1,087 research outputs found
Sixth Graders Investigate Models and Designs through Teacher-Directed and Student-Centered Inquiry Lessons: Effects on Performance and Attitudes
Science inquiry has been found to be effective with students from diverse backgrounds and varied academic abilities. This study compared student learning, enjoyment, motivation, perceived understanding, and creativity during a science unit on Models and Designs for 38 sixth grade students (20 male, 18 female; 1 Black, 1 Hispanic and 36 White). The unit began with a very teacher-centered approach, then became increasingly student-centered, employing more inquiry with each lesson set to determine the effects of student-centered instruction on performance and attitudes. Pretest-posttest data with specific questions tied to each lesson set were collected, as well as repeated measures attitude surveys administered at the conclusion of each of the six sets of lessons. The surveys included ratings of lesson enjoyment, student motivation, perceived understanding, creativity designed into the lesson, and perceived self-creativity on a scale of one to ten, along with open ended responses of reasons for the ratings. Results indicate a trend of improving knowledge retention as student-centeredness and inquiry increased until the last lesson set, which a few students found too challenging. Additionally, reported levels of enjoyment, motivation, and creativity increased as the instructional approaches became more student-centered until the challenge became too great for some students, causing a small dip in the upward trend. Greater experience with science inquiry may assist students in extending their confidence, inquiry leadership, and achievement
Commensurate Fluctuations in the Pseudogap and Incommensurate spin-Peierls Phases of TiOCl
X-ray scattering measurements on single crystals of TiOCl reveal the presence
of commensurate dimerization peaks within both the incommensurate spin-Peierls
phase and the so-called pseudogap phase above T_c2. This scattering is
relatively narrow in Q-space indicating long correlation lengths exceeding ~
100 A below T* ~ 130 K. It is also slightly shifted in Q relative to that of
the commensurate long range ordered state at the lowest temperatures, and it
coexists with the incommensurate Bragg peaks below T_c2. The integrated
scattering over both commensurate and incommensurate positions evolves
continuously with decreasing temperature for all temperatures below T* ~ 130 K.Comment: To appear in Physical Review B: Rapid Communications. 5 page
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Tubular secretion of creatinine and kidney function: an observational study.
BackgroundPrior papers have been inconsistent regarding how much creatinine clearance (CrCl) overestimates glomerular filtration rate (GFR). A recent cross-sectional study suggested that measurement error alone could entirely account for the longstanding observation that CrCl/GFR ratio is larger when GFR is lower among patients with chronic kidney disease (CKD); but there have been no validation of this in other cohorts.MethodsTo fill these gaps in knowledge regarding the relation between CrCl and GFR, we conducted cross-sectional and longitudinal analysis of the Modification of Diet in Renal Disease study (MDRD) and African American Study of Kidney Disease and Hypertension (AASK); and cross-sectional analysis of a clinical dataset from the Mayo Clinic of four different patient populations (CKD patients, kidney transplant recipients, post kidney donation subgroup and potential kidney donors). In the cross-sectional analyses (MDRD, AASK and Mayo Clinic cohort), we examined the relation between the CrCl/iothalamate GFR (iGFR) ratio at different categories of iGFR or different levels of CrCl. In the MDRD and AASK longitudinal analyses, we studied how the CrCl/iGFR ratio changed with those who had improvement in iGFR (CrCl) over time versus those who had worsening of iGFR (CrCl) over time.ResultsObserved CrCl/iGFR ratios were generally on the lower end of the range reported in the literature for CKD (median 1.24 in MDRD, 1.13 in AASK and 1.25 in Mayo Clinic cohort). Among CKD patients in whom CrCl and iGFR were measured using different timed urine collections, CrCl/iGFR ratio were higher with lower iGFR categories but lower with lower CrCl categories. However, among CKD patients in whom CrCl and iGFR were measured using the same timed urine collections (which reduces dis-concordant measurement error), CrCl/iGFR ratio were higher with both lower iGFR categories and lower CrCl categories.ConclusionsThese data refute the recent suggestion that measurement error alone could entirely account for the longstanding observation that CrCl/GFR ratio increases as GFR decreases in CKD patients. They also highlight the lack of certainty in our knowledge with regard to how much CrCl actually overestimates GFR
Gains from the upgrade of the cold neutron triple-axis spectrometer FLEXX at the BER-II reactor
The upgrade of the cold neutron triple-axis spectrometer FLEXX is described.
