Representation Theory of Quantized Poincare Algebra. Tensor Operators and Their Application to One-Partical Systems

A representation theory of the quantized Poincar\'e ($\kappa$-Poincar\'e) algebra (QPA) is developed. We show that the representations of this algebra are closely connected with the representations of the non-deformed Poincar\'e algebra. A theory of tensor operators for QPA is considered in detail. Necessary and sufficient conditions are found in order for scalars to be invariants. Covariant components of the four-momenta and the Pauli-Lubanski vector are explicitly constructed.These results are used for the construction of some q-relativistic equations. The Wigner-Eckart theorem for QPA is proven.Comment: 18 page

Correlated decay of triplet excitations in the Shastry-Sutherland compound SrCu2_2(BO3_3)2_2

The temperature dependence of the gapped triplet excitations (triplons) in the 2D Shastry-Sutherland quantum magnet SrCu$_2$(BO$_3$)$_2$ is studied by means of inelastic neutron scattering. The excitation amplitude rapidly decreases as a function of temperature while the integrated spectral weight can be explained by an isolated dimer model up to 10~K. Analyzing this anomalous spectral line-shape in terms of damped harmonic oscillators shows that the observed damping is due to a two-component process: one component remains sharp and resolution limited while the second broadens. We explain the underlying mechanism through a simple yet quantitatively accurate model of correlated decay of triplons: an excited triplon is long-lived if no thermally populated triplons are near-by but decays quickly if there are. The phenomenon is a direct consequence of frustration induced triplon localization in the Shastry--Sutherland lattice.Comment: 5 pages, 4 figure

The axonally secreted protein axonin-1 is a potent substratum for neurite growth

Axonin-1 is a neuronal glycoprotein occurring both as a membrane-bound and a secreted form. Membrane-bound axonin-1 is predominantly located in membranes of developing nerve fiber tracts and has recently been characterized as a cell adhesion molecule; the soluble form is secreted from axons and accumulates in the cerebrospinal fluid and the vitreous fluid of the eye. In the present study, we addressed the question as to whether secreted axonin-1 was released in a functionally competent form and we found that it strongly promotes neurite outgrowth when presented to neurons as an immobilized substratum. Neurite lengths elaborated by embryonic dorsal root ganglia neurons on axonin-1 were similar to those on the established neurite-promoting substrata L1 and laminin. Fab fragments of axonin-1 antibodies completely inhibited neurite growth on axonin-1, but not on other substrata. In soluble form, axonin-1 had an anti-adhesive effect, as revealed by perturbation of neurite fasciculation. In view of their structural similarity, we conclude that secreted and membrane-bound axonin-1 interact with the same growth-promoting neuritic receptor. The fact that secreted axonin-1 is functionally active, together with our previous findings that it is secreted from an internal cellular pool, suggests a functional dualism between membrane-bound and secreted axonin-1 at the site of secretion, which is most likely the growth cone. The secretion of adhesion molecules could represent a powerful and rapidly acting regulatory element of growth cone-neurite interactions in the control of neurite elongation, pathway selection, and possibly target recognition

E.C.G. Stueckelberg: a forerunner of modern physics II

We will investigate some aspects of Stueckelberg's work, which have contributed to the development of modern physics. On the one hand, the definition of diffuse boundaries in the calculation of scattering amplitudes will be reviewed, and compared with the other proposals by physicists of that time. On the other hand, the applications of Stueckelberg's description of a massive vector field in the Standard Model will be discussed.Comment: 8 pages, no figures, to appear in Proceedings of the II Stueckelberg Workshop - Int. J. Mod. Phys.

Repro Money: An Extension Program to Improve Dairy Farm Reproductive Performance

A farmer-directed, team-based Extension program (Repro Money) was developed and executed by the University of Wisconsin–Madison Department of Dairy Science in collaboration with University of Wisconsin–Extension. The goal of the Repro Money program was to help Wisconsin dairy farmers increase reproductive performance and profitability through identification of areas for improvement and implementation of action plans. For the 40 Wisconsin dairy farms that completed the Repro Money program, mean 21-day pregnancy rate increased by 2 percentage points, which was estimated to result in an economic net gain of $31 per cow per year. Extension professionals can apply similar team-based programs to tackle multifaceted, interrelated problems that may be only partially addressed by other, more traditional programming

Financial loss and depressive symptoms in university students during the first wave of the COVID-19 pandemic: comparison between 23 countries

Objectives: To assess the association between students’ financial loss and depressive symptoms during the first wave of the coronavirus disease 2019 (COVID-19) pandemic and whether this association varied by countries having different levels of lockdown measures. Methods: This cross-sectional survey, conducted in spring 2020, included 91,871 students from 23 countries. Depressive symptoms were measured using the shortened Center for Epidemiological Studies Depression Scale and information on lockdowns retrieved from the COVID-19 government response tracker. The association between financial loss and depressive symptoms was investigated estimating prevalence ratios (PR) with multilevel Poisson models. Results: Some 13% of students suffered financial loss during the lockdown and 52% had a relatively high depression score, with large between-countries differences. Minimally and maximally adjusted models showed a 35% (PR = 1.35, 95% Confidence Interval (CI) = 1.29–1.42) and 31% (PR = 1.31, 95% CI = 1.26–1.37) higher prevalence of depressive symptoms in students who lost economic resources compared to students with stable economic resources. No substantial differences in the association were found across countries. Conclusion: Depressive symptoms were more frequent among students who suffered financial loss during the pandemic. Policy makers should consider this issue in the implementation of COVID-19 mitigating measure

