336 research outputs found
Some exact solutions to the Lighthill Whitham Richards Payne traffic flow equations II: moderate congestion
We find a further class of exact solutions to the Lighthill Whitham Richards
Payne (LWRP) traffic flow equations. As before, using two consecutive
Lagrangian transformations, a linearization is achieved. Next, depending on the
initial density, we either obtain exact formulae for the dependence of the car
density and velocity on x, t, or else, failing that, the same result in a
parametric representation. The calculation always involves two possible
factorizations of a consistency condition. Both must be considered. In physical
terms, the lineup usually separates into two offshoots at different velocities.
Each velocity soon becomes uniform. This outcome in many ways resembles not
only Rowlands, Infeld and Skorupski J. Phys. A: Math. Theor. 46 (2013) 365202
(part I) but also the two soliton solution to the Korteweg-de Vries equation.
This paper can be read independently of part I. This explains unavoidable
repetitions. Possible uses of both papers in checking numerical codes are
indicated at the end. Since LWRP, numerous more elaborate models, including
multiple lanes, traffic jams, tollgates etc. abound in the literature. However,
we present an exact solution. These are few and far between, other then found
by inverse scattering. The literature for various models, including ours, is
given. The methods used here and in part I may be useful in solving other
problems, such as shallow water flow.Comment: 15 pages, 7 figure
Electromagnetic Oscillations in a Spherical Conducting Cavity with Dielectric Layers. Application to Linear Accelerators
We present an analysis of electromagnetic oscillations in a spherical
conducting cavity filled concentrically with either dielectric or vacuum
layers. The fields are given analytically, and the resonant frequency is
determined numerically. An important special case of a spherical conducting
cavity with a smaller dielectric sphere at its center is treated in more
detail. By numerically integrating the equations of motion we demonstrate that
the transverse electric oscillations in such cavity can be used to accelerate
strongly relativistic electrons. The electron's trajectory is assumed to be
nearly tangential to the dielectric sphere. We demonstrate that the interaction
of such electrons with the oscillating magnetic field deflects their trajectory
from a straight line only slightly. The Q factor of such a resonator only
depends on losses in the dielectric. For existing ultra low loss dielectrics, Q
can be three orders of magnitude better than obtained in existing cylindrical
cavities.Comment: Extended version with one new section, modified title and new
abstract, 10 pages, 13 figure
Theoretical confirmation of Feynman's hypothesis on the creation of circular vortices in Bose-Einstein condensates: III
In two preceding papers (Infeld and Senatorski 2003 J. Phys.: Condens. Matter
15 5865, and Senatorski and Infeld 2004 J. Phys.: Condens. Matter 16 6589) the
authors confirmed Feynman's hypothesis on how circular vortices can be created
from oppositely polarized pairs of linear vortices (first paper), and then gave
examples of the creation of several different circular vortices from one linear
pair (second paper). Here in part III, we give two classes of examples of how
the vortices can interact. The first confirms the intuition that the
reconnection processes which join two interacting vortex lines into one,
practically do not occur. The second shows that new circular vortices can also
be created from pairs of oppositely polarized coaxial circular vortices. This
seems to contradict the results for such pairs given in Koplik and Levine 1996
Phys. Rev. Lett. 76 4745.Comment: 10 pages, 7 figure
Nonlinear Electron Oscillations in a Viscous and Resistive Plasma
New non-linear, spatially periodic, long wavelength electrostatic modes of an
electron fluid oscillating against a motionless ion fluid (Langmuir waves) are
given, with viscous and resistive effects included. The cold plasma
approximation is adopted, which requires the wavelength to be sufficiently
large. The pertinent requirement valid for large amplitude waves is determined.
