40 research outputs found
Color Effects Associated with the 1999 Microlensing Brightness Peaks in Gravitationally Lensed Quasar Q2237+0305
Photometry of the Q2237+0305gravitational lens in VRI spectral bands with the
1.5-m telescope of the high-altitude Maidanak observatory in 1995-2000 is
presented. Monitoring of Q2237+0305 in July-October 2000, made at nearly daily
basis, did not reveal rapid (night-to-night and intranight) variations of
brightness of the components during this time period. Rather slow changes of
magnitudes of the components were observed, such as 0.08 mag fading of B and C
components and 0.05 mag brightening of D in R band during July 23 - October 7,
2000. By good luck three nights in 1999 were almost at the time of the strong
brightness peak of image C, and approximately in the middle of the ascending
slope of the image A brightness peak. The C component was the most blue one in
the system in 1998 and 1999, having changed its (V-I) color from 0.56 mag to
0.12 mag since August 1997, while its brightness increased almost 1.2 mag
during this time period. The A component behaved similarly between August 1998
and August 2000, having become 0.47 mag brighter in R, and at the same time,
0.15 mag bluer. A correlation between the color variations and variations of
magnitudes of the components is demonstrated to be significant and reaches
0.75, with a regression line slope of 0.33. A color (V-I) vrs color (V-R) plot
shows the components settled in a cluster, stretched along a line with a slope
of 1.31. Both slopes are noticeably smaller than those expected if a standard
galactic interstellar reddening law were responsible for the differences
between the colors of images and their variations over time. We attribute the
brightness and color changes to microlensing of the quasar's structure, which
we conclude is more compact at shorter wavelengths, as predicted by most quasar
models featuring an energizing central source.Comment: 14 pages, 7 figures, LaTeX, submitted to A&
Microlensing in the double quasar SBS1520+530
We present the results of a monitoring campaign of the double quasar
SBS1520+530 at Maidanak observatory from April 2003 to August 2004. We obtained
light curves in V and R filters that show small-amplitude \Delta m~0.1 mag
intrinsic variations of the quasar on time scales of about 100 days. The data
set is consistent with the previously determined time delay of \Delta
t=(130+-3) days by Burud et al. (2002). We find that the time delay corrected
magnitude difference between the quasar images is now larger by (0.14+-0.03)
mag than during the observations by Burud et al. (2002). This confirms the
presence of gravitational microlensing variations in this system.Comment: 6 pages, 7 figures. Accepted for publication in A&
Measuring anisotropic scattering in the cuprates
A simple model of anisotropic scattering in a quasi two-dimensional metal is
studied. Its simplicity allows an analytic calculation of transport properties
using the Boltzmann equation and relaxation time approximation. We argue that
the c-axis magnetoresistance provides the key test of this model of transport.
We compare this model with experiments on overdoped Tl-2201 and find reasonable
agreement using only weak scattering anisotropy. We argue that optimally doped
Tl-2201 should show strong angular-dependent magnetoresistance within this
model and would provide a robust way of determining the in-plane scattering
anisotropy in the cuprates.Comment: 12 pages, 8 figures, typset in REVTeX 4. Version 2; added references
and corrected typo
Band-structure trend in hole-doped cuprates and correlation with Tcmax
By calculation and analysis of the bare conduction bands in a large number of
hole-doped high-temperature superconductors, we have identified the energy of
the so-called axial-orbital as the essential, material-dependent parameter. It
is uniquely related to the range of the intra-layer hopping. It controls the Cu
4s-character, influences the perpendicular hopping, and correlates with the
observed Tc at optimal doping. We explain its dependence on chemical
composition and structure, and present a generic tight-binding model.Comment: 5 pages, Latex, 5 eps figure
Time delay of SBS 0909+532
The time delays between the components of a lensed quasar are basic tools to
analyze the expansion of the Universe and the structure of the main lens galaxy
halo. In this paper, we focus on the variability and time delay of the double
system SBS 0909+532A,B as well as the time behaviour of the field stars. We use
VR optical observations of SBS 0909+532A,B and the field stars in 2003. The
frames were taken at Calar Alto, Maidanak and Wise observatories, and the VR
light curves of the field stars and quasar components are derived from aperture
and point-spread function fitting methods. We measure the R-band time delay of
the system from the chi-square and dispersion techniques and 1000 synthetic
light curves based on the observed records. One nearby field star (SBS
0909+532c) is found to be variable, and the other two nearby field stars are
non-variable sources. With respect to the quasar components, the R-band records
seem more reliable and are more densely populated than the V-band ones. The
observed R-band fluctuations permit a pre-conditioned measurement of the time
delay. From the chi-square minimization, if we assume that the quasar emission
is observed first in B and afterwards in A (in agreement with basic
observations of the system and the corresponding predictions), we obtain a
delay of - 45 (+ 1)/(- 11) days (95% confidence interval). The dispersion
technique leads to a similar delay range. A by-product of the analysis is the
determination of a totally corrected flux ratio in the R band (corrected by the
time delay and the contamination due to the galaxy light). Our 95% measurement
of this ratio (0.575 +/- 0.014 mag) is in excellent agreement with previous
results from contaminated fluxes at the same time of observation.Comment: 26 pages, 15 figures, Astronomy and Astrophysics (see also
http://www.astro.ulg.ac.be/RPub/Colloques/JENAM/proceedings/proceedings.html
- Quasars Section
Correlation functions for a two-dimensional electron system with bosonic interactions and a square Fermi surface
We calculate zero-temperature correlation functions for a model of 2D
interacting electrons with short-range interactions and a square Fermi surface.
