10,650 research outputs found
New thermocouple-based microwave/millimeter-wave power sensor MMIC techniques in GaAs
We describe a new RF and microwave power sensor monolithic microwave integrated circuit design. The circuit incorporates a number of advances over existing designs. These include a III–V epitaxial structure optimized for sensitivity, the figure-of-merit applicable to the optimization, a mechanism for in-built detection of load ageing and damage to extend calibration intervals, and a novel symmetrical structure to linearize the high-power end of the scale
Towards a High Energy Theory for the Higgs Phase of Gravity
Spontaneous Lorentz violation due to a time-dependent expectation value for a
massless scalar has been suggested as a method for dynamically generating dark
energy. A natural candidate for the scalar is a Goldstone boson arising from
the spontaneous breaking of a U(1) symmetry. We investigate the low-energy
effective action for such a Goldstone boson in a general class of models
involving only scalars, proving that if the scalars have standard kinetic terms
then at the {\em classical} level the effective action does not have the
required features for spontaneous Lorentz violation to occur asymptotically in an expanding FRW universe. Then we study the large limit of
a renormalizable field theory with a complex scalar coupled to massive
fermions. In this model an effective action for the Goldstone boson with the
properties required for spontaneous Lorentz violation can be generated.
Although the model has shortcomings, we feel it represents progress towards
finding a high energy completion for the Higgs phase of gravity.Comment: 20 pages, 5 figures;fixed typos and added reference
Adolescent BMI trajectories with clusters of physical activity and sedentary behavior: An exploratory analysis
Objective: The purpose of this study is to identify distinct body mass index (BMI) trajectories associated with weight classification, and to examine demographic characteristics and clusters of obesogenic behaviours in adolescents with these trajectories.
Methods: Data were extracted from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (n = 1,006, Grades 5–8). The independent variables were physical activity (accelerometer and child report), sports participation, television/video watching time and recreational computer use. The dependent variable was raw BMI. Growth mixture modelling, mixture modelling and independent t-test analyses were used.
Results: Two distinct BMI trajectories were identified – one with the mean BMI within the Overweight–Obese classification (≥85th percentile) and the other within the healthy weight classification (5th– 84th percentile). Two clusters of physical and sedentary behaviours were identified in adolescents with the Overweight–Obese BMI trajectory. These clusters differed in the type of sedentary behaviour (computer vs. television/video). Three clusters were identified in adolescents with the Healthy Weight BMI trajectory. These clusters differed in levels of physical activity and types of sedentary behaviour.
Conclusion: This study contributes to the understanding of multi-dimensional obesogenic behavioural patterns and highlights the importance of understanding types of sedentary behaviour in adolescents
Kinematics of women's sprint canoeing technique
Little is known about the biomechanics of sprint canoeing, especially for women’s
canoeing, and a quantitative kinematic description of the motion would help coaches to
develop valid technique coaching models. Five highly-trained female canoeists were
filmed at 150 Hz while undertaking a 50 s maximal effort on a canoe ergometer, whose
trolley motions were taken to represent those of the boat. Selected boat, body and paddle
kinematics were evaluated at three key stroke cycle events (Contact, Paddle Vertical, and
End of Drive) and their patterns monitored across the stroke cycle. While no clear trends
between the kinematics and power output emerged, a range of strategies were identified
and the data represent an initial step in the construction of detailed technique models that
can be used to evaluate and monitor individual athletes
Density, Velocity, and Magnetic Field Structure in Turbulent Molecular Cloud Models
We use 3D numerical MHD simulations to follow the evolution of cold,
turbulent, gaseous systems with parameters representing GMC conditions. We
study three cloud simulations with varying mean magnetic fields, but identical
initial velocity fields. We show that turbulent energy is reduced by a factor
two after 0.4-0.8 flow crossing times (2-4 Myr), and that the magnetically
supercritical cloud models collapse after ~6 Myr, while the subcritical cloud
does not collapse. We compare density, velocity, and magnetic field structure
in three sets of snapshots with matched Mach numbers. The volume and column
densities are both log-normally distributed, with mean volume density a factor
3-6 times the unperturbed value, but mean column density only a factor 1.1-1.4
times the unperturbed value. We use a binning algorithm to investigate the
