13,632 research outputs found
Comparison of flight data and analysis for hingeless rotor regressive inplane mode stability
Analytical and experimental data obtained during the development of the AH-56A covering stability of the regressive inplane mode, including coupling with other modes such as body and rotor plunge are reported. Data were obtained on two distinctly different control systems; both gyro controlled, but one with feathering moment feedback and the other with direct flapping feedback. A review was made of analytical procedures employed in investigating the stability of this mode and a comparison was made of the analytical and experimental data. The effect of certain parameters including blade droop, sweep, delta 3, alpha 1, vehicle roll inertia, inplane frequency, and rpm and forward speed on the mode were also reviewed. It was shown that the stability of this mode is treatable by analysis and that adequate stability is achievable without recourse to auxiliary inplane damping devices
Double-layer Color Effects in Porcelain Systems
The color of an unshaded body porcelain was determined at three thicknesses on white, gray, and three chromatic backings. Spectral absorption and scattering coefficients of the porcelain were determined from the diffuse reflectance at one thickness on the white and gray backings. These optical coefficients, when utilized with the Kubelka-Munk reflectance theory, accurately predicted the color of the other sample configurations studied. The scattering of the body porcelain was found to decrease with increasing wavelength within the visible spectrum, in accordance with scattering theory for particles not substantially less than the wavelength of the scattered light. For the filtering effects of a translucent material in optical contact with a backing, the Kubelka-Munk reflectance theory described the interaction between the optical absorption and scattering within the translucent material and the reflectance of the backing.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67139/2/10.1177_00220345850640061801.pd
Examples of mathematical modeling tales from the crypt
Mathematical modeling is being increasingly recognized within the biomedical sciences as an important tool that can aid the understanding of biological systems. The heavily regulated cell renewal cycle in the colonic crypt provides a good example of how modeling can be used to find out key features of the system kinetics, and help to explain both the breakdown of homeostasis and the initiation of tumorigenesis. We use the cell population model by Johnston et al. (2007) Proc. Natl. Acad. Sci. USA 104, 4008-4013, to illustrate the power of mathematical modeling by considering two key questions about the cell population dynamics in the colonic crypt. We ask: how can a model describe both homeostasis and unregulated growth in tumorigenesis; and to which parameters in the system is the model most sensitive? In order to address these questions, we discuss what type of modeling approach is most appropriate in the crypt. We use the model to argue why tumorigenesis is observed to occur in stages with long lag phases between periods of rapid growth, and we identify the key parameters
On the proportion of cancer stem cells in a tumour
It is now generally accepted that cancers contain a sub-population, the cancer stem cells (CSCs), which initiate and drive a tumour’s growth. At least until recently it has been widely assumed that only a small proportion of the cells in a tumour are CSCs. Here we use a mathematical model, supported by experimental evidence, to show that such an assumption is unwarranted. We show that CSCs may comprise any possible proportion of the tumour, and that the higher the proportion the more aggressive the tumour is likely to be
Kertesz on Fat Graphs?
The identification of phase transition points, beta_c, with the percolation
thresholds of suitably defined clusters of spins has proved immensely fruitful
in many areas of statistical mechanics. Some time ago Kertesz suggested that
such percolation thresholds for models defined in field might also have
measurable physical consequences for regions of the phase diagram below beta_c,
giving rise to a ``Kertesz line'' running between beta_c and the bond
percolation threshold, beta_p, in the M, beta plane.
Although no thermodynamic singularities were associated with this line it
could still be divined by looking for a change in the behaviour of high-field
series for quantities such as the free energy or magnetisation. Adler and
Stauffer did precisely this with some pre-existing series for the regular
square lattice and simple cubic lattice Ising models and did, indeed, find
evidence for such a change in high-field series around beta_p. Since there is a
general dearth of high-field series there has been no other work along these
lines.
