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Both double-crystal and triple-axis x-ray diffraction techniques have been used to study complex SiGe/Si structures. A novel method for measuring the nucleation activation energy of dislocations in strain relaxed SiGe/Si structures is presented to illustrate the usefulness of these techniques.
Seed–soil contact plays an essential role in the process of germination as seeds absorb water through direct contact with the moist soil aggregates that surround them. Factors influencing seed–soil contact can be considered as those pertaining to soil physical properties (e.g. texture, bulk density, porosity, etc.) and those related to environmental conditions (e.g. temperature, rainfall, frost). Seed–soil contact is furthermore influenced by the specific field management processes that farmers apply, which have developed significantly over the last 30 years. However, the precise effect of cultivation on the actual contact area of the seed with the surrounding soil is based on a series of assumptions and is still largely unknown. This review considers the influence of soil management and its direct impact on seed–soil contact and establishment. We review the state of the art in methodology for measuring seed–soil contact and assess the potential for soil amendments such as plant residues and waste materials to improve seed–soil contact. Engineering the ‘optimal’ seed–soil contact remains a challenge due to the localized variation between the interaction with field management techniques and soil texture, climatic conditions and crop type. The latest imaging approaches show great promise to assess the impact of management on germination. Combining the techniques with the latest network models offers great potential to improve our ability to accurately predict germination, emergence and establishment.
CVD accounted for 27 % of all deaths in the UK in 2014, and was responsible for 1·7 million hospital admissions in 2013/2014. This condition becomes increasingly prevalent with age, affecting 34·1 and 29·8 % of males and females over 75 years of age respectively in 2011. The dysregulation of cholesterol metabolism with age, often observed as a rise in LDL-cholesterol, has been associated with the pathogenesis of CVD. To compound this problem, it is estimated by 2050, 22 % of the world's population will be over 60 years of age, in culmination with a growing resistance and intolerance to pre-existing cholesterol regulating drugs such as statins. Therefore, it is apparent research into additional therapies for hypercholesterolaemia and CVD prevention is a growing necessity. However, it is also imperative to recognise this complex biological system cannot be studied using a reductionist approach; rather its biological uniqueness necessitates a more integrated methodology, such as that offered by systems biology. In this review, we firstly discuss cholesterol metabolism and how it is affected by diet and the ageing process. Next, we describe therapeutic strategies for hypercholesterolaemia, and finally how the systems biology paradigm can be utilised to investigate how ageing interacts with complex systems such as cholesterol metabolism. We conclude by emphasising the need for nutritionists to work in parallel with the systems biology community, to develop novel approaches to studying cholesterol metabolism and its interaction with ageing.
We sought to determine the frequency with which hospice and palliative social workers encounter patients, family caregivers, and other clients at risk of suicide, and to discover the extent to which hospice and palliative social workers feel prepared to address issues related to suicide in their professional practice.
We conducted a cross-sectional survey of hospice and palliative social workers, recruiting a convenience sample of volunteer respondents through advertisements at professional conferences and listservs, and via social media accounts associated with national organizations, state hospice and palliative care associations, and individual healthcare professionals.
Most respondents reported having worked with patients, family caregivers, or other clients who had exhibited warning signs of suicide during the previous year. Fewer respondents indicated that they had worked with patients and family members who had attempted or died by suicide. While the majority of respondents believed they possessed sufficient knowledge and skills to intervene effectively with individuals at risk of suicide, they indicated that additional education on this topic would be valuable for their professional practice.
Significance of results:
These study results suggest that suicide-related competencies are important in the practice of hospice and palliative social work. Future education and training efforts should include skill development in addition to knowledge building.
The benefits of reduced and zero-tillage systems have been presented as reducing runoff, enhancing water retention and preventing soil erosion. There is also general agreement that the practice can conserve and enhance soil organic carbon (C) levels to some extent. However, their applicability in mitigating climate change has been debated extensively, especially when the whole profile of C in the soil is considered, along with a reported risk of enhanced nitrous oxide (N2O) emissions. The current paper presents a meta-analysis of existing literature to ascertain the climate change mitigation opportunities offered by minimizing tillage operations. Research suggests zero tillage is effective in sequestering C in both soil surface and sub-soil layers in tropical and temperate conditions. The C sequestration rate in tropical soils can be about five times higher than in temperate soils. In tropical soils, C accumulation is generally correlated with the duration of tillage. Reduced N2O emissions under long-term zero tillage have been reported in the literature but significant variability exists in the N2O flux information. Long-term, location-specific studies are needed urgently to determine the precise role of zero tillage in driving N2O fluxes. Considering the wide variety of crops utilized in zero-tillage studies, for example maize, barley, soybean and winter wheat, only soybean has been reported to show an increase in yield with zero tillage (7·7% over 10 years). In several cases yield reductions have been recorded e.g. c. 1–8% over 10 years under winter wheat and barley, respectively, suggesting zero tillage does not bring appreciable changes in yield but that the difference between the two approaches may be small. A key question that remains to be answered is: are any potential reductions in yield acceptable in the quest to mitigate climate change, given the importance of global food security?
