679 research outputs found
Acoustic Emission Multi-Parameter Analyzer—AEMPA
A multi-parameter measurement system was designed and built to process signals from acoustic emission (AE) transducers in real time. The system makes selected measurements of each detected AE event as it occurs and stores 23 measured parameters which describe that event in digital form on a standard diskette with IBM format. Measurements recorded on the diskette include information on the shape, magnitude, and frequency content of each AE burst, its timing with respect to location on the specimen under test and its timing with respect to load conditions, pressure, test time, and event count. Over 8000 AE events can be stored on a single diskette at a maximum instantaneous rate of 6000 events/sec and a maximum average rate of 1000 events/sec. Two floppy disk units are included in the system so one can be operational while the diskette is being changed in the other. After a specimen test, the data are transmitted to a remote minicomputer with a standard RS232 interface. Rapid analysis and display of the data by the computer has been demonstrated using up to 8 of the AE parameters at one time in a pattern recognition routine
RELIABILITY OF JUMP AND PERFORMANCE MEASURES IN RUGBY UNION PLAYERS
The current study examined the reliability of countermovement (CMJ), squat (SJ), and rebound jumps (RBJ) to sprint and estimated 1RM back squat (SQ) of sub-elite Rugby Union players drawn from two teams of similar competitive level. Comparisons of mean performance on all tests were made via Student t-tests. The three trial reliability of jump height for the SJ, CMJ, RBJ, contact time (CT) and Reactive Strength Index for the RBJ, T-Test agility run (TA-Test), 30 and 36.58 m (40 yd) sprint times were estimated via ICC and ReANOVA. All variables displayed Average measures ICC ≥ .900; and except for the TA-Test, the three trials did not differ from each other. The performance of the two teams was found to be similar on all tests except the 30 m and 40 yd sprint tests. All the studied performance measures could be reliably assessed with one trial, except the TA-test
POWER OUTPUT, MUSCLE ACTIVITY, AND FRONTAL AREA OF A CYCLIST IN DIFFERENT CYCLING POSITIONS
Nine cyclists completed three trials of cycling 25W below lactate threshold (LT) with 1) hands on top of the brake hoods (BH); 2) hands below the dropped, curved, portion of the handlebars (DH); and 3) using clip-on triathlon aerobars (AB). Each trial lasted three minutes and was immediately followed by a 20sec maximal sprint during which power output and muscle EMG were measured. Frontal projection area (FPA) differed across all three positions. EMG did not differ between positions during submax or sprint cycling. Submax power output also did not differ, but during the sprint AB was lower
than BH, while DH did not differ from the other conditions. Although power output was 8.1% less while cycling in the AB position than BH, its FPA was 17.4% less, indicating the AB position allows a savings in resistive power greater than that lost in power production
Effective Actions, Boundaries and Precision Calculations of Casimir Energies
We perform the matching required to compute the leading effective boundary
contribution to the QED lagrangian in the presence of a conducting surface,
once the electron is integrated out. Our result resolves a confusion in the
literature concerning the interpretation of the leading such correction to the
Casimir energy. It also provides a useful theoretical laboratory for
brane-world calculations in which kinetic terms are generated on the brane,
since a lot is known about QED near boundaries.Comment: 5 pages. revtex; Added paragraphs describing finite-conductivity
effects and effects due to curvatur
Dimensional Reduction of Fermions in Brane Worlds of the Gross-Neveu Model
We study the dimensional reduction of fermions, both in the symmetric and in
the broken phase of the 3-d Gross-Neveu model at large N. In particular, in the
broken phase we construct an exact solution for a stable brane world consisting
of a domain wall and an anti-wall. A left-handed 2-d fermion localized on the
domain wall and a right-handed fermion localized on the anti-wall communicate
with each other through the 3-d bulk. In this way they are bound together to
form a Dirac fermion of mass m. As a consequence of asymptotic freedom of the
2-d Gross-Neveu model, the 2-d correlation length \xi = 1/m increases
exponentially with the brane separation. Hence, from the low-energy point of
view of a 2-d observer, the separation of the branes appears very small and the
world becomes indistinguishable from a 2-d space-time. Our toy model provides a
mechanism for brane stabilization: branes made of fermions may be stable due to
their baryon asymmetry. Ironically, our brane world is stable only if it has an
extreme baryon asymmetry with all states in this ``world'' being completely
filled.Comment: 26 pages, 7 figure
The Sloan Lens ACS Survey. VII. Elliptical Galaxy Scaling Laws from Direct Observational Mass Measurements
We use a sample of 53 massive early-type strong gravitational lens galaxies
with well-measured redshifts (ranging from z=0.06 to 0.36) and stellar velocity
dispersions (between 175 and 400 km/s) from the Sloan Lens ACS (SLACS) Survey
to derive numerous empirical scaling relations. The ratio between central
stellar velocity dispersion and isothermal lens-model velocity dispersion is
nearly unity within errors. The SLACS lenses define a fundamental plane (FP)
that is consistent with the FP of the general population of early-type
galaxies. We measure the relationship between strong-lensing mass M_lens within
one-half effective radius (R_e/2) and the dimensional mass variable M_dim =
G^-1 sigma_e2^2 R_e/2 to be log_10 [M_lens/10^11 M_Sun] = (1.03 +/- 0.04)
log_10 [M_dim/10^11 M_Sun] + (0.54 +/- 0.02) (where sigma_e2 is the projected
stellar velocity dispersion within R_e/2). The near-unity slope indicates that
the mass-dynamical structure of massive elliptical galaxies is independent of
mass, and that the "tilt" of the SLACS FP is due entirely to variation in total
(luminous plus dark) mass-to-light ratio with mass. Our results imply that
dynamical masses serve as a good proxies for true masses in massive elliptical
galaxies. Regarding the SLACS lenses as a homologous population, we find that
the average enclosed 2D mass profile goes as log_10 [M(<R)/M_dim] = (1.10 +/-
0.09) log_10 [R/R_e] + (0.85 +/- 0.03), consistent with an isothermal (flat
rotation curve) model when de-projected into 3D. This measurement is
inconsistent with the slope of the average projected aperture luminosity
profile at a confidence level greater than 99.9%, implying a minimum
dark-matter fraction of f_DM = 0.38 +/- 0.07 within one effective radius.
