885 research outputs found
Photometric Studies of a WZ Sge-Type Dwarf Nova Candidate, ASAS160048-4846.2
We report on our time-resolved CCD photometry during the 2005 June
superoutburst of a WZ Sge-type dwarf nova candidate, ASAS 160048-4846.2. The
ordinary superhumps underwent a complex evolution during the superoutburst. The
superhump amplitude experienced a regrowth, and had two peaks. The superhump
period decreased when the superhump amplitude reached to the first maximum,
successively gradually increased until the second maximum of the amplitude, and
finally decreased again. Investigating other SU UMa-type dwarf novae which show
an increase of the superhump period, we found the same trend of the superhump
evolution in superoutbursts of them. We speculate that the superhump regrowth
in the amplitude has a close relation to the increase of the superhump period,
and all of SU UMa-type dwarf novae with a superhump regrowth follow the same
evolution of the ordinary superhumps as that of ASAS 160048-4846.2.Comment: 7 pages, 4 figure
A battery-operated, stabilized, high-energy pulsed electron gun for the production of rare gas excimers
We report on the design of a new type of electron gun to be used for
experiments of infrared emission spectroscopy of rare gas excimers. It is based
on a filament heated by means of a pack of rechargeable batteries floated atop
the high-voltage power supply. The filament current is controlled by a feedback
circuit including a superluminescent diode decoupled from the high voltage by
means of an optical fiber. Our experiment requires that the charge injection is
pulsed and constant and stable in time. This electron gun can deliver several
tens of nC per pulse of electrons of energy up to keV into the sample
cell. This new design eliminates ripples in the emission current and ensures up
to 12 hrs of stable performance.Comment: 1o pages, 8 figures, to be submitted to Review of Scientific
Instrument
On the rotation periods of the components of the triple system TYC9300-0891-1AB/TYC9300-0529-1 in the Octans Association
Stellar rotation depends on different parameters. The range of values of
these parameters causes the dispersion in the rotation period distributions
observed in young stellar clusters/associations. We focus our investigation on
the effects of different circumstellar environments on stellar rotation. More
specifically, we are searching in stellar Associations for visual triple
systems where all stellar parameters are similar, with the only exceptions of
the unknown initial rotation period, and of the circum-stellar environment, in
the sense that one of the two about equal-mass components has a close-by third
'perturber' component. In the present study we analyse the 35-Myr old visual
triple system TYC 9300-0891-1AB + TYC 9300-0529-1 in the young Octans stellar
association consisting of three equal-mass K0V components. We collected from
the literature all information that allowed us to infer that the three
components are actually physically bound forming a triple system and are
members of the Octans Association. We collected broad-band photometric
timeseries in two observation seasons. We discovered that all the components
are variable, magnetically active, and from periodogram analysis we found the
unresolved components TYC 9300-0891-1AB to have a rotation period P = 1.383d
and TYC 9300-0529-1 a rotation period P = 1.634d. TYC 9300-0891-1A, TYC
9300-0891-1B, and TYC 9300-0529-1 have same masses, ages, and initial chemical
compositions. The relatively small 16% rotation period difference measured by
us indicates that all components had similar initial rotation periods and disc
lifetimes, and the separation of 157AU between the component A and the
'perturber' component B (or vice-versa) has been sufficiently large to prevent
any significant perturbation/shortening of the accretion-disc lifetime.Comment: Accepted by New Astronomy 201
Effect of hot-dip galvanization on the fatigue behaviour of welded structural steel
Abstract This paper investigates the effect of a galvanizing coating on the fatigue strength of S355 structural steel. While in the literature some results from fatigue tests made on unnotched specimens can be found, very few results are available dealing with notched components and, at the best of authors' knowledge, no results are available dealing with welded joints. The aim of the present paper is to partially fill this lack of knowledge. A comparison is carried out, between hot dip galvanized fillet welded cruciform joints made by S355 structural steel and not treated welded joints characterized by the same geometry, subjected to a load cycle R = 0. 34 new experimental data are summarized in the present contribution, in terms of stress range Δσ and averaged strain energy density range ΔW in a control volume of radius R0 = 0.28 mm
