On the semiclassical theory for universal transmission fluctuations in chaotic systems: the importance of unitarity

The standard semiclassical calculation of transmission correlation functions for chaotic systems is severely influenced by unitarity problems. We show that unitarity alone imposes a set of relationships between cross sections correlation functions which go beyond the diagonal approximation. When these relationships are properly used to supplement the semiclassical scheme we obtain transmission correlation functions in full agreement with the exact statistical theory and the experiment. Our approach also provides a novel prediction for the transmission correlations in the case where time reversal symmetry is present

Semiclassical Description of Wavepacket Revival

We test the ability of semiclassical theory to describe quantitatively the revival of quantum wavepackets --a long time phenomena-- in the one dimensional quartic oscillator (a Kerr type Hamiltonian). Two semiclassical theories are considered: time-dependent WKB and Van Vleck propagation. We show that both approaches describe with impressive accuracy the autocorrelation function and wavefunction up to times longer than the revival time. Moreover, in the Van Vleck approach, we can show analytically that the range of agreement extends to arbitrary long times.Comment: 10 pages, 6 figure

Orthogonality Catastrophe in Parametric Random Matrices

We study the orthogonality catastrophe due to a parametric change of the single-particle (mean field) Hamiltonian of an ergodic system. The Hamiltonian is modeled by a suitable random matrix ensemble. We show that the overlap between the original and the parametrically modified many-body ground states, $S$, taken as Slater determinants, decreases like $n^{-k x^2}$, where $n$ is the number of electrons in the systems, $k$ is a numerical constant of the order of one, and $x$ is the deformation measured in units of the typical distance between anticrossings. We show that the statistical fluctuations of $S$ are largely due to properties of the levels near the Fermi energy.Comment: 12 pages, 8 figure

Pulping and pretreatment affect the characteristics of bagasse inks for 3D printing

Bagasse is an underutilized agro-industrial residue with great potential as raw material for the production of cellulose nanofibrils (CNF) for a range of applications. In this study, we have assessed the suitability of bagasse for production of CNF for three-dimensional (3D) printing. First, pulp fibers were obtained from the bagasse raw material using two fractionation methods, i.e. soda and hydrothermal treatment combined with soda. Second, the pulp fibers were pretreated by TEMPO-mediated oxidation using two levels of oxidation for comparison purposes. Finally, the CNF were characterized in detail and assessed as inks for 3D printing. The results show that CNF produced from fibers obtained by hydrothermal and soda pulping were less nanofibrillated than the corresponding material produced by soda pulping. However, the CNF sample obtained from soda pulp was cytotoxic, apparently due to a larger content of silica particles. All the CNF materials were 3D printable. We conclude that the noncytotoxic CNF produced from hydrothermally and soda treated pulp can potentially be used as inks for 3D printing of biomedical devices.Fil: Chinga Carrasco, Gary. RISE PFI; NoruegaFil: Ehman, Nanci Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Pettersson, Jennifer. RISE Bioscience and Materials; SueciaFil: Vallejos, María Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Felissia, Fernando Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Hakansson, Joakim. RISE Bioscience and Materials; SueciaFil: Area, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentin

Adaptation of the Bergen Social Media Addiction Scale (BSMAS) in Spanish

The impact of social networks on people's daily lives is worrisome, particularly in adolescents and young people, who seem to exceed the limits of normal use. Constant excessive use can lead to pathological behaviors linked to social media addiction (SMA). Our objectives were to 1) adapt the Bergen Social Media Addiction Scale (BSMAS) to Spanish and 2) evaluate its psychometric properties in a young population. The BSMAS was adapted to Spanish, involving experts on social media addiction and people from the target population during the adaptation process. For the psychometric evaluation, 650 Peruvian college students responded to the Spanish version (53.5 % women aged 18 to 40, M = 21.5 SD = 2.7). The one-dimensional measurement model proposed for the original BSMAS was confirmed for our version (X2(9) = 23.9315, CFI = 0.994, TLI = 0.990, SRMR = 0.032, RMSEA = 0.061). The reliability was good (α = 0.863; 95 % CI: 0.848–0.870; ω = 0.864; 95 % CI: 0.846–0.844), and the measurement invariance was confirmed for sex and age by fitting models. The concurrent validity with external social media addiction and mental health indicators was also confirmed. This study provides new and relevant information on the BSMAS validity and allows its application to Spanish-speaker college students from Peru and similar countries

