2,481 research outputs found
On knotted streamtubes in incompressible hydrodynamical flow and a restricted conserved quantity
For certain families of fluid flow, a new conserved quantity --
stream-helicity -- has been established.Using examples of linked and knotted
streamtubes, it has been shown that stream-helicity does, in certain cases,
entertain itself with a very precise topological meaning viz, measure of the
degree of knottedness or linkage of streamtubes.As a consequence,
stream-helicity emerges as a robust topological invariant.Comment: This extended version is the basically a more clarified version of
the previous submission physics/0611166v
Analysis and Modeling Experiment Performance Parameters of Routing Protocols in MANETs and VANETs
In this paper, a framework for experimental parameters in which Packet
Delivery Ratio (PDR), effect of link duration over End-to-End Delay (E2ED) and
Normalized Routing Overhead (NRO) in terms of control packets is analyzed and
modeled for Mobile Ad-Hoc NETworks (MANETs) and Vehicular Ad-Hoc NETworks
(VANETs) with the assumption that nodes (vehicles) are sparsely moving in two
different road. Moreover, this paper contributes the performance comparison of
one Proactive Routing Protocol; Destination Sequenced Distance vector (DSDV)
and two reactive protocols; DYnamic Source Routing (DSR) and DYnamic MANET
On-Demand (DYMO). A novel contribution of this work is enhancements in default
versions of selected routing protocols. Three performance parameters; PDR, E2ED
and NRO with varying scalabilities are measured to analyze the performance of
selected routing protocols with their original and enhanced versions. From
extensive simulations, it is observed that DSR outperforms among all three
protocols at the cost of delay. NS-2 simulator is used for simulation with
TwoRayGround propagation model to evaluate analytical results
Energy Injection in GRB Afterglow Models
We extend the standard fireball model, widely used to interpret gamma-ray
burst (GRB) afterglow light curves, to include energy injections, and apply the
model to the afterglow light curves of GRB 990510, GRB 000301C and GRB 010222.
We show that discrete energy injections can cause temporal variations in the
optical light curves and present fits to the light curves of GRB 000301C as an
example. A continuous injection may be required to interpret other bursts such
as GRB 010222. The extended model accounts reasonably well for the observations
in all bands ranging from X-rays to radio wavelengths. In some cases, the radio
light curves indicate that additional model ingredients may be needed.Comment: Accepted for publication in the Astrophysical Journa
Emission from Bow Shocks of Beamed Gamma-Ray Bursts
Beamed gamma-ray burst (GRB) sources produce a bow shock in their gaseous
environment. The emitted flux from this bow shock may dominate over the direct
emission from the jet for lines of sight which are outside the angular radius
of the jet emission, theta. The event rate for these lines of sight is
increased by a factor of 260*(theta/5_degrees)^{-2}. For typical GRB
parameters, we find that the bow shock emission from a jet with half-angle of
about 5 degrees is visible out to tens of Mpc in the radio and hundreds of Mpc
in the X-rays. If GRBs are linked to supernovae, studies of peculiar supernovae
in the local universe should reveal this non-thermal bow shock emission for
weeks to months following the explosion.Comment: ApJ, submitted, 15 pages, 3 figure
The nature of GRB-selected submillimeter galaxies: hot and young
We present detailed fits of the spectral energy distributions (SEDs) of four
submillimeter (submm) galaxies selected by the presence of a gamma-ray burst
(GRB) event (GRBs 980703, 000210, 000418 and 010222). These faint ~3 mJy submm
emitters at redshift ~1 are characterized by an unusual combination of long-
and short-wavelength properties, namely enhanced submm and/or radio emission
combined with optical faintness and blue colors. We exclude an active galactic
nucleus as the source of long-wavelength emission. From the SED fits we
conclude that the four galaxies are young (ages <2 Gyr), highly starforming
(star formation rates ~150 MSun/yr), low-mass (stellar masses ~10^10 MSun) and
dusty (dust masses ~3x10^8 MSun). Their high dust temperatures (Td>45 K)
indicate that GRB host galaxies are hotter, younger, and less massive
counterparts to submm-selected galaxies detected so far. Future facilities like
Herschel, JCMT/SCUBA-2 and ALMA will test this hypothesis enabling measurement
of dust temperatures of fainter GRB-selected galaxies.Comment: 9 pages, 2 figures, submitted to ApJ, for SED templates, see
http://archive.dark-cosmology.dk
CCD photometric and mass function study of 9 young Large Magellanic Cloud star clusters
We present CCD photometric and mass function study of 9 young Large
Magellanic Cloud star clusters namely NGC 1767, NGC 1994, NGC 2002, NGC 2003,
NGC 2006, SL 538, NGC 2011, NGC 2098 and NGC 2136. The BVRI data reaching down
to V ~ 21 mag, are collected from 3.5-meter NTT/EFOSC2 in sub-arcsec seeing
conditions. For NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2011 and NGC 2136,
broad band photometric CCD data are presented for the first time. Seven of the
9 clusters have ages between 16 to 25 Myr while remaining two clusters have
ages Myr (NGC 2098) and Myr (NGC 2136). For 7 younger
clusters, the age estimates based on a recent model and the integrated spectra
are found to be systematically lower ( 10 Myr) from the present estimate.
