NASA Scientific and Technical Aerospace Reports

20040073668 Princeton Univ., NJ
Investigations of Operational Lifetime and Modes of Failure of Organic Light Emitting Devices
Forrest, Stephen R.; Thompson, Mark; Barbara, Paul; Brown, Julia J.; Feb. 2004; 87 pp.; In English
Contract(s)/Grant(s): MDA-972-01-1-0032; Proj-H731
Report No.(s): AD-A422559; AFRL-HE-WP-TR-2003-0154; No Copyright; Avail: CASI; A05, Hardcopy
Reliability limitations of organic light emitting devices (OLEDs) were explored in a joint effort project lead by Princeton
University, with subcontracting efforts by the University of Southern California, the University of Texas and Universal Display
Corporation. Methodologies and protocols for screening of device structures and materials were developed. Extended lifetimes
of red, green and blue phosphorescent OLEDs were achieved. For example, lifetimes of over 50,000 hours were obtained for
both red and green devices. Blue device lifetimes observed were still less than 1000 hours. This difference in blue lifetime was
studied using through both photo- and electro-luminescence methods, and was determined to be due, in part, to the high
energies needed to excite the blue lumophores, which results in charge imbalance in the emission layers of the OLEDs. Contact
degradation was also studied at the microscopic scale using near-field scanning optical microscopy (NSOM) in concert with
our transparent OLED structure (TOLED). It was found that defects introduced during processing are largely responsible for
the formation and growth of dark spots.
DTIC
Failure; Light Emitting Diodes
20040073745 Naval Research Lab., Washington, DC
Bacterial Metabolism, Aromatic Biodegradation, and Lignin Biogeochemistry in Sediment Cores from Pearl Harbor,
Hawaii
Montgomery, Michael T.; Osburn, Christopher L.; Apr. 14, 2004; 18 pp.; In English
Report No.(s): AD-A422667; NRL/FR/6114--04-10077; No Copyright; Avail: CASI; A03, Hardcopy
Heterotrophic bacteria require a source of oxygen to rapidly metabolize complex and recalcitrant carbon sources like
lignin, 2,4,6 trinitrotoluene (TNT) , and polycyclic aromatic hydrocarbons (PAHs). The activities of burrowing macrofauna
can increase oxygenation, which may stimulate bacterial metabolism of PAHs and heterotrophic production. We measured
bacterial production, PAH mineralization, and lignin subunit concentration with depth in cores taken from South Loch and
Bishop’s Point in Pearl Harbor, Hawaii. Bacterial metabolism decreased rapidly with depth but was much higher at South Loch
than Bishop’s Point. PAH mineralization rates were higher at South Loch than at Bishop’s Point and extended down to the
depths of bioturbation at each site: upper 4 to 6 cm at Bishop s Point and upper 9 cm at South Loch. Phenolic moieties of lignin
at South Loch and Bishop’s Point suggest there are different sources of organic matter to the two sites. PAH mineralization
was elevated in bioturbated zones from both sites relative to those below this zone. Ambient PAH concentrations were also
higher at the less bioturbated site. This is consistent with the hypothesis that benthic infauna stimulate PAH metabolism.
DTIC
Bacteria; Biodegradation; Biogeochemistry; Cores; Harbors; Hydrocarbons; Lignin; Metabolism; Sediments
24
COMPOSITE MATERIALS
Includes physical, chemical, and mechanical properties of laminates and other composite materials.
20040068310 Wichita State Univ., Wichita, KS, USA
Damage Resistance and Tolerance of Composite Sandwich Panels: Scaling Effects
Tomblin, J. S.; Raju, K. S.; Arosteguy, G.; Feb. 2004; In English
Report No.(s): PB2004-105464; No Copyright; Avail: National Technical Information Service (NTIS)
The impact responses and the damage states in flat sandwich panels with thin facesheets are known to be dependent on
the diameter of the spherical steel impactor. The residual strength of impact-damaged sandwich panels under static in-plane
compressive loads was dependent on the nature of the damage state. The coupon sizes used in these investigations were
relatively small, and the finite size effects may be embedded in the observed trends. The effects of scaling the planar
dimensions of sandwich specimens on the damage resistance were studied by conducting experiments and finite element
analysis. The impact force and the damage size were observed to decrease as both the planar dimensions were increased. These
effects were negligible when only a single dimension was scaled. The off-center impacts indicated that for a given energy level,
the impacts occurring closer to the boundary supports were more severe compared to those farther away from the boundaries.
The impacts on sandwich specimens supported by a rigid base proved to be the most severe case in terms of the impact
36