Synthesis and characterization of a chiral antiferroelectric series with new SmC A*-L transition

Two new chiral series with a tolane core: (S) 4-(1-methylheptyloxycarbonyl)phenyl (series IB) and (S) 4-(1-ethylheptyloxycarbonyl)phenyl (series IC) 4-alkanoyloxytolane-4'-carboxylates have been synthesized and characterized. All the compounds are mesomorphic, and most of them display the antiferroelectric SmC*A phase. The mesomorphic properties have been analysed by optical microscopy, DSC, helical pitch and electro-optical measurements and X-ray diffraction study. Series IB exhibits a very rich polymesomorphism with SmC*alpha, SmC*, SmC* F12, SmC* F11 and SmC*A phases, like the previously reported series IA, [(S) 4-(1-methylheptyloxycarbonyl)phenyl 4-alkyloxytolane-4-carboxylates]. Series IC is more interesting because it presents for the first time in antiferroelectric series the liquid-like phase (L phase) between the SmC*A and isotropic phases. Preliminary optical studies plead in favour of a helical short range structure for this new liquid-like L phase.     

Key properties of monohalogen substituted phenols: interpretation in terms of the electron localization function

This paper is an attempt to bridge the key properties of monohalogen substituted phenols with the electronic localization function, which has a vivid 3D topological pattern and the vector gradient field of which is determined by the electron transition current density. A primary goal is to interpret the ‘anomalous’ strength of the intramolecular hydrogen bond O—H···X formed in cis ortho-X substituted phenols, depending upon the halogen atom (X = F, Cl, and Br) in terms of the populations of the electronic localization function basins and a so-called core valence bifurcation index. A theoretical model is considered aiming to explain convincingly the cis-trans conversion in ortho-X phenols occurring in some solvents and resulting in the experimentally observed splitting of the ν_OH stretch and based on the Pauling model. Characteristic harmonic vibrational modes of all monohalogen substituted phenols are discussed thoroughly. The order of stability of monohalogen substituted phenols is established at a high level of computational performance, showing the ‘anomalous’ order of stability of fluorophenols, the result being that, in contrast to Cl and Br, the F atom favours the trans meta position over the cis ortho with formation of the intramolecular hydrogen bond.     

Synthesis,properties and crystal structure of chiral semiperfluorinated liquid crystals with ferro and anticlinic smectic phases

A new chiral and semiperfluorinated series with ferro and anticlinic properties has been synthesized and characterized. The mesomorphic behaviour has been established on the grounds of both microscopic observations and DSC measurements. The non-chiral intermediate ethyl 4-semiperfluorinated alkyloxybenzoates exhibit SmA phases, unusual for compounds with a single phenyl ring. The final derivatives display SmA, SmC* and in several cases SmC*A phases. The longer fluorinated chains favour the SmA and SmC* phases at the expense of the SmC*A phase. Electro-optical measurements were carried out with the classical SSFLC geometry. The spontaneous polarization and tilt angle at saturation are higher than those of the hydrogenous homologues, around 140 nCcm-2 at 40 degrees C. One compound of the series, the 4,4,5,5,6,6,7,7,8,8,8-nonafluoroheptyloxy derivative, C36H35O7F9, Mx=750.6 g mol-1, crystallizes in the triclinic system, space group P1 with four independent molecules in the asymmetric unit (Z=4). The molecules are arranged in a head-to-tail fashion with two molecules oriented in the same direction and the two others in the opposite direction. They give rise to sheets with a smectic C-like arrangement. The final reliability factors were R=0.117 and wR=0.134; the goodness of fit was S=1.366.     

BIOECONOMIC MODEL OF EASTERN BALTIC COD UNDER THE INFLUENCE OF NUTRIENT ENRICHMENT

Abstract The objective of this paper is to study the economic management of Eastern Baltic cod (Gadus morhua) under the influence of nutrient enrichment. Average nitrogen concentration in the spawning areas during the spawning season of cod stock is chosen to be an indicator of nutrient enrichment. The optimal cod stock is defined using a dynamic bioeconomic model for the cod fisheries. The results show that the current stock level is about half of the estimated optimal stock level and that the current total allowable catch (TAC) is about one‐fourth of the optimal equilibrium yield. The results also indicate that the benefit from a reduction in nitrogen very much depends on the harvest policies. If the TAC is set equal to the optimal equilibrium yield, the benefit of a nitrogen reduction from the 2009 level to the optimal nitrogen level would be about 604 million DKK over a 10‐year time horizon, given a discount rate of 4% per year. However, if a recovery management plan is chosen, the benefit would only be about 49 million DKK over a 10‐year time horizon.     

