1,011 research outputs found
Big Changes in How Students are Tested
For the past decade, school accountability has relied on tests for which the essential format has remained unchanged. Educators are familiar with the yearly testing routine: schools are given curriculum frameworks, teachers use the frameworks to guide instruction, students take one big test at yearâs end which relies heavily upon multiple-choice bubble items, and then school leaders wait anxiously to find out whether enough of their students scored at or above proficiency to meet state standards. All this will change with the adoption of Common Core standards. Testing and accountability arenât going away. Instead, they are developing and expanding in ways that aim to address many of the present shortcomings of state testing routines. Most importantly, these new tests will be computer-based. As such, they will potentially shorten testing time, increase testsâ precision, and provide immediate feedback to students and teachers
Geometric phases for neutral and charged particles in a time-dependent magnetic field
It is well known that any cyclic solution of a spin 1/2 neutral particle
moving in an arbitrary magnetic field has a nonadiabatic geometric phase
proportional to the solid angle subtended by the trace of the spin. For neutral
particles with higher spin, this is true for cyclic solutions with special
initial conditions. For more general cyclic solutions, however, this does not
hold. As an example, we consider the most general solutions of such particles
moving in a rotating magnetic field. If the parameters of the system are
appropriately chosen, all solutions are cyclic. The nonadiabatic geometric
phase and the solid angle are both calculated explicitly. It turns out that the
nonadiabatic geometric phase contains an extra term in addition to the one
proportional to the solid angle. The extra term vanishes automatically for spin
1/2. For higher spin, however, it depends on the initial condition. We also
consider the valence electron of an alkaline atom. For cyclic solutions with
special initial conditions in an arbitrary strong magnetic field, we prove that
the nonadiabatic geometric phase is a linear combination of the two solid
angles subtended by the traces of the orbit and spin angular momenta. For more
general cyclic solutions in a strong rotating magnetic field, the nonadiabatic
geometric phase also contains extra terms in addition to the linear
combination.Comment: revtex, 18 pages, no figur
Keck/Palomar Cosmic Web Imagers (KCWI/PCWI) Reveal an Enormous Ly Nebula in an Extremely Overdense QSO Pair Field at
Enormous Ly nebulae (ELANe) represent the extrema of Ly
nebulosities. They have detected extents of kpc in Ly and
Ly luminosities erg s. The ELAN population is an
ideal laboratory to study the interactions between galaxies and the
intergalactic/circumgalactic medium (IGM/CGM) given their brightness and sizes.
The current sample size of ELANe is still very small, and the few
ELANe discovered to date are all associated with local overdensities of active
galactic nuclei (AGNs). Inspired by these results, we have initiated a survey
of ELANe associated with QSO pairs using the Palomar and Keck Cosmic Web
Imagers (PCWI/KCWI). In this letter, we present our first result: the discovery
of ELAN0101+0201 associated with a QSO pair at . Our PCWI discovery
data shows that, above a 2- surface brightness of
\sbunit, the end-to-end size of ELAN0101+0201 is kpc. We have
conducted follow-up observations using KCWI, resolving multiple Ly
emitting sources within the rectangular field-of-view of
projected kpc, and obtaining their emission line profiles at high
signal-to-noise ratios. Combining both KCWI and PCWI, our observations confirm
that ELAN0101+0201 resides in an extremely overdense environment. Our
observations further support that a large amount of cool (K) gas
could exist in massive halos (MM) at .
Future observations on a larger sample of similar systems will provide
statistics of how cool gas is distributed in massive overdensities at
high-redshift and strongly constrain the evolution of the intracluster medium
(ICM).Comment: Submitted to Astrophysical Journal Letter, 9 pages, 4 figures,
Comments Welcom
Efficient hole abstraction for highly selective oxidative coupling of methane by Au-sputtered TiO2 photocatalysts
Photocatalytic oxidative coupling of methane (OCM) produces C2 molecules that can be used as building blocks for synthesis of fuels and chemicals. However, the yield rate and the selectivity of C2 products are still moderate due to the stable nature of methane molecules. Here we develop a Au nanocluster-loaded TiO2 photocatalyst by a sputtering approach, achieving a high methane conversion rate of 1.1âmmolâhâ1, C2 selectivity of ~90% and apparent quantum efficiency of 10.3â±â0.6%. The high C2/C2+ yield rate is on the same order of magnitude as the benchmark thermal catalysts in OCM processes operated at high temperature (>680â°C). Au nanoparticles are shown to prolong TiO2 photoelectron lifetimes by a factor of 66 for O2 reduction, together with Au acting as a hole acceptor and catalytic centre to promote methane adsorption, CâH activation and CâC coupling. This work underscores the importance of multifunctional co-catalysts and mechanistic understanding to improve photocatalytic OCM
Adding Value to JWST Spectra and Photometry: Stellar Population and Star Formation Properties of Spectroscopically Confirmed JADES and CEERS Galaxies at
In this paper, we discuss measurements of the stellar population and star
forming properties for 43 spectroscopically confirmed publicly available
high-redshift JWST galaxies in the JADES and CEERS observational
programs. We carry out a thorough study investigating the relationship between
spectroscopic features and photometrically derived ones, including from
spectral energy distribution (SED) fitting of models, as well as morphological
and structural properties. We find that the star formation rates (SFRs)
measured from H line emission are higher than those estimated from
Bayesian SED fitting and UV luminosity, with ratios SFR/ SFR
ranging from 2~13. This is a sign that the star formation history is
consistently rising given the timescales of H vs UV star formation
probes. In addition, we investigate how well equivalent widths (EWs) of
H 4861, [O III] 4959, and [O III] 5007 can be
measured from photometry, finding that on average the EW derived from
photometric excesses in filters is 30% smaller than the direct spectroscopic
