[en] In this work we study the pairing symmetry in a square lattice within a generalized Hubbard model, in which a second-neighbor correlated hopping is included in addition to the on-site and nearest-neighbor repulsions. When an infinitesimal distortion of the right angles in the square lattice is considered, we observe a spin triplet p-wave ground state for the case of electrons, but for holes a finite distortion is required, contrary to the d-wave case. In general, this spatial distortion induces a splitting of the doubly degenerate p-wave pairing states and one of them could become the ground state. On the other hand, this study has been extended to a finite density of electrons within the BCS formalism and the results show a maximum critical temperature of p-wave superconductivity around a 2/3 band-filling, close to the Fermi energy in the γ-band of Sr₂RuO₄ estimated by band-structure calculations

[en] Purpose: To evaluate the antitumor activity of recombinant human tumor necrosis factor-alpha (rHuTNF-α) on a human glioblastoma multiforme (U87) xenograft in nude mice, and to study the effect of combining rHuTNF-α with local radiation on the tumor control probability of this tumor model. Methods and Materials: U87 xenograft was transplanted SC into the right hindleg of NCr/Sed nude mice (7-8 weeks old, male). When tumors reached a volume of about 110 mm³, mice were randomly assigned to treatment: rHuTNF-α alone compared with normal saline control; or local radiation plus rHuTNF-α vs. local radiation plus normal saline. Parameters of growth delay, volume doubling time, percentage of necrosis, and cell loss factor were used to assess the antitumor effects of rHuTNF-α on this tumor. The TCD₅₀ (tumor control dose 50%) was used as an endpoint to determine the effect of combining rHuTNF-α with local radiation. Results: Tumor growth in mice treated with a dose of 150 μg/kg body weight rHuTNF-α, IP injection daily for 7 consecutive days, was delayed about 8 days compared to that in controls. Tumors in the treatment group had a significantly longer volume doubling time, and were smaller in volume and more necrotic than matched tumors in control group. rHuTNF-α also induced a 2.3 times increase of cell loss factor. The administration of the above-mentioned dose of rHuTNF-α starting 24 h after single doses of localized irradiation under hypoxic condition, resulted in a significant reduction in TCD₅₀ from the control value of 60.9 Gy to 50.5 Gy (p < 0.01). Conclusion: rHuTNF-α exhibits an antitumor effect against U87 xenograft in nude mice, as evidenced by an increased delay in tumor growth as well as cell loss factor. Also, there was an augmentation of tumor curability when given in combination with radiotherapy, resulting in a significantly lower TCD₅₀ value in the treatment vs. the control groups

[en] Purpose: To study the impact of the overall treatment time of fractionated irradiation on the tumor control probability (TCP) of a human soft tissue sarcoma xenograft growing in nude mice, as well as to compare the pretreatment potential doubling time (T_pot) of this tumor to the effective doubling time (T_eff) derived from three different schedules of irradiation using the same total number of fractions with different overall treatment times. Methods and Materials: The TCP was assessed using the TCD₅₀ value (the 50% tumor control dose) as an end point. A total of 240 male nude mice, 7-8 weeks old were used in three experimental groups that received the same total number of fractions (30 fractions) with different overall treatment times. In group 1, the animals received three equal fractions/day for 10 consecutive days, in group 2 they received two equal fractions/day for 15 consecutive days, and in group 3 one fraction/day for 30 consecutive days. All irradiations were given under normal blood flow conditions to air breathing animals. The mean tumor diameter at the start of irradiation was 7-8 mm. The mean interfraction intervals were from 8-24 h. The T_pot was measured using Iododeoxyuridine (IudR) labeling and flow cytometry and was compared to T_eff. Results: The TCD₅₀ values of the three different treatment schedules were 58.8 Gy, 63.2 Gy, and 75.6 Gy for groups 1, 2, and 3, respectively. This difference in TCD₅₀ values was significant (p < 0.05) between groups 1 and 2 (30 fractions/10 days and 30 fractions/15 days) vs. group 3 (30 fractions/30 days). The loss in TCP due to the prolongation of the overall treatment time from 10 days to 30 days was found to be 1.35-1.4 Gy/day. The pretreatment T_pot (2.4 days) was longer than the calculated T_eff in groups 2 and 3 (1.35 days). Conclusion: Our data show a significant loss in TCP with prolongation of the overall treatment time. This is most probably due to an accelerated repopulation of tumor clonogens. The pretreatment T_pot of this tumor model does not reflect the actual doubling of the clonogens in a protracted regimen

