754 research outputs found
A model of quantum collapse induced by gravity
We discuss a model where a spontaneous quantum collapse is induced by the
gravitational interaction, treated classically. Its dynamics couples the
standard wave function of a system with the Bohmian positions of its particles,
which are considered as the only source of the gravitational attraction. The
collapse is obtained by adding a small imaginary component to the gravitational
coupling. It predicts extremely small perturbations of microscopic systems, but
very fast collapse of QSMDS (quantum superpositions of macroscopically distinct
quantum states) of a solid object, varying as the fifth power of its size. The
model does not require adding any dimensional constant to those of standard
physics.Comment: Version pubished in EPJ
Modified Sch\"odinger dynamics with attractive densities
The linear Schr\"{o}dinger equation does not predict that macroscopic bodies
should be located at one place only. Quantum mechanics textbooks generally
solve the problem by introducing the projection postulate, which forces
definite values to emerge during position measurements; many other
interpretations have also been proposed.\ Here, in the same spirit as the GRW
and CSL theories, we modify the Schr\"{o}dinger equation in a way that
efficiently cancels macroscopic density fluctuations in space.\ Instead of
introducing the stochastic dynamics of GRW or CSL, we assume a deterministic
dynamics that includes an attraction term towards the density in space of the
de Broglie-Bohm position of particles. This automatically ensures macroscopic
uniqueness, so that the state vector can be considered as a direct
representation of physical reality.Comment: 14 pages, no figure. This is the version accepted by the European
Physical Journal, with a few additions in the text and a few more references.
A typo has been corrected in Eq (4
Detection of dependence patterns with delay
The Unitary Events (UE) method is a popular and efficient method used this
last decade to detect dependence patterns of joint spike activity among
simultaneously recorded neurons. The first introduced method is based on binned
coincidence count \citep{Grun1996} and can be applied on two or more
simultaneously recorded neurons. Among the improvements of the methods, a
transposition to the continuous framework has recently been proposed in
\citep{muino2014frequent} and fully investigated in \citep{MTGAUE} for two
neurons. The goal of the present paper is to extend this study to more than two
neurons. The main result is the determination of the limit distribution of the
coincidence count. This leads to the construction of an independence test
between neurons. Finally we propose a multiple test procedure via a
Benjamini and Hochberg approach \citep{Benjamini1995}. All the theoretical
results are illustrated by a simulation study, and compared to the UE method
proposed in \citep{Grun2002}. Furthermore our method is applied on real data
Self-immolation a common suicidal behaviour in eastern Sri Lanka.
A high number of self-burning injuries are noted in Batticaloa. The epidemiology, outcome and psychosocial aspects of 87 patients admitted with such burns over a 2-year-period was studied. The patients were compared with accidental burns and patients using other methods of suicide. Seventy nine percent of the victims were females and 72% were in the 15-34 years age-group. Most had marital problems. The majority were Tamils, but Muslims were fairly well represented. The median extent of burn was 48% of total body surface area (TBSA), with the top of the body mainly affected. The use of fire proved to have a high mortality in a group of patients who did not really want to die; 61 (70%) died. Mortality was higher than for accidental burns after matching for age and burn extent. The survivors had long hospital stays and suffered severe disfigurement. The cases where the patient denied self-harm, but in which the injuries were suggestive of this motive, were strikingly similar in age, sex and burn extent to the suicide group. In contrast, poison suicide records showed a male predominance and a gross under-representation of Muslims. Fire is a very significant method of suicide in our area. Social make-up and poor problem-solving ability may be contributing factors
Quantum properties of a single beam splitter
When a single beam-splitter receives two beams of bosons described by Fock
states (Bose-Einstein condensates at very low temperatures), interesting
generalizations of the two-photon Hong-Ou-Mandel effect take place for larger
number of particles. The distributions of particles at two detectors behind the
beam splitter can be understood as resulting from the combination of two
effects, the spontaneous phase appearing during quantum measurement, and the
quantum angle. The latter introduces quantum "population oscillations", which
can be seen as a generalized Hong-Ou-Mandel effect, although they do not always
correspond to even-odd oscillations.Comment: 14 pages, 11 figure
Angular momentum conservation in measurements on spin Bose-Einstein condensates
We discuss a thought experiment where two operators, Alice and Bob, perform
transverse spin measurements on a quantum system; this system is initially in a
double Fock spin state, which extends over a large distance in space so that
the two operators are far away from each other. Standard quantum mechanics
predicts that, when Alice makes a few measurements, a large transverse
component of the spin angular momentum may appear in Bob's laboratory. A
paradox then arises since local angular momentum conservation seems to be
violated. It has been suggested that this angular momentum may be provided by
the interaction with the measurement apparatuses. We show that this solution of
the paradox is not appropriate, so that another explanation must be sought. The
general question is the retroaction of a quantum system onto a measurement
apparatus. For instance, when the measured system is entangled with another
quantum system, can its reaction on a measurement apparatus be completely
changed? Is angular momentum conserved only on average over several
measurements, but not during one realization of the experiment?Comment: 11 pages, 3 figure
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