Mode division multiplexing using an orbital angular momentum mode sorter and MIMO-DSP over a graded-index few-mode optical fibre

Mode division multiplexing (MDM)– using a multimode optical fiber’s N spatial modes as data channels to transmit N independent data streams – has received interest as it can potentially increase optical fiber data transmission capacity N-times with respect to single mode optical fibers. Two challenges of MDM are (1) designing mode (de)multiplexers with high mode selectivity (2) designing mode (de)multiplexers without cascaded beam splitting’s 1/N insertion loss. One spatial mode basis that has received interest is that of orbital angular momentum (OAM) modes. In this paper, using a device referred to as an OAM mode sorter, we show that OAM modes can be (de)multiplexed over a multimode optical fiber with higher than −15 dB mode selectivity and without cascaded beam splitting’s 1/N insertion loss. As a proof of concept, the OAM modes of the LP11 mode group (OAM−1,0 and OAM+1,0), each carrying 20-Gbit/s polarization division multiplexed and quadrature phase shift keyed data streams, are transmitted 5km over a graded-index, few-mode optical fibre. Channel crosstalk is mitigated using 4 × 4 multiple-input-multiple-output digital-signal-processing with <1.5 dB power penalties at a bit-error-rate of 2 × 10−3

Provably Secure and Practical Quantum Key Distribution over 307 km of Optical Fibre

Proposed in 1984, quantum key distribution (QKD) allows two users to exchange provably secure keys via a potentially insecure quantum channel. Since then, QKD has attracted much attention and significant progress has been made in both theory and practice. On the application front, however, the operating distance of practical fibre-based QKD systems is limited to about 150 km, which is mainly due to the high background noise produced by commonly used semiconductor single-photon detectors (SPDs) and the stringent demand on the minimum classical- post-processing (CPP) block size. Here, we present a compact and autonomous QKD system that is capable of distributing provably-secure cryptographic key over 307 km of ultra-low-loss optical fibre (51.9 dB loss). The system is based on a recently developed standard semiconductor (inGaAs) SPDs with record low background noise and a novel efficient finite-key security analysis for QKD. This demonstrates the feasibility of practical long-distance QKD based on standard fibre optic telecom components.Comment: 6+7 pages, 3 figure

Chandra pulsar survey (ChaPS)

Taking advantage of the high sensitivity of the Chandra Advanced CCD Imaging Spectrometer, we have conducted a snap-shot survey of pulsars previously undetected in X-rays. We detected 12 pulsars and established deep flux limits for 11 pulsars. Using these new results, we revisit the relationship between the X-ray luminosity, L_psr_x, and spin-down power, Edot. We find that the obtained limits further increase the extremely large spread in the non-thermal X-ray efficiencies, eta_psr_x=L_psr_x/Edot, with some of them being now below 1e-5. Such a spread cannot be explained by poorly known distances or by beaming of pulsar radiation. We also find evidence of a break in the dependence of L_psr_x on Edot, such that pulsars become more X-ray efficient at Edot<~ 1e34-1e35 erg/s. We examine the relationship between the gamma-ray luminosity, L_psr_g, and Edot, which exhibits a smaller scatter compared to that in X-rays. This confirms that the very large spread in the X-ray efficiencies cannot be explained just by beaming because the gamma-ray emission is generally expected to be beamed stronger than the X-ray emission. Intriguingly, there is also an indication of a break in the L_psr_g(Edot) dependence at Edot~1e35 erg/s, with lower-Edot pulsars becoming less gamma-ray efficient. We also examine the distance-independent L_psr_f/L_psr_x ratio as a function of Edot for a sample of gamma-ray pulsars observed by Chandra and find that it peaks at Edot~1e35 erg/s, showing that the breaks cannot originate from poorly measured distances. We discuss the implications of our findings for existing models of magnetospheric emission and venues for further exploration.Comment: Submitted to Ap

Extending Metal-to-Polyoxometalate Charge Transfer Lifetimes: The Effect of Heterometal Location

