排序方式: 共有17条查询结果,搜索用时 15 毫秒
1.
Vieyra HA Oeschler N Seiro S Jeevan HS Geibel C Parker D Steglich F 《Physical review letters》2011,106(20):207001
The tetragonal heavy-fermion compound CeCu?Si? exhibits a superconducting ground state (S type, T(c) = 0.67 K) close to a magnetic instability. Here, we present angle-resolved resistivity measurements of the upper critical field H(c2). In-plane rotation of S-type CeCu?Si? single crystals reveals a fourfold oscillation of H(c2). An extended weak-coupling BCS model for a d-wave symmetry including strong Pauli-limiting effects confirms the aforementioned angular dependence and points towards d(xy) symmetry of the order parameter. 相似文献
2.
It is shown that the F
4 rational and trigonometric integrable systems are exactly solvable for arbitrary values of the coupling constants. Their spectra are found explicitly while eigenfunctions are obtained by pure algebraic means. For both systems new variables are introduced in which the Hamiltonian has an algebraic form being also (block)-triangular. These variables are a certain invariants of the F
4 Weyl group. Both Hamiltonians preserve the same (minimal) flag of spaces of polynomials, which is found explicitly. 相似文献
3.
Menéndez FE Espina Aránzazu Trobajo Camino García José R. Rodríguez Julio 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(3):215-230
Journal of Inclusion Phenomena and Macrocyclic Chemistry - The intercalation reactions betweenn-alkylamines and α-titanium phosphate in aqueous media have been investigated. The compounds with... 相似文献
4.
José?L.?Jiménez-PérezEmail author Pavel?Vieyra?Pincel Alfredo?Cruz-Orea Zormy?N.?Correa-Pacheco 《Applied Physics A: Materials Science & Processing》2016,122(5):556
Thermal properties of a liquid resin were studied by thermal lens spectrometry (TLS) and open photoacoustic cell (OPC), respectively. In the case of the TLS technique, the two mismatched mode experimental configuration was used with a He–Ne laser, as a probe beam and an Argon laser was used as the excitation source. The characteristic time constant of the transient thermal lens was obtained by fitting the theoretical expression to the experimental data in order to obtain the thermal diffusivity (α) of the resin. On the other hand, the sample thermal effusivity (e) was obtained by using the OPC technique. In this technique, an Argon laser was used as the excitation source and was operated at 514 nm with an output power of 30 mW. From the obtained thermal diffusivity (α) and thermal effusivity (e) values, the thermal conductivity (k) and specific heat capacity per unit volume (ρc) of resin were calculated through the relationships k = e(α)1/2 and ρc = e/(α)1/2. The obtained thermal parameters were compared with the thermal parameters of the literature. To our knowledge, the thermal characterization of resin has not been reported until now. The present study has applications in laser stereo-lithography to manufacture 3D printing pieces. 相似文献
5.
The steady-state UVA (350 nm) photolysis of ( E )-β-ionone ( 1 ) in aerated toluene solutions was studied by 1 H NMR spectroscopy. The formation of the 1,2,4-trioxane ( 2 ) and 5,8-endoperoxide ( 5 ) derivatives in the ratio of 4:1 was observed. Time-resolved laser induced experiments at 355 nm, such as laser-flash photolysis, photoacoustic and singlet oxygen 1 O2 phosphorescence detection, confirmed the formation of the excited triplet state of 1 with a quantum yield Φ T = 0.50 as the precursor for the generation of singlet oxygen 1 O2 ( Φ Δ = 0.16) and the isomeric α-pyran derivative ( 3 ), which was a reaction intermediate detected by NMR. In turn, the reaction of 1 O2 with 1 and 3 occurred with rate constants of 1.0 × 106 and 2.5 × 108 m −1 s−1 to yield the oxygenated products 5 and 2 , respectively, indicating the relevance of the fixed s-cis configuration in the α-pyran ring in the concerted [2+4] cycloaddition of 1 O2 . 相似文献
6.
Enhancement of Photophysical and Photosensitizing Properties of Flavin Adenine Dinucleotide by Mutagenesis of the C‐Terminal Extension of a Bacterial Flavodoxin Reductase
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Dr. Lorena Valle Dr. Inés Abatedaga Dr. Faustino E. Morán Vieyra Dr. Ana Bortolotti Prof. Dr. Néstor Cortez Prof. Dr. Claudio D. Borsarelli 《Chemphyschem》2015,16(4):872-883
The role of the mobile C‐terminal extension present in Rhodobacter capsulatus ferredoxin–NADP(H) reductase (RcFPR) was evaluated using steady‐state and dynamic spectroscopies for both intrinsic Trp and FAD in a series of mutants in the absence of NADP(H). Deletion of the six C‐terminal amino acids beyond Ala266 was combined with the replacement A266Y to emulate the structure of plastidic reductases. Our results show that these modifications of the wild‐type RcFPR produce subtle global conformational changes, but strongly reduce the local rigidity of the FAD‐binding pocket, exposing the isoalloxazine ring to the solvent. Thus, the ultrafast charge‐transfer quenching of 1FAD* by the conserved Tyr66 residue was absent in the mutant series, producing enhancement of the excited singlet‐ and triplet‐state properties of FAD. This work highlights the delicate balance of the specific interactions between FAD and the surrounding amino acids, and how the functionality and/or photostability of redox flavoproteins can be modified. 相似文献
7.
