3,880 research outputs found
Visualising apoptosis in live zebrafish using fluorescence lifetime imaging with optical projection tomography to map FRET biosensor activity in space and time
Fluorescence lifetime imaging (FLIM) combined with optical projection tomography (OPT) has the potential to map Förster resonant energy transfer (FRET) readouts in space and time in intact transparent or near transparent live organisms such as zebrafish larvae, thereby providing a means to visualise cell signalling processes in their physiological context. Here the first application of FLIM OPT to read out biological function in live transgenic zebrafish larvae using a genetically expressed FRET biosensor is reported. Apoptosis, or programmed cell death, is mapped in 3-D by imaging the activity of a FRET biosensor that is cleaved by Caspase 3, which is a key effector of apoptosis. Although apoptosis is a naturally occurring process during development, it can also be triggered in a variety of ways, including through gamma irradiation. FLIM OPT is shown here to enable apoptosis to be monitored over time, in live zebrafish larvae via changes in Caspase 3 activation following gamma irradiation at 24 hours post fertilisation. Significant apoptosis was observed at 3.5 hours post irradiation, predominantly in the head region
Geometric Parameterization of Absorption in Heavy Ion Collisions
We calculate the survival probability of particles in various
colliding systems using a Glauber model. An analysis of recent data has
reported a -nucleon breakup cross section of 6.20.7 mb derived
from an exponential fit to the ratio of to Drell-Yan yields as a
function of a simple, linearly-averaged mean path length through the nuclear
medium. Our calculations indicate that, due to the nature of the calculation,
this approach yields an apparent breakup cross section which is systematically
lower than the actual value.Comment: LaTex, 7 pages, 2 figure
MiFID II Unbundling and Sell Side Analyst Research
We examine the effect of MiFID II, which mandated the unbundling and separate pricing of analyst research in Europe beginning in 2018. We find that the requirements of MiFID II were associated with a reduction in analyst following for European firms relative to US firms, with decreases in coverage greatest for firms that were larger, older and less volatile, and had greater coverage and more accurate consensus forecasts. Remaining analysts follow fewer firms and issue fewer forecasts, consistent with increased focus, and appear to increase their efforts on the firms they continue to cover. In particular, forecasts become more accurate, are more likely to be disaggregated and include recommendations, and are accompanied by larger stock price reactions. Consistent with increased effort to curry favor with management, analysts issue more optimistic recommendations and beatable earnings forecasts. While individual forecasts are more informative, the overall information environment for the average firm tends to deteriorate, with less aggregate information conveyed by analyst forecasts, a greater proportion of information delayed to earnings announcements and higher average bid-ask spreads. Taken as a whole, results are consistent with a reduction in analyst following mitigated by an increase in focus and effort by remaining analysts, but with an overall negative effect on the information environment
Modeling seismic wave propagation and amplification in 1D/2D/3D linear and nonlinear unbounded media
To analyze seismic wave propagation in geological structures, it is possible
to consider various numerical approaches: the finite difference method, the
spectral element method, the boundary element method, the finite element
method, the finite volume method, etc. All these methods have various
advantages and drawbacks. The amplification of seismic waves in surface soil
layers is mainly due to the velocity contrast between these layers and,
possibly, to topographic effects around crests and hills. The influence of the
geometry of alluvial basins on the amplification process is also know to be
large. Nevertheless, strong heterogeneities and complex geometries are not easy
to take into account with all numerical methods. 2D/3D models are needed in
many situations and the efficiency/accuracy of the numerical methods in such
cases is in question. Furthermore, the radiation conditions at infinity are not
easy to handle with finite differences or finite/spectral elements whereas it
is explicitely accounted in the Boundary Element Method. Various absorbing
layer methods (e.g. F-PML, M-PML) were recently proposed to attenuate the
spurious wave reflections especially in some difficult cases such as shallow
numerical models or grazing incidences. Finally, strong earthquakes involve
nonlinear effects in surficial soil layers. To model strong ground motion, it
is thus necessary to consider the nonlinear dynamic behaviour of soils and
simultaneously investigate seismic wave propagation in complex 2D/3D geological
structures! Recent advances in numerical formulations and constitutive models
in such complex situations are presented and discussed in this paper. A crucial
issue is the availability of the field/laboratory data to feed and validate
such models.Comment: of International Journal Geomechanics (2010) 1-1
Bcar1/p130Cas is essential for ventricular development and neural crest cell remodelling of the cardiac outflow tract.
