Piezoresponse force microscopy for polarity imaging of GaN

The polarity distribution of GaN based lateral polarity heterostructures is investigated by piezoresponse force microscopy (PFM). Simultaneous imaging of surface morphology, as well as the phase and magnitude of the piezoelectric response, is performed by PFM on a GaN film with patterned polarities on a c-Al2O3 substrate. We demonstrate that the polarity distribution of GaN based lateral polarity heterostructures can be deduced from the phase image of the piezoresponse with nanometer scale spatial resolution

An evaluation of enhanced geotextile layer in permeable pavement to improve stormwater infiltration and attenuation

This paper reports on an evaluation of the properties of a novel structure known as OASIS® which was designed at Coventry University as an enhancement of the commercially available geotextiles when incorporated in the permeable pavement system (PPS). The impact on the hydraulic behaviour of a PPS was analysed through the study of infiltration rate, throughout the PPS and time required to reach the steady-state stage behaviour of the water within the PPS, under extreme rainfall intensities of 100 mm/hr, 200 mm/hr and 400 mm/hr, corresponding to a 100-year return period rainfall over a duration of 15 min in different parts of the world. The result indicated that the novel structure provides an extra benefit when incorporated in PPSs, delaying peak flow of a rainfall event by retaining and storing great volumes of water within its structure. These additional benefits are especially important under extreme rainfall events

The transition from linear to highly branched poly(beta-amino ester)s: Branching matters for gene delivery

Nonviral gene therapy holds great promise but has not delivered treatments for clinical application to date. Lack of safe and efficient gene delivery vectors is the major hurdle. Among nonviral gene delivery vectors, poly(beta-amino ester)s are one of the most versatile candidates because of their wide monomer availability, high polymer flexibility, and superior gene transfection performance both in vitro and in vivo. However, to date, all research has been focused on vectors with a linear structure. A well-accepted view is that dendritic or branched polymers have greater potential as gene delivery vectors because of their three-dimensional structure and multiple terminal groups. Nevertheless, to date, the synthesis of dendritic or branched polymers has been proven to be a well-known challenge. We report the design and synthesis of highly branched poly(beta-amino ester)s (HPAEs) via a one-pot "A2 + B3 + C2"&-type Michael addition approach and evaluate their potential as gene delivery vectors. We find that the branched structure can significantly enhance the transfection efficiency of poly(beta-amino ester)s: Up to an 8521-fold enhancement in transfection efficiency was observed across 12 cell types ranging from cell lines, primary cells, to stem cells, over their corresponding linear poly(beta-amino ester)s (LPAEs) and the commercial transfection reagents polyethyleneimine, SuperFect, and Lipofectamine 2000...This work was funded by Science Foundation Ireland (SFI), a Technology Innovation and Development Award (14/TIDA/2367), an Industry Fellowship (15/IFA/3037), the Principal Investigator Program [10/IN.1/B2981(T)], an Investigator Award (12/IP/1688), the Health Research Board of Ireland (HRA-POR-2013-412), and the National Natural Science Foundation of China (130-0401180007). The atomic force microscope used for this work was funded by SFI (SFI07/IN1/B931

Geomorphological significance of Ontario Lacus on Titan: Integrated interpretation of Cassini VIMS, ISS and RADAR data and comparison with the Etosha Pan (Namibia)

