263 research outputs found
Pienten karboksyylihappojen nestekromatografiassa käytettävät detektorit
Tiivistelmä. Korkean erotuskyvyn nestekromatografia (HPLC) on monipuolisesti hyödynnetty analyysimenetelmä orgaanisten yhdisteiden analysoinnissa kvalitatiivisesti sekä kvantitatiivisesti. Nestekromatografiassa kriittinen osa analyysiä on detektointi. Käytetyt detektorit havaitsevat analyytin, jollain kemiallisella tai fysikaalisella ilmiöllä tai ominaisuudella, mikä on ominaista juuri kyseiselle detektorityypille. Ihanteellisesti yhdellä detektorilla pystyttäisiin analysoimaan kaikkien mahdollisten näytetyyppien kaikki analyytit, mutta tämä ei käytännössä ole mahdollista, vaan detektori tulee valita ja menetelmä tulee soveltaa tietylle analyytille sopivaksi.
Pienet suoraketjuiset karboksyylihapot ovat orgaanisia yhdisteitä, joissa funktionaalisena ryhmänä on karboksyyliryhmä (-COOH). Tutkielmassa käsiteltiin spektrofotometrisen ultraviolettiabsorptioon ja näkyvän valon absorptioon perustuvan detektorin, taitekerroindetektorin sekä valonsirontadetektorin toimintaa ja soveltuvuutta pienten, maksimissaan noin kuuden hiilen mittaisten, suoraketjuisten karboksyylihappojen analysointiin nestekromatografialla.
Yleisimmillä detektorityypeillä voidaan analysoida pieniä suoraketjuisia karboksyylihappoja hyvin. Parhaiten karboksyylihapoille vaikuttaisi soveltuvan valonsirontadetektori sekä spektrofotometriseen ultraviolettiabsorptioon ja näkyvän valon absorptioon perustuva detektori. Taitekerroindetektorilla toteamis- ja määritysrajat jäävät merkittävästi korkeammiksi kuin edellä mainituilla. Taitekerroindetektorilla myös analyysiä häiritsevät ulkoiset tekijät, kuten ympäristön lämpötila, vaikuttavat menetelmän toimivuuteen. Huolellisesti kehitetyllä menetelmällä analyytit voidaan havaita luotettavasti, toistettavasti, nopeasti ja helposti
Free digital image analysis software helps to resolve equivocal scores in HER2 immunohistochemistry
Evaluation of human epidermal growth factor receptor 2 (HER2) immunohistochemistry (IHC) is subject to interobserver variation and lack of reproducibility. Digital image analysis (DIA) has been shown to improve the consistency and accuracy of the evaluation and its use is encouraged in current testing guidelines. We studied whether digital image analysis using a free software application (ImmunoMembrane) can assist in interpreting HER2 IHC in equivocal 2+ cases. We also compared digital photomicrographs with whole-slide images (WSI) as material for ImmunoMembrane DIA. We stained 750 surgical resection specimens of invasive breast cancers immunohistochemically for HER2 and analysed staining with ImmunoMembrane. The ImmunoMembrane DIA scores were compared with the originally responsible pathologists' visual scores, a researcher's visual scores and in situ hybridisation (ISH) results. The originally responsible pathologists reported 9.1 % positive 3+ IHC scores, for the researcher this was 8.4 % and for ImmunoMembrane 9.5 %. Equivocal 2+ scores were 34 % for the pathologists, 43.7 % for the researcher and 10.1 % for ImmunoMembrane. Negative 0/1+ scores were 57.6 % for the pathologists, 46.8 % for the researcher and 80.8 % for ImmunoMembrane. There were six false positive cases, which were classified as 3+ by ImmunoMembrane and negative by ISH. Six cases were false negative defined as 0/1+ by IHC and positive by ISH. ImmunoMembrane DIA using digital photomicrographs and WSI showed almost perfect agreement. In conclusion, digital image analysis by ImmunoMembrane can help to resolve a majority of equivocal 2+ cases in HER2 IHC, which reduces the need for ISH testing.Peer reviewe
Linear stability analysis of retrieval state in associative memory neural networks of spiking neurons
We study associative memory neural networks of the Hodgkin-Huxley type of
spiking neurons in which multiple periodic spatio-temporal patterns of spike
timing are memorized as limit-cycle-type attractors. In encoding the
spatio-temporal patterns, we assume the spike-timing-dependent synaptic
plasticity with the asymmetric time window. Analysis for periodic solution of
retrieval state reveals that if the area of the negative part of the time
window is equivalent to the positive part, then crosstalk among encoded
patterns vanishes. Phase transition due to the loss of the stability of
periodic solution is observed when we assume fast alpha-function for direct
interaction among neurons. In order to evaluate the critical point of this
phase transition, we employ Floquet theory in which the stability problem of
the infinite number of spiking neurons interacting with alpha-function is
reduced into the eigenvalue problem with the finite size of matrix. Numerical
integration of the single-body dynamics yields the explicit value of the
matrix, which enables us to determine the critical point of the phase
transition with a high degree of precision.Comment: Accepted for publication in Phys. Rev.
