374,581 research outputs found
Novel nonalloyed thermally stable Pd/Sn and Pd/Sn/Au ohmic contacts for the fabrication of GaAs MESFETs
No full textGaAs metal-semiconductor field-effect transistors (MESFETs) have been fabricated utilizing thermally stable Pd/Sn and Pd/Sn/Au ohmic contacts for the first time. MESFETs with Pd/Ge ohmic contacts are fabricated for comparison. The thermal stability of the Pd/Sn, Pd/Ge and Pd/Sn/Au ohmic contacts is also presente
Astrophysical S-factors and reaction rates of (p,n)-reactions on ¹¹⁷Sn, ¹¹⁸Sn, ¹²²Sn, and ¹²⁴Sn
No full textAstrophysical S-factors and reaction rates were derived from available cross sections of (p,n)-reactions on Sn-117, Sn-118, Sn-122, and Sn-124 isotopes at incident proton energies up to 9 MeV. The statistical theory predictions of the observable quantities are similar to 2 times smaller at near threshold energies and have better agreement at higher energies
Explosion Parameters of SN 2013df and Properties of Its Progenitor Star
No full textType IIb supernovae have only recently been identified as a distinct flavor of core-collapse stellar explosions. These supernovae represent a transitional type between Type II and Type Ib supernovae. Here I present a multi-wavelength (UV-optical) analysis of Type IIb SN 2013df, with the primary goals to (i) constrain the radius of the progenitor star and (ii) determine properties of the stellar explosion. From the analysis of the cooling envelope emission from SN 2013df I constrain the progenitor radius to be R < 7.8X1014 cm. I then analyze the main supernova peak that is powered by freshly synthesized 56Ni and find that the total ejecta mass is Mej = 5.0 Mʘ and the explosion kinetic energy is Ek = 3 X 1051 erg. Finally, I compare my findings with the explosion and progenitor properties of the currently known and studied sample of Type IIb supernovae from the literature
Precipitation processes in Al-Cu-Mg-Sn and Al-Cu-Mg-Sn-Ag
No full textMicroalloying trace elements into aluminum alloys have been shown to improve mechanical properties by altering the precipitation process. Here, trace amounts of Sn and (Sn + Ag) have been added to Al-1.1Cu-1.7Mg (at.%) and the effects have been investigated by a combination of hardness testing and transmission electron microscopy (TEM). Hardness testing shows that the addition of Sn increases the hardness throughout the ageing process, and in combination with Ag, further increases the hardness and shortens the time to reach the peak hardness. The increase in hardness via Sn microalloying is attributed to the homogeneous distribution of S phase (Al2CuMg) precipitates. In the alloy microalloyed with both Sn and Ag, the microstructure is dominated by homogeneously distributed Ω phase (Al2Cu) precipitates in the peak strengthened condition. Given that neither spherical β-Sn precipitates, nor any other obvious nucleation sites for the Ω phase precipitates were observed using TEM, the mechanism for development of such homogeneous precipitation remains to be determined
A trio of gamma-ray burst supernovae : GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu
No full textWe present optical and near-infrared (NIR) photometry for three gamma-ray burst supernovae (GRB-SNe): GRB 120729A, GRB 130215A/SN 2013ez, and GRB 130831A/SN 2013fu. For GRB 130215A/SN 2013ez, we also present optical spectroscopy at t − t0 = 16.1 d, which covers rest-frame 3000–6250 Å. Based on Fe ii λ5169 and Si ii λ6355, our spectrum indicates an unusually low expansion velocity of ~4000–6350 km s-1, the lowest ever measured for a GRB-SN. Additionally, we determined the brightness and shape of each accompanying SN relative to a template supernova (SN 1998bw), which were used to estimate the amount of nickel produced via nucleosynthesis during each explosion. We find that our derived nickel masses are typical of other GRB-SNe, and greater than those of SNe Ibc that are not associated with GRBs. For GRB 130831A/SN 2013fu, we used our well-sampled R-band light curve (LC) to estimate the amount of ejecta mass and the kinetic energy of the SN, finding that these too are similar to other GRB-SNe. For GRB 130215A, we took advantage of contemporaneous optical/NIR observations to construct an optical/NIR bolometric LC of the afterglow. We fit the bolometric LC with the millisecond magnetar model of Zhang & Mészáros (2001, ApJ, 552, L35), which considers dipole radiation as a source of energy injection to the forward shock powering the optical/NIR afterglow. Using this model we derive an initial spin period of P = 12 ms and a magnetic field of B = 1.1 × 1015 G, which are commensurate with those found for proposed magnetar central engines of other long-duration GRBs
Finding the Largest Flares on Ultracool Dwarfs with ASAS-SN
No full textQuiescent chromospheric activity, as measured through Halpha emission, is ubiquitous on ultracool (late-M and early-L) dwarfs, but the rate of white-light flares on these objects is still under investigation. Recent work with Kepler and K2 has revealed that flares occur less frequently than on more massive M dwarfs, but the strongest flares are sufficiently rare that they are unlikely to be observed in the 90 day observational windows. The All Sky Automated Search for Supernovae (ASAS-SN) survey scans the entire sky once every two days in V band down to V> 17. In addition to discovering hundreds of Supernovae, the ASAS-SN survey has also observed hundreds of stellar flares, including two particularly dramatic flares in the ultracool regime; a ΔV ~ -9 on an M8 dwarf, and a ΔV ~ -10 flare on an L1 dwarf. Both flares radiated ~1034 ergs in the V-band, placing them among the strongest observed white-light flares. While flares this strong are expected to occur less than once per year on individual ultracool dwarfs, the all-sky coverage of ASAS-SN presents a unique opportunity to detect strong flares (ΔV < -5) on all ultracool dwarfs within ~100pc. We discuss the two most dramatic ASAS-SN flares and present our initial constraints on the rate of large flares on ultracool dwarfs.Poster #05
