Diffusive stability for periodic metric graphs

Analysis and Stochastic

Organization of the Drosophila larval visual circuit

Visual systems transduce, process and transmit light-dependent environmental cues. Computation of visual features depends on the types of photoreceptor neurons (PR) present, the organization of the eye and the wiring of the underlying neural circuit. Here, we describe the circuit architecture of the visual system of Drosophila larvae by mapping the synaptic wiring diagram and neurotransmitters. By contacting different targets, the two larval PR-subtypes create parallel circuits potentially underlying the computation of absolute light intensity and temporal light changes already within this first visual processing center. Locally processed visual information then signals via dedicated projection interneurons to higher brain areas including the lateral horn and mushroom body. The stratified structure of the LON suggests common organizational principles with the adult fly and vertebrate visual systems. The complete synaptic wiring diagram of the LON paves the way to understanding how circuits with reduced numerical complexity control wide ranges of behaviors

Evidence of kaon nuclear and Coulomb potential effects on soft K+ production from nuclei

The ratio of forward K+ production on copper, silver and gold targets to that on carbon has been measured at proton beam energies between 1.5 and 2.3 GeV as a function of the kaon momentum p_K using the ANKE spectrometer at COSY-Juelich. The strong suppression in the ratios observed for p_K<200-250 MeV/c can be ascribed to a combination of Coulomb and nuclear repulsion in the K+A system. This opens a new way to investigate the interaction of K+-mesons in the nuclear medium. Our data are consistent with a K+A nuclear potential of V_K~20 MeV at low kaon momenta and normal nuclear density. Given the sensitivity of the data to the kaon potential, the current experimental precision might allow one to determine V_K to better than 3 MeV.Comment: 9 pages, 3 figures; changed conten

Stable mode-locked pulses from mid-infrared semiconductor lasers

We report the unequivocal demonstration of mid-infrared mode-locked pulses from a semiconductor laser. The train of short pulses was generated by actively modulating the current and hence the optical gain in a small section of an edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch equations in an open two-level system. We anticipate our results to be a significant step toward a compact, electrically-pumped source generating ultrashort light pulses in the mid-infrared and terahertz spectral ranges.Comment: 26 pages, 4 figure

Towards Quantum Repeaters with Solid-State Qubits: Spin-Photon Entanglement Generation using Self-Assembled Quantum Dots

In this chapter we review the use of spins in optically-active InAs quantum dots as the key physical building block for constructing a quantum repeater, with a particular focus on recent results demonstrating entanglement between a quantum memory (electron spin qubit) and a flying qubit (polarization- or frequency-encoded photonic qubit). This is a first step towards demonstrating entanglement between distant quantum memories (realized with quantum dots), which in turn is a milestone in the roadmap for building a functional quantum repeater. We also place this experimental work in context by providing an overview of quantum repeaters, their potential uses, and the challenges in implementing them.Comment: 51 pages. Expanded version of a chapter to appear in "Engineering the Atom-Photon Interaction" (Springer-Verlag, 2015; eds. A. Predojevic and M. W. Mitchell

Forward K+ production in subthreshold pA collisions at 1.0 GeV

K+ meson production in pA (A = C, Cu, Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Juelich accelerator. The complete momentum spectrum of kaons emitted at forward angles, theta < 12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.Comment: 4 pages, 3 figure

OGLE-2009-BLG-092/MOA-2009-BLG-137: A Dramatic Repeating Event With the Second Perturbation Predicted by Real-Time Analysis

