Relating breakup and incomplete fusion of weakly bound nuclei through a classical trajectory model with stochastic breakup

A classical dynamical model that treats breakup stochastically is presented for low energy reactions of weakly bound nuclei. The three-dimensional model allows a consistent calculation of breakup, incomplete, and complete fusion cross sections. The model is assessed by comparing the breakup observables with continuum discretized coupled-channel quantum mechanical predictions, which are found to be in reasonable agreement. Through the model, it is demonstrated that the breakup probability of the projectile as a function of its distance from the target is of primary importance for understanding complete and incomplete fusion at energies near the Coulomb barrier.     

Growth mechanism of nanocrystals in solution: ZnO, a case study

We investigate the mechanism of growth of nanocrystals from solution using the case of ZnO. Spanning a wide range of values of the parameters, such as the temperature and the reactant concentration that control the growth, our results establish a qualitative departure from the widely accepted diffusion controlled coarsening (Ostwald ripening) process quantified in terms of the Lifshitz-Slyozov-Wagner theory. Further, we show that these experimental observations can be qualitatively and quantitatively understood within a growth mechanism that is intermediate between the two well-defined limits of diffusion control and kinetic control.     

Effect of headgroup on DNA-cationic surfactant interactions

The interaction behavior of DNA with different types of hydroxylated cationic surfactants has been studied. Attention was directed to how the introduction of hydroxyl substituents at the headgroup of the cationic surfactants affects the compaction of DNA. The DNA-cationic surfactant interaction was investigated at different charge ratios by several methods like UV melting, ethidium bromide exclusion, and gel electrophoresis. Studies show that there is a discrete transition in the DNA chain from extended coils (free chain) to a compact form and that this transition does not depend substantially on the architecture of the headgroup. However, the accessibility of DNA to ethidium bromide is preserved to a significantly larger extent for the more hydrophilic surfactants. This was discussed in terms of surfactant packing. Observations are interpreted to reflect that the surfactants with more substituents have a larger headgroup and therefore form smaller micellar aggregates; these higher curvature aggregates lead to a less efficient, "patch-like" coverage of DNA. The more hydrophilic surfactants also presented a significantly lower cytotoxicity, which is important for biotechnological applications.     

Characterization of novel myelin components 3-O-acetyl-sphingosine galactosylceramides by electrospray ionization Q-TOF MS and MS/CID-MS of Li+ adducts

Glycosphingolipids with R(f) values higher than those of monoglycosylceramides (MGCs) in normal phase HPTLC appear to be normal components of myelin. A series of such low polarity components, referred to as 'fast moving cerebrosides' (FMCs), have been isolated from rat brain, and two of these fractions (FMC-1 and FMC-2) were found to be novel derivatives of galactosylceramide (GalCer) exhibiting O-acetylation at the 3-hydroxy group of the sphingoid moiety, and incorporating either non-hydroxy or 2-hydroxy fatty-N-acylation (Dasgupta S, Levery SB, Hogan EL. J. Lipid Res. 2002; 43: 751-761). Similar to the parent compounds, the 3-O-acetyl-sphingoid derivatives exhibit considerable diversity with respect to fatty-N-acyl chain length, manifested by heterogeneous molecular ion (Li(+) adduct) profiles. However, a detailed analysis of the individual molecular variants ('lipoforms'), e.g. by tandem MS/CID-MS analysis, was not carried out. In addition, several other FMCs distinguished by even lower polarity (higher HPTLC R(f) values) were isolated but have remained uncharacterized. For this study, analysis of both the known and unknown FMC components was carried out by positive ion ESI-MS and MS/CID-MS of their Li(+) adducts on a Q-TOF mass spectrometer. Since a Q-TOF instrument has not yet been applied to MS of lithiated cerebrosides and FMCs, MS/CID-MS spectra of bovine brain GalCer (both types) and the previously characterized rat brain FMCs (FMC-1 and FMC-2), having 3-O-acetylation of the sphingoid, were systematically acquired and their fragmentation behavior compared. This was followed by systematic analysis of previously uncharacterized FMC fractions (FMC-3 through FMC-5/6/7). The GalCer and FMC components proved to be amenable to analysis by this technique, and the data confirm that the latter are all related 3-O-acetyl-sphingoid derivatives, with the higher R(f) components carrying additional O-acetyl modifications on the galactosyl residue, which further reduce their polarity. The utility of the technique, the structures of unknown FMCs, and their characteristic fragmentation patterns are described.     

Stability of an internally damped non-ideal flexible spinning shaft

The stability domain of an internally damped flexible spinning shaft, which is driven by a non-ideal source, is studied in this paper. It is found that the higher transverse modes may become unstable before the lower ones under certain conditions. In particular, we find the entrainment of the shaft spinning speed at specific values corresponding to the lowest stability threshold among all transverse modes. Moreover, the steady state amplitude of the transverse vibrations when the shaft spinning speed is stuck at the stability threshold is determined analytically. The analytical results thus obtained are validated with numerical simulations.     

Implementation of optical logic gates using closed packed 2D-photonic crystal structure

A proposal for implementation of optical logic gates using a two dimensional closed packed photonic crystal structure is presented here. The logic operations are realized by a control signal and the input signal(s) applied across two adjacent faces, while the output is obtained along one of the remaining faces. Finite Difference Time Domain simulations show that, this structure can be used to realize AND, OR, NOT, XNOR, NAND operations, if phase difference of π/2 is maintained between the control and the input signal. Further it is found that the same structure can be used as a switch, if Kerr nonlinearity is introduced to the dielectric rods constituting the photonic crystal structure.     

Loss and dispersion tailoring in 1D photonics band gap Bragg reflection waveguides: finite chirped claddings as a design tool

We exploit a simple and accurate matrix method to analyze the effects of introducing a linear chirp either in thickness or in refractive index of the cladding layers on the propagation characteristics (loss and dispersion) of 1D photonic band gap planar Bragg reflection waveguides (BRWs). We show that an appropriate chirp in the otherwise periodic claddings of finite extent BRWs could be gainfully exploited to tailor its leakage loss and waveguide dispersion features. In particular, we theoretically demonstrate that for some reported sample BRWs, leakage loss and waveguide dispersion could be significantly reduced by a factor of 30–50 and by about two orders of magnitude, respectively as compared to un-chirped BRWs. Furthermore, we also show that in contrast to un-chirped BRWs, how chirped BRWs could be designed with attractive feature like much less number of cladding layers and nearly wavelength independent losses. Our analysis and proposal should serve as a useful design tool to tailor the propagation characteristics of BRWs.     

Doped soap membranes selectively permeate a chiral isomer

Soap films can not only be made with sub-μm thickness, they can have intrinsic permeabilities comparable to many commercial membranes, permitting very high transmembrane flux. Soap films readily incorporate a wide range of modifiers to allow highly tailored selectivity: We show that incorporating α-cyclodextrin in an 890 nm thick Triton-X-100 film allows, in a single stage, a high degree of chirally selective transport (1.6:1) of α(+)-pinene over α(-)-pinene.