2,141 research outputs found
Low-Temperature Phase Transition near V_3H_2
Heat capacity measurements have been made on the V-H alloys with the compositions VH_ to VH_ in the temperature range from -140 to 50â. Anomalous heat absorptions are observed at -100 to -50â depending on composition, indicating the occurrence of a phase transition attributed to the hydrogen ordering. A model of the superstructure of V_3H_2 is proposed for the low-temperature form on the basis of electron diffraction work by Wanagel et al
Measuring the brightness temperature distribution of extragalactic radio sources with space VLBI
We have used VSOP space very long baseline interferometry observations to
measure the brightness temperature distribution of a well-defined sub-set of
the Pearson-Readhead sample of extragalactic radio sources. VLBI which is
restricted to Earth-diameter baselines is not generally sensitive to emitting
regions with brightness temperatures greater than approximately K,
coincidentally close to theoretical estimates of brightness temperature limits,
K. We find that a significant proportion of our sample have
brightness temperatures greater than K; many have unresolved
components on the longest baselines, and some remain completely unresolved.
These observations begin to bridge the gap between the extended jets seen with
ground-based VLBI and the microarcsecond structures inferred from intraday
variability, evidenced here by the discovery of a relationship between intraday
variability and VSOP-measured brightness temperature, likely due to the effects
of relativistic beaming. Also, lower limits on jet Lorentz factors, estimated
from space VLBI observations, are starting to challenge numerical simulations
that predict low Lorentz factor jets.Comment: 4 pages + 1 figure, ApJ letters, accepte
The ability of freeze-dried bull spermatozoa to induce calcium oscillations and resumption of meiosis
The objective was to investigate the ability of freeze-dried (FD) bull spermatozoa to induce calcium oscillations in mouse oocytes and meiosis resumption in in vitro-matured bovine oocytes after intracytoplasmic sperm injection (ICSI). Bull spermatozoa were freeze-dried and stored for 1 y at +25, +4, or -196 degrees C. In the first experiment, rehydrated sperm heads were microinseminated into hybrid mouse oocytes loaded with fluo-3/AM, and the kinetics of intracellular calcium concentration was monitored for I h. Repetitive increases of intracellular calcium concentration were recorded in the majority of injected oocytes, with exception of a few oocytes injected with FD sperm heads stored at +4 degrees C (11%) and +25 degrees C (8%) that exhibited a single increase or no response (non-oscillated). The proportion of oocytes that oscillated with high frequency (>= 10 spikes/h) was higher in the non-dried control group (79%; P < 0.05) than in the FD groups (58, 55, and 54% for storage at -196, +4, and +25 degrees C, respectively). In the second experiment, control and FD spermatozoa were microinseminated into in vitro-matured, denuded bovine oocytes. The oocytes were fixed and stained 12 h after ICSI. A higher proportion of bovine oocytes injected with control spermatozoa (70%; P < 0.05) resumed meiosis than those injected with +25, +4 and -196 degrees C stored FD spermatozoa (53, 48, and 57%, respectively). The proportion of ICSI oocytes that developed to the pronuclear stage (complete activation) was higher in the control group (64%; P < 0.05) than those in all the FD groups (34, 27, and 28% for storage at -196, +4, and +25 degrees C, respectively). Thus, the ability of bull spermatozoa to induce frequent intracellular calcium spikes in mouse oocytes was impaired by the process of freeze-drying, without differences among storage at +25, +4 or -196 degrees C, probably resulting in a lower proportion of bovine oocytes that resumed meiosis and/or developed to the pronuclear stage.ArticleTHERIOGENOLOGY. 71(3):543-552 (2009)journal articl
Space VLBI Observations of 3C 279 at 1.6 and 5 GHz
We present the first VLBI Space Observatory Programme (VSOP) observations of
the gamma-ray blazar 3C 279 at 1.6 and 5 GHz. The combination of the VSOP and
VLBA-only images at these two frequencies maps the jet structure on scales from
1 to 100 mas. On small angular scales the structure is dominated by the quasar
