This study discusses an evacuated tube collector-type solar water heater (ETCSWH) using a phase change material (PCM) chamber with fins, nanofluid, and nano-enhanced phase change material (NEPCM). ...First, the charging phenomena in a horizontal triplex tube heat exchanger (TTHX) equipped with fins, natural convection, and an ETCSWH system without PCM is simulated to validate the solution. The impact of adding fins and nanoparticles with a volume fraction of 3% of Al
O
and Cu to paraffin wax and water-based fluid, respectively, on the unit's efficiency has been examined. The proposed system for the PCM melting process, heat storage, fluid flow behavior in the system, and velocity distribution and temperature contour in the storage tank and three parts of the absorber tube have been evaluated using ANSYS FLUENT software in a three-dimensional and transient simulation. The results show that Case 8 has improved by 39.7% compared to Case 1 and Case 4 by 5.2% compared to Case 1 within 4 h of the melting process. Also, Case 8 with a 43% and 6.4% shorter melting time than Cases 1 and 5 has the best performance and the greatest heat transfer rate. The productivity of the ETCSWH system is considerably enhanced by the use of fins, NEPCM, and nanofluid.
Varieties of Roman domination II Chellali, M.; Jafari Rad, N.; Sheikholeslami, S. M. ...
AKCE international journal of graphs and combinatorics,
09/2020, Letnik:
17, Številka:
3
Journal Article
Recenzirano
Odprti dostop
In this work, we continue to survey what has been done on the Roman domination. More precisely, we will present in two sections several variations of Roman dominating functions as well as the signed ...version of some of these functions. It should be noted that a first part of this survey comprising 9 varieties is published as a chapter book in “Topics in domination in graphs” edited by T.W. Haynes, S.T. Hedetniemi and M.A. Henning. We recall that a function is a Roman dominating function (or just RDF) if every vertex u for which f(u) = 0 is adjacent to at least one vertex v for which f(v) = 2. The Roman domination number of a graph G, denoted by is the minimum weight of an RDF on G.
Let G be a simple graph of order n. The matrix S(G) = D(G) + A(G) is called the signless Laplacian matrix of G, where D(G) and A(G) denote the diagonal matrix of vertex degrees and the adjacency ...matrix of G, respectively. Let s
1
(G) and λ
1
(G) be the largest eigenvalue of S(G) and A(G), respectively. In this paper, we first present sharp upper and lower bounds for s
1
(G) and λ
1
(G) involving the maximum degree, the minimum degree, order, size and sum-connectivity F-index. Moreover, we investigate the relation between s
1
(G) and λ
1
(G).
In this study natural convection heat transfer of Cu–water nanofluid in a cold outer circular enclosure containing a hot inner sinusoidal circular cylinder in the presence of horizontal magnetic ...field is investigated numerically using the Control Volume based Finite Element Method (CVFEM). Both circular enclosure and inner cylinder are maintained at constant temperature. The governing equations of fluid motion and heat transfer in their vorticity stream function form are used to simulate the fluid flow and heat transfer. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. The calculations were performed for different governing parameters such as the Hartmann number, Rayleigh number, values of the number of undulations of the inner cylinder and nanoparticle volume fraction. The results indicate that in the absence of magnetic field, enhancement ratio decreases as Rayleigh number increases while an opposite trend is observed in the presence of magnetic field. Also it is found that the average Nusselt number is an increasing function of nanoparticle volume fraction, the number of undulations and Rayleigh numbers while it is a decreasing function of Hartmann number.
A set S of vertices is a perfect dominating set of a graph G if every vertex not in S is adjacent to exactly one vertex of S. The minimum cardinality of a perfect dominating set is the perfect ...domination number γp(G). A perfect Roman dominating function (PRDF) on a graph G=(V,E) is a function f:V→{0,1,2} satisfying the condition that every vertex u with f(u)=0 is adjacent to exactly one vertex v for which f(v)=2. The weight of a PRDF is the sum of its function values over all vertices, and the minimum weight of a PRDF of G is the perfect Roman domination number γRp(G). Obviously, for every graph G, γRp(G)≤2γp(G), and those graphs attaining the equality are called perfect Roman graphs. In this paper, we provide a characterization of perfect Roman trees.
