1,159 research outputs found
Assessment of detectability of neutral interstellar deuterium by IBEX observations
The abundance of deuterium in the interstellar gas in front of the Sun gives
insight into the processes of filtration of neutral interstellar species
through the heliospheric interface and potentially into the chemical evolution
of the Galactic gas. We investigate the possibility of detection of neutral
interstellar deuterium at 1 AU from the Sun by direct sampling by the
Interstellar Boundary Explorer (IBEX). We simulate the flux of neutral
interstellar D at IBEX for the actual measurement conditions. We assess the
number of interstellar D atom counts expected during the first three years of
IBEX operation. We also simulate observations expected during an epoch of high
solar activity. In addition, we calculate the expected counts of D atoms from
the thin terrestrial water layer, sputtered from the IBEX-Lo conversion surface
by neutral interstellar He atoms. Most D counts registered by IBEX-Lo are
expected to originate from the water layer, exceeding the interstellar signal
by 2 orders of magnitude. However, the sputtering should stop once the Earth
leaves the portion of orbit traversed by interstellar He atoms. We identify
seasons during the year when mostly the genuine interstellar D atoms are
expected in the signal. During the first 3 years of IBEX operations about 2
detectable interstellar D atoms are expected. This number is comparable with
the expected number of sputtered D atoms registered during the same time
intervals. The most favorable conditions for the detection occur during low
solar activity, in an interval including March and April each year. The
detection chances could be improved by extending the instrument duty cycle,
e.g., by making observations in the special deuterium mode of IBEX-Lo.Comment: Accepted for Astronomy & Astrophysic
Effect of freezer storage on quality of M. longissimus lumborum from fallow deer (Dama dama L.)
The aim of this study was to analyse changes in the quality of meat (M. longissimus lumborum) from 11 fallow deer (Dama dama L.) bucks, which had been deep-frozen (-26 °C) for 10 months. The proximate chemical composition, physico-chemical properties and sensory properties of the meat were analysed. Fallow deer aged 17–18 months were hunter-harvested in north-eastern Poland in November and December of the same hunting season. The results revealed that freezer storage did not influence the proximate chemical composition of meat (protein, fat, ash) or the content of water-soluble nitrogen compounds. An analysis of the physico-chemical properties of meat revealed that long-term freezer-stored meat was characterized by higher pH, lower contribution of redness (a*) and yellowness (b*), lower chroma (C*), greater natural drip loss, lower ability to bind added water, and greater cooking loss. Freezer storage improved meat tenderness but reduced meat juiciness. The results of the study also indicated that long-term freezer storage (-26 °C) of vacuum-packaged meat allowed it to maintain its good quality, which indicates that this storage method could help meet consumer demand for fallow deer meat between hunting seasons.Keywords: Freezing, game meat, meat quality, vacuum packagin
Elemental boron doping behavior in silicon molecular beam epitaxy
Boron-doped Si epilayers were grown by molecular beam epitaxy (MBE) using an elemental boron source, at levels up to 2×1020 cm−3, to elucidate profile control and electrical activation over the growth temperature range 450–900 °C. Precipitation and surface segregation effects were observed at doping levels of 2×1020 cm−3 for growth temperatures above 600 °C. At growth temperatures below 600 °C, excellent profile control was achieved with complete electrical activation at concentrations of 2×1020 cm−3, corresponding to the optimal MBE growth conditions for a range of Si/SixGe1−x heterostructures
Application of Silicon Carbide Chills in Controlling the Solidification Process of Casts Made of IN-713C Nickel Superalloy
The paper presents the method of manufacturing casts made of the IN-713C nickel superalloy using the wax lost investment castingprocess and silicon carbide chills. The authors designed experimental casts, the gating system and selected the chills material. Wax pattern,ceramic shell mould and experimental casts were prepared for the purposes of research. On the basis of the temperature distributionmeasurements, the kinetics of the solidification process was determined in the thickened part of the plate cast. This allowed to establish thequantity of phase transitions which occurred during cast cooling process and the approximate values of liquidus, eutectic, solidus andsolvus temperatures as well as the solidification time and the average value of cast cooling rate. Non-destructive testing and macroscopicanalysis were applied to determine the location and size of shrinkage defects. The authors present the mechanism of solidification andformation of shrinkage defects in casts with and without chills. It was found that the applied chills influence significantly the hot spots andthe remaining part of the cast. Their presence allows to create conditions for solidification of IN-713C nickel superalloy cast withoutshrinkage defects
Antisite effect on ferromagnetism in (Ga,Mn)As
We study the Curie temperature and hole density of (Ga,Mn)As while
systematically varying the As-antisite density. Hole compensation by
As-antisites limits the Curie temperature and can completely quench long-range
ferromagnetic order in the low doping regime of 1-2% Mn. Samples are grown by
molecular beam epitaxy without substrate rotation in order to smoothly vary the
As to Ga flux ratio across a single wafer. This technique allows for a
systematic study of the effect of As stoichiometry on the structural,
electronic, and magnetic properties of (Ga,Mn)As. For concentrations less than
1.5% Mn, a strong deviation from Tc ~ p^0.33 is observed. Our results emphasize
that proper control of As-antisite compensation is critical for controlling the
Curie temperatures in (Ga,Mn)As at the low doping limit.Comment: 10 pages, 7 figure
Very high two-dimensional hole gas mobilities in strained silicon germanium
We report on the growth by solid source MBE and characterization of remote doped Si/SiGe/Si two-dimensional hole gas structures. It has been found that by reducing the Ge composition to <=13% and limiting the thickness of the alloy layer, growth temperatures can be increased up to 950 °C for these structures while maintaining good structural integrity and planar interfaces. Record mobilities of 19 820 cm2 V−1 s−1 at 7 K were obtained in normal structures. Our calculations suggest that alloy scattering is not important in these structures and that interface roughness and interface charge scattering limit the low temperature mobilities
Growth studies on Si0.8Ge0.2 channel two-dimensional hole gases
We report a study of the influences of MBE conditions on the low-temperature mobilities of Si/Si0.8Ge0.2 2DHG structures. A significant dependence of 2DHG mobility on growth temperature is observed with the maximum mobility of 3640 cm2 V−1 s−1 at 5.4 K being achieved at the relatively high-growth temperature of 640 °C. This dependence is associated with a reduction in interface charge density. Studies on lower mobility samples show that Cu contamination can be reduced both by growth interruptions and by modifications to the Ge source; this reduction produces improvements in the low-temperature mobilities. We suggest that interface charge deriving from residual metal contamination is currently limiting the 4-K mobility
The Optical Gravitational Lensing Experiment. Short Distance Scale to the LMC
We present {\it UBVI} photometry of the eclipsing binary HV2274 - the system
which has been recently used for distance determination to the LMC by Guinan et
al. (1998). We determine the interstellar reddening to the star,
E(B-V)=0.149+/-0.015 mag, based on observed colors of the star. This value is
in excellent agreement with the mean reddening towards HV2274 obtained from
photometry of the red clump stars in the surrounding field. The reddening is
almost twice as large as determined by Guinan et al. (1998).
We discuss the consequences of reddening underestimate. Most likely HV2274 is
located much closer with the distance modulus to the star and the LMC: m-M =
18.22+/-0.13 mag supporting the short distance scale to the LMC. Such a
distance modulus is in excellent agreement with the recent distance
determinations with RR Lyr and red clump stars.Comment: 11 pages, Latex, 2 Figures. Accepted for publication in Astrophysical
Journal Letters. New version - trimmed to fit ApJL. Additional determination
of the reddening towards HV2274 with OB star
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