200 research outputs found

    Observation and Spectroscopy of a Two-Electron Wigner Molecule in an Ultra-Clean Carbon Nanotube

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    Coulomb interactions can have a decisive effect on the ground state of electronic systems. The simplest system in which interactions can play an interesting role is that of two electrons on a string. In the presence of strong interactions the two electrons are predicted to form a Wigner molecule, separating to the ends of the string due to their mutual repulsion. This spatial structure is believed to be clearly imprinted on the energy spectrum, yet to date a direct measurement of such a spectrum in a controllable one-dimensional setting is still missing. Here we use an ultra-clean suspended carbon nanotube to realize this system in a tunable potential. Using tunneling spectroscopy we measure the excitation spectra of two interacting carriers, electrons or holes, and identify seven low-energy states characterized by their spin and isospin quantum numbers. These states fall into two multiplets according to their exchange symmetries. The formation of a strongly-interacting Wigner molecule is evident from the small energy splitting measured between the two multiplets, that is quenched by an order of magnitude compared to the non-interacting value. Our ability to tune the two-electron state in space and to study it for both electrons and holes provides an unambiguous demonstration of the fundamental Wigner molecule state.Comment: SP and FK contributed equally to this wor

    Some consequences of a spatially varying cosmological constant in a spherically symmetric distribution of matter

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    This paper investigates the effects of the spatial variation of the cosmological constant Λ on the spacetime geometry within and outside a massive object. It is seen that the variation of Λ with the radial coordinate introduces non-trivial changes leading to spacetime closing on itself around a massive object. It may also be possible to generate interior solutions that lead to flat rotation curves of galaxies

    Electron density in the quiet solar coronal transition region from SoHO/SUMER measurements of S VI line radiance and opacity

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    Context: The sharp temperature and density gradients in the coronal transition region are a challenge for models and observations. Aims: We set out to get linearly- and quadratically-weighted average electron densities in the region emitting the S VI lines, using the observed opacity and the emission measure of these lines. Methods: We analyze SoHO/SUMER spectroscopic observations of the S VI lines, using the center-to-limb variations and radiance ratios to derive the opacity. We also use the Emission Measure derived from radiance at disk center. Results: We get an opacity at S VI line center of the order of 0.05. The resulting average electron density is 2.4 10^16 m^-3 at T = 2 10^5 K. This value is higher than the values obtained from radiance measurements. Conversely, taking a classical value for the density leads to a too high value of the thickness of the emitting layer. Conclusions: The pressure derived from the Emission Measure method compares well with previous determinations and implies a low opacity of 5 10^-3 to 10^-2. The fact that a direct derivation leads to a much higher opacity remains unexplained, despite tentative modeling of observational biases. Further measurements need to be done, and more realistic models of the transition region need to be used.Comment: 11 pages, 9 figure

    The Radiative Transport of Dust in Primordial Galaxies and Second-Generation Star Formation

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    We investigate the radiative transport of dust in primordial galaxies in the presence of the UV radiation field from the first metal-free stars. We find that dust created in the first supernova (SN) explosions can be driven through the interior of the SN remnant to accumulate in the SN shells, where second-generation stars may form from compressed cooling gas. This scenario requires metal-free stars to form continuously over timescales of up to 10 Myr, consistent with recent estimates. Silicate and graphite grains, as well as iron-bearing magnetites, are transported to the shells for reasonable parameter assumptions, but their relative yields from primordial SNe is an important factor in the resulting abundance ratios. We compare the results of segregated grain transport with the current nucleosynthetic data on extremely metal-poor Galactic halo stars. Fossil signatures of this process may already have been detected in those iron-poor stars with enhanced carbon and silicate elements such as magnesium, silicon and oxygen. We discuss the implications of our results for the transition from first- to second-generation star formation in primordial galaxies, and the role played by the radiative transport of dust in this process.Comment: Accepted by ApJ; 10 ApJ-style pages, 5 figures. Minor revisions with added text, results and figures unchanged. Will appear in ApJ v. 640, 20 March 2006 issu

