Showing papers by "Shiv Nadar University published in 2015"
TL;DR: This review mainly focuses on the influence of spin canting effects, introduced by the variations in size, shape, and organic/inorganic surface coatings, on the magnetic properties of SPIONs.
301 citations
TL;DR: Concentrated weighted trajectory (CWT) analysis reveals that the potential sources for the carbonaceous aerosols and pollutants are local emissions within the urban environment and transported smoke from agricultural burning in northwest India during post-monsoon.
148 citations
TL;DR: In this article, the seasonality, dust-plume altitudinal variation and affected areas for dust storms originated from the Sistan region, southeastern Iran during the summer (June-September) months of the period 2001-2012 synthesizing local meteorological records, satellite observations (TOMS, OMI, METEOSAT, MODIS) and HYSPLIT forward trajectories.
101 citations
TL;DR: In this article, the authors examined the synoptic and dynamic meteorological conditions associated with dust-storms in the Sistan region, southeastern Iran during the summer season (June-September) of the years 2001-2012.
Abstract: Dust storms are considered natural hazards that seriously affect atmospheric conditions, ecosystems and human health. A key requirement for investigating the dust life cycle is the analysis of the meteorological (synoptic and dynamic) processes that control dust emission, uplift and transport. The present work focuses on examining the synoptic and dynamic meteorological conditions associated with dust-storms in the Sistan region, southeastern Iran during the summer season (June–September) of the years 2001–2012. The dust-storm days (total number of 356) are related to visibility records below 1 km at Zabol meteorological station, located near to the dust source. RegCM4 model simulations indicate that the intense northern Levar wind, the high surface heating and the valley-like characteristics of the region strongly affect the meteorological dynamics and the formation of a low-level jet that are strongly linked with dust exposures. The intra-annual evolution of the dust storms does not seem to be significantly associated with El-Nino Southern Oscillation, despite the fact that most of the dust-storms are related to positive values of Oceanic Nino Index. National Center for Environmental Prediction/National Center for Atmospheric Research reanalysis suggests that the dust storms are associated with low sea-level pressure conditions over the whole south Asia, while at 700 hPa level a trough of low geopotential heights over India along with a ridge over Arabia and central Iran is the common scenario. A significant finding is that the dust storms over Sistan are found to be associated with a pronounced increase of the anticyclone over the Caspian Sea, enhancing the west-to-east pressure gradient and, therefore, the blowing of Levar. Infrared Difference Dust Index values highlight the intensity of the Sistan dust storms, while the SPRINTARS model simulates the dust loading and concentration reasonably well, since the dust storms are usually associated with peaks in model simulations.
94 citations
TL;DR: Grapes extract was explored as a green reducing agent for the preparation of reduced graphene oxide (RGO) from graphene oxide as mentioned in this paper, and the effect of reduction time on physical, chemical and optical properties of the RGO was also investigated.
87 citations
TL;DR: Molecular fluorophores based on N,C-chelate, four-coordinate organoborons exhibit tunable solid-state emission colors that cover the whole visible region from blue to red.
83 citations
TL;DR: In this paper, a sustainable origin phenol was utilized as a reactive diluent to mediate solventless Mannich-type condensation reaction with para-formaldehyde and primary aromatic amines to form a homologous series of benzoxazine (Bz) monomers namely C-a, C-ddm, c-trisapm and C-tetraapm which differ in their degree of oxazine functionality as mono-, di-, tri- and tetra-oxazine respectively.
Abstract: Cardanol, a sustainable origin phenol, was utilized as a reactive diluent to mediate solventless Mannich-type condensation reaction with para-formaldehyde and primary aromatic amines to form a homologous series of benzoxazine (Bz) monomers namely C-a, C-ddm, C-trisapm and C-tetraapm which differ in their degree of oxazine functionality as mono-, di-, tri- and tetra-oxazine respectively. A strong correlation is reflected between the number of oxazine rings in the monomer and the polymerization behavior, thermo-mechanical transitions, and properties of the polybenzoxazine synthesized. The monomer structure was confirmed by FTIR, 1H-, 13C-NMR spectroscopy and mass spectrometry. The curing, rheological, thermo-mechanical and thermal properties were determined using DSC, FTIR, rheometer, DMTA, LSS and TGA studies. The curing characteristic due to ROP of Bz monomers was supported both by DSC and FTIR studies. The presence of neighboring oxazine group in monomers (C-a to C-tetraapm) strongly attenuates the curing temperature (Ti = 225–140 °C), enhances Tg, thermal stability, and mechanical properties. Interestingly, DFT calculations also supported the lowest curing temperature for highest oxazine functionality monomer (C-tetraapm). The interplay between the degree of oxazine functionality in the monomer; extent of H-bonding and crosslink density values in sustainable origin synthesized polybenzoxazines is suggested. The thermoset showed an increasing trend (PC-a < PC-ddm < PC-trisapm < PC-tetraapm) in Tg (58–109 °C), thermal stability (355–391 °C), char yield (13–37%), LOI (23–31) and storage modulus (3.6–66.5 MPa) values. The monomers are liquid to semi-viscous paste at room temperature and showed potential for solventless processing in adhesive applications.
