Shell (United Kingdom)

In the recent years, lithium-ion batteries have become the battery technology of choice for portable devices, electric vehicles and grid storage. While increasing numbers of car manufacturers are introducing electrified models into their offering, range anxiety and the length of time required to recharge the batteries are still a common concern. The high currents needed to accelerate the charging process have been known to reduce energy efficiency and cause accelerated capacity and power fade. Fast charging is a multiscale problem, therefore insights from atomic to system level are required to understand and improve fast charging performance. The present paper reviews the literature on the physical phenomena that limit battery charging speeds, the degradation mechanisms that commonly result from charging at high currents, and the approaches that have been proposed to address these issues. Special attention is paid to low temperature charging. Alternative fast charging protocols are presented and critically assessed. Safety implications are explored, including the potential influence of fast charging on thermal runaway characteristics. Finally, knowledge gaps are identified and recommendations are made for the direction of future research. The need to develop reliable onboard methods to detect lithium plating and mechanical degradation is highlighted. Robust model-based charging optimisation strategies are identified as key to enabling fast charging in all conditions. Thermal management strategies to both cool batteries during charging and preheat them in cold weather are acknowledged as critical, with a particular focus on techniques capable of achieving high speeds and good temperature homogeneities.

Furfural offers a promising, rich platform for lignocellulosic biofuels. These include methylfuran and methyltetrahydrofuran, valerate esters, ethylfurfuryl and ethyltetrahydrofurfuryl ethers as well as various C(10)-C(15) coupling products. The various production routes are critically reviewed, and the needs for improvements are identified. Their relative industrial potential is analysed by defining an investment index and CO(2) emissions as well as determining the fuel properties for the resulting products. Finally, the most promising candidate, 2-methylfuran, was subjected to a road trial of 90,000 km in a gasoline blend. Importantly, the potential of the furfural platform relies heavily on the cost-competitive production of furfural from lignocellulosic feedstock. Conventional standalone and emerging coproduct processes-for example, as a coproduct of cellulosic ethanol, levulinic acid or hydroxymethyl furfural-are expensive and energetically demanding. Challenges and areas that need improvement are highlighted. In addition to providing a critical review of the literature, this paper also presents new results and analysis in this area.

Fully decarbonizing global industry is essential to achieving climate stabilization, and reaching net zero greenhouse gas emissions by 2050–2070 is necessary to limit global warming to 2 °C. This paper assembles and evaluates technical and policy interventions, both on the supply side and on the demand side. It identifies measures that, employed together, can achieve net zero industrial emissions in the required timeframe. Key supply-side technologies include energy efficiency (especially at the system level), carbon capture, electrification, and zero-carbon hydrogen as a heat source and chemical feedstock. There are also promising technologies specific to each of the three top-emitting industries: cement, iron & steel, and chemicals & plastics. These include cement admixtures and alternative chemistries, several technological routes for zero-carbon steelmaking, and novel chemical catalysts and separation technologies. Crucial demand-side approaches include material-efficient design, reductions in material waste, substituting low-carbon for high-carbon materials, and circular economy interventions (such as improving product longevity, reusability, ease of refurbishment, and recyclability). Strategic, well-designed policy can accelerate innovation and provide incentives for technology deployment. High-value policies include carbon pricing with border adjustments or other price signals; robust government support for research, development, and deployment; and energy efficiency or emissions standards. These core policies should be supported by labeling and government procurement of low-carbon products, data collection and disclosure requirements, and recycling incentives. In implementing these policies, care must be taken to ensure a just transition for displaced workers and affected communities. Similarly, decarbonization must complement the human and economic development of low- and middle-income countries.

