9,084 research outputs found
Analytical Estimation of the Beam-Beam Interaction Limited Dynamic Apertures and Lifetimes in e^+e^- Circular Colliders
Physically speaking, the delta function like beam-beam nonlinear forces at
interaction points (IPs) act as a sum of delta function nonlinear multipoles.
By applying the general theory established in ref. 1, in this paper we
investigate analytically the beam-beam interaction limited dynamic apertures
and the corresponding beam lifetimes for both the round and the flat beams.
Relations between the beam-beam limited beam lifetimes and the beam-beam tune
shifts are established, which show clearly why experimentally one has always a
maximum beam-beam tune shift, \xi_{y, max}, around 0.045 for e-^+e$^- circular
colliders, and why one can use round beams to double this value approximately.
Comparisons with some machine parameters are given. Finally, we discuss the
mechanism of the luminosity reduction due to a definite collision crossing
angle.Comment: 25 page
High Dynamic-Range and Very Low Noise K-Band p-HEMT LNA MMIC for LMDS and Satellite Communication
An excellent noise figure and high linearity, K-band p-HEMT LNA MMIC, that incorporates single-bias configuration and negative feedback circuit, has be en developed for LMDS (Local Multi-point Distribution Service) and satellite communication. The third order intercept point (IP3) of this MMIC is 20 dBm, while output power at 1-dB gain compression is 8.5 dBm. The IP3 and noise figure is 19.5 +/- 1 dBm and 1.8 +/- 0.2 dB, respectively, at frequencies between 24 and 32 GHz. The die size of the MMIC is 1.9 mm. This MMIC shows a potential reliable application in high-speed wireless access system
Resonant recoil in extreme mass ratio binary black hole mergers
The inspiral and merger of a binary black hole system generally leads to an
asymmetric distribution of emitted radiation, and hence a recoil of the remnant
black hole directed opposite to the net linear momentum radiated. The recoil
velocity is generally largest for comparable mass black holes and particular
spin configurations, and approaches zero in the extreme mass ratio limit. It is
generally believed that for extreme mass ratios eta<<1, the scaling of the
recoil velocity is V {\propto} eta^2, where the proportionality coefficient
depends on the spin of the larger hole and the geometry of the system (e.g.
orbital inclination). Here we show that for low but nonzero inclination
prograde orbits and very rapidly spinning large holes (spin parameter
a*>0.9678) the inspiralling binary can pass through resonances where the
orbit-averaged radiation-reaction force is nonzero. These resonance crossings
lead to a new contribution to the kick, V {\propto} eta^{3/2}. For these
configurations and sufficiently extreme mass ratios, this resonant recoil is
dominant. While it seems doubtful that the resonant recoil will be
astrophysically significant, its existence suggests caution when extrapolating
the results of numerical kick results to extreme mass ratios and near-maximal
spins.Comment: fixed references; matches PRD accepted version (minor revision); 9
pages, 2 figure
Detection of large scale intrinsic ellipticity-density correlation from the Sloan Digital Sky Survey and implications for weak lensing surveys
The power spectrum of weak lensing shear caused by large-scale structure is
an emerging tool for precision cosmology, in particular for measuring the
effects of dark energy on the growth of structure at low redshift. One
potential source of systematic error is intrinsic alignments of ellipticities
of neighbouring galaxies (II correlation) that could mimic the correlations due
to lensing. A related possibility pointed out by Hirata and Seljak (2004) is
correlation between the intrinsic ellipticities of galaxies and the density
field responsible for gravitational lensing shear (GI correlation). We present
constraints on both the II and GI correlations using 265 908 spectroscopic
galaxies from the SDSS, and using galaxies as tracers of the mass in the case
of the GI analysis. The availability of redshifts in the SDSS allows us to
select galaxies at small radial separations, which both reduces noise in the
intrinsic alignment measurement and suppresses galaxy- galaxy lensing (which
otherwise swamps the GI correlation). While we find no detection of the II
correlation, our results are nonetheless statistically consistent with recent
detections found using the SuperCOSMOS survey. In contrast, we have a clear
detection of GI correlation in galaxies brighter than L* that persists to the
largest scales probed (60 Mpc/h) and with a sign predicted by theoretical
models. This correlation could cause the existing lensing surveys at z~1 to
underestimate the linear amplitude of fluctuations by as much as 20% depending
on the source sample used, while for surveys at z~0.5 the underestimation may
reach 30%. (Abridged.)Comment: 16 pages, matches version published in MNRAS (only minor changes in
presentation from original version
Postcolonialism and the Marshallese Diaspora: Structural Violence and Health in the Marshallese Community in Springdale, Arkansas
Despite moving to the United States for better healthcare, among other benefits, Marshallese Compact of Free Association (COFA) migrants residing in Springdale, Arkansas continue to face similar acute health problems as Marshallese living in the Republic of the Marshall Islands (RMI), and often without access to health services. These problems include high rates of noncommunicable diseases, such as type 2 diabetes and thyroid cancer, as well as rare conditions such as Hansen’s Disease.
