4,993 research outputs found
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 artÃculo, 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
lÃneas 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 matrÃcula, 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 autonomÃa 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 autonomÃa
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
Insecurity for compact surfaces of positive genus
A pair of points in a riemannian manifold 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 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
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
XCC: An X-ray FEL-based Compton Collider Higgs Factory
This report describes the conceptual design of a 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 second year, roughly the same
as the ILC Higgs rate at =250 GeV. The electron accelerator is based
on cold copper distributed coupling (C) accelerator technology. Unlike the
center-of-mass energy spectra of previous optical wavelength
collider designs, the sharply peaked center-of-mass energy
spectrum of XCC produces model independent Higgs coupling measurements with
precision on par with colliders. For the triple Higgs coupling
measurement, the XCC center-of-mass energy can be upgraded to 380 GeV, where
the cross section for is twice that of at =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
Assessing NARCCAP climate model effects using spatial confidence regions
We assess similarities and differences between model effects for the North American Regional
Climate Change Assessment Program (NARCCAP) climate models using
varying classes of linear regression models. Specifically, we
consider how the average temperature effect differs for the various
global and regional climate model combinations, including assessment
of possible interaction between the effects of global and regional
climate models. We use both pointwise and simultaneous inference
procedures to identify regions where global and regional climate model effects differ. We also show
conclusively that results from pointwise inference are misleading, and
that accounting for multiple comparisons is important for making
proper inference
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