Superfluidity of Dense 4^4He in Vycor

We calculate properties of a model of $^4$He in Vycor using the Path Integral Monte Carlo method. We find that $^4$He forms a distinct layered structure with a highly localized first layer, a disordered second layer with some atoms delocalized and able to give rise to the observed superfluid response, and higher layers nearly perfect crystals. The addition of a single $^3$He atom was enough to bring down the total superfluidity by blocking the exchange in the second layer. Our results are consistent with the persistent liquid layer model to explain the observations. Such a model may be relevant to the experiments on bulk solid $^4$He, if there is a fine network of grain boundaries in those systems.Comment: 4 pages, 4 figure

Effect of manganese doping on the size effect of lead zirconate titanate thin films and the extrinsic nature of dead layers

We have investigated the size effect in lead zirconate titanate (PZT) thin films with a range of manganese (Mn) doping concentrations. We found that the size effect in the conventional Pt/PZT/Pt thin-film capacitors could be systematically reduced and almost completely eliminated by increasing Mn doping concentration. The interfacial layer at the electrode-film interface appears to disappear almost entirely for the PZT films with 2% Mn doping levels, confirmed by the fits using the conventional in-series capacitor model. Our work indicates that the size effect in ferroelectrics is extrinsic in nature, supporting the work by Saad et al. Other implications of our results have also been discussed. By comparing a variety of experimental studies in the literature we propose a scenario that the dead layer between PZT (or barium strontium titanate, BST) and metal electrodes such as Pt and Au might have a defective pyrochlore/fluorite structure (possibly with a small portion of ferroelectric perovskite phase).Comment: 21 pages, 6 figure

Površinska obrada polimera u tinjavom argonskom izboju

Surface treatment of polymer material (thin polyester samples) was performed in the DC glow discharge, using Ar gas. The effect of the experimental parameters of the glow discharge (the gas pressure and the sample treatment time) on the wettability of the samples was studied. The wettability was characterized by the water repellency (water spray test). In the present work, it was shown that at a constant gas pressure (270 or 670 Pa), the wettability of the polyester sample was decreased by increasing the exposure time of the sample in the glow discharge. At constant exposure times (2, 5, 10 or 15 min) the wettability of the polyester sample was increased by increasing the gas pressure. This is due to the formation of hydrophilic groups, which increased by increasing the density of electrons and/or metastables.Površinski smo obrađivali polimerni materijal (tanke uzorke poliestera) u istosmjernom tinjavom argonskom izboju. Proučavali smo učinke eksperimentalnih parametara izboja (tlaka plina i vremena izlaganja u izboju) na močivost uzoraka. Močivost smo određivali mjerenjem odbojnosti vode (metoda prskanjem vode). U ovom se radu pokazuje da se na stalnom tlaku plina (270 ili 670 Pa), močivost uzoraka poliestera smanjuje za dulja vremena izlaganja u izboju. Za određena vremena izlaganja (2, 5, 10 ili 15 min), močivost uzoraka je porasla pri povećanom tlaku argona. Razlog tome je stvaranje hidrofilnih grupa koje su bile brojnije pri povećanoj gustoći elektrona i/ili metastabila

Površinska obrada polimera u tinjavom argonskom izboju

Surface treatment of polymer material (thin polyester samples) was performed in the DC glow discharge, using Ar gas. The effect of the experimental parameters of the glow discharge (the gas pressure and the sample treatment time) on the wettability of the samples was studied. The wettability was characterized by the water repellency (water spray test). In the present work, it was shown that at a constant gas pressure (270 or 670 Pa), the wettability of the polyester sample was decreased by increasing the exposure time of the sample in the glow discharge. At constant exposure times (2, 5, 10 or 15 min) the wettability of the polyester sample was increased by increasing the gas pressure. This is due to the formation of hydrophilic groups, which increased by increasing the density of electrons and/or metastables.Površinski smo obrađivali polimerni materijal (tanke uzorke poliestera) u istosmjernom tinjavom argonskom izboju. Proučavali smo učinke eksperimentalnih parametara izboja (tlaka plina i vremena izlaganja u izboju) na močivost uzoraka. Močivost smo određivali mjerenjem odbojnosti vode (metoda prskanjem vode). U ovom se radu pokazuje da se na stalnom tlaku plina (270 ili 670 Pa), močivost uzoraka poliestera smanjuje za dulja vremena izlaganja u izboju. Za određena vremena izlaganja (2, 5, 10 ili 15 min), močivost uzoraka je porasla pri povećanom tlaku argona. Razlog tome je stvaranje hidrofilnih grupa koje su bile brojnije pri povećanoj gustoći elektrona i/ili metastabila

