Phonon promoted charge density wave in topological kagome metal ScV6Sn6

Charge density wave (CDW) orders in vanadium-based kagome metals have recently received tremendous attention, yet their origin remains a topic of debate. The discovery of ScV6Sn6, a bilayer kagome metal featuring an intriguing [Formula: see text] CDW order, offers a novel platform to explore the underlying mechanism behind the unconventional CDW. Here, we combine high-resolution angle-resolved photoemission spectroscopy, Raman scattering and density functional theory to investigate the electronic structure and phonon modes of ScV6Sn6. We identify topologically nontrivial surface states and multiple van Hove singularities (VHSs) in the vicinity of the Fermi level, with one VHS aligning with the in-plane component of the CDW vector near the [Formula: see text] point. Additionally, Raman measurements indicate a strong electron-phonon coupling, as evidenced by a two-phonon mode and new emergent modes. Our findings highlight the fundamental role of lattice degrees of freedom in promoting the CDW in ScV6Sn6.

Thermal and electrostatic tuning of surface phonon-polaritons in LaAlO3/SrTiO3 heterostructures

Phonon polaritons are promising for infrared applications due to a strong light-matter coupling and subwavelength energy confinement they offer. Yet, the spectral narrowness of the phonon bands and difficulty to tune the phonon polariton properties hinder further progress in this field. SrTiO3 - a prototype perovskite oxide - has recently attracted attention due to two prominent far-infrared phonon polaritons bands, albeit without any tuning reported so far. Here we show, using cryogenic infrared near-field microscopy, that long-propagating surface phonon polaritons are present both in bare SrTiO3 and in LaAlO3/SrTiO3 heterostructures hosting a two-dimensional electron gas. The presence of the two-dimensional electron gas increases dramatically the thermal variation of the upper limit of the surface phonon polariton band due to temperature dependent polaronic screening of the surface charge carriers. Furthermore, we demonstrate a tunability of the upper surface phonon polariton frequency in LaAlO3/SrTiO3 via electrostatic gating. Our results suggest that oxide interfaces are a new platform bridging unconventional electronics and long-wavelength nanophotonics.

Multiple antiferromagnetic phases and magnetic anisotropy in exfoliated CrBr3 multilayers

In twisted two-dimensional (2D) magnets, the stacking dependence of the magnetic exchange interaction can lead to regions of ferromagnetic and antiferromagnetic interlayer order, separated by non-collinear, skyrmion-like spin textures. Recent experimental searches for these textures have focused on CrI3, known to exhibit either ferromagnetic or antiferromagnetic interlayer order, depending on layer stacking. However, the very strong uniaxial anisotropy of CrI3 disfavors smooth non-collinear phases in twisted bilayers. Here, we report the experimental observation of three distinct magnetic phases-one ferromagnetic and two antiferromagnetic-in exfoliated CrBr3 multilayers, and reveal that the uniaxial anisotropy is significantly smaller than in CrI3. These results are obtained by magnetoconductance measurements on CrBr3 tunnel barriers and Raman spectroscopy, in conjunction with density functional theory calculations, which enable us to identify the stackings responsible for the different interlayer magnetic couplings. The detection of all locally stable magnetic states predicted to exist in CrBr3 and the excellent agreement found between theory and experiments, provide complete information on the stacking-dependent interlayer exchange energy and establish twisted bilayer CrBr3 as an ideal system to deterministically create non-collinear magnetic phases.

Flat Γ Moiré Bands in Twisted Bilayer WSe_{2}

The recent observation of correlated phases in transition metal dichalcogenide moiré systems at integer and fractional filling promises new insight into metal-insulator transitions and the unusual states of matter that can emerge near such transitions. Here, we combine real- and momentum-space mapping techniques to study moiré superlattice effects in 57.4° twisted WSe_{2} (tWSe_{2}). Our data reveal a split-off flat band that derives from the monolayer Γ states. Using advanced data analysis, we directly quantify the moiré potential from our data. We further demonstrate that the global valence band maximum in tWSe_{2} is close in energy to this flat band but derives from the monolayer K states which show weaker superlattice effects. These results constrain theoretical models and open the perspective that Γ-valley flat bands might be involved in the correlated physics of twisted WSe_{2}.

