75 research outputs found
Constraining the variation of fundamental constants using 18cm OH lines
We describe a new technique to estimate variations in the fundamental
constants using 18cm OH absorption lines. This has the advantage that all lines
arise in the same species, allowing a clean comparison between the measured
redshifts. In conjunction with one additional transition (for example, an
HCO line), it is possible to simultaneously measure changes in ,
and . At present, only the 1665 MHz and 1667 MHz lines
have been detected at cosmological distances; we use these line redshifts in
conjunction with those of HI 21cm and mm-wave molecular absorption in a
gravitational lens at to constrain changes in the above three
parameters over the redshift range . While the constraints
are relatively weak ( 1 part in ), this is the first
simultaneous constraint on the variation of all three parameters. We also
demonstrate that either one (or more) of , and must vary with
cosmological time or there must be systematic velocity offsets between the OH,
HCO and HI absorbing clouds.Comment: 5 pages, no figures. Accepted for publication in Phys. Rev. Let
The use of OH "main" lines to constrain the variation of fundamental constants
We describe a new technique to measure variations in the fundamental
parameters and , using the sum of the frequencies of
cm-wave OH ``main'' lines. The technique is three orders of magnitude
more sensitive than that of Chengalur & Kanekar (2003), which utilised only the
four 18cm OH lines. The increase in sensitivity stems from the use of OH
``main'' lines arising from different rotational states, instead of the
frequency difference between lines from the same state. We also show that
redshifts of the main OH 18cm and 6cm lines can be combined with the redshift
of an HCO transition to measure any evolution in and . Both
18cm main lines and a number of HCO lines have already been detected in
absorption in four cosmologically distant systems; the detection of the main
6cm OH line in any of these systems would thus be sufficient to simultaneously
constrain changes in and between the absorption redshift and
today.Comment: 5 pages, no figures. MNRAS (Letters), in pres
Constraining fundamental constants of physics with quasar absorption line systems
We summarize the attempts by our group and others to derive constraints on
variations of fundamental constants over cosmic time using quasar absorption
lines. Most upper limits reside in the range 0.5-1.5x10-5 at the 3sigma level
over a redshift range of approximately 0.5-2.5 for the fine-structure constant,
alpha, the proton-to-electron mass ratio, mu, and a combination of the proton
gyromagnetic factor and the two previous constants, gp(alpha^2/mu)^nu, for only
one claimed variation of alpha. It is therefore very important to perform new
measurements to improve the sensitivity of the numerous methods to at least
<0.1x10-5 which should be possible in the next few years. Future
instrumentations on ELTs in the optical and/or ALMA, EVLA and SKA pathfinders
in the radio will undoutedly boost this field by allowing to reach much better
signal-to-noise ratios at higher spectral resolution and to perform
measurements on molecules in the ISM of high redshift galaxies.Comment: 11 pages, 3 figure
Detection of 21-cm, H2 and Deuterium absorption at z>3 along the line-of-sight to J1337+3152
We report the detection of 21-cm and H2 absorption lines in the same DLA
system (log N(HI)=21.36+-0.10) at zabs=3.17447 towards SDSSJ133724+315254
(z=3.174). We estimate the spin temperature of the gas to be, Ts~600 K,
intermediate between the expected values for cold and warm neutral media. This
suggests that the HI absorption originates from a mixture of different phases.
The total molecular fraction is low, f=10^-7, and H2 rotational level
populations are not in equilibrium. The average abundance of the alpha-elements
is, [S/H]=-1.45. N and Fe are found underabundant with respect to
alpha-elements by ~1.0 dex and ~0.5 dex respectively. Using photoionization
models we conclude that the gas is located more than 270 kpc away from the QSO.
