Particle Production in a Gravitational Wave Background

In this article, the authors study the possibility that massless particles, such as photons, are produced by a gravitational wave. That such a process should occur is implied by tree-level Feynman diagrams such as two gravitons turning into two photons, i.e., g + g → γ + γ. Here we calculate the rate at which a gravitational wave creates a massless scalar field. This is done by placing the scalar field in the background of a plane gravitational wave and calculating the 4-current of the scalar field. Even in the vacuum limit of the scalar field it has a nonzero vacuum expectation value (similar to what occurs in the Higgs mechanism) and a nonzero current. We associate this with the production of scalar field quanta by the gravitational field. This effect has potential consequences for the attenuation of gravitational waves since the massless field is being produced at the expense of the gravitational field. This is related to the time-dependent Schwinger effect, but with the electric field replaced by the gravitational wave background and the electron/positron field quanta replaced by massless scalar “photons.” Since the produced scalar quanta are massless there is no exponential suppression, as occurs in the Schwinger effect due to the electron mass

Particle Production in a Gravitational Wave Background

In this article, the authors study the possibility that massless particles, such as photons, are produced by a gravitational wave. That such a process should occur is implied by tree-level Feynman diagrams such as two gravitons turning into two photons, i.e., g + g → γ + γ. Here we calculate the rate at which a gravitational wave creates a massless scalar field. This is done by placing the scalar field in the background of a plane gravitational wave and calculating the 4-current of the scalar field. Even in the vacuum limit of the scalar field it has a nonzero vacuum expectation value (similar to what occurs in the Higgs mechanism) and a nonzero current. We associate this with the production of scalar field quanta by the gravitational field. This effect has potential consequences for the attenuation of gravitational waves since the massless field is being produced at the expense of the gravitational field. This is related to the time-dependent Schwinger effect, but with the electric field replaced by the gravitational wave background and the electron/positron field quanta replaced by massless scalar “photons.” Since the produced scalar quanta are massless there is no exponential suppression, as occurs in the Schwinger effect due to the electron mass

Scalar Field Vacuum Expectation Value Induced by Gravitational Wave Background

We show that a massless scalar field in a gravitational wave background can develop a non-zero vacuum expectation value. We draw comparisons to the generation of a non-zero vacuum expectation value for a scalar field in the Higgs mechanism and with the dynamical Casimir vacuum. We propose that this vacuum expectation value, generated by a gravitational wave, can be connected with particle production from gravitational waves and may have consequences for the early Universe where scalar fields are thought to play an important role

Development of Anti-Selective Aldol Additions and a Convergent Assembly of Polycyclic Ethers: Synthesis of the ABCDE Fragment of Brevetoxin A

Anti-selective aldol additions between the titanium enolates of N-glycolyl oxazolidinethiones and simple aldehydes are described. Variation to the Lewis acid stoichiometry of known syn aldol conditions led to a reversal of stereoselectivity favoring formation of one anti diastereomer. Highest selectivity and yield were observed using alpha,beta-allyloxy glycolylimides and aliphatic, unbranched aldehydes. Other suitably protected imides and alpa,beta-unsaturated or aromatic aldehydes were also viable reacting partners. Application of the anti glycolate aldol additions toward the stereoselective synthesis of the BCDE fragment of the potent red tide neurotoxin brevetoxin A is also described. Synthesis of the B ring began with an anti aldol addition to set the C3 and C4 stereogenic centers. Further elaboration using glycolate alkylation and ring-closing metathesis reactions provided the B ring core. The E ring fragment likewise utilized anti aldol methodology to rapidly access a diene fragment needed to close the nine-membered ring. A novel convergent coupling strategy was developed for the synthesis of the completed trans-fused BCDE tetracycle from the individual B and E units. This approach relied on a Horner-Wadsworth-Emmons reaction to join the two complex fragments. Enone reduction and subsequent cyclodehydration generated an intermediate endocyclic enol ether representing the B, C, and E rings. Elaboration of the enol ether intermediate via oxidation, cyclization of the D ring, and ketal reduction then provided the completed BCDE fragment. A revised synthesis of this molecule was subsequently developed to provide the onecarbon homologated version needed for eventual completion of the natural product. The E ring revision is highlighted by a novel glycolate alkylation using bromoacetonitrile and several protecting group alterations. Significant improvements to the convergent assembly were realized during the revision, providing the BCDE fragment in significantly higher yield from the individual rings and in fewer synthetic steps. Finally, the A ring lactone was formed, providing the complete ABCDE pentacycle

Sign language interpreter space : a phenomenological case study of interpreted theatre

This qualitative, phenomenological study explores the production of space by sign language interpreters in the theatre, and the influence of multiple interacting spaces on the co-construction of meaning between participants of these interpreted interactions. A sign language interpreted performance (SLIP) of Disney’s The Lion King serves as a case study of the placed strategy, which situates the interpreters on the outer edges of the performance space. Placed interpreting is the dominant SLIP strategy. Applications of Lefebvre’s (1991) spatial trialectics in deaf spaces and in theatre spaces contribute to the study’s conceptual framework for considering interpreted theatre spaces, the SLIP Spatial Framework. Experiences of the SLIP described by deaf audience members, actors, and the interpreting team combine with observation data and secondary references to form a composite narrative re-telling of the experiences of the SLIP from multiple perspectives. Deaf people are shown to produce deaf spaces within the multiple, highly orchestrated incumbent physical and fictional spaces of the theatre. Meaning co-construction occurs between all three groups, not as a process channelled through the interpreters. The study offers a foundational discussion of sign language interpreter space and a tool for researchers and practitioners: the SLIP Spatial Framework. Application of Lefebvrian spatial trialectics aligns the study with a growing body of deaf space research, while demonstrating ways in which interpreters blend features of deaf spatial production with those of the situations in which they operate

