1,921 research outputs found
Linear recurrences and asymptotic behavior of exponential sums of symmetric boolean functions
In this paper we give an improvement of the degree of the homogeneous linear
recurrence with integer coefficients that exponential sums of symmetric Boolean
functions satisfy. This improvement is tight. We also compute the asymptotic
behavior of symmetric Boolean functions and provide a formula that allows us to
determine if a symmetric boolean function is asymptotically not balanced. In
particular, when the degree of the symmetric function is a power of two, then
the exponential sum is much smaller than .Comment: 18 pages, 3 figure
Toward a test of angular momentum coherence in a twin-atom interferometer
We present a scheme well-suited to investigate quantitatively the angular
momentum coherence of molecular fragments. Assuming that the dissociated
molecule has a null total angular momentum, we investigate the propagation of
the corresponding atomic fragments in the apparatus. We show that the
envisioned interferometer enables one to distinguish unambiguously a
spin-coherent from a spin-incoherent dissociation, as well as to estimate the
purity of the angular momentum density matrix associated with the fragments.
This setup, which may be seen as an atomic analogue of a twin-photon
interferometer, can be used to investigate the suitability of molecule
dissociation processes -- such as the metastable hydrogen atoms H()-H() dissociation - for coherent twin-atom optics.Comment: 6 pages, 3 Figures. Final version accepted for publication in
Europhysics Letter
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Evolution of substrate specificity in a retained enzyme driven by gene loss.
The connection between gene loss and the functional adaptation of retained proteins is still poorly understood. We apply phylogenomics and metabolic modeling to detect bacterial species that are evolving by gene loss, with the finding that Actinomycetaceae genomes from human cavities are undergoing sizable reductions, including loss of L-histidine and L-tryptophan biosynthesis. We observe that the dual-substrate phosphoribosyl isomerase A or priA gene, at which these pathways converge, appears to coevolve with the occurrence of trp and his genes. Characterization of a dozen PriA homologs shows that these enzymes adapt from bifunctionality in the largest genomes, to a monofunctional, yet not necessarily specialized, inefficient form in genomes undergoing reduction. These functional changes are accomplished via mutations, which result from relaxation of purifying selection, in residues structurally mapped after sequence and X-ray structural analyses. Our results show how gene loss can drive the evolution of substrate specificity from retained enzymes
Facile synthesis of low band gap ZnO Microstructures
Abstract In this work a simple chemical route was employed to synthesize ZnO microparticles by precipitation from aqueous solution of ZnCl2 as precursor, NaOH as oxidizing and sodium dodecyl sulfate (SDS) as surfactant. Samples of ZnO microparticles were analyzed by scanning electron microscopy (SEM), FTIR spectroscopy, Raman spectroscopy, X-Ray diffraction, UV/Vis-NIR diffusereflectance,highresolutiontransmissionelectronmicroscopy(HR-TEM),andN2 adsorption-desorption.Itwasobserved from SEM analysis that ZnO microparticles with morphologies resembling six-blade impeller with diameters in the range of 500 nm to 1 m, and sheet-like (approximately 200 nm×300 nm) were obtained through this technique. X-Ray diffraction and Raman analyses confirmed the obtaining of hexagonal wurtzite ZnO crystal structure. The calculated band gap energy was 3.19 eV, which is slightly lower than the average value reported in the literature. Specific BET area of ZnO microparticles was 26.5 m2/g. Keywords: ZnO, microstructures, band gap energy, SEM, morphology.
