1,606 research outputs found
Low-speed stability and control characteristics of a transport model with aft-fuselage-mounted advanced turboprops
A limited experimental investigation was conducted in the Langley 4- by 7-Meter Tunnel to explore the effects of aft-fuselage-mounted advanced turboprop installations on the low-speed stability and control characteristics of a representative transport aircraft in a landing configuration. In general, the experimental results indicate that the longitudinal and lateral-directional stability characteristics for the aft-fuselage-mounted single-rotation tractor and counter-rotation pusher propeller configurations tested during this investigation are acceptable aerodynamically. For the single-rotation tractor configuration, the propeller-induced aerodynamics are significantly influenced by the interaction of the propeller slipstream with the pylon and nacelle. The stability characteristics for the counter-rotation pusher configuration are strongly influenced by propeller normal forces. The longitudinal and directional control effectiveness, engine-out characteristics, and ground effects are also presented. In addition, a tabulated presentation of all aerodynamic data presented in this report is included as an appendix
Diquat Derivatives: Highly Active, Two-Dimensional Nonlinear Optical Chromophores with Potential Redox Switchability
In this article, we present a detailed study of structureâactivity relationships in diquaternized 2,2â˛-bipyridyl (diquat) derivatives. Sixteen new chromophores have been synthesized, with variations in the amino electron donor substituents, Ď-conjugated bridge, and alkyl diquaternizing unit. Our aim is to combine very large, two-dimensional (2D) quadratic nonlinear optical (NLO) responses with reversible redox chemistry. The chromophores have been characterized as their PF_6^â salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Their visible absorption spectra are dominated by intense Ď â Ď^* intramolecular charge-transfer (ICT) bands, and all show two reversible diquat-based reductions. First hyperpolarizabilities β have been measured by using hyper-Rayleigh scattering with an 800 nm laser, and Stark spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities β_0. The directly and indirectly derived β values are large and increase with the extent of Ď-conjugation and electron donor strength. Extending the quaternizing alkyl linkage always increases the ICT energy and decreases the E_(1/2) values for diquat reduction, but a compensating increase in the ICT intensity prevents significant decreases in Stark-based β_0 responses. Nine single-crystal X-ray structures have also been obtained. Time-dependent density functional theory clarifies the molecular electronic/optical properties, and finite field calculations agree with polarized HRS data in that the NLO responses of the disubstituted species are dominated by âoff-diagonalâ β_(zyy) components. The most significant findings of these studies are: (i) β_0 values as much as 6 times that of the chromophore in the technologically important material (E)-4â˛-(dimethylamino)-N-methyl-4-stilbazolium tosylate; (ii) reversible electrochemistry that offers potential for redox-switching of optical properties over multiple states; (iii) strongly 2D NLO responses that may be exploited for novel practical applications; (iv) a new polar material, suitable for bulk NLO behavior
Evolution of Linear Absorption and Nonlinear Optical Properties in V-Shaped Ruthenium(II)-Based Chromophores
In this article, we describe a series of complexes with electron-rich cis-{Ru^(II)(NH_3)_4}^(2+) centers coordinated to two pyridyl ligands bearing N-methyl/arylpyridinium electron-acceptor groups. These V-shaped dipolar species are new, extended members of a class of chromophores first reported by us (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845â4859). They have been isolated as their PF_6â salts and characterized by using various techniques including ^1H NMR and electronic absorption spectroscopies and cyclic voltammetry. Reversible Ru^(III/II) waves show that the new complexes are potentially redox-switchable chromophores. Single crystal X-ray structures have been obtained for four complex salts; three of these crystallize noncentrosymmetrically, but with the individual molecular dipoles aligned largely antiparallel. Very large molecular first hyperpolarizabilities β have been determined by using hyper-Rayleigh scattering (HRS) with an 800 nm laser and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d â Ď^* metal-to-ligand charge-transfer (MLCT) and Ď â Ď^* intraligand charge-transfer (ILCT) bands. The latter measurements afford total nonresonant β_0 responses as high as ca. 600 Ă 10^(â30) esu. These pseudo-C_(2v) chromophores show two substantial components of the β tensor, β_(zzz) and β_(zyy), although the relative significance of these varies with the physical method applied. According to HRS, β_(zzz) dominates in all cases, whereas the Stark analyses indicate that β_(zyy) is dominant in the shorter chromophores, but β_(zzz) and β_(zyy) are similar for the extended species. In contrast, finite field calculations predict that β_(zyy) is always the major component. Time-dependent density functional theory calculations predict increasing ILCT character for the nominally MLCT transitions and accompanying blue-shifts of the visible absorptions, as the ligand Ď-systems are extended. Such unusual behavior has also been observed with related 1D complexes (Coe, B. J. et al. J. Am. Chem. Soc. 2004, 126, 3880â3891)
