228 research outputs found
Refractive indices, density and order parameter of two liquid crystals HBT and OBT
The temperature variation of refractive indices (ne ne), birefringence (δn), density (ρ) and order parameter (S) of two liquid crystals, namely, N-(p-hexyloxybenzylidene)-p-toluidine (HBT) and N-(p-octyloxybenzylidene)-p-toluidine (OBT) are reported in the smectic (SA in OBT and SB in HBT), nematic and isotropic phases. For accurate measurement of δn, the wedge method was modified to eliminate the need to measure the wedge angle. Density measurements indicate that the smectic-nematic and nematic-isotropic phase transitions in these materials are of first order. Using refractive index values and the density data, the internal field factors (γe, γo), the ratio of principal polarizabilities f(=αeαo) and the order parameter, S, have been evaluated and their temperature dependence discussed in the light of molecular geometry. The order parameter has been determined using the isotropic internal field model (Vuks approach) and the anisotropic internal field model (Neugebauer's approach). The S values determined using these two models agree in the nematic phase but differ considerably in the smectic phase
Refractive indices, density and order parameter of some technologically important liquid crystalline mixtures
Temperature variation of the refractive indices, birefringence, density and order parameter of liquid crystalline mixtures E7, E8, N10 and PCH-1132 are reported. The birefringence of PCH-1132 is found to be abnormally low compared to other mixtures
Refractive indices, density and order parameter of some liquid crystals
The temperature variation of the refractive indices (no, ne) and density are reported for two liquid crystals. The order parameter is evaluated by both Vuks' and Neugebauer's approaches. The possible sources of error in evaluating the order parameter from refractive indices measurements have been discussed. The contradictory behavior of Δ n and ΔX during the nematic-smectic B phase transition of HBT has been explained on the basis of polydomain formation and the order parameter in the SB phase is estimated. The order parameter of two liquid crystals, HBT and OBT, is also evaluated by NMR measurements, confirming the polydomain formation in the SB phase of HBT
From the Heart of The Ghoul: C and N Abundances in the Corona of Algol B
Chandra Low Energy Transmission Grating Spectrograph observations of Algol
have been used to determine the abundances of C and N in the secondary star for
the first time. The analysis was performed relative to similar observations of
an adopted "standard" star HR 1099. It is demonstrated that HR 1099 and Algol
are coronal twins in many respects and that their X-ray spectra are very
similar in nearly all details, except for the observed strengths of C and N
lines. The H-like transitions of C and N in the coronae of Algol and HR 1099
demonstrate that the surface abundances of Algol B have been strongly modified
by CN-processing, as shown earlier by Schmitt & Ness (2002). It is found that N
is enhanced in Algol B by a factor of 3 compared to HR 1099. No C lines are
detected in the Algol spectrum, indicating a C depletion relative to HR 1099 by
a factor of 10 or more. These C and N abundances indicate that Algol B must
have lost at least half of its initial mass, and are consistent with
predictions of evolutionary models that include non-conservative mass transfer
and angular momentum loss through magnetic activity. Little or no dredge-up of
material subjected to CN-processing has occurred on the subgiant component of
HR 1099. It is concluded that Fe is very likely depleted in the coronae of both
Algol and HR 1099 relative to their photospheres by 0.5 dex, and C, N and O by
0.3 dex. Instead, Ne is enhanced by up to 0.5 dex.Comment: 17 pages, 4 figures, ApJ accepte
Wavelength-resolved Reverberation Mapping of quasar CTSC30.10: Dissecting MgII and FeII emission regions
We present the results of the reverberation monitoring aimed at MgII broad
line and FeII pseudocontinuum for the luminous quasar CTS C30.10 (z = 0.90052)
with the Southern African Large Telescope covering the years 2012-2021. We
aimed at disentangling the MgII and UV FeII variability and the first
measurement of UV FeII time delay for a distant quasar. We used several methods
for time-delay measurements and determined both FeII and MgII time delays as
well as performed a wavelength-resolved time delay study for a combination of
MgII and FeII in the 2700 - 2900 \AA restframe wavelength range. We obtain the
time delay for MgII of days in the rest frame, while
for FeII we have two possible solutions of days and
in the rest frame. Combining this result with the old
measurement of FeII UV time delay for NGC 5548 we discuss for the first time
the radius-luminosity relation for UV FeII with the slope consistent with
within uncertainties. Since FeII time delay has a shorter time-delay component
but lines are narrower than MgII, we propose that the line delay measurement is
biased towards the BLR part facing the observer, with the bulk of the Fe II
emission may arise from the more distant BLR region, one that is shielded from
the observer.Comment: 22 pages, 19 Figures, 6 Tables, Submitted to Astronomy and
Astrophysics, Comments are welcom
Wavelength-resolved reverberation mapping of intermediate redshift quasars HE 0413-4031 and HE 0435-4312: Dissecting Mg II, optical Fe II, and UV Fe II emission regions
We present the wavelength-resolved reverberation mapping (RM) of combined
MgII and UV FeII broad-line emissions for two intermediate redshifts
(z1), luminous quasars - HE 0413-4031 and HE 0435-4312, monitored by the
SALT and 1-m class telescopes between 2012-2022. Through this technique, we aim
to disentangle the Mg II and FeII emission regions and to build a
radius-luminosity relation for UV FeII emission, which has so far remained
unconstrained. Several methodologies have been applied to constrain the time
delays for total MgII and FeII emissions. In addition, this technique is
performed to quantify the inflow or outflow of broad-line region gas around the
supermassive black hole and to disentangle the emission/emitting regions from
lines produced in proximity to each other. The mean total FeII time delay is
nearly equal to the mean total Mg II time delay for HE 0435-4312 suggesting a
co-spatiality of their emissions. However, in HE 0413-4031, the mean FeII time
delay is found to be longer than the mean MgII time delay, suggesting that FeII
