533 research outputs found
Speaking Ill of the Dead: Anonymity and Communication About Suicide on MyDeathSpace.com
From birth to death, many individuals chronicle their lives online through blogs, pictures, games, Web sites, and social networks. Online spaces, created by the living about the dead, provide a glimpse into often invisible or silent grieving practices. To investigate the role computer-mediated communication (CMC) plays in influencing communication surrounding the often private and taboo topic of suicide, we analyzed the comments sections of MyDeathSpace.com. Our results suggest both a breaking down of social taboos (speaking ill of the dead) and a reaffirming of strict social norms (enforcing a narrow range of acceptable presentation of identity and purpose in life), highlighting how anonymity as a characteristic of CMC can influence our online communication about death
Observers and Measurements in Noncommutative Spacetimes
We propose a "Copenhagen interpretation" for spacetime noncommutativity. The
goal is to be able to predict results of simple experiments involving signal
propagation directly from commutation relations. A model predicting an energy
dependence of the speed of photons of the order E/E_Planck is discussed in
detail. Such effects can be detectable by the GLAST telescope, to be launched
in 2006.Comment: 10 pp; v2: equivalence of observers explicitely stated; v3: minor
changes, references and remarks added, burst spreading with energy emphasized
as a signature rather than nois
Non locality and causal evolution in QFT
Non locality appearing in QFT during the free evolution of localized field
states and in the Feynman propagator function is analyzed. It is shown to be
connected to the initial non local properties present at the level of quantum
states and then it does not imply a violation of Einstein's causality. Then it
is investigated a simple QFT system with interaction, consisting of a classical
source coupled linearly to a quantum scalar field, that is exactly solved. The
expression for the time evolution of the state describing the system is given.
The expectation value of any arbitrary ``good'' local observable, expressed as
a function of the field operator and its space and time derivatives, is
obtained explicitly at all order in the field-matter coupling constant. These
expectation values have a source dependent part that is shown to be always
causally retarded, while the non local contributions are source independent and
related to the non local properties of zero point vacuum fluctuations.Comment: Submitted to Journal of Physics B: 16 pages: 1 figur
Events in a Non-Commutative Space-Time
We treat the events determined by a quantum physical state in a
noncommutative space-time, generalizing the analogous treatment in the usual
Minkowski space-time based on positive-operator-valued measures (POVMs). We
consider in detail the model proposed by Snyder in 1947 and calculate the POVMs
defined on the real line that describe the measurement of a single coordinate.
The approximate joint measurement of all the four space-time coordinates is
described in terms of a generalized Wigner function (GWF). We derive lower
bounds for the dispersion of the coordinate observables and discuss the
covariance of the model under the Poincare' group. The unusual transformation
law of the coordinates under space-time translations is interpreted as a
failure of the absolute character of the concept of space-time coincidence. The
model shows that a minimal length is compatible with Lorents covariance.Comment: 13 pages, revtex. Introductory part shortened and some arguments made
more clea
Maximal Acceleration Effects in Reissner-Nordstrom Space
The dynamics of a relativistic particle in a Reissner-Nordstrom background is
studied using Caianiello model with maximal acceleration. The behaviour of the
particle, embedded in a new effective geometry, changes with respect to the
classical scenario because of the formation of repulsive potential barriers
near the horizon. Black hole formation by accretion of massive particles is not
therefore a viable process in the model. At the same time, the naked
singularity remains largely unaffected by maximal acceleration corrections.Comment: LaTex file, 5 figures, no tables, to appear in Phys. Lett.
Radiation Bursts from Particles in the Field of Compact, Impenetrable, Astrophysical Objects
The radiation emitted by charged, scalar particles in a Schwarzschild field
with maximal acceleration corrections is calculated classically and in the tree
approximation of quantum field theory. In both instances the particles emit
radiation that has characteristics similar to those of gamma-ray bursters.Comment: 11 pages, three figure
Ameloblastic fibroma in a 6-year old child:case report.
Ameloblastic fibroma (AF) is defined in WHO classification as a ''neoplasm composed of proliferating odontogenic epithelium embedded in a cellular ectomesenchymal tissue that resembles dental papilla, and with varying degrees of inductive change and dental hard tissue formation''. AF is a rather uncommon tumor, accounting for only 2.5% of all odontogenic tumors. AF is a true mixed tumor, in which the epithelial and ectomesenchymal elements are neoplastic. AF raises at any age, ranging from 6 months to 42 years (mean 14.6 to 15.5 years); it does not show sex predilection. The lesion occurs in nearly 70% of cases in posterior areas of the mandible. Patients exhibit swelling of the jaw; pain is not usually described. Authors present a clinical and surgical management of an early onset of a large mandibular ameloblastic fibroma in a 6-year-old girsl
Shadows of a maximal acceleration
A quantum mechanical upper limit on the value of particle accelerations, or
maximal acceleration (MA), is applied to compact stars. A few MA fermions are
at most present in canonical white dwarfs and neutron stars. They drastically
alter a star's stability conditions.Comment: 11 page
Optimality-preserving Reduction of Chemical Reaction Networks
Across many disciplines, chemical reaction networks (CRNs) are an established
population model defined as a system of coupled nonlinear ordinary differential
equations. In many applications, for example, in systems biology and
epidemiology, CRN parameters such as the kinetic reaction rates can be used as
control inputs to steer the system toward a given target. Unfortunately, the
resulting optimal control problem is nonlinear, therefore, computationally very
challenging. We address this issue by introducing an optimality-preserving
reduction algorithm for CRNs. The algorithm partitions the original state
variables into a reduced set of macro-variables for which one can define a
reduced optimal control problem from which one can exactly recover the solution
of the original control problem. Notably, the reduction algorithm runs with
polynomial time complexity in the size of the CRN. We use this result to reduce
reachability and control problems of large-scale protein-interaction networks
and vaccination models with hundreds of thousands of state variables
Lower Neutrino Mass Bound from SN1987A Data and Quantum Geometry
A lower bound on the light neutrino mass is derived in the framework
of a geometrical interpretation of quantum mechanics. Using this model and the
time of flight delay data for neutrinos coming from SN1987A, we find that the
neutrino masses are bounded from below by eV, in
agreement with the upper bound
eV currently available. When the model is applied to photons with effective
mass, we obtain a lower limit on the electron density in intergalactic space
that is compatible with recent baryon density measurements.Comment: 22 pages, 3 figure
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