Numerical analysis of filmwise condensation in a plate fin-and-tube heat exchanger in presence of non-condensable gas

In the present paper, a numerical model of a fin-and-tube heat exchanger is proposed. The simulation of water vapor condensation in presence of non-condensable gas (air) between two vertical plane plates and in a plate fin-and-tube heat exchanger in a stationary mode is performed using Fluent software. The differential equations that describe the heat and mass transfer were integrated by the finite volume method, in two and three dimensions.     

Recovery from Numerical Instability during Basis Reinversion

Most of the preassigned pivot agenda algorithms that extend the Hellerman-Rarick P3 algorithm assume that the input matrix is nonsingular. Due to numerical instability, this assumption may be violated and these algorithms fail. We present a modification of theP3 algorithm which includes a procedure to recover from this type of numerical instability.The recovery procedure is integrated into P3 in such a way that all previous work can be maintained and it reduces the likelihoodthat additional recovery will be required.     

Nonvanishing of Hecke L-Functions for CM Fields and Ranks of Abelian Varieties

In this paper we prove a nonvanishing theorem for central values of L-functions associated to a large class of algebraic Hecke characters of CM number fields. A key ingredient in the proof is an asymptotic formula for the average of these central values. We combine the nonvanishing theorem with work of Tian and Zhang [TiZ] to deduce that infinitely many of the CM abelian varieties associated to these Hecke characters have Mordell–Weil rank zero. Included among these abelian varieties are higher-dimensional analogues of the elliptic \mathbb Q{{\mathbb Q}} -curves A(D) of B. Gross [Gr].     

Nonvanishing of Rankin–Selberg L-functions for Hilbert modular forms

Let F be a totally real number field of degree n over $\mathbb{Q}$ with ring of integers $\mathcal{O}$ and narrow class number one. Let S _2k (Γ) be the vector space of cuspidal Hilbert modular forms of parallel weight 2k for $\varGamma=\mathrm{SL}_{2}(\mathcal{O})$ , and let B _2k be an orthogonal Hecke eigenbasis for this space. For any fixed Hecke eigenform f∈S _2k (Γ) and any ε>0, we prove that $$\# \biggl\{ g \in B_{2k}: L \biggl(f \times g, \frac{1}{2} \biggr) \ne0 \biggr\} \gg k^{n- \varepsilon}, $$ where L(f×g,s) is the Rankin–Selberg L–function of f and g.     

Directive metamaterial-based subwavelength resonant cavity antennas – Applications for beam steering

This article presents the use of composite resonant metamaterials for the design of highly directive subwavelength cavity antennas. These metamaterials, composed of planar metallic patterns periodically organized on dielectric substrates, exhibit frequency dispersive phase characteristics. Different models of metamaterial-based surfaces (metasurfaces), introducing a zero degree reflection phase shift to incident waves, are firstly studied where the bandwidth and operation frequency are predicted. These surfaces are then applied in a resonant Fabry–Perot type cavity and a ray optics analysis is used to design different models of ultra-compact high-gain microstrip printed antennas. Another surface presenting a variable reflection phase by the use of a non-periodic metamaterial-based metallic strips array is designed for a passive low-profile steering beam antenna application. Finally, the incorporation of active electronic components on the metasurfaces, allowing an electronic control of the phase responses, is applied to an operation frequency reconfigurable cavity and a beam steering cavity. All these cavity antennas operate on subwavelength modes, the smallest cavity thickness being of the order of λ/60. To cite this article: A. Ourir et al., C. R. Physique 10 (2009).     

The Herglotz-Zagier function, double zeta functions, and values of L-series

In this paper, we define L-series generalizing the Herglotz-Zagier function (Ber. Verhandl. Sächsischen Akad. Wiss. Leipzig 75 (3-14) (1923) 31, Math. Ann. 213 (1975) 153), and the double zeta function (First European Congress of Mathematics, Vol. II, Paris, 1992, pp. 497-512; Progress in Mathematics, Vol. 120, Birkhäuser, Basel, 1994) and evaluate them after meromorphic continuation at integer points in their extended domains. This is accomplished in three steps. First, when is a periodic function and are the harmonic numbers, we establish identities relating these series to the L-series

     

Fresnel phase matching: a universal phase matching scheme

We present new theoretical concepts for Fresnel phase matching. A guided wave approach is described, which allows us to intrinsically take into account all the physical processes involved. To cite this article: M. Raybaut et al., C. R. Physique 8 (2007).     

Sculpting the bicyclo[3.1.0]hexane template of carbocyclic nucleosides to improve recognition by herpes thymidine kinase

The replacement of the furanose ring by a cyclopentane in nucleosides generates a group of analogues known generically as carbocyclic nucleosides. These compounds have increased chemical and enzymatic stability due to the absence of a true glycosyl bond that characterizes conventional nucleosides. The additional fusion of a cyclopropane ring to the cyclopentane produces a bicyclo[3.1.0]hexane system that depending on its location relative to the nucleobase is able to lock the embedded cyclopentane ring into conformations that mimic the typical north and south conformations of the furanose ring in conventional nucleosides. These bicyclo[3.1.0]hexane templates have already provided important clues to differentiate the contrasting conformational preferences between kinases and polymerases. Herein, we describe the design, synthesis, and phosphorylation pattern of a new bicyclo[3.1.0]hexane thymidine analogue that seems to possess an ideal spatial distribution of pharmacophores for an optimal interaction with herpes simplex 1 thymidine kinase. The bicyclo[3.1.0]hexane template represents a privileged rigid template for sculpting other carbocyclic nucleosides to meet the demands of specific receptors.     

Cytotoxic triterpenoid saponins from the roots of Cephalaria gigantea

Three new oleanane-type saponins, giganteosides L (1), M (2) and N (3) along with eight known ones were isolated from the roots of Cephalaria gigantea. Their structures were established as 3-O-[beta-D-galactopyranosyl-(1-->2)-beta-D-glucuronopyranosyl]-28-O-[beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl]-oleanolic acid, 3-O-[beta-D-galactopyranosyl-(1-->2)-beta-D-glucuronopyranosyl]-28-O-[beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl]-hederagenin, 3-O-[alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucuronopyranosyl]-28-O-[beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl]-hederagenin, respectively, by means of spectroscopic methods (1D and 2D NMR, HR-ESI-MS). Cytotoxic activity of monodesmosides was investigated in vitro using three cancer cell lines, namely, human non pigmented melanoma MEL-5 and human leukemia HL-60. Giganteosides D (4) and E (5) showed antiproliferative effect on human cell lines with IC(50) values in the range 3.15-7.5 microM.     

Antiplasmodial activity of three bisbenzylisoquinoline alkaloids from the tuber of Stephania rotunda

Three bisbenzylisoquinoline alkaloids were isolated for the first time from Stephania rotunda tuber. Their structures were elucidated by spectroscopic methods and their antiplasmodial activity was investigated in vitro on chloroquine resistant Plasmodium falciparum strain W2. These alkaloids were identified as 2-norcepharanthine (1), cepharanoline (2) and fangchinoline (3). In vitro, they displayed significant antiplasmodial activity with inhibitory concentration 50 values of 0.3, 0.2 and 0.3 μM.