To research this, I studied the limited texts surrounding the Marshallese diaspora, as well as relevant bodies of literature: postcolonialism, Pacific migration theory, and global health and structural violence. I also conducted topical interviews with Marshallese and non-Marshallese community members, health workers, and government officials in Springdale, Arkansas.
The two biggest barriers to healthcare in the Springdale Marshallese community are poverty and a lack of health insurance. These and the Springdale Marshallese’ biggest health problems can be traced to the structural violence caused by the continuing colonial relationship between the United States (US) and the RMI. Many existing health conditions carried over from the RMI are a result of the poverty, slum conditions, displacement, and irradiation present there, all of which can be traced back to US military occupation and intervention. Current US social services laws have stripped COFA migrants of the publicly funded health benefits (e.g., Medicaid) they were promised in the original COFA. While Marshallese COFA migrants are eligible for subsidized health insurance plans offered by the Affordable Care Act (ACA) of 2010, the Marshallese
community’s low income qualifies them for the health plan bracket reserved for the poorest: Medicaid expansion. Due to their COFA migrant status, however, they are ineligible for Medicaid in Arkansas. Practically, the ACA does little for Marshallese COFA migrants living in Springdale, of which even those with health insurance struggle to afford healthcare.
I recommend reinstating federally-funded social services such as Medicaid and the Department of Agriculture’s Supplemental Nutrition Assistance Program to COFA migrants, as this was prematurely removed from the first Compact between the US and the RMI to the continuing detriment of Marshallese COFA migrants in the US
Trunk muscle activity during drop jump performance in adolescent athletes with back pain
It was with great interest we read the recently published article “Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain.” Investigating back pain (BP) in adolescents is commendable as there is growing evidence that for many, an experience of BP as early as 14 years of age may relate to ongoing pain in adulthood (Coenen et al., 2017). Indeed, the conventional narrative is changing as individual physical factors such as posture, use of schoolbags, and hypermobility are only weakly associated with adolescent BP. Rather, factors which predict BP at a young age are considered to be multi-dimensional and include gender, negative BP beliefs and poor mental health (O\u27Sullivan et al., 2017; Smith et al., 2017). Mueller et al. (2017) have focused on a single physical factor (trunk muscle activation patterns) drawing inferences regarding BP prevention and treatment. This article prompts consideration of three essential aspects regarding research design and interpretation of findings:
1. Interpreting results from cross-sectional designs
2. Interpreting pain-related differences in motor behavior
3. Translating and conveying scientific results to the end-user (patients, healthcare professionals and policy makers)
Slepton pair production in e+e- collision in supersymmetric left-right model
The pair production of sleptons in electron-positron collisions is
investigated in a supersymmetric left-right model. The cross section is found
considerably larger than in the minimal supersymmetric version of the Standard
Model (MSSM) because of more contributing graphs. A novel process is a doubly
charged higgsino exchange in u-channel, which makes the angular distribution of
the final state particles and the final state asymmetries to differ from those
of the MSSM. It also allows for the flavour non-diagonal final states , and , forbidden in the
MSSM. These processes also give indirect information about neutrino mixings
since they depend on the same couplings as the Majorana mass terms of the
right-handed neutrinos.Comment: 13 pages + 4figures available upon request, HU-SEFT R 1993-1
Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile
We present results of theoretical study and numerical calculation of the
dynamics of molecular liquids based on combination of the memory equation
formalism and the reference interaction site model - RISM. Memory equations for
the site-site intermediate scattering functions are studied in the
mode-coupling approximation for the first order memory kernels, while
equilibrium properties such as site-site static structure factors are deduced
from RISM. The results include the temperature-density(pressure) dependence of
translational diffusion coefficients D and orientational relaxation times t for
acetonitrile in water, methanol in water and methanol in acetonitrile, all in
the limit of infinite dilution. Calculations are performed over the range of
temperatures and densities employing the SPC/E model for water and optimized
site-site potentials for acetonitrile and methanol. The theory is able to
reproduce qualitatively all main features of temperature and density
dependences of D and t observed in real and computer experiments. In
particular, anomalous behavior, i.e. the increase in mobility with density, is
observed for D and t of methanol in water, while acetonitrile in water and
methanol in acetonitrile do not show deviations from the ordinary behavior. The
variety exhibited by the different solute-solvent systems in the density
dependence of the mobility is interpreted in terms of the two competing origins
of friction, which interplay with each other as density increases: the
collisional and dielectric frictions which, respectively, increase and decrease
with increasing density.Comment: 13 pages, 8 eps-figures, 3 tables, RevTeX4-forma
Solar Neutrinos with Three Flavor Mixings
The recent 71Ga solar neutrino observation is combined with the 37Cl and
Kamiokande-II observations in an analysis for neutrino masses and mixings. The
allowed parameter region is found for matter enhanced mixings among all three
neutrino flavors. Distortions of the solar neutrino spectrum unique to three
flavors are possible and may be observed in continuing and next generation
experiments.Comment: August 1992 (Revised) PURD-TH-92-
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