Factorization in retrocausality: a response to O. Costa de Beauregard

Costa de Beauregard's reformulation of joint probability, in connection with retrocausality, reveals a mathematical paradox independent of time-reversal. That paradox is intrinsic to Bell's theorem and has a physical manifestation in the Orsay experiments.     

Etude conformationnelle,par rmn du 13C,d'ethers d'enol renfermant un noyau aromatique

Two series of aromatic enol ethers deriving from 1-methoxy-1-phenyl ethylene and from 1-methoxy-1-phenyl 2-methyl propene have been studied by ¹³C NMR. Comparisons between the chemical shifts of these enol ethers and those of styrene on the one hand, and aliphatic enol ethers on the other, led us to conclude that the non-coplanarity of the phenyl ring with the double bond and/or the non-coplanarity of the OCH₃ group with the same double bond play a prominent role in determining the chemical shift values of the ethylenic carbons. Para-substitution on the phenyl ring induces chemical shift variation not only in the aromatic moiety itself but also in the ethylene part of the molecule. The significance of the observed Hammett correlation is discussed.     

Neutron diffraction evidence for anion sublattice disordering in alkali earth fluorides at high temperatures

High temperature powder neutron diffraction studies of calcium, strontium and barium fluorides indicate that there are large thermal motions associated with the anions. This suggests that the anion sublattice in these compounds with the fluoride structure may disorder at temperatures below the melting points. In S:F₂ this disordering appears at about 1370 K and for BaF₂ at about 1300 K. This is in good agreement with transitions of 1440 K and 1240 K, predicted from thermodynamic data.     

Phase diagram of a two-dimensional electron system

The melting curve of the two-dimensional electron system is interpolated between the known classical and ground state limits. The coexistence curve encloses a finite solid-phase domain, as in the three-dimensional case.     

Time-resolved excitation spectra of xenon vapor in the 1500 Å region

Time-integrated and time-resolved excitation spectra, as well as fluorescence lifetimes, have been measured for xenon vapor as a funtion of pressure (for pure xenon as well as with different collision partners: krypton and helium), monitoring the 1700 Å second continuum afterglow. Three very different decay components have been observed: (a) A short component with lifetimes of the order of 2 ns, which is attributed to emission from the upper vibrational levels of the O⁺_u(¹Σ⁺_u) state of Xe*₂. (b) A long component with τ ≈ 60 ns, corresponding to emission from thermally relaxed vibrational levels of the 1_u,O^?_u(³Σ⁺_u) states of Xe*₂. No intervention of any Xe atomic excited species is invoked to explain the excitation and deactivation processes of Xe₂ molecules for these two components of the fluorescence. (c) A very long component with lifetimes in the 150–500 ns range, having a broad ? 1000 cm^?1 - excitation band, centered at ≈ 1470 Å and showing a striking screening and self-absorption effect as well as a strong effect when the partial pressure of a collision partner (Kr, He) is increased. The mechanism of this last excitation is not yet very well understood.     

RMN 13C d'α alcoxy-indenes et d'α alcoxy-styrenes : Topologie electronique du systeme Π et une reflexion sur la relation entre deplacement chimique et reactivite dans les ethers d'enol

¹³C NMR chemical shifts of ethylenic carbon atom C_β of α alkoxy-indenes and α-alkoxy-styrenes are affected by the conformation of the OR group with respect to the double bond and hence the efficiency of p- Π conjugation but, contrary to previous results, δC_α is not affected. The phenyl group exerts a diamagnetic Π- effect on C_α and C_β which is a function of its dihedral angle with the double bond. Although δC_β is especially sensitive to the Π-electron density, the chemical shifts of the ethylenic carbons are best understood by considering the total charge density. The σ and Π contributions to the total charge density are discussed using the preferred conformation of the molecules. This approach strongly suggests that the correlation between the gradual shift of δC_α to low frequency and the gradual shift of δC_β to high frequency (relative to TMS) as R changes from RCH₃ to RtC₄H₉ in certain series of enol-ethers is not due to pΠ conjugation variations. This method of interpreting ¹³C NMR shifts, as opposed to previous methods, is compatible with explanations of other physico-chemical properties of alkyl vinyl ethers. Although it is sometimes possible to correlate the gradual shifts of δC_β with (σ + Π) electron density variations in a homogeneous series, it seems impossible to predict the relation. In all cases, there is no evident correlation between gradual shifts of δC_β(orδC_α) and the reactivity of enol ethers because one cannot consider the role of the out-of-plane conformation of the alkoxy group (which increases from RCH₃ to RtC₄H₉); however, the out of plane conformation does not have an identical effect on δC_β and the reactivity.     

AdA:The First Electron-Positron Collider

I review the origin of AdA, the first electron-positron collider at Frascati, Italy, in the early 1960s. I describe the problems that were tackled to produce the positron beam, the vacuum, and the injection system that were necessary to observe the electron-positron beam-beam collisions. Accidents and incidents occurred, such as the unpredicted Touschek effect, and were surmounted. I discuss the roles of the physicists involved in this work and the state of physics at the time, and I sketch subsequent work on larger collider rings. My recollections are based on the original literature and unpublished documents, photographs, and drawings.