1,086 research outputs found
Limitations on Ku-band communications due to multipath
The earth and orbiter body reflections involving the Tracking Data Relay Satellite (TDRS)/orbiter communications link are evaluated. Recommendations address operational conditions in order to avoid critical multipath impacts, modulation preferences during acquisition, and preferred scan limit implementation
Generalized Strong Curvature Singularities and Cosmic Censorship
A new definition of a strong curvature singularity is proposed. This
definition is motivated by the definitions given by Tipler and Krolak, but is
significantly different and more general. All causal geodesics terminating at
these new singularities, which we call generalized strong curvature
singularities, are classified into three possible types; the classification is
based on certain relations between the curvature strength of the singularities
and the causal structure in their neighborhood. A cosmic censorship theorem is
formulated and proved which shows that only one class of generalized strong
curvature singularities, corresponding to a single type of geodesics according
to our classification, can be naked. Implications of this result for the cosmic
censorship hypothesis are indicated.Comment: LaTeX, 11 pages, no figures, to appear in Mod. Phys. Lett.
Circularly polarized microwaves for magnetic resonance study in the GHz range: application to nitrogen-vacancy in diamonds
The ability to create time-dependent magnetic fields of controlled
polarization is essential for many experiments with magnetic resonance. We
describe a microstrip circuit that allows us to generate strong magnetic field
at microwave frequencies with arbitrary adjusted polarization. The circuit
performance is demonstrated by applying it to an optically detected magnetic
resonance and Rabi nutation experiments in nitrogen-vacancy color centers in
diamond. Thanks to high efficiency of the proposed microstrip circuit and
degree of circular polarization of 85% it is possible to address the specific
spin states of a diamond sample using a low power microwave generator.Comment: 4 pages, 7 figures, nitrogen-vacancy, microwave circular
polarization, spin-state addressin
The vibration based diagnostics of ship propulsion systems
The article has been worked out on the basis of the report devoted to the
conducted diagnostic investigations of the ship main propulsion unit’s mechanical system.
Gdansk University of Technology has been ordered with such investigations by the repair
Shipyard carrying out the ship’s overhaul. Diagnostic tests involved measurements and
analyses of the vibration signals generated in selected constructional kinematic pairs of the
identical (twin) starboard and portside marine propulsion lines. The vibration signals have
been registered at the representative load ranges. By this way the stability of the considered
mechanical unit has been estimated both in a global and local sense. Appearing at that time the
resonance phenomena which result in a kinetic energy dissipation of the ship main
propulsion unit’s masses being in a rotational movement have been identified. There
have been also localized places of the largest growth of the changeable internal
tensions’ amplitudes, what considerably constrains cycles number of the load alterations
at which elements transmitting the propulsion torque from engines to propellers crack, as a result
of the material fatigue phenomenon.
The most probable reasons of the mechanical unit’s enlarged vibration level have been pointed out
on the basis of a carried out analysis of the alignment results, the specifity of the applied main
engine running on the partial loads as well as the range of constructional changes
that had been made during the propulsion unit’s overhaul. Results of the repeated
diagnostic sea trials, carried out after the reduction gears’ modification recommended by the
Authors, confirmed a relevance of the earlier formulated diagnosis. The modification works aimed
to perform a resonance offset by the damping correction of hydraulic devices
additionally founded on the gears frames.
