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991.
Roberto Laos Christos Lampropoulos Steven A. Benner 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(1):22-28
Synthetic biologists demonstrate their command over natural biology by reproducing the behaviors of natural living systems on synthetic biomolecular platforms. For nucleic acids, this is being done stepwise, first by adding replicable nucleotides to DNA, and then removing its standard nucleotides. This challenge has been met in vitro with `six‐letter' DNA and RNA, where the Watson–Crick pairing `concept' is recruited to increase the number of independently replicable nucleotides from four to six. The two nucleobases most successfully added so far are Z and P , which present a donor–donor–acceptor and an acceptor–acceptor–donor pattern, respectively. This pair of nucleobases are part of an `artificially expanded genetic information system' (AEGIS). The Z nucleobase has been already crystallized, characterized, and published in this journal [Matsuura et al. (2016). Acta Cryst. C 72 , 952–959]. More recently, variants of Taq polymerase have been crystallized with the pair P : Z trapped in the active site. Here we report the crystal structure of the nucleobase 2‐aminoimidazo[1,2‐a][1,3,5]triazin‐4‐one (trivially named P ) as the monohydrate, C5H5N5O·H2O. The nucleobase P was crystallized from water and characterized by X‐ray diffraction. Interestingly, the crystal structure shows two tautomers of P packed in a Watson–Crick fashion that cocrystallized in a 1:1 ratio. 相似文献
992.
A static meshfree implementation of the bond-based peridynamics formulation for linearly elastic solids is applied to the study of the transition from local to nonlocal behavior of the stress and displacement fields in the vicinity of a crack front and other sources of stress concentration. The long-range nature of the interactions between material points that is intrinsic to and can be modulated within peridynamics enables the smooth transition from the square-root singular stress fields predicted by the classical (local) linear theory of elasticity, to the nonsingular fields associated with nonlocal theories. The accuracy of the peridynamics scheme and the transition from local to nonlocal behavior, which are dictated by the lattice spacing and micromodulus function, are assessed by performing an analysis of the boundary layer that surrounds the front of a two dimensional crack subjected to mode-I loading and of a cracked plate subjected to far-field tension. 相似文献
993.
Roberto?Zitzumbo-Guzman Felipe?Avalos-Belmontes Luis?F.?Ramos-De Valle Jose?C.?Ortiz-Cisneros Sergio?Alonso-Romero Anayansi?Estrada-MonjeEmail author 《Rheologica Acta》2018,57(5):397-404
The rheological properties in the transient state of PP/EPDM blends with carbon nanofillers had been studied. The carbon nanofillers were incorporated into molten EPDM in an internal mixer at 150 °C. The rheological variables were determined in rotational rheometry at constant temperature of 200 °C. The results suggest that the magnitude of the difference of the normal stress differences (N1-N2) of PP/EPDM blends through the time, with and without nanofillers, and has a transition cycle from positive to negative values and vice versa, at constant and at zero shear rate in previously sheared samples. At constant shear rate, the transition cycle is random; meanwhile, it is constant at zero shear rate. This behavior is attributed to the polymeric chain movement, considering that the sheared samples have two molecular reorder processes: an immediate mechanism and another one slower. The fastest reorder process is attributed to the polymeric chains entanglement forming non-stable and stressed molecular structures. In the other hand, the second process is referred to the molecular mobility that takes place inside the stressed entangled polymer, in such a way that its structure tends to molecular stability as the rest time increases. 相似文献
994.
Jurgen Lange Natalia Davidenko Roberto Sastre 《Macromolecular theory and simulations》2009,18(9):511-527
Mathematical modeling of the thermopolymerization of FM and CMFMA was carried out using a cross‐linked kinetic model proposed for the photo‐initiated polymerization of acryl‐furanic compounds. In this model, the photochemical initiation step was substituted by a thermal one and it was assumed that the constant of radical termination was time‐dependent, which allowed the gel effect (Trommsdorff) at high monomer conversion to be simulated. Optimization of all kinetic constants was achieved and the results of simulation suitably fitted the experimental data of the monomer conversion. The contribution of each step in the mechanism and its dependence on the experimental conditions were estimated by a sensitivity analysis technique.
995.
