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Preparation of multiblock copolymers via step-wise addition of l-lactide and trimethylene carbonate.
Poly(l-lactide) (PLA) is a bioderived and biodegradable polymer that has limited applications due to its hard and brittle nature. Incorporation of 1,3-trimethylene carbonate into PLA, in a block copolymer fashion, improves the mechanical properties, while retaining the biodegradability of the polymer, and broadens its range of applications. However, the preparation of 1,3-trimethylene carbonate (TMC)/l-lactide (LA) copolymers beyond diblock and triblock structures has not been reported, with explanations focusing mostly on thermodynamic reasons that impede the copolymerization of TMC after lactide. We discuss the preparation of multiblock copolymers via the ring opening polymerization (ROP) of LA and TMC, in a step-wise addition, by a ferrocene-chelating heteroscorpionate zinc complex, {[fc(PPh2)(BH[(3,5-Me)2pz]2)]Zn(μ-OCH2Ph)}2 ([(fcP,B)Zn(μ-OCH2Ph)]2, fc = 1,1'-ferrocenediyl, pz = pyrazole). The synthesis of up to pentablock copolymers, from various combinations of LA and TMC, was accomplished and the physical, thermal, and mechanical properties of the resulting copolymers evaluated
The Mass of the Compact Object in the X-Ray Binary Her X-1/HZ Her
We have obtained the first estimates of the masses of the components of the
Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the
formation of the H_gamma absorption line: mx=1.8Msun and mv=2.5Msun. These mass
estimates were made in a Roche model based on the observed radial-velocity
curve of the optical star, HZ Her. The masses for the X-ray pulsar and optical
star obtained for an LTE model lie are mx=0.85\pm0.15Msun and
mv=1.87\pm0.13Msun. These mass estimates for the components of Her X-1/HZ Her
derived from the radial-velocity curve should be considered tentative. Further
mass estimates from high-precision observations of the orbital variability of
the absorption profiles in a non-LTE model for the atmosphere of the optical
component should be made.Comment: 20 pages, 4 tables, 8 figure
How is Binary Radio-Pulsars with Black Holes Population Rich?
Using "Scenario Machine" we have carried out population synthesis of radio
pulsar with black hole binaries (BH+Psr) in context of the most wide
assumptions about star mass loss during evolution, binary stars mass ratio
distribution, kick velocity and envelope mass lost during collapse. Our purpose
is to display that under any suppositional parameters of evolution scenario
BH+Psr population have to be abundant in Galaxy. It is shown that in the all
models including models evolved by Heger et al. (2002), Woosley et al. (2002),
Heger et al. (2003) expected number of the black holes paired with radio
pulsars is sufficient enough to discover such systems within the next few
years.Comment: 8 pages, 4 figures, accepted to MNRA
Switchable Polymerization of Norbornene Derivatives by a Ferrocene‐Palladium(II) Heteroscorpionate Complex
The ferrocene-chelating heteroscorpionate complex [(fc(PPh2){BH{(3,5-Me)2pz}2})PdMe] {(fcP,B)PdMe, fc = 1,1′-ferrocenediyl, pz = pyrazole} catalyzes the addition polymerization of norbornene and norbornene derivatives upon oxidation with [AcFc][BArF] {acetyl ferrocenium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate}. In situ reduction of [(fcP,B)PdMe][BArF] in the presence of a substituted norbornene results in significant decrease of catalytic activity. Addition of one equivalent of oxidant restores the activity
The mass of the compact object in the low-mass X-ray binary 2S 0921-630
We interpret the observed radial-velocity curve of the optical star in the low-mass X-ray binary 2S 0921-630 using a Roche model, taking into account the X-ray heating of the optical star and screening of X-rays coming from the relativistic object by the accretion disk. Consequences of possible anisotropy of the X-ray radiation are considered. We obtain relations between the masses of the optical and compact (X-ray) components, m v and m x , for orbital inclinations i = 60°, 75°, and 90°. Including X-ray heating enabled us to reduce the compact object's mass by ∼0.5-1 M ⊙, compared to the case with no heating. Based on the K0III spectral type of the optical component (with a probable mass of m v ≈ 2.9 M ⊙), we concluded that m x ≈ 2.45-2.55 M ⊙ (for i = 75°-90°). If the K0III star has lost a substantial part of its mass as a result of mass exchange, as in the V404 Cyg and GRS 1905+105 systems, and its mass is m v ≈ 0.65-0.75 M ⊙, the compact object's mass is close to the standard mass of a neutron star, m x ≈ 1.4 M ⊙ (for i = 75°-90°). Thus, it is probable that the X-ray source in the 2S 0921-630 binary is an accreting neutron star. © Pleiades Publishing, Inc., 2006
The mass of the compact object in the X-ray binary her X-1/HZ her
We have obtained the first estimates of the masses of the components of the Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the formation of the H γ absorption line: m x = 1.8 M⊙ and mv = 2.5 M⊙. These mass estimates were made in a Roche model based on the observed radial-velocity curve of the optical star, HZ Her. The masses for the X-ray pulsar and optical star obtained for an LTE model lie are m x = 0.85 ± 0.15 M⊙ and mv = 1.87 ± 0.13 M⊙. These mass estimates for the components of Her X-1/HZ Her derived from the radial-velocity curve should be considered tentative. Further mass estimates from high-precision observations of the orbital variability of the absorption profiles in a non-LTE model for the atmosphere of the optical component should be made. © 2008 Pleiades Publishing, Ltd
Continuous monitoring of pulse period variations in Her X-1 using Swift/BAT
Context: Monitoring of pulse period variations in accreting binary pulsars is
an important tool to study the interaction between the magnetosphere of the
neutron star and the accretion disk. While the X-ray flux of the brightest
X-ray pulsars have been successfully monitored over many years (e.g. with
RXTE/ASM, CGRO/BATSE, Swift/BAT), the possibility to monitor their pulse timing
properties continuously has so far been very limited. Aims: In our work we show
that the Swift/BAT observations can be used to monitor coherent pulsations of
bright X-ray sources and use the Swift archival data to study one of the most
enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the
pulse period and the pulse period derivative of an X-ray pulsar, here Her X-1,
is achieved over a long time (<~ 4 yrs). We compare our observational results
with predictions of accretion theory and use them to test different aspects of
the physical model of the system. Methods: In our analysis we use the data
accumulated with Swift/BAT starting from the beginning of 2005 (shortly after
launch) until the present time. To search for pulsations and for their
subsequent analysis we used the count rate measured by the BAT detector in the
entire field of view. Results: The slope of the correlation between the locally
determined spin-up rate and the X-ray luminosity is measured for Her X-1 and
found to be in agreement with predictions of basic accretion torque theory. The
observed behaviour of the pulse period together with the previously measured
secular decrease of the system's orbital period is discussed in the frame of a
model assuming ejection of matter close to the inner boundary of the accretion
disk.Comment: 7 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
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