566 research outputs found
Spin and Statistics in Galilean Covariant Field Theory
The existence of a possible connection between spin and statistics is
explored within the framework of Galilean covariant field theory. To this end
fields of arbitrary spin are constructed and admissible interaction terms
introduced. By explicitly solving such a model in the two particle sector it is
shown that no spin and statistics connection can be established
Against a proposed alternative explanation of the Aharonov-Bohm effect
The Aharonov-Bohm effect is understood to demonstrate that the Maxwell fields
can act nonlocally in some situations. However it has been suggested from time
to time that the AB effect is somehow a consequence of a local classical
electromagnetic field phenomenon involving energy that is temporarily stored in
the overlap between the external field and the field of which the beam particle
is the source. That idea was shown in the past not to work for some models of
the source of the external field. Here a more general proof is presented for
the magnetic AB effect to show that the overlap energy is always compensated by
another contribution to the energy of the magnetic field in such a way that the
sum of the two is independent of the external flux. Therefore no such mechanism
can underlie the Aharonov-Bohm effect.Comment: 7 pages, 1 figur
Topology, Locality, and Aharonov-Bohm Effect with Neutrons
Recent neutron interferometry experiments have been interpreted as
demonstrating a new topological phenomenon similar in principle to the usual
Aharonov-Bohm (AB) effect, but with the neutron's magnetic moment replacing the
electron's charge. We show that the new phenomenon, called Scalar AB (SAB)
effect, follows from an ordinary local interaction, contrary to the usual AB
effect, and we argue that the SAB effect is not a topological effect by any
useful definition. We find that SAB actually measures an apparently novel spin
autocorrelation whose operator equations of motion contain the local torque in
the magnetic field. We note that the same remarks apply to the Aharonov-Casher
effect.Comment: 9 page
Task planning and control synthesis for robotic manipulation in space applications
Space-based robotic systems for diagnosis, repair and assembly of systems will require new techniques of planning and manipulation to accomplish these complex tasks. Results of work in assembly task representation, discrete task planning, and control synthesis which provide a design environment for flexible assembly systems in manufacturing applications, and which extend to planning of manipulatiuon operations in unstructured environments are summarized. Assembly planning is carried out using the AND/OR graph representation which encompasses all possible partial orders of operations and may be used to plan assembly sequences. Discrete task planning uses the configuration map which facilitates search over a space of discrete operations parameters in sequential operations in order to achieve required goals in the space of bounded configuration sets
Remarks on the Configuration Space Approach to Spin-Statistics
The angular momentum operators for a system of two spin-zero
indistinguishable particles are constructed, using Isham's Canonical Group
Quantization method. This mathematically rigorous method provides a hint at the
correct definition of (total) angular momentum operators, for arbitrary spin,
in a system of indistinguishable particles. The connection with other
configuration space approaches to spin-statistics is discussed, as well as the
relevance of the obtained results in view of a possible alternative proof of
the spin-statistics theorem.Comment: 18 page
Creation of prompt and thin-sheet splashing by varying surface roughness or increasing air pressure
A liquid drop impacting a solid surface may splash by emitting a thin liquid
sheet that subsequently breaks apart or by promptly ejecting droplets from the
advancing liquid-solid contact line. Using high-speed imaging, we show that air
pressure and surface roughness influence both splash mechanisms. Roughness
increases prompt splashing at the advancing contact line but inhibits the
formation of the thin sheet. If the air pressure is lowered, droplet ejection
is suppressed not only during thin-sheet formation but for prompt splashing as
well. The threshold pressure depends on impact velocity, liquid viscosity and
surface roughness
Combinatorial approach to generalized Bell and Stirling numbers and boson normal ordering problem
We consider the numbers arising in the problem of normal ordering of
expressions in canonical boson creation and annihilation operators. We treat a
general form of a boson string which is shown to be associated with
generalizations of Stirling and Bell numbers. The recurrence relations and
closed-form expressions (Dobiski-type formulas) are obtained for these
quantities by both algebraic and combinatorial methods. By extensive use of
methods of combinatorial analysis we prove the equivalence of the
aforementioned problem to the enumeration of special families of graphs. This
link provides a combinatorial interpretation of the numbers arising in this
normal ordering problem.Comment: 10 pages, 5 figure
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