2,635 research outputs found
A 275–425-GHz Tunerless Waveguide Receiver Based on AlN-Barrier SIS Technology
We report on a 275–425-GHz tunerless waveguide receiver with a 3.5–8-GHz IF. As the mixing element, we employ a high-current-density Nb–AlN–Nb superconducting–insulating– superconducting (SIS) tunnel junction. Thanks to the combined use of AlN-barrier SIS technology and a broad bandwidth waveguide to thin-film microstrip transition, we are able to achieve an unprecedented 43% instantaneous bandwidth, limited by the receiver's corrugated feedhorn.
The measured double-sideband (DSB) receiver noise temperature, uncorrected for optics loss, ranges from 55 K at 275 GHz, 48 K at 345 GHz, to 72 K at 425 GHz. In this frequency range, the mixer has a DSB conversion loss of 2.3 1 dB. The intrinsic mixer noise is found to vary between 17–19 K, of which 9 K is attributed to shot noise associated with leakage current below the gap. To improve reliability, the IF circuit and bias injection are entirely planar by design. The instrument was successfully installed at the Caltech Submillimeter Observatory (CSO), Mauna Kea, HI, in October 2006
Vaccinia virus immune evasion: mechanisms, virulence and immunogenicity
Virus infection of mammalian cells is sensed by pattern recognition receptors and leads to an innate immune response that restricts virus replication and induces adaptive immunity. In response, viruses have evolved many countermeasures that enable them to replicate and be transmitted to new hosts, despite the host innate immune response. Poxviruses, such as vaccinia virus (VACV), have large DNA genomes and encode many proteins that are dedicated to host immune evasion. Some of these proteins are secreted from the infected cell, where they bind and neutralize complement factors, interferons, cytokines and chemokines. Other VACV proteins function inside cells to inhibit apoptosis or signalling pathways that lead to the production of interferons and pro-inflammatory cytokines and chemokines. In this review, these VACV immunomodulatory proteins are described and the potential to create more immunogenic VACV strains by manipulation of the gene encoding these proteins is discussed
Measuring random force noise for LISA aboard the LISA Pathfinder mission
The LTP (LISA Testflight Package), to be flown aboard the ESA / NASA LISA
Pathfinder mission, aims to demonstrate drag-free control for LISA test masses
with acceleration noise below 30 fm/s^2/Hz^1/2 from 1-30 mHz. This paper
describes the LTP measurement of random, position independent forces acting on
the test masses. In addition to putting an overall upper limit for all source
of random force noise, LTP will measure the conversion of several key
disturbances into acceleration noise and thus allow a more detailed
characterization of the drag-free performance to be expected for LISA.Comment: 7 pages, 3 figures. To be published in Classical and Quantum Gravity
with the proceedings of the 2003 Amaldi Meetin
Participatory Militias: An Analysis of an Armed Movement's Online Audience
Armed groups of civilians known as "self-defense forces" have ousted the
powerful Knights Templar drug cartel from several towns in Michoacan. This
militia uprising has unfolded on social media, particularly in the "VXM"
("Valor por Michoacan," Spanish for "Courage for Michoacan") Facebook page,
gathering more than 170,000 fans. Previous work on the Drug War has documented
the use of social media for real-time reports of violent clashes. However, VXM
goes one step further by taking on a pro-militia propagandist role, engaging in
two-way communication with its audience. This paper presents a descriptive
analysis of VXM and its audience. We examined nine months of posts, from VXM's
inception until May 2014, totaling 6,000 posts by VXM administrators and more
than 108,000 comments from its audience. We describe the main conversation
themes, post frequency and relationships with offline events and public
figures. We also characterize the behavior of VXM's most active audience
members. Our work illustrates VXM's online mobilization strategies, and how its
audience takes part in defining the narrative of this armed conflict. We
conclude by discussing possible applications of our findings for the design of
future communication technologies.Comment: Participatory Militias: An Analysis of an Armed Movement's Online
Audience. Saiph Savage, Andres Monroy-Hernandez. CSCW: ACM Conference on
Computer-Supported Cooperative Work 201
Environmental chemicals in dog testes reflect their geographical source and may be associated with altered pathology
In humans and dogs, a temporal decline in semen quality and increased incidence of testicular cancer is hypothesised to be associated with exposure to anthropogenic chemicals, particularly during fetal development. Human studies suggest that differential exposures to environmental chemicals may be associated with geographical differences in male reproductive health. Here we investigate testicular chemical profiles and pathologies in dogs residing in the UK [West Midlands (WM), East Midlands (EM), South East (SE)], Denmark (Copenhagen) and Finland (Vantaa). Testes, surplus from routine castrations, contained region specific differences in relative concentrations of diethylhexyl phthalate (DEHP), polybrominated diphenyl ethers (PBDE) and polychlorinated biphenyls (PCB). Relative to UK regions, testes from dogs living in Finland and Denmark had higher concentrations of PBDE and lower concentrations of DEHP and PCBs. Regional differences in the UK in PCB concentrations were also observed. Dog testes from Finland had fewer pathologies, reduced testicular area stained for Sertoli and germ cells and evidence of reduced cellular proliferation. Since the geographical differences in testis pathologies in dogs parallel reports of regional differences in human testicular cancer, we postulate that this may reflect chemical effects within the testis and that this may be related to environmental influences on male reproductive function.Peer reviewe
Effective decrease of photoelectric emission threshold from gold plated surfaces
Many applications require charge neutralisation of isolated test bodies and
this has been successfully done using photoelectric emission from surfaces
which are electrically benign(gold) or superconducting (niobium). Gold surfaces
nominally have a high work function (\,eV)which should require deep
UV photons for photoemission. In practice it has been found that it can be
achieved with somewhat lower energy photons with indicative work functions of
(\,eV). A detailed working understanding of the process is lacking
and this work reports on a study of the photoelectric emission properties of
4.6x4.6 cm^2 gold plated surfaces, representative of those used in typical
satellite applications with a film thickness of 800 nm, and measured surface
roughnesses between 7 and 340 nm. Various UV sources with photon energies from
4.8 to 6.2 eV and power outputs from 1 nW to 1000 nW, illuminated a ~0.3 cm^2
of the central surface region at angles of incidence from 0 to 60 degrees.
Final extrinsic quantum yields in the range 10 ppm to 44 ppm were reliably
obtained during 8 campaigns, covering a ~3 year period, but with intermediate
long-term variations lasting several weeks and, in some cases, bake-out
procedures at up to 200 C. Experimental results were obtained in a vacuum
system with a baseline pressure of ~10^{-7} mbar at room temperature. A working
model, designed to allow accurate simulation of any experimental configuration,
is proposed.Comment: 35 pages, 12 figure
Structural and electrostatic differences between actinidin and papain account for differences in activity
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