29,574 research outputs found
Probing Hadronic Structure with The Decay
We compute the branching ratio for and
in chiral perturbation theory and find that
both decays should be observable at CEBAF. With sufficiently low thresholds on
the invariant mass a branching ratio of may be observed
for . For the decay
mode we predict a branching ratio of . The dependence of the
M1 and E2 amplitudes on the momentum transfer will provide a useful test of
chiral perturbation theory which predicts variation over the
allowed kinematic range.Comment: 6 pages, 3 figures, UCSD/PTH 93-06, QUSTH-93-02, Duke-TH-93-4
Effects of 3-d and 4-d-transition metal substitutional impurities on the electronic properties of CrO2
We present first-principles based density functional theory calculations of
the electronic and magnetic structure of CrO2 with 3d (Ti through Cu) and 4d
(Zr through Ag) substitutional impurities. We find that the half-metallicity of
CrO2 remains intact for all of the calculated substitutions. We also observe
two periodic trends as a function of the number of valence electrons: if the
substituted atom has six or fewer valence electrons (Ti-Cr or Zr-Mo), the
number of down spin electrons associated with the impurity ion is zero,
resulting in ferromagnetic (FM) alignment of the impurity magnetic moment with
the magnetization of the CrO2 host. For substituent atoms with eight to ten
(Fe-Ni or Ru-Pd with the exception of Ni), the number of down spin electrons
contributed by the impurity ion remains fixed at three as the number
contributed to the majority increases from one to three resulting in
antiferromagnetic (AFM) alignment between impurity moment and host
magnetization. The origin of this variation is the grouping of the impurity
states into 3 states with approximate "t2g" symmetry and 2 states with
approximate "eg" symmetry. Ni is an exception to the rule because a
Jahn-Teller-like distortion causes a splitting of the Ni eg states. For Mn and
Tc, which have 8 valence electrons, the zero down spin and 3 down spin
configurations are very close in energy. For Cu and Ag atoms, which have 11
valence electrons, the energy is minimized when the substituent ion contributes
5 Abstract down-spin electrons. We find that the interatomic exchange
interactions are reduced for all substitutions except for the case of Fe for
which a modest enhancement is calculated for interactions along certain
crystallographic directions.Comment: 26 pages, 10 figures, 2 table
Subjectivation and performative politics—Butler thinking Althusser and Foucault: intelligibility, agency and the raced-nationed-religioned subjects of education
Judith Butler is perhaps best known for her take-up of the debate between Derrida and Austin over the function of the performative and her subsequent suggestion that the subject be understood as performatively constituted. Another important but less often noted move within Butler‘s consideration of the processes through which the subject is constituted is her thinking between Althusser‘s notion of subjection and Foucault‘s notion of subjectivation. In this paper, I explore Butler‘s understanding of processes of subjectivation; examine the relationship between subjectivation and the performative suggested in and by Butler‘s work, and consider how the performative is implicated in processes of subjectivation – in =who‘ the subject is, or might be, subjectivated as. Finally, I examine the usefulness of understanding the subjectivating effects of discourse for education, in particular for educationalists concerned to make better sense of and interrupt educational inequalities. In doing this I offer a reading of an episode of ethnographic data generated in an Australian high School. I suggest that it is through subjectivating processes of the sort that Butler helps us to understand that some students are rendered subjects inside the educational endeavour, and others are rendered outside this endeavour or, indeed, outside student-hood
Measuring surface-area-to-volume ratios in soft porous materials using laser-polarized xenon interphase exchange NMR
We demonstrate a minimally invasive nuclear magnetic resonance (NMR)
technique that enables determination of the surface-area-to-volume ratio (S/V)
of soft porous materials from measurements of the diffusive exchange of
laser-polarized 129Xe between gas in the pore space and 129Xe dissolved in the
solid phase. We apply this NMR technique to porous polymer samples and find
approximate agreement with destructive stereological measurements of S/V
obtained with optical confocal microscopy. Potential applications of
laser-polarized xenon interphase exchange NMR include measurements of in vivo
lung function in humans and characterization of gas chromatography columns.Comment: 14 pages of text, 4 figure
Electromagnetic Moments of the Baryon Decuplet
We compute the leading contributions to the magnetic dipole and electric
quadrupole moments of the baryon decuplet in chiral perturbation theory. The
measured value for the magnetic moment of the is used to determine
the local counterterm for the magnetic moments. We compare the chiral
perturbation theory predictions for the magnetic moments of the decuplet with
those of the baryon octet and find reasonable agreement with the predictions of
the large-- limit of QCD. The leading contribution to the quadrupole
moment of the and other members of the decuplet comes from one--loop
graphs. The pionic contribution is shown to be proportional to (and so
will not contribute to the quadrupole moment of nuclei), while the
contribution from kaons has both isovector and isoscalar components. The chiral
logarithmic enhancement of both pion and kaon loops has a coefficient that
vanishes in the limit. The third allowed moment, the magnetic octupole,
is shown to be dominated by a local counterterm with corrections arising at two
loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using
uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5