measurement. We also discover that a stack of the line emitting galaxies shows
a distinct morphology after subtracting imaging that contains only the
continuum. This gives us a first view of the line or ionized gas emission from
galaxies, demonstrating that this material has a similar distribution,
statistically, as the continuum. We also compare the derived SFRs and stellar
masses for both parametric and non-parametric star formation histories, where
we find that 35% of our sample formed at least 30% of their stellar mass in
recent (< 10 Myr) starburst events.Comment: 17 Pages, 13 Figures, 4 Tables, submitted to MNRA
Multiple Lines of Evidence from Mitochondrial Genomes Resolve Phylogenetic Relationships of Parasitic Wasps in Braconidae
The rapid increase in the number of mitochondrial genomes in public databases provides opportunities for insect phylogenetic studies; but it also provides challenges because of gene rearrangements and variable substitution rates among both lineages and sites. Typically, phylogenetic studies use mitochondrial sequence data but exclude other features of the mitochondrial genome from analyses. Here, we undertook large-scale sequencing of mitochondrial genomes from a worldwide collection of specimens belonging to Braconidae, one of the largest families of Metazoa. The strand-asymmetry of base composition in the mitochondrial genomes of braconids is reversed, providing evidence for monophyly of the Braconidae. We have reconstructed a backbone phylogeny of the major lineages of Braconidae from gene order of the mitochondrial genomes. Standard phylogenetic analyses of DNA sequences provided strong support for both Cyclostomes and Noncyclostomes. Four subfamily complexes, that is, helconoid, euphoroid, sigalphoid, and microgastroid, within the Noncyclostomes were reconstructed robustly, the first three of which formed a monophyletic group sister to the last one. Aphidiinae was recovered as a lineage sister to other groups of Cyclostomes, while the Ichneutinae was recovered as paraphyletic. Separate analyses of the subdivided groups showed congruent relationships, employing different matrices and methods, for the internal nodes of the Cyclostomes and the microgastroid complex of subfamilies. This research, using multiple lines of evidence from mitochondrial genomes, illustrates multiple uses of mitochondrial genomes for phylogenetic inference in Braconidae
Effects of dimers on cooperation in the spatial prisoner's dilemma game
We investigate the evolutionary prisoner's dilemma game in structured
populations by introducing dimers, which are defined as that two players in
each dimer always hold a same strategy. We find that influences of dimers on
cooperation depend on the type of dimers and the population structure. For
those dimers in which players interact with each other, the cooperation level
increases with the number of dimers though the cooperation improvement level
depends on the type of network structures. On the other hand, the dimers, in
which there are not mutual interactions, will not do any good to the
cooperation level in a single community, but interestingly, will improve the
cooperation level in a population with two communities. We explore the
relationship between dimers and self-interactions and find that the effects of
dimers are similar to that of self-interactions. Also, we find that the dimers,
which are established over two communities in a multi-community network, act as
one type of interaction through which information between communities is
communicated by the requirement that two players in a dimer hold a same
strategy.Comment: 12 pages and 3 figure
Time evolution, cyclic solutions and geometric phases for general spin in an arbitrarily varying magnetic field
A neutral particle with general spin and magnetic moment moving in an
arbitrarily varying magnetic field is studied. The time evolution operator for
the Schr\"odinger equation can be obtained if one can find a unit vector that
satisfies the equation obeyed by the mean of the spin operator. There exist at
least cyclic solutions in any time interval. Some particular time
interval may exist in which all solutions are cyclic. The nonadiabatic
geometric phase for cyclic solutions generally contains extra terms in addition
to the familiar one that is proportional to the solid angle subtended by the
closed trace of the spin vector.Comment: revtex4, 8 pages, no figur
Enormous lithium isotopic variations of abyssal peridotites reveal fast cooling and Melt/Fluid-rock interactions
Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(9),(2020): e2020JB020393, doi:10.1029/2020JB020393.Fast diffusing Li isotopes provide important insights into the ârecentâ transient events or processes for both modern and ancient times, but questions remain concerning the large Li isotopic variations of mantle peridotites, which greatly hampers their usage as a geochemical tracer. This study investigates in situ Li content and isotopic profiles of the constituent minerals of abyssal peridotites from the Gakkel Ridge and Southwest Indian Ridge. The complicated and large variations of Li isotopic profiles in Clinopyroxene (Cpx) and Orthopyroxene (Opx) indicate Li isotopic disequilibrium at millimeter scale. The negative correlations of a wide range of Li contents (0.5 to 6.5 ppm) and ÎŽ7Li values (â10 to +20â°) of olivine, Opx and Cpx grains/relicts, trace element zoning of Cpx, the occurrence of plagioclase, olivine serpentinization along cracks, together with numerical modeling demonstrate the observed Li characteristics to be a manifestation of highâtemperature mineralâmelt Li diffusion during melt impregnation overprinted by lowâtemperature mineralâfluid Li diffusion during dissolution and serpentinization. The preservation of the Li isotopic diffusion profiles requires rapid cooling of 0.3â5°C/year after finalâstage melt impregnation at the Moho boundary, which is consistent with the low temperature at very slow spreadin g ridges caused by conductive cooling. Compared with the wellâstudied meltârock interaction process, our study indicates that lowâtemperature fluidârock interaction can induce Li diffusion even in the visibly unaltered mineral relicts of partially altered rocks.This study was financially supported by the National Science Foundation of China (grant no. 41872058) and the U.S. National Science Foundation grant.2021-03-0
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