An Inconvenient History: the Nuclear-Fission Display in the Deutsches Museum

One of the longstanding attractions of the Deutsches Museum in Munich, Germany, has been its display of the apparatus associated with the discovery of nuclear fission. Although the discovery involved three scientists, Otto Hahn, Lise Meitner, and Fritz Strassmann, the fission display was designated for over 30 years as the Arbeitstisch von Otto Hahn (Otto Hahn’s Worktable), with Strassmann mentioned peripherally and Meitner not at all, and it was not until the early 1990s that the display was revised to include all three codiscoverers more equitably. I examine the creation of the fission display in the context of the postwar German culture of silencing the National Socialist past, and trace the eventual transformation of the display into a contemporary exhibit that more accurately represents the scientific history of the fission discovery.     

Facile synthesis of (±)-, (+)-, and (-)-galanthamine

The Amarylidacea alkaloid galanthamine ( 1a ) is an acetylcholinesterase inhibitor that has been evaluated as a potential agent for the treatment of Alzheimer's disease. We report a very efficent synthesis of (±)-galanthamine [(±)- 1a ] from readily available isovanillin and tyramine. We have separated racemic galanthamine into its diastereoisomeric (1S)-camphanate esters and obtained both natural (-)- and unnatural (+)-galanthamine by lithium aluminum hydride removal of the acyl group.     

Reactions of methyl(pentafluorophenyl)- and methyl(pentafluorophenyl)phenylsilanes with electrophiles. A convenient preparative route to halogeno(methyl)pentafluorophenylsilanes C6F5SiMe2X and C6F5SiMeX2 (X=F, Cl and Br)

Halogeno(methyl)pentafluorophenylsilanes C₆F₅SiMe_nX_3−n (n=1, 2) (X=F, Cl, Br) were prepared in good yields from the corresponding phenylsilanes C₆F₅SiMe_nPh_3−n by reactions with the electrophiles aHF, HCl–AlCl₃, Br₂–AlBr₃ or AlX₃ (X=Cl, Br) halogenated hydrocarbons. Additionally, reactions of C₆F₅SiMe₃ and (C₆F₅)₂SiMe₂ with selected electrophiles were studied.     

Ion-Interaction Approach: Pressure Effect on the Solubility of Some Minerals in Submarine Brines and Seawater

The pressure dependence of salt solubility in multiple electrolyte solutions was estimated to 1000 atm. The activity coefficients, thermodynamic solubility products, degrees of saturation, and mineral solubility were calculated with high precision only up to 300 atm because of the absence of compressibility data for mixed electrolyte solutions. The ion-interaction approach developed during the last 2 decades allows the prediction of various thermodynamic properties, including volumetric ones for multiple-solute natural solutions. This approach was applied to the estimation of the depth dependence of solubility for certain evaporite minerals in natural brines. The influence of pressure on solubility products, mean activity coefficients, and degrees of saturation of minerals, such as, halite (NaCl), anhydrite (CaSO₄), gypsum (CaSO₄·2 H₂O), celestite (SrSO₄), and barite (BaSO₄) were calculated for in situ depths in the Orca Basin (Gulf of Mexico), the Tyro and Bannock II depressions (the Mediterranean Sea), and for average seawater.     

Discrete angle rotations of Bi nanoparticles embedded in a Ga matrix

Spontaneous instabilities of nanoparticles are known to be influenced by the temperature, and strongly depend on the particle size. However, it is not clear what is the role of the surrounding material that is in contact with the particle. Here we report on the difference between spontaneous rotations of Bi nanoparticles embedded in amorphous SiO and those embedded in liquid Ga. The phenomenon was studied quantitatively by time resolved transmission electron microscopy using Fourier Transform analysis of highresolution electron microscopy images. While rotations of Bi nanoparticles embedded in amorphous SiO occur by all angles, the rotations of Bi nanoparticles embedded in liquid Ga occur by discrete angles. Our results point quantitatively, for the first time, to the role and importance of the contacting surrounding surface during the rotation of nanoparticles.     

