Magnetic structure and ferroelectric polarization of MnWO4 investigated by density functional calculations and classical spin analysis

The ordered magnetic states of MnWO4 at low temperatures were examined by evaluating the spin exchange interactions between the Mn2+ ions of MnWO4 on the basis of first principles density functional calculations and by performing classical spin analysis with the resulting spin exchange parameters. Our work shows that the spin exchange interactions are frustrated within each zigzag chain of Mn2+ ions along the c-direction and between such chains of Mn2+ ions along the a-direction. This explains the occurrence of a spiral-spin order along the c- and a-directions in the incommensurate magnetic state AF2, and that of a uudd spin order along the c- and a-directions in the commensurate magnetic state AF1. The ferroelectric polarization of MnWO4 in the spiral-spin state AF2 was examined by performing Berry phase calculations for a model superstructure to find that the ferroelectric polarization occurs along the b-direction, in agreement with experiment.Comment: 30 pages, 10 figures, 4 figure

High-pressure phase transitions and compressibility of wolframite-type tungstates

This paper reports an investigation on the phase diagram and compressibility of wolframite-type tungstates by means of x-ray powder diffraction and absorption in a diamond-anvil cell and ab initio calculations. X-ray diffraction experiments show that monoclinic wolframite-type MgWO4 suffers at least two phase transitions, the first one being to a triclinic polymorph with a structure similar to that of CuWO4 and FeMoO4-II. The onset of each transition is detected at 17.1 and 31 GPa. In ZnWO4 the onset of the monoclinic-triclinic transition has been also found at 16.7 GPa. This transition does not involve any change in the atomic coordination as confirmed by x-ray absorption measurements. These findings are supported by density-functional theory calculations, which predict the occurrence of additional transitions upon further compression. Calculations have been also performed for wolframite-type MnWO4, which is found to have an antiferromagnetic configuration. In addition, our study reveals details of the local-atomic compression in MgWO4 and ZnWO4. In particular, below the transition pressure the ZnO6 and equivalent polyhedra tend to become more regular, whereas, the WO6 octahedra remain almost unchanged. Fitting the pressure-volume data we obtained the equation of state for the low-pressure phase of MgWO4 and ZnWO4. These and previous results on MnWO4 and CdWO4 are compared with the calculations. The compressibility of wolframite-type tungstates is also systematically discussed. Finally Raman spectroscopy measurements and lattice dynamics calculations are presented for MgWO4

High-pressure structural phase transitions in CuWO4

We study the effects of pressure on the structural, vibrational, and magnetic behavior of cuproscheelite. We performed powder x-ray diffraction and Raman spectroscopy experiments up to 27 GPa as well as ab initio total-energy and lattice-dynamics calculations. Experiments provide evidence that a structural phase transition takes place at 10 GPa from the low-pressure triclinic phase (P-1) to a monoclinic wolframite-type structure (P2/c). Calculations confirmed this finding and indicate that the phase transformation involves a change in the magnetic order. In addition, the equation of state for the triclinic phase is determined: V0 = 132.8(2) A3, B0 = 139 (6) GPa and = 4. Furthermore, experiments under different stress conditions show that non-hydrostatic stresses induce a second phase transition at 17 GPa and reduce the compressibility of CuWO4, B0 = 171(6) GPa. The pressure dependence of all Raman modes of the triclinic and high-pressure phases is also reported and discussed.Comment: 33 pages, 9 figures, 5 table

Bioassays for the optimization of Hermetia illucens (L.) egg laying in a prototype of industrial plant

The black soldier fly Hermetia illucens (L.) (Diptera: Stratiomyidae) presents a particular interest for the feed and food industry as its larvae have the capacity to convert quickly and efficiently large quantities of organic waste or byproducts into a protein biomass rich in fats. Although the information on larvae development is abundant, the necessary knowledge of adult biology to produce large amounts of eggs remains a great challenge. This work represents a part of a regional project (ValoriBio, Emilia Romagna, Italy) where one of the main outputs is the construction of a pilot plant for H. illucens mass rearing, which includes a module for adult rearing. Therefore, a specific custom-made climatic chamber was developed and it consisted in a thermally insulated container (1m3 volume), with a transparent window bearing a light-emitting diode (LED) lights source (UV, green and blue LEDs) on top. Temperature and humidity were controlled through a Peltier cooler/heater system, an ultrasound humidifier and several humidity-temperature digital sensors. An exterior electronic board connected to a touch screen was developed to control and record the rearing parameters. The biological parameters used to establish the functionality of the prototype were the patterns of oviposition, the egg weight and adult longevity. Bioassays were conducted in tree types of climatic chambers at 27°C ± 0,5°C and 70 ± 5% relative humidity considering as treatments the use of different light sources (fluorescent tubes, white LEDs and the UV-green-blue combination of LEDs) and the flies diet (water and sugar, just water or nothing). The results allowed to identify the better conditions to obtain the highest amounts of eggs in the shortest time

Evaluation of biological parameters and the lipid profile of black soldier fly (Hermetia illucens, Stratiomyidae) reared on byproducts from different food chains

The total amount of bio-waste produced annually in the EU by the food and beverage value chains is estimated at 37 Mtons. The possibility to use insects for the valorization of byproducts from these chains may represent a sustainable and valuable solution. This study aimed to analize the development parameters and the lipid content of black soldier fly (Hermetia illucens, Stratiomyidae) prepupae reared on byproducts obtained from different food chains. The substrates used for this experiment were: beer brewery byproducts, tomato skins and seeds, spent ground coffee, grape stalks and marcs, bread dough, cow milk whey and fish-waste material. H. illucens larvae were reared on each substrate within glass containers at 28 ± 0.5 °C and 98% relative humidity. Biological parameters such as larval weight, prepupae weight and development time were recorded. Obtained prepupae were frozen before fractionation and chemical characterization. Lipid extraction was carried out using the Folch method, adjusted for the specific samples. The total lipid content was calculated and the quantitative characterization of the fatty acid profile was performed through GC-FID analysis. The best larval performance was obtained when specimens were reared on byproducts from beer, tomato and cheese food chains. The different substrate composition was reflected in the lipid profile of H. illucens larvae. In particular, the saturated to unsaturated fatty acid ratio showed marked changes according to the substrate. The high content and type of lipids, together with the proteins and chitin extracted from the prepupae represent high-value biobased products that might be used in the feed/food industry as well as for the development of innovative biomaterials for different technological purposes. These results suggest that mass rearing of H. illucens larvae, especially on some of the tested byproducts, may be exploited for an alternative employment of the food/beverage bio-waste

A Statistical Analysis Plan: Validity of ROX index for Nasal High Flow Therapy in Critical Care Patients, including those with hypercapnic respiratory failure

A statistical analysis proposal to use critical care data to assess the use of the ROX index in predicting failure of patients to respond to high flow nasal therap