Book chapters will be unavailable on Saturday 24th August between 8am-12pm BST. This is for essential maintenance which will provide improved performance going forwards. Please accept our apologies for any inconvenience caused.
To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
In order to understand the transport of fast electrons within solid density targets driven by an optical high power laser, we have numerically investigated the dynamics and structure of strong self-generated magnetic fields in such experiments. Here we present a systematic study of the bulk magnetic field generation due to the ponderomotive current, Weibel-like instability and resistivity gradient between two solid layers. Using particle-in-cell simulations, we observe the effect of varying the laser and target parameters, including laser intensity, focal size, incident angle, preplasma scale length, target thickness and material and experimental geometry. The simulation results suggest that the strongest magnetic field is generated with laser incident angles and preplasma scale lengths that maximize laser absorption efficiency. The recent commissioning of experimental platforms equipped with both optical high power laser and X-ray free electron laser (XFEL), such as European XFEL-HED, LCLS-MEC and SACLA beamlines, provides unprecedented opportunities to probe the self-generated bulk magnetic field by X-ray polarimetry via Faraday rotation with simultaneous high spatial and temporal resolution. We expect that this systematic numerical investigation will pave the way to design and optimize near future experimental setups to probe the magnetic fields in such experimental platforms.
Shunt-related adverse events are frequent in infants after modified Blalock–Taussig despite use of acetylsalicylic acid prophylaxis. A higher incidence of acetylsalicylic acid-resistance and sub-therapeutic acetylsalicylic acid levels has been reported in infants. We evaluated whether using high-dose acetylsalicylic acid can decrease shunt-related adverse events in infants after modified Blalock–Taussig.
In this single-centre retrospective cohort study, we included infants ⩽1-year-old who underwent modified Blalock–Taussig placement and received acetylsalicylic acid in the ICU. We defined acetylsalicylic acid treatment groups as standard dose (⩽7 mg/kg/day) and high dose (⩾8 mg/kg/day) based on the initiating dose.
There were 34 infants in each group. Both groups were similar in age, gender, cardiac defect type, ICU length of stay, and time interval to second stage or definitive repair. Shunt interventions (18 versus 32%, p=0.16), shunt thrombosis (14 versus 17%, p=0.74), and mortality (9 versus 12%, p=0.65) were not significantly different between groups. On multiple logistic regression analysis, single-ventricle morphology (odds ratio 5.2, 95% confidence interval of 1.2–23, p=0.03) and post-operative red blood cells transfusion ⩾24 hours [odds ratio 15, confidence interval of (3–71), p<0.01] were associated with shunt-related adverse events. High-dose acetylsalicylic acid treatment [odds ratio 2.6, confidence interval of (0.7–10), p=0.16] was not associated with decrease in these events.
High-dose acetylsalicylic acid may not be sufficient in reducing shunt-related adverse events in infants after modified Blalock–Taussig. Post-operative red blood cells transfusion may be a modifiable risk factor for these events. A randomised trial is needed to determine appropriate acetylsalicylic acid dosing in infants with modified Blalock–Taussig.
A number of laser facilities coming online all over the world promise the capability of high-power laser experiments with shot repetition rates between 1 and 10 Hz. Target availability and technical issues related to the interaction environment could become a bottleneck for the exploitation of such facilities. In this paper, we report on target needs for three different classes of experiments: dynamic compression physics, electron transport and isochoric heating, and laser-driven particle and radiation sources. We also review some of the most challenging issues in target fabrication and high repetition rate operation. Finally, we discuss current target supply strategies and future perspectives to establish a sustainable target provision infrastructure for advanced laser facilities.