International audienceOntario Lacus is the largest lake of the whole southern hemisphere of Titan, Saturn's major moon. It has been imaged twice by each of the Cassini imaging systems (Imaging Science Subsystem (ISS) in 2004 and 2005, Visual and Infrared Mapping Spectrometer (VIMS) in 2007 and 2009 and Radar in 2009 and 2010). In this study, we take advantage of each imaging dataset to establish a global survey of Ontario Lacus' environment from 2005 to 2010. We perform a geomorphological mapping and interpretation of Ontario Lacus, mainly based on a joint analysis of VIMS and Radar SAR datasets, along with the T49 altimetric profile acquired in December 2008. The morphologies observed on Ontario Lacus are compared to landforms of a semi-arid terrestrial analog, which closely resembles Titan's lakes: the pans of the Etosha Basin, located in Namibia. From this comparison, we infer that Ontario Lacus is an extremely flat depression where liquids, only located in the darkest areas in the Radar data, cover topographic lows where the "alkanofer" would raise above the depression floor. The rest of the depression appears rather as a muddy flat surface likely composed of a thick coating of photon-absorbing materials, explaining its still rather dark appearance in the infrared and radar data. We also determined whether surface changes occurred during the 5 years time interval between 2005 and 2010. We found that the depression contour is constant at the resolution of ISS and VIMS data, both being consistent with the depression contour derived from the Radar data. Our interpretation, in which the liquids are located only in some parts of Ontario Lacus, agrees with the lack of significant change of the depression contour between 2007 (and 2005 with more uncertainties) and 2010

Average Lattice Symmetry and Nanoscale Structural Correlations in Magnetoresistive Manganites

We report x-ray scattering studies of nanoscale structural correlations in the paramagnetic phases of the perovskite manganites La$_{0.75}$(Ca$_{0.45}$Sr$_{0.55}$)$_{0.25}$MnO$_3$, La$_{0.625}$Sr$_{0.375}$MnO$_3$, and Nd$_{0.45}$Sr$_{0.55}$MnO$_3$. We find that these correlations are present in the orthorhombic $O$ phase in La$_{0.75}$(Ca$_{0.45}$Sr$_{0.55}$)$_{0.25}$MnO$_3$, but they disappear abruptly at the orthorhombic-to-rhombohedral transition in this compound. The orthorhombic phase exhibits increased electrical resistivity and reduced ferromagnetic coupling, in agreement with the association of the nanoscale correlations with insulating regions. In contrast, the correlations were not detected in the two other compounds, which exhibit rhombohedral and tetragonal phases. Based on these results, as well as on previously published work, we propose that the local structure of the paramagnetic phase correlates strongly with the average lattice symmetry, and that the nanoscale correlations are an important factor distinguishing the insulating and the metallic phases in these compounds.Comment: a note on recent experimental work, and a new reference adde

Comparing typologies of violence exposure and associations with syndemic health outcomes among cisgender and transgender female sex workers living with HIV in the Dominican Republic

Violence against women research largely excludes transgender women’s experiences and violence from perpetrators other than intimate partners. This study compares patterns of violence exposure among cisgender and transgender female sex workers (FSWs) and the associations with syndemic health outcomes. We used cross-sectional surveys from samples of cisgender and transgender FSWs living with HIV in the Dominican Republic (N = 211 and 100, respectively). We used latent class analysis to identify patterns of emotional, physical and sexual violence and harassment by partners, clients, and police. We assessed sociodemographic and occupational predictors in relation to class membership, and class membership in relation to health (HIV continuum of care outcomes, mental health, substance use), using logistic regression. Two classes were identified in cisgender sample: Low Reported Violence Exposure (Class 1) and Sex Work-related Police Harassment (Class 2). Class 2 participants had greater odds of scoring abnormal or borderline abnormal anxiety on the Hospital Anxiety and Depression Scale (HADS-A) (adjusted OR = 3.97 p<0.01), moderate-to-severe depression per the Patient Health Questionnaire-9 (PHQ-9) (aOR = 5.74, p<0.01), and any illicit drug use in the past six months (aOR = 3.06, p<0.05) compared to Class 1. The transgender sample produced three classes: Low Reported Violence Exposure (Class 1); Sex Work-related Police Harassment (Class 2); and Sex Workrelated Violence and Harassment (Class 3). Class 3 participants had greater odds of having anxiety (aOR = 6.65, p<0.01) and depression (aOR = 4.45, p<0.05), while Class 2 participants had greater odds of perfect ART adherence during the previous four days (aOR = 2.78, p<0.05), compared to Class 1. The more diverse and extreme violence patterns uncovered for the transgender sample show this group’s heightened risk, while similar patterns across groups regarding police abuse highlight a need for police-focused violence prevention interventions. Each sample’s highest violence class was associated with poor mental health, underscoring the need for mental health interventions for all FSWs

