Topological aspects of multi-kantiferromagnetism in cubic rare-earth compounds.

We advertise rare-earth intermetallics with high-symmetry crystal structures and competing interactions as a possible materials platform hosting spin structures with non-trivial topological properties. Focusing on the series of cubicRCu compounds, whereR= Ho, Er, Tm, the bulk properties of these systems display exceptionally rich magnetic phase diagrams hosting an abundance of different phase pockets characteristic of antiferromagnetic order in the presence of delicately balanced interactions. The electrical transport properties exhibit large anomalous contributions suggestive of topologically non-trivial winding in the electronic and magnetic structures. Neutron diffraction identifies spontaneous long-range magnetic order in terms of commensurate and incommensurate variations of(ππ0)antiferromagnetism with the possibility for various multi-kconfigurations. Motivated by general trends in these materials, we discuss the possible existence of topologically non-trivial winding in real and reciprocal space in the class ofRCu compounds including antiferromagnetic skyrmion lattices. Putatively bringing together different limits of non-trivial topological winding in the same material, the combination of properties inRCu systems promises access to advanced functionalities.

Phonon Topology and Winding of Spectral Weight in Graphite.

The topology of electronic and phonon band structures of graphene is well studied and known to exhibit a Dirac cone at the K point of the Brillouin zone. Here, we applied inelastic x-ray scattering (IXS) along with ab initio calculations to investigate phonon topology in graphite, the 3D analog of graphene. We identified a pair of modes that form a very weakly gapped linear anticrossing at the K point that can be essentially viewed as a Dirac cone approximant. The IXS intensity in the vicinity of the quasi-Dirac point reveals a harmonic modulation of the phonon spectral weight above and below the Dirac energy, which was previously proposed as an experimental fingerprint of the nontrivial topology. We illustrate how the topological winding of IXS intensity can be understood in terms of atomic displacements and highlight that the intensity winding is not in fact sensitive in telling quasi- and true Dirac points apart.

Kondo quasiparticle dynamics observed by resonant inelastic x-ray scattering.

Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd3 to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature-the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.

Selective probing of magnetic order on Tb and Ir sites in stuffed Tb2Ir2O7  using resonant x-ray scattering.

We study the magnetic structure of the 'stuffed' (Tb-rich) pyrochlore iridate Tb2+x Ir2-x O7-y  (x ∼ 0.18), using resonant elastic x-ray scattering (REXS). In order to disentangle contributions from Tb and Ir magnetic sublattices, experiments were performed at the Ir L 3 and Tb M 5 edges, which provide selective sensitivity to Ir 5d and Tb 4f  magnetic moments, respectively. At the Ir L 3 edge, we found the onset of long-range [Formula: see text] magnetic order below [Formula: see text] K, consistent with the expected signal of all-in all-out (AIAO) magnetic order. Using a single-ion model to calculate REXS cross-sections, we estimate an ordered magnetic moment of [Formula: see text] at 5 K. At the Tb M 5 edge, long-range [Formula: see text] magnetic order appeared below ∼[Formula: see text] K, also consistent with an AIAO magnetic structure on the Tb site. Additional insight into the magnetism of the Tb sublattice is gleaned from measurements at the M 5 edge in applied magnetic fields up to 6 T, which is found to completely suppress the Tb AIAO magnetic order. In zero applied field, the observed gradual onset of the Tb sublattice magnetisation with temperature suggests that it is induced by the magnetic order on the Ir site. The persistence of AIAO magnetic order, despite the greatly reduced ordering temperature and moment size compared to stoichiometric Tb2Ir2O7, for which [Formula: see text] K and [Formula: see text], indicates that stuffing could be a viable means of tuning the strength of electronic correlations, thereby potentially offering a new strategy to achieve topologically non-trivial band crossings in pyrochlore iridates.

All-in-all-Out Magnetic Order and Propagating Spin Waves in Sm_{2}Ir_{2}O_{7}.

Using resonant magnetic x-ray scattering we address the unresolved nature of the magnetic ground state and the low-energy effective Hamiltonian of Sm_{2}Ir_{2}O_{7}, a prototypical pyrochlore iridate with a finite temperature metal-insulator transition. Through a combination of elastic and inelastic measurements, we show that the magnetic ground state is an all-in-all-out (AIAO) antiferromagnet. The magnon dispersion indicates significant electronic correlations and can be well described by a minimal Hamiltonian that includes Heisenberg exchange [J=27.3(6) meV] and Dzyaloshinskii-Moriya interactions [D=4.9(3) meV], which provides a consistent description of the magnetic order and excitations. In establishing that Sm_{2}Ir_{2}O_{7} has the requisite inversion symmetry preserving AIAO magnetic ground state, our results support the notion that pyrochlore iridates may host correlated Weyl semimetals.