The Antarctic Roadmap Challenges (ARC) project identified critical requirements to deliver high priority Antarctic research in the 21st century. The ARC project addressed the challenges of enabling technologies, facilitating access, providing logistics and infrastructure, and capitalizing on international co-operation. Technological requirements include: i) innovative automated in situ observing systems, sensors and interoperable platforms (including power demands), ii) realistic and holistic numerical models, iii) enhanced remote sensing and sensors, iv) expanded sample collection and retrieval technologies, and v) greater cyber-infrastructure to process ‘big data’ collection, transmission and analyses while promoting data accessibility. These technologies must be widely available, performance and reliability must be improved and technologies used elsewhere must be applied to the Antarctic. Considerable Antarctic research is field-based, making access to vital geographical targets essential. Future research will require continent- and ocean-wide environmentally responsible access to coastal and interior Antarctica and the Southern Ocean. Year-round access is indispensable. The cost of future Antarctic science is great but there are opportunities for all to participate commensurate with national resources, expertise and interests. The scope of future Antarctic research will necessitate enhanced and inventive interdisciplinary and international collaborations. The full promise of Antarctic science will only be realized if nations act together.
This study presents accelerator mass spectrometry (AMS) radiocarbon dates and pollen assemblages of 400-cm core sediments collected from the Karekare Swamp in Rarotonga, Southern Cook Islands, to investigate vegetation changes on the island, in particular those induced by human impacts. Eight 14C dates of charcoal and higher plant fragment samples indicate that the sediments accumulated since ∼6.0 cal kBP, with an apparent interruption of deposition (hiatus) from 130 to 132 cm in depth, corresponding to ∼2.8 to 0.7 cal kBP. The appearance of Chenopodiaceae pollen from upland weeds, and Cucurbitaceae and Vigna pollen grains from cultivated plants suggest that human influence existed in core sediments above 130 cm in depth. The increased abundance of Pandanus pollen and monolate-type fern spores also implies the existence of human activity.
There is limited evidence on the acceptability, feasibility and cost-effectiveness of task-sharing interventions to narrow the treatment gap for mental disorders in sub-Saharan Africa. The purpose of this article is to describe the rationale, aims and methods of the Africa Focus on Intervention Research for Mental health (AFFIRM) collaborative research hub. AFFIRM is investigating strategies for narrowing the treatment gap for mental disorders in sub-Saharan Africa in four areas. First, it is assessing the feasibility, acceptability and cost-effectiveness of task-sharing interventions by conducting randomised controlled trials in Ethiopia and South Africa. The AFFIRM Task-sharing for the Care of Severe mental disorders (TaSCS) trial in Ethiopia aims to determine the acceptability, affordability, effectiveness and sustainability of mental health care for people with severe mental disorder delivered by trained and supervised non-specialist, primary health care workers compared with an existing psychiatric nurse-led service. The AFFIRM trial in South Africa aims to determine the cost-effectiveness of a task-sharing counselling intervention for maternal depression, delivered by non-specialist community health workers, and to examine factors influencing the implementation of the intervention and future scale up. Second, AFFIRM is building individual and institutional capacity for intervention research in sub-Saharan Africa by providing fellowship and mentorship programmes for candidates in Ethiopia, Ghana, Malawi, Uganda and Zimbabwe. Each year five Fellowships are awarded (one to each country) to attend the MPhil in Public Mental Health, a joint postgraduate programme at the University of Cape Town and Stellenbosch University. AFFIRM also offers short courses in intervention research, and supports PhD students attached to the trials in Ethiopia and South Africa. Third, AFFIRM is collaborating with other regional National Institute of Mental Health funded hubs in Latin America, sub-Saharan Africa and south Asia, by designing and executing shared research projects related to task-sharing and narrowing the treatment gap. Finally, it is establishing a network of collaboration between researchers, non-governmental organisations and government agencies that facilitates the translation of research knowledge into policy and practice. This article describes the developmental process of this multi-site approach, and provides a narrative of challenges and opportunities that have arisen during the early phases. Crucial to the long-term sustainability of this work is the nurturing and sustaining of partnerships between African mental health researchers, policy makers, practitioners and international collaborators.