Translucent in air and iridescent in water: structural analysis of a salamander egg sac

Females of some Asian salamanders of the genus Hynobius deposit in streams their eggs embedded in a translucent envelope called an 'egg sac'. The edges of the envelope exhibit a spectacular blue-to-yellow iridescent glow, which instantaneously disappears when the sac is removed from water. First, our scanning electron microscopy analyses reveal that the inner surface of the 100 μm-thick envelope displays striations (length scale of about 3 μm), which are themselves covered by much smaller (190 ± 30 nm) and quasi-periodic corrugations. The latter could constitute a surface diffraction grating generating iridescence by light interference. Second, our transmission electron microscopy and focused-ion-beam scanning electron microscopy analyses show that the bulk of the egg sac wall is composed of meandering fibres with a quasi-periodic modulation of 190 ± 60 nm along the thickness of the envelope, generating a photonic crystal. Third, Fourier power analyses of 450 electron microscopy images with varying incident angles indicate that changing the surrounding medium from water to air shifts most of the backscattered power spectrum to the ultraviolet range, hence, explaining that the egg sac loses visible iridescence when removed out of the water. Fourth, the results of our photography and optical spectroscopy experiments of submerged and emerged egg sacs rule out the possibility that the iridescence is due to a thin film or a multilayer, whereas the observed non-specular response is compatible with the backscattering expected from surface diffraction gratings and volumetric photonic crystals with spatial 1D modulation. Finally, although we mention several potential biological functions of the egg sac structural colours and iridescence, we emphasise that these optical properties might be the by-products of the envelope material internal structure selected during evolution for its mechanical properties.

High sensitivity variable-temperature infrared nanoscopy of conducting oxide interfaces

Probing the local transport properties of two-dimensional electron systems (2DES) confined at buried interfaces requires a non-invasive technique with a high spatial resolution operating in a broad temperature range. In this paper, we investigate the scattering-type scanning near field optical microscopy as a tool for studying the conducting LaAlO₃/SrTiO₃ interface from room temperature down to 6 K. We show that the near-field optical signal, in particular its phase component, is highly sensitive to the transport properties of the electron system present at the interface. Our modeling reveals that such sensitivity originates from the interaction of the AFM tip with coupled plasmon-phonon modes with a small penetration depth. The model allows us to quantitatively correlate changes in the optical signal with the variation of the 2DES transport properties induced by cooling and by electrostatic gating. To probe the spatial resolution of the technique, we image conducting nano-channels written in insulating heterostructures with a voltage-biased tip of an atomic force microscope.

Suppressed Magnetic Circular Dichroism and Valley-Selective Magnetoabsorption due to the Effective Mass Anisotropy in Bismuth

We measure the far-infrared reflectivity and Kerr angle spectra on a high-quality crystal of pure semimetallic bismuth as a function of magnetic field, from which we extract the conductivity for left- and right-handed circular polarizations. The high spectral resolution allows us to separate the intraband Landau level transitions for electrons and holes. The hole transition exhibits 100% magnetic circular dichroism; it appears only for one polarization as expected for a circular cyclotron orbit. However, the dichroism for electron transitions is reduced to only 13±1%, which is quantitatively explained by the large effective mass anisotropy of the electron pockets of the Fermi surface. This observation is a signature of the mismatch between the metric experienced by the photons and the electrons. It allows for a contactless measurement of the effective mass anisotropy and provides a direction towards valley polarized magnetooptical pumping with elliptically polarized light.

Versatile setup for optical spectroscopy under high pressure and low temperature

We present an optical setup for spectroscopic measurements in the infrared and of Raman shift under high pressure and at low temperature. Using a membrane-driven diamond anvil cell, the pressure can be tuned in situ up to 20 GPa and the temperatures ranges from room temperature down to 18 K in transmission mode and 13 K in reflection mode. In transmission, the setup is entirely working under vacuum to reduce the water absorption features and obtain a higher spectral stability. Since the infrared throughput obtained with a thermal source is limited, the use of a synchrotron source allowed to enhance the performance, as illustrated with results obtained with various materials. The analysis of the reflectivity is adapted so that it benefits from ambient pressure data and produces quantitative optical conductivity curves that can be easily compared to the results at ambient pressure.