The RING-CH ligase K5 antagonizes restriction of KSHV and HIV-1 particle release by mediating ubiquitin-dependent endosomal degradation of tetherin
Tetherin (CD317/BST2) is an interferon-induced membrane protein that inhibits the release of diverse enveloped viral particles. Several mammalian viruses have evolved countermeasures that inactivate tetherin, with the prototype being the HIV-1 Vpu protein. Here we show that the human herpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV) is sensitive to tetherin restriction and its activity is counteracted by the KSHV encoded RING-CH E3 ubiquitin ligase K5. Tetherin expression in KSHV-infected cells inhibits viral particle release, as does depletion of K5 protein using RNA interference. K5 induces a species-specific downregulation of human tetherin from the cell surface followed by its endosomal degradation. We show that K5 targets a single lysine (K18) in the cytoplasmic tail of tetherin for ubiquitination, leading to relocalization of tetherin to CD63-positive endosomal compartments. Tetherin degradation is dependent on ESCRT-mediated endosomal sorting, but does not require a tyrosine-based sorting signal in the tetherin cytoplasmic tail. Importantly, we also show that the ability of K5 to substitute for Vpu in HIV-1 release is entirely dependent on K18 and the RING-CH domain of K5. By contrast, while Vpu induces ubiquitination of tetherin cytoplasmic tail lysine residues, mutation of these positions has no effect on its antagonism of tetherin function, and residual tetherin is associated with the trans-Golgi network (TGN) in Vpu-expressing cells. Taken together our results demonstrate that K5 is a mechanistically distinct viral countermeasure to tetherin-mediated restriction, and that herpesvirus particle release is sensitive to this mode of antiviral inhibition
Genome derived insights into the biology of the hepatotoxic bloom forming cyanobacterium Anabaena sp. strain 90
Background Cyanobacteria can form massive toxic blooms in fresh and brackish bodies of water and are frequently responsible for the poisoning of animals and pose a health risk for humans. Anabaena is a genus of filamentous diazotrophic cyanobacteria commonly implicated as a toxin producer in blooms in aquatic ecosystems throughout the world. The biology of bloom-forming cyanobacteria is poorly understood at the genome level. Results Here, we report the complete sequence and comprehensive annotation of the bloom-forming Anabaena sp. strain 90 genome. It comprises two circular chromosomes and three plasmids with a total size of 5.3 Mb, encoding a total of 4,738 genes. The genome is replete with mobile genetic elements. Detailed manual annotation demonstrated that almost 5% of the gene repertoire consists of pseudogenes. A further 5% of the genome is dedicated to the synthesis of small peptides that are the products of both ribosomal and nonribosomal biosynthetic pathways. Inactivation of the hassallidin (an antifungal cyclic peptide) biosynthetic gene cluster through a deletion event and a natural mutation of the buoyancy-permitting gvpG gas vesicle gene were documented. The genome contains a large number of genes encoding restriction-modification systems. Two novel excision elements were found in the nifH gene that is required for nitrogen fixation. Conclusions Genome analysis demonstrated that this strain invests heavily in the production of bioactive compounds and restriction-modification systems. This well-annotated genome provides a platform for future studies on the ecology and biology of these important bloom-forming cyanobacteria.Peer reviewe
Detection of Gamma-Ray Emission from the Starburst Galaxies M82 and NGC 253 with the Large Area Telescope on Fermi
We report the detection of high-energy gamma-ray emission from two starburst
galaxies using data obtained with the Large Area Telescope on board the Fermi
Gamma-ray Space Telescope. Steady point-like emission above 200 MeV has been
detected at significance levels of 6.8 sigma and 4.8 sigma respectively, from
sources positionally coincident with locations of the starburst galaxies M82
and NGC 253. The total fluxes of the sources are consistent with gamma-ray
emission originating from the interaction of cosmic rays with local
interstellar gas and radiation fields and constitute evidence for a link
between massive star formation and gamma-ray emission in star-forming galaxies.Comment: Submitted to ApJ Letter
Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B
We present an analysis of the gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of
SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a
significance of 38 sigma is found to coincide with SNR W49B. The energy
spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The
luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy
range. There is no indication that the gamma-ray emission comes from a pulsar.
