2,326 research outputs found
Experimental X-ray Stress Analysis Procedures for Ultra High Strength Materials
X-ray stress analysis procedures for accurate measurement of elastic strain in high strength steel
Damping capacity of a model steel structure
The damping capacities of seven model steel structures, each consisting of a heavy steel platform supported on four columns, have been determined from forced vibration tests. The vibrations were produced by an eccentric-mass vibration generator, and the amplitudes ranged from small displacements up to slightly greater than yield displacement. The tests were terminated at the higher amplitudes once fatigue cracks formed in any of the joint welds in the columns. For vibration amplitudes up to a critical amplitude slightly less than yield displacement, the damping factors of the structures were constant, independent of amplitude, and ranged between .15 and .25~ for different structures. At vibration amplitudes greater than the critical amplitude, the damping factors of the structures became functions of amplitude. For example, the damping factor of one test structure increased from .15 to 1.~ as the displacement amplitude increased from 1.1 to 1.4 inches. The last structure tested revealed that a few cycles of vibration at amplitudes greater than the critical amplitude would increase these values slightly. Finally, the results summarized above are compared with the results of: {i) experimental work conducted by Lazan; {ii) reversed loading tests conducted on cantilever beams of similar construction to those tested in the work described in this report; and (iii) experimental work conducted by Hanson
The dynamic behavior of steel frame and truss buildings
This report describes experimental and analytical studies of the dynamic behavior of the East Building of the University of California\u27s new Medical Center at San Francisco, California. It also describes experimental tests conducted on the East Building\u27s mechanical service tower and on an adjacent elevator tower. Experimental tests on the East Building were conducted in the summers of 1964 and 1965. Vibrations were produced by eccentric-masstype vibration generators. Frequency responses, time responses, and mode shapes were observed. In the summer 1964 tests, the first mode east-west had 2% of critical damping and the first mode north-south had 1.8%; the values of damping for the higher modes lay in the range 0.4% to 0.9% of critical In the summer 1965 tests, the damping capacity measurements were mostly in the range 5 to 10% of critical. The cause of this increase in damping capacity was investigated in the fall 1965 tests. The fall 1965 tests showed that although the East Building was designed as free-standing, it was dynamically coupled to its adjacent buildings The relatively large damping capacity of this coupled system has been attributed to the Coulomb damping provided by non-structural connections between buildings An analytical model of the East Building was formulated to provide behavior corresponding to the summer 1964 test results. A standard openframe- type model was found capable of representing the dynamic behavior of the real structure. The analytical model was subjected to the El Centro earthquake ground acceleration record in a digital computer analysis. With 5% critical damping in the first few modes, no members of the frame yielded, but when the intensity of the earthquake was increased by a factor of 1.3, some members did yield
The Haupt Effect: Coupled rotational and dipolar relaxation of methyl groups
A theory is described for the dynamic proton dipolar polarization observed by Haupt (1972) in 4-methylpyridine following a sudden temperature change. The theory differs from that of Haupt in assuming that transitions which change the rotational quantum number of the 4-methyl group by +or-3 occur very rapidly, maintaining thermal equilibrium within each of the three subsets of rotational levels corresponding to the three methyl group proton spin symmetry species A, Ea and Eb. The difference of A and E species populations approaches the new equilibrium value slowly and exponentially, following the temperature jump, and generates dipolar polarization in the process. Transitions between Ea and Eb species lead to destruction of the polarization, whose evolution from zero due to these competing processes has the simple form C(exp(-at)-exp(-bt)). This is checked by a modified version of Haupt\u27s experiment in which the initial temperature jump is followed by a later burst of RF pulses which reduces the dipolar polarization to zero
The Haupt Effect: Coupled rotational and dipolar relaxation of methyl groups
