1,374,726 research outputs found
Evaluating cumulative ascent: Mountain biking meets Mandelbrot
The problem of determining total distance ascended during a mountain bike
trip is addressed. Altitude measurements are obtained from GPS receivers
utilizing both GPS-based and barometric altitude data, with data averaging used
to reduce fluctuations. The estimation process is sensitive to the degree of
averaging, and is related to the well-known question of determining coastline
length. Barometric-based measurements prove more reliable, due to their
insensitivity to GPS altitude fluctuations.Comment: 10 pages, 9 figures (v.2: minor revisions
The Star Formation Histories and Efficiencies of Two Giant HII Regions in M33
photometry is used to re-identify the OB associations which power the
two most luminous HII regions in M33, NGC 604 and NGC 595. There is a
significant difference (2-3 Myr) in the ages of the most recent star formation
episode in these two regions, while NGC 595 also has undergone a prior episode
of star formation (10-15 Myr ago). These data, combined with the presence of
molecular clouds in the heart of NGC 604, suggest that molecular clouds may
survive at least one intense episode of massive star formation. The star
formation efficiencies (mass of stars per mass of gas) of these two HII regions
are up to a factor of 3 larger than the average efficiency in the inner disk of
M33 or in Galactic molecular clouds, but are still only 2-5\%.Comment: 26 pages including 2 figures, uuencoded compressed postscript file
(Figure 1 not available electronically). Accepted to Ap
Expression patterns of chondrocyte genes cloned by differential display in tibial dyschondroplasia
AbstractTibial dyschondroplasia (TD) appears to involve a failure of the growth plate chondrocytes within growing long bones to differentiate fully to the hypertrophic stage, resulting in a mass of prehypertrophic chondrocytes which form the avascular TD lesion. Many biochemical and molecular markers of chondrocyte hypertrophy are absent from the lesion, or show reduced expression, but the cause of the disorder remains to be identified. As differentiation to the hypertrophic state is impaired in TD, we hypothesised that chondrocyte genes that are differentially expressed in the growth plate should show altered expression in TD. Using differential display, four genes, B-cadherin, EF2, HT7 and Ex-FABP were cloned from chondrocytes stimulated to differentiate to the hypertrophic stage in vitro, and their differential expression confirmed in vivo. Using semi-quantitative RT-PCR, the expression patterns of these genes were compared in chondrocytes from normal and TD growth plates. Surprisingly, none of these genes showed the pattern of expression that might be expected in TD lesion chondrocytes, and two of them, B-cadherin and Ex-FABP, were upregulated in the lesion. This indicates that the TD phenotype does not merely reflect the absence of hypertrophic marker genes, but may be influenced by more complex developmental mechanisms/defects than previously thought
Double distributions: Loose ends
We point out that double distributions need not vanish at their boundary.
Boundary terms do not change the ambiguity inherent in defining double
distributions; instead, boundary conditions must be satisfied in order to
switch between different decompositions. We analyze both the spin zero and spin
one-half cases.Comment: 4 pages, 0 figures, RevTex 4, Brief Repor
Relationship between ferroelectricity and Dzyaloshinskii-Moriya interaction in multiferroics and the effect of bond-bending
We studied the microscopic mechanism of multiferroics, in particular with the
"spin current" model (Hosho Katsura, Naoto Nagaosa and Aleander V. Balatsky,
Phys. Rev. Lett. 95, 057205 (2005)). Starting from a system with helical spin
configuration, we solved for the forms of the electron wave functions and
analyzed their characteristics. The relation between ferroelectricity and
Dzyaloshinskii-Moriya interaction (I. Dzyaloshinskii, J. Phys. Chem. Solids 4,
241 (1958) and T. Moriya, Phys. Rev. 120, 91 (1960)) is clearly established.
There is also a simple relation between the electric polarization and the wave
vector of magnetic orders. Finally, we show that the bond-bending exists in
transition metal oxides can enhance ferroelectricity.Comment: 14 pages, 3 figures. acceptby Physical Review
Feedback laws for fuel minimization for transport aircraft
The Theoretical Mechanics Branch has as one of its long-range goals to work toward solving real-time trajectory optimization problems on board an aircraft. This is a generic problem that has application to all aspects of aviation from general aviation through commercial to military. Overall interest is in the generic problem, but specific problems to achieve concrete results are examined. The problem is to develop control laws that generate approximately optimal trajectories with respect to some criteria such as minimum time, minimum fuel, or some combination of the two. These laws must be simple enough to be implemented on a computer that is flown on board an aircraft, which implies a major simplification from the two point boundary value problem generated by a standard trajectory optimization problem. In addition, the control laws allow for changes in end conditions during the flight, and changes in weather along a planned flight path. Therefore, a feedback control law that generates commands based on the current state rather than a precomputed open-loop control law is desired. This requirement, along with the need for order reduction, argues for the application of singular perturbation techniques
Cloud-free resolution element statistics program
Computer program computes number of cloud-free elements in field-of-view and percentage of total field-of-view occupied by clouds. Human error is eliminated by using visual estimation to compute cloud statistics from aerial photographs
Complex temperatures zeroes of partition function in spin-glass models
An approximate method is proposed for investigating complex-temperature
properties of real-dimensional spin-glass models. The method uses the
complex-temperature data of the ferromagnetic model on the same lattice. The
universality line in the complex-temperature space is obtained.Comment: latex, corrected some misprint
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