Phase behavior and material properties of hollow nanoparticles

Effective pair potentials for hollow nanoparticles like the ones made from carbon (fullerenes) or metal dichalcogenides (inorganic fullerenes) consist of a hard core repulsion and a deep, but short-ranged, van der Waals attraction. We investigate them for single- and multi-walled nanoparticles and show that in both cases, in the limit of large radii the interaction range scales inversely with the radius, $R$, while the well depth scales linearly with $R$. We predict the values of the radius $R$ and the wall thickness $h$ at which the gas-liquid coexistence disappears from the phase diagram. We also discuss unusual material properties of the solid, which include a large heat of sublimation and a small surface energy.Comment: Revtex, 13 pages with 8 Postscript files included, submitted to Phys. Rev.

Elastic Interactions of Cells

Biological cells in soft materials can be modeled as anisotropic force contraction dipoles. The corresponding elastic interaction potentials are long-ranged ($\sim 1/r^3$ with distance $r$) and depend sensitively on elastic constants, geometry and cellular orientations. On elastic substrates, the elastic interaction is similar to that of electric quadrupoles in two dimensions and for dense systems leads to aggregation with herringbone order on a cellular scale. Free and clamped surfaces of samples of finite size introduce attractive and repulsive corrections, respectively, which vary on the macroscopic scale. Our theory predicts cell reorientation on stretched elastic substrates.Comment: Revtex, 6 pages, 2 Postscript files included, to appear in Phys. Rev. Let

Neutrino and astroparticle physics : Working group report

The contributions made to the Working Group activities on neutrino and astroparticle physics are summarised in this article. The topics discussed were leptogenesis in Left-Right symmetric model, inflationary models in Raman-Sundrum scenarios, ultra high energy cosmic rays and neutrino oscillations in 4 flavour and decaying neutrino models.Comment: 11 pages; arXiv copy of contribution to WHEPP-6 proceeding

Deformation and tribology of multi-walled hollow nanoparticles

Multi-walled hollow nanoparticles made from tungsten disulphide (WS$_2$) show exceptional tribological performance as additives to liquid lubricants due to effective transfer of low shear strength material onto the sliding surfaces. Using a scaling approach based on continuum elasticity theory for shells and pairwise summation of van der Waals interactions, we show that van der Waals interactions cause strong adhesion to the substrate which favors release of delaminated layers onto the surfaces. For large and thin nanoparticles, van der Waals adhesion can cause considerable deformation and subsequent delamination. For the thick WS$_2$ nanoparticles, deformation due to van der Waals interactions remains small and the main mechanism for delamination is pressure which in fact leads to collapse beyond a critical value. We also discuss the effect of shear flow on deformation and rolling on the substrate.Comment: Latex, 13 pages with 3 Postscript figures included, to appear in Europhysics Letter

Assessment of Occupational Diseases among Artisans and Factory Workers in Ifo, Nigeria

The ever increasing incidences of occupational diseases among workers have continually drawn the attention of researchers towards ameliorating the situation. Investigation was launched to assess occupational diseases among artisans and factory workers in Ifo, Nigeria. Structured questionnaires with oral interview were employed to complement the health records of the respondents at the Government accredited health center. Of the one hundred and fifty six (156) respondents, ninety six (62%) are males and sixty one (38%) female, sixty one point fifty four percent (61.54%) are youths of age 20 to 39 years, fifty one (32.69%) are illiterates and one hundred and eight (69.21%) earn N100, 000 ($615) and below as monthly wages. The diseases prevalent in these workers were evaluated to include but not limited to disorders of muscles, bones, joints, skin and the respiratory organs indicating that most of the jobs are such that causes damages to these special parts of the body and could lead to deformities/incapacitation in old age. Common amongst these diseases are Pre-patellar bursitis and Eczema (1.92% each), Tuberculosis, Asthma and Sunburn (5.77% each). Toxic/inflammatory syndrome, hearing impairment, allergies and computer vision syndrome (7.69% each). Two (1.28% in each case) have been diagnosed of Lead poisoning, Lung cancer, Carpal tunnel syndrome, Pulmonary fibrosis, Meniscus lesion and Olecranon bursitis. Upper airway disorders (4.49%), Irritations (3.21%), Post-traumatic stress syndrome (11.54%), skin allergies (13.46%). Chronic bronchitis; Pneumonia; Pneumoconiosis; Hepatitis and Anthrax-like infection (0.64 % each). The causes of these diseases/disorders include dusts from quarry, textile, cotton, metal, paper, mineral, wood, cereals, cement, and chemical fumes industries, extreme posture of wrist, repetitive movements, inhalations from petrol fuel, prolonged pressure of the elbow region, prolonged kneeling/ squatting position, forceful exertions and microorganisms. Adequate occupational health and safety awareness through training and campaign should be provided. The use of personal protective equipment among workers should also be encouraged