On a problem of A. Weil

A topological invariant of the geodesic laminations on a modular surface is constructed. The invariant has a continuous part (the tail of a continued fraction) and a combinatorial part (the singularity data). It is shown, that the invariant is complete, i.e. the geodesic lamination can be recovered from the invariant. The continuous part of the invariant has geometric meaning of a slope of lamination on the surface.Comment: to appear Beitr\"age zur Algebra und Geometri

Role of PknB Kinase in Antibiotic Resistance and Virulence in Community-Acquired Methicillin-Resistant Staphylococcus aureus Strain USA300

The regulation of cellular processes by eukaryote-like serine/threonine kinases is widespread in bacteria. In the last 2 years, several studies have examined the role of serine/threonine kinases in Staphylococcus aureus on cell wall metabolism, autolysis, and virulence, mostly in S. aureus laboratory isolates in the 8325-4 lineage. In this study, we showed that the pknB gene (also called stk1) of methicillin-resistant S. aureus (MRSA) strain COL and the community-acquired MRSA (CA-MRSA) strain USA300 is involved in cell wall metabolism, with the pknB mutant exhibiting enhanced sensitivity to β-lactam antibiotics but not to other classes of antibiotics, including aminoglycosides, ciprofloxacin, bactrim, and other types of cell wall-active agents (e.g., vancomycin and bacitracin). Additionally, the pknB mutant of USA300 was found to be more resistant to Triton X-100-induced autolysis and also to lysis by lysostaphin. We also showed that pknB is a positive regulator of sigB activity, resulting in compromise in its response to heat and oxidative stresses. In association with reduced sigB activity, the expression levels of RNAII and RNAIII of agr and the downstream effector hla are upregulated while spa expression is downmodulated in the pknB mutant compared to the level in the parent. Consistent with an enhanced agr response in vitro, virulence studies of the pknB mutant of USA300 in a murine cutaneous model of infection showed that the mutant was more virulent than the parental strain. Collectively, our results have linked the pknB gene in CA-MRSA to antibiotic resistance, sigB activity, and virulence and have highlighted important differences in pknB phenotypes (virulence and sigB activity) between laboratory isolates and the prototypic CA-MRSA strain USA300

Estado y mercado en el financiamiento de la educación superior

Se revisa en este artículo, desde una perspectiva histórica, los tres modelos de financiamiento de la educación superior vigentes en las universidades públicas latinoamericanas: la asignación de fondos del Estado, la resultante del patrimonio propio o de donaciones, y la obtención de rentas por venta de servicios. Según el autor, cada uno de estos modelos corresponde a un modo de funcionamiento de las instituciones: el burocrático, el corporativo y el de mercado, respectivamente. En el primero de ellos, el financiamiento de tipo burocrático, los gobiernos deciden de forma centralizada cuántos recursos serán destinados a las universidades, y, dentro de ellas, cuánto a cada sector y tipo de actividad. En el modelo corporativo, poco común en América Latina, la distribución de recursos entre los diferentes usuarios y sectores es realizada por la propia institución, a través de sus órganos colegiados y administrativos, que establecen prioridades y líneas de acción. Finalmente, el financiamiento de mercado depende de la capacidad de las instituciones de obtener recursos propios, cuya forma más tradicional en América Latina es el cobro por matrícula, y las formas más modernas van desde la venta de servicios hasta la lucha por recursos públicos a través de mecanismos competitivos. El análisis de los tres modelos muestra que ninguno de ellos puede funcionar aisladamente: la coordinación burocrática no garantiza la autonomía de los sistemas universitarios, el mantenimiento de su calidad y la eficiencia en el uso de los recursos; la coordinación corporativa sucumbe con facilidad a la oligarquización y al corporativismo, y no consigue adaptarse a la diferenciación y masificación de la enseñanza superior; la coordinación de mercado pone en riesgo el desempeño de actividades de largo plazo y de utilidad práctica poco clara, y puede destruir los mecanismos de autoregulación y autonomía de las instituciones. Por otro lado, cierta organización burocrática es necesaria, ya que los gobiernos deben participar en la conducción de la educación superior en tanto ésta debe responder al interés general; los mecanismos corporativos son esenciales para el buen desempeño de actividades que dependen de la iniciativa, de la creatividad y del mantenimiento de tradiciones intelectuales y culturales; la operación del mercado en cierta medida es esencial para controlar los efectos nocivos del corporativismo, de la oligarquización y de la burocratización estatal. La conclusión es bastante simple: los tres tipos de financiamiento y coordinación académicas son «tipos puros», y sólo pueden existir de manera combinada. Según el autor, el buen desempeño de un sistema de educación superior depende del tipo de combinación que se consiga establecer