Infrared- and Raman-spectroscopy measurements of a transition in the crystal structure and a closing of the energy gap of BiTeI under pressure

BiTeI is a giant Rashba spin splitting system, in which a noncentrosymmetric topological phase has recently been suggested to appear under high pressure. We investigated the optical properties of this compound, reflectivity and transmission, under pressures up to 15 GPa. The gap feature in the optical conductivity vanishes above p∼9  GPa and does not reappear up to at least 15 GPa. The plasma edge, associated with intrinsically doped charge carriers, is smeared out through a phase transition at 9 GPa. Using high-pressure Raman spectroscopy, we follow the vibrational modes of BiTeI, providing additional clear evidence that the transition at 9 GPa involves a change of crystal structure. This change of crystal structure possibly inhibits the high-pressure topological phase from occurring.

Precise colocalization of interacting structural and pigmentary elements generates extensive color pattern variation in Phelsuma lizards

BACKGROUND

Color traits in animals play crucial roles in thermoregulation, photoprotection, camouflage, and visual communication, and are amenable to objective quantification and modeling. However, the extensive variation in non-melanic pigments and structural colors in squamate reptiles has been largely disregarded. Here, we used an integrated approach to investigate the morphological basis and physical mechanisms generating variation in color traits in tropical day geckos of the genus Phelsuma.

RESULTS

Combining histology, optics, mass spectrometry, and UV and Raman spectroscopy, we found that the extensive variation in color patterns within and among Phelsuma species is generated by complex interactions between, on the one hand, chromatophores containing yellow/red pteridine pigments and, on the other hand, iridophores producing structural color by constructive interference of light with guanine nanocrystals. More specifically, we show that 1) the hue of the vivid dorsolateral skin is modulated both by variation in geometry of structural, highly ordered narrowband reflectors, and by the presence of yellow pigments, and 2) that the reflectivity of the white belly and of dorsolateral pigmentary red marks, is increased by underlying structural disorganized broadband reflectors. Most importantly, these interactions require precise colocalization of yellow and red chromatophores with different types of iridophores, characterized by ordered and disordered nanocrystals, respectively. We validated these results through numerical simulations combining pigmentary components with a multilayer interferential optical model. Finally, we show that melanophores form dark lateral patterns but do not significantly contribute to variation in blue/green or red coloration, and that changes in the pH or redox state of pigments provide yet another source of color variation in squamates.

CONCLUSIONS

Precisely colocalized interacting pigmentary and structural elements generate extensive variation in lizard color patterns. Our results indicate the need to identify the developmental mechanisms responsible for the control of the size, shape, and orientation of nanocrystals, and the superposition of specific chromatophore types. This study opens up new perspectives on Phelsuma lizards as models in evolutionary developmental biology.

Study of the Fermi surface of ZrB12 using the de Haas-van Alphen effect

The de Haas-van Alphen (dHvA) effect in the cluster superconductor ZrB12 was studied by magnetic torque measurements in magnetic fields up to 28 T at temperatures down to 0.07 K. The dHvA oscillations due to orbits from the neck sections and "cubic box" of the Fermi surface were detected. The dHvA frequencies as well as the cyclotron effective masses were calculated using the full-potential linear muffin-tin orbitals method within the generalized gradient approximation. A comparison of the experimental and calculated cyclotron mass shows unusually large electron-phonon interaction on the neck (lambdaep=0.95) and box (lambdaep=1.07) sections of the Fermi surface on the Brillouin zone boundaries.

