864 research outputs found
CRASHWORTHY RAILING FOR TIMBER BRIDGES
Bridge railing systems in the United States have historically beers designed based on static load criteria given in the American Association of State Highway and Transportation 0fficials (AASHTO) Standard Specifications for Highway Bridges. In the past decade, full-scale vehicle crash testing has been recognized as a more appropriate and reliable method of evaluating bridge railing acceptability. In 1993, the National Cooperative Highway Research Program published Report 350, Recommended Procedures for the Saftey Performance Evaluation of Highway Features, which provides new criteria for evaluating longitudinal barriers. Based on these specifications, a cooperative research program is continuing between the USDA Forest Service, Forest Products Laboratory, the Midwest Roadside Saftety Facility of the University of Nebraska- Lincoln; and the Federal Highway Administration to develop and crash test bridge railings for wood bridge decks. This paper describes research that resulted in the successful development and testing of several bridge railings for longitudinal and transverse wood decks in accordance with NCHRP Report 350 requirements
Crash-Tested Bridge Railings for Timber Bridges
Bridge railing systems in the United States historically have been designed on the basis of static load criteria given in the AASHTO Standard Specifications for Highway Bridges. In the past decade, full-scale vehicle crash testing has been recognized as a more appropriate and reliable method of evaluating bridge railing acceptability. In 1989 AASHTO published Guide Specifications for Bridge Railings, which gives the recommendations and procedures to evaluate bridge railings by full-scale vehicle crash testing. In 1993 NCHRP published Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features, which provides criteria for evaluating longitudinal barriers. From these specifications, a cooperative research program was initiated to develop and crash test several bridge railings for longitudinal wood decks. The research resulted in the successful development and testing of five bridge railing systems for longitudinally laminated wood bridge decks in accordance with the AASHTO Performance Level 1 and Performance Level 2 requirements and the Test Level 4 requirements of NCHRP Report 350
CRASHWORTHY RAILING FOR TIMBER BRIDGES
Bridge railing systems in the United States have historically beers designed based on static load criteria given in the American Association of State Highway and Transportation 0fficials (AASHTO) Standard Specifications for Highway Bridges. In the past decade, full-scale vehicle crash testing has been recognized as a more appropriate and reliable method of evaluating bridge railing acceptability. In 1993, the National Cooperative Highway Research Program published Report 350, Recommended Procedures for the Saftey Performance Evaluation of Highway Features, which provides new criteria for evaluating longitudinal barriers. Based on these specifications, a cooperative research program is continuing between the USDA Forest Service, Forest Products Laboratory, the Midwest Roadside Saftety Facility of the University of Nebraska- Lincoln; and the Federal Highway Administration to develop and crash test bridge railings for wood bridge decks. This paper describes research that resulted in the successful development and testing of several bridge railings for longitudinal and transverse wood decks in accordance with NCHRP Report 350 requirements
Two Test Level 4 Bridge Railing and Transition Systems for Transverse Timber Deck Bridges
The Midwest Roadside Safety Facility, in cooperation with the Forest Products Laboratory, which is part of the U.S. Department of Agriculture’s Forest Service, and FHWA, designed two bridge railing and approach guardrail transition systems for use on bridges with transverse glue-laminated timber decks. The bridge raging and transition systems were developed and crash tested for use on higher-service-level roadways and evaluated according to the Test Level 4 safety performance criteria presented in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The first railing system was constructed with glulam timber components, whereas the second railing system was configured with steel hardware. Eight full-scale crash tests were performed, and the bridge railing and transition systems were acceptable according to current safety standards
Hybrid apparatus for Bose-Einstein condensation and cavity quantum electrodynamics: Single atom detection in quantum degenerate gases
We present and characterize an experimental system in which we achieve the
integration of an ultrahigh finesse optical cavity with a Bose-Einstein
condensate (BEC). The conceptually novel design of the apparatus for the
production of BECs features nested vacuum chambers and an in-vacuo magnetic
transport configuration. It grants large scale spatial access to the BEC for
samples and probes via a modular and exchangeable "science platform". We are
able to produce \87Rb condensates of five million atoms and to output couple
continuous atom lasers. The cavity is mounted on the science platform on top of
a vibration isolation system. The optical cavity works in the strong coupling
regime of cavity quantum electrodynamics and serves as a quantum optical
detector for single atoms. This system enables us to study atom optics on a
single particle level and to further develop the field of quantum atom optics.