We discuss the characterisation of the gains from the new primary spectrometer,
including a larger guide and double focussing monochromator, and present
measurements of the energy and momentum resolution and of the neutron flux of
the instrument. We found an order of magnitude gain in intensity (at the cost
of coarser momentum resolution), and that the incoherent elastic energy widths
are measurably narrower than before the upgrade. The much improved count rate
should allow the use of smaller single crystals samples and thus enable the
upgraded FLEXX spectrometer to continue making leading edge measurements.Comment: 8 pages, 7 figures, 5 table
Critical X-ray Scattering Studies of Jahn-Teller Phase Transitions in TbVAsO
The critical behaviour associated with cooperative Jahn-Teller phase
transitions in TbVAsO (where \textit{x} = 0, 0.17, 1)
single crystals have been studied using high resolution x-ray scattering. These
materials undergo continuous tetragonal orthorhombic structural phase
transitions driven by Jahn-Teller physics at T = 33.26(2) K, 30.32(2) K and
27.30(2) K for \textit{x} = 0, 0.17 and 1 respectively. The orthorhombic strain
was measured close to the phase transition and is shown to display mean field
behavior in all three samples. Pronounced fluctuation effects are manifest in
the longitudinal width of the Bragg scattering, which diverges as a power law,
with an exponent given by , on approaching the transition from
either above or below. All samples exhibited twinning; however the disordered x
= 0.17 sample showed a broad distribution of twins which were stable to
relatively low temperatures, well below T. This indicates that while the
orthorhombic strain continues to develop in a conventional mean field manner in
the presence of disorder, twin domains are easily pinned by the quenched
impurities and their associated random strains.Comment: 8 pages, 6 figure
Quantum phase transitions and decoupling of magnetic sublattices in the quasi-two-dimensional Ising magnet Co3V2O8 in a transverse magnetic field
The application of a magnetic field transverse to the easy axis, Ising
direction in the quasi-two-dimensional Kagome staircase magnet, Co3V2O8,
induces three quantum phase transitions at low temperatures, ultimately
producing a novel high field polarized state, with two distinct sublattices.
New time-of-flight neutron scattering techniques, accompanied by large angular
access, high magnetic field infrastructure allow the mapping of a sequence of
ferromagnetic and incommensurate phases and their accompanying spin
excitations. At least one of the transitions to incommensurate phases at \mu
0Hc1~6.25 T and \mu 0Hc2~7 T is discontinuous, while the final quantum critical
point at \mu 0Hc3~13 T is continuous.Comment: 5 pages manuscript, 3 pages supplemental materia
Suppression of the commensurate spin-Peierls state in Sc-doped TiOCl
We have performed x-ray scattering measurements on single crystals of the
doped spin-Peierls compound Ti(1-x)Sc(x)OCl (x = 0, 0.01, 0.03). These
measurements reveal that the presence of non-magnetic dopants has a profound
effect on the unconventional spin-Peierls behavior of this system, even at
concentrations as low as 1%. Sc-doping suppresses commensurate fluctuations in
the pseudogap and incommensurate spin-Peierls phases of TiOCl, and prevents the
formation of a long-range ordered spin-Peierls state. Broad incommensurate
scattering develops in the doped compounds near Tc2 ~ 93 K, and persists down
to base temperature (~ 7 K) with no evidence of a lock-in transition. The width
of the incommensurate dimerization peaks indicates short correlation lengths on
the order of ~ 12 angstroms below Tc2. The intensity of the incommensurate
scattering is significantly reduced at higher Sc concentrations, indicating
that the size of the associated lattice displacement decreases rapidly as a
function of doping.Comment: 7 pages, 5 figure
Asymmetric Thermal Lineshape Broadening in a Gapped 3-Dimensional Antiferromagnet - Evidence for Strong Correlations at Finite Temperature
It is widely believed that magnetic excitations become increasingly
incoherent as temperature is raised due to random collisions which limit their
lifetime. This picture is based on spin-wave calculations for gapless magnets
in 2 and 3 dimensions and is observed experimentally as a symmetric Lorentzian
broadening in energy. Here, we investigate a three-dimensional dimer
antiferromagnet and find unexpectedly that the broadening is asymmetric -
indicating that far from thermal decoherence, the excitations behave
collectively like a strongly correlated gas. This result suggests that a
temperature activated coherent state of quasi-particles is not confined to
special cases like the highly dimerized spin-1/2 chain but is found generally
in dimerized antiferromagnets of all dimensionalities and perhaps gapped
magnets in general
Luttinger-Liquid Behavior in the Alternating Spin-Chain System Copper Nitrate
We determine the phase diagram of copper nitrate Cu(NO)2.5DO
in the context of quantum phase transitions and novel states of matter. We
establish this compound as an ideal candidate to study quasi-1D Luttinger
liquids, 3D Bose-Einstein-Condensation of triplons, and the crossover between
1D and 3D physics. Magnetocaloric effect, magnetization, and neutron scattering
data provide clear evidence for transitions into a Luttinger liquid regime and
a 3D long-range ordered phase as function of field and temperature. Theoretical
simulations of this model material allow us to fully establish the phase
diagram and to discuss it in the context of dimerized spin systems.Comment: 5 pages, 4 figure
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