34,949 research outputs found
Pressure Calculation in Polar and Charged Systems using Ewald Summation: Results for the Extended Simple Point Charge Model of Water
Ewald summation and physically equivalent methods such as particle-mesh
Ewald, kubic-harmonic expansions, or Lekner sums are commonly used to calculate
long-range electrostatic interactions in computer simulations of polar and
charged substances. The calculation of pressures in such systems is
investigated. We find that the virial and thermodynamic pressures differ
because of the explicit volume dependence of the effective, resummed Ewald
potential. The thermodynamic pressure, obtained from the volume derivative of
the Helmholtz free energy, can be expressed easily for both ionic and rigid
molecular systems. For a system of rigid molecules, the electrostatic energy
and the forces at the atom positions are required, both of which are readily
available in molecular dynamics codes. We then calculate the virial and
thermodynamic pressures for the extended simple point charge (SPC/E) water
model at standard conditions. We find that the thermodynamic pressure exhibits
considerably less system size dependence than the virial pressure. From an
analysis of the cross correlation between the virial and thermodynamic
pressure, we conclude that the thermodynamic pressure should be used to drive
volume fluctuations in constant-pressure simulations.Comment: RevTeX, 19 pages, 2 EPS figures; in press: Journal of Chemical
Physics, 15-August-199
The Ursinus Weekly, October 6, 1905
Football • Alumni • Society notes • Old fashioned corn roast • Oyster supper • College world • School of Theology • Songshttps://digitalcommons.ursinus.edu/weekly/2951/thumbnail.jp
The Ursinus Weekly, June 9, 1905
Baccalaureate sermon • Class Day exercises • Commencement • Reunion • Junior oratorical contest • Society notes • College notes • Farewell reception • Baseball • Alumni Day • Alumni oration • President\u27s receptionhttps://digitalcommons.ursinus.edu/weekly/3019/thumbnail.jp
The Ursinus Weekly, March 2, 1906
1907 stag party • Intercollegiate oratorical contest • Mr. Keiner entertains • Alumni • Baseball outlook • Society notes • Glee and orchestra at Conshohocken • Philadelphia letter • Personalshttps://digitalcommons.ursinus.edu/weekly/2971/thumbnail.jp
The Ursinus Weekly, April 21, 1905
Baseball • The Reverend J. H. Sechler, D. D. • Resolutions • Society notes • College sermon • Seminary notes • Alumni noteshttps://digitalcommons.ursinus.edu/weekly/3012/thumbnail.jp
Resonant Clumping and Substructure in Galactic Discs
We describe a method to extract resonant orbits from N-body simulations
exploiting the fact that they close in a frame rotating with a constant pattern
speed. Our method is applied to the N-body simulation of the Milky Way by Shen
et al. (2010). This simulation hosts a massive bar, which drives strong
resonances and persistent angular momentum exchange. Resonant orbits are found
throughout the disc, both close to the bar itself and out to the very edges of
the disc. Using Fourier spectrograms, we demonstrate that the bar is driving
kinematic substructure even in the very outer parts of the disc. We identify
two major orbit families in the outskirts of the disc that make significant
contributions to the kinematic landscape, namely the m:l = 3:-2 and 1:-1
families resonating with the pattern speed of the bar. A mechanism is described
that produces bimodal distributions of Galactocentric radial velocities at
selected azimuths in the outer disc. It occurs as a result of the temporal
coherence of particles on the 3:-2 resonant orbits, which causes them to arrive
simultaneously at pericentre or apocentre. This resonant clumping, due to the
in-phase motion of the particles through their epicycle, leads to both inward
and outward moving groups which belong to the same orbital family and
consequently produce bimodal radial velocity distributions. This is a possible
explanation of the bimodal velocity distributions observed towards the Galactic
anti-Centre by Liu et al. (2012). Another consequence is that transient
overdensities appear and dissipate (in a symmetric fashion) on timescales equal
to the their epicyclic period resulting in a periodic pulsing of the disc's
surface density.Comment: 11 Figures, 1 Table. Accepted for publication in ApJ. Version 2
reflects minor changes to the text. Animation referenced in Figure 7 is
available at http://hubble.shao.ac.cn/~shen/resonantclumping/DensMovie.mp
The Ursinus Weekly, February 9, 1906
The Angelus by Millet • Characters of The Bells entertained • Administration Committee • Society notes • Philadelphia letter • A glance in passing • Union programhttps://digitalcommons.ursinus.edu/weekly/2968/thumbnail.jp
The Ursinus Weekly, November 10, 1905
Football • Alumni • Week of Prayer • Seniors • Ursinus Union • Society notes • College notes • College world • Gettysburg game • New football songhttps://digitalcommons.ursinus.edu/weekly/2956/thumbnail.jp
The Ursinus Weekly, May 26, 1905
Baseball • Junior boating party • Alumni notes • Commencement • Pupils\u27 recital • Society notes • College notes • Noticehttps://digitalcommons.ursinus.edu/weekly/3017/thumbnail.jp
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