563 research outputs found
Raising standards in American schools: the case of No Child Left Behind
In January 2002, President George W Bush signed into law what is arguably the most important piece of US educational legislation for the past 35 years. For the first time, Public Law 107-110 links high stakes testing with strict accountability measures designed to ensure that, at least in schools that receive government funding, no child is left behind. The appropriately named No Child Left Behind Act (NCLB) links government funding to strict improvement policies for America’s public schools. Much of what is undertaken in NCLB is praiseworthy, the Act is essentially equitable for it ensures that schools pay due regard to the progress of those sections of the school population who have traditionally done less well in school, in particular, students from economically disadvantaged homes, as well as those from ethnic minority backgrounds and those who have limited proficiency to speak English. However, this seemingly salutatory aspect of the Act is also the one that has raised the most objections. This paper describes the key features of this important piece of legislation before outlining why it is that a seemingly equitable Act has produced so much consternation in US education circles. Through an exploration of school level data for the state of New Jersey, the paper considers the extent to which these concerns have been justified during the early days of No Child Left Behind
Generalized Flows around Neutron Stars
In this chapter, we present a brief and non-exhaustive review of the
developments of theoretical models for accretion flows around neutron stars. A
somewhat chronological summary of crucial observations and modelling of timing
and spectral properties are given in sections 2 and 3. In section 4, we argue
why and how the Two-Component Advective Flow (TCAF) solution can be applied to
the cases of neutron stars when suitable modifications are made for the NSs. We
showcase some of our findings from Monte Carlo and Smoothed Particle
Hydrodynamic simulations which further strengthens the points raised in section
4. In summary, we remark on the possibility of future works using TCAF for both
weakly magnetic and magnetic Neutron Stars.Comment: 15 pages, 7 figures. arXiv admin note: text overlap with
arXiv:1901.0084
Phenoloxidase activity acts as a mosquito innate immune response against infection with semliki forest virus
Several components of the mosquito immune system including the RNA interference (RNAi), JAK/STAT, Toll and IMD pathways have previously been implicated in controlling arbovirus infections. In contrast, the role of the phenoloxidase (PO) cascade in mosquito antiviral immunity is unknown. Here we show that conditioned medium from the Aedes albopictus-derived U4.4 cell line contains a functional PO cascade, which is activated by the bacterium Escherichia coli and the arbovirus Semliki Forest virus (SFV) (Togaviridae; Alphavirus). Production of recombinant SFV expressing the PO cascade inhibitor Egf1.0 blocked PO activity in U4.4 cell- conditioned medium, which resulted in enhanced spread of SFV. Infection of adult female Aedes aegypti by feeding mosquitoes a bloodmeal containing Egf1.0-expressing SFV increased virus replication and mosquito mortality. Collectively, these results suggest the PO cascade of mosquitoes plays an important role in immune defence against arboviruses
Hyperaccretion after the Blandford-Znajek Process: a New Model for GRBs with X-Ray Flares Observed in Early Afterglows
We propose a three-stage model with Blandford-Znajek (BZ) and hyperaccretion
process to interpret the recent observations of early afterglows of Gamma-Ray
Bursts (GRBs). In the first stage, the prompt GRB is powered by a rotating
black hole (BH) invoking the BZ process. The second stage is a quiet stage, in
which the BZ process is shut off, and the accretion onto the BH is depressed by
the torque exerted by the magnetic coupling (MC) process. Part of the
rotational energy transported by the MC process from the BH is stored in the
disk as magnetic energy. In the third stage, the MC process is shut off when
the magnetic energy in the disk accumulates and triggers the magnetic
instability. At this moment, the hyperaccretion process may onset, and the jet
launched in this restarted central engine generates the observed X-ray flares.