Antarctic and Southern Ocean science is vital to understanding natural variability, the processes that govern global change and the role of humans in the Earth and climate system. The potential for new knowledge to be gained from future Antarctic science is substantial. Therefore, the international Antarctic community came together to ‘scan the horizon’ to identify the highest priority scientific questions that researchers should aspire to answer in the next two decades and beyond. Wide consultation was a fundamental principle for the development of a collective, international view of the most important future directions in Antarctic science. From the many possibilities, the horizon scan identified 80 key scientific questions through structured debate, discussion, revision and voting. Questions were clustered into seven topics: i) Antarctic atmosphere and global connections, ii) Southern Ocean and sea ice in a warming world, iii) ice sheet and sea level, iv) the dynamic Earth, v) life on the precipice, vi) near-Earth space and beyond, and vii) human presence in Antarctica. Answering the questions identified by the horizon scan will require innovative experimental designs, novel applications of technology, invention of next-generation field and laboratory approaches, and expanded observing systems and networks. Unbiased, non-contaminating procedures will be required to retrieve the requisite air, biota, sediment, rock, ice and water samples. Sustained year-round access to Antarctica and the Southern Ocean will be essential to increase winter-time measurements. Improved models are needed that represent Antarctica and the Southern Ocean in the Earth System, and provide predictions at spatial and temporal resolutions useful for decision making. A co-ordinated portfolio of cross-disciplinary science, based on new models of international collaboration, will be essential as no scientist, programme or nation can realize these aspirations alone.
In this paper we illustrate the application of electron beam techniques to the measurement of strain, defect and alloy concentrations in nitride thin films. We present brief comparative studies of CL spectra of AlGaN and InGaN epilayers and EBSD patterns obtained from two silicon-doped 3 μm thick GaN epilayers grown on an on-axis (0001) sapphire substrate and a sapphire substrate misoriented by 10° toward the m-plane (10 0).
In this paper we illustrate the application of electron beam techniques to the measurement of strain, defect and alloy concentrations in nitride thin films. We present brief comparative studies of CL spectra of AlGaN and InGaN epilayers and EBSD patterns obtained from two silicon-doped 3 μm thick GaN epilayers grown on an on-axis (0001) sapphire substrate and a sapphire substrate misoriented by 10° toward the m-plane (1010).
The relationship between the supramolecular conformational structure of assembled chromophores and their susceptibility to electric field poling is of interest for maximizing the bulk alignment achievable in an electro-optic material. We have employed solution phase dielectric constant measurements to investigate possible enhancements in dipolar susceptibility as a function of connectivity and state of aggregation in rationally synthesized chromophore assemblies, including conformationally defined head-to-tail oligomers. On the other hand, conformationally unrestricted, highly dipolar azo dyes behave as relatively isolated molecules even when present in supersaturated solutions and in close proximity on polymer chains.
The design of molecular crystals with specific optical properties, which are thought to arise from constituent molecules’ polarizability properties, is a desirable but currently unachievable goal. One can partially achieve this goal by choosing compounds with specific molecular attributes and empirically determining the manner in which these are translated into crystal properties. Besides the fact that there are no certain rules for prediction of crystal packing arrangements, there is also a problem in specifying molecular properties from what are today incomplete polarizability structure-property relationships. We have, realizing these limitations, identified new molecular crystals by a nonlinear optical (powder-SHG) scouting-screening program from lists of compounds chosen because of desirable molecular properties. Examination of successful materials has revealed interesting, new alignment motifs. Some of these materials, a set of halogen and cyano derivatives of aromatic compounds, are described relating properties and structures of molecules and crystals. In particular, the orientation directing influence of intermolecular halogen-cyano interactions and the use of heterocyclic compounds to improve transparency in the near infrared and in the blue and near ultraviolet spectral regions are demonstrated.
Recently we have synthesized several new aryl compounds substituted with two or more trinitromethyl groups. Vacuum pyrolysis of one of these—±,±,±,±’,±’,±’-hexanitro-p-xylene (p-HNX)—gave the title compound via 1,6-elimination of N2O4. Structural assignment of TNQ is based on spectral evidence (UV, 1H NMR and mass spectrometry) and conversion to the known l,4-bis(bromodinitromethyl)benzene. Evidence for the formation of the TNQ radical anion has been obtained.