In this study, critical temperature and frequency characteristics of a doubly curved panel are reinforced by graphene nanoplatelets (GPLs) with the aid of a two-dimensional generalized differential ...quadrature method (2D-GDQM) are investigated. The size effects are included using nonlocal strain gradient theory (NSGT) that has two length scale parameters, and the panel is modeled as a panel using high order shear deformation theory (HSDT). The mechanical properties of GPLs are calculated based on the rule of mixtures and the modified Halpin–Tsai model. The novelty of the current study is in considering the effects of the thermal environment, various boundary conditions, and size effects on the frequency and critical temperature of the GPLRC panel. The validation is performed through the comparison of the numerical results for the frequency of the GPLRC panel and the literature. For more verification, a finite element model is presented using the finite element package to simulate the response of the current structure. The results created from a finite element simulation illustrate a close agreement with the numerical method results. The results demonstrate that GPLs’ weight function, the ratio of panel curvature (R1/R2), GPLs’ pattern, and size-dependent parameters have noticeable effects on the frequency and critical temperature characteristics of the GPLs-reinforced composite (GPLRC) curved panel. The favorable suggestion of this survey is that when designing the GPLRC structure, special attention should be paid to size-dependent parameters because the nonlocal and length scale parameters have an essential role in the static and dynamic behaviors of the GPLRC panel.
A two-dimensional numerical study has been performed to investigate natural convection in a square cavity with curve boundaries filled with Cu–water nanofluid. Lattice Boltzmann Method (LBM) is used ...to simulate this problem. The effective thermal conductivity and viscosity of nanofluid are calculated by the Maxwell–Garnetts (MG) and Brinkman models, respectively. This investigation was compared with other numerical methods and was found to be in excellent agreement. Effects of nanoparticle volume fraction, Rayleigh numbers and inclination angle on flow and heat transfer are considered. The results proved that the change of inclination angle has a significant impact on the thermal and hydrodynamic flow fields. Also it can be found that maximum values of enhancement are obtained at Ra=103 and Ra=105 for γ>0° and γ<0°, respectively.
Display omitted
•Natural convection of nanofluid filled cavity was investigated.•LBM is used to solve this problem.•Nusselt number increases with increase of ϕ and Ra.•Emax is obtained at Ra=103 and Ra=105 for γ>0° and γ<0°, respectively.
Global triple Roman dominating function Nahani Pour, F.; Abdollahzadeh Ahangar, H.; Chellali, M. ...
Discrete Applied Mathematics,
06/2022, Letnik:
314
Journal Article
Recenzirano
Let k be a positive integer and G=(V,E) a graph. A k-Roman dominating function is a function f:V→{0,1,2,…,k+1} such that for every v∈V(G) with f(v)<k, f(ANv)≥|AN(v)|+k, where AN(v) is the set of ...neighbors of v assigned a non-zero value under f and ANv=AN(v)∪{v}. When k=3, the function f is called a triple Roman dominating function (TRD-function). A global triple Roman dominating function (GTRD-function) on a graph G=(V,E) is a TRD-function for both G and its complement graph G¯. The global triple Roman domination number of a graph G is the minimum weight over all GTRD-functions on G. In this paper, we start the study of the global triple Roman domination number and we obtain various tight bounds for it. Moreover, we prove that the global triple Roman domination problem is NP-complete for bipartite and chordal graphs.
(SARS-CoV-2), was first identified in December 2019 as the cause of a respiratory illness designated coronavirus disease 2019, or Covid-19. Several therapeutic agents have been evaluated for the ...treatment of Covid-19, but none have yet been shown to be efficacious. Remdesivir (GS-5734), an inhibitor of the viral RNA-dependent, RNA polymerase with inhibitory activity against SARS-CoV and the Middle East respiratory syndrome (MERS-CoV), was identified early as a promising therapeutic candidate for Covid-19 because of its ability to inhibit SARS-CoV-2 in vitro. Besides, in nonhuman primate studies, remdesivir initiated 12 hours after inoculation with MERS-CoV9,10 reduced lung virus levels and lung damage. In the field of Medical Science, concerning the definition of the topological index on the molecular structure and corresponding medical, biological, chemical, pharmaceutical properties of drugs can be studied by the topological index calculation. In this paper, we compute some of the general temperature topological properties of remdesivir that the results in this paper may be useful in finding new drug and vaccine for the treatment and prevention of COVID-19.
Let G be a subcubic graph of order n and minimum degree at least 2. In this paper, we prove the conjecture of Bermudo and Fernau that if n≥23, then ∂(G)≥5n∕18, where ∂(G) is the differential of G. To ...do this, we use the Gallai-type result involving the Roman domination number γR(G) and ∂(G) by proving that, with the exception of thirteen graphs of order at most 22, every connected graph G satisfies γR(G)≤13n18.
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