79 citations
TL;DR: The Ganges Valley Aerosol Experiment (GVAX) was initiated in Nainital from June 2011 to March 2012 with the aim of examining the aerosol properties, source regions, uplift mechanisms and aerosol-radiation-cloud interactions.
Abstract: . Light scattering and absorption properties of atmospheric aerosols are of vital importance for evaluating their types, sources and radiative forcing. This is of particular interest over the Gangetic–Himalayan (GH) region due to uplift of aerosol from the plains to the Himalayan range, causing serious effects on atmospheric heating, glaciology and monsoon circulation. In this respect, the Ganges Valley Aerosol Experiment (GVAX) was initiated in Nainital from June 2011 to March 2012 with the aim of examining the aerosol properties, source regions, uplift mechanisms and aerosol–radiation–cloud interactions. The present study examines the temporal (diurnal, monthly, seasonal) evolution of scattering (σ
77 citations
TL;DR: In this paper, columnar and vertical aerosol characteristics and estimates the shortwave (0.25-4.0μm) aerosol radiative forcing (ARF) and atmospheric heating rates over Kanpur, central IGB, during three intense dust-storm events in the pre-monsoon season of 2010.
75 citations
01 Jan 2015
TL;DR: In this paper, the authors describe the origin and evolution of systems biology, as a formal discipline, steps and challenges in building models and their potential applications, and the potential applications of these models.
Abstract: In the mid 1990s when Leroy Hood reintroduced the term “Systems Biology”, the fusion of ideas gave rise to confusion to such an extent that there used to be special talks on ‘what is systems biology’? Over the last decade, Systems Biology has undergone directed evolution leading to the emergence of personalized versions of this term. Irrespective of this, strong computational dependency and a significant increase in the scale of investigation often appear as constant features in the systems biology background. In our opinion, Systems Biology is an approach that involves the following (a) experimental and computational studies describing collective behavior of molecules in relation to the pathway and networks, and with the higher-level physiological outcome (b) new experimental and mathematical methods important to study group behavior of interacting components. This chapter describes the origin and evolution of systems biology, as a formal discipline, steps and challenges in building models and their potential applications.
69 citations
TL;DR: A library comprising of hydantoin and thiohydantoin derivatives and thiophenyl as the central moiety exhibited potent inhibition of human Top1 (HTop1) through stabilization of Top1-DNA cleavage complexes and showed selective anticancer activity against human cervical carcinoma and breast carcinoma cell lines.
TL;DR: While ferromagnetic interactions seem to be predominant, the presence of antiferromagnetic interaction was also observed and free spins available via the conversion of sp2 to sp3 hybridized structures, and the possibility of unpaired electrons from defects induced upon hydrogenation are thought to be likely mechanisms for the observedferromagnetic orders.
Abstract: We report an investigation into the magnetic and electronic properties of partially hydrogenated vertically aligned few layers graphene (FLG) synthesized by microwave plasma enhanced chemical vapor deposition. The FLG samples are hydrogenated at different substrate temperatures to alter the degree of hydrogenation and their depth profile. The unique morphology of the structure gives rise to a unique geometry in which graphane/graphone is supported by graphene layers in the bulk, which is very different from other widely studied structures such as one-dimensional nanoribbons. Synchrotron based x-ray absorption fine structure spectroscopy measurements have been used to investigate the electronic structure and the underlying hydrogenation mechanism responsible for the magnetic properties. While ferromagnetic interactions seem to be predominant, the presence of antiferromagnetic interaction was also observed. Free spins available via the conversion of sp2 to sp3 hybridized structures, and the possibility of unpaired electrons from defects induced upon hydrogenation are thought to be likely mechanisms for the observed ferromagnetic orders.