AIM: The adapter protein p130Cas, encoded by the Bcar1 gene, is a key regulator of cell movement, adhesion, and cell cycle control in diverse cell types. Bcar1 constitutive knockout mice are embryonic lethal by embryonic days (E) 11.5-12.5, but the role of Bcar1 in embryonic development remains unclear. Here, we investigated the role of Bcar1 specifically in cardiovascular development and defined the cellular and molecular mechanisms disrupted following targeted Bcar1 deletions. METHODS AND RESULTS: We crossed Bcar1 floxed mice with Cre transgenic lines allowing for cell-specific knockout either in smooth muscle and early cardiac tissues (SM22-Cre), mature smooth muscle cells (smMHC-Cre), endothelial cells (Tie2-Cre), second heart field cells (Mef2c-Cre), or neural crest cells (NCC) (Pax3-Cre) and characterised these conditional knock outs using a combination of histological and molecular biology techniques.Conditional knockout of Bcar1 in SM22-expressing smooth muscle cells and cardiac tissues (Bcar1SM22KO) was embryonically lethal from E14.5-15.5 due to severe cardiovascular defects, including abnormal ventricular development and failure of outflow tract (OFT) septation leading to a single outflow vessel reminiscent of persistent truncus arteriosus. SM22-restricted loss of Bcar1 was associated with failure of OFT cushion cells to undergo differentiation to septal mesenchymal cells positive for SMC-specific α-actin, and disrupted expression of proteins and transcription factors involved in epithelial-to-mesenchymal transformation (EMT). Furthermore, knockout of Bcar1 specifically in NCC (Bcar1PAX3KO) recapitulated part of the OFT septation and aortic sac defects seen in the Bcar1SM22KO mutants, indicating a cell-specific requirement for Bcar1 in NCC essential for OFT septation. In contrast, conditional knockouts of Bcar1 in differentiated smooth muscle, endothelial cells, and second heart field cells survived to term and were phenotypically normal at birth and post-natally. CONCLUSIONS: Our work reveals a cell-specific requirement for Bcar1 in NCC, early myogenic and cardiac cells, essential for OFT septation, myocardialisation and EMT/cell cycle regulation and differentiation to myogenic lineages. TRANSLATIONAL PERSPECTIVE: The molecular pathways coordinating cardiogenesis and the remodelling of the OFT are complex, and dysregulation of these pathways causes human heart defects. Our findings highlight a specific requirement for Bcar1 essential for cardiogenesis. Furthermore, the failure of OFT septation in Bcar1SM22KO mice resembles persistent truncus arteriosus (PTA), a feature of several human congenital heart diseases, including DiGeorge Syndrome. Our findings have implications for the mechanisms underlying the pathogenesis of congenital heart disease, and suggest that mice with conditional Bcar1 deletions may be useful models for dissecting mechanisms involved in the pathogenesis of human heart defects
Unraveling the ecological processes modulating the population structure of Escherichia coli in a highly polluted urban stream network
Escherichia coli dynamics in urban watersheds are affected by a complex balance among external inputs, niche modulation and genetic variability. To explore the ecological processes influencing E. coli spatial patterns, we analyzed its abundance and phylogenetic structure in water samples from a stream network with heterogeneous urban infrastructure and environmental conditions. Our results showed that environmental and infrastructure variables, such as macrophyte coverage, DIN and sewerage density, mostly explained E. coli abundance. Moreover, main generalist phylogroups A and B1 were found in high proportion, which, together with an observed negative relationship between E. coli abundance and phylogroup diversity, suggests that their dominance might be due to competitive exclusion. Lower frequency phylogroups were associated with sites of higher ecological disturbance, mainly involving simplified habitats, higher drainage infrastructure and septic tank density. In addition to the strong negative relationship between phylogroup diversity and dominance, the occurrence of these phylogroups would be associated with increased facilitated dispersal. Nutrients also contributed to explaining phylogroup distribution. Our study proposes the differential contribution of distinct ecological processes to the patterns of E. coli in an urban watershed, which is useful for the monitoring and management of fecal pollution.Fil: Saraceno, MartĂn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de EcologĂa, GenĂ©tica y EvoluciĂłn de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de EcologĂa, GenĂ©tica y EvoluciĂłn de Buenos Aires; ArgentinaFil: GĂłmez Lugo, Sebastian. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de EcologĂa, GenĂ©tica y EvoluciĂłn; ArgentinaFil: Ortiz, NicolĂĄs. Provincia de Mendoza. Ministerio de Infraestructura y Vivienda. Secretaria de Obras Publicas. Instituto Nacional del Agua; ArgentinaFil: GĂłmez, BĂĄrbara M.. Provincia de Mendoza. Ministerio de Infraestructura y Vivienda. Secretaria de Obras Publicas. Instituto Nacional del Agua; ArgentinaFil: Sabio y GarcĂa, Carmen Alejandra. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de EcologĂa, GenĂ©tica y EvoluciĂłn; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Frankel, NicolĂĄs. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FisiologĂa, BiologĂa Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FisiologĂa, BiologĂa Molecular y Neurociencias; ArgentinaFil: Graziano, MartĂn. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de EcologĂa, GenĂ©tica y EvoluciĂłn de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de EcologĂa, GenĂ©tica y EvoluciĂłn de Buenos Aires; Argentin
Effect of pulsed magnetic field pre-treatment of AISI 52100 steel on the coefficient of sliding friction and wear in pin-on-disk tests
Disc specimens manufactured from commercial bearing rollers (AISI 52100 steel, 62â63 HRC) in initial state and after pre-treatment by pulsed magnetic field (PMF) with a magnetic field strength of 1â7 MA/m were tested with sunflower oil using pin-on-disk apparatus. According to the obtained results the treatment causes a reduction in the coefficient of friction and wear. To explain the results, nano- and microhardness tests as well as optical and atomic force microscopy were used. Reasons of the effect of PMF on the friction and wear were discussed.Peer reviewe
Subpicosecond carrier lifetime in GaAs grown by molecular beam epitaxy at low temperatures
Epitaxial GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures is observed to have a significantly shorter carrier lifetime than GaAs grown at normal substrate temperatures. Using femtosecond timeâresolvedâreflectance techniques, a subâpicosecond (<0.4 ps) carrier lifetime has been measured for GaAs grown by MBE at âŒ200°C and annealed at 600â°C. With the same material as a photoconductive switch we have measured electrical pulses with a fullâwidth at halfâmaximum of 0.6 ps using the technique of electroâoptic sampling. Good responsivity for a photoconductive switch is observed, corresponding to a mobility of the photoexcited carriers of âŒ120â150 cm2/Vâs. GaAs grown by MBE at 200â°C and annealed at 600â°C is also semiâinsulating, which results in a low dark current in the switch application. The combination of fast recombination lifetime, high carrier mobility, and high resistivity makes this material ideal for a number of subpicosecond photoconductive applications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71318/2/APPLAB-59-25-3276-1.pd
Wigner's little group and Berry's phase for massless particles
The ``little group'' for massless particles (namely, the Lorentz
transformations that leave a null vector invariant) is isomorphic to
the Euclidean group E2: translations and rotations in a plane. We show how to
obtain explicitly the rotation angle of E2 as a function of and we
relate that angle to Berry's topological phase. Some particles admit both signs
of helicity, and it is then possible to define a reduced density matrix for
their polarization. However, that density matrix is physically meaningless,
because it has no transformation law under the Lorentz group, even under
ordinary rotations.Comment: 4 pages revte
Erratum: ââPicosecond largeâsignal switching characteristics of a pseudomorphic AlGaAs/InGaAs modulationâdoped fieldâeffect transistorââ [Appl. Phys. Lett. 61, 1187 (1992)]
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70138/2/APPLAB-61-26-3194-1.pd
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