The role of asynapsis in human spermatocyte failure.

The basic molecular mechanisms by which chromosomal rearrangements in heterozygous state produce spermatogenic disturbances are poorly understood. Testicular biopsies from five patients - one carrier of a Robertsonian translocation rob t(13;14), two carriers of two different Y-autosome translocations, a t(Y;6) and a t(Y;11), one carrier of a reciprocal translocation t(3;13) and one carrier of a heterochromatin duplication in chromosome 9 - were processed for histopathological analysis, electron microscopy and fluorescent immunolocalization of meiotic proteins. In all the patients, the asynaptic regions during pachytene are labelled by BRCA1 and retained RAD51 foci. The variant histone γ-H2AX is located on the chromatin domains of the asynaptic regions and the XY body. In contrast, these meiotic proteins are absent in those chromosomal segments that are non-homologously synapsed. The present observations on five new cases and a review of recent studies show that the common features shared by all these cases are the abnormal location of some meiotic proteins and the presence of transcriptionally silenced chromatin domains on asynaptic regions. The frequent association of these silenced regions with the XY body and the rescue of spermatocyte viability through non-homologous synapsis are also shared by all these carriers. A passive, random mechanism of clustering of asynaptic regions with the XY body is suggested.

Focal spermatogenesis originates in euploid germ cells in classical Klinefelter patients.

BACKGROUND: Klinefelter syndrome is the most frequent chromosome abnormality in human males. This paper aims to investigate the ploidy of meiotic and pre-meiotic germ cells found in spermatogenic foci, and furthermore, the sex chromosome constitution of Sertoli cells which surround these germ cells in non-mosaic Klinefelter patients. METHODS AND RESULTS: A survey of 11 adult patients diagnosed with classical, non-mosaic Klinefelter syndrome who underwent testicular biopsies, showed that six of them had spermatogenesis foci. The topographical study of the biopsies showed that tubuli with germ cells are a minor fraction (8-24%) of all tubuli, although the overwhelming majority is devoid of germ cells. Using fluorescence in situ hybridization (FISH) with probes for the X-centromere and immunolocalization of meiotic proteins, the present work shows that all the 92 meiotic spermatocytes analyzed with FISH were euploid, 46,XY, and thus can form normal, haploid gametes. On the other hand, Sertoli cells show two marks for the X chromosome, meaning that they are 47,XXY. CONCLUSIONS: These results provide a rationale for the high rate of success in the testicular sperm extraction plus ICSI procedures when applied to Klinefelter patients. It is also in agreement with previous studies in the XXY-mouse model. These spermatogenic foci most probably originate from clones of spermatogonia that have randomly lost one of the X chromosomes, probably during periods of life when high spermatogonial mitotic activity occurs.

The asynaptic chromatin in spermatocytes of translocation carriers contains the histone variant gamma-H2AX and associates with the XY body.

BACKGROUND: The close apposition of multivalents with the XY body has been repeatedly described in heterozygous carriers of chromosomal rearrangements. Because in many of these carriers spermatogenesis is deeply disturbed at the spermatocyte level, the association of autosomal chromatin with the XY body may impair the spermatocyte life. METHODS: Testicular biopsies from three men carriers of three different chromosomal rearrangements have been analysed by electron microscopy (EM) and immunolocalization of meiotic proteins. RESULTS: There is an ordered transition from isolated multivalents at early pachytene to XY body association in late pachytene, as shown in a carrier of a rob t(13;14) translocation by EM and in a reciprocal translocation t(9;14) carrier by immunofluorescence. The non-synapsed ends of the quadrivalent show BRCA1 located on the axes and the variant histone gamma-H2AX located on the chromatin. The area covered by gamma-H2AX increases with the association of the asynaptic ends with the XY body in the t(9;14) carrier, and the area covered with gamma-H2AX in the t(Y;15) carrier is larger than that of the XY body of controls. CONCLUSIONS: The affinity between the inactive XY body and asynaptic regions of multivalents is given a material basis, and transcriptional inactivation is probably shared by these two chromatin types.

An azoospermic man with a double-strand DNA break-processing deficiency in the spermatocyte nuclei: case report.

