Subfields of Solvable Sextic Field Extensions

Let F be a field, f(x) in F[x] an irreducible polynomial of degree six, K the stem field of f, and G the Galois group of f over F. We show G is solvable if and only if K/F has either a quadratic or cubic subfield. We also show that G can be determined by: the size of the automorphism group of K/F, the discriminant of f, and the discriminants of polynomials defining intermediate fields. Since most methods for computing polynomials defining intermediate subfields require factoring f over its stem, we include a method that does not require factorization over K, but rather only relies factoring two linear resolvent polynomials over F

Feasibility and Limitations of High-Voltage Lithium-Iron-Manganese Spinels

Positive electrodes with high energy densities for Lithium-ion batteries (LIB) almost exclusively rely on toxic and costly transition metals. Iron based high voltage spinels can be feasible alternatives, but the phase stabilities and optimal chemistries for LIB applications are not fully understood yet. In this study, LiFe$_{x}$Mn$_{2-x}$O$_{4}$ spinels with x = 0.2 to 0.9 were synthesized by solid-state reaction at 800 °C. High-resolution diffraction methods reveal gradual increasing partial spinel inversion as a function of x and early secondary phase formation. Mössbauer spectroscopy was used to identify the Fe valences, spin states and coordination. The unexpected increasing lattice parameters with Fe substitution for Mn was explained considering the anion-cation average bond lengths determined by Rietveld analysis and Mn$^{3+}$ overstoichiometries revealed by cyclic voltammetry. Finally, galvanostatic cycling of Li-Fe-Mn-spinels shows that the capacity fading is correlated to increased cell polarization for higher upper charging cut-off voltage, Fe-content and C-rate. The electrolyte may also contribute significantly to the cycling limitations

The effect of chair massage on muscular discomfort in cardiac sonographers: a pilot study

<p>Abstract</p> <p>Background</p> <p>Cardiac sonographers frequently have work-related muscular discomfort. We aimed to assess the feasibility of having sonographers receive massages during working hours in an area adjacent to an echocardiography laboratory and to assess relief of discomfort with use of the massages with or without stretching exercises.</p> <p>Methods</p> <p>A group of 45 full-time sonographers was randomly assigned to receive weekly 30-minute massage sessions, massages plus stretching exercises to be performed twice a day, or no intervention. Outcome measures were scores of the <it>Quick</it>DASH instrument and its associated work module at baseline and at 10 weeks of intervention. Data were analyzed with standard descriptive statistics and the separation test for early-phase comparative trials.</p> <p>Results</p> <p>Forty-four participants completed the study: 15 in the control group, 14 in the massage group, and 15 in the massage plus stretches group. Some improvement was seen in work-related discomfort by the <it>Quick</it>DASH scores and work module scores in the 2 intervention groups. The separation test showed separation in favor of the 2 interventions.</p> <p>Conclusion</p> <p>On the basis of the results of this pilot study, larger trials are warranted to evaluate the effect of massages with or without stretching on work-related discomfort in cardiac sonographers.</p> <p>Trial Registration</p> <p>NCT00975026 ClinicalTrials.gov</p

Strategies towards enabling lithium metal in batteries: interphases and electrodes

Despite the continuous increase in capacity, lithium-ion intercalation batteries are approaching their performance limits. As a result, research is intensifying on next-generation battery technologies. The use of a lithium metal anode promises the highest theoretical energy density and enables use of lithium-free or novel high-energy cathodes. However, the lithium metal anode suffers from poor morphological stability and Coulombic efficiency during cycling, especially in liquid electrolytes. In contrast to solid electrolytes, liquid electrolytes have the advantage of high ionic conductivity and good wetting of the anode, despite the lithium metal volume change during cycling. Rapid capacity fade due to inhomogeneous deposition and dissolution of lithium is the main hindrance to the successful utilization of the lithium metal anode in combination with liquid electrolytes. In this perspective, we discuss how experimental and theoretical insights can provide possible pathways for reversible cycling of twodimensional lithium metal. Therefore, we discuss improvements in the understanding of lithium metal nucleation, deposition, and stripping on the nanoscale. As the solid–electrolyte interphase (SEI) plays a key role in the lithium morphology, we discuss how the proper SEI design might allow stable cycling. We highlight recent advances in conventional and (localized) highly concentrated electrolytes in view of their respective SEIs. We also discuss artificial interphases and three-dimensional host frameworks, which show prospects of mitigating morphological instabilities and suppressing large shape change on the electrode level

Directed plant cell-wall accumulation of iron: embedding co-catalyst for efficient biomass conversion

Plant lignocellulosic biomass is an abundant, renewable feedstock for the production of biobased fuels and chemicals. Previously, we showed that iron can act as a co-catalyst to improve the deconstruction of lignocellulosic biomass. However, directly adding iron catalysts into biomass prior to pretreatment is diffusion limited, and increases the cost of biorefinery operations. Recently, we developed a new strategy for expressing iron-storage protein ferritin intracellularly to accumulate iron as a catalyst for the downstream deconstruction of lignocellulosic biomass. In this study, we extend this approach by fusing the heterologous ferritin gene with a signal peptide for secretion into Arabidopsis cell walls (referred to here as FerEX). The transgenic Arabidopsis plants. FerEX. accumulated iron under both normal and iron-fertilized growth conditions; under the latter (iron-fertilized) condition, FerEX transgenic plants showed an increase in plant height and dry weight by 12 and 18 %, respectively, compared with the empty vector control plants. The SDS- and native-PAGE separation of cell-wall protein extracts followed by Western blot analyses confirmed the extracellular expression of ferritin in FerEX plants. Meanwhile, Perls' Prussian blue staining and X-ray fluorescence microscopy (XFM) maps revealed iron depositions in both the secondary and compound middle lamellae cell-wall layers, as well as in some of the corner compound middle lamella in FerEX. Remarkably, their harvested biomasses showed enhanced pretreatability and digestibility, releasing, respectively, 21 % more glucose and 34 % more xylose than the empty vector control plants. These values are significantly higher than those of our recently obtained ferritin intracellularly expressed plants. This study demonstrated that extracellular expression of ferritin in Arabidopsis can produce plants with increased growth and iron accumulation, and reduced thermal and enzymatic recalcitrance. The results are attributed to the intimate colocation of the iron co-catalyst and the cellulose and hemicellulose within the plant cell-wall region, supporting the genetic modification strategy for incorporating conversion catalysts into energy crops prior to harvesting or processing at the biorefinery.https://doi.org/10.1186/s13068-016-0639-

