17 research outputs found
Electron and nuclear pressures in electron-nucleus mixtures
It is shown for an electron-nucleus mixture that the electron and nuclear
pressures are defined clearly and simply by the virial theorem; the total
pressure of this system is a sum of these two pressures. The electron pressure
is different from the conventional electron pressure being expressed as the sum
of two times of kinetic energy and the potential energy in that the nuclear
virial term is subtracted; this fact is exemplified by several kinds of
definitions for the electron pressure enumerated in this work. The conventional
definition of the electron pressure in terms of the nuclear virial term is
shown inappropriate. Similar remarks are made about the definition of the
stress tensor in this mixture. It is also demonstrated that both of the
electron and nuclear pressures become zero at the same time for a metal in the
vacuum, in contrast to the conventional viewpoint that the zero pressure is
realized by a result of the cancellation between the electron and nuclear
pressures, each of which is not zero. On the basis of these facts, a simple
equation of states for liquid metals is derived, and examined numerically for
liquid alkaline metals by use of the quantum hypernetted chain equation and the
Ashcroft model potential.Comment: 24pages. 2 ps-figures, use epsf.sty, namelist.sty,REVtex macro
Pressure formulas for liquid metals and plasmas based on the density-functional theory
At first, pressure formulas for the electrons under the external potential
produced by fixed nuclei are derived both in the surface integral and volume
integral forms concerning an arbitrary volume chosen in the system; the surface
integral form is described by a pressure tensor consisting of a sum of the
kinetic and exchange-correlation parts in the density-functional theory, and
the volume integral form represents the virial theorem with subtraction of the
nuclear virial. Secondly on the basis of these formulas, the thermodynamical
pressure of liquid metals and plasmas is represented in the forms of the
surface integral and the volume integral including the nuclear contribution.
From these results, we obtain a virial pressure formula for liquid metals,
which is more accurate and simpler than the standard representation. From the
view point of our formulation, some comments are made on pressure formulas
derived previously and on a definition of pressure widely used.Comment: 18 pages, no figur
Radiotherapy using a laser proton accelerator
Laser acceleration promises innovation in particle beam therapy of cancer
where an ultra-compact accelerator system for cancer beam therapy can become
affordable to a broad range of patients. This is not feasible without the
introduction of a technology that is radically different from the conventional
accelerator-based approach. The laser acceleration method provides many
enhanced capabilities for the radiation oncologist. It reduces the overall
system size and weight by more than one order of magnitude. The characteristics
of the particle beams (protons) make them suitable for a class of therapy that
might not be possible with the conventional accelerator, such as the ease for
changing pulse intensity, the focus spread, the pinpointedness, and the dose
delivery in general. A compact, uncluttered system allows a PET device to be
located in the vicinity of the patient in concert with the compact gantry. The
radiation oncologist may be able to irradiate a localized tumor by scanning
with a pencil-like particle beam while ascertaining the actual dosage in the
patient with an improved in-beam PET verification of auto-radioactivation
induced by the beam therapy. This should yield an unprecedented flexibility in
the feedback radiotherapy by the radiation oncologist. Laser accelerated
radiotherapy has a unique niche in a current world of high energy accelerator
using synchrotron or cyclotron.Comment: 26 pages, 8 figures, 2 tables, 69 references. International Symposium
on Laser-Driven Relativistic Plasmas Applied for Science, Industry and
Medicine, Kyoto, Japan, 17-20 September (2007
A parameter study of pencil beam proton dose distributions for the treatment of ocular melanoma utilizing spot scanning
Results of Monte Carlo calculated dose distributions of proton treatment of ocular melanoma are presented. An efficient spot-scanning method utilizing active energy modulation which also minimizes the number of target spots was developed. We simulated various parameter values for the particle energy spread and the pencil-beam diameter in order to determine values suitable for medical treatment. We found that a 2.5-mm-diameter proton beam with a 5% Gaussian energy spread is suitable for treatment of ocular melanoma while preserving vision for the typical case that we simulated. The energy spectra and required proton current were also calculated and are reported. The results are intended to serve as a guideline for a new class of low-cost, compact accelerators