Dual differential interferometer

A dual two-beam differential interferometer that measures both the amplitude and orientation of propagating, broadband surface acoustic waves is disclosed. Four beams are focused on a surface. The four reflected beams are separated into two pairs. The two pairs are detected to produce two signals that are used to compute amplitude and orientation

A Machian Model of Dark Energy

Einstein believed that Mach's principle should play a major role in finding a meaningful spacetime geometry, though it was discovered later that his field equations gave some solutions which were not Machian. It is shown, in this essay, that the kinematical $\Lambda$ models, which are invoked to solve the cosmological constant problem, are in fact consistent with Mach's ideas. One particular model in this category is described which results from the microstructure of spacetime and seems to explain the current observations successfully and also has some benefits over the conventional models. This forces one to think whether the Mach's ideas and the cosmological constant are interrelated in some way.Comment: Received an Honorable mention in the Essay Contest-2002 sponsored by the Gravity Research Foundation; A paragraph added on how the model can explain the CMB anisotropy observations; To appear in the Classical and Quantum Gravit

Optical fiber interferometer for the study of ultrasonic waves in composite materials

The possibility of acoustic emission detection in composites using embedded optical fibers as sensing elements was investigated. Optical fiber interferometry, fiber acoustic sensitivity, fiber interferometer calibration, and acoustic emission detection are reported. Adhesive bond layer dynamical properties using ultrasonic interface waves, the design and construction of an ultrasonic transducer with a two dimensional Gaussian pressure profile, and the development of an optical differential technique for the measurement of surface acoustic wave particle displacements and propagation direction are also examined

The Tensile Root Strength of Spartina Patens Declines with Exposure to Multiple Stressors

Coastal wetlands may be subjected to numerous biotic and abiotic stressors from natural and anthropogenic forces in the landscape. The influx of nutrients, inorganic compounds and xenobiotics are suspected of degrading the belowground biomass of coastal macrophytes. Spartina patens acts as an ecosystem engineer for lower salinity coastal marshes and its biomechanical properties are vital to the stability and resilience of coastal wetlands. S.patens was exposed to one natural (flooding) and two anthropogenic stressors (atrazine and nutrient addition) in a greenhouse experiment to test the hypothesis that these three stressors reduce the tensile root strength of S. patens. A one-way Welch’s analysis of variance revealed that the tensile root strength S. patens significantly declined after exposure to two flood duration regimes, three levels of atrazine exposure, and two levels of nutrient addition that consisted of nitrogen-phosphorus combinations. A one-way ANOVA of tensile root strength with an atrazine flood duration-nutrient addition combination treatment as the main effect resulted in a 52 to 63% loss in tensile strength, while the individual atrazine, flooding, and nutrient treatments produced 40, 39, and 37% losses in tensile root strength, respectively. These results indicate that the effects of multiple natural and/ or anthropogenic stressors may degrade the tensile root strength of S. patens, which could facilitate coastal erosion and subsequent collapse of the wetland ecosystem

The Tensile Root Strength of Spartina patens Varies with Soil Texture and Atrazine Concentration

The widely used agricultural herbicide atrazine enters wetlands and may potentially affect wetland plants that provide critical reinforcement of soil strength and contribute to ecosystem stability in ways that may vary among soil types. We conducted greenhouse experiments using four levels of atrazine doses and three different soil textures to test for differences between control and experimental treatments and interactive effects of soil texture and atrazine exposure by using the tensile root strength of the coastal wetland emergent macrophyte Spartina patens as the response variable. The tensile root strength of S. patens was not affected after 50days of atrazine exposure in an organic soil, but was 29-55% lower vs. controls in a 204-day experiment in sand-, clay-, and organic-dominated soil textures after atrazine exposure with the greatest decline in the sand-atrazine treatment. But there was no statistically significant difference in the distribution of the tensile root strength data of the main effects from individual treatments compared with the soil texture and atrazine combination treatments or any difference in the magnitude of the tensile root strength means. These results indicate that there were no synergistic interactive effects of soil texture and atrazine exposure on S. patens tensile root strength. However, the biogeochemical characteristics of soil texture may play an important role in the plant absorption of xenobiotics

What role do teaching mentors play in supporting new university lecturers to develop their teaching practices?

