496 research outputs found
A problem solving approach in mathematics for second grade children based on cognitive guided instruction
Virtually all young children like mathematics (National Research Council, 1989, p.43). They come to school with knowledge assimilated naturally, based upon observations and experience. Unfortunately, instead of taking advantage of those experiences, teachers can close the door on that natural knowledge by teaching a prescribed curriculum based on accuracy, speed, and memory. Traditionally, elementary mathematics classrooms give little attention to thinking and reasoning. It is a common view under this approach, that facts and skills must first be mastered before students can reason about mathematics. The child\u27s view of mathematics can change from enthusiasm to apprehension, from confidence to fear. (National Research Council, 1989) Eventually the students can become convinced that mathematics is only for the smart kids
Biochemical profile of heifers with spontaneous humeral fractures suggest that protein-energy malnutrition could be an important factor in the pathology of this disease.
CAUL Read and Publish Agreement.CASE HISTORY: Serum and liver samples from 35, 2-year-old dairy heifers that had fractured one or both humeri post-calving between July and December 2019 were submitted to a diagnostic laboratory for analysis. Serum samples were analysed for albumin, ÎČ-hydroxybutyrate (BHB), creatinine, Ca, Mg, phosphate, non-esterified fatty acids (NEFA), and serum Cu concentration. Liver samples were analysed for liver Cu concentration. Data were compared to published reference intervals. Data values for heifers that prior to fracture had grazed fodder beet were also compared to values for those that had grazed pasture. CLINICAL FINDINGS: Sixty-nine percent of heifers with humeral fracture had serum creatinine concentrations below the lower value of the reference range (55-130 ”mol/L). In 3/32 (9%) heifers, serum NEFA concentrations were increased above the reference value indicating body fat mobilisation (â„1.2â
mmol/L for peri-partum cows) and in 20/35 (57%) heifers BHB serum concentrations were above the reference value indicating subclinical ketosis (â„1.1â
mmol/L for peri-partum cows). In 24/35 (69%) heifers, liver Cu concentration was low (†44 ”mol/kg) or marginal (45-94 ”mol/kg). The concentration of Cu in serum was low (†4.5â
”mol/L) in 2/33 (6%) heifers and marginal (4.6-7.9 ”mol/L) in 5/33 (15%) heifers. There was moderate positive correlation between the logged concentrations of Cu in paired liver and serum samples, r(31)â=â0.43; (95% CIâ=â0.1-0.79; pâ=â0.014). One heifer had a serum phosphate concentration below the lower limit of the reference range (< 1.10â
mmol/L). For all heifers, the concentrations of albumin, Ca, and Mg in serum were within the reference intervals (23-38â
g/L, 2.00-2.60â
mmol/L, and 0.49-1.15â
mmol/L respectively). Over winter, 15/35 (43%) heifers grazed predominantly pasture, 14/35 (40%) grazed fodder beet and 6/35 (17%) had a mixed diet. CLINICAL RELEVANCE: In some of these heifers with humeral fractures, there was evidence for protein and/or energy malnutrition in the form of elevated NEFA and BHB concentrations and low creatinine concentrations in serum. Liver Cu concentrations were also reduced in most affected heifers. However, the absence of a control group means it is not possible to determine if these are risk factors for fracture or features common to all periparturient heifers. Clinical trials and molecular studies are needed to determine the true contribution of Cu and protein-energy metabolism to the pathogenesis of spontaneous humeral fractures in dairy heifers. ABBREVIATIONS: BHB: Ă-hydroxybutyrate; NEFA: Non-esterified fatty acids.Publishe
Bone quality changes as measured by Raman and FTIR spectroscopy in primiparous cows with humeral fracture from New Zealand.
