Six new candidate ultracompact X-ray binaries

Ultracompact X-ray binaries (UCXBs) appear able to sustain accretion onto the compact accretor at rates lower than in wider X-ray binaries. This may be understood by the smaller accretion disks in UCXBs: a lower X-ray luminosity suffices to keep a disk completely ionized through irradiation and, thus, keep the viscosity at a sufficiently high level to allow effective transport of matter to the compact object. We employ this distinguishing factor on data from RXTE and BeppoSAX to identify six new candidate UCXBs, thus increasing the population by one quarter. The candidates are drawn from the population of persistently accreting and type-I X-ray bursting low-mass X-ray binaries. The X-ray bursts establish the low-mass X-ray binary nature and provide a handle on the accretion rate. We find that the low accretion rates are supported by the long burst recurrence times and the hard X-ray spectra of the persistent emission as derived from the 2nd INTEGRAL catalog of soft gamma-ray sources. We discuss the peculiar light curves of some new UCXB candidates.Comment: Section 2 corrected and improved thanks to comments by J.-P. Lasota. Accepted for publication in Astronomy and Astrophysic

Independent Loop Invariants for 2+1 Gravity

We identify an explicit set of complete and independent Wilson loop invariants for 2+1 gravity on a three-manifold $M=\R\times\Sigma^g$, with $\Sigma^g$ a compact oriented Riemann surface of arbitrary genus $g$. In the derivation we make use of a global cross section of the $PSU(1,1)$-principal bundle over Teichm\"uller space given in terms of Fenchel-Nielsen coordinates.Comment: 11pp, 2 figures (postscript, compressed and uu-encoded), TeX, Pennsylvania State University, CGPG-94/7-

Flow-Responsive Vascular Endothelial Growth Factor Receptor-Protein Kinase C Isoform Epsilon Signaling Mediates Glycolytic Metabolites for Vascular Repair

Aims: Hemodynamic shear stress participates in maintaining vascular redox status. Elucidating flow-mediated endothelial metabolites enables us to discover metabolic biomarkers and therapeutic targets. We posited that flow-responsive vascular endothelial growth factor receptor (VEGFR)-protein kinase C isoform epsilon (PKCɛ)-6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) signaling modulates glycolytic metabolites for vascular repair. Results: Bidirectional oscillatory flow (oscillatory shear stress [OSS]: 0.1 ± 3 dyne·cm^(−2) at 1 Hz) upregulated VEGFR-dependent PKCɛ expression to a greater degree than did unidirectional pulsatile flow (pulsatile shear stress [PSS]: 23 ± 8 dyne·cm^(−2) at 1 Hz) in human aortic endothelial cells (p < 0.05, n = 3). PSS and OSS further upregulated PKCɛ-dependent PFKFB3 expression for glycolysis (p < 0.05, n = 4). Constitutively active PKCɛ increased, whereas dominant-negative PKCɛ reduced both basal and maximal extracellular acidification rates for glycolytic flux (p < 0.01, n = 4). Metabolomic analysis demonstrated an increase in PKCɛ-dependent glycolytic metabolite, dihydroxyacetone (DHA), but a decrease in gluconeogenic metabolite, aspartic acid (p < 0.05 vs. control, n = 6). In a New Zealand White rabbit model, both PKCɛ and PFKFB3 immunostaining was prominent in the PSS- and OSS-exposed aortic arch and descending aorta. In a transgenic Tg(flk-1:EGFP) zebrafish model, GATA-1a morpholino oligonucleotide injection (to reduce viscosity-dependent shear stress) impaired vascular regeneration after tail amputation (p < 0.01, n = 20), which was restored with PKCɛ messenger RNA (mRNA) rescue (p < 0.05, n = 5). As a corollary, siPKCɛ inhibited tube formation and vascular repair, which were restored by DHA treatment in our Matrigel and zebrafish models. Innovation and Conclusion: Flow-sensitive VEGFR-PKCɛ-PFKFB3 signaling increases the glycolytic metabolite, dihydroxyacetone, to promote vascular repair