Fueling the future: Valeric esters can be produced by acid hydrolysis of lignocellulose to levulinic acid, followed by hydrogenation to valeric acid and its subsequent esterification (see scheme). Valeric biofuels are fully compatible for blending with gasoline or diesel, and have passed a road trial of 250 000 km. At the beginning of the 21st century mankind is facing an energy challenge as a consequence of the world’s increasing energy demand, the depletion of “easy” oil and gas fields, and the impact of CO2 emissions on the Earth’s climate (“three hard truths”).1 Much research is therefore being devoted to the exploration and development of new, carbon-lean energy sources. These include biofuels, which are the most promising option for the transportation sector in the coming decades.2 The first generation of biofuels is presently produced from sugars, starches, and vegetable oil. Although instrumental in developing the market, these biofuels are not likely to deliver the large volumes needed for the transport sector because they directly compete with food for their feedstock. A more promising feedstock is lignocellulosic material, which is more abundant, has a lower cost, and is potentially more sustainable.3 Lignocellulose is recalcitrant and, therefore, requires complex and expensive processes for upgrading to biofuels.4 Interestingly, it has been claimed that levulinic acid (LA) can be easily and cheaply produced from lignocellulosic materials by using a simple and robust hydrolysis process.5 Several LA derivatives have been proposed for fuel applications, for instance ethyl levulinate (EL), γ-valerolactone (gVL), and methyl tetrahydrofuran (MTHF).5, 6 However, these components do not exhibit satisfactory properties when blended in current fuels. Herein, we present a new platform of LA derivatives, the “valeric biofuels”, which we have been developing since 2004 and which can deliver both gasoline and diesel components that are fully compatible with transportation fuels. The manufacture of valeric biofuels (Scheme 1) consists of the acid hydrolysis of lignocellulosic materials to LA, the hydrogenation of the acid to gVL and valeric acid (VA), and finally esterification to alkyl (mono/di)valerate esters. One of these steps, the hydrogenation of gVL to VA (Scheme 1, step 3), has not been reported in the literature and was developed in our laboratory. All the other steps are known but were nevertheless revisited and, wherever possible, improved. This holds for the acid-catalyzed hydrolysis of lignocellulose to LA,5, 7 the hydrogenation of LA to gVL with the use of supported metal catalysts,8 as well as the familiar esterification of carboxylic acids. Herein, we present the main results of the hydrogenation of gVL to VA (Scheme 1, step 3), key improvements in the hydrogenation of LA to gVL (step 2), options for integrating steps 2–4, and finally a thorough evaluation of the fuel performance of the resulting valeric biofuels. Details of the experimental procedures and secondary results are available in the Supporting Information. Platform of valeric biofuels: reaction scheme and key performance factors for the individual process steps (selectivity [mol %], productivity [tproduct m−3reactor h−1], and concentration [wt %]). EV: ethyl valerate; EG: ethylene glycol; PG: propylene glycol; IER: acidic ion-exchange resin. gVL is a relatively stable product under hydrogenation conditions. It was, nevertheless, hydrogenated to VA in the presence of bifunctional catalysts that contain both hydrogenation and acidic functions. An evaluation of about 150 catalysts in a continuous high-pressure plug-flow reactor identified Pt-loaded SiO2-bound H-ZSM-5 as a very effective catalyst (Figure 1 a). However, good yields were also achieved with other zeolites and hydrogenation metals. Promising zeolites included the small-pore TON, the medium-pore PSH-3 (also called MCM-22), and the large-pore mordenite and Beta. The acidic zeolites can be replaced by other strong or weak solid acids, such as W/ZrO2 and amorphous silica–alumina (ASA). Clearly, the conversion of gVL to VA is not very demanding in terms of “shape selectivity” or acid strength. Pt, Pd, and Rh from among the noble metals are all particularly active; however, Rh was not desirable because it co-produced significant amounts of gas. Alloying Pt or Pd with other noble metals did not deliver measurable improvements. Conversion of gVL to VA over Pt/H-ZSM-5/SiO2 catalysts. a) Conversion and selectivity; b) long-term operation with multiple regeneration by hot H2 strips at 10 bar H2 and 400 °C (0.7 % metal loading; run conditions: 250 °C, 10 bar, H2/gVL molar ratio 9:1, weight hourly space velocity (WHSV)=2 h). C5−: C1–C4 hydrocarbons, PV: pentyl valerate, PeOH: 1-pentanol. The reaction mechanism of step 3 (Scheme 1) is believed to proceed by acid-catalyzed ring opening of gVL to pentenoic acid and subsequent hydrogenation to VA (Scheme 2). The production of VA requires a balancing of the acidic and hydrogenation functionalities of the catalyst: changing the metal/zeolite ratio either increases the co-production of pentenoic acid (low metal loading) or favors the formation of MTHF, pentanal/pentanol, and/or pentane/butane (high metal loading). Pentyl valerate (PV) was observed as a minor co-product (Figure 1 a) and is likely to have formed by the esterification of VA with an over-hydrogenation product, such as 1-pentanol or MTHF. For instance, co-feeding MTHF to the gVL feed resulted in a significant increase in PV production. Probable reaction mechanism for the conversion of gVL to VA over bifunctional catalysts. Catalyst extrudates of Pt/ZSM-5 bound with SiO2 (1.6 mm diameter) were operated with high activity (differential VA productivity of approximately 2 gVA gcat−1 h−1) and high selectivity (>90 mol %). This performance could be maintained for more than 1500 h with intermittent catalyst regeneration under hot H2 and/or airflow at 400 °C (Figure 1 b). Once unloaded, the spent catalyst showed marginal loss of Pt and Al (from the zeolite framework), marginal decrease in support surface area, and no measurable loss of mechanical strength of the catalyst extrudates. Pt/ASA catalysts were also very promising candidates. Although they had a lower initial activity, they showed no sign of deactivation over runs of 200–300 h. Their stability is tentatively attributed to their weaker acidity, which may facilitate the desorption of reactive intermediates, such as pentenoic acid, and thereby depress their tendency to form oligomeric deposits that poison the catalyst surface. The literature available on the hydrogenation of LA to gVL (Scheme 1, step 2) provides no information on the long-term stability of the catalysts or their resistance to leaching when operating in liquid LA.8 These issues were addressed through leaching tests of various supports, catalyst evaluation over >100 h, and analysis of spent catalyst samples. Carbon supports are known to resist aggressive aqueous media but do not survive frequent regeneration by coke burn-off. Preference was therefore given to SiO2, TiO2, and ZrO2 supports, which are stable to “decoking” conditions and appeared to retain their integrity after a week’s exposure to hot carboxylic acid (LA or VA). This contrasts with other oxidic materials (e.g., alumina, silica–alumina, and oxides of magnesium, barium, and antimony) that are leached or even dissolve under these conditions. Evaluation of some 50 catalysts showed the best performance was with Pt supported on TiO2 or ZrO2: LA was hydrogenated with high activity (differential productivity 10 ggVL gcat−1 h−1), high selectivity to gVL (>95 mol %), and marginal deactivation over 100 h (Figure 2). The main by-products, VA and MTHF, were formed with <0.5 mol % selectivity. Carbon and SiO2 supports provided a tenth of the activity observed with TiO2 and ZrO2 supports (see the Supporting Information). Pd-based catalysts also showed a much lower activity and selectivity than their Pt counterparts. Alloying the Pt with other noble metals did not improve catalytic performance (see the Supporting Information). Finally, the resistance to leaching was further confirmed by X-ray photoelectron spectroscopy analyses of spent Pt/TiO2 and