Coulomb blockade conductance peak fluctuations in quantum dots and the independent particle model

We study the combined effect of finite temperature, underlying classical dynamics, and deformations on the statistical properties of Coulomb blockade conductance peaks in quantum dots. These effects are considered in the context of the single-particle plus constant-interaction theory of the Coulomb blockade. We present numerical studies of two chaotic models, representative of different mean-field potentials: a parametric random Hamiltonian and the smooth stadium. In addition, we study conductance fluctuations for different integrable confining potentials. For temperatures smaller than the mean level spacing, our results indicate that the peak height distribution is nearly always in good agreement with the available experimental data, irrespective of the confining potential (integrable or chaotic). We find that the peak bunching effect seen in the experiments is reproduced in the theoretical models under certain special conditions. Although the independent particle model fails, in general, to explain quantitatively the short-range part of the peak height correlations observed experimentally, we argue that it allows for an understanding of the long-range part.Comment: RevTex 3.1, 34 pages (including 13 EPS and PS figures), submitted to Phys. Rev.

Spin and e-e interactions in quantum dots: Leading order corrections to universality and temperature effects

We study the statistics of the spacing between Coulomb blockade conductance peaks in quantum dots with large dimensionless conductance g. Our starting point is the ``universal Hamiltonian''--valid in the g->oo limit--which includes the charging energy, the single-electron energies (described by random matrix theory), and the average exchange interaction. We then calculate the magnitude of the most relevant finite g corrections, namely, the effect of surface charge, the ``gate'' effect, and the fluctuation of the residual e-e interaction. The resulting zero-temperature peak spacing distribution has corrections of order Delta/sqrt(g). For typical values of the e-e interaction (r_s ~ 1) and simple geometries, theory does indeed predict an asymmetric distribution with a significant even/odd effect. The width of the distribution is of order 0.3 Delta, and its dominant feature is a large peak for the odd case, reminiscent of the delta-function in the g->oo limit. We consider finite temperature effects next. Only after their inclusion is good agreement with the experimental results obtained. Even relatively low temperature causes large modifications in the peak spacing distribution: (a) its peak is dominated by the even distribution at kT ~ 0.3 Delta (at lower T a double peak appears); (b) it becomes more symmetric; (c) the even/odd effect is considerably weaker; (d) the delta-function is completely washed-out; and (e) fluctuation of the coupling to the leads becomes relevant. Experiments aimed at observing the T=0 peak spacing distribution should therefore be done at kT<0.1 Delta for typical values of the e-e interaction.Comment: 15 pages, 4 figure

Interactions in Chaotic Nanoparticles: Fluctuations in Coulomb Blockade Peak Spacings

We use random matrix models to investigate the ground state energy of electrons confined to a nanoparticle. Our expression for the energy includes the charging effect, the single-particle energies, and the residual screened interactions treated in Hartree-Fock. This model is applicable to chaotic quantum dots or nanoparticles--in these systems the single-particle statistics follows random matrix theory at energy scales less than the Thouless energy. We find the distribution of Coulomb blockade peak spacings first for a large dot in which the residual interactions can be taken constant: the spacing fluctuations are of order the mean level separation Delta. Corrections to this limit are studied using the small parameter 1/(kf L): both the residual interactions and the effect of the changing confinement on the single-particle levels produce fluctuations of order Delta/sqrt(kf L). The distributions we find are significantly more like the experimental results than the simple constant interaction model.Comment: 17 pages, 4 figures, submitted to Phys. Rev.

Conductance fluctuations and weak localization in chaotic quantum dots

We study the conductance statistical features of ballistic electrons flowing through a chaotic quantum dot. We show how the temperature affects the universal conductance fluctuations by analyzing the influence of dephasing and thermal smearing. This leads us to two main findings. First, we show that the energy correlations in the transmission, which were overlooked so far, are important for calculating the variance and higher moments of the conductance. Second, we show that there is an ambiguity in the method of determination of the dephasing rate from the size of the of the weak localization. We find that the dephasing times obtained at low temperatures from quantum dots are underestimated.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let