Arlindo Csar Matias Pereira Helison de Oliveira Carvalho Danna Emanuelle Santos Gonalves Karyny Roberta Tavares Picano Abraho Victor Tavares de Lima Teixeira dos Santos Heitor Ribeiro da Silva Francinaldo Sarges Braga Roberto Messias Bezerra Alessandro de Sousa Nunes Maira Tiyomi Sacata Tongo Nazima Júlia Gomes Cerqueira Talisson Taglialegna Janayra Maris Teixeira Jos Carlos Tavares Carvalho 《Molecules (Basel, Switzerland)》2021,26(16)
This study aimed to evaluate and compare the effects of co-treatment with purified annatto oil (PAO) or its granules (GRA, Chronic®) with that of testosterone on the orchiectomy-induced osteoporosis in Wistar rats. After surgery, rats were treated from day 7 until day 45 with testosterone only (TES, 7 mg/kg, IM) or TES + PAO or GRA (200 mg/kg, p.o.). The following parameters were evaluated: food/water intake, weight, HDL, LDL, glucose, triglycerides (TG), total cholesterol (TC), alkaline phosphatase levels, blood phosphorus and calcium contents, femur weight, structure (through scanning electron microscopy), and calcium content (through atomic absorption spectrophotometry). Our results show that orchiectomy could significantly change the blood lipid profile and decrease bone integrity parameters. Testosterone reposition alone could improve some endpoints, including LDL, TC, bone weight, and bone calcium concentration. However, other parameters were not significantly improved. Co-treatment with PAO or GRA improved the blood lipid profile and bone integrity more significantly and improved some endpoints not affected by testosterone reposition alone (such as TG levels and trabeculae sizes). The results suggest that co-treatment with annatto products improved the blood lipid profile and the anti-osteoporosis effects of testosterone. Overall, GRA had better results than PAO. 相似文献
996.
In this paper we study the growth probability and cluster morphologies which emerge in an off-lattice, two-dimensional, colored diffusion-limited aggregation model for urban dynamics, particularly migration. To reach this goal, three immobile interacting clusters that include the geographical concept of gravity are studied by exact enumeration. In our simulations we find a strong correlation between the seed’s distance, migration rules and number of aggregated particles. The growth probability of a certain angular subset and its rate and route of convergence to a Normal distribution when migration cost is acting are also shown. We search how all the factors mentioned above determine the cluster morphologies. 相似文献
997.
Roberto Boada María ángeles Laguna‐Marco Jesús Chaboy 《Journal of synchrotron radiation》2009,16(1):38-42
An X‐ray magnetic circular dichroism (XMCD) study performed at the Ho L2,3‐edges in Ho6Fe23 as a function of temperature is presented. It is demonstrated that the anomalous temperature dependence of the Ho L2‐edge XMCD signal is due to the magnetic contribution of Fe atoms. By contrast, the Ho L3‐edge XMCD directly reflects the temperature dependence of the Ho magnetic moment. By combining the XMCD at both Ho L2‐ and L3‐edges, the possibility of determining the temperature dependence of the Fe magnetic moment is demonstrated. Then, both μHo(T) and μFe(T) have been determined by tuning only the absorption L‐edges of Ho. This result opens new possibilities of applying XMCD at these absorption edges to obtain quantitative element‐specific magnetic information that is not directly obtained by other experimental tools. 相似文献
998.
Jesús Chaboy María ángeles Laguna‐Marco Cristina Piquer Roberto Boada Neculai Plugaru Hiroshi Maruyama Naomi Kawamura 《Journal of synchrotron radiation》2009,16(3):405-412
An X‐ray magnetic circular dichroism (XMCD) study performed at the rare‐earth L2,3‐edges in the RxR1?x′Al2 compounds is presented. It is shown that both R and R′ atoms contribute to the XMCD recorded at the L‐edges of the selected rare‐earth, either R or R′. The amplitude of the XMCD signal is not directly correlated to the magnetization or to the value of the individual (R, R′) magnetic moments, but it is related to the molecular field acting on the rare‐earth tuned in the photoabsorption process. This result closes a longstanding study of the origin of the XMCD at the L‐edge of the rare‐earths in multi‐component systems, allowing a full understanding of the exact nature of these signals. 相似文献
999.
We review the General Relativistic model of a (quasi) point-like particle represented by a massive shell of neutral matter which has vanishing total energy in the small-volume limit. We then show that, by assuming a Generalised Uncertainty Principle, which implies the existence of a minimum length of the order of the Planck scale, the total energy instead remains finite and equal to the shell's proper mass both for very heavy and very light particles. This suggests that the quantum structure of space–time might be related to the classical Equivalence Principle and possible implications for the late stage of evaporating black holes are briefly mentioned. 相似文献
1000.
Roberto Giambò Fabio Giannoni Paolo Piccione 《Communications in Mathematical Physics》2009,287(3):903-923
Given a Lorentzian manifold (M, g), an event p and an observer U in M, then p and U are light conjugate if there exists a lightlike geodesic γ : [0, 1] → M joining p and U whose endpoints are conjugate along γ. Using functional analytical techniques, we prove that if one fixes p and U in a differentiable manifold M, then the set of stationary Lorentzian metrics in M for which p and U are not light conjugate is generic in a strong sense. The result is obtained by reduction to a Finsler geodesic problem via a second
order Fermat principle for light rays, and using a transversality argument in an infinite dimensional Banach manifold setup. 相似文献