Variable friction secondary seal for face seals

Vibration and stability of a primary seal ring is controlled by a secondary seal system. An inflatable bladder which forms a portion of the secondary seal varies the damping applied to this seal ring. The amplitude of vibration of the primary seal ring is sensed with a proximity probe that is connected to a microprocessor in a control system. The bladder pressure is changed by the control system to mitigate any sensed instability or vibration

Design analysis of a self-acting spiral-groove ring seal for counter-rotating shafts

A self-acting spiral groove inter-shaft ring seal of nominal 16.33 cm (6.43 in.) diameter for sealing fan bleed air between counter rotating shafts in advanced turbofan engines was analyzed. The analysis focused on the lift force characteristics of the spiral grooves. A NASA Lewis developed computer program for predicting the performance of gas lubricated face seals was used to optimize the spiral groove geometry to produce maximum lift force. Load capacity curves (lift force as function of film thickness) were generated for four advanced turbofan engine operating conditions at relative seal speeds ranging from 17,850 to 29,800 rpm, sealed air pressures from 6 to 42 N/sq cm (9 to 60 psi) absolute and temperatures from 95 to 327 C (203 to 620 F). The relative seal sliding speed range was 152 to 255 m/sec (500 to 836 ft/sec). The analysis showed that the spiral grooves are capable of producing sufficient lift force such that the ring seal will operate in a noncontacting mode over the operating range of typical advanced turbofan engines

Experimental evaluation of a tuned electromagnetic damper for vibration control of cryogenic turbopump rotors

Experiments were performed on a passive tuned electromagnetic damper that could be used for damping rotor vibrations in cryogenic turbopumps for rocket engines. The tests were performed in a rig that used liquid nitrogen to produce cryogenic turbopump temperatures. This damper is most effective at cryogenic temperatures and is not a viable damper at room temperature. The unbalanced amplitude response of the rotor shaft was measured for undamped (baseline) and damped conditions at the critical speeds of the rotor (approx. 5900 to 6400 rpm) and the data were compared. The tests were performed for a speed range between 900 and 10 000 rpm. The tests revealed that the damper is very effective for damping single-mode narrow bandwidth amplitude response but is less effective in damping broadband response or multimode amplitude response

Intentions and Behaviors: Testing Spiral of Silence in a Social Media Context

This study tests for a spiral of silence effect on Facebook using vaccination as the controversial topic. Participants were required to have a Facebook account and to log in to their account to participate in the experiment. The three experimental conditions were real Facebook posts containing a meme about vaccines and a comment thread, where the manipulation occurred. The anti-vaccination condition had mostly anti-vaccination comments (9 of 10); the pro-vaccination condition had mostly pro-vaccination comments (9 of 10); and the mixed condition had an equal number of pro- and anti-vaccination comments (4 pro and 4 anti). Participants could leave a comment on the Facebook post; commenting on the post and intentions to engage with the post were the two dependent variables. Results found no difference in commenting or in intentions among the experimental conditions. Vaccination attitudes did not predict commenting but did predict intentions. There were no interaction effects of condition and attitudes on either commenting or intentions. A total of six comments were made across all conditions. Most of the comments supported vaccines. Results indicate vaccination did not inspire strong enough attitudes to create a spiral of silence effect on Facebook in this experiment

Active vibration control for flexible rotor by optimal direct-output feedback control

Experimental research tests were performed to actively control the rotor vibrations of a flexible rotor mounted on flexible bearing supports. The active control method used in the tests is called optimal direct-output feedback control. This method uses four electrodynamic actuators to apply control forces directly to the bearing housings in order to achieve effective vibration control of the rotor. The force actuators are controlled by an analog controller that accepts rotor displacement as input. The controller is programmed with experimentally determined feedback coefficients; the output is a control signal to the force actuators. The tests showed that this active control method reduced the rotor resonance peaks due to unbalance from approximately 250 micrometers down to approximately 25 micrometers (essentially runout level). The tests were conducted over a speed range from 0 to 10,000 rpm; the rotor system had nine critical speeds within this speed range. The method was effective in significantly reducing the rotor vibration for all of the vibration modes and critical speeds

Primary Sequence of the \u3ci\u3eEscherichia coli fadBA\u3c/i\u3e Operon, Encoding the Fatty Acid-Oxidizing Multienzyme Complex, Indicates a High Degree of Homology to Eucaryotic Enzymes

In Escherichia coli at least five enzyme activities required for the beta-oxidation of fatty acids are associated with a multienzyme complex composed of two subunits in α2β2 conformation (A. Pramanik et al., J. Bacteriol. 137:469-473, 1979). In the present work, the DNA sequence of the genes encoding these two subunits, fadB and fadA, has been determined. The direction of transcription was from fadB to fadA rather than from fadA to fadB, as suggested previously (S. K. Spratt et al., J. Bacteriol. 158:535-542, 1984). Only 10 nucleotides separated the coding sequences for the two peptides, confirming the suggestion that these genes form an operon. The peptides encoded by fadB and fadA were 729 amino acids and 387 amino acids, respectively, in length. The larger and smaller peptides had predicted molecular masses of 79,678 and 40,876 Da, respectively. Recently, the sequence of thefadA gene was published in a separate report (Yang et al., J. Biol. Chem. 265:10424-10429, 1990). In this work, most of the DNA sequence for fad4 was confirmed, and 10 errors were corrected. Three of these nucleotide changes resulted in five amino acid residue changes predicted in the carboxy terminus of the fadA-encoded peptide. By comparison to other peptide sequences, the a subunit encoded withinfadB had 31% perfect identity with the rat peroxisomal enoyl-coenzyme A:hydratase-3-hydroxyacyl-coenzyme A dehydrogenase trifunctional enzyme over the entire length of the two peptides. In agreement with the work of Yang et al., the β subunit encoded within fadA had 35 to 45% perfect identity with five thiolase genes from different eucaryotic sources over the entire length of the peptide

American Nonprofit Law in Comparative Perspective

The article presents a comparative law which explores approaches to nonprofit regulations in several countries in Europe and Asia. It discusses the basic laws for the nonprofit sector in the U.S. and is then contrasted with the approach for nonprofit laws in other countries. It explores the two distinctive themes of the American nonprofit regulations, which is its difference in primary relational focus and its property of being unusually tax-centric in its regulatory scheme

Charity at Work: Proposing a Charitable Flexible Spending Account

The current federal system of tax law, in attempting to encourage the shift of assets from private individuals to charitable organizations, fails to reach significant portions of Americans. Not all donors are equal in the eyes of the law; donors with particular demographic characteristics—ranging from income, to race, to state of residence—are more likely to itemize than others. Despite its aim to reflect a pluralistic society, the charitable deduction sanctions the privileging of one-third of American voices over the rest. If taxes are ballots, the election is rigged