Quantum and Classical in Adiabatic Computation

Adiabatic transport provides a powerful way to manipulate quantum states. By preparing a system in a readily initialised state and then slowly changing its Hamiltonian, one may achieve quantum states that would otherwise be inaccessible. Moreover, a judicious choice of final Hamiltonian whose groundstate encodes the solution to a problem allows adiabatic transport to be used for universal quantum computation. However, the dephasing effects of the environment limit the quantum correlations that an open system can support and degrade the power of such adiabatic computation. We quantify this effect by allowing the system to evolve over a restricted set of quantum states, providing a link between physically inspired classical optimisation algorithms and quantum adiabatic optimisation. This new perspective allows us to develop benchmarks to bound the quantum correlations harnessed by an adiabatic computation. We apply these to the D-Wave Vesuvius machine with revealing - though inconclusive - results

Influence of Y2O3 addition on the mechanical and oxidation behaviour of carbon fibre reinforced ZrB2/SiC composites

The influence of Y2O3 addition on the microstructure, thermo-mechanical properties and oxidation resistance of carbon fibre reinforced ZrB2/SiC composites was investigated. Y2O3 reacted with oxide impurities present on the surface of ZrB2 and SiC grains and formed a liquid phase, effectively lowering the sintering temperature and allowing to reach full density at 1900 °C. The presence of a carbon source (fibres) led to additional reactions which resulted in the formation of new secondary phases such as yttrium boro-carbides. Mechanical properties were significantly enhanced compared to the un-doped composite. Further tests at high temperatures resulted in strength increase up to 700 MPa at 1500 °C which was attributed to stress relaxation. Oxidation tests carried out at 1500 °C and 1650 °C in air showed that the presence of the Y-based secondary phases enhanced the growth of ZrO2 grains, but offered limited protection to oxygen due to the lower availability of surficial SiO2 formed from SiC

Toughening effect of non-periodic fiber distribution on crack propagation energy of UHTC composites

Different configurations of continuous carbon fiber-reinforced ultrahigh temperature ceramics (UHTCs), by combining coatings and matrix, were produced via electrophoretic deposition (EPD) and slurry infiltration. The toughening of non-periodic fiber distribution induced by the EPD process was investigated through work of fracture analysis. The results show that a non-periodic fiber distribution results in toughness increase from 8 MPa√m to 11 MPa√m with respect to a periodic fiber distribution. This toughness improvement does not strongly affect the flexural strength, which is mainly related to the fiber volumetric amount. It is shown that the assembling of carbon fibers into bundles (i.e. by dispersing the fibers with a non-periodic distribution) increases the crack propagation energy dissipated on the crack-wake from 0.5 kJ/m2 to 1 kJ/m2, which can be mainly ascribed to the fiber/bundle pull-out. On the other hand, the energy dissipated on the crack-tip (as fiber/matrix debonding) is fiber distribution-independent and increases from 0.3 kJ/m2 to 0.4 kJ/m2 with increasing the fiber amount from 33 vol% to 40 vol%. Finally, WoF analysis is proposed as test to evaluate pull-out toughening instead of push-in and push-out tests

Development of UHTCMCs via water based ZrB2 powder slurry infiltration and polymer infiltration and pyrolysis

Cf/ZrB2-SiC ultra-high temperature composites were manufactured via aqueous slurry impregnation coupled with polymer infiltration and pyrolysis, using a allylhydrido polycarbosilane precursor. For the first time we used ultra-high modulus pitch-based carbon fibres for the PIP process, investigating three different architectures, 0/0°, 0/90°, and 2D. Microstructure, mechanical properties and oxidation resistance in air at 1650 °C were investigated. As expected, the mechanical properties showed the tendency to decrease with increase of the preforms complexity, due to the higher amount of flaws and residual stresses. For instance, the flexural strength was approaching 500 MPa for 0/0°, 370 MPa for 0/90° and 190 MPa for 2D. The materials showed an optimal resistance to oxidation at 1650 °C thanks to formation of a viscous borosilicate glass that guaranteed a self-healing functionality

Reactive melt infiltration of carbon fibre reinforced ZrB2/B composites with Zr2Cu

The microstructure and mechanical properties of carbon fibre reinforced ZrB2 composites produced by slurry infiltration and consolidated by reactive melt infiltration were investigated. Fibres were preliminary infiltrated with ZrB2/B slurries with varying ZrB2/B ratios. Then the composites were infiltrated with Zr2Cu melt at 1200 °C under vacuum. Boron was chosen as the reactant phase, while raw ZrB2 was added as a filler to prevent excessive swelling. With increase of boron content the infiltration becomes more difficult due to the reaction of alloy and boron. The boron is completely converted to nano ZrB2 grains. Some ZrC is produced from the side reaction between Zr2Cu and the carbon fibre, resulting in reduction of fibre diameter. The flexural strength increased from 360 to 560 MPa with the increase of boron content, while KIc amounted to 10 MPa⋅m0.5 but was affected by large scatter. The mechanical behaviour was mostly dominated by matrix properties

Effect of PAN-based and pitch-based carbon fibres on microstructure and properties of continuous Cf/ZrB2-SiC UHTCMCs