Biochar has been reported to improve soil quality and crop yield; however, less is known about its effects on the physical and, in particular, structural properties of soil. This study examines the potential ability of biochar to improve water retention and crop growth through a pot trial using biochar concentrations of 0%, 1·5%, 2·5% and 5% w/w. X-ray computed tomography was used to measure soil structure via pore size characteristics; this showed that pore size is significantly affected by biochar concentration. Increasing biochar is associated with decreasing average pore size, which we hypothesise would impact heavily on hydraulic performance. At the end of the experiment, average pore size had decreased from 0·07 mm2 in the 0% biochar soil to 0·046 mm2 in the 5% biochar soil. Increased biochar concentration also significantly decreases saturated hydraulic conductivity and soil bulk density. It was also observed that increased biochar significantly decreases soil water repellency. Increased water retention was also observed at low matric potentials, where it was shown that increased biochar is able to retain more water as the soil dried out. The application of biochar had little effect on short-term (<10 weeks) wheat growth, but did improve water retention through a change in soil porosity, pore size, bulk density and wetting ability.
We consider a class of convex non-linear boundary value problems of the form
where L is a linear, uniformly elliptic, self-adjoint differential expression, f is a given non-linear function, B is a boundary differential expression of either Dirichlet or Neumann type and D is a bounded open domain with boundary ∂D. Particular problems of this class arise in the process of thermal combustion .
In this paper we show that stable solutions of this class can be bounded from below (above) by a monotonically increasing (decreasing) sequence of Newton (Picard) iterates. The possibility of using these schemes to construct unstable solutions is also considered.
The mechanical properties of alginate hydrogels are critical to their successful use in tissue engineering. We hypothesized that combining alginates of differing molecular weights would allow one to readily control and decouple the viscosity of the pre-gel solution from the post-gel stiffness. To test this, binary hydrogels were prepared by incorporating low molecular weight (MW) alginate (Mn ~ 3.3 x 104 g/mol) into 1 %(w/w) alginate solutions composed of high MW alginate (Mn ~ 2.2 x 105 g/mol). The addition of low MW alginate had minimal effects on the solution viscosity, allowing high solids loading in the solution while maintaining a workable solution. However, the increased mass loading resulted in much higher stiffness gels following ionic cross-linking with calcium. These data may be interpreted in relation to the microstructure of the solution versus hydrogel.
The strain relaxation and threading dislocation density of He-implanted and annealed SiGe/Si heterostructures have been studied. For He doses above a threshold of 8×1015 cm−2, the degree of strain relaxation depends primarily on the SiGe layer thickness; a similar degree of strain relaxation is obtained when the He dose and energy are varied over a relatively wide range. In contrast, the threading dislocation density is strongly influenced by the implantation depth. There is a strong correlation between the parameter He(SiGe), the He dose in the SiGe layer calculated from He profiles simulated using the program Stopping and Range of Ions in Matter (SRIM), and the threading dislocation density. We find that to achieve a low threading dislocation density, <5×107 cm−2, He(SiGe) must be less than 1015 cm−2. The strain relaxation mechanism is also discussed.
Growth factor delivery using polymer matrices is one exciting approach to replace or regenerate tissues. Most growth factor delivery systems, however, have been designed to operate under static conditions, regardless of dynamic environments in the body. Considering the dynamic environment of our body (e.g., bone, muscle, and blood vessel), mechanical stimulation is an important signal that could be readily exploited. We hypothesize that polymer matrices, which release growth factors in response to mechanical stimulation, could provide a novel approach to engineer tissues in mechanically stressed environments. We report here a model system, comprised of alginate hydrogel and vascular endothelial growth factor (VEGF), which upregulates the release of the growth factor in response to mechanical stimulation and subsequently promotes granulation tissue formation in animals. This approach may find a number of potential applications in tissue engineering, as well as in drug delivery.
Thick films of high-temperature superconductors have been deposited electrophoretically using techniques developed for office copier toning. The resultant films are dense because of the high charge density per particle and the high fields during deposition. Orientation by electrostatic and magnetic fields has been demonstrated.
A series of PtSi on p-type Si diodes have been characterized in order to establish correlations among processing parameters, metallurgical features and electrical properties. Characterization techniques include analytical (TED, TEM), electrical (current-voltage characteristics), and optical (photoemission and absorption). The fabrication techniques involve e-beam evaporation of platinum layers at UHV levels onto VLSI grade (100) p-type silicon substrates. The silicide layers are formed via sub-eutectic solid state diffusion at 350°C. The main trends with thickness as well as possible interrelationships are described. An unexpected result is the presence of unreacted polycrystalline Pt and Pt2Si at the interface.
A computer program is developed using the classical oscillator model of Hans W. Verleur  to study the transmittance and reflectance spectra of pre- and post radiation damaged optical components such as color glass filters, multilayer bandpass filters and band reject filters irradiated by one megárad gamma radiation from a 60Co source. In the classical oscillator model, the complex dielectric constant ε(ω) is represented as the sum of classical oscillators with oscillator strength Si, resonance frequency ωi, linewidth Γi and high frequency dielectric constant ε∞ which are the adjustable parameters to fit the experimental transmittance and reflectance data over a limited range of frequency. The parameters have physical significance in the lattice vibrational region. In the spectral regions corresponding to electronic transitions, the spectra can be fitted accurately with no physical meaning associated with the parameters. The present work has concentrated on the calculations of the optical constants n and k of the radiation damaged optical components to determine the effects of 60Co gamma radiation on the optical constants of both films and substrates in these components.
We review three important experimental results which suggest that electron capture and emission by the DX center in AlxGa1-xAs proceeds via an excited intermediate state: the very different dependencies of the thermal capture and emission rates on alloy composition, the exponential dependence of the thermal capture rate on the quasi-equilibrium Fermi energy, and the thermal activation of the hot electron capture rate. None of these results is readily explained by a conventional lattice relaxation model, in which an electron is captured directly from the lowest lying band edge, but each can be simply explained if the dominant channel for multiphonon capture is via a transition state which lies well above the band edge. This picture is consistent with recent pseudopotential calculations which predict that the lattice relaxed state (the DX state) is stabilized by capture of more than one electron, since such a model naturally admits the possibility of an intermediate one-electron state.
Effects of ion bombardment during deposition on the environmental durability of silver coatings have been examined. Films deposited under otherwise identical conditions were bombarded at different levels with 300 eV argon ions. Examination of the environmental durability of coatings revealed that films deposited with ion assisted deposition are more durable than evaporated coatings. Adhesion and scratch resistance of coatings were also improved as a result of ion bombardment.
Optical thin films of nitrides, oxynitrides and oxides of aluminum and silicon were deposited using ion assisted deposition. Coatings were deposited by thermal evaporation of AlN and e-beam evaporation of Si with simultaneous bombardment with 300 eV ions of nitrogen, a mixture of nitrogen and oxygen or oxygen. The chemical composition and the index of refraction of the coating was varied by varying the gas mixture in the ion beam. Optical properties of and environmental stability of coatings were examined. Results indicated that coatings are stable even under severe conditions of humidity and temperature.
Electron density fluctuations associated with microstructural features on a scale from about 1 to 25 nm in glow-discharge-deposited a-Si1-xGex:H films were studied by the technique of small-angle x-ray scattering (SAXS). Films prepared in four different deposition systems (in different laboratories) have been characterized and a general increase in the SAXS signal with increasing x is observed. Density deficiencies determined from film flotation measurements lead to the correlation of the increased scattering intensities with increases in the volume fractions of micro voids. Modeling of the data yields void size distributions that demonstrate significantly more of the larger voids (2 to 6 nm) than found at x=0 (around 1 nm). For the alloys with x>0.4, the scattering at the smallest angles was observed to decrease substantially upon tilting of the sample relative to the x-ray beam. This result contrasts with the small or no changes in SAXS upon tilting device-quality x=0 films. This anisotropie scattering associated with the tilting experiments has been modeled with distributions of ellipsoidal microvoids that are preferentially oriented with their major axes normal to the film plane. This latter result is consistent with a columnar-like microstructure. However, one film with x=0.37 shows no evidence for such microstructure.
Engineering liver tissue using hepatocyte transplantation may provide a new approach for treating a variety of liver diseases. However, techniques to transplant hepatocytes and promote their survival must be developed. We have developed systems to transplant hepatocytes on highly porous (95%), biodegradable sponges, and to regulate the survival of cultured hepatocytes by releasing specific growth factors in the cellular environment. Sponges were fabricated from poly (L, lactic acid) (PLLA) and polyvinyl alcohol using a particulate leaching technique. Epidermal growth factor and insulin, critical factors for hepatocyte growth and survival in culture, were incorporated into microspheres fabricated from poly (lactic-co-glycolic acid) (PLGA) utilizing a double emulsion technique. The incorporated factors were released in a controlled manner over one month in vitro, and the released factors maintained their biological activity, as measured by their ability to promote hepatocyte growth and survival in culture. The growth factor-containing microspheres could be transplanted with hepatocytes using the porous sponges, and the localized, sustained release of these factors improved hepatocyte engraftment 2-fold. These studies suggest that hepatocyte containing tissues can be engineered using cell transplantation, and that regulating the microenvironment of transplanted cells can control their engraftment.
We present an x-ray diffraction study of the variation of the tilt angle between a relaxed Si1−xGex epitaxial layer and the Si (001) substrate. Such measurements provide the basis for a new method to determine the nucleation activation energy of misfit dislocations. We show that the nucleation activation energy for 60° dislocations in the case of the multiplication mechanism observed in graded SiGe layers grown by UHV-CVD at low temperature is 4 eV.