Prolificacy genes in sheep: the French genetic programmes

It has been demonstrated that variations in litter size or ovulation rate in different breeds of sheep can be associated with the segregation of several major genes. This set of natural mutants constitutes a valuable resource to determine key points in the biochemical pathways controlling the development of ovarian follicles. The French genetic programmes were devised to identify two of these genes: the Booroola (FecB) and Lacaune genes. The FecB prolific mutation corresponds to a non-conservative mutation (Q249R) in the intracellular kinase-signalling domain of the bone morphogenetic protein receptor type IB (BMPR-IB) gene. The Lacaune gene is situated on ovine chromosome 11. Positional cloning is currently in progress to identify the relevant gene and mutation. A similar approach, limited to linkage testing of candidate genes, is proposed to classify the different prolificacy genes in sheep.

Mutation in bone morphogenetic protein receptor-IB is associated with increased ovulation rate in Booroola Mérino ewes

Ewes from the Booroola strain of Australian Mérino sheep are characterized by high ovulation rate and litter size. This phenotype is due to the action of the FecB(B) allele of a major gene named FecB, as determined by statistical analysis of phenotypic data. By genetic analysis of 31 informative half-sib families from heterozygous sires, we showed that the FecB locus is situated in the region of ovine chromosome 6 corresponding to the human chromosome 4q22-23 that contains the bone morphogenetic protein receptor IB (BMPR-IB) gene encoding a member of the transforming growth factor-beta (TGF-beta) receptor family. A nonconservative substitution (Q249R) in the BMPR-IB coding sequence was found to be associated fully with the hyperprolificacy phenotype of Booroola ewes. In vitro, ovarian granulosa cells from FecB(B)/FecB(B) ewes were less responsive than granulosa cells from FecB(+)/FecB(+) ewes to the inhibitory effect on steroidogenesis of GDF-5 and BMP-4, natural ligands of BMPR-IB. It is suggested that in FecB(B)/FecB(B) ewes, BMPR-IB would be inactivated partially, leading to an advanced differentiation of granulosa cells and an advanced maturation of ovulatory follicles.

Characterization of Brucella suis clpB and clpAB mutants and participation of the genes in stress responses

Pathogens often encounter stressful conditions inside their hosts. In the attempt to characterize the stress response in Brucella suis, a gene highly homologous to Escherichia coli clpB was isolated from Brucella suis, and the deduced amino acid sequence showed features typical of the ClpB ATPase family of stress response proteins. Under high-temperature stress conditions, ClpB of B. suis was induced, and an isogenic B. suis clpB mutant showed increased sensitivity to high temperature, but also to ethanol stress and acid pH. The effects were reversible by complementation. Simultaneous inactivation of clpA and clpB resulted in a mutant that was sensitive to oxidative stress. In B. suis expressing gfp, ClpA but not ClpB participated in degradation of the green fluorescent protein at 42 degrees C. We concluded that ClpB was responsible for tolerance to several stresses and that the lethality caused by harsh environmental conditions may have similar molecular origins.

Association between expression of reproductive seasonality and alleles of the gene for Mel(1a) receptor in the ewe

To determine whether a link exists between reproductive seasonality and the structure of the gene for melatonin receptor Mel(1a), the latter was studied in two groups of Mérinos d'Arles (MA) ewes previously chosen for their genetic value, which took into account their own out-of-season ovulatory activity adjusted by environmental parameters and that of their relatives. The genomic DNA of 36 ewes found regularly cycling in spring (group H) and that of 35 ewes never cycling in spring (group L) during the 2-3 yr before the present study was prepared, and the cDNA corresponding to almost all exon II was amplified and checked for the presence of MnlI restriction sites. The presence (+) or absence (-) of an MnlI site at position 605 led to genotypes "++", "+-", and "--", whose frequencies differed significantly (P < 0.001) between the H and L groups: 52.8%, 47.2%, and 0% vs. 28.5%, 42.9%, and 28.5%, respectively. Sequencing of exon II cDNA in group L ewes with genotype -- showed the presence of only one allele - with 4 mutations, while that in ewes with genotype ++ showed different types of alleles unrelated to the H or L groups. These + alleles exhibited a combination of 1 to 7 of the 8 mutations recorded in the part of exon II studied. The genotyping of 29 ewes from the more seasonal Ile-de-France breed indicated that 38% of animals had a -- genotype and exhibited the same mutations as in the MA ewes. Finally, a comparison of (125)I-melatonin binding to membrane preparations of pars tuberalis showed a lower number of binding sites (P < 0. 0005) in MA ewes with genotype ++ than in those with genotype -- (43. 2 +/- 4.4 vs. 75.4 +/- 8.4 fmol/mg protein in genotype ++ and genotype --, respectively). In conclusion, the data show an association between genotype -- for site MnlI at position 605 and seasonal anovulatory activity in MA ewes.