While the position of 21-cm absorption line coincides with the H2 velocity
profile, their centroid are shifted by 2.7+-1.0 km/s from each other. However,
the position of the strongest metal absorption component matches the position
of the 21-cm absorption line within 0.5 km/s. From this, we constrain the
variation of the combination of fundamental constants x=alpha^2 Gp/mu, Delta
x/x=-(1.7+-1.7)x10^-6. This system is unique as we can at the same time have an
independent constrain on mu using H2 lines. However only Werner band absorption
lines are seen and the range of sensitivity coefficients is too narrow to
provide a stringent constraint: Delta mu/mu <= 4.0x10^-4. The VLT/UVES spectrum
reveals another DLA at zabs=3.16768 with log N(HI)=20.41+-0.15 and low
metallicity, [Si/H]=-2.68+-0.11. We derive log N(DI)/N(HI)=-(4.93+-0.15) in
this system. This is a factor of two smaller than the value expected from the
best fitted value of Omega_b from the WMAP 5 yr data. This confirms the
presence of astration of deuterium even at very low metallicity. [abridged]Comment: 14 pages, 11 figures, 4 tables, accepted for publication in MNRA
Ferroelectric Phase Transitions in Films with Depletion Charge
We consider ferroelectric phase transitions in both short-circuited and
biased ferroelectric-semiconductor films with a space (depletion) charge which
leads to some unusual behavior. It is shown that in the presence of the charge
the polarization separates into `switchable' and `non-switchable' parts. The
electric field, appearing due to the space charge, does not wash out the phase
transition, which remains second order but takes place at somewhat reduced
temperature. At the same time, it leads to a suppression of the
ferroelectricity in a near-electrode layer. This conclusion is valid for
materials with both second and first order phase transitions in pure bulk
samples. Influence of the depletion charge on thermodynamic coercive field
reduces mainly to the lowering of the phase transition temperature, and its
effect is negligible. The depletion charge can, however, facilitate an
appearance of the domain structure which would be detrimental for device
performance (fatigue). We discuss some issues of conceptual character, which
are generally known but were overlooked in previous works. The present results
have general implications for small systems with depletion charge.Comment: 11 pages, REVTeX 3.1, five eps-figures included in the text. Minor
clarifications in the text. To appear in Phys. Rev. B 61, Apr 1 (2000
Helium and Deuterium Abundances as a Test for the Time Variation of the Fine Structure Constant and the Higgs Vacuum Expectation Value
We use the semi-analytic method of \citet{Esma91} to calculate the abundances
of Helium and Deuterium produced during Big Bang nucleosynthesis assuming the
fine structure constant and the Higgs vacuum expectation value may vary in
time. We analyze the dependence on the fundamental constants of the nucleon
mass, nuclear binding energies and cross sections involved in the calculation
of the abundances. Unlike previous works, we do not assume the chiral limit of
QCD. Rather, we take into account the quark masses and consider the one-pion
exchange potential, within perturbation theory, for the proton-neutron
scattering. However, we do not consider the time variation of the strong
interactions scale but attribute the changes in the quark masses to the
temporal variation of the Higgs vacuum expectation value. Using the
observational data of the helium and deuterium, we put constraints on the
variation of the fundamental constants between the time of nucleosynthesis and
the present time.Comment: 27 pages, 1 figure, replaced to match published version, new
references adde
Laser frequency comb techniques for precise astronomical spectroscopy
Precise astronomical spectroscopic analyses routinely assume that individual
pixels in charge-coupled devices (CCDs) have uniform sensitivity to photons.
Intra-pixel sensitivity (IPS) variations may already cause small systematic
errors in, for example, studies of extra-solar planets via stellar radial
velocities and cosmological variability in fundamental constants via quasar
spectroscopy, but future experiments requiring velocity precisions approaching
~1 cm/s will be more strongly affected. Laser frequency combs have been shown
to provide highly precise wavelength calibration for astronomical
spectrographs, but here we show that they can also be used to measure IPS
variations in astronomical CCDs in situ. We successfully tested a laser
frequency comb system on the Ultra-High Resolution Facility spectrograph at the
Anglo-Australian Telescope. By modelling the 2-dimensional comb signal recorded
in a single CCD exposure, we find that the average IPS deviates by <8 per cent
if it is assumed to vary symmetrically about the pixel centre. We also
demonstrate that series of comb exposures with absolutely known offsets between
them can yield tighter constraints on symmetric IPS variations from ~100
pixels. We discuss measurement of asymmetric IPS variations and absolute
wavelength calibration of astronomical spectrographs and CCDs using frequency
combs.Comment: 11 pages, 7 figures. Accepted for publication in MNRA
Этиология фатальной внебольничной пневмонии у взрослых
Pathogens of fatal community-acquired pneumonia have been studied in 63 adult patients from Smolensk city and Yartsevo town of Smolensk region using autopsy material. Pneumonia was confirmed during histological exanimation in 57 (90.5 %) of the patients. Bacterial pathogens were identified in 91.2 % of the confirmed pneumonias, among them one type of pathogens was yielded in 75% and bacterial associations were identified in 25 % of the cases. The most prevalent pathogens were K. pneumoniae, S. aureus, S. pneumoniae and H. influenzae (31.4, 28.6, 12.9 and 11.4 % of all the identified strains, respectively). Comorbidity (alcohol abuse, chronic heart disease, chronic respiratory disease) was an important factor predetermining pathogen spectrum and poor outcome of the disease.Изучена структура возбудителей фатальной внебольничной пневмонии (ВП) у 63 взрослых пациентов в городах Смоленске и Ярцеве (Смоленская обл.). Гистологически подтвержденная пневмония имела место у 57 (90,5 %) пациентов. Материалом для исследования служил аутопсийный материал, полученный у пациентов, умерших от ВП. Бактериальная этиология ВП была установлена в 91,2 % случаев при гистологически подтвержденной пневмонии, при этом монокультура выделена в 75,0 %, микробные ассоциации – в 25,0 % случаев. Преобладающими возбудителями ВП были K. pneumoniae, S. aureus, S. pneumoniae и H. influenzae (31,4; 28,6; 12,9 и 11,4 % от всех выделенных штаммов соответственно). Важным фактором, определяющим структуру возбудителей и неблагоприятный исход заболевания, являлось наличие и характер сопутствующей патологии (алкоголизм, хронические заболевания сердечно-сосудистой и бронхолегочной системы)
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