2,320 research outputs found
Theorem on the proportionality of inertial and gravitational masses in classical mechanics
We considered the problem of the proportionality of inertial and
gravitational masses in classical mechanics. We found that the kinetic energy
of a material mass point m in a circular motion with a constant angular
velocity around another material point M depends only on its gravitational
mass. This fact, together with the known result that the straight line is a
circumference with an infinite radius, allowed us to prove the proportionality
between the inertial and gravitational masses.Comment: ReVTeX file, 10p
David P. Forsythe and Charles J. Mach on Empire of Humanity: A History of Humanitarianism. By Michael Barnett. Ithaca, NY: Cornell University Press, 2011. 312pp.
A review of:
Empire of Humanity: A History of Humanitarianism. By Michael Barnett. Ithaca, NY: Cornell University Press, 2011. 312pp
Leptons, quarks, and their antiparticles from a phase-space perspective
It is argued that antiparticles may be interpreted in macroscopic terms
without explicitly using the concept of time and its reversal. The appropriate
framework is that of nonrelativistic phase space. It is recalled that a quantum
version of this approach leads also, alongside the appearance of antiparticles,
to the emergence of `internal' quantum numbers identifiable with weak isospin,
weak hypercharge and colour, and to the derivation of the Gell-Mann-Nishijima
relation, while simultaneously offering a preonless interpretation of the
Harari-Shupe rishon model. Furthermore, it is shown that - under the assumption
of the additivity of canonical momenta - the approach entails the emergence of
string-like structures resembling mesons and baryons, thus providing a
different starting point for the discussion of quark unobservability.Comment: Talk given at Fifth Int. Workshop DICE2010 Space-Time-Matter,
Castiglioncello, Italy, September 13-17, 201
Coherent resonant tunneling in ac fields
We have analyzed the tunneling transmission probability and electronic
current density through resonant heterostructures in the presence of an
external electromagnetic field. In this work, we compare two different models
for a double barrier : In the first case the effect of the external field is
taken into account by spatially dependent AC voltages and in the second one the
electromagnetic field is described in terms of a photon field that irradiates
homogeneously the whole sample. While in the first description the tunneling
takes place mainly through photo sidebands in the case of homogeneous
illumination the main effective tunneling channels correspond to the coupling
between different electronic states due to photon absorption and emission. The
difference of tunneling mechanisms between these configurations is strongly
reflected in the transmission and current density which present very different
features in both cases. In order to analyze these effects we have obtained,
within the Transfer Hamiltonian framework, a general expression for the
transition probability for coherent resonant tunneling in terms of the Green's
function of the system.Comment: 16 pages,Figures available upon request,to appear in Phys.Rev B (15
April 1996
Dislodged But Not Dead: Survivorship of a High Intertidal Snail Following Wave Dislodgement
Waves breaking on rocky shorelines impart large forces on intertidal organisms, sometimes dislodging individuals. Dislodged individuals may be deposited in habitats that have a greater risk of predation or that prevent return to preferred regions on the shore. Thus, dislodgement is often assumed to be lethal. We experimentally dislodged Littorina keenae snails from high in the intertidal zone to test the likelihood of survival. Under a variety of wave conditions, we measured return rates to the high shore of 54–90%, so in this species, dislodgement is not equal to death. Snails showed a strong preference for returning to the approximate tidal height from which they were dislodged, but we found no evidence of widespread homing behaviour back to the original site of dislodgement
Jacobi's Principle and the Disappearance of Time
Jacobi's action principle is known to lead to a problem of time. For example,
the timelessness of the Wheeler-DeWitt equation can be seen as resulting from
using Jacobi's principle to define the dynamics of 3-geometries through
superspace. In addition, using Jacobi's principle for non-relativistic
particles is equivalent classically to Newton's theory but leads to a
time-independent Schrodinger equation upon Dirac quantization. In this paper,
we study the mechanism for the disappearance of time as a result of using
Jacobi's principle in these simple particle models. We find that the path
integral quantization very clearly elucidates the physical mechanism for the
timeless of the quantum theory as well as the emergence of duration at the
classical level. Physically, this is the result of a superposition of clocks
which occurs in the quantum theory due to a sum over all histories.
Mathematically, the timelessness is related to how the gauge fixing functions
impose the boundary conditions in the path integral.Comment: Published version. Significant amendments to presentation. 27 page
Three Questions on Lorentz Violation
We review the basics of the two most widely used approaches to Lorentz
violation - the Stardard Model Extension and Noncommutative Field Theory - and
discuss in some detail the example of the modified spectrum of the synchrotron
radiation. Motivated by touching upon such a fundamental issue as Lorentz
symmetry, we ask three questions: What is behind the search for Lorentz
violation? Is String Theory a physical theory? Is there an alternative to
Supersymmetry?Comment: 16 pages; invited luecture at DICE2006 - Piombino, Italy - September
200
Transplantation of a Human Mammary Carcinoma Cell Line (BT 20) Into Nude Mice
Cell suspensions of a human mammary carcinoma cell line (BT 20), when injected subcutaneously into nude athymic mice (BALB/c Nu/Nu), produced tumor nodules at the injection site. Subsequent serial transplantations also gave rise to neoplastic nodules after latency periods averaging 3 weeks. The nodules displayed morphologic and functional characteristics comparable to those of the original tumor cells. Metastases, however, were not observed in any of the tumor-bearing mic
New insight into cataract formation -- enhanced stability through mutual attraction
Small-angle neutron scattering experiments and molecular dynamics simulations
combined with an application of concepts from soft matter physics to complex
protein mixtures provide new insight into the stability of eye lens protein
mixtures. Exploring this colloid-protein analogy we demonstrate that weak
attractions between unlike proteins help to maintain lens transparency in an
extremely sensitive and non-monotonic manner. These results not only represent
an important step towards a better understanding of protein condensation
diseases such as cataract formation, but provide general guidelines for tuning
the stability of colloid mixtures, a topic relevant for soft matter physics and
industrial applications.Comment: 4 pages, 4 figures. Accepted for publication on Phys. Rev. Let
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