Caloric effects around phase transitions in magnetic materials described by ab initio theory : the electronic glue and fluctuating local moments

We describe magneto-, baro-, and elastocaloric effects (MCEs, BCEs, and eCEs) in materials, which possess both discontinuous (first-order) and continuous (second-order) magnetic phase transitions. Our ab initio theory of the interacting electrons of materials in terms of disordered local moments has produced explicit mechanisms for the drivers of these transitions, and here, we study associated caloric effects in three case studies where both types of transition are evident. Our earlier work had described FeRh’s magnetic phase diagram and large MCE. Here, we present calculations of its substantial BCE and eCE. We describe the MCE of dysprosium and find very good agreement with experimental values for isothermal entropy ((ΔSiso) and adiabatic temperature (ΔTad) changes over a large temperature span and different applied magnetic field values. We examine the conditions for optimal values of both ΔSiso and ΔTad that comply with a Clausius–Clapeyron analysis, which we use to propose a promising elastocaloric cooling cycle arising from the unusual dependence of the entropy on temperature and biaxial strain found in our third case study—the Mn3GaN antiperovskite. We explain how both ΔSiso and ΔTad can be kept large by exploiting the complex tensile strain–temperature magnetic phase diagram, which we had earlier predicted for this material and also propose that hysteresis effects will be absent from half of the caloric cycle. This rich and complex behavior stems from the frustrated nature of the interactions among the Mn local moments

Probabilistic metrology or how some measurement outcomes render ultra-precise estimates

We show on theoretical grounds that, even in the presence of noise, probabilistic measurement strategies (which have a certain probability of failure or abstention) can provide, upon a heralded successful outcome, estimates with a precision that exceeds the deterministic bounds for the average precision. This establishes a new ultimate bound on the phase estimation precision of particular measurement outcomes (or sequence of outcomes). For probe systems subject to local dephasing, we quantify such precision limit as a function of the probability of failure that can be tolerated. Our results show that the possibility of abstaining can set back the detrimental effects of noise.Comment: Improved version of arXiv:1407.6910 with an extended introduction where we clarify our approach to metrology, and probabilistic metrology in particular. Changed titl

First-order ferromagnetic transitions of lanthanide local moments in divalent compounds: An itinerant electron positive feedback mechanism and Fermi surface topological change

Around discontinuous (first-order) magnetic phase transitions the strong caloric response of materials to the application of small fields is widely studied for the development of solid-state refrigeration. Typically strong magnetostructural coupling drives such transitions and the attendant substantial hysteresis dramatically reduces the cooling performance. In this context we describe a purely electronic mechanism which pilots a first-order paramagnetic-ferromagnetic transition in divalent lanthanide compounds and which explains the giant non-hysteretic magnetocaloric effect recently discovered in a Eu$_2$In compound. There is positive feedback between the magnetism of itinerant valence electrons and the ferromagnetic ordering of local $f$-electron moments, which appears as a topological change to the Fermi surface. The origin of this electronic mechanism stems directly from Eu's divalency, which explains the absence of a similar discontinuous transition in Gd$_2$In.Comment: 8 pages, 7 figure

