1,540 research outputs found
Deuteron and proton NMR study of Dâ, p-dichlorobenzene and 1,3,5-trichlorobenzene in bimesogenic liquid crystals with two nematic phases
The solutes dideuterium, 1,3,5-trichlorobenzene and p-dichlorobenzene (pdcb) are co-dissolved in a 61/39 wt% mixture of CBC9CB/5CB, a bimesogenic liquid crystal with two nematic phases. NMR spectra are collected for each solute. The local electric field gradient (FZZ) is obtained from the dideuterium spectrum. A double Maier-Saupe potential (MSMS) is used to rationalize the order parameters of pdcb. The liquid-crystal fields Gâ and Gâ are taken to be due to size and shape interactions and interactions between the solute molecular quadrupole and the mean FZZ of the medium. The FZZâs obtained from Dâ and Gâ (from pdcb) are compared and discussed
Origin of Superconductivity in Boron-doped Diamond
Superconductivity of boron-doped diamond, reported recently at T_c=4 K, is
investigated exploiting its electronic and vibrational analogies to MgB2. The
deformation potential of the hole states arising from the C-C bond stretch mode
is 60% larger than the corresponding quantity in MgB2 that drives its high Tc,
leading to very large electron-phonon matrix elements. The calculated coupling
strength \lambda ~ 0.5 leads to T_c in the 5-10 K range and makes phonon
coupling the likely mechanism. Higher doping should increase T_c somewhat, but
effects of three dimensionality primarily on the density of states keep doped
diamond from having a T_c closer to that of MgB2.Comment: Four pages with two embedded figures, corrected fig1. (To appear in
Physical Review Letters(2004)
The stabilisation of the Nx phase in mixtures
The phase behaviour of mixtures between two symmetric dimers, CBC9CB and the ether-linked analogue CBOC9OCB was investigated by Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) studies. The dimeric constituents are fully miscible and the construction of a temperature-composition phase diagram reveals a surprising amplification of the stability of the Nx phase in compositions of up to 37 wt% of CBOC9OCB in CBC9CB. The origin for this enhancement of stability is discussed and an explanation based on chiral recognition is developed
NMR study of a bimesogenic liquid crystal with two nematic phases
Recent interest in bimesogenic liquid crystals showing two nematic phases has led us to investigate the nematic mean-field interactions in these nematic phases by using rigid solutes as probes. The nematic potential that is modelled by two independent Maier-Saupe terms is successful in fitting the observed dipolar couplings (order parameters) of para-, meta- and ortho-dichlorobenzene solutes in both the nematic phases of 39 wt% of 4-n-pentyl-4â˛-cyanobiphenyl (5CB) in Îą,Ď-bis(4-4â˛-cyanobiphenyl)nonane (CB_C9_CB) to better than the 5% level. The derived liquid-crystal potential parameters Gâ and Gâ for each solute in the N and Ntb phases will be discussed. The most interesting observation is that G1 (associated with size and shape interactions) is almost constant in the Ntb phase, whereas Gâ (associated with longer-range electrostatic interactions) has large variation, even changing sign
Noninvasive Measurement of Dissipation in Colloidal Systems
According to Harada and Sasa [Phys. Rev. Lett. 95, 130602 (2005)], heat
production generated in a non-equilibrium steady state can be inferred from
measuring response and correlation functions. In many colloidal systems,
however, it is a nontrivial task to determine response functions, whereas
details about spatial steady state trajectories are easily accessible. Using a
simple conditional averaging procedure, we show how this fact can be exploited
to reliably evaluate average heat production. We test this method using
Brownian dynamics simulations, and apply it to experimental data of an
interacting driven colloidal system
Late GlacialâHolocene climatic transition record at the Argentinian Andean piedmont between 33 and 34° S
The Arroyo La Estacada (~ 33°28' S,
69°02' W), eastern Andean piedmont of Argentina, cuts
through an extensive piedmont aggradational unit composed of a dominant Late
Pleistoceneâearly Holocene (LPâEH) alluvial sequence that includes several
paleosols.
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One of these paleosols developed affecting the topmost part of likely
Late Glacial aeolian deposits aggraded into a floodplain environment by the
end of the Late Pleistocene. The paleosol shows variable grade of
development along the arroyo outcrops. Organic matter humification,
carbonate accumulation and redox processes were the dominant processes
associated with paleosol formation. By the early Holocene, when the
formation of the paleosol ended, renewed alluvial aggradation and high
magnitude flooding events affected the arroyo's floodplain environment. Accordignly,
a period of relative landscape stability in the Arroyo La Estacada basin is
inferred from the paleosol developed by the LPâEH transition in response to
the climatic conditions in the Andes cordillera piedmont after the
Late Glacial arid conditions. The analyzed Late GlacialâHolocene alluvial record of the Andean
piedmont constitutes a suitable record of the LPâEH climatic transition in
the extra-Andean region of Argentina. It is in agreement with regional
paleoclimatic evidence along the southern tip of the South American
continent, where other pedosedimentary sequences record similar late
Quaternary paleoenvironmental changes over both fluvial and interfluvial
areas
Solving singular generalized eigenvalue problems. Part II: projection and augmentation
Generalized eigenvalue problems involving a singular pencil may be very
challenging to solve, both with respect to accuracy and efficiency. While Part
I presented a rank-completing addition to a singular pencil, we now develop two
alternative methods. The first technique is based on a projection onto
subspaces with dimension equal to the normal rank of the pencil while the
second approach exploits an augmented matrix pencil. The projection approach
seems to be the most attractive version for generic singular pencils because of
its efficiency, while the augmented pencil approach may be suitable for
applications where a linear system with the augmented pencil can be solved
efficiently
Produção de biomassa e padrão de decomposição de adubos verdes cultivados nas entrelinhas de acerola orgânica.
A utilização de adubos verdes constitui uma opção para o adequado aporte de matÊria orgânica em solos arenosos sujeitos a um alto grau de degradação. O objetivo deste trabalho foi quantificar a produção e o padrão de decomposição de biomassa de seis espÊcies de adubos verdes e da vegetação espontânea
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