Multi-graviton theory, a latticized dimension, and the cosmological constant

Beginning with the Pauli-Fierz theory, we construct a model for multi-graviton theory. Couplings between gravitons belonging to nearest-neighbor ``theory spaces'' lead to a discrete mass spectrum. Our model coincides with the Kaluza-Klein theory whose fifth dimension is latticized. We evaluate one-loop vacuum energy in models with a circular latticized extra dimension as well as with compact continuous dimensions. We find that the vacuum energy can take a positive value, if the dimension of the continuous space time is $6, 10,...$. Moreover, since the amount of the vacuum energy can be an arbitrary small value according to the choice of parameters in the model, our models is useful to explain the small positive dark energy in the present universe.Comment: 10 pages, No figure. Needs REVTeX4. citations are corrected and minor correction

Acute mTOR inhibition induces insulin resistance and alters substrate utilization in vivo.

The effect of acute inhibition of both mTORC1 and mTORC2 on metabolism is unknown. A single injection of the mTOR kinase inhibitor, AZD8055, induced a transient, yet marked increase in fat oxidation and insulin resistance in mice, whereas the mTORC1 inhibitor rapamycin had no effect. AZD8055, but not rapamycin reduced insulin-stimulated glucose uptake into incubated muscles, despite normal GLUT4 translocation in muscle cells. AZD8055 inhibited glycolysis in MEF cells. Abrogation of mTORC2 activity by SIN1 deletion impaired glycolysis and AZD8055 had no effect in SIN1 KO MEFs. Re-expression of wildtype SIN1 rescued glycolysis. Glucose intolerance following AZD8055 administration was absent in mice lacking the mTORC2 subunit Rictor in muscle, and in vivo glucose uptake into Rictor-deficient muscle was reduced despite normal Akt activity. Taken together, acute mTOR inhibition is detrimental to glucose homeostasis in part by blocking muscle mTORC2, indicating its importance in muscle metabolism in vivo

Crustal structure of active deformation zones in Africa: Implications for global crustal processes

The Cenozoic East African rift (EAR), Cameroon Volcanic Line (CVL), and Atlas Mountains formed on the slow-moving African continent, which last experienced orogeny during the Pan-African. We synthesize primarily geophysical data to evaluate the role of magmatism in shaping Africa's crust. In young magmatic rift zones, melt and volatiles migrate from the asthenosphere to gas-rich magma reservoirs at the Moho, altering crustal composition and reducing strength. Within the southernmost Eastern rift, the crust comprises ~20% new magmatic material ponded in the lower crust sills, and intruded as sills and dikes at shallower depths. In the Main Ethiopian rift, intrusions comprise 30% of the crust below axial zones of dike-dominated extension. In the incipient rupture zones of the Afar rift, magma intrusions fed from crustal magma chambers beneath segment centers create new columns of mafic crust, as along slow-spreading ridges. Our comparisons suggest that transitional crust, including seaward-dipping sequences, is created as progressively smaller screens of continental crust are heated and weakened by magma intrusion into 15-20 km-thick crust. In the 30Ma-Recent CVL, which lacks a hotspot age-progression, extensional forces are small, inhibiting the creation and rise of magma into the crust. In the Atlas orogen, localized magmatism follows the strike of the Atlas Mountains from the Canary Islands hotspot towards the Alboran Sea. CVL and Atlas magmatism has had minimal impact on crustal structure. Our syntheses show that magma and volatiles are migrating from the asthenosphere through the plates, modifying rheology and contributing significantly to global carbon and water fluxes

Could dark energy be vector-like?

In this paper I explore whether a vector field can be the origin of the present stage of cosmic acceleration. In order to avoid violations of isotropy, the vector has be part of a ``cosmic triad'', that is, a set of three identical vectors pointing in mutually orthogonal spatial directions. A triad is indeed able to drive a stage of late accelerated expansion in the universe, and there exist tracking attractors that render cosmic evolution insensitive to initial conditions. However, as in most other models, the onset of cosmic acceleration is determined by a parameter that has to be tuned to reproduce current observations. The triad equation of state can be sufficiently close to minus one today, and for tachyonic models it might be even less than that. I briefly analyze linear cosmological perturbation theory in the presence of a triad. It turns out that the existence of non-vanishing spatial vectors invalidates the decomposition theorem, i.e. scalar, vector and tensor perturbations do not decouple from each other. In a simplified case it is possible to analytically study the stability of the triad along the different cosmological attractors. The triad is classically stable during inflation, radiation and matter domination, but it is unstable during (late-time) cosmic acceleration. I argue that this instability is not likely to have a significant impact at present.Comment: 28 pages, 6 figures. Uses RevTeX4. v2: Discussion about relation to phantoms added and additional references cite