1,115 research outputs found
Non-Fourier heat transport in metal-dielectric core-shell nanoparticles under ultrafast laser pulse excitation
Relaxation dynamics of embedded metal nanoparticles after ultrafast laser
pulse excitation is driven by thermal phenomena of different origins the
accurate description of which is crucial for interpreting experimental results:
hot electron gas generation, electron-phonon coupling, heat transfer to the
particle environment and heat propagation in the latter. Regardingthis last
mechanism, it is well known that heat transport in nanoscale structures and/or
at ultrashort timescales may deviate from the predictions of the Fourier law.
In these cases heat transport may rather be described by the Boltzmann
transport equation. We present a numerical model allowing us to determine the
electron and lattice temperature dynamics in a spherical gold nanoparticle core
under subpicosecond pulsed excitation, as well as that of the surrounding shell
dielectric medium. For this, we have used the electron-phonon coupling equation
in the particle with a source term linked with the laser pulse absorption, and
the ballistic-diffusive equations for heat conduction in the host medium.
Either thermalizing or adiabatic boundary conditions have been considered at
the shell external surface. Our results show that the heat transfer rate from
the particle to the matrix can be significantly smaller than the prediction of
Fourier's law. Consequently, the particle temperature rise is larger and its
cooling dynamics might be slower than that obtained by using Fourier's law.
This difference is attributed to the nonlocal and nonequilibrium heat
conduction in the vicinity of the core nanoparticle. These results are expected
to be of great importance for analyzing pump-probe experiments performed on
single nanoparticles or nanocomposite media
Analytic Approximate Solutions for MHD Boundary-Layer Viscoelastic Fluid Flow over Continuously Moving Stretching Surface by Homotopy Analysis Method with Two Auxiliary Parameters
In this study, a steady, incompressible, and laminar-free convective flow of a two-dimensional electrically conducting viscoelastic fluid over a moving stretching surface through a porous medium is considered. The boundary-layer equations are derived by considering Boussinesq and boundary-layer approximations. The nonlinear ordinary differential equations for the momentum and energy equations are obtained and solved analytically by using homotopy analysis method (HAM) with two auxiliary parameters for two classes of visco-elastic fluid (Walters’ liquid B and second-grade fluid). It is clear that by the use of second auxiliary parameter, the straight line region in ℏ-curve increases and the convergence accelerates. This research is performed by considering two different boundary conditions: (a) prescribed surface temperature (PST) and (b) prescribed heat flux (PHF). The effect of involved parameters on velocity and temperature is investigated
Pan-PPAR Agonist, Bezafibrate, Restores Angiogenesis in Hindlimb Ischemia in Normal and Diabetic Rats
Introduction. The aim of this study was to investigate the effect of bezafibrate as a pan-PPAR agonist on angiogenesis and serum nitrite, the main metabolite of nitric oxide (NO), vascular endothelial growth factor (VEGF) and VEGF receptor-2 (VEGFR-2) concentrations in hindlimb ischemia model of normal and type I diabetic rats. Methods. 28 male Wistar rats were divided into control and diabetic groups. Then, all rats underwent unilateral hindlimb ischemia. After recovery, they were randomly assigned to one of the following experimental groups: (1) control; (2) control + bezafibrate (400 mg/kg/day); (3) diabetic; (4) diabetic + beztafibrate. After three weeks, blood samples were taken and capillary density was evaluated in the gasterocnemius muscle of ischemic limb. Results. Bezafibrate increased capillary density and capillary/fiber ratio in ischemic leg of diabetic and control rats (P < 0.05). Serum VEGF and VEGFR-2 concentrations did not alter after bezafibrate administration, however, serum nitrite concentration was significantly higher in bezafibrate-treated groups than non-treated groups (P < 0.05). Discussion. It seems that bezafibrate, as a pan PPAR agonist, restores angiogenesis in hindlimb ischemic diabetic animals and is useful for prevention and/or treatment of peripheral artery disease in diabetic subjects
Using of a New Carbon Nano Tube Version in Sheet Shape for Water and Wastewater Treatment
Removal of xylene (a toxic compound) from aqueous solution by modified multi wall carbon nano tubes
(MWCNT) via silica as sheeted carbon nanotube (SCNT) was evaluated. The physicochemical properties of
MWCNT such as structure and availability surface were improved due to convert tubes into sheets that
cause significantly increase in xylene adsorption. The equilibrium amount (qe (mg/g)) in nano material's
dose of 1g/l, xylene concentration of 10mg/l, contact time of 10min, and pH 7, for SCNT (qe 9.8 mg/g) was
higher than single wall carbon nano tubes (SWCNT) (qe 9.2 mg/g) and MWCNT (qe 8.9 mg/g). It is concluded
that sheeted carbon nanotube due to their large surface area improve performance of xylene adsorption.