The model was arrived at by mapping electronic states near a square Fermi
surface with Hubbard-like interactions onto one-dimensional quantum chains,
retaining terms which can be written in terms of bosonic density operators.
Interactions between orthogonal chains, corresponding to orthogonal faces of
the square Fermi surface, are neglected. The correlation functions become sums
of Luttinger-type correlation functions due to the bosonic model. However, the
correlation function exponents differ in form from those of the Luttinger
model. As a consequence, the simple scaling relations found to exist between
the Luttinger model exponents, do not carry over to the leading exponents of
our model. We find that for repulsive effective interactions, charge-density
wave/spin-density wave instabilities are dominant. We do not consider d-wave
instabilities here.Comment: 12 pages, no figures; to be published in Physical Review
PG 1115+080: variations of the A2/A1 flux ratio and new values of the time delays
We report the results of our multicolor observations of PG 1115+080 with the
1.5-m telescope of the Maidanak Observatory (Uzbekistan, Central Asia) in
2001-2006. Monitoring data in filter R spanning the 2004, 2005 and 2006 seasons
(76 data points) demonstrate distinct brightness variations of the source
quasar with the total amplitude of almost 0.4 mag. Our R light curves have
shown image C leading B by 16.4d and image (A1+A2) by 12d that is inconsistent
with the previous estimates obtained by Schechter et al. in 1997 - 24.7d
between B and C and 9.4d between (A1+A2) and C. The new values of time delays
in PG 1115+080 must result in larger values for the Hubble constant, thus
reducing difference between its estimates taken from the gravitational lenses
and with other methods. Also, we analyzed variability of the A2/A1 flux ratio,
as well as color changes in the archetypal "fold" lens PG 1115+080. We found
the A1/A2 flux ratio to grow during 2001-2006 and to be larger at longer
wavelengths. In particular, the A2/A1 flux ratio reached 0.85 in filter I in
2006. We also present evidence that both the A1 and A2 images might have
undergone microlensing during 2001-2006, with the descending phase for A1 and
initial phase for A2. We find that the A2/A1 flux ratio anomaly in PG 1115 can
be well explained both by microlensing and by finite distance of the source
quasar from the caustic fold.Comment: 14 pages, 7 figures, 8 tables, Accepted for publication in MNRA
Hypertension control during the COVID-19 pandemic: results of the MMM2021 in Russia
Repetitive quarantines and social restrictions during the coronavirus disease 2019 (COVID-19) pandemic have negatively affected the population health in general, and the control of hypertension (HTN) in particular.Aim. To evaluate the control of HTN in the Russian population during the COVID-19 period based on the results of screening for HTN May Measurement Month 2021 (MMM2021).Material and methods. During May-August 2021, 2491 participants from 11 Russian regions took part in the screening. Participation was voluntary without restrictions on sex. All participants were over 18 years of age. During the screening, blood pressure (BP) was measured three times using automatic and mechanical BP monitors. In addition, a questionnaire was filled out on behavioral risk factors, comorbidities and therapy. HTN was diagnosed with systolic BP ≥140 mmHg and/ or diastolic blood pressure ≥90 mmHg and/or taking antihypertensive therapy. The questionnaire included questions about prior COVID-19, vaccinations and their impact on the intake of antihypertensive drugs.Results. The analysis included data from 2461 respondents aged 18 to 92, of which 963 were men (39,1%). The proportion of hypertensive patients was 41,0%, while among them 59,0% took antihypertensives and 30,9% were effectively treated. In comparison with pre-pandemic period according to MMM2018-2019, the higher proportion of HTN patients in the Russian sample was revealed during MMM2021 (41,0% vs 31,3%, p<0,001) with a comparable proportion of patients receiving antihypertensive therapy (60,7% vs 59,0%, p=0,05) and treatment efficacy (28,7% vs 30,9%, p=0,36). Monotherapy was received in 44,7% of cases, while dual and triple combination therapy — in 30,9% and 14,1%, respectively. The majority of respondents (~90%) did not adjust their antihypertensive therapy during the COVID-19 pandemic.Conclusion. According to HTN screening in Russia, there is persistent ineffective control of HTN, which may be due to both the worsening pattern of behavioral risk factors, limited access to healthcare during COVID-19, and the inertia of physicians and low adherence of patients due to the asymptomatic HTN course in the majority