An update on the human and animal enteric pathogen Clostridium perfringens

Clostridium perfringens, a rapid-growing pathogen known to secrete an arsenal of >20 virulent toxins, has been associated with intestinal diseases in both animals and humans throughout the past century. Recent advances in genomic analysis and experimental systems make it timely to re-visit this clinically and veterinary important pathogen. This Review will summarise our understanding of the genomics and virulence-linked factors, including antimicrobial potentials and secreted toxins of this gut pathogen, and then its up-to-date clinical epidemiology and biological role in the pathogenesis of several important human and animal-associated intestinal diseases, including pre-term necrotising enterocolitis. Finally, we highlight some of the important unresolved questions in relation to C. perfringens-mediated infections, and implications for future research directions

Supersonic Jet Noise from Round and Chevron Nozzles: Experimental Studies

High speed exhaust noise reduction continues to be a research challenge for supersonic cruise business jets as well as for current and future tactical military aircraft. Significant noise reduction may be possible from advanced concepts for controlling instability generated large-scale turbulence structures in the jet shear layer, generally accepted to be the source of aft-angle noise. In response to this opportunity, our team is focused on experimental diagnostic studies and unique instability modeling suited for identifying control strategies to reduce large scale structure noise. The current paper benchmarks the jet noise from supersonic nozzles designed to provide the supporting experimental data and validation of the modeling. Laboratory scale jet noise experiments are presented for a Mach number of Mj = 1.5 with stagnation temperature ratios ranging from Tr = 0.75 to 2. The baseline configuration is represented by a round converging-diverging (CD) ideal expansion nozzle. A round CD nozzle with chevrons is included as the first of several planned non-circular geometries directed at demonstrating the impact on large scale structure noise and validating noise prediction methods for geometries of future technological interest. Overexpanded and underexpanded conditions were tested on both nozzle configurations. The resulting data base provides an opportunity to benchmark the statistical characteristics of round and chevron nozzle data. The current paper examines far field spectra, directivity patterns, and overall sound pressure level dependence comparing observed characteristics with the fine scale turbulence noise and large-scale turbulence structure noise characteristics identified by Tam. In addition, the paper probes the effect of chevrons on the developing flow field and suppression of screech tones. Measurements are also reported from a far-field narrow aperture phased array system used to map the acoustic source distribution on the jet axis. The dominant source region, situated between the end of the potential core and the sonic point, was found to agree with the peak amplitude location of the jet near field wavepackets measured using a unique near field array. This observation supports the cause-effect link between large-scale turbulence structures in the shear layer and their dominant contribution to aft radiated far field noise

Keberkesanan Kaedah Pembelajaran Dalam Talian Ke Atas Kursus Terpilih Bagi Komponen Kesenian Dan Kebudayaan Pusat Kokurikulum Dan Pemajuan Pelajar, Universiti Malaysia Sabah

Susulan penularan wabak COVID-19, institusi pendidikan termasuk Pusat Kokurikulum dan Pemajuan Pelajar (PKPP), Universiti Malaysia Sabah (UMS) telah membuat penyelarasan kurikulum mereka. Pendidikan secara dalam talian adalah kaedah utama penyampaian kurikulum bagi komponen Kesenian dan Kebudayaan dalam Fasa Perintah Kawalan Pergerakan (PKP) hinggalah ke Fasa Pelan Pemulihan Negara (PPN). Selepas lapan minggu pembelajaran dalam talian diadakan, tinjauan persepsi pelajar terhadap kaedah pengajaran dan pembelajaran khususnya komponen Kesenian dan Kebudayaan ini telah dijalankan. Tujuan kajian ini adalah untuk menilai pengalaman baharu pelajar dengan pembelajaran dalam talian dan daya maju pendekatan kaedah pengajaran dan pembelajaran dalam talian bagi komponen Kesenian dan Kebudayaan, Pusat Kokurikulum dan Pemajuan Pelajar. Matlamat kajian ini dapat dicapai dengan meneliti respons daripada 226 pelajar terhadap soal selidik berasaskan kaedah tinjauan. Maklum balas pelajar dalam bentuk skala Likert dianalisis menggunakan kaedah statistik deskriptif. Dapatan kajian menunjukkan bahawa majoriti pelajar berpuas hati dengan pembelajaran dalam talian yang berterusan kerana mereka menikmati akses berterusan ke atas bahan dalam talian, fleksibiliti untuk belajar mengikut keupayaan mereka sendiri, suasana yang selesa dan keupayaan untuk bercakap dengan bebas. Namun, masalah teknikal dan isu peralatan merupakan halangan yang ketara ke atas pembelajaran bidang Kesenian dan Kebudayaan dalam talian semasa pandemik COVID-19. Pembelajaran dalam talian adalah diterima baik oleh pelajar yang mendaftar dalam komponen Kebudayaan dan Kesenian. Namun, penyepaduan pembelajaran talian terhadap kurikulum bidang Kesenian dan Kebudayaan memerlukan strategi yang lebih baik dan pendekatan yang lebih proaktif

On local linearization of control systems

We consider the problem of topological linearization of smooth (C infinity or real analytic) control systems, i.e. of their local equivalence to a linear controllable system via point-wise transformations on the state and the control (static feedback transformations) that are topological but not necessarily differentiable. We prove that local topological linearization implies local smooth linearization, at generic points. At arbitrary points, it implies local conjugation to a linear system via a homeomorphism that induces a smooth diffeomorphism on the state variables, and, except at "strongly" singular points, this homeomorphism can be chosen to be a smooth mapping (the inverse map needs not be smooth). Deciding whether the same is true at "strongly" singular points is tantamount to solve an intriguing open question in differential topology

Decomposition of High Speed Jet Noise: Source Characteristics and Propagation Effects

Current research programs directed at supersonic engine exhaust noise reduction are demonstrating benefits of 3-4 dBA using passive methods to increase jet mixing and break up shock cells in over-expanded flows. While progress is being made, high speed jet noise continues to be a research challenge for small business jets and tactical military aircraft. The current work benchmarks high speed jet noise using laboratory scale jets for the purpose of a) identifying source and propagation mechanisms, and b) providing validation data for simulation/modeling methods. Laboratory scale experiments are presented over a Mach number range of M = 0.68 to 1.5 with static temperature ratio ranging from Tr = 0.68 to 2. A unique near field rotating phased microphone array technique was used to identify the large-scale turbulence structure noise source and Mach waves in supersonic shock-free jets. A companion paper documents the near field pressure statistics and projection of the convected wave packet to the far field. Validation against the directly measured far field levels quantitatively establishes the large scale structure noise contributions. The combined studies underpin a long term effort to develop modeling methods and new concepts for jet noise suppression based on controlling the evolution of the large-scale turbulence structures