3,077 research outputs found
Carta de Pawan Kumar Kamthan a M. Carbona Balaguer
No full textCarta de condol escrita per Pawan Kumar Kamthan a M. Carbona Balaguer, amb motiu de la mort de Ferran Sunyer
Simulations Of Accretion Powered Supernovae In The Progenitors Of Gamma-Ray Bursts
No full textObservational evidence suggests a link between long-duration gamma-ray bursts (LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. We present spherically symmetric hydrodynamic simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in one spatial dimension and with rotation, an explicit shear viscosity, and convection in the mixing length theory approximation. Once the accretion flow becomes rotationally supported outside of the black hole, an accretion shock forms and traverses the stellar envelope. Energy is carried from the central geometrically thick accretion disk to the stellar envelope by convection. Energy losses through neutrino emission and nuclear photodisintegration are calculated but do not seem important following the rapid early drop of the accretion rate following circularization. We find that the shock velocity, energy, and unbound mass are sensitive to convective efficiency, effective viscosity, and initial stellar angular momentum. Our simulations show that given the appropriate combinations of stellar and physical parameters, explosions with energies similar to 5 x 10(50) erg, velocities similar to 3000 km s(-1), and unbound material masses greater than or similar to 6 M-circle dot are possible in a rapidly rotating 16 M-circle dot main-sequence progenitor star. Further work is needed to constrain the values of these parameters, to identify the likely outcomes in more plausible and massive LRGB progenitors, and to explore nucleosynthetic implications.National Science Foundation AST-0708795, AST-1009928, AST-0909110DOEAstronom
Collapsar accretion and the gamma-ray burst X-ray light curve
No full texttextWe present axisymmetric hydrodynamical simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in two spatial dimensions and with an explicit shear viscosity. The evolution of the central accretion rate exhibits phases reminiscent of the long GRB [gamma]-ray and X-ray light curve, which lends support to the proposal by Kumar et al. (2008a,b) that the luminosity is modulated by the central accretion rate. In the first "prompt" phase, the black hole acquires most of its final mass through supersonic quasiradial accretion occurring at a steady rate of [scientific symbols]. After a few tens of seconds, an accretion shock sweeps outward through the star. The formation and outward expansion of the accretion shock is accompanied with a sudden and rapid power-law decline in the central accretion rate Ṁ [proportional to] t⁻²̇⁸, which resembles the L[subscript x] [proportional to] t⁻³ decline observed in the X-ray light curves. The collapsed, shock-heated stellar envelope settles into a thick, low-mass equatorial disk embedded within a massive, pressure-supported atmosphere. After a few hundred seconds, the inflow of low-angular-momentum material in the axial funnel reverses into an outflow from the thick disk. Meanwhile, the rapid decline of the accretion rate slows down, which is potentially suggestive of the "plateau" phase in the X-ray light curve. We complement our adiabatic simulations with an analytical model that takes into account the cooling by neutrino emission and estimate that the duration of the prompt phase can be ~ 20 s. The model suggests that the steep decline in GRB X-ray light curves is triggered by the circularization of the infalling stellar envelope at radii where the virial temperature is below 10¹⁰ K, such that neutrino cooling is inefficient and an outward expansion of the accretion shock becomes imminent; GRBs with longer prompt [gamma]-ray emission should have more slowly rotating envelopes.Astronom
Bibliographics for the 983 eprints in the live archives of E-LIS : trends and status report up to 7th July 2004, based on author-self-archiving metadata
No full textThe priority for ideas and philosophy related to "Network Theory" have been traced back and documented by Braun(2004),and credit goes to Karinthy(1929).The IT has empowered to realise it, as the most practical phenomena and it is no more a humour. The OAI (Open Archives Initiatives)and ACIS (Academic Contributor Information System)are progressive in the direction ,which may lead to realise the "Collective Genius" at global level. Focus of present study is on Author-Self-Archiving (A-S-A)Metadata of the 983 Eprints in the Live Archives of the E-LIS (EPrints of Library and Information Science),which were approved till 7th July 2004.The A-S-A Metadata was used for librametric analysis. Self-explanatory bibliographics are illustrated.The highlights include: Conference papers (34%); highest approval, June 2004 (28%); published archives (76%);not refereed (52%); not in public domain (60%); highest self-archiving-author (De Robbio, Antonella).The Nos. of EPrints having single JITA domain specifications were: Theoretical and general aspects of libraries and information(27); Information use and sociology of information(80);Users,literacy and reading(13);Libraries as physical collections(30);Publishing and legal issues(57);Management(13);Industry, profession and education(36);Information sources, supports, channels(113) ; Information treatment for information services, Information functions and techniques (101); Technical services libraries, archives and museums(25); Housing technologies(1); Information technology and library technology(92); and Inter-domainery (395) i.e. having specifications of two or more than two JITA classes