TL;DR: In this paper, the detection of fault occurred during friction stir welding using discrete wavelet transform on force and torque signals, and statistical features like variance and square of errors of detail coefficients are implemented to localize the defective zone properly as it shows better variations (in defective area) than the detail coefficient itself.
TL;DR: In this paper, the authors consider the non-dissipative multi-fluid equations and demonstrate how multi-Beltrami equilibria emerge as natural relaxed states of the model, representing an evolution towards the minimum energy.
Abstract: We consider the non-dissipative multi-fluid equations, and demonstrate how multi-Beltrami equilibria emerge as natural relaxed states of the model, representing an evolution towards the minimum energy. General properties of these states are studied, and a wide class of solutions is obtained. We specialize to the cases of double and triple Beltrami states and highlight their connections with the appropriate physical invariants, viz., the generalized helicities and the energy. In particular, we demonstrate that different field configurations can give rise to distinct or identical values of the invariants, depending on the nature of the roots of the multi-Beltrami equation. Moreover, we also highlight equivalences between (outwardly) unconnected models allowing us to treat them in a unified manner. Some observations regarding the nature of the solutions for certain special cases of these models are presented. Potential applications for astrophysical plasmas are also highlighted.
TL;DR: An algorithm for maintaining maximal matching in a graph under addition and deletion of edges that can maintain a factor 2 approximate maximum matching in expected amortized $O(\log n )$ time per update as a direct corollary of the maximal matching scheme.
Abstract: We present an algorithm for maintaining maximal matching in a graph under addition and deletion of edges. Our algorithm is randomized and it takes expected amortized $O(\log n)$ time for each edge update, where $n$ is the number of vertices in the graph. While there exists a trivial $O(n)$ time algorithm for each edge update, the previous best known result for this problem is due to Ivkovicź and Lloyd [Lecture Notes in Comput. Sci. 790, Springer-Verlag, London, 1994, pp. 99--111]. For a graph with $n$ vertices and $m$ edges, they gave an $O( {(n+ m)}^{0.7072})$ update time algorithm which is sublinear only for a sparse graph. For the related problem of maximum matching, Onak and Rubinfeld [Proceedings of STOC'10, Cambridge, MA, 2010, pp. 457--464] designed a randomized algorithm that achieves expected amortized $O(\log^2 n)$ time for each update for maintaining a $c$-approximate maximum matching for some unspecified large constant $c$. In contrast, we can maintain a factor 2 approximate maximum matching in expected amortized $O(\log n )$ time per update as a direct corollary of the maximal matching scheme. This in turn also implies a 2-approximate vertex cover maintenance scheme that takes expected amortized $O(\log n )$ time per update.
TL;DR: In this article, a discrete wavelet transform has been applied on FSW images to extract useful features for describing the good and defective welds and these obtained features have been fed to support vector machine based classification model for classification with 99% and 97% accuracy with Gaussian and polynomial kernel.
TL;DR: In this article, a coordination-coupled deprotonation (CCD) driven signaling and signal enhancement sequences were developed for proton relay in the context of molecular switches.
Abstract: Proton relay plays an important role in many biocatalytic pathways. In order to mimic such processes in the context of molecular switches, we developed coordination-coupled deprotonation (CCD) driven signaling and signal enhancement sequences. This was accomplished by using the zinc(ii)-initiated CCD of a hydrazone switch to instigate an acid catalyzed imine bond hydrolysis that separates a quencher from a fluorophore thus leading to emission amplification. Because CCD is a reversible process, we were able to show that the catalysis can be regulated and turned "on" and "off" using a metalation/demetalation cycle.
TL;DR: 3D particle-in-cell simulations demonstrate that the enhanced transparency of a relativistically hot plasma is sensitive to how the energy is partitioned between different degrees of freedom.
Abstract: 3D particle-in-cell simulations demonstrate that the enhanced transparency of a relativistically hot plasma is sensitive to how the energy is partitioned between different degrees of freedom. For an anisotropic electron distribution, propagation characteristics, like the critical density, will depend on the polarization of the electromagnetic wave. Despite the onset of the Weibel instability in such plasmas, the anisotropy can persist long enough to affect laser propagation. This plasma can then function as a polarizer or a wave plate to dramatically alter the pulse polarization.