MP Serrano C Lorente FE Morán Vieyra CD Borsarelli AH Thomas 《Physical chemistry chemical physics : PCCP》2012,14(33):11657-11665
UV-A radiation (320-400 nm) induces damage to the DNA molecule and its components through photosensitized reactions. Biopterin (Bip) and its photoproducts 6-formylpterin (Fop) and 6-carboxypterin (Cap) accumulate in the skin of human beings suffering from vitiligo, a depigmentation disorder where the protection against UV radiation fails because of the lack of melanin. This study was aimed to evaluate the photosensitizing properties of oxidized pterins present in the skin and to elucidate the mechanisms involved in the photosensitized oxidation of purine nucleotides by pterins in vitro. For this purpose, steady-state and time-resolved experiments in acidic (pH 5.0-5.8) aqueous solution were performed using Bip, Fop and Cap as photosensitizers and the nucleotide 2'-deoxyguanosine 5'-monophosphate (dGMP) as an oxidizable target. The three pterin derivatives are able to photosensitize dGMP, being Fop the most efficient sensitizer. The reactions proceed through two competing pathways: (1) electron transfer from dGMP to triplet excited-state of pterins (type I mechanism) and (2) reaction of dGMP with (1)O(2) produced by pterins (type II mechanism). Kinetic analysis revealed that the electron transfer pathway is the main mechanism and the interaction of dGMP with the triplet excited-state of pterins and the formation of the corresponding dGMP radicals were demonstrated by laser flash photolysis experiments. The biological implications of the results obtained are also discussed. 相似文献
8.
Rosa Linares Xchitl N. Acua Gabriela Rosas Elizabeth Vieyra Deyra A. Ramírez Andrea Chaparro Julieta A. Espinoza Roberto Domínguez Leticia Morales-Ledesma 《Molecules (Basel, Switzerland)》2021,26(18)
In rats with polycystic ovary syndrome (PCOS) induced by injection of estradiol valerate (EV), unilateral or bilateral section of the vagus nerve restores ovulatory function in 75% of animals, suggesting that the vagus nerve participates in the development of PCOS. Since the vagus nerve is a mixed nerve through which mainly cholinergic-type information passes, the objective of the present study was to analyze whether acetylcholine (ACh) is involved in the development of PCOS. Ten-day-old rats were injected with 2.0 mg EV, and at 60 days of age, they were microinjected on the day of diestrus in the bursa of the left or right ovary with 100 or 700 mg/kg of ovarian weight atropine, a blocker of muscarinic receptors, and sacrificed for histopathological examination after the surgery. Animals with PCOS microinjected with 100 mg of atropine showed a lack of ovulation, lower serum concentrations of progesterone and testosterone, and cysts. Histology of the ovaries of animals microinjected with 700 mg of atropine showed corpus luteum and follicles at different stages of development, which was accompanied by a lower concentration of progesterone and testosterone. These results allow us to suggest that in animals with PCOS, ACh, which passes through parasympathetic innervation, is an important component in the persistence and development of the pathophysiology. 相似文献
9.
The Fe14.5Co16.5Ni55B15 and the Fe13Co15.5Ni51.5B20 ferromagnetic nanowires were deposited using the electrochemical deposition method. The structure of these nanowires was investigated using X-ray diffraction. Squid magnetometer was used to investigate the magnetic behavior. The hysteresis loops of 50 μm long nanowire arrays were studied as a function of boron concentration, nanowire diameter and field orientation. The competition between shape anisotropy and magnetostatic interactions played a vital role in determining the magnetic field necessary to saturate an array. The decrease in coercive field (Hc) and the squareness (SQ) of the hysteresis loop from 100 to 200 nm wire diameter for both types of compositions suggests the formation of multidomains in the nanowire. 相似文献
10.
Konstantin G.?BoreskovEmail author Alexander V.?Turbiner Juan Carlos Lopez?Vieyra 《Communications in Mathematical Physics》2005,260(1):17-44
Solvability of the rational quantum integrable systems related to exceptional root spaces G2,F4 is re-examined and for E6,7,8 is established in the framework of a unified approach. It is shown that Hamiltonians take algebraic form being written in certain Weyl-invariant variables. It is demonstrated that for each Hamiltonian the finite-dimensional invariant subspaces are made from polynomials and they form an infinite flag. A notion of minimal flag is introduced and minimal flag for each Hamiltonian is found. Corresponding eigenvalues are calculated explicitly while the eigenfunctions can be computed by pure linear algebra means for arbitrary values of the coupling constants. The Hamiltonian of each model can be expressed in the algebraic form as a second degree polynomial in the generators of some infinite-dimensional but finitely-generated Lie algebra of differential operators, taken in a finite-dimensional representation.Alexander V. Turbiner: On leave of absence from the Institute for Theoretical and Experimental Physics, Moscow 117259, Russia. 相似文献