Sodium: a charge-transfer insulator at high pressures

By means of first-principles methods we analyze the optical response of transparent dense sodium as a function of applied pressure. We discover an unusual kind of charge-transfer exciton that proceeds from the interstitial distribution of valence electrons repelled away from the ionic cores by the Coulomb interaction and the Pauli repulsion. The predicted absorption spectrum shows a strong anisotropy with light polarization that just at pressures above the metal-insulator transition manifests as sodium being optically transparent in one direction but reflective in the other. This result provides a key information about the crystal structure of transparent sodium, a new unconventional inorganic electride.Comment: revtex4, 5+8 page

Positronium signature in organic liquid scintillators for neutrino experiments

Electron anti-neutrinos are commonly detected in liquid scintillator experiments via inverse beta decay, by looking at the coincidence between the reaction products, neutron and positron. Prior to positron annihilation, an electron-positron pair may form an orthopositronium (o-Ps) state, with a mean life of a few ns. Even if the o-Ps decay is speeded up by spin flip or pick off effects, it may introduce distortions in the photon emission time distribution, crucial for position reconstruction and pulse shape discrimination algorithms in anti-neutrino experiments. Reversing the problem, the o-Ps induced time distortion represents a new signature for tagging anti-neutrinos in liquid scintillator. In this paper, we report the results of measurements of the o-Ps formation probability and lifetime, for the most used solvents for organic liquid scintillators in neutrino physics (pseudocumene, linear alkyl benzene, phenylxylylethane, and dodecane). We characterize also a mixture of pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength shifter. In the second part of the paper, we demonstrate that the o-Ps induced distortion of the scintillation photon emission time distributions represent an optimal signature for tagging positrons on an event by event basis, potentially enhancing the anti-neutrino detection.Comment: 6 pages, 9 figure

vibration mitigation of a linear host structure using a passive neutralizer effect of nonlinearity in the neutralizer suspension

Abstract Motivated by some experimental results on a test-rig, this paper presents some observations on the frequency response of a primary linear oscillator when an auxiliary nonlinear oscillator is attached to it, acting as a vibration neutralizer. In the experiments, an electro-dynamic shaker is used as the linear one-degree-of-freedom primary oscillator, and it is excited by an harmonic force. The nonlinear neutralizer is attached to the moving head of the shaker, and it is assembled to achieve a cubic stiffness characteristics, due to geometrical arrangement of linear elastic elements. For very low vibration amplitudes, the whole system behaves predominantly as a two-degree-of-freedom linear oscillator, but when the force excitation to the shaker is increased the shape of the frequency response curve changes, and exhibits resonance peak bending, jump phenomena and instabilities of the harmonic response. A theoretical model of the system is presented, with the aim to capture the qualitative phenomena observed in the experiments

Spatial correlations in hexagons generated via a Kerr nonlinearity

We consider the hexagonal pattern forming in the cross-section of an optical beam produced by a Kerr cavity, and we study the quantum correlations characterizing this structure. By using arguments related to the symmetry broken by the pattern formation, we identify a complete scenario of six-mode entanglement. Five independent phase quadratures combinations, connecting the hexagonal modes, are shown to exhibit sub-shot-noise fluctuations. By means of a non-linear quantum calculation technique, quantum correlations among the mode photon numbers are demonstrated and calculated.Comment: ReVTeX file, 20 pages, 7 eps figure

Acceleration with Self-Injection for an All-Optical Radiation Source at LNF

We discuss a new compact gamma-ray source aiming at high spectral density, up to two orders of magnitude higher than currently available bremsstrahlung sources, and conceptually similar to Compton Sources based on conventional linear accelerators. This new source exploits electron bunches from laser-driven electron acceleration in the so-called self-injection scheme and uses a counter-propagating laser pulse to obtain X and gamma-ray emission via Thomson/Compton scattering. The proposed experimental configuration inherently provides a unique test-bed for studies of fundamental open issues of electrodynamics. In view of this, a preliminary discussion of recent results on self-injection with the FLAME laser is also given.Comment: 8 pages, 10 figures, 44 references - Channeling 2012 conferenc

The Drosophila Protein Asp Is Involved in Microtubule Organization during Spindle Formation and Cytokinesis

Abnormal spindle (Asp) is a 220-kD microtubule-associated protein from Drosophila that has been suggested to be involved in microtubule nucleation from the centrosome. Here, we show that Asp is enriched at the poles of meiotic and mitotic spindles and localizes to the minus ends of central spindle microtubules. Localization to these structures is independent of a functional centrosome. Moreover, colchicine treatment disrupts Asp localization to the centrosome, indicating that Asp is not an integral centrosomal protein. In both meiotic and mitotic divisions of asp mutants, microtubule nucleation occurs from the centrosome, and γ-tubulin localizes correctly. However, spindle pole focusing and organization are severely affected. By examining cells that carry mutations both in asp and in asterless, a gene required for centrosome function, we have determined the role of Asp in the absence of centrosomes. Phenotypic analysis of these double mutants shows that Asp is required for the aggregation of microtubules into focused spindle poles, reinforcing the conclusion that its function at the spindle poles is independent of any putative role in microtubule nucleation. Our data also suggest that Asp has a role in the formation of the central spindle. The inability of asp mutants to correctly organize the central spindle leads to disruption of the contractile ring machinery and failure in cytokinesis

7th–8th Grade: English Level 3, Learning Packet #4 • Theme: Disasters #4

Exploring Survivor Stories, Grades 7-8 We\u27ve already explored a few survivor stories, but we\u27re going to look at a few other experiences. This week we are going to take a look at the stories of people, kids in particular, who have experienced disasters and lived to tell about them. We\u27re going to take a look at their encounters with natural disasters to understand how they withstood these dangers. Lesson 1 • It\u27s going to BLOW!, Mountain of fire, Meetings challenges Lesson 2 • Too hot to handle, Lost in Death Valley, Meeting challenges Lesson 3 • Cold enough for you?, Lost in a blizzard, Meeting challenges Lesson 4 • Land falls away, Sinkhole excerpt from Tangerine, Meeting challenges Lesson 5 • Review the week\u27s learning, Write a first-person story of getting heat stroke What will you learn in this packet? - Learn/refine (make better) your understanding of vocabulary and sentence structure - Explore cause and effect relationships of disasters, actions, and physical conditions - Make and explain predictions and inferences about people, actions, or events - Reflect on your learning and how you can use it in the real world Answer Keys W aa a , b a a c.W aa a , b a a c. Detected language : Englis

Nature of light correlations in ghost imaging

We investigate the nature of correlations in Gaussian light sources used for ghost imaging. We adopt methods from quantum information theory to distinguish genuinely quantum from classical correlations. Combining a microscopic analysis of speckle-speckle correlations with an effective coarse-grained description of the beams, we show that quantum correlations exist even in `classical'-like thermal light sources, and appear relevant for the implementation of ghost imaging in the regime of low illumination. We further demonstrate that the total correlations in the thermal source beams effectively determine the quality of the imaging, as quantified by the signal-to-noise ratio.Comment: 12 pages, 5 figures. To appear in Scientific Reports (NPG