PtRe/ZrO2 catalysts, which showed no significant decrease of Pt/Ti or Pt/Re/Zr ratios, and thereby no significant loss or sintering of active metal. Hydrogenation of LA to gVL over Pt/TiO2 (1 wt % metal, 200 °C, 40 bar H2, H2/LA molar ratio 5:1, WHSV=9 h). The four-step process discussed so far provides flexibility and robustness, which are invaluable in work toward deploying a novel technology. However, options for future cost reductions through process integrations have additionally been identified; for example, combining the LA and VA hydrogenation steps with the possibility of even integrating the esterification step. These schemes are described in the Supporting Information; however, one of them is worth presenting here. This is the single-step conversion of gVL to PV, which is a promising diesel component (see below). PV was indeed produced with 20–50 % selectivity upon passing gVL over Pt or Pd/TiO2 catalysts at 275–300 °C (see the Supporting Information). Pt-based catalysts tend to provide higher PV/VA ratios but also produce more undesired light hydrocarbons. VA can be recycled to the reactor for further conversion to PV. Note that PV can also be co-produced over bifunctional VA catalysts (e.g., Pt/ZSM-5) upon increasing the hydrogenation activity to produce more MTHF and/or pentanal, and recycling these co-products over the reactor for upgrading to PV. Beyond developing the manufacturing route, we also carried out a thorough study of the fuel properties of the “valeric biofuels”. In a first step, we focused on their compatibility with current fuels. The components that fail on these criteria would require modifications of vehicles and/or the distribution network and would, therefore, suffer from a slow and costly deployment. Fuel compatibility was assessed against a few basic properties such as polarity, (volumetric) energy content, boiling point, and ignition indices, for example octane or cetane number (CN) for gasoline and diesel, respectively (Figure 3). The components that successfully passed this screening were then evaluated against additional properties, such as oxidation stability, fouling tendency, corrosion, lubricity, water affinity, and response to conventional fuel additives. Screening parameters for fuel performance (MV, EV, PrV, and PV: methyl, ethyl, propyl, and pentyl valerates, respectively). The blending research octane number (BRON) values of PrV, PV, and fatty acid methyl ester (FAME) are estimated from a CN–RON correlation;10 gray shading represents the property windows of hydrocarbon fuels. Valeric biofuels passed all these tests (Figure 3). They have acceptable energy densities and more appropriate polarities than current and alternative candidate biofuels (ethanol, n-butanol, EL, gVL, and MTHF). Their volatility–ignition properties make them compatible for either gasoline or diesel applications, depending on their alkyl chain length. For example, regular gasoline splash blended with ethyl valerate (EV) at 10 and 20 vol % still meets the research (RON) and motor octane number (MON) specification for European gasoline (EN 228; see the Supporting Information). The relatively low polarity of EV makes it less sensitive to elastomer swell or water pickup than EtOH or EL (Figure 4). EV also offers the advantages of a higher energy density and lower blending volatility (dry vapor pressure equivalent, DVPE) than EtOH. This eliminates the need to remove light hydrocarbons from the base fuel prior to introducing the biocomponent. Interestingly, ethyl pentenoate (EP), which is readily produced from gVL,9 is also a promising gasoline component; it presented better octane properties than its saturated analogue EV without showing detrimental effects on other properties. Fuel performance of EV, ethanol (EtOH), and EL blended at 5 % in gasoline (the water affinity is measured for neat biofuel). RVP: Reid vapor pressure. Heavier esters, such as butyl and pentyl valerates, showed polarity, volatility, and ignition properties that are suitable for diesel (Figure 3). PV has better volatility and cold-flow property match with diesel than FAME. However, this is at the cost of a lower energy density. Di- and trivalerates, which can be produced by esterifying VA with ethylene and propylene glycols as well as glycerol, are compatible with diesel with respect to solubility and volatility. However, their modest cetane properties become limiting to the blend ratio at which they can be used in diesel. All these heavy valerate esters are soluble in diesel to high concentrations, a feature that does not apply to heavy levulinates (e.g., pentyl levulinate, PL). Valerate esters, such as FAME, provide lubricity benefits to diesel. The fuel evaluation was complemented by a road trial run on a blend of 15 vol % EV in regular gasoline. The trial was based on ten vehicles (both new and used cars) that are representative of current market technologies. Mileage was accumulated by contract drivers who followed a mixed driving pattern (500 km day−1) for a cumulative distance of 250 000 km. Attention was paid to exhaust emissions, performance, drivability, oil quality, status of engine and fuel lines, and information from the engine management system (see the Supporting Information). The presence of EV in gasoline showed no measurable impact on engine wear, oil degradation, vehicle durability, engine deposits, or regulated tailpipe emissions (EURO 4 and 5 specifications). Some power benefits were realized as a result of the good octane properties of EV. However, the lower energy density did result in a small loss in volumetric fuel economy compared to nonoxygenated gasoline. The 15 vol % EV blend was stable over the four-month period of the test and had no negative impact on the fuel storage and dispensing equipment (tanks, pipes, pumps, and filters). In summary, valeric esters represent a new class of cellulosic biofuels that can outperform previously identified candidate molecules in terms of both their manufacture and fuel properties. The initial production step, LA manufacture, is simple and robust. However, it is the advance in the conversion of LA to VA that has opened up the complete manufacturing process. The valeric platform potentially offers cellulosic biofuels that can be used as components in both gasoline and diesel up to high blend ratios. Note added upon revision: The potential of LA and gVL as intermediates for biofuel manufacture is further confirmed by a paper that appeared during revision of this communication. It reports the conversion of gVL to kerosene- and diesel-range hydrocarbons through decarboxylation to butenes and subsequent butene oligomerization.11 The catalysts were prepared by incipient wetness impregnation of various supports with soluble salts of noble metals, followed by drying at 120 °C and calcination at approximately 450 °C. The supports were commercial extrudates, where available, or based on commercial powders that were extruded in our laboratory. The catalytic tests were carried out in high-pressure steel or Hastelloy reactors equipped with liquid feed pumps, gas manifold, and cold gas–liquid product separators. The catalysts were loaded either as full extrudates or as 0.2–0.5 mm crushed particles, diluted with inert particles of SiC. The catalysts were reduced under H2 flow at atmospheric pressure and 300 °C prior to operation. The liquid product was collected and analyzed off-line by means of gas chromatography. The gaseous products were analyzed on-line by gas chromatography. More details of the procedures are reported in the Supporting Information. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Educational research is not very influential, useful, or well funded. This article explores why and suggests ways that the situation could be improved. Our focus is on the processes that link the development of good ideas and insights, the development of tools and structures for implementation, and the enabling of robust implementation in realistic practice. We suggest that educational research and development should be restructured so as to be more useful to practitioners and to policymakers, allowing the latter to make better-informed, less-speculative decisions that will improve practice more reliably.