(abridged)Comment: 13 pages emulateapj; accepted for publication in the Ap
Radion effects on unitarity in gauge-boson scattering
The scalar field associated with fluctuations in the positions of the two
branes, the ``radion'', plays an important role determining the cosmology and
collider phenomenology of the Randall-Sundrum solution to the hierarchy
problem. It is now well known that the radion mass is of order the weak scale,
and that its couplings to standard model fields are order 1/TeV to the trace of
the energy momentum tensor. We calculate longitudinal vector boson scattering
amplitudes to explore the constraints on the radion mass and its coupling from
perturbative unitarity. The scattering cross section can indeed become
non-perturbative at energies prior to reaching the TeV brane cutoff scale, but
only when some curvature-Higgs mixing on the TeV brane is present. We show that
the coefficient of the curvature-Higgs mixing operator must be less than about
3 for the 4-d effective theory to respect perturbative unitarity up to the TeV
brane cutoff scale. Mass bounds on the Higgs boson and the radion are also
discussed.Comment: 17 pages, LaTeX, 5 eps figures, uses epsf.sty and axodraw.st
4D Constructions of Supersymmetric Extra Dimensions and Gaugino Mediation
We present 4D gauge theories which at low energies coincide with higher
dimensional supersymmetric (SUSY) gauge theories on a transverse lattice. We
show that in the simplest case of pure 5D SUSY Yang-Mills there is an
enhancement of SUSY in the continuum limit without fine-tuning. This result no
longer holds in the presence of matter fields, in which case fine-tuning is
necessary to ensure higher dimensional Lorentz invariance and supersymmetry. We
use this construction to generate 4D models which mimic gaugino mediation of
SUSY breaking. The way supersymmetry breaking is mediated in these models to
the MSSM is by assuming that the physical gauginos are a mixture of a number of
gauge eigenstate gauginos: one of these couples to the SUSY breaking sector,
while another couples to the MSSM matter fields. The lattice can be as coarse
as just two gauge groups while still obtaining the characteristic
gaugino-mediated soft breaking terms.Comment: 32 pages LaTeX; missing factor in two-loop gauge-mediated scalar mass
estimate fixed, comments on unification revise
Single-Scale Natural SUSY
We consider the prospects for natural SUSY models consistent with current
data. Recent constraints make the standard paradigm unnatural so we consider
what could be a minimal extension consistent with what we now know. The most
promising such scenarios extend the MSSM with new tree-level Higgs interactions
that can lift its mass to at least 125 GeV and also allow for flavor-dependent
soft terms so that the third generation squarks are lighter than current bounds
on the first and second generation squarks. We argue that a common feature of
almost all such models is the need for a new scale near 10 TeV, such as a scale
of Higgsing or confinement of a new gauge group. We consider the question
whether such a model can naturally derive from a single mass scale associated
with supersymmetry breaking. Most such models simply postulate new scales,
leaving their proximity to the scale of MSSM soft terms a mystery. This
coincidence problem may be thought of as a mild tuning, analogous to the usual
mu problem. We find that a single mass scale origin is challenging, but suggest
that a more natural origin for such a new dynamical scale is the gravitino
mass, m_{3/2}, in theories where the MSSM soft terms are a loop factor below
m_{3/2}. As an example, we build a variant of the NMSSM where the singlet S is
composite, and the strong dynamics leading to compositeness is triggered by
masses of order m_{3/2} for some fields. Our focus is the Higgs sector, but our
model is compatible with a light stop (with the other generation squarks heavy,
or with R-parity violation or another mechanism to hide them from current
searches). All the interesting low-energy mass scales, including linear terms
for S playing a key role in EWSB, arise dynamically from the single scale
m_{3/2}. However, numerical coefficients from RG effects and wavefunction
factors in an extra dimension complicate the otherwise simple story.Comment: 32 pages, 3 figures; version accepted by JHE
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