556 research outputs found
The development of CFD methods for rotor applications
The optimum design of the advancing helicopter rotor for high-speed forward flight always involves a tradeoff between transonic and stall limitations. However, the preoccupation of the rotor industry was primarily concerned with stall until well into the 1970s. This emphasis on stall resulted from the prevalent use of low-solidity rotors with rather outdated airfoil sections. The use of cambered airfoil sections and higher-solidity rotors substantially reduced stall and revealed the advancing transonic flow to be a more persistent limitation to high-speed rotor performance. Work in this area was spurred not only by operational necessity but also by the development of a tool for the prediction of these flows (the method of computational fluid dynamics). The development of computational fluid dynamics for these rotor problems was a major Army and NASA achievement. This work is now being extended to other rotor flow problems. The developments are outlined
Preliminary analysis of an instructional alternative to exclusionary discipline
37 pagesDecades of research have shown that exclusionary discipline practices are not only ineffective
for changing student behavior, they lead to worse social, behavioral, and academic outcomes for
students. This article explores the findings from a pilot study of the Inclusive Skill-Building
Learning Approach (ISLA), an instructional alternative to exclusionary discipline practices. The
purposes of ISLA are to improve student social and behavioral problem-solving, teacher and
administrator practices, and student-teacher relationships while also reducing lost instructional
time for student excluded from their learning environment. Results from the pilot indicated that
implementation of ISLA was associated with reductions in exclusionary discipline practices
(Cohen’s h effect sizes ranged from .06 to .18 across schools and outcomes), and a substantial
decrease in instructional minutes lost (~ 92%). Educational staff also reported favorable
impressions of the intervention. Practical and conceptual implications, limitations of this study,
and directions for future research are further discussed.The research reported here was supported by the Fairway Fund, a College of Education Faculty
Research Award at the University of Oregon and by the Institute of Education Sciences, U.S.
Department of Education, through Grant R305A180006 to the University of Oregon
Control of rotorcraft retreating blade stall using air-jet vortex generators
A series of low-speed wind tunnel tests were carried out on an oscillating airfoil fitted with two rows of air-jet vortex generators (AJVGs). The airfoil used had an RAE 9645 section and the two spanwise arrays of AJVGs were located at x/c=0.12 and 0.62. The devices and their distribution were chosen to assess their ability to modify/control dynamic stall; the goal being to enhance the aerodynamic performance of helicopter rotors on the retreating blade side of the disc. The model was pitched about the quarter chord with a reduced frequency
(k) of 0.1 in a sinusoidal motion defined by a=15o+10sin_ t. The measured data indicate that, for continuous blowing from the front row of AJVGs with a momentum blowing coefficient (C μ) greater than 0.008, modifications to the stalling process are encouraging. In particular, the pitching moment behavior exhibits delayed stall and there is a marked reduction in the normal force hysteresis
Training in crisis communication and volcanic eruption forecasting:Design and evaluation of an authentic role-play simulation
We present an interactive, immersive, authentic role-play simulation designed to teach tertiary geoscience students
in New Zealand to forecast and mitigate a volcanic crisis. Half of the participating group (i.e., the Geoscience Team)
focuses on interpreting real volcano monitoring data (e.g., seismographs, gas output etc.) while the other half of the
group (i.e., the Emergency Management Team) forecasts and manages likely impacts, and communicates emergency
response decisions and advice to local communities. These authentic learning experiences were aimed at enhancing
upper-year undergraduate students’ transferable and geologic reasoning skills. An important goal of the simulation was
specifically to improve students’ science communication through interdisciplinary team discussions, jointly prepared,
and delivered media releases, and real-time, high-pressure, press conferences.
By playing roles, students experienced the specific responsibilities of a professional within authentic organisational
structures. A qualitative, design-based educational research study was carried out to assess the overall student experience
and self-reported learning of skills. A pilot and four subsequent iterations were investigated.
Results from this study indicate that students found these role-plays to be a highly challenging and engaging learning
experience and reported improved skills. Data from classroom observations and interviews indicate that the students
valued the authenticity and challenging nature of the role-play although personal experiences and team dynamics
(within, and between the teams) varied depending on the students’ background, preparedness, and personality.
During early iterations, observation and interviews from students and instructors indicate that some of the goals of the
simulation were not fully achieved due to: A) lack of preparedness, B) insufficient time to respond appropriately, C)
appropriateness of roles and team structure, and D) poor communication skills. Small modifications to the design of
Iterations 3 and 4 showed an overall improvement in the students’ skills and goals being reached.