Recent results indicate that certain organic molecules whose electronic structures are characterized by extended pi-molecular orbitals can exhibit significant second and third order nonlinear optical (NLO) effects . Unfortunately, this same arrangement which leads to the NLO effects, can also result in essentially one-dimensional bonding coordination. This in turn means that crystals grown from these materials do not readily form good three-dimensional optical-quality crystals, but rather tend to form needles. In addition, pure organic crystals are usually bonded by weak van der Waals forces, often resulting in poor mechanical properties. Indeed, organic impurities are frequently incorporated into these systems during crystallization resulting in poor crystallinity, spurious absorptions, and low damage thresholds. This is particularly true in the case of polymeric NLO materials, where impurities result from the polymerization steps and/or starting materials.
(2-Methoxy)ethoxy substituted anilines have been polymerized by chemical and electrochemical methods in hydrochloric acid (HC1) and p-toluenesulphonic acid(TsOH). Electrical conductivity, optical properties, solubility and charge capacity of these polymers are discussed.
The electron-donating [n]radialenes (n=3,4,5) were prepared with the aim of developing both new type of organic (super)conductors and unprecedented organic/molecular ferromagnets. The charge-transfer (CT) complexes of 1,3-dithioleradialene with TCNQ and of 1,3-benzodithiole-radialene with TCNQF4 and DDQ showed comparatively high electrical conductivities in compressed pellets. The single crystals of PF6 and CIO4 salts of 1,3-benzodithioleradialene radical cation revealed temperature change of electrical conductivity characteristic of a semiconductor. The magnetic properties of the bis(trifluoroacetate)salt of thioxanthene-radialene dication and of the CT complexes of 1,3-benzodithiole-radialene with DDQ, TCNQF4, and hexacyanohexamethylenecyclopropane, were also investigated from the ESR and/or magnetic susceptibility measurements.
The synthesis and second-order nonlinear optical (NLO) properties of a new family of optically nonlinear coumarin dye-containing polymers is reported. Polymerizable coumaromethacrylate (CMA) monomers having various alkyl spacers (C2 to C5) between the polymerizable group and the chromophore were prepared and copolymerized with methylmethacrylate (MMA) and other vinyl monomers. The CMA copolymers had high chromophoric content (up to 18 × 1020) and glass transitions as high as 132°C. Spin cast films were prepared on BK7 substrates and oriented by corona-onset poling at elevated temperatures (COPET). The poled CMA copolymer films were characterized for spectroscopic absorption and second harmonic properties. A comparison of the nonlinear optical properties of poled CMA-MMA copolymers to poled guest-host systems is made. Relative to guest/host systems, CMA-MMA copolymer films exhibit larger and much more stable second-order nonlinear optical properties.
New organic nonlinear optical crystal : dicyanovinyl anisole (DIVA) has been grown from vapor by low pressure sublimation and from saturated solution by solvent evaporation. Crystallographic structure and quadratic nonlinear optical properties were investigated. Molecular orientation in DIVA crystal with space group P21, is favorable for the highest possible value of bulk phase-matchable coefficient. Both type I and type II phase matched second harmonic generation (PMSHG) were observed from naturally grown faces of single crystals. Efficient PMSHG was achieved at a fundamental wavelength of 812 and 1064 nm. The efficient type I PMSHG coefficient was determined as deff = 4.9 × 10−8 esu = 40 × (d11 of α-quartz) at a wave.LH length of 1064 nm. Blue light generation was demonstrated by both PMSHG and sum-frequency mixing of the 812 nm laser with 1064 nm.
We report a new organic nonlinear optical crystal, 2, 6-dibromo-N-methyl-4-nitroaniline (DBNMNA). The refractive indices of DBNMNA were measured at several wavelengths between 500 and 1100 in and fit to a single oscillator Sellmeier equation. Second harmonic Maker fringe data yielded d33 values through comparison with y-cut crystalline quartz. We also report measurements of the electro-optic coefficients, (na3r13-nc3r33) r42, and r51 at several wavelengths. We find good agreement between the observed dispersion and that predicted by the simple two level dispersion model. However, the second order susceptibility is not well described by a single tensor component hyperpolarizability.