The salt 1ṁ4PF6·3CH3CN is a new type of host molecule, which shows similarities to zeolites but is constructed from organic and inorganic ions. The macrocyclic tetracation 1 can be prepared in two steps from bipyridine and 1,4-bis(bromomethyl)benzene. Calculations and X-ray crystallography showed the tetracation to have a box-like structure in which the p-phenylene and paraquat units are slightly bent. The PF-salt of 1 is soluble in organic solvents, the Cl⊖ salt in water. 1·4PF6 in acetonitrile forms weak inclusion complexes with dimethoxybenzenes, which are stabilized by charge-transfer interactions. Structural studies of the inclusion complexes show that the electron-rich guest molecules are located in the cavities (2); because of the stapling of the alternating tetraction and anion/neutral molecule layers these cavities take the form of channels.

Battery thermal management systems are critical for high performance electric vehicles, where the ability to remove heat and homogenise temperature distributions in single cells and packs are key considerations. Immersion cooling, which submerges the battery in a dielectric fluid, has the potential of increasing the rate of heat transfer by 10,000 times relative to passive air cooling. In 2-phase systems, this performance increase is achieved through the latent heat of evaporation of the liquid-to-gas phase transition and the resulting turbulent 2-phase fluid flow. However, 2-phase systems require additional system complexity, and single-phase direct contact immersion cooling can still offer up to 1,000 times improvements in heat transfer over air cooled systems. Fluids which have been considered include: hydrofluoroethers, mineral oils, esters and water-glycol mixtures. This review therefore presents the current state-of-the-art in immersion cooling of lithium-ion batteries, discussing the performance implications of immersion cooling but also identifying gaps in the literature which include a lack of studies considering the lifetime, fluid stability, material compatibility, understanding around sustainability and use of immersion for battery safety. Insights from this review will therefore help researchers and developers, from academia and industry, towards creating higher power, safer and more durable electric vehicles.

