3D LASER FABRICATION OF CONICAL FIBER TIPS

This paper investigates the 3D laser fabrication of microoptics with sharp conical tips as focusing elements that can control the focusing of light below the diffraction limit. The conical tips were obtained by 3D laser lithography method and two-photon photopolymerization in a photosensitive resin. The processing time and the scanning path were optimized by a Python code that we developed. The light propagation through the optical microstructure was simulated with the aid of the COMSOL Multiphysics software within the Electromagnetic Waves, Frequency Domain approximation. The propagation of the light was visualized and analyzed from the spatial distribution of the intensity of light traversing an optical fiber with conical fiber tips

Shortness coefficient of cyclically 4-edge-connected cubic graphs

Grünbaum and Malkevitch proved that the shortness coefficient of cyclically 4-edge-connected cubic planar graphs is at most 76/77. Recently, this was improved to 359/366 (< 52/53) and the question was raised whether this can be strengthened to 41/42, a natural bound inferred from one of the Faulkner-Younger graphs. We prove that the shortness coefficient of cyclically 4-edge-connected cubic planar graphs is at most 37/38 and that we also get the same value for cyclically 4-edge-connected cubic graphs of genus g for any prescribed genus g ≥ 0. We also show that 45/46 is an upper bound for the shortness coefficient of cyclically 4-edge-connected cubic graphs of genus g with face lengths bounded above by some constant larger than 22 for any prescribed g ≥ 0

Results regarding compatibility of some plum cultivars grafted on different rootstocks

In Romania, the most used plum rootstock, ‘Mirobalan’ does not any problems in terms of graft compatibility and that is why it is widely used. However, it was found that this generative rootstock has low compatibility with the ‘Tuleu gras’ cv. and with all the plum cultivars obtained from it. In this paper, we study the degree of compatibility of 5 plum cultivars (‘Andreea’, ‘Pitestean’, ‘Romanța’, ‘Čačanska Lepotiča’, ‘Jojo’) with 7 Romanian rootstocks (‘Adaptabil’, ‘Mirobolan dwarf’, ‘Mirodad 1’, ‘Mirodad 2’, ‘Redutabil’, ‘BN-4Kr’ and ‘B 83/8’). The evaluation of graft compatibility of these cultivar-rootstock combinations was made through two indices: morphological thickness index of the grafting area (IMÎZA - as a result of the ratio between the surfaces section of the scion, rootstock and grafting union) and anatomical similarity index of the symbionts (IMAAtS) calculated based on the number and diameter of the woody vessels in the scion, rootstock and graft union. Following the measurements, very significant results were obtained, which can explain the degree of affinity between cultivars and rootstocks. The morphological thickness index of the grafting area had values above 0.300, which indicates good and very good graft compatibility in most of the cultivar-rootstock combinations studied, with the exception of the association with ‘Redutabil’ rootstock which have values below 0.300, and the thickness differences between scion, rootstock and graft union were very large, indicating a low level of compatibility between the cultivars studied and this rootstock. The anatomical similarity index of the symbionts had values close to 1, indicating good and very good compatibility. The exception was the combinations of cultivars with the ‘Redutabil’ rootstock, the anatomical similarity index of the symbionts having values below

Femtosecond laser ablation and structuring of a hard bi-layered coating

We studied surface modification of a bi-layered coating (Al2O3/TiAlN/steel) induced by fs laser with single and multi-pulse irradiation. The laser pulses (λ=775 nm, τ=200 fs) were generated by a Ti:sapphire laser. The single pulse threshold fluence for ablation of the top Al2O3 layer was Dath =0.56 Jcm-2. Single pulse actions with fluence increased up to 16.47 Jcm-2 caused widening of ablated area without significant change of the TiAlN layer underneath. In case of multipulse irradiation, periodical surface structures (LIPSS) were induced on the TiAlN layer surface. The average periodicity of created LIPSS was 600 nm.Physical chemistry 2012 : 11th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 201

A topological classification of convex bodies

The shape of homogeneous, generic, smooth convex bodies as described by the Euclidean distance with nondegenerate critical points, measured from the center of mass represents a rather restricted class M_C of Morse-Smale functions on S^2. Here we show that even M_C exhibits the complexity known for general Morse-Smale functions on S^2 by exhausting all combinatorial possibilities: every 2-colored quadrangulation of the sphere is isomorphic to a suitably represented Morse-Smale complex associated with a function in M_C (and vice versa). We prove our claim by an inductive algorithm, starting from the path graph P_2 and generating convex bodies corresponding to quadrangulations with increasing number of vertices by performing each combinatorially possible vertex splitting by a convexity-preserving local manipulation of the surface. Since convex bodies carrying Morse-Smale complexes isomorphic to P_2 exist, this algorithm not only proves our claim but also generalizes the known classification scheme in [36]. Our expansion algorithm is essentially the dual procedure to the algorithm presented by Edelsbrunner et al. in [21], producing a hierarchy of increasingly coarse Morse-Smale complexes. We point out applications to pebble shapes.Comment: 25 pages, 10 figure

On the equilibria of finely discretized curves and surfaces

Our goal is to identify the type and number of static equilibrium points of solids arising from fine, equidistant $n$-discretrizations of smooth, convex surfaces. We assume uniform gravity and a frictionless, horizontal, planar support. We show that as $n$ approaches infinity these numbers fluctuate around specific values which we call the imaginary equilibrium indices associated with the approximated smooth surface. We derive simple formulae for these numbers in terms of the principal curvatures and the radial distances of the equilibrium points of the solid from its center of gravity. Our results are illustrated on a discretized ellipsoid and match well the observations on natural pebble surfaces.Comment: 21 pages, 2 figure

Comprehensive ablation study of near-IR femtosecond laser action on the titanium-based alloy Ti6Al4V: morphological effects and surface structures at low and high fluences

The surface of a titanium-based alloy Ti6Al4V was subjected to modifications by a near-IR femtosecond Ti:Sapphire laser, emitting at 775 nm pulses of 200 fs duration, in single-pulse and multi-pulse regimes, with up to 400 accumulated pulses, and pulse energies ranging from 2.5 to 250 \upmu J. The whole range of induced effects is presented, from gentle ablation and pattern occurrence to substantial crater formation. Very observable laser-induced parallel periodic surface structures are reported, appearing both within the damage spot area, with low fluences, and at the peripheries of the craters, with higher fluences—but also on crater walls, and inside the crater structures. Damage threshold fluences $$({F}_{\mathrm{th}})$$and the incubation factor $$(\zeta )$$were also determined