305 research outputs found

    The acoustic phase resonances and surface waves supported by a compound rigid grating (article)

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    This is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this record.The dataset associated with this article is located in ORE at: https://doi.org/10.24378/exe.606We study the radiative and bound acoustic modes supported by a rigid grating formed of three same-depth, narrow grooves per unit cell. One of the grooves is twice the width of the other two, forming a ‘compound’ grating. The structure supports so-called ‘phase’ resonances where the phase difference of the pressure field between the grooves on resonance varies by multiples of π. We explore the dispersion of these modes experimentally by monitoring the specularly reflected signal as a function of the angle of incidence. In addition, by near-field excitation, the dispersion of the non-radiative surface modes has been characterised. Our results are compared with the predictions of a finite element method model.The authors wish to acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom, via the EPSRC Centre for Doctoral Training in Metamaterials (Grant No. EP/L015331/1), QinetiQ and DSTL

    Experimental characterisation of the bound acoustic surface modes supported by honeycomb and hexagonal hole arrays

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    This is the final version. Available from Nature Research via the DOI in this record. The Dirac point and associated linear dispersion exhibited in the band structure of bound (non-radiative) acoustic surface modes supported on a honeycomb array of holes is explored. An aluminium plate with a honeycomb lattice of periodic sub-wavelength perforations is characterised by local pressure field measurements above the sample surface to obtain the full band-structure of bound modes. The local pressure fields of the bound modes at the K and M symmetry points are imaged, and the losses at frequencies near the Dirac frequency are shown to increase monotonically as the mode travels through the K point at the Dirac frequency on the honeycomb lattice. Results are contrasted with those from a simple hexagonal array of similar holes, and both experimentally obtained dispersion relations are shown to agree well with the predictions of a numerical model.Defence Science and Technology Laboratory (DSTL)Engineering and Physical Sciences Research Council (EPSRC

    International Students’ Transition Experiences in Rural Texas: A Phenomenological Study

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    Due to the growth in the number of international students attending universities in Texas and the need to provide appropriate counseling services to them, nine international students were interviewed about their experiences of transitioning from their home country to college in rural Texas. The authors employed the transcendental phenomenological approach to qualitative research (Moustakas, 1994) which allowed for the following seven emergent themes were identified that described the participants’ experiences: American TV; Knowing Someone; Like a Movie; Everybody Saying Hi; Transportation is Inconvenient; I Miss Noodles; and Being Optimistic. The emergent themes provided the basis for implications and recommendations for counseling services with the international student populations. Implications and recommendations for counselors on college campuses include, but are not limited to: actively collaborating with international student services, participating in new international student orientation services, and developing preemptive approaches to assisting international student during their transitions The authors make recommendations for further qualitative research and focus groups inquiries should be conducted by college counselors to better inform outreach services, for campus counseling and career service center, directed at assisting international students during their numerous transitions (Lértora et al., 2017)

    Underwater acoustic surface waves on a periodically perforated metal plate

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    This is the final version. Available from Acoustical Society of America via the DOI in this record. Acoustic surface waves are supported at the surface of appropriately structured elastic materials. Here the excitation and propagation of the lowest-order surface mode supported by a square array of open-ended cavities on a metal plate submerged in water is demonstrated. This mode, which has a half-wavelength character in the cavity, arises due to inter-cavity interaction by evanescent diffraction of the pressure field, and forms a band from zero-frequency to an asymptotic limit frequency. The authors perform an acoustic characterization of the pressure field close to the surface of the perforated plate in the 60–100 kHz frequency range; sound is pulsed from a fixed point-like acoustic source, and the evolution of the acoustic field across the sample surface is measured as a function of time and space with a traversing detector. Using Fourier analysis, the dispersion is imaged between points of high-symmetry (C; X; M) and at planes in momentum-space at fixed frequencies. Beaming of acoustic energy on the surface over a narrow frequency band was observed, caused by the anisotropic mode dispersion of the acoustic surface wave on the square lattice. The measured dispersion shows good agreement with the predictions of a numerical model.Defence Science and Technology Laboratory (DSTL)Engineering and Physical Sciences Research Council (EPSRC)Thales U

    Experimental characterization of acoustic beaming from an elastic plate by coupled symmetric leaky Lamb modes

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    This is the final version. Available from the American Physical Society via the DOI in this recordDesigner mode dispersions with properties such as negative or zero group velocities have applications in tailored wave propagation and energy redistribution. The modes of elastic plates can readily exhibit such phenomena by virtue of their bulk elastic properties and thickness. Here, we investigate the symmetric leaky Lamb modes within a thin flat aluminum-alloy plate submerged in water using pulsed broadband ultrasound, and experimentally characterize acoustic beaming from the plate caused by resonant transmission, which is enhanced via intrinsic negative dispersion of energy within the plate. The beaming of acoustic power occurs within a narrow frequency band in transmission over the negative group velocity region of the first-order symmetric leaky Lamb mode. Experimental characterization utilizes Fourier analysis and measurements of transmitted fields in time and space to obtain the leaky Lamb modes dispersion, which agree well with the predictions of a numerical model. This model is then used to visualize the pressure field and confirm the nature of the energy flow inside the plate. The properties of the acoustic focusing depend on the plate thickness and elastic material parameters, and may be readily controlled for a range of applications. Such phenomena may be exploited in other areas, such as in the microwave domain where designer mode dispersions can be developed using metamaterial conceptsEngineering and Physical Sciences Research Council (EPSRC)Thales UKDST

