36,079 research outputs found
Study of Scalar Mesons and Related Radiative Decays
After a brief review of the puzzling light scalar meson sector of QCD, a
brief summary will be given of a paper concerning radiative decays involving
the light scalars. There, a simple vector meson dominance model is constructed
in an initial attempt to relate a large number of the radiative decays
involving a putative scalar nonet to each other. As an application it is
illustrated why mixing is not expected to greatly alter the
production ratio for radiative decays.Comment: 9 pages, 3 figures, Talk presented at SUNYIT (Utica/NY) conference on
High Energy Physics, June 6, 200
Use of cohesive elements in fatigue analysis
Cohesive laws describe the resistance to incipient separation
of material surfaces. A cohesive finite element
is formulated on the basis of a particular cohesive
law. Cohesive elements are placed at the boundary
between adjacent standard volume finite elements
to model fatigue damage that leads to fracture at the
separation of the element boundaries per the cohesive
law. In this work, a cohesive model for fatigue
crack initiation is taken to be the irreversible loadingunloading
hysteresis that represents fatigue damage
occuring due to cyclic loads leading to the initiation of
small cracks. Various cohesive laws are reviewed and
one is selected that incorporates a hysteretic cyclic
loading that accounts for energetic dissipative mechanisms.
A mathematical representation is developed
based on an exponential effective load-separation cohesive
relationship. A three-dimensional cohesive element
is defined using this compliance relationship integrated
at four points on the mid-surface of the area
element. Implementation into finite element software
is discussed and particular attention is applied to numerical
convergence issues as the inflection point between
loading and 'unloading in the cohesive law is
encountered. A simple example of a displacementcontrolled
fatigue test is presented in a finite element
simulation. Comments are made on applications of
the method to prediction of fatigue life for engineering
structures such as pressure vessels and piping
A basic lock-in amplifier experiment for the undergraduate laboratory
We describe a basic experiment for the undergraduate laboratory that demonstrates aspects of both, the science and the art of precision electronic measurements. The essence of the experiment is to measure the resistance of a small length of brass-wire to high accuracy using a simple voltage divider and a lock-in amplifier. By performing the measurement at different frequencies and different drive currents, one observes various random noise sources and systematic measurement effects
Topological superconductivity in the extended Kitaev-Heisenberg model
We study superconducting pairing in the doped Kitaev-Heisenberg model by
taking into account the recently proposed symmetric off-diagonal exchange
. By performing a mean-field analysis, we classify all possible
superconducting phases in terms of symmetry, explicitly taking into account
effects of spin-orbit coupling. Solving the resulting gap equations
self-consistently, we map out a phase diagram that involves several
topologically nontrivial states. For , we find a competition between
a time-reversal symmetry breaking chiral phase with Chern number and a
time-reversal symmetric nematic phase that breaks the rotational symmetry of
the lattice. On the other hand, for we find a time-reversal
symmetric phase that preserves all the lattice symmetries, thus yielding
clearly distinguishable experimental signatures for all superconducting phases.
Both of the time-reversal symmetric phases display a transition to a
non-trivial phase at high doping levels. Finally, we also
include a symmetry-allowed spin-orbit coupling kinetic energy and show that it
destroys a tentative symmetry protected topological order at lower doping
levels. However, it can be used to tune the time-reversal symmetric phases into
a non-trivial phase even at lower doping
Macroscopic coherence effects in a mesoscopic system: Weak localization of thin silver films in an undergraduate lab
We present an undergraduate lab that investigates weak localization in thin
silver films. The films prepared in our lab have thickness, , between 60-200
\AA, a mesoscopic length scale. At low temperatures, the inelastic dephasing
length for electrons, , exceeds the thickness of the film (), and the films are then quasi-2D in nature. In this situation, theory
predicts specific corrections to the Drude conductivity due to coherent
interference between conducting electrons' wavefunctions, a macroscopically
observable effect known as weak localization. This correction can be destroyed
with the application of a magnetic field, and the resulting magnetoresistance
curve provides information about electron transport in the film. This lab is
suitable for Junior or Senior level students in an advanced undergraduate lab
course.Comment: 16 pages, 9 figures. Replaces earlier version of paper rejected by
Am. J. Phys. because of too much content on vacuum systems. New version deals
with the undergraduate experiment on weak localization onl
A benign, low Z electron capture agent for negative ion TPCs
We have identified nitromethane (CHNO) as an effective electron
capture agent for negative ion TPCs (NITPCs).
