Direct experimental limit on neutron-mirror-neutron oscillations

In case a mirror world with a copy of our ordinary particle spectrum would exist, the neutron n and its degenerate partner, the mirror neutron n', could potentially mix and undergo nn' oscillations. The interaction of an ordinary magnetic field with the ordinary neutron would lift the degeneracy between the mirror partners, diminish the n' amplitude in the n wave function and, thus, suppress its observability. We report an experimental comparison of ultracold neutron storage in a trap with and without superimposed magnetic field. No influence of the magnetic field is found and, assuming negligible mirror magnetic fields, a limit on the oscillation time taunn' > 103 s (95% C.L.) is derived.     

On damped linear dynamical systems

Summary This paper is concerned with damped linear dynamical systems which fail to satisfy the socalled convenience hypothesis, an assumption that guarantees the existence of classical normal modes. Under suitable conditions, estimates are given for the error committed when such a system is described approximately by a differential equation which does satisfy the convenience hypothesis. One of these estimates is used to derive an upper bound on the frequency response of systems which do not violate the convenience hypothesis too severely.

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Ein Beitrag zu den gedämpften, linearen, dynamischen Systemen

Übersicht Die Arbeit befaßt sich mit gedämpften, linearen, dynamischen Systemen, welche die Bequemlichkeitshypothese nicht erfüllen. Dabei wird untersucht, welchen Fehler man macht, wenn man eine allgemeine viskose Dämpfung durch eine zugeordnete modale Dämpfung entsprechend dieser Hypothese ersetzt. Eine der Fehlerabschätzungen wird verwendet zur Herleitung einer oberen Schranke der Antwortamplitude von Systemen, welche die Bequemlichkeitshypothese nicht allzu sehr verletzen.

     

A real-space perturbation theory for electronic correlation

We introduce a method for treating electronic correlation in which a correlation factor is optimized using Hylleraas variational perturbation theory. The factor is defined by a number of parameters which grows only linearly with system size. We test the theory on two-electron atoms using the shielded-nucleus Hamiltonian at zeroth order, obtaining −2.9035 a.u. for helium. The convergence of the method is investigated, and energies and intracule densities are compared with accurate variational results. The application of the theory to an N-electron problem with a Hartree–Fock Hamiltonian at zeroth order is discussed.     

Gender in mathematics relationality: counseling underprepared college students

As a professional tutor practicing primarily in the Northeast of the USA, I have noticed gender differences in how college students approach required mathematics courses and in how I approach tutoring them. I conducted a relational mathematics counseling pilot study, where I was a participant researcher in an introductory statistics for psychology class, ran a study group for the class, and offered individual tutor-counseling to ten volunteer participants, four males, and six females. I found that while students’ expressions of gender were unique and more or less salient to their mathematical progress, there were also some patterns of interest. My analysis suggests that gender difference in underprepared students, on whom I focus in this paper, was a key in the development of differing efforts to protect underdeveloped mathematics selves: typically overconfident grandiosity and/or resistance in the men and underconfident depression or anxiety and troubled tutor attachment relationships in the women. To the concomitant question with respect to effective support that emerged, I show that key relational changes I made and approaches I developed to help, needed also to be gender-sensitive.     

A linked electron pair functional

A modification of the variational configuration interaction functional in the first-order interacting space for molecular electronic structure is presented. The modified functional is a fully linked expression that by construction is extensive and invariant to transformations of the underlying orbital basis and is exact for an ensemble of separated two-electron subsystems. In addition, an approximation to variational coupled cluster is generated through truncation of the exponential cluster operator. When combined, these methods demonstrate accuracy that exceeds that of the standard coupled-cluster method, in particular in situations where the reference Slater determinant is not a good approximation.