Size-dependent electronic-transport mechanism and sign reversal of magnetoresistance in Nd0.5Sr0.5CoO3

A detailed investigation of electronic-transport properties of Nd0.5Sr0.5CoO3 has been carried out as a function of grain size ranging from micrometer order down to an average size of 28 nm. Interestingly, we observe a size induced metal-insulator transition in the lowest grain size sample while the bulk-like sample is metallic in the whole measured temperature regime. An analysis of the temperature dependent resistivity in the metallic regime reveals that the electron-electron interaction is the dominating mechanism while other processes like electron-magnon and electron-phonon scatterings are also likely to be present. The fascinating observation of enhanced low temperature upturn and minimum in resistivity on reduction of grain size is found due to electron-electron interaction (quantum interference effect). This effect is attributed to enhanced disorder on reduction of grain size. Interestingly, we observed a cross over from positive to negative magnetoresistance in the low temperature regime as the grain size is reduced. This observed sign reversal is attributed to enhanced phase separation on decreasing the grain size of the cobaltite

The inequality of charge and spin diffusion coefficients

Since spin and charge are both carried by electrons (or holes) in a solid, it is natural to assume that charge and spin diffusion coefficients will be the same. Drift-diffusion models of spin transport typically assume so. Here, we show analytically that the two diffusion coefficients can be vastly different in quantum wires. Although we do not consider quantum wells or bulk systems, it is likely that the two coefficients will be different in those systems as well. Thus, it is important to distinguish between them in transportmodels, particularly those applied to quantum wire based devices

Bounds for anisotropic Carleson operators

We prove weak $(2,2)$ bounds for maximally modulated anisotropically homogeneous smooth multipliers on $\mathbb{R}^n$. These can be understood as generalizing the classical one-dimensional Carleson operator. For the proof we extend the time-frequency method by Lacey and Thiele to the anistropic setting. We also discuss a related open problem concerning Carleson operators along monomial curves.Comment: 26 page

Multidimensional assessment of smallholder farming systems’ sustainability

A holistic systems-oriented approach is strongly recommended to address the intractable challenges of complex smallholder farm and food systems in different ecologies, and cultures. In the present study, we have developed and piloted a multidimensional framework for assessing farming systems sustainability and resilience (FSSR) which is easily measurable and comparable. It considers five major sustainability domains: environmental, economic, productivity, social and human well-being. Further each domain is divided into different themes, sub-themes and indicators. The indicators have been finalized with rounds of stakeholders’ consultations involving farmers, researchers, development actors besides literature. We identified 115 measurable indicators: environmental (34), economic (29), productivity (12), social (25) and human well-being (15) in the final framework which are aggregated into an index with a maximum value of 100 representing the level of sustainability and resilience at different scales. In our case study the overall sustainability index scores ranged between 42 to 47 across farm types. The overall and domain level sustainability scores varied widely across individual households and farm types. The present framework could be very useful tool for researchers, development actors and institutions to identify entry points to design context-specific strategies to improve sustainability and resilience of farming systems in vulnerable regions

Field Emission from Self-Assembled Arrays of Lanthanum Monosulfide Nanoprotrusions

The field emission properties of LaS nanoprotrusions called nanodomes, formed by pulsed laser deposition on porous anodic alumina films, have been analyzed with scanning anode field emission microscopy. The voltage necessary to produce a given field emission current is 3.5 times less for nanodomes than for thin films. Assuming the same work function for LaS thin films and nanoprotrusions, that is, 1 eV, a field enhancement factor of 5.8 is extracted for the nanodome emitters from Fowler-Nordheim plots of the field emission data. This correlates well with the aspect ratio of the tallest nanodomes observed in atomic force micrograph measurements

Multidimensional framework for measuring sustainability and resilience of farming systems