Constitutive and inducible expression of green fluorescent protein in Brucella suis

A gene fusion system based on plasmid pBBR1MCS and the expression of green fluorescent protein was developed for Brucella suis, allowing isolation of constitutive and inducible genes. Bacteria containing promoter fusions of chromosomal DNA to gfp were visualized by fluorescence microscopy and examined by flow cytometry. Twelve clones containing gene fragments induced inside J774 murine macrophages were isolated and further characterized.

Participation of the molecular chaperone DnaK in intracellular growth of Brucella suis within U937-derived phagocytes

In the intracellular bacterium Brucella suis, the molecular chaperone DnaK was induced under heat-shock conditions and at low pH. Insertional inactivation of dnaK and dnaJ within the dnaK/J locus led to the conclusion that DnaK, but not DnaJ, was required for growth at 37 degrees C in vitro. Viability of the dnaK null mutant was also greatly affected at low pH. Under conditions allowing intracellular multiplication, the infection of U937-derived phagocytes resulted in long-lasting DnaK induction in the wild-type bacteria. In infection experiments performed with both mutants at the reduced temperature of 30 degrees C, the dnaK mutant of B. suis survived but failed to multiply within U937 cells, whereas the wild-type strain and the dnaJ mutant multiplied normally. Complementation of the dnaK mutant with the cloned dnaK gene restored growth at 37 degrees C, increased resistance to acid pH, and increased intracellular multiplication. This is the first report of the effects of dnaK inactivation in a pathogenic species, and of the temperature-independent contribution of DnaK to intracellular multiplication of the pathogen B. suis.

Cloning and characterization of the Brucella ovis heat shock protein DnaK functionally expressed in Escherichia coli

The Brucella ovis dnaK gene, homolog to the eukaryotic hsp70 genes, was cloned by using a Drosophila melanogaster probe. Comparison of B. ovis and Escherichia coli sequences revealed a similar organization for the dnaK and dnaJ genes and putative regulatory signals. In E. coli transfected with the cloned fragment, B. ovis hsp70 was expressed at 30 and 50 degrees C apparently under the control of its own promoter. The recombinant protein and a B. ovis native protein displaying the same molecular weight were both recognized by anti-E. coli DnaK serum. Native B. ovis protein was also recognized by sera of sheep either infected or vaccinated with an attenuated Brucella strain, suggesting that Brucella hsp70 could be up-regulated during host colonization. A thermosensitive E. coli dnaK mutant transfected with the cloned fragment recovered colony-forming ability at 42 degrees C, showing that the B. ovis DnaK protein could behave as a functional heat shock protein in E. coli.

[Neonatal mortality factors at the Dakar General Hospital]

The authors studied 223 new-borns in an African Pediatric Department over a eight month period. The death rate was 47.5 p. cent (106 cases). It was explained by infectious diseases in 53 cases, respiratory distress syndrome in 37 cases, acute foetal distress in 9 cases, jaundice in 6 cases, and malformation syndrome in one case. A birth-weight less than 2.500 g is correlated with a poor prognosis. The authors define target populations in tropical zones to be looked after by aims of prophylactic and curative actions.

[Intolerance to metoclopramide (apropos of 22 case reports of infants of the black race)]

The authors report on 22 observations made from june 1982 to december 1984 in African children having presented an intolerance against metoclopramide. After recalling briefly the pharmacology of this drug, they describe the symptomatology similar to neuroleptic intoxication syndrome: parkinsonian syndrome, motor excitation syndrome. Posology was correct in 2/3 of the cases, when it was known. Overdose was observed in 5 cases only. Recovery was complete after the administration of the drug was stopped, but it was accelerated by antiparkinsonian drugs.