The occurrence of spontaneous humeral fractures in primiparous dairy cows from New Zealand prompted the study of bone material from affected cows to further characterize this condition and to outline a likely pathogenesis. Previous studies indicate that these cows developed osteoporosis due to periods of suboptimal bone formation followed by increased bone resorption during the period of lactation complicated by copper deficiency. We hypothesized that there are significant differences in the chemical composition/bone quality in bones from cows with spontaneous humeral fracture compared to cows without humeral fractures. In this study, Raman and Fourier transform infrared spectroscopy band ratios were, for the first time, measured, calculated, and compared in bone samples from 67 primiparous dairy cows that suffered a spontaneous fracture of the humerus and 14 age-matched post-calving cows without humeral fractures. Affected bone showed a significantly reduced mineral/matrix ratio, increased bone remodeling, newer bone tissue with lower mineralization and, lower carbonate substitution, and reduced crystallinity. As such, is likely that these have detrimentally impacted bone quality and strength in affected cows.Published onlin
In the Shadow of the Accretion Disk: Higher Resolution Imaging of the Central Parsec in NGC 4261
The physical conditions in the inner parsec of accretion disks believed to
orbit the central black holes in active galactic nuclei can be probed by
imaging the absorption (by ionized gas in the disk) of background emission from
a radio counterjet. We report high angular resolution VLBI observations of the
nearby (about 40 Mpc) radio galaxy NGC 4261 that confirm free-free absorption
of radio emission from a counterjet by a geometrically thin, nearly edge-on
disk at 1.6, 4.8, and 8.4 GHz. The angular width and depth of the absorption
appears to increase with decreasing frequency, as expected. We derive an
average electron density of ~10E4 per cc at a disk radius of about 0.2 pc,
assuming that the inner disk inclination and opening angles are the same as at
larger radii. Pressure balance between the thermal gas and the magnetic field
in the disk implies an average field strength of 0.1 milligauss at a radius of
0.2 pc. These are the closest-in free-free absorption measurements to date of
the conditions in an extragalactic accretion disk orbiting a black hole with a
well-determined mass. If a standard advection-dominated accretion flow exists
in the disk center, then the transition between thin and thick disk regions
must occur at a radius less than 0.2 pc (4000 Schwarzschild radii).Comment: 20 pages including 12 figures. Accepted for publication in Ap
Relation between millimeter wavelengths emission and high-energy emission for active galactic nuclei
After comparing the flux densities of a sample of active galactic nuclei
detected by energetic gamma-ray experiment telescope at 90 and 230 GHz with the
-ray emissions detected by Compton Gamma Ray Observatory and x-ray
emission, a strong correlation between the emissions at the millimeter
wavelength and the -ray emission is found. The average flux density of
x-ray is almost proportional to the average flux density at the millimeter
wavelength for quasars detected by energetic gamma-ray experiment telescope,
which strongly supports the previous idea that the x-ray emissions of this kind
sources are mainly produced by Synchrotron Self-Compton process.Comment: 6 pages, Chinese Physics Letters in pres
VSOP and Ground-based VLBI Imaging of the TeV Blazar Markarian 421 at Multiple Epochs
We present thirty VLBI images of the TeV blazar Markarian 421 (1101+384) at
fifteen epochs spanning the time range from 1994 to 1997, and at six different
frequencies from 2.3 to 43 GHz. The imaged observations include a
high-resolution 5 GHz VLBI Space Observatory Programme (VSOP) observation with
the HALCA satellite on 1997 November 14; full-track VLBA observations from 1994
April, 1996 November, and 1997 May at frequencies between 5 and 43 GHz; six
epochs of VLBA snapshot observations at frequencies between 2 and 15 GHz from
Radio Reference Frame studies; and five geodetic VLBI observations at 2 and 8
GHz from the archive of the Washington VLBI Correlator Facility located at the
U.S. Naval Observatory. The dense time coverage of the images allows us to
unambiguously track components in the parsec-scale jet over the observed time
range. We measure the speeds of three inner jet components located between 0.5
and 5 mas from the core (0.3 to 3 pc projected linear distance) to be 0.19 +/-
0.27, 0.30 +/- 0.07, and -0.07 +/- 0.07 c (H_{0}=65 km s^{-1} Mpc^{-1}). If the
sole 43 GHz image is excluded, all measured speeds are consistent with no
motion. These speeds differ from tentative superluminal speeds measured by
Zhang & B\aa\aa th from three epochs of data from the early 1980's. Possible