In the mass range of , the MF slopes for 8 out of nine
clusters were found to be similar with the value of ranging from
to . For NGC 1767 it is flatter with . Mass segregation effects are observed for NGC 2002, NGC 2006,
NGC 2136 and NGC 2098. This is consistent with the findings of Kontizas et al.
for NGC 2098. Presence of mass segregation in these clusters could be an
imprint of star formation process as their ages are significantly smaller than
their dynamical evolution time. Mean MF slope of
derived for a sample of 25 young ( Myr) dynamically unevolved LMC
stellar systems provide support for the universality of IMF in the intermediate
mass range .Comment: To appear in MNRA
Fossil biomass preserved as graphitic carbon in a late paleoproterozoic banded iron formation metamorphosed at more than 550°C
Metamorphism is thought to destroy microfossils, partly through devolatilization and graphitization of biogenic organic matter. However, the extent to which there is a loss of molecular, elemental and isotope signatures from biomass during high-temperature metamorphism is not clearly established. We report on graphitic structures inside and coating apatite grains from the c. 1850 Ma Michigamme silicate banded iron formation from Michigan, metamorphosed above 550°C. Traces of N, S, O, H, Ca and Fe are preserved in this graphitic carbon and X-ray spectra show traces of aliphatic groups. Graphitic carbon has an expanded lattice around 3.6 Å, forms microscopic concentrically-layered and radiating polygonal flakes and has homogeneous δ13C values around −22‰, identical to bulk analyses. Graphitic carbon inside apatite is associated with nanometre-size ammoniated phyllosilicate. Precursors of these metamorphic minerals and graphitic carbon originated from ferruginous clayrich sediments with biomass. We conclude that graphite coatings and inclusions in apatite grains indicate fluid remobilization during amphibolite-facies metamorphism of precursor biomass. This new evidence fills in observational gaps of metamorphosed biomass into graphite and supports the existence of biosignatures in the highly metamorphosed iron formation from the Eoarchean Akilia Association, which dates from the beginning of the sedimentary rock record
Effects of non-denumerable fixed points in finite dynamical systems
The motion of a spinning football brings forth the possible existence of a
whole class of finite dynamical systems where there may be non-denumerably
infinite number of fixed points. They defy the very traditional meaning of the
fixed point that a point on the fixed point in the phase space should remain
there forever, for, a fixed point can evolve as well! Under such considerations
one can argue that a free-kicked football should be non-chaotic.Comment: This paper is a replaced version to modify the not-so-true claim,
made unknowingly in the earlier version, of being first to propose the
peculiar dynamical systems as described in the paper. With respect to the
original workers, we present here our original finding
Resolving the Image of Gamma-Ray Burst Afterglows with Gravitational Microlensing
Microlensing of a gamma-ray burst afterglow by an intervening star can be
used to infer the radial structure of the afterglow image. Near the peak of the
microlensing event, the outer edge of the image is more highly magnified than
its central region, whereas the situation is reversed at later times due to the
rapid radial expansion of the image on the sky. Thus, the microlensed afterglow
light curve can be inverted to recover the self-similar radial intensity
profile of the afterglow image. We calculate the expected errors in the
recovered intensity profile as a function of the number of resolution elements,
under the assumption that the afterglow and microlensing event parameters are
known. For a point-mass lens and uniform source, we derive a simple scaling
relation between these parameters and the resultant errors. The afterglow need
not be monitored for its entire duration; rather, observations from the peak
magnification time t_p of the microlensing event until 7 t_p are sufficient to
resolve the majority of the image. Thus, microlensing events can be alerted by
relatively infrequent observations of afterglows and then monitored
intensively, without significant loss of information about the afterglow
intensity profile. The relative intensity profile of about 1% of all afterglows
can be measured with 10 resolution elements to an accuracy of 1% in the optical
and 10% in the infrared, using 4m-class telescopes. Weak microlensing events
with large impact parameters are more common; we estimate that for about 10% of
afterglows the image profile may be inverted to a fractional accuracy 20%
through frequent optical observations. We also calculate the effects of
external shear due to the host galaxy or a binary companion, and contamination
by background light from the host galaxy.Comment: Minor changes. 32 pages, 9 figures. Accepted to ApJ. To appear in
Sept 10, 2001 issue (v558
DEVELOPMENT OF pH-DEPENDENT CHRONOMODULATED DELIVERY SYSTEMS OF 5-FLUOROURACIL AND OXALIPLATIN TO TREAT COLON CANCER
Objective: To develop two different oral formulations such as 5-fluorouracil (5-FU) tablets and oxaliplatin (OX) microspheres which were further filled into capsules and coated with pH-sensitive polymer (eudragit S-100) for the chronotherapeutic treatment of colon cancer (Fluorouracil: Oxaliplatin regimen) to perform as a substitute for intravenous (IV) route based chronomodulated chemotherapy.
Methods: The 5-FU tablet formulation was prepared with alginate and guar gum polymers in varied concentrations using wet granulation technique in two varieties such as granules coated and tablet coated formulations using eudragit RSPO as coating material to achieve controlled drug release. Alongside OX microspheres were formulated using the ionotropic gelation methodology in combination with alginate and chitosan polymers in varying concentrations to accomplish a time-controlled drug release. Prepared formulations were evaluated for pre-compression and post-compression parameters, percentage yield, percentage drug entrapment, Fourier transformed infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM), In vitro and Ex vivo dissolution studies.
Results: Pre-compression and post-compression parameters for 5-FU tablets were satisfied with Indian pharmacopeia specifications. The entrapment efficiency of OX microspheres were increased due to the elevated concentration of polymers up to a certain level as seen in A7M, further greater the concentration of polymer resulted in a decline of entrapment efficiency as seen in A4M and A8M. The optimized formulations A14T and A14M were shown in vitro drug release of 90.36 % by 24 h and 79.63 % by 9 h respectively.
Conclusion: The two different oral formulations of 5-FU (Tablets) and OX (Microspheres) were found to be successful in controlled drug release. Therefore they can be efficiently used to control the rate of drug release to the colon in synchronization with the circadian timing system in the belief of improved therapeutic efficacy, tolerability and overall survival rate of cancer patients. Hence it is promised to be a better alternative for intravenous route based chronomodulated chemotherapy
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