869 research outputs found
Reciprocity-based experimental determination of dynamic forces and moments: A feasibility study
BBN Systems and Technologies has been tasked by the Georgia Tech Research Center to carry Task Assignment No. 7 for the NASA Langley Research Center to explore the feasibility of 'In-Situ Experimental Evaluation of the Source Strength of Complex Vibration Sources Utilizing Reciprocity.' The task was carried out under NASA Contract No. NAS1-19061. In flight it is not feasible to connect the vibration sources to their mounting points on the fuselage through force gauges to measure dynamic forces and moments directly. However, it is possible to measure the interior sound field or vibration response caused by these structureborne sound sources at many locations and invoke principle of reciprocity to predict the dynamic forces and moments. The work carried out in the framework of Task 7 was directed to explore the feasibility of reciprocity-based measurements of vibration forces and moments
Electron Correlations in the Low Carrier Density LaFeAsO0.89F0.11 Superconductor (Tc = 28 K)
The crystal structure and numerous normal and superconducting state
properties of layered tetragonal (P4/nmm) LaFeAsO, with F-doping of 11 %, are
reported. Resistivity measurements give an onset transition temperature Tc =
28.2 K, and low field magnetic susceptibility data indicate bulk
superconductivity. In applied magnetic field, analysis of the resistive
transition results in a critical field Hc2 = 30 T and a coherence length 35 A.
An upper limit for the electron carrier concentration of 1 x 10^21 cm-3 is
inferred from Hall data just above Tc. Strong electron-electron correlations
are suggested from temperature-dependent resistivity, Seebeck coefficient, and
thermal conductivity data. Anomalies near Tc are observed in both Seebeck
coefficient and thermal conductivity data.Comment: 13 pages, 8 figure
Notes on Fleshy Fungi in Iowa. III
Ninety-nine sporocarps of fleshy fungi were collected during the summer and fall of 1964. In the collections were six species, Boletus piperatus Bull., Clitopilus subplanus Pk., Collybia strictipes Pk., Cortinarius duracinus Fr., Cortinarius imbutus Fr., and Tricholoma acre Pk. not previously reported for the State of Iowa
Microwave Sinterator Freeform Additive Construction System (MS-FACS)
The harmful properties of lunar dust, such as small size, glass composition, abnormal surface area, and coatings of imbedded nanophase iron, lead to a unique coupling of the dust with microwave radiation. This coupling can be exploited for rapid sintering of lunar soil for use as a construction material that can be formed to take on an infinite number of shapes and sizes. This work describes a system concept for building structures on the lunar surface using lunar regolith (soil). This system uses the ATHLETE (All-Terrain Hex- Limbed Extra-Terrestrial Explorer) mobility system as a positioning system with a microwave print head (similar to that of a smaller-scale 3D printer). A processing system delivers the lunar regolith to the microwave print head, where the microwave print head/chamber lays down a layer of melted regolith. An arm on the ATHLETE system positions the layer depending on the desired structure
Some Systematics of the Coupling Constant Dependence of N=4 Yang-Mills
The operator, O_\tau, that generates infinitesimal changes of the coupling
constant in N=4 Yang-Mills sits in the same supermultiplet as the
superconformal currents. We show how superconformal current Ward identities
determine a class of terms in the operator product expansion of O_\tau with any
other operator. In certain cases, this leads to constraints on the coupling
dependence of correlation functions in N=4 Yang-Mills. As an application, we
demonstrate the exact non-renormalization of two and certain three-point
correlation functions of BPS operators.Comment: 56 pages, LaTeX; amended and expanded arguments, added reference
The Large-scale J=3-2 and J=2-1 CO Emission from M17 and its Implications for Extragalactic CO Observations
We observed a 10x20 pc region of the molecular cloud M17 in the 12CO and 13CO
J=3-2 and J=2-1 transitions to determine their global behavior and to assess
the reliability of using ratios of CO line intensities integrated over an
entire cloud to determine the physical conditions within the cloud. Both the
12CO/13CO J=2-1 and J=3-2 line ratios correlate with the 13CO integrated
intensity, with smaller line ratios observed at locations with large integrated
intensities. This correlation is likely due to variations in the column density
from one position to another within M17. The 12CO and 13CO (J=3-2/J=2-1) line
ratios show no significant variation from place to place within M17, even on
the peak of the photon-dominated region. A Large Velocity Gradient analysis of
globally averaged line ratios gives results in reasonable agreement with the
results obtained for individual lines-of-sight through the cloud, which
suggests that the typical physical conditions in a molecular cloud can be
determined using CO line ratios integrated over the entire cloud. There appears
to be a clear trend of increasing 12CO/13CO J=2-1 and J=3-2 line ratios as one
moves from Galactic molecular cloud cores to entire Galactic molecular clouds
to normal galaxies. The most likely explanation of the high line ratios for
normal galaxies is a significant contribution to the CO emission by low column
density material, such as diffuse molecular clouds or the outer envelopes of
giant molecular clouds.Comment: 26 pages, 6 figures, 2 tables. Accepted for publication in Ap