core and the bright secondary component `C4' located 3 milliarcseconds from the
core (at this epoch). On larger angular scales the structure is dominated by a
jet extending to the southwest, which at the largest scale seen in these images
connects with the smallest scale structure seen in VLA images. We have
exploited two of the main strengths of VSOP: the ability to obtain
matched-resolution images to ground-based images at higher frequencies and the
ability to measure high brightness temperatures. A spectral index map was made
by combining the VSOP 1.6 GHz image with a matched-resolution VLBA-only image
at 5 GHz from our VSOP observation on the following day. The spectral index map
shows the core to have a highly inverted spectrum, with some areas having a
spectral index approaching the limiting value for synchrotron self-absorbed
radiation of 2.5. Gaussian model fits to the VSOP visibilities revealed high
brightness temperatures (>10^{12} K) that are difficult to measure with
ground-only arrays. An extensive error analysis was performed on the brightness
temperature measurements. Most components did not have measurable brightness
temperature upper limits, but lower limits were measured as high as 5x10^{12}
K. This lower limit is significantly above both the nominal inverse Compton and
equipartition brightness temperature limits. The derived Doppler factor,
Lorentz factor, and angle to the line-of-sight in the case of the equipartition
limit are at the upper end of the range of expected values for EGRET blazars.Comment: 11 pages, 6 figures, emulateapj.sty, To be published in The
Astrophysical Journal, v537, Jul 1, 200
Dual-Frequency VSOP Observations of AO 0235+164
AO 0235+164 is a very compact, flat spectrum radio source identified as a BL
Lac object at a redshift of z=0.94. It is one of the most violently variable
extragalactic objects at both optical and radio wavelengths. The radio
structure of the source revealed by various ground-based VLBI observations is
dominated by a nearly unresolved compact component at almost all available
frequencies.
Dual-frequency space VLBI observations of AO 0235+164 were made with the VSOP
mission in January-February 1999. The array of the Japanese HALCA satellite and
co-observing ground radio telescopes in Australia, Japan, China and South
Africa allowed us to study AO 0235+164 with an unprecedented angular resolution
at frequencies of 1.6 and 5 GHz. We report on the sub-milliarcsecond structural
properties of the source. The 5-GHz observations led to an estimate of T_B >
5.8 x 10^{13} K for the rest-frame brightness temperature of the core, which is
the highest value measured with VSOP to date.Comment: 8 pages, 8 figures, to appear in Publ. Astron. Soc. Japa
Multiple aster formation is frequently observed in bovine oocytes retrieved from 1 day-stored ovaries
We have recently reported that multiple aster formation after IVF was one of the factors negatively affecting to developmental competence of vitrified-warmed bovine matured oocytes, and that a short-term culture of the post-warm oocytes with an inhibitor of Rho-associated coiled-coil kinase (ROCK) suppressed the multiple aster formation and improved the blastocyst yield. The present study was conducted to investigate whether increased multiple aster formation following IVF can be involved in impaired developmental competence of stored ovary-derived bovine oocytes. Oocytes retrieved from 1-day stored ovaries had lower developmental potential to Day 8 blastocysts when compared with those from fresh ovaries (37 vs 63%). Immunostaining against -tubulin 10 h post-IVF revealed that the higher incidence of multiple aster formation occurred in oocytes retrieved from stored ovaries than fresh ovaries (31 vs 15%). Treatment of post-IVM oocytes with ROCK inhibitor for 2 h significantly suppressed the incidence of multiple aster formation (10 vs 32% in control group). However, the suppressing effect of ROCK inhibitor on multiple aster formation in IVM/IVF oocytes did not improve blastocyst yield from stored ovary-derived oocytes (41 vs 37% in control group). These results suggest that higher incidence of multiple aster formation by bovine ovary storage was not responsible for decreased developmental competence of IVF oocytes.ArticleZYGOTE.24(1):115-120(2015)journal articl
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