SU(5) Heterotic Standard Model Bundles

We construct a class of stable SU(5) bundles on an elliptically fibered Calabi-Yau threefold with two sections, a variant of the ordinary Weierstrass fibration, which admits a free involution. The bundles are invariant under the involution, solve the topological constraint imposed by the heterotic anomaly equation and give three generations of Standard Model fermions after symmetry breaking by Wilson lines of the intermediate SU(5) GUT-group to the Standard Model gauge group. Among the solutions we find some which can be perturbed to solutions of the Strominger system. Thus these solutions provide a step toward the construction of phenomenologically realistic heterotic flux compactifications via non-Kahler deformations of Calabi-Yau geometries with bundles. This particular class of solutions involves a rank two hidden sector bundle and does not require background fivebranes for anomaly cancellation.Comment: 17 page

Resolution of Nested Neuronal Representations Can Be Exponential in the Number of Neurons

Collective computation is typically polynomial in the number of computational elements, such as transistors or neurons, whether one considers the storage capacity of a memory device or the number of floating-point operations per second of a CPU. However, we show here that the capacity of a computational network to resolve real-valued signals of arbitrary dimensions can be exponential in N, even if the individual elements are noisy and unreliable. Nested, modular codes that achieve such high resolutions mirror the properties of grid cells in vertebrates, which underlie spatial navigation

Group 13 Decamethylmetallocenium Cations

Salts containing the decamethylmetallocenium cations, [( C5Me5) M-2](+) ( or Cp*M-2(+)) of the group 13 "metals" B, Al and Ga have been prepared using a variety of synthetic routes. Precursor molecules of the type Cp*2MX ( X = Cl, Br, Me) exhibit structural features that vary significantly depending on the size and electronegativity of the central atom. While salt metathesis, halide abstraction and methanide abstraction methods represent viable routes for the preparation of salts of Cp*B-2(+) and Cp*Al-2(+), acidolysis of a Cp* group from Cp*Ga-3 is the most reliable method for the synthesis of the analogous gallium cation. Gallocenium cations are less stable than either of the lighter congeneric cations since they prove to be susceptible to decomposition reactions involving the "back-transfer" of ligands from the counter anion. Density functional theory (DFT) calculations revealed that, whereas Cp*Ga-2(+) is predicted to adopt a molecular structure more similar to that of Cp*B-2(+), the electronic structure of the gallium cation bears a greater resemblance to that of Cp*Al-2(+).Chemistr

A 2D quantum antiferromagnet with a four-fold degenerate valence-bond-solid ground state

We study the competition between antiferromagnetic order and valence bond solid formation in a two-dimensional frustrated spin-1/2 model. The J1-J2 model on the square lattice is further frustrated by introducing products of three-spin projectors which stabilize four dimer-product states as degenerate ground states. These four states are reminiscent of the dimerized singlet ground state of the Shastry-Sutherland model. Using exact diagonalizations, we study the evolution of the ground state by varying theratio of interactions. For a large range of parameters (J2 > 0.25J1), our model shows a direct transition between the valence-bond-solid phase and the collinear antiferromagnetic phase. For small values of J2, several intermediate phases appear which are also analyzed

Kondo screening in a magnetically frustrated nanostructure: Exact results on a stable, non-Fermi-liquid phase

Triangular symmetry stabilizes a novel non-Fermi-liquid phase in the three-impurity Kondo model with frustrating antiferromagnetic interactions between half-integer impurity spins. The phase arises without fine-tuning of couplings, and is stable against magnetic fields and particle-hole symmetry breaking. We find a conformal field theory describing this phase, verify it using the numerical renormalization group, and extract various exact, universal low-energy properties. Signatures predicted in electrical transport may be testable in scanning tunneling microscopy or quantum-dot experiments.Comment: 4 pages, published version (shortened, minor corrections

The effect of Coulombic friction on spatial displacement statistics

The phenomenon of Coulombic friction enters the stochastic description of dry friction between two solids and the statistic characterization of vibrating granular media. Here we analyze the corresponding Fokker-Planck equation including both velocity and spatial components, exhibiting a formal connection to a quantum mechanical harmonic oscillator in the presence of a delta potential. Numerical solutions for the resulting spatial displacement statistics show a crossover from exponential to Gaussian displacement statistics. We identify a transient intermediate regime that exhibits multiscaling properties arising from the contribution of Coulombic friction. The possible role of these effects during observations in diffusion experiments is shortly discussed.Comment: 11 pages, 9 figure

