Generation and characterization of stable, highly concentrated titanium dioxide nanoparticle aerosols for rodent inhalation studies

The intensive use of nano-sized titanium dioxide (TiO₂) particles in many different applications necessitates studies on their risk assessment as there are still open questions on their safe handling and utilization. For reliable risk assessment, the interaction of TiO₂ nanoparticles (NP) with biological systems ideally needs to be investigated using physico-chemically uniform and well-characterized NP. In this article, we describe the reproducible production of TiO₂ NP aerosols using spark ignition technology. Because currently no data are available on inhaled NP in the 10?C50 nm diameter range, the emphasis was to generate NP as small as 20 nm for inhalation studies in rodents. For anticipated in vivo dosimetry analyses, TiO₂ NP were radiolabeled with ⁴⁸V by proton irradiation of the titanium electrodes of the spark generator. The dissolution rate of the ⁴⁸V label was about 1% within the first day. The highly concentrated, polydisperse TiO₂ NP aerosol (3?C6 × 10⁶ cm^?3) proved to be constant over several hours in terms of its count median mobility diameter, its geometric standard deviation, and number concentration. Extensive characterization of NP chemical composition, physical structure, morphology, and specific surface area was performed. The originally generated amorphous TiO₂ NP were converted into crystalline anatase TiO₂ NP by thermal annealing at 950 °C. Both crystalline and amorphous 20-nm TiO₂ NP were chain agglomerated/aggregated, consisting of primary particles in the range of 5 nm. Disintegration of the deposited TiO₂ NP in lung tissue was not detectable within 24 h.     

Spiky strings on NS5-branes

We study rigidly rotating strings in the near-horizon geometry of a stack of Neveu-Schwarz (NS) 5-branes. We solve the Nambu-Goto action of the fundamental string in the presence of a NS-NS two form (Bμν) and find out limiting cases corresponding to magnon and spike like solutions.     

Thermodynamics of Lema$$\hat{i}$$ tre−Tolman−Bondi Model

Here we consider our universe as inhomogeneous spherically symmetric Lema [^(i)]{\hat{i}} tre−Tolman−Bondi Model and analyze the thermodynamics of this model of the universe. The trapping horizon is calculated and is found to coincide with the apparent horizon. The Einstein field equations are shown to be equivalent with the unified first law of thermodynamics. Finally assuming the first law of thermodynamics validity of the generalized second law of thermodynamics is examined at the apparent horizon for the perfect fluid and at the event horizon for holographic dark energy.     

Particle multiplicities in the fission-like reactions of 340 MeV Si on Th

Pre-scission and post-scission multiplicities of neutrons and alpha particles have been simultaneously measured for the fission-like reactions of 340 MeV ²⁸Si on ²³²Th. Dynamical model calculations using HICOL code predict that about 90% of the observed events are of quasi-fission type while the remaining 10% are from compound nucleus fission decay. Moving source fits were carried out to the observed neutron and alpha particle spectra, measured at different angles with respect to the fragment directions. The pre-scission and post-scission neutron multiplicities are deduced to be 8.7±2.0 and 9.4±2.0, respectively. The corresponding multiplicity values for alpha particles are found to be 0.22±0.08 and 0.1±0.03. From the measured post-scission neutron multiplicity, it is inferred that about 65±20 MeV of the initial excitation energy remains at scission. This may be compared to the value of 85±30 MeV estimated from PACE2 statistical model calculations, adjusted to reproduce the measured pre-scission neutron multiplicity. From a comparison of the Statistical Model predictions with the measured pre-scission neutron multiplicity, the fission delay is estimated to be of 5⁺⁷₋₃×10⁻²⁰ s which overlaps with the average duration of fission-like process from the contact to the scission point (2×10⁻²⁰ s) as determined from HICOL-based dynamical calculations. For the delay time deduced as above, the pre-scission alpha particle multiplicity calculated by the PACE2 code is about a factor two larger than the experimental one, demonstrating the difficulties in modelling the alpha particle emission from highly elongated shapes that characterize the fissioning system from the contact point to scission.     

Simulation model for shapiro time delay and light deflection experiments

The time delay experiment proposed by I.I. Shapiro in 1964 and conducted in the seventies was the most precise experiment of general relativity until that time. Further experimentation has improved the accuracy level of both the time delay and the light deflection experiments. A simulation model is proposed that involves only a simple mass and time transformation factor involving velocity of light. The light deflection and the time delay experiments are numerically simulated using this model that does not use the general relativistic equations. The computed values presented in this paper compare well with recent levels of accuracy of their respective experimental results.     

Morphology and bilayer integrity of small liposomes during aerosol generation by air-jet nebulisation

Small liposome suspensions (hydrodynamic diameter, 80–130 nm) were nebulised, and the resulting changes in morphology and bilayer integrity were found to be related to surface properties controlled by bilayer composition. Four separate liposome compositions (or liposome types) were investigated using three different phospholipids with unique properties. Morphological changes were studied using light scattering and imaging of liposomes before and after nebulisation, and structural integrity was investigated on the basis of the retention of an encapsulated dye (probe molecule). Nebulisation generated droplets contained liposomes. The liposome particles generated on droplet evaporation had a hollow structure as evidenced by electron imaging, indicating that the lipid bilayer does not collapse on evaporation. The particles of all compositions had mobility diameters between 50 and 90 nm, 1.4–1.6 times smaller than their diameters (hydrodynamic) measured before nebulisation, implying considerable volume shrinkage. Liposomes that had polymer-conjugated lipids covering their external surface underwent aggregation during nebulisation, evidenced by increased diameter after nebulisation. Incorporation of charged lipids reduced nebulisation-induced aggregation, but induced greater membrane rupture during aerosol generation, causing leakage of encapsulated probe molecules. Incorporation of both cholesterol and charged lipids prevented aggregation, but also preserved bilayer integrity, evidenced by the maximum retention of encapsulated dye observed in these conditions (>85%). The findings suggest that liposome bilayer composition can be manipulated to improve the efficiency of liposome aerosol delivery.     

Attenuation and modal dispersion models for spatially multiplexed co-propagating helical optical channels in step index fibers

Spatial reuse of optical frequencies has been shown to be possible through a novel spatial domain multiplexing (SDM) technique that uses spatial multiplexer at the input end to launch multiple channels of the same wavelength inside a single strand of carrier fiber and then employs spatial filtering methods to de-multiplex the different optical channels at the output end. The individual SDM channels are confined to dedicated spatial locations inside the fiber while traversing through it owing to helical propagation of light. This presents attenuation and dispersion models of such a system. Experimentally obtained beam profile and resultant crosstalk of two such spatially multiplexed co-propagating SDM channels of the same wavelength over standard step index multimode optical fibers are also presented.     

Exact solutions for Ostrovsky equation

This paper obtains solutions to the Ostrovsky equation by employing the mapping method. Several solutions are determined including the cnoidal waves, shock waves, solitary waves, periodic singular waves and others in the case of no rotation. Finally, the ansatz method is applied to solve the equation with the rotation term present.