Photodiode-Based Chua＇s Circuit with Light Controllability

We present a photodiode-based Chua＇s chaotic circuit that is controllable by light. The proposed circuit consists of an inductor, two passive capacitors, a photodiode-based variable resistor, and a positive feedback trans- conductor with negative nonlinearity. The chaotic dynamics of the circuit were verified by using the simulation program with integrated circuit emphasis analysis using the 0.35 #m complementary metal-oxide-semiconductor process parameters. The gain results （such as the time waveform~ frequency analysis, three-dimensional attractor, bifurcation and Lyapunov exponents diagrams） confirm that the chaotic behavior of the circuit could be controlled by light intensity via the photodiode-based variable resistor.     

Viscosity: From air to hot nuclei

After a brief review of the history of viscosity from classical to quantal fluids, a discussion of how the shear viscosity η of a finite hot nucleus is calculated directly from the width and energy of the giant dipole resonance (GDR) of the nucleus is given in this paper. The ratio η/s with s being the entropy volume density, is extracted from the experimental systematic of GDR in copper, tin and lead isotopes at finite temperature T. These empirical results are compared with the results predicted by several independent models, as well as with almost model-independent estimations. Based on these results, it is concluded that the ratio η/s in medium and heavy nuclei decreases with increasing T to reach \((1.3 - 4) \times \hbar /(4\pi k_{\mathrm {B}})\) at T = 5 MeV, which is almost the same as that obtained for quark-gluon plasma at T > 170 MeV.     

A SPECTRAL METHOD FOR UNSTEADY FLOW AND HEAT TRANSFER PAST A SPHERICAL DROPLET: PRIMITIVE VARIABLE FORMULATION

Abstract

A spectral method is developed based on the primitive variables for the time-dependent solution of the flow and the temperature past a spherical droplet. Both Chebyshev and Legendre polynomials are used to expand the velocity, pressure, and temperature in the radial and angular directions, respectively. The fractional time-stepping method suggested by Orszag (Orszag et al., 1980) is used for solving the flow and the pressure fields. Euler backward differencing is used for the integration of the energy equation. The computed steady-state drag coefficients are compared to those found in the literature for Reynolds numbers in the range from 0.5 to 50 for both the continuous and the dispersed phase. The transient drag coefficients and Nusselt numbers are compared with our previous study using a stream function-vorticity formulation (Nguyen et al, 1993). The comparison indicates that the present model is capable of predicting the correct nature of the flow and heat transfer associated with a droplet.     

Direct smectic A-smectic C*A phase transition

The anticlinic smectic CA phase belongs to the class of tilted smectic phases with an azimuthal angle alternating from one direction (theta=0) to the other (theta=pi) in successive layers. It occurs in general at lower temperature than the uniformly tilted smectic C phase, but may be obtained directly from the untilted smectic A phase. We use the chiral nCTBB9* series synthesized in this laboratory, in order to obtain a phase transition as close as possible to second order, as revealed by DSC. We measure the temperature behaviour of the birefringence and of the optical rotatory power across the transition in order to characterize the tilt angle. We finally study the optical response to a periodic electric field which excites separately the smectic C* and C*A soft modes. The main conclusion is that the only order parameter governing the critica Al behaviour of the phase transition is the tilt angle theta, as we get common divergence of both soft modes at the same temperature. This confirms previous high resolution calorimetric studies by Ema et al. that saw in MHPOBC an initial mean-field second order phase transition when the tilt appears, followed by sharp first order restructuring transitions between the tilted subphases.     

Rotational Forms of Large Eddy Simulation Turbulence Models

In this paper the authors present a derivation of a back-scatter rotational Large Eddy Simulation model,which is the extension of the Baldwin&Lomax model to nonequilibrium problems.The model is particularly designed to mathematically describe a fluid filling a domain with solid walls and consequently the differential operators appearing in the smoothing terms are degenerate at the boundary.After the derivation of the model,the authors prove some of the mathematical properties coming from the weighted energy estimates,which allow to prove existence and uniqueness of a class of regular weak solutions.     

Negative Index Materials and Their Applications: Recent Mathematics Progress

Negative index materials are artificial structures whose refractive index has negative value over some frequency range.These materials were first investigated theoretically by Veselago in 1946 and were confirmed experimentally by Shelby,Smith,and Schultz in 2001.Mathematically,the study of negative index materials faces two difficulties.Firstly,the equations describing the phenomenon have sign changing coefficients,hence the ellipticity and the compactness are lost in general.Secondly,the localized resonance,i.e.,the field explodes in some regions and remains bounded in some others as the loss goes to 0,might appear.In this survey,the author discusses recent mathematics progress in understanding properties of negative index materials and their applications.The topics are reflecting complementary media,superlensing and cloaking by using complementary media,cloaking a source via anomalous localized resonance,the limiting absorption principle and the well-posedness of the Helmholtz equation with sign changing coefficients.