TL;DR: In this paper, the authors examined the characteristics (source regions, pathways, vertical profiles) as well as the meteorological conditions and the role of the Inter-Tropical Convergence Zone (ITCZ) during a dust event on 1-3 July 2014 over southwest (SW) Asia.
TL;DR: In this article, simultaneous measurements of number concentration of condensation nuclei (NCCN) and NCCN activation were obtained at Nainital, in the Gangetic-Himalayan (GH) region, during the frameworks of Ganges Valley Aerosol Experiment (GVAX), June 2011 to March 2012.
TL;DR: The finding of a bowl-shaped quasi-planar structure of a B84 cluster with four hexagonal holes and a three-chain ring all around the edges using ab initio calculations suggests that quasi-Planar structures may be among the low energy structures for larger clusters as well.
Abstract: We report the finding of a bowl-shaped quasi-planar structure of a B84 cluster with four hexagonal holes and a three-chain ring all around the edges using ab initio calculations. A large number of other isomers including those explored earlier such as an empty cage, a filled cage, and a disordered structure, have been found to lie in a significantly higher energy band. A tubular structure, however, is only about 0.45 eV higher in energy. Calculations of the infrared and Raman spectra show that the quasi-planar structure is dynamically stable. These results suggest that quasi-planar structures may be among the low energy structures for larger clusters as well. Accordingly we have calculated the optimal quasi-planar structures stabilized with 2, 3, 5, 6, and 7 hexagonal holes also. The stability of quasi-planar structures is discussed in terms of multi-center two-electron bonding and it is shown that with increasing size their binding energy tends to approach the value for an α-boron sheet.
TL;DR: It could be shown that N-methylimidazole based thiones/selones having an N-CH2CH2OH substituent are remarkably effective in detoxifying various organomercurials to produce less toxic HgE (E=S, Se) nanoparticles.
Abstract: Organomercurials including methylmercury are ubiquitous environmental pollutants and highly toxic to humans. Now it could be shown that N-methylimidazole based thiones/selones having an N-CH2CH2OH substituent are remarkably effective in detoxifying various organomercurials to produce less toxic HgE (E=S, Se) nanoparticles. Compounds lacking the N-CH2CH2OH substituent failed to produce HgE nanoparticles upon treatment with organomercurials, suggesting that this moiety plays a crucial role in the detoxification by facilitating the desulfurization and deselenization processes. This novel way of detoxifying organomercurials may lead to the discovery of new compounds to treat patients suffering from methylmercury poisoning.
TL;DR: Examination, expression knockdown of different molecules and pull down experiments suggest that EhARPC1 interacts with EhAK1 and that it is required during initiation of phagocytosis and phagosome formation, suggesting a novel mechanism of recruitment of Arp 2/3 complex during phagocytetosis in E. histolytica.
Abstract: The parasite Entamoeba histolytica is the etiological agent of amoebiasis and phagocytosis plays a key role in virulence of this organism. Signaling pathways involved in activation of cytoskeletal dynamics required for phagocytosis remain to be elucidated. Phagocytosis is initiated with sequential recruitment of EhC2PK, EhCaBP1, EhCaBP3 and an atypical kinase EhAK1 after particle attachment. Here we show that EhARPC1, an essential subunit of the actin branching complex Arp 2/3 is recruited to the phagocytic initiation sites by EhAK1. Imaging, expression knockdown of different molecules and pull down experiments suggest that EhARPC1 interacts with EhAK1 and that it is required during initiation of phagocytosis and phagosome formation. Moreover, recruitment of EhARPC2 at the phagocytosis initiation by EhAK1 is also observed, indicating that the Arp 2/3 complex is recruited. In conclusion, these results suggests a novel mechanism of recruitment of Arp 2/3 complex during phagocytosis in E. histolytica.
TL;DR: This paper reports for the first time the mechanistic insight of alcohol oxidation with Fe(V)(O) complex of biuret TAML (bTAML), which is isoelectronic withFe(IV)(O)-porphyrin(•+) intermediate form in CytP450, and proposes an ET/PT process after C-H abstraction leading to formation of the aldehyde similar to what has been proposed for the heme and nonheme model compounds.