BACKGROUND: The mechanisms of meiotic arrest in human spermatogenesis are poorly known. METHODS AND RESULTS: A testicular biopsy from an azoospermic male showed complete spermatogenesis arrest at the spermatocyte stage, asynapsis, lack of formation of the XY body, partial reversion to a mitotic-like division and cell degeneration both at the prophase and at the abnormal cell divisions. Synaptonemal complex analysis showed minor segments of synapsis and mainly single axes. Fluorescent immunolocalization of meiotic proteins showed normal SYCP3, scarcity of SYCP1, null MLH1 foci, about 10 patches of gamma-H2AX, abnormal presence of BRCA1 among autosomal axes, absence of RAD51 in early and advanced spermatocytes and permanence of gamma-H2AX labelling up to the abnormal spermatocyte divisions that are the most advanced stage reached. There are at least six dominions of evenly packed chromatin resembling that of the normal XY body, but no true XY body. CONCLUSIONS: The protein phenotype and the fine structure of the nuclei are compatible with a deficiency of the processing of double-strand DNA breaks in the zygotene-like spermatocytes, but the features of this defect do not agree with Spo11, Sycp1, Atm and Dmc1 null mutations, which give absence of XY body, synapsis disturbances and spermatocyte apoptosis in mice.

Fine structure and meiotic behaviour of the male multiple sex chromosomes in the genus Alouatta.

The meiotic cytology and fine structure of the sex multiples in males from two species of the genus Alouatta are presented and compared with descriptions from other species of this genus. As shown in pachytene by synaptonemal complex analysis and in metaphase I by spreading, there is a quadrivalent in male meiosis in A. caraya, which is formed by an X(1)X(2)Y(1)Y(2) complex, while in A. palliata there is a trivalent formed by an X(1)X(2)Y(1) complex. Chromosome painting with human probes shows that A. caraya sex multiples share the same components as those of A. seniculus sara and A. seniculus arctoidea. However, as shown here for A. palliata and by others in A. fusca, there are differences among the multiples of some species. It is shown that in this genus there are several varieties of sex multiples that share some features, and that the origin of these multiples is most probably a primitive development in the genus Alouatta.

A constitutional complex chromosome rearrangement involving meiotic arrest in an azoospermic male: case report.

Complex chromosome rearrangements are rare aberrations that frequently lead to reproductive failure and that may hinder assisted reproduction. A 25-year-old azoospermic male was studied cytogenetically with synaptonemal complex analysis of spermatocytes from a testicular biopsy and fluorescence in situ hybridization (FISH) of lymphocytes. The spermatocytes showed a pentavalent plus a univalent chromosome. Cell death occurred mainly at advanced pachytene stages. The sex chromosomes were involved in the multiple, as shown by their typical axial excrescences. Two autosomal pairs, including an acrocentric chromosome (15), were also involved in the multiple. FISH allowed the definite identification of all the involved chromosomes. An inverted chromosome 12 is translocated with most of one long arm of chromosome 15, while the centromeric piece of this chromosome 15 is translocated with Yqh, forming a small marker chromosome t(15;Y). The euchromatic part of the Y chromosome is joined to the remaining piece of chromosome 12, forming a neo-Y chromosome. The patient shows azoospermia and a normal phenotype. The disruption of spermatogenesis is hypothetically due to the extent of asynaptic segments and to sex-body association during pachytene. This CCR occurred 'de novo' during paternal spermatogenesis. Meiotic analysis and FISH are valuable diagnostic tools in these cases.

Intractable ventricular tachycardia and bridging to heart transplantation with a non-pulsatile flow assist device in a patient with isolated left-ventricular non-compaction.

Intractable ventricular tachycardia was investigated in a 51-year-old man with isolated left ventricular non-compaction during implantation of an automated internal cardioverter-defibrillator. Favorable bridging to cardiac transplantation was achieved with the DeBakey left ventricular assist device (LVAD).