interpretations of these subluminal speeds in terms of the high Doppler factor
demanded by the TeV variability of this source are discussed.Comment: 18 pages, including 7 figures, emulateapj.sty, accepted by The
Astrophysical Journal; modified text describing Radio Reference Frame
observation
MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. VII. Blazar Jet Acceleration
We discuss acceleration measurements for a large sample of extragalactic
radio jets from the MOJAVE program which studies the parsec-scale jet structure
and kinematics of a complete, flux-density-limited sample of Active Galactic
Nuclei (AGN). Accelerations are measured from the apparent motion of individual
jet features or "components" which may represent patterns in the jet flow. We
find that significant accelerations are common both parallel and perpendicular
to the observed component velocities. Parallel accelerations, representing
changes in apparent speed, are generally larger than perpendicular acceleration
that represent changes in apparent direction. The trend for larger parallel
accelerations indicates that a significant fraction of these changes in
apparent speed are due to changes in intrinsic speed of the component rather
than changes in direction to the line of sight. We find an overall tendency for
components with increasing apparent speed to be closer to the base of their
jets than components with decreasing apparent speed. This suggests a link
between the observed pattern motions and the underlying flow which, in some
cases, may increase in speed close to the base and decrease in speed further
out; however, common hydro-dynamical processes for propagating shocks may also
play a role. About half of the components show "non-radial" motion, or a
misalignment between the component's structural position angle and its velocity
direction, and these misalignments generally better align the component motion
with the downstream emission. Perpendicular accelerations are closely linked
with non-radial motion. When observed together, perpendicular accelerations are
usually in the correct direction to have caused the observed misalignment.Comment: 17 pages, 11 figures, 1 table, accepted by the Astrophysical Journa
High-Energy Neutrinos from Photomeson Processes in Blazars
An important radiation field for photomeson neutrino production in blazars is
shown to be the radiation field external to the jet. Assuming that protons are
accelerated with the same power as electrons and injected with a -2 number
spectrum, we predict that km^2 neutrino telescopes will detect about
1-to-several neutrinos per year from flat spectrum radio quasars (FSRQs) such
as 3C 279. The escaping high-energy neutron and photon beams transport inner
jet energy far from the black-hole engine, and could power synchrotron X-ray
jets and FR II hot spots and lobes.Comment: revised paper (minor revisions), accepted for publication in PR
Adaptive optics near infrared integral field spectroscopy of NGC 2992
NGC 2992 is an intermediate Seyfert 1 galaxy showing outflows on kilo parsec
scales which might be due either to AGN or starburst activity. We therefore aim
at investigating its central region for a putative starburst in the past and
its connection to the AGN and the outflows. Observations were performed with
the adaptive optics near infrared integral field spectrograph SINFONI on the
VLT, complemented by longslit observations with ISAAC on the VLT, as well as N-
and Q-band data from the Spitzer archive. The spatial and spectral resolutions
of the SINFONI data are 50 pc and 83 km/s, respectively. The field of view of
3" x 3" corresponds to 450 pc x 450 pc. Br_gamma equivalent width and line
fluxes from PAHs were compared to stellar population models to constrain the
age of the putative recent star formation. A simple geometric model of two
mutually inclined disks and an additional cone to describe an outflow was
developed to explain the observed complex velocity field in H_2 1-0S(1). The
morphologies of the Br_gamma and the stellar continuum are different suggesting
that at least part of the Br_gamma emission comes from the AGN. This is
confirmed by PAH emission lines at 6.2 micron and 11.2 micron and the strength
of the silicon absorption feature at 9.7 micron, which point to dominant AGN
activity with a relatively minor starburst contribution. We find a starburst
age of 40 Myr - 50 Myr from Br_gamma line diagnostics and the radio continuum;
ongoing star formation can be excluded. Both the energetics and the timescales
indicate that the outflows are driven by the AGN rather than the starburst. The
complex velocity field observed in H_2 1-0S(1) in the central 450 pc can be
explained by the superposition of the galaxy rotation and an outflow.Comment: 10 pages, 8 figures, accepted for publication in A&
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