Impact of layer defects in ferroelectric thin films

Based on a modified Ising model in a transverse field we demonstrate that defect layers in ferroelectric thin films, such as layers with impurities, vacancies or dislocations, are able to induce a strong increase or decrease of the polarization depending on the variation of the exchange interaction within the defect layers. A Green's function technique enables us to calculate the polarization, the excitation energy and the critical temperature of the material with structural defects. Numerically we find the polarization as function of temperature, film thickness and the interaction strengths between the layers. The theoretical results are in reasonable accordance to experimental datas of different ferroelectric thin films.Comment: 17 pages, 8 figure

Strain Gradients in Epitaxial Ferroelectrics

X-ray analysis of ferroelectric thin layers of Ba1/2Sr1/2TiO3 with different thickness reveals the presence of internal strain gradients across the film thickness and allows us to propose a functional form for the internal strain profile. We use this to calculate the direct influence of strain gradient, through flexoelectric coupling, on the degradation of the ferroelectric properties of thin films with decreasing thickness, in excellent agreement with the observed behaviour. This work highlights the link between strain relaxation and strain gradients in epitaxial films, and shows the pressing need to avoid strain gradients in order to obtain thin ferroelectrics with bulk-like properties.Comment: 4 pages, 3 embedded figures (1 color), revTex

User friendly system for the visually impaired in learning Al-Quran

This study presents a method to enable the visually impaired Muslim to learn and read the Al-Quran using Braille Display with software help. The system reads the database which contains all verses of Al-Quran and user will need to select the verse and ayah to read. Besides that, this system can be used in a class to teach visually impaired students to learn Al-Quran. Every word or character typed by the instructor in the main Braille Panel will be transmitted to the sub Braille Panel that is connected to the main Braille Panel. The selected verse of Al-Quran and ayah will also generate an index before being transmitted to the Braille Panel. The index will be transmitted to the Braille Display for people to touch and read the display. A user friendly Graphical User Interface (GUI) will be used to fulfill the ergonomics for the visually impaired user's physical capabilities. Several approaches are used to design and implement the interface for the visually impaired like speech or sound output and Braille display. The Braille codes can be displayed using the Braille panel. The design interface and structure of the system for the visually impaired users in learning Al-Quran is presented

Criterion for polynomial solutions to a class of linear differential equation of second order

We consider the differential equations y''=\lambda_0(x)y'+s_0(x)y, where \lambda_0(x), s_0(x) are C^{\infty}-functions. We prove (i) if the differential equation, has a polynomial solution of degree n >0, then \delta_n=\lambda_n s_{n-1}-\lambda_{n-1}s_n=0, where \lambda_{n}= \lambda_{n-1}^\prime+s_{n-1}+\lambda_0\lambda_{n-1}\hbox{and}\quad s_{n}=s_{n-1}^\prime+s_0\lambda_{k-1},\quad n=1,2,.... Conversely (ii) if \lambda_n\lambda_{n-1}\ne 0 and \delta_n=0, then the differential equation has a polynomial solution of degree at most n. We show that the classical differential equations of Laguerre, Hermite, Legendre, Jacobi, Chebyshev (first and second kind), Gegenbauer, and the Hypergeometric type, etc, obey this criterion. Further, we find the polynomial solutions for the generalized Hermite, Laguerre, Legendre and Chebyshev differential equations.Comment: 12 page