dependence of kinetic quantities on spatial scale for regions of column density
contrast (ROCs). The average velocity dispersion for the ROCs is only weakly
correlated with scale, similar to the mean size-linewidth relation for clumps
within GMCs. ROCs are often superpositions of spatially unconnected regions
that cannot easily be separated using velocity information; the same difficulty
may affect observed GMC clumps. We analyze magnetic field structure, and show
that in the high density regime, total magnetic field strengths increase with
density with logarithmic slope 1/3 -2/3. Mean line-of-sight magnetic field
strengths vary widely across a projected cloud, and do not correlate with
column density. We compute simulated interstellar polarization maps at varying
orientations, and determine that the Chandrasekhar-Fermi formula multiplied by
a factor ~0.5 yields a good estimate of the plane-of sky magnetic field
strength provided the dispersion in polarization angles is < 25 degrees.Comment: 56 pages, 25 figures; Ap.J., accepte
Binding of Basic Dyes by the Algae, Chara aspera
Non-living biomass of the algae Chara aspera is capable of binding two basic dyes, methylene blue and basic blue 3, from aqueous solution. Factors such as dye concentration, contact time, sorbent dosage and pH of solution were
studied. Maximum sorption capacities of the algae for methylene blue and basic blue 3 are 139.4 and 17.8 mg/g, respectively, as determined from the
Langmuir isothenns
Age Dating of a High-Redshift QSO B1422+231 at Z=3.62 and its Cosmological Implications
The observed Fe II(UV+optical)/Mg II lambda lambda 2796,2804 flux ratio from
a gravitationally lensed quasar B1422+231 at z=3.62 is interpreted in terms of
detailed modeling of photoionization and chemical enrichment in the broad-line
region (BLR) of the host galaxy. The delayed iron enrichment by Type Ia
supernovae is used as a cosmic clock. Our standard model, which matches the Fe
II/Mg II ratio, requires the age of 1.5 Gyr for B1422+231 with a lower bound of
1.3 Gyr, which exceeds the expansion age of the Einstein-de Sitter Omega_0=1
universe at a redshift of 3.62 for any value of the Hubble constant in the
currently accepted range, H_0=60-80 km,s^{-1},Mpc^{-1}. This problem of an age
discrepancy at z=3.62 can be unraveled in a low-density Omega_0<0.2 universe,
either with or without a cosmological constant, depending on the allowable
redshift range of galaxy formation. However, whether the cosmological constant
is a required option in modern cosmology awaits a thorough understanding of
line transfer processes in the BLRs.Comment: 7 pages including 3 figures, to appear in ApJ Letter
On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening
We assess the contribution of dynamical hardening by direct three-body
scattering interactions to the rate of stellar-mass black hole binary (BHB)
mergers in galactic nuclei. We derive an analytic model for the single-binary
encounter rate in a nucleus with spherical and disk components hosting a
super-massive black hole (SMBH). We determine the total number of encounters
needed to harden a BHB to the point that inspiral due to
gravitational wave emission occurs before the next three-body scattering event.
This is done independently for both the spherical and disk components. Using a
Monte Carlo approach, we refine our calculations for to include
gravitational wave emission between scattering events. For astrophysically
plausible models we find that typically 10.
We find two separate regimes for the efficient dynamical hardening of BHBs:
(1) spherical star clusters with high central densities, low velocity
dispersions and no significant Keplerian component; and (2) migration traps in
disks around SMBHs lacking any significant spherical stellar component in the
vicinity of the migration trap, which is expected due to effective orbital
inclination reduction of any spherical population by the disk. We also find a
weak correlation between the ratio of the second-order velocity moment to
velocity dispersion in galactic nuclei and the rate of BHB mergers, where this
ratio is a proxy for the ratio between the rotation- and dispersion-supported
components. Because disks enforce planar interactions that are efficient in
hardening BHBs, particularly in migration traps, they have high merger rates
that can contribute significantly to the rate of BHB mergers detected by the
advanced Laser Interferometer Gravitational-Wave Observatory.Comment: 13 pages, 9 figures, accepted for publication in MNRA
decays revisited: branching ratios and T-odd momenta correlations
We calculate the branching ratios of the decays, and the T-odd triple momenta correlations
, due to the
electromagnetic final state interaction, in these processes. The contributions
on the order of and to the corresponding amplitudes
are treated exactly. For the branching ratios, the corrections on the order of
are estimated and demonstrated to be small. We compare the results
with those of other authors. In some cases our results differ considerably from
the previous ones.Comment: 13 pages, 11 figures; references adde
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