[Morbidity and mortality in a pediatric department in Dakar]

The authors study, for the year 1983, the morbidity and the mortality in a pediatrics department in Dakar. Despite the fact that the patients admitted belong to a privileged group of the senegalese population, the mortality rate is high (17%), mainly during the neonatal period (51.5%), and within the age group of 1 to 23 months (21%). Seasonal influence is obvious. Admissions and deaths are significantly more numerous from june to december. The diseases of concern are still diarrhea, malnutrition and respiratory diseases.

[Acute poisoning by ingestion of ditakh. Apropos of 8 cases]

In connection with eight pediatric observations, the authors recall the existence and its feature of acute intoxication by Detarium Sp (Heudelotianum), toxic variety of Ditakh (Detarium senegalensis) which is a fruit commonly consumed in Senegal. They stress on the importance of interrogation taking in account the diagnosis of this intoxication which may be fatal.

Longitudinal study of adipose cell size in the dorsoscapular and perirenal depots of the growing rabbit

The changes in fat cell size during normal growth of New Zealand rabbits were investigated longitudinally with serial dorsoscapular and perirenal fat biopsies. A remarkably complex pattern of changes appeared when individual evolutions were considered. About 50% of the rabbits were characterized by "significant drops" of mean diameter during fat tissue growth with shifting of distributions toward the smaller cells. These "drops" could not be attributed to regional variation observed within each depot or to growth or food intake disorders. Differences in behavior of perirenal and dorsoscapular depots were noted. The "drops" occurred earlier in perirenal than in dorsoscapular depots. The meaning of these "drops" remains unclear, but the results suggest that they may be due to a discontinuous recruitment of new observable cells. These results are discussed in relation to the hypothesis of a "critical size" of adipocytes.

alpha-Thalassemia among sickle cell anemia patients in various African populations

We have studied the incidence of alpha-thalassemia in normal and SS individuals from Senegal, Benin, Upper Volta, and Central Republican Africa. The alpha thal gene frequency is not significantly different in the controls from the various populations and in the SS patients from Senegal. In contrast it is compatible with increased survival of SS patients in Benin, Upper Volta. The data suggest epistatic effects of other factors in the Senegalese population.

Kinetics of the uptake of rifampicin and tetracycline into mouse macrophages. In vitro study of the early stages

The in vitro uptake by mouse peritoneal macrophages, of chlortetracycline (by fluorescence microscopy) and of tetracycline and rifampicin (by scintillation spectrometry of radioactive antibiotics) has been studied over a six hours period, using various concentrations of the antibiotics, close to the therapeutic concentrations. The incidence of the conditions of the assays, especially that of the use of heterologous serum for the cultivation of cells, has been investigated; a medium supplemented with homologous serum at low concentration has been devised with the technique. The uptake of these antibiotics was a three-phases process suggesting the superposition to a passive diffusion of either an active incorporation, or a restriction of the outflow (perhaps associated). This led to a rather high concentration of the antibiotics into cells, although other studies have shown that this concentration is not as active on intracellular bacteria as one could expect from the in vitro sensitivity.

[Hemorrhagic dengue fever: evidence of consumption coagulopathy (author's transl)]

Coagulation is explored in 129 children infected by dengue virus and presenting either banal symptoms, or an hemorrhagic fever. Results are given, and commented according to the disease's clinical staging. A disseminated intravascular coagulation symdrome is brought out in all the cases, but with less or more intensity, though it belongs to dengue virus infection. Etio-pathogenic mechanism is then discussed.

[Children typhoid fever in Saigon (Vietnam) : epidemiological and biological aspects (author's transl)]

A review of 130 children cases of typhoid fever in Saigon (Vietnam). Leuco-neutropenia is far from regular but thrombopenia is frequent. The typhoid bacillus is generally cultivated from blood during the first two weeks of the evolution. There is evidence in most S. typhi strains of a plasmid resistance for streptomycine, chloramphenicol, tetracycline and sulfamides. Strains of the various other enterobacteria of the intestinal flora are generally resistant for many more antibiotics than S. typhi.