The general non-linear solution of the continuity and momentum transfer
equations for the electron fluid along with Poisson's equation is obtained in
simple parametric form. It is shown that in all typical hydrogen plasmas, the
influence of plasma resistivity on the modes in question is negligible. Within
the limitations of the solution found, the non-linear time evolution of any
(periodic) initial electron number density profile n_e(x, t=0) can be
determined (examples). For the modes in question, an idealized model of a
strictly cold and collisionless plasma is shown to be applicable to any real
plasma, provided that the wavelength lambda >> lambda_{min}(n_0,T_e), where n_0
= const and T_e are the equilibrium values of the electron number density and
electron temperature. Within this idealized model, the minimum of the initial
electron density n_e(x_{min}, t=0) must be larger than half its equilibrium
value, n_0/2. Otherwise, the corresponding maximum n_e(x_{max},t=tau_p/2),
obtained after half a period of the plasma oscillation blows up. Relaxation of
this restriction on n_e(x, t=0) as one decreases lambda, due to the increase of
the electron viscosity effects, is examined in detail. Strong plasma viscosity
is shown to change considerably the density profile during the time evolution,
e.g., by splitting the largest maximum in two.Comment: 16 one column pages, 11 figures, Abstract and Sec. I, extended, Sec.
VIII modified, Phys. Rev. E in pres
Evaluation of Weight Change During Carboplatin Therapy in Dogs With Appendicular Osteosarcoma.
BackgroundThe prevalence of cancer cachexia in veterinary medicine has not been studied widely, and as of yet, no definitive diagnostic criteria effectively assess this syndrome in veterinary patients.Objectives(1) To determine the patterns of weight change in dogs with appendicular osteosarcoma treated with amputation and single-agent carboplatin during the course of adjuvant chemotherapy; and (2) to determine whether postoperative weight change is a negative prognostic indicator for survival time in dogs with osteosarcoma.AnimalsEighty-eight dogs diagnosed with appendicular osteosarcoma. Animals were accrued from 3 veterinary teaching hospitals.MethodsRetrospective, multi-institutional study. Dogs diagnosed with appendicular osteosarcoma and treated with limb amputation followed by a minimum of 4 doses of single-agent carboplatin were included. Data analyzed in each patient included signalment, tumor site, preoperative serum alkaline phosphatase activity (ALP), and body weight (kg) at each carboplatin treatment.ResultsA slight increase in weight occurred over the course of chemotherapy, but this change was not statistically significant. Weight change did not have a significant effect on survival. Institution, patient sex, and serum ALP activity did not have a significant effect on survival.Conclusions and clinical importanceWeight change was not a prognostic factor in these dogs, and weight loss alone may not be a suitable method of determining cancer cachexia in dogs with appendicular osteosarcoma
Fasting Reduces the Incidence of Delayed-Type Vomiting Associated with Doxorubicin Treatment in Dogs with Lymphoma.
Fasting reduces gastrointestinal cellular proliferation rates through G1 cycle blockade and can promote cellular protection of normal but not cancer cells through altered cell signaling including down-regulation of insulin-like growth factor 1 (IGF-1). Consequently, the purpose of this study was to determine the effects of fasting on delayed-type chemotherapy-induced nausea and vomiting in dogs receiving doxorubicin. This prospective randomized crossover study involved intended administration of two doses of doxorubicin. Cancer-bearing dogs were randomized to be fasted for 24 hours beginning at 6 P.M. the night before the first or second doxorubicin administration, and all treatments were administered within an hour before or after 12 P.M. Dogs were fed normally before the alternate dose. Circulating IGF-1 concentrations were determined from serum samples obtained immediately before each doxorubicin treatment. Data from 35 doses were available from 20 dogs enrolled. Dogs that were fasted exhibited a significantly lower incidence of vomiting, when compared to fed dogs (10% compared to 67%, P = .020). Furthermore, among the 15 dogs that completed crossover dosing, vomiting was abrogated in four of five dogs that experienced doxorubicin-induced vomiting when fed normally (P = .050). No differences in other gastrointestinal, constitutional, or bone marrow toxicities or serum IGF-1 levels were observed
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