36 research outputs found
Resistivity and optical conductivity of cuprates within the t-J model
The optical conductivity and the d.c. resistivity
within the extended t-J model on a square lattice, as relevant to high-
cuprates, are reinvestigated using the exact-diagonalization method for small
systems, improved by performing a twisted boundary condition averaging. The
influence of the next-nearest-neighbor hopping is also considered. The
behaviour of results at intermediate doping is consistent with a
marginal-Fermi-liquid scenario and in the case of for follows
the power law with consistent
with experiments. At low doping for develops a
shoulder at , consistent with the observed mid-infrared
peak in experiments, accompanied by a shallow dip for . This
region is characterized by the resistivity saturation, whereas a more coherent
transport appears at producing a more pronounced decrease in
. The behavior of the normalized resistivity is within a
factor of 2 quantitatively consistent with experiments in cuprates.Comment: 8 pages, 10 figure
Thermoelectric power in one-dimensional Hubbard model
The thermoelectric power S is studied within the one-dimensional Hubbard
model using the linear response theory and the numerical exact-diagonalization
method for small systems. While both the diagonal and off-diagonal dynamical
correlation functions of particle and energy current are singular within the
model even at temperature T>0, S behaves regularly as a function of frequency
and T. Dependence on the electron density n below the half-filling
reveals a change of sign of S at n_0=0.73+/-0.07 due to strong correlations, in
the whole T range considered. Approaching half-filling S is hole-like and can
become large for U>>t although decreasing with T.Comment: 6 pages, 4 figure
From thermal rectifiers to thermoelectric devices
We discuss thermal rectification and thermoelectric energy conversion from
the perspective of nonequilibrium statistical mechanics and dynamical systems
theory. After preliminary considerations on the dynamical foundations of the
phenomenological Fourier law in classical and quantum mechanics, we illustrate
ways to control the phononic heat flow and design thermal diodes. Finally, we
consider the coupled transport of heat and charge and discuss several general
mechanisms for optimizing the figure of merit of thermoelectric efficiency.Comment: 42 pages, 22 figures, review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
Adhesion of perfume-filled microcapsules to model fabric surfaces
The retention and adhesion of melamine formaldehyde (MF) microcapsules on a model fabric surface in aqueous solution were investigated using a customised flow chamber technique and atomic force microscopy (AFM). A cellulose film was employed as a model fabric surface. Modification of the cellulose with chitosan was found to increase the retention and adhesion of microcapsules on the model fabric surface. The AFM force–displacement data reveal that bridging forces resulting from the extension of cellulose chains dominate the adhesion between the microcapsule and the unmodified cellulose film, whereas electrostatic attraction helps the microcapsules adhere to the chitosan-modified cellulose film. The correlation between results obtained using these two complementary techniques suggests that the flow chamber device can be potentially used for rapid screening of the effect of chemical modification on the adhesion of microparticles to surfaces, reducing the time required to achieve an optimal formulation
The impact of social networks on knowledge transfer in long-term care facilities: Protocol for a study
<p>Abstract</p> <p>Background</p> <p>Social networks are theorized as significant influences in the innovation adoption and behavior change processes. Our understanding of how social networks operate within healthcare settings is limited. As a result, our ability to design optimal interventions that employ social networks as a method of fostering planned behavior change is also limited. Through this proposed project, we expect to contribute new knowledge about factors influencing uptake of knowledge translation interventions.</p> <p>Objectives</p> <p>Our specific aims include: To collect social network data among staff in two long-term care (LTC) facilities; to characterize social networks in these units; and to describe how social networks influence uptake and use of feedback reports.</p> <p>Methods and design</p> <p>In this prospective study, we will collect data on social networks in nursing units in two LTC facilities, and use social network analysis techniques to characterize and describe the networks. These data will be combined with data from a funded project to explore the impact of social networks on uptake and use of feedback reports. In this parent study, feedback reports using standardized resident assessment data are distributed on a monthly basis. Surveys are administered to assess report uptake. In the proposed project, we will collect data on social networks, analyzing the data using graphical and quantitative techniques. We will combine the social network data with survey data to assess the influence of social networks on uptake of feedback reports.</p> <p>Discussion</p> <p>This study will contribute to understanding mechanisms for knowledge sharing among staff on units to permit more efficient and effective intervention design. A growing number of studies in the social network literature suggest that social networks can be studied not only as influences on knowledge translation, but also as possible mechanisms for fostering knowledge translation. This study will contribute to building theory to design such interventions.</p
Manufacture Techniques of Chitosan-Based Microcapsules to Enhance Functional Properties of Textiles
