699 research outputs found
Low Degree Metabolites Explain Essential Reactions and Enhance Modularity in Biological Networks
Recently there has been a lot of interest in identifying modules at the level
of genetic and metabolic networks of organisms, as well as in identifying
single genes and reactions that are essential for the organism. A goal of
computational and systems biology is to go beyond identification towards an
explanation of specific modules and essential genes and reactions in terms of
specific structural or evolutionary constraints. In the metabolic networks of
E. coli, S. cerevisiae and S. aureus, we identified metabolites with a low
degree of connectivity, particularly those that are produced and/or consumed in
just a single reaction. Using FBA we also determined reactions essential for
growth in these metabolic networks. We find that most reactions identified as
essential in these networks turn out to be those involving the production or
consumption of low degree metabolites. Applying graph theoretic methods to
these metabolic networks, we identified connected clusters of these low degree
metabolites. The genes involved in several operons in E. coli are correctly
predicted as those of enzymes catalyzing the reactions of these clusters. We
independently identified clusters of reactions whose fluxes are perfectly
correlated. We find that the composition of the latter `functional clusters' is
also largely explained in terms of clusters of low degree metabolites in each
of these organisms. Our findings mean that most metabolic reactions that are
essential can be tagged by one or more low degree metabolites. Those reactions
are essential because they are the only ways of producing or consuming their
respective tagged metabolites. Furthermore, reactions whose fluxes are strongly
correlated can be thought of as `glued together' by these low degree
metabolites.Comment: 12 pages main text with 2 figures and 2 tables. 16 pages of
Supplementary material. Revised version has title changed and contains study
of 3 organisms instead of 1 earlie
Boundary Shear Stress Distribution in Smooth and Rough Open Channel Flow
Boundary shear distribution in open channel flow is a crucial issue for river engineer and researchers working in this area.An experimental investigation has been carried out to measure the boundary shear stress distribution along the wetted perimeter of the smooth and rough channel using piston tube technique the accuracy of the method has been compared and checked with another convention method,NDM, VDM,MPM,Velocity Profile Method and energy gradient approach.The boundary shear along the bed and wall of the channel are different for different flow depth and for different roughness conditions.The percentage of boundary shear carried by the wall and bed has been analysed and found to depends on upon non-dimensional geometry and hydraulic parameters such as Aspect ratio,Reynolds number and Froude’s number.A multi linear regression model has been applied to predict the boundary shear distribution for bed.The equation is useful to calculate the roughness coefficient (friction factor) of the wall and bed of the channel separately,which further determines the composite roughness of the open channel flow accuracy.The methodology has been applied successfully to calculate the stage discharge relationship of the open channel flow.The methodology has been validated against other experimental data, other researcher’s models and Natural Rive
Exploring Foundations of Time-Independent Density Functional Theory for Excited-States
Based on the work of Gorling and that of Levy and Nagy, density-functional
formalism for many Fermionic excited-states is explored through a careful and
rigorous analysis of the excited-state density to external potential mapping.
It is shown that the knowledge of the ground-state density is a must to fix the
mapping from an excited-state density to the external potential. This is the
excited-state counterpart of the Hohenberg-Kohn theorem, where instead of the
ground-state density the density of the excited-state gives the true many-body
wavefunctions of the system. Further, the excited-state Kohn-Sham system is
defined by comparing it's non-interacting kinetic energy with the true kinetic
energy. The theory is demonstrated by studying a large number of atomic
systems.Comment: submitted to J. Chem. Phy
W40 region in the Gould Belt : An embedded cluster and H II region at the junction of filaments
We present a multiwavelength study of W40 star-forming region using IR
observations in UKIRT JHK bands, Spitzer IRAC bands & Herschel PACS bands; 2.12
micron H2 narrow-band imaging; & radio observations from GMRT (610 & 1280 MHz),
in a FoV of ~34'x40'. Spitzer observations along with NIR observations are used
to identify 1162 Class II/III & 40 Class I sources in the FoV. The NN stellar
surface density analysis shows that majority of these YSOs constitute the
embedded cluster centered on the source IRS1A South. Some YSOs, predominantly
younger population, are distributed along & trace the filamentary structures at
lower stellar surface density. The cluster radius is obtained as 0.44pc -
