5,567 research outputs found

    Measurement of the Gravity-Field Curvature by Atom Interferometry

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    We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed.Comment: 5 pages, 3 figure

    Inhibition of phosphoinositide 3-kinase/protein kinase B signaling hampers the vasopressin-dependent stimulation of myogenic differentiation

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    Arginine-vasopressin (AVP) promotes muscle differentiation, hypertrophy, and regeneration through the combined activation of the calcineurin and Calcium/Calmodulin-dependent Protein Kinase (CaMK) pathways. The AVP system is impaired in several neuromuscular diseases, suggesting that AVP may act as a physiological factor in skeletal muscle. Since the Phosphoinositide 3-kinases/Protein Kinase B/mammalian Target Of Rapamycin (PI3K/Akt/mTOR) signaling plays a significant role in regulating muscle mass, we evaluated its role in the AVP myogenic effect. In L6 cells AKT1 expression was knocked down, and the AVP-dependent expression of mTOR and Forkhead box O3 (FoxO) was analyzed by Western blotting. The effect of the PI3K inhibitor LY294002 was evaluated by cellular and molecular techniques. Akt knockdown hampered the AVP-dependent mTOR expression while increased the levels of FoxO transcription factor. LY294002 treatment inhibited the AVP-dependent expression of Myocyte Enhancer Factor-2 (MEF2) and myogenin and prevented the nuclear translocation of MEF2. LY294002 also repressed the AVP-dependent nuclear export of histone deacetylase 4 (HDAC4) interfering with the formation of multifactorial complexes on the myogenin promoter. We demonstrate that the PI3K/Akt pathway is essential for the full myogenic effect of AVP and that, by targeting this pathway, one may highlight novel strategies to counteract muscle wasting in aging or neuromuscular disorders

    Long-lived Bloch oscillations with bosonic Sr atoms and application to gravity measurement at micrometer scale

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    We report on the observation of Bloch oscillations on the unprecedented time scale of severalseconds. The experiment is carried out with ultra-cold bosonic strontium-88 loaded into a vertical optical standing wave. The negligible atom-atom elastic cross section and the absence of spin makes 88^{88}Sr an almost ideal Bose gas insensitive to typical mechanisms of decoherence due to thermalization and to external stray fields. The small size enables precision measurements of forces at micrometer scale. This is a challenge in physics for studies of surfaces, Casimir effects, and searches for deviations from Newtonian gravity predicted by theories beyond the standard model

    Quantum test of the equivalence principle for atoms in superpositions of internal energy eigenstates

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    The Einstein Equivalence Principle (EEP) has a central role in the understanding of gravity and space-time. In its weak form, or Weak Equivalence Principle (WEP), it directly implies equivalence between inertial and gravitational mass. Verifying this principle in a regime where the relevant properties of the test body must be described by quantum theory has profound implications. Here we report on a novel WEP test for atoms. A Bragg atom interferometer in a gravity gradiometer configuration compares the free fall of rubidium atoms prepared in two hyperfine states and in their coherent superposition. The use of the superposition state allows testing genuine quantum aspects of EEP with no classical analogue, which have remained completely unexplored so far. In addition, we measure the Eotvos ratio of atoms in two hyperfine levels with relative uncertainty in the low 10−910^{-9}, improving previous results by almost two orders of magnitude.Comment: Accepted for publication in Nature Communicatio

    Cooling of Sr to high phase-space density by laser and sympathetic cooling in isotopic mixtures

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    Based on an experimental study of two-body and three-body collisions in ultracold strontium samples, a novel optical-sympathetic cooling method in isotopic mixtures is demonstrated. Without evaporative cooling, a phase-space density of 6×10−26\times10^{-2} is obtained with a high spatial density that should allow to overcome the difficulties encountered so far to reach quantum degeneracy for Sr atoms.Comment: 5 pages, 4 figure

    Case Study—Co-Creating School Meals Services

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    All children in Italy receive free, compulsory schooling and have all the rights to school and community education services, including school meals, according to constitutionally founded basic educational principles. To operate a school meals service, the municipal authorities must set up a School Meals Joint Committee (SMJC) composed of the Councillor for Education (CEd), pupil-parent representatives, teachers and a council expert. Mapping the experience of the SMJC set up in Abbiategrasso, a town in the Metropolitan City of Milan, Lombardy, northern Italy, identifies some interconnected drivers of co-production in a basic school and community education service. Hence, the SMJC has become a major enabling force in the school meals monitoring operations, allowing the council to take on education-related challenges that were previously beyond its limited capabilities. The involvement of the SMJC members in the diverse stages of the decision-making process has created a new institutional arena in which the actors play a central role in shaping the school meals service

    Inhibition causes ceaseless dynamics in networks of excitable nodes

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    The collective dynamics of a network of excitable nodes changes dramatically when inhibitory nodes are introduced. We consider inhibitory nodes which may be activated just like excitatory nodes but, upon activating, decrease the probability of activation of network neighbors. We show that, although the direct effect of inhibitory nodes is to decrease activity, the collective dynamics becomes self-sustaining. We explain this counterintuitive result by defining and analyzing a "branching function" which may be thought of as an activity-dependent branching ratio. The shape of the branching function implies that for a range of global coupling parameters dynamics are self-sustaining. Within the self-sustaining region of parameter space lies a critical line along which dynamics take the form of avalanches with universal scaling of size and duration, embedded in ceaseless timeseries of activity. Our analyses, confirmed by numerical simulation, suggest that inhibition may play a counterintuitive role in excitable networks.Comment: 11 pages, 6 figure