Dense electron-positron plasmas and ultraintense γ rays from laser-irradiated solids

In simulations of a 10 PW laser striking a solid, we demonstrate the possibility of producing a pure electron-positron plasma by the same processes as those thought to operate in high-energy astrophysical environments. A maximum positron density of 10(26) m(-3) can be achieved, 7 orders of magnitude greater than achieved in previous experiments. Additionally, 35% of the laser energy is converted to a burst of γ rays of intensity 10(22) W cm(-2), potentially the most intense γ-ray source available in the laboratory. This absorption results in a strong feedback between both pair and γ-ray production and classical plasma physics in the new "QED-plasma" regime.     

Computer experiment and global optimization of layered monocentric lens systems

In this paper we derive a general analytical solution for a monocentric lens system and present a global optimization method combining sequential design for global optimization and an expected improvement algorithm for global optimization for the design and analysis of a layered monocentric lens system, which provides an “intelligent” way to search the optimization space based on accumulated experience. We then apply these methods to an example of monocentric lens design, and explore the improvement in system performance obtained through increasing the system volume.     

Intermolecular interactions in the chiral and racemic forms of 3‐­hydroxy‐2‐(1‐oxoisoindolin‐2‐yl)­butanoic acid derived from threonine

The title compounds, C₁₂H₁₃NO₄, are derived from l ‐threonine and dl ‐threonine, respectively. Hydro­gen bonding in the chiral derivative, (2S/3R)‐3‐hydroxy‐2‐(1‐oxoisoindolin‐2‐yl)­butanoic acid, consists of O—H_acid?O_alkyl—H?O=C_indole chains [O?O 2.659 (3) and 2.718 (3) Å], Csp³—H?O and three C—H?π_arene interactions. In the (2R,3S/2S,3R) racemate, conventional carboxylic acid hydrogen bonding as cyclical (O—H?O=C)₂ [graph set R₂²(8)] is present, with O_alkyl—H?O=C_indole, Csp³—H?O and C—H?π_arene interactions. The COOH group geometry differs between the two forms, with C—O, C=O, C—C—O and C—C=O bond lengths and angles of 1.322 (3) and 1.193 (3) Å, and 109.7 (2) and 125.4 (3)°, respectively, in the chiral structure, and 1.2961 (17) and 1.2210 (18) Å, and 113.29 (12) and 122.63 (13)°, respectively, in the racemate structure. The O—C=O angles of 124.9 (3) and 124.05 (14)° are similar. The differences arise from the contrasting COOH hydrogen‐bonding environments in the two structures.     

(E)‐6‐Methoxy‐3‐(α‐methoxybenzyl­idene)benzo[b]furan‐2(3H)‐one at 173 K

The title compound, C₁₇H₁₄O₄, is an unprecedented new synthetic isoaurone‐type enol ether that has the E configuration. The planar furanone ring is fused to a methoxy­benzene ring system, with an interplanar angle of 175.7 (1)°. Due to this ring fusion, the six‐membered ring has a significant amount of ring strain, as shown by the internal ring angle range of 115.8 (1)–124.7 (1)°, whereas the vinylic phenyl ring has internal angles between 119.7 (1) and 120.2 (1)°. The mol­ecules form infinite hydrogen‐bonding layers along the b direction of the form C—H?O, where the keto O atom acts as a bifurcated acceptor. These layers are connected along the c direction by another hydrogen bond with a methoxy H atom as donor. In addition to this connection, the layers are stacked via centres of symmetry by a pair of symmetry‐related benzo­furan­one ring systems.     

Entourage uniformities for frames

The purpose of this paper is to define a uniformity on a frame using entourages. A definition of uniformities in terms of covers has been given byA. Pultr ([8], [10]). We introduce two new symmetry conditions for a quasi-uniform space, open-set symmetry and small-set symmetry. We prove that a quasi-uniformityU is a uniformity if and only if it is both open-set symmetric and small-set symmetric. The category of (covering) uniform frames is isomorphic with the category of entourage uniform frames.     

Energy release in the reaction of metal powders with fluorine containing polymers

Fluorine and its derivatives have been used as a substitute to oxygen-containing oxidizers in higher performing propellants and other energetic materials. They typically react rapidly with metals or thin oxide layers of the metals to produce metal fluorides, generally in the gaseous state.Thermal reactions of stoichiometric mixtures of metal (M=Al, Ti) -F containing polymers have been studied using thermal analyzers and their energetics are compared with the metals in other halogen element containing oxidizers. The experimental results indicated that thermal reaction becomes more exothermic as the bond strength between Al-X (X=F, Br, I) becomes stronger. It was also found that oxidation of metal powders is largely affected by the size of metal powders as well as the nature of existing oxide layer.