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 email@example.com
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.
At the first retinal synapse, horizontal cells (HCs) contact both photoreceptor terminals and bipolar cell dendrites, modulating information transfer between these two cell types to enhance spatial contrast and mediate color opponency. The synaptic mechanisms through which these modulations occur are still debated. The initial hypothesis of a GABAergic feedback from HCs to cones has been challenged by pharmacological inconsistencies. Surround antagonism has been demonstrated to occur via a modulation of cone calcium channels through ephaptic signaling and pH changes in the synaptic cleft. GABAergic transmission between HCs and cones has been reported in some lower vertebrates, like the turtle and tiger salamander. In these reports, it was revealed that GABA is released from HCs through reverse transport and target GABA receptors are located at the cone terminals. In mammalian retinas, there is growing evidence that HCs can release GABA through conventional vesicular transmission, acting both on autaptic GABA receptors and on receptors expressed at the dendritic tips of the bipolar cells. The presence of GABA receptors on mammalian cone terminals remains equivocal. Here, we looked specifically for functional GABA receptors in mouse photoreceptors by recording in the whole-cell or amphotericin/gramicidin-perforated patch clamp configurations. Cones could be differentiated from rods through morphological criteria. Local GABA applications evoked a Cl− current in cones but not in rods. It was blocked by the GABAA receptor antagonist bicuculline methiodide and unaffected by the GABAC receptor antagonist TPMPA [(1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid]. The voltage dependency of the current amplitude was as expected from a direct action of GABA on cone pedicles but not from an indirect modulation of cone currents following the activation of the GABA receptors of HCs. This supports a direct role of GABA released from HCs in the control of cone activity in the mouse retina.
Important data in the investigation of laser-produced plasmas will be provided by studies of the X-ray emission characteristics in the range 1-10 keV, with time resolution comparable to plasma heating times. Present techniques using conventional photomultipliers or photodiodes are not suitable for time measurements on plasma heated by short optical pulses of several hundred picoseconds or less. The development of new X-ray cameras is also necessary. Their photocathodes must be chosen with care. In this paper we describe an initial study of the characteristics of metallic photocathodes: quantum efficiency, energy distribution of emitted photoelectrons, etc. Then we worked out the provisional sensitivity, spatial and temporal resolution of cameras in the streak mode or in shutter mode.
Several infections have been linked to telomere shortening and in some cases these associations have varied by sex. We assessed the association between seropositivity to four persistent pathogens (cytomegalovirus (CMV), herpes simplex virus-1, Helicobacter pylori, Chlamydia pneumoniae), and total pathogen burden on leukocyte telomere length in a diverse US sample. Data came from the Multi-Ethnic Study of Atherosclerosis, a population-based cohort study. We utilized cross-sectional survey data, and biological samples from participants tested for pathogens and telomere length (N = 163). Linear regression was used to examine the association between seropositivity for individual pathogens as well as total pathogen burden and telomere length, adjusting for various confounders. CMV seropositivity and increased total pathogen burden level were significantly associated with shorter telomere length among females (β = −0·1204 (standard error (s.e.) 0·06), P = 0·044) and (β = −0·1057 (s.e. = 0·05), P = 0·033), respectively. There was no statistically significant association among males. Our findings suggest that prevention or treatment of persistent pathogens, in particular CMV, may play an important role in reducing telomere shortening over the life course among women. Future research is needed to confirm these novel findings in larger longitudinal samples.
To examine the child outcomes at 18-months post-birth of a population cohort of women with antenatal depressed mood, half of whom were randomly chosen to receive perinatal home visits from community health workers during pregnancy.
Pregnant women in 24 neighbourhoods (98% participation) were randomised by neighbourhood to: (1) standard clinic care (SC; 12 neighbourhoods; n = 594) or (2) the Philani Intervention Program, a home visiting intervention plus standard care (12 neighbourhoods; n = 644). The physical and cognitive outcomes of children of mothers with antenatally depressed mood (Edinburg Perinatal Depression Scale >13) in the intervention condition were compared at 18-months post-birth to children of mothers without depressed mood in pregnancy in both conditions.
More than a third of mothers had heightened levels of antenatal depressed mood (35%), similar across conditions. Antenatal depressed mood was significantly associated with being a mother living with HIV, using alcohol and food insecurity. At 18-months, the overall cognitive and motor scale scores on the Bayley Scales of Development were similar. However, 10.3% fewer children of mothers with antenatal depressed mood in the intervention condition had cognitive scores on the Bayley Scales that were less than 85 (i.e., s.d. = 2 lower than normal) compared with children of mothers with antenatal depressed mood in the SC condition. Intervention children of mothers with antenatal depressed mood were also significantly less likely to be undernourished (Weight-for-Age Z-scores < −2).
Cognitive development and child growth among children born to mothers with antenatal depressed mood can be improved by mentor mother home visitors, probably resulting from better parenting and care received early in life.