We describe the technological modules and the operation of the combined BEC
cavity apparatus. Its performance is characterized by single atom detection
measurements for thermal and quantum degenerate atomic beams. The atom laser
provides a fast and controllable supply of atoms coupling with the cavity mode
and allows for an efficient study of atom field interactions in the strong
coupling regime. Moreover, the high detection efficiency for quantum degenerate
atoms distinguishes the cavity as a sensitive and weakly invasive probe for
cold atomic clouds
Two Test Level 4 Bridge Railing and Transition Systems for Transverse Timber Deck Bridges
The Midwest Roadside Safety Facility, in cooperation with the Forest Products Laboratory, which is part of the U.S. Department of Agriculture’s Forest Service, and FHWA, designed two bridge railing and approach guardrail transition systems for use on bridges with transverse glue-laminated timber decks. The bridge raging and transition systems were developed and crash tested for use on higher-service-level roadways and evaluated according to the Test Level 4 safety performance criteria presented in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The first railing system was constructed with glulam timber components, whereas the second railing system was configured with steel hardware. Eight full-scale crash tests were performed, and the bridge railing and transition systems were acceptable according to current safety standards
Railing Systems for Use on Timber Deck Bridges
Bridge railing systems in the United States have historically been designed based on static load criteria given in the AASHTO Standard Specifications for Highway Bridges. In the past decade, full-scale vehicle crash testing has been recognized as a more appropriate and reliable method of evaluating bridge railing acceptability. In 1989, AASHTO published the Guide Specifications for Bridge Railings, which gave the recommendations and procedures to evaluate bridge rails by full-scale vehicle crash testing. In 1993, the National Cooperative Highway Research Program (NCHRP) published Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features, which provided criteria for evaluating longitudinal barriers. Based on these specifications, a cooperative research program was initiated between the University of Nebraska-Lincoln and the Forest Products Laboratory, and later the FHWA, to develop and crash test 11 bridge rails for wood deck bridges. The research that resulted in successful development and testing of 11 bridge railing systems for longitudinally and transversely laminated wood bridge decks in accordance with AASHTO Performance Level 1 and 2 (PL-1 and PL-2) requirements and Test Levels 1, 2, and 4 (TL-1, TL-2, and TL-4) requirements of NCHRP Report 350 are described here
Minority-carrier mobility enhancement in p+ InGaAs lattice matched to InP
Minority electron mobilities in pf-In0.ssGac4, As have been measured with the zero field time-of-flight technique. The room-temperature (297 K) minority electron mobilities for p+-In,, 53Gac47A~ doped 0.9 and 3.1 x 10” cmm3 are found to be 2900 and 3300 cm* V-’ s-l, respectively. These are the first measurements to demonstrate enhancement in minority-carrier mobility as doping is increased for heavily doped Ines3Gae.4+s. This enhancement in mobility as doping is increased is similar to that observed in p+-GaAs, which has been attributed to reductions in plasmon and carrier-carrier scattering between minority electrons and majority holes
The Post-Common Envelope and Pre-Cataclysmic Binary PG 1224+309
We have made extensive spectroscopic and photometric observations of PG
1224+309, a close binary containing a DA white dwarf primary and an M4+
secondary. The H alpha line is in emission due to irradiation of the M-star by
the hot white dwarf and is seen to vary around the orbit. From the radial
velocities of the H alpha line we derive a period of P = 0.258689 +/- 0.000004
days and a semi-amplitude of K_Halpha = 160 +/- 8 km/s. We estimate a
correction Delta_K = 21 +/- 2 km/s, where K_M = K_Halpha + Delta_K. Radial
velocity variations of the white dwarf reveal a semi-amplitude of K_WD = 112
+/- 14 km/s. The blue spectrum of the white dwarf is well fit by a synthetic
spectrum having T_eff = 29,300 K and log(g) = 7.38. The white dwarf contributes
97% of the light at 4500 Angstroms and virtually all of the light blueward of
3800 Angstroms. No eclipses are observed. The mass inferred for the white dwarf
depends on the assumed mass of the thin residual hydrogen envelope: 0.40 < M_WD
< 0.45 solar masses for hydrogen envelope masses of 0 < M_H < 4.0E-4 solar
masses. We argue that the mass of the white dwarf is closer to 0.45 solar
masses, hence it appears that the white dwarf has a relatively large residual
hydrogen envelope. The mass of the M-star is then M_M = 0.28 +/- 0.05 solar
masses, and the inclination is i = 77 +/- 7 degrees. We discuss briefly how PG
1224+309 may be used to constrain theories of close binary star evolution, and
the past and future histories of PG 1224+309 itself. The star is both a
``post-common envelope'' star and a ``pre-cataclysmic binary'' star. Mass
transfer by Roche-lobe overflow should commence in about 10 Gyr.Comment: 17 pages, 8 figures, AAS LaTeX, to appear in AJ, March 199
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