A unique mechanism of nuclear division in Giardia lamblia involves components of the ventral disk and the nuclear envelope

The fine structure of the binucleate, parasitic protist Giardia lamblia during interphase and divisional stages was studied by serial thin sectioning and three-dimensional reconstructions. The earlier sign of nuclear division is the development of a few peripheral areas of densely packed chromatin directly attached to the inner nuclear envelope. An intracytoplasmic sheet of ventral disk components grows from the cell periphery towards one of the nuclei, apparently constricting this nucleus, which becomes located at a ventral bulge. After the basal bodies become duplicated, a full nuclear division occurs in trophozoites, giving two pairs of parent-daughter nuclei. This full division occurs in a dorsal-ventral direction, with the resulting nuclear pairs located at the sides of the two sets of basal bodies. A new ventral disk is formed from the disk-derived sheets in the cell harboring the four nuclei. Cytokinesis is polymorphic, but at early stages is dorsal-to-dorsal. Encysting trophozoites show the development of Golgi cisternae stacks and dense, specific secretory granules. 3-D reconstructions show that cysts contain a single pair of incompletely strangled nuclei. The dividing Giardia lacks a typical, microtubular spindle either inside or outside the nuclei. The nuclear envelope seems to be the only structure involved in the final division of the parent-daughter nuclei. (AU)

A unique mechanism of nuclear division in Giardia lamblia involves components of the ventral disk and the nuclear envelope

The fine structure of the binucleate, parasitic protist Giardia lamblia during interphase and divisional stages was studied by serial thin sectioning and three-dimensional reconstructions. The earlier sign of nuclear division is the development of a few peripheral areas of densely packed chromatin directly attached to the inner nuclear envelope. An intracytoplasmic sheet of ventral disk components grows from the cell periphery towards one of the nuclei, apparently constricting this nucleus, which becomes located at a ventral bulge. After the basal bodies become duplicated, a full nuclear division occurs in trophozoites, giving two pairs of parent-daughter nuclei. This full division occurs in a dorsal-ventral direction, with the resulting nuclear pairs located at the sides of the two sets of basal bodies. A new ventral disk is formed from the disk-derived sheets in the cell harboring the four nuclei. Cytokinesis is polymorphic, but at early stages is dorsal-to-dorsal. Encysting trophozoites show the development of Golgi cisternae stacks and dense, specific secretory granules. 3-D reconstructions show that cysts contain a single pair of incompletely strangled nuclei. The dividing Giardia lacks a typical, microtubular spindle either inside or outside the nuclei. The nuclear envelope seems to be the only structure involved in the final division of the parent-daughter nuclei.

Long-term follow up of children with congenital complete atrioventricular block and the impact of pacemaker therapy.

AIMS: This study assessed survival, morbidity and impact of pacemaker (PM) therapy in children with Congenital Complete Atrioventricular Block (CCAVB). METHODS AND RESULTS: Data of 32 children, diagnosed as showing CCAVB at a median age of 0.4 years (range foetal-10 years), were retrospectively analysed. For comparison of clinical data patients were separated into two groups: CCAVB without structural heart disease (group 1; n = 23) and with structural heart disease (group 2; n = 9). Median follow-up time was 10.2 years. Pacemakers (PM) were implanted in 17 group 1 and all group 2 children. Frequency of PM therapy, age and symptoms before PM implantation did not differ significantly between the groups. Indications for PM implantation were bradycardia in 15, decreased exercise tolerance in 6, syncope in 3 and heart failure in 2 children. PM system related complications occurred in 11/26 (42%) children. Although 1 child died due to PM exit block no further CCAVB related symptoms were recorded in children with PM. CONCLUSION: PM therapy reduces mortality and morbidity in children with CCAVB when compared with natural history data. Although children with PM are free from CCAVB related symptoms limited morbidity remains due to PM system related complications.

I was sick and you came to visit me: time spent at the bedsides of seriously ill patients with poor prognoses.

PURPOSE: To learn how much time hospital staff and families spend at the bedsides of seriously ill patients with poor prognoses. SUBJECTS AND METHODS: An observational study was made of 58 inpatients with cancer, acquired immunodeficiency syndrome, heart failure, obstructive lung disease, or advanced dementia, along with their families and the physicians and nurses working on the medical floors of a university hospital, using direct videotape surveillance of patients' doorways. RESULTS: The mean (+/-SD) total visitor-minutes spent in the rooms of these patients was 321 +/- 297 minutes per day. On average, patients spent 18 hours 39 minutes per day alone. Mean visit durations were 3 +/- 3 minutes for attending physicians (including consultants), 3 +/- 2 minutes for house officers, 2 +/- 1 minutes for nurses, and 24 +/- 51 minutes for family. The total person-visits per patient per day were 3 +/- 3 for attending physicians, 9 +/- 8 for house officers, 45 +/- 23 for nurses, and 13 +/- 21 for family. Patient sex and age were not significantly associated with total visitor-minutes. In a repeated-measures analysis of variance model, nonwhite patients received fewer total visitor-minutes than did white patients, and patients with dementia received fewer total visitor-minutes than did patients with other diagnoses, especially those with malignancy. Do-not-resuscitate orders were associated with slightly more total visitor-minutes. CONCLUSIONS: These seriously ill patients with poor prognoses spent most of their time in the hospital alone. Staff visits were frequent but brief. These data do not confirm anecdotal reports that staff members spend less time at the bedsides of patients with do-not-resuscitate orders. Patients with advanced dementia and minority patients appear to have less bedside contact. Further study is required to confirm these findings and to understand optimal visit time for medical inpatients with poor prognoses.

