Compensator design for low-sensitivity linear time-invariant systems (COMPDES)

Digital computer program written in FORTRAN 4 has capability of synthesizing low order compensators to stabilize dynamical system in presence of parameter variations. Design scheme is accomplished by means of sensitivity function which is minimized with respect to eigenvalues

User's guide for computer program COMPDES, volume 4 Final report, 4 Nov. 1969 - 4 Apr. 1971

User guide for use of compensator design program /COMPDES/ - Vol.

Mid-Infrared Galaxy Morphology Along the Hubble Sequence

The mid-infrared emission from 18 nearby galaxies imaged with the IRAC instrument on Spitzer Space Telescope samples the spatial distributions of the reddening-free stellar photospheric emission and the warm dust in the ISM. These two components provide a new framework for galaxy morphological classification, in which the presence of spiral arms and their emission strength relative to the starlight can be measured directly and with high contrast. Four mid-infrared classification methods are explored, three of which are based on quantitative global parameters (colors, bulge-to-disk ratio) similar to those used in the past for optical studies; in this limited sample, all correlate well with traditional B-band classification. We suggest reasons why infrared classification may be superior to optical classification.Comment: ApJS (in press), Spitzer Space Telescope Special Issue; 13 pages, LaTeX (or Latex, etc); Figure 1ab is large, color plate; full-resolution plates in .pdf format available at http://cfa-www.harvard.edu/irac/publications

Star-Like Micelles with Star-Like Interactions: A quantitative Evaluation of Structure Factor and Phase Diagram

PEP-PEO block copolymer micelles offer the possibility to investigate phase behaviour and interactions of star polymers (ultra-soft colloids). A star-like architecture is achieved by an extremely asymmetric block ratio (1:20). Micellar functionality f can be smoothly varied by changing solvent composition (interfacial tension). Structure factors obtained by SANS can be quantitatively described in terms of an effective potential developed for star polymers. The experimental phase diagram reproduces to a high level of accuracy the predicted liquid/solid transition. Whereas for intermediate f a bcc phase is observed, for high f the formation of a fcc phase is preempted by glass formation.Comment: 5 pages, 4 figures, PRL in pres

Abundances in galactic H2 regions, 3: G25.4-0.2, G45.5+0.06, M8, S159 and DR22

Measurements of the ARII (6.99 microns), ArIII (8.99 microns), NeII (12.81 microns), SIII (18.71 microns), and SIV (10.51 microns) lines are presented for five compact HII regions along with continuum spectroscopy. From these data and radio data, lower limits to the elemental abundances of Ar, S, and Ne were deduced. The complex G25.4-0.2 is only 5.5 kpc from the galactic center, and is considerably overabundant in all these elements. Complex G45.5+0.06 is at seven kpc from the galactic center, and appears to be approximately consistent with solar abundance. The complex S159 in the Perseus Arm, at 12 kpc from the galactic center, has solar abundance, while M8 in the solar neighborhood may be somewhat overabundant in Ar and Ne. Complex DR 22, at 10 kpc from the galactic center in the Cygnus Arm, is overabundant in Ar. A summary of results from a series of papers on abundances is given

Spitzer/IRAC Observations of the Variability of Sgr A* and the Object G2 at 4.5 microns

We present the first detection from the Spitzer Space Telescope of 4.5 micron variability from Sgr A*, the emitting source associated with the Milky Way's central black hole. The >23 hour continuous light curve was obtained with the IRAC instrument in 2013 December. The result characterizes the variability of Sgr A* prior to the closest approach of the G2 object, a putative infalling gas cloud that orbits close to Sgr A*. The high stellar density at the location of Sgr A* produces a background of ~250 mJy at 4.5 microns in each pixel with a large pixel-to-pixel gradient, but the light curve for the highly variable Sgr A* source was successfully measured by modeling and removing the variations due to pointing wobble. The observed flux densities range from the noise level of ~0.7 mJy rms in a 6.4-s measurement to ~10 mJy. Emission was seen above the noise level ~34% of the time. The light curve characteristics, including the flux density distribution and structure function, are consistent with those previously derived at shorter infrared wavelengths. We see no evidence in the light curve for activity attributable to the G2 interaction at the observing epoch, ~100 days before the expected G2 periapsis passage. The IRAC light curve is more than a factor of two longer than any previous infrared observation, improving constraints on the timescale of the break in the power spectral distribution of Sgr A* flux densities. The data favor the longer of the two previously published values for the timescale.Comment: 13 pages, 10 figures, 2 tables, accepted for publication in the Ap

Role of interfacial tension for the structure of PEP-PEO polymeric micelles. A combined SANS and pendant drop tensiometry investigation

We investigated the influence of interfacial tension, gamma, on the micellization properties of a highly asymmetric poly(ethylene-co-propylene)-poly(ethylene oxide) (PEP-PEO) block copolymer in mixed solvents consisting of water and dimethyl form ami de (DMF). Both are good solvents for PEO and nonsolvents for PEP but exhibit, a large difference in gamma with respect to the insoluble core block. Micellar characteristics were obtained by small-angle neutron scattering (SANS) and subsequent fitting of a core-shell form factor to the scattering patterns. The curves are perfectly described by a hyperbolic density profile for the shell, n(r) similar to r(-4/3), indicating a starlike structure of the micelles. The aggregation numbers of the micelles decrease with increasing DMF-water ratio from P = 120 in pure water to nonaggregated chains in pure DMF. Corresponding interfacial tensions were determined by pendant drop tensiometry using a PEP homopolymer of equal molar mass. A correlation of P with gamma reveals a power law dependence, P similar to gamma(6/5) in accordance with the scaling prediction of Halperin for starlike micelles. Additionally, it was found that the addition of DMF leads to a considerable decrease in the micelle radii, which cannot be explained by the decrease in P alone. Measurements of the second virial coefficients, A(2), of a PEO homopolymer by SANS reveal clearly reduced values compared to A(2) in pure water but still good solvent conditions for PEO in all water/DMF mixtures. However, a significant reduction in the radius of gyration was not found. Therefore, it was concluded that the reduced solvent quality has a more pronounced effect for the PEO chain dimensions in the confined geometry of a micellar corona