Transport proteins promoting Escherichia coli pathogenesis

Escherichia coli is a genetically diverse species infecting hundreds of millions of people worldwide annually. We examined seven well-characterized E. coli pathogens causing urinary tract infections, gastroenteritis, pyelonephritis and haemorrhagic colitis. Their transport proteins were identified and compared with each other and a non-pathogenic E. coli K12 strain to identify transport proteins related to pathogenesis. Each pathogen possesses a unique set of protein secretion systems for export to the cell surface or for injecting effector proteins into host cells. Pathogens have increased numbers of iron siderophore receptors and ABC iron uptake transporters, but the numbers and types of low-affinity secondary iron carriers were uniform in all strains. The presence of outer membrane iron complex receptors and high-affinity ABC iron uptake systems correlated, suggesting co-evolution. Each pathovar encodes a different set of pore-forming toxins and virulence-related outer membrane proteins lacking in K12. Intracellular pathogens proved to have a characteristically distinctive set of nutrient uptake porters, different from those of extracellular pathogens. The results presented in this report provide information about transport systems relevant to various types of E. coli pathogenesis that can be exploited in future basic and applied studies

Chromatographische Methode zur vollständigen Isolierung der stickstoffendohedralen Fullerene N@C60 und N@C70 sowie deren EPR-Spektren in Flüssigkristallen

Fullerene können als Fallen für Atome oder kleine Cluster angesehen werden. Der Einschluß hochreaktiver Atome wie Stickstoff und Phosphor führen zu isolierten paramagnetischen Systemen. Diese können wie eine gefüllte Einkaufstasche an beliebigen Positionen abgelegt werden. Damit ist eine Nanostrukturierung von paramagnetischen Festkörpern möglich. Das in C60 oder C70 gefangene hochreaktive Stickstoffatom ist aufgrund der sehr langen Spin-Gitter und Spin-Spin Relaxationszeiten und den daraus resultierenden sehr schmalen Absorptionslinien ein interessantes System. Mit der Elektron-Paramagnetischen-Resonanz (EPR) können diese endohedralen Stickstoffullerene auch in hoher Verdünnung (1:10000) detektiert werden. Aufgrund der hohen Stabilität von N@C60 und N@C70 gegenüber Sauerstoff, Licht, Temperatur (bis zu 100 °C) und der Möglichkeit der chemischen Modifikation sind diese Systeme als Spin-Sonde einsetzbar. Der erste Teil der Arbeit beschäftigt sich mit der Isolierung von N@C60 aus einer Mischung von N@C60 und leerem C60 (1:10000) mit der Hochdruckflüssigchromatographie (HPLC). Neben der eigens dafür entwickelten computergesteuerten chromatographischen Anlage werden zwei weitere Trennverfahren vorgestellt. Die Säulenfiltration und das Peakrecycling. Damit konnte erstmals eine Reindarstellung von N@C60 durchgeführt werden. Das optische Spektrum (UV/VIS) von N@C60 zeigt, daß die atomare Wellenfunktion des Stickstoffatoms nicht mit der molekularen Wellenfunktion des Fullerenkäfigs wechselwirkt und bestätigt damit die Ergebnisse früherer Elektron-Kern-Doppelresonanz-Messungen (ENDOR). Der zweite Teil beschreibt die konzentrationsabhängigen EPR-Festkörper-Spektren von N@C60/C60 und die Temperaturabhängigkeit der EPR-Spektren der Reinsubstanz. Die Simulation der Spektren wurde mit einem eigens dafür geschriebenen Computer-Monte-Carlo-Verfahren, basierend auf der Dipol-Dipol-Kopplung, durchgeführt. Der dritte Teil der Arbeit beschreibt die EPR-Spektren der ausgerichteten endohedralen Fullerene N@C60 und N@C70 in einer Flüssigkristallmatrix. Aus diesen Messungen konnte über die Nullfeldaufspaltung zum einen der temperaturabhängige Ordnungsgrad der Flüssigkristalle verfolgt werden. Zum anderen konnte der Nullfeldparameter selbst und das Vorzeichen des Nullfeldparameters von N@C70 bestimmt werden. Dies zeigt eindrucksvoll den Vorteil gegenüber Pulverspektren, bei denen alle Winkel erlaubt sind, und die spektralen Linien verbreitern. Überraschend zeigt auch das N@C60, welches aufgrund seiner sphärischen Symmetrie keine Ausrichtung erfahren dürfte, eine signifikante Orientierung. Diese Pseudo-Orientierung ist auf die anisotrope Spindichteverteilung durch den anisotropen Lösungsmittelkäfig der Flüssigkristalle zurückzuführen. Beide Systeme zeigen eindrucksvoll, wie sie sich als Spin-Sonde in anisotropen Medien einsetzen lassen