Also carbon nano tube (CNT) recycling by heating, showed better adsorption performance for recycled
SCNT. A comparison study on xylene adsorption revealed that sheeted carbon nanotube has better xylene
adsorption performance as compared to CNT, carbon and silica adsorbents. This suggests that the SCNT is
an efficient adsorbent for xylene removal in environmental pollutions cleanup.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3508
Progress in phase change nano-emulsions for energy applications-A concise review
Thermal energy storage and transport are central to the wide application of renewable energy. With excellent storage capacities, latent heat storage is more promising than sensible one. Phase change materials are the primary storage materials for latent heat storage. Phase change nanoemulsions are developed for latent heat storage in flow systems that can be used as heat transport and thermal storage purposes, offering improved heat transfer, pumping power, and higher storage capacities. This review is focused on the new advances in phase change nanoemulsions for energy applications. The phase change nanoemulsions are introduced and their features and classification are provided. The preparation methods and thermophysical properties of these nanostructured phase changeable fluids are discussed and, material synthesis and property characterization are covered. Finally, the applications of this class of fluids in different energy systems are reviewed. The major barriers to the applications of phase change nanoemulsions, including instability and high degree of super-cooling, are discussed
A Facile and Practical p-Toluenesulfonic Acid Catalyzed Route to Dicoumarols Containing an Aroyl group
New and known dicoumarols may be efficiently synthesized employing p-toluenesulfonic acid (p-TSA) as a solid acid catalyst from the reaction of 4-hydroxycoumarin with aryl glyoxal in water. This method offers direct access to structurally diverse coumarin derivatives in moderate to good yields (up to 65%). A total of five new compounds were synthesized.KEYWORDS Dicoumarol, p-toluenesulfonic acid, aryl glyoxal, 4-hydroxycoumarin.PDF and Supp files attache
Study of nonlinear MHD tribological squeeze film at generalized magnetic reynolds numbers using DTM.
In the current article, a combination of the differential transform method (DTM) and Padé approximation method are implemented to solve a system of nonlinear differential equations modelling the flow of a Newtonian magnetic lubricant squeeze film with magnetic induction effects incorporated. Solutions for the transformed radial and tangential momentum as well as solutions for the radial and tangential induced magnetic field conservation equations are determined. The DTM-Padé combined method is observed to demonstrate excellent convergence, stability and versatility in simulating the magnetic squeeze film problem. The effects of involved parameters, i.e. squeeze Reynolds number (N1), dimensionless axial magnetic force strength parameter (N2), dimensionless tangential magnetic force strength parameter (N3), and magnetic Reynolds number (Rem) are illustrated graphically and discussed in detail. Applications of the study include automotive magneto-rheological shock absorbers, novel aircraft landing gear systems and biological prosthetics
A study of cycle systems
A cycle system is a partition of the edges of the complete graph
into cycles. Let be a collection of cycles of length 4 whose edges
partition the edges of . A set of 4-cycles is called a
4-cycle trade if there exists a set of edge-disjoint 4-cycles on the same
vertices, such that also is a collection of
cycles of length 4 whose edges partition the edges of .
We study cycle trades of volume two (double-diamonds) and three and show
that the set of all 4-CS(9) is connected with respect of trading with trades of
volume 2 (double-diamond) and 3.
In addition, we present a full rank matrix whose null-space is containing
trade-vectors
Aquaculture technology transfer to smallholder farmers in Malawi, Southern Africa
Details are given of activities conducted in Zomba, Malawi, in order to demonstrate new aquaculture technologies and encourage their use by smallholder fish farmers. The following technologies were introduced: napier grass as a pond output; use of a reed fence for harvesting fish; developing a high-quality compost as a pond input; vegetable-pond integration; chicken-pond integration; smoking kiln; pond stirring; and rice-fish integration. The reactions of the farmers to these technologies and their testing by the farmers are outlined briefly
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