Search for positively charged strangelets and other related results with E864 at the AGS
We report on the latest results in the search for positively charged
strangelets from E864's 96/97 run at the AGS with sensitivity of about per central collision. This contribution also contains new results of
a search for highly charged strangelets with . Production of light
nuclei, such as and , is presented as well. Measurements of yields
of these rarely produced isotopes near midrapidity will help constrain the
production levels of strangelets via coalescence. E864 also measures antiproton
production which includes decays from antihyperons. Comparisons with antiproton
yields measured by E878 as a function of centrality indicate a large
antihyperon-to-antiproton ratio in central collisions.Comment: 8 pages, 4 figures; Talk at SQM'98, Padova, Italy (July 20-24th,
1998
Line shape diagnostics for solid density plasmas produced by ultra intense subpicosecond laser
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87325/2/158_1.pd
Galaxy clusters at high redshift and evolution of brightest cluster galaxies
Identification of high redshift clusters is important for studies of
cosmology and cluster evolution. Using photometric redshifts of galaxies, we
identify 631 clusters from the Canada-France-Hawaii Telescope (CFHT) Wide
field, 202 clusters from the CHFT Deep field, 187 clusters from the Cosmic
Evolution Survey (COSMOS) and 737 clusters from the Spitzer Wide-area InfraRed
Extragalactic survey (SWIRE) field. The redshifts of these clusters are in the
range of 0.1<z<1.6. Merging these cluster samples gives 1644 clusters in the
four survey fields, of which 1088 are newly identified and more than half are
from the large SWIRE field. Among 228 clusters of z>1, 191 clusters are newly
identified, and most of them from the SWIRE field. With this large sample of
high redshift clusters, we study the color evolution of the brightest cluster
galaxies (BCGs). The colors r'-z' and r^+-m_{3.6\mu m} of the BCGs are
consistent with a stellar population synthesis model in which the BCGs are
formed at redshift z_f>2 and evolved passively. The colors g'-z' and
B-m_{3.6\mu m} of the BCGs at redshifts z>0.8 are systematically bluer than the
passive evolution model for galaxy formed at z_f~2, indicating star formation
in high redshift BCGs.Comment: 10 pages, 14 figures, 2 tables; added reference, corrected typos;
Table 2 is available at http://zmtt.bao.ac.cn/wzl/CV_wen.ht
Catalogue of high-mass X-ray binaries in the Galaxy ( edition)
We present a new edition of the catalogue of high-mass X-ray binaries in the
Galaxy. The catalogue contains source name(s), coordinates, finding chart,
X-ray luminosity, system parameters, and stellar parameters of the components
and other characteristic properties of 114 high-mass X-ray binaries, together
with a comprehensive selection of the relevant literature. The aim of this
catalogue is to provide the reader with some basic information on the X-ray
sources and their counterparts in other wavelength ranges (-rays, UV,
optical, IR, radio). About 60% of the high-mass X-ray binary candidates are
known or suspected Be/X-ray binaries, while 32% are supergiant/X-ray binaries.
Some sources, however, are only tentatively identified as high-mass X-ray
binaries on the basis of their X-ray properties similar to the known high-mass
X-ray binaries. Further identification in other wavelength bands is needed to
finally determine the nature of these sources. In cases where there is some
doubt about the high-mass nature of the X-ray binary this is mentioned.
Literature published before 1 October 2005 has, as far as possible, been taken
into account.Comment: 25 pages, table include
Xâray spectroscopy of hot solid density plasmas produced by subpicosecond high contrast laser pulses at 1018â1019 W/cm2
Analysis is presented of Kâshell spectra obtained from solid density plasmas produced by a high contrast (1010:1) subpicosecond laser pulse (0.5 Îźm) at 1018â1019 W/cm2. Stark broadening measurements of Heâlike and Liâlike lines are used to infer the mean electron density at which emission takes place. The measurements indicate that there is an optimum condition to produce xâray emission at solid density for a given isoelectronic sequence, and that the window of optimum conditions to obtain simultaneously the shortest and the brightest xâray pulse at a given wavelength is relatively narrow. Lower intensity produces a short xâray pulse but low brightness. The xâray yield (and also the energy fraction in hot electrons) increases with the laser intensity, but above some laser intensity (1018 W/cm2 for Al) the plasma is overdriven: during the expansion, the plasma is still hot enough to emit, so that emission occurs at lower density and lasts much longer. Energy transport measurements indicate that approximately 6% of the laser energy is coupled to the target at 1018 W/cm2 (1% in thermal electrons with Teâ0.6 keV and 5% in suprathermal electrons with Thâ25 keV). At IÎť2=1018 WâÎźm2/cm2 (no prepulse) around 1010 photons are emitted per laser shot, in 2Ď srd in cold KÎą radiation (2â9 Ă
, depending on the target material) and up to 2Ă1011 photons are obtained in 2Ď srd with the unresolved transition array (UTA) emission from the Ta target. Š 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69900/2/PHPAEN-2-5-1702-1.pd
- âŚ