Evolution of the Type IIb SN 2011fu
No full textThe UBVRI photometric follow-up of SN 2011fu has been initiated a few days after the explosion, shows a rise followed by steep decay in all bands and shares properties very similar to that seen in case of SN 1993J, with a possible detection of the adiabatic cooling phase at very early epochs. The spectral modeling performed with SYNOW suggests that the early-phase line velocities for H and Fe ii features were ~ 16000 km s−1 and ~ 14000 km s−1, respectively. Studies of rare class of type IIb SNe are important to understand the evolution of the possible progenitors of core-collapse SNe in more details
Crystal growth of PbTe and (Pb, Sn)Te by the bridgman method and by THM
No full textSynthesis and growth of PbTe and (Pb, Sn)Te single crystals by the Bridgman method and by the Travelling Heater Method (THM) from Te-rich solutions are described. It is to be seen from comparative investigations that seeded THM growth reproducibly provides oriented single-crystalline ingots free of low-angle grain boundaries and with etch pit densities of 8-12 × 104 cm-2. All the materials were p-type with carrier concentrations from 1 to 2 × 1018 cm-3
Sn-Doping Enhanced Ultrahigh Mobility In<sub>1–<i>x</i></sub>Sn<sub><i>x</i></sub>Se Phototransistor
No full textTwo-dimensional ternary
materials are attracting widespread interest
because of the additional degree of freedom available to tailor the
material property for a specific application. An In1–xSnxSe phototransistor
possessing tunable ultrahigh mobility by Sn-doping engineering is
demonstrated in this study. A striking feature of In1–xSnxSe flakes is the reduction
in the oxide phase compared to undoped InSe, which is validated by
spectroscopic analyses. Moreover, first-principles density functional
calculations performed for the In1–xSnxSe crystal system reveal the same
effective mass when doped with Sn atoms. Hence, because of an increased
lifetime owing to the enhanced crystal quality, the carriers in In1–xSnxSe
have higher mobility than in InSe. The internally boosted electrical
properties of In1–xSnxSe exhibit ultrahigh mobility of 2560 ± 240
cm2 V–1 s–1 by suppressing
the interfacial traps with substrate modification and channel encapsulation.
As a phototransistor, the ultrathin In1–xSnxSe flakes are highly sensitive
with a detectivity of 1014 Jones. It possesses a large
photoresponsivity and photogain (Vg =
40 V) as high as 3 × 105 A W–1 and
0.5 × 106, respectively. The obtained results outperform
all previously reported performances of InSe-based devices. Thus,
the doping-engineered In1–xSnxSe-layered semiconductor finds a potential
application in optoelectronics and meets the demand for faster electronic
technology
SN 2018jmt and SN 2019cj opt and NIR obs. mag.[Dataset]
No full textZ.-Y. Wang et al. -- We conducted multi-band optical (Sloan griz, Johnson-Cousins UBV) and near-infrared (NIR; JHK) follow-up campaigns of SNe 2018jmt and 2019cj starting shortly after their classification. Photometry tables for two Ibn supernovae (SN 2018jmt, SN 2019cj).We present optical and near-infrared observations of two Type Ibn supernovae (SNe), SN 2018jmt and SN 2019cj. Their light curves have rise times of about 10 days, reaching an absolute peak magnitude of Mg(SN 2018jmt)=-19.07+/-0.37 and MV(SN 2019cj)=-18.94+/-0.19mag, respectively. The early-time spectra of SN 2018jmt are dominated by a blue continuum, accompanied by narrow (600-1000km/s) HeI lines with P-Cygni profile. At later epochs, the spectra become more similar to those of the prototypical SN Ibn 2006jc. At early phases, the spectra of SN 2019cj show flash ionisation emission lines of CIII, NIII and HeII superposed on a blue continuum. These features disappear after a few days, and then the spectra of SN 2019cj evolve similarly to those of SN 2018jmt. The spectra indicate that the two SNe exploded within a He-rich circumstellar medium (CSM) lost by the progenitors a short time before the explosion. We model the light curves of the two SNe Ibn to constrain the progenitor and the explosion parameters. The ejecta masses are consistent with either that expected for a canonical SN Ib (~2M_{sun}_) or those from a massive WR star (>~4M_{sun}_), with the kinetic energy on the order of 1051 erg. The lower limit on the ejecta mass (>~2M_{sun}_) argues against a scenario involving a relatively low-mass progenitor (e.g., MZAMS~10M_{sun}_). We set a conservative upper limit of ~0.1M_{sun}_ for the 56Ni masses in both SNe. From the light curve modelling, we determine a two-zone CSM distribution, with an inner, flat CSM component, and an outer CSM with a steeper density profile. The physical properties of SN 2018jmt and SN 2019cj are consistent with those expected from the core collapse of relatively massive, stripped-envelope (SE) stars.Peer reviewe
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