[en] The effects of quantum confinement on the superconducting ground state are studied within the Bogoliubov-de Gennes (BdG) formalism and an attractive Hubbard model. We consider a periodic arrangement of two-dimensional superconducting grains composed by N x N atoms surrounded by insulating, metallic or superconducting stripes with a thickness of s atoms, leading to 2(N + s)² coupled self-consistent BdG equations for a supercell of (N + s) x (N + s) atoms. These equations determine the spatial variation of superconducting gap as functions of temperature, electron-electron interaction, and hopping integrals analyzing three types of boundary stripes. The results show a clear enhancement of the superconducting gap and critical temperature induced by the electron confinement in the grain, being larger for the insulating boundary case. Finally, the numerical solutions of BdG equations are compared with those obtained by applying the BCS theory to each grain site. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] Based on the BCS formalism, the electronic specific heat of d-symmetry superconducting states is studied. This study is performed on a square lattice described by a generalized Hubbard model, in which correlated-hopping interactions are included in addition to the repulsive Coulomb ones. Instead of the exponential temperature dependence for the s-channel, the results show second and higher power-law behaviors for d-wave superconducting specific heat, depending on the angular dependence of the single-excitation energy gap occurred at different carrier concentrations. The results of this study could help to understand a variety of power-law behaviors observed in La_2-xSr_xCuO₄ superconductors

[en] In this work, a comparative study of pairing and superconducting states in square lattices with s-, p- and d-symmetries is performed within the BCS formalism and a generalized Hubbard model, in which correlated-hopping interactions are considered in addition to the repulsive Coulomb interactions. The two-particle analysis reveals the importance of the van Hove singularity in the formation of pairs and then the two-particle states with different pairing symmetry have their maximum binding energies at the same hopping strength. This feature is confirmed by the superconducting critical temperature (T _c) calculation at the low-density regime. However, a different picture is found for the high-density regime, i.e., the maxima of the s- and d-channel T _c split from the expected value and no p-wave superconducting state is found. This study suggests that the three superconducting symmetries can be analyzed within a single framework

[en] Based on the BCS formalism, we propose a unified description of the anisotropic p- and d-wave superconducting states by using a local interacting electron model with a unique second-neighbour correlated-hopping interaction. In this work, we study the dependence of both p- and d-channel critical temperatures (T_c) on the electron concentration (n), as well as the angular dependence of single-particle excitation energy gaps (Δ₀), which can be measured by the angle-resolved photoemission spectroscopy (ARPES) and the tunnelling spectroscopy. The effects of an external magnetic field on T_c and Δ₀ in anisotropic superconductors are also investigated within the rigid band-shift approximation.

[en] We report a comparative study of the s-, p- and d-symmetry superconducting states in square lattices within a Hubbard model, in which correlated-hopping interactions are considered in addition to the repulsive Coulomb interactions. This study is carried out by means of the BCS formalism. The results show that the first and second neighbors correlated hoppings favour s- and d-symmetry pairings, respectively. Moreover, an infinitesimal distortion of the right angles in the square lattice induces the appearance of a p-wave (spin-triplet) superconducting state

[en] In this Letter, we consider a two-dimensional Hubbard model that includes a second-neighbor correlated hopping interaction, and we find a triplet p-wave superconducting ground state within the BCS formalism. A small distortion of the square-lattice right angles is introduced in order to break the degeneracy of kx+/-ky oriented p-wave pairing states. For the strong coupling limit, analytical results are obtained. An analysis of the superconducting critical temperature reveals the existence of an optimal electron density and the gap ratio exhibits a non-BCS behavior. Finally, the particular case of strontium ruthenate is examined

[en] The formation of p- and d-wave superconducting ground states on a square lattice is studied within the BCS formalism and a generalized Hubbard model, in which a second-neighbor correlated hopping (Δt₃) is included in addition to the on site and nearest neighbor repulsions. The triplet superconductivity is obtained when a small distortion of the right angles in the square lattice is introduced. This distortion can be characterized by the difference between the values of Δt₃^± in the x ± y directions, i.e., δ₃=(Δt₃⁺-Δt₃^-)/2. The phase diagram is analyzed in the space of the electron density (n) and δ₃. The results show that the p- and d-channel superconductivities are respectively enhanced in the low and high electron density regions