Abstract The success or otherwise of catalyst preparation or modification depends on the availability of suitable characterization techniques to determine the condition of the catalyst. There are many techniques available for this purpose including x-ray powder diffraction, electron microscopy, photoelectron spectroscopy, and infrared spectroscopy. However, none of these techniques has proved to be wholly reliable or generally applicable to the characterization of catalysts under working conditions.

Abstract The lift-off heights and visible-flame lengths of jet diffusion flames in still air have been determined for hydrogen, propane, methane and ethylene. The flame lift-off height varies linearly with the jet exit velocity and is independent of the burner diameter for a given gas. The results support the assumption that if the burner exit flow is choked the burner can be approximated by an equivalent convergent-divergent nozzle at whose exit the flow has expanded to ambient pressure. The data for different gases can be collapsed onto a single curve if they are plotted in terms of the appropriate non-dimensional groupings. These results and previous results for blow-out stability suggest that diffusion flames blow out when the base is lifted to between 0.65 and 0.75 times the height at which stoichiometric concentration is reached at the jet axis. It can be deduced from the experimental results that, at the base of the flame. the ratio of turbulent burning velocity to laminar burning velocity varies as the square root of the local turbulence Reynolds number based on the integral length scale. The predicted correlation for the turbulent burning velocity agrees well with the experimental data presented in the literature. The flame length results for different gases and burner diameters can be collapsed onto a single curve if plotted in terms of the non-dimensional groupings suggested by Becker and Liang (Combust. Flame. 32, p. 115, 1978). The results near the forced convection limit are in line with the theoretical work presented by Becker and Liang but disagree with their final recommendation. Away from the forced convection limit, the flame length correlation is similar to that proposed by Becker and Liang.

A double-blind, randomised, placebo-controlled 8-week study was conducted to evaluate the efficacy and safety of gabapentin in the treatment of neuropathic pain, using doses up to 2400 mg/day. The study used a novel design that was symptom- rather than syndrome-based; an approach that aimed to reflect the realities of clinical practice. Participants had a wide range of neuropathic pain syndromes, with at least two of the following symptoms: allodynia, burning pain, shooting pain, or hyperalgesia. Patients were randomised to gabapentin (n=153) or placebo (n=152). Gabapentin was given in three divided doses, initially titrated to 900 mg/day over 3 days, followed by two further increases, to a maximum of 2400 mg/day if required by the end of week 5. The primary outcome measure was changed in average daily pain diary score (baseline versus final week). Over the 8 week study, this score decreased (i.e. improved) by 1.5 (21%) in gabapentin treated patients and by 1.0 (14%) in placebo treated patients (P=0.048, rank-based analysis of covariance). Significant differences were shown in favour of gabapentin (P<0.05) for the Clinician and Patient Global Impression of Change, and some domains of the Short Form-McGill Pain Questionnaire. Improvements were also shown in patient-reported outcomes in quality of life, as seen by significant differences in favour of gabapentin in several domains of the Short-Form-36 Health Survey. Gabapentin was well tolerated and the majority of patients completed the study (79 versus 73% for placebo). The most common adverse events were mild to moderate dizziness and somnolence, most of which were transient and occurred during the titration phase. This study shows that gabapentin reduces pain and improves some quality-of-life measures in patients with a wide range of neuropathic pain syndromes.