The invertebrate diet of northern bobwhite chicks in Georgia, United States
Dieta a base de invertebrados de las crías del colín de Virginia en Georgia, Estados Unidos
El establecimiento de hábitats de cría a lo largo de los márgenes de los campos se ha convertido en una norma agro–medioambiental muy popular, para ayudar a invertir la disminución de las poblaciones del colín de Virginia (Colinus virginianus) en Georgia, Estados Unidos. En este estudio se examina la dieta a base de invertebrados de los pollos, con hábitats de cría bien establecidos, que forrajean en las tierras de labrantío, en comparación con la de las crías de un coto de caza de colines de Virginia salvajes gestionado intensivamente. En los años 2001 y 2002 se recogieron muestras fecales de los lugares de descanso nocturnos de las crías, y se analizaron. Se investigaron las diferencias en cuanto a la composición de invertebrados entre los lugares de estudio, utilizando un análisis composicional. Mientras que la dieta de los pollos de ambos lugares contenía grupos de invertebrados similares, la composición de las dietas variaba significativamente. A pesar de que las crías de los cultivos habían comido 1,7 veces menos coleópteros, habían devorado 1,7 veces más hemípteros. Estos datos sugieren que aunque la composición de invertebrados de la dieta de las crías difería entre los dos tipos de hábitat, en ambos contenía grandes proporciones de las presas más importantes.Dieta a base de invertebrados de las crías del colín de Virginia en Georgia, Estados Unidos
El establecimiento de hábitats de cría a lo largo de los márgenes de los campos se ha convertido en una norma agro–medioambiental muy popular, para ayudar a invertir la disminución de las poblaciones del colín de Virginia (Colinus virginianus) en Georgia, Estados Unidos. En este estudio se examina la dieta a base de invertebrados de los pollos, con hábitats de cría bien establecidos, que forrajean en las tierras de labrantío, en comparación con la de las crías de un coto de caza de colines de Virginia salvajes gestionado intensivamente. En los años 2001 y 2002 se recogieron muestras fecales de los lugares de descanso nocturnos de las crías, y se analizaron. Se investigaron las diferencias en cuanto a la composición de invertebrados entre los lugares de estudio, utilizando un análisis composicional. Mientras que la dieta de los pollos de ambos lugares contenía grupos de invertebrados similares, la composición de las dietas variaba significativamente. A pesar de que las crías de los cultivos habían comido 1,7 veces menos coleópteros, habían devorado 1,7 veces más hemípteros. Estos datos sugieren que aunque la composición de invertebrados de la dieta de las crías difería entre los dos tipos de hábitat, en ambos contenía grandes proporciones de las presas más importantes.The establishment of brood–rearing habitats along field margins has become a popular agri–environmental prescription to help reverse population declines of northern bobwhite (Colinus virginianus) in Georgia, United States. Here, the invertebrate–diet of chicks foraging on farmland with established brood–rearing habitats is examined and compared to those of chicks on an intensively managed wild bobwhite shooting estate. In 2001 and 2002, faecal samples were collected and analysed from nocturnal roost sites of bobwhite broods. Differences in invertebrate composition between the study sites were investigated using compositional analysis. While the diet of chicks on both sites contained similar invertebrate groups, the composition of the diets varied significantly. Although chicks on farmland had eaten 1.7 times fewer Coleoptera, they had 1.7 times more Hemiptera in their diet. These data suggest that although the invertebrate composition in the diet of chicks differed between the two landscapes, both contained high proportions of important prey items
Dissipation in nanocrystalline-diamond nanomechanical resonators
We have measured the dissipation and frequency of nanocrystalline-diamond nanomechanical resonators with resonant frequencies between 13.7 MHz and 157.3 MHz, over a temperature range of 1.4–274 K. Using both magnetomotive network analysis and a time-domain ring-down technique, we have found the dissipation in this material to have a temperature dependence roughly following T^(0.2), with Q^(–1) ≈ 10^(–4) at low temperatures. The frequency dependence of a large dissipation feature at ~35–55 K is consistent with thermal activation over a 0.02 eV barrier with an attempt frequency of 10 GHz
Time-varying Learning and Content Analytics via Sparse Factor Analysis
We propose SPARFA-Trace, a new machine learning-based framework for
time-varying learning and content analytics for education applications. We
develop a novel message passing-based, blind, approximate Kalman filter for
sparse factor analysis (SPARFA), that jointly (i) traces learner concept
knowledge over time, (ii) analyzes learner concept knowledge state transitions
(induced by interacting with learning resources, such as textbook sections,
lecture videos, etc, or the forgetting effect), and (iii) estimates the content
organization and intrinsic difficulty of the assessment questions. These
quantities are estimated solely from binary-valued (correct/incorrect) graded
learner response data and a summary of the specific actions each learner
performs (e.g., answering a question or studying a learning resource) at each
time instance. Experimental results on two online course datasets demonstrate
that SPARFA-Trace is capable of tracing each learner's concept knowledge
evolution over time, as well as analyzing the quality and content organization
of learning resources, the question-concept associations, and the question
intrinsic difficulties. Moreover, we show that SPARFA-Trace achieves comparable
or better performance in predicting unobserved learner responses than existing
collaborative filtering and knowledge tracing approaches for personalized
education
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