Dissipative quantum mechanics beyond Bloch-Redfield: A consistent weak-coupling expansion of the ohmic spin boson model at arbitrary bias

We study the time dynamics of the ohmic spin boson model at arbitrary bias $\epsilon$ and small coupling $\alpha$ to the bosonic bath. Using perturbation theory and the real-time renormalization group (RG) method we present a consistent zero-temperature weak-coupling expansion for the time evolution of the reduced density matrix one order beyond the Bloch-Redfield solution. We develop a renormalized perturbation theory and present an analytical solution covering the whole range from small to large times, including further results for exponentially small or large times. Resumming all secular terms in all orders of perturbation theory we find exponential decay for all terms of the time evolution. We determine the preexponential functions and find slowly varying logarithmic terms with the renormalized Rabi frequency $\Omega$ as energy scale together with strongly varying parts falling off asymptocially as $1/t$ in leading order, in contrast to the unbiased case. Resumming all logarithmic terms in all orders of perturbation theory via real-time RG we find the correct renormalized tunneling and a power-law behaviour for the oscillating modes with exponent crossing over from $2\alpha$ for exponentially small times to a bias-dependent value $2\alpha \epsilon^2/\Omega^2$ for exponentially large times. Furthermore, we present a degenerate perturbation theory to calculate consistently the purely decaying mode one order beyond Bloch-Redfield.Comment: 27 pages, 2 figure

RG transport theory for open quantum systems: Charge fluctuations in multilevel quantum dots in and out of equilibrium

We present the real-time renormalization group (RTRG) method as a method to describe the stationary state current through generic multi-level quantum dots with a complex setup in nonequilibrium. The employed approach consists of a very rudiment approximation for the RG equations which neglects all vertex corrections while it provides a means to compute the effective dot Liouvillian self-consistently. Being based on a weak-coupling expansion in the tunneling between dot and reservoirs, the RTRG approach turns out to reliably describe charge fluctuations in and out of equilibrium for arbitrary coupling strength, even at zero temperature. We confirm this in the linear response regime with a benchmark against highly-accurate numerically renormalization group data in the exemplary case of three-level quantum dots. For small to intermediate bias voltages and weak Coulomb interactions, we find an excellent agreement between RTRG and functional renormalization group data, which can be expected to be accurate in this regime. As a consequence, we advertise the presented RTRG approach as an efficient and versatile tool to describe charge fluctuations theoretically in quantum dot systems

Substrate and sequential site specificity of cytoplasmic histone acetyltransferases of maize and rat liver

AbstractThe cytoplasmic B-type histone acetyltransferase was purified to apparent homogeneity from maize embryos. We established a novel protocol for easy large-scale preparation of acetylated core histone species, using preparative acetic acid-urea-Triton PAGE. The pure maize histone acetyltransferase B was highly specific for histone H4 under various assay conditions, modifying H4 up to the di-acetylated isoform. Only non-acetylated H4 isoform was accepted as substrate, whereas mono-acetylated H4 could not be further acetylated. The enzyme selectively acetylated lysines 12 and 5 in a sequential manner. The same results were obtained with a partially purified cytoplasmic histone acetyltransferase of rat liver. Protein sequencing results were supported by immunological characterization of acetylated H4 subspecies with site-specific H4-acetyllysine antibodies

Flavor fluctuations in 3-level quantum dots: Generic SU(3)-Kondo fixed point in equilibrium and non-Kondo fixed points in nonequilibrium

We study a $3$-level quantum dot in the singly occupied cotunneling regime coupled via a generic tunneling matrix to several multi-channel leads in equilibrium or nonequilibrium. We derive an effective model where also each reservoir has three channels labelled by the quark flavors $u$, $d$ and $s$ with an effective d.o.s. polarized w.r.t. an eight-dimensional $F$-spin corresponding to the eight generators of $SU(3)$. In equilibrium we perform a standard poor man scaling analysis and show that tunneling via virtual intermediate states induces flavor fluctuations on the dot which become $SU(3)$-symmetric at a characteristic and exponentially small low-energy scale $T_K$. Using the numerical renormalization group (NRG) we study in detail the linear conductance and confirm the $SU(3)$-symmetric Kondo fixed point with universal conductance $G=2.25 e^2/h$ for various tunneling setups by tuning the level spacings on the dot. In contrast to the equilibrium case, we find in nonequilibrium that the fixed point model is not $SU(3)$-symmetric but characterized by rotated $F$-spins for each reservoir with total vanishing sum. At large voltage we analyse the $F$-spin magnetization and the current in golden rule as function of a magnetic field for the isospin of the up/down quark and the level spacing to the strange quark. As a smoking gun to detect the nonequilibrium fixed point we find that the curve of zero $F$-spin magnetization has a particular shape on the dot parameters. We propose that our findings can be generalized to the case of quantum dots with an arbitrary number $N$ of levels.Comment: 24 pages, 8 figure

Atomic mutagenesis of stop codon nucleotides reveals the chemical prerequisites for release factor-mediated peptide release.

Termination of protein synthesis is triggered by the recognition of a stop codon at the ribosomal A site and is mediated by class I release factors (RFs). Whereas in bacteria, RF1 and RF2 promote termination at UAA/UAG and UAA/UGA stop codons, respectively, eukaryotes only depend on one RF (eRF1) to initiate peptide release at all three stop codons. Based on several structural as well as biochemical studies, interactions between mRNA, tRNA, and rRNA have been proposed to be required for stop codon recognition. In this study, the influence of these interactions was investigated by using chemically modified stop codons. Single functional groups within stop codon nucleotides were substituted to weaken or completely eliminate specific interactions between the respective mRNA and RFs. Our findings provide detailed insight into the recognition mode of bacterial and eukaryotic RFs, thereby revealing the chemical groups of nucleotides that define the identity of stop codons and provide the means to discriminate against noncognate stop codons or UGG sense codons

Integrative transcriptome and proteome analysis of the tube foot and adhesive secretions of the sea urchin paracentrotus lividus

IF/00006/2015/CP1276/CT0001 P 25404-B25 P 30347Echinoderms, such as the rock-boring sea urchin Paracentrotus lividus, attach temporarily to surfaces during locomotion using their tube feet. They can attach firmly to any substrate and release from it within seconds through the secretion of unknown molecules. The composition of the adhesive, as well as the releasing secretion, remains largely unknown. This study re-analyzed a differential proteome dataset from Lebesgue et al. by mapping mass spectrometry-derived peptides to a P. lividus de novo transcriptome generated in this study. This resulted in a drastic increase in mapped proteins in comparison to the previous publication. The data were subsequently combined with a differential RNAseq approach to identify potential adhesion candidate genes. A gene expression analysis of 59 transcripts using whole mount in situ hybridization led to the identification of 16 transcripts potentially involved in bioadhesion. In the future these data could be useful for the production of synthetic reversible adhesives for industrial and medical purposes.publishersversionpublishe

Distinct pathways for zinc metabolism in the terrestrial slug Arion vulgaris

In most organisms, the concentration of free Zn is controlled by metallothioneins (MTs). In contrast, no significant proportions of Zn are bound to MTs in the slug, Arion vulgaris. Instead, this species possesses cytoplasmic low-molecular-weight Zn (LMW Zn) binding compound that divert these metal ions into pathways uncoupled from MT metabolism. Zn is accumulated in the midgut gland calcium cells of Arion vulgaris, where they associate with a low-molecular-weight ligand with an apparent molecular mass of ~ 2,000 Da. Mass spectrometry of the semi-purified LMW Zn binding compound combining an electrospray ion source with a differential mobility analyser coupled to a time-of-flight mass spectrometer revealed the presence of four Zn-containing ion signals, which arise from disintegration of one higher MW complex resulting in an ion-mobility diameter of 1.62 nm and a molecular mass of 837 Da. We expect that the novel Zn ion storage pathway may be shared by many other gastropods, and particularly species that possess Cd-selective MT isoforms or variants with only very low affinity to Zn

Likert Versus Cronbach's Psychometric Thresholds: Reducing Error and Maximizing Agricultural Education's Scholarship Impacts

Instrumentation is a critical function in measuring social and behavioral science impacts on stakeholders, teachers, and change agents. Internal validity and reliability have long been considered social sciences’ quality gatekeepers. A systematic review uses a comprehensive search based on explicit protocols to review existing literature with a synthesis of data focusing on key questions. Systematic reviews are five steps; identify the critical question, formulate search parameters, systematically search databases, analyze data, and data summary interpretation (Lee et al., 2021). Using the five steps, authors systematically reviewed all articles from Advancements in Agricultural Development (AAD), Journal of Agricultural Education (JAE), Journal of Extension (JOE), and The Journal of Agricultural Education and Extension (TJAEE) from 2018 to 2022. The authors reviewed eight hundred ninety-six (N = 896) articles from the four publications. Fewer items produced lower construct reliability coefficients and thus, produced higher levels of error. Much of agricultural education’s, broadly defined, published scholarship has not utilized instruments to collect data over the last five years; when they have, smaller numbers of items measured constructs. Likert’s convention in his quintessential work on measuring social variables suggested that for measurements to be reliable an alpha of .9 should be achieved. Researchers should include a maximum number of statements and questions and eliminate those that do not contribute to reliability and add additional questions when acceptable levels of reliability are not achieved.USDA NIFA Hatch Project 09890 “The Adoption Impact of Food and Agricultural Sciences Curricula on Public Health.