406 research outputs found
Interaction of laser generated ultrasonic waves with wedge-shaped samples
Wedge-shaped samples can be used as a model of acoustic interactions with samples ranging from ocean wedges, to angled defects such as rolling contact fatigue, to thickness measurements of samples with non-parallel faces. We present work on laser generated ultrasonic waves on metal samples; one can measure the dominant Rayleigh-wave mode, but longitudinal and shear waves are also generated. We present calculations, models, and measurements giving the dependence of the arrival times and amplitudes of these modes on the wedge apex angle and the separation of generation and detection points, and hence give a measure of the wedge characteristics
Solar Cycle Variation of 0.3-1.29 MeV/nucleon Heavy Ion Composition during Quiet Times near 1 AU in Solar Cycles 23 and 24
We report on the annual variation of quiet-time suprathermal ion composition
for C through Fe using Advanced Composition Explorer (ACE)/Ultra-Low Energy
Isotope Spectrometer (ULEIS) data over the energy range 0.3 MeV/nuc to 1.28
MeV/nuc from 1998 through 2019, covering solar cycle 23's rising phase through
Solar Cycle 24's declining phase. Our findings are (1) quiet time suprathermal
abundances resemble CIR-associated particles during solar minima; (2) quiet
time suprathermals are M/Q fractionated in a manner that is consistent with M/Q
fractionation in large gradual solar energetic particle events (GSEP) during
solar maxima; and (3) variability within the quiet time suprathermal pool
increases as a function of M/Q and is consistent with the analogous variability
in GSEP events. From these observations, we infer that quiet time suprathermal
ions are remnants of CIRs in solar minima and GSEP events in solar maxima.
Coincident with these results, we also unexpectedly show that S behaves like a
low FIP ion in the suprathermal regime and therefore drawn from low FIP solar
sources.Comment: Accepted in Astrophysical Journal. 19 pages, 10 figures, 4 table
A Majority of Solar Wind Intervals Support Ion-Driven Instabilities
We perform a statistical assessment of solar wind stability at 1 AU against
ion sources of free energy using Nyquist's instability criterion. In contrast
to typically employed threshold models which consider a single free-energy
source, this method includes the effects of proton and He temperature
anisotropy with respect to the background magnetic field as well as relative
drifts between the proton core, proton beam, and He components on
stability. Of 309 randomly selected spectra from the Wind spacecraft,
are unstable when the ion components are modeled as drifting bi-Maxwellians;
only of the spectra are unstable to long-wavelength instabilities. A
majority of the instabilities occur for spectra where a proton beam is
resolved. Nearly all observed instabilities have growth rates slower
than instrumental and ion-kinetic-scale timescales. Unstable spectra are
associated with relatively-large He drift speeds and/or a departure of
the core proton temperature from isotropy; other parametric dependencies of
unstable spectra are also identified.Comment: 6 pages, 3 figures, 2 tables, accepted in Physical Review Letters;
fixed typos in version
The Prevalence of Children with a History of Sexual Abuse Hospitalized in the Psychiatric Setting
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72548/1/j.1744-6171.1991.tb00489.x.pd
Nonlinear viscosity and velocity distribution function in a simple longitudinal flow
A compressible flow characterized by a velocity field is
analyzed by means of the Boltzmann equation and the Bhatnagar-Gross-Krook
kinetic model. The sign of the control parameter (the longitudinal deformation
rate ) distinguishes between an expansion () and a condensation ()
phenomenon. The temperature is a decreasing function of time in the former
case, while it is an increasing function in the latter. The non-Newtonian
behavior of the gas is described by a dimensionless nonlinear viscosity
, that depends on the dimensionless longitudinal rate . The
Chapman-Enskog expansion of in powers of is seen to be only
asymptotic (except in the case of Maxwell molecules). The velocity distribution
function is also studied. At any value of , it exhibits an algebraic
high-velocity tail that is responsible for the divergence of velocity moments.
For sufficiently negative , moments of degree four and higher may diverge,
while for positive the divergence occurs in moments of degree equal to or
larger than eight.Comment: 18 pages (Revtex), including 5 figures (eps). Analysis of the heat
flux plus other minor changes added. Revised version accepted for publication
in PR
Parker Solar Probe observations of proton beams simultaneous with ion-scale waves
Parker Solar Probe (PSP), NASA's latest and closest mission to the Sun, is on
a journey to investigate fundamental enigmas of the inner heliosphere. This
paper reports initial observations made by the Solar Probe Analyzer for Ions
(SPAN-I), one of the instruments in the Solar Wind Electrons Alphas and Protons
(SWEAP) instrument suite. We address the presence of secondary proton beams in
concert with ion-scale waves observed by FIELDS, the electromagnetic fields
instrument suite. We show two events from PSP's 2nd orbit that demonstrate
signatures consistent with wave-particle interactions. We showcase 3D velocity
distribution functions (VDFs) measured by SPAN-I during times of strong wave
power at ion-scales. From an initial instability analysis, we infer that the
VDFs departed far enough away from local thermodynamic equilibrium (LTE) to
provide sufficient free energy to locally generate waves. These events
exemplify the types of instabilities that may be present and, as such, may
guide future data analysis characterizing and distinguishing between different
wave-particle interactions.Comment: 24 pages, 9 figures, 2 table
Evaluation of equity in informal land development systems in two Nigerian cities
The informal land development system in Sub-Saharan Africa (SSA) is perceived to promote equity and could be leveraged to support sustainable urban development and management. However, scanty empirical evidence exists on the extent of the system’s provision of equity to support policy formulation and practice in the region. Based on stakeholder workshops, focus group discussions and questionnaire surveys, this study analyses the system’s provision of equity in Nigeria. The study finds all categories of people undertake informal developments. Consistent with literature, this finding reflects wide patronage of the informal land development system and its relevance. Nevertheless, contrary to the existing perception, the system’s provision of equity is low. The study recommends for the institution of pro-poor and gender sensitive land development and management policies and programmes to increase the levels of equity to support the achievement of the country’s sustainable urban development and management agenda
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