An expansion of the field modulus suitable for the description of strong field gradients in axisymmetric magnetic fields: Application to single-sided magnet design, field mapping and STRAFI

International audienceMapping (or plotting) the magnetic field has a critical importance for the achievement of the homogeneous magnetic field necessary to standard MR experiments. A powerful tool for this purpose is the Spherical Harmonic Expansion (SHE), which provides a simple way to describe the spatial variations of a field in free space. Well-controlled non-zero spatial variations of the field are critical to MRI. The resolution of the image is directly related to the strength of the gradient used to encode space. As a result, it is desirable to have strong variations of the field. In that case, the SHE cannot be used as is, because the field modulus variations are affected by the variations of all components of the field. In this paper, we propose a method based on the SHE to characterize such variations, theoretically and experimentally, in the limit of an axisymmetric magnetic field. Practical applications of this method are proposed through the examples of single-sided magnet design and characterization, along with Stray-Field Imaging (STRAFI)

Spray drying of fenofibrate loaded nanostructured lipid carriers

AbstractThe conversion of aqueous dispersion of nanostructured lipid carriers (NLCs) into dry powder by spray drying could be a useful approach to render NLCs with better physical chemical stability than the aqueous dispersion. In this study, aqueous NLC dispersion containing fenofibrate was converted into dry, easily reconstitutable powder using spray drying. A central composite face centered design (CCFD) was used to investigate the influence of the ratio of lipid to protectant (mannitol and trehalose) and crystallinity of spray-dried powder on the particle size, yield and residual moisture content of the dried powder. A linear relationship (R2 = 0.9915) was established between the crystalline content of the spray-dried powders against the ratio of mannitol to trehalose from 3:7 to 10:0 (w/w). Spray drying of NLC aqueous dispersion using a mannitol and trehalose mixture resulted in an increase in particle size of the NLCs after reconstitution in water as compared to that in the initial aqueous dispersion. The decrease in crystallinity of the dry powder by reducing the ratio of mannitol to trehalose could improve the reconstitution of the NLCs in water. However the yield and residual moisture content of dry powder decreased with an increase in the ratio of mannitol to trehalose. Lipid nanoparticles were able to retain the drug incorporation and the prolonged drug release profile after spray drying. The experimental model was robust, and suggested that spray drying is a viable technique for the conversion of NLCs into dry powder

Finding The Sweet Spot Of Cause-Related Marketing: Consumer Response To Campaign Tactics

Cause-related marketing is an effective promotional tool that connects with consumers’ emotions and increases sales. Two essays are presented that explore how consumers respond to different marketing tactics. The first essay presents two studies that examine cause-related marketing (CRM) promotions that require consumers’ active participation. Requiring a follow-up behavior has very valuable implications for maximizing marketing expenditures and customer relationship management. Theories related to ethical behavior, like motivated reasoning and defensive denial, are used to explain when and why consumers respond negatively to these effort demands. The first study finds that consumers rationalize not participating in CRM by devaluing the sponsored cause. The second study identifies a tactic marketers can utilize to neutralize consumers’ use of defensive denial. Allowing the consumer to choose the sponsored cause seems to effectively refocus their attention and increases consumers’ threshold for campaign requirements. Implications for nonprofits and marketing managers include a tendency for consumers to be more likely to perceive a firm as ethical and socially responsible when they are alloto choose the specific cause that is supported. The second essay addresses promotions that donate the same product purchased by the consumer, like Tom’s shoes, and creates a connection between the consumer and donation recipient. The identified victim effect is proposed to explain the success of “one for one” style donation programs. Compared to monetary donations, matched product donations lead consumers to feel more empathy for the needy recipients and also to perceive the donation has more impact. Perceptions about the transparency of the donation are also found to be an important driver of the differences between product and monetary differences

What Next-Generation 21 cm Power Spectrum Measurements Can Teach Us About the Epoch of Reionization

A number of experiments are currently working towards a measurement of the 21 cm signal from the Epoch of Reionization. Whether or not these experiments deliver a detection of cosmological emission, their limited sensitivity will prevent them from providing detailed information about the astrophysics of reionization. In this work, we consider what types of measurements will be enabled by a next-generation of larger 21 cm EoR telescopes. To calculate the type of constraints that will be possible with such arrays, we use simple models for the instrument, foreground emission, and the reionization history. We focus primarily on an instrument modeled after the $\sim 0.1~\rm{km}^2$ collecting area Hydrogen Epoch of Reionization Array (HERA) concept design, and parameterize the uncertainties with regard to foreground emission by considering different limits to the recently described "wedge" footprint in k-space. Uncertainties in the reionization history are accounted for using a series of simulations which vary the ionizing efficiency and minimum virial temperature of the galaxies responsible for reionization, as well as the mean free path of ionizing photons through the IGM. Given various combinations of models, we consider the significance of the possible power spectrum detections, the ability to trace the power spectrum evolution versus redshift, the detectability of salient power spectrum features, and the achievable level of quantitative constraints on astrophysical parameters. Ultimately, we find that $0.1~\rm{km}^2$ of collecting area is enough to ensure a very high significance ($\gtrsim30\sigma$) detection of the reionization power spectrum in even the most pessimistic scenarios. This sensitivity should allow for meaningful constraints on the reionization history and astrophysical parameters, especially if foreground subtraction techniques can be improved and successfully implemented.Comment: 27 pages, 18 figures, updated SKA numbers in appendi

LSST: from Science Drivers to Reference Design and Anticipated Data Products

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg$^2$ field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$\sigma$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $\delta<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures available from https://www.lsst.org/overvie

Durable Hydrophobic Polymer Surfaces

Highly hydrophobic materials and surfaces are useful for a wide range of applications such as waterproof clothing, self-cleaning windows, reducing drag on watercraft, preventing ice buildup, and designing oil/water separators. However, the hydrophobicity of these materials decreases over time though surface wear, presenting a significant drawback. In this work, we demonstrate a solution to this poor durability through surfaces which are renewed with wear, continually exposing a new hydrophobic surface. Materials can be made more hydrophobic through the addition of surface texture or microstructure. Typically, as this texture is worn smooth through use and abrasion, the material steadily loses its hydrophobic property. This can be overcome by designing materials with a consistent, textured microstructure through the entire bulk, not only at the surface. This consistent morphology can be produced from interconnected microparticles. Materials produced in this way can retain a rough surface texture despite wear; as each layer is worn away, a new layer with an identical morphology is exposed and the material remains hydrophobic. The hydrophobicity of this structure is demonstrated both before and after abrasion wear. The hydrophobicity of these surfaces is compared to similar textured surfaces that lack this “renewability.