Natural resources, are fundamental for the structure and function of agricultural systems and for social and environmental sustainability in support of life on earth. Historically, global agricultural development has been narrowly focused on increased productivity rather than on a more holistic integration of natural resource management with food and nutritional security. Now it is strongly suggested that a holistic, or systems-oriented approach, will be needed to address the intractable challenges associated with the complexity of food and other production systems in different ecologies, locations and cultures. In the present study we have developed and piloted a multidimensional framework for assessing farming systems sustainability and resilience (FSSR). The quantification framework is easily measurable and comparable across farm households, farming systems and beyond. It considers five major domains of the farming systems namely environmental, economic, productivity, social and human well-being. In the subsequent stages of measurement each domain is divided into different themes, then sub-themes and indicators. The indicators in our study have been finalized with rounds of stakeholders’ consultations involving farmers, researches, development experts besides literature. Finally, we identified a total of 115 indicators: environmental (34), economic (29), productivity (12), social (25) and human well-being (15) in the final framework which are measurable and would be able to provide an index value representing level of sustainability of farming systems at different scales: farm household, domain and farming system considering appropriate weights of different domains. The FSSR framework could be a very useful tool for designing the context specific strategies to address farm sustainability challenges

Fragmentation of exotic oxygen isotopes

Abrasion-ablation models and the empirical EPAX parametrization of projectile fragmentation are described. Their cross section predictions are compared to recent data of the fragmentation of secondary beams of neutron-rich, unstable 19,20,21O isotopes at beam energies near 600 MeV/nucleon as well as data for stable 17,18O beams

Single-Proton Removal Reaction Study of 16B

The low-lying level structure of the unbound system $^{16}$B has been investigated via single-proton removal from a 35 MeV/nucleon $^{17}$C beam. The coincident detection of the beam velocity $^{15}$B fragment and neutron allowed the relative energy of the in-flight decay of $^{16}$B to be reconstructed. The resulting spectrum exhibited a narrow peak some 85 keV above threshold. It is argued that this feature corresponds to a very narrow ($\Gamma \ll$100 keV) resonance, or an unresolved multiplet, with a dominant $\pi (p_{3/2})^{-1} \otimes \nu (d_{5/2}^3)_{J=3/2^+}$ + $\pi (p_{3/2})^{-1} \otimes \nu (d_{5/2}^2,s_{1/2})_{J=3/2^+}$ configuration which decays by d-wave neutron emission.Comment: 16 pages, 5 figures, 1 table, submitted to Phys. Lett.

Boron carbide amorphous solid with tunable band gap

Boron carbide BxC (x = 1/6 − 10) powders were synthesized through a microwave-assisted carbothermic reduction reaction as a potential clean energy material. Their crystallographic structures and optical properties were characterized. X-ray diffraction and electron diffraction indicated that the synthesized BxC powders were amorphous. Electron energy-loss spectroscopy demonstrated that the composition of boron and carbon was in amorphous materials, and their chemical bonding were disclosed from Raman scattering spectroscopy. UV–vis absorption spectroscopy indicated that the bandgap of the bulks varied from 2.30eV to 3.90eV, tuned by the boron/carbon element ratio. The synthesized powders were potential photovoltaic materials. A short-range ordering model was established to explain the optical properties

An optical coherence photoacoustic microscopy system using a fiber optic sensor

In this work, a novel fiber optic sensor based on Fabry-Pérot interferometry is adopted in an optical coherence photoacoustic microscopy (OC-PAM) system to enable high-resolution in vivo imaging. The complete OC-PAM system is characterized using the fiber optic sensor for photoacoustic measurement. After characterization, the performance of the system is evaluated by imaging zebrafish larvae in vivo. With a lateral resolution of 3.4 μm and an axial resolution of 3.7 μm in air, the optical coherence microscopy subsystem visualizes the anatomy of the zebrafish larvae. The photoacoustic microscopy subsystem reveals the vasculature of the zebrafish larvae with a lateral resolution of 1.9 μm and an axial resolution of 37.3 μm. As the two modalities share the same sample arm, we obtain inherently co-registered morphological and vascular images. This OC-PAM system provides comprehensive information on the anatomy and vasculature of the zebrafish larvae. Featuring compactness, broad detection bandwidth, and wide detection angle, the fiber optic sensor enables a large field of view with a static sensor position. We verified the feasibility of the fiber optic sensor for dual-modality in vivo imaging. The OC-PAM system, as a non-invasive imaging method, demonstrates its superiority in the investigation of zebrafish larvae, an animal model with increasing significance in developmental biology and disease research. This technique can also be applied for functional as well as longitudinal studies in the future