In this paper the microstructure and mechanical properties of two different Cf/ZrB2-SiC composites reinforced with continuous PyC coated PAN-derived fibres or uncoated pitch-derived fibres were compared. Pitch-derived carbon fibres showed a lower degree of reaction with the matrix phase during sintering compared to PyC/PAN-derived fibres. The reason lies in the different microstructure of the carbon. The presence of a coating for PAN-derived fibres was found to be essential to limit the reaction at the fibre/matrix interface during SPS. However, coated bundles were more difficult to infiltrate, resulting in a less homogeneous microstructure. As far as the mechanical properties are concerned, specimens reinforced with coated PAN-derived fibres provided higher strengths and damage tolerance than uncoated pitch-derived fibres, due to the higher degree of fibre pull-out. On the other hand, the weaker fibre/matrix interface resulted in lower interlaminar shear, off-axis strength and ablation resistance

Fertilisation with compost mitigates salt stress in tomato by affecting plant metabolomics and nutritional profiles

Background: Salinity is one of the major threats for crop growth and yield and its rate of expansion is expected to increase. We conducted a pot experiment to evaluate and compare the effect of a green compost addition and mineral fertilisation, on growth, nutrition and metabolites of tomato plants, exposed to increasing doses of NaCl. Results: Although the development of stressed plants was lower than the corresponding controls, compost-treated plants performed better than mineral-amended plants watered with the same amount of salt. The different plant growth was related to an increased nutritional status. Namely, compost-treated plants showed a larger content of macro- and micronutrients, and a greater accumulation of osmoprotectants, such as soluble sugars and amino acids. Moreover, compost-treated plants showed a larger content of metabolites involved in modulating the response to salt stress, such as molecules related to energy transfer in plants and precursors of Reactive Oxygen Species scavenging compounds. Overall, the better performance of compost-added plants may be attributed to a greater availability of the organic forms of nutrients and to the positive bioactivity of compost-derived humic substances. Conclusions: Compost application efficiently mitigated salt stress in tomato plants in respect to mineral fertilisation. This alleviating role was associated to the induction of a more efficient metabolic response that increased accumulation of metabolites involved in modulating the salinity stress. Therefore, fertilising with composted agricultural residue may represent a convenient alternative to mineral fertilisers to grow tomato plants in the presence of salt stres

Cognitive Impairment and Age-Related Vision Disorders: Their Possible Relationship and the Evaluation of the Use of Aspirin and Statins in a 65 Years-and-Over Sardinian Population

Neurological disorders (Alzheimer’s disease, vascular and mixed dementia) and visual loss (cataract, age-related macular degeneration, glaucoma, and diabetic retinopathy) are among the most common conditions that afflict people of at least 65 years of age. An increasing body of evidence is emerging, which demonstrates that memory and vision impairment are closely, significantly, and positively linked and that statins and aspirin may lessen the risk of developing age-related visual and neurological problems. However, clinical studies have produced contradictory results. Thus, the intent of the present study was to reliably establish whether a relationship exist between various types of dementia and age-related vision disorders, and to establish whether statins and aspirin may or may not have beneficial effects on these two types of disorders. We found that participants with dementia and/or vision problems were more likely to be depressed and displayed worse functional ability in basic and instrumental activities of daily living than controls. Mini mental state examination scores were significantly lower in patients with vision disorders compared to subjects without vision disorders. A closer association with macular degeneration was found in subjects with Alzheimer’s disease than in subjects without dementia or with vascular dementia, mixed dementia, or other types of age-related vision disorders. When we considered the associations between different types of dementia and vision disorders and the use of statins and aspirin, we found a significant positive association between Alzheimer’s disease and statins on their own or in combination with aspirin, indicating that these two drugs do not appear to reduce the risk of Alzheimer’s disease or improve its clinical evolution and may, on the contrary, favor its development. No significant association in statin use alone, aspirin use alone, or the combination of these was found in subjects without vision disorders but with dementia, and, similarly, none in subjects with vision disorders but without dementia. Overall, these results confirm the general impression so far; namely, that macular degeneration may contribute to cognitive disorders (Alzheimer’s disease in particular). In addition, they also suggest that, while statin and aspirin use may undoubtedly have some protective effects, they do not appear to be magic pills against the development of cognitive impairment or vision disorders in the elderly

Is spark plasma sintering suitable for the densification of continuous carbon fibre - UHTCMCs?

For the first time we show that spark plasma sintering can efficiently replace hot pressing for the densification of UHTCMCs, in the present case ZrB2/SiC composites reinforced with continuous carbon fibres. To this purpose, the same materials were first produced by hot pressing as baseline samples and then by spark plasma sintering (SPS) to compare microstructure and basic mechanical properties. A special emphasis was given to the study of interfaces, in case of both coated and uncoated carbon fibres. SPS allowed for faster sintering but required an adjustment of the temperature to avoid fibre degradation compared to hot pressing. With similar porosity levels, we observed a slight decrease of flexural strength (300 vs 470 MPa), and an improvement of fracture toughness (15 vs 10 MPa√m) for SPSed samples. SPS was proved to be an effective method for the consolidation of continuous fibre reinforced UHTC composites