The mechanisms by which a wetting, non-saturating liquid bestows macroscopic cohesion and strength to a granular material are usually not accessible to micromechanical investigations for saturations exceeding the pendular regime of isolated menisci, easily studied by discrete element models (DEM). The paper by Delenne et al. (J. Fluid Mech., 2015, vol. 762, R5) exploiting a multiphase lattice Boltzmann approach, pioneers the simulation of the micromorphology and of the mechanical effects on grains of an interstitial liquid, in equilibrium with its vapour, for the whole saturation range. Interestingly, in accordance with some experiments and phenomenological models, the results suggest that the mechanical effect of capillary forces is maximized for some intermediate saturation level (near 40 % in the model), well beyond the pendular range. In general, the proposed simulation technique opens the way to many studies of partially saturated granular assemblies, for different saturation or imbibition processes and histories.
We investigated temporal trends in BMI, and assessed hypothesized predictors of trends including socio-economic position (SEP) and province-level economic development, in Argentina.
Using multivariable linear regression, we evaluated cross-sectional patterning and temporal trends in BMI and examined heterogeneity in these associations by SEP and province-level economic development with nationally representative samples from Argentina in 2005 and 2009. We calculated mean annual changes in BMI for men and women to assess secular trends.
Women, but not men, exhibited a strong cross-sectional inverse association between SEP and BMI, with the lowest-SEP women having an average BMI 2·55 kg/m2 greater than the highest-SEP women. Analysis of trends revealed a mean annual increase in BMI of 0·19 kg/m2 and 0·15 kg/m2 for women and men, respectively, with slightly greater increases occurring in provinces with greater economic growth. No significant heterogeneity in trends existed by individual SEP.
BMI is increasing rapidly over time in Argentina irrespective of various sociodemographic characteristics. Higher BMI remains more common in women of lower SEP compared with those of higher SEP.
Dwarf (Kogia sima) and pygmy (K. breviceps) sperm whales occur in pelagic waters around southern Africa. Here we report the first record of K. sima from Namibia and provide information on the basic morphometrics and diet of that record and of two recent strandings of K. breviceps. All known records (N = 29) of K. breviceps from Namibia are also collated. Eight families of cephalopod were identified in the stomach contents of the K. sima but no fish remains and few crustacean parts were present. Nine and ten families of cephalopod were identified in the stomachs of the two K. breviceps specimens respectively. This report expands the known range of K. sima by more than 1000 km from previous published records in the region. The sparsely populated nature of the Namibian coast and bias of records towards centres of human habitation suggest Kogia strandings are under reported. The low number of stranded specimens of K. sima from Namibia and west South Africa, in comparison to K. breviceps suggests that K. sima occur rarely or at very low densities in the area influenced by the Benguela current ecosystem. Specimens from Namibia are valuable due to uncertainties about taxomony of kogiids in the region.
Nanoparticles (NPs) have attracted a considerable interest in the last decades, owing to their remarkable physical and chemical properties. The most important characteristic of NPs is the size effect, that is, their properties differ from that of the corresponding bulk material. We will focus here on Electron Energy-Loss Spectroscopy (EELS) investigations of Gd2O3 NPs of different and controlled sizes. EELS spectra near the O-K edge of Gd2O3 were recorded and compared with feff8.2 ELNES simulations. The calculation of the EELS response from small particles by the feff code raises some particular problems which have been carefully examined and partially solved. The simulations are in fair agreement with experiment and reveal the existence of size effects.
The sol-gel process opens new possibilities in the field of biotechnologies. Sol-gel glasses are formed at room temperature via the polymerization of molecular precursors. Enzymes can be added to the solution of precursors and trapped within the growing silica network. Small substrate molecules can diffuse through the pores allowing reactions to be performed in-situ, within the silica gels. Enzyme are encased by the hydrated silica in a cage tailored to their size, they retain their biocatalytic activity and may even be stabilized within the sol-gel matrix.
Whole cell bacteria have also been immobilized within sol-gel glasses. They behave as a "bag of enzymes" and their membrane protects enzymes against denaturation and leaching. The cellular organization of bacteria cells is preserved upon encapsulation. Experiments performed with Escherichia coli induced to β-galactosidase show that they still exhibit noticeable enzymatic activity. Some degradation of the cell walls may even occur increasing the “measured” activity. However silica gels made from aqueous precursors seem to prevent bacteria from natural degradation upon ageing.
Antibody-antigen recognition has been shown to be feasible within sol-gel matrices. Trapped antibodies bind specifically the corresponding haptens and can be used for the detection of traces of chemicals. Even whole cell protozoa have been encapsulated without any alteration of their cellular organization. For medical applications, trapped parasitic protozoa have been used as antigens for blood tests with human sera. Antigen-antibody interactions were followed by the so-called Enzyme Linked ImmunoSorbent Assays (ELISA).
We have prepared a wide Ba1−xSrxCl1+yF1−y solid solution (0<x<0.25, −0.20<y<0.20) that has the BaClF structure without any sign of lattice distortion or ordering of the cations or of the anions other than that already present in BaClF. Furthermore, 119Sn Mossbauer spectroscopy shows that tin(ll) is present in this material in the form of Sn2+ ions instead of being covalently bonded Sn(ll) with a stereoactive lone pair of electrons, which is nearly always the case when the anions are small and strongly electronegative, like for F and Cl. The tin situation is similar to that observed in SnCl2.
