Search results for " Tau"

Ķīniešu pasakas

1936

Šmits, Pēteris (sastādītājs)

Zinātņu vēsture un muzejniecība

2001

Krājumā ievietotie raksti veltīti Latvijas Universitātē pārstāvēto zinātņu vēstures izpētei - kā atsevišķām zinātnes nozarēm un specialitātēm laikposmā kopš universitātes dibināšanas līdz mūsdienām, tā arī zinātniskiem kolektīviem, institūtiem, katedrām, zinātniskām skolām un virzieniem, tāpat pazīstamiem LU mācībspēkiem un pētniekiem, viņu dzīvei, darbībai un ieguldījumam augstskolas virzībā. Daļa rakstu veltīta zinātņu vēsturei Latvijā laikposmā pirms LU nodibināšanas, lai parādītu arī to pamatu un saknes, no kurām izauga mūsu pirmā nacionālā augstskola.

Alpu kreimules herbāriji Latvijas Universitātes Muzejā

1922

Alpu kreimule Pinguicula alpina L. ir rets augs, kurš šobrīd vairs nav sastopams Latvijas flora. Tā vienīgā dabīgā augtene bija uz Staburaga Daugavas krastā. Pļaviņu HES būvniecibas rezultātā tā tika iznīcināta. Latvijas Universitātes Muzeja herbārijā Botānikas un mikoloģijas kolekcijās glabājas šā auga herbāriji gan no Latvijas, gan Igaunijas. Šeit atrodas gan senākais ievāktais herbārijs uz Staburaga, gan pēdējais, kas tika šeit ievākts 1961. gadā.

Latviešu tautasdziesmu totēmiskā simbolika (radību, krustību un kāzu rituāli)

2006

Limit on the diffuse flux of ultrahigh energy tau neutrinos with the surface detector of the Pierre Auger Observatory

2009

Data collected at the Pierre Auger Observatory are used to establish an upper limit on the diffuse flux of tau neutrinos in the cosmic radiation. Earth-skimming ντ may interact in the Earth's crust and produce a τ lepton by means of charged-current interactions. The τ lepton may emerge from the Earth and decay in the atmosphere to produce a nearly horizontal shower with a typical signature, a persistent electromagnetic component even at very large atmospheric depths. The search procedure to select events induced by τ decays against the background of normal showers induced by cosmic rays is described. The method used to compute the exposure for a detector continuously growing with time is de…

Updated measurement of the τ lepton lifetime

1997

A new measurement of the mean lifetime of the tau lepton is presented. Three different analysis methods are applied to a sample of 90000 tau pairs, collected in 1993 and 1994 with the ALEPH detector at LEP. The average of this measurement and those previously published by ALEPH is tau_tau = 290.1 +- 1.5 +- 1.1 fs.

X-rays from accretion shocks in classical T Tauri stars: 2D MHD modeling and the role of local absorption

2013

AbstractIn classical T Tauri stars (CTTS) strong shocks are formed where the accretion funnel impacts with the denser stellar chromosphere. Although current models of accretion provide a plausible global picture of this process, some fundamental aspects are still unclear: the observed X-ray luminosity in accretion shocks is order of magnitudes lower than predicted; the observed density and temperature structures of the hot post-shock region are puzzling and still unexplained by models.To address these issues we performed 2D MHD simulations describing an accretion stream impacting onto the chromosphere of a CTTS, exploring different configurations and strengths of the magnetic field. From th…

UV variability and accretion dynamics in the young open cluster NGC 2264

2015

We explore UV and optical variability signatures for several hundred members of NGC 2264 (3 Myr). We performed simultaneous u- and r-band monitoring over two full weeks with CFHT/MegaCam. About 750 young stars are probed; 40% of them are accreting. Statistically distinct variability properties are observed for accreting and non-accreting cluster members. The accretors exhibit a significantly higher level of variability than the non-accretors, especially in the UV. The amount of u-band variability correlates statistically with UV excess in disk-bearing objects, which suggests that accretion and star-disk interaction are the main sources of variability. Cool magnetic spots, several hundred de…

UV And X-Ray Emission from Impacts of Fragmented Accretion Streams on Classical T Tauri Stars

2016

According to the magnetoshperic accretion scenario, during their evo- lution, Classical T Tauri stars accrete material from their circumstellar disk. The accretion process is regulated by the stellar magnetic eld and produces hot and dense post-shocks on the stellar surface as a result of impacts of the downfalling material. The impact regions are expected to strongly radiate in UV and X-rays. Several lines of evidence support the magnetospheric accretion scenario, especially in optical and infrared bands. However several points still remain unclear as, for instance,where the complex-pro le UV lines originate, or whether and how UV and X-ray emission is produced in the same shock region. Th…

Redshifted X-rays from the material accreting onto TW Hya: evidence of a low-latitude accretion spot

2017

High resolution spectroscopy, providing constraints on plasma motions and temperatures, is a powerful means to investigate the structure of accretion streams in CTTS. In particular, the accretion shock region, where the accreting material is heated to temperatures of a few MK as it continues its inward bulk motion, can be probed by X-ray spectroscopy. To attempt to detect for the first time the motion of this X-ray-emitting post-shock material, we searched for a Doppler shift in the deep Chandra/HETGS observation of the CTTS TW Hya. This test should unveil the nature of this X-ray emitting plasma component in CTTS, and constrain the accretion stream geometry. We searched for a Doppler shift…