Resumen En este trabajo se empleó un a ruta química sencilla para sintetizar micropartículas de ZnO mediante precipitación en solución acuosa de ZnCl2 como precursor, NaOH como oxidante y dodecil sulfato de sodio (SDS) como tensoactivo. Las muestras de ZnO fueron analizadas mediante microscopía de barrido electrónico (SEM), espectroscopía de FTIR, espectroscopía Raman, difracción de rayos-X, reflectancia difusa de UV/Vis-NIR, microscopía de transmisión de electrones de alta resolución (HRTEM), y mediante adsorción-desorción de N2. Se observó mediante análisis de SEM que mediante esta técnica se obtienen micropartículas de ZnO con morfologías similares a impulsores de seis-aspas con diámetros entre 500 nm y 1 m, morfologías tipo-hojas(deaproximadamente200nm×300nm).Losanálisisdedifracciónderayos-XydeRamanconfirmaronlaobtención de ZnO con estructura cristalina wurtzita hexagonal. La energía de band gap calculada fue de 3.19 eV, la cual es ligeramente menor que el valor promedio reportado en la literatura. El área superficial BET de las nanopartículas de ZnO fue de 26.5 m2/g Palabras clave: ZnO, microestructuras, energía de band gap, SEM, morfología
Equine lamellar energy metabolism studied using tissue microdialysis
Failure of lamellar energy metabolism may contribute to the pathophysiology of equine laminitis. Tissue microdialysis has the potential to dynamically monitor lamellar energy balance over time. The objectives of this study were to develop a minimally invasive lamellar microdialysis technique and use it to measure normal lamellar energy metabolite concentrations over 24h. Microdialysis probes were placed (through the white line) into either the lamellar dermis (LAM) (n=6) or the sublamellar dermis (SUBLAM) (n=6) and perfused continuously over a 24h study period. Probes were placed in the skin dermis (SKIN) for simultaneous comparison to LAM (n=6). Samples were collected every 2h and analysed for glucose, lactate, pyruvate, urea and glycerol concentrations. LAM was further compared with SUBLAM by simultaneous placement and sampling in four feet from two horses over 4h. Horses were monitored for lameness, and either clinically evaluated for 1month after probe removal (n=4) or subjected to histological evaluation of the probe site (n=10).There were no deleterious clinical effects of probe placement and the histological response was mild. Sample fluid recovery and metabolite concentrations were stable for 24h. Glucose was lower (and lactate:glucose ratio higher) in LAM compared with SUBLAM and SKIN (
Reference ranges for Doppler indices of umbilical and fetal middle cerebral arteries and cerebroplacental ratio: systematic review.
OBJECTIVE: To assess studies reporting reference ranges for umbilical artery (UA) and fetal middle cerebral artery (MCA) Doppler indices and cerebroplacental ratio (CPR), using a set of predefined methodological quality criteria for study design, statistical analysis and reporting methods. METHODS: This was a systematic review of observational studies in which the primary aim was to create reference ranges for UA and MCA Doppler indices and CPR in fetuses of singleton gestations. A search for relevant articles was performed in MEDLINE, EMBASE, CINAHL, Web of Science (from inception to 31 December 2016) and references of the retrieved articles. Two authors independently selected studies, assessed the risk of bias and extracted the data. Studies were scored against a predefined set of independently agreed methodological criteria and an overall quality score was assigned to each study. Linear multiple regression analysis assessing the association between quality scores and study characteristics was performed. RESULTS: Thirty-eight studies met the inclusion criteria. The highest potential for bias was noted in the following fields: 'ultrasound quality control measures', in which only two studies demonstrated a comprehensive quality-control strategy; 'number of measurements taken for each Doppler variable', which was apparent in only three studies; 'sonographer experience', in which no study on CPR reported clearly the experience or training of the sonographers, while only three studies on UA Doppler and four on MCA Doppler did; and 'blinding of measurements', in which only one study, on UA Doppler, reported that sonographers were blinded to the measurement recorded during the examination. Sample size estimations were present in only seven studies. No predictors of quality were found on multiple regression analysis. Reference ranges varied significantly with important clinical implications for what is considered normal or abnormal, even when restricting the analysis to the highest scoring studies. CONCLUSIONS: There is considerable methodological heterogeneity in studies reporting reference ranges for UA and MCA Doppler indices and CPR, and the resulting references have important implications for clinical practice. There is a need for the standardization of methodologies for Doppler velocimetry and for the development of reference standards, which can be correctly interpreted and applied in clinical practice. We propose a set of recommendations for this purpose. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd
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