Volume 74, Issue 2

An extra energy shift between emitted and received radiation on a rotating disc – next to the conventionally recognised second-order Doppler shift – has been revealed in a series of recent Mössbauer experiments, where a radioactive source is fixed at the centre and an absorber is attached to the rim of the rotating disc. This disclosure gives indication to a possible violation of the “clock hypothesis” by Einstein: i.e. the independence of the rate of a clock on its acceleration. At the moment, there seem to be two plausible interpretations of this result: (i) the deviation of the geometry of the rotating disc from that predicted by the general theory of relativity (GTR), or (ii) the existence of a specific maximal acceleration in nature, when transformation between two accelerated frames differs from the corresponding transformation of the relativity theory. We take a closer look at both ways leading to the violation of the clock hypothesis; particularly, by analysing the outcomes of recent experiments in rotating systems and by suggesting a new Mössbauer rotor experiment to determine the most feasible mechanism for testing the dependence of the rate of a clock on its acceleration.

A novel dual Fabry–Pérot (F-P) interferometric carbon monoxide gas sensor based on polyaniline/Co 3 O 4 (PANI/Co 3 O 4 ) sensing film coated on the optical fibre end face is proposed and fabricated. Its structure is composed of standard single-mode-fibre (SMF), endlessly photonic crystal fibre (EPCF), and PANI/Co 3 O 4 sensing membrane (PCSM). Therefore, they form three F-P reflectors, the reflector between SMF and EPCF, that between EPCF and PCSM, and interface between PCSM and air. So, the dual F-P interferometer is achieved. The results show that in the range of 0–70 ppm, the interference spectra appear red shift with the increasing carbon monoxide concentration. In addition, the high sensitivity of 21.61 pm/ppm, the excellent linear relationship ( R 2 = 0.98476), and high selectivity for carbon monoxide are achieved. The response and recovery time are 35 and 84 s, respectively. The sensor has the advantages of high sensitivity, strong selectivity, low cost, and simple structure and is suitable for sensitive detection of trace carbon monoxide gas.

A joint investigation based on an unbiased CALYPSO structure searching method and density functional theory calculation is performed to obtain the most stable structures of the neutral and anionic Al n Sb ( n = 1–16) clusters. The relative stability analysis reveals that the Al 3 Sb, Al 5 Sb, Al 5 Sb − and Al 14 Sb − clusters are more stable than their neighbouring clusters. The studies of electronic properties, especially in the consistency of the simulated photoelectron spectra and the experimental results for small clusters, further confirm that the predicted most stable structures are the global minima. Compared with pure aluminium (Al) clusters, the effect of impurity Sb atom on structural evolution of the neutral and anionic Al n Sb( n = 1–16) clusters may be neglected, revealing that the most stable structures can be obtained by replacing one Al atom with an Sb atom in the corresponding neutral and anionic Al n +1 ( n = 1–16) clusters except for 8, 11 and 12. Moreover, the discussion concerning the magnetic properties indicates that the 3p state of the Al atom in the neutral and anionic Al n Sb( n = 1–16) clusters is the main contributor to the total magnetic moment.

The effects of halogen element X (X = Br, I) doping on the geometrical structures and electronic properties of neutral aluminium clusters are systematically studied by utilising the density functional theory calculations. The structures of X-doped clusters show the three-dimensional forms with increasing atomic number except for n = 3 and X (X = Br, I) atom prefer to occupy the surface site of the host Al n clusters. BrAl 7 and IAl 7 clusters are the most stable geometries. The HOMO-LUMO energy gap and chemical hardness show an odd–even alternative phenomenon. The charges always transfer from the Al atoms to the X (X = Br, I) atom. Finally, the dipole and polarisability are discussed.

Nonlinearity properties of obliquely wave propagation and instability in collisionless magnetized nonthermal dusty plasmas containing fluid of negative-positive grains are investigated. Zakharov-Kuznetsov equation is obtained and the three-dimensional wave instability is studied. The parameters such as polarity charge ratio, cyclotron frequency and fast nonthermal effectiveness of the instability properties and growth rate are theoretically studied. It is found that both positive and negative soliton profiles are formed depending on the fraction ratio of electron-ion nonthermality. Also, the growth rate was dependent nonlinearly on the direction cosines, the cyclotron frequency and the positive (negative) grain charge ratio, but independent of the fractional ratio of electron-ion nonthermality. Present discussion may be very significant regarding the observations of nonlinear phenomena in space.