A Method for Integrating Network-on-Chip Topologies with 3D ICs
No full textThree dimensional integration is a promising approach for reducing the form factor of chips. Scalable Networks on Chips (NoCs) are a necessity to support the communication requirements of such 3D ICs. Mapping of NoC topologies onto the different layers of the 3D stack, while meeting the 3D technology requirements and application power-performance constraints is an important problem. In this paper, we present an algorithm that addresses this issue of performing 3D layer assignment of NoC components. We also integrate the algorithm with an existing NoC interconnect floor planner. Our experiments on many SoC benchmarks show a reduction of 8 - 10% in the NoC power consumption and a 49% reduction in the number of vertical links (and hence, the Through Silicon Vias (TSVs)) when compared to existing approaches
A Simulation Based Buffer Sizing Algorithm for Network on Chips
No full textBuffers in on-chip networks constitute a significant proportion of the power consumption and area of the interconnect. Hence, reducing the buffering overhead of Networks on Chips (NoCs) is an important problem. For application-specific designs, the network utilization across the different links and switches is non-uniform, thereby requiring a buffer sizing approach that tackles the non uniformity. Moreover, congestion effects that occur during network operation needs to be captured when sizing the buffers. To this end, we propose a two-phase algorithm to size the switch buffers in NoCs. Our algorithm considers both the static (based on bandwidth and latency requirements) and dynamic (based on simulation) effects when sizing buffers. Our experiments show that the application of the algorithm results in 42% reduction in amount of buffering required to meet the application constraints when compared to a standard buffering approach
A Buffer-Sizing Algorithm for Network-on-Chips with Multiple Voltage-Frequency Islands
No full textBuffers in on-chip networks constitute a significant
proportion of the power consumption and area of the
interconnect, and hence reducing them is an important problem.
Application-specific designs have nonuniform network
utilization, thereby requiring a buffer-sizing approach that
tackles the nonuniformity. Also, congestion effects that occur
during network operation need to be captured when sizing the
buffers. Many NoCs are designed to operate in multiple voltage/frequency islands, with interisland communication taking
place through frequency converters. To this end, we propose
a two-phase algorithm to size the switch buffers in network-on-chips (NoCs) considering support for multiple-frequency
islands. Our algorithm considers both the static and dynamic
effects when sizing buffers. We analyze the impact of placing
frequency converters (FCs) on a link, as well as pack and send
units that effectively utilize network bandwidth. Experiments
on many realistic system-on-Chip (SoC) benchmark show
that our algorithm results in 42% reduction in amount of
buffering when compared to a standard buffering approach
Fabrication of a Flexible UV Band-Pass Filter Using Surface Plasmon Metal-Polymer Nanocomposite Films for Promising Laser Applications
No full textWe introduce a strategy for the fabrication of silver/polycarbonate (Ag/PC) nanocomposite flexible films of (20 +/- 0.01) mu m thickness with different filling factor of surface plasmon metal using customized solution cast thermal evaporation method. Structural characterizations confirmed the good crystallinity with cubic phase of Ag nanoparticles in PC films. Moreover, the microstructural evolutions of nanocomposite films are investigated by transmission electron microscopy, which indicates that the metal fraction is in the form of fractals. Additionally, the surface plasmonic behavior of nanocomposite films has been explored in detail to examine the distribution of Ag nanoparticles in PC film by spectroscopic technique. Furthermore, the obtained transmittance spectral features of this nanocomposite film are suitable for the applications of band-pass filter at 320 nm UV range, which is highly desirable for a HeCd laser
Multivariate Quantitative Representativeness and Constituency Analysis of Ecological Observation Networks
No full textCite this code as: Kumar, J. (2023). Multivariate Quantitative Representativeness and Constituency Analysis of Ecological Observation Networks (Version 1.0) [Computer software]. https://doi.org/10.5281/zenodo.8048530
Multivariate Quantitative Representativeness and Constituency Analysis of Ecological Observation Networks
Author: Jitendra (Jitu) Kumar ([email protected]), Oak Ridge National Laboratory
Regional and global ecological research networks, representing coordinated and standardized as well as adhoc networks of observation sites, provide valuable observations necessary for ecological modeling and synthesis studies. Studies conducted across observational networks strive to scale up their results to larger areas, trying to reach conclusions that are valid throughout regional, continental, and even global scales. Network representativeness and constituency can show how well conditions at those locations represent conditions elsewhere within a larger area containing the network and can be used to help scale-up results over larger regions.