In an effort to develop robust molecular sensitizers for solar fuel production, the electronic structure and photodynamics of transition-metal-substituted polyoxometalates (POMs), a novel class of compound in this context, was examined. Experimental and computational techniques including femtosecond (fs) transient absorption spectroscopy have been used to study the cobalt-containing Keggin POMs, [CoIIW12O40]6− (1 a), [CoIIIW12O40]5− (2 a), [SiCoII(H2O)W11O39]6− (3 a), and [SiCoIII(H2O)W11O39]5− (4 a), finding the longest lived charge transfer excited state so far observed in a POM and elucidating the electronic structures and excited-state dynamics of these compounds at an unprecedented level. All species exhibit a bi-exponential decay in which early dynamic processes with time constants in the fs domain yield longer lived excited states which decay with time constants in the ps to ns domain. The initially formed states of 1 a and 3 a are considered to result from metal-to-polyoxometalate charge transfer (MPCT) from CoII to W, while the longer-lived excited state of 1 a is tentatively assigned to a localized intermediate MPCT state. The excited state formed by the tetrahedral cobalt(II) centered heteropolyanion (1 a) is far longer-lived (τ=420 ps in H2O; τ=1700 ps in MeCN) than that of 3 a (τ=1.3 ps), in which the single CoII atom is located in a pseudo-octahedral addendum site. Short-lived states are observed for the two CoIII-containing heteropolyanions 2 a (τ=4.4 ps) and 4 a (τ=6.3 ps) and assigned solely to OCoIII charge transfer. The dramatically extended lifetime for 1 a versus 3 a is ascribed to a structural change permitted by the coordinatively flexible central site, weak orbital overlap of the central Co with the polytungstate framework, and putative transient valence trapping of the excited electron on a single W atom, a phenomenon not noted previously in POMs

Endothelial Cells Expressing Endothelial and Mesenchymal Cell Gene Products in Lung Tissue From Patients With Systemic Sclerosis-Associated Interstitial Lung Disease.

OBJECTIVE: To examine whether lung endothelial cells (ECs) from patients with systemic sclerosis (SSc)-associated interstitial lung disease (ILD) express mesenchymal cell-specific proteins and gene transcripts, indicative of the occurrence of endothelial-to-mesenchymal phenotypic transition (EndoMT). METHODS: Lung tissue from 6 patients with SSc-associated pulmonary fibrosis was examined by histopathology and immunohistochemistry. Confocal laser microscopy was utilized to assess the simultaneous expression of EC and myofibroblast molecular markers. CD31+CD102+ ECs were isolated from the lung tissue of 2 patients with SSc-associated ILD and 2 normal control subjects, and the expression of EC and mesenchymal cell markers and other relevant genes was analyzed by quantitative polymerase chain reaction, immunofluorescence microscopy, and Western blotting. RESULTS: Immunohistochemical staining revealed cells expressing the EC-specific marker CD31 in the subendothelial, perivascular, and parenchymal regions of the lungs from all SSc patients. Confocal microscopy identified cells displaying simultaneous expression of von Willebrand factor and α-smooth muscle actin in small and medium-sized arterioles in the SSc lung tissue but not in normal control lungs. CD31+CD102+ ECs isolated from SSc lungs expressed high levels of mesenchymal cell-specific genes (type I collagen, type III collagen, and fibronectin), EC-specific genes (type IV collagen and VE-cadherin), profibrotic genes (transforming growth factor β1 and connective tissue growth factor), and genes encoding EndoMT-related transcription factors (TWIST1 and SNAI2). CONCLUSION: Cells coexpressing EC- and mesenchymal cell-specific molecules are present in the lungs of patients with SSc-associated ILD. CD31+CD102+ ECs isolated from SSc lungs simultaneously expressed mesenchymal cell- and EC-specific transcripts and proteins. Collectively, these observations demonstrate the occurrence of EndoMT in the lungs of patients with SSc-associated ILD

Will the US Economy Recover in 2010? A Minimal Spanning Tree Study

We calculated the cross correlations between the half-hourly times series of the ten Dow Jones US economic sectors over the period February 2000 to August 2008, the two-year intervals 2002--2003, 2004--2005, 2008--2009, and also over 11 segments within the present financial crisis, to construct minimal spanning trees (MSTs) of the US economy at the sector level. In all MSTs, a core-fringe structure is found, with consumer goods, consumer services, and the industrials consistently making up the core, and basic materials, oil and gas, healthcare, telecommunications, and utilities residing predominantly on the fringe. More importantly, we find that the MSTs can be classified into two distinct, statistically robust, topologies: (i) star-like, with the industrials at the center, associated with low-volatility economic growth; and (ii) chain-like, associated with high-volatility economic crisis. Finally, we present statistical evidence, based on the emergence of a star-like MST in Sep 2009, and the MST staying robustly star-like throughout the Greek Debt Crisis, that the US economy is on track to a recovery.Comment: elsarticle class, includes amsmath.sty, graphicx.sty and url.sty. 68 pages, 16 figures, 8 tables. Abridged version of the manuscript presented at the Econophysics Colloquim 2010, incorporating reviewer comment

Halophilic Actinomycetes in 1 Saharan Soils of Algeria: Isolation, Taxonomy and Antagonistic Properties

The diversity of a population of 52 halophilic actinomycetes was evaluated by a polyphasic approach, which showed the presence of Actinopolyspora, Nocardiopsis, Saccharomonospora, Streptomonospora and Saccharopolyspora genera. One strain was considered to be a new member of the last genus and several other strains seem to be new species. Furthermore, 50% of strains were active against a broad range of indicators and contained genes encoding polyketide synthetases and nonribosomal peptide synthetases