Abstract A brief historical review has been made of the values assigned to the binding energy of C 1s electrons from hydrocarbon contamination on sample surfaces. The particular energy calibration technique used for each electron spectrometer on which the C 1s determination was made has been identified. There are notable variations in the C 1s electron binding energy for a hydrocarbon contamination layer with respect to the substrate on which it was measured. The possible source and nature of adventitious carbon have been discussed, as have factors which can affect its C 1s binding energy value. Sodium phosphate salts have been used to illustrate the relative merits of using an internal energy reference line rather than the C 1s electrons from the adventitious carbon layers of these salts. Alternative energy referencing techniques, which include deposition of soot from a candle flame and deliberate ‘ in situ ’ condensation of a volatile organic compound onto the sample surface, have been compared with the method under review. Another possible method is the mixing of powdered samples with reference compounds (e.g. graphite). It is concluded that, although the use of C 1s electrons from adventitious carbon layers is often a convenient method of energy referencing, interpretation of binding energy data obtained should be treated with caution.

In a double-blind trial of vitamin D supplements in pregnant Asian women calciferol (ergocalciferol, 1000 IU/day) was administered to 59 women and placebo to 67 controls during the last trimester. The two groups had similar distributions of maternal age, height, parity, number of vegetarians, countries of origin, and sex and gestation of the infants. At entry to the trial maternal serum 25-hydroxy vitamin D (25-OHD) concentrations were low in both treatment and control groups and significantly lower in vegetarians than non-vegetarians. Mothers in the treatment group gained weight faster in the last trimester than those in the control group, and at term they and their infants all had adequate plasma 25-OHD concentrations, Mothers and infants in the control group, however, had low plasma concentrations of 25-OHD and calcium and raised plasma alkaline phosphatase (bone isoenzyme) activity. Five of these infants developed symptomatic hypocalcaemia. Almost twice as many infants in the control group were small for gestational age (29% v 15%), but there were no significant differences between the two groups of infants in antropometric measurements. Infants in the control group, however, had larger fontanelles, suggesting impaired ossification of the skull. Because of the benefits to mothers and infants in the treatment group and the absence of side effects, vitamin D supplements should be given to all pregnant Asian women in the United Kingdom.

&lt;div class="htmlview paragraph"&gt;The auto-ignition or anti-knock quality of a practical fuel is defined by the Octane Index, OI = (1-K)RON + KMON where RON and MON are the Research and Motor Octane numbers and K is a constant depending only on the pressure and temperature variation in the engine. K decreases as the compression temperature in the unburnt gas at a given pressure in the engine decreases and can be negative if this temperature is lower than in the RON test. As spark ignition (SI) engine designers seek higher efficiency knock becomes more likely. Moreover such initiatives - direct injection, higher compression ratios, downsizing and turbocharging - will reduce the unburnt gas temperature for a given pressure and push the value of K downwards. In Europe there is evidence of a monotonic decrease in the average K value from 1987 to 1992. In 37 different Japanese and European cars (34 models) equipped with knock sensors that have been tested K has been found to be negative in most cases. Thus for a given RON, a fuel of &lt;i&gt;lower&lt;/i&gt; MON has &lt;i&gt;higher&lt;/i&gt; OI and will give &lt;i&gt;better&lt;/i&gt; acceleration and higher power in a car equipped with a knock sensor. Such fuels are also the most appropriate for Homogeneous Charge Compression Ignition (HCCI) engines. Current fuel specifications as well as other initiatives like the World Wide Fuels Charter impose restrictions on fuel composition in order to control emissions. However modern engine and catalyst technology is more tolerant of fuel composition than before. Hence such restrictions might not be as important in controlling emissions as they were when they were first proposed especially if other fuel specifications, such as low sulphur, are left in place. Such pressures will force gasolines to become less sensitive and also make it more difficult to attain high RON. This trend is directly opposed to the fuel requirements of future engines. These issues need to be considered jointly by the various stakeholders to align future fuels with the requirements of future engines. The paper is a review of these points.&lt;/div&gt;

While axial capacity is often the governing design criterion with driven piles, the reliability of predictions made by conventional procedures is generally poor. A long-term research program run at Imperial College London in conjunction with Industry, the UK's Health and Safety Executive and Engineering and Physical Sciences Research Council led to the new design recommendations published by Jardine and Chow in 1996. Their procedures offered considerable improvements and have been applied worldwide in many offshore, marine and onshore projects.