Assuming that the SNR shell is the site of gamma-ray production, the observed
spectrum can be explained either by the decay of neutral pi mesons produced
through the proton-proton collisions or by electron bremsstrahlung. The
calculated energy density of relativistic particles responsible for the LAT
flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either
gamma-ray production mechanism.Comment: 9 pages, 10 figure
Fermi LAT Observations of the Supernova Remnant W28 (G6.4-0.1)
We present detailed analysis of the two gamma-ray sources,1FGL J1801.3-2322c
and 1FGL J1800.5-2359c,that have been found toward the supernova remnant(SNR)
W28 with the Large Area Telescope(LAT) on board the Fermi Gamma-ray Space
Telescope.1FGL J1801.3-2322c is found to be an extended source within the
boundary of SNR W28,and to extensively overlap with the TeV gamma-ray source
HESS J1801-233,which is associated with a dense molecular cloud interacting
with the supernova remnant.The gamma-ray spectrum measured with LAT from
0.2--100 GeV can be described by a broken power-law function with a break of
~1GeV,and photon indices of 2.090.08(stat)0.28(sys) below the break
and 2.740.06(stat)0.09(sys) above the break.Given the clear
association between HESS J1801-233 and the shocked molecular cloud and a
smoothly connected spectrum in the GeV--TeV band,we consider the origin of the
gamma-ray emission in both GeV and TeV ranges to be the interaction between
particles accelerated in the SNR and the molecular cloud.The decay of neutral
pions produced in interactions between accelerated hadrons and dense molecular
gas provide a reasonable explanation for the broadband gamma-ray spectrum. 1FGL
J1800.5-2359c, located outside the southern boundary of SNR W28, cannot be
resolved.An upper limit on the size of the gamma-ray emission was estimated to
be ~16 using events above ~2GeV under the assumption of a circular shape
with uniform surface brightness. It appears to coincide with the TeV source
HESS J1800-240B,which is considered to be associated with a dense molecular
cloud that contains the ultra compact HII region W28A2(G5.89-0.39).We found no
significant gamma-ray emission in the LAT energy band at the positions of TeV
sources HESS J1800-230A and HESS J1800-230C.The LAT data for HESS J1800-230A
combined with the TeV data points indicate a spectral break between 10GeV and
100GeV.Comment: 23 pages, 6 figures. Accepted for publication in the Astrophysical
Journal. Corresponding authors: H. Katagiri, H. Tajima, T. Tanaka, and Y.
Uchiyam
Fermi-LAT observations of the exceptional gamma-ray outbursts of 3C 273 in September 2009
We present the light curves and spectral data of two exceptionally luminous
gamma-ray outburts observed by the Large Area Telescope (LAT) experiment on
board Fermi Gamma-ray Space Telescope from 3C 273 in September 2009. During
these flares, having a duration of a few days, the source reached its highest
gamma-ray flux ever measured. This allowed us to study in some details their
spectral and temporal structures. The rise and decay are asymmetric on
timescales of 6 hours, and the spectral index was significantly harder during
the flares than during the preceding 11 months. We also found that short, very
intense flares put out the same time-integrated energy as long, less intense
flares like that observed in August 2009.Comment: Corresponding authors: E. Massaro, [email protected]; G.
Tosti, [email protected]. 15 pages, 4 figures, published in The
Astrophysical Journal Letters, Volume 714, Issue 1, pp. L73-L78 (2010
GeV Gamma-ray Flux Upper Limits from Clusters of Galaxies
The detection of diffuse radio emission associated with clusters of galaxies
indicates populations of relativistic leptons infusing the intracluster medium.
Those electrons and positrons are either injected into and accelerated directly
in the intracluster medium, or produced as secondary pairs by cosmic-ray ions
scattering on ambient protons. Radiation mechanisms involving the energetic
leptons together with decay of neutral pions produced by hadronic interactions
have the potential to produce abundant GeV photons. Here, we report on the
search for GeV emission from clusters of galaxies using data collected by the
Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi) from
August 2008 to February 2010. Thirty-three galaxy clusters have been selected
according to their proximity and high mass, X-ray flux and temperature, and
indications of non-thermal activity for this study. We report upper limits on
the photon flux in the range 0.2-100 GeV towards a sample of observed clusters
(typical values 1-5 x 10^-9 ph cm^-2 s^-1) considering both point-like and
spatially resolved models for the high-energy emission, and discuss how these
results constrain the characteristics of energetic leptons and hadrons, and
magnetic fields in the intracluster medium. The volume-averaged
relativistic-hadron-to-thermal energy density ratio is found to be < 5-10% in
several clusters.Comment: 9 pages, 3 tables, 1 figure, accepted for publication in ApJ Letter
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