1,085 research outputs found
Microwave cavity light shining through a wall optimization and experiment
It has been proposed that microwave cavities can be used in a photon
regeneration experiment to search for hidden sector photons. Using two isolated
cavities, the presence of hidden sector photons could be inferred from a 'light
shining through a wall' phenomenon. The sensitivity of the experiment has
strong a dependence on the geometric construction and electromagnetic mode
properties of the two cavities. In this paper we perform an in depth
investigation to determine the optimal setup for such an experiment. We also
describe the results of our first microwave cavity experiment to search for
hidden sector photons. The experiment consisted of two cylindrical copper
cavities stacked axially inside a single vacuum chamber. At a hidden sector
photon mass of 37.78 micro eV we place an upper limit on the kinetic mixing
parameter chi = 2.9 * 10^(-5). Whilst this result lies within already
established limits our experiment validates the microwave cavity `light shining
through a wall' concept. We also show that the experiment has great scope for
improvement, potentially able to reduce the current upper limit on the mixing
parameter chi by several orders of magnitude.Comment: To be published in PR
Quasinormal modes of asymptotically flat rotating black holes
We study the main properties of general linear perturbations of rotating
black holes in asymptotically flat higher-dimensional spacetimes. In
particular, we determine the quasinormal mode (QNM) spectrum of singly spinning
and equal angular momenta Myers-Perry black holes (MP BHs). Emphasis is also
given to the timescale of the ultraspinning and bar-mode instabilities in these
two families of MP BHs. For the bar-mode instabilities in the singly spinning
MP BH, we find excellent agreement with our linear analysis and the non-linear
time evolution of Shibata and Yoshino for d=6,7 spacetime dimensions. We find
that d=5 singly spinning BHs are linearly stable. In the context of studying
general relativity in the large dimension limit, we obtain the QNM spectrum of
Schwarzschild BHs and rotating MP BHs for large dimensions. We identify two
classes of modes. For large dimensions, we find that in the limit of zero
rotation, unstable modes of the MP BHs connect to a class of Schwarzschild QNMs
that saturate to finite values.Comment: 52 pages. 25 figure
High Resolution Flicker-Noise-Free Frequency Measurements of Weak Microwave Signals
Amplification is usually necessary when measuring the frequency instability
of microwave signals. In this work, we develop a flicker noise free frequency
measurement system based on a common or shared amplifier. First, we show that
correlated flicker phase noise can be cancelled in such a system. Then we
compare the new system with the conventional by simultaneously measuring the
beat frequency from two cryogenic sapphire oscillators with parts in 10^15
fractional frequency instability. We determine for low power, below -80 dBm,
the measurements were not limited by correlated noise processes but by thermal
noise of the readout amplifier. In this regime, we show that the new readout
system performs as expected and at the same level as the standard system but
with only half the number of amplifiers. We also show that, using a standard
readout system, the next generation of cryogenic sapphire oscillators could be
flicker phase noise limited when instability reaches parts in 10^16 or betterComment: Accepted for publication in IEEE Transactions on Microwave Theory &
Technique
Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures
We report on extremely sensitive measurements of changes in the microwave
properties of high purity non-intentionally-doped single-crystal semiconductor
samples of gallium phosphide, gallium arsenide and 4H-silicon carbide when
illuminated with light of different wavelengths at cryogenic temperatures.
Whispering gallery modes were excited in the semiconductors whilst they were
cooled on the coldfinger of a single-stage cryocooler and their frequencies and
Q-factors measured under light and dark conditions. With these materials, the
whispering gallery mode technique is able to resolve changes of a few parts per
million in the permittivity and the microwave losses as compared with those
measured in darkness. A phenomenological model is proposed to explain the
observed changes, which result not from direct valence to conduction band
transitions but from detrapping and retrapping of carriers from impurity/defect
sites with ionization energies that lay in the semiconductor band gap.
