406 research outputs found
The Parsec-Scale Jets of the TeV Blazars H 1426+428, 1ES 1959+650, and PKS 2155-304: 2001-2004
We present Very Long Baseline Array (VLBA) observations of the TeV blazars H
1426+428, 1ES 1959+650, and PKS 2155-304 obtained during the years 2001 through
2004. We observed H 1426+428 at four epochs at 8 GHz, and found that its
parsec-scale structure consisted of a ~17 mJy core and a single ~3 mJy jet
component with an apparent speed of 2.09 +/- 0.53c. The blazar 1ES 1959+650 was
observed at three epochs at frequencies of 15 and 22 GHz. Spectral index
information from these dual-frequency observations was used to definitively
identify the core of the parsec-scale structure. PKS 2155-304 was observed at a
single epoch at 15 GHz with dual-circular polarization, and we present the
first VLBI polarimetry image of this source. For 1ES 1959+650 and PKS 2155-304,
the current observations are combined with the VLBA observations from our
earlier paper to yield improved apparent speed measurements for these sources
with greatly reduced measurement errors. The new apparent speed measured for
component C2 in 1ES 1959+650 is 0.00 +/- 0.04c (stationary), and the new
apparent speed measured for component C1 in PKS 2155-304 is 0.93 +/- 0.31c. We
combine the new apparent speed measurements from this paper with the apparent
speeds measured in TeV blazar jets from our earlier papers to form a current
set of apparent speed measurements in TeV HBLs. The mean peak apparent pattern
speed in the jets of the TeV HBLs is about 1c. We conclude the paper with a
detailed discussion of the interpretation of the collected VLBA data on TeV
blazars in the context of current theoretical models for the parsec-scale
structure of TeV blazar jets.Comment: 16 pages, Astrophysical Journal, in pres
Heat capacity and magnetoresistance in Dy(Co,Si)2 compounds
Magnetocaloric effect and magnetoresistance have been studied in
Dy(Co1-xSix)2 [x=0, 0.075 and 0.15] compounds. Magnetocaloric effect has been
calculated in terms of adiabatic temperatue change (Delta Tad) as well as
isothermal magnetic entropy change (Delta SM) using the heat capacity data. The
maximum values of DeltaSM and DeltaTad for DyCo2 are found to be 11.4 JKg-1K-1
and 5.4 K, respectively. Both DSM and DTad decrease with Si concentration,
reaching a value of 5.4 JKg-1K-1 and 3 K, respectively for x=0.15. The maximum
magnetoresistance is found to about 32% in DyCo2, which decreases with increase
in Si. These variations are explained on the basis of itinerant electron
metamagnetism occurring in these compounds.Comment: Total 8 pages of text and figure
Heat capacity and magnetocaloric effect in polycrystalline Gd1-xSmxMn2Si2
We report the magnetocaloric effect in terms of isothermal magnetic entropy
change as well as adiabatic temperature change, calculated using the heat
capacity data. Using the zero field heat capacity data, the magnetic
contribution to the heat capacity has been estimated. The variations in the
magnetocaloric behavior have been explained on the basis of the magnetic
structure of these compounds. The refrigerant capacities have also been
calculated for these compounds
Multiple magnetic transitions and magnetocaloric effect in Gd1-xSmxMn2Ge2 compounds
Magnetic and magnetocaloric properties of polycrystalline samples of
Gd1-xSmxMn2Ge2 have been studied. All the compounds except GdMn2Ge2 show
re-entrant ferromagnetic behavior. Multiple magnetic transitions observed in
these compounds are explained on the basis of the temperature dependences of
the exchange strengths of the rare earth and Mn sublattices. Magnetocaloric
effect is found to be positive at the re-entrant ferromagnetic transition,
whereas it is negative at the antiferro-ferromagnetic transition. In SmMn2Ge2,
the magnetic entropy change associated with the re-entrant transition is found
to decrease with field, which is attributed to the admixture effect of the
crystal field levels. The isothermal magnetic entropy change is found to
decrease with increase in Sm concentration.Comment:
Pseudotumor cerebri and ciprofloxacin: a case report
INTRODUCTION: We present a case of ciprofloxacin-associated pseudotumor cerebri in a 22-year-old African American woman. Withdrawal of ciprofloxacin in our patient resulted in complete resolution of ciprofloxacin-associated pseudotumor, as evidenced by a normal neuro-ophthalmic examination and a cerebrospinal fluid opening pressure of 140 mmH20. CASE PRESENTATION: A 22-year-old African American woman presented with a headache of two weeks duration, visual blurring and horizontal diplopia after starting ciprofloxacin for pyelonephritis. An ophthalmic examination revealed that she had left eye esotropia, and a picture of the fundus demonstrated bilateral disc swelling without spontaneous venous pulsations. Magnetic resonance imaging of the brain and a magnetic resonance venogram were normal. A diagnostic lumbar puncture demonstrated an elevated opening pressure of 380mmH2O in a supine position. Laboratory examinations, including a cerebrospinal fluid exam, were unremarkable. CONCLUSION: ciprofloxacin-associated pseudotumor can cause chronic disabling headache and visual complications. Therapy is sub-optimal, often symptomatic, insufficient and complicated by side effects. When ciprofloxacin-associated pseudotumor presents in an atypical population, an inciting agent must be suspected because prompt withdrawal of the agent may lead to complete resolution of symptoms and prevent recurrence of similar episodes
