160 research outputs found
Features of recording the time profile of single picosecond pulses in the real-time mode
A technique for measuring the time profile of a beam-current pulse of runaway electrons that are generated in atmospheric-pressure air is described. The analysis of changes in the pulse shape depending on the bandwidth of the registration path with a temporal resolution of up to 20 ps was performed. It was shown that the electron beam detected behind small-diameter diaphragms has a complicated structure, which depends on the parameters of the gas diode. The issues related to the interpretation of subnanosecond pulses that are picked off capacitive voltage sensors are discussed
Kinematics of Tycho-2 Red Giant Clump Stars
Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95 633
red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort
constants have been found: A = 15.9+-0.2 km/s/kpc and B = -12.0+-0.2 km/s/kpc.
Using 3632 RGC stars with known proper motions, radial velocities, and
photometric distances, we show that, apart from the star centroid velocity
components relative to the Sun, only the model parameters that describe the
stellar motions in the XY plane differ significantly from zero. We have studied
the contraction (a negative K-effect) of the system of RGC stars as a function
of their heliocentric distance and elevation above the Galactic plane. For a
sample of distant (500--1000 pc) RGC stars located near the Galactic plane
(|Z|<200 pc) with an average distance of d=0.7 kpc, the contraction velocity is
shown to be Kd= -3.5+-0.9 km/s; a noticeable vertex deviation, lxy = 9.1+-0.5
degrees, is also observed for them. For stars located well above the Galactic
plane (|Z|>=200 pc), these effects are less pronounced, Kd = -1.7+-0.5 km/s and
lxy = 4.9+-0.6 degrees. Using RGC stars, we have found a rotation around the
Galactic X axis directed toward the Galactic center with an angular velocity of
-2.5+-0.3 km/s/kpc, which we associate with the warp of the Galactic
stellar-gaseous disk.Comment: 23 pages, 7 figures, 4 table
Astrometric Control of the Inertiality of the Hipparcos Catalog
Based on the most complete list of the results of an individual comparison of
the proper motions for stars of various programs common to the Hipparcos
catalog, each of which is an independent realization of the inertial reference
frame with regard to stellar proper motions, we redetermined the vector
of residual rotation of the ICRS system relative to the extragalactic
reference frame. The equatorial components of this vector were found to be the
following: mas yr,
mas yr, and mas yr.Comment: 8 pages, 1 figur
The OSACA Database and a Kinematic Analysis of Stars in the Solar Neighborhood
We transformed radial velocities compiled from more than 1400 published
sources, including the Geneva--Copenhagen survey of the solar neighborhood
(CORAVEL-CfA), into a uniform system based on the radial velocities of 854
standard stars in our list. This enabled us to calculate the average weighted
radial velocities for more than 25~000 HIPPARCOS stars located in the local
Galactic spiral arm (Orion arm) with a median error of +-1 km/s. We use these
radial velocities together with the stars' coordinates, parallaxes, and proper
motions to determine their Galactic coordinates and space velocities. These
quantities, along with other parameters of the stars, are available from the
continuously updated Orion Spiral Arm CAtalogue (OSACA) and the associated
database. We perform a kinematic analysis of the stars by applying an
Ogorodnikov-Milne model to the OSACA data. The kinematics of the nearest single
and multiple main-sequence stars differ substantially. We used distant
(r\approx 0.2 kpc) stars of mixed spectral composition to estimate the angular
velocity of the Galactic rotation -25.7+-1.2 km/s/kpc, and the vertex
deviation,l=13+-2 degrees, and detect a negative K effect. This negative K
effect is most conspicuous in the motion of A0-A5 giants, and is equal to
K=-13.1+-2.0 km/s/kpc.Comment: 16 pages, 8 figure
Doce de umbu.
O umbu apresenta sabor, aroma e textura exóticos e se destaca entre as frutas nativas da Caatinga por sua maior representatividade quanto à produção extrativista com fins alimentícios. As atividades agroindustriais geradas na cadeia produtiva desse fruto movimentam número expressivo de empreendimentos familiares no Semiárido do Brasil. O doce de umbu é indicado pelos empreendedores como o produto mais popular. A facilidade na elaboração, na aquisição das matérias-primas e nos equipamentos utilizados provavelmente justifica essa posição.bitstream/item/222451/1/AG-FAMILIAR-Doce-de-umbu-ed-01-2021-publicacao-digital.pd
Decaying Dark Matter can explain the electron/positron excesses
PAMELA and ATIC recently reported excesses in e+ e- cosmic rays. Since the
interpretation in terms of DM annihilations was found to be not easily
compatible with constraints from photon observations, we consider the DM decay
hypothesis and find that it can explain the e+ e- excesses compatibly with all
constraints, and can be tested by dedicated HESS observations of the Galactic
Ridge. ATIC data indicate a DM mass of about 2 TeV: this mass naturally implies
the observed DM abundance relative to ordinary matter if DM is a quasi-stable
composite particle with a baryon-like matter asymmetry. Technicolor naturally
yields these type of candidates.Comment: 20 pages, 7 figure
The Palomar Testbed Interferometer Calibrator Catalog
The Palomar Testbed Interferometer (PTI) archive of observations between 1998
and 2005 is examined for objects appropriate for calibration of optical
long-baseline interferometer observations - stars that are predictably
point-like and single. Approximately 1,400 nights of data on 1,800 objects were
examined for this investigation. We compare those observations to an
intensively studied object that is a suitable calibrator, HD217014, and
statistically compare each candidate calibrator to that object by computing
both a Mahalanobis distance and a Principal Component Analysis. Our hypothesis
is that the frequency distribution of visibility data associated with
calibrator stars differs from non-calibrator stars such as binary stars.
Spectroscopic binaries resolved by PTI, objects known to be unsuitable for
calibrator use, are similarly tested to establish detection limits of this
approach. From this investigation, we find more than 350 observed stars
suitable for use as calibrators (with an additional being
rejected), corresponding to sky coverage for PTI. This approach
is noteworthy in that it rigorously establishes calibration sources through a
traceable, empirical methodology, leveraging the predictions of spectral energy
distribution modeling but also verifying it with the rich body of PTI's on-sky
observations.Comment: 100 pages, 7 figures, 7 tables; to appear in the May 2008ApJS, v176n
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