Thermodynamic quantum critical behavior of the Kondo necklace model

We obtain the phase diagram and thermodynamic behavior of the Kondo necklace model for arbitrary dimensions $d$ using a representation for the localized and conduction electrons in terms of local Kondo singlet and triplet operators. A decoupling scheme on the double time Green's functions yields the dispersion relation for the excitations of the system. We show that in $d\geq 3$ there is an antiferromagnetically ordered state at finite temperatures terminating at a quantum critical point (QCP). In 2-d, long range magnetic order occurs only at T=0. The line of Neel transitions for $d>2$ varies with the distance to the quantum critical point QCP $|g|$ as, $T_N \propto |g|^{\psi}$ where the shift exponent $\psi=1/(d-1)$. In the paramagnetic side of the phase diagram, the spin gap behaves as $\Delta\approx \sqrt{|g|}$ for $d \ge 3$ consistent with the value $z=1$ found for the dynamical critical exponent. We also find in this region a power law temperature dependence in the specific heat for $k_BT\gg\Delta$ and along the non-Fermi liquid trajectory. For $k_BT \ll\Delta$, in the so-called Kondo spin liquid phase, the thermodynamic behavior is dominated by an exponential temperature dependence.Comment: Submitted to PR

The chloroplast of chlamydomonas reinhardtii as a testbed for engineering nitrogen fixation into plants

Eukaryotic organisms such as plants are unable to utilise nitrogen gas (N2) directly as a source of this essential element and are dependent either on its biological conversion to ammonium by diazotrophic prokaryotes, or its supply as chemically synthesised nitrate fertiliser. The idea of genetically engineering crops with the capacity to fix N2 by introduction of the bacterial nitrogenase enzyme has long been discussed. However, the expression of an active nitrogenase must overcome several major challenges: the coordinated expression of multiple genes to assemble an enzyme complex containing several different metal cluster co-factors; the supply of sufficient ATP and reductant to the enzyme; the enzyme’s sensitivity to oxygen; and the intracellular accumulation of ammonium. The chloroplast of plant cells represents an attractive location for nitrogenase expression, but engineering the organelle’s genome is not yet feasible in most crop species. However, the unicellular green alga Chlamydomonas reinhardtii represents a simple model for photosynthetic eukaryotes with a genetically tractable chloroplast. In this review, we discuss the main advantages, and limitations, of this microalga as a testbed for producing such a complex multi-subunit enzyme. Furthermore, we suggest that a minimal set of six transgenes are necessary for chloroplast-localised synthesis of an ‘Fe-only’ nitrogenase, and from this set we demonstrate the stable expression and accumulation of the homocitrate synthase, NifV, under aerobic conditions. Arguably, further studies in C. reinhardtii aimed at testing expression and function of the full gene set would provide the groundwork for a concerted future effort to create nitrogen-fixing crops

Lanthanides in granulometric fractions of Mediterranean soils. Can they be used as fingerprints of provenance?

Highlights Are lanthanides from fine sand and clay genetically related to the geological materials? Lanthanide concentrations of fine sand and clay fit chronofunctions Pearson's r of lanthanide couples decreases when separation increases in the periodic table Free forms of clay are scavengers of lanthanides and concentrate HREE and ceriumSample preparation and chemical analysis were conducted by Emma Humphreys-Williams and Stanislav Strekopytov (Imaging and Analysis Centre, Natural History Museum, London, UK). This work was supported by a grant from Ministerio de Economía, Industria y Competitividad de España (‘Tipologías de Suelos Mediterráneos versus Cuarzo. En la frontera del conocimiento edafogenético’; Ref. CGL2016-80308-P). The authors thank Professor Margaret A. Oliver, an anonymous editor and two anonymous reviewers for helpful comments and suggestions that improved the final manuscript. We also thank Robert Abrahams (Bsc) for revising the English language.There is geochemical interest in the lanthanides because they behave like a group that is closely related to the parent materials during surface processes, although they also undergo fractionation as a result of supergene dynamics. We analysed lanthanide concentrations (ICPms) in the granulometric fractions fine sand, clay and free forms of clay (FFclay‐CDB and FFclay‐Ox: extracted with citrate‐dithionite‐sodium bicarbonate and with ammonium oxalate, respectively) from a soil chronosequence of Mediterranean soils. There was a relative enrichment of heavy rare earth elements (HREE) in the clay fraction and its free forms with respect to fine sand. The clay free forms behaved as scavengers of lanthanides, and oxidative scavenging of cerium (Ce) in FFclay‐CDB was also detected. Lanthanide concentrations (lanthanum to gadolinium in fine sand; terbium to lutetium in clay) varied with soil age, and chronofunctions were established. There was a strong positive collinearity between most of the lanthanide concentrations. Furthermore, the value of the correlation index (Pearson's r ) of the concentrations between couples of lanthanides (r CLC) decreased significantly with increasing separation between the elements in the periodic table; this has never been described in soils. Several geochemical properties and indices in the fine sand and clay soil fractions and in the geological materials of the Guadalquivir catchment showed, on the one hand, a genetic relation between them all, enabling the lanthanides to be used as fingerprints of provenance; on the other hand, fractionation between fine sand and clay showed these are actively involved in soil lanthanide dynamics.Secretaría de Estado de Investigación, Desarrollo e Innovación. Grant Number: CGL2016‐80308‐