Three-dimensional effects on cracked discs and plates under nominal Mode III loading
The existence of three-dimensional effects at cracks has been known for many years, but understanding has been limited, and for some situations still is. Understanding improved when the existence of corner point singularities and their implications became known. Increasingly powerful computers made it possible to investigate three-dimensional effects numerically in detail. Despite increased understanding, threedimensional effects are sometimes ignored in situations where they may be important. The purpose of the present contribution is to review the study carried out by the same authors in some recent investigations, in which a coupled fracture mode generated by anti-plane loading of a straight through-the-thickness crack in linear elastic discs and plates has been analysed by means of accurate 3D finite element (FE) models. The results obtained from the highly accurate finite element analyses have improved understanding of the behaviour of through cracked components under anti-plane loading. The influence of plate bending is increasingly important as the thickness decreases. It appears that a new field parameter, probably a singularity, is needed to describe the stresses at the free surfaces. Discussion on whether KIII tends to zero or infinity as a corner point is approached is futile because KIII is meaningless at a corner point. The intensity of the local stress and strain state through the thickness of the cracked components has been evaluated by using the strain energy density (SED) averaged over a control volume embracing the crack tip. The SED has been considered as a parameter able to control fracture in some previous contributions and can easily take into account also coupled three-dimensional effects. Calculation of the SED shows that the position of the maximum SED in the discs case is a function of the thickness. In the plates case instead the position of the maximum SED is independent of plate thickness, contrary to disc results
Discovery of a Promissing Candidate of WZ Sge-Type Dwarf Novae, ASAS 160048-4846.2: Evidence for Double-Peaked Humps
We report on time-resolved CCD photometry during the 2005 June outburst of a
dwarf nova, ASAS160048-4846.2. The observed light curves unambiguously showed
embryonic humps with a period of 0.063381(41) days, after which genuine
superhumps emerged with a period of 0.064927(3) days. Based on evidence for
double-peaked humps in the earlier stage of the outburst, this object might be
qualified as the seventh member of WZ Sge-type dwarf novae after Var Her 04. If
the former period is the same as, or very close to the orbital period of the
system, as in other WZ Sge systems, the fractional superhump excess is about
2.4{%}. This value is unexpectedly larger than that of other WZ Sge-type
dwarf novae. The early phase of our observing run provided evidence for the
transition from chaotic humps to genuine superhumps, together with increasing
the amplitude.Comment: 4 pages, 6 figures, submitted to PAS
Efeito da altura do resíduo sobre a produção e a estrutura de sorgo forrageiro.
O cultivo de sorgo forrageiro (Sorghum bicolor (L.) Moench.) tem crescido na região Noroeste do Rio Grande do Sul nos últimos anos. Os produtores rurais estão sendo orientados a manejar o sorgo forrageiro em pastejo rotacionado, respeitando uma altura de entrada dos animais acima de 70 cm e altura de saída (resíduo) em torno de apenas 5 cm.bitstream/item/63868/1/BP31.pd
Effect of heat treatment and defects on the tensile behavior of a hot work tool steel manufactured by laser powder bed fusion
Microstructure and tensile properties of a hot work tool steel manufactured via laser powder bed fusion (LPBF) were investigated. Specimens were built under two different orientations and subjected to two quenching and tempering heat treatments, featuring different austenitizing and tempering temperatures and the eventual presence of a sub-zero step. Microstructural analyses revealed a homogeneous tempered martensite structure after both heat treatments, with the only distinction of a higher alloying segregation at a sub micrometric scale length in samples subjected to the highest tempering temperatures. Hardness and tensile tests indicated a negligible effect of building orientation on mechanical properties, but a significant influence of heat treatment parameters. The treatment featuring the lower tempering temperatures and the sub-zero step resulted in higher hardness, tensile strength, and elongation, attributed to a lower martensite tempering and alloying segregation. Tensile fracture occurred via crack initiation and unstable propagation from large LPBF defects in all the investigated conditions
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