is produced at longer distances from the black hole. The UV Fe II R-L relation
is updated with these two quasars and compared with the optical FeII relation,
which suggests that the optical FeII region is located further than the UV FeII
by a factor of 1.7-1.9 i.e. . We
detected a weak pattern in the time delay vs. wavelength relation, suggesting
that the MgII broad-line originates a bit closer to the SMBH than the UV FeII,
however, the difference is not very significant. Comparison of MgII, UV, and
optical FeII R-L relations suggests that the difference may be larger for
lower-luminosity sources, possibly with the MgII emission originating further
from the SMBH. In the future, more RM data will be acquired to put better
constraints on these trends, in particular the UV FeII R-L relation.Comment: 24 pages, 16 figures, 5 tables, Accepted for publication in A&A, in
Pres
Hubble Space Telescope Spectroscopy of V471 Tauri: Oversized K Star, Paradoxical White Dwarf
We have used the GHRS onboard the HST to obtain Lyman-alpha spectra of the
hot white-dwarf (WD) component of the short-period eclipsing DA+dK2
pre-cataclysmic binary V471 Tauri, a member of the Hyades star cluster. Radial
velocities of the WD, combined with ground-based measurements of the dK
velocities, eclipse timings, and a determination of the dK star's rotational
velocity, yield dynamical masses for the components of M(WD)=0.84 and
M(dK)=0.93 Msun. Model-atmosphere fitting of the Ly-alpha profile provides the
effective temperature (34,500 K) and surface gravity (log g=8.3) of the WD. The
radius of the dK component is 18% larger than that of a normal Hyades dwarf of
the same mass. This expansion is attributed to the extensive coverage of the
surface by starspots, causing the star to expand in response. The WD radius,
determined from a radiometric analysis and from eclipse ingress timings, is
0.0107 Rsun. The position of the star in the M-R plane is in full accord with
theory for a degenerate CO WD. The high temperature and mass of the WD present
an evolutionary paradox: the WD is the most massive known in the Hyades, but
also the hottest and youngest. We suggest that the explanation is that the WD
is indeed very young, and is descended from a triple consisting of a blue
straggler and a more-distant dK companion. We estimate that the common-envelope
efficiency parameter, alpha_CE, was of order 0.3-1.0, in good agreement with
recent hydrodynamical simulations.Comment: Astrophysical Journal, in press. 34 text pages, 8 figure
Living arrangements and place of death of older people with cancer in England and Wales: a record linkage study
The main objectives of the study were to (1) see whether the household circumstances of people aged 50 years and over with cancer, and trends in these, differ from those of the rest of the population and (2) whether living arrangements and presence and health status of a primary coresident are associated with place of death among older people dying of cancer and those dying from other causes. The design included prospective record linkage study of people aged 50 years and over included in a 1% sample of the population of England and Wales (the Office for National Statistics Longitudinal Study). The main outcome measures comprised family and household type, and death at home. The household circumstances of older people with cancer were very similar to those of the rest of the population of the same age and both showed a large increase in living alone, and decrease in living with relatives, between 1981 and 1991. The primary coresident of cancer sufferers who did not live alone was in most cases a spouse, with much smaller proportions living with a child, sibling or other person. In all, 30% of spouse, and 23% of other, primary coresidents had a limiting long-term illness. Compared with people who lived alone in 1991, odds of a home death among those dying of cancer between 1991 and 1995 were highest for those who lived with a spouse who had no limiting long-term illness (odds ratio (OR) 2.52, 95% confidence interval (CI) 2.15-2.97) and raised for those living with a spouse with a long-term illness (OR 2.14, CI 1.79-2.56) and those living with someone else who was free of long-term illness (OR 2.13, CI 1.69-2.68). Higher socioeconomic status, both individual and area, was positively associated with increased chance of a home death, while older age reduced the chance of dying at home. The changing living arrangements of older people have important implications for planning and provision of care and treatment for cancer sufferers
Protection of Melanized Cryptococcus neoformans from Lethal Dose Gamma Irradiation Involves Changes in Melanin's Chemical Structure and Paramagnetism
Certain fungi thrive in highly radioactive environments including the defunct Chernobyl nuclear reactor. Cryptococcus neoformans (C. neoformans), which uses L-3,4-dihydroxyphenylalanine (L-DOPA) to produce melanin, was used here to investigate how gamma radiation under aqueous aerobic conditions affects the properties of melanin, with the aim of gaining insight into its radioprotective role. Exposure of melanized fungal cell in aqueous suspensions to doses of γ-radiation capable of killing 50 to 80% of the cells did not lead to a detectable loss of melanin integrity according to EPR spectra of melanin radicals. Moreover, upon UV-visible (Xe-lamp) illumination of melanized cells, the increase in radical population was unchanged after γ-irradiation. Gamma-irradiation of frozen cell suspensions and storage of samples for several days at 77 K however, produced melanin modification noted by a reduced radical population and reduced photoresponse. More direct evidence for structural modification of melanin came from the detection of soluble products with absorbance maxima near 260 nm in supernatants collected after γ-irradiation of cells and cell-free melanin. These products, which include thiobarbituric acid (TBA)-reactive aldehydes, were also generated by Fenton reagent treatment of cells and cell-free melanin. In an assay of melanin integrity based on the metal (Bi+3) binding capacity of cells, no detectable loss in binding was detected after γ-irradiation. Our results show that melanin in C. neoformans cells is susceptible to some damage by hydroxyl radical formed in lethal radioactive aqueous environments and serves a protective role in melanized fungi that involves sacrificial breakdown
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