Bethe Ansatz solution of a new class of Hubbard-type models

We define one-dimensional particles with generalized exchange statistics. The exact solution of a Hubbard-type Hamiltonian constructed with such particles is achieved using the Coordinate Bethe Ansatz. The chosen deformation of the statistics is equivalent to the presence of a magnetic field produced by the particles themselves, which is present also in a ``free gas'' of these particles.Comment: 4 pages, revtex. Essentially modified versio

Microscopic features of moving traffic jams

Empirical and numerical microscopic features of moving traffic jams are presented. Based on a single vehicle data analysis, it is found that within wide moving jams, i.e., between the upstream and downstream jam fronts there is a complex microscopic spatiotemporal structure. This jam structure consists of alternations of regions in which traffic flow is interrupted and flow states of low speeds associated with "moving blanks" within the jam. Empirical features of the moving blanks are found. Based on microscopic models in the context of three-phase traffic theory, physical reasons for moving blanks emergence within wide moving jams are disclosed. Structure of moving jam fronts is studied based in microscopic traffic simulations. Non-linear effects associated with moving jam propagation are numerically investigated and compared with empirical results.Comment: 19 pages, 12 figure

Mental Toughness in Strength and Conditioning Training: Is it really necessary? Perspectives of elite NCAA Strength and Conditioning coaches

In recent years, there has been an increased awareness and consideration of the association of mental toughness (MT) in high performance in sports. However, MT remains both one of the most accepted and misunderstood terms in applied sport psychology, especially when it comes to strength and conditioning training and female student-athletes. PURPOSE: To investigate the beliefs of Strength and Conditioning Coaches (SSC) of women’s collegiate basketball in regards to MT. In more detail, based on the literature, field tendencies, and practice, 8 areas of interest were covered: 1) Conceptualization, 2) Value, 3) Development, 4) Gender Differences, 5) Measurement, 6) Differences in the responsibilities to develop MT when compared to basketball coaches, 7) Implementation, and 8) Level of interest in learning more. METHODS: Ten National Collegiate Athletic Association (NCAA) Division 1 SCCs for women’s basketball from the same Power 5 conference were recruited via email. The study followed an observational and cross-sectional model while a fixed and convergent mixed-method design was used. Data were collected on a quantitative instrument (i.e., questionnaire) and on a qualitative instrument (i.e., interview). Eight SCCs completed the Stronger Than Average Mentality (S.T.A.M.) questionnaire on Qualtrics. S.T.A.M. is a 34-item instrument, which was piloted first. In addition, its items’ reliability was estimated using Guttman’s λ2. Six participated in a semi-structured interview of 10 open-ended questions. Both instruments’ items were developed based on the same 8 areas of interest stated above. Capturing the descriptive information about the sample was the goal of analysis of the quantitative data (i.e., descriptive statistics), while data reduction was the goal of analysis of the qualitative data (i.e., thematic analysis). Then, integration of the results from the two strands was performed looking for corroborating or complementary information, which resulted in a 90% inter-rater agreement. In cases of conflict, analytic induction was run. RESULTS: There was convergence of the findings in all 8 areas of interest. In more detail, all SCC’s find MT to be important and would like to know more about it. The majority of SCC’s claimed that they know what MT is, that MT can be developed, that the head coach has more responsibility towards developing MT, and that they know how to measure it. However, there was high variability when ranking MT’s key attributes, while there was no consensus on whether MT can be developed in student-athletes or on whether there are gender differences in MT. None SCC reported use of an instrument for measurement. CONCLUSION: MT is of value in strength and conditioning in this conference. The findings confirm conclusions of previous research, which indicated that –although MT is reported to be widely used– at the same time, it is a very unclear term. More education of the coaches is necessary, especially in regards to the key components of MT, MT training, and MT measurement. Future research should perhaps use a more grounded theory approach and recruit SCC’s from other sports and different environments (e.g., conference, level, country). The development in this age and the transferability outside sports are two issues that should be addressed in future research efforts