5,479 research outputs found
Evidence for the Strong Effect of Gas Removal on the Internal Dynamics of Young Stellar Clusters
We present detailed luminosity profiles of the young massive clusters M82-F,
NGC 1569-A, and NGC 1705-1 which show significant departures from equilibrium
(King and EFF) profiles. We compare these profiles with those from N-body
simulations of clusters which have undergone the rapid removal of a significant
fraction of their mass due to gas expulsion. We show that the observations and
simulations agree very well with each other suggesting that these young
clusters are undergoing violent relaxation and are also losing a significant
fraction of their stellar mass. That these clusters are not in equilibrium can
explain the discrepant mass-to-light ratios observed in many young clusters
with respect to simple stellar population models without resorting to
non-standard initial stellar mass functions as claimed for M82-F and NGC
1705-1. We also discuss the effect of rapid gas removal on the complete
disruption of a large fraction of young massive clusters (``infant
mortality''). Finally we note that even bound clusters may lose >50% of their
initial stellar mass due to rapid gas loss (``infant weight-loss'').Comment: 6 pages, 3 figures, MNRAS letters, accepte
Dispersive analysis of omega --> 3pi and phi --> 3pi decays
We study the three-pion decays of the lightest isoscalar vector mesons, omega
and phi, in a dispersive framework that allows for a consistent description of
final-state interactions between all three pions. Our results are solely
dependent on the phenomenological input for the pion-pion P-wave scattering
phase shift. We predict the Dalitz plot distributions for both decays and
compare our findings to recent measurements of the phi --> 3pi Dalitz plot by
the KLOE and CMD-2 collaborations. Dalitz plot parameters for future precision
measurements of omega --> 3pi are predicted. We also calculate the pi-pi P-wave
inelasticity contribution from omega-pi intermediate states.Comment: 23 pages, 18 figures; discussion extended, Appendix D added, matches
version published in EPJ
Dispersion relations for
We present a dispersive analysis of the decay amplitude for
that is based on the fundamental principles of analyticity
and unitarity. In this framework, final-state interactions are fully taken into
account. Our dispersive representation relies only on input for the
and scattering phase shifts. Isospin symmetry allows us to describe
both the charged and neutral decay channel in terms of the same function. The
dispersion relation contains subtraction constants that cannot be fixed by
unitarity. We determine these parameters by a fit to Dalitz-plot data from the
VES and BES-III experiments. We study the prediction of a low-energy theorem
and compare the dispersive fit to variants of chiral perturbation theory.Comment: 22 pages, 10 figures; v2: added footnote, version published in EPJ
PENGARUH PENGGUNAAN CUTTING FLUID DAN PEMILIHAN FEED RATE TERHADAP KEKASARAN PERMUKAAN DAN KEPRESISIAN MATERIAL ALUMINIUM MENGGUNAKAN MESIN MILLING CNC
Ada banyak faktor yang mempengaruhi kualitas produk yang dihasilkan dari proses milling. Kualitas produk kebanyakan tentang kekasaran permukaan dan kepresisian. Faktor-faktor yang mempengaruhi adalah pemilihan parameter pemotongan dan penggunaan cutting fluid. Penelitian ini dilakukan untuk mengetahui pengaruh penggunaan cutting fluid dan pemilihan feed rate terhadap kekasaran permukaan dan kepresisian material aluminium menggunakan mesin milling CNC. Pada penelitian ini menggunakan mesin milling CNC Mitsubishi M70. Variabel bebas feed rate 20, 32, 45, 69, 108 mm/min. Tiap variasi feed rate diberi perlakuan menggunakan cutting fluid dan tanpa menggunakan cutting fluid. Cutting fluid yang digunakan yaitu oli bromus yang dicampur dengan air. Pengujian yang dilakukan adalah uji kakasaran permukaan, dan uji kepresisian. Hasil penelitian ini menunjukkan bahwa semakin tinggi feed rate maka kekasaran permukaan semakin tinggi (berbanding lurus). Penggunaan cutting fluid berpengaruh terhadap kekasaran permukaan. Nilai kekasaran pada variasi feed rate 20, 32, 45, 69, 108 mm/min menggunakan cutting fluid, menunjukkan nilai kekasaran berturut-turut sebesar 0,442; 0,484; 0,553; 0,643; 0,797 µm. Nilai kekasaran permukaan tanpa menggunakan menggunakan cutting fluid menunjukkan nilai kekasaran 0,470; 0,517; 0,582; 0;662; 0,847 µm. Berdasarkan hasil analisis statistik menggunakan two way ANOVA, disimpulkan bahwa penggunaan cutting fluid dan variasi feed rate berpengaruh terhadap kepresisian dengan tingkat keyakinan 95 %. Pada pengukuran dimensi A variasi feed rate 20, 32, 45,69,108 mm/min menggunakan cutting fluid, tingkat kepresisiannya sebesar 99,999348; 99,99929; 99,999304; 99,999261; 99,9992 %. Pada variasi tanpa menggunakan cutting fluid, tingkat kepresisiannya sebesar 99,999188; 99,999184; 99,999037; 99;998884; 99,998684 %
Dispersive analysis of the pion transition form factor
We analyze the pion transition form factor using dispersion theory. We
calculate the singly-virtual form factor in the time-like region based on data
for the cross section, generalizing previous studies on
decays and scattering, and verify our
result by comparing to data. We perform the analytic
continuation to the space-like region, predicting the poorly-constrained
space-like transition form factor below 1 GeV, and extract the slope of the
form factor at vanishing momentum transfer .
We derive the dispersive formalism necessary for the extension of these results
to the doubly-virtual case, as required for the pion-pole contribution to
hadronic light-by-light scattering in the anomalous magnetic moment of the
muon.Comment: 13 pages, 5 figures, journal versio
Thermophysical properties of warm dense hydrogen
We study the thermophysical properties of warm dense hydrogen using quantum
molecular dynamics simulations. New results are presented for the pair
distribution functions, the equation of state, the Hugoniot curve, and the
reflectivity. We compare with available experimental data and predictions of
the chemical picture. Especially, we discuss the nonmetal-to-metal transition
which occurs at about 40 GPa in the dense fluid
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