Systematic review of diagnostic tests for reproductive-tract infection and inflammation in dairy cows

The objective of this study was to conduct a systematic and critical appraisal of the quality of previous publications and describe diagnostic methods, diagnostic criteria and definitions, repeatability, and agreement among methods for diagnosis of vaginitis, cervicitis, endometritis, salpingitis, and oophoritis in dairy cows. Publications (n = 1,600) that included the words "dairy," "cows," and at least one disease of interest were located with online search engines. In total, 51 papers were selected for comprehensive review by pairs of the authors. Only 61% (n = 31) of the 51 reviewed papers provided a definition or citation for the disease or diagnostic methods studied, and only 49% (n = 25) of the papers provided the data or a citation to support the test cut point used for diagnosing disease. Furthermore, a large proportion of the papers did not provide sufficient detail to allow critical assessment of the quality of design or reporting. Of 11 described diagnostic methods, only one complete methodology, i.e., vaginoscopy, was assessed for both within- and between-operator repeatability (κ = 0.55-0.60 and 0.44, respectively). In the absence of a gold standard, comparisons between different tests have been undertaken. Agreement between the various diagnostic methods is at a low level. These discrepancies may indicate that these diagnostic methods assess different aspects of reproductive health and underline the importance of tying diagnostic criteria to objective measures of reproductive performance. Those studies that used a reproductive outcome to select cut points and tests have the greatest clinical utility. This approach has demonstrated, for example, that presence of (muco)purulent discharge in the vagina and an increased proportion of leukocytes in cytological preparations following uterine lavage or cytobrush sampling are associated with poorer reproductive outcomes. The lack of validated, consistent definitions and outcome variables makes comparisons of the different tests difficult. The quality of design and reporting in future publications could be improved by using checklists as a guideline. Further high-quality research based on published standards to improve study design and reporting should improve cow-side diagnostic tests. Specifically, more data on intra- and interobserver agreement are needed to evaluate test variability. Also, more studies are necessary to determine optimal cut points and time postpartum of examination

Enantioselective Total Synthesis of Brevetoxin A: Convergent Coupling Strategy and Completion

A highly convergent, enantioselective total synthesis of brevetoxin A is reported. The development of a [X + 2 + X] Horner–Wadsworth–Emmons/cyclodehydration/reductive etherification convergent coupling strategy allowed for a unified approach to the synthesis of two advanced tetracyclic fragments from four cyclic ether subunits. The Horner–Wittig coupling of the two tetracyclic fragments provided substrates that were explored for reductive etherification, the success of which delivered a late-stage tetraol intermediate. The tetraol was converted to the natural product through an expeditious selective oxidative process, followed by methylenation

Total Synthesis of Brevetoxin A

A total synthesis of brevetoxin A is reported. Two tetracyclic coupling partners, prepared from previously reported advanced fragments, were effectively united via a Horner—Wittig olefination. The resulting octacycle was progressed to substrates that were explored for reductive etherification, the success of which led to a penultimate tetraol intermediate. The tetraol was converted to the natural product through an expeditious selective oxidative process, followed by methylenation

Enantioselective Total Synthesis of Brevetoxin A: Unified Strategy for the B, E, G, and J Subunits

Brevetoxin A is a decacyclic ladder toxin that possesses five-,six-, seven-, eight-, and nine-membered oxacycles, as well as 22 tetrahedral stereocenters. Herein, we describe a unified approach to the B, E, G, and J rings predicated upon a ring-closing metathesis strategy from the corresponding dienes. The enolate technologies developed in our laboratory allowed access to the precursor acyclic dienes for the B, E, and G medium ring ethers. The strategies developed for the syntheses of these four monocycles ultimately provided multigram quantities of each of the rings, supporting our efforts toward the convergent completion of brevetoxin A

Tectonics of SE China: New insights from the Lushan massif (Jiangxi Province)

International audienceIn south China the Lushan massif forms a topographic high of the South China Block south of the Qinling-Dabie belt. The Lushan massif consists of two main lithotectonic units separated by a major tectonic contact: a Neoproterozoic (upper Sinian)-Paleozoic unit comprising primarily unmetamorphosed sandstones overlies a Paleoproterozoic unit mainly composed of low-pressure, high-temperature gneisses and micaschists. Both units are cut by Cretaceous granitic intrusions. Three primary tectono-metamorphic and magmatic events are recognized. The eastern part of the Lushan massif is cut by a NNE-SSW trending ductile normal fault (D3 deformation) coeval to the emplacement of a 100-110 Ma leucogranite dated by 40Ar/39Ar laserprobe on biotite and muscovite. D2 deformation is responsible for the formation of a decakilometer-scale NE-SW trending upright anticline characterized by NE-SW stretching and NW-SE shortening. The age of this folding event is defined by a 127±1 (2σ) Ma U/Pb titanite date obtained for a syntectonic granodiorite and 40Ar/39Ar ages of 133 Ma for amphibole. This Cretaceous age also corresponds to the 40Ar/39Ar ages of 126 Ma found on syntectonic muscovites at the base of the Sinian unit. An older deformation event, D1, characterized by a top-to-the-NW extensional decollement of the Sinian-Paleozoic series above Proterozoic metamorphic rocks is related to the Triassic tectonics of the Dabieshan. Lastly, in the lower part of Sinian rocks, the occurrence of kyanite cataclased during D1 documents an older, poorly preserved, late Paleozoic-early Mesozoic tectonometamorphic event (Dx) related to a blind thrust in the continental crust of the South China Block in the southern foreland of the Dabieshan