Horizon Mass Theorem

A new theorem for black holes is found. It is called the horizon mass theorem. The horizon mass is the mass which cannot escape from the horizon of a black hole. For all black holes: neutral, charged or rotating, the horizon mass is always twice the irreducible mass observed at infinity. Previous theorems on black holes are: 1. the singularity theorem, 2. the area theorem, 3. the uniqueness theorem, 4. the positive energy theorem. The horizon mass theorem is possibly the last general theorem for classical black holes. It is crucial for understanding Hawking radiation and for investigating processes occurring near the horizon.Comment: A new theorem for black holes is establishe

Manifestations of professional identity work: An integrative review of research in professional identity formation

Professional identity formation (PIF) is an integral part of educating professionals. A well-formed professional identity helps individuals to develop a meaningful professional self-understanding that facilitates their transition to and sustainability in professional work. Although professional identity and its formation are well theorized, it is largely unclear how the underpinning interpretive process of professional identity work leads to observable changes in thoughts, feelings and behaviours, and how these insights can be used in educational practice. To address this gap, we conducted an integrative review of 77 empirical articles on professional identity formation and inductively developed a four-fold typology of professional identity work, through which individuals reportedly make the shift from individual to professional. The theoretical contribution of this article is a more nuanced understanding of the practical manifestations of professional identity work. As a practical contribution, the typology may be used as a heuristic through which educators of professionals can support their students’ professional identity formation, particularly where this is halted or complicated by obstructions

Shear Lag in Corrugated Sheets Used for the Chord Member of a Box Beam

The problem of the distribution of normal stress across a wide corrugated sheet used as the chord of a box-beam-like structure is investigated theoretically and experimentally. Expressions are developed giving the stress distribution in beams, symmetrical or unsymmetrical, about a plane passed spanwise through the center of the sheet. The experiments were arranged to insure bending without torsion and surveys of the normal stresses were made by means of mechanical and electrical strain gages. The experimental data showed very good agreement with the new b of the theoretical curves, especially at the highly stressed sections, for both the symmetrical and unsymmetrical beams. Several suggestions for future research are included

Electrically charged fluids with pressure in Newtonian gravitation and general relativity in d spacetime dimensions: theorems and results for Weyl type systems

Previous theorems concerning Weyl type systems, including Majumdar-Papapetrou systems, are generalized in two ways, namely, we take these theorems into d spacetime dimensions (${\rm d}\geq4$), and we also consider the very interesting Weyl-Guilfoyle systems, i.e., general relativistic charged fluids with nonzero pressure. In particular within Newton-Coulomb theory of charged gravitating fluids, a theorem by Bonnor (1980) in three-dimensional space is generalized to arbitrary $({\rm d}-1)>3$ space dimensions. Then, we prove a new theorem for charged gravitating fluid systems in which we find the condition that the charge density and the matter density should obey. Within general relativity coupled to charged dust fluids, a theorem by De and Raychaudhuri (1968) in four-dimensional spacetimes in rendered into arbitrary ${\rm d}>4$ dimensions. Then a theorem, new in ${\rm d}=4$ and ${\rm d}>4$ dimensions, for Weyl-Guilfoyle systems, is stated and proved, in which we find the condition that the charge density, the matter density, the pressure, and the electromagnetic energy density should obey. This theorem comprises, as particular cases, a theorem by Gautreau and Hoffman (1973) and results in four dimensions by Guilfoyle (1999). Upon connection of an interior charged solution to an exterior Tangherlini solution (i.e., a Reissner-Nordstr\"om solution in d-dimensions), one is able to give a general definition for gravitational mass for this kind of relativistic systems and find a mass relation with the several quantities of the interior solution. It is also shown that for sources of finite extent the mass is identical to the Tolman mass.Comment: 27 page

See a Black Hole on a Shoestring

The modes of vibration of hanging and partially supported strings provide useful analogies to scalar fields travelling through spacetimes that admit conformally flat spatial sections. This wide class of spacetimes includes static, spherically symmetric spacetimes. The modes of a spacetime where the scale factor depends as a power-law on one of the coordinates provide a useful starting point and yield a new classification of these spacetimes on the basis of the shape of the string analogue. The family of corresponding strings follow a family of curves related to the cycloid, denoted here as hypercycloids (for reasons that will become apparent). Like the spacetimes that they emulate these strings exhibit horizons, typically at their bottommost points where the string tension vanishes; therefore, hanging strings may provide a new avenue for the exploration of the quantum mechanics of horizons.Comment: 5 pages, 1 figure, extensive changes to refect version accepted to PR

Black string and velocity frame dragging

We investigate velocity frame dragging with the boosted Schwarzschild black string solution and the boosted Kaluza-Klein bubble solution, in which a translational symmetry along the boosted $z$-coordinate is implemented. The velocity frame dragging effect can be nullified by the motion of an observer using the boost symmetry along the $z-$coordinate if it is not compact. However, in spacetime with the compact $z-$coordinate, we show that the effect cannot be removed since the compactification breaks the global Lorentz boost symmetry. As a result, the comoving velocity is dependent on $r$ and the momentum parameter along the $z-$coordinate becomes an observer independent characteristic quantity of the black string and bubble solutions. The dragging induces a spherical ergo-region around the black string.Comment: 8 pages, no figure, some correction

Elucidating the Performance Limitations of Alkaline Electrolyte Membrane Electrolysis: Dominance of Anion Concentration in Membrane Electrode Assembly

Anion exchange membrane water electrolyzers (AEMWEs) offer a cost-effective technology for producing green hydrogen. Here, an AEMWE with atmospheric plasma spray non-precious metal electrodes was tested in 0.1 to 1.0 M KOH solution, correlating performance with KOH concentration systematically. The highest cell performance was achieved at 1.0 M KOH (ca. 0.4 A cm−2 at 1.80 V), which was close to a traditional alkaline electrolysis cell with ≈6.0 M KOH. The cell exhibited 0.13 V improvement in the performance in 0.30 M KOH compared with 0.10 M KOH at 0.5 A cm−2. However, this improvement becomes more limited when further increasing the KOH concentration. Electrochemical impedance and numerical simulation results show that the ohmic resistance from the membrane was the most notable limiting factor to operate in low KOH concentration and the most sensitive to the changes in KOH concentration at 0.5 A cm−2. It is suggested that the effect of activation loss is more dominant at lower current densities; however, the ohmic loss is the most limiting factor at higher current densities, which is a current range of interest for industrial applications

Quantum Corrections to the Reissner-Nordstrom and Kerr-Newman Metrics: Spin 1

A previous evaluation of one-photon loop corrections to the energy-momentum tensor has been extended to particles with unit spin and speculations are presented concerning general properties of such forms.Comment: 21 pages, 1 Figur