    Knowledge of fertility and perception of fertility treatment among adults with sickle cell disease (KNOW FERTILITY)

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    IntroductionThis study assessed fertility knowledge in adults with sickle cell disease using the Cardiff Fertility Knowledge Scale and Fertility Treatment Perception Survey and compared knowledge scores in respondents with sickle cell disease to previously reported unaffected cohorts.MethodsThis cross-sectional study surveyed adults over age 18 with sickle cell disease at an adult sickle cell disease center using a 35-question survey addressing infertility risk factor knowledge and perceptions of fertility treatment. Analyses included summary statistics for continuous and categorical variables, univariate linear regression, and Mann-Whitney U tests for group comparisons of Fertility Knowledge Scale scores. Fertility Treatment Perception Survey scores were measured by medians of the two positive statements and four negative statements to generate separate positive and negative treatment belief scores. Statistical significance was set at p < 0.05 for all analyses.ResultsNinety-two respondents (71 female, 21 male) with median age of 32 years (IQR: 25.0, 42.5) completed the survey between October 2020-May 2021. Sixty-five percent of respondents reported taking sickle cell disease treatment and 18% reported refusing at least one sickle cell disease treatment due to fertility concerns. The mean Fertility Knowledge Score was 49% (SD: 5.2), lower than reported in an international cohort (57% vs. 49%, p = 0.001), and higher than in a cohort of reproductive-aged Black women in the USA (49% vs. 38%, p = 0.001). Less than 50% of respondents correctly identified common infertility risk factors including sexually transmitted infections, advanced age, and obesity. Mean positive fertility perception score was 3 (IQR 3, 4), and negative fertility perception score was 3.5 (IQR 3, 4). Factors associated with agreement with negative fertility perception statements included: trying to conceive, refusing sickle cell disease treatment, and undergoing fertility treatment.DiscussionOpportunities exist to improve knowledge of infertility risk factors among adults with sickle cell disease. This study raises the possibility that nearly one in five adults with sickle cell disease refuse SCD treatment or cure due to infertility concerns. Education about common infertility risks factors needs to be addressed alongside disease- and treatment- associated fertility risks

    Agronomic performance and transcriptional analysis of carotenoid biosynthesis in fruits of transgenic HighCaro and control tomato lines under field conditions

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    Genetic manipulation of carotenoid biosynthesis in higher plants has been the objective of a number of biotechnology programs, e.g. the Golden Rice Program. However, tomato (Solanumlycopersicum L.), which naturally accumulates lycopene in fruits, has attracted the attention of many groups who have manipulated it to increase or diversify carotenoid accumulation. One of the most significant achievements was “HighCaro (HC),” a transgenic tomato plant constitutively expressing the tomato lycopene beta-cyclase (tLcy-b), that produces orange fruits due to the complete conversion of lycopene to β-carotene. In this article we report the results of a field trial conducted in Metaponto (Italy) on HC and on two control genotypes to evaluate the stability of the transgenic trait and their yield performances. Transcriptional regulation of eight genes involved in carotenogenesis was assayed by quantitative real-time PCR (qRT-PCR) analysis on fruits collected at four distinct development stages. Statistical analysis results demonstrated that in field conditions the transgene maintained its ability to induce the conversion of lycopene to β-carotene. Moreover, agronomic performances and fruit quality in the transgenic line were not impaired by this metabolic disturbance. Results of qRT-PCR analysis suggested that transcription of PSY-1, PDS and ZDS genes were developmentally regulated in both genotypes. Unexpectedly, Lcy-b expression in transgenic fruits was also developmentally regulated, despite the fact that the gene was driven by a constitutive promoter. Our data provide evidence that in photosynthetic cells a strict and aspecific mechanism controls the level of transcripts until the onset of chromoplasts differentiation, at which point a gene-specific control on transcription takes place

    Isolation and functional characterization of a lycopene β-cyclase gene that controls fruit colour of papaya (Carica papaya L.)