Abstract: Selective oxidation of alcohol to its corresponding carbonyl compound is an important chemical process in biological as well as industrial reactions. The heme containing enzyme CytP450 has been known to selectively oxidize alcohols to their corresponding carbonyl compounds. The mechanism of this reaction, which involves high-valent Fe(IV)(O)-porphyrin(•+) intermediate with alcohol, has been well-studied extensively both with the native enzyme and with model complexes. In this paper, we report for the first time the mechanistic insight of alcohol oxidation with Fe(V)(O) complex of biuret TAML (bTAML), which is isoelectronic with Fe(IV)(O)-porphyrin(•+) intermediate form in CytP450. The oxidations displayed saturation kinetics, which allowed us to determine both the binding constants and first-order rate constants for the reaction. The K and k values observed for the oxidation of benzyl alcohol by Fe(V)(O) at room temperature (K = 300 M(-1), k = 0.35 s(-1)) is very similar to that obtained by CytP450 compound I at -50 °C (K = 214 M(-1), k = 0.48 s(-1)). Thermodynamic parameters determined from van't Hoff's plot (ΔH∼ -4 kcal/mol) suggest hydrogen bonding interaction between substrate and bTAML ligand framework of the Fe(V)(O) complex. Analysis of H/D KIE (kH/kD ∼ 19 at 303 K), Hammett correlation and linearity in Bell-Evans-Polyanski plot points to the C-H abstraction as the rate determination step. Finally, experiments using Fe(V)(O(18)) for benzyl alcohol oxidation and use of the "radical clock" cyclobutanol as a substrate shows the absence of a rebound mechanism as is observed for CytP450. Instead, an ET/PT process is proposed after C-H abstraction leading to formation of the aldehyde, similar to what has been proposed for the heme and nonheme model compounds.
TL;DR: In this article, the authors deal with the fatigue crack growth simulations of three-dimensional linear elastic cracks by XFEM under cyclic thermal load, where both temperature and displacement approximations are extrinsically enriched by Heaviside and crack front enrichment functions.
Abstract: This paper deals with the fatigue crack growth simulations of three-dimensional linear elastic cracks by XFEM under cyclic thermal load. Both temperature and displacement approximations are extrinsically enriched by Heaviside and crack front enrichment functions. Crack growth is modelled by successive linear extensions, and the end points of these linear extensions are joined by cubic spline segments to obtain a modified crack front. Different crack geometries such as planer, non-planer and arbitrary spline shape cracks are simulated under thermal shock, adiabatic and isothermal loads to reveal the sturdiness and versatility of the XFEM approach.
TL;DR: In this article, the low-energy structures of PtnSnn and Pt3mSnm clusters were determined using genetic algorithm incorporated with density functional theory, and the results provided the general trends for the structural and bonding characteristics of the Pt-Sn alloy clusters and help understand their catalytic behavior.
Abstract: The low-energy structures of PtnSnn (n = 1–10) and Pt3mSnm (m = 1–5) clusters have been determined using genetic algorithm incorporated with density functional theory Platinum and tin atoms tend to mix with each other due to the energetically favorable Pt–Sn bonds However, due to the larger atomic radius of Sn atoms, we find segregation of Sn atoms on the surface of PtnSnn clusters This leaves one or two Pt atoms available for reaction and for larger clusters segregation of Sn could block the Pt sites For Pt3mSnm clusters, Sn atoms are well separated in the cluster structures and prefer to form sharp vertices leaving triangular faces of three Pt atoms available for reactivity The electronic properties such as highest occupied molecular orbital–lowest unoccupied molecular orbital gap, distribution of frontier orbitals, Mayer bond order, Mulliken atomic charge, and the density of states are discussed Significant hybridization between the d orbitals of Pt and the p orbitals of Sn is revealed These theoretical results provide the general trends for the structural and bonding characteristics of the Pt–Sn alloy clusters and help understand their catalytic behavior
TL;DR: In this article, a hexagonal-shaped fractal antenna with triangular slot for super wideband (SWB) application is presented, which has total size of 20 × 33.4 × 1.57 mm3.