Influence of nesting shell size on brightness longevity and resistance to ultrasound-induced dissolution during enhanced B-mode contrast imaging

This study aims to bridge the gap between transport mechanisms of an improved ultrasound contrast agent (UCA) and its resulting behavior in a clinical imaging study. Phospholipid-shelled microbubbles nested within the aqueous core of a polymer microcapsule are examined for their use and feasibility as an improved UCA. The nested formulation provides contrast comparable to traditional formulations, specifically an SF₆ microbubble coated by a DSPC PEG-3000 monolayer, with the advantage that contrast persists at least nine times longer in a mock clinical, in vitro setting. The effectiveness of the sample was measured using a contrast ratio in units of decibels (dB) which compares the brightness of the nested microbubbles to a reference value of a phantom tissue mimic. During a 40 min imaging study, six nesting formulations with average outer capsule diameters of 1.95, 2.53, 5.55, 9.95, 14.95, and 20.51 μm reached final contrast ratio values of 0.25, 2.35, 3.68, 4.51, 5.93, and 8.00 dB, respectively. The starting contrast ratio in each case was approximately 8 dB and accounts for the brightness attributed to the nesting shell. As compared with empty microcapsules (no microbubbles nested within), enhancement of the initial contrast ratio increased systematically with decreasing microcapsule size. The time required to reach a steady state in the temporal contrast ratio profile also varied with microcapsule diameter and was found to be 420 s for each of the four smallest shell diameters and 210 s and 150 s, respectively, for the largest two shell diameters. All nested formulations were longer-lived and gave higher final contrast ratios than a control sample comprising un-nested, but otherwise equivalent, microbubbles. Specifically, the contrast ratio of the un-nested microbubbles decreased to a negative value after 4 min of continuous ultrasound exposure with complete disappearance of the microbubbles after 15 min whereas all nested formulations maintained positive contrast ratio values for the duration of the 40 min trial. The results are consistent with two distinct stages of gas transport: in the first stage, passive diffusion occurs under ambient conditions across the microbubble monolayer within the first few minutes after formulation until the aqueous interior of the microcapsule is saturated with gas; in the second stage ultrasound drives additional gas dissolution even further due to pressure modulation. It is important to understand the chemistry and transport mechanisms of this contrast agent under the influence of ultrasound to attain better perspicacity for enhanced applications in imaging. Results from this study will facilitate future preclinical studies and clinical applications of nested microbubbles for therapeutic and diagnostic imaging.     

The Politics of Forgetting: Otto Hahn and the German Nuclear-Fission Project in World War II

As the co-discoverer of nuclear fission and director of the Kaiser Wilhelm Institute for Chemistry, Otto Hahn (1879–1968) took part in Germany‘s nuclear-fission project throughout the Second World War. I outline Hahn’s efforts to mobilize his institute for military-related research; his inclusion in high-level scientific structures of the military and the state; and his institute’s research programs in neutron physics, isotope separation, transuranium elements, and fission products, all of potential military importance for a bomb or a reactor and almost all of it secret. These activities are contrasted with Hahn’s deliberate misrepresentations after the war, when he claimed that his wartime work had been nothing but “purely scientific” fundamental research that was openly published and of no military relevance.     

Sensitivity of ultrasonic hydrophone probes below 1 MHz

Frequency responses of different PVDF polymer hydrophone probes, including membrane and needle designs, were measured and are presented in terms of end-of-cable voltage sensitivity versus frequency over a wide, 4.5 octave bandwidth ranging from 0.25 to 2.5 MHz. The probes are seldom, if at all, characterized in this frequency range due to the difficulties associated with a lack of adequate and readily implementable calibration techniques. To this end, a technique, which uses a combination of swept frequency chirp and reciprocity, so that both the relative and absolute plots of sensitivity versus frequency can be obtained, was developed and tested. Salient features of the technique including the design of a 6 octave auxiliary acoustic source are described. The experimental data indicate that a majority of the PVDF membrane hydrophones exhibit a relatively uniform (to within +/- 2 dB) response. While, in general, this is not the case for commercially available needle hydrophone probes, it is evidenced that a careful attention to the PVDF probe design results in frequency characteristics fairly close to those achievable with a membrane design. The overall uncertainty of the calibration technique was estimated to be better than +/- 1.5 dB in the considered frequency range. The results of this work are important to implement procedures for adequate determination of the Mechanical Index (MI) of ultrasound imaging devices. MI is widely accepted as a predictor of potential bioeffects associated with cavitation phenomena. Current efforts are focused on extending the applicability of the technique to frequencies below 100 kHz.