A theory is described for the dynamic proton dipolar polarization observed by Haupt (1972) in 4-methylpyridine following a sudden temperature change. The theory differs from that of Haupt in assuming that transitions which change the rotational quantum number of the 4-methyl group by +or-3 occur very rapidly, maintaining thermal equilibrium within each of the three subsets of rotational levels corresponding to the three methyl group proton spin symmetry species A, Ea and Eb. The difference of A and E species populations approaches the new equilibrium value slowly and exponentially, following the temperature jump, and generates dipolar polarization in the process. Transitions between Ea and Eb species lead to destruction of the polarization, whose evolution from zero due to these competing processes has the simple form C(exp(-at)-exp(-bt)). This is checked by a modified version of Haupt\u27s experiment in which the initial temperature jump is followed by a later burst of RF pulses which reduces the dipolar polarization to zero
A New Approach to Environmental Valuation for New Zealand
New Zealand’s Resource Management Act is frequently criticised for the costs and delays it imposes on activities, but less attention is given to the consistency of values it applies to environmental effects through its decisions. The wide variety of parties who exercise decision roles under the act lack guidance on the economic value of the environment, and non-market valuation studies are too costly to be widely used and too few and varied to infer reliable generic values. Drawing on experience in estimating the public value of safety improvements, this article proposes an alternative approach that measures people’s aversion to the risk of environmental impacts of different scales and severity which could yield values sufficiently generic to be widely used, and outlines its uses both within and beyond the RMA applications
Synthesis and characterization of polyimides containing 4,4'-hexafluoroisopropylidene-bisphthalic
Effects of Intraventricular Locus Coeruleus Transplants on Seizure Severity in Genetically Epilepsy-Prone Rats Following Depletion of Brain Norepinephrine
Audiogenic seizures (AGS) in genetically
epilepsy-prone rats (GEPR) of the moderateseizure
substrain (GEPR-3s) were investigated
to determine whether norepinephrine (NE)
depletion induced by 6-hydroxydopalnine (6-OHDA)
microinfusion into the locus coeruleus
(LC) could alter the efficacy of intraventricular
NE tissue grafts in promoting reductions in
seizure severity in AGS. GEPR-3s were
stereotaxically infused with 6-OHDA
(4ÎĽg/side/rat), or vehicle into the region of the
LC. Following 6-OHDA treatment all animals
were subjected to 3 AGS tests. GEPR-3s seizure
severities were increased in 39.5% of the
animals after microinfusion of 6-OHDA into the
region of the LC. Following the third AGS test,
each rat was stereotaxicaily implanted with 17
gestational day rat fetal tissue obtained from the
dorsal pons and containing the primordia of the
LC or with tissue obtained from the neocortex
or were sham-grafted. Subsequent to grafting,
rats were subjected to 3 additional AGS tests.
53% (10/19) of 6-OHDA treated GEPRs showed
a significant reduction in seizure severity
following transplantation of fetal LC tissue. In
contrast, only 20% (1/5) of GEPRs infused with
saline rather than 6-OHDA showed, a reduction
of seizure severity following fetal LC
transplantation. NE content in the cortex and
pons/medulla was decreased by 78% and 46%
respectively following 6-OHDA microinfusion
into the LC. Prominent grafts with numerous
TH positive neurons and neurites were present
within the third ventricle of grafted animals,
while cortex grafts contained no TH
immunostained structures. These findings
suggest that the efficacy of fetal LC tissue to
promote reductions in seizure severity in GEPRs
is increased following depletion of central NE by
microinfusion of 6-OHDA
Easy on that trigger dad: a study of long term family photo retrieval
We examine the effects of new technologies for digital photography on people's longer term storage and access to collections of personal photos. We report an empirical study of parents' ability to retrieve photos related to salient family events from more than a year ago. Performance was relatively poor with people failing to find almost 40% of pictures. We analyze participants' organizational and access strategies to identify reasons for this poor performance. Possible reasons for retrieval failure include: storing too many pictures, rudimentary organization, use of multiple storage systems, failure to maintain collections and participants' false beliefs about their ability to access photos. We conclude by exploring the technical and theoretical implications of these findings
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Thin liquid water clouds: their importance and our challenge
Many clouds important to the Earth’s energy balance contain small amounts of liquid water, yet despite many improvements, large differences in retrievals of their liquid water amount and particle size still must be resolved
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