Small representations of finite classical groups
Finite group theorists have established many formulas that express
interesting properties of a finite group in terms of sums of characters of the
group. An obstacle to applying these formulas is lack of control over the
dimensions of representations of the group. In particular, the representations
of small dimensions tend to contribute the largest terms to these sums, so a
systematic knowledge of these small representations could lead to proofs of
important conjectures which are currently out of reach. Despite the
classification by Lusztig of the irreducible representations of finite groups
of Lie type, it seems that this aspect remains obscure. In this note we develop
a language which seems to be adequate for the description of the "small"
representations of finite classical groups and puts in the forefront the notion
of rank of a representation. We describe a method, the "eta correspondence", to
construct small representations, and we conjecture that our construction is
exhaustive. We also give a strong estimate on the dimension of small
representations in terms of their rank. For the sake of clarity, in this note
we describe in detail only the case of the finite symplectic groups.Comment: 18 pages, 9 figures, accepted for publications in the proceedings of
the conference on the occasion of Roger Howe's 70th birthday (1-5 June 2015,
Yale University, New Haven, CT
Stringy KLT relations, global symmetries, and E_7(7) violation
We study consequences of the Kawai-Lewellen-Tye (KLT) relations applied to
tree amplitudes in toroidal compactifications of string theory to four
dimensions. The closed string tree amplitudes with massless external states
respect a global SU(4)xSU(4) symmetry, which is enhanced to the SU(8)
R-symmetry of N=8 supergravity in the field theory limit. Our analysis focuses
on two aspects: (i) We provide a detailed account of the simplest
SU(8)-violating amplitudes. We classify these processes and derive explicit
superamplitudes for all local 5- and 6-point operators with SU(4)xSU(4)
symmetry at order alpha'^3. Their origin is the dilatonic operator exp(-6 phi)
R^4 in the closed-string effective action. (ii) We expand the 6-point closed
string tree amplitudes to order alpha'^3 and use two different methods to
isolate the SU(8)-singlet contribution from exp(-6 phi) R^4. This allows us to
extract the matrix elements of the unique SU(8)-invariant supersymmetrization
of R^4. Their single-soft scalar limits are non-vanishing. This demonstrates
that the N=8 supergravity candidate counterterm R^4 is incompatible with
continuous E_7(7) symmetry. From the soft scalar limits, we reconstruct to
quadratic order the SU(8)-invariant function of scalars that multiplies R^4,
and show that it satisfies the Laplace eigenvalue equation derived recently
from supersymmetry and duality constraints.Comment: 23 pages, published versio
Socioeconomic differences in childhood length/height trajectories in a middle-income country: a cohort study:a cohort study
Published: 8 September 2014Socioeconomic disadvantage is associated with shorter adult stature. Few studies have examined socioeconomic differences in stature from birth to childhood and the mechanisms involved, particularly in middle-income former Soviet settings.The sample included 12,463 Belarusian children (73% of the original cohort) born in 1996-1997, with up to 14 stature measurements from birth to 7 years. Linear spline multi-level models with 3 knots at 3, 12 and 34 months were used to analyse birth length and growth velocity during four age-periods by parental educational achievement (up to secondary school, advanced secondary/partial university, completed university) and occupation (manual, non-manual).Girls born to the most (versus least) educated mothers were 0.43 cm (95% confidence interval (CI): 0.28, 0.58) longer at birth; for boys, the corresponding difference was 0.30 cm (95% CI: 0.15, 0.46). Similarly, children of the most educated mothers grew faster from birth-3 months and 12-34 months (p-values for trend ≤ 0.08), such that, by age 7 years, girls with the most (versus least) educated mothers were 1.92 cm (95% CI: 1.47, 2.36) taller; after controlling for urban/rural and East/West area of residence, this difference remained at 1.86 cm (95% CI: 1.42, 2.31), but after additionally controlling for mid-parental height, attenuated to 1.10 cm (95% CI: 0.69, 1.52). Among boys, these differences were 1.95 cm (95% CI: 1.53, 2.37), 1.89 cm (95% CI: 1.47, 2.31) and 1.16 cm (95% CI: 0.77, 1.55), respectively. Additionally controlling for breastfeeding, maternal smoking and older siblings did not substantively alter these findings. There was no evidence that the association of maternal educational attainment with growth differed in girls compared to boys (p for interaction = 0.45). Results were similar for those born to the most (versus least) educated fathers, or who had a parent with a non-manual (versus manual) occupation.In Belarus, a middle-income former Soviet country, socioeconomic differences in offspring growth commence in the pre-natal period and generate up to approximately 2 cm difference in height at age 7 years. These associations are partly explained by genetic or other factors influencing parental stature.Current Controlled Trials: NCT01352247 assigned 9 Sept 2005; ClinicalTrials.gov. Identifier: NCT01561612 received 20 Mar 2012.Rita Patel, Kate Tilling, Debbie A Lawlor, Laura D Howe, Natalia Bogdanovich, Lidia Matush, Emily Nicoli, Michael S Kramer and Richard M Marti
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