L’évolution des enfants difficiles

Dans cet article, les auteurs relatent une recherche faite, dans le cadre du projet Concordia Longitudinal Risk Project, sur l'ajustement des enfants socialement atypiques durant l'adolescence. Plus précisément, ils tentent de répondre à la question suivante: Quels comportements de l'enfant et quelles tangentes de son développement mènent à des problèmes psychologiques majeurs à l'adolescence et à l'âge adulte? Après une analyse complexe de divers facteurs, leurs résultats indiquent que les enfants perçus comme agressifs, repliés sur eux-mêmes ou souvent agressifs et repliés sur eux-mêmes par leur camarades, sont susceptibles d'avoir des problèmes à l'adolescence. Ils explicitent ensuite selon ces trois groupes les difficultés de chacun.In this article, the authors discuss a study carried out during a Concordia Longitudinal Risk Project that deals with the adjustment of socially atypical children in their adolescent years. More precisely, they try to answer the following question : What child behaviors and which tangents of their development lead to major psychological problems as an adolescent and as an adult? After a complex analysis of various factors, their results indicate that children perceived as aggressive, keeping to themselves or often aggressive and keeping to themselves because of peer pressure, are liable to have problems in their adolescent years. The authors then elaborate on the difficulties experienced by each of these three groups

Response of VIRGO detectors to pre-big-bang gravitons

The sensitivity achievable by a pair of VIRGO detectors to stochastic and isotropic gravitational wave backgrounds produced in pre-big-bang models is discussed in view of the development of a second VIRGO interferometer. We describe a semi-analytical technique allowing to compute the signal-to-noise ratio for (monotonic or non-monotonic) logarithmic energy spectra of relic gravitons of arbitrary slope. We apply our results to the case of two correlated and coaligned VIRGO detectors and we compute their achievable sensitivities. We perform our calculations both for the usual case of minimal string cosmological scenario and in the case of a non-minimal scenario where a long dilaton dominated phase is present prior to the onset of the ordinary radiation dominated phase. In this framework, we investigate possible improvements of the achievable sensitivities by selective reduction of the thermal contributions (pendulum and pendulum's internal modes) to the noise power spectra of the detectors. Since a reduction of the shot noise does not increase significantly the expected sensitivity of a VIRGO pair (in spite of the relative spatial location of the two detectors) our findings support the experimental efforts directed towards a substantial reduction of thermal noise.Comment: 23 pages in Latex styl

Exploring multiple steady states in Earth's long-term carbon cycle

The long-term carbon cycle regulates Earth's climate and atmospheric CO2 levels over multimillion-year timescales, but it is not clear that this system has a single steady state for a given input rate of CO2. In this paper we explore the possibility for multiple steady states in the long-term climate system. Using a simple carbon cycle box model, we show that the location of precipitation bands around the tropics and high mid-latitudes, coupled with the response of the terrestrial biosphere to local surface temperature, can result in system bi-stability. Here, maximum CO2 drawdown can occur when either the tropics or high mid-latitudes are at the photosynthetic optimum temperature of around 25°C, and a period of instability can exist between these states. We suggest that this dynamic has influenced climate variations over Phanerozoic time, and that higher steady state surface temperatures may be easier to reach than is commonly demonstrated in simple ‘GEOCARB style’ carbon cycle models

Insecurity for compact surfaces of positive genus

A pair of points in a riemannian manifold $M$ is secure if the geodesics between the points can be blocked by a finite number of point obstacles; otherwise the pair of points is insecure. A manifold is secure if all pairs of points in $M$ are secure. A manifold is insecure if there exists an insecure point pair, and totally insecure if all point pairs are insecure. Compact, flat manifolds are secure. A standing conjecture says that these are the only secure, compact riemannian manifolds. We prove this for surfaces of genus greater than zero. We also prove that a closed surface of genus greater than one with any riemannian metric and a closed surface of genus one with generic metric are totally insecure.Comment: 37 pages, 11 figure

XCC: An X-ray FEL-based γγ\gamma\gamma Compton Collider Higgs Factory

This report describes the conceptual design of a $\gamma\gamma$ Higgs factory in which 62.8 GeV electron beams collide with 1 keV X-ray free electron laser (XFEL) beams to produce colliding beams of 62.5 GeV photons. The Higgs boson production rate is 80,000 Higgs bosons per 10$^7$ second year, roughly the same as the ILC Higgs rate at $\sqrt{s}$=250 GeV. The electron accelerator is based on cold copper distributed coupling (C$^3$) accelerator technology. Unlike the center-of-mass energy spectra of previous optical wavelength $\gamma\gamma$ collider designs, the sharply peaked $\gamma\gamma$ center-of-mass energy spectrum of XCC produces model independent Higgs coupling measurements with precision on par with $e^+e^-$ colliders. For the triple Higgs coupling measurement, the XCC center-of-mass energy can be upgraded to 380 GeV, where the cross section for $\gamma\gamma\rightarrow HH$ is twice that of $e^+e^- \rightarrow ZHH$ at $\sqrt{s}$=500 GeV. Design challenges are discussed, along with the R\&D to address them, including demonstrators.Comment: 30 pages, 21 figures, submitted to JINST. arXiv admin note: substantial text overlap with arXiv:2203.0848