Piezoelectric devices for vibration suppression: Modeling and application to a truss structure

For a space structure assembled from truss members, an effective way to control the structure may be to replace the regular truss elements by active members. The active members play the role of load carrying elements as well as actuators. A piezo strut, made of a stack of piezoceramics, may be an ideal active member to be integrated into a truss space structure. An electrically driven piezo strut generates a pair of forces, and is considered as a two-point actuator in contrast to a one-point actuator such as a thruster or a shaker. To achieve good structural vibration control, sensing signals compatible to the control actuators are desirable. A strain gage or a piezo film with proper signal conditioning to measure member strain or strain rate, respectively, are ideal control sensors for use with a piezo actuator. The Phase 0 CSI Evolutionary Model (CEM) at NASA Langley Research Center used cold air thrusters as actuators to control both rigid body motions and flexible body vibrations. For the Phase 1 and 2 CEM, it is proposed to use piezo struts to control the flexible modes and thrusters to control the rigid body modes. A tenbay truss structure with active piezo struts is built to study the modeling, controller designs, and experimental issues. In this paper, the tenbay structure with piezo active members is modelled using an energy method approach. Decentralized and centralized control schemes are designed and implemented, and preliminary analytical and experimental results are presented

First Report of the Mayan Cichlid, Cichlasoma urophthalmus (Günther 1862) Collected in the Southern Littoral Zone of Lake Okeechobee, Florida

Here we report the collection of five juvenile Mayan cichlids in Lake Okeechobee, a large, shallow subtropical lake (26°60\u27N, 80°50\u27W). These specimens were collected on 4 and 10 November 2003 in the southern littoral zone of Lake Okeechobee at a site off the southwest tip of Torry Island (26°42\u27N, 80°44\u27W). The lake stage of this densely vegetated area is highly variable. Nico (in press) reported a single collection of 16 juvenile Mayan cichlids in 2001 from a backwater area in the rim-canal along the NE portion of Lake Okeechobee; an area that is hydrologically isolated from the lake proper, except for several navigation locks and water control structures

Polymer-Based Composite Catholytes for Li Thin-Film Cells

Polymer-based composite catholyte structures have been investigated in a continuing effort to increase the charge/discharge capacities of solid-state lithium thin-film electrochemical cells

Assessing Potential Winter Weather Response to Climate Change and Implications for Tourism in The U.S. Great Lakes and Midwest

Study Region: Eight U.S. states bordering the North American Laurentian Great Lakes. Study Focus: Variable Infiltration Capacity (VIC) model simulations, based on data from an en- semble of atmospheric-ocean general circulation models (AOGCMs) used for the Intergovernmental Panel on Climate Change\u27s (IPCC\u27s) Fifth Assessment Report (AR5), were used to quantify potential climate change impacts on winter weather and hydrology in the study re- gion and understand implications for its tourism sector. New Hydrologic Insights for the Region: By the 2080s, climate change could result in winters that are shorter by over a month, reductions of over a month in days with snow depths required for many kinds of winter recreation, declines in average holiday snow depths of 50 percent or more, and reductions in the percent area of the study region that would be considered viable for winter tourism from about 22 percent to 0.3 percent. Days with temperatures suitable for artificial snowmaking decline to less than a month annually, making it potentially less feasible as an adaptation strategy. All of the region\u27s current ski resorts are operating in areas that will become non-viable for winter tourism businesses under a high emissions scenario. Given the economic importance of the winter tourism industry in the study region, businesses and communities should consider climate change and potential adaptation strategies in their future planning and overall decision-making

Improved Instrument for Detecting Water and Ice in Soil

An instrument measures electrical properties of relatively dry soils to determine their liquid water and/or ice contents. Designed as a prototype of instruments for measuring the liquid-water and ice contents of lunar and planetary soils, the apparatus could also be utilized for similar purposes in research and agriculture involving terrestrial desert soils and sands, and perhaps for measuring ice buildup on aircraft surfaces. This instrument is an improved version of the apparatus described in Measuring Low Concentrations of Liquid Water and Ice in Soil (NPO-41822), NASA Tech Briefs, Vol. 33, No. 2 (February 2009), page 22. The designs of both versions are based on the fact that the electrical behavior of a typical soil sample is well approximated by a network of resistors and capacitors in which resistances decrease and capacitances increase (and the magnitude and phase angle of impedance changes accordingly) with increasing water content. The previous version included an impedance spectrometer and a jar into which a sample of soil was placed. Four stainless-steel screws at the bottom of the jar were used as electrodes of a fourpoint impedance probe connected to the spectrometer. The present instrument does not include a sample jar and can be operated without acquiring or handling samples. Its impedance probe consists of a compact assembly of electrodes housed near the tip of a cylinder. The electrodes protrude slightly from the cylinder (see Figure 1). In preparation for measurements, the cylinder is simply pushed into the ground to bring the soil into contact with the electrodes

Monitoring the Effects of Anti-angiogenesis on the Radiation Sensitivity of Pancreatic Cancer Xenografts Using Dynamic Contrast-Enhanced CT

Purpose To image the intra-tumor vascular physiological status of pancreatic tumors xenografts and their response to anti-angiogenic therapy using Dynamic Contrast-Enhanced CT (DCE-CT), and to identify parameters of vascular physiology associated with tumor X-ray sensitivity following anti-angiogenic therapy. Methods and Materials Nude mice bearing human BxPC-3 pancreatic tumor xenografts were treated with 5Gy of radiation therapy (RT), either a low-dose (40mg/kg) or a high-dose (150mg/kg) of DC101, the anti-VEGF receptor-2 anti-angiogenesis antibody, or with combination of low or high dose DC101 and 5Gy RT (DC101-plus-RT). DCE-CT scans were longitudinally acquired over three week period post-DC101 treatment. Parametric maps of tumor perfusion and fractional plasma volume (Fp) were calculated and their averaged values and histogram distributions evaluated and compared to controls, from which a more homogeneous physiological window was observed 1-week post-DC101. Mice receiving a combination of DC101-plus-RT(5Gy) were imaged baseline prior to receiving DC101 and 1-week after DC101 (prior to RT). Changes in perfusion and Fp were compared with alternation in tumor growth delay for RT and DC101-plus-RT(5Gy) treated tumors. Results Pretreatment with low or high doses of DC101 prior to RT significantly delayed tumor growth by an average 7.9 days compared to RT alone (p≤0.01). The increase in tumor growth delay for the DC101-plus-RT treated tumors was strongly associated with changes in tumor perfusion (ΔP>−15%) compared to RT treated tumors alone (p=0.01). In addition, further analysis revealed a trend linking the tumor’s increased growth delay to its tumor volume-to-DC101 dose ratio. Conclusions DCE-CT is capable of monitoring changes in intra-tumor physiological parameter of tumor perfusion in response to anti-angiogenic therapy of a pancreatic human tumor xenograft that was associated with enhanced radiation response