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    The colour of papaya fruit flesh is determined largely by the presence of carotenoid pigments. Red-fleshed papaya fruit contain lycopene, whilst this pigment is absent from yellow-fleshed fruit. The conversion of lycopene (red) to β-carotene (yellow) is catalysed by lycopene β-cyclase. This present study describes the cloning and functional characterization of two different genes encoding lycopene β-cyclases (lcy-β1 and lcy-β2) from red (Tainung) and yellow (Hybrid 1B) papaya cultivars. A mutation in the lcy-β2 gene, which inactivates enzyme activity, controls lycopene production in fruit and is responsible for the difference in carotenoid production between red and yellow-fleshed papaya fruit. The expression level of both lcy-β1 and lcy-β2 genes is similar and low in leaves, but lcy-β2 expression increases markedly in ripe fruit. Isolation of the lcy-β2 gene from papaya, that is preferentially expressed in fruit and is correlated with fruit colour, will facilitate marker-assisted breeding for fruit colour in papaya and should create possibilities for metabolic engineering of carotenoid production in papaya fruit to alter both colour and nutritional properties

    Scale relativity and fractal space-time: theory and applications

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    In the first part of this contribution, we review the development of the theory of scale relativity and its geometric framework constructed in terms of a fractal and nondifferentiable continuous space-time. This theory leads (i) to a generalization of possible physically relevant fractal laws, written as partial differential equation acting in the space of scales, and (ii) to a new geometric foundation of quantum mechanics and gauge field theories and their possible generalisations. In the second part, we discuss some examples of application of the theory to various sciences, in particular in cases when the theoretical predictions have been validated by new or updated observational and experimental data. This includes predictions in physics and cosmology (value of the QCD coupling and of the cosmological constant), to astrophysics and gravitational structure formation (distances of extrasolar planets to their stars, of Kuiper belt objects, value of solar and solar-like star cycles), to sciences of life (log-periodic law for species punctuated evolution, human development and society evolution), to Earth sciences (log-periodic deceleration of the rate of California earthquakes and of Sichuan earthquake replicas, critical law for the arctic sea ice extent) and tentative applications to system biology.Comment: 63 pages, 14 figures. In : First International Conference on the Evolution and Development of the Universe,8th - 9th October 2008, Paris, Franc

    Glutathione Deficiency in Cardiac Patients Is Related to the Functional Status and Structural Cardiac Abnormalities

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    International audienceBACKGROUND: The tripeptide glutathione (L-gamma-glutamyl-cysteinyl-glycine) is essential to cell survival, and deficiency in cardiac and systemic glutathione relates to heart failure progression and cardiac remodelling in animal models. Accordingly, we investigated cardiac and blood glutathione levels in patients of different functional classes and with different structural heart diseases. METHODS: Glutathione was measured using standard enzymatic recycling method in venous blood samples obtained from 91 individuals, including 15 healthy volunteers and 76 patients of New York Heart Association (NYHA) functional class I to IV, undergoing cardiac surgery for coronary artery disease, aortic stenosis or terminal cardiomyopathy. Glutathione was also quantified in right atrial appendages obtained at the time of surgery. RESULTS: In atrial tissue, glutathione was severely depleted (-58%) in NYHA class IV patients compared to NYHA class I patients (P = 0.002). In patients with coronary artery disease, this depletion was related to the severity of left ventricular dysfunction (P = 0.006). Compared to healthy controls, blood glutathione was decreased by 21% in NYHA class I patients with structural cardiac disease (P<0.01), and by 40% in symptomatic patients of NYHA class II to IV (P<0.0001). According to the functional NYHA class, significant depletion in blood glutathione occurred before detectable elevation in blood sTNFR1, a marker of symptomatic heart failure severity, as shown by the exponential relationship between these two parameters in the whole cohort of patients (r = 0.88). CONCLUSIONS: This study provides evidence that cardiac and systemic glutathione deficiency is related to the functional status and structural cardiac abnormalities of patients with cardiac diseases. These data also suggest that blood glutathione test may be an interesting new biomarker to detect asymptomatic patients with structural cardiac abnormalities
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