matching well with the extent of radio emission - with a peak density of
650pc^-2. The JHK data is used to map the extinction which is subsequently used
to compute the cloud mass. It has resulted in 126 Msun & 71 Msun for the
central cluster & the northern IRS5 region, respectively. H2 narrow-band
imaging displays significant emission, which prominently resembles fluorescent
emission arising at the borders of dense regions. Radio analysis shows this
region as having blister morphology, with the radio peak coinciding with a
protostellar source. Free-free emission SED analysis is used to obtain physical
parameters of the overall region & the IRS5 sub-region. This multiwavelength
scenario is suggestive of star formation having resulted from merging of
multiple filaments to form a hub. Star formation seems to have taken place in
two successive epochs, with the first epoch traced by the central cluster & the
high-mass star(s) - followed by a second epoch which is spreading into the
filaments as uncovered by the Class I sources & even younger protostellar
sources along the filaments. The IRS5 HII region displays indications of
swept-up material which has possibly led to the formation of protostars.Comment: 17 pages, 12 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Young stellar population and ongoing star formation in the HII complex Sh2-252
In this paper an extensive survey of the star forming complex Sh2-252 has
been undertaken with an aim to explore its hidden young stellar population as
well as to understand the structure and star formation history. This complex is
composed of five embedded clusters associated with the sub-regions A, C, E, NGC
2175s and Teu 136. Using 2MASS-NIR and Spitzer-IRAC, MIPS photometry we
identified 577 young stellar objects (YSOs), of which, 163 are Class I, 400 are
Class II and 14 are transition disk YSOs. Spatial distribution of the candidate
YSOs shows that they are mostly clustered around the sub-regions in the western
half of the complex, suggesting enhanced star formation activity towards its
west. Using the spectral energy distribution and optical colour-magnitude
diagram based age analyses, we derived probable evolutionary status of the
sub-regions of Sh2-252. Our analysis shows that the region A is the youngest (~
0.5 Myr), the regions B, C and E are of similar evolutionary stage (~ 1-2 Myr)
and the clusters NGC 2175s and Teu 136 are slightly evolved (~ 2-3 Myr).
Morphology of the region in the 1.1 mm map shows a semi-circular shaped
molecular shell composed of several clumps and YSOs bordering the western
ionization front of Sh2-252. Our analyses suggest that next generation star
formation is currently under way along this border and that possibly
fragmentation of the matter collected during the expansion of the HII region as
one of the major processes responsible for such stars. We observed the densest
concentration of YSOs (mostly Class I, ~ 0.5 Myr) at the western outskirts of
the complex, within a molecular clump associated with water and methanol masers
and we suggest that it is indeed a site of cluster formation at a very early
evolutionary stage, sandwiched between the two relatively evolved CHII regions
A and B.Comment: 19 pages, 13 figures, Accepted for publication in MNRA
Star Formation and Young Population of the HII Complex Sh2-294
The Sh2-294 HII region ionized by a single B0V star features several infrared
excess sources, a photodissociation region, and also a group of reddened stars
at its border. The star formation scenario in the region seems to be quite
complex. In this paper, we present follow-up results of Sh2-294 HII region at
3.6, 4.5, 5.8, and 8.0 microns observed with the Spitzer Space Telescope
Infrared Array Camera (IRAC), coupled with H2 (2.12 microns) observation, to
characterize the young population of the region and to understand its star
formation history. We identified 36 young stellar object (YSO, Class I, Class
II and Class I/II) candidates using IRAC color-color diagrams. It is found that
Class I sources are preferentially located at the outskirts of the HII region
and associated with enhanced H2 emission; none of them are located near the
central cluster. Combining the optical to mid-infrared (MIR) photometry of the
YSO candidates and using the spectral energy distribution fitting models, we
constrained stellar parameters and the evolutionary status of 33 YSO
candidates. Most of them are interpreted by the model as low-mass (< 4 solar
masses) YSOs; however, we also detected a massive YSO (~9 solar masses) of
Class I nature, embedded in a cloud of visual extinction of ~24 mag. Present
analysis suggests that the Class I sources are indeed younger population of the
region relative to Class II sources (age ~ 4.5 x 10^6 yr). We suggest that the
majority of the Class I sources, including the massive YSOs, are
second-generation stars of the region whose formation is possibly induced by
the expansion of the HII region powered by a ~ 4 x 10^6 yr B0 main-sequence
star.Comment: 12 pages, 7 figures, 2 tables. Accepted for publication in The
Astrophysical Journa
Effect of chronic administration of nicorandil (a potassium channel activator) on body weight of two different experimental animal species
