay proposed in the literature: the Stretched Exponential Law in two forms
(including and not including a time shift) and the band Limited Power Law
(LPL). We found that such models perform worse than the Modified Omori Model
(MOM) and other Omori-type models for the large majority of sequences, although
for LPL, the relatively short duration of the analyzed sequences (one year)
might also contribute to its poor performance.Comment: 33 pages, 10 figures, 1 tabl
Alzheimer's Disease and Small Vessel Disease Differentially Affect White Matter Microstructure
OBJECTIVE: Alzheimer's disease (AD) and cerebral small vessel disease (cSVD), the two most common causes of dementia, are characterized by white matter (WM) alterations diverging from the physiological changes occurring in healthy aging. Diffusion tensor imaging (DTI) is a valuable tool to quantify WM integrity non-invasively and identify the determinants of such alterations. Here, we investigated main effects and interactions of AD pathology, APOE-ε4, cSVD, and cardiovascular risk on spatial patterns of WM alterations in non-demented older adults.METHODS: Within the prospective European Prevention of Alzheimer's Dementia study, we selected 606 participants (64.9 ± 7.2 years, 376 females) with baseline cerebrospinal fluid samples of amyloid β 1-42 and p-Tau 181 and MRI scans, including DTI scans. Longitudinal scans (mean follow-up time = 1.3 ± 0.5 years) were obtained in a subset (n = 223). WM integrity was assessed by extracting fractional anisotropy and mean diffusivity in relevant tracts. To identify the determinants of WM disruption, we performed a multimodel inference to identify the best linear mixed-effects model for each tract. RESULTS: AD pathology, APOE-ε4, cSVD burden, and cardiovascular risk were all associated with WM integrity within several tracts. While limbic tracts were mainly impacted by AD pathology and APOE-ε4, commissural, associative, and projection tract integrity was more related to cSVD burden and cardiovascular risk. AD pathology and cSVD did not show any significant interaction effect.INTERPRETATION: Our results suggest that AD pathology and cSVD exert independent and spatially different effects on WM microstructure, supporting the role of DTI in disease monitoring and suggesting independent targets for preventive medicine approaches.</p
Intranasal Delivery of MVA Vector Vaccine Induces Effective Pulmonary Immunity Against SARS-CoV-2 in Rodents
Antigen-specific tissue-resident memory T cells (Trms) and neutralizing IgA antibodies provide the most effective protection of the lungs from viral infections. To induce those essential components of lung immunity against SARS-CoV-2, we tested various immunization protocols involving intranasal delivery of a novel Modified Vaccinia virus Ankara (MVA)-SARS-2-spike vaccine candidate. We show that a single intranasal MVA-SARS-CoV-2-S application in mice strongly induced pulmonary spike-specific CD8+ T cells, albeit restricted production of neutralizing antibodies. In prime-boost protocols, intranasal booster vaccine delivery proved to be crucial for a massive expansion of systemic and lung tissue-resident spike-specific CD8+ T cells and the development of Th1 - but not Th2 - CD4+ T cells. Likewise, very high titers of IgG and IgA anti-spike antibodies were present in serum and broncho-alveolar lavages that possessed high virus neutralization capacities to all current SARS-CoV-2 variants of concern. Importantly, the MVA-SARS-2-spike vaccine applied in intramuscular priming and intranasal boosting treatment regimen completely protected hamsters from developing SARS-CoV-2 lung infection and pathology. Together, these results identify intramuscular priming followed by respiratory tract boosting with MVA-SARS-2-S as a promising approach for the induction of local, respiratory as well as systemic immune responses suited to protect from SARS-CoV-2 infections
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