Bioencapsulation in sol-gel materials has been widely studied during the past decade. Trapped species appear to retain their bioactivity in the porous silica matrix. Small analytes can diffuse through the pores allowing bioreactions to be performed in-situ, inside the sol-gel glass. A wide range of biomolecules and micro-organisms have been encapsulated. The catalytic activity of enzymes is used for the realization of biosensors or bioreactors. Antibody-antigen recognition has been shown to be feasible within sol-gel matrices. Trapped antibodies bind specifically the corresponding haptens and can be used for the detection of traces of chemicals. Even whole cells are now encapsulated without any alteration of their cellular organization. They can be used for the production of chemicals or as antigens for immunoassays.
A number of experimental techniques were used to characterize structural quality, ultrafast carrier dynamics and deep center properties of low-temperature-grown GaAs doped with Be. GaAs layers grown at 280 °C, doped with the Be concentration from 5×1017 cm-3 to 2×1019 cm-3 and annealed at temperatures between 500 and 800 °C were studied. Electron trapping times in these samples varied from hundreds of femtoseconds to several picoseconds. A non-monotonous electron trapping time dependence on Be doping level is explained by the influence of triple-charged gallium vacancies and single-charged Be-acceptors on the number of ionized As antisite defects.
The discipline of ecology has evolved through several phases as it has developed and defined itself and its relationship with human society. While it initially had little to do with human concerns, it has become more applied, and is today more integrated with the human element in the way it conceptualizes complex social-ecological systems. As the science has developed, so too have its relationships with other disciplines, as well as people and processes outside the domain of science. However, it is unclear how far ecology has progressed in developing these relationships and where it should best focus its efforts in the future in order to increase its relevance and role in society. The concept of ecosystem services (the benefits people get from nature) has the potential to further this integration and clarify ecology's role and relevance in society, however doubt remains as to whether the concept has helped ecology in developing disciplinary and societal relationships. This review assesses the progress of ecology in relation to a transdisciplinary knowledge hierarchy (empirical, pragmatic, normative and purposive) where all levels of the hierarchy are coordinated on the basis of an overall purpose introduced from the purposive level down. At each of the levels of the knowledge hierarchy, the principles of transdisciplinarity, ecology's progress, the contribution of ecosystem services to this progress and future directions for a transdisciplinary ecology are explored. Ecology has made good progress in developing an interdisciplinary dialogue between the natural and social sciences and sectors. It is well-integrated with empirical and pragmatic disciplines and coordinates research at these two levels. At the normative level, the absence of collaborative frameworks and planning instruments is a major gap limiting the influence that ecology can have on land and resource use decisions at this level. At the purposive level, ecology has limited interactions with a narrow set of values associated with ecological ethics and economics. There is an obvious need for ecology to engage with the purposive disciplines of philosophy, ethics and theology, but also a need for ecological research to transform itself into a social process dealing with values and norms of both society and science. Ecosystem services have helped ecology to make links with many disciplines at the empirical and pragmatic levels, provided a useful concept and framework for interactions at the normative level requiring further examination, and helped make values explicit, allowing ecologists to begin to interact with the purposive level. The Western ecological economic origins of the ecosystem service concept presents a potential constraint to interactions at the purposive level, and must be considered and addressed if ecosystem services are to further the development of a transdisciplinary ecology, the joint ecology-society debate and the formulation and execution of policy.
Because insects are ectotherms, their physiology, behaviour and fitness are influenced by the ambient temperature. Any changes in environmental temperatures may impact the fitness and life history traits of insects and, thus, affect population dynamics. Here, we experimentally tested the impact of heat shock on the fitness and life history traits of adults of the aphid parasitoid Aphidius avenae and on the later repercussions for their progeny. Our results show that short exposure (1 h) to an elevated temperature (36°C), which is frequently experienced by parasitoids during the summer, resulted in high mortality rates in a parasitoid population and strongly affected the fitness of survivors by drastically reducing reproductive output and triggering a sex-dependent effect on lifespan. Heat stress resulted in greater longevity in surviving females and in shorter longevity in surviving males in comparison with untreated individuals. Viability and the developmental rates of progeny were also affected in a sex-dependent manner. These results underline the ecological importance of the thermal stress response of parasitoid species, not only for survival, but also for maintaining reproductive activities.
We present the latest results of our on-going closed-loop “end-to-end” numerical adaptive optics (AO) simulations concerning both a standard-AO and a three-star
ground-layer AO system for a near-infrared 2-m class telescope at Dome C, Antarctica. We demonstrate that Dome C is an ideal site for wide-field AO-aided astronomy,
define in details the AO system(s) optimized for the median turbulence profile considered, and finally show that a ~0.3 Strehl ratio and 200-mas-wide stable point-spread
function is reached in band J on at least a 15'-diameter field.