    Excitation of airborne acoustic surface modes driven by a turbulent flow

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    This is the author accepted manuscript. The final version is available from AIAA via the DOI in this recordThis experiment demonstrated the generation of trapped acoustic surface waves excited by a turbulent flow source through the coupling of pressure fluctuations at the interface between an acoustic metamaterial and a flow environment. The turbulent flow, which behaves as a stochastic pressure source, was produced using a fully developed turbulent wall jet. The plate in the wall jet was perforated with a single cavity. On the flow-side it was capped by a Kevlar weave to ensure the cavity did not significantly disturb the flow, whilst on the adjacent side the cavity was open to the quiescent (static) environment. The through-cavity opening, on the quiescent side, was flush with an acoustic metasurface waveguide, which, through evanescent diffractive coupling of the pressure field, produced an acoustic surface mode. This acoustic mode was trapped at the plate surface, with its mode dispersion determined by the surface geometry. The results of two different metasurface geometries are discussed; (1) a slotted cavity array, and (2) a meander connected cavity array, each demonstrating a different trapped surface wave dispersion behavior. Fourier transform and correlation analyses of spatially-resolved temporal acoustic signals, measured close to the metamaterial surface, were used to construct the frequency and wave vector-dependent acoustic mode dispersion. Results demonstrated the flow can indeed be used to excite these acoustic modes and that their mode dispersion can be tailored towards realizing novel control of turbulent flow through acoustic-flow interactionsDefence Science and Technology Laboratory (DSTL

    The Environmental History of Cetaceans in Portugal: Ten Centuries of Whale and Dolphin Records

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    The history between cetaceans and humans is documented throughout time not only in reports, descriptions, and tales but also in legal documents, laws and regulations, and tithes. This wealth of information comes from the easy spotting and identification of individuals due to their large size, surface breathing, and conspicuous above water behaviour. This work is based on historical sources and accounts accounting for cetacean presence for the period between the 12th and 17th centuries, as well as scientific articles, newspapers, illustrations, maps, non-published scientific reports, and other grey literature from the 18th century onwards. Information on whale use in Portugal's mainland has been found since as early as the 12th century and has continued to be created throughout time. No certainty can be given for medieval and earlier events, but both scavenging of stranded whales or use of captured ones may have happened. There is an increasing number of accounts of sighted, stranded, used, or captured cetaceans throughout centuries which is clearly associated with a growing effort towards the study of these animals. Scientific Latin species denominations only started to be registered from the 18th century onwards, as a consequence of the evolution of natural sciences in Portugal and increasing interest from zoologists. After the 19th century, a larger number of observations were recorded, and from the 20th century to the present day, regular scientific records have been collected. Research on the environmental history of cetaceans in Portugal shows a several-centuries-old exploitation of whales and dolphins, as resources mainly for human consumption, followed in later centuries by descriptions of natural history documenting strandings and at sea encounters. Most cetaceans species currently thought to be present in Portuguese mainland waters were at some point historically recorded

    Altered Retinoic Acid Metabolism in Diabetic Mouse Kidney Identified by 18O Isotopic Labeling and 2D Mass Spectrometry

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    Numerous metabolic pathways have been implicated in diabetes-induced renal injury, yet few studies have utilized unbiased systems biology approaches for mapping the interconnectivity of diabetes-dysregulated proteins that are involved. We utilized a global, quantitative, differential proteomic approach to identify a novel retinoic acid hub in renal cortical protein networks dysregulated by type 2 diabetes.Total proteins were extracted from renal cortex of control and db/db mice at 20 weeks of age (after 12 weeks of hyperglycemia in the diabetic mice). Following trypsinization, (18)O- and (16)O-labeled control and diabetic peptides, respectively, were pooled and separated by two dimensional liquid chromatography (strong cation exchange creating 60 fractions further separated by nano-HPLC), followed by peptide identification and quantification using mass spectrometry. Proteomic analysis identified 53 proteins with fold change >or=1.5 and p<or=0.05 after Benjamini-Hochberg adjustment (out of 1,806 proteins identified), including alcohol dehydrogenase (ADH) and retinaldehyde dehydrogenase (RALDH1/ALDH1A1). Ingenuity Pathway Analysis identified altered retinoic acid as a key signaling hub that was altered in the diabetic renal cortical proteome. Western blotting and real-time PCR confirmed diabetes-induced upregulation of RALDH1, which was localized by immunofluorescence predominantly to the proximal tubule in the diabetic renal cortex, while PCR confirmed the downregulation of ADH identified with mass spectrometry. Despite increased renal cortical tissue levels of retinol and RALDH1 in db/db versus control mice, all-trans-retinoic acid was significantly decreased in association with a significant decrease in PPARbeta/delta mRNA.Our results indicate that retinoic acid metabolism is significantly dysregulated in diabetic kidneys, and suggest that a shift in all-trans-retinoic acid metabolism is a novel feature in type 2 diabetic renal disease. Our observations provide novel insights into potential links between altered lipid metabolism and other gene networks controlled by retinoic acid in the diabetic kidney, and demonstrate the utility of using systems biology to gain new insights into diabetic nephropathy
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