Quantum Critical Ferromagnetism in Ni x Pd1- x Alloys

We analyze the non-Fermi liquid behavior in the proximity of the quantum phase transition induced by the strong polarization of the electrons due to local magnetic moments in Ni _x Pd_1-x alloys. We use the renormalization group approach introduced by Hertz–Mi11is–Moriya (HMM) to estimate the temperature dependence of the electrical resistivity for the case of three dimensional itinerant ferromagnets. We study two different cases, namely, the clean and disordered ferromagnets, and argue that at the present time more experimental data are needed to decide if the HMM theory can accurately describe the physical properties in Ni _x Pd_1-x alloys.     

Educational recommender systems and their application in lifelong learning

The almost unlimited access to educational information plethora came with a drawback: finding meaningful material is not a straightforward task anymore. Recommender algorithms can be used to make smart decisions in complex information systems and help the users decide upon useful materials; therefore, they become a promising area in academia and industry. The current paper presents a survey on educational recommender systems (RS): a set of analysis criteria are exposed and the technological specifications and challenges of each analysed system are provided, in the context of the main trends in the development of RS. Also, an ontology-based educational recommendation mechanism is proposed and its application to lifelong learning is highlighted, proving that RS can successfully support new learning paradigms.     

Low Temperature Behavior of a Two-Dimensional Quantum Antiferromagnet

We analyze the two-dimensional antiferromagnet with a quantum disordered ground state and a gap to bosonic excitations with finite spin. The zero temperature (T = 0) quantum phase transition is studied, and the finite temperature effects are also considered in the low temperature approximation of the Renormalization Group Method. The violation of the universality expected for d = 2 system has been shown to be logarithmic for T = 0 and T 0. We showed that chemical potential and the ground state energy depends on the interaction parameters at T = 0 and T 0. but this dependence is logarithmic.     

Small-molecule vacuum processed melamine-C60, organic field-effect transistors

The transfer of benchtop knowledge into large scale industrial production processes represents a challenge in the field of organic electronics. Large scale industrial production of organic electronics is envisioned as roll to roll (R2R) processing which nowadays comprises usually solution-based large area printing steps. The search for a fast and reliable fabrication process able to accommodate the deposition of both insulator and semiconductor layers in a single step is still under way. Here we report on the fabrication of organic field effect transistors comprising only evaporable small molecules. Moreover, both the gate dielectric (melamine) and the semiconductor (C₆₀) are deposited in successive steps without breaking the vacuum in the evaporation chamber. The material characteristics of evaporated melamine thin films as well as their dielectric properties are investigated, suggesting the applicability of vacuum processed melamine for gate dielectric layer in OFETs. The transistor fabrication and its transfer and output characteristics are presented along with observations that lead to the fabrication of stable and virtually hysteresis-free transistors. The extremely low price of precursor materials and the ease of fabrication recommend the evaporation processes as alternative methods for a large scale, R2R production of organic field effect transistors.     

Non-Fermi Behavior Near Ferromagnetic Quantum Phase Transition

We propose a model for the explanation of the non-Fermi behavior near the ferromagnetic quantum phase transition. The scaling equations have been used to calculate the specific heat and we showed that the quantum effects are responsible for the T ln T term from the specific heat. The results are in agreement with recent experimental data obtained in the Ni _x Pd_{1 – x} system. The relation with the other approaches was also discussed.     

Non-Fermi Behavior of the Itinerant-Electron Ferromagnet near the Quantum Phase Transition Point

We used the Renormalization Group (RG) method in the Hertz–Millis version to study the quantum phase transition of the itinerant-electron ferromagnet. Near the quantum phase transition point the system present a non-Fermi behavior in agreement with the experimental results. The importance of long-range interactions considered by Belitz–Kirkpatrick–Vojta was taken into consideration, showing the importance of the marginal parameters.     

Metallic Glass in Two Dimensional Disordered Bose Systems; A Renormalization Group Approach

We consider the quantum critical properties of a disordered two dimensional Bose gas based on the renormalization group approach. To account for disorder, we consider that the Bose gas interacts with an external random field. The system’s behavior in the critical region of the quantum phase transition is obtained in the universality class z=2 and includes contributions beyond the Gaussian approximation by considering interactions between bosonic degrees of freedom. The evaluation of the system’s conductivity close to the transition point proves the occurrence of a nonzero conductivity (metallic-like) state in the system in the ω=0 and T→0 K limit.     

Biocompatible and Biodegradable Materials for Organic Field‐Effect Transistors

Biocompatible‐ingestible electronic circuits and capsules for medical diagnosis and monitoring are currently based on traditional silicon technology. Organic electronics has huge potential for developing biodegradable, biocompatible, bioresorbable, or even metabolizable products. An ideal pathway for such electronic devices involves fabrication with materials from nature, or materials found in common commodity products. Transistors with an operational voltage as low as 4–5 V, a source drain current of up to 0.5 μA and an on‐off ratio of 3–5 orders of magnitude have been fabricated with such materials. This work comprises steps towards environmentally safe devices in low‐cost, large volume, disposable or throwaway electronic applications, such as in food packaging, plastic bags, and disposable dishware. In addition, there is significant potential to use such electronic items in biomedical implants.