RESUMO
An annihilation signal of dark matter is searched for from the central region of the Milky Way. Data acquired in dedicated on-off observations of the Galactic center region with H.E.S.S. are analyzed for this purpose. No significant signal is found in a total of â¼9 h of on-off observations. Upper limits on the velocity averaged cross section, ⟨σv⟩, for the annihilation of dark matter particles with masses in the range of â¼300 GeV to â¼10 TeV are derived. In contrast to previous constraints derived from observations of the Galactic center region, the constraints that are derived here apply also under the assumption of a central core of constant dark matter density around the center of the Galaxy. Values of ⟨σv⟩ that are larger than 3×10^{-24} cm^{3}/s are excluded for dark matter particles with masses between â¼1 and â¼4 TeV at 95% C.L. if the radius of the central dark matter density core does not exceed 500 pc. This is the strongest constraint that is derived on ⟨σv⟩ for annihilating TeV mass dark matter without the assumption of a centrally cusped dark matter density distribution in the search region.
RESUMO
Gamma-ray line signatures can be expected in the very-high-energy (E(γ)>100 GeV) domain due to self-annihilation or decay of dark matter (DM) particles in space. Such a signal would be readily distinguishable from astrophysical γ-ray sources that in most cases produce continuous spectra that span over several orders of magnitude in energy. Using data collected with the H.E.S.S. γ-ray instrument, upper limits on linelike emission are obtained in the energy range between â¼ 500 GeV and â¼ 25 TeV for the central part of the Milky Way halo and for extragalactic observations, complementing recent limits obtained with the Fermi-LAT instrument at lower energies. No statistically significant signal could be found. For monochromatic γ-ray line emission, flux limits of (2 × 10(-7) -2 × 10(-5)) m(-2) s(-1) sr(-1) and (1 × 10(-8) -2 × 10(-6)) m(-2) s(-1)sr(-1) are obtained for the central part of the Milky Way halo and extragalactic observations, respectively. For a DM particle mass of 1 TeV, limits on the velocity-averaged DM annihilation cross section ⟨σv⟩(χχ â γγ) reach â¼ 10(-27) cm(3)s(-1), based on the Einasto parametrization of the Galactic DM halo density profile.
RESUMO
A search for a very-high-energy (VHE; ≥100 GeV) γ-ray signal from self-annihilating particle dark matter (DM) is performed towards a region of projected distance râ¼45-150 pc from the Galactic center. The background-subtracted γ-ray spectrum measured with the High Energy Stereoscopic System (H.E.S.S.) γ-ray instrument in the energy range between 300 GeV and 30 TeV shows no hint of a residual γ-ray flux. Assuming conventional Navarro-Frenk-White and Einasto density profiles, limits are derived on the velocity-weighted annihilation cross section (σv) as a function of the DM particle mass. These are among the best reported so far for this energy range and in particular differ only little between the chosen density profile parametrizations. In particular, for the DM particle mass of â¼1 TeV, values for (σv) above 3×10(-25) cm(3) s(-1) are excluded for the Einasto density profile.
RESUMO
Dark matter (DM) particle annihilation or decay can produce monochromatic gamma rays readily distinguishable from astrophysical sources. gamma-ray line limits from 30 to 200 GeV obtained from 11 months of Fermi Large Area Space Telescope data from 20-300 GeV are presented using a selection based on requirements for a gamma-ray line analysis, and integrated over most of the sky. We obtain gamma-ray line flux upper limits in the range 0.6-4.5x10{-9} cm{-2} s{-1}, and give corresponding DM annihilation cross-section and decay lifetime limits. Theoretical implications are briefly discussed.
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A psychological autopsy of 20 children and adolescents aged 12-19 years who had committed suicide and a matched-pair control group revealed that 85% of the victims and 18% of the control subjects had expressed suicidal ideation. A statistically significant number of the victims had a history of suicide threats (55%), suicide attempts (40%), drug or alcohol abuse (70%), antisocial behavior (70%), or inhibited personality (65%). Suicidal behavior of parents, relatives, or friends and a parental history of emotional problems and absence or abusiveness were also significant factors for the victims.
