Free-field propagation of high intensity noise

Research on high intensity (finite amplitude) acoustic waves shows that nonlinear distortion effects generally result in a shift of energy to higher frequencies. The higher intensities associated with supersonic jets would therefore indicate that high frequency enhancement of the spectrum should occur, resulting in the differences observed between subsonic and supersonic jets. A 10,000 acoustic watt source installed in an anechoic chamber generates sound levels such that acoustic shocks are readily observable. Dual frequency excitation of the source produces a strong parametric effect with a difference frequency comparable in level to the primary frequency. The test set up and recording equipment being used to determine the finite amplitude noise representative of an actual supersonic jet are described as well as the development of a computer program based on Burger's equation. The spectra of 1/2 octave band, 1 kHz sine wave, and dual frequency input and output are presented in graphs along with waveforms at Z = .025, 0.1, and 1.0

Longitudinal excitations in quantum antiferromagnets

By extending our recently proposed magnon-density-waves to low dimensions, we investigate, using a microscopic many-body approach, the longitudinal excitations of the quasi-one-dimensional (quasi-1d) and quasi-2d Heisenberg antiferromagnetic systems on a bipartite lattice with a general spin quantum number. We obtain the full energy spectrum of the longitudinal mode as a function of the coupling constants in the original lattice Hamiltonian and find that it always has a non-zero energy gap if the ground state has a long-range order and becomes gapless for the pure isotropic 1d model. The numerical value of the minimum gap in our approximation agrees with that of a longitudinal mode observed in the quasi-1d antiferromagnetic compound KCuF${}_3$ at low temperature. It will be interesting to compare values of the energy spectrum at other momenta if their experimental results are available.Comment: 19 pages, 4 figure

Description of an ancient social bee trapped in amber using diagnostic radioentomology

The application of non-invasive imaging technologies using X-radiation (diagnostic radioentomology, ‘DR’) is demonstrated for the study of amber-entombed social bees. Here, we examine the external and internal morphology of an Early Miocene (Burdigalian) stingless bee (Apinae: Meliponini) from the Dominican Republic using non-destructive X-ray microtomography analysis. The study permits the accurate reconstruction of features otherwise obscured or impossible to visualize without destroying the sample and allows diagnosis of the specimen as a new species, Proplebeia adbita Greco and Engel

Status quo and sector readiness for (bio)plastic food and beverage packaging in the 4IR

Single-use plastics emanating from the food and beverage industry are polluting the environment, and there is increasing public pressure to find ‘green’ solutions to plastic pollution. The introduction of more bio-based and biodegradable plastics (possibly manufactured by disruptive technologies), increased plastic recycling, and enhanced degradation of plastics (micro, meso, and macro) in the environment can holisticallycontribute to solving the problem for future generations. In order to inform future research, it is imperative that robust background data and information are available. This review provides details about the volumes and categories of food and beverage packaging manufactured and recycled, and available data (qualitative and quantitative) on environmental plastic pollution in South Africa, and to a lesser extent, in Europe andglobally. In addition, current and future trends and technologies for recycling, enhanced degradation, and manufacturing of plastics are discussed, with an emphasis on the manufacture of bioplastics. Significance: Plastic pollution needs to be tackled through a holistic combination of reduced use, enhanced recycling efforts, public education about littering, replacement of selected conventional plastics by degradable alternatives, and enhanced degradation of plastics in the environment

Evidence for a second class of S-adenosylmethionine riboswitches and other regulatory RNA motifs in alpha-proteobacteria

BACKGROUND: Riboswitches are RNA elements in the 5' untranslated leaders of bacterial mRNAs that directly sense the levels of specific metabolites with a structurally conserved aptamer domain to regulate expression of downstream genes. Riboswitches are most common in the genomes of low GC Gram-positive bacteria (for example, Bacillus subtilis contains examples of all known riboswitches), and some riboswitch classes seem to be restricted to this group. RESULTS: We used comparative sequence analysis and structural probing to identify five RNA elements (serC, speF, suhB, ybhL, and metA) that reside in the intergenic regions of Agrobacterium tumefaciens and many other α-proteobacteria. One of these, the metA motif, is found upstream of methionine biosynthesis genes and binds S-adenosylmethionine (SAM). This natural aptamer most likely functions as a SAM riboswitch (SAM-II) with a consensus sequence and structure that is distinct from the class of SAM riboswitches (SAM-I) predominantly found in Gram-positive bacteria. The minimal functional SAM-II aptamer consists of fewer than 70 nucleotides, which form a single stem and a pseudoknot. Despite its simple architecture and lower affinity for SAM, the SAM-II aptamer strongly discriminates against related compounds. CONCLUSION: SAM-II is the only metabolite-binding riboswitch class identified so far that is not found in Gram-positive bacteria, and its existence demonstrates that biological systems can use multiple RNA structures to sense a single chemical compound. The two SAM riboswitches might be 'RNA World' relics that were selectively retained in certain bacterial lineages or new motifs that have emerged since the divergence of the major bacterial groups

Quasi-1D spin-1/2 Heisenberg magnets in their ordered phase: correlation functions

We study weakly coupled antiferromagnetic spin chains in their ordered phase by combinining an exact solution of the single-chain problem with an RPA analysis of the interchain interaction. A single chain is described by a quantum Sine-Gordon model and dynamical staggered susceptibilities are determined by employing the formfactor approach to quantum correlation functions. We consider both antiferromagnetic order encountered in quasi-1D materials like $KCuF_3$ and spin-Peierls order as found in $CuGeO_3$.Comment: 16 pages of revtex, 12 figure

Feeding the rural tourism strategy? Food and notions of place and identity

The humble rural cuisine has now been thrust at the forefront of economic development strategies. This conceptual paper is a contribution to a growing critical awareness of the operations of the food industry and helps to foster a critical understanding of how, if at all, local food and its associated culture can help sustain rural tourism particularly and rural communities generally. It is inspired by literature about the international political economy of food and the many experiences of local food development, and is aware of the contrast between the structure of the industry and the hopes associated with its practice on the ground. The paper thus argues that, beyond the glamour and hype, there are those who gain, as well as those who lose, from the current food fad. While it explains the causes of the contemporary craze with food, the paper also interrogates the naı¨ve expectations often placed in food as a motor of rural development, and as the panacea for struggling rural communities. The empirical data on which this chapter is based are drawn from 18 short chapters explaining the history of various “traditional dishes” from the islands of the broad North Atlantic that feature in a recent food publication.peer-reviewe

The visible human slice Web server: a first assessment

The visible human slice server started offering its slicing services at the end of June 1998. From that date until the end of May, more than 280000 slices were extracted from the Visible Man, by laymen interested in anatomy, by students and by specialists. The Slice Server is based one Bi-Pentium PC and 16 disks. It is a scaled down version of a powerful parallel server comprising 5 Bi-Pentium Pro PCs and 60 disks. The parallel server program was created thanks to a computer-aided parallelization framework, which takes over the task of creating a multithreaded pipelined parallel program from a high-level parallel program description. On the full blown architecture, the parallel program enables the extraction and resampling of up to 5 color slices per second. Extracting 5 slice/s requires to access the disks and extract subvolumes of the Visible Human at an aggregate throughput of 105 MB/s. The publicly accessible server enables to extract slices having any orientation. The slice position and orientation can either be specified for each slice separately or as a position and orientation offered by a Java applet and possible future improvements. In the very near future, the Web Slice Server will offer additional services, such as the possibility to extract ruled surfaces and to extract animations incorporating slices perpendicular to a user defined trajector