Tropical deserts have existed sporodically on our planet from the Precambrian to the Present, and seem not to have been a permanent feature of its surface (Glennie 1987). Depending on their definition, tropical deserts and semi-deserts currently occupy between approximately one fifth and one third of the Earth's land surface, of which only about 4 ~ is covered by that popular concept of what a desert consists of--sand dunes. The remaining area comprises barren rock (both hill and plateau) with a variable cover of sediments transported by ephemeral streams (wadis, arroyos) to form the deposits at the terminal points of these streams. Varying with the ratio of water supply to the annual potential rate of evaporation, those terminal areas may be occupied by desert lakes that are generally of a temporary nature (permanent only if the water is provided from beyond the margins of the desert or is fed by groundwater), and become more saline as they become desiccated. The end product of such a situation is a salina or sabkha (area of sand, silt or clay, commonly encrusted with halite). There is no universally accepted definition of a desert. In its simplest form it can be defined as a barren tract of land over which rainfall is too limited or spasmodic to support vegetation adequately. Very few desert areas are completely devoid of vegetation, and many areas that fall within a desert in terms of average annual rainfall may have an even though sparse cover of plants that have adapted to the relatively arid environment in which they live. In this context, some writers define deserts as areas that have an average upper limit of 250 mm of annual rainfall, even though it may all fall in one storm and rainfall may not recur for several years. Perhaps more important than the rainfall itself is the ratio between it and the potential rate of evaporat ion-the aridity or desiccation factor. This is about 1 : 10 in some parts of the Australian Desert and up to 1:500 in areas of the Sahara (Cooke & Warren 1973). Tropical deserts exist either because the winds that cross their surfaces have a low relative humidity or there are no hills to push the winds up to colder cloud-forming altitudes; the Southwest Monsoon gives torrential rain over the Western Ghats of peninsular India but little over the arid low-lying Rajasthan Desert further to the N. Drawn from the high-pressure area of the Mediterranean Sea, the North African trade winds blow south and southwestward under clear skies, warming as they cross the Sahara, and so becoming capable of absorbing more moisture without condensation. By contrast, the southern hemisphere coastal deserts of the Namib and Atacama are often shrouded in mist but rarely experience rain. Cold deserts also occur in areas of low precipitation but lack a protective cover of vegetation because the moisture necessary for growth is frozen for a large part of the year. Allied to the low temperature, peri-glacial dune fields exist because of adequate supplies of fluvioglacial sediments that are unprotected by vegetation and have a grain size that is suitable for deflation once the summer melt-floods have ceased. Dunes are formed because strong dry winds can transport sand-size particles as a saltation load within a few metres of the land surface (sand storm). Because winds can drive sand over a hard immobile surface faster than over one of loose sand (Bagnold 1941), sand tends to accumulate in areas that are already sand covered. These sand patches grow in size whenever the velocity of the wind lessens and is no longer capable of keeping the grains in motion; dunes eventually result. Silt and clay-size particles, however, can be carried in suspension (dust storm) and by this means may be transported right out of the desert to be deposited elsewhere, as a marine horizon in the ocean or on land as loess. A cover of vegetation on the land surface tends to inhibit the aeolian transport of sand. Some ancient dune sequences that were deposited before higher plants began to colonize extensive areas of land during the Devonian (eg Precambrian dunes; Ross 1983) may reflect the ease with which sand could be moved by the wind in the absence of vegetation rather than any long-term aridity. The Devonian Old Red Sandstone sequences of Britain, for instance, are dominated by fluvial and lacustrine sediment that must indicate a fairly high annual rainfall, and yet dune sands have accumulated locally (Mykura 1983; Carruthers, this volume). To confirm a true desert origin for ancient sequences, additional evidence of aridity is needed. In hot deserts this is most easily recog-

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Earlier studies of pre-ignitions at hot surfaces are first reviewed. The concept of a critical radius of a hot pocket of gas, closely related to the laminar flame thickness, that is necessary to initiate a propagating flame, has been used successfully to predict relative tendencies of different fuel–air mixtures to pre-ignite. As the mixture is compressed, the thickness of potential laminar flames decreases, and when this becomes of the order of the thermal sheath thickness at the hottest surface, pre-ignition can occur there, creating a propagating flame. Measured engine pre-ignition ratings are shown to correlate well with laminar flame thicknesses. Predictions are made concerning the effects of changes in intake temperature and pressure on the pre-ignition of different fuels. A growing current concern is occasional gas-phase, autoignitive, pre-ignitions that can occur in turbo-charged engines, giving rise to very severe autoignition and knock. It is concluded from the evidence of engine pressure records and autoignition delay times of the mixtures that such pre-ignitions have not arisen from autoignition of the fuel, but of a mixture with a smaller autognition delay time than stoichiometric n -heptane–air. One possibility is that autoignition occurs at hot spots containing some lubricating oil. It is shown that such pre-ignitions, particularly with catalytic enhancement, could initiate a propagating flame, rather than autoignitive propagation. In the later, much more severe autoignition arising after pre-ignition, autoignitive propagation velocities at a hot spot are estimated from computed values of the ignition delay times and assumed reactivity gradients in the fuel–air mixture at the hot spot. The severity of the associated pressure pulse is dependent upon the ratios <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>ξ</mml:mi> </mml:mrow> </mml:math> , of the acoustic speed to the localised autoignitive velocity, and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> </mml:math> , of the residence time of the acoustic wave in the hot spot to the short excitation time in which most of the chemical energy is released. The regime in which a localised detonation can be generated in the hot spot is defined by a peninsula on a plot of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>ξ</mml:mi> </mml:mrow> </mml:math> against <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> </mml:math> . A locus is plotted on this figure corresponding to the growing measured intensities of the engine knock as the pressure increases. This is based on computed autoignition delays and excitation times, for an appropriate surrogate fuel. These changes are characterised by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>ξ</mml:mi> </mml:mrow> </mml:math> tending to unity and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>ε</mml:mi> </mml:mrow> </mml:math> tending to ever-higher values, with increasingly intense, localised, developing detonations.