Assuntos
Entrevista Psicológica , Suicídio/psicologia , Adolescente , Fatores Etários , Agressão/psicologia , Transtorno da Personalidade Antissocial/psicologia , Criança , Família , Feminino , Humanos , Relações Interpessoais , Masculino , Transtornos Mentais/genética , Pais/psicologia , Transtornos Relacionados ao Uso de Substâncias/psicologia , Tentativa de Suicídio/psicologiaRESUMO
Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce pi(0) decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.
RESUMO
The very large collection area of ground-based gamma-ray telescopes gives them a substantial advantage over balloon or satellite based instruments in the detection of very-high-energy (>600 GeV) cosmic-ray electrons. Here we present the electron spectrum derived from data taken with the High Energy Stereoscopic System (H.E.S.S.) of imaging atmospheric Cherenkov telescopes. In this measurement, the first of this type, we are able to extend the measurement of the electron spectrum beyond the range accessible to direct measurements. We find evidence for a substantial steepening in the energy spectrum above 600 GeV compared to lower energies.
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In the past few decades, several models have predicted an energy dependence of the speed of light in the context of quantum gravity. For cosmological sources such as active galaxies, this minuscule effect can add up to measurable photon-energy dependent time lags. In this Letter a search for such time lags during the High Energy Stereoscopic System observations of the exceptional very high energy flare of the active galaxy PKS 2155-304 on 28 July 2006 is presented. Since no significant time lag is found, lower limits on the energy scale of speed of light modifications are derived.
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The detection of fast variations of the tera-electron volt (TeV) (10(12) eV) gamma-ray flux, on time scales of days, from the nearby radio galaxy M87 is reported. These variations are about 10 times as fast as those observed in any other wave band and imply a very compact emission region with a dimension similar to the Schwarzschild radius of the central black hole. We thus can exclude several other sites and processes of the gamma-ray production. The observations confirm that TeV gamma rays are emitted by extragalactic sources other than blazars, where jets are not relativistically beamed toward the observer.
RESUMO
The detection of gamma rays from the source HESS J1745-290 in the Galactic Center (GC) region with the High Energy Spectroscopic System (HESS) array of Cherenkov telescopes in 2004 is presented. After subtraction of the diffuse gamma-ray emission from the GC ridge, the source is compatible with a point source with spatial extent less than 1.2;{'}(stat) (95% C.L.). The measured energy spectrum above 160 GeV is compatible with a power law with photon index of 2.25+/-0.04(stat)+/-0.10(syst) and no significant flux variation is detected. It is finally found that the bulk of the very high energy emission must have non-dark-matter origin.
RESUMO
Torsional parameters for MM3(96) were derived for the missing atom types present in the natural product camptothecin (CPT). Potential energy curves were calculated via ab initio calculations on representative compounds for dihedral angles containing these missing parameters. Gaussian 92 at the restricted Hartree-Fock level of theory using the standard 6-31G** and 4-31G** basis sets, was used for all the quantum-mechanics calculations. Missing MM3 torsional terms were obtained by optimizing the V1, V2 and V3 parameters such that MM3 could reproduce the ab initio torsional profile. MM3 calculated molecular structures that compare well with the ab initio results. Using the newly developed parameters, conformational analyses and QSAR studies of camptothecin analogs were undertaken. MM3 predicts two distinct 'boatlike' conformations for the alpha-hydroxy lactone moiety. The low-energy lactone conformation predicted by MM3 is in general agreement with reported X-ray crystal structures of CPT iodoacetate and 7-ethyl-10-(4-piperidino)piperidinylcarbonyloxy CPT HCl as well as the ab initio structure of a CPT-like alpha-hydroxy lactone.