Background: Potassium channel openers (Nicorandil being the prototype) are a distinct class of drugs, used in the management of chronic stable angina pectoris. Obesity is a frequent co-morbid condition and also a risk factor for angina pectoris. Anti-obesity drugs are used more frequently these days than ever before. Therefore, it is more likely that physician would be prescribing at least 2 or more drugs while treating such comorbid conditions. This generates a need for the development of a new drug which would work against both angina and obesity. The resultant effect would be a reduction in the cost burden, incidences of side effects and possible drug- drug interactions as compared to multidrug therapy. The purpose of this study is evaluating the chronic effect of Nicorandil (graded doses) on the body weight in 2 different species of animals i.e. rabbits and mice.Methods: In this study, 30 experimental animals of each species were selected. Pretreatment weight (Mean body weight±SEM) of each group were recorded and compared with the post-treatment values of the respective group in every week up to a period of 4 weeks. The route of administration was an intraperitoneal injection.Results: Chronic administration of nicorandil causes a significant reduction in body weight at moderate to high doses in both species of the study group. (p <0.05).Conclusions: Body weight reducing, an effect of nicorandil in animals, if established in human, could enhance its acceptability in obesity with various ischemic heart diseases including angina
Deep optical survey of the stellar content of Sh2-311 region
The stellar content in and around Sh2-311 region have been studied using the
deep optical observations as well as near-infrared (NIR) data from 2MASS. The
region contains three clusters, viz. NGC 2467, Haffner 18 and Haffner 19. We
have made an attempt to distinguish the stellar content of these individual
regions as well as to re-determine their fundamental parameters such as
distance, reddening, age, onto the basis of a new and more extended optical and
infrared photometric data set. NGC 2467 and Haffner 19 are found to be located
in the Perseus arm at the distances of 5.0 0.4 kpc and 5.7 0.4 kpc,
respectively, whereas Haffner 18 is located at the distance of 11.2 1.0
kpc. The clusters NGC 2467 and Haffner 19 might have formed from the same
molecular cloud, whereas the cluster Haffner 18 is located in the outer
galactic arm, i.e. the Norma-Cygnus arm. We identify 8 class II young stellar
objects (YSOs) using the NIR two colour diagram. We have
estimated the age and mass of the YSOs identified in the present work and those
by Snider et al. (2009) using the colour-magnitude diagram. The
estimated ages and mass range of the majority of the YSOs are 1 Myr
and 0.4 - 3.5 \msun, respectively, indicating that these sources could be
T-Tauri stars or their siblings. Spatial distribution of the YSOs shows that
some of the YSOs are distributed around the H II region Sh2-311, suggesting a
triggered star formation at its periphery.Comment: 19 pages, 13 figures, 9 table; Accepted for publication in New
Astronom
Optical and Near-infrared survey of the stellar contents associated with the star-forming Complex Sh2-252
We present the analyses of the stellar contents associated with the HII
region Sh2-252 using UBVRI photometry, slit and slitless spectroscopy along
with the NIR data from 2MASS for an area ~1 degree x 1 degree. We studied the
sub-regions of Sh2-252 which includes four compact-HII (CHII) regions, namely
A, B, C and E and two clusters NGC 2175s and Teutsch 136 (Teu 136). Of the
fifteen spectroscopically observed bright stars, eight have been identified as
massive members of spectral class earlier than B3. From the spectro-photometric
analyses, we derived the average distance of the region as 2.4+/-0.2 kpc and
the reddening of the massive members is found to vary between 0.35 to 2.1 mag.
We found that NGC 2175s and Teu 136, located towards the eastern edge of the
complex are the sub-clusters of Sh2-252. The stellar surface density
distribution in K-band shows clustering associated with the regions A, C, E,
NGC 2175s and Teu 136. We have also identified the candidate ionizing sources
of the CHII regions. 61 H_alpha emission sources are identified using slitless
spectroscopy. The distribution of the H_alpha emission sources and candidate
YSOs with IR excess on the V/(V-I) CMD shows that a majority of them have
approximate ages between 0.1 - 5 Myr and masses in the range of 0.3 - 2.5
M_sun. The CMDs of the candidate YSOs in the individual regions also show an
age spread of 0.1 - 5 Myr for each of them. We calculated the KLFs for the
sub-regions A, C, E, NGC 2175s and Teu 136. Within errors, the KLFs for all the
sub-regions are found to be similar and comparable to that of young clusters of
age < 5 Myr. We also estimated the mass functions (MFs) of the PMS sample of
the individual regions in the mass range of 0.3 - 2.5 M_sun. In general, the
slopes of the MFs of all the sub-regions are found comparable to the Salpeter
value.Comment: published in MNRA
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