Productive and reproductive performance of local cows under farmer’s management in central Tigray, Ethiopia
The study was conducted on 408 indigenous cows maintained under farmer’s management in eight districts of central Tigray, Ethiopia. A total of 208 small-scale dairy farm owners were randomly selected and interviewed with structured questionnaire to obtain information on the productive and reproductive performance of indigenous cows. The results of the study showed that the mean age at first calving (AFC) was 43.3 ±2.7 months, number of services per conception (NSC) was 2.7±0.5, days open (DO) was 201.47±61.21 days, calving interval (CI) was 468.33±71.42 days, lactation length (LL) was 206.17±32.33 days, lactation milk yield (LMY) was 414.65±53.69 litres for indigenous cows. The estimated value for productive and reproductive traits had higher than normal range in indigenous cows. This calls for a planned technical and institutional intervention for improved support services for appropriate breeding programs, improved cows and adequate veterinary health services.
Key words: Productive and Reproductive Performance, Local Cows
Spatially Resolved Galaxy Star Formation and its Environmental Dependence I
We use the photometric information contained in individual pixels of 44,964
(0.019<z<0.125 and -23.5<M_r<-20.5) galaxies in the Fourth Data Release (DR4)
of the Sloan Digital Sky Survey to investigate the effects of environment on
galaxy star formation (SF). We use the pixel-z technique, which combines
stellar population synthesis models with photometric redshift template fitting
on the scale of individual pixels in galaxy images. Spectral energy
distributions are constructed, sampling a wide range of properties such as age,
star formation rate (SFR), dust obscuration and metallicity. By summing the
SFRs in the pixels, we demonstrate that the distribution of total galaxy SFR
shifts to lower values as the local density of surrounding galaxies increases,
as found in other studies. The effect is most prominent in the galaxies with
the highest star formation, and we see the break in the SFR-density relation at
a local galaxy density of (Mpc/h). Since our method
allows us to spatially resolve the SF distribution within galaxies, we can
calculate the mean SFR of each galaxy as a function of radius. We find that on
average the mean SFR is dominated by SF in the central regions of galaxies, and
that the trend for suppression of SFR in high density environments is driven by
a reduction in this nuclear SF. We also find that the mean SFR in the outskirts
is largely independent of environmental effects. This trend in the mean SFR is
shared by galaxies which are highly star forming, while those which are weakly
star forming show no statistically significant correlation between their
environment and the mean SFR at any radius.Comment: 37 pages, 11 figures. Referee's comments included and matches version
accepted for publication in the Astrophysical Journal. For high resolution
figures, see http://www.phyast.pitt.edu/~welikala/pixelz/paper1
Exact Distributions for Stochastic Gene Expression Models with Bursting and Feedback
Stochasticity in gene expression can give rise to fluctuations in protein
levels and lead to phenotypic variation across a population of genetically
identical cells. Recent experiments indicate that bursting and feedback
mechanisms play important roles in controlling noise in gene expression and
phenotypic variation. A quantitative understanding of the impact of these
factors requires analysis of the corresponding stochastic models. However, for
stochastic models of gene expression with feedback and bursting, exact
analytical results for protein distributions have not been obtained so far.
Here, we analyze a model of gene expression with bursting and feedback
regulation and obtain exact results for the corresponding protein steady-state
distribution. The results obtained provide new insights into the role of
bursting and feedback in noise regulation and optimization. Furthermore, for a
specific choice of parameters, the system studied maps on to a two-state
biochemical switch driven by a bursty input noise source. The analytical
results derived thus provide quantitative insights into diverse cellular
processes involving noise in gene expression and biochemical switching.Comment: Accepted in Phys. Rev. Let
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