58,806 research outputs found
Conceptual design and structural analysis of the spectroscopy of the atmosphere using far infrared emission (SAFIRE) instrument
The conceptual design and structural analysis for the Spectroscopy of the Atmosphere using Far Infrared Emission (SAFIRE) Instrument are provided. SAFIRE, which is an international effort, is proposed for the Earth Observing Systems (EOS) program for atmospheric ozone studies. A concept was developed which meets mission requirements and is the product of numerous parametric studies and design/analysis iterations. Stiffness, thermal stability, and weight constraints led to a graphite/epoxy composite design for the optical bench and supporting struts. The structural configuration was determined by considering various mounting arrangements of the optical, cryo, and electronic components. Quasi-static, thermal, modal, and dynamic response analyses were performed, and the results are presented for the selected configuration
Recasting results in equivariant geometry: affine cosets, observable subgroups and existence of good quotients
Using the language of stacks, we recast and generalize a selection of results
in equivariant geometry
A New Species of Mite (Acari: Podapolipidae) From a Michigan Carabid Beetle, \u3ci\u3eChlaenius Pennsylvanicus\u3c/i\u3e
Eutarsopolipus regenfussi n. sp. is described from the Michigan carabid beetle, Chlaenius pennsylvanicus (L.)
Beyond Chernobyl: Radiating A New Word Meaning Mistrust Authentic human development by ecological and transnational moral interdependence (Solicitudo Rei Socialis, 1987)
Female Fighting and Host Competition Among Four Sympatric Species of \u3ci\u3eMelittobia\u3c/i\u3e (Hymenoptera: Eulophidae)
Melittobia is a genus of parasitic wasps well known for high levels of inbreeding and violent male combat. Casual observations of groups of sisters of M. femorata placed with hosts revealed a surprising incidence of body mutilations (broken or missing tarsi, antennae, and wings). Replicated conspecific groups of 1, 2, or 3 females of M. femorata, M. digitata, and M. australica and interspecific groups of M. femorata and M. australica (2:1) were observed over their first 10 days in newly established cultures, and the incidence of mutilation was recorded. In some groups females were dye-fed, allowing us to subsequently chart their individual activity patterns on or near the host based on patterns of their colored fecal droppings. For M. australica and M. digitata, no conspecific females in any group size ever showed mutilation. However, in M. femorata nearly 3/4ths of the females in conspecific groups of two or three acquired body damage beginning about the time of first oviposition on the host. In 4 of 5 replicates of the interspecific groups, M. femorata females killed the female of M. australica. Patterns of dyed fecal droppings that developed over several days showed that individual females in groups of both M. femorata and M. australica increasingly restricted their activities to a small portion of the host. These âmicroâ territories were non-overlapping and appeared to be actively defended. In contrast, M. digitata females in groups never displayed obvious territoriality or interference. Possible reasons for these differences in female behavior are discussed
Heavy mineral stratigraphy of the Unayzah Formation and Basal Khuff Clastics (Carboniferous to Permian) of Central Saudi Arabia
A study of heavy mineral assemblages in the Unayzah Reservoir sandstones of central Saudi Arabia has
identified successive changes in provenance signature. These define four heavy mineral units that are of
regional extent and largely coincident with the four main depositional units defined by previous authors:
Unayzah C, Unayzah B, Unayzah A and the Basal Khuff Clastics. Sandstone bodies with anomalous mineral
signatures also occur, however, especially within the Unayzah B Member. These are attributed to local
supply of sand from pre-Unayzah Paleozoic sandstones exposed on the Central Arabian Arch and on intrabasinal
highs.
The stratigraphic changes in mineralogy reflect successive developments in the geography and climate of the
region and in the pattern of sand sourcing and transport. The Unayzah C sands and the majority of Unayzah
B sands were derived from the south but whereas the southerly derived Unayzah C sands appear to have
been derived from pre-existing mature sandstones, those of Unayzah B were sourced from a wider range of
rock types including crystalline basement. This contrast is interpreted as indicating that a significant hiatus
may separate the two units. The Unayzah B sands are also characterised by the common presence of apatite,
indicating that the source rocks were relatively unweathered. This observation is compatible with the glacial
origin attributed to many of the Unayzah B sediments.