Under investigation in this article is the integrable spin-1 Gross–Pitaevskii (SGP) equations, which can be used to describe light transmission in bimodal nonlinear optical fibres. The spectral analysis with 4 × 4 Lax pairs is performed for the integrable SGP equations, from which a Riemann Hilbert problem is formulated. Furthermore, N -soliton solutions of this integrable SGP equations are expressed in terms of solutions of the Riemann–Hilbert problem by using the Plemelj formulae. Finally, collision dynamics between two solitons is also analyzed. Our results can be used to enrich and explain some related nonlinear phenomena.

We propose that space-time results from collapse of the wave function of macroscopic objects, in quantum dynamics. We first argue that there ought to exist a formulation of quantum theory which does not refer to classical time. We then propose such a formulation by invoking an operator Minkowski space-time on the Hilbert space. We suggest relativistic spontaneous localisation as the mechanism for recovering classical space-time from the underlying theory. Quantum interference in time could be one possible signature for operator time, and in fact may have been already observed in the laboratory, on attosecond time scales. A possible prediction of our work seems to be that interference in time will not be seen for ‘time slit’ separations significantly larger than 100 attosecond, if the ideas of operator time and relativistic spontaneous localisation are correct.

Assuming a closed universe with slight positive curvature, cosmic expansion can be modeled as a heat engine where we define the “system,” collectively, as those regions of space within the observable universe, which will later evolve into voids. We identify the “surroundings,” collectively, as those pockets of space that will eventually develop into matter-filled galaxies, clusters, superclusters, and filament walls. Using this model, we can find the energy needed for cosmic expansion using basic thermodynamic principles and show that cosmic expansion had as its origin a finite initial energy density, pressure, volume, and temperature. Inflation in the traditional sense, with the inflaton field, may also not be required. We also argue that homogeneities and inhomogeneities in the WMAP temperature profile are attributable to quantum mechanical fluctuations about a fixed background temperature in the initial isothermal expansion phase of the cycle, which we identify with inflation. Fluctuations in temperature can cause certain regions of space to lose heat while other regions will absorb that heat. The voids, being those regions that absorb the heat, will expand, thereby leaving slightly cooler temperatures for the surroundings, where matter will later congregate. Upon freeze-out, this could produce the observed WMAP signature with its associated inhomogeneity. Finally, using the uncertainty relation, we estimate that the temperature and time for formation of WMAP inhomogeneities occurred at roughly 3.02 × 10 27 K and 2.54 × 10 −35 s, respectively, after first initiation of volume expansion. This is in line with current estimates for the end of the inflationary epoch. The heat input in the inflationary phase is calculated as roughly Q = 1.81 × 10 94 J (photons only); the collective void volume increases by a factor of only 5.65. The bubble voids in the observable universe increase in size from about 0.046 to 0.262 m 3 within this inflationary period in our model.

An exact formula for the limit of the safety factor q at a magnetic axis is derived for the general up-down asymmetric plasma equilibria possessing axial symmetry, generalizing Bellan’s formula for the up-down symmetric ones. New exact axisymmetric plasma equilibria depending on arbitrary parameters α , ξ , b kn , z kn , where k = 1, ⋯, M , n = 1⋯, N , are constructed ( α ≠ 0 is a scaling parameter), which are up-down asymmetric in general. The equilibria are not force-free if ξ ≠ 0 and satisfy Beltrami equation if ξ = 0. For some values of ξ the magnetic field and electric current fluxes have isolated invariant toroidal magnetic rings, for another ξ they have invariant spheroids (blobs) and for some values of ξ both invariant toroidal rings and spheroids (blobs). A generalization of the Chandrasekhar – Fermi – Prendergast magnetostatic model of a magnetic star is presented where plasma velocity V ( x ) is non-zero.