This model can account for energies and timescales of GRBs with X-ray flares
observed in early afterglows.Comment: 10 pages, 2 figures. Accepted by ChJA
Energy Release During Disk Accretion onto a Rapidly Rotating Neutron Star
The energy release L_s on the surface of a neutron star (NS) with a weak
magnetic field and the energy release L_d in the surrounding accretion disk
depend on two independent parameters that determine its state (for example,
mass M and cyclic rotation frequency f) and is proportional to the accretion
rate. We derive simple approximation formulas illustrating the dependence of
the efficiency of energy release in an extended disk and in a boundary layer
near the NS surface on the frequency and sense of rotation for various NS
equations of state. Such formulas are obtained for the quadrupole moment of a
NS, for a gap between its surface and a marginally stable orbit, for the
rotation frequency in an equatorial Keplerian orbit and in the marginally
stable circular orbit, and for the rate of NS spinup via disk accretion. In the
case of NS and disk counterrotation, the energy release during accretion can
reach . The sense of NS rotation is a factor that strongly
affects the observed ratio of nuclear energy release during bursts to
gravitational energy release between bursts in X-ray bursters. The possible
existence of binary systems with NS and disk counterrotation in the Galaxy is
discussed. Based on the static criterion for stability, we present a method of
constructing the dependence of gravitational mass M on Kerr rotation parameter
j and on total baryon mass (rest mass) m for a rigidly rotating neutron star.
We show that all global NS characteristics can be expressed in terms of the
function M(j, m) and its derivatives.Comment: 42 pages, 12 figures, to appear in Astronomy Letters, 2000, v.26,
p.69
Energy Release on the Surface of a Rapidly Rotating Neutron Star during Disk Accretion: A Thermodynamic Approach
The total energy E of a star as a function of its angular momentum J and mass
M in the Newtonian theory: E = E(J, M) [in general relativity, the
gravitational mass M of a star as a function of its angular momentum J and rest
mass m, M = M(J, m)], is used to determine the remaining parameters (angular
velocity, equatorial radius, chemical potential, etc.) in the case of rigid
rotation. Expressions are derived for the energy release during accretion onto
a cool (with constant entropy), rapidly rotating neutron star (NS) in the
Newtonian theory and in general relativity. A separate analysis is performed
for the cases where the NS equatorial radius is larger and smaller than the
radius of the marginally stable orbit in the disk plane. An approximate formula
is proposed for the NS equatorial radius for an arbitrary equation of state,
which matches the exact one at J = 0.Comment: 12 pages, 0 figures (Astronomy Letters in press
Gravitational Waves from Gravitational Collapse
Gravitational wave emission from the gravitational collapse of massive stars
has been studied for more than three decades. Current state of the art
numerical investigations of collapse include those that use progenitors with
realistic angular momentum profiles, properly treat microphysics issues,
account for general relativity, and examine non--axisymmetric effects in three
dimensions. Such simulations predict that gravitational waves from various
phenomena associated with gravitational collapse could be detectable with
advanced ground--based and future space--based interferometric observatories.Comment: 68 pages including 13 figures; revised version accepted for
publication in Living Reviews in Relativity (http://www.livingreviews.org
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
Accretion of helium and metal-rich gas onto neutron stars and black holes at high luminosities
Ultraluminous X-ray sources fed by Wolf-Rayet star winds and X-ray bursters
in ultracompact binaries with He or C white dwarfs have accretion disks, whose
properties may significantly differ from those of pure H alpha-accretion disks.
We have therefore included the dependence on charge number Z and mean molecular
weights mu_{e/I} into the Shakura and Sunyaev (1973) scaling relations for the
key parameters of the disk. Furthermore, we also consider the case of the
pseudo-Newtonian potential of Paczynsky and Wiita (1980). These scaling
relations might become useful, e.g., when estimating the illumination
efficiency of the external parts of the disk. We also address the changes in
the structure of the boundary (spreading) layer on the surface of neutron
stars, occurring in the case of H depleted accretion disks.Comment: 10 page
The origin and early evolution of vascular plant shoots and leaves
The morphology of plant fossils from the Rhynie chert has generated longstanding questions about vascular plant shoot and leaf evolution, for instance, which morphologies were ancestral within land plants, when did vascular plants first arise and did leaves have multiple evolutionary origins? Recent advances combining insights from molecular phylogeny, palaeobotany and evo-devo research address these questions and suggest the sequence of morphological innovation during vascular plant shoot and leaf evolution. The evidence pinpoints testable developmental and genetic hypotheses relating to the origin of branching and indeterminate shoot architectures prior to the evolution of leaves, and demonstrates underestimation of polyphyly in the evolution of leaves from branching forms in ‘telome theory’ hypotheses of leaf evolution. This review discusses fossil, developmental and genetic evidence relating to the evolution of vascular plant shoots and leaves in a phylogenetic framework.
This article is part of the themed issue ‘The Rhynie chert: our earliest terrestrial ecosystem revisited’
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