Detrapping and retrapping relaxation times have been evaluated from comparison
with measured data.Comment: 7 pages, 6 figure
Modified permittivity observed in bulk Gallium Arsenide and Gallium Phosphide samples at 50 K using the Whispering Gallery mode method
Whispering Gallery modes in bulk cylindrical Gallium Arsenide and Gallium
Phosphide samples have been examined both in darkness and under white light at
50 K. In both samples we observed change in permittivity under light and dark
conditions. This results from a change in the polarization state of the
semiconductor, which is consistent with a free electron-hole
creation/recombination process. The permittivity of the semiconductor is
modified by free photocarriers in the surface layers of the sample which is the
region sampled by Whispering Gallery modes.Comment: 8 pages, 3 figure
Regulation of pro-apoptotic phosphorylation of Kv2.1 K<sup>+</sup> channels
Caspase activity during apoptosis is inhibited by physiological concentrations of intracellular K+. To enable apoptosis in injured cortical and hippocampal neurons, cellular loss of this cation is facilitated by the insertion of Kv2.1 K+ channels into the plasma membrane via a Zn2+ /CaMKII/SNARE-dependent process. Pro-apoptotic membrane insertion of Kv2.1 requires the dual phosphorylation of the channel by Src and p38 at cytoplasmic N- and C- terminal residues Y124 and S800, respectively. In this study, we investigate if these phosphorylation sites are mutually co-regulated, and whether putative N- and C-terminal interactions, possibly enabled by Kv2.1 intracellular cysteine residues C73 and C710, influence the phosphorylation process itself. Studies were performed with recombinant wild type and mutant Kv2.1 expressed in Chinese hamster ovary (CHO) cells. Using immunoprecipitated Kv2.1 protein and phospho-specific antibodies, we found that an intact Y124 is required for p38 phosphorylation of S800, and, importantly, that Src phosphorylation of Y124 facilitates the action of the p38 at the S800 residue. Moreover, the actions of Src on Kv2.1 are substantially decreased in the non-phosphorylatable S800A channel mutant. We also observed that mutations of either C73 or C710 residues decreased the p38 phosphorylation at S800 without influencing the actions of Src on tyrosine phosphorylation of Kv2.1. Surprisingly, however, apoptotic K+ currents were suppressed only in cells expressing the Kv2.1(C73A) mutant but not in those transfected with Kv2.1(C710A), suggesting a possible structural alteration in the C-terminal mutant that facilitates membrane insertion. These results show that intracellular N-terminal domains critically regulate phosphorylation of the C-terminal of Kv2.1, and vice versa, suggesting possible new avenues for modifying the apoptotic insertion of these channels during neurodegenerative processes
Link Between Mathematics Pedagogy and Missouri Assessment
Abstract
The researcher studied the correlation between mathematics pedagogy and fifth grade test scores on the Missouri Achievement Program Mathematics Test, utilizing data from 2019 to avoid the effects Covid-19 had on the education system. All fifth graders attending public schools in Saint Louis County were studied using the data released by the Department of Elementary and Secondary Education. The first research question pertained to a correlation between mathematics pedagogy (Spiral, Strand or Blended Method) and overall fifth grade test scores on the Missouri Assessment Program Mathematics Test. The second question tested whether correlation existed between mathematics pedagogy and test scores for Lower SES students. The third question tested whether correlation existed between mathematics pedagogy and Black fifth grade test scores on the Missouri Assessment Program Mathematics Test. The final research question tested whether pedagogy closed the achievement gap between Low SES, minority students and the overall population on the fifth grade MAP Mathematics Test (MAPMT). The researcher found the Strand Method correlated with higher test scores for the overall population and the Low SES population, but the Black population scored best utilizing the Spiral Method. The Blended Method had the lowest difference between all subgroups. The researcher recommends that districts adopt a methodical mathematics program that utilizes the Strand Method. Further, the researcher suggests students be grouped by both learning style and ability. Mastery is required before students proceed to subsequent concepts.
Keywords: mathematics, pedagogy, MA
OAK Fund Annual Report: 2015-2016
2016 Annual report of the OAK FundThe Open Access to Knowledge Fund (OAK Fund) at Texas A&M University is a program for underwriting publication fees for scholarly journal articles, book chapters, and monographs in fully Open Access publications. The OAK Fund was established in 2013 to help fulfill Texas A&M University’s commitment to the “Compact for Open Access Publishing Equity.” The goals of OAK Fund at Texas A&M University are to support and encourage: (1) Texas A&M University faculty, research staff, and graduate students (as of fiscal year 2015/2016) who lack another source of funding to publish in Open Access venues; (2) innovative scholarly publishing that takes advantage of digital networking technologies for distribution and Open Access; and (3) greater public access to Texas A&M University research and scholarship.
The OAK Fund has been available to Texas A&M University authors for three years. In the 2015/2016 fiscal year, the Vice President for Research (VPR) and the Texas A&M University Libraries committed 50,000 to the fund, respectively. For the first time, additional funds were allocated to support graduate student authors; the Office of Graduate and Professional Studies (OGAPS) and the VPR each committed $2,500. This document reports on outcomes of the 2015/2016 OAK Fund program
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