A further change in provenance signature takes place at the base the newly recognised âun-named middle
Unayzah memberâ, equivalent to the base of Unayzah A of previous authors. This is associated with the onset
of red-bed sedimentation throughout the area. Unayzah A sedimentation was terminated by a fall in sea level
that led to the formation of a widespread unconformity and to the development of deeply incised valleys along
the western basin margin. In most of the study area this unconformity corresponds to the base of the Khuff
Formation, but in the east of the area, where the succession is more complete, it is believed to occur within the
Unayzah Formation, at a level equivalent to the base of the Upper Gharif Member of Oman.
By identifying lateral and vertical changes in sand provenance, heavy mineral analysis provides an important
additional tool in the stratigraphic analysis of the Permian sandstone succession of Saudi Arabia, both at the
regional scale and wand at the scale of individual reservoir sandstone successions
A geometric approach to three-dimensional hipped bipedal robotic walking
This paper presents a control law that results in stable walking for a three-dimensional bipedal robot with a hip. To obtain this control law, we utilize techniques from geometric reduction, and specifically a variant of Routhian reduction termed functional Routhian reduction, to effectively decouple the dynamics of the three-dimensional biped into its sagittal and lateral components. Motivated by the decoupling afforded by functional Routhian reduction, the control law we present is obtained by combining three separate control laws: the first shapes the potential energy of the sagittal dynamics of the biped to obtain stable walking gaits when it is constrained to the sagittal plane, the second shapes the total energy of the walker so that functional Routhian reduction can be applied to decoupling the dynamics of the walker for certain initial conditions, and the third utilizes an output zeroing controller to stabilize to the surface defining these initial conditions. We numerically verify that this method results in stable walking, and we discuss certain attributes of this walking gait
Finite Source Sizes and the Information Content of MACHO-Type Lens Search Light Curves
If the dark halo matter is primarily composed of MACHOs toward the lower end
of the possible detection range ( ) a fraction of the
lens detection events should involve the lens crossing directly in front of the
disk of the background star. Previously, Nemiroff (1987) has shown that each
crossing would create an inflection point in the light curve of the MACHO
event. Such inflection points would allow a measure of the time it took for the
gravitational lens to cross the stellar disk. Given an independent estimate of
the stellar radius by other methods, one could then obtain a more accurate
estimate of the velocity of the lens. This velocity could then, in turn, be
used to obtain a more accurate estimate of the mass range for the MACHO or disk
star doing the lensing.Comment: in press: ApJ (Lett.), 10 pages in Plain TeX version 3.0, 1 figure
available by FA
Trends in Self-Employment Among White and Black Men: 1910-1990
We examine trends in self-employment among white and black men from 1910 to 1990 using Census and CPS microdata. Self-employment rates fell over most of the century and then started to rise after 1970. For white men, we find that the decline was due to declining rates within industries, but was counterbalanced somewhat by a shift in employment towards high self-employment industries. Recently, the increase in self-employment was caused by an end to the within industry decline and the continuing shift in employment towards high self-employment industries. We find that the trends in self-employment average returns do not easily explain the decline in self-employment from 1950 to 1970, nor the increase from 1970 to 1990. We also find that changes in tax rates, social security benefits, and immigration patterns do not explain the recent upturn in self-employment. For black men, we find that the self-employment rate remained at a level of roughly one-third the white rate from 1910 to 1990. The large and constant gap between the black and the white rates is not due to blacks being concentrated in low self-employment rate industries, but is consistent with job opportunities outside of self-employment increasing relative to those in self-employment. However, more recently the relative earnings of blacks in self-employment rose more than relative earnings for whites the near constancy of the relative self-employment rates more surprising. We also find that absent continuing forces holding down black self-employment, a simple inter-generational model of self-employment suggests that black and white rates would converge quickly.
- âŠ