Exploring the vicinity of the Bogomol'nyi-Prasad-Sommerfield bound

We investigate systems of real scalar fields in bidimensional spacetime, dealing with potentials that are small modifications of potentials that admit supersymmetric extensions. The modifications are controlled by a real parameter, which allows implementing a perturbation procedure when such parameter is small. The approach allows obtaining the energy and topological charge in closed forms, up to first order in the parameter. We illustrate the procedure with some examples. In particular, we show how to remove the degeneracy in energy for the one-field and the two-field solutions that appear in a model of two real scalar fields.Comment: Revtex, 9 pages, To be published in J. Phys.

Mild place illusion: a virtual reality factor to spark creativity in writing

Developments in Virtual Reality (VR) technology have modified the creative potential of each individual. We introduce a new con cept, called "mild place illusion", as a new paradigm for designing VR-based user interfaces targeted at stimulating creativity. We show that for creative tasks - such as creative writing, new product ideation, and brainstorming - a "just-enough" amount of place illu sion leads to a greater self-perception of creativity, as opposed to a "full-level" place illusion. This is a somewhat unexpected result since one would suppose, a priori, to have the full-level place illu sion as the optimal setup for stimulating creativity. We considered that the methodology in this work was fairly complex, but our re sults show – through a data triangulation approach – that we were able to identify more consistent and personal creative experiences. Therefore, the main contribution of this paper is a new paradigm for designing VR user interfaces targeted at stimulating creativity by showing that a “one-illusion interspace” leads to a greater self perception of creativity.info:eu-repo/semantics/publishedVersio

Invasive Streptococcus pneumoniae in Children, Malawi, 2004–2006

Of 176 invasive Streptococcus pneumoniae isolates from children in Malawi, common serotypes were 1 (23%), 6A/B (18%), 14 (6%), and 23F (6%). Coverage with the 7-valent pneumococcal conjugate vaccine (PCV) was 39%; PCV10 and PCV13 increased coverage to 66% and 88%, respectively. We found chloramphenicol resistance in 27% of isolates and penicillin nonsusceptibility in 10% (by using meningitis breakpoints); all were ceftriaxone susceptible

Metric of a tidally perturbed spinning black hole

We explicitly construct the metric of a Kerr black hole that is tidally perturbed by the external universe in the slow-motion approximation. This approximation assumes that the external universe changes slowly relative to the rotation rate of the hole, thus allowing the parameterization of the Newman-Penrose scalar $\psi_0$ by time-dependent electric and magnetic tidal tensors. This approximation, however, does not constrain how big the spin of the background hole can be and, in principle, the perturbed metric can model rapidly spinning holes. We first generate a potential by acting with a differential operator on $\psi_0$. From this potential we arrive at the metric perturbation by use of the Chrzanowski procedure in the ingoing radiation gauge. We provide explicit analytic formulae for this metric perturbation in spherical Kerr-Schild coordinates, where the perturbation is finite at the horizon. This perturbation is parametrized by the mass and Kerr spin parameter of the background hole together with the electric and magnetic tidal tensors that describe the time evolution of the perturbation produced by the external universe. In order to take the metric accurate far away from the hole, these tidal tensors should be determined by asymptotically matching this metric to another one valid far from the hole. The tidally perturbed metric constructed here could be useful in initial data constructions to describe the metric near the horizons of a binary system of spinning holes. This perturbed metric could also be used to construct waveforms and study the absorption of mass and angular momentum by a Kerr black hole when external processes generate gravitational radiation.Comment: 17 pages, 3 figures. Final PRD version, minor typos, etc corrected. v3: corrected typo in Eq. (35) and (57

On the equivalence principle and gravitational and inertial mass relation of classical charged particles

We show that the locally constant force necessary to get a stable hyperbolic motion regime for classical charged point particles, actually, is a combination of an applied external force and of the electromagnetic radiation reaction force. It implies, as the strong Equivalence Principle is valid, that the passive gravitational mass of a charged point particle should be slight greater than its inertial mass. An interesting new feature that emerges from the unexpected behavior of the gravitational and inertial mass relation, for classical charged particles, at very strong gravitational field, is the existence of a critical, particle dependent, gravitational field value that signs the validity domain of the strong Equivalence Principle. For electron and proton, these critical field values are $g_{c}\simeq 4.8\times 10^{31}m/s^{2}$ and $g_{c}\simeq 8.8\times 10^{34}m/s^{2}$, respectively

CreaSenses: fostering creativity through olfactory cues

Smell is a strong trigger of memories and creativity. Different smells can create sensitive environments that can foster creative tasks. In this paper, we present CreaSenses, a study that includes olfactory cues, representing different types of sensitive environ ments such as “food” and “ambience” in a within-subject design. Our aim was to obtain a deeper understanding of which smell cues promote higher levels of creativity during the process of creative writing. We discuss the results in the light of creative senses and potential implications for the design of creativity support tools. In addition, our study was evaluated trough the Creativity Support Index.info:eu-repo/semantics/publishedVersio

Exactly Solvable Hydrogen-like Potentials and Factorization Method

A set of factorization energies is introduced, giving rise to a generalization of the Schr\"{o}dinger (or Infeld and Hull) factorization for the radial hydrogen-like Hamiltonian. An algebraic intertwining technique involving such factorization energies leads to derive $n$-parametric families of potentials in general almost-isospectral to the hydrogen-like radial Hamiltonians. The construction of SUSY partner Hamiltonians with ground state energies greater than the corresponding ground state energy of the initial Hamiltonian is also explicitly performed.Comment: LaTex file, 21 pages, 2 PostScript figures and some references added. To be published in J. Phys. A: Math. Gen. (1998

Bags, junctions, and networks of BPS and non-BPS defects

We investigate several models of coupled scalar fields that present discrete Z_2, Z_2 x Z_2, Z_3 and other symmetries. These models support topological domain wall solutions of the BPS and non-BPS type. The BPS solutions are stable, but the stability of the non-BPS solutions may depend on the parameters that specify the models. The BPS and non-BPS states give rise to bags, and also to three-junctions that may allow the presence of networks of topological defects. In particular, we show that the non-BPS defects of a specific model that engenders the Z_3 symmetry give rise to a stable regular hexagonal network of domain walls.Comment: Revtex, 16 pages, 6 ps figures; Shorter version to be published in Phys. Rev.

Subsynchronous Vibration Problem And Solution In Multistage Centrifugal Compressor.

LecturePg. 65-74The investigation of a subsynchronous vibration problem encountered in a six stage centrifugal compressor is discussed. At a running speed of approximately 9000 rpm, a subsynchronous vibration (at 4200 rpm) of nearly two times the synchronous vibration level was encountered. A systematic program was undertaken to identify the problem and correct it. A detailed analysis of the floating ring annular oil seals, balance piston labyrinth seals and impeller aerodynamic cross coupling was conducted. The oil seals were identified as the primary cause of the subsynchronous vibration due to lock up, and a modified seal design incorporating circumferential grooves was developed. This radically reduced the seal cross coupled stiffness. Further, a modified bearing design was investigated to increase the rotor logarithmic decrement. Changes were implemented in the compressor with the result of no subsynchronous vibrations for the operating conditions of the compressor thus far