Development of mass spectrometry techniques for analysis of biomedical systems

2020 Spring.Includes bibliographical references.The advances of modern mass spectrometry (MS) have allowed MS to become one of the essential analytical tools for biological and biomedical research. Mass spectrometry's ability to provide rapid and sensitive analysis of many types of analytes made it an excellent candidate to study the polysaccharide dextran, biodegradable poly(organophosphazene) and polyester derived polymers, as well as interfering species in commonly used cell viability studies. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS) was used to analyze the polysaccharide dextran. Polysaccharides, including dextran, are difficult to ionize due to their inherent neutrality. Ionization efficiency is poor in negative polarity ESI because they lack acidic groups typically needed for proton abstraction, and ionization efficiency in positive polarity ESI is poor because polysaccharides have low proton affinity. In efforts to circumvent the issue of low ionization efficiency, dextran was derivatized to try mimicking protein-like ionization. Dextran was derivatized using a one-pot derivatization procedure with ethylenediamine, thus, giving dextran free terminal amine groups. The derivatization procedure attached up to four ethylenediamine groups and allowed dextran to have up to four protonations (or positive charges). The ability to carry up to four charges shifted the molecular weight of dextran to a lower m/z, similar to protein supercharging ionization. Mass spectrometric analysis was successfully applied to identify potential degradation products during the catalytic release of nitric oxide (NO) from S-nitrosoglutathione (GSNO) when it was exposed to metal-organic frameworks (MOFs) embedded onto chitosan polymer support systems. Oxidized glutathione (GSSG) was confirmed to be the reaction byproduct of the release of NO from GSNO, and glucosamine and N-acetylglucosamine were identified as the degradation products from the chitosan polymer support system. In a similar use of MS, potential interferences in the commonly used CellTiter Blue and MTT cell viability assays were studied. When the UV-vis spectroscopic assays suggested interferences or produced inconclusive results, mass spectrometric analyses accurately determined whether selected small molecules were responsible for conversion of resazurin to resorufin, MTT to formazan, or if they were responsible for severe signal suppression on the UV-vis spectroscopic assays. MS was also successfully used to study the biodegradable poly(phosphazene), polyester polymers and their nitrosated analogues. The purpose of the studies was to investigate the potential degradation products from the degradation of these polymers. In-depth understanding of the degradation products from these polymers may aid in determining potential unwanted side effects that may render the polymeric devices unusable. A combination of direct flow injection MS, liquid chromatography mass spectrometry (LC-MS), and tandem mass spectrometry (LC-MS/MS) were successfully applied to identify the degradation products from each polymer system investigated. Identification of each degradation product from these polymers strongly suggests the implementation of LC-MS/MS when biodegradable polymers are developed for biomedical applications. Particularly because these methods can be used when a device intended for medical use undergoes the ISO 10993 series Biological Evaluation of Medical Devices. Additionally, in a highly collaborative effort, a chiral metal-organic framework (MOF) was used as a chiral stationary phase (CSP) for chiral resolution. The chiral-MOF (TAMOF-1) was packed in-house into an empty HPLC column and successfully used to resolve chiral compounds efficiently using normal and reversed phase solvent systems, highlighting the versatility of the chiral-MOF

Chromatographic analysis of fatty acids using 9-chloromethyl-anthracene and 2-bromomethyl-anthraquinone

Fatty acids are carboxylic acids with long alkane or alkene chains and are important components of living organisms. The presence of the carboxylic acid is analytically very important since it allows for derivatization with fluorescence reagents such as 9-chloromethyl-anthracene (9-CMA) for HPLC analysis. A method for the analysis of fatty acids using 9-CMA and 2-bromomethyl-anthraquinone (MAQ-Br) was developed. The method utilizes a modified protocol previously used for the analysis of short-chain carboxylic acids with 9-CMA. The modified protocol was applied to medium- and long-chain fatty acids for analysis by HPLC with UV-visible and fluorescence detection. After successful derivatization and analysis using 9-CMA, MAQ-Br was used for derivatization with successful results. Six fatty acid standards were derivatized with 9-CMA and utilized to develop a separation method and quantification. With the use of a Zorbax Rx C8 column, good separation was achieved and calibration curves ranging from 1 to 100 pmol with good linearity and R2 values. The limit of detection was approximately 50 fmol and the maximum limit of quantitation was approximately 100 pmol for the 9-CMA derivatives. After successful separation and quantitation, analyses of fat-free cooking spray and cloprostenol, a prostaglandin, were performed

Investor protection and corporate control

We argue that investor protection changes the relative importance of productivity and scale as drivers of corporate control transfers. Using a large sample of European firms we find that control transfers are more correlated with increasing profitability and less correlated with increasing size when investor protection is strong. This suggests that improving productivity is more important as a driver of acquisitions when investor protection is strong, and alleviating financial constraints or empire building are more important when investor protection is weak. Our evidence is consistent with the idea that good investor protection promotes a more productive use of corporate assets