Assuntos
Camptotecina/análogos & derivados , Camptotecina/química , Conformação Molecular , Estrutura Molecular , Estereoisomerismo , Relação Estrutura-Atividade , TermodinâmicaRESUMO
Recruitment of polymorphonuclear leucocytes (PMN) across the intestinal epithelium is dependent on specific adhesion molecules and chemoattractants diffusing from the intestinal lumen. The present understanding is that in response to fMLP, PMN migration across a T84 colon carcinoma monolayer is dependent on the beta(2) integrin, Mac-1 (CD11b/CD18). To further understand PMN transepithelial migration, we sought to determine whether migration to C5a, IL-8 and LTB(4) was similarly Mac-1-, or even CD18-dependent. T84 epithelial cell monolayers growing on Transwell filters were used in combination with radiolabelled peripheral blood PMN. The number of migrated PMN was established by the amount of radioactivity recovered from the well after the migration period. Monoclonal antibodies were used to block integrin function. Whereas essentially all migration to fMLP across T84 monolayers was prevented by anti-CD18 antibody, significant migration to C5a, IL-8 or LTB(4) persisted despite anti-CD18 antibody, indicating PMN are capable of beta(2) integrin-independent transepithelial migration. An antibody to CD11b but not CD11a blocked migration to an extent similar as with anti-CD18. CD18-independent PMN migration to C5a occurred only in the basolateral-to-apical direction across epithelial cells. Co-stimulation of PMN with C5a and fMLP or IL-8 plus LTB(4) and fMLP still resulted in CD18-independent migration. Thus CD18 use during PMN migration across this model epithelium is a function of the chemoattractant inducing migration. The finding of CD18-independent migration mechanisms needs to be considered when developing antiadhesion molecule strategies to reduce or reverse intestinal inflammation.
Assuntos
Células Epiteliais , Doenças Inflamatórias Intestinais/imunologia , Mucosa Intestinal/imunologia , Neutrófilos/citologia , Análise de Variância , Anticorpos Monoclonais/farmacologia , Antígenos CD18/imunologia , Adesão Celular , Contagem de Células , Linhagem Celular Tumoral , Movimento Celular , Complemento C5a/farmacologia , Humanos , Interleucina-8/farmacologia , Leucotrieno B4/farmacologia , N-Formilmetionina Leucil-Fenilalanina/farmacologia , Ativação de Neutrófilo , Neutrófilos/imunologiaRESUMO
Conformational studies and comparative molecular field analysis (CoMFA) were undertaken for a series of camptothecin (CPT) analogs to correlate topoisomerase I inhibition with the steric and electrostatic properties of 32 known compounds. The resulting CoMFA models have been used to make predictions on novel CPT derivatives. Using the newly derived MM3 parameters, a molecular database of the 32 CPT analogs was created. Various point atomic charges were generated and assigned to the MM3 minimized structures, which were used in partial least-squares analyses. Overall, CoMFA models with the greatest predictive validity were obtained when both the R- and S-isomers were included in the data set, and semiempirical charges were calculated for MM3 minimized low-energy lactone structures. A cross-validated R2 of 0.758 and a non-cross-validated R2 of 0.916 were obtained for MM3 minimized structures with PM3 ESP charges for the 32 CPT analogs. The derived QSAR equations were used to assign topoisomerase I inhibition values for compounds in this study and compounds not included in the original data set. Prior to its appearance in the literature, an IC50 of 103 nM was predicted for the 10,11-oxazole derivative. This CoMFA predicted value compared favorably with the recently reported value of 150 nM. The CoMFA model was also evaluated by predicting the activities of recently reported 11-aza CPT and trione derivatives. The predicted activity (IC50 = 249 nM) for 11-aza CPT compared well with the reported value of 383 nM.
Assuntos
Antineoplásicos/química , Camptotecina/análogos & derivados , Inibidores Enzimáticos/química , Inibidores da Topoisomerase I , Antineoplásicos/farmacologia , Camptotecina/química , Camptotecina/farmacologia , Simulação por Computador , Bases de Dados Factuais , Inibidores Enzimáticos/farmacologia , Humanos , Modelos Moleculares , Conformação Molecular , Relação Estrutura-Atividade , TermodinâmicaRESUMO
Although the gas chromatographic separation of the isomers of BHC was demonstrated two decades ago, the present AOAC method of analysis of BHC for gamma-isomer (lindane) content is based on a separation carried out on a liquid chromatographic partition column. A method of analysis has been developed that uses an OV-210 column for separation of the gamma-isomer from the other isomers and impurities in technical BHC. Di-n-propyl phthalate was chosen as an internal standard. The same system allows quantitation of lindane in lotion and shampoo after these products are extracted with ethyl acetate-isooctane (1 + 4). The analytical methods were subjected to a collaborative trial with 10 laboratories. The coefficient of variation for technical BHC was 2.83%. For the water-dispersible powder and emulsifiable concentrate, the coefficients of variation were 2.89% and 4.62%, respectively. Coefficients of variation for 1% lindane lotion and shampoo were 4.36% and 11.92%, respectively. The method has been adopted official first action.