A look with BeppoSAX at the low-luminosity Galactic X-ray source 4U 2206+54

A pointed observation of the low-luminosity galactic source 4U 2206+54 was carried out in November 1998 with BeppoSAX. The light curve of 4U 2206+54 shows erratic variability on a timescale of about 1 hour; neither hardness variations nor time periodicities are detected throughout this 67 ks long observation. Thanks to the wide spectral coverage capabilities of BeppoSAX we could observe the source X-ray continuum over three energy decades, from 0.6 to 60 keV. The spectrum could be equally well fitted either with a blackbody plus Comptonization or with a high energy cutoff power law. No iron emission around 6.5 keV was detected, while a tentative detection of a cyclotron resonant feature in absorption is presented. Comparison of the present BeppoSAX data with the information available in the literature for this source suggests that 4U 2206+54 is a close binary system in which a (possibly magnetized) NS is accreting from the companion star wind.Comment: 9 pages, 5 figures, 2 tables; accepted for publication on Astronomy & Astrophysics, main journal. Final version of the paper including the A&A Language Editor's comment

Scientific Opinion on the safety and efficacy of disodium 5?-ribonucleotides, disodium 5?-guanylate, disodium 5?-inosinate for all animal species and categories

The flavours included in this assessment are widely present in nature as the building blocks of DNA and RNA. In the absence of any information on the microbial strains or substrates used for the production of the additives, and with little information on the manufacturing process, the FEEDAP Panel is unable to ascertain whether the manufacturing process introduces any safety concerns. Disodium 5′-guanylate and disodium 5′-inosinate and their mixture are considered to be safe for the target animals and the consumer. However, considering the lack of information on the production process, these conclusions apply only to the compounds ‘per se’ and their extrapolation to any feed additive containing these compounds is not possible. In the absence of any data related to hazard to the user, it would be prudent to regard disodium 5′-guanylate and disodium 5′-inosinate and their mixture as potentially hazardous to workers by skin or inhalation exposure. The compounds under assessment are naturally present in feed materials; therefore, no risk to the safety for the environment is foreseen. Since these compounds are used in food as flavourings, and their function in feed is essentially the same as that in food, no further demonstration of efficacy is necessary

Direct Higgs production and jet veto at the Tevatron and the LHC in NNLO QCD

We consider Higgs boson production through gluon--gluon fusion in hadron collisions, when a veto is applied on the transverse momenta of the accompanying hard jets. We compute the QCD radiative corrections to this process at NLO and NNLO. The NLO calculation is complete. The NNLO calculation uses the recently evaluated NNLO soft and virtual QCD contributions to the inclusive cross section. We find that the jet veto reduces the impact of the NLO and NNLO contributions, the reduction being more sizeable at the LHC than at the Tevatron.Comment: 22 pages, 12 postscript figure

Warped Higgsless Models with IR--Brane Kinetic Terms

We examine a warped Higgsless $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ model in 5--$d$ with IR(TeV)--brane kinetic terms. It is shown that adding a brane term for the $U(1)_{B-L}$ gauge field does not affect the scale ($\sim 2-3$ TeV) where perturbative unitarity in $W_L^+ W_L^- \to W_L^+ W_L^-$ is violated. This term could, however, enhance the agreement of the model with the precision electroweak data. In contrast, the inclusion of a kinetic term corresponding to the $SU(2)_D$ custodial symmetry of the theory delays the unitarity violation in $W_L^\pm$ scattering to energy scales of $\sim 6-7$ TeV for a significant fraction of the parameter space. This is about a factor of 4 improvement compared to the corresponding scale of unitarity violation in the Standard Model without a Higgs. We also show that null searches for extra gauge bosons at the Tevatron and for contact interactions at LEP II place non-trivial bounds on the size of the IR-brane terms.Comment: 23 pages, 8 figure

Carrier generation and transport in bulk heterojunction films processed with 1,8-octanedithiol as a processing additive

Improved performance of polymer-based solar cells based on poly[2,6-(4,4-bis-(2-ethylhexyl)- 4H -cyclopenta[2,1-b;3,4- b???] dithiophene)-alt-4,7-(2,1,3-benzo-thiadiazole)] PCPDTBT has been obtained by using 1,8-octanedithiol (ODT) as a processing additive in the polymer solution used to spin cast the bulk heterojunction films. Although ultrafast spectroscopy studies indicate that the carrier losses are reduced in the films processed with ODT [similar to the reduced carrier losses after thermal annealing of bulk heterojunction (BHJ) materials made from P3HT:PCBM], the magnitude of the reduction is not sufficient to explain the observed factor of 2 increase in the power conversion efficiency. From the analysis of carrier transport in field effect transistors, we find increased electron mobility in the PCPDTBT: PC70 BM composites when fabricated with ODT, which is indicative of enhanced connectivity of PC70 BM networks. The improved electron mobility appears to be the primary origin of the improved power conversion efficiency in BHJ films.open453