Can a light beam be considered to be the sum of a completely polarized and a completely unpolarized beam?

In a classic paper that may be regarded as the starting point of polarization optics, G. G. Stokes [Trans. Cambridge Philos. Soc.9, 399 (1852)] presented a theorem according to which any light beam is equivalent to the sum of two light beams, one of which is completely polarized and the other completely unpolarized. We show that Stokes' proof of this theorem is flawed. We present a condition for the theorem to be valid.     

Can the photon velocity be derived from the Klein-Gordon equation?

In their most recent article, Grado-Caffaro et al. have addressed the question of the ‘photon velocity’. They have expressed the photon velocity in terms of the wavefunctions of the Klein-Gordon equation (Grado-Caffaro and Grado-Caffaro [4]). In this note, we closely follow their work and explicitly obtain the photon velocity using the free solutions of the Klein-Gordon equation. It is shown that the plane wave solutions give rise to six possible values of the photon velocity. Two of these solutions are the most expected (v=±c). The remaining four solutions, the real pair ±0.786c and the imaginary pair ±1.272ic are difficult to comprehend.     

Can the crystallization rate be independent from the crystallization enthalpy? The case of amorphous silicon

The crystallization enthalpy measured in a large series of amorphous silicon (a-Si) materials varies within a factor of 2 from sample to sample (Kail et al 2011 Phys. Status Solidi RRL 5 361). According to the classical theory of nucleation, this variation should produce large differences in the crystallization kinetics leading to crystallization temperatures and activation energies exceeding 550?°C and 1.7 eV, respectively, the 'standard' values measured for a-Si obtained by self-implantation. In contrast, the observed crystallization kinetics is very similar for all the samples studied and has no correlation with the crystallization enthalpy. This discrepancy has led us to propose that crystallization in a-Si begins in microscopic domains that are almost identical in all samples, independently of their crystallization enthalpy. Probably the existence of microscopic inhomogeneities also plays a crucial role in the crystallization kinetics of other amorphous materials and glasses.     

Can a Higgs boson be produced at the LHC?

A simple model is designed to simulate, by using the mean free path method, the probability of Higgs boson production at the Large Hadron Collider (LHC). The probability that the colliding particles could get close to a given distance with different colliding energies is discussed in this model. Calculated results imply that the probability of producing a Higgs boson is near zero according to the existing theoretical mechanism for Higgs boson production.     

Can the states of the W-class be suitable for teleportation?

Entangled states of the W-class are considered as a quantum channel for teleportation of an entangled state and as well the state to be teleported via a multiparticle quantum channel. Using an introduced unitary transformation in the teleportation schemes based on the multiparticle Greenberger–Horne–Zeilinger channel it is found a set of protocols main feature of which is a collection of non-local recovering operators.     

Can surfactant be present at pinch-off of a liquid filament?

Surfactants lower surface tension and are used to facilitate breakup and spreading. How much surfactant remains where a filament of initial radius R breaks is set by the ratio of convection, which sweeps surfactant away, to diffusion, which replenishes it, or Peclet number Pe proportional, variantR. Thus, as is well known, surfactant concentration Gamma-->0 when a macroscale filament breaks. Here theory and simulation are used to investigate pinch-off of microscopic filaments. At breakup, Gamma is shown to be nonzero but uniform on a filament of negligible Pe. Since R must be finite, the zero-Pe limit is transitory and yields to a final regime. Two such regimes with distinct dynamics characterized by different scaling exponents are reported.     

Can the eigenstates of a many-body Hamiltonian be represented exactly using a general two-body cluster expansion?

It is proved that a recent conjecture that the exact ground-state wave function of an arbitrary many-fermion system with one- and two-body interactions may be represented by an exponential cluster expansion employing finite two-body operators, starting from any reference function sufficiently close to the exact eigenfunction, is not valid. We show that the space of initial reference functions which lead to the exact ground state is of dimension equal to the number of two-body operators. If the dimension of the multiparticle space is greater than the number of two-body operators, then the space of good reference functions is of measure zero in it.     

Do unpolarized electrons affect the polarization of a stored beam?

We present a short overview of the PAX physics case for polarized antiprotons. In order to progress towards a stored polarized antiproton beam, it is crucial to understand the interaction of polarized protons with unpolarized electrons. Therefore investigations that address in particular the contributions of electrons to the polarization buildup of a stored proton beam are presented here in more detail. The measurement of the depolarizing p e cross section settled a long-standing controversy about the role of electrons in the polarization buildup of a stored beam by spin-filtering. Instead of studying the buildup of polarization in an initially unpolarized beam, here the inverse situation was investigated by observation of the depolarization of an initially polarized beam. For the first time, electrons in the electron cooler have been used as a target to study their depolarizing effect on a 49.3 MeV proton beam orbiting in COSY. The foreseen spin-filtering experiments at COSY–Jülich and at the AD of CERN are briefly discussed as well.     

Can mobile defects be the source of 1/f noise in a semiconductor?

We discuss two alternative approaches relating the occurrence of 1/f noise in semiconductors with fluctuations in the mobility of current carriers. In the first approach, 1/f noise is associated with fluctuations in scattering of the carriers by the acoustic phonons of the lattice. According to the second approach, the source of 1/f noise is fluctuations in the scattering cross section of mobile defects. Experimental data in favor of the first approach are analyzed. It is shown that, to explain the data in terms of the model of fluctuations in the scattering cross section of mobile defects, a new effect must exist. Namely, manufacturing a semiconductor with an increased degree of doping must result in a proportional decrease in the density of mobile defects that are responsible for the generation of 1/f noise. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 6, pp. 590–594, June 1999.     

Can one count the shape of a drum?

Sequences of nodal counts store information on the geometry (metric) of the domain where the wave equation is considered. To demonstrate this statement, we consider the eigenfunctions of the Laplace-Beltrami operator on surfaces of revolution. Arranging the wave functions by increasing values of the eigenvalues, and counting the number of their nodal domains, we obtain the nodal sequence whose properties we study. This sequence is expressed as a trace formula, which consists of a smooth (Weyl-like) part which depends on global geometrical parameters, and a fluctuating part, which involves the classical periodic orbits on the torus and their actions (lengths). The geometrical content of the nodal sequence is thus explicitly revealed.     

Can one hear the dimension of a fractal?

We consider the spectrum of the Laplacian in a bounded open domain of ⁿ with a rough boundary (i.e. with possibly non-integer dimension) and we discuss a conjecture by M. V. Berry generalizing Weyl's conjecture. Then using ideas Mark Kac developed in his famous study of the drum, we give upper and lower bounds for the second term of the expansion of the partition function. The main thesis of the paper is to show that the relevant measure of the roughness of the boundary should be based on Minkowski dimensions and on Minkowski measures rather than on Haussdorff ones.Dedicated to the memory of Mark Kac