In recent years, the textile industry has been moving to novel concepts of products, which could deliver to the user, improved performances. Such smart textiles have been proven to have the potential to integrate within a commodity garment advanced feature and functional properties of different kinds. Among those functionalities, considerable interest has been played in functionalizing commodity garments in order to make them positively interact with the human body and therefore being beneficial to the user health. This kind of functionalization generally exploits biopolymers, a class of materials that possess peculiar properties such as biocompatibility and biodegradability that make them suitable for bio-functional textile production. In the context of biopolymer chitosan has been proved to be an excellent potential candidate for this kind of application given its abundant availability and its chemical properties that it positively interacts with biological tissue. Notwithstanding the high potential of chitosan-based technologies in the textile sectors, several issues limit the large-scale production of such innovative garments. In facts the morphologies of chitosan structures should be optimized in order to make them better exploit the biological activity; moreover a suitable process for the application of chitosan structures to the textile must be designed. The application process should indeed not only allow an effective and durable fixation of chitosan to textile but also comply with environmental rules concerning pollution emission and utilization of harmful substances. This chapter reviews the use of microencapsulation technique as an approach to effectively apply chitosan to the textile material while overcoming the significant limitations of finishing processes. The assembly of chitosan macromolecules into microcapsules was proved to boost the biological properties of the polymer thanks to a considerable increase in the surface area available for interactions with the living tissues. Moreover, the incorporation of different active substances into chitosan shells allows the design of multifunctional materials that effectively combine core and shell properties. Based on the kind of substances to be incorporated, several encapsulation processes have been developed. The literature evidences how the proper choices concerning encapsulation technology, chemical formulations, and process parameter allow tuning the properties and the performances of the obtained microcapsules. Furthermore, the microcapsules based finishing process have been reviewed evidencing how the microcapsules morphology can positively interact with textile substrate allowing an improvement in the durability of the treatment. The application of the chitosan shelled microcapsules was proved to be capable of imparting different functionalities to textile substrates opening possibilities for a new generation of garments with improved performances and with the potential of protecting the user from multiple harms. Lastly, a continuous interest was observed in improving the process and formulation design in order to avoid the usage of toxic substances, therefore, complying with an environmentally friendly approach
INSIGHT INTO SORPTION AND ANTIOXIDANT PROPERTIES OF ANTIBACTERIAL WOUND DRESSINGS COMPOSED OF VISCOSE FABRICS FUNCTIONALIZED WITH CHITOSAN AND CHITOSAN-BASED NANOPARTICLES
Wound dressings designed with simultaneously adequate antibacterial, sorption, and antioxidant properties enable proper wound healing. Since the antibacterial properties have already been proven in our previous studies, the sorption and antioxidant properties of raw and differently pretreated (TEMPO-oxidized and TEMPO-oxidized cellulose nanofibrils (TOCN) coated) viscose fabrics (CVs), functionalized with chitosan (CH) and chitosan-based nanoparticles with (NCH+Zn) and without incorporated zinc (NCH), were investigated. The sorption properties were evaluated by absorbency rate and capacity, contact angle, zeta potential, and moisture sorption, whereas the antioxidant properties were determined by the ABTS method. The morphological properties of CVs were investigated by SEM. By using pretreatments, the sorption and antioxidant properties of CVs were improved, while subsequent functionalization with CH, NCH and NCH+Zn decreased both properties. However, TOCN-coated CV functionalized with CH and TEMPO-oxidized CV functionalized with NCH still have sorption and antioxidant properties better than raw CV. The obtained results allow the design of antibacterial wound dressings with predefined sorption and antioxidant properties
Funkcjonalizacja chitozanem i miodem włókniny wiskozowej do zastosowań medycznych
The aim of this research was to develop the formulation of chitosan in combination with honey in different mass proportions of each of the components within the separate mixture. Such a formulation could serve as a functional coating suitable for wound healing. From the perspective of different formulations used within research presented, it is assumed that the different mass fraction of components will affect antimicrobial and antioxidant activity of the functionalised substrate differently. To apply the separate formulation onto a non-woven viscose substrate, the conventional pad-drying process was selected. Moreover a study of the effectiveness of the individual treatment was performed systematically, which is also reflected in the systematics of the experimental techniques selected. Considering antioxidant and antimicrobial action, honey-functionalised non-woven viscose shows higher effectiveness if compared to non-woven viscose functionalized with the chitosan:honey combination.Celem pracy było opracowanie z kombinacji chitozanu i miodu preparatu służącego jako przyspieszająca gojenie ran powłoka włóknin wiskozowych. W prezentowanych badaniach założono, że różna frakcja masowa składników wpływa odmiennie na działanie przeciwdrobnoustrojowe i przeciwutleniające funkcjonalizowanego podłoża. W celu zastosowania oddzielnego preparatu na nietkanym podłożu wiskozy, wybrano konwencjonalny proces osuszania. Biorąc pod uwagę działanie przeciwutleniające i przeciwbakteryjne, włóknina funkcjonalizowana miodem wykazywała większą skuteczność w porównaniu z włókniną wiskozową funkcjonalizowaną kombinacją chitozanu i miodu