Abstract Diffusion‐ordered spectroscopy (DOSY) is a powerful method for the NMR analysis of mixtures such as crude synthetic products, biofluids or biological extracts. Mixtures can be analysed without the need for any physical separation, and the method requires only standard NMR pulsed field gradient hardware. Existing pulse sequences for DOSY require extensive and time‐consuming phase cycling for clean results. A new sequence is reported here which allows clean spectra with good lineshapes to be obtained using as little as one transient per gradient value. Asymmetric bipolar field gradient pulse pairs are used in conjunction with extra balancing gradient pulses, selecting a unique coherence transfer pathway but minimizing eddy current effects and field‐frequency lock disturbance. Using the new sequence, high‐resolution proton DOSY spectra can be obtained in less than 1 min. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Cells of mucoid and non-mucoid Pseudomonas aeruginosa in colonies were at least one-thousandfold less sensitive to the antibiotics tobramycin or cefsulodin than were cells of the same bacteria in dispersed suspension. We did not detect any difference between the mucoid form and the non-mucoid form in the antibiotic sensitivity of colonies, from which we infer that the exopolysaccharide of the mucoid form does not contribute to colony-resistance by forming a barrier to antibiotic diffusion. Mathematical models were constructed in order to estimate time-courses of penetration of tobramycin and cefsulodin into biofilms and microcolonies of mucoid and non-mucoid P. aeruginosa. For tobramycin penetration, adsorption of antibiotic to the exopolysaccharide of the glycocalyx and antibiotic uptake by cells were taken into account in the calculations. The longest time-period for the concentration of tobramycin at the base of a biofilm 100 micron deep to rise to 90% of the concentration outside the biofilm was predicted to be 2.4 h. For cefsulodin penetration, irreversible hydrolysis catalysed by beta-lactamase was taken into account, using beta-lactamase levels taken from the literature. The calculations predicted that the cefsulodin concentration at the base of a biofilm 100 micron deep would rise to 90% of the external concentration in 29 s when the beta-lactamase was synthesized at the basal level. For a similar biofilm of bacteria synthesizing enhanced levels of beta-lactamase ('derepressed'), the concentration of cefsulodin at the base was calculated to rise to 41% of the external concentration in about 50 s and then remain at that level. This was despite the fact that cefsulodin is a poor substrate for this beta-lactamase.

Xylan comprises up to one-third of plant cell walls, and it influences the properties and processing of biomass. Glucuronoxylan in Arabidopsis is characterized by a linear β-(1,4)-linked backbone of xylosyl residues substituted by glucuronic acid and 4-O-methylglucuronic acid (collectively termed [Me]GlcA). The role of these substitutions remains unclear. GUX1 (glucuronic acid substitution of xylan 1) and GUX2, recently identified as glucuronyltransferases, are both required for substitution of the xylan backbone with [Me]GlcA. Here, we demonstrate clear differences in the pattern of [Me]GlcA substitution generated by each of these glucuronyltransferases. GUX1 decorates xylan with a preference for addition of [Me]GlcA at evenly spaced xylosyl residues. Intervals of eight or 10 residues dominate, but larger intervals are observed. GUX2, in contrast, produces more tightly clustered decorations with most frequent spacing of five, six or seven xylosyl residues, with no preference for odd or even spacing. Moreover, each of these GUX transferases substitutes a distinct domain of secondary cell wall xylan, which we call the major and minor domains. These major and minor xylan domains were not separable from each other by size or charge, a finding that suggests that they are tightly associated. The presence of both differently [Me]GlcA decorated domains may produce a xylan molecule that is heterogeneous in its properties. We speculate that the major and minor domains of xylan may be specialised, such as for interaction with cellulose or lignin. These findings have substantial implications for our understanding of xylan synthesis and structure, and for models of the molecular architecture of the lignocellulosic matrix of plant cell walls.