Abstract: A hexagonal-shaped fractal antenna with triangular slot for super wideband (SWB) application is presented. The proposed antenna has total size of 20 × 33.4 × 1.57 mm3.The proposed antenna is designed of iterations of triangular slot on a hexagonal metallic patch with tapered microstrip line feed. A combination of semicircular and rectangular shaped partial ground plane is used to achieve a super wide bandwidth from 3 to 35 GHz with bandwidth ratio of 11.6:1. The antenna design, simulation and optimization are performed using IE3D Full Wave Electromagnetic Simulator. The proposed antenna is compact and has stable radiation pattern. The simulation and measured results are compared to demonstrate the performance of proposed antenna. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1659–1662, 2015
TL;DR: Furosemide (FS), a loop diuretic drug commonly used for the treatment of hypertension and edema, exhibited color cocrystal polymorphism with coformer 4,4′-bipyridine (4BPY) in the stoichiometry 2:1 as mentioned in this paper.
Abstract: Furosemide (FS), a loop diuretic drug commonly used for the treatment of hypertension and edema, exhibited color cocrystal polymorphism with coformer 4,4′-bipyridine (4BPY) in the stoichiometry 2:1, albeit both the API and the cocrystal former are colorless. Crystallization from ethanol, isopropanol, ethanol–water (v/v, 1/1) mixture, and acetonitrile yielded pale yellow (form 1I, thin needles) and orange (form 1II, blocks) cocrystals concomitantly. Needles appeared from solution within a day, while the blocks were obtained after 1–2 days from the same flask, indicating that yellow needles were formed faster and the orange blocks were perhaps formed under thermodynamic conditions. Form 1I cocrystals could also be produced from the variety of common solvents. Cocrystallization of FS with 2,2′-bipyridine (2BPY) and 4-aminopyridine (4AP) gave colorless cocrystals 2 and 3, respectively, and did not exhibit polymorphism. The single-crystal X-ray structures, powder X-ray diffraction, photophysical characterizati...
TL;DR: In this article, the authors analyzed the percentage departure of rainfall for nearly two decades (1997-2014) along with crop statistics and showed that the SW monsoon rainfall in the NER has gradually dropped in recent years compared to the 1980s and 1990s as a result, these regions have witnessed frequent unprecedented drought than Western India.
Abstract: The rainfall distribution over Western and North East India during the southwest (SW) monsoon season is geographically distinct with the heaviest seasonal rainfall occurs over the North Eastern Region (NER), while the lowest rainfall occurs over the Western region (Saurashtra and Kutch in Gujarat, and also in Rajasthan) Gujarat is located in arid to semiarid region and has more drought-prone areas In contrast, Assam and Meghalaya have humid climate and occurrence of drought is unusual Here, we analyse the percentage departure of rainfall for nearly two decades (1997-2014) along with crop statistics Our results indicate that the SW monsoon rainfall in the NER has gradually dropped in recent years compared to the 1980s and 1990s As a result, these regions have witnessed frequent unprecedented drought than Western India In NER, probability of drought occurrence was 54%, and it is 27% for Western India in the recent decade (2000-2014) The frequent drought has caused adverse agricultural impacts and our results show a significant negative rice production anomaly during drought years 2005-06 and 2009 in Assam Drought impacts were also reported from other states in NER during 2010-11 and 2013 Drought associated with El Nino was not so strong; however, increasing temperature and increased monsoon season rainfall variability have an impact on global climate change This may cause warming-induced drought leading to adverse impact on agriculture and food security in the NER
15 May 2015
TL;DR: An overview of the different type of graph databases, applications, and comparison between their models based on some properties is given.
Abstract: In the era of big data, data analytics, business intelligence database management plays a vital role from technical business management and research point of view. Over many decades, database management has been a topic of active research. There are different type of database management system have been proposed over a period of time but Relational Database Management System (RDBMS) is the one which has been most popularly used in academic research as well as industrial setup[1]. In recent years, graph databases regained interest among the researchers for certain obvious reasons. One of the most important reasons for such an interest in a graph database is because of the inherent property of graphs as a graph structure. Graphs are present everywhere in the data structure, which represents the strong connectivity within the data. Most of the graph database models are defined in which data-structure for schema and instances are modeled as graph or generalization of a graph. In such graph database models, data manipulations are expressed by graph-oriented operations and type constructors [9]. Now days, most of the real world applications can be modeled as a graph and one of the best real world examples is social or biological network. This paper gives an overview of the different type of graph databases, applications, and comparison between their models based on some properties.