Solving Fuzzy Job-Shop Scheduling Problems with a Multiobjective Optimizer

International audienceIn real-world manufacturing environments, it is common to face a job-shop scheduling problem (JSP) with uncertainty. Among different sources of uncertainty, processing times uncertainty is the most common. In this paper, we investigate the use of a multiobjective genetic algorithm to address JSPs with uncertain durations. Uncertain durations in a JSP are expressed by means of triangular fuzzy numbers (TFNs). Instead of using expected values as in other work, we consider all vertices of the TFN representing the overall completion time. As a consequence, the proposed approach tries to obtain a schedule that optimizes the three component scheduling problems (corresponding to the lowest, most probable, and largest durations) all at the same time. In order to verify the quality of solutions found by the proposed approach, an experimental study was carried out across different benchmark instances. In all experiments, comparisons with previous approaches that are based on a single-objective genetic algorithm were also performed

Spin-Charge Separation in the t−Jt-J Model: Magnetic and Transport Anomalies

A real spin-charge separation scheme is found based on a saddle-point state of the $t-J$ model. In the one-dimensional (1D) case, such a saddle-point reproduces the correct asymptotic correlations at the strong-coupling fixed-point of the model. In the two-dimensional (2D) case, the transverse gauge field confining spinon and holon is shown to be gapped at {\em finite doping} so that a spin-charge deconfinement is obtained for its first time in 2D. The gap in the gauge fluctuation disappears at half-filling limit, where a long-range antiferromagnetic order is recovered at zero temperature and spinons become confined. The most interesting features of spin dynamics and transport are exhibited at finite doping where exotic {\em residual} couplings between spin and charge degrees of freedom lead to systematic anomalies with regard to a Fermi-liquid system. In spin dynamics, a commensurate antiferromagnetic fluctuation with a small, doping-dependent energy scale is found, which is characterized in momentum space by a Gaussian peak at ($\pi/a$, $\pi/a$) with a doping-dependent width ($\propto \sqrt{\delta}$, $\delta$ is the doping concentration). This commensurate magnetic fluctuation contributes a non-Korringa behavior for the NMR spin-lattice relaxation rate. There also exits a characteristic temperature scale below which a pseudogap behavior appears in the spin dynamics. Furthermore, an incommensurate magnetic fluctuation is also obtained at a {\em finite} energy regime. In transport, a strong short-range phase interference leads to an effective holon Lagrangian which can give rise to a series of interesting phenomena including linear-$T$ resistivity and $T^2$ Hall-angle. We discuss the striking similarities of these theoretical features with those found in the high-$T_c$ cuprates and give aComment: 70 pages, RevTex, hard copies of 7 figures available upon request; minor revisions in the text and references have been made; To be published in July 1 issue of Phys. Rev. B52, (1995

Singular regional brightening events on Titan as seen by Cassini/VIMS

Titan, the largest satellite of Saturn, is the only satellite in the solar system with a dense atmosphere. The close and continuous observations of Titan by the Cassini spacecraft, in orbit around Saturn since July 2004, bring us evidences that Titan tropo-sphere and low stratosphere experience an exotic, but complete meteorological cycle similar to the Earth hy-drological cycle, with hydrocarbons evaporation, con-densation in clouds, and rainfall. Cassini monitoring campaigns also demonstrate that Titan’s cloud cover-age and climate vary with latitude. Titan’s tropics, with globally weak meteorological activity and widespread dune fields, seem to be slightly more arid than the poles, where extensive and numerous liquid reservoirs and sustained cloud activity were discovered. Only a few tropospheric clouds have been observed at Titan’s tropics during the southern summer [2-4]. As equinox was approaching (in August 2009), they oc-curred more frequently and appeared to grow in strength and size [5-7]

Can forest management based on natural disturbances maintain ecological resilience?

Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance