Two-channel Kondo physics in odd impurity chains

We study odd-membered chains of spin-(1/2) impurities, with each end connected to its own metallic lead. For antiferromagnetic exchange coupling, universal two-channel Kondo (2CK) physics is shown to arise at low energies. Two overscreening mechanisms are found to occur depending on coupling strength, with distinct signatures in physical properties. For strong inter-impurity coupling, a residual chain spin-(1/2) moment experiences a renormalized effective coupling to the leads; while in the weak-coupling regime, Kondo coupling is mediated via incipient single-channel Kondo singlet formation. We also investigate models where the leads are tunnel-coupled to the impurity chain, permitting variable dot filling under applied gate voltages. Effective low-energy models for each regime of filling are derived, and for even-fillings where the chain ground state is a spin singlet, an orbital 2CK effect is found to be operative. Provided mirror symmetry is preserved, 2CK physics is shown to be wholly robust to variable dot filling; in particular the single-particle spectrum at the Fermi level, and hence the low-temperature zero-bias conductance, is always pinned to half-unitarity. We derive a Friedel-Luttinger sum rule and from it show that, in contrast to a Fermi liquid, the Luttinger integral is non-zero and determined solely by the `excess' dot charge as controlled by gate voltage. The relevance of the work to real quantum dot devices, where inter-lead charge-transfer processes fatal to 2CK physics are present, is also discussed. Physical arguments and numerical renormalization group techniques are used to obtain a detailed understanding of these problems.Comment: 21 pages, 19 figure

Living Collection Curation

The necessity to redesign and relandscape the interior of the Temperate Palmhouse at the Royal Botanic Garden Edinburgh (RBGE) created the opportunity to undertake a full curatorial survey of the palms and other plants contained in the Palmhouse. This paper gives the background to, and describes the process of, undertaking the survey. It stresses the need for maximum consultation with all interested parties to decide the fate of existing plants and make recommendations for new plantings. The result was a booklet describing the history and development of the Palmhouse, listings of all existing plants with notes on ethnobotanical use, value in teaching or research and final destination and suggestions for new species to meet the new design along with educational and interpretation opportunities. The resultant survey could act as a model for other projects

Angiogenesis in human parathyroid disease and chronic allograft nephropathy

Angiogenesis in parathyroid disease and association with VEGFAngiogenesis has been demonstrated in normal parathyroid tissue in vitro and must occur in vivo to allow for successful transplantation. Here we present data that angiogenesis also occurs in parathyroid disease states and that VEGF (a known endothelial cell mitogen) expression is not evident in these tissues.Formalin fixed, paraffin embedded sections of human parathyroid tissue were stained with an antibody to CD31 to visualise endothelial cells and separate sections stained with antibody to VEGF using standard immunohistochemistry techniques. Microvessel counts were performed by two (blinded) investigators. Western blot analysis of protein lysate of parathyroid tissue was also performed using antibody to VEGF.123 patients were studied (44 normal, 27 hyperplasia and 52 adenoma). Microvessel counts showed a statistically significant (p < 0.05 compared with normal) and step-wise increase in microvessel count between the different types of tissue. 120 parathyroid sections stained with antibody to VEGF with positive control of normal kidney showed non-specific staining in all tissue types, a finding which was repeated with Western blot analysis of protein derived from 1 normal, 2 adenomas and 2 hyperplasia samples.Here we have demonstrated evidence of angiogenesis that occurs in human parathyroid tissue when diseased. Our data have not shown a significant expression ofVEGF in these samples. This finding implies that either VEGF does not mediate angiogenesis in these tissues or that it does so transiently. Alternatively VEGF may act in concentrations too small to be detected with these techniques. Gaining a better understanding ofthe progression of angiogenesis in parathyroid disease may lead to the development of novel therapeutic strategies.Changes in Vascularity Associated with Chronic Allograft NephropathyThis study aims to compare vascularity of kidneys with CAN versus normal. In addition, validation of renal biopsy samples in the assessment of angiogenesis has been performed.Tissue from transplant nephrectomies performed because of CAN (n=29), antecedent biopsies from these grafts (n=18) and normal kidneys (n=61) were studied. Protocol renal transplant biopsies were also studied. Tissue sections were immunostained with the endothelial cell antibody to CD31. Changes in overall vascular patterns were noted and microvessel counts performed. Sections were dual-stained with antibody to CD31 and the proliferation marker, MIB-1, to determine the presence of proliferating endothelial cells. Microvessel counts were performed on paired samples of core biopsies and cross-section of normal kidney and were compared in early protocol biopsy specimens from grafts which develop CAN (n=10) with those where stable graft function continued (n=20). Macrophage infiltration was studied using immunostaining to CD68.CD31 staining from CAN nephrectomies exhibited diminished cortical and medullary staining and was accompanied by a significant increase in proliferation index when compared with normal. There was significant correlation in microvessel counts in core biopsies and the corresponding kidney crosssection. Early biopsies from grafts which developed CAN show significantly higher microvessel counts compared with the corresponding nephrectomy. The number ofproliferating ECs was significantly increased in this biopsy group compared with normal kidney but was not significantly different compared with the CAN nephrectomy group. Early protocol biopsies from grafts which developed CAN showed significantly higher microvessel counts compared with those with stable graft function. A significant increase in macrophage infiltration was seen in CAN nephrectomies compared with normal kidney.This study demonstrates reduced density of CD31-positive microvessels in CAN compared with normal. In addition, the investigation of changes in the microvasculature in CAN by study of core biopsies has been validated and confirms preservation of normal vasculature in early CAN. Together with evidence ofproliferating endothelial cells these findings support a hypothesis that, early in the development ofCAN, angiogenesis is stimulated, but despite this attempt at tissue repair, progressive microvascular loss occurs. The presence of significant numbers of macrophages may be of aetiological importance or reflect changes relating to cessation of immunosuppression

Characterization of Alkali Metal Dispensers and Non-Evaporable Getter Pumps in Ultra-High Vacuum Systems for Cold Atomic Sensors

A glass ultrahigh vacuum chamber with rubidium alkali metal dispensers and non-evaporable getter pumps has been developed and used to create a cold atomic sample in a chamber that operates with only passive vacuum pumps. The ion-mass spectrum of evaporated gases from the alkali metal dispenser has been recorded as a function of dispenser current. The efficacy of the non-evaporable getter pumps in promoting and maintaining vacuum has been characterized by observation of the Rb vapor optical absorption on the D2 transition at 780 nm and vacuum chamber pressure rate of rise tests. We have demonstrated a sample of laser-cooled Rb atoms in this chamber when isolated and operating without active vacuum pumps

Response to Crocetti et al.

No abstract available

\u3cem\u3eChlamydomonas\u3c/em\u3e mutants display reversible deficiencies in flagellar beating and axonemal assembly

Axonemal complexes in flagella are largely prepackaged in the cell body. As such, one mutation often results in the absence of the co-assembled components and permanent motility deficiencies. For example, a Chlamydomonas mutant defective in RSP4 in the radial spoke (RS), which is critical for bend propagation, has paralyzed flagella that also lack the paralogue RSP6 and three additional RS proteins. Intriguingly, recent studies showed that several mutant strains contain a mixed population of swimmers and paralyzed cells despite their identical genetic background. Here we report a cause underlying these variations. Two new mutants lacking RSP6 swim processively and other components appear normally assembled in early log phase indicating that, unlike RSP4, this paralogue is dispensable. However, swimmers cannot maintain the typical helical trajectory and reactivated cell models tend to spin. Interestingly the motile fraction and the spokehead content dwindle during stationary phase. These results suggest that (1) intact RS is critical for maintaining the rhythm of oscillatory beating and thus the helical trajectory; (2) assembly of the axonemal complex with subtle defects is less efficient and the inefficiency is accentuated in compromised conditions, leading to reversible dyskinesia. Consistently, several organisms only possess one RSP4/6 gene. Gene duplication in Chlamydomonas enhances RS assembly to maintain optimal motility in various environments

Conductance fingerprint of Majorana fermions in the topological Kondo effect

We consider an interacting nanowire/superconductor heterostructure attached to metallic leads. The device is described by an unusual low-energy model involving spin-1 conduction electrons coupled to a nonlocal spin-1/2 Kondo impurity built from Majorana fermions. The topological origin of the resulting Kondo effect is manifest in distinctive non-Fermi-liquid (NFL) behavior, and the existence of Majorana fermions in the device is demonstrated unambiguously by distinctive conductance lineshapes. We study the physics of the model in detail, using the numerical renormalization group, perturbative scaling and abelian bosonization. In particular, we calculate the full scaling curves for the differential conductance in AC and DC fields, onto which experimental data should collapse. Scattering t-matrices and thermodynamic quantities are also calculated, recovering asymptotes from conformal field theory. We show that the NFL physics is robust to asymmetric Majorana-lead couplings, and here we uncover a duality between strong and weak coupling. The NFL behavior is understood physically in terms of competing Kondo effects. The resulting frustration is relieved by inter-Majorana coupling which generates a second crossover to a regular Fermi liquid.Comment: 17 pages, 8 figure