Algorithms For Extracting Timeliness Graphs

We consider asynchronous message-passing systems in which some links are timely and processes may crash. Each run defines a timeliness graph among correct processes: (p; q) is an edge of the timeliness graph if the link from p to q is timely (that is, there is bound on communication delays from p to q). The main goal of this paper is to approximate this timeliness graph by graphs having some properties (such as being trees, rings, ...). Given a family S of graphs, for runs such that the timeliness graph contains at least one graph in S then using an extraction algorithm, each correct process has to converge to the same graph in S that is, in a precise sense, an approximation of the timeliness graph of the run. For example, if the timeliness graph contains a ring, then using an extraction algorithm, all correct processes eventually converge to the same ring and in this ring all nodes will be correct processes and all links will be timely. We first present a general extraction algorithm and then a more specific extraction algorithm that is communication efficient (i.e., eventually all the messages of the extraction algorithm use only links of the extracted graph)

The lower limit of pitch perception for pure tones and low-frequency complex sounds

The lower limit of pitch (LLP) perception was explored for pure tones, sinusoidally amplitude-modulated (SAM) tones with a carrier frequency of 125 Hz, and trains of 125-Hz tone pips, using an adaptive procedure to estimate the lowest repetition rate for which a tonal/humming quality was heard. The LLP was similar for the three stimulus types, averaging 19 Hz. There were marked individual differences, which were correlated to some extent across stimulus types. The pure-tone stimuli contained a single resolved harmonic, whereas the SAM tones and tone-pip trains contained only unresolved components, whose frequencies did not necessarily form a harmonic series. The similarity of the LLP across stimulus types suggests that the LLP is determined by the repetition period of the sound for pure tones, and the envelope repetition period for complex stimuli. The results are consistent with the idea that the LLP is determined by a periodicity analysis in the auditory system, and that the longest time interval between waveform or envelope peaks for which this analysis can be performed is approximately 53 ms

A Simple Technology for Generating Marker-Free Chloroplast Transformants of the Green Alga Chlamydomonas reinhardtii.

The availability of routine methods for the genetic engineering of the chloroplast genome of Chlamydomonas reinhardtii is allowing researchers to explore the use of this microalga as a phototrophic cell platform for synthesis of high value recombinant proteins and metabolites. However, the established method for delivering transforming DNA into the algal chloroplast involves microparticle bombardment using an expensive "gene gun". Furthermore, selection of transformant lines most commonly involves the use of a bacterial antibiotic resistance gene. In this chapter, we describe a simple and cheap delivery method in which cell-DNA suspensions are agitated with glass beads: a method that is more commonly used for nuclear transformation of Chlamydomonas. We also describe the use of plasmid expression vectors that target transgenes to a neutral site within the chloroplast genome between psbH and trnE2, and employ psbH as the selectable marker-thereby avoiding issues of unwanted antibiotic resistance genes in the resulting transgenic lines. Finally, we highlight a feature in our latest vectors in which the presence of a novel tRNA gene on the plasmid results in recognition within the chloroplast of UGA stop codons in transgenes as tryptophan codons. This feature simplifies the cloning of transgenes that are normally toxic to E. coli, serves as a biocontainment strategy restricting the functional escape of transgenes from the algal chloroplast to environmental microorganisms, and offers a simple system of temperature-regulated translation of transgenes

Circuit architecture explains functional similarity of bacterial heat shock responses

Heat shock response is a stress response to temperature changes and a consecutive increase in amounts of unfolded proteins. To restore homeostasis, cells upregulate chaperones facilitating protein folding by means of transcription factors (TF). We here investigate two heat shock systems: one characteristic to gram negative bacteria, mediated by transcriptional activator sigma32 in E. coli, and another characteristic to gram positive bacteria, mediated by transcriptional repressor HrcA in L. lactis. We construct simple mathematical model of the two systems focusing on the negative feedbacks, where free chaperons suppress sigma32 activation in the former, while they activate HrcA repression in the latter. We demonstrate that both systems, in spite of the difference at the TF regulation level, are capable of showing very similar heat shock dynamics. We find that differences in regulation impose distinct constrains on chaperone-TF binding affinities: the binding constant of free sigma32 to chaperon DnaK, known to be in 100 nM range, set the lower limit of amount of free chaperon that the system can sense the change at the heat shock, while the binding affinity of HrcA to chaperon GroE set the upper limit and have to be rather large extending into the micromolar range.Comment: 17 pages, 5 figure

Microfluidic Continuous Approaches to Produce Magnetic Nanoparticles with Homogeneous Size Distribution

We present a gas-liquid microfluidic system as a reactor to obtain magnetite nanoparticles with an excellent degree of control regarding their crystalline phase, shape and size. Several types of microflow approaches were selected to prevent nanomaterial aggregation and to promote homogenous size distribution. The selected reactor consists of a mixer stage aided by ultrasound waves and a reaction stage using a N2-liquid segmented flow to prevent magnetite oxidation to non-magnetic phases. A milli-fluidic reactor was developed to increase the production rate where a magnetite throughput close to 450 mg/h in a continuous fashion was obtained

General and specific culture learning in EFL textbooks aimed at adult learners in Spain

Since language teaching in modern-day society is closely linked to cultural instruction, this study employs the model of a cultural learning analysis based on the earlier work of Paige and Lee. Using this model, the authors analysed the cultural content of six B1 and B2-level textbooks for teaching English to adults in Spain, and carried out a comparative study of the results, contrasting the two levels. Findings show that the subjective aspects of culture receive less coverage in textbooks, despite being fundamental to an understanding of the values of a society. Regarding the comparison between B1 and B2 levels, the data indicate that the number of big “C” Culture occurrences is similar for both levels, although there are differences in other cultural aspects. So, for example, culture in general is dealt with more at the B1 level, whereas small “c” culture is dealt with more at the B2 level