Digital holographic data storage in a high-performance photorefractive polymer composite.

Binary information in the form of a 256 x 256 pixel array has been stored holographically within a polymeric photorefractive composite of 130-mum thickness. Devices used consisted of 55-wt. % organic chromophore 1-(2?-ethylhexyloxy)-2, 5-dimethyl-4-(4?nitrophenylazo) benzene and up to 11.2-wt. % 2, 4, 7-trinitro-9-fluorenone (TNF) dispersed within a poly(N-vinyl carbazole) matrix. In a degenerate four-wave mixing arrangement, the refractive-index modulation and speed were 10(-3) and 200 ms, respectively. The high TNF concentration leads to short digital hologram recording times of 2 s without detriment in optical quality. Although not yet optimized, a figure of merit, M#, for holographic storage in this composite has been measured to be 0.017, and this is estimated to reach 0.18 in a revised experimental geometry.

Methyl bromide 1-year dietary study in dogs.

Average human exposure resulting from consumption of methyl I bromide (MB)-fumigated food has been estimated to be 0.00125 mg/kg/day. A 1-yr feeding study in beagle dogs was conducted as a safety study in which the high-dose diet was intended to yield a methyl bromide dose of at least 100 times the calculated human dietary exposure. Diets were fumigated with MB and fed to the dogs daily, except for weekends and holidays. MB consumption each feeding day was calculated as a time weighted average (TWA) that accounted for the rate of degassing from the fumigated diet and the rate of feed consumption during the feeding period. TWA compound consumption in the loss-, mid- and high-dose groups, respectively, averaged 0.06 ¿ 0.02, 0.13 ¿ 0.03 and 0.28 ¿ 0.08 mg/kg/day in males and 0.07 ¿ 0.03, 0.12 ¿ 0.03 and 0.27 ¿ 0.09 mg/kg/day in females. Clinical observations, body weight and feed consumption, ophthalmology, clinical pathology, urinalysis, organ weights and macroscopic and microscopic pathology were comparable in control and MB-treated dogs. Under the conditions of this study. the no-observed-effect level (NOEL) for MB was at least 0.28 mg/ kg/day, or approximately 200 times the expected average human dietary exposure.

The impact of automatic threshold tracking on pulse generator longevity in patients with different chronic stimulation thresholds.

Automatic adjustment of the stimulation output of pacemakers to changing stimulation thresholds using the Autocapture feature increases patient safety and decreases energy consumption. This study examined the impact of Autocapture on pulse generator longevity in patients with different chronic stimulation thresholds. Eighty patients (mean age 79 +/- 9 years; 37 men, 43 women) with Pacesetter Regency SR+ pacemakers were included in the study. Data were collected before discharge of the patients from the hospital, 6-12 weeks postimplant, and then every 6-12 months. Pulse generator longevity was calculated theoretically, assuming 100% stimulation with a stable threshold, at a pacing rate of 65 +/- 6 beats/min and 1% backup pulses. Theoretical pulse generator longevity was calculated for low (< 1 V), intermediate (> or = 1 V and < 2 V), and high (> or = 2 V) stimulation thresholds. Pulse generator longevity was compared among three groups: (A) Autocapture programmed On, (B) Autocapture programmed Off, (C) theoretical calculations using thresholds of patients in group A with the stimulation voltage programmed at twice pacing threshold, or at a minimum of 2.4 V. The mean follow-up time since implantation was 19 +/- 8 months. The calculated longevity benefits for patients in group A were 36%, 59%, and 30% compared to group B, and 19%, 32%, and 49% compared to group C in patients with low, intermediate, and high chronic stimulation thresholds, respectively. Theoretical calculations based on chronic stimulation thresholds in our patient population with Regency SR+ pacemakers suggest that Autocapture may markedly prolong pulse generator longevity in patients with a broad range of long-term pacing thresholds.