Representativeness: Euclidean distance between two sites plotted in multivariate environmental space can be used as an inverse measure of multivariate similarity to quantify representativeness. Close sites in environmental space have a similar combination of environmental factors, and therefore are highly representative of each other.
Constituency: For any site in the network, its Constituency represent all locations that are best represented by the multivariate environmental drivers at that site.
Code Compilation:
make
Edit the ```makefile``` as needed for your platform.
CC=gcc
CFLAGS= -O3
hpea: network_representativeness.o\
utility.o
(CFLAGS) *.o -lm -o network_representativeness
.o:
(CFLAGS) -c $<
clean:
\rm *.o network_representativeness
Running the representativeness analysis:
Usage: network_representativeness -infile input data file [ASCII]
-coordsfile coordinate file name
-clustfile coordinate file name [OPTIONAL -- must be used with -siteclustfile]
-sitefile site data file name
-siteclustfile site data file name [OPTIONAL -- must be used with -clustfile]
-nsites No. of sites
-minmaxfile minmax file name
-outfile output file name
-nrows No. of rows in input data
-ncols No. of variables
-details [OPTIONAL -- turn on output representativeness for each site, default is to write network representativeness and constituency only.]
-help program usage help.
Publications using ```network_reprentativeness``` code:
Kumar, J., Coffin, A. W., Baffaut, C., Ponce-Campos, G., Witthaus, L., and Hargrove, W. W. (2023) "Quantitative Representativeness and Constituency of the Long-Term Agroecosystem Research Network, and Analysis of Complementarity with Other Existing Ecological Networks", Environmental Management (in press)
M. M. T. A. Pallandt, J. Kumar, M. Mauritz, E. A. G. Schuur, A.-M. Virkkala, G. Celis, F. M. Hoffman, and M. Göckede. Representativeness assessment of the pan-arctic eddy covariance site network and optimized future enhancements. Biogeosciences, 19(3):559--583, 2022. https://doi.org/10.5194/bg-19-559-2022
J. Kumar, F. M. Hoffman, W. W. Hargrove, and N. Collier. Understanding the representativeness of FLUXNET for upscaling carbon flux from eddy covariance measurements. Earth System Science Data Discussion, 2016:1--25, August 2016. https://doi.org/10.5194/essd-2016-36.If you use this software, please cite it as below.
Kumar, J. (2023). Multivariate Quantitative Representativeness and Constituency Analysis of Ecological Observation Networks (Version 1.0) [Computer software]. https://doi.org/10.5281/zenodo.804853
Advancement of brazing filler alloy: An Overview
No full textThe brazing is a special type of joining technique for the complex parts of any engineering components, such as, heat exchangers, turbine engine parts of aircraft, spacecraft etc. In this method, joining area is significantly narrow (~1mm), which demands a specific joining method with optimum heat input to achieve a near net shape fabricated component. A suitable brazing filler alloy in this respect offers specific characteristics like adequate wetting, low thickness, narrow melting zone, avoidance of intermetallic formation and limited extent of stress generation at joint interface. The methodology is applicable for both similar and dissimilar combination of materials depending on particular requirement. Due to minimal thickness constraint, the brazing filler alloy is synthesized in the form of fine powders, paste, thin foils and controlled coating between / over the substrate to be joined. The thin foils (~50 µm thickness) are fabricated by rapid solidification technique. Paste of suitable composition is produced by mechanical alloying to obtain fine grain structure with overall chemical homogeneity. The mixed product is further wetted by chemical fluid, which is non-reactive to the components of mixture, however can provide substantial fluidity of the paste. There are several methods to produce thin foils. Once the composition is achieved by conventional melting and casting, the desired thickness is obtained by repetitive forging or rolling of the stock. Controlled coating of single / multiple metal can be produced by spattering, physical vapour deposition and chemical vapour deposition of pre-determined thickness over the substrate to be joined. The controlled thickness in all the above cases is apposite to bridge narrow crack or join components. This methodology is also lucrative considering ease in process control as the variables are limited to four only i.e. temperature, normal pressure, time and atmosphere. Thus a transition joint with satisfactory efficiency and structural homogeneity can be easily achieved
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