In this paper we use the solution of the Ising model in field on planar
random graphs by Boulatov and Kazakov to carry out a similar exercise for the
Ising model on random graphs (i.e. coupled to 2D quantum gravity). We generate
a high-field series for the Ising model on random graphs and examine
its behaviour for evidence of a Kertesz line
Polarized radio emission from the magnetar XTE J1810-197
We have used the Parkes radio telescope to study the polarized emission from
the anomalous X-ray pulsar XTE J1810-197 at frequencies of 1.4, 3.2, and 8.4
GHz. We find that the pulsed emission is nearly 100% linearly polarized. The
position angle of linear polarization varies gently across the observed pulse
profiles, varying little with observing frequency or time, even as the pulse
profiles have changed dramatically over a period of 7 months. In the context of
the standard pulsar "rotating vector model," there are two possible
interpretations of the observed position angle swing coupled with the wide
profile. In the first, the magnetic and rotation axes are substantially
misaligned and the emission originates high in the magnetosphere, as seen for
other young radio pulsars, and the beaming fraction is large. In the second
interpretation, the magnetic and rotation axes are nearly aligned and the line
of sight remains in the emission zone over almost the entire pulse phase. We
deprecate this possibility because of the observed large modulation of thermal
X-ray flux. We have also measured the Faraday rotation caused by the Galactic
magnetic field, RM = +77 rad/m^2, implying an average magnetic field component
along the line of sight of 0.5 microG.Comment: Accepted for publication in ApJ Letters. Six pages with 4 figure
A Search for the Optical Counterpart of the Luminous X-ray Source in NGC 6652
We examine images of the field of X1832-330, the luminous (Lx ~ 10^36 erg/s)
X-ray burst source near the center of the globular cluster NGC 6652, in order
to identify the optical counterpart for further study. U and B ground-based
images allow us to set a limit M_B > 3.5 for the counterpart at the time of
those observations, provided that the color is (U-B)_0 ~ -1, similar to the
sources known in other clusters. Archival Hubble Space Telescope observations
survey most but not all of the 1 sigma X-ray error circle, and allow us to set
limits M_B > 5.9 and M_B > 5.2 in the WF/PC and WFPC2 regions, respectively. In
the WF/PC images we do weakly detect a faint object with UV-excess, but it is
located 11.7'' from the ROSAT X-ray position. This considerable (2.3 sigma)
discrepancy in position suggests that this candidate be treated with caution,
but it remains the only reasonable one advanced thus far. We measure for this
star m_439 = 20.2 +- 0.2, (m_336 - m_439) = -0.5 +- 0.2, and estimate M_B =
5.5, (U-B)_0 = -0.9, similar to other known optical counterparts. If this
candidate is not the identification, our limits imply that the true
counterpart, not yet identified, is probably the optically-faintest cluster
source yet known, or alternatively that it did not show significant UV excess
at the time of these observations. Finally, we assess the outlook for the
identification of the remaining luminous globular cluster X-ray sources.Comment: 15 pages including 5 figures and no tables. Accepted for publication
in The Astronomical Journal; to appear in Volume 116, September 1998. A
preprint with full resolution figures may be downloaded from
http://www.astro.washington.edu/deutsch/pubs
The Surface Roughness and Gloss of Composites
The contrast gloss and the average roughness were measured for four commercial composite filling materials. Using a factorial design, each material was subjected to four available finishing methods. A significant difference was found in the contrast gloss among finishing methods, and a significant linear regression is given which relates the inverse of the contrast gloss to the average roughness. Surface gloss is proposed as playing a major role in the esthetic appearance of composite restorations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68215/2/10.1177_00220345840630051601.pd
Are Child's Class C Patients With Acute Variceal Bleeding Worth Treating?
In the ten year period January 1980 to December 1989, 102 patients with Child’s Class C liver disease
(Pugh's Modification) were admitted with acute variceal bleeding to one surgical unit with a policy of
early sclerotherapy. There were 56 males and 46 females; the average age was 55 years (range 28–77).
Fifty-three suffered from alcoholic cirrhosis. Four died before definitive treatment could be carried out,
three from liver failure and one from uncontrolled bleeding. Of the remaining 98 patients, eight had
urgent oesophageal transection with three deaths from hepatorenal failure; 90 had sclerotherapy with 19
hospital deaths, nine from recurrent bleeding, eight from liver failure often coupled with renal failure
and two from respiratory complications. Of the 76 who survived to leave hospital, 52 received chronic
injection sclerotherapy, 10 had elective oesophageal transection and 14 did not have further elective
intervention for various reasons. Surviving patients have been followed up at a special Liver Clinic with
minimum follow up of one year. Although no patient has yet survived ten years, the one, five and eight
year survivals of 50%, 21% and 13% suggest that salvage of thdse patients is worthwhile
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