We report the result of the analysis of a dramatic repeating gravitational microlensing event OGLE-2009-BLG-092/MOA-2009-BLG-137, for which the light curve is characterized by two distinct peaks with perturbations near both peaks. We find that the event is produced by the passage of the source trajectory over the central perturbation regions associated with the individual components of a wide-separation binary. The event is special in the sense that the second perturbation, occurring $\sim 100$ days after the first, was predicted by the real-time analysis conducted after the first peak, demonstrating that real-time modeling can be routinely done for binary and planetary events. With the data obtained from follow-up observations covering the second peak, we are able to uniquely determine the physical parameters of the lens system. We find that the event occurred on a bulge clump giant and it was produced by a binary lens composed of a K and M-type main-sequence stars. The estimated masses of the binary components are $M_1=0.69 \pm 0.11\ M_\odot$ and $M_2=0.36\pm 0.06\ M_\odot$, respectively, and they are separated in projection by $r_\perp=10.9\pm 1.3\ {\rm AU}$. The measured distance to the lens is $D_{\rm L}=5.6 \pm 0.7\ {\rm kpc}$. We also detect the orbital motion of the lens system.Comment: 18 pages, 5 figures, 1 tabl

Role of 20-Hydroxyeicosatetraenoic Acid in Mediating Hypertension in Response to Chronic Renal Medullary Endothelin Type B Receptor Blockade

BACKGROUND: The renal medullary endothelin (ET-1) system plays an important role in the control of sodium excretion and arterial pressure (AP) through the activation of renal medullary ET-B receptors. We have previously shown that blockade of endothelin type B receptors (ET-B) leads to salt-sensitive hypertension through mechanisms that are not fully understood. One possible mechanism is through a reduction in renal medullary production of 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE, a metabolite of arachidonic acid, has natriuretic properties similar to ET-B activation. While these findings suggest a possible interaction between ET-B receptor activation and 20-HETE production, it is unknown whether blockade of medullary ET-B receptors in rats maintained on a high sodium intake leads to reductions in 20-HETE production. METHODOLOGY/PRINCIPAL FINDINGS: The effect of increasing sodium intake from low (NS = .8%) to high (HS = 8%) on renal medullary production of 20-HETE in the presence and absence of renal medullary ET-B receptor antagonism was examined. Renal medullary blockade of ET-B receptors resulted in salt sensitive hypertension. In control rats, blood pressure rose from 112.8±2.4 mmHg (NS) to 120.7±9.3 mmHg (HS). In contrast, when treated with an ET-B receptor blocker, blood pressure was significantly elevated from 123.7±3.2 (NS) to 164.2±7.1 (HS). Furthermore, increasing sodium intake was associated with elevated medullary 20-HETE (5.6±.8 in NS vs. 14.3±3.7 pg/mg in HS), an effect that was completely abolished by renal medullary ET-B receptor blockade (4.9±.8 for NS and 4.5±.6 pg/mg for HS). Finally, the hypertensive response to intramedullary ET-B receptor blockade was blunted in rats pretreated with a specific 20-HETE synthesis inhibitor. CONCLUSION: These data suggest that increases in renal medullary production of 20-HETE associated with elevating salt intake may be, in part, due to ET-B receptor activation within the renal medulla

Molecular and cellular mechanisms underlying the evolution of form and function in the amniote jaw.

The amniote jaw complex is a remarkable amalgamation of derivatives from distinct embryonic cell lineages. During development, the cells in these lineages experience concerted movements, migrations, and signaling interactions that take them from their initial origins to their final destinations and imbue their derivatives with aspects of form including their axial orientation, anatomical identity, size, and shape. Perturbations along the way can produce defects and disease, but also generate the variation necessary for jaw evolution and adaptation. We focus on molecular and cellular mechanisms that regulate form in the amniote jaw complex, and that enable structural and functional integration. Special emphasis is placed on the role of cranial neural crest mesenchyme (NCM) during the species-specific patterning of bone, cartilage, tendon, muscle, and other jaw tissues. We also address the effects of biomechanical forces during jaw development and discuss ways in which certain molecular and cellular responses add adaptive and evolutionary plasticity to jaw morphology. Overall, we highlight how variation in molecular and cellular programs can promote the phenomenal diversity and functional morphology achieved during amniote jaw evolution or lead to the range of jaw defects and disease that affect the human condition