56,328 research outputs found
Predicting vibrational failure of flexible ducting
Technique applies to liquid or gas transfer through flexible ducting and proves valuable in high velocity fluid flow cases. Fluid mechanism responsible for free bellows vibrational excitation also causes flexible hose oscillation. Static pressure stress influences flexible ducting fatigue life and is considered separately
Magnetometer and direct-current resistivity studies in Alaska
During the past year and a half, the territorial Department of Mines in Alaska has conducted a modest experimental program for the purpose of determining the extent to which magnetic and resistivity methods can be used in interior Alaska in connection with prospecting, mining and geological studies. Since little information is available concerning previous work, and since conditions differ considerably from those in most other regions, it was considered advisable to make a general study of the possibilities and limitation[s] of the two methods, rather than a detailed study of any single problem.Foreword -- Problems -- Instruments and methods -- Location of buried placers -- Thawed and permanently frozen overburden -- Underground water -- Conclusions -- References
Saltation on Mars and expected lifetime of Viking 75 wind sensors
With the use of the wind-tunnel measurements of Bagnold and Zingg, a model is developed for estimating the parameters that describe the flux of sand on Mars. Application of this model to the sensor-breakage problem indicates that the expected lifetime on Mars of the wind sensors of the Viking 75 Meteorology Instrument System is about 40 earth years. This expected lifetime is adequate for both the primary Viking 75 mission and for a proposed extended mission
Optimum Repair Level Analysis (ORLA) for the Space Transportation System (STS)
A repair level analysis method applied to a space shuttle scenario is presented. A determination of the most cost effective level of repair for reparable hardware, the location for the repair, and a system which will accrue minimum total support costs within operational and technical constraints over the system design are defined. The method includes cost equations for comparison of selected costs to completion for assumed repair alternates
Pressure wave propagation through annular and mist flows
One dimensional models of pressure wave propagation through annular and mist flow
Subgroup separability in residually free groups
We prove that the finitely presentable subgroups of residually free groups
are separable and that the subgroups of type are virtual
retracts. We describe a uniform solution to the membership problem for finitely
presentable subgroups of residually free groups.Comment: 8 pages, no figure
On the difficulty of presenting finitely presentable groups
We exhibit classes of groups in which the word problem is uniformly solvable
but in which there is no algorithm that can compute finite presentations for
finitely presentable subgroups. Direct products of hyperbolic groups, groups of
integer matrices, and right-angled Coxeter groups form such classes. We discuss
related classes of groups in which there does exist an algorithm to compute
finite presentations for finitely presentable subgroups. We also construct a
finitely presented group that has a polynomial Dehn function but in which there
is no algorithm to compute the first Betti number of the finitely presentable
subgroups.Comment: Final version. To appear in GGD volume dedicated to Fritz Grunewal
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