A technology of the marine propulsion shaft line’s transverse and longitudinal vibration
measurements carried out by means of the portable vibration register as well as a method of the
vibration spectral analysis have been focused within the program description of the
performed diagnostic investigations. They represented the base for a diagnostic
inference
about the considered mechanical unit’s dynamic state
Effects of fault interaction on moment, stress drop, and strain energy release
Solutions for collinear shear cracks are used to examine quantitatively the effects of fault slip zone interaction on determinations of moment, stress drop, and static energy release. Two models, the barrier model and the asperity model, are considered. In the asperity model, the actual distribution of strengths on a fault plane is idealized as a combination of two limiting cases: areas which slip freely at a uniform value of a residual friction stress and unbroken ligaments or ‘asperities’ across which slip occurs only at the time of a seismic event. In the barrier model, slip zones separated by unbroken ligaments (barriers) are introduced into a uniformly stressed medium to approximate the nonuniform fault propagation proposed by Das and Aki. The strain energy change due to introducing collinear slip zones or due to breaking the asperities between them is shown to be given by the usual formula for an isolated slip zone with the stress drop replaced by the effective stress. Significant interaction between slip zones occurs only if the length of the asperity is less than half the length of the slip zones. For the case of two collinear slip zones, fracture of the asperity between them is shown to cause a large moment primarily because of the additional displacement which is induced on the adjacent slip zones. For example, if the asperity length is 0.05l, where l is the length of each adjacent slip zone, then fracture of the asperity causes a moment almost 1.8 times the moment caused by introducing a slip zone of length l. For two collinear slip zones, the local stress drop due to fracture of the separating asperity is shown to become unbounded as the asperity length goes to zero, but in the same limit the stress drop averaged over the entire fault length is approximately equal to the apparent stress drop inferred for an isolated fault of the same moment and total fault length. This apparent stress drop is approximately equal (within a factor of 2 or 3) to the effective stress and hence can be used in the usual formula to give a good estimate of the strain energy change. For the barrier model, numerical results are given for the ratio of the stress drop calculated on the assumption of an isolated slip zone to the true stress drop. For example, in the case of two collinear slip zones of length l separated by a barrier of length 0.2l, this ratio is 0.5, whereas for a barrier length equal to that of the adjacent slip zones, the ratio is 0.24. Stress drop estimates become worse with increasing number of fault segments
Coherent population oscillations with nitrogen-vacancy color centers in diamond
We present results of our research on two-field (two-frequency) microwave
spectroscopy in nitrogen-vacancy (NV-) color centers in a diamond. Both fields
are tuned to transitions between the spin sublevels of the NV- ensemble in the
3A2 ground state (one field has a fixed frequency while the second one is
scanned). Particular attention is focused on the case where two microwaves
fields drive the same transition between two NV- ground state sublevels (ms=0
-> ms=+1). In this case, the observed spectra exhibit a complex narrow
structure composed of three Lorentzian resonances positioned at the pump-field
frequency. The resonance widths and amplitudes depend on the lifetimes of the
levels involved in the transition. We attribute the spectra to coherent
population oscillations induced by the two nearly degenerate microwave fields,
which we have also observed in real time. The observations agree well with a
theoretical model and can be useful for investigation of the NV relaxation
mechanisms.Comment: 17 page
An Ontological Approach to Representing the Product Life Cycle
The ability to access and share data is key to optimizing and streamlining any industrial production process. Unfortunately, the manufacturing industry is stymied by a lack of interoperability among the systems by which data are produced and managed, and this is true both within and across organizations. In this paper, we describe our work to address this problem through the creation of a suite of modular ontologies representing the product life cycle and its successive phases, from design to end of life. We call this suite the Product Life Cycle (PLC) Ontologies. The suite extends proximately from The Common Core Ontologies (CCO) used widely in defense and intelligence circles, and ultimately from the Basic Formal Ontology (BFO), which serves as top level ontology for the CCO and for some 300 further ontologies. The PLC Ontologies were developed together, but they have been factored to cover particular domains such as design, manufacturing processes, and tools. We argue that these ontologies, when used together with standard public domain alignment and browsing tools created within the context of the Semantic Web, may offer a low-cost approach to solving increasingly costly problems of data management in the manufacturing industry
Testing for entanglement with periodic coarse-graining
Continuous variables systems find valuable applications in quantum
information processing. To deal with an infinite-dimensional Hilbert space, one
in general has to handle large numbers of discretized measurements in tasks
such as entanglement detection. Here we employ the continuous transverse
spatial variables of photon pairs to experimentally demonstrate novel
entanglement criteria based on a periodic structure of coarse-grained
measurements. The periodization of the measurements allows for an efficient
evaluation of entanglement using spatial masks acting as mode analyzers over
the entire transverse field distribution of the photons and without the need to
reconstruct the probability densities of the conjugate continuous variables.
Our experimental results demonstrate the utility of the derived criteria with a
success rate in entanglement detection of relative to studied
cases.Comment: V1: revtex4, 10 pages, 4 figures + supp. material (4 pages, 1 figure)
V2: Substantial revisions implemented both in theory and experimental data
analysi
- …