A communication skills instrument (SPCC) was used to measure self-reported pre- and post- communication competence
in the last two iterations. Results showed that this instrument recorded positive shifts in all categories of self-perceived
abilities, the largest shifts seen in students who participated in press conferences. Future research will be aimed
at adapting this curricula to new volcanic and earthquake scenarios
Search for right-handed W bosons in top quark decay
We present a measurement of the fraction f+ of right-handed W bosons produced
in top quark decays, based on a candidate sample of events in the
lepton+jets decay mode. These data correspond to an integrated luminosity of
230pb^-1, collected by the DO detector at the Fermilab Tevatron
Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the
kinematics of the and decay products, which allows for the
measurement of the leptonic decay angle for each event. By comparing
the distribution from the data with those for the expected
background and signal for various values of f+, we find
f+=0.00+-0.13(stat)+-0.07(syst). This measurement is consistent with the
standard model prediction of f+=3.6x10^-4.Comment: Submitted to Physical Review D Rapid Communications 7 pages, 3
figure
Search for R-parity violating supersymmetry via the LLE couplings lambda_{121}, lambda_{122} or lambda_{133} in ppbar collisions at sqrt(s)=1.96 TeV
A search for gaugino pair production with a trilepton signature in the
framework of R-parity violating supersymmetry via the couplings lambda_121,
lambda_122, or lambda_133 is presented. The data, corresponding to an
integrated luminosity of L~360/pb, were collected from April 2002 to August
2004 with the D0 detector at the Fermilab Tevatron Collider, at a
center-of-mass energy of sqrt(s)=1.96 TeV. This analysis considers final states
with three charged leptons with the flavor combinations eel, mumul, and eetau
(l=e or mu). No evidence for supersymmetry is found and limits at the 95%
confidence level are set on the gaugino pair production cross section and lower
bounds on the masses of the lightest neutralino and chargino are derived in two
supersymmetric models.Comment: 9 pages, 4 figures (fig2 includes 3 subfigures
Measurement of Semileptonic Branching Fractions of B Mesons to Narrow D** States
Using the data accumulated in 2002-2004 with the DO detector in
proton-antiproton collisions at the Fermilab Tevatron collider with
centre-of-mass energy 1.96 TeV, the branching fractions of the decays B ->
\bar{D}_1^0(2420) \mu^+ \nu_\mu X and B -> \bar{D}_2^{*0}(2460) \mu^+ \nu_\mu X
and their ratio have been measured: BR(\bar{b}->B) \cdot BR(B-> \bar{D}_1^0
\mu^+ \nu_\mu X) \cdot BR(\bar{D}_1^0 -> D*- pi+) =
(0.087+-0.007(stat)+-0.014(syst))%; BR(\bar{b}->B)\cdot BR(B->D_2^{*0} \mu^+
\nu_\mu X) \cdot BR(\bar{D}_2^{*0} -> D*- \pi^+) =
(0.035+-0.007(stat)+-0.008(syst))%; and (BR(B -> \bar{D}_2^{*0} \mu^+ \nu_\mu
X)BR(D2*0->D*- pi+)) / (BR(B -> \bar{D}_1^{0} \mu^+ \nu_\mu X)\cdot
BR(\bar{D}_1^{0}->D*- \pi^+)) = 0.39+-0.09(stat)+-0.12(syst), where the charge
conjugated states are always implied.Comment: submitted to Phys. Rev. Let
Measurement of the Lifetime Difference in the B_s^0 System
We present a study of the decay B_s^0 -> J/psi phi We obtain the CP-odd
fraction in the final state at time zero, R_perp = 0.16 +/- 0.10 (stat) +/-
0.02 (syst), the average lifetime of the (B_s, B_sbar) system, tau (B_s^0)
=1.39^{+0.13}_{-0.16} (stat) ^{+0.01}_{-0.02} (syst) ps, and the relative width
difference between the heavy and light mass eigenstates, Delta Gamma/Gamma =
(Gamma_L - Gamma_H)/Gamma =0.24^{+0.28}_{-0.38} (stat) ^{+0.03}_{-0.04} (syst).
With the additional constraint from the world average of the B_s^0$lifetime
measurements using semileptonic decays, we find tau (B_s^0)= 1.39 +/- 0.06 ~ps
and Delta Gamma/\Gamma = 0.25^{+0.14}_{-0.15}. For the ratio of the B_s^0 and
B^0 lifetimes we obtain tau(B_s^0)/tau(B^0)} = 0.91 +/- 0.09 (stat) +/- 0.003
(syst).Comment: submitted to Phys. Rev. Lett. FERMILAB-PUB-05-324-
Measurement of the Lifetime Using Semileptonic Decays
We report a measurement of the lifetime in the semileptonic decay
channel (and its charge conjugate), using
approximately 0.4 fb of data collected with the D0 detector during 2002
-- 2004. We have reconstructed 5176 signal events, where the
is identified via the decay , followed by . Using these events, we have measured the lifetime to be
. This is the most precise measurement of the lifetime to date.Comment: To appear in Phys. Rev. Lett., 7 pages, 2 figure
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