We present drift velocity and longitudinal diffusion measurements for
negative ion gas mixtures using nitromethane as the capture agent.
Not only is nitromethane substantially more benign than the only other
identified capture agent, CS, but its low atomic number will enable the use
of the NITPC as a photoelectric X{}-ray polarimeter in the 1{}-10 keV band
Aerodynamic design and performance testing of an advanced 30 deg swept, eight bladed propeller at Mach numbers from 0.2 to 0.85
The increased emphasis on fuel conservation in the world has stimulated a series of studies of both conventional and unconventional propulsion systems for commercial aircraft. Preliminary results from these studies indicate that a fuel saving of from 15 to 28 percent may be realized by the use of an advanced high speed turboprop. The turboprop must be capable of high efficiency at Mach 0.8 above 10.68 km (35,000 ft) altitude if it is to compete with turbofan powered commercial aircraft. An advanced turboprop concept was wind tunnel tested. The model included such concepts as an aerodynamically integrated propeller/nacelle, blade sweep and power (disk) loadings approximately three times higher than conventional propeller designs. The aerodynamic design for the model is discussed. Test results are presented which indicate propeller net efficiencies near 80 percent were obtained at high disk loadings at Mach 0.8
Variable pitch fan system for NASA/Navy research and technology aircraft
Preliminary design of a shaft driven, variable-pitch lift fan and lift-cruise fan was conducted for a V/STOL Research and Technology Aircraft. The lift fan and lift-cruise fan employed a common rotor of 157.5 cm diameter, 1.18 pressure ratio variable-pitch fan designed to operate at a rotor-tip speed of 284 mps. Fan performance maps were prepared and detailed aerodynamic characteristics were established. Cost/weight/risk trade studies were conducted for the blade and fan case. Structural sizing was conducted for major components and weights determined for both the lift and lift-cruise fans
Evaluation of wind tunnel performance testings of an advanced 45 deg swept 8-bladed propeller at Mach numbers from 0.45 to 0.85
The increased emphasis of fuel conservation in the world and the rapid increase in the cost of jet fuel has stimulated a series of studies of both conventional and unconventional propulsion systems for commercial aircraft. The results of these studies indicate that a fuel saving of 15 to 30 percent may be realized by the use of an advanced high-speed turboprop (Prop-Fan) compared to aircraft equipped with high bypass turbofan engines of equivalent technology. The Prop-Fan propulsion system is being investigated as part of the NASA Aircraft Energy Efficient Program. This effort includes the wind tunnel testing of a series of 8 and 10-blade Prop-Fan models incorporate swept blades. Test results indicate efficiency levels near the goal of 80 percent at Mach 0.8 cruise and an altitude of 10.67 km (35,000 ft). Each successive swept model has shown improved efficiency relative to the straight blade model. The fourth model, with 45 deg swept blades reported herein, shows a net efficiency of 78.2 at the design point with a power loading of 301 kW/sq meter and a tip speed of 243.8 m/sec (800 ft/sec.)
Physical Activity and Mental Well-being in a Cohort Aged 60–64 Years
Introduction: Although evidence suggests physical activity (PA) may be associated with mental well-being at older ages, it is unclear whether some types of PA are more important than others. The purpose of this study is to investigate associations of monitored total PA under free-living conditions, self-reported leisure-time PA (LTPA), and walking for pleasure with mental well-being at age 60–64 years. Methods: Data on 930 (47%) men and 1,046 (53%) women from the United Kingdom MRC National Survey of Health and Development collected in 2006–2011 at age 60–64 were used in 2013–2014 to test the associations of PA (PA energy expenditure and time spent in different intensities of activity assessed using combined heart rate and acceleration monitors worn for 5 days, self-reported LTPA, and walking for pleasure) with the Warwick-Edinburgh Mental Well-being Scale (WEMWBS; range, 14–70). Results: In linear regression models adjusted for gender, long-term limiting illness, smoking, employment, socioeconomic position, personality, and prior PA, those who walked for >1 hour/week had mean WEMWBS scores 1.47 (95% CI=0.60, 2.34) points higher than those who reported no walking. Those who participated in LTPA at least five times/month had WEMWBS scores 1.25 (95% CI=0.34, 2.16) points higher than those who did not engage in LTPA. There were no statistically significant associations between free-living PA and WEMWBS scores. Conclusions: In adults aged 60–64 years, participation in self-selected activities such as LTPA and walking are positively related to mental well-being, whereas total levels of free-living PA are not
- …