Luís Nobre Gonçalves

Universidade NOVA de Lisboa | NOVA · Department of Physics

Advanced fitting of ordinary differential equations models to experimental results is presented within the context of different academic levels of students and diverse research fields. In many areas, the analysis of experimental results cannot be restricted to cases where particular solutions of the models' differential equations, valid only for sp...

A detailed analysis of pendular motion is presented. Inertial effects, self-oscillation, and memory, together with non-constant moment of inertia, hysteresis, and negative damping are shown to be required for the comprehensive description of the free pendulum oscillatory regime. The effects of very high initial amplitudes, friction in the roller be...

A detailed analysis of three pendular motion models is presented. Inertial effects, self-oscillation, and memory, together with non-constant moment of inertia, hysteresis and negative damping are shown to be required for the comprehensive description of the free pendulum oscillatory regime. The effects of very high initial amplitudes, friction in t...

A presente invenção resolve o problema de conceber uma cúpula poliédrica com defeito angular nulo em todos os vértices interiores. É aqui apresentada uma solução que permite o acoplamento de estruturas a coberturas, quando a cobertura é uma tela inicialmente plana, garantindo assim a estanquidade da cobertura. Esta solução é um conjunto estrutura/c...

Oscillatory motion is a main topic in physics at all levels of undergraduate courses. In this work, we study the damping of a bar acting as a physical pendulum subjected to air drag.

Esta apresentação foi produzida para a segunda Ignite da Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa com o tema "Sociedade e Tecnologia" e tem como objectivo alertar as consciências para a encruzilhada sociológica em nos encontramos. A esta encruzilhada corresponde o famoso "tipping point" dos ecossistemas terrestres. O códi...

We propose that by using the concept of negative mass, the dynamics of objects embedded in fluids can be considerably simplified. For example, helium balloons, whose motion can be puzzling in a non-inertial reference frame, can be easily explained using the concept of negative mass. Two experiments have been carried out to demonstrate this idea. Th...

The Shree Yantra Core is a figure composed of nine interlocking isosceles trian- gles, all inside a circle. This figure is found in some of the oldest hindu temples and contains, in itself, a series of interesting mathematical problems. This arti- cle describes an attempt to solve the problem of drawing the Shree Yantra Core with METAPOST.

The three bars kit is constituted by three kinds of bars, where the bar of kind (1), has uniform square convex hull section along its length, and both the other two bars, the bars of kind (2) and (3), have equal and uniform regular hexagonal convex hull sections along their lengths, such that the height H of the hexagonal convex hull section is rel...

UMA ESTRUTURA POLIÉDRICA É UM CONJUNTO DE POLÍGONOS PLANOS LIGADOS ENTRE SI DE TAL FORMA QUE ARESTAS DE DOIS POLÍGONOS ADJACENTES SE SOBREPOEM NA MESMA LINHA RECTA. PROPÕE-SE AGORA UM SISTEMA QUE PERMITE CONSTRUIR A MÁXIMA DIVERSIDADE DE ESTRUTURAS POLIÉDRICAS DESMONTÁVEIS COM UM NÚMERO MÍNIMO DE PEÇAS (SEIS). ESTA AUSÊNCIA DE RESTRICÇÕES RESULTA D...

The molecular dynamics in a series of halogen liquid crystals exhibiting smectic B phases is presented. Standard and fast field cycling NMR techniques were used to obtain the proton spin-lattice relaxation dispersion over a broad frequency range. The results are analyzed is terms of potential contributions of different molecular motions. At high fr...

metapost is able to produce figures that look almost like ray-traced raster images but that remain vector-based. A small review of three-dimensional perspective implementations with metapost is presented. Special emphasis is given to the abilities of the author’s implementation: fetapost.

We present an analysis of the formation and evolution of the transient periodic pattern in the nematic director field reorientation in the magnetic non-Fréedericksz twist geometry and compare with experiments. The stability analysis of the magnetically induced director reorientation in a planar oriented nematic slab with rigid anchoring and with th...

The occurrence of periodically distorted director structures in planar and pre-tilted nematic slabs above the magnetically driven Fréedericksz transition is investigated in the intermediate geometries between the pure splay, twist and bend Fréedericksz transition geometries. Considering rigid boundary conditions the domain of existence of the perio...

We present an experimental study of the transient periodic structures appearing in the nematic director field in the magnetically induced reorientation of the director in the vicinity of the twist Fréedericksz geometry. Thin nematic samples (50 µm thick) were exposed to magnetic fields of variable intensity and orientation relative to the surface a...

Estudamos teoricamente as transições de Fréedericksz nas geometrias intermédias entre: (i) afunilamento e torção; (ii) torção e flexão; e (iii) flexão e afunilamento. Foram determinadas as condições em que a transição entre o estado não deformado e o estado homogeneamente deformado (transição de Fréedericksz usual) é substituida pela transição entr...

The appearance of periodically distorted director structures in pretilted nematic slabs with rigid boundary conditions above the Fréedericksz transition is determined as a function of the Frank elastic constant ratios K(2)/K(1), K(3)/K(1), and the pretilt angle. It is found that the periodically distorted state can be reached either directly from t...

The phase diagram in the vicinity of the Fréedericksz transition from the uniform to the deformed homogeneous or periodic states of a nematic slab under a magnetic field with rigid boundary conditions was qualitatively calculated in the mean-field approximation for intermediate geometries between the splay and twist Fréedericksz transition geometri...

We study the influence of the anisotropy of the Frank elastic constants on the magnetic reorientation of the nematic phase of polymer liquid crystals. In the magnetic reorientation following a 90° director rotation with respect to an aligning magnetic field, a pattern of inversion walls develops which depends on the relative magnitude of the elasti...

A novel continuum theory of nematic liquid crystalline polymers has been recently proposed (Martins, 1993) and is applied here to interpret new and quoted data, for concentrated solutions of hydroxypropylcellulose (HPC) in acetic acid and poly(γ-benzil)L-glutamate (PBLG) in m-cresol, on shear rate ( ), molecular mass, and concentration dependence o...

The magnetic field reorientation of an initially aligned sample of a nematic polymer liquid crystal was followed by proton NMR. Evolution to a metastable (banded) state was considered using a Rheo-NMR technique developed previously. Late stage reorientation was studied by taking into account the dynamics of defects following the formation of splay–...