We examine the support mentors provide to new lecturers as part of a postgraduate programme designed to familiarise them with university teaching. Drawing on qualitative data collected from 13 new lecturers and nine mentors, we document the support new lecturers’ call upon to shape their practice. We identify important issues surrounding the significance of mentor choice, in terms of a mentor’s experience, position and knowledge of their role, which determine the effectiveness of professional learning. Difficult issues were observed relating to prioritisation and workload for new lecturers and their mentors, and as a consequence the wider networks of colleagues and peers that new lecturers drew upon were seen as an essential source of advice. Indeed, the extent of their use depended on assistance available from mentors. Our data indicate the need for careful framing of mentoring relationships in terms of professional development and teaching enhancement to ensure the benefits of these interactions are realised. Equally both parties need to be encouraged to use reflection to scaffold interactions to promote professional learning. Our data also identify the need for recognition for those performing mentoring roles, to ensure they can dedicate necessary time so that productive relationships are sustained for the duration over which support is required

Quantitative T1 mapping using multi-slice multi-shot inversion recovery EPI

An efficient multi-slice inversion–recovery EPI (MS-IR-EPI) sequence for fast, high spatial resolution, quantitative T1 mapping is presented, using a segmented simultaneous multi-slice acquisition, combined with slice order shifting across multiple acquisitions. The segmented acquisition minimises the effective TE and readout duration compared to a single-shot EPI scheme, reducing geometric distortions to provide high quality T1 maps with a narrow point-spread function. The precision and repeatability of MS-IR-EPI T1 measurements are assessed using both T1-calibrated and T2-calibrated ISMRM/NIST phantom spheres at 3 and 7 T and compared with single slice IR and MP2RAGE methods. Magnetization transfer (MT) effects of the spectrally-selective fat-suppression (FS) pulses required for in vivo imaging are shown to shorten the measured in-vivo T1 values. We model the effect of these fat suppression pulses on T1 measurements and show that the model can remove their MT contribution from the measured T1, thus providing accurate T1 quantification. High spatial resolution T1 maps of the human brain generated with MS-IR-EPI at 7 T are compared with those generated with the widely implemented MP2RAGE sequence. Our MS-IR-EPI sequence provides high SNR per unit time and sharper T1 maps than MP2RAGE, demonstrating the potential for ultra-high resolution T1 mapping and the improved discrimination of functionally relevant cortical areas in the human brain

On wave interference in planet migration: dead zone torques modified by active zone forcing

We investigate planetary migration in the dead zone of a protoplanetary disk where there are a set of spiral waves propagating inward due to the turbulence in the active zone and the Rossby wave instability (RWI), which occurs at the transition between the dead and active zones. We perform global 3D unstratified magnetohydrodynamical (MHD) simulations of a gaseous disk with the FARGO3D code, using weak gradients in the static resistivity profiles that trigger the formation of a vortex at the outer edge of the dead zone. We find that once the Rossby vortex develops, spiral waves in the dead zone emerge and interact with embedded migrating planets by wave interference, which notably changes their migration. The inward migration becomes faster depending on the mass of the planet, due mostly to the constructive (destructive) interference between the outer (inner) spiral arm of the planet and, the destruction of the dynamics of the horseshoe region by means of the set of background spiral waves propagating inward. The constructive wave interference produces a more negative Lindblad differential torque which inevitably leads to an inward migration. Lastly, for massive planets embedded in the dead zone, we find that the spiral waves can create an asymmetric wider and depeer gap than in the case of $\alpha$-disks, and can prevent the formation of vortices at the outer edge of the gap. The latter could generate a faster or slower migration compared to the standard type-II migration.Comment: 18 pages, 14 figures, accepted for publication in Ap

Особливості зачину актів купівлі-продажу (на матеріалі Пирятинських міських книг)

У статті розглянуто особливості структурних компонентів початкового протоколу актів купівлі-продажу в українській мові кінця ХVІІ – другої третини ХVІІІ ст. На численних прикладах проілюстровано специфічні ознаки власне пирятинських актів, а також виявлено спільні риси, характерні для тогочасного діловодства взагалі